A metal-organic catalyst for C-H bond activation
Ljubljana, April 16, 2020 - Metal-catalysed activation of C–H bonds has attracted much attention over the past decade for its potential to efficiently introduce complexity in organic molecules, without the need for prefunctionalization. One of the most interesting C–H activation reactions is the oxidative alkenylation of arenes, which yields vinylated aromatic motifs that are abundantly present in pharmaceuticals, natural products, agrochemicals, and other fine chemicals.
In this work the authors developed a heterogeneous single-site catalyst that combines the precise active site design of organometallic complexes with the efficient recovery of solid catalysts. The catalyst is based on the porous metal-organic material MOF-808 ([Zr6(μ3-O)4(μ3–OH)4(btc)2(CH3COO)6]; btc3– = 1,3,5-benzenetricarboxylate), functionalized by the tetrahydrothiophene-2,5-dicarboxylic acid ligands, which effectively entrap and stabilize Pd(II) centres. In the large cages of MOF-808 with an internal pore diameter of 18.4 Å the introduced ligands and Pd(II) centres do not limit the diffusion of reactants and products. The high oxidation state of Zr(IV) centres ensures a strong bond between the Zr6-cluster and the carboxylate group of the ligand, yielding chemically and thermally stable functionalized materials.
The developed heterogeneous single-site catalyst has a three times higher turnover frequency (8.4 h–1 reached after 1 h of reaction time) than the standard Pd(OAc)2 and can be ranked among the most active heterogeneous catalysts ever reported for the nondirected oxidative alkenylation of arenes. It promotes the oxidative alkenylation of a broad range of electron-rich arenes. Its practical applicability was demonstrated by the gram-scale synthesis of industrially relevant products.
The structure of the new catalyst was characterized in detail via solid-state nuclear magnetic resonance spectroscopy by Andraž Krajnc and Gregor Mali from the Department of Inorganic Chemistry and Technology of the National Institute of Chemistry.
For further information please contact: andraz.krajnc[at]ki.si