Imidazoline-Functionalized Diphosphines:Models for N-Heteroeyclic Carbene-Diphosphinocarbene Coupling

摘要

N-Heterocyclic carbenes I derived from imidazol-2-ylidene,also referred to as Arduengo carbenes,are important compounds whose isolation as stable,free molecules has greatly contributed to the development of carbene chemistry in recent years.They show no tendency to dimerize to afford tetraazafulvalenes II,except under special circumstances,unlike the corresponding saturated N-heterocyclic carbenes.In contrast,related diphosphinocarbenes III are not isolable,and have been reported in the literature only as transient species,whereas their corresponding dimers IV are known to be stable.As far as we are aware,no example of coupling of both types of carbenes (V in Figure 1) has been described.