Vanadium-iron complexes featuring metal-metal multiple bonds

A series of V/Fe heterobimetallic complexes supported by phosphinoamide ligands, [Ph sub(2)PN super(i)Pr] super(-), is described. The V(iii) metalloligand precursor [V( super(i)PrNPPh sub(2)) sub(3)] can be treated with Fe(ii) halide salts under reducing conditions to afford [V( super(i)PrNPPh sub(2)) sub(3)FeX] (X = Br (2), I (3)). These complexes feature multiple bonds between Fe and V, leading to an intermetallic distance of similar to 2.07 Aa. Exploration of the one-electron reduction of complex 3 allows isolation of [V( super(i)PrNPPh sub(2)) sub(3)Fe(PMe sub(3))] (5), which also features metal-metal multiple bonding and a nearly identical Fe-V distance. Mossbauer spectroscopy of complexes 2 and 5 suggest that the most reasonable oxidation state assignments for these complexes are V super(III)Fe super(I) and V super(III)Fe super(0), respectively, and that reduction occurs solely at the Fe center in these bimetallic complexes. A theoretical investigation confirms this description of the electronic structure, providing a description of the metal-metal bonding manifolds as ( sigma ) super(2)( pi ) super(4)(Fe sub(nb)) super(3) and ( sigma ) super(2)( pi ) super(4)(Fe sub(nb)) super(4) for complexes 3 and 5, consistent with a metal-metal bond order of three. One electron-oxidation of complex 3 results in halide abstraction from PF sub(6) super(-), forming FV( super(i)PrNPPh sub(2)) sub(3)FeI (6). Complex 6 has a much weaker V-Fe interaction as a result of axial fluoride ligation at the V center.