Multistep Photochemical Reactions of Polypyridine-Based Ruthenium Nitrosyl Complexes in Dimethylsulfoxide

The photorelease of nitric oxide (NO·) has been investigated in dimethylsulfoxide (DMSO) on two compounds of formula [Ru(R-tpy)(bpy)(NO)](PF(6))(3), in which bpy stands for 2,2′-bipyridine and R-tpy for the 4′-R-2,2′:6′,2″-terpyridine with R = H and MeOPh. It is observed that both complexes are extremely sensitive to traces of water, leading to an equilibrium between [Ru(NO)] and [Ru(NO(2))]. The photoproducts of formula [Ru(R-tpy)(bpy)(DMSO)](PF(6))(2) are further subjected to a photoreaction leading to a reversible linkage isomerization between the stable Ru-DMSO((S)) (sulfur linked) and the metastable Ru-DMSO((O)) (oxygen linked) species. A set of 4 [Ru(R-tpy)(bpy)(DMSO)](2+) complexes (R = H, MeOPh, BrPh, NO(2)Ph) is investigated to characterize the ratio and mechanism of the isomerization which is tentatively related to the difference in absorbance between the Ru-DMSO((S)) and Ru-DMSO((O)) forms. In addition, the X-ray crystal structures of [Ru(tpy)(bpy)(NO)](PF(6))(3) and [Ru(MeOPh-tpy)(bpy)(DMSO((S)))](PF(6))(2) are presented.