Radical Formation and Oxidative Reactivity of a Square Planar Rhenium(III)/Tin(IV) Bimetallic Nitrido Complex

A fundamental challenge in catalytic dinitrogen (N2) fixation is synthesizing stable metal nitrido (M≡N) complexes that are sufficiently reactive for subsequent functionalization. We report the isolation of [ReIII(PNP)(N)·Sn(Bu)3(Cl)] (3; PNP = 2,6-bis[(dicyclohexylphosphino)ethyl]amine), a rare rhenium(III)/tin(IV) bimetallic molecule resulting from the reaction of a rhenium(V) nitrido precursor with tributyltin hydride. Complex 3 features an exceptionally rare square planar geometry around the rhenium(III) center, which was confirmed by X-ray crystallography and DFT calculations. Mechanistic studies involving radical initiators and traps indicate that the formation of this rhenium(III) complex proceeds via a radical reduction pathway involving tributyltin hydride. Furthermore, 3 exhibits interesting reactivity, undergoing oxidative addition with HCl to regenerate a rhenium(V) nitrido species, showcasing an initial reduction and reoxidation sequence relevant to catalytic cycles. The synthesis and reactivity of this bimetallic complex, featuring a metal nitride in an uncommon oxidation state and geometry, provides significant insight for the development of new catalytic design strategies for N2 functionalization.