Understanding the synergistic effects observed when using tethered dual catalysts for heat and light activated catalysis

Dual catalysis, where two different catalysts work cooperatively to promote a chemical reaction, is an important synthetic approach as it can allow a wide range of unique reactivity to be accessed. Whilst most dual catalysis strategies utilise separate catalysts in the reaction mixture, there is a growing interest in using tethered dual catalysts to increase cooperativity between the catalytic centres. In this current work we sought to determine the origin of the catalytic synergy observed for a series of Ir(I) based complexes tethered to a BODIPY type photocatalyst through different tethering modes. Kinetic analyses revealed that the tethered dual catalysts were more effective at promoting heat activated intermolecular hydroamination than the un-tethered analogues. The tethering mode had a significant influence on the magnitude of this synergistic enhancement observed for the hydroamination reaction, likely due to a combination of steric and electronic ligand effects. Investigations into the effect of the tethered dual catalysts on the light activated oxidation of thioanisole demonstrated that chemical tethering leads to substantial increases in photocatalytic activity, which was once again impacted by the tethering mode. The origin of the observed enhancement was found to be due to both increased singlet oxygen generation through the heavy atom effect, as well as direct involvement of the Ir centre in the oxidation reaction pathway.