4 years ago

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

An Ion-Responsive Pincer-Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization
Matthew R. Kita, Alexander J. M. Miller
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 abstraction 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.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201701006

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