Modifying electron injection kinetics for selective photoreduction of nitroarenes into cyclic and asymmetric azo compounds

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 products from the nitroarenes photoreduction. The strategy includes the orchestration of capsule openings to control the electron injection kinetics of electron donors, and the capsule’s pocket to encapsulate more than one nitroarene molecules, facilitating a condensation reaction between the in situ formed azanol and nitroso species to produce azo product. The conceptual microenvironment catalyst endows selective conversion of asymmetric azo products from different nitroarenes, wherein, the estimated diameter and inclusion Gibbs free energy of substrates are used to control and predict the selectivity of products. Inhibition experiments confirm a typical enzymatic conversion, paving a new avenue for rational design of photocatalysts toward green chemistry.


Synthesis of dinitro substrates
2-nitrotoluene (1.00 g, 7.5 mmol) was dissolved in tetrahydrofuran at 0 ⸰ C, followed by addition of potassium butoxide as bases. After 10 min agitation, the reaction mixture was then added bromine (1.60 g, 10.0 mmol) and further stirred for 10 min before addition of 250 mL of ice/water. The precipitate was filtered and the filtrate was extracted with CH2Cl2 (3 × 50 mL). The organic layers were combined and washed with saturated sodium thiosulfate solution and saturated sodium. After dried over Na2SO4, the solution was concentrated under reduced pressure. The final product 2,2'-Dinitrodibenzyl was purified by crystallization and collected as a white solid. 1 To a solution of o-nitrophenol (1.0 mmol) in DMSO (20 mL), anhydrous potassium carbonate (1.0 mmol) was added in small portion and the reaction mixture was stirred continuously with the inert atmosphere. Then the dibromo substrate (0.5 mmol) was injected into the reaction solution and was further stirred for 2 h. After the completion of the reaction, the mixture was extracted with ethyl acetate (2 × 10 mL) and washed successively with HCl (2 N, 2×5 mL), and cold water. After treated with Na2SO4, the finale product was collected by evaporating the solvent under reduced pressure. 2

Crystallography
The intensities were collected on a Bruker SMART APEX CCD diffractometer equipped with a graphite-monochromated Mo-Kα (λ = 0.71073 Å) radiation source; the data were acquired using the SMART and SAINT programs 3,4 . The structures were solved by direct methods and refined on F 2 by full-matrix least-squares methods using the SHELXTL version 5.1 software 5 .

Crystal data for H1
Crystal data for H1: C375H401Co6F24N38O40P16 For the refinement of H1, except the solvent molecules, other non-hydrogen atoms were refined anisotropically, hydrogen atoms were fixed geometrically at calculated distances and allowed to ride on the parent non-hydrogen atoms. Two of the benzene rings in the ligands, and several F aoms in the counter PF6ions were disordered into two parts with the site occupied factors of each part being fixed as 0.5, respectively. The related bond distances in the solvent molecules were restrained as idealized values. Thermal parameters on adjacent atoms of several solvent molecules were restrained to be similar.
In the checkcif file, the A alert is caused by the weak diffraction intensity of the poor quality crystal, and the "short inter D…A contact" is caused by the presence of partly occupied solvent molecules with highly disordered atoms. The crystal analysis here could offer the structure of the cage compound and estimate the size of the cavity, which is helpful for the research of the catalytical chemistry of the cage compound.   The cage was used as the recipient in the docking calculation. The models of the cage were refined by adding hydrogen atoms, followed by the assignment of Kollman charges, fragmental volumes, and atomic solvation parameters to adhesive by means of AutoDock Tools. For the ligand, Fluorescein molecule was refined by adding hydrogen atoms in a similar manner to that for adhesive. Next, Gasteiger partial charges were assigned to the ligands, and nonpolar hydrogens were merged. All torsions were allowed to rotate during docking. The Lamarckian genetic algorithm was used to determine the appropriate binding positions, orientations, and conformations of the ligands. Default parameters were used, except for the number of runs was set to 100. The blind docking strategy was used with a 54 Å × 66 Å × 68Å (x, y and z, respectively). grid box which ensured sufficient spaced to cover the entire surface of the cage. The Lamarckian genetic algorithm was chosen with default parameters, which was set to 100 for more accurate docking results. The best docking mode of the host-guest complex was chosen based on the binding energy score, clustering, and chemical reasonableness.

Kinetics experiments of photocatalytic of nitro substrates reduction using Na2S as reductant.
During the reaction process, the tracking of the reaction process was carried by extraction of 50 μL reaction mixture every 5 minutes with a long needle and followed by HPLC analysis after the quick flush through the silica gel. The reaction rates in the first 5 minutes were regarded as the initial rate of the reactions.     14. Characterization of the azo products.