Ring-Opening Polymerization of Strained, Ring-Tilted

Chapter 33

Ring-Opening Polymerization of Strained, Ring-Tilted Metallocenophanes

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New Route to Polymers Based on Transition Metals Daniel A. Foucher, Ralf Ziembinski, Rudy Rulkens, James Nelson, and Ian Manners 1

Department of Chemistry, University of Toronto, 80 Saint George Street, Toronto M5S 1A1, Ontario, Canada Recent developments involving the use of ring-opening polymerization (ROP) as a new route to high molecular weight polymers containing skeletal transition metal atoms are described ROP of strained, ring-tilted silicon-bridged [1]ferrocenophanes provides a route to high molecular weight poly(ferrocenylsilanes). These polymers possess an unusual backbone of alternating ferrocene groups and silicon atoms and the current knowledge of the properties of these interesting materials is reviewed with emphasis on their electrical and electrochemical properties, thermal transition behavior, and morphology. Related [1]ferrocenophanes containing germanium or phosphorus in the bridge also undergo ROP to yield poly(ferrocenylgermanes) and poly(ferrocenylphosphines), respectively. The recent extension of this ROP approach to [2]metallocenophanes to yield new iron and ruthenium containing polymers is also discussed. Polymers containing transition elements in the main chain are of considerable interest because of their potentially attractive physical and chemical properties. However, until very recendy, most routes to these materials have yielded products which are either insoluble, of low molecular weight, or of poorly defined structure (116). Ring-opening polymerization (ROP) reactions generally occur via chain-growth processes which are not subject to the stringent stoichiometry and conversion requirements which often impede the preparation of high molecular weight polymers via condensation (step-growth) routes. Indeed, ROP provides a versatile route to organic (17,18) and, increasingly, to inorganic and organosiHcon-based macromolecules (19-30). In contrast, ROP represents a virtually unexplored methodology for the preparation of transition metal-based polymers and very few examples of the ROP of cyclic compounds containing skeletal transition elements have been reported (31,32). As part of our studies of new classes of polymers based on main group elements (28-30) or transition metals (33-44) we recendy reported the discovery of a novel, ROP route which provided access to the first examples of high molecular weight poly(ferrocenylsilanes) (33). This involved the thermal ROP of [l]ferrocenophanes 1 1

Corresponding author 0097-6156/94/0572-0442S08.00/0 © 1994 American Chemical Society In Inorganic and Organometallic Polymers II; Wisian-Neilson, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

33. FOUCHER ET A L .

Strained, Ring-Tilted Metallocenophanes

443


containing a silicon atom in the bridge and the resulting macromolecules 2 possess an unusual main chain comprising ferrocene units and silicon atoms. In this Chapter we provide an overview of recent work in this area and the extension of the ROP route to prepare other classes of transition metal-based macromolecules (33-44).

1

2

ROP of Silicon-Bridged [l]Ferrocenophanes Previous work on [l]ferrocenophanes such as 1 has shown that they possess strained, ring-tilted structures and that stoichiometric ring-opening processes readily occur (45-47). The strain is apparent in the molecular structure of 1 (R = R' = Me) (Figure 1) where the planes of the cyclopentadienyl ligands are tilted with respect to one another by an angle of 20.8(5)°(35). We found that when 1 (R = R* = Me) is heated at 130°C thermal ROP takes place to yield the corresponding poly(ferrocenylsilane) 2 in essentially quantitative yield (33). Gel permeation chromatography (GPC) indicated that 2 (R = R' = Me) possessed an approximate weight average molecular weight (M ) of 5.2 χ 10 and a number average molecular weight (Mn) of 3.4 χ 10 . Because the polymerizations of [l]silaferrocenophanes are essentially quantitative it is possible to use differential scanning calorimetry (DSC) to obtain an estimate of the strain energy present in the monomers 1. A DSC thermogram for 1 (R = R' = Me) indicates that this species melts at 78°C and then polymerizes exothermically at 120-170°C. Integration of the latter exotherm for a known amount of the monomer indicated the strain energy to be £â 80 kJmoF (33). The phenylated [l]silaferrocenophane 1 (R = R = Ph) was similarly studied and in this case the strain energy was estimated to be ea 60 kJmoF (33). These values are quite large and lie inbetween those found for cyclopentane (ça 42 kJmol' ) and cyclobutane (ça 118 kJmol" ) and are far greater than the value reported for the cyclotrisiloxane [Me2SiO]3 (19 kJmoF). Because of die substantial instrinsic strain energy present we have found that thermal polymerization is quite general for species 1 and even species with bulky substituents such as phenyl (as mentioned above), ferrocenyl, or norbornyl undergo ROP. Representative examples of the poly(ferrocenylsilanes) prepared to date are given in Table 1. These polymers are of high molecular weight which contrasts with the materials previously prepared by condensation routes (48). In addition, virtually all of the poly(ferrocenylsilanes) dissolve in polar organic solvents and polymers such as 2 (R = R* = η-Hex) are even soluble in non-polar solvents such as hexanes. However, the phenylated poly(ferrocenylsilane) 2 (R = R* = Ph) is insoluble although lower molecular weight fractions can be extracted using hot THF (34). The detailed properties of poly(ferrocenylsilanes) are under active investigation and the published results in this area from their discovery up to mid-1993 have been recently reviewed (38). One of the most interesting characteristics of these polymers involves their use as pyrolytic precursors to magnetic ceramics (36). However, in this Chapter we focus in some detail on the electrical and thermal characteristics of these novel materials. 5

w

5

1

1

1

In Inorganic and Organometallic Polymers II; Wisian-Neilson, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.


444

INORGANIC AND ORGANOMETALLIC POLYMERS II

Figure 1

The Molecular Structure of 1 (R = R' = Me). Reproduced with permission from reference 35.


33.

FOUCHER ET AL.


445


Table 1 Characterization Data for Selected Poly(ferrocenylsilanes) 2 R

R'

MB

MB

Et nBu nHex Ph

Et nBu nHex Ph H TFPd Fed n-CisH37 Vinyl Ph Nor* Vinyl

MB

Me Ms Me MB

Ms MB

Ph a b c d e

Μη» s

1

5.2 x 1 0 7.4 χ 10 1.1 χ 106 1.2 χ 105 5.1 χ 10* 8.6 χ 10 2.7 χ 106 1.6 χ 105 1.4 χ 106 1.6 χ 105 3.0 χ 105 1.6 χ 105 1.1 χ 105 5

5

3.4 χ 4.8 χ 4.9 χ 7.6 χ 3.2 χ 4.2 χ 8.1 χ 7.1 χ 5.6 χ 7.7 χ 1.5 χ 1.1 χ 7.6 χ

5

10 10 105 10 10 105 105 10 105 10 105 10 10 s

4

4

4

4

4

4

8(29Si)b

Tc

T C

-6.4 -2.7 -4.9 -2.3 -12.9 -20.0 -4.3 -9.8 -5.3 -10.3 -7.7 -3.4 -12.6

33 22 3 -26 9 59 99 1 28 54 81

122 108 116,129 87, 102 16 -

e

g

_

M

A

m

Polymer molecular weights were determined by Gel Permeation Chromatogaphy in THF containing 0.1 % by weight of [NBu4]Br using polystyrene standards, S i NMR data recorded in CfcDe Tg and T values were determined by Differential Scanning Calorimetry, the latter generally after annealing, Fc = ferrocenyl, TFP = trifluoropropyl, and Nor = norbornyl Determined by solid state S i N M R

29

m

29

Electrical and Electrochemical Properties of Poly(ferrocenylsilanes) The electrochemical properties of poly(ferrocenylsilanes) are quite intriguing. In contrast to organic polymers with ferrocenyl side groups such as poly(vinylferrocene) which show die presence of a single reversible oxidation wave, poly(ferrocenylsilanes) show two reversible oxidation waves (33,37-39). This is illustrated by the cyclic voltammograms for 2 (R = R' = Me) dissolved in CH2CI2 (Figure 2a) and as a (initially) surface confined species which dissolves on oxidation so as to give rise to progressively weaker traces (Figure 2b). In the latter case the different shapes of the two waves are probably a consequence of solvation effects. The presence of two waves for poly(ferrocenylsilanes) in solution has been explained in terms of the presence of cooperative interactions between the iron centers. In contrast, in rx)ly(vinylferrocene) the ferrocenyl groups do not interact with one another. Thus, the initial oxidation of poly(ferrocenylsilanes) is believed to occur at alternating iron sites and the subsequent oxidation of iron centers next to those already oxidized is more difficult and occurs at higher potentials (33,39). Interestingly, comparative studies of different poly(ferrocenylsilanes) show that the peak separation, AE, which is a measure of die interaction between the iron centers, changes with the substituents at silicon and increases in the order (Me < Et < n-Bu). Molecular modelling indicates that the distance between the iron centers in poly(ferrocenylsilanes) is probably over 6 À which suggests that the interactions probably occur through the bridge rather than through space.



446


E(mV)

JeO.OO μΑ

b)

-600.0

-400.0

-200.0

0.0 mV

2ÔUO

4ÔOÔ

600JÔ

80ΊΓΟ"

E(mV)

Figure 2

f

Cyclic Voltammograms for 2 (R = R = Me) a) 5 χ 1(H M in 0.1 M [NBu4][PF6] in CH2CI2 (Scans at 500 and 1000 mVs" ) b) as a Film on at Pt Electrode dipped in 0.1M [NBu4][PF6] in MeCN (Scans at 250 mVs- ). Potentials are relative to the ferroœne/ferroœmum couple at Ε = 0.00 Vfigure 2a is reproduced with permission from reference 39. 1

1


33.


FOUCHER ET AL.

In view of the evidence for interactions between the iron atoms in the polymer main chain and the appreciable σ-delocalization in polysilanes the electrical conductivity of poly(ferrocenylsilanes) has been studied. In the undoped state poly(ferrocenylsilanes) are insulators with conductivities of ca 10" Scnr . The lack of ^localization in these undoped materials is supported by UV/vis spectroscopy which shows the polymers possess spectra similar to those for monomelic ferrocenes such as bis(trimeÂylsnyl)ferrocene (34,38). Oxidation of poly(ferrocenylsilanes) can be achieved in solution using a variety of reagents such as I2, o-quinones, and FeCl3 and is accompanied by the growth of a characteristic "ferrocenium-type" visible absorption with Xmax = ca 645 nm as the colors of the solution change from amber to blue. Similar behavior is detected for poly(ferrocenylsilane) films which are electrochromic and can be cycled between amber and dark blue-green states. Conductivities forfe-dopedsamples of 2 (R = R' = Me) rise into the weak semiconductor range (ca 10 Scnr ) which is consistent with an electron hopping model (38). An essentially localized structure for this particular polymer is supported by Môssbauer spectroscopy which shows the presence of both an outer (IS = 0.38 mms- , AEq = 2.27 mms ) and an inner (IS = 0.29 mms , AEq = 0.69 mms ) quadrupolar doublet. These were assigned to discrete Fe and Fe sites, respectively (Figure 3). This indicates that at least for doped samples of 2 (R = R = Me) at 25°C delocalization does not occur on the Môssbauer timescale. Nevertheless, work on small molecule [m,m]ferrocenophanes indicates that die factors that influence delocalization in these types of materials are likely to be very complex and so some further understanding of structure-property relations is probably required in order to access more highly conducting materials in the future (38,39). 14


447

7

1

1

1

1

1

n

1

111

1

Thermal Transition Behavior and Morphology of Poly(ferrocenylsilanes) In order to investigate the thermal properties of poly(ferrocenylsilanes) studies by DSC, thermogravimetric analysis (TGA) and Dynamic Mechanical Analysis (DMA) were carried out In addition, in order to gain insight into the morphology of these materials Wide Angle X-Ray Scattering (WAXS) studies of poly(ferrocenylsilanes) were also performed (34,38,40). Studies of the glass transition temperatures of poly(ferrocenylsilanes) by DSC have indicated that the TgS are generally higjher than those of polysilanes which can be attributed to the relative rigidity and bulk of the skeletal ferrocenyl units. In addition, the T s decrease with the length of the side group in die series 2 (R = R' = Me, Et, nBu, and η-Hex) which can be rationalized by free volume effects (Table 1) (34). Studies of the polymers by TGA have shown that they are thermally stable to ca 350°C but above this temperature they decompose to yield interesting ceramic and (^polymerization products (36). The melting characteristics and morphology of poly(ferrocenylsilanes) has been studied by DSC and WAXS, respectively, and have been found to be very sensitive to sample thermal history (38,40). Samples of the symmetrically substituted poly(ferrocenylsilanes) 2 (R = R = Me, Et, η-Bu, and η-Hex) have been studied in some detail. WAXS of unannealed samples of the polymers with methyl and ethyl side groups show diffractograms which are indicative of the presence of some order with broad lines superimposed on typical amorphous halos (Figures 4a and 4b). The amorphous halos, which correspond to a d-spacing of ça 6.0 Â in 2 (R = R' = Me) and 6.9 Â in 2 (R = R' = Et), probably arise from the contribution of the first coordination sphere of the iron-iron correlation function. Samples of these polymers show melting transitions (T s) at 122°C and 108°C, respectively, when annealed at ca 90 - 100°C and sometimes without annealing which indicates that sample thermal history is important This behavior is illustrated by the DSC thermograms for 2 (R = g

1

m




448


33.

FOUCHER ET AL.

Strained, Ring- Tilted Metallocenophanes

449

1

R = Et) for an annealed sample (90°C, 2 h) (Figure 5a) and for a subsequent run where a T was not detected (Figure 5b). A WAXS study of the poly(ferrocenylsilane) with η-Bu side groups, 2 (R = R* = nBu), shows much more evidence of order with several sharp peaks (Figure 4c) and a T is observed at 129°C for annealed samples and often for samples that were not deliberately annealed prior to study. Interestingly, annealing of 2 (R = R = η-Bu) at ca 80 - 90°C for 2 h - 3 days leads to a new endotherm at 116°C in addition to that at 129°C. One of these peaks may be a consequence of side chain crystallization, which is a well-known phenomenon for poly(di(n-alkyl)silanes) (27), and further studies in this area are in progress. In contrast to die poly(ferrocenylsilanes) with shorter n-alkyl groups, the n-hexyl substituted polymer 2 (R = R' = η-Hex) shows only very broad amorphous halos at d-spacings of 5.3 Â and 13.6 À (Figure 4d) and a T has not yet been detected for this material. m

m


1

m

ROP of Germanium- and Phosphorus-Bridged [l]Ferrocenophanes The discovery of the facile thermal ring-opening polymerization of [l]silaferrocenophanes suggested that [l]ferrocenophanes with other elements in the bridge structure might also polymerize (33). This has been found to be the case and [l]ferrocenqphanes with germanium in the bridge 3 also undergo ROP to yield poly(ferrocenylgermanes) 4 (Table 2) (38,41,42).

3

4

Table 2 Molecular Weight and Glass Transition Dam for Selected Poly(ferrocenylgermanes) 4

a b

R

R'

Me Et nBu Ph

Me Et nBu Ph

M a

Tb

M„*

w

6

2.0 χ 10 7.4 χ 10 8.9 χ 10 1.0 χ 106 5

5

T

g

5

8.5 χ 10 4.8 χ 10 3.4 χ 10 8.2x105

5 5

28 12 -7 114

m

-

88, 94

-

Polymer molecular weights were determined by Gel Permeation Chromatogaphy in THF containing 0.1 % by weight of [NBu4]Br using polystyrene standards, Tg and T values were determined by Differential Scanning Calorimetry. m

The properties of these polymers are under investigation and some characterization data for selected examples is given in Table 2. Interestingly, electrochemical studies have shown that similar cooperative interactions exist between the iron centers in poly(ferrocenylgermanes) to those detected for their silicon analogues (39). In addition, phosphorus-bridged [l]ferrocenophanes such as 5 (R = Ph) and related species also polymerize thermally to yield poly(ferrocenylphosphines) such as




450

b)

Figure 4

Wide Angle X-Ray Scattering (WAXS) Powder Diffractograms of Poly(ferrocenylsilanes) a) 2 (R = R' = Me) b) 2 (R = R' = Et), c) 2 (R = R' = nBu) and d) 2 (R = R' = nHex). Continued on next page


FOUCHER ET AL.



C)

S

10

IS

20

25

Figure 4. Continued


451


48.40·


Tin 41.20· 48.0047.80-

SΒ

47.60·

£

47.40-

i

47.20-

—

47.00« 44.S044.00 ·

—ι— 2S.0

Figure 5

—Τ— 50.0 Temperature *C

DSC Thermogram for 2 (R = R = Et) a) After annealing at 90°C for 2 h showing both aTVandaT b) Subsequent scan showing only a T . m

g


33.


FOUCHER ET A L .

453


6 (R = Ph). These materials are of identical structure to the polymers prepared previously by condensation routes (49). It should be noted that stoichiometric ringopening reactions of species of type 5 are also known and in fact oligomers with 2-5 repeat units can be formed with certain anionic reagents. However, previous attempts to induce the ROP of species 5 were unsuccessful (49). Poly(ferrocenylphosphines) 6 also show evidence for interactions between the iron centers in their electrochemical behavior (39).

Fe

heat

F

Fe

R

ROP of [2]Metallocenophanes with a Hydrocarbon Bridge Although [l]ferrocenophanes with a single silicon, germanium, or phosphorus atom were found to readily polymerize, to date, our attempts to extend the ROP methodology to [2]ferrocenophanes which possess two silicon atoms in the bridge using either thermal or catalytic initiation have been unsuccessful (35). The reduced propensity for such species to polymerize has been attributed to the lower degree of ring strain present which is reflected by the very small cyclopentadienyl ring tilt-angle of only ca 4 °in compounds such as Fe(n-C5H4)2(SiMe2)2 (35). However, [2]ferrocenophanes with a hydrocarbon bridge 7, are significantly more strained than disilane-bridged analogues because of the smaller size of carbon relative to silicon and these compounds can possess ringtilt-anglesof ca 21°. We have found that the hydrocarbon bridged species 7 will undergo ROP which has provided access to the first examples of well-characterized rx)ly(ferrocenylethylenes) 8 (44). These polymers possess backbones consisting of alternating ferrocene groups and aliphatic C2 units and are insoluble if R = H but are readily soluble in solvents such as THF if R is an organic group such as methyl.

CH

CH -CH f2

9

heat

2

M

-Jn

7 M = Fe 9 M = Ru

8 M = Fe 10 M = Ru

Poly(ferrocenylethylenes) 8 possess ferrocene units which are further separated from one another than in polymers derived from [l]ferrocenophanes such as the poly(ferrocenylsilanes) 2. As mentioned above, the electrochemistry of the latter polymers is indicative of the presence of substantial cooperative interactions between the iron centers. In contrast, studies of the electrochemistry of 8 (R = Me) showed the presence of only a single reversible oxidation wave which indicated that the ferrocene groups interact to much less significant extent (39).



454


In order to prepare [2]metallocenophanes that are even more strained than 7 we attempted to synthesize analogous species with a larger ruthenium atom in the place of iron. Such [2]ruthocenophanes would be expected to possess much greater ring tiltangles and, as ruthenocene is known to possess significandy different electrical properties compared to ferrocene, the ruthenium analogues of poly(ferrocenylethylenes) would be very interesting to investigate. We have recendy synthesized the first examples of [2]ruthenocenophanes and 9 (R = H) possesses atiltangle of 29.6(5)°, which is the largest known to date for any neutral iron group metallocenophane (40). In addition, we have found that such species with hydrocarbon bridges undergo ROP more readily than their iron analogues to yield poly(ruthenocenylethylenes) 10 (40). These results indicate that ROP provides a versatile route to a variety of high molecular weight transition metal-based polymers. We are now attempting to extend the ROP route still further whilst concentrating on detailed studies of the properties of the polymers prepared to date, and also their mechanisms of formation. The different possible pathways for the ROP processes are outlined in a forthcoming review article (50). Acknowledgements Our work on the ring-opening polymerization of strained rings containing transition elements was initially supported by the Ontario Center of Materials Research (OCMR) and has subequendy been funded by the ACS Petroleum Research Fund (PRF), the Institute of Chemical Science and Technology (ICST), and the Natural Sciences and Engineering Research Council of Canada (NSERC). The research on the detailed properties of the polymers is being carried out in collaboration with the Polymer Materials Science Research Group of Professor G. Julius Vancso at the University of Toronto. Literature Cited 1. Wright, M. E.; Sigman M.S. Macromolecules, 1992, 25, 6055. 2. Fyfe, H.B.; Mlekuz, M.; Zargarian, D.; Taylor, N.J.; Marder, T.B.J.Chem. Soc. Chem. Commun. 1991, 188. 3. Davies, S.J.; Johnson, B.F.G.; Khan, M.S.; Lewis, J. J. Chem.Soc.,Chem. Commun., 1991, 187. 4. Tenhaeff, S.C. and Tyler, D.R. J. Chem. Soc. Chem. Commun. 1989, 1459. 5. Neuse, E.W.; Bednarik, L. Macromolecules, 1979, 12, 187. 6. Sturge, K. C. ; Hunter, A. D. ; McDonald, R. ; Santarsiero, B. D. Organometallics, 1992, 11, 3056. 7. Pollagi, T.P.; Stoner, T.C.; Dallinger, R.F.; Gilbert, T.M.; Hopkins, M.D. J. Am. Chem.Soc.,1991, 113, 703. 8. Bayer, R.; Pohlmann, T.; Nuyken, O. Makromol. Chem. Rapid Commun. 1993, 14, 359. 9. Gonsalves, K.; Zhanru, L.; Rausch, M.V. J. Am. Chem.Soc.,1984, 106, 3862. 10. Brandt, P.F.; Rauchfuss, T.B.J. Am. Chem. Soc., 1992, 114, 1926. 11. Dembek,Α.Α.;Fagan, P.J.; Marsi, M . Macromolecules, 1993, 26, 2992. 12. Gilbert, A.M.; Katz, T.J.; Geiger, W.E.; Robben, M.P.; Rheingold, A.L. J. Am. Chem.Soc.,1993,115,3199. 13. Nugent, H.M.; Rosenblum, M.; Klemarczyk, P. J. Am. Chem. Soc., 1993, 115, 3848. 14. Sheats, J.E.; Carraher, C.E.; Pittman, C.U. Metal Containing Polymer Systems, Plenum, 1985. 15. Neuse, E.W.; Rosenburg, H. J. Macromol. Sci. Revs., Macromol. Chem. 1970, C4(l), 1. 16. Manners, I. J. Chem.Soc.Ann. Rep. Prog. Chem. (A) 1991, 77. In Inorganic and Organometallic Polymers II; Wisian-Neilson, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.


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17. Ring Opening Polymerization Ivin, K.J. and Saegusa, T. Eds, Elsevier, New York, 1984. 18. Ring Opening Polymerization McGrath, J.E.; Ed.; ACS Symp. Ser. 286, Washington D.C. 1985. 19. Sargeant, S. J.; Zhou, S. Q.; Manuel, G.; Weber, W. P. Macromolecules, 1992, 25, 2832. 20. West, R.; Hayase, S.; Iwahara, T. J. Inorg. Organomet. Polym. 1991, 1, 545. 21. Anhaus, J.T.; Clegg, W.; Collingwood, S.P.; Gibson, V.C. J. Chem. Soc. Chem. Commun. 1991, 1720. 22. Manners, I.; Renner, G.; Allcock, H.R.; Nuyken, O. J. Am. Chem. Soc., 1989, 111, 5478. 23. Ngo, D.C.; Rutt, S.J., Allcock, H.R. J. Am. Chem.Soc.,1991, 113, 5075. 24. Wu, H.J.; Interrante, L.V. Chem. Mater., 1989, 1, 564. 25. Allcock, H.R.; Dodge, J. Α.; Manners, I.; Riding, G. H.; J. Am. Chem. Soc., 1991, 113, 9596. 26. Cypryk, M.; Gupta, Y.; Matyjaszewski, K. J. Am. Chem.Soc.,1991, 113, 1046. 27. Mark, J.E.; Allcock, H.R.; West, R. Inorganic Polymers, Prentice Hall, 1992. 28. Liang, M.; Manners, I. J. Am. Chem. Soc., 1991, 113, 4044. 29. Ni, Y.; Stammer, Α.; Liang, M.; Massey, J.; Vancso, G.J.; Manners, I Macromolecules 1992, 25, 7119. 30. Manners, I. Polymer News 1993, 18, 133. 31. Rœsky, H.W.; Lücke, M . Angew. Chem. Int. Ed. Engl., 1989, 28, 493. 32. Rœsky, H.W.; Lücke, M . J. Chem.Soc.,Chem. Commun, 1989, 748. 33. Foucher, D.A.; Tang, B.Z., Manners, I. J. Am. Chem.Soc.,1992, 114, 6246. 34. Foucher, D.A.; Ziembinski, R.; Tang, B.Z.; Macdonald, P.M.; Massey, J.; Jaeger, R.; Vancso, G.J.; Manners, I. Macromolecules, 1993, 26, 2878. 35. Finckh, W.; Tang, B.Z.; Foucher, D.A.; Zambie, D.B.; Ziembinski, R.; Lough, Α.; Manners, I. Organometallics, 1993, 12, 823. 36. Tang, B.Z., Petersen, R.; Foucher, D.A.; Lough, Α.; Coombs, N.; Sodhi, R.; Manners, I. J. Chem. Soc. Chem. Commun. 1993, 523. 37. Foucher, D.A.; Petersen, R.; Tang, B.Z.; Ziembinski, R.; Coombs, N.; MacDonald, P.M.; Sodhi, R.N.S.; Massey, J.; Vancso, J.G.; Manners, I. Polymer Prepr. (Am. Chem.Soc.,Div. Polym. Chem.) 1993, 34(1), 328. 38. Manners, I. J. Inorg. Organomet. Polym. 1993, 3, 185. 39. Foucher, D.A.; Honeyman, C.; Nelson, J.M.; Tang, B.Z.; Manners, I. Angew Chem Int. Ed. Engl. 1993, 32, 1703. 40. Manners, I. Advanced Materials 1994, 6, 68. 41. Honeyman, C.; Foucher, D.A.; Mourad, O.; Rulkens, R.; Manners, I. Polymer Prepr. (Am. Chem. Soc. Div. Polym. Chem.) 1993, 34(1), 330. 42. Foucher, D.A.; Manners, I. Makromol. Chem., Rapid Commun. 1993, 14, 63. 43. Ziembinski, R.; Honeyman, C.; Mourad, O.; Foucher, D.A.; Rulkens, R.; Liang, M.; Ni, Y.; Manners, I. Phosphorus, Sulfur, Silicon and Rel. Elem., 1993, 76, 219. 44. Nelson, J.M.; Rengel, H.; Manners, I. J. Am. Chem. Soc 1993, 115, 7035. 45. Stœckli-Evans, H.; Osborne, A.G.; Whiteley, R.H.; Helv. Chim. Acta. 1976, 59, 2402. 46. Osborne, A.G.; Whiteley, R.H.; Meads, R.E.; J. Organomet. Chem. 1980, 193, 345. 47. Fischer, A.B.; Bruce, J.A.; McKay, D.R.; Maciel, G.E.; Wrighton, M.S.; Inorg. Chem.. 1982, 21, 1766. 48. Rosenberg, H.; U.S. Patent 3,426,053 (1969). 49. Withers, H.P.; Seyferth, D.; Fellmann, J.D.; Garrou, P.; Martin, S. Organometallics, 1982, 1, 1283. 50. Manners, I. Adv. Organomet. Chem. 1995, 37, in press. RECEIVED July 14, 1994 In Inorganic and Organometallic Polymers II; Wisian-Neilson, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

Ring-Opening Polymerization of Strained, Ring-Tilted

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