Photoredox Heterobimetallic Dual Catalysis Using Engineered Covalent Organic Frameworks

The functionalization of an imine-based layered covalent organic framework (COF), containing phenanthroline units as ligands, has allowed the obtention of a heterobimetallated material. Photoactive Ir and Ni fragments were immobilized within the porous structure of the COF, enabling heterogeneous light-mediated Csp3–Csp2 cross-couplings. As radical precursors, potassium benzyl- and alkoxy-trifluoroborates, organic silicates, and proline derivatives were employed, which brings out the good versatility of Ir,Ni@Phen-COF. Moreover, in all the studied cases, an enhanced activity and stability have been observed in comparison with analogous homogenous systems.

As control experiment, a blank carbon paste containing only high purity carbon and Nujol was obtained and measured under the same conditions. Thermogravimetric analyses (TGA) were performed on a TGA Q500 Thermobalance from TA instruments, heating the sample from 25 o C to 900 o C at 10 o C/min under air atmosphere.
X Ray Photoelectron Spectroscopy (XPS) were performed with a Phoibos 150 analyzer (SPECS GmbH) in ultra-high vacuum conditions (base pressure 410 -10 mbar) with a monochromatic aluminum K α x-ray source (1486.74 eV) at 300 W. The energy resolution as measured by the FWHM of the Ag 3d 5/2 peak for a sputtered silver foil was 0.62 eV. The binding energy was corrected by using the C 1s line at 284.5 eV as the reference. A flood gun was used during acquisition to compensate the surface charging of the samples.
Qualitative and quantitative Total X-Ray Fluorescence analyses (TXRF) were performed with a benchtop S2 PicoFox TXRF spectrometer from Bruker Nano (Germany) 1,2 . TXRF system was equipped with a Mo X-ray source working at 50 kV and 600 μA, a multilayer monochromator with 80% of reflectivity at 17.5 keV (Mo K α ), a XFlash SDD detector with an effective area of 30 mm 2 and an energy resolution better than 150 eV for 5.9 keV (Mn K α ). For deconvolution and integration commercial Spectra v. 7.5.3 software package from Bruker was used. Previously to the measurements, sample acid digestions were performed in a high pressure and temperature microwave. Acid digestion technology was used by mean of an UltraWAVE digestion system from Millestone (Italy) with a single reaction chamber able of operates up to 199 bar pressure and 270 °C.
Volumetric N 2 sorption isotherms were collected at 77 K (N 2 ) using an ASAP 2460 HD (Micromeritics). Temperature was controlled by using a liquid nitrogen bath.

Synthesis of building blocks and metal complexes.
Synthesis of 1: 3,8-dibromo-1,10-phenanthroline (1 g, 2.96 mmol), (4-formylphenyl)boronic acid (930 mg, 6.20 mmol) and K 2 CO 3 (1.625 g, 8.87 mmol) were introduced into a 100 mL Schlenk equipped with a stir bar. Three vacuum-Ar cycles were performed. Then, 20 mL of purged THF and 4 mL of distilled water were added under Ar atmosphere. Finally, Pd(PPh 3 ) 4 (512 mg, 0.443 mmol) was added under Ar atmosphere. The reaction was heated at 70 0 C during 48 hours in presence of Ar. A white solid was precipitated. Then, the reaction was cool down and filtered. The white solid was washed with water and acetone. Finally, it was recrystallized in a mixture of hot CHCl 3 -acetone, in order to afford white crystals of 1, that were isolated by filtration and dried under vacuum. 1118 mg obtained (97 % of yield).

Synthesis of the Ir precursor.
Step 1 -Synthesis of 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine (L1) 3 Potassium (2,4-difluorophenyl)trifluoroborate (1.1 g, 5 mmol), 2-bromo-5-(trifluoromethyl)pyridine (753 mg, 3.33 mmol), K 2 CO 3 (2.3 g, 16.7 mmol) and Pd(PPh 3 ) 4 (390 mg, 0.33 mmol) were placed into a 100 mL Schlenk equipped with a stir bar. Three vacuum-Ar cycles were performed. Then, 12 mL of degassed THF and 6 mL of degassed distilled water were added. The reaction was stirred at 80 o C under Ar atmosphere for 24 hours. After cooling to room temperature, it was extracted with 3x20 mL of dichloromethane. The organic layers were combined and dried with Na 2 SO 4 , filtrated and evaporated under reduced pressure. After purification by silica gel chromatography (cyclohexane-AcOEt 20:1), L1 was isolated as a white solid (847 mg, 97 %). Step 2 -Synthesis of dimer [(dF(CF 3 )ppy) 2 -Ir-µ-Cl] 2 4 L1 (840 mg, 3.24 mmol) and IrCl 3 (440 mg, 1.47 mmol) were placed into a 100 mL Schlenk equipped with a stir bar. Three vacuum-Ar cycles were performed. Then, 18 mL of degassed 2ethoxyethanol and 6 mL of degassed distilled water were added. The reaction was stirred at 120 o C under Ar atmosphere for 24 hours. After cooling to room temperature, the yellow solid formed was filtrated and gently washed with deionized water and cyclohexane, and finally dried under vacuum. 1.639 g obtained, 75 % yield.  5 A 50 mL Schlenk flask was charged with a stir bar, NiCl 2 (77.7 mg, 0.6 mmol), and 1,10phenanthroline (108,1 mg, 0.6 mmol). Three vacuum/Ar cycles were performed. Then, 5 mL of degassed EtOH were added. The pink reaction mixture was stirred at room temperature overnight. A green solid appeared, indicating the completion of the reaction. The solvent was evaporated under reduced pressure, and the crude was suspended in 10 mL of THF. The green solid was isolated by filtration and dried overnight under vacuum.

Synthesis of PF-Crystalline Laminar COF
A 45 mL solvothermal reactor was charged with TAPB (100.0 mg, 0.285 mmol), BTCA (46.0 mg, 0.285 mmol), 8.9 mL of a mixture of anhydrous dioxane : mesitylene (1:9) and 0.9 mL of 6 M acetic acid in water. The reactor was heated at 120 ˚C for 72 h, yielding a brown solid which was isolated by filtration and washed with DMSO, methanol and THF. The resulting powder was immersed in anhydrous THF for 24 h and dried first at room temperature under vacuum for 12 h, and then at 100 ˚C for 2 h to afford a brown powder. Its characterization agreed well with previous works. 6 Then, an analogous post-functionalization protocol than the used for the synthesis of Ir,Ni@Phen-COF was followed. In a 100 mL round bottom-flask, 140 mg of Crystalline Laminar COF were suspended on 50 mL of dry acetonitrile and 1 mL of aqueous acetic acid 6 M during 30 minutes with an ultrasound bath. Then, [(dF(CF 3 )ppy) 2 -Ir-µ-Cl] 2 (33 mg, 0.022 mmol) and NiCl 2 ·glyme (19.6 mg, 0.089 mmol) were added. The mixture was stirred at 70 o C for 16 hours, yielding a yellow powder that was isolated by filtration and washed with hot DMF, acetonitrile and THF. The resulting powder was washed with acetone using Soxhlet extraction, then filtered and dried first at room temperature under vacuum for 12 h, and then at 100 ˚C for 2 h to afford an orange powder, PF-Crystalline Laminar COF. 138 mg obtained. In order to determine the quantity of Ir and Ni incorporated into the material, quantitative TXRF analyses were performed. Very low quantities of both Ir and Ni can be observed.

S28
General procedure for the light-mediated cross-coupling between potassium benzyltrifluoroborate and aryl bromides An oven-dried 10 mL vial equipped with a magnetic stir bar was charged with catalyst (1.2 mg), corresponding potassium trifluoroborate salt 2 (0.15 mmol) and the corresponding aryl bromide 3 (0.075 mmol). Then, 950 L of dry acetone and 50 L of dry MeOH were added. Finally, 2,6lutidine (30.5 L, 0.26 mmol) was added. The vial was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum / Ar of "freeze-pump-thaw". Then the vial was placed on a blue light LED photoreactor (450 nm) with an Ar balloon and the reaction mixture was stirred at 25 ˚C. The reaction was monitored by TLC and 1 H-NMR. The yield was determined by 1 H-NMR using nitromethane as internal standard. S29 a This result was obtained when the reaction was sealed using a typical rubber septum instead of a PTFE-rubber septum. The reproducibility and the yields were significantly increased. b This material was obtained after the functionalization of the Phen-COF synthesized following the procedure presented in entry 14 of Table S1.

Variation of catalytic activity of the material depending on metal loading and Ir/Ni ratio
For the study of the influence of metal loading in the catalytic activity under the optimal conditions, a series of 6 different Ir,Ni@Phen-COF were obtained variating the amount of metal precursors on the post-functionalization stage. The results obtained appear in the following table:

Recyclability experiment
An oven-dried 10 mL vial equipped with a magnetic stir bar was charged with catalyst (5 mg), corresponding potassium trifluoroborate salt 2a (0.15 mmol) and the corresponding aryl bromide 3b (0.075 mmol). Then, 950 L of dry acetone and 50 L of dry MeOH were added. Finally, 2,6-lutidine (30.5 L, 0.26 mmol) was added. The vial was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum / Ar of "freeze-pump-thaw". Then the vial was placed on a blue light LED photoreactor (450 nm) with an Ar balloon and the reaction mixture was stirred at 25 ˚C. After 26 h of reaction, an aliquot is analyzed by NMR to determine the yield using nitromethane as internal standard. Then, the reaction crude is centrifuged and washed with acetone 3 times. The catalyst is recovered as a yellow powder and was dried under vacuum during 2 hours before the next catalytic run. When the reaction was catalyzed by Ir,Ni@Phen-COF, 7 catalytic runs were performed, producing 0.92 mmol of diphenylmethane 4b.

Leaching experiments
Once the first catalytic run was completed, the reaction was filtered in order to remove the catalyst. The supernatant was transferred to an oven-dried 10 mL vial equipped with a magnetic stir bar. The vial was closed with a PTFE / rubber septum and the reaction mixture was degassed by three cycles vacuum / oxygen of "freeze-pump-thaw". Then the vial was placed on a blue light LED photoreactor (450 nm) and the reaction mixture was stirred at 25 ˚C. The reaction was monitored by 1 H-NMR, observing that it did not advance further for the next 16 h. In addition, ICP-AES measurements confirmed that no detectable Ir and Ni quantities were observed in the supernatant.
Procedure for the light-mediated cross-coupling between potassium tert-butoxymethyltrifluoroborate and aryl bromides.
An oven-dried 10 mL vial equipped with a magnetic stir bar was charged with catalyst (1.2 mg), corresponding potassium (tert-butoxymethyl)trifluoroborate 5 (0.15 mmol) and the corresponding aryl bromide 3e (0.075 mmol). Then, 950 L of dry acetone and 50 L of dry MeOH were added. Finally, 2,6-lutidine (30.5 L, 0.26 mmol) was added. The vial was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum / Ar of "freeze-pump-thaw". Then the vial was placed on a blue light LED photoreactor (450 nm) with an Ar balloon and the reaction mixture was stirred at 25 ˚C. The reaction was monitored by TLC and 1 H-NMR. The yield was determined by 1 H-NMR using nitromethane as internal standard. An oven-dried 10 mL vial equipped with a magnetic stir bar was charged with catalyst (2.5 mg), radical precursor 7 (102 mg, 0.225 mmol) and the corresponding aryl bromide 3e (27.3 mg, 0.15 mmol). Then, 3 L of dry DMF were added. The vial was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum / Ar of "freeze-pump-thaw". Then the vial was placed on a blue light LED photoreactor (450 nm) with an Ar balloon and the reaction mixture was stirred at 25 ˚C. The reaction was monitored by TLC and 1 H-NMR. When total conversion was observed, the crude was filtered through membrane filter and extracted with 3 x 15 mL of diethyl ether and aqueous saturated solution of NaHCO 3 . The organic phases were dried over Na 2 SO 4 , filtered, and evaporated under reduced pressure. The yield was determined by 1 H-NMR using nitromethane as internal standard. Procedure for the light-mediated decarboxylative arylation of -aminoacids with aryl bromides.
An oven-dried 10 mL vial equipped with a magnetic stir bar was charged with catalyst (2.5 mg), Cs 2 CO 3 (73 mg, 0.225 mmol) radical precursor 9 (48.4 mg, 0.225 mmol) and the corresponding aryl bromide 3e (27.3 mg, 0.15 mmol). Then, 4 L of dry DMF were added. The vial was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum / Ar of "freeze-pump-thaw". Then the vial was placed on a blue light LED photoreactor (450 nm) with an Ar balloon and the reaction mixture was stirred at 25 ˚C. The reaction was monitored by TLC and 1 H-NMR. When total conversion was observed, the crude was filtered through membrane filter and extracted with 3 x 15 mL of diethyl ether and aqueous saturated solution of NaHCO 3 .
The organic phases were dried over Na 2 SO 4 , filtered, and evaporated under reduced pressure. The yield was determined by 1 H-NMR using nitromethane as internal standard.

S36
Benchmarking of catalytic results.