Synthesis and Characterization of Siloxane Contained Liquid Crystalline Polymers with Two Symmetric Mesogens
摘要:
New thermotropic siloxane contained liquid crystalline polymers with two symmetric mesogens were prepared by hydrosilation with Rh(PPh(3))(3)Cl catalyst. It was found that Rh(PPh(3))(3)Cl catalyst was effective for low molecular weight polymerization. The resulting polymers exhibited good solubility in organic solvents such as tetrahydrofuran(THF), chloroform, and so on. The structures of the monomer and polymers were confirmed by IR, H-1 and C-13 NMR spectra The number average molecular weight(<(Mn)over bar>) values of the polymers were in the range of 2000 similar to 6000. Thermal properties of the monomers and the polymers were analyzed by differential scanning calorimetry(DSC), and polarized optical microscopy. Monomers did not show liquid crystalline phase but the polymers exhibited nematic phases.
Chiral Benzoquinones as a New Class of Ligands for Asymmetric Catalysis: Synthesis and Application to the Palladium(II)-Catalyzed 1,4-Dialkoxylation of 1,3-Dienes
Chiral C-2-symmetric 2,5-bisamide hydroquinone ligands, with beta-amino alcohols as chiral building units, were synthesized in excellent overall yields. The ligands gave up to 54.4% ee in the palladium-catalyzed 1,4-dialkoxylation of 1,3-dienes. These findings demonstrate the potential of asymmetric induction utilizing chiral benzoquinones as ligands in palladium(II) catalysis, albeit with modest enantiomeric excesses. Weakly coordinating hydroxyl groups of the ligand appear to be crucial for the success of the reaction. Mechanistic aspects and the origin of enantioselectivity are also discussed.