Synthesis, Structure, and Olefin Polymerization Activity of Titanium Complexes Bearing Asymmetric Tetradentate [OSNO]-Type Bis(phenolato) Ligands

Abstract

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)}X(2)] [R(1) = Me (a), (t)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 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.