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

Raubenheimer H.G. ; Du Toit A. ; Du Toit M. ; An J. ; Van Niekerk L. ; Cronje S. ; Esterhuysen C. ; Crouch A.M. (2004)


New polynuclear complexes, (L1)3 M2{M 2 = 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 {M 2 = V(IV) (6)} and L1M2Cp2 {M 2 = Ti(III) (10)} with L1 = (CO)M1=C{C=NC(CH 3)=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.

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