Nucleophilic Addition to π‑Allyl Gold(III) Complexes: Evidence for Direct and Undirect Paths

π-Allyl complexes play a prominent role in organometallic chemistry and have attracted considerable attention, in particular the π-allyl Pd­(II) complexes which are key intermediates in the Tsuji–Trost allylic substitution reaction. Despite the huge interest in π-complexes of gold, π-allyl Au­(III) complexes were only authenticated very recently. Herein, we report the reactivity of (P,C)-cyclometalated Au­(III) π-allyl complexes toward β-diketo enolates. Behind an apparently trivial outcome, i.e. the formation of the corresponding allylation products, meticulous NMR studies combined with DFT calculations revealed a complex and rich mechanistic picture. Nucleophilic attack can occur at the central and terminal positions of the π-allyl as well as the metal itself. All paths are observed and are actually competitive, whereas addition to the terminal positions largely prevails for Pd­(II). Auracyclobutanes and π-alkene Au­(I) complexes were authenticated spectroscopically and crystallographically, and Au­(III) σ-allyl complexes were unambiguously characterized by multinuclear NMR spectroscopy. Nucleophilic additions to the central position of the π-allyl and to gold are reversible. Over time, the auracyclobutanes and the Au­(III) σ-allyl complexes evolve into the π-alkene Au­(I) complexes and release the C-allylation products. The relevance of auracyclobutanes in gold-mediated cyclopropanation was demonstrated by inducing C–C coupling with iodine. The molecular orbitals of the π-allyl Au­(III) complexes were analyzed in-depth, and the reaction profiles for the addition of β-diketo enolates were thoroughly studied by DFT. Special attention was devoted to the regioselectivity of the nucleophilic attack, but C–C coupling to give the allylation products was also considered to give a complete picture of the reaction progress.