Highly Efficient and Selective Photocatalytic Oxidation of Sulfide by a Chromophore–Catalyst Dyad of Ruthenium-Based Complexes

Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

Photocatalytic Oxygenation Reactions Using Water and Dioxygen

Water (H₂ O) is the most environmentally benign reductant and is oxidized to evolve dioxygen (O₂ )-the greenest oxidant-in photosystem II. This Minireview focuses on photocatalytic oxygenation of substrates with H₂ O as an oxygen source and O₂ as an oxidant. Metal complexes can be oxidized by two molecules of one-electron oxidants with H₂ O to produce high-valent metal-oxo complexes, which act as active oxidants for oxygenating organic substrates. When an appropriate oxidant is employed for the substrate oxidation, the reduced oxidant can be oxidized by dioxygen to regenerate the oxidant when water and dioxygen are used as an oxygen source and an oxidant, respectively. Photoinduced electron transfer from a substrate (S) to the excited state of complex [(L)M^III ]⁺ produces a substrate radical cation (S^.+ ), accompanied by the regeneration of [(L)M^II ]. S^.+ then reacts with H₂ O to produce an OH adduct radical that is oxidized by [(L)M^III ]⁺ to yield an oxygenated product (SO), in which the oxygen atom originates from H₂ O, accompanied by regeneration of [(L)M^II ]. Photocatalytic oxidation of H₂ O by O₂ to produce H₂ O₂ is combined with the catalytic oxygenation of substrates with H₂ O₂ to produce the oxygenated products, in which the oxygen atom originates from O₂ at the beginning but later from water. This Minireview provides a promising strategy for oxygenation of substrates by using H₂ O as an oxygen source and O₂ as the greenest oxidant.

A Bpp-based dinuclear ruthenium photocatalyst for visible light-driven oxidation reactions

The photocatalytic oxidation of organic substrates in water using a diruthenium chromophore-catalyst dyad molecule can be tuned by the nature of the bridging ligand.

Terpyridine-functionalized stimuli-responsive microgels and their assembly through metal–ligand interactions

We developed a terpyridine-functionalized microgel (tpy-mG) for its supramolecular assembly.

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

A molecular chromophore-catalyst assembly containing a chromophore ruthenium(II) center (RuIIchro ) and a catalytic copper(II) center (CuIIcat ) has been prepared easily. The assembly was employed for photocatalytic oxidation of sulfides without sacrificial reagent in the presence of dioxygen under blue light irradiation. Unprecedented turnover number (TON) up to 32 000 was achieved. It was elucidated that an electron transferred from excited state of chromophore RuII*chro to CuIIcat along with generation of CuIcat that was further activated by O₂ . These results demonstrate a promising strategy for efficient cooperative photocatalytic reactions under air using the chromophore-catalyst assembly.

Repairable photoactive polymer systems via metal–terpyridine-based self-assembly

The photocatalytic activity of polymeric systems ceased upon disassembly and was restored upon assembly through metal ion–ligand interaction.

Highly selective oxidation of sulfides on a CdS/C3N4 catalyst with dioxygen under visible-light irradiation

A CdS/C₃N₄ visible-light catalyst exhibits high product selectivity towards photocatalytic oxidation of sulfides into corresponding sulfoxides with dioxygen in methanol.

A pyrene-modified cobalt salophen complex immobilized on multiwalled carbon nanotubes acting as a precursor for efficient electrocatalytic water oxidation

Highly efficient electrocatalytic water oxidation with an immobilized pyrene-modified cobalt salophen complex: molecular catalysis or heterogeneous catalysis?

Visible-light-driven selective oxidation of benzyl alcohol and thioanisole by molecular ruthenium catalyst modified hematite

Molecular ruthenium catalysts were found to selectively catalyze the oxidation of thioanisole to sulfoxide with a yield up to 100% in the presence of visible light and sacrificial reagents when they were anchored onto hematite powder. The composite photocatalysts also showed about 5 times higher efficiencies in benzyl alcohol oxidation than the system composed of dispersed molecular catalysts and hematite particles in aqueous solution. A photoelectrochemical cell based on a molecular catalyst modified hematite photoanode was further fabricated, which exhibited high activity towards the oxidation of organic substrates.

Photocatalytic oxidation of alkenes and alcohols in water by a manganese(v) nitrido complex

Mn(v) nitrido complex [Mn(N)(CN)4](2-) is an efficient catalyst for visible-light induced oxidation of alkenes and alcohols in water using [Ru(bpy)3](2+) as a photosensitizer and [Co(NH3)5Cl](2+) as a sacrificial oxidant. Alkenes are oxidized to epoxides and alcohols to carbonyl compounds.

Efficient Light-Driven Oxidation of Alcohols Using an Organic Chromophore-Catalyst Assembly Anchored to TiO2

The ligand 5-PO3H2-2,2':5',2″-terthiophene-5-trpy, T3 (trpy = 2,2':6',2″-terpyridine), was prepared and studied in aqueous solutions along with its metal complex assembly [Ru(T3)(bpy)(OH2)](2+) (T3-Ru-OH2, bpy = 2,2'-bipyridine). T3 contains a phosphonic acid group for anchoring to a TiO2 photoanode under aqueous conditions, a terthiophene fragment for light absorption and electron injection into TiO2, and a terminal trpy ligand for the construction of assemblies comprising a molecular oxidation catalyst. At a TiO2 photoanode, T3 displays efficient injection at pH 4.35 as evidenced by the high photocurrents (∼350 uA/cm(2)) arising from hydroquinone oxidation. Addition of [Ru(bpy)(OTf)][OTf]2 (bpy = 2,2'-bipyridine, OTf(-) = triflate) to T3 at the free trpy ligand forms the molecular assembly, T3-Ru-OH2, with the oxidative catalyst fragment: [Ru(trpy)(bpy)(OH2)](2+). The new assembly, T3-Ru-OH2, was used to perform efficient light-driven oxidation of phenol (230 μA/cm(2)) and benzyl alcohol (25 μA/cm(2)) in a dye-sensitized photoelectrosynthesis cell.

Synergistic "ping-pong" energy transfer for efficient light activation in a chromophore-catalyst dyad

The synthesis of a porphyrin-Ru(II) polypyridine complex where the porphyrin acts as a photoactive unit and the Ru(II) polypyridine as a catalytic precursor is described. Comparatively, the free base porphyrin was found to outperform the ruthenium based chromophore in the yield of light induced electron transfer. Mechanistic insights indicate the occurrence of a ping-pong energy transfer from the (1)LC excited state of the porphyrin chromophore to the (3)MCLT state of the catalyst and back to the (3)LC excited state of the porphyrin unit. The latter, triplet-triplet energy transfer back to the chromophore, efficiently competes with fast radiationless deactivation of the excited state at the catalyst site. The energy thus recovered by the chromophore allows improved yield of formation of the oxidized form of the chromophore and concomitantly of the oxidation of the catalytic unit by intramolecular charge transfer. The presented results are among the rare examples where a porphyrin chromophore is successfully used to drive an oxidative activation process where reductive processes prevail in the literature.

pH-Dependence of the Aqueous Phase Room Temperature Brønsted Acid-Catalyzed Chemoselective Oxidation of Sulfides with H₂O₂

A pH-dependence of the Brønsted acid-catalyzed oxidation of sulfides to the corresponding sulfoxides with H₂O₂ is reported for the first time based on our systematic investigation of the catalytic performance of a series of Brønsted acids. For all of the Brønsted acids investigated, the catalytic performances do not depend on the catalyst loading (mol ratio of Brønsted acid to substrate), but rather depend on the pH value of the aqueous reaction solution. All of them can give more than 98% conversion and selectivity in their aqueous solution at pH 1.30, no matter how much the catalyst loading is and what the Brønsted acid is. This pH-dependence principle is a very novel perspective to understand the Brønsted-acid catalysis system compared with our common understanding of the subject.

Crystal structure of a mononuclear Ru(II) complex with a back-to-back terpyridine ligand: [RuCl(bpy)(tpy-tpy)](.)

In this first crystal structure of an Ru complex with 6′,6"-bis­(pyridin-2-yl)-2,2′:4′,4":2",2"’-quaterpyridine, a ‘half’ of the ligand (one of the two terpyridyl units) is N^N^N mer-coordinated, whereas the other is free and adopts a trans,trans conformation about the inter­annular C—C bonds. The crystal packing features π–π stacking inter­actions between tpy–tpy ligands.

We report the structural characterization of [6′,6′′-bis­(pyridin-2-yl)-2,2′:4′,4′′:2′′,2′′′-quaterpyridine](2,2′-bi­pyridine)­chlorido­ruthenium(II) hexa­fluorido­phosphate, [RuCl(C₁₀H₈N₂)(C₃₀H₂₀N₆)]PF₆, which contains the bidentate ligand 2,2′-bi­pyridine (bpy) and the tridendate ligand 6′,6′′-bis­(pyridin-2-yl)-2,2′:4′,4′′:2′′,2′′′-quaterpyridine (tpy–tpy). The [RuCl(bpy)(tpy–tpy)]⁺ monocation has a distorted octa­hedral geometry at the central Ru^II ion due to the restricted bite angle [159.32 (16)°] of the tridendate ligand. The Ru-bound tpy and bpy moieties are nearly planar and essentially perpendicular to each other with a dihedral angle of 89.78 (11)° between the least-squares planes. The lengths of the two Ru—N bonds for bpy are 2.028 (4) and 2.075 (4) Å, with the shorter bond being opposite to Ru—Cl. For tpy–tpy, the mean Ru—N distance involving the outer N atoms trans to each other is 2.053 (8) Å, whereas the length of the much shorter bond involving the central N atom is 1.936 (4) Å. The Ru—Cl distance is 2.3982 (16) Å. The free uncoordinated moiety of tpy–tpy adopts a trans,trans conformation about the inter­annular C—C bonds, with adjacent pyridyl rings being only approximately coplanar. The crystal packing shows significant π–π stacking inter­actions based on tpy–tpy. The crystal structure reported here is the first for a tpy–tpy complex of ruthenium.