Palladium and Platinum

Synthesis, catalytic activity, and leaching studies of a heterogeneous Pd-catalyst including an immobilized bis(oxazoline) ligand

The synthesis and characterization of a novel catalytic system including Pd(OAc)(2) attached to a bis(oxazoline) (=BOX) ligand that is covalently bonded to 3-mercaptopropyl-functionalized silica gel is presented. The catalyst was tested for Suzuki-Miyaura reactions of different aryl halides with phenylboronic acid. The heterogeneity of the catalytic system was investigated using different approaches, indicating that there is virtually no Pd leaching into the reaction solution under the applied reaction conditions. Furthermore, our results show that the catalytic system can be reused multiple times without significant loss of stability or structure.

Investigation of Pd Leaching from Supported Pd Catalysts during the Heck Reaction

Palladium supported on amorphous silica, mercapto-functionalized silica, amine functionalized silica, and zeolite Y has been studied as a catalyst in the Heck reaction of iodobenzene with butyl acrylate in the presence of triethylamine base and dimethylformamide solvent. Trapping of soluble Pd with poly(4-vinylpyridine), hot filtration tests during the batchwise Heck reaction, and reaction tests of effluents from a fixed bed continuous reactor support the conclusion that leached Pd is the active phase in the Heck reaction for all of the catalysts tested. Two different paths of Pd leaching that depend on the chemical state of the Pd were elucidated in this study. Oxidative addition of aryl halide to reduced Pd caused leaching of samples containing metallic particles. However, for a zeolite Y sample containing unreduced cationic Pd, the presence of triethylamine base was required to leach Pd into solution. These two paths of Pd leaching are consistent with the generally accepted mechanism of the Heck reaction.