Lanthanide borohydride complexes with an aryloxide ligand: Synthesis, structural characterization and polymerization activity

Reactions of LnCl3, NaBH4 and ArONa (Ar = C6H2-t-Bu3-2,4,6) in a molar ratio of 1:3:1 in THF afforded the aryloxide lanthanide borohydrides of (ArO)Ln(BH4)2(THF)2 (Ln = Yb (1), Er (2)). They were characterized by elemental analysis, infrared spectrum and X-ray crystallography. The two complexes are neutral and isostructural. The lanthanide atom is nine-coordinated by an aryloxide ligand, two borohydride ligands and two THF ligands in a trigonal bipyramidal geometry. Both of the BH4 ligands in each monomeric complex are η3-coordinated. These complexes displayed moderate high catalytic activities for the polymerization of methyl methacrylate. The polymerization temperature had great influence on the catalysis. At about 0 °C, the catalysts showed the polymerization activity best.