Mechanistic examination of AuIII-mediated 1,5-enyne cycloisomerization by AuBr2(N-imidate)(NHC)/AgX precatalysts - is the active catalyst AuIII or AuI?Electronic supplementary information (ESI) available: Representative NMR spectra and other characterization data. See DOI: 10.1039/c4cy00617h

• Main Authors: Reeds, Jonathan P, Healy, Mark P, Fairlamb, Ian J. S
• Format: Journal Article
• Published: 08.09.2014
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/c4cy00617h

Gold( iii ) catalysts mediate 1,5-enyne cycloisomerization or tandem nucleophilic substitution-1,5-enyne cycloisomerization processes in an efficient manner. This study examines the reaction kinetics of 1,5-enyne cycloisomerization, mediated by AuBr 2 ( N -imidate)(NHC) catalysts {where N -imidate = N -tetrafluorosuccinimide ( N -TFS) or N -phthalimide ( N -phthal) and NHC = N , N ′-di- tert -pentylimidazol-2-ylidene (I t Pe)}, in the presence of AgOTf, in comparison with Au III Br 3 (NHC) and Au I Br(NHC). The nature of N -imidate anion influences catalyst efficacy. NMR spectroscopic investigations have allowed the ease of reduction of AuBr 2 ( N -TFS)(NHC) to Au I X(NHC) (where X = N -TFS or Br) to be examined. Br 2 is liberated from Au III , which has been trapped by a sacrificial alkene. Under working catalyst conditions cationic Au III is reduced to Au I . The role of Au I and Au III species in 1,5-enyne cycloisomerization reactions has been examined in this paper.