“…However, one way to overcome this is by using a water-stable molecular Lewis acid such as ytterbium or scandium triflate (Ding et al, 2006). It was recently discovered that rate enhancements could be achieved by adding small amounts of ligand to ytterbium triflate-catalyzed Michael addition reactions in water (Ding et al, 2006). Although in this study a recycling study on the catalyst was not performed, it is likely that these species can be easily recycled in a similar way to related nitration catalysts previously reported (Waller et al, 1997).…”