Synthesis, characterization and catalytic activity of novel monometallic and bimetallic Mn(II) complexes with thiocarboxamide and phenanthroline ligands

Novel manganese(II) complexes, 1-3, involving 1,10-phenanthroline and thiocarboxamide ligands, were prepared and characterized structurally using single-crystal X-ray diffraction that revealed monometallic and bimetallic nature of the octahedral complexes. The catalytic activities of 1-3 were investigated in the oxidation of selected primary and secondary alcohols. During the optimization of the oxidation reactions, 1, a bimetallic manganese(II) complex bearing phenanthroline and bridging anthranilate showed higher activity as catalyst precursor than monometallic 2 or 3 in the oxidation of primary alcohols. The catalytic reactions were carried out in the presence of various oxidants such as molecular oxygen, hydrogen peroxide and tert-butyl hydroperoxide (TBHP) and additives such as acetic acid and imidazole. In this study, the oxidant/additive combination of TBHP and imidazole was shown to be effective for the oxidation of substrates investigated and the degree of their impact on oxidation reaction is highly dependent on a balanced ratio between them. 1 and 2 were selected as the most effective catalyst precursor under optimized reaction conditions and revealed efficient for the oxidation of selected primary and secondary alcohols, respectively.