measured by the turnover number (TON), especially for industrial applications (up
to 10
6 –10
7 !). Around 80% of the chemical products elaborated in the chemical
industry are produced with at least one step involving a catalyst. For the more recent
processes, 90% of the products are in contact with a catalyst during their elaboration. Indeed numerous compounds or intermediates for the efficient synthesis of
pharmaceuticals, natural products, agrochemicals, fine chemicals, plastics, synthetic fibers, dyes, perfumes, etc.,
4 require the presence of a catalyst. In addition,
the same statement prevails for the crude oil processing in petrochemistry and the
purification of exhaust gas from automobiles or off-gas from many industrial
plants.
5
Among the three main catalytic domains, which include heterogeneous and
homogeneous systems and biocatalysts, homogeneous transition metal complexes
account for around 15%. Many organometallic complexes have been synthesized
during the last years, and the various steps of a catalytic cycle are in many cases
well understood. It is now possible to adjust the electronic effects of the ligands, as
well as their steric hindrance, and to coordinate them to a metal center, most of the
time a transition metal, in order to obtain good catalytic performances. Various in
situ infrared and NMR studies, performed at the temperature and pressure of
catalytic conditions, have allowed to identify all the steps and among them to
discriminate the rate-determining step. In this coordination catalysis domain, the
coordination sphere of the metal needs to be flexible enough in order to coordinate
the substrates, to activate them, to induce the reaction between the appropriate
activated fragments, and in time to eliminate the expected product and recover the
active species. Mostly, this catalysis involves mononuclear complexes containing
sophisticated ligands, adjusted with reacting fragments such as carbon monoxide,
and hydride, alkyl, and acyl groups, to achieve the electron density at the right time
(step) and at the right position.
In addition, dinuclear complexes have recently been shown to be an elegant way
to manage these variations of electron flexibility along all the catalytic cycle, one
metal center being able to produce the classical and expected activation of one
reactant whereas the other center being able to provide the required flexibility. In
some cases, the second metal complex is able to unblock a step in which the
activation energy is too high, most of the time inducing the decoordination of a
ligand.
Thus, this issue is especially dedicated to dinuclear (homo- as well as heterodinuclear complexes) entities which are clearly more active than the mononuclear
counterparts and for which the dinuclear framework is maintained along all the
catalytic cycle.
4 F. Hartwig, Organotransition Metal Chemistry – From Bonding to Catalysis, 2010, University
Science Books.
5 H.-J. Arpe, Industrial Organic Chemistry, 5
th Edition, 2010, Wiley-VCH.
vi
Preface
to 10
6 –10
7 !). Around 80% of the chemical products elaborated in the chemical
industry are produced with at least one step involving a catalyst. For the more recent
processes, 90% of the products are in contact with a catalyst during their elaboration. Indeed numerous compounds or intermediates for the efficient synthesis of
pharmaceuticals, natural products, agrochemicals, fine chemicals, plastics, synthetic fibers, dyes, perfumes, etc.,
4 require the presence of a catalyst. In addition,
the same statement prevails for the crude oil processing in petrochemistry and the
purification of exhaust gas from automobiles or off-gas from many industrial
plants.
5
Among the three main catalytic domains, which include heterogeneous and
homogeneous systems and biocatalysts, homogeneous transition metal complexes
account for around 15%. Many organometallic complexes have been synthesized
during the last years, and the various steps of a catalytic cycle are in many cases
well understood. It is now possible to adjust the electronic effects of the ligands, as
well as their steric hindrance, and to coordinate them to a metal center, most of the
time a transition metal, in order to obtain good catalytic performances. Various in
situ infrared and NMR studies, performed at the temperature and pressure of
catalytic conditions, have allowed to identify all the steps and among them to
discriminate the rate-determining step. In this coordination catalysis domain, the
coordination sphere of the metal needs to be flexible enough in order to coordinate
the substrates, to activate them, to induce the reaction between the appropriate
activated fragments, and in time to eliminate the expected product and recover the
active species. Mostly, this catalysis involves mononuclear complexes containing
sophisticated ligands, adjusted with reacting fragments such as carbon monoxide,
and hydride, alkyl, and acyl groups, to achieve the electron density at the right time
(step) and at the right position.
In addition, dinuclear complexes have recently been shown to be an elegant way
to manage these variations of electron flexibility along all the catalytic cycle, one
metal center being able to produce the classical and expected activation of one
reactant whereas the other center being able to provide the required flexibility. In
some cases, the second metal complex is able to unblock a step in which the
activation energy is too high, most of the time inducing the decoordination of a
ligand.
Thus, this issue is especially dedicated to dinuclear (homo- as well as heterodinuclear complexes) entities which are clearly more active than the mononuclear
counterparts and for which the dinuclear framework is maintained along all the
catalytic cycle.
4 F. Hartwig, Organotransition Metal Chemistry – From Bonding to Catalysis, 2010, University
Science Books.
5 H.-J. Arpe, Industrial Organic Chemistry, 5
th Edition, 2010, Wiley-VCH.
vi
Preface