Limiting the relative orientation of bridged cyclopentadienyl anions. Mono- and dianions derived from 4,4,8,8-tetramethyltetrahydro-4,8-disila-s-indacenes

Abstract

Two isomers of 4,4,8,8-tetramethyltetrahydro-4,8-disila-s-indacene have been deprotonated under various conditions to give novel anions in which a cyclopentadienyl (Cp) and a cyclopentadiene or two Cp's are doubly bridged by Me 2 Si fragments to give the monoanion 3 or the dianion 4. Use of NaH or 1 equiv of n-BuLi selectively yielded 3 whereas KH or 2 equiv of n-BuLi gave 4. Temperature-dependent NMR spectroscopy showed the two enantiomers 3a/b of the monoanion to undergo both a degenerate and a nondegenerate silatropic rearrangement with a barrier of E a =48.5 kJ mol −1 . The solid-state structure of 4Li 2 (TMEDA) 2 was determined by X-ray structure analysis