Titanium Catalysts

Monopentamethylcyclopentadienyltitanium triflate and bistriflimide (bistrifluoromethylsulfonylimide) complexes of the form Cp*TiRLn (for R = OH, Me, OMe, O-C6H2(Me)3, n = 2, L = OTf, NTf2; for R = o-O2C6H4, n = 1; L = OTf) and titanocene bistriflimide Cp2Ti(NTf2)2 were obtained by displacement of the chloride ligand using silver salts of the triflate or bistriflimide.

Single crystal X-ray diffraction studies of five derivatives (R = OH, Me, OMe, O-C6H2(Me)3, o-O2C6H4) showed most of the triflates as dimers with one bridging and one terminal triflate group per titanium center while the bulky phenoxy derivative with its three methyl substituents existed as a monomer. Characterization of a metallocene derivative, the titanocene bistriflimide complex by single crystal X-ray studies revealed coordination through one of the oxygens of the sulfonimide group (Figure shown below). On the other hand, the monopentamethylcyclopentadienyltitanium bistriflimide complexes proved to be very moisture-sensitive as attempts to obtain X-ray quality crystals invariably resulted in either decomposition or hydrolysis. We report here an unusual chelating mode of the bistriflimide ligand as well as an 'adamantyl-like' structure for one of the complexes.

The reactivity of these complexes as polymerization catalysts was tested with styrene. Results of polymerizations with methylaluminoxane (MAO) as activator showed syndiospecific polymerization with activities slightly better than the parent trichloro complex. Stereoselectivity was not appreciably affected by changes in the R groups but the catalytic activity was observed to decrease with an increase in steric bulk of the R ligand. Atactic polystyrene was obtained from polymerizations without the use of MAO. The bistriflimide complexes exhibited higher polymerization activity compared to the triflate complexes.