Ca. Bessel et al., SYNTHESIS AND CHARACTERIZATION OF RUTHENIUM COMPLEXES WHICH UTILIZE ANEW FAMILY OF TERDENTATE LIGANDS BASED UPON 2,6-BIS(PYRAZOL-1-YL)PYRIDINE, Journal of the Chemical Society. Dalton transactions, (10), 1993, pp. 1563-1576
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.