Multiple Bonds between Main-Group Elements and Transition Metals. 85.¹ Tetramethyloxoosmium(VI): Synthesis, Gas-Phase Molecular Structure, Photoelectron Spectroscopy, and Electrochemistry

Tetramethyloxoosmium(VI) (2a), the first example of methylosmium oxides (CH₃)_xOs_yO_z, has been synthesized from osmium tetraoxide (la) and dimethylzinc (19% yield) or methyltris(isopropoxy)titanium (50% yield). A more directed synthesis (60% yield) is methylation of the glycolate osmium(VI) complex 0=Os(OCH₂CH₂O)2 (1b), which precursor compound is in turn accessible from la in quantitative yield. The thermally labile ethyl derivative tetraethyloxoosmium(VI) (2b), the first well-characterized example of its class (C₂H₅)_xOs_yO;, 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).