Synthesis, structure, and olefin polymerization activity of titanium complexes bearing asymmetric tetradentate [OSNO]-type bis(phenolato) ligands.

A series of chiral linear tetradentate bis(phenols) that contain both sulfur and nitrogen donors of the type [2,2'-(HOC 6 H 2 -6- t Bu-4-R 1 ) 2 SC 6 H 10 NR 2 ] [R 1 = Me (a), t Bu (b); R 2 =H (1), Me (2)], [2,2'-(HOC 6 H 2 -4,6- t Bu 2 ) 2 SC 6 H 10 N=CH] (3), and [2,2'-(HOC 6 H 2 -4,6- t Bu 2 ) 2 SC 6 H 10 NHCH 2 ] (4) were synthesized. The reaction of these bis(phenols) with TiX 4 (X=Cl O i Pr) afforded the corresponding C 1 -symmetric titanium complexes [Ti{2,2'-(OC 6 H 2 -6- t Bu-4-R 1 ) 2 SC 6 H 10 NR 2 }-X2] [R 1 = Me (a), 'Bu (b); R 2 = H, X = Cl (5a, 5b), O i Pr (6a); R 2 = Me, X = Cl (7a, 7b), O i Pr (8a)], [Ti{2,2'-(OC 6 H 2 -4,6- t Bu 2 ) 2 SC 6 H 10 N=CH}Cl 2 ] (9), and [Ti{2,2'-(OC 6 H 2 -4,6- t Bu 2 ) 2 SC 6 H 10 NHCH 2 }Cl 2 ] (10). The formation of titanium complexes 5-8 proceeded diastereoselectively, but a mixture of two isomers (a and b) was obtained for 9 and 10. The configuration of the ligand around the metal center was determined by a combination of NMR spectroscopy and single-crystal X-ray diffraction studies of 5b, 7b, 8a, 9b, 10a, and 10b. All titanium complexes were configurationally stable in solution up to 100 °C. For compounds 5-8, cis-α and cis-β 2 coordination modes of the ligand were observed, depending on the nitrogen substituent and the auxiliary ligand. In compounds 9 and 10, both configurations coexist and do not interconvert at elevated temperatures, but HCI catalyzes the isomerization of 10a to 10b. Upon activation with methylaluminoxane, [Ti{OSNO}X 2 complexes show moderate activity in the polymerization of styrene and trace activity in the polymerization of 1-hexene.