Galactose Oxidase Models: Creation and Modification of Proton Transfer Coupled to Copper(II) Coordination Processes in Pro-Phenoxyl Ligands

Authors

  • Fabien Michel,

    1. Laboratoire de Chimie Biomimétique, LEDSS, UMR CNRS 5616, ICMG FR CNRS 2607, Université J. Fourier, B. P. 53, 38041 Grenoble cedex 9, France, Fax: +33-4-7651-4836
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  • Fabrice Thomas,

    1. Laboratoire de Chimie Biomimétique, LEDSS, UMR CNRS 5616, ICMG FR CNRS 2607, Université J. Fourier, B. P. 53, 38041 Grenoble cedex 9, France, Fax: +33-4-7651-4836
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  • Sylvain Hamman,

    1. Laboratoire de Chimie Biomimétique, LEDSS, UMR CNRS 5616, ICMG FR CNRS 2607, Université J. Fourier, B. P. 53, 38041 Grenoble cedex 9, France, Fax: +33-4-7651-4836
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  • Christian Philouze,

    1. Laboratoire de Chimie Biomimétique, LEDSS, UMR CNRS 5616, ICMG FR CNRS 2607, Université J. Fourier, B. P. 53, 38041 Grenoble cedex 9, France, Fax: +33-4-7651-4836
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  • Eric Saint-Aman,

    1. Pr. E. Saint-Aman, LEOPR, UMR CNRS 5630, ICMG FR CNRS 2607, Université J. Fourier, B. P. 53, 38041 Grenoble Cedex 9, France
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  • Jean-Louis Pierre

    1. Laboratoire de Chimie Biomimétique, LEDSS, UMR CNRS 5616, ICMG FR CNRS 2607, Université J. Fourier, B. P. 53, 38041 Grenoble cedex 9, France, Fax: +33-4-7651-4836
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Abstract

Two tripodal ligands containing two pyridyl and one 4-(benzimidazol-2-yl)-2-tert-butylphenol (HLH) and one 2-tert-butyl-4-(N-methylbenzimidazol-2-yl)phenol (HLMe) unit have been synthesized. They possess a N3O donor set that is known to stabilize phenoxyl radicals more efficiently than the corresponding N2O2 donor unit. Reaction of one molar equiv. of Cu(ClO4)2·6H2O with HLH or HLMe affords the zwitterionic benzimidazolium phenolate complexes [CuII(HLH)]2+ and [CuII(HLMe)]2+ via a proton transfer reaction coupled to copper(II) coordination. Addition of HClO4 to [CuII(HLH)]2+ and [CuII(HLMe)]2+ results in the formation of the benzimidazolium phenol complexes [CuII(H2LH)]3+ and [CuII(H2LMe)]2+, while addition of NEt3 affords the benzimidazol-phenolate complexes [CuII(LH)]2+ and [CuII(LMe)]2+, respectively. The phenol’s pKa is remarkably low due to the strong withdrawing effect of the benzimidazolium substituent. X-ray crystallographic analysis of the copper(II) complexes shows that deprotonation of the axial phenol forces the metal to move out of the square plane towards the oxygen atom, and one (or two) Cu–Npyridine equatorial bond length increases. The copper(II) phenoxyl species [CuII(HLH)]·3+ and [CuII(HLMe)]·3+ were prepared electrochemically, or by addition of two molar equiv. of copper(II) to HLH or HLMe. Under these conditions, radical formation has never been observed for tripodal ligands containing two pyridyl and one 2,4-di-tert-butylphenol group. This difference is explained in terms of the proton transfer mechanism and redox potentials. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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