Storey, Caroline M., Gyton, Matthew R., Andrew, Rhiann E. and Chaplin, Adrian B. (2020) Terminal alkyne coupling reactions through a ring : effect of ring size on rate and regioselectivity. Chemistry - A European Journal . doi:10.1002/chem.202002962 (In Press)

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Abstract

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)(C2H4)][BArF4] (n = 12, 14, 16; ArF = 3,5‐(CF3)2C6H3) – have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr′ (Ar′ = 3,5‐tBu2C6H3) 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(=CH2)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)(C2H4)][BArF4] and solvent effects.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Divisions:	Faculty of Science > Chemistry
Library of Congress Subject Headings (LCSH):	Organometallic compounds -- Synthesis, Chemical reactions, Chemistry, Organic, Organometallic compounds -- Reactivity
Journal or Publication Title:	Chemistry - A European Journal
Publisher:	Wiley - V C H Verlag GmbH & Co. KGaA
ISSN:	0947-6539
Official Date:	17 July 2020
Dates:	Date Event 17 July 2020 Available 17 July 2020 Accepted
Date of first compliant deposit:	22 July 2020
DOI:	10.1002/chem.202002962
Status:	Peer Reviewed
Publication Status:	In Press
Publisher Statement:	This is the peer reviewed version of the following article: Storey, C..M., Gyton, M..R., Andrew, R..E. and Chaplin, A..B. (2020), Terminal alkyne coupling reactions through a ring: effect of ring size on rate and regioselectivity. Chem. Eur. J.. Accepted Author Manuscript. doi:10.1002/chem.202002962, which has been published in final form at https://doi.org/10.1002/chem.202002962. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.
Access rights to Published version:	Open Access
RIOXX Funder/Project Grant:	Project/Grant ID RIOXX Funder Name Funder ID 637313 H2020 European Research Council http://dx.doi.org/10.13039/100010663 UF150675 [RS] Royal Society http://dx.doi.org/10.13039/501100000288 UF100592 [RS] Royal Society http://dx.doi.org/10.13039/501100000288

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