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

Salt elimination protocols using Ap*K {Ap*H = (2,6-diisopropyl-phenyl)[6-(2,4,6-triisopropyl-phenyl)-pyridin-2-y1]-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 epsilon-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 alpha,omega-dihydroxytelechelic polymers with high molar mass ((M) over bar (n) up to 50,000) and moderate molar mass distributions (1.3 (w)/(M) over bar (n) < 1.6). (C) 2007 Wiley Periodicals, Inc