Synthesis, Characterization, and Homopolymerization and

Kai C. Hultzsch, James M. Nelson, Alan J. Lough, and Ian Manners ... D. Dewhurst , Jan Mies , Krzysztof Radacki , Sascha Stellwag-Konertz , and Alfred...
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Organometallics 1995, 14, 5496-5502

5496

Articles Synthesis, Characterization, and Homopolymerization and Copolymerization Behavior of the Silicon-Bridged [11Chromarenophane Cr(q =CeH5)2SiMe2 Kai C. Hultzsch, James M. Nelson, Alan J . Lough, and Ian Manners* Department of Chemistry, University of Toronto, 80 St. George Street, Toronto M5S lA1, Ontario, Canada Received June 21, 1995@ The silicon-bridged [llchromarenophane Cr(?pC&)2SiMe2 (7) was synthesized by the reaction of [Cr(r-CsHsLi)al.TMEDA (TMEDA, NJV,N,N-tetramethyl-1,2-ethylenediamine) with MezSiCl2 in hexanes. The molecular structure of 7 was determined by single-crystal X-ray diffraction and was shown to be strained, with an angle between the planes of the arene rings of 16.6(3)". In addition, significant distortion from planarity was detected in 7 for the arene carbon atom bonded to the bridging silane moiety, with angles between the planes of the arene ligands and the C(arene)-Si bonds of 37.9(4)" and 38.2(4)". Compound 7 does not undergo thermal ring-opening polymerization at temperatures approaching 180 "C, but instead decomposes to yield chromium metal and Ph2SiMe2. This behavior contrasts with that of silicon-bridged [llferrocenophanes such as Fe(~-CsH4)2SiMez(l),which readily thermally polymerize t o yield poly(femocenylsi1anes) at 130 "C and above. However, thermal treatment of equimolar mixtures of 7 and 1 at 140 "C for 72 h resulted in the formation of the air-sensitive, heterobimetallic copolymer [Cr(r-CgH5)2SiMeglr[Fe(r-C~H4)aSiMe21, (9a), which was identified by lH, 13C,and 29SiNMR. Treatment of equimolar mixtures of 7 and 1 in THF with anionic initiators such as BuLfiexanes resulted in the formation of an analogous copolymer 9b. 'H NMR integration and, after selective cleavage of the siliconarene bonds in the copolymers by treatment with methanol, analysis of the residual ferrocenylsilane segments by GPC allowed an estimate of the molecular weights of 9a and 9b. These results indicated that the minimum value of M, for 9a was ea. 2.4 x lo3 and that for 9b was ea. 1.2 x lo4.

Introduction Well-defined,high molecular weight, transition-metalcontaining polymers currently are a topic of considerable interest due to their interesting properties and potential applications.lI2 In 1992, we reported3 that strained, ring-tilted, silicon-bridged [llferrocenophanes ( e g . , 1) undergo ring-opening polymerization (ROP) t o yield @Abstractpublished in Advance ACS Abstracts, October 15,1995. (1)(a) Pittman, C. U., Jr.; Carraher, C. E., Jr.; Reynolds, J . R. In Encyclopedia ofPolymer Science and Engineering; Mark, H. F., Bikales, N. M., Overberger, C. G., Menges, G., Eds.; Wiley: New York, 1989; Val. 10,p 541. (b) Mark, J. E.; Allcock, H. R.; West, R. Inorganic Polymers; Prentice Hall: Englewood Cliffs, NJ, 1992. (c) Allcock, H. R. Adu. Mater. 1994,6 , 106. (d) Manners, I. Adu. Muter. 1994,6 , 68. (2)For recent examples of transition-metal-based polymeric materials, see the following: (a) Fyfe, H. B., Mlekuz, M.; Zargarian, D.; Taylor, N. J.; Marder, T. B. J . Chem. Soc., Chem. Commun. 1991, 188. (b) Tenhaeff, S. C.; Tyler, D. R. Organometallics 1992, 11, 1466. (c) Davies, S.J . ; Johnson, B. F. G.; Khan, M. S.; Lewis, J. J . Chem. Soc., Chem. Commun. 1991, 187. (d) Lewis, J.;Khan, M. S.; Kakkar, A. K.; Johnson, B. F. G.; Marder, T. B.; Fyfe, H. B.; Whittmann, F.; Friend, R. H.; Dray, A. E. J . Organomet. Chem. 1992,425,165. (e) Nugent, H. M.; Rosenblum, M.; Klemarczyk, P. J . A m . Chem. Sac. 1993,115, 3848. (D Dembek, A. A.; Fagan, P. J.;Marsi, M. Macromolecules 1993, 26,2992. (g) Brandt, P. F.; Rauchfuss, T. B. J . A m . Chem. Soc. 1992, 114,1926.(h) Roesky, H.W.; Liicke, M. Angew. Chem., Int. Ed. Engl. 1989,28,493. (i) Bayer, R.; Pohlmann, T.; Nuyken, 0. Makromol. Chem., Rapid Commun. 1993,114,6246. (3)Foucher, D. A.; Tang, B. Z.; Manners, I. J . A m . Chem. SOC.1992, 114,6246.

high molecular weight poly(ferroceny1silanes)2.4-6 These silicon-bridged [llferrocenophaneshave also been shown to undergo anionic ring-opening oligomerization and polymerization in solution in the presence of anionic initiators to produce, in some cases, living system^.^^^^ In addition, transition-metal-catalyzed ROP of species such as 1 has recently been reported.8 We have also described the successful extension of this ROP methodology to related species, such as other [llferrocenophanes and hydrocarbon-bridged [2lmetallocenophanes 3.9J0 In all cases in which ROP has been shown (4)Manners, I. Adu. Organomet. Chem. 1995,37, 131. (5)(a) Foucher, D. A.; Ziembinski, R.; Tang, B.-2.; Macdonald, P. M.; Massey, J.;Jaeger, C. R.; Vancso, G. J.; Manners, I. Macromolecules 1993,26,2878.(b) Foucher, D.; Ziembinski, R.; Petersen, R.; Pudelski J . ; Edwards, M.; Ni, Y.; Massey, J.; Jaeger, C. R.; Vancso, G. J.; Manners, I. Macromolecules 1994,27,3992. (c) Rulkens, R.; Ni, Y.; Manners, I. J . A m . Chem. SOC.1994,116,12121. (d) Foucher, D. A.; Honeyman, C. H.; Nelson, J. M.; Tang, B. Z.; Manners, I. Angew. Chem., Int. Ed. Engl. 1993,32,1709. (6)For the work of other groups on poly(ferrocenylsi1anes) and related materials, see the following: (a) Rosenberg, H. U.S. Patent 3,426,053,1969. (b) Tanaka, M.; Hayashi, T. Bull. Chem. SOC.Jpn. 1993, 66,334. (c) Nguyen, M. T.; Diaz, A. F.; Dement'ev, V. V.; Pannell, K. H. Chem. Mater. 1993,5,1389. (7)Rulkens, R.; Lough, A. J.; Manners, I. J . A m . Chem. SOC.1994, 116,797. (8)Ni, Y.; Rulkens, R.; Pudelski, J. K.; Manners, I. Makromol. Chem., Rapid Commun. 1995,16,637.

0276-733319512314-5496$09.00/00 1995 American Chemical Society

Silicon-Bridged [lIChromarenophane CdrpCsHdZSiMez

to take place, the monomers have been found to possess strained structures in which the cyclopentadienyl ligands are tilted substantially by ca. 18-31".4J1J2

3 M

2

1

= Fe, Ru

The first silicon-bridged [llchromarenophane, Cr(qCsH5)zSiPhg (41, was synthesized in 1990 by Elschenbroich and c o - ~ o r k e r s . 'An ~ X-ray diffraction study of this species indicated that this compound possesses a strained structure with a tilt angle between the planes of the arene ligands of ca. 14". Related compounds such as 5 and 6 have also been characterized, and these also have strained, ring-tilted structures. These results suggest that [nlmetalloarenophanes may also function as precursors to novel transition-metal-based polymers via ROP. In this paper, we report on the synthesis, molecular structure, and polymerization behavior of Cr(?pCsH&SiMeg (7), the chromarenophane analog of l.14

4

5

CHI

si'

'CH2

6

Results and Discussion Various silicon-bridged [1lmetalloarenophanes have previously been synthesized and structurally characterized. For example, the previously mentioned species 4 was found to possess a substantially ringtilted structure with a tilt angle of 14.4".13 In addition, the siliconbridged [llvanadarenophanes 6 and 6 were found t o possess tilt angles of 20.8" l5 and 19.9",16respectively. (9)(a) Nelson, J.M.; Rengel, H.; Manners, I. J . Am. Chem. Soc. 1993, 115, 7035. (b) Nelson, J. M.; Lough, A. J.; Manners, I. Angew. Chem., Int. Ed. Engl. 1994,33, 989. (10)Foucher, D. A.; Edwards, M.; Burrow, R. A.; Lough, A. J.; Manners, I. Organometallics 1994,13,4959. (11)(a) Stoeckli-Evans, H.; Osborne, A. G.; Whiteley, R. H. Helu. Chim. Acta 1976,59, 2402. (b) Stoeckli-Evans, H.; Osborne, A. G.; Whiteley, R. H. J . Organomet. Chem. 1980,194,91. (c) Seyferth, D.; Withers, H. P. Organometallics, 1982,I , 1275. (d) Butler, I. R.; Cullen, W. R.; Einstein, F. W. B.; Rettig, S. J.; Willis, A. J. Organometallics 1983,2,128. (e) Fischer, A.B.; Bruce, J. A.; McKay, D. R.; Maciel, G. E.; Wrighton, M. S. Inorg. Chem. 1982,21,1766. (0 Osborne, A. G.; Whiteley, R. H.; Meads, R. E. J . Organomet. Chem. 1980,193, 345. (12)Pudelski, J.&; Gates, D. P.; Rulkens, R.; Lough, A. J.;Manners, I. Angew. Chem., Int. Ed. Engl. 1995,34,1506. (13)Elschenbroich, C.; Hurley, J.; Metz, B.; Massa, W.; Baum, G. Organometallics 1990,9,889. (14) Elschenbroich and co-workers have mentioned in a footnote in a paper published in 1990 that they have prepared compound 7, but no characterization data were reported (see ref 13,footnote 16). After this manuscript was submitted, we were informed by Professor Elschenbroich that the characterization data are described in a Ph.D. Thesis (Hurley, J. Doktorarbeit, Philipps-Universitilt Marburg, 1989). (15)Elschenbroich, C.;Bretschneider-Hurley, A.; Hurley, J.;Massa, W.; Wocadio, S.; Pebler, J.;Reijerse, E. Inorg. Chem. 1993,32,5421.

Organometallics, Vol. 14,No. 12, 1995 5497 The structures of these species are strikingly similar to those of silicon-bridged Cllferrocenophanes, and this suggests that similar ROP behavior might be anticipated. To study the ROP behavior of these siliconbridged chromarenophanes, we targeted the chromarenophane analog of the ferrocenophane 1rather than phenylated 4, as the ferrocenophane analog of the latter yields a poly(ferrocenylsi1ane) that is insoluble and difficult to c h a r a ~ t e r i z e . ~ ~ ~ ~ Synthesis and Characterization of the SiliconBridged [lIChromarenophane Cr(q-CsH&SiMez (7). The [llchromarenophane 7 was prepared as a maroon crystalline material in 56% yield via the reaction of [Cr(q-CsH&i)21*TMEDAwith MezSiClz in hexanes, a route analogous t o that previously reported by Elschenbroich and co-workers for the synthesis of 4.13 The synthesis [C~(~;~-C~HSL~)~I*TMEDA was carried out by reaction of bis(benzene)chromiumwith BuLirrMEDA in refluxing cyclohexane.

The identity of 7 was confirmed by lH, 13C,and 29Si NMR and mass spectrometry, which gave data consistent with the assigned structure. Significantly, the 13C NMR spectroscopic data for 7 indicated that this species is significantly strained. Thus, an upfield 13C NMR chemical shift for the ipso-arene carbons bonded to silicon was found (39.5 ppm) compared t o bidbenzene)chromium (73.2 ppm).17 By comparison, a similar trend has been found for strained, ring-tilted [llferrocenophanes (eg., l),where the ipso-cyclopentadienylcarbon atom bonded to silicon is shifted 35-60 ppm upfield compared to analogous unstrained species.Ig To allow a comparison of the molecular structure of compound 7 with those of related species, a single-crystal X-ray diffraction study was carried out. Discussion of the X-ray Structure of 7. Marooncolored single crystals of 7 suitable for an X-ray diffraction study were obtained from a solution of the compound in hexanes a t -30 "C. Two alternative views of the molecular structures of 7 are shown in Figure la,b. A summary of cell constants and data collection parameters is included in Table 1,the fractional coordinates are listed in Table 2, and important bond lengths and angles are listed in Table 4 of the supporting information for 7. The angles a,p, 8, and 6 used in discussing the structures are defined in Figure 2.18 The most interesting structural feature of 7 is the tilt of the virtually planar arene ligands with respect to one another (Figure 1). The tilt angle of 16.6(3)' in 7 is slightly larger than that in the previously characterized phenylated analog 4 (a= 14.4"). The degree of tilting in 7 can also be appreciated by considering the arene(16)Elschenbroich, C.;Bretschneider-Hurley, A.; Hurley, J.; Behrendt, A.; Massa, W.; Wocadlo, S.; Reijerse, E. Inorg. Chem. 1995, 34, 743. (17)Elschenbroich, C.; Koch, J. J . Organomet. Chem. 1982,229,139. (18)Osborne, A. G.; Whiteley, R. H.; Meads, R. E. J . Organomet. Chem. 1980,193,345.

Hultzsch et al.

5498 Organometallics, Vol. 14, No. 12, 1995

Table 1. Summary of Crystal Data and Intensity Collection Parametersa

a

7

empirical formula

M, crystal class

:p(r," (11) b

c

(11,

v (113)

z

Y

d

b

&led (g ~ m - ~ ) p(Mo K)(cm-l) F(OO0) w scan width (deg) range 0 collected (deg) total no. rflns no. of unique flns refinement coefficient no. of data used no. of obsd data [I > 2dZ)I weighting a , b Ri [I > 2403 R,2 (all data) GOF (Nu),, in last cycle no. of params refined A e (max)'in final A F map (e

c1141

C14H16CrSi 264.36 orthorhombic Pbca 13.773(2) 10.829(3) 16.180(3) 2413.2(9) 8 1.455 0.10 1104 0.57 3.47-25.0 1981 1981

F

1981 1066 0.0282,O.OO 0.067 0.144 1.03 0.00

150 0.43

a Definition ofR indices: R1= Xw(Fo - F,)/XF,); R,z = {X[w(Fo2 - Fc2)12~[~(Fo2)21}"2.

d

Figure 1. (a)Molecular structure of 7 and (b) alternative view of the molecular structure of 7 (vibrational ellipsoids at the 50% probability level; hydrogen atoms are shown

as small spheres for clarity). (centroid)-Cr-arene(centroid1 angle (61, which is 167.6(3)" compared t o 180" in bis(benzene)chromium.lg The tilting of the arene rings results in a displacement (away from silicon) of the chromium atom from the line joining the two centroids of the arene ligands of 0.173(8) Additionally, the tilting of the arene ligands in 7 results in a significant distortion from planarity at the arene carbon bonded to silicon, with angles between the planes of the arene ligands and the C(arene)-Si bonds in 7 of 37.9(4)"and 38.2(4)",which are slightly smaller than that for 4 (40.8"). This substantial deviation from planarity also helps to explain the large upfield 13C NMR shift associated with the arene carbon atom bonded to silicon. The C(arene)-Si-C(arene) angle 8 in 7 [92.9(3)"1is smaller than that of 4 [96.0(2)"1and in both cases is substantially less than the ideal angle for a sp3-hybridized silicon atom. The smaller 8 angle results in a slight scissoring effect at silicon, with a widening of the C(R)-Si-C(R) [7, C(R) = Me; 4, C(R) = Phl angle to values of 111.0(4)"in 7 and 110.9(2)"in 4. The Si-C(arene) bond lengths in 7 [1.868(8) and 1.881(8)AI are essentially identical to those in 4 l1.882(4) AI. The Cr-Si distance in 7 of 2.906(1) A is longer than both the sum of the covalent radii (2.42 A)20and the corresponding value in 4 [2.842(2) AI. These distances indicate that any interaction between the Cr center and silicon is weak at best. The arene ligands in 7 are essentially eclipsed with a staggering angle of O.l(S)O. There is a n appreciable variance in the C-C bond lengths associated with the arene ligands. The

A.

(19)Keulen, E.; Jellinek, F. J. Orgunomet. Chem. 1966, 5,490. (20)Stark, J. G.; Wallace, H. G. Chemistry Datu Book; John Murray: London, 1975.

Figure 2. Distortions in arenophanes defining angles a,

p, 6, and 8.

Table 2. Final Fractional Coordinates ( x lo4) and Equivalent Isotropic Displacement Coefficients (kx 10s) for the Non-Hydrogen Atoms of 7 X

1120(1) 1286(2) 457(5) 898(5) 722(5) 57(6) -422(5) -235(5) 1964(5) 2565(5) 2598(5) 2041(5) 1466(5) 1440(5) 622(6) 2048(5)

V

732(1) 1245(2) 1824(7) 2611(7) 2476(8) 1575(7) 833(8) 941(8) 214(7) 835(7) 458(8) -535(8) -1195(7) -839(7) 371(8) 2478(7)

z

Ueai

6462(1) 8219(1) 7381(5) 6778(5) 5929(5) 5641(5) 6228(5) 7071(5) 7497(4) 6899(4) 6057(5) 5777(5) 6348(5) 7190(5) 9026(5) 8688(5)

bond lengths for the carbon atoms directly bonded to the ipso-carbons [C(l)-C(6) = 1.441(10) A,C(l)-C(2) = 1.431(10) A] are significantly longer than the other , = 1.403(10)AI. This C-C bond lengths [ e g g .C(2)-C(3) lengthening is consistent with the substantial deviation from sp2hybridization for the arene carbon atom bonded to silicon.

Silicon-Bridged [llChromarenophane Cr(q-C&&SiMe2

Thermal and Anionic Homopolymerization Behavior of 7. Attempts to thermally polymerize 7 involved heating this species in the melt in a manner analogous to that used to successfully polymerize 1. However, when 7 was heated in an evacuated tube at a temperature of 180 "C for 1h, a substantial amount of lustrous metallic chromium coated the sides of the tube and no increase in viscosity was detected. Analysis of the tube contents by IH and 29SiNMR, as well as by mass spectrometry, showed only the presence of Ph2SiMe2. Anionic ROP has previously been reported for cyclic tetrasilanesZ1 and also for the ROP of the [llferroSimilar anionic ROP methods were cenophane investigated in an attempt to induce 7 to polymerize under more mild conditions. Initial experiments focused on stoichiometric ringopening reactions of 7. When a solution of 7 in THF was treated with 1molar equiv of MeLi in diethyl ether followed by quenching of the reaction with MesSiCl, examination of the reaction products by NMR spectroscopy provided evidence for the formation of the bis[(trimethylsilyl)benzenelchromium species 8. A lH NMR spectrum (in CsD6) of the products revealed that, in fact, no monomer remained and displayed only broad resonances at 4.33-4.25 (br s, arene) and 0.25 (s, SiMe3) ppm. Further evidence for the formation of 8 was provided by a 29SiNMR (in C6D6) spectrum, which displayed a sharp resonance a t 1.9 ppm that was identical t o that of an authentic sample of 8 prepared via reaction of [Cr(q-C6H5Li)*TMEDAwith MesSiCl in hexanes. The formation of 8 demonstrated that 7 can indeed be ring-opened stoichiometrically by anionic reagents. To explore whether oligomerization or polymerization could be induced, the reaction of 7 with low concentrations (10%) of alkyllithium reagents was investigated. However, only uncharacterized mixtures of products were formed in these reactions according to 29Si NMR analysis. GPC analysis was unsuccessful, presumably as a consequence of the acute air and moisture sensitivity of the material. Mass spectral analysis also provided no useful information in the form of peaks assignable t o monomeric or oligomeric fragments. In an attempt t o yield products that were amenable to characterization, the thermal and anionic copolymerization reactions of 7 with the silicon-bridged [llferrocenophane 1 were explored. Thermal and Anionic Copolymerization of 7 with 1. A sealed tube containing an equimolar ratio of 7 and 1 was heated for 3 h a t 140 "C. No significant increase in viscosity was detected. Analysis of the tube contents by lH NMR and GPC showed a significant amount of the two starting monomers and small quantities (yield = 10%)of the poly(ferrocenylsilane)2. Under identical conditions, as a control, a pure sample of 1 underwent ROP t o yield poly(ferrocenylsi1ane) 2 in greater than 80-90% yield.22 Extended heating (72 h) of a 1:l molar mixture of 1and 7 at 140 "C in a sealed Pyrex tube produced an immobile black solid, which l.5c17

(21) Cypryk, M.; Gupta, Y.; Matyjaszewski, K. J.Am. Chem. SOC. 1991,113,1046. (22) Interestingly, in other experiments it was found that the addition of 10-25% of 7 to 1 led to a n effective inhibition of the thermally induced ROP process, with dramatic redudions in both yield and molecular weight. In contrast, polymerizations of 1 carried out in 1:l molar ratios with bis(benzene)chromium showed no signs of significant inhibition. See the Experimental Section for details.

Organometallics, Vol. 14, No. 12, 1995 5499

Figure 3. lH NMR spectrum of copolymer 9b in C6D6. showed partial solubility in hexanes and good solubility in C6D6. Analysis of this material by multinuclear (lH, 29Si,I3C)NMR afforded data consistent with the formation of a cooligomer or copolymer 9a, presumably mixed with poly(ferrocenylsi1ane) 2 on the basis of the results of the 3 h e ~ p e r i m e n t .Treatment ~~ of an equimolar amount of 7 and 1 in THF with 10 mol % n-BuLi in THF yielded an analogous copolymer 9b. The IH NMR spectra of the poly(ferrocenylsi1ane)-poly(chr0marenosilane) copolymers displayed broad resonances a t 4.24.3 ppm assigned to both arene and Cp protons, 4.14.2 ppm assigned t o Cp protons, and 0.5-0.6 ppm assigned to SiMe2 protons (see Figure 3 for 9b). The integration ratio for the arene and cyclopentadienyl regions of the IH NMR spectrum showed that the ratios of Cr:Fe in the copolymers were ca. 1:4.6 in 9a and 1:1.6 in 9b. Further structural characterization of 9a and 9b was provided by 29Siand I3C NMR spectroscopy. Analysis of the copolymers by 29SiNMR (in CsD6) showed resonances for the ferrocenyldimethylsilane units at -6.4 ppm3 and a broad resonance for chromarenodimethylsilane segments at f 3 . 7 ppm and also revealed a small peak for a SiMea crossover group between the ferrocenyldimethylsilane and chromarenodimethylsilane segments a t -1.3 ppm (see Figure 4 for 9b). Very little information has been published concerning the 29SiNMR shifts of ring substituted bis(benzene)chromium compounds, and to provide additional support for our assignments, we synthesized the biddimethylphenylsi1ane)-substituted species 10 by reaction of [Cr(q-C&&Li)2l-TMElDA with MezPhSiCl in hexanes. Compound 10 was found t o display a 29SiNMR resonance at +0.7 ppm. As uncomplexed Ph2SiMe2 displays a 29Si NMR resonance at -7.9 ppm, a comparison suggests that complexation of both phenyl groups in PhzSiMez chromium would result in a significant downfield chemical shift from $0.7 ppm, which is reasonably consistent with our value for a ring-opened chromarenosilane segment in 9a and 9b a t +3.4 ppm. The 13C NMR spectra of 9a and 9b were also consistent with the assigned copolymer structure. Further evidence for the copolymeric nature of these materials was provided by mass spectrometric analysis of samples, which were heated under vacuum at 100 "C in the mass spectrometer probe, and the thermal decomposition (23) Elemental analysis data for 9a and 9b were repeatedly low for C (e.g.,for 9b Anal. calcd C, 61.10;H, 5.89.Found: C, 53.70; H, 5.64). Similar problems have been noted for Cr-arene compounds (see footnote 13 in ref 15).

Hultzsch et al.

5500 Organometallics, Vol. 14, No. 12, 1995

8 R=Me

9a-b

10RsPh

Summary and Conclusions

Figure 4. 29SiNMR spectrum of copolymer 9b in C&.

products were found to contain the oligomer species CsHsSiMe2((r-CsH4)Fe(r-CsH~)SiMe2)~C6Hs ( x = 1-4). GPC analysis of the molecular weights of the copolymers 9a and 9b was not possible due to the acute air sensitivity of the materials. An alternative method to measure the molecular weights of the copolymers 9a and 9b involved treatment with methanol, which is known to cleave arene-silicon bonds in these bis(benzenelchromium-based systems to afford C6H6 and SiOH group^.^^^^^ This resulted in partial, but controlled decomposition of the copolymer to leave the ferrocenyldimethylsilane segments intact. Similar partial decomposition techniques using W light were previously used to confirm the nature of poly(ferroceny1silane)-poly(si1ane) copolymer^.^^ GPC analysis of 9a after methanolysis provided a minimum molecular weight estimate (assuming a block copolymer) and gave an approximate weight-average molecular weight (M,) of 2.0 x lo3 and a number-average molecular weight (M,)of 0.9 x lo3. This suggests that the M, for the copolymer 9a is at least 2.4 x lo3 on the basis of the Cr:Fe ratio from lH NMR integration. The polymeric nature of this methanolysis product was confirmed by lH NMR spectroscopy, which showed characteristic resonances associated with the poly(ferroceny1dimethylsilane) (2).3An analogous procedure for 9b showed that the value of M, is a t least 1.2 x lo4. The lower molecular weight for the thermally derived copolymer 9a is also consistent with the partial solubility of this material in hexanes, which is a nonsolvent for 9b and 2. (24) In a n attempt to estimate of the molecular weights of 9a and 9b,these materials were first oxidized with [Fe(q-C6H5)21[PFelin THF. However, analysis of the oxidized materials by GPC showed only peaks with M , < ca. 2000, which trailed into that ofthe solvent. Presumably due to the ionomeric nature of oxidized 9a and 9b,the use of GPC analysis with polystyrene standards provides a poor estimate of the molecular weight. (25) Fossum, E.; Matyjaszewski, K.; Rulkens, R.; Manners, I. Macromolecules 1995,28, 401.

The silicon-bridged [llchromarenophane 7 has been synthesized and structurally characterized. Unlike the silicon-bridged [llferrocenophane 1, this compound is resistant to thermal and anionic homopolymerization via ROP; however, through thermal and anionic copolymerization with polymerizable 1,the bimetallic airsensitive oligomeridpolymeric materials 9a and 9b have been prepared. Recent work has shown that the thermal ROP of silicon-bridged [llferrocenophane occurs by cleavage of the cyclopentadienyl carbon-bridging atom (Le., silicon) bond via a process that is probably heterolytic in nature.26 The difference in polymerization behavior observed for the [llchromarenophane 7 compared to the analogous [llferrocenophane 1 can be attributed to the lower Cr-arene bond energy, which is ca. 170 kJ molv1 compared to ca. 220 kJ mol-l for a Fe-Cp bond.27 Thus, at elevated temperatures ( e g . , 180 "C) exclusive extrusion of Cr is detected. At lower temperatures (ca. 140 "C), this extrusion process is much slower and it is possible t o induce copolymerization with 1. Analogous air- and moisture-sensitive copolymers were also formed by anionic copolymerization of 7 with 1. We are now investigating the synthesis and polymerization behavior of other strained, transition-metalcontaining rings, and our results will be the subject of future publications. Experimental Section Materials. Dimethyldichlorosilane (MezSiClz), dimethylphenylchlorosilane (MezPhSiCl),trimethylchlorosilane (MeaSiCl),1.6 M butyllithium in hexanes, 1.4 M methyllithium in diethyl ether, tetramethylethylenediamine (TMEDA),ferrocenium hexafluorophosphate,and chromium(II1)chloride were purchased from Aldrich. Bis(benzene)chromium,dilithio[bis(benzene)chromium].TMEDA, and dilithioferrocene.TMEDA were synthesized by literature p r ~ c e d u r e s . ~ ~ J ~ Equipment. All reactions and manipulations were carried out under an atmosphere of prepurified nitrogen using either Schlenk techniques or an inert-atmosphere glove box (Vacuum Atmospheres). Solvents were dried by standard methods, distilled, and stored under nitrogen over activated molecular sieves. lH NMR spectra (200 MHz) and 13CNMR spectra (50.3 MHz) were recorded on either a Varian Gemini 200 or a Varian XL 400 spectrometer, respectively. The 79.4 MHz 29SiNMR spectra were referenced externally to SiMe4 (TMS)and were recorded on a Varian XL 400 spectrometer utilizing either a normal (proton-coupled) or a DE€" pulse sequence (protondecoupled) with a VS,-H coupling of 6.7 Hz. All NMR spectra were performed in benzene-&, which was dried over sodium and stored under nitrogen over activated molecular sieves, and were referenced internally to TMS. Mass spectra were obtained with the use of a VG 70-250s mass spectrometer (26) Pudelski, J . K.;Manners, I. J . Am. Chem. SOC.1995,117,7265. (27) (a) The Cr-(rp&H6) bond energy of Cr(v-C6H& is ca. 170 kJ/ mol, and the Fe-(pCbH5) bond energy of Fe(v-CsH& is ca. 220-270 kJ/mol [see Elschenbroich, C.; Salzer, A. Organometallics; VCH: Weinheim, Germany, 19921.

Silicon-Bridged [llChromarenophane Cr(q-C&&SiMeZ operating in an electron impact (EI) mode. Molecular weights were estimated by gel permeation chromatography (GPC) by using a Waters Associates liquid chromatograph equipped with a 510 HPLC pump, U6K injector, and ultrastyragel columns packed with high-performance, fully porous, highly crosslinked styrene-divinylbenzene copolymer particles, with a pore size between lo3and lo5A, and a Waters 410 differential refractometer. A flow rate of 1.0 m u m i n was used, and the eluent was a solution of 0.1%tetra-n-butylammonium bromide in THF. Polystyrene standards were used for calibration purposes.

Synthesis of the Silicon-Bridged[lIChromarenophane 7. To a suspension of [Cr(l;l-C6HbLi)z*TMEDA(2.42 g, 7.2 mmol) in hexane (40 mL) was added MezSiClz (0.93 g, 7.4 mmol) at -78 "C. The reaction mixture was stirred a t this temperature for 3 h and was then allowed to warm to room temperature over a 12 h period. Removal of solvent under vacuum left 7 as a black powder that was isolated and purified by recrystallization from hexanes a t -20 "C (yield, 1.04 g (56%)). 'H NMR (200 MHz) (CDC13): 6 4.7 (t, 3 5= 5.3 ~ Hz, ~ 2H,p-C&), 4.5 (t, 35HH = 5.4 HZ, 4H,m-CsHd, 3.9 (d, 35HH = 5.1 Hz, 4H,o-CsHb), 0.3 (5, 6H, SiMe). I3C NMR (CDC13): 6 82.7 (p-C6H5),79.1 (o-C6H5),75.4 (m-CsHs),39.5 (ipso, c p s i ) , -4.9 (SiMe). 29SiNMR (79.5 MHz) (CsDs): 6 21.0. MS (EI, 70 eV): m l z 264 (M+, 1001, 249 (M+ - CH3, 391, in good agreement with isotopic abundance calculations. HRMS calculated for C14H1ss2crz8Si264.0426, found 264.0427. Synthesis of Bis[(trimethylsilyl)benzene]chromium (8). To a suspension of [Cr(r-CsHsLi)z].TMEDA(0.20 g, 0.6 mmol) in cyclohexane (40 mL) was added Me3SiCl(0.40 g, 3.2 mmol) at -20 "C. The reaction mixture was stirred a t this temperature for 3 h and was then allowed t o warm to room temperature over a 12 h period. Removal of solvent under vacuum left 8 as a black powder that was isolated and purified by sublimation at high vacuum (70 "ClO.005 mmHg) to give very air-sensitive dark brown crystals (yield, 0.15 g (72%)). 'H NMR (200 MHz) (C6Ds): 6 4.33-4.25 (br S, 10H, C&), 0.25 (br s, 18H, SiMe3). 29SiNMR (79.5 MHz) (C6Ds): 6 1.9 (s, SiMe3). MS (EI, 70 eV): m l z 352 (M+, 35), 280 (M+ SiMe3, 121, 135 (SiPhMez, 1001, in good agreement with isotopic abundance calculations. Synthesis of Bis[(dimethylphenylsilyl)benzene]chromium (10). To a suspension of [Cr(l;l-CsHsLi)z].TMEDA (0.22 g, 0.7 mmol) in cyclohexane (40 mL) was added PhMezSic1 (0.34g, 3.2 mmol) at -20 "C. The reaction mixture was stirred a t this temperature for 3 h and was then allowed t o warm t o room temperature over a 12 h period. Removal of solvent under vacuum left 9 as a black powder that was isolated and purified by sublimation a t high vacuum (70 "Cl 0.005 mmHg) to give very air-sensitive dark brown crystals (yield, 0.21 g (72%)). 'H NMR (200 MHz) (CsDs): 6 7.77 (m, 2H, SiPh), 7.16-7.19 (m, 3H, SiPh), 4.38 (br s, 3H, C&), 4.28 (br s, 2H, CsH5), 0.25 (br s, 6H, SiMez). 29SiNMR (79.5 MHz) (CsDs): 6 0.7 (s, SiPhMez). MS (EI, 70 eV): m / z 476 (M+,381, 341 (M+ - SiPhMez, 91,135 (SiPhMez, 1001, in good agreement with isotopic abundance calculations. HRMS calculated for C ~ & Z ~Si2~476.1448, C ~ ~ found ~ 476.1450. Attempted Thermal ROP of 7. Samples of 7 (ca. 120 mg, 0.43 mmol) were heated in evacuated, sealed Pyrex glass tubes a t temperatures of 180 "C for 1 h, resulting in the production of chromium metal and PhzSiMez, as confirmed by 'H and 29Si NMR and mass spectrometry. 'H NMR (200 MHz) (CsDs): 6 7.45 (m, 4H, SiPh), 7.15-7.19 (m, 6H, SiPh), 0.41 (br s, 6H, SiMez). 29SiNMR (79.5 MHz) (CsDs): 6 -7.9 (s, MezSiPhz). MS (EI, 70 eV): m l z 212 (M+, 26), 197 (M+ - Me, 9), 135 (SiPhMez, 12). No increase in melt viscosity was noted, and analysis of the tube contents by mass spectrometry and GPC in THF showed that no high molecular weight ( M , > lOOO), GPC-active material was present. (28)Sheldrick, G. M. SHELXA-90, Program for Absorption Correction;University of Gottingen: Gottingen, Germany, 1994.

Organometallics, Vol. 14,No. 12, 1995 5501 Anionic Ringopening Reactions of 7. (a)To a solution of 7 (30 mg, 0.11 mmol) in 2 mL of THF was added 0.08 mL (0.11 mmol) of a 1.4 M solution of MeLi in diethyl ether The reaction mixture was stirred for 1.5 h and quenched with an excess of Me3SiC1. Analysis of the reaction mixture by 'H and 29SiNMR showed resonances consistent with the formation of bis[(trimethylsilyl)benzene]chromium (8). 'H NMR (200 MHz) (CsDs): 6 4.33-4.25 (br s, 10H, C&), 0.25 (br s, 18H, SiMe3). 29SiNMR (79.5 MHz) (CsDs): 6 1.9 (s, SiMe3). (b) To a solution of 7 (100 mg, 0.38 mmol) in 3 mL of THF was added 0.027 mL (0.038 mmol) of a 1.4 M solution of MeLi in diethyl ether. The reaction mixture was stirred for 1.5 h and quenched with 0.04 mL of Me3SiCl(O.38 mmol). 'H NMR (200 MHz) (CsDs): 6 4.40-4.10 (br s, arene), 0.54 (br s). 29si NMR (79.5 MHz) (CsDs): 6 30.6, 7.6, and 4.8. Analysis of this solid by GPC was not possible due to the acute air sensitivity of the material. (c) To a solution 7 (100 mg, 0.38 mmol) in 3 mL of THF was added 0.023 mL (0.037 mmol) of a 1.6 M solution of BuLU hexanes. The reaction mixture was stirred for 1.5 h and quenched with 0.04 mL of MesSiCl(O.38mmol). 'H NMR (200 MHz) (CsDs): 6 4.40-4.10 ( b r s , arene), 0.54 (br s). z9SiNMR (79.5 MHz) (C&): 6 27.5, 7.6, and 4.6. Analysis of this solid by GPC was not possible due to the acute air sensitivity of the material. Attempted Thermal Copolymerization of 7 with the [lIFerrocenophane 1. (a) A mixture consisting of a 1:l molar ratio of 7 (100 mg, 0.38 mmol) and 1 (90 mg, 0.37 mmol) was heated a t 140 "C for (i) 1, (ii) 3, (iii) 47, and (iv) 72 h. In the cases of i-iii, no significant increase in melt viscosity was noted, and analysis of the tube contents by 'H and 29SiNMR revealed that a varying amount of the poly(ferrocenylsi1ane) 2 was either (i) not detectable, (ii) ca. 10%and (iii) 50%based on 'H NMR integration together with the two starting monomers. In the case of iv, heat treatment resulted in the formation of an immobile black solid, which was analyzed by multinuclear ('H, 29Si, I3C) NMR and found to possess resonances consistent with the formation of a poly(ferroceny1silane)-poly(chromarenosi1ane) copolymer 9a. For 9a: 'H NMR (200 MHz) (C&) 6 4.28 (br s), 4.11 (br s), 0.55 (br s); I3C NMR (50.3 MHz) (CsDs) 6 79.1 (s, arene), 76.5 (s, arene), 74.8 (s, arene), 74.1 (9, ipso-arene), 73.7 (s, Cp), 71.9 (s, ipso-Cp), 71.4 (s, Cp), -0.5 (s, CpSiMezCp), -1.0 (s, CpSiMez-arene), -1.6 (s, arene-SiMez-arene);29SiNMR (79.5 MHz) (CsDs) 6 3.4 (br s, arene-Si-arene), -1.3 (br s, CpSi-arene), -6.4 (br s, CpSiCp). This material was treated with methanol (20 mL) and filtered, and the solvent was removed in vacuo, leaving a brown residue. Analysis of this material by 'H NMR in CsDs showed resonances a t 4.28 (br s, 4H, l;l-C5H4),4.11 (br s, 4H, l;l-C5H4), and 0.56 (br s, 6H, SiMe) ppm, consistent with the formation of poly(ferrocenylsi1ane) 2. Analysis of this solid by GPC revealed that this material possesses a weight-average molecular weight (M,) of ca. 2.0 x lo3 and a number-average molecular weight (M,) of ca. 0.9 x lo3. On the basis of 'H NMR integration, this suggests that a minimum estimate of molecular weight for this material is ca. 2.4 x lo3. (b) A mixture consisting of a 1:4 molar ratio of 7 (20 mg, 0.076 mmol) of l ( 7 0 mg, 0.29 mmol) was heated for (i) 3 and (ii) 47 h a t 140 "C. In each case, no increase in melt viscosity was noted, and analysis of the tube contents by 'H and 29Si NMR and GPC revealed that a small to moderate amount of the poly(ferrocenylsi1ane)2 was present: (i) ca. lo%,M,., = 6.6 x lo3, M , = 4.7 x lo3, polydispersity (M,/M,) = 1.4; (ii) 55%,M , = 5.5 x lo3, M , = 4.3 x lo3,polydispersity (M,lM,) = 1.4. The two starting monomers were also identified by 'H NMR. Influence of Bis(benzene)chromiumon the Thermal ROP of the [lIFerrocenophane 1. A mixture consisting of a 1:l molar ratio of bis(benzene1chromium (50 mg, 0.24 mmol) and 1 (58 mg, 0.24 mmol) was heated for 10 min at 150 "C, a t which point a considerable increase in viscosity was noted and the tube contents became immobile. Analysis of the tube

Hultzsch et al.

5502 Organometallics, Vol. 14, No. 12, 1995 contents by lH NMR revealed that the poly(ferrocenylsi1ane) 2 (approximately 10%based on NMR integrations) was present along with the two starting monomers. For polymer 2: M, = 3.6 x lo5, M, = 2.3 x lo5, polydispersity (M,/M,) = 1.6. Anionic Copolymerization of 7 with the [lIFerrocenophane 1. To a 1:lmolar mixture of 7 (50 mg, 0.19 mmol) and 1 (45 mg, 0.19 mmol) in 10 mL of THF was added 0.01 mL (0.016 mmol) of a 1.6 M solution of BuLi in hexanes. The reaction mixture was stirred for 1.5 h and quenched with 0.02 mL of MeaSiCl (0.16 mmol). Analysis of the black reaction product 9b by lH and 29SiNMR showed resonances consistent with the formation of a poly(ferrocenylsi1ane)-poly(chromarenosilane) copolymer. lH NMR (200 MHz) (CsDs): 6 4.37 (br s, arene), 4.26 (br s, Cp), 4.10 (br s, Cp), 0.54 (br s, SiMe2). 13C NMR (50.3 MHz) (C6D6): 6 79.1 (s, arene), 76.5 (s, arene), 74.8 (s, arene), 74.1 (s, ipso-arene), 73.7 (s, Cp), 71.9 (s, ipso-Cp), 71.4 (s, Cp), -0.5 (s, CpSiMezCp), -1.0 (s, CpSiMe2-srene), -1.6 (s, arene-SiMe2-arene). 29SiNMR (79.5 MHz) (CsD6): 6 3.4 (br s, arene-Si-arene), -1.3 (br s, CpSi-arene), -6.4 (br s, CpSiCp). MS (EI, 70 eV): m l z 1180 (((Fe(r-C5H4)2SiMe2)4(C&)2SiMe2, 81, 938 ((Fe(rl-CsH4)2SiMe2)3(CsHs)zSiMez), 41, 726 (((Fe(rl-C5H4)2SiMe2)3,30), 696 ((Fe(q-CsH4)2SiMe2)2(C6Hs)2SiMe2),5), 528 ((C6H&CrSiMe2)2), 361, 502 ((Fe(r-C5H5)(r-C5H4)(SiMe20SiMe2)(Fe(r-CsH4)(r-CsH5)), 751, 484 ((Fe(r-CsH4)2SiMez)z,361,454 ((Fe(r-CsH4)2SiMez)((CsH5)2SiMez), 1001, 428 ((Fe(r-CsH4)2SiMe2(Fe(r-C5H4)2, 61, 363 ((Fe(r-C5H4)2SiMe2(r-C5H4)Fet 141, 243 ((Fe(rl-CsH&SiMez+ H, 33), 197 (PhzSiMe,18), 186 ((Fe(r-CbH&, 12), 135 (PhSiMe2, 49). This material was treated with methanol (20 mL) and filtered, and solvent was removed in vacuo, leaving a brown residue. Analysis of this material by 'H NMR in CsDs showed resonances a t 4.28 (br s, 4H, q-C5H4),4.11 (br s, 4H, l;l-C5H4), and 0.56 (br s, 6H, SiMe) ppm, consistent with the formation of poly(ferrocenylsi1ane) 2. Analysis of this solid by GPC revealed that this material possesses a weight-average molecular weight (M,) of ca. 7.5 x lo3 and a number-average molecular weight (M,) of ca. 6.7 x lo3. On the basis of 'H NMR integration, which showed a 1:1.6, Cr:Fe ratio, this suggests that a minimum estimate of molecular weight for this material is ca. 1.2 x IO4. X-ray Structural Determination Technique. Intensity data were collected on an Enraf-Nonius CAD4 (Siemens P4) diffractometer a t 173 K, using graphite monochrominated Mo K a radiation (2. = 0.710 73 A). The w scan technique was

applied with variable scan speeds (4 to 45 deg/min in 0).The intensities of three standard reflections measured every 97 reflections showed no decay. The data were corrected for Lorentz and polarization effects. A semiempirical absorption correction was carried out using SHELXA-9028(in SHELXL93). The program used for absorption correction was SHEIXAwhich uses A F refinement for corrections. The structure was solved by direct methods. Non-hydrogen atoms were refined with anisotropic thermal parameters by full-matrix least squares t o minimize Cw(F, - Fc)2,where W-l= u2(F,) bP, where P = (F,2 2FC2)/3.Hydrogen atoms were included in calculated positions (C-H distance of 0.96 A) with U,,, of 0.030(6)A2 for ring hydrogens and O.Ol(2)A2 for methyl hydrogens. Crystal data, data collection, and least-squares parameters are listed in Table 1. All calculations were performed and structural diagrams were created by using SHELXTL PC29 on a 486-66 personal computer. Atomic coordinates are listed in Table 2; other data concerning the crystal structure are given in the supporting information.

+

+

+

Acknowledgment. This work was supported by the Petroleum Research Fund (PRF), administered by the American Chemical Society, and the Natural Science and Engineering Research Council of Canada (NSERC). We also thank the University of Toronto for an Open Research Fellowship for J.M.N., the Deutscher Akademischer Austauchdienst (DAAD)for an overseas exchange award for K.C.H., and Mr. Nick Plavac for obtaining the 29SiNMR spectra. In addition, I.M. is grateful to the Alfred P. Sloan Foundation for a Fellowship (1994-1996). Supporting Information Available: Tables of atomic coordinates, complete bond lengths and angles, anisotropic thermal parameters, hydrogen atom coordinates,torsion angles, and least squares plane data and a figure showing the structure of 7 (9 pages). Ordering information is given on any current masthead page. OM950477X (29) Sheldrick, G. M. SHELXTL-93, Program for Crystal Structure Refinement; Gottingen, Germany, 1994.