Rhenium(III), (IV) and (V) complexes with 6-hydroxypicolinic acid

• Published in: Polyhedron Vol. 110; pp. 106 - 113
• Main Authors: Mukiza, J., Hosten, E.C., Gerber, T.I.A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 28.05.2016
• Subjects: 6-Hydroxypicolinic acid; Bridging chelate; Rhenium(IV) dimers; X-ray crystal structures; X-ray crystal structures; Bridging chelate; 6-Hydroxypicolinic acid; Rhenium(IV) dimers
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2016.02.036

The reaction of trans-[ReOBr3(PPh3)2] with 6-hydroxypicolinic acid (H2hpa) in ethanol led to the isolation of the doubly chelate-bridged complex (μ-O)(μ-hpa)2[ReIV2Br(OEt)(PPh3)2] (1). By using [ReOCl3(PPh3)2] as precursor, two products were isolated, i.e. (μ-Cl)(μ-O)(μ-hpa)-[ReIV2Cl2(OEt)(PPh3)2] (2) and [ReIIICl2(Hhpa)(PPh3)2] (3). The bromide equivalent of 3, i.e. [ReIIIBr2(Hhpa)(PPh3)2] (6), was obtained from the reaction of [ReOBr3(PPh3)2] with H2hpa in 2-propanol. The complexes cis-[ReOX2(Hhpa)(PPh3)] (X=Br (4); Cl (5)) were the only products formed by the reaction of [ReOX3(PPh3)2] with H2hpa in acetonitrile. [Display omitted] The reaction of trans-[ReOBr3(PPh3)2] with 6-hydroxypicolinic acid (H2hpa) in ethanol led to the isolation of the ReIVReIV dimer (μ-O)(μ-hpa)2[Re2Br(OEt)(PPh3)2] (1). Each hpa2− anion acts as a bridging ligand with the coordination of a neutral pyridol oxygen to one rhenium ion, and the coordination of a carboxylate oxygen and a pyridinate nitrogen to the other rhenium ion. By using [ReOCl3(PPh3)2] as precursor in ethanol, two products were isolated, i.e. (μ-Cl)(μ-O)(μ-hpa)[ReIV2Cl2(OEt)(PPh3)2] (2) and [ReIIICl2(Hhpa)(PPh3)2] (3). The complexes cis-[ReOX2(Hhpa)(PPh3)] (X=Br (4); Cl (5)) were the only products formed by the reaction of [ReOX3(PPh3)2] with H2hpa in acetonitrile. The bromide equivalent of 3, i.e. [ReIIIBr2(Hhpa)(PPh3)2] (6), was obtained from the reaction of [ReOBr3(PPh3)2] with H2hpa in 2-propanol. Coordination of Hhpa− in 3–6 occurs through the carboxylate oxygen and neutral pyridyl nitrogen. In addition to the X-ray crystal structures, infra-red, 1H NMR, electrochemical and electronic properties are also reported.