Electrochemical Reduction of Homo– and Hetero–tri(aryl)borohydrides

Authentic terminal homo– and hetero–tri(aryl)borohydrides of the form [HB(C₆F₅)_x{m,m–(CF₃)₂C₆H₃}_y(C₆Cl₅)_z]⁻ have been synthesised by reaction of their parent borane with a hydride source; their electrochemical properties have been studied, together with a computational investigation using density functional theory (DFT). The three of these compounds incorporating at least two pentachlorophenyl rings have been identified as, upon electrochemical oxidation, regenerating their parent borane, one of the essential steps (together with rapid cleavage under mild conditions of H₂ together with an appropriate Lewis base), in implementing the electrochemically coupled – frustrated Lewis pair concept. The resulting mechanism upon oxidation is supported by modelling the cyclic voltammetry data obtained. The DFT studies have allowed for the structures of these compounds to be assessed, along with quantifying their hydride ion affinities (HIAs).