Chemoselective single-site Earth-abundant metal catalysts at metal–organic framework nodes

Earth-abundant metal catalysts are critically needed for sustainable chemical synthesis. Here we report a simple, cheap and effective strategy of producing novel earth-abundant metal catalysts at metal–organic framework (MOF) nodes for broad-scope organic transformations. The straightforward metalation of MOF secondary building units (SBUs) with cobalt and iron salts affords highly active and reusable single-site solid catalysts for a range of organic reactions, including chemoselective borylation, silylation and amination of benzylic C–H bonds, as well as hydrogenation and hydroboration of alkenes and ketones. Our structural, spectroscopic and kinetic studies suggest that chemoselective organic transformations occur on site-isolated, electron-deficient and coordinatively unsaturated metal centres at the SBUs via σ-bond metathesis pathways and as a result of the steric environment around the catalytic site. MOFs thus provide a novel platform for the development of highly active and affordable base metal catalysts for the sustainable synthesis of fine chemicals.

. The disappearance of ν µ3O-H band (~3640 cm -1 , KBr) suggests post-synthetic metalation at Zr 3 -µ 3 -OH sites. Each sample was dried under vacuum at 100 °C overnight before sample preparation. (b) IR spectra of UiO-CoH (black) and UiO-CoD (red). We assigned the weak peak at ~2350 cm -1 to the Co-H stretching, which disappeared in the UiO-CoD analog. The even weaker Co-D stretching peak is expected to be buried under the strong carboxylate stretching at ~1662 cm -1 .

Supplementary Tables
Supplementary Fits of the EXAFS region were performed using the Artemis program of the IFEFFIT package. Fits were performed with a k-weight of 2 in R-space. Refinement was performed by optimizing an amplitude factor S 0 2 and energy shift ΔE 0 which are common to all paths, in addition to parameters for bond length (ΔR) and Debye-Waller factor (σ 2 ). The fitting models were obtained from Material Studio 7.0, based on the crystal structure of UiO-68 or Zr 6 (OH) 4 O 4 (OMc) 12 (reference). Unique parameters for ΔR and σ 2 were provided for all scattering paths in all fits.    Supplementary Supplementary  Figure 8).

Test of "heterogeneity" of the MOF catalysis in alkyl C-H borylation.
In a glovebox, UiO-CoCl (1.0 mg, 0.2 mol % Co) was charged into a small vial and 0.5 mL THF was added.
Then, 15 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox.
The solid was centrifuged out of suspension and washed twice with THF and then once with p-xylene. B 2 pin 2 (43.0 mg, 0.169 mmol) in 2.0 mL p-xylene was added to the vial and the resultant mixture was transferred to a Schlenk tube. The tube was heated under nitrogen at 103 °C for 48 h to obtain the alkyl boronate ester in 89% yield as determined by GC analysis.
In a glovebox, UiO-CoCl (1.0 mg, 0.2 mol % Co) was charged into a small vial and 0.5 mL THF was added.
Then, 15 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox.
The solid was centrifuged out of suspension and washed twice with THF and then once with p-xylene. Investigation of substrate size effect on catalytic activity in benzylic C-H borylation.
In a glovebox, UiO-CoCl (1.0 mg, 0.2 mol % Co) was charged into a small vial and 0.5 mL THF was added.
Then, 15 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox.
The solid was centrifuged out of suspension and washed with THF twice and then once with heptane. B 2 pin 2 (43.0 mg, 0.169 mmol) and p-xylene (41.8 µL, 0.34 mmol) in 2.0 mL heptane was added to the vial and the resultant mixture was transferred to a Schlenk tube. The tube was heated under nitrogen at 103 °C for 2.5 d to obtain the alkyl boronate ester in 94% yield as determined by GC analysis.
The borylation reaction of 4-tert-butyl-toluene and 3,5-di-tert-butyl-toluene were conducted using the same procedure described above under identical reaction conditions and the results are summarized in Supplementary Table   7. The yield of the boronate ester decreased dramatically on increasing the size of the substrates. Therefore, this experiment demonstrates that catalysis is facilitated by Co-sites both inside the pores and on the outside of the MOFs, not the framework surface alone.

Test of "heterogeneity" of the MOF catalysis in alkene hydrogenation.
In were then added. The resulting mixture was sealed in a pressure vessel under nitrogen and stirred at 80 o C for 3 days.
After cooling to room temperature, the reaction mixture was mixed with H 2 O (20 mL), and centrifuged to obtain solid crude compound. The solid was then washed sequentially with H 2 O, dimethoxylethane, and THF to remove impurities and dried in vacuo to afford 1,4-bis(4-methoxycarbonylphenyl)benzene as a white solid (420 mg,  Figure 1).   4 and refined by a full-matrix least-squares procedure using OLEX2 5 software packages (XL refinement program version 2014/7) 6 . Crystallographic data and details of the data collection and structure refinement are listed in Supplementary Table 1.

X-Ray Absorption Spectroscopic Analysis
X-ray absorption data were collected at Beamline 9-BM-C at the Advanced Photon Source (APS) at Argonne National Laboratory. Spectra were collected at the iron or cobalt K-edge in transmission mode. The X-ray beam was monochromatized by a Si(111) monochromater and detuned by 25% to minimize harmonics. A metallic iron or cobalt foil standard was used as the reference for energy calibration and was measured simultaneously with experimental samples. The incident beam intensity (I 0 ) was measured by an ionization chamber with 30% N 2 and 70% He gas composition. Data was collected in three regions: a pre-edge region -150 to -20 eV (5 eV step size, dwell time 1.0 s), XANES region -20 to 50 eV (0.5 eV step size, dwell time 1.0 s), and EXAFS region 3.62 Å -1 to 13.93 Å -1 (0.05 Å -1 step size, dwell time increased linearly from 1.0 to 3.9 seconds over the region to facilitate higher k-weighted data processing). All energies are listed relative to the elemental Fe K-edge (7112 eV) of Co K-edge (7709 eV). Multiple X-ray absorption spectra were collected at room temperature for each sample. Samples were ground and mixed with polyethyleneglycol (PEG) and packed into a 6-shooter sample holder to achieve adequate absorption length.
Data were processed using the Athena and Artemis programs of the IFEFFIT package based on FEFF 6. 7,8 Prior to merging, spectra were calibrated against the reference spectra (metallic Co or Fe) and aligned to the first peak in the smoothed first derivative of the absorption spectrum, background removed, and spectra processed to obtain a normalized unit edge step.

A typical procedure for UiO-Co catalyzed benzylic C-H borylation of arenes.
In a glovebox, UiO-CoCl (1.0 mg, 0.2 mol % Co) was charged into a small vial and 0.5 mL THF was added.
Then, 15 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox.
The solid was centrifuged out of suspension and washed with THF twice and then once with m-xylene. Quantification of hydrogen production in the reaction of UiO-CoH with HBpin.
In a J. Young NMR tube, 2.25 mg of UiO-CoH in heptane was added. Then, HBpin (1.2 equiv. w.r.t. Co) was added to the mixture and then the tube was sealed quickly. The tube was left for 4 h. The headspace gas (total volume 1.5 mL) was analyzed by gas chromatography to give a hydrogen content of 2.8157% (v/v). The total amount of hydrogen in the headspace was then calculated to be: The amount of hydrogen expected from the reaction of UiO-68-CoH and HBpin is 3.85 mol, which is close to the experimental value.

Determination of the rate law for UiO-Co-catalyzed benzylic C-H borylation of p-xylene.
The rate law of the benzylic C-H borylation of p-xylene was determined by the method of initial rates (up to
In a glovebox, UiO-CoCl (1.0 mg, 0.4 mol % Co) was charged into a small vial and 0.5 mL THF was added.
Then, 15 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox.
The solid was centrifuged out of suspension and washed with THF twice and then once with toluene. The solid suspended in 2 mL toluene was transferred to a Schlenk tube and (EtO) 3  General procedure for UiO-Co catalyzed hydrogenation of olefins. In a nitrogen-filled glove box, UiO-CoCl (0.5 mg, 0.1 mol % Co) in 1.0 mL THF was charged into a glass vial. NaBEt 3 H (10 μL, 1.0 M in THF) was then added to the vial and the mixture was stirred for 1 h. The solid was then centrifuged, washed with THF twice, and transferred to a glass vial in 0.5 mL THF. The olefin substrate (0.34 mmol) was added to the vial. Then the vial was placed in a Parr reactor which was sealed under nitrogen atmosphere and charged with hydrogen to 40 bar. After stirring at room temperature for 12 h -3 d, the pressure was released and the MOF catalyst was removed from the reaction mixture via centrifugation. Mesitylene (internal standard) was added to the organic extracts and the yield of the product was determined by integrations of the product and mesitylene peaks in the 1 H NMR spectra in CDCl 3 .

A typical procedure for UiO-Co catalyzed hydrogenation of olefins.
In a glovebox, UiO-CoCl in THF (0.5 mg, 0.1 mol% Co) was charged into a small vial and 0.5 mL THF was added. Then, 10 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox. The solid was centrifuged out of suspension and then washed with THF two times. Then, the black solid in 0.5 mL THF was transferred to a vial containing 0.5 mL THF solution of trans-α-methylstilbene (65.9 mg, 0.34 mmol). The vial was placed into a Parr pressure reactor in a nitrogen-filled glovebox. The reactor was then pressurized to 40 bar. After stirring at room temperature for 2 d, the solid was centrifuged out of suspension and extracted three times with THF. The combined organic extracts were concentrated in vacuo to afford crude 1,2-diphenylpropane in quantitatively yield, which was sufficiently pure as shown in 1 H NMR spectrum (Supplementary Figure 39).

Reuse and recycle experiment procedure for UiO-Co-catalyzed hydrogenation of 1-octene.
In a glovebox, a vial was charged with UiO-CoCl (2.0 mg, 0.01 mol % Co) in 1 mL THF. 20 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox. The solid was centrifuged out of suspension and washed with THF two times. Then, the solid in 1.0 mL THF was transferred to a vial and 1-octene (2 mL, 12.7 mmol) was added. The vial was placed into a Parr pressure reactor in a nitrogen-filled glovebox. The reactor was then pressurized to 40 bar. After 2 h, hydrogen was released and the solid was centrifuged out of suspension and extracted 2-3 times with THF in the glovebox. Quantitative yield of n-octane was obtained as determined by GC-MS and 1 H NMR with mesitylene as the internal standard. The recovered solid catalyst was added to a vial containing 1-octene (2 mL, 12.7 mmol) in 1.0 mL THF. The vial was placed into a Parr pressure reactor in a nitrogen-filled glovebox. The reactor was then pressurized to 40 bar.
After 16 h, the solid was centrifuged out of suspension and extracted 2-3 times with THF in the glovebox. n-Octane was obtained in quantitative yield as determined by GC-MS and 1 H NMR with mesitylene as the internal standard.
UiO-Co was recovered and reused at least 16 times without loss of catalytic activity.

Procedures for UiO-Co-catalyzed hydroboration of carbonyl compounds.
In a glovebox, UiO-CoCl (1.0 mg, 0.01 mol % Co) was charged into a small vial and 0.5 mL THF was added.
Then, 8 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox.
The solid was centrifuged out of suspension and washed with THF two times. Then, THF was removed and the aldehyde or ketone (6.78 mmol) and pinacolborane (7.40 mmol) were added. The resultant mixture was transferred to a Schlenk tube and then heated at 60 °C outside of the glovebox and the progress of the reaction was monitored by GC. After complete conversion, the solid was centrifuged out of suspension and extracted with hexane 2-3 times. The combined organic extracts were concentrated in vacuo to yield the pure product.
A typical procedure for UiO-Co catalyzed hydroboration of ketones.
In a glovebox, UiO-CoCl (1.0 mg, 0.01 mol % Co) was charged into a small vial and 0.5 mL THF was added.
Then, 8 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox.
The solid was centrifuged out of suspension and washed with THF two times. Then, THF was removed and acetophenone (0.81 g, 6.78 mmol) and pinacolborane (0.95 g, 7.40 mmol) was added. The resultant mixture was transferred to a Schlenk tube and then heated at 60 °C outside of the glovebox for 2 d. Then, the solid was centrifuged out of suspension and extracted with hexane 2-3 times. The combined organic extracts were concentrated in vacuo to yield 4,4,5,5-Tetramethyl-2-(1-phenylethoxy)-1,3,2-dioxaborolane as a colorless oil (1.63 g, 6.57 mmol, 96.9%). The crude borate ester was sufficiently pure for further uses as shown by 1 H NMR spectrum (Supplementary Figure 41).
In a glovebox, UiO-CoCl (10 mg, 0.2 mol% Co) was charged into a small vial and 0.5 mL THF was added.
Then, 8 µL NaBEt 3 H (1.0 M in THF) was added to the vial and the mixture was stirred slowly for 1 h in the glovebox.
The solid was centrifuged out of suspension and washed with THF two times. Then, THF was removed and alkene (3.39 mmol) and pinacolborane (5.08 mmol) were added. The resultant mixture was transferred to a Schlenk tube and then heated at 100 °C outside of the glovebox and the progress of the reaction was monitored by GC. After complete conversion, the solid was centrifuged out of suspension and extracted with hexane 2-3 times. The combined organic extracts were concentrated in vacuo to yield the pure product.

A typical procedure of catalytic alkene hydroboration
In a glovebox, UiO-CoCl (8 mol Co) was charged into a small vial and 0.5 mL THF was added. Then, 80