Following on from a search for long C-C bonds, here is the same repeated for C=C double bonds. The query restricts the search to each carbon having just two non-metallic substituents. To avoid conjugation with these, they each are 4-coordinated; the carbons themselves are three-coordinated.
Abstract 2,3,6,7-Tetrakis(trimethylsilyl)-1,1,4,4,5,5,8,8-octamethyl-1,4,5,8-tetrasila-1,4,5,8-tetrahydroanthracene (3) was prepared starting from 2,3,6,7-tetrakis(dimethylsilyl)-1,1,4,4,5,5,8,8-octamethyl-1,4,5,8-tetrasila-1,4,5,8-tetrahydroanthracene (1). The molecular structures of 1 and 3 have been determined by X-ray crystallography. Compound 1 has an almost planar structure, whereas compound 3 exhibits a highly folded structure due to the steric repulsion of the trimethylsilyl groups. Treatment of 1 and 3 with lithium metal yielded the corresponding tetralithium salts of the tetraanions 4 and 5, in which the two tetrasilylethylene units were subjected to two-electron reduction. 2,3-Bis(dimethylsilyl)-1,1,4,4-tetramethyl-1,4-disila-1,4-dihydronaphthalene (6), which has a half unit of 1, was reacted with lithium metal to give the dilithium salt of the dianion (7). Evidence for an interaction between the Si-H and the Li+ ion of 4 and 7 in both solid state and solution is also given.