Coordination chemistry and catalytic activity of N-heterocyclic carbene iridium(i) complexes

Article abstract of DOI:10.1039/b906016b

Iridium complexes [(CO)₂Ir(NHC-R)Cl] (R = Et-, 3a; PhCH ₂-, 3b; CH₃OCH₂CH₂-, 3c; o-CH ₃OC₆H₄CH₂-, 3d; NHC: N-heterocyclic carbene) are prepared via the carbene transfer from [(NHC-R)W(CO)₅] to [Ir(COD)Cl]₂. By using substitution with ¹³CO, we are able to estimate the activation energy (ΔG^?) of the CO-exchange in 3a-d, which are in the range of 12-13 kcal mol^-1, significantly higher than those for the phosphine analog [(CO) ₂Ir(PCy₃)Cl]. Reactions of 3b and 3d with an equimolar amount of PPh₃ result in the formation of the corresponding [(NHC-R)Ir(CO)(PPh₃)Cl] with the phosphine and NHC in trans arrangement. In contrast, the analogous reaction of 3a or 3c with phosphine undergoes substitution followed by the anion metathesis to yield the corresponding di-substituted [(NHC-R)Ir(CO)(PPh₃)₂]BF ₄ (5) directly. Treatment of 3b or 3d with excess of PPh₃ leads to the similar product of disubstitution 5b and 5d. The analysis for the IR data of carbonyliridium complexes provides the estimation of electron-donating power of NHCs versus phosphines. The NHC moiety on the iridium center cannot be replaced by phosphines, even 1,2-bis(diphenylphohino)ethane (dppe). All the carbene moieties on the iridium complexes are inert toward sulfur treatment, indicating a strong interaction between NHC and the iridium centers. Complexes 3a-c are active on the catalysis of the oxidative cyclization of 2-(o-aminophenyl)ethanol to yield the indole compound. The phosphine substituted complexes or analogs are less active.

Full text of DOI:10.1039/b906016b

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N-Heterocyclic Carbenes
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Westfälische Wilhelms-Universität, Münster, Germany
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PAPER
www.rsc.org/dalton | Dalton Transactions
Coordination chemistry and catalytic activity of N-heterocyclic carbene
iridium(I) complexes†
Ching-Feng Fu,a Yung-Hung Chang,a Yi-Hong Liu,a Shei-Ming Peng,a Cornelis J. Elsevier,*b Jwu-Ting Chen*a
and Shiuh-Tzung Liu*a
Received 26th March 2009, Accepted 4th June 2009
First published as an Advance Article on the web 2nd July 2009
DOI: 10.1039/b906016b
Iridium complexes [(CO)2Ir(NHC-R)Cl] (R = Et–, 3a; PhCH2–, 3b; CH3OCH2CH2–, 3c;
o-CH3OC6H4CH2–, 3d; NHC: N-heterocyclic carbene) are prepared via the carbene transfer from
[(NHC-R)W(CO)5] to [Ir(COD)Cl]2. By using substitution with 13CO, we are able to estimate the
activation energy (DG‡) of the CO-exchange in 3a–d, which are in the range of 12–13 kcal mol-1,
significantly higher than those for the phosphine analog [(CO)2Ir(PCy3)Cl]. Reactions of 3b and 3d with
an equimolar amount of PPh3 result in the formation of the corresponding [(NHC-R)Ir(CO)(PPh3)Cl]
with the phosphine and NHC in trans arrangement. In contrast, the analogous reaction of 3a or 3c with
phosphine undergoes substitution followed by the anion metathesis to yield the corresponding
di-substituted [(NHC-R)Ir(CO)(PPh3)2]BF4 (5) directly. Treatment of 3b or 3d with excess of PPh3 leads
to the similar product of disubstitution 5b and 5d. The analysis for the IR data of carbonyliridium
complexes provides the estimation of electron-donating power of NHCs versus phosphines. The NHC
moiety on the iridium center cannot be replaced by phosphines, even 1,2-bis(diphenylphohino)ethane
(dppe). All the carbene moieties on the iridium complexes are inert toward sulfur treatment, indicating
a strong interaction between NHC and the iridium centers. Complexes 3a–c are active on the catalysis
of the oxidative cyclization of 2-(o-aminophenyl)ethanol to yield the indole compound. The phosphine
substituted complexes or analogs are less active.
particularly by comparison with phosphines. The catalytic
activities of these iridium complexes on oxidative cyclization of
2-(o-aminophenyl)ethanol are also studied for comparison.
Introduction
Since the stable diaminocarbene was first isolated by Arduengo1,
N-heterocyclic carbenes (NHCs) have appeared as an prominent
class of ligands in both realms of organometallic chemistry and
catalysis.2–4 The NHC ligands have been considered to offer
even stronger s-donation that is able to stabilize the metal
complexes or catalyst-precursors than phosphines.3–6 Unlike the
steric and electronic effects of phosphines toward metal ions are
well established, however, the coordination behaviour of NHC is
less understood.2–8 Thus, numerous NHCs with the incorporation
of steric bulky substituents, other donors, rigid systems and chiral
functionality have been developed.3–5 In this context, we have
focused our research on the NHC character by means of the
investigation of structures, substitution and catalytic activity.
In recent work, evidenced by the studies of Tolman, electronic
parameters6a,7a, computation6b and calorimetric analysis of bond
strength7b, both Nolan and Crabtree’s groups concluded that
NHCs are more electron-donating than the phosphines. In this
paper we describe the preparation of a series of iridium(I) com-
plexes containing various substituted 4,5-dihydroimidazolylidene
ligands (denoted as NHC-R) and their coordination behaviours,
Results and discussion
Preparation of carbene complexes
The desired iridium carbene complexes were prepared via the
carbene transfer from tungsten carbene complex to [(COD)IrCl]2,
which we have reported previously (Scheme 1).9a–b Deprotonation
of the parent compound 1 was followed by quenching with the
appropriate electrophile to install the substituents at both nitrogen
positions of the imidazolidine ring. Treatment of 2 with an equal
molar amount of [(COD)IrCl]2 provides the corresponding irid-
ium complex [(CO)2Ir(NHC-R)Cl] 3 in excellent yields, in which
both carbonyl and carbene ligands are apparently transferred from
aDepartment of Chemistry, National Taiwan University, Taipei, 106, Taiwan.
E-mail: stliu@ntu.edu.tw, jtchen@ntu.edu.tw; Fax: +886 2 2363-6359
bVan ‘t Hoff Institute of Molecular Sciences, University of Amsterdam,
Amsterdam, Netherlands. E-mail: elsevier@science.uva.nl
† Electronic supplementary information (ESI) available: Table of kinetic
data from CO exchanging on 3b–3d and (PCy3)Ir(CO)2Cl. CCDC reference
numbers for 3a and 5b: 725408–725409. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/b906016b
Scheme 1 Preparation of NHC–iridium complexes.
Dalton Trans., 2009, 6991–6998 | 6991
This journal is
The Royal Society of Chemistry 2009
©

Table 1 Selected spectral data for iridium carbene and phosphine
W(0) to Ir(I). In this work, various intramolecular hemi-labile
ether donors are also introduced into the ligand system.
complexesa
The structural formulas for 3a–d are consistent with their NMR
and IR spectroscopic data. The IR spectra of 3 in the carbonyl
stretching region shows two vibrations in comparable intensity,
which indicates the cis arrangement of these two CO ligands.6a,9e
Two 13CO shifts are also observed by 13C NMR spectroscopy.
Furthermore, the molecular structure of 3a, determined by single-
crystal X-ray diffraction, is depicted in Fig. 1, along with selected
bond distances and angles. The crystal structure confirms the
details of the proposed formulation of 3. By monitoring the
samples of 3c and 3d in various solvents, there is no indication
for the interaction between the ether functionality on the NHC
substituents and the iridium center.
13C NMR,
C(NHC)–Ir/ppm
13C NMR,
C(CO)–Ir/ppm
Complex
31P NMR/ppm
3a
3bb
3c
197.8
198.6
199.3
198.6
181.7 (trans-CO),
168.2 (cis-CO)
181.4 (trans-CO)
168.3 (cis-CO)
181.6 (trans-CO),
168.1 (cis-CO)
181.5 (trans-CO),
168.1 (cis-CO)
—
—
—
3d
—
4bb
4d
5a
5b
5c
5d
6a
6b
202.1 (JP–C = 108.2) 171.7 (JP–C = 9.8)
24.6
201.9 (JP–C = 108.6) 171.4 (JP–C = 18.3) 24.9
201.8 (JP–C = 11.5)
203.1 (JP–C = 11.0)
204.5 (JP–C = 11.7)
204.2 (JP–C = 11.5)
203.8 (JP–C = 99.4)
204.9 (JP–C = 99.4)
184.3 (JP–C = 11.9) 20.1
183.6 (JP–C = 12.5) 19.8
184.2 (JP–C = 15.9) 19.7
184.2 (JP–C = 12.2) 19.7
171.4 (JP–C = 10.7) 29.9
172.0 (JP–C = 10.6) 29.5
a In CDCl3. J in Hz. b Ref. 9e.
◦
˚
Table 2 Selected bond distances (A) and bond angles ( ) of 5b
˚
Bond distances/A
Ir(1)–C(1)
Ir(1)–C(2)
Ir(1)–P(1)
Ir(1)–P(2)
C(1)–O(1)
N(1)–C(2)
N(2)–C(2)
1.836(8)
2.075(7)
2.328(2)
2.316(2)
1.156(8)
1.359(8)
1.324(8)
Ir(2)–C(55)
Ir(2)–C(56)
Ir(2)–P(3)
1.874(8)
2.092(7)
2.319(2)
2.329(2)
1.126(8)
1.312(8)
1.340(8)
Fig. 1 ORTEP plot of 3a (drawn with 30% probability ellipsoids).
Ir(1)–C(1) 1.88(1) A, Ir(1)–C(2) 2.110(9) A, Ir(1)–C(3) 1.77(1) A,
˚
˚
˚
Ir(2)–P(4)
˚
˚
˚
Ir(1)–Cl(1) 2.352(2) A, C(3)–O(2) 1.17(1) A, C(1)–O(1) 1.13(2) A,
C(2)–Ir(1)–C(3) 91.6(4)◦.
C(55)–O(2)
N(3)–C(56)
N(4)–C(56)
Treatment of 3b or 3d with triphenylphosphine in methy-
lene chloride at room temperature yielded the corresponding
phosphine-substituted complexes 4b and 4d, respectively. A car-
bonyl ligand trans to carbene moiety is found to be readily
displaced by the phosphine in a few minutes, as evidenced by
a color change from pale to deep yellow. Both 4b and 4d can
be isolated as stable species. However, the reaction of 3a with
an equimolar amount of PPh3 yields a di-substituted product 5a
instantaneously even at -50 ◦C, and left 50% of the starting 3a
un-reacted. Treatment of 3a with an excess of triphenylphosphine
followed by the anion metathesis leads to 5a, quantitatively. Com-
plex 3c behaves similarly as 3a. On the other hand, the substitution
reaction of 3a with one equivalent of tricyclohexylphosphine
results in the formation of mono-phosphine substituted product
6a. Clearly, the steric bulkiness of phosphines influences the
substitution reaction.
Bond angles/◦
C(1)–Ir(1)–C(2)
C(1)–Ir(1)–P(2)
P(2)–Ir(1)–P(1)
O(1)–C(1)–Ir(1)
176.2(3)
90.2(2)
175.91(7)
177.2(7)
C(55)–Ir(2)–C(56)
C(55)–Ir(2)–P(3)
P(3)–Ir(2)–P(4)
173.6(3)
90.3(2)
176.25(7)
178.3(7)
O(2)–C(55)–Ir(2)
dichloromethane–methanol. There are two independent molecules
co-existed in the unit cell. Relevant bond distances and angles are
reported in Table 2, while ORTEP plot for cationic part of 5b is pre-
sented in Fig. 2. The complexes show the expected square-planar
geometry around the iridium with a slight distortion of bond
angles around the metal center. As expected, the imidazolidine
ring is tilted by 86.9◦ relative to the square-planar coordination
All of the carbene iridium complexes were characterized by
NMR and IR spectroscopic methods. The selected spectral data
are listed in Table 1. The 31C NMR spectra of complexes 3–5 have
a characteristic shift for the carbenic carbon resonance around
200 ppm, while the carbonyl carbon resonance is found at upper
field in the range of 168–185 ppm (Table 1). 1H NMR spectra of all
iridium complexes exhibit a singlet resonance around 3.0–3.5 ppm
for the protons of imidazole ring (–CH2CH2–), indicating the
symmetrical environment for this ethylene moiety. The structure
of compound 5b was further determined using single-crystal X-ray
diffraction.
Suitable crystals of 5b (0.5CH2Cl2)(0.5MeOH) for X-ray
analysis were grown by slow evaporation from a solution of
Fig. 2 ORTEP plot of the cationic portion of 5b (drawn with 30%
probability ellipsoids).
6992 | Dalton Trans., 2009, 6991–6998
This journal is
The Royal Society of Chemistry 2009
©

Table 3 Carbonyl stretching frequencies for [(NHC-R)Ir(CO)2Cl]a
Complex
Solvent
uCO
uaverage
TEP
3a
3b
3c
3d
CHCl3
CHCl3
CH2Cl2
CHCl3
2067, 1983
2067, 1983
2072, 1987
2070, 1986
2025
2025
2030
2028
2051
2051
2055
2053
a In cm-1.
sphere of the iridium, indicating that the N-benzyl groups are
seated on the axial positions of the coordination plane. All bond
lengths and angles of 5b are in the normal range as compared to
those of the related species.
Fig. 4 Comparison of spectral data for 6b, 7b and Vaska’s complex.
the minimal differences in chemical shifts of carbonyl-carbons,
carbonyl stretching frequencies or 31P shifts are somewhat surpris-
ing. Accordingly, the ligand strength of NHC and phosphines is
not directly reflected by the spectroscopic observations.
Spectroscopic comparison
There is growing experimental evidence that NHC donors are
stronger s-donors toward transition metal ions when compared
to their phosphine-based counterparts. Among this context,
the carbonyl-containing transition metal complexes are often
employed to illustrate the donating property of the NHC donors.6–8
From a linear correlation between the average infrared stretching
frequency of the [(L)Ir(CO)2Cl] (L: NHC and phosphine) sys-
tem and the Tolman electronic parameter (TEP), Crabtree and
co-workers concluded that N-heterocyclic carbenes are stronger
electron donors than most of the phosphine ligands.6a Such
a correlation was further modified by Nolan’s group and an
equation for the estimation of TEP is formulated as: TEP (cm-1) =
0.847[uCO(average)] + 336 cm-1.7c By adopting this equation, we
calculate the TEP values for the NHC-R prepared in this work
(Table 3). As shown in the table, TEP values for NHC-R are in
Treatment of 4b or 4d with triphenylphosphine promptly gen-
erated the corresponding cationic complexes 5b or 5d (scheme 1),
wherein the phosphines are seated in trans fashion. However,
the PCy3-disubstituted species was not detected under similar
conditions, presumably due to the steric hindrance from tricyclo-
hexylphosphine. We examine the infrared stretching frequencies of
carbonyls in 5b and [{(PPh3)3Ir(CO)}PF6] (Fig. 5), a substantial
red shift over 20 cm-1 in the NHCs-Ir species (1992–1994 cm-1)
than in [(PPh3)3Ir(CO)]+ (2017 cm-1) is shown, indicating that
the extent of a back-bonding to a CO group increases as the
s-donating ability of its trans ligand increases, i.e. NHC > PPh3.
excellent agreement with most of the reported NHC ligands6,7
,
indicating that the ether functionality on the NHC substituents
has little influence on the coordination, i.e. the ether donors ought
to remain non-coordination mode.
In order to further learn about the ligand effect, selected
spectroscopic data of triphenylphosphine substituted iridium
carbene complexes 4b and 7a9e, as well as the Vaska’s complex
8a are summarized in Fig. 3. Both complexes 4b and 7a have
similar NMR measurements, except the data for NHC carbon.
The saturated backbones in 4b and unsaturated in 7a show a
significant difference in 13C chemical shifts of carbene-carbon by
about 25 ppm. However, other spectral data such as 31P shifts
or carbonyl stretching frequencies are generally negligible. Such
kind of observation is also applicable for tricyclohexylphosphine
substituted iridium complexes (Fig. 4). Considering that the NHCs
are expected to be stronger s-donating donors than phosphines,
Fig. 5 Comparison of spectral data for 5b, 7c and Vaska’s complex.
Reaction with sulfur
It is well documented that the reaction of tetraamino-substituted
olefins or diamino-substituted carbenes with sulfur yields the
corresponding thiourea.9b Thus, the reactions of 3, 4 and 5 with
sulfur were investigated to probe the stability of NHC carbene
complexes. A sample of an equal molar amount of 3b and S8
in CDCl3 was monitored by NMR spectroscopy. We did not
observe the formation of thiourea (1,3-dibenzylimidazolidine-2-
thione) even under refluxing temperature for 24 h. In fact, the
complex remains intact without decomposition as confirmed by
its NMR spectrum.
On the other hand, reaction of 4b or 5b with sulfur readily results
in the disappearance of the starting material accompanied with the
formation of triphenylphosphine sulfide. In these reactions, the
thiourea compound was not detected by 1H NMR measurement.
By carrying out these reactions in the presence of CO, we were
able to isolate the iridium complex 3b quantitatively by separating
it from the phosphine sulfide, suggesting that the metal–carbene
Fig. 3 Comparison of spectral data for 4b, 7a and Vaska’s complex.
This journal is
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Dalton Trans., 2009, 6991–6998 | 6993
©

Table 4 Kinetic data for CO exchanging on 3aa
[CO]/mM
[3a]/mM
Half-height Width/Hz
Dv/Hz
k
obs/s-1
k/M-1.s-1
DG‡/kcal mol-1
DG‡(average)/kcal mol-1
0
9.8
9.8
9.8
0.66
10.60
11.20
17.71
0
—
—
—
—
—
12.7
—
1.5
3.1
4.4
9.94
10.54
17.05
31.2
33.1
53.6
3.2 ¥ 103
3.4 ¥ 103
2.7 ¥ 103
12.7
12.7
12.8
19.5
a See Experimental.
Table 5 Activation energy for CO exchange of Ir carbonyl complexesa
bonds are rather stable. This outcome is quite different from the
carbene tungsten complexes, which we have studied previously.9b
Scheme 2 summarizes the reactivity of W–C(carbene) toward sulfur.
[(NHC-CH2Ph)W(CO)5] (2b) does not react with sulfur in a
THF solution, whereas M–C bonds in the phosphine substituted
complexes undergo the cleavage reaction to yield 9. Apparently,
the stability of M–carbene also depends on the nature of metal
ion.
Complex
3a
3b
3c
3d
[cis-(PCy3)Ir(CO)2Cl]
~10.6
DG‡/kcal mol-1
12.7
12.9
12.8
12.9
a See ESI.†
[cis-(PPh3)Ir(CO)2Cl] is found to undergo the disproportionation
to yield [(PPh3)2Ir(CO)3]+[(CO)2IrCl2]-.12
Under the CO atmosphere, the phosphine substituted com-
plexes 4–6 are readily converted into 3. In a typical case, a CDCl3
solution of 5b was bubbled with CO at room temperature for
5 min, and then monitored by 31P NMR spectrometry. The signal
at 19.8 ppm (31P shift for 5b) disappeared accompanied with the
occurrence of free PPh3 shown at 5 ppm, indicating the dissociation
1
of phosphine from the complex. Both H and 13C NMR spectra
of the resulting solution further confirm the formation of 3b.
We also noticed that treatment of 4b with AgBF4 in CD3CN
promptly caused the formation of 3b and 5b via disproportiona-
tion, as evidenced by the 1H NMR measurement. Presumably, the
abstraction of chloride from 4b readily generates the free site for
the coordination of PPh3 or CO donors and leads to the products.
The lack of detection for bis-carbene iridium species indicates
no dissociation of NHC donors from the complex during this
disproportionation process.
Scheme 2 Cleavage of W–ccarbene bonds by sulfur.
Ligand substitution-CO exchange
In order to understand the substitution of carbonyl in NHC
iridium complexes, reactions of 3 with 13CO was examined. A
NMR tube loaded with 3 in CDCl3 was exposed to the atmosphere
of 13CO and the sample was monitored by 13C NMR spectroscopy.
Ligand substitution-bis(diphenylphosphino)ethane (dppe)
A
13C shift at 168 ppm appears immediately, which is due to
It is known that the coordination ability of a bidentate toward
the metal ion is generally stronger than that of a monodentate
due to the chelation. Thus, the reaction of [cis-(PPh3)Ir(CO)2Cl]
with an equimolar amount of dppe yields [(dppe)Ir(CO)2]Cl via
the substitution of PPh3 and chloride, in agreement with the
rules of trans effect. However, reaction of 3b with excess of
dppe results in the formation of 10(Scheme 4), in which the bis-
phosphine ligand replaces chloride and a CO. The NHC moiety
remains intact, again demonstrating the good strength of Ir–CNHC
bond. Substitution also occurs from the reaction of 5b with dppe
the replacement of CO cis to the NHC moiety. Eventually all
carbonyls in 3 are replaced upon prolong standing (Scheme 3).
The first carbonyl substitution may be attributed to the cis
labilization.10 The rate of CO self-exchange in 3a was determined
by 13C NMR line broadening techniques.11 The change in the line
width at half-height of the resonance at 168 ppm is measured as
a function of the concentration of 13CO, and the rate constants
are estimated for complex 3a (Table 4), which provides the
evaluation of the activation energy (DG‡). The analogous kinetic
analysis for 3b–3d and [cis-(PCy3)Ir(CO)2Cl] were estimated in a
similar manner and are listed in Table 5. There is no significant
difference in DG‡ for all carbene complexes 3a–3d, which are
higher than that for [cis-(PCy3)Ir(CO)2Cl]. In contrast, complex
Scheme 3 CO exchange on complex 3
Scheme 4 Substitution with dppe.
6994 | Dalton Trans., 2009, 6991–6998
This journal is
The Royal Society of Chemistry 2009
©

to yield 10 exclusively, i.e. both triphenylphosphine ligands are
replaced by dppe. From the above observation, it can be concluded
that NHC ligands are not likely to dissociate from the metal
center presumably due to the stronger basicity of NHCs versus
phosphines.5f
According to the reported work14, the postulated pathway for
the catalytic reactions is shown in Scheme 5. The formation of
alkoxy-metal species I under basic conditions, which undergoes
b-elimination to yield the corresponding aldehyde II. Nucleophilic
attack of the amine to the aldehyde moiety generates the imine
III. The isomerization of double bond affords the final product
indole. The oxidation of alcohol facilitated by the NHC–iridium
complexes appears to be crucial in such a catalytic process. But
the generally better activity of the NHC-coordinating species
rather than the phosphine-coordinating species is likely due to
the stability of the complex.
Catalysis
According to the coordination behaviour presented above, it
would be interesting to test the catalytic activity of NHC iridium
complexes. In recent studies, we have shown that the NHC
complexes of iridium(I) are excellent pre-catalysts for N-alkylation
of amines with alcohols (eqn (1))9e, which involves the metal-
assisted hydrogen transfer reactions.13 Adopting this type of
reaction, we investigate the activity of iridium complexes 3–6 as
well as Vaska’s complexes on the catalysis of oxidative cyclization
of 2-(o-aminophenyl)ethanol leading to the formation of the
indole molecule (eqn (2)), aiming to confirm if the electronic
modification would have any significant effect on the catalytic
activity.
Scheme 5 Catalytic pathway of the indole formation.
(1)
From our results, we can conclude that the NHC-carbonyl pre-
catalysts 3a–c showed higher activity than the related phosphine
complexes except 3d, indicating that the coordination of NHC
ligands to the metal center significantly enhance the activity of
catalysis. For the relatively low efficiency of pre-catalyst 3d, it is
presumably due to the anisole–ether donor. We believe that the
coordination of a rigid donor toward the metal center during the
catalytic cycle brings down the activity. For the reaction performed
with the mono-triphenylphosphine substituted complex 4b as
the catalyst the product was efficiently obtained, but not the
tricyclohexylphosphine substituted ones 6a,b.
After several attempts, we found that the quantitative conver-
sion of 2-(o-aminophenyl)ethanol into indole can be achieved by
carrying out the reaction in 0.5 mmol scale with the use of 20 mol%
CsOH as the base and 1 mol% loading of 3a in toluene at 100 ◦C
for 1.5 h. The indole compound was obtained as the single product
without any other side product. When the optimized reaction
conditions are applied to various iridium complexes, Table 6 shows
the catalytic results for the cyclization. Comparison of the catalysts
for activity under the same conditions shows that 3a is the best
catalyst among all iridium complexes.
(2)
Summary
With this work we have provided the influence of NHC donor on
the ligand substitution on iridium(I) ions as well as the stability
toward ligand substitution. The IR analysis of carbonyl complexes
offers the donating ability of NHCs versus phosphines. These
effects have important implications on the catalytic properties
of 3a–c, these being considerably enhanced when compared to
the related phosphine complexes in the oxidative cyclization of
2-aminophenylethanol. We are currently performing methods for
catalytically activity of these NHC iridium complexes on other
reactions.
We find complexes 3 and 4 are all active for the oxidative cycliza-
tion of 2-aminophenylethanol. Comparison of the catalysts for
activity in this reaction (Table 6) shows that 3a is the most active,
with 100% conversion in 1.5 h. corresponding to a TOF of 66 h-1.
This system is among the most active oxidative cyclization that
forms indole, and comparable with that for RuCl2(PPh3)3complex
(TOF: 10 h-1 at 110 ◦C)14, with that for [Cp*IrCl2]2 complex for a
cascade cyclization and alkylation (TOF: < 4 h-1 at 110 ◦C).15
Table 6 Oxidative cyclization catalyzed by various Ir(I) complexesa
Complex
Yield (%)b
Complex
Yield (%)b
Experimental
3a
3b
3c
3d
4b
4d
5a
100
92 (88)c
93
53
85
25
16
5b
10
29
12
52
33
66
8
General information
6a
6b
All reactions, manipulations and purification steps were per-
formed under a dry nitrogen atmosphere. Tetrahydrofuran
was distilled under nitrogen from sodium benzophenone ketyl.
Dichloromethane and acetonitrile were dried over CaH2 and
distilled under nitrogen. Other chemicals and solvents were of
analytical grade and were used after degassed process. Tungsten
carbene complex 1, 2a, 2b, 3b, 4b and 7a,b were prepared
accordingly to the method reported previously.9d,9e
cis-(PPh3)Ir(CO)2Cl
cis-(PCy3)Ir(CO)2Cl
trans-(PPh3)2Ir(CO)Cl
trans-(PCy3)2Ir(CO)Cl
a Reaction conditions: 2-(o-aminophenyl)ethanol (0.5 mmol), 1 mol%
loading of Ir(I) complex, 20 mol% CsOH in toluene (0.25 mL) at 100 ◦
C
for 1.5 h. b Based on the NMR integration with the internal standard.
c Isolated yield.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 6991–6998 | 6995
©

=
Nuclear magnetic resonance spectra were recorded in CDCl3 on
a Bruker AVANCE 400 spectrometer. Chemical shifts are given
in parts per million relative to Me4Si for 1H and 13C NMR,
and relative 85% H3PO4 for 31P NMR. Infrared spectra were
measured on a Nicolet Magna-IR 550 spectrometer (Series-II)
as KBr pallets, unless otherwise noted.
–OCH3). 13C NMR (CDCl3, 100.6 MHz) d/ppm: 199.3 (M C),
181.6 (trans-CO), 168.1 (cis-CO), 71.1, 58.9, 50.9, 50.1. IR (KBr)
u
CO: 2062, 1978 cm-1. IR (CHCl3) uCO: 2072, 1987 cm-1. Anal. calcd
for C11H18ClIrN2O4: C 28.11, H 3.86, N 5.96. Found: C 27.82, H
3.55, N 6.03.
Preparation of 3d. This procedure was similar to that for 3a
except the use of 2d as the carbene source. Complex 3d was
obtained as yellow solids (yield 56%). 1H NMR (CDCl3, 300 MHz)
d/ppm: 7.38–7.40 (m, 2 H, Ar–H), 7.25–7.31 (m, 2 H, Ar–H),
6.92–6.97 (m, 2 H, Ar–H), 6.86–6.89 (m, 2 H, Ar–H), 5.34 (d, 2
Preparation of 2c. A 20 mL Schlenk tube loaded with 55%
NaH (0.166 g, 3.81 mmol) was washed with hexane (3 ¥ 5 mL).
Compound 1 (0.15 g, 0.381 mmol) and anhydrous THF (5 mL)
were added to the above tube. The suspended solution was stirred
at ambient temperature for 24 h. 2-Bromoethyl methyl ether
(0.18 mL, 1.91 mmol) was then syringed into the reaction vessel
and stirred for another 12 h. Upon the addition of water to quench
the excess of NaH, dichloromethane (2 ¥ 20 mL) was added
for the extraction. The organic layer was collected, dried with
Na2SO4, and concentrated. The crude product was passed through
a filtration column to yield 2d as yellow oil (0.17 g, 87%). 1H NMR
(CDCl3, 400 MHz) d/ppm: 3.92 (t, 4 H, –CH2–, 3JHH = 5.1 Hz),
2
H, –N–CHH–Ph, JHH = 14.9 Hz), 4.75 (d, 2 H, –N–CHH–Ph,
2JHH = 14.9 Hz), 3.82 (s, 6 H, –OCH3), 3.43–3.50 (m, 4 H, imi–
H). 13C NMR (CDCl3, 100.6 MHz) d/ppm: 198.6 (M C), 181.5
=
(trans-CO), 168.1 (cis-CO), 157.4, 129.8, 129.2, 123.3, 120.6, 110.3
(Ar–C), 55.3 (ArCH2N), 49.1 (NCH2–CH2N), 48.7 (OCH3). IR
(KBr) uCO: 2070, 1986 cm-1. Anal. calcd for C21H22ClIrN2O4:
C 42.46, H 3.73, N 4.72. Found: C 42.09, H 3.46, N 4.52.
Preparation of 4d. A solution of PPh3 (4.2 mg, 0.0160 mmol)
in CH2Cl2(1 mL) was added to a solution of complex 3b (10.0 mg,
0.0168 mmol) in CH2Cl2 (1 mL) under N2. The resulting solution
was stirred at ambient temperature for 1 h. Upon concentration
of the reaction mixture, the residue was washed by ether (2 ¥
1 mL). The desired product 5b was obtained as a pale yellow solid
3
3.68 (s, 4 H, imi–H), 3.61 (t, 4 H, –CH2–, JHH = 5.1 Hz), 3.35
13
=
(s, 6 H, –OCH3). C NMR (100.6 MHz) d/ppm: 208.6 (M C),
200.9(trans-CO), 198.2 (cis-CO), 72.3, 58.9, 52.7, 49.9 (sp3-C).
IR (KBr) uCO: 2062, 1901 cm-1. Anal. calcd for C14H18N2O7W:
C 32.96, H 3.56, N 5.49. Found: C 32.71, H 3.66, N 5.20.
1
Preparation of 2d. This procedure was similar to that for 2c
except the electrophile. Complex 2d was obtained as pale yellow
solids (yield 62%). 1H NMR (CDCl3, 400 MHz) d/ppm: 7.26 (t, 2
H, Ar–H, 3JHH = 5.6 Hz), 7.16 (d, 2 H, Ar–H, 3JHH = 5.6 Hz), 6.95
(t, 2 H, Ar–H, 3JHH = 5.6 Hz), 6.89 (d, 2 H, Ar–H, 3JHH = 5.6 Hz),
5.01 (s, 4 H, –CH2–), 3.84 (s, 6 H, –OCH3), 3.50 (s, 4 H, imi–
(11.1 mg, 65%). H NMR (CDCl3, 400 MHz) d/ppm: 7.65–7.69
3
(m, 6 H, Ar–H), 7.58 (d, 2 H, Ar–H, JHH = 7.1 Hz), 7.30–7.50
3
(m, 9 H, Ar–H), 7.24–7.27 (t, 2 H, Ar–H, JHH = 8.0), 6.92 (t,
3
3
2 H, Ar–H, JHH = 7.1 Hz), 6.87 (d, 2 H, Ar–H, JHH = 8.0),
5.67 (d, 2 H, –CHHAr, 2JHH = 14.9 Hz), 5.06 (d, 2 H, –CHHAr,
2JHH = 14.9 Hz), 3.80 (s, 6 H, –OCH3), 3.41–3.56 (m, 4 H, imi–H).
H). 13C NMR (CDCl3, 100.6 MHz) d/ppm: 209.6 (M C), 201.3
C NMR (CDCl3, 100.6 MHz) d/ppm: 201.9 (d, M C, JC–P
=
=
13
=
=
(trans-CO), 198.0 (cis-CO), 157.6, 129.0, 128.4, 124.3, 120.6, 110.4
(Ar–C), 55.3 (ArCH2N), 51.6 (NCH2–CH2N), 48.3 (OCH3). IR
(KBr) uCO: 2061, 1909 cm-1. HR-FAB-MS m/z: 634.0926 ([M]+,
calcd for C24H22N2O7W: 634.0936). Anal. calcd for C24H22N2O7W:
C 45.37, H 3.65, N 4.41. Found: C 45.03, H 3.35, N 4.21.
108.6 Hz), 171.4 (d, cis-CO, JC–P = 18.3 Hz), 157.5, 134.6 (d, JC–P
11.5 Hz), 133.6 (d, JC–P = 48.9 Hz), 130.2, 129.6, 128.6, 127.7 (d,
1
JC–P = 10.0 Hz), 124.6, 120.7, 110.2, 55.3, 48.7, 48.5. 31P { H}
NMR (CDCl3, 162 MHz) d/ppm: 24.9. IR (KBr) uCO: 1946 cm-1.
Anal. calcd for C38H37ClIrN2O3P: C 55.10, H 4.50, N 3.38. Found:
C 54.82, H 4.19, N 3.01.
Preparation of 3a. A mixture of 2a (75.0 mg, 0.167 mmol) and
[Ir(COD)Cl]2 (0.118 g, 0.175 mmol) in a 50 mL flask was evacuated
and re-filled with N2 three times. Anhydrous CH2Cl2 (15 mL)
was added to the above mixture and then stirred at ambient
temperature for 72 h. The colour of the solution changed from
yellow to black slowly. The resulting mixture was filtered through
Celite and concentrated. The brown residue was chromatographed
on silica gel with elution of hexane–ethyl acetate (3 : 1) and a
yellow band was collected. Upon concentration, the product was
Preparation of 5a. To a flask was placed with 3a (5.0 mg,
0.0122 mmol) in anhydrous CH2Cl2 (1 mL) under N2. A solution
of triphenylphosphine (6.7 mg, 0.0256 mmol) in CH2Cl2 was slowly
syringed into the above flask. The resulting solution was stirred at
room temperature for 3 h and then concentrated. To this residue
was added a solution of KPF6 (4.3 mg, 0.0232 mmol) in CH3CN
(1 mL). After stirring at room temperature for another hour, the
solution was concentrated, extracted with CH2Cl2–H2O, collected
the organic layer, dried with Na2SO4, and re-precipitated by
CH2Cl2–ether. The desired product 6a was obtained as a yellow
solid (5.8 mg, 47%). 1H NMR (CDCl3, 400 MHz) d/ppm: 7.41–
7.52 (m, 30 H, Ar–H), 3.01 (s, 4 H, imi–H) 2.89 (q, 4 H,
1
obtained as a yellow solid (56.2 mg, 82%). H NMR (CDCl3,
400 MHz) d/ppm: 3.87 (dq, 1 H, –NCHH–Me, J = 14, 7 Hz),
3
3.77 (dq, 1 H, –NCHH–Me,2J = 14 Hz, J = 7.0 Hz), 3.65 (s, 4
H, imi–H), 1.23 (t, 6 H, –CH3, 3J = 7.0 Hz). 13C NMR (CDCl3,
100.6 MHz) d/ppm: 197.8 (M C), 181.7 (trans-CO), 168.2 (cis-
–CH2–CH3, 3JHH = 7.2 Hz), 0.31 (t, 6 H, –CH3, 3JHH = 7.2 Hz).
=
13
=
CO), 48.0 (NCH2–CH2N), 45.1 (NCH2–Me), 13.0 (–CH3). IR
(KBr) uCO: 2057, 2001 cm-1. Anal. calcd for C9H14ClIrN2O2:
C 26.37, H 3.44, N 6.83. Found: C 26.57, H 3.57, N 6.33.
C NMR (d6-DMSO, 100.6 MHz) d/ppm: 201.9 (M C), 184.3
(trans-CO), 133.7, 131.5, 128.7, 47.6, 45.0, 11.8. 31P { H} NMR
1
(CDCl3, 121 MHz) d/ppm: 20.1, -143.7 (septet). IR (KBr) uCO
:
1993 cm-1. Anal. calcd for C44H44F6IrN2OP3: C 52.02, H 4.37,
N 2.76. Found: C 51.77, H 4.84, N 2.42.
Preparation of 3c. This procedure was similar to that for 3a
except the use of 2c as the carbene source. Complex 3c was
obtained as yellow oil (yield 83%): 1H NMR (CDCl3, 400 MHz)
d/ppm: 4.02–4.08 (m, 2 H), 3.76–3.84 (m, 2 H), 3.78 (s, 4 H,
imi–H), 3.66–3.71 (m, 2 H), 3.58–3.63 (m, 2 H), 3.34 (s, 6 H,
Preparation of 5b. As described above for 5a, the addition of
triphenylphosphine (2 equivalent) to 3b gave 5b as yellow solids
(92%). 1H NMR (400 MHz, CDCl3) d/ppm: 7.67–7.46 (m, 30 H,
6996 | Dalton Trans., 2009, 6991–6998
This journal is
The Royal Society of Chemistry 2009
©

Ar–H), 7.13 (t, J = 7 Hz, 2 H, Ar–H), 6.92 (t, J = 7 Hz, 4 H, Ar–
H), 6.43 (d, J = 7 Hz, 4 H, Ar–H), 3.85 (s, 4 H, ArCH2N), 2.82
(s, 4 H, NCH2–CH2N). 13C NMR (100 MHz, CDCl3) d/ppm:
H, NCH2–CH2N), 2.32–1.13 (m, 33 H, Cy). 13C NMR (100 MHz,
=
CDCl3) d/ppm: 204.9 (d, JP–C = 99.4 Hz, Ir C), 172.0 (d, JP–C
=
10.6 Hz, CO), 136.8, 128.6, 127.6 (Ar–C), 54.5 (ArCH2N), 48.1
(d, JP–C = 3.5 Hz, NCH2–CH2N), 33.6 (d, JP–C = 25.4 Hz, Cy),
=
203.1 (t, JP–C = 11.0 Hz, Ir C), 183.6 (t, JP–C = 12.5 Hz, CO),
1
133.6, 133.5, 133.4, 132.7, 131.6, 131.5, 131.4, 131.1, 128.8, 128.7,
30.1 (s, Cy), 27.7 (d, JP–C = 10.4 Hz, Cy), 26.8 (s, Cy). 31P { H}
128.6, 128.4, 128.1 (phenyl), 54.7 (ArCH2N), 48.2 (NCH2–CH2N).
(161.9 MHz, CDCl3) d/ppm: 29.5 (s). IR (KBr) nCO: 1932 cm-1.
Anal. calcd for C36H51ClIrN2OP: C 54.98, H 6.54, N 3.56. Found:
C 54.71, H 6.61, N 3.23.
1
31P { H} NMR (161.9 MHz, CDCl3) d/ppm: 19.8 (s), -144.0
(sept, JP–F = 712.4 Hz). IR (KBr) uCO: 1994 cm-1. Anal. calcd for
C54H48F6IrN2OP3: C 56.89, H 4.24, N 2.46. Found: C 57.03,
H 4.62, N 2.33.
Preparation of 7c. The preparation of 7c is similar to that of 5b.
Yield 80%. IR (KBr) uCO: 1992 cm-1. 1H NMR (400 MHz, CDCl3)
d/ppm: 7.55–7.51 (m, 6 H, Ar–H), 7.43–7.39 (m, 12 H, Ar–H),
7.32–7.31 (m, 12 H, Ar–H), 7.14 (t, J = 7.4 Hz, 2 H, Ar–H), 6.96
Preparation of 5c. As described above for 5a, addition of
triphenylphosphine (2 equivalent) to 3c gave 5c as yellow solids
(yield 66%). 1H NMR (CDCl3, 400 MHz) d/ppm: 7.52–7.57 (m,
12 H, Ar–H), 7.48–7.50 (m, 18 H, Ar–H), 3.05 (s, 4 H, imi–H),
2.96 (t, 4 H, N–CH2–CH2–O, 3JHH = 5.4 Hz), 2.79 (s, 6 H, –OCH3),
2.75 (t, 4 H, N–CH2–CH2–O, 3JHH = 5.4 Hz). 13C NMR (CDCl3,
=
(t, J = 7.5 Hz, 4 H, Ar–H), 6.52 (s, 2 H, C CHN), 6.50 (d, J =
7.3 Hz, 4 H, Ar–H), 4.19 (s, 4 H, ArCH2N). 13C NMR (100 MHz,
CDCl3) d/ppm: 183.6 (t, JP–C = 12.5 Hz, CO), 173.5 (t, JP–C
=
=
11.0 Hz, Ir C), 133.6, 133.5, 133.4, 132.6, 131.8, 131.5, 131.2,
=
100.6 MHz) d/ppm: 204.5 (M C), 184.2 (t, trans-CO, JC–P
=
=
129.1, 129.1, 129.0, 128.9, 128.8 (Ar–C), 122.2 (NCH CHN),
1
54.7. 31P { H} (161.9 MHz, CDCl3) d/ppm: 20.4, 143.9 (septet).
15.9 Hz), 133.9 (t, JC–P = 6.1 Hz), 131.9 (t, JC–P = 27.5 Hz), 131.5,
128.8 (t, JC–P = 5.2 Hz), 68.6, 58.1, 49.8, 48.9. 31P { H} NMR
1
Anal. calcd for C54H46F6IrN2OP3: C 56.99, H 4.07, N 2.46. Found:
C 56.59, H 4.57, N 2.22.
(CDCl3, 162 MHz) d/ppm: 19.7, -143.9 (septet). IR (KBr) uCO
:
1991 cm-1. Anal. calcd for C46H48F6IrN2O3P3: C 51.35, H 4.50, N
2.60. Found: C 50.98, H 4.24, N 2.38.
Preparation of 10. A mixture of 3b (7 mg, 0.013 mmol) and
dppe (5.2 mg, 0.013 mmol) in CHCl3 (1 mL) was stirred for
10 min. The mixture was concentrated and then added a solution of
NaPPh4 (4.5 mg, 0.013 mmol) in pre-dried CH3CN (1 mL). After
stirring for 30 min, the acetonitrile was removed under vacuum
and extracted with CHCl3. Complex 9 was obtained as yellow
solids. 1H NMR (400 MHz, CDCl3) d/ppm: 7.54–7.29 (m, 36 H,
Ar–H), 7.12–7.00 (m, 4 H, Ar–H), 6.89–6.85 (m, 6 H, Ar–H),
6.77–6.73 (m, 4 H, Ar–H), 5.08 (d, J = 14.8 Hz, 2 H, ArCH2N),
3.44 (d, J = 14.8 Hz, 2 H, ArCH2N), 3.15–2.90 (m, 4 H, NCH2–
CH2N), 2.31–2.09 (m, 4 H, PCH2–CH2P). 13C NMR (100 MHz,
Preparation of 5d. As described above for 5a, addition of
triphenylphosphine (2 equivalent) to 3d gave 5b as yellow solids
(yield 40%). 1H NMR (CDCl3, 400 MHz) d/ppm: 7.54–7.59 (m,
18 H, Ar–H), 7.46–7.49 (m, 12 H, Ar–H), 7.13 (t, 2 H, Ar–H,
3
3JHH = 8.0 Hz), 6.75 (d, 2 H, Ar–H, JHH = 8.0 Hz), 6.35 (t, 2
3
3
H, Ar–H, JHH = 7.0 Hz), 6.11 (d, 2 H, Ar–H, JHH = 7.0 Hz),
4.02 (s, 4 H, –CH2Ar), 3.53 (s, 6 H, –OCH3), 2.71 (s, 4 H, imi–
H). 13C NMR (CDCl3, 100.6 MHz) d/ppm: 204.2 (M C), 184.2
=
(trans-CO), 134.0 (t, JC–P = 6 Hz), 132.0 (t, JC–P = 27 Hz), 131.6
(s), 130.6, 130.1, 129.0 (t, JC–P = 5 Hz), 55.0, 49.1, 48.6. 31P { H}
1
=
CDCl3) d/ppm: 191.45 (dd, JP–C = 155, 87.4 Hz, Ir C), 163.9
NMR (CDCl3, 162 MHz) d/ppm: 19.7, 144.0 (septet). IR (KBr)
(dd, JP–C = 100, 49.4 Hz, CO), 136.1, 134.7, 132.9, 132.7, 132.3,
132.2, 132.0, 131.8, 131.3, 130.1, 129.6, 129.3, 129.2, 129.1, 129.0,
128.9, 128.1, 127.5, 125.3, 121.5 (Ar–C), 54.4, 48.4, 27.5, 26.0.
u
CO: 1991 cm-1. Anal. calcd for C56H52F6IrN2OP3: C 56.04, H 4.37,
N 2.33. Found: C 55.78, H 4.02, N 2.11.
1
31P { H} (161.9 MHz, CDCl3) d/ppm: 49.6 (d, J = 14.8 Hz),
Preparation of 6a. As described above for 4d, addition of
tricyclohexylphosphine (1 equivalent) to 3a gave 6b as light yellow
solids (88%). 1H NMR (CDCl3, 300 MHz) d/ppm: 4.15 (dq, 2 H,
–CHH–, 2JHH = 14.1 Hz, 3JHH = 7.0 Hz), 3.83 (dq, 2 H, –CHH–,
2JHH = 14.1 Hz, 3JHH = 7.0 Hz), 3.84 (m, 2 H, –CH2–), 3.61 (s, 4
H, imi–H), 1.21–3.32 (m, 39 H, Cy and –CH3). 13C NMR (CDCl3,
100.6 MHz) d/ppm: 203.8 (d, JC–P = 99.4 Hz), 171.7 (d, cis-CO,
48.0 (d, J = 14.8 Hz). IR (KBr) nCO: 1992 cm-1. Anal. calcd for
C44H42F6IrN2OP3: C 52.12, H 4.18, N 2.76. Found: C 51.82,
H 3.97, N 2.45.
Reaction of 3b with sulfur. Iridium complex 3b (10 mg) was
treated with sulfur S8 (2 mg) in CDCl3 (0.7 mL). After sonication
1
for 2 h, the H NMR spectrum of the sample was taken. The
JC–P = 10.7 Hz), 48.0 (d, JC–P = 3.8 Hz), 45.0, 33.6 (d, JC–P
=
obtained spectral data are essentially identical to those for 3b.
25.3 Hz), 31.7, 30.2, 27.8 (d, JC–P = 10.7 Hz), 27.0, 22.8, 14.3, 13.2.
1
31P { H} NMR (CDCl3, 121 MHz) d/ppm: 29.9. IR (KBr) uCO
:
Reaction of 4b or 5b with sulfur in the presence of CO atmosphere.
Iridium complex 4b or 5b (50 mg) was treated with sulfur S8
(1.2 mg) in CHCl3 (3 mL) in the presence of CO atmosphere. After
refluxing for 24 h, the 31P NMR spectrum of the reaction mixture
showed one signal corresponding to the triphenylphosphine
sulfide. The reaction mixture was concentrated and the residue
was chromatographed on silica gel with elution of hexane–ethyl
acetate. A yellow band was collected and concentrated to give
yellow solids (40 mg). The 1H NMR spectrum of this yellow sample
is essentially identified to that for 3b.
1930 cm-1. Anal. calcd for C26H47ClIrN2OP: C 47.15, H 7.15, N
4.23. Found: C 46.93, H 7.01, N 3.98.
Preparation of 6b. Anhydrous CH2Cl2 (5 mL) was added
to a mixture of 3b (72 mg, 0.135 mmol) and PCy3 (37.9 mg,
0.135 mmol) with stirring under nitrogen atmosphere. After
stirring at room temperature for 2.5 h, the reaction mixture was
concentrated and the residue was chromatographed on silica gel
with elution of ethyl acetate–hexane (1 : 3). A yellow band was
collected and concentrated to yield 6b as yellow solids (98 mg,
92%). 1H NMR (400 MHz, CDCl3) d/ppm: 7.51 (d, J = 7.4 Hz, 4
H, Ar–H), 7.39–7.26 (m, 6 H, Ar–H), 5.52 (d, J = 14.6 Hz, 2 H,
ArCH2N), 5.01 (d, J = 14.6 Hz, 2 H, ArCH2N), 3.43–3.38 (m, 4
CO exchange rates in 3a–d. The corresponding complex was
weighed (4.88 ¥ 10-6 mol) into a NMR tube and then dissolved in
pre-dried and degassed CDCl3 (0.60 mL) to give a homogeneous
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 6991–6998 | 6997
©

solution. After capping with a septum, the NMR spectrum was
acquired at 25 ◦C for each complex. 13CO gas was added via a
gastight syringe. The tube was immersed into a water bath at
25 ◦C for 2 h. Linewidths (w) were measured at half-height in units
of Hertz for carbonyl-carbon. Linewidths (w0) in the absence of
CO were also measured. The second-order exchange rates were
determined from the equation for the exchange approximation:
k = p(Dv)/[13CO], where Dv is equal to w - w0 and [13CO] is the
molar concentration of free 13CO.
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2485.
(0.5 mmol), CsOH (0.1 mmol) and 1 mol% iridium complex was
placed in flask. Toluene (0.25 mL) was added subsequently to
the above mixture. The resulting solution was heated at 100 ◦C
by an oil bath for 1.5 h. After the completion of the reaction,
brine (3 mL) and CH2Cl2(5 mL) were added. The organic layer
was separated and the aqueous layer was extracted with CH2Cl2.
The combined organic extract were dried over magnesium sulfate
1
and concentrated. Product yields are obtained by the H NMR
integration compared to the internal standard. Indole product
was purified by chromatography and characterized by NMR
spectroscopy. The spectral data are essentially identical to the
authentic sample. 1H NMR (400 MHz, CDCl3) d/ppm: 8.13 (br,
1 H, NH), 7.64 (d, J = 7.2 Hz, 1 H), 7.39 (d, J = 8 Hz, 1 H),
7.21–7.19 (m, 2 H), 7.11 (t, J = 7.2 Hz, 1 H), 6.55 (s, 1 H). 13C
NMR (100 MHz, CDCl3) d/ppm: 136.1, 128.6, 125.1, 122.7,
121.6, 120.2, 111.8, 102.6.
Crystallography. Crystals suitable for X-ray determination
were obtained for 3a and 5b [5b·0.5(CH2Cl2)·0.5 (CH3OH)]
by recrystallization at room temperature. Cell parameters were
determined either by a Siemens SMART CCD diffractometer. The
structure was solved using the SHELXS-97 program16 and refined
using the SHELXL-97 program17 by full-matrix least-squares on
F2 values. Crystal data of the complex3a: C9H14ClIrN2O2, Mw=
8 (a) D. M. Khramov, V. M. Lynch and C. W. Bielawski, Organometallics,
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Liu, Organometallics, 1999, 18, 2145; (c) S.-T. Liu and K. R. Reddy,
Chem. Soc. Rev., 1999, 315; (d) C.-Y. Liu, D.-Y. Chen, G.-H. Lee, S.-M.
Peng and S.-T. Liu, Organometallics, 1996, 15, 1055; (e) Y.-H. Chang,
C.-F. Fu, Y.-H. Liu, S.-M. Peng, J.-T. Chen and S.-T. Liu, Dalton Trans.,
2009, 861.
10 R. D. Davy and M. B. Hall, Inorg. Chem., 1989, 28, 3524.
11 M. Shiotsuki, P. S. White, M. Brookhart and J. L. Templeton, J. Am.
Chem. Soc., 2007, 129, 4058.
12 (a) D. E. Morris, and H. B. Tinker, US Pat., 3 948 962, 1976;
(b) W. M. Rees, M. R. Churchill, J. C. Fettinger and J. D. Atwood,
Organometallics, 1985, 4, 2179.
13 (a) H. Tuerkmen, T. Pape, F. E. Hahn and B. Cetinkaya,
Organometallics, 2008, 27, 571; (b) C.-Y. Wang, C.-F. Fu, Y.-H.
Liu, S.-M. Peng and S.-T. Liu, Inorg. Chem., 2007, 46, 5779; (c) D.
Gnanamgari, A. Moores, E. Rajaseelan and R. H. Crabtree,
Organometallics, 2007, 26, 1226; (d) F. Hanasaka, K.-i. Fujita and R.
Yamaguchi, Organometallics, 2005, 24, 3422; (e) J. R. Miecznikowski
and R. H. Crabtree, Organometallics, 2004, 23, 629; (f) R.-Y. Lai, C.-I.
Lee and S.-T. Liu, Tetrahedron, 2008, 64, 1213.
˚
˚
409.87, monoclinic, P21/n, a = 13.2977(2) A, b = 8.0898(2) A, c =
◦
3
˚
˚
12.7385(3) A, b = 107.271(1) , V = 1308.57(5) A , Z = 4, Dcalcd
=
2.080 Mg m-3, F(000) = 768, 0.20 ¥ 0.15 ¥ 0.10 mm3, 2q = 1.60–
27.44◦, 9649 reflections collected, 2978 independent reflections
[Rint = 0.1176], full-matrix least-squares on F2, R1 = 0.0593, wR2 =
0.1466 [I > 2s(I)]. Complex 5b: C110H102Cl2F12Ir2N4O3P6, Mw=
˚
˚
2397.08, monoclinic, P21/n, a = 21.7662(3) A, b = 19.3288(3) A,
◦
3
˚
˚
c = 27.6600(4) A, b = 109.458(2) , V = 10 972.3(3) A , Z = 4,
Dcalcd = 1.451 Mg m-3, F(000) = 4800, 0.15 ¥ 0.15 ¥ 0.10 mm3,
2q = 2.46–27.50◦, 69 291 reflections collected, 24 038 independent
reflections [Rint = 0.0891], full-matrix least-squares on F2, R1 =
0.0420, wR2 = 0.0800 [I > 2s(I)].
Acknowledgements
We thank the National Science Council (NSC97-2113-M-002-
013) and NSC-NWO Project (NSC97-2911-I-002-007) for their
financial support.
14 Y. Tsuji, S. Kotachi, K.-T. Huh and Y. Watanabe, J. Org. Chem., 1990,
55, 580.
15 S. Whitney, R. Grigg, A. Derrick and A. Keep, Org. Lett., 2007, 9,
3299.
16 G. M. Sheldrick, SHELXS-97, Program for solution of crystal struc-
tures, University of Go¨ttingen, Germany, 1997.
17 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Go¨ttingen, Germany, 1997.
Notes and references
1 A. J. Arduengo III, R. L. Harlow and M. Kline, J. Am. Chem. Soc.,
1991, 113, 361.
6998 | Dalton Trans., 2009, 6991–6998
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