The prindpal findings of the project, which was initiated August 15, 1990, are summarized in the sections below. Reduction of Coordinated Thiophenes This study probed the relative accepter abilities of arene and thiophene ligands through the study of complexes containing both thiophenes and arenes. It was found that thiophene ligands are reduced in preference to arenes (eq. 1), This is evident not only in the structures and spectroscopy but also by the reduction potentials. The Eo's for

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... 4S)(C6Me6)] 2+/+/0(-442, -607 mV) are closer to those for [Ru(C4Me4S)2] 2+/+/0(-392, 568 mV) but far more cathodic than for [Ru(CeMee)2] 2+/o(-976 mV). The ease of electrochemical reduction is one of the defining differences between arenes and thiophenes. Interestingly thiophenes are also better donors than arenes. This trend reflects their decreased homo/lumo gap compared to arches. Using methods developed for the mixed arene/thiophene complexes, we have isolated and characterized Ru(C4Me4S)2. This complex is thermally unstable (>-20°C ), as one would expect for an active desulfurization agent (Ru 0) attached only to its own substrate (thiophene). It exbJbits a simple two line 1H NMR spectrum indicative of a dynamic averaging via rapid making and breaking of the Ru-S bonds. The 13C NMR shifts aupport this proposal as they occur near the average seen for q4. and q5.