Iridium(I) complex of chelating pyridine-2-thiolate ligand: Synthesis, reactivity, and application to the catalytic E-selective terminal alkyne dimerization via C-H activation

Article abstract of DOI:10.1016/j.jorganchem.2007.06.030

A novel iridium(I) complex bearing a chelate-coordinated pyridine-2-thiolate ligand [Ir(η²-SNC₅H₄)(PPh₃)₂] (2) was prepared by the reaction of iridium ethylene complex [IrCl(C₂H₄

Full text of DOI:10.1016/j.jorganchem.2007.06.030

Journal of Organometallic Chemistry 692 (2007) 4139–4146
www.elsevier.com/locate/jorganchem
Iridium(I) complex of chelating pyridine-2-thiolate ligand:
Synthesis, reactivity, and application to the catalytic E-selective
terminal alkyne dimerization via C–H activation
*
*
Kenichi Ogata , Akinori Toyota
Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei-shi, Tokyo 184-8588, Japan
Received 22 May 2007; received in revised form 20 June 2007; accepted 21 June 2007
Available online 24 June 2007
Abstract
A novel iridium(I) complex bearing a chelate-coordinated pyridine-2-thiolate ligand [Ir(g2-SNC5H4)(PPh3)2] (2) was prepared by the
reaction of iridium ethylene complex [IrCl(C2H4)(PPh3)2] (1) with lithium salt of pyridine-2-thiol (Li[SNC5H4]). On the treatment of irid-
ium(I) complex 2 with chloroform, iridium(III) dichloro-complex [IrCl2(g2-SNC5H4)(PPh3)2] (3) was formed. Reactions of complex 2
with methyldiphenylsilane, acetic acid, and p-tolylacetylene afforded iridium(III) hydride complexes [IrH(SiMePh2)(g2-SNC5H4)(PPh3)2]
(4), [IrH(O2CCH3)(g2-SNC5H4)(PPh3)2] (5), and [IrH(C„C(p-tolyl))(g2-SNC5H4)(PPh3)2] (6), respectively. Complex 2 catalyzed dimer-
ization of terminal alkynes leading to enynes (7) with high E-selectivity via C–H bond activation.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Iridium complex; Pyridine-2-thiolate; Hydride complex; Dimerization of alkyne
1. Introduction
(L = COD, (CO)2), generated from the reaction of [IrCl-
(COD)]2 with lithium salt of pyridine-2-thiol, Li[SNC5H4],
has been reported [8]. The binuclear iridium(I) complex
[Ir(l-SNC5H4)(CO)2]2 reacted with CH3I or CH2I2 to give
iridium(II) complexes [Ir2(CH3)I(l-SNC5H4)2(CO)4] or
[Ir2(CH2I)I(l-SNC5H4)2(CO)4] through oxidative addition
between two metal centers. The reaction of [Ir(OMe)-
(COD)]2 with sterically hindered pyridine-2-thiol bearing
tert-butyl group in the ortho-position generated S-bridging
binuclear complex [Ir(l-SNC5H3-o-tBu)(COD)]2 [9].
Low valent iridium(I) complex bearing chelate-coordi-
nated pyridine-2-thiolate ligand has not been reported,
though many other transition metal complexes bearing
chelate-coordinated pyridine-2-thiolate ligand has been
reported. Chelating pyridine-2-thiolate ligand have an abil-
ity to act as a bifunctional ligand (hard N-donor and soft
S-donor), and we had an interest in the chemistry of its
four-coordinated iridium(I) complex.
Pyridine-2-thiolate has been used as supporting ligand
for transition metal complexes because of the versatility
in their coordination modes [1]. Neutral monodentate [2],
anionic S-monodentate [3], chelating [4], and bridging [5]
pyridine-2-thiolate complexes have been reported. In the
chemistry of iridium, several S-monodentate and chelating
pyridine-2-thiolate iridium complexes which are four- and
six-coordinate structure [6] and Cp* iridium(III) complex
bearing a chelating pyridine-2-thiolate ligand [Cp*Ir(g2-
SNC5H4)N3] [7] were reported. Photolysis of the Cp*Ir
complex [Cp*Ir(g2-SNC5H4)N3] gave a pyridine-1-imido-
2-thiolato complex, in which one of the nitrogen atoms
of the azido ligand has been inserted into the iridium-
N(Py) bond. In case of bridging pyridine-2-thiolate com-
plexes, binuclear iridium(I) complexes [Ir(l-SNC5H4)L]2
In this paper, we describe synthesis and reactivity of an
iridium(I) complex. In addition, the catalytic activity in
dimerization of terminal alkynes is also described.
*
Corresponding authors. Tel./fax: +81 42 388 7162.
E-mail addresses: kogata@cc.tuat.ac.jp (K. Ogata), a-toyota@cc.tuat.
ac.jp (A. Toyota).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.030

4140
K. Ogata, A. Toyota / Journal of Organometallic Chemistry 692 (2007) 4139–4146
1
2. Experimental
2.1. General procedures
(18 mg, 0.020 mmol, 47%). H NMR (CDCl3): d 5.8–8.9
(m, Ph and Pyridine unit). 31P{1H} NMR (CDCl3): d
À12.7 (s, PPh3). Anal. Calc. for C41H34Cl2IrNP2S Æ
0.5CH2Cl2: C, 53.01; H, 3.75; N, 1.49. Found: C, 53.44;
H, 3.93; N, 1.52%.
All manipulations involving air- and moisture-sensitive
organometallic compounds were carried out under dry
argon 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/benzophenone prior to
use. Chloroform was distilled over CaH2 prior to use.
[IrCl(ethylene)(PPh3)2] (1) [10], [Ir(l-SNC5H4)(COD)]2 [8]
were prepared according to the literature methods. Other
reagents employed in this research were commercially
available and used without further purification. The
NMR spectra were recorded on a JEOL Delta-400 spec-
2.3.2. Preparation of [IrH(SiMePh2)(g2-SNC5H4)-
(PPh3)2] (4)
To solution of complex 2 (64 mg, 0.077 mmol) in tolu-
ene (5 mL), methyldiphenylsilane (16 lL, 0.080 mmol)
was added at room temperature. After 5 min, the solvent
was removed under high vacuum and the residue was
washed with hexane (3 · 5 mL) and then dried in vacuo,
1
giving yellow powder of 4 (50 mg, 0.049 mmol, 63%). H
NMR (C6D6): d À19.60 (t, JPH = 16.5 Hz, 1 H, Ir–H),
0.80 (s, 3H, CH3), 6.8–8.5 (m, 39H, Ph and Py), 31P{1H}
1
trometer at ambient temperature. H NMR spectra and
NMR (C6D6):
d
5.8 (s, PPh3). Anal. Calc. for
13C{1H} NMR spectra were measured using Me4Si as
an internal reference, and 31P{1H} NMR spectra were
measured using 85% H3PO4 as an external reference. All
chemical shifts were recorded in ppm and all coupling
constants were recorded in Hz. Fast atom bombardment
(FAB) mass spectra were measured on a JEOL JMS-
SX102 spectrometer using m-nitrobenzylalcohol as matrix.
Elementary analyses were measured on a Perkin–Elmer
240C.
C54H48IrNP2SSi: C, 63.26; H, 4.72; N, 1.37. Found: C,
63.38; H, 4.86; N, 1.40%.
2.3.3. Preparation of [IrH(O2CCH3)(g2-SNC5H4)-
(PPh3)2] (5)
To solution of complex 2 (54 mg, 0.065 mmol) in tolu-
ene (5 mL), acetic acid (5 lL, 0.087 mmol) was added at
room temperature. After 5 min, the solvent was removed
under high vacuum and the residue was washed with hex-
ane (3 · 5 mL) and then dried in vacuo, giving yellow pow-
1
2.2. Preparation of iridium(I)pyridine-2-thiolate complex
[Ir(g2-SNC5H4)(PPh3)2] (2)
der of 5 (52 mg, 0.059 mmol, 90%). H NMR (CD2Cl2): d
2
2
À17.53 (dd, JP1H = 16.8 Hz, JP2H = 20.2 Hz, 1 H, Ir–
H), 1.12 (s, 3H, CH3), 2.8–8.0 (m, 34H, Ph and Py).
2
A solution of ethylene complex [IrCl(C2H4)(PPh3)2] (1)
(276 mg, 0.35 mmol) in THF (5 mL) was cooled to
À78 ꢁC, and then a THF solution of Li[SNC5H4], which
was prepared by the reaction of the parent H[SNC5H4]
31P{1H} NMR (CD2Cl2): d À0.9 (d, Jpp = 18.4 Hz,
2
PPh3), 5.7 (d, Jpp = 18.4 Hz, PPh3). Anal. Calc. for
C43H38IrNO2P2S: C, 58.23; H, 4.32; N, 1.58. Found: C,
58.08; H, 4.46; N, 1.50%.
n
(41 mg, 0.37 mmol) with BuLi (1.58 M in a hexane solu-
tion, 0.24 mL, 0.38 mmol) at À78 ꢁC, was added. The mix-
ture was allowed to warm to room temperature. After
several hours, the volatiles were removed under reduced
pressure. The residual solid was washed with hexane sev-
eral times and then extracted with toluene. The filtrate
was evaporated off under high vacuum to give red complex
2 (250 mg, 0.151 mmol, 85%). FAB mass (m/z): 827 ([M]+).
1H NMR (C6D6): d 6.0–9.2 (m, Ph and Pyridine unit).
31P{1H} NMR (C6D6): d 20.9 (d, Jpp = 20.4 Hz, PPh3),
22.8 (d, Jpp = 20.4 Hz, PPh3). Anal. Calc. for C41H34Ir-
NP2S: C, 59.55; H, 4.14; N, 1.69. Found: C, 59.07; H,
4.17; N, 1.61%.
2.3.4. Preparation of [IrH(C„CC6H4CH3)(g2-SNC5H4)-
(PPh3)2] (6)
To solution of complex 2 (46 mg, 0.056 mmol) in tolu-
ene (2 mL), p-tolylacetylene (10 ll, 0.079 mmol) was added
at room temperature. After 5 min, the solvent was removed
under high vacuum and the residue was washed with hex-
ane (3 · 5 mL) and then dried in vacuo, giving yellow pow-
der of 6 (42 mg, 0.045 mmol, 80%). FAB mass (m/z): 942
1
([M–H]+). IR (KBr): 2300 (Ir–H), 2106 cmÀ1(C„C). H
NMR (C6D6): d À9.56 (dd, JP(trans)H = 171 Hz, JP(cis)H
=
16.5 Hz, 1H, Ir–H), 1.92(s, 3H, CH3), 6.8–8.5 (m, 38H,
Ph, Py). 31P{1H} NMR (C6D6): d À3.9 (d, Jpp = 6.9 Hz,
PPh3), 12.2 (d, Jpp = 6.9 Hz, PPh3).
2.3. Preparation of iridium(III)pyridine-2-thiolate
complexes
2.4. General procedure for catalytic alkyne dimerization
2.3.1. Preparation of [IrCl2(g2-SNC5H4)(PPh3)2] (3)
To solution of complex 2 (35 mg, 0.042 mmol) in tolu-
ene (3 mL), chloroform (0.1 mL, 1.25 mmol) was added
at room temperature. After 1 h, the solvent was removed
under high vacuum and the residue was recrystallized from
CH2Cl2 and diethyl ether, affording yellow crystals of 3
The mixture of iridium complex 2 (0.030 mmol), toluene
(3 mL) and terminal alkyne (1.0 mmol) charged in a sealed
tube under argon. After stirring for 6 h at 80 ꢁC, the sol-
vent was removed and the residue was chromatographed
on silica gel, using ether/hexane (1:3) as eluent. The solvent
was removed to give dimeric product 7. All products were

K. Ogata, A. Toyota / Journal of Organometallic Chemistry 692 (2007) 4139–4146
4141
Table 1
Crystal data for [Ir(g2-SC5H4N)(PPh3)2] Æ 0.5CH2Cl2 (2 Æ 0.5CH2Cl2), [IrCl2(g2-SC5H4N)(PPh3)2] (3) and [IrH(SiMePh2)(g2-SC5H4N)(PPh3)2] (4)
Compound
2 Æ 0.5CH2Cl2
41.5H35ClIrNP2S
3
4
Formula
C
C41H34NCl2IrSP2
897.86
C54H48NSSiP2Ir
1025.29
Molecular weight
Crystal color, habit
Crystal size (mm)
Crystal system
Space group
869.42
Red, prismatic
0.23 · 0.05 · 0.02
Monoclinic
P21/n (No. 14)
10.471(2)
29.975(5)
11.596(3)
90.0
103.009(5)
90.00
3546.2(12)
4
Yellow, prismatic
0.24 · 0.14 · 0.11
Monoclinic
P21/m (No. 11)
9.4642(10)
24.510(3)
15.4529(17)
90.0
90.0917(16)
90.0
3584.5(7)
4
Yellow, block
0.08 · 0.08 · 0.03
Monoclinic
C2/c (No. 15)
35.4026(6)
12.1561(2)
25.0020(5)
90.0
123.9410(7)
90.0
8926.4(3)
8
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
˚
V (A)
Z
Dcalc (g cmÀ3
)
1.628
40.314
–
1.664
40.631
–
1.526
–
73.243
l (Mo Ka) (cmÀ1
)
)
l (Cu Ka) (cmÀ1
Reflections measured
2h (ꢁ)
Independent reflections (Rint
Number of variables
Reflection/parameter ratio
Residuals: R; Rw
22339
55.0
7988 (0.040)
434
18.41
72781
60.1
10703 (0.091)
464
23.07
45941
136.5
8172 (0.066)
546
14.97
)
0.0589; 0.0811
0.0421
0.0613; 0.1398
0.0551
0.0357; 0.0850
0.0322
Residuals: R1
Number of reflections to calculated R1
Goodness-of-fit indicator
6259 (I > 2.0r(I))
1.197
9163 (I > 2.0r(I))
1.162
7463 (I > 2.0r(I))
1.066
identified by comparison of the observed chemical shifts
with literature data [11].
2.6. Determination of structure
The crystal parameters along with data collections are
summarized in Table 1. These structures were solved by
direct methods (SIR92) [12] for 2 Æ 0.5CH2Cl2, (SIR2004)
[13] for 3 and (SHELX97) [14] for 4 and expanded using Fou-
rier techniques [15]. All of non-hydrogen atoms were
refined anisotropically. In complex 2 Æ 0.5CH2Cl2 and 3,
all hydrogen atoms were refined using riding model. In
complex 4, some hydrogen atoms were refined isotropically
and others were refined using the riding model. All calcula-
tions were performed using the CrystalStructure [16] crys-
tallographic software package except for refinement,
which was performed using SHELXL-97 [14].
2.5. Experimental procedure for X-ray crystallography
Suitable single crystals were obtained by recrystalliza-
tion from CH2Cl2/diethyl ether for 2 Æ 0.5CH2Cl2 and 4,
and toluene/hexane for 3. Crystal of 2 Æ 0.5CH2Cl2 and 3
were mounted at the top of nylon loop using liquid paraf-
fin, which was set on a Rigaku Saturn CCD/Rigaku AFC 8
diffractometer. The measurement was made by using Mo
˚
Ka radiation (k = 0.7107 A) at À183 ꢁC under a cold nitro-
gen stream. Indexing of crystals of 2 Æ 0.5CH2Cl2 and 3
were performed from six images that were exposed for
5 s. The crystal-to-detector distances were 40.06 mm for
2 Æ 0.5CH2Cl2 and 40.05 mm for 3. A total of 556 oscilla-
tion for 2 Æ 0.5CH2Cl2 and 1440 oscillation for 3 images
were collected. Readout was performed in the 0.137 mm
pixel mode for 2 Æ 0.5CH2Cl2 and 3.
3. Results and discussion
3.1. Synthesis of iridium(I)pyridine-2-thiolate complex
[Ir(SNC5H4)(PPh3)2](2)
Crystal of 4 was mounted at the top of nylon loop using
liquid paraffin, which was set on a Rigaku RAXIS RAPID
imaging plate/ultra X18 diffractometer. The data were
corrected for Lorentz and polarization effects. The mea-
surement was made by using Cu Ka radiation (k =
Iridium(I) complex 2 bearing pyridine-2-tholate was pre-
pared by the reaction of ethylene complex [IrCl(C2H4)-
(PPh3)2] (1) with lithium salt of pyridine-2-thiolate
Li[SNC5H4] in THF at À78 ꢁC (Scheme 1).
˚
1.54187 A) at À175 ꢁC under a cold nitrogen stream. Index-
Molecular peak of m/z = 827 in the FAB mass spec-
trometry and elementary analysis corresponded to the
formula of [Ir(SNC5H4)(PPh3)2]. The 31P{1H} NMR spec-
ing was performed from three oscillations that were
exposed for 150 s. The crystal-to-detector distance was
127.40 mm. A total of 160 oscillation images were collected.
Readout was performed in the 0.100 mm pixel mode.
tra of 2 showed two doublets at 20.9 and 22.8 ppm (Jpp
=
20.4 Hz) assigned to two PPh3 ligands.

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K. Ogata, A. Toyota / Journal of Organometallic Chemistry 692 (2007) 4139–4146
3.2. Reactions of iridium(I)pyridine-2-thiolate complex 2
N
S
PPh3
PPh3
+
IrCl(C2H4)(PPh3)2
Ir
3.2.1. Reaction of complex 2 with chloroform
THF
SLi
N
-78 oC → r.t.
The complex 2 reacted readily with chloroform at room
temperature to afford the dichloro complex 3 in 47% yield
(Scheme 2). The structure of complex 3 was confirmed by
X-ray analysis. The ORTEP drawing of complex 3 is dis-
played in Fig. 2. Selected bond distances and angles are
listed in Table 3. The crystal contained two independent
iridium complex having Ir(1) and Ir(2). The complex has
1
2
Scheme 1. Synthesis of Ir(I)pyridine-2-thiolate complex.
The structure of complex 2 was also confirmed by X-ray
analysis. The ORTEP drawing of complex 2 is shown in
Fig. 1. Selected bond distances and angles are listed in
Table 2. The crystal contained CH2Cl2 in the lattice. The
complex have square planar geometry around iridium
metal. The sum of angles around iridium atom is 359.9ꢁ.
The Ir–N and Ir–S bond distances were 2.117(4) and
PPh3
N
S
Cl
Cl
N
S
CHCl3
PPh3
PPh3
Ir
Ir
˚
toluene
r.t.
2.3910(12) A, respectively. The N–Ir–S bond angle was
PPh3
68.28(12)ꢁ. The Ir–S bond distance was shorter than
that for previously reported iridium(III)pyridine-2-thiolate
complexes [6].
2
3
Scheme 2. Reaction of Ir(I)pyridine-2-thiolate complex with chloroform.
An attempted substitution of the coordinated pyridine
unit of pyridine-2-thiolate ligand by the reaction of com-
plex 2 with triphenylphosphine in refluxing toluene resulted
in no reaction (recovering yield: 90%). This result showed
high stability of the chelating pyridine-2-thiolate ligand in
complex 2. On the other hand, complex 2 was unstable
toward air in solution and color changed from red to yel-
low for a few seconds.
Fig. 2. ORTEP drawing of complex 3 with thermal ellipsoids drawn at the
50% probability level. All hydrogen atoms are omitted for clarity.
Table 3
2
˚
Fig. 1. ORTEP drawing of complex 2 with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms and CH2Cl2 molecule are omitted
for clarity.
Selected bond distances (A) and angles (ꢁ) for [IrCl2(g -C5H3NS)(PPh3)2]
(3)
Ir(1)–Cl(1)
Ir(1)–N(1)
Ir(1)–P(1)
Ir(2)–Cl(4)
Ir(2)–S(2)
2.405(2)
2.051(8)
2.3452(14)
2.405(2)
2.391(2)
Ir(1)–Cl(2)
Ir(1)–S(1)
Ir(2)–Cl(3)
Ir(2)–N(2)
Ir(2)–P(2)
2.400(2)
2.3988(19)
2.403(2)
2.037(8)
2.3447(16)
Table 2
Selected bond distances (A) and angles (ꢁ) for [Ir(g2-C5H3NS)-
˚
(PPh3)2] Æ 0.5CH2Cl2 (2 Æ 0.5CH2Cl2)
Cl(1)–Ir(1)–Cl(2)
Cl(1)–Ir(1)–S(1)
P(1)–Ir(1)–P(1*)
N(2)–Ir(2)–S(2)
Cl(4)–Ir(2)–N(2)
97.64(6)
101.51(7)
175.17(5)
68.4(2)
N(1)–Ir(1)–S(1)
Cl(2)–Ir(1)–N(1)
Cl(3)–Ir(1)–Cl(4)
Cl(3)–Ir(2)–S(2)
P(2)–Ir(2)–P(2*)
68.0(2)
92.8(2)
96.51(8)
102.86(8)
176.05(8)
Ir(1)–N(1)
Ir(1)–P(1)
2.117(4)
2.2266(12)
Ir(1)–S(1)
Ir(1)–P(2)
2.3910(12)
2.2119(14)
N(1)–Ir(1)–S(1)
P(2)–Ir(1)–S(1)
68.28(12)
98.50(4)
N(1)–Ir(1)–P(1)
P(1)–Ir(1)–P(2)
96.86(12)
96.26(5)
92.3(2)

K. Ogata, A. Toyota / Journal of Organometallic Chemistry 692 (2007) 4139–4146
4143
octahedral geometry around a iridium metal, and the pyr-
dine-2-thiolate ligand was located on a coplanar with two
chloride ligands. Two phosphine ligands of complex 3 are
located in mutually trans position. Ir(1)–N(1) bond dis-
˚
tance (2.051(8) A) of complex 3 is shorter than that for
˚
complex 2 (2.117(4) A). These observation reflect the differ-
ence of electron density on iridium metals between irid-
ium(III) and iridium(I). The axial P(1)–Ir(1) bond
distance was longer than that for complex 2. Other bond
distances and angles of pyridine-2-thiolate ligand of com-
plex 3 are similar to those of complex 2.
The 31P{1H} NMR spectrum showed one singlet signal
at À12.7 ppm. This result indicate the symmetrical struc-
ture of complex 3 in solution as well as structure in the
solid state. The formation of dichloro complex 3 suggested
the strong oxidative tendency of complex 2.
3.2.2. Reaction of complex 2 with methyldiphenylsilane
On the treatment of complex 2 with methyldiphenylsi-
lane at room temperature, oxidative addition of Si–H to
iridium(I) metal was occurred and hydride-silyl complex
4 was isolated in 63% yield (Scheme 3).
Fig. 3. ORTEP drawing of complex 4 with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms are omitted for clarity.
1
The H NMR spectrum of 4 showed hydride signal at
À19.60 ppm as triplet with a P–H coupling constant of
16.5 Hz. The 31P{1H} NMR spectrum shows a singlet at
5.8 ppm assignable for PPh3 ligands. The 31P{1H} NMR
spectrum of complex 4 suggested that the complex 4 has
a symmetrical structure with mutually trans phosphine
ligands.
Table 4
Selected bond distances (A) and angles (ꢁ) for [IrH(SiMePh2)(g2-
˚
C5H3NS)(PPh3)2] (4)
Ir(1)–H(1)
Ir(1)–S(1)
Ir(1)–P(1)
1.50(4)
2.5114(8)
2.3501(9)
Ir(1)–N(1)
Ir(1)–Si(1)
Ir(1)–P(2)
2.172(3)
2.3810(9)
2.3059(9)
The structure of complex 4 was also confirmed by X-ray
analysis. The ORTEP drawing of complex 4 is displayed in
Fig. 3. Selected bond distances and angles are listed in
Table 4. Two phosphine ligands of complex 4 are located
in mutually trans position as well as complex 3. Silyl ligand
is trans to sulfur atom, and the hydride ligand is trans to
nitrogen atom. Similar cationic iridium(III) hydride
complex bearing pyridine-2-thiolate ligand [IrH(g2-SN-
C5H4)(CO)(PPh3)2][BF4] had been reported by Dahlenburg
[6b]. The hydride ligand of the reported cationic complex is
trans to sulfur atom. The crystal structure of complex 4
coincide with solution-state geometry which observed by
1H and 31P{1H} NMR spectra.
H(1)–Ir(1)–Si(1)
N(1)–Ir(1)–S(1)
P(1)–Ir(1)–P(2)
79.4(16)
65.61(7)
163.83(3)
H(1)–Ir(1)–S(1)
N(1)–Ir(1)–Si(1)
110.6(16)
104.31(8)
3.2.3. Reaction of complex 2 with acetic acid
When complex 2 was treated with acetic acid at room
temperature, hydride-acetate complex was formed
(Scheme 4). The result of elementary analysis corresponded
to formula of [Ir(CH3COOH)(NSC5H4)(PPh ) ]. The H
5
1
3 2
NMR spectrum of 5 showed hydride signal at À17.53
ppm as double doublet with a P–H coupling constant of
16.5 and 20.2 Hz. In 31P{1H} NMR spectrum of 5, two
doublets at À0.9 and 5.7 ppm with P–H coupling constants
˚
The Ir–Si bond distance of complex 4 is 2.3810(9) A.
The bond distance is in good agreement with reported
value for the normal iridium(III)–Si bond distances [17].
of 18.4 Hz were observed. These H and 31P{1H} NMR
1
spectra show that two phosphine ligands of complex 5
˚
˚
The Ir–N (2.172(3) A) and Ir–S (2.5114(8) A) bond dis-
tances of complex 4 were slightly longer than those for
dichloro-iridium complex 3.
are located in mutually cis position and by the P–
H(hydride) coupling constants (2JP1H = 16.8 Hz, JP2H
=
2
PPh3
OOCCH3
HSiMePh2
N
S
N
S
SiPh2Me
H
PPh3
PPh3
N
Ir
PPh3
Ir
N
Ir
PPh3
PPh3
CH3COOH
toluene
r.t., 5 min
Ir
H
S
PPh3
4
toluene
r.t., 5 min
S
PPh3
2
2
5
Scheme 3. Reaction of Ir(I)pyridine-2-thiolate complex with methyldi-
phenylsilane.
Scheme 4. Reaction of Ir(I)pyridine-2-thiolate complex with acetic acid.

4144
K. Ogata, A. Toyota / Journal of Organometallic Chemistry 692 (2007) 4139–4146
20.2 Hz) of 1H NMR measurement, hydride and two phos-
phine ligands are located in mutually cis position [18].
R
H
H
R
cat.
H
R
H
R
+
toluene, 80 oC, 6 h
H
R
3.2.4. Reaction of complex 2with p-tolylacetylene
When complex 2 was treated with p-tolylacetylene at
7-Z
7-E
Scheme 6. Catalytic dimerization of terminal alkyne.
room temperature, hydride-acetylide complex
6 was
formed (Scheme 5). Molecular peak of m/z = 942 in the
FAB mass spectrometry corresponded to the formula of
[Ir(HC”C(p-tolyl))(NSC5H4)(PPh3)2]–H]. In the IR spec-
tra, the most noticeable absorption were observed at
2300 and 2106 cmÀ1, which were assigned to Ir–H and
the C„C vibration of acetylide ligand, respectively. The
1H NMR spectrum showed hydride signal as a double dou-
blet at À9.56 ppm with a P–P coupling constant of 16.5 and
171 Hz was observed. The coupling constant of 171 Hz
indicate that hydride locate in the trans to PPh3 ligand
[6a]. In 31P{1H} NMR spectrum of 6, two doublets assign-
able to mutually cis phosphine ligands at À3.9 and
12.2 ppm with P–H coupling constants of 6.9 Hz were
observed. These spectroscopic results indicate that struc-
ture of 6 is 6A or 6B as shown in Scheme 5. The similar
hydride-acetylide complex of iridium(III) bearing acetyl-
acetonato complex [IrH(C„CR)(g2-acac)(PPh3)2] (R =
Ph, Cy, SiMe3) has been reported [17]. In case of the
acetylacetonato complex, two phosphine ligands located
in mutually trans position.
Table 5
Results of catalytic dimerization reaction catalyzed by complex 2a
Entry
R
Yield (%)b
Ratio (7-E/7-Z)c
1
2
3
4
5
a
p-toly
Ph
72
65
42
54
55
92:8
91:9
91:9
95:5
100:0
nBu
tBu
TMS
Reaction conditions; alkyne (1.0 mmol), complex 2 (0.03 mmol), tol-
uene (3 mL), temperature (80 ꢁC), reaction time (6 h).
b
Isolated yields.
Determined by 1H NMR measurement.
c
ucts and trimerization products were not generated. In
case of bimetallic pyridine-2-thiolate catalytic system
([Ir(l-SNC5H4)(COD)]2/2PPh3), dimerization of p-tolyl-
acetylene proceeded in low yield (36%) with low stereose-
lectivity (E/Z = 65:35). These results clearly demonstrated
that the use of bidentate pyridine-2-thiolate complexes
enables high E-selectivity. The complex 2 also showed
moderate activity and high E-selectivity for dimerization
of alkylacetylene (entries 3 and 4) and trimethylsilylacet-
ylene (entry 5).
3.3. Alkyne dimerization reaction catalyzed by iridium(I)
complex 2
The possible pathway for the formation of dimerization
product 7 is shown in Scheme 7. An oxidative addition of
the alkyne C–H bond to iridium(I) affords hydride-acetylide
complex 6. Addition of the iridium hydride to the another
alkyne then provides intermediate A. It is probably prefer
to form E-type intermediate A due to the fact that A has a
stable structure to avoid steric repulsion between alkene
unit and other ligands around iridium metal. Reductive
elimination furnishes enyne 7-E, and regenerates the
hydride-acetylide complex 6. Recently, mechanistic study
for dimerization of terminal alkynes in iridium complex
bearing PCP pincer ligand had been reported by Goldman
et al. [25], which showed that alkyne insertion into Ir–H
bond followed by reductive elimination affords an enyne.
The transition-metal-catalyzed dimerization of alkynes
has received much attention as a useful method for the syn-
thesis of substituted enynes [19]. Many late transition metal
complexes such as ruthenium [20], rhodium [21], iridium
[22], nickel [23], and palladium [24] have been used in the
dimerization of alkynes. Miyaura et al. reported that
[IrCl(COD)]2/PR3 system catalyzed head-to-head dimer-
ization of terminal alkynes leading to enynes with high
stereoselectivity [11b]. However, iridium-catalyzed dimer-
ization has not been well examined other than [IrCl-
(COD)]2/phosphine system. Accordingly, we investigated
alkyne dimerization by using iridium(I) complex 2 (Scheme
6).
The results and reaction conditions are listed in Table
5. In the presence of complex 2, head-to-head dimeriza-
tion of p-tolylacetylene or phenylacetylene proceeded with
high E-selectivity (entries 1 and 2). In this reaction, cou-
pling by-products such as head-to-tail dimerization prod-
4. Summary
A novel iridium(I) complex bearing chelating pyridine-
2-thiolate ligand was prepared. The complex was readily
PPh3
PPh3
Ir
p
-tolyl
C
N
S
C
N
PPh3
N
S
PPh3 HC C(p-tolyl)
Ir
or
-tolyl
Ir
PPh3
C
toluene
S
PPh3
C
p
H
r.t., 5 min
H
6A
2
6B
Scheme 5. Reaction of Ir(I) pyridine-2-thiolate complex with p-tolylacetylene.

K. Ogata, A. Toyota / Journal of Organometallic Chemistry 692 (2007) 4139–4146
4145
H
R
H
[Ir]
[Ir]
H
R
H
R
H
R
H
[Ir]
R
R
H
R
6
A
R
H
7-E
Scheme 7. Possible pathway for catalytic dimerization of alkyne catalyzed by complex 2.
[5] (a) M.A. Ciriano, J.J.P. Torrente, F. Viguri, F.J. Lahoz, L.A. Oro,
A. Tiripicchio, M.T. Camellini, J. Chem. Soc. Dalton Trans. (1990)
1493;
reacted with chloroform, methyldiphenylsilane, acetic acid
and alkyne to give iridium(III) complexes. Two phosphine
ligands of hydride-acetate and hydride-acetylide complex
were mutually cis position whereas for dichloro-complex
and hydride-silyl complex, phosphine ligands were
positioned mutually trans. The iridium(I) complex was
active for catalytic dimerization of terminal alkynes, which
proceeded with high E-selectivity. Further investigation of
reactivity of these complexes is underway in our
laboratory.
(b) J.G. Reynolds, S.C. Sendlinger, A.M. Murray, J.C. Huffman, G.
Christou, Angew. Chem. Int. Ed. Engl. 31 (1992) 1253;
(c) R.M. Tylicki, W. Wu, P.E. Fanwick, R.A. Walton, Inorg. Chem.
34 (1995) 988;
(d) E.W. Ainscough, A.M. Brodie, R.K. Coll, T.G. Kotch, A.J.
Lees, A.J.A. Mair, J.M. Waters, J. Organomet. Chem. 517 (1996)
173.
[6] (a) S. Park, A.J. Lough, R.H. Morris, Inorg. Chem. 35 (1996) 3001;
(b) L. Dahlenburg, M. Kuhnlein, Eur. J. Inorg. Chem. (2000) 2117.
¨
[7] Y. Sekioka, S. Kaizaki, J.M. Mayer, T. Suzuki, Inorg. Chem. 44
(2005) 8173.
[8] M.A. Ciriano, F. Viguri, L.A. Oro, A. Tiripicchio, M.T. Camellini,
Angew. Chem. Int. Ed. Engl. 26 (1987) 444.
Acknowledgements
The authors are grateful to Dr. Noriyuki Suzuki and
Daisuke Hashizume (RIKEN) for their kind help in X-
ray measurement.
[9] V.M. Soto, J.J.P. Torrente, L.A. Oro, F.J. Lahoz, M.L. Mart´ın,
M.P. Hake, D.B. Grotjahn, Organometallics 25 (2006) 4374.
[10] A. van der Ent, A.L. Onderdelinden, Inorg. Chim. Acta 7 (1973) 203.
[11] (a) C.S. Yi, N. Lin, Organometallics 15 (1996) 3968;
(b) T. Ohmura, S. Yorozuya, Y. Yamamoto, N. Miyaura, Organo-
metallics 19 (2000).
Appendix A. Supplementary material
[12] SIR92: A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 27 (1994)
435.
[13] SIR2004: M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L.
Cascarano, L. De Caro, C. Giacovazzo, G. Polidori, R. Spagna
(2005).
CCDC 646693, 646694 and 646695 contain the supple-
mentary crystallographic data for 2, 3 and 4. These data
can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; 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.2007.06.030.
[14] SHELX97: G.M. Sheldrick, 1997.
[15] DIRDIF99: P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman,
R. de Gelder, R. Israel, J.M.M. Smits, The DIRDIF-99 program
system, Technical Report of the Crystallography Laboratory, Uni-
versity of Nijmegen, The Netherlands, 1999.
[16] Crystal Structure 3.8.0: Crystal Structure Analysis Package, Rigaku
and Rigaku/MSC (2000–2006). 9009 New Trails Dr. The Woodlands,
TX 77381, USA.
References
´
[17] M.A. Esteruelas, F.J. Lahoz, E. Onate, L.A. Oro, L. Rodrıguez,
˜
Organometallics 15 (1996) 823.
[18] J.A. van Doorn, C. Masters, C. van der Woude, J. Chem. Soc.,
Dalton 1213 (1978).
[1] (a) E.R. Raper, Coord. Chem. Rev. 153 (1996) 199;
(b) E.R. Raper, Coord. Chem. Rev. 165 (1997) 475.
[2] (a) K. Umakoshi, A. Ichimura, I. Kinoshita, S. Ooi, Inorg. Chem. 29
(1990) 4005;
[19] B.M. Trost, Science 254 (1991) 1471.
[20] (a) For ruthenium-catalyzed dimerization of alkynes, see: Y. Sasaki,
P.H. Dixneuf, J. Chem. Soc., Chem. Commun. (1986) 790;
(b) C. Bianchini, M. Peruzzini, F. Zanobini, P. Frediani, A. Albinati,
J. Am. Chem. Soc. 113 (1991) 5453;
(b) E.C. Constable, A.C. King, C.A. Palmer, P.R. Raithby, Inorg.
Chem. Acta 184 (1991) 43.
[3] (a) P.D. Cookson, E.R.T. Tiekink, J. Chem. Soc., Dalton Trans.
(1993) 259;
(c) L. Dahlenburg, K.-M. Frosin, S. Kerstan, D. Werner, J.
Organomet. Chem. 407 (1991) 115;
(b) P. Aslanidis, S.K. Hadgikakou, P. Karagiannidis, B. Kojicprodic,
M. Luic, Polyhedron 13 (1994) 3119;
(d) A.M. Echavarren, J. Lopez, A. Santos, J. Montoya, J. Organomet.
Chem. 414 (1991) 393;
(c) C. Vetter, C. Wagner, J. Schmidt, D. Steinborn, Inorg. Chim.
Acta 359 (2006) 4326.
(e) C. Bianchini, M. Peruzzini, F. Zanobini, P. Frediani, A. Albinati,
J. Am. Chem. Soc. 113 (1991) 5453;
[4] (a) Y. Nakatsu, Y. Nakamura, K. Matsumoto, S. Ooi, Inorg. Chim.
Acta 196 (1992) 81;
(f) C. Bianchini, P. Frediani, D. Masi, M. Peruzzini, F. Zanobini,
Organometallics 13 (1994) 4616;
(b) M. Gupta, R.E. Cramer, K. Ho, C. Pettersen, S. Mishina, J.
Belli, C.M. Jensen, Inorg. Chem. 34 (1995) 60;
(g) C.S. Yi, N. Liu, A.L. Rheingold, L.M.L. Sands, Organometallics
15 (1996) 5275;
´
´
(c) A.S. Pedrares, M.L. Duran, J. Romero, J.A.G. Vazquez, J.C.
Monteagudo, A. Sousa, J.R. Dilworth, Inorg. Chim. Acta 359 (2006)
863.
(h) J.-P. Gu, D. Masui, Y. Ishii, M. Hidai, Chem. Lett. (1998) 1003;
¨

4146
K. Ogata, A. Toyota / Journal of Organometallic Chemistry 692 (2007) 4139–4146
(i) K. Melis, D.D. Vos, P. Jacobs, F. Verpoort, J. Organomet. Chem.
659 (2002) 159;
(j) Y. Gao, R.J. Puddephatt, Inorg. Chim. Acta 350 (2003) 101;
(k) H. Katayama, H. Yari, M. Tanaka, F. Ozawa, Chem. Commun.
(2005) 4336, and [11a].
[22] (a) For iridium-catalyzed dimerization of alkynes, see: C.-H. Jun, Z.
Lu, R.H. Crabtree, Tetrahedron Lett. 34 (1992) 7119;
(b) T. Hirabayashi, S. Sakaguchi, Y. Ishii, Adv. Synth. Catal. 347
(2005) 872, and Ref. [11b].
[23] (a) For Nickel-catalyzed dimerization of alkynes, see: G. Giacomelli, F.
Marcacci, A.M. Caporusso, L. Lardicci, Tetrahedron Lett. (1979) 3217;
(b) M. Ishikawa, J. Ohshita, Y. Ito, A. Minato, J. Chem. Soc., Chem.
Commun. (1988) 804;
[21] (a) For recent example of rhodium-catalyzed dimerization of alkynes,
see: J. Ohshita, K. Furumori, A. Matsuguchi, M. Ishikawa, J. Org.
Chem. 55 (1990) 3277;
(b) I.P. Kovalev, K.V. Yevakov, Y.A. Strelenko, M.G. Vinogradov,
G.I. Nikishin, J. Organomet. Chem. 386 (1990) 139;
(c) W.T. Boese, A.S. Goldman, Organometallics 10 (1991) 782;
(d) M. Scha¨fer, N. Mohr, J. Wolf, H. Werner, Angew. Chem., Int.
Ed. Engl. 32 (1993) 1315;
(c) S. Ogoshi, M. Ueta, M. Oka, H. Kurosawa, Chem. Commun. (2004)
2732.
[24] (a) For palladium-catalyzed dimerization of alkynes, see: H. Singer,
G. Wilkinson, J. Chem. Soc., A (1968) 190;
(b) E.T. Sabourin, J. Mol. Catal. 26 (1984) 363;
(e) C.-C. Lee, Y.-C. Lin, Y.-H. Liu, Y. Wang, Organometallics 24
(2005) 136;
(c) F.A. Selimov, O.G. Rutman, U.M. Dzhemilev, J. Organomet.
Chem. 346 (1988) C58.
(f) W. Weng, C. Guo, R. Celenligil-Cetin, B.M. Foxman, O.V.
Ozerov, Chem. Commun. (2006) 197.
[25] R. Ghosh, X. Zhang, P. Achord, T.J. Emge, K.K. Jespersen, A.S.
Goldman, J. Am. Chem. Soc. 129 (2007) 853.