STUDIES ON POLYMERIZATION MECHANISM OF CONJUGATED DIENE WITH η~3-ALLYL RARE EARTH MODEL COMPLEX

(η^-C_H_5)_2CeCl_5Mg_2(tmed)_2 was used as a catalyst to polymerize isoprene,Terminal ends of polyisoprene were identified as -CH_2-CH=CH_,which indicates that the insertion reaction of the monomer occurred between η^-allyl and cerium ion and gives a direct evidence for the η^-allyl mechanism of conjugated diene polymerzation with rare earth coordination catalysts.

Nickel-Catalyzed Regioselective Hydrosilylation of Conjugated Dienes

With the increasing demand for homoallylic silanes and allylic silanes,the highly efficient and regioselective hydrosilylations of conjugated dienes are urgently needed.Herein,we developed a Ni-catalyzed regiodivergent hydrosilylation of aromatic conjugated dienes by adjusting the temperature and ligands.Under low temperature(-30℃),an eternal-ligand-free system(Ni/t-BuOk)can efficiently facilitate the 3,4-anti-Markovnikov hydrosilylation to provide homoallylic silanes via electrophilic activation process;under room temperature(25℃),a ligand-controlled system(Ni/t-BuOk/PPh3)can eventuate the 3,4-Markovnikov hydrosilylation to produce allylic silanes via Chalk-Harrod process.Both systems are compatible with various conjugated dienes and primary silanes in excellent yields andregioselectivities.

Palladium-catalyzed 3,4-hydroaminocarbonylation of conjugated dienes for formation ofβ,γ-unsaturated amides

Hydrocarbonylation of conjugated dienes is one of the most promising yet challenging methods for the synthesis of carbonyl compounds.Herein,we reported the development of an unprecedented palladium-catalyzed branched selective 3,4-hydroaminocarbonylation of 1,3-dienes with CO and amines hydrochloride to affordβ,γ-unsaturated amides.This reaction employs readily available starting materials(including anilines,amines,amino acids,peptides,aryl-1,3-dienes,alyl-1,3-dienes)and tolerates a wide range of functional groups,thus providing a facile and effective approach to access a diverse array ofα-substitutedβ,γ-unsaturated amides.Mechanistic investigations suggested that the hydropalladation of dienes is irreversible,and the insertion of CO into the allyl-Pd species is probably the rate-limiting step.

Copolymers of Styrene with Conjugated Dienes by Titanium Catalysts:Synthesis,Characterization and Evaluation of the Mechanical Properties

1 Results Polymerization of butadiene,isoprene and styrene and binary copolymerization of styrene with butadiene and isoprene were investigated using the catalyst Ti(η5-C5H5)(η2-MBMP)Cl (1) (MBMP=2,2′-methylenebis(6-tert-butyl-4-methylphenoxo) activated with methylaluminoxane (MAO).Syndiotactic polystyrene, cis-1,4- polybutadiene and cis-1,4-polyisoprene were obtained in good yields at 50 °C.Binary copolymerization of styrene with butadiene yielded block copolymers containing segments of cis-1,4-polybut...

A HIGHER ACTIVE LANTHANIDE CHLORIDE CATALYST FOR STEREOSPECIFIC POLYMERIZATION OF CONJUGATED DIENE

It is known that the first lanthanide （Ln） catalyst used for stereospecific polymeriza-tion of conjugated diene is composed of LnCl3 and R3Al.It initiates stereospecific polymeri-zation of butadiene with a very high cis-1, 4 content（98%）, yet owns poor activity. This paper presents the new results obtained in our laboratory. By adding alcohol tothis binary system （LnCl3-R3Al）, the catalytic activity is greatly enhanced without any losson its high stereospecificity. It is shown that the catalytic activity is dependent on the ratioof its components and their order of addition. Furthermore, we have ascertained that itis the alcohol complex of LnCl3 with a definite composition LnCl3.R3OH, that turns out tobe an active catalyst when treated with R3Al.

The Wittig sigmatropic rearrangement in a conjugated diene system Ⅰ

A conjugated dienic benzyl ether was shown to undergo Wittig sigmatropic rearrangement to give a mixture of[1,2]and[1,4]besides the expected[2,3]rearrangement product.The solvent effect as well as the reaction pathways were discussed.

Studies on sulfinatodehalogenation——ⅪⅩ.The reaction of perfluoroalkyl iodides and perfluoroalkane-sulfonyl bromides with conjugated dienes

The reaction of TbCl_3 with K[2,4-(CH_2)_2C_5H_5] at 0℃ in THF followed by crystalliza- tion at -90℃ led to a pale yellow hexagonal prismatic crystalline product [2,4-[CH_3)_2-η~5-C_5H_5]_(2-) Tb·1/2THF, which is highly sensitive to air and water and rapidly efflorescent at ambient temper- ature. The single Crystal X-ray diffraction data of the compound have been collected at low tem- perature (-60℃) and the crystal structure has been solved by heavy atom method. It belongs to triclinic system, space group Pl with lattice parameters a=8.477 (?),b=12.583 (?),c=12.858 (?), a=118.08°,β=91.38°,γ=108.75°,V=1120.36 (?)~ 3 and Z=2. Least-squares refinement converged to a final value R=0.043. The compound possesses an idealized G_(2h) symmetry、with three 2,4- dimethylpentadienyl ligands bound to the central terbium atom in a pentahapto mode (η~5). Each unit cell contains two molecules of[2,4-(CH_3)_2-η~5-C_5H_5]_3Tb and one molecule of solvent THF, of which the role in the lattice has been discussed in detail.

Iron-Catalyzed Alkenylzincation of Internal Alkynes

The alkenylzincation of internal alkynes is an effective method for the synthesis of multi-substituted conjugated dienes;however,the current catalytic systems for this reaction are limited in terms of substrate scope and selectivity control,which restricts its practical applications.Herein,we report the first iron-catalyzed alkenylzincation of internal alkynes,which features mild conditions,simple operation,broad substrate scope (including aryl/alkyl,diaryl,and dialkyl acetylenes),excellent functional group tolerance (tolerating highly active functional groups such as ester,methylthio,amide,sulfonyl,cyano,etc.),and high activity (with a turnover number of up to 11500,the highest record for carbometallation reactions).Notably,the catalytic system described in this article also realized the highly selective vinylzincation of unfunctionalized internal alkynes as well as the alkenylzincation of unsymmetrical diarylacetylenes and dialkyl acetylenes,which have not been achieved with other catalytic systems reported in the literatures.The current study provides a highly selective access to synthetically important multi-substituted conjugated dienes.