Switching electronic effects of UiO-67-Pd using fluorinated ligands for catalytic oxidative arylation of bio-based furfuryl alcohol

Abstract

An efficient and novel approach is proposed for oxidative arylation of bio-based furfuryl alcohol (FA) to aryl furans (AFs), a versatile monomer of photoelectric materials, in the presence of UiO-67-Pd(F) with phenanthroline/ bipyridine, and poly-F substituted phenyl ligands as the mixture linkers. The results of control experiments and theoretical calculations reveal that the –F on the phenyl linkers efficiently tunes the electron-deficient nature of Pd through the Zr₆ clusters bridges, which favors the adsorption and activation of the furan ring. Furthermore, the conjugation of different nitrogen-containing ligands facilitates Pd coordination for the Heck-type insertion and subsequent electrophilic palladation, respectively. As a result, the oxidative arylation of FA derivatives is substantially enhanced because of these electronic and steric synergistic effects. Under the optimized conditions, 72.2% FA conversion and 74.8% mono aryl furan (MAF) selectivity are shown in the Heck-type insertion. Meanwhile, 85.3% of MAF is converted, affording 74.8% selectivity of final product (AFs) in the subsequent electrophilic palladation reaction. This process efficiency is remarkably higher than that with homogeneous catalysts. In addition, furan-benzene polymer obtained from the halogen-free synthesis catalyzed by UiO-67-Pd(F) show significantly better properties than that from conventional Suzuki coupling method. Therefore, the present work provides a new insight for useful AFs synthesis by oxidative arylation of bio-furan via rational tunning the metal center micro-environment of heterogeneous catalyst.