title: Base-free molybdenum and tungsten bicyclic silylene complexes stabilized by a homoaromatic contribution.
abstract: Unprecedented base-free bicyclic silylene complexes of molybdenum and tungsten 3a,b (a, M = Mo; b, M = W) were prepared by the reaction of the calcium salt of 1,2,3,4-tetrakis(di-tert-butylmethylsilyl)tetrasilabicyclo[1.1.0]butane-2,4-diide 2(2-) x Ca(2+) with Cp(2)MCl(2) (M = Mo, W). The unusual structural features of 3b (long SiW double bond, short skeletal (sp(2)-Si)-(sp(3)-Si) bonds and extremely long Si-Si bridge) are indicative of a contribution from the zwitterionic resonance form W(delta-)-Si(delta+), in which the electrophilic silicon center is stabilized by the Si(3)-homoaromatic conjugation. This was supported by the theoretical calculations (NBO, NPA) revealing the presence of pi(WSi) and sigma(Si-Si bridge) interactions.
authors.affiliation: Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Takanashi
authors.forename: Vladimir Ya
authors.initials: VY
authors.lastname: Lee
authors.forename: Taka
authors.initials: T
authors.lastname: Yokoyama
authors.forename: Akira
authors.initials: A
authors.lastname: Sekiguchi