Synthesis of binuclear iridium(III) and rhodium(III) complexes bearing methylnaphthalene-linked N-heterocyclic carbenes, and application to intramolecular hydroamination

Article abstract of DOI:10.1016/j.jorganchem.2010.04.006

New methylnaphthalene-linked imidazolium salts 1 were synthesized through the reaction of 1,8-dibromomethylnaphthalene and N-alkylimidazole. On treatment of imidazolium salt 1 with silver oxide followed by [CpMCl₂] ₂ (M = Ir, Rh), binuclear iridium and rhodium complexes 2 were formed. Reaction of these complexes 2 with AgPF₆ afforded Cl-bridged cationic binuclear iridium and rhodium complexes 3. X-ray crystallographic analysis of 3 revealed that the two imidazole rings of the carbene ligand are in a parallel geometry. The cationic binuclear iridium complexes 3-Ir could be applied to the intramolecular hydroamination reaction of 2-ethynylaniline to give the corresponding indole compound.

Full text of DOI:10.1016/j.jorganchem.2010.04.006

Journal of Organometallic Chemistry 695 (2010) 1675e1681
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of binuclear iridium(III) and rhodium(III) complexes bearing
methylnaphthalene-linked N-heterocyclic carbenes, and application to
intramolecular hydroamination
Kenichi Ogata , Toshinori Nagaya, Shin-ichi Fukuzawa*
*
Department of Applied Chemistry, Institute of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 February 2010
Received in revised form
New methylnaphthalene-linked imidazolium salts 1 were synthesized through the reaction of 1,8-
dibromomethylnaphthalene and N-alkylimidazole. On treatment of imidazolium salt 1 with silver oxide
followed by [Cp*MCl
of these complexes 2 with AgPF
. X-ray crystallographic analysis of 3 revealed that the two imidazole rings of the carbene ligand are in
2
]
2
(M ¼ Ir, Rh), binuclear iridium and rhodium complexes 2 were formed. Reaction
5
April 2010
6
afforded Cl-bridged cationic binuclear iridium and rhodium complexes
Accepted 9 April 2010
Available online 21 April 2010
3
a parallel geometry. The cationic binuclear iridium complexes 3-Ir could be applied to the intramolecular
hydroamination reaction of 2-ethynylaniline to give the corresponding indole compound.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
N-heterocyclic carbene
Iridium complex
Rhodium complex
Binuclear complex
Intramolecular hydroamination
1. Introduction
metalemetal separation have been prepared using a bridging
diphosphine ligand [5]. However, synthesis of the corresponding
N-heterocyclic carbenes (NHCs) have emerged as an extremely
useful class of ligands for use in transition-metal complexes [1]. It is
well recognized that replacement of phosphines by NHCs can
provide complexes with enhanced stability and catalytic perfor-
mance due to the higher electron-donor ability. The majority of
NHC ligands used are monodentate, and much fewer complexes are
known that include bidentate bis-NHC ligands, in which a pair of
NHC groups is joined by an appropriate linker group. The use of
chelating bis-NHC and pincer NHC ligands has allowed for the
preparation of new complexes which show increased catalytic
activity [2] along with improved stability due to the entropic
advantages of chelation. In contrast to chelated NHC complexes, the
reactivity and catalytic application of binuclear bridging NHC
complex has scarcely been studied [3] even though several binu-
clear complexes with alkyl chain-linked NHC ligand have been
prepared [4]. In order to bring the metals together such that
cooperative interaction is possible, the bridging NHC complex
needs to have short metalemetal separation. In the case of phos-
phine ligands, various late-transition-metal complexes with short
bridging bis-NHC complexes such as halogen bridged complex has
not been developed in detail. On the basis of this concept, Cowie
et al. recently reported on rhodium complexes which were bridged
by a bis-NHC ligand and halogen using a bridging dppm ligand as
a second bridging group [4e].
In this report, we describe the synthesis of a new flexible bis-NHC
ligand linked by a methylnaphthalene unit, which is used to form
complexes with iridium and rhodium (Fig. 1). Because the methyl-
naphthalene-linked ligand is flexible due to rotation around the
methylene groups, it is possible to obtain a structural complex with
short metalemetal separation. To evaluate the properties of the ligand,
we selected a Cp* iridium(III) system as a metal-complex fragment
because stable complexes bearing a monodentate NHC ligand had
been reported in Ref. [6], and were found to be of application in
intramolecular hydroamination of 2-ethynylaniline derivatives.
2. Results and discussion
2.1. Synthesis of imidazolium salts and binuclear neutral
iridium(III) and rhodium(III) complexes
*
Corresponding author. Tel./fax: þ81 3 3817 1916.
The methylnaphthalene-linked imidazolium salts 1a and
1b were readily obtained as white powders by the reaction of
E-mail addresses: kogata@kc.chuo-u.ac.jp (K. Ogata), orgsynth@kc.chuo-u.ac.jp
(
S.-i. Fukuzawa).
0
022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.04.006

1676
K. Ogata et al. / Journal of Organometallic Chemistry 695 (2010) 1675e1681
R
N
RM
N
R
R
R
N
N
H
N
H
2Br-
Cl
N
M
M Cl
N
Cl
Cl
Rotation of
methylene chain
R
R
M
N
N
N
N
N
M
N
1. Ag2O
2. [Cp*MCl2]2
N
N
N
R
M
1
a (R = Me)
2a-Ir (R = Me, M = Ir), y. 50%
i
i
1
b (R = Pr)
2b-Ir (R = Pr, M = Ir), y. 75%
2
a-Rh (R = Me, M = Rh), y. 98%
Long metal-metal separation
Short metal-metal separation
Scheme 2. Synthesis of binuclear carbene complex 2
Fig. 1. Methylnaphthalene-linked bis-NHC ligand.
complex 3a (Scheme 3). The 13C{ H} NMR resonances for the
characteristic carbene carbons are observed at 156.9 ppm for 3a-Ir,
and 167.5 (JRhC ¼ 58.8 Hz) ppm for 3a-Rh, which are similar to those
reported for similar cationic iridium and rhodium carbene
complexes [6]. The complex 3b-Ir bearing an isopropyl group was
also prepared by a similar procedure. In contrast, the reaction of
1
ꢀ
1
(
,8-dibromomethylnaphthalene with N-alkylimidazole at 140 C
Scheme 1). In the 1H NMR spectra of 1a and 1b, the characteristic
imidazolium proton appeared at 9.98 ppm for 1a and 10.19 ppm for 1b.
For synthesis of the binuclear carbene complexes, trans-
metallation from the corresponding silver carbene complexes
generated in situ was carried out. Transmetallation has proved to be
promising procedure for obtaining N-heterocyclic carbene
complexes, typically involving treatment of an imidazolium salt
with silver oxide to form a silver N-heterocyclic carbene complex
7]. Treatment of imidazolium salt 1 with 1 equiv. of silver oxide
in dichloromethane afforded the
binuclear carbene complex 2-Ir as an orange solid (Scheme 2).
corresponding monodentate N-heterocyclic carbene complex
i
(
[Cp*IrCl
2
(I Pr)]) with AgPF
6
resulted in complex mixture.
a
Orange single crystals of complex 3a-Ir suitable for X-ray
diffraction were grown from dichloromethane and diethyl ether.
The ORTEP drawing of 3a-Ir is shown in Fig. 3. Selected bond
distances and angles are listed in Table 2. X-ray analysis of complex
[
followed by 1 equiv. of [Cp*IrCl
2 2
]
3a-Ir revealed the existence of a chloride-bridged binuclear skel-
eton with a pair of N-heterocyclic carbene ligands. The two imid-
azole rings of the N-heterocyclic carbene ligand are parallel to each
In the case of the rhodium complex, the analogous reaction with
[
Cp*RhCl
2
]
2
took place to give 2a-Rh as a red solid. In the case of the
with 2 equiv. of silver carbene generated by
other. The two Ir-C(carbene) bond distances of 3a-Ir (2.059(5) and
reaction of [Cp*IrCl
]
2 2
ꢀ
2
.069(5) A) are slightly longer than those for the neutral complex
in situ reaction of 1a and silver oxide, the binuclear complex 2a-Ir
was obtained in preference to the mononuclear chelating carbene
complex.
2b-Ir, and are in good agreement with the distances reported for
cationic iridium(III) N-heterocyclic carbene complexes [6]. The
ꢀ
The 1 C{ H} NMR spectra of 2a-Ir, 2a-Rh and 2b-Ir showed
3
1
IreIr separation of 3.7701(3) A corresponds to nonbonding.
Complex 3a-Ir reacted readily with trimethylphosphite to give
the phosphite complex 4a-Ir (Scheme 4). In contrast, triethylphos-
phine and triphenylphosphine did not react with complex 3a-Ir. The
signals characteristic of the carbene carbon at 157.3, 170.8
(J
RhC ¼ 58.8 Hz) and 157.7 ppm, respectively. These carbene signals
have the same chemical shifts as those for previously reported
neutral Cp* iridium(III) and rhodium(III) complexes bearing
a monodentate N-heterocyclic carbene ligand [6,8].
31
P NMR spectrum of 4a-Ir showed a singlet at 78.2 ppm and a septet
at ꢁ144.5 ppm, assignable to the trimethylphosphite ligand and PF
6
13
anion, respectively. In C NMR, a doublet assignable to the carbene
carbon was observed at 161.1 ppm with a coupling constant of
The structure of complex 2b-Ir was also confirmed by X-ray
analysis. The ORTEP drawing of 2b-Ir is shown in Fig. 2. Selected
bond distances and angles are listed in Table 1. The molecule has
a dimeric structure connected by the carbene ligand, and the Cp*
Ir moieties occupy each side of the naphthalene ring. The two
25.2 Hz consistent with coupling to the phosphorus atom of trime-
thylphosphite. This spectral data suggested a structure in which
phosphite was coordinated to the iridium metals, and indicated
a weak coordinate bond for the bridging chlorides in complex 3.
ꢀ
Ir-C(carbene) distances are 2.037(6) and 2.053(5) A, respectively.
These bond distances are the same as those previously reported
for a neutral Cp* iridium(III) complex bearing a monodentate
N-heterocyclic carbene ligand [6].
2.3. Application to intramolecular hydroamination
The transition-metal-catalyzed intramolecular hydroamination
of 2-ethynylaniline has received much attention as a simple
2.2. Synthesis of Cl-bridged binuclear iridium(III)
and rhodium(III) complexes
We next prepared Cl-bridged binuclear iridium and rhodium
complexes. The complex 2a reacted readily with 2 equiv. of AgPF
6
at
room temperature to afford the Cl-bridged cationic binuclear
R
N
R
H
N
H
2Br-
N
Br
Br
R
N
2eq.
N
N
1
40 C
°
1
a (R = Me), y. 95%
i
1
b (R = Pr), y. 82%
Fig. 2. ORTEP drawing of complex 2b-Ir with thermal ellipsoids drawn at the 50%
Scheme 1. Synthesis of imidazolium salt 1
2 2
probability level. Hydrogen atoms and CH Cl molecules are omitted for clarity.

K. Ogata et al. / Journal of Organometallic Chemistry 695 (2010) 1675e1681
1677
Table 1
Selected bond distances (A) and angles ( ) for [(Cp*IrCl
CH Cl (2b-Ir$5CH Cl
ꢀ
ꢀ
2 2 2 10 6 2
) (I PrCH C H CH
IiPr)]$
i
5
2
2
2
2
)
Ir(1)-Ir(2)
Ir(1)-Cl(2)
Ir(2)-Cl(3)
Ir(2)-C(21)
N(2)-C(1)
N(4)-C(21)
8.1178(2)
2.4055(15)
2.4265(11)
2.053(5)
1.370(7)
1.350(7)
Ir(1)-Cl(1)
Ir(1)-C(1)
Ir(2)-Cl(4)
N(1)-C(1)
N(3)-C(21)
2.4298(10)
2.037(6)
2.4520(12)
2.037(6)
1.361(5)
Ir(1)-C(1)-N(1)
Ir(2)-C(21)-N(3)
N(1)-C(1)-N(2)
129.0(4)
127.9(3)
103.5(5)
Ir(1)-C(1)-N(2)
Ir(2)-C(21)-N(4)
N(3)-C(21)-N(4)
126.9(3)
128.0(3)
104.0(4)
method for the synthesis of indole compounds. Many late-transi-
tion-metal complexes have been used in this reaction [9]. Crabtree
et al. recently reported that an iridium(III)-hydride complex effec-
tively catalyzed intramolecular hydroamination of 2-ethynylaniline
[9n]. However, intramolecular hydroamination using a cationic
iridium(III) catalyst has not been well examined with the exception
of this iridium-hydride system. In the following, we describe the
intramolecular hydroamination of 2-ethynylaniline using the
cationic Cl-bridged iridium (III) complex 3-Ir (Schemes 5 and 6).
First, catalysts and solvents were screened in the intramolecular
hydroamination reaction of 2-aminodiphenyl acetylene (5a), as
shown in Scheme 5 and Table 3. In the presence of the Cl-bridged
iridium complex 3a-Ir in acetonitrile, the intramolecular hydro-
amination reaction proceeded effectively under reflux conditions to
afford 6a in good yield (entry 1). While the use of 3b-Ir and
rhodium complex 3a-Rh resulted in slightly lower yields of 6a
Fig. 3. ORTEP drawing of complex 3a-Ir with thermal ellipsoids drawn at the 50%
probability level. Hydrogen atoms, PF6 anions and CH Cl molecules are omitted for
2
2
clarity.
(
entries 2 and 3), the neutral iridium complex 2a-Ir did not catalyze
3
. Conclusion
the reaction (entry 4). Other solvents such as propionitrile, 1,2-
dichloroethane, THF, 1,4-dioxane, DMF, PrOH were significantly
less effective (entries 5e10). The reaction using iridium complex
bearing monodentate N-heterocyclic carbene ligand ([Cp*Ir-
Cl
1
i
Novel binuclear iridium(III) and rhodium(III) complexes bearing
methylnaphthalene-linked N-heterocyclic carbenes were prepared.
The neutral bimetallic iridium and rhodium complexes could easily
be converted to cationic Cl-bridged complexes by reaction with 2
i
2
(I Pr)]) in the presence of AgPF
6
resulted in moderate yield (entry
1). Among the catalysts and solvents screened, the highest yield of
6
equiv. of AgPF , and the resulting iridium complex reacted with 2
the hydroamination product 6a was achieved using the Cl-bridged
cationic iridium complex 3a-Ir in acetonitrile.
equiv. of trimethylphosphite to yield the phosphite complex by
cleavage of the Ir-Cl coordinate bond. These results indicate the
flexible nature of the methylnaphthalene-linked N-heterocyclic
carbene ligand. The Cl-bridged cationic iridium(III) complex was
active for catalytic intramolecular hydroamination of 2-ethynyla-
nilines leading to indole compounds. Further investigation into the
reactivity of these complexes is underway in our laboratory.
On the basis of the screening results, the iridium complex 3a-Ir
was examined in the catalysis of intramolecular hydroamination of
various 2-ethynylanilines 5, as shown in Scheme 6 and Table 4. The
alkyl-substituted alkynes (5b, 5c and 5d) underwent reaction to the
corresponding products in good yields (entries 1e3). Similarly, the
use of o-, m-, and p-methyl-substituted aryl alkynes afforded the
corresponding products 5 in good yields (entries 4e6). However,
the reaction of p-methoxy-, trifluoromethyl-, and nitro-substituted
aryl alkynes led to lower yields (entries 7e9). Alkyne 5k, which
possesses a pyridyl group, did not undergo reaction (entry 10). In
contrast, replacement of the pyridyl group with a thiophenyl group
4. Experimental
4.1. General procedures
(
5l) resulted in the formation of the corresponding hydroamination
All manipulations involving air- and moisture-sensitive organ-
ometallic compounds were carried out under dry nitrogen or argon
product 6l in good yield (entry 11).
2
+
2
PF -
6
M Cl
Cl
N
M
Cl
Cl
Cl
R
R
M
M
N
N
2eq. AgPF6
Cl
N
N
R
N
R
N
CH Cl /acetone
2
2
r.t.
N
3
a-Ir (R = Me, M = Ir), y. 78%
2
a-Ir (R = Me, M = Ir)
i
i
3b-Ir (R = Pr, M = Ir), y. 76%
a-Rh (R = Me, M = Rh), y. 68%
2
b-Ir (R = Pr, M = Ir)
a-Rh (R = Me, M = Rh)
3
2
Scheme 3. Synthesis of Cl-bridged binuclear complex 3

1678
K. Ogata et al. / Journal of Organometallic Chemistry 695 (2010) 1675e1681
Table 2
Selected bond distances (A) and angles ( ) for [(Cp*IrCl)
PF $2CH Cl (3a-Ir$2CH Cl
ꢀ
ꢀ
2 2 10 6 2
(IMeCH C H CH IMe)]
(
6
)
2
2
2
2
2
)
5
mol% catalyst
Ir(1)-Ir(2)
3.7701(3)
2.4534(13)
2.4643(12)
2.069(5)
1.344(6)
1.356(6)
Ir(1)-Cl(1)
Ir(1)-C(1)
Ir(2)-Cl(2)
N(1)-C(1)
N(3)-C(19)
2.4497(12)
2.059(5)
2.4665(14)
1.366(6)
Ir(1)-Cl(2)
Ir(2)-Cl(1)
Ir(2)-C(19)
N(2)-C(1)
N(4)-C(19)
solvent, reflux, 24 h
N
H
NH2
6
a
1.358(6)
5a
Scheme 5. Intramolecular hydroamination of 5a
Ir(1)-C(1)-N(1)
Ir(2)-C(19)-N(3)
N(1)-C(1)-N(2)
130.0(3)
128.1(3)
104.0(4)
Ir(1)-C(1)-N(2)
Ir(2)-C(19)-N(4)
N(3)-C(19)-N(4)
126.0(3)
126.3(3)
104.3(4)
and dried in vacuo to yield 1b as a white solid (230 mg, 0.430 mmol,
1
i
8
4
2%). H NMR (400 MHz, CDCl
.81 (sep, J ¼ 6.4 Hz, Pr-CH), 6.51 (s, 4H, eCH2e), 7.2e8.1 (m, 10H,
3
):
d
1.65 (d, J ¼ 6.4 Hz, 12H, Pr-CH
3
),
i
atmosphere, which was purified by SICAPENT (Merck Co., Inc.), by
using a standard Schlenk tube or high vacuum techniques. Toluene,
hexane, diethyl ether and THF were distilled over Na/benzophe-
none prior to use. Dichloromethane was distilled over CaH
use. 1,8-Dibromomethylnaphthalene [10], [Cp*IrCl
[11], alkyne
a [12], 5b [13], 5c [14], 5d [13], 5e [15], 5f [16], 5g [17], 5h [14], 5i
18], 5j [19], 5k [20] and 5l [21] were prepared according to the
13
1
CH]CH, naphthalene), 10.19 (s, NCHN). C{ H} NMR (100 MHz,
i
i
CDCl
25.8, 128.7, 129.7, 129.8, 131.6, 135.6, 135.8 (s, CH]CH, naphtha-
lene, NCHN). Anal. Calc. for C24 : C, 53.95; H, 5.66; N, 10.49.
Found: C, 53.78; H, 5.75; N, 10.53%.
3 3
): d 22.9 (s, Pr-CH ), 53.4, 53.7 (s, Pr-CH, eCH2e), 120.2, 123.0,
1
2
prior to
2 4
H30Br N
2 2
]
5
[
literature methods. Other reagents employed in this research were
commercially available and used without further purification. The
4
4
.3. Preparation of iridium and Rhodium complexes
NMR spectra were recorded on JEOL Delta-400 or Varian Mercury
.3.1. Preparation of [(Cp*IrCl
The mixture of 1,1 -(1,8-dimethylnaphthalene)-3,3 -dime-
2
)
2
(IMeCH
2
C
10
H
6
CH
2
IMe)] (2a-Ir)
1
3
00 spectrometers at ambient temperature. H NMR spectra and
0
0
1
3
1
4
C{ H} NMR spectra were measured using Me Si as an internal
thyldiimidazolium dibromide (1a) (153 mg, 0.32 mmol), silver(I)
oxide (91 mg, 0.39 mmol) and CH Cl (5 mL) charged in Schlenk
tube under nitrogen and stirring for 2 h. The resulting mixture was
added to the CH Cl (259 mg,
solution (5 mL) of [Cp*IrCl
.33 mmol). After stirring for 2 h, the mixture was filtrated through
reference. All chemical shifts were recorded in ppm and all
coupling constants were recorded in Hz. Elementary analyses were
measured on a Perkin-Elmer 240C.
2
2
2
2
2 2
]
0
celite, and the volatiles were removed under reduced pressure. The
residual solid was washed with diethyl ether several times, and
4
.2. Preparation of imidazolium salts (1)
0
0
then dried in vacuo to give 2a-Ir as a orange solid (267 mg,
4
.2.1. Preparation of 1,1 -(1,8-dimethylnaphthalene)-3,3 -
1
0
4
.24 mmol, 73%). H NMR (400 MHz, CDCl
3
):
), 7.0e7.8 (m, CH]CH, naph-
): 9.20 (s, C Me ), 38.7 (s,
). 122e135 (s, CH]CH, naph-
thalene,), 157.3 (s, NCN). Anal. Calc. for C40H50Cl Ir N $0.5CH Cl : C,
5 5
d 1.61 (s, 30H, C Me ),
dimethyldiimidazolium dibromide [(IMeCH
1a)
The mixture of 1,8-dibromonaphthalene (250 mg, 0.80 mmol)
2 10 6 2 2
C H CH IMe)$(HBr) ]
.05 (s, 6H, NMe), 5.6 (br, 4H, NCH
thalene). C{ H} NMR (100 MHz, CDCl
NMe), 53.4 (s, NCH ), 89.0 (s, C Me
2
(
13
1
3
d
5
5
and N-methylimidazole (5mL) charged in Schlenk tube under
argon. After stirring for 1 h at 140 C, the supernatants were
2
5
5
ꢀ
4
2
4
2
2
42.90; H, 4.45; N, 4.85. Found: C, 42.33; H, 4.47; N, 4.94%.
removed. The residual solid was washed with toluene (3 ꢂ10 mL)
and dried in vacuo to yield 1a as a white solid (360 mg, 0.753 mmol,
1
4
.3.2. Preparation of [(Cp*RhCl
2
)
2
(IMeCH CH IMe)] (2a-Rh)
2
C
10
H
6
2
9
6
5%). H NMR (400 MHz, CDCl
3
):
d
3.70 (s, CH
3
), 6.47 (s, 4H, eCH2e),
0
Complex 2a-Rh was prepared from 1,1 -(1,8-dimethylnaph-
.89 (s, 2H, CH]CH), 7.06 (s, 2H, CH]CH), 7.1e8.0 (m, 6H, naph-
13
1
0
thalene)-3,3 -dimethyldiimidazolium dibromide (1a) (262 mg,
thalene), 9.98 (s, NCHN). C{ H} NMR (100 MHz, CDCl
2.7 (s, CH , eCH2e), 120.7, 122.8, 124.4, 126.0, 128.2, 129.0, 130.1,
31.1, 137.2 (s, CH]CH, naphthalene, NCHN). Anal. Calc. for
: C, 50.23; H, 4.64; N, 11.72. Found: C, 49.36; H, 4.70; N,
3
): d 36.2,
0
.55 mmol), silver(I) oxide (154 mg, 0.66 mmol), and [Cp*RhCl
340 mg, 0.55 mmol) in the same manner as that for 2a-Ir.
Complex 2a-Rh was isolated as a orange solid (505 mg, 0.54 mmol,
2 2
]
5
1
3
(
20 2 4
C H22Br N
1
3
1
9
8%). C{ H} NMR (125 MHz, CDCl
NMe), 55.6 (s, NCH
), 96.3 (d, J ¼ 6.0 Hz, C
CH, naphthalene), 170.8 (d, J ¼ 58.8 Hz, NCN). Anal. Calc. for
Rh $CH Cl : C, 48.31; H, 5.14; N, 5.50. Found: C, 48.31;
H, 5.37; N, 5.77%. In the H NMR, 2a-Rh showed broadened signals
3
):
d
9.49 (s, C
5 5
Me ), 39.1 (s,
11.60%.
2
5
Me ), 122e135 (s, CH]
5
0 0
.2.2. Preparation of 1,1 -(1,8-dimethylnaphthalene)-3,3 -
4
i
2 10 6 2 2
C H CH ]
IiPr)$(HBr)
C
40
H
50Cl
4
N
4
2
2
2
diisopropyldiimidazolium dibromide [(I PrCH
1b)
The mixture of 1,8-dibromonaphthalene (16 mg, 0.53 mmol)
1
(
ꢀ
ꢀ
1
in the temperature range from ꢁ60 C to 60 C. The satisfactory H
NMR data could not be observed.
and N-isopropylimidazole (5 mL) charged in Schlenk tube under
argon. After stirring for 1 h at 160 C, the supernatants were
removed. The residual solid was washed with toluene (3 ꢂ10 mL)
ꢀ
i
IiPr)] (2b-Ir)
O (118 mg,
4
.3.3. Preparation of [(Cp*IrCl
2
)
2
(I PrCH
2
C
10
H
6
CH
2
The mixture of 1b (253 mg, 0.47 mmol) and Ag
2
0.51 mmol) in CH
2
Cl
2
was stirred for 1 h at room temperature
2
+
2
+
2
PF6-
PF6-
2
Cl
Cl
N
Ir
Me Me
Ir
(MeO) P Ir
3
Ir P(OMe)3
R
2
eq.P(OMe)3
Cl
Cl
R
N
R
N
N
N
N
CH2Cl2
r.t.
N
N
5 mol% 3a-Ir
R
N
H
CH CN, reflux, 24 h
3
3
a-Ir
NH2
4
a-Ir y. 73%
6
5
Scheme 4. Reaction of Cl-bridged iridium(III) binuclear complex 3a-Ir with
trimethylphosphite
Scheme 6. Intramolecular hydroamination of 5

K. Ogata et al. / Journal of Organometallic Chemistry 695 (2010) 1675e1681
1679
3
1
1
Table 3
P{ H} NMR (CDCl
) ꢁ143.8 (sep, J ¼ 713 Hz, PF
$2CH Cl
33.81 H, 3.72; N, 3.35%.
). Anal. Calc. for
2
: C, 33.59; H, 3.62; N, 3.73. Found: C,
3
6
a
Screening of reaction conditions for intramolecular hydroamination of 5a.
C
40
H50Cl
2
F12Ir
2
N
4
P
2
2
Entry
Catalyst
Solvent
GC yield (%)
1
2
3
4
5
6
7
8
9
3a-Ir
3b-Ir
3a-Rh
2a-Ir
3a-Ir
3a-Ir
3a-Ir
3a-Ir
3a-Ir
3a-Ir
[Cp*IrCl
CH
CH
CH
CH
CH
CH
3
3
3
3
3
2
CN
CN
CN
CN
CH
73
55
52
5
62
32
15
19
38
33
52
4.3.5. Preparation of [(Cp*RhCl)
PF (3a-Rh)
Complex 3a-Rh was prepared from 3a (173 mg, 0.19 mmol), and
AgPF (94 mg, 0.37 mmol) in the same manner as that for 3a-Ir.
Complex 3a-Rh was isolated as a orange solid (154 mg, 0.13 mmol,
2 2 10 6 2
(IMeCH C H CH IMe)]-
(
6 2
)
2
CN
Cl
ClCH
2
6
THF
1
6
1,4-dioxane
DMF
68%). H NMR (400 MHz, acetone-d ):
NMe), 5.16 (d, J ¼ 14.6 Hz, 2H, NCH ), 6.28 (s, 2H, CH]CH), 7.05 (s,
2H, CH]CH), 7.01 (d, J ¼ 14.6 Hz, NCH ), 7.70 (t, J ¼ 7.6 Hz, 2H,
naphthalene), 7.92 (d, J ¼ 6.4 Hz, 2H, naphthalene), 8.28 (d, J ¼ 7.6 Hz,
d
1.78 (s, 30 H, Cp*), 3.88 (s, 6H,
i
2
1
1
0
1
PrOH
b
i
2
2
(I Pr)]/AgPF
6
3
CH CN
a
Reaction conditions: carbene complex (0.0125 mmol), alkyne (0.25 mmol),
13
1
2
H, naphthalene). C{ H} NMR (100 MHz, CDCl
39.3 (s, NMe), 55.6 (s, NCH
),100.3 (d, J ¼ 8.4 Hz, C
26.8, 128.8, 132.2, 133.9, 137.7, 137.9 (s, CH]CH, naphthalene,),167.5
3
):
d
9.91(s, C
5 5
Me ),
solvent (2 mL).
b
i
5
Me
5
).124.3,125.6,
[
Cp*IrCl
2 6
(I Pr)] (0.025 mmol), AgPF (0.025 mmol)
2
1
(
3
1
1
d, J ¼ 58.8 Hz, NCN). P{ H} NMR (CDCl
3
):
d
ꢁ143.8 (sep, J ¼ 713 Hz,
under argon atmosphere. The resulting solution was added to the
solution of [Cp*IrCl
(375 mg, 0.471 mmol) in CH Cl (5 mL). After
PF ). Anal. Calc. for C40H50Cl2F12N P Rh $2CH Cl : C, 38.12; H, 4.11;
6
4
2
2
2
2
2
]
2
2
2
N, 4.23. Found: C, 38.87 H, 4.16; N, 3.74%.
being stirred at room temperature for 4 h, the solution was filtered
and the filtrate was evaporated off under high vacuum. The residual
solid was washed with diethyl ether at several times, and dried in
i
i
4.3.6. Preparation of [(Cp*IrCl) (I PrCH C H CH I Pr)](PF )
(3b-Ir)
2
2
10
6
2
6 2
1
vacuo to give yellow solid of 2b-Ir (409 mg, 0.35 mmol, 75%). H
Complex 3b-Ir was prepared from 3a (160 mg, 0.14 mmol), and
AgPF6 (69 mg, 0.27 mmol) in the same manner as that for 3a-Ir.
Complex 3b-Ir was isolated as a orange solid (88 mg, 0.064 mmol,
NMR (400 MHz, CDCl
3
):
), 5.35 (sep, J ¼ 6.4 Hz, 2H, Pr-CH), 5.58 (d, J ¼ 17.4 Hz, 2H,
), 5.66 (d, J ¼ 17.4 Hz, 2H, CH ), 6.5e7.9 (m, 10H, C]C, naph-
d
1.59 (s, 30 H, Cp*), 1.59 (d, J ¼ 6.4 Hz, 12H,
i
i
Pr-CH
CH
thalene). C{ H} NMR (100 MHz, CDCl
Me ), 51.6 (s, NCH ), 89.0 (s, C Me
naphthalene,), 157.7 (s, NCN). Anal. Calc. for C44
C, 43.10; H, 4.82; N, 4.47. Found: C, 43.44; H, 4.96; N, 4.81%.
3
1
6
2
2
47%). H NMR (400 MHz, acetone-d ): d
1.5e2.0 (br, 30 H, Cp*), 1.62
13
1
i
i
i
3
):
). 122e135 (s, CH]CH,
Ir $CH Cl
d
8.23, 9.13, 13.9 (s, Pr,
(br-d, J ¼ 5.9 Hz, 12 H, Pr-CH ), 4.85 (br-s, 2H, Pr-CH), 6.27 (br, 4H,
3
13 1
C
5
5
2
5
5
NCH ), 7.4e8.2 (m, 10 H, CH]CH, naphthalene). C{ H} NMR
2
i
H58Cl
4
2
N
4
2
2
:
3 5 5 3 2
(100 MHz, CDCl ): d 9.63 (s, C Me ), 22.6 (s, Pr-CH ), 54.2 (s, NCH ),
92.2 (s, C Me ), 122.0, 123.8, 126.7, 129.6, 130.5, 131.2, 132.4, 136.2 (s,
CH]CH, naphthalene,). P{ H} NMR (CDCl
PF ). Correct elemental analysis data could not be obtained.
5
5
31
1
3
) ꢁ143.8 (sep, J ¼ 713 Hz,
4
(
.3.4. Preparation of [(Cp*IrCl)
PF (3a-Ir)
Mixture of complex 2a-Ir (267 mg, 0.24 mmol), AgPF
.48 mmol), CH Cl (5 mL), and acetone (5 mL) were stirred at
2
(IMeCH
2
C
10
H
6
CH
2
IMe)]-
6
6 2
)
6
(121 mg,
4.3.7. Preparation of [{Cp*IrCl(P(OMe) )} (IMeCH C H CH IMe)]
3
2
2
10
6
2
0
2
2
6 2
(PF ) (4-Ir)
room temperature. After being stirred for 2 h, the volatiles were
removed under reduced pressure. The residue was extracted with
2 2
Mixture of complex 3a-Ir (167 mg, 0.13 mmol), CH Cl (5 mL),
and trimethylphosphite (30 ml, 0.25 mmol) were stirred at room
CH
2
Cl
2
and the volatiles were removed under reduced pressure.
temperature. After being stirred for 3 h, the volatiles were removed
under reduced pressure. The residue was washed with diethylether,
and was recrystallized from acetone/hexane. The orange crystal of
The residual solid was washed with diethyl ether several times, and
then dried in vacuo to give 3a-Ir as a orange solid (197 mg,
.15 mmol, 63%). 1H NMR (400 MHz, acetone-d ):
6
d
1.77 (s, 30H,
), 6.28 (d,
J ¼ 2.3 Hz, 2H, CH]CH), 7.05 (d, J ¼ 2.3 Hz, 2H, CH]CH), 7.07 (d,
J ¼ 14.7 Hz, 2H, NCH ), 7.70 (dd, J ¼ 8.0, 5.9 Hz, 2H, naphthalene),
.89 (d, J ¼ 5.9 Hz, 2H, naphthalene), 8.27 (d, J ¼ 8.0 Hz, 2H, naph-
1
0
3a-Ir were obtained (79 mg, 0.092 mmol, 73%). H NMR (400 MHz,
6
Cp*), 3.88 (s, 6H, NMe), 5.12 (d, J ¼ 14.7 Hz, 2H, NCH
2
acetone-d ):
d
1.76 (s, 30H, Cp*), 3.72 (d, J ¼ 11.5 Hz, 18 H, P
(OCH ) ), 3.99 (s, 6H, NMe), 6.2e8.0 (m, 14H, NCH , CH]CH,
naphthalene). C{ H} NMR (100 MHz, acetone-d ):
3
3
2
1
3
1
6
2
d 9.36 (s,
7
C Me ), 40.0 (s, NMe), 54.6 (d, J ¼ 7.2 Hz, P(OCH ) ), 56.4 (s, NCH ),
5
5
3 3
2
13
1
thalene). C{ H} NMR (100 MHz, CDCl
NMe), 53.4 (s, NCH ), 93.3 (s, C Me
3
):
d
9.67 (s, C
5
Me
5
), 39.1 (s,
98.7 (d, J ¼ 3.5 Hz, C Me ). 126.0, 126.4, 126.9, 127.0, 130.2, 130.9,
5
5
2
5
5
). 124.0, 125.1, 126.9, 128.8,
135.7, 136.7 (s, CH]CH, naphthalene), 161.1 (d, J ¼ 25.2 Hz, NCN).
3
1
1
6
132.4, 134.1, 137.8, 138.0 (s, CH]CH, naphthalene), 156.9 (s, NCN).
P{ H} NMR (acetone-d ):
d
78.2(s, P(OCH ) ), ꢁ144.5 (sep,
3
3
J ¼ 713 Hz, PF
6
2 12 4 3 4 2 2 2
). Anal. Calc. for C46H68Cl F N O P Ir $CH Cl : C,
3
3.90; H, 4.24; N, 3.36. Found: C, 33.70 H, 4.35; N, 3.59%.
Table 4
Intramolecular hydroamination of 5 using iridium complex 3a-Ir
a
4.3.8. Preparation of [Cp*IrCl
2
(IiPr)]
The mixture of 1,3-diisopropylimidazolium chloride (150 mg,
.80 mmol), silver(I) oxide (111 mg, 0.48 mmol) and CH Cl (5 mL)
charged in Schlenk tube under nitrogen and stirring for 3 h. The
resulting mixture was added to the CH Cl solution (5 mL) of
Cp*IrCl
(317 mg, 0.40 mmol). Ater stirring for 15vh, the mixture
Entry
5
R
6
Isolated yield (%)
0
2
2
1
2
3
4
5
6
7
8
9
5b
5c
5d
5e
5f
5g
5h
5i
nC
6
H
13
6b
6c
6d
6e
6f
6g
6h
6i
80
75
69
78
70
68
37
24
15
0
Cyclopropyl
CH Ph
o-CH
m-CH
p-CH
p-CH
p-CF
p-NO
2-Pyridyl
2-Thiophenyl
2
2
2
[
2 2
]
3 6 4
C H
3
C
6
H
4
was filtrated through celite, and the volatiles were removed under
reduced pressure. The residual solid was purified by alumina
column chromatography using methanol, and then dried in vacuo to
3
C
6
H
4
3
OC
6
H
4
3 6 4
C H
i
1
give [Cp*IrCl
2
(I Pr)] as a yellow solid (99 mg, 0.18 mmol, 23%). H
5j
5k
5l
2
C
6
H
4
6j
6k
6l
i
10
1
NMR (300 MHz, CDCl
3
):
d
1.45 (t, J ¼ 6.9 Hz, 12H, Pr-CH
3
), 1.72 (s, 15
i
13
1
76
H, Cp*), 4.79 (sep, J ¼ 6.9 Hz, 2H, Pr-CH), 6.99 (s, 2H, CH]CH).
C
),
1
i
a
{ H} NMR (100 MHz, CDCl
):
d
9.43 (s, C
5 5 3
Me ), 24.0, 25.0 (s, Pr-CH
Reaction conditions: carbene complex (0.0125 mmol), alkyne (0.25 mmol),
CN (2 mL).
3
i
CH
3
52.1 (s, Pr-CH), 85.8 (s, C
5
Me
5
), 117.6 (s, CH]CH), 160.4 (s, NCN).

1680
K. Ogata et al. / Journal of Organometallic Chemistry 695 (2010) 1675e1681
4.4. General procedure for intramolecular hydroamination
CrystalStructure [30] crystallographic software package except for
of alkyne
refinement, which was performed using SHELXL-97 [27].
The mixture of iridium complex 3a-Ir (12 mg, 0.0092 mmol),
Acknowledgements
alkyne 5 (36 mg, 0.18 mmol) and acetonitrile (2 mL) charged in
Schlenk tube under nitrogen atmosphere. After stirring for 24 h in
reflux conditions, the solution filtered through a small amounts of
silica gel using ethyl acetate. The residue was purified by silica gel
preparative TLC (hexane/ethyl acetate ¼ 10:1). The solvent was
removed to give corresponding indole compound 6 as white solid.
The structures of 6a [22], 6b [23], 6c [21], 6d [24], 6e [25], 6f [22], 6g
This work is supported by a Joint Research Grant from the
Institute of Science and Engineering, Chuo University.
Appendix. Supplementary data
CCDC 760813 for 2b-Ir and 760814 for 3a-Ir contains the
supplementary crystallographic data for this paper. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223-
[25], 6h [22], 6i [23], 6j [19] and 6l [26] were referred to the
reported data.
4.5. X-ray Crystal structure determinations
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at:
doi:10.1016/j.jorganchem.2010.04.006.
Suitable single crystals were obtained by recrystallization from
CH Cl /diethyl ether. Crystal of 2b-Ir$5CH Cl and 3a-Ir$2CH Cl
2 2 2 2 2 2
were mounted at the top of nylon loop using liquid paraffin, which
was set on a Rigaku Saturn CCD/Rigaku AFC 8 diffractometer and
Rigaku RAXIS RAPID diffractometer, respectively. The measurement
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(
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Crystal data for [(Cp*IrCl
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2
(I PrCH
2
C
10
H
$2CH
6
CH
2
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[
(Cp*IrCl)
2
(IMeCH CH
2
C
10
H
6
2
IMe)](PF
6
)
2
2
2
2
2
)
7
Compound
2b-Ir$5CH
68Cl14Ir
1593.89
Yellow, prism
Cl
2 2
3a-Ir$2CH
2
Cl
2
(
1
Formula
Mol. Wt.
C
49
H
N
2 4
C
42
H
54
F
12
N
4
Cl Ir P
6 2 2
1502.00
Red, block
(
(
(
(
c) Y. Yamamoto, F. Miyauchi, Inorg. Chim. Acta. 334 (2002) 77;
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Crystal color, habit
Crystal size (mm)
Crystal system
Space group
0.44 ꢂ 0.38 ꢂ 0.35 0.50 ꢂ 0.40 ꢂ 0.30
Triclinic
Monoclinic
P2 /n (No 14)
e) K. Fujita, H. Nakaguma, T. Hamada, R. Yamaguchi, J. Am. Chem. Soc. 125
P ꢁı (No 2)
1
(2003) 12368.
ꢀ
a/A
11.160(3)
16.506(4)
18.146(5)
102.504(5)
100.806(2)
108.201(3)
2980.4(13)
2
12.0378(2)
28.0984(5)
15.8868(3)
90.0
105.2221(7)
90.0
5185.05(16)
4
1.924
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826;
ꢀ
b/A
ꢀ
c/A
ꢀ
ꢀ
a
/
(d) H. Aktas, J.C. Slootweg, A.W. Ehlers, M. Lutz, A.L. Spek, K. Lammertsma,
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/
ꢀ
g
/
ꢀ
V/A
(f) M. Viciano, M. Feliz, R. Corbern, J.A. Mata, E. Clot, E. Peris, Organometallics
Z
(g cmꢁ3
(Mo K
(Cu K
26 (2007) 5304.
D
m
m
c
)
1.776
51.367
[
7] (a) H.M.J. Wang, I.J.B. Lin, Organometallics 17 (1998) 972;
ꢁ
1
a
a
) (cm
)
e
(b) J.C. Garrison, W.J. Youngs, Chem. Rev. 105 (2005) 3978.
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e
137.018
95498
136.5
9493 (Rint ¼ 0.143)
[
[
8] X.-Q. Xiao, G.-X. Jin, J. Org. Chem. 693 (2008) 316.
Reflections measured
34383
60.2
17166
(
623
27.55
0.0539; 0.1439
0.0460
9] (a) For recent transition-metal-catalyzed intramolecular hydroamination, for
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ꢀ
2
q
( )
Independent reflections (Rint
)
R
int ¼ 0.038)
Number of variables
Reflection/parameter ratio
Residuals: R; Rw
Residuals: R
Number of reflections to calculated R
614
15.46
0.0425; 0.1096
0.0417
(
(
(
(
e) L.D. Field, B.A. Messerle, S.L. Wren, Organometallics 22 (2003) 4393;
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1
1
13738 (I >2.0
s
(I)) 9275 (I >2.0s(I))
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GOF indicator
1.081
1.109
Commun. 8 (2005) 65;

K. Ogata et al. / Journal of Organometallic Chemistry 695 (2010) 1675e1681
1681
(
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(
(
(
(
(
(
j) R.S. Robinson, M.C. Dovey, D. Gravestock, Eur. J. Org. Chem. (2005) 505;
k) K.C. Hultzsch, Adv. Synth. Catal. 347 (2005) 367;
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