281 Journal of Organometallic Chemistry, 341 (1988) 281-291 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM Structure and dynamics of hindered organosilicon compounds. The conformation and enantiotopomerization of (chlorodiphenylsilyl) (methoxydimethylsilyl) - bis( trimethylsilyl) methane * Anthony G. Avent, Paul D. Lickiss, School of Chemistry and Molecular Sciences, University of Sussex, Brighton BNl 9QJ (Great Bntain) and Alan Pidcock School of Chemistry, Lancashire Polytechnic, Preston PRI 2TQ (Great Bntain) (Received October 20th, 1987) Abstract At low temperatures, the ‘H and 13C NMR spectra of (chlorodiphenylsilyl)(meth- oxydimethylsilyl)bis(trimethylsilyl)methane show resonances from nine non-equiv- alent methyl groups, and are consistent with the presence in solution of enantio- topomeric molecules with conformations very similar to those found in the solid state by an X-ray crystal structure determination. By means of NOESY and COSY 2D NMR experiments, the ‘H and 29Si resonances have been assigned to particular sites in the molecule, and the enantiotopomerization has been shown to be of ESSS type, with free energy of activation 43.3 kJ mol-‘. Some aspects of the structure and chirality of hindered molecules, such as those containing (Me,Si),C groups, are discussed. Introduction During the last ten years, Eaborn and co-workers have used bulky groups such as (Me,Si),C (“Trisyl” denoted Tsi) and (PhMe,Si),C to stabilize many novel organometallic compounds and to prepare and study the unusual reactions of highly hindered organosilicon compounds [l]. X-Ray crystal structure determinations have shown that as well as providing steric protection for atoms to which it is attached, the trisyl group is itself strained internally, and the bonds from silicon to the central * Dedicated to Professor Cohn Eabom on the occasion of his 65th birthday and in gratitude for many (continuing) years of friendly and fruitful collaboration. 0022-328X/88/$03.50 0 1988 Elsevier Sequoia S.A.