Portal de Periódicos da CAPES

Synthesis and Catalytic Properties of Molybdenum(VI) Complexes with Tris(3,5-dimethyl-1-pyrazolyl)methane

2011; American Chemical Society; Volume: 50; Issue: 8 Linguagem: Inglês

10.1021/ic102456z

1520-510X

Patrícia Neves, Sandra Gago, Salete S. Balula, André D. Lopes, Anabela A. Valente, Luís Cunha‐Silva, Filipe A. Almeida Paz, Martyn Pillinger, João Rocha, Carlos M. Silva, Isabel S. Gonçalves,

Metal-Organic Frameworks: Synthesis and Applications

The complex [MoO2Cl{HC(3,5-Me2pz)3}]BF4 (1) (HC(3,5-Me2pz)3 = tris(3,5-dimethyl-1-pyrazolyl)methane) has been prepared and examined as a catalyst for epoxidation of olefins at 55 °C using tert-butyl hydroperoxide (TBHP) as the oxidant. For reaction of cis-cyclooctene, epoxycyclooctane is obtained quantitatively within 5 h when water is rigorously excluded from the reaction mixture. Increasing amounts of water in the reaction mixture lead to lower activities (without affecting product selectivity) and transformation of 1 into the trioxidomolybdenum(VI) complex [{HC(3,5-Me2pz)3}MoO3] (4). Complex 4 was isolated as a microcrystalline solid by refluxing a suspension of 1 in water. The powder X-ray diffraction pattern of 4 can be indexed in the orthorhombic Pnma system, with a = 16.7349(5) Å, b = 13.6380(4) Å, and c = 7.8513(3) Å. Treatment of 1 in dichloromethane with excess TBHP led to isolation of the symmetrical [Mo2O4(μ2-O){HC(3,5-Me2pz)3}2](BF4)2 (2) and unsymmetrical [Mo2O3(O2)2(μ2-O)(H2O){HC(3,5-Me2pz)3}] (3) oxido-bridged dimers, which were characterized by single-crystal X-ray diffraction. Complex 2 displays the well-known (Mo2O5)2+ bridging structure where each dioxidomolybdenum(VI) center is coordinated to three N atoms of the organic ligand and one μ2-bridging O atom. The unusual complex 3 comprises dioxido and oxidodiperoxo molybdenum(VI) centers linked by a μ2-bridging O atom, with the former center being coordinated to the tridentate N-ligand. The dinuclear complexes exhibit a similar catalytic performance to that found for mononuclear 1. For complexes 1 and 2 use of the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate and N-butyl-3-methylpyridinium tetrafluoroborate as solvents allowed the complexes to be completely dissolved, and in each case the catalyst and IL could be recycled and reused without loss of activity.