Department of Chemistry, Georgetown University, Box 571227-1227, Washington, District of Columbia 20057, United States.
J Am Chem Soc. 2020 Oct 28;142(43):18483-18490. doi: 10.1021/jacs.0c07137. Epub 2020 Oct 19.
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]-C≡CAr (Ar = 2,6-ClCH) forms upon reaction of the alkyne H-C≡CAr with the copper(II) -butoxide complex [Cu]-OBu. In solution, this [Cu]-C≡CAr species cleanly transforms to the Glaser coupling product ArC≡C-C≡CAr and Cu. Addition of nucleophiles R'C≡C-Li (R' = aryl, silyl) and Ph-Li to [Cu]-C≡CAr affords the corresponding C-C and C-C coupled products RC≡C-C≡CAr and Ph-C≡CAr with concomitant generation of Cu and {[Cu]-C≡CAr}, respectively. Supported by density functional theory (DFT) calculations, redox disproportionation forms Cu(R) species that reductively eliminate R-C≡CAr products. [Cu]-C≡CAr also captures the trityl radical PhC· to give PhC-C≡CAr. Radical capture represents the key C-C 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-C coupled products R-C≡CR via radical relay with BuOOBu as oxidant.
铜（II）炔基物种被认为是许多铜催化 C-C 偶联反应中的关键中间体。在β-二酮亚胺配体的支持下，三配位的铜（II）炔基 [Cu]-C≡CAr（Ar = 2,6-ClCH）通过炔烃 H-C≡CAr 与铜（II）-丁氧基配合物 [Cu]-OBu 的反应形成。在溶液中，这种 [Cu]-C≡CAr 物种可以干净地转化为 Glaser 偶联产物 ArC≡C-C≡CAr 和 Cu。向 [Cu]-C≡CAr 中添加亲核试剂 R'C≡C-Li（R' = 芳基，硅基）和 Ph-Li，可得到相应的 C-C 和 C-C 偶联产物 RC≡C-C≡CAr 和 Ph-C≡CAr，同时分别生成 Cu和 {[Cu]-C≡CAr}。密度泛函理论（DFT）计算支持，氧化还原歧化形成 Cu(R)物种，该物种可还原消除 R-C≡CAr 产物。[Cu]-C≡CAr 还捕获三苯甲基自由基 PhC·以生成 PhC-C≡CAr。自由基捕获代表了铜催化苄基底物 R-H 与炔烃 H-C≡CR'（R' = (杂)芳基，硅基）的 C-H 官能化反应中关键的 C-C 键形成步骤，该反应通过自由基接力提供 C-C 偶联产物 R-C≡CR，其中 BuOOBu 作为氧化剂。
