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 (<b>5</b>) to hold both a photosensitizer part, [Ru^II(terpy)­(bpy)­X]^<i>n</i>+ (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