title: Synthesis and catalytic properties of molybdenum(VI) complexes with tris(3,5-dimethyl-1-pyrazolyl)methane.
abstract: The complex [MoO(2)Cl{HC(3,5-Me(2)pz)(3)}]BF(4) (1) (HC(3,5-Me(2)pz)(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-Me(2)pz)(3)}MoO(3)] (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 [Mo(2)O(4)(μ(2)-O){HC(3,5-Me(2)pz)(3)}(2)](BF(4))(2) (2) and unsymmetrical [Mo(2)O(3)(O(2))(2)(μ(2)-O)(H(2)O){HC(3,5-Me(2)pz)(3)}] (3) oxido-bridged dimers, which were characterized by single-crystal X-ray diffraction. Complex 2 displays the well-known (Mo(2)O(5))(2+) bridging structure where each dioxidomolybdenum(VI) center is coordinated to three N atoms of the organic ligand and one μ(2)-bridging O atom. The unusual complex 3 comprises dioxido and oxidodiperoxo molybdenum(VI) centers linked by a μ(2)-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.
authors: Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal.
authors: Patrícia
authors: P
authors: Neves
authors: Sandra
authors: S
authors: Gago
authors: Salete S
authors: SS
authors: Balula
authors: André D
authors: AD
authors: Lopes
authors: Anabela A
authors: AA
authors: Valente
authors: Luís
authors: L
authors: Cunha-Silva
authors: Filipe A Almeida
authors: FA
authors: Paz
authors: Martyn
authors: M
authors: Pillinger
authors: João
authors: J
authors: Rocha
authors: Carlos M
authors: CM
authors: Silva
authors: Isabel S
authors: IS
authors: Gonçalves
mesh_terms: D002384:Catalysis; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D011720:Pyrazoles / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D011720:Pyrazoles; C573422:tris(3,5-dimethyl-1-pyrazolyl)methane; D008982:Molybdenum