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Mechanism of the Transition-Metal-Catalyzed Hydroarylation ofBromo-Alkynes Revisited: Hydrogen versus Bromine Migration
Huang, Genping; Cheng, Bing; Xu, Liang; Li, Yahong; Xia, Yuanzhi
2012
Source PublicationCHEMISTRY-A EUROPEAN JOURNAL
ISSN0947-6539
Volume18Issue:17Pages:5401-5415
AbstractA comprehensive mechanistic study of the InCl3-, AuCl-, and PtCl2-catalyzed cycloisomerization of the 2-(haloethynyl)biphenyl derivatives of Furstner et al. was carried out by DFT/M06 calculations to uncover the catalyst-dependent selectivity of the reactions. The results revealed that the 6-endo-dig cyclization is the most favorable pathway in both InCl3- and AuCl-catalyzed reactions. When AuCl is used, the 9-bromophenanthrene product could be formed by consecutive 1,2-H/1,2-Br migrations from the Wheland-type intermediate of the 6-endo-dig cyclization. However, in the InCl3-catalyzed reactions, the chloride-assisted intermolecular H-migrations between two Wheland-type intermediates are more favorable. These Cl-assisted H-migrations would eventually lead to 10-bromophenanthrene through proto-demetalation of the aryl indium intermediate with HCl. The cause of the poor selectivity of the PtCl2 catalyst in the experiments by the Furstner group was predicted. It was found that both the PtCl2-catalyzed alkynevinylidene rearrangement and the 5-exo-dig cyclization pathways have very close activation energies. Further calculations found the former pathway would lead eventually to both 9- and 10-bromophenanthrene products, as a result of the Cl-assisted H-migrations after the cyclization of the Ptvinylidene intermediate. Alternatively, the intermediate from the 5-exo-dig cyclization would be transformed into a relatively stable Ptcarbene intermediate irreversibly, which could give rise to the 9-alkylidene fluorene product through a 1,2-H shift with a 28.1 kcal?mol-1 activation barrier. These findings shed new light on the complex product mixtures of the PtCl2-catalyzed reaction. A comprehensive mechanistic study of the InCl3-, AuCl-, and PtCl2-catalyzed cycloisomerization of the 2-(haloethynyl)biphenyl derivatives of Furstner et al. was carried out by DFT/M06 calculations to uncover the catalyst-dependent selectivity of the reactions. The results revealed that the 6-endo-dig cyclization is the most favorable pathway in both InCl3- and AuCl-catalyzed reactions. When AuCl is used, the 9-bromophenanthrene product could be formed by consecutive 1,2-H/1,2-Br migrations from the Wheland-type intermediate of the 6-endo-dig cyclization. However, in the InCl3-catalyzed reactions, the chloride-assisted intermolecular H-migrations between two Wheland-type intermediates are more favorable. These Cl-assisted H-migrations would eventually lead to 10-bromophenanthrene through proto-demetalation of the aryl indium intermediate with HCl. The cause of the poor selectivity of the PtCl2 catalyst in the experiments by the Furstner group was predicted. It was found that both the PtCl2-catalyzed alkynevinylidene rearrangement and the 5-exo-dig cyclization pathways have very close activation energies. Further calculations found the former pathway would lead eventually to both 9- and 10-bromophenanthrene products, as a result of the Cl-assisted H-migrations after the cyclization of the Ptvinylidene intermediate. Alternatively, the intermediate from the 5-exo-dig cyclization would be transformed into a relatively stable Ptcarbene intermediate irreversibly, which could give rise to the 9-alkylidene fluorene product through a 1,2-H shift with a 28.1 kcal?mol-1 activation barrier. These findings shed new light on the complex product mixtures of the PtCl2-catalyzed reaction.
KeywordAlkynes Cycloisomerization Density Functional Calculations
Indexed BySCI
Document Type期刊论文
Identifierhttp://ir.isl.ac.cn/handle/363002/2060
Collection青海盐湖研究所知识仓储
Recommended Citation
GB/T 7714
Huang, Genping,Cheng, Bing,Xu, Liang,et al. Mechanism of the Transition-Metal-Catalyzed Hydroarylation ofBromo-Alkynes Revisited: Hydrogen versus Bromine Migration[J]. CHEMISTRY-A EUROPEAN JOURNAL,2012,18(17):5401-5415.
APA Huang, Genping,Cheng, Bing,Xu, Liang,Li, Yahong,&Xia, Yuanzhi.(2012).Mechanism of the Transition-Metal-Catalyzed Hydroarylation ofBromo-Alkynes Revisited: Hydrogen versus Bromine Migration.CHEMISTRY-A EUROPEAN JOURNAL,18(17),5401-5415.
MLA Huang, Genping,et al."Mechanism of the Transition-Metal-Catalyzed Hydroarylation ofBromo-Alkynes Revisited: Hydrogen versus Bromine Migration".CHEMISTRY-A EUROPEAN JOURNAL 18.17(2012):5401-5415.
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