Synthesis of Tetranuclear, Four-Coordinate Manganese Clusters with 'Pinned Butterfly' Geometry Formed by Metal-Mediated N-N Bond Cleavage in Diphenylhydrazine

摘要

The preparation of four-coordinate tetra-manganese-amide-hydrazide clusters is described. Reaction of Mn(NR_2)_2 (R = SiMe_3) with N,N'-diphenylhydra-zine resulted in the formation of a black intermediary mixture that converted to a four-coordinate tetranuclear "pinned butterfly" duster, Mn_4(μ_3-N_2Ph_2)_2(μ-N_2Ph_2)(μ-NHPh)_2(THF)_4. This compound was isolated in ～90% yield and identified by single-crystal X-ray diffraction analysis. In pyridine, the THF ligands were replaced, giving the pyridyl complex Mn_4(μ_3-N_2Ph_2)_2(μ-N_2Ph_2)(μ-NHPh)_2-(py)_4. Charge counting considerations indicate that the clusters had gained two protons and two electrons in addition to the formative fragments. Isolation of the black mixture was achieved by extraction techniques from a reaction with a decreased loading of hydrazine run at low temperatures with decreased solvent polarity. The black mixture was characterized by FT-IR, UV-vis, and ~1H NMR spectroscopy. In addition, an isolable, colorless dimer, Mn_2-(μ-NHPh)_2(NR_2)_2(THF)_2, was present in the mixture and identified by single-crystal X-ray diffraction. These intermediates are discussed in light of possible mechanisms for formation of the tetranuclear cluster.