The first divalent ytterbium complex supported by a diaminobis(phenolate) ligand, YbL(THF)(2)center dot 0.5C(7)H(8) (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-Bu-2(t))(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 PhCCH, as a single electron-transfer reagent, to give the corresponding reduction coupling product [(YbLOCNPh)(THF)](2)center dot 4THF (2) and the alkynide complex YbLCCPh(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 mu,eta(4) fashion. Complex 3 has a monomeric structure with a Yb-C(terminal phenylacetynide) bond length of 2.374(3) angstrom. Complex 1 is also a highly efficient catalyst for ring-opening polymerization of epsilon-caprolactone.