Controlled photosubstitution of Ru(II) polypyridyl complexes with gold chloride.

The well-known chloride (Cl-)-ion-induced photosubstitution (PS) reaction of ruthenium tris-polypyridyl complexes [Ru(PP)3]2+ deals with HCl and tetraalkylammonium chloride (TEACl) as sources of Cl- ions. However, these reported Cl- ion sources could not show any restriction on the PS reaction irrespective of the nature of the [Ru(PP)3]2+ complexes. In this study, the glutathione (GSH)-mediated reduction of [AuCl4]- in methanol (MeOH) or acetonitrile (MeCN), as a new alternate source of Cl- ions, demonstrates restrictions in the PS reaction of [Ru(PP)3](PF6)2 complexes 1 and 2 (PP = 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen), respectively). However, a similar study with complexes 3 and 4 (PP = 2,2'-bipyrazine (bpz) and 1,4,5,8-tetraazaphenanthrene (tap), respectively) shows a facile PS reaction with quantum yields (Φphotosub) of 0.36 and 0.30, respectively. A mechanistic investigation by XPS analysis of the reaction mixture with complex 1 suggests the presence of not only of Au+ and oxidized glutathione (GSSG) but also of Au3+ and GSH during photoirradiation. These equilibria in the presence of 1 or 2 restrict the attack of a Cl- ion on the Ru2+ center. In contrast, in the case of complexes 3 and 4, Cl- attacks the more electropositive Ru2+ center, and there is no trace of Au3+ in XPS. Further reactions without GSH have been carried out between [AuCl4]- and 1 or 3 in aqueous medium. Immediate red precipitates from the reaction generate single crystals of [Ru(bpy)3][AuCl4]2 (1'), and [Ru(bpz)3]2[AuCl6][AuCl4]3 (3') upon crystallization. [AuCl6]- in 3' oxidizes [Ru(bpz)3]2+ to [Ru(bpz)3]3+ and itself reduces to produce [AuCl2]- and Cl- in the crystal structure of [RuII(bpz)3][RuIII(bpz)3][AuCl2]2Cl3 (3''). The selective PS reaction (Φphotosub = 0.01) in 3' is attributed to the presence of octahedral [AuCl6]- as a source of Cl- ions, which has been obtained for the first time. Conversely, 1' with [AuCl4]- as a counterion does not show any PS reaction.