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

The tris­(phosphinoamide)-bridged FeIIFeII di­iron complex Fe­(μ-iPrNPPh2)3Fe­(η2-iPrNPPh2) (1) can be reduced in the absence or presence of PMe3 to generate the mixed-valence FeIIFeI complexes Fe­(μ-iPrNPPh2)3Fe­(PPh2NHiPr) (2) or Fe­(μ-iPrNPPh2)3Fe­(PMe3) (3), respectively. Following a typical oxidative group transfer procedure, treatment of 2 or 3 with organic azides generates the mixed-valent FeIIFeIII imido complexes Fe­(iPrNPPh2)3FeNR (R = tBu (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, Mössbauer 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.