@article{14409, abstract = {We present a photon- and metal-free approach for the radical fluorination of aliphatic oxalate-activated alcohols. The method relies on the spontaneous generation of the N-(chloromethyl)triethylenediamine radical dication, a potent single electron oxidant, from Selectfluor and 4-(dimethylamino)pyridine. The protocol is easily scalable and provides the desired fluorinated products within only a few minutes reaction time.}, author = {Baunis, Haralds and Pieber, Bartholomäus}, issn = {1099-0690}, journal = {European Journal of Organic Chemistry}, number = {42}, publisher = {Wiley}, title = {{Formal radical deoxyfluorination of oxalate-activated alcohols triggered by the selectfluor-DMAP charge-transfer complex}}, doi = {10.1002/ejoc.202300769}, volume = {26}, year = {2023}, } @article{13970, author = {Madani, Amiera and Sletten, Eric T. and Cavedon, Cristian and Seeberger, Peter H. and Pieber, Bartholomäus}, issn = {2333-3553}, journal = {Organic Syntheses}, pages = {271--286}, publisher = {Organic Syntheses}, title = {{Visible-light-mediated oxidative debenzylation of 3-O-Benzyl-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose}}, doi = {10.15227/orgsyn.100.0271}, volume = {100}, year = {2023}, } @article{13972, abstract = {This Special Collection is dedicated to the field of photocatalytic synthesis and contains a diverse selection of original research contributions. It includes studies on catalyst development, mechanistic investigations, method development and the use of enabling technologies, illustrating the many facets of state-of-the-art research in photocatalytic synthesis. Further, emerging topics are surveyed and discussed in three reviews and a concept article.}, author = {Næsborg, Line and Pieber, Bartholomäus and Wenger, Oliver S.}, issn = {1867-3899}, journal = {ChemCatChem}, publisher = {Wiley}, title = {{Special Collection: Photocatalytic synthesis}}, doi = {10.1002/cctc.202300683}, year = {2023}, } @article{12919, abstract = {We report the visible light photocatalytic cleavage of trityl thioethers or ethers under pH-neutral conditions. The method results in the formation of the respective symmetrical disulfides and alcohols in moderate to excellent yield. The protocol only requires the addition of a suitable photocatalyst and light rendering it orthogonal to several functionalities, including acid labile protective groups. The same conditions can be used to directly convert trityl-protected thiols into unsymmetrical disulfides or selenosulfides, and to cleave trityl resins in solid phase organic synthesis.}, author = {Murakami, Sho and Brudy, Cosima and Bachmann, Moritz and Takemoto, Yoshiji and Pieber, Bartholomäus}, issn = {1437-210X}, journal = {Synthesis}, keywords = {Organic Chemistry, Catalysis}, number = {09}, pages = {1367--1374}, publisher = {Georg Thieme Verlag}, title = {{Photocatalytic cleavage of trityl protected thiols and alcohols}}, doi = {10.1055/a-1979-5933}, volume = {55}, year = {2023}, } @article{12920, abstract = {The multicomponent approach allows to incorporate several functionalities into a single covalent organic framework (COF) and consequently allows the construction of bifunctional materials for cooperative catalysis. The well-defined structure of such multicomponent COFs is furthermore ideally suited for structure-activity relationship studies. We report a series of multicomponent COFs that contain acridine- and 2,2’-bipyridine linkers connected through 1,3,5-benzenetrialdehyde derivatives. The acridine motif is responsible for broad light absorption, while the bipyridine unit enables complexation of nickel catalysts. These features enable the usage of the framework materials as catalysts for light-mediated carbon−heteroatom cross-couplings. Variation of the node units shows that the catalytic activity correlates to the keto-enamine tautomer isomerism. This allows switching between high charge-carrier mobility and persistent, localized charge-separated species depending on the nodes, a tool to tailor the materials for specific reactions. Moreover, nickel-loaded COFs are recyclable and catalyze cross-couplings even using red light irradiation.}, author = {Traxler, Michael and Reischauer, Susanne and Vogl, Sarah and Roeser, Jérôme and Rabeah, Jabor and Penschke, Christopher and Saalfrank, Peter and Pieber, Bartholomäus and Thomas, Arne}, issn = {1521-3765}, journal = {Chemistry – A European Journal}, keywords = {General Chemistry, Catalysis, Organic Chemistry}, number = {4}, publisher = {Wiley}, title = {{Programmable photocatalytic activity of multicomponent covalent organic frameworks used as metallaphotocatalysts}}, doi = {10.1002/chem.202202967}, volume = {29}, year = {2023}, } @article{12921, abstract = {Visible-light photocatalysis provides numerous useful methodologies for synthetic organic chemistry. However, the mechanisms of these reactions are often not fully understood. Common mechanistic experiments mainly aim to characterize excited state properties of photocatalysts and their interaction with other species. Recently, in situ reaction monitoring using dedicated techniques was shown to be well-suited for the identification of intermediates and to obtain kinetic insights, thereby providing more holistic pictures of the reactions of interest. This minireview surveys these technologies and discusses selected examples where reaction monitoring was used to elucidate the mechanism of photocatalytic reactions.}, author = {Madani, Amiera and Pieber, Bartholomäus}, issn = {1867-3899}, journal = {ChemCatChem}, keywords = {Inorganic Chemistry, Organic Chemistry, Physical and Theoretical Chemistry, Catalysis}, number = {7}, publisher = {Wiley}, title = {{In situ reaction monitoring in photocatalytic organic synthesis}}, doi = {10.1002/cctc.202201583}, volume = {15}, year = {2023}, } @article{12922, abstract = {The influence of structural modifications on the catalytic activity of carbon materials is poorly understood. A collection of carbonaceous materials with different pore networks and high nitrogen content was characterized and used to catalyze four reactions to deduce structure–activity relationships. The CO2 cycloaddition and Knoevenagel reaction depend on Lewis basic sites (electron-rich nitrogen species). The absence of large conjugated carbon domains resulting from the introduction of large amounts of nitrogen in the carbon network is responsible for poor redox activity, as observed through the catalytic reduction of nitrobenzene with hydrazine and the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine using hydroperoxide. The material with the highest activity towards Lewis acid catalysis (in the hydrolysis of (dimethoxymethyl)benzene to benzaldehyde) is the most effective for small molecule activation and presents the highest concentration of electron-poor nitrogen species.}, author = {Lepre, Enrico and Rat, Sylvain and Cavedon, Cristian and Seeberger, Peter H. and Pieber, Bartholomäus and Antonietti, Markus and López‐Salas, Nieves}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, keywords = {General Chemistry, Catalysis}, number = {2}, publisher = {Wiley}, title = {{Catalytic properties of high nitrogen content carbonaceous materials}}, doi = {10.1002/anie.202211663}, volume = {62}, year = {2023}, } @article{11955, abstract = {Covalent organic frameworks (COFs) are structurally tuneable, porous and crystalline polymers constructed through the covalent attachment of small organic building blocks as elementary units. Using the myriad of such building blocks, a broad spectrum of functionalities has been applied for COF syntheses for broad applications, including heterogeneous catalysis. Herein, we report the synthesis of a new family of porous and crystalline COFs using a novel acridine linker and benzene-1,3,5-tricarbaldehyde derivatives bearing a variable number of hydroxy groups. With the broad absorption in the visible light region, the COFs were applied as photocatalysts in metallaphotocatalytic C−N cross-coupling. The fully β-ketoenamine linked COF showed the highest activity, due to the increased charge separation upon irradiation. The COF showed good to excellent yields for several aryl bromides, good recyclability and even catalyzed the organic transformation in presence of green light as energy source.}, author = {Traxler, Michael and Gisbertz, Sebastian and Pachfule, Pradip and Schmidt, Johannes and Roeser, Jérôme and Reischauer, Susanne and Rabeah, Jabor and Pieber, Bartholomäus and Thomas, Arne}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, number = {21}, publisher = {Wiley}, title = {{Acridine‐functionalized covalent organic frameworks (COFs) as photocatalysts for metallaphotocatalytic C−N cross‐coupling}}, doi = {10.1002/anie.202117738}, volume = {61}, year = {2022}, } @article{12067, abstract = {We present a divergent strategy for the fluorination of phenylacetic acid derivatives that is induced by a charge-transfer complex between Selectfluor and 4-(dimethylamino)pyridine. A comprehensive investigation of the conditions revealed a critical role of the solvent on the reaction outcome. In the presence of water, decarboxylative fluorination through a single-electron oxidation is dominant. Non-aqueous conditions result in the clean formation of α-fluoro-α-arylcarboxylic acids.}, author = {Madani, Amiera and Anghileri, Lucia and Heydenreich, Matthias and Möller, Heiko M. and Pieber, Bartholomäus}, issn = {1523-7052}, journal = {Organic Letters}, number = {29}, pages = {5376–5380}, publisher = {American Chemical Society}, title = {{Benzylic fluorination induced by a charge-transfer complex with a solvent-dependent selectivity switch}}, doi = {10.1021/acs.orglett.2c02050}, volume = {24}, year = {2022}, } @article{12923, abstract = {Photoredox-mediated Ni-catalyzed cross-couplings are powerful transformations to form carbon–heteroatom bonds and are generally photocatalyzed by noble metal complexes. Low-cost and easy-to-prepare carbon dots (CDs) are attractive quasi-homogeneous photocatalyst alternatives, but their applicability is limited by their short photoluminescence (PL) lifetimes. By tuning the surface and PL properties of CDs, we designed colloidal CD nano-photocatalysts for a broad range of Ni-mediated cross-couplings between aryl halides and nucleophiles. In particular, a CD decorated with amino groups permitted coupling to a wide range of aryl halides and thiols under mild, base-free conditions. Mechanistic studies suggested dynamic quenching of the CD excited state by the Ni co-catalyst and identified that pyridinium iodide (pyHI), a previously used additive in metallaphotocatalyzed cross-couplings, can also act as a photocatalyst in such transformations.}, author = {Zhao, Zhouxiang and Pieber, Bartholomäus and Delbianco, Martina}, issn = {2155-5435}, journal = {ACS Catalysis}, keywords = {Catalysis, General Chemistry}, number = {22}, pages = {13831--13837}, publisher = {American Chemical Society}, title = {{Modulating the surface and photophysical properties of carbon dots to access colloidal photocatalysts for cross-couplings}}, doi = {10.1021/acscatal.2c04025}, volume = {12}, year = {2022}, } @article{12924, abstract = {We demonstrate that several visible-light-mediated carbon−heteroatom cross-coupling reactions can be carried out using a photoactive NiII precatalyst that forms in situ from a nickel salt and a bipyridine ligand decorated with two carbazole groups (Ni(Czbpy)Cl2). The activation of this precatalyst towards cross-coupling reactions follows a hitherto undisclosed mechanism that is different from previously reported light-responsive nickel complexes that undergo metal-to-ligand charge transfer. Theoretical and spectroscopic investigations revealed that irradiation of Ni(Czbpy)Cl2 with visible light causes an initial intraligand charge transfer event that triggers productive catalysis. Ligand polymerization affords a porous, recyclable organic polymer for heterogeneous nickel catalysis of cross-coupling reactions. The heterogeneous catalyst shows stable performance in a packed-bed flow reactor during a week of continuous operation.}, author = {Cavedon, Cristian and Gisbertz, Sebastian and Reischauer, Susanne and Vogl, Sarah and Sperlich, Eric and Burke, John H. and Wallick, Rachel F. and Schrottke, Stefanie and Hsu, Wei‐Hsin and Anghileri, Lucia and Pfeifer, Yannik and Richter, Noah and Teutloff, Christian and Müller‐Werkmeister, Henrike and Cambié, Dario and Seeberger, Peter H. and Vura‐Weis, Josh and van der Veen, Renske M. and Thomas, Arne and Pieber, Bartholomäus}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, keywords = {General Chemistry, Catalysis}, number = {46}, publisher = {Wiley}, title = {{Intraligand charge transfer enables visible‐light‐mediated Nickel‐catalyzed cross-coupling reactions}}, doi = {10.1002/anie.202211433}, volume = {61}, year = {2022}, } @article{11956, abstract = {Controlling the selectivity of a chemical reaction with external stimuli is common in thermal processes, but rare in visible-light photocatalysis. Here we show that the redox potential of a carbon nitride photocatalyst (CN-OA-m) can be tuned by changing the irradiation wavelength to generate electron holes with different oxidation potentials. This tuning was the key to realizing photo-chemo-enzymatic cascades that give either the (S)- or the (R)-enantiomer of phenylethanol. In combination with an unspecific peroxygenase from Agrocybe aegerita, green light irradiation of CN-OA-m led to the enantioselective hydroxylation of ethylbenzene to (R)-1-phenylethanol (99 % ee). In contrast, blue light irradiation triggered the photocatalytic oxidation of ethylbenzene to acetophenone, which in turn was enantioselectively reduced with an alcohol dehydrogenase from Rhodococcus ruber to form (S)-1-phenylethanol (93 % ee).}, author = {Schmermund, Luca and Reischauer, Susanne and Bierbaumer, Sarah and Winkler, Christoph K. and Diaz‐Rodriguez, Alba and Edwards, Lee J. and Kara, Selin and Mielke, Tamara and Cartwright, Jared and Grogan, Gideon and Pieber, Bartholomäus and Kroutil, Wolfgang}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, number = {13}, pages = {6965--6969}, publisher = {Wiley}, title = {{Chromoselective photocatalysis enables stereocomplementary biocatalytic pathways}}, doi = {10.1002/anie.202100164}, volume = {60}, year = {2021}, } @article{11965, abstract = {Metallaphotocatalytic cross-coupling reactions are typically carried out by combining homogeneous or heterogeneous photocatalysts with a soluble nickel complex. Previous attempts to realize recyclable catalytic systems use immobilized iridium complexes to harvest light. We present bifunctional materials based on semiconductors for metallaphotocatalytic C−S cross-coupling reactions that can be reused without losing their catalytic activity. Key to the success is the permanent immobilization of a nickel complex on the surface of a heterogeneous semiconductor through phosphonic acid anchors. The optimized catalyst harvests a broad range of the visible light spectrum and requires a nickel loading of only ∼0.1 mol %.}, author = {Reischauer, Susanne and Pieber, Bartholomäus}, issn = {2367-0932}, journal = {ChemPhotoChem}, number = {8}, pages = {716--720}, publisher = {Wiley}, title = {{Recyclable, bifunctional metallaphotocatalysts for C−S cross‐coupling reactions}}, doi = {10.1002/cptc.202100062}, volume = {5}, year = {2021}, } @article{11972, abstract = {Carbon dots have been previosly immobilized on titanium dioxide to generate photocatalysts for pollutant degradation and water splitting. Here we demonstrate that these nanocomposites are valuable photocatalysts for metallaphotocatalytic carbon–heteroatom cross-couplings. These sustainable materials show a large applicability, high photostability, excellent reusability, and broadly absorb across the visible-light spectrum.}, author = {Zhao, Zhouxiang and Reischauer, Susanne and Pieber, Bartholomäus and Delbianco, Martina}, issn = {1463-9270}, journal = {Green Chemistry}, number = {12}, pages = {4524--4530}, publisher = {Royal Society of Chemistry}, title = {{Carbon dot/TiO₂ nanocomposites as photocatalysts for metallaphotocatalytic carbon-heteroatom cross-couplings}}, doi = {10.1039/d1gc01284c}, volume = {23}, year = {2021}, } @article{11974, abstract = {Visible light photocatalysis has become a powerful tool in organic synthesis that uses photons as traceless, sustainable reagents. Most of the activities in the field focus on the development of new reactions via common photoredox cycles, but recently a number of exciting new concepts and strategies entered less charted territories. We survey approaches that enable the use of longer wavelengths and show that the wavelength and intensity of photons are import parameters that enable tuning of the reactivity of a photocatalyst to control or change the selectivity of chemical reactions. In addition, we discuss recent efforts to substitute strong reductants, such as elemental lithium and sodium, by light and technological advances in the field.}, author = {Reischauer, Susanne and Pieber, Bartholomäus}, issn = {2589-0042}, journal = {iScience}, number = {3}, publisher = {Elsevier}, title = {{Emerging concepts in photocatalytic organic synthesis}}, doi = {10.1016/j.isci.2021.102209}, volume = {24}, year = {2021}, } @article{11981, abstract = {The cleavage of benzyl ethers by catalytic hydrogenolysis or Birch reduction suffers from poor functional group compatibility and limits their use as a protecting group. The visible-light-mediated debenzylation disclosed here renders benzyl ethers temporary protective groups, enabling new orthogonal protection strategies. Using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as a stoichiometric or catalytic photooxidant, benzyl ethers can be cleaved in the presence of azides, alkenes, and alkynes. The reaction time can be reduced from hours to minutes in continuous flow.}, author = {Cavedon, Cristian and Sletten, Eric T. and Madani, Amiera and Niemeyer, Olaf and Seeberger, Peter H. and Pieber, Bartholomäus}, issn = {1523-7052}, journal = {Organic Letters}, number = {2}, pages = {514--518}, publisher = {American Chemical Society}, title = {{Visible-light-mediated oxidative debenzylation enables the use of benzyl ethers as temporary protecting groups}}, doi = {10.1021/acs.orglett.0c04026}, volume = {23}, year = {2021}, } @unpublished{12068, abstract = {Metallaphotocatalysis typically requires a photocatalyst to harness the energy of visible-light and transfer it to a transition metal catalyst to trigger chemical reactions. The most prominent example is the merger of photo- and nickel catalysis that unlocked various cross-couplings. However, the high reactivity of excited photocatalyst can lead to unwanted side reactions thus limiting this approach. Here we show that a bipyridine ligand that is subtly decorated with two carbazole groups forms a nickel complex that absorbs visible-light and promotes several carbon–heteroatom cross-couplings in the absence of an exogenous photocatalysts. The ligand can be polymerized in a simple one-step procedure to afford a porous organic polymer that can be used for heterogeneous nickel catalysis in the same reactions. The material can be easily recovered and reused multiple times maintaining high catalytic activity and selectivity.}, author = {Cavedon, Cristian and Gisbertz, Sebastian and Vogl, Sarah and Richter, Noah and Schrottke, Stefanie and Teutloff, Christian and Seeberger, Peter H. and Thomas, Arne and Pieber, Bartholomäus}, publisher = {ChemRxiv}, title = {{Photocatalyst-free, visible-light-mediated nickel catalyzed carbon–heteroatom cross-couplings}}, doi = {10.26434/chemrxiv-2021-kt2wr}, year = {2021}, } @unpublished{12070, abstract = {Controlling the selectivity of a chemical reaction with external stimuli is common in thermal processes, but rare in visible-light photocatalysis. Here we show that the redox potential of a carbon nitride photocatalyst (CN-OA-m) can be tuned by changing the irradiation wavelength to generate electron holes with different oxidation potentials. This tuning was the key to realizing photo-chemo-enzymatic cascades that give either the (S)- or the (R)-enantiomer of phenylethanol. In combination with an unspecific peroxygenase from Agrocybe aegerita, green light irradiation of CN-OA-m led to the enantioselective hydroxylation of ethylbenzene to (R)-1-phenylethanol (99% ee). In contrast, blue light irradiation triggered the photocatalytic oxidation of ethylbenzene to acetophenone, which in turn was enantioselectively reduced with an alcohol dehydrogenase from Rhodococcus ruber to form (S)-1-phenylethanol (93% ee).}, author = {Schmermund, Luca and Reischauer, Susanne and Bierbaumer, Sarah and Winkler, Christoph and Diaz-Rodriguez, Alba and Edwards, Lee J. and Kara, Selin and Mielke, Tamara and Cartwright, Jared and Grogan, Gideon and Pieber, Bartholomäus and Kroutil, Wolfgang}, publisher = {ChemRxiv}, title = {{Switching between enantiomers by combining chromoselective photocatalysis and biocatalysis}}, doi = {10.26434/chemrxiv.13521527}, year = {2021}, } @article{11954, abstract = {The combination of nickel and photocatalysis has unlocked a variety of cross-couplings. These protocols rely on a few photocatalysts that can only convert a small portion of visible light (<500 nm) into chemical energy. The high-energy photons that excite the photocatalyst can result in unwanted side reactions. Dyes that absorb a much broader spectrum of light are not applicable because of their short-lived singlet excited states. Here, we describe a self-assembling catalyst system that overcomes this limitation. Immobilization of a nickel catalyst on dye-sensitized titanium dioxide results in a material that catalyzes carbon–heteroatom and carbon–carbon bond formations. The modular approach of dye-sensitized metallaphotocatalysts accesses the entire visible light spectrum and allows tackling selectivity issues resulting from low wavelengths strategically. The concept overcomes current limitations of metallaphotocatalysis by unlocking the potential of dyes that were previously unsuitable.}, author = {Reischauer, Susanne and Strauss, Volker and Pieber, Bartholomäus}, issn = {2155-5435}, journal = {ACS Catalysis}, number = {22}, pages = {13269–13274}, publisher = {American Chemical Society}, title = {{Modular, self-assembling metallaphotocatalyst for cross-couplings using the full visible-light spectrum}}, doi = {10.1021/acscatal.0c03950}, volume = {10}, year = {2020}, } @article{11966, abstract = {The front cover artwork is provided by the group of Dr. Bartholomäus Pieber at the Max Planck Institute of Colloids and Interfaces (Germany). The image symbolizes the activation of a heterogeneous photocatalyst by visible light and its application for organic synthesis. Read the full text of the Review at 10.1002/cptc.202000014.}, author = {Gisbertz, Sebastian and Pieber, Bartholomäus}, issn = {2367-0932}, journal = {ChemPhotoChem}, number = {7}, pages = {454--454}, publisher = {Wiley}, title = {{Heterogeneous photocatalysis in organic synthesis}}, doi = {10.1002/cptc.202000137}, volume = {4}, year = {2020}, }