Styrene is polymerized isospecifically by group 4 metal complexes that contain a C2-symmetrically coordinated 1,4-dithiabutane-linked bis(phenolato) ligand activated by methylaluminoxane.

The effect of ethyl benzoate (EB) as a component of the solid catalyst ("internal" base) and/or of the co-catalyst ("external" base) on propene polymerization in the presence of different MgClz-supported Ziegler-Natta systems was investigated systematically. From the experimental results, it is suggested that internal EB mainly prevents TiCb from coordination on the MgClz crystal faces where mostly non-stereospecific active sites would be formed, whereas external EB inhibits selectively the non-stereospecific centres and decreases the reaction of the alkylaluminium with the internal base. A possible model of active sites for isotactic 1-alkenes polymerization in the presence of MgC12-supported catalysts is presented, which is in good agreement with a large number of known experimental facts.

The stereoregularity of polystyrenes prepared in the presence of different syndiotactic specific homogeneous catalysts, at different temperatures and monomer concentrations, has been evaluated by I3C NMR. It is confirmed that the statistical model of the stereospecific propagation is first-order Markovian. The stereoregularity of the polymers decreases while increasing the polymerization temperature and is affected by the concentration of the monomer, by the ligands of the transition metal precursor of the catalyst, and is higher in the presence of titanium based catalysts. Polymerization of substituted styrenes is increasingly stereospecific in the order p-chlorostyrene < styrene < p-methylstyrene. The results strongly support the polyinsertion mechanism proposed in a previous paper by some of us.

The present work deals with the production of glycidol through a new synthetic approach based on the conversion of 2-chloro-1,3-propanediol (β-MCH), a by-product in the epichlorohydrin production plant.

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A series of titanium dichloro and di(isopropoxy) complexes with a 1,4-dithiabutanediyllinked 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 delta and lambda 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 helical structure in solution up to 100 °C. The helical structure with trans-O,O, cis-S,S, cis-Cl,Cl (“alpha-cis”) is confirmed by the single-crystal structure analysis of two dichloro complexes [Ti(OC6H2-6-R1-4-R2)2{S(CH2)2S}Cl2] (2e, R1 ) tBu, R2 ) Me; 2i, R1, R2 ) 2-phenyl-2-propyl). Related dichloro and di(isopropoxy) complexes that contain a 1,5-dithiapentanediyl-linked bis(4,6-disubstituted phenolato) ligand [Ti(OC6H2-6-R1-4-R2)2{S(CH2)3S}X2] (R1 ) tBu; R2 ) Me, tBu, OMe; X ) Cl, 5a-c; OiPr, 6a-c) were synthesized in an analogous fashion and shown by NMR spectroscopy to be conformationally flexible at room temperature. This fluxionality can be explained by a twisting of one fivemembered chelate ring, converting the trans-O,O (“alpha-cis”) to the cis-O,O (“beta-cis”) isomer. A crystal structure determination of ligand [Ti(OC6H2tBu2-4,6)2{S(CH2)3S}(OiPr)2] (6b) revealed the trans-O,O, cis-S,S, cis-Cl,Cl (“alpha-cis”) isomer. Upon activation with methylaluminoxane, the stereorigid derivatives 2e-i efficiently polymerize styrene to give isotactic polystyrene, whereas the conformationally flexible complexes 2a-d produce atactic polystyrene with negligible activity. Under the same conditions, complexes with the 1,5-dithiapentanediyllinked ligand 5a,b and 6b,c polymerized styrene syndiospecifically with low activity

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