Lanthanide borohydrido complexes for MMA polymerization: syndio- vs iso-stereocontrol

This paper presents an extensive study of the polymerization of MMA with borohydrido lanthanide complexes for the first time. Catalytic systems are made from a lanthanide derivative bearing zero one, or two bulky ligands: substituted cyclopentadienyl (Cp*' = C(5)Me(4)nPr, Cp-4i = C(5)HiPr(4), Cp-Ph3 = H2C5Ph3-1,2,4), and/or diketiminate ([(p-tol)NN] = [(p-CH3C6H4)N(CH3)C](2)CH), in the presence of variable quantities of alkylating agent. With BuLi in apolar medium, highly isotactic polymer (up to 95.6%) is formed. In THF, syndiotactic-rich PMMA is obtained whatever the nature of the co-catalyst (BuLi or (MgBu2)-Bu-n). The presence of an electron-withdrawing ligand such as Cp-Ph3 allows high syndioregularity, up to 81.8% at 0 degrees C, together with the highest conversion. There is quite good concordance between calculated and experimental molecular data in THF. Divalent CP*'Sm-2(II)(THF) and (Cp-Ph3)(2)Sm-II(THF) are active as single-component initiators; the former affords PMMA 88% syndiotactic at 0 degrees C. Copyright (c) 2005 John Wiley & Sons, Ltd.