Chiral Palladium(II) and Nickel(II) Complexes with <i>C</i>₂‑Symmetrical Tridentate Bis(oxazoline) Ligands: Synthesis, Characterization, and Catalytic Norbornene Polymerization

A series of chiral palladium­(II) and nickel­(II) complexes bearing a <i>C</i>₂-symmetric monoanionic tridentate bis­(oxazoline) ligand, (R₂-(<i>S</i>,<i>S</i>)-BOZ)­M­(X) (<b>1</b>–<b>6</b>: R = CH­(CH₃)₂, M = Pd, X = OAc (<b>1</b>); R = CH­(CH₃)₂, M = Pd, X = Cl (<b>2</b>); R = Ph, M = Pd, X = Cl (<b>3</b>); R = Ph, M = Ni, X = Cl (<b>4</b>); R = CH­(CH₃)₂, M = Ni, X = Cl (<b>5</b>); R = CH­(CH₃)₂, M = Pd, X = OTf (<b>6</b>)), have been synthesized and structurally characterized. The experimental results demonstrate that such chiral palladium­(II) and nickel­(II) complexes bearing <i>C</i>₂-symmetric tridentate ligands in which the monoanionic group is located inside are effective for norbornene polymerization. In the presence of various cocatalysts such as MAO, MMAO, and activator/AlR₃, these chiral palladium­(II) complexes exhibit much higher activities of up to 4.8 × 10⁸ g of PNB (mol of Pd)⁻¹ h^–1 for the vinylic polymerization of norbornene, affording insoluble polynorbornenes with high packing density. In contrast, the chiral nickel­(II) complexes show relatively low activities of ca. 4.5 × 10⁷ g of PNB (mol of Ni)⁻¹ h^–1 and produce both insoluble polynorbornenes and soluble high-molecular-weight polynorbornenes with moderate molecular weight distributions

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%

Quasi-Living <i>trans</i>-1,4-Polymerization of Isoprene by Cationic Rare Earth Metal Alkyl Species Bearing a Chiral (<i>S</i>,<i>S</i>)‑Bis(oxazolinylphenyl)amido Ligand

A series of chiral mononuclear dialkyl complexes [(<i>S</i>,<i>S</i>)-BOPA]­Ln­(CH₂SiMe₃)₂ (<b>1</b>, <b>2</b>) (BOPA = (<i>S</i>,<i>S</i>)-bis­(oxazolinylphenyl)­amido; Ln = Sc (<b>1</b>); Ln = Lu (<b>2</b>)) and binuclear alkyl complexes [<i>ο</i>-(<i>S</i>)-OPA–C₆H₄–(CH₂SiMe₃)­CN–CH­(^<i>i</i>Pr)­CH₂–O]­Ln­(CH₂SiMe₃)}₂ (<b>3</b>,<b> </b><b>4</b>) (OPA = (oxazolinylphenyl)­amine; Ln = Y (<b>3</b>); Ln = Tm (<b>4</b>)) have been synthesized in moderate yields via one-pot acid–base reactions by use of the tris­(trimethylsilylmethyl) rare earth metal complexes with the chiral tridentate (<i>S</i>,<i>S</i>)-bis­(oxazolinylphenyl)­amine ligand. In the presence of activator with or without a small amount of Al^<i>i</i>Bu₃, the dialkyl complexes <b>1</b> and <b>2</b> exhibit very high activities (up to 6.8 × 10⁵ g mol_Ln^–1 h^–1) and <i>trans</i>-1,4-selectivity (up to 100%) in the quasi-living polymerization of isoprene, yielding the <i>trans</i>-1,4-PIPs with moderate molecular weights (<i>M</i>_n = (0.2–1.0) × 10⁵ g/mol) and narrow molecular weight distributions (<i>M</i>_w/<i>M</i>_n = 1.02–2.66)