Biomimetic catalysis with immobilized transition metal complexes

The tetradentate chelate ligand tris[(1-vinylimidazol-2-yl)methyl]amine (10) was synthesized in five steps from commercially available starting materials. Upon reaction with MCl2 (M = Zn, Cu, Ni, Co) in the presence of NH4PF6, the complexes [M(10)Cl]PF6 (M = Zn (11), Cu (12), Co (14)) and [Ni(10)Cl]2(PF6)2 (13) were obtained. The structure of all complexes was determined by single crystal X-ray crystallography. Immobilization of 11 and 12 was achieved by copolymerization with ethyleneglycol dimethacrylate (EGDMA) to obtain P11-Zn and P12-Cu. Immobilized versions of 13 and 14 have been generated by cleavage the metal from P12-Cu and subsequent assembly of MCl2 (M = Ni (P12-Ni), Co (P12-Co)). The supported complexes P11-Zn, P12-Cu, P12-Ni, and P12-Co were found to be efficient catalysts for the hydrolysis of bis(ρ-nitrophenyl)phosphate (BNPP) at 50 °C. At pH 9.5, the heterogeneous catalyst P12-Cu was 56 times more active than the homogeneous catalyst 12. Partitioning effects, which increase the local concentration of BNPP in the polymer, are shown to contribute to the enhanced activity of the immobilized catalyst. The tridentate N,N',N''-chelate ligand tris(1-vinylimidazol-2-yl)phosphine (20) was synthesized from commercially available starting materials. Three immobilized Cu(II) complexes were generated by the following: (a) homopolymerization of 20 and subsequent metalation with CuCl2; (b) copolymerization of 20 with EGDMA and subsequent metalation with CuCl2; or (c) molecular imprinting with the organometallic Mo-complex [Mo(η3-C4H7)(CO)2(20)](TsO) (28) and EGDMA and subsequent replacement of Mo(II) by Cu(II). All three polymeric Cu complexes were found to very efficiently promote the hydrolysis of activated phosphoesters with the relative activity being dependent on the nature of the polymer and the substrate. The complex [Fe2O(CH3COO)(10)2](NO3)3 (42) was synthesized and structurally investigated by single crystal X-ray crystallography. After copolymerization with EGDMA and subsequent replacement of Fe(III) by Cu(II), Zn(II) or Mn(III), hydrolysis and oxidation reactions were investigated. A higher activity compared to the corresponding monometallic immobilized complexes was observed. This increase in activity is most likely caused by cooperative effects.


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