Synthesis of a Novel Cellulose Microencapsulated Palladium Nanoparticle and Its Catalytic Activities in Suzuki-Miyaura and Mizoroki-Heck Reactions

Palladium nanoparticles microencapsulated by cellulose (CelMcPd(0)) were, for the first time, developed via reduction of Pd(OAc)(2) or PdCl2 in a cellulosic ionic liquid solvent, in which the Pd-II species were synchronously reduced to Pd-0 nanoparticles in situ with the ionic liquid itself or with NaBH4, followed by enveloping the Pd-0 cores with cellulosic films using anhydrous ethanol as a coagulant. The as-prepared novel hybrid material CelMcPd(0) proved to be a versatile and highly catalytically efficient, recyclable, and robust catalyst for a range of phosphine-free crossing Suzuki-Miyaura and Mizoroki-Heck reactions under mild aerobic conditions. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and inductively coupled plasma atomic emission spectroscopy (ICP-AES) measurements have been used to characterize the catalysts. The results revealed that the palladium particles are mostly spherical in shape and estimated to be range of 5-20 nm in CelMcPd(0)-1, 5-40 nm in CelMcPd(0)-2, and 3-15 nm in CelMcPd(0)-3. Moreover, homogeneous catalysis in Suzuki-Miyaura couplings catalyzed by CelMcPd(0)-1 was evidenced from CS2 poisoning tests. After the completion of the reaction, catalyst separation could be easily achieved by simple filtration, and the catalyst could be recycled at least six times without any loss of its high catalytic activity.