Reaction of bromopentacarbonylrhenium(I) with ferrocenylcarbaldehyde thiosemicarbazones: the first X-ray diffraction studies of metal carbonyl complexes containing bidentate thiosemicarbazone ligands

The reactions of [ReBr(CO)5] with ferrocenylcarbaldehyde thiosemicarbazones HL with different groups attached to the amide nitrogen (R=H, Me, Ph) yielded complexes [ReBr(CO)3(HL)] (1) in which, according to X-ray studies of 1a·{(CH3)2CO} and 1b·1/2{CH2Cl2}, the thiosemicarbazone is N,S-bidentate and the geometry around the metal fac-octahedral. Compounds of formula [ReL(CO)3]2 (2) were then prepared by reaction of the corresponding adduct 1 with NaOMe in acetone. A complex of formula [ReL2(CO)3]2 (2b′) was also obtained as a dissolvate by slow concentration of a solution of 1b in acetone. Single crystals of 2a and 2b obtained from the mother liquors are composed of centrosymmetric dimers formed by ReSRe bridges, where S is the thiolic sulfur of an N,S-bidentate thiosemicarbazonato ligand. Although 2b·2{(CH3)2CO} and 2b′·2{(CH3)2CO} have similar co-ordination spheres, they differ as regards the configuration of the thiosemicarbazonato ligand about the azomethine bond and certain bond lengths (notably ReN); it seems likely that the configuration of L2− determines how close the rhenium can approach the N atom of the ligand, and hence the delocalization of the π electrons in the CNN fragment of the thiosemicarbazide chain. The mass, IR and UV–vis spectra of the complexes, and their electrochemical behavior, are also discussed.