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

Summary: The performances of readily available Ln(allyl) 2 Cl(MgCl 2 ) 2  · (THF) 4 precursors (Ln = Nd, 1 ; Y, 2 ; La, 3 ), in combination with alkyl aluminum activators [MAO, AlMe 3 , AlEt 3 , Al( i Bu) 3 ], have been studied in isoprene polymerization. The catalyst combination 1 /MAO (1:30) shows a high activity (average TOFs up to ca. 5 × 10 4 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 ( $\overline M _{\rm w} /\overline M _{\rm n}$  = 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 AlEt 3 or Al( i Bu) 3 , respectively.Formation of 1,4‐ cis ‐ or 1,4‐ trans ‐enriched polyisoprenes upon activation with MAO.