Bioinspired cobalt cubanes with tunable redox potentials for photocatalytic water oxidation and CO₂ reduction

• Zhishan Luo,
• Yidong Hou,
• Jinshui Zhang,
• Sibo Wang and
• Xinchen Wang

Beilstein J. Org. Chem. 2018, 14, 2331–2339, doi:10.3762/bjoc.14.208

• photocatalytic conversions has been the Achilles’ heel of solar energy utilization. Here, we report on a chemical approach based on ligand designed architectures to fabricate unique structural molecular catalysts coupled with appropriate light harvesters (e.g., carbon nitride and Ru(bpy)32+) for photoredox

• reactions. The “Co4O4” cubane complex Co4O4(CO2Me)4(RNC5H4)4 (R = CN, Br, H, Me, OMe), serves as a molecular catalyst for the efficient and stable photocatalytic water oxidation and CO2 reduction. A comprehensive structure–function analysis emerged herein, highlights the regulation of electronic

• favorable electrochemical potential for 1-R with tunable ligand substitutions suggests their great potential as redox catalysts for water oxidation and CO2 reduction reactions. Next, we studied the photocatalytic activity of a series of the 1-R molecular complexes in the water oxidation reaction to release

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• -photocatalytic or transition metal photocatalysed processes. The reported chemistry has no precedent in the literature and is only possible using organophotoredox chemistry. The products presented must always be somehow important in medicinal chemistry. A combination of some of the above conditions. As such, the

Graphitic carbon nitride prepared from urea as a photocatalyst for visible-light carbon dioxide reduction with the aid of a mononuclear ruthenium(II) complex

• Kazuhiko Maeda,
• Daehyeon An,
• Ryo Kuriki,
• Daling Lu and
• Osamu Ishitani

Beilstein J. Org. Chem. 2018, 14, 1806–1812, doi:10.3762/bjoc.14.153

• activity obtained at 873–923 K. This trend was also consistent with that observed in photocatalytic H2 evolution using Pt-loaded g-C3N4. The photocatalytic activities of RuP/g-C3N4 for CO2 reduction and H2 evolution were thus shown to be strongly associated with the generation of the crystallized g-C3N4

• emerging material as an organic semiconductor photocatalyst active for various kinds of reactions such as water splitting, CO2 reduction, and degradation of harmful organic compounds, because of its non-toxic, stable, and earth-abundant nature [2][3][4][5][6][7]. Our group has developed photocatalytic CO2

• temperature. In this work, we investigated photocatalytic activities of g-C3N4, which was synthesized by heating urea at different temperatures, for visible-light CO2 reduction with the aid of a mononuclear Ru(II) complex, RuP (see Scheme 1). As mentioned earlier, g-C3N4 has been studied as a visible-light

Functionalization of N-arylglycine esters: electrocatalytic access to C–C bonds mediated by n-Bu₄NI

• Mi-Hai Luo,
• Yang-Ye Jiang,
• Kun Xu,
• Yong-Guo Liu,
• Bao-Guo Sun and
• Cheng-Chu Zeng

Beilstein J. Org. Chem. 2018, 14, 499–505, doi:10.3762/bjoc.14.35

• ., wherein simple copper salts were used as catalysts and oxygen as the co-oxidant (Scheme 1) [17]. Alternatively, photocatalytic versions of CDC reactions of glycine derivatives with C-nucleophiles were also developed [18][19]. For example, combining the visible light catalyst Ru(bpy)3Cl2, and the

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• conditions. The key concepts of photocatalysis and photoredox-catalyzed reactions for carbon–carbon and carbon–heteroatom (C–X) bond formation have been reviewed in detail. However, several new photocatalytic methods for the formation of carbon–sulfur (C–S) bonds were recently reported and we aim to

• radical initiators as well as photocatalytic reactions, where sulfur-containing substrates act as a sacrificial agent are not discussed in this review [23][24][25][26][27][28]. Review Thiols Formation of sulfides and sulfoxides A large number of photocatalytic C–S bond-forming methods report the

• preparation of sulfides. Non-photocatalytic procedures apply the so-called radical thiol–ene or radical thiol–yne reactions for efficient cross-coupling of thiols with olefins [24][29][30]. In 2013, Yoon and co-workers developed a photoredox-catalyzed version of the radical thiol–ene reaction (Scheme 2) [31

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• tandem trifluoromethylation/cyclisation processes. Dolbier and co-workers first proposed the use of N-arylacrylamides 3 to access trifluoromethylated 3,3-disubstituted 2-oxindoles 4 under photocatalytic conditions (Scheme 4) [11]. In the presence of Ru(phen)3Cl2 (phen = phenanthroline), a variety of N

• then be involved in another photocatalytic sequence in the presence of α-methylstyrene and water to access β-hydroxysulfones 27 in moderate to good yields (Scheme 22) [29]. Interestingly, this process can be realised in one-pot. Reiser and co-workers also envisioned that using alkenols as substrates in

• reaction, in classical solvents or in an ionic liquid media, to yield the corresponding CF3 alkenes (Scheme 28) [35][36]. As for Yu, Zhang and co-workers, they described the trifluoromethylation of two enamides under photocatalytic conditions, using similar conditions as those they proposed for the

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• this work, it should be noted that Davies, MacMillan and co-workers have designed an integrated small-scale photoreactor that enabled acceleration of this photocatalytic reaction [75]. Trifluoromethylation of arenediazonium compounds: Langlois’ conditions were applied in the copper-mediated Sandmeyer

Ni nanoparticles on RGO as reusable heterogeneous catalyst: effect of Ni particle size and intermediate composite structures in C–S cross-coupling reaction

• Debasish Sengupta,
• Koushik Bhowmik,
• Goutam De and
• Basudeb Basu

Beilstein J. Org. Chem. 2017, 13, 1796–1806, doi:10.3762/bjoc.13.174

• nanocomposites [30]. Therefore, RGO is considered an excellent candidate for catalyst support [31][32]. To date, various magnetic or semiconducting nanoparticles (NPs) have been incorporated in GO surfaces and thoroughly studied in terms of their photocatalytic and electrochemical properties [33][34][35][36][37

Mechanochemical synthesis of graphene oxide-supported transition metal catalysts for the oxidation of isoeugenol to vanillin

• Ana Franco,
• Sudipta De,
• Alina M. Balu,
• Araceli Garcia and
• Rafael Luque

Beilstein J. Org. Chem. 2017, 13, 1439–1445, doi:10.3762/bjoc.13.141

• production via simple oxidation pathways [12][13][14]. Photocatalytic oxidation has been reported for the production of vanillin where TiO2-based materials have been used as effective catalysts in recent years [15][16][17][18]. Although the conversion was high in some cases, vanillin selectivity was never

Contribution of microreactor technology and flow chemistry to the development of green and sustainable synthesis

• Flavio Fanelli,
• Giovanna Parisi,
• Leonardo Degennaro and
• Renzo Luisi

Beilstein J. Org. Chem. 2017, 13, 520–542, doi:10.3762/bjoc.13.51

• reported a metal-free photocatalytic aerobic oxidation of thiols to disulfides under continuous-flow conditions [64]. Disulfides are useful molecules employed as drugs, anti-oxidants or pesticides as well as rubber vulcanizating agents [65]. Symmetric disulfides are generally obtained by oxidative coupling

• disulfide 12 (Scheme 12), used as food flavour additive [67]. To demonstrate the usefulness of the flow methodology, and its applicability, the photocatalytic aerobic oxidation of a peptide to obtain oxytocin in continuous flow was reported (Scheme 12). Full conversion was achieved in water with 200 s of

• . (Adapted with permission from [53], copyright 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim). Continuous flow process setup for the preparation of 11 (Reproduced with permission from [54], copyright 2015 American Chemical Society). Continuous-flow photocatalytic oxidation of thiols to disulfides

Stabilization of nanosized titanium dioxide by cyclodextrin polymers and its photocatalytic effect on the degradation of wastewater pollutants

• Tamás Zoltán Agócs,
• István Puskás,
• Erzsébet Varga,
• Mónika Molnár and
• Éva Fenyvesi

Beilstein J. Org. Chem. 2016, 12, 2873–2882, doi:10.3762/bjoc.12.286

• carboxymethyl β-cyclodextrin polymer (CMBCD-P) for stabilization of nanoTiO2 dispersions. The photocatalytic degradation of methylene blue and ibuprofen as model organic pollutants in various media (distilled water, NaCl solution and tap water) has been studied using nanoTiO2 as catalyst stabilized by CMBCD-P

• pollutant of emerging concern (EP), was protected by CMBCD-P against the photocatalytic degradation showing that inclusion complex formation can result in opposite effects depending on the structure of the host–guest complex. Keywords: carboxymethyl β-cyclodextrin polymer; colloid stability; ibuprofen

• catalyst for photodecomposition of various organic pollutants [31]. The photocatalytic reactions take place on the surface of the catalyst on the effect of solar light or of artificial UV light irradiation. In the practice, TiO2 is immobilized on a surface, e.g., glass wool mats or ceramic plates and a

Solvent-free, visible-light photocatalytic alcohol oxidations applying an organic photocatalyst

• Martin Obst and
• Burkhard König

Beilstein J. Org. Chem. 2016, 12, 2358–2363, doi:10.3762/bjoc.12.229

• Martin Obst Burkhard Konig Institute of Organic Chemistry, University of Regensburg, Universitätsstraße 31, 93040 Regensburg, Germany 10.3762/bjoc.12.229 Abstract A method for the solvent-free photocatalytic conversion of solid and liquid substrates was developed, using a novel rod mill apparatus

• . In this setup, thin liquid films are realized which is crucial for an effective photocatalytic conversion due to the low penetration depth of light in heterogeneous systems. Several benzylic alcohols were oxidized with riboflavin tetraacetate as photocatalyst under blue light irradiation of the

• solvent like hydrogen-atom transfer or the formation of byproducts could be excluded. For liquid substrates, some examples for photocatalytic, solvent-free conversions are reported, such as the oxidation of benzyl alcohol to benzaldehyde [4] and the oxidation of benzenes to phenols [5]. Another field of

Copper-mediated arylation with arylboronic acids: Facile and modular synthesis of triarylmethanes

• H. Surya Prakash Rao and
• A. Veera Bhadra Rao

Beilstein J. Org. Chem. 2016, 12, 496–504, doi:10.3762/bjoc.12.49

• [52]. The reaction was conducted in the presence of 20 mol % Cu(OTf)2 under optimized conditions, providing triarylmethane 21 in 76% yield. Deprotection of the phenolic hydroxy group in 21 was facile under photocatalytic conditions by using UV LED lamps in wet acetonitrile. The reaction furnished the

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• excitation wavelength 385 nm, band gap 3.2 eV). Whilst this is less convenient than visible light, the band edge positions are consequently more powerful redox agents. Of the naturally occurring crystal structures of TiO2, anatase is superior to rutile for photocatalytic activity [12]. For semiconductor

• 64 but a significant quantity of ring opened byproduct was also formed. Carbonyl compounds are also good electron acceptors and so SCPC hydrogenations seemed likely. Actually there is a literature precedent for photocatalytic hydrogenation of acetophenone derivatives with TiO2 [80][81]. We studied a

CO₂ Chemistry

• Thomas E. Müller and
• Walter Leitner

Beilstein J. Org. Chem. 2015, 11, 675–677, doi:10.3762/bjoc.11.76

• fixation of CO2, which can be applied in the synthesis of carboxylic acids [8]. Also highly interesting is the combination of enzymatic and photocatalytic approaches for activating CO2 [9]. Bifunctional catalyst systems are frequently needed and well-understood in the synthesis of cyclic carbonates [10

Photocatalytic nucleophilic addition of alcohols to styrenes in Markovnikov and anti-Markovnikov orientation

• Martin Weiser,
• Sergej Hermann,
• Alexander Penner and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2015, 11, 568–575, doi:10.3762/bjoc.11.62

• additive. Photocatalytic additions of a variety of alcohols gave the corresponding products in good to excellent yields. The proposed photocatalytic electron transfer mechanism was supported by detection of the PDI radical anion as key intermediate and by comparison of two intramolecular reactions with

• [8]. The way towards a really complete organo-type photoredox catalysis has mainly been established for eosin Y as an important alternative for [Ru(bpy)3]2+ [9]. Photocatalytic nucleophilic additions of amines and alcohols to olefins, especially styrenes, became an increasingly important task due to

• /70s, and Lewis identified exciplex states as key intermediates [13][14]. The corresponding photohydration worked only if the aromatic olefins as starting material were directly excited by UV light [15][16]. The first approach towards a photocatalytic version of this type of reaction came from Arnold

An improved procedure for the preparation of Ru(bpz)₃(PF₆)₂ via a high-yielding synthesis of 2,2’-bipyrazine

• Danielle M. Schultz,
• James W. Sawicki and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2015, 11, 61–65, doi:10.3762/bjoc.11.9

• properties of these complexes is well understood [6][7][8]. As a result, a variety of Ru and Ir based chromophores spanning a range of redox potentials have recently become widely utilized in the design of new photocatalytic transformations [9]. In particular, the homoleptic tris(bipyrazyl) complex 2 (Ru(bpz

Visible-light-induced bromoetherification of alkenols for the synthesis of β-bromotetrahydrofurans and -tetrahydropyrans

• Run Lin,
• Hongnan Sun,
• Chao Yang,
• Youdong Yang,
• Xinxin Zhao and
• Wujiong Xia

Beilstein J. Org. Chem. 2015, 11, 31–36, doi:10.3762/bjoc.11.5

• alkenols with CBr4 as the bromine source, utilizing visible-light-induced phototedox catalysis. The reaction proceeds with high efficiency and regioselectivity for the synthesis of β-bromotetrahydrofurans and -tetrahydropyranes. Experimental General procedure for the photocatalytic bromoetherification of

• bromoethrification of alkenols. Proposed mechanism for the photocatalytic bromoetherification of alkenols. Survey on the photocatalytic bromoetherification of alkenols. Photocatalytic bromoetherification of butenols.a Photocatalytic bromoetherification of pentenolsa. Supporting Information Supporting Information

An integrated photocatalytic/enzymatic system for the reduction of CO₂ to methanol in bioglycerol–water

• Michele Aresta,
• Angela Dibenedetto,
• Tomasz Baran,
• Antonella Angelini,
• Przemysław Łabuz and
• Wojciech Macyk

Beilstein J. Org. Chem. 2014, 10, 2556–2565, doi:10.3762/bjoc.10.267

• , 70126 Bari, Italy Department of Chemistry, University of Bari, Via Orabona 4, 70125 Bari, Italy Faculty of Chemistry Jagiellonian University Ingardena 3, 30-060 Kraków, Poland 10.3762/bjoc.10.267 Abstract A hybrid enzymatic/photocatalytic approach for the conversion of CO2 into methanol is described

• gap energy of 3.2 eV (which is not compatible for use with visible light), modified TiO2 is known to be more suitable for carrying out photocatalytic processes utilizing the visible part of the solar spectrum [17]. In previous work, systems based on stable, encapsulated enzymes [7] for the enzymatic

• , and the in situ photocatalytic reduction of NAD+ to NADH under visible-light irradiation, using semiconductors in water/bioglycerol mixtures. Bioglycerol is being produced in increasing volumes for bio-diesel production from oleaginous seeds. New applications for this product are being investigated [7

Visible-light photoredox catalyzed synthesis of pyrroloisoquinolines via organocatalytic oxidation/[3 + 2] cycloaddition/oxidative aromatization reaction cascade with Rose Bengal

• Carlos Vila,
• Jonathan Lau and
• Magnus Rueping

Beilstein J. Org. Chem. 2014, 10, 1233–1238, doi:10.3762/bjoc.10.122

• examples of lamellarin alkaloids. Photocatalytic metal free construction of pyrrolo[2,1-a]isoquinolines. Evaluation of the substrate scope. Evaluation of the substrate scope with activated alkynes. Optimization of the reaction conditions.a Supporting Information Supporting Information File 56

Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

• Axel G. Griesbeck and
• Melissa Reckenthäler

Beilstein J. Org. Chem. 2014, 10, 1143–1150, doi:10.3762/bjoc.10.114

• visible region and appropriate redox activity in the excited states. Many potent photoredox catalysts with sufficient long-term stability are transition metal complexes with excited MLCT states that can be generated in the visible. Another important group of photocatalytic active compounds are

• the homogeneous catalytic titanium species The original protocol for photocatalytic hydroxymethylation involves titanium tetrachloride in methanol as the reactive catalyst/donor mixture and carbonyl compounds as the acceptor components. During the exothermic dissolution process of TiCl4 in methanol

Direct C–H trifluoromethylation of di- and trisubstituted alkenes by photoredox catalysis

• Ren Tomita,
• Yusuke Yasu,
• Takashi Koike and
• Munetaka Akita

Beilstein J. Org. Chem. 2014, 10, 1099–1106, doi:10.3762/bjoc.10.108

• CF3-substituted alkenes via direct Calkenyl–H trifluoromethylation. 1,1-Di- and trisubstituted alkenes were applicable to this photocatalytic system, providing the corresponding multisubstituted CF3-alkenes. In addition, use of an excess amount of the CF3 source induced double C–H trifluoromethylation

• trifluoromethylating reagents (+CF3) can serve as more efficient CF3 radical sources under mild photocatalytic reaction conditions. In addition, the putative β-CF3 carbocation intermediate formed through SET photoredox processes is playing a key role in our reaction systems (vide infra). Trifluoromethylated alkenes

• trisubstituted alkenes (Scheme 3c). Herein we disclose a highly efficient direct C–H trifluoromethylation of di- and trisubstituted alkenes with easy-handling and shelf-stable Umemoto’s reagent 1a by visible-light-driven photoredox catalysis under mild conditions. This photocatalytic protocol allows us easy

On the mechanism of photocatalytic reactions with eosin Y

• Michal Majek,
• Fabiana Filace and
• Axel Jacobi von Wangelin

Beilstein J. Org. Chem. 2014, 10, 981–989, doi:10.3762/bjoc.10.97

• discussed on the basis of pH, solvent polarity, lamp type, absorption properties, and quantum yields. Determination of the latter proved to be an especially valuable tool for the distinction between radical chain and photocatalytic reactions. Keywords: mechanism; organocatalysis; photocatalysis; photoredox

• visible range of the solar spectrum have been demonstrated to catalyze light-driven organic reactions. The use of the pyridyl-based complexes [Ru(bpy)3]2+, [Ir(ppy)3] and [Ir(ppy2)(dtbbpy)]+ for the mediation of redox processes has certainly attracted the most interest, incipiently in photocatalytic

• no appreciable absorption at this wavelength. However, the addition of minor quantities of base (TBAOH) to the reaction mixture resulted in strong absorption at 535 nm and good photocatalytic activity under irradiation. The substitution of acetonitrile with DMSO in the same reaction gave strong

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

• Christian Ley,
• Julien Christmann,
• Ahmad Ibrahim,
• Luciano H. Di Stefano and
• Xavier Allonas

Beilstein J. Org. Chem. 2014, 10, 936–947, doi:10.3762/bjoc.10.92

• kinetics occuring in so called photocatalytic systems. The simple kinetic model used is enough to outline the benefit of the cyclic system and to give the basic requirements in term of chemical combination needed to be fulfilled in order to obtain a photocatalytic behavior. Keywords: computation; electron

• responsible for the higher efficiency of PCIS [9][31][53][54][55] in photopolymerization reactions. Therefore, as the dye is regenerated during the photochemical reaction, a catalytic behavior appears, leading to the so-called photocatalytic system. In this paper an experimental and mechanistic study of Type

• II PIS will be given and compared with a PCIS. Then, in order to improve the knowledge of PCIS, a thermodynamic and mechanistic approach of PCIS exhibiting an ideal photocatalytic behavior will be presented. The proposed scheme will be used as model to run some computation. This will permit to

Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

• Jacques Lalevée,
• Sofia Telitel,
• Pu Xiao,
• Marc Lepeltier,
• Frédéric Dumur,
• Fabrice Morlet-Savary,
• Didier Gigmes and
• Jean-Pierre Fouassier

Beilstein J. Org. Chem. 2014, 10, 863–876, doi:10.3762/bjoc.10.83

• anion. Later on, other amines (N,N-diisopropylethylamine, N,N-dimethylformamide) and bromides (ethyl 2-bromoisobutyrate, benzyl bromide) were proposed for the photocatalytic radical polymerization of various methacrylates [53]. Ir complexes can also be used. As only carbon centered radicals can be