Effect of single-wall carbon nanotubes on direct epoxidation of cyclohexene catalyzed by new derivatives of cis-dioxomolybdenum(VI) complexes with bis-bidentate Schiff-base containing aromatic nitrogen-nitrogen linkers

The synthesis and characterisation of three dimeric cis-dioxomolybdenum(VI) complexes involving Schiff-base ligands is described. Ligands were obtained by condensation of salicylaldehyde with aromatic nitrogen-nitrogen linkers (4,4'-diaminodiphenylmethane; 4,4'-diaminodiphenylether; 4,4'-diaminodiphenylsulfone). [MoO2(acac)(2)] reacted with the prepared ligands; bis[(N,O-salicylidene)-4,4'diaminodiphenyl]methane, H2L2; his [(N,O-salicylidene)-4,4-diaminodiphenyl]ether, H2L2; bis[(N,O-salicy]idene)-4,4'-diaminodiphenyl]sulfone, H2L3; forming six-coordinated cis-dioxoMo(VI) complexes; [MoO2L1-3](2). The yellow colored, non-electrolytic and diamagnetic compounds were characterized by elemental analyses and spectroscopic techniques (IR, H-1 NMR and UV-vis). These complexes show good catalytic activity and selectivity in the epoxidation of cyclohexene with t-butylhydroperoxide (TBHP), especially for complex [MoO2L3](2), which could give a nearly 88% of epoxidation conversion and 94% of selectivity. Introduction of the electron-withdrawing group to the aromatic nitrogen-nitrogen linkers of complex strongly increases the effectiveness of a catalyst. The addition of single-wall carbon nanotubes (SWNT) can enhance the activity of the Mo complexes and the selectivity toward epoxide. It is also better for the recycling of the Mo complex, the catalytic activity and the selectivity toward which still held at a high level after four times using. (c) 2007 Elsevier B.V. All rights reserved.