Solvent-free mechanochemical synthesis of dithiophosphonic acids and corresponding nickel(II) complexes

Abstract

<p>We report a green chemistry route for dithiophosphonic acids of the type [HS₂P(OR)(4-MeOC₆H₄)] [R = H, (<b>1</b>); Me (<b>2</b>); Et (<b>3</b>); <i>ⁱ</i>Pr (<b>4</b>)]. The different dithiophosphonic acids formed through the stoichiometric addition of water or alcohols to Lawesson's Reagent (molar ratio 2:1), followed by an intimate grinding of the mixture (mechanochemistry). The products formed without the use of solvent or external heat in less than 5 minutes. The acids are formed with 100% atom economy, and because they form in essentially quantitative yield, are also formed with >98% atom efficiency and an E-factor = 0, because no waste is produced. Of importance is that this methodology is different from conventional methods in forming dithiophosphonic acids where the use of organic solvents, added heat, long reaction times and lower yields are commonplace. We further demonstrate that nickel(II) complexes can form directly from the <i>in situ</i> generated acids. Thus, the reaction between <b>1–4</b> and NiCl₂ ‧ 6 H₂O (molar ratio 2:1) lead to complexes of the type [Ni{S₂P(OR)(4-MeOC₆H₄)}₂] [R = H, (<b>5</b>); Me (<b>6</b>); Et (<b>7</b>); ⁱPr (<b>8</b>)] with no use of organic solvent. All compounds were characterized or verified by a combination of ¹H, ³¹P NMR, elemental analysis (solids), and FT-IR.</p