Anionic Monosubstituted Cyclopentadienylsamarium Derivatives: Catalysts for a Stereospecific Isoprene Polymerization

Abstract

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 the formation of the carbene adduct Cp′2Sm(C3H5)[C(NiPr)2(CMe)2] (1′). Crystals of 1′ were isolated but this new compound undergoes a partial rearrangement into a tris-Cp′ species in solution. Similar behaviour is observed for the analogous complex Cp′2SmCl[C(NiPr)2(CMe)2] (1′′). The X-ray crystal structure revealed the formation of the adduct, as a toluene solvate, which exists in benzene solution in equilibrium with Cp′3Sm and Cp′SmCl2[C(NiPr)2(CMe)2]2. The catalytic behaviour of 2 is compared with that of other early lanthanide derivatives.