Diverse Pathways of Activation and Deactivation of Half-Sandwich Aryloxide Titanium Polymerization Catalysts

A series of half-sandwich aryloxide titanium complexes, [CpTi(OAr)Me 2 ] (Cp = C 5 H 5 ; OAr = OC 6 H 3 -Me 2 -2,6, OC 6 H 3 Et 2 -2,6, OC 6 H 3 i Pr 2 -2,6, OC 6 H 3 t Bu 2 -2,6, and OC 6 HPh 4 -2,3,5,6), have been synthesized. These compounds react with B(C 6 F 5 ) 3 to give thermally unstable complexes [CpTi(OAr)Me[MeB(C 6 F 5 ) 3 ]. Two different deactivation pathways have been identified within the series. The tetraphenylphenoxide cationic methyl compound decomposes cleanly at room temperature to give [CpTi(OC 6 HPh 4 -2,3,5,6)-(C 6 F 5 ){CH 2 B(C 6 F 5 ) 2 }] and methane with a first-order rate constant of 7.6(2) × 10 -4 s -1 at 25 °C. For relatively smaller aryloxide ligands, OAr = OC 6 H 3 i Pr 2 -2,6, OC 6 H 3 t Bu 2 -2,6, a Me/C 6 F 5 exchange takes place, yielding CpTi(OAr)Me(C 6 F 5 ) and MeB(C 6 F 5 ) 2 . The cationic titanium complexes are shown to be active for the polymerization of 1-hexene. At -20 and 0 °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 = OC 6 HPh 4 -2,3,5,6.