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

Abstract

Diphosphene Ter^MesP = PTer^Mes (1; Ter^Mes = 2,6-Mes₂C₆H₃; Mes = 2,4,6-Me₃C₆H₂) and NHC^Me₄2 (NHC^Me₄ = 1,3,4,5-tetramethylimidazol-2-ylidene) exist in an equilibrium mixture with the NHC^Me₄-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 NHC^Me₄. On this basis, conditions suitable for the catalytic use of NHC^Me₄ were identified. Similarly, while the hydrogenation of free diphosphene 1 with H₃N·BH₃ is very slow, 3 reacts instantaneously with H₃N·BH₃ at room temperature to afford a dihydrodiphosphane.