Copper(I)-anilide complex [Na(phen)3][Cu(NPh2) 2]: An intermediate in the copper-catalyzed N-Arylation of N-Phenylaniline

Article abstract of DOI:10.1002/chem.201002661

Complex [Na(phen)₃][Cu(NPh₂)₂] (2), containing a linear bis(N-phenylanilide)copper(I) anion and a distorted octahedral tris(1,10-phenanthroline)sodium counter cation, has been isolated from the catalytic C-N cross-coupling reaction with the CuI/phen/tBuONa (phen=1,10-phenanthroline) catalytic system. Complex 2 can react with 4-iodotoluene to produce 4-methyl-N,N-diphenylaniline (3a) with 70.6% yield. In addition, 2 can work as an effective catalyst for Ci￡N coupling under the same reaction conditions, thus indicating that 2 is the intermediate of the catalytic system. Both [Cu(NPh₂) ₂]^- and [Cu(NPh₂)I]^- have been observed by in situ electron ionization mass spectrometry (ESI-MS) under catalytic reaction conditions, thus confirming that they are intermediates in the reaction. A catalytic cycle has been proposed based on these observations. The molecular structure of 2 has been determined by single-crystal X-ray diffraction analysis.

Full text of DOI:10.1002/chem.201002661

DOI: 10.1002/chem.201002661
Copper(I)–Anilide Complex [NaACTHNUTRGENNG(U phen)3][CuACHTUNTGREN(NUGN NPh2)2]: An Intermediate in
the Copper-Catalyzed N-Arylation of N-Phenylaniline
Chia-Kai Tseng,[a, b] Chi-Rung Lee,[c] Chien-Chung Han,[b] and Shin-Guang Shyu*[a, d]
Abstract: Complex [Na
(NPh2)2] (2), containing a linear bis(N-
phenylanilide)copper(I) anion and
distorted octahedral tris(1,10-phenan-
throline)sodium counter cation, has
G
(3a) with 70.6% yield. In addition, 2
can work as an effective catalyst for
have been observed by in situ electron
ionization mass spectrometry (ESI-MS)
under catalytic reaction conditions,
thus confirming that they are inter-
mediates in the reaction. A catalytic
cycle has been proposed based on
these observations. The molecular
structure of 2 has been determined by
single-crystal X-ray diffraction analysis.
G
À
C N coupling under the same reaction
conditions, thus indicating that 2 is the
intermediate of the catalytic system.
been isolated from the catalytic C N
Both [CuACTHNGUTRENUNG ACHTUGNTRENNNUG
(NPh2)2]À and [Cu(NPh2)I]À
À
cross-coupling reaction with the CuI/
phen/tBuONa
(phen=1,10-phenan-
Keywords: copper · cross-coupling ·
mass spectrometry N ligands
reactive intermediates
throline) catalytic system. Complex 2
can react with 4-iodotoluene to pro-
·
·
duce
4-methyl-N,N-diphenylaniline
Introduction
plexes with the corresponding amido ligand have been pre-
pared, and their catalytic activities have been evaluated.[5b,6]
However, direct isolation of the intermediates from the cat-
alytic reaction has not been achieved.
À
Catalytic systems for copper-catalyzed C N cross-coupling
reactions usually consist of a ligand, a base, and a copper
salt.[1] In addition, copper complexes with various ligands
have been synthesized[2] and have served as the catalytic
center in the catalytic system.[3] During the copper-catalyzed
In the copper-catalyzed N-arylation of amines, the most
commonly used catalyst system consists of CuI, 1,10-phenan-
throline (phen) and sodium tert-butoxide. The reaction is
typically carried out in toluene at 1208C under an inert at-
mosphere. However, although the mechanism is still not
well-established, the bis(1,10-phenanthroline)copper(I) com-
À
C N coupling reaction, the proton of the amide may be re-
moved by the base to generate an amido anion, which may
then replace the counter anion of the copper source and
produce a copper complex with the amido ligand.[4] Mecha-
nistic studies show that formation of the copper complex
with the amido ligand may be the first step in the catalytic
cycle of the copper-catalyzed N-arylation of amides, fol-
lowed by the oxidative addition of the aryl halide.[5] Com-
plex, [CuACTHNUTRGNEUNG
(phen)2]I (1)[7] may be formed in situ in the first
step. To verify the proposed catalytic cycle, the intermediate
of the reaction should be isolated from the catalytic reaction
and checked for catalytic activity. Herein, we report the iso-
lation, structural characterization, and catalytic activity of
[NaACHTUNGRTENNUG(phen)3][CuACHTUNGTREN(NUGN NPh2)2] (2). Electron ionization mass spec-
trometry (ESI-MS) analysis of the catalytic system in situ
under the catalytic reaction conditions indicating the pres-
ence of [Cu
also reported.
[a] C.-K. Tseng, S.-G. Shyu
Institute of chemistry
(NPh2)2]À and [Cu(NPh2)I]À in the reaction is
ACHUTGTNRENNUG CAHTUNGTRENNUGN
Academia Sinica
Taipei 115, Taiwan (Republic of China)
Fax : (+886)2-2783-1237
E-mail: sgshyu@chem.sinica.edu.tw
[b] C.-K. Tseng, C.-C. Han
Results and Discussion
Department of Chemistry
National Tsing Hua University
Hsinchu, Taiwan (Republic of China)
Separation and characterization of 2: General procedures
reported in the literature[8] were followed to investigate the
[c] C.-R. Lee
À
copper-catalyzed C N coupling reaction between an aryl
Department of Chemical and Materials Engineering
Minghsin University of Science and Technology
Taiwan (Republic of China)
iodide (4-iodotoluene) and an amine (N-phenylaniline). A
mixture of N-phenylaniline (1.2 equiv), 4-iodotoluene
(1 equiv), sodium tert-butoxide (2 equiv), CuI (10 mol%)
and phen (20 mol%) was allowed to stir in toluene at room
temperature. A yellow precipitate (denoted as Y) was ob-
served after five minutes. The mixture was then allowed to
stir for additional 20 min. At this stage, 4-iodotoluene was
[d] S.-G. Shyu
Department of Chemistry
National Central University
Jhong Li, Taiwan (Republic of China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002661.
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Chem. Eur. J. 2011, 17, 2716 – 2723

FULL PAPER
found by GC analysis to be essentially unchanged. When
the above reaction mixture was heated to 1208C, the precip-
itate Y redissolved, and the reaction solution became red-
dish-brown. After 40 h, the reaction was worked up to give
4-methyl-N,N-diphenylaniline (3a) in 66.4% isolated yield
(79.1% GC yield). These results imply that Y, which is
formed at room temperature during the initial stage, may
contain the intermediate of the catalytic reaction.
Compound 1 was also prepared from a mixture of phen
(2 equiv) and CuI (1 equiv) in toluene as a purple powder in
high yield by following a previously reported method.[7]
À
Complex 1 could effectively catalyze the C N coupling reac-
tion between 4-iodotoluene and N-phenylaniline under simi-
lar reaction conditions to form 3a with a similar isolated
yield of 68.0% (74.0% GC yield). In addition, 2 could also
be formed by the reaction of 1, sodium tert-butoxide
(2 equiv), N-phenylaniline (1.2 equiv), and 4-iodotoluene
(1.0 equiv), in toluene at room temperature. Whether 1 was
formed as a precursor complex in the CuI/phen/tBuONa
system prior to formation of 2, or whether it just provides
the copper(I) and phen in the reaction (the phen ligand can
readily interchange) is still not clear. Scheme 1 shows the
formation of 2 through different reaction routes.
In another batch of experiments, the room temperature
precipitate Y was collected in a glove box and subjected to
more detailed characterizations. As observed under a micro-
scope, Y was found to be composed of a mixture of yellow
crystals and a white powder. Mixture Y could also be ob-
tained from a similar reaction mixture in the absence of 4-
1
iodotoluene. H NMR spectroscopic analysis indicated that
Y was composed of a mixture of sodium tert-butoxide and
À
an unknown compound containing three phen, two NPh2 ,
and one toluene moieties. This yellow crystalline complex
was separated from Y by hand-picking, giving a respectable
yield of 48.1% (based on the mol% of CuI) or as 72.1% (if
the limited reagent of phen is used as the calculation base),
and its structure was identified as 2·toluene by single-crystal
X-ray diffraction studies as shown in Figure 1, which is con-
Scheme 1. The formation of 2 through different reaction routes. i) N-Phe-
nylaniline; ii) N-phenylaniline, 4-iodotoluene; iii) remove THF, add N-
phenylaniline, tBuONa, toluene.
Molecular structure of 2·toluene: Complex 2·toluene con-
sists of a bis(N-phenylanilide)copper(I) anion, a distorted
octahedral tris(1,10-phenanthroline)sodium counter cation,
ACTHNUTRGNEUNG
and one solvated toluene. The Na+ in [Na(phen)3]+ is six-
coordinated by the nitrogen atoms of the three phen ligands,
À
with Na N distances in the range of 2.504(3)–2.424(3) ꢁ.
À
These distances are very similar to the reported Na N dis-
tances in the tris(1,10-phenanthroline)sodium cation in com-
plexes
(C3H2N3S3),[11] [Na
[Na(phen)3][Ln
(C5H5)3Cl].[13] In the bis(N-phenylanilide)-
copper(I) anion, the N1-Cu-N2 angle is 169.9(1)8 and is
slightly nonlinear. The N-Cu-N angle in [{Li(OEt2)2}][Cu-
(NPh2)3],[14] which also has a [Cu(NPh2)2]À portion, is
177.4(2)8. Unlike [{Li(OEt2)2}][Cu(NPh2)3], in which each of
the two nitrogen atoms in the [Cu
(NPh2)2]À unit is coordi-
nated to a lithium cation, the [Cu
(NPh2)2]À in 2·toluene is
an outer sphere counterion of [Na
(phen)3]+, and there is no
[Na
G
N
[Na
ACHTUNGTRENNUNG(phen)3]-
G
N
(C9H6NO)],[12] and
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Figure 1. The ORTEP drawing of 2·toluene with 50% ellipsoids. Hydro-
gen atoms and the solvated toluene are omitted for clarity. Selected bond
A
ACHTUNGTRENNUNG
À
À
lengths (ꢁ): Cu N1 1.854(3), Cu N2 1.862(3).
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
sistent with its 1H NMR and elemental analyses. Alterna-
tively, 2 could be separated by recrystallization of Y in anhy-
drous CH2Cl2 and n-hexane with comparable yield (36.2%,
based on the mol% of CuI) as a yellow crystalline solid.
The formation of 2 may proceed through initial formation
of cuprous tert-butoxide, followed by substitution of the tert-
butoxide ligand with the N,N-diphenylamino anion. Thus,
cuprous iodide was allowed to react with sodium tert-butox-
ide in tetrahydrofuran (THF) to generate cuprous tert-bu-
toxide.[5b,6b,9] The solvent was then removed and toluene
(4 mL), N-phenylaniline, and sodium tert-butoxide (1:1
ratio) were added to the system. After stirring the mixture
for 30 min, Y was obtained as indicated by its 1H NMR
spectroscopic analysis.
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
bonding between the Na ion and the nitrogen atoms in [Cu-
À
À
G
which is slightly shorter than that in [{Li
À
AHCTUNTGRENGUN(N NPh2)3] (1.895(2) ꢁ). This indicates that the Cu N coordi-
nation bonding in 2·toluene is stronger than the correspond-
À
ing Cu N bonding in [{Li
nation of the nitrogen atoms to the lithium cation in [{Li-
G
G
ACHTUNERGN(UNG OEt2)2}][CuACHTUTGNRNEN(UGN NPh2)3] may reduce the electron density on N
and weaken its coordination to Cu as compared with the
À
corresponding Cu N coordination bonding in 2·toluene, in
which the nitrogen atom is not coordinated to the sodium
cation.
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2717

S.-G. Shyu et al.
Catalytic cycle of the copper-
catalyzed N-arylation of ani-
line: If compound 2 is the inter-
mediate, it should effectively
react with 4-iodotoluene alone
to form the product. Hence, 2
was allowed to react with two
equivalents of 4-iodotoluene in
the absence of sodium tert-but-
oxide, assuming that the role of
base is only to remove the
proton from N-phenylaniline to
generate the N,N-diphenylami-
no anion. The GC yield of the
reaction was 70.6% (based on
the 4-iodotoluene used). In ad-
dition, 2 also worked as an ef-
fective catalyst for the catalytic
À
C N coupling reaction of
N-phenylaniline and 4-iodoto-
luene. For example, when
10 mol% of 2 was added into a
mixture of N-phenylaniline
Figure 2. ESI(+)(À)-MS from the solution taken during the reaction of N-phenylaniline with tBuONa in the
presence of CuI and phen in toluene at room temperature.
(1.2 equiv), 4-iodotoluene (1 equiv), and sodium tert-butox-
tion (see the Supporting Information). Peaks at m/z 563.2
and 383.1 corresponding to [Na
(phen)3]+ and [Na(phen)2]+,
À
ide (2 equiv) in toluene, the catalytic C N coupling reaction
G
ACHTUNGTRENNUNG
proceeded effectively at 1208C to give 3a in 99.1% GC
yield (in 40 h). These observations suggest that 2 is an inter-
mediate in the CuI/phen/tBuONa catalytic system. The pro-
posed catalytic cycle is shown in Scheme 2. Complex 2 first
reacts with 4-iodotoluene to form A through an oxidative
respectively, were also observed in the positive-ion mode.
No other Cu species were found in either positive-ion or
negative-ion modes. No signal of [CuACTHNUTRGNEUNG
(phen)2]+ was ob-
served, indicating that [CuACHTNUGRTENUNG(phen)2]I may not be formed
during the formation of 2 at room temperature. Because IÀ
addition reaction. Reductive elimination of 3a produces
was observed in the negative-ion mode, the presence of [Na-
À
[Cu
A
(phen)2]+ in the ESI-MS and the isolation of 2 may indicate
ACHTUNGTRENNUNG
and complete the catalytic cycle.
that [NaACHTNGUTRENNUG CAHTUNGTRNE(NUNG phen)2]I.
(phen)2]+ arises from [Na
Because the catalytic reaction is carried out at 1208C,
ESI-MS analysis was carried out in situ at 1208C to detect
the intermediates (Figure 3). A solution of N-phenylaniline
(1.2 equiv), 4-iodotoluene (1 equiv), sodium tert-butoxide
(2 equiv), CuI (10 mol%), and phen (30 mol%) in toluene
was stirred at 1208C for 2 h. The solution was then trans-
ferred to a GC vial in a dry-box. The temperature of the so-
lution was kept at 1208C by immersing the GC vial in a
sand bed and ESI-MS spectra of the solution were taken.
The ESI-MS spectra recorded in the negative-ion mode
showed two peaks at m/z 399.1 and 357.9, which were identi-
fied as [CuACTHNUTRGENNUG ACHTUNGTRENNGUN
(NPh2)2]À and [Cu(NPh2)I]À, respectively, accord-
ing to their isotopic distributions (see the Supporting Infor-
mation).
Scheme 2. The proposed catalytic cycle.
Peaks at m/z 423.1 and 383.1 corresponding to
[CuACTHNUGRTNENUG ACHUTNGTRENNUGN
(phen)2]+ and [Na(phen)2]+, respectively, were also ob-
To gain a better insight into the reaction path, ESI-MS
analysis was carried out in situ. A solution of N-phenylani-
line (1.2 equiv), sodium tert-butoxide (2 equiv), CuI
(10 mol%), and phen (30 mol%) in toluene was stirred at
room temperature for 1 h, and ESI-MS analysis of the reac-
tion solution was undertaken (Figure 2). The ESI-MS in
negative-ion mode showed a peak m/z 399.1, which was
served in the positive-ion mode of ESI-MS, indicating that
ligand redistribution had occurred under the catalytic reac-
tion conditions. The amount of [NaACHTUNGTRNEUNG
(phen)3]+ was much less
in the in situ ESI-MS recorded under catalytic conditions
than observed under similar temperatures in the absence of
4-iodotoluene, indicating that this ligand redistribution
favors the formation of [Cu
tion (see the Supporting Information).
(phen)2]+ in the catalytic reac-
ACHTUNGTRENNUNG
identified as [Cu
ACHTUNGTRENNUNG
(NPh2)2]À according to its isotopic distribu-
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N-Arylation of N-Phenylaniline
FULL PAPER
been reported that CuI can
À
work as a catalyst in the C N
coupling reaction in the ab-
sence of ligand.[15] As shown in
the catalytic cycle, the CuI of 2
is the catalytic site. This may
imply that, in the absence of
phen, the catalytic system
should still be active. In fact,
when phen is absent, under sim-
ilar reaction conditions (1 equiv
of 4-iodotoluene, 1.2 equiv of
N-phenylaniline, 2 equiv of
sodium
tert-butoxide,
and
10 mol% of CuI; 1208C for
40 h), the yield of the reaction
was 22.0% (35.4% GC yield).
The reaction is still catalytic, al-
though the turnover number
(TON) is much lower (2.2).
Attempts to isolate the pro-
posed intermediate Na[Cu-
Figure 3. ESI(+)(À)-MS from the solution taken during the reaction of N-phenylaniline and 4-iodotoluene
with tBuONa in the presence of CuI and phen in toluene at 1208C.
AHCTUNGTRENNUNG
In the positive-ion mode, a peak at m/z 513.1 was ob-
served that corresponded to Na[Cu(NPh2)2A
(p-tolyl)]+; its
isotopic distribution was consistent with this assignment.
The [Cu(NPh2)2A(p-tolyl)] portion of this cation might come
from Na[Cu(NPh2)2A(p-tolyl)I], the sodium salt of proposed
intermediate A, which fragmented into IÀ and Na[Cu-
(NPh2)2A
(p-tolyl)]+. The iodide anion was observed in the
negative-ion mode of the ESI-MS.
The presence of [Cu
(phen)2]+ and [Cu
cate the formation of [Cu(phen)2][Cu(NPh2)2] in the reac-
tion. It has been reported that in polar solvent (N,N-dime-
thylformamide (DMF)) at À258C, [Cu(phen)(phth)] and
[Cu(phen)(pyrr)] can form [Cu(phen)2][Cu(phth)2] and [Cu-
(phen)2][Cu(pyrr)2] (phth=phthalimidate, pyrr=pyrrolidin-
onate), respectively.[6b] We did not observe [Cu
(phen)-
(NPh2)] in the reaction solution either at 1208C or at room
ACHTUNGTRENNUNG
G
CHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
E
G
intermediate in the reaction. The lower TON of the catalytic
reaction in the absence of phen suggests that the reactivity
of the catalyst depends on the counter cation. At 1208C,
R
CHTUNGTRENNUNG
G
N
both [CuACTHNGUTRENUNG ACHTUGNTRENNNUG
(phen)2]+ and [Na(phen)2]+ were observed when
three equivalents of phen was used, indicating that the
actual counter cations in the reaction system are [Cu-
A
(NPh2)2]À may indi-
ACHTUNGTRENNUNG
E
R
(phen)2]+ and [Na(phen)2]+. Thus, although phen ligand is
ACHUTGTNRENNUG CAHTUNGTRENNUGN
not essential in the catalytic system, it may greatly promote
the catalytic activity by stabilizing the [Cu
(NPh2)2]À with the
large [Cu
(phen)2]+ or [Na(phen)2]+.
G
R
ACHTUNGTRENNUNG
N
G
R
G
U
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
E
Comparison of the selectivities of stoichiometric and catalyt-
ic reactions: Based on the proposed catalytic cycle, NaNR2
should also be able to enter the catalytic cycle through the
ACHTUNGTRENNUNG
temperature in the ESI-MS, indicating that [Cu
the catalytic center in the system.
(NPh2)2]À is
ACHTUNGTRENNUNG
reaction between NaNR2 and [Cu
(NPh2)I]À to generate
ACHTUNGTRENNUNG
[Cu(NPh2)
N
ACHTUNGTRENNUNG
Effect of phen in the CuI/phen/tBuONa catalytic system: In
compound 2, the counter cation is tris(1,10-phenanthroline)-
sodium. This implies that three equivalents of phen (relative
to CuI) are needed to optimize the yield from the catalytic
system. Indeed, when the catalytic reaction was carried out
under similar reaction conditions with three equivalents of
phen, the yield of the reaction was found to be greatly en-
hanced to 95.2% (vs. 79.1% with two equivalents of phen).
Furthermore, when three equivalents of phen were used, the
isolated yield of 2 was also enhanced from 36.2 to 56.7%
(based on the amount of CuI used).
methylaniline (1.2 equiv), 4-iodotoluene (1 equiv), sodium
tert-butoxide (2 equiv), and 2 (10 mol%) was allowed to stir
in toluene at 1208C for 40 h (Scheme 3). The results showed
that both 3a and N,4-dimethyl-N-phenylaniline (3b) were
Theoretically, when two equivalents of phen were used,
only 66.7% of CuI could be converted into 2; the rest of the
CuI (33.3%) should remain in the reaction mixture. It has
Scheme 3. Comparison of selectivities in the catalytic reaction.
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2719

S.-G. Shyu et al.
that the higher formation yield
of 3a (vs. 3b) may be attributed
to both a faster reductive elimi-
À
nation between NPh2 and p-
À
tolyl (vs. that between NPhMe
and p-tolyl) and the easier gen-
eration of the catalyst species
[Cu
(NPh2)2]À (vs. that of [Cu-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
the fact that the NH of N-phe-
nylaniline has a lower pKa than
that of N-methylaniline.
Similar catalytic and stoichio-
metric reactions between 2 and
4-methyl-N-phenylaniline were
carried out and the results are
listed in Schemes 3 and 4. Re-
sults indicate that the rate of re-
ductive elimination between
À
NPh2 and p-tolyl to produce
3a is similar to that between
Figure 4. ESI(À)-MS from the solution taken during the reaction of N-phenylaniline with tBuONa in the pres-
ence of CuI in toluene at 1208C.
obtained with 14.9 and 30.2% GC yield, respectively (based
on the amount of 4-iodotoluene used). The reaction is
indeed catalytic, with a TON of 4.5. This observation indi-
cates that NaNPhMe, which is generated from the reaction
between sodium tert-butoxide and N-methylaniline, may
enter the reaction cycle by reaction with [Cu
form [Cu(NPh2)
(NPhMe)]À, which reacts further with 4-io-
(NPh2)I]À to
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Scheme 5. Comparison of selectivities in the catalytic reaction.
dotoluene to produce 3a or 3b. To compare the reactivity of
À
NPh2 and NMePhÀ, a stoichiometric reaction using the
same amount of reagents but with 50 mol% of 2 was carried
out (Scheme 4). Under these conditions, coupling products
À
NPhACHTNGUTERNNU(G p-tolyl) and p-tolyl to produce 4-methyl-N-(4-methyl-
phenyl)-N-phenylaniline (3c). When a stoichiometric reac-
tion was carried out by using 50 mol% of 2, products 3a
and 3c were obtained in 42.3 and 53.7% GC yield (based
on the amount of 4-iodotoluene used), respectively. This
result indicates that the reductive elimination rate ratio be-
À
tween NPh2 and p-tolyl (forming 3a) compared to that be-
À
tween NPh
A
dition, in the catalytic reaction (using 10 mol% of 2) 3a and
3c were obtained in 9.5 and 68.1% GC yield (based on the
amount of 4-iodotoluene used), respectively. Although, the
Scheme 4. Comparison of selectivities in the stoichiometric reaction.
À
yield ratio (1:7) appears different to the feed ratio of NPh2
À
versus NPh
A
3a and 3b were obtained in 60.4 and 25.7% GC yield
(based on the amount of 4-iodotoluene used), respectively.
consistent with the expected yield of 1:7.2 after adjustment
for the reductive elimination rate ratio (1:1.2).
À
This result indicates that reductive elimination of NPh2
and p-tolyl to produce 3a is more favorable than that of
When a similar reaction was carried out by using CuI
(10 mol%), phen (30 mol%), 4-methyl-N-phenylaniline
À
NPhMe and p-tolyl to produce 3b.
(1 equiv),
N-phenylaniline
(1 equiv),
4-iodotoluene
When a similar reaction was carried out by using CuI
(10 mol%), phen (30 mol%), N-methylaniline (1 equiv),
N-phenylaniline (1 equiv), 4-iodotoluene (1 equiv), and
sodium tert-butoxide (2 equiv), 3a and 3b were obtained in
80.1 and 8.1% GC yield (based on the amount of 4-iodoto-
luene used), respectively (Scheme 5). The results suggest
(1 equiv), and sodium tert-butoxide (2 equiv), 3a and 3c
were obtained in 49.0 and 48.4% GC yield (based on the
amount of 4-iodotoluene used), respectively (Scheme 5).
The results suggest that not only is the rate of reductive
elimination between NPh2 and p-tolyl (forming 3a) similar
to that between NPh
À
À
(p-tolyl) and p-tolyl (forming 3c), but
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N-Arylation of N-Phenylaniline
FULL PAPER
stirred and heated at 1208C in an oil bath for 40 h. The pure product 3a
(172.0 mg, 66.4%) was obtained as a white solid after separation. GC
yield: 79.1% (1,4-di-tert-butylbenzene was used as the internal standard,
correction factor for 3a: 0.787).
that the generation rate of the catalyst species of
[Cu
in the catalytic reaction.
ACHTUNGTRENNUNG ACHTUNRTEGG[NNUN NPhACTHNUGTRENNGUN
(NPh2)2]À is also similar to that of {Cu (p-tolyl)]2}À
À
Copper-catalyzed C N coupling reaction with 1: In a glove box, 1
(55.0 mg, 0.10 mmol, 10 mol%), tBuONa (192.0 mg, 2.0 mmol), and tolu-
ene (4 mL) were transferred to a Pyrex tube fitted with a Teflon screw-
cap. N-Phenylaniline (203.0 mg, 1.2 mmol) and 4-iodotoluene (218.0 mg,
1.0 mmol) were then added at RT. The mixture was stirred and heated at
1208C in an oil bath for 40 h. The pure product 3a (176.1 mg, 68.0%)
was obtained as a white solid after separation. GC yield: 74.0% (1,4-di-
tert-butylbenzene was used as the internal standard, correction factor for
3a: 0.787).
Conclusion
This paper describes the isolation of 2 as an intermediate in
the catalytic C N coupling reaction between 4-iodotoluene
and N-phenylaniline in the CuI/phen/tBuONa catalytic
system. When 1 was used as the copper(I) and phen source,
2 was also obtained under similar reaction conditions. The
isolated 2 can work as an effective catalyst to carry out the
À
À
Copper-catalyzed C N coupling reaction with CuI and three equivalents
of Phen: In a glove box, CuI (19.0 mg, 0.10 mmol, 10 mol%), 1,10-phe-
nanthroline (54.0 mg, 0.3 mmol, 30 mol%), tBuONa (192.0 mg,
2.0 mmol), and toluene (4 mL) were transferred to a Pyrex tube fitted
with a Teflon screw-cap. N-Phenylaniline (203.0 mg, 1.2 mmol) and 4-io-
dotoluene (218.0 mg, 1.0 mmol) were then added at RT. The mixture was
stirred and heated at 1208C in an oil bath for 40 h. GC yield: 95.2%
(1,4-di-tert-butylbenzene was used as the internal standard, correction
factor for 3a: 0.787).
À
C N coupling under the same reaction conditions. Cop-
per(I) fragments of [Cu
G
E
Na[CuACHTUNGTRENNUNG(NPh)2ACHTUNGTRENNUNG
(p-tolyl)]+ were observed in situ by ESI-MS
analysis under the catalytic reaction conditions. Based on
these observations, a catalytic cycle involving the formation
of 2 was proposed.
Separation of 2·toluene and 2 from the reaction mixture: In a glove box,
CuI (19.0 mg, 0.10 mmol, 10 mol%), 1,10-phenanthroline (36.0 mg,
0.2 mmol, 20 mol%), tBuONa (192.0 mg, 2.0 mmol), and toluene (4 mL)
were transferred into a 15 mL Pyrex tube fitted with a Teflon screw-cap.
After stirring for 5 min, N-phenylaniline (203.0 mg, 1.2 mmol) was added,
and the resulting mixture was stirred for an additional 20 min at RT. A
yellow precipitation was obtained. The mixture was then heated to
1208C in an oil bath for 30 min to give a transparent reddish-brown solu-
tion. The solution was cooled to RT, and a yellow precipitation contain-
Experimental Section
All reagents were purchased from commercial sources and used without
further purification. Copper(I) iodide (fine grey powder), N-phenylani-
line, 4-iodotoluene, 1,10-phenanthroline, and 1,4-di-tert-butylbenzene
were purchased from ACROS. tBuONa was purchased from Alfa Aesar.
Toluene (dried, seccoSolvꢂ) was purchased from Merck and purged with
argon for 15 min before use. All reagents were transferred to the reaction
vessel (Pyrex tube with a Teflon screw cap) in a glove box. 1H NMR
spectra were recorded with Bruker AV 300 and Bruker AMX 400 instru-
ments. GC experiments were performed with an Agilent 6890N gas chro-
ing both crystals of [NaACHTNURGTENNG(U phen)3][CuACHTUGNTERN(NUGN NPh2)2]·toluene and tBuONa as indi-
cated by its 1H NMR spectrum was obtained. 1H NMR (300 MHz,
CD2Cl2): d=1.22 (s, tBuONa), 2.32 (s, 3H), 6.89 (t, J=7.5 Hz, 4H), 7.08
(d, J=7.8 Hz, 8H), 7.25 (m, 13H), 7.74–7.78 (m, 6H), 7.96 (s, 6H), 8.44
(d, J=7.8 Hz, 6H), 9.01 ppm (d, J=3.6 Hz, 6H). Yellow crystals of 2·tol-
uene were separated by hand-picking. Yield: 50.8 mg (48.1%). 1H NMR
(300 MHz, CD2Cl2): d=2.33 (s, 3H), 6.90 (t, J=7.2 Hz, 4H), 7.08 (d, J=
8.1 Hz, 8H), 7.22–7.27 (m, 13H), 7.75–7.79 (m, 6H), 7.97 (s, 6H), 8.45 (d,
J=7.8 Hz, 6H), 9.02 ppm (br. s, 6H); elemental analysis calcd (%) for
C67H52CuN8Na (1055.72): C 76.22, H 4.96, N 10.61; found: C 75.83, H
5.01, N 10.76.
matograph equipped with
a 30 mꢃ0.53 mmꢃ3.0 mm HP-1 capillary
column and a FID detector. Elemental analyses were performed with a
Thermo CHNS-O analyzer (FlashEA 1112 series). High-resolution ESI-
MS were measured with a Waters LCT Premier XE with a dual ioniza-
tion ESCiꢂ in the Mass Spectrometry Facility in the Institute of Chemis-
try, Academia Sinica. Leucine Enkephalin m/z 556.277 [M+H]+ was
used as a reference standard.
In another batch of experiments, the yellow precipitation containing both
complex 2·toluene and tBuONa obtained after the reaction, was recrys-
tallized in dried CH2Cl2 and n-hexane. Complex 2 was obtained as a
yellow powder. Yield: 35.0 mg (36.2%). 1H NMR (400 MHz, CD2Cl2):
d=6.91 (br, 5H), 7.08 (br, 8H), 7.25 (br, 7H), 7.72 (br, 6H), 7.91 (br,
6H), 8.38 (br, 6H), 9.05 ppm (br, 6H); elemental analysis calcd (%) for
C60H44CuN8Na (963.56): C 74.79, H 4.60, N 11.63; found: C 74.83, H 4.38,
N 11.60.
À
Typical procedure for copper(I)-catalyzed C N coupling: In a glove box,
CuI (19.0 mg, 0.10 mmol, 10 mol%), tBuONa (192.0 mg, 2.0 mmol), and
toluene (4 mL) were transferred to a Pyrex tube fitted with a Teflon
screw-cap. After stirring for 5 min, N-phenylaniline (203.0 mg, 1.2 mmol)
and 4-iodotoluene (218.0 mg, 1.0 mmol) were added, and the resulting
mixture was stirred for an additional 20 min at RT. The mixture was then
heated at 1208C in an oil bath for 40 h. The tube was removed from the
oil bath, and the resulting solution was allowed to cool to RT. Water
(20 mL) was added into the above solution at RT, and the resulting mix-
ture was extracted with CH2Cl2 (3ꢃ15 mL). The collected CH2Cl2 frac-
tion was dried over MgSO4, filtered, and the solvent was removed under
reduced pressure. The crude product was purified by chromatography on
silica gel (CH2Cl2/hexane, 1:30). The pure product 3a (58.0 mg, 22.0%)
was obtained as a white solid after removing the solvent. GC yield was
established as follows: CH2Cl2 (10 mL) was added into the resulting solu-
tion, and the mixture was filtered through Celite to remove any insoluble
residues. The solvent was diluted with CH2Cl2. GC quantitative analysis
by using 1,4-di-tert-butylbenzene as the internal standard (correction
factor for 3a: 0.787) indicated that 3a was obtained in 35.4% GC yield.
Synthesis 2·toluene and 2 from 1: In a glove box, 1 (55.0 mg, 0.10 mmol,
10 mol%), tBuONa (192.0 mg, 2.0 mmol), and toluene (4 mL) were
transferred into a 15 mL Pyrex tube fitted with a Teflon screw-cap, and
the mixture was stirred for 5 min. N-Phenylaniline (203.0 mg, 1.2 mmol)
was then added and the mixture was stirred for an additional 20 min. The
mixture was then heated to 1208C in an oil bath for 30 min, and a trans-
parent reddish-brown solution was obtained. The brown solution was
cooled to RT, and a yellow precipitation containing both crystals of com-
plex 2·toluene and tBuONa were obtained. The yellow crystals of 2·tolu-
ene were obtained by hand-packing. Yield: 40.8 mg (38.7%). 1H NMR
(300 MHz, CD2Cl2): d=2.33 (s, 3H), 6.90 (t, J=8.1 Hz, 4H), 7.08 (t, J=
1.2 Hz, 8H), 7.15–7.28 (m, 13H), 7.77 (br. s, 6H), 7.95 (s, 6H), 8.40 (d,
J=8.1 Hz, 6H), 9.02 ppm (brs, 6H); elemental analysis calcd (%) for
C67H52CuN8Na (1055.72): C 76.22, H 4.96, N 10.61; found: C 76.02, H
4.92, N 10.77.
À
Copper-catalyzed C N coupling reaction with CuI and two equivalents
of phen: In a glove box, CuI (19.0 mg, 0.10 mmol, 10 mol%), 1,10-phe-
nanthroline (36.0 mg, 0.20 mmol, 20 mol%), tBuONa (192.0 mg,
2.0 mmol), and toluene (4 mL) were transferred to a Pyrex tube fitted
with a Teflon screw-cap. N-Phenylaniline (203.0 mg, 1.2 mmol) and 4-io-
dotoluene (218.0 mg, 1.0 mmol) were then added at RT. The mixture was
Stoichiometric reaction of
2 and 4-iodotoluene: In a glove box, 2
(43.7 mg, 0.045 mmol), 4-iodotoluene (19.6 mg, 0.09 mmol), 1,4-di-tert-bu-
tylbenzene (19.0 mg, 0.1 mmol), and toluene (1 mL) were transferred
Chem. Eur. J. 2011, 17, 2716 – 2723
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2721

S.-G. Shyu et al.
into a 15 mL Pyrex tube fitted with a Teflon screw-cap. The mixture was
stirred and heated at 1208C in an oil bath for 40 h, to give 3a with a
70.6% GC yield (1,4-di-tert-butylbenzene as internal standard, correction
factor for 3a: 0.787).
N-methylaniline (53.6 mg, 0.5 mmol), and 4-iodotoluene (109.0 mg,
0.5 mmol) were added, and the resulting mixture was stirred for an addi-
tional 20 min at RT then heated at 1208C in an oil bath for 40 h. Prod-
ucts 3a and 3b were obtained in 80.1 and 8.1% GC yield, respectively
(1,4-di-tert-butylbenzene as internal standard, correction factor for 3a:
0.787; 3b: 1.232).
À
Copper-catalyzed C N coupling reaction with 2 as catalyst: In a glove
box, 2 (20.0 mg, 0.02 mmol), 4-iodotoluene (43.6 mg, 0.2 mmol), N-phe-
nylaniline (40.6 mg, 0.24 mmol), tBuONa (38.4 mg, 0.4 mmol), 1,4-di-tert-
butylbenzene (19.0 mg, 0.1 mmol), and toluene (1 mL) were transferred
into a 15 mL Pyrex tube fitted with a Teflon screw-cap. The above mix-
ture was heated at 1208C in an oil bath for 40 h, and 3a was obtained
with a 99.1% GC yield. (1,4-di-tert-butylbenzene as internal standard,
correction factor for 3a: 0.787).
À
Competitive catalytic C N coupling of 4-iodotoluene with N-phenylani-
line and 4-methyl-N-phenylaniline by CuI and three equivalents of phen:
In a glove box, CuI (8.3 mg, 0.044 mmol, 10 mol%), 1,10-phenanthroline
(23.6 mg, 0.132 mmol, 30 mol%), tBuONa (83.9 mg, 0.88 mmol), and tol-
uene (2 mL) were transferred into a 15 mL Pyrex tube fitted with a
Teflon screw-cap. After stirring for 5 min, N-phenylaniline (73.9 mg,
0.44 mmol), 4-methyl-N-phenylaniline (80.0 mg, 0.44 mmol), and 4-iodo-
toluene (95.3 mg, 0.44 mmol) were added, and the resulting mixture was
stirred for an additional 20 min at RT then heated at 1208C in an oil
bath for 40 h. Products 3a and 3c were obtain in 49.0 and 48.4% GC
yield respectively (1,4-di-tert-butylbenzene as internal standard, correc-
tion factor for 3a: 0.787; 3c: 0.773).
Synthesis of 2 with three equivalents of phen: In a glove box, CuI
(19.0 mg, 0.10 mmol), 1,10-phenanthroline (54.0 mg, 0.3 mmol), tBuONa
(192.0 mg, 2.0 mmol), and toluene (4 mL) were transferred into a 15 mL
Pyrex tube fitted with a Teflon screw-cap. After stirring for 5 min, N-phe-
nylaniline (203.0 mg, 1.2 mmol) was added, and the resulting mixture was
stirred for an additional 20 min at RT. A yellow precipitation was ob-
tained. The mixture was then heated to 1208C in an oil bath for 30 min,
and a transparent reddish-brown solution was obtained. The brown solu-
tion was cooled to RT and the yellow precipitation, containing both 2
and sodium tert-butoxide, were recrystallized from anhydrous CH2Cl2
and n-hexane to obtain 2 as a yellow powder. Yield: 54.6 mg (56.7%).
Crystal structure determination of complex 2·toluene: A mixture of N-
phenylaniline (203.0 mg, 1.2 mmol), tBuONa (192 mg, 2.0 mmol),
10 mol% CuI (19.0 mg, 0.10 mmol), and 20 mol% 1,10-phenanthroline
(36.0 mg, 0.2 mmol) (CuI/phen in 1:2 ratio) was stirred in toluene at RT
in a 15 mL Pyrex tube fitted with a Teflon screw-cap. The mixture was
then stirred and heated to 1208C in an oil bath for 30 min. After cooling
to RT, a yellow precipitation containing both 2·toluene and tBuONa was
obtained. Single crystals of 2·toluene were separated from the yellow pre-
cipitation by hand-picking. A crystal of 2·toluene was mounted on a glass
fiber for data collection by using MoKa radiation with a Bruker X8 Apex
CCD diffractometer at 100 K. Structure refinement was performed using
SHELXL97-2[16] with full-matrix least-squares on F2, using all the unique
data. The Thermal ellipsoid diagram was obtained by using the ORTEP-
3 program for windows.[17] All programs were run with the WinGX pack-
age[18] of crystallographic programs. Details of the crystal data and refine-
ments are summarized in Table 1.
À
C
N coupling reaction between 4-iodotoluene and N-methylaniline with
10 mol% of 2: In a glove box, 2 (20 mg, 0.02 mmol, 10 mol%), tBuONa
(38.4 mg, 0.40 mmol), and toluene (2 mL) were transferred into a 15 mL
Pyrex tube fitted with a Teflon screw-cap. After stirring for 5 min, N-
methylaniline (25.7 mg, 0.24 mmol) and 4-iodotoluene (43.6 mg,
0.20 mmol) were added, and the resulting mixture was stirred for an addi-
tional 20 min at RT then heated at 1208C in an oil bath for 40 h. Prod-
ucts 3a and 3b were obtained in 14.9 and 30.2% GC yield, respectively
(1,4-di-tert-butylbenzene as internal standard, correction factor for 3a:
0.787; 3b: 1.232).
À
C
N coupling reaction between 4-iodotoluene and N-methylaniline with
50 mol% of 2: In a glove box, 2 (48.3 mg, 0.05 mmol), tBuONa (9.6 mg,
0.1 mmol), and toluene (2 mL) were transferred into a 15 mL Pyrex tube
fitted with a Teflon screw-cap. After stirring for 5 min, N-methylaniline
(10.7 mg, 0.1 mmol) and 4-iodotoluene (21.8 mg, 0.1 mmol) were added,
and the resulting mixture was stirred for an additional 20 min at RT then
heated at 1208C in an oil bath for 40 h. Products 3a and 3b were ob-
tained in 60.4 and 25.7% GC yield, respectively (1,4-di-tert-butylbenzene
as internal standard, correction factor for 3a: 0.787; 3b: 1.232).
Table 1. Crystallographic data for 2·toluene.
formula
Mr
C67H52CuN8Na
1055.7
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
triclinic
P1
¯
12.0093(3)
14.6694(4)
15.4984(5)
78.986(2)
89.131(2)
87.341(2)
2677.11(13)
2
À
C
N coupling reaction between 4-iodotoluene and 4-methyl-N-phenyl-
aniline with 10 mol% of 2: In
a glove box, 2 (20 mg, 0.02 mmol,
10 mol%), tBuONa (38.4 mg, 0.40 mmol), and toluene (2 mL) were
transferred into a 15 mL Pyrex tube fitted with a Teflon screw-cap. After
stirring for 5 min, 4-methyl-N-phenylaniline (44.0 mg, 0.24 mmol) and 4-
iodotoluene (43.6 mg, 0.20 mmol) were added, and the resulting mixture
was stirred for an additional 20 min at RT then heated at 1208C in an oil
bath for 40 h. Products 3a and 3c were obtained in 9.5 and 68.1% GC
yield, respectively (1,4-di-tert-butylbenzene as internal standard, correc-
tion factor for 3a: 0.787; 3c: 0.773).
a [8]
b [8]
g [8]
V [ꢁ3]
Z
1calcd [gcmÀ3
]
1.31
0.467
1100
m [mmÀ1
(000)
]
F
A
À
C
N coupling reaction between 4-iodotoluene and 4-methyl-N-phenyl-
independent reflns (Rint
R1, wR2 (I>2s)
)
10923 (0.0494)
0.0576, 0.1575
aniline with 50 mol% of 2: In a glove box, 2 (48.3 mg, 0.05 mmol),
tBuONa (9.6 mg, 0.1 mmol), and toluene (2 mL) were transferred into a
15 mL Pyrex tube fitted with a Teflon screw-cap. After stirring for 5 min,
4-methyl-N-phenylaniline (18.3 mg, 0.1 mmol) and 4-iodotoluene
(21.8 mg, 0.1 mmol) were added, and the resulting mixture was stirred for
an additional 20 min at RT then heated at 1208C in an oil bath for 40 h.
Products 3a and 3c were obtained in 42.3 and 53.7% GC yield respec-
tively (1,4-di-tert-butylbenzene as internal standard, correction factor for
3a: 0.787; 3c: 0.773).
Acknowledgements
We are grateful to the National Science Council, Republic of China, and
to the Academia Sinica for financial support of this work.
À
Competitive catalytic C N coupling of 4-iodotoluene with N-phenylani-
line and N-methylaniline by CuI and three equivalents of phen: In a
glove box, CuI (9.5 mg, 0.05 mmol, 10 mol%), 1,10-phenanthroline
(27.0 mg, 0.15 mmol, 30 mol%), tBuONa (96 mg, 1.0 mmol), and toluene
(2 mL) were transferred into a 15 mL Pyrex tube fitted with a Teflon
screw-cap. After stirring for 5 min, N-phenylaniline (84.5 mg, 0.5 mmol),
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Chem. Eur. J. 2011, 17, 2716 – 2723

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Received: September 16, 2010
Published online: January 26, 2011
Chem. Eur. J. 2011, 17, 2716 – 2723
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2723