Comparison of binuclear phospholyl chromium carbonyl derivatives with their cyclopentadienyl analogues: Role of the phosphorus atom in ligand-metal bonding

Abstract

The structures and energetics of the binuclear phospholyl chromium carbonyl derivatives (C4H4P)2Cr2(CO)n (n = 6, 5, 4, 3) have been investigated by density functional theory. The lowest energy (C4H4P)2Cr2(CO)n (n = 6, 4, 3) structures are completely analogous to their Cp2Cr2(CO)n analogues with two terminal pentahapto phospholyl rings. However, for the pentacarbonyl (C4H4P)2Cr2(CO)5 the lowest energy structure has a bridging seven-electron donor η5,η1-C4H4P ligand using the phosphorus lone pair in addition to the π-system of the phospholyl ligand as well as a Cr-Cr single bond. Thus, except for the pentacarbonyl the phosphorus lone pair of the phospholyl ligand is seen to play a minor role in the energetically preferred structures of the binuclear phospholyl chromium carbonyl derivatives.