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-(SiMe3)2C3H3] =
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.