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  • Title: Imidazole substituent effects on oxidative reactivity of tripodal(imid)2(thioether)CuI complexes.
    Author: Zhou L, Nicholas KM.
    Journal: Inorg Chem; 2008 May 19; 47(10):4356-67. PubMed ID: 18399624.
    Abstract:
    In the search for new bis(imidazole)thioether (BIT) copper complexes that accurately mimic the electronic and reactivity features of the CuM site of copper hydroxylase enzymes, a set of tripodal BIT ligands 4a, b- 6a, b has been synthesized that vary according to the imidazole C-(Ph or H) and N-(H or Me) substituents, as well as the position (2- or 4-) of the tripodal attachment. Corresponding [(BIT)Cu(L)](PF6) complexes 7a, b', 8a, b', and 9a', b' [L=CO (a), CH3CN (b)] have been prepared and characterized spectroscopically. The IR spectra of 7a- 9a (L=CO), specifically nu(CO), show little variation (2090-2100 cm(-1)), suggesting a similar electronic character of the Cu centers. In contrast, cyclic voltammetric analysis of these compounds (L=CH3CN) reveals quasi-reversible oxidation waves with significant variation of Epa in the range of + 0.45-0.57 V vs Fc/Fc(+), depending on the imidazole substituents. Each of the [(BIT)Cu(CH 3CN)]PF6 complexes reacts with dioxygen to form [(BIT)Cu(II) 2(mu-OH) 2](PF6)2 derivatives, 10- 12, but they vary considerably in their relative reactivity, following the same trend as the ease of their electrochemical oxidation, that is, [(2-BIT (NMe))Cu(CH 3CN)](+) ( 9b')>[(4-BIT (Ph,NMe))Cu(CH3CN)](+) ( 8b')>[(2-BIT (Ph2,NMe))Cu(CH3CN)](+) (1a')>[(4-BIT (Ph,NH))Cu(CH3CN)](+) (7b'). Thus, N-Me substitution and 4-tethering on the imidazole unit increase oxidation and oxygenation reactivity, while Ph-substitution and 2-tethering decrease reactivity. PM3 and DFT calculations are employed to analyze the relative stability, the electronic features, the Cu-CO vibrtional frequency, and the electrochemical and oxidative reactivity of the complexes.
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