Vanadium-iron complexes featuring metal-metal multiple bonds

Abstract

A series of V/Fe heterobimetallic complexes supported by phosphinoamide ligands, [Ph2PNiPr]-, is described. The V(III) metalloligand precursor [V(iPrNPPh2)3] can be treated with Fe(III) halide salts under reducing conditions to afford [V(iPrNPPh2)3FeX] (X = Br (2), I (3)). These complexes feature multiple bonds between Fe and V, leading to an intermetallic distance of ∼2.07 å. Exploration of the one-electron reduction of complex 3 allows isolation of [V(iPrNPPh2)3Fe(PMe3)] (5), which also features metal-metal multiple bonding and a nearly identical Fe-V distance. Mössbauer spectroscopy of complexes 2 and 5 suggest that the most reasonable oxidation state assignments for these complexes are VIIIFeI and VIIIFe0, 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 (σ)2(π)4(Fenb)3 and (σ)2(π)4(Fenb)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 PF6 -, forming FV(iPrNPPh2)3FeI (6). Complex 6 has a much weaker V-Fe interaction as a result of axial fluoride ligation at the V center. © 2013 Royal Society of Chemistry.