Small Pd Nanoparticles Supported in Large Pores of Mesocellular Foam: An Excellent Catalyst for Racemization of Amines

Abstract

Highly dispersed palladium nanoparticles (1-2 nm) supported in large-pore mesocellular foam (MCF; 29 nm) were synthesized. The Pd-nanocatalyst/MCF system was characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The performance of the Pd nanocatalyst obtained was examined for amine racemization. The Pd nanocatalyst showed higher activity and selectivity toward racemization of (S)-1-phenylethyl amine than any other amine racemization catalyst reported so far and it could be reused several times. Our data from TEM and XRD suggest a restructuring of the Pd nanocatalyst from amorphous to crystalline and an increase in Pd nanocatalyst size during the racemization reaction. This led to an unexpected increase of activity after the first use. The Pd nanocatalyst obtained can be integrated with other resolving processes of racemic organic compounds to increase the yield of chiral organic products.

Cycloisomerization of Acetylenic Acids to γ-Alkylidene Lactones using a Palladium(II) Catalyst Supported on Amino-Functionalized Siliceous Mesocellular Foam

“…In the presence of benzoquinone the Pd(0) species formed in situ is efficiently reoxidized to active Pd(II), and the recovered heterogeneous catalyst maintains its high catalytic and can be reused four times without detectable deactivation. In a control experiments, we found that in the presence of benzoquinone also the Pd(0)-AmP-MCF 30,31 was activated and shown to catalyze the lactonization of 4-pentynoic acid in good yield.…”

“…24,25,29 We have recently reported on the preparation of a heterogeneous catalyst based on Pd nanoparticles immobilized on amino-functionalized siliceous mesocellular foam (Pd(0)-AmP-MCF). 30,31 Mesocellular foam (MCF) is a mesoporous material that has proven to be an excellent support for both chemical as well as biological catalysts, mainly due to its high surface area, high pore volume and adjustable pore size. [32][33][34] Several organic transformations have successfully been accomplished with our novel Pd(0)-catalyst, such as aerobic oxidation of primary and secondary alcohols, 31 transfer effect of the change in the different reaction parameter, the reaction time for the screen was chosen to 1 h. The optimization of the reaction conditions commenced with a screening of a series of bases.…”

Combined heterogeneous metal/organic catalysts for eco-friendly synthesis

“…Among the reactions explored, we had developed an allylic alcohol oxidation/Michael/ carbocyclization catalytic relay using a bench-stable palladium complex (Pd(PPh 3 ) 4 ) and a simple chiral amine with molecular oxygen as the terminal oxidant [48]. Palladium is a powerful and versatile transition metal, which can be immobilized on various solid supports and next be used as a heterogeneous catalyst for efficient chemical reactions [49][50][51][52][53][54][55][56]. In this context, we recently disclosed that enantioselective carbocyclizations could be performed by the synergistic action of a heterogeneous palladium catalyst and a chiral amine co-catalyst [57].…”

Nanocatalysts for Hiyama, Stille, Kumada, and Negishi C–C Coupling Reactions

“…Other siliceous materials, such as mesocellular foams, ordered mesoporous materials, and mesoporous spheres, have been similarly used for nanoparticle stabilization. 78,79 Choudhary et al, for instance, has used layered double hydroxides for encapsulating Pd-NPs that are active for Stille C C coupling reactions. 80 Merrifield resins, usually used for automated peptide synthesis, have also been used as metal nanoparticle supports, albeit with added functionalities.…”