Hyper-Cross-Linked Porous Polymer Featuring B–N Covalent Bonds (HCP-BNs): A Stable and Efficient Metal-Free Heterogeneous Photocatalyst

The first example of a porous polymer containing B–N covalent bonds, prepared from a tetraphene B–N monomer and biphenyl as a comonomer, is reported. It was prepared using the solvent knitting strategy, which allows the connection between the aromatic rings of the two monomers through methylene groups provided by an external cross-linking agent. The new polymer exhibited micromeso porosity with an SBET of 612 m2/g, high thermal stability, and potential properties as a heterogeneous photocatalyst, since it is very active in the aza-Henry coupling reaction (>98% of conversion and selectivity). After the first run, the catalyst improves its photocatalytic activity, shortening the reaction time to only 2 h and maintaining this activity in successive runs. The presence of a radical in this structure that remains stable with successive runs makes it a new type of material with potential applications as a highly stable and efficient photocatalyst.

Solvents were dried by elution through a PureSolv Innovative Technology column drying system.
ATR-FTIR spectra were recorded (cm −1 ) on a PerkinElmer Spectrum Two spectrometer with a Fourier equipped with a diamond internal element. 13 C solid-state MAS-NMR measurements were recorded with a Bruker AV400 WB spectrometer.
Thermogravimetric and differential thermal analyses (TGA-DTA) were conducted on a with a TA Instruments Model TA-Q500 analyzer. The samples were heated from 40 to 800 ºC under N 2 atmosphere with a heating rate 10 ºC/min. The photoreactor used the reactions tested was lab-made and has one LED blue lamps of 50 W. The progress of the C-C aza Henry reactions was followed by 1

H-NMR in Varian
Inova 300 MHz and a JEOL JNM-ECZ400R. Figure S1. Photoreactor used (lab-made) and Light-emitting spectrum of the used blue LEDs.

Synthesis of photocatalyst HCP-BNT2Ph
A solution of 0.5 mmol of BN-tetraphene monomer (BNT) and 0.5 mmol of biphenyl in 10 mL of anhydrous dichloroethane was placed in a Schlenk. h. Finally, the polymer was washed with THF under stirring. A green product was obtained as fine powder and was dried at 100°C overnight.

DFT Calculations
The reported structures were optimized at Density Functional Theory level as implemented in Gaussian 16 (3). The geometry optimizations were performed using M062X functional (4) with 6-311++g(d,p) basis set for all atoms. Solvent effects were considered in the calculations applying the polarizable continuum model (IEFPCM) using 1,2-dichloroethane as solvent at 273.15 K. The bonding situation in the complexes was studied using Natural Bond Orbital (5) analysis (NBO, 3.1 version) (6). Main atomic charges (NPA) (7) have been calculated.

Catalytic activity
General procedure: The aza-Henry couplings were done in a glass microreactor. 2-phenyl-1,2,3,4tetrahydroisoquinoline (314 mg, 1.5 mmol), K-BNT2Ph (40 mg, 5 mmol %) and the corresponding nucleophile (115 mmol) were added. The reaction mixture was purged with air and maintained with an air or N 2 balloon (see Table 2). The mixture was stirred under blue LED light (50 W) irradiation, the time indicated in Table 1 (4h or 2h). The catalyst was separated by filtration and the solvent was removed by rotation under vacuum. The residue was analyzed by 1 H-NMR.

Recycling experiments:
The recyclability of K-BNT2Ph was evaluated using nitromethane as a nucleophile. After completion of the first reaction (4 h), the K-BNT2Ph catalyst was separated from the reaction medium by Büchner funnel, washed with acetone, and dried at 90-100 °C under vacuum overnight. Afterward, it was used in a new reaction for 2 hours, since when studying its kinetics, it is observed that it reaches the maximum conversion in that time.
The solvent was removed after each operation as above and the corresponding residues were analyzed by 1 HNMR. This procedure was repeated three more times.      Figure S16. Scavengers tested in the aza-Henry photoreaction using HCP-BNT2Ph as photocatalyst.