New aspect of chemoselective hydrogenation utilizing heterogeneous palladium catalysts supported by nitrogen- and oxygen-containing macromolecules
Heterogeneous palladium catalysts supported on nitrogen-containing macromolecules, such as fibroin (Fib), polyethyleneimine (PEI), boron nitride (BN), and molecular sieves (MS), oxygen-containing macromolecules were developed. The Pd/Fib, Pd/PEI, Pd/BN, Pd/MS3A and Pd/MS5A were used for the novel chemoselective hydrogenation of the reducible functionalities. These catalysts were easy to handle and easily prepared by stirring a macromolecule-suspended palladium diacetate solution in methanol at room temperature. The absorption effect of the Pd species to the macromolecules and the catalyst activity were partially controlled by the lone pairs of the nitrogen atoms in the macromolecule. Pd/Fib, Pd/MS or Pd/BN mainly enabled the chemoselective hydrogenation of azide, alkene and alkyne in the presence of other reducible functionalities. Furthermore, the chemoselective semi-hydrogenation of alkynes to alkenes could be achieved using Pd/PEI or Pd/BN with a nitrogen-containing base catalyst.