Gold(III) NHC Complexes for Catalyzing Dihydroalkoxylation and Hydroamination Reactions

Article abstract of DOI:10.1021/acs.inorgchem.7b02161

A gold(III) complex of an N-heterocyclic carbene based hemilabile ligand with two pendant pyrazole arms (1,3-bis((1H-pyrazol-3-yl)methyl)-2,3-dihydro-1H-imidazole, LH) was synthesized. Complex [LAu(III)Cl₃] is an excellent catalyst for promoting dihydroalkoxylation at room temperature, even catalyzing this reaction at 0 °C. [LAu(III)Cl₃] is one of the most efficient catalysts reported to date for the spirocyclization of alkynyl diols. Furthermore, [LAu(III)Cl₃] catalyzed intra- and intermolecular hydroamination reactions, achieving good to excellent conversions. [LAu(III)Cl₃] is a more efficient catalyst than a gold(I) analogue, [LAu(I)Cl]. The dependence of the quantity of weakly coordinating anion [BAr^F₄]^- ((3,5-trifluoromethyl)phenyl borate) present on catalysis efficiency was probed for the dihydroalkoxylation reaction. X-ray diffraction analysis of single crystals demonstrated the solid-state structure of gold complexes [LAu(III)Cl₃] and [LAu(I)Cl], which displayed the expected square-planar and linear coordination geometries, respectively.

Full text of DOI:10.1021/acs.inorgchem.7b02161

Article
pubs.acs.org/IC
Gold(III) NHC Complexes for Catalyzing Dihydroalkoxylation and
Hydroamination Reactions
Ashwin G. Nair, Roy T. McBurney, Mark R. D. Gatus, Samantha C. Binding,
and Barbara A. Messerle*
Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney 2109, Australia
*
S Supporting Information
ABSTRACT: A gold(III) complex of an N-heterocyclic
carbene based hemilabile ligand with two pendant pyrazole
arms (1,3-bis((1H-pyrazol-3-yl)methyl)-2,3-dihydro-1H-imi-
dazole, LH) was synthesized. Complex [LAu(III)Cl ] is an
3
excellent catalyst for promoting dihydroalkoxylation at room
temperature, even catalyzing this reaction at 0 °C. [LAu(III)-
Cl ] is one of the most efficient catalysts reported to date for
3
the spirocyclization of alkynyl diols. Furthermore, [LAu(III)-
Cl ] catalyzed intra- and intermolecular hydroamination
3
reactions, achieving good to excellent conversions. [LAu(III)-
Cl ] is a more efficient catalyst than a gold(I) analogue,
3
[
LAu(I)Cl]. The dependence of the quantity of weakly
F
−
coordinating anion [BAr ] ((3,5-trifluoromethyl)phenyl
4
borate) present on catalysis efficiency was probed for the dihydroalkoxylation reaction. X-ray diffraction analysis of single
crystals demonstrated the solid-state structure of gold complexes [LAu(III)Cl ] and [LAu(I)Cl], which displayed the expected
3
square-planar and linear coordination geometries, respectively.
1
4g,j
17
INTRODUCTION
bond,
gands,
or bidentate N,O-donor or N,N′-donor li-
■
1
4d,f,h
1
see Figure 1. However, in designing and selecting
Gold catalysis is a vitally important area with many reported
2
Au(III) complexes as catalysts, a balance needs to be struck
between stability and catalytic activity. Highly efficient Au(III)
catalysts offering good stability that operate across a range of
reactions would be welcome. We reasoned that a ligand with a
strong σ-donor to act as an anchor for gold(III) in combination
examples of gold(I)-catalyzed reactions including C−O and
3
C−N bond formations, C−C bond forming cyclization
4
5
6
reactions, applications to total synthesis, and photocatalysis.
Conversely, gold(III)-catalyzed reactions are still in their
infancy. The vast majority of reports use inorganic gold(III)
salts, typically AuCl , primarily for promoting hydroamina-
3
7
8
9
tions, hydroalkoxylations, intramolecular hydroarylation,
1
0
11
oxidations, rearrangements, and C−C bond forming
8
g,12
cyclizations.
There are a growing number of reports using
13
14
4b
organometallic Au(III) complexes as catalysts, aided by
Hashmi’s method for oxidizing Au(I) to Au(III).
Organometallic gold(III) complexes have been used for
1
1
4b,c
14d
catalyzing isomerizations,
hydroaminations,
hydrations, and three component couplings.
A recent communication by Toste highlighted the need to
C−C cou-
1
4e−k
14l
14m,n
plings,
15
further develop the area of gold(III) catalysis. Increasing the
scope of organogold(III) catalysis is important to enable a
greater level of regio-, chemo-, and enantioselectivity over the
products generated, to achieve vastly increased reaction rates
and to avoid in situ reduction of Au(III) by substrates,
intermediates, or products.
Figure 1. Gold(III) catalysts featuring (a−d) strong and (e) hemilable
The choice of ligand to support gold(III) is crucial for
achieving optimal catalytic activity. Common structural motifs
found in the ligands of reported organogold(III) catalysts
coordination motifs; (f) our design features both.
14k,16
include a central N-heterocyclic carbene (NHC);
some
Received: August 22, 2017
feature a biphenyl ligand coordinated through a gold-aryl
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b02161
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Article
with hemilabile pendant arms to stabilize intermediates/
transition states during the catalytic cycle should be a promising
catalyst. Given our past success with complexes based on such
ligands, an NHC-based ligand with two pyrazole pendant
arms was selected. These ligands were specifically targeted
because of the range of coordination modes accessible, as well
[LAu(I)Cl] and gold(III) square planar in [LAu(III)Cl ], see
Figure 2. In both structures the gold ion is coordinated to the
3
1
8
1
3c,14g
as the known stability of NHC−gold(III) complexes.
Herein, we report the synthesis and catalytic activity of a
novel Au(III) complex containing a hemilabile bis-pyrazole
carbene ligand (1,3-bis((1H-pyrazol-3-yl)methyl)-2,3-dihydro-
18
1
H-imidazole, LH). Ligand LH has accommodated a range of
18a 18b
transition metals including Rh(I) and Ir(I), Ru(II), and
1
8c
Ni(II). We were interested to discover if gold(III) catalyst
LAu(III)Cl ] could be stabilized by its pendant pyrazole arms
Figure 2. X-ray crystal structures of (a) [LAu(I)Cl] and (b)
[
3
[
LAu(III)Cl ]. Nitrogen atoms are shown in purple, carbons gray,
3
after addition of a halide abstraction agent. Catalyst [LAu(III)-
gold yellow, and chloride green; hydrogens are omitted for clarity.
Cl ] was found to efficiently catalyze the dihydroalkoxylation of
3
Selected bond lengths (Å) and angles (deg): [LAu(I)Cl], C1−Au(I)
a series of alkynyl diols at room temperature under mild
1.973, (C2−C3)
−C1−Au(I) 175.57; [LAu(III)Cl ], C1−Au-
centroid
centroid
3
conditions. [LAu(III)Cl ] also catalyzed intra- and intermo-
(III) 2.007, (C2−C3)
−C1−Au(III) 178.7.
3
lecular hydroamination reactions. The catalytic efficiency of
[
LAu(III)Cl ] was compared against that of a related Au(I)
carbenic atom in the NHC unit (∼2 Å) and the (C2−
C3) −C1−Au angle is close to linear. The pendant
3
catalyst, [LAu(I)Cl].
centroid
pyrazole groups were uncoordinated (N−Au distances are all
greater than 3.1 Å), though in the Au(III) example the nitrogen
in the pyrazole ring would be available for coordination upon
displacement of a chloride ion by a suitable weakly coordinating
RESULTS AND DISCUSSION
Synthesis and Characterization. Ligand 1,3-bis((1H-
pyrazol-3-yl)methyl)-2,3-dihydro-1H-imidazole, LH, was syn-
■
18a,b
F
−
thesized according to our previous report, see Scheme 1.
counterion such as [BAr ] (tetrakis[3,5-bis(trifluoromethyl)-
4
phenyl]borate).
Scheme 1. Synthesis of [LAu(III)Cl ] and [LAu(I)Cl]
Dihydroalkoxylation Catalysis. Dihydroalkoxylations are
atom efficient C−O bond forming reactions between two
alcohols and an alkyne, affording ethers as the final product.
Dihydroalkoxylations lead to spiroketals, which are important
structural motifs found in many natural products. We
examined the dihydroalkoxylation spirocyclization of alkynyl
diol containing substrates, specifically 2-(5-hydroxypent-1-
ynyl)benzyl alcohol 1 (Scheme 2).
3
19
Scheme 2. Conversion of 1 to 2a and 2b
[
LAu(I)Cl] was prepared by stirring a suspension of
The dihydroalkoxylation reactions were first attempted at 70
chloroauric acid in the presence of triethylamine, dichloro-
methane, methanol, and LH at room temperature for 16 h. The
resulting reduced gold(I) complex, [LAu(I)Cl], was precipi-
tated from a dichloromethane solution by addition of pentane
°C in C
2
D
2
Cl
] (1.1 mol %) was added and the substrate alkynyl
4
4
with a catalyst loading of 1 mol % to which
F
Na[BAr
diol, 1. The reaction was monitored at regular intervals using
H NMR spectroscopy. The Au(III) catalyzed reaction reached
1
and isolated as a white/gray solid. [LAu(III)Cl ] was prepared
completion (>98% conversion) in less than 1 min, with the
Au(I) catalyzed reaction completing soon after (Figure 3a).
Given the excellent reaction progress at 70 °C, we repeated the
reactions at room temperature (25 °C). The Au(III) catalyst
was significantly faster than the Au(I) catalyst for this reaction,
achieving completion within 9.3 min. Pleasingly, [LAu(III)Cl3]
still gave excellent conversion of 1 to 2a and 2b at 0 °C, albeit
over a much longer time frame (>170 min). We did not test
[LAu(I)Cl] at 0 °C as we expected the reaction to take
3
1
8b
via a transmetalation from [L Ag(I)][BPh ]
using chlor-
2
4
oauric acid in dichloromethane and ethanol. Precipitation from
1
pentane produced [LAu(III)Cl ] as a yellow solid. The H
3
NMR spectra (see Figure S6 and Figure S8) show that
[
LAu(I)Cl] and [LAu(III)Cl ] are symmetrical species; each
3
has a plane of symmetry passing through an axis defined by the
carbene−gold bond. There are clear differences in the H NMR
spectra of complexes [LAu(III)Cl ] and [LAu(I)Cl], indicating
1
3
that the different oxidation states and number of chloride
coligands present have a clear effect on the chemical
environment of the ligand backbone.
Crystals suitable for crystallographic analysis were obtained,
and X-ray crystallography demonstrated that the coordination
environments were as expected, with gold(I) being linear in
significantly longer than [LAu(III)Cl ] did at 0 °C.
3
Lowering the gold(III) catalyst loading to 0.1 mol % resulted
in a significant decrease of reaction progress, with only 30%
conversion of substrate 1 to 2a and 2b after 2.2 min, Figure 3b.
Further decreasing to 0.01 mol % resulted in just 10%
conversion of substrate after 3.3 min. The time conversion
B
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Figure 3. Comparison of Au(III) and Au(I) catalysts, loadings, and
additives for the conversion of 1 to 2a and 2b. (a) Reagents and
F
−
F
Figure 4. Effect of increasing equivalents of added Na[BAr ] (from
conditions: gold catalyst (1 mol %), Na[BAr ] (1.1 mol %), substrate
4
4
0
to 4 equiv) on catalytic efficiency. Catalytic efficiency was measured
1
, C D Cl . (b) Reagents and conditions: [LAu(III)Cl ], substrate 1,
2
2
4
3
−1
F
by the TOF (h ) calculated from the first data point after >50%
conversion of substrate 1 to product (2a + 2b), as the amount of
product formed by one mole of catalyst per hour.
Na[BAr ] or Ag[SbF ] (1.1 equiv wrt [LAu(III)Cl ]), C D Cl , 25
4
6
3
2
2
4
°
C. Conversion was determined by integration of the product
1
resonances relative to the substrate resonances using H NMR
spectroscopy. Empty columns denote that experiment was not
performed.
reach completion. This increase in catalysis rate with increase in
counterion concentration was expected when coordinated
chloride ions are replaced by hemilabile pyrazole arms and
weakly coordinating anions. Furthermore, the catalyst remains
stable and active under these conditions. As a control
experiment, we have shown that Na[BAr ] alone will not
graphs for these reactions (see Figure S2) show that the
1
conversion to product essentially plateaued after the first H
F
NMR spectrum was recorded, although good turnover numbers
4
22
of over 1000 were achieved when using [LAu(III)Cl ] at 0.1
catalyze dihydroalkoxylation reactions of 1.
3
1
mol % catalyst loading.
Separate from the catalysis reactions, H NMR spectra of
[LAu(III)Cl ] on addition of counterion in tetrachloroethane-
d4 were obtained (Scheme 3 and Figure S10). Addition of just 1
The use of different counterions has been found to have an
impact on the efficiency of a number of charged catalysts, and
3
in particular gold catalysts. Our use of [SbF6]− as a
counterion at 1 mol % catalyst loading of [LAu(III)Cl3]
catalyst resulted in a 4-fold decrease in reaction rate and a lower
conversion (Figure 3b). At 0.1 mol % catalyst loading using
20
F
Scheme 3. Addition of Na[BAr ] to [LAu(III)Cl ]
4
3
Ag[SbF ] no conversion to spiroketal products was observed.
6
We therefore did not attempt any lower catalyst loading
reactions with Ag[SbF ]. These results would indicate that for
6
F
−
−
this specific reaction [BAr ] clearly outperforms [SbF ] .
4
6
Screenings of other weakly coordinating anions were deemed
F
−
F
4
unnecessary given the excellent performance of [BAr ] .
equiv of Na[BAr ] resulted in a complicated spectrum, with
4
When using any silver halide abstraction agent, it is necessary
to consider any potential effect that silver may have on the
reaction. Zhdanko and Maier reported a detailed study on the
effects of silver on gold(I) catalyzed hydroalkoxylations where
silver was found to be innocent with regard to the catalytic
cycle but either decreased or increased catalysis rate. We thus
deemed any silver effect to be negligible.
contributions from the original complex [LAu(III)Cl ], and
3
additional species where one or more chlorides have been
removed resulting most likely in one pyrazole arm coordinating
to the gold ion. This mixture could also contain a bridged
23
auro−chloro dimer species. Upon of addition of 3 equiv of
21
F
Na[BAr ] the spectrum is composed of one species (>95%),
4
presumably a species where all chlorides have been removed,
the two pyrazole arms coordinate the gold ion, and one vacant
site is available at the gold(III) center. This assumption is
backed up by a related study from Miqeu, Amgoune, and
Bourissou, who used detailed NMR investigations to prove a
cationic gold(III) species, which was later used for insertion of
Our catalyst design features hemilabile pendant pyrazole
arms that can coordinate to the gold ion. Progressively
−
stripping Cl from the gold(III) ion in [LAu(III)Cl ] should
3
allow these pyrazole arms to coordinate, thereby stabilizing the
−
complex, and the removal of coordinated Cl should improve
1
4j
substrate access to the gold ion, increasing the rate of catalysis.
Focusing on the reaction shown in Scheme 2, for the
conversion of 1 to 2a and 2b using 1 mol % of catalyst
olefins into gold−aryl bonds.
Control studies were performed to assess substrate
conversion (1 to 2a and 2b) using gold salts to promote the
[
LAu(III)Cl ] at room temperature, we gradually increased the
reactions. Chloroauric acid (HAuCl ) led to no conversion of
3
4
F
F
equivalents of Na[BAr ] relative to [LAu(III)Cl ] and
substrate at room temperature, with or without Na[BAr ]
4
3
4
observed the resulting effect on the reaction rate (Figure 4).
present. However, AuCl has been reported to catalyze the
3
F
As more equivalents of Na[BAr ] were added, the reaction rate
dihydroalkoxylation of a similar substrate, proceeding to 41%
4
8a
increased and time to completion (>98% conversion)
yield with a 5 mol % catalyst loading after 30 min.
shortened considerably. The reaction promoted using [LAu-
Au(I)Cl(SMe ) catalyzed the reaction of 1 to 2a and 2b at
2
F
(
III)Cl ] and 3 equiv of Na[BAr ] was complete after just 5
25 °C, which was greatly accelerated in the presence of 1 equiv
3
4
F
F
min, whereas when no Na[BAr ] was present it took 68 min to
of Na[BAr ] (Figure S1). Au(I)Cl(SMe ) proved a much
4
4
2
C
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more efficient catalyst than [LAu(I)Cl]. On undertaking the
catalysis of the conversion of 1 to 2a and 2b using
substrate 9 proceeded to a greater level of conversion to
product than substrate 7.
[
LAu(III)Cl ] as a catalyst, nanoparticles were observed as a
Hydroamination Catalysis. Having established that gold-
3
broad peak between 260 and 340 nm in the UV/vis spectra
Figure S5). However, a mercury drop test ruled out any
nanoparticle contribution to the catalysis reaction forming 2a
(III) catalyst [LAu(III)Cl ] was an excellent catalyst for
3
(
dihydroalkoxylation reactions, we set out to investigate other
potential heterobond-forming applications. Hydroamination
reactions involve the addition of an N−H bond across an
unsaturated C−C bond and are atom economical processes for
2
4
and 2b.
Spirocyclization of substrate 1 leads to a pair of isomeric
spiroketal products 2a and 2b. Previous reports have shown
that it is difficult to achieve regioselectivity between these two
27
the formation of C−N bonds. A few organometallic gold(III)
catalyzed hydroaminations have been reported including
22,25
14d,28
29
spiroketal isomers.
Here, using both gold(I) and gold(III)
intramolecular cyclizations onto alkyne,
alkene, and
3
0
catalysis we found that the product distributions were
uniformly 3:1. We had hoped that reducing the reaction
temperature to 0 °C may have an effect on selectivity by
favoring formation of one ring size over the other. However,
this was not fruitful, with the same ratio of isomers of the
spiroketal being observed as at elevated temperatures.
We also investigated the gold catalyzed cyclizations of
substrates with varying lengths of alkyl chain between the
alkyne and the aliphatic alcohol. Using catalyst [LAu(III)Cl3]
the substrate 2-(4-hydroxybut-1-ynyl)benzyl alcohol (3) with a
shorter alkyl chain was cyclized to give the 5,5-spiroketal
product, 4, with >99% conversion to product observed after 15
min (Scheme 4a). In comparison, when using catalyst
allene acceptors, and also intermolecular additions to
allenes. The activity of catalysts [LAu(I)Cl] and [LAu(III)-
31
Cl ] was assessed for the intramolecular cyclization of 4-
3
pentyne-1-amine, 11, to 2-methyl-1-pyrroline, 12 (Scheme 5a).
Scheme 5. Gold Catalyzed Intra- and Intermolecular
Hydroamination Reactions
Scheme 4. Au(III) Catalyzed Dihydroalkoxylation
Spirocyclizations of Alkynyl Diols
Given the slower progress of hydroamination reactions, a
catalyst loading of 2 mol % was used and the reaction was
conducted in toluene-d at 100 °C; the conversions were
8
determined by integration of the product resonances relative to
the substrate resonances. The gold(III) catalyst led to a
maximum conversion to product 12 of 97% after 15 min,
outperforming the gold(I) catalyst. The substrate containing an
internal alkyne 5-phenyl-4-pentyn-1-amine, 13, also gave
complete conversion to 14 after 24 min no matter what
catalyst was used, Scheme 5b. The performance of both gold
catalysts matches our fastest reports for the cyclizations of
pentynamine and phenylpentynamine using Rh(I) and Ir(I)
[
LAu(I)Cl] the reaction took almost 2 h to reach near
completion (96% conversion) for the cyclization of 3. The
catalyzed cyclization of 2-(6-hydroxyhex-1-ynyl)benzyl alcohol
32
catalysts.
(
5) using [LAu(III)Cl ] required heating at 40 °C and gave just
The gold-catalyzed intermolecular hydroamination reactions
between either phenylacetylene or pentyne and either aniline or
benzylamine were investigated. The only combination of
substrates that gave rise to any reaction when using our gold
catalysts was phenylacetylene 15 with aniline 16 to give imine
17 (Scheme 5c). While both gold catalysts gave low
conversions (approximately 30%) to the imine product, it
was notable that gold(III) outpaced gold(I). Extended reaction
times at 100 °C did not improve the conversions. Lowering the
reaction temperature to 70 °C and lengthening reaction times
did not lead to improved conversions. Catalyst [LAu(III)Cl3]
also promoted the intermolecular hydroamination between
phenylacetylene, 15, and sterically hindered mesitylamine, 18,
3
3
(
8% conversion to the 6,6-spiroketal product 6 after 3 min
Scheme 4b). The conversion did not increase with longer
reaction times. No reaction was observed when using
LAu(I)Cl] at 40 °C with substrate 5. The differing rates of
- and 6-membered ring closure have been noted for Rh(I) and
[
5
26
Ir(I) catalysts previously by us. The results here would
indicate that Au-catalyzed sequential 6-exo and 6-endo
spirocyclizations are much slower than 5-membered cycliza-
tions resulting in lower yields of the 6,6-spiroketal product 6.
The catalyzed cyclization of symmetric alkynyl diols 7 and 9
gave excellent conversion to products 8 and 10 using
[LAu(III)Cl ] (Scheme 4c,d). Unsurprisingly, less hindered
3
D
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Article
giving a good conversion to 19 of 61% (Scheme 5d). This was
unexpected given the steric hindrance around the amino site.
The reaction between phenylacetylene, 15, and 4-
CONCLUSIONS
■
In summary, we have found that a simple NHC-based gold(III)
organometallic catalyst based on complex [LAu(III)Cl ] is a
3
(
(
trifluoromethyl)aniline, 20, gave only 49% conversion to 21
Scheme 5e). Clearly the electron withdrawing CF group
more efficient catalyst than gold(I) analogue [LAu(I)Cl]. The
gold(III) catalyst reported here is the most efficient system to
the best of our knowledge for promoting the cyclization of
alkynyl diols to form spiroketals under mild conditions.
Furthermore, this gold(III) catalyst can achieve TONs of
1000 while avoiding reduction to gold(I). Control experi-
ments proved that this was an organogold(III)-catalyzed
process, with no competing gold(III) salt catalyzed reaction
or contribution from gold nanoparticles. Adding more
equivalents of Na[BAr ] accelerated the rate of reactions
producing spiroketal products. Intramolecular hydroaminations
were also studied with both catalysts performing well, achieving
excellent conversions in less than 30 min, which places them on
3
decreases the reactivity of the aniline. Our gold NHC-based
catalysts proved more efficient for intra- than intermolecular
hydroaminations.
Catalyst Investigations. Our results in the dihydroalkox-
ylation and hydroamination catalysis reactions demonstrated
the high levels of reaction efficiency achieved using catalyst
3
3
[
LAu(III)Cl ]. It was also evident that, despite our attempt at
3
F
creating a stable gold(III) catalyst based on a hemilabile NHC
ligand, the catalysis results were quite mixed. To further our
understanding of the shortcomings of our gold(III) catalyst we
revisited the dihydroalkoxylation reaction of substrate 1,
4
3
2
a par with our previously reported Rh(I) and Ir(I) catalysts.
Intermolecular catalyzed hydroamination reactions were also
found to proceed with good conversions using catalyst
Scheme 2. We ran the reaction at 25 °C using [LAu(III)Cl ]
3
F
4
(
1 mol %) and Na[BAr ] (1.1 mol %) in C D Cl . After the
2
2
4
1
reaction was complete (<15 min) as judged by H NMR
spectroscopy, another equivalent of substrate 1 was added and
the reaction progress monitored. Interestingly, the reaction
only reached ∼1% conversion after 20 min, indicating that the
catalyst was no longer active. This result, coupled with
examination of time-course plots (Figure S2 and Figure S3)
for selected dihydroalkoxylation reactions, points to the
[
LAu(III)Cl ]. Given the interest and activity in the area, it
3
will not be long before gold(III) catalysis achieves the same
status as gold(I) catalysis, opening up a wider array of useful
catalysts and potential new reactivity to be explored and
exploited.
EXPERIMENTAL SECTION
■
conclusion that [LAu(III)Cl ] is extremely active in the early
3
General Methods and Materials. All manipulations of metal
complexes and air sensitive reagents were carried out using standard
Schlenk techniques; catalysis experiments were prepared in an LC
stages of the catalysis reaction (50−70% conversion) but suffers
deactivation in the final stages. However, for substrate 6,
deactivation occurs much earlier (<10 min), and when using
Technologies Solutions Inc. glovebox under N atmosphere. Unless
2
lower catalyst loadings of [LAu(III)Cl ], such as 0.1 mol % or
otherwise stated, chemicals were purchased from Alfa Aesar Inc. or
Aldrich Chemical Co. Inc. and used as received. Gold(III) chloride
hydrate was purchased from Matthey Garrett Pty Ltd. and used
18b
3
0.01 mol %, deactivation occurs even sooner (<3 min),
although turnover numbers of up to 1000 were achieved, Table
S2.
To determine a possible cause of catalyst deactivation, we
investigated the stability of the Au(III) complex. [LAu(III)Cl3]
1
8a
without further purification. [LH][BPh4]
and [L Ag][BPh ]
2 4
were prepared according the literature reports. For the purposes of air
sensitive manipulations and preparation of metal complexes, solvents
were dispensed from a LC Technology Solutions Inc. solvent
purification system and transferred directly to Schlenk flasks
containing nitrogen/vacuum which were fitted with Young Teflon
is stable as a solid, stored in air over a period of two months.
[
LAu(III)Cl ] remains intact for at least 1 h in a C D Cl
3
2
2
4
1
F
valves. The H NMR spectra were recorded on Bruker Avance 400,
solution at 80 °C. Addition of Na[BAr ] to a room
4
Avance III 400, and DMX600 spectrometers. All spectra were
recorded at 298 K unless stated otherwise, and chemical shifts (δ)
are quoted in ppm. Coupling constants (J) are quoted in Hz and have
temperature C D Cl solution of [LAu(III)Cl ] gives a stable
2
2
4
3
species for at least 16 h but when heated to 80 °C
LAu(III)Cl ] decomposes after just 10 min. With regard to
[
1
3
uncertainties of ±0.05 Hz. H NMR chemical shifts were referenced
stability in the presence of substrates, [LAu(III)Cl ] remains
internally to residual solvent resonances. The following abbreviations
are used to report the multiplicity of NMR resonances: s, singlet; d,
doublet; t, triplet; q, quartet; m, multiplet. Proton and carbon
resonances were assigned using COSY (correlation spectroscopy),
3
intact after 2 h in the mixture of either phenylacetylene, aniline,
or methanol at room temperature. [LAu(III)Cl ] will also
3
survive catalysis conditions at 100 mol % catalyst loading.
1
13
HSQC ( H− C) (heteronuclear single quantum coherence), and
Thus, taking into account the results for catalyst loading,
1
13
HMBC ( H− C) (heteronuclear multiple bond coherence) experi-
ments. All NMR data was acquired and processed using TopSpin
version 3.2 from Bruker NMR software.
F
4
catalyst stability to heat, and presence of Na[BAr ] and/or
substrates, it is clear that [LAu(III)Cl ] is stable at least long
3
enough to perform the required number of turnovers to achieve
complete conversion. Hence, it would appear that the
deactivation of the gold catalysts is due to formation of gold
nanoparticles, as observed by UV/vis spectroscopy, Figures S4
[LAu(I)Cl]. [LH][BPh
were suspended in 20 mL of dry CH Cl , and [H][AuCl ]·3H O
0.036 g, 0.092 mmol) dissolved in 5 mL of methanol was added to
the mix. The resulting gray-white suspension was stirred at room
temperature for 16 h. The resulting suspension was filtered using a
GF/C filter cannula producing a clear colorless solution. Reduction in
volume of solution to 10 mL followed by addition of pentane (40 mL)
resulted in a gray-white solid; the solid was washed with distilled water
4
] (0.050 g, 0.092 mmol) and NEt (1 mL)
3
2
2
4
2
(
2a
and S5. These findings echo those of Hashmi and team,
where the use of a gold(I) complex of an N-acyclic carbene
possessing a bulky siloxane arm proved essential to achieving
high turnover numbers at low catalyst loadings by preventing
undesired nanoparticle formation. The decomposition pathway
during the hydroamination reactions is likely to be very similar
but will happen at a quicker rate due to the elevated reaction
temperature (100 °C).
(
(
25 mL) and diethyl ether (25 mL) and dried under Schlenk vacuum
1
3
40%). H NMR (600 MHz, (CD ) CO): δ 8.07 (d, J = 2.5 Hz, 2H,
3
2
3
H3), 7.54 (s, 2H, H5), 7.53 (d, J = 1.5 Hz, 2H, H1), 6.55 (s, 4H, H4),
13
1
6
(
.33 (br dd, 2H, H2). C{ H} NMR (150 MHz, (CD ) CO): δ 172.9
3 2
C6), 141.9 (C1), 131.5 (C3), 122.6 (C5), 107.6 (C2), 65.1 (C4).
Elemental analysis found: C, 30.06; H, 2.91; N, 17.62. Calcd for
E
DOI: 10.1021/acs.inorgchem.7b02161
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Au C H N Cl.0.2C H : C, 30.34; H, 3.06; N, 17.69. ESI MS: m/z
1
11 12
6
5
12
ACKNOWLEDGMENTS
■
calcd for Au C H N = 425.0789, found m/z = 425.0778.
1
11 12
6
This work was supported under Australian Research Council’s
Discovery Projects funding scheme (Project No.
DP110101611). We thank Macquarie University and the
Australian Government for financial support. A.G.N. is a
grateful recipient of an Australian Postgraduate Award (APA)
awarded by the Australian Government, administered by the
University of New South Wales and Macquarie University. We
acknowledge the Macquarie University NMR Facility and Prof.
Yves De Deene for access to NMR instrumentation.
[
LAu(III)Cl ]. [L Ag][BPh ] (0.100 g, 0.11 mmol) was dissolved in
3 2 4
2
0 mL of dry CH Cl to which an ethanolic solution (5 mL) of
2 2
[
H][AuCl ]·3H O (0.090 g, 0.22 mmol) was added. The resulting
4 2
yellow suspension was stirred at room temperature in an N2
atmosphere for 16 h. Filtration using GF/C filter paper (cannulation)
produced a clear yellow solution, which was reduced to 10 mL in
volume. Pentane (40 mL) was added to the solution slowly until first
indication of precipitation. The mixture was filtered using GF/B filter
(
cannulation), yielding a yellow solid, which was dried under Schlenk
1
3
vacuum (50%). H NMR (600 MHz, (CD ) CO): δ 8.08 (d, J = 2.4
Hz, 2H, C3), 7.82 (s, 2H, C5), 7.60 (d, J = 1.6 Hz, 2H, C1), 6.78 (s,
4
3
2
3
1
3
1
H, C4), 6.37 (br dd, 2H, C2). C{ H} NMR (150 MHz,
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Corresponding Author
*E-mail: barbara.messerle@mq.edu.au.
ORCID
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Roy T. McBurney: 0000-0002-2383-8450
Samantha C. Binding: 0000-0003-4402-0313
Barbara A. Messerle: 0000-0002-1928-5961
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The authors declare no competing financial interest.
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Inorg. Chem. XXXX, XXX, XXX−XXX

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