HIGHLY TWISTED ETHYLENE DIANION DILITHIUM STABILIZED BY PHENYL AND SILYL GROUPS

Phenyl- and silyl-substituted ethylene dianion dilithiums, [1-phenyl-1 ,2,2-tris(trimethylsilyl)ethylene]{bis [(dimethoxyethane)lithium(I)]} (2) and [1,1-diphenyl-2,2-bis(trimethylsilyl)ethylene] [tris(tetrahydr ofuran)dilithium(I)] (4), were prepared and characterized by X-ray cry stallography as well as NMR spectra. The crystal structures of 2 and 4 revealed interesting structural features. One of the lithium cations was located near to the two central carbon atoms, ipso and ortho carbo ns of the phenyl ring, while the other one was found above the benzene ring. The central C-C bond is twisted by ca. 90 degrees for 2 and ca. 70 degrees for 4.