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 n Pr, Cp 4i = C 5 H i Pr 4 , Cp Ph3 = H 2 C 5 Ph 3 ‐1,2,4), and/or diketiminate ([( p ‐tol)NN] = [( p ‐CH 3 C 6 H 4 )N(CH 3 )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 Mg n Bu 2 ). The presence of an electron‐withdrawing ligand such as Cp Ph3 allows high syndioregularity, up to 81.8% at 0 °C, together with the highest conversion. There is quite good concordance between calculated and experimental molecular data in THF. Divalent Cp *′ 2 Sm II (THF) and (Cp Ph3 ) 2 Sm II (THF) are active as single‐component initiators; the former affords PMMA 88% syndiotactic at 0 °C. Copyright © 2005 John Wiley & Sons, Ltd.