Visible-Light
Activation of the Bimetallic Chromophore–Catalyst
Dyad: Analysis of Transient Intermediates and Reactivity toward Organic
Sulfides
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Abstract
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<sup>II</sup>(terpy)(bpy)X]<sup><i>n</i>+</sup> (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<sup>III</sup> to photooxidized
Ru<sup>III</sup> chromophore yielding the catalytically active high-valent
salen–Mn<sup>IV</sup> species was proposed. To examine the
reactivity of such photogenerated salen–Mn<sup>IV</sup>, we
employed organic sulfide as substrate. Detection of the formation
of a Mn<sup>III</sup>–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<sup>IV</sup> catalytic center