Selective Formation and Characterization of Oxorhenium(V) Complexes with 2-Methylquinolin-8-ylamido (Hamq). Interconversion between [ReOX2(Hamq)(PPh3)] and [ReOX2(Hamq)(OPPh3)] (X = Cl, Br)

The reactions of Re(V) precursors [ReOX3(PPh3)2] (X = Cl, Br) with 8-amino-2-methylquinoline (H2amq) gave [ReOX2(Hamq)(PPh3)] (X = Cl, 1; Br, 2) as major products and [ReOX2(Hamq)(OPPh3)] (X = Cl, 3; Br, 4) as minor products. 3 and 4 were also obtained from the reaction of 1 and 2 with an excess of free OPPh3 ligand. The crystal structures of 1, 3, and 4 were determined by X-ray analyses. These complex molecules have a distorted octahedral geometry. The Re=O bond in 1 occupies the trans position to the amido N atom of the partially deprotonated H2amq ligand. Its distance (1.724(4) ?) is long due to the trans influence of the amido N atom. The Re=O bonds in 3 and 4 occupy the trans position to the O atom of the OPPh3 ligand, indicating a geometrical conversion during the ligand substitution reaction. Some intramolecular and/or intermolecular stacking interactions are also observed in the crystalline state. All complexes were characterized in the solid state by IR, far-IR, diffuse reflectance, and 31P{1H} CP-MAS NMR spectra. From UV-vis absorption and 31P{1H} NMR spectra, it was indicated that the PPh3 and OPPh3 ligands in 1-4 are released in solution.