Reactivity of [K3(phen)8][Cu(NPh2) 2]3 - A possible intermediate in the copper(i)-catalyzed N-arylation of N-phenylaniline

Article abstract of DOI:10.1039/c4dt00051j

Complex [K₃(phen)₈][Cu(NPh₂) ₂]₃ (1, phen = phenanthroline) was isolated from the catalytic C-N cross coupling reaction based on the CuI-phen-tBuOK catalytic system. Complex 1 can react with 4-iodotoluene to give 4-methyl-N,N- diphenylaniline (3a) in 50% yield (based on all available NPh₂ ^- ligands of complex 1). In addition, 1 can also work as an effective catalyst for the C-N coupling reactions under the same reaction conditions, indicating that 1 may be an effective intermediate of the catalytic system. In the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), a radical scavenger, the stoichiometric reaction between complex 1 and 4-iodotoluene was significantly quenched to give a low yield of 12%. The results suggest that the radical path dominates in the reaction, with (phen)KNPh₂ as the possible radical source. The structures of 1 and (phen)KNPh₂ were both determined by single crystal X-ray diffraction studies.

Full text of DOI:10.1039/c4dt00051j

Volume 43 Number 19 21 May 2014 Pages 6937–7332
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An international journal of inorganic chemistry
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COVER ARTICLE
Han, Shyu et al.
Reactivity of [K3(phen)8][Cu(NPh2)2]3—a possible intermediate in the
copper(I)-catalyzed N-arylation of N-phenylaniline

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PAPER
Reactivity of [K3(phen)8][Cu(NPh2)2]3—a possible
intermediate in the copper(I)-catalyzed N-arylation
of N-phenylaniline†
Cite this: Dalton Trans., 2014, 43,
7020
Chia-Kai Tseng,a,b Chi-Rung Lee,c Mei-Chun Tseng,a Chien-Chung Han*b and
Shin-Guang Shyu*a
Complex [K3(phen)8][Cu(NPh2)2]3 (1, phen = phenanthroline) was isolated from the catalytic C–N cross
coupling reaction based on the CuI-phen-tBuOK catalytic system. Complex 1 can react with 4-iodo-
−
toluene to give 4-methyl-N,N-diphenylaniline (3a) in 50% yield (based on all available NPh2 ligands of
complex 1). In addition, 1 can also work as an effective catalyst for the C–N coupling reactions under the
same reaction conditions, indicating that 1 may be an effective intermediate of the catalytic system. In the
presence of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), a radical scavenger, the stoichiometric reac-
tion between complex 1 and 4-iodotoluene was significantly quenched to give a low yield of 12%. The
results suggest that the radical path dominates in the reaction, with (phen)KNPh2 as the possible radical
source. The structures of 1 and (phen)KNPh2 were both determined by single crystal X-ray diffraction
studies.
Received 7th January 2014,
Accepted 27th January 2014
DOI: 10.1039/c4dt00051j
www.rsc.org/dalton
have also been reported.5 Among all these studies, the influ-
ence of a base is however seldom addressed. Recently, the
Introduction
The C–N cross coupling reaction is a useful procedure for aryl copper(II) complex {K[Cu(phen)(NPh2)(p-tolyl)]}+ was found by
amine synthesis in biological, pharmaceutical, and chemical in situ ESI-MS study to be present in the CuI-phen-(tBuONa/
materials.1 The catalytic reaction has been intensively studied K2CO3) mixed-base catalytic system, and a dual reaction path
due to its economic attractiveness, low toxicity, and air and involving both the 2e oxidative addition path and the free
moisture stability.2 The formation of the copper complex with radical path was thus proposed.6 These observations suggest
the amido ligand may be the first step in the catalytic cycle of that the cross coupling reaction may undergo a different cata-
the copper-catalyzed N-arylation of amides, followed by the oxi- lytic path when tBuOK is used as the base instead of tBuONa.
dative addition of the aryl halide.3 We have reported the iso-
In this study, we have isolated 1 from the CuI-phen-tBuOK
lation of [Na(phen)3][Cu(NPh2)2] (2) from the CuI-phen- catalytic system, which showed quite a different reactivity from
tBuONa catalytic system. In addition, [Cu(NPh2)2]−, {Na[Cu- 2, consistent with our finding that the reactivity of the cross
(NPh2)2(p-tolyl)]}+ and [Cu(NPh2)I]− were observed by in situ coupling reaction depends significantly on the counter cation
electrospray ionization mass spectrometry (ESI-MS) analysis of the base, tBuOM (M = Na, K).
for the catalytic reaction, indicating that they are intermediates
We report herein the isolation, structure characterization and
of the reaction. A catalytic cycle was proposed based on these reactivity of complex 1 from the CuI-phen-tBuOK catalytic system.
observations.4 Mechanisms involving either the 2e oxidative
addition path or the free radical path for the activation of aryl
halide in the copper-catalyzed C–N cross coupling reaction
Results and discussion
We followed the general procedure reported in the literature to
investigate the copper-catalyzed C–N cross coupling reaction
between aryl iodide and amine.7 Toluene is chosen as the
solvent, instead of the frequently used DMF or DMSO, because
it is a greener solvent and easier to work up. Typical catalytic
reactions were performed by heating a mixture of aniline
(1.2 equiv.), aryl iodide (1.0 equiv.), tBuOM (M = Na or K;
3 equiv.), CuI (10 mol%) and phen (30 mol%) in toluene at
aInstitute of Chemistry, Academia Sinica, Taipei 115, Taiwan, Republic of China.
E-mail: sgshyu@gate.sinica.edu.tw
bDepartment of Chemistry, National Tsing Hua University, Hsinchu, Taiwan,
Republic of China. E-mail: cchan@mx.nthu.edu.tw
cDepartment of Chemistry and Materials Engineering, Minghsin University of Science
and Technology, Hsinchu, Taiwan, Republic of China
†Electronic supplementary information (ESI) available. CCDC 979244–979245.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4dt00051j
7020 | Dalton Trans., 2014, 43, 7020–7027
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Table 1 Cu(I) catalyzed C–N coupling reaction with different base
systemsa
Conversion/GC yield (%)
Fig. 1 ORTEP drawing of 1, with 50% thermal ellipsoids. Hydrogen
atoms are omitted.
tBuONa
(3 equiv.)
tBuOK
(3 equiv.)
Entry
ArI
Ar′2NH
1
2
3
C6H5I
Ph2NH
Ph2NH
Ph2NH
Ph2NH
Ph2NH
Ph2NH
Ph2NH
Ph2NH
(p-Tolyl)2NH
49/47
48/33
46/38
53/35
61/40
—
—
22/12
44/42
98/95
91/76
99/80
100/50
90/45
46/43
57/35
63/52
100/74
4-MeOC6H4I
4-MeC6H4I
4-MeC6H4I
4-MeC6H4I
4-MeC6H4I
4-MeC6H4I
2-MeC6H4I
C6H5I
If 1 is the effective catalytic intermediate, it alone should be
sufficient to react with 4-iodotoluene stoichiometrically to
form the product 3a without requiring the use of potassium
tert-butoxide, assuming that the base only serves to convert
N-phenylaniline to an N,N-diphenylamide anion.
4b
5c
6d
7e
8
Hence, 1 (containing 3 equiv. of Cu species) was allowed to
react with an excess amount (12 equiv.) of 4-iodotoluene (with
4-iodotoluene/Cu = 4) in toluene at 120 °C for 6 h to form 3a
in 50.0% yield, counted against all NPh2− ligands of complex 1
(Table 2, entry 1). In addition, 1 also works as an effective cata-
lyst for the catalytic C–N cross coupling reaction between
N-phenylaniline and 4-iodotoluene. For example, when
3.3 mol% of 1 (containing 10 mol% of Cu(I) species) was
added into a mixture of N-phenylaniline (1.2 equiv.), 4-iodo-
toluene (1 equiv.), and potassium tert-butoxide (3 equiv.) in
toluene, the catalytic C–N cross coupling reaction proceeded
effectively at 120 °C in 6 h to give 3a in 47% yield (based on
the used 4-iodotoluene). These observations suggest that 1
could be an effective catalytic intermediate in the CuI-phen-
tBuOK catalyst system.
9
a 1.0 mmol ArI, 1.2 mmol N-phenylaniline, 4 mL toluene, 0.1 mmol
CuI, 0.3 mmol phen, 3 mmol base. b Add 3 mmol TEMPO. c Add
0.5 mmol cumene. d Reaction time: 30 min. e Add 0.3 mmol TEMPO
and use 30 min reaction time.
120 °C for 6 h. The results are summarized in Table 1; the
yields of these catalytic reactions were measured based on the
aryl iodides used. The results showed that the reactions based
on the CuI-phen-tBuOK catalytic system give about twice better
yields than those reactions with the CuI-phen-tBuONa catalytic
system (Table 1, entries 1–3). The reaction of 2-iodotoluene
(1 equiv.) with N-phenylaniline (1.2 equiv.) catalyzed by CuI-
phen-tBuONa gave 2-methyl-N,N-diphenylaniline (3b) in 12%
yield, which is four times lower than the yield (52%) of the
same reaction based on the CuI-phen-tBuOK catalytic system
(Table 1, entry 8) under the same reaction conditions. The
results imply that the more hindered 2-iodotoluene can
somehow be better activated by the CuI-phen-tBuOK catalytic
system. In addition, the free radical path is present because
the addition of the free radical scavenger TEMPO or cumene
reduces the turnover frequency of the reaction (Table 1, entries
4, 5, and 7). In order to investigate the reason for their different
reactivity behaviours, intermediates [K3(phen)8][Cu(NPh2)2]3 (1)
and [Na(phen)3][Cu(NPh2)2] (2) were isolated from the corres-
ponding catalytic systems,4 and their structures and activities
were studied.
In order to obtain a better understanding of the catalytic
cycle of the C–N cross coupling reaction, we have compared
the activities of the stoichiometric reactions between the Cu
complexes (1 and 2) and 4-iodotoluene, and the results are dis-
played in Table 2. The yields for these stoichiometric reactions
−
were respectively measured based on all available NPh2
ligands within the corresponding complexes. Under the same
reaction conditions (e.g., in toluene at 120 °C for 6 h), complex
1 (1 equiv.; corresponding to 3 equiv. of Cu(I) species) reacted
with 4-iodotoluene (12 equiv.) to give 3a in 50.0% yield (based
Table 2 Stoichiometric reaction between Cu(I) complexes and
4-iodotoluenea
Entry Radical scavenger Cu(I) complex Conversion/GC yieldd (%)
Structure of 1 and reactivity of 1 and 2
Complex 1 is characterized by single-crystal X-ray analysis and
its structure is shown in Fig. 1, which contains three K+ ions
ligated by eight phen and three bis(N-phenylanilide)copper(I)
anions. Quite interestingly, complex 1 also contains the ana-
logous counter anion [Cu(NPh2)2]− as found in the previously
reported complex of [K(phen)3][Cu(NPh2)2], which was syn-
thesized from the reaction mixture of tBuOCu, HNPh2, KNPh2
and phen.8,4b
1
—
—
—
1
1
2
1
2
51/50
99/81
61/61
12/12
51/50
2b
3
4
5
TEMPOc
TEMPOc
a 0.08 mmol 4-iodotoluene, 0.007 mmol complex 1 or 0.02 mmol
complex 2, 1 mL toluene. b Add 0.08 mmol tBuOK. c 0.02 mmol
TEMPO was used; with TEMPO/Cu = 1. d Based on all available NPh2
−
ligands in the corresponding complex.
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−
on NPh2 ligands of complex 1) (Table 2, entry 1), while
complex 2 (3 equiv.) reacted with 4-iodotoluene (12 equiv.) to
−
give 3a in 61.0% yield (based on NPh2 ligands of complex 2)
(Table 2, entry 3). The higher turnover frequency of 2 than 1
implies that the counter cation may have an influence on the
reactivity of the Cu(I) complex, and this may also imply that
different catalytic mechanisms may be involved.
It has been reported that when a mixed base (tBuONa/
K2CO3) is used in a copper-catalyzed C–N cross coupling reac-
tion, the radical path is also involved in the mechanism.6 This
may imply that if solely tBuOK is used, the radical path may
even dominate the mechanism of aryl halide activation. In
order to clarify the existence of the free radical path, the effect
of free radical scavenger TEMPO on the coupling reaction was
examined. When the same amount of TEMPO (e.g., with
1 equiv. TEMPO per Cu species) was added, the yield for the
reaction of complex 1 reduced dramatically from 50% to 12%
(Table 2, entry 4), while the yield for the reaction of complex 2
Fig. 2 (a) ESI(+)-MS and (b) ESI(−)-MS from the reaction solution taken
during the reaction of 4-iodotoluene, N-phenylaniline with complex 2 in
reduced only slightly from 61% to 50% (Table 2, entry 5) under toluene at 120 °C.
the same reaction conditions. The results suggest that the reac-
tion involving complex 1 may mainly go through a radical
path, whereas the reaction involving complex 2 mainly under-
goes a 2e oxidative addition path.
In situ ESI-MS analyses of the stoichiometric reactions of
1 and 2 with aryl iodide
To further clarify these possibilities, in situ ESI-MS analyses
were carried out to investigate the reactions. A similar reaction
mixture of complex 1 (or complex 2) and 4-iodotoluene in
toluene was stirred at 120 °C for 1 h. The solution was then
transferred to a GC vial in a dry box. The temperature was kept
at 120 °C by immersing the GC vial in a sand bed, and ESI-MS
spectra of the solution were taken.
The ESI-MS results indeed showed different spectral beha-
viours for these two reaction systems. For complex 2, all the
intermediates previously reported for the reaction based on
the CuI-phen-tBuONa catalytic system were also observed in
the stoichiometric reaction of 2 with 4-iodotoluene, while not
all the intermediates were observed in the stoichiometric reac-
Fig. 3 Simulated and experimental isotopic distributions of (a) [Cu(NPh)2-
(p-tolyl)Na]+ and (b) [Cu(NPh2)2]−.
tion of 1 with 4-iodotoluene. Only [K(phen)3]+, [Cu(phen)2]+
and [K(phen)2]+ were detected.
For the stoichiometric reaction of 2 with 4-iodotoluene,
peaks at m/z = 563.2, 423.1, 383.1 and 513.1 corresponding to
[Na(phen)3]+, [Cu(phen)2]+, [Na(phen)2]+ and {Na[Cu(NPh2)2-
(p-tolyl)]}+ respectively were observed in the positive-ion mode
of ESI-MS, and their measured accurate mass and isotopic dis-
tribution patterns are consistent with the assigned species
(Fig. 2). These observations indicate that the ligand redistribu-
tion had occurred in the stoichiometric reaction. In addition,
the ESI-MS in the negative-ion mode shows a peak at m/z =
399.1, which is identified as [Cu(NPh2)2]−, and its measured
accurate mass and isotopic distribution patterns are consistent
with the assigned species (Fig. 3). The observed Cu(III) complex
of {Na[Cu(NPh2)2(p-tolyl)]}+ implies the presence of Cu-
reaction mixture, which may have resulted from [Cu(NPh2)2-
(p-tolyl)I]− by losing the iodide anion. As expected, the iodide
anion was also observed in the negative-ion mode of ESI-MS.
The result implies that 4-iodotoluene reacts with [Cu(NPh2)2]−
to form [Cu(NPh2)2(p-tolyl)I]− through a 2e oxidative addition
path (Scheme 1). Thus, these observations indicate that
[Cu(NPh2)2]− is indeed the active catalyst species in the stoi-
chiometric reaction of complex 2. These results are consistent
with the previously reported data for the catalytic reaction
using the CuI-phen-tBuONa catalyst system.4
Reaction paths of the C–N coupling reactions of 1 and 2
(NPh2)2(p-tolyl) species (that pick up a Na+ and are detected by During the reaction of 1 with 4-iodotoluene, redistribution of
−
the positive-ion mode of the ESI-MS measurement) in the the phen and NPh2 ligands among metal cations may occur
7022 | Dalton Trans., 2014, 43, 7020–7027
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Fig. 4 ORTEP drawing of (phen)KNPh2, with 30% thermal ellipsoids.
Hydrogen atoms are omitted.
Scheme 1 The proposed mechanism of the reaction between 2 and
4-iodotoluene.
to form the observed cationic complex [Cu(phen)2]+ (by the
ESI-MS spectra in the positive ion mode), and possibly also the
neutral complexes such as Cu(phen)(NPh2) and (phen)KNPh2
(which were not detectable by ESI-MS, because they are neu-
trally charged). The observed ESI-MS data behaviors may be
accounted by the fact that the radical path dominates the reac-
tion mechanism when complex 1 is used. Presumably, the
radical mechanism involves neutrally charged intermediate
species, which are invisible to ESI-MS.
Scheme 2 Reaction between (phen)KNPh2 and 4-iodotoluene with
and without radical scavenger TEMPO.
that (phen)KNPh2, similar to (phen)KOtBu, can act as a single
electron donor toward aryl iodide. A plausible mechanism for
the reaction between 1 and 4-iodotoluene is shown in
Scheme 3.
Although the CuI-phen-tBuOK catalytic system produced
twice higher turnover frequency than the CuI-phen-tBuONa
catalytic system, the yield for the stoichiometric reaction of
For example, a p-tolyl free radical [p-CH3C6H4]• may be gen-
erated from the radical anions [p-CH3C6H4I]•− that resulted
from the reaction between 4-iodotoluene and a potential
single electron donor, such as (phen)KNPh2. The p-tolyl free
radical may add to the Cu(I) complex, Cu(phen)(NPh2), to
generate a neutral Cu(II) complex, [Cu(phen)(NPh2)(p-tolyl)],
which is not detectable by ESI-MS in this reaction. Actually,
such a species has been previously observed by ESI-MS as a K+
complex, {K[Cu(phen)(NPh2)(p-tolyl)]}+, in other radical-based
reaction systems such as the CuI-phen-(tBuONa/K2CO3) mixed-
base catalytic system.6
The (phen)KOtBu complex was reported to act as a single
electron donor toward aryl iodide and led to the coupling
between aryl halide and benzene without the need of a tran-
sition metal catalyst.9 If (phen)KNPh2 can work as a single
electron donor just like (phen)KOtBu, then similar C–C coup-
ling products should also be observed in a similar reaction.
For this purpose, (phen)KNPh2 was prepared as a red-brown
powder by the reaction between tBuOK and N-phenylaniline in
the presence of 1,10-phenanthroline. The structure of (phen)-
KNPh2 was characterized by NMR and single crystal X-ray diffr-
action analysis and is shown in Fig. 4.
A stoichiometric reaction between (phen)KNPh2 (1 equiv.)
and 4-iodotoluene (1 equiv.) was carried out in toluene at
120 °C for 6 h. The products of C–C coupling between 4-iodo-
toluene and toluene, identified by GC-MS, were indeed
observed. But, when TEMPO (1 equiv.) was added to the same
reaction, the yield of the C–C coupling reaction products
reduced from 17.8% to 5.6% (Scheme 2). The results indicate
Scheme 3 The proposed radical path of the reaction between 1 and
4-iodotoluene.
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complex 1 with 4-iodotoluene is somewhat lower than that of catalyzed by CuI-phen-tBuONa and CuI-phen-tBuOK respecti-
complex 2 with 4-iodotoluene (Table 2, entries 1 and 3). This vely. Both complexes can catalyze the C–N coupling reaction
may be due to the presence of fewer radical donor species in between aryl iodide and N-phenylaniline, indicating that they
the stoichiometric reaction of complex 1. When an additional could be the intermediates of the reaction. The different reac-
4.0 equiv. of tBuOK was added to the stoichiometric reaction tivities of complexes 1 and 2 towards 4-iodotoluene imply that
of complex 1, the yield increased to 81% (Table 2, entry 2). The they have undergone different reaction pathways. A drastic
additional tBuOK provides additional (phen)KOtBu as an elec- yield reduction occurred in the reaction between 1 and 4-iodo-
tron donor, and thus increases the overall yield of the reaction. toluene in the presence of TEMPO, which implies that the
radical path dominates the reaction. In contrast, 2e oxidative
The role of phen and tBuOK
addition is the major path for the reaction between 2 and
4-iodotoluene.
In order to evaluate whether the radical path is existing in the
absence of phen, catalytic reactions with and without the
addition of radical scavenger were carried out using the CuI/
tBuOK catalytic system. Thus, a toluene solution of N-phenyl- Experimental
aniline (1.2 equiv.), tBuOK (2.0 equiv.), CuI (10 mol%) and
4-iodotoluene (1 equiv.) was stirred at 120 °C for 30 min to
give products in 18.9%. With the addition of TEMPO
(1 equiv.), the reaction gave almost the same yield (i.e., 17.6%)
within the experimental errors. This indicates that, in the
absence of phen, the radical path does not exist.
General procedures
All reagents were purchased from commercial sources and
used without further purification. Copper(I) iodide (fine grey
powder), N-phenylaniline, iodobenzene, 2-iodotoluene,
4-iodoanisole, 4-iodotoluene, 1,10-phenanthroline, tBuOK,
tBuONa, and 1,4-di-tert-butylbenzene were purchased from
ACROS. Toluene (dried, SeccoSolv®) was purchased from
Merck and purged with argon for 15 min before use. All
reagents were transferred to the reaction vessel (Pyrex tube
Ligand redistribution (or exchange) between the metal
cations has surely occurred in the stoichiometric reactions of
both 1 and 2 as well as in the catalytic reaction of CuI-phen-
tBuOK and CuI-phen-tBuONa, as confirmed by the observation
of the ligand-exchanged cationic species [Cu(phen)2]+ in their
ESI-MS spectra. Conceivably, the stable complex species
formed during the intermediate ligand-exchange stage, i.e.,
(phen)CuNPh2, should have also existed in all the above reac-
tions. It is envisaged that the complex (phen)CuNPh2 can
accept the p-tolyl free radical [p-CH3C6H4]•, which results from
the electron transfer reaction between 4-iodotoluene and the
single electron donor (phen)MOtBu or (phen)MNPh2 (M = K
or Na), to generate the neutrally charged intermediate of
[Cu(phen)(NPh2)(p-tolyl)] and further complete the reaction.
The fact that reactions of 1 mainly go through the free radical
path implies that the electron donation ability of the potass-
ium complex, (phen)KNPh2, is stronger than that of the
sodium complex, (phen)NaNPh2. Similarly, the stronger elec-
tron donating ability of (phen)KOtBu versus (phen)NaOtBu has
also been reported in the study of C–H arylation with MOtBu
(M = Na or K) in the presence of phen or other ligands.9 Fur-
thermore, the fact that the CuI/phen/tBuONa catalytic system
also shows far less radical path contribution than the CuI/
phen/tBuOK catalytic system further supports the above
argument.6
1
with a Teflon screw cap) in a glove box. H NMR spectra were
recorded using Bruker AV 300 and Bruker AMX 400 instru-
ments. GC-MS experiments were performed on an Agilent
7890A gas chromatograph equipped with a 30 m × 0.25 mm ×
3.0 m HP-5 capillary column and an MSD detector. GC experi-
ments were performed on an Agilent 6890N gas chromato-
graph equipped with a 30 m × 0.53 mm × 3.0 μm HP-1
capillary column and a FID detector. Elemental analysis was
performed on a Thermo CHNS-O analyzer (FlashEA 1112
series). High resolution ESI-MS were measured using a Waters
LCT Premier XE with a dual ionization ESCi® in the Mass
Spectrometry Facility in the Institute of Chemistry, Academia
Sinica. Leucine enkephalin [M + H]+ 556.277 was used as a
reference standard.
Crystal structure determination of complex 1
A single crystal of a suitable size was attached to a glass fiber
and mounted on a goniometer head. Data were collected on a
Bruker SMART CCD diffractometer at 100 K using graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å). A total of
47 735 reflections were sorted and merged using a Bruker
SAINT, giving 11 597 independent data. Structure refinement
with SHELXL97-210 was undertaken using full-matrix least-
squares on F2 and all of the unique data. All of the non-H
atoms are refined anisotropically. The refinement details are
given in the ESI.† The thermal ellipsoid plot was obtained
using ORTEP-311 program for Windows; all of the calculations
were carried out using the WinGX12 package.
Apparently, the use of both phen and tBuOK is essential for
the reaction to proceed through a radical path, because it pro-
vides not only (phen)KOtBu or (phen)KNPh2 as an effective
free radical source,9 but also (phen)CuNPh2 as an acceptor for
the p-tolyl radical to form [CuII(phen)(NPh2)(p-tolyl)].
[Cu(NPh2)2]3[K3(phen)8] is crystallized in the monoclinic
space group P21/c. An overview and the numbering scheme are
Conclusions
In summary, complexes 1 and 2 have been isolated from the displayed in Fig. 1. The molecule consists of a discrete tri-
3+
−
reaction mixture of catalytic C–N cross coupling reactions cationic K3(phen)8 and three Cu(NPh2)2 anions. For the
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−
Cu(NPh2)2 anions, there are two different Cu atoms in the
Reaction between N-phenylaniline and 4-iodotoluene with
crystal. The Cu(1) and K(1) sit in general positions in the unit tBuOK for 6 h: GC yield: 80% (correction factor for 4-methyl-
cell, and Cu(2) and K(2) are located at the inversion center. N,N-diphenylaniline (3a): 0.818).
Each Cu atom is coordinated with two NPh2− ligands.
Reaction between N-phenylaniline and 4-iodotoluene with
The torsion angle between two diphenyl amine ligands tBuOK and 3.0 equiv. of TEMPO (488 mg, 3.0 mmol) for 6 h: GC
built from four phenyl groups is flatter in the Cu(2) fragment yield: 50% (correction factor for 4-methyl-N,N-diphenylaniline
than that in the Cu(1) fragment with torsion angles 5.2° (3a): 0.818).
(∠C28–N27–N27i–C34i, i: −x, −y, −z) and 54.9° (∠C8–N1–N14–
C15) respectively.
Reaction between N-phenylaniline and 4-iodotoluene with
tBuOK for 30 min: GC yield: 43% (correction factor for
4-methyl-N,N-diphenylaniline (3a): 0.818).
Crystal structure determination of (phen)KNPh2
Reaction between N-phenylaniline and 4-iodotoluene with
Intensity data were collected on an Oxford Atlas-CCD diffracto- tBuOK and 3.0 equiv. of TEMPO (488 mg, 3.0 mmol) for 30 min:
meter for (phen)KNPh2 single crystal at 100 K, using graphite GC yield: 35% (correction factor for 4-methyl-N,N-diphenyl-
monochromated Mo-Kα radiation (λ = 0.71073 Å). Integration aniline (3a): 0.818).
on the intensity measurement was performed using the CrysA-
Reaction between N-phenylaniline and 2-iodotoluene with
lisPro13 package. Structure was refined using SHELXL97-2 with tBuOK for 6 h: GC yield: 52% (correction factor for 2-methyl-
full-matrix least-squares on F2. All programs were performed N,N-diphenylaniline (3b): 0.818).
using WinGX software. Detailed information is summarized in
the ESI.†
Reaction between di-p-tolylaniline and iodobenzene with
tBuOK for 6 h: GC yield: 74% (correction factor for 4-methyl-N-
(phen)KNPh2 is crystallized in an orthorhombic space phenyl-N-p-tolylaniline (3e): 0.735).
group Pbca. Potassium ion is four-coordinated, with one phen
Reaction between N-phenylaniline and iodobenzene with
and two NPh2− ligands. The nitrogen atom of the NPh2− anion tBuONa for 6 h: GC yield: 47% (correction factor for triphenyl-
bridges two potassium ions and each metal is again linked by amine (3c): 0.827).
two NPh2− resulting in an infinite chain type packing.
Reaction between N-phenylaniline and 4-iodoanisole with
tBuONa for 6 h: GC yield: 33% (correction factor for 4-methoxy-
N,N-diphenylaniline (3d): 0.843).
Typical procedure of the copper(I) catalyzed C–N coupling
reaction
C–N coupling reaction between N-phenylaniline and 4-iodoto-
In a glove box, CuI (19.0 mg, 0.10 mmol, 10 mol%), 1,10-phen- luene with tBuONa for 6 h: GC yield: 38% (correction factor for
anthroline (54.0 mg, 0.30 mmol, 30 mol%), base (3.0 mmol), 4-methyl-N,N-diphenylaniline (3a): 0.818).
1,4-di-tert-butylbenzene (19.0 mg, 0.1 mmol) and toluene
Reaction between N-phenylaniline and 2-iodotoluene with
(4 mL) were transferred to a Pyrex tube with a Teflon screw tBuONa for 6 h: GC yield: 12% (correction factor for 2-methyl-
cap. After stirring for 5 min, aryl amine (1.2 mmol) and aryl N,N-diphenylaniline (3b): 0.818).
halide (1.0 mmol) were added, and the resulting mixture was
Reaction between di-p-tolylaniline and iodobenzene with
stirred for an additional 20 min at room temperature. The reac- tBuONa for 6 h: GC yield: 42% (correction factor for 4-methyl-
tion mixture was then heated at 120 °C in an oil bath for 6 h. N-phenyl-N-p-tolylaniline (3e): 0.735).
After the reaction, the tube was removed from the oil bath and
Copper catalyzed C–N cross coupling reaction based on CuI/
phen/tBuOK
allowed to cool to room temperature. The reaction mixture was
first diluted with CH2Cl2 (10 mL), and then filtered to remove
any insoluble residues by Celite. All products were identified Without TEMPO: In a glove box, CuI (19.0 mg, 0.1 mmol),
by GC-MS, and the yield was determined by quantitative GC 4-iodotoluene (218.0 mg, 1.0 mmol), N-phenylaniline
analysis by adding 1,4-di-tert-butylbenzene as the internal stan- (203.0 mg, 1.2 mmol), 1,10-phenanthroline (54.0 mg, 30 mol
dard. All GC data are provided in the ESI.†
%), tBuOK (336 mg, 3.0 mmol), 1,4-di-tert-butylbenzene
(19.0 mg, 0.1 mmol) and 4 mL of toluene were transferred into
a 15 mL Pyrex tube with a Teflon screw cap. The above mixture
was stirred and heated at 120 °C in an oil bath for 30 minutes.
Reaction of copper(I) catalyzed C–N coupling with different
base systems
The same procedure, amount of reagents and reaction con- The GC yield of 3a was 43.4% (correction factor for 3a: 0.688).
ditions as in the typical procedure stated above was applied to Another reaction was carried out for longer reaction time,
the reaction. For reactions using tBuOK as the base, 336.0 mg, i.e., 6 h using the same procedure, amount of reagents and
3.0 mmol of tBuOK was used. For reactions using tBuONa as reaction conditions. The GC yield of 3a was 80.0% (correction
the base, 288.0 mg, 3.0 mmol of tBuONa was used.
factor for 3a: 0.787).
Reaction between N-phenylaniline and iodobenzene with
With TEMPO: The same procedure, amount of reagents and
tBuOK for 6 h: GC yield: 95% (correction factor for triphenyl- reaction conditions as above was applied to the reaction except
amine (3c): 0.827). that 3.0 equiv. of TEMPO (488 mg, 3.0 mmol) was used. The
Reaction between N-phenylaniline and 4-iodoanisole with GC yield of 3a for 30 min reaction time was 34.7%. The GC
tBuOK for 6 h: GC yield: 76% (correction factor for 4-methoxy- yield of 3a for 6 h reaction time was 50.0% (correction factor
N,N-diphenylaniline (3d): 0.843).
for 3a: 0.688).
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Separation of 1 from the reaction mixture
bath for 6 h, and 3a was obtained with an 81.0% GC yield
based on all available NPh2 ligands in complex 1 (correction
−
In a glove box, CuI (19.0 mg, 0.10 mmol, 10 mol%), 1,10-phen-
anthroline (54.0 mg, 0.3 mmol, 30 mol%), tBuOK (224.0 mg,
2.0 mmol) and toluene (4 mL) were transferred into a 15 mL
Pyrex tube 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 additional 20 min at room
temperature. A reddish brown precipitation was obtained. The
mixture was then heated up to 120 °C in an oil bath for
30 min, and a transparent reddish brown solution was
obtained. The brown solution was cooled to room temperature,
and a reddish brown crystal of [K3(phen)8][Cu(NPh2)2]3 was
separated from other solid precipitates by hand-picking. Yield:
factor for 3a: 0.818).
Synthesis of complex (phen)KNPh2
In a glove box, tBuOK (180.0 mg, 1.6 mmol), N-phenylaniline
(676.0 mg, 4.0 mmol), 1,10-phenanthroline (290.0 mg,
1.6 mmol) and 12 mL of toluene were transferred into a 50 mL
Pyrex tube with a Teflon screw cap. The above mixture was
stirred at room temperature for 24 h. The resultant red precipi-
tation was collected by filtration, which was washed several
times with toluene and then dried under reduced pressure.
Complex of (phen)KNPh2 was obtain in 187.0 mg (30%). 1H
NMR (300 MHz, CD2Cl2): δ = 6.80 (d, J = 1.2 Hz, 2H), 7.08 (m,
2H), 7.16–7.28 (m, 4H), 7.65 (q, J = 2.34 Hz, 2H), 7.83 (d, J =
2.34 Hz, 2H), 8.29 (q, J = 1.74 Hz, 2H), 9.13 ppm (q, J =
1.74 Hz, 2H). Elemental analysis calcd (%) for C24H18KN3:
C 74.39, H 4.68, N 10.84; found: C 74.39, H 4.83, N 10.87.
1
36.0 mg (39.2%). H NMR (300 MHz, CD2Cl2): δ = 6.90 (s, br,
18H), 7.02–7.09 (m, 30H), 7.25 (t, J = 7.2 Hz, 16H), 7.58 (d, J =
3.3 Hz, 15H), 7.82 (s, 15H), 8.28 (d, J = 7.8 Hz, 15H), 8.98 ppm
(s, br, 15H); elemental analysis calcd (%) for
C168H124Cu3K3N22: C 73.14, H 4.53, N 11.17; found: C 73.01, H
4.51, N 11.14.
Stoichiometric reaction between (phen)KNPh2 and
4-iodotoluene
Stoichiometric reaction between complex 1 and 4-iodotoluene
Without TEMPO: In a glove box, (phen)KNPh2 (38.7 mg,
0.10 mmol), 4-iodotoluene (21.8 mg, 0.10 mmol), 1,4-di-tert-
butylbenzene (19.0 mg, 0.10 mmol) and 2 mL of toluene were
transferred into a 15 mL Pyrex tube with a Teflon screw cap.
The above mixture was stirred and heated at 120 °C in an oil
bath for 6 h, and 3a was obtained with a 2.0% GC yield (correc-
tion factor for 3a: 0.818). Byproducts (biphenyl isomers) were
obtained with a 17.8% GC yield (correction factor for bypro-
duct: 1.17).
With TEMPO: 100 mol% of TEMPO (15.6 mg, 0.1 mmol) was
added to the above reaction mixture. 3a was obtained with a
0% GC yield. Byproducts (biphenyl isomers) were obtained
with a 5.6% GC yield (correction factor for byproduct: 1.17).
Without TEMPO: In a glove box, 1 (18.4 mg, 0.007 mmol),
4-iodotoluene (17.5 mg, 0.08 mmol), 1,4-di-tert-butylbenzene
(19.0 mg, 0.1 mmol) and 1 mL of toluene were transferred into
a 15 mL Pyrex tube with a Teflon screw cap. The above mixture
was stirred and heated at 120 °C in an oil bath for 6 h, and 3a
was obtained with a 50.0% GC yield based on all available
NPh2− ligands in complex 1 (correction factor for 3a: 0.818).
With TEMPO: 100 mol% (vs. overall Cu species) of TEMPO
(3.2 mg, 0.02 mmol) was added into the mixture as stated
above. 3a was obtained with a 12.0% GC yield based on all
−
available NPh2 ligands in complex 1 (correction factor for 3a:
0.818).
Stoichiometric reaction between complex 2 and 4-iodotoluene
Copper catalyzed C–N cross coupling reaction based on
CuI/tBuOK
Without TEMPO: In a glove box, 2 (19.4 mg, 0.02 mmol), 4-iodo-
toluene (17.5 mg, 0.08 mmol), 1,4-di-tert-butylbenzene
(19.0 mg, 0.1 mmol) and 1 mL of toluene were transferred into
a 15 mL Pyrex tube with a Teflon screw cap. The above mixture
was stirred and heated at 120 °C in an oil bath for 6 h, and 3a
was obtained with a 61.0% GC yield based on all available
NPh2− ligands in complex 1 (correction factor for 3a: 0.818).
Addition with 100 mol% TEMPO: TEMPO (3.2 mg,
0.02 mmol; 100 mol% (vs. overall Cu species) was added into
the mixture. 3a was obtained with a 50.0% GC yield based on
Without TEMPO: In a glove box, CuI (19.0 mg, 0.1 mmol),
4-iodotoluene (218.0 mg, 1.0 mmol), N-phenylaniline
(203.0 mg, 1.2 mmol), tBuOK (224 mg, 2.0 mmol), 1,4-di-tert-
butylbenzene (19.0 mg, 0.1 mmol) and 4 mL of toluene were
transferred into a 15 mL Pyrex tube with a Teflon screw cap.
The above mixture was stirred and heated at 120 °C in an oil
bath for 30 minutes. The GC yield of 3a was 18.9% (correction
factor for 3a: 0.818).
With 200 mol% TEMPO: The same procedure, amount of
reagents and reaction conditions as above was applied to the
reaction except that 2.0 equiv. of TEMPO (312 mg, 2.0 mmol)
was used. The GC yield of 3a was 17.6% (correction factor for
3a: 0.818).
−
all available NPh2 ligands in complex 2 (correction factor for
3a: 0.818).
Stoichiometric reaction between complex 1 and 4-iodotoluene
plus additional tBuOK
Copper catalyzed C–N cross coupling reaction based on 1
In a glove box, 1 (18.4 mg, 0.007 mmol), 4-iodotoluene
(17.5 mg, 0.08 mmol), tBuOK (9.0 mg, 0.08 mmol), 1,4-di-tert- In a glove box, 1 (47.0 mg, 0.017 mmol), 4-iodotoluene
butylbenzene (19.0 mg, 0.1 mmol) and 1 mL of toluene were (109.0 mg, 0.5 mmol), N-phenylaniline (102.0 mg, 0.6 mmol),
transferred into a 15 mL Pyrex tube with a Teflon screw cap. tBuOK (112.0 mg, 1.0 mmol), 1,4-di-tert-butylbenzene
The above mixture was stirred and heated at 120 °C in an oil (19.0 mg, 0.1 mmol) and toluene (2 mL) were transferred into
7026 | Dalton Trans., 2014, 43, 7020–7027
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Paper
a 15 mL Pyrex tube with a Teflon screw cap. The above mixture
was heated at 120 °C in an oil bath for 6 h, and 3a was
obtained with a 46.5% GC yield (1,4-di-tert-butylbenzene as an
internal standard; correction factor for 3a: 0.688).
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Acknowledgements
We acknowledge the National Science Council of the Republic of
China and Academia Sinica for financial support of this work.
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