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 dioxo-osmium(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 [O sO(C8H9)(4)] (4) (4%) while that with C8H9OMgBr (C8H9O = 4-methoxy-2-methyl phenyl) afforded [OsO(C8H9O)(4)] (5) in 20% yield. Oxidation of 3 with 3-ch loroperoxybenzoic acid afforded 4 in good yield. The solid-state structures of 1 and 4 have been established by X-ray crystallography. Crystals of 1 a re tetragonal with a = 13.080(1) and c = 6.6506(5) Angstrom, V = 1137.9(1) Angstrom (3), Z = 2, and space group of P4/n; while those of 4 are tetragon al with a = 13.593(2) and c = 7.377(2) Angstrom, V = 1363.0(5) Angstrom (3) , Z = 4, and space group of P4/n. The geometry around osmium in both comple xes 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) Angstrom, respective ly, while those in 4 are 1.688(7) and 2.088(4) Angstrom, respectively. The cyclic voltammograms of the monooxo aryl osmium(VI) compounds show reversib le Os(VI/V) couple at around -1.4 V vs. ferrocene/ferrocenium couple.