Selective formation of biaryls via interaction of polynuclear arylcopper compounds with copper(I) trifluoromethanesulfonate [copper(I) triflate]
article
Selective formation of biaryls is observed upon interacting well-defined arylcopper cluster compounds (2-Me2NCH2C6H4)4Cu 4, (4-MeC6H4)4Cu4, (2-Me2NC6H4)4Cu6Br 2, and (2-Me2NC6H4)4Cu6OTf 2 with equimolar amounts of CuOTf in benzene. It is shown that complex formation of the arylcopper cluster with CuOTf precedes the C-C-coupling process. In some cases these complexes are sufficiently stable to be isolated, e.g., (2-Me2NC6H4)4Cu6OTf 2 (from the 2/1 reaction of 2-Me2NC6H4Cu with CuOTf). Decomposition of the 2-MeC6H4Cu/CuOTf complex with NH3/H2O in the presence of oxygen affords, in addition to toluene and 2,2′-bitolyl, 2-H2NC6H4Me and 2-HOC6H4Me. The formation of the arylcopper-CuOTf complexes and hence biaryl formation can be inhibited by suitable ligands such as PPh3. In the absence of built-in ligands in the arylcopper compound, e.g., (4-MeC6H4)4Cu4, the reaction with CuOTf can be made catalytic in CuOTf. The selective C-C-coupling reaction has been explained in terms of intraaggregate electron-transfer processes occurring in the intermediate arylcopper-copper triflate complexes. A mechanism is proposed based on valence disproportionation inside the copper core induced by charge transfer from the core to the electron-accepting OTf anions.
TNO Identifier
228236
ISSN
00223263
Source
Journal of Organic Chemistry, 42(12), pp. 2047-2053.
Pages
2047-2053
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