Novel High-Efficiency Single-Site Rare Earth (RE) Catalyst System for Isoprene Polymerization

Bis-(<i>o</i>-dipheylphosphinophenyl)amine, a tridentate (PNP) chelating ligand, and several of their Rare Earth (RE) metal complexes, [bis-(<i>o</i>-dipheylphosphinophenyl)amido]-RER₂, {[(C₆H₅)₂P-<i>o</i>-(C₆H₄)]₂NMR₂ (R = -CH₂-<i>o</i>-(C₆H₄)NMe₂: M = Y, <b>1</b>; Nd, <b>2</b>; Gd, <b>3</b>;), are prepared in high yields. When activated with the strong Lewis acid MMAO-7, all these complexes exhibit catalytic activity toward the polymerization of isoprene (IP) in non-protic hydrocarbons. While the Nd complex (<b>2</b>) showed moderate activity and stereoselectivity, the Y and Gd complexes (<b>1</b> and <b>3</b>) exhibited extremely high catalytic efficiency in IP homo-polymerization, and produced polyisoprene rubber (PI) with 95% to over 99% <i>cis</i>-1,4 stereoselectivity and narrow polydispersity indices (<2.0). Moreover, under industrially relevant conditions, complex <b>3</b> can catalyze IP to produce ultrahigh molecular weight PI (UHMW-PI, MW up to 1200-2600 kg/mol) rubber with a very narrow polydispersity index (PDI ca. 1.1-1.6), a high-performance elastomeric material mimic of natural rubber (NR).