As published in Organic Letters, the Gagné Group has shown that the resting state of a gold(I)-catalyzed hydroarylation reaction changes in the presence of Ag+, with silver free catalysts resting at a dinuclear gold and Ag+ containing solutions resting at a heteronuclear gold-silver species with an asymmetric 3-center-2-electron Au-C-Ag bond stablizied by an auro-argentophilic interaction.
Adventitious Ag+, typically from LAuCl activation, can therefore intercept key organogold intermediates and effect the catalysis even when it does not effect the reaction in Au free control experiments. Key observations point to Ag+ ions intercepting Au(I) catalytic intermediates and subsequently effecting catalyst speciation and reaction kinetics; a structural model is also suggested. The discovery of dinuclear gold-silver intermediates may rationalize known Ag+ effects in gold(I) catalysis.
Under experimental conditions chosen to establish constitutional equilibration, it is possible to amplify unusual structures that maximally lower the system free energy. In cases where a template is added to the system, new host-guest pairs can be identified from complex mixtures. The Gagné Group has discovered a situation where one of the components recognizes itself and interlocks two 56-membered rings, each of which is composed of 1 A unit and 3 B units.
The X-ray structure shows two rings mutually grabbing each other. The self-recognition occurs via the usual suspects of protein recognition; π-stacking, H-bonding, and C-H–π interactions. NMR analysis shows that the solid state structure is maintained in solution, and thus serves as an excellent structural model for cases where these subunits assemble into tight-binding hosts for various guests.