Facile Synthesis of Lanthanidocenes by the Borohydride/Alkyl Route and Their Application in Isoprene Polymerization

Several borohydridolanthanidocenes were synthesized by means of a straightforward approach starting from equimolar amounts of Ln(BH(4))(3)(thf)(3) (Ln = Nd, Sm) and n-butylethylmagnesium (BEM) in the presence of 2 equiv. of a cyclopentadiene derivative. Depending on the nature of the cyclopentadiene, monometallic Cp(2)(center dot)Nd(BH(4))(thf) (Cp(center dot) = C(5)Me(5)) (1), heterodimetallic [Cp(2)Nd(BH(4)) (mu-BH(4))](2)Mg(thf)(4) (Cp = C(5)H(5)) (2), [(CMe(2)C(5)H(4))(2)Ln(BH(4)) (mu-BH(4))](2)Mg(thf)(3) (Ln = Nd, 3a; Ln = Sm, 3b), and monometallic anilidocyclopentadienyl compounds (C(5)Me(4)CH(2)SiMe(2)NPh)Ln(BH(4))(thf)(2) (Ln = Nd, 4a; Ln = Sm, 4b) were isolated. The complexes were characterized by (1)H NMR spectroscopy, elemental analysis, and X-ray structural analysis. Mg(BH(4))(2)(thf)(3) (5) was isolated as a by-product and structurally characterized, revealing an unprecedented structural arrangement. In combination with BEM, complexes 2a, 3a, and 4a were found to be efficient in isoprene polymerization to afford highly stereoregular transpolyisoprene. Similar results were obtained by an all in situ approach starting from Nd(BH(4))(3)(thf)(3)/BEM mixtures in the presence of 2 equiv. of cyclopentadiene derivative.