title: Synthesis, properties, and reactions of a series of stable dialkyl-substituted silicon-chalcogen doubly bonded compounds.
abstract: The first dialkyl-substituted silicon-chalcogen doubly bonded compounds [R2Si=X; R2=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 dialkylsilylene R2Si: (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.
authors.affiliation: Department of Chemistry, and Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. iwamoto@mail.tains.tohoku.ac.jp
authors.forename: Takeaki
authors.initials: T
authors.lastname: Iwamoto
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Sato
authors.forename: Shintaro
authors.initials: S
authors.lastname: Ishida
authors.forename: Chizuko
authors.initials: C
authors.lastname: Kabuto
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Kira