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  • Title: Ruthenium(II) complexes incorporating 2-(2'-pyridyl)pyrimidine-4-carboxylic acid.
    Author: Nickita N, Gasser G, Pearson P, Belousoff MJ, Goh LY, Bond AM, Deacon GB, Spiccia L.
    Journal: Inorg Chem; 2009 Jan 05; 48(1):68-81. PubMed ID: 19053847.
    Abstract:
    A new bidentate ligand bearing a single carboxylate functionality, 2-(2'-pyridyl)pyrimidine-4-carboxylic acid (cppH), has been prepared and applied in the synthesis of a series of ruthenium(II) complexes. Reaction of this new ligand with Ru(II)(bpy)(2)Cl(2) led to the unexpected oxidation of the starting material to give [Ru(III)(bpy)(2)Cl(2)]Cl.H(2)O and a low yield of [Ru(II)(bpy)(2)(cppH)](PF(6))(2).H(2)O (1) on addition of an aqueous KPF(6) solution (bpy = 2,2'-bipyridine and cpp = 4-carboxylate-2'-pyridyl-2-pyrimidine). An X-ray crystal structure determination on crystals of 1a, [Ru(II)(bpy)(2)(cpp)](PF(6)), obtained from slow evaporation of an aqueous solution of 1 revealed that the nitrogen para to the carboxylate group in the cpp(-) ligand coordinates to the ruthenium(II) center rather than that ortho to this group. The same complex was prepared via decarbonylation of [Ru(II)(cppH)(CO)(2)Cl(2)].H(2)O in the presence of bpy and an excess of trimethylamine-N-oxide (Me(3)NO), as the decarbonylation agent. The coordination of cppH in the precursor is the same as in the final product. The related complex [Ru(II)(phen)(2)(cppH)](PF(6))(2).2H(2)O (2) (phen = 1,10-phenanthroline) was similarly synthesized. [Ru(II)(bpy)(dppz)(cppH)](PF(6))(2).CH(3)CN (3) (dppz = dipyrido[3,2,-a;2',3-c]phenazine) was also prepared by photochemical decarbonylation of [Ru(II)(bpy)(CO)(2)Cl(2)] giving [Ru(II)(bpy)(CO)Cl(2)](2) followed by bridge splitting with dppz to generate [Ru(II)(bpy)(dppz)(CO)Cl](PF(6)).H(2)O. This intermediate was then reacted with cppH to produce 3, as a mixture of geometric isomers. In contrast to 1, X-ray crystallography on the major product isolated from this mixture, [Ru(II)(bpy)(dppz)(cpp)](NO(3)).10H(2)O, 3(N3) indicated that the nitrogen adjacent to the carboxylate was coordinated to ruthenium(II). Full characterization of these complexes has been undertaken including the measurement of UV-visible and emission spectra. Electrochemical and spectroelectrochemical studies in acetonitrile show that these complexes undergo reversible oxidation from Ru(II) to Ru(III) at potentials of 983 +/- 3 mV, 1004 +/- 5 mV, and 1023 +/- 3 mV versus Fc(0/+) (Fc = Ferrocene) for 1, 2, and 3(N3), respectively.
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