Linkage isomerization and electrochemical behavior of two geometrical isomers of dichlorobis(dimethylsulfoxide)bis(t-butylpyridine)ruthenium(II)

The reaction of cis-[RuCl2(dmso)4] (dmso = dimethylsulfoxide) with 4-tert-butylpyridine (tbpy) in chloroform leads to the all cis (ccc) and the cis,cis,trans (cct) geometrical isomers of [RuCl2(S-dmso)2(tbpy)2]. The cct isomer exhibits a reversible cyclic voltammogram, ascribed to the RuIII/II redox couple with E1/2 = 1.12 V versus SHE. The ccc isomer can be oxidized at E1/2 = 1.27 V; however, the oxidized species undergoes a relaxation equilibrium, (Ks→o = 1.59), involving the S-to-O linkage isomerization of a coordinated dmso ligand (ks→o = 1.9 s−1 and kO→S = 1.2 s−1). The isomerization reaction in the RuIIIccc isomer is discussed in terms of the competitive effects between the S-bound dmso and the tbpy ligands.