Anionic Monosubstituted Cyclopentadienylsamarium Derivatives: Catalysts for a Stereospecific Isoprene Polymerization

New alkyl and allyl complexes 1–3 {1: [Cp′2Sm(C3H5)]n, Cp′ = Me3CC5H4; 2: [Me4C2(C5H4)2]Sm(C3H5)2Li(dme),dme = (CH3OCH2CH2OCH3); 3: Cp′2SmMe2Li(dioxane)} were synthesized from (Cp′2SmCl)2and from the magnesium derivative [Me4C2(C5H4)2]SmCl · MgCl2(THF)4 (4). The ansa anionic complex 2 exhibited good activity for the stereospecific 1,4-trans polymerization of isoprene, whereas the neutral derivative 1 was inactive. In the same way, the anionic complex [Cp′2SmMe2]Li(dioxane) (3) was found to be an ethylene polymerization catalyst of very short lifetime. The lack of reactivity of 1 is related to the associated structure of this coordinatively unsaturated complex: this fact was established by t…