chapter 30. inorganic and organometallic polymers

job:L00985F 9-9-1998 page:1 colour:0

30 Inorganic and organometallic polymers

By IAN MANNERSDepartment of Chemistry, University of Toronto, 80 St. George St., Toronto M5S 3H6,

Ontario, Canada

1 Introduction

Polymeric materials based on inorganic elements continue to attract attention as aresult of their interesting and unusual properties and applications as speciality ma-terials.1—4 This review focuses on developments in inorganic and organometallicpolymer science published in 1997 and has a similar format as and follows on from thethree previous articles in the series which cover the years 1991—1996.5—10 The firstsections of the review cover new developments concerning the inorganic polymersystems based on main group elements including the well established polysiloxanes,polyphosphazenes and polysilanes.1—3 A brief introduction to each of these classes ofinorganic polymer systems was included in the appropriate sections of the first articleof this series.5 Following this section, recent developments concerning polymers basedon transitionmetals are discussed.4 As with previous articles in this series,5—10 the mainemphasis is placed on polymers with inorganic elements within the main chain ratherthan in the side group structure. A review of inorganic polymer science, which focusesmainly on the new polymer systems prepared recently was published in 1996 and mayalso be of interest to readers.11

2 Polysiloxanes (silicones), polysilanes and other silicon-containingpolymers

Molenberg and Moller have reported detailed studies of the structure and phasetransitions in poly(diethylsiloxanes) using differential scanning calorimetry (DSC) andtransmission electron microscopy (TEM) studies on replicas of freeze-fracturedsamples.12 The diethyl-substituted polymer is the first member of the series ofpoly(dialkylsiloxanes) which is capable of forming a mesophase and forms differentcrystalline polymorphs. Narrow molecular weight samples were prepared via anionicring-opening polymerization (ROP) of hexaethylcyclotrisiloxane (Scheme 1). Usingthis system, above M

n[ 105 the polydispersity broadens to above 1.3. A number of

interesting observations were apparent from studies of samples with different molecu-lar weights. Thus, the isotropization temperature was found to strongly depend onmolecular weight. In addition, no mesophase was formed below a critical value ofM

n\ 28 000.

Royal Society of Chemistry — Annual Reports — Book A

603

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http://dx.doi.org/10.1039/ic094603

http://pubs.rsc.org/en/journals/journal/IC

http://pubs.rsc.org/en/journals/journal/IC?issueid=IC998094


OSi

O

SiO

Si EtEt

Et Et

Et Et

O Si

Et

O SiMe3

Et

BusEt2Si

BusEt2SiOLicryptand 211 Me3SiCl

n

Scheme 1

Si(OEt)2(EtO)2SiClCH2Si(OEt)2ClMg

THF

OEt

Si CH2

OEt n

Karstedt

catalyst1

2

1

1 or 2 Si(O) CH2n

H2O(H+)

hydrolysis

–H2O/EtOH

condensation

N2, pyrolysisSiOxCy

Scheme 2

CH2 CHPh

CH2 CH MePhSiBus Hn m

3

BusLi i Si4Ph4Me4

ii H+

Scheme 3

In other areas of polysiloxane chemistry, research has focused on ferroelectric liquidcrystalline materials based on biphenylcarboxylate mesogenic groups andoligooxyethylene spacers.13 In addition, work on the ethanol permselectivity ofpoly(dimethylsiloxane) membranes and the control by surface modification by addi-tives has been described.14 Research targeting silicon oxycarbide ceramics via thepyrolysis of polycarbosilane/polysiloxane hybrid polymers has also been reported.The hybrid materials were prepared via sol—gel processing of cyclic carbosilanes 1 andpolycarbosilanes 2 containing ethoxysilane moieties (Scheme 2).15

Moller and co-workers have reported studies of a polystyrene—polysilane blockcopolymer 3 with a polystyrene block with M

n\ 18 700 and poly(methylphenylsilane)

block with Mn\ 9000.16 This material was prepared via the anionic ROP of cyclo-

silane using living polystyrene anions (Scheme 3). Microphase separation was ob-served and for the aforementioned material by TEM of a thin section of a film whichwas cast from THF, which is slightly selective for the polystyrene block. Poorly definedwormlike domains of polysilane were observed in a polystyrene matrix. After exposureto UV light which photodegrades the polysilane blocks, a texture consistent with theTEM results was detected by scanning force microscopy.

A remarkable thermo- and ion-responsive non-ionic water soluble polysilane 4 hasalso been reported.17 This polymer shows a j

.!9\ 281nm which is blue shifted from

the usual value when dissolved in water. This was attributed to the reduction in thedegree of conjugation due to the presence of a more distorted polymer backbone as a

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Si Si

R RR

R n

BunLi

THF

MeOH

5 6

Scheme 4

consequence of strong solute—solvent interactions. Above the lower critical solutiontemperature at 46 °C (concentration\ 0.40m) the solution turns opaque due to theabrupt onset of light scattering due to association. In addition, an instantaneousbathochromic shift of j

.!9from 281 to 320nm is observed suggesting increasing

p-delocalization. Interestingly, the LCST can be tuned via the addition of inorganicsalts.

Me

Si

OO

Me3

n

4

Studies of the photodegradation of poly(phenylmethylsilane) using GPC/light scat-tering analysis have also been reported.18 In addition, adjacent reentry of foldedpoly(dimethylsilane) polymer chains has been established using atomic force micro-scopy.19 Molecular scale resolution of poly(dimethylsilane) single crystals using AFMrevealed rows of rod-like features which were much longer than the Si—Si bond lengthwhich were assigned to chain folds at the single crystal surface, as expected for theregular adjacent reentry model.

Anionic polymerization of 3-methylenesilacyclobutanes has been reported byYamaoka and co-workers.20 Reaction of the silacyclobutane 5 wih BuLi in THF at[78 °C followed by treatment with methanol yielded the novel polycarbosilane 6.This material could be hydroborated with BH

3·THF and after alkaline hydrolysis a

hydroxyl functionalized material could be isolated (Scheme 4). Cyclopropanation wasalso attempted but side reactions were also observed.

Yokoyma and co-workers have described the formation of gold colloids inAu/poly(methylphenylsilane) layered films by heat treatment which depends on UV-light pre-exposure (Fig. 1).21 Colour variations were detected only in the areas of thepolysilane films which were exposed to UV light prior to Au film deposition. Studiesindicated that the thermally induced Au colloid formation is strictly related to thedegree of photodecomposition of the polysilane surface. The Au/polysilane layeredfilms were used as novel materials for write-once laser optical disc memory. To achievethis a Ti phthalocyanine layer was vacuum deposited under the polysilane layer.Optical recording was performed using a laser disc head equipped with a diode laser(830nm) focused on a tiny spot in the TiOpc layer. The recording process of pitregistration was monitored by the reflection of a stationary low power laser. A distinctdecrease in the reflectance of the monitor light intensity from the Au surface wasobserved on Au colloid formation. The recording contrast (R

1/R

2) where R

1and R

2are the reflected intensity before and after laser recording was monitored as a functionof laser power.

605Inorganic and organometallic polymers

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Fig. 1

Photoconductivity of poly(disilyleneoligothienylene)s 7 with SiEt2SiEt

2and

thiophene groups in the polymer main chain has been studied.22 These materialspossess photocarrier generation maxima in accordance with their optical absorptionspectra. The polymer with four thiophene groups per repeat unit was photoconductingwhen irradiated with visible light and the quantum efficiency for photocarrier gener-ation was 2% at 480nm (electric field strength\ 6] 105V cm~1). The hole mobilitieswere found to be ca. 1—2] 10~4 cm2V~1 s~1 at room temperature at fields of2—6] 105V cm~1. Addition of C

60enhanced the photoconductivity quantum effi-

ciency effectively to 85% at 470nm (field strength\ 3] 105Vcm~1) via a photoin-duced charge transfer mechanism.

SSi

Et

Et

Si

Et

Etn

x

7 x = 2–4

3 Polyphosphazenes and other polymers based on main groupelements

Further developments in the novel ambient temperature synthesis of polyphos-phazenes reported in 1995 have been described.23 Polyphosphazene block copolymersare available via the controlled cationic ambient temperature polymerization of phos-phoranimines.24 Thus sequential copolymerization of Cl

3P——NSiMe

3and

RR@ClP——NSiMe3

yields the novel materials after halogen atom replacement withOCH

2CF

3groups (Scheme 5).

Novel triarmed star polyphosphazenes have also been reported.25 The key to thesynthesis procedure is the preparation of the trifunctional initiator from a trifunctionalamine (Scheme 6). Materials with molecular weights of ca. 12 000—42 000 and polydis-persities of 1.05—1.36 were prepared.

A detailed study of a range of poly(N-methyldisilazanes) 8 has been published byTang and co-workers.26 Three polysilazanes were studied with methyl or methyl andvinyl substituents with M

n\ 2500—38 000 and these materials were prepared via the

ring-opening polymerization of cyclic monomers. Each possesses two endothermictransitions by DSC and the first involved a change from a three- to a two-dimenional

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Cl

PCl

Cl

NSiMe3

Cl

PN

Cl

NCl3P PCl3 [PCl6]–

Cl

P

Cl

N P

R

R′

N

OCH2CF3

P

OCH2CF3

N P

R

R′

N

n

n m n m

+

PCl5

CH2Cl2

RR′ClP=NSiMe3

R = Ph, R′ = Cl

R = Me, R′ = Et

R = R′ = Me

NaOCH2CF3

Dioxane

Scheme 5

CH2CH2NH2

NH2NH2CH2C CH2CH2NH2 CH2CH2N(H)R2P=NSiMe3

NMe3SiN=PR2(H)NH2CH2C CH2CH2N(H)R2P=NSiMe3R

PBr NSiMe3

R

+

THF/NEt3

–[HNEt3]Br

CH2CH2N(H)[R2P=NPCl3+]PCl6–

NPCl6–[+Cl3PN=PR2](H)NH2CH2C CH2CH2N(H)[R2P=NPCl3+]PCl6–

6 PCl5/CH2Cl2

CH2CH2N(H)R2P[N=PR2]n

N[R2P=N]nPR2(H)NH2CH2C CH2CH2N(H)R2P[N=PR2]n

i CH2Cl2ii NaOCH2CF3/dioxane

Scheme 6

ordered phase. The second transition, at higher temperatures, is a melting transitionaccording to X-ray and polarizing microscopy results.

Si

R

Me

N

Me

Si

R′

Me

N

Men

8 R,R′ = Me or CH=CH2

In other work, chain flexibility and 31P NMR spin—lattice relaxation measurementson melts of halogenated poly(thionylphosphazenes) have been reported.27 A brief


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Si Si SiO

SiO

n m

Si Si SiO

SiO

n m

Co(CO)3

Co(CO)3

Co2(CO)8

Scheme 7

review of work on functional main group element based dendrimers has been pub-lished.28

4 Polymers containing skeletal transition metal atoms

Macromolecules containing skeletal transition metal atoms represent a continuallygrowing area of research.

In some interesting work on metal-containing silicon-containing polymers Brookand co-workers have described a series of oligomers and polymers with Co

2fragments

(Scheme 7) complexed to alkyne moieties and Cr(CO)3

fragments complexed to areneligands.29 Materials with molecular weights up to 155 000 were reported for a siliconepolymer derivative. Novel, Cr/Mo and Cr/Co mixed-metal species were also prepared.

Zhu and Swager have reported interesting studies of conducting polymetal-larotaxanes (Fig. 2).30 Combined electrochemical and conductivity studies of thepoly(metallarotaxanes) showed that the Lewis acidity and redox properties of themetal center have a profound effect on the redox and conducting properties of thematerial. Lewis acidity leads to charge localization and a redox conduction process ineach of the systems studied. Matching of the polymer and the Cux` (x\ 1 or 2) redoxpotentials resulted in a contribution of Cu to the conductivity.

Full details of the synthesis and properties of poly(ferrocenylsilane)—polysilanerandom copolymers 9 have been published. These interesting materials were preparedvia the thermal ring-opening copolymerization of silicon-bridged [1]ferrocenophanewith cyclotetrasilane.31

Si

Me

Me

Si

Me

Ph4

Fe

n

9

The materials were shown to have iodine doped conductivities in the range10~5—10~6S cm~1 and appreciable hole mobilities. The corresponding poly[ferro-cenyldi(n-butyl)silane] was shown to have a conductivity of ca. 2] 10~4S cm~1 fororiented films. Poly(ferrocenylmethylphenylsilane) possessed a comparable hole mo-bility to the random copolymers.

Transition metal catalyzed ROP of silicon-bridged [1]ferrocenophanes has beenshown to provide a versatile route to controlling the molecular weight and architec-ture of poly(ferrocenes).32 Thus the use of Et

3Si—H in the presence of the metal catalyst

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Fig. 2

allows chain end functionalization and reaction with poly(siloxanes) 10 with Si—Hgroups allows the preparation of graft copolymers 11 (Scheme 8). Regioregular poly-mers are also formed from [1]silaferrocenophanes with different cyclopentadienylgroups.

In the past year full details have been reported on the synthesis and ring-openingpolymerization of sulfur- and selenium-bridged [1]ferrocenophanes (Scheme 9).33 Thepoly(ferrocenylsulfides) (e.g. 12) possess significantly more strongly interacting metalatoms than in their counterparts with silicon spacers.

In 1997 the first [1]ferrocenophane was reported with a first row element (boron) inthe bridge.34 So far ring-opening polymerization of such species has afforded onlyinsoluble poly(boraferrocene) materials.

Southard and Curtis have reported a well defined condensation route to orange-redpoly(ferrocenes) with arene 13 and thiophene 14 spacers.35 The reported values of M

nwere 3600—4000 and the materials possessed broad polydispersities (PDI\ 10—14).


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Me

Si

H

O Si

Me

Me

O

n

Me

Si O Si

Me

Me

O

n

Si

Me

Me

H

Fe

n

Fe SiMe

Me

Pt0

10

11

Scheme 8

Fe S Fe

Me

Me Me

Me

S

n

12

heat or BuLi

Scheme 9

Significantly, two redox waves were detected by cyclic voltammetry (redox splitting,*E\ 170—190mV in CH

2Cl

2) indicating that a significant interaction occurs through

the arene bridge.Interesting studies of redox-active ferrocene-based dendrimers have been reported

by Cuadrado and co-workers. Thermodynamics and kinetics of adsorption, in situelectrochemical quartz crystal microbalance studies and tapping mode AFM imagingwere reported.36

FeMe

C6H13

Me

C6H13 n

FeMe

C6H13

Me

C6H13 n

S

13 14

Photopolymerization of metal-containing liquid crystalline monomers has beenreported as a method for preparing polymer films with a high content of metal centers(Zn, Cu and Mg).37

Interesting soluble organoiron derivatives of poly(pyrrole) have also been re-ported.38 Oxidative polymerization of the monomer 15 with persulfate as oxidant was

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Fe

CO

N

FeC N N

Fe COCO

O

[O] heat

n

m+

n

m+

15 16 17

Scheme 10

claimed to yield 16 which on reflux afforded the polyazaferrocene 17 (Scheme 10).Films of 16 and 17 possessed conductivities of 10~3—10~4S cm~1. Raithby andco-workers prepared novel pyridyl-stabilized rigid rod polymers containing Pt.39

Cameron and Pickup have reported enhanced electrochemical charge transportrates in a conjugated benzimidazole-based polymer via complexation of [Ru-(bipy)

2]2` moieties to the polymer backbone. Electron diffusion coefficients reported

for materials 18 (with 60% occupation of the co-ordinating sites) indicated that theconjugated backbone enhances communication between the ruthenium centers.40

N

N

N

H

N

NRu(bipy)2

H

2+

n18

The first generation of chiral metallodendrimers have been reported by MacDonnelland co-workers.41 These tetranuclear D3-symmetric tetranuclear complexes 19 weremade via a stereoselective synthesis which function as prototypes for polymers and areof interest as chiral hosts and catalysts.

Very interesting soluble, well characterized, conformationally rigid, ribbon-likeruthenium() co-ordination polymers 20 have been reported by Kelch and Rehahn(Scheme 11).42

Degrees of polymerization (DP)[ 30 were assumed based on the lack of detectableend groups in the NMR spectra of the materials. This estimate was verified by smallangle X-ray scattering (SAXS) which gave M

8\ ca. 47 000 and a radius of gyration of

8.4mm.In other work, studies of model complexes with different chain lengths which aim to

provide insight into the photochemical degradation of polymers with M—M bonds inthe main chain have been reported.43 Previous studies have shown that the quantumyields for these polymers decrease with increasing chain length. A possible explanationis that radiationless decay is faster in molecules with more vibrational modes. Inaddition, Newkome and co-workers have reported novel palladium containing cas-cade structures.44


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References

1 Silicon-Based Polymer Science, eds. J.M. Zeigler and F.W.G. Fearon, Advances in Chemistry 224, Ameri-can Chemical Society, Washington, DC, 1990.

2 Siloxane Polymers, eds. J. A. Semlyen and S. J. Clarson, Prentice Hall, Englewood Cliffs, NJ, 1991.3 J. E. Mark, H. R. Allcock and R. West, Inorganic Polymers, Prentice Hall, Englewood Cliffs, NJ, 1992.4 I. Manners, Chem. Br., 1996, 32, 46.5 I. Manners, Ann. Rep. Prog. Chem., Sect. A, Inorg. Chem., 1991, 88, 77.6 I. Manners, Ann. Rep. Prog. Chem., Sect. A, Inorg. Chem., 1992, 89, 93.7 I. Manners, Ann. Rep. Prog. Chem., Sect. A, Inorg. Chem., 1993, 90, 103.8 I. Manners, Ann. Rep. Prog. Chem., Sect. A, Inorg. Chem., 1994, 91, 131.9 I. Manners, Ann. Rep. Prog. Chem., Sect. A, Inorg. Chem., 1995, 92, 127.

10 I. Manners, Ann. Rep. Prog. Chem., Sect. A, Inorg. Chem., 1996, 93, 129.11 I. Manners, Angew. Chem., Int. Ed. Engl., 1996, 35, 1602.12 A. Molenberg and M. Moller, Macromolecules, 1997, 30, 8332.13 Jr.H. Chen, G.-H. Hsiue and C.-P. Hwang, Chem. Mater., 1997, 9, 51.14 T. Miyata, Y. Nakanishi and T. Uragami, Macromolecules, 1997, 30, 5563.15 Q. Liu, W. Shi, F. Babonneau and L.V. Interrante, Chem. Mater., 1997, 9, 2434.16 E. Fossum and K. Matyjaszewski, S. S. Sheiko and M. Moller, Macromolecules, 1997, 30, 1765.17 T. J. Clejj, L.W. Jenneskens and S.G. J.M. Kluijtmans, Adv. Mater., 1997, 9, 961.

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Scheme 11

18 J. A. Villegas, R. Olayo and J. Cervantes, J. Inorg. Organomet. Polym., 1997, 51.19 R.D. Boyd and J. P. S. Badyal, Adv. Mater., 1997, 9, 895.20 K. Matsumoto, K. Miyagawa and H. Yamaoka, Macromolecules, 1997, 30, 2524.21 N. Nagayama, K. Itagaki and M. Yokoyama, Adv. Mater., 1997, 9, 71.22 M. Kakimoto, H. Kashihara, T. Kashiwagi, T. Takiguchi, J. Ohshita and M. Ishikawa, Macromolecules,

1997, 30, 7816.23 C.H. Honeyman, I. Manners, C. Morissey and H.R. Allcock, J. Am. Chem. Soc., 1995, 117, 7035.24 H.R. Allcock, S.D. Reeves, J.M. Nelson, C.A. Crane and I. Manners, Macromolecules, 1997, 30, 2213.25 J.M. Nelson and H.R. Allcock, Macromolecules, 1997, 30, 1854.26 H. Tang, R. E. Prud’homme, A. Mingotaud, M. Schappacher and A. Soum, Macromolecules, 1997, 30, 1400.27 R. Jaeger, G. J. Vancso, D. Gates, Y. Ni and I. Manners, Macromolecules, 1997, 30, 6869.28 D. Gudat, Angew. Chem., Int. Ed. Engl., 1997, 36, 1951.29 T. Kuhnen, M. Stradiotto, R. Ruffolo, D. Ulbrich, M. J. McGlinchey and M.A. Brook, Organometallics,

1997, 16, 5048.30 S. S. Zhu and T.M. Swager, J. Am. Chem. Soc., 1997, 119, 12 568.31 R. Rulkens, R. Resendes, A. Verma, I. Manners, K. Murti, E. Fossum, P. Miller and K. Martjaszewski,

Macromolecules, 1997, 30, 8165.32 P. Gomez-Elipe, P.M. Macdonald and I. Manners, Angew. Chem., Int. Ed. Engl., 1997, 36, 762.33 R. Rulkens, D. P. Gates, J.K. Pudelski, D. Balaishis, D. F. McIntosh, A. J. Lough and I. Manners, J. Am.

Chem. Soc., 1997, 119, 10 976.34 H. Braunschweig, R. Dirk, M. Muller, P. Nguyen, R. Resendes, D. P. Gates and I. Manners, Angew. Chem.,

Int. Ed. Engl., 1997, 36, 2338.35 G.E. Southard and M. D. Curtis, Organometallics, 1997, 16, 5618.36 K. Takada, D. J. Diaz, H.D. Abrun8 a, I. Cuadrado, C. Casado, B. Alonso, M. Moran and J. Losada, J. Am.

Chem. Soc., 1997, 119, 10 763.37 L. Marcot, P. Maldivi and J.-C. Marchon, Chem. Mater., 1997, 9, 2051.38 K.F. Martin and T.W. Hanks, Organometallics, 1997, 16, 4857.39 C. J. Adams, S. L. James and P.R. Raithby, Chem. Commun., 1997, 2155.40 C.G. Cameron and P.G. Pickup, Chem. Commun., 1997, 303.41 S. Bodige, A. S. Torres, D. J. Maloney, D. Tae, G.R. Kinsel, A. K. Walker and F.M. MacDonnell, J. Am.

Chem. Soc., 1997, 119, 10 364.


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42 S. Kelch and M. Rehahn, Macromolecules, 1997, 30, 6185.43 J. L. Male, B. E. Lindfors, K. J. Covert and D.R. Tyler, Macromolecules, 1997, 30, 6404.44 G.R. Newkome, J. Rob, C. N. Moorfield and B.D. Woosley, Chem. Commun., 1997, 515.

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chapter 30. inorganic and organometallic polymers

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