Gold(I) Complexes Stabilized by Nine- and Ten-Membered N-Heterocyclic Carbene Ligands

Article abstract of DOI:10.1002/chem.201902458

Nine- and ten-membered N-heterocyclic carbene (NHC) ligands have been developed and for the first time their gold(I) complexes were synthesized. The protonated NHC pro-ligands 2 a–h were prepared by the reaction of readily available N,N′-diarylformamidines with bis-electrophilic building blocks, followed by anion exchange. In situ deprotonation of the tetrafluoroborates 2 a–h with tBuOK in the presence of AuCl(SMe₂) provided fast access to NHC-gold(I) complexes 3–10. These new NHC-gold(I) complexes show very good catalytic activity in a cycloisomerization reaction (0.1 mol % catalyst loading, up to 100 % conversion) and their solid-state structures reveal high steric hindrance around the metal atom (%V_bur up to 53.0) which is caused by their expanded-ring architecture.

Full text of DOI:10.1002/chem.201902458

A Journal of
Accepted Article
Title: Gold(I) Complexes Stabilized by Nine- and Ten-Membered N-
Heterocyclic Carbene Ligands
Authors: Alejandro Cervantes Reyes, Frank Rominger, Matthias
Rudolph, and A. Stephen K. Hashmi
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Chemistry - A European Journal
10.1002/chem.201902458
Gold(I) Complexes Stabilized by Nine- and Ten-Membered N-Heterocyclic
Carbene Ligands
[
a]
[a],[+]
[a]
Alejandro Cervantes Reyes, Frank Rominger,
Hashmi*[a,b]
Matthias Rudolph, A. Stephen K.
[
a] M. Sc. A. Cervantes-Reyes, Dr. F. Rominger, Dr. M. Rudolph, Prof. Dr. A. S. K.
Hashmi
Organisch-Chemisches Institut
Heidelberg University
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: (+49)-6221-54-4205
E-mail: hashmi@hashmi.de
Homepage: http://www.hashmi.de
[b] Prof. Dr. A. S. K. Hashmi
Chemistry Department, Faculty of Science
King Abdulaziz University, Jeddah 21589, Saudi Arabia
[+] Crystallographic investigation
Keywords: gold, carbene, expanded-ring, NHC, ligands
Abstract
Nine- and ten-membered N-heterocyclic carbene (NHC) ligands have been developed
and for the first time their gold(I) complexes are synthesized. The protonated NHC pro-
ligands 2a-h were prepared by the reaction of readily available N,N’-
diarylformamidines with bis-electrophilic building blocks, followed by anion exchange.
In-situ deprotonation of the tetrafluoroborates 2a-h with tBuOK in the presence of
AuCl(SMe
gold(I) complexes show very good catalytic activity in a cycloisomerization reaction
0.1 mol% catalyst loading, up to 100% conversion) and their solid-state structures
2
) provided fast access to NHC-gold(I) complexes 3-10. These new NHC-
(
reveal high steric hindrance around the metal atom (%Vbur up to 53.0), that is caused
by their expanded-ring architecture.
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Introduction
The chemistry of N-heterocyclic carbenes (NHC) has become a major area of
research, since these stable carbenes have proven to be outstanding ligands for
[
1]
transition metals. These ligands also offer certain advantages, such as their thermal
stability, low toxicity and stability against oxidation, enabling their application in many
different classes of metal-mediated reactions.[2] Among them, NHC-gold(I)
complexes[3] have shown good catalytic activities[4] in the activation of alkynes or
alkenes for nucleophilic additions, leading to cyclizations, cycloadditions, or
heteroatom additions.[5,6] Overall, homogeneous gold catalysis has become an
important tool in all fields of synthetic organic chemistry as one of the fast-growing
sectors of modern chemistry.[7] Accordingly, the development of NHC ligands for
gold(I)[7h] is an important goal, given the strong σ-donating capability of these species,
to which the different reactivity and selectivity of the gold(I) complexes can be
ascribed.[8, 9]
Figure 1. Milestones in the development of NHC-gold(I) complexes with NHC rings
containing more than five atoms.
In the last few years, the synthesis and application of a new type of NHC ligands,
containing a backbone ring with more than five atoms, has emerged.[10] These
expanded-ring NHC ligands demonstrated unique steric and electronic properties in
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comparison to the traditional five-membered counterparts.[11] Complexes of this class,
with a broad variety of metal atoms (e.g. Cu, Ni, Fe, Pd, Pt, Ir, Rh, Ga, In) can be found
in the current literature.[11b,12] Nevertheless, only a few expanded-ring NHC-gold(I)
complexes have been presented up to now (Figure 1).[9,11a,13,14] To the best of our
knowledge, no NHC-gold(I) complexes with a ring size larger than eight have been
reported to date, thus their chemistry represents an intriguing field to be explored.
In this contribution we report the synthesis of the first nine- and ten-membered ring
NHC ligands featuring biphenyl and diphenyl ether moieties at the backbone, and the
preparation of their gold(I) complexes. The structural characteristics of both NHC salts
and metal complexes are investigated, and a preliminary survey of the catalytic activity
of gold(I) complexes 3-10 on the cycloisomerization of a N-propargyl carboxamide is
presented.
Results and Discussion
expanded-ring NHC pro-ligands
Various reaction conditions have been previously reported for the synthesis of six- and
seven-membered protonated NHC salts, including the classic ring-closure of a
disubstituted alkyl- or aryl-amino moiety with a pre-carbenic unit (e.g. HC(OEt) or
3
formaldehyde).[15] Despite the good yields, those conditions are limited with regard to
the bulkiness of the N-substituted backbone. Larger eight-membered ring NHC salts
have been synthesized by the reaction of a functionalized formamidine with a
dihaloalkane moiety, typically in the presence of a base in a polar solvent.[10,1c,4] In
pursuit of these reported protocols, we envisioned that the new NHC pro-ligands with
expanded backbone might be generated via formamidine ring-closure. Therefore, this
approach was employed to synthesize the amidinium salts 1a-h starting from
dibromoalkane I and a series of N,N’-diarylformamidines II (Scheme 1).
Scheme 1. Synthetic strategy for the synthesis of NHC pro-ligands 1a-h.
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Our initial experiments followed well-known literature methods; for instance, employing
reaction conditions reported by Jazzar et. al. (n-BuLi/hexane, THF, r.t.)[1b] and
Kolychev et. al. (DIPEA, DMF, 120°C),[16] the expected nine- and ten-membered cyclic
amidinium bromides could not be obtained. By refluxing a mixture of Dibromide I and
N,N’-dimesitylformamidine, in presence of K
Iglesias et. al.,[1c] we obtained the desired amidinium bromides, but in low yields
<12%). Recently Huynh et. al.[12e] synthesized various eight-membered NHC salts by
2
CO
3
in CH
3
CN for 24 h, as reported by
(
isolating the monoalkylated synthetic intermediates (compound A in Table 1) and
conducting the cyclization of the medium-sized eight-membered ring in a second step
however, despite the addition of NaI to accelerate the reaction, yields were not
significantly improved. Guided by those observations, we decided to increase the
-1
reaction time and work in diluted solutions (0.005 mol·L ) for the challenging synthesis
of the nine- and ten-membered rings; first at room temperature and then under
conventional heating, to induce a full consumption of the dibromide. The yields
increased considerably with this optimized procedure (45–84%, Table 1).
Table 1. Synthesis of amidinium bromides 1a-h
Ar
Y
none
O
Product
Yield (%)[a]
[(9-Mes)H][Br] 1a
[(10-Mes)H][Br] 1e
[(9-Dipp)H][Br] 1b
[(10-Dipp)H][Br] 1f
[(9-Xyl)H][Br 1c
69
48
54
45
84
48
66
51
2
,4,6-trimethylphenyl
none
O
2
,6-diisopropylphenyl
none
O
2
,6-dimethylphenyl
[(10-Xyl)H][Br] 1g
[(9-Dietph)H][Br] 1d
[(10-Dietph)H][Br] 1h
none
O
2
,6-diethylphenyl
[a] Reaction conditions: Dibromoalkane I (1.1 mmol), N,N-diarylformamidine II (1.0
mmol, 1.0 equiv), K CO (1.0 equiv), CH CN (400 mL), r.t. 24 h, then 85°C, 3-4 days.
2
3
3
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In general, the yields of the nine-membered NHC salts (1a-d, 54%–84%) are notably
higher than those of the ten-membered ones (1e-h, 45%–51%). The less sterically
hindered representative (1e, 84%) is obtained in a higher yield than the sterically more
hindered one (1b, 54%). The resulting bromides 1a-h are air-stable colorless to slightly
colored solids that can be easily purified by recrystallization and stored without
precautions for weeks.
Anion exchange at 1a-h with NaBF in an acetone:water mixture smoothly produced
4
the tetrafluoroborates 2a-h in excellent yields (Table 2). Tetrafluoroborate anion has a
lower ability to coordinate to the amidinium proton than bromide,[1c] presumably since
the bromide anion is bonded to the amidinium proton through a hydrogen bond,[12d]
and thus, the subsequent deprotonation reaction takes place more efficiently. The
resulting tetrafluoroborate salts are usually colorless solids and no further
recrystallization is needed. In some cases, crystalline salts can be observed due to
presence of residual water from the reaction media. To purify these, the crude material
can be re-dissolved in CH
2
Cl
2
and dried over Na
2
SO .
4
Table 2. Preparation of tetrafluoroborates 2a-h by anion exchange.[a]
Product
Yield (%)
Product
2e
Yield (%)
2a
2b
2c
2d
94
94
92
95
91
86
86
87
2f
2g
2h
[
a] Reaction conditions: Amidinium bromide 1a-h (1.0 mmol) in acetone (100 mL),
NaBF (660 mg, 6.0 equiv) in water (75 mL), r.t, 45 min.
4
1
13
1
An inspection into the H NMR and C{ H} NMR signals of amidinium salts 1a-h and
a-h, offers relevant information about these new class of NHC pro-ligands (Table 3).
2
On one hand, a trend in upfield shift of the proton resonance is observed when
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increasing the heterocycle ring size from nine (8.17–8.54 ppm) to ten (7.26–7.73 ppm).
This implies that the amidinium proton in the ten-membered ring NHC salts is less
acidic than that of its nine-membered analogues, which agrees with previous
observations made by Cavell and co-workers for six- and seven-membered ring NHC
salts.[10,12h,13c] On the other hand, a similar trend is noted in the carbon resonance
whose 13C{ H} NMR signals reveal an upfield shift when the heterocycle ring size
increases from nine (164.2–165.6 ppm) to ten (156.9–157.7 ppm).
1
1
Finally, the anion exchange was also confirmed by H NMR. The signals of compounds
2a-d are notably displaced upfield (7.25–8.03 ppm) relative to their precursors 1a-d
(7.26–8.54 ppm) which also is an evidence of the diminished acidity of the amidinium
proton. Displacement of proton resonance is almost unnoticeable in 2e and 2g (<0.01
ppm). The signals of the amidinium carbon are essentially unaltered after anion
exchange (<0.3 ppm).
1
13
1
[a]
Table 3. H and C{ H} NMR shifts of NHC-HX salts 1a-h and 2a-h
1H NMR shift N-CH-C
13
C{ H} NMR shift
1
1
2
X = BF
7.81
1
2
Substrate
X = Br-
8.45
7.26
8.46b
7.40
8.54
7.29
8.17c
7.73
-
X = Br-
165.6
157.7
164.4
156.9
165.5
157.4
164.2
157.3
X = BF
165.0
157.9
163.6
157.4
165.7
157.6
164.1
157.5
-
4
4
[
(9-Mes)H]+
(10-Mes)H]+
(9-Dipp)H]+
(10-Dipp)H]+
(9-Xyl)H]+
(10- Xyl)H]+
(9-Dietph)H]+
(10-Dietph)H]+
a
e
b
f
[
7.25
[
7.91b
7.46d
8.03
[
[
c
g
d
h
[
7.30
[
7.84c
[
7.29
[a] Values are given in ppm. Unless other stated, values were determined in CDCl
3
at
1
13
1
1
4
00 MHz ( H) and 101 MHz ( C{ H}). [b] Determined in CDCl
3
at 500 MHz ( H) and
1
3
1
1
13
1
1
26 MHz ( C{ H}). [c] Determined in CDCl
Cl
3
at 600 MHz ( H) and 151 MHz ( C{ H}).
[
d] Determined in CD
2
2
.
Single crystals suitable for X-ray crystal structure analysis of 1b, 1c, 1f and 1g were
obtained by slow diffusion of hexane, into concentrated solutions of the compound in
CH
2
Cl
2
or CHCl
3
, followed by evaporation of solvents at room temperature, typically
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after one day. The solid-state structures show a wide N-CH-N angle (127.2–134.5°)
Figure 2).[17]
(
Figure 2. Molecular structure (ORTEP representation) of bromides 1b (top left), 1f (top
right), 1c (bottom left) and 1g (bottom right) in the solid state. Thermal ellipsoids are
shown at 50% probability level. Bromide anion and all hydrogen atoms have been
omitted for clarity.
NHC-gold(I) complexes
Despite several attempts employing various reaction conditions, efforts to isolate the
free carbene species were unsuccessful.[18] Instead, a mixture of starting material
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10.1002/chem.201902458
and/or decomposition products were observed by NMR analysis of the resulting solids
or the crude reaction mixtures. To circumvent these problems, we investigated the
reaction of tetrafluoroborate salts in in-situ deprotonation in presence of AuCl(SMe ),
2
as the method to directly access the NHC-gold(I) complexes (Table 4).
The
treatment
of
selected
substrates
with
recurrently
employed
bis(trimethylsilyl)amides (e.g. NaHMDS, LiHMDS) gave only traces of product as
judged by TLC (entries 1–3, 5, 8). Interestingly, small quantities of the desired gold(I)
complex were isolated when (9-Dipp)HBF
4
2b, reacted with KHMDS (entry 4). Other
CO ) were unable to deprotonate to the
examined bases (MeONa, NaH, Et N, K
3
2
3
substrate under the explored conditions (entries 9, 10, 21 and 22) instead, a purple to
dark solid corresponding to colloidal gold, appeared.
Table 4. Screening of conditions for the synthesis of NHC-gold(I) complexes
Entry
Substrate
2a
Base
LiHMDS[d]
LiHMDS
KHMDS
KHMDS
NaHMDS[d]
KHMDS
LiHMDS
KHMDS
MeONa
NaH
Conditions[a, b]
Yield(%)[c]
traces
traces
traces
12
1
2
3
4
5
6
7
8
9
-40°C
2a
-78°C
2a
-40°C
2b
-78°C
2b
-78°C
traces
N.R
2f
-78°C
2e
-78°C
N.R
2e
-78°C
traces
N.R
2b
0°C
10
11
12
13
14
15
16
17
2b
0°C
N.R
2b
NaH
0°C, tBuOK 10 mol%
8
2f
NaH
0°C, tBuOK 10 mol%
traces
15
2b
tBuOK
0°C
0°C
2b
tBuONa[e]
tBuONa[e]
tBuOK
10
2b
-40°C
-40°C
-78°C
19
2b
21
2b
tBuOK
31
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18
19
20
21
22
23
2a
2a
2f
tBuOK[d]
tBuOK[d]
tBuOK[d]
-40°C
-78°C
27
42
-78°C
38
2f
Et
3
N
0°C, DCM, open-air
60°C, acetone, open-air
60°C, acetone, open-air
N.R
N.R
N.R
2b
2f
K
2
2
CO
CO
3
3
K
[
a] Reaction conditions: Tetrafluoroborate salt (0.1 mmol, 1.0 equiv), [AuCl(SMe
mmol, 1.0 equiv), Base (1.0 equiv), THF (10 mL); Excluding Et N, all bases were
employed as solids directly from the containing bottle. [b] Unless other stated,
reactions were carried out under an inert atmosphere of N using dry THF. [c] Isolated
yields are presented. [d] 1.0 M in dry THF (commercially available) was employed. [e]
.0 M in dry THF (commercially available) was employed.
2
)] (0.1
3
2
2
When tBuOK was employed as an additive to NaH (entry 11), isolable quantities of
gold(I) complex 2b (8%) were obtained. An equivalent quantity of tBuOK gave 15%
when used under same conditions (entry 13). The experiment at -40°C increased the
yield to 21% (entry 16) while the reaction at -78°C yielded 31% of the gold(I) complex
(
entry 17). The employment of a solution of tBuONa also showed a promising result
19% yield, entry 15) relative to that using solid tBuOK under same conditions (21%
(
yield, entry 16). When using a solution of tBuOK, 27% yield at -40°C (entry 18) and
2% yield at -78°C (entry 19), could be achieved. These preliminary observations
4
indicated that an environment free of possible contaminants (water, KOH or tBuOH),
as well as temperature below -40°C, are optimal factors for the generation and stability
of the carbene in the reaction media, and thus, determine the NHC-gold(I) formation.
With this set of experiments, we partially concluded that tBuOK is a feasible
deprotonating agent for the current NHC salts 2a-h.
Table 5. Optimization of the synthesis of NHC-AuCl complexes
Entry
1
Variation of the stated conditions
none
Yield(%)[a]
35
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2
3
4
5
6
7
-40°C to r.t, 0.2 mmol tBuOK
0.20 mmol tBuOK
28
44
45
52
58
67
65
0.30 mmol tBuOK
0.15 mmol 2a, 0.20 mmol tBuOK
0.20 mmol 2a, 0.20 mmol tBuOK[b]
0.20 mmol 2a, 0.30 mmol tBuOK[b]
8
0.20 mmol 2a, 0.30 mmol tBuOK, 40 mg 4Å MS additive.
[
a] Isolated yield. [b] 1.0 M in dry THF (commercially available) was employed.
The original conditions afforded 35% of complex 3 (entry 1). When the quantity of
tBuOK was doubled and temperature lowered to -40°C, the yield dropped to 28% (entry
2). A slight improvement was observed when maintaining the initial temperature in -
78°C and using 0.20 mmol of base (44%, entry 3). Increasing the ratio of tBuOK (0.3
mmol, 3.0 equiv, entry 4), did not considerably impact on the yield (45%). Increasing
the quantity of substrate 2a to 0.15 mmol in the presence of 0.20 mmol tBuOK gave a
comparatively good result (52%, entry 5). A slight rise in the yield was achieved (58%)
when employing 0.20 mmol of both substrate 2a and tBuOK in solution (entry 6).
Furtherly, increasing the quantity of tBuOK to 0.30 mmol, presented an improved yield
(
67%, entry 7). Moreover, with the employment of solid tBuOK and freshly activated 4
Å molecular sieves as an additive, the reaction also occurred in good yield (65%, entry
). Thus, the reaction conditions presented in the entries 7 and 8 (Table 5) seemed to
8
be the optimal for the synthesis of further examples of NHC-gold(I) complexes using
the salts 2a-h. To our delight, the representative series of gold(I) complexes 3-10,
bearing the newly developed NHC ligands, could be successfully synthesized (Figure
3
).
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Figure 3. First examples of nine- and ten-membered-ring NHC-gold(I) complexes.
Regardless of the inert conditions and the use of degassed solvent or molecular sieves
as additive, the work-up procedure can be performed under open-air conditions at
room temperature since the gold(I) complexes are very stable solids. Through this
straightforward approach, the direct complexation of the gold(I) with the free carbene
in solution, led to the desired NHC-gold(I) complexes in good yields and purity, making
the overall synthesis a one-step process in-lieu of the classical procedure (isolation of
the free carbene and subsequent reaction with a metal source).[6b]
Analysis of the compounds by 1H NMR spectroscopy reveals the disappearance of the
characteristic amidinium proton between 7.29–8.03 ppm in accordance with gold(I)
1
3
complex formation. In the C NMR spectra, the chemical shifts for the carbene carbon
atoms (N-CNHC-N) are found between 208.9–214.8 ppm (Table 6). These values are
significantly shifted downfield (~50 ppm), relative to that of the amidinium carbon peak
1
3
1
(
N-CH-N) of the starting precursors ( C{ H} NMR peaks: 157.4–165.7 ppm, Table 2)
which confirms the complex formation. This new series of NHC-gold(I) complexes
show a N-CNHC-N signal evidently less shielded by more than ∆δ 7 ppm in the spectra,
1
3
when compared to examples reported in the literature (Table 6, entries 1–5). C NMR
signals of nine-membered NHC complexes (211.7–214.8 ppm) are slightly more
deshielded than the ten-membered ones (208.9–210.3 ppm).
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1
3
Table 6. C NMR displacement shifts of carbene carbon (N-CNHC-N) in complexes 3-
0 and selected examples found in literature.
1
Entry
Complex
Au(IPr)Cl
Reference
[19]
C
NHC (ppm)
175.9
192.6
193.1
200.9
201.7
211.9
212.6
214.8
211.7
209.3
210.3
208.9
209.9
1
2
3
4
5
6
7
8
9
Au(6-Mes)Cl
Au(7-Dipp)Cl
Au(6-Dipp)Cl
Au(7-Dietph)Cl
Au(9-Mes)Cl
Au(9-Dipp)Cl
Au(9-Xyl)Cl
[11a]
[11a]
[14]
[13a]
3
This work
This work
This work
This work
This work
This work
This work
This work
4
5
6
7
8
9
Au(9-Dietph)Cl
Au(10-Mes)Cl
Au(10-Dipp)Cl
Au(10-Xyl)Cl
10
11
12
13
Au(10-Dietph)Cl 10
The structures of complexes 3, 4, 6 and 7 were confirmed by X-ray crystallography
Table 7). Single crystals were grown by layering pentane into a solution of the gold(I)
(
complex at room temperature followed by slow evaporation of solvents. The crystal
structures do not show any aurophilic interactions (Au–Au) and were found to adopt a
relative common spatial conformation. An inspection into the angles and bond
distances revealed some insightful characteristics. As can be seen from Table 7, the
four complexes show the two-coordinated gold(I) atom in a nearly linear arrangement,
with CNHC–Au–Cl bond angles close to 180° (175.39(7)–179.46(8)°). The CNHC–Au
bond lengths range from 1.991(6) to 2.007(6)Å and fall within the range of previously
reported values found in other essentially comparable compounds such as Au(7-
Dipp)Cl (2.01 Å),[11a] Au(6-Dipp)Cl (2.01 Å),[14] Au(6-Mes)Cl (1.99 Å)[11a] or Au(IPr)Cl
(
1.94 Å).[19]
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Table 7. X-ray structure of complexes 3, 4, 6 and 7,[17] and their corresponding
Topographic Steric Maps (TSM).[20, 24]
[a] Ellipsoids are shown at 50% probability level with all hydrogen atoms and solvent
molecules omitted for clarity. [b] Only one of the two symmetry-independent molecules
in the unit cell is shown for clarity.
A notable change is the decrease in the N-CNHC-N angle upon coordination of the NHC
ligand. For instance, the N-CH-N angle of amidinium bromide 1b changes from
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1
27.1(3)° to 117.2(5)° in the gold(I) complex 4. The wider angle is observed in the ten-
membered-ring complex 7 (119.5(2)°) which is ca. 0.9° larger than that of complexes
and 6 (with angles 118.6(2) and 118.6(5)°) and ca. 2.3° than that of complex 4
117.2(5)°), that possess a nine-membered NHC ligand. If compared to other NHC-
3
(
gold(I) complexes found in literature, the N-CNHC-N angles of 3, 4 and 6 are evidently
larger than those in Au(IPr)Cl (102.4°)[19] and Au(IMes)Cl (107.0°),[21] but similar to
those of the six-membered counterparts Au(6-Dipp)Cl (119.0°)[14] and Au(6-Mes)Cl
(
118.6°).[11a] To our surprise, the major difference in the structures of complexes 3, 4,
6
and 7 is that the N-CNHC-N angles are significantly smaller than that found in complex
Au(7-Dipp)Cl (121.2°).[11a]
Figure 4. Torsional angle α° in expanded-ring NHC complexes.
The torsional angle α° between the planes, defined by the CAr–N···N–CAr atoms (Figure
4
), was introduced by Iglesias et. al.[1c,12j] as a measurement of the spatial twist and
the relative position of the aromatic substituents, which point into the metal’s
coordination sphere. The torsional angle α found in complex 3 is 39.3° while in 7 it is
52.4°. Complex 6 exhibits the most pronounced twisting ( = 53.6°). The relative
orientation of aryl substituents in 4 ( = 48.2°) places one of the isopropyl groups of
each aryl substituent slightly away from the metal center.
A closer inspection of the biphenyl and diphenyl ether backbones offered some
interesting characteristics. In 7 the angle CAr-O-CAr’ is 120.2°, while the angle between
the phenyl ring planes PL1 and PL2, is 69.9° (with PL1 = C1Ar···C6Ar and PL2 =
C1Ar’···C6Ar’). This value is smaller than that observed by least-squares in either of the
two crystallized forms of diphenyl ether molecule that showed angles of 87.6–88.4°
between the phenyl ring planes PL1 and PL2[22] indicating a highly strained
conformation, upon NHC formation. Torsion angles, formed by intersection of the two
aryl planes in the backbone of complexes 3, 4 and 6, were found to be 54.6°, 48.7°,
and 57.0°, respectively.
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The percent of buried volume (%Vbur)[23] and topographic steric map (TSM)[20,24] have
emerged as molecular descriptors of the spatial distribution of steric bulk in N-
heterocyclic carbenes. Using the method developed by Cavallo,[25] we have derived
topographic steric maps and %Vbur values for the ligands (Table 7). As can be
expected, complex 4 possessing diisopropylphenyl substituents at the arms is the
more sterically hindered example (%Vbur 53.0). Nonetheless, its TSM reveals some
unfilled space and a heterogeneous steric distribution. Complexes 3 and 7 exhibit the
same %Vbur values (43.6) and share a basically common steric distribution around
the metal atom. Complex 6 shows a slightly higher %Vbur value (48.4) but its TSM
showed a non-uniform steric distribution towards the gold(I) center. In order to gain
insight into the steric characteristics of the current gold(I) complexes, we made a brief
comparison with other related NHC complexes bearing expanded-ring cores and
bulkier ligands (Table 8).
Table 8. %Vbur values of some previously reported NHC-AuCl complexes[a]
Entry
Complex
Au(6-Mes)Cl
Au(7-Dietph)Cl
Au(9-Mes)Cl 3
Au(10-Mes)Cl 7
Au(IPr)Cl
Reference
[11a]
%Vbur
42.2
43.3
43.6
43.3
45.6
48.4
49.4
50.4
50.8
51.3
51.5
52.6
53.0
1
2
3
4
5
6
7
8
9
[13a]
This work
This work
[19]
Au(Dietph)Cl 6
Au(IPent)Cl
This work
[26]
Au(IPr*)Cl
[27]
Au(6-Dipp)Cl
Au(INon)Cl
[14]
10
11
12
13
[28]
Au(IHept)Cl
[28]
Au(7-Dipp)Cl
Au(9-Dipp)Cl 4
[11a]
This work
[
a] %Vbur values were taken directly as reported or from CIF files available in CCDC
using SambVca 2.0[25a, c]
Notably, the five-membered NHC-gold(I) complexes bearing the bulky IPr, IPent and
IPr* (entries 5, 7 and 8) possess higher %Vbur values (45.6–50.4) relative to complexes
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3
and 7 (entries 3 and 4), both with a %Vbur value of 43.6. Moreover, they all are still
smaller than those complexes with 6-Dipp and 7-Dipp ligands with %Vbur values of 50.8
and 51.6 respectively (entries 9 and 10). To the best of our knowledge, the complex 4
has the largest %Vbur value of any expanded-ring NHC-AuCl complex reported to date,
surpassing the %Vbur 52.6 of Au(7-Dipp)Cl reported by Dunsford et. al.[11a] (entry 12).
While the alkyl chain-containing cores of six- to eight-membered-ring NHC ligands, can
adopt flexible conformations, leading to less predictable features,[11a] the presence of
a relatively rigid biphenyl and diphenyl ether moieties at the backbone ring, can
contribute to the structural stability of the metal complexes. This pattern also might
establish certain limits for the construction of larger and rigid ring systems of similar
nature (i.e. eleven-membered NHC ligands).
In general, the metal complexes 3-10 are easy to purify by recrystallization. The solids
are stable in open-air conditions at room temperature and can be stored indefinitely in
a freezer. The melting points of these species lie around 300°C. All the complexes are
stable in CDCl
observed on storage (>6 weeks). Solutions of the complexes (~0.1M) in wet solvents
CH Cl or THF) can be preserved at low temperatures (below 4°C) for several weeks,
3
or CD
2
Cl
2
solutions at room temperature, but decomposition might be
(
2
2
but if kept on the bench at room temperature, colloidal gold (purple-dark), might
appear. We have found the complexes to be resilient to chromatographic purification
(
SiO ) with no significant loss of yield (<7%).
2
First study of the catalytic activity of NHC-gold(I) complexes
Given the continuously growing field of catalyzed reactions using expanded-ring NHC-
gold(I) complexes,[29] we selected the gold(I)-catalyzed oxazole synthesis[30] as a
benchmark reaction for the assessment of the catalytic activity of the gold(I) complexes
3-10. Thus, 4-Methoxy-N-(2-propyn-1-yl)benzamide B, acted as a model substrate and
initially 1.0 mol% pre-catalyst loading was investigated in the presence of AgNTf
employed as the chloride scavenger (Table 13).
2
Table 13. NHC-gold(I)-catalyzed cycloisomerization of propargylamide.
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[
a] Reactions were carried out at room temperature at 100 µmol scale in CDCl (500
3
1
µL). [b] Determined by H NMR as an average of two runs, using hexamethylbenzene
as internal standard. [c] Carried out in CD
2
Cl .
2
Employing 1.0 mol% catalyst loading, a complete conversion (<99%) was observed for
complexes 3, 5, 6, 7 and 9 (entries 2, 9, 13, 16 and 24) after 24 hours of reaction.
Complex 10 reached 90% (entry 28) and 8 offered 44% yield (entry 20) at the same
reaction time. While complex 4 needed 24 hours (entry 6), complexes 3, 5 and 9
required only 3 hours to reach a 50% conversion (entries 1, 8 and 23). Interestingly,
catalysts 6 and 7 surpassed 60% conversion after 3 hours (entries 12 and 15) and
complexes 5, 8 and 10 achieved 17–42% yield, at same reaction time (3 h, entries 5,
1
9 and 27). Outstandingly, after 72 hours of reaction, complex 3 offered 98% yield at
.3 mol% loading (entry 4) while complex 5 reached 91% yield at 0.15 mol% loading
0
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10.1002/chem.201902458
(entry 10). We then reduced catalyst loadings to 0.1 mol%. Complex 3 furnished 82%
yield (entry 3) and complexes 7, 9 and 10, overcome the 50% mark (entries 17, 25 and
29), after 48 hours. Catalyst 5 and 8 showed a lower catalytic activity (<33%, entries
11 and 21). Despite the need for longer times (>5 days), conversion was still notable
for 4 (92%, entry 7), 8 (85%, entry 22), 9 (100%, entry 26) and 10 (96%, entry 30).
Complex 6 showed a slow activity through the days (6 d, 20%, entry 14). At 0.05 mol%
loading, complex 7 afforded 24% conversion after 6 days (entry 18).
We next investigated whether the scope with regard to the gold(I) complexes could be
improved by heating (Table 14). Total reaction time was 24 hours and testing
temperature was 50°C. Thus, a 91% conversion was achieved with 0.05 mol% of 3
(entry 1), while a 60% conversion was observed when loading was reduced to 0.025
mol% (entry 2). Complexes 8 and 9 reached 14% and 15% yield under the same
conditions (entries 8 and 9) whereas only 7% conversion was observed for catalyst 10
(
entry 10). As expected from the prior experiments, complex 3 proved to be a very
active catalyst at a 0.005 mol% loading, affording 19% yield which corresponds to a
TON = 3800 (entry 3). The more sterically encumbered complex 4 offered only 6%
yield employing five times more of catalyst (0.025 mol%, entry 4). Despite the heating
conditions, a 0.025 mol% loading of complexes 5, 6 and 7 proved insufficient for
effecting cycloisomerization (<11% yield, entries 5–7).
Table 14. NHC-gold(I)-catalyzed cycloisomerization of B under heating.a
[
Au]
Pre-catalyst
loading
Yield
(%)
Entry
TON
b
complex
1
2
3
4
5
6
7
8
9
3
0.050 mol%
0.025 mol%
0.005 mol%
0.025 mol%
0.025 mol%
0.025 mol%
0.025 mol%
0.025 mol%
0.025 mol%
0.025 mol%
91
60
19
6
1820
2400
3800
240
440
400
440
560
600
280
3
3
4
5
11
10
11
14
15
7
6
7
8
9
10
10
aReactions were carried out at 200 µmol scale in CHCl
(2.0 mL). Determined by GC-
b
3
MS using dodecane as internal standard.
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Previous studies on this cycloisomerization reaction, have shown 95% yield in 12 hours
[
30a]
using 5 mol% of AuCl
3
or 79% after 36 hours, employing a lower catalyst loading
PAuNTf
, 1.0 mol%).[31] Recently, some examples
of a phosphine-based complex (Ph
3
2
of HAAC (Hydrazino amino acyclic carbene) complexes were developed in our group,
that yielded up to 100%, but at the expense of a prolonged reaction time (2 days).[32]
If we consider the steric characteristics of the complexes 3, 4, 6 and 7, we can
appreciate a closer relationship with their catalytic activity. Under exactly the same
experimental conditions (1.0 mol% catalyst, 24 h, r.t), complex 4 (%Vbur 53.0) afforded
50% conversion, whereas complexes 3 (%Vbur 43.6), 6 (%Vbur 48.4) and 7 (%Vbur 43.6)
achieved 99–100% conversion. The steric maps also support these results; in
complexes 3, 6 and 7 the steric hindrance around the metal atom seems to be more
homogeneously distributed, despite some uncovered field, in a difference to 4, where
two quadrants appear to be bulkier, while the other two show a lower steric hindrance;
in other words, only two (of the four) isopropyl groups of aryls are pointing down to
metal atom and remaining two have a negligible steric influence in the metal’s
coordination sphere. The observed distortion between (N-attached) aryl planes 4 ( =
49.2°) irrevocably confirms this postulate, in contrast to 3 ( = 39.3°) where the four
methyl substituents of aryls are pointing towards gold center in a relative uniform
manner. This steric distribution might explain the high catalytic activity of complex 3 in
the given reaction.
Overall, we have shown that a well-sterically distributed ligand, can deliver a better
catalytic activity than a sterically bulkier one, confirming certain limits on the larger is
more efficient concept,[33] particularly when designing expanded-ring NHC ligands.
Conclusions
The development of amidinium bromides 1a-h as NHC pro-ligands, is reported for the
first time. The synthesis of gold(I) complexes 3-10 is accomplished by in-situ proton
abstraction of tetrafluoroborates 2a-h, with tBuOK in the presence of AuCl(SMe ) in
2
acceptable yields (36–70%). Solid state structures of NHC-gold(I) complexes 3, 4, 6
and 7 revealed NCN angles in the range 118.61–119.48°, and a common spatial
conformation. Calculated %Vbur values lie between 43.6–53.0, being Au(9-Dipp)Cl 4
(
%Vbur 53.0), the more sterically hindered. Gold(I) complexes 3, 5, 6, 7 and 9 exhibited
exceptional catalytic activity in a selected cycloisomerization reaction (1.0 mol%, up to
100% conversion). Importantly, heating conditions can help shorten reaction times
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without decreasing the catalyst performance (3, 0.05 mol%, up to 91% conversion).
The most effective catalyst of the tested gold(I) species was 3 at relatively low loadings
(0.05–0.025 mol%), followed by 7, 9 and 10 at 0.1 mol% loadings. Furthermore, gold(I)
catalysis imparted for these complexes can be performed in air, under open-flask
conditions or prolonged reaction times without detrimental effects. Owing to this
exceptional performance, current gold(I) complexes have the potential to be
tremendously useful in gold(I) catalyzed reactions.
Experimental Section
General considerations
NMR characterization data was collected at 296 K (unless otherwise stated) at the
department of chemistry of the University of Heidelberg in Bruker Avance DRX 300
(300 MHz), Bruker Avance III 400 (400 MHz), Bruker Avance III 500 (500 MHz) and
1
13
Bruker Avance III 600 (600 MHz). H and C spectra are given relative to TMS (0.00
ppm) or to the residual protons in deuterated solvents (CD
2
Cl : 5.22 ppm, 53.84 ppm;
2
1
and CDCl
3
: 7.19 ppm, 77.16 ppm). Data for H NMR are reported as follows: chemical
shift ꢀ are quoted in parts per million (ppm), multiplicity (s = singlet, d = doublet, t =
triplet, q = quartet, m = multiplet, dd = double doublet, td = triple doublet, br s = broad
singlet) and coupling constant J in hertz (Hz), integration. 13C NMR spectra were
1
measured with H‐decoupling. The multiplicities mentioned in these spectra [s (singlet,
quaternary carbon), d (doublet, CH‐group), t (triplet, CH
2
‐group), q (quartet, CH ‐
3
group)] were determined with help of DEPT135, HSBC and HMQC experiments.
Melting points were determined in a BÜCHI automated B-545 apparatus and are
uncorrected. High resolution mass spectra (HRMS) were recorded on a Bruker Apex-
‐
1
Qe hybrid 9.4 FT‐ICR spectrometer (ESI+, MALDI). IR spectra (in cm ) were recorded
on a Bruker Vector 22 Lumos FT‐IR. GC/MS spectra were measured using an Agilent
7890A gas chromatograph with an Agilent 5975C Series MSD mass analyzer and
using helium as a carrier gas. UV-Vis were accomplished in a V-670 UV-VIS-NIR
Spectrophotometer. For the X-Ray diffraction analyses, the intensity data were
collected at 200(2) K on Bruker Smart CCD or Bruker APEX-II diffractometers (Mo-Kα
radiation, λ=0.71073 Å). The structures were solved by direct methods with SHELXT-
2
014[34] and refined by full-matrix least-squares procedures using the SHELXL-2017/1
software[35] with anisotropic thermal parameters for all the non-hydrogen atoms. A
summary of crystal data and structure refinement is available in the Electronic
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Supporting Information and the structures in the Cambridge Structural Database
CCDC) with deposition numbers 1918016–1918023.
(
General procedure for the synthesis of amidinium bromides 1a-h
To a stirred solution of N,N´-diarylformamidine (1.0 mmol) in CH CN (400 mL) was
added finely grinded K CO (1.0 mmol, 1.0 equiv) and mixture was stirred for 45 min.
3
2
3
at room temperature. Then, the corresponding dibromoalkane (1.1 mmol, 1.1 equiv)
was added to the suspension in one portion, and the mixture was stirred 24 hours at
same temperature after which it was heated to 85°C for 3-4 days till consumption of
the dibromoalkane (monitored by TLC). The suspension was cooled down to room
temperature and filtered. The solvent was removed under reduced pressure, CH
2
Cl
2
(100 mL) was added and solids were filtered off. The filtrate was evaporated till dryness
to give a solid which was recrystallized from toluene:n-hexane to give amidinium
bromides as white or yellowish solids.
1
1
a: Colorless solid. Yield: 367 mg. (68 %). m.p: 239-240°C. H NMR (400 MHz, CDCl
3
)
δ 8.45 (s, 1H), 7.57–7.46 (m, 2H), 7.37 (t, J = 7.0 Hz, 4H), 7.05 (d, J = 7.4 Hz, 2H),
7.01 (d, J = 7.2 Hz, 4H), 5.05 (d, J = 14.7 Hz, 2H), 4.70 (d, J = 14.7 Hz, 2H), 2.30 (s,
13
6
H), 2.28 (s, 6H), 2.20 (s, 6H). C NMR (101 MHz, CDCl ) δ 165.60 (d, 1C), 141.20
3
(s, 2C), 139.66 (s, 2C), 137.94 (s, 2C), 135.82 (s, 2C), 133.08 (s, 2C), 132.64 (s, 2C),
131.66 (d, 2C), 131.41 (d, 2C), 130.85 (d, 2C), 130.50 (d, 2C), 129.61 (d, 2C), 129.26
-1
(
d, 2C), 59.61 (t, 2C), 21.22 (q, 2C), 19.27 (q, 2C), 18.45 (q, 2C). IR (ATR, cm ): 3066,
2
1
997, 2866, 2740, 1644, 1585, 1473, 1441, 1403, 1380, 1350, 1308, 1291, 1204, 1177,
121, 1094, 1036, 997, 949, 913, 883, 852, 826, 793, 776, 776, 754, 658, 621. UV-vis
in CH
2
Cl
59.2795, found: 459.2795.
b: Colorless solid. Yield: 508 mg. (81%). m.p: 169°C. H NMR (500 MHz, CDCl
2
: λmax (log ε): 272 (3.73) nm. HR-MS (ESI+) m/z calcd. for C33
H
35
N
[M-Br]+:
2
4
1
8
0
7
1
3
) δ
.46 (s, 1H), 7.54 (td, J = 7.6, 1.0 Hz, 2H), 7.50 (t, J = 7.8 Hz, 2H), 7.39 (dd, J = 7.7,
.9 Hz, 2H), 7.34 (td, J = 7.6, 1.2 Hz, 2H), 7.31 (dd, J = 7.8, 1.3 Hz, 2H), 7.27 (dd, J =
.9, 1.3 Hz, 2H), 6.89 (d, J = 7.6 Hz, 2H), 5.16 (d, J = 14.6 Hz, 2H), 4.65 (d, J = 14.6
Hz, 2H), 2.74–2.62 (m, 4H), 1.27 (d, J = 6.7 Hz, 6H), 1.23 (d, J = 6.6 Hz, 6H), 1.18 (d,
1
3
J = 6.7 Hz, 6H), 1.10 (d, J = 7.0 Hz, 6H). C NMR (126 MHz, CDCl
46.80 (s, 2C), 143.69 (s, 2C), 139.22 (s, 2C), 136.39 (s, 2C), 132.05 (d, 2C), 131.74
d, 2C), 131.61 (s, 2C), 131.27 (d, 2C), 129.87 (d, 2C), 129.02 (d, 2C), 127.13 (d, 2C),
3
) δ 164.35 (d, 1C),
1
(
125.21 (d, 2C), 61.69 (t, 1C), 61.65 (t, 1C), 29.58 (d, 1C), 29.54 (d, 1C), 29.14 (d, 1C),
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2
2
2
1
8
9.10 (d, 1C), 27.04 (q, 1C), 27.00 (q, 1C), 25.56 (q, 1C), 25.51 (q, 1C), 25.39 (q, 1C),
-1
5.34 (q, 1C), 22.62 (q, 1C), 22.57 (q, 1C). IR (ATR, cm ): 3064, 3026, 2956, 2927,
865, 2814, 2754, 2704, 2104, 1735, 1624, 1585, 1440, 1405, 1385, 1364, 1347, 1324,
302, 1289, 1270, 1256, 1236, 1202, 1172, 1127, 1101, 1055, 1001, 953, 933, 920,
53, 800, 781, 752, 666, 632. UV-vis in CH
2
Cl : λmax (log ε): 275 (3.77), 348 (3.38) nm.
2
+
HR-MS (ESI+) m/z calcd. for C39
H
47
N
2
[M-Br] : 543.3734, found: 543.3743.
1
1
c: Colorless solid. Yield: 498 mg. (72%). m.p: 229-230°C. H NMR (500 MHz, CDCl
3
)
δ 8.54 (s, 1H), 7.52 (t, J = 7.6 Hz, 2H), 7.38 (t, J = 7.2 Hz, 4H), 7.31 (t, J = 7.6 Hz, 2H),
7
1
1
.22 (t, J = 6.6 Hz, 4H), 7.04 (d, J = 7.5 Hz, 2H), 5.08 (d, J = 14.7 Hz, 2H), 4.75 (d, J =
1
3
4.7 Hz, 2H), 2.35 (s, 6H), 2.26 (s, 6H). C NMR (126 MHz, CDCl
3
) δ 165.45 (d, 1C),
40.24 (s, 2C), 139.51 (s, 2C), 136.00 (s, 2C), 132.95 (s, 2C), 132.81 (s, 2C), 131.35
(
d, 2C), 130.95 (d, 2C), 130.94 (d, 2C), 130.82 (d, 2C), 129.78 (d, 2C), 129.45 (d, 2C),
29.20 (d, 2C), 59.53 (t, 1C), 59.49 (t, 1C), 19.30 (q, 1C), 19.27 (q, 1C), 18.49 (q, 1C),
1
1
1
9
2
4
1
-1
8.45 (q, 1C). IR (ATR, cm ): 2982, 2951, 2917, 2859, 2830, 2774, 2739, 1735, 1633,
584, 1469, 1441, 1399, 1344, 1396, 1295, 1204, 1156, 1122, 1092, 1033, 1006, 962,
48, 915, 892, 823, 801, 789, 770, 756, 731, 659, 618. UV-vis in CH
2
Cl : λmax (log ε):
2
+
72 (3.84) nm. HR-MS (ESI+) m/z calcd. for C31
H
31
N
2
[M-Br] : 431.2482, found:
31.2482.
1
d: Pale brown solid. Yield: 394 mg. (83%). m.p: 159-161°C. H NMR (600 MHz,
CDCl
3
) δ 8.17 (s, 1H), 7.53 (td, J = 7.6, 1.1 Hz, 2H), 7.45 (t, J = 7.8 Hz, 2H), 7.39–7.33
(m, 4H), 7.29 (t, J = 8.1 Hz, 4H), 6.99 (d, J = 7.7 Hz, 2H), 5.13 (d, J = 14.7 Hz, 2H),
4
6
2
1
.70 (d, J = 14.7 Hz, 2H), 2.67–2.55 (m, 4H), 2.54–2.44 (m, 4H), 1.23 (t, J = 7.5 Hz,
1
3
H), 1.19 (t, J = 7.5 Hz, 6H). C NMR (151 MHz, CDCl ) δ 164.24 (d, 1C), 141.43 (s,
3
C), 139.50 (s, 2C), 139.13 (s, 2C), 138.39 (s, 2C), 132.44 (s, 2C), 131.58 (d, 2C),
31.57 (d, 2C), 131.11 (d, 2C), 129.66 (d, 2C), 129.12 (d, 2C), 128.73 (d, 2C), 127.50
(d, 2C), 60.73 (t, 2C), 24.80 (t, 2C), 23.95 (t, 2C), 15.06 (q, 2C), 14.79 (q, 2C). IR (ATR,
-1
cm ): 2970, 2933, 2871, 1722, 1642, 1585, 1446, 1411, 1393, 1371, 1351, 1308, 1292,
237, 1202, 1171, 1124, 1055, 1006, 955, 942, 913, 880, 853, 820, 784, 665, 627. UV-
1
vis in CH
2
Cl
2
: λmax (log ε): 277 (3.60), 355 (3.21). HR-MS (ESI+) m/z calcd. for
+
C
35
H
39
N
2
[M-Br] : 487.3108, found: 487.3109.
1
1
e: colorless solid. Yield: 264 mg. (48%). m.p: 199-200°C. H NMR (400 MHz, CDCl
δ 7.58 (d, J = 7.8 Hz, 2H), 7.36 (td, J = 8.2, 1.7 Hz, 2H), 7.26 (s, 1H), 7.00 (td, J = 7.5,
.8 Hz, 2H), 6.91 (dd, J = 7.5, 1.5 Hz, 2H), 6.78 (s, 4H), 5.82 (s, 4H), 2.16 (s, 6H), 2.15
3
)
0
1
3
(
s, 12H). C NMR (101 MHz, CDCl ) δ 157.74 (d, 1C), 157.18 (s, 2C), 140.75 (s, 2C),
3
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139.96 (s, 2C), 134.68 (s, 4C), 131.70 (d, 2C), 130.82 (d, 2C), 130.29 (d, 2C), 129.04
(d, 1C), 128.23 (d, 1C), 125.76 (d, 2C), 125.41 (s, 2C), 120.37 (d, 2C), 57.49 (t, 2C),
-
1
2
1
9
0.88 (q, 2C), 18.00 (q, 4C). IR (ATR, cm ): 3462, 3375, 2921, 2861, 2457, 1650,
604, 1581, 1479, 1453, 1398, 1348, 1299, 1236, 1201, 1179, 1155, 1134, 1110, 1031,
87, 949, 877, 854, 791, 744, 702, 656, 637, 617. UV-vis in CH
2
Cl : λmax (log ε): 271
2
+
(3,64) nm. HR-MS (ESI+) m/z calcd. for C33
H
35
N
2
O [M-Br] : 475.2744, found:
4
1
7
7
1
75.2746.
1
f: Pale yellow solid. Yield: 288 mg. (45%). m.p: 281°C. H NMR (400 MHz, CDCl
3
) δ
.64 (dd, J = 8.2, 0.5 Hz, 2H), 7.40 (s, 1H), 7.34 (td, J = 8.2, 1.7 Hz, 2H), 7.29 (t, J =
.8 Hz, 2H), 7.10 (d, J = 7.8 Hz, 4H), 6.98 (td, J = 7.5, 0.9 Hz, 2H), 6.86 (dd, J = 7.6,
1
3
.5 Hz, 2H), 5.95 (s, 4H), 3.45 (s, 4H), 1.10 (d, J = 6.8 Hz, 12H), 0.87 (s, 12H). C
) δ 157.74 (s, 2C), 156.92 (d, 1C), 145.81 (s, 4C), 140.24 (s,
C), 132.05 (d, 4C), 131.06 (d, 2C), 130.63 (d, 2C), 125.68 (d, 4C), 125.57 (s, 2C),
21.35 (d, 2C), 59.42 (t, 2C), 28.07 (d, 4C), 25.81 (q, 4C), 24.63 (q, 4C). IR (ATR, cm-
: 3321, 2967, 2868, 2817, 1638, 1582, 1483, 1466, 1450, 1401, 1364, 1326, 1269,
228, 1185, 1161, 1111, 1098, 1056, 990, 949, 933, 901, 849, 808, 792, 745, 701,
NMR (101 MHz, CDCl
3
2
1
1)
1
6
40, 615. UV-vis in CH
2
Cl : λmax (log ε): 271 (3,72) nm. HR-MS (ESI+) m/z calcd. for
2
+
C
39
H
47
N
2
O [M-Br] : 559.3683, found: 559.3688.
1
1
g: Colorless solid. Yield: 255 mg. (48%). m.p: 200-202°C. H NMR (400 MHz, CDCl
δ 7.59 (d, J = 7.8 Hz, 2H), 7.36 (td, J = 8.1, 1.7 Hz, 2H), 7.29 (s, 1H), 7.14–7.07 (m,
H), 6.99 (t, J = 7.3 Hz, 6H), 6.88 (dd, J = 7.5, 1.5 Hz, 2H), 5.85 (s, 4H), 2.20 (s, 12H).
13C NMR (101 MHz, CDCl
) δ 157.46 (d, 1C), 157.14 (s, 2C), 142.97 (s, 2C), 135.06
s, 4C), 131.65 (d, 2C), 130.91 (d, 2C), 129.97 (d, 2C), 129.76 (d, 4C), 125.60 (s, 2C),
3
)
2
3
(
-
1
1
2
8
25.44 (d, 2C), 120.38 (d, 2C), 57.59 (t, 2C), 18.10 (q, 4C). IR (ATR, cm ): 3377, 3010,
884, 2827, 1650, 1584, 1482, 1450, 1234, 1188, 1164, 1112, 1095, 1034, 986, 950,
88, 847, 756, 701, 634. UV-vis in CH
2
Cl : λmax (log ε): 274 (3,63) nm. HR-MS (ESI+)
2
+
m/z calcd. for C31
H
31
N
2
O [M-Br] : 447.2431, found: 447.2434.
1
1
7
7
1
h: Colorless solid. Yield: 300 mg. (51%). m.p: 180°C. H NMR (400 MHz, CDCl
3
) δ
.63 (dd, J = 8.2, 0.6 Hz, 2H), 7.35 (td, J = 8.0, 1.7 Hz, 2H), 7.29 (s, 1H), 7.22 (t, J =
.7 Hz, 2H), 7.05 (d, J = 7.7 Hz, 4H), 6.96 (td, J = 7.5, 0.9 Hz, 2H), 6.85 (dd, J = 7.5,
13
.6 Hz, 2H), 5.86 (br s, 4H), 2.71–2.45 (m, 8H), 0.95 (t, J = 7.5 Hz, 12H). C NMR
) δ 157.32 (d, 1C), 157.22 (s, 2C), 141.63 (s, 2C), 140.65 (s, 4C),
31.94 (d, 2C), 130.99 (d, 2C), 130.23 (d, 2C), 127.59 (d, 4C), 125.36 (d, 2C), 125.29
(101 MHz, CDCl
3
1
-1
(
s, 2C), 120.31 (d, 2C), 58.34 (t, 2C), 23.27 (t, 4C), 15.04 (q, 4C). IR (ATR, cm ): 3063,
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3
1
8
023, 2968, 2933, 2875, 2818, 1649, 1603, 1584, 1478, 1396, 1366, 1351, 1331, 1306,
275, 1249, 1188, 1160, 1113, 1102, 1052, 1034, 993, 945, 930, 899, 869, 846, 845,
25, 796, 780, 765, 747, 727, 701, 636, 619. UV-vis in CH
2
Cl : λmax (log ε): 266 (3.89)
2
+
nm. HR-MS (ESI+) m/z calcd. for C35
H
39
N
2
O [M-Br] : 503.3057, found: 503.3058.
General procedure for the synthesis of amidinium tetrafluoroborates 2a-h
Anion exchange was undertaken by mixing solutions of amidinium bromide (1.0 mmol,
in 100 mL acetone) and NaBF (660 mg, 6.0 equiv in 75 mL distilled water) and stirring
4
for 45 minutes at room temperature. Acetone was then evaporated under reduced
pressure and the solid was filtered, washed with distilled water (50 mL) taken up in
CH
2
Cl
2
(50 mL) and dried over Na
2
SO . Evaporation of solvent till a minimal amount
4
and adding Et
2
O gave white solids corresponding to tetrafluoroborate salts which were
recovered by filtration and dried under vacuum (5.0 mbar) prior to its use on metal
complexes synthesis.
1
2
7
1
a: Colorless solid. Yield: 516 mg. (94%). m.p: >300°C. H NMR (400 MHz, CDCl
3
) δ
.81 (s, 1H), 7.57–7.48 (m, 2H), 7.41–7.34 (m, 4H), 7.09–6.98 (m, 6H), 5.08 (d, J =
1
3
4.7 Hz, 2H), 4.70 (d, J = 14.7 Hz, 2H), 2.30 (s, 6H), 2.27 (s, 6H), 2.19 (s, 6H). C
) δ 165.03 (d, 1C), 141.36 (s, 2C), 139.73 (s, 2C), 138.05 (s,
C), 135.90 (s, 2C), 133.04 (s, 2C), 132.64 (s, 2C), 131.68 (d, 2C), 131.48 (d, 2C),
30.91 (d, 2C), 130.56 (d, 2C), 129.61 (d, 2C), 129.31 (d, 2C), 59.65 (t, 2C), 21.20 (q,
NMR (101 MHz, CDCl
3
2
1
2
1
7
-1
C), 19.01 (q, 2C), 17.96 (q, 2C). IR (ATR, cm ): 3022, 1738, 1649, 1587, 1473, 1442,
404, 1382, 1348, 1309, 1293, 1260, 1165, 1095, 1050, 1031, 959, 914, 883, 852,
89, 754, 732, 657, 621. UV-vis in CH
2
Cl : λmax (log ε): 272 (3.86) nm. HR-MS (ESI+)
2
m/z calcd. for C33
H
35
N
2
[M-BF
4
]+: 459.2795, found: 459.2796.
1
2
b: Colorless solid. Yield: 576 mg. (94%). m.p: 279-280°C. H NMR (500 MHz, CDCl
3
)
δ 7.91 (s, 1H), 7.59–7.53 (m, 4H), 7.42 (d, J = 7.6 Hz, 2H), 7.39–7.32 (m, 6H), 6.93 (d,
J = 7.6 Hz, 2H), 5.23 (d, J = 14.6 Hz, 2H), 4.71 (d, J = 14.7 Hz, 2H), 2.76–2.70 (m,
4
H), 1.31 (d, J = 6.6 Hz, 6H), 1.27 (d, J = 6.5 Hz, 6H), 1.18 (d, J = 6.6 Hz, 6H), 1.11
d, J = 6.9 Hz, 6H). 13C NMR (126 MHz, CDCl
) δ 163.60 (d, 1C), 147.14 (s, 2C),
43.87 (s, 2C), 139.42 (s, 2C), 136.50 (s, 2C), 132.21 (d, 2C), 131.89 (d, 2C), 131.64
(
3
1
(s, 2C), 131.34 (d, 2C), 129.96 (d, 2C), 129.09 (d, 2C), 127.27 (d, 2C), 125.40 (d, 2C),
6
2
1
1.84 (t, 2C), 29.64 (d, 1C), 29.60 (d, 1C), 29.17 (d, 1C), 29.14 (d, 1C), 27.09 (q, 1C),
7.05 (q, 1C), 25. 46 (q, 1C), 25.41 (q, 2C), 25. 35 (q, 1C), 22.64 (q, 1C), 22.59 (q,
-1
C). IR (ATR, cm ): 3065, 2964, 2931, 2872, 1737, 1626, 1586, 1466, 1440, 1391,
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1
348, 1325, 1303, 1267, 1238, 1204, 1171, 1053, 934, 919, 854, 810, 778, 755, 728,
99, 667, 632. UV-vis in CH Cl : λmax (log ε): 253 (3.76), 273 (3.85) nm. HR-MS (ESI+)
[M-BF
6
2
2
m/z calcd. for C39
H
47
N
2
4
]+: 543.3734, found: 543.3735.
1
2
c: Pale pinkish solid. Yield: 477 mg. (92%). m.p: >300°C. H NMR (400 MHz, CDCl
3
)
δ 8.04 (s, 1H), 7.53 (td, J = 7.6, 1.2 Hz, 2H), 7.40–7.37 (m, 4H), 7.33 (t, J = 7.6 Hz,
2
=
1
1
H), 7.27–7.22 (m, 4H), 7.06 (d, J = 8.4 Hz, 2H), 5.12 (d, J = 14.7 Hz, 2H), 4.74 (d, J
13
14.7 Hz, 2H), 2.34 (s, 6H), 2.27 (s, 6H). C NMR (101 MHz, CDCl ) δ 165.77 (d,
3
C), 140.56 (s, 2C), 139.79 (s, 2C), 136.32 (s, 2C), 133.20 (s, 2C), 133.14 (s, 2C),
31.50 (d, 2C), 131.11 (d, 2C), 131.08 (d, 2C), 130.92 (d, 2C), 129.95 (d, 2C), 129.69
-1
(
d, 2C), 129.34 (d, 2C), 59.66 (t, 2C), 19.17 (q, 2C), 18.13 (q, 2C). IR (ATR, cm ):
3
021, 2918, 1647, 1473, 1442, 1402, 1382, 1347, 1309, 1293, 1206, 1165, 1096, 1050,
030, 998, 959, 914, 883, 852, 789, 773, 753, 732, 657, 620. UV-vis in CH Cl
[M-BF
]+: 431.2482,
1
2
2
: λmax
(log ε): 271 (3.97) nm. HR-MS (ESI+) m/z calcd. for C31
H
31
N
2
4
found: 431.2489.
1
2
d: Colorless solid. Yield: 545 mg. (95%). m.p: 279°C. H NMR (600 MHz, CDCl
3
) δ
7.84 (s, 1H), 7.54 (t, J = 7.6 Hz, 2H), 7.47 (t, J = 7.8 Hz, 2H), 7.42–7.35 (m, 4H), 7.31
(t, J = 6.8 Hz, 4H), 7.00 (d, J = 7.6 Hz, 2H), 5.16 (d, J = 14.7 Hz, 2H), 4.69 (d, J = 14.7
Hz, 2H), 2.67–2.56 (m, 4H), 2.56–2.43 (m, 4H), 1.24 (t, J = 7.5 Hz, 6H), 1.21 (t, J = 7.5
1
3
Hz, 6H). C NMR (151 MHz, CDCl
39.25 (s, 2C), 138.49 (s, 2C), 132.49 (s, 2C), 131.62 (d, 2C), 131.59 (d, 2C), 131.11
d, 2C), 129.69 (d, 2C), 129.13 (d, 2C), 128.78 (d, 2C), 127.57 (d, 2C), 60.74 (t, 2C),
3
) δ 164.09 (d, 1C), 141.62 (s, 2C), 139.60 (s, 2C),
1
(
-
1
2
2
1
4.80 (t, 2C), 23.79 (t, 2C), 15.04 (q, 2C), 14.79 (q, 2C). IR (ATR, cm ): 2973, 2937,
877, 1731, 1642, 1584, 1448, 1411, 1396, 1371, 1351, 1308, 1295, 1240, 1204, 1171,
093, 1050, 1008, 957, 943, 913, 881, 854, 815, 783, 758, 728, 665, 624. UV-vis in
+
CH
2
Cl
87.3111, found: 487.3108.
e: Colorless solid. Yield: 512 mg. (91%). m.p: 227°C. H NMR (400 MHz, CDCl
2
: λmax (log ε): 278 (3.78) nm. HR-MS (ESI+) m/z calcd. for C35
H
39
N
2
[M-BF
4
] :
4
2
7
7
2
2
1
4
1
1
3
) δ
.62 (dd, J = 8.2, 0.7 Hz, 1H), 7.40 (td, J = 8.0, 1.7 Hz, 1H), 7.25 (s, 1H), 7.02 (td, J =
.5, 0.9 Hz, 1H), 6.89 (dd, J = 7.5, 1.5 Hz, 1H), 6.81 (s, 2H), 5.48 (s, 2H), 2.18 (s, 3H),
1
3
.09 (s, 6H). C NMR (101 MHz, CDCl ) δ 157.87 (d, 1C), 157.19 (s, 2C), 140.57 (s,
3
C), 140.18 (s, 2C), 134.67 (s, 4C), 131.68 (d, 2C), 131.17 (d, 2C), 130.45 (d, 4C),
25.54 (d, 2C), 125.37 (s, 2C), 120.45 (d, 2C), 55.72 (t, 2C), 20.93 (q, 2C), 17.46 (q,
-1
C). IR (ATR, cm ): 2959, 2926, 2869, 1738, 1654, 1605, 1581, 1483, 1454, 1414,
364, 1237, 1205, 1182, 1059, 1032, 950, 860, 818, 790, 758, 731, 704, 640, 617. UV-
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vis in CH
2
Cl : λmax (log ε): 246 (3.83), 272 (3.59), 363 (2.63) nm. HR-MS (ESI+) m/z
2
calcd. for C33
H
35
N
2
O [M-BF
4
]+: 475.2744, found: 475.2744.
1
2
f: Colorless solid. Yield: 512 mg. (86%). m.p: 286-287°C. H NMR (400 MHz, CD
2
Cl )
2
δ 7.70 (d, J = 8.3 Hz, 2H), 7.46 (s, 1H), 7.42 (td, J = 8.2, 1.6 Hz, 2H), 7.34 (t, J = 7.8
Hz, 2H), 7.15 (d, J = 7.8 Hz, 4H), 7.05 (td, J = 7.5, 0.9 Hz, 2H), 6.88 (dd, J = 7.6, 1.4
Hz, 2H), 5.46 (br s, 4H), 3.15–2.97 (m, 4H), 1.08 (d, J = 6.8 Hz, 12H), 0.86 (d, J = 6.4
1
3
Hz, 12H). C NMR (101 MHz, CD
2
Cl
C), 139.58 (s, 2C), 131.66 (d, 4C), 130.94 (d, 2C), 125.84 (d, 2C), 125.79 (d, 4C),
24.42 (s, 2C), 121.61 (d, 2C), 57.49 (t, 2C), 28.24 (d, 4C), 25.46 (q, 4C), 23.98 (q,
2
) δ 157.61 (s, 2C), 157.35 (d, 1C), 145.21 (s,
4
1
4
1
7
3
5
2
-1
C). IR (ATR, cm ): 2969, 2929, 2872, 1647, 1583, 1485, 1469, 1454, 1407, 1388,
364, 1329, 1299, 1282, 1237, 1186, 1162, 1096, 1029, 932, 900, 879, 848, 812, 788,
67, 748, 699, 657, 639, 617. UV-vis in CH
2
Cl : λmax (log ε): 248 (3.94), 270 (3.73),
2
12 (2.97) nm. HR-MS (ESI+) m/z calcd. for C39
H
47
N
2
O [M-BF
]+: 559.3683, found:
4
59.3683.
1
g: Colorless solid. Yield: 464 mg. (87%). m.p: 281-282°C. H NMR (400 MHz, CDCl
3
)
δ 7.64 (d, J = 7.7 Hz, 2H), 7.41 (td, J = 8.2, 1.7 Hz, 2H), 7.30 (s, 1H), 7.19–7.11 (m,
1
3
2
H), 7.05–6.98 (m, 6H), 6.87 (dd, J = 7.5, 1.5 Hz, 2H), 5.51 (s, 4H), 2.14 (s, 12H). C
NMR (101 MHz, CDCl ) δ 157.60 (d, 1C), 157.15 (s, 2C), 142.77 (s, 2C), 135.02 (s,
C), 131.61 (d, 2C),131.28 (d, 2C), 130.15 (d, 2C), 129.93 (d, 4C), 125.57 (s, 2C),
3
4
1
1
1
-1
25.18 (d, 2C), 120.48 (d, 2C), 55.75 (t, 2C), 17.54 (q, 4C). IR (ATR, cm ): 3006, 1656,
605, 1583, 1485, 1473, 1454, 1436, 1411, 1386, 1362, 1318, 1298, 1240, 1190, 1161,
057, 1026, 942, 897, 880, 848, 825, 793, 771, 754, 734, 704, 636, 615. UV-vis in
CH
2
Cl
2
: λmax (log ε): 250 (3.78), 268 (3.62) nm. HR-MS (ESI+) m/z calcd. for C31
H
31
2
N O
[
M-BF
4
]+: 447.2431, found: 447.2432.
1
2
7
7
1
h: Colorless solid. Yield: 464 mg. (87%). m.p: 284°C. H NMR (400 MHz, CDCl
3
) δ
.68 (dd, J = 8.2, 0.6 Hz, 2H), 7.40 (td, J = 8.0, 1.7 Hz, 2H), 7.29 (s, 1H), 7.27 (t, J =
.7 Hz, 2H), 7.09 (d, J = 7.7 Hz, 4H), 6.99 (td, J = 7.5, 0.9 Hz, 2H), 6.85 (dd, J = 7.5,
1
3
.6 Hz, 2H), 5.52 (s, 4H), 2.65–2.45 (m, 8H), 0.97 (t, J = 7.5 Hz, 12H). C NMR (101
) δ 157.50 (d, 1C), 157.27 (s, 2C), 141.49 (s, 2C), 140.61 (s, 4C), 131.88
d, 2C), 131.37 (d, 2C), 130.44 (d, 2C), 127.69 (d, 4C), 125.51 (d, 2C), 124.88 (s, 2C),
MHz, CDCl
3
(
-
1
1
2
9
20.41 (d, 2C), 56.60 (t, 2C), 22.97 (t, 4C) 14.96 (q, 4C). IR (ATR, cm ): 3071, 2968,
934, 2878, 1650, 1605, 1584, 1480, 1451, 1329, 1246, 1183, 1156, 1105, 1050, 1021,
43, 931, 893, 869, 840, 813, 777, 744, 702, 634, 613. UV-vis in CH
2
Cl : λmax (log ε):
2
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+
2
47 (4.04), 272 (3.93) nm. HR-MS (ESI+) m/z calcd. for C35
03.3057, found: 503.3059.
H
39
N
2
O [M-BF
4
] :
5
General procedure for the synthesis of gold(I) NHC complexes 3-10
A 4.5 mL screw-cap vial provided with a stirring bar, was charged with tetrafluoroborate
salt (0.10 mmol), [AuCl(SMe )] (15 mg, 0.05 mmol), tBuOK (40 mg or 0.35 mL, 1.0 M
in THF; 0.35 mmol) and 4ꢁ MS (40 mg) in air conditions at room temperature. Vial was
sealed with Teflon/silicone septa and purged-backfilled with N three times. After
2
2
cooling to -78°C, dry degassed THF (3.0 mL) was added to the mixture via syringe and
suspension was stirred overnight, allowing to warm up slowly to room temperature.
The resulting suspension was directly filtered through a pad of silica gel (1.5 x 3.0 cm),
followed by washing the plug with absolute CH
evaporated, and the residue was taken up in CH Cl
hexane (ca. 35 mL) which gave a cloudy white suspension. The liquor was removed
by decantation and solid residue was recrystallized from CH Cl :npentane (1:4) to yield
2
Cl
2
(15 mL). The solvent was
2
2
(2 mL), followed by addition of n-
2
2
pure NHC-AuCl complexes as colorless microcrystalline solids.
1
Au(9-Mes)Cl 3: Yield: 23 mg. (67%). m.p: 269°C. H NMR (600 MHz, CDCl
3
) δ 7.37 (t,
J = 8.0 Hz, 2H), 7.26 (d, J = 7.6 Hz, 2H), 7.22 (t, J = 7.6 Hz, 2H), 6.98 (s, 2H), 6.89 (s,
H), 6.85 (d, J = 7.7 Hz, 2H), 4.99 (d, J = 14.9 Hz, 2H), 4.49 (d, J = 14.9 Hz, 2H), 2.27
2
1
3
(
d, J = 2.3 Hz, 12H), 2.05 (s, 6H). C NMR (151 MHz, CDCl
s, 2C), 139.76 (s, 2C), 138.72 (s, 2C), 136.94 (s, 2C), 134.85 (s, 2C), 133.52 (s, 2C),
31.44 (d, 2C), 130.89 (d, 2C), 129.89 (d, 2C), 129.86 (d, 2C), 129.64 (d, 2C), 128.72
3
) δ 211.93 (NCN), 142.76
(
1
-1
(
d, 2C), 59.29 (t, 2C), 21.49 (q, 2C), 19.77 (q, 2C), 18.74 (q, 2C). IR (ATR, cm ): 3950,
3020, 2955, 2921, 2858, 1674, 1634, 1609, 1480, 1436, 1373, 1383, 1303, 1286, 1241,
1208, 1193, 1161, 1122, 1034, 1010, 952, 886, 853, 828, 774, 753, 735, 706, 637. UV-
vis in CH
2
Cl
2
: λmax (log ε): 277 (3.98), 335 (3.44), 452 (2.88), 484 (2.97) nm. HR-MS
+
(
ESI+) m/z calcd. for C33
H34AuClN
2
Na [M+Na] : 713.1968, found: 713.1972.
1
Au(9-Dipp)Cl 4: Yield: 20 mg. (52%). m.p: >300°C. H NMR (600 MHz, CDCl
3
) δ 7.40
(t, J = 7.7 Hz, 4H), 7.32–7.28 (m, 2H), 7.28–7.25 (m, 2H), 7.24–7.20 (m, 2H), 7.20–
7
2
6
1
.16 (m, 2H), 6.78 (d, J = 7.6 Hz, 2H), 5.18 (d, J = 14.8 Hz, 2H), 4.54 (d, J = 14.9 Hz,
H), 2.89–2.75 (m, 4H), 1.38 (d, J = 6.7 Hz, 6H), 1.29 (d, J = 6.9 Hz, 6H), 1.23 (d, J =
1
3
.8 Hz, 6H), 1.11 (d, J = 6.7 Hz, 6H). C NMR (151 MHz, CDCl
3
) δ 212.56 (NCN),
47.33 (s, 2C), 144.96 (s, 2C), 142.23 (s, 2C), 139.58 (s, 2C), 133.95 (s, 2C), 131.25
(
d, 2C), 130.72 (d, 2C), 130.06 (d, 2C), 129.84 (d, 2C), 128.64 (d, 2C), 126.68 (d, 2C),
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2
1
1
24.42 (d, 2C), 61.60 (t, 2C), 29.41 (d, 2C), 29.23 (d, 2C), 26.30 (q, 2C), 25.47 (q, 2C),
-1
5.40 (q, 2C), 23.07 (q, 2C). IR (ATR, cm ): 3060, 3027, 2960, 2925, 2867, 1626,
588, 1474, 1440, 1386, 1348, 1323, 1300, 1281, 1251, 1226, 1180, 1162, 1125, 1102,
056, 1015, 960, 948, 935, 887, 811, 778, 767, 754, 729, 666, 639, 620. UV-vis in
CH
2
Cl
2
: λmax (log ε): 253 (4.21), 278 (3.83) nm. HR-MS (ESI+) m/z calcd. for
+
C
39
H46AuClN
2
Na [M+Na] : 797.2913, found: 797.2923.
1
Au(9-Xyl)Cl 5: Yield: 16 mg. (49%). m.p: 229-230°C. H NMR (500 MHz, CDCl
3
) δ 7.38
(t, J = 10.9, 4.1 Hz, 2H), 7.27 (d, J = 7.6 Hz, 2H), 7.23 (t, J = 7.5 Hz, 4H), 7.18 (d, J =
7.6 Hz, 2H), 7.11 (d, J = 7.4 Hz, 2H), 6.85 (d, J = 7.8 Hz, 2H), 5.03 (d, J = 14.9 Hz,
1
3
2
H), 4.53 (d, J = 14.9 Hz, 2H), 2.31 (s, 6H), 2.12 (s, 6H). C NMR (126 MHz, CDCl ):
3
δ 214.76 (NCN), 144.87 (s, 2C), 139.48 (s, 2C), 137.00 (s, 2C), 134.49 (s, 2C), 133.79
s, 2C), 130.68 (d, 2C), 130.46 (d, 2C), 129.54 (d, 2C), 129.45 (d, 2C), 128.93 (d, 2C),
28.86 (d, 2C), 128.51 (d, 2C), 59.05 (t, 2C), 19.57 (q, 2C), 18.56 (q, 2C). IR (ATR,
(
1
-1
cm ): 3058, 3026, 2987, 2950, 2916, 2858, 2235, 1943, 1871, 1590, 1491, 1434, 1376,
1345, 1290, 1241, 1206, 1181, 1164, 1123, 1094, 1009, 960, 941, 912, 825, 779, 769,
7
52, 731, 654, 630, 609. UV-vis in CH
2
Cl
2
: λmax (log ε): 281 (3.72), 257 (4.13) nm. HR-
+
MS (ESI+) m/z calcd. for C31
H
30AuClN
2
Na [M+Na] : 685.1655, found: 685.1676.
1
Au(9-Dietph)Cl 6: Yield: 13 mg. (36%). m.p: >300°C. H NMR (600 MHz, CDCl
3
) δ 7.38
(td, J = 7.6, 1.0 Hz, 2H), 7.35 (t, J = 7.7 Hz, 2H), 7.27 (t, J = 8.0 Hz, 4H), 7.20 (t, J =
7
2
2
.6 Hz, 2H), 7.16 (d, J = 7.6 Hz, 2H), 6.79 (d, J = 7.7 Hz, 2H), 5.10 (d, J = 14.9 Hz,
H), 4.45 (d, J = 14.9 Hz, 2H), 2.70–2.63 (m, 2H), 2.58–2.50 (m, 2H), 2.50–2.44 (m,
1
3
H), 2.43–2.37 (m, 2H), 1.30 (t, J = 7.5 Hz, 6H), 1.22 (t, J = 7.5 Hz, 6H). C NMR (151
) δ 211.72 (NCN), 144.08 (s, 2C), 142.21 (s, 2C), 139.54 (s, 2C), 139.45
s, 2C), 134.23 (s, 2C), 130.85 (d, 2C), 129.83 (d, 2C), 129.59 (d, 2C), 129.31 (d, 2C),
MHz, CDCl
3
(
1
2
1
8
28.35 (d, 2C), 128.07 (d, 2C), 126.37 (d, 2C), 60.57 (t, 2C), 25.24 (t, 2C), 23.93 (t,
-1
C), 14.63 (q, 2C), 14.52 (q, 2C). IR (ATR, cm ): 3063, 3026, 2969, 2924, 2868, 1589,
476, 1448, 1427, 1388, 1345, 1282, 1226, 1180, 1124, 1108, 1055, 1007, 946, 867,
05, 769, 752, 730, 700, 658, 631. UV-vis in CH
2
Cl
2
: λmax (log ε): 253 (4.28), 281 (3.91)
+
nm. HR-MS (ESI+) m/z calcd. for C35
41.2297.
H
38AuClN
2
Na [M+Na] : 741.2287, found:
7
1
Au(10-Mes)Cl 7: Yield: 22 mg. (61%). m.p: 286°C. H NMR (600 MHz, CD
2
Cl ) δ 7.25
2
(
t, J = 7.7 Hz, 2H), 7.17 (d, J = 8.1 Hz, 2H), 6.92 (t, J = 8.0 Hz, 2H), 6.89 (s, 4H), 6.58
d, J = 7.6 Hz, 2H), 4.98 (s, 4H), 2.24 (s, 6H), 2.09 (s, 12H). 13C NMR (151 MHz,
(
CD
2
Cl
2
) δ 209.32 (NCN), 156.29 (s, 2C), 142.40 (s, 2C), 138.73 (s, 4C), 135.58 (s,
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Chemistry - A European Journal
10.1002/chem.201902458
2
1
2
1
2
C), 132.21 (d, 2C), 130.78 (d, 2C), 130.15 (d, 2C), 127.52 (d, 2C), 125.32 (d, 2C),
-1
21.75 (d, 2C), 54.95 (t, 2C), 21.13 (q, 2C), 18.80 (q, 4C). IR (ATR, cm ): 2962, 2920,
857, 2124, 1722, 1678, 1633, 1605, 1580, 1554, 1484, 1451, 1376, 1261, 1235, 1182,
105, 1028, 947, 854, 800, 754, 702, 636. UV-vis in CH
2
Cl
2
: λmax (log ε): 267 (4.03),
+
78 (3.93) nm. HR-MS (ESI+) m/z calcd. for C33
H
34AuClN
2
NaO [M+Na] : 729.1918,
found: 729.1922.
1
Au(10-Dipp)Cl 8: Yield: 28 mg. (70%). m.p: >300°C. H NMR (600 MHz, CD
2
Cl ) δ 7.37
2
(t, J = 7.7 Hz, 2H), 7.27–7.23 (m, 2H), 7.16 (d, J = 7.5 Hz, 4H), 6.92 (t, J = 7.5 Hz, 2H),
6
1
1
.58 (d, J = 7.6 Hz, 2H), 5.78 (br s, 2H), 4.36 (br s, 2H), 2.91–2.87 (m, 4H), 1.29 (br s,
1
3
2H), 0.89 (br s, 12H). C NMR (151 MHz, CD
2
Cl
2
) δ 210.27 (NCN), 156.12 (s, 2C),
46.91 (s, 1C), 145,47 (s, 1C), 142.06 (s, 2C), 132.68 (d, 2C), 131.11 (d, 4C), 129.82
(d, 2C), 127.49 (s, 2C), 126.13(s, 1C) 125.31 (d, 4C), 124.44 (s, 1C), 121.89 (d, 2C),
-
1
5
1
1
6.90 (t, 2C), 29.27 (d, 4C), 25.41 (q, 8C). IR (ATR, cm ): 3063, 2962, 2927, 2868,
605, 1587, 1454, 1426, 1385, 1352, 1324, 1296, 1272, 1232, 1176, 1111, 1099, 1056,
018, 957, 942, 932, 888, 877, 819, 800, 762, 738, 638, 611. UV-vis in CH
2
Cl
2
: λmax
(log ε): 271 (4.06) nm. HR-MS (ESI+) m/z calcd. for C39
H
46AuClN
2
NaO [M+Na]+:
813.2862, found: 813.2882.
1
Au(10-Xyl)Cl 9: Yield: 16 mg. (48%). m.p: >300°C. H NMR (600 MHz, CD
t, J = 6.9 Hz, 2H), 7.21 (d, J = 8.1 Hz, 2H), 7.18 (t, J = 7.6 Hz, 2H), 7.08 (d, J = 7.5
Hz, 4H), 6.93 (t, J = 6.9 Hz, 2H), 6.58 (d, J = 7.6 Hz, 2H), 5.02 (br s, 4H), 2.14 (s, 12H).
13C NMR (151 MHz, CD
Cl ) δ 208.93 (NCN), 156.50 (s, 2C), 145.17 (s, 2C), 136.11
s, 2C), 132.22 (d, 2C), 130.99 (d, 4C), 129.63 (d, 2C), 128.95 (d, 2C), 127.49 (s, 4C),
2
Cl
2
) δ 7.27
(
2
2
(
125.47 (d, 2C), 121.98 (d, 1C), 121.93 (d, 1C), 55.08 (t, 2C), 18.97 (q, 4C). IR (ATR,
-1
cm ): 3068, 2950, 2917, 2859, 1680, 1603, 1574, 1492, 1377, 1343, 1310, 1279, 1236,
1206, 1173, 1159, 1108, 1094, 1034, 1012, 950, 927, 889, 819, 786, 765, 742, 703,
6
68, 650, 631, 607. UV-vis in CH
2
Cl
2
: λmax (log ε): 261 (3.93), 362 (2.31) nm. HR-MS
+
(
ESI+) m/z calcd. for C31
H30AuClN
2
NaO [M+Na] : 701.1605, found: 701.1629.
1
Au(10-Dietph)Cl 10: Yield: 19 mg. (52%). m.p: 283-285°C. H NMR (600 MHz, CD
2
Cl )
2
δ 7.31 (td, J = 7.6, 3.4 Hz, 2H), 7.28–7.23 (m, 2H), 7.22–7.10 (m, 6H), 6.90 (t, J = 7.5
Hz, 2H), 6.53 (t, J = 7.3 Hz, 1H), 5.01 (br s, 4H), 2.80–2.52 (m, 4H), 2.47–2.24 (m, 4H),
1
3
1
.18 (t, J = 7.2 Hz, 12H). C NMR (151 MHz, CD
2
Cl ) δ 209.83 (NCN), 156.28 (s, 2C),
2
143.72 (s, 2C), 141.46 (s, 2C), 132.36 (d, 2C), 130.99 (d, 2C), 129.23 (d, 2C), 127.28
(d, 4C), 127.21 (s, 4C), 125.30 (d, 2C), 121.83 (d, 2C), 56.53 (t, 2C), 24.51 (t, 4C),
-1
1
4.51 (q, 4C). IR (ATR, cm ): 3058, 3031, 2964, 2927, 2868, 1949, 1602, 1577, 1485,
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