Background: Organic polymer supported palladium nanoparticles (NPs) are important for
use as heterogeneous catalyst in various organic reactions. This works describes Pd Nps immobilized on
to polystyrene-based ion-exchange resin surface for use as catalyst in the reduction of nitrobenzenes.
The heterogeneous catalyst was found useful for hydrogenation of nitro group under both catalytic
transfer hydrogenation (CTH) as well as by using molecular hydrogen (H2).
Methods: The catalyst was prepared from Amberlite IRA 900 Cl after rinsing with formic acid (10%)
and subsequent treatment with Na2PdCl4 in DMF. The resulting Pd Nps immobilized resins was designated
as VersaCat Pd and used for CTH of nitrobenzenes in the presence of H-donors (sodium formate,
formic acid, hydrazine hydrate) and also for hydrogenation with H2 gas. The catalyst was characterized
by FT-IR, MAS-NMR, SEM, TEM and XPS and surface morphologies were studied before and after
Results: Hydrogenations of nitrobenzenes under CTH using different H-source and direct use of H2 gas
were achieved successfully with good to excellent yields. Reactions were performed under mild conditions
and high degree of chemoselectivity was also observed. The catalyst was recyclable, used for six
consecutive runs with appreciable conversions and showed higher activity (> 3 times) in terms of metalcontent
than commercially available Pd/C (10%) in the hydrogenation of nitrobenzenes using H2 gas.
The TEM images showed that Pd Nps are evenly distributed with size 50-200 mm on polymeric matrices
and there was no significant changes observed after the first catalytic run. However, considerable
rupture of the polymeric surface occurred after six runs, as seen from SEM studies.
Conclusion: The present study establishes high catalytic efficiency and chemoselectivity of the newly
developed organic polystyrene-based resin-soaked Pd NPs (VersaCat Pd) in the reduction of nitrobenzenes.
Both CTH and hydrogenation using H2 gas were successfully done. Interestingly, hydrazine hydrate
offered excellent control over chemoselectivity under CTH conditions and allowed clean conversion
from nitro to amine, while keeping a chloro substitutent unaffected. Hydrogenation using molecular
H2 gave maximum TOF. Easy preparation, high efficacy, TOF, chemoselectivity, and versatile applications
are notable features for this heterogeneous palladium catalyst (VersaCat Pd). These features
are often required in chemical industries.