Decarbonylative coupling of fluorobenzoyl chlorides with hexamethyldisilane in the presence of a palladium complex catalyst: Extremely facile decarbonylation of pentafluorobenzoyl-Pd complex relevant to C6F 5SiMe3 formation

Article abstract of DOI:10.1021/om060479p

Palladium-phosphite complexes catalyze the reaction of pentafluorobenzoyl chloride with hexamethyldisilane to selectively form pentafluorophenytrimethylsilane as virtually the sole product. The reaction of 3,5-difluoro- or 4-fluorobenzoyl chloride was less selective, giving a mixture of corresponding benzoyl-and phenylsilanes. Oxidative addition of pentafluorobenzoyl chloride with Pd(PPh₃)₄ or with Pd[P(OEt)₃]₂ generated in situ proceeds readily, but decarbonylation occurs, giving trans-C₆F₅PdClL₂ (L = PPh₃, P(OEt)₃), selectively.

Full text of DOI:10.1021/om060479p

4648
Organometallics 2006, 25, 4648-4652
Decarbonylative Coupling of Fluorobenzoyl Chlorides with
Hexamethyldisilane in the Presence of a Palladium Complex
Catalyst: Extremely Facile Decarbonylation of
Pentafluorobenzoyl-Pd Complex Relevant to C6F5SiMe3 Formation
Taigo Kashiwabara and Masato Tanaka*
Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
ReceiVed May 31, 2006
Palladium-phosphite complexes catalyze the reaction of pentafluorobenzoyl chloride with hexameth-
yldisilane to selectively form pentafluorophenytrimethylsilane as virtually the sole product. The reaction
of 3,5-difluoro- or 4-fluorobenzoyl chloride was less selective, giving a mixture of corresponding benzoyl-
and phenylsilanes. Oxidative addition of pentafluorobenzoyl chloride with Pd(PPh3)4 or with Pd[P(OEt)3]2
generated in situ proceeds readily, but decarbonylation occurs, giving trans-C6F5PdClL2 (L ) PPh3,
P(OEt)3), selectively.
Scheme 1
Introduction
We previously reported a rhodium-catalyzed addition reaction
of perfluorinated acid chlorides across alkynes, which affords
2-chloroalken-1-yl perfluoroorganyl ketones.1 This reaction is
quite different from the reaction of nonfluorinated aroyl chloride
with alkynes, which gives (2-chloroalken-1-yl)arenes,2 in that
it is a nondecarbonylative addition reaction. This observation
seems to suggest that the ease of decarbonylation of aroyl-
rhodium species is highly dependent on the electronic nature
of the aroyl group, as electronegative groups bound to the
carbonyl prevent the decarbonylation. With the significant effect
of the fluorine substituent in mind, we became interested in
decarbonylation in palladium-catalyzed reactions. We chose the
reaction of pentafluorobenzoyl chloride with hexamethyldisilane
as a probe. Palladium-catalyzed reactions of aroyl chlorides with
disilanes, first reported by Yamamoto and Tsuji using [Pd(η3-
C3H5)Cl]2 as a precatalyst3 and later by Rich using PdCl2-
(PhCN)2,4 are straightforward and high-yielding synthetic routes
for aroylsilanes.5 To our knowledge, pentafluorobenzoyl chloride
has never been examined as a substrate for the reaction. At least
three reactions could have taken place: (i) the nondecarbonyl-
ative metathesis leading to fluorinated aroylsilanes,6 which are
valuable in synthetic applications;7 (ii) decarbonylative metath-
esis forming fluorinated arylsilanes, which are also useful in
organic and inorganic syntheses;8 (iii) decarbonylative reduc-
tive coupling leading to fluorinated biaryls, similarly to the
desulfonylative reductive coupling of arenesulfonyl chloride.9
The real event observed in practice was the second, which will
be reported in this paper. Very rapid decarbonylation of the
pentafluorobenzoyl-palladium species, different from the slow
decarbonylation of the pentafluorobenzoyl-rhodium complex,
is also described.
* To whom correspondence should be addressed. E-mail: m.tanaka@
res.titech.ac.jp.
(1) (a) Kashiwabara, T.; Kataoka, K.; Hua, R.; Shimada, S.; Tanaka, M.
Org. Lett. 2005, 7, 2241. See also: (b) Hua, R.; Onozawa, S.; Tanaka, M.
Chem. Eur. J. 2005, 11, 3621. (c) Hua, R.; Tanaka, M. Tetrahedron Lett.
2004, 45, 2367. (d) Hua, R.; Tanaka, M. J. Am. Chem. Soc. 1998, 120,
12365.
Results and Discussion
Catalytic Reactions. In a representative reaction (entry 1,
Table 1), pentafluorobenzoyl chloride and hexamethyldisilane
(2) Kokubo, K.; Matsumasa, K.; Miura, M.; Nomura, M. J. Org. Chem.
1996, 61, 6941.
(3) (a) Yamamoto, K.; Suzuki, S.; Tsuji, J. Tetrahedron Lett. 1980, 1653.
(b) Yamamoto, K.; Hayashi, A.; Suzuki, S.; Tsuji, J. Organometallics 1987,
6, 974.
(6) Kondo, J.; Inoue, A.; Ito, Y.; Shinokubo, H.; Oshima, K. Tetrahedron
2005, 61, 3361.
(7) (a) Ricci, A.; Degl’Innocenti, A. Synthesis 1989, 647. (b) Page, P.
C. B.; Klair, S. S.; Rosenthal, S. Chem. Soc. ReV. 1990, 19, 147.
(8) (a) Furin, G. G. Russ. J. Org. Chem. 1997, 33, 11209. (b) Huang,
D.; Renkema, K. B.; Caulton, K. G. Polyhedron 2006, 25, 459. (c)
Babadzhanova, L. A.; Kirij, N. V.; Yagupolskii, Y. L. J. Fluorine Chem.
2004, 125, 1095. (d) Panne, P.; Naumann, D.; Hoge, B. J. Fluorine Chem.
2001, 112, 283. (e) Nishida, M.; Ono, T.; Abe, T. Nippon Kagaku Kaishi
2000, 817. See also: (f) Bardin, V. V.; Pressman, L. S.; Rogoza, L. N.;
Furin, G. G. J. Fluorine Chem. 1991, 53, 213.
(4) Rich, J. D. J. Am. Chem. Soc. 1989, 111, 5886.
(5) Both [Pd(η3-allyl)Cl]2 and PdCl2(PhCN)2 are envisioned to be
converted to the same PdLn species upon treatment with hexamethyldisilane
in the presence of a phosphorus ligand (L). On the basis of this assump-
tion, we presume it reasonable to compare current results obtained using
PdCl2(PhCN)2 with those in ref 3. However, we cannot rule out the
possibility that catalytic activity may be dependent on the structure of the
precursor complex, in view of the difference in the quantity of the coproduct
(SiClMe3) generated during the conversion of the precursor to the active
species.
(9) (a) Krafft, T. E.; Rich, J. D.; McDermott, P. J. J. Org. Chem. 1990,
55, 5430. (b) Kashiwabara, T.; Tanaka, M. Tetrahedron Lett. 2005, 46,
7125.
10.1021/om060479p CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/09/2006

Decarbonylation of Pentafluorobenzoyl-Pd Complex
Organometallics, Vol. 25, No. 19, 2006 4649
Table 1. Ligand Effect in the Reaction of 1a with 2aa
Table 2. Dependence of the Extent Fluorine Substitution on
the Selectivitya
time
(day)
conversion of
yield of
entry
ligand
1a (%)b
4aa (%)b
yield (%)b
time conversion
1
P(OEt)3
5
5
3
3
3
5
3
3
5
5
5
5
97
40
100
78
45
5
69
55
5
38
2
10
44
5
94 (85)
40
95
68
42
3
62
53
5
30
2
10
40
3
entry
ArfCOCl
solvent (day) of 1 (%)b
3xa
4xa
2c
P(OMe)3
P[O(n-Pr)]3
P[O(i-Pr)]3
P[O(n-Bu)]3
P(OPh)3
PPh(OEt)2
PPh2(OEt)
PPh3
3c
1
C6F5COCl 1a
3,5-F2C6H3COCl 1b toluene
none
toluene
5
2
2
97
69
90
∼0
94 (85)
2c
15
32
2
4c
3c,d 4-FC6H4COCl 1c
57 (51)
5c
6d
a Arf stands for a fluorinated aryl group. Reaction was carried out at
110 °C using 1 (2 mmol), 2a (2 mmol), PdCl2(PhCN)2 (5 mol %), P(OEt)3
(10 mol %), and solvent (2 mL) in a sealed tube. b Determined by 19F NMR
spectroscopy. The figure in parentheses is isolated yield. c Pd mirror was
formed. d The quantity of PdCl2(PhCN)2 and P(OEt)3 was doubled.
7c
8c
9d
10e
11d
12
13c
14c
15c
16c
17c
18c
19g
PPh3
P(p-FC6H4)3
P(p-Tol)3
furyl)phosphine, triphenylarsine, and triphenylstibine are com-
pletely ineffective.
f
P(Mes)3
5
dppe
dppp
dppp
PMe3
P(t-Bu)3
P(OEt)3
0.5
0.5
0.5
1
5
5
In the reactions with the Pd-P(OPh)3, -PPh3, and -P(p-
FC6H4)3 catalyst systems, a white precipitate was observed soon
after the reaction started. With the Pd-PPh3 catalyst system,
the precipitate was trans-C6F5PdCl(PPh3)2, an intermediate
involved in the catalytic cycle (vide infra). It is reasonable to
assume that the low solubility of this intermediate was respon-
sible, at least in part, for the yield being poor (5% yield). When
sym-tetrachloroethane, a better solvent than toluene, was used,
the conversion of the acid chloride and the yield of 4aa after 5
days improved to 38% and 30%, respectively (entry 10).
Finally, an attempted reaction under pressurized CO (10 atm)
to prevent decarbonylation was run using the PdCl2(PhCN)2-
P(OEt)3 catalyst system. However, only a decrease in catalytic
activity resulted (entry 19).
The above results clearly suggest that the pentafluorophenyl
group strongly promotes decarbonylation. This conclusion is
further reinforced by the following results observed in the
reactions of partially fluorinated aroyl chlorides (Table 2). The
reaction of 3,5-difluorobenzoyl chloride (1b) gave 3,5-difluo-
rophenylsilane (4ba) in 32% yield, together with 3,5-difluo-
robenzoylsilane (3ba) in 15% yield, suggesting less decarbo-
nylation (entry 2). The reaction of 4-fluorobenzoyl chloride (1c)
carried out without solvent afforded the corresponding aroyl-
silane (3ca) more selectively (entry 3).10 In these reactions of
3,5-difluorobenzoyl chloride and 4-fluorobenzoyl chloride,
material balance was not so satisfactory as compared with the
reaction of pentafluorobenzoyl chloride. A careful search for
minor byproducts formed in the reaction of 4-fluorobenzoyl
chloride revealed the presence of chlorofluorobenzene (3%),
4,4′-difluorobiphenyl (4%), and diethyl 4-fluorobenzoylphos-
phonate (3%). However, neither fluorobenzene nor 4,4′-difluo-
robenzophenone was detected.11
2
5
2
20
58
2
5
2
1
42
a Reaction conditions: 1a (2 mmol), 2a (2 mmol), toluene 2 mL,
PdCl2(PhCN)2 (5 mol %), ligand/Pd ) 2, 110 °C. b Determined by 19F NMR
spectroscopy. The figure in parentheses is isolated yield. c Pd mirror was
formed. d Reaction mixture became heterogeneous as the reaction proceeded.
e Run in sym-tetrachloroethane. f Mes ) 2,4,6-trimethylphenyl. g Run under
a CO atmosphere (10 atm).
in toluene were heated at 110 °C in the presence of PdCl2-
(PhCN)2 and triethyl phosphite (P/Pd ) 2). 19F NMR spectros-
copy showed that the reaction proceeded cleanly to give
pentafluorophenyltrimethylsilane (4aa) as nearly the sole product
in 94% yield after 5 days, eq 1. Unlike the reaction of plain
benzoyl chloride in the presence of [Pd(η3-C3H5)Cl]2 as pre-
catalyst,3 nondecarbonylative coupling forming pentafluoro-
bezoylsilane (3aa) did not proceed at all. Decafluorobiphenyl,
a possible product of decarbonylative reductive coupling,9a was
not formed either. The reaction was slow, taking 5 days for
completion, compared with only 24 h for the reaction of plain
benzoyl chloride3,4 under similar conditions.
Various catalyst systems comprising a phosphorus ligand and
PdCl2(PhCN)2 promote the decarbonylative silylation as sum-
marized in Table 1. The performance depended on the nature
of the ligand, but none of the ligands listed in Table 1 promoted
the formation of 3aa.
The reaction of tetrafluoroterephthaloyl dichloride smoothly
conformed to the decarbonylative coupling at both acid chloride
moieties to afford bis(trimethylsilyl)tetrafluorobenzene (5) in a
high yield, eq 2.
As observed by Yamamoto in the CO-retentive metathesis
of aroyl chloride with disilane forming aroylsilane, the present
decarbonylative silylation is also best accomplished using
phosphites, particularly trialkyl phosphites (entries 2-5).3 Of
the trialkyl phosphites, tri-n-propyl phosphite is the ligand of
choice, which generates the most active palladium species, while
higher or lower alkyl phosphites are somewhat inferior, and
triphenyl phosphite displays only a marginal activity. Phospho-
nite and phosphinite ligands are moderately active (entries 7,
8). Phosphines in general are not capable ligands, as compared
with phosphites. As far as triarylphosphines are concerned, a
more donating phosphine is better performing than a less
donating phosphine (entries 9, 11-13). However, more electron-
donating trialkylphosphines and more strongly coordinating
diphosphines are much more inferior (entries 14-18). Tris(2-
(10) When the reaction was run in a toluene solution under the standard
conditions, the catalyst species decomposed rapidly, as judged by the
development of a palladium mirror, and the yield of 3ca was only 7% after
4 days. Another reaction using [Pd(η3-C3H5)Cl]2 and P(OEt)3 under the
standard conditions afforded 3ca and 4ca in yields of 27% and 3%,
respectively.
(11) The 19F NMR spectrum and gas chromatogram of the reaction
mixture showed the formation of other byproducts. Despite much effort,
including performing GC-MS analyses, we were unable to identify the
byproducts. However, integration of the 19F NMR signals of all unknown
byproducts accounted for the discrepancy between the conversion of the
acid chloride and the yield of the identified products. For the 19F NMR
spectrum of the reaction mixture, see Supporting Information.

4650 Organometallics, Vol. 25, No. 19, 2006
Kashiwabara and Tanaka
On the other hand, the reaction of heptafluorobutyryl chloride
under the standard conditions was not clean, resulting in a messy
mixture; although complete consumption of the starting hep-
tafluorobutyryl chloride was confirmed by 19F NMR spectros-
copy, neither heptafluorobutyrylsilane nor heptafluoropropyl-
silane was detected.
Unlike hexamethyldisilane, sym-dichlorotetramethyldisilane
was quite reluctant to react with fluorinated benzoyl chloride
when the reaction was effected in the presence of the phosphite-
Pd catalysts or PdCl2(PPh3)2 under similar conditions. Only
traces (<7%) of decarbonylative coupling products were formed
in the reactions of 3,5-difluorobenzoyl chloride and 4-fluo-
robenzoyl chloride. Pentafluorobenzoyl chloride was even less
reactive. This is somewhat peculiar in view of the successful
formation of benzoylsilane from plain benzoyl chloride and sym-
dichlorotetramethyldisilane reported by Rich. The low reactivity
of sym-dichlorotetramethyldisilane in the reaction with pen-
tafluorobenzoyl chloride is presumably associated with the
difficulty of Si-C reductive elimination from C6F5-Pd-SiMe2-
Cl species (vide infra), in which both C6F5-Pd12 and Pd-SiMe2-
Cl13 are thermodynamically strong bonds.
Figure 1. Molecular structure of complex 6. Thermal ellipsoids
are drawn at the 30% probability level, and hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Pd1-C1 ) 2.011(2), Pd1-Cl1 ) 2.3552(5), Pd1-P1 ) 2.3228-
(7), Pd1-P2 ) 2.3264(7), Cl1-Pd1-P1 ) 89.68(2), Cl1-Pd1-
P2 ) 88.47(2), Cl1-Pd1-C1 ) 179.58(7), P1-Pd1-P2 )
177.93(2), P1-Pd1-C1 ) 90.61(7), P2-Pd1-C1 ) 91.23(7).
in Figure 1. The sum of the bond angles around Pd being 360°
indicates that the complex has a square planar configuration.
The length of the Pd-C bond is 2.011 Å, which, as anticipated,
is remarkably shorter than that in trans-C6H5PdCl(PPh3)2 (2.407
Å).16
Mechanistic Aspects of the Reaction. As Yamamoto sug-
gested, the reaction mechanism is best explained by Scheme 2,
Scheme 2
To gain a more realistic view of the mechanism, oxidative
addition of pentafluorobenzoyl chloride with a Pd-phosphite
complex was also examined. In our literature search for relevant
precedents, we have found only two articles describing oxidative
addition of organic halides with Pd-phosphite complexes,17 one
of which reports that benzoyl chloride reacts with [Pd-
{P(OPh)3}2]n.17a In our experiment, a benzene solution of PdCl2-
(PhCN)2, P(OEt)3 (2.0 equiv), hexamethyldisilane (1.0 equiv),
and C6F5COCl (1.0 equiv) was heated at 80 °C. The reaction
was slow at this temperature, and 19F NMR spectroscopy
which is well supported by the following observations. Pd(II)
precatalyst is readily reduced to catalytically active Pd(0)
species, as evidenced by the quantitative formation of chloro-
trimethylsilane (30.1 ppm in 29Si{1H} NMR spectroscopy) upon
treatment of PdCl2(PhCN)2 with hexamethyldisilane (1 equiv)
in toluene at room temperature, eq 3.
(12) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 2nd ed.; John Wiley & Sons: New York, 1993; Chapter 3, p 48.
(b) Albe´niz, A. C.; Espinet, P.; Mart´ın-Ruiz, B.; Milstein, D. Organome-
tallics 2005, 24, 3679. See also: (c) Bennett, M. A.; Chee, H.-K.; Robertson,
G. B. Inorg. Chem. 1979, 18, 1061. (d) Green, M. L. H. Organometallic
Compounds, 3rd ed.; Methuen: London, 1968; Vol. 2, p 263. (e) Treichel,
P. M.; Stone, F. G. A. AdV. Organomet. Chem. 1968, 1, 143. (f) Stone, F.
G. A. EndeaVour 1966, 25, 33.
(13) (a) Manojloviæ-Muir, L.; Muir, K. W.; Ibers, J. A. Inorg. Chem.
1970, 9, 447. (b) Aylett, B. L. AdV. Inorg. Chem. Radiochem. 1982, 25, 1.
(c) Yamashita, H.; Kobayashi, T.; Hayashi, T.; Tanaka, M. Chem. Lett.
1990, 1447. (d) Lichtenberger, D. L.; Rai-Chaudhuri, A. J. Am. Chem. Soc.
1991, 113, 2923. (e) Aizenberg, M.; Milstein, D. J. Am. Chem. Soc. 1995,
117, 6456.
Oxidative addition of pentafluorobenzoyl chloride with Pd-
(PPh3)4 took place readily and cleanly at both 110 °C and room
temperature. In striking contrast with the reaction of plain
benzoyl chloride, in which benzoyl-palladium complex is
formed,14 the present reaction afforded trans-C6F5PdCl(PPh3)2
(6)15 in excess of 80% isolated yield, suggesting that the
pentafluorobenzoyl complex initially generated rapidly extruded
carbon monoxide even at room temperature, eq 4. The structure
of complex 6 was characterized by X-ray crystallography. The
ORTEP drawing and selected bond lengths and angles are shown
(14) Koide, Y.; Bott, S. G.; Barron, A. R. Organometallics 1996, 15,
2213.
(15) Complex 6 is a known compound, which was synthesized via a
different route. (a) Casado, A. L.; Espinet, P.; Gallego, A. M. J. Am. Chem.
Soc. 2000, 122, 11771. (b) Uso´n, R.; Fornie´s, J.; Espinet, P.; Lalinde, E.;
Jones, P. G.; Sheldrick, G. M. J. Organomet. Chem. 1985, 288, 249.
(16) Flemming, J. P.; Pilon, M. C.; Borbulevitch, O. Y.; Antipin, M.
Y.; Grushin, V. V. Inorg. Chim. Acta 1998, 280, 87.

Decarbonylation of Pentafluorobenzoyl-Pd Complex
Organometallics, Vol. 25, No. 19, 2006 4651
on a Shimadzu GC-MS QP-1100EX mass spectrometer. High-
resolution mass spectra were obtained with a JEOL JMS-700 mass
spectrometer at an ionization potential of 70 eV. Melting points
were measured on a IA9100 micro melting point apparatus (Iuchi-
Seieido Ltd.). X-ray crystal structure was determined on a Rigaku
AFC10 diffractometer.
Acid chlorides, hexamethyldisilane, and liquid phosphorus-
containing ligands were distilled before use. Solid phosphine ligands
were recrystallized from EtOH or hexane. The following ligands/
complexes were prepared according to the literature: PhP(OEt)2,19
Ph2P(OEt),20 P(OnBu),21 P(OnPr),21 PMe3,22 PdCl2(PhCN)2,23 Pd-
(PPh3)4,24 Pd2(dba)3‚CHCl3,25 Si2Me4Cl2.26
revealed that only a trace of trans-C6F5PdCl[P(OEt)3]2 (7) had
formed after 14 h. In another experiment run at 110 °C for 12
h, C6F5COCl was completely consumed and complex 7 was
formed in 48% yield, although extensive metallic palladium pre-
cipitation was visible and decafluorobiphenyl was also formed
in 34% yield (in terms of the C6F5 group). Since complex 7
turned out to be an oil, it could be only partially purified. How-
ever, the purity of complex 7 obtained after partial purification
was >90%, slightly contaminated with decafluorobiphenyl and
other unknown compounds, and provided satisfactory 31P NMR
and HRMS data to support the structure. The result suggests
that, as was observed in the above reaction with Pd(PPh3)4, the
initial adduct, C6F5COPdCl[P(OEt)3]2, is labile, allowing it to
undergo decarbonylation under the oxidative addition reaction
conditions. Furthermore, in view of decafluorobiphenyl being
formed in the absence of extra hexamethyldisilane, complex 7
appears somewhat more labile than complex 6.
Pentafluorophenyl-palladium complex 6 was found to react
with hexamethyldisilane (10 equiv), forming 4aa in 11% yield
(110 °C, 2 h; estimated by 19F NMR spectroscopy), eq 5.
Complex 7 behaved similarly (110 °C, 5 h) to give 4aa and
decafluorobiphenyl in yields of 71% and 6%, respectively. The
mechanism of this transformation is as yet unclear, but presum-
ably proceeds via trans-C6F5-Pd-Si species formed by σ-bond
metathesis (only this possibility is illustrated in Scheme 1) or
oxidative addition-reductive elimination involving Si-Si and
C6F5-Pd-Cl linkages, isomerization to cis-C6F5-Pd-Si spe-
cies, and Si-C reductive elimination.18
Typical Procedure for the Catalytic Silylation: The Reaction
of Pentafluorobenzoyl Chloride with Hexamethyldisilane Af-
fording 4aa. In a 5 mL Schlenk tube equipped with a three-way
stopcock and a magnetic stirring bar were placed PdCl2(PhCN)2
(39.2 mg, 0.10 mmol), toluene (2 mL), triethyl phosphite (34 µL,
0.20 mmol), pentafluorobenzoyl chloride (0.3 mg, 2.0 mmol),
hexamethyldisilane (0.41 mL, 2.0 mmol), and hexafluorobenzene
(62.1 mg, an internal standard for 19F NMR analysis) under argon.
The mixture was stirred at 110 °C for 5 days. After NMR analysis
of the reaction mixture, volatiles were removed under reduced
pressure. The residue was purified by Kugelrohr distillation to afford
pentafluorophenyltrimethylsilane (4aa) as a pale yellow oil in 85%
yield, bp 37-38 °C/3 mmHg (lit.27 43-45 °C/5 mmHg). 1H NMR
5
(300 MHz, CDCl3): δ 0.39 (t, 9H, JFH ) 1.3 Hz, SiMe3). 19F
NMR (282.4 Hz, CDCl3): δ -127.6 (quart, 2F, J ) 14.2 Hz, o-F),
-152.52 (t, 1F, J ) 19.7 Hz, p-F), -161.9 (m, 2F, m-F). The
structure was further confirmed by comparing the spectral data with
those of an authentic sample prepared via a different route.27
(3,5-Difluorobenzoyl)trimethylsilane (3ba). An authentic sample
was synthesized from ethyl 3,5-difluorobenzoate by the procedure
reported for benzoyltrimethylsilane.28 The yellow oil we obtained,
even after repeated fractional distillation (bp 40-42 °C/0.1 mmHg),
was an approximately 1:2 mixture of ethyl 3,5-difluorobenzoate
and 3ba. However, careful analysis of the mixture by comparing
with pure ethyl 3,5-difluorobenzoate allowed us to characterize 3ba
In summary, pentafluorobenzoyl chloride reacts cleanly with
hexamethyldisilane in the presence of trialkyl phosphite-
palladium complexes to give pentafluorophenyltrimethylsilane
as nearly the sole product. The reaction proceeds with con-
comitant decarbonylation, which is very rapid even at room
temperature, as evidenced by the selective formation of trans-
C6F5PdCl(PPh3)2 in the reaction of pentafluorobenzoyl chloride
with Pd(PPh3)4.
1
as follows. H NMR (CDCl3, 300 MHz): δ 7.31 (m, 2H, o-Ph),
6.97 (m, 1H, p-Ph), 0.38 (s, 9H, Me). 13C{1H} NMR (75 MHz,
CDCl3): δ 232.8 (CO), 163.1 (dd, 1JCF ) 252 Hz, 3JCF ) 11.5 Hz,
2
m-Ph), 133.7 (3JCF ) 9.3 Hz, ipso-Ph), 110.0 (AB coupling, JCF
) 17.1 Hz, 4JCF ) 7.9 Hz, o-Ph), 107.8 (t, 2JCF ) 30.2 Hz, p-Ph),
-1.6 (TMS). 19F NMR (282 MHz, CDCl3): δ -108.1 (m). 29Si-
{1H} NMR (75 MHz, CDCl3): δ -5.43 (br s). IR (neat, cm-1):
1627 (νCO). MS (EI, 20 eV): m/z (relative intensity) 214 ([M]+,
5), 199 (8), 171 (12), 73 (100). HRMS (EI, 70 eV): calcd for
C10H12F2OSi 214.0625, found 214.0623. For 1H and 13C{1H} NMR
of 3ba (an approximately 1:2 mixture of ethyl 3,5-difluorobenzoate
and 3ba), see Supporting Information.
Experimental Section
General Procedures. All manipulations involving air- and
moisture-sensitive compounds were carried out under an atmosphere
of dry argon or nitrogen, by using standard Schlenk tube techniques.
All solvents were distilled over appropriate drying agents prior to
use. IR spectra were recorded on a HORIBA FT/IR 730 spectrom-
(3,5-Difluorophenyl)trimethylsilane (4ba). The synthetic pro-
cedure reported by Dunogues and co-workers29 afforded an
1
eter. H NMR (300 MHz), 13C{1H} NMR (75 MHz), 19F NMR
(282 MHz), and 29Si{1H} NMR (60 MHz) spectra were recorded
on a Bruker DPX300 spectrometer at ambient temperatures. 31P-
{1H} NMR (162 MHz) spectra were recorded on a JEOL JNM-
(19) Collins, D. J.; Drygala, P. F.; Swan, M. Aust. J. Chem. 1983, 36,
2095.
(20) Quin, L. D.; Anderson, H. G. J. Organomet. Chem. 1964, 29, 1859.
(21) Prishchenko, A. A.; Litantsov, M. V.; Boganova, N. V.; Lutsenko,
I. F. Zh. Obs. Khim. 1988, 58, 2168.
(22) Luetkens, M. L.; Sattelberger, A. P.; Basil, M. J. D.; Fackler, J. P.
Inorg. Synth. 1990, 28, 7.
(23) Doyle, J. R.; Slade, P. E.; Jonassen, H. B. Inorg. Synth. 1960, 6,
218.
1
EX400 spectrometer. H, 13C{1H}, and 29Si{1H} NMR chemical
shifts were reported in ppm relative to internal Me4Si. 19F NMR
chemical shifts were reported in ppm relative to external CFCl3.
31P{1H} NMR chemical shifts were reported in ppm relative to
external aqueous 85% H3PO4. GC was run on a GL Sciences
GC390B chromatograph (silicone OV17 5% on Chromosorb W
(60/80 mesh), SUS column 2.0 mm φ × 2.0 m). GC-MS was run
(24) Coulson, D. R. Inorg. Synth. 1972, 13, 121.
(25) Ukai, T.; Kawazura, H.; Ishii, Y. J. Organomet. Chem. 1974, 65,
253.
(17) (a) Urata, H.; Suzuki, H.; Morooka, Y.; Ikawa, T. J. Organomet.
Chem. 1989, 364, 235. (b) Trzeciak, A. M.; Wojtko´w, W.; Ciunik, Z.;
Ziołkowski, J. J. Catal. Lett. 2001, 77, 245.
(18) We are unable to rigorously exclude the possibility of σ-bond
metathesis between Si-Si and C6F5-Pd bonds forming the C6F5SiMe3
product, followed by Si-Cl reductive elimination to regenerate Pd(0)
species.
(26) Denmark, S. E.; Kallemeyn, J. M. Org. Lett. 2003, 5, 3483.
(27) Gostevskii, B. A.; Kruglaya, O. A.; Albaov, A. I.; Vyazankin, N.
S. J. Organomet. Chem. 1980, 187, 157.
(28) Picard, J.-P.: Calas, R.; Dunogues, J.; Duffaut, N.; Gerval, J.;
Lapouyade, P. J. Org. Chem. 1979, 44, 420.
(29) Babin, P.; Bennetau, B.; Theurig, M.; Dunogues, J. J. Organomet.
Chem. 1993, 446, 135-138.

4652 Organometallics, Vol. 25, No. 19, 2006
Kashiwabara and Tanaka
authentic sample as a pale yellow oil, bp 75-77 °C/20 mmHg (lit.29
73 °C/20 mmHg). Spectroscopic data, which have not been
mmol). After stirring at room temperature for 5 min, the mixture
was treated with pentafluorobenzoyl chloride (46 µL, 0.32 mmol)
and was heated at 110 °C for 12 h, while a black powdery material
gradually precipitated. Volatiles were evaporated, and benzene-d6
(1.0 mL) and hexafluorobenzene (26 µL, internal standard for 19F
NMR analysis) were added. Analysis of the mixture by 19F NMR
spectroscopy showed that complex 7 had been formed in 48% yield
together with decafluorobiphenyl (34% in terms of the pentafluo-
rophenyl group). Addition of hexane (10 mL), filtration to remove
the black powder and majority of decafluorobiphenyl, and evapora-
tion of volatiles (40 °C/0.01 mmHg) afforded a colorless oil (71
mg). Analysis by 31P and 19F NMR spectroscopies confirmed its
1
described, are as follows. H NMR (CDCl3, 300 MHz): δ 6.91
(m, 2H, o-H), 6.69 (m, 1H, p-H), 0.21 (s, 9H, Me). 19F NMR (282
MHz, CDCl3): δ -111.1 (t, J ) 9.2 Hz).
(4-Fluorobenzoyl)trimethylsilane (3ca). 4-Fluorobenzoyl chlo-
ride (2 mmol) and hexamethyldisilane (2 mmol) were heated in a
sealed tube at 110 °C for 2 days in the presence of PdCl2(PhCN)2
(10 mol %) and P(OEt)3 (20 mol %). After 19F NMR analysis of
the reaction mixture (57% 19F NMR yield), the mixture was
subjected to Kugelrohr distillation to afford 3ca as a pale yellow
oil in 51% yield, bp 95-100 °C/20 mmHg. This compound has
been documented30 without spectral data, which are as follows. 1H
NMR (300 MHz, CDCl3): δ 7.88-7.83 (m, 2H, o-H), 7.16-7.11
(m, 2H, m-H), 0.37 (s, 9H, Me). 19F NMR (282 MHz, CDCl3): δ
-106.2 (m). 13C{1H} NMR (75 MHz, CDCl3): δ 233.5 (CO), 165.4
(d, J ) 254.4 Hz, p-C), 130.0 (d, J ) 9.1 Hz, o-C), 115.4 (d, J )
9.2 Hz, m-C), 115.3 (d, J ) 21 Hz, ipso-Ph), -1.4 (s, Me). 29Si-
{1H} NMR (60 MHz, CDCl3): δ -50.0. Anal. Calcd for C10H13-
FOSi: C, 61.19; H, 6.68. Found: C, 60.97; H, 6.64.
1
purity being in excess of 90%. H NMR (300 MHz, benzene-d6):
δ 4.19 (m, 12H, OCH2CH3), 1.08 (m, 18H, OCH2CH3). 13C{1H}
NMR (75 MHz, benzene-d6): δ 62.5 (br s, OCH2CH3), 16.1 (virtual
t, J ) 3.17 Hz, OCH2CH3). Signals associated with carbons in the
pentafluorophenyl group were too weak to be observable due
presumably to multiple couplings with F nuclei. 19F NMR (282
MHz, benzene-d6): δ -139.6 (m, 2F, o-F), -162.3 (m, 1F, p-F),
-165.4 (t, 2F, J ) 19.7 Hz, m-F). 31P{1H } NMR (162 MHz,
benzene-d6): δ 105.2 (t, J ) 11.6 Hz). HRMS (FAB, matrix )
3-nitrobenzyl alcohol): calcd for C18H31ClF5O6P2106Pd (value for
(4-Fluorophenyl)trimethylsilane (4ca). The synthetic procedure
reported by Dunogues and co-workers29 afforded an authentic
sample as a yellow oil. Spectroscopic data, which have not been
1
[M + 1]+) 641.0239, found 641.0233. For H, 13C{1H}, 19F, and
31P{1H} NMR spectra of this material of >90% purity, see
Supporting Information.
1
reported, are as follows. H NMR (CDCl3, 300 MHz): δ 7.43-
7.37 (dd, 2H, JFH ) 4.9 Hz, JHH ) 1.1 Hz, FCCHCHCSiMe3),
6.93-6.87 (dd, 2H, JFH ) 8.5 Hz, JHH ) 1.1 Hz, FCCHCHCSiMe3),
0.01 (s, 9H, Me). 19F NMR (282 MHz, CDCl3): δ -115.5 (m).
Reaction of trans-Pd(C6F5)Cl(PPh3)2 with Si2Me6. A mixture
of trans-Pd(C6F5)Cl(PPh3)2 (4.2 mg, 5.0 µmol), Si2Me6 (10 µL, 49
µmol), and toluene-d8 (0.5 mL) was heated in a sealed NMR tube
at 110 °C for 2 h. 19F NMR spectroscopy revealed the formation
of C6F5SiMe3 in 11% yield.
Reaction of trans-Pd(C6F5)Cl[P(OC2H5)3]2 with Si2Me6. To
trans-Pd(C6F5)Cl[P(OEt)3]2 (>90% purity, 25.6 mg, 0.0399 mmol
on the assumption of 100% purity) placed in an NMR tube were
added toluene-d8 (0.5 mL), Si2Me6 (5.6 µL, 0.03 mmol), and
hexafluorobenzene (2.2 mg, internal standard for 19F NMR analysis).
Heating the mixture at 80 °C for 1 h did not promote the reaction
to an appreciable extent. Further heating for 5 h at 110 °C resulted
in deposition of palladium mirror. 19F NMR analysis showed signals
arising from C6F5SiMe3 (71% based on Si2Me6), decafluorobiphenyl
(approximately 6% based on complex 7), and a trace of unreacted
7 (approximately 3%).
Molecular Structure Analysis of Complex 6. Single crystals
were grown from a CH2Cl2 solution. A suitable colorless crystal
(0.18 × 0.15 × 0.10 mm) was used for X-ray diffraction data
collection with Mo KR radiation (λ ) 0.7107 Å). Crystal data for
6: Cl2F10P2Pd2C84H60, M ) 1605.04, monoclinic, space group )
P21/a (#14), a ) 23.287(4) Å, b ) 11.9507(17) Å, c ) 25.667(4)
Å, â ) 90.019(2)°, V ) 7143.1(18) Å3. Z ) 4, density(calc) )
1.492, 2θmax ) 55.0°. Total reflections collected ) 16 228, GOF
) 1.031. The final R factor was 0.0747 (Rw ) 0.0773 for all data).
The structure was solved by direct methods (SIR97) and refined
by full-matrix least-squares method by using the SHELXL program.
1,4-Bis(trimethylsilyl)tetrafluorobenzene (5). After the reaction
of tetrafluoroterephthaloyl dichloride (1.0 mmol) with hexameth-
yldisilane (2.0 mmol) under the standard conditions for 10 days,
the mixture was evaporated. Dichloromethane was added to the
residue, and the mixture was filtered. The filtrate was evaporated
and was purified by preparative TLC (hexane) to afford an
analytically pure sample of compound 5, 76% isolated yield, mp
1
53.5-54.7 °C (lit.31 53-55 °C). H NMR (CDCl3, 300 MHz): δ
0.83 (t, J ) 6.95 Hz, 18H, Me). 19F NMR (282 MHz, CDCl3): δ
-128.5 (br s). Anal. Calcd for C12H18F4Si2: C, 48.95; H, 6.16.
Found: C, 48.83; H, 6.28.
Reaction of PdCl2(PhCN)2 with Si2Me6. A mixture of PdCl2-
(PhCN)2 (15.7 mg, 0.041 mmol), Si2Me6 (0.041 mmol), and toluene
(2.0 mL) was stirred at room temperature for 5 min. Metallic
palladium precipitated immediately. Analysis of the resulting
mixture by 29Si{1H} NMR spectroscopy (CDCl3) revealed complete
consumption of Si2Me6 and displayed only one singlet assignable
to SiClMe3 (30.1 ppm).
Synthesis of trans-Pd(C6F5)Cl(PPh3)2 (6). Pentafluorobenzoyl
chloride (20 µL, 0.139 mmol) was added to a greenish-yellow
solution of Pd(PPh3)4 (141 mg, 0.122 mol) in toluene (3.0 mL)
placed in a Schlenk tube. Gas evolution started immediately, and
the solution became colorless in less than 10 min to afford a white
participate. The mixture was stirred for 1 h at room temperature
under argon. Volatiles were removed in vacuo, and the residue was
washed with Et2O (5 mL × 2) to afford the title complex as a
white powder in 85% yield, mp 233.0-235.0 °C (under Ar, dec).
1H NMR (300 MHz, CDCl3): δ 7.89-7.18 (m, 30H, Ph). 19F NMR
(282 MHz, CDCl3): δ -119.17 (m, 2F, o-F), -164.6 (t, 1F, J )
19.8 Hz, p-F), -164.9 (t, 2F, J ) 19.8 Hz, m-F). 31P{1H} NMR
(162 MHz, CDCl3): δ 24.9 (t, J ) 7.3 Hz). Anal. Calcd for C42H30-
ClF5P2Pd: C, 60.52; H, 3.63. Found: C, 60.15; H, 3.31.
Acknowledgment. We thank the Japan Society for the
Promotion of Science and Technology for a research fellowship
to T.K. and Dr. Makoto Tanabe for his assistance in X-ray
crystallography.
Supporting Information Available: 1H and 13C{1H} NMR
1
spectra of compound 3ba, H, 13C{1H}, 19F, and 31P{1H} NMR
spectra of complex 7, 19F NMR spectrum of the reaction mixture
of entry 3, Table 2, and crystallographic data for 6 in CIF format.
The material is available free of charge via the Internet at
http://pubs.acs.org.
Synthesis of trans-Pd(C6F5)Cl[P(OC2H5)3]2 (7). To a toluene
(5.0 mL) solution of PdCl2(PhCN)2 (122.3 mg, 0.32 mmol) was
added P(OEt)3 (110 µL, 0.64 mmol) and Si2Me6 (65 µL, 0.32
(30) Dondy, B.; Doussot, P.; Portella, C. Synthesis 1992, 995.
(31) Tamborski, C.; Soloski, E. J. J. Organomet. Chem. 1969, 17, 185-
192.
OM060479P