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

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.