Linked Constrained Geometry Type Half-Titanocenes

2 Linked (Constrained Geometry Type) Half-Titanocenes 

Linked half-titanocenes (so-called constrained geometry-type titanium complexes) like [Me2Si(C5Me4)(N Bu)]TiCl2 have also shown to be efficient catalyst precursors [2,16-19], although they have shown extremely low activity for syndiospecific styrene polymerization [16a,19a]. It has also been reported that styrene incorporation by linked Cp-amide Ti catalyst (constrained geometry 

Complex Ethylene (bar) [S]/[E] Temperature (°C) Activity MjMt Styrene (mol %y 

TABLE 5.4 Copolymerization of Ethylene with Styrene Using Different Linked Half-Titanocenes (lb,4 )-MAO Catalyst Systems (2)[16h]  

Styrene incorporation in ethylene/styrene dramatically improved with the use of a dinuclear catalyst system (Ti22Bi), and a copolymer with a high styrene content (76mol %) has been synthesized with this catalysis (Table 5.5). Therefore, this catalyst system afforded broad-range controllable styrene incorporation (styrene contents 39-76mol %) in copolymerization, although the observed activities should be further improved [19a]. Resonances ascribed to the three consecutive head-to-tail coupled styrene units in addition to tail-to-tail coupled dyads were observed in the NMR spectra of the resultant copolymers (styrene 50 mol %) [19a]. They assumed that the arene ring of the last-inserted styrene may preferentially coordinate with the adjacent Ti 

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