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

<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

Innovative Efficient Method for the Synthesis of 1,4-Dihydropyridines Using Y₂O₃ Loaded on ZrO₂ as Catalyst

In this study a highly efficient protocol is reported to synthesize 1,4-dihydropyridine derivatives using 2.5% Y₂O₃/ZrO₂ as heterogeneous catalyst. The one-pot, four-component reaction involves substituted aldehyde, malononitrile, 4-bromoaniline, and dimethylacetylenedicarboxylate in the green solvent ethanol. The new catalyst material is characterized by powder X-ray diffraction, TEM, SEM, and nitrogen adsorption/desorption analysis techniques. The key benefits of this novel approach are easy workup, green solvent, short reaction times (<20 min), energy efficient reaction conditions, and no chromatographic separation techniques plus excellent yields (88–95%)