A metallacyclic alkyl-amido carbene complex (MCAAC)

Abstract

The activation of the CN moiety in the redox-active metalloligand [CpRu{κ³N_pz-1}][PF₆] (2) (1: ambidentate hybrid ligand, NC–C(pz)₃, with pz = pyrazolyl) was observed in the reaction with [Ir(cod)Cl]₂ (cod = 1,5-cyclooctadiene). By performing detailed NMR spectroscopic and X-ray crystallographic investigations the product was found to be a bimetallic Ru^II–Ir^III complex of the composition [CpRu{μ-1′}Ir(cod)Cl₂][PF₆] (3) consisting of a chemically modified ligand 1′. Most notably, the heterobimetallic complex 3 features an unprecedented metallacyclic alkyl-amido carbene (MCAAC) core structure, which is coordinated to an Ir^III centre. Density functional theory (DFT) calculations as well as cyclic voltammetry (CV) studies were performed in an effort to establish the formal oxidation states of the metal atoms in 3. Indeed, a quasi-reversible oxidation wave was detected at E⁰_1/2 = 0.36 V, which was attributed to the Ru^II/Ru^III redox couple, while two irreversible reduction processes were observed at very negative potentials and have been assigned to the stepwise reduction of Ir^III to Ir^I. First efforts to elucidate the reaction mechanism have also been performed.