Theoretical study on the reaction between phosphacyclopropenylidene and ethylene: An alternative approach to the formation of phosphorus-bearing heterocyclic compounds

The reaction mechanism between phosphacyclopropenylidene and ethylene has been systematically investigated at the B3LYP/6-311++G(d,p) level of theory in order to better understand the reactivity of unsaturated cyclic phosphorus-bearing carbene. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surface of the system. Calculations show that the spiro bicyclic intermediate could be produced through the cycloaddition process between phosphacyclopropenylidene and ethylene initially. The reaction mechanism is illustrated with the frontier molecular orbital theory. Introduction of electron-withdrawing group in phosphacyclopropenylidene will better facilitate the addition process. Through subsequent ring-expanding and hydrogen-migrating process, fuse-ring and allene compounds could be produced, respectively. Furthermore, it's easy for spiro bicyclic intermediate and another ethylene to form a spiro tricyclic compound. This study is helps to understand the reactivity of phosphacyclopropenylidene, the evolution of phosphorus-bearing molecules in space, and to offer an alternative approach to the formation of phosphorus-bearing heterocyclic compound.