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
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Abstract
A series of chiral mononuclear dialkyl
complexes [(<i>S</i>,<i>S</i>)-BOPA]Ln(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub> (<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–C<sub>6</sub>H<sub>4</sub>–(CH<sub>2</sub>SiMe<sub>3</sub>)CN–CH(<sup><i>i</i></sup>Pr)CH<sub>2</sub>–O]Ln(CH<sub>2</sub>SiMe<sub>3</sub>)}<sub>2</sub> (<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<sup><i>i</i></sup>Bu<sub>3</sub>, the dialkyl complexes <b>1</b> and <b>2</b> exhibit very high activities (up to 6.8 × 10<sup>5</sup> g mol<sub>Ln</sub><sup>–1</sup> h<sup>–1</sup>) 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><sub>n</sub> = (0.2–1.0)
× 10<sup>5</sup> g/mol) and narrow molecular weight distributions
(<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> = 1.02–2.66)
