THE CHEMICAL AND ELECTROCHEMICAL OXIDATION OF PYRIDONATE-BRIDGED RUTHENIUM(I) DIMERS - X-RAY STRUCTURE OF [RU2(MU-PYO)2(CO)4(PYOH)2] (PYOH = 2-PYRIDONE)

Chemical and electrochemical studies have shown that the pyridonate-bridged ruthenium(I) dimers [Ru2(mu-pyO)2(CO)4(L)2] (1) (L = PPh3, 1a; P(i)Pr3, 1b; or pyOH, 1c; pyOH = 2-pyridone) can be oxidized to the cationic paramagnetic species [Ru2(mu-pyO)2(CO)4(L)2]+ (2). The species 2 are very unstable at room temperature, decomposing into a mixture of 1 and the ruthenium(II) cations [Ru(pyO)(CO)2(L)]+ (3). The latter can be obtained quantitatively by reaction of 1 with two equivalents of oxidant. The structure of complex 1c, which has an oxidation peak in its cyclic voltammogram at an unexpectedly high potential (1.11 versus 0.47 V for 1a and 0.33 V for 1b), has been determined by X-ray crystallography, revealing the presence of two intramolecular hydrogen bonds between the oxygen atoms of the bridging and the terminal pyO fragments.