Chiral NCN pincer rhodium(III) complexes with bis(imidazolinyl)phenyl ligands: Synthesis and enantioselective catalytic alkynylation of trifluoropyruvates with terminal alkynes

Article abstract of DOI:10.1002/adsc.201200967

A series of new chiral C₂-symmetrical NCN pincer rhodium(III) complexes with bis(imidazolinyl)phenyl ligands have been conveniently synthesized from easily available materials. The complexes were subsequently applied in the enantioselective add

Full text of DOI:10.1002/adsc.201200967

FULL PAPERS
DOI: 10.1002/adsc.201200967
Chiral NCN Pincer Rhodium(III) Complexes with
G
Bis(imidazolinyl)phenyl Ligands: Synthesis and Enantioselective
Catalytic Alkynylation of Trifluoropyruvates with Terminal
Alkynes
Tao Wang,a Jun-Long Niu,a Shuang-Liang Liu,a Juan-Juan Huang,a
Jun-Fang Gong,a,* and Mao-Ping Songa,*
a
The College of Chemistry and Molecular Engineering, Henan Key Laboratory of Chemical Biology and Organic
Chemistry, Zhengzhou University, Zhengzhou 450052, Peopleꢀs Republic of China
Fax : (+86)-371-6778-3012; phone: (+86)-371-6778-3012; e-mail: gongjf@zzu.edu.cn or mpsong@zzu.edu.cn
Received: November 12, 2012; Published online: February 28, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200967.
Abstract: A series of new chiral C2-symmetrical enantioselectivities of up to >99% ee and high
NCN pincer rhodiumACTHNUTRGNE(NUG III) complexes with bis(imida- yields. Although good to excellent enantioselectivi-
zolinyl)phenyl ligands have been conveniently syn- ties (85–98% ee) could be achieved only for some of
thesized from easily available materials. The com- the aliphatic terminal alkynes under the optimized
plexes were subsequently applied in the enantiose- conditions, the enantioselectivities were consistently
lective addition of terminal alkynes to trifluoropyru- excellent (94% to >99% ee) in the case of aromatic
vates. With catalyst loading of 1.5–3.0 mol%, the al- as well as heteroaromatic alkynes and enynes.
kynylation of ethyl or methyl trifluoropyruvate with
a variety of electronically and structurally diverse Keywords: asymmetric alkynylation; Phebim ligands;
terminal alkynes gave the optically active trifluoro- pincer rhodium
ACHTUNGTRENN(UNG III) complexes; terminal alkynes; tri-
methyl-substituted tertiary propargylic alcohols with fluoropyruvates
Introduction
excess dimethylzinc) was added to aryl methyl ke-
tones in the presence of a catalytic amount of
The synthesis of optically active propargylic alcohols Cu
(OTf)2/chiral
camphorsulfonamide
complex
by enantioselective alkynylation of carbonyl com- (10 mol%) as the catalyst, high yields and enantiose-
pounds[1] has received much attention in recent years, lectivities (up to 97% ee) could be achieved.[4b,i] Alk-
because propargylic alcohols can serve as useful
ACHTUNGTRENyNUGN nylsilanes such as (trimethoxy)(phenylethynyl)silane
building blocks for a wide range of natural products were also successfully used as alternative alkynylating
and pharmaceutical molecules. Although the catalytic reagents.[5] In addition, Jiang and co-workers demon-
asymmetric alkynylation of aldehydes has been well strated that terminal alkynes were viable nucleophiles
studied and great progresses have been made,[2] the for the alkynylation of a-keto esters in the presence
alkynylation of ketones is still regarded as a challeng- of catalytic ZnACTHNUGTRENUNG(OTf)2/chiral amino alcohol (20 mol%)
ing task mostly due to their lower reactivities. In re- and the corresponding tertiary propargylic alcohols
ported alkynylation of ketones, stoichiometric were produced in high yields with up to 94% ee.[6] Al-
amounts of metal acetylides, which were generated in though the catalyst loading of 20 mol% is relatively
situ from terminal alkynes and excess metal reagents high, this may represent the most atom-economical
such as organolithium, organomagnesium or diorga- strategy for the asymmetric alkynylation of ketones
nozinc compounds, were usually employed as nucleo- since both the metal and ligand are substoichiometric.
philes (alkynylating reagents) with stoichiometric[3] or On the other hand, the alkynylation of a-CF3-substi-
catalytic amounts[4] of chiral ligands (in some cases tuted carbonyl compounds, which are the highly acti-
with chiral metal complexes) for controlling the abso- vated ketones, is particularly appealing since the ob-
lute configurations. For example, when zinc phenyla- tained a-CF3-substituted chiral tertiary alcohols are
cetylide (prepared in situ from phenylacetylene and important intermediates for drugs or candidates with
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Tao Wang et al.
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unusual biological activities such as efavirenz.[7] Efa- fluoropyruvate.[12] In the presence of 3.0 mol% of C1-
virenz is a potent non-nucleoside HIV reverse tran- symmetrical Rh complexes with 1,3-bis(2’-oxazolinyl)-
scriptase inhibitor for AIDS treatment. Its synthesis phenyl ligands (Phebox) as the catalysts, the alkynyla-
was realized by the addition of stoichiometric metal tion proceeded well in Et2O at room temperature
acetylide (in situ formed) to trifluoromethyl ketone in without addition of an external base, giving the corre-
the presence of a stoichiometric chiral auxiliary, sponding tertiary propargylic alcohols in high yields
which is also in fact the first report on enantioselec- and enantioselectivities (up to >99% ee).
tive alkynylation of a ketone.[3,8] Later, Shibasaki and
Although excellent results have been obtained with
co-workers disclosed preliminary results on the asym- C1-symmetrical Rh/Phebox complexes[14] for the
metric alkynylation of trifluoroacetophenone with direct catalytic asymmetric alkynylation of ethyl tri-
phenylacetylene catalyzed by copper-diphosphine or fluoropyruvate, the design and development of easily
Cu-Pybox complex (10–20 mol%).[9] Similar to what accessible, economical and highly enantioselective
was reported by Jiang,[6] this direct catalytic alkynyla- chiral catalysts as well as an extension of the substrate
tion procedure was quite simple, unfortunately, only scope are still worthwhile projects. In the previous
moderate enantioselectivity was observed (up to 52% studies, we have synthesized a series of C2-symmetri-
ee). Recently, Ma and co-workers developed an effi- cal NCN pincer Pt(II), Pd(II) and Ni(II) complexes
cient titanium(IV)-catalyzed enantioselective addition with anionic tridentate 1,3-bis(2’-imidazolinyl)phenyl
of zinc alkynylides to various trifluoromethyl ketones ligands (abbreviated as Phebim) via the direct metal-
À
by using catalytic chiral Cinchona alkaloids as li- induced C H bond activation of the Phebim-H li-
gands.[10] Both enantiomers of trifluoromethylated ter- gands.[15,16] And the cationic Pt-aquo complex was
tiary propargylic alcohols could be accessed in good found to be an effective catalyst for the asymmetric
to high yields (up to 98%) and enantioselectivities Friedel–Crafts alkylation of indoles with nitroalkenes
(up to 94% ee) with the aid of BaF2 as an additive. (up to 83% ee).[15d] Similar to the Phebox ligands, the
Besides trifluoromethyl ketones, the commercially electronic and conformational properties of Phebim
available trifluoropyruvates can also be used as versa- ligands can be easily tuned by using different chiral
tile fluorine-containing reagents for the construction amino alcohols. Moreover, a further tune of these
of chiral fluorinated products. Unlike catalytic asym- properties for Phebim ligands can be achieved by ap-
metric carbonyl-ene, aldol as well as Friedel–Crafts propriate choice of substituent on the additional ni-
reactions with trifluoropyruvate,[7] much less work on trogen atom. Following our interest in the pincer
the catalytic enantioselective alkynylation of trifluoro- metal complexes[17] and particularly, as a continuation
pyruvates has been reported. To the best of our of our studies on the pincer metal complexes with
knowledge, there are only two examples of this reac- Phebim ligands, herein we report the first synthesis of
tion.[11,12,13] One was by Mikami and co-workers, who C2-symmetrical
Rh
G
complexes
used alkynylsilanes as nucleophiles and a dicationic (Scheme 1) and their application in the catalytic
Pd/(S)-BINAP complex (5.0 mol%) as the catalyst.[11] asymmetric alkynylation of trifluoropyruvates with
In this case, high enantioselectivities (up to >99% ee) various terminal alkynes. The complexes were found
were obtained and the system could also be applied to be effective and highly enantioselective not only
to polyynylsilanes. The other was reported by Ohshi- for the reactions of ethyl trifluoropyruvate but also
ma, Mashima and co-workers, who directly used ter- for those of methyl trifluoropyruvate with a catalyst
minal alkynes including aryl- as well as alkyl-substi- loading of 1.5–3.0 mol%. The terminal alkynes used
tuted alkynes as nucleophiles to react with ethyl tri- in the alkynylation can be aromatic including phenyl-
Scheme 1. Synthesis of chiral C2-symmetrical NCN pincer rhodiumACTHUNTGRNEUNG(III) complexes with bis(imidazolinyl)phenyl ligands.
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Chiral NCN Pincer RhodiumACTHNUTRGNE(UNG III) Complexes with Bis(imidazolinyl)phenyl Ligands
acetylene, substituted phenylacetylenes and naphthy-
lacetylene as well as heteroaromatic ones such as
thiophene acetylenes. They can also be enynes and
other aliphatic alkynes. Furthermore, in the alkynyla-
tion of ethyl trifluoropyruvate the C2-symmetrical Rh/
Phebim complexes gave better enantioselectivities
than the reported C1-symmetrical Rh/Phebox com-
plexes under similar reaction conditions and the enan-
tioselectivities were >97% ee in most cases.
Results and Discussion
As shown in Scheme 1, the rhodium
ACHTUNGTREN(NUNG III) chloride
complexes (Phebim)RhCl2A(H2O) 2a–e with different
CTHUNGTRENNUNG
electronic and conformational properties could be
conveniently prepared in a way similar to that report-
Figure 2. Molecular structure of 2d’. Hydrogen atoms are
omitted for clarity.
ed for (Phebox)RhCl2ACTHNUTRGNEUNG
(H2O) complexes[18] by heating
the Phebim-H ligands 1 and triply hydrated rhodium
trichloride in wet methanol in the presence of sodium
bicarbonate. Then the chloride complexes were readi-
With the C2-symmetrical NCN pincer RhACHTUNGTRENNUNG(III)/
ly converted to the corresponding acetate complexes Phebim complexes in hand, their potential in the cata-
(Phebim)Rh(OAc)2A(H2O) 3a–e by reaction with an lytic enantioselective alkynylation of trifluoropyru-
A
CHTUNGTRENNUNG
excess of silver acetate in CH2Cl2. All of the new vates with terminal alkynes was then evaluated. In
compounds were fully characterized by elemental the beginning, the addition of phenylacetylene to
analysis (HR-MS for the new ligands 1d and 1e), ethyl trifluoropyruvate was chosen as a model with
1H NMR, 13C NMR, and IR spectra. The elemental the acetate complex 3a as the catalyst. A rough
1
analysis and some of the H NMR spectra of the Rh/ survey of reaction conditions indicated that the yields
Phebim complexes indicated the coordination of one of the catalysis products were largely dependent on
molecule of H2O to the rhodium atom. In addition, the reaction temperature and the solvent used, al-
the formation of the expected NCN pincer RhACTHNUTRGNEUNG(III) though good to excellent enantioselectivities (88–98%
complexes is unambiguously confirmed by the single ee) could be obtained in all cases (Table 1, entries 1–
crystal X-ray diffraction analysis of complexes 2c’ and 6). Higher temperature was beneficial for the reaction
2d’ (Figure 1 and Figure 2, respectively), in which a di- and Et2O was found to be the most appropriate sol-
chloromethane or acetone molecule, the solvent used vent among the tested solvents including CH2Cl2,
in recrystallization takes the place of the H2O mole- Et2O, toluene and THF. The alkynylation proceeded
cule in complexes 2c and 2d. A similar phenomenon very well at 258C in Et2O with 3.0 mol% of 3a giving
was observed with (Phebox)RhCl
2ACHTUNGTREN(NGNU H2O) com- the tertiary propargylic alcohol in 98% yield and 97%
plexes.[19]
ee after 24 h (Table 1, entry 4). In contrast, no reac-
tion occurred when the related chloride complex 2a
was employed as the catalyst under the same reaction
conditions. This was in accordance with the literature
results for RhACHTUNTRGNEUNG(III)/Phebox complexes suggesting that
the acetate moiety on the Rh may act as an internal
base to deprotonate the terminal alkyne.[12] Further
studies revealed that in the reaction with 4-methoxy-
phenylacetylene as an alkynylating reagent complex
3a only afforded a 86% yield with 83% ee (entry 7)
although it gave excellent results in the reaction with
phenylacetylene. Then the performance of the other
four Rh complexes 3b–e in this reaction was exam-
ined. It was found that the ligand structure of the
RhACTHUNRTGNEUNG(III)/Phebim complexes had an obvious effect on
both yield and enantioselectivity. In comparison with
3a which has an (S)-phenyl substituent, complex 3b
with an (S)-benzyl substituent resulted in a lower
yield and enantioselectivity (entry 8). Complex 3c
Figure 1. Molecular structure of 2c’. Hydrogen atoms are
omitted for clarity.
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Table 1. Optimization of conditions for the catalytic asymmetric alkynylation of ethyl trifluoropyruvate using the NCN
pincer Rh
(III)/Phebim complexes 3 as the catalysts.[a]
ACHTUNGTRENNUNG
Entry
Catalyst (mol%)
R
Solvent
Temperature [8C]
Product
Yield[b] [%]
ee[c,d] [%]
1
2
3
4
5
6
7
8
3a (3.0 mol%)
3a (3.0 mol%)
3a (5.0 mol%)
3a (3.0 mol%)
3a (3.0 mol%)
3a (3.0 mol%)
3a (3.0 mol%)
3b (3.0 mol%)
3c (3.0 mol%)
3d (3.0 mol%)
3e (3.0 mol%)
H
H
H
H
H
H
MeO
MeO
MeO
MeO
MeO
CH2Cl2
Et2O
Et2O
Et2O
toluene
THF
Et2O
Et2O
Et2O
Et2O
Et2O
r.t.[e]
r.t.[e]
25
25
25
25
25
25
25
4a
4a
4a
4a
4a
4a
4b
4b
4b
4b
4b
24
62
99
98
15
21
86
84
36
89
99
95
98
97
97
96
88
83
75
97
97
98
9
10
11
25
25
[a]
The reaction was run with terminal alkyne (0.24 mmol), ethyl trifluoropyruvate (0.20 mmol), solvent (2 mL) for 24 h.
Isolated yields.
[b]
[c]
[d]
[e]
Enantiomeric excess was determined by chiral HPLC analysis.
The absolute configurations of the products were assigned to be S by comparison of optical rotations with those in ref.[12]
About 148C.
with (S,S)-phenyl substituents and an N-Cy substitu- Br, F, CF3, NO2 or CHO. And it can be located at the
ent produced a rather modest yield (36%), however, 2-, 3- or 4-position of the alkynyl group. For example,
we were happy to see that an excellent enantioselec- excellent yields and enantioselectivities were achieved
tivity (97% ee) could be obtained (entry 9). Replace- with the 2-, 3- and 4-methylphenylacetylenes (90–96%
ment of the N-Cy substituent in complex 3c by N-p- yields, 99% ee, entries 2–4). In fact, complex 3d could
tolyl substituent furnished complex 3d and the use of also give excellent enantioselectivities in these reac-
3d led to a significant increase in yield (89% vs. 36%) tions except for 3-methylphenylacetylene (see also en-
without loss of enantioselectivity (entry 10). Finally, tries 1–11). In comparison with 3e, complex 3d result-
complex 3e, which has the same imidazoline ring as ed in slightly lower yields and/or enantioselectivities.
3d and an additional NO2 group at the para position Among the substituted phenylacetylenes, the 4-ethy-
to the metal, was found to be the best catalyst with nylbenzaldehyde was somewhat special since it bore
excellent yield and enantioselectivity (99% yield and a reactive aldehyde group. In this case, the two Rh
98% ee, entry 11).
complexes could still produce the desired propargylic
Since both complexes 3d and 3e performed rather alcohol in good yields and excellent enantioselectivi-
well in the selected alkynylation, they were both ap- ties (75–80% yields, 96% ee, entry 11). It should be
plied as the catalysts in the following experiments to mentioned that in the above alkynylation the C2-sym-
explore the scope of the alkynylation. It was found metrical Rh/Phebim complexes 3d and 3e consistently
that the two complexes were really effective and provided better enantioselectivities than the reported
highly enantioselective catalysts for the alkynylation C2- or C1-symmetrical Rh/Phebox complexes.[12] Fur-
of ethyl and methyl trifluoropyruvates with various thermore, with the current two Rh catalysts the aro-
aromatic terminal alkynes (Table 2). In all cases, the matic terminal alkynes can be extended to 1-naphthy-
corresponding a-CF3 substituted tertiary propargylic lacetylene (entry 12) as well as heteroaromatic termi-
alcohols were isolated in good to excellent chemical nal alkynes[20] such as thiophene acetylenes (entries 13
yields. When phenylacetylene and substituted phenyl- and 14), and excellent stereocontrol (97 to >99% ee)
acetylenes acted as alkynylating reagents to react with was also observed. Although complex 3d gave compa-
ethyl trifluoropyruvate, complex 3e afforded ee values rable enantioselectivities to complex 3e in the alkyny-
higher than 96% regardless of the electronic property lation of ethyl trifluoropyruvate, in the reaction of
and the position of the substituent in the alkynes (en- methyl trifluoropyruvate it was obviously inferior to
tries 1–11). The substituent can be an electron-donat- complex 3e (entries 15–18). With the latter as the cat-
ing group such as Me or the aforementioned OMe alyst, alkynylations of methyl trifluoropyruvate with
and also be an electron-withdrawing group such as some representative aromatic and heteroaromatic al-
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Chiral NCN Pincer RhodiumACTHNUTRGNE(UNG III) Complexes with Bis(imidazolinyl)phenyl Ligands
Table 2. Catalytic asymmetric alkynylation of ethyl and methyl trifluoropyruvate with aromatic and heteroaromatic terminal
alkynes using complex 3d and 3e as the catalyst.[a]
Entry
Ar
R
Product
Catalyst 3d
Catalyst 3e
Yield[b] [%]
ee[c,d] [%]
Yield[b] [%]
ee[c,d] [%]
1
2
3
4
5
6
7
8
Ph
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
4a
4c
4d
4e
4f
4g
4h
4i
99
88
92
87
90
80
86
83
82
80
75
97
97
88
99
98
99
99
97
98
97
96
99
91
96
90
91
86
89
87
84
85
80
98
99
99
99
98
>99
99
99
98
97
96
4-Me-C6H4
3-Me-C6H4
2-Me-C6H4
4-F-C6H4
2-F-C6H4
4-Br-C6H4
3-Br-C6H4
4-CF3-C6H4
4-O2N-C6H4
4-OHC-C6H4
9
10
11
4j
4k
4l
12
Et
4m
89
98
93
98
13
14
Et
Et
4n
4o
83
84
99
97
85
88
>99
98
15
16
17
Ph
Me
Me
Me
4p
4q
4r
89
85
85
86
46
88
95
91
90
99
95
94
3-Me-C6H4
4-MeO-C6H4
18
Me
4s
86
99
90
>99
[a]
The reaction was run with aryl-substituted terminal alkyne (0.24 mmol), trifluoropyruvate (0.20 mmol), 3.0 mol% of Rh
complex at 258C for 24 h in Et2O (2 mL).
Isolated yields.
[b]
[c]
[d]
Enantiomeric excess was determined by chiral HPLC analysis.
The absolute configurations of the known products were assigned to be S by comparison of optical rotations with those
in ref.[12] and the configurations of the new products were assigned by analogy.
kynes all afforded the expected products in excellent 708C in the presence of complex 3e with the ratio of
yields and ee values (90–95% yields, 94 to >99% ee). alkyne and trifluoropyruvate being 3:1 (entry 2). In
Encouraged by the remarkable results with aromat- contrast with 4-phenyl-1-butyne, the related 4-phenyl-
ic or heteroaromatic alkynes, our attention was next 1-butyn-3-ene which is an enyne readily reacted with
turned to alkynylation with aliphatic terminal alkynes. ethyl trifluoropyruvate under the aforementioned
However, it was found that the reactions did not pro- standard conditions to produce the addition product
ceed as smoothly as expected. For example, when 4- in good yields with excellent enantioselectivities (82–
phenyl-1-butyne reacted with ethyl trifluoropyruvate 86% yields, 99% ee, entry 3). Similarly, cyclohexenyl-
under the above standard conditions low yields (29–
ACHTUNGTRENaNGNU cetylene, a cyclic enyne could also afford the corre-
34%) were obtained after 48 h although the enantio- sponding product in good yields after 48 h with excel-
selectivities were excellent (96–97% ee, Table 3, lent enantioselectivities (80–81% yields, 97–98% ee,
entry 1). Then numerous attempts including varying entry 4). The results suggested that the alkynylation
the solvent, temperature, the ratio of alkyne and tri- with aliphatic terminal alkynes might be correlated
fluoropyruvate as well as the addition of additive with the acidity of the alkynes. With the more acidic
were made to improve the yield of this alkynylation alkynes like enynes, the reaction became easier. Final-
reaction.[21] After much effort, a 77% yield with 98% ly, addition of several other aliphatic terminal alkynes
ee could be finally achieved when the reaction was to ethyl trifluoropyruvate under the modified condi-
conducted in a mixed solvent of toluene and Et2O at tions was investigated with the complex 3e as the cat-
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Table 3. Catalytic asymmetric alkynylation of ethyl trifluoropyruvate with aliphatic terminal alkynes using complex 3d or 3e
as the catalyst.[a]
Entry
R
Temperature [8C] Solvent
Product
Catalyst 3d
Catalyst 3e
Yield[b] [% ] ee[c,d] [%] Yield[b] [%] ee[c,d] [%]
1[e]
2
PhCH2CH2
PhCH2CH2
25
70
Et2O
toluene-Et2O 4t
4t
29
–
96
–
34
77
97
98
3[e,f]
25
25
Et2O
4u
82
80
99
97
86
81
99
4[e]
Et2O
4v
98
5
6
t-Bu
70
70
toluene-Et2O 4w
toluene-Et2O 4x
–
–
–
–
68
85
95[g]
85[g]
7
8
9
n-Pr
n-C6H13
(EtO)2CH
70
70
70
toluene-Et2O 4y
toluene-Et2O 4z
toluene-Et2O 4#
–
–
–
–
–
–
71
73
80
85[g]
52
63
[a]
The reaction was run with aliphatic terminal alkyne (0.60 mmol), ethyl trifluoropyruvate (0.20 mmol), 3.0 mol% of Rh
complex for 48 h in Et2O or toluene-Et2O (2 mL).
Isolated yields.
Enantiomeric excess was determined by chiral HPLC analysis.
The absolute configurations of the known products were assigned to be S by comparison of optical rotations with those
in ref. [12] and the configurations of the new products were assigned by analogy.
Terminal alkyne (0.24 mmol), ethyl trifluoropyruvate (0.20 mmol).
Reaction time was 24 h.
[b]
[c]
[d]
[e]
[f]
[g]
The absolute configurations of the products were assigned to be R.
alyst (entries 5–9). Overall, the results were not as Conclusions
good as those in the alkynylation with aromatic al-
kynes and enynes although in some cases good to ex- In conclusion, a new class of NCN pincer RhACHTUNGTRENNUNG(III)
cellent enantioselectivities were achieved (entries 5– complexes with Phebim ligands as chiral catalysts has
7). been developed. These complexes are easy to prepare
To further extend the potential application of the and their structures can be readily modified as well.
present system, the alkynylation of ethyl trifluoropyr- Furthermore, they have revealed high activity and
uvate with phenylacetylene was carried out on enantioselectivity in the catalytic asymmetric alkyny-
a larger scale (2.0 mmol) with the loading of complex lation of trifluoropyruvates with terminal alkynes.
3e being reduced from 3.0 mol% to 1.5 mol%. An With a typical catalyst loading of 3.0 mol%, a variety
89% yield with 96% ee could still be obtained of electronically and structurally diverse terminal al-
(Scheme 2).
kynes including phenylacetylenes, naphthylacetylene,
thiophene acetylenes, enynes as well as some other
aliphatic alkynes reacted smoothly with ethyl or
methyl trifluoropyruvate to afford the optically active
CF3-substituted tertiary propargylic alcohols in high
yields with enantioselectivities of up to >99% ee. Fur-
ther modification of the pincer Rh/Phebim complexes
and their applications in asymmetric catalysis are in
progress.
Scheme 2. Scaled-up version of the asymmetric alkynylation
of ethyl trifluoropyruvate with phenylacetylene.
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Chiral NCN Pincer RhodiumACTHNUTRGNE(UNG III) Complexes with Bis(imidazolinyl)phenyl Ligands
6.65 (m, 3H, ArH), 5.35 (app t, J=11.5 Hz, 2H, NCH), 4.49
(app t, J=10.2 Hz, 2H, NCHH), 3.83 (dd, J=9.6, 12.3 Hz,
2H, NCHH), 2.41 (s, 6H, CH3), 1.97 (br s, 2H, OH2);
13C NMR (100 MHz, CDCl3): d=168.6, 140.2, 138.2, 137.8,
134.7, 130.3, 128.6, 128.3, 128.2, 126.4, 121.2, 66.5, 64.0, 21.2;
Experimental Section
General Procedures
Solvents were dried with standard methods and freshly dis-
tilled prior to use if needed. The 1,3-bis(2’-imidazolinyl)ben-
zene ligands 1a–e were synthesized according to the litera-
ture method reported by us.[15b] Melting points were mea-
sured on a WC-1 instrument and are uncorrected. Infrared
spectra were obtained with a Bruker VECTOR 22 spectro-
photometer in KBr pellets. NMR spectra were recorded on
a Bruker DPX 400 instrument using TMS as an internal
standard. HR-MS were determined on a Waters Q-Tof
Micro MS/MS system ESI spectrometer. Elemental analyses
were measured on a Thermo Flash EA 1112 elemental ana-
lyzer. Optical rotations were recorded on a Perkin–Elmer
341 polarimeter.
aal. found:
C
60.48,
H
4.91,
N
6.98; calcd. for
C38H35Cl2N4ORh·0.25CH2Cl2: C 60.55, H 4.72, N 7.38.
Complex (2b): Yield: 52%; mp 228–2308C; [a]2D0: +369 (c
0.170, CHCl3). IR (KBr): n=3415, 2923, 1757, 1580, 1512,
1405, 1300, 1158, 1095, 817, 702, 466 cmÀ1
;
1H NMR
(400 MHz, CDCl3): d=7.31–7.26 (m, 7H, ArH), 7.23–7.17
(m, 7H, ArH), 7.11 (d, J=8.3 Hz, 4H, ArH), 6.69–6.63 (m,
3H, ArH), 4.71–4.63 (m, 2H, NCH), 4.07 (app t, J=
10.0 Hz, 2H, NCHH), 3.81 (dd, J=7.2, 9.7 Hz, 2H, NCHH),
3.72 (dd, J=3.8, 14.0 Hz, 2H, CH2Ph), 2.91 (dd, J=10.5,
14.0 Hz, 2H, CH2Ph), 2.81 (br s, 2H, OH2), 2.38 (s, 6H,
CH3); 13C NMR (100 MHz, CDCl3): d=166.5, 138.1, 138.0,
137.5, 134.6, 130.1, 129.3, 128.6, 128.0, 126.4, 126.2, 121.4,
63.4, 59.8, 41.0, 21.1; anal. found: C 60.75, H 4.68, N 6.92;
calcd. for C40H39Cl2N4ORh·0.5CH2Cl2: C 60.20, H 4.99; N
6.93.
General Procedure for the Synthesis of
(Phebim)RhCl2ACHTUNGTRENNUNG(H2O) Complexes 2a–e
Complex (2c): Yield: 26%; mp 221–2238C; [a]2D0: +432 (c
0.116, CHCl3). IR (KBr): n=3421, 3193, 2929, 2854, 1704,
Bis(imidazoline)benzene
1
(0.55 mmol), RhCl3·3H2O
1569, 1531, 1486, 1403, 1270, 1094, 756, 700, 475 cmÀ1
;
(131 mg, 0.50 mmol), and sodium bicarbonate (46 mg,
0.55 mmol) were added in a 50-mL flask. After addition of
methanol (20 mL) and H2O (2 mL), the resulting solution
mixture was stirred at 658C for 14 h. After cooling, filtra-
tion, and evaporation, the residue was purified by prepara-
tive TLC on silica gel plates using CH2Cl2 (for 2a, 2c–e) or
CH2Cl2/ethyl acetate 20/1 (for 2b) as the eluent.
1H NMR (400 MHz, CDCl3): d=7.82 (d, J=8.0 Hz, 2H,
ArH), 7.36–7.24 (m, 21H, ArH), 4.84 (d, J=8.4 Hz, 2H,
NCH), 4.75 (d, J=8.4 Hz, 2H, NCH), 4.48–4.41 (m, 2H,
NCy-H), 2.00–1.74 (m, 4H, CyH), 1.68–1.53 (m, 4H, CyH),
1.44–1.23 (m, 6H, CyH), 0.98–0.87 (m, 6H, CyH). 13C NMR
(100 MHz, CDCl3): d=169.2, 143.6, 141.0, 136.2, 128.8,
128.4, 128.0, 127.9, 127.8, 127.4, 127.1, 122.7, 75.9, 71.7, 57.6,
33.8, 30.9, 26.0, 25.8, 25.2; anal. found: C 63.90, H 5.89, N
6.17; calcd. for C48H51Cl2N4ORh·0.5CH2Cl2: C 63.58, H 5.72,
N 6.11.
New ligand (1d): Yield: 53%; mp 117–1198C; [a]2D0: +444
(c 0.540, CHCl3). IR (KBr): n=3421, 3027, 2920, 2363, 1618,
1569, 1511, 1383, 1266, 1110, 813, 754, 697, 516 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=8.25 (s, 1H, ArH), 7.73
(dd, 2H, J=1.7, 7.8 Hz, ArH), 7.43–7.40 (m, 4H, ArH),
7.37–7.32 (m, 10H, ArH), 7.28–7.25 (m, 7H, ArH), 6.90 (d,
J=8.2 Hz, 4H, ArH), 6.59 (d, J=8.2 Hz, 4H, ArH), 5.07 (d,
J=6.5 Hz, 2H, NCH), 4.59 (d, J=6.5 Hz, 2H, NCH), 2.24
(s, 6H, CH3); 13C NMR (100 MHz, CDCl3): d=164.5, 145.2,
144.8, 142.6, 136.2, 132.6, 132.3, 131.7, 130.9, 130.5, 130.2,
129.5, 129.2, 128.8, 128.0, 127.9, 126.0, 80.4, 80.1, 22.3; MS
(ESI+): m/z=699.5 (M+H); HR-MS (positive ESI): m/z=
699.3486 [M+H]+, calcd. for C50H43N4: 699.3488.
Complex (2d): Yield: 34%; mp 216–2188C; [a]2D0: +646 (c
0.118, CHCl3). IR (KBr): n=3420, 3167, 1701, 1576, 1483,
1403, 1158, 1103, 751, 698 cmÀ1
;
1H NMR (400 MHz,
CDCl3): d=7.41 (d, J=6.9 Hz, 4H, ArH), 7.36–7.24 (m,
18H, ArH), 7.13–7.06 (m, 5H, ArH), 6.75 (br s, 1H, ArH),
6.70–6.66 (m, 1H, ArH), 6.59 (d, J=8.0 Hz, 2H, ArH), 5.25
(d, J=10.0 Hz, 2H, NCH), 4.76 (d, J=10.0 Hz, 2H, NCH),
2.32 (s, 6H, CH3); 13C NMR (100 MHz, CDCl3): d=168.5,
140.1, 139.6, 138.3, 137.6, 134.9, 130.2, 128.9, 128.6, 128.5,
128.4, 128.3, 128.1, 128.0, 121.7, 80.4, 76.0, 21.2; anal. found:
Ligand (1e): Yield: 30%; mp 123–1258C; [a]2D0: +385 (c
0.300, CHCl3). IR (KBr): n=3463, 3113, 2961, 2231, 1757,
C
65.79,
H
5.01,
N
5.70;
calcd.
for
1441, 1293, 1233, 1191, 1121, 1023, 985, 852, 810, 710 cmÀ1
;
C50H43Cl2N4ORh·0.25CH2Cl2: C 66.25, H 4.81, N 6.15.
1H NMR (400 MHz, CDCl3): d=8.58 (d, J=1.5 Hz, 2H,
ArH), 8.38 (t, J=1.5 Hz, 1H, ArH), 7.45–7.35 (m, 10H,
ArH), 7.32–7.28 (m, 6H, ArH), 7.26–7.24 (m, 4H, ArH),
6.96 (d, J=8.2 Hz, 4H, ArH), 6.60 (d, J=8.2 Hz, 4H, ArH),
5.11 (d, J=7.4 Hz, 2H, NCH), 4.58 (d, J=7.4 Hz, 2H,
NCH), 2.27 (s, 6H, CH3); 13C NMR (100 MHz, CDCl3): d=
161.4, 147.8, 142.9, 142.8, 140.5, 136.1, 135.5, 132.9, 130.0,
129.1, 128.9, 128.1, 127.7, 126.8, 126.6, 125.4, 125.3, 79.7,
78.9, 21.0; MS (ESI+): m/z=744.5 (M+H); HR-MS (posi-
tive ESI): m/z=744.3333 [M+H]+, calcd. for C50H42N5O2:
744.3339.
Complex (2e): Yield: 31%; mp 255–2578C; [a]2D0: +678 (c
0.134, CHCl3). IR (KBr): n=3423, 3168, 1698, 1590, 1513,
1486, 1452, 1398, 1329, 1271, 1106, 746, 699, 471 cmÀ1.
1H NMR (400 MHz, CDCl3): d=7.40–7.38 (m, 6H, ArH),
7.34–7.25 (m, 17H, ArH), 7.21–7.13 (m, 5H, ArH), 6.82 (br
s, 2H, ArH), 5.26 (d, J=11.2 Hz, 2H, NCH), 4.86 (d, J=
11.2 Hz, 2H, NCH), 2.35 (s, 6H, CH3); 13C NMR (100 MHz,
CDCl3): d=167.8, 143.7, 139.4, 139.2, 138.7, 136.5, 135.3,
130.6, 129.0, 128.9, 128.6, 128.4, 128.3, 128.1, 122.3, 80.4,
76.2, 21.2; anal. found: C 63.23, H 4.64, N 6.97; calcd. for
C50H42Cl2N5O3Rh·0.25CH2Cl2: C 63.14, H 4.48, N, 7.33.
Pincer RhACHTUNGTRENNUNG(III) chloride complex (2a): Yield: 57%; mp
199–2028C; [a]2D0: +912 (c 0.176, CHCl3). IR (KBr): n=
3422, 3177, 3029, 2921, 2857, 1577, 1490, 1404, 1254, 1159,
1106, 1038, 1022, 823, 762, 699, 522 cmÀ1
;
1H NMR
(400 MHz, CDCl3): d=7.58 (d, J=7.1 Hz, 4H, ArH), 7.36
(t, J=7.3 Hz, 4H, ArH), 7.32–7.22 (m, 10H, ArH), 6.73–
Adv. Synth. Catal. 2013, 355, 927 – 937
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
933

Tao Wang et al.
FULL PAPERS
141.4, 141.0, 137.9, 137.3, 135.1, 130.1, 129.0, 128.6, 128.5,
127.84, 127.80, 127.4, 127.2, 127.0, 121.4, 79.2, 75.5, 23.3,
21.2; anal. found: C 65.80, H 5.12, N 5.34; calcd. for
C54H49N4O5Rh·0.75CH2Cl2: C 65.72, H 5.09, N 5.60.
General Procedure for the Synthesis of
(Phebim)RhACHTUNGTRENNUNG(OAc)2ACHTUNGTREN(NNGU H2O) Complexes 3a–e
To a stirred solution of 2 (0.20 mmol) in CH2Cl2 (5 mL) was
added AgOAc (67 mg, 0.40 mmol), the resulting solution
mixture was stirred at room temperature for 12 h. After fil-
tration and concentration under vacuum, the residue was
purified by preparative TLC on silica gel plates eluting with
CH2Cl2/ethyl acetate (10/1) to afford the corresponding
complexes 3a–e.
Complex (3e): Yield: 90%; mp 269–2718C; [a]2D0: +160 (c
0.124, CHCl3); IR (KBr): n=3416, 3165, 3031, 2924, 2361,
1757, 1630, 1590, 1488, 1396, 1326, 1104, 821, 758, 696 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=7.48 (s, 2H, ArH), 7.32–
7.28 (m, 18H, ArH), 7.22–7.01 (m, 8H, ArH), 6.81 (br s,
2H, ArH), 5.17 (d, J=7.0 Hz, 2H, NCH), 5.16 (br s, 2H,
OH2), 4.97 (d, J=7.0 Hz, 2H, NCH), 2.37 (s, 6H, CH3), 1.59
(s, 6H, OAc); 13C NMR (100 MHz, CDCl3): d=207.3 (d, J=
26.4 Hz), 181.0, 167.5, 143.3, 140.7, 140.3, 138.9, 136.2, 135.3,
130.5, 129.1, 128.74, 128.69, 128.2, 127.4, 127.2, 121.8, 79.3,
75.5, 23.3, 21.2; anal. found: C 63.06, H 4.75, N 6.58; calcd.
for C54H48N5O7Rh·0.75CH2Cl2: C 62.89, H 4.77, N 6.70.
Pincer RhACHTUNGTRENNUNG(III) acetate complex (3a): Yield: 95%; mp
154–1568C; [a]2D0: +325 (c 0.156, CHCl3). IR (KBr): n=
3416, 3168, 1757, 1626, 1578, 1514, 1400, 1321, 1158, 1104,
696, 476 cmÀ1 1H NMR (400 MHz, CDCl3): d=7.43–7.41
;
(m, 4H, ArH), 7.31–7.22 (m, 14H, ArH), 6.72 (s, 3H, ArH),
5.39 (dd, J=8.6, 11.1 Hz, 2H, NCH), 4.49 (dd, J=9.7,
11.1 Hz, 2H, NCHH), 4.03 (dd, J=8.6, 9.7 Hz, 2H, NCHH),
3.60 (br s, 2H, OH2), 2.41 (s, 6H, CH3), 1.54 (s, 6H, OAc);
13C NMR (100 MHz, CDCl3): d=181.0, 168.1, 141.6, 138.2,
137.6, 135.0, 130.3, 128.4, 127.9, 127.82, 127.76, 126.2, 121.2,
66.3, 63.6, 23.7, 21.2; anal. found: C 60.80, H 5.14, N 6.50;
calcd. for C42H41N4O5Rh·0.75CH2Cl2: C 60.52, H 5.05, N
6.60.
General Procedure for the Asymmetric Alkynylation
of Trifluoropyruvate with Aromatic Terminal Alkynes
by (Phebim)RhACTHNUTRGENN(UG OAc)2ACHTUNTGRENN(UGN H2O) Complexes 3
Under an argon atmosphere, the (Phebim)RhACTHNUTRGNEN(UG OAc)2ACHTUNGTRENNUNG(H2O)
Complex (3b): Yield: 82%; mp 195–1978C; [a]2D0: +336 (c
0.128, CHCl3). IR (KBr): n=3416, 3167, 1758, 1622, 1582,
complex 3 (0.006 mmol, 3.0 mol%) was dissolved in 2 mL of
Et2O. Ethyl trifluoropyruvate or methyl trifluoropyruvate
(0.20 mmol) was added, followed by aromatic terminal
alkyne (0.24 mmol), then the resulting solution mixture was
stirred at 258C for 24 h. The residue was purified by prepa-
rative TLC on silica gel plates eluting with CH2Cl2/petrole-
um ether to afford the desired product.
1536, 1513, 1494, 1400, 1326, 1097, 819, 705, 472 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=7.51 (br s, 2H, OH2), 7.32
(d, J=7.1 Hz, 4H, ArH), 7.29–7.25 (m, 4H, ArH), 7.21–7.13
(m, 6H, ArH), 7.04 (d, J=7.9 Hz, 4H, ArH), 6.68–6.61 (m,
3H, ArH), 4.75–4.67 (m, 2H, NCH), 4.14–4.05 (m, 2H,
NCHH), 3.83 (dd, J=7.4, 9.6 Hz, 2H, NCHH), 3.65 (dd, J=
3.9, 13.7 Hz, 2H, PhCH2), 2.86 (dd, J=9.1, 13.7 Hz, 2H,
PhCH2), 2.37 (s, 6H, CH3), 1.83 (s, 6H, OAc); 13C NMR
(100 MHz, CDCl3): d=191.9 (d, J=26.8 Hz), 182.3, 167.5,
137.98, 137.95, 137.4, 135.0, 130.1, 129.7, 128.4, 127.5, 126.4,
126.0, 121.2, 63.6, 59.3, 40.3, 23.9, 21.1; anal. found: C 63.92,
H 5.49, N 6.67; calcd. for C44H45N4O5Rh·0.25CH2Cl2: C
63.73, H 5.50, N 6.72.
General Procedure for the Asymmetric Alkynylation
of Trifluoropyruvate with Aliphatic Terminal Alkynes
by (Phebim)RhACTHNUTRGENN(UG OAc)2ACHTUNTGRENN(UGN H2O) Complexes 3
Under an argon atmosphere, the (Phebim)RhACTHNUTRGNEN(UG OAc)2ACHTUNGTRENNUNG(H2O)
complex 3 (0.006 mmol, 3.0 mol%) was dissolved in a mixed
solvent of toluene and Et2O (2 mL, v/v=1:1). Ethyl trifluor-
opyruvate (0.20 mmol) was added, followed by aliphatic ter-
minal alkyne (0.60 mmol), then the resulting solution mix-
ture was stirred at 708C for 48 h. The residue was purified
by preparative TLC on silica gel plates eluting with CH2Cl2/
petroleum ether to afford the desired product.
The analytical data of the new catalysis products are
given here and those of the known products are given in
Supporting Information.
Compound (4g): The ee was determined on a Daicel Chir-
alcel OD-H column with hexane/2-propanol=300/1, flow=
0.25 mLminÀ1, and detected at a UV wave length of
228 nm; retention times: 97.7 min, 104.4 min (major), >99%
ee; [a]2D0: +52.3 (c 0.911, CHCl3). 1H NMR (400 MHz,
CDCl3): d=7.51–7.47 (m, 1H, Ar-H), 7.41–7.35 (m, 1H, Ar-
H), 7.15–7.07 (m, 2H, Ar-H), 4.47 (q, J=7.1 Hz, 2H,
OCH2CH3), 4.33 (br s, 1H, OH), 1.40 (t, J=7.1 Hz, 3H,
OCH2CH3); 13C NMR (100 MHz, CDCl3): d=166.3, 163.3
(d, JC,F =253 Hz), 133.9, 131.6 (d, JC,F =8.0 Hz), 124.0 (d,
Complex (3c): Yield: 92%; mp 151–1538C; [a]2D0: À14.0 (c
0.142, CHCl3). IR (KBr): n=3417, 3172, 2928, 2854, 1758,
1626, 1531, 1488, 1400, 1320, 1095, 758, 698, 472 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=7.80 (d, J=8.0 Hz, 2H,
ArH), 7.37 (t, J=7.9 Hz, 1H, ArH), 7.28–7.22 (m, 16H,
ArH), 7.18–7.15 (m, 4H, ArH), 4.87 (d, J=4.7 Hz, 2H,
NCH), 4.82 (d, J=4.7 Hz, 2H, NCH), 4.63 (br s, 2H, OH2),
4.51–4.45 (m, 2H, NCy-H), 2.04–1.75 (m, 6H, CyH), 1.69–
1.53 (m, 6H, CyH), 1.40 (s, 6H, OAc), 1.35–1.24 (m, 2H,
CyH), 1.00–0.84 (m, 6H, CyH); 13C NMR (100 MHz,
CDCl3): d=194.8 (d, J=27.2 Hz), 180.8, 168.7, 144.2, 142.3,
136.3, 129.1, 128.6, 128.1, 127.7, 127.1, 126.7, 126.3, 122.5,
74.9, 70.7, 56.7, 34.0, 31.9, 29.8, 25.9, 25.2, 23.2; anal. found:
C 67.30, H 6.57, N 5.35; calcd. for C52H57N4O5Rh·C3H6O: C
67.47, H 6.49, N 5.72.
Complex (3d): Yield: 85%; mp 255–2588C; [a]2D0: +198 (c
0.104, CHCl3). IR (KBr): n=3416, 3197, 3030, 2922, 1628,
1575, 1534, 1485, 1403, 1318, 1158, 1108, 1018, 751,696 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=7.36–7.25 (m, 18H, ArH),
7.24–7.20 (m, 5H, ArH), 7.10 (br s, 5H, ArH), 6.76–6.72 (m,
1H, ArH), 6.69–6.66 (m, 2H, ArH), 5.21 (d, J=6.5 Hz, 2H,
NCH), 5.10 (br s, 2H, OH2), 4.90 (d, J=6.5 Hz, 2H, NCH),
2.34 (s, 6H, CH3), 1.58 (s, 6H, OAc); 13C NMR (100 MHz,
CDCl3): d=193.4 (d, J=26.7 Hz), 181.0, 167.99, 167.96,
J
C,F =3.7 Hz), 121.7 (q, JC,F =285 Hz), 115.7 (d, JC,F =20 Hz),
109.4 (d, JC,F =15 Hz), 84.7, 80.8, 71.7 (q, JC,F =34 Hz), 65.2,
13.8; 19F NMR (376 MHz, CDCl3): d=À78.1, À108.8; IR
(KBr): n=3467, 2991, 2245, 1752, 1494, 1452, 1234, 1195,
1129, 1052, 760 cmÀ1; HR-MS (positive ESI): m/z=313.0467
[M+Na]+, calcd. for C13H10O3F4Na: 313.0464.
934
asc.wiley-vch.de
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2013, 355, 927 – 937

Chiral NCN Pincer RhodiumACTHNUTRGNE(UNG III) Complexes with Bis(imidazolinyl)phenyl Ligands
Compound (4i): The ee was determined on a Daicel Chir-
alcel OD-H column with hexane/2-propanol=99/1, flow=
0.5 mLminÀ1, and detected at a UV wave length of 228 nm;
retention times: 24.3 min (major), 27.9 min, 99% ee; [a]2D0:
+49.7 (c 0.535, CHCl3); 1H NMR (400 MHz, CDCl3): d=
7.65 (s, 1H, Ar-H), 7.52 (d, J=7.9 Hz, 1H, Ar-H), 7.43 (d,
J=7.9 Hz, 1H, Ar-H), 7.21 (t, J=7.9 Hz, 1H, Ar-H), 4.54–
4.40 (m, 2H, OCH2CH3), 4.31 (br s, 1H, OH), 1.40 (t, J=
7.1 Hz, 3H, OCH2CH3); 13C NMR (100 MHz, CDCl3): d=
7.43 (d, J=8.8 Hz, 2H, Ar-H), 6.85 (d, J=8.8 Hz, 2H, Ar-
H), 4.27 (br s, 1H, OH), 4.00 (s, 3H, COOCH3), 3.81 (s, 3H,
OCH3); 13C NMR (100 MHz, CDCl3): d=167.2, 160.6, 133.8,
121.8 (q, JC,F =285 Hz), 114.0, 112.5, 87.6, 78.3, 71.8 (q, JC,F
=
34 Hz), 55.3, 55.2; 19F NMR (376 MHz, CDCl3): d=À78.3;
IR (KBr): n=3459, 2962, 2845, 2235, 1756, 1607, 1512, 1250,
1194, 1125, 1052, 986, 835, 802, 740, 540 cmÀ1; HR-MS (posi-
tive
ESI):
m/z=311.0506,
[M+Na]+,
calcd.
for
C13H11O4F3Na: 311.0507.
Compound (4q): The ee was determined on a Daicel Chir-
alcel OD-H column with hexane/2-propanol=99/1, flow=
0.5 mLminÀ1, and detected at a UV wave length of 228 nm;
retention times: 31.7 min (major), 36.3 min, 95% ee; [a]2D0:
+63.1 (c 0.408, CHCl3). 1H NMR (400 MHz, CDCl3): d=
7.33–7.30 (m, 2H, Ar-H), 7.24–7.18 (m, 2H, Ar-H), 4.28 (br
s, 1H, OH), 4.01 (s, 3H, COOCH3), 2.33 (s, 3H, CH3);
13C NMR (100 MHz, CDCl3): d=167.1, 138.2, 132.7, 130.6,
129.3, 128.3, 121.7 (q, JC,F =285 Hz), 120.3, 87.6, 79.1, 71.7
(q, JC,F =34 Hz), 55.3, 21.1; 19F NMR (376 MHz, CDCl3): d=
À78.3. IR (KBr): n=3465, 2961, 2238, 1756, 1444, 1399,
1290, 1238, 1184, 1123, 1057, 988, 787, 739, 689 cmÀ1; HR-
MS (positive ESI): m/z=295.0555, [M+Na]+ calcd for
C13H11O3F3Na: 295.0558.
Compound (4s): The ee was determined on a Daicel Chir-
alcel OD-H column with hexane/2-propanol=300/1, flow=
0.8 mLminÀ1, and detected at a UV wave length of 254 nm;
retention times: 62.8 min, 68.2 min (major), >99% ee; [a]2D0:
+70.6 (c 0.795, CHCl3). 1H NMR (400 MHz, CDCl3): d=
7.34–7.33 (m, 2H, Ar-H), 7.00–6.99 (m, 1H, Ar-H), 4.28 (br
s, 1H, OH), 4.00 (s, 3H, CH3); 13C NMR (100 MHz, CDCl3):
d=166.8, 134.4, 129.0, 127.1, 121.6 (q, JC,F =285 Hz), 120.2,
83.2, 81.0, 71.9 (q, JC,F =34 Hz), 55.3; 19F NMR (376 MHz,
CDCl3): d=À78.1; IR (KBr): n=3463, 3113, 2961, 2231,
1757, 1441, 1293, 1233, 1191, 1121, 1023, 985, 852, 810,
710 cmÀ1; HR-MS (positive ESI): m/z=286.9968, [M+Na]+,
calcd. for C10H7O3F3SNa: 286.9966.
166.3, 134.9, 132.9, 130.7, 129.9,122.6, 122.2, 121.7 (q, JC,F
=
285 Hz), 85.5, 81.0, 71.7 (q,
JC,F =34 Hz), 65.2, 13.8;
19F NMR (376 MHz, CDCl3): d=À78.1; IR (KBr): n=3466,
2988, 2242, 1751, 1473, 1227, 1195, 1127, 1053, 786 cmÀ1
;
HR-MS (positive ESI): m/z=372.9664 [M+Na]+, calcd. for
C13H10O3F3BrNa: 372.9663..
Compound (4k): The ee was determined on a Daicel Chir-
alcel OD-H column with hexane/2-propanol=99/1, flow=
1.0 mLminÀ1, and detected at a UV wave length of 254 nm;
retention times: 46.3 min (major), 59.2 min, 97% ee; [a]2D0:
+39.8 (c 0.688, CHCl3). 1H NMR (400 MHz, CDCl3): d=
8.23 (d, J=8.9 Hz, 2H, Ar-H), 7.68 (d, J=8.9 Hz, 2H, Ar-
H), 4.57–4.42 (m, 2H, OCH2CH3), 1.41 (t, J=7.1 Hz, 3H,
OCH2CH3); 13C NMR (100 MHz, CDCl3): d=165.9, 148.0,
133.1, 127.3, 123.6, 120.1 (q, JC,F =285 Hz), 84.8, 84.4, 71.5
(q, JC,F =34 Hz), 65.4, 13.9; 19F NMR (376 MHz, CDCl3): d=
À78.0; IR (KBr): n=3447, 3178, 2925, 1757, 1638, 1526,
1456, 1398, 1351, 1195, 1129, 1095, 858, 751, 698 cmÀ1; HR-
MS (positive ESI): m/z=340.0411 [M+Na]+, calcd. for
C13H10O5F3NNa: 340.0409.
Compound (4n): The ee was determined on a Daicel Chir-
alcel OD-H column with hexane/2-propanol=300/1, flow=
0.8 mLminÀ1, and detected at a UV wave length of 254 nm;
retention times: 41.0 min, 46.2 min (major), >99% ee; [a]2D0:
+52.5 (c 0.828, CHCl3). 1H NMR (400 MHz, CDCl3): d=
7.35–7.33 (m, 2H, Ar-H), 6.99 (dd, J=5.0, 3.8 Hz, 1H, Ar-
H), 4.53–4.39 (m, 2H, OCH2CH3), 4.34 (br s, 1H, OH), 1.39
(t, J=7.1 Hz, 3H, OCH2CH3); 13C NMR (100 MHz, CDCl3):
d=166.3, 134.2, 129.0, 127.1, 120.3, 121.7 (q, JC,F =285 Hz),
Compound (4z): The ee was determined on a Daicel Chir-
alcel OD-H column with hexane/2-propanol=100/0.5,
flow=0.3 mLminÀ1, and detected at a UV wave length of
215 nm; retention times: 22.9 min, 26.7 min (major), 52%
ee; [a]2D0: +15.6 (c 0.680, CHCl3). 1H NMR (400 MHz,
CDCl3): d=4.48–4.35 (m, 2H, OCH2CH3), 4.21 (br s, 1H,
OH), 2.26 (t, J=7.1 Hz, 2H, CH2CH2CH2CH2CH2CH3),
1.59–1.50 (m, 2H, CH2CH2CH2CH2CH2CH3), 1.43–1.34 (m,
5H, CH2CH2CH2CH2CH2CH3), 1.32–1.26 (m, 4H,
CH2CH2CH2CH2CH2CH3), 0.89 (t, J=6.9 Hz, 3H,
OCH2CH3); 13C NMR (100 MHz, CDCl3): d=166.9, 120.4
(q, JC,F =284 Hz), 89.2, 71.5, 71.2 (q, JC,F =34 Hz), 64.8, 31.3,
28.4, 27.8, 22.5, 18.7, 14.0, 13.8; 19F NMR (376 MHz,
CDCl3): d=À78.7; IR (KBr): n=3480, 2935, 2864, 1750,
1463, 1299, 1244, 1170, 1103, 1016, 692 cmÀ1; HR-MS (posi-
83.5, 80.8, 71.9 (q,
J
C,F =34 Hz), 65.2, 13.8; 19F NMR
(376 MHz, CDCl3): d=À78.0; IR (KBr): n=3463, 2988,
2231, 1751, 1300, 1190, 1120, 1023, 855, 710 cmÀ1; HR-MS
(positive ESI): m/z=301.0124, [M+Na]+, calcd. for
C11H9O3F3SNa: 301.0122.
Compound (4u): The ee was determined on a Daicel Chir-
alpak AD-H column with hexane/2-propanol=97/3, flow=
1.0 mLminÀ1, and detected at a UV wave length of 254 nm;
retention times: 17.0 min (major), 24.2 min, 99% ee; [a]2D0:
+47.0 (c 0.858, CHCl3). 1H NMR (400 MHz, CDCl3): d=
7.40–7.31 (m, 5H, Ar-H), 7.09 (d, J=16.4 Hz, 1H, -CH=
CH), 6.15 (d, J=16.4 Hz, 1H, -CH=CH), 4.53–4.38 (m, 2H,
OCH2CH3), 1.39 (t, J=7.1 Hz, 3H, OCH2CH3); 13C NMR
(100 MHz, CDCl3): d=166.5, 144.7, 135.4, 129.4, 128.8,
tive
ESI):
m/z=303.1183,
[M+Na]+,
calcd.
for
C13H19O3F3Na: 303.1184.
126.6, 120.3 (q, JC,F =285 Hz), 105.6, 86.5, 81.4, 71.6 (q, JC,F
=
34 Hz), 65.1, 13.8; 19F NMR (376 MHz, CDCl3): d=À78.2.
IR (KBr): n=3448, 3175, 2925, 2857, 1751, 1626, 1456, 1399,
1179, 1107, 960, 750, 696 cmÀ1; HR-MS (positive ESI): m/z=
299.0893 [M+H]+, calcd. for C15H14O3F3: 299.0895.
Supporting Information
Compound (4r): The ee was determined on a Daicel Chir-
alcel OD-H column with hexane/2-propanol=97/3, flow=
0.5 mLminÀ1, and detected at a UV wave length of 254 nm;
retention times: 31.4 min (major), 39.9 min, 94% ee; [a]2D0:
+55.2 (c 0.308, CHCl3). 1H NMR (400 MHz, CDCl3): d=
CCDC 880619 (for 2c’) and CCDC 880618 (for 2d’) contain
the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
Adv. Synth. Catal. 2013, 355, 927 – 937
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
935

Tao Wang et al.
FULL PAPERS
Crystal structure determination and crystallographic data
of pincer Rh complexes 2c’ and 2d’, additional results on the
catalytic alkynylation of ethyl trifluoropyruvate with aliphat-
ic terminal alkynes, characterization data of the known
asymmetric catalysis products, figures of the 1H and
13C NMR spectra of the new compounds 1–3, 1 H, 13C and
19F NMR spectra of the catalysis products 4 as well as their
chiral HPLC spectra are available in the Supporting Infor-
mation.
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