10.1002/anie.201814577
Angewandte Chemie International Edition
COMMUNICATION
optimal orientation of the mesitylidenes for trans-C1-C1 bond
formation, can evolve via TSIntII-IV (G‡ = 6.2 kcal/mol) to form E-
2b. At -35 ºC, the calculated E/Z-2b ratio (G‡= 0.6 kcal/mol, 3:1
E/Z) is in close agreement with the experimental results (2.4:1
E/Z). Related mechanisms have been proposed for the formation
of alkenes from rhenium[23] and ruthenium[25] carbenes.
cycloheptatrienes (retro-Buchner reaction). In the absence of
other reagents, we observed dimerization to form preferentially
the E-configured alkene by a process similar to that followed by
other well-known metal carbenes, which places these highly
electrophilic species among the metal carbene family, despite the
weak back donation from gold(I) to the carbenic carbon.
We also examined theoretically the reaction pathways for the
cyclopropanation of Z-2b and E-2b by gold carbene 5b´.[32] As we
have found before for intermolecular cyclopropanations of
intermediate gold(I) carbenes,[33] these reactions proceed by an
asynchronous concerted mechanism with an activation barrier for
E-2b (G‡ = 12.7 kcal/mol), 8.5 kcal/mol lower than that for Z-2b
(G‡ = 21.2 kcal/mol).[32]
Acknowledgements
We thank the Agencia Estatal de Investigación (AEI)/FEDER, UE
(CTQ2016-75960-P and FPI predoctoral fellowship to C. G.-M.),
H2020-Marie Sklodowska-Curie program (postdoctoral fellowship
to X.-L. P.), Swiss National Science Foundation (Early Postdoc
Mobility fellowship to J. M. S. T.), the AGAUR (2017 SGR 1257),
and CERCA Program/Generalitat de Catalunya for financial
support. We also thank the ICIQ NMR and X-ray diffraction units
for technical support and Ángel L. Mudarra (ICIQ) for helpful
discussions.
In summary, we have generated and characterized
spectroscopically monosubstituted gold(I) carbenes for the first
time in solution, which undergo representative transformations of
intermediate gold(I) carbenes formed under catalytic conditions
such as cyclopropanation, oxidation, and CH insertion reactions.
These aryl gold(I) carbenes correspond to the intermediates
generated in the gold(I)-catalyzed decarbenation of
Keywords: carbenes • carbenoids • gold • cyclopropane • CH
insertion
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