Catalytic homogeneous CH-activation reactions of cyclooctane with [Ir(cod)LL]X complexes (LL = N,N-chelating ligands, amines, phosphines; X = Cl, PF6)

Article abstract of DOI:10.1016/j.molcata.2008.01.023

A series of new [Ir(cod)LL]X complexes (LL = chelating ligands, amines, phosphines; X = Cl, PF₆) was synthesized. The complexes catalyzed the selective homogeneous dehydrogenation of cyclooctane to give cyclooctene up to a rate of 61 turnovers. The activity and selectivity depends on the ligand structure of the corresponding coordination compound. The addition of external additives (amines and phosphines) increased the activities up to 100% in case of PCy₃ and NHPh₂. The dehydrogenation reaction showed a high temperature dependence.

Full text of DOI:10.1016/j.molcata.2008.01.023

Available online at www.sciencedirect.com
Journal of Molecular Catalysis A: Chemical 284 (2008) 134–140
Catalytic homogeneous CH-activation reactions of cyclooctane with
[Ir(cod)LL]X complexes (LL = N,N-chelating ligands,
amines, phosphines; X = Cl, PF6)
Silke Taubmann, Helmut G. Alt∗
Laboratorium fu¨r Anorganische Chemie, Universita¨t Bayreuth, Universita¨tsstraße 30,
D-95440 Bayreuth, Germany
Received 20 December 2007; accepted 13 January 2008
Available online 20 January 2008
Abstract
A series of new [Ir(cod)LL]X complexes (LL = chelating ligands, amines, phosphines; X = Cl, PF6) was synthesized. The complexes catalyzed
the selective homogeneous dehydrogenation of cyclooctane to give cyclooctene up to a rate of 61 turnovers. The activity and selectivity depends
on the ligand structure of the corresponding coordination compound. The addition of external additives (amines and phosphines) increased the
activities up to 100% in case of PCy3 and NHPh2. The dehydrogenation reaction showed a high temperature dependence.
© 2008 Elsevier B.V. All rights reserved.
Keywords: CH bond activation; Homogeneous catalyst; Dehydrogenation; Iridium complexes
1. Introduction
complex by thermal activation [8]. This reaction is a trans-
fer dehydrogenation reaction, which catalyzes the transfer of
hydrogen from an alkane to a sacrificial olefinic hydrogen accep-
tor. In the following many transfer dehydrogenation reactions
were reported in the literature [9–20]. Brookhart et al. described
turnover numbers higher than 1000 per 30 min [21] using an
iridium bis(phosphinite) p-XPCP pincer complex. The disad-
vantage of a transfer dehydrogenation reaction is the necessity
of a hydrogen acceptor, like tert-butylethylene. This makes such
areactionuneconomic. CH-activationreactionswithoutahydro-
gen acceptor are hard to find. The activities of these reaction are
mostly lower than the transfer dehydrogenation results [22]. To
carry out acceptorless CH-activation reactions [Ir(cod)LL]PF6
(LL = chelating ligands, amines, phosphines; X = Cl, PF6) com-
plexes should be promising candidates.
Saturated hydrocarbons are still abundant and inexpensive
chemical feedstocks. Therefore it is a challenge and an attractive
goal in research to convert alkanes into alkenes in order to use
their synthetic potential [1–3]. Olefins are valuable educts and/or
intermediates in many industrial processes.
The key step of a catalytic CH-activation reaction is the for-
mation of an electronically and coordinatively unsaturated active
species. Low valent transition metal species have the potential
to insert into an alkane CH-bond to give an alkyl metal hydride
complex (oxidative addition of an alkane at a transition metal).
A subsequent ␤-hydrogen elimination produces the olefin and
hydrogen [4]. Crabtree et al. first reported the stoichiometric
dehydrogenation of cyclooctene to cyclooctadiene with an irid-
ium phosphine complex [5]. In the early 1980s, examples were
discovered of oxidative addition of CH bonds to late transi-
tion metal complexes [6,7]. Perhaps the most remarkable report
was the one of Baudry and Ephritikhine of the first catalytic
dehydrogenation of cyclooctane with a rhenium polyhydride
2. Results and discussion
2.1. Syntheses of the complexes
The pyridine imine ligand precursors were synthesized via an
acid catalyzed condensation reaction of acetyl pyridine with a
phenylamine as reported in the literature [23,24]. The ligand pre-
cursors have to be transformed into the corresponding sodium
∗
Corresponding author. Tel.: +49 921 55 2555; fax: +49 921 55 2044.
E-mail address: helmut.alt@uni-bayreuth.de (H.G. Alt).
1381-1169/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2008.01.023

S. Taubmann, H.G. Alt / Journal of Molecular Catalysis A: Chemical 284 (2008) 134–140
135
Scheme 1. Synthesis of iridium complexes with N,N-chelating ligands (1a–d and 2a–c).
alcoholates, which reacts directly with [Ir(cod)Cl]2 yielding
the new pyridine imine iridium complexes 1a–d (Scheme 1).
The yields of compounds 1a–d are generally high (95–99.5%).
Another kind of iridium complexes with N,N-chelating lig-
ands are complexes 2a–c. The reaction of 1 equiv. of the
corresponding N,N-chelating ligand precursor with 0.5 equiv.
of [Ir(cod)Cl]2 yields the new complexes 2a–c (Scheme 1).
These complexes were formed by a breakdown of the dimeric
[Ir(cod)Cl]2 complexes. The chlorides formed the anions of the
new ionic iridium complexes. Complexes [Ir(cod)bipy]Cl (2d)
and [Ir(cod)phen]Cl (2e) were prepared according to published
procedures [25].
Scheme 3. Equilibrium of tetra- and pentacoordinated species of ionic iridium(I)
complexes [29].
The novel complexes 3a–c and 4a were prepared from the
reaction of [Ir(cod)Cl]2 with NaPF6 and an excess of the amine
resp. phosphine (Scheme 2).
Scheme 4. Catalytic activation of cyclooctane.
The complexes [Ir(cod)(PR3)2]PF6 (R = Ph (4b), Cy (4c),
p-Tol (4d), m-Tol (4e)) were prepared according to published
procedures [26–29].
2.2. Dehydrogenation of cyclooctane
Jensen postulated coordinatively and electronically unsatu-
rated intermediates as the active species [4]. Therefore ionic
complexes as 16 e− species are promising candidates for dehy-
drogenation reactions (Scheme 3).
Various coordination compounds were tested as catalysts for
the dehydrogenation of cyclooctane to form cyclooctene and
hydrogen (Scheme 4) in a homogeneous reaction. The catalysts
were used without any activation.
Scheme 2. Syntheses of bis(amine)-1,5-cyclooctadiene iridium complexes and bis(phosphine)-1,5-cyclooctadiene iridium complexes.

136
S. Taubmann, H.G. Alt / Journal of Molecular Catalysis A: Chemical 284 (2008) 134–140
Table 1
TONs and selectivities of complexes 1a–d
Catalyst no.
Products
TON
Selectivity (%)
1a
1b
1c
1d
Cyclooctene, toluene
Cyclooctene
Cyclooctene
3.4
21.5
13.9
7.9
55.4
100
100
Cyclooctene
100
Table 2
TONs and selectivities of complexes 2a–e
Catalyst no.
Products
TON
Selectivity (%)
2a
2b
2c
2c
2d
2e
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
32.5
40.1
20.5
18.9
12.9
10.7
100
100
100
100
100
100
Scheme5. TONsofbis(amine)1,5-cyclooctadieneiridium(I)complexes(3a–c).
For CH-activation reactions the corresponding complex was
dissolved in degassed cyclooctane. The solution was transferred
into an autoclave and heated to 200–400 ◦C. The standard reac-
tion temperature was 300 ◦C. After the reaction period, the
autoclave was cooled to room temperature. The reaction gas
and the reaction solution were characterized by GC analysis.
The selectivity for the dehydrogenation reaction was calculated
by the conversion of cyclooctane to cyclooctene.
At high temperatures most of the organometallic com-
pounds do no longer have the original composition. Remarkably,
structure-efficiency relationships showed that the nature of the
organic ligands has a relevant impact on the activity and selec-
tivity of the corresponding catalyst.
Complexes 1a–d converted cyclooctane to cyclooctene in a
catalytic reaction with TONs between 3.4 and 21.5 (Table 1).
The selectivities were 100% with the exception of complex 1a
which produced toluene as secondary product.
Scheme 6. TONs of bis(phosphine) 1,5-cyclooctadiene iridium(I) complexes
The complexes 2a–e, especially 2a and 2b, showed a high
dehydrogenation potential for homogeneous dehydrogenation
reactions without a hydrogen acceptor (Table 2). The high TONs
of 2a and 2b can be interpreted with the more flexible ligand
backbone of the chelating ligand.
The iridium complexes 3a–c showed catalytic dehydrogena-
tion activities (Scheme 5). The dehydrogenation results of the
[Ir(cod)NN]PF6 catalysts indicated that a para-substitution (3b)
of the amino phenyl group has a positive effect on the activ-
ity (TON = 61). The TON of 3b describes a thoroughly active
iridium catalyst in a homogeneous dehydrogenation reaction
without any hydrogen acceptor. The catalysts 3a–c produced
cyclooctene with a selectivity of 96–100%.
The [Ir(cod)PP]PF6 (P = P(o-Tol)3, P(m-Tol)3, P(p-Tol)3,
PPh3, PCy3) complexes yielded cyclooctene in catalytic
amounts (Scheme 6). The activities of complexes 4a–e are gen-
erally lower than the activities of amine containing complexes
(3a–c). Only the complexes 4a (TON = 31) and 4b (TON = 31)
showed TONs in the range of the activities of [Ir(cod)NN]PF6
complexes.
(4a–e).
2.3. Temperature dependence of dehydrogenation reactions
The CH-activation reaction is an endothermic process.
Thereforeatemperaturedependencecanbeexpected. Inthetem-
perature range from 200 to 350 ◦C a continuous increase of the
activity can be observed with the catalysts [Ir(cod)(NPh3)2]PF6
(3a) and [Ir(cod)(PPh3)2]PF6 (4d). Remarkably, the activities
showed a sudden increase at a reaction temperature of 350 ◦C
(Scheme 7). This suggests that a new active species is formed. In
this process the ligands are involved. Obviously the phosphine
(4d) is better than the amine ligand (3a) forming such a catalytic
species at higher temperatures in a homogeneous system.
2.4. Influence of additives on the dehydrogenation reaction
of cyclooctane
Since the positive influence of the heteroatomic ligands was
obvious from numerous experiments, it made sense to add exter-

S. Taubmann, H.G. Alt / Journal of Molecular Catalysis A: Chemical 284 (2008) 134–140
137
Scheme 8. Activities of complex 2c depending on different additive amounts.
Scheme 7. Temperature dependence of the activities of catalysts 3a and 4d.
1:16. The ideal additive concentration was 4 equiv. (Scheme 8).
The increase of the additive concentration gave no higher
TON. NHPh2 ratios of 1:8, 1:12 and 1:16 decreased the TON.
These experiments with Lewis basic additives are another
argument for the formation of a new active species in the
process.
nal additives (amines and phosphines) in order to increase the
activities. The complex [Ir(cod)dichinolin)]PF6 (2c) was sus-
pended in 20 ml cyclooctane and the respective additive was
added in a ratio of metal:additive = 1:4.
The TON of complex 2c (without additive) was 19.7. The
catalysts 5a and 5c–e showed lower TONs than 2c (Table 3).
The phosphine additive PCy3 was responsible for a decrease
of the activity with the exception of catalyst 5b (Table 3). The
addition of PCy3 increased the TON to 36.9 (100% higher than
2c).
The amine additives (catalysts 6a–h) showed generally an
increase of the activities (TON = 19.9–33.5) in comparison to
catalyst 2c (TON = 19.7). The highest TON was obtained for cat-
alyst 6c, which contained 4 equiv. NHPh2 (Table 4). The amines
proved as better additives than phosphines. In all cases, cata-
lysts 6a–h showed selectivities of 100% for the production of
cyclooctene.
3. Summary and conclusions
Novel complexes of the type [Ir(cod)LL]X (LL = pyridine
imine (1a–d), N,N-chelating ligand (2a–c), amine (3a–c), phos-
phine (4a); X = Cl, PF6) were synthesized. The advantage of
these complexes is an existing equilibrium between penta- and
tetra-coordinated species. Because of this dynamic equilibrium
which depends on the anion and the solvent, these com-
plexes are promising candidates as dehydrogenation catalysts
for alkanes. The prepared complexes catalyzed the dehydro-
genation of cyclooctane at a reaction temperature of 300 ◦C.
The catalysts showed relatively high activities (maximum of
In another series of experiments the amount of additives
was varied with metal:additive ratios of 1:2, 1:4, 1:8, 1:12 and
Table 3
TONs and selectivities depending on phosphine additives
Coordination compound
Catalyst no.
Additive [M:additive]
TON
Selectivity (%)
5a
5b
5c
5d
5e
PPh3 [1:4]
PCy3 [1:4]
P(p-Tol)3 [1:4]
P(n-Bu) [1:4]
PH(t-Bu) [1:4]
14.1
36.9
18.0
7.1
100
100
93.5
53.0
57.8
4.2
Table 4
TONs and selectivities depending on amine additives
Coordination compound Catalyst no.
Additive [M:additive]
TON
Selectivity (%)
6a
6b
6c
6d
6e
6f
NPh3 [1:4]
NEt3 [1:4]
24.1
29.7
33.5
26.5
19.9
24.1
25.7
27.4
100
100
100
100
100
100
100
100
NHPh2 [1:4]
NH2Ph [1:4]
NH2pyr [1:4]
NH(i-prop)2 [1:4]
NHCy2 [1:4]
NMe2Et [1:4]
6g
6h

138
S. Taubmann, H.G. Alt / Journal of Molecular Catalysis A: Chemical 284 (2008) 134–140
61 turnovers) for homogeneous dehydrogenation reactions.
The activity and selectivity depends on the heteroatomic lig-
and. For most ligands selectivities of 100% monoolefin were
obtained. In the homogeneous system the catalysts with amine
ligands achieved the highest TONs with selectivities of 100%.
At higher temperatures most catalysts have no longer the
original compositions. Obviously the ligands of the original
organometallic compound contribute to the formation of the new
active species. The formation of a new active species using the
heteroatomic ligand is supported by experiments with exter-
nal additives. The addition of amine additives increased the
activities of the corresponding catalysts. The ideal additive con-
centration proved as metal:additive = 1:4. The activities of the
ionic iridium(I) complexes also depend on the reaction temper-
ature and show a sudden increase at a temperature >350 ◦C.
This result is another argument for the formation of a new
active species at elevated temperatures. Its composition is still
unknown.
(1a). From 196 mg (1 mmol) of 1-(2-pyridyl)-2-phenyl-2-
aza-ethene and 336 mg (0.5 mmol) [Ir(cod)Cl]2 was obtained
519 mg (0.98 mmol, 98%) of 1a as a dark blue powder. MS data
for 1a: 495 (M•+ − Cl) (24), 493 (20), 295 (10), 269 (4), 195
(61), 181 (37), 118 (85), 77 (100).
(1b). From 224 mg (1 mmol) of 1-(2-pyridyl)-2-(2,6-
dimethylphenyl)-2-aza-ethene and 336 mg (0.5 mmol)
[Ir(cod)Cl]2 was obtained 539 mg (0.96 mmol, 96%) of
1b as a dark blue powder. MS data for 1b: 524 (M•+ − Cl) (25),
412 (11), 295 (17), 269 (4), 224 (31), 209 (100), 146 (45), 105
(24), 77 (31).
(1c). From 280 mg (1 mmol) of 1-(2-pyridyl)-2-(2,6-
diisopropylphenyl)-2-aza-ethene and 336 mg (0.5 mmol)
[Ir(cod)Cl]2 was obtained 578 mg (0.995 mmol, 99.5%) of 1c
1
as a dark blue powder. Spectroscopic data for 1c: H NMR
(250 MHz, 21 ◦C, CDCl3): 8.25 (d, breit, 1H), 8.08–8.03 (m,
1H), 7.70–7.65 (m, 4H), 7.25–7.20 (m, 1H), 3.64 (s, breit, 2H),
3.30–3.19 (m, 4H), 2.24–2.18 (m, 4H), 1.84 (s, 3H), 1.72–1.63
1
(m, 4H), 1.26 (d, 6H), 1.02 (d, 6H). 13C { H} (62 MHz, 21 ◦C,
4. Experimental
CDCl3): 169.9 (Cq), 157.5 (Cq), 146.9 (CH), 142.2 (Cq), 140.6
(Cq), 136.6 (CH), 127.7 (CH), 127.3 (CH), 127.0 (CH), 124.2
(CH), 63.3 (CH), 31.8 (CH2), 27.4 (CH), 25.1 (CH3), 20.7
(CH3). MS data for 1c: 580 (M•+) (3), 565 (1), 468 (5), 280 (6),
265 (18), 237 (100), 202 (12).
4.1. General considerations
All manipulations were carried out using standard Schlenk
techniques under argon, which was purified by passage through
(1d). From 303 mg (1 mmol) of 1-(2-pyridyl)-2-(4-brom-
2,6-dimethylphenyl)-2-aza-ethene and 336 mg (0.5 mmol)
[Ir(cod)Cl]2 was obtained 607 mg (0.95 mmol, 95%) of 1d as
a dark blue powder. MS data for 1d: 602 (M•+ − HCl) (45), 492
(17), 303 (43), 295 (20), 287 (71), 223 (99), 208 (100), 145 (63),
104 (88).
˚
columns of BTS catalyst and 4 A molecular sieves. NMR spec-
tra were measured on a Bruker ARX250 instrument. Chemical
shifts (δ, ppm) were recorded relative to the residual solvent
peak at δ = 7.26 ppm for chloroform-d. The multiplicities were
1
assigned as follows: s, singlet; m, multiplet. 13C { H} NMR
spectra were fully proton decoupled and the chemical shifts
(δ, ppm) are relative to the solvent peak (77.0 ppm). The gas
chromatograph Agilent 6890 was used to monitor the dehy-
drogenation reactions. The identification of dehydrogenation
products and the reaction control were carried out by a FOCUS
DSQ instrument (Thermo). Elemental analyses were performed
using a VarioEl III instrument.
4.4. General procedure for the synthesis of iridium
complexes with N,N-chelating ligands (2)
A suspension of the N,N-chelating ligand (2.5 mmol) in 30 ml
of THF was added to a solution of 1 mmol [Ir(cod)Cl]2 in 30 ml
THF. The mixture was stirred at RT for 2 h. A color change
from red to yellow resp. ocher was observed. The solvent was
reduced to 30 and 50 ml pentane were added. The precipitated
solid was filtered, washed with pentane and diethylether and
dried in vacuo. The products were obtained as yellow and ocher
solids.
4.2. Materials
Tetrahydrofuran, n-pentane and toluene were distilled from
Na/K alloy. Diethylether was distilled from LiAlH4 and methy-
lene chloride from P2O5. All solvents were stored under argon.
Cyclooctane (COA) was degassed and stored under argon.
[Ir(cod)Cl]2 and [Ir(cod)(OMe)]2 were synthesized in analogy
to known procedures [26,30–32]. The organic starting materials
were purchased from Aldrich or Arcos.
(2a). From 290 mg (2.5 mmol) of N,N,Nꢀ,Nꢀ-
tetramethylethyldiamine and 671 mg (1 mmol) [Ir(cod)Cl]2 was
obtained 670 mg (0.74 mmol, 74%) of 2a as a yellow powder.
1
Spectroscopic data for 2a: 13C { H} (62 MHz, 21 ◦C, CDCl3):
67.3 (CH), 63.4 (CH2), 59.7 (CH3), 50.2 (CH3), 32.0, 30.4
(CH2).
4.3. General synthesis of the pyridine imine iridium(I)
complexes (1)
(2b). From 361 mg (2.5 mmol) of N,N,Nꢀ,Nꢀ-tetramethyl-1,4-
butanediamine and 671 mg (1 mmol) [Ir(cod)Cl]2 was obtained
494 mg (0.51 mmol, 51%) of 2b as a yellow powder. Spectro-
0.5 mmol [Ir(cod)Cl]2 were dissolved in 20 ml CH2Cl2. After
addition of 1 mmol of the respective pyridine imine, the mixture
was stirred at RT for 2 h. The solvent was reduced in vacuo and
the remained suspension was filtered. The solid was washed with
pentane and dried in vacuo. The products were obtained as dark
blue solids.
1
scopic data for 2b: H NMR (250 MHz, 21 ◦C, CDCl3): 4.07
(s, breit, 4H), 2.96–2.95 (m, 4H), 2.43 (s, 6H), 2.29 (s, 6H),
1
2.08–2.01 (m, 8H), 1.34–1.15 (m, 4H). 13C { H} (62 MHz,
21 ◦C, CDCl3): 65.1 (CH2), 59.1 (CH2), 49.2 (CH2), 45.0 (CH3),
31.8 (CH2), 30.5 (CH2).

S. Taubmann, H.G. Alt / Journal of Molecular Catalysis A: Chemical 284 (2008) 134–140
139
(2c). From641 mg(2.5 mmol)of2,2ꢀ-biquinolineand336 mg
4.7. Addition of external additives (amines, phosphines)
(0.5 mmol) [Ir(cod)Cl]2 was obtained 1150 mg (0.97 mmol,
97%) of 2c as a ocher powder. MS data for 2c: 592 (M•+) (5),
296 (5), 256 (100), 128 (18).
To test the influence of additives on the activities of the metal
complexes, a four molar ratio of the respective additive was
added directly to a solution of complex 2c and 20 ml cyclooc-
tane resulting in the formation of the phosphine resp. amine
containing catalysts 5a–e and the amine containing catalysts
6a–h. The corresponding mixture was used for dehydrogenation
experiments (see Section 4.8).
4.5. General synthesis of bis(amine) iridium(I) complexes
(3)
A suspension of NaPF6 (3.5 mmol) in 20 ml of H2O was
added to a solution of 1 mmol [Ir(cod)Cl]2 in 30 ml THF. After
addition of 8 mmol of the respective amine, the mixture was
stirred at RT for 4 h. The solvent was removed in vacuo and
the remaining solid was suspended in pentane. The solid was
filtered, washed with pentane, toluene and H2O and dried in
vacuo. The complexes were obtained as light yellow and orange,
voluminous powders.
4.8. Homogeneous dehydrogenation of cyclooctane
The respective complex was dissolved resp. suspended in
20 ml cyclooctane. The mixture was transferred into a 250 ml
autoclave. The autoclave was closed gastight and heated to
200–400 ◦C, the standard temperature was 300 ◦C. After the
desired reaction time (4 h), the autoclave was removed from the
oven and cooled to room temperature. The gas and the solution
were analyzed by GC.
(3a). From 1.96 g (8 mmol) of tri-phenylamine and 671 mg
(1 mmol) [Ir(cod)Cl]2 was obtained 1.58 g (0.84 mmol, 84%) of
3a as apricot, voluminous powder. Spectroscopic data for 3a:
1H NMR (250 MHz, 21 ◦C, CDCl3): 7.18–6, 90 (m, 30H), 4.16
1
(s, breit, 4H), 2.26–2.15 (m, 4H), 1.48–1.42 (m, 4H). 13C { H}
Acknowledgment
(62 MHz, 21 ◦C, CDCl3): 147.9 (Cq), 129.2 (CH), 124.2 (CH),
122.7 (CH), 62.2 (CH), 31.8 (CH2).
We thank ConocoPhillips, Bartlesville, USA, for the financial
support of the project.
(3b). From 1.15 g (4 mmol) of tri-(p-toluyl)amine and 336 mg
(0.5 mmol) [Ir(cod)Cl]2 was obtained 723 mg (0.71 mmol, 71%)
1
of 3b as yellow solid. Spectroscopic data for 3b: H NMR
References
(250 MHz, 21 ◦C, CDCl3): 7.32–6.96 (m, 24H), 4.27 (s, 4H),
2.31 (s, 18H), 1.57–1.53 (m, 8H). 13C { H} (62 MHz, 21 ◦C,
1
[1] G.W. Parshwell, Catalysis 1 (1977) 335.
[2] A.E. Shilov, Coord. Chem. Rev. 24 (1977) 97.
[3] D.E. Webster, Adv. Organomet. Chem. 15 (1977) 147.
[4] C.M. Jensen, Chem. Commun. (1999) 2443.
CDCl3): 145.7 (Cq), 131.7 (Cq), 129.7 (CH), 123.9 (CH), 62.8
(CH), 31.8 (CH2), 20.8 (CH3).
(3c). From 1.15 g (4 mmol) of tri-benzylamine, 336 mg
(0.5 mmol) [Ir(cod)Cl]2 and 588 mg (3.5 mmol) NaPF6 was
obtained 300 mg (0.29 mmol, 29%) of 3c as light yellow pow-
der. Anal. Calcd for C50H54N2PF6Ir 3c: C, 58.87; H, 5.34; N,
2.75. Found: C, 57.30; H, 5.32; N, 2.92. Spectroscopic data for
[5] R.H. Crabtree, J.M. Mihelcic, J.-M. Quirk, J. Am. Chem. Soc. 101 (1979)
7738.
[6] J.H. Hoyano, W.A.G. Graham, J. Am. Chem. Soc. 104 (1982) 3723.
[7] R.G. Bergman, A.H. Janowicz, J. Am. Chem. Soc. 104 (1982) 352.
[8] D. Baudry, M. Ephritikhine, H. Felkin, R. Holmes-Smith, J. Am. Chem.
Soc. (1983) 788.
[9] M.J. Burk, R.H. Crabtree, C.P. Parnell, R.J. Uriarte, Organometallics 3
(1984) 816.
[10] H. Felkin, T. Fillebeen-Khan, Y. Gault, R. Holmes-Smith, J. Zakrzewski,
Tetrahedron Lett. 25 (1984) 1999.
1
3c: H NMR (250 MHz, 21 ◦C, CDCl3): 7.39–7.33 (m, 30H),
4.23 (s, breit, 4H), 3.97 (s, 12H), 2.27–2.23 (m, 4H), 1.55–1.46
1
(m, 4H). 13C { H} (62 MHz, 21 ◦C, CDCl3): 129.5 (CH), 129.1
(CH), 62.2 (CH), 57.6 (CH2), 31.7 (CH2).
[11] M.J. Burk, R.H. Crabtree, D.V. McGrath, J. Chem. Soc., Chem. Commun.
1985 (1829).
4.6. Synthesis of 1,5-cyclooctadiene bis(phosphine)
iridium(I) complex (4a)
[12] M. Gupta, C. Hagen, R.J. Flesher, W.C. Kaska, C.M. Jensen, Chem. Com-
mun. (1996) 2083.
[13] R.H. Crabtree, C.P. Parnell, Organometallics 4 (1985) 519.
[14] M.J. Burk, R.H. Crabtree, J. Am. Chem. Soc. 109 (1987) 8025.
[15] J.A. Maguire, W.T. Boese, A.S. Goldman, J. Am. Chem. Soc. 111 (1989)
7088.
[16] J.A. Maguire, A.S. Goldman, J. Am. Chem. Soc. 113 (1991) 6706.
[17] J.A. Maguire, A. Petrillo, A.S. Goldman, J. Am. Chem. Soc. 114 (1992)
9492.
[18] J. Belli, C.M. Jensen, Organometallics 15 (1996) 1532.
[19] P. Braunstein, Y. Chauvin, J. Nahring, A. DeCian, J. Fischer, A. Tiripicchio,
F. Ugozzoli, Organometallics 15 (1996) 5551.
[20] J.A. Miller, L.K. Knox, J. Chem. Soc., Chem. Commun. (1994) 1449.
[21] I. Go¨ttker-Schnetmann, gen. Schnetmann, P. White, M. Brookhart, J. Am.
Chem. Soc. 126 (2004) 1804.
[22] W.-W. Xu, G.P. Rosini, M. Gupta, C.M. Jensen, W.C. Kaska, K. Krogh-
Jespersen, A.S. Goldman, Chem. Commun. (1997) 2273.
[23] K.J. Miller, T.T. Kitagawa, M.M. Abu-Omar, Organometallics 20 (2001)
4403.
To a THF solution (30 ml) of [Ir(cod)Cl]2 [Ir(cod)Cl]2
(0.5 mmol) was added 1.75 mmol NaPF6, dissolved in 20 ml
H2O. After addition of 3 mmol tri-(ortho-toluyl)-phosphine
under stirring, the mixture was stirred at RT for 2 h. The sol-
vent was removed in vacuo and the crude product suspended in
pentane. The solid was filtered off, washed with pentane, toluene
and H2O and dried in high vacuum. The reaction yielded 430 mg
complex (0.41 mmol, 41%) as an orange powder. Spectroscopic
data for 4a: 1H NMR (250 MHz, 21 ◦C, CDCl3): 7.47–7.04 (m,
24H), 4.22 (s, br, 4H), 2.47 (s, 18H), 2.36–2.24 (m, 8H). 13C
1
{ H} (62 MHz, 21 ◦C, CDCl3): 133.0 (CH, 2J(C,P) = 13.0 Hz),
132.1 (CH, 3J(C,P) = 4.6 Hz), 131.7 (CH, 3J(C,P) = 4.3 Hz),
130.4 (CH), 62.2 (CH), 31.8 (CH2), 22.0 (CH3). 31P{ H} NMR
1
(101 MHz, 21 ◦C, CDCl3): 20.17.
[24] A. Ko¨ppl, H.G. Alt, J. Mol. Cat. A: Chem. 154 (2000) 45.

140
S. Taubmann, H.G. Alt / Journal of Molecular Catalysis A: Chemical 284 (2008) 134–140
[25] G.S. Rodman, K.R. Mann, Inorg. Chem. 27 (1988) 3338.
[26] R.H. Crabtree, G.E. Morris, J. Organomet. Chem. 135 (1977) 395.
[29] G. Mestroni, A. Camus, G. Zassinovich, J. Organomet. Chem. 73 (1974)
119.
[27] R.H. Crabtree, H. Felkin, G.E. Morris, J. Organomet. Chem. 141 (1977)
[30] R.H. Crabtree, J.M. Quirk, H. Felkin, T. Fillebeen-Khan, Synth. React.
Inorg. Met.-Org. Chem. 12 (1982) 407.
205.
[28] D. Hesk, P.R. Das, B. Evans, J. Labelled Compd. Radiopharm. 36 (1995)
497.
[31] J.L. Herde, J.C. Lambert, C.V. Senoff, Inorg. Syn. 15 (1974) 18.
[32] S.D. Robinson, B.L. Shaw, J. Am. Chem. Soc., Abstr. (1965) 4997.