Di- and trivalent rare earth complexes stabilized by sterically demanding aminopyridinato ligands as initiators in ring-opening polymerization reactions of ϵ-caprolactone

Salt elimination protocols using Ap*K {Ap*H = (2,6‐diisopropyl‐phenyl)‐[6‐(2,4,6‐triisopropyl‐phenyl)‐pyridin‐2‐yl]‐amine} lead to the rare earth aminopyridinato complex [Ap*LuCl2(thf)2], 4. Results of X‐ray crystal structure analyses of 4 and the corresponding single THF coordinated dimer are discussed. Ring‐opening polymerization of ε‐caprolactone initiated by complexes [Ap*LaBr2(thf)3], 2, [Ap*YbI(thf)2]2, 3 or 4 in the presence of NaBH4 allows the preparation, in a short reaction time, of α,ω‐dihydroxytelechelic polymers with high molar mass ( $ \bar{M}_{\rm n} $ up to 50,000) and moderate molar mass distributions (1.3 < $ \bar{M}_{\rm w} $/$ \bar{M}_{\rm n} $< 1.6). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3611–3619, 2007 The rare earth aminopyridinato complexes [Ap*LaBr2(thf)3], 2, [Ap*YbI(thf)2]2, 3, and [Ap*LuCl2(thf)2], 4 initiate, in the presence of NaBH4, the ring‐opening polymerization of ε‐caprolactone to give α,ω‐dihydroxytelechelic polymers with controlled molecular features ( $ \bar{M}_{\rm n} $ and end‐groups).