Spectroscopy and Electrochemistry of mer-[RuCl_3(dmso)(tmen)]. Dimethylsulfoxide Is Sulfur-Bonded to Ru(II), Ru(III), and Ru(IV)

Abstract

The discovery that halo−ruthenium(sulfoxide) complexes exhibit anticancer activity has stimulated interest in the nature of bonding of metal ions to dimethylsulfoxide (dmso). Both M−S and M−O bonds are observed in metal complexes containing dmso, with the former mode prevalent with "soft" metal centers. The importance of dπ-S back-bonding in S-bonded complexes has been addressed by several investigators. Especially revealing was the finding by Taube and co-workers that S to O linkage isomerism can be induced by oxidation of pentaammineruthenium(II) to ruthenium(III), thereby suggesting that dπ-S bonding is a stabilizing factor only in the lower oxidation state. However, the observation that other Ru(III)(chloro)(dmso) complexes are S-bonded led Alessio and Calligaris to propose a role for dπ-S bonding in Ru(III) as well. In the course of our work on a related complex, mer-[RuCl_3(dmso)(tmen)] (dmso is dimethylsulfoxide; tmen is N,N,N',N'-tetramethylethylenediamine), we have found that dmso also can be S-bonded to Ru(IV). Our findings suggest that S(dmso) σ-donation to Ru is extensive in the Ru(III) and Ru(IV) states.

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