Anionic Fischer-type carbene complexes as bidentate (N,O) ligands

Abstract

New polynuclear complexes, (L¹)₃M² {M² = Cr(III) (4a, 4b), Fe(III) (5), Co(III) (8)}, (L¹)₂M²(L²)₂ {M² = Co(II) (7), Ni(II) (9)}, (L¹)₂M²(O)L² {M² = V(IV) (6)} and L¹M²Cp₂ {M² = Ti(III) (10)} with L¹ = (CO)₅M¹C{CNC(CH₃)CHS}O⁻ (M¹ = Cr or W) and L² = 4-methylthiazole or THF, are described. The molecular structures of these complexes determined by X-ray diffraction show that the Fischer-type carbene complexes act as bidentate ligands towards the second metal centre, coordinating through C(carbene)-attached O-atoms and imine N-atoms of the thiazolyl groups to form five-membered chelates with the oxygen atoms in the mer configuration. Isostructural complexes have similar characteristic band patterns in their far-IR spectra. Cyclic voltammetry of selected complexes reveals the oxidation of the carbene complex ligand between 1.01 and 1.29 V. Oxidation of the central metal (M²) takes place at 0.56 and 0.86 V for 7 and 9, respectively. Three stepwise reductions of Cr(III) to Cr(0) occur for 4a and 4b in the region −0.51 to −1.58 V. These new ligand types and other variants thereof should find application in ligand design with the first metal – and other ligands attached thereto – in the carbene complex ligand, playing an important role.