title: Isomeric metamorphosis: Si3E (E = S, Se, and Te) bicyclo[1.1.0]butane and cyclobutene.
abstract: Group 14 and 16 hybrid heavy bicyclo[1.1.0]butanes (tBu2MeSi)4Si3E (E = S, Se, and Te) 2a-c have been prepared by the [1 + 2] cycloaddition reaction of trisilirene 1 and the corresponding chalcogen. Bicyclo[1.1.0]butanes 2 have exceedingly short bridging Si-Si bonds (2.2616(19) A for 2b and 2.2771(13) A for 2c), a phenomenon explained by the important contribution of the trisilirene-chalcogen pi-complex character to the overall bonding of 2. Photolysis of 2a and 2b produced their valence isomers, the heavy cyclobutenes 3a and 3b, featuring flat four-membered Si3E rings and a planar geometry of the Si=Si double bond. The mechanism of such isomerization was studied using deuterium-labeled 2a-d6 to ascertain the preference of the pathway, involving the direct concerted symmetry-allowed transformation of bicyclo[1.1.0]butane 2 to cyclobutene 3.
authors.affiliation: Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Vladimir Ya
authors.initials: VY
authors.lastname: Lee
authors.forename: Shogo
authors.initials: S
authors.lastname: Miyazaki
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yasuda
authors.forename: Akira
authors.initials: A
authors.lastname: Sekiguchi