Background: The N-aryl piperazines are an important component of many drug products
used for the treatment of malaria, depression, anxiety and Parkinson diseases. Buchwald-Hartwig
amination is the latest and well-known reaction for Pd catalyzed direct synthesis of N-aryl piperazine
from aryl halides. Although several Pd-ligand systems have already been discovered for this conversion,
Pd nanoparticles are recently being used for this useful coupling reaction due to their recyclability
and durability. Metal nanoparticles show enhanced catalytic activity compared to their bulk counterparts
due to increased surface area at the edges and corners. The use of green algal extract in place
of chemical ligands makes this process more environment-friendly and cost-effective. In this research,
Pd nanoparticles synthesized using green alga C. Vulgaris were utilized as an alternative approach
for the coupling reaction during the preparation of N-aryl piperazines.
Methods: Synthesized Pd nanoparticles from C. Vulgaris were characterized by FTIR, SEM and
XRD techniques. The catalytic activity of the synthesized nanoparticles was monitored for the synthesis
of N-aryl piperazines by Buchwald-Hartwig reaction. The synthesized N-aryl piperazines were
characterized by NMR, FTIR and mass analysis.
Results: A very good catalytic activity of the synthesized Pd nanoparticles from green alga Chlorella
vulgaris extract was observed. The green alga not only reduces the size of the Pd metal to nanoparticles
but also acts as a green ligand for reduction of Pd(II) to Pd(0) during nanoparticle synthesis. Using
this Pd nanoparticles-green ligand system, several N-aryl piperazines were synthesized in good to
excellent yields. Reaction conditions for better conversion were optimized. The comparative advantage
of the catalytic system with recently published works on Buchwald-Hartwig C-N coupling
reaction is given. Recyclability and durability of the catalyst were explored and the results were
found to be promising. A plausible mechanism of Pd nanoparticle catalyzed reaction is also proposed.
Conclusion: Catalytic activity of the Pd nanoparticle synthesized from Chlorella vulagris in the synthesis
of N-aryl piperazines by Buchwald-Hartwig reaction is reported first time to the best of our
knowledge and understanding. The green approach of Pd catalyst to facilitate the reaction and its environmental
impact is the main characteristic of the process.