Bdmpp complexes of Ru(II) as structural analogs for Ru(II)-2,2′:6′,2"-terpyridine species (where bdmpp is 2,6-bis(3,5-dimethyl-N-pyrazoyl)pyridine

The complexes, [Ru(bdmpp)(bpy)Cl](PF6) (1a), [Ru(bdmpp)(phen)Cl](PF6) (2a), and [Ru(bdmpp)(Me(2)bpy)Cl](PF6) (3a) (where bdmpp is 2,6-bis(3,5-dimethyl-N-pyrazoyl)pyridine bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline and Me(2)bpy is 4,4'-dimethyl-2,2'-dipyridyl) were synthesized and characterized by H-1 NMR, electronic absorption spectroscopy and cyclic voltammetry. 1a and 3a were also characterized by X-ray crystallography. The chloride salt of 1a, [Ru(bdmpp)(bpy)Cl]Cl . 1.25CHCl(3), crystallizes in the monoclinic space group P2(1)/n with Z = 4, a = 13.551(2), b = 8.556(1), c = 29.994(3) Angstrom, beta = 100.28(1)degrees, V = 3421.8(7) Angstrom(3) with 4486 unique data yielding R-1 = 0.0715 (I > 2 sigma(I)). The chloride salt of 3a crystallizes in the triclinic space group P (1) over bar with 1.25 chloroform solvate and a = 8.656(1), b = 10.685(2), c = 18.729(3) Angstrom, alpha = 94.394(6), beta = 99.72(1), gamma = 98.61(1)degrees, V = 1679.0(4) Angstrom(3), Z = 2, and R-1 = 0.066 (I > 2 sigma(I)) with 4403 unique reflections. Compounds 1a, 2a, and 3a are converted to their corresponding aqua complexes, 1b, 2b, and 3b upon treatment with aqueous silver ion, and to the acetonitrile species, 1c, 2c, and 3c, by dissolution in acetonitrile. Cyclic voltammograms in acetonitrile of 1a, 2a, and 3a display one-electron oxidations at 0.72, 0.71, 0.63 V, respectively, consistent with a Ru(III/II) couple. Compounds 1b, 2b, and 3b show a pH independent couple at pH < 2 and a pH dependent couple consistent with a one-electron, one-proton process at pH values from ca. 2 to Il. Past pH II this redox process becomes pH independent again, and the compounds become unstable. The one-electron nature was verified by bulk electrolysis and spectroelectrochemical measurements. (C) 1999 Elsevier Science S.A. All rights reserved.