Cycloaurated phosphinothioic amide complex as a precursor of gold(I) nanoparticles: Efficient catalysts for A3 synthesis of propargylamines under solvent-free conditions

Abstract

A C,S-cycloaurated complex based on an ortho-substituted phosphinothioic amide framework has been synthesized in high yield through tin(IV)-Au(III) transmetalation from the corresponding chlorodimethylstannyl derivative. The latter was prepared in a two-step process involving directed ortho lithiation/quenching with MeSnCl followed by Me/Cl exchange. The tin(IV) and gold(III) complexes have been characterized in solution and in the solid state. In both complexes, the phosphinothioic amide moiety acts as a C-C-P-S pincer ligand with formation of five-membered-ring metalacycles. The use of the gold(III) complex in the amine-aldehyde-alkyne (A) three-component coupling synthesis of propargylamines showed that the compound is transformed into the Sonogashira-type o-alkynylphosphinothioic amide with generation of Au(I) nanoparticles with an average size of around 7 nm. These nanoparticles proved to be excellent catalysts in A coupling processes, providing propargylamines in high yields under solvent-free conditions with loadings as low as 0.1 mol % and without the use of additives.