MOLECULAR-ORBITAL STUDY OF THE VINYLPHOSPHINIDENE TO PHOSPHAPROPYNE REARRANGEMENT

MNDO and ab initio studies of interconversions on the C2H3P potential surface point to 1-phosphapropyne (1) as the global minimum and suggest that, under vigorous reaction conditions, vinylphosphinidene 2 will interconvert with its ring-closed isomer 5. At the reported experimental temperature of 700-degrees-C, the conversion of 2 or 5 to phosphaallene (3) will occur much more rapidly than their conversion to 1. The lowest-energy pathway for conversion of 3 to 1 involves reversion of 3 to 2, and subsequent rearrangement of 2 to 1. It is predicted that, at high temperatures, an equilibrium mixture of 2, 5, and 3 will be depleted by the conversion of 2 to 1. Thus, the net reaction will be the direct rearrangement of 2 to 1, in which a hydrogen shifts away from an electron-deficient center. These results agree well with experimental studies in which the flash vacuum thermolysis of vinylphosphirane at 700-degrees-C led to 1 as the sole product.