Effect of Cyclopentadienyl and Amide Fragment in Olefin Polymerization by Nonbridged (Amide)(cyclopentadienyl)titanium(IV) Complexes of the Type Cp‘TiCl2[N(R)R]−Methylaluminoxane (MAO) Catalyst Systems
journal contributionposted on 05.03.2003 by Kotohiro Nomura, Kensaku Fujii
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Cp*TiCl2[N(Me)R1] [R1 = Me (1), Et (2), Cy (3), Cp* = C5Me5, Cy = cyclohexyl], and (1,3-Me2C5H3)TiCl2[N(Cy)R2] [R2 = Me (4), Cy (5)] have been prepared from the reaction of Cp‘TiCl3 (Cp‘ = cyclopentadienyl) with the corresponding lithium amide in toluene or n-hexane. The structures for 3, 4, and 5 have been determined by X-ray crystallography. The catalytic activity for ethylene polymerization in the presence of d-MAO [prepared by removing toluene and AlMe3 from ordinary methylaluminoxane (MAO) solution] increased in the order: 3 (4540 kg-PE/mol-Ti·h, in toluene, ethylene 6 atm, 25 °C, 10 min) ≫ 5 (2000 kg-PE/mol-Ti·h) > 2 (1680), 1 (1600), and 4 (1520). In particular, 3 exhibited the highest catalytic activity, suggesting both electronic and steric factors play a role. On the other hand, 4 exhibited the highest catalytic activity for syndiospecific styrene polymerization, and the results clearly show that efficient catalyst for the desired polymerization can be modified only by replacing the substituent on Cp‘. 3 exhibited better 1-hexene incorporation than 1, affording poly(ethylene-co-1-hexene) with high molecular weight. 4 exhibited both the highest catalytic activity and efficient 1-hexene incorporation, and the 1-hexene incorporation as well as the monomer sequence distributions were affected by the substituents on both cyclopentadienyl and amide ligands. On the other hand, Cp*TiCl2[N(2,6-Me2C6H3)(SiMe3)] (6) showed poor 1-hexene incorporation under the same conditions, affording the copolymer with relatively low molecular weight. The resultant rErH values by 3 and 4 were 0.38−0.48, which showed that these copolymerizations did not proceed in a random manner that can be seen in ordinary metallocene and linked half-metallocene catalysts.