Structural variations and magneto-structural correlations in two new dinuclear bis(µ2-phenoxido)-bridged CuII Schiff-base complexes and their catalytic potential for the peroxidative oxidation of cycloalkanes

Two new dinuclear bis(mu(2)-phenoxo)-bridged copper(II) complexes [Cu(NCS)L-1](2) (1) and [Cu(NCS)L-2](2) (2) have been synthesized using two tridentate NNO-donor Schiff-base ligands, (LH)-H-1 (Me2N(CH2)(3)N=CHC6H3(OMe)(OH)) and (LH)-H-2 (Me2N(CH2)(3)N=C(CH3)C6H4(OH)), respectively. They have been characterized by elemental analyses, IR, UV-visible, and electron paramagnetic resonance (EPR) spectroscopy, cyclic voltammetry, and magnetic susceptibility measurements. X-Ray single-crystal structures reveal a central Cu2O2 core in each complex with an isothiocyanate ligand coordinated terminally to each metal centre. The coordination environments around the Cu-II ions in 1 and 2 are a distorted trigonal bipyramid and a quasi-regular square pyramid, respectively, with significant differences in the Cu-O-Cu bridging angles (100.22(5)degrees for 1 and 95.64(7)degrees for 2). Although both Cu-II dimers present intradimer antiferromagnetic exchange interactions, the magnitudes of the coupling constants in 1 and 2 (J = -119(1) and -0.361(3) cm(-1), respectively) are quite different as a result of the different coordination geometries and Cu-O-Cu bridging angles. Both complexes act as promising catalysts or catalyst precursors for the efficient peroxidative oxidation of cycloalkanes (cyclohexane and cycloheptane) to the corresponding cyclic alcohols and ketones, with maximum overall yields of 53% and 56% for 1 and 2, respectively.