Acid Chloride Synthesis by the Palladium-Catalyzed Chlorocarbonylation of Aryl Bromides

Article abstract of DOI:10.1002/chem.201500476

We report a palladium-catalyzed method to synthesize acid chlorides by the chlorocarbonylation of aryl bromides. Mechanistic studies suggest the combination of sterically encumbered PtBu₃ and CO coordination to palladium can rapidly equilibrate the oxidative addition/reductive elimination of carbon-halogen bonds. This provides a useful method to assemble highly reactive acid chlorides from stable and available reagents, and can be coupled with subsequent nucleophilic reactions to generate new classes of carbonylated products. The Good, the Bad and the Bulky! By employing a sterically encumbered phosphine ligand, tri-tert-butyl phosphine, under palladium catalysis inert aryl bromides are chlorocarbonylated to create reactive acid chlorides by reversible carbon-halogen bond reductive elimination. This general platform allows for an expanded scope of the Heck carbonylation reaction to include previously incompatible nucleophiles.

Full text of DOI:10.1002/chem.201500476

DOI: 10.1002/chem.201500476
Full Paper
&
Organic Synthesis
Acid Chloride Synthesis by the Palladium-Catalyzed
Chlorocarbonylation of Aryl Bromides
Jeffrey S. Quesnel, Laure V. Kayser, Alexander Fabrikant, and Bruce A. Arndtsen*[a]
Abstract: We report a palladium-catalyzed method to syn-
thesize acid chlorides by the chlorocarbonylation of aryl bro-
mides. Mechanistic studies suggest the combination of steri-
cally encumbered PtBu3 and CO coordination to palladium
can rapidly equilibrate the oxidative addition/reductive elim-
ination of carbon–halogen bonds. This provides a useful
method to assemble highly reactive acid chlorides from
stable and available reagents, and can be coupled with sub-
sequent nucleophilic reactions to generate new classes of
carbonylated products.
Introduction
Palladium-catalyzed bond-forming reactions have become
among the most heavily exploited transformations in synthetic
chemistry. A common feature of these reactions is the genera-
tion of a robust and inert CÀC, CÀN, or CÀO bond, which to-
gether with the byproducts (e.g. metal salts) provide a strong
driving force for reaction. In contrast, there has been recent in-
terest in using palladium catalysis to create more reactive co-
valent bonds, such as carbon–halogen containing products.
Hartwig illustrated this potential in the stoichiometric reductive
elimination of aryl halides induced by sterically encumbered li-
gands.[1] Lautens, Buchwald, Tong, Jiang, and others have
shown these reactions can be applied in catalysis, thereby al-
lowing the efficient generation of carbon–halogen containing
products.[2,3] These methods typically involve halide (or pseu-
dohalide) metathesis (Scheme 1a) or alkene/alkyne insertion
followed by reductive elimination (Scheme 1b). We have simi-
larly reported that the palladium-catalyzed carbonylation of
aryl iodides can allow the synthesis of acid chlorides.[4] In con-
trast to many the above examples, acid chlorides are them-
selves reactive towards oxidative addition to Pd0 complexes.[5]
However, the aryl iodide bond in the substrate is significantly
weaker than in the acid chloride, and allows it to compete for
addition to palladium.
Scheme 1. Catalytic sp2- and sp3-carbon–halogen bond-forming reactions.
more reactive bonds than in the substrate. A practical limita-
tion of the catalytic synthesis of acid chlorides is its reliance on
aryl iodides, which are often as expensive as acid chlorides, are
unstable, and can be challenging to prepare. In contrast, aryl
bromides are attractive building blocks in synthesis, less ex-
pensive, and, with the advent of cross-coupling reactions, are
now generally available. Employing aryl bromides in palladi-
um-catalyzed transformations is often a matter of overcoming
the higher kinetic barrier for oxidative addition. However, an
unusual challenge in this case is relative bond strengths, as the
aryl bromide bond is not only stronger than that of aryl io-
dides (PhÀBr, Ph-I: 75 and 65 kcalmolÀ1, respectively), but is
also as strong as the CÀCl bond in the acid chloride product
(PhCOÀCl: 74 kcalmolÀ1).[6] More importantly, the aryl bromide
substrate is orders of magnitude less reactive towards the Pd0
From an energetic standpoint, the use of catalytic bond-
forming reactions to convert stable building blocks into prod-
ucts that are themselves reactive can provide a useful ap-
proach in synthesis. In considering these features, we became
interested in whether reactions such as carbonylations could
be extended to form products with a weak and significantly
[a] J. S. Quesnel, L. V. Kayser, A. Fabrikant, Prof. B. A. Arndtsen
Department of Chemistry, McGill University
801 Sherbrooke Street West, Montreal
H3A 0B8 Quebec (Canada)
E-mail: bruce.arndtsen@mcgill.ca
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201500476.
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catalyst than acid chlorides. This can be seen in the reaction of
Pd(PtBu3)2 with benzoyl chloride in bromobenzene solvent,
which leads to the exclusive oxidative addition of the CÀCl
bond [Eq. (1)].[7] This reaction would therefore require what is
to our knowledge the unique use of palladium-catalyzed car-
bonylations to create a product that has both a weak bond
and is orders of magnitude more reactive than the substrate,
without becoming inhibited by product growth (Scheme 1c).
Table 1. Ligand screening for catalytic acid chloride synthesis.[a,b]
Entry
L
Yield
1
2
3
4
5
6
PtBu3
PPh3
P(o-tolyl)3
PCy3
PtBu2(neopentyl)
PtBu3
34[c]
2
2
0
41
54 (56)[d]
7
11
We describe below how sterically encumbered phosphines
can overcome the relative barriers of aryl bromide and acid
chloride oxidative addition. Mechanistic studies suggest this re-
flects the ability of phosphine and carbonyl-coordinated palla-
dium to rapidly equilibrate the oxidative addition/reductive
elimination of carbon–halogen bonds. From a synthetic per-
spective, coupling the catalytic formation of acid chlorides
with their subsequent reactivity allows the application of car-
bonylations to nucleophiles not typically viable in this chemis-
try.
8
9
5
0
10
11
39
4
Results and Discussion
Catalyst development
12
13
14
15
dcpe
dppe
dppp
dppb
0
1
2
1
Initial studies examined the reaction of the electron-rich 4-bro-
moanisole in the presence of chloride salts. The use of our pre-
vious conditions for aryl iodide carbonylation leads to a low
yield of acid chloride together with catalyst decomposition
(Table 1, entry 1). We therefore examined lower temperatures
and higher catalyst loadings with a broad range of ligands, in-
cluding trialkyl-, triaryl-, and dialkylarylphosphines, as well as
N-heterocyclic carbenes (for the full scope of ligands, see Sup-
porting Information). In contrast to our results with aryl io-
dides, a number of sterically encumbered ligands allow the for-
mation of acid chloride in low yield (entries 5–8, and 10). The
influence of ligand sterics on this reaction is dramatic: relative
to PtBu3 (entry 6), the slightly smaller PtBu2(neopentyl)
(entry 5) and P(1-adamantyl)2nbutyl (entry 7) lead to lower
yields, while PCy3, triarylphosphines, and aryldialkylphosphines
show very little catalytic activity, nor do NHCs. As a palladium
precipitate is generated during many of these reactions, che-
lating phosphines were also examined. While most of these
are also inactive, the large bite angle Xantphos (entry 16) pro-
vides comparable yields to PtBu3.
16
17
48 (47)[d]
5
18
19
0
PtBu3
84[e] (74)[f]
[a] 4-Bromoanisole (47 mg, 0.25 mmol), Ph3PBnCl (146 mg, 0.375 mmol),
[Pd2(dba)3]·CHCl3 (13 mg, 12.5 mmol), L (25 mmol), CO (4 atm), 2 mL PhMe,
110 8C, 24 h. [b] NMR yield. [c] 2.5 mol% [Pd2(dba)3]·CHCl3, 1308C.
[d] 10 mol% [PdL2]. [e] 10 mol% [PdL2], CO (20 atm.). [f] 5 mol%
[Pd(PtBu3)2], CO (20 atm.). dba=dibenzalacetone; dcpe=1,2-bis(dicyclo-
hexylphosphino)ethane;
dppp=1,2-bis(diphenylphosphino)propane; dppb=1,2-bis(diphenylphos-
phino)butane.
dppe=1,2-bis(diphenylphosphino)ethane;
The limitation of even the best catalyst systems at approxi-
mately 50% conversion is presumably the result of product in-
hibition, as the acid chloride generated in the reaction can
preferentially add to palladium relative to the aryl bromide
substrate. In probing methods to overcome this limitation, we
found that CO pressure can itself facilitate catalysis. Although
added CO pressure has minimal influence with many of the li-
gands in Table 1, performing the catalytic reaction with the
largest ligand, PtBu3, at high CO pressure leads to high yield of
acid chloride (Table 1, entry 19). Under these conditions, the
catalyst loading can be lowered without a significant loss in ac-
tivity, and proceeds equally well with Pd(PtBu3)2. Bu4NCl can
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also be employed as a chloride source, albeit in diminished
yields (see Supporting Information for other chloride sources).
Mechanistic studies
The above studies suggest that the sterically encumbered
PtBu3 ligand and CO pressure can favor both the reductive
elimination of a weak and reactive ArCOÀCl bond, and at the
same time the competitive activation of the significantly less
reactive ArÀBr reagent. This catalyst is the same to that identi-
fied as being unique for acid chloride synthesis from aryl io-
dides.[4] Nevertheless, it is notable that a number of ligands
can allow acid chloride formation from aryl bromides in mod-
erate yield, which suggests that acid chloride reductive elimi-
nation may be more common than previously considered in
carbonylations.
To gain a more complete mechanistic understanding of this
reaction, we have prepared and structurally characterized
a series of palladium–aroyl complexes, including that of the
moderately active P(1-Ad)2nBu ligand, and compared it to com-
plexes of highly active (PtBu3) and inactive (PPh3) ligands
(Scheme 2a). Unlike the rapid, room temperature reductive
elimination of acid chloride from 2a we have previously noted
with aryl iodide trap [(PtBu3)Pd0],[4] complexes 2a–c do not un-
dergo a similar exchange with the significantly less reactive
aryl bromide substrate. However, these experiments probe two
steps: the rate of elimination of acid chloride and of aryl halide
addition to palladium. A more accurate method to examine re-
ductive elimination from complexes 2 is by scrambling experi-
ments. As shown in Scheme 2b, no reaction is observed be-
tween p-toluoyl chloride and any of these complexes alone,
but the addition of CO initiates a rapid reaction with the PtBu3
complex 2a, and the near quantitative liberation of p-anisoyl
chloride after 1 h. The monophosphine complex 2b undergoes
slower exchange, and this rate becomes insignificant with the
bis-PPh3 complex 2c.
The relative reactivity of these complexes parallels the cata-
lytic activity in Table 1 (PtBu3 >P(1-Ad)2nBu@PPh3). It is also
consistent with marked differences in the coordination envi-
ronments of complexes 2a–c. The larger catalytically active li-
gands in 2a and 2b generate monophosphine complexes that
would be amenable for CO coordination, and CO-assisted re-
ductive elimination.[4] Comparison of the structures of 2a and
2b provides potential insight into the significantly higher reac-
tivity of 2a. Relative to the pseudo-square-planar P(1-Ad)2nBu
complex 2b, the PtBu3 complex 2a adopts a three-coordinate,
T-shaped structure due to the disfavored occupation of the
fourth coordination site on palladium by the three sterically
congested tBu units.[8] One possibility for the unusual ability of
2a to undergo rapid reductive elimination may therefore be
the steric strain induced upon CO association to palladium,
which together with the withdrawal of electron density by CO
leads to favorable, strain-relief reductive elimination of acid
chloride. This phenomenon would be expected to be most
pronounced with three large units on the phosphine (e.g.
Table 1, entries 5, 6, and 10), relative to other seemingly large
ligands lacking this tertiary steric bulk (entries 7–9).[9] Neverthe-
Scheme 2. a) Atoms are represented by Gaussian ellipsoids at the 50% prob-
ability level. Hydrogen atoms are omitted for clarity and only half of palladi-
um dimer 2b shown. b) Data in brackets at 508C. PMP=p-methoxyphenyl.
less, even moderately sized ligands such as P(1-Ad)2nBu can
undergo acid chloride elimination at temperatures well below
that of catalysis (Scheme 2b).
CO also appears to influence the thermodynamics of reduc-
tive elimination. Subjecting the PtBu3 complex 2a to 1 atm. of
CO without any trapping reagent results in the rapid equilibri-
um formation of acid chloride within minutes at ambient tem-
perature [Eq. (2)]. Removal of CO regenerates 2a, and increas-
ing CO pressures further favors this equilibrium. These results
suggest that CO can itself favor the formation of acid chloride
elimination from 2a, likely by generating an electron-poor Pd0-
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carbonyl complex that is less reactive towards the electrophilic
acid chloride.[10] Complexes 2b and 2c undergo a similar CO-
induced acid chloride elimination, but at significantly slower
rates.[11]
Table 2. Palladium-catalyzed carbonylation of aryl bromides to acid chlor-
ides.[a]
The rapid formation of acid chloride from 2a with CO
(within minutes at ambient temperature) shows that reductive
elimination is unlikely to be rate-determining in catalysis. Pre-
liminary kinetic experiments on the catalytic reaction are con-
sistent with the stoichiometric studies. These show a linear
rate dependence on CO pressure with the first order disap-
pearance of aryl bromide (see the Supporting Information),
and in situ 31P NMR spectroscopic analysis (at 5 atm. CO) re-
veals that complex 2a is the major catalyst resting state. Over-
all, these data suggest that the catalytic generation of acid
chloride from aryl bromides proceeds by the reversible build-
up of product and Pd0 from 2a. This equilibrium is favored by
the large PtBu3 ligand (Scheme 2c) and high CO pressure.[12] In
this scenario, catalyst turnover is dependent upon aryl bromide
oxidative addition. The latter is also facilitated by sterically en-
cumbered and strong donor ligands such at PtBu3. These
mechanistic features are summarized in Scheme 3.
[a] Aryl bromide (1.25 mmol), Ph3PBnCl (1.9 mmol), Pd(PtBu3)2 (31.9 mg,
62.5 mmol), 20 atm. CO, PhMe (10 mL), 110 8C, 24 h; isolated yield of the
derivatized products (see Supporting Information). [b] 7.5 mol%
Pd(PtBu3)2; [c] 48 h; [d] 15 mol% PtBu3 added. [e] 1H NMR yield of ester
derivative of 3o. Determined by comparison to data reported in ref. [14].
[f] Standard conditions using 4-methoxychlorobenzene. [g] In neat chloro-
benzene solvent at 1508C.
Scheme 3. Proposed catalytic cycle for aryl bromide chlorocarbonylation.
Scope of catalysis
As shown in Table 2, a range of aryl bromides can be carbony-
lated into acid chlorides with this catalyst system.[13] This in-
cludes arenes with functionality such as aldehydes (3d), nitriles
(3i), and ketones (3 f). Heteroaromatic aryl bromides, which are
much more available and stable than their iodide counterparts,
are also compatible in this reaction manifold (3k, 3l). For nitro-
gen-containing 3m, additional PtBu3 is required to accelerate
the slow reaction, presumably due to the competitive coordi-
nation of the pyridine moiety to the catalyst. Substitution at
the ortho-position is tolerated (3n), although the reaction is
slightly more sluggish, likely as a result of the slower oxidative
addition with the bulkier aryl bromide. Unsymmetrical dibro-
mides can also be carbonylated to diacid chlorides (3o). Inter-
estingly, only minimal monoacid chloride is generated from
this reagent, even at short reaction times,[14] which suggests
the first chlorocarbonylation facilitates a rapid second carbony-
lation to form 3o. Conversely, the more atom-economical car-
bonylation of aryl chlorides to acid chlorides is not kinetically
viable, even with this optimized catalyst system. The latter pre-
sumably reflects the extreme kinetic challenge of activating
aryl chloride bonds in the presence of reactive ArCOCl. Overall,
considering the low cost and broad availability of aryl bro-
mides, and the other reagents (CO, ClÀ), this provides an effec-
tive method to assemble aromatic or heteroaromatic acid
chlorides.
The catalytic generation of acid chlorides offers the potential
to apply aryl bromide carbonylations to new classes of sub-
strates. A traditional limitation in Pd-catalyzed carbonylations
is the scope of nucleophiles that can be employed. For exam-
ple, sterically encumbered, weakly nucleophilic, or palladium-
reactive substrates have traditionally proven problematic in
carbonylations. This is believed to arise from the limited elec-
trophilicity of in situ generated palladium–acyl intermediates,
and the required initial coordination of nucleophiles to palladi-
um for reductive elimination.[15] In contrast, as acid chlorides
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bond-forming reactions, their application to assemble reactive
products such as acid chlorides from stable building blocks
could provide a useful general direction for such systems.
Studies directed towards the latter are currently underway.
Table 3. Synthesis of benzohydrazides by carbonylation.[a]
Experimental Section
In a steel Parr autoclave in a nitrogen glovebox was added 4-bro-
moanisole (234 mg, 1.25 mmol), benzyltriphenyl phosphonium
chloride (727 mg, 1.88 mmol, 1.5 equiv), Pd(PtBu3)2 (32 mg,
0.062 mmol, 5 mol%) and a stir bar. The autoclave was placed in
a Parr system, then charged with carbon monoxide by evacuating
and filling the system three times, and finally pressurized to 20 atm
CO. The reaction was then heated to 110 8C for 24 h with a stirring
rate of 600 RPM. The vessel was then allowed to cool to room tem-
perature, the headspace was evacuated and the vessel was
brought back into the glovebox. The product solution was filtered
over a fine sintered glass frit to remove the insoluble phosphoni-
um salt, the solid rinsed with toluene (3”1 mL), and the reaction
solution derivatized.
Acknowledgements
We thank NSERC, CFI, and FQRNT-supported Centre for Green
Chemistry and Catalysis for their financial support of this work.
[a] 1. Procedure from Table 2; 2. hydrazine hydrate (85%, 0.6 mL), 08C,
2 h.
Keywords: acid chloride
· carbonylation · mechanism ·
palladium · reductive elimination
are highly electrophilic reagents, their catalytic generation can
allow the extension of palladium-catalyzed carbonylations to
nonclassical coupling partners.[16] As an example, simple hydra-
zine is an attractive building block in synthesis but rarely em-
ployed in palladium-catalyzed coupling reactions,[17] including
carbonylations, due in part to the ability of this small nucleo-
phile to coordinate and interfere with bond activation.[18,19] As
shown in Table 3, the in situ generation of acid chloride fol-
lowed by hydrazine addition can provide a straightforward
route to form benzohydrazide derivatives. A diverse range of
aryl- and heteroaryl bromides can be employed in this one
pot, two-step chemistry, each of which undergo rapid reaction
with the in situ formed acid chloride. In light of the rich and
highly-developed chemistry of acid chlorides, this approach
should prove viable in the synthesis of many products typically
inaccessible by carbonylations.
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Conclusion
In summary, we have described the preparation of acid chlor-
ides by carbonylation from aryl bromides. In contrast to tradi-
tional approaches to acid chloride synthesis with high energy
and toxic halogenating agents (e.g. SOCl2, PCl3), or the use of
aryl iodides, this reaction provides an approach to these elec-
trophiles from reagents that are inexpensive, readily available,
and stable (aryl bromides, CO, ClÀ). Catalyst effects are found
to be critical for the generation of the weak and reactive acid
chloride bond, with both sterically encumbered PtBu3 and CO
required to achieve rapid and favored reductive elimination.
Considering the growing significance of palladium-catalyzed
[6] BDE values can vary with the technique employed. Those quoted used
the same method: a) Ph-Br BDE: R. J. Kominar, M. J. Krech, S. J. W. Price,
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Can. J. Chem. 1978, 56, 1589; b) Ph-I BDE: R. J. Kominar, M. J. Krech,
S. J. W. Price, Can. J. Chem. 1976, 54, 2981; c) PhCO-Cl BDE: M. Szwarc,
J. W. Taylor, J. Chem. Phys. 1954, 22, 270; for other sources: d) Y. R. Luo,
Comprehensive Handbook of Chemical Bond Energies, CRC Press, Boca
Raton, 2007 and references therein.
[13] Due to the similar boiling points and solubility of aryl bromides and
acid chlorides, acid chlorides were converted to the corresponding
esters for isolation and characterization (see the Supporting Information
for details).
[14] 1H NMR spectroscopic analysis of crude mixture at 24 h shows 36%
diacid chloride relative to 14% monoacid chloride, and 50% starting
material, by comparison to known ester derivatives: a) L. Anzalone, J. A.
Hirsch, J. Org. Chem. 1985, 50, 2128; b) K. S. Song, S. K. Lee, M. J. Kim,
H. J. Seo, J. Lee, S. H. Lee, M. E. Jung, E. J. Son, M. Lee, J. Kim, J. Lee, ACS
Med. Chem. Lett. 2011, 2, 182.
[15] Carbonylations typically show significant nucleophile scope limitations
relative to acid chlorides. For reviews, see: a) X.-F. Wu, H. Neumann, M.
Beller, Chem. Rev. 2013, 113, 1; b) R. Grigg, S. P. Mutton, Tetrahedron
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[7] While the rate constant for PhBr oxidative addition to Pd(PtBu3)2 is not
known due to complications of product decomposition, the half-life of
this reaction is approximately 6.5 h at 708C (F. Barrios-Landeros, B. P.
Carrow, J. F. Hartwig, J. Am. Chem. Soc. 2008, 130, 5842), relative to ca.
10 min for PhCOCl at 258C. Conversely, PhI oxidative addition rates sug-
gest an approximate half-life of 25 min in neat PhI at 258C (F. Barrios-
Landeros, B. P. Carrow, J. F. Hartwig, J. Am. Chem. Soc. 2009, 131, 8141).
[8] Related [RCOPdX(L)] complexes: a) S. Korsager, R. H. Taaning, T. Skrydstr-
up, J. Am. Chem. Soc. 2013, 135, 2891; b) S. Bontemps, J. S. Quesnel, K.
Worrall, B. A. Arndtsen, Angew. Chem. Int. Ed. 2011, 50, 8948; Angew.
Chem. 2011, 123, 9110; c) D. Gauthier, A. T. Lindhardt, E. P. K. Olsen, J.
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geev, A. Spannenberg, M. Beller, J. Am. Chem. Soc. 2008, 130, 15549.
[9] The more accessible coordination site in 2a may also facilitate CO asso-
ciation and elimination. However, we see no evidence for CO binding
to 2a, even at elevated pressures, which suggests this association is
not favored. Similarly, excess PtBu3 does not affect the rate of elimina-
tion, which suggests PtBu3 is not displaced by CO.
[10] For other examples of CO-induced reductive elimination: a) R. Pulukko-
dy, S. J. Kyran, R. D. Bethel, C.-H. Hsieh, M. B. Hall, D. J. Darensbourg,
M. Y. Darensbourg, J. Am. Chem. Soc. 2013, 135, 8423; b) Y. Gloaguen,
L. M. Jongens, J. N. H. Reek, M. Lutz, B. de Bruin, J. I. van der Vlugt, Orga-
nometallics 2013, 32, 4284; c) M. Montag, I. Efremenko, R. Cohen,
L. J. W. Shimon, G. Leitus, Y. Diskin-Posner, Y. Ben-David, H. Salem,
J. M. L. Martin, D. Milstein, Chem. Eur. J. 2010, 16, 328; d) N. M. West, S.
Reinartz, P. S. White, J. L. Templeton, J. Am. Chem. Soc. 2006, 128, 2059;
for a computational study of the role of palladium electronics on CÀX
reductive elimination:e) Y. Lan, P. Liu, S. G. Newman, M. Lautens, K. N.
Houk, Chem. Sci. 2012, 3, 1987.
[17] R. J. Lundgren, M. Stradiotto, Angew. Chem. Int. Ed. 2010, 49, 8686;
Angew. Chem. 2010, 122, 8868.
[18] We are aware of only one report of hydrazine in carbonylative coupling,
and this required high Pd loading (30 mol%), 1508C, and was per-
formed on a 2–3 mg scale: a) F. Karimi, B. Langstrom, J. Chem. Soc.
Perkin Trans. 1 2002, 2111; b) unsuccessful use: D. Marosvçlgyi-Haskó, A.
Petz, A. Takµcs, L. Kollµr, Tetrahedron 2011, 67, 9122.
[19] Examples of the reaction of hydrazine with carbonylated products:
a) M. S. Mohamed Ahmed, K. Kobayashi, A. Mori, Org. Lett. 2005, 7,
4487; b) S. T. Staben, N. Blaquiere, Angew. Chem. Int. Ed. 2010, 49, 325;
Angew. Chem. 2010, 122, 335; for an alternative use of reactive nitrogen
nucleophiles in carbonylation, see: c) F. M. Miloserdov, V. V. Grushin,
Angew. Chem. Int. Ed. 2012, 51, 3668; Angew. Chem. 2012, 124, 3728.
[11] See the Supporting Information for details.
[12] As acid chloride builds up in catalysis, the equilibrium elimination in
Equation (2) will become disfavored. As such, the role CO pressure may
be to make this step kinetically viable near the end of the reaction
(Table 1, entry 19).
Received: February 5, 2015
Published online on May 15, 2015
Chem. Eur. J. 2015, 21, 9550 – 9555
www.chemeurj.org
9555
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