Cooperative Metal–Ligand Reactivity and Catalysis
in Low-Spin Ferrous Alkoxides
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Abstract
This report describes examples of
combined Fe- and O-centered reactivity
of Fe(P<sub>2</sub>O<sub>2</sub>)(CO)<sub>2</sub> (<b>1</b>),
where P<sub>2</sub>O<sub>2</sub> is the diphosphinoglycolate (Ph<sub>2</sub>PC<sub>6</sub>H<sub>4</sub>CHO)<sub>2</sub><sup>2–</sup>. This 18e low-spin ferrous dialkoxide undergoes substitution of
CO to give the labile monosubstituted derivatives Fe(P<sub>2</sub>O<sub>2</sub>)(CO)(L) (L = PMe<sub>3</sub>, pyridine, MeCN). Treatment
of Fe(P<sub>2</sub>O<sub>2</sub>)(CO)<sub>2</sub> 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)NH<sub>2</sub>) proceeds with binding
of the carbonyl and formation of an intramolecular hydrogen bond between
N<i>H</i> and the neighboring alkoxo ligand. This two-site
binding was confirmed with crystallographic characterization of the
thiourea-substituted derivative. Fe(P<sub>2</sub>O<sub>2</sub>)(CO)<sub>2</sub> reacts with Ph<sub>2</sub>SiH<sub>2</sub> to give the O-silylated
hydrido complex, which is inactive for hydrosilylation. The monocarbonyl
derivatives Fe(P<sub>2</sub>O<sub>2</sub>)(CO)(L) (L = NCMe, PMe<sub>3</sub>, acetamide) are precursors to catalysts for the hydrosilylation
of benzaldehyde, acetophenone, and styrene
