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Photocatalyzed reduction of dinitro substrates using different reductants Isolated yields are reported. Standard conditions for cyclic azo product conversion were as follows: 1.0 mol% HF (0.50 μmol), substrate (0.05 mmol) and tripropylamine (1.20 mmol) under light irradiation for 10 h. Standard conditions for diamino product conversion were as follows: 1.0 mol % of HF (0.50 μmol), substrate (0.05 mmol) and Na2S (1.20 mmol) under light irradiation for 2 h.
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Modifying the reactivity of substrates by encapsulation is essential for microenvironment catalysts. Herein, we report an alternative strategy that modifies the entry behaviour of reactants into the microenvironment and substrate inclusion thermodynamics related to the capsule to control the electron injection kinetics and the selectivity of produc...
Citations
... 24 So far, few catalysts have been reported to further reduce the unsaturated bond (C═C, C═O, N═O) by using the H species product generated by green water. [25][26][27] In particular, the literature of the photocatalytic semihydrogenation reaction of alkynes reduced by proton from H 2 O is scarce. [28][29][30] In this work, we reported the "one-pot" tandem conversion of a photocatalytic hydrogen evolution reaction and an alkyne semi-hydrogenation reaction, which achieved high conversion and selectivity of alkynes to Z-alkenes (Scheme 1). ...
The semi‐hydrogenation of alkyne to form Z‐olefins with high conversion and high selectivity is still a huge challenge in the chemical industry. Moreover, flammable and explosive hydrogen as the common hydrogen source of this reaction increases the cost and danger of industrial production. Herein, we connect the photocatalytic hydrogen evolution reaction and the semi‐hydrogenation reaction of alkynes in series and successfully realize the high selective production of Z‐alkenes using low‐cost, safe, and green water as the proton source. Before the cascade reaction, a series of isomorphic metal–organic cage catalysts ( Co x Zn 8− x L 6 , x = 0, 3, 4, 5, and 8) are designed and synthesized to improve the yield of the photocatalytic hydrogen production. Among them, Co 5 Zn 3 L 6 shows the highest photocatalytic activity, with a H 2 generation rate of 8.81 mmol g ⁻¹ h ⁻¹ . Then, Co 5 Zn 3 L 6 is further applied in the above tandem reaction to efficiently reduce alkynes to Z‐alkenes under ambient conditions, which can reach high conversion of >98% and high selectivity of >99%, and maintain original catalytic activity after multiple cycles. This “one‐pot” tandem reaction can achieve a highly selective and safe stepwise conversion from water into hydrogen into Z‐olefins under mild reaction conditions.
... Among azobenzene modifications, so-called diazocines enjoy special attention because the relative thermodynamical stability of their photoswitchable isomers is reversed compared to the parent azobenzene: the bent (Z) isomer is thermodynamically favored, Among azobenzene modifications, so-called diazocines enjoy special attention because the relative thermodynamical stability of their photoswitchable isomers is reversed compared to the parent azobenzene: the bent (Z) isomer is thermodynamically favored, and the elongated (E) form is metastable [23]. Synthetic procedures to obtain functionalized diazocines include the reduction of 2,2'-dinitrobibenzyl [24], oxidation of 2,2'-diaminobibenzyl [25] and the cascade amidation reaction of 2,2'-dihalobibenzyl compounds via Boc-protected diazocines [26]. The photoconversion of the yellow (Z) to the red (E) isomer occurs at an irradiation wavelength of 405 nm, resulting in an energetic increase of 37.08 kJ/mol (Scheme 1) [27]. ...
Unlike azobenzene, the photoisomerization behavior of its ethylene-bridged derivative, diazocine, has hardly been explored in synthetic polymers. In this communication, linear photoresponsive poly(thioether)s containing diazocine moieties in the polymer backbone with different spacer lengths are reported. They were synthesized in thiol-ene polyadditions between a diazocine diacrylate and 1,6-hexanedithiol. The diazocine units could be reversibly photoswitched between the (Z)- and (E)-configurations with light at 405 nm and 525 nm, respectively. Based on the chemical structure of the diazocine diacrylates, the resulting polymer chains differed in their thermal relaxation kinetics and molecular weights (7.4 vs. 43 kDa) but maintained a clearly visible photoswitchability in the solid state. Gel permeation chromatography (GPC) measurements indicated a hydrodynamic size expansion of the individual polymer coils as a result of the Z→E pincer-like diazocine switching motion on a molecular scale. Our work establishes diazocine as an elongating actuator that can be used in macromolecular systems and smart materials.
This review summarises and discusses aryl amine and azide syntheses from aryl halides employing azides. The majority of the reported reactions proceed with copper catalysis or mediation. Often, an aryl azide is formed in the first step, which is then reduced in situ to an aryl amine in a second step. The occurrence of the second step, the reduction, depends on the chosen reaction conditions and the substrates. The formation of only aryl azides through Cu‐mediated C−N bond formations is discussed, followed by mediated and catalytic aryl azide reduction employing different catalytic systems, and azidation with in situ azide reduction to amines, viz. azidation‐amination strategies. The azidation‐amination allows for the synthesis of complex heterocycles in multi‐step one‐pot procedures, of which several are summarised here. Examples of the application of azidation‐amination for synthesising important aryl amines employed in or as biologically active compounds, catalysis and materials science are also summarised. Finally, conducted control reactions have been collected and discussed in combination with mechanistic proposals. This literature survey allows us to pinpoint design criteria for the azide reduction to valuable amines, which includes the choice of reaction conditions such as solvent system and additives, involved metal and promising substrates.
A new site-selective methodology for C-H nitration of 2H-indazoles has been accomplished at the C7 position using iron(III) nitrate. This strategy enables a practical access to an array of 7-nitroindazoles...
Hydrogen atom transfer from commonly used solvents to nitroarenes occurred. Such solvents required C(sp³)H‐C(sp³)H bond adjacent to oxygen atoms, such as 1,4‐dioxane, tetrahydrofuran, alkanol, ethylene glycol, glycerol and bis(2‐methoxyethyl) ether. The transformation was transition‐metal free and the reduced nitroarenes were trapped by naphthols and their analogues at ortho‐position. The protocol provided a favourable and efficient route to access ortho‐arylaminonaphthols and a possible mechanism is depicted.
Modifying redox potential of substrates and intermediates to balance pairs of redox steps are important stages for multistep photosynthesis but faced marked challenges. Through co‐clathration of iridium photosensitizer and imine substrate within one packet of a metal‐organic capsule to shift the redox potentials of substrate, herein, we reported a multiphoton enzymatic strategy for the generation of heterocycles by intramolecular C‐X hydrogen evolution cross‐couplings. The cage facilitated a pre‐equilibrium substrate‐involving clathrate that cathodic shifts the oxidation potential of the substrate‐dye‐host ternary complex and configuration inversion of substrate via spatial constraints in the confined space. The new two photon excitation strategy enabled the precise control of the multistep electron transfer between each pair (photosensitizer, substrate and the capsule), endowing the catalytic system proceeding smoothly with an enzymatic fashion. Three kinds of 2‐subsituted (‐OH, ‐NH2, and ‐SH) imines and N‐aryl enamines all give the corresponding cyclization products efficiently under visible light irradiation, demonstrating the promising of the microenvironment driven thermodynamic activation in the host‐dye‐substrate ternary for synergistic combination of multistep photocatalytic transformations.
Modifying redox potential of substrates and intermediates to balance pairs of redox steps are important stages for multistep photosynthesis but faced marked challenges. Through co‐clathration of iridium photosensitizer and imine substrate within one packet of a metal‐organic capsule to shift the redox potentials of substrate, herein, we reported a multiphoton enzymatic strategy for the generation of heterocycles by intramolecular C−X hydrogen evolution cross‐couplings. The cage facilitated a pre‐equilibrium substrate‐involving clathrate that cathodic shifts the oxidation potential of the substrate‐dye‐host ternary complex and configuration inversion of substrate via spatial constraints in the confined space. The new two photon excitation strategy enabled the precise control of the multistep electron transfer between each pair (photosensitizer, substrate and the capsule), endowing the catalytic system proceeding smoothly with an enzymatic fashion. Three kinds of 2‐subsituted (−OH, −NH2, and −SH) imines and N‐aryl enamines all give the corresponding cyclization products efficiently under visible light irradiation, demonstrating the promising of the microenvironment driven thermodynamic activation in the host‐dye‐substrate ternary for synergistic combination of multistep photocatalytic transformations.
