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Assessing the Metal–Metal Interactions in a Series of Heterobimetallic Nb/M Complexes (M = Fe, Co, Ni, Cu) and Their Effect on Multielectron Redox Properties

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journal contribution
posted on 20.12.2018 by Brett A. Barden, Gursu Culcu, Jeremy P. Krogman, Mark W. Bezpalko, Gregory P. Hatzis, Diane A. Dickie, Bruce M. Foxman, Christine M. Thomas
A one-pot synthetic procedure for a series of bimetallic Nb/M complexes, Cl–Nb­(iPrNPPh2)3M–X (M = Fe (2), Ni (4), Cu (5)), is described. A similar procedure aimed at synthesizing a Nb/Co analogue instead affords iPrNNb­(iPrNPPh2)2(μ-PPh2)­Co–I (3) through cleavage of one phosphinoamide P–N bond under reducing conditions. Complexes 4 and 5 are found to have short Nb-M distances, corresponding to unusual metal–metal bonds between Nb and these first row transition metals. For comparison, a series of heterobimetallic ONb­(iPrNPPh2)3M–X complexes (M = Fe (7), Co (8), Ni (9), Cu (10)) was synthesized. In these complexes, the NbV center is engaged in sufficient π-bonding to the terminal oxo ligand to remove the driving force for direct metal–metal interactions. A comparison of the cyclic voltammograms of 2 and 410 reveals that the presence of a second metal shifts the redox potentials of both Nb and the late metal center anodically, even when direct metal–metal interactions are not present.