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Nouch, R., Woodward, S., Willcox, D., Robinson, D. 
ORCID: 0000-0003-2760-7163 and Lewis, W.,
2020.
Mechanistic-insight-driven rate enhancement of asymmetric copper-catalyzed 1,4-addition of dialkylzinc reagents to enones.
Organometallics, 39 (6), pp. 834-840.
ISSN 0276-7333
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Abstract
The combination of [Cu(MeCN)4]TFA·TFAH (TFA = O2CCF3) with Feringa’s phosphoramidite ligand (LA) provides an exceptionally active (0.75 mol %) catalyst for asymmetric conjugate additions of ZnR2 (R = Et and Me at −40 to −80 °C) to enones. Kinetic and other studies of the addition of ZnEt2 to cyclohex-2-en-1-one indicate a transition state stoichiometry composition of (ZnEt2)3(enone)4Cu2(LA)3 that is generated by transmetalation from Et2Zn(enone)2. Catalyst genesis is significantly slower than turnover (which has limited previous attempts to attain useful kinetic data); in the initial stages, varying populations of catalytically inactive, off-cycle, species are present. These issues are overcome by a double-dose kinetic analysis protocol. A rest state of [LACu(Et)(μ-TFA)(μ-{(enone)(ZnEt)2(enolate)})CuLA2]+ (through the equivalence of enolate = enone + ZnEt2) is supported by DFT studies (ωB97X-D/SRSC). Rate-determining ZnEt2(enone)2 transmetalation drives the exceptionally high catalytic activity of this system.
| Item Type: | Journal article | ||||||
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| Publication Title: | Organometallics | ||||||
| Creators: | Nouch, R., Woodward, S., Willcox, D., Robinson, D. and Lewis, W. | ||||||
| Publisher: | American Chemical Society | ||||||
| Date: | 2020 | ||||||
| Volume: | 39 | ||||||
| Number: | 6 | ||||||
| ISSN: | 0276-7333 | ||||||
| Identifiers: |
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| Divisions: | Schools > School of Science and Technology | ||||||
| Record created by: | Jonathan Gallacher | ||||||
| Date Added: | 17 Mar 2020 16:58 | ||||||
| Last Modified: | 31 May 2021 15:06 | ||||||
| URI: | https://irep.ntu.ac.uk/id/eprint/39409 |
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