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Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity
Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC‐based pincer ligands—which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC‐n)(C(2)H(4))][BAr(F) (4)] (n=12, 14, 16; Ar(F)=3,5‐(CF(3))(2)C(6)H(3))—have been investigate...
Autores principales: | , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
John Wiley and Sons Inc.
2020
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7756505/ https://www.ncbi.nlm.nih.gov/pubmed/32677713 http://dx.doi.org/10.1002/chem.202002962 |
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author | Storey, Caroline M. Gyton, Matthew R. Andrew, Rhiann E. Chaplin, Adrian B. |
author_facet | Storey, Caroline M. Gyton, Matthew R. Andrew, Rhiann E. Chaplin, Adrian B. |
author_sort | Storey, Caroline M. |
collection | PubMed |
description | Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC‐based pincer ligands—which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC‐n)(C(2)H(4))][BAr(F) (4)] (n=12, 14, 16; Ar(F)=3,5‐(CF(3))(2)C(6)H(3))—have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr’ (Ar’=3,5‐tBu(2)C(6)H(3)) as substrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives and produce rhodium(I) complexes of conjugated 1,3‐enynes by C−C bond reductive elimination through the annulus of the ancillary ligand. The intermediates are formed with orthogonal regioselectivity, with E‐alkenyl complexes derived from HC≡CtBu and gem‐alkenyl complexes derived from HC≡CAr’, and the reductive elimination step is appreciably affected by the ring size of the macrocycle. For the homocoupling of HC≡CtBu, E‐tBuC≡CCH=CHtBu is produced via direct reductive elimination from the corresponding rhodium(III) alkynyl E‐alkenyl derivatives with increasing efficacy as the ring is expanded. In contrast, direct reductive elimination of Ar'C≡CC(=CH(2))Ar’ is encumbered relative to head‐to‐head coupling of HC≡CAr’ and it is only with the largest macrocyclic ligand studied that the two processes are competitive. These results showcase how macrocyclic ligands can be used to interrogate the mechanism and tune the outcome of terminal alkyne coupling reactions, and are discussed with reference to catalytic reactions mediated by the acyclic homologue [Rh(CNC‐Me)(C(2)H(4))][BAr(F) (4)] and solvent effects. |
format | Online Article Text |
id | pubmed-7756505 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2020 |
publisher | John Wiley and Sons Inc. |
record_format | MEDLINE/PubMed |
spelling | pubmed-77565052020-12-28 Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity Storey, Caroline M. Gyton, Matthew R. Andrew, Rhiann E. Chaplin, Adrian B. Chemistry Full Papers Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC‐based pincer ligands—which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC‐n)(C(2)H(4))][BAr(F) (4)] (n=12, 14, 16; Ar(F)=3,5‐(CF(3))(2)C(6)H(3))—have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr’ (Ar’=3,5‐tBu(2)C(6)H(3)) as substrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives and produce rhodium(I) complexes of conjugated 1,3‐enynes by C−C bond reductive elimination through the annulus of the ancillary ligand. The intermediates are formed with orthogonal regioselectivity, with E‐alkenyl complexes derived from HC≡CtBu and gem‐alkenyl complexes derived from HC≡CAr’, and the reductive elimination step is appreciably affected by the ring size of the macrocycle. For the homocoupling of HC≡CtBu, E‐tBuC≡CCH=CHtBu is produced via direct reductive elimination from the corresponding rhodium(III) alkynyl E‐alkenyl derivatives with increasing efficacy as the ring is expanded. In contrast, direct reductive elimination of Ar'C≡CC(=CH(2))Ar’ is encumbered relative to head‐to‐head coupling of HC≡CAr’ and it is only with the largest macrocyclic ligand studied that the two processes are competitive. These results showcase how macrocyclic ligands can be used to interrogate the mechanism and tune the outcome of terminal alkyne coupling reactions, and are discussed with reference to catalytic reactions mediated by the acyclic homologue [Rh(CNC‐Me)(C(2)H(4))][BAr(F) (4)] and solvent effects. John Wiley and Sons Inc. 2020-10-12 2020-11-17 /pmc/articles/PMC7756505/ /pubmed/32677713 http://dx.doi.org/10.1002/chem.202002962 Text en © 2020 The Authors. Published by Wiley-VCH GmbH This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc-nd/4.0/ License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. |
spellingShingle | Full Papers Storey, Caroline M. Gyton, Matthew R. Andrew, Rhiann E. Chaplin, Adrian B. Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity |
title | Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity |
title_full | Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity |
title_fullStr | Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity |
title_full_unstemmed | Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity |
title_short | Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity |
title_sort | terminal alkyne coupling reactions through a ring: effect of ring size on rate and regioselectivity |
topic | Full Papers |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7756505/ https://www.ncbi.nlm.nih.gov/pubmed/32677713 http://dx.doi.org/10.1002/chem.202002962 |
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