Ru Photocatalyst Research Articles

Template-Directed Fabrication of Highly Efficient Metal-Organic Framework Photocatalysts.

Photocatalysis is a powerful and versatile tool widely applied in the areas of synthesis chemistry. However, most of the photocatalysts currently used are homogeneous catalysts, which inevitably face issues such as product-catalyst separation and recyclability. Addressing this challenge, we utilized a homogeneous Ru photocatalyst as a structure-directing template to fabricate a series of isostructural photocatalyst-encapsulating metal-organic frameworks (photocatalyst@MOFs) with high porosity, robustness, and photocatalyst loading. The regular channels of MOF can disperse the encapsulated photocatalysts, promote the mass transfer of substrates and products, and provide an outstanding substrate confinement effect, thereby dramatically improving the catalytic activity and excellent recyclability toward valuable organic reactions. For instance, the MOF photocatalysts can catalyze the asymmetric Mannich reaction with ketones with high yields and excellent enantioselectivities (up to 99% ee), better than the reported photocatalyst. Significantly, this was the first case that heterogeneous MOF-based photocatalyst can catalyze the asymmetric Mannich reaction without cocatalysts under room temperature and visible light. This work not only explores an avenue to prepare heterogeneous photocatalysts but also broadens the application scope of MOF-based photocatalysts.

Long wavelength visible light-responsive SrTiO3 photocatalysts doped with valence-controlled Ru for sacrificial H2 and O2 evolution

H2-Reduced SrTiO3:Ru photocatalyst is active for O2 evolution under a wide range of visible light up to 750 nm.

An Olefinic 1,2‐Boryl‐Migration Enabled by Radical Addition: Construction ofgem‐Bis(boryl)alkanes

A series of in situ formed alkenyl diboronate complexes from alkenyl Grignard reagents (commercially available or prepared from alkenyl bromides and Mg) with B2 Pin2 (bis(pinacolato)diboron) react with diverse alkyl halides by a Ru photocatalyst to give various gem-bis(boryl)alkanes. Alkyl radicals add efficiently to the alkenyl diboronate complexes, and the adduct radical anions undergo radical-polar crossover, specifically, a 1,2-boryl-anion shift from boron to the α-carbon sp2 center. This transformation shows good functional-group compatibility and can serve as a powerful synthetic tool for late-stage functionalization in complex compounds. Measurements of the quantum yield reveal that a radical-chain mechanism is operative in which the alkenyl diboronates acts as reductive quencher for the excited state of the photocatalyst.

Nickel Dual Photoredox Catalysis for the Synthesis of Aryl Amines

In this work, a new dual photoredox nickel catalysis system has been utilized for the synthesize of aryl amines. Previously, our group has shown that a nickel catalyst in conjunction with a photosensitizer and a sacrificial electron donor can cross-couple C–C bonds via photoredox-assisted reductive coupling. Here we have built upon that system to develop a redox-neutral cross-coupling system for the formation of C–N bonds. The catalytic system is composed of just a nickel cross-coupling catalyst, a Ru photocatalyst, and base and is capable of coupling amines with aryl halides in good to excellent yields. Furthermore, it was found that these reactions are functional under ambient conditions with catalyst loadings of 1 mol %. Spectroscopic studies provide support that this amination mechanism proceeds via a nitrogen-based radical intermediate. This N-radical mechanism offers direct synthetic access to di- and triaryl amines from nickel photocatalysis.

A bridged ruthenium dimer (Ru–Ru) for photoreduction of CO2 under visible light irradiation

A bridged binuclear complex consisting of two ruthenium units (Ru–Ru) connected through a bridging ligand was synthesized, in which one unit serves as a photosensitizer, while another unit works as a catalyst. The synthesized Ru–Ru photocatalyst was tested for photoreduction of CO2 to give CO and HCOOH under visible light irradiation in the presence of triethanolamine as a sacrificial donor. The yield of CO and HCOOH was found to be 54ppm and 28ppm respectively after 12h of irradiation. Due to the binding of photosensitizer and catalyst units in a single molecule via bridging ligand provides faster and efficient electron transfer from sensitizer to catalyst unit which resulted in the higher activity and better product yields.

Substituent Effect of the Bridging Ligand in the Trinuclear Ru Complexes on Photocatalytic Oxygenation of a Sulfide and Alkenes.

To examine the effect of tuning the electron transfer ability between photosensitizers and reaction centers on the activity of visible-light-driven catalysts, a series of trinuclear Ru photocatalysts containing two Ru(II) photosensitizers and a Ru(II) reaction center bridged by a substituted bipyrimidine was prepared. The introduction of electron-donating or electron-withdrawing groups on the ligands was found to affect the photophysical and electrochemical properties of these catalysts. Density functional theory calculations of the mononuclear Ru complexes with nonsubstituted and substituted bipyrimidine ligands, which correspond to the reaction center of the trinuclear complexes, revealed how the electronic effect of the substituents affect the frontier orbital energies. For photocatalytic oxygenation of a sulfide and terminal alkenes, the catalyst with a 5,5'-dibromo-2,2'-bipyrimidine ligand showed higher activity than the catalyst with 5,5'-dimethyl-2,2'-bipyrimidine and nonsubstituted bipyrimidine ligands, as expected according to the electronic effects of these ligands. In contrast, the catalyst with the nonsubstituted bipyrimidine ligand showed the highest activity toward inner alkenes, which may be due to steric effects.

Probing Co-Assembly of Supramolecular Photocatalysts and Polyelectrolytes Using Isothermal Titration Calorimetry.

The creation of renewable fuels to replace dwindling fossil energy resources is one of the greatest challenges facing the scientific community. Generating H2 fuel from water is a carbon-neutral strategy that demonstrates great promise. Photocatalysts of the molecular architecture [{(TL)2Ru(BL)}2RhX2]5+ (BL = bridging ligand, TL = terminal ligand, X = halide) catalyze the formation of H2 in deoxygenated organic solvents but are limited by poor performance in air-saturated aqueous solutions. Addition of the water-soluble polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) was recently shown as being a promising new strategy to increase efficiency and stability of H2 evolving photocatalysts in air-saturated aqueous solutions. Herein we investigate intermolecular interactions between Ru,Rh,Ru photocatalysts and water-soluble polyelectrolytes using isothermal titration calorimetry (ITC). ITC studies provide insight into the thermodynamic forces that drive assembly of PSS-photocatalyst aggregates and give new evidence for the intermolecular forces that lead to increased photocatalytic efficiency.

ChemInform Abstract: Trifluoromethylation of Aromatic Alkenes by Visible‐Light‐Driven Photoredox Catalysis: Direct Conversion of Alkenes to 3‐Trifluoromethyl‐1‐propenyl and 1,3‐Bis(trifluoromethyl)‐1‐propenyl Derivatives.

Abstract Photoredox-catalyzed trifluoromethylation of alkenes using Umemoto's reagent as a CF3 source under visible light irradiation has been developed. A Ru photocatalyst, [Ru(bpy)3](PF6)2 (bpy = 2,2′-bipyridine), is useful for the present trifluoromethylation and preferable formation of 3-trifluoromethyl-1-propenyl derivatives is observed. Use of an excess amount of Umemoto's reagent readily induces double trifluoromethylation of electron-rich alkenes, resulting in 1,3-bis(trifluoromethyl)-1-propenyl skeleton.

Photocatalytic production of hydrogen peroxide from water and dioxygen using cyano-bridged polynuclear transition metal complexes as water oxidation catalysts

H2O2 was produced from H2O and O2 using cyano-bridged polynuclear transition metal complexes as water oxidation catalysts with a Ru photocatalyst in water under visible light irradiation.

A new hydrophilic supramolecular photocatalyst for the production of H2 in aerobic aqueous solutions.

Addition of sulfonated terminal ligands into a Ru,Rh,Ru photocatalyst has a significant impact on the excited-state properties of the complex. The hydrophilic photocatalyst demonstrates increased solubility and H2 production in aqueous solutions. H2 production is observed under aerobic conditions for the new complex, a stark contrast to the hydrophobic analog in organic solvents.

Trifluoromethylation of aromatic alkenes by visible-light-driven photoredox catalysis: Direct conversion of alkenes to 3-trifluoromethyl-1-propenyl and 1,3-bis(trifluoromethyl)-1-propenyl derivatives

Photoredox-catalyzed trifluoromethylation of alkenes using Umemoto's reagent as a CF3 source under visible light irradiation has been developed. A Ru photocatalyst, [Ru(bpy)3](PF6)2 (bpy = 2,2′-bipyridine), is useful for the present trifluoromethylation and preferable formation of 3-trifluoromethyl-1-propenyl derivatives is observed. Use of an excess amount of Umemoto's reagent readily induces double trifluoromethylation of electron-rich alkenes, resulting in 1,3-bis(trifluoromethyl)-1-propenyl skeleton.

ChemInform Abstract: Visible‐Light Sensitization of Vinyl Azides by Transition‐Metal Photocatalysis.

Irradiation of vinyl and aryl azides with visible light in the presence of Ru photocatalysts results in the formation of reactive nitrenes, which can undergo a variety of C-N bond-forming reactions. The ability to use low-energy visible light instead of UV in the photochemical activation of azides avoids competitive photodecomposition processes that have long been a significant limitation on the synthetic use of these reactions.

Highly Regio- and Diastereoselective Synthesis of CF3-Substituted Lactones via Photoredox-Catalyzed Carbolactonization of Alkenoic Acids

Trifluoromethylative lactonization of both terminal and internal alkenoic acids by photoredox catalysis has been developed. The use of a Ru photocatalyst and Umemoto's reagent as a CF3 source is key in the present carbolactonization. This is the first example of a highly endo- and diastereoselective synthesis of CF3-substituted five-, six-, and seven-membered ring lactones from internal alkenoic acids.

Visible‐Light Sensitization of Vinyl Azides by Transition‐Metal Photocatalysis

Irradiation of vinyl and aryl azides with visible light in the presence of Ru photocatalysts results in the formation of reactive nitrenes, which can undergo a variety of C-N bond-forming reactions. The ability to use low-energy visible light instead of UV in the photochemical activation of azides avoids competitive photodecomposition processes that have long been a significant limitation on the synthetic use of these reactions.

Efficient Photocatalytic Hydrogen Production in a Single‐Component System Using Ru,Rh,Ru Supramolecules Containing 4,7‐Diphenyl‐1,10‐Phenanthroline

Small changes go a long way: Modification of the terminal ligand to incorporate 4,7-diphenyl-1,10-phenanthroline has generated superior Ru,Rh,Ru photocatalysts (see scheme; ochre Ru, red Rh, blue N, yellow Cl or Br) displaying significantly enhanced photocatalytic H2 production from H2O with long-term functioning: H2O is reduced to H2 with over 1300 turnovers per Rh site and a maximum efficiency of 7.3 %.