New Functionalized Vinyl Monomers by Ethylene-(Functionalized)Norbornene Hetero-Trimerization Catalyzed by CoII-(Imino)pyridine Complexes

On activation by MAO the (imino)pyridine cobalt(II) complex CoCl2N2Ph/i-Pr2 catalyzes the enchainment of one norbornene (NB) molecule with two ethylene molecules to give exo-2,exo-3-ethylvinylnorbornane with high activity and complete diastereoselectivity. Turnover frequencies [TOF, mol NB (mol Co>h)1] as high as 270,000 have been obtained. The 2E-1NB hetero-trimerization reaction has been also accomplished with NBs bearing polar substituents such as norbornenemethanol and norbornenecarboxylic acid provided that the substrate is protected with triisobutylaluminum and the less sterically demanding complex CoCl2N2 Ph/Me2 is used as catalyst precursor. A mechanism for the hetero-trimerization reactions is proposed on the basis of experimental evidence.