A bis(phosphaethenyl)pyridine complex of iridium(I): Synthesis and catalytic application to N-alkylation of amines with alcohols

Article abstract of DOI:10.1021/om4000743

The iridium(I) complex [IrCl(BPEP-H)] (1), coordinated with 2,6-bis[2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine (BPEP-H) as a PNP-pincer-type phosphaalkene ligand, has been synthesized and fully characterized by elemental analysis, NMR spectroscopy, and X-ray diffraction analysis. Complex 1 (1 mol %) catalyzes N-alkylation of primary and secondary amines with alcohols, leading to the selective formation of secondary and tertiary amines, respectively. Primary amines are smoothly alkylated with a variety of benzylic and aliphatic alcohols (1 or 3 equiv) at 100 C under basic conditions (CsOH, 10 mol %) to give the corresponding secondary amines in good to high yields. On the other hand, N-alkylation of secondary amines with benzyl alcohol (3 equiv) proceeds in the presence of KH₂PO₄ (5 mol %) at 140 C to afford tertiary amines in high yields.

Full text of DOI:10.1021/om4000743

Article
pubs.acs.org/Organometallics
A Bis(phosphaethenyl)pyridine Complex of Iridium(I): Synthesis and
Catalytic Application to N‑Alkylation of Amines with Alcohols
Yung-Hung Chang,† Yumiko Nakajima,†,‡ and Fumiyuki Ozawa*,†
†International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto University, Uji, Kyoto
611-0011, Japan
‡JST-PRESTO, Uji, Kyoto 611-0011, Japan
S
* Supporting Information
ABSTRACT: The iridium(I) complex [IrCl(BPEP-H)] (1),
coordinated with 2,6-bis[2-(2,4,6-tri-tert-butylphenyl)-2-
phosphaethenyl]pyridine (BPEP-H) as a PNP-pincer-type
phosphaalkene ligand, has been synthesized and fully charac-
terized by elemental analysis, NMR spectroscopy, and X-ray
diffraction analysis. Complex 1 (1 mol %) catalyzes N-alkylation
of primary and secondary amines with alcohols, leading to the
selective formation of secondary and tertiary amines, respec-
tively. Primary amines are smoothly alkylated with a variety of
benzylic and aliphatic alcohols (1 or 3 equiv) at 100 °C under
basic conditions (CsOH, 10 mol %) to give the corresponding
secondary amines in good to high yields. On the other hand, N-
alkylation of secondary amines with benzyl alcohol (3 equiv) proceeds in the presence of KH2PO4 (5 mol %) at 140 °C to afford
tertiary amines in high yields.
analogues and proven to be a valuable structural scaffold for
developing functional transition-metal complexes.10 We have
considered that the meridional coordination of the pincer
ligands can be utilized as a useful structural motif also in
phosphaalkene chemistry. Thus, in this geometry, the two P
C bonds in BPEP-Y adopt a parallel orientation to the
coordination plane, suitable to undergo a dπ−pπ interaction
with central metals. We have confirmed the occurrence of such
orbital interactions in Fe(I) and Cu(I) complexes.7a−c
This paper reports the synthesis of [IrCl(BPEP-H)] (1) and
its catalytic application to N-alkylation of amines with alcohols.
This catalysis has attracted a great deal of attention in recent
years as an environmentally benign process of synthesizing
amines, which produces water as the sole byproduct.11 While
both heterogeneous and homogeneous catalysts have been
known to promote the reaction,11b ruthenium12−14 and
iridium15−19 complexes have constituted a vast majority of
the homogeneous catalysts because of their relatively high
catalytic performance with high product selectivity.11c We have
found that complex 1 exhibits catalytic activity comparable to
that of those complexes.
INTRODUCTION
■
There has been considerable interest in the coordination
chemistry of low-coordinate phosphorus compounds, owing to
their unique ligand properties.1,2 Phosphaalkenes having a P
C bond are among the central subjects in such chemistry.2,3
They possess an extremely low lying π* orbital around the
phosphorus atom and thus exhibit a marked tendency to
engage in effective π back-bonding with transition metals. We
have demonstrated with bidentate diphosphinidenecyclobutene
ligands (DPCB-Y) that this property is useful for catalysis,
leading to highly efficient organic transformations in con-
junction with group 8−10 metals.2c,d Representative examples
include hydroamination of 1,3-dienes (Pd),4 dehydrative
allylation with allylic alcohols (Pd),5 and Z-selective hydro-
silylation of alkynes (Ru).6
Our recent efforts have been devoted to the coordination
chemistry of PNP-pincer type phosphaalkene ligands (BPEP-
Y),7,8 in which two phosphaethenyl groups are connected to
the 2,6-positions of a pyridine ring (Chart 1).9 The PNP-pincer
ligands of this type have been extensively studied for phosphine
Chart 1. BPEP-Y Ligands
RESULTS AND DISCUSSION
■
Synthesis and Characterization of [IrCl(BPEP-H)] (1).
The reaction of BPEP-H with 1/2 mol of [Ir(μ-Cl)(coe)2]2 (coe
= cyclooctene) in CH2Cl2 afforded [IrCl(BPEP-H)] (1), which
Received: January 28, 2013
© XXXX American Chemical Society
A
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was isolated as a green crystalline solid in 61% yield and
characterized by elemental analysis, NMR spectroscopy, and X-
ray diffraction analysis (eq 1). Complex 1 is stable under a
nitrogen atmosphere and can be stored at ambient temperature
without decomposition.
Table 1. Effects of Bases on N-Alkylation of Aniline with
Benzyl Alcohol Catalyzed by 1
a
b
c
entry
base (amt, mol %)
conversn, %
yield, %
1
2
3
4
5
6
7
none
6
15
<1
<1
15
44
63
80
K2CO3 (30)
KOAc (30)
K3PO4 (30)
KO(t-Bu) (30)
KOH (30)
CsOH (10)
23
52
67
81
The NMR data observed in CD2Cl2 at room temperature
were consistent with a PNP-pincer-type square-planar structure
with C2v symmetry. The two phosphorus atoms were observed
equivalently at δ 249.1 in the 31P NMR spectrum; the chemical
100
94 (90)
a
Reactions were carried out at 100 °C for 24 h using PhNH2 (1
mmol), PhCH2OH (1 mmol), 1 (1 mol %), and base in toluene (0.3
b
1
mL). Conversion of PhCH2OH as confirmed by NMR spectroscopy
shift is in a typical range for phosphaalkene ligands. The H
c
using anisole as an internal standard. NMR yield of PhNHCH2Ph.
The value in parentheses is the isolated yield.
NMR spectrum exhibited two singlet signals assignable to ortho
and para t-Bu groups of BPEP-H at δ 1.71 (36 H) and 1.39 (18
H), respectively.
Figure 1 depicts the X-ray structure of 1, which adopts a
slightly distorted square planar geometry; the sum of the four
Scheme 1. Plausible Catalytic Cycle for N-Alkylation
Figure 1. Molecular structure of [IrCl(BPEP-H)](2Et2O) (1·2Et2O)
with thermal ellipsoids at the 50% probability level. Hydrogen atoms
and two Et2O molecules are omitted for clarity. Selected bond
distances (Å) and angles (deg): Ir−P1 = 2.2312(10), Ir−P2 =
2.2313(10), Ir−N = 2.046(4), Ir−Cl = 2.3134(11), P1−C1 =
1.651(4), P2−C2 = 1.668(4); N−Ir−P1 = 80.95(8), N−Ir−P2 =
80.83(8), P1−Ir−Cl = 98.99(4), P2−Ir−Cl = 99.45(4), P1−Ir−P2 =
161.41(4), N−Ir−Cl = 175.78(9).
bond angles around iridium is 360.22°. This structure is
superimposable on that of the rhodium analogue [RhCl(BPEP-
H)].7d The P−C bond lengths (1.651(4), 1.668(4) Å) are
comparable to those of BPEP-H complexes (1.66−1.67 Å)7d
but slightly shorter than those of BPEP-Ph complexes (1.68−
1.72 Å).7a−c The Ir−N and Ir−P distances are in the typical
range for PNP-pincer iridium(I) complexes (2.05−2.09 and
2.27−2.36 Å, respectively).20,21
N-Alkylation of Amines with Alcohols Catalyzed by 1.
The catalytic performance of 1 was examined in N-alkylation of
aniline with benzyl alcohol in the presence of a catalytic amount
of base (Table 1). This catalysis is considered to proceed via
the (benzyloxy)iridium intermediate A, which undergoes β-
hydrogen elimination to give the iridium hydride B and
PhCHO (step b in Scheme 1).11,15−19 Dehydrative con-
densation of PhCHO with aniline forms PhNCHPh (step c).
Insertion of PhNCHPh into the Ir−H bond of B (step d),
followed by alcoholysis of the resulting (amido)iridium species
C (step e), affords PhNHCH2Ph as the N-alkylation product
and reproduces the (benzyloxy)iridium intermediate A, which
further completes the catalytic cycle.
So far, iridium-catalyzed reactions of this sort have been
examined with Cp*IrIII complexes,15−17 taking advantage of the
findings of Fujita and Yamaguchi.15a On the other hand,
iridium(I) complexes that are catalytically active for N-
alkylation of amines with alcohols have been limited.18,19
This is probably because transition-metal complexes with an
electron-deficient metal center, which is often in a high
oxidation state, are advantageous in nature to the catalysis. For
example, complexes in a high oxidation state should be
favorable for step b in Scheme 1, involving oxidation of
alcohols to aldehydes. Moreover, step e, which affords N-
alkylation products, very probably proceeds via the coordina-
tion of alcohols, which enhances the acidity of alcohols, thereby
facilitating the alcoholysis of Ir−N bonds. In this case, an
electron-deficient metal center with enhanced Lewis acidity
exhibits high reactivity. We have considered that the unique
ligand property of BPEP-H with strong π-accepting ability
B
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Article
possibly forms a highly electron-deficient Ir(I) complex,
sufficiently reactive to a variety of amines and alcohols.
The reaction of aniline and benzyl alcohol was performed at
100 °C for 24 h in toluene using each 1 mmol of substrates and
1 mol % of 1. As seen from Table 1, the catalytic reaction did
not proceed well in the absence of a base or in the presence of
weak bases (entries 1−4). This is probably because the
formation of PhCH2O− ion is essential for the displacement of
the Cl ligand in 1 to form the (benzyloxy)iridium species A as a
key intermediate (step a). Thus, the catalytic reaction
successfully proceeded in the presence of strong bases, and
N-benzylaniline was obtained in 94% yield in the presence of a
catalytic amount of CsOH (10 mol %) (entries 5−7), where no
formation of PhN(CH2Ph)2 as a dialkylation product was
detected.
Table 3. N-Alkylation of Primary Amines with Benzyl
Alcohol Catalyzed by 1
a
c
yield, %
b
entry
RNH2
conversn, %
RNHCH2Ph RNCHPh
1
2
3
4-MeOC6H4NH2
4-MeC6H4NH2
4-ClC6H4NH2
4-NCC6H4NH2
4-NCC6H4NH2
2-aminopyridine
3-aminopyridine
4-aminopyridine
PhCH2NH2
95
96
84 (83)
86 (83)
100 (97)
72 (69)
69
0
0
100
91
0
d
4
0
e
5
78
0
6
7
8
89
80 (76)
87 (85)
94 (90)
92 (84)
76 (70)
45
0
87
0
Under similar reaction conditions, several kinds of alcohols
successfully reacted with aniline (Table 2). Benzyl alcohols with
94
0
f
9
0
f
10
PhCH2CH2NH2
n-C6H13NH2
23
39
30
f
11
Table 2. N-Alkylation of Aniline with Alcohols Catalyzed by
a
f
12
cyclo-C6H13NH2
60
1
a
Reactions were carried out at 100 °C for 24 h using RNH2 (1 mmol),
PhCH2OH (1 mmol), 1 (1 mol %), and CsOH (10 mol %) in toluene
b
(0.3 mL), unless otherwise noted. Conversion of PhCH2OH as
confirmed by NMR spectroscopy using anisole as an internal standard.
c
c
NMR yield of RNHCH2Ph. The values in parentheses are isolated
yield, %
d
yields. The reaction was accompanied by production of p-
b
entry
RCH2OH
conversn, %
PhNHCH2R PhNCHR
e
H2NCOC6H4NHCH2Ph (18%). Molecular sieves 4 Å was added.
f
1
2
3
4-MeOC6H4CH2OH
4-MeC6H4CH2OH
4-ClC6H4CH2OH
4-CF3C6H4CH2OH
(2-pyridyl)CH2OH
(2-furyl)CH2OH
99
97
91
89
90
89
80
80
95 (93)
95 (91)
91 (86)
81 (73)
90 (84)
80 (76)
60 (52)
77 (75)
0
0
The reaction was carried out using excess PhCH2OH (3 mmol)
without solvent.
0
d
4
0
equiv); otherwise, the formation of imines predominated
(entries 9−12). As another attempt, the reaction of 1-
phenethylamine with benzyl alcohol was examined. However,
the catalytic reaction was significantly slow even at 140 °C, and
the desired product (PhCH(Me)NHCH2Ph) was formed in
low yield (38%).
Complex 1 also exhibited the catalytic activity for N-
alkylation of secondary amines with benzyl alcohol. Unlike the
reactions of primary amines, so far only a few examples have
been documented for catalytic N-alkylation of secondary
amines with alcohols.12c,13b,15b Table 4 summarizes the results.
The reactions required a temperature of 140 °C, higher than
that used for primary amines. As previously reported for related
iridium(III)-catalyzed reactions,15b the N-alkylation of dibenzyl-
amine was retarded by a simple base such as K2CO3 (entries 1
and 2) but successfully proceeded in the presence of bases with
d
5
0
6
0
d
7
(2-thienyl)CH2OH
Me(CH2)6CH2OH
18
0
8
a
Reactions were carried out at 100 °C for 24 h using PhNH2 (1
mmol), RCH2OH (1 mmol), 1 (1 mol %), and CsOH (10 mol %) in
toluene (0.3 mL), unless otherwise noted. Conversion of RCH2OH
as confirmed by NMR spectroscopy using anisole as an internal
standard. NMR yield of PhNHCH2R. The values in parentheses are
b
c
d
isolated yields. The reaction was carried out for 48 h.
electron-donating as well as electron-withdrawing substituents
at the para position formed N-benzylaniline derivatives in high
yields, though the reactivity somewhat decreased with the
increasing electron-withdrawing ability of the substituents
(entries 1−4). 2-Pyridinemethanol and 2-furanmethanol also
reacted with aniline to afford the desired products in 90 and
80% yields, respectively (entries 5 and 6). On the other hand,
the reaction with 2-thiophenemethanol formed PhNCH(2-
thenyl) (18%) in addition to PhNHCH2(2-thenyl) (60%)
(entry 7). The present catalytic system was applicable to 1-
octanol as an aliphatic alcohol, giving N-octylaniline in 77%
yield (entry 8).
Table 3 summarizes the results of catalytic N-alkylation of
several kinds of amines with benzyl alcohol. Anilines with p-
MeO, p-Me, and p-Cl substituents were N-alkylated in high
yields (entries 1−3). 4-Aminobenzonitrile was also N-alkylated,
but a part of the product was hydrated to 4-(benzylamino)-
benzamide (entry 4). This side reaction was prevented by
addition of molecular sieves to the system (entry 5). Three
isomers of aminopyridine reacted with benzyl alcohol in high
yields (entries 6−8). Alkylamines were also converted to N-
benzylamines in good yields, by using excess benzyl alcohol (3
Table 4. N-Alkylation of Secondary Amines with Benzyl
a
Alcohol Catalyzed by 1
b
entry
RR′NH
base
none
yield of RR′NCH2Ph, %
1
2
3
4
5
6
(PhCH2)2NH
(PhCH2)2NH
(PhCH2)2NH
(PhCH2)2NH
(PhCH2)(Me)NH
morpholine
68
12
K2CO3
NaHCO3
KH2PO4
KH2PO4
KH2PO4
63
83
100
78
a
Reactions were carried out at 140 °C for 24 h using RR′NH (1
mmol), PhCH2OH (3 mmol), 1 (1 mol %), and base (5 mol %),
without solvent. NMR yield of RR′NCH2Ph.
b
C
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p-t-Bu). 13C{1H} NMR (CD2Cl2, 25 °C): δ 174.2 (s, 2,6-Py), 157.3 (s,
o-PAr), 154.0 (s, p-PAr), 143.2 (t, JPC = 27 Hz, PC), 135.8 (s, 4-Py),
127.2 (m, ipso-PAr), 123.5 (s, m-PAr), 108.4 (t, JPC = 16 Hz, 3,5-Py),
39.5 (s, o-C(CH3)3), 36.0 (s, p-C(CH3)3), 34.4 (s, o-C(CH3)3), 31.6
(s, p-C(CH3)3). 31P{1H} NMR (CD2Cl2, 25 °C): δ 249.1 (s). Anal.
Calcd for C43H63ClIrNP2: C, 58.31; H, 7.40; N, 1.59. Found: C, 58.45;
H, 7.19; N, 1.59.
X-ray Crystal Structure Determination of 1. The intensity data
were collected on a Rigaku Mercury CCD diffractometer with
monochromated Mo Kα radiation (λ = 0.71070 Å). The data set
was corrected for Lorentz and polarization effects and absorption. The
structure was solved by Patterson methods (DIRDIF-2008)23 and
refined by least-squares calculations on F2 for all reflections (SHELXL-
97)24 using Yadokari-XG 2009.25 Two Et2O molecules were
incorporated in the unit cell. Anisotropic refinement was applied to
all non-hydrogen atoms, except for disordered groups. Hydrogen
atoms were placed at calculated positions. The crystallographic data
and the summary of solution and refinement are reported as
Supporting Information.
Catalytic Reactions. A typical procedure (entry 7 in Table 1) is as
follows. Benzyl alcohol (103 μL, 1.0 mmol), aniline (91 μL, 1.0
mmol), and toluene (0.3 mL) were added to a Schlenk tube containing
1 (8.8 mg, 0.010 mmol) and CsOH (15 mg, 0.10 mmol). The solution
was degassed by freeze−pump−thaw cycles, the tube was filled with
dry nitrogen gas, and the contents were stirred at 100 °C for 24 h. The
solution was diluted with CDCl3 (0.5 mL) at room temperature, and
anisole (108 μL, 1.0 mmol) was added as an internal standard. The
NMR analysis of the resulting solution revealed the formation of N-
benzylaniline (0.94 mmol, 94%). The solution was concentrated to
dryness under vacuum, and the residue was subjected to column
chromatography (SiO2, ethyl acetate/hexane 1/10) to afford N-
benzylaniline (164.7 mg, 0.90 mmol, 90%).
a proton source (entries 3 and 4). In the present catalytic
system using 1, KH2PO4 was particularly effective for the
conversion of dibenzylamine into tribenzylamine (entry 4).
Similarly, benzylmethylamine and morpholine were N-alkylated
with benzyl alcohol in high yields (entries 5 and 6). As has been
discussed by Fujita and Yamaguchi,15b it is reasonable that the
proton facilitates dehydrative condensation of PhCHO with
secondary amines (corresponding to step c in Scheme 1).
Unlike the hemiaminals (PhCH(OH)NHR) formed from
primary amines, those derived from secondary amines (i.e.,
PhCH(OH)NRR′) are poorly reactive toward dehydration
under basic conditions, due to the lack of a proton on the
nitrogen atom, but converted to iminium ions ([PhC
NRR′]+) via protonation.
CONCLUSION
■
We have synthesized the iridium(I) complex 1 bearing a PNP-
pincer-type phosphaalkene ligand (BPEP-H), which exhibits
high catalytic activity toward N-alkylation of primary and
secondary amines with alcohols, leading to the selective
formation of secondary and tertiary amines, respectively. In
addition to iridium(III) complexes,15−17 Kempe and co-
workers have recently developed novel iridium(I) complexes
coordinated with PN chelate ligands, which are inactive to
aliphatic amines but exhibit extremely high catalytic perform-
ance in N-alkylation of aromatic primary amines, in conjunction
with a stoichiometric amount of t-BuOK.18 On the other hand,
while the catalytic activity is lower than that of Kempe’s
catalysts, complex 1 has proven to be reactive to a variety of
amine substrates, including aromatic and aliphatic primary
amines as well as secondary amines in the presence of a
catalytic amount of a base. It is reasonable that the strong π-
accepting ability of BPEP-H, which provides a highly electron-
deficient Ir(I) center, is responsible for this high catalytic
performance.
The catalytic reactions given in Tables 1−4 were similarly
conducted. The resulting amines were identified by comparison of
1
the H and 13C{1H} NMR data with those previously reported.
N-Benzylaniline.18a 1H NMR (CDCl3): δ 7.37−7.30 (m, 4H),
7.28−7.26 (m, 1H), 7.16 (t, J = 8.1 Hz, 2H), 6.73 (t, J = 7.3 Hz, 1H),
6.65 (d, J = 7.6 Hz, 2H), 4.32 (s, 2H). 13C{1H} NMR (CDCl3): δ
147.6, 139.0, 129.3, 128.6, 127.6, 127.3, 118.0, 113.3, 48.6.
N-(4-Methoxybenzyl)aniline.26 1H NMR (CDCl3): δ 7.28 (d, J =
8.6 Hz, 2H), 7.16 (dd, J = 8.5 and 7.5 Hz, 2H), 6.86 (d, J = 8.6 Hz,
2H), 6.71 (t, J = 7.5 Hz, 1H), 6.64 (d, J = 8.5 Hz, 2H), 4.24 (s, 2H),
3.79 (s, 3H). 13C{1H} NMR (CDCl3): δ 158.9, 147.9, 131.2, 129.2,
128.9, 117.8, 114.0, 113.1, 55.3, 47.9.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were carried under a
nitrogen atmosphere using Schlenk techniques. Nitrogen gas was
passed through a P2O5 column (Merck, SICAPENT). Toluene
(Kanto, dehydrated) and CH2Cl2 and Et2O (Wako, dehydrated)
were used as received. Benzene was dried over sodium benzophenone
ketyl and distilled. CsOH was dried overnight under vacuum prior to
use. Alcohols and amines were purchased from commercial sources
and used without purification. [Ir(μ-Cl)(coe)2]222 and BPEP-H8 were
prepared according to literature procedures. NMR spectra were
recorded on a Bruker AVANCE 400 spectrometer (1H NMR, 400.13
MHz; 13C NMR, 100.62 MHz; 31P NMR, 161.98 MHz). Chemical
N-(4-Methylbenzyl)aniline.27 1H NMR (CDCl3): δ 7.24 (d, J = 7.8
Hz, 2H), 7.16 (dd, J = 8.5 and 7.4 Hz, 2H), 7.12 (d, J = 7.8 Hz, 2H),
6.75 (t, J = 7.3 Hz, 1H), 6.68 (d, J = 7.8 Hz, 2H), 4.27 (s, 2H), 2.31 (s,
3H). 13C{1H} NMR (CDCl3): δ 148.0, 136.9, 136.2, 129.3, 129.2,
127.5, 117.6, 113.0, 48.2, 21.1.
N-(4-Chlorobenzyl)aniline.28 1H NMR (CDCl3): δ 7.29 (s, 4H),
7.16 (t, J = 7.5 Hz, 2H), 6.72 (t, J = 7.3 Hz, 1H), 6.61 (d, J = 7.7 Hz,
2H), 4.30 (s, 2H). 13C{1H} NMR (CDCl3): δ 147.5, 137.8, 132.9,
129.3, 128.8, 128.7, 118.1, 113.1, 47.8.
shifts are recorded in δ (ppm), referenced to H (residual) and 13C
1
N-(4-(Trifluoromethyl)benzyl)aniline.29 1H NMR (CDCl3): δ 7.56
(d, J = 8.1 Hz, 2H), 7.47 (d, J = 8.1 Hz, 2H), 7.17 (dd, J = 8.1 and 7.4
Hz, 2H), 6.77 (t, J = 7.4 Hz, 1H), 6.65 (d, J = 8.1 Hz, 2H), 4.40 (s,
2H). 13C{1H} NMR (CDCl3): δ 147.5, 143.6, 129.6, 129.3, 127.5,
125.5 (q, JCF = 3.7 Hz), 122.8, 118.1, 113.0, 47.9.
signals of deuterated solvents as internal standards or to the 31P signal
of 85% H3PO4 as an external standard. Elemental analysis was
performed by ICR Analytical Laboratory, Kyoto University.
Synthesis of [IrCl(BPEP-H)] (1). To a CH2Cl2 (4 mL) solution of
BPEP-H (0.205 g, 0.31 mmol), was added a CH2Cl2 solution (4 mL)
of [Ir(μ-Cl)(coe)2]2 (0.140 g, 0.16 mmol) at −78 °C. The cold bath
was removed, and the reaction mixture was warmed to room
temperature. The mixture was stirred for an additional 30 min, and
volatile materials were removed under vacuum. The residue was
washed with benzene (ca. 1 mL) and dried under vacuum to give
analytically pure 1 as an olive solid (0.17 g, 0.19 mmol, 61%), which
was dissolved in Et2O, and allowed to stand at −35 °C overnight to
give single crystals, suitable for an X-ray diffraction study.
N-(Pyridin-2-ylmethyl)aniline.30 1H NMR (CDCl3): δ 8.58 (d, J =
4.7 Hz, 1H), 7.69 (td, J = 7.7 and 1.8 Hz, 1H), 7.38 (d, J = 7.8 Hz,
1H), 7.22−7.20 (m, 1H), 7.16 (dd, J = 8.5 and 7.4 Hz, 2H), 6.70 (t, J
= 7.4 Hz, 1H), 6.65 (d, J = 8.5 Hz, 2H), 4.50 (s, 2H). 13C{1H} NMR
(CDCl3): δ 158.5, 149.1, 147.8, 136.6, 129.2, 122.0, 121.6, 117.5,
113.0, 49.2.
N-(Furan-2-ylmethyl)aniline.26 1H NMR (CDCl3): δ 7.36−7.34
(m, 1H), 7.17 (dd, J = 8.5 and 7.4 Hz, 2H), 6.72 (t, J = 7.4 Hz, 1H),
6.66 (d, J = 8.5 Hz, 2H), 6.31−6.29 (m, 1H), 6.22−6.19 (m, 1H), 4.30
(s, 2H), 4.00 (br, 1H). 13C{1H} NMR (CDCl3): δ 152.7, 147.5, 141.9,
129.2, 118.1, 113.2, 110.3, 107.0, 41.5.
1H NMR (CD2Cl2, 25 °C): δ 8.42 (t, JPH = 4.4 Hz, 2H, PCH),
7.72 (m, 1H, 4-Py), 7.63 (t, JPH = 2.0 Hz, 4H, Mes*), 6.97 (dt, 3JHH
=
7.6 Hz, JPH = 2.8 Hz, 2H, 3,5-Py), 1.71 (s, 36H, o-t-Bu), 1.39 (s, 18H,
D
dx.doi.org/10.1021/om4000743 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
N-(Thiophen-2-ylmethyl)aniline.31 1H NMR (CDCl3): δ 7.21−
7.16 (m, 3H), 7.01−6.98 (m, 1H), 6.95−6.93 (m, 1H), 6.73 (t, J = 7.4
Hz, 1H), 6.66 (d, J = 7.8 Hz, 2H), 4.50 (s, 2H), 4.03 (br, 1H).
13C{1H} NMR (CDCl3): δ 147.6, 142.9, 129.3, 126.8, 125.0, 124.6,
118.1, 113.1, 43.5.
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N-Benzylpyridin-2-amine.18c 1H NMR (CDCl3): δ 8.09−8.06 (m,
1H), 7.42−7.25 (m, 6H), 6.58 (dd, J = 7.0 and 5.2 Hz, 1H), 6.37 (d, J
= 8.4 Hz, 1H), 5.00 (br, 1H), 4.49 (d, J = 5.8 Hz, 2H). 13C{1H} NMR
(CDCl3): δ 158.6, 148.0, 139.1, 137.5, 128.6, 127.4, 127.2, 113.1,
106.8, 46.3.
N-Benzylpyridin-3-amine.35 1H NMR (CDCl3): δ 8.15 (br, 1H),
7.93 (d, J = 4.3 Hz, 1H), 7.34−7.26 (m, 5H), 7.11 (dd, J = 8.3 and 4.8
Hz, 1H), 6.92 (dd, J = 8.4 and 1.7 Hz, 1H), 4.55 (br, 1H), 4.35 (d, J =
4.2 Hz, 2H). 13C{1H} NMR (CDCl3): δ 144.1, 138.6, 138.4, 135.9,
128.7, 127.5, 127.4, 123.7, 118.7, 47.8.
N-Benzylpyridin-4-amine.36 1H NMR (CDCl3): δ 8.10 (d, J = 6.3
Hz, 2H), 7.35−7.25 (m, 5H), 6.48 (d, J = 6.3 Hz, 2H), 5.24 (br, 1H),
4.35 (d, J = 5.6 Hz, 2H). 13C{1H} NMR (CDCl3): δ 153.7, 148.8,
137.7, 128.8, 127.6, 127.2, 107.7, 46.8.
Dibenzylamine.37 1H NMR (CDCl3): δ 7.35−7.30 (m, 8H), 7.27−
7.22 (m, 2H), 3.80 (s, 4H). 13C{1H} NMR (CDCl3): δ 140.3, 128.4,
128.1, 126.9, 53.2.
N-Benzyl-2-phenylethanamine.38 1H NMR (CDCl3): δ 7.31−7.25
(m, 7H), 7.21−7.18 (m, 3H), 3.79 (s, 2H), 2.91−2.88 (m, 2H), 2.83−
2.79 (m, 2H). 13C{1H} NMR (CDCl3): δ 140.3, 140.0, 128.7, 128.4,
128.3, 128.1, 126.9, 126.1, 53.9, 50.5, 36.4.
ASSOCIATED CONTENT
■
S
* Supporting Information
A CIF file giving crystallographic data for 1. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
(11) (a) Hamid, M. H. S. A.; Slatford, P. A.; Williams, J. M. J. Adv.
Synth. Catal. 2007, 349, 1555. (b) Guillena, G.; Ramon
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Corresponding Author
*E-mail for F.O.: ozawa@scl.kyoto-u.ac.jp.
́
, D. J.; Yus, M.
̈
Notes
The authors declare no competing financial interest.
M. Chem. Asian J. 2007, 2, 403. (b) Bahn, S.; Tillack, A.; Imm, S.;
Mevius, K.; Michalik, D.; Hollmann, D.; Neubert, L.; Beller, M.
ChemSusChem 2009, 2, 551. (c) Tillack, A.; Hollmann, D.; Mevius, K.;
̈
ACKNOWLEDGMENTS
■
This work was supported by a MEXT Grant-in-Aid for
Scientific Research on Innovative Areas “Stimuli-responsive
Chemical Species” (No. 24109010) and a JSPS Grant-in-Aid
for JSPS Fellows (No. 24·3950). This work was partially
supported by MEXT program “Elements Strategy Initiative to
Form Core Research Center”.
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