Cooperative Metal–Ligand Reactivity and Catalysis in Low-Spin Ferrous Alkoxides

Abstract

This report describes examples of combined Fe- and O-centered reactivity of Fe(P2O2)(CO)2 (1), where P2O2 is the diphosphinoglycolate (Ph2PC6H4CHO)22–. This 18e low-spin ferrous dialkoxide undergoes substitution of CO to give the labile monosubstituted derivatives Fe(P2O2)(CO)(L) (L = PMe3, pyridine, MeCN). Treatment of Fe(P2O2)(CO)2 with Brønsted acids results in stepwise O-protonation, affording rare examples of low-spin Fe(II) complexes containing alcohol ligands. Substitution reactions with amides (RC(O)NH2) proceeds with binding of the carbonyl and formation of an intramolecular hydrogen bond between NH and the neighboring alkoxo ligand. This two-site binding was confirmed with crystallographic characterization of the thiourea-substituted derivative. Fe(P2O2)(CO)2 reacts with Ph2SiH2 to give the O-silylated hydrido complex, which is inactive for hydrosilylation. The monocarbonyl derivatives Fe(P2O2)(CO)(L) (L = NCMe, PMe3, acetamide) are precursors to catalysts for the hydrosilylation of benzaldehyde, acetophenone, and styrene.