Heterogeneous catalysts have been developed for homo and cross coupling reactions, but the great majority of these involve precious metals such as Pd or Au, and catalysts based on less expensive metals are clearly desirable. We describe two binary Metal Oxide species based on Ag and Fe3O4 that can serve as heterogeneous catalysts for C(sp2) Hydrogen heteroarylation and also magnetically recyclable. One of these is an “inverse” Oxide Metal composite comprised of Fe3O4 islands on colloidal Ag. These silver iron oxide (SIO) particles are precatalysts that can be activated by cathodic charging at mild potentials or by short term light exposure, and can be reused multiple times without further activation. Electrochemical analysis of SIO supports a model in which Ag ions or clusters adsorbed on Fe3O4 are reduced into catalytically active forms. The second catalyst is a Metal Oxide composite comprised of Ag islands on colloidal Fe3O4. This system has several advantages over the first: The amount of Ag involved is reduced by at least 11 fold and is more stable against acid, enabling cross coupling to be performed with in situ diazotization of aniline derivatives. We have also found Ag decorated Fe3O4 to be an efficient catalyst for the reduction of nitro groups, permitting us to design one pot reaction conditions for converting nitroarenes into heterobiaryl compounds.

Silver iron oxide particles: Magnetically recyclable redox catalysts for cross coupling reactions

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