Binuclear phospholyl iron carbonyls: The limited role of the phosphorus atom in metal complexation

The structures and thermodynamics of the binuclear phospholyl iron carbonyls (C4H4P)2Fe2(CO)n (n = 6, 5, 4, 3, 2) have been investigated using density functional theory. The low-energy singlet (C4H4P)2Fe2(CO)n (n = 4, 3, 2) structures are found to have direct iron-iron bonds and terminal five-electron donor pentahapto η5-C4H4P rings with the phosphorus lone pairs not involved in the bonding to the iron atoms.