Catalytic dehydrogenation of cyclooctane with neutral iridium(I) complexes

Article abstract of DOI:10.1016/j.jorganchem.2008.02.003

A series of new 1,5-cyclooctadiene iridium(I) complexes with chelating ligands has been synthesized. The ligands are naphthoxyimines, carboxylates and alcoholates. The complexes catalyze the homogeneous dehydrogenation of cyclooctane to give cyclooctene and hydrogen without an external hydrogen acceptor up to rates of 75 turnovers. The catalysts are active for at least 48 h at a temperature of 300 °C. The ligand structure has an influence on the activity and selectivity of the corresponding catalysts.

Full text of DOI:10.1016/j.jorganchem.2008.02.003

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1808–1814
www.elsevier.com/locate/jorganchem
Catalytic dehydrogenation of cyclooctane with neutral
iridium(I) complexes
Silke Taubmann, Helmut G. Alt *
Laboratorium fu¨r Anorganische Chemie, Universita¨t Bayreuth, Universita¨tsstraße 30, 95440 Bayreuth, Germany
Received 21 December 2007; received in revised form 24 January 2008; accepted 1 February 2008
Available online 7 February 2008
Abstract
A series of new 1,5-cyclooctadiene iridium(I) complexes with chelating ligands has been synthesized. The ligands are naphthoxyi-
mines, carboxylates and alcoholates. The complexes catalyze the homogeneous dehydrogenation of cyclooctane to give cyclooctene
and hydrogen without an external hydrogen acceptor up to rates of 75 turnovers. The catalysts are active for at least 48 h at a temper-
ature of 300 °C. The ligand structure has an influence on the activity and selectivity of the corresponding catalysts.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: CH bond activation; Homogeneous catalyst; Dehydrogenation; Iridium
1. Introduction
reported in the literature [4–15]. In the year 2004, Brookhart
et al. described turnover numbers of 1000 per 30 min using
an iridium bis(phosphinite) p-XPCP pincer complex [16].
The disadvantage of this transfer dehydrogenation is the
necessity of a hydrogen acceptor, like tert-butylethylene,
making this reaction uneconomic. CH bond activation reac-
tions without a hydrogen acceptor are very rare [17,18]. The
yields of these reactions are mostly lower than the transfer
dehydrogenation results [19]. To carry out acceptor less
dehydrogenation reactions, neutral iridium(I) complexes
with heteroatomic N,O-chelating ligands were synthesized.
The selective, catalytic activation of chemical bonds
remains a challenging and significant goal of modern
research in chemistry. An attractive area is the transforma-
tion of relatively inexpensive hydrocarbon feedstocks into
more useful value-added products by low energy processes
[1]. In this respect, catalytic alkane dehydrogenation with
coordination compounds is a significant reaction convert-
ing alkanes into the corresponding olefins and hydrogen.
The products are valuable educts or intermediates for
industrial processes.
In the year 1979, Crabtree et al. reported the stoichio-
metric dehydrogenation of cyclooctene to cyclooctadiene
with an iridium phosphine complex [2]. Four years later,
Baudry and Ephritikhine described the first catalytic dehy-
drogenation of cyclooctane with a rhenium polyhydride
complex under thermal conditions [3]. This process repre-
sents a transfer dehydrogenation reaction, because a
‘‘sacrificing” olefin reacts with the generated hydrogen. In
the following, transfer dehydrogenation reactions were
2. Results and discussion
2.1. Syntheses of the complexes
The hydroxyimine ligand precursors were synthesized
via an acid-catalyzed condensation reaction of 2-hydroxy-
1-naphthaldehyde with a phenylamine as reported in the
literature [20]. The ligand precursors have to be trans-
formed into the corresponding sodium alcoholates. The
typical procedure is the reaction of the ligand precursor
with NaH to produce the sodium alcoholate and hydrogen.
The reaction of 1 equiv. of the alcoholate with 0.5 equiv. of
*
Corresponding author. Tel.: +49 921 55 2555; fax: +49 921 55 2044.
E-mail address: helmut.alt@uni-bayreuth.de (H.G. Alt).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.02.003

S. Taubmann, H.G. Alt / Journal of Organometallic Chemistry 693 (2008) 1808–1814
1809
[Ir(cod)Cl]2 yielded the corresponding, new naphthoxy irid-
ium complexes 1a–d (Scheme 1). The complexes were
obtained with yields of 65–85%.
Similar complexes like the naphthoxyimine iridium(I)
compounds are the alcoholate iridium(I) complexes 2a–c
(the hetero atoms nitrogen and oxygen coordinating to irid-
ium). The synthesis was performed as described in Scheme 2.
The complexes were obtained as yellow and orange solids.
neous reaction. The catalysts could be used without any
activation or additives.
The corresponding coordination compound was dis-
solved in cyclooctane, the solution was transferred into
an autoclave and heated to 300 °C. This temperature is use-
ful because the dehydrogenation of alkanes is an endother-
mic reaction. At higher temperatures most of the
organometallic compounds have no longer their original
compositions but they are still catalytically active. Remark-
ably, the investigations of structure–efficiency relationships
of catalysts showed that the nature of the organic ligands
has a relevant impact on the activity and selectivity of
the corresponding catalyst and its ‘‘decomposition prod-
uct”. The identity of the decomposition products is still
unclear.
The
complex
1,5-cyclooctadiene
8-oxychinoline
iridium(I) (2d) was prepared in an analogous manner [21].
The third type with an N,O-chelating ligand are carbox-
ylate iridium(I) complexes. The novel complexes 3a–c were
synthesized from the reaction of [Ir(cod)(OMe)]2 with pyr-
idine 2-acetic acid, 6-methylpyridine 2-carboxylic acid and
indol 2-carboxylic acid (Scheme 3).
For investigations of structure–efficiency relationships
in CH-activation reactions, the known iridium(I) com-
plexes 3d–h were synthesized. The procedure is known in
the literature [22,23].
The results of the naphthoxyimine iridium(I) catalysts
(Scheme 5) indicated that a meta-substitution (1d) gave a
higher TON (44) than the ortho-substituted derivative
(1a) with 28 turnovers. The highest activity (TON = 75)
was obtained for catalyst 1c. This could be due to the elec-
tron withdrawing effect of the para-Br substituent. This
electronic deficit could favor an oxidative addition reaction
of the alkane at the metal which is the starting step of the
CH-activation reaction. Catalysts 1a–c produced 100%
cyclooctene.
2.2. Catalytic dehydrogenation of cyclooctane
The synthesized coordination compounds were tested as
catalysts for the dehydrogenation of cyclooctane to gener-
ate cyclooctene and hydrogen (Scheme 4) in a homoge-
R2
R2
R2
R3
R4
R3
R4
R3
R4
R1
R1
R1
+ 0.5 eq
[Ir(cod)Cl]2
+ NaH
N
HO
N
NaO
N
O
Ir
- H2
-NaCl
RT, THF
RT, THF
2a
R1, R4 = Me; R2, R4 = H
R1, R4 = i-prop; R2, R4 = H
R1, R4 = Me; R2 = H; R3 = Br
R1, R2 = Me; R3, R4 = H
2b
2c
2d
Scheme 1. Synthesis of naphthoxy iridium(I) complexes.
+ 0.5 eq
N
N
N
+ NaH
-H2
[Ir(cod)Cl]2
Ir
- 2 NaCl
RT, THF
HO
NaO
O
RT, THF
N
O
N
O
N
O
N
O
=
2a
2b
2c
Scheme 2. Synthesis of the alcoholate iridium(I) complexes 2a–c.

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S. Taubmann, H.G. Alt / Journal of Organometallic Chemistry 693 (2008) 1808–1814
Me
O
N
N
O
RT
Ir
Ir
Ir
2
2
- 2MeOH
O
HO
Me
NH
O
N
O
N
O
N
=
O
O
O
O
3a
3b
3c
Scheme 3. Synthesis of carboxylate iridium(I) complexes.
Table 1
cat.
TONs and selectivities of the dehydrogenation of cyclooctane catalyzed by
2a–h
+
H2
ΔT
Metal complex
Catalyst no.
TON
14.12
Selectivity [%]
100
Scheme 4. Catalytic activation of cyclooctane.
2a
N
Ir
75
80
O
70
60
50
40
30
20
10
0
44
N
Ir
2b
2c
2d
10.59
9.21
78.4
55.3
100
35
28
O
N
Ir
Br
O
N
10.34
Ir
O
1a
1b
1c
1d
Scheme 5. TONs of the dehydrogenation of cyclooctane catalyzed with
1a–d.
The alcoholate iridium(I) catalysts also achieved a cata-
lytic dehydrogenation reaction of cyclooctane to give
cyclooctene and hydrogen. The activities of catalysts 2a–d
were constant within the scope of measuring accuracy
(TON = 9–14). Compared with the naphthoxy iridium(I)
catalysts, the alcoholate ligands of catalysts 2a–d showed
no influence (Table 1). In contrast to the activities, the
selectivities varied depending on the hetero atoms of the
ligand. The results in Table 1 show that a substitution at
the pyridine (2b) reduced the selectivity to produce the
monoolefin. Another decrease of selectivity (55.3%) was
observed with catalyst 2c. The unfavorable seven-mem-
bered ring of the chelating ligand could be the reason for
this behavior.
The carboxylate iridium(I) complexes 3a–h achieved
excellent selectivities (100%). Depending on the organic
ligand, the activities of complexes 3a–h varied between 5
and 35 turnovers (Table 2).
Complexes 3a with a six-membered ring of chelating
ligand and metal showed the highest catalytic activity
(TON = 35). The NH-structure unit reduced the activity
of catalysts 3c and 3h. A steric influence of the isochinoline

S. Taubmann, H.G. Alt / Journal of Organometallic Chemistry 693 (2008) 1808–1814
1811
Table 2
H
H
H
H
TONs and selectivities of the dehydrogenation of cyclooctane catalyzed
with 3a–h
Ln-1M
LnM
+
H2
Ln-1M
-L
Metal complex
Catalyst no.
TON
34.53
Selectivity [%]
100
3a
R
R
Ln-1
M
LnM
+
N
-L
Ir
Scheme 6. Coordination of an alkene and hydrogen at the metal center of
the active species.
O
O
2.3. Time dependence of homogeneous dehydrogenation
N
Ir
3b
17.41
100
100
The catalytic dehydrogenation of alkanes produces
alkenes and hydrogen. These products are potential ligands
(Scheme 6) and can block the first step of the CH-activa-
tion reaction.
In a homogeneous system, the reaction products cannot
be isolated or separated from the catalytic centers. This
explains the time dependence of the TONs of catalyst 3a
(Scheme 7). The curve is indicative of a permanent reduc-
tion of the dehydrogenation reaction. The catalyst per-
formed 29 turnovers in 8 h. An extension of the reaction
time of 48 h gave 43 turnovers. In spite of the activity
decrease, catalyst 3a was still active after 48 h.
O
O
3c
4.88
NH
Ir
O
O
N
Ir
3d
3e
28.02
18.81
100
100
O
O
N
3. Summary and conclusion
Novel naphthoxyimine (1a–d), alcoholate (2a–d) and
carboxylate iridium(I) complexes (3a–c) have been synthe-
sized. The hydroxyimine ligand precursors can be prepared
from relatively inexpensive starting materials. The alcohol-
ates and carboxylic acid ligand precursors are commer-
cially available. The prepared complexes catalyzed the
homogeneous dehydrogenation of cyclooctane without a
‘‘sacrificing” olefin at a reaction temperature of 300 °C
(maximum of 75 turnovers). The activity and selectivity
depends on the nature of the heteroatomic ligand. For
most ligands a selectivity of 100% monoolefin was
obtained. The naphthoxyimine ligand with a para-bro-
mine-substituent (1c) gave the highest conversion, obvi-
ously because of the electron pulling effect of the ligand
favoring the oxidative addition of alkanes at the iridium
atom. The time dependence of the homogeneous dehydro-
genation reaction of catalyst 3a was almost a parabolic
curve. This is indicative of a permanent reduction of the
activity. The reason for this behavior is primarily the con-
tamination of the catalysts by its own products (hydrogen
and alkene) in a closed system. In order to gain more infor-
mation it is planned to perform these reactions in open sys-
tems (fixed bed reactor) at various temperatures.
N
Ir
O
O
3f
25.02
100
N
Ir
O
O
N
Ir
3g
3h
20.57
10.09
100
100
O
O
O
H
H
N
O
Ir
and the quinoline carbonic acid ligand could not be
observed. The simpler the structure of hetero atomic
ligands (pyridine carboxylate) the higher the activities
(complexes 3a and 3d). In a similar manner also cationic
iridium complexes of the type [Ir(cod)LL]X (LL = chelat-
ing ligand; X = Cl, PF6) are able to activate cyclooctane
in homogeneous solution [24].
4. Experimental
4.1. General considerations
Air- and moisture-sensitive reactions were carried out
under an atmosphere of argon employing standard Schlenk

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S. Taubmann, H.G. Alt / Journal of Organometallic Chemistry 693 (2008) 1808–1814
50
45
40
35
30
25
20
15
10
5
N
Ir
O
O
3a
0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
reaction time [h]
Scheme 7. Time dependence of the dehydrogenation of cyclooctane in a closed system catalyzed with 3a.
techniques. NMR spectra were measured on a Bruker
ARX 250 instrument. Chemical shifts (d, ppm) were
recorded relative to the residual solvent peak
(d = 7.24 ppm for chloroform-d). The multiplicities were
designated as follows: s = singlet; d = doublet; m = multi-
plet. 13C{1H} NMR spectra were fully proton decoupled
and the chemical shifts (d, ppm) are relative to the solvent
peak (d = 77.0 ppm). Elemental analyses were performed
using a VarioEl III instrument. A gas chromatograph Agi-
lent 6890 was used to register the dehydrogenation reaction
products. The identification of dehydrogenation products
and the reaction control were carried out by FOCUS
DSQ (Thermo) mass spectrometer.
dried in vacuo. The complexes were obtained as yellow
powders.
4.3.1. Compound 1a
From 275 mg (1 mmol) of 1-[(2,6-dimethylphenyl)
imino]methylenyl]-2-naphthalenol, 24 mg (1 mmol) of
NaH, and 336 mg (0.5 mmol) [Ir(cod)Cl]2 was obtained
372 mg (0.65 mmol, 65%) of 1a as an orange powder. Spec-
troscopic data for 1a: 1H NMR (250 MHz, 21 °C, CDCl3):
9.04 (s, 1H), 7.89–7.03 (9H), 4.46–4.41 (m, 2H), 2.66–2.56
(m, 2H), 2.30 (s, 6H), 2.21–2.09 (m, 4H), 1.80–1.62 (4H).
13C {1H} (62 MHz, 21 °C, CDCl3): 166.5 (Cq), 157.5
(CH), 150.2 (Cq), 136.2 (CH), 134.7 (Cq), 130.8 (Cq),
129.2 (CH), 128.3 (CH), 127.5 (CH), 127.3 (Cq), 126.3
(CH), 125.3 (CH), 122.8 (CH), 118.9 (CH), 110.2 (Cq),
69.1 (CH), 57.4 (CH), 32.5 (CH2), 29.5 (CH2), 18.7
(CH3). MS data for 1a: 575 (MÅ+) (100), 573 (60), 545
(9), 463 (17), 295 (6), 77 (7).
4.2. Materials
Tetrahydrofuran, n-pentane, diethylether, methylene-
chloride and toluene were refluxed over the appropriate
drying agents and distilled under argon. NaH was washed
with toluene and pentane before use to remove mineral oil.
CDCl3 was stored over molecular sieves. Cyclooctane
(COA) was degassed and stored under argon. [Ir(cod)Cl]2
and [Ir(cod)(OMe)]2 were synthesized in analogy to known
procedures [25–28]. The organic starting materials were
purchased from Aldrich or Arcos.
4.3.2. Compound 1b
From 331 mg (1 mmol) of 1-[(2,6-diisopropyl-
phenyl)imino]methylenyl]-2-naphthalenol, 24 mg (1 mmol)
of NaH, and 336 mg (0.5 mmol) [Ir(cod)Cl]2 was obtained
530 mg (0.84 mmol, 84%) of 1b as a yellow powder. Anal.
Calc. for C31H36NOIr (1b): C, 58.93; H, 5.90; N, 2.22.
Found: C, 59.06; H, 6.10; N, 2.30%. Spectroscopic data
1
4.3. General procedure for the synthesis of the complexes
N,O-imine-Ir(cod) (1)
for 1b: H NMR (250 MHz, 21 °C, CDCl3): 9.09 (s, 1H),
7.90–7.22 (m, 9H), 4.46–4.44 (m, 2H), 3.43–3.37 (m, 2H),
2.77–2.74 (m, 2H), 2.24–2.16 (m, 4H), 1.77–1.66 (m, 4H),
1.35 (d, 6H, 3J(H,H) = 6.86 Hz), 1.02 (d, 6H,
3J(H,H) = 6.80 Hz). 13C {1H} (62 MHz, 21 °C, CDCl3):
166.5 (Cq), 157.5 (CH), 157.4 (CH), 146.9 (Cq), 136.3
(CH), 134.5 (Cq), 129.2 (CH), 127.7 (CH), 127.4 (CH),
127.2 (Cq), 125.4 (CH), 125.2 (CH), 123.3 (CH), 122.8
(CH), 118.5 (CH), 109.5 (Cq), 69.2 (CH), 57.4 (CH), 32.3
(CH2), 29.5 (CH2), 27.8 (CH3), 22.4 (CH3). MS data for
1b: 631 (MÅ+) (100), 629 (72), 519 (28), 295 (12).
To a THF solution (30 ml) of the respective hydroxyi-
mine (1 mmol) was added 1 mmol of NaH. The mixture
was stirred for 2 h at RT. A solution of 0.5 mmol of
[Ir(cod)Cl]2 in 20 ml THF was then added and the mixture
was stirred for 2 h at RT. After evaporation of the solvent
in vacuo, the residue was dissolved in CH2Cl2. The solution
was filtered over Na2SO4, the solvent was then removed in
vacuo. The crude product was washed with pentane and

S. Taubmann, H.G. Alt / Journal of Organometallic Chemistry 693 (2008) 1808–1814
1813
4.3.3. Compound 1c
(CH), 31.4 (CH2), 30.5 (CH2). MS data for 2a: 409 (MÅ+)
From 354 mg (1 mmol) of 1-[(4-brom-2,6-dimethyl-
phenyl)imino]methylenyl]-2-naphthalenol, 24 mg (1 mmol)
of NaH, and 336 mg (0.5 mmol) [Ir(cod)Cl]2 was obtained
490 mg (0.75 mmol, 75%) of 1c as a yellow powder. Spec-
troscopic data for 1c: 1H NMR (250 MHz, 21 °C, CDCl3):
9.00 (s, 1H), 7.90–7.22 (m, 8H), 4.48 (s, br, 2H), 2.62–2.53
(m, 2H), 2.28 (s, 6H), 2.20–2.14 (m, 4H), 1.80–1.64 (m,
4H). 13C {1H} (62 MHz, 21 °C, CDCl3): 166.6 (Cq), 157.5
(CH), 149.0 (Cq), 136.6 (CH), 134.3 (Cq), 131.1 (CH),
129.3 (CH), 127.8 (CH), 127.3 (Cq), 125.5 (CH), 123.2
(CH), 119.3 (Cq), 118.9 (CH), 110.4 (Cq), 70.4 (CH), 68.9
(CH), 32.8 (CH2), 29.7 (CH2), 18.6 (CH3), 18.5 (CH3).
MS data for 1c: 653 (MÅ+) (100), 623 (7), 573 (7), 541
(10), 295 (9).
(17), 407 (20), 375 (39), 296 (20), 269 (9), 108 (100).
4.4.2. Compound 2b
From 146 mg (1 mmol) of 8-hydroxyquinaldine, 24 mg
(1 mmol) of NaH, and 336 mg (0.5 mmol) [Ir(cod)Cl]2
was obtained 305 mg (0.73 mmol, 73%) of 2b as an orange
1
powder. Spectroscopic data for 2b: H NMR (250 MHz,
21 °C, CDCl3): 8.00 (d, 1H), 7.27 (dd, 1H), 7.01 (dd, 1H),
6.93 (dd, 1H), 6.78 (dd, 1H), 4.43 (s, 2H), 4.11 (s, 2H),
2.50 (s, 3H), 2.29–2.21 (m, 4H), 1.61–1.50 (m, 4H). 13C
{1H} (62 MHz, 21 °C, CDCl3): 161.7 (Cq), 144.3 (Cq),
140.0 (CH), 129.4 (CH), 128.7 (Cq), 124.1 (CH), 115.8
(CH), 113.5 (CH), 67.2 (CH), 55.4 (CH), 33.8 (CH2), 29.6
(CH2), 23.8 (CH3). MS data for 2b: 459 (MÅ+) (100), 457
(75), 429 (55), 294 (13), 269 (6).
4.3.4. Compound 1d
From 275 mg (1 mmol) of 1-[[(2,3-dimethylphenyl)
imino]methylenyl]-2-naphthalenol, 24 mg (1 mmol) of
NaH, and 336 mg (0.5 mmol) [Ir(cod)Cl]2 was obtained
488 mg (0.85 mmol, 85%) of 1d as a yellow powder. Spec-
troscopic data for 1d: 1H NMR (250 MHz, 21 °C, CDCl3):
9.13 (s, 1H), 7.89–6.89 (m, 9H), 5.49–4.42 (m, 2H), 3.19–
3.16 (m, 2H), 2.67–2.61 (m, 4H), 3.34 (s, 3H), 2.21 (s,
3H), 1.78–1.59 (m, 4H). 13C {1H} (62 MHz, 21 °C, CDCl3):
166.3 (Cq), 157.4 (CH), 151.1 (Cq), 137.6 (Cq), 136.3 (CH),
129.2 (CH), 134.4 (Cq), 129.8 (Cq), (Cq), 128.2 (CH), 127.9
(CH), 127.6 (CH), 127.4 (Cq), 125.4 (CH), 122.9 (CH),
122.1 (CH), 119.1 (CH), 110.0 (Cq), 69.0 (CH), 56.7
(CH), 32.4 (CH2), 29.6 (CH2), 20.6 (CH3), 14.3 (CH3).
MS data for 1d: 575 (MÅ+) (100), 573 (70), 545 (8), 463
(25), 295 (17), 77 (10).
4.4.3. Compound 2c
From 137 mg (1 mmol) of 3-pyridinepropanol, 24 mg
(1 mmol) of NaH, and 336 mg (0.5 mmol) [Ir(cod)Cl]2
was obtained 196 mg (0.45 mmol, 45%) of 2c as an orange
1
powder. Spectroscopic data for 2c: H NMR (250 MHz,
21 °C, CDCl3): 8.35–8.33 (m, 1H), 7.55–7.43 (m, 1H),
7.05–7.02 (m, 1H), 7.00–6.95 (m, 1H), 3.55 (t, 2H), 3.27
(s, 2H), 2.81 (t, 2H), 2.35 (s, 2H), 1.85–1.81 (m, 2H), 1.37
(s, 4H), 1.11 (s, 4H).
4.5. General procedure for the synthesis of N-carboxylate
iridium complexes (3)
The respective carbonic acid (1 mmol) was dissolved in
10 ml THF by heating. The solvent was added to a solu-
tion of 0.5 mmol [Ir(cod)(OMe)]2 in 10 ml THF. The
mixture was stirred for 3 h at RT. A color change from
yellow to red resp. brown was observed. After reducing
the solvent in vacuo, the precipitated solid was filtered,
washed with pentane and diethylether and dried in
vacuo. The products were obtained as red and brown
powders.
4.4. General procedure for the synthesis of N-alcoholate
iridium complexes (2)
A Schlenk tube was charged with 1 mmol of the respec-
tive alcoholate and 5 ml THF. After addition of 1 mmol
NaH, the mixture was stirred for 2 h at RT. The suspension
was slowly added to a solution of 0.5 mmol [Ir(cod)Cl]2 in
10 ml THF and stirred for 1 h at RT. The solvent was
removed in vacuo and the crude product was dissolved in
CH2Cl2. After filtration through Na2SO4, the solvent was
reduced in vacuo until a solid precipitated. The solid was
washed with pentane and diethylether and dried in vacuo.
The products were obtained as yellow and orange powders.
4.5.1. Compound 3a
From 486 mg (2.5 mmol) of 2-pyridine acetic acid and
662 mg (1 mmol) [Ir(cod)OMe]2 was obtained 859 mg
(0.98 mmol, 98%) of 3a as an orange powder. Spectro-
1
scopic data for 3a: H NMR (250 MHz, 21 °C, CDCl3):
8.40 (d, 1H), 7.82 (dd, 1H), 7.40–7.36 (m, 1H), 7.05–7.02
(m, 1H), 4.61 (s, 2H), 4.18–4.16 (m, 2H), 3.11–3.09 (m,
2H), 2.21–2.14 (m, 4H), 1.62–1.57 (m, 4H). 13C {1H}
(62 MHz, 21 °C, CDCl3): 171.0 (Cq), 156.0 (Cq), 148.5
(CH), 139.2 (CH), 126.3 (CH), 125.2 (CH), 79.2 (CH),
46.1 (CH2), 45.1 (CH2). MS data for 3a: 453 (MÅ+ÀH)
(3), 297 (100), 295 (98), 269 (26), 91 (4), 77 (7).
4.4.1. Compound 2a
From 109 mg (1 mmol) of hydroxymethylpyridine,
24 mg (1 mmol) of NaH, and 336 mg (0.5 mmol)
[Ir(cod)Cl]2 was obtained 91 mg (0.23 mmol, 23%) of 2a
1
as a yellow powder. Spectroscopic data for 2a: H NMR
(250 MHz, 21 °C, CDCl3): 8.76 (d, 1H), 8.09 (d, 1H),
7.81 (dd, 1H), 7.05 (d, 1H), 4.61 (s, 2H), 4.17 (s, 2H),
3.10 (s, 2H), 2.21–2.14 (m, 4H), 1.62–1.57 (m, 4H). 13C
{1H} (62 MHz, 21 °C, CDCl3): 148.1 (CH), 136.9 (CH),
121.7 (CH), 120.0 (CH), 68.4 (CH), 63.7 (CH2), 53.3
4.5.2. Compound 3b
From 137 mg (1 mmol) of 6-picolinic-acid and 331 mg
(0.5 mmol) [Ir(cod)OMe]2 was
obtained 415 mg
(0.95 mmol, 95%) of 3b as an orange powder. Spectro-

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S. Taubmann, H.G. Alt / Journal of Organometallic Chemistry 693 (2008) 1808–1814
scopic data for 3b: MS data for 3b: 437 (MÅ+) (59), 391 (83),
389 (90), 387 (100), 296 (38), 294 (38), 269 (14).
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4.5.3. Compound 3c
From 403 mg (2.5 mmol) of indol-2-carbonic-acid and
662 mg (1 mmol) [Ir(cod)OMe]2 was obtained 424 mg
(0.46 mmol, 46%) of 3c as an orange powder. Anal. Calc.
for C17H18NO2Ir (3c): C, 45.75; H, 3.84; N, 2.96. Found:
C, 45.27; H, 3.85; N, 2.85%. Spectroscopic data for 3c:
1H NMR (250 MHz, 21 °C, CDCl3): 8.92 (s, 1H), 7.71–
7.11 (m, 5H), 4.38 (s, breit, 4H), 2.83 (s, breit, 4H), 2.22
(s, breit, 4H).
4.6. Homogeneous dehydrogenation of cyclooctane
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Krogh-Jespersen, A.S. Goldman, Chem. Commun. (1997) 2273.
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The respective complex was dissolved resp. suspended in
20 ml of cyclooctane. The mixture was transferred into a
250 ml autoclave. The autoclave was closed gastight and
heated to 300 °C. The standard reaction time was 4 h. After
the desired reaction time, the autoclave was removed from
the oven and cooled to room temperature. The reaction gas
and the solution were analyzed by GC.
Acknowledgment
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507.
We thank ConocoPhillips, Bartlesville, USA, for the
financial support of the project.
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