Toluene and anisole have low Lewis basicities, and are thus not likely to disproportionate [Co2(CO)8]. Inspired by Dong et al., the substrate itself may be proposed as responsible for the generation of the active species, a reasoning which may be extended to all solvents: a suitable active species would be generated by disproportionation of [Co2(CO)8] by either the solvent, or the substrate, or both. A high CO pressure disfavours such disproportionation, hence the quasi-systematic lower PL conversion at higher pressure.