Mixed Aluminum-Magnesium-Rare Earth Allyl Catalysts for Controlled Isoprene Polymerization: Modulation of Stereocontrol

Summary: The performances of readily available Ln(allyl)2Cl(MgCl2)2 · (THF)4 precursors (Ln = Nd, 1; Y, 2; La, 3), in combination with alkyl aluminum activators [MAO, AlMe3, AlEt3, Al(iBu)3], have been studied in isoprene polymerization. The catalyst combination 1/MAO (1:30) shows a high activity (average TOFs up to ca. 5 × 104 mol (Ip) · mol (Nd)−1 · h−1 at 20 °C) and produces polyisoprene in a controlled fashion with up to 98.5% cis content, number-average molecular weights in reasonable agreement with calculated values, and relatively narrow polydispersities index ( = 1.20–1.70). The yttrium precursor 2 affords systems with much lower activity and degree of control, but enables the formation of either 1,4-cis-enriched (75%) or 1,4-trans-enriched (91%) polyisoprenes, simply replacing the MAO activator by AlEt3 or Al(iBu)3, respectively. Formation of 1,4-cis- or 1,4-trans-enriched polyisoprenes upon activation with MAO.