Isospecific Styrene Polymerization by Chiral Titanium Complexes That Contain a Tetradentate [OSSO]-Type Bis(phenolato) Ligand

Abstract

A series of titanium dichloro and di(isopropoxy) complexes with a 1,4-dithiabutanediyl-linked bis(4,6-disubstituted phenolato) ligand [Ti(OC6H2-6-R1-4-R2)2{S(CH2)2S}X2] (X = Cl, 2a−i, OiPr, 3a−i; R1 = H, Me, iPr, tBu, 2-phenyl-2-propyl; R2 = H, Me, tBu, OMe, 2-phenyl-2-propyl) were synthesized by reacting the corresponding linked bis(phenol) (HOC6H2-6-R1-4-R2)2{S(CH2)2S} (1a−i) with the titanium precursor TiX4. The NMR spectra of the dichloro complexes Ti(OC6H2-6-R1-4-R2)2{S(CH2)2S}Cl2] (2a−d) with small ortho substituents R1 = H, Me, iPr are in agreement with a C2-symmetrical helical structure, but the complexes become fluxional at higher temperatures. The corresponding di(isopropoxy) complexes [Ti(OC6H2-6-R1-4-R2)2{S(CH2)2S}(OiPr)2] (3a−d) are fluxional in solution at room temperature due to rapid interconversion between the Δ and Λ isomers. In contrast, both dichloro and di(isopropoxy) complexes 2e−i and 3e−i with bulky ortho substituents R1 = tBu and 2-phenyl-2-propyl exhibit a rigid C2-symmetrical he...