To assess whether this synthetic procedure would tolerate a large degree of steric bulk on the P and N substituents, the analogous reaction of HP t Bu2•BH3 with [MesN2][BF4] was attempted, and gratifyingly gave MesN2P t Bu2•BH3 (2•BH3) as a purple solid after work-up in 55% yield (Scheme 2). To etsablish that the Mes group on the nitrogen is not a prerequisite for the formation of azophosphine boranes, (p-NMe2)C6H4N2P t Bu2•BH3 (3•BH3) was prepared from the corresponding diazonium salt as a red solid in an excellent yield of 84% (Scheme 2).