Rare earths/main group metal alkyls catalytic systems for the 1,4‐<i>trans</i> stereoselective coordinative chain transfer polymerization of isoprene

Abstract

Abstract A series of lanthanum and neodymium complexes comprising the half‐lanthanidocenes Cp*La(BH 4 ) 2 (THF) 2 (Cp* = C 5 Me 5 ) ( 1 ) and Cp*Nd(BH 4 ) 2 (THF) 2 ( 2 ), the trisborohydrides La(BH 4 ) 3 (THF) 3 ( 3 ) and Nd(BH 4 ) 3 (THF) 3 ( 4 ), the trichlorides LaCl 3 (THF) 3 ( 5 ) and NdCl 3 (THF) 3 ( 6 ), the triisopropoxides La(O i Pr) 3 ( 7 ) and Nd(O i Pr) 3 ( 8 ), and the triaryloxide Nd(OC 6 H 3 ‐ t Bu 2 ‐2,6) 3 ( 9 ) has been assessed for the chain transfer polymerization of isoprene. A transmetalation process is occurring efficiently with the borohydride complexes in the presence of magnesium dialkyl. A gradual decrease of the 1,4‐ trans stereoselectivity of the reaction is observed at the benefit of 3,4‐selectivity with increasing quantities of magnesium dialkyl. This can be at least partially attributed to the growth of 3,4 polyisoprene units onto the magnesium atom. By combining dialkylmagnesium and trialkylaluminum, a 1,4‐ trans stereospecific reversible coordinative chain transfer polymerization of isoprene is reached using the half‐lanthanocene Cp*La(BH 4 ) 2 (THF) 2 . © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010