A molecular Pd(II) complex incorporated into a MOF as a highly active single-site heterogeneous catalyst for C–Cl bond activation
The organic palladium complex Pd(H2bpydc)Cl2 (H2bpydc = 2,2′-bipyridine-5,5′-dicarboxylic acid) was immobilized on a porous metal–organic framework UiO-67 (Zr6O4(OH)4(bpdc)6, bpdc = para-biphenyldicarboxylate) using a direct incorporation strategy. The use of a large amount of the H2bpdc ligand (90 mol% of the mixed ligands) that can't chelate the Pd complex allowed the formation of isolated Pd single active sites uniformly distributed in the MOF network. Pd(II) doped UiO-67 is isostructural to the parent UiO-67 framework, with a high surface area and pore volume of ca. 2000 m2 g−1 and 0.79 cm3 g−1, respectively. The material was highly efficient in the catalytic conversion of aryl chlorides, showing remarkably higher activity than the homogeneous Pd counterparts. High yields were achieved in Heck and Suzuki–Miyaura coupling reactions of chloroarenes bearing a wide range of substituents. Moreover, the catalyst was recoverable and reusable, giving essentially identical activity after at least 5 cycles. The combination of the advantages of both homogeneous molecular Pd catalysts and solid MOF structures in this system may bring new opportunity in the development of highly active heterogeneous palladium catalysts for a variety of Pd-catalyzed transformations.