β-Hydride Elimination at Low-Coordinate Gold(III) Centers

F. Rekhroukh , L. Estevez , Sonia Mallet-Ladeira (1) , Karinne Miqueu (2) , A. Amgoune (3) , D. Bourissou (3)

1 ICT - Institut de Chimie de Toulouse
2 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux
3 LHFA - Laboratoire Hétérochimie Fondamentale et Appliquée

This Article reports the first comprehensive study of β-hydride elimination at gold(III). The stability/fate of gold(III) alkyl species have been investigated experimentally and computationally. A series of well-defined cationic cyclometalated gold(III) alkyl complexes [(P,C)gold(III)(R)][NTf2] [(P,C) = 8-diisopropylphosphino-naphthyl; R = Me, nPr, nBu] have been synthesized and spectroscopically characterized. While the cationic gold(III) methyl derivative 3c is stable for days at room temperature, the gold(III) n-propyl and n-butyl complexes 3a,b readily undergo β-hydride elimination at low temperature to generate propylene and 2-butenes, respectively. The formation of internal olefins from the gold(III) n-butyl complex 3b shows that olefin isomerization takes place after β-hydride elimination. Computational studies indicate that this isomerization proceeds through a chain-walking mechanism involving a highly reactive gold(III) hydride intermediate and a sequence of β-hydride elimination/reinsertion into the Au-H bond. The reaction of the cationic gold(III) methyl complex 3c with ethylene was also explored. According to 1H and 13C NMR spectroscopy, a mixture of propylene, 1-butene, and 2-butenes is formed. DFT calculations provide detailed mechanistic insights and support the occurrence of migratory insertion of ethylene, β-hydride elimination, and olefin exchange at gold(III). © 2016 American Chemical Society.

Mots clés: 13C NMR spectroscopy; Computational studies; Ethylene; gold; Gold compounds; Hydride elimination; Hydrides; Isomerization; Isomers; Methyl complexes; Methyl derivatives; Migratory insertion; Nuclear magnetic resonance spectroscopy; Olefin isomerization; Olefins; Propylene; Synthesis (chemical); Temperature; Walking mechanism

Domaines: Chimie

F. Rekhroukh, L. Estevez, Sonia Mallet-Ladeira, Karinne Miqueu, A. Amgoune, et al.. β-Hydride Elimination at Low-Coordinate Gold(III) Centers. Journal of the American Chemical Society, 2016, 138 (36), pp.11920--11929. ⟨10.1021/jacs.6b07035⟩. ⟨hal-01495769⟩