Redox Control of a Dendritic Ferrocenyl-Based Homogeneous Catalyst

The application of a dendrimer in a redox‐switchable catalytic process is reported. A monomeric and the corresponding dendritic ferrocenylphosphane ligand were used to develop well‐defined controllable catalysts with distinct redox states. The corresponding ruthenium(II) complexes catalyze the isomerization of the allylic alcohol 1‐octen‐3‐ol. By adding a chemical oxidant or reductant, it was possible to reversibly switch the catalytic activity of the complexes. On oxidation, the ferrocenium moiety withdraws electron density from the phosphane, thereby lowering its basicity. The resulting electron‐poor ruthenium center shows much lower activity for the redox isomerization and the reaction rate is markedly reduced. Under control: Both monomeric and dendritic (see picture) ferrocenylphosphane ruthenium(II) catalysts were reversibly switched off and on by chemical oxidation and reduction during isomerization of the allylic alcohol 1‐octen‐3‐ol. This outcome is mainly due to electronic communication between the redox‐active unit and the catalytic center. Such redox control could facilitate the development of catalysts with orthogonal activity for different substrates.