Improved synthetic routes to rhodium bipyridine complexes: Comparison of microwave vs. conventional synthesis

• Published in: Inorganica Chimica Acta Vol. 358; no. 7; pp. 2231 - 2238
• Main Authors: Amarante, Daniel, Cherian, Cheryl, Emmel, Christopher, Chen, Hui-Yun, Dayal, Saraswati, Koshy, Mary, Megehee, Elise G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2005
• Subjects: Conventional synthesis; Microwave synthesis; Rhodium(III) bipyridine complexes; Rhodium(III) bipyridine complexes; Conventional synthesis; Microwave synthesis
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2005.01.024

Two new, high purity, high yield, one-step syntheses of cis-[Rh(bpy) 2X 2][PF 6] {X = Cl, Br, I, bpy = 2,2′-bipyridine} – one conventional and one microwave – are described and compared. In order to obtain pure cis-[Rh(bpy) 2X 2][PF 6], it is essential to maintain a 2:1 ratio of rhodium to bipyridine throughout the reaction. The complexes were characterized by 1H and 13C NMR, elemental analysis, cyclic voltammetry, electronic absorption and emission spectroscopies. The first cyclic voltammetry data on the cis-[Rh(bpy) 2I 2][PF 6] complex are reported and compared with the chloro and bromo complexes. We report here two new, high purity, high yield, one-step syntheses of cis-[Rh(bpy) 2X 2][PF 6] {X = Cl, Br, I, bpy = 2,2′-bipyridine} directly from the RhX 3 · nH 2O starting materials – one conventional and one microwave. The key to obtaining the pure complexes appears to be maintaining a 2:1 ratio of bipyridine to rhodium in solution; thus all reactants must be completely dissolved prior to the start of the reaction. Comparison of the two methods is also discussed. These complexes are pure enough for emission spectroscopy after minimal work-up. The complete characterization of all the halide complexes and the first cyclic voltammetry data on the cis-[Rh(bpy) 2I 2][PF 6] complex are reported. The irreversible Rh(III)–Rh(I) redox potential becomes more positive from Cl to I. All three complexes show two reversible redox potentials corresponding to the bipyridine reductions. These data are consistent with the loss of the two halide ligands and formation of [Rh(bpy) 2] + upon reduction of Rh(III) to Rh(I).