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Discovery of Molecular Oxidation Catalysts Using Metallo-Enzyme Mimicry and Combinatorial Chemistry Stephen B. Colbran & D. Brynn Hibbert, School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia Aims • To synthesize and screen a library of molecules combining an organometallic N-heterocyclic carbene (NHC) centre and one or more ‘classical’ metal sites as homogeneous catalysts for selective oxidations of organic substrates. Results • Routes to the precursor polytopic ligands with the NHC and bis(pyridylmethyl)amine (bpa) donor domains to make multi-metallic complexes were developed. • Problems of metal selectivity between the ligand domains restricted the library of complexes to the novel bi- and tri-metallic systems 1 and 2. • Serial screens for catalysis of styrene oxidation using series 1 and 2 were conducted. Catalytic activity above that found for the monomeric constituent metal centres was not uncovered. • Density functional calculations of M(IV)=O (M = Ti–Cu) species were undertaken and point to peak activity for the latter transition metals ... NiIV, CuIV (Zn is inactive and does form a M=O species). The reactivity scales with increasing radical character for the oxo ligand (i.e. as the metal centre becomes more MIII–O• like) M1 N N N N N N N 1. M1{(NHC)--(bpa)}Ma M1 = RhCl(cyclooctadiene) Ma = Co2+, Ni2+, Cu2+, Zn2+ N N N M1 N N Ma N Ma Mb N N N M1 = PdCl: Ma,b = Co2+, Cu2+, Zn2+ Ma,b = PdCl: M1 = RhCl, PdCl, AgCl 2. M1{(py-NHC2)--(bpa)2}Ma,Mb