Diboranyl Phosphonium Cations: Synthesis and Chemical Properties

Hydride abstraction from the diborane [HB(hpp)] 2 (hpp = 1,3,4,6,7,8‐hexahydro‐2 H ‐pyrimido[1,2‐ a ]pyrimidinate) followed by base stabilization led to the first (highly water sensitive) diboranyl phosphonium cations of the general formulas [HB(hpp) 2 BPR 3 ] + and [HB(hpp) 2 BPHR 2 ] + . The B–P bond strength could be varied over a relatively large range by choice of the substituents R on the phosphine. The cation [HB(hpp) 2 BPCy 3 ] + (Cy = cyclohexyl) was structurally characterized. The PCy 3 base of this cation could be substituted by a stronger base (a carbene or a bicyclic guanidine). In solution, [HB(hpp) 2 BPCy 3 ] + very slowly decomposes, and [HB(hpp) 3 BH] + was identified as one of the decomposition products.