Ethoxysilane appended M(II) complexes and their SiO2/MCM-41 supported forms as catalysts for efficient oxidation of secondary alcohols

Divalent transition metal complexes ML2 (M = Mn 1; Co 2; Cu 3; Zn 4), possessing an ethoxysilane group as a part of the bidentate Schiff base ((E)-1-((3-(triethoxysilyl) propylimino) methyl)naphthalen-2-ol (L)), have been synthesized. While the copper complex 3 has been isolated in an analytically pure form and characterized by spectroscopic and single crystal XRD studies, the formation of complexes 1, 2, and 4 in solution has been verified by ESI mass spectroscopy and subsequently used for further catalyst preparation without their isolation. Treatment of the in situ formed 1-4 with pre-activated silica in boiling toluene produces the catalysts 5-8, respectively. The copper complex 3 was also treated with MCM-41 in boiling toluene to obtain CuL2@MCM-41 (9). Elemental analysis (CHN), ESI MS, IR, UV-vis., C-13 & Si-29 NMR, EPR, P-XRD, TGA, BET, SEM and TEM have been used to characterize the compounds. Compounds 3 (homogeneous) and 5-9 (heterogeneous) have been utilized as catalysts in the oxidation of secondary alcohols to corresponding carbonyls in the presence of H2O2, t-BuOOH, and C6H5C (CH3)(2)OOH. 3 and 9 have shown better catalytic activity than the rest of the catalysts investigated. Combination of 9 with H2O2 is the best catalytic system due to its efficiency and reusability besides being environment friendly. (C) 2017 Elsevier B.V. All rights reserved.