Catalysis with complexes -: LIII.: Synthesis and characterization of the bis-(η3-ally)lanthanum halide complexes La(η3-C3H5)2X.2THF (X = Cl, Br, I) precatalysts for stereospecific butadiene polymerization -: Further clarification of the catalytic structure-activity relationship

La(eta(3)-C3H5)(3) . 1,5-dioxane 5 can be transformed into the bis(eta(3)-allyl) lanthanum(III) halides La(eta(3)-C3H5)(2)X . 2THF (X = CI 1, Br 2, I 3) by partial protolysis with the trimethylaminhydrohalides [Me3NH]X (X = Cl, Br, I) in THF in high yields. The complexes are characterized by lanthanum and propene determination after protolysis, as well as H-1-, C-13- and La-139-NMR spectroscopy. By X-ray crystal structure analysis of the chloride complex, crystallized from THF, a dimeric structure according to the formula [{La(eta(3)-C3H5)(2)Cl(THF)(2)}(2) . 2THF] is found, corresponding to the composition La(C3H5)(2)Cl . 3THF 4. After activation with methylaluminoxane (MAO) these complexes catalyze the 1,4-cis polymerization of butadiene with increasing activity and cis selectivity along the series 1 < 2 < 3. The mechanism of activation and stereoregulation is discussed.