Computational Study on Cycloisomerization/Oxidative Dimerization of Aryl Propargyl Ethers Catalyzed by Gold Nanoclusters: Mechanism and Selectivity

Abstract

A theoretical analysis of the cycloisomerization and oxidative dimerization of phenyl propargyl ether catalyzed by the Au 38 cluster is performed by means of density functional theory. The role of the cationic gold species is also clarified. The substituent effect at the para site of phenyl is studied to explore the selectivity of cycloisomerization and oxidative dimerization. Phenyl propargyl ether preferred to adsorb at the T1 site of the Au 38 surface with an adsorption energy of −10.61 kcal/mol. The 6-endo pathway to give 2Hchromene is the most feasible pathway, with an energy barrier of 20.50 kcal/mol in dichloroethane solvent. The energy barriers of the 5-exo and oxidative dimerization pathways in dichloroethane solvent are 25.81 and 30.14 kcal/mol, respectively. 2H-Chromene is the main product of the cycloisomerization of phenyl propargyl ether catalyzed by the gold cluster. The presence of the cationic gold species can increase the yield of dimeric 2H-chromene, which is in agreement with experiment results. The binding strength between the active sites and 2H-chromen-3-yl is crucial for oxidative dimerization. Substituents at the para site of phenyl have only a slight influence on the 6-endo pathway, except for the methoxyl group. The differences in the energy barriers between cycloisomerization and oxidative dimerization are in agreement with the ratio of 2Hchromenes and 2H,2′H-4,4′-bichromenes obtained in experiments. The selectivity for the 6-endo/dimeric pathways is sensitive to the substituents of the substrates and the electronic prosperities of the active site of the catalysts. Our theoretical results are in agreement with the product distribution and phenomena in experiments.

A DFT Insight into Hashmi Phenol Synthesis Catalyzed by M6@Au32 (M=Ag, Cu, Pd, Pt, Ru, Rh) Core–Shell Nanoclusters

“…All transition states were further confirmed by the nudged elastic band (NEB) calculations or relaxed potential energy surface scans . Many theoretical studies indicated that the variation of the geometric structure of the Au 38 cluster may be neglected during the reaction process . Hence, the position of the M 6 @Au 32 clusters were fixed to those in the isolated clusters during structural optimizations.…”

“…During the reaction process, four bonds are broken and four new bonds are formed. In our previous work, we analyzed the alkyne activation reactions in detail, including the cycloisomerization of 1,6‐enyne and the cycloisomerization/oxidative dimerization of phenyl propargyl ether, which are catalyzed by Au 38 cluster . We also investigated the full reaction mechanism of ω‐alkynylfuran cycloisomerization using Au 38 as the catalyst .…”

DFT insights into the cycloisomerization of ω-alkynylfuran catalyzed by planar gold clusters: mechanism and selectivity, as compared to Au(i)-catalysis

“…The interaction between the alkyne fragment and Au 3 is similar to that of alkyne fragments of 1,6-enyne and aryl propargyl ether with the surface gold atom of the Au 38 clusters. 22,23 The adsorption of substrate causes the net transfer of electron from Au 3 fragment to substrate fragment (the natural charge on the Au 3 fragment is about 0.17|e|). The received electron from the substrate fragment is mainly distributed on the C^C bond, which enhances the nucleophilicity of two carbon atoms.…”

“…18,21 In our previous papers, the alkyne activation reactions including the cycloisomerization of 1,6-enyne and the cycloisomerization/oxidative dimerization of phenyl propargyl ether catalyzed by the Au 38 cluster were investigated. 22,23 The present theoretical mechanistic investigations are aimed at extending the understanding of u-alkynylfuran cycloisomerization catalyzed by the planar gold clusters by elucidating the following intriguing, but not yet rmly resolved aspects: (1) which is the preferred mechanism for the u-alkynylfuran cycloisomerization catalyzed by the planar gold clusters? (2) What is the source of product selectivity?…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…Potential involvement of gold carbene complexes in the cycloisomerization reaction of enynes bridged through a cyclopropane was noted in a combined experimental and computational study [1250]. Involvement of gold carbene complexes was noted in a computational study of intramolecular hydroarylation reactions catalyzed by the Au 38 cluster [1251].…”