The Diels-Alder reactivity of different bowl-shaped polycyclic aromatic hydrocarbons (namely, corannulene, cyclopentacorannulene, diindenochrysene, hemifullerene, and circumtrindene) has been explored computationally within the Density Functional Theory framework. To this end, both the increase of the reactivity with the size of the buckybowl and the complete [6,6]-regioselectivity in the process have been analyzed in detail using the activation strain model of reactivity in combination with the energy decomposition analysis method. Our results have been compared to the parent C 60 fullerene, which also produces the corresponding [6,6]-cycloadduct exclusively. It is found that the behavior of the considered buckybowls resembles, in general, that of C 60 . Whereas the interaction energy between the deformed reactants along the reaction coordinate mainly controls the regioselectivity of the process, it is the interplay between the activation strain energy and the transition state interaction which governs the reactivity of the system.

The Diels-Alder reactivity of maleic anhydride to the bay regions of planar polycyclic aromatic hydrocarbons has been explored computationally within the Density Functional Theory framework. It is found that the process becomes more and more exothermic and the associated activation barriers become lower and lower when the size of the system increases. This enhanced reactivity follows an exponential behavior reaching its maximum for systems having 18-20 benzenoid rings in their structures. This peculiar behavior has been analyzed in detail using the activation strain model of reactivity in combination with the energy decomposition analysis method. In addition, the influence of the change in the aromaticity strength of the polycyclic compound during the process on the respective activation barriers has been also studied.

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.

A new mode of bond activation involving M→Z interactions is disclosed. Coordination to transition metals as-acceptor ligands was found to enable the activation of fluoro silanes, opening the way to the first transition metal-catalyzed Si-F bond activation. Using phosphines as directing groups, sila-Negishi couplings were developed by combining Pd and Ni complexes with external Lewis acids such as MgBr2. Several key catalytic intermediates have been authenticated spectroscopically and crystallographically. Combined with DFT calculations, all data support cooperative activation of the fluoro silane via Pd/Ni→Si-F→Lewis acid interaction with conversion of the Z-type fluoro silane ligand into an X-type silyl moiety.