Synthesis and catalytic applications of 1,2,3-triazolylidene gold(i) complexes in silver-free oxazoline syntheses and C-H bond activation

Article abstract of DOI:10.1039/c6dt02181f

A series of novel 1,2,3-triazolylidene gold(i) chloride complexes have been synthesised and fully characterised. Silver-free methodologies for chloride ion abstraction of these complexes were evaluated for their potential as Au-based catalyst precursors. Using simple potassium salts or MeOTf as chloride scavengers produced metal complexes that catalyse both the regioselective synthesis of oxazolines and the C-H activation of benzene or styrene for carbene transfer from ethyl diazoacetate. These results indicate that Ag-free activation of 1,2,3-triazolylidene gold(i) chloride complexes is feasible for the generation of catalytically active Au triazolylidene species. However, silver-mediated activation imparts substantially higher catalytic activity in oxazoline synthesis.

Full text of DOI:10.1039/c6dt02181f

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Synthesis and catalytic applications of 1,2,3-triazolylidene gold(I) complexes in silver-free
DOI: 10.1039/C6DT02181F
oxazoline syntheses and C–H bond activation
a,b
c
b
a,d
René Pretorius, Manuel R. Fructos, Helge Müller-Bunz, Robert A. Gossage, Pedro J.
c
a,b
Pérez,* and Martin Albrecht*
a
Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012
Bern, Switzerland
b
School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4,
Ireland
c
Laboratorio de Catálisis Homogénea, Unidad Asociada al CSIC, CIQSO-Centro de
Investigación en Química Sostenible and Departamento de Química, Universidad de Huelva,
Campus de El Carmen 21007 Huelva, Spain
d
Department of Chemistry & Biology, Ryerson University, 350 Victoria Street, Toronto ON
M5B 2K3 Canada
E-mail: perez@dqcm.uhu.es; martin.albrecht@dcb.unibe.ch
Abstract
A series of novel 1,2,3-triazolylidene gold(I) chloride complexes have been synthesised and
fully characterised. Silver-free methodologies for chloride ion abstraction of these complexes
were evaluated for their potential as Au-based catalyst precursors. Using simple potassium salts
or MeOTf as chloride scavengers produced metal complexes that catalyse both the
regioselective synthesis of oxazolines and the C–H activation of benzene or styrene for carbene
transfer from ethyl diazoacetate. These results indicate that Ag-free activation of 1,2,3-
triazolylidene gold(I) chloride complexes is feasible for the generation of catalytically active
Au triazolylidene species. However, silver-mediated activation imparts substantially higher
catalytic activity in oxazoline synthesis.
1

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DOI: 10.1039/C6DT02181F
Introduction
Homogeneous catalysts comprised of gold as the active centre have enjoyed increased attention
1
in recent years as more and more unique reactivity patterns have been revealed. In particular,
ligation by N-heterocyclic carbenes (NHCs) as for example in AuCl(IPr) (IPr = N,N’-bis(2,6-
1
k,2
diisopropylphenyl)imidazolylidene) imparted exceptionally high catalytic activity,
which
spurred widespread efforts in this burgeoning area of catalysis. In comparison to classical,
3
imidazole-derived NHCs, structurally related 1,2,3-triazolylidene (trz) ligands have been
4
significantly less studied as ligands in gold chemistry. The triazole framework offers several
benefits when compared with NHCs, including for example the ease of functional group
3
a,5
3,6
incorporation,
increased σ-donation compared to classical NHCs, and a mesoionic
7
resonance form which is able to potentially stabilise different metal oxidation states. Catalytic
activity in carbene gold complexes has typically been instigated by using a silver(I) salt as
8
+
halide scavenger for catalyst activation. However, Ag can be a non-innocent activator in
many Au-catalysed transformations, and often plays an active (and not always beneficial) role
1
d,9
in the catalytic cycle. Current trends in Au catalysis are therefore focusing on using Ag-free
protocols to avoid any undesired side-reactions. For example, pre-activation and subsequent
silver salt removal from a stable cationic gold(I) complex as catalyst precursor has been
1
0
11
12
13
described by Gagosz Echavarren, and others. Also, the use of a gold(I) hydroxide or
1
4
acetate pre-catalyst in lieu of gold(I) chloride complexes has also been shown to be an
effective method to avoid the necessity of silver salts for catalyst activation. Several approaches
towards Ag-free activation have been probed, though almost none are based on simple and
inexpensive (commercial) salts. Thus, the in situ generation of active gold(I) catalysts has been
1
5
explored by using Lewis acids as activators such as metal triflates, and alkali metal salts of
4
a,16
17
borates,
activators are typically non-commercial and customised salts.
We have recently demonstrated the non-innocent behaviour of silver(I) salts when activating
2 3 3
to name a few. However, with the exception of Cu(OTf) (OTf = CF SO ), the
1
8
1
,2,3-triazolylidene gold complexes. Specifically, silver mediated carbene transfer reactions
have been demonstrated, likely via a reverse carbene transfer from gold(I) to silver(I).
Considering the significant complications arising from such ligand transfer, we endeavoured
to establish alternative procedures for the activation of AuCl(trz) complexes for catalytic bond
+
activation purposes, which do not rely on Ag for chloride abstraction. Herein we demonstrate
that simple potassium salts can be used to form catalytically active triazolylidene gold
2

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complexes. These methodologies are of further use for exploring the specific impact of
DOI: 10.1039/C6DT02181F
triazolylidene ligands in gold(I)-mediated catalytic activity.
Results and discussion
Synthesis of Triazolylidene Gold Complexes. A set of novel triazolylidene gold complexes
AuCl(trz) were synthesised as representative examples intending to probe ligand induced
catalytic effects. The ligand precursor triazolium salts 1a–e (Scheme 1) were readily available
through copper(I)-catalysed [2+3] dipolar cycloaddition reactions and subsequent alkylation
–
–
3 4 3 3
with either (Me O)BF , MeI, or MeOTf (OTf = SO CF ). Of note, triazolium 1b, which
contains a pendant acetate group was highly sensitive to hydrolysis and hence the alkylation
of the triazole with MeOTf was performed at low temperature (below 0 °C). Subsequent storage
of the triazolium salt 1b below –20 °C is paramount to avoid spontaneous degradation over
time. Salt 1c was obtained in relatively low yields (about 30%) when compared to the other
triazolium salts (≥79%), presumably because the electron withdrawing nature of the
perfluorinated tail decreases the nucleophilicity of the triazole unit. The influence of the
1
fluorocarbon unit is supported by the H NMR chemical shifts for the NCH
2
signals, which are
shifted downfield by 0.72 and 0.38 ppm, for N1 and N3 respectively, in comparison with the
1
3
analogous protons of 1a. Moreover, the N-bound methylene group appears in the C NMR
3
spectrum as a triplet ( JCF = 21 Hz), indicating an interaction between the perfluorinated tail
1
3
and the methylene group. In contrast, the C NMR chemical shifts do not show any significant
variation due to the more electron withdrawing nature of the fluoro-chain.
The AuCl(trz) complexes were synthesised from the triazolium salts 1a–f using well
4
g,18,19
established methodologies (Scheme 1).
triazolium salt with Ag O yielded the corresponding carbene silver intermediate, which was
not isolated and used in situ for transmetallation with AuCl(SMe ). To ensure that chlorido
complexes were formed exclusively, all novel AuCl(trz) complexes were prepared from
Accordingly, treatment of the appropriate
2
2
–
–
triazolium salts containing either a BF
4
or a OTf counterions, or alternatively by counterion
exchange with AgBF directly before the reaction with Ag
4
2
O (for 1c). Only traces of
triazolylidene silver intermediate were formed in the absence of a chloride source according to
1
H NMR spectroscopic monitoring of the reaction, while clean and essentially quantiative
4
formation of the intermediate was observed in the presence of Me NCl. The subsequent
transmetalation was straightforward and good yields ranging from 64–88% were obtained for
all gold complexes 2a–f (see Experimental section)
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DOI: 10.1039/C6DT02181F
Scheme 1. Synthesis of triazolylidene gold(I) complexes 2.
Metallation of the hydroxyl-functionalised triazolium salt 1f gave a mixture of products, with
ratios that were dependent on the reaction conditions. In the presence of an excess Ag O and
in moist solvents, complex 2f was obtained in nearly 90% yield. Metallation of 1f under an
atmosphere of dry nitrogen and substoichiometric amounts of Ag O afforded significant
2
2
amounts (up to 46%) of complexes 2g and 2g’ as the major products (Scheme 2). We have not
been able to separate these two products preparatively, though fractional crystallisation
afforded single crystals of pure 2g that were suitable for X-ray diffraction analysis (see below).
Dissociation of the C-bound substituent in 2g and 2g’ with formal loss of acetone was indicated
by NMR spectroscopy. Two sets of resonances were observed, both featuring an additional
resonance in the aromatic region and the disappearance of the two methyl groups of the wingtip
1
unit of 1f. Integration of the H NMR resonances of the NCH
2
and NCH
3
signals suggest a 5:4
1
13
ratio of 2g and 2g’. The spectroscopic assignment was based on long range H– C correlation
spectroscopy (HMBC). Accordingly, the NCH group of the C4-metallated complex 2g
resonantes at 4.20 ppm (cf. δ = 4.17 ppm in the C5-metallated homologue 2g’), whereas the
NCH group in 2g’ appears at lower field than in 2g (δ = 4.50 vs 4.38 ppm) and provides the
3
H
2
H
clearest spectroscopic distinction between the two isomers. The Ctrz–H resonance shift is
essentially identical in both complexes and appears at 7.58 and 7.57 ppm, respectively.
1
3
Similarly, the C NMR shifts of the two isomers are only marginally disparate. In agreement
1
with the H NMR data, the largest difference again pertains to the NCH
3
group (δ
C
= 42.1 and
3
8.8) and the NCH
2
group (δ
C
= 52.5 and 55.4 for 2g and 2g’, respectively). The resonances
C
due to the CtrzH carbons were significantly upfield shifted (δ = 134±0.4) when compared to
4

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the normal 145–150 ppm range observed for C5-alkylated or -arylated triazolylidene gold
DOI: 10.1039/C6DT02181F
complexes.
Scheme 2. Transmetallation of 1f and concurrent partial formal loss of acetone resulting in the
formation of 2f, 2g, and 2g’.
Formation of complexes 2g and 2g’ may be rationalised by deprotonation of the hydroxyl
group, which is followed by elimination of acetone from the ligand. The observation of isomers
suggests that the ligand degraded before the triazolylidene silver intermediate is formed.
Metallation of a C4,C5-diprotonated triazolium salt is unselective and may thus account for the
formation of a mixture of 2g and 2g’. The influence of Ag
detail. Using various 1f/Ag O ratios (0.5, 1, 2) and monitoring of the triazolylidene silver
complex formation indicated that higher equivalents of Ag O promoted the preservation of the
wingtip group and hence promoted the formation of the silver intermediate that eventually leads
to complex 2f, while sub-stoichiometric quantities of Ag O increased substituent degradation.
2
O was therefore investigated in more
2
2
2
The isomeric ratio of the unsubstituted triazolylidene silver complexes is independent of the
quantity of silver salt (cf. Table S1), remains unchanged over time, and is in good agreement
with the final product distribution observed for formation of complexes 2g and 2g’. These data
therefore suggest that wingtip degradation of the ligand occurs prior to transmetallation and
that acetone elimination is a competitive process to triazolium Ctrz–H bond activation.
Moreover, these results indicate that wingtip degradation only takes place from the triazolium
salt, yet it is suppressed once the carbene silver precursor is formed. Otherwise, larger
2
quantities of Ag O should shift the isomeric ratio due to degradation of the silver precursor of
2
f.
1
3
Characterisation of triazolylidene gold complexes. The C NMR spectra of all
triazolylidene gold complexes feature a resonance in the 156–162 ppm range for the Au-bound
4
,18–20
C
trz nucleus, consistent with related triazolylidene gold complexes.
The carbenic carbon
= 162.1 ppm), and resonates at higher field in the alkyl-
= 157.5 ± 2.3 ppm) than in aryl-substituted
is most deshielded in complex 2e (δ
C
substituted triazolylidene complexes (δ
C
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triazolylidene complexes, suggesting that the electronic configuration of this carbon is affected
DOI: 10.1039/C6DT02181F
by the triazolylidene substitution pattern. The polyfluorinated tail had no significant influence
2
on the NMR frequency of the carbenic carbon. However, the NCH group in complex 2c is
1
deshielded by 0.4 ppm ( H NMR) when compared to the butyl homolog 2a, and likewise
1
3
shielded by about 8 ppm in the C NMR spectrum.
Single crystal X-ray diffraction analysis of complexes 2b, 2f, and 2g confirmed the bonding
situation in these complexes and in particular demonstrated the wingtip dissociation in 2g
(Figure 1). Bond lengths and angles of these complexes (Table 1) do not significantly deviate
4
,18–20
from related carbene gold complexes characterised previously.
However, some packing
trends are worth noting. Complex 2g displays a head-to-tail type packing, attributed to
presumably weak aurophilic interactions (Au···Au separation of 3.46 Å) which may add to the
1
f,21
electrostatic interaction between the chlorido ligand and the heterocyclic ring.
This
arrangement may be preferred due to the low steric demand of this ligand system, and hence
allows for much closer packing than that of, for example, complex 2b.
Figure 1. ORTEP representations of complex 2b (a), 2f (b), and 2g (c; all 50% probability
ellipsoids, H-atoms and second independent molecule of 2g in the unit cell omitted for clarity).
Table 1. Selected bond lengths [Å] and angles [°] in complexes 2b and 2g
Complex
Au-C1
Au-Cl
C1-Au-Cl
178.08(7)
178.1(2)
2
2
2
b
f
1.995(2)
1.976(6)
1.984(2)
2.2896(6)
2.2873(19)
2.2978(6)
a)
g
175.90(7)
a)
Only for one of the two non-related molecules in the unit cell of 2g
6

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Catalysis results and activation studies. Previous work has clearly shown that Ag(I) can be
DOI: 10.1039/C6DT02181F
1
d,9c,9d,18,22
a non-innocent activator for Au-catalysed transformations.
In particular when using
AuCl(trz) system, silver has multiple roles beyond solely abstracting the gold-bound chlorido
ligand and likely induces a retro-transmetallation to (transiently) yield catalytically active
9
c,18,23
triazolylidene silver complexes.
Because of these complications and the associated
uncertainty whether the true catalytic species is (are) based on silver or gold, silver-free catalyst
1
6
activation methodologies are of paramount importance. We considered two specific routes:
+
(i) halide abstraction with a potassium salt, and (ii) the use of CH
3
as an electrophile. Even
though methyl cations are only rarely used to scavenge chloride, chloride to halide exchange
2
4
reactions at the metal centre have been performed successfully with methyl iodide. Moreover,
C–C bond formation by electrophilic activation of (NHC)Au(Aryl) complexes has been
2
5
reported. To probe this methodology, complex 2a was reacted with stoichiometric equivalents
of MeOTf in MeCN. Initial attempts to isolate the putative cationic solvent complex
[(trz)Au(solv)]OTf from the reaction mixture only afforded Au(0), indicated by the gold mirror
1
9
that formed upon evaporation of all volatiles. Monitoring the reaction by F NMR
spectroscopy (CD Cl ) indicated a new resonance that is shifted 5 ppm upfield from MeOTf,
2
2
attributed to the gradual formation of a new ion pair in solution (see ESI, Figure S1). The
1
corresponding H NMR data showed only minor changes in the ligand, and a new resonance
3
around 3 ppm which has been assigned to CH Cl. In order to overcome the apparent instability
of the cationic species resulting from 2a, it was trapped by the addition of an exogenous ligand.
Addition of isonitrile (methyl isocyanoacetate) gave the corresponding cationic complex (see
1
8
3
ESI). Likewise, addition of PPh before evaporation of the solvent afforded the cationic gold
species 3a. This complex was unambiguously identified by NMR spectroscopy and X-ray
diffraction (Figure 2). However, it should be noted that the phosphine carbene gold complex
3
cation is also formed upon treatment of 2a with PPh in the absence of any electrophilic
chloride scavenger (albeit with a chloride counterion), which limits the relevance of phosphines
as trapping reactions. In contrast, isonitrile binding does not occur with the [(trz)AuCl]
complexes 2 spontaneously and was only observed in the presence of MeOTf, suggesting that
isonitriles are more diagnostic trapping agents.
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DOI: 10.1039/C6DT02181F
Figure 2. Synthesis and ORTEP representation of complex 3a (50% probability, hydrogens
–
and OTf anion omitted for clarity); Au1–C1 2.046(3) Å, Au1–P1 2.2817(8), Cl1–Au–P1
1
72.57(9)°.
1
3
31
Analysis of complex 3a by C and P NMR spectroscopy reveals similar features when
+
+
compared to related [(trz)Au(PPh
3
)] and [(NHC)Au(PPh
The carbenic nucleus is deshielded by about 15 ppm compared to the chlorido analogue
a and appears at δ = 172, in agreement with a more electron-deficient metal fragment. X-ray
3 P
)] complexes (e.g. δ = 39.4 for
1
8,26
3
2
a).
C
diffraction analysis of single crystals of 3a indicates an elongation of the gold carbene distance
compared to 2a (Au–C1 2.046(3) Å in 3a vs 1.98 Å in complexes 2), a consequence of the
3
higher trans influence of PPh compared to the chlorido ligand. The coordination geometry
slightly deviates from linearity, P–Au–C1 172.57(9)°, presumably due to packing constraints.
Alternating layers of triflate ions and triazolium units with close contacts of 3.13 and 3.53 Å
suggest electrostatic interactions in the solid state between the formally negatively charged
triflate oxygen sites and the partially positively charged heterocycle.
Catalytic activity in oxazoline synthesis. Halide abstraction under catalytically relevant
conditions was probed in the presence of isonitriles and bromobenzaldehyde to promote the
1
2d-g,18,27
catalytic formation of oxazolines.
Complex 2a was chosen as a representative
AuCl(trz) complex because of the simple ligand design and the established benefit of the
7
d
triazolylidene substitution pattern for monitoring catalytic reactions. Activation of this
complex for initiating catalytic activity was investigated using MeOTf as well as different
potassium salts (Table 2).
a
Table 2. Catalytic oxazolines synthesis with various AuCl(trz) complexes and activators
8

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DOI: 10.1039/C6DT02181F
Entry
[Au]
---
---
2a
2a
2a
2a
2a
2a
2b
2c
Additive
base
---
conversion (%)
cis/trans
---
1
2
3
4
5
6
7
8
9
---
6
KPF
6
NiPr
NiPr
---
2
Et
Et
25
24
<2
93
21
61
62
88
75
87
---
---
2
23/77
---
KPF
6
6
KPF
NiPr
NiPr
NiPr
NiPr
NiPr
NiPr
NiPr
2
2
2
2
2
2
2
Et
Et
Et
Et
Et
Et
Et
26/74
18/82
28/72
27/73
27/73
29/71
29/71
KBF
4
KOTf
MeOTf
KPF
KPF
KPF
6
6
6
1
1
0
1
2d
a
General conditions: 4-bromobenzylaldehyde (1.6 mmol), methyl isocyanoacetate (1.4 mmol),
NiPr Et (0.14 mmol), AuCl(trz) (0.014 mmol), additive (0.028 mmol), trimethoxybenzene
0.36 mmol, internal standard), CH Cl (4 mL), 40 °C, 8 h; yields and cis/trans ratio determined
2
(
2
2
1
by H NMR spectroscopy, averaged of at least 2 runs.
A systematic variation of the different reaction parameters revealed that the gold complex,
2
8
amine, and a chloride scavenger are needed for generating an active species (entries 1–5).
Comparison of different chloride scavenging additives revealed that KPF (entry 5) is superior
to other potassium salts (entries 6,7). The addition of NiPr Et is essential for catalytic turnover,
as no catalytic activity was observed in the absence of base (entry 4). Likewise the reaction
is very slow when no scavenger was used (entry 3). Interestingly, KBF has no activating effect
cf entries 3 and 6). The utilisation of MeOTf enhanced catalytic activity (entry 8), suggesting
6
2
1
8
4
(
that chloride methylation is a viable strategy to generate the labile coordination site at the gold
centre. It is remarkable that KOTf and MeOTf result in the same catalytic activity (entries 7
–
and 8) and give identical conversions, suggesting a distinct role for the OTf anion in levelling
1
e
catalyst activity. Tentatively, weak triflate coordination may be surmised to slow down the
–
turnover frequency when compared to the analogous species containing a PF
6
counterion. The
9

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relevance of the counterion is also indicated by the variable catalytic activity in dependence of
DOI: 10.1039/C6DT02181F
different anions in the potassium salts (entries 5–7).
Further studies on using MeOTf to activate the AuCl(trz) catalyst precursor included the
variation of the equivalents of this activator, a modification which affected the conversion rates
markedly. Using only 1.1 instead of 2 equiv. MeOTf with respect to 2a reduced the activity to
about half (e.g. 21% vs 38% conversion after 4 h, Figure 3 and Table S2). In the presence of 5
equiv. MeOTf, the catalytic activity is doubled and almost full conversion was accomplished
after 8 h (45% already after 2 h), which matches the conversion rates achieved upon activation
of the gold complex with KPF
6
. The need for higher relative ratios of additive may be because
Et or undergo partial hydrolysis.
MeOTf may interact with NiPr
2
Figure 3. Comparison of the conversion for catalytic oxazoline synthesis using 2a in
combination with varying amounts of MeOTf (red, green, and purple traces), and using MeOTf
in the absence of a gold complex (blue trace).
The enhancement of catalytic activity in the presence of KOTf, MeOTf and in particular KPF
6
+
suggests the successful formation of a [(trz)Au] species for substrate conversion. Therefore,
6
KPF , was utilised as activator for a catalytic screening of the AuCl(trz) complexes 2a–d
(entries 5,9-11). In this series, the catalytic activity of 2a, 2b, and 2d is identical within the
measurement errors (±5%). Complex 2c containing perfluorinated substituents on the
triazolylidene induced slightly lower catalytic activity. This effect is particularly pronounced
at early conversion stages. Thus after 2 h and 4 h, runs with complex 2c achieved 25% and
4
3
3% conversion, respectively, while the other complexes are considerably more active (average
8% and 65% conversion after the same reaction time). The lower performance of complex 2c
may be associated with the specific solubility and aggregation properties imparted by the
perfluorinated substituents. Variation of the hydrocarbon substituents on the triazolylidene
1
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ligand from linear or branched alkyl groups to aryl substituents does not affect the catalytic
DOI: 10.1039/C6DT02181F
performance (cf 2a vs 2b and 2d). These results therefore suggest that the catalytic rate-
determining step is not significantly governed by steric or electronic effects induced by the
triazolylidene ligand. This conclusion is further supported by the essentially unaltered cis/trans
ratio, even when a sterically demanding adamantyl group was included in the ligand scaffold
(
2d, entry 11).
Importantly, activation of complex 2a with AgBF
of magnitude more active than the species generated with KPF
4
affords a species that is two to three orders
or triflates, reaching
6
1
8
quantitative oxazoline formation within 15 min at 0.5 mol% loading. Similarly high activities
have been recorded when related triazolylidene silver complexes (trz)AgCl were used for
2
9
catalysis in the absence of gold. Thus, the gold-based active species are considerably less
competitive than their triazolylidene silver analogues in this catalytic heterocycle synthesis.
These data further suggest that the catalytically active component in the AuCl(trz) / AgBF
4
+
system may be a [(trz)Ag] species resulting from a retro-transmetallation or the formation of
1
5a,18,29
Au nanoparticles.
C–H bond activation in metal-mediated carbene transfer from ethyl diazoacetate. The
+
application of Ag-free [(trz)Au] catalysis was further probed in carbene transfer chemistry by
the metal-mediated decomposition of diazo compounds. This catalytic system is attractive for
F
F
several reasons. Firstly, NaBAr
4 4
(BAr = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) has
been shown to be an excellent activator for AuCl(NHC) catalysts in this area of catalysis and
3
0
F
hence allows for Ag-free activation. In particular the AuCl(IPr)/NaBAr
4
system has given
3
1
promising results with arenes as substrates. With previously described catalytic systems, the
reaction of benzene and ethyl diazoacetate (EDA) led to cycloheptatriene (4 in Table 3), as the
result of consecutive double bond cyclopropanation and ring expansion in the so-called
Buchner reaction . However, the gold-based system is selective towards C-H bond
functionalisation of benzene and other arenes by formal carbene insertion affording an alkyl-
3
0a–c
arene (5 in Table 3).
6
Furthermore, it was shown that AuCl(trz)/AgSbF systems are useful
4
g
carbene transfer reagents from EDA to both reactive N- or O-containing substrates. Since the
activity of the AuCl(trz) systems for C–H insertion has not been studied, the catalytic C–H
activation with EDA seems an attractive expansion to investigate Ag-free activation of
AuCl(trz). Benzene was chosen as a representative substrate for preliminary screening, and the
F
activity of complexes 2a–2e in catalytic carbene transfer was monitored using NaBAr
4
as
additive (Table 3). While a mixture of the aforementioned cycloheptatriene 4 and benzyl
1
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acetate 5 is expected, these two products are easily distinguishable by their diagnostic NMR
DOI: 10.1039/C6DT02181F
signals.
a
Table 3. Triazolylidene gold-mediated carbene transfer from EDA to benzene
b
Entry
[Au]
Additive
Product ratio
c
4
5
DEF/DEM
F
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2a
2a
2e
NaBAr
NaBAr
NaBAr
NaBAr
NaBAr
4
68
65
61
57
67
77
64
62
17
18
19
17
16
9
15
17
21
26
17
14
18
F
F
F
F
4
4
4
4
AgBF
4
AgSbF
AgSbF
6
6
18
22
16
a
F
General conditions: [Au] (0.012 mmol), benzene (3 mL), EDA (0.44 mmol), NaBAr
4
(0.015
b
1
mmol), ratios in % of product mixture; distribution of products according to H NMR
spectroscopy, ca. 15% of EDA were remaining after 24 h as quantified with benzaldehyde as
c
internal standard; DEF/DEM: diethyl fumarate/diethyl maleate, by products of the carbene
coupling reaction from two molecules of EDA.
All AuCl(trz) complexes 2a–e favoured the formation of the cycloheptatriene product 4 over
the product from C–H insertion in approximately a 3:1 ratio (Table 3, entries 1–5). The catalytic
activity is essentially insensitive to the substitution pattern on the triazolylidene heterocycle
with overall product ratios, i.e. 4 + 5, all in the 75–85% range. The influence of silver salts as
halide scavengers was also considered to determine potential interactions of silver in the
catalytic cycle (entries 6–8). While the use of AgBF
yielded a 8:1 selectivity towards 4 (entry 6), AgSbF
compared to the activation of AuCl(trz) with NaBAr
4
further promoted cyclopropanation and
6
did not alter the product distribution when
F
4
(entries 7,8). We also noted that the
consumption of EDA was not complete (ca. 85%, see Table 3) even after 24 h. Furthermore,
1
2

Page 13 of 27
Dalton Transactions
F
View Article Online
DOI: 10.1039/C6DT02181F
the species generated from AuCl(trz) and NaBAr
4
in CH
2
Cl
2
was unstable in the absence of
coordinating substrates as displayed by the immediate formation of gold(0) and gold
nanoparticles observed as purple particles in solution. This instability required addition of EDA
before introducing the additive for generating the active catalyst. This sequence of addition
resulted in the formation of fumarate and maleate as minor by-products. Such side-product
3
2
formation is typically suppressed by slow addition of EDA, though this procedure is
+
F
prohibited here because of the instability of the [Au(trz)] /BAr
Similar reactivity patterns were observed when using selected AuCl(trz) complexes for carbene
transfer to styrene (Table 4). These runs were performed in CH Cl solution, in contrast to the
neat benzene catalysis. The results indicate that the active species is solvent tolerant and
apparently does not react with CH Cl but instead selectively activates the aromatic C–H
4
species.
2
2
2
2
bonds. As in the case of benzene, full conversion of EDA was not achieved within 24 h and
about 10% EDA remained unconverted after that time, which resulted in a complex reaction
mixture for NMR analysis. Nonetheless, the ratio of products confirmed the same trend noted
for diazocarbene transfer to benzene. Thus, carbene addition to a C=C double bond and
formation of the phenyl cyclopropane 6 is the major outcome of the reaction, while carbene
insertion into a Caryl–H bond and formation of styryl acetate 7 is less favoured. The ratio
between cyclopropanation and C–H bond activation is about 3:1 for complexes 2b,d,e and
hence very similar to the ratios obtained when using benzene as substrate (entries 2–4). In
contrast, complex 2a is considerably more selective and reaches a 6.5:1 product ratio (entry 1).
a
Table 4. Triazolylidene gold-mediated carbene transfer from EDA to styrene
b
Entry
[Au]
Additive
Product ratio
c
6
7
DEF/DEM
F
1
2
3
4
5
2a
NaBAr
NaBAr
NaBAr
NaBAr
4
77
65
59
66
74
12
20
17
21
13
11
15
24
13
12
b
F
F
F
2b
4
4
4
2d
2e
2a
AgSbF
6
1
3

Dalton Transactions
Page 14 of 27
F
View Article Online
13
DOI: 10.1039/C6DT02181F
6
2d
NaBAr
4
, Hg drop 67
20
a
F
General conditions: [Au] (0.012 mmol), styrene (2.3 mmol), EDA (0.44 mmol), NaBAr
4
b
1
(
2 2
0.015 mmol), CH Cl (2 mL); average of 2 runs; distribution of products according to H
NMR spectroscopy, ca. 10% of EDA were remaining after 24 h as quantified with
c
benzaldehyde as internal standard; DEF/DEM: diethyl fumarate/diethyl maleate, by products
of the carbene coupling reaction from two molecules of EDA.
No significant change in activity or selectivity was observed upon substituting the chloride
F
scavenger from NaBAr
4
to a silver salt (entry 5). The similar performance suggests that unlike
in the oxazoline syntheses (vide supra), the catalytically active species in the carbene transfer
+
reaction remains the [(trz)Au] species. Finally, a Hg-drop test was performed using catalyst
2
d. No significant deviation was noted when compared to the parent run (cf. entries 3 and 6),
which is indicative of a homogeneous catalytic cycle rather than one involving nanoparticles
as an active species.
It is worthwhile to compare complexes AuCl(trz) and AuCl(IPr) as catalyst precursors to give
+
some insight into the ligand effects. Firstly, the activity of the [(trz)Au] species is substantially
+
lower than that of [(IPr)Au] , requiring more than 24 h rather than just 6 h to reach complete
3
0c
conversion under identical conditions. Secondly, and perhaps more importantly, the active
species resulting from AuCl(trz) strongly favours cyclopropanation over C–H bond activation
and carbene insertion, while the use of AuCl(IPr) favours C–H bond activation. However, the
product ratio for the AuCl(trz) systems closely matches those found for functionalised
3
0d
AuCl(NHC) systems. As the reactivity pattern was essentially identical for all the evaluated
triazolylidene complexes, this facet likely reflects the different properties induced by
triazolylidenes vs classical NHC ligands. Previous work has suggested that decreasing electron
density on the metal centre favours C–H insertion. In agreement with such a model, the
increased σ-donor properties of mesoionic triazolylidenes indeed results in preferential
3
0a,33
cyclopropanation as compared to carbene insertion via C–H activation.
Accordingly, an
increased electron density at the metal centre favours a carbene type resonance structure for
the diazo fragment (A, Scheme 3) while electron-poorer metal centres induce a carbocationic
3
4
structure (B, Scheme 3). It is very likely that the relative weight of each limiting structure in
the real structure influences the reaction outcome toward the addition (Buchner) or insertion
(alkyl-carbene) products.
1
4

Page 15 of 27
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DOI: 10.1039/C6DT02181F
Scheme 3. Resonance forms for the gold-carbene intermediate
Conclusions
A range of Ag-free chloride scavenger reagents for application with triazolylidene gold(I)
complexes has been tested and shown to be useful for the activation of these complexes prior
to catalysis. The results indicate that the Au complexes are less active catalysts for oxazoline
2
9
synthesis than the analogous silver complexes such as AgCl(trz). Also, due to the linear
coordination sphere around the metal centre, variation of the ligand substituents only
moderately modulated catalytic activity and did not alter the diastereoselectivity of the
F
resulting product profile. The AuCl(trz)/NaBAr
4
system also catalysed the carbene transfer
from EDA via benzene and styrene C–H bond activation. This activity demonstrated further
+
applications of Ag-free [(trz)Au] catalysis. In this case, cyclopropanation products were
favoured over C-H insertions, in contrast to the AuCl(IPr) system, indicating that the strong σ-
donor properties of triazolylidene can be used to modulate the selectivity of gold in catalytic
processes. Considering these results in combination with previous studies, it can be concluded
that the choice of chloride scavenger is important to effectively identify the activity of gold-
based catalysts and to assess the impact of the metal, as well as that of the ligand framework.
Experimental
General
The precursor 4-butyl-1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-1H-1,2,3-triazole for the
3
5
36
3d
triazolium salts 1c, the triazolium salts 1a, and 1e, and the triazolylidene gold complex 2d
1
8
were synthesised using literature procedures. The synthesis of all novel triazoles and
triazolium salts is described in the ESI. Ag O was used after regeneration by heating >160° C
under vacuum. Dry, degassed solvents were purified using an alumina/catalyst column
Thermovac Co.). All other reagents are commercially available and were used as received. All
microwave experiments were carried out using a Biotage Initiator 2.5 instrument, operating at
2
(
1
5

Dalton Transactions
Page 16 of 27
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0
-400 W irradiation power. Unless specified otherwise NMR were recorded at 25° C, on Varian
DOI: 10.1039/C6DT02181F
1
and Bruker spectrometers operating at 300, 400, or 500 MHz ( H NMR) and 75, 100, 125 MHz
1
3
1
(
C{ H} NMR) respectively. Chemical shifts (δ in ppm, coupling constants J in Hz) were
referenced to residual solvents. Assignments are based on homo- and heteronuclear shift
correlation spectroscopy. Elemental analyses were performed by the Microanalytical
Laboratory at University College Dublin, Ireland using an Exeter Analytical CE-440 Elemental
Analyzer, with the exception of complex 2d which was performed in Unidad de Análisis
Elemental of the Universidad de Huelva. Residual solvents were identified by NMR
spectroscopy GC analysis were recorded on a Varian CP-3800 instrument. High-resolution
mass spectrometry was carried out with a Micromass/Waters Corp. USA liquid
chromatography time-of-flight spectrometer equipped with an electrospray source.
Complex 2a
To a solution of 1a (290 mg, 1.0 mmol) in dry CH
Ag O (134 mg, 0.58 mmol), and NMe Cl (140 mg, 1.3 mmol), and the suspension was stirred
for 16 h under the exclusion of light under a N atmosphere. AuCl(SMe ) (309 mg, 1.1 mmol)
was added and stirring continued for 2 h. The reaction mixture was filtered through Celite and
volatiles were removed under reduced pressure. The residue was redissolved in CH Cl and
2 2
Cl /MeCN (20 mL, 1:1 v/v) were added
2
4
2
2
2
2
filtered through Celite a second time to remove residual salts. Volatiles were removed under
reduced pressure yielding the product as a brown oil, which became crystalline after several
1
days of drying in vacuo (0.376 g, 0.88 mmol, 86 %). H NMR (500 MHz, CDCl
3
): δ 0.95 (m,
CH ), 1.98-
), 4.42 (t, JHH
CH CH ), 13.9
), 24.9 (CtrzCH
6
2
H, 2 x CH
2
CH
3
), 1.32-1.44 (m, 4H, 2 x 2 CH
2
CH
3
), 1.68-1.74 (m, 2H, CtrzCH
), 4.02 (s, 3H, NCH
): δ 13.4 (NCH CH
), 22.5 (CtrzCH CH CH
), 55.1 (NCH ), 147.5 (CtrzCH
2
2
3
.04 (m, 2H, NCH
2
CH
2
), 2.76 (t, JHH = 7.8Hz, 2H, CtrzCH
2
3
1
3
1
=
7.3Hz, 2H, NCH
2
)
C{ H} (126 MHz, CDCl
), 19.8 (NCH CH CH
CH ), 36.4 (NCH
3
2
2
2
3
(
C
trzCH
trzCH
2
CH
2
CH
2
CH
3
2
2
2
2
2
2
2
), 31.4
(C
2
CH
2
), 32.3 (NCH
2
2
3
2
2
), 157.0 (Ctrz-Au)
+
HRMS (ESI+): m/z Found 450.0987 [M + Na] (calcd. for C11
H
21
N
3
AuClNa, 450.1028) Anal.
Calcd. for C11H N AuCl: C, 30.89; H, 4.97; N, 9.82%. Found: C, 31.04; H, 4.72; N, 9.69%.
21 3
Complex 2b
This complex was prepared according to the procedure described for 2a starting from
triazolium salt 1b (200 mg, 0.51 mmol), Ag O (60 mg, 0.26 mmol), NMe Cl (60 mg, 0.55
2
4
1
6

Page 17 of 27
Dalton Transactions
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2
DOI: 10.1039/C6DT02181F
mmol), and AuCl(SMe ) (156 mg, 0.53 mmol). After filtration through Celite and
concentration under reduced pressure, pentane was added. The formed black coloured solids
were removed by filtration and the supernatant evaporated to dryness. The residue was
2 2 2
repeatedly dissolved in CH Cl and precipitated with Et O until a minor amount of white
precipitate was observed . The supernatant was then decanted, evaporated to dryness, washed
with pentane, and dried in vacuo. This procedure yielded complex 2b as a white solid (0.19 g,
0
.40 mmol, 78 %). Crystals were obtained by slow diffusion of Et
2
O into a CH
CH ), 1.33-1.40 (m, 2H,
), 2.10 (s, 3H, C=OCH ), 4.14 (s, 3H,
) C{ H} (126 MHz, CDCl ): δ 13.6 (CH CH ), 19.8
), 29.1 (C(CH ), 32.3 (NCH CH ), 39.6 (NCH ), 56.1 (NCH ),
2 2
Cl solution.
1
3
H NMR (500 MHz, CDCl
CH ), 2.04-2.07(m, 8H, NCH
NCH ), 4.49 (t, JHH = 7.1 Hz, 2H, NCH
3
): δ 0.96 (t, JHH = 7.4Hz, 3H, CH
2
3
CH
2
3
2
CH
2
and C(CH
3
)
2
3
3
13
1
3
2
3
2
3
(
CH
2
CH
3
), 22.0 (C=OCH
3
3
)
2
2
2
3
2
7
6.7 (CCtrz), 149.4 (CCtrz), 156.6 (Ctrz-Au), 169.5 (C=O) HRMS (ESI+): m/z Found 494.0886
+
[
M + Na ] (calcd. for C12
H
21
N
3
O
2
ClAuNa, 494.0886) Anal. Calc. for C12
H
21
N
3
AuClO
2
: C,
3
0.55; H, 4.49; N, 8.91%. Found: C, 30.28; H, 4.31; N, 8.63%.
Complex 2c
AgBF (41 mg, 0.21 mmol) was added to a solution of 1c (0.18 g, 0.19 mmol) in dry
CH Cl /MeCN (30 mL, 1:1 v/v), an stirred with the exclusion of light under a N atmosphere
for 5 min. This mixture was treated with Ag O (27 mg, 0.12 mmol) and NMe Cl (26 mg, 0.24
mmol) and the reaction was stirred for 16 h in the dark. Then AuCl(SMe ) (56 mg, 0.19 mmol)
4
2
2
2
2
4
2
was added and the reaction stirred for a further 2 h. The reaction mixture was exposed to air
and the product was purified as described for 2a by repeated filtering through Celite, affording
1
complex 2c as a pale yellow solid (150 mg, 0.14 mmol, 75 %). H (500 MHz, CDCl
3
): δ 0.97
CH ),
), 4.82 (t, JHH = 6.8Hz,
3
(
t, JHH =7.3 Hz, 3H, CH
2
CH
3
), 1.39-1.47 (m, 2H, CH
2
CH
3
), 1.73-1.79 (m, 2H, CCH
2
2
3
3
2
2
3
4
1
1
2
.8-3.01 (m, CCH
2
, 6H, 2xNCH
2
CH
) C{ H}(126 MHz, CDCl
CH
2
), 4.62 (t, JHH = 7.1Hz, 2H, N3CH
2
1
3
1
H, N1CH
2
3
): δ 13.8 (CH
2
CH
3
) , 22.4 (CH
2
CH
), 31.6 (CtrzCH
), 158.5 (Ctrz-Au) F{ H}(470MHz, CDCl
26.27-(-126.12) (m, 4F), -123.4, -123.2 (2xbr, 2x2F), -122.9 (br, 4F), -121.97-(-121.79), -
3
) , 24.9 (CtrzCH
2
),
3
3
0.9 (t, JCF = 22.2 Hz, N3CH
2
2
), 31.3 (t, JCF = 20.1 Hz, N1CH
2
CH
2
2
CH
2
),
1
9
1
2.2 (N3CH
2
) , 47.7 (N1CH
2
), 146.7 (CtrzCH
2
3
: δ -
14.23-(-14.05) (2xm, 2x4F), -80.88-(-80.80) (m, 6F) Anal. Calcd for C22
5.17; H, 1.63; N, 4.00%. Found: C, 25.18: H, 1.30; N, 3.80%.
3
H17AuClF26N : C,
Complex 2e
1
7

Dalton Transactions
Page 18 of 27
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DOI: 10.1039/C6DT02181F
Triazolium salt 1e (87 mg, 0.9 mmol), Ag
2
O (29.8 mg, 0.13 mmol), and NMe
4
Cl (20.1 mg,
0
.18 mmol) were stirred in dry CH
2
Cl
2
2
/MeCN (10 mL, 1:1 v/v) under a N atmosphere, for 17
h with the exclusion of light. Volatiles were removed in vacuo, and the residue was suspended
in dry CH Cl (15 mL), and stirred with AuCl(SMe ) (54.9 mg, 0.19 mmol) in the dark for 2
h. The reaction mixture was filtered through Celite, eluted with CH Cl and all volatiles were
2
2
2
2
2
removed. The product was obtained as a white solid (65 mg, 0.12 mmol, 64 % yield). Crystals
1
were obtained by slow diffusion of dry Et
2
O into a CH
2
Cl
2
solution at –20°C. H (500 MHz,
3
3
CDCl
3
): δ 1.14 (d, JHH = 6.9Hz , 6H, CH(CH
3
)
2
3 2
), 1.34 (d, JHH = 6.9Hz , 6H, CH(CH ) ), 2.31
3
3
(
sept, JHH = 6.9Hz, 2H, 2xCH(CH
3
)
2
), 4.25 (s, 3H, NCH
3
), 7.31 (d, JHH = 7.8Hz, 2H, CDiIPr
1
3
1
H), 7.53-7.58 (m, 4H, CArH), 7.80-7.82 (m, 2H, CArH) C{ H}(126 MHz, CDCl
2 x CHCH ), 28.9 (CDiIPrH), 38.4 (NCH ), 124.4 (CArH), 126.0 (CPh), 129.4, 129.8, 130.7 (3 x
PhH), 131.6 (CArH), 135.2, 145.2 (2 x CAr), 146.8 (CtrzC), 162.1 (Ctrz-Au) Anal. Calcd for
25AuClN • ½ CH Cl : C, 43.45; H, 4.41; N,7.07%. Found: C, 43.28; H, 4.50; N, 6.79%.
3
): δ 24.2, 24.5
(
3
3
C
C
21
H
3
2
2
Complex 2f
The triazolium tetrafluoroborate 1f (77.5 mg, 0.27 mmol), NMe
Ag O (31.9 mg, 0.14 mmol) were stirred in CH Cl /MeCN (5 mL, 1:1 v/v) for 16 h protected
from light. To this mixture was added AuCl(SMe ) (79.5mg, 0.27 mmol) and stirring was
continued for 2 h. The suspension was filtered through Celite, eluted with CH Cl and the
volatiles were removed under reduced pressure yielding the crude product as an off-white solid
98 mg 23 mmol, 88%). Crystals were grown by slow evaporation of a CH Cl /Et O solution
), 1.33-1.43 (m, 2H,
), 4.29 (s, 3H, NCH ), 4.47 (t,
), 21.2 (CH CH ), 32.6, 32.7
), 151.7 (CtrzC), 155.2 (Ctrz-Au).
4
Cl (29 mg, 0.26 mmol), and
2
2
2
2
2
2
(
2
2
2
1
3
of 2f. H (400 MHz, CD
2
Cl
2
): δ 0.97 (t, JHH = 7.4 Hz, 3H, CH
) 1.99-2.06 (m, 2H, NCH CH
Cl ): δ 13.8 (CH CH
), 56.2 (NCH
2 3
CH
CH
2
CH
3
), 1.89 (s, 6H, C(CH
3
)
2
2
2
3
3
13
1
J
HH = 7.3 Hz) C{ H}(101MHz, CD
2
2
2
3
2
3
(
NCH CH and C(CH ), 41.0 (NCH
2
2
3
)
2
3
2
Complex 2g and 2g’
A suspension of the triazolium tetrafluoroborate 1f (100 mg, 0.35 mmol), Ag
mmol), NMe Cl (80 mg, 0.73 mmol), and activated molecular sieves in dry CH
was stirred under the exclusion of light for 3 days, under a N atmosphere. AuCl(SMe
2
O (80 mg, 0.35
Cl (25 mL)
) (103
4
2
2
2
2
mg, 0.35 mmol) was added and the reaction stirred for 2 h. The reaction mixture was then
filtered through Celite, and all volatiles were removed under reduced pressure, which yielded
2
g as a pale yellow solid (37 mg, 0.10 mmol, 28 % yield). Crystals were grown by slow
1
8

Page 19 of 27
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evaporation of CH
triazolium triflate analogue of 1f. H (400MHz, CDCl
.44 (m, 2H, CH CH ), 1.89-1.98 (m, 2H, NCH CH ), 4.20 (s, 3H, NCH
Hz, 2H, NCH ), 7.57 (s, 1H, CtrzH) C{ H}(101MHz, CDCl ): δ 13.4 or 13.6 (CH
), 31.6 (NCH CH ), 42.1 (NCH ), 52.5 (NCH ), 133.6 (CtrzH), 158.4 (Ctrz-Au). 2g H
400 MHz, CDCl ): δ 0.94-1.01 (m, 3H, CH
), 4.17 (s, 3H, NCH
): δ 13.4 or 13.6 (CH
), 134.7 (CtrzH), 157.7 (Ctrz-Au) Anal. (%):Found: C, 23.66; H, 3.55; N,
13AuClN : C, 22.62; H,3.53; N,11.31.
2 2
DOI: 10.1039/C6DT02181F
Cl . The same result was obtained when the reaction was started from the
1
3
): δ 0.94-1.01 (m, 3H, CH
2
3
CH ), 1.32-
3
1
2
3
2
2
3
), 4.38 (t, JHH = 7.3
1
3
1
2
3
2 3
CH ), 19.7
’
1
(
(
CH
2
CH
2
2
2
3
2
3
2
CH
3
), 1.32-1.44 (m, 2H, CH
2
CH
), 7.58 (s, 1H, CtrzH)
), 32.4 (NCH CH ), 38.8
3
), 1.99-2.06 (m,
3
2
H, NCH
2
CH
2
3
), 4.50 (t, 2H, JHH = 7.3 Hz, NCH
2
1
3
1
C{ H}(101 MHz, CDCl
3
2
CH
3
), 19.7 (CH
2
CH
3
2
2
(NCH
3 2
), 55.4 (NCH
1
1.08; Calcd for C
7
H
3
Compound 3a
Neat MeOTf (12.5 µL, 0.11 mmol) was added to a solution of 2a (40 mg, 0.094 mmol) in dry
MeCN (2 mL), and the reaction mixture stirred protected from light for 5 min. PPh (31 mg,
.12 mmol) was added, and the reaction stirred for a further 15 min. The solvent was removed
in vacuo, and the residue was purified by dissolving the product in CH Cl and precipitation
with pentane, followed by drying in vacuo. Complex 3a was obtained as a white solid in
quantitative yield (76 mg, 0.095 mmol). Crystals were grown by slow diffusion of Et O into a
CH ), 0.92
), 1.79-1.87 (m, 2H,
), 2.90 (t, JHH = 7.8 Hz, 2H, CTrzCH ), 4.18 (s, 3H,
), 7.44-7.54 (m, 12H, CArH), 7.54-7.59 (m, 3H, CArH)
): δ 13.6 (N(CH CH ),13.9 (CTrz(CH CH ), 19.9 (N(CH CH ),
), 24.7 (CTrzCH ), 31.7 (CCH CH ), 32.9 (NCH CH ), 37.2 (NCH ), 55.5
), 129.7 (d, JPC = 11.0 Hz, CArH), 132.1 (d, JPC = 2.2 Hz, CArH), 134.1 (d, JPC = 14.2 Hz,
3
0
2
2
2
1
3
CH
2
Cl
2
solution of 3a. H (400 MHz, CDCl
3
): δ 0.88 (t, JHH = 7.3 Hz, 3H, C(CH
2
)
3
3
3
(
t, JHH = 7.3 Hz, 3H, N(CH
2
)
3
CH ), 1.32-1.49 (m, 4H, CH
3
2
CH
3
3
C
TrzCH
2
CH
2
), 2.00-2.08 (m, 2H, NCH
2
CH
2
2
3
NCH
3
), 4.46 (t, JHH = 7.3 Hz, 2H, NCH
2
1
3
1
C{ H}(101 MHz, CDCl
3
2
)
3
3
2
)
3
3
2
)
2
2
2
2.5 (CTrz(CH
2
)
2
CH
2
2
2
2
2
2
3
(NCH
2
3
1
1
19
1
C
ArH), 149.9 (CtrzC), 172.0 (Ctrz-Au) P{ H}(162 MHz,CDCl
3
): δ 39.4 (br) F{ H} (282
+
MHz, CDCl
3
): δ -78.12 (s) HRMS (ESI+): m/z Found 654.2339 [M – OTf] (calcd. for
29 36 3
C H N
PAu, 654.2312)
Catalytic procedures
General Procedure for the Catalytic Synthesis of Oxazolines. To a solution of 4-
bromobenzaldehyde (290 mg, 1.57 mmol) and trimethoxybenzene (60. mg, 0.36 mmol, internal
2 2
standard) in CH Cl (4 mL) in thick walled 5 mL vail was added methyl isocyanoacetate (130
1
9

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2
µL, 1.43 mmol), followed by NiPr Et (25 µL, 0.14 mmol), complex 2 (14 µmol), and the
DOI: 10.1039/C6DT02181F
additive according to Table 2 (28 µmol). The vial was sealed, protected from light, and heated
1
to 40° C in an oil bath. Conversions and cis/trans ratios were monitored by H NMR
3
7
spectroscopy in CDCl
For reactions involving 1.1 mol% and 2 mol% MeOTf, a solution of MeOTf (0.265 M in dry,
degassed CH Cl ) was used and added before NiPr Et. The volume of CH Cl was adjusted to
a total reaction volume of 4 mL.
3
and compared to previously reported literature values.
2
2
2
2
2
General procedure for catalytic carbene transfer of EDA to benzene. Under a N
2
atmosphere and protected from light, anhydrous benzene (3 mL) was added to a Schlenk flask
F
containing 2 (12 µmmol). Then EDA (53 µL, 0.44 mmol) was added and either NaBAr
4
(13.7
mg, 15 µmol) or the appropriate silver salt (13 µmol, see Table 3). The reaction was monitored
by GC at 3–5 h and 20–24h. After 24 h, the reaction was filtered, concentrated, and analysed
1
30c,38
by H NMR spectroscopy (CDCl
3
solution).
For runs with 2c, the quantities were lower:
F
2
a (6.1 mg, 5.8 µmol), benzene (2 mL), EDA (25 µL, 0.21 mmol) and NaBAr
µmol).
For experiments probing the carbene transfer to styrene, the experimental procedure was
4
(7.6 mg, 8.6
3
0c,39
identical to that described above,
2 2
except benzene was replaced by a mixture of CH Cl (2
mL) and styrene (267 µL, 2.3 mmol).
Crystal structure determinations. Crystal data for 2b,f,g, and 3a were collected using a
Rigaku (former Agilent Technologies) Oxford Diffraction SuperNova A diffractometer fitted
α
with an Atlas detector and using monochromated Mo–K radiation (0.71073 Å). A complete
dataset was collected, assuming that the Friedel pairs are not equivalent. The intensities were
corrected for Lorentz and polarisation effects, and a numerical absorption correction based on
Gaussian integration over a multifaceted crystal model was applied. The structures were solved
2
by direct methods using SHELXS-97 and refined by full-matrix least squares fitting on F for
4
0
all data using SHELXL-97. Hydrogen atoms were added at calculated positions and refined
by using a riding model. Anisotropic thermal displacement parameters were used for all
nonhydrogen atoms. Further crystallographic details are compiled in Tables S5–S8.
Crystallographic data for all four complexes have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC 1481152 (2b), 1481154
(
2f), 1481151 (2g), and 1481153 (3a).
2
0

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DOI: 10.1039/C6DT02181F
Supporting Information
Synthesis of all novel triazoles and triazolium salts, NMR spectra of 2c, tables of catalytic runs
and crystallographic details.
Acknowledgements
This work was financially supported by the European Research Council (CoG 615653), the
European Science Foundation (COST Action CM 1205), MINECO (CTQ2014-52769-CO3-1-
R), the Junta de Andalucía (P10-FQM-06292), Ryerson University (R.A.G.), and the Irish
Research Council through a fellowship to. R.P. We thank Dr. D. Conseco-Gonzales for the
synthesis of complex 2e. We thank the group of Chemical Crystallography of the University
of Bern (PD Dr. P. Macchi) for the X-ray structure solution of 2f and the Swiss National
Science Foundation (R'equip project 206021_128724) for co-funding the single crystal X-ray
diffractometer at the department of Chemistry and Biochemistry of the University of Bern
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Table of contents entry:
Novel triazolylidene gold(I) complexes were synthesized and activated by silver-free
methodologies to generate catalysts for oxazoline synthesis and the C–H activation of arenes.
2
7