Rhenium is different: CO tetramerization induced by a divalent lanthanide complex in rhenium carbonyls

The reduction of M$_{2}$(CO)$_{10}$ (M = Mn, Re) with different divalent lanthanide (Ln = Sm, Yb) compounds was investigated. Depending on the steric demand of the ligand, either unusual CO tetramerization or formation of a new Re carbonyl anion occurred in the case of Re. Theoretical calculations were performed for a better understanding of the nature of bonding in the newly formed species