Mechanistic insights into the one-pot synthesis of propargylamines from terminal alkynes and amines in chlorinated solvents catalyzed by gold compounds and nanoparticles

Article abstract of DOI:10.1002/chem.201000587

Propargylamines can be obtained from secondary amines and terminal alkynes in chlorinated solvents by a three-and two-component synthesis catalyzed by gold compounds and nanoparticles (Au-NP) under mild conditions. The use of dichloromethane allows for the activation of two C-Cl bonds and a clean transfer of the methylene fragment to the final product. The scope of the reaction as well as the influence of different gold(III) cycloaurated complexes and salts has been investigated. The involvement of gold nanoparticles generated in situ in the process is discussed and a plausible reaction mechanism is proposed on the basis of the data obtained.

Full text of DOI:10.1002/chem.201000587

FULL PAPER
DOI: 10.1002/chem.201000587
Mechanistic Insights into the One-Pot Synthesis of Propargylamines from
Terminal Alkynes and Amines in Chlorinated Solvents Catalyzed by Gold
Compounds and Nanoparticles
David Aguilar,[a] Maria Contel,*[b] and Esteban P. Urriolabeitia*[a]
This paper is dedicated to Professor Richard H. Fish on the occasion of his 70th birthday
Abstract: Propargylamines can be ob-
tained from secondary amines and ter-
minal alkynes in chlorinated solvents
by a three- and two-component synthe-
sis catalyzed by gold compounds and
nanoparticles (Au-NP) under mild con-
ditions. The use of dichloromethane
bonds and a clean transfer of the meth-
ylene fragment to the final product.
The scope of the reaction as well as the
rated complexes and salts has been in-
vestigated. The involvement of gold
nanoparticles generated in situ in the
process is discussed and a plausible re-
action mechanism is proposed on the
basis of the data obtained.
influence of different goldACTHNUTRGNE(NUG III) cycloau-
À
Keywords: alkynes · C C coupling ·
À
C Cl activation · catalysis · gold
À
allows for the activation of two C Cl
Introduction
The synthesis of propargylic amines has attracted considera-
ble attention over the last few years due to their pharma-
ceutical relevance and their importance as building blocks in
the preparation of nitrogen-containing molecules, and as
key intermediates for natural product synthesis.[1] There are
three main synthetic pathways to obtain propargylamines:[2]
1) by stoichiometric nucleophilic reactions; 2) by transition-
metal-catalyzed reactions of imines (or enamines), which
Scheme 1. Methods available to form propargylamines.[2]
can be generated from aldehydes and amines; or 3) by the
3
À
catalytic coupling of a sp C H adjacent to nitrogen with a
terminal alkyne (Scheme 1). Gold, silver, and copper com-
pounds have also provided efficient catalysts in the imine-,
enamine-, or imine-generated addition to alkynes,[3,4] includ-
ing recyclable gold compounds[5] or nanoparticles.[6] The first
example of a CuI-catalyzed alkynylation of tertiary amines
with terminal alkynes in the presence of tBuOOH
3
À
[a] Dr. D. Aguilar, Dr. E. P. Urriolabeitia
Departamento de Compuestos Organometꢀlicos
Instituto de Ciencia de Materiales de Aragꢁn
CSIC-Universidad de Zaragoza, Pedro Cerbuna 12
50009 Zaragoza (Spain)
(Scheme 1, pathway c; through sp C H activation) was re-
ported.[2]
We report herein on a gold-catalyzed three- and two-com-
ponent synthesis of propargylamines by an alternative route
to those outlined in Scheme 1. Gold compounds and nano-
particles (Au-NP) are found to be efficient catalysts for the
coupling of secondary amines and terminal alkynes in
chlorinated solvents. In dichloromethane, we discovered that
the coupling involves the methylene fragment from the sol-
vent, which constitutes an unexpected role for dichlorome-
Fax : (+34)976761187
E-mail: esteban@unizar.es
[b] Prof. M. Contel
Chemistry Department, Brooklyn College and the Graduate Center
The City University of New York, New York 11210 (USA)
Fax : (+1)718-951-4607
E-mail: mariacontel@brooklyn.cuny.edu
À
thane as a CH2 partner, by a gold-catalyzed C Cl bond acti-
vation.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000587.
Chem. Eur. J. 2010, 16, 9287 – 9296
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9287

Activation of carbon–halogen bonds by transition-metal
compounds is involved in various organic processes, but the
dition of 2-methylfuran and electron-rich arenes to methyl
vinyl ketone,[19a,b] and the synthesis of 2,5-disubstituted oxa-
zoles through cyclization of N-propargylcarboxamides.[19b]
Iminophosphoranes (R3P=NR’) constitute a class of com-
pounds that can be readily prepared by different synthetic
routes,[20] and their electronic and steric properties may be
tuned through appropriate choice of R and R’. Not only
does the iminophosphorane C,N-backbone confer a marked
stability to the metallic center in d8 square-planar com-
plexes, but also the PR3 fragment can be used as a spectro-
scopic marker to follow reactions by 31P NMR spectroscopic
analysis. We demonstrated that the real catalytic species in
À
activation of the relatively stable C Cl bond is an important
subject in environmental chemistry (due to the possible deg-
radation of harmful chlorinated compounds).[7] The activa-
tion of CH2Cl2 by late transition metals has been document-
ed for CoI,[8] RhI,[9] RhIII,[10] RuII,[11] Pd,[12] and Pt0[12] com-
À
À
plexes. The activation of the C Cl bond usually affords M
À
À
CH2Cl or M CH2 M organometallic compounds. Dinuclear
gold(I) ylide complexes are also known to add CH2Cl2 to
afford dinuclear AuII derivatives with a methylene bridge.[13]
The activation of CH2Cl2 (wherein CH2Cl2 serves as a CH2
partner) by early transition metals has also been ach-
ieved.[14,15] CrII complexes are able to promote methylene
transfer from CH2Cl2 to an alkene (cyclopropanation, but
only in 2% yield) and the direct stoichiometric methynela-
tion of ketones and aldehydes has been recorded for a bi-
metallic Mg/TiCl4/THF system.[15] The heterolytic thermal or
photocatalytic degradation of CH2Cl2 to HCl and CO under
aerobic conditions has been described for heterogeneous
these processes were cationic goldACHTUNTRGNEUNG(III) cycloaurated com-
plexes generated by abstraction of the chloride ligands in
polar solvents further assisted by silver salts.[19a]
catalysts and chlorocuprate ions.[16] The C Cl bond activa-
À
tion described here represents an elegant example of the ac-
tivation of CH2Cl2, which generates and transfers the meth-
ylene fragment catalytically (typically 5 mol% catalyst and
amounts as low as 1 mol% for longer reaction times) under
mild reaction conditions (508C). AuIII complexes and AgI
Encouraged by these results, we decided to study hydro-
À
salts have proven to be effective in similar C Cl bond acti-
ACHTUNGTRENNUNG
vations,[17] but details of these findings were never published.
We report herein on the effects of gold compounds and
nanoparticles in different oxidation states in such coupling
reactions, and suggest a plausible reaction mechanism.
Although gold-catalyzed reactions have been thoroughly
studied in the past decade,[18] the study of reaction mecha-
nisms and the isolation/characterization of gold intermedi-
ates and/or catalytically active species has not received the
same attention. Clarification of the reaction mechanisms is
crucial for the rational design of more efficient molecular
catalysts.
Results and Discussion
Scope of the gold-catalyzed synthesis of propargylamines in
chlorinated solvents: Formation and catalytic activity of
gold nanoparticles: The cyclization of 5-trimethylsilyl-4-pen-
tynylamine (3)[21] was catalyzed by 1, 2, and gold
ACTHUNRTGNE(GNU III) salts
(Table 1), affording yields of the intramolecular hydroami-
nation product 4 comparable to those reported for Na-
We reported on the catalytic and cytotoxic/apoptotic
ACHTUNGRTEN[NGNU AuCl4] with 5-alkynylamines to give tetrahydropyridines
properties[19] of gold
(III) compounds containing iminophos-
(see the Supporting Information).[22]
phorane ligands (such as 1 and 2)[19a,c] that catalyzed the ad-
Table 1. Catalytic preparation of 4 through intramolecular hydroamina-
tion of 3.
Abstract in Spanish: Se han obtenido propargilaminas a
partir de aminas secundarias y alquinos terminales en disol-
ventes clorados a travꢀs de una sꢁntesis de dos o tres compo-
nentes catalizada por compuestos de oro y nanoparticulas
(Au-NP) en condiciones de reacciꢂn suaves. El uso de diclo-
Entry
Catalyst ([mol%])
AuCl3 (5)
Ag+ ([mol%])
Time [h]
Yield [%][a]
À
rometano permite la activaciꢂn de dos enlaces C Cl y la pos-
terior trasferencia del fragmento metileno al producto final.
El alcance de la reacciꢂn asꢁ como la influencia de diferentes
1
2
3
4
5
6
7
8
–
–
–
2
2
2
2
2
2
2
2
64
85
61
80
73
65
79
70
Na
N
1 (5)
1 (5)
1 (5)
1 (5)
2 (5)
2 (5)
compuestos ortometalados y sales de oroACTHNUTRGNEUNG(III) han sido inves-
AgOTf (11)
AgOTf (6.1)
–
AgOTf (11)
AgOTf (6.1)
tigados. Los resultados obtenidos son la base de la discusiꢂn
sobre la participaciꢂn de nanopartꢁculas de oro generadas in
situ en el proceso asꢁ como del posible mecanismo de reac-
ciꢂn.
[a] Isolated yields.
9288
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Chem. Eur. J. 2010, 16, 9287 – 9296

One-Pot Synthesis of Propargylamines
FULL PAPER
We have also studied the catalytic activity of 1 in intermo-
lecular hydroamination processes with terminal alkynes and
secondary amines. However, when Bu2NH (5b) was added
vents, such as CHCl3 or (ClCH2)2, did not give detectable
coupling products (see below). Preliminary reactions with a
higher catalyst loading (10 mol%) and a 1:1.2 molar ratio of
alkyne to amine afforded higher yields (Table 3 below and
ꢀ
to HC CPh (6a) in either THF or toluene in the presence
of 1 (5 mol%, 508C, 24 h), the expected intermolecular hy-
droamination product was not obtained and the unreacted
starting materials were recovered instead (Scheme 2). Sur-
Table 3. Synthesis of progargylamines 7ba, 7bd, and 8bd in CH2Cl2 with
isolated Au-NP (nano-12) synthesized by the Brust[26] method. A compar-
ison with K
ACHTUNGRTEN[NUNG AuCl4] is given in the table.
Cat.
7bd+8bd [%]
7ba [%]
Nano-12[a]
94 (7bd/8bd, 1:0.5)
93 (7bd/8bd, 1:0.5)
90 (7bd/8bd, 1:0.05)
91 (7bd/8bd, 1:0.08)
75
75
76
83
KACTHNUTRGNEUNG
[AuCl4][a]
Nano-12[b]
[AuCl4][a]
KACHTUNGTRENNUNG
[a] Reaction conditions: cat. (10 mol%), solvent (5 mL), 508C, 24 h,
alkyne/amine (1:1). [b] Reaction conditions: cat. (1 mol%), solvent
(5 mL), 508C, 72 h, alkyne/amine (1:1.2).
Scheme 2. Three-component synthesis of propargylamines.
Table 1 in the Supporting Information), but the reaction
conditions were subsequently optimized to lower the
amount of catalyst and to use a 1:1 molar ratio (alkyne/
amine).
The nature of the alkyne has a critical influence over the
general process, as depicted in Scheme 3. The reaction of
prisingly, when CH2Cl2 was employed we obtained propar-
gylamine 7ba. This compound comes from a three-compo-
nent coupling of the amine 5b, the alkyne 6a and the CH2
fragment from the solvent CH2Cl2 as will be demonstrated
below.
ꢀ
We explored the scope of the reaction for the cycloaurat-
ed gold compound 1 as a catalyst under the same reaction
conditions (alkyne (2 mmol), amine (2 mmol), 1 (5 mol%),
24 h, 508C) for three different terminal alkynes and for five
different secondary amines (Table 2). No reaction was ob-
Me3SiC CH (6d) with R’2NH (5a–e) in CH2Cl2 under the
same conditions gave two different propargylamines
(Table 4). The main product of the mixture was the CH2Cl2
activation product (7ad–ed), whereas the minor product
(8ad–ed) arose from the formal coupling of one R’2N frag-
ꢀ
ment, one Me3SiC C unit, and a CH(Me) group that comes
ꢀ
from a second Me3SiC CH alkyne molecule (see below).
Table 2. Three-component synthesis[a,b] of propargylamines in CH2Cl2
with 1 as the catalyst (Scheme 2).
The nature of the silyl substituent is crucial for the synthesis
of compound 8. For instance, the terminal alkyne Me3CC
CH (6b) did not afford propargylamines of the type 8 with
ꢀ
Amine
6a [%]
6b [%]
6c [%]
5a
5b
5c
5d
5e
15 (7aa)
58 (7ba)
22 (7ca)
70 (7da)
60 (7ea)
17 (7ab)
71 (7bb)
21 (7cb)
36 (7db)
70 (7eb)
0 (7ac)
57 (7bc)
30 (7cc)
51 (7dc)
55 (7ec)
ꢀ
a Me3CC C unit.
Compound 8ed was not formed under the reaction condi-
tions. Compound 8bd was obtained as the exclusive product
under similar reaction conditions in chlorinated solvents,
such as CHCl3 or ClCH2CH2Cl, with yields of 90%. A simi-
lar reaction between Et2NH and acetylene (13.6 atm) to
afford 3-diethylaminobut-1-yne, catalyzed by CuBr
(20 mol%) in THF at 1008C, was described as early as
1949.[23]
[a] Isolated yields. [b] Reaction conditions: cat.
1
(5 mol%), CH2Cl2
(5 mL), alkyne (2 mmol), amine (2 mmol), 24 h, 508C.
served between 1-decyne and HNMe2. Better yields were
obtained with Bu2NH than with Me2NH, probably due to
the high volatility of the dimethylamino derivatives. The re-
action seems to be very sensitive to the nature of the amine
because no reaction was observed between the above-men-
tioned alkynes and Ph2NH, Cy2NH, iPr2NH, or MeBnNH.
Amines with linear N-alkylic chains are best tolerated and
we observed that more basic amines such as Bu2NH and pi-
peridine also gave better results
We tested other gold
es, such as the simple gold
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
new cationic cycloaurated phosphane-containing derivatives
9 and 10 (Scheme 4).
The synthesis and characterization of 9 and 10 are de-
scribed in the Experimental Section. Mono- and dicationic
derivatives 9 and 10, respectively, are cleanly obtained from
(dimethylamino
derivatives
were more volatile and gave
lower isolated yields). The reac-
tion is also sensitive to the
nature of the solvent: whereas
CH2Br2 can be used instead of
CH2Cl2, other chlorinated sol- Scheme 3. Two- versus three-component synthesis with trimethylsilylacetylene.
Chem. Eur. J. 2010, 16, 9287 – 9296
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9289

M. Contel, E. P. Urriolabeitia, and D. Aguilar
Table 4. Two- versus three-component synthesis[a,b] of propargylamines in
CH2Cl2 with 1 as the catalyst (Scheme 3).
Moreover, the catalytic activity and selectivity of K-
AHCTUNGTRENNUNG
Amine
6d [%]
ꢀ
the terminal alkyne Me3SiC CH (6d) (Table 6 and
5a
5b
5c
5d
5e
55 (7ad/8ad, 1:0.2)
95 (7bd/8bd, 1:0.5)
39 (7cd/8cd, 1:0.05)
40 (7dd/8dd, 1:0.3)
65 (7ed/8ed, 1:0.0)
Scheme 3). With more basic amines, the selectivity towards
the CH2Cl2 activation product was higher. Again 8ed (with
piperidine) could not be obtained under these reaction con-
ditions.
[a] Isolated yields. [b] Reaction conditions: cat.
1
(5 mol%), CH2Cl2
Table 6. Two- versus three-component synthesis[a,b] of propargylamines in
(5 mL), alkyne (2 mmol), amine (2 mmol), 24 h, 508C.
CH2Cl2 with K
ACHTUNGERTN[NUNG AuCl4] as the catalyst (Scheme 3).
Amine
6d [%]
5a
5b
5c
5d
5e
60 (7ad/8ad, 1:0.3)
90 (7bd/8bd, 1:0.1)
46 (7cd/8cd, 1:0.05)
42 (7dd/8dd, 1:0.8)
73 (7ed/8ed, 1:0.0)
[a] Isolated yields. [b] Reaction conditions: cat.
KACHTNGUTRENNU[G AuCl4] (5 mol%),
CH2Cl2 (5 mL), alkyne (2 mmol), amine (2 mmol), 24 h, 508C.
With KACTHUNTGRNE[UNG AuCl4], the catalyst load (Table 3) could be re-
duced to 1 mol% (for amine 5b and alkyne 6d) to give the
mixture of products in 91% yield in a similar ratio 7bd/8bd
(1:0.08) but after longer reaction times (72 vs. 24 h). Ex-
changing CH2Cl2 with other chlorinated solvents resulted in
the clean synthesis of product 8bd; with CHCl3 or
ClCH2CH2Cl the yields of isolated product were 90 and
93%, respectively. In the case of the reaction of amine 5b
and alkyne 6d in nonchlorinated solvents, such as THF or
Scheme 4. Synthesis of new cationic cycloaurated endo derivatives 9 and
10 with phosphane ligands. Dppe=1,2-bis(diphenylphosphino)ethane.
À
CH3CN, the C Cl activation product 7bd was clearly not
the organometallic gold
al of one or two chloride ligands with a silver salt and addi-
tion of a mono- (PPh3) or bis-phosphane (dppe), respective-
ly.
With the salt KACHTUNGTRENNUNG[AuCl4] as a catalyst, we studied the addi-
(III) endo derivative 1[19a] by remov-
observed and, instead, the chiral product 8bd was obtained
in low yields (40 and 10%, respectively) together with start-
ing materials and some unidentified amine derivatives.
The results of our study on the catalytic activity of the
mono- and dicationic cycloaurated derivatives 9 and 10 are
collected in Table 7. We investigated the standard reaction
tion reaction of the secondary amines 5a–e to the terminal
alkynes 6a–c in CH2Cl2 (Scheme 2, Table 5). The results
ꢀ
in CH2Cl2 and the particular case of the Me3SiC CH alkyne
(6d) with nBu2NH (5b). The catalytic activity was similar to
that observed for 1 and KACTHNUTRGNE[UGN AuCl4] for phenylacetylene (6a),
Table 5. Three-component synthesis[a,b] of propargylamines in CH2Cl2
with KACHTUNGTRENNUNG
but decreased for the other alkynes. In the case of trimethyl-
silylacetylene (6d), the propargylamine obtained was exclu-
sively derived from CH2Cl2 activation (7ba).
Amine
6a [%]
6b [%]
6c [%]
5a
5b
5c
5d
5e
35 (7aa)
76 (7ba)
32 (7ca)
61 (7da)
78 (7ea)
30 (7ab)
80 (7bb)
30 (7cb)
41 (7db)
80 (7eb)
0 (7ac)
60 (7bc)
35 (7cc)
73 (7dc)
68 (7ec)
Table 7. Two- versus three-component synthesis[a,b] of propargylamines
derived from nBu2NH (5b) in CH2Cl2 with cationic cycloaurated gold-
AHCTUNGTREG(NNNU III) derivatives 9 and 10 as catalysts (Equations 2 and 3).
Cat.
6a [%]
6b [%]
6c [%]
6d [%]
[a] Isolated yields. [b] Reaction conditions: cat.
KACHTNGUTRENNU[G AuCl4] (5 mol%),
CH2Cl2 (5 mL), alkyne (2 mmol), amine (2 mmol), 24 h, 508C.
9
10
80 (7ba)
75 (7ba)
60 (7bb)
65 (7bb)
47 (7bc)
43 (7bc)
34 (7bd/8bd, 1:0.0)
30 (7bd/8bd, 1:0.0)
[a] Isolated yields. [b] Reaction conditions: cat.
9
or 10 (5 mol%),
CH2Cl2 (5 mL), alkyne (2 mmol), amine (2 mmol), 24 h, 508C.
were comparable to those obtained with the cycloaurated
derivative 1 (slightly higher yields in this case). More basic
amines gave better isolated yields. We could also reduce the
catalyst loading to 1 mol% without loss of conversion
(83%), at the expense of longer reaction times (72 h), to
obtain propargylamine 7ba (Table 3 below).
In contrast to our previous studies with gold
plexes, for which we demonstrated that the catalytically
active species were discrete gold
(III) derivatives,[19] it seems
that the real catalytically active species here are gold nano-
ACHTUNGTRENN(UNG III) com-
AHCTUNGTRENNUNG
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Chem. Eur. J. 2010, 16, 9287 – 9296

One-Pot Synthesis of Propargylamines
FULL PAPER
particles (Au-NP) generated in situ at the beginning of the
reaction by reduction of the gold precursors with the amine.
We always observed an immediate change of the color of
(5b) in CDCl3; as expected, compound 8bd did not show in-
corporation of H in the C(H)Me unit. The generation of
the C(H)Me unit can be explained by a desilylation reaction
of the starting alkyne. The reaction of an equimolar mixture
2
the goldACHTUNGTRENNUNG(III)-containing solutions from yellow to deep red
ꢀ
ꢀ
upon addition of the amine in all reactions. Au-NP were re-
of Me3SiC CH (6d) and PhC CH (6a) with two equiva-
lents of Bu2NH (5b) in CH2Cl2, gave the cross-coupling
ported to be formed by reduction of goldACTHNUGRTENUNG(III) salts with
amines.[24] Moreover, AuI halides, AuCl, and AuBr can also
generate Au-NP with narrow size distribution under mild
conditions (608C)[25] similar to those used in the catalytic
conditions reported herein (508C).
product PhC C-C(H)Me-NBu2 (13) in 15% yield, together
ꢀ
with the expected products 7ba (4%), 7bd (41%), and 8bd
(40%) (see Scheme 5 and the Supporting Information). This
result clearly showed that the incorporation of the C(H)Me
unit is related to the presence of the silylalkyne in the start-
ing mixture because the reaction of PhC CH (6a) with
Bu2NH (5b) gave only 7ba.
We have been able to characterize these deep-red solu-
tions to test for the presence of gold colloids in the forma-
ꢀ
tion of 7ba with K
N
of these gold materials (aliquot of the solution deposited
onto a carbon-coated copper grid and blotted) as well as X-
ray diffraction studies (from the powdered sample after re-
moval of all solvents) confirmed the formation of homoge-
neous nanoparticles with a 3 nm radius (see the Supporting
Information). As expected, isolable gold nanoparticles pre-
pared by literature methods (nano-12),[26] were also catalyti-
cally active in CH2Cl2 in the reactions described herein
(Table 3) and the yields of products 7ba and 7bd/8bd ob-
tained were similar to those achieved with KACTHNUGTRENUNG[AuCl4].
Reaction mechanism: We have elucidated the origin of the
CH2 (in propargylamines of type 7) and C(H)Me (in propar-
gylamines of type 8) fragments. NMR spectroscopy experi-
ments proved that the CH2 fragment in 7ba comes from the
Scheme 5. Gold-catalyzed cross-coupling reaction of Bu2NH (5b) with
two different alkynes (trimethylsilylacetylene (6d) and phenylacetylene
(6a)) in CH2Cl2.
CH2Cl2 solvent. When the KACHTUNTRGNE[UNG AuCl4]-catalyzed reaction of
ꢀ
PhC CH (6a) and Bu2NH (5b) was performed in CD2Cl2,
the signal in the H NMR spectra corresponding to the CH2
1
fragment at d=3.63 ppm in the final product ([D2]7ba) dis-
appeared (Figure 1). The fact that the new isolated com-
pound incorporated deuterium (CD2 fragment) was further
The definitive proof of the origin of the C(H)Me frag-
ment came from the reaction of isotopically enriched alkyne
13
Me3Si C 13CH (13C-6d) with Bu2NH (5b) (CH2Cl2, 24 h,
ꢀ
2
confirmed by H NMR analysis and mass spectrometry (see
508C). The 13C{1H} NMR spectrum of the resulting mixture
the Supporting Information).
shows unambiguously the presence of a spin system due to
13
13
13
the
C
C(H) 13CH3 skeleton: the signal at about d=
ꢀ
À
C
À
50 ppm, which was assigned to the 13CH carbon, appears as
a ddd by coupling with the other three 13C nuclei (13C-8bd,
see Figure 2 and detailed assignment of signals in the Sup-
Figure 1. 1H NMR spectra of: a) 7ba and b) [D2]7ba.
In the case of the C(H)Me fragment, we excluded the the-
oretical possibility of participation by the solvent by per-
13
Figure 2. 13C NMR spectrum of 13C-8bd showing the
spin system (CH and CH3 signals).
13C13CH13CH3
ꢀ
C
ꢀ
forming an experiment with Me3SiC CH (6d) and Bu2NH
Chem. Eur. J. 2010, 16, 9287 – 9296
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9291

M. Contel, E. P. Urriolabeitia, and D. Aguilar
porting Information). A proposal to account for the forma-
tion of propargylamines of the type 8 is outlined in
Scheme 6.
geneous sample such as this one (see Figure SI 1 in the Sup-
porting Information), the composition in the surface is rep-
resentative of the whole sample. Thus, no goldACTHNUTRGNEUG(N III) was
found in these solutions or in
the nanoparticles. In the three-
component coupling of alde-
hydes, terminal alkyne, and
amine catalyzed by supported
Au-NP on CeO2 or ZrO2, it was
demonstrated that the catalytic
Scheme 6. Formation of propargylamines of type 8 from trimethylsilylacetylene (6d).
At this point, we considered what role the gold nanoparti-
cles could play in the catalytic process. One important factor
is the oxidation state of the gold-containing species (mainly
nanoparticles) that are generated in situ by reduction of the
Table 8. Assignation of oxidation states in the XPS deconvolution ex-
periment from nano-14 (Figure 3).
Binding energy [eV]
Assignation
Area [%]
4f7/2
4f5/2
Au0
AuI
83.8
84.6
87.7
88.3
16
84
goldACHTUNGTRENNUNG(III) complexes by the secondary amine before the ad-
dition of the terminal alkyne and subsequent catalytic reac-
tion. To gain some insight into this aspect of the reaction,
we ran an X-ray photoelectron spectroscopy (XPS) experi-
ment (see explanations in the Supporting Information) on
activity was directly related to the content of AuIII in these
nanoparticles.[5a] The authors claimed that the support led to
the solution generated by the reduction of KACTHNUGTRENUNG[AuCl4] with
Bu2NH (5b) in CH2Cl2 (nano-14). The XPS spectrum
(Figure 3) shows the typical doublet (due to spin–orbital
stabilization of the gold
tion to gold(I) or metallic gold and a higher catalytic activi-
ty. However, gold(III) and gold(I) derivatives and unsup-
ACHTUNGTRNE(NUNG III) species and allowed its reduc-
AHCTUNGTRENNUNG
ported Au-NP were also catalytically active in these cou-
plings.[4,5b,c,6] In Scheme 7, we propose a plausible reaction
mechanism for the formation of propargylamines of type 7
(Scheme 2) in CH2Cl2.
The first step of the proposed catalytic cycle is the reduc-
tion of all goldACHTUNTRGNEUNG(III) complexes and salts by the amine to Au-
NP in the oxidation states AuI–Au0. The working hypothesis
here is that the AuI fragments are the catalytically active
species in this process. The next step is the addition of the
terminal alkynes and the formation of alkynylgold(I) spe-
cies. The synthesis of ethynylACHTNUGTRENNUNG
gold(I) derivatives such as [AuClACTHUNGTRENNNUG
kynes and NEt3 as a base has been previously reported.[27]
Moreover, the formation of alkynylgold(I) and alkynylgold-
AHCTUNGTRENNUNG
(III) species has been proposed as the first step in the A3
coupling reaction of terminal alkynes, amines, and aldehydes
to afford propargylamines.[4,5] The alkynylgold(I) species 16
should react with the CH2Cl2 and give the AuIII species 17
by oxidative addition of the CH2Cl2 through activation of
Figure 3. XPS deconvolution spectra from nano-14 generated by reduc-
tion of KACHTUNGTRENNUNG[AuCl4] by amine (Scheme 2, Table 5, Table 8).
À
one C Cl bond. Such an oxidative addition has been report-
splitting) for an electron on a 4f level of gold. Each compo-
nent of the doublet is called 4f7/2 and 4f5/2. The deconvolu-
tion of the resulting signal indicates that two different oxida-
tion states are contributing to each component of the dou-
blet, and the values for the binding energy for each peak are
in good agreement with the presence of gold in the oxida-
tion states 0 and +1. The subsequent assignment of oxida-
tion states in these colloids is shown in Table 8.
Most of the gold species (84%) were found to be in the
oxidation state +1, and 16% in oxidation state 0. The XPS
technique can measure the composition of the examined sur-
face up to a depth of 10 nm. We can assume that, in a homo-
ed for dinuclear gold(I) ylide derivatives in the formation of
dinuclear gold(II) complexes with the methylene group as a
bridge ligand.[13] The addition of CH2X2 with X=Br or I to
dinuclear gold(I) derivatives is also known[28,29] to afford
either dinuclear gold(II) complexes with the methylene
bridging the gold centers[28] or to mononuclear gold
ACHTUNGTRENNUNG(III) de-
rivatives.[29] Subsequent reductive elimination of highly reac-
tive 17 would afford the corresponding propargylchloride 19
and gold(I) species 18. Reductive eliminations on
alkynylgoldACTHNUGTRNEUNG(III) derivatives have been described before to
afford RC C-containing products and gold(I) complexes.
The reaction of propargylchloride with an amine may
[30]
ꢀ
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One-Pot Synthesis of Propargylamines
FULL PAPER
goldACTHNUGRTNEUNG(III) precursors, and a 52–
60% yield of the mixture 7bd–
8bd compared with an average
value of 90% using neutral or
anionic goldACTHNUTRGNE(NUG III) compounds. In
the case of trimethylsilylacety-
lene, complete selectivity to-
wards the CH2Cl2 activation
product 7bd was found when
[AuClACTHNUGRTENUNG(PPh3)] was used as the
catalyst. Interestingly, the cata-
lytic reactions performed with
AuI complexes did not develop
the deep-red color observed in
reactions using AuIII complexes.
Since we have shown that
gold(I) catalyzes efficiently the
formation of propargylamines,
we wondered about the pres-
ence of NP in these reaction
mixtures. Transmission electron
microscopy (TEM) analysis of
the mixture of [AuClACHTNUTGRNEUNG(tht)] and
HNBu2 (5b) shows a very small
amount (almost zero) of very
small nanoparticles (approxi-
mately 2–3 nm, see TEM image
of 22 in the Supporting Infor-
Scheme 7. Proposed reaction mechanism for the gold-catalyzed synthesis of propargylamines of type 7 in
CH2Cl2.
render the final product 7. The catalytic cycle can close be-
cause the AuI species 18 could further react with more
alkyne to give 16. Alternatively, the cycle could be closed by
further oxidative addition of propargyl chloride to the
mation). The influence of the ligand coordinated to the AuI–
Cl, either tetrahydrothiophene or PPh3, on the stability of
the AuI compound must be strong. Gold(I) halides without
other stabilizing ligands are able to afford stable nanoparti-
cles of 12 nm radius by reduction with alkylamines.[25] In our
case, it seems that the AuI derivatives with other stabilizing
ligands do not produce Au-NP under the reaction conditions
(508C) in the presence of alkylamines.
gold(I) species 18 to afford gold
with quaternary ammonium salts, compound 20 would gen-
erate a gold(III) intermediate 21 containing the propargylic
ACHTUNGTNER(NUNG III) species 20. By reaction
ACHTUNGTRENNUNG
fragment and the amine, which, by reductive elimination,
would afford propargylamines 7ae–7de and the gold(I) spe-
cies that is able to restart the catalytic cycle.
The interaction of the Au-NP with the alkyne should
result in a plausible alkynyl–AuI compound that could also
We performed a set of experiments to provide evidence
for some steps of this proposed mechanism. We tested the
be catalytically active. We have checked this possibility, and
[31]
ꢀ
have found that the complex [Ph3PAuC CPh] efficiently
catalytic activity of gold(I) derivatives such as [AuCl
N
catalyzes the coupling between Bu2NH (5b) and PhCCH
(6a), giving the propargylamine 7ba in 61% yield, and pro-
viding proof that the alkynyl species could be involved in
the catalytic cycle.
(tht=tetrahydrothiophene) and [AuCl(PPh3)] in the forma-
AHCTUNGTRENNUNG
tion of propargylamines 7ba and 7bd–8bd in CH2Cl2 under
the standard reaction conditions (alkyne (2 mmol), amine
(2 mmol), cat. (5 mol%), 24 h, 508C) and found that both
compounds were able to catalyze the reactions (Table 9).
However, slightly lower yields were obtained: a 40–65%
yield of 7ba, compared with an average value of 75% using
The next step is the oxidative addition of CH2Cl2 to the
formed alkynyl–AuI complex. In this respect, we have per-
ꢀ
formed a comparative study of the reaction of PhC CH
(6a) with Bu2NH (5b) in either CH2Cl2 or CH2Br2. Monitor-
ing the reaction leading to 7ba by NMR spectroscopic anal-
ysis, revealed that the process is more rapid for CH2Br2 (see
the Supporting Information). This fact strongly suggests that
incorporation of the solvent onto the gold catalyst proceeds
through an oxidative addition reaction. At this point, we can
consider two ways to close the catalytic cycle, as proposed
before. In the first, a reductive elimination in 17 gives prop-
argyl chloride and an AuI species 18, which could restart the
catalytic cycle. We found that the reaction between propar-
Table 9. Synthesis of progargylamines 7ba, 7bd, and 8bd in CH2Cl2 with
gold(I) compounds.
Cat.[b]
[ClAu
ACHTUNGTRENNUNG[ClAuPPh3]
7bd+8bd [%][a]
7ba [%][a]
N
(tht)]
52 (7bd/8bd, 0.7:1)
60 (7bd/8bd, 1:0.0)
65
40
[a] Isolated yields. [b] Reaction conditions: cat. (5 mol%), solvent
(5 mL), 508C, 72 h, alkyne/amine (1:1.2).
Chem. Eur. J. 2010, 16, 9287 – 9296
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9293

M. Contel, E. P. Urriolabeitia, and D. Aguilar
gylchloride (from Aldrich) and Bu2NH (5b) to afford prop-
argylamine 7ba proceeds cleanly in CH2Cl2 without the as-
sistance of a catalyst (with a slight excess of amine, and a
1:1.2 molar ratio of propargylchloride/alkylamine). This in-
dicates that the key step of the catalytic process may indeed
be the activation of CH2Cl2 by an alkynyl–gold(I) species
(mono or polynuclear) formed in situ by reduction of gold-
Experimental Section
General methods: Solvents and amines were dried and distilled under
argon by using standard procedures before use. Elemental analyses were
carried out with a Perkin–Elmer 2400-B microanalyser. Infrared spectra
(4000–200 cmÀ1) were recorded with a Perkin–Elmer Spectrum One IR
spectrophotometer from nujol mulls between polyethylene sheets. The
1H, 2H, 13C{1H}, and 31P{1H} NMR spectra were recorded in CDCl3,
CD2Cl2, or CH2Cl2 ([D2]7ba) at 258C with Bruker ARX-300, AvanceII-
300, Avance-400, or Avance-500 spectrometers (d, ppm; J, Hz); 1H and
13C{1H} were referenced by using the solvent signal as internal standard;
31P{1H} was externally referenced to H3PO4 (85%). The mass spectra
(MALDI+) and (ESI+) were recorded from solutions in CH2Cl2 or
ACHTUNGTRENNUNG(III) complexes by the amine, and subsequent reaction of
the gold(I) species with terminal alkynes in basic media. An
alternative way to close the catalytic cycle involves the oxi-
dative addition of propargylchloride to AuI species 18,
À
amine coordination, further C N coupling, and reductive
elimination. With the data thus far obtained, we cannot yet
discriminate between these two pathways.
MeOH with
(DCTB as matrix). Compounds 1,[18a] 3,[20] nano-12,[26] [Au
(PPh3)],[31] [AuCl(tht)],[32] and [AuCl(PPh3)][33] were synthesized as re-
ported before. All other chemicals and reagents were commercially avail-
able and used without further purification.
a MALDI-TOF MICROFLEX (Bruker) spectrometer
ꢀ
ACHTUNGTRENNUNG(C CPh)-
G
R
ACHTUNGTRENNUNG
The fact that the more basic amines give better yields in
these processes confirms our hypothesis that gold
be reduced to lower oxidation states to achieve higher cata-
lytic activity. K[AuCl4] and cyclometalated 1 give similar
ACHTUNGTRENUN(NG III) has to
Propargylamines 7 and 8: Typical optimized procedure: The gold catalyst
ꢀ
(1, K
[AuCl4], 9, 10, nano-12, [AuCl
E
E
U
ACHTUNGTRENNUNG
(PPh3)]; 5 mol%) was added to a solution of amine 5a–e (2 mmol) in
CH2Cl2 (5 mL). The corresponding alkyne 6a–d (2 mmol) was subse-
quently added to the resulting mixture, which was stirred at 508C for
24 h. Subsequent filtration through Celite and complete removal of the
solvent gave the crude mixture, which afforded the final products after
purification by column chromatography on silica gel. Details of the pu-
rification procedures used for the different propargylamines, as well as
spectroscopic data and selected spectra, are provided in the Supporting
Information.
yields, whereas the more cationic species with phosphane
derivatives give lower yields of product. This may arise from
a combination of factors, such as the higher stability of the
cationic pincer derivatives towards reduction and/or the
ease of formation/stability of the alkynylgold derivatives
formed in situ. The nanoparticle size may also play an im-
portant role. It has been demonstrated that in the A3 cou-
pling of aldehyde, terminal alkyne, and aldehyde by recycla-
ble gold nanoparticles, a size of 20 nm was optimal to afford
high yields of products at 75–808C in 12 h, with a catalyst
load of 10 mol% Au-NP.[6] We think that cationic derivatives
may afford Au-NP with a lower content of AuI and/or a dif-
ferent size, and that this may be the reason for the lower
yield. We have already seen that, although gold(I) com-
pounds have proven to be catalytically active in the forma-
tion of propargylamine 7ba, the yields of isolated product
are lower; this could be correlated to the fact that they did
not produce considerable amounts of nanoparticle under the
reaction conditions (see TEM image of 22 in the Supporting
Information). What seems clear is that the key steps in the
Experiments with deuterated CH2Cl2 and CD2Cl2 to give [D2]7ba: Cata-
lyst KACHTNURGTNE[NUG AuCl4] (5 mol%) was added to a solution of Bu2NH (5a; 2 mmol)
in CDCl2 (5 mL), then phenylacetylene (6b; 2 mmol) was added to the
resulting mixture, which was stirred at 508C for 24 h. Subsequent filtra-
tion through Celite and complete removal of the solvent gave a crude
mixture that afforded pure [D2]7ba after purification by column chroma-
tography on silica gel (n-hexane/AcOEt, 95:5). Yield: 60%. MS (ESI+):
m/z (%): 246 (100) [M]+. For the relevant spectra, see Figure 2 and the
Supporting Information.
Reaction with CH2Br2 to give 7ba: Catalyst KACTHUNGRTNEUNG[AuCl4] (5 mol%) was
added to a solution of Bu2NH (5a; 2.4 mmol) in CH2Br2 (5 mL), followed
by phenylacetylene (6b; 2 mmol). The resulting mixture was stirred at
508C for 24 h. Subsequent filtration through Celite and complete remov-
al of the solvent gave a crude mixture that afforded the final product 7ba
after purification by column chromatography on silica gel (n-hexane/
AcOEt, 95:5). Yield: 73%. For NMR spectra, see the Supporting Infor-
mation.
catalytic process involve the reduction of goldACTHNUTRGNEUG(N III) com-
plexes to gold(I)-containing nanoparticles, and the produc-
Gold-catalyzed cross-coupling reaction of Bu2NH (5b) with trimethyl-
À
silylacetylene (6d) and phenylacetylene (6a) in CH2Cl2: Catalyst K-
AHCTUNTGREGN[NNU AuCl4] (5 mol%) was added to a solution of Bu2NH (5a; 3.1 mmol) in
tion of catalytically active species able to activate C Cl
bonds in the CH2Cl2.
CH2Br2 (5 mL), followed by either phenylacetylene (6a; 1.6 mmol) or tri-
methylsilylacetylene (6d; 1.6 mmol). The resulting mixture was stirred at
508C for 24 h. Subsequent filtration through Celite and complete remov-
al of the solvent gave a crude mixture that afforded the products 7ba,
7bd, 8bd, and 13 after purification by column chromatography on silica
gel (n-hexane/AcOEt, 80:20).
Conclusion
Reduction of goldACHTUNGTRENNUNG(III) compounds and salts in situ gener-
Experiments with 13C-enriched trimethylsilylacetylene (13C-6d) to give
ates gold(I)-containing nanoparticles that are efficient cata-
lysts for the one-pot synthesis of propargylamines from al-
kynes and amines in chlorinated solvents under mild condi-
tions. Importantly, we have shown that CH2Cl2 can be acti-
vated by these nanoparticles, and some other gold(I) species,
to serve as a CH2 partner that could lead to potentially rele-
vant gold-catalyzed chemical processes.
13C-8bd: Catalyst K
ACTHNUTRGEN[UGN AuCl4] (5 mol%) was added to a solution of Bu2NH
(5a; 1 mmol) in CH2Br2 (5 mL), followed by 13C-enriched trimethylsilyl-
acetylene (1 mmol). The resulting mixture was stirred at 508C for 24 h.
Subsequent filtration through Celite and complete removal of the solvent
gave a crude mixture of products 13C-7bd and 13C-8bd.
Synthesis of [9: Catalyst AgClO4 (0.074 g, 0.36 mmol) was added to a so-
lution of orthoaurated complex 1 (0.201 g, 0.32 mmol) in anhydrous THF
(20 mL). The resulting suspension was stirred for 30 min at RT with ex-
clusion of light, and then filtered through a Celite pad to remove the in-
soluble AgCl formed. The freshly prepared solution was treated with
PPh3 (0.085 g, 0.32 mmol) and stirred for 2 h at RT. The solvent was sub-
9294
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Chem. Eur. J. 2010, 16, 9287 – 9296

One-Pot Synthesis of Propargylamines
FULL PAPER
sequently evaporated to a small volume and the residue was treated with
Et2O (20 mL). Further stirring resulted in the precipitation of 9 as an
orange solid that was filtered and vacuum-dried. Yield: 0.193 g (63.1%).
1H NMR (CDCl3): d=6.91–7.00 (m, 5H; Ho +Hp, NPh H-5+H-6, C6H4),
The specimen was imaged with a JEOL-2000FXII high-resolution trans-
mission electron microscope (point to point resolution 0.28 nm) and
images were recorded on a Gatan MSC-794 camera, by using the Digital
Micrograph software (from Gatan).
7.09 (t, 3J
ACHTUNGTRENNUNG(H,H)=7.1 Hz, 2H; Hm, NPh), 7.29–7.34 (m, 2H; H-3+H-4,
X-ray photoelectron spectroscopy: XPS measurements of nano-14, which
C6H4), 7.54 (m, 6H; Hm, PPh3), 7.60–7.70 (m, 13H; Hm, PPh2 +Hp +Ho,
PPh3), 7.77–7.85 ppm (m, 6H; Hp +Ho, PPh2); 13C{1H} NMR (CDCl3):
was prepared by reduction of KACHTNUGTRENUNG[AuCl4] with Bu2NH (5b), were taken
with a Kratos AXIS Ultra DLD (Kratos Tech.) spectrometer. Samples
were prepared under a cover of argon gas and placed in a vacuum before
measurement. While collecting the survey scans, the following parameters
were used: AlKa monochromatic excitation source (1486.6 eV) working at
15 kV and 10 mA, pass energy=120 eV. To confirm the oxidation state of
the various gold species, high-resolution scans were also taken by using a
pass energy of 20 eV.
d=123.9 (d, 1J(P,C)=67.7 Hz; Ci, PPh3), 124.4 (d, 1J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
2
4
(d, J
C6H4 overlapped), 135.0 (d, J
10.8 Hz; Co, PPh3), 136.1 (d, 1J
(P,C)=2.2 Hz; C-1’, NPh), 151.6 ppm (d, 2J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(P,C)=10.7 Hz; Co, PPh2), 133.9 (d, JAHCTUNGTRNE(NUNG P,C)=3.1 Hz; Cp, PPh3 +C-6,
4
4
G
ACHTUNGTRNE(NUNG P,C)=
AHCTUNGTRENNUNG
E
31P{1H} NMR (CDCl3): d=40.46 (PPh3), 60.09 ppm (PPh2). IR: n˜ =1277
(nP=N) cmÀ1; MS (MALDI+): m/z (%): 846 (100) [MÀClO4]+; elemental
analysis calcd (%) for C42H34AuCl2NO4P2 (946.54): C 53.29, H 3.62, N
1.48; found: C 53.09, H 3.45, N 1.21.
Acknowledgements
Funding from MICINN (CTQ2008-01784, Spain) and Brooklyn College
(US) is gratefully acknowledged. D.A. thanks DGA (Spain) for a Ph.D.
grant. The authors also thank Prof. Fernando Lꢁpez Ortiz (Universidad
de Almeria, Spain) for his stimulating and constructive comments and
Prof. Jesffls Santamaría and Dr. Silvia Irusta (INA, Universidad de Zara-
goza) for facilitating the XPS measurements.
Synthesis of 10. Catalyst AgClO4 (0.135 g, 0.65 mmol) was added to a so-
lution of 1 (0.184 g, 0.30 mmol) in anhydrous THF (20 mL). The resulting
suspension was stirred for 30 min with exclusion of light, and then fil-
tered through a Celite pad to remove the insoluble AgCl formed. Dppe
(0.118 g, 0.30 mmol) was added to the freshly prepared solution and the
resulting pale-yellow solution was stirred at RT for 2 h. After the reac-
tion time, the solvent was evaporated to a small volume (ca. 1 mL) and
Et2O (30 mL) was added. By continuous stirring, compound 10 was ob-
tained as a yellow solid that was filtered and vacuum-dried. Yield:
[1] Two relevant examples: a) Y. Yamamoto, H. Hayashi, T. Saigoku,
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Hm, NPh), 6.55 (t, 3J(H,H)=7.3 Hz, 1H; Hp, NPh), 6.62 (d, 3J
7.6 Hz, 2H; Ho, NPh), 7.04 (td, 4J(H,P)=3.0 Hz, 3J
(H,H)=7.3 Hz, 1H;
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
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A
ACHTUNGTRENNUNG
H-4, C6H4), 7.23–7.31 (m, 3H; H-3+H-5+H-6, C6H4), 7.46–7.52 (m,
10H; Hm +Hp +Ho, Ph2-dppe), 7.59–7.63 (m, 4H; Hm, PPh2- C6H4), 7.67–
7.75 (m, 12H; Hm +Hp, Ph2-dppe+Hp +Ho, PPh2- C6H4), 7.99–8.05 ppm
(m, 4H; Ho, Ph2-dppe); 13C{1H} NMR (CDCl3): d=28.9 (d, 1J
ACHTUNGTRENNUNG
36.8 Hz; CH2, dppe), 30.6 (d, 1J
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
137.19 ppm (C6H4). Signals due to C-1’ (NPh) and C-1, C-2 (C6H4) were
not observed, in spite of long time accumulation trials. 31P{1H} NMR
(CDCl3): d=61.01 (d, 4J(P,P)=2.4 Hz; PPh2), 64.75 (d, 3J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
dppe), 72.38 ppm (dd, 3J(P,P)=14.8 Hz, 4J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
1284 (nP=N) cmÀ1; MS (MALDI+): m/z (%): 1046 (95) [MÀClO4]+; ele-
mental analysis calcd (%) for C50H43AuCl2NO8P3: C 52.37, H 3.78, N
1.22; found: C 51.91, H 3.50, N 1.05.
Preparation and X-ray/TEM characterization of gold nanoparticles nano-
11: An aliquot of nano-11 (1 mL), generated from a solution of nBu2NH
(2 mmol) in CH2Cl (5 mL) with KACHTUNTRGNE[NUG AuCl4] (5 mol%), after stirring for
5 min at RT, was applied to a glow-discharged carbon-coated copper grid
and blotted. The specimen was imaged with a JEOL-2000FXII high-reso-
lution transmission electron microscope (point-to-point resolution:
0.28 nm) and images were recorded with a Gatan MSC-794 camera, by
using the Digital Micrograph software (from Gatan). A step-scanned
powder diffraction pattern of nano-11 was collected at RT by using a Sie-
mens D500/501 diffractometer with a Cu X-ray tube. The diffractometer
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used to select the CuKa1,2 radiation. Data were collected from 5 to 808
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Chem. Eur. J. 2010, 16, 9287 – 9296
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9295

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Received: March 5, 2010
Published online: June 25, 2010
9296
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ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 9287 – 9296