Selectivity switch in the synthesis of vinylgold(I) intermediates

Article abstract of DOI:10.1021/om2009556

An unexpected regioselectivity reversal was observed in the synthesis of vinylgold(I) complexes from propargyl carboxamides. The use of [Au(IPr)(OH)] affords preferentially vinylgold(I) complexes resulting from a 5-exo-dig cyclization, whereas the use [Au(IPr)]⁺ species, generated in situ starting from [Au(IPr)(Cl)] and AgOTf, leads to vinylgold(I) complexes which form via a 6-endo-dig cyclization, This unexpected "selectivity switch" for this cyclization led us to propose two different reaction pathways enabling the formation of the two different products. One mechanism involves the [Au(IPr)]⁺ species with "classical" I activation of the alkyne framework of the carboxamides, and the second represents an "unusual" use of the basic Bronsted character of [Au(IPr)(OH)]. Mechanistic and DFT studies support the mechanistic hypotheses.

Full text of DOI:10.1021/om2009556

Article
pubs.acs.org/Organometallics
Selectivity Switch in the Synthesis of Vinylgold(I) Intermediates
A. Stephen K. Hashmi,*,† Andreas M. Schuster,† Sylvain Gaillard,‡,§ Luigi Cavallo,∥,# Albert Poater,⊥
and Steven P. Nolan*,‡
†Organisch-Chemisches Institut, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
̈
‡EaStCHEM School of Chemistry, University of St Andrews, St Andrews KY16 9ST, U.K.
§Laboratoire de Chimie Molec
Marechal Juin 14050 Caen, France
∥Dipartimento di Chimica, Universita
́ ́
ulaire et Thioorganique, UMR 6507, INC3M, FR 3038, ENSICAEN-Universite de Caen, 6 bd.
́
̀
di Salerno, Via ponte don Melillo, 84084, Fisciano, Italy
#KAUST Catalysis Center and Division of Chemicals and Life Sciences & Engineering 4700, King Abdullah University of Science and
Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
⊥Catalan Institute for Water Research (ICRA), H2O Building, Scientific and Technological Park of the University of Girona, Emili
Grahit 101, E-17003 Girona, Spain
S
* Supporting Information
ABSTRACT: An unexpected regioselectivity reversal was
observed in the synthesis of vinylgold(I) complexes from
propargyl carboxamides. The use of [Au(IPr)(OH)] affords
preferentially vinylgold(I) complexes resulting from a 5-exo-
dig cyclization, whereas the use [Au(IPr)]+ species, generated
in situ starting from [Au(IPr)(Cl)] and AgOTf, leads to
vinylgold(I) complexes which form via a 6-endo-dig
cyclization, This unexpected “selectivity switch” for this
cyclization led us to propose two different reaction pathways
enabling the formation of the two different products. One mechanism involves the [Au(IPr)]+ species with “classical” π activation
of the alkyne framework of the carboxamides, and the second represents an “unusual” use of the basic Brønsted character of
[Au(IPr)(OH)]. Mechanistic and DFT studies support the mechanistic hypotheses.
heterocyclic carbene),6 one of which has been demonstrated to
INTRODUCTION
■
act as a versatile synthon in organometallic chemistry7 as well as
Gold-catalyzed organic transformations represent a truly
proving quite useful in homogeneous catalysis.8 In the course of
these synthetic and catalytic studies, [Au(IPr)(OH)] (3) (IPr =
1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) displayed in-
teresting Brønsted basic properties which were envisaged to
possibly trigger novel reactivity.6,8e,f The use of [Au(IPr)(OH)]
(3) as a mechanistic probe in the cyclization of propargyl
carboxamides 1 is now examined and compared to the
previously reported procedure leading to vinylgold(I) inter-
mediates.4d Herein, results on new selectivity brought about by
the use of 3 for cyclization of N-propargyl carboxamide
derivatives 1 are presented.
prolific area of research in organic chemistry.1 This is certainly
due to the wide range of organic transformations gold has
successfully mediated thus far. Of utmost importance in such
reactions is the propensity of gold to act as an electrophilic
activator for C−C multiple bonds.2 It is commonly accepted
that nucleophiles can attack C−C multiple bonds that have
been activated by cationic gold(I) complexes. For an in-depth
understanding of the mechanism involving these cationic
gold(I) complexes, trapping such intermediates has become a
desirable goal that some may characterize as essential.3 With
this aim in mind, Hashmi et al. succeeded in the isolation of a
vinylgold(I) complex intermediate (2a)4 resulting from a 6-
endo-dig cyclization of N-propargyl carboxamides (1a)5 (eq 1).
RESULTS AND DISCUSSION
■
Various N-propargyl carboxamides 1, bearing an internal
alkyne, were prepared and reacted with 3 (condition A) or
with in situ generated cationic [Au(IPr)]+ (from [AuCl(IPr)]
and AgOTs in presence of triethylamine) (condition B) (Table
1). Results of the selectivity between the 5-exo-dig and the 6-
In a related area, Nolan and co-workers have reported the
synthesis of novel [Au(NHC)(OH)] complexes (NHC = N-
Received: October 10, 2011
Published: October 28, 2011
© 2011 American Chemical Society
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a
Table 1. Synthesis of Vinylgold(I) Complexes 2 and 4 from N-Propargyl Carboxamides 1
a
Conditions: (A) reaction carried out in a NMR tube with propargyl carboxamide 1 (85 μmol) and [Au(IPr)(OH)] (3; 85 μmol) in THF-d8 at
room temperature; (B) reaction carried out in a Schlenk tube with [Au(IPr)Cl] (161 μmol), AgOTs (161 μmol), triethylamine (100 μL), and
propargyl carboxamide 1 (153 μmol) in dry THF at room temperature.
endo-dig cyclization of compounds 1, respectively yielding the
vinylgold(I) complexes 4 and/or 2, are presented in Table 1.
All propargyl carboxamides 1a−h were fully converted into a
mixture of vinylgold(I) complexes 2 and 4 under both reaction
conditions (Table 1, entries 1−16). Propargyl carboxamides
1i−k were only subjected to reaction conditions A, and only
compound 1j did not furnish the expected vinylgold(I)
complexes 2j and/or 4j, instead yielding decomposition of
the starting material (Table 1, entry 18). Nevertheless, 1i,k gave
only the vinylgold(I) complexes 4i,k, respectively. Noteworthy,
all propargyl carboxamide derivatives 1 gave quantitatively a
mixture of 2 and 4 under reaction conditions A, whereas
reaction conditions B afforded these mixtures in yields ranging
from 58% to 88% (Table 1, entries 1−16). The most important
observation was the reversal in expected regioselectivity
between reaction conditions A and B. Indeed, using conditions
A, the major vinylgold(I) complexes 4 result from a 5-exo-dig
cyclization, whereas under conditions B, the major products
formed were vinylgold(I) complexes 2, which are formed via a
6-endo-dig cyclization. Among these observations, only one
exception in this reactivity trend was observed, for 1h, which
selectively afforded, using either protocol, the vinylgold(I)
complex 4h (Table 1, entries 15 and 16). Finally, 3 (conditions
A) proved more selective than [Au(IPr)]+ (conditions B), as
better 4/2 ratios were obtained using this well-defined complex.
The electronic effects of substituents R1 and R2 were both
obviously involved in this selectivity. Indeed, when R1 remained
constant, if R2 was an alkyl group, formation of 2 was favored
(Table 1, entries 2, 4, 6, and 8), whereas the presence of an aryl
group favored the formation of 4 (Table 1, entry 16). Such
dramatic selectivity does not appear so clear-cut under reaction
conditions A. Nevertheless, when R1 and R2 are two aromatic
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groups, total selectivity in favor of 4 was observed (Table 1,
entries 15, 17, and 19). This was confirmed when 5 (bearing
two alkynylcarboxamide frameworks substituted at both R1 and
R2 positions by aromatic groups) was employed. Indeed, under
conditions A, 5 afforded quantitatively and selectively the
divinylgold(I) complex 6, resulting from two 5-exo-dig
cyclizations (eq 2).
appears clear. The question we next tackled was by which
pathway 7 evolved into 4.
The gold-catalyzed cyclization of 2-alkynylphenol (8) leading
to furans has already been reported.9 Formation of vinylgold(I)
from 2-alkynylphenol (8) and 2-alkylaniline (11) is also known
to proceed in the presence of cationic gold complexes.4a
Therefore, it appeared worthwhile to examine the reactivity
differences between 3 and cationic gold(I) leading to the
formation of vinylgold(I) complexes 9 and 12 obtained from 2-
alkynylphenol 8 and 2-alkylaniline 11, respectively. Gratifyingly,
compounds 8 and 11 in the presence of 3 afforded the
corresponding vinylgold(I) complexes 9 and 12, respectively
(eqs 3 and 4).
The selectivity switch observed with neutral 3, possessing basic
properties, in comparison to the use of a “classical” cationic
gold(I) source raised questions about the mechanistic pathway
preferred when 3 is employed. Under regime B, the
regioselectivity observed in favor of the 6-endo-dig cyclization4d
can be attributed to electronic effects. Indeed, the inductive
effect, brought about by the terminal substituent, leads to a
positive partial charge on Ca instead of Cb during the π
activation of the alkyne, resulting in the selectivity observed
(Scheme 1). To support this argument, when the inductive
effect is absent, which is the case when a terminal alkyne is
employed, this reaction leads to the sole formation of the 5-exo-
dig cyclized product 4 (Scheme 1).5
The pKa values for phenol or aniline clearly indicate these
substrates compatible with a deprotonation reaction by 3.10
The reactions above clearly show that the C−C triple bond is
capable of being inserted into Au−O and Au−N bonds.
Thereafter, the proto-deaurated compound 104a was observed,
which could originate from the hydrolysis of the Au−C bond4d
by the water generated from the deprotonation of 10 by 3. As
water cannot be involved in the proto-deauration when
conditions B are used, a complementary experiment using
TsOH for the cleavage of this Au−C bond in 4h was
undertaken (eq 5).
Therefore, to understand this switch in regioselectivity in
favor of 4 when reactions were performed under conditions A,
1
attempts to observe intermediate(s) were carried out using H
NMR spectroscopy. Compounds 1i and 3 were introduced into
an NMR tube, and spectra were recorded every 4 min (THF-d8,
298 K, 300.13 MHz, NS = 64, DS = 2) (Figure 1).
1
Initial H NMR spectra revealed immediate formation of a
new intermediate (7i) attributed to the deprotonated 1i with a
[Au(IPr)] group N-ligated. Then, 7i disappeared in favor of the
formation of 4i. This observation is in good agreement with the
basic properties displayed by 3. Indeed, 3 can deprotonate
compounds with pKa(DMSO) up to 30.3 pKa units.8f In view of
this acid−base reactivity, the pathway leading to the cyclization
Unexpectedly, ring opening of 4h occurs and 1h is
regenerated with concomitant formation of [Au(IPr)][OTs].
Scheme 1. Proposed Reaction Mechanism for the Formation of Complexes 2 and 4 in the Presence of a Cationic Gold(I)
Source
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Figure 1. Isomerization of amide gold(I) complex 7i into the vinylgold(I) complex 4i.
water to afford the oxazole derivative 14 or [Au(IPr)Cl] to
obtain 4h was achieved (Scheme 2). After 13 was treated with
n-BuLi and the preformed vinyl anion was quenched with
water, oxazole 14 and ring-opening product 1h were observed
in a 1:1 ratio. The same reactivity was observed when water was
replaced by [Au(IPr)Cl]. Indeed, under these conditions, a
mixture of 4h and the amidogold(I) complex 7h was obtained
in a 1:1 ratio. These two experiments revealed the instability of
the vinyl anion when lithium is the countercation, yielding the
ring-opened product. This result is in agreement with the
experiment involving 4h in the presence of TsOH, where the
acid proton activates the oxazole nitrogen to afford the ring-
opened product 1h.
It is worth noting that no interconversion of 4h into 2h was
observed. This is not surprising, as these reaction conditions do
not lead to the reaction conditions used in Table 1 with
conditions B. This experiment highlights the crucial role of
triethylamine under conditions B, which traps the liberated
proton during the course of the reaction and avoids the re-
formation of the starting material 1h. Finally, the absence of
acidolysis of the Au−C bond in complex 4h by TsOH is due to
the basic character of the nitrogen atom of the oxazole, which
reacts with the strong Brønsted acid TsOH.4a This led us to
consider these vinylgold(I) complexes as vinyl anions highly
stabilized by very sterically demanding cations. To test this
hypothesis, attempts to generate this vinyl anion by reacting
iodovinyloxazole (13) with n-BuLi followed by addition of
Finally, these experiments led us to propose a mechanism for
the formation of 4. Initially, 1 is deprotonated in the presence
of [Au(IPr)(OH)] (3), affording as an intermediate the
1
amidogold complex 7, observed by H NMR spectroscopy
(Figure 1). Then, 7 is involved in an equilibrium with the
amidogold complex intermediate 15, which could be stabilized
by coordination to the alkyne moiety.
Scheme 2. Evolution of the Vinyloxazole Anion in the Presence of Water or [Au(IPr)Cl]
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DFT calculations permit us to draw a complete picture using
the experimental information at hand, and energy profiles are
presented in Figures 2 and 3.11 Focusing on the reactivity of 1h
(see Figure 2). Structure 7h is 1.6 kcal/mol more stable than
the starting neutral species 3 plus free 1h and is the resting state
of the reaction pool. The key intermediate 15h, at 22.4 kcal/
mol in energy above 3 + 1h, is formed through the rather high
energy transition state 7h-15h, 27.9 kcal/mol above the resting
state 7h. However, the key intermediate 15h can be also
reached via coordination of the alkyne functionality of 1h to the
gold center of 3 to yield 16h, an endergonic step costing 22.2
kcal/mol, followed by a low-energy proton transfer step
through transition state 16h-17h, which leads to intermediate
17h, lying 21.5 kcal/mol above 3 + 1h. Loss of the coordinated
water molecule finally leads to intermediate 15h. Considering
that transition state 7h-15h is only 1.6 kcal/mol above
transition state 16h-17h, calculations suggest that 15h can be
formed both along the sequence 3 + 1h →16h → 17h → 15h
and along the sequence 3 + 1h → 7h → 15h. Furthermore, 7h
can react reversibly with a liberated H2O molecule to form 3 +
1h, thus allowing the initially formed 7h to reach the key
intermediate 15h through the slightly more stable transition
state 16h-17h rather than the slightly higher in energy
transition state 7h-15h.
The regioselectivity in favor of the 5-exo-dig pathway occurs
at the level of the rate-determining cyclization step, with
transition state 15h-4h, some 3.6 kcal/mol below transition
state 15h-2h. At the product level, the five-membered Au
species 4h is only 1.0 kcal/mol more stable than the six-
membered Au species 2h. The higher stability of transition state
15h-4h originates from the polarity of the alkyne bond, induced
by the Ph group. Natural population analysis results with
charges of −0.114e and −0.027e on the C1 and C2 atoms of
15h, which drives O attack toward the less negatively (more
positively) charged C2 atom. Similar results are obtained with
substrate 1a (see the numbers in brackets in Figure 2). In short,
the data reported in Figure 2 provide a rationale for the
experimentally observed preferential 5-cyclization promoted by
neutral 3.
Figure 2. DFT energy profile for the cyclization of 1h promoted by 3
(energy values in parentheses). The energy values for the cyclization of
1a are reported in brackets. [Au] represents [Au(IPr)].
Moving to cyclization in the presence of the cationic
[Au(IPr)]+ species, the corresponding energy profiles are
shown in Figure 3. After initial coordination of 1h to the
cationic Au species, leading to intermediate 18h, with a release
of 19.4 kcal/mol, the question is whether cyclization occurs
before or after deprotonation of the NH functionality of 1h by
NEt3, leading thus to a competition between cyclization-then-
deprotonation and deprotonation-then-cyclization pathways. Along
the cyclization-then-deprotonation pathway (Figure 3a), the 6-
endo-dig cyclization transition state 18h-19h is strongly favored
over the 5-exo-dig cyclization transition state 18h-20h, which is
calculated to be 9.5 kcal/mol higher in energy. Deprotonation
of the NH functionality of the cyclized intermediates 19h and
20h with the transfer of the proton from the substrate to the H-
bonded NEt3 is not an issue, with an energetic cost of less than
5 kcal/mol, and leads to the intermediates 21h and 22h.
+
Dissociation of HNEt3 , perhaps assisted by the tosylate,
liberates the final products 2h and 4h. Along the deprotona-
tion-then-cyclization pathway (Figure 3b), NEt3 deprotonates
the NH functionality of the coordinated substrate in 18h prior
cyclization. This step proceeds through transition state 18h-
23h, requiring 7.4 kcal/mol, and leads to the neutral Au species
Figure 3. DFT energy profiles for the cyclization of 1h promoted by
the cationic [Au(IPr)]+ species (energy values in parentheses). Energy
values for the cyclization of 1a are reported in brackets. [Au]
represents [Au(IPr)].
+
23h with a HNEt3 molecule H-bonded to the N atom of the
substrate. Cyclization from 23h gives the intermediates 21h and
22h through transition states 23h-21h and 23h-22h. As in
Figure 3a, dissociation of the H-bonded HNEt3+ from 21h and
22h liberates the final products 4h and 2h. Consistent with the
with neutral 3, formation of 7h with concomitant release of a
water molecule requires overcoming a barrier of 19.2 kcal/mol
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atmosphere of dry argon or in a MBraun glovebox containing dry
argon and less than 1 ppm of oxygen. Anhydrous solvents were either
distilled from appropriate drying agents or purchased from Aldrich and
degassed prior to use by purging with dry argon and kept over
molecular sieves. Solvents for NMR spectroscopy were degassed with
argon and dried over molecular sieves. NMR spectra were recorded on
a 400 MHz Varian Gemini spectrometer. Elemental analyses were
performed by St Andrews analytical services. Complex 3 was prepared
according to the procedure described in the literature.6 Chemicals
were purchased from the indicated supplier in the indicated purity:
triethylamine (Acros, 99%), [AuCl(IPr)] (Strem, 95%). Dry solvents
were obtained from a Braun MB-SPS 800 solvent purification system.
Deuterated solvents were purchased from Euriso-top and used from
the bottle without further drying. NMR spectra were recorded on a
Bruker Avance DRX-300 MHz spectrometer. Mass spectra were taken
with a JEOL JMS-700 spectrometer. As a FAB matrix either NBA (3-
nitrobenzyl alcohol) or NPOE (o-nitrophenyl octyl ether) was used.
IR spectroscopy was processed on a FT-IR Bruker Vector 22. IUPAC
names of the compounds were determined with ACDLabs 12.0.
General Procedure for the Synthesis of Vinylgold Com-
pounds (GP1). In a NMR tube propargylamide and [Au(OH)(IPr)]
(3) were dissolved in THF-d8 at room temperature. The reaction was
monitored by NMR. To obtain the product, the solvent was removed
at the rotary evaporator without heating.
General Procedure for the Synthesis of Vinylgold Com-
pounds (GP2). In a 25 mL Schlenk tube 100 mg (161 μmol) of
[AuCl(IPr)] and 45 mg (161 μmol) of AgOTs were dissolved in 6 mL
of dry THF and stirred for 1 h. Then 100 μL of triethylamine and 153
mmol amide were added. The reaction mixture was stirred for a further
16 h at room temperature, filtered over a small column of basic Alox,
and washed with 50 mL of dry THF. To obtain the product, the
solvent was removed at the rotary evaporator without heating.
Synthesis of 4a and 2a. According to GP1, 14.7 mg (85.0 μmol)
of N-(but-2-ynyl)benzamide and 51.2 mg (85.0 μmol) of [Au(OH)-
(IPr)] (3) were used. After 1 day, 4a and 2a were obtained as a white
foam in quantitative yield (4a/2a = 1/0.14). According to GP2, 26.3
mg (152 μmol) N-(but-2-ynyl)benzamide was used. After 1 d, 4a and
2a were obtained as a white foam in 82% yield (Ratio 4a/2a = 0.04/1).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}[(1E)-1-(2-phenyl-1,3-oxazol-5(4H)-ylidene)ethyl]gold
(4a). 1H NMR (300 MHz, THF-d8): δ 1.23 (d, J = 7.0 Hz, 12 H),
1.40 (d, J = 7.0 Hz, 12 H), 1.57 (t, J = 2.5 Hz, 3 H), 2.61−2.77 (m, 4
H), 3.88 (q, J = 2.5 Hz, 2 H), 7.25−7.40 (m, 7 H), 7.44−7.57 (m, 4
H), 7.79−7.88 (m, 2 H). 13C NMR (75 MHz, THF-d8): δ 21.05 (q),
24.30 (q, 4 C), 25.06 (q, 4 C), 29.84 (d, 4 C), 59.08 (t), 124.38 (d, 2
C), 124.77 (d, 4 C), 128.45 (d, 2 C), 128.86 (d, 2 C), 129.19 (s),
130.72 (s), 131.06 (d, 2 C), 131.24 (d), 136.18 (s, 2 C), 146.96 (s, 4
C), 151.11 (s), 163.96 (s), 198.08 (s).
energetic plot of Figure 2, a neutral Au species such as 23h
interacting with a HNEt3 molecule H-bonded to the N atom
+
of the substrate, 5-exo-dig cyclization is favored over 6-endo,dig
cyclization. This preference is calculated to be 3.5 kcal/mol,
which is nearly identical with the preference of 3.6 kcal/mol in
favor of the 5-exo-dig cyclization in the case of 1h cyclization
promoted by neutral 3 (see Figure 2), indicating a minor effect
of the H-bonded HNEt3+ molecule. Focusing on a comparison
between the cyclization-then-deprotonation and deprotonation-
then-cyclization pathways, it is noteworthy that, with the
exception of transition state 18h-20h leading to 4h along the
cyclization-then-deprotonation pathway, the key transition
states 18h-23h, 23h-21h, 23h-22h, and 18h-19h are of similar
energy and are thus in competition. This indicates that in the
case of a cationic Au species the 5-exo-dig product 4h can be
formed along both the cyclization-then-deprotonation and
deprotonation-then-cyclization pathways, whereas the 6-endo-
dig product 2h can be formed along the cyclization-then-
deprotonation pathway only. However, as an initial step the
deprotonation is favored by 1.8 kcal/mol with respect to the
competitive cyclization. A similar chemical scenario is
calculated when 1a is the substrate; see the energy values in
brackets in Figure 3. In summary, calculations provide a
rationale for the increased amount of six-membered vinylgold
products promoted by the cationic [Au(IPr)]+ species. Finally,
in the case of the deprotonation-then-cyclization pathway,
formation of the five-membered vinylgold species is favored
over formation of the six-membered vinylgold species by 3.5
kcal/mol in the case of 1h, whereas this preference is reduced
to only 0.5 kcal/mol in the case of 1a. This result is also
consistent with the experimental finding that 1h cyclization
promoted by the cationic [Au(IPr)]+ species yields only the
five-membered vinylgold species 4h.
To further support the computational work and proposed
reaction pathways, the kinetics of formation of 4i from 1i were
investigated under conditions A at four temperatures (50, 40,
25, and 10 °C) and an Arrhenius plot constructed (see the
Supporting Information). The effective energy EA was
calculated as 24.2 kcal/mol, which is in good agreement with
the value estimated by DFT calculations of compound 1h
converting into vinylgold(I) 4h passing through intermediate
15h. This compares to the theoretical value for the activation
energy of 22.4 kcal/mol and is consistent with the experimental
value if substituent variations between 1h and 1i are
considered.
{1,3-bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}(6-methyl-2-phenyl-4H-1,3-oxazin-5-yl)gold (2a). 1H NMR
(300 MHz, THF-d8): δ 1.23 (d, J = 7.0 Hz, 12 H), 1.38 (d, J = 7.0 Hz,
12 H), 1.43 (t, J = 1.6 Hz, 3 H), 2.61−2.77 (m, 4 H), 3.68 (q, J = 1.6
Hz, 2 H), 7.14−7.25 (m, 4 H), 7.25−7.40 (m, 3 H), 7.44−7.57 (m, 4
H), 7.79−7.88 (m, 2 H). 13C NMR (75 MHz, THF-d8): δ 22.06 (q),
24.30 (q, 4 C), 25.03 (q, 4 C), 30.82 (d, 4 C), 53.04 (t), 124.45 (d, 2
C), 124.77 (d, 4 C), 127.58 (d, 2 C), 128.30 (d, 2 C), 130.13 (d),
131.02 (d, 2 C), 135.92 (s), 136.14 (s, 2 C), 145.92 (s), 146.92 (s, 4
C), 147.25 (s), 153.96 (s), 197.90 (s). HRMS (FAB(+), matrix
NPOE): [C38H47ON3Au]+ calcd 758.3385, found 758.3358. IR (KBr):
CONCLUSION
■
An unprecedented regioselectivity switch in vinylgold(I) complex
synthesis from propargyl carboxamides 1 as a function of the
gold(I) source has been reported. Indeed, the use of 3
preferentially leads, via a 5-exo-dig cyclization, to vinylgold(I)
complexes 4, whereas the use of the [Au(IPr)]+ species
provided, via a 6-endo-dig cyclization, leads to complexes of
type 2. This switch in regioselectivity can be attributed to the
basic properties of [Au(IPr)(OH)] (3), confirming our hope
that this stable and easily synthesized complex might lead to
novel reactivities. Further investigations focusing on the use of
3 and related complexes are ongoing in our laboratories.
ν̃
(cm−1) 2962, 2927, 2868, 2282, 1680, 1470, 1459, 1415, 1385, 1365,
1337, 1285, 1147, 1102, 1067, 1024, 804, 758, 696, 512, 501.
Synthesis of 4b and 2b. According to GP1, 14.6 mg (85.0 μmol)
of N-(pent-2-ynyl)benzamide and 51.2 mg (85.0 μmol) of [Au(OH)-
(IPr)] (3) were used. After 1 day, 4b and 2b were obtained as a pale
yellow foam in quantitative yield (4b/2b = 1/0.16). According to GP2,
28.6 mg (152 μmol) of N-(pent-2-ynyl)benzamide was used. After 1
day, 4b and 2b were obtained as a pale yellow foam in 81% yield (4b/
2b = 0.20/1).
EXPERIMENTAL SECTION
General Considerations. All reactions were carried out in air
unless otherwise stated. In such exceptions, manipulations were
performed using standard Schlenk techniques using an inert
■
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}[(1E)-1-(2-phenyl-1,3-oxazol-5(4H)-ylidene)propyl]gold
(4b). 1H NMR (300 MHz, THF-d8): δ 0.56 (t, J = 7.6 Hz, 3 H), 1.23
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Organometallics
Article
(d, J = 6.9 Hz, 12 H), 1.39 (d, J = 6.9 Hz, 12 H), 2.11 (tq, J = 7.6 Hz, J
= 2.1 Hz, 2 H), 2.60−2.78 (m, 4 H), 3.86 (t, J = 2.1 Hz, 2 H), 7.26−
7.38 (m, 7 H), 7.45−7.56 (m, 4 H), 7.76−7.84 (m, 2 H). 13C NMR
(75 MHz, THF-d8): δ 17.47 (q), 24.38 (q, 4 C), 25.01 (q, 4 C), 28.25
(t), 29.86 (d, 4 C), 58.93 (t), 124.31 (d, 2 C), 124.75 (d, 4 C), 128.44
(d, 2 C), 128.85 (d, 2 C), 131.03 (d, 2 C), 131.23 (d), 136.24 (s, 2 C),
137.97 (s), 146.72 (s), 147.01 (s, 4 C), 150.01 (s), 163.97 (s), 198.91
(s).
130.75 (s), 131.06 (d, 2 C), 131.20 (d), 136.02 (s), 136.24 (s, 2 C),
147.01 (s, 4 C), 150.52 (s), 163.99 (s), 198.82 (s).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}(6-pentyl-2-phenyl-4H-1,3-oxazin-5-yl)gold (2d). 1H NMR
(300 MHz, THF-d8): δ 0.76 (t, J = 7.3 Hz, 3 H), 0.89−1.14 (m, 4 H),
1.23 (d, J = 6.9 Hz, 12 H), 1.38 (d, J = 6.9 Hz, 12 H), 1.83 (t, J = 7.1
Hz, 2 H), 2.61−2.79 (m, 4 H), 3.67 (s, 2 H), 7.16−7.40 (m, 7 H),
7.45−7.57 (m, 4 H), 7.75−7.86 (m, 2 H). 13C NMR (75 MHz, THF-
d8): δ 14.91 (q), 23.24 (t), 24.33 (q, 4 C), 25.24 (q, 4 C), 29.85 (d, 4
C), 35.40 (t), 37.48 (t), 53.04 (t), 124.44 (d, 2 C), 124.76 (d, 4 C),
127.56 (d, 2 C), 128.32 (d, 2 C), 131.03 (d, 2 C), 131.20 (d), 131.58
(s), 136.02 (s), 136.16 (s, 2 C), 146.90 (s, 4 C), 150.08 (s), 154.12 (s),
197.96 (s). HRMS (FAB(+), matrix NPOE): [C41H53ON3Au]+ calcd
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}(6-ethyl-2-phenyl-4H-1,3-oxazin-5-yl)gold (2b). 1H NMR
(300 MHz, THF-d8): δ 0.75 (t, J = 7.5 Hz, 3 H), 1.23 (d, J = 6.9
Hz, 12 H), 1.38 (d, J = 6.9 Hz, 12 H), 1.75 (tq, J = 7.6 Hz, J = 0.7 Hz,
2 H), 2.60−2.78 (m, 4 H), 3.68 (t, J = 0.7 Hz, 2 H), 7.26−7.38 (m, 7
H), 7.45−7.56 (m, 4 H), 7.76−7.84 (m, 2 H). 13C NMR (75 MHz,
THF-d8): δ 13.93 (q), 24.33 (q, 4 C), 25.03 (q, 4 C), 29.86 (d, 4 C),
30.61 (t), 53.06 (t), 124.43 (d, 2 C), 124.77 (d, 4 C), 127.57 (d, 2 C),
128.32 (d, 2 C), 130.71 (s), 131.01 (d, 2 C), 131.18 (d), 136.15 (s, 2
C), 146.63 (s), 146.93 (s, 4 C), 151.70 (s), 154.12 (s), 197.97 (s).
HRMS (FAB(+), matrix NPOE): [C39H49ON3Au]+ calcd 772.3541,
800.3854, found 800.3872. IR (KBr): ν̃
(cm−1) 3434, 3421, 2961,
2926, 2869, 1653, 1634, 1471, 1458, 1451, 1414, 1385, 1364, 1337,
1060, 1025, 849, 803, 758, 696.
Synthesis of 4e and 2e. According to GP1, 21.4 mg (85.0 μmol)
of 4-bromo-N-(but-2-ynyl)benzamide and 51.2 mg (85.0 μmol) of
[Au(OH)(IPr)] 3 were used. After 1 day, 4e and 2e were obtained as a
pale yellow foam in quantitative yield (4e/2e = 1/0.22). According to
GP2, 38.3 mg (152 μmol) of 4-bromo-N-(but-2-ynyl)benzamide was
used. After 1 day, 4e and 2e were obtained as a pale yellow foam in
81% yield (4e/2e = 0.07/1).
found 772.3543. IR (KBr): ν
̃
(cm−1) 3440, 2962, 2926, 2868, 1675,
1653, 1632, 1471, 1459, 1414, 1384, 1364, 1336, 1086, 1062, 1043,
1025, 804, 758, 694.
Synthesis of 4c and 2c. According to GP1, 17.1 mg (85.0 μmol)
of N-(hex-2-ynyl)benzamide and 51.2 mg (85.0 μmol) of [Au(OH)-
(IPr)] (3) was used. After 1 day, 4c and 2c were obtained as a white
foam in quantitative yield (4c/2c = 1/0.14). According to GP2, 30.8
mg (152 μmol) of N-(hex-2-ynyl)benzamide was used. After 1 day, 4c
and 2c were obtained as a white foam in 85% yield (4c/2c = 0.26/1).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}[(1E)-1-(2-phenyl-1,3-oxazol-5(4H)-ylidene)butyl]gold
(4c). 1H NMR (300 MHz, THF-d8): δ 0.58 (t, J = 7.4 Hz, 3 H), 0.91−
1.05 (m, 2 H), 1.23 (d, J = 6.9 Hz, 12 H), 1.39 (d, J = 6.9 Hz, 12 H),
2.10 (tt, J = 7.1 Hz, J = 2.1 Hz, 2 H), 2.61−2.78 (m, 4 H), 3.86 (t, J =
2.1 Hz, 2 H), 7.17−7.38 (m, 7 H), 7.45−7.56 (m, 4 H), 7.75−7.86 (m,
2 H). 13C NMR (75 MHz, THF-d8): δ 14.73 (q), 24.40 (q, 4 C), 24.96
(q, 4 C), 26.05 (t), 29.85 (d, 4 C), 37.40 (t), 59.01 (t), 124.28 (d, 2
C), 124.75 (d, 4 C), 128.44 (d, 2 C), 128.84 (d, 2 C), 130.75 (s),
131.02 (d, 2 C), 131.21 (d), 135.95 (s), 136.26 (s, 2 C), 147.01 (s, 4
C), 150.66 (s), 164.01 (s), 198.89 (s).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}(6-butyl-2-phenyl-4H-1,3-oxazin-5-yl)gold (2c). 1H NMR
(300 MHz, THF-d8): δ 0.64 (t, J = 7.4 Hz, 3 H), 0.91−1.05 (m, 2
H), 1.23 (d, J = 6.9 Hz, 12 H), 1.39 (d, J = 6.9 Hz, 12 H), 1.79 (tt, J =
7.1 Hz, J = 0.8 Hz, 2 H), 2.61−2.78 (m, 4 H), 3.67 (t, J = 0.8 Hz, 2
H), 7.17−7.38 (m, 7 H), 7.45−7.56 (m, 4 H), 7.75−7.86 (m, 2 H).
13C NMR (75 MHz, THF-d8): δ 14.35 (q), 24.33 (q, 4 C), 25.05 (q, 4
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}{(1E)-1-[2-(4-bromophenyl)-1,3-oxazol-5(4H)-ylidene]ethyl}
gold (4e). 1H NMR (300 MHz, C6D6): δ 0.96 (d, J = 6.9 Hz, 12 H),
1.30 (d, J = 6.9 Hz, 12 H), 2.06 (t, J = 2.5 Hz, 3 H), 2.38 −2.58 (m, 4
H), 4.27 (q, J = 2.5 Hz, 2 H), 6.21 (s, 2 H), 8.87−7.00 (m, 4 H),
7.00−7.09 (m, 2 H), 7.84−7.97 (m, 4 H). 13C NMR (75 MHz, C6D6):
δ 21.25 (q), 24.03 (q, 4 C), 24.71 (q, 4 C), 29.14 (d, 4 C), 57.64 (t),
122.48 (d, 2 C), 124.41 (d, 4 C), 129.16 (d, 2 C), 130.65 (d, 2 C),
131.04 (d, 2 C), 134.96 (s, 2 C), 136.67 (s), 145.70 (s), 146.01 (s, 4
C), 151.00 (s), 163.40 (s), 169.96 (s), 197.93 (s).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-2,3-dihydro-1H-imidazol-2-
yl}[2-(4-bromophenyl)-6-methyl-4H-1,3-oxazin-5-yl]gold (2e). 1H
NMR (300 MHz, C6D6): δ 0.96 (d, J = 6.9 Hz, 12 H), 1.30 (d, J =
6.9 Hz, 12 H), 2.06 (t, J = 1.5 Hz, 3 H), 2.38−2.58 (m, 4 H), 4.21 (q, J
= 1.5 Hz, 2 H), 6.21 (s, 2 H), 8.87−7.00 (m, 4 H), 7.00−7.09 (m, 2
H), 7.84−7.97 (m, 4 H). 13C NMR (75 MHz, C6D6): δ 22.10 (q),
23.92 (q, 4 C), 24.66 (q, 4 C), 29.04 (d, 4 C), 52.77 (t), 122.53 (d, 2
C), 124.17 (d, 4 C), 129.14 (d, 2 C), 130.59 (d, 2 C), 131.04 (d, 2 C),
131.91 (s), 132.40 (s), 134.31 (s), 134.93 (s, 2 C), 145.94 (s, 4 C),
146.14 (s), 153.32 (s), 197.96 (s). HRMS (FAB(+), matrix NBA):
[C38H46ON379BrAu]+ calcd 836.2490, found 836.2509. IR (KBr): ν
(cm−1) 2963, 2927, 2868, 2279, 1681, 1592, 1471, 1415, 1385, 1364,
1332, 1285, 1147, 1110, 1092, 1010, 837, 806, 759, 728.
̃
Synthesis of 4f and 2f. According to GP1, 16.3 mg (85.0 μmol)
of N-(but-2-ynyl)-2,5-dimethylfuran-3-carboxamide and 51.2 mg (85.0
μmol) of [Au(OH)(IPr)] (3) were used. After 1 day, 4f and 2f were
obtained as a pale yellow foam in quantitative yield (4f/2f = 1/0.14).
According to GP2, 19.1 mg (152 μmol) of N-(but-2-ynyl)-2,5-
dimethylfuran-3-carboxamide was used. After 1 day, 4f and 2f were
obtained as a pale yellow foam in 76% yield (4f/2f = 0.17/1).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}{(1E)-1-[2-(2,5-dimethylfuran-3-yl)-1,3-oxazol-5(4H)-
C), 26.09 (t), 29.97 (d, 4 C), 39.61 (t), 53.05 (t), 124.43 (d, 2 C),
124.78 (d, 4 C), 127.57 (d, 2 C), 128.32 (d, 2 C), 131.04 (d, 2 C),
131.39 (d), 131.76 (s), 136.03 (s), 136.16 (s, 2 C), 146.92 (s, 4 C),
149.93 (s), 154.14 (s), 197.96 (s). HRMS (FAB(+), matrix NPOE):
[C40H51ON3Au]+ calcd 786.3698, found 786.3730. IR (KBr): ν
̃
(cm−1) 3439, 3072, 2962, 2927, 2868, 1633, 1557, 1470, 1460, 1415,
1385, 1364, 1337, 1058, 804, 758, 698, 549, 452, 420.
Synthesis of 4d and 2d. According to GP1, 18.3 mg (85.0 μmol)
of N-(hept-2-ynyl)benzamide and 51.2 mg (85.0 μmol) of [Au(OH)-
(IPr)] (3) were used. After 1 day, 4d and 2d were obtained as a white
foam in quantitative yield (4d/2d = 1/0.12). According to GP2, 32.9
mg (152 μmol) of N-(hept-2-ynyl)benzamide was used. After 1 day,
4d and 2d were obtained as a white foam in 88% yield (4d/2d = 0.31/
1).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}[(1E)-1-(2-phenyl-1,3-oxazol-5(4H)-ylidene)pentyl]gold
(4d). 1H NMR (300 MHz, THF-d8): δ 0.67 (t, J = 6.9 Hz, 3 H),
0.89−1.14 (m, 4 H), 1.23 (d, J = 6.9 Hz, 12 H), 1.39 (d, J = 6.9 Hz, 12
H), 2.13 (tt, J = 7.3 Hz, J = 2.0 Hz, 2 H), 2.61−2.79 (m, 4 H), 3.84 (t,
J = 2.0 Hz, 2 H), 7.16−7.40 (m, 7 H), 7.45−7.57 (m, 4 H), 7.75−7.86
(m, 2 H). 13C NMR (75 MHz, THF-d8): δ 14.86 (q), 23.47 (t), 24.38
(q, 4 C), 25.01 (q, 4 C), 29.85 (d, 4 C), 34.87 (t), 35.57 (t), 58.96 (t),
124.29 (d, 2 C), 124.76 (d, 4 C), 128.43 (d, 2 C), 128.84 (d, 2 C),
ylidene]ethyl}gold (4f). 1H NMR (300 MHz, C6D6): δ 1.09 (d, J =
6.9 Hz, 12 H), 1.44 (d, J = 6.9 Hz, 12 H), 1.84 (s, 3 H), 2.16 (t, J = 2.4
Hz, 3 H), 2.47 (s, 3 H), 2.51−2.71 (m, 4 H), 4.36 (q, J = 2.4 Hz, 2 H),
6.37 (s, 2 H), 6.44 (s), 7.08 (d, J = 7.8 Hz, 4 H), 7.27 (t, J = 7.8 Hz, 2
H). 13C NMR (75 MHz, C6D6): δ 13.05 (q), 13.65 (q), 21.44 (q),
23.91 (q, 4 C), 24.69 (q, 4 C), 29.04 (d, 4 C), 58.09 (t), 107.01 (d),
112.73 (s), 122.48 (d, 2 C), 124.18 (d, 4 C), 128.15 (s), 130.65 (d, 2
C), 135.02 (s, 2 C), 146.00 (s, 4 C), 149.64 (s), 151.60 (s), 153.17 (s),
160.68 (s), 198.37 (s).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}[2-(2,5-dimethylfuran-3-yl)-6-methyl-4H-1,3-oxazin-5-yl]
gold (2f). 1H NMR (300 MHz, C6D6): δ 1.08 (d, J = 6.9 Hz, 12 H),
1.41 (d, J = 6.9 Hz, 12 H), 1.80 (t, J = 1.6 Hz, 3 H), 1.89 (s, 3 H), 2.46
(s, 3 H), 2.51−2.71 (m, 4 H), 4.29 (q, J = 1.6 Hz, 2 H), 6.38 (s, 2 H),
6.43 (s), 7.05 (d, 7.8 Hz, 4 H), 7.21 (t, J = 7.8 Hz, 2 H). 13C NMR (75
MHz, C6D6): δ 13.13 (q), 13.94 (q), 22.18 (q), 23.94 (q, 4 C), 24.66
6334
dx.doi.org/10.1021/om2009556|Organometallics 2011, 30, 6328−6337

Organometallics
Article
(q, 4 C), 29.16 (d, 4 C), 52.40 (t), 107.25 (d), 117.87 (s), 122.55 (d, 2
C), 124.42 (d, 4 C), 130.54 (d, 2 C), 130.90 (s), 134.99 (s, 2 C),
145.96 (s, 4 C), 146.18 (s), 148.48 (s), 151.52 (s), 151.76 (s), 198.26
(s). HRMS (FAB(+), matrix NPOE): [C38H49O2N3Au]+ calcd
131.10 (d, 2 C), 131.21 (d, 2 C), 131.90 (d), 133.24 (s), 135.99 (s, 2
C), 144.51 (s), 147.05 (s, 4 C), 155.41 (s), 155.45 (s), 164.01 (s),
195.35 (s). HRMS (FAB(+), matrix NPOE): [C43H48O3N4Au]+ calcd
865.3392, found 865.3392. IR (KBr): ν
̃
(cm−1) 3426, 2962, 2926,
776.3490, found 776.3436. IR (KBr): ν
̃
(cm−1) 2962, 2925, 2868,
2869, 1652, 1582, 1499, 1471, 1417, 1385, 1325, 1107, 1075, 1059,
1025, 850, 804, 758, 696.
1680, 1585, 1470, 1460, 1415, 1385, 1366, 1349, 1330, 1275, 1226,
1147, 1079, 1042, 1023, 805, 758.
Synthesis of 7i and 4i. According to GP1, 14.5 mg (52.0 μmol)
of N-(3-(4-nitrophenyl)prop-2-ynyl)benzamide and 31.3 mg (52.0
μmol) of [Au(OH)(IPr)] (3) were used. After 30 min at room
temperature, the mixture was measured in NMR at −80 °C. After the
intermediate amide complex 7i was characterized, the solution was
measured for 16 h with continuous 1H NMR to investigate the
conversion of the amide complex 7i to vinylgold intermediate 4i.
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}{N-[3-(4-nitrophenyl)prop-2-yn-1-yl]benzamidato-κN}gold
(7i). 1H NMR (300 MHz, THF-d8): δ 0.88−1.44 (m, 24 H), 2.33−
2.63 (m, 4 H), 1.12 (s, 2 H), 6.79 (t, J = 7.4 Hz, 2 H), 7.09 (t, J = 6.91
Hz, 1 H), 7.29−7.50 (m, 6 H), 7.53−7.71 (m, 4 H), 7.88 (s, 2 H), 8.32
(d, J = 8.5, 2 H). 13C NMR (75 MHz, THF-d8): δ 23.99 (q, 4 C),
24.95 (q, 4 C), 29.67 (d, 4 C), 38.51 (t), 79.05 (s), 97.60 (s), 124.42
(d, 2 C), 125.10 (d, 4 C), 125.21 (d, 2 C), 128.05 (d, 2 C), 128.19 (d,
2 C), 128.90 (d), 131.43 (d, 2 C), 132.32 (s), 133.63 (d, 2 C), 135.36
(s, 2 C), 142.67 (s), 146.27 (s, 4 C), 147.22 (s), 174.56 (s), 174.96 (s).
Synthesis of 7k and 4k. According to GP1, 21.5 mg (85.0 μmol)
of N-(3-(5-formylfuran-2-yl)prop-2-ynyl)benzamide and 51.2 mg
(12.3 μmol) of [Au(OH)(IPr)] (3) were used. After 1 day, the
conversion of the amide complex was not complete, and so both amide
complex 7k and vinylgold intermediate 4k were analyzed by NMR.
After an additional 2 days the conversion to vinylgold intermediate 4k
was complete and the product was obtained as a pale yellow solid in
quantitative yield.
{1,3-bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}{N-[3-(5-formylfuran-2-yl)prop-2-yn-1-yl]benzamidato-κN}
gold (7k). 1H NMR (300 MHz, THF-d8): δ 1.17 (d, J = 6.9 Hz, 12
H), 1.21 (d, J = 6.9 Hz, 12 H), 2.50−2.66 (m, 4 H), 4.14 (s, 2 H), 6.61
(d, J = 3.6 Hz, 1 H), 6.75 (t, J = 7.6 Hz, 2 H), 7.01 (t, J = 7.6 Hz, 1 H),
7.56 (s, 2 H), 7.26−7.60 (m, 9 H), 9.57 (s, 1 H). 13C NMR (75 MHz,
THF-d8): δ 24.23 (q, 4 C), 24.65 (q, 4 C), 29.70 (d, 4 C), 38.55 (t),
70.24 (s), 100.05 (s), 116.79 (d), 124.89 (d, 2 C), 125.05 (d, 4 C),
126.43 (d), 127.85 (d, 2 C), 128.16 (d, 2 C), 128.46 (d), 131.39 (d, 2
C), 135.63 (s, 2 C), 143.36 (s), 143.80 (s), 146.49 (s, 4 C), 153.21 (s),
175.39 (s), 176.59 (s), 177.19 (d).
Synthesis of 4g and 2g. According to GP1, 19.7 mg (85.0 μmol)
of N-(but-2-yn-1-yl)adamantylamide and 51.2 mg (85.0 μmol) of
[Au(OH)(IPr)] (3) were used. After 1 day, 4g and 2g were obtained
as a white foam in quantitative yield (4g/2g = 1/0.15). According to
GP2, 35.1 mg (152 μmol) of N-(but-2-yn-1-yl)adamantylamide was
used. After 1 day, 4g and 2g were obtained as a white foam in 58%
yield (4g/2g = 0.50/1).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}{(1E)-1-[2-(tricyclo[3.3.1.13,7]dec-1-yl)-1,3-oxazol-5(4H)-
ylidene]ethyl}gold (4g). 1H NMR (300 MHz, C6D6): δ 1.08 (d, J =
6.9 Hz, 12 H), 1.41 (d, J = 6.9 Hz, 12 H), 1.52−1.58 (m, 6 H), 1.80−
1.86 (m, 3 H), 2.05−2.10 (m, 6 H), 2.16 (t, J = 2.5 Hz, 3 H), 2.50−
2.66 (m, 4 H), 4.24 (q, J = 2.5 Hz, 2 H), 6.33 (s, 2 H), 7.05 (d, J = 7.5
Hz, 4 H), 7.25 (t, J = 7.5 Hz, 2 H). 13C NMR (75 MHz, C6D6): δ
21.31 (q), 23.90 (q, 4 C), 24.69 (q, 4 C), 28.53 (d, 3 C), 29.03 (d, 4
C), 36.39 (s), 37.06 (t, 3 C), 39.96 (t, 3 C), 58.10 (t), 122.36 (d, 2 C),
124.15 (d, 4 C), 130.63 (d, 2 C), 173.07 (s), 170.94 (s), 152.30 (s),
145.97 (s, 4 C), 135.00 (s, 2 C), 198.62 (s).
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}[6-methyl-2-(tricyclo[3.3.1.13,7]dec-1-yl)-4H-1,3-oxazin-5-yl]
gold (2g). 1H NMR (300 MHz, C6D6): δ 1.06 (d, J = 6.9 Hz, 12 H),
1.40 (d, J = 6.9 Hz, 12 H), 1.52−1.58 (m, 6 H), 1.75−1.81 (m, 3 H),
1.83 (t, J = 1.6 Hz, 3 H), 1.98−2.02 (m, 6 H), 2.50−2.66 (m, 4 H),
4.20 (q, J = 1.6 Hz, 2 H), 6.33 (s, 2 H), 7.04 (d, J = 7.5 Hz, 4 H), 7.16
(t, J = 7.5 Hz, 2 H). 13C NMR (75 MHz, C6D6): δ 22.18 (q), 24.08 (q,
4 C), 24.67 (q, 4 C), 28.91 (d, 3 C), 29.14 (d, 4 C), 37.45 (t, 3 C),
39.08 (s), 40.64 (t, 3 C), 52.47 (t), 122.44 (d, 2 C), 124.12 (d, 4 C),
130.52 (d, 2 C), 134.97 (s, 2 C), 145.92 (s, 4 C), 146.46 (s), 162.69
(s), 173.06 (s), 198.56 (s). HRMS (FAB(+), matrix NPOE):
[C42H57ON3Au]+ calcd 816.4167, found 816.4158. IR (KBr): ν
̃
(cm−1). 2962, 2905, 2851, 2279, 1689, 1659, 1640, 1455, 1414, 1385,
1365, 1332, 1273, 1144, 1103, 1078, 990, 807, 759.
Synthesis of 4h. According to GP1, 20.0 mg (85.0 μmol) of N-
(3-phenylprop-2-ynyl)benzamide and 51.2 mg (85.0 μmol) [Au(OH)-
(IPr)] (3) were used. After 1 day, 4h was obtained as a pale yellow
solid in quantitative yield. According to GP2, 35.8 mg (152 μmol) of
N-(3-phenylprop-2-ynyl)benzamide was used. After 1 day, 4h was
obtained as a pale yellow solid in 60% yield.
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}[(E)-phenyl(2-phenyl-1,3-oxazol-5(4H)-ylidene)methyl]gold
(4h). 1H NMR (300 MHz, THF-d8): δ 1.25 (d, J = 6.9 Hz, 12 H),
1.37 (d, J = 6.9 Hz, 12 H), 2.64−2.82 (m, 4 H), 4.06 (s, 2 H), 6.71−
6.80 (m, 1 H), 6.85−6.94 (m, 2 H), 7.13−7.21 (m, 2 H), 7.29−7.45
(m, 7 H), 7.52−7.62 (m, 4 H), 7.82−7.91 (m, 2 H). 13C NMR (75
MHz, THF-d8): δ 24.34 (q, 4 C), 24.83 (q, 4 C), 29.79 (d, 4 C), 60.93
(t), 123.56 (d), 124.29 (d, 2 C), 124.78 (d, 4 C), 127.32 (d, 2 C),
128.44 (d, 2 C), 128.92 (d, 2 C), 130.01 (s), 131.04 (d, 2 C), 131.13
(d, 2 C), 131.45 (d), 134.68 (s), 136.13 (s, 2 C), 146.97 (s, 4 C),
147.30 (s), 151.30 (s), 164.20 (s), 196.78 (s). HRMS (FAB(+), matrix
NPOE): [C43H49ON3Au]+ calcd 819.3463, found 819.3451. IR (KBr):
ν (cm−1) 3441, 3067, 2962, 2925, 2869, 1745, 1646, 1471, 1415, 1385,
1364, 1332, 1257, 1181, 1061, 1025, 866, 804, 758, 696.
{1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihydro-2H-imidazol-2-
ylidene}[(E)-(5-formylfuran-2-yl)(2-phenyl-1,3-oxazol-5(4H)-
ylidene)methyl]gold (4k). 1H NMR (300 MHz, THF-d8): δ 1.26 (d, J
= 6.9 Hz, 12 H), 1.41 (d, J = 6.9 Hz, 12 H), 2.65−2.82 (m, 4 H), 4.06
(s, 2 H), 6.26 (d, J = 3.6 Hz, 1 H), 7.03 (d, J = 3.6 Hz, 1 H), 7.36−7.48
(m, 7 H), 7.56 (t, J = 8.0 Hz, 2 H), 7.62 (s, 2 H), 7.92−8.02 (m, 2 H),
9.30 (s, 1 H). 13C NMR (75 MHz, THF-d8): δ 24.26 (q, 4 C), 25.01
(q, 4 C), 29.83 (d, 4 C), 61.80 (t), 110.91 (d), 120.74 (s), 124.55 (d),
124.84 (d, 4 C), 128.62 (d, 2 C), 129.15 (d), 129.18 (d, 2 C), 131.13
(d, 2 C), 131.97 (d, 2 C), 135.98 (s, 2 C), 146.98 (s, 4 C), 150.94 (s),
157.47 (s), 164.16 (s), 166.94 (s), 176.58 (s), 176.64 (d), 194.65 (s).
HRMS (FAB(+), matrix NPOE): [C42H47O3N3Au]+ calcd 838.3283,
found 838.3292. IR (KBr): ν
̃
(cm−1) 3434, 2962, 2926, 2869, 1653,
1616, 1553, 1471, 1417, 1386, 1364, 1328, 1214, 1076, 1059, 1025,
917, 803, 757, 696.
Synthesis of p-Bis{1,3-bis[2,6-bis(propan-2-yl)phenyl]-1,3-
dihydro-2H-imidazol-2-ylidene}[(E)-phenyl(1,3-oxazol-5(4H)-
ylidene)methyl]gold}benzene (6). According to GP1, 10.2 mg
(52.0 μmol) of N1,N4-bis(3-phenylprop-2-ynyl)terephthalamide and
62.6 mg (104 μmol) of [Au(OH)(IPr)] (3) was used. After 1 day, 6
was obtained as a pale yellow solid in quantitative yield.
Synthesis of 1,3-Bis[2,6-bis(propan-2-yl)phenyl]-1,3-dihy-
dro-2H-imidazol-2-ylidene}[(E)-(4-nitrophenyl)(2-phenyl-1,3-
oxazol-5(4H)-ylidene)methyl]gold (4i). According to GP1, 23.8
mg (85.0 μmol) N-(3-(4-nitrophenyl)prop-2-ynyl)benzamide and 51.2
mg (85.0 μmol) [Au(OH)(IPr)] 3 was used. After 1 d, 4i was
obtained as a pale yellow solid in quantitative yield.
1H NMR (300 MHz, THF-d8): δ 1.23 (d, J = 6.9 Hz, 24 H), 1.35
(d, J = 6.9 Hz, 24 H), 2.62−2.80 (m, 8 H), 4.04 (s, 4 H), 6.70−6.79
(m, 2 H), 6.83−6.92 (m, 4 H), 7.09−7.17 (m, 4 H), 7.35−7.43 (m, 8
H), 7.52−7.61 (m, 8 H), 7.84 (s, 4 H). 13C NMR (75 MHz, THF-d8):
δ 24.45 (q, 8 C), 24.93 (q, 8 C), 29.91 (d, 8 C), 61.09 (t, 2 C), 123.73
(d, 2 C), 124.42 (d, 4 C), 124.90 (d, 8 C), 127.46 (d, 4 C), 128.34 (d,
4 C), 131.16 (d, 4 C), 131.21 (d, 4 C), 132.03 (s, 2 C), 135.05 (s, 2
C), 136.23 (s, 4 C), 147.08 (s, 8 C), 147.27 (s, 2 C), 151.14 (s, 2 C),
1H NMR (300 MHz, THF-d8): δ 1.26 (d, J = 6.9 Hz, 12 H), 1.36
(d, J = 6.9 Hz, 12 H), 2.61−2.80 (m, 4 H), 4.07 (s, 2 H), 7.24−7.31
(m, 2 H), 7.32−7.46 (m, 7 H), 7.58−7.68 (m, 4 H), 7.77−7.83 (m, 2
H), 7.84−7.91 (m, 2 H). 13C NMR (75 MHz, THF-d8): δ 24.29 (q, 4
C), 24.86 (q, 4 C), 29.82 (d, 4 C), 61.46 (t), 122.92 (d, 2 C), 124.50
(d, 2 C), 124.90 (d, 4 C), 128.48 (d, 2 C), 129.14 (d, 2 C), 129.28 (s),
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Organometallics
Article
163.99 (s, 2 C), 196.81 (s, 2 C). HRMS (FAB(+), matrix NPOE):
ACKNOWLEDGMENTS
■
[C80H91O2N6Au2]+ calcd 1561.6535, found 1561.6538. IR (KBr): ν
(cm−1) 2962, 2926, 2868, 1648, 1622, 1592, 1486, 1470, 1414, 1385,
1364, 1327, 1254, 1214, 1062, 1019, 864, 803, 758, 694.
̃
The ERC (FUNCAT to SPN) and the EPSRC are gratefully
acknowledged for support of this work. A.P. thanks the Spanish
MICINN for a Ramón y Cajal contract (RYC-2009-04170).
Synthesis of {1,3-Bis[2,6-bis(propan-2-yl)phenyl]-
imidazolidin-2-ylidene}(4-methylphenolato)gold ([Au(O-p-
Tol)(IPr)]). [Au(OH)(IPr)] (3; 50 mg, 0.083 mmol) and p-cresol
(9.0 mg, 0.083 mmol) were introduced into a vial containing toluene
(0.8 mL). The reaction mixture was stirred at 60 °C for 14 h. The
reaction mixture was cooled to room temperature, and the solvent
volume was reduced by half, under vacuum. Pentane (6 mL) was
added, and the resulting precipitate was collected on a frit and washed
with pentane (3 × 3 mL). The solid was dried under vacuum to afford
[Au(O-p-Tol)(IPr)] as a white microcrystalline solid (51.1 mg, 89%).
1H NMR (300 MHz, CD2Cl2): δ 7.58 (t, J = 7.8 Hz, 2H, CH
aromatic), 7.36 (d, J = 7.8 Hz, 4H, CH aromatic), 7.26 (s, 2H, CH
imidazole), 6.59 (br d, J = 8.2 Hz, 2H, CH p-cresol), 6.10 (br d, J = 8.2
Hz, 2H, CH p-cresol), 2.60 (sept, J = 6.9 Hz, 4H, CH(CH3)2), 2.07 (s,
3H, CH3 p-cresol), 1.34 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.23 (d, J =
6.9 Hz, 12H, CH(CH3)2). 13C NMR (75 MHz, CD2Cl2): δ 169.8 (s, C
carbene), 166.0 (s, C aromatic p-cresol), 146.3 (s, C aromatic NHC),
134.7 (s, C aromatic), 131.0 (s, CH imidazole), 129.2 (s, CH aromatic
p-cresol), 124.6 (s, CH aromatic), 123.7 (s, CH aromatic), 123.4 (s, C
aromatic p-cresol), 118.1 (s, CH aromatic p-cresol), 29.2 (s,
CH(CH3)2), 24.5 (s, CH(CH3)2), 24.3 (s, CH(CH3)2), 20.3 (s, CH3
p-cresol) ppm. Anal. Calcd for C34H43AuN2O: C, 58.95; H, 6.26; N,
4.04. Found: C, 59.21; H, 6.58; N, 3.91.
Synthesis of {1,3-Bis[2,6-bis(propan-2-yl)phenyl]-
imidazolidin-2-ylidene}(4-methylanilinato)gold ([Au(NH-p-
Tol)(IPr)]). [Au(OH)(IPr)] (3; 50 mg, 0.083 mmol) and p-toluidine
(8.9 mg, 0.083 mmol) were introduced into a vial containing toluene
(0.8 mL). The reaction mixture was stirred at 100 °C for 24 h. The
reaction mixture was cooled to room temperature, at which point the
solvent volume was reduced by half, under vacuum. Pentane (6 mL)
was added, and the resulting precipitate was collected on a frit and
washed with pentane (3 × 3 mL). The solid was dried under vacuum
to afford [Au(NH-p-Tol)(IPr)] as a brown microcrystalline solid (49
mg, 85%).
Umicore AG and Chemetall AG are thanked for their generous
gifts of materials. S.P.N. is a Royal Society Wolfson Research
Merit Award holder. We thank Dr. Pierrick Nun for valuable
discussions.
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ASSOCIATED CONTENT
■
́
S
* Supporting Information
Text, tables, and figures giving an Arrhenius plot for the
formation of vinylgold(I) complex 4i, a detailed procedure for
the synthesis of IPrAuOH (3) on a large scale, calculations for a
(3) For a review and discussion on recent isolated intermediates
involved in gold homogeneous catalysis, see: (a) Hashmi, A. S. K.
Angew. Chem., Int. Ed. 2010, 49, 5232−5241. For a more recent
example, see: (b) Melchionna, M.; Nieger, M.; Helaja, J. Chem. Eur. J.
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1
mechanism involving 3 and cationic gold(I) species, and H
and 13C NMR spectra of complexes 2−4, 6, 7, [Au(O-p-
Tol)(IPr)], and [Au(O-p-Tol)(IPr)]. This material is available
free of charge via the Internet at http://pubs.acs.org.
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studies on gold-catalyzed oxazole synthesis from propargyl carbox-
amide, see: (d) Milton, M. D.; Inada, Y.; Nishibayashi, Y.; Uemura, S.
Chem. Commun. 2004, 2712−2713.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: snolan@st-andrews.ac.uk (S.P.N.); hashmi@hashmi.
de (A.S.K.H.).
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complexes in 89% and 85% isolated yields, respectively.
(11) The DFT optimizations were performed with the BP86 GGA
functional using the SDD ECP on Au and the SVP basis set on all
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single-point calculations on the BP86 geometries using the M06
functional. Solvent effects (THF) were introduced with the PCM
approach.
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