Metal-metal interactions in C3-symmetric diiron imido complexes linked by phosphinoamide ligands

Abstract

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(PPh 2NHiPr) (2) or Fe(μ-iPrNPPh 2)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. © 2012 American Chemical Society.