Mo(II) complexes of 8-aminoquinoline and their immobilization in MCM-41

Two new Mo(II) complexes [MoBr(η3-C3H5)(CO)2(8-aq)] (1) and [MoI2(CO)3(8-aq)] (2) containing the bidentate 8-aminoquinoline ligand (8-aq) were synthesized and characterized. They were immobilized in MCM-41. A 3-iodopropyltrimethoxysilane spacer reacted both with the surface, through the silane, and through the other end, with the coordinated 8-aq of complexes 1 and 2, leading to an immobilized form of the complex (MCM-Pr-1,2). In an alternative route, 8-aq reacted with 3-iodopropyltrimethoxysilane to form a new ligand L1, which could be supported in the MCM-41 and then react with the metal precursors to afford (MCM-L1-1,2). The complexes and the materials were characterized using FTIR and NMR spectroscopies, and the structure of the materials was checked with powder X-ray diffraction and nitrogen adsorption isotherms. The first synthetic procedure was less efficient in terms of metal load inside the channels of the materials.The complexes and the new materials were tested as catalytic precursors in the epoxidation of cis-cycloctene, styrene, 1-octene, R-(+)limonene, geraniol, cis-3-hexene-1-ol and trans-2-hexene-1-ol, using tert-butylhydroperoxide (TBHP) as oxidant. Although almost all the catalysts were 100% selective toward the epoxide, the conversions were in general poor. The best catalyst was complex 1, but the conversions dropped after immobilization. Conversions could be a bit improved by a careful choice of reaction conditions, the most effective being the absence of added solvent (the substrate acted as solvent).

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► Two new Mo(II) complexes with the 8-aminoquinoline ligand were prepared.
► The Mo(II) complexes were immobilized in MCM-41 using two different methodologies.
► MCM-Mo(II) materials were active pre-catalysts for olefin epoxidation.
► Homogeneous catalysts are more active than their heterogeneous counterparts.
► All catalysts epoxidize allylic alcohols selectively.