Synthesis and molecular structures of monooxo aryl complexes of osmium(VI)

Reaction of [OsO4] with C7H7MgBr (C7H7= 2-methylphenyl) followed by column chromatography afforded the reported osmium tetraaryl [Os(C7H7)4] along with the oxo-osmium(VI) ([OsO(C7H7)4]) (1) (13%) and the dioxoosmium(VI) ([OsO2(C7H7)2]) (2) (25%) complexes. Treatment of [OsO4] with C8H9MgBr (C8H9= 2,5-dimethylphenyl) gave a mixture of [Os(C8H9)4] (3) (34%) and [OsO(C8H9)4] (4) (4%) while that with C8H9OMgBr (C8H9O = 4-methoxy-2-methylphenyl) afforded [OsO(C8H9O)4] (5) in 20% yield. Oxidation of 3 with 3-chloroperoxybenzoic acid afforded 4 in good yield. The solid-state structures of 1 and 4 have been established by X-ray crystallography. Crystals of 1 are tetragonal with a = 13.080(1) and c = 6.6506(5) Å, V = 1137.9(1) Å3, Z = 2, and space group of P4/n; while those of 4 are tetragonal with a = 13.593(2) and c = 7.377(2) Å, V = 1363.0(5) Å3, Z = 4, and space group of P4/n. The geometry around osmium in both complexes is square pyramidal with the oxo ligand occupying apical position. The Os - O and Os - C distances in 1 are 1.652(2) and 2.084(1) Å, respectively, while those in 4 are 1.688(7) and 2.088(4) Å, respectively. The cyclic voltammograms of the monooxo aryl osmium(VI) compounds show reversible Os(VI/V) couple at around -1.4 V vs. ferrocene/ferrocenium couple.