Cu(II) complexes with labile apical coordination: Synthesis, crystal structure, 1H NMR investigation, and oxidation properties of mononuclear [CuII(dien)(2-PhIm)(ClO4)]+ (1), [CuII(dien)(2-MeBzIm)]2+ (2), complexes

The compounds [Cu(dien)(2-PhIm)(ClO4)](ClO4) (1); [Cu(dien)(2-MeBzIm)](ClO4)2 (2); where dien = diethylenetriamine, 2-PhIm = 2-phenylimidazole and 2-MeBzIm = 2-methylbenzimidazole, were synthesized and characterized. The complexes possessing [Cu(II)dien] moiety as common, the former containing 2-phenylimidazole, yielded square pyramidal geometry with apical perchlorate coordination [Cu1–O(5) = 2.449 Å], while the latter with 2-methylbenzimidazole formed square planar geometry with weak perchlorate contact [Cu1–O(8) = 2.596 Å] in its apical position. The effect of solvent and the variable temperature 1H NMR investigation combinedly explore the geometrical rearrangement towards five coordination around Cu(II) metal center by accommodating the solvent molecule in its fifth coordination. Possessing easily labile perchlorate anion, both these complexes were investigated for their oxidation capability using 3,5-di-tert-butyl catechol (DTBC). The rate constant determined for the oxidation of DTBC to corresponding quinone indicates that they are catalytically quite similar and the kcat of 1 ≈ 2. The crystal structure and the NMR investigations are discussed in detail.

Graphical abstractTwo mononuclear ternary Cu(II) complexes containing diethylenetriamine and imidazole derivatives were synthesized and characterized. The effect of solvent and the variable temperature 1H NMR investigation combinedly explore the geometrical rearrangements from square planar to square pyramidal. The weak apical coordination observed by single crystal X-ray structure was exploited to understand the catalytic property of these compounds promoting oxidation of DTBC to DTBQ.Figure optionsDownload full-size imageDownload as PowerPoint slide