Cationic allyl complexes of the rare-earth metals: synthesis, structural characterization, and 1,3-butadiene polymerization catalysis.

Monocationic bis-allyl complexes Ln(eta(3)-C(3)H(5))(2)(thf)(3)B(C(6)X(5))(4) (Ln = Y, La, Nd; X = H, F) and dicationic mono-allyl complexes of yttrium and the early lanthanides Ln(eta(3)-C(3)H(5))(thf)(6)BPh(4)(-) (Ln = La, Nd) were prepared by protonolysis of the tris-allyl complexes [Ln(eta(3)-C(3)H(5))(3)(diox)] (Ln = Y, La, Ce, Pr, Nd, Sm; diox = 1,4-dioxane) isolated as a 1,4-dioxane-bridged dimer (Ln = Ce) or THF adducts [Ln(eta(3)-C(3)H(5))(3)(thf)(2)] (Ln = Ce, Pr). Allyl abstraction from the neutral tris-allyl complex by a Lewis acid, ER(3) (Al(CH(2)SiMe(3))(3), BPh(3)) gave the ion pair Ln(eta(3)-C(3)H(5))(2)(thf)(3)ER(3)(eta(1)-CH(2)CH=CH(2)) (Ln = Y, La; ER(3) = Al(CH(2)SiMe(3))(3), BPh(3)). Benzophenone inserts into the La-C(allyl) bond of La(eta(3)-C(3)H(5))(2)(thf)(3)BPh(4) to form the alkoxy complex La{OCPh(2)(CH(2)CH=CH(2))}(2)(thf)(3)BPh(4). The monocationic half-sandwich complexes Ln(eta(5)-C(5)Me(4)SiMe(3))(eta(3)-C(3)H(5))(thf)(2)B(C(6)X(5))(4) (Ln = Y, La; X = H, F) were synthesized from the neutral precursors [Ln(eta(5)-C(5)Me(4)SiMe(3))(eta(3)-C(3)H(5))(2)(thf)] by protonolysis. For 1,3-butadiene polymerization catalysis, the yttrium-based systems were more active than the corresponding lanthanum or neodymium homologues, giving polybutadiene with approximately 90% 1,4-cis stereoselectivity.