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'-(HOC6H2-6-Bu-t-4-R-1)(2)SC6H10NR2] [R-1 = Me (a), Bu-t (b); R-2 = H (1), Me (2)], [2,2'-(HOC6H2-4,6-Bu-t(2))(2)SC6H10N = CH] (3), and [2,2'-(HOC6H2-4,6-Bu-t(2))(2)SC6H10NHCH2] (4) were synthesized. The reaction of these bis(phenols) with TiX4 (X=Cl, (OPr)-Pr-i) afforded the corresponding C-1-symmetric titanium complexes [Ti{2,2'-(OC6H2-6-Bu-t-4-R-1)(2)SC6H10NR2}-X-2] [R-1 = Me (a), Bu-t (b); R-2 = H, X = Cl (5a, 5b), (OPr)-Pr-i (6a); R-2 = Me, X = Cl (7a, 7b), (OPr)-Pr-i (8a)], [Ti{2,2'-(OC6H2-4,6-Bu-2)(2)SC6H10N=CH}Cl-2] (9), and [Ti{2,2'-(OC6H2-4,6- Bu-t(2))(2)SC6H10NHCH2}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 degrees C. For compounds 5-8, cis-alpha and cis-beta(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 HCl 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.