Low-coordinate rare-earth complexes of the asymmetric 2,4-di-tert- butylphenolate ligand prepared by redox transmetallation/protolysis reactions, and their reactivity towards ring-opening polymerisation

New trivalent lanthanoid aryloxide complexes have been prepared by redox transmetallation/protolysis (rtp) reactions using 2,4-di-tert-butylphenol (dbpH). Mononuclear octahedral complexes from tetrahydrofuran (thf) were of the type [Ln(dbp)3(thf)3] (Ln = La ( 1), Pr ( 2), Nd ( 3), Gd ( 4), Er ( 5)). The lanthanoid contraction results in the rather subtle change in stereochemistry from meridional (La, Pr, Nd, Gd) to facial (Er). An analogous reaction with neodymium in dimethoxyethane (dme), resulted in the isolation of the seven coordinate [Nd(dbp)3(dme)2] ( 6), and this is comparable with the thf complexes in terms of steric crowding. Dinuclear complexes of the type [Ln2(dbp)6(thf)2], (Ln = Nd ( 7), Er ( 8)) were obtained when 1 and 5 were recrystallised from toluene. These dimeric complexes contain two bridging and four terminal phenolates, as well as a single coordinated molecule of thf at each metal.