International audienc

A series of lanthanum and neodymium complexes comprising the half-lanthanidocenes Cp*La(BH 4 ) 2 (THF) 2 (Cp* ¼ 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 . V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: [4640][4641][4642][4643][4644][4645][4646][4647] 2010