New copper(II) salicylaldimine derivatives for mild oxidation of cyclohexane

Abstract: Two new salicylaldiminato-copper(II) complexes, [Cu(L1)2] (1) and [Cu(L2)2] (2) (where HL¹= 4 -tert-Butyl-2-[(thiophen-2-ylmethylimino)-methyl]-phenol and HL²= 2 , 4 -Di-tert-butyl-6-[(thiophen-2-ylmethylimino)-methyl]-phenol), endowed with a pendant thiophenyl moiety, were synthesized and characterized using standard spectroscopic techniques (FT-IR, UV-Vis, MS) and elemental analysis. Complexes 1 and 2 were unequivocally characterized by single crystal X-ray crystallography, which confirmed bidentate bis-chelation of the deprotonated -L¹ and -L² ligands to the copper (II) centres via the phenoxo and imine atoms forming square planar complexes. The copper(II)-hydroperoxo derivatives of 1 and 2 ([(L1)2CuII-OOH] (3) and [(L2)2CuII-OOH] (4)) were also synthesized and the formation of the active intermediate in solution studied. Complexes 1 and 2 were tested as catalyst precursors in cyclohexane oxidation under mild reaction conditions using hydrogen peroxide (H ₂O ₂) as a terminal oxidant, and were found to catalyse oxidation of the substrate with yields comparable to similar mononuclear and even multinuclear copper complexes. Graphical Abstract: Synopsis Synthesis, characterisation, and molecular structure of salicylaldiminato-copper(II) complexes, and their catalytic evaluation in the oxidation of cyclohexane employing hydrogen peroxide as a terminal oxidant have been studied. The complexes catalysed conversion of cyclohexane with appreciable yields. [Figure not available: see fulltext.].