Catalytic isomerization and disproportionation of olefins promoted by group 4/d0 benzamidinate complexes

The group 4/d(0) benzamidinate complexes cis-[p-CH3-C6H4C(NSiMe3)(2)](2)Zr(CH3)(2) (1), C-3-tris([N-trimethylsilyl] [N'-myrtanyl]benzamidinate)zirconium chloride (2) and cis-[p-CH3C6H4C(NSiMe3)(2)](2)Ti(CH3)(2) (3) were found to be active catalytic precursors, in the presence of MAO (methylalumoxane), for the isomerization of aliphatic olefins (1-octene, 3-E-octene, 3-methyl-1-butene, 2-methyl-1-butene, allylbenzene) and the disproportionation of 1,4- and 1,3-cyclohexadienes. The active species was found to be the cationic hydride complex obtained for aliphatic olefins by the insertion of the methyl ligand with concomitant beta-hydrogen elimination, and for the alicyclic dienes by an activation of the allylic hydrogen and accompanying elimination of methane. Kinetic studies and Eyring analysis for the isomerization of allylbenzene show that the reaction is first order in both complex and olefin with Delta H+ 17.8(6) kcal.mol(-1) and Delta S+ = -25.1(2) eu. These findings support the epimerization mechanism proposed for these types of cationic complexes, in the polymerization of propylene, toward isotactic polypropylene. To the best of our knowledge, this is the first study in which high oxidation state group 3 complexes are able to induce the catalytic isomerization of olefins or the disproportionation of cyclic olefins.