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

Abstract

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)=tBu, iPr, H; R(2)=tBu, iPr, 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, OiPr) proceeds in a diastereoselective fashion to give only the Lambda,R,R and Delta,S,S enantiomers. Racemic [Ti{(OC(6)H(2)-6-tBu-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 degrees 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}(OiPr)(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=tBu and 1290 g mol(-1) for R=Me. Below M(n) approximately 5000 these oligostyrenes show optical activity.

Titanium complexes with sulfur-linked bis(phenolate) ligands

“…Comparatively good results were obtained recently for a routine crystal structure determination of (I) (Meppelder et al, 2008). We have now obtained high-quality crystals of this compound by reactive crystallization.…”

“…Compound (I) was prepared as described previously (Meppelder et al, 2008). High-quality crystals were obtained by reactive crystallization.…”

Synthesis and olefin homo- and copolymerization behavior of new vanadium complexes bearing [OSSO]-type ligands

“…For example, catalysts based on phenoxy-imine complexes may be not only more active than the metallocene catalysts, but they make it possible to produce a variety of polyolefinic materials, inclusive of ultra-high-molecular-weight PEs, welldefined multimodal PEs, selective vinyl-and Al-terminated PEs, isotactic and syndiotactic PPs, as well as stereo-and regioirregular high-molecular weight poly(1-olefin)s [1]. Group 4 transition metal complexes which incorporate tetradentate [OSSO]-type bis(phenolate) ligands have also been quite extensively studied in homo-and copolymerization of olefins as well as in polymerization of styrene and its derivatives, and in olefin-styrene copolymerization [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The titanium complex of the tetradentate [OSSO]-type diphenolate ligand with the 1,4-dithiabutanediyl-bridge yielded isotactic PS at very high activity.…”

“…That catalyst was also active in the copolymerization of conjugated dienes with ethylene and provided prevailingly alternating copolymers [13], in the copolymerization of ethylene with 4-methyl-1,3-pentadiene [17], and it catalyzed the homopolymerization of conjugated dienes as well [18]. Enantiomerically pure titanium complexes which contained trans-1,2-cyclohexanediyl-linked [OSSO]-type bis(phenolate) ligand were found to produce low-molecular-weight homochiral isotactic oligostyrenes which showed optical activity [14]. There are also known group 4 metal complexes with o-carborane-bridged [OSSO]-type tetradentate ligands with high activity towards ethylene homo-and copolymerization [19].…”

A vanadium(V) complex with a tetradentate [OSSO]-type bis(phenolato) ligand: Synthesis, structure, and ethylene polymerization activity

“…Recently, several research groups have reported new post-metallocene vanadium catalysts featuring aryloxide-based ligands [7], since aryloxides are known to give highly active olefin polymerization catalysts [8] and are of potential interest as chemical models for the active site of vanadium nitrogenase [9]. We have recently introduced a new family of chiral-at-metal group IV metal catalysts precursors supported by linear, tetradentate 1,x-dithiaalkanediyl-bridged bis(phenolato) [OSSO] ligands, which show interesting reactivity towards a variety of olefins [10]. Here, we report the synthesis, structure and olefin polymerization study of a vanadium(V) complex that contains a trans-1,2-dithiacyclohexane-bridged bis(phenolato) ligand.…”