Ab initio SCF-MO study of the Staudinger phosphorylation reaction between a phosphane and an azide to form a phosphazene †

The lowest energy pathway for a Staudinger reaction between a phosphane and an azide is predicted at the RHF and DFT ab initio SCF-MO level to proceed via an s-cis intermediate 7, followed by cyclisation and elimination of N2 to form a phosphazene. When suitable stabilising substituents are present, 7 can instead isomerise to the isolable s-trans intermediate 9. Natural bond orbital perturbation theory analysis has been employed to identify the factors influencing the relative stability of the s-cis phosphazide and the s-trans isomers.