Three-Coordinate Copper(II) Alkynyl Complex in C–C Bond Formation: The Sesquicentennial of the Glaser Coupling
Year: 2020
Type: article
Abstract: Copper(II) alkynyl species are proposed as key intermediates in numerous Cu-catalyzed C–C coupling reactions. Supported by a β-diketiminate ligand, the three-coordinate copper(II) alkynyl [Cu II ]–C≡CAr (Ar = 2,6-Cl 2 C 6 H 3 ) forms upon reaction of the alkyne H–C≡CAr with the copper(II) tert -butoxide complex [Cu II ]–O t Bu. In solution, this [Cu II ]–C≡CAr species cleanly transforms to the Glaser coupling product ArC≡C–C≡CAr and [Cu I ](solvent). Addition of nucleophiles R′C≡C–Li (R′ = aryl, silyl) and Ph–Li to [Cu II ]–C≡CAr affords the corresponding C sp –C sp and C sp –C sp2 coupled products RC≡C–C≡CAr and Ph–C≡CAr with concomitant generation of [Cu I ](solvent) and {[Cu I ]–C≡CAr} −, respectively. Supported by density functional theory (DFT) calculations, redox disproportionation forms [Cu III ](C≡CAr)(R) species that reductively eliminate R–C≡CAr products. [Cu II ]–C≡CAr also captures the trityl radical Ph 3 C· to give Ph 3 C–C≡CAr. Radical capture represents the key C sp –C sp3 bond-forming step in the copper-catalyzed C–H functionalization of benzylic substrates R–H with alkynes H–C≡CR′ (R′ = (hetero)aryl, silyl) that provide C sp –C sp3 coupled products R–C≡CR via radical relay with t BuOO t Bu as oxidant.
DOI: 10.1021/jacs.0c07137
Institution: Georgetown University
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3087117466