Multiple bonds between main-group elements and transition metals. 85. Tetramethyloxoosmium(VI): Synthesis, gas-phase molecular structure, photoelectron spectroscopy, and electrochemistry

Article abstract of DOI:10.1021/om00051a024

Tetramethyloxoosmium(VI) (2a), the first example of methylosmium oxides (CH₃)_xOs_yO_z, has been synthesized from osmium tetraoxide (1a) and dimethylzinc (19% yield) or methyltris(isopropoxy)titanium (50% yield). A more directed synthesis (60% yield) is methylation of the glycolate osmium(VI) complex O=Os(OCH₂CH₂O)₂ (1b), which precursor compound is in turn accessible from 1a in quantitative yield. The thermally labile ethyl derivative tetraethyloxoosmium(VI) (2b), the first well-characterized example of its class (C₂H₅)_xOs_yO_z, is also reported. The title compound 2a is an orange, air-stable, volatile, crystalline compound that melts at 74°C without decomposition. The gas-phase average molecular structure of 2a, as determined by electron diffraction techniques, is consistent with a theoretical model having C₄ symmetry, with the most important parameters being r_a(Os-C) = 209.6 (3) pm, r_a (Os=O) = 168.1 (4) pm, and 〈(OOsC) = 112.2 (5)°. According to PE spectroscopic data, the d ionization of 2a occurs at 8.55 eV. The title compound 2a undergoes irreversible oxidation at +2.2 V, reversible reduction at -1.58 V (cyclic voltammetry).