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

Cp*TiCl2,(L) [L = C4H4N (1), 2,5-Me2C4H2,N(2), 2,4-Me2C4HN (3), 2,4-Me-2,-3-EtC4HN (4)], Cp*TiCl(2A-Me,-3-EtC4HN)2 (5), and Cp*Ti(C4H4N)3 (6) were prepared by treating Cp*TiCl3 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 eta(l) fashion. The dimethyl analogues Cp*TiMe2,,(L) [L = C4H4N (7), 2.5-Me2C4H2,N (8)] could be prepared by adopting a route that involves in situ generation of Cp*Ti(CI)Me,. prepared by the reaction of Cp*TiCl3 with 2.0 equiv of MeLi in Et2O, and the subsequent treatment with the corresponding lithium salts. The Cp analogues CpTiCl2,(L) [L = C4H4N (9), 2,5-Me2C4H2N (10), 2.4-Me2C4H2,N (11), 2,4-Me-2-3-EtC4HN (12)] were also prepared by treating CpTiCl3 with the corresponding lithium salts in Et2O or n-hexane. The crystallographic analyses of 9-11 indicate that the dimethylpyrrolide ligand in 10 coordinates to Ti in eta(5) mode, whereas the nitrogen atom in the pyrrolide ligand (in complexes 9 and 11) binds to Ti in an eta(l) fashion (a bonding in addition to T 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 I exhibited the highest catalytic activity, and ail 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 (Bu3Al)-Bu-i/[Ph3C][B(C6F5)(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.