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Synthesis and crystal structures of Group 6 metal carbonyl complexes containing S-rich bis(pyrazol-1-yl)methane ligands
Authors:Liang-Fu Tang  Wen-Li JiaZhi-Hong Wang  Ji-Tao WangHong-Gen Wang
Institution:a Department of Chemistry, Nankai University, Tianjin 300071, People's Republic of China
b Central Laboratory of Nankai University, Tianjin 300071, People's Republic of China
Abstract:The reaction of 3(5)-methylthio-5(3)-phenylpyrazole with dibromomethane under phase-transfer catalytic conditions only affords a new ligand, bis(3-phenyl-5-methylthiopyrazol-1-yl)methane. However, the reaction of 3(5)-methylthio-5(3)-p-methoxyphenylpyrazole or 3(5)-methylthio-5(3)-tert-butylpyrazole with dibromomethane under the same conditions yields three isomers, respectively, indicating that the substituents significantly affect the steric and electronic properties of pyrazole ring during the formation of ligands. Treatment of these potential polydentate ligands with M(CO)6 (M=Cr, Mo or W) under UV irradiation at room temperature affords (NN)M(CO)4 derivatives, in which some complexes contain asymmetric substituted bis(pyrazol-1-yl)methane ligands. The X-ray crystal structure analyses indicate that the sulfur atoms in these complexes do not take part in the coordination to the metal centers, and S-rich bis(pyrazol-1-yl)methanes actually act as bidentate chelating ligands by two nitrogen atoms. It is also interesting that in order to reduce the repulsion of methyl groups with carbonyls, the methyl groups in these complexes are oriented away from the metal centers.
Keywords:Bis(pyrazol-1-yl)methane  Group 6 metal carbonyl complexes  X-ray crystal structures
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