[Pd(IPr*OMe)(acac)Cl]: Tuning the N-heterocyclic carbene in catalytic C-N bond formation

Article abstract of DOI:10.1021/om3011867

A new N-heterocyclic ligand IPr*^OMe [N,N′-bis(2,6- bis(diphenylmethyl)-4-methoxyphenyl)imidazol-2-ylidene] has been synthesized and compared with its earlier methyl-substituted congener IPr* [N,N′-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene]. IPr*^OMe was successfully bound to palladium, and the catalytic activity of the resulting complex [Pd(IPr*^OMe)(acac)Cl] was investigated in Buchwald-Hartwig arylamination. Catalytic activity was compared to that of [Pd(IPr*)(acac)Cl].

Full text of DOI:10.1021/om3011867

Article
pubs.acs.org/Organometallics
[Pd(IPr*OMe)(acac)Cl]: Tuning the N‑Heterocyclic Carbene in Catalytic
C−N Bond Formation
Sebastien Meiries,‡ Klaus Speck,‡ David B. Cordes, Alexandra M. Z. Slawin, and Steven P. Nolan*
EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, KY16 9ST, U.K.
S
* Supporting Information
ABSTRACT: A new N-heterocyclic ligand IPr*OMe [N,N′-bis(2,6-bis(diphenylmethyl)-4-methoxyphenyl)imidazol-2-ylidene]
has been synthesized and compared with its earlier methyl-substituted congener IPr* [N,N′-bis(2,6-bis(diphenylmethyl)-4-
methylphenyl)imidazol-2-ylidene]. IPr*OMe was successfully bound to palladium, and the catalytic activity of the resulting
complex [Pd(IPr*OMe)(acac)Cl] was investigated in Buchwald−Hartwig arylamination. Catalytic activity was compared to that of
[Pd(IPr*)(acac)Cl].
Interestingly, an optimum combination of steric and electronic
effects in the guise of substituents appended to the NHC
frameworks may result in the design of even better performing
NHCs in catalysis.7 To date, however, very few studies have
focused on modifying electronic properties of existing NHC
ligand architectures.7 The use of aniline-containing NHCs
offers a great opportunity for such a chemical modification and
the ultimate fine-tuning of the NHC properties. Indeed,
anilines can be decorated by countless substituents and provide
access to tailor-made NHCs. In this study and to examine the
effects of such a variation, the bulky and electron-rich IPr*OMe
ligand was prepared and coordinated to palladium. The result-
ing complex 2 was then tested as a precatalyst in the Buchwald−
Hartwig arylamination reaction (Figure 1).
INTRODUCTION
■
Palladium-catalyzed arylamination has become an important
and widely employed method for the formation of C−N
bonds.1 As opposed to the phosphine-based ligands commonly
used for this reaction,2 relatively fewer studies have been
reported using N-heterocyclic carbene (NHC)-based catalysts.3
The catalytic activity of Pd-NHC complexes is directly related
to the unique properties of the supporting NHC. Spectacular
reactivity observed using the Pd-NHC systems has been
attributed to a “flexible steric bulk” in which the ligands can
adjust to incoming substrates, while enabling the stabilization of
a low-valent active intermediate.4 As an example, the precatalyst
[Pd(IPr*)(acac)Cl] (1) (Figure 1) bearing the very bulky IPr*
RESULTS AND DISCUSSION
■
The IPr* ligand previously reported by Marko
́
et al.8 was
recently applied to diverse metal-catalyzed transformations.9
The preparation of the IPr* aniline 6, involving the high
yielding o,o′-dialkylation of p-toluidine with benzhydryl groups,
initially reported by Howell,10 was actually found to be a unique
case of Freidel−Crafts alkylation (Scheme 1). Indeed, as
opposed to phenols that can readily undergo Friedel−Crafts
alkylation/acylation, very few literature examples involve their
aniline equivalents.11 This is believed to be associated with the
stronger affinity of nitrogen toward Lewis acids together with
their higher reactivity, which induces undesired side-reactions.12
Consequently, we decided to take advantage of this reaction to
access other bulky substituted anilines. Surprisingly, in our
hands, the reaction proved to be extremely intolerant to diverse
Figure 1. [Pd(IPr*)(acac)Cl] (1) and [Pd(IPr*OMe)(acac)Cl] (2).
ligand proved to be highly efficient in the catalytic Buchwald−
Hartwig arylamination reaction.5 Another important parameter
accounting for the utility of NHC ligands in catalysis is their
strong σ-donor character, which plays a major role in their
ability to perform the oxidative-addition of aryl halides.6
Received: December 8, 2012
© XXXX American Chemical Society
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a
Scheme 1. Preparation of p-Substituted 2,6-Dibenzhydryl
Anilines by Friedel−Crafts Alkylation
Scheme 3. Preparation of [Ni(IPr*OMe)(CO)3] 13
a
a
Reagents and conditions: (i) aniline (1.0 equiv), diphenylmethanol
(1.1 equiv), ZnCl2, HCl (37% in H2O), 160 °C.
a
electronic or steric modifications. The introduction of nitro,
thio, or amino groups in the para position as well as bulkier
substituents all failed to give the desired anilines in a clean and
efficient manner. However, the CF3 and OMe para-substitued
aniline analogues 7 and 8 were efficiently obtained in good
yields (Scheme 1).
Reagents and conditions: (i) HBF4 (48% in H2O), THF, H2O, rt,
150 min; (ii) NaH, KOtBu, THF, rt, 19 h; (iii) Ni(CO)4, THF, 5 h, rt.
Unfortunately, the unreactive CF3 aniline 7 could not be
converted to the corresponding diimine, and our efforts then
turned to the OMe modification of the IPr*. The IPr*OMe·HCl
10 was accessed through a series of transformations in a similar
fashion as described by Marko
́
(Scheme 2).8 The purification of
a
Scheme 2. Preparation of IPr*OMe·HCl 8
a
Reagents and conditions: (i) glyoxal (40% in H2O), MgSO4,
3 days, rt; (ii) (CHO)n, ZnCl2, HCl (4.0 M in 1,4-dioxane), THF,
70 °C, 2 h.
Figure 2. Molecular structure of [Ni(IPr*OMe)(CO)3] 13. Hydrogens
have been omitted for clarity. Selected bond lengths (Å) and angles
(deg): Ni1−C1 = 1.971(0); Ni1−C72 = 1.809(2); Ni1−C73 =
1.787(2); Ni1−C74 = 1.794(2); O72−C72 = 1.150(3); O73−C73 =
1.134(0); O74−C74 = 1.147(5); C73−Ni1−C1 = 112.99(6); C74−
Ni1−C1 = 119.24(3); C72−Ni1−C1 = 107.78(3).
each intermediates appeared to be greatly facilitated by the
presence of the methoxy substituent, and the process proved to
be easily scalable.
IPr*OMe·HCl 10 was successfully converted to the more
soluble IPr*OMe·HBF4 11 salt as a precursor to the free carbene
IPr*OMe 12. The latter was prepared in multigram quantity and
stored in the glovebox for several weeks with no observed
degradation. Compound 12 was finally reacted with Ni(CO)4
to prepare the [Ni(IPr*OMe)(CO)3] 13 complex and obtain
information about the steric and electronic properties of the
new IPr*OMe (Scheme 3).
Ultimately, IPr*OMe·HCl 10 was reacted with Pd(acac)2, as
described in the literature,3m,5 to afford, in high yield and
purity, the well-defined [Pd(IPr*OMe)(acac)Cl] (2) as an air-
and moisture-stable compound (eq 1).
Crystals of 13 were successfully obtained by slow diffusion of
pentane into a saturated benzene solution of 13, and X-ray dif-
fraction confirmed the expected tricarbonyl structure (Figure 2).13
Bond lengths and angles around the metal center in
[Ni(IPr*OMe)(CO)3] 13 (Figure 2) and [Ni(IPr*)(CO)3]8a
proved nearly identical. The percent buried volume (%VBur
)
of the latter nickel complexes, calculated via the application
SambVca,14 were very similar [%VBur (IPr*OMe) = 39.8 and %VBur
(IPr*) = 38.8].8a,14 Information about the IPr*OMe electronic
properties was obtained from the TEP value (Tolman electronic
parameter = νCO (A1)) band measured by infrared spectroscopy.15
As expected, the slightly more electron-donor property of IPr*OMe
(νCO = 2051.1 cm−1) versus IPr* (νCO = 2052.7 cm−1)8a was
confirmed.16
Suitable X-ray quality single crystals were obtained by
diffusion of pentane into an ethanol solution of 2, and its
structure was confirmed by X-ray diffraction study (Figure 3).13
Molecular structures of both 15 and 2 allowed for the
comparison of their steric properties. Despite a small difference
in their percent buried volumes [(%VBur = 39.3) and (%VBur
=
42.2), respectively],14 identical bond lengths/angles (Figure 3)
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were tested with four different base/solvent systems. Results
were very dependent on the substrates used, and no further
information was obtained to help refine our initial screening
(see the Supporting Information). For practical reasons and
comparison purposes between 1 and 2, 1,4-dioxane and KOtAm
were used to conduct the remainder of the study.
The kinetic profile of the reaction at room temperature and
110 °C was determined by gas chromatography in using 1.0
Figure 3. X-ray structure of [Pd(IPr*OMe)(acac)Cl] 2. Hydrogens have
been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Pd1−C1 = 2.020(1); Pd1−O73 = 2.042(1); Pd1−O75 = 2.063(9); Pd1−
Cl1 = 2.281(7); C1−Pd1−O73 = 92.21(1); O73−Pd1−O75 = 92.92(6);
C1−Pd1−Cl1 = 88.23(5); O75−Pd1−Cl1 = 86.64(8).
were observed in the two complexes, clearly suggesting their
steric similarity.
Figure 4. Kinetic profile of 1 vs 2 in arylamination (involving
nonhindered C−N bond) at rt and 110 °C.
The catalytic properties of 2 in the Buchwald−Hartwig
arylamination reaction were then explored by screening several
base/solvent systems, as previously performed with 1.5 The
results gave preliminary guidelines showing that several bases
(LiHMDS, KHMDS, NaOtBu, KOH, Cs2CO3) were inefficient
for the coupling, giving only low to modest GC conversions.
Interestingly, despite the minor structural difference between
1 and 2, a dramatic difference was already observed during
the preliminary optimization of the conditions. Whereas 1,4-
dioxane appeared to be suitable for both precatalysts, the choice
of the base was critical. LiHMDS (pKa ∼ 30 in DMSO),17 ideal
in the case of 1,5 proved to be highly inefficient with 2. Toluene
and 1,4-dioxane, with KOtAm and KOtBu (pKa ∼ 29.4−32.2 in
DMSO),18 were identified as the best solvent/base combina-
tions for the reaction and gave the best GC conversions at
room temperature and 80 °C (Table 1, entries 1, 2, 4, and 5).
A second optimization was performed by extending the
previous best conditions (Table 1, entries 1, 2, 4, and 5) to
other substrates. Seven different couples of aryl chloride/amine
Figure 5. Kinetic profiles of 1 vs 2 in arylamination (involving
sterically encumbered C−N bond) at rt and 110 °C.
a
Table 1. Initial Screening for Arylamination with 2
bc
,
bd
,
entry
solvent/base
conversion (%) at rt
conversion (%) at 80 °C
1
2
3
4
5
6
7
8
9
toluene/KOtBu
1,4-dioxane/KOtBu
DME/KOtBu
toluene/KOtAm
1,4-dioxane/KOtAm
DME/KOtAm
39
31
5
100
100
100
93
47
25
1
100
100
15
toluene/LiHMDS
1,4-dioxane/LiHMDS
DME/LiHMDS
19
5
40
4
48
a
b
4-Chloroanisole (0.50 mmol), morpholine (0.55 mmol), Pd precatalyst 2 (0.50 mol %), solvent (0.5 mL), base (0.55 mmol). GC conversions of
c
d
coupling product were based on starting aryl halide. GC conversion obtained with 2 (0.50 mol %), room temperature, 20 h. GC conversion
obtained with 2 (0.20 mol %), 80 °C, 5 h.
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ab
,
and 0.05 mol % of catalyt loading, respectively. Two different
benchmark arylamination reactions were examined under the
previously optimized conditions for each catalyst (LiHMDS/
1,4-dioxane for 15 and KtOAm/1,4-dioxane for 2). Only a small
increase of the reaction rate was noticed at room temperature
with 2 (Figures 4 and 5, dashed lines). However, at 110 °C, a
dramatic change was observed in favor of 2. In both cases,
monitoring by gas chromatography indicated complete conversion
within the first hours with 2, whereas no or very low conversion
was observed with 1 (Figures 4 and 5, solid lines).
Table 2. Room-Temperature Arylamination Reactions
As both IPr* and IPr*OMe ligands can be considered sterically
quite similar as the OMe substituent resides away from the
immediate metal coordination environment, the stronger
σ-donor character of IPr*OMe compared with IPr* can pre-
sumably account for the difference in the catalytic performance
observed. Extra σ-donation may help in a number of ways: in
the initial reduction step (PdII to Pd0) and/or offer greater
stabilization of the Pd0-NHC complex at high temperature.3f,7
Similar to its earlier nonoxygenated congener,5 2 was tested
in Buchwald−Hartwig arylamination at room temperature with
1.0 mol % catalyst loading (Table 2). Under these conditions,
the couplings of hindered substrates (Table 2, entries 1 and 6),
deactivated aryl halides (Table 2, entries 3 and 5), and
heterocyclic halides (Table 2, entries 2 and 4) were successfully
achieved. Almost identical results were obtained with 1,5
indicating that both precatalysts possess very similar catalytic
activities at room temperature. The coupling of 2-chloro-m-
xylene and 2,6-di-iso-propylaniline (Table 2, entry 6) previously
studied (Figure 5) lead to the desired heteroadduct in 92%
yield after purification by flash column chromatography. The
similarity of both precatalysts’ activities at room temperature
(Figures 4 and 5, dashed lines) for the nonhindered substrates
led us to explore the limitations of the novel system and
attempt to identify any marked differences between 1 and 2.
Moreover, [Pd(NHC)(acac)Cl] precatalysts generally require
higher temperature for their activation to Pd0-NHC, and con-
sequently, efforts focused on high-temperature reactions that
should show greater scope and we had hoped differences in
catalytic behavior (Table 3).
a
Aryl halide (0.50 mmol), amine (0.55 mmol), Pd precatalyst 2 (1.0
mol %), 1,4-dioxane (0.5 mL), KtOAm (0.55 mmol), room
temperature, 22 h. Isolated yield after optimal GC conversion,
followed by chromatography on silica gel, average of two runs.
b
To compare our results to the literature data,5,19 our
arylamination scope was limited to the reported very chal-
lenging substrates. Hindered (Table 3, entries 1, 2, and 3) and
unactivated substrates (Table 3, entries 2−8), reported to be
highly disfavored coupling partners,19 were successfully coupled
under these conditions. The catalyst loading was dramatically
reduced to 0.05 mol % with no loss of efficiency and excellent
isolated yields. This is in contrast to [Pd(IPr)(acac)Cl]3m and
15 that required much higher loadings for the couplings of
simpler substrates. The secondary biaryl anilines of entries 1, 3,
and 5 were obtained in similar yields as with 1, but with a
catalyst loading 8 times lower! More interestingly, highly
deactivated heteroadducts illustrated in entries 4, 6, 7, and 8
were successfully isolated in 62, 86, 91, and 76% with 0.05−
0.40 mol % of 2. For comparison’s sake, the highly active
Pd-PEPPSI-IPent afforded the same compounds in 90, 75, 65
and 66%, respectively, with the much milder Cs2CO3 as the
base, but at a much higher catalyst loading of 4.0 mol %!19
Finally, our catalytic system was tested at very low catalyst
loading with more classical substrates (Table 4).
that activate significantly more easily than the [Pd(acac)(NHC)Cl]
system,3t this bodes well for the synthesis of even more activate
palladium systems.
CONCLUSION
■
We have reported the preparation and characterization of
IPr*OMe as a new NHC ligand and its application in palladium-
catalyzed arylamination reactions. [Pd(IPr*OMe)(acac)Cl] 2
was obtained as a well-defined air- and moisture-stable pre-
catalyst and proved to be superior to its [Pd(IPr*)(acac)Cl] 1
congener. This observation is in line with previous observations
that have highlighted that sterically demanding and electron-
rich phosphine ligands yielded higher activity in palladium
catalysis,20 but this simple ligand modification leads to a re-
markable increase in catalyst activity and, probably more im-
portantly, stability. A close look at the reaction profiles together
with an optimization of the catalyst loading was necessary
to fully appreciate the gain in activity brought about by the
presence of a simple methoxy substituent; yet, the magnitude of
this difference is, in the end, surprising. Most importantly, the
study has demonstrated that NHC ligands can be further tuned
Good to excellent yields were obtained with as low as
50 ppm of 2, which is comparable with results obtained with
the most efficient phosphine ligands for similar substrates
(≥0.005 mol %).20 As we have previously investigated systems
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ab
,
Table 3. Arylamination Reactions at 110 °C
Table 4. Arylamination Reactions with Low Catalyst Loading
at 110°C
a b
,
a
Reagents and conditions: aryl halide (0.50 mmol), amine (0.55 mmol),
b
1,4-dioxane (0.5 mL), KtOAm (0.55 mmol), 110 °C, 21 h. Isolated
yield after optimal GC conversion, followed by chromatography on
silica gel, average of two runs.
solution in vacuo under nitrogen. 1,2-Dimethoxyethane (DME) was
distilled on sodium/benzophenone, degassed, and stored in a glovebox.
Gas chromatography was performed on an Agilent Technologies 7890A
GC-System equipped with a 7683B series injector and a 7683 series
autosampler. Analytical thin-layer chromatography (TLC) was carried
out using Merck silica gel 60 F254 glass-backed plates and visualized
under UV light (254 and/or 366 nm). Flash column chromatography
was performed on silica gel with a 60 Å pore diameter and 40−63 μm
a
Aryl halide (0.50 mmol), amine (0.55 mmol), 1,4-dioxane (0.5 mL),
1
particle size. H and 13C nuclear magnetic resonance (NMR) spectra
b
KtOAm (0.55 mmol), 110 °C. Isolated yield after optimal GC
conversion, followed by chromatography on silica gel, average of two
runs. This lower yield is likely to be associated with purification issues.
were recorded on a Bruker-400 or 300 MHz spectrometer at ambient
temperature in CDCl3 without TMSCl as an internal standard.
Elemental analyses were performed at London Metropolitan University
(166-220 Holloway Road, London, N7 8DB, U.K.). High-resolution
mass spectrometry was performed by the EPSRC National Mass
Spectrometry Service Centre (NMSSC) (Grove Building Extn., Swansea
University, Singleton Park, Swansea, SA2 8PP, U.K.).
c
by simple (and, in this case, quite remote) structural modifi-
cations. In this context, and opposed to alkylamine-containing
NHCs, aniline-containing NHCs offer almost unlimited possi-
bilities. Indeed, the more or less simple “chemical decoration”
of the aniline aromatic unit can be seen as an efficient way of
fine-tuning existing NHC ligands. The precatalyst 2 is an early
example of this concept, and further investigations are currently
on going in our laboratory to obtain mechanistic evidence and
demonstrate the generality of this concept.
2,6-Bis(diphenylmethyl)-4-trifluoromethylaniline 7. A 50 mL
round-bottom flask was loaded with p-trifluoromethylaniline (2.25 g,
14.0 mmol, 1.0 equiv) and diphenylmethanol (5.14 g, 27.9 mmol,
2.0 equiv) and heated to 160 °C. The eutectic homogeneous liquid
was then treated with a premade solution of anhydrous zinc chloride
(934 mg, 6.85 mmol, 0.5 equiv) in conc. hydrochloric acid (37% in
H2O, 1.20 mL, 14.4 mol, 1.0 equiv) (exothermic + intense bubbling).
After 30 min at 160 °C, the reaction was placed under high vacuum at
160 °C for 15 min before the crude solid was dissolved in hot DCM
(200 mL). The DCM layer was washed with water (3 × 100 mL), then
dried over anhydrous magnesium sulfate. The solvent was evaporated,
and the resulting brownish powder (7.18 g) was dissolved in the
minimum amount of hot toluene. Crystallization was initiated by
addition of pentane, and the process was repeated until no more
crystals formed. The pure desired aniline 7 was obtained as a yellowish
crystalline solid (6.20 g, 90%).
EXPERIMENTAL SECTION
■
General Information. Special care was taken while manipulating
the EXTREMELY TOXIC Ni(CO)4. Ni(CO)4 was constantly
maintained at −50 °C and kept in the glovebox at all times. Unreacted
Ni(CO)4 was quenched with a solution containing triphenylphosphine
in organic solvent. All aryl halides and amines were used as purchased
except 2-chloro-5-methoxy-1,3-dimethylbenzene (Table 3, entries 3
and 4), which was prepared by methylation of the corresponding
4-chloro-3,5-dimethylphenol. Bases (NaOtBu, KOtBu, Na2CO3,
K3PO4, Cs2CO3, K2CO3, NaOH, KOH), anhydrous 1,4-dioxane, and
anhydrous toluene were used as received and stored in a glovebox.
KOtAm was prepared by evaporation of the solvent of a commercial
1H NMR (400 MHz, CDCl3): δ 3.85 (2H, bs, NH2), 5.50 (2H, s,
2 × CHPh2), 6.93 (2H, s, 2 × CHAr), 7.16−7.19 (8H, m, CHAr),
7.30−7.42 (12H, m, CHAr). 13C {1H} NMR (100 MHz, CDCl3): δ
52.4 (2 × CHPh2), 119.2 (q, JCF = 32.1 Hz, CF3), 125.5 (q, JCF = 3.9 Hz,
E
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2 × CHm‑Ar), 127.0 (CHAr), 128.6 (2 × CIVAr), 128.7 (CHAr), 129.3
(CHAr), 141.5 (4 × CIVp‑Ar), 145.2 (N-CIVAr). 19F {1H} NMR (282
MHz, CDCl3): δ = −61.4. HRMS (NSI): found m/z [M + H]+
494.2086; calcd for C33H27NF3, 494.2090.
m, CHAr), 7.25−7.32 (18H, m, CHAr), 12.79 (1H, s, N-CH-N). 13C
{1H} NMR (100 MHz, CDCl3): δ 51.4 (4 × CHPh2), 55.1 (2 ×
OCH3), 115.5 (4 × CHAr), 123.4 (2 × NCH), 125.2 (CHAr), 126.8
(CHAr), 126.9 (CHAr), 128.5 (CHAr), 128.6 (CHAr), 129.0 (CHAr),
129.9 (CHAr), 141.6 (2 × N-CIVAr), 142.2 (CIVAr), 142.6 (CIVAr), 143.0
(N-CH-N), 160.7 (2 × O-CIVp‑Ar). HRMS (NSI): found m/z [M −
Cl]+ 945.4414; calcd for C69H57O2N2, 945.4415. Anal. Calcd for
C69H57ClN2O2: C, 84.42; H, 5.85; N, 2.85. Found: C, 84.37; H, 5.85;
N, 2.95.
2,6-Bis(diphenylmethyl)-4-methoxyaniline 8. A 250 mL
round-bottom flask was loaded with p-anisidine (14.9 g, 0.12 mol,
1.0 equiv) and diphenylmethanol (44.6 g, 0.24 mol, 2.0 equiv) and
heated to 160 °C. The eutectic homogeneous liquid was then treated
with a premade solution of anhydrous zinc chloride (8.09 g, 0.06 mol,
0.5 equiv) in conc. hydrochloric acid (37% in H2O, 10.2 mL, 0.12 mol,
1.0 equiv) (exothermic + intense bubbling). The reaction darkened
and got more and more viscous until it turned completely solid within
20 min. The reaction was placed under high vacuum at 160 C for
15 min before the crude solid was dissolved in hot DCM (300 mL).
The DCM layer was washed with water (3 × 200 mL), then dried over
anhydrous sodium sulfate. The solvent was evaporated, and the
resulting purple viscous oil was dissolved in the minimum amount of
hot toluene. Crystallization was initiated by addition of pentane, and
the process was repeated until no more crystals formed. The pure
desired aniline 8 was obtained as a white crystalline solid (49.3 g,
89%). 1H NMR (400 MHz, CDCl3): δ 3.24 (2H, bs, NH2), 3.55 (3H,
s, OCH3), 5.64 (2H, s, 2 × CHPh2), 6.40 (2H, s, 2 × CHAr), 7.25−
7.43 (20H, m, CHAr). 13C {1H} NMR (100 MHz, CDCl3): δ 52.3 (2 ×
CHPh2), 54.9 (OCH3), 114.2 (2 × CHm‑Ar), 126.6 (CHAr), 128.4
(CHAr), 129.4 (CHAr), 130.6 (2 × CIVo‑Ar), 135.8 (N-CIVAr), 142.4
(CIVAr), 151.7 (O-CIVp‑Ar). HRMS (NSI): found m/z [M + H]+
456.2319; calcd for C33H30ON, 456.2322.
IPr*OMe·HBF4 11. A suspension of imidazolium chloride 10 (9.90 g,
10.1 mmol, 1.0 equiv) in distilled water (300 mL) was treated with
THF (25 mL, helps improve solubility), followed by an aqueous
solution of tetrafluoroboric acid (48%, 1.50 mL, 15.3 mmol, 1.50 equiv).
After 150 min at room temperature, the suspension was extracted with
DCM (3 × 200 mL) and the DCM layer was dried over anhydrous
sodium sulfate. The solvent was evaporated under vacuum until the
apparition of a solid, and the suspension was diluted in pentane. The
solid was isolated by filtration, washed with pentane, and dried under
high vacuum to yield the pure desired imidazolium tetrafluoroborate 11
as an off-white powder (8.49 g, 81%). 1H NMR (400 MHz, CDCl3): δ
3.55 (6H, s, 2 × OCH3), 5.07 (4H, s, 4 × CHPh2), 5.63 (2H, d, J = 1.54
Hz, 2 × NCH), 6.86 (8H, m, 8 × CHAr), 7.07 (8H, m, 8 × CHAr),
7.15−7.29 (18H, m, CHAr), 10.09 (1H, s, N-CH-N). 13C {1H} NMR
(100 MHz, CDCl3); δ 51.6 (4 × CHPh2), 55.1 (2 × OCH3), 115.4 (4 ×
CHAr), 124.3 (2 × NCH), 124.8 (CIVAr), 127.0 (CHAr), 127.2
(CHAr), 128.7 (CHAr), 128.7 (CHAr), 129.1 (CHAr), 129.6 (CHAr),
140.5 (N-CH-N), 141.2 (CIVAr), 142.0 (CIVAr), 142.5 (2 × N-CIVAr),
161.0 (2 × O-CIVp‑Ar). 19F NMR (400 MHz, CDCl3); δ 150.6 (BF4).
HRMS (NSI): found m/z [M − BF4]+ 945.4411; calcd for C69H57O2N2,
945.4415. Anal. Calcd for C69H57BF4N2O2: C, 80.23; H, 5.56; N, 2.71.
Found: C, 80.12; H, 5.48; N, 2.65.
N,N′-Bis(2,6-bis(diphenylmethyl)-p-anisidyl)diazabutadiene 9.
A solution of aniline 8 (44.3 g, 96.9 mmol, 2.0 equiv) in regular DCM
(1000 mL) was treated with anhydrous magnesium sulfate (24.5 g,
203 mmol, 4.2 equiv), followed by an aqueous solution of glyoxal
(40% in H2O, 5.40 mL, 49.1 mmol, 1.0 equiv) and formic acid
(0.5 mL, 13 mmol, 0.3 equiv). The reaction was stirred at room
temperature until complete consumption of the starting aniline, as
indicated by 1H NMR analysis ( 4 days). The magnesium sulfate was
filtered off, and the filtrate was concentrated under vacuum to afford a
brownish solid (47.8 g). The crude solid was recrystallized from
boiling toluene to provide the pure diimine 9 as a bright yellow solid
IPr*OMe 12. In a glovebox, a white suspension of imidazolium
tetrafluoroborate 11 (8.05 g, 7.79 mmol, eq) in anhydrous and
degassed THF (200 mL) was treated with sodium hydride (neat,
280 mg, 11.7 mmol, 1.5 equiv) and a small quantity of KtOBu (tip of
spatula) at room temperature. Very slow bubbling was observed, and
the stirring was continued overnight (19 h) at room temperature. The
2
resulting clear orange solution was filtered through Celite, and /3 of
1
the solvent was evaporated under reduced pressure. The resulting
white suspension was diluted with pentane (100 mL), and the solid
was isolated by filtration. The solid was washed with pentane (3 × 20 mL)
and dried under high vacuum to yield the pure desired free carbene 12 as a
white powder (5.44 g, 74%, containing 2% of THF w/w calculated by
1H NMR). Traces of THF could not be removed from the solid even
(38.8 g, 90%). H NMR (400 MHz, CDCl3): δ 3.53 (6H, s, 2 ×
OCH3), 5.28 (4H, s, 4 × CHPh2), 6.44 (4H, s, 4 × CHAr), 6.99−7.02
(16H, m, HAr), 7.15−7.25 (26H, m, HAr). 13C {1H} NMR (100 MHz,
CDCl3): δ 51.2 (2 × CHPh2), 55.0 (OCH3), 114.1 (2 × CHm‑Ar),
126.4 (CHAr), 128.3 (CHAr), 129.4 (CHAr), 133.7 (2 × CIVo‑Ar), 142.8
(2 × N-CIVAr), 143.5 (CIVAr), 156.1 (2 × O-CIVp‑Ar), 164.2 (2 × NCH).
HRMS (NSI): found m/z [M + H]+ 933.4416; calcd for C68H57O2N2,
933.4416.
1
after prolonged evaporation under high vacuum (cf. NMR data). H
NMR (400 MHz, d8-THF): δ 3.51 (6H, s, 2 × OCH3), 5.64 (4H, s, 4 ×
CHPh2), 5.68 (2H, d, J = 1.54 Hz, 2 × NCH), 6.58 (4H, m, 4 ×
CHAr), 6.89−6.92 (8H, m, 8 × CHAr), 7.04−7.14 (32H, m, CHAr).
Residual THF 1.68 (bs) and 3.64 (bs). 13C {1H} NMR (100 MHz, d8-
THF): δ 52.1 (4 × CHPh2), 55.3 (2 × OCH3), 115.0 (4 × CHAr), 123.0
(2 × NCH), 127.0 (CHAr), 127.0 (CHAr), 128.9 (CHAr), 129.0
(CHAr), 130.3 (CHAr), 130.6 (CHAr), 134.3 (CIVAr), 143.7 (CIVAr),
144.2 (CIVAr), 145.4 (2 × N-CIVAr), 159.9 (2 × O-CIVAr), 221.8 (N-C-N).
Residual THF 26.4 and 68.3 ppm. Anal. Calcd for C69H56N2O2: C, 87.68;
H, 5.97; N, 2.96. Found: C, 87.56; H, 5.88; N, 2.84.
IPr*OMe·HCl 10. A solution of diimine 9 (15.1 g, 16.2 mmol,
1.0 equiv) in regular THF (550 mL) was treated with anhydrous zinc
chloride (2.21 g, 16.2 mmol, 1.0 equiv) at 70 °C, causing the
yellow solution to turn red. After 5 min under stirring at 70 C,
p-formaldehyde (507 mg, 16.9 mmol, 1.0 equiv) was added, followed
by the slow addition of HCl (4.0 M in dioxane, 6.10 mL, 24.4 mmol,
1.50 equiv), which caused the reaction mixture to darken. The reaction
slowly lightened up over 20 min, and the stirring was continued for 2 h
at 70 C. The solvent was evaporated in vacuuo and replaced by ethyl
acetate (550 mL). The organic fraction was washed with water
(3 × 200 mL), then brine (200 mL), before being dried over anhyd-
rous sodium sulfate. The solvent was partially evaporated under
reduced pressure until the formation of a white solid, and the
remaining solution was diluted in pentane (300 mL). The off-white
solid was isolated by filtration and dried under high vacuum. The off-
white crude product (13.7 g) was washed with boiling toluene (3 ×
100 mL), and the remaining off-white solid (9.45 g) was isolated by
filtration. The filtrate was diluted in pentane and provided more
crystals (2.90 g) over 1 h at room temperature. The solids were
combined, washed with pentane, and dried under high vacuum to
provide the pure desired imidazolium chloride 10 as an off-white
crystalline powder (12.4 g, 78%). 1H NMR (400 MHz, CDCl3): δ 3.53
(6H, s, 2 × OCH3), 5.32 (4H, s, 4 × CHPh2), 5.46 (2H, s, 2 × N
CH), 6.49 (4H, s, 4 × CHAr), 6.85 (8H, m, CHAr), 7.12−7.22 (16H,
[Ni(IPr*OMe)(CO)3] 13. In a glovebox, a precooled solution of free
carbene 102 (400 mg, 0.42 mmol, 1.0 equiv) in anhydrous THF was
treated with precooled neat Ni(CO)4 (100 μL, ∼0.77 mmol, ∼1.8 equiv)
under stirring. After 5 h at room temperature, the volatiles were
evaporated in vaccuo to yield a brownish solid. The solid was washed with
pentane (2 × 15 mL) and was dried under high vacuum to afford the
pure desired nickel complex 13 as a light gray powder (430 mg, 93%,
containing 3% of THF and 3% of pentane w/w calculated by 1H
NMR). The complete removal of volatiles (THF and pentane) was
proved impossible even after prolonged drying under high vacuum
(cf. NMR data). 1H NMR (400 MHz, d8-THF): δ 3.50 (6H, s,
2 × OCH3), 5.05 (4H, s, 4 × CHPh2), 5.31 (2H, d, J = 1.54 Hz, 2 ×
NCH), 6.60 (4H, m, 4 × CHAr), 6.80 (8H, app bd, J = 6.3 Hz, 8 ×
CHAr), 7.04−7.26 (32H, m, CHAr). Residual solvents (THF 1.68 (bs)
and 3.64 (bs) and pentane 0.86 (t) and 1.26 (m)). 13C {1H} NMR
F
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(100 MHz, d8-THF): δ 52.9 (4 × CHPh2), 55.4 (2 × OCH3), 115.5
(4 × CHAr), 124.1 (2 × NCH), 127.2 (CHAr), 127.4 (CHAr), 129.0
(CHAr), 130.3 (CHAr), 131.1 (CHAr), 133.6 (CHAr), 144.0 (CIVAr),
144.3 (CIVAr), 144.8 (2 × N-CIVAr), 160.7 (2 × O-CIVAr), 197.6 (N-C-N),
198.4 (3 × CO). Residual solvents (THF 26.4 and 68.3 ppm and
pentane 14.4, 23.2, and 35.1 ppm). IR νCO (CH2Cl2, cm−1): 2051.1 (s),
1976.2 (s), 1961.9 (s). (3 mg/mL). Anal. Calcd for C72H56N2NiO5: C,
79.49; H, 5.19; N, 2.57. Found: C, 79.34; H, 5.28; N, 2.67.
solid. Data were in full agreement with those reported in the
literature.5 1H NMR (CDCl3, 300 MHz): δ = 3.05−3.08 (4H, m, 2 ×
N-CH2), 3.78 (3H, s, OCH3), 3.86−3.89 (4H, m, 2 × O-CH2), 6.85−
6.92 (4H, m, HAr). 13C NMR (CDCl3, 75 MHz): δ = 50.8 (2 × N-
CH2), 55.5 (O-CH3), 67.0 (2 × O-CH2), 114.5 (CHAr), 117.8 (CHAr),
145.6 (N-CIVAr), 154.0 (O-CIVAr).
N-Methyl-N-phenylpyridin-2-amine (Table 2, Entry 4). The
general procedure yielded (181.1 mg, 98%) the pure arylamine as a
yellow oil. Data were in full agreement with those reported in the
literature.5 1H NMR (CDCl3, 400 MHz): δ = 3.47 (3H, s, CH3), 6.53
(1H, dt, J = 8.6, 0.9 Hz, CHPyr), 6.60 (1H, ddd, J = 7.1, 5.0, 0.9 Hz,
CHPyr), 7.15−7.32 (4H, m, CHPyr + CHAr), 7.36−7.42 (2H, m, HAr),
8.23 (1H, ddd, J = 5.0, 2.0, 0.9 Hz, CHPyr). 13C NMR (CDCl3, 100 MHz):
δ = 38.3 (N-CH3), 109.1 (CHPyr), 112.3 (CHPyr), 113.0 (CHAr), 125.3
(CHAr), 126.2 (CHAr), 129.1 (CHAr), 129.6 (CHAr), 136.5 (CHPyr), 146.8
(CIVAr), 147.7 (CHPyr), 158.7 (2 − CIVPyr).
4-(4-Methoxyphenyl)morpholine (Table 2, Entry 5). The general
procedure yielded (161.2 mg, 83%) the pure arylamine as a white
solid. Data were in full agreement with those reported in the
literature.5 1H NMR (CDCl3, 300 MHz): δ = 3.05−3.08 (4H, m, 2 ×
N-CH2), 3.78 (3H, s, OCH3), 3.86−3.89 (4H, m, 2 × O-CH2), 6.85−
6.92 (4H, m, HAr). 13C NMR (CDCl3, 75 MHz): δ = 50.8 (2 ×
N-CH2), 55.5 (O-CH3), 67.0 (2 × O-CH2), 114.5 (CHAr), 117.8 (CHAr),
145.6 (N-CIVAr), 154.0 (O-CIVAr).
N-(2,6-Di-iso-propylphenyl)-2,6-dimethylaniline (Table 2, Entry 6).
The general procedure yielded (258.0 mg, 92%) the pure arylamine
as a colorless oil. Data were in full agreement with those reported in
the literature.5 1H NMR (CDCl3, 400 MHz): δ = 1.22 (12H, d, J =
6.9 Hz, 4 × CH3), 2.08 (6H, s, 2 × CH3), 6.53 (1H, app hept, J =
6.9 Hz, CHMe2), 4.89 (1H, bs, NH), 6.81 (1H, t, J = 7.4 Hz, CHAr),
7.03 (2H, d, J = 7.4 Hz, CHAr), 7.18−7.25 (3H, m, HAr). 13C NMR
(CDCl3, 100 MHz): δ = 19.3 (CH3), 23.4 (CH3), 28.0 (Me2CH),
119.6 (CHAr), 123.2 (CHAr), 124.8 (CHAr), 125.6 (CIVAr), 129.5
(CHAr), 138.8 (CIVAr), 143.1 (CIVAr), 144.1 (CIVAr).
[Pd(IPr*OMe)(acac)Cl] 2. A solution ofIPr*OMe·HCl 10 (2.40 g,
2.44 mmol, 1.4 equiv) in dry 1,4-dioxane (40 mL) was treated with
Pd(acac)2 (550 mg, 1.79 mmol, 1.0 equiv) under an atmosphere of
nitrogen. The reaction mixture was stirred for 24 h (time not
optimized) at 100 C before being concentrated under reduced
pressure. The resulting crude product was dissolved in DCM, the
solution was filtered through a pad of silica covered with Celite, and
the pad was eluted with DCM. After evaporation of the solvents, the
complex was triturated with pentane and dried under high vacuum to
1
yield the pure complex 2 as a yellow powder (2.05 g, 96%). H NMR
(400 MHz, d8-THF): δ 0.93 (3H, s, CH3acac), 2.16 (3H, s CH3acac),
3.61 (6H, s, 2 × OCH3), 5.00 (2H, s, 2 × NCH), 5.26 (1H, s,
CHacac), 6.01 (4H, vbs, 4 × CHPh2), 6.67 (4H, s, 4 × CHArN), 6.86
(8H, vbs, 8 × CHAr), 7.21 (32H, vbs, 32 × CHAr), 7.62 (4H, vbs,
CHAr). 13C {1H} NMR (100 MHz, d8-THF): δ 26.3 (CH3acac), 27.1
(CH3acac), 50.9 (4 × CHPh2), 54.8 (2 × OCH3), 77.2 (residual
CHCl3), 100.0 (CHacac), 115.2 (broad, 4 × CHArN), 124.2 (2 × N
CH), 126.1 (broad, CHAr), 127.7 (CHAr), 127.9 (CHAr), 129.3
(CHAr), 130.1 (broad, CHAr), 130.3 (CIVAr), 130.6 (broad, CHAr),
143.4 (CIVAr), 144.1 (2 × N-CIVAr), 154.9 (N-C-N), 159.1 (2 × O-
CIVAr), 185.1 (C-Oacac), 186.7 (C-Oacac). HRMS (NSI): found m/z [M
+ NH4]+ 1198.3880; calcd for C74H67O4N3Cl102Pd, 1198.3871. Anal.
Calcd for C35H53ClN2: C, 74.87; H, 5.43; N, 2.36. Found: C, 74.95; H,
5.30; N, 2.28.
General Procedure for the Buchwald−Hartwig Cross-
Coupling of Aryl Halides with Amines. In a glovebox, a glass
vial was charged with KOtAm (0.55 mmol), equipped with a magnetic
stir bar, and sealed with a screw cap fitted with a septum. The vial was
then loaded with the neat amine (0.55 mmol) and the aryl halide
(0.50 mmol) outside the glovebox. Finally, a premade solution of
[Pd(IPr*OMe)(acac)Cl] 2 in anhydrous 1,4-dioxane (prepared in a
glovebox) was subsequently injected at room temperature under
argon, and the reaction mixture was stirred until optimal conversion, as
indicated by GC chromatography. The final reaction mixture was
diluted with a minimum amount of dichloromethane and directly
loaded onto silica gel to be purified by flash column chromatography
(silica gel, diethyl ether in pentane). The reported yields are based on
the average of two runs. In the case of solid starting materials, the solid
was quickly added to the vial containing KOtAm outside the glovebox
and the vial was purged using classical Schlenk techniques.
2,6-Dimethyl-N-(o-tolyl)aniline (Table 2, Entry 1). The general
procedure yielded (202.3 mg, 96%) the pure arylamine as a white
solid. Data were in full agreement with those reported in the liter-
ature.5 1H NMR (CDCl3, 400 MHz): δ = 2.28 (6H, s, 2 × CH3), 2.42
(3H, s, CH3), 5.01 (1H, vbs, NH), 6.25 (1H, d, J = 8.1 Hz, HAr), 6.80
(1H, t, J = 7.3 Hz, HAr), 7.06 (1H, t, J = 7.7 Hz, HAr), 7.15−7.23
(4H, m, HAr). 13C NMR (CDCl3, 100 MHz): δ = 17.6 (CH3), 18.2
(2 × CH3), 111.7 (CHAr), 118.0 (CHAr), 122.4 (CIVAr), 125.5 (CHAr),
126.9 (CHAr), 128.5 (CHAr), 130.2 (CHAr), 135.5 (CIVAr), 138.7
(CIVAr), 144.1 (CIVAr).
N-Methyl-N-phenylpyridin-2-amine (Table 2, Entry 2). The
general procedure yielded (171.4 mg, 93%) the pure arylamine as a
yellow oil. Data were in full agreement with those reported in the
literature.5 1H NMR (CDCl3, 400 MHz): δ = 3.48 (3H, s, CH3), 6.53
(1H, dt, J = 8.6, 0.9 Hz, CHPyr), 6.60 (1H, ddd, J = 7.1, 5.0, 0.9 Hz,
CHPyr), 7.16−7.31 (4H, m, CHPyr + CHAr), 7.37−7.42 (2H, m, HAr),
8.23 (1H, ddd, J = 5.0, 2.0, 0.9 Hz, CHPyr). 13C NMR (CDCl3,
100 MHz): δ = 38.3 (N-CH3), 109.1 (CHPyr), 112.3 (CHPyr), 113.0
(CHAr), 125.3 (CHAr), 126.2 (CHAr), 129.1 (CHAr), 129.6 (CHAr),
136.5 (CHPyr), 146.8 (CIVAr), 147.7 (CHPyr), 158.7 (2 − CIVPyr).
4-(4-Methoxyphenyl)morpholine (Table 2, Entry 3). The general
procedure yielded (138.2 mg, 72%) the pure arylamine as a white
N-(2,6-Di-iso-propylphenyl)-2,6-dimethylaniline (Table 3, Entry 1).
The general procedure yielded (262.6 mg, 93%) of the pure arylamine
as a yellow oil. Data were in full agreement with those reported in the
literature.5 1H NMR (CDCl3, 400 MHz): δ = 1.19 (12H, d, J = 6.9 Hz,
4 × CH3), 2.04 (6H, s, 2 × CH3), 3.22 (1H, app hept, J = 6.9 Hz,
CHMe2), 4.86 (1H, bs, NH), 6.78 (1H, t, J = 7.4 Hz, CHAr), 7.00 (2H,
d, J = 7.4 Hz, CHAr), 7.15−7.23 (3H, m, HAr). 13C NMR (CDCl3, 100
MHz): δ = δ 19.3 (CH3), 23.4 (CH3), 28.0 (Me2CH), 119.6 (CHAr),
123.2 (CHAr), 124.8 (CHAr), 125.6 (CIVAr), 129.5 (CHAr), 138.8
(CIVAr), 143.1 (CIVAr), 144.1 (CIVAr).
2,6-Di-iso-propyl-N-(2-methoxyphenyl)aniline (Table 3, Entry 2).
The general procedure yielded (262.4 mg, 93%) the pure arylamine as
a colorless oil. Data were in full agreement with those reported in the
literature.22 1H NMR (CDCl3, 300 MHz): δ = 1.21 (6H, s, CH3), 3.23
(2 H, h, J = 6.8 Hz, 2 × Me2CH), 4.01 (3H, s, O-CH3), 5.70 (1H, bs,
NH), 6.19 (1H ddd, J = 7.2, 2.5, 1.0 Hz, HAr), 6.70−6.80 (2H, m,
HAr), 6.92 (1H, dd, J = 7.2, 2.1 Hz, HAr), 7.27−7.38 (3H, m, HAr). 13
C
NMR (CDCl3, 75 MHz): δ = 23.8 and 23.9 (app b peak, 2 × CH3),
28.1 (Me2CH), 55.6 (O-CH3), 109.7 (CHAr), 110.9 (CHAr), 116.7
(CHAr), 121.1 (CHAr), 123.7 (CHAr), 127.0 (CHAr), 135.4 (CIVAr),
137.9 (CIVAr), 146.2 (CIVAr), 147.6 (CIVAr).
N-(2,6-Di-iso-propylphenyl)-4-methoxy-2,6-dimethylaniline
(Table 3, Entry 3). The general procedure yielded (270.0 mg, 87%) the
pure arylamine as an orange oil. Data were in full agreement with those
reported in the literature.5 1H NMR (CDCl3, 300 MHz): δ = 1.15
(12H, d, J = 6.9 Hz, 4 × CH3), 2.04 (6H, s, 2 × CH3), 3.11 (2H, app
hept, J = 6.9 Hz, 2 × Me2CH), 3.80 (3H, s, OCH3), 4.67 (1H, bs,
NH), 6.59 (2H, bs, J = 7.6 Hz, HAr), 7.05−7.15 (3H, m, HAr). 13C
NMR (CDCl3, 75 MHz): δ = 19.5 (CH3), 23.5 (CH3), 27.9
(Me2CH), 55.4 (OCH3), 114.4 (CHAr), 123.0 (CHAr), 123.4 (CHAr),
129.9 (Me-CIVAr), 136.5 (N-CIVAr), 139.7 (N-CIVAr), 141.5 (iPr-CIVAr),
153.9 (MeO-CIVAr).
4-(4-Methoxy-2,6-dimethylphenyl)morpholine (Table 3, Entry 4).
The general procedure yielded (138.3 mg, 62%) the pure arylamine as
an orange solid. Data were in full agreement with those reported in the
literature.3h 1H NMR (CDCl3, 300 MHz): δ = 2.34 (6H, s, 2 × CH3),
G
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3.07 (4H, app t, J = 4.5 Hz, 2 × N-CH2), 3.76 (3H, s, OCH3), 3.80
(4H, app t, J = 4.5 Hz, 2 × O-CH2), 6.56 (2H, s, HAr). 13C NMR
(CDCl3, 75 MHz): δ = 19.7 (CH3), 50.2 (N-CH2), 55.2 (O-CH3),
68.2 (O-CH2), 113.8 (CIV), 138.4 (CHAr), 141.1 (N-CIVAr), 156.6
(O-CIVAr).
4-(4-Methoxyphenyl)morpholine (Table 3, Entry 5). The general
procedure yielded (179.0 mg, 93%) the pure arylamine as a white
solid. Data were in full agreement with those reported in the
literature.5 1H NMR (CDCl3, 300 MHz): δ = 3.05−3.08 (4H, m, 2 ×
N-CH2), 3.78 (3H, s, OCH3), 3.86−3.89 (4H, m, 2 × O-CH2), 6.85−
6.92 (4H, m, HAr). 13C NMR (CDCl3, 75 MHz): δ = 50.8 (2 ×
N-CH2), 55.5 (O-CH3), 67.0 (2 × O-CH2), 114.5 (CHAr), 117.8 (CHAr),
145.6 (N-CIVAr), 154.0 (O-CIVAr).
4-Fluoro-N-(4-methoxyphenyl)aniline (Table 3, Entry 6). The
general procedure yielded (187.3 mg, 86%) the pure arylamine as an
orange beige solid. Data were in full agreement with those reported in
the literature.2i,23 1H NMR (CDCl3, 300 MHz): δ = 3.81 (3H, s,
CH3), 5.38 (1H, bs, NH), 6.84−7.04 (8H, m, HAr). 13C NMR (CDCl3,
75 MHz): δ = 55.6 (O-CH3), 114.7 (CHAr), 115.6 (d, J = 22 Hz,
CHAr), 115.9 (CHAr), 117.7 (d, J = 8 Hz, CHAr), 117.8 (CHAr), 121.2
(CHAr), 136.5 (N-CIVAr), 141.1 (N-CIVAr), 155.0 (O-CIVAr), 155.5
(CHAr), 158.7 (d, J = 238 Hz, CIVAr). 19F NMR (CDCl3, 282 MHz):
δ = −124.8
(CHAr), 128.3 (CHAr), 128.9 (CHAr), 131.3 (CHAr), 136.8 (CIVAr),
146.8 (N-CIVAr), 149.1(N-CIVAr).
N,2-Dimethyl-N-phenylaniline (Table 4, Entry 4). The general
procedure yielded (192.7 mg, 98%) the pure arylamine as a pale yellow
oil. Data were in full agreement with those reported in the literature.25
1H NMR (CDCl3, 300 MHz): δ = 2.18 (3H, s, CH3), 3.25 (3H, s,
N-CH3), 6.57 (2H, d, J = 8.9 Hz, HAr), 6.74 (1H, t, J = 7.3 Hz, HAr),
7.16−7.33 (6H, m, HAr). 13C NMR (CDCl3, 75 MHz): δ = 17.8
(CH3), 39.0 (CH3), 112.8 (CHAr), 116.8 (CHAr), 126.4 (CHAr), 127.5
(CHAr), 128.3 (CHAr), 128.9 (CHAr), 131.3 (CHAr), 136.8 (CIVAr),
146.8 (N-CIVAr), 149.1(N-CIVAr).
4-Methoxy-N-methyl-N-phenylaniline (Table 4, Entry 5). The
general procedure yielded (195.5 mg, 92%) the pure arylamine as a
pale yellow oil. Data were in full agreement with those reported in the
literature.9c 1H NMR (CDCl3, 300 MHz): δ = 3.71 (3H, s, CH3), 4.26
(3H, s, O-CH3), 7.22−7.28 (3H, m, HAr), 7.32−7.38 (2H, m, HAr),
7.53−7.58 (2H, m, HAr), 7.62−7.69 (2H, m, HAr). 13C NMR (CDCl3,
75 MHz): δ = 40.4 (CH3), 55.4 (O-CH3), 114.7 (CAr), 115.6 (CAr),
118.3 (CAr), 126.2 (CAr), 128.9 (CAr), 142.2 (CIVAr), 149.7 (CIVAr),
156.2 (CIVAr).
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra for all compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
2-Fluoro-N-(4-methoxyphenyl)aniline (Table 3, Entry 7). The
general procedure yielded (198.6 mg, 91%) the pure arylamine as an
off-white solid. Data were in full agreement with those reported in the
literature.17c 1H NMR (CDCl3, 300 MHz): δ = 3.83 (3H, s, CH3),
AUTHOR INFORMATION
Corresponding Author
*E-mail: snolan@st-andrews.ac.uk.
5.66 (1H, bs, NH), 6.77 (1H, bm, HAr), 6.90−7.15 (7H, m, HAr). 13
C
■
NMR (CDCl3, 75 MHz): δ = 55.5 (CH3), 114.7 (CHAr), 115.0 (d, J =
1 Hz, CHAr), 115.0 and 115.2 (d, J = 19 Hz, CHAr), 118.8 (d, J = 7 Hz,
CHAr), 123.0 (CHAr), 124.2 (d, J = 3 Hz, CHAr), 133.8 (d, J = 11 Hz,
CIVAr), 134.4 (CIVAr), 150.5 and 153.7 (d, J = 240 Hz, CIV-F), 155.8
(CIVAr). 19F NMR (CDCl3, 282 MHz): δ = −135.3.
Author Contributions
‡These authors contributed equally.
Notes
N-(4-Methoxyphenyl)-3-(trifluoromethyl)aniline (Table 3, Entry 8).
The general procedure yielded (201.8 mg, 76%) the pure arylamine as
a yellowish solid. Data were in full agreement with those reported in
the literature.24 1H NMR (CDCl3, 300 MHz): δ = 3.83 (3H, s, CH3),
5.64 (1H, bs, NH), 6.89−6.94 (2H, m, HAr), 7.00−7.13 (5H, m, HAr),
7.27−7.32 (1H, m, HAr). 13C NMR (CDCl3, 75 MHz): δ = 55.5
(CH3), 111.3 (q, J = 4 Hz, CHAr), 114.8 (CHAr), 115.6 (q, J = 4 Hz,
CHAr), 117.9 (CHAr), 122.4 and 126.0 (d, J = 272 Hz, CIVAr), 123.5
(CHAr), 129.7 (CHAr), 131.7 (q, J = 32 Hz, CIVAr), 134.2 (CIVAr),
146.0 (CIVAr), 156.1 (CIVAr). 19F NMR (CDCl3, 282 MHz): δ = −63.3.
N,4-Dimethyl-N-phenylaniline (Table 4, Entry 1). The general
procedure yielded (143.0 mg, 72%) the pure arylamine as a slightly
yellow oil. Data were in full agreement with those reported in the
literature.9c 1H NMR (CDCl3, 300 MHz): δ = 7.29 (2H, t, J = 7.6 Hz,
HAr), 7.18 (2H, d, J = 8.1 Hz, HAr), 7.07 (2H, d, J = 8.3 Hz, HAr), 6.99
(2H, d, J = 7.9 Hz, HAr), 6.93 (1H, t, J = 7.3 Hz, HAr), 3.35 (3H, s,
N-CH3), 2.39 (3H, s, CH3). 13C NMR (CDCl3, 75 MHz): δ = 20.7
(CH3), 40.3 (N-CH3), 118.2 (CHAr), 119.7 (CHAr), 122.5 (CHAr),
129.0 (CHAr), 129.9 (CHAr), 132.0 (CIVAr), 146.6 (N-CIVAr), 149.3
(N-CIVAr).
N,4-Dimethyl-N-phenylaniline (Table 4, Entry 2). The general
procedure yielded (180.3 mg, 91%) the pure arylamine as a slightly
yellow oil. Data were in full agreement with those reported in the
literature.9c 1H NMR (CDCl3, 300 MHz): δ = 7.30 (2H, m, HAr), 7.19
(2H, d, J = 8.1 Hz, HAr), 7.07 (2H, m, HAr), 7.00 (2H, d, J = 7.9 Hz,
HAr), 6.94 (1H, t, J = 7.3 Hz, HAr), 3.36 (3H, s, N-CH3), 2.40 (3H, s,
CH3). 13C NMR (CDCl3, 75 MHz): δ = 20.7 (CH3), 40.3 (N-CH3),
118.2 (CHAr), 119.8 (CHAr), 122.5 (CHAr), 129.0 (CHAr), 129.9
(CHAr), 132.0 (CIVAr), 146.6 (N-CIVAr), 149.3 (N-CIVAr).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the EC for funding through the
seventh framework programme SYNFLOW and the ERC for an
Advanced Researcher Award to S.P.N. (FUNCAT). Umicore
AG is thanked for its generous gifts of materials. We thank the
EPSRC National Mass Spectrometry Service Center in Swansea
for mass spectroscopic analyses. S.P.N. is a Royal Society
Wolfson Research Merit Award holder.
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