Synthesis and Structure of an o-Carboranyl-Substituted Three-Coordinate Borane Radical Anion

Abstract

Bis(1-(4-tolyl)-carboran-2-yl)-(4-tolyl)-borane [(1-(4-MeC6H4)-closo-1,2-C2B10H10-2-)2(4-MeC6H4)B] (1), a new bis(o-carboranyl)-(R)-borane was synthesised by lithiation of the o-carboranyl precursor and subsequent salt metathesis reaction with (4-tolyl)BBr2. Cyclic voltammetry experiments on 1 show multiple distinct reduction events with a one-electron first reduction. In a selective reduction experiment the corresponding paramagnetic radical anion 1.− was isolated and characterized. Single-crystal structure analyses allow an in-depth comparison of 1, 1.−, their calculated geometries, and the S1 excited state of 1. Photophysical studies of 1 show a charge transfer (CT) emission with low quantum yield in solution but a strong increase in the solid state. TD-DFT calculations were used to identify transition-relevant orbitals.