An Ion‐Responsive Pincer‐Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization

Rapid, selective, and highly controllable iridium‐catalyzed allylbenzene isomerization is described, enabled by tunable hemilability based on alkali metal cation binding with a macrocyclic “pincer‐crown ether” ligand. An inactive chloride‐ligated complex can be activated by halide ion with sodium sa...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2017-05, Vol.56 (20), p.5498-5502
Main Authors: Kita, Matthew R., Miller, Alexander J. M.
Format: Article
Language:English
Subjects:
Binding
Catalysts
Chloride
Chlorides
Coordination compounds
Crown ethers
Ethers
hemilability
homogeneous catalysis
Iridium
Isomerization
olefin isomerization
Salts
Sodium
Sodium salts
Substrates
switchable catalysis
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Summary:Rapid, selective, and highly controllable iridium‐catalyzed allylbenzene isomerization is described, enabled by tunable hemilability based on alkali metal cation binding with a macrocyclic “pincer‐crown ether” ligand. An inactive chloride‐ligated complex can be activated by halide ion with sodium salts, with the resulting catalyst [κ5‐(15c5NCOPiPr)Ir(H)]+ exhibiting modest activity. Addition of Li+ provides a further boost in activity, with up to 1000‐fold rate enhancement. Ethers and chloride salts dampen or turn off reactivity, leading to three distinct catalyst states with activity spanning several orders of magnitude. Mechanistic studies suggest that the large rate enhancement and high degree of tunability stem from control over substrate binding. Multi‐stage cati‐ON booster: Complete control over activity is achieved for olefin isomerization with the system shown. Mechanistic studies suggest that cations help control substrate binding through interaction with the hemilabile macrocycle of “pincer‐crown ether” ligands. Acceleration using an appropriate cation and deceleration using ether or chloride sources provide exquisite control over the catalytic activity.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201701006