Photoredox catalysis by [Ru(bpy)3]2+ to trigger transformations of organic molecules. Organic synthesis using visible-light photocatalysis and its 20th century roots

Efficient Visible-Light-Driven Carbon Dioxide Reduction using a Bioinspired Nickel Molecular Catalyst

Inspired by natural enzymes, this study presents a nickel-based molecular catalyst, [Ni‖(N2S2)]Cl2 (NiN2S2, N2S2=2,11-dithia[3,3](2,6)pyridinophane), for the photochemical catalytic reduction of CO2 under visible light. The catalyst was synthesized and characterized using various techniques, including liquid chromatography-high resolution mass spectrometry (LC-HRMS), UV-Visible spectroscopy, and X-ray crystallography. The crystallographic analysis revealed a slightly distorted octahedral coordination geometry with a mononuclear Ni2+ cation, two nitrogen atoms and two sulfur atoms. Photocatalytic CO2 reduction experiments were performed in homogeneous conditions using the catalyst in combination with [Ru(bpy)3]Cl2 (bpy=2,2'-bipyridine) as a photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as a sacrificial electron donor. The catalyst achieved a high selectivity of 89 % towards CO and a remarkable turnover number (TON) of 7991 during 8 h of visible light irradiation under CO2 in the presence of phenol as a co-substrate. The turnover frequency (TOF) in the initial 6 h was 1079 h-1, with an apparent quantum yield (AQY) of 1.08 %. Controlled experiments confirmed the dependency on the catalyst, light, and sacrificial electron donor for the CO2 reduction process. These findings demonstrate this bioinspired nickel molecular catalyst could be effective for fast and efficient photochemical catalytic reduction of CO2 to CO.

Electrochemiluminescence of a First-Row d6 Transition Metal Complex

We report the electrochemiluminescence (ECL) of a 3d6 Cr(0) complex ([Cr(LMes)3]; λem=735 nm) with comparable photophysical properties to those of ECL-active complexes of 4d6 or 5d6 precious metal ions. The electrochemical potentials of [Cr(LMes)3] are more negative than those of [Ir(ppy)3] and render the [Cr(LMes)3]* excited state inaccessible through conventional co-reactant ECL with tri-n-propylamine or oxalate. ECL can be obtained, however, through the annihilation route in which potentials sufficient to oxidise and reduce the luminophore are alternately applied. When combined with [Ir(ppy)3] (λem=520 nm), the annihilation ECL of [Cr(LMes)3] was greatly enhanced whereas that of [Ir(ppy)3] was diminished. Under appropriate conditions, the relative intensities of the two spectrally distinct emissions can be controlled through the applied potentials. From this starting point for ECL with 3d6 metal complexes, we discuss some directions for future development.

Harnessing the Potential of Electron Donor-Acceptor Complexes and N-Centered Radicals: Expanding the Frontiers of Isoquinoline Derivative Synthesis

Research on synthesizing nitrogen-containing heterocyclic scaffolds is important because these structures are commonly found in Nature, such as in the alkaloids' family. In our study, we propose a new method to synthesize the isoquinoline core using an electron donor-acceptor (EDA) complex strategy. Our mechanistic investigations have confirmed that our synthesis process operates through an EDA mechanism, which is not extensively discussed in the literature, particularly regarding its applications on alkynyl substrates. This EDA strategy has proven to be a simple and straightforward way to produce isoquinoline scaffolds and their derivatives without the need for metal catalysts.

Ruthenium(II) complexes with phosphonate-substituted phenanthroline ligands as reusable photoredox catalysts

Ru(II) complexes with polypyridyl ligands (2,2'-bipyridine = bpy, 1,10-phenanthroline = phen) play a central role in the development of photocatalytic organic reactions. In this work, we synthesized four mixed-ligand [Ru(phen)(bpy)2]2+-type complexes (Ru-Pcat-A) bearing two phosphonate substituents P(O)(OH)(OR) (R = H, Et) attached to the phen core at positions 3,8 (Ru-3,8PH and Ru-3,8PHEt) and 4,7 (Ru-4,7PH and Ru-4,7PHEt) of the heterocycle in high yields (87-99%) and characterized them using spectral methods. Single crystal X-ray diffraction was employed to determine the coordination mode of the ditopic phen ligand in Ru-4,7PH. This complex exists as the neutral species and forms a 1D hydrogen-bonded framework in the crystals. The light absorption characteristics were found to be similar for all complexes prepared in this work. However, the emission maxima in aqueous solutions were significantly affected by the substitution of the heterocycle, ranging from 629 nm for Ru-4,7PH to 661 nm for Ru-3,8PHEt. The emission quantum yields in Ar-saturated deionized water showed a strong dependence on the substitution pattern of the phen ligand, with maximal values reaching approximately 0.11 for Ru-4,7PHEt and Ru-4,7PH, which is twice as high as that of the classical [Ru(bpy)3]2+ complex (Ru-bpy). The photocatalytic performance of Ru-Pcat-A was investigated using visible light photoredox catalytic transformations of tertiary amines. With Ru-Pcat-A, we achieved the phosphonylation of N-aryl-1,2,3,4-tetrahydroisoquinolines (THIQs) and cyanation of THIQs and N,N-dimethylaniline in methanol, while a mixture of nitromethane/methanol (1 : 1 v/v) proved to be the optimal solvent for conducting the nitromethylation of THIQs. In the majority of the studied reactions, Ru-4,7PHEt exhibited greater efficiency compared to Ru-bpy, and it could be easily separated from the products using water extraction and reused in the next catalytic cycle. We successfully performed seven consecutive nitromethylation and phosphonylation of N-phenyl-1,2,3,4-tetrahydroisoquinoline using the recycled homogeneous photoredox catalyst.

Visible Light Induced C-H/N-H and C-X Bonds Reactions

Herein, we report efficient visible light-induced photoredox reactions of C–H/N–H and C–X Bonds. These methods have provided access to varied portfolio of synthetically important γ-ketoesters, azaspirocyclic cyclohexadienones spirocyclohexadienones, multisubstituted benzimidazole derivatives, substituted N,2-diarylacetamide, 2-arylpyridines and 2-arylquinolines in good yields and under mild conditions. Moreover, we have successfully discussed the construction through visible light-induction by an intermolecular radical addition, dearomative cyclization, aryl migration and desulfonylation. Similarly, we also spotlight the visible light-catalyzed aerobic C–N bond activation from well-known building blocks through cyclization, elimination and aromatization. The potential use of a wide portfolio of simple ketones and available primary amines has made this transformation very attractive.

Visible Light-Promoted Green and Sustainable Approach for One-Pot Synthesis of 4,4'-(Arylmethylene)bis(1H-pyrazol-5-ols), In Vitro Anticancer Activity, and Molecular Docking with Covid-19 Mpro

A visible light-promoted, efficient, green, and sustainable strategy has been adopted to unlatch a new pathway toward the synthesis of a library of medicinally important 4,4'-(arylmethylene)bis(1H-pyrazol-5-ols) moieties using substituted aromatic aldehydes and sterically hindered 3-methyl-1-phenyl-2-pyrazoline-5-one in excellent yield. This reaction shows high functional group tolerance and provides a cost-effective and catalyst-free protocol for the quick synthesis of biologically active compounds from readily available substrates. Synthesized compounds were characterized by spectroscopic techniques such as IR, 1HNMR, 13CNMR, and single-crystal XRD analysis. All the synthesized compounds were evaluated for their antiproliferative activities against a panel of five different human cancer cell lines and compared with Tamoxifen using MTT assay. Compound 3m exhibited maximum antiproliferative activity and was found to be more active as compared to Tamoxifen against both the MCF-7 and MDA-MB-231 cell lines with an IC50 of 5.45 and 9.47 μM, respectively. A molecular docking study with respect to COVID-19 main protease (Mpro) (PDB ID: 6LU7) has also been carried out which shows comparatively high binding affinity of compounds 3f and 3g (-8.3 and -8.8 Kcal/mole, respectively) than few reported drugs such as ritonavir, remdesivir, ribacvirin, favipiravir, hydroxychloroquine, chloroquine, and olsaltamivir. Hence, it reveals the possibility of these compounds to be used as effective COVID-19 inhibitors.

Photoredox catalysis powered by triplet fusion upconversion: arylation of heteroarenes

In this work, the feasibility of triplet fusion upconversion (TFU, also named triplet-triplet annihilation upconversion) technology for the functionalization (arylation) of furans and thiophenes has been successfully proven. Activation of aryl halides by TFU leads to generation of aryl radical intermediates; trapping of the latter by the corresponding heteroarenes, which act as nucleophiles, affords the final coupling products. Advantages of this photoredox catalytic method include the use of very mild conditions (visible light, standard conditions), employment of commercially available reactants and low-loading metal-free photocatalysts, absence of any sacrificial agent (additive) in the medium and short irradiation times. The involvement of the high energetic delayed fluorescence in the reaction mechanism has been evidenced by quenching studies, whereas the two-photon nature of this photoredox arylation of furans and thiophenes has been manifested by the dependence on the energy source power. Finally, the scaling-up conditions have been gratifyingly afforded by a continuous-flow device.

Photoredox-Catalyzed C-H Functionalization Reactions

The fields of C-H functionalization and photoredox catalysis have garnered enormous interest and utility in the past several decades. Many different scientific disciplines have relied on C-H functionalization and photoredox strategies including natural product synthesis, drug discovery, radiolabeling, bioconjugation, materials, and fine chemical synthesis. In this Review, we highlight the use of photoredox catalysis in C-H functionalization reactions. We separate the review into inorganic/organometallic photoredox catalysts and organic-based photoredox catalytic systems. Further subdivision by reaction class─either sp2 or sp3 C-H functionalization─lends perspective and tactical strategies for use of these methods in synthetic applications.

Visible-light-mediated copper photocatalysis for organic syntheses

Photoredox catalysis has been applied to renewable energy and green chemistry for many years. Ruthenium and iridium, which can be used as photoredox catalysts, are expensive and scarce in nature. Thus, the further development of catalysts based on these transition metals is discouraged. Alternative photocatalysts based on copper complexes are widely investigated, because they are abundant and less expensive. This review discusses the scope and application of photoinduced copper-based catalysis along with recent progress in this field. The special features and mechanisms of copper photocatalysis and highlights of the applications of the copper complexes to photocatalysis are reported. Copper-photocatalyzed reactions, including alkene and alkyne functionalization, organic halide functionalization, and alkyl C-H functionalization that have been reported over the past 5 years, are included.

The Impact of Ligand Carboxylates on Electrocatalyzed Water Oxidation

Fossil fuel shortage and severe climate changes due to global warming have prompted extensive research on carbon-neutral and renewable energy resources. Hydrogen gas (H₂), a clean and high energy density fuel, has emerged as a potential solution for both fulfilling energy demands and diminishing the emission of greenhouse gases. Currently, water oxidation (WO) constitutes the bottleneck in the overall process of producing H₂ from water. As a result, the design of efficient catalysts for WO has become an intensively pursued area of research in recent years. Among all the molecular catalysts reported to date, ruthenium-based catalysts have attracted particular attention due to their robust nature and higher activity compared to catalysts based on other transition metals.Over the past two decades, we and others have studied a wide range of ruthenium complexes displaying impressive catalytic performance for WO in terms of turnover number (TON) and turnover frequency (TOF). However, to produce practically applicable electrochemical, photochemical, or photo-electrochemical WO reactors, further improvement of the catalysts' structure to decrease the overpotential and increase the WO rate is of utmost importance. WO reaction, that is, the production of molecular oxygen and protons from water, requires the formation of an O-O bond through the orchestration of multiple proton and electron transfers. Promotion of these processes using redox noninnocent ligand frameworks that can accept and transfer electrons has therefore attracted substantial attention. The strategic modifications of the ligand structure in ruthenium complexes to enable proton-coupled electron transfer (PCET) and atom proton transfer (APT; in the context of WO, it is the oxygen atom (metal oxo) transfer to the oxygen atom of a water molecule in concert with proton transfer to another water molecule) to facilitate the O-O bond formation have played a central role in these efforts.In particular, promising results have been obtained with ligand frameworks containing carboxylic acid groups that either are directly bonded to the metal center or reside in the close vicinity. The improvement of redox and chemical properties of the catalysts by introduction of carboxylate groups in the ligands has proven to be quite general as demonstrated for a range of mono- and dinuclear ruthenium complexes featuring ligand scaffolds based on pyridine, imidazole, and pyridazine cores. In the first coordination sphere, the carboxylate groups are firmly coordinated to the metal center as negatively charged ligands, improving the stability of the complexes and preventing metal leaching during catalysis. Another important phenomenon is the reduction of the potentials required for the formation of higher valent intermediates, especially metal-oxo species, which take active part in the key O-O bond formation step. Furthermore, the free carboxylic acid/carboxylate units in the proximity to the active center have shown exciting proton donor/acceptor properties (through PCET or APT, chemically noninnocent) that can dramatically improve the rate as well as the overpotential of the WO reaction.

Enantioenriched Ruthenium-Tris-Bipyridine Complexes Bearing One Helical Bipyridine Ligand: Access to Fused Multihelicenic Systems and Chiroptical Redox Switches

The synthesis and photophysical and chiroptical properties of novel aza[n]helicenes (6a-d, 10a,b, n = 4-7) substituted with one or two 2-pyridyl groups are described. The preparation was performed via an adapted Mallory reaction using aromatic imines as precursors. The obtained novel class of helical 2,2'-bipyridine ligands was then coordinated to Ru(bipy)₂²⁺ units, thus affording the first diastereomerically and enantiomerically pure [RuL(bipy)₂]²⁺ (11a,c, L = 6a,c) or [Ru₂L'(bipy)₄]⁴⁺ (12, L' = 10b) complexes. The topology and stereochemistry of these novel metal-based helical architectures were studied in detail, notably using X-ray crystallography. Interestingly, the coordination to ruthenium(II) enabled the preparation of fused multihelical systems incorporating aza- and ruthena-helicenes within the same scaffold. The photophysical, chiroptical, and redox properties of these complexes were examined in detail, and efficient redox-triggered chiroptical switching activity was evidenced.

Strategic Use of Visible-Light Photoredox Catalysis in Natural Product Synthesis

Recent progress in the development of photocatalytic reactions promoted by visible light is leading to a renaissance in the use of photochemistry in the construction of structurally elaborate organic molecules. Because of the rich functionality found in natural products, studies in natural product total synthesis provide useful insights into functional group compatibility of these new photocatalytic methods as well as their impact on synthetic strategy. In this review, we examine total syntheses published through the end of 2020 that employ a visible-light photoredox catalytic step. To assist someone interested in employing the photocatalytic steps discussed, the review is organized largely by the nature of the bond formed in the photocatalytic step.

Photoinduced Borylation for the Synthesis of Organoboron Compounds

Organoboron compounds have important synthetic value and can be applied in numerous transformations. The development of practical and convenient ways to synthesize boronate esters has thus attracted significant interest. Photoinduced borylations originated from stoichiometric reactions of alkanes and arenes with well-defined metal-boryl complexes. Now, photoredox-initiated borylations, catalyzed by either transition metal or organic photocatalysts, and photochemical borylations with high efficiency have become a burgeoning area of research. In this Focus Review, we summarize research on photoinduced borylations, especially emphasizing recent developments and trends. This includes the photoinduced borylation of arenes, alkanes, aryl/alkyl halides, activated carboxylic acids, amines, alcohols, and so on based on transition metal catalysis, metal-free organocatalysis, and direct photochemical activation. We focus on reaction mechanisms involving single-electron transfer, triplet-energy transfer, and other radical processes.

Recent Progress in Designing Halide-Perovskite-Based System for the Photocatalytic Applications

The halide perovskite material has attracted vast attention as a versatile semiconductor in the past decade. With the unique advantages in physical and chemical properties, they have also shown great potential in photocatalytic applications. This review aims at the specific design principles triggered by the unique properties when employing halide-perovskite-based photocatalytic systems from the following perspectives: (I) Design of photoelectrocatalytic device structures including the n-i-p/p-i-n structure, photoelectrode device encapsulation, and electrolyte engineering. (II) The design of heterogeneous photocatalytic systems toward the hydrogen evolution reaction (HER) and CO2 reduction reaction, including the light management, surface/interface engineering, stability improvement, product selectivity engineering, and reaction system engineering. (III) The photocatalysts for the environmental application and organic synthesis. Based on the analyses, the review also suggests the prospective research for the future development of halide-perovskite-based photocatalytic systems.

Highly chemoselective deoxygenation of N-heterocyclic N-oxides under transition metal-free conditions

Because their site-selective C-H functionalizations are now considered one of the most useful tools for synthesizing various N-heterocyclic compounds, the highly chemoselective deoxygenation of densely functionalized N-heterocyclic N-oxides has received much attention from the synthetic chemistry community. Here, we provide a protocol for the highly chemoselective deoxygenation of various functionalized N-oxides under visible light-mediated photoredox conditions with Na2-eosin Y as an organophotocatalyst. Mechanistic studies imply that the excited state of the organophotocatalyst is reductively quenched by Hantzsch esters. This operationally simple technique tolerates a wide range of functional groups and allows high-yield, multigram-scale deoxygenation.

A supramolecular bifunctional iridium photoaminocatalyst for the enantioselective alkylation of aldehydes

The construction of a hybrid metal-organo-photoredox catalyst based on the conjugation of an imidazolidinone organocatalyst and Ir(ppy)2(bipy) (ppy = 2-phenylpyridine, bipy = bipyridine) is described. The introduction of the desired organocatalyst into the bipyridine moiety is quite modular, allowing the preparation of different hybrid photocatalysts, and is realized though a simple click reaction. The hybrid photocatalysts obtained were employed in the benchmark photoredox alkylation of aldehydes. Remarkably, the conjugation of a first-generation MacMillan catalyst produces an active and stereoselective hybrid photoredox catalyst.

The Different Faces of [Ru(bpy)3Cl2] and fac[Ir(ppy)3] Photocatalysts: Redox Potential Controlled Synthesis of Sulfonylated Fluorenes and Pyrroloindoles from Unactivated Olefins and Sulfonyl Chlorides

A cascade alkene sulfonylation that simultaneously forges C-S and C-C bonds is a highly efficient and powerful approach for directly accessing structurally diverse sulfonylated compounds in a single operation. The reaction was enabled by visible-light-mediated regioselective radical addition of sulfonyl chlorides to 2-arylstyrenes using fac[Ir(ppy)₃] as a photocatalyst, demonstrating its unique role in a photocascade process to execute atom transfer radical addition (ATRA) followed by photocyclization. A new class of sulfonyl-substituted fluorenes and pyrroloindoles, which are useful in the field of photoelectronic materials and medicinal chemistry, was produced in excellent yields by this photocascade reaction. In contrast, the cyclization was interrupted when using the [Ru(bpy)₃Cl₂] catalyst having lower reduction potential, leading only to the formation of a C-S bond and the production of acyclic sulfonylated 2-arylstyrenes under identical reaction conditions. The synthetic utility of the present room-temperature photocatalysis is enhanced by the broad availability of bench-stable sulfonyl chlorides and unactivated olefins, thereby providing a cost-effective and broad-scope protocol.

Facile Light-Induced Transformation of [RuII(bpy)2(bpyNO)]2+ to [RuII(bpy)3]2

Ru-based coordination compounds have important applications as photosensitizers and catalysts. [Ru^II(bpy)₂(bpyNO)]²⁺ (bpy = 2,2'-bipyridine and bpyNO = 2,2'-bipyridine-N-oxide) was reported to be extremely light-sensitive, but its light-induced transformation pathways have not been analyzed. Here, we elucidated a mechanism of the light-induced transformation of [Ru^II(bpy)₂(bpyNO)]²⁺ using UV-vis, EPR, resonance Raman, and NMR spectroscopic techniques. The spectroscopic analysis was augmented with the DFT calculations. We concluded that upon 530-650 nm light excitation, ³[Ru^III(bpyNO^-•)(bpy)₂]²⁺ is formed similarly to the ³[Ru^III(bpy^-•)(bpy)₂]²⁺ light-induced state of the well-known photosensitizer [Ru^II(bpy)₃]²⁺. An electron localization on the bpyNO ligand was confirmed by obtaining a unique EPR signal of reduced [Ru^II(bpy)₂(bpyNO^-•)]⁺ (g_xx = 2.02, g_yy = 1.99, and g_zz = 1.87 and ¹⁴N hfs A_xx = 12 G, A_yy = 34 G, and A_zz = 11 G). ³[Ru^III(bpyNO^-•)(bpy)₂]²⁺ may evolve via breaking of the Ru-O-N fragment at two different positions resulting in [Ru^IV═O(bpy)₂(bpy_out)]²⁺ for breakage at the O-|-N bond and [Ru^II(H₂O)(bpy)₂(bpyNO_out)]²⁺ for breakage at the Ru-|-O bond. These pathways were found to have comparable ΔG. A reduction of [Ru^IV═O(bpy)₂(bpy_out)]²⁺ may result in water elimination and formation of [Ru^II(bpy)₃]²⁺. The expected intermediates, [Ru^III(bpy)₂(bpyNO)]³⁺ and [Ru^III(bpy)₃]³⁺, were detected by EPR. In addition, a new signal with g_xx = 2.38, g_yy = 2.10, and g_zz = 1.85 was observed and tentatively assigned to a complex with the dissociated ligand, such as [Ru^III(H₂O)(bpy)₂(bpyNO_out)]³⁺. The spectroscopic signatures of [Ru^IV═O(bpy)₂(bpy_out)]²⁺ were not observed, although DFT analysis and [Ru^II(bpy)₃]²⁺ formation suggest this intermediate. Thus, [Ru^II(bpy)₂(bpyNO)]²⁺ has potential as a light-induced oxidizer.

Shining Visible Light on Vinyl Halides: Expanding the Horizons of Photocatalysis

ConspectusOver the past decade, photoredox catalysis has blossomed as a powerful methodology because of its wide applicability in sustainable free-radical-mediated processes, in which light is used as a cleaner energy source to alter the redox properties of organic molecules and to drive unique chemical transformations. Numerous examples of highly selective C-C and C-heteroatom bond formation processes have been achieved this way in an efficient and waste-reducing way. Therein, the activation of widely available organic halides via single-electron reduction has been broadly applied for organic synthesis. However, in comparison with alkyl and aryl halides, the analogous utilization of vinyl halides is less developed, most likely as a consequence of the highly unstable vinyl radicals generated as intermediates along with their strong tendency to abstract hydrogen atoms from a suitable source (e.g., the solvent), resulting in a synthetically less useful reduction.Nevertheless, during the last years, a number of photocatalytic processes involving vinyl halides have been developed, featuring the generation of vinyl radicals, diradicals, or radical cations as the key transient species. Moreover, photoredox processes in which a radical reacts with a vinyl halide or with an in situ-generated vinylmetal halide have been developed. Thus, identifying suitable conditions to generate and manipulate these reactive species has resulted in novel synthetic processes in a controllable manner. Moreover, in view of the great versatility of vinyl halides in palladium-catalyzed cross-coupling reactions, their activation by visible light might provide an attractive alternative to such processes, especially when non-noble metals could be used as photoinitiators in the future.In this Account, we discuss the various strategies of photoredox processes involving vinyl halides, classifying the material into four categories: (a) formation of a vinyl radical upon receipt of an electron from the photocatalyst, (b) formation of a radical cation after donation of an electron to the photocatalyst, (c) energy transfer corresponding to diradical formation upon triplet-triplet sensitization, and (d) dual transition metal and photocatalysis employing vinyl halides as precursors. While in the first three approaches the activation of vinyl halides is part of the photochemical step, the fourth one involves the interaction of a photochemically generated radical with a vinylnickel(II) halide obtained in turn by the oxidative addition of nickel(0) to the vinyl halide. Therefore, we highlight these important developments for conceptual comparison to the direct activation of vinyl halides by light, but they are not covered in depth in this Account.

Heterogeneous water oxidation photocatalysis based on periodic mesoporous organosilica immobilizing a tris(2,2'-bipyridine)ruthenium sensitizer

A periodic mesoporous organosilica (PMO) containing 2,2′-bipyridine groups (BPy-PMO) has been shown to possess a unique pore wall structure in which the 2,2′-bipyridine groups are densely and regularly packed. The surface 2,2′-bipyridine groups can function as chelating ligands for the formation of metal complexes, thus generating molecularly-defined catalytic sites that are exposed on the surface of the material. We here report the construction of a heterogeneous water oxidation photocatalyst by immobilizing several types of tris(2,2′-bipyridine)ruthenium complexes on BPy-PMO where they function as photosensitizers in conjunction with iridium oxide as a catalyst. The Ru complexes produced on BPy-PMO in this work were composed of three bipyridine ligands, including the BPy in the PMO framework and two X₂bpy, denoted herein as Ru(X)-BPy-PMO where X is H (2,2′-bipyridine), Me (4,4′-dimethyl-2,2′-bipyridine), t-Bu(4,4′-di-tert-butyl-2,2′-bipyridine) or CO₂Me (4,4′-dimethoxycarbonyl-2,2′-bipyridine). Efficient photocatalytic water oxidation was achieved by tuning the photochemical properties of the Ru complexes on the BPy-PMO through the incorporation of electron-donating or electron-withdrawing functionalities. The reaction turnover number based on the amount of the Ru complex was improved to 20, which is higher than values previously obtained from PMO systems acting as water oxidation photocatalysts.

Ruthenium complex photosensitizer fixed on 2,2′-bipyridine bridged-periodic mesoporous organosilica with iridium oxide exhibits an efficient photocatalytic water oxidation.

Porous Ru(bpy)32+-Linked Polymers for Recyclable Photocatalysis of Enantioselective Alkylation of Aldehydes

Two metal porous organic polymers (POPs) that contain the [Ru(bpy)₃]²⁺ cores are prepared via one-pot Suzuki-Miyaura coupling reactions. Both Ru-POPs are thermally stable at up to 340 °C in air and do not dissolve in all solvents tested. One of the POPs has been revealed to be highly effective and reusable as a heterogeneous photocatalyst for visible light-driven enantioselective alkylation of aldehydes. After 10 cycles, the catalyst still maintains the enantioselectivity, while the activity just decreases slightly.

Facile synthesis of 1,5-disubstituted tetrazoles by reacting a ruthenium acetylide complex with trimethylsilyl azide

Treatment of [Ru]-C[triple bond, length as m-dash]CPh (1, [Ru] = (η⁵-C₅H₅)(dppe)Ru, dppe = Ph₂PCH₂CH₂PPh₂) with trimethylsilyl azide afforded the cationic nitrile complex {[Ru]NCCH₂Ph}[N₃] (2) and the further cycloaddition of 2 with trimethylsilyl azide at 60 °C afforded the N(2)-bound tetrazolato complex [Ru]N₄CCH₂Ph (3). The regiospecific alkylation of 3 gave a series of cationic N(2)-bound N(4)-alkylated-5-benzyl tetrazolato complexes {[Ru]N₄(CH₂R)CCH₂Ph}[Br] (4a, R = C₆F₅; 4b, R = Ph; 4c, R = 4-CN-C₆H₄; 4d, R = 2,6-F₂-C₆H₃; 4e, R = 6-CH₂Br-C₅NH₃) and the subsequent cleavage of the Ru-N bond of 4a-4e gave N(1)-alkylated-5-benzyl tetrazoles N₄(CH₂R)CCH₂Ph (5a-5e) in good to excellent yields and [Ru]-Br, which, on reacting with phenylacetylene, resulted in the formation of 1 thus forming a reaction cycle. The structures of 2, 3, 4a, 4c and 5a were confirmed by single-crystal X-ray diffraction analysis.

Helical-Ribbon and Tape Formation of Lipid Packaged [Ru(bpy)3]2+ Complexes in Organic Media

Anionic lipid amphiphiles with [RuII(bpy)3]2+ complex have been prepared. The metal complexes have been found to form ribbon and tape structures depending on chemical structures of lipid amphiphiles. Especially, the composites showed hypochromic effect and induced circular dichroism in organic media, and flexibly and weakly supramolecular control of morphological and optical properties have been demonstrated.