Organic Chemistry, Poster
Gold-Catalyzed Alkynylation of Arenes: Mechanistic Insights and Evidence for AuI/AuIII Redox Catalytic Cycles
M. Hofer1, T. De Haro1, E. Gomez-Bengoa2, R. Kumar1, C. Nevado1
1University of Zurich, 2Universidad del PaĆ­s Vasco
AuI/AuIII-catalyzed, oxidative cross-coupling reactions have been developed in recent years as a powerful tool for C-C and C-X bond formation. However, the mechanistic understanding of these transformations is still limited and detailed investigations to elucidate their mechanism are rare.1 Given our ongoing interest in the oxidative chemistry of gold,2 we decided to investigate the mechanism of the gold catalyzed alkynylation of arenes previously developed in our group. This reaction enables the intermolecular coupling of Csp2-centers of electron rich arenes with Csp-centers of electron deficient terminal alkynes in presence of gold as catalyst and PhI(OAc)2 as stoichiometric, external oxidant.3 Kinetic analysis and NMR monitoring of species formed in the reaction mixture together with control experiments and DFT calculations, have unravelled a sequence of steps to generate the product including: 1) Transfer of the alkyne to the gold(I) complex via C-H activation; 2) Oxidation to an alkynylgold(III) complex by an in situ generated oxidant; 3) C-H Activation of the arene on the gold(III) oxidation state and subsequent reductive elimination. Interestingly, the reactivity of the gold(III) intermediates is governed by the anionic ligands: only the acetato ligands are displaced by the arene yielding the Csp2-Csp coupling products, while chloride ligands show no reactivity thus highlighting the importance of catalyst and oxidant speciation in gold-catalyzed oxidative couplings.4
1. Liam T. Ball, Guy C. Lloyd-Jones, Christopher A. Russell, J. Am. Chem. Soc. 2014, 136, 254-264.
2. (a) Manuel Hofer, Cristina Nevado, Eur. J. Inorg. Chem. 2012, 9, 1338-1341; (b) Manuel Hofer, Cristina Nevado, Tetrahedron 2013, 69, 5751-5757; (c) Manuel Hofer, Cristina Nevado, Organometallics 2014, 33, 1328-1332.
3. Teresa de Haro, Cristina Nevado J. Am. Chem. Soc. 2010, 132, 1512-1513.
4. Manuel Hofer, Teresa de Haro, Enrique Gomez-Bengoa, Roopender Kumar, Cristina Nevado, submitted for publication