om5009499_si_002.xyz (349.85 kB)
Computational Study on Cycloisomerization/Oxidative Dimerization of Aryl Propargyl Ethers Catalyzed by Gold Nanoclusters: Mechanism and Selectivity
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posted on 2014-11-24, 00:00 authored by Dianyong Tang, Zhongzhu Chen, Jin Zhang, Ying Tang, Zhigang XuA theoretical
analysis of the cycloisomerization and oxidative dimerization of phenyl
propargyl ether catalyzed by the Au38 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 Au38 surface with an adsorption energy
of −10.61 kcal/mol. The 6-endo pathway to
give 2H-chromene 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 2H-chromenes 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.