Extension of the Pnictinous Acid Series: Rational Synthesis of a Stibinous Acid and Exploration of Its Reactivity

Abstract

The oxyacids of the heavy group 15 elements remain underexplored despite the important role that main-group oxyacids play in academic and industrial chemistry. Higher-valent oxyacids of heavier main-group elements readily polymerize because of their ability to expand their coordination spheres and the polarity of their terminal E–O (E = P, As, Sb, Bi) bonds. As a result, no free R2SbO2H stibinic acids have yet been prepared. Lower-valent R2SbOH stibinous acids should be less susceptible to such polymerization, but there are no reported rational syntheses of molecules belonging to this class. We report here the first controlled synthesis and isolation of a molecular stibinous acid, Dipp2SbOH, where Dipp = 2,6-diisopropylphenyl. We also report an initial exploration of the chemistry of this class of compounds, including their Brønsted acidity and Lewis basicity. The hydroxyl group of Dipp2SbOH is weakly acidic as probed via reaction with the very strong base DBU. We also prepared the analogous arsinous acid Dipp2AsOH and demonstrated that it can support oxidation to the well-defined monomeric arsinic acid Dipp2AsO2H. We therefore investigated the oxidation of Dipp2SbOH. Reaction with PhIO and H2O2 produced oxo-bridged clusters, suggesting the formation of a transient stibinic acid of the form Dipp2SbO2H.