Chemo- And regioselective hydroformylation of alkenes with CO2/H2over a bifunctional catalyst

Article abstract of DOI:10.1039/d0gc03913f

As is well known, CO2 is an attractive renewable C1 resource and H2 is a cheap and clean reductant. Combining CO2 and H2 to prepare building blocks for high-value-added products is an attractive yet challenging topic in green chemistry. A general and selective rhodium-catalyzed hydroformylation of alkenes using CO2/H2 as a syngas surrogate is described here. With this protocol, the desired aldehydes can be obtained in up to 97% yield with 93/7 regioselectivity under mild reaction conditions (25 bar and 80 °C). The key to success is the use of a bifunctional Rh/PTA catalyst (PTA: 1,3,5-triaza-7-phosphaadamantane), which facilitates both CO2 hydrogenation and hydroformylation. Notably, monodentate PTA exhibited better activity and regioselectivity than common bidentate ligands, which might be ascribed to its built-in basic site and tris-chelated mode. Mechanistic studies indicate that the transformation proceeds through cascade steps, involving free HCOOH production through CO2 hydrogenation, fast release of CO, and rhodium-catalyzed conventional hydroformylation. Moreover, the unconventional hydroformylation pathway, in which HCOOAc acts as a direct C1 source, has also been proved to be feasible with superior regioselectivity to that of the CO pathway.

Full text of DOI:10.1039/d0gc03913f

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DOI: 10.1039/D0GC03913F
ARTICLE
Chemo- and Regioselective Hydroformylation of Alkenes with
CO /H over a Bifunctional Catalyst
Received 00th
January 20xx,
2
2
a,b
a
a,c
a
a,c
a,c
Kaimin Hua , Xiaofang Liu ,* Baiyin Wei , Zilong Shao , Yuchao Deng , Liangshu Zhong , Hui
a
a,c,d
Wang ,* Yuhan Sun
*
As is well known, CO
to prepare building blocks for high-value-added products is an attractive yet challenging topic in green chemistry. A general
and selective rhodium-catalyzed hydroformylation of alkenes using CO /H as a syngas surrogate is described here. With this
protocol, the desired aldehydes can be obtained in up to 97% yield and 93/7 regioselectivity under mild reaction conditions
25 bar, 80 °C). Key-to-success is the use of bifunctional Rh/PTA catalyst (PTA: 1,3,5-triaza-7-phosphaadamantane), which
facilitates both CO hydrogenation and hydroformylation. Notably, monodentate PTA exhibited better activity and
2 2 2 2
is an attractive renewable C1 resource and H is a cheap and clean reductant. Combining CO and H
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
2
2
(
2
regioselectivity than common bidentate ligands, which might be ascribed to its built-in basic site and tris-chelated mode.
Mechanistic studies indicate that the transformation proceeds through cascade steps, involving free HCOOH production
2
through CO hydrogenation, fast release of CO, and rhodium-catalyzed conventional hydroformylation. Moreover, the
unconventional hydroformylation pathway, in which HCOOAc acts as a direct C1 source, has also been proved feasible with
superior regioselectivity than that of CO pathway.
50
carboxylic acids . However, owing to the intrinsic
Introduction
With the concerns surrounding global warming caused by the
ever-increasing carbon dioxide emissions, the catalytic reduction
thermodynamic stability of CO and the resulting deoxygenative
2
cleavage of O=CO bond, reverse water gas shift (RWGS)
(
Scheme 1, Pathway 131,50 and 240,51,52) generally requires high
temperatures, which lead to overreduction of the carbonyl group,
precluding the isolation of aldehydes and/or restricting the
function of the ligands. As a result, poor regioselectivity is
observed in this reaction. Recently, Ding and Xia et al. realized
selective hydroformylation of alkenes with CO /H to obtain
2 2
aldehydes in good yields and regioselectivities (up to 70% and 90/10
l/b, respectively) through a sophisticated strategy, in which additional
of CO
high-value-added chemicals and energy-related products1-11 such
as CO12,13, formic acid14-16, methanol17-20, and gasoline21,22. CO
reduction to CO is of particular interest, as it can bridge the gap
between CO utilization and carbonylation of alkenes, the latter
2
has been extensively explored as a strategy to generate
2
2
of which represents a major industrial technology for the
production of valuable chemicals23,24 such as aldehydes,
alcohols, carboxylic acids, esters, though suffering from high
toxicity and unsustainable fossil fuels source of CO.
Therefore, reductive transformations using CO
carbonylative alkene functionalization25-27 with reductants28
such as hydrosilane29,30, hydroborane, or CH OH31,32 have
emerged as elegant alternative strategies. From a sustainable
reductant hydrosilane was required to mediate reduction of CO
Scheme 1, Pathway 3) 29. Therefore, new strategies using
CO /H as a syngas surrogate (especially with H as the exclusive
reductant) for chemo- and regioselective hydroformylation of
2
to CO
(
2
2
2
2
for
53
alkenes are required .
3
3
3
point of view, H
generated by the photolysis of water34-36
combination of CO and H for carbonylative alkene
2
is a better choice of reductant , as it can be
.
Hence, the
2
2
functionalization15,37-39 has attracted much attention, which is
one of the major areas in green chemistry, and it has been
demonstrated to afford high-value-added alcohols40-49 and
COY
H2 / MeOH
CO
Pathway 1 RWGS
+ HY
+ H2
+ H2
R
R
Y = OH, OCH3
CH2OH
R
H2
R
CO
Pathway 2 RWGS
a. CAS key Laboratory of Low-carbon Conversion Science and Engineering, Shanghai
Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (P.
R. China).
CO2
hydrosilane
CO
Pathway 3
CHO
R
R
b.
University of Chinese Academy of Science, Beijing 100049 (P. R. China).
ShanghaiTech University, Shanghai 201210 (P. R. China).
Shanghai Institute of Clean Technology, Shanghai, 201620 (P. R. China).
c.
d.
†
this work
H2
HCOOAc
+ H
2
R
CHO
Ac2O
HCOOH
or
R
Pathway 4
Electronic
Supplementary
Information
(ESI)
available.
See
CO
DOI: 10.1039/x0xx00000x
2
Scheme 1 Strategies for the carbonylation of alkenes with CO /H2.
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ARTICLE
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As is well known, HCOOH can be obtained by the catalytic Table 1 Ligand screening and optimization of reactionVcieowndArittiicolenOsnfloinre
14-16,54,55. On the other hand, effective the hydroformylation of 1-decene 1a with CO
DOI: 10.10
[a]39/D0GC03913F
2
and H
.
hydrogenation of CO
2
2
CHO
regioselective hydroformylation of alkenes with HCOOH has
been realized56-58 in which HCOOAc (generated from HCOOH
[Rh]/L
CHO
nC8H17
+
CO2 + H2
8 17
nC H
+
nC8H17
Ac2O , NMP
80 °C, 12 h
2
0 bar 5 bar
57
1a
and Ac
Therefore, we envisaged the possibility of utilizing CO
the hydroformylation of alkenes via HCOOH. To achieve such a
transformation, rapid production of HCOOH through CO
2
O) instead of conventional CO acts as intermediate .
2a
2a'
O
O
NaO3S
SO3Na
O
O
2
/H for
P
2
P
P
O POOP O
OO
P
PPh2
PPh2
PPh2
PPh2
PPh2
O
Ph2P
Fe
N
N
N
PPh2
PPh2
SO3Na
O
PMeOPh3
Xantphos
Biphephos
BISBI
dppf
dppb
PTA
PPh3
TPPTS
2
hydrogenation, HCOOAc formation/CO release should be
coupled with regioselective hydroformylation in a single process
[
b]
[b]
l/b[b] Iso /% H /%
[b]
[b]
Entry
L
Conv /% 2a+2a’ /%
1
2
3
4
5
6
7
8
9
PPh
3
94
82
95
95
94
90
73
99
99
98
99
99
15
14
26
5
74/26
90/10
76/24
50/50
-
37
33
24
2
41
5
9
(
Scheme 1, Pathway 4) . Herein, a bifunctional catalytic system
composed of rhodium and PTA (1,3,5-triaza-7-
phosphaadamantane), where Rh/PTA facilitates both CO
TPPTS
33
PMeOPh
Xantphos
Biphephos
BISBI
dppf
44
3
2
86
hydrogenation and hydroformylation, is developed for the
efficient and selective hydroformylation of alkenes using
CO /H as a syngas surrogate.
2 2
0
2
91
20
6
92/8
13
6
55
93/7
60
dppb
87
90
80
74
92
78/22
89/11
90/10
94/6
4
8
PTA
5
3
Results and discussion
Effects of ligands and reaction parameters
1
0[c]
PTA
8
9
11[d]
PTA
11
3
13
3
1
2[e]
PTA
90/10
Initially, Rh-catalyzed hydroformylation of 1-decene 1a under
[
a] Reaction conditions: 1-decene 1a (1 mmol), Rh(acac)(CO)
ligand (0.12 mmol), Ac O (2.0 mmol), CO /H
4 mL). [b] Determined by GC analysis with benzyl alcohol or isooctane as
the internal standard. Iso = isomerized alkenes, H = decane. [c] 0.02 mmol
Rh(OAc) instead of Rh(acac)(CO) . [d] CO /H = 7/3 bar. [e] 2.2 mol %
Rh(acac)(CO)
2
(0.02 mmol),
2
5 bar CO
using different ligands (Table 1). It should be mentioned that
Ac O could be regenerated through dehydration of CH COOH.
With the simple ligand PPh , the aldehydes were obtained in
5% yield with a linear to branched ratio (l/b) of 74/26, which
proved that the tandem transformation was feasible (Table 1,
entry 1). Derivatives of PPh substituted with an electron-
withdrawing or electron-donating group, such as TPPTS and
PMeOPh
, showed slightly improved activity or regioselectivity
entries 2-3). The commonly used ligands Xantphos and
2 2 2
/H (4/1) in the presence of Ac O was investigated
2
2
2
= 20/5 bar, 80 ºC, 12 h, NMP
(
2
3
3
1
3
2
2
2
2
.
3
ratio on the aldehyde yield and regioselectivity. It is worth
mentioning that the catalytic performance of (PPh (CO)Rh-H
is similar to that of PPh , which implied that L (CO)Rh-H could
3
3 3
)
(
3
3
Biphephos, which are well known to mediate highly
regioselective hydroformylation, afforded negligible amounts of
the aldehydes or no aldehydes, and hydrogenated byproducts
dominated in both cases. In contrast, BISBI and metallocene-
modified dppf displayed poor activity with excellent
regioselectivity (entries 4-7). These results imply that
be the active intermediate (Table S3, SI). Specifically, a similar
yield (80%) and regioselectivity (90/10) of the aldehyde were
achieved when using Rh(OAc) (Table 1, entry 10), Other
3
rhodium salts could also promote this transformation but more
isomerization/hydrogenation products were observed (Table S3,
SI). Decreasing or increasing the amount of PTA also weakened
the aldehyde yield (Table S4, SI). A quick screening of solvents
showed that a solvent with high polarity, such as 1,3-dimethyl-
2 2
hydroformylation with CO /H was blocked by the deficient
CO/HCOOAc and that the critical step might be CO
2
hydrogenation into HCOOH, which promotes the subsequent
hydroformylation, suppressing possible hydrogenation of
2-imidazolidinone (DMI), N-methylpyrrolidone (NMP), or
dimethyl sulfoxide (DMSO), was beneficial for the
transformation; Among these, NMP was the optimal solvent. In
contrast, the reactions carried out in toluene and THF afforded
the aldehyde in a mediocre yield but with excellent
regioselectivity (Table S5, SI). The aldehyde yield and l/b ratio
could be maintained well when the reaction temperature was
between 70 and 90 °C (Table S6, SI). The aldehyde yield and l/b
6
0
14
alkene. Therefore, dppb and PTA , which show an outstanding
ability for the hydrogenation of CO to free HCOOH (as acetic
acid from Ac O created a weakly acidic medium), were explored
for use in hydroformylation with CO /H . Indeed, when the
reaction was performed with dppb, the aldehyde was obtained in
7% yield with an l/b ratio of 78/22 (entry 8). Even better
2
2
2
2
8
regioselectivity (89/11) but with a similar aldehyde yield was
observed when using PTA (entry 9). Ten additional mono- and
bidentate phosphine ligands, such as CgPPh with a cage structure
similar to that of PTA and dppp, were also screened, and inferior
results were obtained (Tables S1 and S2, SI). Hence, PTA was
considered as the optimal ligand for this reaction.
Further investigations of the reaction conditions using the
optimal ligand PTA revealed substantial effects of the rhodium
precursor, PTA/Rh ratio, solvent type, temperature, and PCO2/PH2
ratio fluctuated marginally when the pressure of CO
doubled or halved (Table S7, SI). Notably, reducing the CO
pressure to 7 bar increased the regioselectivity (up to 94/6 l/b),
but slightly decreased the aldehyde yield (Table 1, entry 11).
Finally, the aldehyde yield could be improved to 92% with 90/10
l/b by optimizing the catalyst loading (Table 1, entry 12).
2 2
/H is
2
Substrate scope
2
| J. Name., 2012, 00, 1-3
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ARTICLE
Table 2 Substrate scope.[a]
As shown in Table 1, the ligand plays a critica
V
l
iewro
DOI: 10.1039/D0GC03913F
2 2
/H . Therefore, we selected
Article Online
le in the
Rh(acac)(CO)2 (2 mol%)
R2
CHO
R2
hydroformylation of alkene with CO
typical ligands including PPh , Xantphos, dppb, and PTA to
R2
Rh/PTA=1/6
Ac2O (2 equiv.), NMP
80 °C, 12 h
R1
R1
+
CO2 + H2
+
R1
CHO
3
20 bar
5 bar
compare the aldehyde yield, regioselectivities, and CO
production under identical conditions (Figure 1). Analysis of gas
products formed during the hydroformylation of 1a promoted by
1
2
2'
Conv /% Yield [b]/% l/b[b] Iso /% H /%
[b]
[b]
[b]
Entry
1
Alkene
9
9
9
9
9
9
9
9
92
96
96
95
97
95
77
73
72
87
92
90/10
90/10
88/12
86/14
85/15
86/14
93/7
3
1
2
2
2
2
-
3
1
1
1
<1
2
-
Rh/PPh
3
revealed that the amount of CO remained
2
3
approximately 0.1 mmol. The low CO content (decomposed
from HCOOAc) led to the mediocre yield and regioselectivity.
Although Xantphos exhibited excellent regioselective
4
5
1
00
23, it afforded
hydroformylation with CO/H
2
a
major
6
9
9
hydrogenated by-product instead of the desired aldehyde, which
can be attributed to its inferior ability to produce HCOOH
through CO hydrogenation and the resulting HCOOAc/CO. In
2
the presence of dppb, the amount of produced CO increased and
remained constant at a high level (over 0.5 mmol), which
effectively promoted the subsequent hydroformylation to furnish
aldehydes in 92% yield and with modest linear regioselectivity
7[c]
-
8[c]
-
-
85/15
-
-
-
9[c]
-
-
1
1
0
1
Cl
9
8
9
87/13
73/27
2
1
8
6
HO
O
9
9
(80/20 l/b ratio). Gratifyingly, Rh/PTA displayed a better ability
1
2
8
6
90
75
85/15
-
3
0
4
1
O
to generate CO, as 0.9 mmol CO in the initial 30 min could be
detected and over 0.4 mmol CO could be maintained throughout.
Notably, as CO was derived from HCOOH/HCOOAc
decomposition, appreciable amounts of CO in the gas phase
implied accumulation of HCOOH/HCOOAc in the liquid phase
3[d]
1
1
7
3
1
4[e]
9
9
9
0
9
8
64
90
47
-
25
0
1
1
4
2
(actually, HCOOH production increased gradually over time, see
1
5
6
10/90
17/83
Figure S2, SI). Therefore, the possibility of HCOOH/HCOOAc
acting as a direct C1 source could not be ruled out. These
observations revealed that the key to distinguish PTA from other
ligands is the efficient and rapid production of HCOOAc or CO,
which originates from its outstanding ability to produce HCOOH
1
0
Cl
1
7
9
4
91
16/84
0
<1
H3CO
14
through CO
2
hydrogenation in acidic media . After excluding
[
a] Reaction conditions: Alkene (1 mmol), Rh(acac)(CO)
PTA (0.132 mmol), Ac O (2.0 mmol), NMP (4 mL), CO /H
ºC, 12 h. [b] Determined by GC analysis with benzyl alcohol or isooctane
as the internal standard. [c] Alkene (3 mmol), Ac O (4.5 mmol). [d] T = 90
2
(0.022 mmol),
the influence of acids (Tables S10, SI) and sterically rigid
2
2
2
= 20/5 bar, 80
2
ºC. selectivity of exo-product 99%. [e] T=100 ºC, 24 h. 1-CHO: 2-CHO: 3-
CHO=16:60:24.
Yield/%
00
CO/mmol
Yield/%
100
CO/mmol
1.0
1
1.0
a) PPh3
b) Xantphos
2
2
a'
a
CO
2a'
2a
CO
80
60
40
20
0
0.8
0.6
0.4
0.2
80
60
40
20
0
0.8
0.6
0.4
0.2
0.0
With the optimized reaction conditions in hand, the generality of
the reaction was investigated. As shown in Table 2, terminal
alkenes (C5-C10) demonstrated similar reactivity irrespective of
the carbon chain length, affording the corresponding aldehydes
in over 90% yields with good linear regioselectivities (l/b =
0.0
12
0.5
1
2
6
0.5
1
2
6
12
8
5/15–90/10) (entries 1-6), which were obviously higher than
those of reported systems. Bulk aldehydes were also achieved in
2% – 77% yield with good linear regioselectivity for the
time/h
time/h
Yield/%
c) dppb
CO/mmol Yield/%
CO/mmol
d) PTA
100
1.0
0.8
0.6
0.4
0.2
0.0
100
1.0
7
2
2a
a'
CO
2a'
2a
CO
hydroformylation of ethene, propene, and butene (entries 7-9).
Remarkably, good functional-group tolerance was observed for
chloro, hydroxyl and ester groups (entries 10-12). The more
challenging internal alkenes, norbornene and 2-octene, were
transformed into corresponding aldehydes in good yield (entries
80
80
0.8
0.6
0.4
0.2
0.0
6
0
0
60
4
40
20
0
20
1
3-14). Finally, the reaction proceeded smoothly with styrene
0
0.5
1
2
6
12
0.5
1
2
6
12
derivatives, furnishing aldehydes in moderate to excellent yields,
though with opposite regioselectivities (entries 15-17).
time/h
time/h
Figure 1. Control experiments with different ligands. (a) PPh , (b) Xantphos,
3
(c) dppb, and (d) PTA in 0.5, 1, 2, 6, and 12 h. Reaction conditions: 1a (1.0
Role of the PTA ligand
mmol), Rh(acac)(CO) (2 mol%), L (12 mol%), Ac O (2.0 mmol), CO / H = 20/5
2
2
2
2
bar, 80 ºC, NMP (4 mL) in a 50 mL autoclave.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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ARTICLE
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structure of PTA (ligand CgPPh with similar cage structure
showed poor activity and regioselectivity, see Tables S1, L6, SI),
we presume it’s the characteristic nitrogen atom in PTA acting
as a built-in basic site61-64 that thermodynamically shift the
equilibrium towards formation of free HCOOH. Another
possible reason for superior regioselectivity of PTA over dppb is
the tris-chelated mode of PTA towards Rh, similar to that of
2a/2a'
Yield/%
View Article Online
DOI: 10.1039/D280GC03913F
100
2a+2a'%
H%
iso%
2a/2a'
2
4
0
80
60
40
20
0
2
16
12
8
6
5
monodentate PPh
3
(Table S3, SI) , and the resultant steric-
hindered (PTA) (CO)Rh-H (confirmed by ESI-MS, see Figure
3
S3, SI) induces formation of linear aldehydes.
4
Isotope-labelling and Control experiments
0
0
1
2
3
4
5
6
7
8
9
10 11 12
To gain insight into the details of alkene hydroformylation with
Time/h
Figure 2. Reaction profiles for the hydroformylation of 1a with CO
Reaction conditions: 1a (1.0 mmol), Rh(acac)(CO) (2 mol%), PTA (12 mol%),
Ac O (2.0 mmol), CO /H = 20/5 bar, 80 ºC, NMP (4 mL) in a 50 mL autoclave.
CO
). Isotope-labeling experiments were performed using CO
verify the source of the carbon in the formyl group. Incorporation
of 13CO into the formyl group was confirmed by 13C NMR
Figure S4, SI) analysis. 13CO was also detected by MS in the
gas phase (Figure S6, SI). These results confirmed that CO was
2 2
/H , a series of control experiments were designed (Scheme
2 2
/H .
13
2
2
to
2
2
2
2
2
(
5
7
coordination of HCOOAc with Rh/PTA . In a word, two
compatible pathways (HCOOAc one with 92/8 regioselectivity
and CO one with 78/22) generates overall 90/10 regioselectivity.
2
53
involved in the formation of the formyl group (Scheme 2a) .
Formation of HCOOH and CO was detected from the liquid and
gas phases, respectively, under standard conditions (Scheme 2b).
Time course of the reaction
2
To explore the HCOOH source, hydrogenation of CO was
conducted in the presence of Rh/PTA. Signals attributed to Results of the kinetic study (Figure 2) also confirmed the
1
HCOOH could be clearly observed in the H NMR spectrum coexistence of both conventional and unconventional reaction
(
Figure S7, SI). The addition of 2.0 mmol acetic anhydride to the pathways. In the first 10 min, 14% yield of aldehydes (2a+2a’)
above reactor generated 1.3 mmol CO (Scheme 2c). HCOOAc along with excellent 96/4 regioselectivity was observed.
could not be detected in the system as it’s highly reactive. Based Subsequently, the yield exceeded 50% with the l/b ratio of 95/5
on the above results, we speculated that CO
hydrogenated to HCOOH, which produced HCOOAc in the was approximately 90% with an l/b ratio of 90:1066,67. Hence, the
presence of Ac
O. HCOOAc would be rapidly decomposed to exceptionally high regioselectivity at the initial stage is attributed
CO. All these results together proved the feasibility of the CO
to the accumulation of HCOOAc, which follows the
2
was readily in 1 h. When 1a was fully converted after 6 h, the aldehyde yield
2
2
-
HCOOH-HCOOAc-CO-formyl pathway in obtaining aldehydes. unconventional hydroformylation pathway. With time,
Similar aldehyde yields could be obtained, albeit with lower HCOOAc rapidly decomposes to CO. High concentration of CO
regioselectivity, when CO is used instead of CO
A similar performance compared with that of CO
2
(Scheme 2d). will divert the reaction to the conventional pathway, reducing the
2
/H
2
was regioselectivity.
achieved with HCOOH as the C1 source (Scheme 11, SI).
Notably, with HCOOAc as the direct carbon source, the reaction Proposed mechanism
proceeded with superior regioselectivity and similar aldehyde
On the basis of all these results and previous reports53,57, we
yield (Scheme 2e). This unconventional pathway contributed to
the exceptional regioselectivity, possibly owing to the
suggest the following reaction pathways for the
hydroformylation of alkenes with CO /H (Scheme 3). Initially,
CO is hydrogenated by Rh/PTA to produce HCOOH, which
readily decomposes to CO with the assistance of Ac O. In the
presence of H and in situ generated CO, Rh/PTA-catalyzed
conventional hydroformylation proceeds smoothly (pathway I).
2
Compared with the conventional hydroformylation using CO/H ,
2
2
2
2
13CHO
CHO
nC8H17
nC8H17
+
13CO2
+
H2
Rh(acac)(CO)2 /PTA
Ac2O (2 equiv.), NMP
nC H
+ 13CO
(
a)
8
17
2
8
0 °C, 12 h


CHO
Rh(acac)(CO)2 /PTA
Ac2O (2 equiv.), NMP
(
b)
+
CO2
+
H2
nC H
17
8
+
nC8H17
+
CO
+
HCOOH
8
0 °C, 12 h
2
0 bar 5 bar
Yield: 90%; l/b: 89/11


unconventional pathway II in which HCOOAc acts as a direct
carbon source proves plausible . Pathway II dominates the early
stage of the reaction and generates more linear aldehydes. Hence,
two compatible pathways contribute to the excellent yield and
2 2
regioselectivity in the hydroformylation of alkenes with CO /H ,
Rh(acac)(CO)2 /PTA
NMP
(c)
CO2
+
H2
+
Ac2O
-
HCOOH
+
CO
57
8
0 °C, 12 h
no CO
20 bar 5 bar


1.3 mmol
2
0 bar 5 bar 2 mmol
CHO
Rh(acac)(CO)2 /PTA
NMP
CHO
(d)
nC8H17
+
CO
+
H2
nC8H17
+
nC H
8 17
8
0 °C, 12 h
1
5
bar 5 bar
bar 5 bar
Yield: 90%; l/b: 77/23
Yield: 92%; l/b: 78/22
wherein the bifunctional Rh/PTA system plays a crucial role.
Rh(acac)(CO)2 /PTA
NMP
CHO
CHO
(
e)
nC8H17
+
HCOOAc
equiv.
indicated the typical substance was detected.
+
H2
8 17
nC H
+
nC8H17
+ CO
8
0 °C, 12 h
3
5 bar
Yield: 88%; l/b: 92/8

Conclusions

Scheme 2. Isotope-labeling experiments and control experiments.
4
| J. Name., 2012, 00, 1-3
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Page 5 of 7
Please Gd roe en no tC ha ed mj u iss tt r my argins
Journal Name
ARTICLE
P
CO2
+
H2
with a FID detector and a Stabilwax®-DA columnVie(w60Artmicle,O0n.l5in3e
DOI: 10.1039/D0GC03913F
mm, 0.5 μm). The gaseous mixture was collected and analyzed
L :
N
N
N
RhLn
by gas chromatography equipped with thermal conductivity
detector (Shimadzu GC-2014C) with Argon as the carrier gas.
ESI-MS analysis was performed on WATERS 2695+ZQ2000.
Detected masses are given in m/z and correlated to calculated
masses of the respective species. High resolution MS (omni star
gas analysis system) analyses were performed to detect 13CO
Path II
Path I
HCOOH
H
H
H
RhL3
H
RhL3
C=O
Ac2O
AcO RhL3
CHO
R
CO
AcO
H2
HCOOAc
CO
H
R
O
C
CO
R
RhL3
RhL3(CO)
RhL3
OAc
RhL3
AcOH
AcOH
R
H2
after 13CO
Isotope experiment. Detected masses are given in
2
O
RhL3
CO
C RhL3
OAc
H
R
R
m/z and correlated to calculated masses of the respective species.
1H- and 13C- NMR spectra were recorded on Bruker Avance III
R
CHO
R
Scheme 3. Proposed mechanism.
400 MHz spectrometers. Chemical shifts (δ values) were
In summary, Rh/PTA, a bifunctional catalytic system that
couples CO hydrogenation and hydroformylation of alkenes,
has been developed for the efficient production of linear
aldehydes using CO /H
innovative way for chemo- and regioselective synthesis of
aldehyde. A number of aliphatic alkenes can be transformed in
good to excellent yields and regioselectivities under mild
conditions. Mechanistic studies revealed that the reaction
proceeded through two pathways: via CO or via HCOOAc,
where the HCOOAc pathway generated more linear aldehydes.
reported in ppm relative to internal TMS.
2
2
2
as a syngas surrogate, which paves an Author contributions
K. Hua, Dr. X. Liu, Prof. H. Wang and Prof. Y. Sun designed
and developed this project. K. Hua and Dr. X. Liu performed the
catalytic experiments and data analysis. K. Hua, Dr. X. Liu and
Prof. H. Wang wrote the manuscript. B. Wei, Z. Shao, Y. Deng,
and Prof. L. Zhong performed some experiments and discussed
the work.
2 2
We demonstrate the possibility of using CO and H for the
selective hydroformylation of alkenes without any additional
reductants. We believe that this paper will trigger the design of
Conflicts of interest
There are no conflicts to declare.
other routes for efficient hydroformylation of alkenes using CO
and H in green chemistry.
2
2
Acknowledgements
Experimental Section
This work was supported by the National Natural Science
Foundation of China (21776296, 21905291), The National Key
General procedure for the hydroformylation reaction
All reactions and operations involving air- or moisture-sensitive
compounds were performed in Ar-filled glove box. All reactions
were carried out in a Teflon-lined stainless steel reactor of 50 mL
capacity equipped with a magnetic stirrer. Typically, in a
Research
and
Development
Program
of
China
(2017YFB0602203), Strategic Priority Research Program of the
Chinese Academy of Sciences (XDA21090201), Key Research
Program of the Chinese Academy of Sciences (ZDRW-ZS-2018-
glovebox, 1-decene (1.0 mmol), Rh(acac)(CO)
ligand (0.12 mmol), Ac O (2.0 mmol) and NMP (4 mL) were
loaded into the reactor. The autoclave was sealed and purged
three times with CO gas, subsequently charged with CO (20
bar), then H (5 bar) to total pressure of 25 bar. The autoclave
2
(0.02 mmol),
1-3), and the Shanghai Sailing Program (19YF1453000).
2
2
2
Notes and references
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| J. Name., 2012, 00, 1-3
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Page 7 of 7
Green Chemistry
View Article Online
DOI: 10.1039/D0GC03913F
Marrying CO and H for chemo- and regioselective hydroformylation of alkenes has been
2
2
realized. Key-to-success is the use of bifunctional Rh/PTA catalyst, which can ingeniously
combine efficient CO hydrogenation and hydroformylation
.
2