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 (M w / M ₙ = 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. magnified image Formation of 1,4‐cis‐ or 1,4‐trans‐enriched polyisoprenes upon activation with MAO.