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), in which bpy stands for 2,2'-bipyridine and R-tpy for the 4'--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)]. The photoproducts of formula Ru(R-tpy)(bpy)(DMSO) are further subjected to a photoreaction leading to a reversible linkage isomerization between the stable Ru-DMSO (sulfur linked) and the metastable Ru-DMSO (oxygen linked) species. A set of 4 [Ru(R-tpy)(bpy)(DMSO)] complexes (R = H, MeOPh, BrPh, NOPh) is investigated to characterize the ratio and mechanism of the isomerization which is tentatively related to the difference in absorbance between the Ru-DMSO and Ru-DMSO forms. In addition, the X-ray crystal structures of Ru(tpy)(bpy)(NO) and Ru(MeOPh-tpy)(bpy)(DMSO) are presented.