Binuclear CuII complexes as catalysts for hydrocarbon and catechol oxidation reactions with hydrogen peroxide and molecular oxygen

Journal of the Brazilian Chemical Society

Faria, Roberto B.¹  Mangrich, Antonio S.¹  Martins, Luciana R.¹  Rachinski, Sílvio¹  Souza, Bernardo de¹  Universidade Federal de Santa Catarina, Florianópolis, Brazil¹  Machado, Sérgio P.¹  Souza, Elizabeth T.¹  Universidade Federal de Minas Gerais, Belo Horizonte, Brazil¹  Casellato, Annelise¹  Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil¹  Scarpellini, Marciela¹  Universidade Federal do Paraná, Curitiba, Brazil¹  Pinheiro, Carlos B.¹  Fernandez, Tatiana L.¹ 

关键词: binuclear copper complexes;    molecular structure;    hydrocarbon oxidation;    catechol oxidase;   

DOI  :  10.1590/S0103-50532010000700009

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

The tridentate ligands HL1, [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine, and HL2, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine, were used to synthesize binuclear CuII complexes, [Cu2(L1)2]Cl2•2H2O, complex 1, and [Cu2(L2)2](ClO4)2•1.5H2O, complex 2, in order to obtain catalysts for oxidative processes. Both complexes were characterized by elemental analysis, IR, UV-Vis and EPR spectroscopies. In addition, they were studied by cyclic voltammetry and potentiometric titration in order to investigate their behavior in solution. The crystal structure of complex 1 revealed a binuclear cation where the metal centers are bridged by two phenoxo groups. This arrangement provides a Cu...Cu distance of 3.043(10) Å, which is similar to the observed for catechol oxidase (2.90 Å). The catalytic reactivities of both complexes were investigated for hydrocarbon and catechol oxidations. Complexes 1 and 2 led to low overall hydrocarbon oxidation conversion values of 6.34 % and 7.15 %, respectively. However, for complex 1, only cyclohexanol (Cy-OH) and cyclohexanone (Cy=O) were isolated as reaction products, with selectivities of 68.1% for Cy-OH. This low overall conversion is tentatively attributed to steric hindrance effects produced by the non-coplanar aromatic rings of the ligand scaffolds, which suggest that the access of the hydrocarbon molecule to the binuclear active center is a determinant step in the reaction mechanism. Investigation of catecholase activities has shown high efficiencies, with complex 2 being more active than complex 1. It indicates that the pyridine-containing ligand is able to stabilize the intermediate CuICuI center which is proposed to be formed in this process. This is corroborated by the strong participation of pyridine in the LUMO (lowest unoccupied molecular orbital) of complex 2, which can help to accommodate the additional negative charge when the complex is reduced from CuIICuII to CuICuI.

【 授权许可】

Unknown