1,4-Selective Polymerization of 1,3-Cyclohexadiene and Copolymerization with Styrene by Cationic Half-Sandwich Fluorenyl Rare Earth Metal Alkyl Catalysts

The regioselective coordination–insertion polymerization of 1,3-cyclohexadiene (CHD) and copolymerization with styrene (S) could be achieved by cationic half-sandwich fluorenyl rare earth metal alkyl catalysts generated by treating half-sandwich fluorenyl rare earth metal dialkyl complexes Flu′Ln­(CH₂SiMe₃)₂(THF)_n (<b>1</b>–<b>10</b>) with an activator (such as [Ph₃C]­[B­(C₆F₅)₄] (<b>A</b>), [PhNHMe₂]­[B­(C₆F₅)₄] (<b>B</b>), or B­(C₆F₅)₃ (<b>C</b>)) and Al^<i>i</i>Bu₃. The homopolymerization of CHD afforded poly­(CHD)­s with complete 1,4 selectivity (1,4 selectivity up to 100%). The copolymerization of CHD with styrene gave new random CHD–S copolymers with CHD content ranging from 22 to 74 mol % containing 1,4-linked CHD–CHD, alternating CHD–S, and syndiotactic S–S sequences unavailable previously. The activity of the copolymerization and the comonomer compositions and sequences of the resulting CHD–S copolymers could be easily controlled by changing the substituted fluorenyl ligand, the metal center, the activator, the temperature, and the molar ratio of comonomers. The residual C–C double bonds of the random CHD–S copolymers could be further epoxidized by <i>meta</i>-chloroperoxybenzoic acid (<i>m</i>CPBA) at room temperature to prepare high-performance polymers with polar groups and reactive sites in the polymer backbone. Such functionalization could improve the solubility, dying, acidity, and surfactivity of these copolymer materials

1,4-Selective Polymerization of 1,3-Cyclohexadiene and Copolymerization with Styrene by Cationic Half-Sandwich Fluorenyl Rare Earth Metal Alkyl Catalysts

The regioselective coordination–insertion polymerization of 1,3-cyclohexadiene (CHD) and copolymerization with styrene (S) could be achieved by cationic half-sandwich fluorenyl rare earth metal alkyl catalysts generated by treating half-sandwich fluorenyl rare earth metal dialkyl complexes Flu′Ln­(CH₂SiMe₃)₂(THF)_n (<b>1</b>–<b>10</b>) with an activator (such as [Ph₃C]­[B­(C₆F₅)₄] (<b>A</b>), [PhNHMe₂]­[B­(C₆F₅)₄] (<b>B</b>), or B­(C₆F₅)₃ (<b>C</b>)) and Al^<i>i</i>Bu₃. The homopolymerization of CHD afforded poly­(CHD)­s with complete 1,4 selectivity (1,4 selectivity up to 100%). The copolymerization of CHD with styrene gave new random CHD–S copolymers with CHD content ranging from 22 to 74 mol % containing 1,4-linked CHD–CHD, alternating CHD–S, and syndiotactic S–S sequences unavailable previously. The activity of the copolymerization and the comonomer compositions and sequences of the resulting CHD–S copolymers could be easily controlled by changing the substituted fluorenyl ligand, the metal center, the activator, the temperature, and the molar ratio of comonomers. The residual C–C double bonds of the random CHD–S copolymers could be further epoxidized by <i>meta</i>-chloroperoxybenzoic acid (<i>m</i>CPBA) at room temperature to prepare high-performance polymers with polar groups and reactive sites in the polymer backbone. Such functionalization could improve the solubility, dying, acidity, and surfactivity of these copolymer materials

Cationic Tropidinyl Scandium Catalyst: A Perfectly Acceptable Substitute for Cationic Half-Sandwich Scandium Catalysts in <i>cis</i>-1,4-Polymerization of Isoprene and Copolymerization with Norbornene

Different nonmetallocene rare earth metal alkyl complexes such as monotropidinyl (Trop) scandium dialkyl complex (Trop)­Sc­(CH₂SiMe₃)₂(THF) (<b>1</b>), ditropidinyl yttrium alkyl complex (Trop)₂Y­(CH₂SiMe₃)­(THF) (<b>3</b>) as well as binuclear lutetium alkyl complex bearing one tetradentate dianionic 6-<i>N</i>-methyl-1,4-cycloheptadienyl (NMCH) ligand [(NMCH)­Lu­(CH₂SiMe₃)­(THF)]₂ (<b>2</b>) have been synthesized in high yields via one-pot acid–base reaction by using of the tris­(trimethylsilylmethyl) rare earth metal complexes with the readily available natural product tropidine. The polymerization experiments indicate that the monotropidinyl scandium dialkyl complex <b>1</b> displays reactivity akin to that of the analogous monocyclopentadienyl scandium dialkyl complexes. In the presence of activator and a small amount of AlMe₃, complex <b>1</b> exhibits similar activities (up to 1.6 × 10⁶ g mol_Sc^–1 h^–1) but higher <i>cis</i>-1,4-selectivities (up to 100%) than (C₅H₅)­Sc­(CH₂SiMe₃)₂(THF) (<i>cis</i>-1,4-selectivity as 95%) in the isoprene polymerization, yielding the pure <i>cis</i>-1,4-PIPs with moderate molecular weights (<i>M</i>_n = 0.5–11.2 × 10⁴ g/mol) and bimodal molecular weight distributions (<i>M</i>_w/<i>M</i>_n = 1.48–6.07). Moreover, the complex <b>1</b>/[Ph₃C]­[B­(C₆F₅)₄/Al^<i>i</i>Bu₃ ternary system also shows good comonomer incorporation ability in the copolymerization of isoprene and norbornene similar to the [C₅Me₄(SiMe₃)]­Sc­(η³-CH₂CHCH₂)₂/activator binary system, affording the random isoprene/norbornene copolymers with a wide range of isoprene contents around 57–91 mol % containing <i>cis</i>-1,4 configuration up to 88%