Design of a Bimetallic Au/Ag System for Dechlorination of Organochlorides: Experimental and Theoretical Evidence for the Role of the Cluster Effect

The experimental study of dechlorination
activity of a Au/Ag bimetallic
system has shown formation of a variety of chlorinated bimetallic
Au/Ag clusters with well-defined Au:Ag ratios from 1:1 to 4:1. It
is the formation of the Au/Ag cluster species that mediated C–Cl
bond breakage, since neither Au nor Ag species alone exhibited a comparable
activity. The nature of the products and the mechanism of dechlorination
were investigated by ESI-MS, GC-MS, NMR, and quantum chemical calculations
at the M06/6-311G­(d)&SDD level of theory. It was revealed that
formation of bimetallic clusters facilitated dechlorination activity
due to the thermodynamic factor: C–Cl bond breakage by metal
clusters was thermodynamically favored and resulted in the formation
of chlorinated bimetallic species. An appropriate Au:Ag ratio for
an efficient hydrodechlorination process was determined in a joint
experimental and theoretical study carried out in the present work.
This mechanistic finding was followed by synthesis of molecular bimetallic
clusters, which were successfully involved in the hydrodechlorination
of CCl4 as a low molecular weight environment pollutant
and in the dechlorination of dichlorodiphenyl­trichloroethane
(DDT) as an eco-toxic insecticide. High activity of the designed bimetallic
system made it possible to carry out a dechlorination process under
mild conditions at room temperature.