THE TRANS-CIS ISOMERIZATION OF BIS(DIOXOLENE)BIS(PYRIDINE) RUTHENIUM COMPLEXES

The isomerisation of trans to cis bis(3,5-di-t-butylbenzosemiquinonato)bis(R-pyridine)ruthenium, Ru(R-Py)2(DTBDiox)2, is induced by warming with an excess of R-pyridine, where R = 3-chloro, 4-methyl, 4-phenyl, or 4-butyl. The rates of these reactions, for the species with R-Py = 3-chloropyridine, were monitored in o-dichlorobenzene by UV-visible spectroscopy against varying 3-chloropyridine and varying trans-[Ru(3-ClPy)2(DTBDiox)2] concentration. The data were found to obey first-order kinetics, -d[Ru(3-ClPy)2(DTBDiox)2/dt = k(obsd)[Ru(3-ClPy)2(DTBDiox)2], over a considerable range of pyridine concentration. A plot of 1/k(obsd) vs. [3-chloropyridine] is linear with a positive intercept. A dissociative mechanism is proposed for the isomerisation reaction. The activation parameters were determined for the specific case of R-Py = 3-chloropyridine. Electronic and electrochemical features of these species are briefly discussed.