Efficient fluoride-catalyzed conversion of CO2 to CO at room temperature

Article abstract of DOI:10.1021/ja502911e

A protocol for the efficient and selective reduction of carbon dioxide to carbon monoxide has been developed. Remarkably, this oxygen abstraction step can be performed with only the presence of catalytic cesium fluoride and a stoichiometric amount of a disilane in DMSO at room temperature. Rapid reduction of CO₂ to CO could be achieved in only 2 h, which was observed by pressure measurements. To quantify the amount of CO produced, the reduction was coupled to an aminocarbonylation reaction using the two-chamber system, COware. The reduction was not limited to a specific disilane, since (Ph ₂MeSi)₂ as well as (PhMe₂Si)₂ and (Me₃Si)₃SiH exhibited similar reactivity. Moreover, at a slightly elevated temperature, other fluoride salts were able to efficiently catalyze the CO₂ to CO reduction. Employing a nonhygroscopic fluoride source, KHF₂, omitted the need for an inert atmosphere. Substituting the disilane with silylborane, (pinacolato)BSiMe₂Ph, maintained the high activity of the system, whereas the structurally related bis(pinacolato)diboron could not be activated with this fluoride methodology. Furthermore, this chemistry could be adapted to ¹³C-isotope labeling of six pharmaceutically relevant compounds starting from Ba¹³CO ₃ in a newly developed three-chamber system.

Full text of DOI:10.1021/ja502911e

Article
pubs.acs.org/JACS
Efficient Fluoride-Catalyzed Conversion of CO2 to CO at Room
Temperature
Camille Lescot,† Dennis U. Nielsen,† Ilya S. Makarov,† Anders T. Lindhardt,*,‡ Kim Daasbjerg,†
and Troels Skrydstrup*,†
†The Center for Insoluble Protein Structures (inSPIN), the Interdisciplinary Nanoscience Center (iNANO) and Department of
Chemistry, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus, Denmark
‡The Interdisciplinary Nanoscience Center (iNANO), Biological and Chemical Engineering, Department of Engineering, Aarhus
University, Finlandsgade 22, 8200 Aarhus N, Denmark
S
* Supporting Information
ABSTRACT: A protocol for the efficient and selective reduction of
carbon dioxide to carbon monoxide has been developed. Remarkably,
this oxygen abstraction step can be performed with only the presence of
catalytic cesium fluoride and a stoichiometric amount of a disilane in
DMSO at room temperature. Rapid reduction of CO2 to CO could be
achieved in only 2 h, which was observed by pressure measurements. To
quantify the amount of CO produced, the reduction was coupled to an
aminocarbonylation reaction using the two-chamber system, COware. The reduction was not limited to a specific disilane, since
(Ph2MeSi)2 as well as (PhMe2Si)2 and (Me3Si)3SiH exhibited similar reactivity. Moreover, at a slightly elevated temperature,
other fluoride salts were able to efficiently catalyze the CO2 to CO reduction. Employing a nonhygroscopic fluoride source,
KHF2, omitted the need for an inert atmosphere. Substituting the disilane with silylborane, (pinacolato)BSiMe2Ph, maintained
the high activity of the system, whereas the structurally related bis(pinacolato)diboron could not be activated with this fluoride
methodology. Furthermore, this chemistry could be adapted to 13C-isotope labeling of six pharmaceutically relevant compounds
starting from Ba13CO3 in a newly developed three-chamber system.
arbon monoxide (CO) is an industrially important gas for
stoichiometric amounts of CO. As the carbon monoxide
Cthe production of aldehydes, carboxylic acids, alcohols, precursors were prepared from CO2, we speculated whether we
and hydrocarbons.1 This diatomic molecule also serves as a
could replace these precursors by CO2 and thereby identify
suitable conditions for the reduction of CO2 to CO in this two-
chamber system. Furthermore, this deoxygenation step should
be sufficiently rapid in order to be useful for a Pd-catalyzed
carbonylation reaction.
In this paper, we report the successful identification of a
simple, efficient, and stoichiometric conversion of CO2 to CO
performed at room temperature with catalytic cesium fluoride
in the presence of a disilane. In particular, the process can be
coupled up to Pd-catalyzed amino- and alkoxycarbonylations
with aryl bromides and iodides, thereby allowing for the
synthesis of a range of known pharmaceuticals directly from
this greenhouse gas.
Our inspiration for the development of the catalytic
transformation of CO2 to CO came from the work of Sadighi9
and Kleeberg,10 demonstrating the possibility of the copper(I)
complex, (IPr)Cu−OtBu (IPr = 1,3-bis(2,6-diisopropyl-
phenyl)imidazolidene), to catalyze this oxygen abstraction
process in the presence of excess bis(pinacolato)diboron or
(pinacolato)BSiMe2Ph (Scheme 1). In the proposed catalytic
cycles, the copper(I) complexes (IPr)Cu−Bpin and (IPr)Cu−
SiMe2Ph formed from a σ-bond metathesis pathway represent
useful C1-building block in numerous transition-metal-
catalyzed transformations for the construction of relevant
compounds of pharmaceutical and agrochemical interest.2
Nevertheless, its high toxicity remains a significant disadvantage
requiring specialized facilities for its handling. On the other
hand, if CO could be generated from a safe and inexpensive
precursor, this would considerably enhance the utility of this
gas. Carbon dioxide could represent a valuable CO source
being abundant, nonflammable, and nontoxic in low concen-
trations.3 Furthermore, there is an increasing interest in
identifying useful applications of this greenhouse gas as a
source for chemical production.4,5 A significant hurdle, though,
for the transformation of CO2 to CO is the need to cleave a
strong CO bond (bond energy = 804 kJ/mol).6 Although
considerable advances have been made applying photo- and
electrocatalytic processes, such systems are complex and their
optimization can be difficult.7
We recently demonstrated the usefulness of a two-chamber
reactor for performing a number of Pd-catalyzed carbonylation
reactions.8 In this setup, the chemically controlled release of the
diatomic gas from a carbon monoxide precursor is spatially
separated from the CO consuming reaction (carbonylation
reaction) being connected by a bridge, thus simplifying workup
and allowing carbonylation reactions to be run with just
Received: March 22, 2014
Published: April 4, 2014
© 2014 American Chemical Society
6142
dx.doi.org/10.1021/ja502911e | J. Am. Chem. Soc. 2014, 136, 6142−6147

Journal of the American Chemical Society
Article
Scheme 1. Selected Approaches for the Reduction of CO2 to
CO
Table 1. Copper Source Screening for the Reduction of CO2
to CO with Disilane
a
bc
,
b
entry
copper source
R3SiOSiR3 1 % conv
amide 2 % conv
key intermediates followed by CO2 insertion to generate
(IPr)Cu−O2CBpin and (IPr)Cu−O2CSiMe2Ph, respectively.
Initial efforts were set out to explore this reduction chemistry
applying the two-chamber reactor for trapping the synthesized
CO in a Pd-catalyzed aminocarbonylation. Furthermore,
another goal was to simplify the catalytic protocol for this
reduction step. After considerable experimentation, we
discovered that the combination of a catalyst derived from
Cu(OAc)2 and the bidentate ligand, DPPBz,11 with stoichio-
metric amounts of dimethyltetraphenyldisilane in N-methyl-
pyrrolidinone (NMP) at 150 °C, efficiently reduced CO2 to
carbon monoxide as measured by the formation of the
corresponding disiloxane 1. Coupling of this process in a
two-chamber system with the Pd-catalyzed carbonylative
coupling of p-iodoanisole and n-hexylamine at 80 °C for 18 h
provided the amide 2 in a 96% yield, as depicted in Scheme 2.12
1
2
3
4
5
CuI
0
0
CuCN
0
0
Cu(acac)2
Cu(OCOCF3)2
Cu(OTf)2
67
94
0
100
100
0
a
Conditions: Chamber A was loaded with (MePh2Si)2 (0.75 mmol),
copper salt (0.075 mmol), DPPBz (0.083 mmol), NMP (3.0 mL), and
last CO2 (21 mL, 0.85 mmol) by injection through the septum.
Chamber B was loaded with p-iodoanisole (0.50 mmol), n-hexylamine
(1.0 mmol), Pd(dba)2 (0.025 mmol), PPh3 (0.050 mmol), Et3N (1.0
mmol), and dioxane (3.0 mL). The reaction mixture in Chamber B
was stirred at 80 °C for 18 h and in Chamber A at 150 °C for 18 h.
Conversions were measured by analysis of the H NMR spectra of
the crude product mixtures in the individual chambers (see Supporting
Information). Since 1.5 equiv of the disilane was used, only 67%
conversion is needed for the full conversion to the amide 2.
b
1
c
conversion was observed at all in both chambers (entries 2 and
3).
Scheme 2. Initial Experiment on the CO2 Reduction and
Application in a Pd-Catalyzed Aminocarbonylation
An increase in reactivity was nevertheless noted when
potassium acetate was replaced with 10 mol % potassium
fluoride. Hence, at 80 °C and even at 40 °C, the conversions to
1 and 2 were high (entries 4 and 5) implying that the CO2
reduction step was indeed effective at these temperatures. On
the other hand, negligible reactivity was again observed at 20
°C (entry 6). A screening of various solvents (entries 7−13)
proved rewarding and revealed that the use of DMSO
permitted the effective transformation of CO2 to CO at 20
°C (entry 13). Finally, after examining other fluoride sources
including TBAF, LiF, NaF, and CsF (entries 14−17), the latter
was found to exhibit the highest reactivity leading to complete
conversion in both chambers. Hence, cesium fluoride proved to
be an excellent catalyst for the room temperature and
stoichiometric reduction of CO2 to carbon monoxide with
the disilane, (MePh2Si)2.
Furthermore, the catalyst loading could be reduced down to
5 mol% without lowering the conversions in both chambers
(entry 18). Less reactive substrates for the aminocarbonylation
reaction generally need a slight excess of CO.8 To meet this
requirement a slight excess of CO was indirectly applied by
increasing the amount of disilane. With these conditions, a 99%
isolated yield of amide 2 could be secured (entry 19).14
After optimizing the parameters for the catalytic activation of
diphenylmethyldisilane for the reduction of CO2, it was decided
to screen other disilanes (Table 3). Having only methyl or
phenyl groups present on the disilane proved detrimental for
the reaction (entries 1 and 2). However, it is worth noting that
hexaphenyldisilane was insoluble in DMSO, which could
explain its lack of reactivity. Substituting two of the phenyl
substituents with methyl groups provided the high activity of
the system (entry 3). The presence of o-methoxy substituents
on the aromatic rings completely shuts down the reaction,
which could possibly be explained by coordination between the
In our efforts to optimize these new reduction conditions for
the transformation of CO2 to CO with disilane, we decided to
investigate the effect of the copper source (Table 1). The two
copper(I) salts that were examined were ineffective as shown in
entries 1 and 2. Cu(acac)2 furnished disiloxane 1 from the
disilane with a conversion of 67% (entry 3), while Cu-
(OCOCF3)2 in entry 4 proved to be almost as efficient as
Cu(OAc)2 (94% conversion). On the other hand, Cu(OTf)2
did not lead to any conversion at all (entry 5). Due to the large
influence of the different counterions of the Cu(II) salts, we
speculated whether they would exhibit catalytic activity in the
absence of copper. Hence, a similar set of experiments were
performed as illustrated in Scheme 2, though with the
exception that the Cu(OAc)2/DPPBz combination was
replaced with KOAc.13 To our delight, complete conversion
to the disiloxane 1 and amide 2 was observed (Table 2, entry 1)
with only 10 mol % of added potassium acetate suggesting that
indeed CO2 reduction to CO could be catalyzed by this simple
salt. Lowering the reaction temperature to 80 °C led to a
substantial drop in the conversion, whereas, at 20 °C, no
6143
dx.doi.org/10.1021/ja502911e | J. Am. Chem. Soc. 2014, 136, 6142−6147

Journal of the American Chemical Society
Article
Table 2. Optimization of the Reduction of CO2 to CO with
Disilane Catalyzed by Simple Salts
Table 3. Screening of Disilanes for the Reduction of CO2 at
Room Temperature
a
a
R3SiOSiR3 1
amide 2
b
b
entry
cat.
solvent T [°C]
% conv
% conv
1
KOAc
KOAc
KOAc
KF
NMP
150
80
20
80
40
20
20
20
20
20
20
20
20
20
20
20
20
20
20
100
50
0
100
50
0
2
NMP
3
NMP
4
NMP
100
95
4
99
95
4
5
KF
NMP
6
KF
NMP
7
KF
THF
0
0
8
KF
dioxane
MeCN
toluene
DCE
0
0
9
KF
0
0
10
11
12
13
14
15
16
17
18
KF
0
0
KF
0
0
KF
DMF
75
90
0
75
90
0
KF
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
TBAF
LiF
0
0
NaF
CsF
0
0
100
100
100
100
100
a
Conditions: Chamber A was loaded with disilane (0.50 mmol), CsF
c
CsF
(0.050 mmol), DMSO (3.0 mL), and last CO2 (21 mL, 0.85 mmol) by
injection through the septum. Chamber B was loaded with p-
iodoanisole (0.50 mmol), n-hexylamine (1.0 mmol), Pd(dba)2 (0.025
mmol), PPh3 (0.050 mmol), Et3N (1.0 mmol), and dioxane (3.0 mL).
The reaction mixture in Chamber B was stirred at 80 °C for 18 h and
d
e
19
CsF
100[99]
a
Conditions: Chamber A was loaded with (MePh2Si)2 (0.50 mmol),
activator (0.050 mmol), solvent (3.0 mL), and last CO2 (21 mL, 0.85
mmol) by injection through the septum. Chamber B was loaded with
p-iodoanisole (0.50 mmol), n-hexylamine (1.0 mmol), Pd(dba)2
(0.025 mmol), PPh3 (0.050 mmol), Et3N (1.0 mmol), and dioxane
(3.0 mL). The reaction mixture in Chamber B was stirred at 80 °C for
b
1
in Chamber A at 20 °C for 18 h. Based on H NMR conversion.
c
Disilane (0.17 mmol).
b
18 h. Conversions were measured by analysis of the 1H NMR spectra
of the crude product mixtures in the individual chambers (see
c
Supporting Information). Loading of CsF was reduced to 0.025
d
e
mmol. Loading of disilane was increased to 0.75 mmol. Isolated yield
(%) of amide 2.
silicon and oxygen. Interestingly, as opposed to hexamethyl-
disilane (entry 1), tris(trimethylsilyl)silane proved to be very
efficient even with a loading approximately 3 times less than
that for the other disilanes, which is undoubtedly due to the
presence of multiple Si−Si bonds in this structure (entry 5).
Surprisingly, it does not appear that the Si−H bond is involved
in this reduction step, as neither the silyl formate nor the
methoxysilane could be observed in the crude NMR.11,15
To further quantify the reactivity of the system, we followed
the reduction of CO2 to CO by measuring the pressure of the
system over time without the CO-consuming reaction (Figure
1). After the injection, carbon dioxide rapidly goes into
solution, causing a quick pressure decay. As the reaction
proceeds, the less soluble carbon monoxide is produced and
after 30 min the pressure commences to increase, achieving a
constant value after approximately 2 h when the reduction is
complete.
Figure 1. Profile of the pressure measurement experiment.
Conditions: (PhMe2Si)2 (0.50 mmol), CsF (0.050 mmol), DMSO
(3.0 mL), CO2 (0.85 mmol) injected through a septum. The reaction
mixture was stirred at 20 °C.
(IPr)Cu−OtBu. Therefore, the substitution of CsF with a
nonhygroscopic fluoride source should allow these trans-
formations to be carried out without the need for an inert
atmosphere. Gratifyingly, the reaction setup in air with KHF2 as
a catalyst (10 mol %) under the otherwise optimal conditions
(Scheme 3) provided 63% conversion of p-iodoanisole into the
amide 2 after 18 h. The conversion is incomplete due to the
lower reactivity of potassium hydrogen fluoride; however, it can
Cesium fluoride is hygroscopic, and hence an inert
atmosphere should be applied when working with this salt.
This is also the case with the previously reported systems for
the CO2 to CO reduction by Sadighi9 and Kleeberg,10 when
utilizing the air- and moisture-sensitive copper(I) complex,
6144
dx.doi.org/10.1021/ja502911e | J. Am. Chem. Soc. 2014, 136, 6142−6147

Journal of the American Chemical Society
Article
a
Scheme 3. Reduction of CO2 in the Presence of Air
Scheme 5. Proposed Mechanism for CO2 Reduction with
CsF and Disilane
a
Conditions: Chamber A was loaded with (Ph2MeSi)2 (0.50 mmol),
KHF2 (0.050 mmol), DMSO (3.0 mL), and last CO2 (21 mL, 0.85
mmol) by injection through the septum. Chamber B was loaded with
p-iodoanisole (0.50 mmol), n-hexylamine (1.0 mmol), Pd(dba)2
(0.025 mmol), PPh3 (0.050 mmol), Et3N (1.0 mmol), and dioxane
(3.0 mL). The reaction mixture in Chamber B was stirred at 80 °C for
18 h and in Chamber A at specified temperature for 18 h.
be increased to 100% by performing the CO2 reduction in
chamber A at 30 °C.
It was also interesting to compare the reactivity of the
disilanes with the two related reductants used in the copper(I)-
catalyzed variants of the transformations of carbon dioxide to
carbon monoxide.9,10 Similar experiments were therefore
carried out as in the case for the disilanes applying a two-
chamber system whereby chamber A was instead loaded with
either bis(pinacolato)diboron or (pinacolato)BSiMe2Ph
(Scheme 4). The reduction of CO2 with pinBSiMe2Ph led to
Whether CO2 reacts with a free silyl anion under our reaction
conditions or a hypervalent species A by fluoride coordination
to one of the two silyl atoms is at the moment not clear.
Nevertheless, subsequent CO2 insertion into A would generate
the O-silylated silacarboxylic acid B. Liberation of the
silacarboxylate generates the corresponding cesium salt C,
which possibly undergoes a Brook rearrangement to liberate
CO and a silyloxide, in analogy to similar observations on the
fluoride and hydroxide promoted generation of CO from
silacarboxylic acids.8b,17 Subsequent generation of the disilox-
ane from attack of the siloxide with the silyl fluoride regenerates
the cesium fluoride.
Scheme 4. CsF-Catalyzed Reduction of CO2 with B2pin2 and
a
pinBSiMe2Ph
With this surprisingly simple catalytic protocol in hand for
the efficient conversion of CO2 into CO without the need of a
transition metal catalyst, we proceeded to investigate its
usefulness for the preparation of a number of pharmaceutically
relevant molecules as depicted in Scheme 6. As with the
optimization studies, all reactions were run in a two-chamber
system and, for best coupling yields, 1.5 equiv of CO were
applied. Gratifyingly, all the amino- and alkoxycarbonylations
proved to be highly efficient, indicating again that the CO2
reduction step to CO performed exceptionally well.
Further studies were also undertaken to validate this protocol
for selective 13C-carbon isotope labeling of the same bioactive
compounds. As a convenient source of 13CO2, we chose
commercially available 13C-labeled Ba13CO3. This required a
closed three-chamber system, whereby CO2 is liberated in one
of the three chambers by the treatment of the barium carbonate
with camphorsulfonic acid.18 As shown in the results in Scheme
6, the addition of a third reaction in an additional chamber did
not have a detrimental effect on the efficiency of the carbon
dioxide reduction step or the Pd-catalyzed transformation, and
hence, all 13C-isotopically labeled pharmaceutical compounds
were prepared in good yields.
In conclusion, a simple and mild protocol for the conversion
of CO2 to CO has been developed, which does not require a
transition metal catalyst. Notably, this transformation is
promoted by catalytic cesium fluoride in the presence of a
disilane and at room temperature. This is the first example
utilizing a disilane for the reduction of CO2 to CO.19
Furthermore, the process can be coupled to Pd-catalyzed
amino- and alkoxycarbonylations in a two-chamber system
providing excellent coupling yields of a range of pharmaceuti-
cally relevant compounds. Finally, with a three-chamber system,
13C-isotope labeling of the same compounds with Ba13CO3
a
Conditions: Chamber A was loaded with pinBSiMe2Ph (0.50 mmol)
or B2pin2 (0.50 mmol), CsF (0.050 mmol), DMSO (3.0 mL), and last
CO2 (21 mL, 0.85 mmol) by injection through the septum. Chamber
B was loaded with p-iodoanisole (0.50 mmol), n-hexylamine (1.0
mmol), Pd(dba)2 (0.025 mmol), PPh3 (0.050 mmol), Et3N (1.0
mmol), and dioxane (3.0 mL). The reaction mixture in Chamber B
was stirred at 80 °C for 18 h and in Chamber A at 20 °C for 18 h.
an 89% conversion of p-iodoanisole into the amide 2 and full
consumption of the silylborane after 18 h at room temperature.
The incomplete conversion of CO2 into CO is most likely due
to some unidentified side reactions.10 This experiment
demonstrates that cesium fluoride is a more active catalyst for
deoxygenating CO2 with pinBSiMe2Ph than (IPr)Cu−OtBu
used by Kleeberg. Indeed, with 20 mol % of this copper species,
1 equiv of carbon dioxide is completely consumed after 79 h
giving approximately 70% of CO,10 whereas with CsF (10 mol
%) the same consumption is achieved after only 18 h and the
yield of carbon monoxide is higher. Unlike the disilanes and
silylborane, B2pin2 was unreactive under our optimized
conditions. These results suggest that the presence of a silicon
atom is necessary for the fluoride to be an active catalyst for the
CO2 to CO reduction.
A possible catalytic cycle for the fluoride promoted reduction
of CO2 to carbon monoxide with disilane is depicted in Scheme
5. Hiyama and co-workers have earlier demonstrated the ability
to generate metal-free silyl anions from the treatment of
disilanes with tetrabutylammonium fluoride in HMPA.16
6145
dx.doi.org/10.1021/ja502911e | J. Am. Chem. Soc. 2014, 136, 6142−6147

Journal of the American Chemical Society
Article
Scheme 6. Combining the CO2 to CO Reduction Protocol with the Pd-Catalyzed Amino- and Alkoxycarbonylation
Notes
could be achieved. Further work is currently in progress to
provide a more detailed understanding of this intriguing oxygen
abstraction step from CO2. This work will be reported in due
course.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are deeply appreciative of generous financial support from
the Danish National Research Foundation, (Grant No.
DNRF59), the Villum Foundation, the Danish Council for
Independent Research: Technology and Production Sciences,
the Carlsberg Foundation, and Aarhus University for generous
financial support of this work.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Copies of H NMR, 13C and 19F NMR spectra for all the
coupling products, and details on experimental procedures.
This material is available free of charge via the Internet at
http://pubs.acs.org.
REFERENCES
■
AUTHOR INFORMATION
■
(1) For recent publications on these industrial processes: (a) Melaet,
G.; Ralston, W. T.; Li, C. S.; Alayoglu, S.; An, K.; Musselwhite, N.;
Kalkan, B.; Somorjai, G. A. J. Am. Chem. Soc. 2014, 136, 2260.
(b) Dydio, P.; Detz, R. J.; Reek, J. N. J. Am. Chem. Soc. 2013, 135,
Corresponding Authors
lindhardt@eng.au.dk
ts@chem.au.dk
6146
dx.doi.org/10.1021/ja502911e | J. Am. Chem. Soc. 2014, 136, 6142−6147

Journal of the American Chemical Society
Article
10817. (c) Wu, L.; Fleischer, I.; Jackstell, R.; Profir, I.; Franke, R.;
Beller, M. J. Am. Chem. Soc. 2013, 135, 14306. (d) Haynes, A.; Maitlis,
P. M.; Morris, G. E.; Sunley, G. J.; Adams, H.; Badger, P. W.; Bowers,
C. M.; Cook, D. B.; Elliott, P. I.; Ghaffar, T.; Green, H.; Griffin, T. R.;
Payne, M.; Pearson, J. M.; Taylor, M. J.; Vickers, P. W.; Watt, R. J. J.
Am. Chem. Soc. 2004, 126, 2847.
(2) For some recent reviews on transition-metal-catalyzed carbon-
ylations, see: (a) Wu, X.-F.; Neumann, H.; Beller, M. Chem. Rev. 2013,
113, 1. (b) Wu, X.-F.; Neumann, H.; Beller, M. ChemCatChem 2012,
4, 447. (c) Wu, X.-F.; Neumann, H.; Beller, M. Chem. Soc. Rev. 2011,
40, 4986. (d) Magano, J.; Dunetz, J. R. Chem. Rev. 2011, 111, 2177.
(e) Grigg, R.; Mutton, S. P. Tetrahedron 2010, 66, 5515.
(f) Brennfuhrer, A.; Neumann, H.; Beller, M. Angew. Chem., Int. Ed.
2009, 48, 4114.
(3) (a) Wu, L.; Liu, Q.; Fleischer, I.; Jackstell, R.; Beller, M. Nat.
Commun. 2014, 5, doi: 10.1038/ncomms4091. (b) Yu, B.; Zhao, Y.;
Zhang, H.; Xu, J.; Hao, L.; Gao, X.; Liu, Z. Chem. Commun. 2014, 50,
2330. (c) Dobrovetsky, R.; Stephan, D. W. Angew. Chem., Int. Ed.
2013, 52, 2516.
(4) For selected reviews on the valorization of CO2, see: (a) Jessop,
P. G.; Ikariya, T.; Noyori, R. Chem. Rev. 1995, 95, 259. (b) Jessop, P.
G.; Joo, F.; Tai, C.-C. Coord. Chem. Rev. 2004, 248, 2425. (c) Aresta,
́
M.; Dibenedetto, A. Dalton Trans. 2007, 2975. (d) Sakakura, T.; Choi,
J.-C.; Yasuda, H. Chem. Rev. 2007, 107, 2365. (e) Correa, A.; Martin,
R. Angew. Chem., Int. Ed. 2009, 48, 6201. (f) Benson, E. E.; Kubiak, C.
P.; Sathrum, A. J.; Smieja, J. M. Chem. Soc. Rev. 2009, 38, 89.
(g) Appel, A. M.; Bercaw, J. E.; Bocarsly, A. B.; Dobbek, H.; Dubois,
D. L.; Dupuis, M.; Ferry, J. G.; Fujita, E.; Hille, R.; Kenis, P. J. A.;
Kerfeld, C. A.; Morris, R. H.; Peden, C. H. F.; Portis, A. R.; Ragsdale,
S. W.; Rauchfuss, T. B.; Reek, J. N. H.; Seefeldt, L. C.; Thauer, R. K.;
Waldrop, G. L. Chem. Rev. 2013, 113, 6621. (h) Wang, W.; Wang, S.;
Ma, X.; Gong, J. Chem. Soc. Rev. 2011, 40, 3703. (i) Huang, K.; Sun,
C.-L.; Shi, Z.-J. Chem. Soc. Rev. 2011, 40, 2435. (j) Martin, R.; Kleij, A.
W. ChemSusChem 2011, 4, 1259. (k) Cokoja, M.; Bruckmeier, C.;
W.; Lee, S. H.; Shin, J. W.; Lee, S. P.; Kim, Y. J. Am. Chem. Soc. 2003,
125, 14688. (e) DiMeglio, J. L.; Rosenthal, J. J. Am. Chem. Soc. 2012,
135, 8798. (f) Keith, J. A.; Grice, K. A.; Kubiak, C. P.; Carter, E. A. J.
Am. Chem. Soc. 2013, 135, 15823. (g) Lu, Q.; Rosen, J.; Zhou, Y.;
Hutchings, G. S.; Kimmel, Y. C.; Chen, J. G.; Jiao, F. Nat. Commun.
2014, 5, 3242.
(8) (a) Hermange, P.; Lindhardt, A. T.; Taaning, R. H.; Bjerglund,
K.; Lupp, D.; Skrydstrup, T. J. Am. Chem. Soc. 2011, 133, 6061.
(b) Friis, S. D.; Taaning, R. H.; Lindhardt, A. T.; Skrydstrup, T. J. Am.
Chem. Soc. 2011, 133, 18114. (c) Nielsen, D. U.; Lescot, C.; Lindhardt,
A. T.; Gøgsig, T. M.; Skrydstrup, T. Chem.Eur. J. 2013, 19, 17926.
(d) Korsager, S.; Taaning, R. H.; Lindhardt, A. T.; Skrydstrup, T. J.
Org. Chem. 2013, 78, 6120 and references cited therein.
(9) Laitar, D. S.; Muller, P.; Sadighi, J. P. J. Am. Chem. Soc. 2005, 127,
̈
17196.
(10) Kleeberg, C.; Cheung, M. S.; Lin, Z.; Marder, T. B. J. Am. Chem.
Soc. 2011, 133, 19060.
(11) Motokura, K.; Kashiwame, D.; Takahashi, N.; Miyaji, A.; Baba,
T. Chem.Eur. J. 2013, 19, 10030.
(12) This amide coupling is one of the most efficient and has been
repeatedly used by us for investigations of CO release in a two-
chamber reactor (see refs 8a and 8b).
(13) For the metal-free reduction of CO2 to CO using a disilyne
biphosphine adduct, see: Gau, D.; Rodriguez, R.; Kato, T.; Saffon-
Merceron, N.; de Cozar, A.; Cossío, F. P.; Baceiredo, A. Angew. Chem.,
́
Int. Ed. 2011, 50, 1092.
(14) The rate of CO release is undoubtedly faster with 10 mol%,
which proved necessary for the good conversions with the more
complex substrates in the second chamber as illustrated in Scheme 6.
(15) (a) Zhang, L.; Cheng, J.; Hou, Z. Chem. Commun. 2013, 49,
4782. (b) Riduan, S. N.; Zhang, Y.; Ying, J. Y. Angew. Chem., Int. Ed.
2009, 48, 3322.
(16) (a) Hiyama, T.; Obayashi, M.; Mori, I.; Nozaki, H. J. Org. Chem.
1983, 48, 912. (b) Hiyama, T.; Obayashi, M. Tetrahedron Lett. 1983,
24, 4109. (c) Hiyama, T.; Obayashi, M.; Sawahata, M. Tetrahedron
Rieger, B.; Herrmann, W. A.; Kuhn, F. E. Angew. Chem., Int. Ed. 2011,
̈
Lett. 1983, 24, 4113. See also (d) Wagler, J.; Bohme, U.; Roewer, G.
̈
50, 8510. (l) Tsuji, Y.; Fujihara, T. Chem. Commun. 2012, 48, 9956.
(m) Omae, I. Coord. Chem. Rev. 2012, 256, 1384. (n) Schneider, J.; Jia,
H.; Muckerman, J. T.; Fujita, E. Chem. Soc. Rev. 2012, 41, 2036.
(o) Lu, X.-B.; Darensbourg, D. J. Chem. Soc. Rev. 2012, 41, 1462.
(p) Zhang, L.; Hou, Z. Chem. Sci. 2013, 4, 3395. (q) Aresta, M.;
Dibenedetto, A.; Angelini, A. Chem. Rev. 2014, 114, 1709. (r) Tlili, A.;
Frogneux, X.; Blondiaux, E.; Cantat, T. Angew. Chem., Int. Ed. 2014,
53, 2543. (s) Lanzafame, P.; Centi, G.; Perathoner, S. Chem. Soc. Rev.
2014, DOI: 10.1039/C3CS60396B. (t) Fontaine, F.-G.;
Organometallics 2004, 23, 6066. (e) Mita, T.; Chen, J.; Sugawara, M.;
Sato, Y. Org. Lett. 2012, 14, 6202.
(17) Friis, S. D.; Andersen, T. L.; Skrydstrup, T. Org. Lett. 2013, 15,
1381.
(18) See Supporting Information for the design and dimensions of
the three-chamber system.
(19) An intriguing follow-up to this work would be to identify
reaction conditions for the conversion of the disiloxane back to the
disilane, possibly via an electrochemical setup.
Courtemanche, M.-A.; Leg
(5) For some recent publications on the CO2 valorization, see:
(a) Correa, A.; Leon, T.; Martin, R. J. Am. Chem. Soc. 2014, 136, 1062.
́
are,
́
M.-A. Chem.Eur. J. 2014, 20, 2990.
́
(b) Wu, J.; Kozak, J. A.; Simoen, F.; Hatton, T. A.; Jamison, T. F.
Chem. Sci. 2014, 5, 1227. (c) Studt, F.; Sharafutdinov, I.; Abild-
Pedersen, F.; Elkjær, C. F.; Hummelshøj, J. S.; Dahl, S.; Chorkendorff,
́
I.; Nørskov, J. K. Nat. Chem. 2014, 6, 320. (d) Leon, T.; Correa, A.;
Martin, R. J. Am. Chem. Soc. 2013, 135, 1221. (e) Sasano, K.; Takaya,
J.; Iwasawa, N. J. Am. Chem. Soc. 2013, 135, 10954. (f) Ostapowicz, T.
G.; Schmitz, M.; Krystof, M.; Klankermayer, J.; Leitner, W. Angew.
Chem., Int. Ed. 2013, 52, 12119. (g) Bontemps, S.; Sabo-Etienne, S.
Angew. Chem., Int. Ed. 2013, 52, 10253. (h) Kozak, J. A.; Wu, J.; Su, X.;
Simoen, F.; Hatton, T. A.; Jamison, T. F. J. Am. Chem. Soc. 2013, 135,
18497. (i) Zhang, L.; Cheng, J.; Carry, B.; Hou, Z. J. Am. Chem. Soc.
2012, 134, 14314. (j) Wesselbaum, S.; Vom Stein, T.; Klankermayer,
J.; Leitner, W. Angew. Chem., Int. Ed. 2012, 51, 7499. (k) Angamuthu,
R.; Byers, P.; Lutz, M.; Spek, A. L.; Bouwman, E. Science 2010, 327,
313.
(6) (a) Sanderson, R. T. Chemical bonds and bond energy, 2nd ed.;
Academic Press: New York, NY, 1976. (b) Sanderson, R. T. Polar
Covalence; Academic Press: New York, NY, 1983.
(7) For a current status and a few recent and notable exemptions,
́
see: (a) Costentin, C.; Robert, M.; Saveant, J.-M. Chem. Soc. Rev. 2013,
42, 2423. (b) Oh, Y.; Hu, X. Chem. Soc. Rev. 2013, 42, 2253. (c) Qiao,
J.; Liu, Y.; Hong, F.; Zhang, J. Chem. Soc. Rev. 2014, 43, 631. (d) Shin,
6147
dx.doi.org/10.1021/ja502911e | J. Am. Chem. Soc. 2014, 136, 6142−6147