Ansa-metallocene titanium complexes

Alt, H. G Foettinger, K. Milius, W. Synthesis, characterization and polymerization potential of ansa-metallocene dichloride complexes of titanium, zirconium and hafnium containing a Si-N-Si bridging... 

Constrained-geometry catalysts for C2H4 polymerization 88 that are counterparts of well-known ansa-metallocene systems have been prepared and shown to be active, in combination with MAO, toward polymerization of ethylene the product is almost entirely polyethylene, with ca. 1% of 1-octene obtained. The titanium complex was found to be four times as active as the zirconium species.1... 

Brintzinger and coworkers produced a titanium complex with a binaphthyl linked ansa metallocene ligand [56[. Upon activation with nBuLi, this complex catalyzed the reductions of B and 2 phenyl 1 pyrroline in 76 and 98% ee, respectively. Titanium catalysts with chiral amido cyclopentadienyl ligands have also been reported, but were considerably less stereoselective than the metallocene based ones [57]. 

Biscyclopentadienyl complexes and bridged metallocene complexes of titanium show lower polymerization activities than the monocyclopentadienyl complexes (39). The catalytic activity and S5nidiospecificity for bridged metallocenes does increase by decreasing the bite-angle (51). Although ansa-monocyclopentadienyl-amido titanium complexes are essentially inactive for homopolymerization of styrene, efficient sPS formation with nonbridged amido cylcopentadienyl complexes of titanium has been reported (52). 

The first isospecific propene polymerization with an ethanediyl-bridged bis (indenyl)-titanium complex demonstrated in 1983 the capability of ansa-metaUocenes to control the tacticity of a growing polypropylene chain [4, 48], thus creating a strong interest in exploring the potential use of ansa-metallocenes for industrial polypropylene production. A first step towards industrially suitable systems was the use of much more stable zirconium complexes, which when activated by the methylaluminoxane co-catalyst [3] allowed higher polymerization temperatures and thus higher activities [5]. 

---