Indazolin- S -ylidene-N-heterocyclic carbene complexes of rhodium, palladium, and gold: Synthesis, characterization, and catalytic hydration of alkynes

Article abstract of DOI:10.1021/om4002928

A novel series of Indy-N-heterocyclic carbene ligands (Indy = indazolin-s-ylidene) have been developed and investigated. Via a mild Ag carbene transfer route, these new carbene ligands reacted with rhodium, palladium, and gold salts to yield the correspon

Full text of DOI:10.1021/om4002928

Article
pubs.acs.org/Organometallics
Indazolin‑s‑ylidene−N-Heterocyclic Carbene Complexes of Rhodium,
Palladium, and Gold: Synthesis, Characterization, and Catalytic
Hydration of Alkynes
Yang Zhou,† Qingjie Liu,‡ Weifeng Lv,‡ Qingyu Pang,§ Rong Ben,† Yong Qian,*,† and Jing Zhao*,†,‡,§
†Institute of Chemistry and Biomedical Sciences, State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences,
Nanjing University, Nanjing 210093, People’s Republic of China
‡Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, People’s Republic of China
§Shenzhen Key Laboratory of Nano-Micro Material Research, Key Laboratory of Chemical Genomics, Shenzhen Graduate School of
Peking University, Shenzhen 518055, People’s Republic of China
S
* Supporting Information
ABSTRACT: A novel series of Indy-N-heterocyclic carbene ligands (Indy = indazolin-
s-ylidene) have been developed and investigated. Via a mild Ag carbene transfer route,
these new carbene ligands reacted with rhodium, palladium, and gold salts to yield the
corresponding air-stable metal complexes. The product complexes were characterized
by NMR spectroscopic methods and X-ray diffraction analysis. The electronic
properties of these complexes were modified by the introduction of different
substituents at the coordinated NHC ligands. Catalytic properties of the gold complex
were evaluated in the hydration of alkynes to give the corresponding ketone products.
This new type of gold N-heterocyclic carbene complex showed a high catalytic activity
in the hydration of alkyne at room temperature.
Huynh and co-workers pioneered the design and synthesis of
indazolin-s-ylidene (Indy) carbenes in 2009, which showed
even stronger donating capacities than the classical NHC
ligands.7 However, examples of Indy-NHC complexes and
catalytic activities of these Indy-NHC complexes are still rather
limited.8,9 As the electronic properties and chemical activities of
transition-metal complexes are often determined by the
electronic and steric effects of their ligands,10 we were
interested in introducing an aryl group with different
substituents on the central nitrogen atom of the Indy-NHCs,
hoping to discover new reactive species. Herein, we report the
design and synthesis of a novel series of Indy-NHC complexes
which allow modifications at the coordinated Indy-N-
heterocyclic carbene ligands. These complexes were isolated
in good yields and were unambiguously characterized by X-ray
crystallography and NMR spectroscopic methods. We have also
investigated the catalytic activity of an NHC-Au complex and
found that the gold Indy-NHC complex showed superior
catalytic activities in the hydration of alkynes (80−99%).
INTRODUCTION
■
Since N-heterocyclic carbenes (NHCs) were first isolated in the
free state by Arduengo and co-workers in 1991,1 NHCs have
been studied extensively as ligands in organometallic chemistry
and in catalysis. Owing to their strong σ donation and the
excellent stability of NHC complexes toward air and moisture,2
N-heterocyclic carbenes often can promote higher catalytic
activity than phosphane ligands.3 In addition to the normal
imidazole derivatives, Crabtree and co-workers first discovered
the abnormal carbenes,4 which have a carbenoid center adjacent
to only one nitrogen atom. These abnormal carbenes have
proven to be more donating than the normal carbenes.5 Since
then, various classes of NHC ligands such as py-NHCs, remote
py-NHCs, have been developed6 (Figure 1).
Received: May 5, 2013
Figure 1. Some representatives for the subclasses of NHC ligands.
© XXXX American Chemical Society
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Scheme 1. Synthesis of Indazole N-Heterocyclic Carbene Ligands
Scheme 2. Synthesis of Various Metal Complexes (Rh, Pd)
copy. We hypothesized that a change in steric bulkiness on the
aryl group (C ring, Scheme 2) might stabilize the desired Rh(I)
complex. After replacing the substituted group with 2,6-
dimethylphenyl (3c), we obtained the Rh Indy-NHC complex
4c successfully without the isolation of the presumed silver
carbene intermediate. Complex 4c was isolated and charac-
terized by NMR spectroscopy, and the signal of the ylidene
carbon atom was observed at 196.49 ppm in the 13C NMR
spectrum.
We further explored the effect of different substituents on the
phenyl ring on the coordination process. When the para
position of ring C was substituted with a methyl group (3d),
the reaction rate and yield remained the same as for 3c. When
the para position of ring C was substituted with halogens
(3e,f), the silver carbene intermediates were inclined to
precipitate. Thus, to obtain high yields of rhodium complexes
4e,f, addition of [Rh(COD)Cl]2 needed to be executed in 20
min after mixing Ag2O and ligands 3e,f. When ring C had two
sterically bulky iPr substituents at the 2,6-positions, the silver
carbene intermediate was stable, and the corresponding metal
complex 4g was obtained in almost quantitative yield (93%).
RESULTS AND DISCUSSION
■
Synthesis of the Indy-NHC Ligands. The synthetic route
of these novel Indy-NHC ligands is outlined in Scheme 1,
following a previous report.11
Compounds 1 were prepared by a condensation reaction of
2-nitrobenzaldehyde and aniline in excellent yield (89−93%).
Then, through the Cadogan reaction,12 intramolecular
cyclization was performed after adding excessive triethyl
phosphate and refluxing for 12 h under an inert atmosphere
to give the indazole compounds 2 in 60−68% yield. Finally, the
NHC ligands 3 were conveniently synthesized in 79−90% yield
by reacting indazoles with CH3I in CH3CN at 80 °C (Scheme
1). Synthetic details and ligand characterization data are given
in the Supporting Information.
Synthesis and Structure of Rh Indy-NHC Complexes.
In an initial attempt, the reactions of [Rh(COD)Cl]2 with the
corresponding Indy-NHC (substitution of nitrogen with phenyl
(3a) and o-tolyl (3b)) via a silver−carbene transfer method
failed to yield products. Stirring 3a,b with silver oxide for 30
min in CD2Cl2 at room temperature in the glovebox did not
form stable silver complexes, as monitored by NMR spectros-
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Figure 2. Molecular structure of complex 4g. Hydrogen atoms are omitted for clarity.
Scheme 3. Comparison of Donating Abilities of Different NHC Ligands on the IR Scale
Interestingly, when the NHC precursor 3h with iodine ion
reacted with Ag2O and then [Rh(COD)Cl]2, a mixture of two
complexes was observed with similar NMR resonance patterns.
This phenomenon has been noted previously by Crabtree et al.
and was assigned to a mixture of a chloride complex and an
iodide complex.13 An exchange of the iodide ion in compound
3h with chloride ion by stirring compound 3h with DOWEX
21K exchange resin for 12 h circumvented this problem.
Subsequently Rh complex 4h was obtained in pure form in 89%
yield.
As depicted in Figure 2, the molecular structure of complex
4g was confirmed by single-crystal X-ray analysis. Selected
geometrical parameters of complex 4g are as follows: Rh(2)−
C(34) = 1.981(11) Å, Rh(2)−C(55) = 2.073(12) Å, Rh(2)−
C(52) = 2.185(15) Å, Rh(2)−C(51) = 2.181(14) Å, Rh(2)−
C(48) = 2.049(13) Å, and Rh(2)−Cl(2) = 2.374(4) Å. Bond
lengths were in the expected range.8
C
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Synthesis of Rh−CO Indy-NHC Complexes and
Comparison of Donating Abilities of Different Indy-
NHC Ligands. Complexes 5 were easily prepared by treating
complexes 4 with CO in CH2Cl2 at room temperature for 10
min, resulting in a quick substitution of the COD ligand by a
CO ligand (Scheme 2).
The IR stretching frequencies of CO groups in the
dicarbonyl rhodium complex RhCl(CO)2L are commonly
used to assess the electronic properties of a given ligand
L.10,14,15 Normally a more donating ligand would result in a
lower CO stretching frequency. Some reports used average
values, while others compared the stretching frequencies of the
trans-CO (νasym). To evaluate the donating abilities of these
novel Indy-NHC ligands, complexes 4c−h were converted to
the corresponding carbonyl complexes 5c−h. The stretching
frequencies of these trans-CO ligands (1985−1996 cm−1) were
lower than those for most previously reported NHCs.15 This
observation indicated that this series of new ligands might have
stronger donating abilities (Scheme 3). However, metal−CO
stretching frequencies are not always accurate in measuring the
13
donating capacity of the ligands. The
C
signals of the
carbene
complexes RhCl(CO)2L appeared at 183.00−183.35 ppm,
which also showed that most of these ligands have stronger
donating abilities than other NHCs.8,15b
Synthesis of the Pd Indy-NHC Complexes. The
versatility of the Indy-NHC ligands was further demonstrated
through transmetalation with [Pd(allyl)Cl]2 to yield PdI
complexes. However, the reaction of the NHC precursor of
3h with both iodide ion and chloride counterion failed to give a
stable PdI Indy-NHC complex by using the same route. Steric
hindrance plays an important role in chelating with transition
metals, and in our hands, more than one methyl group of R1 or
R2 was needed to promote the formation of the desired
complex.
Figure 3. Molecular structure of complex 6g. Hydrogen atoms are
omitted for clarity.
Scheme 4. Synthesis of Au Complex 7
As depicted in Figure 3, the molecular structure of complex
6g was also unambiguously confirmed by single-crystal X-ray
analysis. Selected geometrical parameters of complex 6g are as
follows: Pd(1)−C(6) = 2.035(3) Å, Pd(1)−Cl(8) = 2.353(9)
Å, Pd(1)−C(30) = 2.094(3) Å, Pd(1)−C(20) = 2.111(5) Å,
Pd(1)−C(21) = 2.181(6) Å, Cl(8)−Pd(1)−C(6) = 92.94(8)°.
Bond lengths were in the expected range.16
Synthesis of an Au Indy-NHC Complex and Its
Catalytic Application. The Indy-NHC ligands failed to
react with [AuCl(SMe2)] by a silver carbene transfer method to
give AuI Indy-NHC complexes. One exception is for the ligand
with iPr (3g), which gave complex 7 in 94% yield (Scheme 4).
The combination of steric bulkiness and strong electron
donating ability of ligand 3g might contribute to the successful
formation of complex 7.
achieve an efficient catalytic hydration of alkynes. The reaction
occurred at room temperature in air, affording products in high
yields after a short reaction time.
We initiated our investigation on the model reaction of
hydration of 1-phenylpropargyl ester using the gold Indy-NHC
complex 7 as a catalyst. To optimize the reaction parameters,
solvents and catalyst loadings were screened (Table 1). The
CH3CN/H2O solvent mixture (40/1) provided the best results,
giving the desired α-acetoxy ketone in nearly quantitative yield
(96% isolated yield) (entry 9).
Interestingly, the amount of water had no obvious effect on
the product yield (entries 8, 10, 7, and 11). As for the catalyst
loadings, 3 mol % of NHC-Au complex/AgSbF6 provided an
excellent yield (95% isolated yield) (entry 12). However, the
yield decreased to 70% when the catalyst loading was reduced
to 1 mol % (entry 14). Taken together, we used the
combination of 3 mol % of AuI Indy-NHC complex/AgSbF6
and CH3CN/H2O (40/1) at room temperature as the
optimized reaction conditions for this transformation.
With the optimized reaction conditions in hand, we next
evaluated the scope of substrates. The results are summarized
in Table 2. A series of substrates with different functional
groups were examined; the products were isolated in moderate
to excellent yield (83−99%, 9a−l). The AuI Indy-NHC
complex catalyst was shown to be highly effective for this
transformation. As shown, electron-withdrawing groups includ-
Figure 4 shows the molecular structure of gold complex 7.
The Au(1)−C(7) (2.015(10) Å) and Au(1)−Cl(1) (2.285(3)
Å) bond lengths were within the expected ranges.9
There have been several reports on cationic gold-catalyzed
hydration of alkynes. The product α-hydroxyl methyl ketone
skeleton has proven to be a useful building block in organic
synthesis and natural products. It widely exists in biologically
relevant molecules, such as cytochalasin, sesquiterpene, and
secokotomolide.17 The catalytic hydration of alkynes is an
environmentally friendly and cost-effective synthetic method.
However, most of the reported procedures required mineral
acid as promoters or high temperature.18 A simple, efficient,
and stable catalyst is highly desired from a practical viewpoint.
Herein we applied our air-stable gold Indy-NHC complex to
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Figure 4. Molecular structure of complex 7. Hydrogen atoms are omitted for clarity.
of rhodium/palladium/gold Indy-NHC complexes. All com-
plexes have been fully characterized and molecular structures of
representative examples were determined by X-ray diffraction
analysis. Among them, the isopropyl-substituted ligand (3g)
not only coordinated with rhodium and palladium but also
reacted with the gold salt to form an air-stable AuI Indy-NHC
complex in high yield. Finally, the gold iPr-NHC complex
showed high activity in catalyzing the hydration of alkynes
(83−99%). Further studies on tuning the properties of these
types of N-heterocyclic ligands and other transition-metal
carbene complexes are in progress.
Table 1. Survey of Reaction Conditions
entry
solvent
amt of catalyst (mol %)
yield (%)
a
1
acetone/H2O (20/1)
dioxane/H2O (20/1)
DCM/H2O (20/1)
THF/H2O (20/1)
4
4
4
4
4
4
4
4
4
4
4
3
2
1
34
a
2
60
a
3
trace
a
4
80
a
5
MeOH/H2O (20/1)
DMF/H2O (20/1)
85
a
6
51
a
EXPERIMENTAL SECTION
7
CH3CN/H2O (20/1)
CH3CN/H2O (50/1)
CH3CN/H2O (40/1)
CH3CN/H2O (30/1)
CH3CN/H2O (10/1)
CH3CN/H2O (40/1)
CH3CN/H2O (40/1)
90
■
a
8
83
All solvents were distilled under N2 before use and were stored in a
drybox. All chemicals were purchased and used without any further
purification unless otherwise specified. Column chromatography was
performed on 200−300 mesh silica gel (Qingdao Haiyang Chemical).
Analytical thin-layer chromatography (TLC) was performed using
Huanghai silica gel plates with HSGF 254. Melting points (mp) were
determined on a DR-2 MP apparatus (New Skylight Corp., Tianjin,
People’s Republic of China). 1H NMR and 13C NMR data were
obtained on a Bruker 400 MHz nuclear resonance spectrometer unless
otherwise specified. The chemical shifts are given as dimensionless δ
values and are referenced relative to TMS. Gas chromatographs were
recorded on a Shimadzu GC-2014 spectrometer. HRMS spectra were
obtained in ESI mode and performed by The Analytical
Instrumentation Center at Peking University Shenzhen Graduate
School.
a
b
9
99; 96
a
10
11
12
13
14
92
a
62
b
95
b
80
b
CH3CN/H2O (40/1)
70
a
b
GC yield. Isolated yield.
ing halogen groups at the 4- or 3-positions on the aromatic ring
gave the desired products in excellent yield (9b−f). Hydration
of the terminal triple bond with an electron-poor ortho
substituent on the aromatic ring of propargyl acetates also
produced the corresponding ketones (9g−j) in excellent yields.
Importantly, 1-(naphthalen-1-yl)prop-2-ynyl acetate substrate
and an aliphatic ring derived ester were also examined and
afforded the expected product in good yields (83% yield of 9k,
86% yield of 9l, respectively).
Synthesis and Characterization of 1g. A mixture of 2-
nitrobenzaldehyde (2.30 g, 15.2 mmol) and 2,6-diisopropylaniline
(1.2 equiv.) was stirred at 90 °C for 3 h and then cooled to room
temperature. Ethanol (10 mL) was added to the reaction mixture, and
the solution was placed in a refrigerator overnight for recrystallization.
The resulting precipitate was filtered and washed with 3 × 4 mL of
1
cold ethanol to give a yellow solid. Yield: 93%. Mp: 67−68 °C. H
CONCLUSION
■
NMR (400 MHz, CDCl3): δ 8.65 (s, 1H), 8.34 (dd, J = 7.8, 1.4 Hz,
1H), 8.13 (dd, J = 8.2, 1.1 Hz, 1H), 7.80 (m, 1H), 7.68 (m, 1H), 7.17
(m, 3H), 3.03 (m, 2H), 1.22 (d, J = 6.9 Hz, 12H). 13C NMR (100
MHz, CDCl3): δ 158.22, 149.34, 148.31, 137.52, 133.77, 131.35,
In summary, we have reported the synthesis of a serial of new
Indy-N-heterocyclic carbene ligands with strong donating
ability. Utilizing these ligands, we synthesized a novel series
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a
Table 2. AuI Indy-NHC Complex Catalyzed Hydration of Alkynes
a
Reaction conditions: 3% catalyst, 0.5 M substrate in CH3CN/H2O (40/1) at room tempertaure for 3 h. Isolated yields are given.
131.04, 129.70, 124.77, 124.59, 123.14, 27.95, 23.50. HRMS (ESI+):
311.1755; calcd mass for [C19H23N2O2]+ 311.1760.
29.05 (CH2 of COD), 28.321 (C(CH3)2), 28.21 (CH2 of COD),26.34
(CH2 of COD), 25.18 (CH3), 24.64 (CH3), 23.60 (CH2 of COD).
Synthesis and Characterization of Rh−CO Complex 5g.
Carbon monoxide was bubbled in a suspension of complex 4g (20 mg)
in CH2Cl2 (2 mL) for 10 min at room temperature. The solvent was
subsequently removed under reduced pressure. The resulting residue
was washed with hexane or ether to give complex 5g as a yellow solid.
Synthesis and Characterization of 2g. Compound 1g (10
mmol) and triethyl phosphate (10 equiv) were loaded into a 100 mL
sealed tube and stirred at 160 °C for 12 h. The solvent was then
removed under reduced pressure. The residue obtained was purified
by silica gel chromatography to give 2g as a white solid. Yield: 68%.
Mp: 138−139 °C. 1H NMR (400 MHz, CDCl3): δ 8.01 (s, 1H), 7.85
(d, J = 8.8 Hz, 1H), 7.78 (d, J = 8.5 Hz, 1H), 7.49 (t, J = 7.8 Hz, 1H),
7.38 (dd, J = 11.6, 3.8 Hz, 1H), 7.29 (d, J = 7.8 Hz, 2H), 7.19 (m, 1H),
2.18 (m, 2H), 1.16 (d, J = 6.8 Hz, 6H), 1.11 (d, J = 6.9 Hz, 6H). 13C
NMR (100 MHz, CDCl3): δ 148.88, 146.15, 137.13, 130.17, 126.12,
125.67, 123.51, 122.09, 121.64, 120.38, 118.21, 28.20, 24.65, 24.02.
HRMS (ESI+): 279.1837; calcd mass for [C19H23N2]+ 279.1861.
Synthesis and Characterization of 3g. An excess of CH3I (5
equiv) was added to a solution of compound 2 (1 mmol) in CH3CN,
and the reaction mixture was stirred at 80 °C for 5 h. The solvent was
then removed under reduced pressure. The residue was subsequently
washed with diethyl ether (3 × 2 mL) to give 3g as a yellow solid.
Yield: 90%. Mp: 195−197 °C. 1H NMR (400 MHz, CDCl3): δ 9.77 (s,
1H), 8.50 (d, J = 8.5 Hz, 1H), 8.25 (d, J = 8.8 Hz, 1H), 7.94 (m, 1H),
7.71 (t, J = 7.9 Hz, 1H), 7.56 (m, 1H), 7.43 (d, J = 7.9 Hz, 2H), 4.11
(s, 3H), 1.92 (dd, J = 13.6, 6.8 Hz, 2H), 1.18 (dd, J = 6.6, 5.4 Hz,
12H). 13C NMR (100 MHz, CDCl3): δ 147.00, 140.76, 135.66,
135.27, 134.16, 127.55, 126.45, 125.55, 124.62, 119.88, 112.13, 35.32,
29.09, 25.33, 23.04. HRMS (ESI+): 293.2025; calcd mass for
[C20H25N2]+ 293.2012.
1
Yield: 89%. Mp: 197−198 °C. H NMR (400 MHz, CDCl3): δ 8.51
(d, J = 7.8 Hz, 1H), 7.72 (t, J = 7.6 Hz, 1H), 7.63 (t, J = 7.6 Hz, 1H),
7.38 (m, 3H), 3.58 (s, 3H), 2.48 (m, 2H), 1.36 (d, J = 6.3 Hz, 6H),
1.11 (d, J = 6.5 Hz, 6H). 13C NMR (100 MHz, CDCl3): δ 187.51(d,
J(Rh, Cco) = 39 Hz, CO), 185.64(d, J(Rh−CCO) = 52 Hz, CO),
183.35(d, J(Rh−C) = 75 Hz, Ccarbene), 147.41, 140.83, 132.83, 132.65,
131.95, 131.63, 131.20, 125.05, 122.79, 109.04, 34.44, 28.41, 24.85,
24.50. FT-IR (CH2Cl2): ν(COsym) 2066 cm−1 (s) and ν(COasym) 1991
cm−1 (s).
Synthesis and Characterization of Palladium Complex 6g. A
mixture of Ag2O (0.06 mmol, 14 mg) and complex 3g (50 mg, 0.12
mmol) in anhydrous CH2Cl2 was stirred at room temperature in the
dark under an argon atmosphere for 90 min. [Pd(allyl)Cl]2 (0.06
mmol, 22 mg) was then added to the mixture, which was then stirred
for another 3 h to give complex 6g as a yellow solid. Yield: 94%. Mp:
1
205−207 °C. H NMR (400 MHz, CDCl3): δ 8.64 (d, J = 8.2 Hz,
1H), 7.67 (m, 1H), 7.57 (t, J = 7.8 Hz, 1H), 7.34 (m, 4H), 5.08 (m,
1H), 4.22 (dd, J = 7.6, 1.4 Hz, 1H), 3.56 (s, 3H), 3.18 (d, J = 13.7 Hz,
1H), 2.85 (d, J = 6.5 Hz, 1H), 2.69 (m, 1H), 2.39 (m, 1H), 1.74 (d, J =
11.8 Hz, 1H), 1.38 (d, J = 6.7 Hz, 3H), 1.29 (d, J = 6.7 Hz, 3H), 1.12
(dd, J = 11.4, 6.8 Hz, 6H). 13C NMR (100 MHz, CDCl3): δ 190.85,
147.43, 140.95, 133.83, 132.12, 131.46, 131.42, 124.68, 122.12, 114.77,
109.00, 73.52, 48.53, 34.40, 28.25, 24.73, 24.42, 24.10.
Synthesis and Characterization of Rhodium Complex 4g. A
mixture of Ag2O (0.06 mmol, 14 mg) and compound 3g (50 mg, 0.12
mmol) in anhydrous CH2Cl2 was stirred at room temperature in the
dark under an argon atmosphere for 90 min. [Rh(COD)Cl]2 (0.06
mmol, 29 mg) was then added to the mixture, which was then stirred
for another 3 h to give the yellow solid complex 4g. Yield: 93%. Mp:
Synthesis and Characterization of Gold Complex 7. Ag2O
(0.06 mmol, 14 mg) and complex 3g (50 mg, 0.12 mmol) were
dissolved in anhydrous CH2Cl2, and the mixture was stirred at room
temperature in the dark under an argon atmosphere for 90 min.
[AuCl(SMe2)] (0.12 mmol, 36 mg) was then added to the mixture,
which was then stirred for another 3 h to give complex 7 as a yellow
1
198−200 °C. H NMR (400 MHz, CDCl3): δ 8.85 (d, J = 8.1 Hz,
1H), 7.62 (m, 2H), 7.51 (d, J = 7.2 Hz, 1H), 7.36 (t, J = 7.5 Hz, 1H),
7.24 (m, 3H), 5.15 (s, 1H, CODvinyl), 4.90 (s, 1H, CODvinyl), 3.59 (s,
1H, CODvinyl), 3.41 (s, 3H), 2.86 (s, 1H, CODvinyl), 2.39 (d, J = 37.2
Hz, 2H), 2.08 (s, 2H), 1.72 (m, 6H), 1.14 (m, 12H). 13C NMR (100
MHz, CDCl3): δ 200.64 (d, J(Rh−C) = 45 Hz, Ccarbene),148.68,
146.88, 141.38, 132.83, 132.00, 131.89, 131.10, 125.45, 123.80, 122.29,
109.23, 98.29 (CH of COD), 97.05 (CH of COD), 67.71 (CH of
COD), 34.49 (NCH3), 33.79 (CH of COD), 32.06 (CH of COD),
1
solid. Yield: 94%. Mp: 289−291 °C. H NMR (400 MHz, CDCl3): δ
8.17 (d, J = 8.2 Hz, 1H), 7.75 (t, J = 7.6 Hz, 1H), 7.61 (t, J = 7.8 Hz,
1H), 7.47 (d, J = 8.5 Hz, 1H), 7.37 (dd, J = 14.7, 7.8 Hz, 3H), 3.65 (s,
3H), 2.13 (m, 2H), 1.31 (d, J = 6.7 Hz, 3H), 1.14 (d, J = 6.9 Hz, 3H).
13C NMR (100 MHz, CDCl3): δ 172.72, 146.72, 139.65, 133.05,
132.32, 132.06, 129.93, 128.87, 124.93, 123.00, 109.18, 33.36, 28.67,
24.96, 23.20.
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X-ray Diffraction Studies. All measurements were made on a
Rigaku Saturn70 CCD diffractometer using graphite-monochromated
Cu Kα radiation. Data were collected and processed using
CrystalClear (Rigaku). The data were corrected for Lorentz and
polarization effects. The structures were solved by direct methods19
and expanded using Fourier techniques. Non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were refined using the riding
model. All calculations were performed using the CrystalStructure20
crystallographic software package, except for refinement, which was
performed using SHELXL-97.19
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ASSOCIATED CONTENT
* Supporting Information
■
S
(15) (a) Herrmann, W. A.; Schutz, J.; Frey, G. D.; Herdtweck, E.
̈
Text, tables, figures, and CIF files giving crystallographic data
for complexes 4g (CCDC 929101), 6g (CCDC 929102), and 7
Organometallics 2006, 25, 2437. (b) Furstner, A.; Alcarazo, M.; Krause,
̈
H.; Lehmann, C. W. J. Am. Chem. Soc. 2007, 129, 12676.
1
(CCDC 929103), H and 13C NMR and high-resolution mass
(16) Peng, H.; Song, G.; Li, Y.; Li, X. Inorg. Chem. 2008, 47, 8031.
(17) (a) Liu, R.; Lin, Z.; Zhu, T.; Fang, Y.; Gu, Q.; Zhu, W. J. Nat.
Prod. 2008, 71, 1127. (b) Wang, S.-K.; Huang, M.-J.; Duh, C.-Y. J. Nat.
Prod. 2006, 69, 1411. (c) Chen, F.-C.; Peng, C.-F.; Tasi, I.-L.; Chen, I.-
S. J. Nat. Prod. 2005, 68, 1318. (d) Liu, Y.-B.; Su, E.-N.; Li, J.-L.; Yu, S.-
S.; Qu, J.; Liu, J.; Li, Y. J. Nat. Prod. 2009, 72, 229.
spectral data and spectra of compounds 1−3 and 9 and
complexes 4−7, and experimental details, including exper-
imental procedures. This material is available free of charge via
the Internet at http://pubs.acs.org.
(18) (a) Wang, W.; Jasinshi, J.; Hammond, G. B. Angew. Chem., Int.
Ed. 2010, 49, 7247. (b) Wang, W.; Xu, B.; Hammond, G. B. J. Org.
AUTHOR INFORMATION
Corresponding Author
*E-mail for J.Z.: jingzhao@nju.edu.cn.
Notes
■
Chem. 2009, 74, 1640. (c) Marion, N.; Ramon
Am. Chem. Soc. 2009, 131, 448. (d) Ramon, R. S.; Marion, N.; Nolan,
S. P. Tetrahedron 2009, 65, 1767.
(19) Sheldrick, G. M. SHELX97; University of Gottingen, Gottingen,
́
, R. S.; Nolan, S. P. J.
́
̈
̈
The authors declare no competing financial interest.
Germany, 1997.
(20) CrystalStructure 4.0: Crystal Structure Analysis Package; Rigaku
and Rigaku Americas, 9009 New Trails Dr., The Woodlands, TX
77381, 2000−2009.
ACKNOWLEDGMENTS
■
This work was financially supported by grants from the
National Basic Research Program of China (2010CB923303),
the NCET, and the Doctoral Fund of the Ministry of Education
of China. J.Z. thanks the Natural Science Foundation of Jiangsu
Province (BK2011547) and the Shenzhen Government
(JC201005260103A, KQC201105310016A, SW201110018)
for support.
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dx.doi.org/10.1021/om4002928 | Organometallics XXXX, XXX, XXX−XXX