Synthesis and characterization of rhenium(III) and (V) pyridylimidazole complexes

Reaction of trans-[ReOCl3(PPh3)(2)] with 2-(2'-pyridyl) imidazole (pimH) in methanol led to the isolation of the rhenium(III) salt [ReCl2(pimH)(PPh3)(2)](ReO4) (1). However, with 2-(2'-pyridyl)- 1-methylimidazole (pimMe) as ligand, the complex [ReCl3(pimMe)(PPh3)] (2) was obtained. The monooxorhenium(V) complexes [ReOCl3(pimR)] (R = H, Me) could only be prepared by the reduction of [ReO4](-) with an equimolar amount of PPh3 in the presence of pimR and hydrochloric acid in acetic acid. With four equivalents of PPh3, compounds 1 and 2 were obtained. Using (n-Bu4N)[ReOCl4] as starting material, the mu-oxo dimers [Re2O3(pimR)(2)Cl-4] were isolated as the only products. These new compounds have been characterized by X-ray crystallography, (HNMR)-H-1 and IR spectroscopy. In 1 the [ReO4](-) counterion is tightly associated with the cationic complex through N-(HReO3-)-Re-... hydrogen bonding. Despite being paramagnetic, (HNMR)-H-1 spectra for 1 and 2 could be fully assigned.