Sustainable Catalysis: Rational Pd Loading on MIL‐101Cr‐NH₂ for More Efficient and Recyclable Suzuki–Miyaura Reactions

Abstract

Palladium nanoparticles have been immobilized into an amino-functionalized metal–organic framework (MOF), MIL-101Cr-NH 2 , to form Pd@MIL-101Cr-NH 2 . Four materials with different loadings of palladium have been prepared (denoted as 4-, 8-, 12-, and 16 wt %Pd@MIL-101Cr-NH 2 ). The effects of catalyst loading and the size and distribution of the Pd nanoparticles on the catalytic performance have been studied. The catalysts were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), N 2 -sorption isotherms, elemental analysis, and thermogravimetric analysis (TGA). To better characterize the palladium nanoparticles and their distribution in MIL-101Cr-NH 2 , electron tomography was employed to reconstruct the 3D volume of 8 wt %Pd@MIL-101Cr-NH 2 particles. The pair distribution functions (PDFs) of the samples were extracted from total scattering experiments using high-energy X-rays (60 keV). The catalytic activity of the four MOF materials with different loadings of palladium nanoparticles was studied in the Suzuki–Miyaura cross-coupling reaction. The best catalytic performance was obtained with the MOF that contained 8 wt % palladium nanoparticles. The metallic palladium nanoparticles were homogeneously distributed, with an average size of 2.6 nm. Excellent yields were obtained for a wide scope of substrates under remarkably mild conditions (water, aerobic conditions, room temperature, catalyst loading as low as 0.15 mol %). The material can be recycled at least 10 times without alteration of its catalytic properties.

Highly Functionalized Biaryls via Suzuki–Miyaura Cross‐Coupling Catalyzed by Pd@MOF under Batch and Continuous Flow Regimes

“…After repeated recycling runs, some Pd agglomeration becomes evident under TEM. [18] These results suggest that even if Pd leaching occurs, the redeposition process is extremely efficient and products completely free of contamination can be obtained.…”

“…The material of choice was 8 wt % Pd@MIL-101-NH 2 , which we recently reported to have the optimal amount of palladium impregnated in MIL-101-NH 2 for this type of applications. [18,19] The large majority of these functionalized (hetero)aromatic iodides reacted in excellent yields at mild temperatures (20 or 50 8C) and in very short reaction times (0.5-4 h), leading to the facile synthesis of 3 a-f despite the presence of one or several heteroatoms. Even hindered aryl iodides (2 b) and lengthy substrates (2 f) afforded the coupling products 3 b and 3 f, important building blocks in the synthesis of pharmaceutically active intermediates, [20] in high yields (85 % and 82 %, respectively) after short reaction times (1 and 4 h, respectively).…”

“…Encouraged by the results presented above and the facile recyclability of this catalyst under batch conditions, previously demonstrated by our group, [18] we proceeded to investigate the behavior of Pd@MIL-101-NH 2 under continuous-flow conditions. [28] The catalyst was packed in an Omnifit glass column (d = 10 mm; 70 mm max adjustable bed height).…”

“…ChemSusChem 2015, 8, 123 -130 www.chemsuschem.org 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Experimental Section General procedure for the Suzuki-Miyaura cross-coupling reactions 8 wt % Pd@MIL-101-NH 2 was prepared according to the reported procedure. [18] Unless otherwise stated, in a 20 mL regular vial or Biotage microwave vial, the arylboronic acid (0.83 mmol), the aryl halide (0.158 g, 0.75 mmol), K 2 CO 3 (0.207 g, 1.5 mmol), and 8 wt % Pd@MIL-101Cr-NH 2 (10 mg, 7.5 mmol, 1 mol % Pd) were added together with a magnetic stirring bar. EtOH (5 mL) and H 2 O (5 mL) were added.…”

Chemistry of Metal-organic Frameworks Monitored by Advanced X-ray Diffraction and Scattering Techniques

“…The different amounts of Pd nanoparticles were immobilized within the MIL-101(Cr)-NH 2 material for Suzuki-Miyaura catalytic reactions. 144 The distribution of Pd nanoparticles was determined by XTS. The method includes the extracting of pair distribution function (PDF) from Fourier-transformation of the total scattering intensities (including Bragg peaks and diffuse scattering).…”