affording unsaturated products and relatively sophisticated organic transformations
triggered by substrate dehydrogenation are discussed, and many of the listed catalytic systems are revealed to have become important tools for organic synthesis.
Keywords Cooperative catalysis · Dehydrogenation · Functional ligand · Hydrogen
production · Hydrogen storage · Organic synthesis · Pincer complex
1 Introduction
Catalytic chemistry of iridium for organic synthesis is entering a maturity phase. A
wide variety of reactions using iridium catalysts is continuously being developed,
some of which are indispensable to organic synthesis.
The relative stability of Ir–H and Ir–C bonds allows the isolation of
organoiridium complexes and the investigation of their structural and fundamental
properties, as exemplified by the work of Vaska et al., who uncovered the basics of
the fundamental reactions (e.g., oxidative addition) involved in organometallic
chemistry [1]. However, the catalytic chemistry of Ir has advanced at a considerably
slower pace than that of Rh and Pd. For example, [Ir(cod)(Py)(PCy 3 )]
+ (cod:
1,5-cyclooctadiene; Py: pyridine; Cy: cyclohexyl), which shows a very high activity
for alkene hydrogenation, was reported by Crabtree et al. only in 1977 [2, 3]. This
discovery triggered the development of Ir catalytic chemistry and the discovery of
other high-performance Ir catalysts, as exemplified by the use of [Ir(cod)(phox)]
+
(phox: phosphinooxazoline) for asymmetric hydrogenation, which was reported by
Pfaltz et al. [4].
Although the application scope of Ir catalysts was initially restricted to the hydrogenation of unsaturated organic compounds, it subsequently expanded to include
allylic substitution [5–14] and C–H borylation [15–18] and even the industrial carbonylation of methanol to afford acetic acid (the Cativa process) [19]. In addition,
many other reactions catalyzed exclusively by Ir have been developed [20–22].
The ability of Ir to catalyze hydrogenation reactions suggests that this metal
should also promote the reverse reaction, i.e., dehydrogenation. Indeed, the last
three decades have witnessed the rapid development of Ir-catalyzed dehydrogenative
reactions.
This chapter lists the applications of homogeneous Ir catalysts for the dehydrogenation of hydrogen acceptor-free organic molecules, demonstrating that many of
these catalytic systems have become important organic synthesis tools.
2 Dehydrogenation of Alkanes
Alkenes are one of the most synthetically and industrially important classes of
compounds, featuring high synthetic utility due to the presence of reactive
π-bonds, whereas the reactivity of the parent alkanes is low because of their strong
2
T. Shimbayashi and K. Fujita
triggered by substrate dehydrogenation are discussed, and many of the listed catalytic systems are revealed to have become important tools for organic synthesis.
Keywords Cooperative catalysis · Dehydrogenation · Functional ligand · Hydrogen
production · Hydrogen storage · Organic synthesis · Pincer complex
1 Introduction
Catalytic chemistry of iridium for organic synthesis is entering a maturity phase. A
wide variety of reactions using iridium catalysts is continuously being developed,
some of which are indispensable to organic synthesis.
The relative stability of Ir–H and Ir–C bonds allows the isolation of
organoiridium complexes and the investigation of their structural and fundamental
properties, as exemplified by the work of Vaska et al., who uncovered the basics of
the fundamental reactions (e.g., oxidative addition) involved in organometallic
chemistry [1]. However, the catalytic chemistry of Ir has advanced at a considerably
slower pace than that of Rh and Pd. For example, [Ir(cod)(Py)(PCy 3 )]
+ (cod:
1,5-cyclooctadiene; Py: pyridine; Cy: cyclohexyl), which shows a very high activity
for alkene hydrogenation, was reported by Crabtree et al. only in 1977 [2, 3]. This
discovery triggered the development of Ir catalytic chemistry and the discovery of
other high-performance Ir catalysts, as exemplified by the use of [Ir(cod)(phox)]
+
(phox: phosphinooxazoline) for asymmetric hydrogenation, which was reported by
Pfaltz et al. [4].
Although the application scope of Ir catalysts was initially restricted to the hydrogenation of unsaturated organic compounds, it subsequently expanded to include
allylic substitution [5–14] and C–H borylation [15–18] and even the industrial carbonylation of methanol to afford acetic acid (the Cativa process) [19]. In addition,
many other reactions catalyzed exclusively by Ir have been developed [20–22].
The ability of Ir to catalyze hydrogenation reactions suggests that this metal
should also promote the reverse reaction, i.e., dehydrogenation. Indeed, the last
three decades have witnessed the rapid development of Ir-catalyzed dehydrogenative
reactions.
This chapter lists the applications of homogeneous Ir catalysts for the dehydrogenation of hydrogen acceptor-free organic molecules, demonstrating that many of
these catalytic systems have become important organic synthesis tools.
2 Dehydrogenation of Alkanes
Alkenes are one of the most synthetically and industrially important classes of
compounds, featuring high synthetic utility due to the presence of reactive
π-bonds, whereas the reactivity of the parent alkanes is low because of their strong
2
T. Shimbayashi and K. Fujita