Diverse Pathways of Activation and Deactivation of Half-Sandwich Aryloxide Titanium Polymerization Catalysts
作者:Khamphee Phomphrai、Andrew E. Fenwick、Shalini Sharma、Phillip E. Fanwick、James M. Caruthers、W. Nicholas Delgass、Mahdi M. Abu-Omar、Ian P. Rothwell
DOI:10.1021/om0507272
日期:2006.1.1
A series of half-sandwich aryloxide titanium complexes, [CpTi(OAr)Me-2] (CP = C5H5; OAr = OC6H3-Me-2-2,6, OC6H3Et2-2,6, (OC6H3Pr2)-Pr-i-2,6, (OC6H3Pr2)-Pr-t-2,6, and OC6HPh4-2,3,5,6), have been synthesized. These compounds react with B(C6F5)(3) to give thermally unstable complexes [CpTi(OAr)Me][MeB(C6F5)(3)]. Two different deactivation pathways have been identified within the series. The tetraphenylphenoxide, cationic methyl compound decomposes cleanly at room temperature to give [CpTi(OC6HPh4-2,3,5,6)(C6F5)CH2B(C6F5)(2)}] and methane with a first-order rate constant of 7.6(2) x 10(-4) s(-1) at 25 degrees C. For relatively smaller aryloxide ligands, OAr = (OC6H3Pr2)-Pr-i-2,6, (OC6H3Bu2)-Bu-t-2,6, a Me/C6F5 exchange takes place, yielding CpTi(OAr)Me(C6F5) and MeB(C6F5)(2). The cationic titanium complexes are shown to be active for the polymerization of 1-hexene. At -20 and 0 degrees C, first-order dependence on the concentration of 1-hexene is observed. The rate of polymerization decreases with increasing steric hindrance of aryloxides except for OAr = OC6HPh4-2,3,5,6.