Preparation and Characterization of Half‐Sandwich (Pentamethylcyclopentadienyl)(triflato)titanium(IV) Complexes: Solid‐State Structural Motifs and Catalysis Studies

Half‐sandwich (pentamethylcyclopentadienyl)(triflato)titanium(IV) complexes of the type Ti(Cp*)(TfO)₂X] (X=MeO ( 1 ), Me ( 2 ), 2,4,6‐Me₃C₆H₂O ( 5 )) or Ti(Cp*)(o‐OC₆H₄O)(TfO)] ( 7 ) were readily synthesized via methathesis of the corresponding chloride complexes with silver triflate (Cp*=(η⁵‐1,2,3,4,5‐pentamethylcyclopenta‐2,4‐dien‐1‐yl)). In addition, the complex 3 with X=OH was prepared by controlled hydrolysis of 2 . The solid‐state structures of these new complexes were determined by single‐crystal X‐ray‐diffraction techniques. Three different structural motifs were identified; 1, 2, 3 , and 7 are dimeric, while 5 is monomeric. The complexes were screened for their ability to stereospecifically polymerize styrene under homogeneous conditions. In the absence of activators, such as MAO (methylaluminoxane), 1 and 2 readily catalyzed the formation of atactic polystyrene; a strong dependence on the steric size of X was noted. In the presence of MAO, all of the complexes showed high activity and strong preference for the synthesis of syndiotactic polystyrene that was superior to that of TiCl₃(Cp*)]/MAO.