Reactivity enhancement of a diphosphene by reversible N-heterocyclic carbene coordination.

Diphosphene TerMes P = PTerMes ( 1 ; TerMes = 2,6-Mes2 C6 H3 ; Mes = 2,4,6-Me3 C6 H2 ) and NHCMe4 2 (NHCMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) exist in an equilibrium mixture with the NHCMe4 -coordinated diphosphene 3 . While uncoordinated 1 is inert to hydrolysis, the NHC adduct 3 readily undergoes hydrolysis to afford a phosphino-substituted phosphine oxide with the liberation of NHCMe4 . On this basis, conditions suitable for the catalytic use of NHCMe4 were identified. Similarly, while the hydrogenation of free diphosphene 1 with H3 N·BH3 is very slow, 3 reacts instantaneously with H3 N·BH3 at room temperature to afford a dihydrodiphosphane.