Angewandte
Chemie
DOI: 10.1002/anie.201105516
CO2 Recycling
A Diagonal Approach to Chemical Recycling of Carbon Dioxide:
Organocatalytic Transformation for the Reductive Functionalization of
CO2**
Christophe Das Neves Gomes, Olivier Jacquet, Claude Villiers, Pierre Thuꢀry,
Michel Ephritikhine, and Thibault Cantat*
CO2 recycling is a priority to reduce our dependence on
petrochemicals to produce chemical commodities and, in a
broader context, to develop new fuels.[1] With 6.8 Gt of
recyclable CO2 produced each year at point sources,[2] carbon
dioxide is a very attractive, nontoxic and abundant C1
building block.[1,3] Yet, only a handful processes utilizing
CO2 have been industrialized to date.[3] Urea synthesis is the
main process utilizing carbon dioxide[1,3] and more recently,
reaction of CO2 and epoxides in the presence of a catalyst was
developed to commercialize new polycarbonates and cyclic
carbonates.[4] Importantly, in these processes new C O and
À
À
C N bonds are formed but there is no formal reduction of the
carbon center and therefore no significant energy storage. In
parallel to this “horizontal approach” to CO2 utilization
(Figure 1), extensive research efforts have been devoted to
CO2 reduction to formic acid, formaldehyde, and methanol
Figure 1. Approaches to recycling transformations of CO2 as alterna-
tives to petrochemical methods.
using electrochemical, photo-electrochemical, and chemical
methods (“vertical approach”, Figure 1).[5] For example, CO2
could be reduced to formic acid derivatives with H2 using a
homogenous catalytic system and highly efficient catalysts
have been proposed recently for this reaction.[6–7] Though it is
expected that formic acid and methanol will play a growing
role in future nonfossil fuel economies, these chemicals do not
cover the whole feedstock necessary for fine chemicals
synthesis or high-energy fuels production.[1] In contrast,
petrochemicals (hydrocarbons) are extensively used as fuels
and basic reagents to access other chemicals, because they are
energetic and easy to derivatize. Novel methods for CO2
recycling that aim to compete with petrochemistry require
new processes that combine both reduction of CO2 and
enlarge the spectrum of compounds directly available from
CO2. Ideally, these “diagonal transformations” are catalytic
and proceed in a single step to ensure energy economy and a
positive carbon balance; yet, viable examples remain scarce
and lack generality because the functionalization is induced
by the reductant itself.[8] In this context, we have investigated
three-component systems where CO2 is reacted, in a single
step, with a functionalization reagent and a reducing reagent
which can be modified independently. Herein we report novel
diagonal transformations for CO2 recycling, including an
unprecedented organocatalytic synthesis of formamides from
CO2.
À
À
À
formation of C C, C N, and C O bonds (Figure 1), to
Amines and alcohols react with CO2 in the presence of a
base to afford carbamate and carbonate salts, respectively,
and were thus chosen as functionalization reagents.[9] On the
other hand, organosilanes are attractive reducing agents
because they are cheap and nontoxic. In addition, they have a
mild reducing potential and are thus an attractive energy
source to reduce CO2-derived systems without wasting
energy.[10] Our entry point into developing new reductive
functionalization of CO2 was therefore to explore the reaction
chemistry of the CO2/alcohol/silane and CO2/amine/silane
three-component systems.
[*] C. Das Neves Gomes, Dr. O. Jacquet, Dr. C. Villiers, Dr. P. Thuꢀry,
Dr. M. Ephritikhine, Dr. T. Cantat
CEA, IRAMIS, SIS2M, CNRS UMR 3299
91191 Gif-sur-Yvette (France)
E-mail: thibault.cantat@cea.fr
[**] For financial support of this work, we acknowledge the CEA, CNRS,
ANR (Fellowship to C.G. and Starting Grant to T.C.), the FP7
Eurotalents Program (PD Fellowship to O.J.), and the CEA Physical
Sciences Division (PD Fellowship to O.J., Basic Research on Low
Carbon Energies Grant to T.C.). We thank the CINES for the
allowance of computer time (Project No. c2011086494).
1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) was chosen as
Supporting information for this article including detailed descrip-
tions of experimental, spectroscopic, crystallographic, and quantum
chemical methods and results is available on the WWW under
À
À
a base to promote the insertion of CO2 to O H and N H
bonds. Indeed, we have recently isolated the first CO2 adduct
of a nitrogen base, using TBD [1, Eq. (1)], enabling the
Angew. Chem. Int. Ed. 2012, 51, 187 –190
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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