2-Aminoalkylgold Complexes: The Putative Intermediate in Au-Catalyzed Hydroamination of Alkenes Does Not
Joël Gubler1, Mitar Radić1, Yannick Stöferle1
1Laboratorium für Organische Chemie, ETH Zürich, Rämistrasse 101, 8092, Zürich, Switzerland.
Abstract:
Au-catalyzed hydroamination proceeds well for alkynes but not alkenes. We report gas-phase binding energies of alkenes and alkynes to a cationic Au center, which indicate that differences in binding are not the origin of the disparate chemical behavior. We further report the synthesis and characterization of 2-aminoalkylgold complexes, which would be the intermediates in a hypothetical Au-catalyzed hydroamination of styrene. The reactivity of the well-characterized and isolable complexes reveals that protonation or alkylation of the 2-aminoalkylgold complexes results in amine elimination in solution, and in the gas phase, indicating that the failure of Au-catalyzed alkene hydroamination derives from a non-competitive protodeauration step. We analyze possible transition states for the protodeauration, and identify an insufficiently strong Au-proton interaction as the reason that the transition states lie too high in energy to compete.
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