Open-shell Mo(V) nitrides, phosphides, and carbides: Does radical character dictate coupling chemistry?

Abstract

Ammonia and water oxidn. are of interest for renewable energy conversion technologies, but further understanding is necessary to harness these reactions in a controlled, sustainable, and cost-efsfective manner. Terminal M=E species have been invoked in oxidatively-induced E-E coupling chemistries, including for E = O and N.[1] Spin leakage onto E is thought to be an important determinant for the reactivity of such species. However, the impact of the triply-bonded element on the extent of spin leakage and E-E coupling is poorly understood. A significant challenge in probing this question rests in finding a system capable of supporting a series of open-shell M»E complexes with varying E (e.g., E = N, P, C), leaving the metal center and ligand scaffold unperturbed. Here we target a series of M=E complexes (M = Mo; E = P, N, C) supported by terphenyl-diphosphine ligand L. L has already been shown to be extraordinarily versatile in its ability to enable a range of small mol. activation chemistries on Mo, including deoxygenative reductive coupling of CO,[2a] ammonia-borane dehydrogenation,[2b] and nitride-CO coupling.[2c] In the present context, the targeted complexes are prepd. via oxidn. of the resp. isoelectronic Mo(IV) species. Pulse ESR expts. are conducted to det. the extent of spin delocalization on E. The obsd. spin delocalization is correlated to the propensity of the resp. Mo»E complexes to undergo E-E coupling, as a function of the triply-bonded element.