Development of in situ generated nanoparticle catalysts for selective hydrogenation reactions

Abstract

Catalytic semihydrogenation of alkynes and azoarenes are considered the most efficient and straightforward approaches for the preparation of corresponding (Z)-alkenes and hydrazoarenes. Considering the wide use of (Z)-alkenes and hydraozoarenes in manufacturing fine chemicals or synthesizing pharmaceutically active compounds, various catalytic methods have been developed and is currently developed. However, in developing new catalysts, predicting the combination of metals, ligands, and supports that would exhibit maximum synergistic effect is difficult. Furthermore, preparation of catalysts commonly require multiple synthesis steps which involve the use of chemical reagents, solvents, and energy. These processes fare poorly from the green matrices perspective and limit their applicability for development of environmentally benign and sustainable hydrogenation reactions. In this light, an in situ generated catalytic system offers advantages over conventional approaches by eliminating time-consuming catalyst synthesis or characterization steps. To this end, catalytic systems comprising commercially available metal salts, ligands, and supports would likely be attractive. In this dissertation, an in situ generation of nanoparticle catalysts using commercially available metal salts and ammonia borane (NH3BH3) is described which were applied for the transfer semihydrogenation of alkynes to (Z)-alkenes and azoarenes to hydrazoarenes. First, in situ generation of copper nanoparticles for (Z)-selective semihydrogenation of alkynes is described. Then, to enhance the catalytic efficiency of these in situ generated copper nanoparticles, various supports were introduced. For efficient screening of catalytic efficiency of various in situ generated copper nanoparticle-support composites for (Z)-selective semihydrogenation, fluorescence-based high-throughput screening method was applied. Finally, development of in situ generated bimetallic nanoparticle catalysts for transfer semihydrogenation of azoarenes to hydrazoarenes is described.