Highly trans-Stereospecific Isoprene Polymerization by Neodymium Borohydrido Catalysts

Highly stereospecific polymerization of isoprene was achieved using borohydridoneodymium complexes. In combination with stoichiometric amounts of dialkylmagnesium, Nd(BH 4 ) 3 (THF) 3 ( 1 ) and Cp*‘Nd(BH 4 ) 2 (THF) 2 ( 2 ) (Cp*‘ = C 5 Me 4 n Pr) afford very efficient catalysts. The activity reaches 37300 (g of polyisoprene/mol of Nd)/h. Half-lanthanidocene 2 gives rise to polyisoprene, 98.5% trans -regular, the highest content yet described for a homogeneous organometallic catalyst. NMR experiments argue for the formation of bimetallic Nd(μ-BH 4 )Mg active species.