623
The first report on methanol synthesis using hydrosilane as a reducing agent was
reported by Eisenberg et al. The iridium pincer carbonyl complexes (39) are efficient at ambient temperature (40 °C) with low TON [129]. In 2010, Guan adopted
the Ni PNP hydride complex (40) for the hydrogenation reaction in the presence of
organoboranes [130, 131]. The cobalt PNP hydride complex (41) promoted the
hydrosilylation of CO 2 using PhSiH 3 leading to the mixture of silyl formate,
bis(silyl)acetals, and methoxysilyl derivatives [132]. The ruthenium catalyst (42) in
the presence of monohydrosilanes, with selectivity towards bis(silyl)acetals or
methoxysilyl products at high temperature (150 °C), takes long reaction time with
better selectivity [133]. Mazzota et al. have reported an oxorhenium PNN pincer
complex (43) in the presence of PhMe 2 SiH, and PhSiH 3 reduces the CO 2 to
methoxysilyl [134, 135]. Mn(I)-PNP complex (44) catalyzed CO 2 hydrosilylation to
silyl derivative of methanol under mild reaction conditions (80 °C, 1 bar CO 2 ). The
mechanistic pathway suggesting the reaction proceeds via formato complexes by
hydride transfer to CO 2 followed by hydrogenation of silyl formate to silyl acetal
species [136].
3.2.4 Formic Acid
As we know formic acid is the most widely used fine chemicals in various industries. Formic acid having an excellent application as hydrogen source contains
4.4 wt% of H 2 with volume capacity of 53.4 g/L at STP. The hydrogen can be
released by decomposing the formic acid; hence, it is used as energy material [137,
138]. As formic acid is being recognized as best storage material, varieties of homogeneous and heterogeneous catalysts have been explored for the hydrogen production. Similarly, formic acid production from CO 2 can also be possible; various
P
P
Ph
Ph
Ph
Ph
Ir
CN
CO
N
P t Bu 2
Co
P t Bu 2
H
N
O P t Bu 2
Ni
O P t Bu 2
H
N
P t Bu 2
Re
NEt 2
O
O
N
N P i Pr 2
Mn
N P i Pr 2
CO
CO
H
R
R
R = -H, -CH 3
S
Ru
PR 3
(39)
(40)
(41)
(42)
(43)
(44)
Scheme 16 Homogeneous catalyst for methanol synthesis from CO 2 and hydrosilane
Efficient Homogeneous Catalysts for Conversion of CO 2 to Fine Chemicals
The first report on methanol synthesis using hydrosilane as a reducing agent was
reported by Eisenberg et al. The iridium pincer carbonyl complexes (39) are efficient at ambient temperature (40 °C) with low TON [129]. In 2010, Guan adopted
the Ni PNP hydride complex (40) for the hydrogenation reaction in the presence of
organoboranes [130, 131]. The cobalt PNP hydride complex (41) promoted the
hydrosilylation of CO 2 using PhSiH 3 leading to the mixture of silyl formate,
bis(silyl)acetals, and methoxysilyl derivatives [132]. The ruthenium catalyst (42) in
the presence of monohydrosilanes, with selectivity towards bis(silyl)acetals or
methoxysilyl products at high temperature (150 °C), takes long reaction time with
better selectivity [133]. Mazzota et al. have reported an oxorhenium PNN pincer
complex (43) in the presence of PhMe 2 SiH, and PhSiH 3 reduces the CO 2 to
methoxysilyl [134, 135]. Mn(I)-PNP complex (44) catalyzed CO 2 hydrosilylation to
silyl derivative of methanol under mild reaction conditions (80 °C, 1 bar CO 2 ). The
mechanistic pathway suggesting the reaction proceeds via formato complexes by
hydride transfer to CO 2 followed by hydrogenation of silyl formate to silyl acetal
species [136].
3.2.4 Formic Acid
As we know formic acid is the most widely used fine chemicals in various industries. Formic acid having an excellent application as hydrogen source contains
4.4 wt% of H 2 with volume capacity of 53.4 g/L at STP. The hydrogen can be
released by decomposing the formic acid; hence, it is used as energy material [137,
138]. As formic acid is being recognized as best storage material, varieties of homogeneous and heterogeneous catalysts have been explored for the hydrogen production. Similarly, formic acid production from CO 2 can also be possible; various
P
P
Ph
Ph
Ph
Ph
Ir
CN
CO
N
P t Bu 2
Co
P t Bu 2
H
N
O P t Bu 2
Ni
O P t Bu 2
H
N
P t Bu 2
Re
NEt 2
O
O
N
N P i Pr 2
Mn
N P i Pr 2
CO
CO
H
R
R
R = -H, -CH 3
S
Ru
PR 3
(39)
(40)
(41)
(42)
(43)
(44)
Scheme 16 Homogeneous catalyst for methanol synthesis from CO 2 and hydrosilane
Efficient Homogeneous Catalysts for Conversion of CO 2 to Fine Chemicals