Syntheses of dinuclear titanium constrained geometry complexes with polymethylene bridges and their copolymerization properties

The polymethylene bridged dinuclear half-sandwich constrained geometry catalyst (CGC) [Ti(η5:η1-C9H5SiMe2NCMe3)]2 [(CH2)n] (n=6 (10), n=9 (11), n=12 (12)) have been prepared by treating two equivalents of TiCl3(THF)3 with the corresponding tetralithium salts of the ligands followed by oxidation by AgCl. Proton and Carbon-13 NMR spectra of the synthesized complexes provide firm evidence for the anticipated dinuclear structure. The important feature associated with the chemical shift of Carbon-13 NMR is the downfield chemical shift of 63.0 ppm due to the ipso-carbon of t-butyl group bonded at the coordinated nitrogen. In addition the chemical shift of the bridge head carbon at the indenyl ring is shifted toward highfield from 119 to 97 ppm. In order to investigate the catalytic behaviors of the prepared dinuclear catalysts copolymerization of ethylene and styrene was conducted in the presence of modified methylaluminoxane. The prime observance is that their activities increase in the order of 10<11<12 which indicates the presence of longer bridge between two active sites contributes to facilitate the polymerization activity of the dinuclear CGC. The melting points of the generated copolymers decrease as the styrene portion in feed increases. An interesting point is that styrene content in copolymers formed by the dinuclear catalysts is actually bigger than that in copolymer formed by the mononuclear CGC, which demonstrates the superior comonomer response of the dinuclear CGC comparing to the normal CGC.