C-N bond insertion of a complexed phosphinidene into a bis(imine) - A novel 2,3-sigmatropic shift

The electrophilic phosphinidene complex PhPW(CO)₅ reacts with bis(imine) 5, possessing a single carbon spacer, to give the C-N insertion product 6. B3LYP/6-31G* calculations indicate that this process occurs by way of a 2,3-sigmatropic shift from the initially formed phosphane ylide. The alternative, 1,3-dipolar cycloaddition, followed by ring-opening of the bicyclic structure, can be ruled out since both steps are energetically much more demanding. Ring-closure to an azaphosphirane is also less favorable than the C-N insertion, which is in agreement with the absence of such a product in the experiment.