A series of C3-symmetric heterobimetallic Cr-M (M = Fe, Co and Cu) complexes

A series of tris(phosphinoamide) heterobimetallic Cr-M (M = Fe, Co and Cu) complexes has been investigated in an effort to probe and contribute to the understanding of the electronic structure and metal-metal bonding in heterobimetallic complexes of the first row transition metals. The chromium tris(phosphinoamide), [Cr((PrNPPh2)-Pr-i)(3)] (1), is a useful isolable precursor and can be treated with MI2 under reducing conditions to form [Cr((PrNPPh2)-Pr-i)(3)M-I] (M = Fe (2), Co (3)). Both of these complexes can be reduced by one electron to generate [Cr((PrNPPh2)-Pr-i)(3)M-PMe3] (M = Fe (4), Co (5)). The Cr-Cu complex [Cr((PrNPPh2)-Pr-i)(3)Cu-I] (6) has also been synthesized for comparison. The solid state structures of 2-6 have been determined crystallographically, revealing relatively short metal-metal interatomic distances. Mossbauer spectroscopy, cyclic voltammetry, and computational methods have been used to evaluate the electronic structure and metal-metal interactions in these unique bimetallic complexes in an effort to uncover the underlying factors that affect metal-metal bonding between elements of the first row transition series.