Selective CO2 Splitting by Doubly Reduced Aryl Boranes to Give CO and [CO3]2?

Article abstract of DOI:10.1002/anie.201811135

Alkali metal salts M₂[1] (M=Li, Na) of doubly reduced 9,10-dimethyl-9,10-dihydro-9,10-diboraanthracene (1) instantaneously add the C=O bond of CO₂ across their boron centers to furnish formal [4+2]-cycloadducts M₂[2]. If only 1 equiv of CO₂ is supplied, these products are stable. In the presence of excess CO₂, however, C?O bond cleavage occurs and an O^2? equivalent is transferred to CO₂ to furnish CO and [CO₃]^2?. With M=Li, Li₂CO₃ precipitates and the neutral 1 is liberated such that it can be reduced again to establish a catalytic cycle. With M=Na, [CO₃]^2? remains coordinated to both boron atoms in a bridging mode (Na₂[4]). A mechanistic scenario is proposed, based on isolated intermediates and model reactions.

Full text of DOI:10.1002/anie.201811135

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Selective CO2 Splitting by Doubly Reduced Aryl Boranes to Give
CO and [CO3]2–
Authors: Esther von Grotthuss, Sven Erik Prey, Michael Bolte, Hans-
Wolfram Lerner, and Matthias Wagner
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201811135
Angew. Chem. 10.1002/ange.201811135
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10.1002/anie.201811135
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COMMUNICATION
Selective CO2 Splitting by Doubly Reduced Aryl Boranes to Give
CO and [CO3]2–
Esther von Grotthuss, Sven E. Prey, Michael Bolte, Hans-Wolfram Lerner, and Matthias Wagner*
Abstract: Alkali metal salts M2[1] (M = Li, Na) of doubly reduced
9,10-dimethyl-9,10-dihydro-9,10-diboraanthracene (1)
Since the advent of frustrated Lewis pair (FLP) chemistry,
increasing efforts have been devoted to the replacement of
transition-metal catalysts by appropriate combinations of main-
group Lewis acids and bases. In the context of CO2 activation, a
plethora of capture products such as R3P‒C(O)‒O‒BR’3 are
nowadays known. Follow-up reactions with various reducing
agents have been studied and the palette of obtainable
compounds encompasses CO, HC(O)OH, H3COH, and CH4.[11]
Despite these impressive achievements, examples of catalytic
instantaneously add the C=O bond of CO2 across their boron
centers to furnish formal [4+2]-cycloadducts M2[2]. If only 1 equiv of
CO2 is supplied, these products are stable. In the presence of
excess CO2, however, C‒O-bond cleavage occurs and an O2–
equivalent is transferred to CO2 to furnish CO and [CO3]2–. With M =
Li, Li2CO3 precipitates and the neutral 1 is liberated such that it can
be reduced again to establish a catalytic cycle. With M = Na, [CO3]2–
remains coordinated to both boron atoms in a bridging mode (Na2[4]). CO2 reductions with FLPs are still scarce and often require
A mechanistic scenario is proposed, based on isolated intermediates
and model reactions.
drastic reaction conditions, extended periods of time, as well as
rather expensive hydride donors (e.g., HB(OR)2, HSiR3). The
reduction products are mainly obtained in the form of
organyloxyboranes and -silanes (e.g., H3CO‒B(OR)2) and the
released O atoms appear incorporated in dibor- or disiloxanes
(e.g., (RO)2B‒O‒B(OR)2).[11]
In the quest for more atom economic main-group reduction
catalysts, arylboranes with two cooperating boron centers and
the ability to accept two electrons from an electropositive metal
or a negative electrode bear particular promise. In 2010, our
group reported the activation of C(sp)‒H ([B]2–) and C=O ([C]2–)
The exhaust gas CO2 has long been neglected as a ubiquitous
and potentially valuable C1 building block for chemical synthesis.
Today, however, this situation is dramatically changing, driven
by the general awareness that fossil oil and gas are limited
resources and that the accumulation of CO2 in the earth’s
atmosphere significantly contributes to climate change.[1]
Conversion of the thermodynamically stable CO2 molecule into
useful chemicals requires the input of energy and reduction
equivalents. As an additional challenge, high-pressure
conditions are only avoidable with the help of carefully designed
catalysts.
bonds
by
the
doubly
reduced
9,10-dihydro-9,10-
Later we also
13]
diboraanthracene [A]2– (Scheme 1a).[12,
succeeded in the cleavage of H2 on the [A]2– platform and
proposed a concerted addition of the H2 molecule to the two
Prospective technologies for the renewable production of
organic compounds from CO2 are often based on the
heterogeneous CO2 → CO electroreduction at metal surfaces
and nanoparticles (e.g., Cu, Ag, Au),[2-4] Bi-modified glassy
carbon cathodes,[5] or metal-organic frameworks.[6] Common
obstacles include high electrode overpotentials, low energetic
efficiencies, rapid deactivation of the systems, and poor product
selectivities.[3] The one-electron reduction of CO2 occurs only at
very cathodic potential values, mainly because of the energy
penalty associated with bending of the linear molecule upon
electron uptake to furnish the [CO2]•– radical. Correspondingly,
the bent [CO2]•– is predisposed to accept a second electron.[1a]
Some transition-metal compounds can act as nucleophiles
toward CO2 molecules and thereby transfer two electrons
simultaneously onto the substrate, which is afterwards stabilized
through  backbonding (see below). Indeed, several metal
complexes exist that are capable of achieving the CO2 → CO
reduction under mild conditions, albeit not always in a catalytic
fashion.[7-10]
(a) Wagner 2010
tBu
pTol
pTol
H
H
2
2
2
H
O
B
B
OC(pTol)2
HCCtBu
B
B
B
B
H
H
H
H
[A]2
[B]2
[C]2
(b) Kinjo 2015
Kinjo 2016
Harman 2017
O
O
O
NHC
Ph
Ph
O
B
B
O
O
B
B
N
O
O
N
B
B
N
N
N
N
Ph
NHC
Ph
D
E
F
reversible
irreversible
O
irreversible
(c) Braunschweig 2018
O
O
C
NHC
Br
Br
CO2
NHC
Br
B
B
B
B
B
B
Br
NHC
[*]
M. Sc. E. von Grotthuss, B. Sc. S. E. Prey, Dr. M. Bolte, Dr. H.-W.
Lerner, Prof. Dr. M. Wagner
NHC
NHC
Br
O
NHC
Br
Institut für Anorganische Chemie, Goethe-Universität Frankfurt
Max-von-Laue-Strasse 7, 60438 Frankfurt (Main) (Germany)
E-mail: Matthias.Wagner@chemie.uni-frankfurt.de
G
H
I
Scheme 1. (a) Activation of C(sp)‒H and C=O bonds by a doubly
reduced 9,10-dihydro-9,10-diboraanthracene ([A]2–). (b) Cycloaddition
products of CO2 with neutral boron-containing heterocycles (D-F). (c)
Reaction of the diborene G with CO2 to furnish I via H. NHC = 1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidene.
Supporting information for this article (including all experimental
procedures together with further spectroscopic, crystallographic, and
computational details) is available on the WWW under http://...
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10.1002/anie.201811135
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COMMUNICATION
boron atoms.[14] In the meantime, related systems have been
disclosed by Kinjo[15, 16] and Harman[17] and shown to add CO2
through one of its C=O bonds (D-F; Scheme 1b). Even under a
CO2 atmosphere no further transformation took place.
Braunschweig et al. encountered a different situation when they
treated the diborene G with CO2 (Scheme 1c).[18] As a thermally
unstable primary intermediate, they observed the dibora--
lactone H, which rearranged with CO2 splitting to form the
isomeric 2,4-diboraoxetan-3-one I.
Herein, we report that reactions of CO2 with alkali metal salts
M2[1] (M = Li, Na; cf. Scheme 2) do not stop at the stage of F-
type cycloadducts, but proceed further to furnish CO and O2–
equivalents. Contrary to the stoichiometric system G-I, however,
CO is released and the O2– equivalent transferred to CO2 with
formation of [CO3]2–. The reaction is quantitative and the scaffold
of 1 remains fully intact, which renders the system catalytic.
Stirring of the known 1[19] in THF over lithium or sodium metal
quantitatively provides the respective M2[1] salts. Exposure of a
red solution of Li2[1] in [D8]THF to excess CO2 resulted in an
immediate decolorization (room temperature, 1 atm). After an
induction period of several minutes, gas evolution set in,
Na···COG = 2.268 Å; COG: centroid of the B2C4 ring). Upon
addition of CO2, decolorization of the solution and CO evolution
occurred as before, but no Na2CO3 precipitated and the reaction
mixture also contained no free 1. Rather, the 11B NMR spectrum
was characterized by a broad resonance at 2.7 ppm, indicating
tetracoordinate boron nuclei.[23] In line with that, the three signals
observed in the 1H NMR spectrum [7.25 (4H), 6.71 (4H), 0.31
(6H) ppm] and the corresponding 13C resonances were
considerably shifted upfield compared to those of 1. An
additional 13C signal appeared at  = 163.5 ppm and the IR
spectrum of the product contained two strong stretches in the
1
carbonyl region ( = 1399, 1523 cm– ). Taken together, the
spectroscopic results indicated the presence of a symmetric
diadduct of 1, which was finally identified as the [CO3]2– complex
Na2[4] by X-ray crystallography. The thf-solvated salt forms C1-
symmetric tetramers [Na8(thf)14][4]4 in the solid state (see the
Supporting Information). The bicyclo[3.2.2] ion [4]2– acquires its
negative charges from a bridging [CO3]2– ion (Figure 1). The
average lengths of the formal C=O double and C–OB single
bonds are 1.252 Å and 1.302 Å, respectively,[24] with an
unstrained O–C–O bond angle of 123°. The comparatively large
spread of the individual B–O bond lengths (1.600(8)-1.646(8) Å)
indicates a soft bonding potential. Together with the large
average B–O bond length of 1.626 Å,[25] this points toward a
weak interaction. Consequently, the extra thermodynamic
driving force provided by the higher lattice energy of Li2CO3 vs
Na2CO3 (UPOT = 2523 vs 2301 kJ mol–1)[26] suffices to cause the
precipitation of the former while the latter remains coordinated to
the ditopic Lewis acid 1.
accompanied by the formation of
a colorless precipitate
(Scheme 2). An NMR spectroscopic investigation of the
supernatant after 30 min revealed the selective and quantitative
conversion of Li2[1] to 1. A solution of the precipitate in D2O
We next treated M2[1] (M = Li, Na) with only 1 equiv of CO2. The
bicyclo[2.2.2] adducts M2[2] formed quantitatively (Scheme
3a).[27] Na2[2] gives rise to two 11B NMR signals: a broad one at
 = 2.0 ppm, similar to the [CO3]2– adduct Na2[4], is assignable
to the BO atom. A sharp one at  = –14.6 ppm corresponds to
the boron center attached to the carbonyl carbon atom. The
carbonyl 13C resonance ( = 219.9 ppm; cf. F: 198.4 ppm) is
Scheme 2. Highly selective transformation of CO2 to CO and Li2CO3 with
lithium metal and 1 as the redox catalyst (THF, room temperature, 1 atm).
showed only one resonance in the 13C{1H} and one in the 7Li
NMR spectrum (
= 167.7 and 0.11 ppm, respectively).
Moreover, the precipitate gave rise to a prominent IR stretch at
1
1435 cm– with a shoulder at higher wavenumbers. These
values are in accordance with corresponding data recorded on
commercial samples of Li2CO3. On a preparative scale, Li2[1]
and CO2 gave Li2CO3 in yields of 83%. When the reaction was
carried out in a sealed NMR tube, also the resonances of newly
formed CO ((13C) = 184.9 ppm[20]) and residual CO2 ((13C) =
125.7 ppm[21]) were detected. Further evidence for the formation
of CO was gathered from a chemical analysis technique based
on the reduction of colorless, aqueous PdCl2 to black Pd
metal.[22] In conclusion, 1 equiv of Li2[1] transforms 2 equiv of
CO2 into 1 equiv of CO and 1 equiv of Li2CO3. Importantly, the
reaction can also be performed in a catalytic fashion: as a proof
of principle, we have treated the 1-containing supernatant first
with lithium metal, then with CO2, and harvested a second crop
of Li2CO3/CO.
Given that the rate of H2 activation with M2[A] salts is
significantly influenced by the choice of the counter cation M+,[14]
the CO2 reduction was next repeated with the green-colored
Na2[1]. An X-ray crystal-structure analysis of the polymeric
inverse sandwich complex [Na2(thf)3][1] is shown in Figure 1 (av.
Figure 1. Molecular structures of [Na2(thf)3][1], [Na][Na3(thf)6][2]2,
[Na8(thf)14][4]4, and [Na(thf)2][Na(thf)][5] in the solid state. Na+ cations and
coordinating thf molecules are only shown for [Na2(thf)3][1]; all CH atoms
are omitted for clarity.
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10.1002/anie.201811135
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broadened almost beyond detection due to the effect of the
boron quadrupole moment. According to the overall numbers
and patterns of the 1H and 13C NMR signals, [2]2– possesses
average Cs symmetry in solution. The NMR data of Li2[2] are
essentially the same as those of Na2[2]. Single crystals of
[Na][Na3(thf)6][2]2 grew directly from the reaction mixture. Its
2 M
2 M
(a)
B
B
B
B
M2[1]
M2[1]*
CO2
solid-state
structure
contains
two
crystallographically
2 M
O
independent [2]2– ions with identical geometric parameters within
experimental error (Figure 1). The B–O bond length of [2]2– (av.
1.589 Å) lies between that of Harman’s neutral derivative F
(1.509(2) Å) and that of the [CO3]2– adduct [Na8(thf)14][4]4 (av.
1.626 Å). The formal C–O single bond of the CO2 bridge in [2]2–
(av. 1.319 Å) is longer by 0.053 Å than the C=O double bond (av.
1.266 Å). The primary C=O-activation step is reminiscent of
O
O
C
O
O
2 M
O
B
B
B
CO2
B
M2[2]
O
common [4+2]-cycloaddition reactions across the two central
O
2
carbon atoms of anthracene,[28] an isoelectronic analog of [1] .
2 M
–
O
O
2 M
O
Alternatively, one can view the [1]2– ion as containing ambiphilic
boron centers, which concertedly act on the substrate as a
frustrated B+I/B+III Lewis pair (see the resonance form M2[1]* in
Scheme 3a).[16] Analogous to the µ-[CO3]2– adduct Na2[4], the
primary product Na2[2] may be described as featuring a [CO2]2–
dianion, simultaneously bonded to the two boron atoms of
neutral 1.
O
O
B
B
B
B
CO
M2[4]
M2[3]
O
O
(b)
O
O
O
O
CO
[Mn]
When M2[2] was put under a blanket of CO2 ([D8]THF, room
temperature, 1 atm), we obtained the same product mixtures as
before when we had treated M2[1] directly with excess CO2,
which confirmed the role of M2[2] as an intermediate in the CO2-
reduction sequence. The elongated B–O bond likely constitutes
the weak link of [2]2– and the site of attack of a second CO2
molecule, which reacts through the insertion of one C=O bond. A
plausible mechanism of this insertion involves an equilibrium in
which ring-opening occurs through B–O bond heterolysis. The
transient intramolecular B/O-FLP could activate the substrate
CO2 in the usual manner to afford compound M2[3] (Scheme 3a).
Its [R3B–O–C(O)–O–C(O)–BR3]2– fragment has a structural
analog in the mixed carboxylic-carbonic anhydrides (MCCAs)
R3C–O–C(O)–O–C(O)–CR3,[29] which often suffer from low
stability. In the case of [3]2–, decomposition is even too rapid to
allow an NMR-spectroscopic characterization. The molecular
structure of this putative intermediate was therefore investigated
by quantum-chemical calculations. The computed dianion [3c]2–
represents a local minimum on the energy surface (Figure 2).
Regarding the release of CO, the most noteworthy structural
peculiarity lies in the pronounced difference between the two
C(sp2)–O bond lengths within the central C–O–C unit: the one
belonging to the CO3 moiety is 1.357 Å, whereas the one
belonging to the CO2 fragment amounts to 1.437 Å. We
therefore assume that the latter heterolytically dissociates in the
course of the subsequent reaction step, whereupon a species is
formed, which contains an 1-coordinated [CO3]2– ligand on one
boron atom and a CO ligand on the other. Ample precedence
exists for R3B–CO complexes and association/dissociation
equilibria with their free components R3B/CO.[30] In this vein, loss
of CO should readily occur also in the present situation and the
generated Lewis-acidic B center can subsequently bind to the
[CO3]2– ligand to give the µ-complex M2[4], which persists in the
case of M = Na, but dissociates in the case of M = Li. We note
that the mechanistic scenario outlined in Scheme 3a is strikingly
similar to the CO2-activation reaction mediated by the transition-
I
CO2
CO2
[Mn]
[Mn]
[Mn]
2
CO3
(c)
O
2 Na
2 Na
O
O
O
OCMe2
CO2
B
B
Na2[1]
B
B
Na2[5]
Na2[6]
Scheme 3. (a) Proposed mechanism for the reaction of M2[1] (M = Li,
Na) with CO2. (b) Related transformation mediated by the anionic fac-
[Mn–I(CO)3(bis-MeNHC)]– complex containing
a
methylene bis(N-
methylimidazol-2-ylidene) ligand. (c) Stable model complex Na2[6] of the
putative intermediate Na2[3], obtained by treatment of Na2[1] with
acetone and then with CO2.
metal complex fac-[Mn+I(CO)3(bis-MeNHC)Br] with a chelating
methylene bis(N-methylimidazol-2-ylidene) ligand (Figure 3b):[10]
In the course of the catalytic cycle, the metal-centered HOMO of
an electrogenerated [Mn–I]– intermediate nucleophilically attacks
an incoming CO2 molecule and forms a [Mn+I‒CO2]– anion,
which subsequently chains
up with a second equivalent
of CO2. Finally, [CO3]2–
dissociates from the complex
to leave a [Mn+I‒CO]+ cation
behind.
In order to gain further proof
for the intermediacy of Na2[3],
we decided to replace the
carbonyl group marked in
blue in Scheme 3a by a
CMe2 group, which should
be less easily extricable than
CO. The addition of 1 equiv
of acetone to Na2[1] gave
Figure 2. Calculated structure of [3c]2–
at the PBE0D/TZVP level of theory
with the SMD polarized continuum
model for solvation in THF.
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[10] F. Franco, M. F. Pinto, B. Royo, J. Lloret-Fillol, Angew. Chem. Int. Ed.
2018, 57, 4603-4606; Angew. Chem. 2018, 130, 4693-4696.
[11] a) A. E. Ashley, A. L. Thompson, D. O'Hare, Angew. Chem. Int. Ed.
2009, 48, 9839-9843; Angew. Chem. 2009, 121, 10023-10027; b) A.
Berkefeld, W. E. Piers, M. Parvez, J. Am. Chem. Soc. 2010, 132,
10660-10661; c) D. W. Stephan, G. Erker, Chem. Sci. 2014, 5, 2625-
2641; d) D. W. Stephan, Acc. Chem. Res. 2015, 48, 306-316; e) Z. Lu,
H. Hausmann, S. Becker, H. A. Wegner, J. Am. Chem. Soc. 2015, 137,
5332-5335; f) R. Declercq, G. Bouhadir, D. Bourissou, M.-A. Légaré,
M.-A. Courtemanche, K. S. Nahi, N. Bouchard, F.-G. Fontaine, L.
Maron, ACS Catal. 2015, 5, 2513-2520; g) F.-G. Fontaine, D. W.
Stephan, Current Opinion in Green and Sustainable Chemistry 2017, 3,
28-32; h) F.-G. Fontaine, É. Rochette, Acc. Chem. Res. 2018, 51, 454-
464.
Na2[5] in a clean reaction (Scheme 3c). X-ray crystallography on
[Na(thf)2][Na(thf)][5] (Figure 1) revealed a B–O bond length of
1.562(6) Å, which is shorter by 0.027
Å than that of
[Na][Na3(thf)6][2]2, but still longer by 0.053 Å than that of
Harman’s CO2-inert adduct F. Upon exposure to CO2 (room
temperature, 1 atm), Na2[5] was converted further to Na2[6]
(Scheme 3c). The NMR spectra of this product are in line with
the uptake of 1 equiv of CO2: (i) all 1H, 11B, and 13C{1H}
resonances were shifted compared to the starting material
Na2[5], but the signal patterns remained compatible with a
bridged derivative of 1 with average Cs symmetry. (ii) A new
13C{1H} resonance appeared at  = 159.1 ppm, which we assign
to the carbonyl carbon atom of the activated CO2 molecule (cf.
the [CO3]2– signal of Na2[4] at  = 163.5 ppm). (iii) The IR
spectrum of Na2[6] (but not of Na2[5]) contains strong absorption
bands at = 1358 and 1397 cm–1, in the typical region of C=O
stretches. Notably, even if the reaction was carried out in a
sealed NMR tube, no resonance of CO could be detected. This
result strongly indicates that the CO released in the course of
the reaction between M2[1] and CO2 indeed originates from the
first incorporated molecule of CO2.
To conclude, the presence of 9,10-dimethyl-9,10-dihydro-9,10-
diboraanthracene (1) as a redox catalyst enables the clean
reduction of CO2 with lithium metal under ambient conditions
and with selective formation of CO and Li2CO3 (the main
products of the corresponding uncatalyzed reaction are Li2O and
elemental carbon[31]). Notwithstanding the relevance of Li2CO3
for the chemical and pharmaceutical industry,[32] it would be
desirable to prepare also Na2CO3 in the same way. The reaction
currently stops at the stage of an isolable Na2CO3–1 aggregate,
but our system offers multiple options to promote the release of
Na2CO3, e.g., by adjusting the steric demand of the boron-
bonded substituents.
[12] A. Lorbach, M. Bolte, H.-W. Lerner, M. Wagner, Organometallics 2010,
29, 5762-5765.
[13] The X-ray crystal-structure analysis of a close derivative of [C]2– is
provided in Figure S49.
[14] E. von Grotthuss, M. Diefenbach, M. Bolte, H.-W. Lerner, M. C.
Holthausen, M. Wagner, Angew. Chem. Int. Ed. 2016, 55, 14067-
14071; Angew. Chem. 2016, 128, 14273-14277.
[15] D. Wu, L. Kong, Y. Li, R. Ganguly, R. Kinjo, Nat. Commun. 2015, 6,
7340.
[16] B. Wang, Y. Li, R. Ganguly, H. Hirao, R. Kinjo, Nat. Commun. 2016, 7,
11871.
[17] J. W. Taylor, A. McSkimming, C. F. Guzman, W. H. Harman, J. Am.
Chem. Soc. 2017, 139, 11032-11035.
[18] A. Stoy, J. Böhnke, J. O. C. Jiménez-Halla, R. D. Dewhurst, T. Thiess,
H. Braunschweig, Angew. Chem. Int. Ed. 2018, 57, 5947-5951; Angew.
Chem. 2018, 130, 6055-6059.
[19] S. N. Kessler, M. Neuburger, H. A. Wegner, Eur. J. Org. Chem. 2011,
3238-3245.
[20] B. von Ahsen, C. Bach, G. Balzer, B. Bley, M. Bodenbinder, G. Hägele,
H. Willner, F. Aubke, Magn. Reson. Chem. 2005, 43, 520-527.
[21] G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb, A.
Nudelman, B. M. Stoltz, J. E. Bercaw, K. I. Goldberg, Organometallics
2010, 29, 2176-2179.
[22] A. F. Holleman, E. Wiberg, N. Wiberg, Lehrbuch der Anorganischen
Chemie, Vol. 102, De Gruyter, Berlin, New York, 2007.
Keywords: boron • CO2 activation • electrocatalysis • main-
[23] H. Nöth, B. Wrackmeyer, Nuclear Magnetic Resonance Spectroscopy
of Boron Compounds, in NMR Basic Principles and Progress (Eds.: P.
Diehl, E. Fluck, R. Kosfeld), Springer, Berlin, 1978.
group ambiphile • reduction
[24] Compare the C–O bond lengths of CaCO3: 1.280(1), 1.2818(9), and
1.2818(9) Å: B. Pokroy, J. S. Fieramosca, R. B. Von Dreele, A. N. Fitch,
E. N. Caspi, E. Zolotoyabko, Chem. Mater. 2007, 19, 3244-3251.
[25] B–O bond lengths for comparison are listed in the legend of Figure S45.
[26] L. Glasser, H. D. B. Jenkins, J. Am. Chem. Soc. 2000, 122, 632-638.
[27] The dianion [2]2– is also comparable to published 9,10-dihydro-9,10-
diboraanthracene- and 1,2-diborylbenzene-diazene adducts: a) A.
Lorbach, M. Bolte, H.-W. Lerner, M. Wagner, Chem. Commun. 2010,
46, 3592-3594; b) Ö. Seven, S. Popp, M. Bolte, H.-W. Lerner, M.
Wagner, Dalton Trans. 2014, 43, 8241-8253; c) Z. Lu, H. Quanz, O.
Burghaus, J. Hofmann, C. Logemann, S. Beeck, P. R. Schreiner, H. A.
Wegner J. Am. Chem. Soc. 2017, 139, 18488-18491.
[1]
a) A. M. Appel, J. E. Bercaw, A. B. Bocarsly, H. Dobbek, D. L. DuBois,
M. Dupuis, J. G. Ferry, E. Fujita, R. Hille, P. J. A. Kenis, C. A. Kerfeld,
R. H. Morris, C. H. F. Peden, A. R. Portis, S. W. Ragsdale, T. B.
Rauchfuss, J. N. H. Reek, L. C. Seefeldt, R. K. Thauer, G. L. Waldrop,
Chem. Rev. 2013, 113, 6621-6658; b) M. Aresta, A. Dibenedetto, A.
Angelini, Chem. Rev. 2014, 114, 1709-1742.
[2]
[3]
[4]
Y. Hori, H. Wakebe, T. Tsukamoto, O. Koga, Electrochim. Acta 1994,
39, 1833-1839.
B. A. Rosen, A. Salehi-Khojin, M. R. Thorson, W. Zhu, D. T. Whipple, P.
J. A. Kenis, R. I. Masel, Science 2011, 334, 643-644.
D. Kim, J. Resasco, Y. Yu, A. M. Asiri, P. Yang, Nat. Commun. 2014, 5,
4948.
[28] a) J. C. C. Atherton, S. Jones, Tetrahedron 2003, 59, 9039-9057.
[29] a) D. S. Tarbell, E. J. Longosz, J. Org. Chem. 1959, 24, 774-778; b) D.
S. Tarbell, Acc. Chem. Res. 1969, 2, 296-300; c) C.-O. Chan, C. J.
Cooksey, D. Crich, J. Chem. Soc., Perkin Trans. 1 1992, 777-780.
[30] H. C. Brown, Acc. Chem. Res. 1969, 2, 65-72.
[5]
[6]
J. L. DiMeglio, J. Rosenthal, J. Am. Chem. Soc. 2013, 135, 8798-8801.
N. Kornienko, Y. Zhao, C. S. Kley, C. Zhu, D. Kim, S. Lin, C. J. Chang,
O. M. Yaghi, P. Yang, J. Am. Chem. Soc. 2015, 137, 14129-14135.
P. Zimmermann, S. Hoof, B. Braun-Cula, C. Herwig, C. Limberg,
Angew. Chem. Int. Ed. 2018, 57, 7230-7233; Angew. Chem. 2018, 130,
7349-7353.
[7]
[31] G. Zhuang, Y. Chen, P. N. Ross, Jr., Surf. Sci. 1998, 418, 139-149. At
–153 °C, the principal reaction products are Li2CO3 and CO (probably
formed via an oxalate intermediate), but even at such low temperatures
the reaction is far less selective than the one mediated by Li2[1].
[32] J. Deberitz, Lithium: production and application of a fascinating and
versatile element, SZ Scala GmbH, München, 2006.
[8]
[9]
S. Fukuzumi, Y.-M. Lee, H. S. Ahn, W. Nam, Chem. Sci. 2018, 9, 6017-
6034.
Z. Cao, J. S. Derrick, J. Xu, R. Gao, M. Gong, E. M. Nichols, P. T.
Smith, X. Liu, X. Wen, C. Copéret, C. J. Chang, Angew. Chem. Int. Ed.
2018, 57, 4981-4985; Angew. Chem. 2018, 130, 5075-5079.
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10.1002/anie.201811135
Angewandte Chemie International Edition
COMMUNICATION
COMMUNICATION
Two in one sweep: A doubly
reduced 9,10-diboraanthracene splits
CO2 quantitatively and under
ambient conditions to give CO and
carbonate ions. If lithium metal is
used as the reducing agent, Li2CO3
precipitates from the reaction mixture
and the CO2 reduction process
becomes catalytic.
E. von Grotthuss, S. E. Prey, M. Bolte,
H.-W. Lerner, and M. Wagner*
Page No. – Page No.
Selective CO2 Splitting by Doubly
Reduced Aryl Boranes to Give CO
and [CO3]2–
This article is protected by copyright. All rights reserved.