Palladium-catalyzed carbonylative coupling reactions of aryl iodides with hexamethyldisilane (HMDS) to benzoyl silanes

Article abstract of DOI:10.1016/j.tetlet.2011.11.104

A novel procedure for the palladium-catalyzed carbonylative synthesis of acyl silanes has been developed. Starting from aryl iodides and hexamethyldisilane (HMDS) various benzoyl silanes are produced in moderate to good yields.

Full text of DOI:10.1016/j.tetlet.2011.11.104

Tetrahedron Letters 53 (2012) 582–584
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Tetrahedron Letters
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Palladium-catalyzed carbonylative coupling reactions of aryl iodides
with hexamethyldisilane (HMDS) to benzoyl silanes
Xiao-Feng Wu a,b, Helfried Neumann b, Matthias Beller b,
⇑
a Department of Chemistry, Zhejiang Sci-Tech University, Xiasha Campus, Hangzhou, Zhejiang Province 310018, People’s Republic of China
b Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Strasse 29a, 18059 Rostock, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel procedure for the palladium-catalyzed carbonylative synthesis of acyl silanes has been devel-
oped. Starting from aryl iodides and hexamethyldisilane (HMDS) various benzoyl silanes are produced
in moderate to good yields.
Received 20 October 2011
Revised 18 November 2011
Accepted 21 November 2011
Available online 26 November 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Palladium
Carbonylation
Aryl iodides
Acyl silane
HMDS
Apart from being synthetically useful as carbonyl anion equiva-
lents, acyl silanes are of interest in organic chemistry due to their
unusual spectroscopic behavior.1,2 In spite of their broad applica-
tions in organic synthesis, methodologies developed for the conve-
nient preparation of acyl silanes are still rare.3 For example,
benzoyl silanes represent an important sub-class of acyl silanes,
which are formed via palladium-catalyzed reactions of benzoyl
chlorides with hexamethyldisilane (HMDS)3d or trimethyl(tributyl-
stannyl)silane (TMSSnBu3).3i In addition, Seyferth and Weinstein
reported the carbonylation of an organolithium compounds at
À110 °C using CO and TMSCl to give acyl silanes in moderate to
good yields.3g,h Clearly, catalytic carbonylations under milder con-
ditions with more easily available substrates are desired. Based on
our continuing interest on palladium-catalyzed carbonylations of
aryl halides,4 here we wish to report a novel protocol for the palla-
dium-catalyzed carbonylative synthesis of acyl silanes from aryl
iodides.5
In the past two decades palladium-catalyzed carbonylations of
aryl halides have become a powerful tool for the synthesis of all
kinds of substituted (hetero) aromatic carboxylic acids and their
derivatives.6 More recently, aminocarbonylation of aryl halides
with ammonia to primary amides,4b,c carbonylative Sonogashira
reactions of aryl bromides and aryl triflates to alkynones,4f,i as well
as carbonylative Heck reactions of aryl halides and aryl/vinyl tri-
flates to chalcones,4d,h,k were developed in our group. But to the
best of our knowledge, there are no methods known, which allow
for a general carbonylative synthesis of synthetically useful acyl si-
lanes under milder reaction conditions.
At the start of our investigations, we selected the carbonylative
silylation of iodobenzene with HMDS as a model reaction. Based on
the known catalytic silylation of benzoyl chloride,3d we investi-
gated different [(cinnamyl)PdCl]2/phosphite catalyst systems for
this transformation (Table 1, entries 1–7).
To our delight, 30% of the desired product was formed in the
presence of the sterically hindered phosphite. However, increasing
the ligand concentration gave only 10% of the product (Table 1,
entry 2). Except for tri-n-butylphosphite, other tested phosphite
ligands gave only traces of benzoyltrimethyl silane. Next, some
typical phosphine ligands were also tested. Unfortunately, no con-
version was observed in our model reaction (Table 1, entries 8–11).
Similarly, in the presence of nitrogen ligands such as phenanthro-
line and bipyridine not even traces of benzoyltrimethyl silane
could be detected (Table 1, entries 12 and 13). On the other hand,
7
to our surprise using triphenylarsine AsPh3 as ligand 49% of ben-
zoyltrimethyl silane was obtained (Table 1, entry 14). Since AsPh3
gave the best results among the tested ligands (Table 1), we
applied it in further optimization reactions. As shown in Table 2,
several organic solvents were used as reaction medium (Table 2,
entries 1–4). While heptane inhibited the reaction totally and no
reaction was observed, DMF and NMP gave low yields of the
desired silane with low selectivity. 1,4-Dioxane was the most suit-
able solvent and we achieved full conversion with 71% of benzoyl-
trimethyl silane (Table 2, entry 2). Next, some more common
palladium salts were tested as catalyst precursor (Table 2, entries
⇑
Corresponding author. Tel./fax: +86 381 1281 5000.
E-mail address: matthias.beller@catalysis.de (M. Beller).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.11.104

X.-F. Wu et al. / Tetrahedron Letters 53 (2012) 582–584
583
Table 1
Table 3
Palladium-catalyzed carbonylative silylation of phenyl iodide: variation of ligandsa
Palladium-catalyzed carbonylative synthesis of benzoyl silanesa
O
O
I
[(cinnamyl)PdCl]2/AsPh3
1, 4-dioxane, 110 oC, 16 h
I
[(cinnamyl)PdCl]2/L
SiMe3
SiMe3
CO
HMDS
CO
HMDS
R
R
Entry
1
Ligand
Conv.b (%)
31
Yieldb (%)
30
Entry
Aryl iodide
Product
Yieldb (%)
88
tBu
I
O
1
2
P
O
tBu
3
SiMe3
O
I
tBu
2c
20
10
62
77
SiMe3
P
O
tBu
3
I
O
3
4
5
6
7
P(OPh)3
P(OBu)3
P[OCH(CF3)2]3
P(OMe)3
P[OCH(CH3)2]3
PPh3
PCy3
TFP
DPPP
2
63
15
100
100
0
0
0
0
0
1
35
11
13
12
0
0
0
0
0
SiMe3
O
3
4
8
9
I
SiMe3
10
11
12
13
14
71
tBu
tBu
Phenanthroline
Bipyridine
AsPh3
I
I
O
0
53
0
49
5
6
69
52
SiMe3
O
a
[(Cinnamyl)PdCl]2 (5 mol %), ligand (10 mol %), iodobenzene (1 mmol), HMDS
(1.5 mmol), toluene (2 ml), CO (10 bar), 110 °C, 16 h.
Conversion and yield were determined by GC using hexadecane as internal
standard based on iodobenzene.
b
SiMe3
c
20 mol % of ligand. TFP: tri(2-furyl)phosphine; DPPP: 1,3-bis(diphenylpho-
sphino)propane.
I
O
SiMe3
7
8
9
74
41
67
F
Table 2
F
Palladium-catalyzed carbonylative synthesis of benzoyltrimethyl silane: Further
I
I
I
O
optimizationa
SiMe3
SiMe3
SiMe3
O
Br
I
[Pd]/AsPh3
Br
CO HMDS
SiMe3
O
Cl
Cl
Entry
[Pd]
Solvent
Conv.b (%)
Yieldb (%)
Cl
Cl
1
2
3
4
5
[(Cinnamyl)PdCl]2
[(Cinnamyl)PdCl]2
[(Cinnamyl)PdCl]2
[(Cinnamyl)PdCl]2
Pd(OAc)2
Pd2(dba)3
PdBr2
PdCl2
[(Cinnamyl)PdCl]2
[(Cinnamyl)PdCl]2
[(Cinnamyl)PdCl]2
[(Cinnamyl)PdCl]2
[(Cinnamyl)PdCl]2
Heptane
1,4-Dioxane
DMF
0
100
46
10
45
30
89
16
100
2
0
71
24
2
29
29
56
15
88
0
O
10
65
NMP
Cl
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
6
7
Cl
a
[(Cinnamyl)PdCl]2 (5 mol %), AsPh3 (10 mol %), aryl iodide (1 mmol), HMDS
8
9c
(2 mmol), 1,4-dioxane (2 ml), CO (10 bar), 110 °C, 16 h.
b
10c,d
11c,e
12c,f
13c,g
Yield was determined by GC using hexadecane as internal standard based on
aryl iodide; the calibration of the product of entry 1 was also used for the other
entries.
61
28
100
60
0
0
a
[Pd] (10 mol %), AsPh3 (10 mol %), iodobenzene (1 mmol), HMDS (1.5 mmol),
while using 1 equiv resulted in only 27% yield, albeit with full con-
version of iodobenzene. No benzoyltrimethyl silane was formed
when the reaction was run at lower temperature (80 °C) even with
2 equiv of HMDS (Table 2, entry10). A lower pressure of CO was
also tested, but again the yield dropped to 60% (Table 2, entry
11). Finally, we tested some additives under the best reaction con-
ditions. Adding NEt3 as base led to the formation of N,N-diethylb-
enzamide (Table 2, entry 12), while exclusive formation of
benzoyl fluoride was observed when we added 1 mmol of CsF to
the reaction mixture (Table 2, entry 13).
solvent (2 ml), CO (10 bar), 110 °C, 16 h.
Conversion and yield were determined by GC using hexadecane as internal
standard based on iodobenzene.
b
c
HMDS (2 mmol).
80 °C.
CO (5 bar).
NEt3 (1 mmol).
d
e
f
g
CsF (1 mmol).
5–8). However, they all gave lower yields and selectivity compared
to [(cinnamyl)PdCl]2. Notably, the amount of HMDS plays a crucial
role for the outcome of this reaction. With 2 equivalents of HMDS
88% yield of the desired product was achieved (Table 2, entry 9),
With the best reaction conditions in our hand, some substrate
variations were carried out. Aryl iodides with simple electron-
donating substituents and even ortho-substituted derivatives were

584
X.-F. Wu et al. / Tetrahedron Letters 53 (2012) 582–584
A. M.; Scheidt, K. A. J. Org. Chem. 2006, 71, 5715–5724; (k) Cunico, R. F.; Pandey,
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transformed into corresponding acyl silanes in good yields (Table
3, entries 2–5). In addition, 52% of 1-naphthoyltrimethyl silane
was produced under our standard conditions (Table 3, entry 6).
Fluoride-, chloride-, and bromide-substituted iodobenzenes were
smoothly carbonylated to the corresponding benzoyl silanes in
the range of 41–74% yield (Table 3, entries 7–10). However, cyano-
and acetyl-substituted aryl iodides gave only traces of the desired
products. Similarly, 3-iodopyridine gave the desired product only
in traces. Notably, the reaction of bromobenzene with HMDS did
not give any desired product under our standard conditions, and
bromobenzene was recovered as it is.
In conclusion, the first catalytic carbonylation of aryl iodides
toward benzoyl silanes has been developed. Notably, electron-poor
phosphites or triphenylarsine has to be applied as ligands in order to
achieve the desired transformation. Under optimized conditions ten
aryl iodides with both electron-donating and electron-withdrawing
substituents were carbonylated to the corresponding benzoyl
silanes in 41–88% yield.
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5. Typical reaction procedure for carbonylation reaction of aryl iodides:
[(Cinnamyl)PdCl]2 (5 mol %) and AsPh3 (10 mol %) were transferred into a vial
(4 mL reaction volume) equipped with a septum, a small cannula and a stirring
bar. After the vials were purged with argon, 1,4-dioxane distilled from sodium
ketyl, 2 ml, iodobenzene (1 mmol), and HMDS (2 mmol) were injected into the
vial by syringe. Then, the vial was placed in an alloy plate, which was transferred
into a 300 mL autoclave of the 4560 series from Parr InstrumentsÒ under argon
atmosphere. After flushing the autoclave three times with CO, a pressure of
10 bar was adjusted and the reaction was performed for 16 h at 110 °C. Due to
the sensitivity of the products no isolation was performed and characterization
was done by GC–MS. Determination of the yield was done using the calibration
factor of benzoyltrimethyl silane.
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Acknowledgments
The authors thank the state of Mecklenburg-Vorpommern, the
Bundesministerium für Bildung und Forschung (BMBF), and the
DFG (Leibniz price) for the financial support. We also thank Drs.
W. Baumann, C. Fischer (LIKAT) for the analytical support.
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