Water-medium organic reactions catalyzed by active and reusable Pd/Y Heterobimetal-organic framework

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)Cl ₂ 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-(tert-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.