the result of the pretreatment temperature. Thus, at very high temperature, more
strained Si–O–Si groups were produced on silica surface and vice versa.
These strained groups exhibit also a typical reactivity with metal alkyls or
metal hydrides
To understand the reaction mechanism for a given reaction on surface and
correlate structure–activity relationship, first of all a well-defined “single-site”
system is needed. To have a well-defined “single-site” system the silanols must
be sufficiently isolated from each other to behave independently. This is the
necessary condition to reach the ultimate goal of making “single-site” catalysts.
Based on the above concepts, flame silica which has a surface area of %200 m
2 g
À1
is usually pretreated at 700, 500, and 200
C under high vacuum (10
À5 mbar) for
16 h. The corresponding number of silanols is equal to 0.26, 0.42, and
0.86 mmolg
À1 , respectively (measured either by
1 H NMR of simple titration
method via MeLi) [17]. For such low values for surface silanol especially in the
case of SiO 2-700 , one can presume that the hydroxyl groups are far away from each
other and so well-defined grafted organometallic isolated species will be expected
upon reaction with these hydroxyl groups. This is the key point of surface organometallic chemistry.
In Table 1, we have mentioned some examples of grafting of organometallic
complexes on various supports by the use of surface organometallic chemistry.
Scheme 2 Various surface silanols and siloxane bridges present on partially dehydroxylated
silica
Table 1 Example of various organometallic complexes on oxide surface prepared by SOMC
approach
Metal
SOMC species
References
Vanadium
(SiOÀ)V(¼NBu
t
)(CH 2 Bu
t ) 2
[18]
Chromium
(SiOÀ)Cr(CH 2 Bu
t ) 3
[19]
Zirconium
(SiOÀ)Zr(CH 2 Bu
t ) 3
[4, 20]
Molybdenum
(SiOÀ)Mo(CMe 3 )(CH 2 Bu
t ) 2
[21]
Tantalum
(SiOÀ)Ta(¼CHBu
t
)(CH 2 Bu
t
) 2
[22]
Tungsten
(SiOÀ)WMe 5
[23]
Rhenium
(SiOÀ)Re(CMe 3 )(CH 2 Bu
t
) 2
[24]
Osmium
(SiOÀ)Os(CMe 3 )(CH 2 Bu
t ) 2
[25]
New Concept of C–H and C–C Bond Activation via Surface Organometallic. . .
159
strained Si–O–Si groups were produced on silica surface and vice versa.
These strained groups exhibit also a typical reactivity with metal alkyls or
metal hydrides
To understand the reaction mechanism for a given reaction on surface and
correlate structure–activity relationship, first of all a well-defined “single-site”
system is needed. To have a well-defined “single-site” system the silanols must
be sufficiently isolated from each other to behave independently. This is the
necessary condition to reach the ultimate goal of making “single-site” catalysts.
Based on the above concepts, flame silica which has a surface area of %200 m
2 g
À1
is usually pretreated at 700, 500, and 200
C under high vacuum (10
À5 mbar) for
16 h. The corresponding number of silanols is equal to 0.26, 0.42, and
0.86 mmolg
À1 , respectively (measured either by
1 H NMR of simple titration
method via MeLi) [17]. For such low values for surface silanol especially in the
case of SiO 2-700 , one can presume that the hydroxyl groups are far away from each
other and so well-defined grafted organometallic isolated species will be expected
upon reaction with these hydroxyl groups. This is the key point of surface organometallic chemistry.
In Table 1, we have mentioned some examples of grafting of organometallic
complexes on various supports by the use of surface organometallic chemistry.
Scheme 2 Various surface silanols and siloxane bridges present on partially dehydroxylated
silica
Table 1 Example of various organometallic complexes on oxide surface prepared by SOMC
approach
Metal
SOMC species
References
Vanadium
(SiOÀ)V(¼NBu
t
)(CH 2 Bu
t ) 2
[18]
Chromium
(SiOÀ)Cr(CH 2 Bu
t ) 3
[19]
Zirconium
(SiOÀ)Zr(CH 2 Bu
t ) 3
[4, 20]
Molybdenum
(SiOÀ)Mo(CMe 3 )(CH 2 Bu
t ) 2
[21]
Tantalum
(SiOÀ)Ta(¼CHBu
t
)(CH 2 Bu
t
) 2
[22]
Tungsten
(SiOÀ)WMe 5
[23]
Rhenium
(SiOÀ)Re(CMe 3 )(CH 2 Bu
t
) 2
[24]
Osmium
(SiOÀ)Os(CMe 3 )(CH 2 Bu
t ) 2
[25]
New Concept of C–H and C–C Bond Activation via Surface Organometallic. . .
159