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Uncovering a copper(II) Alkynyl Complex in C−C Bond Forming Reactions

preprint
submitted on 27.05.2020 and posted on 28.05.2020 by Abolghasem (Gus) Bakhoda, Otome Okoromoba, Christine Greene, Mahdi Raghibi Boroujeni, Jeffery A. Bertke, Timothy H. Warren

Copper(II) alkynyl species are proposed as key intermediates in numerous Cu−catalysed C−C coupling reactions. Supported by a β−diketiminate ligand, the three coordinate copper(II) alkynyl [CuII]−C≡CAr (Ar = 2,6−Cl2C6H3) forms upon reaction of the alkyne H−C≡CAr with the copper(II) tert−butoxide complex [CuII]−OtBu. In solution, this [CuII]−C≡CAr species cleanly transforms the to the Glaser coupling product ArC≡C−C≡CAr and [CuI](solvent). Addition of nucleophiles R′C≡CLi (R′ = aryl, silyl) and Ph–Li to [CuII]−C≡CAr affords the corresponding Csp−Csp and Csp−Csp2coupled products RC≡C−C≡CAr and Ph–C≡CAr with concomitant generation of [CuI](solvent) and {[CuI]−C≡CAr}. Supported by DFT calculations, redox disproportionation forms [CuIII](C≡CAr)(R) species that reductively eliminate R−C≡CAr products. [CuII]−CCAr also captures the trityl radical Ph3C• to give Ph3C−C≡CAr. Radical capture represents the key Csp−Csp3 bond forming step in the copper catalysed C-H functionalization of benzylic substrates R−H with alkynes H−C≡CR′ (R′ = (hetero)aryl, silyl) that provide Csp−Csp3 coupled products R−C≡CR via radical relay with tBuOOtBu as oxidant.

Funding

NSF CHE-1665348

History

Email Address of Submitting Author

thw@georgetown.edu

Institution

Georgetown University

Country

USA

ORCID For Submitting Author

0000-0001-9217-8890

Declaration of Conflict of Interest

No conflict

Exports