7 Heterogeneous Catalysis by Frustrated Lewis Pairs
249
a)
b)
Fig. 7.9 a Z-selective reduction of alkynes to alkenes by a silica-supported Au-NP/piperazine FLP;
b proposed mechanism for the reduction
the heterogeneous catalyst, a magnetic variant of the silica support was used to aid
separation; it was shown that the magnetic Au-NPs could be recycled five times but
that fresh portions of piperazine were also required. A follow-up paper explored the
influence of the capping ligands that are used in the synthesis of the Au-NPs [59]. It
was demonstrated that the removal of these capping ligands by calcination at 400 °C
gave a cleaner gold surface that resulted in significantly enhanced catalytic activity.
7.3 Fully Immobilised FLPs
The majority of the semi-immobilised FLP systems discussed so far can act as heterogeneous catalysts, but suffer from recyclability issues due to the presence of a soluble
component, namely either the Lewis acid or base. There have been many different
approaches to develop fully immobilised FLP systems to overcome this problem,