{μ-PbSe}: A Heavy CO Homologue as an Unexpected Ligand

Abstract

Reactions of [K(18-crown-6)]2[Pb2Se3] and [K([2.2.2]crypt)]2[Pb2Se3] with [Rh(PPh3)3Cl] in en (ethane-1,2-diamine) afforded ionic compounds with [Rh3(PPh3)6(μ3-Se)2]−and [Rh3(CN)2(PPh3)4(μ3-Se)2(μ-PbSe)]3−anions, respectively. The latter contains a PbSe ligand, a rather uncommon homologue of CO that acts as a μ-bridge between two Rh atoms. Quantum chemical calculations yield a significantly higher bond energy for PbSe than for CO, since the size of the ligand orbitals better matches the comparably rigid Rh-Se-Rh angles and the resulting Rh⋅⋅⋅Rh distance. To rationalize the bent coordination of the ligand, orbitals with significant ligand contributions and their dependence on the bonding angle were investigated in detail.