Reactions of Dimesityldioxoosmium(VI) with Bidentate N -Heterocycles. Crystal Structure of a Dioxoosmium(VI) Complex Containing a Molecular Square

The interaction of OsO 2 (mes) 2 (mes = mesityl) with pyz (pyrazine) gave the pyrazine-bridged dimer [OsO 2 (mes) 2 ] 2 (μ-pyz) ( 1 ), which has been characterized by X-ray crystallography. The structure around Os in 1 is square pyramidal, with the pyrazine, two oxo ligands, and one mesityl group in the square plane. The Os−O distance and O−Os−O angle are 1.71 Å and 147.5°, respectively. The reaction of OsO 2 (mes) 2 with 4,4‘-bpy (4,4‘-bipyridyl) and bpe ( trans -1,2-bis(4-pyridyl)ethylene) in Et 2 O gave the oligomeric [OsO 2 (mes) 2 L] n (L = 4,4‘-bpy ( 2 ), bpe ( 3 )) in good yields. The 1 H NMR spectra of 2 and 3 indicate that L's are coordinated in a symmetric fashion in these oligomers. The reaction of OsO 2 (mes) 2 with 4,4‘-bpy in CHCl 3 followed by slow evaporation afforded the crystalline tetramer [OsO 2 (mes) 2 (μ-4,4‘-bpy)] 4 ( 4 ). The crystal structure of the tetramer 4 contains the square-planar [Os(4,4‘-bpy)] 4 core with octahedral local geometry around each Os. The Os−O distance and O−Os−O angle are 1.6 Å and 159°, respectively. Treatment of OsO 2 (mes) 2 with CNpy (4-cyanopyridine) gave [OsO 2 (mes) 2 ]·[OsO 2 (mes) 2 (CNpy)] ( 5 ). The structure of 5 consists of the four-coordinate [OsO 2 (mes) 2 ] and five-coordinate [OsO 2 (mes) 2 (CNpy)] moieties, which are linked together via the Os O···Os interaction. The Os−O distances in the [OsO 2 (mes) 2 ] and [OsO 2 (mes) 2 (CNpy)] moieties in 5 are 1.69 and 1.71 Å, respectively. The (Os)O···Os distance is 2.78 Å, and the Os−O···Os angle is 170°. The Os−O stretching frequency for the above dimesityldioxoosmium(VI) complexes correlates well with the Os−O bond order and the coordination environment around Os.