A Masked Phosphinidene Trapped in a Fluxional NCN Pincer

The trapping of a phosphinidene (R-P) in an NCN pincer is presented.Stabilized phosphinidene 1 was characterized by 31P{1H}, 1H, and 13C{1H} NMR spectroscopy, exhibiting an averaged C2v-symmetry in solution between -60 and 60 °C. In the solid state, the phosphinidene was coordinated by one adjacent N atom featuring a formal P-N bond (1.757(2) A) to give a five-membered ring with some aromatic character, confirmed by DFT calculations (B3LYP-D3/6-311G**++) to be the ground state structure. Equilibration of the two N ligands occurs rapidly in solution via a "bell-clapper" type process through an associative symmetric transition state calculated to lie 4.0 kcal/mol above the ground state.