Insight into decomposition of formic acid to syngas required for Rh-catalyzed hydroformylation of olefins

Article abstract of DOI:10.1016/j.jcat.2020.09.039

Formic acid (FA) is one kind of important bulk chemicals, which is recognized as a sustainable and eco-friendly energy carrier to transport H₂ via dehydrogenation or CO via decarbonylation. Expectantly, FA upon decomposition into H₂ and CO could be used as the syngas alternative for hydroformylation. In this paper, the behaviors of FA to release H₂ as well as CO following the distinct pathways were carefully investigated for the first time, and then established a new hydroformylation protocol free of syngas. It was found that the atmospheric hydroformylation of olefins with formic acid (FA) as syngas alternative was smoothly fulfilled over Xantphos (L1) modified Rh-catalyst under mild conditions (80 °C, Rh concentration 1 mol %, 14 h), resulting in >90% conversion of the olefins along with the high selectivity to the target aldehydes (>93%). By using FA as syngas source, the side-reaction of olefin-hydrogenation was greatly depressed. The in situ FT-IR and the high-pressure ¹H NMR spectroscopic analyses were applied to reveal how FA behaves dually as CO surrogate and hydrogen source over L1-Rh(acac)(CO)₂ catalytic system, based on which the deeply insight into the catalytic mechanism of hydroformylation of olefins with FA as syngas alternative was offered.

Full text of DOI:10.1016/j.jcat.2020.09.039

Journal Pre-proofs
Insight into decomposition of formic acid to syngas required for Rh-catalyzed
hydroformylation of olefins
Lei Liu, Xiao-Chao Chen, Shu-Qing Yang, Yin-Qing Yao, Yong Lu, Ye Liu
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S0021-9517(20)30438-3
https://doi.org/10.1016/j.jcat.2020.09.039
YJCAT 13952
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21 September 2020
Please cite this article as: L. Liu, X-C. Chen, S-Q. Yang, Y-Q. Yao, Y. Lu, Y. Liu, Insight into decomposition of
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Insight into decomposition of formic acid to syngas required for
Rh-catalyzed hydroformylation of olefins
Lei Liu, Xiao-Chao Chen, Shu-Qing Yang, Yin-Qing Yao, Yong Lu, Ye Liu*
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of
Chemistry & Molecular Engineering, East China Normal University, Shanghai
2
00062, PR China. Email: yliu@chem.ecnu.edu.cn.
Abstract
Formic acid (FA) is one kind of important bulk chemicals, which is recognized as a
sustainable and eco-friendly energy carrier to transport H via dehydrogenation or CO
2
via decarbonylation. Expectantly, FA upon decomposition into H and CO could be
2
used as the syngas alternative for hydroformylation. In this paper, the behaviors of FA
to release H as well as CO following the distinct pathways were carefully
2
investigated for the first time, and then established a new hydroformylation protocol
free of syngas. It was found that the atmospheric hydroformylation of olefins with
formic acid (FA) as syngas altrnative was smoothly fulfilled over Xantphos (L1)
o
modified Rh-catalyst under mild conditions (80 C, Rh concentration 1 mol %, 14 h),
resulting in >90% conversion of the olefins along with the high selectivity to the
target aldehydes (>93%). By using FA as syngas source, the side-reaction of
olefin-hydrogenation was greatly depressed. The in situ FT-IR and the high-pressure
1H NMR spectroscopic analyses were applied to reveal how FA behaves dually as CO
surrogate and hydrogen source over L1-Rh(acac)(CO) catalytic system, based on
2
which the deeply insight into the catalytic mechanism of hydroformylation of olefins
with FA as syngas alternative was offered.
1

Keywords: Formic acid; Hydroformylation; Rhodium catalyst; CO surrogate;
Hydrogen carrier; Syngas alternative; In situ FT-IR spectroscopic characterization;
1
High-pressure H NMR spectroscopic characterization
Introduction
Syngas (CO/H ) is indispensably required in hydroformylation of olefins as the most
2
extensively applied homogenous catalytic reaction in industry[1,2], but suffering from
the risk of high-pressure manipulation as well as the explosion of H and the toxicity
2
of CO. In order to eliminate the use of toxic CO, many CO surrogates[3,4] such as
carbon dioxide[5–7], metal carbonyls[8], formate[9,10] have been elaborately utilized
in the carbonylation. Compared to above mentioned CO surrogates, formic acid (FA),
a liquid sustainable and eco-friendly energy carrier derived from biomass[11,12], is an
excellent CO-carrier with 60.9 wt% of CO[13]. Hence, considerable efforts have been
made to utilize FA as CO surrogate by decomposing FA in situ to release CO with the
presence of appropriate activators [14–17]. The acid anhydrides like Ac O were used
2
stoichiometrically to spur FA to release CO thorough forming an more reactive mixed
anhydride with poor thermodynamical stability[18]. For example, the reductive
carbonylation of halohydrocarbons effectively performed with the involvement of
Ac O[19–21]. And Pd-catalyzed regioselective hydroformylation of olefins with FA
2
as CO surrogate along with the presence of Ac O were firstly reported by Shi[22]. In
2
addition, the dehydrant such as DCC (N,N’-dicyclohexylcarbodiimide)[17], the solid
acid zeolite[23] or sulfuric acid[24] have also been applied to react with FA to in situ
or ex situ release CO. Moreover, Ac O-free decarbonylations of FA to in situ generate
2
CO were also explored over Pd-catalysts modified by chelating bis‐phosphines along
2

with pyridine as a base [25,26].
-1
Besides as an ideal CO surrogate, FA also has a high H -content of 53 gL or
2
4
.4 wt%, able to serve as a sustainable biogenic H -carrier through dehydrogenation
2
(i.e. decarboxylation)[27,28], which has been applied in hydroformylation with
presence of gaseous CO[29,30]. It is encouraging that M. Beller recently has made
great efforts to investigate the dehydrogenation of FA over Mn[31], Co[32], Ru[33]
and Fe[34] catalysts. In general, the decomposition of FA can proceed via two
pathways (Scheme 1): dehydrogenation towards H and CO , and decarbonylation
2
2
towards CO and H O, both of which can be controlled selectively by using different
2
catalysts under selected conditions[13,27]. In addition, in our recent study on one-pot
tandem hydroformylation-reduction of olefins, FA was proved to be a hydride-donor
responsible for the effective formation of Ir-H species in charge of the second-step
transfer hydrogenation[35], which had also been verified in many single transfer
hydrogenations[36–38].
The facts that FA could liberate CO as well as H following the district pathways
2
provoked us to explore the use of FA as syngas (CO/H ) alternative and then establish
2
a new hydroformylation protocol free of syngas, which should be advantageous with
the simplified manipulations and no risk of using toxic and pressured gases. In
principle, the required catalyst was required to exhibit multiple catalytic functions for
decarbonylation of FA, dehydrogenation of FA, and hydroformylation of olefins
under the compatible rection conditions. Herein, it was also the first time that the in
1
situ FT-IR and the high-pressure H NMR spectroscopy techniques were applied to
elucidate the decomposing behavior of FA over Rh-catalyst as well as the formation
of Rh-H active species, with an effort to understand the catalytic mechanism of the
hydroformylation of olefins with FA.
3

o
-1
-1
HCOOH (l)
HCOOH (l)
H2(g)
+
CO2(g)
G = -32.9 kJ mol
(1)
(2)
[
Ref. 27]
o
CO(g) + H2O(g)
G = -12.4 kJ mol
HCOOH
Ac O
2
HOAc
Me
O
C
O
H
O
(acetic formic anhydride, AFA)
Cat.: L1-Rh(acac)(CO)2 Decarbonylation
HOAc
Cat.: L1-Rh(acac)(CO)2
CHO
R
+
CO
+
H2
+
R
R
CHO
Hydroformylation
CO2
Cat.: L1-Rh(acac)(CO)2
Dehydrogenation
HCOOH
Scheme 1 The atmospheric hydroformylation of olefins with HCOOH (FA) as syngas alternative
over L1-Rh(acac)CO) catalytic system (L1 = Xantphos)
2
Results and discussion
In the preliminary experiments, the hydroformylation of styrene was chosen as the
model reaction, wherein FA served both as CO surrogate and hydrogen source
without using high-pressure syngas (CO/H ). In addition, Ac O was added
2
2
additionally as an activator along with Rh(acac)(CO) pre-catalyst and the ancillary
2
diphosphine of Xantphos (L1). As shown in Table 1, the hydroformylation of styrene
o
was performed smoothly under the mild reaction conditions (80 C and 14 h), leading
to 94% conversion of styrene and 93% selectivity to the desired aldehyde with B/L of
5
. The side reaction of hydrogenation of styrene was dramatically depressed with
4

indication of merely 2% selectivity to ethylbenzene (Entry 1). The lowered
o
temperature down to 70 and 60 C resulted in the decreased conversion of styrene but
with negligible impact on the high selectivity of aldehyde (Entry 2, Conv. 85%, Sel.
9
3%; Entry 3, Con. 59%, Sel. 94%). The decrease of the amount of FA and Ac O led
2
to the deaccelerated transformation of styrene due to the reduced concentration of
carbon monoxide released in situ (Entry 4). The selection of solvents also had
significant influence on the conversion of styrene. In the ether analogues (THF,
dioxane and n-Bu O) as well as toluene, the conversions of styrene all reached up to
2
9
0% (Entries 1 and 7-9). Obviously, the presence of Ac O as an activator to spur FA
2
to release CO played indispensable role in expediting the reaction rate of
hydroformylation. The hydroformylation didn’t occur at all without the presence of
Ac O wherein 29% of styrene was completely hydrogenated to ethylbenzene (Entries
2
1
0 vs 7), due to the lack of CO liberated from FA. Such outcome verified that only the
use of Ac O as the activator enabled FA to serve as CO surrogate via the formation of
2
acetic formic anhydride (AFA), which was subsequently supported by the evidence
from in situ FT-IR analysis (Fig. 1). In comparison, Ac O itself without the presence
2
of FA just corresponded to the completely stopped hydroformylation (Entry 11),
further indicating that the required CO was just derived from FA. Reasonably, the
decreased amount of Ac O resulted in the less availability of AFA with more free FA
2
retained, corresponding to the prevailing transfer hydrogenations with FA as the
hydrogen source (Entry 12)[35–38]. Consequently, ethylbenzene (3) as the
hydrogenated product of styrene (Sel.ethylbenzene 9%) as well as the other side-products
(Sel.others 19%) was obtained universally in the relatively higher yields (Entries 12 vs
o
7
). As the temperature increased up to 120 C, the selectivity to the aldehydes dropped
obviously accompanied by the concurrent increase to the by-products due to the
5

continuous transformations including transfer hydrogenation of aldehydes by FA and
then alcohol esterification (Entries 13 vs 7). The other anhydrides like propionic
anhydride or butyric anhydride also exhibited the similar behavior of Ac O in
2
promoting the target hydroformylation (Entries 14 and 15). Anyway, the use of HOAc
instead of Ac O only led to the formation of ethylbenzene in the yield of 42% (Entry
2
1
6) because of the failure to provoke the release of CO from FA. Additionally, CO as
well as H was truly detected in the collected gaseous compositions upon completion,
2
further convincing the successful release of CO and H from FA necessitated for
2
hydroformylation (See Fig. S3 in ESI). Because of the limitation of the decomposition
rate of H and CO from FA, the prolonged reaction time was required (Fig. S1 and
2
Fig. S2 in ESI).
6

Table
1
Atmospheric hydroformylation of styrene with FA over L1-modified
a
Rh(acac)(CO) -catalyst with the involvement of Ac O under different conditions
2
2
CHO
Rh(acac)(CO) , L1
2
+
HCOOH
+
CHO +
+
Others
Ac O
2
2a
2b
3
1
Others:
HCOOH
CH OH
2
CH OH
2
HCOOH
(Ac2O/HOAc)
O
O
CH O C H (Me)
2
CH O C H (Me)
2
Entry FA
Anhydride
T.
Sol.
Conv Sel. (%) b
c
(equiv. (equiv.)
)
(ºC)
.
2a+2b Others 3
2b/2a
(%) b
1
6
6
6
4
6
6
6
6
6
6
--
6
6
6
6 (Ac O)
80
70
60
80
80
80
80
80
80
80
80
80
Toluene 94
Toluene 85
Toluene 59
Toluene 78
93
93
94
93
95
97
96
88
96
-
5
2
3
3
4
3
2
3
3
1
5.0
4.9
5.1
2.2
1.6
3.1
3.0
2.6
3.8
2
2
6 (Ac O)
4
2
3
6 (Ac O)
3
2
4
4 (Ac O)
3
2
5
6 (Ac O)
NMP
DMF
THF
56
74
93
2
2
6
7 d
6 (Ac O)
1
2
6 (Ac O)
1
2
8
6 (Ac O)
Dioxane 97
9
2
9
6 (Ac O)
n-Bu O 90
3
2
2
1
1
1
1
1
0
1
2
3
4
--
THF
THF
THF
29
--
-
100 --
6 (Ac O)
--
--
19
24
4
--
9
4
3
--
2
2 (Ac O)
96
98
93
72
72
93
3.1
2.8
2.4
2
6 (Ac O)
120 THF
2
6 (Propionic
anhydride)
80
THF
1
5
6
6
6
6 (Butyric anhydride) 80
12 (HOAc) 80
THF
THF
95
42
95
-
2
-
3
2.5
-
1
100
a
Styrene 4 mmol, Rh(acac)(CO) 0.04 mmol (Rh, 1 mol %), L1 (Xantphos) 0.04 mmol, solvent 3
2
b
c
mL, 14 h; Determined by GC and GC-Mass; “Others” represents the selectivity of the products
d
derived from reduction of 2a and 2b with HCOOH and the subsequent esterification; The gases
were collected and analyzed by GC-TCD to detect the gaseous compositions upon completion
(The GC analytic profiles were provided in Fig. S3 in ESI).
7

The effects of the Rh(I)-complex precursors as well as the phosphine ligands on the
catalytic performance of Rh-catalysts were investigated in Table 2. It was found that
only Rh(acac)(CO) with the involvement of L1 (Xantphos) exhibited the best
2
performance towards the hydroformylation of styrene with FA and Ac O in place of
2
syngas, leading to 94% conversion of styrene with 93% selectivity of the aldehyde
along with the B/L ratio of 5 (Entry 1). The other complexes such as RhCl(PPh ) CO,
3
2
RhCl(PPh ) , and [RhCl(COD)] all corresponded to the much lower yields of the
3
3
2
aldehydes under the same reaction conditions (Entries 2-4). It was reasonable that
Rh(acac)(CO) could more easily dissociate the involved ligands of CO and acac
2
(
acetylacetonate) to make vacancies for the substrates of FA, and L1 as well as the
olefin to coordinate Rh(Ⅰ)-center, in comparison to the other Rh(I)-complexes
Entries 1 vs 2-4). In parallel, the phosphine ligands played remarkable role in
(
modifying the catalytic performance of Rh(acac)(CO) . It was noted that over the
2
different kinds of bidental phosphines (L1-L6) with variant bite angles, L1
(Xantphos) and L2 (Nixantphos) with the similar chelation effect and the wide bite
o
o
angles (111 and 114 respectively) corresponded to the highest yields of the target
aldehyde (Entries 1 and 6), whereas the inefficient hydroformylation was found over
the flexible biphosphines of L3-L5 with the relatively narrow bite angles (92-102 o)
(
Entries 7-9, Conv. 45-63%), implying that rigidly fixed two PPh -fragements in the
2
phosphine structures with the suitable bite angles (like L1 and L2) indeed facilitated
the stability and activity of the corresponding Rh-catalyst. As for L6, its narrow bite
o
angle (83 ) unfavored the stable formation of L6-ligated Rh-catalyst, resulting in the
inefficient conversion of styrene (Entry 10, Conv. 30%). Comparatively, the
mono-phosphines of L7 and L8 or no ligand led to no transformation of styrene
8

(Entries 5, 11 and 12). The GC analysis for the gaseous compositions upon reaction
also indicated that over Rh(acac)(CO) -L7 (Entry 11), no free H was detectable at all
2
2
(See Fig. S4 in ESI), which implied that L7 modified Rh-complex could not activate
FA to release H , leading to the completely failed hydroformylation. The comparison
2
data over L1 and L7 (Entry 1 vs 11), the later was the analogue of L1 but devoid of
the coordinating chelation ability, indicated that the suitable chelation effect from the
biphosphine greatly contributed to the stability of the resultant Rh(I)-catalyst,
corresponding to the warranted activity to the dehydrogenation of FA as well as the
hydroformylation.
Table 2 The effects of Rh(I)-complex precursors and the phosphine ligands on the
hydroformylation of styrene with FA with the involvement of Ac O a
2
H
N
Ph P
2
PPh2
O
O
O
PPh2
PPh2
PPh2
PPh2
PPh2
PPh2
L1
L2
L3
L4
PPh2
PPh2
PPh2
PPh2
P
O
PPh2 Ph2+P
OTf-
L5
L6
L7
L8
Entry Rh-complex
Ligand Bite angle[39]
(o
Conv. Sel. (%) b
2a+2b Others c
3
2
3
3
5
-
2b/2a
5.0
3.3
0.6
0.3
-
)
(%) b
94
48
36
32
0
1
Rh(acac)(CO)2
L1
111
111
111
111
-
93
93
85
80
-
5
2
RhCl(PPh ) CO L1
4
3
2
3
RhCl(PPh3)3
L1
L1
--
12
15
-
4 d
[RhCl(COD)]2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
5
6
L2
L3
L4
L5
L6
L7
L8
114
102
91
92
83
-
88
53
63
45
30
0
98
88
76
63
63
-
-
2
2.5
7
-
12 2.4
15 1.1
8
9
9
31
23
-
6
0.6
1
1
1
0
14 0.7
1 e,f
2 e
-
-
-
-
-
0
-
-
9

a
Styrene 4 mmol, Rh-complex 0.04 mmol (Rh, 1 mol %), ligand 0.04 mmol, toluene 3 mL, 14 h; b
Determined by GC and GC-Mass analyses; c “Others” represents the selectivity of the products
d
derived from reduction of 2a and 2b with HCOOH and the subsequent esterification;
e
f
[
RhCl(COD)] 0.02 mmol (Rh, 1 mol %); L7 or L8 0.08 mmol; The gases were collected and
2
analyzed by GC-TCD to detect the gaseous compositions upon completion (The GC analytic
profiles were provided Fig. S4 in ESI);
In order to further elucidate the dual roles of FA in releasing CO as well as
serving as the hydrogen-source in the way of liberating H (along with CO ),
2
2
whichever is required by the hydroformylation of olefins, the following control
experiments were carried out as shown in Table 3. When gaseous CO (1.4 MPa,
equiv. to 24 mmol released from the reaction of FA with Ac O) coupled with FA was
2
applied instead of the mixture of FA (24 mmol) and Ac O (24 mmol) as CO-source,
2
the comparative styrene conversion (93%) and the aldehyde selectivity (98%) were
obtained (Entry 2 vs 1), revealing that FA indeed was able to serve as the hydrogen
source [30]. However, when FA was used with H (1.4 MPa, ca. 24 mmol) free of
2
Ac O, only the hydrogenated product of ethylbenzene was obtained with 100% yield
2
(Entry 3), indicating that FA itself couldn’t act as CO surrogate without the aid of
Ac O under the applied reaction conditions. When just FA was present free of both
2
Ac O and H , also the hydrogenation of styrene was observed with 29% yield of
2
2
ethylbenzene (Entry 4) and then the dramatically improved yield up to 100% while
o
the temperature increasing from 80 to 120 C (Entry 5), further convincing that FA
itself only could serve as hydrogen source but not CO surrogate. The above results
demonstrated that only the presence of Ac O could guarantee FA to liberate CO.
2
Without the aid of Ac O, FA itself couldn’t decarbonylate to release CO required by
2
hydroformylation, but just served as a hydrogen source in the way of liberating H2
under the applied catalytic condition.
10

11

Table 3 The control experiments using different CO sources and hydrogen sources for
hydroformylation of styrene over L1-modifed Rh-catalyst a
CHO
Hydroformylation
+
CHO +
+
others
L1-Rh(acac)(CO)2
2a
2b
3
1
Entry CO source
Hydrogen source
T.
Conv. Sel. (%) b
(
ºC) (%) b 2a+2b Others c
3
1
2
3
4
FA (24 mmol)-Ac
2
O (24 mmol) FA d
80
80
93
96
98
-
1
3
CO (1.4 MPa, 24 mmol)
FA (24 mmol)
FA (4.8 mmol)
93
trace
2
H
-
2
(1.4 MPa, 24 mmol) 80
80
100
29
-
-
-
100
100
100
FA (24 mmol)
-
5
FA (24 mmol)
-
120 100
-
a
b
Rh(acac)(CO) 0.04 mmol (Rh, 1 mol %), L1 0.04 mmol, styrene 4 mmol, THF 3 mL, 14 h;
2
Determined by GC and GC-Mass analyses; c “Others” represents the selectivity of the products
d
derived from reduction of 2a and 2b with HCOOH and the subsequent esterification; FA was not
added additionally.
It has been well known that FA is widely used as a safe reducing reagent instead
of H due to its ability to directly donate the reductive hydride as observed in many
2
efficient transfer hydrogenation[35–37]. Accordingly, FA is also believed to
contribute to the formation Rh-H species, which is responsible for the efficient
hydroformylation of olefins herein, upon providing hydride-ligand to Rh(I)-center. In
order to elucidate the inherent nature of FA as a hydrogen source to form Rh-H
species as well as an CO surrogate, the evolving processes of FA under the different
conditions were monitored by in situ FT-IR spectroscopy (Fig. 1).
Knowingly, FA can form several hydrogen-bonded dimeric structures at ambient
conditions typically in the forms of trans-trans and trans-cis dimers (see Fig. S5 in
ESI) due to the lowest eneggy level[40,41]. As observed in Fig. 1-A, the involvement
of Ac O even in the absence of any catalyst resulted in the slow release of CO ( 2171
2
-1
o
and 2117 cm ) at ca. 80 C, revealing that the availability of the labile AFA formed
upon the metathesis of FA with Ac O successfully led to the decarbonylation of FA
2
even under the non-catalytic condition. In contrast, without the involvement of Ac O,
2
12

FA couldn’t liberate CO at all even over L1-Rh(acac)(CO) catalytic system (See Fig.
2
S5 in ESI). Reasonably, as demonstrated in Fig. 1-B, the introduction of
L1-Rh(acac)(CO) catalyst could greatly spur the decomposition of AFA into CO (
2
-1
o
2
173 and 2115 cm ). So, even at the much lower temperature of ca. 40 C, the
decarbonylation of AFA happened readily. When the temperature increased up to 80
oC, AFA completely consumed along with the abundantly formed CO with indication
-1
of the most intensive magnitude at  2173 and 2115 cm . Since the rapid
decomposition of AFA over L1-Rh(acac)(CO) led to the release of CO as well as the
2
-1
formation of HOAc, the absorption at ca 1728 cm (attributed to HOAc’s carbonyl
group) synchronously grew stronger and stronger whereas the absorption of 1826 cm-1
(
attributed to Ac O’s carbonyl group) decayed to void due to Ac O’s complete
2
2
consumption. At the same time, the additional weak absorptions at 2037 and 1961
cm-1 appeared gradually, which were coherently attributed to Rh-H and Rh-CO
vibrations respectively[42–44] in the corresponding Rh-complex intermediate in the
o
form of Rh(L1)(H)(CO) (B in Scheme 2). The continuous monitoring at 80 C from
-1
4
5 to 60 min showed that such vibrations ( 2037 and 1961 cm ) were always
available without obvious decay, indicating the acceptable stability of the formed
active Rh-complex intermediate. Since the formation of CO-ligated Rh-H
intermediate undoubtedly corresponded to the efficient hydroformylation of the olefin,
the evolving processes of the real hydroformylation of styrene under the same
conditions applied in Fig. 1-B were monitored in parallel. As demonstrated in Fig.
-1
1
-C, similar to the profiles in Fig. 1-B, the appearance of Rh-CO ( 1968 cm ) as
-1
well as Rh-H species (weak,  2039 cm ) was observed clearly. In addition, the
-1
-1
relatively weak absorption peaks at ca. 2370 cm and 2321 cm was observed, which
was ascribed to the characteristic vibrations of the accumulated CO in the catalytic
2
13

hydroformylation of styrene with FA, implying that the formation of Rh-H species
with FA as the hydrogen source directly accompanied by the formation of CO . The
2
continuous catalytic cycle with the presence of styrene led to the abundant
accumulation of CO released from FA, which accounted for the appearance of CO2
2
vibration only observed in Fig. 1-C but not in Fig. 1-B. On the other hand, the
dramatically increased absorption intensity at ca. 1720 cm-1 (Fig. 1-C) could be
reasonably attributed to the continuous accumulation of the formed aldehydes
(2-/3-phenylpropanal) from styrene under the built catalytic conditions. However, the
characteristic peak of aldehyde group in the product of 2-/3-phenylpropanals mostly
overlapped with the vibrations of HOAc. In order to further prove that the vibration of
-1
2
037 cm (as observed in Fig. 1-B and Fig. 1-C) was indeed attributed to Rh-H
vibration, the deuterated dry FA (DCOOD) instead of HCOOH was used to react with
Ac O with the presence of L1-Rh(acac)(CO) catalytic system to undergo the same
2
2
detection by the FT-IR spectroscopy. As shown in Fig. 1-D, the Rh-H vibration at ca.
-1
2
037 cm completely disappeared whereas the Rh-CO vibration was still observable
-1
-1
at 1940 cm but red-shifted in comparison to those observed at ~1960 cm (Fig. 1-B
and Fig. 1-C). Concurrently, a new weak peak at ca. 1460 cm-1 was observed
-1
indistinctively due to the interference of the strong and broad absorption at 1384 cm ,
which could be ascribed to Rh-D vibration in accordance with the theoretical
calculated value (vibrationRh-H/vibrationRh-D  1.39)[45]. The observations in Fig.
-1
-1
1
-B/C/D confirmed that the absorption band at 2037 cm /1940 cm undoubtedly
corresponded to the formation of Rh-H/Rh-D species wherein the hydrogen source
was originated from HCOOH or DCOOD. In addition, a hydride signal at δ -9.09 ppm
1
belonging to Rh-H species[46] was also clearly detected by the high-pressure H
NMR spectroscopy while the mixture of Rh(acac)(CO) , Xantphos, FA and Ac O was
2
2
14

o
treated in a pressure-tight NMR tube at 60 C (Fig. 2-B), further convincing that FA
could serve as a hydrogen source to form Rh-H species. Accordingly, from the above
1
in situ FT-IR and high-pressure H NMR spectral analyses (Fig. 1 and Fig. 2) were
drawn the following conclusions including that (1) FA could decompose into CO only
upon reacting with Ac O to form more reactive AFA, (2) the introduction of
2
L1-Rh(acac)(CO) could spur the release of CO from AFA, and (3) FA could serve as
2
the hydrogen source in place of H to form Rh-H species along with the formation of
2
CO2.
15

B: FA + AcO + L1 + Rh(acac)(CO)
A: FA + Ac O
2
2
2
o
3
0 C 1min
o
o
30 C 1min
6
0 C 1min
o
4
0 C 1min
o
8
0 C 1min
o
6
0 C 1min
o
o
8
0 C 10min
80 C 5min
o
8
0 C 20min
o
8
0 C 30min
o
8
0 C 35min
o
8
0 C 45min
o
a
8
0 C 50min
o
c
80 C 60 min
b
2117
2171
o
80 C 60min
2
115
1
826
2
173
a: 2037
b: 2002
c: 1961
1826
a
c
b
1723
1728
3000 2750 2500 2250 2000 1750 1500
3000 2750 2500 2250 2000 1750 1500
-1
-1
Wavenumber (cm
)
Wavenumber (cm )
C: FA + Ac O + Styrene + L1 + Rh(acac)(CO)
2
2
D: Rh(acac)(CO) + L1 + DCOOD + Ac O
2
2
o
3
0 C 1 min
o
6
0 C 1 min
o
3
0 C 1 min
o
8
0 C 5 min
o
8
0 C 20 min
o
6
0 C 1 min
o
8
0 C 35 min
o
o
1940
2007
80 C 1 min
2
370 2321
80 C 45 min
a
115
c
b
o
o
2
80 C 60 min
80 C 10 min
2170
1825
o
2
117
1460
80 C 20 min
o
a: 2039
2175
80 C 30 min
b: 2010
c: 1968
o
80 C 60 min
1384
1940
2007
a b c
1720
3
000 2750 2500 2250 2000 1750 1500
3000 2750 2500 2250 2000 1750 1500
-1
-1
Wavenumber (cm )
Wavenumber (cm )
Fig. 1 The in situ evolving processes of FA under different conditions continuously recorded by
o
FT-IR spectroscopy from 30 to 80 C. A: The mixture of FA and Ac O without the presence of L1
2
and Rh(acc)(CO) ; B: the mixture of FA and Ac O with the presence of L1 and Rh(acc)(CO) ; C:
2
2
2
the mixture of FA, Ac O and styrene with the presence of L1 and Rh(acc)(CO) ; D: the mixture of
2
2
deuterated FA (DCOOD) and Ac O with the presence of L1 and Rh(acc)(CO) .
2
2
16

o
A (30 C)
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
Chemical shift (ppm)
o
B (60 C)
-9.09 ppm, Rh-H
-8
-9
-10
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
Chemical shift (ppm)
1
Fig. 2 H NMR spectra (500 MHz, CDCl ) for the mixtures of Rh(acac)(CO) , Xantphos, FA and
3
2
o
Ac O sealed in the high-pressure NMR tube upon treatment at 30 C (A) and 60 C (B)
2
respectively.
1
On the basis of the in situ FT-IR and the high-pressure H NMR analyses (Fig. 1
and Fig. 2) as well as the results in Table 2 (Entry 11 vs 1) and Table 3 (Entry 5), the
catalytic mechanism over L1-Rh(acac)(CO) system for the hydroformylation using
2
17

FA dually as CO surrogate and hydrogen source (in the way of liberating H ) was
2
proposed in Scheme 2. Clearly, as observed in Fig. S5 (in ESI), when the temperature
o
increases up to ca. 80 C, the cis-FA monomer is abundantly available as the
hydride-donor derived from the dissociation of cis-trans FA dimer[35], which
coordinates to Rh(I)-center to form the Rh(I)-complex intermediate of A upon
-
ligand-exchange of acetylacetonate (acac) and CO with formate (HCOO ) and cis-FA
monomer. The formation of thermodynamically stable six-member ring structure
linked by the hydrogen bond between the hydroxy hydrogen atom of cis-FA monomer
and the negative-charged oxygen atom of formate, is the driving forcing to form A.
Subsequently, the discharge of CO along with one molecular FA leads to the release
2
of H , which is able to be activated by L1-modfied Rh(I)-catalyst to afford Rh-H
2
active species (B) after the concomitant coordination of CO (derived from the
catalytic decomposition of AFA). Knowingly, the CO-ligated Rh-H active species
-1
-1
(
B), with the characteristic vibrations of 2037 cm (Rh-H) and 1961 cm (Rh-CO) in
Fig. 1-B/C (or δ -9.09 ppm in Fig. 2-B), is essentially responsible for efficient
2
hydroformylation. Subsequently, the  -coordination of the double bond in the olefin
to Rh(I)-center (C) and then the H-transfer to the double bond leads to the formation
of alkylrhodium intermediate D. Upon CO migration and insertion, D transforms to
the acylrhodium intermediate E, which irreversible corresponds to the formation of
the linear or branched aldehydes after hydrogenolysis by H (originated from FA),
2
along with the regeneration of B. In this catalytic cycle, the linear aldehyde is the
major product, due to the steric hindrance on the bulky L1 in the intermediate of D.
While R is phenyl group like styrene (or its derivatives), the formation of intermediate
3
with stabilized  -benzyl-Rh(I) configuration gives rise to the regioselectivity of the
branched product as observed in Table 1. Reasonably, the availability of excessive FA
18

guaranteed one portion of FA-molecules fully react with Ac O to release CO while
2
the other FA-molecules readily have access to Rh-center to undergo dehydrogenation.
R
P
AFA
R
HOAc
RhI
H
O
O
P
CO
FA + Ac2O
H
O
CH3
CO
(
C)
O
O
L1
Hacac + CO
P
P
H
Hydroformylation
R
+
RhI
P
P
H
H+
P
P
Rh(acac)(CO)2
O-
RhI
H
H2
RhI
O
O
H
O
H
H
O
CO
H
CO
O
(B)
H
H
O
(
A)
(
D)
trans-FA or cis-FA monomer
CO2 +
H
O
L1 + Rh(acac)(CO)2
O
C
R
CO
P
=
H
R
P
P
C
O
RhI
P
O
PPh2
Xantphos (L1)
PPh2
H2
CO
(
E)
Scheme 2 The proposed catalytic mechanism over L1-Rh(acac)(CO) for the hydroformylation of
2
olefins with FA
Finally, the generality of L1-Rh(acac)(CO)2 catalytic system for the
hydroformylation of the different olefins with FA was investigated in Table 4. As for
styrene derivatives, the substituents at para-/meta-position of the phenyl ring, no
matter the electron-donating groups (-OMe, -Me, -OOMe) or the
electronic-withdrawing groups (-F, -Cl, Br), had no obvious effect on the reaction rate
in comparison to that using styrene. The high conversions of styrene derivatives (>
9
2%) and the excellent selectivity to the aldehydes (> 93%) were obtained universally
(Entries 2-8). Notably, the ester functional group in 4-vinylphenyl acetate was tolerant
to the presence of FA in this reaction (Entry 4), which could be utilized to further
produce to the high value chemicals. As for the aliphatic terminal olefins (Entry 9)
were also tolerated well (Conv. 98%, Sel. 92%), but the linear aldehydes were the
major product (B/L = 0.4) resulting from the bulky steric hindrance of ligand
(Xantphos) in intermediate of D. Whereas the internal olefin (Entry 10) could not
19

easily transform into terminal olefins in this reaction condition, thus, moderate yield
was obtained and the almost products were branched aldehydes and only little linear
aldehydes were observed (B/L = 10.2).
Table 4 Generality of L1-Rh(acac)(CO) catalytic system for hydroformylation of olefin with FA
2
a
in the presence of Ac O
2
Rh(acac)(CO) -L1, Ac O
2
2
CHO
+
HCOOH
+
+
+
Others
R
R
R
THF, 80 °C, 14 h
R
CHO
Others:
HCOOH
CH OH
2
R
R
CH OH
2
HCOOH
(Ac2O/HOAc)
O
C
O
C
CH O
H ( Me)
R
2
R
CH O
H (Me)
2
Entry
Olefin
Conv.
Sel. (%) b
Aldehyde
%) b
Others c
(
B/L
Hydrogenation of olefins
1
2
93
92
96
93
3.0
3
1
3.7
3.8
2.4
3
3
2
4
4
3
O
3
4
97
98
93
95
O
O
5
6
7
8
98
96
97
96
95
94
97
94
3.4
2.7
3.2
3.3
2
3
2
4
3
3
1
2
F
Cl
Cl
Br
9d
98
78
92
96
0.4
2
2
4
1
5
4
1
0e
10.2
a
Olefin 4 mmol, Rh(acac)(CO) 0.04 mmol (Rh, 1 mol %), L1 (Xantphos) 0.04 mmol, FA 24
2
mmol, Ac O 24 mmol, THF 3 mL, 80 C, 14 h; Determined by GC and GC-Mass analyses; c
o
b
2
20

“
Others” represents the selectivity of the products derived from reduction of produced aldehyde
with HCOOH and the subsequent esterification; d The isomerized products of the olefin in the
e
yield of 2% were detected; The isomerized products of olefins in the yield of 1% were detected.
Conclusions
Free of the conventional used syngas (CO/H ), the successful hydroformylation of
2
olefins with FA was achieved over L1 modified Rh-catalyst under the mild conditions
o
(
80 C, Rh concentration 1 mol %, 14 h). In this reaction, FA not only served as the
hydrogen source in place of H but also as CO surrogate upon formation of AFA with
2
Ac O. Generally, the prolonged reaction time of 14 h was required, due to the limited
2
decomposition rate of CO and H from FA, to achieve the high conversion of the
2
olefins (92%-98%), along with the excellent selectivity (93%-97%) to the target
1
aldehydes. For the first time, the in situ FT-IR and the high-pressure H NMR
spectroscopic techniques were applied to reveal the mechanism of hydroformylation
of olefins with FA free of syngas over L1-Rh(acac)(CO) catalytic system. It was
2
proved that, over L1-Rh(acac)(CO) catalytic system, AFA formed upon reacting FA
2
reacting with Ac O was effectively promoted to release CO in situ whereas the
2
available cis-FA monomer served as a hydride donor responsible for the liberation of
-1 1
H and then the facilitated formation of Rh-H active species (FT-IR:  2039 cm ; H
2
NMR: -9.09 ppm) in charge of efficient hydroformylation. It should be noticed that
FA self couldn’t be decarbonylated under the applied catalytic condition without the
involvement of Ac O activator.
2
Experimental section
Reagents and analysis
21

The chemical reagents were purchased from Shanghai Aladdin Chemical Reagent Co.
Ltd. and Alfa Aesar China, which were used as received. Gas chromatography (GC)
was performed on a SHIMADZU-2014 equipped with a DM-Wax capillary column
(30 m  0.25 mm  0.25 m) and FID to analyze the conversion of olefin and the
product distributions for hydroformylation. Gas chromatography (GC) was performed
on an Agilent 7890A equipped with Pora PLOT Q (30 m  530 m  40 m), Pora
PLOT Q (2 m  530 m  40 m) and HP-PLOT 5A (60 m  530 m  25 m) and
TCD to analyze the compositions of the collected gases upon reaction completion.
GC-mass spectrometry (GC-MS) was recorded on an Agilent 6890 instrument
1
equipped with an Agilent 5973 mass selective detector. The H NMR spectra were
recorded with a Bruker Avance 500 spectrometer.
General procedures for rhodium-catalyzed the hydroformylation of olefins with
FA and Ac O
2
FA, Ac O and all the solvents were completely dried before use. In a typical
2
experiment, Rh(acac)(CO) (0.04 mmol, Rh, 1 mol %), L1 (0.04 mmol) (or the other
2
ligand) were mixed with styrene (4 mmol, or the other olefin), FA (24 mmol), Ac O
2
(24 mmol) and THF (3 mL). The mixture was added in a 50 mL sealed Teflon-lined
stainless-steel autoclave. Then, the reaction mixture was stirred vigorously at
appointed temperature for some time. Upon completion, the autoclave was cooled
down to room temperature and slowly depressurized. The solution was analyzed by
GC to determine the conversion (n-dodecane as internal standard) and the selectivity
(normalization method), and the products were further identified by GC-mass
spectrometry. If necessary, the gases in the autoclave was collected for GC-TCD
analysis before de-pressure.
22

In situ FT-IR spectroscopic characterization
The in situ FT-IR spectra were recorded on a Nicolet NEXUS 670 spectrometer. 50
μL of reaction mixture was added in the specially designed high-pressure IR cell,
wherein the cylindric CaF was used as the sealing sheets. Then, the sealed cell was
2
purged with N (0.5 MPa) for three times. The real-time monitoring was performed
2
o
under the different reaction temperatures from 30~80 C. The different reaction
mixtures used in Fig. 1 were prepared as follow: Figure 1-A, 1 mmol FA was added
into the solution of 1 mmol Ac O; Figure 1-B, 0.01 mmol Rh(acac)(CO) with 0.01
2
2
mmol L1 was added into the mixture of 1 mmol FA and 1 mmol Ac O; Figure 1-C,
2
0
.02 mmol Rh(acac)(CO) with 0.02 mmol L1 was added into the mixture of 0.2
2
mmol styrene, 1 mmol FA and 1 mmol Ac O (the much higher concentrations of
2
Rh(acac)(CO) and L1 required for the FT-IR spectral detection were loaded
2
compared to the standard experimental conditions in Table 1); Figure 1-D: 0.01 mmol
Rh(acac)(CO) with 0.01 mmol L1 was added into the mixture of 1 mmol deuterated
2
FA (DCOOD) and 1 mmol Ac O.
2
1
High pressure H NMR spectroscopic characterization
1
The high pressure H NMR spectra were recorded by a Bruker Avance 500
spectrometer. In order to monitor the signal of Rh-H species clearly, the concentration
of Rh(acac)(CO) and L1 was much higher than that applied in the real reaction
2
conditions. In a pressure-resistant NMR tube (Wilmad-LabGlass Co.), FA (0.5 mmol)
and Ac O (0.5 mmol) were added sequentially to the solution of Rh(acac)(CO) (0.04
2
2
mmol) and L1 (0.04 mmol) in DCCl (200 uL). Then the obtained mixture which was
3
o
o
sealed in the pressure-tight NMR tube was heated at 30 C and 60 C respectively and
23

then analyzed by the NMR spectrometer.
Acknowledgements
This work was financially supported by National Natural Science Foundation of
China (No. 21673077, 21972045) and Science and Technology Commission of
Shanghai Municipality (18JC1412100).
Supplementary Information
The Electronic Supplementary Information (ESI) associated with this article can be
found online.
References
[
1] R. Franke, D. Selent, A. Börner, Applied Hydroformylation, Chem. Rev. 112 (2012) 5675–
732. https://doi.org/10.1021/cr3001803.
2] S. Hanna, J.C. Holder, J.F. Hartwig,
5
[
A
Multicatalytic Approach to the
Hydroaminomethylation of α-Olefins, Angew. Chem. Int. Ed. 58 (2019) 3368–3372.
https://doi.org/10.1002/anie.201811297.
[3] T. Morimoto, K. Kakiuchi, Evolution of Carbonylation Catalysis: No Need for Carbon
Monoxide,
Angew.
Chem.
Int.
Ed.
43
(2004)
5580–5588.
https://doi.org/10.1002/anie.200301736.
[
4] L. Wu, Q. Liu, R. Jackstell, M. Beller, Carbonylations of Alkenes with CO Surrogates,
Angew. Chem. Int. Ed. 53 (2014) 6310–6320. https://doi.org/10.1002/anie.201400793.
5] X. Ren, Z. Zheng, L. Zhang, Z. Wang, C. Xia, K. Ding, Rhodium-Complex-Catalyzed
[
Hydroformylation of Olefins with CO and Hydrosilane, Angew. Chem. Int. Ed. 56 (2017)
2
3
10–313. https://doi.org/10.1002/anie.201608628.
[6] T.G. Ostapowicz, M. Schmitz, M. Krystof, J. Klankermayer, W. Leitner, Carbon Dioxide as
a C1 Building Block for the Formation of Carboxylic Acids by Formal Catalytic
Hydrocarboxylation,
Angew.
Chem.
Int.
Ed.
52
(2013)
12119–12123.
https://doi.org/10.1002/anie.201304529.
[
[
[
7] Z. Liu, Z. Yang, B. Yu, X. Yu, H. Zhang, Y. Zhao, P. Yang, Z. Liu, Rhodium-Catalyzed
Formylation of Aryl Halides with CO2 and H , Org. Lett. 20 (2018) 5130–5134.
2
https://doi.org/10.1021/acs.orglett.8b02027.
8] J. Wannberg, M. Larhed, Increasing Rates and Scope of Reactions: Sluggish Amines in
Microwave-Heated Aminocarbonylation Reactions under Air, J. Org. Chem. 68 (2003)
5
750–5753. https://doi.org/10.1021/jo034382d.
9] H. Li, H. Neumann, M. Beller, X.-F. Wu, Aryl Formate as Bifunctional Reagent:
Applications in Palladium-Catalyzed Carbonylative Coupling Reactions Using in situ
Generated
CO,
Angew.
Chem.
Int.
Ed.
53
(2014)
3183–3186.
https://doi.org/10.1002/anie.201311198.
[10] Y. Wang, W. Ren, J. Li, H. Wang, Y. Shi, Facile Palladium-Catalyzed Hydrocarboxylation
of Olefins without External CO Gas, Org. Lett. 16 (2014) 5960–5963.
24

https://doi.org/10.1021/ol502987f.
[11] P. Preuster, J. Albert, Biogenic Formic Acid as a Green Hydrogen Carrier, Energy Technol.
6
(2018) 501–509. https://doi.org/10.1002/ente.201700572.
[
12] F. Valentini, V. Kozell, C. Petrucci, A. Marrocchi, Y. Gu, D. Gelman, L. Vaccaro, Formic
acid, a Biomass-Derived Source of Energy and Hydrogen for Biomass Upgrading, Energy
Environ. Sci. 12 (2019) 2646–2664. https://doi.org/10.1039/C9EE01747J.
[
[
[
[
[
13] J. Cao, Z.-J. Zheng, Z. Xu, L.-W. Xu, Transition-Metal-Catalyzed Transfer Carbonylation
with HCOOH or HCHO as Non-Gaseous C1 Source, Coord. Chem. Rev. 336 (2017) 43–53.
https://doi.org/10.1016/j.ccr.2017.01.005.
14] J. Hou, J.-H. Xie, Q.-L. Zhou, Palladium-Catalyzed Hydrocarboxylation of Alkynes with
Formic
https://doi.org/10.1002/anie.201501054.
15] J. Hou, M.-L. Yuan, J.-H. Xie, Q.-L. Zhou, Nickel-Catalyzed Hydrocarboxylation of
Alkynes with Formic Acid, Green Chem. 18 (2016) 2981–2984.
https://doi.org/10.1039/C6GC00549G.
Acid,
Angew.
Chem.
Int.
Ed.
54
(2015)
6302–6305.
16] X.-D. Lang, F. You, X. He, Y.-C. Yu, L.-N. He, Rhodium(I)-Catalyzed Pauson-Khand-Type
Reaction Using Formic Acid as a CO Surrogate: An Alternative Approach for Indirect CO2
Utilization, Green Chem. 21 (2019) 509–514. https://doi.org/10.1039/C8GC03933J.
17] F.-P. Wu, J.-B. Peng, X. Qi, X.-F. Wu, Palladium-Catalyzed Carbonylative Transformation
of Organic Halides with Formic Acid as the Coupling Partner and CO Source: Synthesis of
Carboxylic
https://doi.org/10.1021/acs.joc.7b01808.
18] P. Strazzolini, A. G. Giumanini, S. Cauci, Acetic Formic Anhydride a Review, Tetrahedron.
6 (1990) 1081–1118. https://doi.org/10.1016/S0040-4020(01)86676-X.
19] G. Sun, X. Lv, Y. Zhang, M. Lei, L. Hu, Palladium-Catalyzed Formylation of Aryl Iodides
with HCOOH as CO Source, Org. Lett. 19 (2017) 4235–4238.
https://doi.org/10.1021/acs.orglett.7b01882.
Acids,
J.
Org.
Chem.
82
(2017)
9710–9714.
[
[
4
[
[
[
[
[
[
[
[
20] X. Qi, C.-L. Li, X.-F. Wu, A Convenient Palladium-Catalyzed Reductive Carbonylation of
Aryl Iodides with Dual Role of Formic Acid, Chem. - Eur. J. 22 (2016) 5835–5838.
https://doi.org/10.1002/chem.201600387.
21] F.-P. Wu, J.-B. Peng, L.-S. Meng, X. Qi, X.-F. Wu, Palladium-Catalyzed Ligand-Controlled
Selective Synthesis of Aldehydes and Acids from Aryl Halides and Formic Acid,
ChemCatChem. 9 (2017) 3121–3124. https://doi.org/10.1002/cctc.201700517.
22] W. Ren, W. Chang, J. Dai, Y. Shi, J. Li, Y. Shi, An Effective Pd-Catalyzed Regioselective
Hydroformylation of Olefins with Formic Acid, J. Am. Chem. Soc. 138 (2016) 14864–
1
4867. https://doi.org/10.1021/jacs.6b10297.
23] P. Losch, A.-S. Felten, P. Pale, Easy, Green and Safe Carbonylation Reactions through
Zeolite-Catalyzed Carbon Monoxide Production from Formic Acid, Adv. Synth. Catal. 357
(2015) 2931–2938. https://doi.org/10.1002/adsc.201500384.
24] C. Brancour, T. Fukuyama, Y. Mukai, T. Skrydstrup, I. Ryu, Modernized Low Pressure
Carbonylation Methods in Batch and Flow Employing Common Acids as a CO Source, Org.
Lett. 15 (2013) 2794–2797. https://doi.org/10.1021/ol401092a.
25] L. Wang, H. Neumann, M. Beller, A General, Activator-Free Palladium-Catalyzed
Synthesis of Arylacetic and Benzoic Acids from Formic Acid, Angew. Chem. Int. Ed. 57
(2018) 6910–6914. https://doi.org/10.1002/anie.201802384.
26] R. Sang, P. Kucmierczyk, K. Dong, R. Franke, H. Neumann, R. Jackstell, M. Beller,
Palladium-Catalyzed Selective Generation of CO from Formic Acid for Carbonylation of
Alkenes, J. Am. Chem. Soc. 140 (2018) 5217–5223.
27] D. Mellmann, P. Sponholz, H. Junge, M. Beller, Formic Acid as a Hydrogen Storage
Material -Development of Homogeneous Catalysts for Selective Hydrogen Release, Chem.
Soc. Rev. 45 (2016) 3954–3988. https://doi.org/10.1039/C5CS00618J.
[28] D. Wang, D. Astruc, The Golden Age of Transfer Hydrogenation, Chem. Rev. 115 (2015)
6
621–6686.
29] A. Somasunderam,
,3-Bis(diphenylphosphino)propane to Catalyze the Regioselective Hydroformylation of
[
H.
Alper,
Use
of
Rhodium
on
Carbon
and
1
Alkenes with Formic Acid as the Hydrogen Source, J. Mol. Catal. 92 (1994) 35–40.
https://doi.org/10.1016/0304-5102(94)00054-9.
25

[
30] B. El Ali, G. Vasapollo, H. Alper, A Novel Rh-PCy -CO-HCOOH Catalytic System for the
3
Regioselective Conversion of Alkenes to Aldehydes, J. Mol. Catal. Chem. 112 (1996) 195–
2
01.
[
31] A. Léval, A. Agapova, C. Steinlechner, E. Alberico, H. Junge, M. Beller, Hydrogen
Production from Formic Acid Catalyzed by a Phosphine Free Manganese Complex:
Investigation and Mechanistic insights, Green Chem. 22 (2020) 913–920.
https://doi.org/10.1039/C9GC02453K.
[
[
[
[
32] X. Li, A. Surkus, J. Rabeah, M. Anwar, S. Dastigir, H. Junge, A. Brückner, M. Beller,
Cobalt Single‐Atom Catalysts with High Stability for Selective Dehydrogenation of Formic
Acid, Angew. Chem. Int. Ed. (2020) 15849–15854. https://doi.org/10.1002/anie.202004125.
3
33] A. Léval, H. Junge, M. Beller, Formic Acid Dehydrogenation by a Cyclometalated κ -CNN
Ruthenium
Complex,
Eur.
J.
Inorg.
Chem.
2020
(2020)
1293–1299.
https://doi.org/10.1002/ejic.202000068.
34] A. Boddien, D. Mellmann, F. Gartner, R. Jackstell, H. Junge, P.J. Dyson, G. Laurenczy, R.
Ludwig, M. Beller, Efficient Dehydrogenation of Formic Acid Using an Iron Catalyst,
Science. 333 (2011) 1733–1736. https://doi.org/10.1126/science.1206613.
35] L. Liu, H. Gao, S.-Q. Yang, X.-C. Chen, Y. Lu, Y. Liu, F. Xia, Ir-Catalyzed Tandem
Hydroformylation-TransferHydrogenation of Olefins with (trans-/cis-)Formic Acid as
Hydrogen Source in Presence of 1,10-Phenanthroline, J. Catal. 385 (2020) 183–193.
https://doi.org/10.1016/j.jcat.2020.03.008.
[
36] Z. Yang, Z. Zhu, R. Luo, X. Qiu, J. Liu, J.-K. Yang, W. Tang, Iridium-catalyzed highly
efficient chemoselective reduction of aldehydes in water using formic acid as the hydrogen
source, Green Chem. 19 (2017) 3296–3301. https://doi.org/10.1039/C7GC01289F.
37] X. Wu, J. Liu, X. Li, A. Zanotti-Gerosa, F. Hancock, D. Vinci, J. Ruan, J. Xiao, On Water
and in Air: Fast and Highly Chemoselective Transfer Hydrogenation of Aldehydes with
[
Iridium
Catalysts,
Angew.
Chem.
Int.
Ed.
45
(2006)
6718–6722.
https://doi.org/10.1002/anie.200602122.
[
[
[
[
[
38] J. Liu, S. Yang, W. Tang, Z. Yang, J. Xu, Iridium-Catalyzed Efficient Reduction of Ketones
in Water with Formic Acid as a Hydride Donor at Low Catalyst Loading, Green Chem. 20
(2018) 2118–2124.
39] P. Dierkes, P.W.N.M. van Leeuwen, The Bite Angle Makes the Difference: A Practical
Ligand Parameter for Diphosphine Ligands, J. Chem. Soc. Dalton Trans. (1999) 1519–1530.
https://doi.org/10.1039/a807799a.
40] K. Marushkevich, L. Khriachtchev, J. Lundell, A. Domanskaya, M. Räsänen, Matrix
Isolation and Ab Initio Study of Trans-Trans and Trans-Cis Dimers of Formic Acid, J. Phys.
Chem. A. 114 (2010) 3495–3502.
41] D. Yang, Y. Yang, Yufang. Liu, A Theoretical Study on The Red- and Blue-Shift Hydrogen
Bonds of Cis-Trans Formic Acid Dimer in Excited States, Cent. Eur. J. Chem. 11 (2013)
1
71–179. https://doi.org/10.2478/s11532-012-0143-x.
42] L.A. van der Veen, M.D.K. Boele, F.R. Bregman, P.C.J. Kamer, P.W.N.M. van Leeuwen,
K. Goubitz, J. Fraanje, H. Schenk, C. Bo, Electronic Effect on Rhodium Diphosphine
Catalyzed Hydroformylation: The Bite Angle Effect Reconsidered, J. Am. Chem. Soc. 120
(
1998) 11616–11626. https://doi.org/10.1021/ja981969e.
43] Y.S. Varshavsky, T.G. Cherkasova, I.S. Podkorytov, Action of Triphenylphosphine on
Rh(HCOO)(PPh ) (CO)]. A Novel Synthetic Route to [HRh(PPh ) (CO)], Inorg. Chem.
Commun. 7 (2004) 489–491. https://doi.org/10.1016/j.inoche.2004.01.013.
44] S. Haji, C. Erkey, Investigation of Rhodium Catalyzed Hydroformylation of Ethylene in
Supercritical Carbon Dioxide by in situ FTIR Spectroscopy, Tetrahedron. 58 (2002) 3929–
[
[
[
[
3
2
3 3
3
941. https://doi.org/10.1016/S0040-4020(02)00246-6.
45] Takashi. Ito, Shoji. Kitazume, Akio. Yamamoto, Sakuji. Ikeda, Nitrogen-Coordinated
Complexes. Preparations and Reactions of Hydrido-Phosphine Complexes of Ruthenium
and
Rhodium,
J.
Am.
Chem.
Soc.
92
(1970)
3011–3016.
https://doi.org/10.1021/ja00713a014.
[
46] L.A. van der Veen, P.H. Keeven, G.C. Schoemaker, J.N.H. Reek, P.C.J. Kamer, P.W.N.M.
van Leeuwen, M. Lutz, A.L. Spek, Origin of the Bite Angle Effect on Rhodium
Diphosphine Catalyzed Hydroformylation, Organometallics. 19 (2000) 872–883.
https://doi.org/10.1021/om990734o.
26

Declaration of Interest Statement
There are no conflicts of interest to declare.
Graphical Abstract
HCOOH
Ac O
2
HOAc
O
C
O
H
O
Me
(acetic formic anhydride, AFA)
Cat.: L1-Rh(acac)(CO)2 Decarbonylation
HOAc
Cat.: L1-Rh(acac)(CO)2
CHO
R
+
CO
+
H2
+
R
R
CHO
Hydroformylation
CO2
Cat.: L1-Rh(acac)(CO)2
Dehydrogenation
HCOOH
The atmospheric hydroformylation of olefins with FA as syngas alternative over L1-Rh(acac)CO)2
catalytic system (L1 = Xantphos)
Research Highlights:



Rh-catalyzed hydroformylation of olefins with formic acid as syngas alternative
Formic acid serving as CO-surrogate and H -source respectively
2
Insight into decomposition of formic acid to syngas discerned by in situ FT-IR
1
and high-pressure H NMR spectroscopic techniques
27