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

The new complexes [MoI2(CO)3(L1)] (1) and [MoI2(CO)3(L2)] (2) were prepared from reaction of [MoI2(CO)3(NCMe)2] with the ligands 2-(2′-hydroxyphenyl)imidazoline (L1), and 2-(2′-hydroxyphenyl)benzimidazole (L2). 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(L1)] (1) or [MoI2(CO)3(L2)] (2). All the molybdenum derivatives were characterized by NMR and FTIR spectroscopies, which showed coordination of L1 and L2 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.