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Applicability of nickel-catalysed aryl amination and etherification driven by sunlight and NCNCNx. Yields were determined by ¹H NMR signal referenced to 1,3-benzodioxole. aReaction heated to 55 °C. bDifferent reaction condition, see Section B in the ESI.†c40 hours illumination
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Nickel-catalyzed aryl amination and etherification are driven with sunlight using a surface-modified carbon nitride to extend the absorption of the photocatalyst into a wide range of the visible region. In...
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A visible light-mediated heterogeneous photocatalytic cyanomethylarylation of alkenes with acetonitrile has been established using K-modified carbon nitride (CN-K) as a recyclable semiconductor photocatalyst. This protocol, employing readily accessible alkyl N-hydroxyphthalimide (NHPI) ester as a radical initiator, allows the efficient construction...
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... Therefore, incorporating these privileged bipyridyl-based Ni catalysts into solid-state sensitizer materials holds great potential to furnish a novel heterogeneous platform for metallaphotoredox catalysis. The early research that employed carbon nitride (C 3 N 4 ), perovskite, quantum dot (QDs) as heterogeneous photocatalyst in dual catalysis could only realize partial recycling due to the combined use of homogeneous Ni/ligand [23][24][25][26][27][28][29] . More recently, one approach has been developed to immobilize the engineered Ni complex containing carboxylic/phosphoric acid groups on the surface of dye-/carbon dotsensitized titanium dioxide or carbon nitride photocatalyst 30,31 . ...
The development of heterogeneous metallaphotocatalysis is of great interest for sustainable organic synthesis. The rational design and controllable preparation of well-defined (site-isolated) metal/photo bifunctional solid catalysts to meet such goal remains a critical challenge. Herein, we demonstrate the incorporation of privileged homogeneous bipyridyl-based Ni-catalysts into highly ordered and crystalline potassium poly(heptazine imide) (K-PHI). A variety of PHI-supported cationic bipyridyl-based Ni-catalysts (LnNi-PHI) have been prepared and fully characterized by various techniques including NMR, ICP-OES, XPS, HAADF-STEM and XAS. The LnNi-PHI catalysts exhibit exceptional chemical stability and recyclability in diverse C−P, C−S, C−O and C−N cross-coupling reactions. The proximity and cooperativity effects in LnNi-PHI significantly enhances the photo/Ni dual catalytic activity, thus resulting in low catalyst loadings and high turnover numbers.
... The early research that employed carbon nitride (C 3 N 4 ), perovskite, and quantum dot (QDs) as heterogeneous photocatalysts in dual catalysis could only realize partial recycling due to the combined use of homogeneous Ni/ligand. [23][24][25][26][27][28][29] More recently, one approach has been developed to immobilize the engineered Ni complex containing carboxylic/phosphoric acid groups on the surface of dye-/carbon dot-sensitized titanium dioxide or carbon nitride photocatalyst. 30,31 Another attractive strategy was to incorporate Ni(II) and photosensitizing Ir centers into metal/covalent organic frameworks (MOFs/COFs)/flexible polymers containing chelating bpy/phen sites or directly embed Ni(II) in a photosensitive bpy-functionalized COF or poly-Czbpy. ...
The development of heterogeneous metallaphotocatalysis is of great interest for sustainable organic synthesis. The rational design and controllable preparation of well-defined (site-isolated) metal/photo bifunctional solid catalysts to meet such goals remain a critical challenge. Herein, we demonstrate the incorporation of privileged homogeneous bipyridyl-based Ni-catalysts into highly ordered and crystalline potassium poly(heptazine imide) (K-PHI). A variety of PHI-supported cationic bipyridyl-based Ni catalysts (LnNi-PHI) have been prepared and fully characterized by various techniques, including NMR, ICP-OES, XPS, HAADF-STEM, and XAS. The LnNi-PHI catalysts exhibit exceptional chemical stability and recyclability in diverse C−P, C−S, C−O, and C−N cross-coupling reactions. The proximity and cooperativity effects in LnNi-PHI significantly enhance the photo/Ni dual catalytic activity, thus resulting in low catalyst loadings and high turnover numbers.
... [25][26][27][28] The heterogeneous nature of CN x allow easy isolation and reuse, which is a significant advantage over homogeneous photocatalysts. [29][30][31][32] To overcome associated challenges of the use of CN x in dual catalysis with molecular co-catalysts, e.g., with Ni polypyridyl complexes, [33][34][35][36][37] we and others have recently introduced Ni-deposited carbon nitride as a fully heterogeneous photo-catalytic system to perform CÀ O cross-coupling reactions. [38,39] Ni-mpg-CN x has been synthesized and characterized according to a previously reported procedure and details are presented in the Supporting Information (see Figures S1-S4 for transmission electron microscopy (TEM), powder X-ray diffraction, attenuated total reflectance infrared and UV/Vis spectroscopy). ...
The synthesis of primary anilines via sustainable methods remains a challenge in organic synthesis. We report a photocatalytic protocol for the selective synthesis of primary anilines via cross‐coupling of a wide range of aryl/heteroaryl halides with sodium azide using a photocatalyst powder consisting of nickel(II) deposited on mesoporous carbon nitride (Ni‐mpg‐CNx). This heterogeneous photocatalyst contains a high surface area with a visible light‐absorbing and adaptive “built‐in” solid‐state ligand for the integrated catalytic Ni site. The method displays a high functional group tolerance, requires mild reaction conditions, and benefits from easy recovery and reuse of the photocatalyst powder. Thereby, it overcomes the need of complex ligand scaffolds required in homogeneous catalysis, precious metals and elevated temperatures/pressures in existing protocols of primary anilines synthesis. The reported heterogeneous Ni‐mpg‐CNx holds potential for applications in the academic and industrial synthesis of anilines and exploration of other photocatalytic transformations.
... Another important advantage of the practical potential of heterogeneous catalysts is recyclability 33 . As shown in Supplementary Fig. 3, the catalyst could be recovered and reused for at least ve cycles without signi cant loss in its catalytic performance between 4-chlorobenzonitrile and H 2 O. ...
The proximity of different active sites in multi-catalytic systems is crucial in influencing the catalytic reactions, i.e. , to occur or to be accelerated. Here we reported a heterogeneous metallaphotocatalyst prepared by embedding Ni(II) species in a photosensitive covalent organic framework (COF). A concerted triad catalytic behavior executed by electron, hole, and Ni species triggered a dramatic catalytic enhancement on the activation of aryl chlorides with water to phenols. It demonstrated a 50-fold increment in its activity when compared to homogeneous analog, e.g., NidabpyBr 2 . Also, it was able to tolerate a broad range of functional groups even for those hardly achieved by the thermal catalysts. Based on the detailed study, the proximity of the photoactive COF and Ni(II) sites facilitates rapid electron transfer to produce Ni(I) active sites for the oxidative addition. Meanwhile, the photogenerated holes oxidized water to hydroxyl radical, which then attacked Ni(III) intermediates to complete the catalytic cycle.
... These results demonstrated the great potential of gas-liquid-solid segmented flow in the field of heterogeneous photocatalysis. This process can also be applied in other photocatalytic synthesis of fine chemicals, including but not limited to the bifunctionalization of arenes and heteroarenes [62], esterification of carboxylic acids with aryl halides [63], aryl amination and etherification [64], and C-C coupling of methanol into ethylene glycol reaction [65]. However, it should be pointed out that the throughput of the present microreactor was insufficient in regard to industrial application, which can be overcome by "numbering up" strategy. ...
Difficult handling the solid catalysts remains one of the pain points in the continuous flow photochemistry. In this work, the gas-liquid-solid segmented flow was employed in the photocatalytic production of azo- compounds (azoxybenzene and azobenzene) from nitrobenzene using graphitic carbon nitride (g-C3N4) as solid catalyst. Compared with the batch reactor, the photocatalytic reaction rate was greatly improved in the microreactor, and the reaction time was shortened from 180 min of the batch to 7.5 min for near-full conversion of nitrobenzene. The effects of various reaction parameters (temperature, light source power, catalyst content) in the continuous system were examined, and the reaction kinetic was found in first order. The photocatalytic reaction performance was very sensitive to the gas-liquid-solid segmented flow conditions, which needed to be carefully tuned. With the help of high-speed camera and micro particle image velocimetry (µ-PIV) techniques, it was identified that the increasing inert gas fraction resulted in more stable segmented flow with shorter liquid segments, favoring the reaction rate. With a high gas fraction, the intensity of recirculation in the liquid segments was strengthened by the increasing total flow rate, enhancing the local mass transfer, thereby benefiting the photocatalytic reaction. Overall, the continuous microreactor reached 5.6 times higher productivity per volume (26.1 mmol/h*L) of azo- compounds than the batch reactor under the same conditions. The successful photosynthesis of azo- compounds demonstrated the great potential of the presented gas-liquid-solid segmented flow, and the findings of this work provide useful guidance on its future application in other heterogeneously catalyzed reactions.
... [11,29] The external quantum efficiency (EQE) for the coupling reaction with Ni-mpg-CN x was calculated by assuming that one photon is consumed for a molecule of product (although we note that the number of photons required is not unequivocally known, see below). [40] We obtained an EQE of 2.26 AE 0.1 % at l = 447 (see Supporting Information for more detail). Light-dark experiments showed no product formation in the dark following an irradiation period (Figure S14), which suggests that even though the Ni catalytic cycle is ideally self-sustainable, continuous irradiation is necessary to avoid the deactivation of Ni I /Ni III species by carbon nitride matrix. ...
Ni‐deposited mesoporous graphitic carbon nitride (Ni‐mpg‐CNx) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross‐coupling reactions. The dual catalytic Ni‐mpg‐CNx is demonstrated for C–O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good‐to‐excellent yields (60–92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron‐withdrawing, ‐donating and neutral groups. The heterogeneous Ni‐mpg‐CNx can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system.
... Similarly,the scope of aryl halides was also limited to electron-poor aryl bromides.A nother drawback is the long reaction time for many cases.V ery recently,N ocera and coworkers developed an ew type of surface-modified carbon nitride, NCN CN x ,w hich absorbs sunlight over an extended spectral range (Scheme 16 B). [47] Thus,e fficient and sustainable photoredox nickel-catalyzed aryl amination and etherification driven by readily available sunlight using NCN CN x as the heterogeneous photocatalyst was realized. ...
The formation of C‐heteroatom bonds represents an important type of bond‐forming reaction in organic synthesis and often provides a fast and efficient access to privileged structures found in pharmaceuticals, agrochemical and materials. In contrast to conventional Pd‐ or Cu‐catalyzed C‐heteroatom cross‐couplings under high‐temperature conditions, recent advances in homo‐ and heterogeneous Ni‐catalyzed C‐heteroatom formations under mild conditions are particularly attractive from the standpoint of sustainability and practicability. The generation of NiIII and excited NiII intermediates facilitate the reductive elimination step to achieve mild cross‐couplings. This review provides an overview of the state‐of‐the‐art approaches for mild C‐heteroatom bond formations and highlights the developments in photoredox and nickel dual catalysis involving SET and energy transfer processes; photoexcited nickel catalysis; electro and nickel dual catalysis; heterogeneous photoredox and nickel dual catalysis involving graphitic carbon nitride (mpg‐CN), metal organic frameworks (MOFs) or semiconductor quantum dots (QDs); as well as more conventional zinc and nickel dual catalyzed reactions.
... [11,29] The external quantum efficiency (EQE) for the coupling reaction with Ni-mpg-CN x was calculated by assuming that one photon is consumed for a molecule of product (although we note that the number of photons required is not unequivocally known, see below). [40] We obtained an EQE of 2.26 AE 0.1 % at l = 447 (see Supporting Information for more detail). Light-dark experiments showed no product formation in the dark following an irradiation period (Figure S14), which suggests that even though the Ni catalytic cycle is ideally self-sustainable, continuous irradiation is necessary to avoid the deactivation of Ni I /Ni III species by carbon nitride matrix. ...
A Ni‐deposited carbon nitride material was developed as a fully heterogeneous dual photocatalyst. Visible light‐driven C–O cross‐coupling is demonstrated free of organic ligands and additives. This dual catalytic system operates with very low nickel loadings and the heterogeneous photocatalyst can be easily recycled.
Abstract
Ni‐deposited mesoporous graphitic carbon nitride (Ni‐mpg‐CNx) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross‐coupling reactions. The dual catalytic Ni‐mpg‐CNx is demonstrated for C–O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good‐to‐excellent yields (60–92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron‐withdrawing, ‐donating and neutral groups. The heterogeneous Ni‐mpg‐CNx can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system.
... By order of importance, photocatalysis comes first, with monomeric heptazines and COFs, then sensing applications, using both COFs and MOFs, while gas storage applications are more specific of MOFs because of their nanoporosity. 135 on photocatalysis (in this case the hydrogen evolution reaction (HER)) triggered the appearance of hundreds of similar publications (excluding sheptazine-containing polymers), on so-called "g-CN" or "(graphitic) carbon nitride" or "C 3 N 4 " photocatalytic properties, 136 a field recently well reviewed. 137 It is absolutely surprising that the field of photocatalysis with monomeric sheptazines has basically received almost no attention, except from the groups of Schlenker and, more recently, Audebert and Masson. ...
This review gives an account on the fast expanding field of monomeric (or molecular) heptazines, at the exclusion of their various polymeric forms, often referred to as carbon nitrides. While examples of monomeric heptazines were extremely limited until the beginning of this century, the field has started expanding quickly since then, as has the number of reports on polymeric materials, though previous reviews did not separate these fields. We provide here a detailed report on the synthetic procedures for molecular heptazines. We also extensively report on the different achievements realized from these new molecules, in the fields of physical chemistry, spectroscopy, materials preparation, (photo)catalysis, and devices. After a comprehensive summary and discussion on heptazines syntheses and characteristics, we show that starting from well-defined molecules allows a versatility of approaches and a wide tunability of the expected properties. It comes out that the field of monomeric heptazines is now emerging and possibly heading toward maturity, while diverging from the one of polymeric carbon nitrides. It is likely that this area of research will quickly surge to the forefront of the search for active organic molecules, with special attention to the domains of catalysis and organic-based functional materials and devices.
