these active sites and to draw a reliable and predictive structure–activity
relationship.
In this chapter, we try to describe SOMC strategy in the recent years to achieve
alkane and cycloalkane metathesis with increasing TONs and selectivities. We will
explore the surface organometallic chemistry of Group IV, V and VI metals on
various supports and the properties of these single-site systems in the area of alkane
and cycloalkane metathesis.
2 Surface Organometallic Chemistry (SOMC)
A heterogeneous catalyst is an ideal choice for the great variety of chemical
transformations carried out in industry. Homogeneous catalysts, mostly because
of their fragility, instability at higher temperature, and difficulty to separate them
from the product(s) after reaction, are comparatively less used in industry (although
the number of homogeneous processes is steadily increasing with time). However,
selective utilization of the small number of active sites in heterogeneous catalyst
makes their characterization quasi-impossible, and, as a result, structure–activity
relationship is rarely reached which prevents further improvement of these
catalysts.
In order to bring the concepts of homogeneous catalysis into heterogeneous
catalysis, a new field of catalysis was developed called surface organometallic
chemistry (SOMC) (Scheme 1). SOMC led progressively to the discovery of a
new area of chemistry [13, 14]. It has been found that organometallic complexes
react with surfaces of oxides in a very specific way leading to new materials having
an extremely high electron deficiency. As a consequence a very strong reactivity to
activate the C–H and C–C bonds of paraffin’s was observed. It was discovered when
group IV metal alkyls were reacted with silica surfaces. The first discovery of the
hydrides of group IV was made in the field of olefin polymerization [15]. These group
IV metal alkyls (or hydrides) are tremendously effective for low-temperature
hydrogenolysis of most alkanes and polyolefins (similar to Ziegler–Natta depolymerization), activation of methane, and coupling of methane into ethane and hydrogen.
A series of new reactions were developed by using this approach [16].
After its origin, SOMC has been extended to the full ensemble of metallic
elements of the periodical table, to a huge variety of ligands, and to a huge variety
of supports. In addition, SOMC approach is applied in the area of nanoparticles.
In almost all cases, we could progressively understand reaction mechanisms and
make a clear structure–activity relationship.
SOMC is purely a surface phenomenon where an organometallic complex binds
selectively with the surface by covalent (or sometimes ionic or both) bonds. One can
then access to its electronic configuration and oxidation state, and this leads to a better
understanding of the reaction mechanism. In SOMC, the surface acts as a ligand,
which means one can tune the catalytic activity of the organometallic with the surface
New Concept of C–H and C–C Bond Activation via Surface Organometallic. . .
157
relationship.
In this chapter, we try to describe SOMC strategy in the recent years to achieve
alkane and cycloalkane metathesis with increasing TONs and selectivities. We will
explore the surface organometallic chemistry of Group IV, V and VI metals on
various supports and the properties of these single-site systems in the area of alkane
and cycloalkane metathesis.
2 Surface Organometallic Chemistry (SOMC)
A heterogeneous catalyst is an ideal choice for the great variety of chemical
transformations carried out in industry. Homogeneous catalysts, mostly because
of their fragility, instability at higher temperature, and difficulty to separate them
from the product(s) after reaction, are comparatively less used in industry (although
the number of homogeneous processes is steadily increasing with time). However,
selective utilization of the small number of active sites in heterogeneous catalyst
makes their characterization quasi-impossible, and, as a result, structure–activity
relationship is rarely reached which prevents further improvement of these
catalysts.
In order to bring the concepts of homogeneous catalysis into heterogeneous
catalysis, a new field of catalysis was developed called surface organometallic
chemistry (SOMC) (Scheme 1). SOMC led progressively to the discovery of a
new area of chemistry [13, 14]. It has been found that organometallic complexes
react with surfaces of oxides in a very specific way leading to new materials having
an extremely high electron deficiency. As a consequence a very strong reactivity to
activate the C–H and C–C bonds of paraffin’s was observed. It was discovered when
group IV metal alkyls were reacted with silica surfaces. The first discovery of the
hydrides of group IV was made in the field of olefin polymerization [15]. These group
IV metal alkyls (or hydrides) are tremendously effective for low-temperature
hydrogenolysis of most alkanes and polyolefins (similar to Ziegler–Natta depolymerization), activation of methane, and coupling of methane into ethane and hydrogen.
A series of new reactions were developed by using this approach [16].
After its origin, SOMC has been extended to the full ensemble of metallic
elements of the periodical table, to a huge variety of ligands, and to a huge variety
of supports. In addition, SOMC approach is applied in the area of nanoparticles.
In almost all cases, we could progressively understand reaction mechanisms and
make a clear structure–activity relationship.
SOMC is purely a surface phenomenon where an organometallic complex binds
selectively with the surface by covalent (or sometimes ionic or both) bonds. One can
then access to its electronic configuration and oxidation state, and this leads to a better
understanding of the reaction mechanism. In SOMC, the surface acts as a ligand,
which means one can tune the catalytic activity of the organometallic with the surface
New Concept of C–H and C–C Bond Activation via Surface Organometallic. . .
157