Lanthanide superoxide complexes and a novel μ3-oxo samarium complex with hydrotris(3,5-dimethylpyrazolyl)borate ligand

The lanthanide superoxide complexes Tp2Sm(η2-O2) (1) (Tp=hydrotris-(pyrazolyl)borate), Tp2Yb(η2-O2) (2) and Tp*2Yb(η2-O2) (3) [Tp*=hydrotris(3,5-dimethylpyrazolyl)borate], have been synthesized by the reactions of Tp2Sm, Tp2Yb and Tp*2Yb with dioxygen in toluene at −75°C, respectively. The reaction of Tp*2Sm with a half equivalent of pyridine N-oxide in THF yields complex [Tp*2Sm]2(μ-η2:η2-O2)·2THF (4). The addition of hexane to the mother liquid, which was generated after the separation of complex 4, yields crystals of [Tp*Pz*2-Sm(μ3-O)(BOH)]2·2THF (5) (Pz*=3,5-dimethylpyrazolyl) structurally characterized by X-ray diffraction. Meanwhile 3,5-dimethylpyrazole resulted from the cleaved Tp* was also detected. Complex 5 is a seven-coordinated dimeric molecule with a pseudo-octahedral coordination geometry and crystallizes in the triclinic space group P1̄ (no. 2) with a=13.458(4) Å, b=13.740(5) Å, c=10.198(3) Å, α=105.88(3)°, β=107.99(2)°, γ=86.85(3)°, Z=1. The samarium to nitrogen distances range from 2.516(5) to 2.624(5) Å. The samarium to oxygen distances are 2.249(4)–2.324(4) Å. The complex contains two Tp*, four Pz*, two samarium atoms and two bridged oxygen atoms.