Palladium-catalyzed carbonylative synthesis of acylstannanes from aryl iodides and hexamethyldistannane

Article abstract of DOI:10.1016/j.jorganchem.2020.121351

In this communication, we describe a new method for the carbonylative synthesis of acylstannanes from aryl iodides and hexamethyldistannane. With Pd(PPh₃)₄ as the catalyst and toluene as the solvent at 60 °C under 10 bar CO for 16 h, the desired acylstannanes were obtained in good to excellent yields. In order to facilitate isolation and analysis, the obtained acylstannanes were transformed into the corresponding benzoic acids by simply stirring under air for 5 h.

Full text of DOI:10.1016/j.jorganchem.2020.121351

Journal Pre-proof
Palladium-catalyzed carbonylative synthesis of acylstannanes from aryl iodides and
hexamethyldistannane
Bo Chen, Yang Yuan, Jian-Xing Xu, Robert Franke, Xiao-Feng Wu
PII:
S0022-328X(20)30253-9
DOI:
https://doi.org/10.1016/j.jorganchem.2020.121351
JOM 121351
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 7 May 2020
Revised Date: 19 May 2020
Accepted Date: 21 May 2020
Please cite this article as: B. Chen, Y. Yuan, J.-X. Xu, R. Franke, X.-F. Wu, Palladium-catalyzed
carbonylative synthesis of acylstannanes from aryl iodides and hexamethyldistannane, Journal of
Organometallic Chemistry (2020), doi: https://doi.org/10.1016/j.jorganchem.2020.121351.
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Palladium-Catalyzed Carbonylative Synthesis of Acylstannanes from
Aryl Iodides and Hexamethyldistannane
Bo Chen,a Yang Yuan,a Jian-Xing Xu,a Robert Franke,b Xiao-Feng Wu*a
a. Leibniz-Institut für Katalyse e. V. an der Universität Rostock, Albert-Einstein-Straβe 29a, 18059 Rostock, Germany
E-Mail: Xiao-Feng.Wu@catalysis.de
b. Evonik Industries AG, Paul-Baumann-Str. 1, D-45772 Marl, Germany, and Lehrstuhl für Theoretische Chemie, Ruhr-
Universität Bochum, Universitätsstraße 150, D-44780 Bochum, Germany
Dedicated to Professor Laszlo Kollar on the occasion of his 65th birthday!
ABSTRACT: In this communication, we describe a new method for the carbonylative synthesis of acylstannanes from aryl iodides
and hexamethyldistannane. With Pd(PPh3)4 as the catalyst and toluene as the solvent at 60 ℃ under 10 bar CO for 16 h, the desired
acylstannanes were obtained in good to excellent yields. In order to facilitate isolation and analysis, the obtained acylstannanes
were transformed into the corresponding benzoic acids by simply stirring under air for 5 hours.
Keywords: Palladium catalyst; carbonylation; aryl iodides; acylstannane; cross-coupling
Recently, acylsilanes as versatile synthetic building blocks
have been employed in various interesting transformations in
organic synthesis.[1] Since Brook and Corey independently report-
ed the first example for the synthesis of acylsilanes,[2,3] a number
of methods for synthesis of acylsilanes have been developed.[4,5]
In 2012, a palladium-catalyzed carbonylative coupling of aryl
iodides with TMS-TMS to give the corresponding Acyl-TMS was
developed in Beller’s group.[5] However, their heavier congeners,
acylgermanes and acylstannanes, group-14 element compounds,
don’t get much attention as acylsilanes, despite their theoretical
and practical interest in organic synthesis. Recently, our group
reported a carbonylative method for synthesis of acylgermanes.[6]
From the same strategy, we envisage the synthesis of acylstan-
nanes through a carbonylative reaction. From literature, some
methods have been developed for the preparation of acylstannanes
(Scheme 1). In 1968, Peddle reported the first example for synthe-
sis of acylstannanes by the addition of triphenyltinlithium to acyl
chlorides at -70℃(Scheme 1a).[7] Subsequently, Quintard and co-
workers able to prepare acylstannanes from aldehydes and a Sn-
Mg organometallic reagent (Scheme 1b).[8] In addition, Hassner
and co-workers developed a method for the preparation of
acylstannanes by acidolysis of stannylated alkyl vinyl ethers
(Scheme 1c).[9] In 1983, Klumpp and co-workers obtained
acylstannanes through hydrolysis of a 1,3-dioxane derivative
(Scheme 1d).[10] In 1990, Mitchell and co-workers got acylstan-
nanes by reacting acyl chlorides with hexamethylditin in the
presence of palladium catalysts (Scheme 1e).[11] Additionally,
Sander and co-workers described a method for the preparation of
acylstannanes through photolysis of stannylfuranes (Scheme
1f).[12]
Scheme 1. Methodologies for Acylstannanes Synthesis

On the other hand, since Heck and co-workers reported the
first example in 1970s, Pd-catalyzed coupling reaction of aryl
halides with CO and different nucleophiles has been widely used
not only in academia but also in industry for the preparation of the
carbonyl-containing compounds.[13] In 1985, in their studies on
palladium-catalyzed synthesis of symmetrical ketones or
diketones from aroyl chlorides and Et6Sn2, Bumagin and co-
workers described one example on palladium-catalyzed synthesis
of 4,4’-dimethoxybenzil (71% yield) from 4-iodoanisole (2 equiv)
3
4
5
6
7
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
THF
60
66
THF
80
34
THF
100
60
7
Toluene
92(83)b
1,4-
Dioxane
DCE
60
68
o
in the presence of Et6Sn2 under CO pressure (8 bar) at 111 C.[14]
8
Pd(PPh3)4
Pd(PPh3)4
-
60
60
60
60
60
60
60
57
0
The authors proposed acylstannane as the intermediate, which is
most likely the case, however, no detection of acylstannane was
possible rather than diketone and ketone.
Based on our continual research interests in carbonylation
chemistry, we report here a new method for the synthesis of
acylstannanes by palladium-catalyzed carbonylation of aryl io-
dides with hexamethyldistannane.
9
MeCN
10
11
12
13c
14d
Toluene
Toluene
0
CuI/Bipyridine
0
NiBr2/Bipyridine Toluene
0
The initial investigation was carried out with 1-iodo-4-
methoxybenzene and hexamethyldistannane as the substrates. To
Pd(PPh3)4
Pd(PPh3)4
Toluene
Toluene
61
91
our
delight,
the
desired
product
(4-
methoxy)benzoyltrimethylstannane could be detected on GC-MS
as the major product with Pd(PPh3)4 as the catalyst in THF at 80
°C for 16 hours under 10 bar CO. However, the acylstannane was
sensitive to oxygen and light, we failed to isolate the acylstan-
nanes by column chromatography. In order to obtain isolated
yield and spectroscopic characterization, the acylstannane product
was completely oxidized under air to give the corresponding
benzoic acid. Then we screened parameters to establish the opti-
mal conditions for this reaction (Table 1). In the screening of
reaction temperature, we found that temperature was critical to the
reaction, too high or too low temperature was not conducive to the
improvement of yield and 60 was the best temperature for this
reaction (Table 1, entries 1-5). Low reaction temperature leads to
low conversion of substrates, while arylstannane becomes the
main product under higher reaction temperature. Next, a set of
solvents were tested, and the yield increased significantly to 92%
when toluene was employed (Table 1, entry 6). 1,4-Dioxane and
DCE gave moderate yields (Table 1, entries 7 and 8), no product
was detected in MeCN (Table 1, entry 9). When we removed the
palladium catalyst or changed the catalyst to Cu or Ni, this reac-
tion could not proceed at all (Table 1, entries 10-12). It revealed
the unique and important catalytic role of palladium in this car-
bonylative reaction. The target product can still be produced in
61% yield when we carried out the reaction under atmospheric
pressure CO (Table 1, entry 13). Finally, we were delighted to
find that the catalyst loading can be decreased to 1 mol% while
gave a similar yield 91% (Table 1, entry 14). In order to compare
with Bumagin’s system, 2 equiv of 4-iodoanisole was added
under our standard condition and 4,4’-dimethoxybenzil become
the main product even under lower reaction temperature. Hence,
the product selectivity between arylstannane and ketone is mainly
controlled by the loading aryl iodides added.
aReaction conditions: 1a (0.2 mmol), 2 (0.22 mmol), catalyst (2 mol %), solvent (0.5
mL), 10 bar CO, 16 h, then stirring under air 5 h, NMR yield. bisolated yield. c1 bar
CO. dcatalyst (1 mol %)
With the optimal reaction conditions in hand, we then tested
other aryl iodides in this carbonylative reaction (Table 2). First,
we tried iodobenzene as the starting material, the expected benzo-
ic acid was obtained with 71% yield under the standard conditions
(3b). As shown in Table 2, iodobenzenes with methyl-substituted
at different positions could be well tolerated and delivered the
target products in good to excellent yields (3c-3f). When the
substituents were replaced with ethyl and tert-butyl, the corre-
sponding products were achieved with 64% and 83% yields,
respectively (3g, 3h). Moreover, the reaction with 1-
iodonaphthalene proceeded smoothly as well and gave the desired
product in 87% yield (3i). Gratifyingly, N-pyrrole-substituted
iodobenzene was also well tolerated in this transformation, deliv-
ering the corresponding benzoic acid in 54% yield (3j). When the
methoxy group located in the meta-position, the yield was lower
than in the para-position (3k). As the number of substituted
methoxy groups increased, the yield of the corresponding product
increased (3l). Unfortunately, substrates with electron-
withdrawing groups, such as -Cl, -F, -CF3, -COOMe, lead to low
yields of the target products (< 10%; see Support Information).
One of the main reasons was that the acylstannanes from electron-
withdrawing substituted aryl iodides are easily to go to decar-
bonylation to give ArSnMe3 even under low pressure of carbon
monoxide. ArSnMe3 were detected in these cases. Additionally,
(Bu3Sn)2 and (Et3Sn)2 were tested with 1-iodo-4-methoxybenzene
under our standard conditions as well, but no desired products
could be detected. It is also important to mention that a control
experiment without hexamethyldistannane was carried out as
well. Only trace amount of the corresponding carboxylic acid was
detected in GC-MS which might due to the trace amount of water
in the solvent and produced via hydroxycarbonylation.
Table 1. Optimization of the Reaction Conditions.a
Based on our results and literature,[15-20] a plausible reaction
pathway is proposed in Scheme 2. First, oxidative addition of
palladium to aryl iodide to obtain arylpalladium complex A. Next,
acylpalladium complex B is generated by the migratory insertion
of carbon monoxide. Subsequently, intermediate B undergoes
transmetalation with distannane to give stannyl complex C, and
the by-product ISnMe3 can be detected on GC-MS. The final
acylstannane products can be delivered by reductive elimination
from complex C, and meanwhile regenerate the active palladium
species for the next catalytic cycle.
entry catalyst
solvent
temp
yield
(%)
trace
1
2
Pd(PPh3)4
Pd(PPh3)4
THF
THF
r.t.
40
5

Table 2. Synthesis of Acylstannanes from Aryl Iodides. Reac-
tion scale: 0.50 mmol, isolated yields.
In conclusion, an interesting procedure for the synthesis of
acylstannanes from aryl iodides and hexamethyldistannane by
direct carbonylation has been developed.[16-20] With Pd(PPh3)4 as
the catalyst and toluene as the solvent at 60 under 10 bar CO
for 16 h, the desired acylstannanes were obtained in good to ex-
cellent yields which can be easily converted into the correspond-
ing benzoic acids by simply stirring under air.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
We thank the Chinese Scholarship Council (CSC) for financial
support. The analytical support of Dr W. Baumann, Dr C. Fisher,
S. Buchholz, and S. Schareina is gratefully acknowledged (all in
LIKAT).
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264.

1. The first palladium catalyzed carbonylative synthesis of acylstannanes from aryl iodides and
hexamethyldistannane has been developed.
2. With Pd(PPh3)4 as the catalyst at 60 ℃, the desired acylstannanes were obtained in good to
excellent yields.
3. The obtained acylstannanes can be transformed into the corresponding benzoic acids by simply
stirring under air.

We have no conflict of interest to declaration!