Rare Earths/Main Group Metal Alkyls Catalytic Systems for the 1,4-trans Stereoselective Coordinative Chain Transfer Polymerization of Isoprene

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). (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4640-4647, 2010