7 Heterogeneous Catalysis by Frustrated Lewis Pairs
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7.1 Introduction
Catalysis underpins the vast majority of industrially important reactions. In particular, hydrogenation is employed in upgrading crude oil, as well as in the synthesis of
agrochemicals, pharmaceuticals and materials [1]. Historically, this has been carried
out with transition metal complexes; however, in 2006 Stephan et al. articulated the
concept of frustrated Lewis pairs (FLPs), and showed that unquenched combinations
of bulky Lewis acids and Lewis bases could synergistically and reversibly activate
dihydrogen, H 2 (Fig. 7.1a) [2]. Even more importantly, the protic and hydridic species
derived from the heterolytic cleavage of H 2 could be used to effect the metal-free
hydrogenation of unsaturated organic substrates (Fig. 7.1b) [3–7]. Since the initial
discovery, a huge variety of FLP systems have been explored, most commonly with
a)
b)
c)
Fig. 7.1 a First reversible activation of dihydrogen by an FLP; b general catalytic cycle for FLPcatalysed hydrogenation of an imine (LB = Lewis base; LA = Lewis acid); c selected examples of
intermolecular, intramolecular and chiral FLPs