Synthesis of well-defined diphenylvinyl(cyclopropyl)phosphine-palladium complexes for the Suzuki-Miyaura reaction and Buchwald-Hartwig amination

Article abstract of DOI:10.1002/adsc.201300332

The well-defined diphenylvinylphosphine-palladium complex 1 and the diphenylcyclopropylphosphine-palladium complex 2 were successfully synthesized. The crystal structures of these complexes were obtained by X-ray crystallographic analysis. Both complexes were air- and moisture-stable, and could be prepared on a gram scale. These palladium complexes catalyzed the Suzuki-Miyaura reaction of aryl bromides [turnover numbers (TON) up to 196,000] and aryl chlorides (TON up to 50,000). Furthermore, complex 2 catalyzed the Buchwald-Hartwig amination of aryl chlorides and aromatic/aliphatic amines with a low catalyst loading. These complexes showed different reactivities for the coupling of 2-chloropyridine, and the origin of this difference is discussed. Copyright

Full text of DOI:10.1002/adsc.201300332

UPDATES
DOI: 10.1002/adsc.201300332
Synthesis of Well-Defined Diphenylvinyl(cyclopropyl)phosphine-
Palladium Complexes for the Suzuki–Miyaura Reaction and
Buchwald–Hartwig Amination
Naota Yokoyama,a,* Yuji Nakayama,a Hideki Nara,a and Noboru Sayoa
a
Takasago International Corporation, Corporate Research & Development Division, 4-11, Nishiyawata 1-chome, Hiratsuka
City, Kanagawa 254-0073, Japan
Fax : (+81)-463-25-2084; e-mail: naota_yokoyama@takasago.com
Received: April 19, 2013; Revised: May 21, 2013; Published online: July 12, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300332.
Abstract: The well-defined diphenylvinylphosphine-
palladium complex 1 and the diphenylcyclopropyl-
phosphine-palladium complex 2 were successfully
synthesized. The crystal structures of these com-
plexes were obtained by X-ray crystallographic
analysis. Both complexes were air- and moisture-
stable, and could be prepared on a gram scale.
These palladium complexes catalyzed the Suzuki–
Miyaura reaction of aryl bromides [turnover num-
bers (TON) up to 196,000] and aryl chlorides (TON
up to 50,000). Furthermore, complex 2 catalyzed
the Buchwald–Hartwig amination of aryl chlorides
and aromatic/aliphatic amines with a low catalyst
loading. These complexes showed different reactivi-
ties for the coupling of 2-chloropyridine, and the
origin of this difference is discussed.
Figure 1. BRIDPs.
Suzuki–Miyaura reaction[3b,d] and the a-arylation of
ketones[3d] using aryl chlorides as the substrate. Re-
cently, there has been considerable interest in pre-
formed and well-defined palladium-ligand com-
plexes,[4] which offer greater reproducibility of the cat-
alytic reactions compared to the use of complexes
prepared in situ. We report here the synthesis, charac-
terization and the application of newly developed pal-
ladium complexes of BRIDPs (Pd-BRIDP com-
plexes) for the cross-coupling reactions.
À
Keywords: amination; biaryls; C C coupling; palla-
dium; phosphane ligands
First, we tried to synthesize Pd-BRIDP complexes
by combining four types of BRIDPs and three palla-
dium sources: [PdCl
The palladium-catalyzed cross-coupling reaction is Pd(OAc)2. In all cases, a Pd-BRIDP complex was
one of the most straightforward and reliable tools for formed successfully (confirmed by 31P NMR analysis).
the preparation of the biaryl motifs that are often Among them, PdCl2(cy-vbridp)2 (1) and PdCl(p-
seen in natural products, pharmaceuticals, agrochemi- allyl)(cbridp) (2) were isolated in quantitative yields
ACHTUTNGERNNUG(p-allyl)]2, PdCl2ACHUTNTGERN(NUGN CH3CN)2 and
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
cals and functional materials.[1] To date, various types as yellow powders and gave single crystals from THF/
of ligands, such as trialkylphosphines,[2a] Buchwald li- n-heptane. The results of X-ray crystallographic anal-
gands,[2b] and N-heterocyclic carbenes,[2c] have been ysis of these complexes are shown in Scheme 1. The
developed to increase the catalytic activity. Their X-ray and calculated structures of 3 and 4 are also
ꢀelectron-richꢁ and ꢀbulkyꢁ nature has enabled the use shown. The lone pair of the phosphorus atom of each
of less-reactive substrates such as aryl chlorides for ligand faces toward the cis phenyl group to minimize
the coupling reaction. We have also developed the steric repulsion between the cyclohexyl/tert-butyl
(1,1-diphenylprop-1-en-2-yl)phosphines
[vBRIDP, groups and the cis phenyl group. During the forma-
Cy-vBRIDP (3)][3a,b] and (1-methyl-2,2-diphenylcyclo- tion of complex 1, the dicyclohexylphosphino-carbon
propyl)phosphines [cBRIDP (4), Cy-cBRIDP][3c,d] bond rotates [Eq. (1)]. On the other hand, the di-tert-
(Figure 1), which are efficient ligands for the palladi- butylphosphino-carbon bond does not rotate with the
um-catalyzed Buchwald–Hartwig amination,[3a,c] the formation of complex 2 [Eq. (2)]. The energy barrier
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Naota Yokoyama et al.
UPDATES
Scheme 1. Synthesis of Pd-BRIDP complexes.
for rotation of the latter bond is too high, so that the the reaction. Aryl bromides containing electron-do-
bond does not rotate at the reaction temperature.[5] nating groups (entries 1–4) or electron-withdrawing
Both complexes could be prepared on a gram scale. groups (entries 5–8) were converted into the desired
In addition, the complexes were stable for at least 12 biphenyl compounds with quite low catalyst loadings
months under air at room temperature, and could be (0.01–0.0005 mol%). The addition of water promoted
handled without any special care.
the reaction of 2-bromotoluene (entry 4). The E/Z
Next, we evaluated the catalytic activities of these ratio was retained in the coupling of b-bromostyrene
well-defined Pd-BRIDP complexes in the Suzuki– (entry 10). Complex 2 also smoothly catalyzed the re-
Miyaura reaction[6] of aryl bromides (Table 1). As action (entries 11 and 12).
a result, complex 1 showed high catalytic activity for
The reaction of aryl bromide was also catalyzed by
Pd-BRIDP complexes at lower temperature (Table 2).
Table 1. Suzuki–Miyaura reaction of aryl bromide catalyzed
by Pd-BRIDP complexes.
Table 2. Suzuki–Miyaura reaction of aryl bromides under
mild conditions.
Entry Ar1 Ar2 Pd Temp. [8C] Time [h] Conv. [%][a,b]
Entry Ar1 Pd mol% Temp. [8C] Time [h] Conv. [%][a,b]
1
5a 6a
5b 6a
5b 6a
1
1
1
1
1
1
1
1
1
1
1
2
2
40
40
40
40
40
40
40
40
40
40
60
30
30
21
17
18
15
22
8
6
8
6
24
24
18
5
>99 (99)
>99 (99)
92 (À)
2
1
2
5a
5b
5b
5d
5e
5f
5g
5h
5i
1
1
1
1
1
1
1
1
1
1
2
2
0.001 100
0.001 100
0.0005 100
7
1
8
3
3
10
7
8
2
97 (95)
3[c]
4
>99 (99)
98 (À)
5c
6a
>99 (99)
99 (97)
3
4[c]
5
0.01
80
>99 (99)
>99 (97)
98 (96)[d]
96 (90)
5
6
7
8
9
10
11
5d 6a
5e 6a
99 (97)
>99 (92)
99(95)
>99 (97)
99 (92)
99 (95)
0.001 100
0.002 80
0.002 100
0.001 100
5f
6a
6
7
8
9
10
11[c]
12
5g 6a
5h 6a
5b 6b
5b 6c
96 (94)
0.01
0.01
0.01
0.02
100
80
80
96 (85)[d]
99 (98)[e]
99 (À)
5k
5b
5j
7
5
0.5
12[d,e] 5b 6a
13[d,e] 5g 6a
>99 (À)
>99 (À)
80
>99 (96)
[a]
[a]
GC conversion of aryl bromide.
GC conversion of aryl bromide.
[b]
[c]
[d]
[e]
[b]
[c]
[d]
[e]
Values in parentheses show the isolated yield.
The reaction was carried out in the absence of water.
cBRIDP (4) was added (1.0 equiv. vs. complex 2).
Solvent: toluene/THF/H2O=10/1/6.
Values in parentheses show the isolated yield.
Solvent: toluene/THF/H2O=10/1/6.
Isolated by recrystallization.
The trans:cis ratio was 85:15.
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Synthesis of Well-Defined Diphenylvinyl(cyclopropyl)phosphine-Palladium Complexes
Complexes 1 and 2 catalyzed the reaction at 408C (entries 1–5), electron-withdrawing groups (entries 6–
and 308C, respectively. Interestingly, the presence of 10), and sulfur which often acts as a poison for the
water was a key factor for completion of the reaction catalyst (entry 11), could be used at a low catalyst
(entry 2 vs. entry 3). We thought that water may ac- loading (0.1–0.002 mol%). The reaction of bulky 2-
celerate the transmetalation step by resolving the in- chloro-m-xylene also proceeded smoothly with com-
organic base to promote the formation of a borate plex 1 (entry 15). In contrast to the case of aryl bro-
and/or arylpalladium hydroxide intermediate.[7] The mides, the addition of water was not necessary for
reaction of 4-acetylphenylboronic acid proceeded at completion of the reaction. This result suggests that
608C (entry 11).
the rate-limiting step in the coupling of aryl chlorides
We also tried the Suzuki–Miyaura reaction of aryl was not transmetalation, but rather oxidative addi-
chlorides, which are an inexpensive but less-reactive tion.
substrate (Table 3). As a result, both complexes
Next, the coupling reaction of chloropyridine was
showed high catalytic activity in the reaction of aryl examined with 0.05 mol% of catalysts (Table 4). Sur-
chlorides. Additional ligand 4 was necessary for the prisingly, complex 2 did not work well for the reaction
completion of the reaction when complex 2 was used of 2-chloropyridine (entry 1) and the reaction was not
as catalyst (entry 1 vs. entry 2). To reduce the catalyst completed even if 1.0 mol% of complex 2 was used
loading, an extra ligand is essential for stabilizing the (entry 2). Since 3-chloropyridine reacted smoothly
palladium catalyst, although monoligated Pd(0) com- under the same conditions (entry 3), the coordination
plexes are the active species when electron-rich and of pyridyl group to the catalyst was not the reason for
bulky ligands are used.[8a] When [PdCl
ACHTUNGTRENNUNG
reaction became much slower than that catalyzed by strates (entries 4 and 5). In addition, PdCl
preformed complex 2 (entry 1 vs. entry 3). Various 4 did not work well (entry 6) while [PdCl
aryl chlorides containing electron-donating groups showed high activity (entry 7).
2A
AHCTUNGTRENNUNG
These results suggest that the difference between
the catalytic activities of complexes 1 and 2 was not
due to the difference in their palladium precursors,
but rather to the structures of ligands 3 and 4. In the
course of the coupling reaction of 2-chloropyridine,
Table 3. Suzuki–Miyaura reaction of aryl chlorides catalyzed
by Pd-BRIDP complexes.
Table 4. Suzuki–Miyaura reactions of chloropyridine.
Entry Ar3 Ar2 Pd mol% Time [h] Conv. [%][a,b]
1[c]
2
3
7a
7a
7a
7b
7c
7d
7e
7f
7g
7h
7j
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6b
6a
6a
6a
2
2
–
2
2
2
2
2
2
2
2
2
1
1
1
0.05
0.05
0.05
0.02
0.02
0.005
0.01
0.002
0.005
0.05
0.02
0.1
2
2
2
2
2
2
0.5
6
2.5
1
>99 (97)
93 (À)
[d]
18 (À)
Entry Ar4 Pd
Time [h] Conv. [%][a,b]
4[c]
5[c]
6[c]
7[c]
8[c]
9[c]
10[c]
11[c]
12[c]
13
>99 (97)
>99 (94)
>99 (95)
>99 (96)
>99 (92)
>99 (92)
>99 (97)
>99 (95)
93 (85)
1[c]
2[c,d]
3[c]
4
5
6
8a
8a
8b
8a
8b
8a
8a
2
2
2
1
1
2
2
3
2
1
2
4 (–)
64(–)
98 (–)
>99 (94)
99 (94)
2 (–)
1
PdCl2ACHTNUGTRENNUNG
[PdCl
(CH3CN)2/4[e]
(p-allyl)]2/3[f]
2
3
3
1
7
N
99 (–)
7b
7b
7f
7i
[a]
GC conversion of chloropyridine.
0.05
0.005
0.1
>99 (99)
>99 (93)
>99 (99)
[b]
[c]
[d]
Values in parentheses show the isolated yield.
cBRIDP (4) was added (1.0 equiv. vs. complex 2).
The reaction was carried out in the presence of 1.0 mol%
of complex 2.
14
15
4
[a]
GC conversion of aryl chloride.
Values in parentheses show the isolated yield.
cBRIDP (4) was added (1.0 equiv. vs. complex 2).
The reaction was carried out by use of 4 (0.1 mol%) and
[b]
[c]
[d]
[e]
[f]
The reaction was carried out with a THF solution of 4
(0.1 mol%) and PdCl
The reaction was carried out with a THF solution of 3
(0.1 mol%) and [PdCl(p-allyl)]2 (0.05 mol% Pd).
2ACHTUNGTREN(NUNG CH3CN)2 (0.05 mol% Pd).
[PdCl
N
ACHTUNGTRENNUNG
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Naota Yokoyama et al.
UPDATES
Scheme 2. The different behaviour of monodentate ligands and bidentate ligands for the reaction of 2-chloropyridine.
Table 5. Buchwald–Hartwig amination of aryl chloride.
there is the equilibrium of the 2-pyridylpalladium
chloride and m-pyridinatopalladium chloride dimer,
and it is known that the former complex is active for
the transmetalation, whereas the latter dimer is inac-
tive.[9] When the bidentate ligand was used for the re-
action, the equilibrium would shift to the inactive
dimer which was strongly stabilized by chelate effect
of the ligand.[9c] As a result, the rate of the reaction
would decrease with decreasing amount of the active
species in the reaction system (Scheme 2). The results
with complexes 1 and 2 for the coupling of 2-chloro-
pyridine suggest that 3 behaves as a monodentate
ligand [Figure 2 (a)], whereas 4 act as a hemilabile bi-
dentate ligand, respectively. From the X-ray crystallo-
graphic analysis [Scheme 1, Eq. (2)] and VT-NMR,[10]
we thought that the phenyl group of 4 located near
the palladium in complex 2 would coordinate to the
palladium reversibly [Figure 2 (b)].[11,12]
Entry Ar5 Amine Pd mol% Time [h] Conv. [%][a,b]
1
2
3
7b 9a
7b 9a
7b 9b
7b 9c
2
1
2
2
2
–
2
0.1
0.1
0.1
0.1
1.0
1.0
1.0
2
2
>99 (92)
2 (–)
>99 (95)
>99 (99)
53 (–)
0.5
0.25
2
0.25
0.25
4
5[c]
6
8a
8a
9c
9c
[d]
>99 (97)
96 (80)
7[c]
8b 9c
[a]
[b]
[c]
[d]
Other applications of these complexes were also in-
vestigated and we found that complex 2 was also ef-
fective for the Buchwald–Hartwig amination of aryl
chlorides (Table 5).[8] On the other hand, complex
1 did not work well because the dichloropalladium-
GC conversion of aryl chloride.
Values in parentheses show the isolated yield.
cBRIDP (4) was added (1.0 equiv. vs. complex 2).
The reaction was carried out with a THF solution of 3
(2.0 mol%) and [PdClACHTNUTRGNE(UNG p-allyl)]2 (1.0 mol% Pd).
phosphine complex would not be reduced to afford
an active species by sodium tert-butoxide efficiently
(entry 2). As a result, p-toluidine, morpholine and di-
phenylamine were converted to the corresponding N-
arylated compounds in the presence of complex 2
within a few hours (entries 1, 3 and 4). As mentioned
above, the Suzuki–Miyaura reaction of 2-chlroropyri-
dine was not completed even if 1.0 mol% of complex
2 was used. Therefore, the Buchwald–Hartwig amina-
tion between 2-chloropyridine and diphenylamine was
attempted in the presence of complex 2 (1.0 mol%),
but the reaction was not finished (entry 5). In con-
trast, the reaction was completed within 15 min with
the same catalytic amount of [PdCl
ACHTUNGTRENN(UNG p-allyl)]2/3
Figure 2. Plausible coordination of 3 and 4 to Pd(II).
(entry 6). In the case of 3-chloropyridine, complex 2
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Synthesis of Well-Defined Diphenylvinyl(cyclopropyl)phosphine-Palladium Complexes
128.8, 128.2, 127.8, 127.7, 126.8, 126.3, 124.1 (t, J=11.7 Hz),
smoothly catalyzed the coupling reaction (entry 7).
Because the regioisomers of coupling product were
not observed in the course of the reaction, pyridyne
was not generated under the reaction conditions.[13]
To the best of our knowledge, this is the first report
of the coupling reaction of 3-chloropyridine and dia-
rylamine.
33.3 (t, J=9.5 Hz), 31.1, 29.5, 27.4 (t, J=5.1 Hz), 26.9 (t, J=
6.3 Hz), 26.1, 25.1 (t, J=8.6 Hz); 31P NMR (121 MHz,
CD2Cl2): d=36.8.
Complex 2, PdClACTHNUGRTENNUG(p-allyl)AHCTUNGTRENN(UGN cbridp): An oven-dried, 500-
mL, four-necked, round-bottomed flask equipped with
a Teflonꢃ coated magnetic stirring bar, thermometer and
a gas inlet, was evacuated and backfilled with nitrogen. To
In conclusion, we have succeeded in the synthesis
and characterization of novel Pd-BRIDP complexes
that are highly stable and effective precatalysts for
the Suzuki–Miyaura reaction and Buchwald–Hartwig
amination of aryl halides. The reactivity for the cou-
pling of 2-chloropyridine revealed that ligands 3 and
4 had different coordination properties for the palla-
dium atom. The tert-butyl and cyclohexyl groups on
the phosphorus atom controlled whether or not the
rotation of dialkylphosphino-carbon bond could
occur, which determined both the conformation and
the coordination number of the ligand in the com-
plex.
the flask, [PdClACHTUNRGTNEUNG(p-allyl)]2 (7.4 g, 20.3 mmol, 1.0 equiv.) and
dehydrated THF (104 mL) were charged successively to give
a clear yellow solution. To the solution was added cBRIDP
(4, 15.0 g, 42.6 mmol, 2.1 equiv.) in one potion and a pale
yellow suspension was generated immediately. The suspen-
sion was stirred for 2 h at 308C and n-heptane (370 mL) was
added at the same temperature. The mixture was stirred for
2 h at 308C and filtered, and the wet powder was washed
with n-heptane (50 mLꢄ3) and dried under vacuum
(5 mmHg) for 8 h at 508C to give PdClACHTUNTRGENN(GU p-allyl)ACHTUNGTERN(NUGN cbridp) (2)
as a pale yellow powder; yield: 21.7 g (97%). 1H NMR
(300 MHz, CD2Cl2): d=7.78–6.96 (m, total 10H), 5.31–5.18
(m, 0.80H), 4.28–4.18 (m, 0.89H, major), 4.32–4.02 (br,
0.18H, minor), 4.02–3.90 (m, 1.12H), 3.42–3.30 (m, 1.20H),
2.96–2.84 (m, 0.9H), 2.63–2.57 (br, 0.17H), 1.62–1.30 (m,
23H), 1.08 (d, J=12.3 Hz, 0.88H); 13C NMR (75 MHz,
CDCl3): d=144.5, 142.1 (minor), 132.3, 129.9, 128.0, 127.4,
125.9, 125.4, 112.9 (minor), 80.0, 79.7, 60.1, 42.0 (d, J=
2.9 Hz), 39.5 (d, J=9.8 Hz), 36.8 (d, J=10.4 Hz), 32.0 (d, J=
5.8 Hz), 31.4 (d, J=6.3 Hz), 29.8, 29.2 (d, J=13.2 Hz,
minor), 25.2; 31P NMR (121 MHz, CD2Cl2): d=75.8 (minor),
74.3 (major); see the Supporting Information.
Experimental Section
General Experimental Methods
All reactions were conducted under a nitrogen atmosphere
unless otherwise noted. Cy-vBRIDP (3), cBRIDP (4),
vBRIDP and Cy-cBRIDP were synthesized according to the
previously reported procedure.[3] All of the reagents and de-
hydrated solvents were purchased and used as received.
NMR spectra were obtained on Varian Mercury plus 300
and Bruker BioSpin Avance III 500 systems. NMR chemical
shifts are reported in ppm relative to CHCl3 (7.26 ppm for
1H, and 77.0 ppm for 13C), CH2Cl2 (5.32 ppm for 1H, and
Typical Procedure for the Suzuki–Miyaura Reaction
Catalyzed by Pd-BRIDP Complex (Table 1, entry 1)
An oven-dried, 200-mL, four-necked, round-bottomed flask
equipped with a Teflonꢃ coated magnetic stirring bar, ther-
mometer, condenser and a gas inlet was evacuated and
backfilled with nitrogen. To the flask, 4-bromoanisole (5a)
(12.3 g, 65.6 mmol, 1.0 equiv.), dehydrated toluene (65 mL),
phenylboronic acid (6a) (10.0 g, 82.0 mmol, 1.25 equiv.), po-
tassium carbonate (13.5 g, 97.7 mmol, 1.5 equiv.) and com-
plex 1 (0.6 mg, 0.000656 mmol, 0.001 mol%) in dehydrated
THF (6.5 mL) were charged successively. The reaction mix-
ture was stirred at 1008C for 7 h and cooled to room tem-
perature. To the mixture was added drinking water (40 mL),
and the water phase was separated and extracted with tolu-
ene (40 mL) once. The organic layers were combined and
concentrated under reduced pressure. The residue was puri-
fied by silica gel column chromatography (eluent: toluene/n-
hexane=1/1) to give 4-methoxy-1,1’-biphenyl as a colorless
solid; yield: 13.3 g (95%); see the Supporting Infomation.
1
53.1 ppm for 13C), CH3OH (3.30 ppm for H, and 49.0 ppm
for 13C) or CF3C6H5 (À64.0 ppm for 19F). Mass spectra were
obtained on Shimadzu LCMS-IT-TOF.
Synthesis of Pd-BRIDP Complexes
Complex 1, PdCl2(cy-vbridp)2: An oven-dried, 500-mL,
four-necked, round-bottomed flask equipped with a Teflonꢃ
coated magnetic stirring bar, thermometer and a gas inlet,
was evacuated and backfilled with nitrogen. To the flask,
PdCl2ACHTUNGTRENNUNG(CH3CN)2 (7.0 g, 27.0 mmol, 1.0 equiv.), dehydrated
toluene (56 mL) and Cy-vBRIDP (3, 22.1 g, 57.5 mmol,
2.1 equiv.) were charged successively, and the orange solu-
tion was stirred for 3 h at 308C and yellow precipitate was
generated gradually. Subsequently, to the mixture was added
n-heptane (420 mL) at 308C and the mixture was cooled to
58C and stirred for 2 h at the same temperature. The result-
ing pale yellow suspension was filtered, and the wet powder
was washed with n-heptane (50 mLꢄ3) and dried under
vacuum (5 mmHg) for 8 h at 508C to give PdCl2(cy-vbridp)2
(1) as a yellow powder; yield: 25.4 g (98%). 1H NMR
(300 MHz, CD2Cl2): d=7.56–7.18 (m, 20H), 2.32–2.21 (m,
4H), 2.15 (t, J=6.3 Hz, 6H), 2.10–1.93 (m, 8H), 1.84–1.48
(m, 20H), 1.30–1.12 (m, 4H), 1.10–0.90 (m, 8H); 13C NMR
(75 MHz, CDCl3): d=151.7 (m), 144.9 (t, J=5.1 Hz), 141.9,
Typical Procedure of the Buchwald–Hartwig
Amination Catalyzed by Complex 2 (Table 5, entry 1)
An oven-dried, 200-mL, four-necked, round-bottomed flask
equipped with a Teflonꢃ coated magnetic stirring bar, ther-
mometer, condenser and a gas inlet was evacuated and
backfilled with nitrogen. To the flask, 4-chlorotoluene (8.2 g,
65.0 mmol, 1.0 equiv.), dehydrated toluene (65 mL), dehy-
drated THF (6.5 mL), sodium tert-butoxide (7.5 g,
78.0 mmol, 1.2 equiv.), p-toluidine (7.3 g, 68.3 mmol,
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Naota Yokoyama et al.
UPDATES
1.05 equiv.) and complex 2 (34.8 mg, 0.065 mmol, 0.1 mol%)
were charged successively. The reaction mixture was stirred
at 1008C for 2 h and cooled to room temperature. To the
mixture was added drinking water (40 mL), and the water
phase was separated and extracted with toluene (40 mL)
once. The organic layers were combined and concentrated
under reduced pressure. The residue was purified by silica
gel column chromatography (eluent: n-hexane/ethyl ace-
tate=1/1) to give di-p-tolylamine as colorless solid; yield:
11.8 g (92%); see the Supporting Infomation.
CCDC 933599 and CCDC 933600 contain the supplemen-
tary crystallographic data for complex 1 and complex 2.
These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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Acknowledgements
We thank Prof. Kazushi Mashima (Osaka University) and
Dr. Yusuke Kita (Osaka University) for the X-ray crystallo-
graphic analysis of complexes 1 and 2 and ligand 3. We also
thank Seika Abe (researcher of Takasago International Cor-
poration (TIC)) for performing variable-temperature NMR
spectroscopy for complex 2. Our sincere thanks are due to
Dr. Takeshi Nakai (Professors Emeritus at Tokyo Institute of
Technology) and Dr. Mitsuhiko Fujiwhara (executive director
of TIC) for useful discussion.
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