Unexpected Chemistry of Molecular Precursors to Boron Arsenide Materials

Simple arsine-boranes were explored as precursors to the semiconductor ceramic cubic boron arsenide (BAs). In preparing Ph₂AsHBH₃, spontaneous hydrogen loss was observed to give cyclo-arsine boranes, (Ph₂AsBH₂)_n, and other products. At low temperature, Ph₂AsHBH₃ could be isolated and observed to engage in spontaneous hydrogen to form (Ph₂AsBH₂)_n rings. These rings exhibit dynamic behavior through varying ratios of n = 3 or 4, but n = 5 could be observed and promoted under nonequilibrium conditions. Interestingly, the arsine substrate appears catalyze the decomposition of THF-borane, and simple boranes are catalysts for the dehydrocoupling of Ph₂AsH. However, the most chemically odd observation was the relative lability of As-C bonds under mild conditions. While (Ph₂AsBH₂)_n and Ph₃AsBH₃ are competent substrates for the formation of BAs products under pyrolysis conditions, particularly in air, ceramic yields suffer from from factors including volatility of the substrate under pyrolysis conditions and competitive arsenic oxidation occurred unpredictably. Arsenic chemistry aside, this overall strategy is valid for the production of bulk BAs substrates, though further substrate development is needed.