Arylamidate palladium complexes containing deprotonated phthalimide and p-methylbenzamide: possibility of their participation in reductive elimination

Full text of DOI:10.1016/j.mencom.2007.05.003

Mendeleev
Communications
Mendeleev Commun., 2007, 17, 142–144
Arylamidate palladium complexes containing
deprotonated phthalimide and p-methylbenzamide:
possibility of their participation in reductive elimination
a
a
b
Alexey G. Sergeev, Galina A. Artamkina, Viktor N. Khrustalev,
b
a
Mikhail Yu. Antipin and Irina P. Beletskaya*
a
b
Department of Chemistry, M. V. Lomonosov Moscow State University, 119992 Moscow, Russian Federation.
Fax: +7 495 939 3618; e-mail: beletska@org.chem.msu.ru
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. Fax: +7 495 135 5085
DOI: 10.1016/j.mencom.2007.05.003
Arylamidate palladium complexes containing deprotonated p-methylbenzamide and phthalimide have been synthesised; the latter
has been characterised by X-ray diffraction data. A comparison of the catalytic and stoichiometric versions of N-arylation of
p-methylbenzamide and phthalimide in the presence of palladium complexes and DPPF as a ligand has been carried out.
The steps of oxidative addition, transmetallation and migratory
insertion are the most important steps of the catalytic cycle
determining the overall reaction rate and the very possibility
of reactions catalysed by palladium complexes such as cross-
coupling, Mizoroki–Heck reaction and many others. The
in 92% yield, but phthalimide does not react under these
conditions (Scheme 1).
According to the generally accepted mechanism, the amina-
tion (amidation) catalytic cycle involves three steps: oxidative
addition, substitution of halogen with amine and reductive
1
7
amination of aryl halides (Buchwald–Hartwig reaction) is an
elimination to give a C–N bond. The oxidative addition of
exception: the final step, viz., the reductive elimination of
arylamines from arylamide palladium complexes, plays a key
role in this process. The importance of this step should increase
even more for the arylation of amides because the coordinated
amide fragment should be less able to reduce palladium(II).
Furthermore, the lower nucleophilicity of amides in comparison
with amines can slow down the step of halogen substitution by
an amide fragment. In fact, the arylation of amides occurs less
aryl halides to palladium(0) has been studied fairly well for
complexes with various ligands.8
–15
Oxidative addition of p-bromobenzotrifluoride to Pd(0) in the
presence of DPPF occurs smoothly in toluene at 100 °C to give
the Pd(DPPF)(p-C H CF )Br complex 1 in 83% yield (see
6
4
3
Online Supplementary Materials).
Pd(dba) + DPPF + p-CF C H Br
Pd(DPPF)(p-C H CF )Br
6 4 3
2
3
6
4
toluene,
00 °C,
1
1
83%
readily than that of amines, whereas the arylation of low-basic
1
h
amides seems problematic so far.2–6
In this study, we compared the catalytic and stoichiometric
arylation of two amides with different basicity, namely,
phthalimide and p-methylbenzamide. The catalytic version of
the reaction was carried out in the presence of 2 mol% Pd dba ,
In order to obtain arylamide complexes 2 and 3, we carried
out the reactions of complex 1 and N-metallated amides in
THF.† The reactions occur at room temperature to give
arylamide complexes 2 and 3 in quantitative yields (according
to H and P NMR data). Experiments carried out under the
same conditions showed that aryl bromide complex 1 did not
react with free amides.
2
3
1
31
6
mol% DPPF and Cs CO as a base in dioxane at 100 °C.
2
3
The arylation of p-methylbenzamide gives an arylation product
O
The rate of substitution strongly depends on the nucleophilicity
of the anion: the reaction with the sodium salt of p-methyl-
benzamide was completed in less than 5 min, whereas the
complete conversion of complex 1 with weakly nucleophilic
NH2
Me
CF3
2
mol% Pd2dba3,
mol% DPPF
O
31
potassium phthalimide was observed only after 6 h. In P NMR
6
spectra, the signals of the original complex at d 10.4 and 30.4
Cs2CO3, dioxane,
00 °C, 4.5 h
N
H
2
1
( J 32.5 Hz) disappeared and two new doublets appeared at
PP
2
Me
d 15.2 and 27.7 ( J 30 Hz) for complex 2 and at d 16.6 and
24.0 ( J 30 Hz) for complex 3. In the H NMR spectra of amide
PP
9
2%
2
1
Br
O
PP
complexes, the signals of aromatic protons of coordinated amides
are shifted upfield with respect to the signals of free amides. The
proton signals of coordinated amide in complex 2 are observed
NH
F3C
O
3
at d 6.72 (d) and 6.95 (d) ( J 8 Hz), those of free amide appear
HH
2
mol% Pd2dba3,
mol% DPPF
3
at d 7.14 (d) and 7.71 (d) ( J 8 Hz), and those in complex 3
6
HH
no reaction
appear at d 7.00–7.15 (m) and 7.65–7.80 (m), respectively. In
Cs CO , dioxane,
2
1
3
†
00 °C, 24 h
During the preparation of this paper, a similar paper was published,
which dealt with a synthesis of palladium complexes containing coor-
dinated secondary amides.
Scheme 1
1
6
–
142 –

Mendeleev Commun., 2007, 17, 142–144
CF3
CF3
Ph Ph
O
P
2
p-MeC H C(O)NHNa
N
6
4
Dioxane, 60 °C, 2 h
H
Fe
>
Pd
C H Me-p
THF, 25 °C, < 5 min
6 4
Me
P
HN
2
7%
85%
CF3
O
Ph Ph
Ph Ph
(
in the presence of 1 equiv. of DPPF)
no reaction
2
P
Pd
95% ( H, 31P NMR)
1
3
Fe
Dioxane, 100 °C, 2 h
P
Br
O
Scheme 3
Ph Ph
CF3
Ph Ph
NK
without any ligand gives a mixture of several complexes. An
increase in the yields of products in reductive elimination of
arylamines from Pd(DPPF)(Ar)NRR' complexes due to the
1
P
O
O
Fe
Pd
P
THF, 25 °C, 6 h
19
N
addition of triphenylphosphine was noted by Driver and Hartwig.
A similar result was also observed in reductive elimination with
Ph
Ph O
formation of C–O,20 C–S and C–C bonds.
21
22
3
8
8%
Fe(1)
Fe(2)
95% ( H, 31P NMR)
1
>
P(1)
Scheme 2
P(2)
O(2)
P(4)
Pd(2)
Pd(1)
P(3)
C(51)
C(2)
C(1)
O(4)
C(64)
both cases, amidate complexes are formed irreversibly even
in the reaction with the low-basic phthalimide anion.
Phthalimide complex 3 was isolated in 88% yield. Slow
diffusion of light petroleum into a chloroform solution of
N(1)
C(8)
C(50)
F(3)
F(1)
N(2)
C(57)
C(6)
C(55)
‡
O(1)
O(3)
F(6)
F(5)
F(4)
F(2)
§
A
B
complex 3 gave crystals suitable for X-ray analysis in the form
of the solvate 3·1/2CHCl ·3/4C H ·1/2C H . A unit cell of
3
6
14
7
16
Figure 1 Molecular structure of the 3·1/2CHCl ·3/4C H ·1/2C H
3 6 14 7 16
the complex contains two independent molecules, which have
similar bond lengths and bond angles but differ in the DPPF
conformation with respect to the aryl and amide ligands. Figure 1
demonstrates the structures of both molecules (A and B). Complex
complex, where atoms are presented as thermal vibration ellipsoids (the
probability is 40%). Two independent molecules are shown, differing in the
DPPF conformation with respect to the aryl and amide ligands. Selected
bond lengths (Å) and bond angles (°) for A: Pd(1)–P(1) 2.2715(12), Pd(1)–
P(2) 2.3952(12), Pd(1)–N(1) 2.063(4), Pd(1)–C(1) 2.032(4), P(1)–Pd(1)–
P(2) 102.10(4), C(1)–Pd(1)–P(1) 86.36(13), C(1)–Pd(1)–N(1) 82.54(16),
N(1)–Pd(1)–P(2), 89.07(11), N(1)–Pd(1)–C(1)–C(6) 86.4(4), C(1)–Pd(1)–
N(1)–C(15) 89.3(4); for B: Pd(2)–P(3) 2.3007(13), Pd(2)–P(4) 2.3778(13),
Pd(2)–N(2) 2.078(4), Pd(2)–C(50) 2.035(5), P(3)–Pd(2)–P(4) 102.15(4),
C(50)–Pd(2)–P(3) 85.36(13), C(50)–Pd(2)–N(2) 84.43(17), N(2)–Pd(2)–P(4)
3
has a square-planar configuration. The aryl and phthalimide
ligands are almost orthogonal to the palladium square plane.
We studied the reductive elimination of N-arylamides from
the complexes obtained. The heating of complex 2 at 60 °C
results in a product in a low yield (27%). However, the addition
of 1 equiv. of DPPF allowed us to increase the yield to 85%,
i.e., to obtain the product in a yield approaching that of the
catalytic reaction. This effect of phosphine addition is difficult
to explain. It can be assumed that it is due to the reversibility
of the reaction and the ability of ‘PdDPPF’ to be inserted into
88.08(11), N(2)–Pd(2)–C(50)–C(51) 87.0(4), C(50)–Pd(2)–N(2)–C(57)
75.2(4).
§
Crystallographic data for 3·1/2CHCl3·3/4C6H14·1/2C7H16. Crystals
of C57.5H Cl F FeNO P Pd (M = 1126.39) are monoclinic, space group
55 1.5
3
2 2
P2 /c, a = 19.2799(14), b = 17.4190(13) and c = 30.120(2) Å, b = 93.424(2)°,
1
3
–3
2
V = 10097.2(13) Å , Z = 8, dcalc = 1.482 g cm , l(MoK ) = 0.71073 Å,
m(MoK ) = 0.842 mm , F(000) = 4620, T = 120(2) K.
the Csp –N bond (though it seems problematic) and also due to
–
1
an equilibrium shift to the right upon formation of Pd(DPPF)2.
Another explanation, which is also disputable, involves the
assumption that the N-arylamide is displaced when the phosphine
is added since the electrophilicity of palladium in this complex
decreases. Note that the heating of complex 2 in the presence
of DPPF as the main phosphorus-containing product results in
Crystallographic data for 4. Crystals of C H ClF FeP Pd (M =
4
1
32
3
2
=
841.31) are triclinic, space group P1, a = 11.0112(10), b = 12.0563(12)
and c = 14.2026(13) Å, a = 71.630(2)°, b = 89.028(2)°, g = 78.472(2)°,
3
–3
V = 1751.1(3) Å , Z = 2, d = 1.596 g cm , l(MoK ) = 0.71073 Å,
calc
m(MoK ) = 1.141 mm–1, F(000) = 848, T = 120(2) K.
The experimental data were obtained using a Bruker SMART 1K
three-circle diffractometer. Corrections for the absorption of X-ray
the Pd(DPPF) complex, whereas the same reaction carried out
2
17
irradiation were made semi-empirically using the SADABS software.
‡
Complex 3. Pd(DPPF)(p-C H CF )Br (45 mg, 50.8 mmol), potassium
The structures were determined by direct methods and refined by a full-
matrix least-squares method in an anisotropic approximation for non-
hydrogen atoms. The positions of hydrogen atoms were calculated
geometrically and refined within the riding model with fixed isotropic
temperature parameters. All calculations were carried out using the
6
4
3
phthalimide (11 mg, 59.38 mmol) and THF (2 ml) were placed in a
reactor filled with argon. The solution was stirred for 6 h at room
temperature, diluted with THF (5 ml), filtered, concentrated to 2 ml and
precipitated with light petroleum to give 43 mg of the product as orange-
1
18
yellow crystals (88%). H NMR (THF) d: 7.71–7.79 (m, 4H), 7.56–7.64
SHELXTL PLUS software (PC Version 5.10). For 3: R = 0.0697,
1
(
7
m, 4H), 7.33–7.39 (m, 2H), 7.23–7.29 (dt, 4H, J 2.5 and 8.0 Hz),
.15–7.23 (m, 8H), 7.10–7.15 (m, 2H), 7.00–7.06 (m, 2H), 6.59 (d, 2H,
wR = 0.1431 for 18544 reflections with I > 2s(I), GOF = 0.999. For 4:
2
R = 0.043, wR = 0.101 for 8082 reflections with I > 2s(I), GOF = 1.038.
1
2
J 8 Hz), 4.41–4.45 (m, 4H), 4.35–4.38 (m, 2H), 4.32–4.35 (m, 2H).
Atomic coordinates, bond lengths, bond angles and thermal param-
eters have been deposited at the Cambridge Crystallographic Data Centre
(CCDC). These data can be obtained free of charge via www.ccdc.cam.uk/
conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336 033; or deposit@ccdc.cam.ac.uk).
Any request to the CCDC for data should quote the full literature citation
and CCDC reference numbers 624042 and 624043 for 3 and 4, respectively.
For details, see ‘Notice to Authors’, Mendeleev Commun., Issue 1, 2007.
3
1
P NMR (THF) d: 24.00 (d, J 30 Hz), 16.58 (d, J 30 Hz). 13C NMR
(
(
(
(
CDCl ) d: 177.97, 163.77 (d, J 126 Hz), 137.52, 135.69, 134.63
3
C–P
d, JC–P 12 Hz), 134.31 (d, JC–P 12 Hz), 133.30 (d, JC–P 37 Hz), 131.87
d, JC–P 54 Hz), 130.63, 130.55, 130.35, 128.33 (d, JC–P 10 Hz), 128.23
d, JC–P 10 Hz), 122.90 (m), 120.36, 75.39 (d, JC–P 4.5 Hz), 75.28 (d,
–
1
JC–P 4 Hz), 73.51 (d, JC–P 6.5 Hz), 73.09 (d, JC–P 7 Hz). IR (THF, n/cm ):
665 ( C=O).
1
–
143 –

Mendeleev Commun., 2007, 17, 142–144
Unlike p-methylbenzamide complex 2, phthalimide complex
is stable even when heated at 100 °C.
CF3
3
Ph Ph
O
This result allows us to explain the fact that phthalimide
P
Pd
CHCl3
does not undergo arylation under catalytic conditions. As one
can see from the above examples, the reductive elimination of
N-arylamides from palladium amidate complexes 2 and 3 is
much more sensitive to the basicity of the amide anion than
substitution of bromine with an amidate fragment (‘transmetal-
lation’) and requires much more drastic conditions. The series
of relative facility of reductive elimination to give a C–N bond
from arylpalladium complexes with deprotonated amines and
azoles has been reported by Hartwig.23 The reaction rate increases
with amine basicity: reductive elimination from complexes with
aliphatic amines and anilines occurs at room temperature,
whereas the reaction with diarylamines and azoles requires
3
Fe
NH
THF, 100 °C, 2 h
P
Cl
O
Ph Ph
4
48%
61%
1
1
79% ( H NMR)
80% ( H NMR)
Scheme 4
cleavage of the C–N bond. The participation of chloroform as
an acid in this reaction is unlikely, since the reaction of com-
plex 3 with Bu OH, which has a similar acidity, does not occur
to any noticeable extent under these conditions. Presumably, the
cleavage of the complex at the Pd–N bond occurs due to the
action of HCl that is formed from chloroform.
Thus, we have synthesised the amidate complexes of palladium
with phthalimide and p-methylbenzamide ligands and studied
the ability of these complexes to participate in reductive
elimination resulting in the formation of a C–N bond.
t
1
9,24,25
more drastic conditions: 70 and 100 °C, respectively.
The reductive elimination of N-arylamide from amidate complex
with deprotonated p-methylbenzamide and from complexes
with di(p-tolyl)amine occurs under similar conditions (60 and
2
1
9,25
7
0 °C).
This agrees with the fact that the basicity of anions
of aromatic acid amides is comparable with that of diarylamine
anions. In fact, the pK of benzamide in DMSO is 23.5, while
that of diphenylamine is 24.9. The absence of reductive
a
2
6
elimination from complex 3 is undoubtedly due to the very low
Online Supplementary Materials
basicity of the phthalimide anion (pK 8.3).
Supplementary data associated with this article can be found
in the online version at doi:10.1016/j.mencom.2007.05.003.
a
It is interesting to note that, on heating, the chloroform
solvate of phthalimide complex, 3·1/2CHCl ·3/4C H ·1/2C H ,
3
6
14
7
16
gives the aryl chloride complex Pd(DPPF)(p-C H CF )Cl 4
References
6
4
3
§
,¶
and phthalimide.
1
J. F. Hartwig, in Handbook of Organopalladium Chemistry for Organic
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2001, 42, 4381.
Complex 4 was characterised by X-ray diffraction data§
(
Figure 2). We assume that this process involves the acidic
2
3
4
C(27)
C(26)
F(1)
C(28)
C(29)
F(3)
5
6
A. G. Sergeev, G. A. Artamkina and I. P. Beletskaya, Tetrahedron Lett.,
2003, 44, 4719.
C(7)
C(25)
C(24)
C(5)
C(2)
F(2)
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I. P. Beletskaya, Zh. Org. Khim., 2005, 41, 881 (Russ. J. Org. Chem.,
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C(4)
C(3)
C(23)
C(22)
C(6)
C(10) C(9)
C(11)
C(8)
C(1)
P(1)
7
C(12)
C(21)
Pd(1)
8
9
Fe(1)
C(15)
C(20)
Cl(1)
C(32)
C(31)
10 J. F. Hartwig and F. Paul, J. Am. Chem. Soc., 1995, 117, 5373.
11 L. M. Alcazar-Roman, J. F. Hartwig, A. L. Rheingold, L. M. Liable-
Sands and I. A. Guzei, J. Am. Chem. Soc., 2000, 122, 4618.
P(2)
C(13)
C(33)
C(35)
C(16)
C(17)
C(14)
C(30)
C(36)
C(41)
C(40)
C(39)
12 L. M. Alcazar-Roman and J. F. Hartwig, J. Am. Chem. Soc., 2001, 123,
C(34)
1
2905.
C(37)
C(38)
13 L. M. Alcazar-Roman and J. F. Hartwig, Organometallics, 2002, 21, 491.
4 J. P. Stambuli, C. D. Incarvito, M. Buehl and J. F. Hartwig, J. Am. Chem.
1
Soc., 2004, 126, 1184.
1
1
5 C. Amatore and F. Pfluger, Organometallics, 1990, 9, 2276.
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Incarvito and J. F. Hartwig, J. Am. Chem. Soc., 2006, 128, 9044.
Figure 2 Molecular structure of complex 4, where atoms are presented as
thermal vibration ellipsoids (probability 40%).
¶
A solution of Pd(DPPF)(p-C H CF )[N{(O)C}·2C H ]·1/2CHCl ·
17 G. M. Sheldrick, SADABS, V2.01, Bruker/Siemens Area Detector Absorp-
6
4
3
6
4
3
3
/4C H ·1/2C H (75 mg, 0.0665 mmol) in 2 ml of THF was heated
tion Correction Program, Bruker AXS Inc., Madison, WI, 1998.
6 14 7 16
for 2 h in a sealed tube at 100 °C under argon; the reaction mixture was
then cooled and concentrated. The residue was chromatographed on
18 G. M. Sheldrick, SHELXTL, V5.10, Bruker AXS Inc., Madison, WI,
1
998.
1
2
9 M. S. Driver and J. F. Hartwig, J. Am. Chem. Soc., 1997, 119, 8232.
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2003, 22, 2775.
40–63 m silica gel using a 1:2 ethyl acetate–light petroleum mixture
(
65–68 °C) as an eluent to give 27 mg (48%) of complex 4 as orange-
1
31
yellow crystals and 6 mg (61%) of phthalimide. The H and P NMR
spectra of the products obtained are identical to the spectra of the
products in the reaction mixture.
21 G. Mann, D. Baranano, J. F. Hartwig, A. L. Rheingold and I. A. Guzei,
J. Am. Chem. Soc., 1998, 120, 9205.
2
2
2
2 D. A. Culkin and J. F. Hartwig, Organometallics, 2004, 23, 3398.
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1
Complex 4. H NMR (THF) d: 8.00–8.13 (m, 4H), 7.37–7.47 (m, 6H),
7
.30–7.38 (m, 4H), 7.22–7.30 (m, 2H), 7.00–7.13 (m, 6H), 6.65 (m,
quasi-doublet, 2H, J 7.5 Hz), 4.76–4.80 (m, 2H), 4.51–4.56 (m, 2H),
1
4
.15–4.20 (m, 2H). H NMR (CDCl ) d: 8.00–8.13 (m, 4H), 7.41–7.52
3
25 J. F. Hartwig, Angew. Chem., Int. Ed. Engl., 1998, 37, 2046.
6 F. G. Bordwell, Acc. Chem. Res., 1988, 21, 456.
(
m, 6H), 7.27–7.38 (m, 6H), 7.04–7.17 (6H), 6.76 (m, quasi-doublet,
2
2
3
H, J 8 Hz), 4.67–4.73 (m, 2H), 4.48–4.53 (m, 2H), 4.13–4.19 (m, 2H),
3
1
.55–3.62 (m, 2H). P NMR (THF) d: 31.46 (d, J 31.5 Hz), 11.09 (d,
31
J 31.5 Hz). P NMR (CDCl ) d: 33.25 (d, J 32.5 Hz), 12.38 (d, J 32.5 Hz).
Received: 23rd October 2006; Com. 06/2799
144 –
3
–