Binary ansa-lanthanidocenes/dialkylmagnesium systems versus single-component catalyst: Controlled synthesis of end-capped syndiotactic oligostyrenes

Combinations of the ansa-chloroneodymocene precursor [(Cp–CMe2–Flu)Nd(μ-Cl)]2 (2) and a dialkylmagnesium (1–100 equiv. versus Nd) have been explored for styrene oligomerization and compared to the single-component polymerization catalyst [Cp–CMe2–Flu]Nd(allyl)(THF) (1). Binary systems derived from 2 and Mg(n-Bu)2 or Mg(allyl)2 are moderately active at 60 °C (1–8 kg PS mol Nd−1 h−1), yielding soluble oligostyrenes (Mn = 1600–6500 g mol−1, Mw/Mn = 1.3–2.5), which have an unprecedented high degree of syndiotacticity (Pr = 94%, determined by 13C NMR spectroscopy) and are selectively end-capped by butyl or allyl groups (identified by 1H NMR and/or MALDI-TOF-MS). The formation of the oligostyrenes is proposed to arise exclusively from a coordination/insertion mechanism, involving in situ generated Nd-alkyl species that are active for syndiotactic styrene polymerization and undergo chain transfer via transmetallation to excess dialkylmagnesium reagent.

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