Titre: ''Unusual Regiocontrol in the Carbonâ€“Hydrogen Bond Activation with Intermetallic Catalysts''
Emdroit: Pavillon Roger-Gaudry, Salle G-815
Hôte: Davit Zargarian
Résumé: 'Once unimaginable, catalytic methods that selectively break C–H bonds in organic molecules are now considered indispensable in synthesis. The activation and functionalisation of inert C–H bonds in hydrocarbons from oil refineries, such as benzene, toluene and xylenes, is arguably one of the most challenging facets of this field.1-2 We recently discovered some unusual Pd–Al intermetallic complexes capable of breaking the C–H bond of benzene at 25 oC.3 Here we present the catalytic C–H alumination of benzene, toluene and xylenes using both Al(I) and Al(III) dihydride reagents. (Voir PDF).
Remarkably these reactions proceed primarily with ortho- and meta-selectivity, indicative of a new mode of regiocontrol that is complementary to both C–H borylation and Friedel-Crafts methodology (Figure – b). Preliminary mechanistic analysis suggests that C–H activation is the rate-limiting and selectivity determining step and that weak dispersion forces between the ligands and substrate determine the regiochemistry of C–H functionalisation.
1. Labinger, J. A.; Bercaw, J. E., Nature 2002, 417, 507. 2.Bergman, R. G., Nature 2007, 446, 391. 3. Discovered during mechanistic studies that resulted from: Chen, W.; Hooper, T. N.; Ng, J.; White, A. J. P.; Crimmin, M. R. Angew. Chem., Int. Ed. 2017, 56, 12687. '