Mechanistic Aspects of the Carboxylative Cyclization of Propargylamines and Carbon Dioxide Catalyzed by Gold(I) Complexes Bearing an N-Heterocyclic Carbene Ligand

Article abstract of DOI:10.1021/acscatal.5b01335

The carboxylative cyclization of a range of propargylic amines using carbon dioxide (CO₂) is promoted by IPr-gold(I) (IPr = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene) complexes to afford (Z)-5-alkylidene-2-oxazolidones in methanol under mild conditions, even in the absence of additives such as silver salts and bases. Investigation of the substrate scope shows that the catalytic performance is markedly retarded by the introduction of aromatic substituents at the alkyne terminus. The formation of alkenylgold(I) complexes as catalytic intermediate models is demonstrated by the treatment of methyl- and phenyl-substituted propargylamines with AuOH(IPr) under a CO₂ atmosphere. A comparison of the reactivity of the alkenylgold(I) complexes clearly indicates that the alkenyl ligand attached to an alkyl group at the α position is more susceptible to protonolysis compared with that attached to a phenyl group. These results and kinetic experiments corroborate a catalytic cycle that involves the nucleophilic attack of carbamate at the C-C triple bond bound to the Au center and its subsequent protodeauration to release the cyclic urethane products.

Full text of DOI:10.1021/acscatal.5b01335

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Mechanistic Aspects of the Carboxylative Cyclization of
Propargylamines and Carbon Dioxide Catalyzed by Gold(I)
Complexes Bearing an N-Heterocyclic Carbene Ligand
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Shun Hase, Yoshihito Kayaki,* and Takao Ikariya*
Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama
2-12-1-E4-1, Meguro-ku, Tokyo 152-8552, JAPAN.
Supporting Information Placeholder
propargylamines (1) under ambient CO2 conditions to afford
5-vinylidene-2-oxazolidones (2) (Scheme 1).14b An intensive
comparative study on the choice of ligands and solvents revealed
ABSTRACT: The carboxylative cyclization of a range of
propargylic amines using carbon dioxide (CO2) is promoted by
IPr-gold(I) (IPr
= 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-
that
the
use
of
gold(I)
chloride
with
a
ylidene) complexes to afford (Z)-5-alkylidene-2-oxazolidones in
methanol under mild conditions, even in the absence of additives
such as silver salts and bases. Investigation of the substrate scope
shows that the catalytic performance is markedly retarded by the
introduction of aromatic substituents at the alkyne terminus. The
formation of alkenylgold(I) complexes as catalytic intermediate
models is demonstrated by the treatment of methyl- and
phenyl-substituted propargylamines with AuOH(IPr) under a CO2
atmosphere. A comparison of the reactivity of the alkenylgold(I)
complexes clearly indicates that the alkenyl ligand attached to an
alkyl group at the  position is more susceptible to protonolysis
compared with that attached to a phenyl group. These results
and kinetic experiments corroborate a catalytic cycle that involves
the nucleophilic attack of carbamate at the C-C triple bond bound
to the Au center and its subsequent protodeauration to release the
cyclic urethane products. KEYWORDS: gold catalysis, carbon
dioxide, carboxylative cyclization, alkenyl complex, cyclic
urethane
1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) ligand in
methanol was highly beneficial with respect to productivity and
allowed the reaction to proceed even in the absence of cocatalysts
such as silver salts. A recent computational study suggested that
the ring formation by the nucleophilic attack of a carbamate anion
at an (2-alkyne)gold species is the rate-determining step and that
the use of methanol as a solvent could stabilize the carbamate
anion to lower the energy barrier for the transition state.17
Although the calculations indicated that the resulting cyclized
intermediate is easy for the subsequent protonation, we
successfully synthesized a model alkenylgold(I) complex with a
five-membered urethane moiety from AuOH(IPr) with
1-methylamino-2-butyne (1a) and CO2. In this paper, we disclose
a full account of the 2-oxazolidone synthesis from a range of
propargylic amines as well as the properties of the intermediate
models, which helps provide further insight into the
gold-catalyzed reaction mechanism. In particular, we observed
that the reactivity of the amine substrate is markedly influenced
by the substituents attached to the alkyne moiety, and that this
influence originates from the susceptibility of the alkenylgold(I)
intermediate to protonolysis to liberate the urethane products.
INTRODUCTION
Catalytic CO2 fixation into valuable compounds has received
considerable attention as desirable chemical processes to utilize a
ubiquitous C1 source.1 Because 2-oxazolidones are versatile
intermediates for the production of pharmaceuticals and fine
chemicals and are also chiral auxiliaries, the CO2-based
dehydrative carboxylation of amino alcohols,2 the cycloaddition
of aziridines3 and the cyclization of alkynyl and alkenyl amines
with CO2 have been explored to construct the five-membered
urethane ring structure.4–14 These effective CO2 fixation protocols
are based on the conversion of thermodynamically less stable
carbamic acids generated from amines and CO2 into robust
urethanes.15
As a part of our research directed toward the development of
addition reactions of CO2 to unsaturated molecules,14,16 we
recently observed that N-heterocyclic carbene-coordinated Au(I)
complexes effectively promote the carboxylative cyclization of
Scheme 1. Metal/NH Bifunctionality Based on the
Interconversion Between the Amido and Amine Complexes.
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RESULTS AND DISCUSSION
As evaluated by the screening of group 11 metal complexes in
our previous paper,14b AuCl(IPr)18 catalyzes efficiently under an
atmospheric pressure of CO2 with a substrate/catalyst ratio of 50
in methanol at 40 °C for 15 h (the standard conditions in Table 1).
Various 5-alkylidene-2-oxazolidones were prepared from
alkyl-substituted internal aminoalkynes, which could not be
transformed under catalyst-free supercritical conditions.14a
Using 1-(methylamino)-2-butyne (1a; R1 = R2 = CH3; 2.0
mmol) as a substrate afforded Z-5-ethylidene-2-oxazolidone (2a)
regioselectively as a 5-exo-dig cyclization product in 91% yield
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1
(entry 1). The H NMR spectrum of the reaction mixture clearly
indicates that no other regioisomers or stereoisomers were formed
in the cyclization and that the anti addition of the carbamate anion
to the alkyne moiety therefore occured in a stereoselective
manner.14b The use of methanol as a solvent gave optimal results
compared to CH2Cl2, toluene, or tetrahydrofuran, in which 1a
remained intact (vide infra).
Figure 1. Time dependence on the yield 2a from 1a under the
standard conditions described in the footnote of Table 1.
Table 1. Carboxylative Cyclization with AuCl(IPr)
Catalysta
Table 2. Catalytic activities under mixed gas atmospheresa
entry amine R1
R2
time/h % yieldb
entry
mixed gas
CO2
% yieldb
91
1
2
3
4
5
6
7
1
2c
CH3
CH3
CH3
CH3
CH3
CH3
CH3
15
48
15
15
15
15
91
85
83
87
81
9
1a
1a
1b
1c
1d
1e
CO2/O2
CO2/CO
CO2/H2
CO2/C2H4
CO2/NO
CO2/ N2O
80
CH3
80
3
C2H5
75
4
(CH3)2CH
(CH3)3C
H
77
5
59
6
78
7(2f),
16(2e)
7
(CH3)3Si
CH3
48
1f
aReaction conditions: the reaction was carried out with 1 (2.0
mmol) and catalyst (0.04 mmol) in CH3OH (2.0 mL) under a
gaseous mixture containing CO2 (50% vol) at 40 °C for 15 h.
bDetermined by 1H NMR using durene as an internal standard.
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CH3
CH2C6H5 15
83
1g
1i
C6H5
CH3
CH3
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48
48
48
48
48
48
48
76
10
4-CH3C6H4
75(69)
53
1j
11
12
13
14
15
16
4-CH3OC6H4 CH3
1k
1l
Under the optimized reaction conditions and in the presence of
4-NCC6H4
4-FC6H4
4-ClC6H4
4-BrC6H4
C6H5
CH3
CH3
CH3
CH3
H
45
2
mol%
of
AuCl(IPr)
in
methanol,
aliphatic
N-methylaminoalkyne substrates (1b-1d; R1 = alkyl) were fully
converted into the analogous Z-products (2b-2d) in yields of
85–91% (entries 3–5). A substrate with a terminal alkyne unit,
N-methylpropargylamine (1e), gave only 9% yield with recovery
of 91%, possibly because of the in-situ formation of a gold
acetylide as a less catalytically active species (entry 6). The
incorporation of a trimethylsilyl group at the alkyne terminus was
ineffective and resulted in the formation of the desilylated product
2e coupled with 2f in 16% and 7% yields, respectively, after 48 h
(entry 7). Whereas the desired Z-5-ethylidene-2-oxazolidone
product (2g) was obtained in 83% yield from
1-benzylamino-2-butyne (1g; entry 8), N-propargylated aniline
(1h) gave a mixture of 1,2-dihydroquinoline and quinoline
derivatives in 50% and 41% yields, respectively. These products
were formed via 6-endo-dig cycloisomerization19 without CO2
incorporation, as shown in Scheme 2.
59
1m
1n
1o
1p
56(55)
43(40)
47
aReaction conditions: the reaction was carried out with 1 (2.0
mmol) and AuCl(IPr) (0.04 mmol) in CH3OH (2.0 mL) under
CO2 (1 atm) at 40 °C. bIsolated yield in parentheses. cThe
reaction was conducted with AuCl(IPr) (0.01 mmol) under
otherwise identical conditions.
The time-course of the conversion of 1a into 2a under the
standard conditions indicates that no marked induction period
occurs at the early stage of the carboxylation and that the yield of
2a reaches 77% within 6 h (Figure 1). The reaction with a
reduced catalyst loading of 0.5 mol% from 2 mol% proceeded
smoothly to give 2a in 85% yield after 48 h (entry 2). Notably,
the high efficiency of the gold catalysts was maintained under a
mixed-gas atmosphere; i.e., the reaction of 1a proceeded
smoothly to yield the desired product in comparable yields, even
when the CO2 was diluted with O2, H2, CO, ethylene, NO or
N2O, as shown in Table 2.
Scheme 2. Reaction of 1-anilino-2-butyne 1h.
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When a series of substrates (1i-1p; R1 = aryl) containing
3
4
5
6
7
8
9
aromatic groups attached to the alkyne moiety were subjected to
the reaction, the anti-addition products were obtained in moderate
to good yields and with perfect stereoselectivities (Table 2, entries
9–16). Changing the R1 group from alkyls to aryls resulted in
retardation of the gold-catalyzed carboxylation; in contrast,
aminoalkynes substituted with electrophilic functional groups are
rather susceptible to reaction in scCO2 without any catalysts.14a
The amine conversion was significantly reduced even at elongated
reaction times. A primary amine 1p was also transformed into the
urethane in a reasonable yield (entry 16).
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The stereochemical outcome of the cyclization has a clear
consonance with a catalytic cycle involving the intramolecular
addition of carbamates to the alkyne moiety in an anti fashion, as
depicted in Scheme 3. The chlorogold(I) precursor can form a
catalytically active cationic species via dissociation of the anion in
a polar medium. The alkyne moiety on the propargylic carbamate
formed from the amine substrate and CO2 is activated on the
cationic gold(I) center. The carbamate anion attacks the C–C
triple bond to generate the corresponding neutral alkenylgold
intermediate. After protonolysis, the resulting gold intermediate
releases the urethane product and regenerates the cationic active
species.
Figure 2. Plots of rate against gold concentration under the
conditions of CO2 (1 atm) and [1a] = 1.0 M in methanol (2.0 mL)
at 40 °C.
Figure 3. Plots of log(rate) against log([1a]) under the
conditions of CO2 (1 atm) and [cat] = 2.0  10-2 M in methanol
(2.0 mL) at 40 °C.
Scheme 3. A possible catalytic cycle of the carboxylative
cyclization of propargylamines promoted by IPr–Au complexes.
We envisioned that the treatment of the IPr-Au(I) complex with
propargylic amines under aprotic and non-acidic conditions could
suppress the protodeauration and will permit confirmation of the
formation of alkenylgold species containing cyclic urethane units.
Actually, the alkenylgold complexes (3a14b and 3i) were isolated
To account for the catalytic cycle, the kinetic aspects of the
catalytic urethane formation were analyzed. We determined the
relative rates of the urethane formation by measuring the initial
rates of the reaction of 1a and CO2 (1 atm) in methanol (2.0 mL)
at 40 °C. Under the standard conditions of a substrate/catalyst
ratio of 50 (i.e., [1a] = 1.0 mol dm-3, [cat] = 2.0  10-2 mol dm-3),
the formation of 2a was not influenced by an increase of the CO2
pressure to greater than 0.1 MPa (see Supporting Information). A
linear relationship was observed between the rates and the
concentrations of the gold catalyst, which ranged from 1.0  10-2
to 4.0  10-2 M, as shown in Figure 2. In contrast, the rate
increased nonlinearly with increasing concentration of 1a. The
slopes of the log[rate] vs. log[1a] plots reveal that the rate obeys a
three-fourths-order relationship with [1a], as illustrated in Figure
3. On the basis of the fact that the reaction rate was not affected
by the CO2 concentration and followed first order kinetics with
respect to the gold catalyst, the formation of ammonium
carbamate from 1 and CO2 should be relatively fast. We
postulated that the coordination of the ammonium carbamate is
the rate-determining step under a lower concentration of the
amine substrate. The non-integer reaction order with [1a] was
possibly observed because the protonation of the alkenylgold(I)
intermediate becomes sluggish with the increase in [1a].
from
a
stoichiometric reaction of AuOH(IPr)20 with
1-(methylamino)-2-butyne (1a) or 1-methylamino-3-phenyl-
2-propyne (1i) under a CO2 atmosphere at 40 °C in dry THF
(Scheme 4). Recrystallization by the slow diffusion of n-pentane
into a THF solution of 3a or 3i gave colorless crystals in 54% or
16% yield, respectively. These complexes were fully
characterized by NMR spectroscopy, elemental analysis and
X-ray crystallography. The Au(I) atom is bound to the NHC
carbene and alkenyl carbons in a typical linear two-coordinate
geometry. As observed from Figures 4 and 5, no apparent
structural difference exists between 3a14b and 3i. The gold-carbon
(alkenyl and IPr) bond lengths are in the range of 2.021–2.049 Å,
which are typical values for related alkenylgold compounds.21 The
alkylidene-carbamate scaffold that includes the five-membered
ring is virtually planar, and the geometry is almost identical to
that of the Z-urethanes, 2. These structural data suggest that the
cyclization proceeds via the attack of the carbamate at the alkyne
unit coordinated to the gold center to form the anti addition
product.
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Table 3. Comparison of catalytic activities in the presence
of 3a and 3ia
entry
substrate
Au catalyst
AuCl(IPr)
3a
% yieldb
91
1
2
3
4
5
1a
1a
1a
1i
90
Scheme 4. Synthesis of alkenylgold(I) complexes 3 as model
intermediates in the carboxylative cyclization.
8
9
AuOH(IPr)
AuCl(IPr)
3i
83
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48
1i
aReaction conditions: the reaction was carried out with 1 (2.0
mmol) and catalyst (0.04 mmol) in CH3OH (2.0 mL) under CO2
b
(1 atm) at 40 °C for 15 h. Determined by 1H NMR using durene
as an internal standard.
The stoichiometric reaction of AuOH(IPr) with 1a in THF gave
the alkenylgold complex 3a and H2O as a co-product; this
complex lacks sufficient acidity to cleave the alkenyl–Au bond
(Scheme 4). Nevertheless, AuOH(IPr) was also active for
catalytic carboxylation in CH3OH under catalytic conditions
(entry 3). These results suggest that some acidic compounds such
as methylcarbonic acid22 (CH3OCO2H; vide infra) might be
generated during the carboxylation in CH3OH for the protonolysis
of the alkenylgold intermediate, as shown in Scheme 3. In fact,
the isolated complex 3a was smoothly deaurated upon the
addition of an equimolar amount of acetic acid in CD3OD at room
temperature to give 2a in 83% yield within 1 h, as shown in
Figure 6. In contrast, the phenyl-substituted complex 3i gave 2i in
only 15% yield under identical conditions. The substituents on the
alkenyl carbon proximal to the gold center in 3a and 3i clearly
affect the relative ease of protodeauration; hence, the strong
correlation between the reactivities of the isolated complexes and
the catalytic reaction rates of 1a and 1i was realized.
Figure 4. ORTEP diagram of alkenylgold complexes 3a (left)
and 3i (right) with 50% probability ellipsoids; hydrogen atoms are
omitted for clarity.
Figure 6. Conversion versus time curve for the reactions of 3a
(■) and 3i (●) with equimolar amounts of acetic acid in CD3OD at
room temperature.
Figure 5. Selected bond lengths (Å) and angles (°) for 3a14b
and 3i.
When the alkenyl complexes were treated in CD3OD under an
argon atmosphere (Table 4), 91% of the 3a was remained
untouched and 3i was mostly recovered after 24 h (entries 1 and
2). Although the alkenyl–Au bond proved to be more stable than
expected, the protodeauration of 3a was significantly facilitated
by the exposure to atmospheric CO2 to furnish 2a in 95% yield
after 9 h (entry 3), possibly because the combination of methanol
and CO2 results in the formation of methylcarbonic acid. The
acceleration due to the CO2-mediated protonation was also
confirmed by the reaction of 3i in methanol; however, the phenyl
substituent diminishes the carbanionic character of the alkenyl
groups, leading to a limited yield of 2i (13 %; entry 4).
To corroborate the catalytic mechanism involving the
alkenylgold species, the carboxylative cyclizations of 1a and 1i
were conducted in the presence of 3a and 3i, respectively, for 15 h
under the standard catalytic conditions (Table 3). The isolated
methyl-substituted complex 3a exhibited catalytic activity (90%
yield) comparable with that of AuCl(IPr) in the reaction of 1a
(entries 1 and 2). The lower reactivity of 1i compared to that of 1a
was reproduced in the carboxylation using the phenyl-substituted
complex 3i (48% yield), as shown in entries 4 and 5.
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JNM-ECX400 spectrometers. The NMR chemical shifts were
Table 4 Protodeauration of alkenyl complexes 3a and 3i in
CD3OD a
referenced to SiMe4 by using residual protio impurities in the
1
deuterated solvent. Abbreviations for H NMR are as follows: s
entry Au complex
atmosphere time/h
% yield of 2b
= singlet, d = doublet, t = triplet, q = quartet or m = multiplet.
Elemental analyses were carried out using a PE2400 Series II
CHNS/O Analyser (Parkin Elmer) or a MICRO CORDER JM10
instrument. IR spectra were recorded on a JASCO FT/IR-610
spectrometer. Mass spectra (MS) were obtained with a JEOL
1
2
3
4
Ar
24
24
9
9
3a
3i
Ar
<1
95
13
CO2
CO2
3a
3i
JMS-SX102A
instrument.
Recyclable
preparative
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high-performance liquid chromatography was performed on a
Japan Analytical Industry LC-9225 NEXT system equipped with
JAIGEL-1H and -2H columns using CHCl3 as an eluent at a flow
rate of 14 mL min-1.
aReaction conditions: the reaction was carried out with 3a or
3i(0.020 mmol) in CD3OD (1.0 mL) at room temperature.
bDetermined by 1H NMR using durene as an internal standard.
General procedure for the catalytic carboxylative
cyclization. Propargylamines (2.0 mmol) were added to a
methanol (2.0 mL) suspension of AuCl(IPr) (0.04 mmol) in a 20
mL Schlenk flask under an Ar atmosphere. The flask was charged
with 2.0 L of CO2 through a balloon and stirred at 40 °C. After
evaporation of the resulting mixture under reduced pressure, the
product yield was determined by 1H NMR using durene as an
internal standard. The characterization data for 2a–2e, 2g, 2i, and
2p were described in our previous paper.14b
To further investigate the rate enhancement in acidic reaction
media, a 1:1 mixture of methanol and water was employed as the
solvent in the catalytic reaction involving the less reactive
substrate 1i; however, only a trace amount of the desired
2-oxazolidone 2i was obtained. Presumably, the preferential
formation of ammonium hydrogen carbonate, [RR’NH2]+[HCO3]–,
from the amine substrate, water and CO2 prevented the
carbamate-induced cyclization. However, the catalytic
carboxylation was accelerated in 2,2,2-trifluoroethanol to give 2i
in 71% yield under conditions otherwise identical to the standard
conditions. The positive effect of the acidic alcohol intimates that
the product-releasing protodeauration of the alkenylgold
intermediates governs the overall catalyst performance as the
rate-determining step.
Kinetic experiments. AuCl(IPr) (0.01-0.04 mmol) and durene
(an internal standard for NMR analysis; 0.08 mmol) were
dissolved in methanol (1.0 mL) in a 20 mL Schlenk flask under an
Ar atmosphere. The flask was sealed with a septum, charged with
2.0 L of CO2 through a balloon and stirred at 40 °C. 1a (0.2-1.2
mmol) was added to the solution. A portion of the reaction
mixture was collected every 5 or 10 min and diluted with CDCl3
(0.5 mL) for determination of the product yield by 1H NMR.
Synthesis of alkenylgold complex 3i. To a THF (7 mL)
solution of AuOH(IPr) (0.50 mmol) in a 20 mL Schlenk flask,
1-methylamino-3-phenyl-2-propyne (1i, 0.50 mmol) was added
under an Ar atmosphere. The Schlenk flask was charged with CO2
and stirred at 40 °C for 48 h. The resulting mixture was
evaporated to dryness, and the residue was washed with ether and
then recrystallized from THF and n-pentane to give 3i as colorless
crystals in 16% yield (62 mg). 1H NMR (399.78 MHz, THF-d8, rt,
CONCLUSIONS
We have demonstrated that IPr-Au(I) complexes serve as
efficient catalysts that provide 2-oxazolidones from
propargylamines and CO2. This gold catalyst system exhibits
considerable versatility with respect to the substrate scope,
operational simplicity, and ambient reaction conditions. In
particular, the catalytic intermediates can be successfully isolated
as alkenylgold(I) complexes by treatment of AuOH(IPr) with an
equimolar amount of propargylamines under a CO2 atmosphere in
aprotic THF. The experimental results obtained from kinetic
experiments as well as stoichiometric reactions using the model
intermediates support the validity of the catalytic cycle shown in
Scheme 3 and are congruent with the dramatic CO2-mediated
acceleration of the product-releasing protodeauration step.
 /ppm) : 1.21 (d, 3JHH = 6.7 Hz, 12H, (CH3)2CH), 1.31 (d, 3JHH
=
=
3
6.7 Hz, 12H, (CH3)2CH), 2.61 (s, 3H, NCH3), 2.67 (sept, JHH
6.7 Hz, 4H, (CH3)2CH), 3.40 (s, 2H, CH2), 6.70 (t, 3JHH = 7.3 Hz,
3
3
1H, Ar), 6.80 (t, JHH = 7.6 Hz, 2H, Ar), 7.06 (d, JHH = 7.3 Hz,
3
3
2H, Ar), 7.37 (d, JHH = 7.8 Hz, 4H, Ar), 7.54 (t, JHH = 7.8 Hz,
2H, Ar), 7.58 (s, 2H, NCH=CHN); 13C NMR (100.53 MHz,
THF-d8, rt, /ppm): 23.3, 23.8, 28.8, 29.2, 51.8, 123.0, 123.4,
123.8, 126.3, 130.0, 130.4, 135.2, 135.6, 139.5, 144.9, 146.1,
156.6 (C=O), 195.5 (NCN). Anal. Calcd for C38H46N3O2Au: C,
58.99; H, 5.99; N, 5.43. Found: C, 58.81; H, 5.93; N, 5.19.
EXPERIMENTAL SECTION
Materials. Solvents were purchased from Kanto Chemical Co.,
Inc. or Nacalai Tesque, Inc., and dried by refluxing over sodium
benzophenone ketyl (toluene, THF, ether), P2O5 (CH2Cl2,
n-pentane) or CaH2 (methanol) and distilled under argon. Carbon
dioxide (99.999%) was purchased from Showa Tansan. Other
reagents were used as delivered. (IPr)AuCl18 and (IPr)Au(OH)20
were prepared according to literatures. Aliphatic internal
propargylamines (1a-1d and 1f-1h) were prepared by
propargylation of primary amines by treatment with the propargyl
chlorides or bromides in the presence of base.14b Aromatic
internal propargylamines (1i-1p) were prepared by Sonogashira
reaction of the corresponding aryl halides and terminal
propargylamines.23
Protonolysis of the alkenylgold complexes with acetic acid.
Acetic acid (10 mmol) was added to a CD3OD (0.5 mL) solution
of alkenylgold complex 3a or 3i (10 mmol) in a NMR tube. The
reaction was monitored via 1H NMR spectroscopy at room
temperature.
Reaction of the alkenylgold complexes in deuterated
methanol under CO2. Alkenylgold complex 3a or 3i (20 mmol)
was dissolved in CD3OD (1.0 mL) in a 20 mL Schlenk flask under
an Ar atmosphere. The flask was sealed with a septum, charged
with 2.0 L of CO2 through a balloon and stirred at room
temperature. The reaction was monitored via 1H NMR
spectroscopy.
1
Analytical methods. H(300.40 and 399.78 MHz), 13C(100.53
MHz) NMR were recorded with JEOL JNM-LA300 and
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Supporting Information
Analytical data for new compounds, supplementary data for
catalytic results, and X-ray scrystallographic data for 3i. This
material is available free of charge via the Internet at
http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
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*E-mail: ykayaki@o.cc.titech.ac.jp
*E-mail: tikariya@apc.titech.ac.jp
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENTS
This work was financially supported by JSPS KAKENHI Grant
Numbers 24350079 and 26621043. The authors thank the
Material Analysis Suzukake-dai Center, Technical Department,
Tokyo Institute of Technology, for the HRMS analysis.
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