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

Abstract

The photorelease of nitric oxide (NO·) has been investigated in dimethylsulfoxide (DMSO) on two compounds of formula [Ru(R-tpy)(bpy)(NO)](PF₆)₃, in which bpy stands for 2,2'-bipyridine and R-tpy for the 4'-<i>R</i>-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(NO₂)]. The photoproducts of formula [Ru(R-tpy)(bpy)(DMSO)](PF₆)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, NO₂Ph) 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)](PF₆)₃ and [Ru(MeOPh-tpy)(bpy)(DMSO_(S))](PF₆)₂ are presented.