Ytterbium(II) Complex Bearing a Diaminobis(phenolate) Ligand: Synthesis, Structure, and One-Electron-Transfer and ε-Caprolactone Polymerization Reactions

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Abstract
The first divalent ytterbium complex supported by a diaminobis(phenolate) ligand, YbL(THF)2·0.5C7H8 (1; THF = tetrahydrofuran), was synthesized in good yield by the amine elimination reaction of Yb[N(SiMe3)2]2(THF)2 with H2L (L = [Me2NCH2CH2N(CH2-2-OC6H2-3,5-But2)2]) in a 1:1 molar ratio. X-ray structural determination shows complex 1 to be a THF-solvated monomer, which adopts a distorted octahedral coordination geometry around the Yb atom. Complex 1 can react with PhNCO and PhC⋮CH, as a single electron-transfer reagent, to give the corresponding reduction coupling product [(YbLOCNPh)(THF)]2·4THF (2) and the alkynide complex YbLC⋮CPh(DME) (3; DME = 1,2-dimethoxyethane). Complexes 2 and 3 have been characterized by X-ray crystal structural analysis. In complex 2, the dianionic oxamide ligand resulting from the reductive coupling of two phenyl isocyanate molecules coordinates to two Yb atoms in a μ,η4 fashion. Complex 3 has a monomeric structure with a Yb−C(terminal phenylacetynide) bond length of 2.374(3) Å. Complex 1 is also a highly efficient catalyst for ring-opening polymerization of ε-caprolactone.

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