Mononuclear anionic AO2X3 compounds with non-VSEPR structure

Abstract

The molybdenyl compound [NBu₄][MoO₂(C₆F₅)₃] (1) has been obtained by low-temperature treatment of MoO₂Cl₂ with LiC₆F₅ in Et₂O followed by addition of [NBu₄]Br. This compound of the (AO₂X₃)⁻ type shows an unusual five-coordinate structure not lying in the Berry-pseudorotation path: it can be described rather as an edge-capped tetrahedron (TE-5). The same kind of structure has been found by DFT calculations to be the most energetically favored for the mononuclear (MoO₂X₃)⁻ model species, where X = H, Cl or CN. Compound 1 exhibits marked stereochemical stability, as it shows no sign of exchange between chemically inequivalent C₆F₅ groups even at 150 °C in dmf solution (¹⁹F NMR spectroscopy).