Density Functional Study of Oxygen Insertion into Niobium–Phosphorus Bonds: Novel Mechanism for Liberating P3– Synthons

Abstract

We explore the mechanism of oxygen insertion into niobium–phosphorus bonds to liberate synthetically relevant, phosphorus-containing molecules. Oxygen insertion mechanisms generally proceed through either direct oxygen insertion from an oxo ligand, M═O (oxy-insertion), or an insertion of an oxygen atom from an external oxidant, OY (Baeyer–Villiger, BV). Computational methods were employed to elucidate the preferred mechanism for the liberation of the phosphorus moiety from [(η2-P3)Nb(ODipp)3] (Dipp = 2,6-iPr2C6H3, P3 = P3-SnPh3) when treated with pyridine-N-oxide as an external oxidant. Careful analysis of conformational isomers and energies clearly suggests that the BV mechanism is the preferred pathway toward phosphorus liberation. Once free, the P3 moiety can react with 1,3-cyclohexadiene to form the Diels–Alder product, which is also modeled in the computational study.