N-Heterocyclic Phosphenium Complexes of Vanadium

Isolable N-heterocyclic phosphenium (NHP) complexes of vanadium were prepared by cophotolysis of Na[V(CO)6] and 2-bromo-1,3,2-diazaphospholenes. Single-crystal XRD studies revealed that the complexes exhibit trigonal planar coordination at phosphorus and short P–V distances indicative of phosphorus–metal double bonding. An exemplary reaction with Li[BEt3H] proceeded via hydride transfer to the phosphorus atom to yield an anionic secondary phosphine complex, which resisted protonation by [Et3NH]Cl and differed in this aspect from a previously reported manganese-based analogue. DFT calculations were carried out to analyze metal–ligand interactions in the NHP vanadium complexes and to rationalize the different behavior of the vanadium- and manganese-based species in H–/H+-transfer reactions.