Metal-Metal Interactions in C3-Symmetric Diiron Imido Complexes Linked by Phosphinoamide Ligands

The tris(phosphinoamide)-bridged (FeFeII)-Fe-II diiron complex Fe(mu-PrNPPh2)(3)Fe(eta(2)-(PrNPPh2)-Pr-i) (1) can be reduced in the absence or presence of PMe3 to generate the mixed valence (FeFeI)-Fe-II complexes Fe(mu-(PrNPPh2)-Pr-i)(3)Fe((PPh2NHPr)-Pr-i) (2) or Fe(mu-(PrNPPh2)-Pr-i)(3)Fe(PMe3) (3), respectively. Following a typical oxidative group transfer procedure, treatment of 2 or 3 with organic azides generates the mixed-valent (FeFeIII)-Fe-II imido complexes Fe((PrNPPh2)-Pr-i)(3)Fe NR (R = Bu-t (4), Ad (5), 2,4,6-trimethylphenyl (6)). These complexes represent the first examples of first-row bimetallic complexes featuring both metal-ligand multiple bonds and metal-metal bonds. The reduced complexes 2 and 3 and imido complexes 4-6 have been characterized via X-ray crystallography, Mossbauer spectroscopy, cyclic voltammetry, and SQUID magnetometry, and a theoretical description of the bonding within these diiron complexes has been obtained using computational methods. The effect of the metal-metal interaction on the electronic structure and bonding in diiron imido complexes 4-6 is discussed in the context of similar monometallic iron imido complexes.