Synthesis,Properties,and Reactions of a Series of Stable Dialkyl-Substituted Silicon-Chalcogen Doubly Bonded Compounds

摘要

The first dialkyl-substituted silicon-chalcogen doubly bonded compounds [R_2Si=X; R_2 = 1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl,X = S (4),Se (5),and Te (6) ] were synthesized by the reactions of an isolable diaikylsilylene R_2Si: (3) with phosphine sulfide,elemental selenium,and elemental tellurium,respectively.Systematic changes of characteristics of silicon-chalcogen double bonds are elucidated by X-ray analysis,UV-vis spectroscopy,and DFT calculations.In the solid state,the unsaturated silicon atom in 4-6 adopts planar geometry and the extent of the shortening of Si=X double bonds from the corresponding Si-X single bonds decreases in the order 4 > 5 > 6.In the absorption spectra of 4-6,pi -> pi transition bands are observed distinctly in addition to n -> pi transition bands.Both the n -> pi and pi-> pi transitions are red-shifted in the order 4 < 5 < 6,and the difference between the energies of the two transitions is kept almost constant among 4-6.The tendency is explained using the qualitative perturbation theory and is reproduced by the DFT calculations for model silanechalcogenones.Addition reactions of water,methanol,and isoprene to 4-6 are reported.