Dinuclear gold(i) complexes bearing alkyl-bridged bis(n-heterocyclic carbene) ligands as catalysts for carboxylative cyclization of propargylamine: Synthesis, structure, and kinetic and mechanistic comparison to the mononuclear complex [Au(IPr)Cl]

Tahani A.C.A. Bayrakdar, Fady Nahra, Jack V. Davis, Mohan M. Gamage, Burjor Captain, Manuel Temprado, Marco Marazzi, Marina Saab, Kristof van Hecke, Dominic Ormerod, Carl D. Hoff, Steven P. Nolan

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Eight new dinuclear gold(I) complexes, [Au2(L)X2] (1−8), were synthesized using a straightforward synthetic procedure under very mild conditions. The complexes have been characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray structure analysis. Their catalytic activity was investigated in the carboxylative cyclization of propargylamine (PPA). A superior performance in comparison to [Au(IPr)Cl] (9) was obtained for complexes 1 and 2 having an eight-methylene bridge connecting two NHCs with an arene bearing an isopropyl substituent for X = Cl, Br. This prompted more detailed kinetic and mechanistic studies by FTIR comparing dinuclear complex 2 of X = Cl to complex 9. Fortuitously the FTIR studies allowed monitoring of the formation of the products carbamic acid (CA) and carbamate salt (CS), as well as a key cyclized intermediate first discovered by Ikariya. These data allow additional insight into the mechanism as well as the central role which may be played by Au(I) carbamate formation as a higher energy resting state present in the catalytic cycle. The crystal structures of four of the new complexes and a detailed computational study relevant to the role of carbamic acid (CA) and carbamates in the catalytic cycle are also reported.

Original languageEnglish (US)
Pages (from-to)2907-2916
Number of pages10
JournalOrganometallics
Volume39
Issue number15
DOIs
StatePublished - Aug 10 2020

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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