Tetrasupersilyl-tristannaallene and -tristannacyclopropene (tBu3Si)4Sn3 – Isomers with the Shortest Sn=Sn Double Bonds to Date

Abstract

The dark blue, air- and moisture-sensitive, thermolabile tristannaallene R*2Sn=Sn=SnR*2 (5) (R* = SitBu3) is prepared by reaction of Sn(OtBu)2 or Sn[N(SiMe3)2]2 with R*Na in pentane/benzene at –25°C. The dark red-brown, air-sensitive, moisture-insensitive, and thermostable cyclotri-stannene R*4Sn3 (6) with a –R*Sn=SnR*– moiety as part of a Sn3 ring is obtained from the reaction of Sn(OtBu)2 or Sn[N(SiMe3)2]2 with R*Na in pentane at 25°C or from the isomerization of 5 at room temperature (τ1/2 = 9.8 h). According to the result of X-ray structural analyses the Sn3 framework of chiral 5 is bent (156°) and the terminal Sn atoms have pyramidal surroundings. The SnSn double bonds in 5 (2.68 Å) are shorter than those found for the hitherto structurally investigated distannenes (2.77–2.91 Å). Even shorter is the double bond in 6 (2.59 Å). The unsaturated Sn atoms here have nearly planar surroundings in perfect analogy to the carbon atoms in CC double bonds. The SnSn double bond in 6 can therefore be considered as the first “true” Sn=Sn bond. The structures of 5 and 6 can be deduced also from 119Sn- and 29Si-NMR studies in solution.