Formation of silylcarbaboranes from 1,2-bis(trimethylsilyl)pentaborane(9)

Abstract

By way of an apparent carbon-insertion process, 1,2-bis(trimethylsilyl)pentaborane(9) gives, on flash thermolysis, a number of C-silyl derivatives of the smallest known carbaborane, 1-H₃Si-1,5-C₂B₃H₃, 1-MeH₂Si-1,5-C₂B₃H₄, 2-Me-1-(H₃Si)-1,5-C₂B₃H₃, as well as an equilibrium mixture of 2- and 4-methyl derivatives of CB₅H₇. A total carbaborane yield of ca. 40 mol % has been obtained. Temperature-dependent n.m.r. studies on the B-methyl isomers of CB₅H₇ show a fast bridge-hydrogen tautomerism at ca. 100 °C. A substituent chemical-shift effect has been calculated for Me₃Si and H₃Si groups on all positions of the pentaborane(9) cage.