reconversion catalytic deoxygenation of phenolic functional groups

8/12/2019 Reconversion Catalytic Deoxygenation of Phenolic Functional Groups

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Reconversion Catalytic Deoxygenation of PhenolicFunctional Groups

DE-FG22-93PC93208

Prof. Clifford P. KubiakDepartment of Chemistry

Purdue UniversityWest Lafayette, IN 47907phone: (317) 494-532 3fax: (317) 494-0239

Quarterly Technical Progress Report* for the period.October 1,1995 -December 31,1995

DISCLAIMER IThis report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neithe r the United State s Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsi-bility for the accuracy, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-ence herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by t he Un ited S tate s Government or any agency thereof. The viewsand opinions of authors expressed herein do not necessarily state or reflect those of the

.c4~~ ~

-2 3 0fl p524United States Government or any agency thereof.

*US/DOE Patent Clearance is not required primto the publication of his document


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2

Introduction to Catalytic Deoxygenation of Phenols by CO.

Recent research in our aboratories has established the viability of the catalyticdeoxygenation of phenols by carbon monoxide.' The deoxygenation of phenols is a problem ofboth fundamental and practical importance. The deoxygenation of phenols toarenes is aconceptually simple, yet a very difficult chemical transformation to achieve. The phenolic C-0bond energy of 103 kca.I/mol is as strong as a benzeneC-H ond and over 10kcal/mol strongerthan the C-0 bonds of methanol or ethanol.

D(C-0) = 103 kcal/mol/ 0-H) = 85 kcavmOlD(C-H)I 03 kcaYmo1

H

Catalytic hydrodeoxygenation (HDO)f phenols over sulfided Moly-Al203, Ni-Moly-Al2O3, Co-Moly-AI203 or other supported metal oxide catalysts can be achieved, atexceedingly high hydrogen pressures > 100atm) and temperatures > 200 OC)?-loArene ringhydrogenation generally competes effectively with hydrodeoxygenation,2*10and was found tooccur an order of magnitude faster than HDO.~ As a consequence, mostof the hydrogen isconsumed in hydrogenation of the aromatic rings. HDO catalysts are easily p~isoned.~Moreover, the HDO side product, water, is found to dramatically impairHDO activity byoccupying anion vacancies on the catalyst surfaces?

The im iciency of catalysts or phenol &oxygenation in the presence of hydrogen can beattributed to the absence of a low energy mechanistic pathway for he hydrogenolysis of thestrong phenol C-0bond We are currently studying new transition metal catalysts for theefficient and selective deoxygenationof phenols using the CO/CO2 couple to remove phenolic


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3oxygen atoms. The deoxygenation of phenols by CO, eq 1, is thexmodynamically favored byover 20 kcdmol; however, remarkably no commercial catalystsare yet available for thisimportant reaction.

O O H 1) +AG298= -20.7 kcdmol

The key to our studies involves the exploitation of the recently discovered insertion of CO intothe M - 0 bonds of metal phenoxides, eq 2, and subsequent decarboxylation to afford C02 and ametal phenyl complex,l eq 3,which can produce benzene by protonation or hydrogenation, eq 4and 5.

M a MIn contrast to hydrodeoxygenation of phenols, for which no obvious low energy pathways

exist for C - 0 bond rupture, the thermodynamic driving force forCO; limination, in eq 3, ishigh. Moreover, cooperative metal arene-.rc interactions or metal stabilized benzyneintekediates' are likely to be important in facilitating the deoxygenation by CO2 loss.

Our initialphases of research focus on identifying catalyst requirements essential for lowtemperature deoxygenation of phenols. These studies make use of soluble transition metalcatalysts and phenols. These well defined systems are chosen because they are amenable tofacile characterization by routine spectroscopic methods IR, NMR,UV-Vis) at modest


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4temperatures and pressures. The advantageof transition metal catalystsis that their studyprovides a richly detailed knowledge of fundamental chemical mechanisms for catalysis. Ourongoing studies focus on mono(ary1oxide) potential catalysts of the class: Jr(triphos)(O-Ph),[Pt(triph~~)(O-Ph)and Rh(triphos)(O-Ph).

This provides a series of compounds which are expected to have the following order of reactivitytoward CO insertion: Rh(triphos)(O-Ph)> Ir(triphos)(O-Ph) > [Pt(triphos)(O-Ph)].

Recent Resultson he Mechanism of CO Insertion into Metal-Oxygen Bonds ofPhenoxides. The term insertion is used in organometallic chemistry todescribe a wide varietyof reactions where an incoming group ends up between a metal and a previously bonded ligand.For carbonyl insertions into metal-alkyl bonds a large body of kinetic and mechanistic work savailable, and is the subject of several reviews.1-5 For all the transition metals an example ofcarbon monoxide reacting with a metal alkyl M-R) to produce a metal acyl (M-C(=O)-R) isknown. A variety of detailed mechanistic pathways are available for these reactions6

The first carbonyl insertionreaction to be studied in detail was the carbonylation ofCH3Mn(CO)5. Infrared spectroscopy was used by Calderazzo to study this system? Floodlater re-examined this reaction using 13CNMR and confirmed the stereochemistry at themanganese?y9 Specifically in Floods work, treatment of CH,Mn(CO),with 13C0yields onlyCH,C O))M~I CO), ~CO),here the labeled carbon monoxide is situatedcis to the acyl group,eq. 1.


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5

In addition, the product distribution after insertion was studiedwith cis CH~M~(CO),('~CO).The migration of carbon monoxide into the Mn - Me bond of cis CE~(CO) , ( '~CO)ouldgive a distributionof products where only the cis terminal manganese carbonyls would containthe 3cabel, eq 2. ~nhe reverse case, methyl migration, the ratio ofcis/truns 3cabeledterminal manganese carbonyls would be 2:1, q 3. A ration of 2:1was reported on the basis ofIR 13C stretching frequencies,'' and 13CN M R ntegration , confirming the methyl migration

2cis

1trans

1- (3)

For carbon monoxide insertion into platinum group alkyls one could be tempted by theavailable coordination site to propose a similarmigratory insertion mechanism with a fivecoordinate intermediate. lJ2 While this simple insertion mechanism is known for some squareplanar platinum alkyls, a second mechanism is more pre~a1ent. l~he secondmechanisminvolves dissociation of phosphine and formationof a cis fourcoordinate alkylcarbonylderivative, MXR(C0)L. Insertion then proceeds through a T-shaped 14 electron intermediatefollowed by phosphine filling the vacant site.13714 These reactions are faster for palladium thanfor platinum, and are faster for triarylphosphine complexes;both observationsare consistent witha mechanism involving displacementofphosphine. The necessity for ligand dissociation isunderlined by the inability of organoplatinum complexes containing chelating phosphine ligands


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6to undergo carbonyl insertion reactions. This mechanism is the one most commonly seen forcarbonylation ofplatinum alkyls. Formation of a five coordinate intermediate dominates theprocess in a few cases, but only after isomerization of the alkyl group to the apex of a squarepyramidalconfiguration.

For the late transition metal alkoxides several examples of carbonyl insertion into themetal &oxide bond are known. However, little solid kinetic ormechanistic information hasbeen reported. The best defined examples are thoseof Atwood for Ir(CO)(OPh)(PPh3)2,15-18Bryndza for Pt(dppe)(OMe)2,19S20and [Pt(triphos)(O-Ph)]+ described here.

There are two principal mechanisms by which late transition metal aryloxy complexescan be carbonylated to their respective at-yloxycarbonyls. The first is classical migratoryin~ertion,l-~~*here the aryloxy ligand migrates to a carbon monoxide cis to the aryloxy ligand,eq 4.

A second plausible mechanism is nucleophilic addition of a displaced aryloxide tocoordinated carbon monoxide. Thismechanism must be considered in view of the dissociativemechanisms observed for platinum alkyl ~arbonylat ionl~*~~nd the lower M OAr bondenergies expected for late transition metal aryloxy complexes2' This mechanism would proceedby substitutionofaweakly bound aryloxy ligandwith carbon monoxide, followed bynucleophilic addition of the displaced aryloxide to the carbonyl ligand, eq.5.-coL,,M-OAr ,M CO)+ + - 0A r M CO)OAr(5)

It was concluded by Bryndza that migratory insertion,eq.4, is involved in thecarbonylation of the platinum alkoxy complexes, Pt(dppe)(O-Me)@) R = OMe, Me), eq 6.2'


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7This conclusion was based on low temperature -80C) 13CN M R tudies, whereby a fivecoordinate carbon monoxide platinum adduct was observed, with a chemical shift of 184.9 ppm('J(C-Pt) = 1753Hz with no coupling to phosphorus observed. In the H NMR spectrum, themethoxy protons in Pt(d~pe)(O-Me)~re equivalent, indicating a square pyramidal structure forthis intermediate. Warming the solution to 2OOCresults in coalescence of the platinum adductresonance with that of fr carbon monoxide. These observations suggest that the first step ofthe carbonylation of Pt(dppe)(O-Me)@) R = OMe, Me) is a pre-equilibrium coordinationofcarbon monoxide to form a square pyramidal intermediate. The prospect of methoxidedissociation was ruled out by examiningCD,OD exchange with the complex. Under theseconditions, methoxide/methanol exchange occurs more than threeorders of magnitude slowerthan carbonylation. Furthermore, in the presence of carbon monoxide, the deuteriumincorporation into the finalmethoxycarbonyl is less than 596, the detection limit of protonintegration.

Atwood et al. determined that nucleophilic attack on coordinated carbon monoxidewasthe mechanism for carbon monoxide insertion into the Ir 0ond of Ir(CO)(O-Ph)(PPh,)2.'7During the reaction of Ir(CO)(O-Ph)(PPh3)2with carbon monoxide, the formation of anIr(CO)3(PPh3)z+ intermediate is observed spectroscopically. Infrared spectra taken during thecourse of the carbonylation reaction show the growth and then the loss of IR signals assigned to[Ir(CO),(PPh3)z]+. The amount of this intermediate is dependent on phenoxide nucleophilicity,with the intermediate being undetectable in the presence of more nucleophilic alkoxides.

Trogler found that the increased tendency toward heterolytic dissociation complicated thereaction of carbon monoxide with truns-PtH(O-Ph)(PEg),. Reaction with carbon monoxideyields trans-Pt(CO)z(PEt& as the major product, indicating reductive elimination as the


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8dominent reaction pathway.22 However, someP~H(PEs)~+s produced as a result of theincreased tendency of late transition metal alkoxides toward heterolytic dissociation.

Experimental Section

General Experimental DescriptionsCarbon monoxide (research grade) was purchased from Matheson and usedwithout

further purification. Acetonitrile, methylene chloride, andTH were freshly distilled fromunder a nitrogen atmosphere. THFwas freshly distilled from sodium benzophenone ketal.Deuterated acetonitrile (99.9 )was purchased from Cambridge Isotope Labs, stored undernitrogen, and used as received. All reactions and manipulations were carried out under anitrogen atmosphere using a nitrogen filled glovebox (Vacuum Atmospheres).

'P N M R pectra were recorded on a Varian XL-200 pectmme er. 'P N M R pectrawere referenced to external 85 H3P04 and were all proton decoupled.

Kinetic Experiments31Rates of carbnylation of 2a-c were followed by P{H} NMR at ambient temperatures

under carbon monoxide pressure. In a typical experiment, a pressure NMR tube (Wilmad) wascharged in an inert atmosphere box with a d3-acetonitrile solution of one of the platinum aryloxycomplexes, 2a-c. Experiments with excess aryloxide ligand required a 1:1 d3-acetonitrile:THFsolvent mixture. An initial P{ H}N M R pectrum was taken before the tube was pressurized(10 134 psi gauge) with carbon monoxide according to the procedure in chapter 3. Thereafter,31P{ H} NMR spectrawere taken at regular intervals, Figure 1. These intervals were controlledby arraying the PAD parameter in the Varian XL software package. A typical array in seconds is

31

PAD(1) = 5 , 5 ,a,0 60 60 600 600 600 600 600 600 m,m,m o00mm.Increasing the PAD delay during the experiment in this manner utilizes the software constrained


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9

18 data points more effectively and provides a good balance between obtaining at least 4halflives of data and accurately collecting data during the early part of the experiment.


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10

. . . . . . .a9.n u . s

Figure 1. Overlaid 31P{1H ) spectra showing the disappearanceof resonances correspondingto the aryloxide,2b, and the appearance of the aryloxy carbonyl, b.

2 a e

PB 2b)= 74.7 ppm

PB 3b) = 91.1 ppmt


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11Figure 2. 31P(H) spectra showing the disappearanceof trans phosphine associated withphenoxide and the appearanceof the trans phosphine of the aryloxy carbonyl.


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12l j I I I 10.9

0.8.- 0.7iii6 .60.5Q) 2b) p-Methyl Phenoxide0.4 1 P Y I I I I

0 2 4 6Time hr) 8 10

Figure 3. Reaction profile of the carbon monoxide insertion reaction.

12

0.50- 0.5

EQ, -1n

Q)xrvc- 1.5

-2-2.5

O:OO 01:OO 02:OO 03:OO 04:OO 05:OO 06:OO 07:OO 08:OO 09:OOTime Hrs . )Figure 4. Plot of -ln[Pt-Phenoxide] vs. time for the disappearance of 2b.


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13Figure 1-2 shows a seriesof plots of the peak intensities for the starting aryloxide at 74.7

ppm and product aryloxycarbonyl at 91.1 ppm. Signals corresponding to the starting aryloxycomplexes 2a-c and the carbonylated aryloxycarbonyl products, 3a-c, were integrated and theseintegrations were used in the kinetic data analysis. In the resulting reaction profile, Figure 3, itcan be Seen that the products are quantitatively produced from the reactants. Because thisreaction is under pseudo first order conditions, plotting -ln[Pt-Phenoxide] vs. time gives a slopeequal to the observed rate constant, kobs, Figure4.

Spin lattice relaxation times (TI) for 2a were determined by inversion recovery for PA4.8 s) and P, 3.4 s). Toobtain accurate integrations a 6 second recycle rate was used with a 2second acquisition time and minimized spectral width. It should be noted that care must be takenin obtaining these integrations; baseline correction must be turned off and each full spectrummust be individually phased.

The concentration of carbon monoxide in acetonitrile was determined by Henry's Law?3These calculations were based on the calibrated total volume of the tube and mole fractionsolubility of carbon monoxide in propionitrile 01= 6 . 3 0 ~ 1 0 ) ? ~ ~nder these conditions thecarbon monoxide concentration in solution is greater than the Pt complex, -80 m M s -20 mM,and pseudo first order conditions exist. While these concentration differentials do not meet thestrictest definitions of pseudo first order conditions, commonly a 10-100 fold excess of reagent,the reader is reminded of the low solubility ofcarbon monoxide in these solvents. This poorsolubility requires high pressures to achieve the reported concentrations, and results in thepresence of a large excessof carbon monoxide being present in the head space. The head spacethen acts as a reservoir o keep the carbon monoxide concentration constant, the importantrequirement of pseudo first order kinetics. Furthermore, given that the rates being studied arequite slow, there should not be interferencefrom he CO,,/CO equilibrium.gas

Results and Discussion


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14The kinetics of carbonylation are first order in [2a-c] to better than four half-lives, Figure

3, Table 1. Varying the carbon monoxide pressures from 50to 134 psi also indicated that theobserved rates were firstorder in [CO], Figures 5,Table 2. The reaction shows no observabledependence on the presence of excess aryloxide in solution. The addition of up to 37 equivalentsof aryloxide to the solution does not affect the rate, Table 2. These observations are consistentwith associative kinetics and suggest quite clearly that the carbonylations of2a c do not proceedby initial dissociationof the aryloxide ligand.

Table 1 Pseudo first order rate constants for the carbonylation of the aryloxy complexes(2a-a).

Compound k lo4) Hammett o 5[Pt(tIiphOS)(O-C6H,-F)][PF6] (2d) 1.703 0.06[Ft(triphOS) O-C6H4-H)] [PFg] 2C) 2.308 0.00

1.252 0.17[Pt triphos) O-C6H4-O-Me)]pF6] (2a) 1.031 0.27


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153.3

0 2 4 6 8 10 12 14Time hr)

F i p . Dependence of the observed rate ofpara methyl-phenoxide disappearance oncarbon monoxide pressure for [R(triphos)(C(O)O-C,H,-p-Me)][PFd (2b).

Table 2.[Pt(triphos)(O-C,H,-p-Me)] [pF6] on carbon monoxide pressure.

Dependence of the observed rate of carbon monoxide insertion into

PSI Iptl(mM) [COl(mM) k (IO4) R250 16.4 41 0.67 0.99474 12.6 61 0.98 0.993

100 13.6 82 1.25 0.984134 17.3 110 1.91 0.980


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16

I /

0 20 40 60 80[CO] M 100 120

Figure 6 . Plot of the change in the observed rate of para methyl-phenoxide disappearancevs. carbon monoxide concentration for [Pt(triphos)(C(O)O-C,H,-p-Me)][PFd (2b).

Table 3. Pseudo first order rate constants for the carbnylation of [pt(~phos)(o-c6H4-Me)][PF6] (2b) in the presence of excess phenoxide. Pressure is 100psi, [CO]= 82 mM.

eq.of excess kobs@-q R2. phenoxide

9 1.16 .97419 1.16 .99337 1.49 .982

none 1.36 .962


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17While these observations rule out a dissociative pathway, two associative pathways can

still be considered. The first pathway involves classical migratory insertion: axial association ofcarbon monoxide with the square planar complex followed by insertion into thePt - aryloxidebond, eq 8.

The second pathway involves an associative substitutionof aryloxide for carbonmonoxide, eq. 9-10 ollowed by nucleophilic addition of the displaced aryloxide to thecoordinated carbon monoxide, eq. 11.

l lC1 I l

IllC

(10)isplacement


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18In order to distinguish between the twomechanisms that describe associative kinetics

withcarbon monoxide, aryloxide ligand exchange and crossover were examined. When oneequivalent of Naoc6H4-p-R(R = OMe,H) s added to a sohtion of [P t( t~ ip hO S) (~ ~H ~- p-Me)][PF6] (2b) the 31P{1H}NMR hows twoproducts at equilibrium in solution, Figure 7, eq.12. These two products can be identified as [Pt(triphOS)(~6H4-p-Me)][pFBI 2b) andrPt(triphOS)(~6H4-p-R)]rPF6]221or 2c). The reaction is slow enough to enable theobservation of twodistinct species on the NMR ime scale, and the reaction is complete within20 min. This brackets the rate constant for exchange between 102s-l to 10-1s-. These N M Rstudies also facilitate the measurement of relative stability constants for the different platinumaryloxy complexes, 2a-e. Equilibrium constants of 0.75 f .2 for the ~t(triphos)(OC6H4-p-OMe)]+(2a)/[Pt(triphos)(OC6H4-p-Me)]+(2b)ystem,0.31f .2 for the [Pt(triphos)(OPh)]+(2c)l[Pt(triphos)(oC6H4-p-Me)]+(2b) system, and 0.23 f .2 for the [Pt(triphos)(OPh)]+(2c)[Pt(tripho~)(~~H~-p-OMe)]+(2a)ystem were obtained. These equilibrium constants should beconsidered within the context of the essentially thermoneutral behavior reported earlier for theexchange of platinum methoxides with methanol.2( When the equilibrated mixtures of platinumaryloxide complexes are reacted with carbon monoxide at 100psi, both insertion products appeartogether at rates comparabIe to those Seen for the same aryloxide complexes alone, Table 3.


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19

Pt OPh Me 2b) + Na OPh OMeMixing time = 16 min1P{1H}NMR

.... ....... cI

7 ) 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1

76 0 75.5 I 75 0 74.5 74.0Pt OPh Me tPt OPh OMe

2b) (24

Figure 7. Phenoxide self exchange, upper spectrum shows products at equilibrium after 16minutes.


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20

Table 4.exchanging mixtures.

Insertion rates for complexes 2 a-c), at 100psi as pure compounds and as

Aryloxide exchange is at least a factor of 1,OOO times faster than carbon monoxide insertion.Since aryloxide ligand exchange in these systems is so facile, aryloxide displacement by carbonmonoxide is also expected to be rapid, eq. 10. Thus, unless carbon monoxide coordinationprofoundly affects the rate of aryloxide dissociation,it is difficult to seriously consider aryloxidedissociation as the rate determining step in the carbonylation of 2a-e.

The rate of carbon monoxide insertion is also related to the electronic effects introducedby thepara substituentsof the aryloxides, Table 1. The rateof carbonylation for the morenucleophilic aryloxides is slower than the less nucleophilic aryloxides,Figure 8. These rates alsocorrelate well with Hammett cf values, Figure 9F7 Clearly, the opposite trend would beobserved if nucleophilic addition of the displaced aryloxide, eq 11 was the rate determiningstep. The presence of excess aryloxide would also affect the rate if nucleophilic addition tocoordinated carbon monoxide were rate determining. This was not observed. These resultsremove nucleophilicadditionof displaced aryloxide to coordinated carbon monoxide, eq 11, asa reasonable rate determining step. Overall, the facility of aryloxide exchange together with thedecreased rates of carbonylation for platinum complexes of m r e nucleophilic aryloxide ligands


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21cannot be reconciled with the carbon monoxide induced aryloxide dissociation mechanismsummarizedineq.9-11.

I I I I I I I0 1 2 3 4 5 6 7 8Time Hr.)

Figure 8. Dependence of the observed rate aryloxycarbonyl formation on the aryloxidesubstituent.


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22

tWVIDa

2.600

2.200

1.400

-0.3 -0.2 -0.1Harnmett Sigma

0 0.1

Figure 9. Correlation of the observed rate to Hammett Sigma of the phenoxide substituents.

The relative stability constants of the aryloxide complexes 2a-c and the electronicinfluence of p-substituents on the aryloxide ligands both indicate the importance of Pt 0 bondbreaking in the carbonylation mechanism. When AG, calculatedfrom he relative stabilityconstants, is compared to AE,, calculatedfrom elative rates for carbonylation, a linearrelationship is found,Figure10. For example, the AG or the ~(triphos)(O-Ph-Me)]+2b) /[Pt(triphos)(O-Ph-OMe)] (2a) equilibrium is calculated to be 0.71 kJ/mol and AE, is 0.48kJ/mol. In the [F (triphos)(O-Ph-Me)]' (2b) / [Pt(mphos)(O-Ph)]+ 2c) equilibrium,AG is 2.87kJ/mol and is 1.52 kJ/mol. Finally for the [Pt(triphos)(OPh)]+ 2c) / [Pt(triphos)(OC,H,-p-OMe)]+ 2a) equilibriumAG s 3.59 kJ/mol and LIE is 1.99kJ/mol.


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23

1.6

f(x) =0.534x +0.0; R2 0.9951

0 0.5 1 1.5 2 2.5 3 3.5 4AG (kJ/mol)

Figure 10. Plot of AEa vsAG

From this linear free energy relationship it can be seen that differences in Pt - 0 bond energy,determined from the relative stability constants, contribute to the activation energy forcarbonylation.28 This supports the notion that pt 0 bond breaking is important in theformation of the transition state. This is further supported by the dependence of the observedrates of carbon monoxide insertion on aryloxide ligand p-substitution. More nucleophilicaryloxide ligands are slowerto carbonylate since a strongerpt - 0 bond must be broken.Together these data support our assertion of a classical migratory insertion pathway, eq 4, orthe carbonylation of 2a-e. While little is known of the structureof the transition state involved,we find that approximately half of the difference in Pt 0 ground state bond energies is


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24

contributed to the activation energy for carbonylation. We also note that migratory insertion ofcarbon monoxide only occurs into the Pt 0 bond of Pt(dppe)(Me)(OMe), and not the availablePt C ond.20 This preference was attributed to the interaction of the oxygen lone pairs with thecarbonyl x* orbital,Figure11.

Figure 11. Interaction of the carbonylA orbital with the aryloxide oxygen lone pair.

Thus, part of the C - 0 bond is formed prior to completePt - 0 bond ~leavage.2~his effectwould stabilizethe transition state and accelerate the rates for the more nucleophilic aryloxides, atrend opposite to that observed experimentally. In the [pt(triphos)(O-Ph)]+ system we believethat a transition state model like that shown in Figure 11is plausible for the carbonylation ofaryloxides, but in our system the influence of Pt 0 bond breaking relative to C 0 bond makingdominates.

It is interestingto note that while we arrive at the same mechanistic conclusion asBryndza, regarding the carbonylation of platinum aryloxide complexes, the two systems havediffering exchange conditions. In the Pt(dppe)(OMe), system, methoxide exchange is found tobe slow with respect to insertion.2' In the aryloxide systems, 2a-e, aryloxide exchange is fasterthan insertion. Yet, in both systems, the mechanism of carbonylation is a classical migratoryinsertion of the alkyl or aryloxide ligand to coordinated carbon monoxide.


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25ListofReferencesWojcicki, A. Adv. Organomet.Chem. 1973,11,87.Kuhlman,E. J.; Alexander, J. J Coord Chem. ev. 1980,33,195.Flood,T. C. In Topics in Organic and Organometallic Stereochemistry ;G.L Goeffroy,Ed.; Topics in Stereochemistry; Wiley: New York, 1981; Vol. 12;pp 83.Mechanisms of Inorganic and Orgamm etallic Reactions;Twigg, M . V., Ed.; Plenum:New York, 1984;Vol. 2, pp 259.Alexander, J. J. In The Chemistryof the M etal-Carbon Bond ;F. R. Hartley,Ed.; Wiley:New York, 1985, Vol. 2.Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applica tions ofOrganotransitionMetal Chemistry ;University ScienceBooks: Mill Valley, 1987;Vol.p 989.Calderazzo, F.; Cotton, F. A. Inorg. Chem. 1962,1,30-36.Calderazzo, F. A n g m . Chem. Int. Ed. Engl. 1977,16,299.Flood,T. C.; Jensen, J. E.; Statler,J. A. J. Am. Chem. SOC. 1981,103,4410-14.Noack, K.; Calderazzo, F. J Organomet. Chem . 1967, IO, 101-104.Klein, H. Angew. Chem. Int. Ed. Engl. 1973,12,402.Booth,G.; Chatt, J. J Chem.SOC.A. 1966,634.Anderson, G K.; C ros s , R. J. Acc. Chem.Res. 1984,17,67-74.Garrou, P. E.; Heck, R.F. .Am. Chem.SOC. 1976,944115.Churchill, M. R.; Fettinger,J. C.; Rees, W. M.; Atwood, J. D. J Orgammer. Chem.1986,304,361,Churchill, M. R.; Fettinger,J. C.; Rees, W. M.; Atwood, J. D. J Organomer. Chem.Rees, W. M.; Churchill,M. R.; Fettinger, J. C.; Atwood J D. Organometallics 1985,4,

Rees,W M.; Atwood, J. D. Organometallics 1985,4,402.

1986,304,227-238.

2179-2185.

(19) Bryndza, H. E.; Kretchmar, S. A.; Tulip, T. H. J Chem. OC.,Chem. Commun. 1985,I4,977-8.(20)(21)

Bryndza,H. E. Organometallics 1985,4,1686-7.Bryndza, H. E.; Fong, L. K.; Paciello,R. A.; Tam,W.; ercaw, J. E. J Am. Chem. SOC.1987,109,1444-56,


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26(22) Cowan, R.L.; Trogler, W. C. J .Am. hem. oc. 1989,111,4750-61.(23) Fogg,P.G. T.; erard, W. Solubility of Gases in Liquids, A Critical Evaluation ofGaslLiquid Systems in Theoryand Practice ; ohnWiley and Sons: New York, 1991;VOl. p(24) At the timeofwriting no accurate solubility data for carbon monoxide in acetonitrileexists in the literature.(25) McDaniel, D. H.; Brown,H. C. J Org. Chem. 1958 ,23,420 .(26) Bryndza, H. E.; Domaille, P. J.; Tam, W.; Fong,L.K.; Paciello, R. A.; Bercaw, J. E.Polyhedron 1988,7,1441-52.(27) A plot of the rate ofcarbon monoxide insertion versus Hammet Sigma gives a best fit lineof kobs= 5.16 s + 2.20.(28) Gaset, A.; Constant,G.; Kalck,P.; Villain, G. J Mol. Catal. 1980,7,355.(29) Bryndza, H. E.; Tam,W. hem.Rev. 1988,88,1163-88.

reconversion catalytic deoxygenation of phenolic functional groups

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