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Are β‐H‐Eliminations or Alkene Insertions Feasible Elementary Steps in Catalytic Cycles Involving Gold(I) Alkyl Species or Gold(I) Hydrides?
Author(s) -
Klatt Günter,
Xu Rong,
Pernpointner Markus,
Molinari Lise,
Quang Hung Tran,
Rominger Frank,
Hashmi A. Stephen K.,
Köppel Horst
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201203043
Subject(s) - chemistry , reductive elimination , alkyl , catalysis , elimination reaction , alkene , decomposition , medicinal chemistry , hydride , computational chemistry , metal , organic chemistry
The β‐H‐elimination in the (IPr)AuEt complex and its microscopic reverse, the insertion of ethene into (IPr)AuH, were investigated in a combined experimental and computational study. Our DFT‐D3 calculations predict free‐energy barriers of 49.7 and 36.4 kcal mol −1 for the elimination and insertion process, respectively, which permit an estimation of the rate constants for these reactions according to classical transition‐state theory. The elimination/insertion pathway is found to involve a high‐energy ethene hydride species and is not significantly affected by continuum solvent effects. The high barriers found in the theoretical study were then confirmed experimentally by measuring decomposition temperatures for several different (IPr)Au I ‐alkyl complexes which, with a slow decomposition at 180 °C, are significantly higher than those of other transition‐metal alkyl complexes. In addition, at the same temperature, the decomposition of (IPr)AuPh and (IPr)AuMe, both of which cannot undergo β‐H‐elimination, indicates that the pathway for the observed decomposition at 180 °C is not a β‐H‐elimination. According to the calculations, the latter should not occur at temperatures below 200 °C. The microscopic reverse of the β‐H‐elimination, the insertion of ethene into the (IPr)AuH could neither be observed at pressures up to 8 bar at RT nor at 1 bar at 80 °C. The same is true for the strain‐activated norbornene.