title: Imidazole substituent effects on oxidative reactivity of tripodal(imid)2(thioether)CuI complexes.
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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhou
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Nicholas
mesh_terms: D001665:Binding Sites; D003198:Computer Simulation; D003300:Copper / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D007093:Imidazoles / Q000737:chemistry*; D008024:Ligands; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013055:Spectrophotometry, Infrared
chemical_list: D007093:Imidazoles; D008024:Ligands; D009942:Organometallic Compounds; D003300:Copper; C029899:imidazole; D006899:Mixed Function Oxygenases; D010100:Oxygen