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PLATINUM METALS REVIEW A Quarterly Survey of Research on the Platinum Metals and

of Developments in their Application in Industry www.matthey.com and www.platinurn.matthey.com

VOL. 46 APRIL 2002 NO. 2

Contents

Palladium/Nucleophilic Carbene Catalysts for Cross-Couplmg Reactions By Anna C. Hillier and Steven P. Nolan

Automotive Fuel Cells: A U.K. Perspective By D. M. Jollie

Fuel Cells: Science and Technology 2002

Catalysis for Low Temperature Fuel Cells

Catalysts & Catalysed Reactions A review by Andrew P. E. York

Jewellery-Related Propefties of Platinum By John C. Wright

Laser Drilling of Platinum Cavities

Heterogeneous Catalytic Hydrogenation A review by M. Hayes

Two-Phase Iridium-Based Refractory Superalloys By Y. Yamabe-Mitarai, Y. F. Gu and H. Harada

The Chemistry of the Platinum Group Metals: PGM8

2001 Nobel Prize in Chemistry By Thomas J. Colacot

Abstracts

New Patents

Final Analysis: 5% Pd/C - Precise but Vague By D. E. Grove

50

64

64

64

65

66

72

73

74

81

82

84

89

92

Communications should be addressed to: The Editor, Susan V. Ashton, Platinum Metals Review, [email protected] Johnson Matthey Public Limited Company, Hatton Garden, London EClN 8EE

Palladium/Nucleophlic Carbene Catalysts

Hartwig-Buchwald Amination

for Cross-Coupling Reactions

H N R " R"'

By Anna C. Hillier and Steven P. Nolan' Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, USA., 'E-mail: [email protected]

Palladium complexes bearing N-heterocyclic nucleophilic carbenes can, function as eificient and convenient mediators of C-C and C-N cross-coupling reactions. These phosphine-free systems are highly effective in coupling reactions of aryl bromides and aryl chlorides with a variety of coupling partners. Some applications of these palladium complexes in a range of coupling reactions are described here and catalysts, conditions and results are presented.

Palladium and nickel based catalysts have provided a plethora of new methodologies for synthetic organic chemistry. Palladium-catalysed cross-coupling of aryl halides (or halide analogues) with nudeophiles is firmly established as one of the most important methods available for C-C and C-N bond formation (14). These cross-coupling reactions employ a range of transmetallating agents, examples of which are shown in Figure 1.

Palladium and nickel complexes containing phosphine hgands are among the most successful and widely used catalyst precursors for couphg of sp2 carbons, and bulky electron-rich tertiary alkyl phosphines are particularly effective (5-7). Significant advances have been made in using aryl chlorides as cross-couplug partners, with a

Reaction Reagent, [MI-Ar'

Suzuki-Miyaura Kumada Ar'-MgX Negishi Stille

Ar'-ZnX Ar'-SnR"3 I

Hiyama I Ar'-Si(OR")s I Heck Sonogashira

number of processes mediated by palladium-bulky phosphine systems (8, 9). Their success is explained by reference to the catalytic cyde depicted in Figure 2. The increased electron-richness imparted to the metal centre by the electron-donating phosphine assists in the cleavage of an Ar-X bond in the first, oxidative addition, step, while the steric bulk of the hgand promotes the reductive elimination of the Ar-Ar' coupling product following transmetallation with M-Ar'. While Heck and amination (and CuI-free Sonogashira) reactions do not, strictly speaking, involve a transmetallation step, they are generally included in discussions of cross-couplug chemistry since their catalytic cycles possess essentially the same features.

Recently, alternatives to phosphines have been sought owing to certain of their 'user-unfriendly' properties, namely air- and moisture-sensitivity and thermal instability, which means that excess hgand is often required to stabilise low-valent metal centres during the catalytic cycle.

Highly promising and versatile alternatives to phosphines have been found in the N-heterocyclic nudeophilic carbene (NHC) class of hgand (10) (see Figure 3), often referred to as Arduengo carbenes, following their isolation by Arduengo in 1991 (11). These carbenes are neutral two electron o-donors (12), generally bearing bulky and/or electron-donating N-substituents. Arduengo carbenes exhibit greater thermal stability than phosphines and can bind more strongly to a metal centre (lOa), eliminating the need for excess ligand

Pbhnnm Metah b., 2002,46, (Z), 5 0 6 4 50

Fig. I Coupling partners for cross-coupling with aryl halides

Fig. 2 Catalytic cycle for palladium complex-mediated cross-coupling reactions; where Ar'-M is organoboroni( acid, organostannane, organomagnesium, organosilicon, amine, etc.

R 2,4,6-trirnethylphenyI 2,6-di-iso-propylphenyl 4-rnethylphenyl 2,6-dimethylphenyl cyclohexyl adamantyl

during catalytic processes. They have proven to be extremely effective ancillary lpnds in a broad range of metal complex-catalysed processes (13), with reactivity often surpassing that observed with phosphine Itgation (another notable example being in ruthenium-catalysed olefin metathesis (14)). Some of our recent work, in the area of cross-coupling chemistry employing palladium complexes with N-heterocyclic nudeophilic carbenes as catalyst precursors, is reviewed here.

L lMes IPr ITol I XY ICY IAd

Cross-Coupling via Transmetallation Suzuki-Miyaura Cross-Coupling of Aryl Halides or Pseudo-Halides with Arylboronic Acids (15)

The couphng reaction of aryl and heteroaryl- boronic acids with aryl and heterocyclic halides or d a t e s is a powerful method for preparing various biaryl systems and is .widely used in synthesising natural products (16). The importance of the palladium-catalysed Sd-Miyaura cross-coupling reaction cannot be overstated in view of its general use in a variety of C-C bond formations and is underscored by the large volume of research published in the last year, includmg extension to aqueous and supercritical COZ media and polymer-supported catalysts (17). Indeed, on a

commercial scale the Suzuki-Miyaura reaction is usually preferred to other C-C bond-forming processes since organoboronic acids are conve- niently synthesised reagents (18), and are generally thermally stable and inert to water and oxygen. NHC llgands have been employed with great success in this process (19).

Our initial research in th is area focused on the use of catalytic quantities of zerovalent PdZ(dba), as the precursor in conjunction with the carbene LMes and CsZCO3 as base (19e). This combination afforded a yield of 59% in the coupling of Cchlorotoluene with phenylboronic acid. The catalytic protocol could be simplified and improved by the use of air-stable IMes.HCl as hg- and precursor and deprotonating in sib with Cs2C03. Other combinations of NHC and base were less effective in this reaction.

Subsequently a simpler catalytic system was achieved by using air-stable Pd(II) precursors, eliminating the need for a drybox to load the catalytic components (20). The catalytic system was activated by heating at 80°C for 30 minutes under an argon atmosphere, during which time the base reacts with the PdQl) salt and IMes-HCI to generate the NHC and the active Pd(0) catalyst, prior to ad- substtate. The catalytic activity of the

R, ;; / R N N \=/

Fig. 3 N-Heterocyclic nucleophilic carbenes (NHCs)

51

R 2,4,6-trimethylp henyl 2,6-di-iso-propylphenyl cyclohexyl

L SlMes SlPr SlCy

R

Pd sourccl 2L-HCI C s2COj ( 2 equiv.) dioxane, 80.C

CI R' /

R'

Table I

Functional Group Tolerance of Suzuki-Miyaura Cross-Coupling Using PdAmidazoliurn Salt Catalystsa

Pd source

Pdz(d baI3 Pdz(d bah Pddd bah Pdz(d bah Pd4d bah Pdz(d baI3 Pdz(d halo Pdz(dbaI3 Pddd baI3 Pdz(d bah Pd(0AC)Z Pd( 0Ac)z Pd(0AC)z Pd(0AC)Z Pd( 0Ac)z Pd(0AC)z Pd(0AC)z Pd( 0Ac)z Pd( 0Ac)z Pd(0AC)z

R R' Time, h

1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2 2 2

19 2 8 2 2 2 2

Yield, Yob

IMes-HCI

90 99 88 91 93 95 99 99 ale 80e 99 80 50 93 99 85 989 94 9ah 6gg

IPr-HCI

95 99 97 95 99 95 7ge 98 99'

100' - -

- - - - - - - -

' Reaclion conditions: 1.0 mmol a w l chloride, 1.5 mmol uiylhoronic acid, 2.0 ntmol Cs2 CO1, 2 L/Pd. 80°C; lsolated yields; Pdz(dbu).q/lMe.s.HCl = (1.5 mo1%)/(3.0 mol%), Pd(OAc)?/IMes.HCI = (2.5 mo1%)/(2.5 mol%J: Pdz(dba)j/lPr.HCl = (1.0 mol%)/(2.0 mol%J:

5 mol% of IMes-HCI: ' 16 hours; '3 hours: Pd(OAc)?/lMe.sHCl = (5.0 mo1%)/(5.0 mol%J

system was also investigated as a function of the imidazolium salt (NHC precursor). NHC N- substituents comprising bulky orthesubstituted aryl groups (IMeseHCl, IPr-HCl, JXyHCl) dis- played the highest activities, indicating that steric factors dictate the catalytic system effectiveness.

Both Pd(0) (Pd2(dba)3/IMes.HC1; Pdz(dba),/ Pr-HCl) and PdQI) (Pd(OAc)z/Mes.HCl) systems were found to be exceptionally tolerant to functional groups on the aryl chloride and boronic acid. Excellent yields were obtained with some diverse electron-donatmg and electron-withdraw-

ing substituents, with slightly lower yields observed for sterically-hindered ortho-substituted reagents, see Table I. This protocol could also be applied to the cross-coupling of aryl aiflates with phenylboronic acids, as shown in Table II.

Kumada-Tamao-Corriu Cross-Coupling of Aryl Chlorides with Aryl Grignard Reagents

Arylboronic acids and other organometallic reagents employed in (3-c coup& reactions are often prepared from the corresponding Grignard or organolithium reagents (15a). Three years after

Phinwm Metab Reu., 2002,46, (2) 52

4-CH3 4-CH3 4-CH3 4-CH3

4-OcH3 2,5-(CH3)2

H 4-C(O)OCH3 4-C( 0)CHJ

4-CN 4-CH3 4-CH3 4-CH3 4-CH3

4-C(O)OCH3 4-CH3

3-N(CH3)7 2,5-(CH& 2,5-(CH3)7 2,5-(CH3)z

4-OCH3

H 4-OCH3 2-CH3

3-OCH3 H H

4-OCH3 H H H H

2-CH3 OCH, 3-

H H H

H H

H

R - 8 Pd s u r c e (2.5rnol -1.) IPr.HCI (2.5 rnol */a)

CszCO3 (2equiv.l dioxane, 80-C, 5h

R

/ OTf R’

R’

R

Table II

Functional Group Tolerance of Pd SourceAPr-HCI-Catalysed Suzuki Cross-Coupling of Aryl Triflates with Phenylboronic Acid Derivativesa

R’ Yield, Yob Pd source

Pd (0AC)z Pd(0AC)z Pddd ba)3 Pdz(dbaI3

Pddd bah

Pdz(d baI3

Pd( 0Ac)z

Pd( 0Ac)z Pd(0AC)z

86 81 97 98 85 99 76 77 97

Reaction conditions: 1.0 mmol of aryl trifklte, 1.5 mmol of arylboronic acid, 2.0 mmol of Csl COA 2.5 mol% Pd source, 2.5 mol% IPr.HC1, 80°C; Isolatedyields

the first reports, in 1972, of the Nio-catalysed reaction of Grignards with akenyl or aryl halides (21, 22), the Pd-catalysed reaction was described (23). Several reports have appeared since, d e w phosphine-modified Pd- or Ni-mediated couphg of Grignards with aryl halides (5% 5b, 5n-5v). We recently reported the first example of successful couplmg involving unactivated aryl chlorides and an aryl Gngnard reagent (24).

The reaction between 4-chlorotoluene and phenylmagnesium bromide was selected for the initial screening of the Pd source and hgand. The system Pd2(dba)3/IF’r-HC1 in a l,Cdioxane/THF solvent mixture at 80°C was found to be most effective (quantitative convesion in 3 h), although replacing 1 mol% Pdz(dba)3 with 2 mol% Pd(0Ac)z afforded similar conversions. No additional base was necessary as a small excess of PhMgBr was utilised. The catalytic system was tested with a range of substituted aryl halide substrates and Gngnard reagents Fable III) and found to be extremely tolerant of electronic variation in the substituents; even Cchloroanisole

(which is particularly inactive) afforded quantitative conversion in three hours. Although oho-substituents on the aryl Grignard reagents were tolerated well, ortho-substituted aryl chlorides required a larger excess of Grignard (1.8 equivalents) to achieve good yields. Steric congestion around both reactive centres (as encountered in the reactions of 2-chloro-mxylene or 2-bromo- mesitylene with mesityl magnesium bromide) resulted in no conversion.

Stille Cross-Coupling of Aryl Halides with Hypervalent Organostannanes

The use of readily available, ait- and moisture- stable organotin reagents, SnR”,R, as cross- coupling partners represents one of the most versatile of couplug methods in organic chemistry. One important advantage of tin reagents is their compatibility with a large variety of functional groups. However, there are sgdicant disadvan- tages to their use, most notably the difficulty of removing tin from the product and there are con- cerns regarding the toxicity of tin. A further

P h t i n m Metah Rev., 2002, 46, (2) 53

H H

4-OCH3 4-OCH3 4-OCH3 4-OCH3

4-c 4-c 4-c

0 0 0

CH3 CH3 CH3

4-OCH3

4-OCH3

4-OCH3

H

H

H

4-CH3

4-CH3

4-CH3

Table 1 1 1

Palladium/lmidazolium Salt-Catalysed Cross-Coupling of Aryl Halides with Aryl Grignard Reagentsa

X

CI CI Br CI CI CI Br I CI CI CI CI CI CI Br

R R' Time, h I Yield, Yob

3 3 1 3 3 5 5 3 5 3 3 3 3

24 24

99 9gC 99 97 85 87d 69 96e 95e 99 83 99 95

0 0

rhe wactions were carried out according to the conditions indicated hv the ohove eyuution. 1.2 equivulenrs qfPhMgBr

2.0 mol% of Pd(OAc)> used instead of 1.0 mol% ofPd?(dba),; a 1.8 eyuivulents ofphen>hnugnesium bromide weir used: 2.5 equivalents of phenylmagnesium bmmide were used

(1.0 Msolution in THF) used unless otherwise stated; Isolated vields (average of hvo runs) afierjlush chromatography:

limitation is their hgh stability which results in a slow transmetallation step in the catalytic cycle. To avoid these limitations we investigated the use of hypervalent stannate species. Fluorophilic organostannanes (25) react with fluoride anion to give hypervalent five-coordinate intermediates which are more labile than the parent organostannanes and thus expected to transmetallate more effectively (26).

We identified a hypervalent fluorostannate anion by I9F NMR spectroscopy after treating SnMe3Ph with 2 equivalents of tetrabutylammoni- um fluoride 0. In the presence of catalytic amounts of Pd(0Ac)z and IPr.HC1 this intermecl- ate coupled with Cchlorotoluene to afford the desired biaryl cross-coupling product (27). Other bases that were screened for activity (CsF, KOBu', CszC03, NaOH) were essentially ineffective. The

TBAF appears to play a dual role in the cadytic system, acting both as the base/nudeophile to

deprotonate the NHC precursor imidazolium salt and as the fluorinating agent, accelerating the transmetallation step via formation of the more reactive hypervalent organostannate. An additional advantage of using TBAF is that it serves as a fluorous medium for tin extraction, a i d q the removal of tin by simple water extraction. Both the Pd(II)/IPr.HCl and Pd(II)/IAd-HCl systems were effective in the cross-coupling of electron- neutral and electron-deficient aryl bromides with SnMe3Ph or Sn(Bu")sPh (see Table IV). Electron- rich 4-bromoanisole proved less facile and only coupled rapidly with the more reactive SnMe3Ph employing IPr-HCl as ligand precursor. Odwsub- stituted aryl bromides required longer reaction times with SnMe3Ph. Unactivated aryl chlorides

PMmm Metah Rm, 2002,46, (2) 54

L.HCI (3.0 mol %)

TBAF (2 equiv.) dioxane/THF R

IPr-HCI

Table IV

Pd(OAc)2/L.HCI-Catalysed Stille Couplinga

48 35

X

X R Time, h

Br 4-C(O)CH3 3 Br 4-OCH3 48 Br 2,4,6-(CH3)3 48 Br 4-CH3 48 CI 4-C(O)CH3 3 CI 4-OCH3 24 CI 4-CH3 12

Br Br Br Br Br Br Br CI CI CI GI

Yield, Yob

92 69 25 98 83 15 41

R

4-CH3 4-CH3

4-C( O)CHs 4-C(O)CH3

2,4,6-(CH3)3 4-OCH3 2-CN 4-CH3 4-CH3

4-C( O)CHs 4-OCH3

Tin reagent

SnMe3Ph

SnMesPh SnMe3Ph SnMe3Ph SnMe3Ph SnMe3Ph SnMe3Ph

Sn( Bu"),Ph SnMe3Ph SnMe3Ph

Sn(BU")3Ph IPr-HCI

IPr-HCI

IPr-HCI IPr-HCI IPr-HCI IPr-HCI

IPr-HCI

IAd-HCI

IAd*HCI

IAd*HCI

Time, h

1.5 3 0.5 1

48 2

48 24 12 1

~

Yield, Yob

90 91 92 86 86 92 80 54 45 91

Reaction conditions: 1.0 mmol ofaryl halide. 1.1 mmol of arylstannane. 2 mmol TBAE 3.0 mol% Pd(0Ac)a 3.0 mol% L.HC1. I ml dioxane, 80°C for awl bromides (100% for aryl chlorides); Isolated yie1d.v

were unsuitable couplmg partners for this catalytic system, although good yields were obtained with 4- chloroacetophenone.

couphg of aryl bromides with vinylstannanes in good to moderate yields, (Table V) although for the aryl chlorides, moderate conversion was

The same catalytic method also effected the observed only with the electron-deficient

Reaction conditions: 1.0 mmol aryl halide, 1.1 mmol vinylslannane, 2 mmol TBAE 3.0 mol% Pd(0Ac)a 3.0 mol% IPraHCI, I mi dioxane, 80°C for aryl bromides (100% for aryl chlorides): GCyields

PIpltiwwm Meitah h., 2002,46, (2) 55

Table V

Pd(OAc)2/1Pr.HCI-Catalysed Cross-Coupling of Aryl Halides with Vinylstannanea

Cchloroacetophenone. The results suggest that couplug of aryl chlorides is facilitated by electron- withdrawing substituents, consistent with a rate determining oxidative addition step.

X

Br Br Br Br Br Br Br GI

Organosilanes as Coupling Partners Silicon-derived compounds are viable altema-

tives to other transmetdating agents owing to their low cost, easy availability, low-toxicity byproducts and stability to different reaction conditions (28). However, for electron-rich or -neutral aryl chlorides hgh yields are only obtained with high catalyst and phosphine loadmgs.

The reaction of one equivalent of aryl halide with two of phenyltrimethoxysilane in the presence of 3 mol% each of Pd(OAc)z and IPr-HC1 and two equivalents (per Pd) TBm in 1,4-dioxane at 80°C afforded both the desired couplug products and the homocouplug product (29,30). As in Stille coupling, rapid, quantitative conversion was achieved with aryl bromides and electron-deficient aryl chlorides (4chloroacetophenone, Cchloro- benzonitrile) but poor activity was observed with unactivated chlorides (4chlorotoluene, Cchloro- anisole) despite prolonged reaction times. This protocol was also applicable to heteroaryl halides,

R Time, h Yield, Yob

4-C( 0) H 0.25 100 H 1 100

4-CH3 1.5 100 2-CH3 1 35

3,5-CH3 1 99 4-OCH3 3 99 3-OCH3 2 99

H 2 13

I

Fig. 4 Chelating carbene-phosphine (imidazolium salt depicted)

affordmg moderate yields with longer reaction times. A further analogy with the tin chemistry is suggested by a preliminary study which indicated that substituted styrenes are obtained in quantitative yield (after prolonged reaction times) &om the reaction of aryl halides with vinyltrimethoxysilane.

Cross-Coupling with ALkenes: Heck Reaction The Heck reaction involves initial oxidative

addition of an aryl halide to generate ArPdX, followed by insertion of an alkene into the Pd-Ar bond and subsequent liberation of the new akene by P-hydrogen elimination (as with concomi- tant regeneration of the Pd(0) catalyst. Thus a base is required to promote the removal of HX and provide additional driving force for the reaction. Heck coupling of an aryl moiety to an alkene is widely employed in organic synthesis in the prepa-

I

a Reaction conditions: I mmol aryl halide: 1.4 mmol n-hutyl acrylate: GCvield (diethyleneglycol di-n-butyl ether as GC standard; average of two runs)

56

Table VI

Pd/Chelating Carbene-Phosphine-Catalysed Heck Reaction of Aryl Halides with n-Butyl Acrylatea

Pd(OAc)l (2molV.) I Mes. HCI (4 rnol%) fl OBu"

R R COOB~" c s 2 c o 3 ( 2 equiv.)

DMAc, 120.C

Table VII

Pd(OAc)2/1Mes.HCI-Catalysed Heck Coupling of Aryl Bromides with n-Butyl Acrylatea

Yield, Yob

100 100 97 94 99 16 97 94 65 91 99 88 66 99

'Reaction condilions:1.0 mmol aryl bromide, 1.6 mmol n-buy1 aciylate, 2 ml ojDMAc; ' GC yield (diethyleneglycol di-n-buy1 ether as GC standard); an average oj'lwo runs; with addition of [Bun4NjBr (20 mol%); 2 mol% Pd(dba)> as Pd source; ' 4 mol% ICyHCl as ligand; 4 mol% SlPi-HCI as ligund

ration of substituted olehns, dienes and precursors to conjugated polymers (50,31). While monodentate phosphines have provided efficient catalyst modifiers, in reactions with less reactive aryl bromides and chlorides bulky electron-donating phosphines, such as PBu'3, are necessary (50). At the elevated temperatures required for Heck chem- istty, both phosphines and their Pd complexes are prone to decomposition, so %her catalyst load- ings are needed. Increased stability can be imparted by using chelating phosphines but only limited success has then been achieved in catalysis.

However, a hlgh degree of efficiency has been observed in Heck reactions mediated by palladium carbene complexes (32). Following a recent theoretical study which suggested that mixed carbene-phosphine chelates were suitable for the Pd-catalysed Heck reaction (33), we prepared the carbene-phosphine chelating ligand shown in Figure 4 and investigated its eficacy in the cross-

couphg of aryl bromides with n-butyl acrylate (34).

Optimal conditions were found using Pd(dba)z with one equivalent of L-HBr, & = the &and in Figure 4), two equivalents of CSZCO,, and the polar solvent Nfl-dimethylacetamide (DMAc) at 120°C. Excellent yields were obtained with a range of activated and unactivated aryl bromides (Table vI>. The protocol was, however, intolerant of ster- icdy hindered orlho-substituted substrates and ineffective for unactivated aryl chlorides, with prolonged reaction times resulting in side reactions in both cases.

These results were compared with those obtained employing non-chelating NHC hgands (35). Both Pd(0) and Pd(II) precursors were effective with IMes-HC1 and the system using 2 mol% Pd(OAc)J4 mo1Yo IMes.HC1 was selected for study owing to its greater ease of execution. When the same protocol was used as that for the chelating NHC-phosphine system, htgh yields of franr

coupling products were obtained with a range of aryl bromides (Table VIl). With 4bromoanisole,

Pbtinwm Metah h., 2002,46, (2) 57

Pd(OAc), (3 mol % I I Mes.HCI (6 mol%)

Cul ( 2 mo1v.I.) (&X +

R CS.~CO) (2 equiv.)

DMAC, 8O.C

X R Time, h

Br 4-C(O)H 0.25 Br H 0.5 Br 4-CH3 0.5 Br 4-CH3 0.5 Br 2-CH3 0.5

Br 4-OCH3 3 Br 4-OCH3 0.5 Br 4-OCH3 1 Br 2-OCH3 0.5 Br 2-OCH3 0.5 Br 2,4,6-(CH3)2 1 CI H 1

Br 4-OCH3 0.5

Yield, Yob

100 (92)' 100 (91)'

100 (93) ' azc 946 96 (88) 43 '.

100 (93) 95'

96 (86)' 99

90 (82) 51

O Reaction conditions: 1.0 mmol aryl halide, 1.4 mmol I-phenyl-2-(trimeth~lsilvl)-acehiene. 2 ml of DMAc; GCyields based on aryl halide; Number in parenthesis is isolatedyield (average of two runs); Without Cul: Reaction temperature 60°C; ' 3 mol% Pd(dba)? as Pd source; 6 mol% IPr-HCI us ligund

4bromotoluene and 2-bromotoluene, the conversion was improved when 20 mol?h Pun4N]Br was added to the reaction. Aryl chlorides proved unsuitable for this system.

Cross-Coupling with Terminal Alkynes: Sonogashira Reaction

Palladium complexes are active for the cou- p h g of terminal alkynes with aryl or alkenyl halides to give arylalkynes or conjugated enynes. These are important in assemblulg bioactive natural molecules and for new materials (36,37). The Sonogashira reaction of terminal alkynes with aryl or alkenyl halides provides a straightforward and powerful method for their synthesis (37, 38). The Pd(0)-catalysed Sonogashira couplulg is most efficient when CuI is added as cocatalyst. CuI activates the alkyne by forming copper acetylide, which transmetallates with an arylpalladium halide to form the alkynyl-arylpalladium species.

PIdnun Metals Rcv., 2002,46, (2)

Reductive elimination affords the arylalkyne coupling product and regenerates the Pd(0) catalyst and CuI.

A recent report described the unusually high activity of a palladium system modified by PBu'3 in the Sonogashira coupling of aryl bromides (39). To our knowledge only a handful of Pd/NHC- mediated Sonogashira reactions have been reported, and these deal only with activated aryl bromides (40, 41). After different ligands and bases were screened, a similar set of conditions to that used for Heck coupling was adopted, namely the combination: Pd(OAc)2/IMes-HC1/Cs2 CO3 in DMAc at 80°C. Nitrogen bases are commonly used in the Sonogashira reaction but in this case produced inactive systems. Undesired dimerisa- tion products were obtained when phenylacetylene was employed as the alkyne source. This side reaction was suppressed by using l-phenyl-2- (trimethylsily1)-acetylene as coupltng partner with

58

Table Vl l l

Pd(OAc)2/1Mes.HCI-Catalysed Sonogashira Reaction of Aryl Halides with 1 -Phenyl-2-(trimethylsily1)-acetylenea

Table IX

Pd2(dba)3/1Pr-HCI-Catalysed Amination of Aryl Chloridesa

Amine, HNR'R" R I Kmethylaniline

piperidine piperidine, 4-(tetrahydro-2H-pyran-Cyl)

morpholine HN(Bu")~ HzN(6i1')

aniline mesitylaniline

2,6-( Pr')z-aniline Kmethylaniline

aniline morpholine

Kmethylaniline HN(Bu")z

Yield, %b

99 96 86 82 95 86 96 59 85 91 91 80 98 94

Reaction conditions: 1.0 mmol of aiyl chloride, 1.2 mmol of amine. 1.5 mmol of KOBu ', 1.0 mol% Pd2(dba)j.

Isolated yields 4.0 mol% lPr.HCl(2 L/Pd). 3 ml ofdioxane, 100°C. Reactions were complete in 3-24 hours and reaction times were not minimised;

aryl bromides (35). Under optimised conditions excellent product yields were obtained; however, it is noteworthy that these hgh yields were achieved under Cd-free conditions. Ad- Cul increased reaction rates, most notably with deactivated or sterically encumbered aryl bromides. The catalytic system was even effective for chlorobenzene, although the yield was moderate.

C-N Bond-Forming Reactions Hartwig-Buchwald Amination

Only recently has metal-catalysed displacement of aryl halides with primary and secondary alkyl- and arylamines been developed as a useful synthetic method (42). Pd- and Ni-mediated aminations have attracted significant interest owing to the importance of this reaction in organic synthesis and materials science. The careful selection of hgands dictates the efficiency of a catalytic system, with bulky monodentate and chelaring phosphines giving the best results (43), although a recently reported two-coordinate palladium-carbene system

has proved very effective for amination of aryl chlorides (44). After the success of the Pd/NHC system in mediating C-C bond formation we turned out attention to C-N coupling processes. The use of the bulky NHC precursor IPr-HC1 with KOBu' as base and 1,Cdioxane as solvent permit- ted the catalytic C-N couplulg of aryl iodides and bromides at room temperature and the catalytic couplulg of aryl chlorides at elevated temperature. I-Qh conversions were achieved with primary and secondary, cyclic and acyclic amines with various aryl halides. CChlorotoluene and ortho-substituted aryl halides were aminated in good to excellent yields.

The effective couplulg of Cchloroanisole with sterically unhindered amines makes th is the most effective catalytic system to date (45,46). Data for the coupling of aryl chlorides with a variety of amines are presented in Table IX.

The scope of the Harrwig-Buchwald reaction was extended to the amination of heteroaromatic halides. No problems were encountered with

P/atnnm Metals Rev., 2002,46, (2) 59

Table X

Pd2(dba)3/1Pr.HCI-Catalysed Amination of Chloropyridines and Bromopyridinesa

Aryl halide

2-chloropyridine 2-chloropyridine 2-chloropyridine 3-chloropyridine 3-chloropyridine 3-chloropyridine 4-chloropyridine-HCI 4-chloropyridine-HCI 4-chloropyridine-HCI 2-bromopyridine 2-bromopyridine 2-bromopyridine

Arnine, HNR'R"

morpholine Nmethylaniline

aniline rnorpholine

Nmethylaniline aniline

rnorpholine N-rnethylaniline

aniline morpholine

N-rnethylaniline aniline

Yield, Yob

99 97 88 97 91 98 80 70 83 95 99 96

a Reaction conditions: 1.0 mmol chloro- or hmmopyidine. 1 .1 mmol arnine. 1.5 nimol KOBii'. I L/Pd. 3 ml diorarzr. 3 h. loo'%: Isolated ~vie1d.v

N-Arylation of Aryl Indoles coordination of Ncontaining substrates to the metal, and moderate to hgh conversions were achieved with 2-chloro- and 2-bromopyridine (Table X).

Amination of Aryl Halides with an Ammonia Analogue

Benzophenone imine adducts have been prepared using benzophenone imine as an ammonia surrogate. This represents an efficient alternative route to the synthesis of N-unsubstituted anilines owing to its low cost, availability of reagent and stability to varied reaction conditions (42e, 47). Under the conditions established for catalytic amination, benzophenone imine reacted readily with unactivated and ortb~~substituted aryl chlorides in high yield at 80°C. The reactions with Cchloro- toluene and 4-chloroanisole were faster and cleaner at 100°C, as were reactions with aryl bromides. However, activated aryl halides were incompatible with the strong base KOBu' in this process, resulting in base-promoted cleavage of the substrate. Primary anilines were obtained in good yields by acidic cleavage of the benzophenone imine adducts, see Table XI.

N-Aryl indoles themselves can be biologically active (48), or can be useful intermediates in the synthesis of biologically active agents (49). As such they are attractive synthetic targets. The involve- ment of aromatic nitrogen in the reaction limits the use of the N-arylation of indoles to more reactive aryl iodides and bromides. While our general amination procedure was ineffectual for the arylation of indoles, good results were obtained when coupling a number of aryl bromides and indole derivatives using a Pd(OAc)2/SIPr-HCl/NaOH catalytic system. This protocol additionally over- came a common problem in indole synthesis, namely the formation of C-arylation side products. Results are presented in Table XII.

Conclusions NHCs have been shown to be hghly effective

as supporting ligands in a range of catalytic processes. Their superior thermal stability, together with electronic and steric tunability imparted by facile variation of the N-substituents, and the ease of manipulation (and in siiu deprotonation) of the

Phtinnm Metab b., 2002,46, (2) 60

Pd(dba)z(2Wl %)

Ph IPr.HCI (211701 %) Ph

7ph KOBu'(1.5equiv.) * g++ Ph R

a x + H-N-

dioxanc

Table XI

Arnination of Aryl Chlorides and Bromides with Benzophenone lrninea

X

CI CI CI CI CI Br Br Br Br Br

a Reaction conditions: 1.0 mmol aryl halide, 1.0s mmol benzophenone imine, 1.5 mmol KOBU', 2.0 mol% Pd(dba)2, 2.0 mol% IPr.HC1, 3 ml dioxane. 80°C: Isolated yields; ' The reaction was performed at I00"C

NHC-precursor imidazolium salts, makes NHCs the a n a h y llgands of choice in many pdadiun- catalysed cross-coupling processes. Indeed, chloride substrates.

unprecedented catalytic activity has been observed in some cases, particularly with 'difficult' aryl

Table XI1

Arnination of Aryl Bromides with lndolesa

R R' I Time, h

H H H H Ph Ph Ph

2-F-CsH4 2-F-CsH4

3.5 1 3.5

16 3

18 10 3

10

Yield, Yob

97 100 88 68

1 ooc l o o c 61 97 83'

a Reaction conditions: 1.0 mmol aryl bromide, 1.1 mmol indole. 2 mmol KOBU'. 2.0 mol% Pd(OAc)z. 2.0 mol% SIPr.HCl, 3 ml dioxane. I00"C; Isolated yields; The reaction was performed in toluene

PLahnm Metah Rnr, 2002,46, (2) 61

Acknowledgements The National Science Foundation, the Petroleum Research

Fund administered by the ACS, Albemarle Corporation and Johnson Matthey are gratefully acknowledged for partial support of this work. We would also like to acknowledge our collaborators and coworkers whose names appear in the references.

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13 Recent examples of the use of NHC in coupling chemistry: (a) J. A. Loch, M. Albrecht, E. Peris, J. Mata, J. W. Faller and R. H. Crabtree, Otgunomet&cs, 2002, 21, 700; (b) A. A. D. Tulloch, A. A. Danopoulos, G. J. Tizzard, S. J. Coles, M. B. Hursthouse, R. S. Hay-Motherwell and W. B. Motherwell, Chem. Commun., 2001, 1270; (c) M. V. Baker, B. W. Skelton, A. H. White and C. G. Williams, J. Chem. Soc., Dalton Truns., 2001, 111; (d) D. J. Nielsen, K. J. Cave4 B. W. Skelton and A. H. White, Organometudics, 2001, 20, 995; (e) S. Caddick, F. G. N. Cloke, G. K. B. Clentsmith, P. B. Hitchcock, D. McKerrecher, L. R Titcomb and M. R V. Williams, J. Organornet. Chm., 2001, 617-618, 635; (0 A. M. Magdl, D. S. McGuinness, K. J. Cavell, G. J. P. Britovsek, V. C. Gibson, A. J. P. White, D. J. Williams, A. H. White and B. W. Skelton, ibid, 546; (9) D. S. McGuinness, K. J. Cavell, B. W. Skelton and A. H. White, Orgunometuhs, 1999,18, 1596

14 (a) T. Weskamp, W. C. Schattenmann, M. Spiegler and W. A. Herrmann, Angem Chem., Int. Ed. Engrl, 1998, 37, 2490; (b) M. Scholl, T. M. Tmka, J. P. Morgan and R. H. Grubbs, Tefrubedmn Lett., 1999, 40, 2674; (c) T. M. Tmka and R H. Grubbs, Acc.

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27 28

Reactions”, eds. F. Diederich and P. J. Stang, Wiley- VCH, Weinheim, 1998, pp. 49-97 and references therein; (c) A. Suzuki, J. Organomet. Cbem., 1999,576, 147 S . P. Stanforth, Tetrubedmn, 1998,54,263 (a) L. Botella and C. Nijera, hgew. Cbem., Ink Ed Engl, 2002, 41, 179; (b) N. A. Burnagin and V. V. Bykov, Tehbedmn, 1997, 53, 14437; (c) T. R Early, R. S. Gordon, M. A. Can04 A. B. Holmes, R E. Shute and I. F. McConvey, Cbem. Commun., 2001, 1966 (a) A. Huth, I. Beetz and I. Schurnann, Tetrubedmn, 1989, 45, 6679; (b) D. S. En&, J. McManus, W. Wood-Kaczmar, J. Richardson, G. E. Smith and A. Crastairs, 0%. Pmc. Res. Dev., 1999, 3, 248, (c) T. Oh-e, N. Miyawa and A. S u z a J . 0%. Cbem., 1993, 58, 2201; (d) J. Uenishi, J.-M. Beau, R. W. Armstrong and Y. JSishi, J. Am. Cbem. Soc., 1987, 109,4756; (e) M. Uemura, H. Nishimura, T. Minami and Y. Hayashi, ibid, 1991,113,5402 9. cit., (Refs. 5i, 1Od); (a) M. Regitz, hp. Cbem., Int. Ed Engl, 1996,35,725; @) W. A. Henmaan and C. Kocher, A n p . Cbem., Int. Ed Engl, 1997, 36, 2163; (c) W. A. Herrmann, C. P. Reisinger and M. Spiegler, J. Otgunomet. Cbem., 1998, 557, 93; (d) C. Zhang, J. Huang, M. T. Trudell and S. P. Nolan, J. 0%. Cbem., 1999,64,3804, (e) V. P. W. Bohm, C. W. K. Gstomnayr, T. Weskamp and W. A. Herrmann, J. Otgiznomet. Chem., 2000,595,186; ( f ) M. B. Andrus and C. Song, 0%. Lett., 2001,3,3761; (g) C. Zhang and M. L. Trudell, Tetrubedmn Lett., 2000,41,595; (h) T. Weskamp, V. P. W. Bohm and W. A. Herrmann, J. Organomet. Cbm., 1999,585,348 G. A. Grasa, M. S. Viciu, J. Hung, C. Zhang, M. L. Trudell and S. P. Nolan, submitted for publication K. Tamao, K. Sumitani and M. Kumada, J. Am. Cbem. Soc., 1972,94,4374 R J. P. Corriu and J. P. Masse, J. Cbem. SOC., Cbem. Commun., 1972,144 M. Yamamura, I. Moritan and S. Murahashi, J. Otgunomet. Cbem., 1975,91, C39 J. Huang and S. P. Nolan, J. Am. Cbem. Soc., 1999, 121,9889 P. J. Smith, “Chemistry of Tin”, Bladde, New York, 1998 A. L. Casado and P. Espinet, J. Am. Cbem. Soc., 1998, 120,8978 G. A. Grasa and S. P. Nolan, 0%. Lett., 2001,3,119 (a) M. E. Mowery and P. DeShong, 0%. Letr., 1999, 1,2137; (b) M. E. M o w q and P. DeShong, J. 0%. Chem., 1999, 64, 1684; (c) M. E. Mowery and P. DeShong, ibid, 1999,64,3266; (d) M.-R Brescia and P. DeShong, ibid, 1998, 63, 3156; (e) A. S . Pilcher and P. DeShong, ibid, 1996, 61, 6901; ( f ) S. E. Denmark and 2. Wu, 0% Ltt., 1999,1,1495; (9) S . E. Denmark and J. Y. Choi,]. Am. Cbem. Soc., 1999, 121,5821; (h) K A. Horn, Ckm. Rm, 1995,95,1317; (i) C. Chuit, R J. P. Corriu, C. Reye and J. C. Young, ibid, 1993,93, 1317; (j) K. Gouda, E. Hagiwara, Y. Hatanaka and T. Him]. 0%. Cbm., 1996, 61, 7232; (k) E. Hagiwa~a, K. Gouda, Y. Hatanaka and T. Hiyama, Tehbedmn Lett., 1997,38,439

29 H. M. Lee and S. P. Nolan, 0%. Lett., 2000,2,2053 30 Decreased amounts of homocoupled product were

obtained using 3 equiv. PhSi(OMe), and reducing the temperature to 60°C

31 (a) I. Beletskaya and A. V. Cheprakov, Cbem. Rev., 2000, 100, 3009; (b) M. T. Reetz, in ‘Transition Metal Catalyzed Reactions”, eds. S . G. Davies and %I., Murahashi, Blackwell Science, Oxford, 1999; (c) G. T. Crisp, Cbem. SOC. Rey., 1998, 27, 427; (d) J. T. Link and L. E. Overman, in “Metal-Catalyzed Cross-Couphg Reactions”, eds. F. Diederich and P. J. Stang, Wiley-VCH, New York, 1998, pp. 231-266; (e) J. T. Link and L. E. Overman, Cbemtech, 1998,28, 19; ( f ) S. Brase and A. deMeijere, op. cif., (Ref. d); (g) H. A. Dieck and R F. Heck,J. 0%. Cbem., 1975,40, 1083; (h) H. A. Dieck and R F. Heck,]. Am. Gem. Soc., 1974,96,1133

32 Op. it. , (Ref. 13g); (a) J. Schwan, V. P. W. Bohm, M. G. Gardiner, M. Grosche, W. A. Herrmann, W. Hieringer and G. Raudasd-Sieber, Cbem. Eur. J., 2000, 6, 1773; @) A. A. D. Tulloch, A. A. Danopoulos, R. P. Tooze, S. M. Cafferkey, S. Kleinhenz and M. B. Hursthouse, Cbem. Commun., 2000, 1274; (c) D. S. McGuinness and K. J. Cavell, Otgunomehdics, 2000,19,741; (d) W. A. H-ann, J. Fischer, M. Elison, C. Kocher and G. R J. Artus, Cbm. Eur. J., 1996,2,772; (e) W. A. Herrmann, M. Elison, J. Fischer, C. Kocher and G. R J. A r t u s , Angew. Cbem., Ink Ed Engl, 1995,34,2371

33 K. Albert, P. Gisdakis and N. Rosch, OrganomefuZkcs, 1998,17,1608

34 C. Yang, H. M. Lee and S. P. Nolan, 0% Letr., 2001, 3,1511

35 C. Yang and S. P. Nolan, Synhff, 2001,1539 36 L. Cassar, J. Otgunomet. Cbem., 1975,93,253 37 (a) K. C. Nicolaou and E. J. Sorensen, “Classics in

Total Synthesis”, Wilq-VCH, W e i n h h , 1996, pp. 582-586; (b) L. Brandsma, S. F. Vasilevsky and H. D. Verkruijsse, “Application of Transition Metal Catalysts in Organic Synthesis”, Springer-Verlag, Berlin, 1998, pp. 179-225; (c) A. L. Rusanov, I. A. Khotina and M. M. Begretov, Rurs. Cbem. R#., 1997, 66,1053

38 (a) J. Tsuji, op. cit., (Ref. la), pp. 168-171; (b) K. Sonoeashira. ob. it.. (Ref. 31cf). DD. 203-229: (c) R

39

40

41

a * 1 I \ I , 1 1 . ., Rossi, A. Carpita and F. Bellina, 0%. Pnp. Pmc. Int., 1995,27,127; (d) I. B. Campbell, in “Organocopper Reagents”, ed. R J. K. Taylor, IRL Press, Oxford, 1994, pp. 217-235; (e) K. Sonogashira, in “Comprehensive Organic Synthesis”, ed. B. M. Trost, Pergamon, New York, 1991, pp. 521-549; (0 K. Sonogashira, Y. Tohda and N. Hagihara, Tetrubedmn Lett., 1975,4467 (a) V. P. W. Bohm and W. A. Herrmann, Eur. J. 0%. Cbem., 2000, 22, 3679; (b) T. Hundemnark, A. F. Littke, S. L. Buchwald and C. G. Fu, 0% Lett., 2000, 2,1729 W. A. Hemnann, V. P. W. Bohm, C. W. K. Gstotttnayr, M. Grosche, C.-P. Reisinger and T. Weskamp, J. Otgunomef. Cbem., 2001,617418,616 9. if., (Ref. 19d); (a) D. S. McGuinness and K. J. Cavell, O%unomet&, 2000,19,741s

Platinum Me.& Rm., 2002,46, (2) 63

42 Recent reviews of palladim- and nickel-mediated aryl aminations: (a) J. P. Wolfe, S. Wagaw, J.-F. Marcoux and S. L. Buchwald, A c . Cbem. Res., 1998, 31, 805; (b) J. F. H d g , Act. Chem. Ref., 1998, 31, 852; (c) J. F. Hartwig, Angw. Cbem., Int. Ed Engl.,

44 L. R. Titcomb, S. Caddick, F. G. N. Cloke, D. J. Wilson and D. McKerrecher, Cbem. Commun., 2001, 1388

45 J. Huang, G. A. Grasa and S. P. Nolan, 0% Ltt., 1999,1, 1307

1998, 37, 2046; (dl J. F. Hattwig, Gnktt, 1997, 329; (e) B. H. Ymg and s. L. Buchwald, ]. ofgunornet.

46 G. A. Grass, M. Vidu, J. Huang and S. P. Nolan, J. ofg, ,-hem,, 2001, 86, 7729

47 F. Paul, J. Pan and 1. F. H d g , Oqunometulbcf, Cbem., 1999,576, 125

43 For examples of amination of aryl chlorides, see: q. it., (Refs. 5b, 5n, 5 4 ; (a) J. P. Wolfe and S. L. Buchwald, Angew. Cbem, Znt. Ed, 1999,38,2413; (b) X. Bei, T. Uno, J. Norris, H. W. Turner, W. H. Weinburg, A. S. Guram and J. L. Petersen, O?ganomet&cs, 1999,18,1840, (c) E. Brenner and Y. Fort, Tetrubedmn Lett., 1998, 39, 5359; (d) T. Yamamoto, M. Nishiyama and Y. Kole, ibid, 2367; (e) J. P. Wolfe and S. L. Buchwald,]. h. Cbem. Soc., 1997,119,6054; (0 T. H. Riermeir, A. Zapf and M. Beller, T L ~ . Cu#ul., 1997, 4301; @ N. P. Reddy and M. Tan&, Tetrdedmn Lit., 1997,38,4807; (h) S. R. Stauffer, S. Lee, J. P. Stambuli, S. I. Hauck and J. F. Hartwig, Ox. Lit., 2000,2,1423

- - 1995,14,3030

48 (a) P. Marchini, G. Liso and A. Reho,]. 0%. Cbem., 1975,40,3453; (b) C. F. Lane, Synthesis, 1975,135

49 J. Perregaard, J. ht, K. P. Bogrso, J. Hyttel and C. Sinchez,]. Med Cbern., 1992,35,1090

The Authors Anna Hillier is a Postdoctoral Research Associate at the University of New Orleans. Her main research interests are in organolanthanides, organometallic chemistry and catalysis

Steve Nolan is a University Research Professor in the Department of Chemistry at the University of New Orleans. His main research interests are organornetallic chemistry, organometallic thermochemistry and catalysis.

Automotive Fuel Cells: A U.I<. Perspective The Institution of Mechanical Engineers held a

one-day conference in London on 28th February on Fuel Cells for Automotive Applications. The main topics discussed were technical issues, implementa- tion of the technology and potential markets.

Melanie Sadler (QinetiQ) addressed challenges and developments across the entire spectrum of fuel cell vehicles, payjng attention to fuel storage and cost reduction. Achieving lower costs has been examined for many components, including the noble metal content in electrodes. Careful use of chemistry and engineering ought to optimise the platinum and ruthenium content in a fuel cell.

Work with alkaline fuel cells was described by A. Willett (Fuel Cell Systems). These were the first fuel cells to be seriously demonstrated (by Francis Bacon in 1959). NASA have used alkaline fuel cells with platinum group metal electrodes since the Apollo programme. The low operating temperature provides some benefits for vehicles, but carbon dioxide has to be removed from the air intake. This technology has ‘trickle-charged’ an electric taxi.

Chris Dudfield (Intellgent Energy) gave details on more conventional platinum-based proton

which lie even beyond the immediate technical hur- dles.

Finally, the motion: ‘Th is house believes that the fuel cell electric vehicle will comprise 10% of a new car market in 2010’, was defeated, despite strong support from Gary Acres (Consultant) and many positive comments. Professor James Randle (University of Birmingham) won the day. Nonetheless, the impression was given of a market almost on the verge of expansion.

David Jollie is Manager of the online resource Fuel Cell Today (fuelcelltoday.com), sponsored by Johnson Matthey, Hatton Garden, London. David’s main interests are the industrial development and utilisation of fuel cells.

Fuel Cells: Science and Technology 2002

D. M. JOLLIE

The next Grove-organised fuel cell conference ‘Scientific Advances in Fuel Cell Systems’ takes place in Amsterdam on 25th and 26th September. Topics covered will include materials (and membranes), stack and cell engineering, electrochemisq and catalysis, fuel processing, hydrogen storage and distribution and balance of plant. For further information please contact Ms C. Norris, Fax: +44 (0)118 377 4696; E-mail: [email protected].

exchange membrane technology for sole power in a car. He listed many prototypes using this technology.

A project underway to put a fuel cell into use in the town of Woking, U.K., was described by J. Kenna (Energy for Sustainable Development). He showed the logistical and regulatory challenges

Catalysis for Low Temperature Fuel Cells Unfortunately publication of the second part of

this paper has had to be postponed until a later issue. We apologise to readers who were hoping to read this item in this issue of Phtinum Met& W e w .

Phhvurn Metah h., 2002, 46, (2) 64

Catalysts & Catalysed Reactions EDITOR IN CHIEF: E. G. DEROUANE, The Royal Society of Chemistry, Cambridge, Number 1, January 2002, Items 1-233, ISSN (printed version) 1474-9173, (online version) 1474-91 81, Subscription for 2002 (12 issues): f 395, U.S.$596

Initially I was skeptical when I heard of the publication of another new catalysis journal into this already saturated field. But when I found out it was to be an abstracts journal I was optimistic. There is now a wide range of sources containing literature of interest to the catalysis community, and often important catalysis-related research appears in obscure or non-specialised journals, outside the scope of usual searches, so any help in bringing these sources to light is greatly appreciated.

The stated aim of the new journal, Cata&ts & Catdysed Reactions, is to alert catalysis researchers to new and interesang developments in the field. This is done using graphical synopses of papers published in a wide range of relevant journals over the past 2 to 3 months.

The editors and publishers of the new journal have been partially successful in their aim. The journal is well laid out, with section headlngs allowing simple searches for areas of interest, and covers a wide range of subjects: it does not appear to have a bias towards one area. Most of the abstracts are very informative. In particular, those concerning organic transformations are well dis- played with plenty of useful and relevant information (such as solvent, yield) to supplement the title. In these types of reactions the use of a pictorial representation greatly aids in understand- ing the subject matter of the paper. Nevertheless, a few of the abstracts are no- more than a direct pictorial interpretation of the title, and give no additional information on the content: perhaps a

pictorial abstract is not always required, and more would be gained by the inclusion of a couple of lines of relevant text.

The inclusion of a Chemikaf Abstracts-style index is a good feature, allowing quick and easy scanning for subjects of interest. In particular, brealung the index into separate sections for author, catalyst, reactant, product and journal is useful. However this also reveals the major favouritism of the journal to two or three sources, all of which are major

titles. Indeed, over one third of the abstracts in this edition are drawn from 3 journals (Chemicaf Communications, Journaf of Catabsis and Joutnaf of Mokmkar Cdys is ) includhg all 25 from one issue of Joumd of Cata&k. All of these journals would rank highly in any list of important journals for catalysis research, and therefore it is more than likely that most researchers would already be aware of important papers in these journals long before the three months it takes for the editors to include and publish them in Catdysts Q Ca&ysed Reactions.

Also, although the source list is certainly extensive, it was easy to think of a number of journals that are not included. For example, Journal ofSolid State Cbemistty, Chemishy ofMatetiah and Carbon, to name but three, all of which frequently contain papers of relevance to catalysis. Perhaps it is intended to expand the source list in the future?

Of far more interest would be coverage of the less well known journals, includmg more foreign journals sometimes containing published work in English (for example Shokubai gapan)), and obscure sources, such as solid state chemistry titles. Abstracts from these could be included and, I would argue, should take precedence.

Certainly this journal does not replace the need for regular perusal of the literature and literature searches, but it may, with the inclusion of more obscure journals, become a useful additional tool for keeping aware of current developments in catalysis research, alongside ChemWeb's forum on catalysis (http://catalysis.chemweb.com).

Professor Eric Derouane, the Editor in Chief, states in his hrst editorial that comments are wel- come. I hope that comments are forthcoming from the catalysis community, so that in the future this journal becomes a good source of information for its readers. (http://~.rsc.org/catalysts)

ANDREW P. E. YORK

Andy York is a Research Scientist at the Johnson Matthey Technology Centre. His interests are in the development of computer models for diesel aftertreatment systems.

Phtinwn Metalr Rev., 2002,46, (2), 65 65

Jewellery-Related Properties of Platinum LOW THERMAL DlFFUSlVlTY PERMITS USE OF LASER WELDING FOR JEWELLERY MANUFACTURE

By John C. Wright Consultant, Wilson-Wright Associates, Solihull, West Midlands, 690 4LS, U.K.

The performance ofprecious metal alloys can be usefully compared by the application of engineering design theory and heat flow properties on the small scale that is required for jewellery production. Some of the physical and mechanical properties ofplatinum jewellery alloys differ sufficiently from typical gold and silver alloys to require modifications in the processing techniques, but these properties may allow for stronger slender designs. The thermal difsusivity ofplatinum jewellery alloys is significantly lower than that of other precious metal jewellery alloys. This explains why laser welding is so efficient when used in making platinum jewellery and why it also allows most of the cold work hardening to be retained in components.

Few jewellery designers or manufacturers start

with a design specification, outline a design, detail a materials specification and optimise the production ability - which is the usual procedure in the manufacture of engineering components. Critical engineering design not only integrates mechanical design (such as stress/strain behaviour) with the

properties of the materials and their interaction with the production process, but also has to take into account how all these factors have to operate in an acceptable economic and environmental framework. Most of the worldwide jewellery industry takes a traditional view that depends on a relatively narrow range of processes and materials and favours batch processing rather than mass production.

By applying engineering design theory and heat flow physical properties on the small scale required for jewdery, the performances of precious metal alloys can be compared. For example, properties such as Young’s modulus, elastic limit stress and work hardenability of platinum jewellery alloys are significantly hgher than those of the other precious metal jewdery alloys. This combination of properties can explain the favourable ‘dead-set’ capability of platinum settings, that is, claws/

Fig. I A YAG laser used for jewellery welding ( I ) . Most jewellery lasers are Class 1 lasers. The workpiece IS irradiated by the narrow laser beam which heats up a small, controllable surface area of the platinum or platinum alloy jewellery to well above the melting point ( I 772-2000°C). Precise targeting allows welds to be made - 0.2 rnm,from heat-sensitive parts. Jewellety to be welded is placed in the upper compartment: the stereomicroscope aids positioning Photo courtew of RoJin-Buosrl LIK Lld.

Phfinum Metah Rnr, 2002,46, (2), 6C72 66

Table I

Typical Parameters of Jewellery Laser Welding Machines

Machine size, height x width x depth Weight Input power supply Max average operating power Focal spot diameter Pulse energy Peak pulse power Pulse duration Pulse frequency Pulse energising voltage

700-1 350 x 250-550 x 650-860 mm

11 5 or 200-240 V, 50-60 Hz

0.2-2.0 mm

85-1 50 kg

30-80 W'

0.05-80 J (W S) 4.5-10 kW 0.5-20 ms single to 10 Hz 200-400 V"

Average light bulb power but in-phase, so equivalent to much higher power density Voltage used to trigger xenon jlash. in turn, afects laser beam output power **

prongs and similar settings when pushed against gemstones tend to remain in position and show little 'spring-back'.

The thermal difhsivities of the platinm alloys used for jewellery are significantly lower than those for gold and silver, which explains why laser welding is so efficient and also why it allows more of the cold work hardening of jewellery alloys to be retained in components.

Laser Welding of Jewellery Laser machines for jewellery are compact, low-

powered and safe, see Figure 1. They weld most alloys quickly, repeatably and precisely, but the efficiency of the laser process depends very much on the properties of the target material. The energy that is effectively used in the welding depends on the surface absorption of the target and is controlled by adjusting pulse intensity, duration and pulse frequency. The laser weldmg effectiveness depends on properties of absorption, reflection and any chemical reactions of the target material. Components to be joined, or upgraded (repaired) in the case of castings, are arranged under visual control or jigged, and exposed to one or more laser pulses. A stereomicroscope and cross hairs facilitate the positioning of the parts and help to target the exact position where the laser pulse will strike.

The laser welding machine is easier to use if the shape of the beam in the worlung zone is cylindrical; th is is because the spot diameter does not change over a range of focus of several millimetres, see Figure 2. A typical laser pulse lasts from 1 to 20 milliseconds and suitable adjustments can be made for various materials through trial and error, but certain heat flow data allow good predictions of suitable weldmg parameters. Material properties which need to be taken into account when welding jewellery alloys, includmg latent heats of melung and corresponding thermal conductivities, are available but these values are more accurately known at or near room temperature than around the melting point. Despite the hgh energy needed to melt platinum alloys, their relatively low thermal

Good beam Bad beam quality quality

Misalignment of work piece in due beam to manual direction -E=5!5 positioning Spot diameter Spot diameter

remains nearly changes constant dramatically

Fig. 2 A good quality laser beam is one where the beam shape in the working area is cylindrical so that the spot diameter is constant over several millimetres of.focus.

Phtinum Metah REX, 2002, 46, (2) 67

Table II

Typical Laser Welding Parameters For Some Jewellery Materials

Alloy Pulse energising composition voltage**, V

Pulse duration, ms

Platinum, All Gold, 999 fine Gold, 18 ct yellow Gold, 18 ct white Silver, 925, 835 Titanium Stainless steel

200-300 300-400

250-280 300-400

250-300

200-300 200-300

1.5-1 0 10-20

2.5-1 0 1.7-5.0 7.0-20 2.0-4.0 2.0-15

Comments

Very good welding results Darken target area; high power necessary Good welding results Very good welding results Darken target area; high power necessary Weld in inert gas inside the laser welding machine Weld in inert gas inside the laser welding machine

Voltage used to trigger the xenonJ7ash affecfs the outpuf power of the laser heam used,for the diferent materials I*

diffusivity allows the heat to be retained/concentrated at the target, so they can be efficiently welded. However, platinum jewellery alloys have casting temperatures around 2000°C and high solidification rates, so the challenge is for compact

300V 3 5 0 V 400V

Beam diameter 0.2mm, Pulse 2.5ms

2.5ms lOms 20ms

Beam diameter 0.2mm, Voltage 300V

0.25mm 2.5mm 4 .5mm

Pulse 2.5ms, Voltage 300V

Fig. 3 Effect of diflerent laser settings of voltage. duration of beam pulse and beam diameter on the cross-section of the heat affected zone. (a) Increasing the voltage increases the penetration of the beam. (h) Increasing the duration of the pulse increases the total pulse energy and radial heat Jlow. (c) Increasing the beam diameter at constant pulse energy gives heat spread rather than penetration

laser machines to achieve this. The very hgh intensity laser pulse generates a

surface temperature well above the melting point of platinum over a very small diameter target spot. This allows controlled welding, under ideal conditions, as close as 0.2 rnm from complicated and heat-sensitive component parts, such as hinges, catches, fasteners, settings, most precious stones, and even, with care, pearls and organic materials. Provided that the heat flow away from the target is limited, it is possible to retain heat treated or cold worked hardness in most jewellery alloys; this works particularly well with platinum jewellery

The settings given in Table I1 are based on a beam diameter of about 0.5 mm on the materials stated and may need adjustment for other compo- sitions. The main control settings on the laser machine @ower/energy, beam diameter, dura- tions) have slightly different effects on any one material, as shown in Figure 3. Different materials can have very different values for thermal diffusivity, melting temperatures and latent heats of melting. The way these properties combine together has a marked effect on the energy intensity needed to produce an effective weld. Welding is achieved only when adequate heat is absorbed through the surface, not when the beam is reflected off the surface, so surface colour and reflectivity have to be taken into consideration. Where there is a combination of high reflectivity and high heat dispersion (for instance in silver and hgh carat

alloys.

Phhinwm Met& Rev., 2002,46, (2) 68

golds), it is helpful to mark and darken the target spot or line with a dark blue or black felt tip pen or permanent marker. This effectively increases the absorption coefficient of the surface.

Why Platinum Responds Well The efficiency of a laser welding machine dif-

fers from alloy to alloy. While the same set of control parameters will result in the same power delivered in each weldmg pulse, the melting effect of each pulse depends on the proportion of the heat energy absorbed and then on the rate at which the heat is dissipated from the melting/welding zone. This is not simply a function of the thermal conductivity. Thermal conductivity is defined as the rate of heat transferred through a volume whose two extremes are at different but constant temperatures - a steady state. However, what matters more in dependable practical workshop technology, is how the heat is transferred from a hot-spot, such as where a welding torch touches a surface, through a mass whose temperature rises as a consequence, and thus where the 'low' temperature end is not at constant temperature. This property is best described by thermal diffusivity, stiu very dependent on conductivity but modified by the specific heat of the metal related to the volume:

thermal conductivity specific heat x density

Thermaldiffusivity =

The heat input parameters are: [a] Specific heat of solid up to the melting point [b] Melting (liquidus) temperature [c] Latent heat of melting [d] Specific heat of the superheated melt [el Thermal diffusivity

Melung points for most platinum alloys are hgh, but thermal diffusivities are relatively low Fable III) so the laser is able to deliver enough energy to melt a very small focused spot at each pulse but with only a small heat affected zone. With the possible exception of palladium, all the platinum group jewellery alloys respond in the same way to identical settings of a laser machine. Shght differences in surface colour when melting in air (alloys containing copper and cobalt tend to

be a little greyer) have little effect on the optimum settings. Gold and silver alloys have lower melting points but five to seven times &her capacity to transmit heat away from the target.

The units used in Table I1 are c.g.s. units. This is because they fit the scale of jewellery alloys better than SI units (which rates thermal diffusivity in J m2 s-') and the interest here is in the order of the effect rather than calculating the actual heat flow. The data for the pure metals are known most accurately around room temperature (2, 3) and data for the alloys were calculated from the properties of the pure metals, based on alloy composition by weight. The fullest version of the data was used where available. For instance, data for platinum, gold and silver have been mwe extensively studied than for, say, ruthenium. However, the data in Table ID have been ratio- nalised to two decimal places to give greater uniformity, while acknowledgmg that the accuracy at %her temperatures is questionable.

The laser beam does its most effective work at or near the melting point of the target metal so we should be more interested in data at and near melting point temperatures. Thermal conductivity increases with temperature: for platinum from 0.171 at 300 K to 0.230 at 1800 I Q and at the melting point it is around 0.24. Specific heat (more correctly, molar heat at constant pressure, C,) within a single-phase region also increases with temperature according to a polynomial function:

C, = a + bT + cT2 + dT'I2 + eT-'

For platinum, a = 5.755, b = 0.001505, c = -0.185 x lod, so the specific heat increases from 0.0316 at 273 K to 0.0452 at 2046 K.

Density decreases by the cube of the coefficient of linear expansion with temperature, which for platinum is 8.9 x 10". This means that a cube of platinum, sides of 1 cm, at 273 K (21.40 g) would expand to a 1.016 cn-sided cube at 2046 K, or volume 1.049 an3, which is almost 5% less dense - at 20.04. On these assumptions, the thermal diffusivity of solid platinum at the melting point is approximately 0.265 instead of 0.245, about an 8% increase. All the platinum jewellery alloys have thermal diffusivities of the order of

P&mm Metah Rev., 2002,46, (2) 69

Table 111

Melting Points and Thermal Diffusivities for Platinum Alloys and Other Jewellery Materials

MetaVAlloy

999 Platinum 990 Platinum Copper Pt-5% Copper Cobalt Pt-5% Cobalt Iridium Pt-5% Iridium Pt-10% Iridium Pt-15% Iridium Pt-20% Iridium Palladium Pt-5% Palladium Pt-10% Palladium Pt-15% Palladium Rhodium Pt-5% Rhodium Ruthenium Pt-5% Ruthenium Tungsten Pt-5% Tungsten Fine Gold Fine Silver Sterling Silver

Liquidus temperature,

O C

1772 1772 1084.5 1745 1494 1765 2447 1795 1800 1820 1830 1554 1765 1755 1750 1963 1820 231 0 1795 3387 1845 1064.43 961.93 893

Density, g c m 3

21.45 21.45

8.93 20.38

8.80 20.34 22.55 21 5 1 21 5 6 21 6 2 21 67 12.00 20.98 20.51 20.03 12.42 21 .oo 12.36 21 .oo 19.25 21.34 19.28 10.50 10.40

Thermal conductivity,

cal (s T cm)-’

0.17 0.17 0.96 0.21 0.12 0.17 0.14 0.1 7 0.17 0.17 0.1 6 0.17 0.1 7 0.1 7 0.1 7 0.21 0.17 0.28 0.1 8 0.35 0.1 8 0.76 1.02 1 .oo

0.23 to 0.27. A similar argument applied to silver, shows its thermal diffusivity decreases from 1.74 to 1.31 (near its melting point).

The heat energy contained within 1 cm3 cubes of liquid platinum, gold and silver at 100 K above their respective melting points, are 1854, 956, and 878 cal, respectively. Although the heat contents of molten platinum jewellery alloys are roughly double those of gold or silver, their thermal diffusivities are about one fifth of that for gold and one seventh of that of silver. So the rate of heat input to the ta+- get can still substantially exceed the rate of outward heat diffusion. In effect this means that the laser beam can be placed very close to delicate stones with platinum, and that normally it is unnecessary to remove stones before malung repairs. A skilled

Latent heat,

cal g-’

27.13 27.13 48.90 28.22 63.00 28.68 51.09 28.33 29.53 27.31 31.92 38.00 27.67 28.22 28.76 53.00 28.42 91.19 30.31 61 .OO 29.1 7 15.21 25.30 26.40

Mean specific heat,

cal g-’ OC- ’

at 50°C

0.03 0.03 0.09 0.04 0.10 0.04 0.03 0.03 0.03 0.03 0.03 0.06 0.03 0.04 0.04 0.06 0.03 0.06 0.03 0.03 0.03 0.03 0.06 0.06

Thermal diff usivity,

cm2 s-’

0.25 0.25 1.17 0.29 0.13 0.23 0.20 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.29 0.25 0.40 0.25 0.54 0.27 1.25 1.74 1.66

operator can weld the surface without scarring and most components can be polished to ‘near finish‘ before welding. Alternatively, components can be ‘tack welded’, adjusted to the correct position and final welds made with laser settings that improve the cosmetic finish of the tack welds.

Another feature of the localised heating effect of the laser is that dissimilar alloys can be joined more readily than when using bulk melting. There are incompatible pairs of metals, but a laser welding machine can produce narrow weld zones where the change in colour or texture between the two components is sharper and better delineated than in alternate technologies. The most obvious common feature of a typical range of laser welded platinm jewellery is that remarkably small sections,

PLatinum Metah Rev., 2002, 46, (2) 70

Fig. 4 Platinum jewellery (not to scale) by Tom Rucker, who used laser welding in its assembly: (a) A 16 ct beiylpendant (back view) made in platinum- 5% copper The beryl is held between 2 laser-welded rails. This design could only be achieved by laser welding. (b) This diamond brooch made in platinum-20% iridium and I8 ct yellow gold was complete!y laser welded. (c) Necklace with diamond brilliants. sapphires and pearls (2nd Prize, International Pearl Design Contest, Tokyo, 1999/2000) made in platinum-20% iridium and 18 ct yellow gold. The 0.6 mm diameter wire is assembled crosswise in two levels and laser welded. (d) The 'Sea ofLights ' necklace made in platinum and 18 ct yellow gold with a 1.3 ct diamond brilliant. In the centre ofthe gold bowl is a brilliant cut diamond held in tension by 4 crossing platinum wires - 0.7 mm thick. The setting is so secure that brilliants up to 2 ct are used. The bowl is surrounded at the back by a cage of0.4 mm platinum wire which also holds the bearing. (e) A necklace with pearl clasp made in platinum-20% iridium. Platinum wire was wound onto the surface o f a wooden ball and laser welded. The ball was then burned away. The wire balls appearfragile, but the strong Pt-Ir al1o.v structure gives a solid result

Phtinwr Metah Rev., 2002,46, (1)

thin stampings and fine wire can be at least stitch welded with precision. More extensive welds and repairs of casting defects (see later section) can be made by a series of overlapping pulses. As the laser is limited to joints that can be hit by the direct beam, deep and undercut sites should be avoided.

Jewellery Design Several components in the jewellery shown in

Figure 4 have been elastically stressed to give springiness and rigidity. The tightly localised and limited heat diffusivity allows springy and hard components to be joined with little or no soften- ing. This enables designs that make good use of lightweight springy sections or robust fasteners. The very limited heat affected zones also allow joining of more dissimilar alloys (assay rules permit~@ than would be possible with large scale melting. In good commercial practice all the components could have a high degree of finish prior to joining. Most of the high finish is preserved, and it is clearly easier before welding to dean up and pol- ish separate components than finished pieces.

Upgrading and Repairs There are probably as many laser welding

machines used for upgtadtng castings as there are for makmg welded pieces. Some surface defects can be repaired at the fettllng stage but small pir- holes sometimes show up later during polishing. The expense to both the finisher and caster of returning such components for recasting is often avoidable by using the laser welder to upgrade the castings, particularly when casting and finislung operations are on the same site.

A small area of rough surface texture may be glossed by using a rapid repeat sequence of pulses with the laser beam set relatively wide and shallow. Small pinhole defects (around 0.25 mm) can be filled by similarly pdsing around the edge of the defect. Larger defects can be effectively filled with fine filler wire touched into the defect, cut to size with the laser beam striking the wire and then lev- elling the tiller down to the original surface. The colour of the filler can usually be matched accurately to that of the casting. The principle of relatively low thermal diffusivities of platinum jew-

ellery alloys when used with a laser machine, whether for upgrading castings or for weldmg, are virmally identical.

Conclusion Comparing jewellery alloys, the necessary heat

inputs to melt platinum alloys are high compared with gold and silver alloys, but thermal diffusivities are significantly lower. One effect is that heat is more localised around hot-spots than with gold and silver.

Most platinum jewellery alloys show the relatively high stress necessary to exceed the elastic limit, followed by a hgh rate of plastic work hardening which also raises the ‘bend-back‘ stress. Components may have useful strength and springiness in slender sections, and these extra properties acquired before laser welding can be retained after assembly.

Acknowledgements I gratefully acknowledge technical advice from Michael

Batchelor and David MacLellan of RofimBaasd UK Ltd.; www.rofin.com. I am indebted to Tom Rucker of Anton Rucker, Ottostrasse 80,85521, Ottobrunn, Germany, who puts the technology expressed in this paper into very effective artistic design, and for permission to use several of his designs.

References 1 Rofir-Baasel UK Ltd., (formerly Baasel Lasertech

UK Ltd.), Drayton Fields, Daventry, “11 5RB 2 “Kempe’s Engineers Yearbook 2000”, Miller

Freeman, Tonbridge, U.K., 2000 3 “CRC Handbook of Chemistry and Physics”, 76th

Edn., CRC, Boca Raton, 1995-1996

The Author John Wright is a former Professor of Industrial Metallurgy at the University of Aston in Birmingham. Currently, he is a consultant for the jewellery industry worldwide with Wilson-Wright Associates.

Laser Drilling of Platinum Cavities A copper laser has been used to etch and bore

into coated platinum wire electrodes (outer diameter 50-150 pn) to form - 30 pn diameter cavities for storing enzymes, by P. M. Vadgama of the University of Manchester (WotbiAppr! 01/13,102). Cavities are formed in and along the length of the active electrode core. The enzymes face laterally, instead of being on a mechanically vulnerable tip, which improves effectiveness and ease of use. The electrodes are for in yivo biological sensors.

PLdnwn Metals h., 2002,46, (2) 72

Heterogeneous Catalytic Hydrogenation HANDBOOK OF HETEROGENEOUS CATALYTIC HYDROGENATION FOR ORGANIC SYNTHESIS BY SHIGEO NISHIMURA, John Wiley & Sons, New York. 2001,700 pages, ISBN 0-471-39698-2, US. $185. €217.70, f 137

Catalytic hydrogenation is widely applied for the reduction of a variety of functional groups. It has been and will continue to be a very substantial market for platinum group metal (pgm) catalysts as they tend to be more active for a given transformation than their base metal equivalents. This permits the use of less severe reaction conditions. In the main, though not exclusively, the reactions are carried out over a heterogeneous catalyst. Unsupported catalysts have found application in small-scale laboratory use, though on an industrial scale use of a supported catalyst is usually advanta- geous. The rather diffidt-to-handle Raney Ni catalyst is one of the few unsupported materials which has been utilised industrially.

A diversity of materials can be used as a support to the hydrogenation catalyst and numerous techniques are used to deposit and anchor the active metal on this material. This results in a vast array of catalysts, each of which may be optimal for a given reaction operating under appropriate conditions. Correlating this data to produce a reference book, to enable a researcher to ascertain quickly the favoured catalyst and reaction conditions for the hydrogenation step of a particular functional group is an ambitious and hghly laudable endeav- our. This is exactly what Professor Nishimura has attempted to do with this book.

The book is divided into thirteen chapters. The first chapter gives an overview of hydrogenation catalysts, subdivided into sections on base metal catalysts and one on pgm catalysts. Details are given of methods by which both supported and unsupported catalysts can be prepared. The recipes provide a useful starting point for preparation of an optimised catalyst. The second chapter deals briefly with reactors, then with catalyst inhibitors and poisons, the judicious use of which is seen in the subsequent chapters on hydrogenation chem- istries to be a good control of catalyst selectiviq.

For example, in Chapter 4 on the hydrogenation of alkynes we see that Pb-doped CaC03-

supported Pd (the Lindlar catalyst) is active in the selective hydrogenation of alkynes to alkenes. The catalyst can be further modified for this reaction by addition of a nitrogen base such as quinoline or pyridine. This inhibition of the catalyst prevents further hydrogenation of the alkene product and results in an increase in selectivity. It is important, however, to adjust the concentration of the inhibitor to avoid complete poisoning of the catalyst. Another example of selective poisoning is described in Chapter 13 where a BaSO4-supported Pd catalyst when treated with a sulfur-containing poison, such as thioquinanthrene, becomes selective in the hydrogenation of acid chlorides to give aldehydes (the Rosenmund reduction). Addition of the inhibitor prevents further hydrogenation of the labile aldehyde product.

The specialist nature of this book is reflected not only in the price (an eye-watering E137) but also in the fact that technical terms (explanations being beyond its scope) are used liberally throughout. The reference lists for each chapter, while not meant to be comprehensive, could perhaps benefit from an update as they tend to be biased towards earlier work, sometimes even towards unsupported catalysts.

In conclusion, this book is easy to use to find information quickly on the hydrogenation of a given functional group. In conjunction with other texts (1, 2) it adds to a useful armoury for dealulg with most queries on hydrogenation. It is therefore good value for the specialist practitioner.

References 1

2

R L. Augustine, “Heterogeneous Catalysis for the Synthetic Chemist”, Marcel Dekker, New York, 1995 “Fine Chemicals through Heterogeneous Catalysis” ed. R. A. Sheldon and H. Van Bekkum, Wiley-VCH, weinheim, 2000

M. HAYES

Martin Hayes is a Senior Chemist, Process Catalyst Development Department, Johnson Matthey, Royston. His interests are in the development of heterogeneous platinum group metals catalysts for commercial production of added value chemicals.

Plnttaum Me.& Rev., 2002, 46, (2), 13 73

Two-Phase Iridum-Based Refractory Sup eralloy s THEIR DEVELOPMENT AND POSSIBILITIES AS HIGH TEMPERATURE STRUCTURAL MATERIALS

By Y. Yamabe-Mitarai, Y. F. Gu and H. Harada High-Temperature Materials Group, NIMS, Sengen 1-2-1, Tsukuba. lbaraki 305-0047, Japan

A new class of alloys based on platinum group metals. which are called rejractoty superallo.vs, is proposed. These refractory superalloys have aJc.c. and L 1 2 coherent two-phase structure (similar to that of nickel-based superalloys). high melting temperatures, and good potential as structural materials for use at temperatures up to 1800°C. In this paper. we report our results on the strength behaviour. creep property, ductility and,fracture mode of iridium-based refractory superalloys.

Iridium has a high melting temperature (2447"C), the highest room temperature elastic modulus (570 GPa) (1) and is one of the most sta-

ble elements against corrosion (2). Its main use is for crucibles for growing single crystals of h h melting temperature oxides, but it is also used in catalysts and in ignition devices (spark plugs).

Over the last few decades, the possibility of using iridium Q as a hgh temperature structural material has been evaluated. Several Ir-based intermetallics have been noted as having melting temperatures above 2000"C, such as IrNb with a Llo structure (3), IrAl with a B2 structure (4), and Ir,Nb or Ir3Zr with a L12 structure (5-6). However, Ir is an anomalous metal with a face centred cubic (f.c.c.) lattice that fails due to cleavage

Iridium single crystals fail in a brittle manner under tensile tests after an elongation of about 80 per cent at room temperature (9). However, polycrystalline Ir and its alloys normally exhibit intergranular or mixed intergranular and transgranular cleavage with limited ductility over a wide temperature range (10-1 2). Some researchers believe that intergranular fracture in polycrystalline Ir is caused by non-metallic impurities, such as carbon (C) and oxygen, or that it is environmentally induced (13). Other reports have proposed that the intergranular brittleness in polycrystalline Ir is intrinsic and not due to impurities at the grain boundary (14).

(7,s).

Much work has been done over the past three decades in attempts to prevent brittle fracture of Ir and its alloys and to improve their mechanical properties. Alloying (by macro-addition or micro- d o p a is believed to be one of the most effective ways to achieve this. Liu and colleagues found that adding a trace amount (below 60 ppm) of thorium (Th) to an Ir-0.3W alloy (the alloy currently used as a fuel-clad- material in radioisotope thermo- electric generators) could improve its strength and ductility, and change the fracture mode from intergranular to transgranular (15). A cerium-doped Ir alloy has also shown several similarities to Th- doped alloys (16). Wolff and coworkers reported that the addition of 0.5 at.% boron (B) to an Ir- 16Nb alloy could raise its strength and ductility at lower temperatures but caused a rapid fall in strength above 1100°C (17). Recently, Heatherly and colleagues investgated the effects of impurities in Ir and found that iron, nickel pi), chromium or aluminium (Al) at levels ranging from 50 to 5000 ppm do not embrittle Ir, whereas high levels of silicon cause severe embrittlement

While these research projects concentrated on single-phase alloys based on Ir (which may be less resistant to creep deformation than two-phase alloys) we focused on two-phase Ir-based alloys consisting of f.c.c. and L12 phases (19). We have proposed a new class of alloys based on Ir with a f.c.c. and Llz coherent two-phase structure similar

(18).

Pkzfinum Metalr Rev., 2002, 46, (2), 74-81 74

Fig. 1 Phase diagrams of iridium alloys, determined experimentally: (a) the tertiary system Ir-Nb-Ni at 1300°C (b) the quaternary system Ir-Nb-Ni-A1 at 1300°C

to that of Ni-based super-

(a) Nb

I

Atomic percent of Ni, at.%

I

f.&. f.c.c. + Ir3Nb + Ni3Al

Atomic percent d Ni, at.% alloys, and named them ‘refractory superalloys’ (20, 21). The coherent interface in the alloys appears to play an important role in strengthening alloys by preventing dislocation movements. We considered that if the Ir-based alloys (with melting temperature above 2000°C) have a f.c.c. and L12 two-phase coherent structure, then the alloys should show high

strength at hgh temperature. Such an alloy could then be used at hgh temperawe in situations where Ni-based superalloys cannot be used. A brief introduction to our primary work was given in this Journal by Wolff and W (22). Here, our recent results on the strength behaviour, creep

Phtinnm Me& h., 2002,46, (2) 75

Fig. 2 Precipitate shape of (u) lr-I5 ut.% Nb und (h) I r - I 5 at.% Zr alloys. These durk+eid images were takeii.jrom sirperlattice rejlectionsfrom the L12 phase. (c) Bright$eld image qf'un Ir-15 at. % ZI- ulloy

property, ductility and fracture mode of Ir-based alloys developed under the High-Temperature Materials 21 Project are reported.

Design Concept of Ir-Based Refractory Superalloys

According to the Ir binary phase diagrams given in Massalski (23), the f.c.c. and LlZ two- phase region exists, for example, in the Ir-V, Ir-Ti, Ir-Nb, Ir-Ta, Ir-Hf and Ir-Zr systems. We investigated the strength behaviour and deformation structure in these alloys (24,25), and Ir-Nb and Ir- Zr were found to be the most promising alloys for study with regard to their strength and microstructure up to 1200°C. However, the strength of these two binary alloys dropped off drastically above 1200°C. In attempts to improve the high-temperature strength, additions of molybdenum (Mo),

tantalum pa) and tungsten (W) with hgh melting temperatures (261 7,2977 and 3380"C, respectively) were added to the Ir-Nb alloy.

Another problem is that Ir-based alloys are very brittle and break by the intergranular fracture mode (26). In attempts to improve their ductility and change the fracture mode, different elements were added as the third element to the Ir-Nb alloy. In Ni-based superalloys, B is the element added to improve grain boundary strength and C is added

to stabilise the grain boundary. Therefore B and C were expected to improve grain boundary strength in Ir-based alloys. In addition to these trials, platinum (Pt), Ni and rhodium @) were also added to Ir-Nb alloys to characterise the structural con- nection and to find a suitable quantity of each to replace some of the Ir. These added elements may help to improve ductility.

Another trial involved combining the two- phase Ir-Nb and Ni-Al alloys and also the two-phase Ir-Nb-Ni and Rh-Nb-Ni alloys in order to check the two-phase regions in the combined systems. These two quaternary alloys can be expected to have the advantages of both systems - Q h strength at high temperature from the Ir-Nb and Ir-Nb-Ni alloys, and good ductility and low density from the Ni-Al and Rh-Nb-Ni alloys. These quaternary alloys could be described, respectively, as an Ir-Ni-based alloy or as an Ir-Rh- based alloy, containing some f.c.c. or L1, phase- forming elements.

Experimentally determined phase diagrams of Ir-Nb-Ni and Ir-Nb-Ni-Al at 1300°C are shown in Figure 1 (27,28). In the Ir-Nb-Ni system, the f.c.c. and L12 two-phase region expanded on addition of Ni. However, when too much Ni was added a third phase, Qr, Ni),,Nb,, was formed. In the Ir- Nb-Ni-Al system, contrary to our expectations,

Pkzhn#m Metah b., 2002, 46, (2) 76

Fig. 3 Comparisons of Ihe temperature dependence of the compressive strengths of four iridium-based alloys: Ir-12Zc Ir-l7Nb, Ir-ISNb-5Ni and Ir-13.5Nb-8Ni-2AI; with the nickel-based alloy (CMSX-10) (29), a niobium-based alloy (Nh-Si-Mo- W) (30). and a tungsten-based alloy (31)

2000

1500

a 4 v)- 1000 v)

LL c v)

3

s s z LL

500 lo00 1500 2000 TEMPERATURE, *C

the f.c.c. and Llz two-phase region was not connected from the Ni-Al side to the Ir-Nb side. Instead, a three- phase region, the f.c.c. and Llz-Ir3Nb and L12-Ni& appeared. However, there was no other phase of different structure in addition to the f.c.c. and Llz phase in the alloys that were tested. The quaternary Ir-Nb-Ni-Al alloy is very promising from the point of view of phase structure. Although exact phase diagrams for the Ir-Nb-Mo, Ir-Nb-Ta, Ir-Nb-W, Ir-Nb-Pt, Ir-Nb-B and Ir-Nb- C systems cannot be provided yet, the f.c.c. and Llz two-phase structure was confirmed in the following alloys: Ir-15Nb-5M0, Ir-l5Nb-Ta, Ir-lSNb-lOW, Ir-15Nb-30Pt (all measured in at.%) and in Ir-15 at.% Nb-500 ppm B, and Ir-15 at.% Nb-500 ppm C, by observation of their microstructure. For the Ir-Rh-Nb-Ni system, the f.c.c. and L11 two-phase region was observed over a wide area.

High-Temperature Strength Precipitate Morphology Effect

Precipitate morphology depends on the lattice misfit between the f.c.c. matrix and the Llz precipitates (21). Typical microstructures are shown in Figure 2. In the Ir-Nb alloy with a small lattice mis-

fit of 0.4%, cuboidal Llz precipitates formed, see

Figure 2a. However, plate-like precipitates formed in the Ir-Zr alloys where there was a large lattice misfit of 2% ( F i i e 2b), and a sern-coherent structure with many misfit dislocations also

formed (Figure 2c). Plots of the temperature dependence of the strength showed that the strengths of the Ir-Nb and Ir-Zr alloys were very hgh (> 1000 MPa) below 1200"C, although the strengths decreased dramatically above 1200°C (Figure 3). (Figure 3 also shows the strengths of a typical commercial Ni-based superalloy, CMSX-10 (29), a Nb alloy (30) and a W alloy (31) plotted for comparison as other hgh-temperature materials.) In both the Ir alloys the volume fraction of the L11 precipitates was 50%. Below 1200"C, the strength of the Ir-Zr alloy was higher than that of the Ir-Nb alloy. In these two alloys, solid-solution hardening and precipitation-hardening effects were both observed (32), with precipitation hardening being larger in the Ir-Zr alloy.

The deformation mode in the Ir-Zr alloy was by she- (25); on the other hand, shearing did not occur in the Ir-Nb alloy (33). In the Ir-Zr alloy, when a dislocation moves in the f.c.c. matrix, it

77

140

120

0

‘E, 100 .- tm

2 = 80

I‘ GJ

60 u + u)

U IT 40 U W a u)

-

20

500 1000 1500 201

TEMPERATURE, *C

meets numerous interfaces in the maze structure. The coherent interface has high-coherency strain energy in the maze structure, and a large number of misfit dislocations will prevent the movement of dislocations in a semi-coherent structure. This could be attributed to the high precipitation hardening of the Ir-Zr alloy.

The Effect of Element Addition In attempts to improve the high-temperature

strength of Ir-based alloys above 1200”C, we added Mo, Ta and W to a two-phase 11-15Nb alloy. Only Ta, at concentrations C 20 at.%, was found to be effective at improving the high-temperature strength. Additions of Ta > 20 at.% made the Ir-15Nb lose the f.c.c. and L12 two-phase structure, causing the alloy strength to drop greatly at 1200°C. Ad* W and Mo to the Ir-15Nb alloy only slightly improved its high-temperature strength even though W has a higher melting temperature and larger atomic size than Ta. Similar behaviour was also observed in the Ir-Nb-Ni and Ir-Nb-Ni-Al alloys (Figure 3). These results showed that a third element is not very effective at improving the strength at temperatures over 1200°C.

One of the biggest obstacles to using a two-

Fig. 4 The temperature dependence of the speciJk strength of (I6 Rh)rsNblsNiIn allo.vs. Small udditions of rhodium produce the strongest alloy

phase Ir-based alloy as a structural material at ultra-high temperatures may come from its lower specific strength (normalised strength to density), which is mainly caused by its higher density. To reduce the density, we med replacing Ir by Rh in an Ir-15Nb-1ONi alloy, which has higher strength at both room and high temperature. The effects of the replacement on the strength and ductility are shown in Figure 4. The quaternary (Ir75Rh25)75Nb15Nilo two-phase alloy had the highest specific strength of all the tested Qr, Rh)7sNb15Nilo alloys: 126 MPa g-’ cm-’ at room temperature, 81 MPa g-’ cm-’ at 1200°C, and 24 MPa g-’ cm-3 at 1600°C.

In the trial described previously, after the Ir-Nb alloy had been combined with the Ni-Al alloy, the density decreased; for example, the density of the Ir-lONb-42Ni-8Al alloy with three phases was 14.8 g cm-’. However, the strength and melting temperature also decreased drastically.

Creep Properties Compressive creep curves of the Ir binary and

ternary alloys at 1500 and 1650°C are shown in Figure 5. Although the strength of the Ir-based binary alloys above 1500°C was not very high, the creep strain was below 2% and tertiary creep was

PIatinrrm Met& Rey., 2002,46, (2) i a

Fig. 5 Creep curves (a) for the binary iridium alloys Ir-12.3 and Ir-17Nb at 1500°C under I3 7 MPa (b) for Ir-17Nb alloy and nickel- containing iridium-niobium alloys at 1650%, also under 137 MPa. The alloy containing the least amount ( I at.%) of nickel shows the best creep property

not observed until 300 hours. The creep resistance was %her in the It-Nb alloy than in the Ir- Zr alloy because discontinuous coarsening occurred from the grain boundary in the Ir-Zr alloy and its microstructure changed to a coarse structure during creep (34). This was due to the large lattice misfit in the h-Zr alloy. In the Ir-Zr alloys, the coherency

( a ) 1 M O *C

-? . 3 1

5 2.

L i . Ir-12Zr LL

Ir-17Nb

100 2 0 0 3bO TIME, HOURS

1650.C ( b )

Ir-15Nb-1ONi 3-

z z- a

1

I- v)

1 -

\

1650.C ( b )

I I

100 2 0 0 300

TIME, HOURS

strain energy of the interface was very hgh and coarsening of the maze structure was difficult to achieve. Discontinous coarsening was also observed in the lamellar structure of the Ti-Al alloy, for example (35). When the lamellae are very fine, coarsening often occurs by migration of the grain boundary (36).

At 1650°C, a tertiary creep was observed dear- ly in the binary Ir-Nb alloy after 20 hours, but ad- Ni to this alloy improved its creep resistance dramatically. As long as the Ni content is below 5 at.%, tertiary creep is not observed. The creep strains were below 2% after 300 hours for Ir- 15Nb-xNi alloys (x e 5). The steady-state creep rate for the Ir-15Nb-ZNi was 1.2 x 10" s-I, about three orders of magnitude lower than that of the

binary Ir-17Nb alloy d). The values of the steady-state creep rates for the Ir-15Nb-5Ni and Ir-15Nb-1ONi alloys were 2.1 X lo4 sd and 1.2 x lo-' s-', respectively. The great improvement in creep resistance of the Ir-15Nb alloy on adding Ni might be due to the effect of Ni on improving the grain-boundary strength and reducing the coarsening process.

Ductility and Fracture Mode Our previous investigation showed that poly-

crystalline binary Ir-based two-phase alloys normally exhibit intergranular fracture with limited ductility even in compression tests, as does pure Ir and its single-phase alloys (26). This result implies that the grain boundary in binary Ir-based two-

Phtinnm Me& &., 2002,46, (2) 79

1 o - ~

phase alloys is still a weak point. The large difference between the cohesion of the grain boundary and of the bulk is likely to cause the grain boundary to break before any dislocations form, as discussed by Hack et ul. (37).

An interpretation of the enhanced ductility in alloys prone to intergranular fracture (which hap- pens in many intermetallic alloys and other alloy systems) based on improved grain-boundary cohesion caused by B segregation has been at least partially successful. The fracture behaviour and compression properties of the 11-15Nb alloy doped with 80 to 2000 wppm B were investigated. The results showed that doping with B can change the fracture mode from intergranular (for the binary Ir-l5Nb alloy) to transgranular (for the B-doped alloys). However, we found that doping with B only shghtly improves the ductility of the alloy. We also found that even though the fracture mode for Ir-15Nb can be changed from intergranular to transgranular by adding Ni, W, Ta, Pt or Ni-Al, there is no obvious improvement in compression ductility by this change. The main reason is that the Ir-15Nb alloy, despite having additions of various elements, stiU fractures by transgranular cleavage at room temperature. This is due to apparently very strong and directed atomic bin- forces.

To stabilise the structure of polycrystalline Ni- based superalloys against high-temperature deformation, carbide formation is required. However, C is reported to be the main impurity causing polycrystalline Ir to crack in intergranular fracture (13). Our research has found no harmful effects due to C additions on the properties of the two-phase Ir-Nb refractory superalloy, even when the C additions were up to 2000 wppm. The compression ductility for C-free and C-doped alloys had almost the same value.

Possibilities for Ir-Based Refractory Superalloys

The high-temperature strength of Ir-based refractory superalloys above 1200°C did not improve on addition of a third element. Compared with the Nb-Si-Mo-W d o y in Figure 3, the strength of the Ir-based alloys above 1200°C is not remarkable considering their high melang temper-

ature. On the other hand, the creep property of the Ir-based alloys is remarkable. We tested a Ni- based superalloy, TMS-75, which has a rupture life of 196 hours under 98 MPa in a tensile condition at 1150°C (38). Under compressive stress at 1200”C, the sample buckled, and the strain could not be measured accurately. Another comparative test indicated that the compressive creep strain rates of an IrAl single-phase alloy with a B2 structure at 1100°C were between lo4 and s-’ under 100 to 220 MPa (39). The strain rate of ItAl at 1100°C was one or two orders of magnitude larger than that of our alloys (lo-’ s-’) at 1500°C.

This shows that our alloys, with the f.c.c. and L12 two-phase structure are more promising materials because of their high creep resistance. We also found that the creep life of Ir-Nb increased dramatically at 1650°C by addition of a third element, such as Ni. This shows that the Ir- based refractory superalloys may possibly be regarded as ultra-high temperature materials. Furthermore, the change in fracture mode on addition of Ni showed that there is a potential for designing high-temperature Ir-based alloys with both htgh-temperature strength and good ductility by addition of a suitable element.

Acknowledgement This work was conducted as part of the High-Temperature

Materials 21 Project. We thank Dr X. H. Y u from Manitoba University, who did part of this work during her stay at NIMS. We also thank Mr S. Nishikawa and Mr T. Maruko of Furuya Metal Co., Ltd. for the iridium.

References 1 “International Tables of Selected Constants”,

Vol. 16, ‘Metals: Thermal, and Mechanical Data’, ed. S. Allatd, Pergamon, Oxford, 1969

2 “Metals Handbook”, 9th Edn., ASM, Metals Park, OH, 1979, Vol. 2

3 R. L. Fleisher, R D. Field, K. K. Denke and R J. Zabala, Metal Truns. A, 1990,2lA, 3063

4 P. J. W, L. A. Cornish and M. J. Witcomb,]. A/&s

5 M. Bruemmer, J. Brimhall and C. H. Heneger, Mater. Res. SOC. Symp. Proc., 1990,194, pp. 257-262

6 A. M. Gyurko and J. M. Sanches, M&. Sci Eng., 1993, A170, 169

7 C. Gandhi and M. F. Ashby, Ada Metal., 1979,27, 1565

8 P. Pantilov and A. Yermakov, Platinum Metalr h., 2001, 45, (4), 179

co,.qd, i99a,280,240

Phtinum Metalj Rev., 2002, 46, (2) 80

1 o - ~

9

10

11

12

13 14 15

16

17

18

19

20

21

22

23

24

25

26

27

28

C. A. Brooks, J. H. Greenwood and J. L. Routbort, J. Appl Ply.., 1968,39,2391 C. A. Brooks, J. H. Greenwood and J. L. Routbort, J. IM. Met., 1970, 98,27 R W. Douglass and R I. Jaffee, Proc. ASTM, 1962, 62,627 D. L. Rohr, L. E. Mutr and S. S. Hecker, Metall Tmns., 1979, 1 0 4 399 J. R Handley, PkdnumMetOLr Rev., 1986,30, (l), 12 S. P. Chen, Phil Mag. A, 1992,66, 1 C. T. Liu, H. Inouye and A. C. Schaffhauser, Met& Trans. A, 1981,12A, 993 A. N. Gubbi, E. P. George, E. K. Ohriner and R H. Zee, Metdl Mah. Tmns. A, 1997,28,2049 I. M. Wolff and G. Sauthoff, Metal Trans. A, 1996, 27,2642 L. Heatherly and E. P. George, A& Muter., 2001,49, 289 Y. Ro, Y. Koizumi and H. Harada, Muter. Sci Eng., 1997, A223,59 Y. Yamabe, Y. Koizumi, H. Murakarm, Y. Ro, T. Maruko and H. Harada, Sm Muter., 1996,35, (2), 211 Y. Yamabe-Mtarai, Y. Ro, T. Maruko and H. Harada, Metdl Ma&. Trans. A, 1998,294 537 I. M. Wolff and P. J. W, Phtnum Metals Rm, 2000, 44, (4), 158 “Binary Alloy Phase Diagrams”, 2nd Edn. Suppl., ed. T. B. Massalski, ASM, Materials Park, OH, 1992 Y. Yamabe-Mitarai, Y. Ro, T. Maruko, T. Yokokawa, and H. Harada, “Structural Intermetallics 1997, TMS, Seven Springs, 1997, pp. 805-814 Y. Yamabe-Mitarai, Y. Ro, S. Nakazawa, T. Maruko and H. Harada, Dcf.ct D&. Foam, 2001, 188-190, 171 Yuefeng Gu, Y. Yamabe-Mtarai, Y. Ro and H. Harada, Sm Muter., 1999,40, (ll), 1313 Yuefeng Gu, Y. Yamabe-Mtarai, Y. Ro, T. Yokokawa and H. Harada, Sm Matm., 1998,39, (6), 723 X H. Yu, Y. Yamabe-Mitarai and H. Harada, Scr Muter., 1999,41, (ll), 1153

29 G. L. Elickson, “Superalloys 1996”, TMS, Warrendale, PA, 1996, pp. 35-44

30 C. L. Ma, A. Kasama, Y. Tan, H. Tankaka, R Tanaka, Y. Mishima and S. Hanada, Report of the 123rd Committee on Heat-Resisting Materials and Alloys, JSPS, Tokyo, 1999,40, (3), pp. 349-360

31 W. F. Brown, H. Mindin and N. C. Ho, “Aerospace Structural Metals Handbook”, CIDAS/Purdue University, Weat Lafayette, IN, 1992, Vol. 5, p. 5502

32 Y. Yamabe-Mitarai, Y. Ro, T, Maruko and H. Harada, Intmetaficf, 1999, 7, 49

33 Y. Yamabe-Mitarai, Yuefeng Gu, Y. Ro, S. Nakazawa, T. Maruko and H. Harada, Sm Mafm., 1999, 41, (3), 305

34 Y. Yamabe-Mitarai, S. Nakazawa and H. Harada, Sm Mater., 2000,43,1059

35 Y. Yamabe, N. Honjo and M. Kikuch~, JIMIS-6, Proc. Int. Symp. on Intermetallic Compounds, ed. 0. Izumi, Japan Inst. Metals, Sen& 1991, p. 821

36 J. D. Livingston and J. W. Cahn, A d a Metau., 1974, 22,495

37 J. E. Hack, S. P. Chen and D. J. Srolovitz, A d a Me&’., 1989,37,1957

38 Y. Koizumi, T. Kobayashi, T. Kimwa, M. Osawa and H. Harada, ‘Waterials for Advanced Power Engineering 1998”, Forschungszentrum, Jiilich, pp. 1089-1098

39 A. Chiba, T. Ono, X. G. Li and S. Takahashi, Intemehakcs, 1998, 6, 35

Authors Dr Yoko Yamabe-Mitarai is a Senior Researcher at the National Institute for Materials Science in Tsukuba. Her main professional interests are in high temperature materials, applications of the platinum group metals and intermetallics.

Dr Y. Gu is a Senior Researcher at the National Institute for Materials Science in Tsukuba. His main professional interests are in high temperature materials, applications of the platinum group metals and in intermetallics.

Professor H. Harada is Project Director at the National Institute for Materials Science in Tsukuba. His main professional interests are in high temperature materials, especially nickel-based superalloys.

The Chemistry of the Platinum Group Metals: PGM8 The eighth conference in th is series takes place

at Southampton University, U.K, from 7th to 12th July. Internationally-recognised speakers from the chemistry community will present their work on a wide range of platinum group metals chemistry. The

[email protected], Tel: +44 (0)20 7440 3322; Fax: +44 (0)20 7734 1227; or from the website: http://www.rsc.org/lap/confs/PGM8.hm.

Invitation to Students -~ ~~

main themes include: organometallic chemistry; coordination and supramolecular chemistry; biological and medicinal chemistry; surfaces, materials and crystal enginee-, photochemistty and electrochemistry; catalysis and organic synthesis; and theoretical chemistry and physical methods.

More information may be obtained from Ms P. Mohamed, Royal Society of Chemistry, E-mail:

Students attending the conference are invited to write an article of 300 words for Pkzfinum Metah Reyien, on one of the following a presentation, a series of presentations or an interview with a respect- ed academic attending the conference. The winning article will be published in Ph’iinum Mehah lZeview.

Further details will be available later and at the Ph’inum Metah Review desk at the conference.

Pfatinzm Metah h., 2002,46, (2) 81

2001 Nobel Prize in Chemistry TIMELY RECOGNITION FOR RHODIUM, RUTHENIUM AND OSMIUM-CATALYSED CHIRAL REACTIONS

William S. Knowles, a retired chemist from Monsanto Company, USA., and Professor Ryoji Noyori, Nagoya University, Japan, shared one half of the 2001 Nobel Prize for Chemistry for their work on chiral-catalysed hydrogenation reactions. Professor K. Barry Sharpless, Scripps Research Institute, U.S.A., received the other half of the prize for his work on chiralcatalysed oxidation reactions.

In nature, molecules, such as hormones, DNA, antibodies and enzymes, display the property of chirality. Such molecules have the same chemical formula but different spatial orientations, ma& a significant difference to their biological properties; for example, (R)-limonene smells of oranges, (S)- limonene smells of lemons. Chiral molecules in our nasal receptors can recognise these differences. Biochemical reactions are sensitive to chirality and the activity of a drug depends on the nature of the enantiomer. Many drugs are chiral, and it is essential that a drug is matched to the receptor in the cell to which it is directed. Mismatch will reduce the potency of the drug and could be extremely ham- ful. (S)-(+)-Ibuprofen is an example of a drug where only the (S) isomer is efficacious for anti- inflammatory use (1).

Enantioselective syntheses involve two major approaches: resolution or asymmetric synthesis. In resolution the mixture of chiral compounds is sep- arated by physical means whereas in chiral syntheses the novel concept is that a very small amount of catalyst can drive chemical selectivity towards the desired isomer. As an active catalyst can produce millions of molecules of optically pure compound, the waste associated with racemate resolution can be minimised.

Knowles’ Rh Catalysed Chiral Hydrogenation In the 1960s G. Wilkinson with J. A. Osbom (2)

synthesised the hydrogenation catalyst RhCl(Ph3P)3. At the same time L. Homer and K. M. Mislow synthesised optically active phosphines. Knowles combined these two discoveries. Using a Rh complex of (-)-methylpropylphenylphosphine he was

able to hydrogenate a-phenylacrylic acid to (+)- hydratropic acid in 15% ee. These results, along with reports by Homer, H. B. Kagan, J. D. Morrison and B. Bosnich, prompted him to investigate the prop- er match between ligand, metal and substrate to enhance selectivity. After much systematic work Knowles and colleagues at Monsanto were able to make the rare amino acid, L-DOPA, in 100% yield with 95% ee, using [Rh((R,R)-DiPAMP)COD]BF4 ( F i i e 1). Monsanto commercialised the process in 1974. It is recognised as the first industrial process using catalytic asymmetric synthesis. In the catalytic chiial hydrogenation cycle, Rho becomes R h o by oxidative addition of two H atoms. These H atoms are later transferred to the double bond in the substrate, and the catalyst is regenerated.

Noyori’s Rh and Ru Catalysed Hydrogenations Ryoji Noyori has worked in the area of chiral

catalysis from the mid-1960s and has sought throughout his career to understand chiral hydrogenation. The co-discovery of the ligand BINAP (3) and its applications in chiral synthesis was of great help. Other powerful ligands are now available, but BINAP is still one of the most versatile in chiral synthesis. Noyori’s enantiopure isomerisa- tion reaction of allylic amines to (R)-(-)-&ethyl- (E)-citronellalenamine in the presence of [Rh-(-)- BINAP(COD)]ClO, resulted in commercialisation of a multi-ton L-menthol process (Figure 2).

Noyori also used Rh-BINAP catalysts for the chiral hydrogenation of several a-(acy1amino)- acrylic acids or esters, and his work on BINAP- Ru(II) complexes is used for the enantioselective hydrogenation of a,P- and P,y-unsaturated carboxylic acids. The anti-inflammatory drug (S)-(+)- naproxen (Figure 3) is synthesised in very high ee

A wide range of ketones has also been hydrogenated with the aid of [RuX(arene)BINAP]X or p&(BINAp)] (X = halogen) complexes. The anti- bacterial agent levofloxacin is produced indusmally this way. Ru(II) BINAP complexes are also used in

and yield using ~u(OAC)~((S)-(BINAP)].

P b f i w m Metub &., 2002, 46, (2). 82-83 82

Me0 [Rh((R,R)-(DiPAMP)COD]BFt, - HO

AcO ' AcO ' NHAc no NHAc lobar H2, 25.C

L-DOPA ton 20.000, tof 1000 ti' yield; 95.1aee

Fig. I Industrial production of L-DOPA developed by Knowles using [Rh((R,R)-DiPAMP)COD]BF4'

100.C Fig. 2 [Rh-(-)-BINAP(COD)]ClO4'

manufacture is 'Curalysr the catalyst dotu.Jtom: of used L-menthol. in the

H. U Blaser. F. Spindler and M. Studer. Appl Caral. A . Gen.. 2001. 221. (1-2). 119

~ N E t ~ h - ~ - ) - ~ ~ A z l c l o ~ - tof 440 h-' bNE- b OH

... allylamine ... enamine L- menthol

A 94% ee

Fig. 3 (S)-(+)-Naproxen is

catalyst [Ru(OAC)Z((S)-BINAP)] c-0~ [Ru(OAC),((S)-BINAP)] COO" produced using Noyori k *

M e 0

(S)-(+)-naproxen (92.1. yield; 97% ec)

Me0

cinchona alkaloid (0.13 equiv.) Fig. 4 Catalyst oso4 as used in Sharpless' chiral dihydroxylation

production of chiral propanediol, and for an enantiopure azetidinone for carbapenem synthesis.

In recent years, Noyori has demonstrated asymmetric hydrogen transfer reactions in simple ketones, such as acetophenone. Addtng ethylenediamine in the presence of KOH in isopropanol enhances the activity of the Ru catalysts. The syn- thetically challenging substrates a,P-unsaturated ketones have been reduced with hgh ees and yields. The modified Ru BINAP complex, RuC12- (xylylbinap)(diamine) transforms enone to chiral ally1 alcohol with hgh turnover number. Noyori's work has been used in the pharmaceutical, agro- chemical, flavours and h e chemical industries.

Sharpless' Oxidation Chemistry In the 1980s, Sharpless centred his work on the

chiral oxidation of allyfic alcohols to epoxides, useful synthons for various organic compounds. Transformation utilises T i 0 tetraisopropoxide, t&-butylhydroperoxide, and enantiomerically pure ddkyltartrate. Choice of the appropriate tartrate hgand permits oxygen addition either to the top or bottom face of the ole&. Production methods for (R)- and (9-glycidol and methylglycidol have

resulted. Glycidol is used to produce P-blockers. The Sharpless epoxidation is also used industrially to produce the pheromone (7R,8S)-disparlure.

Sharpless also introduced 'hgand accelerated catalysis' where catalytic amounts of OsO4 and cinchona alkaloid were used with a stoichiometric amount of co-oxidant, N-methylmorpholine N- oxide, to give asymmetric dihydroxylation (Figure 4).

The platinum metals catalysts used in these reactions have contributed to their success and efficacy, and have formed an essential part of this most presugious award to Knowles, Noyori and Sharpless (4). Organometallic chemistry now sits M y in the main-stream of modem chemistry.

References 1

2

3

4 http://www.nobel.se

Thomas Colacot is Senior Development Associate for Chemicals & Catalysts, Johnson Matthey, West Deptford, USA. His interests are high throughput screening of catalysts for organic reactions, supported homogeneous catalysts and process development for new products.

S. C. Stinson, Cbem. Eng. News, 2001, 79, (a), 79; ibid., 2001, 79, (20), 45 M. L. H. Green and W. P. Griffith, Phtinam Met& Rey., 1998, 42, (4). 168 H. Nozaki, S. Moriuti, H. Takaya and R Noyori, Tetrahedron Lett., 1966,5239

THOMAS J . COLACOT

Phtinum Metolr Rev., 2002, 46, (2) 83

ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Palladium Nanoparticles Stabilised by Polyfluorinated Chains M. MORENO-MARAS, R PLEIXATS and s. VILLARROYA, Chem. Cornman., 2002, (l), 6 U l

Pd nanoparticles can be prepared by reduction of Naz(Pd2Ch) in the presence of compounds having long perfluorinated C chains (1) such as 1,5-bis(4,4'- bis@e~uor00ayl)-l,4-pentadien-3~1ne. The reduction is performed in MeOH at 60°C. (1) is the only constituent of the stabilising layer.

Influence of the Thermal Annealing on the Electrical Resistivity and Thermal Diffusivity of Pd:Ag Nanocomposites c . A. s. LIMA, R. OLIVA, G. CARDENAS T., E. N. SILVA and L. C. M. MIRANDA, &futm ha., 2001,51, (4), 357-362

Nanocrystalline Pd:Ag powder was formed by solvent evaporation of metal colloids. The obtained Pd:Ag powder was then compressed into compacts of - 250 p thick, 10 mm diameter wafers, and annealed at different temperatures for - 1 h. The electrical resistivity exhibited a sharp exponential decrease with increasing annealing temperature I 400°C. At > 400"C, electrical resistivity remained almost constant. The dependence of thermal diffusivity on increasing annealing temperature is complex.

CHEMICAL COMPOUNDS Oxidation of [Pt"Cl2(ethane-l ,2-diamine-N,N'- dicarboxylic Acid)] and Ligand Ring Closure in the Platinum(1V) Oxidation State P. N. WONG, M. s. DAVIES and T. w. HAMBLEY, A u s t . J. Chem., 2001,54, (5), 303-306

Oxidation of [Pt"Cl~(H~enda)] using HZOZ gives rise to a variety of products, including three crystal and two isomeric forms. The major product is the ring closed [pt'"Clz(enda)] and if the solution is heated under reflux for 24 h, t h i s is the only product.

Kinetics of Substitution of Aqua Ligands from cis- Diaqua(ethylenediamine)platinum(ll) Perchlorate by DL-Penicillamine in Aqueous Medium P. s. SENGUFTA, R SMHA and G. s. DE, Trunsition Met. Chem., 2001,26, (6), 63%643

The kinetics of the interaction of DL-penidlamine with [Pt(en)(HzO)Z]" were studied spectrophotomet- rically at pH 4.0. The reaction proceeds via rapid outer-sphere-association complex (1) formation, followed by two slow steps. The first is the conversion of (1) into the inner-sphere complex, independent of ltgand concentration, and the second is a slower chelation step, where another aqua ltgand is replaced.

Tris(pyrazoly1)methanesulfonate (Tpms) - A Versatile Alternative to Tris(pyrazoly1)borate in Rhodium(1) Chemistry w. UUI, D. SCHRAMM, w. PETERS, G. RHEINWALD and H. m ~ , Ear.]. Inotg. Cbem., 2001, (6), 1415-1424

TlTpms (Tpms = tris@yrazol-1-y1)methanesulfonate) reacts with m(LL)CI]z (LL = (C0)2, cod and nbd) to give TpmsRh(LL) complex. In solution, TpmsRh(C0)z (1) reversibly forms TpmsRh@-CO)3- RhTpms. TpmsRh(CO)(PR3) (PR3 = PPh3, PMe3, PCy3, P(Ph)2(PhS031C)) were obtained by reaction of (1) with the correspondmg phosphanes. IR studies indicate that Tpms is a weakly donating ligand.

Synthesis of Chloro(2-methylimidazole)ruthenium(lll) Complexes and Their Aqueous Solution Chemisby, and the Crystal Structure of [2-MelmHl2[RuCl52-MeIm1 CANDEMON, Can. J. Chem., 2001,79, (lo), 1477-1482

2-Methylimidazole reacts with RuCl3 in HCI-HzO- EtOH to give (2-MeImH)2~uCl@MeIrn)] and (2-MeImH) puCl@MeIm)~] (2-MeImH = protonat- ed 2-methylimidazole). The ratio of the products depends on the reacuon conditions employed.

ELECTROCHEMISTRY Temperature-Dependent Surface Electrochemistry on Pt Single Crystals in Alkaline Electrolyte: Part 1: CO Oxidation T. J. SCHMIDT, P. N. ROSS and N. M. MARKOVIC. J. Pbys. Chem. B, 2001,105, (48), 12082-12086

The continuous electrooxidation of CO in 0.1 M KOH electrolyte (cob) on Pt(h4 at 275 and 333 K was investigated. Significant reaction rates were observed even in the potential region for H underpo- tentid deposition (Hued). The cob oxidation on Pt (h4 involves a Langmuit-Hinshelwood type reaction between the adsorbed states of CO and 0H.d.

Electrochemical Properties of Pt-Modified Nano-Honeycomb Diamond Electrodes K HONDA, M. YOSHIhiURA, T. N. RAO, D. A. TRYK, A. FUJISHIMA, K. YASUI, Y. SAKAMOTO, K. NISHIO and H. MASUDA, J. EIectounuL Chem., 2001,514, (1-2), 35-50

B-doped nanoporous honeycomb diamond films modified with Pt nanoparticles (10-150 nm) were studied with CV and electrochemical impedance spectroscopy in acid solution. These electrodes showed high electroactivity for H adsorption and oxidation of MeOH, EtOH and 2-propanol. The current density (geometric basis) in the CV for MeOH oxidation at a Pt-modified porous film of pore diameter 400 nm and pore depth 3 p was enhanced by a factor of 16 compared to values obtained with a bulk Pt electrode.

Phfinam Metub Rev., 2002,46, (Z), 8 6 8 8 84

An Electrochemical Impedance Study of the Electrochemical Doping Process of Platinum Phthalocyanine Microcrystals in Non-Aqueous Electrolytes J. JIANG and A. KUCERNAK, J. Ekchand Cbem., 2001,514, (1-2), 1-15

The electrochemical doping process (1) of Pt phthalocyanine microcrystalline film (2) in MeCN was studied using electrochemical impedance spectroscopy. At low doping levels of (l), the rate of the first electrochemical step is slow and determined by the conductivity of (2). Once (2) becomes conductive, the electrochemical reaction is accelerated abruptly. Further increases in doping potential trigger another slow oxidation process.

Formation of Palladium Complex at Carbon Paste Surface in Chloride Solution as Studied by Cyclic Voltammetry IC-H. LUBERT, M. GU?TMA" and L. BEER, CoUect. Cpcb. C k . Co-n., 2001,66, (lo), 1457-1472

The deposition and dissolution of Pd at a non-modified C paste electrode was studied by CV in C1- solutions Q 0.5 M KCl and pH 3-6). Pdo was deposited from Pd"CL]% solution by potential cycling from E 2 0 V (vs. Ag/AgCl) or application of positive potentials or by potentiostatic treatment at E I 0 V. [pdnC1.] was formed on applying anodic potentials.

PHOTOCONVERSION Photochemistry of v-Hydrido-tetrakis(tertiary ph0sphine)diplatinum Complexes R. BOARETTO, S. SOSTERO and 0. TRAVERSO, J. Pbotocbem. Photobid A Cbem., 2001,144, (2-3), 101-106

The primary photoprocesses of trm-trum monohy- drido-bridged [(PEt3),HPt(p-H)PtH(PEt3)~][SPh,] and &u~J-& dihydrido-bridged [(PEt&HPt(p- H2)Pt(PEt3)2][SPh4] are homolyses of their Pt-Pt bonds. The Pt-Pt bond dissociation leads to cleavage of Pt(p-H)Pt and Pt(p-Hz)Pt yieldmg the reactive complexes [(PEt3)~PtHzl and [(PEt3)zPtH(S)] [SPb] (S = solvent).

Dendrimers Based on Ruthenium(l1) and Osmium(l1) Polypyridine Complexes and the Approach of Using Complexes as Ligands and Complexes as Metals S. SERRONI, S. CAMPAGNA, F. PUNTORIERO, C. DI PIETRO, N. D. MCCLENAGHAN and F. LOISEAU, Cbm. SOC. Rm, 2001, 30, (6), 367-375

The use of the 'complexes as hgands and complexes as metals' synthetic strategy for the preparation of luminescent and redox-active Os(Il) and Ru(II) den- h e r s is reviewed. The photophysical and redox properties of such dendrimers containing 2,3-dpp (2,3-bis(2-pyridyl)pyrazine) bridges are included. Alternative approaches to polypyridine dendrimers are briefly discussed. (27 Refs.)

Photochromic Atropisomer Generation and Conformation Determination in a Ruthenium Bis( bipyridine) Phosphonite y-Cyclodextrin System D. HESEK, G. A. HEMBURY. M. G. B. DREW, V. V. BOROVKOV and~ .~~ou~ ,J .h . &. Soc,2001,l23, (49), 1223Z12237

Irradiation of ra~-~u@py)~(PhP(OMe);)(CI)]Cl (1) at h > 460 nrn results in the photochromic generation of a new atropisomer and chirality inversion, via rotation of PhP(0Me)z around the Ru-P bond. The formation of a supramoleculai complex between (1) and y-cydodextrin allows the stabilisation of the new atropisomeric conformation.

Ruthenium Polypyridine Complexes. On the Route to Biomimetic Assemblies as Models for the Photosynthetic Reaction Center H. DURR and S. BOSSMA", Acc. C k . h~., 2001,34, (ll), 905-917

Photophysical data and the preparation of RI& complexes (1) from simple or more complicated bipyridine ligands, L, are reported. (1) with polyether bipyridines as building blocks, such as in Ru podates and coronates, were shown to be among the most photostable Ru complexes. Two-shell biomimetic model systems have more efficient electron transfer than one-shell systems. Covalently linked assemblies are more efficient in electron transfer. (41 Refs.)

ELECT R 0 D E PO S IT I 0 N AN D S U R FACE COATINGS Nanostructured Pt-Doped Tin Oxide Films: Sol-Gel Preparation, Spectroscopic and Electrical Characterization F. MORAZZONI. C. CANEVALI, N. CHIODINf, C. MARI, R RUFFO, R. SCOITI. L. ARMELAO. E. TONDELLO, L. E. DEPERO and E. BONTEMF'I, Cbem. Ma&.., 2001,13, (11), 43554361

Nanostructured (3-6 nm) thin films (80 nm) of SnO, and Pt-doped SnOz (1) were obtained by a sol-gel route using [Sn(OBu'),] and pt(acac)z] precursors. Glancing incidence X-ray diffraction measurements showed that P t o substituted for S n o in the lattice of the air annealed films. X P S established that the reaction of (1) with CO reduces P t o to P t O at 373 K and to Pt(0) at 673 K.

Computed Depth Profile Method of X-Ray Diffraction and Its Application to N iPd Films H. WU. B. LI, W. ML40. X InJ and K TAO, Sw$ Cod. Tecbnol, 2002,149, (2-3), 198-205

A method based on parallel beam XRD for profil- ing structure and phase distributions along with depth was used to characterise Ni/Pd thin films (1) and to obtain their phase depth profile. (1) were annealed at 380°C for 30 min. In the data analysis procession, the non-negative least squares algorithm was employed to resolve the ill-posed inverse problem that emerged in the solving procession.

Pldinnm Mekdr Rm, 2002,46, (2) a5

Electrochemical Evaluation of the Morphology and Enantioselectivity of Pt/Graphite G. A. ATTARD, J. E. GII.LIES, C. A. HARRIS, D. J. JENKINS, P. JOHNSTON, M. A. PRICE, D. J. WATSON and P. B. WELLS, Appl. Cai'al. A: Gen., 2001,222, (1-2), 39-5

Cinchona-modified Pt/graphite (1) is enantioselective for the hydrogenation of ethyl pyruvate to ethyl lactate at 1 bar pressure and 293 K. CV was used to investigate surface morphology, alkaloid adsorption and morphology change on sintering. CVs of (1) were interpreted using literature data for Pt single crystals. 0-induced surface reconstruction is lifted by reduction. Adsorption rates for cinchona alkaloids on (1) are: cinchonine > cinchonidine > dihydrocinchoni- dine. Cinchonidine adsorption is site selective during uptake from the acidic electrolyte solution. Sintering increases particle size.

Kinetics of Hydrogenation of 4-Chloro-2-nitrophenol Catayzed by Pt/Carbon Catalyst s. B. HALLIGUDI ands. s. KHAIREJ Chem. Technol. Biotechnot!, 2002,77, (l), 2528

Hydrogenation of 4-chloro-2-nitrophenol (CNP) catalysed by 1% Pt/C at 300 K and 21.3 a m Hz in a stirred pressure reactor gave 4-chloro-2-aminophenol (CAP) exclusively. Pdly-AlZO3 is also active in the hydrogenation; however, dechlorination of CNP or CAP occurs forming 2-nitrophenol and 2- aminophenol, respectively. From an Arrhenius plot of In rate vs. 1000/Tfor the Pt/C reaction an apparent activation energy of 22 kJ mol-I was estimated.

Molecular Weight Effects in the Hydrogenation of Model Polystyrenes Using Platinum Supported on Wide-Pore Silica J. s. NESS, J. c. BRODIL, F. s. BATES, s. F. HAHN, D. A. HUCUL and M. A. HILLMYER, Mammokaks, 2002,35, (3), 602-609

A kinetic study of the hydrogenation of model polystyrenes (PS) (molecular weight = 1.5276 kg mol-') using Pt/wide-pore SiOz catalyst was car- ded out. The initial rate of hydrogenation, r,, was found to be inversely proportional to the PS MW. For MW I 102 kg mol-I, r, scaled with the number- average degree of polymerisation, X,, to the -0.15 power. The two highest MW samples, 190 and 276 kg mol-', had significantly slower initial rates of hydrogenation and did not follow this trend.

Effect of Transition Metals on Catalytic Performance of Ru/Sepiolite Catalyst for Methanation of Carbon Dioxide L. LUO, S. Ll andJ. GUO, Chin. ]. Cai'd, 2002,23, (I), 85-87

The effects of adding Mo, Mn and Zr to Ru/sepiolite (1) catalyst was investigated for methanation of COz. The activity of (1) is closely associated with the electronic state on the Ru surface. Mo increases the active surface area, Ru dispersity, number of active sites, and poisoning resistance. When T I 674 K, the energy factor predominates and results in S (CHd)/S (CO) decreasing. Otherwise steric factors dominate.

Glucose Sensor Based on Au-Pt Black Electrode- Preparation of Functionally Different Sites on Electrode Surface 0. TAKEI. S. TOYAMA, M. SOMEYA, T. KUROKAWA, R USAMI, IC HORIKOSI and Y. Il(ARIyAMA, Ek&cb&try flpn.), 2001, 69, (12), 956-958

A glucose sensor has been developed based on a composite metal (Au and Pt) black electrode, fabri- cated by simultaneous codeposition of Au and Pt. Enzyme was immobilised at Au sites on the electrode surface, while enzymatic product was oxidised at Pt sites. a 6 0 moWo Au:Pd gave the largest response.

Sputtered, Electroless, and Rolled Platinum-Ceramic Membranes S. TOSTI, L. BETTINALI, S. CASTELLI, F. SARTO, S. SCAGLIONE and V. VIOLANTE,]. Membrane Sci, 2002,196, (2), 241-249

Sputtering, electroless deposition and rolling of thin Pd-Ag alloy films over ceramic porous tubes were used to produce Pd-ceramic composite membranes for Hz separation and production. In the sputtered (0.5-5 p) and electroless (2.5-20 p) membranes, thermal cydulg of the hydrogenated metallic layer produces membrane failures. Rolled (50-70 p) membranes, however, have a complete Hz selectivity and good chemical and physical stability.

H ETERO G EN EO U S CATALYSIS The Effect of Metal Order on the Oxidation of a Hydrocarbon Mixture over Alumina-Supported Combined Platinum/Rhodium Catalysts M. J. PATIERSON, D. E. ANGOVE and N. w. CANT, Appl. Catal. B: Envimn., 2001,35, (l), 5>58

The oxidation of a mixture of benzene, toluene, 1- hexene and isooctane in the absence and presence of CO was investigated over Pt/Al203 and Rh/AlzO, monolith catalysts arranged singly and in various 1:l and 4 1 combinations. Physical mixtures of the Pt and Rh are more active than the individual metals for complete removal of hydrocarbons when CO is present. Without CO, Pt is more active than Rh for aromatic and isooocme oxidation. Removing CO on Rh facilitates oxidation of benzene and isooctane on Pt. If Rh is put ahead of Pt in a sequential bed arrangement, the effect is maximised.

Adsorption and Decomposition of NO on Carbon and Carbon-Supported Catalysts J. ZAWADZKI and M. WI~NIEWSKI, Carbon, 2002, 40, (l), 119-124

The interactions of NO with C and C-supported catalysts have been studied by means FlTR spectroscopy. Direct decomposition of NO over C-supported catalysts (Pt, Cu) was investigated at 47-23 K NO conversion increased with increasing reaction temperature. Pt/C has a very hgh activity for NO decomposition, even in the absence of 0 2 .

Phfinum Metah Rev., 2002, 46, (2) 86

1405

Mw

APPARATUS AND TECHNIQUE

H 0 M 0 G EN EO U S CATALYSIS Stability and Thermodynamics of the PtCh Type Catalyst for Activating Methane to Methanol: A Computational Study J. KUA, x. xu, R. A. PERIANA and w. A. GODDARD, O ~ u n o m ~ f a ~ , 2002,21, (3), 511-525

The relative stability and reaction mechanism of Pt(NH&Clz and Pt@pym)Clz @pym = bipyrimidine) in concentrated H2SO4 were studied. The mechanism was found to involve a series of steps beginning with G H activation to form an intermediate ion-pair Pt(Il)-C& complex prior to forming a PtO-CH3 complex. The calculated relative activation barriers for C-H activation are in good agreement with experimentally observed H/D ratios. Subsequent oxidation to a P t o complex can occur with reduction of SO,. Release of methyl bisulfate regenerates the Pt(II) catalyst.

Microwave Promoted Palladium-Catalyzed Phenylation of Aroyl Chlorides and Sodium Tetraphenylborate J.-X WANG, B. WFJ, Y. HU, Z. LIU and Y. YANG, Jptb. cornrun.., 2001,31, (24), 3885-3890

Unsymmemcal ketones (1) can be synthesised from sodium tetraphenylborate and aroyl chlorides using Pd(pPh3)~Cl~ as the catalyst under microwave iitadia- tion. KF was the best base for the reaction. This method is simple, fast and affords good yield (8748%) of (1). The results show that the synthesis of (1) under microwave irradiation was 133 times faster than with conventional heating.

Synthetic Process Development and Scale Up of Palladium-Catalyzed Alkoxycarbonylation of Chloropyridines R C R E ~ A Z , J. WASER and Y. BESSARD, 0%. Pmte~s Res. Dw., 2001,5, (6), 572-574

Mono- or dicarbonylation of 2,3-dichloropyridines in the presence of CO, EtOH and Pd(OAc)z/dppf or PdCL(ph3P)~/dppb catalyst, gives selectively either alkyl 3-chloropyridine-2-carboxylates or dialkyl pyridine-2,3-dicarboxylates in good yields, depending on the reaction conditions. The process was used for the scale up of the monoalkoxycarbonylation of 2,3- dichloro-5-(trifluoromethyI)pyridine, giving ethyl 3- chloro-5-(trifluoromethyl)pyridine-2-carboxylate with high selectivity and yield.

Palladium-Catalyzed Intramolecular adrylation of a-Amino Acid Esters 0. GAERTZEN and S. L. BUCHWALD, J. erg. Chm., 2002,67, (2), 465475

A simple route to dihydroisoindole and tetrahy- droisoindole carboxylic acid derivatives involves the use of Pd-catalysed intramolecular a-arylation of a- amino acid esters. The best results in the cyclisation reactions used a slight excess of biphenyl-based, sterically hindered phosphines together with Pdz(dba),.

Rhodium-Catalyzed Conjugate Addition of Aryl- and Alkenyl-Stannanes to a,p-Unsaturated Carbonyl Compounds s. 01, M. MORO, H. ITO, Y. HONMA, s. MIYANO and Y. INOUE, Te@abedmn, 2002,58, (l), 91-97

Addition of aryl- or alkenyl-trimethylstannanes to a,P-unsaturated carbonyl compounds in the presence of a catalytic amount of P(cod)(MeCN)z]BF, and HzO affords the conjugate addition products in good yields. The use of HzO allowed the reaction to pro- ceed smoothly. The ary- or alkenyl-Rh complex, which is generated by the transmetallation from the organo-Sn compound, is proposed as the active catalytic species.

Catalyst Screening by Electrospray Ionization Tandem Mass Spectrometry: Hofmann Carbenes for Olefin Metathesis M. A. 0. VOLLAND, c. ADLHART, c. A. KIENER, P. CHEN and P. HOFMA", Cbem. EIK I., 2001,7, (21), 4 6 2 1 4 3 2 In sitrr synthesis of complexes combined with an

assay by electrospray ionisation tandem mass spectrometry has been employed to investigate [{R~P(CH~),PR~-K~P}XRU=CHR~+ in ring-opening metathesis polymerisation. The most reactive complex for acyclic olefin metathesis utilised chloride as the anionic ligand X, had a small chelating angle (n = l), and reduced steric demand of the substituents R (Cy vs. t-Bu). Variation of the carbene moiety CHR' had little influence.

Ring-Closing Metathesis, Kharasch Addition and Enol Ester Synthesis Catalysed by a Novel Class of Ruthenium(ll) Complexes B. DE CLERCQ and F. VERPOORT, Tetrabedmi h#., 2001, 42, (51), 89594963

Ru Schiff base complexes were shown to be good catalysts for the Kharasch addition of CCL across olehns. The yields depended on the catalyst and the substrate used. Also, ring-closing metathesis of diolehns was achieved. The best catalytic system was able to form tri- and tetrasubstituted double bond products. Stereoselective formation of enol esters or enynes in excellent yields was also achieved.

Highly Efficient Use of NaOCl in the Ru-Catalysed Oxidation of Aliphatic Ethers to Esters L. GONSALVI, I. W. C. E. ARENDS and R A. SHELDON, Chem. Commun., 2002, (3), 202-203

Ru-catalysed bleach a-oxidation of ethers was achieved without the need of an excess of oxidant by careful pH control during the reaction. Fast complete conversions (as short as 3 h) and high yields in esters (I 95%) were obtained by efficient reoxidation of Ru to the active catalytic species (Ru04) by optimal use of the terminal oxidant, NaOCl. CH2ClZ and EtOAc were employed as solvents. Using a stoichiometric amount of NaOCl, high substrate to catalyst ratios were possible in biphasic media at room temperature.

Pkdnzm Metah Rm, 2002, 46, (2) 87

FUEL CELLS Chemical and Electronic Effects of Ni in Rlwi and Pt/Ru/Ni Alloy Nanoparticles in Methanol Electrooxidation K.-W. PARK, J.-H. CHOI, B.-K. KWON, S.-A. LEE, Y.-E. SUNG, H.-Y. HA, S.-A. HONG, H. KIM and A. WIECKOWSKI, J. Phy. Chem. B, 2002,106, (8), 1869-1877

The electrooxidation of MeOH in H2SO4 was studied using Pt, Pt/Ni (1:l and 3:1), Pt/Ru/Ni (541 and 6:3.5:0.5) and Pt/Ru (1:l) alloy nanoparticle catalysts, in relation to MeOH oxidation processes in a DMFC. Pt/Ni and Pt/Ru/Ni exhibited excellent catalytic activities compared to pure Pt and Pt/Ru.

Synthesis and Characterization of Osmium Carbonyl Cluster Compounds with Molecular Oxygen Electroreduction Capacity R. H. CASTELLANOS, A. L. OCAMPO, J. MOREIRA-ACOSTA and P. J. SEBASTIAN, Int. 1. Hydrogen Energy, 2001, 26, (12), 1301-1306

A cluster electrocatalyst (1) is based on Os&O). (2) and Vulcan C; (2) w a s prepared by pyrolysis of Os3(CO)l2 in 1,2di&lorobenzene under Nz. The elec- trocatalytic parameters of the 0 reduction reaction for (1) were studied with a rotating disk electrode in 0.5 M H2S04 electrolyte. (1) used in a H2/02 P W C cathode is reported to perform nearly as well as a Pt one.

ELECTRICAL AND ELECTRONIC ENGINEERING Impacts of Postannealing Ambient Atmospheres on Pt/SrBi2.2Ta209/Pt Capacitors A.-D. LI, T. w, H.-Q. LING, D. wu, 2.-G. MU and N.-B. MING, J. Muter. Ref., 2001,16, (12), 35263535 Films of SrBizTa20p (SBT) were formed on

Pt/TiOZ/SiO2/Si substrates at 750°C in 02. SBT film capacitors were postannealed in Ar (Nz) at 356750°C and then reannealed in OZ at 750°C. Composition analyses show that Ar- or Nz-annealing at 750°C leads to Bi evaporation and 0 loss. After 550°C 100% Ar or Nz postannealing, the remnant polarisation decreases and the coercive field increases significantly. The subsequent 0 2 annealing can only partly restore the SBT phase; the ferroelectric properties cannot be rejuvenated.

Preparation of Pt-PtO, Thin Films as Electrode for Memory Capacitors K KURIBAYASHI and s. KITAMURA, Thin Solid Film, 2001, 400, (1-2), 160-164

Pt-PtO, thin films (1) were deposited on Si(100) at substrate temperatures of 36700°C by reactive r.f. magnetron sputtering with a Pt target. (1) mainly con- sisted of amorphous PtO and Pt30, (or Pt203) at < 400°C. The amorphous Pt in (1) increased as deposition temperature increased to 600°C. Pure Pt f h s of (1 1 1) orientation were formed at 700°C. The electr- cal resistivity of (1) was of the order 10-’-10-5 C2 cm.

The Influence of Surface Cleaning on the Stability of Pd/GaAs Contacts P. MACHAt, A. KANTA and v. PE~INA, J. Muter. Sci.: Muter. Ekctmn., 2001,12, (ll), 649-653

The thermal stability of Pd/n’-GaAs ohmic contacts with Ge and Sn layers was studied at 300 and 400°C. The Pd/Ge contact structures have better thermal stability than Pd/Sn. The Ge(20 nm)/Pd(lO nm) structure has two optimum annealing temperatures, the higher one producing ohmic contacts with slightly lower contact resistivity and better stability. Ge/Pd contact structures are based on solid phase regrowth mechanisms. The annealing mechanism is completely different in the Sn/Pd structures. Etching the G a A s wafers before metal deposition in HzS04: H202:HZO (1:8:500) followed by HC1:HzO (1:l) or in concentrated HC1 gives the best thermal stability.

Characterization of Hydrous Ruthenium Oxide/Carbon Nanocomposite Supercapacitors Prepared by a Colloidal Method H. KIM andB. N. POPOV,]. Po~erso#ms, 2002,104, (I), 52-61

Amorphous nanostructured composite electrodes based on RuOz (1) were loaded on C using a colloidal method. The colloids were synthesised from solutions containing various amounts of RuCl3.xH~0 adjusted with NaHC03 to pH 5. The electrochemical performance of the composite material depends on the annealing temperature and the particle size of (1).

MEDICAL USES Voltammetric Studies of the Effect of Cisplatin- Liposome on Hela Cells Y . - X . CI, Q. ZHAI, S. WANG, W.-B. CHANG, C.-Y. ZHANG, H. hiA, D.-Y. CHEN, M.-Z. ZHAO and s.-w. HU, Tuhntu, 2001,55, (4), 69M98

The effect of cisplatin-liposome on HeLa cells was studied using a voltammetric method (1). The peak current decreased with both cisplatin-liposome concentration and increasing treatment time. The decrease of peak current was in accordance with dam- age to the nucleus and loss of mitochondrial membrane potential. (1) may be a useful way to study the electron-transfer mechanism in drug-treated cells.

Study on the Microstructure and the Phase Composition of Two Precious Metal Dental Casting Alloys x ZHAO, x LAN and z. SHANG, Preciour Met. (Chin.), 2001, 22, (4), 13-16

Dental alloys Ag-30Au-15Pd-llCu (1) and Ag- 1 lAu-23Pd-9Cu (2) in the as-cast conditions consist of two phases: Ag-Pd-rich f.c.c. solid solution (a,) and Cu-rich f.c.c. solid solution (012). Au is evenly distributed throughout both phases. The as-cast microstructure of (1) consists of equiaxed g a i n s of al and a small amount of lamellar eutectic structure (a, + a2). (2) consists mainly of lamellar eutectic structure (a, + a2) and a small amount of (al).

Phdnum Met& Rev., 2002, 46, (2) 88

NEW PATENTS ELECTROCHEMISTRY Electrode for Water Purification H. E. ODONNELL et d US. &pL 2001 /0,042,682

An electrode (1) for HzO purification, includes an intermediate layer and a protective pre-coat layer (containing a Pt group metal). The former decreases leakage of current from an electrolyte solution direct- ly to the latter. A method to produce (1) is claimed. (1) has a longer service life and good current yield.

ELECTRODEPOSITION AND SURFACE COATINGS Chemical Vapour Deposition of Ruthenium Films APPLIED MATERIALS INC Ewupean&pL 1,178,131

Thin Ru films are deposited on a substrate by liquid source CVD using bis(ethylcyclopentadienyl)Ru, which is at room temperature. Deposition occurs in the kinetic-limited temperature regime. The bis(ethy1- cyclopentadieny1)Ru is vaporised at 100-300°C to form a CVD source material gas (1). Deposition onto the substrate is performed in a reaction chamber using (1) and 0 source reactant gas at - 10&500"C.

High-Purity Bis(ethylcyclopentadieny1)ruthenium TANAKA KIKINZOKU KOGYO KK wWkJ&pL 01/42,261

High purity bis(ethy1cyclopentadienyI)Ru is produced by hydrogenating bis(acetylcyclopentadieny1)- Ru (1) without causing corrosion. (1) is prepared by reacting bis(cyclopentadieny1)Ru (2) with acetic anhy- dride and H3P04 as catalyst, while (2) is prepared by reacting cyclopentadiene with Ru chloride and Zn powder. CVD formation of thin Ru or Ru compound films is also claimed for use in capacitors for ICs.

Fabrication of X-Ray Masks INT BUSINESS MACHINES cow U.S. Patent 6,287,434

An apparatus, for electroplating one side of a substrate for use in fabricating X-ray masks, has an anode positioned in an electrolyte. A Pt inhibitor electrode (1) is attached to the inner surface of the dielectric plate of the cathode. A Si substrate is attached to the inner surface of the cathode. (1) allows electroplating on one side of the substrate using a rack plating system.

Palladium Plating Solution KOJIMA KAGAKU YAKUHIN KK

Japanese AppL 2001/192,885 A Pd plating solution (l), for decorative and elec-

sonic uses, comprises ( i i g P, as metal equiv. amount): 0 . 1 4 soluble Pd salt, 0.01-10 of pyridine carboxylic acid (Pa) and/or 0.002-1 of soluble salt of Fe, Zn, 'l3, Se or Te, 0.005-10 of amine group derivative of PCA, and 0.001-1.2 of aldehyde benzoic acid derivative, and anionic or amphoteric group surfactant. (1) has stable properties and corrosion resistance and the Pd film has high purity, a mirror-like gloss and plasticity. Crack generation is suppressed.

APPARATUS AND TECHNIQUE Water Denitrification SUD CHEMIE MT Sfl Eampean&pL 1,178,017

Nitrates are removed from H20 by making it flow over a transition metal catalyst, preferably 0.01-5 wt.% Pd, on a porous carrier which can activate applied Hz, forming metallic hydrides (1). Denitr- fying bacteria, which can survive in the presence of Hz, adhere to (1). COZ is used to adjust the pH to 4.57.8. 0, is fed into the tank to convert nitrites.

Detecting Nitric Oxide UNIV DUKE U.S. Patent 6,280,604

An electrode (1) for rapid in vim detection of NO in biological samples, such as blood, urine, synovial fluid, lymph, surgical dramage fluid, etc., has a surface made of material containing Ru and at least one oxide of Ru which complexes with NO when exposed to a NO-containing fluid. (1) exhibits maximal NO response after pre-conditioning. Direct response to NO has been observed for the Ru electrodes at potentials I +675 mV vs. Ag/AgCl, while the para- doxical response of the Ru electrodes to NO occurs at potentials > +675 mV vs. Ag/AgCl.

Material for a Deflecting Colour Filter NATL INST ADV IND SCI TECHNOL

Japane~e &pL 2001 /147,326 Material for a deflecting colour filter comprises a

planar organic metal complex of Pd, Pt or Ni. Lght transmittance can be changed, depending on the viewing angle. By gradually increasing the angle of incidence, light transmittance is decreased. For light hitting vertically to the film surface, transmittance is - 90%. Light transmittance at a s p e d c wavelength depends on the incident angle of the hght.

Gas Sensor to Measure NOx Concentration NGK SPARK PLUG CO LTD ]apanese AppL2001/153,834

A gas sensor, for accurate measurement of NOx concentrations in ICES, motor vehicles, aeroplanes and boilers, comprises an exterior electrode and an internal electrode formed on an 0 ion conducting layer. The internal electrode comprises (ii wt.O/o): 0.1-25 Pd, 0.1-30 Au and remainder Pt An 0 pump cell controls the 0 concentration in the sensor void. 0 pumping capability is maintained for a long time.

Ozone Generator KI SAN JET PLASMA CO LTD b a n AppL 2001/007,966

An 0 3 generator using low activity plasma ion discharge effects to produce purified 0 3 has a discharge plate for low activity plasma ions. The discharge plate is prepared from a composite powder of Zr, Y, Ti, Al oxides and balance SiN. SiOz glass is added to form and sinter the synthetic ceramic sheets. Molten metal between the sheets contains 1.8-2.2 wt.% of Mo and 0.3-0.7 wt.% of Pt group elements.

Pkatinum Mehh Rm, 2002,46, (2), 89-91 89

Production of Epoxycyclododecane Compound UBE IND LTD Eumpean AppL 1,125,934

An epoxycydododecane compound (1) for producing the resin component for paints and adhesives, is produced by hydrogenating 1,2-epoxy-5,9-cyclodo- decadiene with HZ at 0.8-9 MPa pressure, in the presence of a long-life catalyst of Pt supported on activated C, Alz03, SO,, etc. (1) are produced in high yield at a high reaction rate. (1) can also be used to produce a lactam compound which is an intermediate for polyamide 12 and polyesters, useful for producing synthetic resins and fibres.

Purification of Naphthalenic Carboxylic Acid BP cow NORTH AMERICA mc WodiAPp/; 01/56,967

A naphthalenic carboxylic acid, especially 2,6-naphthalene dicarboxylic acid (2,6-NDA), is purified by contacting with a purification solvent in the presence of Hz and a Group VIII catalyst, such as Ru/C, at 52&575"F. 2,6-NDA is useful as a monomer in the production of dimethyl-2,6-naphthalene dicarboxy- late-based polymers for use in films and food and beverage containers. Reduced amounts of organic impurities are obtained in the purified acid.

Palladium Hydrogenation Catalyst SUED-CHEMIE AG WodillppL 01/58,590

A catalyst for hydrogenation of unsaturated hydrocarbons, such as selective hydrogenation of diolefins to monoolefins or of acetylenes to olefins, contains a catalytically-effective amount of Pd and optionally Ag on a support. The support comprises a moulding of tdlobal cross-section with holes through the lobes. Catalysts on a ailobal support have higher activiq and selectivity than usual and can be used at gas hourly spatial velocities of - 12,00&15,000, compared with only 3000-8000 when beads, tablets or extrudates are used. The pressure drop is also lower.

Production of Epoxide ARC0 CHEM TECHNOL LP WorMAppL 01/62,380

An epoxide, such as propylene oxide, is produced by reacting an olefin, HZ and 0 2 in the presence of a catalyst of Ti zeolite, Pd and Au promoter. The Ti zeolite is impregnated with a solution of a Pd compound and Au compound in a solvent, followed by solvent removal and diymg. Adding the Au promoter increases productivity and selectivity to epoxide.

Jet Engine Catalytic Converter P. BOURGON Canadian Appr 2,299,746

A catalytic converter for a jet engine is built into the engine and uses Pt anodised onto all the metal parts of the combustion chamber and turbine, except for any bearings used in these stages. The anodised Pt catalyses some of the &/fuel mixture in the engine. The engine becomes more responsive, smoother, ga ins more thrust across the power band, and lasts longer as there are fewer contaminating byproducts. Fuel economy is increased.

Hydrogenation Catalyst for Anthraquinones ASAHI KASEI KOGYO KK Japanese AppL 2001/170,485

A highly active hydrogenation catalyst (1) for anthraquinones is formed from a Pd component on support particles of diameter < 200 pn and bulk density 0.7-1.5 g ml '. The support is a SOz-based composition, with Alz03 and MgO in atomic ratio MgAI > 1/2. The Pd distribution is controlled and has surface area of 40-300 mz g-'. (1) is almost free from Pd loss and has excellent durability. The support has superior abrasion resistance.

Hydrogenation of Carbonyl Compounds BASF AG G e n n a n e L 1/00/09,817

A catalyst (1) used in hydrogenation of carbonyl compounds to alcohols at relatively low temperature (< 140°C) contains (in part wt.): 0.0001-0.5 Re, 0.00014.5 Pt and 0-0.25 of Ru, Zn, Cu, Ag, Au, Ni, Fe, Mn, Cr, Mo, W and V on activated C, sub- jected to non-oxidative pretreatment. (1) has higher total selectivity for the hydrogenation of carbonyl compounds to alcohols, without ether formation.

Catalyst Preparation by Chemical Vapour Deposition HYOSUNG T & c co LTD Korean Appl 2001 /046,425

A catalyst for the dehydration of hydrocarbons comprises (in wt.Yo): 0.1-2.0 Pt, 0.0-1.0 K, 0.1-1.0 Sn, and 0.0-1 .O Eu or Yb on an A1203-Al borate support. The support is prepared by mixing Al(N03)~ and H3BO3 with NH3 solution. The support has pore volume 0.4-1.0 cc g-', mean pore size 20&3000 A and surface area 25-1 50 mz g-'. CVD impregnates the catalyst active species onto the support by spray injection of the chemicals in the reactor at 800°C.

H 0 M 0 G EN EO U S CATALYSIS Carbonylation of Unsaturated Compounds SHELL INT RES MIJ BV WorM &pL 01 /68,583

Carbonylation of 3C or more ethylenically unsaturated compounds used in the preparation of detergents, involves reacting CO and hydroxyl- group-containing compounds in the presence of a catalyst system (1) in an aprotic solvent. (1) comprises a source of Pd cations, bidentate diphosphine and a source of anions derived from an acid having pK, < 3 at 18°C in an aqueous solution. High regioselec- tivity towards a linear product is obtained.

Manufacture of Cyclic Polyether Compounds KAGAKU GIJUTSU SHINKO JIGYODAN

Japanese AppL 2001/199,987 The manufacture of a cyclic polyether compound

used as s tar t ing material for the synthesis of natural substances, such as ciguatoxin, comprises cross-coupling an alkyl borane and cyclic enol phosphate, in the presence of a basic aqueous solution containing a Pd(0) compound which has a phosphine ligand, as the catalyst. The method can be used to manufacture cyclic polyether product, which is suitable for the synthesis of cyclic compounds larger than six- membered rings.

Pkafinwv Metals Rev., 2002, 46, (2) 90

H ETE R 0 G E N EO U S CATALYSIS

FUEL CELLS Electrode Catalyst for Fuel Cells NE CHEMCAT COW Eunpan AppL 1,156,543

A h@ly active electrode catalyst (1) for a fuel cell electrode, such as for SPEFCs, comprises 20-70 wt.% Pt on conductive C, which has 0 chemically bonded to it, at an atomic ratio of 0.7-3 to the Pt. Also claimed is an alloy catalyst prepared by deposit- ing a metal component which alloys with Pt in a Pt precursor, which is then reduced to form the alloy. (1) is also used in a membrane electrode assembly.

Proton Conducting Polymer Membrane JOHNSON M A m Y PLC WdAppL 01/69,706

A proton conducting polymer membrane of thick- ness < 100 p, for a membrane electrode assembly (MEA) and a fuel cell, comprises channels and/or capillaries (< 50 p) arranged in the z-direction of the membrane. Tow or yarn or Pt or Nb wires are placed or inserted into the membrane during its formation, The tow or yarn is subsequently removed to form channels; and/or the Pt or Nb is left in J-& to form capillaries. The membrane allows the supply of additional HzO to the system to sustain H20 elec- trolysis during cell reversal in a MEA or fuel cell. The hfEA exhibits improved performance at low reactant gas pressure.

Generation of a Hydrogen-Rich Fuel Gas Stream UOP LLC U.S. Patent 6,299,995

A H-rich fuel gas stream (1) is generated by passing a fuel stream over an 0-contahhg preferential oxidation catalyst at 70-160°C. The catalyst comprises Ru metal dispersed on an A1203 carrier with apparent bulk density of 0.2-0.4 g cm-3 and high porosity (average pore size 800-1500 A). (1) containing < 50 ppm of CO is passed to a fuel cell for electric power generation for a motor vehicle. CO is converted and high selectivity to COZ is maintained.

Platinum-Ruthenium Alloy Electrodes for Fuel Cells ISHIFUKU KINZOKU KOGYO KK

]+aneseAppl 2001/205,086 Catalysts loaded with Pt-Ru alloys, for fuel cell elec-

trodes, are prepared by reducing Pt ammine type complexes and Ru salts (not containing Cl) to a state where Ru bonds to C powder. Very fine Pt-Ru alloy particles are dispersed uniformly on the C powder support, and poisoning by CO is inhibited.

Selective Oxidation Catalyst for Fuel Cell MATjUSHITA ELEcTRlC WORKS LTD

J@anueAPpl2001/212,458 A selective oxidation catalyst (1) used for fuel cells,

particularly SPFCs, contains Ru and Pt on a porous carrier, such as a-Alz03, at a Ru:Pt weight ratio of 0.1-9.5. The Ru and/or Pt are localised in a layer 4 100 p under the outer surface of the porous carrier. (1) selectively oxidises CO in a reformed gas, at low temperature, by an 02-contahhg gas. Improved fuel and electricity generation efficiencies are obtained.

ELECTRICAL AND ELECTRONIC ENGINEERING Ceramic Capacitor Electrode-Forming Paste NGK INSULATORS LTD Eun@an&I. 1,178,493

A paste to form a ceramic capacitor electrode con- ta ins (in wt.?h): 10-14 of an organic vehicle and 8690 of Pt powder. The Pt powder contains pow- ders of spherical, flaky and indefinitely-shaped particles. The electrode layer film formed with the paste has density of 1 8W?, surface roughness of 0.44.6 pn and adhesion strength of 2 2 kg. There is improved adhesion to the dielectric layer and small through-holes can be made in the electrode layer.

Oxidation Stabilisation of Semicondutors MICRON TECHNOLOGY INC U.S. P&t 6,291,364

A catalyst matrix is used in high pressure, high temperature oxidation in Nz0 of a gate dielectric layer or cell dielectric layer on Si to stabilise the semiconduc- tor. Oxidation at 5-250 atm pressure and 600-750°C occurs in the presence of a catalyst selected from Pt, Ir, Pd, Rh, Pb, Ni or Ag and their oxides. The method and apparatus prevent N20 from becoming supercritical; temperature and pressure spikes are prevented. The exposure of semiconducting wafers to high temperature is minimised and undesirable diffusion prevented.

Chip-Type Multilayer Electronic Part TDK COW U.S. Patent 6,342,732

A chip-type laminated electronic part, for a multi- layered ceramic capacitor, comprises internal metal electrodes and terminal electrodes (l), which contain Ag and Pd as their main ingredients (&Pd = 7 3 to 3:7 wt. ratio). (1) also contain 0.1-1.0 wt% B. (1) are prevented from oxidising when the electrical part is joined to the substrate, so that improved electtical bonding to the internal electrodes is attained.

High Output Piezoelectric Ceramic NEC HYOGO LTD J+anese Appl. 2001 /146,470

A high output piezoelectric ceramic composition for oscillators, piezoelectric actuators, and ultrasonic motors, consists of ternary composite oxide system of Pb-Mn-Sb, Pb-Zr, and Pb-Ti. Piezoelecmc ceram- ics with a hgh exothermic threshold of oscillating velocity can be manufactured by sintering at low temperature together with Ag-Pd electrodes.

Reflecting Film for Liquid Crystal Display Elements FURIJYA KINZOKU KK [email protected] @I. 2001 /226,765

A heat-resistant reflecting film (1) for a LCD element, consists of Ag alloy material containing 0.1-3.0 wt.% Pd. Also claimed are: a laminate of one or more layers of (1); a LCD element using the laminate; and a portable device which can use the LCD element as reflector, reflecting film or bddmg glass material. (1) has improved heat-resistance, reliability and optical reflecting rate. (1) has enhanced bondmg with the substrate layer, glass substrate or resin substrate. Brightness is improved, due to reduced optical loss.

Phtinum Me& Rcv., 2002,46, (2) 91

5% Pd/C - Precise but Vague

pounds, imines and nitriles to amines; reductive amhadons/alkylations;

For liquid phase batch hydrogenations catalysed by supported platinum group metals ( p g m s ) , the most frequently used combination of metal and support is 5% palladium/carbon (Pd/C) paste (1). Catalytic hydrogenation is very widely used in industrial organic chemistry and includes reactions as diverse as carbon-carbon multiple bond reduction; aromatic ring saturation; reduction of carbonyl groups to alcohols or hydrocarbons;

Pd distribution Eggshell Intermediate Uniform

% Conversion after 1 hour 10 60 a5

metal distribution. At the other extreme the Pd can be evenly distributed throughout the particle: uniform distribution. Somewhere between these two extremes is the intermediate distribution. It does not follow that catalysts with eggshell distributions are invariably the most active. For example:

Pd salt used to impregnate the support; the nature and form of the reducing

- oc5'1. w/c ocoo" 150%. 100tur H2

Types of 5% Pd/C paste catalyst 1 2 3 4 5

Relative reaction rate 0 38 10 7 4

dehdogenation, removal of protecting groups; etc. For some pgm catalysed hydrogenations, Pd

would not necessarily be the metal of choice. For example, the reduction of aliphatic aldehydes to primary alcohols is best performed with a ruthenium catalyst (2).

However, in practice, about three quarters of all

liquid phase batch hydrogenations which use a heterogeneous pgm catalyst are in fact performed with 5% Pd/C paste. Some of the variables exploited in the manufacture of any given 5% Pd/C paste include: source of the acti- f i

At higher pressures, catalysts with the same total metal loading but deeper metal locations tend to be more active than those with eggshell distributions because of their &her metal dispersions.

In some extreme cases, certain 5% Pd/C paste formulations have no catalytic activity whatsoever and others can show a wide variation in reaction rate. For the reaction below, performed in an aka- line methanol solvent, the following relative reaction rates have been observed:

vated carbon support; pretreatment (if any)

crystallites on the support; pH and temperature of both the Pd salt impregnation and reduction steps; rate and order of addition of the reagents; efficiency of the final washing/filtration step; etc.

Clearly a vast number of combinations of the above is possible, all capable of yielding an end product that could accurately be described as '5% Pd/C paste' with each being assigned some unique identification code by the manufacturer.

One of the key parameters that can be controlled is the location of the Pd on the support. At one extreme the Pd can be entirely located at the surface of the individual carbon particle: eggshell

To achieve reproducible results, it is absolutely essential therefore to ensure that the same catalyst formulation, identified by the manufacturer's code, be used throughout any evaluation programme.

D. E. GROVE

References 1 2 See for example, "The Catalyst Technical

D. E. Grove, P&nwnMetalsReu., 2002,46, (l), 48

Handbook", Johnson Matthey, 2001

David E. Grove is a former Marketing Manager in Johnson Matthey Catalysts and Chemicals Division. His many years experience of the platinum group metals catalyst industry gives him a unique insight into typical user problems.

Phz'inum Metals Rev., 2002, 46, (Z), 92 92

- .

reduction of nitro and nitroso compounds, imines and nitriles to amines; reductive aminations/alkylations; hydrogenolysis, for example, hydro-

of the support; the nature of the soluble Pd salt used to impregnate the support; the nature and form of the reducing agent used to produce the Pd metal

platinum metals review · department of chemistry, university of new orleans, new orleans,...

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