Previous Article Next Article ASAP Copper Complexes with NH-Imidazolyl and NH-Pyrazolyl Units and Determination of Their Bond Dissociation Gibbs Energies
† Georg-August-University Göttingen, Tammannstr. 4, D-37077 Göttingen, Germany
Inorg. Chem., Article ASAP
DOI: 10.1021/acs.inorgchem.5b02084
Publication Date (Web): January 20, 2016
Copyright © 2016 American Chemical Society
*E-mail: inke.siewert@chemie.uni-goettingen.de.
Synopsis
The bond dissociation Gibbs energy has been determined for two isoelectronic Cu complexes having an imidazole and pyrazole unit, respectively. Both complexes show a thermodynamic coupling between the redox event at the metal center and the proton transfer event at the ligand backbone.
Abstract
We synthesized two dinuclear copper complexes, which have ionizable N imidazole and Npyrazole protons in the ligand, respectively, and determined the BDFE of the hypothetical H atom transfer reactions CuII(LH–1) + H• ↔ CuI(L) in MeOH/H2O (BDFE: bond dissociation Gibbs (free) energy). The ligands have two adjacent N,N′,O-binding pockets, which differ in one N-heterocycle: La has an imidazole unit and Lc, a pyrazole unit. The copper(II) complexes of La and Lc have been characterized, and the substitution pattern has only little influence on the structural properties. The BDFEs of the hypothetical PCET reactions have been determined by means of the species distribution and the redox potentials of the involved species in MeOH/H2O (80/20 by weight). The pyrazole copper complex 3 exhibits a lower BDFE than the isoelectronic imidazole copper complex 1 (1, 292(3) kJ mol–1; 3, 279(1) kJ mol–1). The difference is mainly caused by the higher acidity of the N pyrazole proton of 3 compared to the N imidazole proton of 1. The redox potentials of 1 and 3 are very similar.
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