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

Abstract Divalent transition metal complexes ML 2 (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 CuL 2 @MCM-41 ( 9 ). Elemental analysis (CHN), ESI MS, IR, UV–vis., 13 C & 29 Si 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 H 2 O 2 , t -BuOOH, and C 6 H 5 C(CH 3 ) 2 OOH. 3 and 9 have shown better catalytic activity than the rest of the catalysts investigated. Combination of 9 with H 2 O 2 is the best catalytic system due to its efficiency and reusability besides being environment friendly.