SYNTHESIS AND CHARACTERIZATION OF RUTHENIUM COMPLEXES WHICH UTILIZE ANEW FAMILY OF TERDENTATE LIGANDS BASED UPON 2,6-BIS(PYRAZOL-1-YL)PYRIDINE

To demonstrate the synthetic utility of a new family of terdentate lig ands based on 2,6-bis(pyrazol-1-yl)pyridine (bpp), reaction conditions were developed to generate a variety of [RuL(NO2)(PMe3)2]+ complexes [L = bpp, 2.6-bis(3,5-dimethylpyrazol-1-yl)pyridine(bdmpp), 2,6-bis(3- phenylpyrazol-1-yl)pyridine (bppp) or 2,6-bis(3-p-chlorophenylpyrazol- 1-yl)pyridine (bcppp)]. These complexes were characterized by elementa l analysis, H-1 and C-13 NMR, infrared and UV/VIS spectroscopies, cycl ic voltammetry, and single-crystal X-ray diffraction studies, The subs tituents of the terdentate bpp ligands sterically affected the Ru-N(py razole) bond lengths, the displacement of the nitrogen atoms of the ni tro ligands from the RuL plane, and the twisting of the N-O vectors of the nitro ligand from that plane. Also the substituents affected the potentials and peak-current ratios of the Ru(III)-Ru(II) couples. The log (i(pc)/i(pa)) values (i(pc) = cathodic peak current, i(pa) = anodi c peak current) are linearly correlated with the steric size of the su bstituents as estimated by Tolman's cone angles and with the distance of the nitro ligand out of the RuL plane. A linear correlation was als o found between the differences in infrared absorbances due to the N-O symmetric and asymmetric stretches and the ratio of the N-O bond dist ances observed from the four crystal structures.