Many of the transformations of biomass discussed here are hydrogenation or
dehydrogenation reactions. In comparison with oil derived platform chemicals,
biomass is highly functionalized with mostly oxygen containing groups. Hydrogenation/dehydrogenation strategies are therefore an efficient way of converting these
compounds. The focus with dehydrogenation reactions can be either on the hydrogen generated or on the dehydrogenated product, while of course always both are
formed. The generation of hydrogen gas from biomass as a renewable fuel will be
discussed in Sect. 5, alongside dehydrogenative strategies for the synthesis of other
compounds. Hydrogenation of CO 2 with H 2 gives formic acid, which has been
widely researched and proposed as a reversible hydrogen carrier. While we mention
the topic of formic acid dehydrogenation in the last section for the hydrogenation of
other substrates, a full discussion of CO 2 hydrogenation was deemed out of scope for
this chapter. For further information on this topic, we refer to this recent review [4].
2 Recent Trends in Iridium-Catalyzed Valorization
of Bio-derived Alcohols
Alcohols, diols, and polyols are indispensable ingredients and reactive materials for
polymers, cosmetics, and pharmaceuticals and their wide range of applications
makes them one of the largest class of chemicals produced in the world [5]. The
C2-C4 diols alone are produced on an annual scale of 18 million tons [6].
In the last two decades, the use of renewable resources for the benign production
of industrially relevant alcohols (see Fig. 1) has received significant interest. In this
regard, fermentative and catalytic processes were developed to obtain the bio-based
versions of the existing fossil-based polyols as well as newly synthesized alcohols,
usually not available from fossil feedstock material [6]. For a detailed overview on
the production of bio-based alcohols, we refer to the recently published review
articles [5, 7]. In this section the use of bio-based polyols in homogenously
iridium-catalyzed reactions is reported.
2.1 Iridium-Catalyzed Reactions Using Ethylene Glycol
2.1.1 Iridium-Catalyzed Selective Cross-Coupling of Ethylene Glycol
Ethylene glycol (EG) is industrially produced from renewable resources on a
multiton scale via the hydrogenolysis of sorbitol using a Ni/Ru catalyst [8]. This
process leads to a mixture of EG and other bio-based polyols. Furthermore, the
dehydration of bio-ethanol to ethylene and its further conversion to EG is an
alternative bio-based route according to the conventional petro-based process
[8]. Finally, the Dutch company Avantium has recently started to build a demonstration plant where EG will be produced directly from renewable sugars [9]. EG is
Homogenous Iridium Catalysts for Biomass Conversion
343
dehydrogenation reactions. In comparison with oil derived platform chemicals,
biomass is highly functionalized with mostly oxygen containing groups. Hydrogenation/dehydrogenation strategies are therefore an efficient way of converting these
compounds. The focus with dehydrogenation reactions can be either on the hydrogen generated or on the dehydrogenated product, while of course always both are
formed. The generation of hydrogen gas from biomass as a renewable fuel will be
discussed in Sect. 5, alongside dehydrogenative strategies for the synthesis of other
compounds. Hydrogenation of CO 2 with H 2 gives formic acid, which has been
widely researched and proposed as a reversible hydrogen carrier. While we mention
the topic of formic acid dehydrogenation in the last section for the hydrogenation of
other substrates, a full discussion of CO 2 hydrogenation was deemed out of scope for
this chapter. For further information on this topic, we refer to this recent review [4].
2 Recent Trends in Iridium-Catalyzed Valorization
of Bio-derived Alcohols
Alcohols, diols, and polyols are indispensable ingredients and reactive materials for
polymers, cosmetics, and pharmaceuticals and their wide range of applications
makes them one of the largest class of chemicals produced in the world [5]. The
C2-C4 diols alone are produced on an annual scale of 18 million tons [6].
In the last two decades, the use of renewable resources for the benign production
of industrially relevant alcohols (see Fig. 1) has received significant interest. In this
regard, fermentative and catalytic processes were developed to obtain the bio-based
versions of the existing fossil-based polyols as well as newly synthesized alcohols,
usually not available from fossil feedstock material [6]. For a detailed overview on
the production of bio-based alcohols, we refer to the recently published review
articles [5, 7]. In this section the use of bio-based polyols in homogenously
iridium-catalyzed reactions is reported.
2.1 Iridium-Catalyzed Reactions Using Ethylene Glycol
2.1.1 Iridium-Catalyzed Selective Cross-Coupling of Ethylene Glycol
Ethylene glycol (EG) is industrially produced from renewable resources on a
multiton scale via the hydrogenolysis of sorbitol using a Ni/Ru catalyst [8]. This
process leads to a mixture of EG and other bio-based polyols. Furthermore, the
dehydration of bio-ethanol to ethylene and its further conversion to EG is an
alternative bio-based route according to the conventional petro-based process
[8]. Finally, the Dutch company Avantium has recently started to build a demonstration plant where EG will be produced directly from renewable sugars [9]. EG is
Homogenous Iridium Catalysts for Biomass Conversion
343