Angewandte
Chemie
Hydrogenation
Highly Efficient Ruthenium-Catalyzed N-Formylation of Amines with
H2 and CO2**
Lei Zhang, Zhaobin Han, Xiaoyu Zhao, Zheng Wang, and Kuiling Ding*
Abstract: A highly efficient catalyst system based on ruthe-
nium-pincer-type complexes has been discovered for
N-formylation of various amines with CO2 and H2, thus
affording the corresponding formamides with excellent pro-
ductivity (turnover numbers of up to 1940000 in a single
batch) and selectivity. Using a simple catalyst recycling
protocol, the catalyst was reused for 12 runs in N,N-dimethyl-
formamide production without significant loss of activity, thus
demonstrating the potential for practical utilization of this cost-
effective process. A one-pot two-step procedure for hydro-
genation of CO2 to methanol via the intermediacy of forma-
mide formation has also been developed.
efficiency by using the bidentade Ru/phosphine complex
[RuCl2(dppe)2] [dppe = (1,2-bis(diphenylphosphino)ethane)]
as the catalyst, and a TON of up to 740000 was attained at
1008C with 130 atm of CO2 and 85 atm of H2.[8] Since 2010,
Beller et al. have reported the development of catalytic
systems based on complexes of nonprecious metals such as
FeII and CoII, complexes which also demonstrated high
activities in the hydrogenation of CO2 for the production of
DMF (TON of up to 5100).[9] At the same time of these
studies, recent progress was made on the hydrogenative
transformation of CO2 into formic acid[10] or methanol,[11] as
well as reductive functionalization of CO2 to produce
methylated amine derivatives[5,12] in the context of chemical
utilization of CO2.[13] Despite these remarkable achievements,
however, the attractive N-formylation of amines by CO2
hydrogenation has not yet found industrial application, and
is presumably hampered by major drawbacks in catalyst
recycling and energy consumption. Herein, we report a highly
efficient and recyclable ruthenium catalyst, based on a pincer-
type complex, for N-formylation of various amines with H2
and CO2, to afford the corresponding formamides with TONs
of up to 1940000 under relatively mild reaction conditions. A
one-pot two-step procedure for the hydrogenation of CO2 to
methanol via the intermediacy of formamide formation has
also been accomplished using morpholine as an example.[14]
We envisioned that the transition-metal complexes 1a–
l (Figure 1), with their robust nature and well-defined pincer-
type structures,[15] might be worthwhile candidates for the
catalysis of N-formylation reactions. Some of the complexes
have been shown to be excellent catalysts for the hydro-
genation of various carboxylic and carbonic acid deriva-
tives.[16,17] Encouraged by these facts, we initiated the study
with N-formylation of morpholine (2a) as the model reaction
and the Ru/PNP pincer complex 1b as the catalyst. A
preliminary survey of various reaction parameters, including
temperature, CO2/H2 partial pressures, and solvent was
performed under a catalyst loading of 0.1 mol% in the
presence of 0.1 mol% tBuOK, and the results are summar-
ized in Table S2 (see the Supporting Information). These data
indicated that the reaction was best performed in THF at
1208C under a CO2/H2 partial pressure of 35/35 atm/atm, to
afford N-formylmorpholine (3a) in good yield (75%).
Further attempts to improve this N-formylation reaction
were made by screening the catalytic activity of ruthenium(II)
or iridium(III) complexes of a variety of tridentate PNP, PNN,
NNN, and SNS ligands (1a–l; Figure 1). The results are shown
in Table 1. At a molar ratio of 2a/catalyst/tBuOK = 1000:1:1,
all the catalysts 1a–l were found to be active for morpholine
N-formylation, but a significant variation in catalytic activity
was observed depending on the type of the supporting ligand
Formamides are a class of chemicals with widespread
applications in industry as solvents and raw materials for
syntheses.[1] For example, N,N-dimethylformamide (DMF),
an industrial solvent with huge annual global market volume,
has also served as an extremely versatile multipurpose
reagent in numerous synthetic processes.[2] Among the
methods developed for the production of various formamides,
the most general approach is the N-formylation of amines
with formic acid or formate in the presence of a catalyst.[3]
Industrially, DMF is produced by a NaOCH3-catalyzed
reaction of dimethylamine with toxic CO in methanol.[4] An
alternative green route for the N-formylation of amines is the
use of cheap, abundant, and safe CO2 along with H2 as
a formylating reagent, and development of this technology
has attracted long-term interest from both academia and
industry.[5] In 1970 Haynes reported the first homogeneous
catalyst for the preparation of DMF from CO2, H2, and
dimethylamine with a turnover number (TON) up to 1200.[6]
An elegant procedure for DMF synthesis was reported by
Noyori and co-workers in 1994, and TONs of up to 370000
were achieved at 1008C with 80 atm H2 in supercritical CO2
(130 atm) using [RuCl2{P(CH3)3}4] as the catalyst.[7] Extension
to bulkier dialkylamines was less successful, and resulted in
lower activity (TON < 820). Baiker et al. improved the
[*] Dr. L. Zhang, Dr. Z. Han, X. Zhao, Dr. Z. Wang, Prof. Dr. K. Ding
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
345 Lingling Road, Shanghai 200032 (P.R. China)
E-mail: kding@mail.sioc.ac.cn
[**] We acknowledge the National Natural Science Foundation of China
(grant nos. 91127041, 20421091, 21472215), a special fund from the
Chinese Academy of Sciences (XDA07040404), and the Science and
Technology Commission of Shanghai Municipality for financial
support of this work.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2015, 54, 1 – 5
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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