Visible-Light Activation of the Bimetallic Chromophore-Catalyst Dyad: Analysis of Transient Intermediates and Reactivity toward Organic Sulfides

In order to develop a new photocatalytic system, we designed a new redox-active module (5) to hold both a photosensitizer part, [Ru-II(terpy)(bpy)X](n+) (where terpy 2,2':6',2 ''-terpyridine and bpy = 2,2'-bipyridine), and a popular Jacobsen catalytic part, salen-Mn(III), covalently linked through a pyridine-based electron-relay moiety. On the basis of nanosecond laser flash photolysis studies, an intramolecular electron transfer mechanism from salen-Mn-III to photooxidized Ru-III chromophore yielding the catalytically active high-valent salen-Mn-IV species was proposed. To examine the reactivity of such photogenerated salen-Mn-IV, we employed organic sulfide as substrate. Detection of the formation of a Mn-III-phenoxyl radical and a sulfur radical cation during the course of reaction using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. This is the first report for the electron transfer reaction of organic sulfide with the photochemically generated salen-Mn-IV catalytic center.