Syntheses, structures, and properties of tricarbonyl (chloro) rhenium(I) complexes with redox-active tetrathiafulvalene-pyrazole ligands

A series of new tetrathiafulvalene-substituted 3,5-dimethylpyrazole ligands, 4-[{2,6,7-tris(methylthio)TTF-3-yl}thio]-3,5-dimethylpyrazole (MTSPz*, Pz* = 3,5-dimethylpyrazole, 4a), 4-[[6,7-benzo-2(methylthio)-TTF-3-yl}thio]-3,5-dimethylpyrazole (BTSPz*, 4b), 4-[{6,7-(ethylenedithio)-2-(methylthio)TTF-3-yl}thio]-3,5-dimethylpyrazole (ETSPz*, 4c) and 4-[16,7-(propylenedithio)-2-(methylthio)-TTF-3-yl}thio]-3,5-dimethylpyrazole (PTSPz*, 4d), have been prepared by an efficient synthetic route. Further coordination reactions of the respective ligands with Re(CO)(5)Cl afford new rhenium(I) tricarbonyl chloro complexes, ClRe(CO)(3)(MTSPz*)(2) (5a), ClRe(CO)(3)(BTSPZ*)(2) (5b), ClRe(CO)(3)(ETSPz*)(2) (5c) and ClRe(CO)(3)(PTSPz*)(2) (5d). The crystal structures of the ligand 4d and complexes 5b-d have been determined by X-ray crystallography, showing nearly planar TTF units in these compounds, and the distorted octahedral geometry in all complexes. The absorption spectra and multiredox behaviors of these new compounds (4a-d, 5a-d) have been studied, and are rationalized based on density functional theory. The results suggest that the novel redox-active tetrathiafulvalene-pyrazole ligands are useful for the syntheses of new metal complexes.