Abstract

Transition metal complexes containing imido ligands (M=NR) are an important class of coordination compounds implicated in nitrogen-group-transfer reactions such as aziridination. The present thesis investigates the formation of iron-imido complexes via deoxygenation of iron-nitroso complexes that have a nitroso (RN=O) functionality tethered to their main ligand framework. This process is at the heart of important oxygen-atom- transfer (OAT) reactions such as the epoxidation of alkenes or the hydroxylation of organic substrates.
For this purpose, the new pentadentate monoanionic ligand BPAEBNHOH was synthesized and disproportionated by Fe(II) salts to yield N-bonded monomeric iron-nitroso complexes [Fe(II)BPAEBNO(OAc)] (1) and [Fe(II)BPAEBNO(MeCN)](OTf) (2) as well as the iron-amine complex [Fe(II)BPAEBNH2(OAc)]. These complexes were characterized by X-ray crystallography and spectroscopic techniques. Complexes (1) and (2) were found to be able to perform OAT to phosphine reagents (PR3) in moderate to high yields. Although not isolated, iron-iminophosphorane (M−N=PR3) compounds were identified as the main products of the reaction. Detailed kinetic and mechanistic studies of this reaction suggest that the mechanism does not involve a simple rate law. Control
experiments and comparisons with the literature suggest that the mechanism involves the replacement of acetate and acetonitrile ligands with a phosphine ligand, before the nitroso group is deoxygenated. These results suggest the formation of an iron-imido intermediate, prior to its trapping by phosphine reagents.