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(II) 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 V^IIIFe^I and V^IIIFe⁰, 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(Fe_nb)³ and (σ)²(π)⁴(Fe_nb)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.