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

Content Provider	Scientific Electronic Library Online (SciELO)
Author	Martins, Luciana R. Souza, Elizabeth T. Fernandez, Tatiana L. Souza, Bernardo de Rachinski, Sílvio Pinheiro, Carlos B. Faria, Roberto B. Casellato, Annelise Machado, Sérgio P. Mangrich, Antonio S. Scarpellini, Marciela
Abstract	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 CuI CuI 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 CuII CuII to CuI CuI.
Related Links	http://www.scielo.br/scielo.php?script=sci_abstract&pid=S0103-50532010000700009&lng=en&nrm=iso http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532010000700009&lng=en&nrm=iso
Starting Page	1218
Ending Page	1229
Page Count	12
File Format	PDF
ISSN	01035053
DOI	10.1590/S0103-50532010000700009
Journal	Journal of the Brazilian Chemical Society
Issue Number	7
Volume Number	21
Language	English
Publisher	Sociedade Brasileira de Química
Publisher Date	2010-01-01
Publisher Institution	Universidade Federal do Rio de Janeiro Instituto de Química Departamento de Química Inorgânica Universidade Federal de Santa Catarina Departamento de Química Universidade Federal do Paraná Departamento de Química Universidade Federal de Minas Gerais Instituto de Ciências Exatas Departamento de Física
Publisher Place	Brazil
Access Restriction	Open
Subject Keyword	Binuclear copper complexes Molecular structure Hydrocarbon oxidation Catechol oxidase
Content Type	Text
Resource Type	Article
Subject	Chemistry

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