Influence of N-heterocyclic carbenes (NHCs) on the hydrolysis of a diphosphene

Abstract

We report the influence of N-heterocyclic carbenes (NHCs) on the hydrolysis of a diphosphene TerPPTer (1; Ter = 2,6-Mes₂C₆H₃; Mes = 2,4,6-Me₃C₆H₂), a phosphorus-analogue of an alkene. The diphosphene 1 itself is completely inert towards water. However, NHCs have been found to activate 1 towards ready hydrolysis. While sterically less-encumbered NHCs react with 1 affording NHC-adducts which are in equilibrium with 1 in solution, sterically encumbered NHCs do not bind to 1 at all. Interestingly, in both of these situations hydrolysis of the PP motif proceeds efficiently. At low temperatures, sterically less-encumbered NHCs are catalytic while the sterically encumbered NHCs play a catalytic role at room temperature. To gain insight on this striking influence of NHCs on the hydrolysis of diphosphene detailed low-temperature ³¹P-NMR studies along with theoretical calculations have been carried out. In addition, systematic hydrolysis studies of all the NHCs used in this study have also been performed.