New Mo(II) complexes in MCM-41 and silica: Synthesis and catalysis

The new complexes [MoI2(CO)(3)(L-1)] (1) and [MoI2(CO)(3)(L-2)] (2) were prepared from reaction of [MoI2(CO)(3)(NCMe)(2)] with the ligands 2-(2'-hydroxyphenyl) imidazoline (L-1), and 2-(2'-hydroxyphenyl)benzimidazole (L-2). These complexes were immobilized in MCM-41 and in silica gel, by grafting (3-chloropropyl)trimethylsilane on the surface of the materials and allowing it to react with [MoI2(CO) 3(L-1)] (1) or [MoI2(CO)(3)(L-2)] (2). All the molybdenum derivatives were characterized by NMR and FTIR spectroscopies, which showed coordination of L-1 and L-2 in neutral form. The structure of the MCM materials was analyzed by powder X-ray diffraction and nitrogen adsorption isotherms. The catalytic activity of the complexes and materials was tested in several substrates (cis-cyclooctene, styrene, 1-octene, R-(+)limonene, geraniol, cis-hex-3-en-1-ol and trans-hex-2-en-1-ol), using tert-butylhydroperoxide (TBHP) as oxidant. Complexes 1 and 2 were in general the more active catalysts and 100% selective towards the epoxide of cis-cyclooctene. Complex 1 immobilized in silica (Si-Pr-1) was the best material, showing higher conversion than 1 in the oxidation of R-(+)limonene, with comparable selectivity towards the ring epoxide. (C) 2013 Elsevier B.V. All rights reserved.