Micelle-Dependent Spontaneous Formation of Gold(I) in Nanodendritic Chloride-Bridged Particles with Catalytic Activity for Cyclization of Alkynylanilines in an Aqueous Environment

A proline-based engineered amphiphile featuring a thiourea functional group has been synthesized for the purpose of controlled reduction of Au(III) to Au(I) with subsequent stabilization of the resulting nanomaterial. This study elucidates the significant role played by the designer amphiphile, alongside chloride ions, in imparting a dendritic morphology to the final nanocatalyst. Such a morphology is pivotal for the catalytic activity of Au(I), as demonstrated in the cyclization reaction of alkynylanilines, conducted in water as a benign reaction medium. The structural characterization of the nanomaterial revealed intriguing associations between dendritic nanocatalysts and nanomicelles, as observed through cryogenic transmission electron microscopy. Spectroscopic analyses, including X-ray photoelectron and X-ray absorption spectroscopy, corroborate the presence of Au in the +1 oxidation state within the dendritic nanomaterial. The metal–amphiphile binding is further supported by an X-ray absorption fine structure analysis. Cyclic voltammetry analysis confirms the amphiphile-mediated reduction of Au(III) to Au(I). Significantly, the dendritic morphology is inaccessible when bromide ions are employed, whose greater nucleophilicity disrupts the bridging linkages formed by the chloride counterpart. Under these conditions, the catalytic activity is adversely affected.