Catalytic isomerization and disproportionation of olefins promoted by group 4/d(0) 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)zirconi um 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-meth yl-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 catio nic hydride complex obtained for aliphatic olefins by the insertion of the methyl ligand with concomitant beta-hydrogen elimination, and for the alicy clic dienes by an activation of the allylic hydrogen and accompanying elimi nation of methane. Kinetic studies and Eyring analysis for the isomerizatio n 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. Thes e findings support the epimerization mechanism proposed for these types of cationic complexes, in the polymerization of propylene, toward isotactic po lypropylene. 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 is omerization of olefins or the disproportionation of cyclic olefins.