Studies on gold(i) and gold(iii) alcohol functionalised NHC complexes

Article abstract of DOI:10.1039/d1dt00387a

Five pairs of novel chiral alcohol functionalised gold(i) and gold(iii) NHC complexes derived from chiral amino alcohols, were synthesized and characterised (NMR, IR, HRMS). Single crystal X-ray diffraction data of gold(i) and gold(iii) complexes are reported and discussed. The chiral imidazolium preligands were readily synthesizedviathe oxalamides, subsequent reduction and final orthoformate condensation. An improved method was used for generation of gold(i) NHC complexes (up to 92%) and further oxidation afforded the corresponding gold(iii) NHC complexes (up to 99%). All the Au(i) and Au(iii) NHC complexes proved far more catalytically active in a 1,6-enyne alkoxycyclization test reaction than our previously testedN,N- andP,N-ligated Au(iii) complexes. Comparative gold(i) and gold(iii) catalytic studies demonstrated different catalytic ability, depending on the NHC ligand flexibility and bulkiness. Excellent yields (92-99%) of target alkoxycyclization product were obtained with both gold(i) and gold(iii) complexes with the bulkyN¹-Mes-N²-ethanol based NHC ligand.

Full text of DOI:10.1039/d1dt00387a

Volume 50
Number 15
21 April 2021
Pages 5053-5372
Dalton
Transactions
An international journal of inorganic chemistry
rsc.li/dalton
ISSN 1477-9226
PAPER
Anne Fiksdahl et al.
Studies on gold(I) and gold(III) alcohol functionalised NHC
complexes
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PAPER
Studies on gold(I) and gold(III) alcohol
functionalised NHC complexes†
Helgi Freyr Jónsson,a Andreas Orthaber b and Anne Fiksdahl
Cite this: Dalton Trans., 2021, 50,
5128
a
*
Five pairs of novel chiral alcohol functionalised gold(I) and gold(III) NHC complexes derived from chiral
amino alcohols, were synthesized and characterised (NMR, IR, HRMS). Single crystal X-ray diffraction data
of gold(I) and gold(III) complexes are reported and discussed. The chiral imidazolium preligands were
readily synthesized via the oxalamides, subsequent reduction and final orthoformate condensation. An
improved method was used for generation of gold(I) NHC complexes (up to 92%) and further oxidation
afforded the corresponding gold(III) NHC complexes (up to 99%). All the Au(I) and Au(III) NHC complexes
proved far more catalytically active in a 1,6-enyne alkoxycyclization test reaction than our previously
tested N,N- and P,N-ligated Au(III) complexes. Comparative gold(I) and gold(III) catalytic studies demon-
strated different catalytic ability, depending on the NHC ligand flexibility and bulkiness. Excellent yields
(92–99%) of target alkoxycyclization product were obtained with both gold(I) and gold(III) complexes with
the bulky N1-Mes-N2-ethanol based NHC ligand.
Received 3rd February 2021,
Accepted 5th March 2021
DOI: 10.1039/d1dt00387a
rsc.li/dalton
lated NHC complex developed by Toste achieved excellent
kinetic resolution of a 1,5-cycloisomerization.27 Additionally,
Introduction
Homogenous gold catalysis is one of the fastest growing fields the study of the biological activity, especially anticancer, of
within homogenous transition metal catalysis. Gold catalysts both gold(I) and gold(III) NHC complexes is an active field.28
display excellent selectivity towards the activation of carbon–
In contrast to the linear coordination mode of gold(I),
carbon multiple bonds, allowing for wide array of gold(III) forms tetracoordinate, square planar complexes, which
a
transformations.1–8 Moreover, in the span of two decades gold presents an opportunity for additional chelating or hemilabile
catalysis has gone from a novelty to a widely recognised and functionalities on the NHC ligand.21,29 Such ligated Au(III) cat-
useful tool in organic synthesis and has found application in alysts might bring a prochiral reacting substrate closer to the
the total synthesis of several complex natural products.9–11 chiral environment of the ligand, improving the enantio-
N-Heterocyclic carbenes (NHCs) have likewise become ubiqui- selectivity of the reaction. Alcohol-functionalised NHC ligands
tous ligands in transition metal catalysis12 since the first iso- have been successfully employed in copper catalysed conjugate
lation of a free NHC in 1991 by Arduengo.13 Their properties addition of enones.30 Additionally, we have previously reported
as strong σ-donors, even stronger than the widely used phos- a series of chiral, alcohol functionalised gold(I) NHC com-
phines, lead to the formation of strong bonds to most tran- plexes, catalytic active in cyclopropanation reactions.31 The
sition metals, gold among them.14 Gold(I) NHC complexes direct and modular template synthesis of NHC–gold com-
have widely been adopted as catalysts,15,16 also within asym- plexes with a free hydoxy group has also been reported.32
metric gold(I) catalysis.17–19 Even though gold(III) NHC com- Herein, we report the synthesis and structure of novel alcohol
plexes are easily prepared from the analogous gold(I) NHC functionalised gold(I) and gold(III) NHC complexes and their
complexes,20 their use as catalysts is so far limited, despite catalytic activity in alkoxycyclisation of 1,6-enynes.
their potential catalytic activity.21–26 Reports of chiral gold(III)
NHC complexes have been scarce, though a chiral cyclometal-
Results and discussion
Preparation of imidazolium preligands
aDepartment of Chemistry, Norwegian University of Science and Technology,
NO-7491 Trondheim, Norway. E-mail: anne.fiksdahl@chem.ntnu.no
bDepartment of Organic Chemistry – Ångström Laboratory, Uppsala University,
The imidazolinium chloride preligands 7a–e were readily avail-
Lägerhyddsvägen 1, 751 20, Uppsala, Sweden
†Electronic supplementary information (ESI) available: Copies of 1H and 13C
able through a slightly modified four-step synthetic method
(Scheme 1a).30 Oxalamide ethyl esters 3a,b were prepared in
NMR spectra. CCDC 2056822, 2056823, 2056825, 2056827, 2056945 and
quantitative yield from mesityl/benzyl amines 2a,b and ethyl
chlorooxoacetate 1. Subsequent condensation with chiral amino-
2056946. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/d1dt00387a
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Scheme 1 Synthesis of (a) imidazolium chloride preligands 7a–e; (b) Au(I)NHC complexes 8a–e and (c) Au(III)NHC complexes 9a–e.
alcohols 4a–c in refluxing ethanol yielded the asymmetric and water (1 : 1) by vigorous stirring and simple work-up (brine
oxalamides 5a–e (76–99%), which were reduced with LiAlH4 to washing of organic phase and filtering through short silica
give the corresponding N1-Mes/Bn-N2-(iPr/Ph)-ethanol dia- plug). This method was used for the synthesis of all gold(I) NHC
mines 6a–d (61–77%) and N1-Mes-N2-indanol diamine 6e complexes 8a–e (Scheme 1b). The flexible N1-Mes-N2-(iPr/Ph)-
(77%). Finally, protonation by anhydrous HCl (1 eq.) followed ethanol–NHC gold(I) complexes 8a,b were more successfully pre-
by cyclocondensation with trimethylorthoformate yielded the pared (91–92%) than the corresponding rigid N1-Mes-N2-
respective imidazolinium chlorides 7a–e in moderate to high indanol complex 8e (69%). The N1-Bn complexes 8c and 8d
yields (49–90%).
proved less stable under the reaction conditions. Hence, lower
isolated yields (52–56%) were obtained, due to significant
decomposition during the course of the reaction.
Synthesis of gold(I) and gold(III) NHC complexes
The NHC ligated gold(I) complexes 8a–e were prepared from
1H NMR studies readily illustrate the course of the K2CO3-
imidazolinium chloride preligands 7a–e. Initially, the most Me2SAuCl reaction (Scheme 1b) with imidazolinium chloride 7e
commonly used route towards gold(I) NHC complexes33 via to give the gold(I) NHC complex 8e (Fig. 1). As reported by both
transmetalation of a silver(I) NHC complex, usually generated Nolan34 and Gimeno,35 this reaction proceeds through an inter-
in situ, was applied. The reaction of imidazolinium chlorides mediate anion exchange of imidazolinium chloride to
−
7a,b,e with Ag2O (0.5–1 eq.) in DCM for 3–24 h, followed by Me2SAuCl, giving the new AuCl2 imidazolinium counterion.
addition of Me2SAuCl, provided gold(I) NHC complexes 8a,b,e The chloride counterion exchange is observed by 1H NMR spec-
in moderate yields (48–69%). However, due to unreacted troscopy, in particular by a shielding effect for the H2 proton
Me2SAuCl, the product isolation required chromatographic (from 8.65 to 8.40 ppm for 7e, Fig. 1a and b). The formation of
purification. A more convenient and atom-efficient method to the desired Au(I) complex is clearly verified by the dis-
generate gold(I) NHC complexes is based on treatment of the appearance of the acidic H2 proton (Fig. 1c). The formation of
imidazolinium salt (Scheme 1b) by a weak base, such as K2CO3, Au(I) NHC was also seen by the large change in chemical shift
in either refluxing acetone34 or in DCM at room temperature.35 of the original imidazolium (7e) C2 13C NMR signal at
Stirring imidazolinium salts 7a,e in refluxing acetone with ∼140 ppm, appearing as a NHC carbenic carbon resonance at
K2CO3 (1 eq.) and Me2SAuCl gave full conversion of imidazoli- ∼195 ppm (8e, which is characteristic for gold(I) NHC com-
nium salts 7a,e in 2 hours, but only low yields of Au(I) com- plexes with a saturated imidazoline backbone.33 1H NMR also
plexes 8a,e (50–56%) and formation of a dark precipitate, indi- demonstrates that most aliphatic indanol protons are clearly
cating significant decomposition to gold(0). The similar reac- affected and mostly experience a shielding effect by ligand
tion of imidazolinium choride 7b in DCM at room temperature coordination and formation of the target Au(I) NHC complex 8e.
with increased amount of K2CO3 (10 eq.) was slow (<35% con-
The Au(III) NHC–alcohol complexes 9a–e were readily pre-
version to complex 8b in 12 hours; 1H NMR). However, fast con- pared by oxidation of the respective (AuI) complexes 8a–e with
version (<2 h) and excellent yield (up to 91% of 8b) was dichloroiodobenzene, PhICl2, in DCM at room temperature
obtained for the corresponding reaction in a mixture of DCM (Scheme 1c).20 The reactions proceeded smoothly and afforded
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−
Fig. 1 1H NMR studies; formation of (c) Au(I) NHC complex 8e from K2CO3, Me2SAuCl and (a) preligand 7e (Scheme 1b), via (b) imidazolium AuCl2
salt.
high yields of complexes 9a and 9c–e (89–96%). The lower yield
Selected bond lengths and bond angles for the analysed
of complex 9b (53%) was due to solubility issues and challen- structures are reported in Table 1. The Au–C bond in the Au(I)
ging product isolation. The successful Au(I)-to-Au(III) oxidation of complexes 8a,b,e is in average significantly shorter (<2.0 Å)
complexes 8a–e was verified by the significant change of chemi- compared to that found in the corresponding Au(III) species
cal shift of the carbenic 13C NMR resonance from ∼195 ppm to 9a,b,e (>2.05 Å). This is in line with reported Au(I) and Au(III)
∼170 ppm, which is characteristic for gold(I)- and gold(III) NHC NHC complexes, which have average NHC-Au(I) and Au(III) dis-
complexes of saturated imidazolines, respectively.36
tances of 1.984 0.022 Å (range 1.897–2.151 Å)37 and 2.004
0.012 Å (range 1.986–2.039 Å).23,38 Notably, 9b shows the
longest NHC–Au(III) distance (2.055 Å) reported so far.
Interestingly, in this series the chloride atom trans to the
carbene centre shows significantly shorter Au–Cl distances in
case of Au(I) (2.28–2.29 Å) compared those in Au(III) (2.32 Å)
complexes. In comparison with literature reported Au(III)–
Cltrans distances the average is slightly longer (2.314 0.010 Å,
range 2.291–2.338 Å)39 compared to the Au(I)–Cl distances
(2.286 0.015 Å, range 2.253–2.350 Å),40 however both classes
XRD, structural discussion
All the gold(I) and gold(III) complexes 8a–e and 9a–e were air
stable, crystalline solids, and could be stored indefinitely in the
freezer under normal atmosphere and were stable for several
days in NMR tubes in CDCl3. Crystals for single crystal X-ray
diffraction were obtained for complexes 8b,d,e and 9a,b,e by
slow diffusion of diethyl ether into saturated dichloromethane
solutions of the complexes (solid state structures Fig. 2).
Fig. 2 Solid state structures of gold(I) and gold(III) NHC complexes 8b,d,e and 9a,b,e obtained by X-ray crystallographic analysis.
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Table 1 Structural parameters of crystallographically characterized gold(I) and gold(III) NHC complexes
Au(I)
Au(I)
8b
8da
8e
9a
9b
9e
C1–Au
1.980(5)
2.2870(13)
177.61(16)
—
—
—
—
—
1.99
2.28
178.3
—
—
—
—
—
125.7
125.3
—
1.972(12)
2.295(3)
178.3(3)
—
—
—
2.016(6)
2.3269(17)
178.1(2)
2.055
2.324
178.7
2.27
2.278
88.6
90.3
176.7
129.2
127.3
85.5
2.009(5)
2.3290(12)
177.26(13)
2.2876(13)
2.2845(12)
87.72(13)
91.10(13)
174.61(6)
125.8(4)
Au–Cltrans
C–Au–Cltrans
AuClcis
2.275(2)
2.265(2)
88.39(19)
91.39(19)
176.05(9)
127.3(5)
127.4(5)
89.8(2)
AuClcis
C–Au–Clcis
C–Au–Clcis
Cl–Au–Cl
C4–N1–C1
C13–N2–C1
Angle of planesb
—
—
126.2(4)
124.7(4)
—
124.2(9)
122.1(10)
—
125.4(4)
100.4(1)
a Average value of two independent molecules. b Dihedral angle between the least square planes spanned by the NHC backbone and the C
̲·AuCl3
motif.
cover a wide ranges of Au–Cltrans distances. The cis-chlorides in elemental gold, as proven by IR (broad OH and new urea CvO
the Au(III) complexes have shorter Au–Cl distances (1672 cm−1) signal) and 13C NMR (urea CvO at 165.0 ppm).
(2.26–2.28 Å), which is not reflected in the structurally reported Lowering the reaction temperature slowed down the unwanted
Au(III) complexes (range 2.227–2.382; average 2.280
0.023 Å).41 There is no noticeable deviation from linearity for
the Au(I) complexes nor from an ideal square planar Au(III)
configuration. The latter plane is significantly distorted from
the least squares plane spanned by the NHC backbone (9b:
85.5°; 9a: 89.8°: 9e: 100.4°) to accommodate for the steric
demand of the N-substituents, which is not uncommon for
this class of complexes.42–45
NHC-oxidation, but still no coordination was observed.
Catalytic activity of Au NHC complexes
The alkoxycyclisation of a 1,6-enyne8,48,49 is known to be cata-
lysed by gold(I) NHC catalysts17–19,50–52 and also by gold(III)
complexes.53,54 Our previous studies on the mechanism55,56 of
the this gold catalysed reaction54 show that initial gold–alkyne
coordination activates towards nucleophilic intramolecular
attack by the alkene, and yields a carbocation which undergoes
nucleophilic attack by methanol. Final proton transfer and
deauration yields the 3-methylene-cyclopentane target product
13 from enyne substrate 12 (Table 2). The exocyclic double bond
of 13 may isomerise to give the endocyclic double bond isomer
14. The alkoxycyclisation of 1,6-enyne 12 into cyclopentane
product 13 was chosen as a model reaction to test the catalytic
activity of the new gold(I)- and gold(III) NHC complexes 8a–e and
9a–e (Table 1). To the best of our knowledge, the reaction has
not previously been catalysed by gold(III) NHC complexes.
The reactions were performed at room temperature with
enyne 12 in MeOH, acting both as a solvent and nucleophile.
For the Au(I) catalyzed reactions (4–6 h, entries 1–5), AgSbF6
(5 mol%) was used for counterion exchange of the non-active
gold(I) NHC–Cl complex (8a–e, 5 mol%). No reaction was
observed in the absence of the silver salt additive. Likewise, no
reaction took place with the silver salt alone. All the Au(I) NHC
complexes 8a–e proved catalytically active and gave the alkoxy-
cyclization product 13 in high to excellent yields (66–99%,
entries 1–5). The N2-ethanol based complexes 8a–d were more
catalytic active (77–99% of 13, 4 h, entries 1–4) than the rigid
cyclic N2-indanol complex 8e (66%, 6 h, entry 5). The two
bulky N1-Mes Au(I)NHC complexes 8a,b gave highest yields of
product 13 (99% and 89%; entries 1,2). Complex 8b also gave
minor amounts of the not previously reported isomer 14 (7%)
with an endocyclic double bond, most likely formed by isomer-
ization of the originally formed product 13. Au(I) NHC com-
Attempted O–Au(III) coordination
Several approaches were attempted to give a bidentate C,O-Au(III)
complex (e.g. 9b′, Scheme 2a) by O-Au(III) coordination of the
alcohol moiety of gold(III) NHC complexes 9a–e. KOAc treatment
for OH deprotonation46 of complex 9b in EtOH gave the unstable
gold(III) acetate derivative 10b (Scheme 2b), by chloride–acetate
1
counterion exchange, as shown by IR (OH-stretch) and H NMR
(OAc), while non-coordinating bases (Cs2CO3 in EtOH) or
Hünig’s base (EtN(i-Pr)2 in DCM) led to black mixtures of un-
identified products (Scheme 2c), presumably due to reduction to
gold(0). As microwave assisted methods have been successfully
applied in the synthesis of gold(III) complexes, e.g. cyclometal-
lated complexes by C–H activation,47 thermal activation
(70–120 °C) was tested for O-Au(III) coordination. No reaction
took place in CH3CN. However, in CH3CN–water (1 : 1, 30 min,
120 °C), the white, crystalline imidazolinone product 11b
(Scheme 2d) was formed by C2 oxidation along with reduction to
Scheme 2 Attempts to coordinate the OH functionality of Au(III) NHC
complex 9b.
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Table 2 Catalytic testing of gold(I) and gold(III) NHC complexes (8a–e
and 9a–e) in gold catalysed alkoxycyclization of 1,6-enyne 12a
were formed (9–32%). This result is consistent with our previous
studies on gold(III) catalysed alkoxycyclisations of 1,6-enynes,
with gold(III) being less suited for this reaction than their gold(I)
counterparts.54,58 The lower selective may be explaned by the
ability of gold(III) complexes to give competing alkyne hydration,
which was supported by the observation of the ketone bypro-
duct (dimethyl 2-cinnamyl-2-(2-oxopropyl)malonate) in some
reactions, together with other non-identified biproducts. High
yield of product 13 (92%) was, however, obtained with the most
bulky N1-Mes-N2-(iPr)ethanol NHC–gold(III) complex 9a.
The bulky N1-Mes Au(I) and Au(III) NHC complexes (8a,b,e
and 9a,b,e) gave minor enantioselectivity. The Au(III) catalysts
9a,b,e afforded slightly higher values (5–6% ee) than the Au(I)
8a,b,e analogues (3–5% ee). The more flexible and less steri-
cally hindered N1-benzyl Au(I) and Au(III) NHC complexes (8c,d
and 9c,d) did not induce enantioselectivity. The lack of stereo-
control is most likely due to the chiral environment provided
by the ligand being too far from the reaction centre.
[Au] catalyst
(ratio AgSbF5 : [Au])
Entry
Timeb
Yieldc
1
2
3
4
5
6
7
8
8a (1 : 1)
8b (1 : 1)
8c (1 : 1)
8d (1 : 1)
8e (1 : 1)
9a (1 : 1)
9a (2 : 1)
9a (3 : 1)
9b (2 : 1)
9c (2 : 1)
9d (2 : 1)
9e (2 : 1)
4 h
4 h
4 h
4 h
6 h
2 h
2 h
2 h
2 h
2 h
2 h
2 h
99% (13)
89% (13) + 7% (14)
79% (13)
77% (13)
66% (13)
44% (13)
92% (13)
38% (13) + 9% (14)
15% (13) + 32% (14)
22% (13) + 15% (14)
38% (13) + 10% (14)
49% (13) + 9% (14)
9
10
11
12
Conclusions
a Reactions were performed on a 0.1 mmole scale in 3 mL MeOH with
5 mol% [Au] and 5–15 mol% AgSbF6. b Full conversion. c Isolated
yields.
Five pairs of chiral gold(I) and gold(III) NHC complexes (8a–e
and 9a–e), derived from chiral amino alcohols, were syn-
thesized and characterised (NMR, IR, HRMS). The chiral imid-
azolium preligands 7a–e were readily synthesized via the oxal-
amides, prepared from the respective chiral aminoalcohols
plexes 8c,d, with the more flexible and less sterically hindered and chlorooxoacetate; subsequent reduction and final ortho-
N1-benzyl substituent, gave product 13 in good yields (79 and formate condensation. An improved method was used for
77%, entries 3,4).
generation of gold(I) NHC complexes (8, up to 92%) and
Thus, our Au(I) NHC complexes gave similar to better yields further oxidation afforded the corresponding gold(III) NHC
and reaction rates in this reaction compared to previously complexes (9, up to 99%). Single crystal X-ray diffraction was
reported Au(I) NHC complexes (48–99% yields, 1–48 h).17–19,50–52 obtained for six gold(I) and gold(III) complexes. Attempts to
The study of the corresponding gold(III) NHC complexes coordinate the pendant alcohol functionality to the gold(III)
were initiated by optimizing the ratio of silver salt additive centre was not successful.
to gold(III) complex 9a (entries 6–8). A 3 : 1 ratio of silver salt/
The synthesised gold(I) and gold(III) NHC complexes (8, 9)
gold(III) catalyst has been used in previous gold(III) catalyzed were studied in an alkoxycyclisation test reaction. All com-
alkoxycyclisations.53 A large increase in yield in AuCl3 cata- plexes were far stronger catalysts than our previously tested
lyzed hydroarylation of alkenes has also been seen by increas- N,N- and P,N-ligated Au(III) complexes in this reaction. Gold(I)
ing the number of equivalents of AgSbF6 from 1 to 3, presum- complexes (8a–e) were most efficient and selective (66–99%
ably due to generation of a more electrophilic gold(III) yield of target product 13, 4 h, r.t.). The gold(III) complexes
species.57 Screening for optimum amount of silver salt to be (9b–e) gave fastest conversion, but were less selective, due to
used with the present gold(III) complex 9a, showed that a competing alkyne hydration. However, excellent yields of
highly increased selectivity (from 44% to 92%) towards the target product 13 (92–99%) were obtained with both gold(I)
main product 13 was obtained going from 1 : 1 to 2 : 1 ratio of and gold(III) complexes (8a, 9a) with the bulky N1-Mes-N2-
AgSbF6/Au(III) catalyst (entries 6 and 7). Further increased ratio ethanol based NHC ligand. Only minor enantioselectivity (up
(3 : 1) had negative impact on the yield and selectivity (entry 8). to 6% ee) was obtained with the most bulky N1-Mes Au(I) and
In general, the other gold(III) NHC complexes 9a–e afforded Au(III)NHC complexes (8a,b,e and 9a,b,e).
faster conversion (100% in 2 h, entries 6–12) than the corres-
ponding gold(I) complexes (4–6 h, entries 1–5), and gave defi-
nitely, more rapid reactions than our previously studied pyri-
Experimental
General
dine-oxazoline-Au(III)51 and P,N-chelated gold(III)51 complexes
(14–62% conversion in 24 h). However, in contrast to Au(I)
NHC complexes 8a–e, the gold(III) NHC 9b–e catalyzed reaction Commercial grade reagents were used without any additional
were less selective, giving poorer yields of target product 13 purification. Dry solvents were collected from a MB SPS-800
(15–49%, entries 9–12), as significant amounts of isomer 14 solvent purification system. All reactions were monitored by
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NMR and/or thin-layer chromatography (TLC) using silic a gel
(S)-N1-(1-Hydroxy-3-methylbutan-2-yl)-N2-mesityloxalamide
60 F254 (0.25 mm thickness). TLC plates were developed using (5a). Following the general procedure, ethyl 2-(mesitylamino)-
UV-light and/or p-anisaldehyde stain. Flash chromatography 2-oxoacetate (3a, 942 mg, 4.00 mmol) and (S)-2-amino-3-
1
was performed with Merck silica gel 60 (0.040–0.063 mm). H methylbutan-1-ol (4a, 413 mg, 4.00 mmol) gave target product
and 13C NMR spectra were recorded either a Bruker Avance 5a as a white solid in 97% yield (1137 mg, 0.89 mmol). 1H
DPX 400 MHz or a Bruker Avance III 600 MHz spectrometer. NMR (600 MHz, CDCl3) δ (ppm) 8.73 (s, 1H, NH), 7.67–7.68 (d,
Chemical shifts are reported in ppm (δ) downfield from tetra- J = 5.4 Hz, 1H, NH), 6.92 (s, 2H, CHAr), 3.74–3.80 (m, 3H, CH +
methylsilane (TMS) as an internal standard. Melting points CH2), 2.28 (s, 3H, CH3), 2.19 (s, 6H, 2 × CH3), 1.97–2.03 (m,
(mp) were determined using a Stuart SMP40 apparatus and are 1H, CH), 1.01–1.02 (d, J = 6.9 Hz, 3H, CH3), 0.98–0.99
uncorrected. Accurate mass determination was performed on a (d, J = 6.9 Hz, 3H, CH3). 1H NMR corresponds to previously
“Synapt G2-S” Q-TOF instrument from Waters. Samples were reported spectra.
ionized with an ASAP probe with no chromatography separ-
((S)-N1-(2-Hydroxy-1-phenylethyl)-N2-mesityloxalamide (5b).
ation performed before mass analysis. IR spectra were Following the general procedure, ethyl 2-(mesitylamino)-2-
recorded with a Nicolet 20SXC FT-IR spectrometer using EZ oxoacetate (3a, 344 mg, 1.56 mmol) and (S)-2-amino-2-phenyl-
OMNIC software to analyse the spectra and a Bruker Alpha ethanol (4a, 214 mg, 1.56 mmol) gave target product 5b as a
FT-IR spectrometer using OPUS V7 software to analyse the white solid in 87% yield (422 mg, 1.36 mmol). 1H NMR
spectra. Single crystal X-ray data were collected on a Bruker D8 (400 MHz, (CD3)2SvO) δ (ppm) 10.06 (s, 1H, NH), 9.10 (d, J =
APEX-II diffractometer equipped with a CCD camera using Mo 8.5 Hz, 1H, NH), 7.32–7.40 (m, 4H, CHAr), 7.25 (tt, J = 7.1, 1.2
Kα radiation (λ = 0.71073 Å).
Hz, 1H, CHAr), 6.89 (s, 2H, CHAr), 4.99 (t, J = 6.0 Hz, 1H, OH),
CCDC ID: 2056822, 2056823, 2056825, 2056827, 2056945, 4.89–4.94 (m, 1H, CH), 3.73–3.79 (m, 1H, CH2), 3.63–3.68 (m,
2056946;† CCDC also included under each complex (8b,d,e 1H, CH2), 2.23 (s, 3H, CH3), 2.07 (s, 6H, CH3).
and, 9b,d,e) below.
((S)-N1-Benzyl-N2-(1-hydroxy-3-methylbutan-2-yl)oxalamide
(5c). Following the general procedure, ethyl 2-(benzylamino)-2-
oxoacetate (3b, 553 mg, 2.67 mmol) and (S)-2-amino-3-methyl-
butan-1-ol (275 mg, 2.67 mmol) gave target product 5c as a
white solid in 93% yield (653 mg, 2.48 mmol). 1H NMR
(400 MHz, CDCl3) δ (ppm) 7.88 (t, J = 6.3 Hz, 1H, NH), (d, J =
7.1 Hz, 1H, NH), 7.27–7.36 (m, 5H, CHAr), 4.43–4.53 (m, 2H,
CH2), 3.68–3.75 (m, 3H, CH + CH2), 2.41 (t, J = 5.7 Hz, 1H,
OH).
General procedure for the synthesis of oxalamide ethyl esters
To a solution of amine 2 (1 eq.) and triethylamine (1 eq.) in
dry DCM (40 mL) was added ethyl chlorooxoacetate 1 (1 eq.).
The resulting solution was stirred at room temperature for
1 hour. The solution was then diluted with 30 mL DCM and
washed with NaHCO3 solution (saturated, 2 × 25 mL) and
brine (25 mL). The organic layer was dryed over anhydrous
Na2SO4, filtered and concentrated in vacuo to afford the pro-
ducts as white solids.
Ethyl 2-(mesitylamino)-2-oxoacetate (3a). Following the
general procedure, mesityl amine (2a, 1.734 g, 12.8 mmol), tri-
ethylamine (1.785 g, 12.8 mmol) and ethyl chlorooxoacetate (1
1.433 g) gave target product 3a as a white solid in 94% yield
(2.843 g, 12.08 mmol). 1H NMR (400 MHz, CDCl3) δ (ppm)
8.33 (s, 1H, NH), 6.92 (s, 2H, CHAr), 4.43 (q, J = 7.0 Hz, 2H,
CH2), 2.28 (s, 3H, CH3), 2.20 (s, 6H, CH3), 1.45 (t, J = 7.0 Hz,
3H, CH3).
Ethyl 2-(benzylamino)-2-oxoacetate (3b). Following the
general procedure, benzyl amine (1293 mg, 12.06 mmol), tri-
ethylamine (1221 mg, 12.06 mmol) and ethyl chlorooxoacetate
(1647 mg, 12.06 mmol) gave target product 3b as a white solid
in 97% yield (2146 mg, 11.70 mmol). 1H NMR (400 MHz,
CDCl3) δ (ppm) 7.50 (s, 1H, NH), 7.27–7.35 (m, 5H, CHAr), 4.50
(d, J = 6.0 Hz, 1H, CH2), 4.32 (q, J = 7.1 Hz, 2H, CH2),
1.36 (t, J = 7.1 Hz, 3H, CH3).
((S)-N1-Benzyl-N2-(2-hydroxy-1-phenylethyl)oxalamide (5d).
Following the general procedure, ethyl 2-(benzylamino)-2-oxo-
acetate(3b, 554 mg, 2.67 mmol) and (S)-2-amino-2-phenyletha-
nol (367 mg, 2.67 mmol) gave target product 5d as a white
1
solid in 99% yield (788 mg, 2.64 mmol). H NMR (400 MHz,
(CD3)2SvO) δ (ppm) 9.29 (t, 1H, J = 6.5 Hz, NH), 8.99 (t, 1H,
J = 8.6 Hz, NH), 7.21–7.35 (m, 10H, CHAr), 4.97 (t, J = 5.7 Hz,
1H, OH), 4.82–4.87 (m, 1H, CH), 4.27–4.37 (m, 2H, CH2),
3.68–3.74 (m, 1H, CH2), 3.60 (m, 1H, CH2). IR ˜υ (cm−1) 3293,
3062, 3031, 2929, 1651, 1515, 1073, 609. HRMS (ESI) m/z
[M + H+]: calcd for C17H19N2O3 299.1396, found 299.1396.
(N1-((1S,2R)-2-Hydroxy-2,3-dihydro-1H-inden-1-yl)-N2-mesityl-
oxalamide (5e). Following the general procedure ethyl 2-(mesi-
tylamino)-2-oxoacetate (3a, 681 mg, 2.90 mmol) and (1S,2R)-1-
amino-1H-inden-2-ol (4c, 432 mg, 2.90 mg) gave target product
5e as a white solid in 76% yield (748 mg, 2.20 mmol). 1H NMR
(600 MHz, (CD3)2SvO) δ (ppm) 10.28 (s, 1H, NH), 8.25–8.27
(d, J = 8.6 Hz, 1H, NH), 7.21–7.28 (m, 4H, CHAr), 6.91 (s, 2H,
CHAr), 5.48–5.49 (d, J = 4.9 Hz, 1H, OH), 5.22–5.25 (dd, J = 8.5,
5.2 Hz, 1H, CH), 4.50–4.54 (m, 1H, CH), 3.11–3.16 (dd, J = 16.2,
5.1 Hz, 1H, CH2), 2.85–2.89 (dd, J = 16.2, 1.4 Hz, 1H, CH2),
General procedure for the synthesis of oxalamides
To a solution of oxalamide ethyl ester 3 (1 eq.) in ethanol 2.23 (s, 3H, CH3), 2.11 (s, 6H, 2 × CH3). 13C (150 MHz,
(10 mL) was added aminoalcohol 4 (1 eq.) and the solution (CD3)2SvO) δ (ppm) 160.1 (CvO), 159.1 (CvO), 141.7 (CAr),
stirred at reflux for 16 hours. The solvent was decanted off and 141.2 (CAr), 136.5 (CAr), 135.2 (CAr), 131.9 (CAr), 128.8 (CHAr),
the solid residue was washed with EtOH (2 × 5 mL). The solid 128.2 (CHAr), 127.0 (CHAr), 125.5 (CHAr), 124.5 (CHAr), 72.1
was then dried in vacuo to yield the oxalamides as white solids. (CHOH), 57.2 (CHNH), 40.3 (CH2), 20.9 (CH3), 18.4 (CH3). M.p
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1
231 °C. HRMS (ESI) m/z [M + H+]: calcd for C20H23N2O3 1.27 mmol). H NMR (400 MHz, CDCl3) δ (ppm) 7.23–7.35 (m,
339.1709, found 339.1713.
10H, CHAr), 3.73–3.75 (m, 2H, PhCH2), 3.69 (dd, J = 10.5, 4.4
Hz, 1H, CH2), 3.54 (dd, 10.5, 8.7 Hz, 1H, CH2), 2.59–2.78 (m,
4H, 2 × CH2). IR ˜υ (cm−1) 3292, 3084, 3060, 2904, 2831, 1493,
General procedure for synthesis of diamines
Oxalamide (1 eq.) and AlCl3 (2 eq.) were placed in a predried 1452, 1359, 1124, 101, 746. HRMS (ESI) m/z [M + H+]: calcd for
Schlenck tube and placed under N2-atmosphere. After dis- C17H23N2O 271.1810, found 271.1815.
solution in dry THF (10 mL), LiAlH4 (5 eq., 1 M, THF) was
added under vigorous stirring. Upon complete addition the 2-ol (6e). Following the general procedure, N1-((1S,2R)-2-
solution was stirred at reflux for 16 hours. The solution was hydroxy-2,3-dihydro-1H-inden-1-yl)-N2-mesityloxalamide
(5e,
(1S,2R)-1-((2-(Mesitylamino)ethyl)amino)-2,3-dihydro-1H-inden-
then cooled with an ice bath and quenched with NaOH (1 M). 381 mg, 1.13 mmol) gave target product 6e in 77% yield
The resulting slurry was filtered and the washed thoroughly (271 mg, 0.87 mmol) as a colourless oil. 1H NMR (400 MHz,
with DCM (150 mL). The organic phase was washed with CDCl3) δ (ppm) 7.21–7.27 (m, 4H, CHAr), 6.82 (s, 2H, CHAr),
NaOH (1 M, 2 × 50 mL) and brine (50 mL) before drying over 4.66 (m, 1H, CH), 4.09 (d, J = 5.0 Hz, 1H, CH), 3.05–3.14 (m,
Na2SO4. After concentration in vacuo the crude oils were puri- 4H, 2 × CH2), 2.95–3.01 (m, 2H, CH2), 2.28 (s, 6H, 2 × CH3),
fied by column chromatography (1 : 10/1 : 20 MeOH : DCM) to 2.22 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3) δ (ppm) 143.1
yield the pure diamines.
(CAr), 142.2 (CAr), 140.9 (CAr), 131.6 (CAr), 129.8 (CAr), 129.5 (2 ×
(S)-2-((2-(Mesitylamino)ethyl)amino)-3-methylbutan-1-ol (6a). CHAr), 128.1 (CHAr), 126.7 (CHAr), 125.6 (CHAr), 123.7 (CHAr),
Following the general procedure (S)-N1-(1-hydroxy-3-methyl- 71.0 (CH), 66.0 (CH), 49.1 (CH2), 48.5 (CH2), 39.6 (CH2), 20.5
butan-2-yl)-N2-mesityloxalamide (5a, 580 mg, 1.98 mmol) gave (CH3), 18.3 (2 × CH3). IR ˜υ (cm−1) 3236, 3068, 2912, 2851, 1483,
target product 6a as a colourless oil in 77% yield (404 mg, 1457, 1112, 1077, 1016, 851. HRMS (ESI) m/z [M + H+]: calcd
1
1.52 mmol). H NMR (400 MHz, CDCl3) δ (ppm) 6.82 (s, 2H, for C20H27N2O 311.2123, found 311.2129.
CHAr), 3.66 (dd, J = 10.6, 4.0 Hz, 1H, CH2), 3.41 (dd, J = 10.6,
7.3 Hz, 1H, CH2), 3.00–3.11 (m, 2H, CH2), 2.90–2.96 (m, 1H,
General procedure for synthesis of imidazolium chlorides
CH2), 2.80–2.85 (m, H, CH2), 2.53 (broad s, 3H, 2 × NH + OH), To a solution of diamine 6 (1 eq.) in dry THF (2 mL) under N2-
2.42–2.48 (m, 1H, CH), 2.27 (s, 6H, 2 × CH3), 2.22 (s, 3H, CH3), atmosphere was added anhydrous HCl (1.25 M in MeOH,
1.81–1.90 (m, 1H, CH), 0.98 (d, J = 6.9 Hz, CH3), 0.92 (d, J = 1 eq.) which lead to immediate precipitation of a white solid.
6.8 Hz, CH3).
The solvent was evaporated off by N2-stream. Toluene (1 mL)
(S)-2-((2-(Mesitylamino)ethyl)amino)-2-phenylethan-1-ol (6b). and trimethyl orthoformate (5 eq.) were added and the suspen-
Following the general procedure, (S)-N1-(2-hydroxy-1-phenyl- sion was stirred at 90 °C for 16 hours. After cooling to room
ethyl)-N2-mesityloxalamide (5b, 422 mg, 1.29 mmol) gave temperature and concentration in vacuo the crude salts were
target product 6b as a colourless oil in 62% yield (239 mg, purified by column chromatography (1 : 10 MeOH : DCM) to
0.80 mmol). 1H NMR (400 MHz, (CDCl3) δ (ppm) 7.31–7.36 yield the pure imidazolium chlorides as white solids.
(m, 2H, CHAr), 7.25–7.29 (m, 3H, CHAr), 6.80 (s, 2H, CHAr),
3.77 (dd, J = 8.7, 4.5 Hz, 1H, CH), 3.71 (dd, J = 10.7, 4.4 Hz, 1H, imidazol-3-ium chloride (7a). Following the general procedure,
CH2), 3.56 (dd, J = 10.7, 8.7 Hz, 1H, CH2), 2.95–30.7 (m, 2H, (S)-2-((2-(mesitylamino)ethyl)amino)-3-methylbutan-1-ol (6a,
CH2), 2.72–2.78 (m, 1H, CH2), 2.65–2.70 (m, 1H, CH2), 2.24 60.0 mg, 0.227 mmol) gave target product 7a as a white solid
(s, 6H, 2 × CH3), 2.21 (s, 3H, CH3).
in 90% yield (63.2 mg, 0.203 mmol). 1H NMR (400 MHz,
(S)-3-(1-Hydroxy-3-methylbutan-2-yl)-1-mesityl-4,5-dihydro-1H-
(S)-2-((2-(Benzylamino)ethyl)amino)-3-methylbutan-1-ol (6c). CDCl3) δ (ppm) 8.79 (s, 1H, NCHN), 6.93 (s, 2H, CHAr), 5.82
Following the general procedure, (S)-N1-benzyl-N2-(1-hydroxy-3- (dd, J = 9.6, 3.7 Hz, 1H, OH), 4.41–4.49 (m, 1H, CH2), 4.28–4.36
methylbutan-2-yl)oxalamide (5c, 525 mg, 1.89 mmol) gave (m, 1H, CH2), 4.09–4.16 (m, 1H, CH2), 3.94–4.08 (m, 3H, CH +
target product 6c in 61% yield (287 mg, 1.15 mmol) as a col- CH2), 3.57–3.65 (m, 1H, CH2), 2.39 (broad s, 3H, CH3), 2.28 (s,
1
ourless oil. H NMR (600 MHz, CDCl3) δ (ppm) 7.31–7.34 (m, 3H, CH3), 2.25 (broad s, 3H, CH3), 1.80–1.89 (m, 1H, CH), 1.05
4H, Ar), 7.24–7.26 (m, 1H, Ar), 3.80 (s, 2H, CH2Ph), 3.61 (dd, (d, J = 6.6 Hz, 3H, CH3), 1.01 (d, J = 6.7 Hz, 3H, CH3). 13C NMR
J = 10.8, 4.1 Hz, 1H, CH2OH), 3.33 (dd, J = 10.8, 7.7 Hz, 1H, (100 MHz, CDCl3) δ (ppm) 160.1 (NCN), 140.3 (CAr), 130.3
CH2OH), 2.81–2.85 (m, 1H, CH2), 2.69–2.80 (m, 3H, CH2
+
(CHAr), 130.1 (broad, CAr), 129.6 (broad, CAr), 66.9 (CH), 58.6
CH2), 2.35–2.38 (m, 1H, CHNH), 1.73–1.78 (m, 1H, CH), 0.96 (CH2), 50.5 (CH2), 44.9 (CH2), 27.7 (CH), 20.9 (CH3), 20.3
(d, J = 6.8 Hz, 3H, CH3), 0.89 (d, J = 6.8 Hz, 3H, CH3). 13C NMR (CH3), 18.9 (CH3), 18.0 (broad, CH3), 17.6 (broad, CH3). IR
(150 MHz, CDCl3) δ (ppm) 140.0 (CAr), 128.5 (CHAr), 128.2 ˜υ (cm−1) 3230, 2962, 2876, 1631, 1505, 1484, 1224, 1075, 1029,
(CHAr), 127.1 (CHAr), 64.5 (CHNH), 61.5 (CH2OH), 53.8 640. m.p: 212 °C. HRMS (ESI) m/z [M+]: calcd for C17H27N2O
(CH2Ph), 49.2 (CH2), 46.7 (CH2), 29.5 (CH), 19.5 (CH3), 18.8 275.2123, found 275.2128.
(CH3). IR ˜υ (cm−1) 3296, 3085, 3062, 2954, 2830, 1494, 1453,
1104, 735.
(S)-3-(2-Hydroxy-1-phenylethyl)-1-mesityl-4,5-dihydro-1H-imid-
azol-3-ium chloride (7b). Following the general procedure,
(S)-2-((2-(Benzylamino)ethyl)amino)-2-phenylethan-1-ol (6d). (S)-2-((2-(mesitylamino)ethyl)amino)-2-phenylethan-1-ol
(6b,
Following the general procedure, (S)-N1-benzyl-N2-(2-hydroxy-1- 239 mg, 0.801 mmol) gave target product 7b as a white solid in
1
phenylethyl)oxalamide (5d, 614 mg, 2.06 mmol) gave target 87% yield (241 mg, 0.697 mmol). H NMR (400 MHz, CDCl3)
product 6d as a colourless oil in 62% yield (343 mg, δ (ppm) 9.27 (s, 1H, NCHN), 7.38–7.44 (m, 3H, CHAr),
5134 | Dalton Trans., 2021, 50, 5128–5138
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7.35–7.36 (m, 2H, CHAr), 6.91 (s, 2H, CHAr), 6.19 (dd, J = 9.2, (2 × CHAr), 127.6 (CHAr), 126.1 (CHAr), 125.1 (CHAr), 70.7
3.9 Hz, 1H, OH), 5.54 (dd, J = 10.6, 4.2 Hz, 1H, CH), 4.28–4.34 (CHOH), 65.5 (PhCH), 50.8 (CH2), 49.0 (CH2), 38.9 (PhCH2),
(M, 1H, CH2), 4.18–4.25 (m, 2H, 2 × CH2), 4.07–4.11 (m, 1H, 20.9 (CH3), 17.9 (2 × CH3). IR ˜υ (cm−1) 3201, 2950, 2918,
CH2), 4.00–4.04 (m, 1H, CH2), 3.90–3.95 (m, 1H, CH2), 2.36 1631, 1482, 1252, 1055, 664. M.p: 255 °C (decomp.). HRMS
(broad s, 3H, CH3), 2.30 (broad s, 3H, CH3), 2.27 (s, 3H, CH3). (ESI) m/z [M+]: calcd for
13C NMR (100 MHz, CDCl3) δ (ppm) 159.5 (NCN), 140.3 (CAr), 319.1973
135.6 (broad CAr), 135.1 (broad CAr), 133.5 (CAr), 130.5 (CAr),
C21H23N2O 321.1967 found
General procedure for the synthesis of gold(I) NHC complexes
130.0 (broad 2 × CHAr), 129.4 (3 × CHAr) 127.7 (2 × CHAr), 63.8
(CH), 59.9 (CH2), 50.6 (CH2), 46.4 (CH2), 21.0 (CH3), 18.0 To a solution of imidazolium chloride 7 (1 eq.) in DCM (2 mL)
(broad 2 × CH3). IR ˜υ (cm−1) 3221, 3032, 2920, 1628, 1483, was added Me2SAuCl (1 eq.) and stirred for 10 minutes. K2CO3
1379, 2276, 1138, 648. M.p: 239 °C HRMS (ESI) m/z [M+]: calcd (10 eq.) and water (2 mL) were then added. The mixture was
for C20H25N2O 309.1967, found 309.1972.
then stirred vigorously for 2–7 hours. After completion of the
(S)-1-Benzyl-3-(1-hydroxy-3-methylbutan-2-yl)-4,5-dihydro-1H- reaction, DCM (15 mL) and water (15 mL) were added and the
imidazol-3-ium chloride (7c). Following the general procedure, phases separated. The organic phase was then washed with
(S)-2-((2-(benzylamino)ethyl)amino)-3-methylbutan-1-ol
(6c, brine (15 mL), dried over Na2SO4 and concentrated in vacuo.
98.0 mg, 0.415 mmol), gave target product 7c in 71% yield The crude complexes were purified by filtering through a short
(83.2 mg, 294 mmol) as a white solid. 1H NMR (400 MHz, silica plug (EtOAc) giving the gold(I) NHC complexes as white
CDCl3) δ (ppm) 9.49 (s, 1H, NCHN), 7.33–7.40 (m, 5H, Ar), 5.81 crystalline solids.
(broad s, 1H, OH), 4.96 (d, J = 14.7 Hz, 1H, CH2Ph), 4.72 (d, J =
14.7 Hz, 1H, CH2Ph), 4.10–4.21 (m, 1H, CH2), 3.94–4.01 (m, 2-ylidene)gold(I) chloride (8a). Following the general pro-
1H, CH2), 3.67–3.87 (m, 4H, CH2 + CH2OH), 3.56–3.62 (m, 1H, cedure, (S)-3-(1-hydroxy-3-methylbutan-2-yl)-1-mesityl-4,5-
NCH), 1.78–1.90 (m, 1H, CH), 0.98 (d, J = 6.6 Hz, CH), 0.97 (d, dihydro-1H-imidazol-3-ium chloride (7a, 37.0 mg,
(S)-(1-(1-Hydroxy-3-methylbutan-2-yl)-3-mesitylimidazolidin-
J = 6.7 Hz, 1H, CH). 13C NMR (100 MHz, CDCl3) δ (ppm) 159.1 0.119 mmol), Me2SAuCl (35.1 mg, 0.119 mmol) and K2CO3
(NCN), 132.8 (CAr), 129.1 (CHAr), 128.7 (CHAr), 128.6 (CHAr), (164 mg, 1.19 mmol) gave target gold(I) NHC complex 8a as a
67.3 (NCH), 58.6 (PhCH2), 52.1 (CH2OH), 47.4 (CH2), 45.7 white, crystalline solid in 92% yield (55.5 mg, 0.109 mmol). 1H
(CH2), 27.5 (CH), 20.1 (CH3), 19.1 (CH3). IR ˜υ (cm−1) 3341, NMR (400 MHz, CDCl3) δ (ppm) 6.90(s, 2H, Ar), 4.28–4.33 (m,
3060, 2965, 1643, 1513, 1205, 635. M.p 125 °C.
1H, CH), 4.00 (dd, J = 11.8, 3.8 Hz, 1H, CH2OH), 3.93–3.99 (m,
(S)-1-Benzyl-3-(2-hydroxy-1-phenylethyl)-4,5-dihydro-1H-imid- 1H, CH2), 3.69–3.84 (m, 4H, CH2OH + CH2), 2.28 (s, 3H, CH3),
azol-3-ium chloride (7d). Following the general procedure, 2.21 (s, 6H, 2 × CH3), 1.99–2.08 (m, 1H, CH), 1.05 (d, J = 6.6
(S)-2-((2-(benzylamino)ethyl)amino)-2-phenylethan-1-ol
(6d,) Hz, 3H, CH3), 1.04 (d, J = 6.6 Hz, 3H, CH3). 13C NMR
gave target product 7d in 49% yield (143 mg, 0.450 mmol) as a (100 MHz, CDCl3) δ (ppm) 193.8 (CAu), 138.6 (CAr), 135.8 (CAr),
pale yellow waxy solid. 1H NMR (400 MHz, CDCl3) δ (ppm) 135.5 (CAr), 134.9 (CAr), 129.6 (CHAr), 129.6 (CHAr), 67.6 (CH),
10.05 (s, 1H, NCHN), 7.30–7.42 (m, 10H, CHAr), 6.21 (broad s, 61.7 (CH2OH), 50.1 (CH2), 45.2 (CH2), 27.0 (CH), 21.0 (CH3Ar),
1H, OH), 5.06 (dd, J = 10.2, 3.7 Hz, 1H, PhCH), 5.00 (d, J = 14.8 21.0 (CH3), 20.2 (CH3), 17.9 (CH3Ar), 17.9 (CH3Ar). M.p. 209 °C
Hz, 1H, PhCH2), 4.75 (d, J = 14.8 Hz, 1H, PhCH2), 4.33 (dd, J = (decomp). HRMS (ESI) m/z [M + −Cl− + CH3CN] calcd for
12.6, 10.3 Hz, 1H, CH2OH), 3.93–4.01 (m, 2H, NCH2
+
C19H29AuN3O 512.1976, found 512.1976.
CH2OH), 3.82–3.90 (m, 1H, NCH2), 3.58–3.75 (m, 2H, NCH2).
(1-((S)-2-Hydroxy-1-phenylethyl)-3-mesitylimidazolidin-2-yl)
13C NMR (100 MHz, CDCl3) δ (ppm) 158.3 (NCN), 133.7 (CAr), gold(I) chloride (8b). Following the general procedure, (S)-3-(2-
132.5 (CAr), 129.2 (2 × CHAr), 129.1 (2 × CHAr), 128.9 (2 × CHAr), hydroxy-1-phenylethyl)-1-mesityl-4,5-dihydro-1H-imidazol-3-ium
128.8 (2 × CHAr), 127.5 (2 × CHAr), 64.5 (PhCH), 60.7 (PhCH2), chloride (7b, 33.1 mg, 0.096 mmol), Me2SAuCl (28.3 mg,
52.4 (CH2OH), 47.2 (CH2), 46.5 (CH2). IR ˜υ (cm−1) 3247, 3032, 0.096 mmol) and K2CO3 (133 mg, 0.96 mmol) gave target gold(I)
2927, 1638, 1512, 1496, 1205, 702. HRMS (ESI) m/z [M+]: calcd NHC complex 8b as a white, crystalline solid in 91% yield
for C18H21N2O 281.1654, found 281.1659.
(47.2 mg, 0.087 mmol). 1H NMR (600 MHz, CDCl3) δ (ppm)
3-((1S,2R)-2-Hydroxy-2,3-dihydro-1H-inden-1-yl)-1-mesityl-4,5- 7.40–7.42 (m, 4H, Ar), 7.37–7.39 (m, 1H, Ar), 6.91 (s, 1H, Ar),
dihydro-1H-imidazol-3-ium chloride (7e). Following the general 6.90 (s, 1H, Ar), 5.94 (dd, J = 8.8, 5.4 Hz, 1H, CH), 4.25–4.33 (m,
procedure,
(1S,2R)-1-((2-(mesitylamino)ethyl)amino)-2,3- 2H, CH2OH), 3.88–3.94 (m, 1H, CH2), 3.78–3.83 (m, 1H, CH2),
dihydro-1H-inden-2-ol (6e, 136 mg, 0.438 mmol) gave target 3.67–3.72 (m, 1H, CH2), 3.50–3.55 (m, 1H, CH2), 2.29 (s, 3H,
product 7e in 87% yield (130 mg, 0.381 mmol) as a white CH3), 2.24 (s, 3H, CH3), 2.20 (s, 3H, CH3), 2.07–2.09 (broad m,
1
solid. H NMR (400 MHz, CDCl3) δ (ppm) 8.65 (s, 1H, NCHN), 1H, OH). 13C NMR (150 MHz, CDCl3) δ (ppm) 194.1 (CAu),
7.28–7.39 (m, 4H, CHAr), 6.92 (broad s, 2H, CHAr), 6.57 (broad 138.9 (CAr), 135.9 (CAr), 135.5 (CAr), 135.2 (CAr), 134.9 (CAr), 129.7
d, J = 4.2 Hz, 1H, OH), 5.41 (d, J = 6.2 Hz, 1H, NCH), 5.02–5.07 (CHAr), 129.7 (CHAr), 129.2 (CHAr), 128.7 (CHAr), 127.4 (CHAr),
(broad m, 1H, CH̲OH), 4.28–4.41 (m, 2H, 2 × CH2), 4.03–4.16 64.0 (CH), 61.1 (CH2OH), 50.5 (CH2), 44.7 (CH2), 21.0 (CH3),
(m, 2H, 2 × CH2), 3.32 (dd, J = 17.0, 7.2 Hz, 1H, PhCH2), 3.04 18.1 (CH3), 18.0 (CH3). IR (cm−1) 3455, 3028, 2917, 2885, 1607,
(dd, J = 16.8, 5.9 Hz, 1H, PhCH2), 2.36 (broad s, 6H, 2 × CH3), 1497, 1452, 1233, 1088, 1040, 854. M.p 175 °C (decomp.) HRMS
2.28 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3) δ (ppm) 159.3 (ESI) m/z [M + −Cl− + CH3CN] calcd for C22H27AuN3O 546.1820,
(NCN), 142.4 (CAr), 140.4 (CAr), 135.7 (CAr), 130.0 (CHAr), 129.9 found 546.1826. CCDC ID: 2056825.†
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(1-Benzyl-3-((S)-1-hydroxy-3-methylbutan-2-yl)imidazolidin-2- General procedure for the synthesis of gold(III) NHC complexes
yl)gold(I) chloride (8c). Following the general procedure, (S)-1-
benzyl-3-(1-hydroxy-3-methylbutan-2-yl)-4,5-dihydro-1H-imida-
To a solution of gold(I) NHC complex 8 in DCM (2 mL) was
zol-3-ium chloride (7c, 39.3 mg, 0.139 mmol), Me2SAuCl added dichloro iodobenzene (PhICl2, 1.1 eq.) and the solution
(40.9 mg, 0.139 mmol) and K2CO3 (192 mg, 1.39 mmol) gave stirred for 15–60 minutes after which the solvent was evapor-
target gold(I) NHC complex 8c as a white, crystalline solid in ated. The solid residue was washed with pentane (3 × 5 mL)
1
50% yield (33.5 mg, 0.0700 mmol). H NMR (400 MHz, CDCl3) and then further purified by column chromatography (EtOAc/
δ (ppm) 7.31–7.38 (m, 5H, CHAr), 4.95 (d, J = 15.0 Hz, 1H, pentane) to yield the pure gold(III) NHC complexes as yellow,
CH2Ph), 4.79 (d, J = 15.0 Hz, 1H, CH2Ph), 4.22–4.27 (m, 1H, crystalline solids.
CH), 3.95–3.98 (m, 1H, CH2OH), 3.77–3.80 (m, 1H, CH2OH),
(1-((S)-1-Hydroxy-3-methylbutan-2-yl)-3-mesitylimidazolidin-
3.71–3.77 (m, 1H, CH2), 3.41–3.57 (m, 3H, CH2), 1.91–2.00 (m, 2-yl)gold(III) chloride (9a). Following the general procedure,
1H, CH), 1.79 (broad s, 1H, OH), 1.01 (d, J = 6.7 Hz, 3H, CH3), (S)-(1-(1-hydroxy-3-methylbutan-2-yl)-3-mesitylimidazolidin-2-
0.99 (d, J = 6.7 Hz, 3H, CH3). 13C NMR (100 MHz, CDCl3) δ ylidene)gold(I) chloride (8a, 31.2 mg, 0.0616 mmol) and PhICl2
(ppm) 193.0 (CAu), 134.9 (CAr), 129.0 (CHAr), 128.3 (CHAr), (18.6 mg, 0.0677 mmol) gave target gold(III) NHC complex 9a
127.9 (CHAr), 67.9 (CH), 61.8 (CH2OH), 55.0 (CH2Ph), 47.4 as
(CH2), 45.3 (CH2), 27.3 (CH), 20.3 (CH3), 19.5 (CH3). M.p 0.0560 mmol). 1H NMR (600 MHz, CDCl3) δ (ppm) 6.95 (s, 1H,
126 °C (Decomp.). Ar), 6.94 (s, 1H, Ar), 4.25–4.29 (m, 1H, CH), 4.19–4.23 (m, 2H,
a yellow crystalline solid in 91% yield (32.5 mg,
(1-Benzyl-3-((S)-2-hydroxy-1-phenylethyl)imidazolidin-2-yl)gold(I) CH2 + CH2OH), 4.06–4.11 (m, 2H, CH2), 3.97–4.01 (m, 2H,
chloride (8d). Following the general procedure, (S)-1-benzyl-3-(2- CH2), 3.73 (dd, J = 12.4, 8.6 Hz, 1H, CH2OH), 2.39 (s, 3H, CH3),
hydroxy-1-phenylethyl)-4,5-dihydro-1H-imidazol-3-ium chloride 2.38 (s, 3H, CH3), 2.30 (s, 3H, CH3), 1.99–2.04 (m, 1H, CH),
(7d, 29.0 mg, 0.092 mmol), Me2SAuCl (27.1 mg, 0.092 mmol) 1.16 (d, J = 6.9 Hz, 3H, CH3), 1.07 (d, J = 6.7 Hz, 3H, CH3). 13C
and K2CO3 (130 mg, 0.92 mmol) gave target gold(I) NMR (150 MHz, CDCl3) δ (ppm) 170.3 (CAu), 140.3 (CAr), 136.4
NHC complex 8d as a white, crystalline solid in 56% yield (CAr), 136.3 (CAr), 131.6 (CAr), 130.2 (CHAr), 67.0 (CH), 61.6
(26.4 mg, 0.052 mmol). 1H NMR (400 MHz, CDCl3) δ (ppm) (CH2OH), 51.8 (CH2), 45.9 (CH2), 28.2 (CH), 21.1 (CH3Ar), 20.9
7.31–7.39 (m, 10H, Ar), 5.87 (dd, J = 8.9, 5.2 Hz, 1H, CH), 5.0 (d, (CH3), 19.1 (CH3), 18.8 (CH3Ar), 18.6 (CH3Ar). IR (cm−1) 3504,
J = 14.9 Hz, 1H, CH2Ph), 4.74 (d, J = 14.8 Hz, 1H, CH2Ph), 2965, 2925, 1537, 1462, 1307, 1069, 855. HRMS (ESI) m/z [M +
4.26–4.32 (m, 1H, CH2OH), 4.17–4.22 (m, 1H, CH2OH), −Cl−] calcd for C17H26AuCl2N2O 541.1088, found 541.1093. M.
3.69–3.77 (m, 1H, CH2), 3.53–3.60 (m, 1H, CH2), 3.25–3.43 (m, p 210 °C (decomp). CCDC ID: 2056823.†
2H, CH2), 2.58–2.61 (broad m, 1H, OH). 13C NMR (100 MHz,
(1-((S)-2-Hydroxy-1-phenylethyl)-3-mesitylimidazolidin-2-yl)
CDCl3) δ (ppm) 192.7 (CAu), 135.2 (CAr), 134.7 (CAr), 129.1 gold(III) chloride (9b). Following the general procedure,
(CHAr), 128.9 (CHAr), 128.6 (CHAr), 128.3 (CHAr), 128.1 (CHAr), (1-((S)-2-hydroxy-1-phenylethyl)-3-mesitylimidazolidin-2-yl)gold(I)
127.5 (CHAr), 64.5 (CH), 61.2 (CH2OH), 55.1 (CH2Ph), 47.8 chloride (8b, 31.4 mg, 0.0581 mmol) and PhICl2 (17.6 mg,
(CH2), 44.7 (CH2). IR (cm−1) 3450, 3060, 3028, 2926, 2883, 1726, 0.0639 mmol) gave target gold(III) NHC complex 9b as a yellow
1
1494, 1239, 1191, 700. HRMS (ESI) m/z [M + −Cl− + CH3CN] crystalline solid in 53% yield (18.9 mg, 0.0309 mmol). H NMR
calcd for C20H23AuN3O: 518.1507, found 518.1514. M.p 145 °C (400 MHz, CD3CN) δ (ppm) 7.57–7.60 (m, 2H, Ar), 7.39–7.49 (m,
(decomp). CCDC ID: 2056945.†
3H, Ar), 7.03 (s, 1H, Ar), 7.02 (s, 1H, Ar), 5.69 (t, J = 6.4 Hz, 1H,
(1-((1S,2R)-2-Hydroxy-2,3-dihydro-1H-inden-1-yl)-3-mesitylimid- CH), 4.18–4.25 (m, 3H, CH2 + CH2OH), 3.99–4.14 (m, 2H, CH2),
azolidin-2-yl)gold(I) chloride (8e). Following the general pro- 3.79–3.87 (m, 1H, CH2), 3.29 (t, J = 6.0 Hz, 1H, OH), 2.41 (s, 3H,
cedure,
(3-((1S,2R)-2-hydroxy-2,3-dihydro-1H-inden-1-yl)-1- CH3), 2.34 (s, 3H, CH3), 2.31 (s, 3H, CH3). 13C NMR (100 MHz,
mesityl-4,5-dihydro-1H-imidazol-3-ium chloride (7e, 21.6 mg, CD3CN) δ (ppm) 169.3 (CAu), 141.1 (CAr), 138.1 (CAr), 137.8 (CAr),
0.061 mmol), Me2SAuCl (17.8 mg, 0.061 mmol) and K2CO3 135.5 (CAr), 133.4 (CAr), 130.7 (CHAr), 130.7 (CHAr), 129.9 (CHAr),
(84 mg, 0.605 mmol) gave target gold(I) NHC complex 8e as a 129.7 (CHAr), 129.4 (CHAr), 65.0 (CH), 61.9 (CH2OH), 52.8 (CH2),
white, crystalline solid in 69% yield (23.2 mg, 0.042 mmol). 1H 48.1 (CH2), 21.1 (CH3), 19.1 (CH3), 19.0 (CH3). IR (cm−1) 3512,
NMR (600 MHz, CDCl3) δ (ppm) 7.30–7.38 (m, 4H, Ar), 6.92 (s, 2947, 1537, 1496, 1461, 1314, 1173, 1139, 1081, 1068, 854, 691.
1H, Ar), 6.91 (s, 1H, Ar), 6.10 (d, J = 6.9 Hz, 1H, NCH), M.p 184 °C (decomp). CCDC ID: 2056946.†
4.91–4.95 (m, 1H, CHOH), 3.67–3.85 (m, 3H, CH2), 3.42–3.48
(m, 1H, CH2), 3.37 (dd, J = 16.2, 7.8 Hz, 1H, CH2), 2.96 (dd, J = yl)gold(III) chloride (9c). Following the general procedure,
16.3, 6.2 Hz, 1H, CH2), 2.29 (s, 3H, CH3), 2.26 (s, 6H, CH3). 13
((1-benzyl-3-((S)-1-hydroxy-3-methylbutan-2-yl)imidazolidin-2-yl)
(1-Benzyl-3-((S)-1-hydroxy-3-methylbutan-2-yl)imidazolidin-2-
C
NMR (150 MHz, CDCl3) δ (ppm) 194.2 (CAu), 140.6 (CAr), 138.9 gold(I) chloride (8c, 17.1 mg, 0.0357 mmol) and PhICl2
(CAr), 136.6 (CAr), 135.8 (CAr), 135.4 (CAr), 134.9 (CAr), 129.7 (10.8 mg, 0.0393 mmol) gave target gold(III) NHC complex 9c
(CHAr), 129.7 (CHAr), 129.6 (CHAr), 127.7 (CHAr), 125.8 (CHAr), as
a yellow crystalline solid in 89% yield (17.5 mg,
1
125.6 (CHAr), 73.0 (CHOH), 66.2 (CHN), 50.7 (CH2), 47.1 (CH2), 0.0318 mmol). H NMR (600 MHz, CDCl3) δ (ppm) 7.38–7.41
40.1 (CH2), 21.1 (CH3), 18.0 (CH3), 18.0 (CH3). IR (cm−1) 3440, (m, 5H, Ar), 5.05 (d, J = 14.8 Hz, 1H, CH2Ph), 4.83 (d, J = 14.8
2919, 1659, 1499, 1456, 1271, 1151, 1088, 818. M.p 155 °C Hz, 1H, CH2Ph), 4.11–4.15 (m, 2H, NCH + CH2OH), 4.00–4.05
(decomp.) HRMS (ESI) m/z [M + Cl−] calcd for C21H24AuCl2N2O (m, 1H, CH2), 3.79–3.81 (m, 1H, CH2), 3.66–3.73 (m, 3H,
587.0931, found 587.0937. CCDC ID: 2056827.†
CH2OH + CH2), 2.09 (broad s, 1H, OH), 1.94–2.00 (m, 1H, CH),
5136 | Dalton Trans., 2021, 50, 5128–5138
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1.09 (d, J = 6.8 Hz, 3H, CH3), 1.04 (d, J = 6.7 Hz, 3H, CH3). 13C pentane : EtOAc) to give products 13 and 14. Results are sum-
NMR (150 MHz, CDCl3) δ (ppm) 168.9 (CAu), 132.2 (CAr), 129.3 marized in Table 2.
(CAr), 129.2 (CAr), 128.7 (CAr), 67.2 (CH), 61.7 (CH2OH), 54.4
Dimethyl 3-(methoxy(phenyl)methyl)-4-methylenecyclopentane-
(CH2), 48.5 (CH2), 46.0 (CH2), 27.9 (CH), 20.8 (CH3), 19.1 1,1-dicarboxylate (13). 1H NMR (400 MHz, CDCl3) δ (ppm)
(CH3). IR (cm−1) 3530, 2962, 2931, 1560, 1497, 1454, 1360, 7.23–7.33 (m, 5H, CHAr), 4.91 (q, J = 1.6 Hz, vCH2), 4.50 (m,
1286, 1077, 928. HRMS (ESI) m/z [M + −Cl− + CH3CN] 1H, vCH2), 4.14 (d, J = 5.9 Hz, 1H, CH), 3.71 (s, 3H, CH3), 3.65
C17H25N3OCl2Au 554.1040, found 554.1041. m.p (185 °C (s, 3H, CH3), 3.18 (s, 3H, CH3), 2.93–3.00 (m, 1H, CH),
(decomp.).
2.85–2.90 (m, 2H, CH2), 2.41 (ddd, J = 13.3, 8.1, 1.4 Hz, 1H,
(1-Benzyl-3-((S)-2-hydroxy-1-phenylethyl)imidazolidin-2-yl) CH), 2.31 (dd, J = 13.4, 9.0 Hz, 1H, CH2). 1H NMR corresponds
gold(III) chloride (9d). Following the general procedure to previously reported data.59
(1-benzyl-3-((S)-2-hydroxy-1-phenylethyl)imidazolidin-2-yl)gold(I)
Dimethyl 4-(methoxy(phenyl)methyl)-3-methylcyclopent-2-
1
chloride (8d, 35.9 mg, 0.070 mmol) and PhICl2 (21.2 mg, ene-1,1-dicarboxylate (14). H NMR (400 MHz, CDCl3) δ (ppm)
0.077 mmol) gave target gold(III) NHC complex 9d as a yellow 7.27–7.37 (m, 5H, CHAr), 5.58–5.59 (m, 1H, vCH), 4.31 (d, J =
1
crystalline solid in 96% yield (39.3 mg, 0.067 mmol). H NMR 4.4 Hz, 1H, CH), 3.75 (s, 3H, CH3), 3.66 (s, 3H, CH3), 3.23 (s,
(400 MHz, CDCl3) δ (ppm) 7.48–750 (m, 2H, Ar), 7.40–7.44 (m, 3H, CH3), 2.92–2.96 (m, 1H, CH), 2.55 (dd, J = 13.6, 7.1 Hz, 1H,
8H, Ar), 5.72 (dd, J = 8.0, 5.4 Hz, 1H, NCH), 4.96 (d, J = 15.0 Hz, CH2), 2.32 (dd, J = 13.7, 8.3 Hz, 1H, CH2), 1.67 (m, 3H, CH3).
1H, CH2Ph), 4.91 (d, J = 15.0 Hz, 1H, CH2Ph), 4.21–4.33 (m, 2H, 13C NMR (100 MHz, CDCl3) δ (ppm) 172.0 (CvO), 146.2
CH2OH), 3.98–4.07 (m, 1H, CH2), 3.71–3.77 (m, 1H, CH2), (CvC), 140.7 (CAr), 128.4 (CHAr), 127.5 (CHAr), 126.8 (CHAr),
3.51–3.64 (m, 2H, CH2). 13C NMR (100 MHz, CDCl3) δ (ppm) 124.9 (CvCH), 82.4 (CH), 57.0 (CH3), 54.7 (CH), 52.6 (CH3),
168.5 (CAu), 132.9 (CAr), 132.1 (CAr), 129.4 (CHAr), 129.3 (CHAr), 52.5 (CH3), 33.2 (CH2), 15.3 (CH3). IR (cm−1) 2952, 2824, 1731,
129.2 (CHAr), 129.2 (CHAr), 128.8 (CHAr), 128.0 (CHAr), 63.7 1492, 1166, 1025. HRMS (ESI) m/z [M + −Cl−] calcd for
(CH), 61.1 (CH2), 54.5 (CH2), 48.6 (CH2), 45.9 (CH2). IR (cm−1
)
C18H22O5Na 341.1365, found 341.1370.
3507, 3061, 3031, 2945, 2890, 1585, 1555, 1356, 648. M.p 183 °C
(decomp.).
(1-((1S,2R)-2-Hydroxy-2,3-dihydro-1H-inden-1-yl)-3-mesityl-
imidazolidin-2-yl)gold(III) chloride (9e). Following the general
Conflicts of interest
procedure, (1-((1S,2R)-2-hydroxy-2,3-dihydro-1H-inden-1-yl)-3- There are no conflicts to declare.
mesitylimidazolidin-2-yl)gold(I) chloride (8e, 33.6 mg,
0.061 mmol) and PhICl2 (18.4 mg, 0.067 mmol) gave target
gold(III) NHC complex 9e as a yellow crystalline solid in 69%
References
yield (26.1 mg, 0.042 mmol). 1H NMR (600 MHz, CDCl3) δ
(ppm) 7.51 (d, J = 7.5 Hz, 1H, Ar), 7.40 (t, J = 7.4 Hz, 1H, Ar),
7.36 (t, J = 7.4 Hz, 1H, Ar), 7.32 (d, J = 7.5 Hz, 1H, Ar), 6.95 (s,
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(decomp). CCDC ID: 2056822.†
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