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

The preparation of four-coordinate tetramanganese−amide−hydrazide clusters is described. Reaction of Mn(NR2)2 (R = SiMe3) with N,N′-diphenylhydrazine resulted in the formation of a black intermediary mixture that converted to a four-coordinate tetranuclear “pinned butterfly” cluster, Mn4(μ3-N2Ph2)2(μ-N2Ph2)(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 Mn4(μ3-N2Ph2)2(μ-N2Ph2)(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, Mn2(μ-NHPh)2(NR2)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.