A theoretical study of the effect of phosphorus and nitrogen heteroatoms on pentahapto coordination of diazaphospholyl ligands in binuclear ruthenium and iron carbonyl derivatives

Abstract

The structures and energies of the (Me2C2N2P)2Ru2(CO)n (n = 4, 3) complexes of the four isomeric diazaphospholyl ligands have been studied by density functional theory. Most of the low-energy structures in these systems have one or both diazaphospholyl rings bridging a central RuRu bond through RuN and/or RuP bonds without involvement of the other three ring atoms. A few higher energy structures are found in these systems having either terminal pentahapto η5-Me2C2N2P ligands or bridging η5,η1-Me2C2N2P ligands bonded to one ruthenium atom as a pentahapto ligand and to the other ruthenium atom through a P → Ru or N → Ru dative bond. The potential surfaces of the analogous iron systems (Me2C2N2P)2Fe2(CO)n (n = 4, 3) are complicated considerably by other triplet and even quintet structures of comparable energies to structures analogous to the low-energy ruthenium structures. This relates to the lower ligand field strengths of iron complexes as compared with their ruthenium analogues.