The role of alkali metal cations in MMA polymerization initiated by neutral and anionic allyl lanthanide complexes

Reaction of 2 or 3 equiv of potassium 1,3-bis(trimethylsilyl)allyl (K[1,3-(SiMe ₃) ₂C ₃H ₃] = K[A′]) with the triflate salts of Ce, Nd, Eu, Tb, and Yb gives the corresponding neutral bis-(Yb, Eu) and tris-(Ce, Nd, Tb) allyl lanthanide complexes in yields ranging from 40 to 80%. These complexes, which have been crystallographically characterized, initiate the polymerization of methyl methacrylate (MMA), but with poor turnover frequencies when compared with the corresponding salt complexes of the type K[LnA′ ₃]. K[A′] itself initiates MMA polymerization, however, and its presence as an ion-pair in the salt complexes may contribute to the activity of heterometallic lanthanide catalysts.