2
D. W. Stephan
Et
Ethyl
FLPs
Frustrated Lewis pairs
h
Hour(s)
Me
Methyl
Mes
Mesityl; 2,4,6-trimethylphenyl
MIC
Meso-ionic carbene
MMA
Methyl methacrylate
MOF
Metal-organic framework
NHC
N-heterocyclic carbene
Ph
Phenyl
Piers’ borane HB(C 6 F 5 ) 2
pin
pinacol
Pr
Propyl
rt
Room temperature
terpy
Terpyridine
THF
Tetrahydrofuran
TMP
Tetramethylpiperidine
1.1 Introduction
In 2006, we described the first metal-free system capable of the reversible activation of H 2 [1]. This finding was based on Mes 2 PC 6 F 4 B(C 6 F 5 ) 2 (Mes = 2,4,6Me 3 C 6 H 2 ), a molecule-containing sterically encumbered phosphine and borane
sites. Subsequently, we further showed that such reactivity could be extended to
simple combinations of sterically demanding boranes and donors [2]. Shortly, thereafter, Erker and coworkers reported the reaction of the intramolecular B/P system
Mes 2 PC 2 H 4 B(C 6 F 5 ) 2 with H 2 [3]. These systems were shown to react with H 2 to
effect heterolytic cleavage as well as effect B/P addition to olefins, prompting the
moniker “frustrated Lewis pairs (FLPs)” for such systems (Scheme 1.1) [4].
The ability to activate H 2 immediately prompted questions regarding the possibility of metal-free catalysis. Moreover, studies probing the notion of FLPs have
also led both to a broadened range of FLP catalysts as well as their application in
a widening range of metal-free catalytic processes. Indeed, the emergence of the
concept has provided a new strategy for synthetic chemists to develop new avenues
for catalytic protocols in the last decade. It has been exploited for a broad range of
applications in asymmetric reductions, metal-free organic synthesis, C–H bond activations, polymer synthesis, in addition to providing new perspectives on transition
metal chemistry in biological systems and heterogeneous catalysis. Several reviews
have appeared that detail specific aspects of FLP chemistry [5–17].
The ever-broadening applications of this remarkably simple concept are impressive, particularly in the context that the origin of this notion emerged from fundamental main group chemistry. In this chapter, we provide a brief account of the
D. W. Stephan
Et
Ethyl
FLPs
Frustrated Lewis pairs
h
Hour(s)
Me
Methyl
Mes
Mesityl; 2,4,6-trimethylphenyl
MIC
Meso-ionic carbene
MMA
Methyl methacrylate
MOF
Metal-organic framework
NHC
N-heterocyclic carbene
Ph
Phenyl
Piers’ borane HB(C 6 F 5 ) 2
pin
pinacol
Pr
Propyl
rt
Room temperature
terpy
Terpyridine
THF
Tetrahydrofuran
TMP
Tetramethylpiperidine
1.1 Introduction
In 2006, we described the first metal-free system capable of the reversible activation of H 2 [1]. This finding was based on Mes 2 PC 6 F 4 B(C 6 F 5 ) 2 (Mes = 2,4,6Me 3 C 6 H 2 ), a molecule-containing sterically encumbered phosphine and borane
sites. Subsequently, we further showed that such reactivity could be extended to
simple combinations of sterically demanding boranes and donors [2]. Shortly, thereafter, Erker and coworkers reported the reaction of the intramolecular B/P system
Mes 2 PC 2 H 4 B(C 6 F 5 ) 2 with H 2 [3]. These systems were shown to react with H 2 to
effect heterolytic cleavage as well as effect B/P addition to olefins, prompting the
moniker “frustrated Lewis pairs (FLPs)” for such systems (Scheme 1.1) [4].
The ability to activate H 2 immediately prompted questions regarding the possibility of metal-free catalysis. Moreover, studies probing the notion of FLPs have
also led both to a broadened range of FLP catalysts as well as their application in
a widening range of metal-free catalytic processes. Indeed, the emergence of the
concept has provided a new strategy for synthetic chemists to develop new avenues
for catalytic protocols in the last decade. It has been exploited for a broad range of
applications in asymmetric reductions, metal-free organic synthesis, C–H bond activations, polymer synthesis, in addition to providing new perspectives on transition
metal chemistry in biological systems and heterogeneous catalysis. Several reviews
have appeared that detail specific aspects of FLP chemistry [5–17].
The ever-broadening applications of this remarkably simple concept are impressive, particularly in the context that the origin of this notion emerged from fundamental main group chemistry. In this chapter, we provide a brief account of the