Nickel-catalyzed direct carboxylation of olefins with CO2: One-pot synthesis of α,β-unsaturated carboxylic acid salts

Article abstract of DOI:10.1002/chem.201405528

The nickel-catalyzed direct carboxylation of alkenes with the cheap and abundantly available C₁ building block carbon dioxide (CO₂) in the presence of a base has been achieved. The one-pot reaction allows for the direct and selective synthesis of a wide range of a,b-unsaturated carboxylates (TON>100, TOF up to 6 h^-1, TON= turnover number, TOF=turnover frequency). Thus, it is possible, in one step, to synthesize sodium acrylate from ethylene, CO₂, and a sodium salt. Acrylates are industrially important products, the synthesis of which has hitherto required multiple steps.

Full text of DOI:10.1002/chem.201405528

DOI: 10.1002/chem.201405528
Communication
&
Alkene Carboxylation
Nickel-Catalyzed Direct Carboxylation of Olefins with CO2:
One-Pot Synthesis of a,b-Unsaturated Carboxylic Acid Salts
Nfflria Huguet,[a] Ivana Jevtovikj,[a] Alvaro Gordillo,[a] Michael L. Lejkowski,[a] Ronald Lindner,[a]
Miriam Bru,[a] Andrey Y. Khalimon,[a] Frank Rominger,[b] Stephan A. Schunk,[c]
Peter Hofmann,[a, b] and Michael Limbach*[a, d]
Dedicated to Prof. Dr. Heinz Hoberg, a pioneer in the field
The hydrocarboxylation of activated unsaturated hydrocar-
Abstract: The nickel-catalyzed direct carboxylation of al-
[3]
bons with CO2 is an established methodology in organic
kenes with the cheap and abundantly available C1 build-
chemistry to yield either a,b- (for alkynes),[4] b,g-unsaturated a-
ing block carbon dioxide (CO2) in the presence of a base
branched (for allenes and 1,3 alkadienes),[5] or a-branched car-
has been achieved. The one-pot reaction allows for the
boxylic acid derivatives (for styrenes),[6] but requires the stoi-
direct and selective synthesis of a wide range of a,b-unsa-
turated carboxylates (TON>100, TOF up to 6 hÀ1, TON=
chiometric use of reductants (i.e., AlEt3, hydrosilanes, Et2Zn,
RMgX) or directing groups in the substrate.[6c]
turnover number, TOF=turnover frequency). Thus, it is
The catalytic carboxylation of unsaturated hydrocarbons
possible, in one step, to synthesize sodium acrylate from
with CO2 to a,b-unsaturated carboxylates (i.e., acrylates) has
ethylene, CO2, and a sodium salt. Acrylates are industrially
been difficult for three decades, although, in the 1980s,
Hoberg et al.[7] reported the nickel-catalyzed reaction of al-
required multiple steps.
important products, the synthesis of which has hitherto
kenes and isocyanates (isoelectronic to CO2) to acrylamides.
Since the early results of Hoberg et al., the cleavage of inter-
mediately formed metallalactones, in particular nickelalac-
tones,[8] has been a challenging route for such catalytic reac-
The exploitation of carbon dioxide (CO2) for the production of
globally used chemicals such as formic acid,[1] is of huge indus-
tions: for stereoelectronic reasons, five-membered “Hoberg
trial interest, because CO2 is a cheap and abundantly available
C1 building block.[2] Nevertheless, only a few reactions and cat-
alysts enable the straightforward catalytic functionalization of,
for example, alkenes with CO2 to industrially relevant target
molecules such as acrylates. Acrylates and their downstream
products are ubiquitous in daily life as hygiene products, coat-
ings, adhesives, and food preservatives and are globally manu-
factured on a multimillion ton level.
complexes” do not readily undergo b-H elimination and their
cleavage with auxiliaries such as electrophiles (i.e., alkyl hal-
ides[9] or protons[9g,10]), Lewis acids,[9g,10,11] a combination of
both,[12] thermally,[9c,10,13] or even sonochemically,[10] has not led
to catalysis. The cleavage of nickelalactones with sterically hin-
dered phosphazene bases is slow[11c] and, due to the mutual in-
compatibility of strong bases, Lewis acids, and CO2, catalysis re-
mained a challenge. The same applies for other metals from
groups 4 (Zr),[14] 6 (Mo),[15] 8 (Fe, Ru),[16] 9 (Rh),[17] and 10 (Pd,
Pt).[18]
Only recently have we been able to disclose the first two-
step catalytic synthesis of sodium acrylate from ethylene and
CO2 based on a nickel catalyst (TON 10),[19] as a) we targeted
the exergonic reaction to an acrylic acid salt instead of the
highly endergonic formation of acrylic acid (DG=21 vs.
À59 kJmolÀ1[20] in THF) and b) overcame the kinetically unfeasi-
ble b-H elimination from the dtbpe-ligated nickelalactone
[a] Dr. N. Huguet, Dr. I. Jevtovikj, Dr. A. Gordillo, Dr. M. L. Lejkowski,
Dr. R. Lindner, Dr. M. Bru, Dr. A. Y. Khalimon, Prof. Dr. P. Hofmann,
Dr. M. Limbach
CaRLa (Catalysis Research Laboratory)
Im Neuenheimer Feld 584, 69120 Heidelberg (Germany)
Fax: (+49)621-60-6648957
E-mail: michael.limbach@basf.com
[b] Dr. F. Rominger, Prof. Dr. P. Hofmann
Ruprecht-Karls-Universitꢀt Heidelberg
Organisch-Chemisches Institut
1 (DG° =103 kJmolÀ1 [19]
by its a-deprotonation with an alkox-
)
ide base. In this communication we will address the develop-
ment of an efficient one-pot catalyst system, which has previ-
ously been hampered by being limited to a small set of ligands
and substrates, and by the need to separate lactone formation
and its cleavage due to the lack of a base capable of tolerating
CO2.
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
[c] Dr. S. A. Schunk
hte GmbH
Kurpfalzring 104, 69123 Heidelberg (Germany)
[d] Dr. M. Limbach
BASF SE
Synthesis and Homogeneous Catalysis
Carl-Bosch-Strasse 38, 67056 Ludwigshafen (Germany)
The reaction of 1 with sodium 2-fluorophenoxide (2 equiv)
led to quantitative decarboxylation to ethylene complex 2 by
31P NMR, whereas acrylate p-complex 3 was formed in a clean
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405528.
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though BenzP* was not the most active ligand at 808C
(Table 1), it turned out to be robust at elevated temperatures
(TON 10 at 808C vs. 35 at 1008C with sodium 2-fluorophenox-
ide, Table 2). At 1208C the reductive decarboxylation of nickel-
alactone 5 was pronounced and the reaction became slug-
gish.[19,30]
Scheme 1. Nickelalactone cleavage by sodium 2-fluorophenoxide.
The electronic and steric influence of substituents on the
phenoxide’s core was crucial for reactivity (Table 2): at 808C
sodium phenoxide (50 equiv with respect to Ni(COD)2) as well
reaction in the presence of 10 equiv of base (Scheme 1). Al-
though alcoholates (or strong N-bases such as 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU)) react irreversibly with CO2 to form
carbonic acid half-esters[21] (or carbaminates),[22] phenoxides are
less nucleophilic. This makes them suitable bases to work with
under CO2-pressure conditions.
Table 2. Variation of phenoxide, temperature, and stoichiometry.
Catalytic reactions under CO2 and ethylene pressure (10 and
5 bar) with sodium 3-fluorophenoxide (50 equiv) and the es-
tablished ligand dtbpe[19] gave a TON of 9 (Table 1). Monoden-
Entry
Phenoxide
TON
Temp.
base/cat.
(DuanPhos)
[8C]
1[a]
3
4
80
80
50
50
Table 1. Variation of ligand and solvent.
2[a]
3[a]
4
80
80
50
50
Ligand
TON
Ligand
TON
dtbpe
dcppe”2 HBF4
dippp
(S)-BINAPINE
(S,S,R,R)-TangPhos
(R,R)-QuinoxP*
9
2
5
10
14
4
Dcpe
3
6
2
16
1
2
dippe
dippb
4[a]
8 (16)
(R,R,S,S)-DuanPhos
Dcpf
(R,R)-Me-DuPhos
5[a]
10 (21)
35 (24)
31 (21)
39 (31)
69 (28)
80
80
50
50
50
100
100
200
300
6[a]
100
120
100
100
100
100
2 (DMF)
10 (PhCl, THF)
13 (dioxane)
17 (toluene)
7[a]
8[b]
9[c]
4
10[c]
11[c]
107
Conditions: Sodium 3-fluorophenoxide (10 mmol), Ni(COD)2 (0.2 mmol),
ligand (0.22 mmol), C2H4 (5 bar), CO2 (10 bar), 20 h.
12[a]
2
1
80
50
13[a]
80
50
tate phosphines (i.e., PPh3, PtBu3) and small bite-angle ligands
(i.e., dtbpm, dppm) failed in the reaction. Comparably high
TONs (10–16) were obtained with the electron-rich P-stereo-
genic bisphosphine ligands (S)-BINAPINE,[23] (S,S’,R,R’)-Tang-
Phos,[24] (1R,1’R,2S,2’S)-DuanPhos,[25] and (R,R)-BenzP*,[26] where-
as dcpf, HiersoPHOS-1,[27] (R,R)-QuinoxP*[28] and the bisphos-
pholane (R,R)-Me-DuPhos were only moderately active (Table 1,
TON 1–4).[11b] In the homologous series of bidentate ligands
dippe, dippp, and dippb, a C2–3 bridge between the donor
atoms turned out to be beneficial (TON up to 6), whereas
[a] Ligand (0.22 mmol), Ni(COD)2 (0.2 mmol), CO2 (10 bar), C2H4 (5 bar),
sodium phenoxide (10 mmol); [b] As [a] but ligand (0.11 mmol), Ni(COD)2
(0.1 mmol), 1008C. [c] As [b] with zinc (10 mmol), CO2 (20 bar), C2H4
(10 bar).
as its derivatives bearing substituents with +I effect in ortho-
position (i.e., sodium 2-methyl- and 2,6-dimethyl-phenoxide,
Table 2, entries 2 and 3) gave comparably low TONs (ca. 4). In
a series of fluoro phenoxides (substituent with ÀI effect), the
meta- or even better ortho-substituted derivative led to an in-
crease in TON but not the para-substituted one (TON 8, 10,
and 2, respectively, cf. Table 2, entries 3, 4, and 12). This trend
holds true for DuanPhos (TON 16 and 21, respectively, cf.
Table 2, entries 4 and 5), albeit at a lower level. The activity of
the phenoxide seems to correlate with its pKa value in H2O
t
i
amongst the substituents at the P-donor a Bu or Pr group
gave the highest activity (TONs of 9 and 6, respectively).
The solvent had a major impact on the reaction outcome
(Table 1), whereas ligands such as BenzP* were only moderate-
ly active in DMF (or inactive in MeOH), apolar and aprotic sol-
vents like ethers (THF, dioxane) or even toluene led to higher
reactivity (TON 17). In chlorobenzene oxidative addition to
form NiII turned out to be a limiting side-reaction.[29] Even
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Communication
Terminal, unactivated alkenes or
internal ones did not react to
give the corresponding acrylates,
most likely due to their lower
tendency to form the initial
BenzP*-Ni0-alkene complex simi-
lar to 4 (e.g., cyclopentene, nor-
bonene,
(Z)-3-hexene;
cf.
Scheme 2), or the corresponding
lactones akin to 5 (e.g., propyl-
ene, 1-hexene).
Apart from ethylene (high
TON of 107; cf. Table 3, entry 1),
the reaction also tolerates differ-
ent functional groups. This is es-
pecially true for 1,3-butadienes:
while n-butylvinylether gave
only traces of sodium 3-me-
thoxy-2-propenoate, the corre-
sponding (E)-1-methoxy-1,3-bu-
tadiene yielded sodium (E,E)-5-
methoxy-2,4-pentadienoate with
a reasonably high TON of 99
(Table 3, entries 5 and 6). Similar-
ly, an (E,Z)-mixture of methyl 2,4-
pentadienoate yielded a mixture
of muconic acid isomers with an
Scheme 2. Catalytic cycle and solid-state structure of lactone 5. Ellipsoids drawn at 50% probability. Hydrogen
atoms are omitted for clarity. Selected bond lengths [Š] and angles [8]: NiÀC 1.955(4), NiÀO 1.890(2), NiÀP1
2.1887(10), NiÀP2 2.1193(9), O-Ni-C 85.61(13), P-Ni-P 89.04(4).
with a maximum for sodium 2-fluorophenoxide (pKa =8.82).[31]
Clearly, a base successful in the reaction is sufficiently Brønst-
ed-basic to deprotonate nickelalactone 5, and of reasonably
poor nucleophilicity to avoid its neutralization by reacting with
CO2 (Scheme 2).
overall TON of 75 (Table 3, entry 7). 2-Vinylpyridine was the
only substrate that produced the salt of an a-branched a,b-un-
saturated acid, albeit with a low TON value (TON 2; Table 3,
entry 8). Out of the three different double bonds of the natural
product myrcene, only the least substituted one was trans-
formed with very high (E)-selectivity to the corresponding
linear a,b-unsaturated carboxylic acid derivative (TON of 11; cf.
Table 3, entry 14).
The addition of finely powdered zinc (100 equiv) had a bene-
ficial effect on the reaction with BenzP* (TON 69 vs. 39;
Table 2, entry 9). A huge excess of base (300 equiv) increased
TON further (107 vs. 69 for BenzP*; Table 2, entry 11). Most
likely the metal reduced intermediately formed NiII species. The
effect was less pronounced for DuanPhos (TON 28 vs. 31;
Table 2, entries 9 and 10).
In conclusion, we have found a robust Nickel catalyst and re-
action setup for the one-pot, direct carboxylation of activated
alkenes, such as ethylene, styrenes, and 1,3-dienes with CO2.
The a,b-unsaturated carboxylic acid salts are formed in high
yields and selectivity for the linear product. This method might
pave the way for more efficient routes to basic chemicals such
as acrylates, methacrylates, and sorbates, but also enrich the
organic chemist’s toolbox to access more complex molecular
architectures.
Amongst a series of activated alkenes, that is, styrenes, Mi-
chael acceptors, and 1,3-butadienes, CO2 was only incorporat-
ed once into the product (Table 3). (E)-Configured starting al-
kenes yielded exclusively (E,E)-configured products. Thus, 1,3-
butadiene and (E)-piperylene gave exclusively the linear mono-
carboxylated a,b,g,d-unsaturated carboxylic acids salts
(TON 116 and 90, respectively; Table 3, entries 9 and 10). One
or even two alkyl substituents on the double bonds significant-
ly reduced reactivity (cyclohexadiene, isoprene, 2,3-dimethyl-
butadiene, TONs from 7–64; Table 3, entries 11–13). In the case
of isoprene, where there are two terminal double bonds for
a potential reaction with CO2, both products were formed in
roughly equimolar amounts (TON 7 and 9; Table 3, entry 12).
The reaction of styrene and CO2 under optimized reaction con-
ditions yielded only sodium (E)-cinnamate (TON 12; Table 3,
entry 2).[32] Electron-donating or -withdrawing groups in the 4-
position of the styrene frame (i.e., R=OMe or CF3) led to a reac-
tivity drop represented by a TON<10 (Table 3, entries 3 and 4).
Acknowledgements
N.H., I.J., A.G., M.L.L., R.L., M.B., A.Y.K., P.H., and M.L. work at
CaRLa of Heidelberg University, which is co-financed by Heidel-
berg University, the state of Baden-Württemberg, and BASF SE.
Support from Bundesministerium für Bildung und Forschung
(BMBF) (grant 01RC1015A) is gratefully acknowledged.
Keywords: carbon dioxide
·
catalysis
·
CÀC coupling
reactions · metallacycles · nickel
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237–246.
[25] (1R,1’R,2S,2’S)-DuanPhos=(1R,1’R,2S,2’S)-2,2’-di-tbutyl-2,3,2’,3’-tetrahy-
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[28] (R,R)-QuinoxP*=(R,R)-(À)-2,3-bis(tbutylmethylphosphino)quinoxaline, cf.
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[23] (S)-BINAPINE=(3S,3’S,4S,4’S,11bS,11’bS)-(+)-4,4’-di-tbutyl-4,4’,5,5’-tetra-
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Received: October 5, 2014
Published online on && &&, 0000
Chem. Eur. J. 2014, 20, 1 – 6
www.chemeurj.org
5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
COMMUNICATION
&
Alkene Carboxylation
N. Huguet, I. Jevtovikj, A. Gordillo,
M. L. Lejkowski, R. Lindner, M. Bru,
A. Y. Khalimon, F. Rominger, S. A. Schunk,
P. Hofmann, M. Limbach*
&& – &&
Dream Reactions: The nickel-catalyzed
one-pot carboxylation of alkenes with
CO2 allows the direct and selective syn-
thesis of a wide range of unsaturated
carboxylates from alkenes and alka-
dienes in high selectivity.
Nickel-Catalyzed Direct Carboxylation
of Olefins with CO2: One-Pot Synthesis
of a,b-Unsaturated Carboxylic Acid
Salts
&
&
Chem. Eur. J. 2014, 20, 1 – 6
www.chemeurj.org
6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!