Syntheses, structures, and properties of oxorhenium(V) complexes with 2-, 5-, and/or 7-substituted 8-quinolinolato ligands

Five mononuclear oxorhenium(V) complexes containing 8-quinolinolato derivatives, [ReOCl2(2-X-5-Y-7-Z-8-Oqn)(PPh3)] (qn=quinoline; PPh3=triphenylphosphine; X=Me, Y=Z=H, 1; X=Z=H, Y=Cl, 2; X=H, Y=Z=Cl, 3; X=H, Y=Cl, Z=I, 4; X=H, Y=Z=Br, 5), were newly synthesized by the reaction of [ReOCl3(PPh3)2] with the corresponding 8-hydroxyquinoline ligands. From X-ray crystal structural analyses, all the obtained complexes have the same geometry; the ReO bond occupies the trans position to the O atom of the deprotonated 8-hydroxyquinoline ligand. The complexes, which retain their structures in solution, were characterized on the basis of IR, UV-vis, 31P NMR spectra, and cyclic voltammetry. Depending on the existence of 2-Me substituent in the ligands, some stereochemical and electrochemical differences were observed. In contrast to the case of the corresponding 2-methylquinolin-8-ylamido complex [ReOCl2(2-Me-8-HNqn)(PPh3)], substitution reaction of PPh3 to OPPh3 (=triphenylphosphine oxide) or pyridine did not take place, reflecting the high stability of the present 8-quinolinolato complexes.