from first principles PP-I-1

OP-II-6Mechanism of the Dimerization of Propene in the Presence of theZiegler-Natta Catalyst Based on Nickel and Aluminum Alkyl HalidesTkach V.S., Suslov D.S., Gubaidulina O.V., Bykov M.V.Irkutsk State University, Irkutsk, Russiatkach@chem.isu.ru; tkach.vitaly@gmail.comThe dimerization of propylene in the presence of the Ziegler-Natta catalyst based on nickeland aluminum alkyl halides leads to three types of structural isomers: linear hexenes,methylpentenes, 2,3-dimethylbutenes. The composition of catalyst system substantiallyinfluences on the ratio of the structural isomers. But the most interesting fact is thecomposition of methylpentenes when dimerization of propene occurs withNi(acac) 2 /Al(i-Bu) 2 Cl/PPh 3 . In this case the content of 4-MP-1 is 24%, which is of two ordersof magnitude higher than the thermodynamically equilibrium amount. The dimerization ofpropylene by nickel hydrides assumes formation of the intermediate with Ni-alkyl bond. TheNi-C bond breaking via the β-hydride elimination mechanism should lead to the formation of4-MP-1 and 4-MP-2 (cis + trans). Their ratio should be close to thermodynamicallyequilibrium. These data can be considered as the experimental reasoning for activity of thereduced forms of nickel in the catalytic cycles, which are included on the first stage oxidativeaddition of substrate to transition metal and on the terminal stage reductive eliminationof 4-MP-1:To elucidate the probable nature of the catalytic action of Ni(0) complexes in alkenes(ethylene, propylene) oligomerization, the model compositions containing mainly nickelcomplexes NiP 4 (P = PR 3 , P(OR) 3 ) and boron trifluoride etherate have been studied. Study ofinteraction of formed complexes of Ni(0) has shown oxidation (NiP 4 ) to Ni(I) by injection tothe system BF 3·OEt 2 . Treatment of the reaction mixture containing Ni(I) complex[(PPh 3 )NiL 2 ]BF 4 with propylene showed it’s high activity in the dimerization of propylene.Activity of the Ni(I) in the dimerization of propylene assumes dissociative oxidative additionof propylene and formation of Ni(III) on the first stage of catalytic cycle. This assumptionwas supported by model reaction of phenylacetylene oxidative addition to Ni(I) monitored byESR which resulted in the formation of Ni(III) complex.41