| Abstrakt: |
The synthesis, spectroscopic characterisation and catalytic olefin polymerisation behaviour of a class of binuclear titanium bis(benzyl) complexes bearing bis-(pyridine-2-phenolate-6-methine)-[μ-(arylene-1,4-diyl-2,3-X2)] ligands [X2 = -C4H4-- (1), F2 (2), H2 (3)], and mononuclear analogues, are described. These bi-metallic catalyst frameworks are designed to exhibit a degree of conformational flexibility, which is regulated by steric effects and crucially permits tuning of intermetallic distances and geometry, yet their shape-persistent nature can also confer favourable entropic terms. Complexes 1-3 are characterised as two diastereomers [meso (RS) and rac (RR,SS)] in ratios of 1.32, 1.18 and 1.13 respectively, according to ¹H NMR spectroscopy. In contrast to 3,[¹H, ¹H]-ROESY experiments for 1 and 2 revealed that the X² substituents can impose preferred conformations with syn orientations of Ti2 centres and benzyl groups, thus implying that the activated catalysts would present binding sites with the same direction of access. For ethylene-(1-octene) copolymerisation reactions, in conjunction with [Ph3C][B(C6F5)4], catalyst 1 displayed superior efficiencies and produced polymers with higher Mw values and enhanced comonomer incorporation ratios (up to 41%), when compared with the mononuclear 5m (22%). These results are indicative of enhanced comonomer enchainment and cooperative reactivity by the Ti2 sites. [ABSTRACT FROM AUTHOR] |
