Facile C=O Bond Splitting of Carbon Dioxide Induced by Metal–Ligand Cooperativity in a Phosphinine Iron(0) Complex

New iron complexes [Cp*FeL]⁻ (1-σ and 1-π, Cp*=C₅Me₅) containing the chelating phosphinine ligand 2-(2′-pyridyl)-4,6-diphenylphosphinine (L) have been prepared, and found to undergo facile reaction with CO₂ under ambient conditions. The outcome of this reaction depends on the coordination mode of the versatile ligand L. Interaction of CO₂ with the isomer 1-π, in which L binds to Fe through the phosphinine moiety in an η⁵ fashion, leads to the formation of 3-π, in which CO₂ has undergone electrophilic addition to the phosphinine group. In contrast, interaction with 1-σ—in which L acts as a σ-chelating [P,N] ligand—leads to product 3-σ in which one C=O bond has been completely broken. Such CO₂ cleavage reactions are extremely rare for late 3d metals, and this represents the first such example mediated by a single Fe centre.