CHEMCATCHEM
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DOI: 10.1002/cctc.201200732
Complete Catalytic Deoxygenation of CO2 into
Formamidine Derivatives
Olivier Jacquet, Christophe Das Neves Gomes, Michel Ephritikhine, and Thibault Cantat*[a]
Because fossil resources are a limited feedstock and their ex-
tensive use results in the problematic accumulation of CO2 in
the atmosphere, the organic-chemical industry will face impor-
tant challenges over the coming few decades to circumvent
the use of raw fossil materials.[1] In particular, the fuel, petro-
chemical, and fine-chemicals industries have to find alternative
feedstocks and carbon-free energy sources to embrace sustain-
ability.[2] In this regard, CO2 has been proposed as an “energy
vector” for renewable energies,[3] as a solution for hydrogen
storage,[4] and as a C1 building block for the synthesis of fine
chemicals.[5,6] Yet, as a waste compound, CO2 is thermodynami-
Scheme 1. Principles of our approach.
cally and kinetically difficult to transform and research efforts
are still needed to promote shifts in technology in the chemi-
cal industry. Among the challenges that are associated with
CO2 transformation, we must acknowledge that, despite recent
progress, the scope of chemical functions that are available
from CO2 is still very limited and mostly consists of molecules
in which at least one CÀO bond from CO2 is retained.[5,6] In
fact, the only catalytic reaction that results in the complete de-
oxygenation of CO2 is its reduction into methane by hydroge-
nation, hydrosilylation, or electrochemical methods.[7] Interest-
ingly, Wehmschulte and co-workers recently observed that tol-
uene and diphenylmethane could be obtained as side-prod-
ucts in the silylium-catalyzed hydrosilylation of CO2 into meth-
ane in the presence of benzene.[7f]
(NHCs), which were found to be efficient at room temperature
for the conversion of a large scope of amines, anilines, imines,
and N heterocycles.[6b] This reaction was mild, robust, and se-
lective; thus, it offered a good starting point for the develop-
ment of new cascade reactions. Alternatively, nitrogen bases,
such 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), were also active
catalysts in this reaction, but at higher temperatures (1008C).[6a]
By using a primary amine as a nucleophile, the condensation
step with a formamide is known to be thermally available
without needing to resort to catalysts. However, hard drying
agents, such as phosphorus oxychloride, trifluoroacetic anhy-
dride, and thionyl chloride, are typically required to promote
this reaction.[8] To avoid the use of such additives, which in-
crease waste formation, we investigated the reactivity of a dia-
mine, o-phenylene diamine (1a), in the presence of CO2 and
hydrosilanes, so as to favor an intramolecular condensation re-
action (Table 1). By using 5.0 mol% of IPr in the presence of
CO2 (2 bar) and 1 equivalent of phenylsilane, compound 1a
was converted in high yield into its formyl and N,N’-bisformyl
derivatives (compounds 2a (31%) and 3a (38%) respectively)
after 24 h at 258C (Table 1, entry 5). To our delight, a significant
amount (16%) of the desired benzimidazole (4a) was also ob-
served in the reaction mixture. This reaction demonstrated
that the complete deoxygenation product (4a) was available
under our reaction conditions. However, the observed selectivi-
ty indicates the high rate of the formylation reaction in the
presence of PhSiH3. Because compound 3a is unreactive to-
wards condensation, a less-reactive silane, that is, poly(methyl-
hydrosiloxane) (PMHS),[6b,9] was employed to avoid the formyla-
tion of both amine functions. By using 3 equivalents of PMHS
under similar reaction conditions (Table 1, entry 6), mono-
formyl derivative 2a was formed as the major compound
(42% yield) and compounds 3a and 4a were formed as side-
products (in 20% and 5% yield, respectively). Therefore, the
condensation step appears to be rate determining in this cas-
cade strategy. As a consequence, raising the operating temper-
To utilize CO2 as a “true” C1 building block and to prepare
a wide spectrum of chemicals, catalytic reactions that are able
to promote the complete deoxygenation of CO2 with the com-
plete reconstruction of the carbon valence sphere are required
(Scheme 1). Herein, we report the first solution to tackling this
problem by using the cascade reductive functionalization of
CO2 into benzimidazoles, quinazolinones, formamidines, and
their derivatives.
We recently reported an organocatalytic formylation reaction
of NÀH bonds by using CO2 and hydrosilanes to yield forma-
mides.[6] To substitute the C=O bond in the formamide deriva-
tive and achieve complete deoxygenation, we reasoned that
the amide function could be reacted in a cascade reaction
with a nucleophile (Scheme 1), such as an amine. The formyla-
tion step was efficiently catalyzed by N-heterocyclic carbenes
[a] Dr. O. Jacquet, C. Das Neves Gomes, Dr. M. Ephritikhine, Dr. T. Cantat
CEA, IRAMIS, SIS2M, CNRS UMR 3299
91191 Gif-sur-Yvette (France)
Fax: (+33)1-6908-6640
Supporting information for this article is available on the WWW under
tion of the experimental and spectroscopic results.
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ChemCatChem 2013, 5, 117 – 120 117