Synthesis and Characterisation of Novel Bis(diphenylphosphane oxide)methanidoytterbium(III) Complexes

Reaction of [YbCp₂(dme)] (Cp = cyclopentadienyl, dme = 1,2 dimethoxyethane) with bis(diphenylphosphano)methane dioxide (H₂dppmO₂) leads to deprotonation of the ligand H₂dppmO₂ and oxidation of ytterbium, forming an extremely air-sensitive product, [Yb^III(HdppmO₂)₃] (1), a six-coordinate complex with three chelating (OPCHPO) HdppmO₂ ligands. Complex 1 was also obtained by a redox transmetallation/protolysis synthesis from metallic ytterbium, Hg(C₆F₅)_2, and H₂dppmO₂. In a further preparation, the reaction of [Yb(C₆F₅)₂] with H₂dppmO₂, not only yielded compound 1, but also gave a remarkable tetranuclear cage, [Yb₄(µ-HdppmO₂)₆(µ-F)₆] (2) containing two [Yb(µ-F)]₂ rhombic units linked by two fluoride ligands and the tetranuclear unit is encapsulated by six bridging HdppmO₂ donors. The fluoride ligands of the cage result from C-F activation of pentafluorobenzene and concomitant formation of p-H₂C₆F₄ and m-H₂C₆F₄, the last being an unexpected product.