Gold‐Palladium Nanocluster Catalysts for Homocoupling: Electronic Structure and Interface Dynamics

Abstract

The gold‐palladium (Au−Pd) bimetallic nanocluster (NC) catalyst in colloidal phase performs the homocoupling reaction of various aryl chlorides (Ar−Cl) under ambient conditions. We have systematically investigated various aspects of the Au−Pd NC catalysts with respect to this homocoupling reaction by using density functional theory (DFT) calculations, genetic algorithm (GA) approaches, and molecular dynamics (MD) simulations. Our findings include the geometric and electronic structures of the Au−Pd NC, the reactive Pd sites on the NC surface, the electron‐donating effects of surrounding polymer matrix, the reaction mechanism of homocoupling reaction and rate‐determining step, the inverse halogen dependence of the reaction, and the solvation dynamics at interface region between NC and polymer matrix in aqueous solution.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

“…(c) Energy profile for the oxidative addition of the second ArCl to the reductive elimination of biphenyl in the pathway I. (a,c) Reproduced with permission from ref . Copyright 2019 Wiley-VCH.…”

“…For instance, AuPd nanoclusters stabilized by poly­( N -vinylpyrrolidone) (PVP) are shown to be efficient catalysts for Ullmann coupling reaction while the monometallic clusters are inactive (see Figure ). Mechanistic study based on theoretical calculations indicate that the Pd ensembles in the AuPd nanoclusters are responsible for the oxidative addition of Ar–Cl) and the role of Au is to improve the stability of the Pd ensembles . The synergy of bimetallic nanoclusters for organic reactions is observed with other reactions, such as hydrosilylation of internal alkynes .…”

Visible Light-Driven, Gold(I)-Catalyzed Preparation of Symmetrical (Hetero)biaryls by Homocoupling of Arylazo Sulfones

“…In addition, the current growing interest for these biaryls is ascribable to their multifaced applications as (stereogenic) ligands, conducting and electroluminescent materials, and key constituents of molecular switches and devices . Thus, it is not surprising that starting from the early synthetic approaches based on the copper-catalyzed coupling of aryl halides under reductive conditions (the so-called Ullmann reaction), an impressive number of transition metal-catalyzed protocols was developed. − In this context, the use of Au salts, complexes, or nanoparticles as the catalysts for homocoupling processes has been widely explored, and different substrates have been successfully employed, including, among the others, aryl boronic acids (in the presence of a stoichiometric amount of an inorganic base), haloarenes (mainly iodides, by following an Ullman-type coupling), and aromatics (via direct C–H bond functionalization under oxidative conditions) . On the other hand, the opportunity to perform efficient and selective syntheses under mild conditions upon visible light irradiation allowed for the emergence of photochemistry as a sustainable synthetic approach.…”

Importance of the Pd and Surrounding Sites in Hydrosilylation of Internal Alkynes by Palladium–Gold Alloy Catalyst

“…Fortunately, it is found that the alloy nanoparticles consisting of two or more kinds of metals show unique catalytic properties due to their different electronic/structural properties and synergic effects compared to the original monometallic nanoparticles. Accordingly, the catalysis based on the alloy catalysts has gained much attention in the field of synthetic chemistry. − In the case of bimetallic catalysts, the palladium–gold (Pd–Au) alloy catalyst is of interest because of the wide variety of catalytic activity, particularly due to the monometallic Pd site. , For example, the Pd–Au alloy nanoparticle shows considerable catalytic activity in the oxidation of alcohols, − polyols, , and hydrocarbons. , The catalytic activity of the Pd–Au alloy nanoparticle was also identified in organic synthesis. − In 2012, the colloidal-phase Pd–Au bimetallic nanoparticle was observed to catalyze Ullmann coupling of aryl chlorides under mild reaction conditions while the monometallic Au or Pd nanoparticle did not show any activity. − Later, Yamamoto and Jin et al reported the 1,4-hydrosilylation of cyclic α,β-unsaturated ketones applying the nanoporous Pd–Au alloy catalyst at elevated temperature . More recently, Miura and Shishido et al have developed highly active supported Pd–Au alloy catalyst for the hydrosilylation of α,β-unsaturated ketones as well as internal alkynes. , They found the catalytic performance was significantly influenced by the atomic ratio of Pd/Au and the supporting material.…”