CARBON-HYDROGEN BOND PROPERTIES AND ALKYL GROUP GEOMETRIES IN CHLORO(ETA(5)-CYCLOPENTADIENYL)-METHYLTITANIUM(IV) AND PENTADIENYL)-ETHYLTITANIUM(IV)[TIR(ETA(5)-C5H5)CL] (R=ME OR ET)

Infrared spectra have been recorded for various isotopomers of [TiMe(c p)Cl-2] (cp = cyclopentadienyl. eta(5)-C5H5 . Me = CH3! CD3 or CHD2) a nd [TiEt(cp)Cl-2] (Et = CH3CH2, CD3CH2 CH3CD2 or CHD2CD2) and assignme nts proposed for the alkyl group vibrations; A method was elaborated f or the calculation of Fermi-resonance-shifts on CH and CD stretching m odes in methyl groups with C-3v and C-s symmetry. Estimates of CH bond lengths, bond strengths and HCH angles were derived;from the resonanc e-corrected frequency data. The results show the methyl group in [TiMe (cp)Cl-2] to be markedly asymmetric, with the CH bond trans to the cyc lopentadienyl ligand being ca. 0.005 Angstrom longer and 15 kJ mol(-1) weaker;than those trans to chlorine. In the ethyl compound, the termi nal methyl group is similarly asymmetric, again with one weak bond and two stronger bonds. The vCH(2), and vCD(2) frequencies fdr the methyl ene group are anomalous and can only be satisfactorily interpreted in terms of a model in which the two methylene CH bonds are inequivalent. The estimated bond lengths are 1.100(5) and 1.105(9) Angstrom, and th e corresponding bond dissociation energies are 403 and 383 kJ mol(-1), respectively. These results appear to point to a direct alpha-interac tion between at least one of the methylene CH bonds and the titanium a tom. A similar effect may also occur in [TiMe(cp)Cl-2].