Access to functionalised silver(I) and gold(I) N-heterocyclic carbenes by [2 + 3] dipolar cycloadditions

Article abstract of DOI:10.1039/c2dt30249g

A new strategy was developed for the modification of silver(i) and gold(i) N-heterocyclic carbenes. Azido groups were grafted and used either by copper-catalysed azide-alkyne cycloaddition before metallation or by thermal and "strain-promoted" 1,3-dipolar cycloaddition after metallation to functionalise the metal-NHCs.

Full text of DOI:10.1039/c2dt30249g

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PAPER
Access to functionalised silver(I) and gold(I) N-heterocyclic carbenes by
[2 + 3] dipolar cycloadditions†
Audrey Hospital,a Clémentine Gibard,a Christelle Gaulier,a Lionel Nauton,a,b Vincent Théry,a
Malika El-Ghozzi,a Daniel Avignant,a Federico Cisnetti*a and Arnaud Gautier*a,b
Received 2nd February 2012, Accepted 22nd March 2012
DOI: 10.1039/c2dt30249g
A new strategy was developed for the modification of silver(I) and gold(I) N-heterocyclic carbenes. Azido
groups were grafted and used either by copper-catalysed azide–alkyne cycloaddition before metallation
or by thermal and “strain-promoted” 1,3-dipolar cycloaddition after metallation to functionalise the
metal-NHCs.
Introduction
Metal N-heterocyclic carbenes have attracted considerable
interest in the last two decades and they can now be considered
as classics in organometallic chemistry.1 Their strong metal–
carbon bonds, their remarkable electron donating properties and
– in the case or NHCs bearing aromatic “wings” – their steric
protection of the metal centre has allowed them to become a
leading family of organometallic catalysts.2 For similar reasons,
their use as metal-based drugs is currently actively explored.3
For both applications it would be highly desirable to develop
concise functionalisation strategies permitting straightforward
structural variations for stability, solubility and activity modula-
tion.4 Azide–alkyne reactivity is nowadays an attractive entry
into the functionalisation of biomolecules, materials and mole-
cular metal complexes.5 Ruthenium and especially Copper-
catalysed Azide Alkyne Cycloaddition (RuAAC and CuAAC,
respectively) are the methods of choice in those modifications
yielding 1,5- and 1,4-disubstituted triazoles, respectively.6
A literature survey reveals few examples of metal-NHCs bearing
a triazole moiety. Indeed, they are obtained by the metallation
of an imidazolium already containing a triazole pendant (pre-
functionalisation)7 or by realizing a click reaction on a metal-
NHC that bears a suitable azide or alkyne (post-functionalisa-
tion).8,9 Both pathways are considered in this paper (Fig. 1).
Fig. 1 Pre- and post-functionalisation paths discussed in this paper.
To the best of our knowledge in the context of metal-NHC
chemistry, all the examples deal with starting materials bearing
alkyne groups.7,8 We hypothesize that the use of azide pendants
would potentially broaden the scope of the functionalisation
strategies by employing metal-catalysed azide–alkyne chemistry
or by the so-called “strain-promoted” azide–alkyne cycloaddi-
tions (SPAAC), a copper-free reaction.10 Moreover we have
chosen aromatic azide sites, which implies that minimal pertur-
bations would be experienced by the coordinating core: the final
complexes will contain peripherial triazole groups sterically
unable to interfere with the metal centre. Here, we report the
synthesis of an azide–bearing imidazolium IPrN3·HCl (IPrN3:
1,3-bis(4-azido-2,6-diisopropylphenyl)imidazol-2-ylidene), the
synthesis of its related Ag(I) and Au(I) complexes and its
CuAAC and “strain-promoted” functionalisation.
aInstitut de Chimie de Clermont-Ferrand, Clermont Université,
Université Blaise Pascal, F-63000 Clermont-Ferrand, France.
E-mail: federico.cisnetti@univ-bpclermont.fr; Fax: +33 473 407 717;
Tel: +33 473 407 110
bCNRS, UMR 6296, F-63177 Aubière, Cedex, France.
E-mail: arnaud.gautier@univ-bpclermont.fr; Fax: +33 473 407 717;
Tel: +33 473 407 646
Results and discussion
†Electronic supplementary information (ESI) available: crystal packing
of 22, selected 1D and 2D NMR spectra, attribution of NMR spectra of
BCN adducts 9 and 24, pictures of the transition states as computed by
DFT. CCDC 864597, 864596 and 864598 (16, 21 and 22 respectively).
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c2dt30249g
1. Pre-functionalisation
Scheme 1 depicts the synthetic route employed in the synthesis
of a bis-azido imidazolium salt selected for the pre-functionalisa-
tion strategy.
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Scheme 1 The synthetic pathway to IPrN3·HCl (5).
Scheme 3 Pre-functionalisation and cyclisation of bisimine precursors
and structure of catalyst 6.
In our effort to access a greater variety of functionalised
metal-NHCs, the pre-functionalisation strategy was also applied
on the precursor 4 (Scheme 3). Indeed, in contrast with imidazo-
lium 5, this bisimine proved easily functionalisable with phenyl-
acetylene, propargyl alcohol and a cationic choline-derived
alkyne using 0.5 mol% of 6. Thus, bisimine 4 was entirely
converted to the 1,2,3-triazoles 10, 11 and 12 bearing phenyl,
hydroxymethyl and (N,N-dimethyl-N-2-hydroxylethyl)ammonio-
methyl groups, respectively. 10 and 11 were efficiently cyclised
to imidazolium cations 13 and 14 according to Hintermann.13
Applying a similar protocol to 12 resulted in partial solvolytic
opening of the starting bisimine. However, this matter was
efficiently circumvented using pivaloyloxymethyl chloride
(POMCl) to yield the imidazolium 15.
Scheme 2 The synthesis of 9 and unsuccessful catalyzed and thermal
Huisgen reactions on 5.
Therefore, para-iodo-aniline 2 was easily obtained through
11
iodination of 1 with I2 and the required 4-azido-aniline 3 was
synthesized taking advantage of the very efficient protocol of
Liang et al.12 The bisimine 4 was obtained after reacting 3 with
0.5 equiv. glyoxal and recovered by a simple filtration. Finally,
Hintermann’s cyclisation procedure13 was applied to obtain 5
(IPrN3·HCl). All the synthetic sequence may be conducted in
2–3 working days, at the gram-scale, with no chromatographic
purification and with an overall yield of 21%. Unfortunately, 5
proved to be unreactive towards cycloaddition with phenylacety-
lene or propargyl alcohol (Scheme 2) under catalysis {Cu(II) +
THPTA + sodium ascorbate14 or with [CuCl(4,7-Cl2-1,10-Phen)
(SIMes)]15 (6), a Cu(I)-NHC catalyst that tolerates oxygen}.
Under thermal conditions with the activated alkyne dimethylace-
tylene dicarboxylate 7, decomposition to an intricate mixture of
products was observed at 90 °C while no Huisgen adduct was
observed at lower temperatures. However, we were pleased to
observe that the reaction with bicyclo[6.1.0]non-4-yn-9-ylmetha-
nol 8 (BCN, a SPAAC reagent) affords a total conversion to 9 at
room temperature. This reaction takes place rapidly and exother-
mically at a concentration of 0.1–0.5 M in methanol.
Thereafter, metallation reactions could be performed using
methods depicted in Scheme 4. Metallation of hydrophobic 13
was performed classically by Lin’s protocol.16 Metallocarbene
16 thus obtained serves as transmetallation synthon to efficiently
access the heteroleptic gold complex 17. Due to their poor solu-
bility in CH2Cl2, metallation procedures of hydrophilic imidazo-
lium salts 14 and 15 are more original and deserve detailed
discussion. Indeed, metallation of 14 with silver(I) oxide is not
feasible in dichloromethane or other aprotic solvents due to
insufficient solubility in these media of the imidazolium salt.
Therefore, methanol was chosen for this reaction. In this solvent,
a slow reaction takes place (several days) at room temperature
affording a mixture of products. However, overnight in refluxing
methanol, a single product is obtained. This product appears to
be the homoleptic complex 18 as shown by elemental, MS
1
and NMR analyses. The observed JC–Ag coupling constants
(186 and 215 Hz) and compare very well with those observed
for homoleptic silver(I) complexes.17 Unfortunately, this
6804 | Dalton Trans., 2012, 41, 6803–6812
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Fig. 2 The thermal ellipsoid plot of silver(I) complex 16. Ellipsoids
were drawn at 50% probability level and H atoms omitted for clarity.
Table 1 Structural features of interest for silver(I) complex 16
Phenyl–triazole
Bonds and angles
interplane angle (°)
C1–Ag (Å)
Ag–Cl (Å)
C1–Ag–Cl (°)
2.058(8)
2.314(2)
177.2(3)
34.7a
43.4a
8.2b
12.7b
a Triazole containing N3, N4, N5. b Triazole containing N6, N7 and N8.
regarding the metal-carbene core, the structure revealed note-
worthy features concerning the peripherial triazoles (Fig. 2 and
Table 1).21
Due to crystal packing – in particular π–π interactions – the
two triazole moieties were found in different positions. One of
them is close to coplanarity with both phenyl and phenylene
planes, while for the other no coplanarity is observed. Overall,
the twist around the latter triazole results in nearly perpendicular
phenyl and phenylene planes.
Scheme 4 Metallation reactions of triazole functionalised NHCs.
complex proved to be unreactive in transmetallation experiments.
Gold(I) complex 19 was instead obtained using an alternative
procedure implying a direct metallation reaction with in situ pre-
pared alcohol-soluble AuCl·tdg (tdg = thiodiglycol, [S(CH2-
CH2OH)2]). The latter species was obtained by the reduction of
HAuCl4 with excess thiodiglycol.18 Despite the high pKa values
reported for the NCHN group – 21.1 in water for IPr·H+ 19 – 19
was obtained after short reaction times at room temperature
using stoichiometric20 sodium hydroxide. This direct metallation
procedure with AuCl·tdg was straightforwardly adapted to obtain
the gold carbene 20 bearing cationic side-chains. The triazole-
functionalised NHC complexes metal carbenes show very vari-
able solubilities extending from dichloromethane for 16 and 17
(R = Ph) to ethanol or methanol for 18, 19 and even to water for
20. The latter complex indeed displayed full hydrosolubility
(>50 mg mL−1).
2. Post-functionalisation
We synthesized [AgCl(IPrN3)] (21) and [AuC(lPrN3)] (22), that
were subjected to cycloaddition reactions. Both materials were
obtained by conventional procedures: 21 by the reaction of
IPrN3·HCl with Ag2O and 22 by the transmetallation of 21 with
AuCl·SMe2 (Scheme 5).
X-ray diffraction-suitable crystals of both metal-NHCs 21 and
22 were grown by vapour diffusion of n-pentane in concen-
trated dichloromethane solutions.†‡ As expected, the bonds and
angles in both complexes proved to be very similar to those of
[AgCl(IPr)] and [AuCl(IPr)] (Fig. 3 and Table 2).
While hydrophilic compounds 18–20 were isolated as analyti-
cally pure solids, unfortunately no monocrystals could be
obtained. Fortunately, X-ray suitable crystals of 16 could be
obtained by layering a dichloromethane solution of this com-
pound with n-pentane.‡ While being very similar to [AgCl(IPr)]
Interestingly, azide–azide dipolar interactions are apparent in
the structures packing (dipole–dipole distances: 3.31 and 3.68 Å)
and may be partly responsible of crystal integrity (ESI†).
ˉ
‡Crystallographic data for 16: C43H46AgClN8, triclinic, space group P1,
a = 11.5948(9) Å, b = 14.2010(12) Å, c = 14.4224(12) Å, α = 74.320
(5), β = 66.567(4), γ = 88.958(4), V = 2087.1(3) Å3, T = 293(2) K, Z =
2, Final R (I > 3σ(I)): R1 = 0.0499, wR2 = 0.0431, s = 1.1601. Crystallo-
graphic data for 21: C27H34AgClN8·CH2Cl2, monoclinic, space group
P21/n, a = 10.0772(3) Å, b = 15.3419(5) Å, c = 21.5215(8) Å, β =
92.1640(10)°, V = 3324.92(19) Å3, T = 293(2) K, Z = 4, Final R (I >
3σ(I)): R1 = 0.0400, wR2 = 0.0473, s = 0.8432. Crystallographic data for
22: C27H34AuClN8, monoclinic, s space group P21/n, a = 9.9292(3) Å,
b = 15.3418(5) Å, c = 21.8821(7) Å, β = 90.9950(10)°, V = 3332.84(18)
Å3, T = 293(2) K, Z = 4, Final R (I > 4σ(I)): R1 = 0.0531, wR2
0.0539, s = 0.9989.
=
Scheme 5 The synthesis of azido-metallocarbenes 21 and 22.
Dalton Trans., 2012, 41, 6803–6812 | 6805
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Fig. 3 Thermal ellipsoid plots of silver and gold complexes 21 and 22.
Ellipsoids were drawn at 50% probability level and H atoms and solvent
molecule (for 21) omitted for clarity.
Scheme 7 Functionalisation of gold complex 22 by the cyclooctyne 8.
(8) and other “copper free click reagents” are now of high inter-
est in biology and material sciences. Even if we have tested this
reaction only with gold(I) species, we are convinced of its appli-
cability to other transition metal complexes.
Table 2 Coordination bond lengths and angles of 21 and 22 in
comparison with the parent IPr complexes
C–M (Å)
M–Cl (Å)
C–M–Cl (°)
[AgCl(IPr)]a
2.056(6)
2.070(3)
1.942(3)
1.985(7)
2.316(17)
2.3141(10)
2.2698(11)
2.276(2)
175.2(2)
174.71(10)
177.0(4)
177.5(2)
21
[AuCl(IPr)]b
3. Quantum calculations
22
We decided to undertake density functional theory (DFT) calcu-
lations in order to further investigate the reactivity in Huisgen
cycloadditions of imidazolium 5 and gold(I)-NHC 22 with
dimethylacetylene dicarboxylate or BCN. Indeed, experi-
mentally, the picture is a priori not completely clear, because in
thermal conditions the Huisgen cycloaddition could not be per-
formed satisfactorily due to decomposition of the starting
material in the case of imidazolium 5. Its reactivity could thus
not be compared with that of 22.
a Ref. 21. b Ref. 22.
Gibbs and transition state energies (TS) for a [2 + 3] dipolar
cycloaddition between imidazolium 5 and the gold(I)-NHC 22
with dimethylacetylene dicarboxylate (7) and BCN (8) were cal-
culated by DFT [B3LYP/6-31G(d,p)] using Gaussian 09 and
B3LYP/genecp (Au SDD; C N H O Cl 6-31G(d,p)) for the
gold(I) complex 22 (Table 3 and Fig. 4).24 For consistency, TS
and Gibbs energies were calculated for all compounds at 75 °C,
which corresponds to the limit of the observed thermal stability
of the diazide 5.
Scheme 6 Thermal Huisgen functionalisation of gold complex 22.
Gold complex 22 was subjected to various functionalisation
experiments. Treatment with diphenylacetylene showed no reac-
tion, even at 160 °C (the total amount of starting material was
recovered unchanged). Also, no reaction with propargyl alcohol
catalysed by Cu(II) + THPTA + sodium ascorbate or by 6 (5 mol
%) at room temperature took place. However, using catalyst
6 (3 mol%) at 45 °C overnight, a 50% conversion of 22 to
triazole-containing species – 19 and an unsymmetrical species
most probably resulting from CuAAC on only one of the two
It can be noticed that the transition state energies associated
with these highly exothermic reactions (in agreement with what
is commonly accepted for an azide–alkyne cycloaddition)
decrease from the linear to the strained alkyne. Indeed, the bar-
riers for the two reactions of 7 are 28.2 and 24.6 kcal mol−1
.
This leads to poor reactivities of 5 + 7 (decomposition occurred
instead) and 22 + 7 (several days of reaction in concentrated sol-
ution to reach completion). The “strain-promoted” 1,3-dipolar
cycloaddition displayed by BCN (8) is evidenced by the two
lowest TS computed: for both the imidazolium 5 and the gold(I)
carbene 22 the transition state energy is 10.9 kcal mol−1. 13.7
and 17.3 kcal mol−1 are gained in comparison with reactions of
the linear alkyne 7. Consequently, this strain effect allows the
cycloadditions to occur efficiently both on azide-tagged gold
1
azide functions – was confirmed by H NMR but with the con-
comitant formation of undefined compounds.
Importantly, we were pleased to observe that 22 could be sub-
jected to thermal Huisgen cycloaddition with the activated
alkyne 7 (Scheme 6).23 While degradation products were
observed at T > 75 °C, a clean and total conversion was reached
after 240 h at 60 °C in CCl4 affording 23.
As far as we know, the functionalisation of 22 is the first
example of thermal Huisgen cycloaddition of a metal NHC.
Although the functionalised gold(I)-NHC 19 was successfully
obtained, the high sensitivity of the reaction to the thermal con-
ditions and the slow rate observed indicates the limited scope of
this method employing a classical activated internal alkyne.
Therefore to enlarge the scope of the reaction, we re-investigated
the “strain-promoted” 1,3-dipolar cycloaddition effect using
BCN 8 (Scheme 7) on gold carbene 22.
Table 3 Gibbs and transition state energies
Reactions
Gibbsa
TSa
5 + 7
5 + 8
22 + 7
22 + 8
−43.7
−59.7
−48.8
−62.3
28.2
10.9
24.6
10.9
a kcal mol−1
.
Gratifyingly, the reaction affords the complex 24 at room
temperature (0.06 mol L−1). This result is of importance as BCN
6806 | Dalton Trans., 2012, 41, 6803–6812
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internal references (1H, 13C). Electrospray (positive mode) high-
resolution mass spectra were recorded on a Q-TOF micro
spectrometer (Waters), using internal (H3PO4) and external lock
masses (leucine-enkephalin [M + H]+: m/z = 556.2766).
IR spectra were recorded on a Shimadzu Fourier Transform
Infrared Spectrophotometer FTIR-8400S. Elemental analyses
were performed at the Service de Microanalyse, Université
Henry Poincaré, Vandoeuvre-les-Nancy, France. All calculations
were conducted using density functional theory (DFT) as imple-
mented in the Gaussian 09 program. Geometry optimizations
were performed using the restricted B3LYP exchange and corre-
lation function and the triple-ζ 6-311G(d,p) basis set for all
atoms except for Au (SDD basis set) [B3LYP/6-311G (C, N, O,
H)/SDD (Au)]. Harmonic frequency analysis based on analytical
second derivatives was used to characterize the optimized geo-
metries as local minima. Diffraction intensity data were collected
at T = 293 K with a Bruker APEX-II CCD diffractometer
[Mo-Kα radiation (λ = 0.7107 Å)]. The structure was solved
by direct methods with SHELXS-9726 and refined with
SHELXL-9727 implemented in the Crystals program package.28
Fig. 4 A simplified picture of the Gibbs and transition state energies.
NHCs and their imidazolium precursors. This confirms that even
though 5 and 22 could not be satisfactorily functionalised by
CuAAC, they possess a moderate and identical reactivity in
Huisgen dipolar cycloadditions and that the strain-promotion is
fully efficient in these systems.
4-Iodo-2,6-diisopropylaniline (2)
Adapted from a literature procedure.11 2,6-Diisopropylaniline (1)
(40.0 mL, 37.6 g, 212 mmol, 1.0 eq.) was added to 200 mL
Et2O. Iodine (59.21 g, 233 mmol, 1.1 eq.) and a saturated
sodium bicarbonate solution (600 mL) were added and the
resulting biphasic mixture was stirred vigorously. Gas evolution
was observed. After 2 h, excess iodine was destroyed by addition
of sodium thiosulfate and 2 was recovered by separation of the
ethereal phase and further extraction (2 × 100 mL Et2O) of the
aqueous phase. The joint organic phases were washed with
200 mL H2O and evaporated to yield 61.7 g (203 mmol, 96%)
Conclusions
In summary, we have reported herein novel silver and gold
N-heterocyclic carbenes both in their azide and “clicked”
versions. Thermal Huisgen reaction with dimethylacetylene
dicarboxylate is feasible on a gold carbene allowing the first
entry into a potentially easily functionalisable tetraester Au(I)-
NHC. In addition, we demonstrate that BCN, a prototype
‘copper-free’ click reagent reacts very easily with an imidazo-
lium and its corresponding Au(I)-NHC, paving the way for
easier functionalisation of metal carbenes. Accordingly, com-
plexes such as 23 and 24 may constitute important complex pre-
cursors for further modification of the ester or the alcohol
moieties. Further studies are underway in our laboratory in order
to explore other applications of these complexes taking advan-
tage of these new functionalisation entries.
1
of 2 as a brown oil. H NMR (400 MHz, DMSO-d6): δ (ppm) =
7.09 (s, 2H, HAr), 4.81 (bs, 2H, NH2), 2.97 (hept, J = 6.7 Hz,
2H, CH(CH3)2), 1.10 (d, J = 6.7 Hz, 12H, CH(CH3)2). Analyses
match previously reported data.29
4-Azido-2,6-diisopropylaniline (3)
2 (30.0 g, 98.9 mmol, 1.0 eq.), NaN3 (12.9 g, 197.9 mmol,
2.0 eq.) and N,N′-dimethylethylenediamine (1.60 mL,
14.9 mmol, 15 mol%) were dissolved in DMSO/water (180 mL/
45 mL). Ascorbic acid (1.70 g, 9.9 mmol, 10 mol%) and NaOH
(400 mg, 9.9 mmol, 10 mol%) were added and the reaction
mixture was degassed by bubbling argon for 20 min at 50 °C.
Then, CuI (1.90 g, 9.9 mmol, 10 mol%) was added and the
resulting mixture was stirred at 50 °C overnight. Brine (200 mL)
was added and the aqueous layer was extracted with 3 × 100 mL
of diethyl ether, then dried over MgSO4 and evaporated under
reduced pressure to afford 20.1 g of a brownish oil (92.1 mmol,
93%). 1H NMR (400 MHz, CDCl3): δ (ppm) = 6.72 (s, 2H,
HAr), 3.70 (s, 2H, NH2), 2.93 (hept, J = 6.8 Hz, 2H, CH(CH3)2),
1.27 (d, J = 6.8 Hz, 12H, CH(CH3)2). 13C NMR (100 MHz,
CDCl3): δ (ppm) = [137.6, 134.2, 129.8, (CqAr)], 113.7 (CHAr),
28.1 (CH(CH3)2), 22.2 (CH(CH3)2). IR ν˜ (cm−1): 2963, 2107
(N3), 1638, 1600, 1571, 1560, 1464, 1257, 1073, 901. HRMS
Experimental
General remarks
Reagents and solvents were purchased from Acros, Sigma-
Aldrich and Fisher Scientific at reagent grade and used without
further purification. Bicyclo[6.1.0]non-4-yn-9-ylmethanol (BCN,
8) was purchased from SynAffix. Warning! Organic and inor-
ganic azides may pose safety concerns due to their potential
explosivity. However, none of the organic azides 3–5 described
herein is to considered to be dangerous according to a commonly
accepted rule (NC/NN ≥ 3).25 The synthesis of N-(2-hydroxy-
ethyl)-N,N-dimethylprop-2-yn-1-aminium chloride is described
elsewhere.15c NMR spectra were recorded in Fourier transform
mode with a Bruker AVANCE 400 spectrometer (1H at
400 MHz, 13C at 100 MHz) at 298 K. Data are reported as
chemical shifts (δ) in ppm. Residual solvent signals were used as
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(ESI+) calculated for C12H20N4 [M + H]+: 219.1610, found:
219.1615.
(d, J = 7.0 Hz, 12H), 0.90 (m, 4H), 0.73 (m, 2H). 13C NMR
(100 MHz, MeOH-d4): δ (ppm) = [149.2, 147.0, 137.3, 132.4,
CqAr], 141.2, 128.1, 124.0, 66.6, 31.02, 29.1, 28.8, 28.3, 26.5,
24.74, 24.72, 24.5, 23.81, 23.78, 23.75, 23.70. See ESI† for
further attributions and 2D NMR data. HRMS (ESI+) calculated
for C47H63N8O2 [M]+: 771.5074, found: 771.5063.
N,N′-Bis(4-azido-2,6-diisopropylphenyl)1,4-diazabuta-1,3-diene
(4)
3 (21.6 g, 98.9 mmol, 1.0 eq.) was dissolved in 55 mL of metha-
nol at 50 °C. Glyoxal (30% w/w in water, 7.2 mL, 44.5 mmol,
0.45 eq.) and acetic acid (0.5 mL, 477 mg, 21.0 mmol, 0.21 eq.)
were added and the resulting mixture was stirred at room
temperature for 4 h. A solid separated. It was filtered and washed
with cold methanol to afford, after drying under vacuum, 17.0 g
of a yellow powder (37.0 mmol, 75%). 1H NMR (400 MHz,
DMSO-d6): δ (ppm) = 8.16 (s, 2H, Himine), 6.90 (s, 4H, HAr),
2.85 (hept, J = 6.8 Hz, 4H, CH(CH3)2), 1.13 (d, J = 6.8 Hz,
24H, CH(CH3)2). 13C NMR (100 MHz, CDCl3): δ (ppm) =
163.5 (Cimine), [145.1, 139.0, 136.8, (CqAr)], 114.1 (CHAr), 28.3
(CH(CH3)2), 23.3 (CH(CH3)2). IR ν˜ (cm−1): 2961, 2101 (N3),
1625 (imine), 1598, 1461, 1442, 1336, 1302, 1233, 1182, 795.
HRMS (ESI+) calculated for C26H35N8 [M + H]+: 459.2985,
found: 459.2993.
N,N′-Bis[2,6-diisopropyl-4-(4-phenyl-1,2,3-1H-triazol-1-yl)-
phenyl]1,4-diazabuta-1,3-diene (10)
To 36 mL of methanol were added 4 (2.00 g, 4.36 mmol, 1.0
eq.), phenyl acetylene (1.05 mL, 9.59 mmol, 2.2 eq.) and 6
(14.0 mg, 21.9 μmol, 0.5 mol%). The reaction mixture was
stirred at 60 °C overnight. The resulting solid was filtered,
washed with cold (0 °C) methanol and dried under reduced
pressure to yield 2.17 g (3.28 mmol, 75%) of a yellow powder.
1H NMR (400 MHz, CDCl3): δ (ppm) = [8.21 (s, 2H), 8.18
(s, 2H), (Himine, Htriazole)], 7.95 (d, J = 7.3 Hz, 4H, HPh), 7.59
(s, 4H, HAr), 7.49 (t, J = 7.3 Hz, 4H, HPh), 7.40 (t, J = 7.3 Hz,
2H, HPh), 3.04 (hept, J = 6.8 Hz, 4H, CH(CH3)2), 1.31 (d, J =
6.8 Hz, 24H, CH(CH3)2). 13C NMR (100 MHz, CDCl3):
δ (ppm) = 163.5 (Cimine), [148.4, 148.3, 138.9, 134.8, 130.5,
(CqAr)], [129.1, 128.5, 126.0, (CHPh)], 118.1 (CHtriazole), 116.3
(CHAr), 28.6 (CH(CH3)2), 23.7 (CH(CH3)2). IR ν˜ (cm−1): 2969,
2358, 1650 (imine), 1472, 1240, 1043, 871, 771. HRMS (ESI+)
calculated for C43H47N8 [M + H]+: 663.3924, found: 663.3910.
N,N′-Bis(4-azido-2,6-diisopropylphenyl)imidazolium chloride (5)
To 200 mL of warm (70 °C) ethyl acetate were added under stir-
ring 4 (11.0 g, 24.0 mmol, 1.0 eq.) and paraformaldehyde
(1.06 g, 35.3 mmol, 1.47 eq.). TMSCl (3.04 mL, 24.0 mmol,
1.0 eq.) diluted in 20 mL of ethyl acetate was added dropwise
and the reaction mixture was stirred overnight. After cooling to
RT, the solvent was evaporated under reduced pressure and the
resulting oil was triturated with tert-butylmethylether until a
solid separated. 6.90 g of a brown powder were recovered by
N,N′-Bis[2,6-diisopropyl-4-(4-hydroxymethyl-1,2,3-1H-triazol-1-
yl)phenyl]-1,4-diazabuta-1,3-diene (11)
To a mixture of ethyl acetate and MeOH (v/v = 4/1, 25 mL)
were added 4 (2.38 g, 5.19 mmol, 1.0 eq.), propargyl alcohol
(674 μL, 11.4 mmol, 2.2 eq.) and 6 (64.0 mg, 44 μmol, 0.8 mol
%). The reaction mixture was stirred at 30 °C for 72 h. The
formed solid was filtered, washed with cold (0 °C) ethyl acetate/
MeOH (v/v = 4/1, 25 mL) and dried under reduced pressure to
1
filtration (13.6 mmol, 57%). H NMR (400 MHz, DMSO-d6):
δ (ppm) = 10.24 (t, J = 1.2 Hz, 1H, NCHN), 8.53 (d, J = 1.2
Hz, 2H, NCHCHN), 7.19 (s, 4H, HAr), 2.30 (hept, J = 6.8 Hz,
4H, CH(CH3)2), [1.23 (d, J = 6.8 Hz, 12H), 1.13 (d, J = 6.8 Hz,
12H), (CH(CH3)2)]. 13C NMR (100 MHz, CDCl3): δ (ppm) =
[147.3, 143.7, 126.9, CqAr], 141.5 (NCHN), 126.3 (NCHCHN),
115.3 (CHAr), 29.5 (CH(CH3)2), [24.7, 23.7 CH(CH3)2].
IR ν˜ (cm−1): 2966, 2929, 2870, 2106 (N3), 1597, 1539, 1464,
1339, 1308, 1249, 1238. HRMS (ESI+) calculated for C27H35N8
[M]+: 471.2979, found: 471.2979.
1
afford 2.54 g of a yellow powder (4.94 mmol, 95%). H NMR
(400 MHz, DMSO-d6): δ (ppm) = 8.79 (s, 2H, Htriazole), 8.29
(s, 2H, Himine), 7.70 (s, 4H, HAr), 5.35 (t, J = 5.8 Hz, 2H, OH),
4.62 (d, J = 5.8 Hz, 4H, CH2OH), 2.94 (hept, J = 6.8 Hz, 4H,
CH(CH3)2), 1.22 (d, J = 6.8 Hz, 24H CH(CH3)2). 13C NMR
(100 MHz, CDCl3): δ (ppm) = 163.9 (Cimine), [148.7, 147.3,
137.7, 133.9, (CqAr)], 120.9 (CHtriazole), 115.0 (CHAr), 54.8
(CH2OH), 27.6 (CH(CH3)2), 22.6 CH(CH3)2). IR ν˜ (cm−1):
3300 (broad, OH) 2962, 1619 (imine), 1481, 1342, 1239, 1020.
HRMS (ESI+): calculated for C33H44N8O2 [M]+: 583.3509
Found: 583.3514.
N,N′-Bis(2,6-diisopropyl-4-(6-(hydroxymethyl)-5,5a,6,6a,7,8-
hexahydrocyclopropa[5,6]cycloocta[1,2-d][1,2,3]triazol-1(4H)-yl)-
phenyl)imidazolium chloride (9)
To 212 μL of methanol were added 5 (16.0 mg, 31.7 μmol, 1.0
eq.) and 8 (10.0 mg, 66.6 μmol, 2.1 eq.). An exothermic reaction
occurred instantaneously. The reaction mixture was stirred for
2 h. Evaporation of the solvent afforded 26.0 mg of a pale
N,N′-Bis{2,6-diisopropyl-4-[4-(N-(2-hydroxyethyl)-N,N-
dimethylammoniomethyl)-1,2,3-1H-triazol-1-yl]phenyl}1,4-
diazabuta-1,3-diene dichloride (12)
1
reddish solid. H NMR (400 MHz, MeOH-d4): δ (ppm) = 10.25
(t, J = 1.5 Hz), 8.51 (d, J = 1.5 Hz, 2H), 7.65 (s, 4H), 3.46 (dd,
J = 7.0 Hz, J = 11.0 Hz, 2H), 3.40 (dd, J = 7.0 Hz, J = 11.0 Hz,
2H), 3.08 (ddd, J = 3.0 Hz, J = 7.5 Hz, J = 16.0 Hz, 2H),
2.99–2.90 (m, 4H), 2.78 (ddd, J = 3.0 Hz, J = 9.5 Hz, J = 16.0
Hz, 2H), 2.61 (hept, J = 7.0 Hz, 4H), 2.48 (m, 2H),
2.39 (m, 2H), 1.51 (m, 4H), 1.41 (d, J = 7.0 Hz, 12 H), 1.33
To a mixture of 7 mL of ethyl acetate and 2 mL of methanol
were added 4 (750 mg, 1.64 mmol, 1.0 eq.), N-(2-hydro-
xyethyl)-N,N-dimethylprop-2-yn-1-aminium chloride (535 mg,
3.27 mmol, 2.0 eq.) and 6 (10.0 mg, 16 μmol, 1 mol%).
The reaction mixture was heated under stirring at 60 °C for 4 h.
A yellow solid formed. The solution was evaporated to dryness,
6808 | Dalton Trans., 2012, 41, 6803–6812
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the solid residue was washed several times with ethyl acetate and
dried in vacuum. Isolated mass: 1.11 g (1.41 mmol, 86%).
1HNMR (400 MHz, MeOH-d4): δ (ppm) = 8.90 (s, 2H, Htriazole),
8.25 (s, 2H, Himine), 7.73 (s, 4H, HAr), 4.86 (s, 4H, CH2N
(CH3)2), 4.18 (t, J = 4.8 Hz, 4H, NCH2CH2OH), 3.47 (t, J = 4.8
Hz, 4H, NCH2CH2OH), 3.27 (s, 12H, N(CH3)2), 3.06 (hept, J =
6.8 Hz, 4H, CH(CH3)2), 1.31 (d, J = 6.6 Hz, 24H, CH(CH3)2).
13C NMR (100 MHz, MeOH-d4): δ (ppm) = 166.6 (Cimine),
[150.2, 140.3, 137.7, 135.7 (CqAr)], 128.0 (CHtriazole), 117.4
(CHAr), 66.8 (NCH2CH2), 60.8 (NCH2Ctriazole), 57.1 (CH2OH),
52.0 (N(CH3)2), 29.7 (CH(CH3)2), 23.5 (CH(CH3)2).
IR ν˜ (cm−1): 3200 (broad, OH), 1627 (imine), 1481, 1250, 1057,
1051, 1011, 907, 880, 801.
29.1 (CH(CH3)2), [23.7, 22.7 (CH(CH3)2)]. IR ν˜ (cm−1): 3300
(broad, OH), 2965. 2360, 1603, 1540, 1481, 1214, 1041. HRMS
(ESI+): calculated for C33H43N8O2 [M − Cl]+: 583.3509,
+
found: 583.3514.
N,N′-Bis{2,6-diisopropyl-4-[4-(N-(2-hydroxyethyl)-N,N-
dimethylammoniomethyl)-1,2,3-1H-triazol-1-yl]phenyl}-
imidazolium trichloride (15)
To 15 mL of warm DMSO (50 °C) was added 12 (1.47 g,
1.87 mmol, 1.0 eq.) and pivaloylmethyl chloride (408 μL,
400 mg, 2.81 mmol, 1.5 eq.). The reaction was complete after
2 days (1H NMR). The solution was poured on 150 mL of
acetone and the resulting mixture was stirred at 0 °C for 1 h.
After filtration, washing with acetone, diethyl ether and drying
under reduced pressure gave 1.35 g of a beige solid (1.62 mmol,
87%). 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 10.71 (s, 1H,
NCHN), 9.62 (s, 2H, Htriazole), 8.72 (s, 2H, NCHCHN), 8.15
(s, 4H, HAr), 5.60 (bs, 2H, OH), 4.91 (s, 4H, CH2N(CH3)2), 3.97
(m, 4H, NCH2CH2OH), 3.48 (m, 4H, NCH2CH2OH), 3.19
(s, 12H, N(CH3)2), 2.51 (hept, J = 6.8 Hz, 4H, CH(CH3)2),
[1.39 (d, J = 6.8 Hz, 12H), 1.27 (d, J = 6.8 Hz, 12H), CH
(CH3)2]. 13C NMR (100 MHz, DMSO-d6): δ (ppm) = [147.4,
140.0, 138.9, 136.7, (CqAr)], 129.9 (NCHN), [127.5, 126.4,
N,N′-Bis(2,6-diisopropyl-4-(4-phenyl-1,2,3-1H-triazol-1-yl)-
phenyl)imidazolium chloride (13)
To 25 mL of warm (70 °C) ethyl acetate were added under vigo-
rous stirring 10 (1.68 g, 3.00 mmol, 1.0 eq.) and paraformalde-
hyde (127 mg, 4.23 mmol, 1.40 eq.). TMSCl (420 μL,
3.30 mmol, 1.1 eq.), in 8 mL of ethyl acetate, was added drop-
wise over 45 min and the reaction mixture was stirred for 2 h
before being cooled at 10 °C after which a solid formed. The
solid was filtered, washed with diethyl ether and dried under
reduced pressure to give 1.12 g (1.57 mmol, 52%) of a off-white
powder. 1H NMR (400 MHz, DMSO-d6) δ (ppm) = 10.41
(s, 1H, NCHN), 9.62 (s, 2H, Htriazole), 8.71 (s, 2H, NCHCHN),
8.13 (s, 4H, HAr), 7.99 (d, J = 7.5Hz, 4H, HPh), 7.55 (t, J = 7.5
Hz, 4H, HPh), 7.43 (t, J = 7.5 Hz, 2H, HPh), 2.48 (hept, 4H, J =
6.7 Hz, CH(CH3)2), [1.40 (d, J = 6.7 Hz, 12H), 1.29 (d, J = 6.7
Hz, 12H), (CH(CH3)2)]. 13C NMR (100 MHz, DMSO-d6/
MeOH-d4 v/v: 1/1): δ (ppm) = [148.9, 148.5, 140.3, 130.9,
130.5, (CqAr)], 140.6 (NCHN), [129.7, 129.2, 126.3 (CHPh)],
127.3 (NCHCHN), 120.4 (CHtriazole), 116.9 (CHAr), 30.2 CH
(CH3)2), [24.3, 23.3, (CH(CH3)2)]. IR ν˜ (cm−1): 2969, 1603,
1540, 1478, 1230, 1018, 759. HRMS (ESI+): calculated for
(CHtriazole
, NCHCHN)], 116.7 (CHAr), 64.3 (NCH2CH2),
58.4 (NCH2Ctriazole), 54.9 (CH2OH), 50.6 (N(CH3)2), 29.2
(CH(CH3)2), [23.9, 22.9, (CH(CH3)2)]. IR ν˜ (cm−1): 3350
(broad, OH), 2965, 1602, 1484, 1468, 1355, 1257, 1051, 1010,
884. HRMS (ESI+) calculated for C41H62N10O2 [M − H]2+:
363.2529, found: 363.2528.
{N,N′-Bis[2,6-diisopropyl-4-(4-phenyl-1,2,3-1H-triazol-1-yl)-
phenyl]imidazol-2-ylidene}chlorosilver(I) (16)
To 25 mL of dichloromethane were added 13 (500 mg,
0.701 mmol, 1.0 eq.) and Ag2O (106 mg, 0.46 mmol, 0.65 eq.).
The reaction mixture was stirred overnight in the dark before
being filtered over celite and evaporated. The resulting solid was
dissolved in 5 mL of dichloromethane and n-pentane (∼25 mL)
was added dropwise to give 387 mg of a white solid
(0.47 mmol, 67%). Monocrystals were grown by layering
n-pentane onto a concentrated solution of 16 in dichloromethane.
1H NMR (400 MHz, DMSO-d6): δ (ppm) = 9.51 (s, 2H,
C43H47N8 [M − Cl]+: 675.3924, found: 675.3939. Anal. calcd
+
for C43H47ClN8: C 72.60, H 6.66, N 15.75, found: C 72.03,
H 6.61, N 15.75.
N,N′-Bis(2,6-diisopropyl-4-(4-hydroxymethyl-1,2,3-1H-triazol-1-
yl)phenyl)imidazolium chloride (14)
H
triazole), 8.21 (s, 2H, NCHCHN), 8.03 (s, 4H, HAr), [7.98 (d,
To 10 mL of warm (40 °C) THF were added under stirring 11
(1.08 g, 1.88 mmol, 1.0 eq.) and paraformaldehyde (80.0 mg,
2.67 mmol, 1.4 eq.). TMSCl (250 μL, 2.26 mmol, 1.2 eq.) was
added dropwise and the reaction was stirred overnight with
vigorous stirring to form a white solid. After cooling to room
temperature, the solid was filtered, washed with diethyl ether and
dried under reduced pressure. Isolated mass: 786 mg
J = 7.3 Hz, 4H), 7.54 (t, J = 7.3 Hz, 4H), 7.42 (t, J = 7.3 Hz,
2H), HPh], 2.59 (hept, J = 6.7 Hz, 4H, CH(CH3)2), 1.33 (m,
24H, CH(CH3)2)). 13C NMR (100 MHz, CDCl3): [149.0, 148.3,
139.2, 134.6, 130.2 (CqAr)] [129.2, 128.8, 126.2 (CHPh)], 124.3
3
(d, JAg–C = 6 Hz, NCHCHN), 118.2 (CHtriazole), 117.3 (CHAr),
29.4 CH(CH3)2), [24.8, 24.1, CH(CH3)2)]; (carbene carbon not
detected). IR ν˜ (cm−1): 2966, 1602, 1478, 1404, 1231, 1046,
1019, 947, 767. Anal. calcd for C43H46AgClN8: C 63.12, H
5.64, N 13.60, found: C 62.78, H 5.64, N 13.60.
1
(1.27 mmol, 68%). H NMR (400 MHz, DMSO-d6): δ (ppm) =
10.34 (s, 1H, NCHN), 9.04 (s, 2H, Htriazole), 8.68 (s, 2H,
NCHCHN), 8.07 (s, 4H, HAr), 5.44 (t, 2H, J = 5.5 Hz, OH) 4.67
(d, J = 5.5 Hz, 4H, CH2OH), 2.56 (hept, J = 6.7 Hz, 4H, CH
(CH3)2), [1.35 (d, J = 6.7 Hz, 12H), 1.25 (d, J = 6.7 Hz, 12H),
(CH(CH3)2)]. 13C NMR (100 MHz, DMSO-d6): δ (ppm) =
[147.2, 149.6, 139.2, 129.3, (CqAr)], 139.7 (NCHN), 126.4
(NCHCHN), 121.5 (CHtriazole), 115.9 (CHAr), 54.9 (CH2OH),
{N,N′-Bis[2,6-diisopropyl-4-(4-phenyl-1,2,3-1H-triazol-1-yl)-
phenyl]imidazol-2-ylidene}chlorogold(I) (17)
To 6 mL of dichloromethane were added under stirring 16
(150 mg, 0.183 mmol, 1.0 eq.) and 56.7 mg of AuCl·Me2S
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(0.192 mmol, 1.05 eq.). The solution was protected from light
and stirred at 30 °C overnight. The solution was filtered over
celite® and evaporated. The solid was taken up with 3 mL of
dichloromethane and n-pentane (∼15 mL) was added dropwise
to give 152 mg of a white powder (0.167 mmol, 91%). 1H NMR
(400 MHz, DMSO-d6): δ (ppm) = 9.52 (s, 2H, Htriazole), 8.21
(s, 2H, NCHCHN), [8.0 (m, 8H), 7.54 (t, J = 7.5 Hz, 4H), 7.42
(t, J = 7.5 Hz, 2H), HAr, HPh], 2.60 (hept, J = 6.8 Hz, 4H, CH
(CH3)2), [1.39 (d, J = 6.8 Hz, 12H), 1.34 (d, J = 6.8 Hz, 12H),
(CH(CH3)2)]. 13C NMR (100 MHz, CDCl3/DMSO-d6 v/v 1/2):
δ (ppm) = 173.6 (Ccarbene), [147.4, 147.3, 138.0, 133.3, 130.0,
(CqAr)], [128.4, 127.8, 125.1 (CHPh)], 124.2 (NCHCN), 119.4
(CHtriazole), 115.4 (CHAr), 28.6 (CH(CH3)2), [23.6, 23.1, (CH
(CH3)2)]. IR ν˜ (cm−1): 2966, 1602, 1478, 1407, 1357, 1230,
1039, 1019, 946, 766. HRMS (ESI+) calculated for
C43H47N8AuCl [M + H]+: 907.3278, found: 907.3260. Anal.
calcd for C43H46AuClN8: C 56.92, H 5.11, N 12.35, found: C
56.53, H 5.02, N 12.22.
performed by the elution of 7 mL of water, followed by 14 mL
of methanol. After evaporation the product was obtained as
72.0 mg (0.088 mmol, 44%) of an off-white solid.
1H NMR (400 MHz, MeOH-d4): δ (ppm) = 8.69 (s, 2H, Htriazole),
7.92 (s, 4H, HAr), 7.90 (s, 2H, NCHCHN), 4.82 (s, 4H,
CH2OH), 2.71 (hept, J = 6.8 Hz, 4H, CH(CH3)2), [1.45 (d,
J = 6.8 Hz, 12H), 1.37 (d, J = 6.8 Hz, 12H), (CH(CH3)2)].
13C NMR (400 MHz, MeOH-d4) δ (ppm) = 175.9 (Ccarbene),
[149.9, 140.8, 135.8, 126.0, (CqAr)], 126.0 (NCCHN), 117.4
(CHAr), 56.7 (CH2OH), 30.8 (CH(CH3)2), [25.0, 24.4, (CH
(CH3)2)]. IR ν˜ (cm−1): 3300 (broad, OH), 2970, 1603, 1484,
1046, 881, 805.HRMS (ESI+) calculated for C33H43N8O2AuCl
[M
+
H]+ 815.2863, found: 815.2879. Anal. calcd for
C33H42AuClN8O2: C 48.62, H 5.19, N 13.75, found: C 48.35,
H 5.26, N 13.35.
(N,N’-Bis{2,6-diisopropyl-4-[4-(N-(2-hydroxyethyl)-N,N-
dimethylammoniomethyl)-1,2,3-1H-triazol-1-yl]phenyl}imidazol-
2-ylidene)chlorogold(I) dichloride (20)
Bis{N,N′-bis[2,6-diisopropyl-4-(4-hydroxymethyl-1,2,3-1H-
triazol-1-yl)phenyl]imidazol-2-ylidene}silver(I) chloride (18)
To 12 mL of methanol were added HAuCl4·3.5H2O (74.0 mg,
0.176 mmol, 1.05 eq.) and thiodiglycol (131.0 mg, 1.07 mmol,
6.1 eq.). The solution was heated at 40 °C for a few minutes
during which it turned from yellow to colourless. To 6 mL of
methanol were added 15 (140 mg, 0.168 mmol, 1.0 eq.) and
NaOH (31.0 mg, 0.763 mmol, 4.55 eq.). This solution was
added to the former to give a dark mixture. After 3 h at room
temperature this mixture was filtered through a nylon membrane
filter (0.2 μm). The resulting solution was evaporated to yield an
oil which was triturated with 3 × 20 mL of ether/acetone (v/v
1/1) to give a powder. The product was dissolved in 7 mL of
water and this solution introduced in a Waters Sep-Pak cartridge.
Desalting was performed by the elution of 7 mL of water, fol-
lowed by 7 mL of methanol. After evaporation, the product was
taken up in 20 mL of water prior to lyophilisation which
afforded 101 mg of 20 as an off-white solid (0.098 mmol, 59%).
1H NMR (400 MHz, MeOH-d4) δ (ppm) = 9.12 (s, 2H, Htriazole),
7.97 (s, 4H, HAr), 7.92 (s, 2H, NCHCHN), 4.92 (s, 4H,
CH2OH), 4.14 (m, 4H, NCH2CH2OH), 3.60 (m, 4H,
NCH2CH2OH), 3.27 (s, 12H, N(CH3)2), 2.72 (hept, J = 6.8 Hz,
4H, CH(CH3)2), [1.44 (d, J = 6.8 Hz, 12H), 1.36 (d, J = 6.8 Hz,
12H), (CH(CH3)2)]. 13C NMR (100 MHz, MeOH-d4):
δ (ppm) = 175.8 (Ccarbene), [149.9, 139.9, 137.9, 136.0, (CqAr)],
128.3 (CHtriazole), 125.9 (NCHCHN), 118.0 (CHAr), 66.7
(NCH2CH2), 60.7 (NCH2Ctriazole), 57.1 (CH2OH), 52.1
(N(CH3)2), 30.7 (CH(CH3)2), [24.5, 24.1 (CH(CH3)2)]. IR ν˜
(cm−1): 3250 (broad, OH), 2967, 2931, 2870, 1603, 1559, 1487,
1466, 1458, 1387, 1351, 1257, 1077, 1050, 1010, 946, 909,
881, 770. HRMS (ESI+) calculated for C41H62AuN10O2 [M]2+:
479.2206, found: 479.2227. Anal. calcd for C41H62AuCl3N10O2:
C 47.79, H 6.07, N 13.59, found: C 48.04, H 6.07, N 13.10.
To 25 mL of methanol were added 14 (250 mg, 0.404 mmol,
1.0 eq.) and Ag2O (60 mg, 0.260 mmol, 0.65 eq.). The suspen-
sion was refluxed overnight. The solution was filtered over
celite®, evaporated and taken up with 1.5 mL of methanol and
20 mL of diethyl ether was added dropwise to give 143 mg of
1
an off-white powder (0.106 mmol, 52%). H NMR (400 MHz,
DMSO-d6) δ (ppm) = 8.83 (s, 4H, Htriazole), 8.00 (s, 4H,
NCHCHN), 7.60 (s, 8H, HAr), 5.48 (br s, 4H, OH), 4.74 (s, 8H,
CH2OH), 2.27 (hept, J = 6.9 Hz, 8H, CH(CH3)2), 1.05 (d, J =
6.9 Hz, 24H, CH(CH3)2), 0.83 (d, J = 6.9 Hz, 24H, CH(CH3)2).
13C NMR (100 MHz, DMSO-d6): δ (ppm) = 181.3 (2 × d,
1JC–Ag = 186/215 Hz, Ccarbene), [149.4, 147.0, 138.1, 133.9,
3
(CqAr)], 125.9 (d, JC–Ag = 6 Hz, NCHCHN), 121.3 (CHtriazole),
115.8 (CHAr), 55.0 (CH2OH), 28.5 (CH(CH3)2), [23.3, 23.2
(CH(CH3)2)]. IR ν˜ (cm−1): 3200 (broad, OH), 2969, 2910, 1602,
1485, 1406, 1234, 1050, 947, 882. HRMS (ESI+) calculated for
C66H85N16O4Ag [M + H]2+: 636.2995, found: 636.2985. Anal.
calcd for C66H84AgClN16O4·2H2O: C 58.86, H 6.74, N 16.64,
found: C 58.69, H 6.34, N 16.39.
{N,N′-Bis[2,6-diisopropyl-4-(4-hydroxymethyl-1,2,3-1H-triazol-
1-yl)phenyl]-imidazol-2-ylidene}chlorogold(I) (19)
To 13 mL of methanol were added HAuCl4·3.5H2O (88.4 mg,
0.210 mmol, 1.05 eq.) and thiodiglycol (156.4 mg, 1.28 mmol,
6.4 eq.). The solution was heated at 40 °C for a few minutes
during which it turned from yellow to colourless. To 7 mL of
methanol were added 14 (123.7 mg, 0.200 mmol, 1.0 eq.) and
NaOH (36.4 mg, 0.91 mmol, 4.55 eq.). This solution was added
to the former to give a dark solution. After 2 h at room tempera-
ture the mixture was filtered through a nylon membrane filter
(0.2 μm). The resulting colourless solution was evaporated to
obtain an oil which was taken up in 3 mL MeOH and 45 mL of
diethyl ether was added dropwise to yield 106.0 mg of a powder.
The latter was suspended in 7 mL of water and this solution
introduced in a Waters Sep-Pak cartridge. Desalting was
[N,N′-Bis(4-azido-2,6-diisopropylphenyl)imidazol-2-ylidene]-
chlorosilver(I) (21)
To 140 mL of dichloromethane, were added 5 (2.00 g,
3.95 mmol, 1.0 eq.) and silver oxide (595 mg, 2.57 mmol, 0.65
eq.). After 2 h under stirring in the dark at room temperature, the
6810 | Dalton Trans., 2012, 41, 6803–6812
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suspension was filtered over celite® and the resulting solution
evaporated under reduced pressure to afford a yellow powder.
The solid was dissolved in 35 mL of dichloromethane and
120 mL of n-pentane was added dropwise under stirring.
Filtration afforded 2.20 g of a pale brown powder (3.28 mmol,
83%). Monocrystals were grown by vapour diffusion at 4 °C of
n-pentane onto a concentrated solution of 21 in dichloromethane.
1H NMR (400 MHz, DMSO-d6): δ (ppm) = 8.01 (s, 2H,
NCHCHN), 7.11 (s, 4H, HAr), 2.44 (hept, J = 6.8 Hz, 4H, CH
(CH3)2), 1.20 (t, J = 6.8 Hz, 24 H, CH(CH3)2). 13C NMR
(d, J = 6.8 Hz, 12H), CH(CH3)2]. 13C NMR (100 MHz, CDCl3):
δ (ppm) = 176.5 (Ccarbene), [160.2, 159.5, (CvO)], [148.4,
139.3, 137.9, 135.4, 133.0, CqAr], 123.5 (NCHCHN), 120.7
(CHAr), [54.5, 53.0, (COOCH3)], 29.5 (CH(CH3)2), [24.4, 24.0,
(CH(CH3)2)]. IR ν˜ (cm−1): 2966, 1738 (CvO), 1482, 1438,
1368, 1329, 1292, 1209, 1153, 1118, 1077, 946. HRMS (ESI+)
calculated for C39H47N8O8AuCl [M + H]+: 987.2871, found:
987.2865. Anal. Calcd for C39H46AuClN8O8: C 47.45, H 4.70,
N 11.35, found: C 47.62, H 4.75, N 10.85.
1
(100 MHz, CDCl3): δ (ppm) = 182.4 (2 × d, JC–Ag = 268/232
3
{N,N′-Bis[2,6-diisopropyl-4-(6-(hydroxymethyl)-5,5a,6,6a,7,8-
hexahydrocyclopropa[5,6]cycloocta[1,2-d][1,2,3]triazol-1(4H)-yl)-
phenyl]-imidazol-2-ylidene}chlorogold(I) (24)
Hz, Ccarbene), [147.5, 141.5, 131.3, (CqAr)], 125.1 (d, JC–Ag
=
7 Hz, NCHCHN), 114.9 (CHAr), 28.5 (CH(CH3)2), [23.9, 23.1
(CH(CH3)2)]. IR ν˜ (cm−1): 2964, 2117 (N3), 1655, 1597, 1469,
1385, 1365, 1337, 1312, 1283, 1273, 1250, 1100, 1073, 880,
858. Anal. Calcd for C27H34AgClN8·2/3CH2Cl2: C 49.56,
H 5.31, N 16.71, found: C 49.73, H 5.38, N 16.27.
To 1060 μL of CCl4 and 266 μL methanol were added 23
(22.8 mg, 32.5 μmol, 1.0 eq.) and 8 (10.0 mg, 66 μmol, 2.05
eq.). The reaction mixture was stirred for 2 h. Evaporation of the
solvent afforded 32.5 mg of a pale reddish solid. 1H NMR
(400 MHz, DMSO-d6): δ (ppm) = 8.22 (s, 2H), 7.54 (s, 4H),
3.28 (d, J = 6.5 Hz, 4H), 3.08 (ddd, J = 2.5 Hz, J = 7.5 Hz, J =
15.5 Hz, 2H), 2.91–2.78 (m, 4H), 2.71 (ddd, J = 3.0 Hz, J =
10.0 Hz, J = 15.5 Hz, 2H), 2.56 (hept, J = 7.0 Hz, 4H), 2.35
(m, 2H), 2.29 (m, 2H), 1.37–1.51 (m, 4H), 1.32 (d, J = 7.0 Hz,
12H), 1.27 (d, J = 7.0 Hz, 12H), 0.76–0.83 (m, 4H), 0.60
(m, 2H). 13C NMR (100 MHz, DMSO-d6): δ (ppm) = 173.2
(Ccarbene), [147.3, 144.7, 138.1, 134.7, 134.3, (CqAr)], 124.8,
121.6, 64.0, 28.8, 27.6, 27.2, 26.6, 25.4, 23.69, 23.66, 23.24,
23.20, 23.1, 21.7, 21.7. See ESI† for further attributions and 2D
NMR data. IR ν˜ (cm−1): 3200 (broad, OH), 2966, 2926, 2870,
1601, 1480, 1420, 1388, 1087, 1048, 947. C47H64AuN8O2Cl
[M + 2H]2+: 502.2248, found: 502.2227.
[N,N′-Bis(4-azido-2,6-diisopropylphenyl)-imidazol-2-ylidene]-
chlorogold(I) (22)
21 (417 mg, 0.68 mmol, 1.0 eq.) and AuCl·Me2S (200 mg,
0.68 mmol, 1.0 eq.) were dissolved in 21 mL of dichloro-
methane. The reaction mixture was stirred for 24 h at 30 °C –
protected from light – before filtration over celite® and evapora-
tion under reduced pressure. The resulting solid was taken up
with dichloromethane (6 mL) and 40 mL of n-pentane was
added dropwise under stirring to afford 345 mg of a white solid
(0.45 mmol, 66%). Monocrystals were grown by vapour diffu-
sion at 4 °C of n-pentane onto a concentrated solution of 22 in
1
dichloromethane. H NMR (400 MHz, DMSO-d6): δ (ppm) =
8.01 (s, 2H, NCHCHN), 7.10 (s, 4H, HAr), 2.44 (hept, J = 6.8
Hz, 4H, CH(CH3)2), [1.25 (d, J = 6.8 Hz, 12H), 1.20 (d, J = 6.8
Hz, 12H), (CH(CH3)2)]. 13C NMR (100 MHz, DMSO-d6):
δ (ppm) = 173.4 (Ccarbene), [147.5, 141.5, 130.7, (CqAr)], 124.7
(NCHCHN), 114.8 (CHAr), 28.6 (CH(CH3)2), (23.6, 23.2, CH
(CH3)2). IR ν˜ (cm−1): 2965, 2115 (N3), 1597, 1472, 1338, 1249,
1075, 949, 880, 858. HRMS (ESI+) calculated for C27H37-
N8AuClNa [M + Na]+: 725.2518, found: 725.2519. Anal. calcd
for C27H34AuClN8·2/3CH2Cl2: C 43.74, H 4.69, N 14.75,
found: C 43.84, H 4.66, N 14.24.
Notes and references
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{N,N′-Bis[2,6-diisopropyl-4-(4,5-dimethoxycarbonyl-1,2,3-1H-
triazol-1-yl)phenyl]-imidazol-2-ylidene}chlorogold(I) (23)
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Into a sealed tube were added 2.5 mL of CCl4, 22 (35.1 mg,
50.0 μmol, 1.0 eq.) and 7 (37.5 μL, 0.30 mmol, 6.0 eq.). The
solution was stirred at 60 °C in the dark for 240 h. The solvent
was removed under reduced pressure and the resulting oil was
triturated with n-pentane (2 × 20 mL). After drying under
vacuum the crude material contained non-aromatic contaminants
probably arising from degradation of 7 (1H NMR). The product
was purified by SiO2 column chromatography (eluent: chloro-
form/acetone v/v 98/2) and 32.0 mg of a powder was obtained
(32.5 μmol, 65% yield).
1H NMR (400 MHz, CDCl3): 7.54 (s, 4H, HAr), 7.33 (s, 2H,
NCHCHN), [4.04 (s, 6H), 3.96 (s, 6H), (COOCH3)], 2.64 (hept,
J = 6.8 Hz, 4H, CH(CH3)2), [1.40 (d, J = 6.8 Hz, 12H), 1.29
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Dalton Trans., 2012, 41, 6803–6812 | 6811

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6812 | Dalton Trans., 2012, 41, 6803–6812
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