Enantiomerically Pure Titanium Complexes Containing an [OSSO]‐Type Bis(phenolate) Ligand: Synthesis, Structure, and Formation of Optically Active Oligostyrenes

Chiral 1,2‐ trans ‐dithiocyclohexanediyl‐bridged bis(phenols) of the type [2,2′‐{HOC 6 H 2 ‐6‐R 1 ‐4‐R 2 } 2 S 2 C 6 H 10 ] ([OSSO]H 2 , R 1 = t Bu, i Pr, H; R 2 = t Bu, i Pr, Me) could be conveniently and selectively synthesized in three steps, starting from cyclohexene oxide and arene thiolate. The racemic bis(phenols) could be resolved using an enantiopure ( S )‐camphorsulfonic ester auxiliary or by (chiral) HPLC. Complexation of the racemic bis(phenols) to TiX 4 (X=Cl, O i Pr) proceeds in a diastereoselective fashion to give only the Λ, R,R and Δ, S,S enantiomers. Racemic [Ti{(OC 6 H 2 ‐6‐ t Bu‐4‐Me) 2 S 2 C 6 H 10 }Cl 2 ] reacts with benzyl magnesium bromide to afford the crystallographically characterized dibenzyl complex. The benzyl cation formed using B(C 6 F 5 ) 3 in C 6 D 5 Br slowly decomposes at temperatures above +10 °C. When treated with methylaluminoxane, the dichloro complexes [Ti{OSSO}Cl 2 ] polymerize styrene with activities up to 146 kg (mol catalyst) −1  [styrene (mol L −1 )] −1  h −1 ; diisopropoxy complexes [Ti{OSSO}(O i Pr) 2 ] show mere trace activity. With 1‐hexene as a chain‐transfer agent, activated enantiopure titanium complexes give low‐molecular‐weight homochiral isotactic oligostyrenes, terminated by one to five 1‐hexene units with M n values as low as 750 g mol −1 for R= t Bu and 1290 g mol −1 for R=Me. Below M n ≈5000 these oligostyrenes show optical activity.