Controlling the Product Platform of Carbon Dioxide Reduction: Adaptive Catalytic Hydrosilylation of CO2 Using a Molecular Cobalt(II) Triazine Complex

Article abstract of DOI:10.1002/ange.202004463

The catalytic reduction of carbon dioxide (CO₂) is considered a major pillar of future sustainable energy systems and chemical industries based on renewable energy and raw materials. Typically, catalysts and catalytic systems are transforming CO₂ preferentially or even exclusively to one of the possible reduction levels and are then optimized for this specific product. Here, we report a cobalt-based catalytic system that enables the adaptive and highly selective transformation of carbon dioxide individually to either the formic acid, the formaldehyde, or the methanol level, demonstrating the possibility of molecular control over the desired product platform.

Full text of DOI:10.1002/ange.202004463

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Titel: Controlling the Product Platform of Carbon Dioxide Reduction:
Adaptive Catalytic Hydrosilylation of CO2 Using a Molecular
Cobalt(II) Triazine Complex
Autoren: Walter Leitner, Christophe Werlé, Thomas Weyhermüller,
Basujit Chatterjee, and Hanna Hinrika Cramer
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10.1002/ange.202004463
Angewandte Chemie
Controlling the Product Platform of Carbon Dioxide Reduction:
Adaptive Catalytic Hydrosilylation of CO2 Using a Molecular Cobalt(II) Triazine
Complex
Hanna H. Cramer,a,b Basujit Chatterjee,a Thomas Weyhermüller,a Christophe Werlé,a, c, * Walter
Leitnera, b,
*
[a] Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 – 36, 45470 Mülheim an der Ruhr,
Germany. Emails: christophe.werle@cec.mpg.de and walter.leitner@cec.mpg.de
[b] Institut für Technische und Makromolekulare Chemie (ITMC), RWTH Aachen University, Worringer Weg 2,
52074 Aachen, Germany.
[c] Ruhr University Bochum, Universitätsstr. 150, 44801 Bochum, Germany.
Abstract
The catalytic reduction of carbon dioxide (CO2) is considered a major pillar of future
sustainable energy systems and chemical industries based on renewable energy and raw
materials. Typically, catalysts and catalytic systems are transforming CO2 preferentially or
even exclusively to one of the possible reduction levels and are then optimized for this specific
product. Here we report a cobalt-based catalytic system that enables the adaptive and highly
selective transformation of carbon dioxide individually to either the formic acid, the
formaldehyde, or the methanol level, demonstrating the possibility of molecular control over
the desired product platform.
1
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10.1002/ange.202004463
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Introduction
The catalytic reduction of carbon dioxide (CO2) is considered central to the future of
sustainable energy systems and chemical industries based on renewable energy and raw
materials.[1] In attempts to “defossilize” the chemical value chain, CO2 utilization techniques
have attracted considerable interest. In particular, the transition metal complex catalyzed
reduction of CO2 can lead to products on the formal oxidation levels of formic acid (HCO2H),[2]
formaldehyde (H2CO),[3] and methanol (H3COH),[4] thus providing access to a broad range of
valuable chemicals and energy carriers. Research efforts worldwide are focusing on catalytic
methods to enable such transformations. Hydro-elementation reactions of CO2 provide in-
situ generated intermediates of the three product platforms that can be further hydrolysed
or trapped by adding nucleophiles (e.g., amines or alcohols) to generate the corresponding
amides or esters, thus creating the opportunity for further functionalization.[5] Catalytic
hydrosilylation of CO2 was used, for example, to activate the notoriously unreactive molecule
en route to challenging N-methylation of amines.[5e, 6]
Typically, catalysts and catalytic systems are amenable to transform CO2 preferentially or
even exclusively to one of the possible reduction levels and are subsequently optimized to
provide the corresponding specific product.[2-4] Following these lines, only very few 3d metal
complexes are capable of reducing CO2 beyond the formate level.[3d, 4g, 7] Selected examples
of first-row transition metals catalysts for CO2 hydrosilylation are depicted in Scheme 1.[8]
Each of these catalysts leads selectively to one product platform. Interestingly, as reported by
Kirchner, Gonsalvi, et al., a manganese complex even allows selective reduction either at the
formate level or at the methoxide level, depending on the reaction conditions.[8d]
2
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10.1002/ange.202004463
Angewandte Chemie
H
N
O
N
F5 3
B(C6
)
H
CO
CO
Mn
CH2SiMe3
tBu2P Co PtBu2
N
O
Ni
B
tBu2P
N
PtBu2
NH
iPr2P
PiPr2
tBu2P
PtBu2
Ni
H
HN
N
NH
2019,
2014,
2016,
2018,
Chem. Comm.
54, 11395
ACS Catal.
Inorg. Chem.
53, 9463
Chem. Comm.
52, 2114
9, 632
or Ph
2SiH
;
D6
D
H
2SiPh
PhSiH
25°C, <0.1 h:
PhSiH3
HSiEt
3, DMSO-d6, 1 bar CO2
2; C6
,
3, C6 6, 4 bar CO2,
2, DMF, 1 bar CO2,
60°C, 54 h;
95% formate
1 bar CO
70°C, 22 h;
2, 25°C, 2 h;
99% methoxide
99% formate
60% acetal
98% methoxide
80°C, 6 h:
Scheme 1: Selected examples of 3d transition metal catalysts used for CO2 hydrosilylation.
Alternatively, one might envisage a single catalyst that is comprehensively controlled by fine
adjustments of reaction conditions to arrive at any of the different formal oxidation levels of
CO2 reduction with high selectivity.[7b, 9] Efforts towards designing such catalytic systems will
contribute to an increased understanding of the fundamental requirements needed for the
development of adaptive and highly efficient catalytic systems for CO2 reduction.
Here, we present a catalytic system that enables the fully controllable and highly selective
transformation of carbon dioxide individually to either the formic acid, the formaldehyde, or
to the methanol level, demonstrating the possibility of molecular control over the desired
product platform (Scheme 2). The catalyst is based on a coordination compound of the earth-
abundant 3d transition metal cobalt, bearing a triazine-core embedded pincer ligand
framework.
3
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10.1002/ange.202004463
Angewandte Chemie
2 e-
-
-
reduction
4 e reduction
6 e reduction
/
H
H
PhSi
0.2 mol%
[Co]
[Co]
3
H
[Si]
0.8 mol% KOtBu,
DMSO-d
O
H
6, 1 bar,
Methoxysilane
99% selectivity
85% conversion*
80 °C, 4h
/
[Si]
O
H
PhSi
0.3 mol%
3
CO2
H
[Si]
[Co]
0.9 mol% KOtBu,
O
H
neat, 1 bar, 80 °C, 8h
Bis(silyl)acetal
71% selectivity
99% conversion*
O
/
H
2Si
Ph
0.2 mol%
[Co]
2
[Si]
H
O
0.8 mol% KOtBu,
neat, 1 bar, 40°C, 4h
N
N
Cl Cl
Co
Silyl formate
96% selectivity
76% conversion*
N
P
N
P
N
N
N
N
N
Formic acid
surrogates
Formaldehyde
surrogates
Methanol
surrogates
Ph
= [Co(
NMePNP)Cl2
platform
1st
2nd platform
3rd platform
1
]
*Based on 13CO2
[Co]
Scheme 2: Controlling the product platform of CO2 reduction: Adaptive hydrosilylation of CO2 using the cobalt
catalyst 1.
4
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10.1002/ange.202004463
Angewandte Chemie
Results and discussion
Motivated by recent examples of organometallic catalysts of 3d metals comprising PNP pincer
type ligands for catalytic CO2 reduction,[2d, 4a, 10] we set out to explore the catalytic system
based on a cobalt complex bearing the triazine ligand 2 (NMePNP) (NMePNP = 2,6-Bis((1,3-
diisopropyl-1,3,2-diazaphospholidin)-N-methylamino)-4-phenyltriazine). Cobalt has been
identified as active 3d metal in formic acid[11] and CO2 reduction[2e, 3e, 4f, 5d, 7a, 12] previously.
Ligand 2 was chosen due to the combination of different electronic effects. The 1,3-
diisopropyl-1,3,2-diazaphospholidine moieties are expected to lower significantly the π-back
bonding abilities, making the phosphortriamidite groups weaker π-acceptor ligands than
phosphines and ultimately leading to higher electron density at the metal center. In contrast,
the vertical plane has electron-withdrawing capabilities, via the triazine core.[13] Together
with the meridional coordination geometry, the ligand defines a well-defined structural and
electronic framework around the metal center (Scheme 3).
π
-donating ability
N
N
Cl Cl
Co
N
P
N
P
N
N
N
N
N
90 °
Ph
1
π
-accepting ability
Scheme 3: Electronic considerations in the design of catalyst 1.
The ligand 2 and the corresponding complex 1 were prepared by following modified reported
procedures in the individual steps as described in Scheme 4. The triazine ligand framework
was synthesized, starting from commercially available 2,4-dichloro-6-phenyl-1,3,5-triazine 3.
The addition of 2-chloro-1,3-diisopropyl-1,3,2-diazaphospholidine to the lithiated organic
backbone in toluene provided the ligand 2. The subsequent overnight reaction at room
temperature of 2 with the CoCl2 in tetrahydrofuran led to the precatalyst [Co(NMePNP)Cl2] 1 in
97% yield.
5
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10.1002/ange.202004463
Angewandte Chemie
N
N
N
N
Cl Cl
Co
H
H
N
N
N
N
P
N
N
P
N
P
N
P
N
N
N
a)
b)
N
N
N
N
N
N
N
N
Ph
Ph
Ph
(97 %)
3
2
1
(85 %)
Scheme 4: Reagents and conditions: a) 2-chloro-1,3-diisopropyl-1,3,2-diazaphospholidine, lithium bis(trimethyl-
silyl)amide, toluene, 25°C, 16 h; b) CoCl2, THF, 25°C, 12 h.
The formation and structural identity of the products was confirmed by spectroscopic
methods in solution and by single crystal X-ray analysis for complex 1. Single crystals suitable
for X-ray diffraction to determine the solid-state molecular structures of 1 were obtained by
slow diffusion of n-pentane into a concentrated solution of 1 in a mixture of toluene and THF.
In Figure 1, the molecular structure of 1 is shown with thermal ellipsoids drawn at the 60%
probability level. For clarity reasons, the hydrogen atoms were omitted. Crystallographic data
of the complex and a the detailed description of the molecular structure are provided in the
supporting information (Table S6). All angles between the cis-coordinated donors are close to
the ideal value of 90° (83.7 – 94.9°). The apical Co-Cl bond is slightly elongated by 0.17 Å as
compared to the Co-Cl bond in the quadratic base. The quadratic pyramidal geometry
matches the expectations for a Cobalt(II) complex with a d7 metal center and is in agreement
with structurally related complexes.[14]
6
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10.1002/ange.202004463
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Figure 1: Molecular structure of 1. The hydrogen atoms are omitted for clarity. Selected interatomic distances
(Å) and angles (°) for 1: Co1-N8 1.924(3), Co1-P1 2.2079(9), Co1-P10 2.2167(9), P1-N2 1.733(3), P10-N9 1.740(3),
Co1-Cl1 2.218(2), Co1-Cl2 2.3885(9), P1-Co1-P10 165.08(4), P1-Co1-N8 83.68(9), P10-Co1-N8 84.79(9)°, N8-Co1-
Cl1 164.90(9), Cl2-Co1-N8 87.27(9), Cl2-Co1-P1 94.00(3), Cl2-Co1-P10 94.89(3).
The catalytic activity of the cobalt complex 1 was examined for the hydrosilylation of carbon
dioxide with phenylsilane (PhSiH3) at 1 bar applied as a continuous CO2 stream by using 1
mol% of pre-catalyst and 4 mol% potassium tert-butoxide (KOtBu; relative to the silane) in
C6D6 at 80 °C for 4 h (Scheme 5). Following previous reports,[7a] conversion and selectivity
were determined by quantitative 13C{1H} NMR spectroscopy. Silyl formate units correspond
to signals at 155-165 ppm, bis(silyl)acetal units to signals at 80-90 ppm, and methoxysilane
units to signals at 50-60 ppm.[7a] The cobalt complex 1 converted the CO2 to silylated products
with a total turnover number of 50 for the CO2, generating the silyl formate, bis(silyl)acetal,
and silyl ether units with 51%, 35% and 14% selectivity (Table S1, entry 1). After hydrolysis of
the silylated products by adding 0.05 ml water to the reaction mixture and heating at 80°C for
12 h, formic acid and methanol were detected by 1H NMR spectroscopy, while the trimer of
formaldehyde trioxane was observed by GC-MS analysis. No formation of methane was
observed in any of these experiments, which is often an undesired side-product in hydro-
elementation reactions.[3d, 7a, 9a, 9c, 15]
7
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Angewandte Chemie
1
1 mol%
4 mol% KOtBu
[Si]
H
R
H
3Si
O
O
+
+
+
H
C
CO2
H
4
[Si]
H
[Si]
[Si]
O
H
O
O
1 bar, C6D6
80°C, 4 h
,
H
H
Silyl formate
Bis(silyl)acetal
Methoxysilane
Methane
Scheme 5: Screening conditions and possible products for the catalytic hydrosilylation of carbon dioxide
using cobalt complex 1.
Control experiments with 1 mol% CoCl2, with the complex 1 in the absence of KOtBu, or with
KOtBu alone resulted in no product formation (Table S1, entries 2-3; Table S3 entry 1).
Hydrosilylation with complex 1 could be achieved, however, even in the absence of KOtBu
under more rigorous conditions. Treating complex 1 (0.2 mol%) with PhSiH3 for 1 h at room
temperature before pressurizing with 40 bar CO2 and prolonging the reaction time to 21 h
resulted in the formation of silyl formates with high selectivity of 91% and a TON of 146
(Table S3, entry 2). The product mixture obtained under the screening conditions revealed a
remarkable reactivity of complex 1, demonstrating that all three reduction levels are
accessible with this catalyst. Therefore, we set out to explore the possibility of controlling the
reduction process to arrive at individual products selectively.
The influence of the reaction conditions on the reduction pathway was studied systematically
using cobalt catalyst 1 with a ratio of 1:4 with potassium tert-butoxide as co-catalyst in a
closed flask with an initial pressure of 1 bar 13CO2 (Table S2). After 4 h at 80°C in C6D6, 97 %
conversion of the CO2 was observed, yielding silyl formate units, bis(silyl)acetal units, and
methoxysilane units in 55%, 35%, and 11% selectivity. Decreased catalyst loading of
0.2 mol% 1 and 0.8 mol% KOtBu resulted in only minor changes of 92% 13CO2 conversion and
provided 63%, 27% and 10% selectivity for the silyl formate, bis(silyl)acetal and methoxysilane
units respectively (Table S2, entries 1-2). Due to the nearly full consumption of 13CO2, the
turnover numbers of 63 relative to CO2 conversion and 93 relative to Si-H conversions,
respectively, define only a lower limit of the catalyst productivity. These data indicate that
the catalyst is able to convert CO2 even under very low partial pressures.
8
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10.1002/ange.202004463
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The catalyst loading of 0.2 mol% 1 and 0.8 mol% KOtBu with 2.5 mmol silane was set as
standard conditions in the subsequent studies. In agreement with previous reports, the
choice of the solvent strongly influenced the selectivity of the reaction (Table S2, entries 3-
6).[16] As displayed in Figure 2, the conversion of 13CO2 was further increased to 94 % under
neat conditions while the selectivity changed from the silyl formats as the main product (63%
selectivity in C6D6) to the bis(silyl)acetals (53% selectivity, neat). Using DMSO-d6 as the
solvent, the reduction reached almost exclusively to the methanol level forming the
methoxysilane units with excellent selectivity of more than 99% with a 13CO2 conversion of
85%. Other polar solvents such as acetonitrile or THF, proved less effective. Conversion of
13CO2 was still significant when the weaker reductant diphenylsilane (Ph2SiH2) was used as the
silylating agent under the standard conditions (Table S2, entries 7-8). The reduction was
steered towards the formate level, with the preferential formation of silyl formates in high
selectivity. 79% selectivity and 70% 13CO2 conversion were observed under neat conditions,
75% selectivity and 57% 13CO2 conversion in C6D6.
Figure 2: Influence of the solvent and the silane for the hydrosilylation of carbon dioxide. 1 bar 13CO2, 0.2 %
catalyst loading, 0.8 % base loading, 80°C, 4 h
The influence of temperature was evaluated under neat conditions under 1 bar of 13CO2
(Table S2, entries 9-12). As shown in Figure 3, the high CO2 conversion of 90% - 94% was
achieved in a range from room temperature to 80°C. At higher temperatures, the conversion
decreased down to only 47% at 120°C. This may be due to catalyst deactivation or non-
productive silane dehydrogenation at higher temperatures. A clear trend for the product
9
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10.1002/ange.202004463
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formation of CO2 reduction can be observed. The formate level is strongly favored at low
temperatures leading to maximum selectivity of 79% for the silyl formates at room
temperature. The reduction beyond the formate level becomes increasingly pronounced at
higher temperatures, with a strong preference for the 53% selective acetal formation at 80°C.
With the formaldehyde platform being the most difficult to reach reduction level, the 53%
selectivity obtained in this parameter study is already quite remarkable.
Figure 3: Influence of the temperature on the hydrosilylation of carbon dioxide with complex 1 and phenylsilane.
1 bar 13CO2, 0.2 mol% catalyst loading, 0.8 mol% base loading, neat, 4 h.
The CO2 pressure had only a small effect on the total CO2 consumption but strongly influenced
the selectivity. As shown in Figure 4, the selectivity towards the silyl formates increases from
53% at 1 bar with a constant gas flow to 83% at 40 bar in a closed vessel. The turnover
numbers (relative to the product formation) for reduction to the formate level correspond to
turnover numbers of 355 at 1 bar and 468 and 508 at 20 and 40 bar (Table S1, entry 4; Table
S3, entries 3-4).
10
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10.1002/ange.202004463
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Figure 4: Influence of the CO2 pressure on the hydrosilylation of carbon dioxide using catalyst 1. Phenylsilane,
0.2 % catalyst loading, 0.8 % base loading, neat, 80°C, 4 h.
Table 1 summarizes the influence of the control parameters on product formation. In a first
approximation, they correspond with the relative kinetic challenge for the reduction levels.[1f,
5f, 15d]
Hydride transfer to reduce CO2 to formate has a relatively low barrier, making this
product accessible at low temperatures and a low Si-H/CO2 ratio corresponding to a weaker
reductant and higher CO2 pressures. Highly polar aprotic solvents, as represented by DMSO,
are beneficial for the further hydride transfer.[16] Additionally, low CO2 pressures (high Si-
H/CO2 ratio) and higher temperatures facilitate the reduction. Most challenging is the control
on the formaldehyde level, which is kinetically disfavored relative to both the formation as
well as the over-reduction.
Table 1: Control parameters for selective product formation
Reduction level /
Parameter
Formic acid
[Si]-O2CH
Formaldehyde
[Si]-OCH2O-[Si]
Methanol
[Si]-OCH3
Solvent
Silane
Broad range
Broad range
Low
Neat
PhSiH3
Dipolar aprotic
PhSiH3
Temperature
CO2 supply
Si-H/CO2
Medium
High
High pressure or
continuous
Low pressure, static or
continuous
Low pressure, static
Medium
Low
High
11
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While the exact nature of the catalytic active species remains at present elusive, the deduced
trends are consistent with hydride transfer to the C=O units of the individual
products/substrates as the major mechanistic control factor. Thus, rational optimization to
maximize the yields for the individual products becomes possible, as outlined below and
summarized in Figure 5.
To reach the formate level in high yields, a low Si-H:CO2 ratio with the use of diphenylsilane
as silylating agent in the absence of solvent was set as primary conditions (2.5 mmol silane,
0.2 mol% Co, 1:KOtBu 1:4). Under 40 bar CO2 pressure, a catalyst solution based on complex 1
produced 1.2 mmol silyl formate units in 93% selectivity in 4 h. This corresponds to a
conversion of Si-H units of 26% and TON relative to the Si-H transfer of 264. Carrying out the
reaction at 1 bar 13CO2 and 40°C under neat conditions for 4 h, 76% of the 13CO2 was converted
to silyl formate units with high selectivity of 96% (Figure 5, column 1 and 3).
Highly selective reduction to the methanol level was achieved in DMSO-d6 at 80°C under a
constant flow of CO2 at 1 bar for 4 h with PhSiH3 (2.5 mmol silane, 0.2 mol% Co, 1:KOtBu 1:4).
The methoxysilane units were formed with 99% selectivity at 68% conversion of silane in
quantities corresponding to a TON of 277 (Figure 5, column 5). Interestingly, increasing the
pressure to 40 bar under otherwise identical conditions led to a drastic change in selectivity
towards the formate units with excellent selectivity of 98% and a turnover number of 262
(Figure 5, column 2). This suggests that for hydrosilylation in DMSO-d6, the Si-H:CO2 ratio is
the predominant control parameter making this reaction highly pressure tunable under these
conditions.[9c]
For the most challenging formaldehyde level, the selectivity was optimized by compromising
between formation and over-reduction. In the optimization sequence, the best selectivity of
53% and a TON of 56 were already obtained in the initially used solvent-free standard
conditions (2.5 mmol silane, 0.2 mol% Co, 1:KOtBu 1:4, 80°C, 1 bar, 4 h) and with phenylsilane
as the silylating agent. Increasing the 1:KOtBu ratio to 1:7 under otherwise identical conditions
gave a similar selectivity of 62% and a TON of 40, although the CO2 conversion was lower (82%
compared to 94%). The highest selectivity of bis(silyl)acetals with 71% was achieved under
neat conditions and a 1 bar 13CO2 by slightly modifying the standard conditions to 0.3% 1,
12
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10.1002/ange.202004463
Angewandte Chemie
0.9% potassium tert-butoxide and 8 h reaction time (Figure 5, column 4). While reduction of
the formate was nearly complete (6%), the over reduction to the methoxysilyl units could not
be fully suppressed and accounted for 23% of products.
Figure 5: Conversion and product selectivity under optimized reaction conditions for the hydrosilylation of
carbon dioxide. Column 1: 0.2% 1, 0.8 % KOtBu, H2SiPh2, 40 bar, neat, 80°C, 4 h; Column 2: 0.2% 1, 0.8 % KOtBu,
H3SiPh, 40 bar, DMSO-d6, 80°C, 4 h; Column 3: 0.2% 1, 0.8 % KOtBu, 1 bar 13CO2, neat, H2SiPh2, 40°C, 4 h;
Column 4: 0.3 % 1, 0.9 % KOtBu, H3SiPh, 1 bar 13CO2, neat, 80°C, 8 h; Column 5: 0.2 % 1, 0.8 % KOtBu, H3SiPh,
1 bar (continuous gas stream), DMSO-d6, 80°C, 4 h.
13
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Conclusion
In conclusion, we have developed an efficient catalyst, which demonstrates remarkable
selectivity in CO2 reduction towards attaining individually the product platforms of formic acid
(HCO2H), formaldehyde (H2CO), and methanol (H3COH). The cobalt-based catalyst bearing a
PNP pincer-type triazine ligand can operate at low catalyst loadings (0.2 mol%), short reaction
times (4 h), and moderate temperatures (r.t. to 80°C) to convert CO2 even at ambient
pressures. The formate level can be adjusted at 96% selectivity via hydrosilylation using
diphenylsilane under solvent-free conditions at 40°C for 4 h, while the methanol level is
reachable in DMSO at 80°C for 4 h in 99% selectivity by using phenylsilane. The formaldehyde
level is accessible in 71% selectivity by using phenylsilane under neat conditions for 8 h at
80°C. These results demonstrate the adaptivity of the catalytic system under varying reaction
conditions for the development of catalytic protocols to selectively access different reduction
levels of CO2 Further studies to elucidate the nature of the active species are currently
underway to fully comprehend the underlying control mechanisms on a molecular basis.
Meanwhile, extending the concept of multi-level CO2 reduction to other reducing agents,
including hydrogen or electrons and protons, seems highly attractive.
Supplementary Information is linked to the online version of the paper at
anie_xxxxxxxxx_sm_miscellaneous_information.pdf
Acknowledgments
We gratefully acknowledge basic support by the Max Planck Society, the RWTH Aachen
University, and the Ruhr University Bochum. The results summarized here have been
assembled as part of our activities in the Kopernikus Project “Power-to-X” (reduction of CO2)
and funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)
under Germany´s Excellence Strategy–Cluster of Excellence 2186 „The Fuel Science Center. “
HHC thanks the “Studienstiftung des deutschen Volkes” for a fellowship, as well as the IMPRS-
RECHARGE School.
14
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Literature
[1]
a) E. A. Quadrelli, G. Centi, J. L. Duplan, S. Perathoner, ChemSusChem 2011, 4, 1194-
1215; b) P. Markewitz, W. Kuckshinrichs, W. Leitner, J. Linssen, P. Zapp, R. Bongartz,
A. Schreiber, T. E. Müller, Energy Environ. Sci. 2012, 5, 7281-7305; c) J. Schneider, H.
Jia, J. T. Muckerman, E. Fujita, Chem. Soc. Rev. 2012, 41, 2036-2051; d) M. Aresta, A.
Dibenedetto, A. Angelini, Chem. Rev. 2014, 114, 1709-1742; e) Q. Liu, L. Wu, R.
Jackstell, M. Beller, Nat. Commun. 2015, 6, 5933; f) J. Klankermayer, S. Wesselbaum,
K. Beydoun, W. Leitner, Angew. Chem. Int. Ed. 2016, 55, 7296-7343; g) J. Artz, T. E.
Müller, K. Thenert, J. Kleinekorte, R. Meys, A. Sternberg, A. Bardow, W. Leitner, Chem.
Rev. 2018, 118, 434-504.
[2]
a) W. Leitner, Angew. Chem. Int. Ed. 1995, 34, 2207-2221; b) R. Tanaka, M. Yamashita,
K. Nozaki, J. Am. Chem. Soc. 2009, 131, 14168–14169; c) C. Federsel, A. Boddien, R.
Jackstell, R. Jennerjahn, P. J. Dyson, R. Scopelliti, G. Laurenczy, M. Beller, Angew.
Chem. Int. Ed. 2010, 49, 9777-9780; d) R. Langer, Y. Diskin-Posner, G. Leitus, L. J.
Shimon, Y. Ben-David, D. Milstein, Angew. Chem. Int. Ed. 2011, 50, 9948-9952; e) M.
S. Jeletic, M. T. Mock, A. M. Appel, J. C. Linehan, J. Am. Chem. Soc. 2013, 135, 11533-
11536; f) C. A. Huff, M. S. Sanford, ACS Catal. 2013, 3, 2412-2416; g) S. Moret, P. J.
Dyson, G. Laurenczy, Nat. Commun. 2014, 5, 4017; h) G. A. Filonenko, R. van Putten,
E. N. Schulpen, E. J. M. Hensen, E. A. Pidko, ChemCatChem 2014, 6, 1526-1530; i) Y.
Zhang, A. D. MacIntosh, J. L. Wong, E. A. Bielinski, P. G. Williard, B. Q. Mercado, N.
Hazari, W. H. Bernskoetter, Chem. Sci. 2015, 6, 4291-4299; j) J. Klankermayer, S.
Wesselbaum, K. Beydoun, W. Leitner, Angew. Chem. Int. Ed. 2016, 55, 7296-7343.
[3]
[4]
a) S. Bontemps, L. Vendier, S. Sabo-Etienne, Angew. Chem. Int. Ed. 2012, 51, 1671-
1674; b) S. Bontemps, L. Vendier, S. Sabo-Etienne, J. Am. Chem. Soc. 2014, 136, 4419-
4425; c) P. Rios, N. Curado, J. Lopez-Serrano, A. Rodriguez, Chem. Commun. (Camb.)
2016, 52, 2114-2117; d) M. Rauch, G. Parkin, J. Am. Chem. Soc. 2017, 139, 18162-
18165; e) B. G. Schieweck, J. Klankermayer, Angew. Chem. Int. Ed. 2017, 56, 10854-
10857; f) N. Del Rio, M. Lopez-Reyes, A. Baceiredo, N. Saffon-Merceron, D. Lutters, T.
Müller, T. Kato, Angew. Chem. Int. Ed. 2017, 56, 1365-1370; g) M. Rauch, Z. Strater, G.
Parkin, J. Am. Chem. Soc. 2019, 141, 17754-17762.
a) S. Chakraborty, J. Zhang, J. A. Krause, H. Guan, J. Am. Chem. Soc. 2010, 132, 8872-
8873; b) G. A. Olah, A. Goeppert, G. K. S. Prakash, Beyond Oil and Gas: The Methanol
Economy, Wiley-VCH, 2011; c) C. A. Huff, M. S. Sanford, J. Am. Chem. Soc. 2011, 133,
18122-18125; d) S. Wesselbaum, T. Vom Stein, J. Klankermayer, W. Leitner, Angew.
Chem. Int. Ed. 2012, 51, 7499-7502; e) N. M. Rezayee, C. A. Huff, M. S. Sanford, J. Am.
Chem. Soc. 2015, 137, 1028-1031; f) J. Schneidewind, R. Adam, W. Baumann, R.
Jackstell, M. Beller, Angew. Chem. Int. Ed. 2017, 56, 1890-1893; g) C. Erken, A. Kaithal,
S. Sen, T. Weyhermüller, M. Hölscher, C. Werlé, W. Leitner, Nat. Commun. 2018, 9,
4521; h) W.-Y. Chu, Z. Culakova, B. T. Wang, K. I. Goldberg, ACS Catal. 2019, 9, 9317-
9326.
15
This article is protected by copyright. All rights reserved.

10.1002/ange.202004463
Angewandte Chemie
[5]
a) O. Jacquet, C. Das Neves Gomes, M. Ephritikhine, T. Cantat, J. Am. Chem. Soc. 2012,
́
134, 2934-2937; b) L. González-Sebastián, M. Flores-Alamo, J. J. Garcıa,
Organometallics 2013, 32, 7186-7194; c) O. Jacquet, C. Das Neves Gomes, M.
Ephritikhine, T. Cantat, ChemCatChem 2013, 5, 117-120; d) P. Daw, S. Chakraborty, G.
Leitus, Y. Diskin-Posner, Y. Ben-David, D. Milstein, ACS Catal. 2017, 7, 2500-2504; e) D.
S. Morris, C. Weetman, J. T. C. Wennmacher, M. Cokoja, M. Drees, F. E. Kühn, J. B.
Love, Catal. Sci. Technol. 2017, 7, 2838-2845; f) Y. Zhang, T. Zhang, S. Das, Green Chem.
2020, 22, 1800-1820.
[6]
[7]
[8]
a) Y. Li, X. Fang, K. Junge, M. Beller, Angew. Chem. Int. Ed. 2013, 52, 9568-9571; b) C.
Darcel, J.-B. Sortais, D. Wei, A. Bruneau-Voisine, in Non-Noble Metal Catalysis, 2018,
pp. 241-264.
a) M. L. Scheuermann, S. P. Semproni, I. Pappas, P. J. Chirik, Inorg. Chem. 2014, 53,
9463-9465; b) F. Bertini, M. Glatz, B. Stöger, M. Peruzzini, L. F. Veiros, K. Kirchner, L.
Gonsalvi, ACS Catal. 2018, 9, 632-639.
a) M. L. Scheuermann, S. P. Semproni, I. Pappas, P. J. Chirik, Inorg. Chem. 2014, 53,
9463-9465; b) P. Ríos, N. Curado, J. López-Serrano, A. Rodríguez, Chem. Comm. 2016,
52, 2114-2117; c) H. Li, T. P. Gonçalves, Q. Zhao, D. Gong, Z. Lai, Z. Wang, J. Zheng, K.-
W. Huang, Chem. Comm. 2018, 54, 11395-11398; d) F. Bertini, M. Glatz, B. Stöger, M.
Peruzzini, L. F. Veiros, K. Kirchner, L. Gonsalvi, ACS Catal. 2019, 9, 632-639.
[9]
a) T. T. Metsänen, M. Oestreich, Organometallics 2014, 34, 543-546; b) M. R. Espinosa,
D. J. Charboneau, A. Garcia de Oliveira, N. Hazari, ACS Catal. 2018, 9, 301-314; c) J.
Guzmán, P. García-Orduña, V. Polo, F. J. Lahoz, L. A. Oro, F. J. Fernández-Alvarez, Catal.
Sci. Technol. 2019, 9, 2858-2867.
[10] A. Kumar, P. Daw, N. A. Espinosa-Jalapa, G. Leitus, L. J. W. Shimon, Y. Ben-David, D.
Milstein, Dalton Trans. 2019, 48, 14580-14584.
[11] T. J. Korstanje, J. Ivar van der Vlugt, C. J. Elsevier, B. de Bruin, Science 2015, 350, 298.
[12] a) C. Federsel, C. Ziebart, R. Jackstell, W. Baumann, M. Beller, Chem.: Eur. J. 2012, 18,
72-75; b) M. S. Jeletic, M. L. Helm, E. B. Hulley, M. T. Mock, A. M. Appel, J. C. Linehan,
ACS Catal. 2014, 4, 3755-3762.
[13] a) M. Joost, L. Estevez, S. Mallet-Ladeira, K. Miqueu, A. Amgoune, D. Bourissou,
Angew. Chem. Int. Ed. 2014, 53, 14512-14516; b) G. Bistoni, S. Rampino, N. Scafuri, G.
Ciancaleoni, D. Zuccaccia, L. Belpassi, F. Tarantelli, Chem. Sci. 2016, 7, 1174-1184.
[14] S. Rösler, J. Obenauf, R. Kempe, J. Am. Chem. Soc. 2015, 137, 7998-8001.
[15] a) T. Matsuo, H. Kawaguchi, J. Am. Chem. Soc. 2006, 128, 12362-12363; b) S. J. Mitton,
L. Turculet, Chem.: Eur. J. 2012, 18, 15258-15262; c) S. Park, D. Bezier, M. Brookhart,
J. Am. Chem. Soc. 2012, 134, 11404-11407; d) F. J. Fernández-Alvarez, A. M. Aitani, L.
A. Oro, Catal. Sci. Technol. 2014, 4, 611-624; e) A. Julián, E. A. Jaseer, K. Garcés, F. J.
Fernández-Alvarez, P. García-Orduña, F. J. Lahoz, L. A. Oro, Catal. Sci. Technol. 2016,
16
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10.1002/ange.202004463
Angewandte Chemie
6, 4410-4417; f) F. J. Fernández-Alvarez, L. A. Oro, ChemCatChem 2018, 10, 4783-4796;
g) J. Chen, M. McGraw, E. Y. Chen, ChemSusChem 2019, 12, 4543-4569.
[16] H. Lv, Q. Xing, C. Yue, Z. Lei, F. Li, Chem. Commun. (Camb.) 2016, 52, 6545-6548.
17
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