Synthesis and Structural Analysis of (Cyclopentadienyl)(pyrrolide)titanium(IV) Complexes and Their Use in Catalysis for Olefin Polymerization

Abstract

Cp*TiCl 2 (L) [L = C 4 H 4 N ( 1 ), 2,5-Me 2 C 4 H 2 N ( 2 ), 2,4-Me 2 C 4 H 2 N ( 3 ), 2,4-Me 2 -3-EtC 4 HN ( 4 )], Cp*TiCl(2,4-Me 2 -3-EtC 4 HN) 2 ( 5 ), and Cp*Ti(C 4 H 4 N) 3 ( 6 ) were prepared by treating Cp*TiCl 3 with the corresponding lithium salts in toluene or n -hexane. The structures of 3 − 6 determined by X-ray crystallography indicate that the complexes have a distorted tetrahedral geometry around Ti, and the nitrogen atom binds to Ti in an η 1 fashion. The dimethyl analogues Cp*TiMe 2 (L) [L = C 4 H 4 N ( 7 ), 2,5-Me 2 C 4 H 2 N ( 8 )] could be prepared by adopting a route that involves in situ generation of Cp*Ti(Cl)Me 2, prepared by the reaction of Cp*TiCl 3 with 2.0 equiv of MeLi in Et 2 O, and the subsequent treatment with the corresponding lithium salts. The Cp analogues CpTiCl 2 (L) [L = C 4 H 4 N ( 9 ), 2,5-Me 2 C 4 H 2 N ( 10 ), 2,4-Me 2 C 4 H 2 N ( 11 ), 2,4-Me 2 -3-EtC 4 HN ( 12 )] were also prepared by treating CpTiCl 3 with the corresponding lithium salts in Et 2 O or n -hexane. The crystallographic analyses of 9 − 11 indicate that the dimethylpyrrolide ligand in 10 coordinates to Ti in η 5 mode, whereas the nitrogen atom in the pyrrolide ligand (in complexes 9 and 11 ) binds to Ti in an η 1 fashion (σ bonding in addition to π donation). These complexes ( 1 − 4, 7 − 12 ) exhibited moderate catalytic activities for ethylene polymerization in the presence of methylaluminoxane (MAO), and the activities were highly affected by the substituent on the pyrrolide ligand. In the polymerization using a series of dichloro complexes, the Cp*-pyrrolide analogue 1 exhibited the highest catalytic activity, and an increase in the steric bulk led to the decrease in activity, whereas the activity of the Cp analogues increased upon increasing the steric bulk in the pyrrolide ligand. The dimethyl complexes ( 7, 8 ) exhibited notable catalytic activities in the presence of MAO, and the activities increased in the presence of i Bu 3 Al/[Ph 3 C][B(C 6 F 5 ) 4 ] cocatalyst in place of MAO. The resultant polymers possessed unimodal molecular weight distributions. These complexes also exhibited moderate catalytic activities for syndiospecific styrene polymerization, and the activities of the Cp* analogues increased at high temperature.