Selective catalytic oxidation of alkenes employing homobinuclear manganese(II) catalysts with TBHP

Abstract

The two novel homobinuclear compounds [Mn-2((II,II)) (mu(1,1)-4-CH3-C6H4COO)(2)(phen)(4)](ClO4)(2) (1) and [Mn-2((II,II)) (mu(1,3)-4-CH3-C6H4COO)(2)(bipy)(4)](ClO4)(2) (2), where bipy=2,2-bipyridine and phen=1,10-phenanthroline, have been synthesized and characterized by elemental analyses and spectral methods (UV-Vis, FTIR, and X-ray). A single-crystal X-ray diffraction structure analysis of the compounds revealed that the manganese atom is octahedrally coordinated. In compound 1, the binuclear(II) structure is monodentate, bridged with one oxygen atom of carboxylate ligand in mu(1,1) mode, and each Mn(II) center is coordinated with two phen ligands. In compound 2, the binuclear(II) structure is synanti bidentate, bridged with two oxygen atoms of carboxylate ligand in mu(1,3) mode, and each Mn(II) center is coordinated with two bipy ligands. The Mn-Mn separation is 3.441 (1)angstrom and 4.450 (1)angstrom for 1 and 2, respectively. The catalytic potentials of these compounds have been tested for the oxidation reaction of various olefins (i.e., styrene, cyclohexene, ethyl benzene, 1-hexene, 1-octene). The oxidation reactions were carried out in the presence of catalytic amounts of 1 and 2 with a peroxide oxygen donor (TBHP=tert-Butyl hydroperoxide) in acetonitrile at 70 degrees C. On comparing the catalytic activities of 1 and 2, both catalysts showed good activity (similar to 100% conv. in 24 h) in the oxidation of studied alkenes, and excellent conversion was obtained for cyclohexene (similar to 100% conv. in 3 h; TON = 265 and TON = 257, respectively, for 1 and 2)