Water–Medium Organic Reactions Catalyzed by Active and Reusable Pd/Y Heterobimetal–Organic Framework

Abstract

A Pd/Y heterobimetallic MOF (denoted as Pd/Y-MOF) catalyst is synthesized by coordination of Pd­(II) and Y­(III) with 2,2′-bipyridine-5,5′-dicarboxylate acid (bpydc) under microwave irradiation condition and is characterized by XRD Rietveld refinement, FTIR, Raman, TG-DTA, and XPS. It is shown that the 3D extended framework is constructed by linking Pd­(bpydc)­Cl₂ building blocks via Y­(III) coordinating to carboxylic groups. Pd/Y-MOF exhibits higher catalytic activity than Pd­(bpydc)­Cl₂ in Suzuki-Miyaura coupling reaction and Sonogashira reaction owing to the highly dispersed Pd­(II) sites in the layered structure of Pd/Y-MOF and the cooperative effect between Pd­(II) and Y­(III). The heterogeneity studies provide mechanistic evidence that the reaction proceeds on the surface of Pd­(II) ions in the crystal framework. Thus, Pd/Y-MOF exhibits impressive size selectivity toward substrates. With the small-sized reactants, it displays comparable activities with Pd­(OAc)₂ homogeneous catalyst. However, extremely poor activity in Suzuki-Miyaura coupling reaction with bulk substrates 1-iodonaphthalene and 4-(<i>tert</i>-butyl) iodobenzene is observed due to the inhibition of diffusion into the micropore channels. In addition, Pd/Y-MOF can be easily recycled and reused owing to the high stability of the framework formed by coordination of Y­(III) with carboxylic group. The incorporation of Pd­(II) into the crystal framework of Pd/Y-MOF prohibits the leaching of Pd­(II) active species