Copper(I) Chelation by Tetradentate NSSN Donor Ligands: Reversible Oxidation but no Oxygenation

The copper(I) complexes [Cu(L4)](ClO4), L4 = 1,6-bis(N-methyl-1H-benzimidazol-2-yl)-2,5-dithiahexane (bmbdh) or 1,7-bis(N-methyl-1H-benzimidazol-2-yl)-2,6-dithiaheptane (bmdhp) were obtained and investigated through structure analysis (bmdhp compounds), cyclic voltammetry, UV/Vis/NIR and EPR spectroelectrochemistry. Structure comparison of the complexes [Cu(bmdhp)](ClO4) (1) and [Cu(bmdhp)](SO3CF3) (2) with the previously reported [CuI(bdhp)(H2O)](PF6)0.66(BF4)0.34 (4), bdhp = 1,7-bis(1H-benzimidazol-2-yl)-2,6-dithiaheptane, with the related [CuI(mmb)2](BF4) (5), mmb = 1-methyl-2-methylthiomethyl-1H-benzimidazole, with the oxidised [CuII(bmdhp)(H2O)](ClO4)2 (7), and with the zinc(II) species [Zn(bmbdh)(H2O)(SO3CF3)](SO3CF3) (8) and {[Zn(μ-bmdhp)(H2O)(SO3CF3)]2}(SO3CF3) (9) reveal a variety of coordination numbers, L4 ligand coordination modes, M–N bond lengths and especially N–M–N angles, affecting the accessibility of the central metal ions. Electronic consequences as evident from oxidation potentials and from EPR and absorption spectra of the copper(II) forms are discussed. The lack of reactivity of the copper(I) compounds towards O2 is attributed to steric shielding and to electronic effects from two π accepting thioether donors.

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