“MoCl3(dme)” (dme = 1,2-dimethoxyethane)
is an important precursor for midvalent molybdenum chemistry, particularly
for triply Mo–Mo bonded compounds of the type Mo2X6 (X = bulky anionic ligand). However, its exact structural
identity has been obscure for more than 50 years. In search of a convenient,
large-scale synthesis, we have found that trans-MoCl4(Et2O)2 dissolved in dme can be cleanly
reduced with dimethylphenylsilane, Me2PhSiH, to provide
khaki Mo2Cl6(dme)2 in ∼90%
yield. If the reduction is performed on a small scale, single crystals
suitable for X-ray crystallography can be obtained. Two different
crystal morphologies were identified, each belonging to the P21/n space group, but with
slightly different unit cell constants. The refined structure of each
form is an edge-shared bioctahedron with overall Ci
symmetry and metal–metal separations on the order
of 2.8 Å. The bulk material is diamagnetic as determined by both
the Gouy method and SQUID magnetometry. Density functional theory
calculations suggest a σ2π2δ*2 ground state for the dimer with the diamagnetism arising
from a singlet diradical “broken symmetry” electronic
configuration. In addition to a definitive structural assignment for
“MoCl3(dme)”, this work highlights the utility
of organosilanes as easy to handle, alternative reductants for inorganic
synthesis.