Investigation of Thiaborane closo- nido Conversion Pathways Promoted by N-Heterocyclic Carbenes.

The 12-X- closo-SBH (X = H or I) thiaboranes react with one or two molar equivalents of various N-heterocyclic carbenes (NHCs) to give the deprotonated 12-vertex species of [12-X-SBH·NHC][NHC-H]composition as kinetic products. The use of one molar equivalent of a sterically more hindered NHC reactant leads to the formation of 12-X-SBH·NHC adducts with a heavily distorted cage and the nido electron count. Further reaction of 12-I-SBH·NHC to deboronated 12-X-SBH·NHC proceeds in acetone to complete the closo- nido reaction pathway under the thermodynamic control. The structures of all compounds have been investigated by NMR spectroscopy and diffraction techniques. The results are supported by theoretical methods.