A Ruthenium(II)–Copper(II) Dyad for the Photocatalytic Oxygenation of Organic Substrates Mediated by Dioxygen Activation

Abstract

Dioxygen activation by copper complexes is a valuable method to achieve oxidation reactions for sustainable chemistry. The development of a catalytic system requires regeneration of the Cu(I) active redox state from Cu(II). This is usually achieved using extra reducers that can compete with the Cu(II)(O2) oxidizing species, causing a loss of efficiency. An alternative would consist of using a photosensitizer to control the reduction process. Association of a Ru(II) photosensitizing subunit with a Cu(II) pre-catalytic moiety assembled within a unique entity is shown to fulfill these requirements. In presence of a sacrificial electron donor and light, electron transfer occurs from the Ru(II) center to Cu(II). In presence of dioxygen, this dyad proved to be efficient for sulfide, phosphine, and alkene catalytic oxygenation. Mechanistic investigations gave evidence about a predominant (3)O2 activation pathway by the Cu(I) moiety.

CuAAC-based assembly and characterization of a ruthenium–copper dyad containing a diimine–dioxime ligand framework

“…Two mechanisms can operate under these photolysis conditions: ( i ) the oxidative quenching pathway, previously discussed in the “steady-state fluorescence spectroscopy” section, which forms a Ru III Cu I intermediate before regeneration of the Ru II centre by the sacrificial electron donor TEA; ( ii ) the reductive quenching pathway, where *Ru is first quenched by TEA, yielding a Ru I Cu II species, that ultimately produced Ru II Cu I . The oxidative quenching process was unambiguously established, on the basis of time-resolved spectroscopic studies, for two dyads we previously studied: a ruthenium-cobalt one, also relying on an imidazo[4,5-f][1,10]phenanthroline bridging ligand,41 and more recently a ruthenium-copper assembly 40. Moreover, previous reports have established that quenching of *[Ru(bpy) 3 ] 2+ and related Ru-based photosensitizers by aliphatic amines (TEA, TEOA) was not efficient, even at high molar concentrations of the quencher,61–63 supporting the fact that a reductive quenching process is quite unlikely to occur in our system.…”

“…EPR spectroscopy is the technique of choice to bring any metal redox state modification to light. It has been previously employed in the literature to characterize light-induced redox processes such as oxidation of a Ni II centre29 or reduction of a Cu II centre40 in ruthenium-based dyads, under photolysis conditions. Reductive photolysis experiments are typically performed in the presence of a large excess of a sacrificial electron donor, such as triethylamine (TEA); the latter rapidly reacts with the oxidized photosensitizer to regenerate Ru II , thus avoiding charge recombination and leading to accumulation of the targeted reduced species.…”

“…Photoinduced electron transfers in heterodinuclear ruthenium copper complexes have for instance been exploited to develop luminescent probes,34–36 molecular switches,37 dye-sensitized solar cells38 and also for the photochemical reduction of nitrite 39. Recently, a RuCu dyad for the photocatalytic oxidation of organic substrates mediated by dioxygen activation has also been reported 40. In this contribution, we describe the synthesis and full characterization of the first ruthenium-copper dinuclear complex assembled by CuAAC click chemistry.…”

Robust Cooperative Photo‐oxidation of Sulfides without Sacrificial Reagent under Air Using a Dinuclear RuII–CuII Assembly

“…Nevertheless, photocatalytic aerobic reactions using copper‐based catalytic sites are rarely investigated . A ruthenium(II)–copper(II) dyad was used for photocatalytic oxidation of organic sulfides in the presence of a sacrificial electron donor (TEOA) under O 2 atmosphere . The highest TON was found to be 300.…”

Sulfur‐Center‐Involved Photocatalyzed Reactions

“…In 2015, Ru‐aqua complex 307 or its chloro form 308 (Scheme ) were synthesized and used to oxidize sulfide to sulfoxide with water as the oxygen source and [Co(NH 3 ) 5 Cl]Cl 2 as a sacrificial electron acceptor [Eq. (119)] . Both catalysts showed significant activity, with TONs of up to 1000 and high product selectivity (>99 %).…”