A μ-Phosphido Diiron Dumbbell in Multiple Oxidation States

The reaction of the ferrous complex [LFe(NCMe)(2)](OTf)(2) (1), which contains a macrocyclic tetracarbene as ligand (L), with Na(OCP) generates the OCP--ligated complex [LFe(PCO)(CO)]OTf (2) together with the dinuclear mu-phosphido complex [(LFe)(2)P](OTf)(3) (3), which features an unprecedented linear Fe-(mu-P)-Fe motif and a naked P-atom bridge that appears at delta=+1480 ppm in the P-31 NMR spectrum. 3 exhibits rich redox chemistry, and both the singly and doubly oxidized species 4 and 5 could be isolated and fully characterized. X-ray crystallography, spectroscopic studies, in combination with DFT computations provide a comprehensive electronic structure description and show that the Fe-(mu-P)-Fe core is highly covalent and structurally invariant over the series of oxidation states that are formally described as ranging from (FeFeIII)-Fe-III to (FeFeIV)-Fe-IV. 3-5 now add a higher homologue set of complexes to the many systems with Fe-(mu-O)-Fe and Fe-(mu-N)-Fe core structures that are prominent in bioinorganic chemistry and catalysis.