Light‐Induced Activation of the Du Bois [RhII2(Esp)2] Catalyst for Nitrogen Atom Transfer Reactions

Abstract

Abstract[Rh2(Esp)2] (Esp=α,α,α′,α′‐tetramethyl‐1,3‐benzenedipropionate) is a well‐established catalyst for intra‐ and intermolecular C(sp)3−H bond amination. We have prepared and isolated complex I, [Rh2(Esp)2(NHTces)2]2−, where the catalyst bears sulfonamidate ligands (−NHTces=−NHSO3CH2CCl3) as nitrogen sources in the coordination sphere of the rhodium centre. The possibility for light activation instead of chemical activation of the [Rh2(Esp)2] catalyst and complex I is demonstrated using [Ru(bpy)3]2+ as the photosensitizer. The oxidation of the two dinuclear Rh complexes occurs through two distinct pathways. On one hand, [Rh2(Esp)2] is oxidized in a bimolecular reaction with the RuIII species formed after excitation of the photosensitizer in the presence of an electron acceptor. In contrast, the lower oxidation potential of complex I allows for its oxidation to occur directly from the excited state of the photosensitizer, helped by ion‐pair formation between the negatively charged complex I with [Ru(bpy)3]2+. The charge‐separated state of the oxidized complex I/reduced photosensitizer had a lifetime of 50 μs.