Direct Synthesis of in-Situ Chirally Modified Palladium Nanocrystals without Capping Agents and Their Application in Heterogeneous Enantioselective Hydrogenations

Abstract

Shape-controlled metal nanocrystals possess the advantages of specific atomic arrangement on the surface and uniform size, which can act as ideal model catalysts for heterogeneous enantioselective catalytic studies. Nevertheless, capping agents are commonly retained on the surface of the as-synthesized metal nanocrystals, which may hinder the necessary interaction between the substrate and the chiral modifiers coadsorbed on the metal surface for chiral recognition. In this paper, we directly synthesized dendritic or cubic palladium nanocrystals in-situ modified by chiral modifiers such as cinchonidine (CD) or S-proline through a one-pot strategy by replacing the conventional capping agents with the chiral modifiers. The as-prepared CD-modified Pd nanodendrite catalyst already exhibits enantioselectivity in the asymmetric hydrogenation of (E)-α-phenylcinnamic acid without subsequent chiral modification processes. The in-situ S-proline-modified Pd nanocube catalyst shows higher enantioselectivity than nanocubes synthesized with polyvinylpyrrolidone (PVP) or cetyltrimethylammonium bromide (CTAB) as traditional capping agents in asymmetric hydrogenation of acetophenone. Chiral modifiers have dual functions (both shape-control agents and catalytic functional molecules), which can not only eliminate the adverse effect of traditional capping agents (such as PVP) on heterogeneous enantioselective hydrogenations but also simplify the follow-up chiral modification step of metal catalysts, providing a simple and efficient synthetic protocol to directly prepare in-situ chirally modified metal nanocrystal catalysts.

Shape-Controlled Synthesis of Concave Pt and Willow-Like Pt Nanocatalysts via Electrodeposition with Hydrogen Adsorption/Desorption and Investigation of Their Electrocatalytic Performances toward Ethanol Oxidation Reaction

“…In addition, no universal method has been found to remove surfactants in different synthesis methods which employed different surfactants . Another strategy to synthesize shaped nanocatalysts with a clean surface is to avoid introducing any surfactants during the process of synthesis; thus, it can guarantee the cleanness of the shaped nanocatalysts as synthesized. − A representative work of the second strategy was the successful synthesis of tetrahexahedral platinum NCs enclosed with (730) high index facets using the square-wave potential (SWP) electrodeposition method . In this method, they employed no surfactants, and the shape-controlled synthesis was achieved just by repeated oxygen adsorption and desorption on the surface or subsurface of the nanoparticles.…”

Facile preparation of hierarchical micro-nano FeF3·0.33H2O by a one-pot method with dual surfactants

“…Compared with FF(nothing), FF(0.5PVP) is stronger at the position of 1600-1650 cm −1 , which is caused by the superposition of the bending δ(H 2 O) bond and characteristic C=O stretching vibrational band at 1670 cm −1 of PVP. In addition, FF(0.5PVP) has several more characteristic peaks, including the C-N stretching vibrational band of N-C=O (1494 cm −1 ), C-H scissoring vibrational mode (1424 cm −1 ), C-H bending vibrational band (1373 cm −1 ) and C-N stretching vibrational mode of N-CH 2 (1288 cm −1 ); they all belong to PVP [38]. However, FF(0.5CTAB 0.5PVP) and FF(1.5CTAB 0.5PVP) did not find the characteristic peak belonging to PVP and CTAB, which further confirmed our guess that the dissolution of FF@PVP by CTAB could better remove the PVP mixed in FF(0.5PVP).…”

Biomimetic Chiral Nanomaterials with Selective Catalysis Activity

“…Chiral cinchonidine or S‐proline was used for one‐pot synthesis of dendritic or cubic Pd NPs by replacing the conventional capping agents. [ 44 ] The fabricated chiral Pd catalyst exhibited asymmetric hydrogenation catalysis activity against (E)‐α‐phenylcinnamic acid with moderate ee as 34% and a yield of 49.8%. The method introduced heterogeneous enantioselective hydrogenations with facile chiral modification step of metal catalysts.…”

“…[ 8 , 42 , 43 ] The synthetic methodology regarding chemical precursors, chiral ligands, growth conditions, and controlling of material compositions and geometries was comprehensively discussed. In the current review, we assess different types of selective catalysis activities including asymmetric hydrogenation, [ 44 , 45 ] asymmetric Aldol reaction, [ 46 , 47 ] selective oxidation, [ 48 , 49 ] asymmetric electroreduction, [ 38 ] and so on. The applications of chiral nanomaterials in enantioselective biocatalysis in‐site in living systems were also explored.…”