Electro- and photoactivation of silver-iron oxide particles as magnetically recyclable catalysts for cross-coupling reactions.

Colloidal Ag particles decorated with FeO islands can be electrochemically or photochemically activated as inverse catalysts for C(sp)-H heteroarylation. The silver-iron oxide (SIO) particles are reduced into redox-active forms by cathodic charging at mild potentials or by short-term light exposure, and can be reused multiple times by magnetic cycling without further activation. A negative shift in the reduction peak is attributed to an overpotential produced by surface FeO which separates residual Ag ions or clusters from bulk silver. The catalytic efficiency of SIO is maintained even with acid degradation, which can be countered simply by adding water to the reaction medium.