Olefin Polymerization by (Cyclopentadienyl)(aryloxy)titanium(IV) Complexes−Cocatalyst Systems

Abstract

Various titanium(IV) complexes of the type Cp′Ti(OAr)Cl2 (Cp′ ) cyclopentadienyl; OAr ) aryloxy) could be prepared in high yields from Cp′TiCl3. Cp*Ti(O-2,6-i Pr2C6H3)Me2 (Cp* ) C5Me5) could also be prepared from Cp*TiMe3 with 2,6-i Pr2C6H3OH in high yield (77%). These complexes showed notable catalytic activities for ethylene polymerization with MAO or Al i Bu3-Ph3CB(C6F5)4: Cp*Ti(O-2,6-i Pr2C6H3)X2 [X ) Cl (2b), Me (8b), CF3SO3 (9b)] showed the highest activities among these complexes. The effects of substituents on both cyclopentadienyl (pentamethylcyclopentadienyl) and aryloxy (2,6diisopropylphenoxy) groups are important for the remarkable activity. The crystallographic analyses of CpTi(O-2,6-i Pr2C6H3)Cl2 (1b), Cp*Ti(O-2,6-i Pr2C6H3)Cl2 (2b), and (1,3-t Bu2C5H3)Ti(O-2,6-i Pr2C6H3)Cl2 (6b) could be performed, and the bond angle of Ti-O-C (phenyl group) for 2b (173.0°) was found to be significantly different from those for other complexes (162.3-163.1°), although no significant differences are observed for other bond lengths and angles among these compounds. CpTi(O-2,4,6-Me3C6H2)2Cl (7a) and CpTi(O-2,6-i Pr2C6H3)2Cl (7b) could be prepared from CpTiCl3 with the corresponding phenol under the refluxing conditions of toluene, and the structure of 7a could be determined by X-ray crystallography. These complexes also exhibited moderate catalytic activities for ethylene polymerization in the presence of MAO, which was prepared by removing toluene and an excess amount of AlMe3, and the effect of the bulk of phenoxy ligand on the activity was demonstrated. 2b was also found to be an effective catalyst precursor for ethylene/1-butene copolymerization, and the smaller rErB values (0.25-0.36) compared to [Me2Si(C5Me4)(N t Bu)]TiCl2 (2.45) were observed by microanalysis of the resultant copolymers.

Olefin Polymerization with Half-Metallocene Catalysts

“…For example, as shown in Scheme 2.3, substituents on both cyclopentadienyl and aryloxo ligands affect the activity for ethylene polymerization (Our initial efforts in olefin polymerization and ethylene/a-olefin copolymerization, for example [60,61] BuC 5 H 4 ) Cp. The similar trend was observed in the syndiospecific styrene polymerization using a series of Cp'Ti(OMe) 3 complexes [40,109,110], and the fact would be assumed as due to a stabilization of the active site by more electron-donating substituents leading for the high activity.…”

“…In order to explore the reason why both the Cp* and 2,6-diisopropylphenoxy ligand in 2a are prerequisite for the remarkable activity in the ethylene polymerization, structures of various Cp and aryloxide analogues were determined by X-ray crystallography [60,61]. On the basis of structural data in Cp'TiCl 2 (O-2,6-i Pr 2 C 6 H 3 ), the bond angle (173.0°) of Ti-O-C (phenoxy) for Cp*TiCl 2 (O-2,6-i Pr 2 C 6 H 3 ) (2a), which was the most effective catalyst precursor, is significantly different from those for the other Cp derivatives, (Cp'=Cp, 1,3-t Bu 2 C 5 H 3 , 163.0-163.1°): the large Ti-O-C bond angle would lead to more O ?…”

“…On the basis of structural data in Cp'TiCl 2 (O-2,6-i Pr 2 C 6 H 3 ), the bond angle (173.0°) of Ti-O-C (phenoxy) for Cp*TiCl 2 (O-2,6-i Pr 2 C 6 H 3 ) (2a), which was the most effective catalyst precursor, is significantly different from those for the other Cp derivatives, (Cp'=Cp, 1,3-t Bu 2 C 5 H 3 , 163.0-163.1°): the large Ti-O-C bond angle would lead to more O ? Ti p donation into Ti (Our initial efforts in olefin polymerization and ethylene/a-olefin copolymerization, for example [60,61] [109,110]. The aryloxo substituent in the ortho position not only affects the stabilization, but also affects the R-Tiethylene bond angle that should be important for the subsequent insertion.…”

“…Many researchers thus focused on designing the catalysts with ''constrained geometry type'' for the above reason (See Reviews for linked halftitanocenes [15][16][17]46]). Scheme 2.2, have been considered as promising candidates for the efficient catalysts (Reviews for cyclic olefin copolymers [9], See Reviews for nonbridged halftitanocenes [18][19][20][40][41][42], Our initial efforts in olefin polymerization and ethylene/a-olefin copolymerization, for example [60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77]81]), because these complex catalysts display unique characteristics especially for synthesis of new polymers (See Reviews for nonbridged half-titanocenes [19,20], Ethylene copolymerization with 2-methyl-1-pentene (disubstited a-olefin) [82,83], Copolymerization with aolefin containing bulky substituents [78][79][80], Copolymerization with norbornene [84][85][86][87], Copolymerization with cyclohexene, cyclopentene [88,89], Copolymerization with styrene with efficient...…”

“…Therefore, there have been many examples concerning syntheses of complexes of this type and their use as olefin polymerization catalysts [19,20], especially for ethylene polymerization. The selected examples in Cp'TiX 2 (Y) that are known to be promising candidates as the efficient catalysts are shown in Scheme 2.2 (See Reviews for nonbridged half-titanocenes [18][19][20]; Our initial efforts in olefin polymerization and ethylene/a-olefin copolymerization [60][61][62][63][64][65][66]), [67-77, 81, 103-108]. …”