DIASTEREOSELECTIVE SYNTHESIS, SPECTROSCOPY, AND ELECTROCHEMISTRY OF RUTHENIUM(II) COMPLEXES OF SUBSTITUTED PYRAZOLYLPYRIDINE LIGANDS

We report the synthesis of the hetero- and homoleptic ruthenium(II) co mplexes Ru(bpy)(2)L(2+), Ru(bpy)L(2)(2+) (bpy is 2,2'-bipyridine), and RuL(3)(2+) of six new bidentates L, the substituted pyrazolylpyridine s 1-6 tuted-3-(2-pyridinyl)-4,5,6,7-tetrahydroindazooles with substitu ents R = H, CH3, Ph, or C6H4-4('')-COOX where X = H, CH3, or C2H5). Th ese were fully characterized by H-1- and C-13-NMR spectroscopy and ele mental analysis. The UV-visible spectra and redox properties of the co mplexes, some in the ruthenium(III) and reduced bipyridine oxidation s tates, are also discussed. The substituents R played a role in determi ning the stereochemistry of the Ru(bpy)L(2)(2+) and RuL(3)(2+) product s. The reaction of Ru(DMSO)(4)Cl-2 with 3 equiv of L bearing aromatic substituents gave only meridional RuL(3)(2+) isomers. The one-step rea ction of Ru(bpy)Cl-3 . H2O with 2 equiv of L provided a mixture of the three possible Ru(bpy)L(2)(2+) isomers, from which one symmetric isom er (labeled beta) was isolated pure. A trans arrangement of the pyrazo le groups was deduced by H-1-NMR and confirmed by X-ray crystallograph y for one such stereomer (beta-[Ru(bpy)(5)(2)](PF6)(2), R = C6H4-4('') -COOC2H5). In contrast, Ru(DMSO)(4)Cl-2 reacted with 2 equiv of L and then 1 equiv of bpy to selectively form the other symmetric isomer (la beled alpha) where the pyridine groups of L are trans. Crystal data fo r beta-[Ru(bpy)(5)(2)](PF6)(2) (C52H50N8O4F12P2Ru) With MO K alpha (la mbda = 0.710 73 Angstrom) radiation at 295 K: a = 28.442(13) Angstrom, b = 18.469(15) Angstrom, c = 23.785(9) Angstrom, beta = 116.76(0)degr ees, monoclinic, space group C2/c, Z = 8. Fully anisotropic (except fo r H and disordered F atoms), full-matrix, weighted least-squares refin ement on F-2 gave a weighted R on F-2 of 0.2573 corresponding to R on F of 0.1031 for data where F > 4 sigma(F).