Synthesis and characterization of Ru(arene) complexes of bispyrazolylazines: Catalytic hydrogen transfer of ketones |
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Authors: | M Laura Soriano Blanca R Manzano |
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Institution: | a Departamento de Química Inorgánica, Orgánica y Bioquímica, Facultad de Químicas-IRICA, UCLM, Avda. Camilo J. Cela 10, 13071 Ciudad Real, Spain b Departamento de Química Fundamental, Universidade da Coruña, 15071 A Coruña, Spain |
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Abstract: | The bis(pyrazol-1-yl)azine ligands 2,3-bis(pyrazol-1-yl)quinoxaline (bpzqnx), 2,3-bis(pyrazol-1-yl)pyrazine (bpzprz) and 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine (bpz*pdz) were prepared by the reaction of pyrazolate salts and the corresponding azine dichloride derivatives. The reaction of these ligands with Ru(arene) precursors led to the mononuclear complexes RuCl(arene)(L)]BPh4 (arene = p-cymene, L = bpzqnx, 1, bpzprz, 5, bpz*pdz, 7; arene = C6H6, L = bpzqnx, 2, bpzprz, 6, bpz*pdz, 8) with the N-donor ligand coordinated in a bidentate chelate way. In general, the ligands coordinate through one pyrazole ring and the azine, except in the cases of 1 and 2 where the two pyrazolyl rings are coordinated to the metal in a symmetrical way. When the reactions between the ruthenium precursors and bpzqnx are carried out in MeOH, the complexes RuCl(arene)(OMepzqnx)]BPh4 with partially methanolyzed ligands are isolated (arene = p-cymene, 3; C6H6, 4). In this process a methoxy group has replaced one of the pyrazole groups in the ligand. The X-ray structures of 6 and 7 have been determined. These compounds have a three-legged piano-stool structure with cations and anions packed through weak interactions. Complexes 1-8 are active in ketone hydrogenation transfer processes even in the absence of base. |
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Keywords: | Ruthenium Pyrazole Catalysis Hydrogen transfer N-donor ligands Arene derivatives |
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