Nickel-catalyzed hydrocarboxylation of alkynes with formic acid

Article abstract of DOI:10.1039/c6gc00549g

A protocol for nickel-catalyzed hydrocarboxylation of alkynes with formic acid was developed. The protocol allowed for highly efficient synthesis of acrylic acid with a TON of up to 7700.

Full text of DOI:10.1039/c6gc00549g

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Nickel-Catalyzed Hydrocarboxylation of Alkynes with Formic Acid
Jing Hou,a Ming-Lei Yuan,a Jian-Hua Xiea and Qi-Lin Zhou*,a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
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A protocol for nickel-catalyzed hydrocarboxylation of alkynes with Supporting Information). Only bidentate phosphine ligands
formic acid was developed. The protocol allowed for highly with a certain bite angle and substituents on the phosphorus
efficient synthesis of acrylic acid with a TON of up to 7700.
atom afforded the desired acrylic acid product, with 3c giving
the highest TON for acrylic acid (130).
Acrylic acid is an important commodity chemical and is widely
used as a base material for the industrial production of paints,
plastics, superabsorbent polymers, rubber, and so on.1
Currently acrylic acid is produced by partial oxidation of
propene,2 which is refined from petroleum. Catalytic
hydrocarboxylation of acetylene with CO is another way to
synthesize acrylic acid with high atom-economy.3 However,
this nonpetroleum process uses toxic CO gas at high pressure.
Formic acid is a renewable, nontoxic liquid and is an ideal
replacement for CO gas for the hydrocarboxylation of alkenes.4
Recently, we developed a method for palladium-catalyzed
hydrocarboxylation of acetylene with formic acid, providing
acrylic acid with a TON of up to 350.5 As part of our search for
low-cost, more-efficient catalysts for the hydrocarboxylation of
acetylene, we studied catalysts based on first-row metals and
found that nickel complexes with diphosphine ligands are
efficient catalysts. Although organonickel chemistry has been
thoroughly explored,6 only limited progress on the nickel-
catalyzed hydrocarboxylation of alkynes has been made.7
Herein, we report the first nickel-catalyzed hydrocarboxylation
of acetylene with formic acid as the CO surrogate (Scheme 1).
A nickel catalyst bearing a di(tert-butylmethylphosphino)-
benzene ligand produced acrylic acid with a TON of up to 7700,
which is much higher than the TONs of previously reported
palladium catalysts.8
Previous work
Pd catalyst
TON up to 350
O
HCO2H
+
OH
This work
Ni catalyst
TON up to 7700
Scheme 1 Hydrocarboxylation of acetylene with formic acid.
Using ligand 3c
, we optimized the other reaction
parameters. Increasing the ratio of ligand to nickel (L/Ni) from
1:1 to 2:1 improved the TON for acrylic acid to 170 (Table 1,
entry 2). However, increasing the L/Ni to 3:1 resulted in a drop
in the TON to 90 (entry 3). Various nickel catalyst precursors
were compared (entries 4
most efficient precursor. Increasing the amount of formic acid
reduced the TON (entries 8 9).
−7), and Ni(acac)2 proved to be the
−
No reaction occurred in the absence of an anhydride, which
is necessary for the decomposition of formic acid to CO. The
experiments showed that the TON of acrylic acid remained
unchanged when 5−25 mol% Ac2O was used (Figure 2). The
effect of solvent on the reaction was also evaluated, and Et2O,
dioxane, and DMF were found to be suitable, although they
gave lower TONs than did THF (for details, see the Supporting
Information).
The hydrocarboxylation of acetylene with formic acid was
initially carried out at 100 °C in THF with Ni(acac)2 as a catalyst
precursor and acetic anhydride as a promoter. The nature of
the ligand markedly affected the reaction (see Figure 1 and the
We next studied the effect of the initial pressure of
acetylene and the effect of the reaction temperature on the
hydrocarboxylation of acetylene. We were delighted to find
that a low pressure of acetylene favored the reaction (Figure
3). Under 1 atm of acetylene, acrylic acid was obtained in 100%
yield with a TON of 300. Investigation of the reaction
temperature showed that the hydrocarboxylation could be
a.State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai
University,Tianjin 300071, China.
b.Collaborative Innovation Center of Chemical Science and Engineering
(Tianjin),Tianjin 300071, China. E-mail: qlzhou@nankai.edu.cn
Electronic Supplementary Information (ESI) available: Full experimental and
characterization data, including 1H, 13C and 31P NMR spectra for all new
compounds. See DOI: 10.1039/x0xx00000x
performed at 60−100 °C (Figure 4).
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Journal Name
S
N
N
PR1R2
PR1R2
PR1R2
PR1R2
the reaction was carried out at a 3c/Ni ratio 20:1 under 1 atm
of acetylene at 100 °C. To our delight, the TON for acrylic acid
could be improved to 7700 (77% yield) when the reaction was
performed under 10 atm of acetylene at a 3c/Ni ratio of 20:1
at 100 °C.
R2P
PR2
n
Cy2
P
PCy2
1a
R = Cy, n = 1
2a R1= R2 = Me
3a R1= R2 = Ph
4
R = R2 = Cy
R = R2 = Cy
1
1
1b R = Cy, n = 2
2b
3b
1c R = Cy, n = 3
2c R1= tBu, R2 = Me
3c R1= tBu, R2 = Me (rac)
t
1d
R = Bu, n= 2
Figure 1. Study on the phosphine ligands in Ni-catalyzed hydrocarboxylation of
acetylene (Reaction conditions: initial pressure P(C2H2) = 10 atm, Ni(acac)2 (5
μmol), ligand (5 μmol), Ac2O (0.75 mmol), HCOOH (1.5 mmol), in THF (3 mL) at
100 °C for 12 h; Yield was determined by GC analysis using n-hexadecane as an
internal standard).
Figure 2. The effect of the concentration of Ac2O on the reaction (Reaction
conditions: initial pressure P(C2H2) = 10 atm, Ni(acac)2 (5 μmol), 3c (10 μmol),
HCOOH (1.5 mmol), in THF (3 mL) at 100 °C for 12 h; Yield was determined by GC
analysis using n-hexadecane as an internal standard).
Table 1. Optimization of the reaction conditions for hydrocarboxylation of acetylene.a
O
[Ni], 3c, Ac2O
HCOOH
+
OH
THF, 100 oC,12 h
Entry
[Ni]
3c/[Ni]
[HCOOH] (mol/L)
TONb
130
170
90
1
2
3
4
5
6
7
8
9
Ni(acac)2
Ni(acac)2
Ni(acac)2
NiCl2
1
2
3
2
2
2
2
2
2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1
2
Figure 3. Effect of the pressure of acetylene on the reaction (Reaction conditions:
Ni(acac)2 (5 μmol), 3c (10 μmol), Ac2O (45 μmol), HCOOH (1.5 mmol), in THF (3
mL) at 100 °C for 12 h; Yield was determined by GC analysis using n-hexadecane
as an internal standard).
NiI2
10
Ni(OAc)2·4H2O
Ni(COD)2
Ni(acac)2
Ni(acac)2
1
27
93
1.5
60
a
Reaction conditions: initial pressure P(C2H2) = 10 atm, [Ni] (5 μmol), Ac2O
(0.75 mmol), HCOOH (1.5 mmol), THF (3 mL). b Yield was determined by GC
analysis using n-hexadecane as an internal standard.
Under the optimal reaction conditions (P(C2H2) = 1 atm,
Ac2O (45 μmol), HCOOH (1.5 mmol), in 3 mL of THF at 60 °C for
12 h), we investigated the effects of lowering the catalyst
loading. When we carried out the hydrocarboxylation of
acetylene using 0.01 mol% of 3c/Ni(acac)2, the desired
hydrocarboxylation product was obtained with a TON of 300,
which was the same as that obtained for the reaction using
0.33 mol% catalyst. We then increased the 3c/Ni ratio and the
reaction temperature. Increasing the 3c/Ni ratio under 1 atm
Figure 4. Effect of the temperature on the reaction (Reaction conditions: initial
pressure P(C2H2) = 1 atm, Ni(acac)2 (5 μmol), 3c (10 μmol), Ac2O (45 μmol),
HCOOH (1.5 mmol), in THF (3 mL) for 12 h; Yield was determined by GC analysis
of acetylene at 60 °C had little influence on the TON (Figure 5). using n-hexadecane as an internal standard).
However, the TON was enhanced substantially to 2400, when
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and
11).
The
α,β-disubstituted
acetylene
1,2-
diphenylacetylene gave only trace amount (<5%) of desired
hydrocarboxylation product under identical reaction
conditions.
To gain insight into the reaction mechanism, we carried out
the hydrocarboxylation of acetylene using 1 atm of CO instead
of Ac2O (P(CO) = 1 atm, P(C2H2) = 1 atm, Ni(acac)2 (5 μmol), 3c
(10 μmol), HCO2H (1.5 mmol), 3 mL of THF). The desired
product was obtained with a TON of 170, which was almost
the same as that obtained from the reaction with catalytic
Ac2O. This result proved that the CO was involved in the
hydrocarboxylation of acetylene with catalytic Ac2O. A possible
mechanism for the nickel-catalyzed hydrocarboxylation of
acetylene is proposed in Scheme 2. First, Ni(acac)2 reacts with
formic acid to produce nickel complex A. Decomposition of A
generates active catalyst B and releases CO2.9 Insertion of
acetylene into the Ni–H bond of B produces intermediate C.
Subsequently, CO, which is generated in situ by decomposition
of the mixed anhydride,10 inserts into the Ni–C bond of C to
form intermediate D. A reductive elimination reaction of D
generates Ni(0) complex E and anhydride F. Oxidative addition
of formic acid to E regenerates catalyst B. In another cycle,
anhydride F decomposes to form the acrylic acid product and
regenerate CO.
Figure 5. Effect of the ratio of 3c/[Ni] on the hydrocarboxylation of acetylene
under the condition of S/C = 10000 (Reaction conditions: Ni(acac)2 (0.15 μmol),
Ac2O (45 μmol), HCOOH (1.5 mmol), in THF (3 mL) at 100 °C for 12 h; Yield was
determined by GC analysis using n-hexadecane as an internal standard).
Table 2. Catalytic hydrocarboxylation of alkynes with formic acid.a
2 mol% Ni(acac)2
4 mol% 3c
O
O
30 mol% Ac2O
HCO2H
R1
+
+
OH
R1
OH
THF, 100 oC, 12 h
R1
5
6
7
entry
1
5
R1
6/7b
97:3
97:3
96:4
98:2
93:7
95:5
97:3
96:4
95:5
93:7
87:13
Yield (%)c
88
5a
C6H5
HCO2H
O
H
Ac2
O
O
LNi
2
5b
5c
5d
5e
5f
4-MeC6H4
3-MeC6H4
2-MeC6H4
4-MeOC6H4
4-ClC6H4
3-ClC6H4
4-BrC6H4
4-CF3C6H4
n-C6H13
89
O
O
C
3
85
CO
H
O
H
O
4
28
O
CO2
O
H
O
LNi
LNi
LNi(OOCH)2
D
OOCH
HO
5
84
A
B
O
O
6d
7d
8d
9d
10
11
83
L, HCOOH
H
O
cac)
Ni(a
2
F
5g
5h
5i
80
L2Ni0
E
HCO2H
82
Figure 6. Proposed mechanism
84
In conclusion, we have developed the first nickel-catalyzed
hydrocarboxylation of acetylene with formic acid. A nickel
catalyst bearing di(tert-butylmethylphosphino)benzene ligands
showed high activity with a TON of up to 7700, which is much
higher than the TONs for previously reported palladium
catalysts. The high efficiency and low cost of nickel catalysts
make this Ni-catalyzed hydrocarboxylation of acetylene a
promising approach to acrylic acids. Detailed studies of the
mechanism and applications of nickel catalysts in other
hydrocarboxylation reactions are in progress.
5j
64
5k
Cy
28
a
b
Reaction conditions: Alkyne (0.5 mmol), HCOOH (1.5 mmol), THF (3 mL).
c
Selectivity determined by NMR spectroscopy. Isolated yield. The transfer
hydrogenation product alkene was detected in all reactions. d 5 h.
The substrate scope of the reaction was investigated, and
the results are summarized in Table 2. Phenylacetylenes
bearing either an electron-donating or electron-withdrawing
group smoothly underwent the hydrocarboxylation reaction,
producing the corresponding α-aryl acrylic acids in good yields;
the only exception was 2-methylphenylacetylene, which gave a
low yield because of the bulky substituent at the ortho
position (entry 4). The hydrocarboxylation reaction was highly
regioselective, with the major products being α-aryl acrylic
acids, which were produced by the addition of the carboxyl
group to the substituted side of the aryl acetylenes. Aryl
acetylenes bearing an electron-withdrawing group showed
We thank the National Natural Science Foundation of China,
the National Basic Research Program of China
(2012CB821600), the “111” project (B06005) of the Ministry of
Education of China, and the National Program for Support of
Top-notch Young Professionals for financial support.
Notes and references
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(a) W. Jr. Bauer, Kirk-OthmerEncyclopedia of Chemical
Technology, Vol. 1 (Ed.: A. Seidel), John Wiley & Sons, Inc.
Hoboken, N. J, 2004, pp. 342; (b) M. Cokoja, C. Bruckmeier,
higher reaction rates (entries 6−9). Compared with
arylacetylenes, alkylacetylenes gave lower yields (entries 10
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