Isocyanide insertion reaction of a carborane-fused borirane and isocyanide affinity of the ring expansion products

Abstract

The reactions of the carborane-fused borirane (B10H10C2)BN(SiMe3)2 (1) with isocyanides proceed, for the first time, a clearly defined sequence of insertion and coordination steps. The first equivalent of isocyanide undergoes selective 1,1-insertion into the borirane unit, affording a four-membered borete ring (2). A second equivalent initially coordinates reversibly to the boron center. Subsequent heating promotes its full insertion to generate the five-membered α-diimine product (3), which can reversibly capture an additional isocyanide molecule. Variable-temperature NMR studies reveal that 3 exhibits a remarkably higher isocyanide affinity than 2.