Cyclopropenylgold(I) Complexes as Aurated Carbenoids or Quasi-Carbenes

Article abstract of DOI:10.1002/adsc.201701526

Highly strained hydrocarbons have always been a research target of high interest. Due to their untypical electronic structure, they show interesting reactivity patterns and can easily be activated by π-coordination to or insertion reactions with metal complexes. Herein we report the synthesis of a range of 3,3-disubstituted cyclopropenylgold(I) complexes. The synthesis of such compounds with a metal, which usually easily activate cyclopropenes is a double-edged sword. We found σ-bound vinylic gold to generally have a strong stabilizing effect in terms of ring strain. The complexes show a strong distortion, preactivating the cyclopropenyls towards the ring-opening mode which thermally generates 1-aurated vinylcarbenes which is reflected by a much faster conversion (E_a of 10 kcal/mol instead of 40 kcal/mol, the reaction proceeds at temperatures as low as ?20 °C instead of 200 °C reported in the literature). In 3-phenyl-cyclopropenyl complexes, these could be trapped intramolecularly to give indenylgold(I) complexes. The properties of these highly strained complexes were investigated, utilizing a range of analytical and experimental procedures and Kohn-Sham density functional theoretic methods. (Figure presented.).

Full text of DOI:10.1002/adsc.201701526

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DOI: 10.1002/adsc.201701526
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Very Important Publication
Cyclopropenylgold(I) Complexes as Aurated Carbenoids or
Quasi-Carbenes
a
a
+a
Florian F. Mulks, Patrick W. Antoni, Frank Rominger, and A. Stephen
a, b,
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K. Hashmi *
a
Organisch-Chemisches Institut, Heidelberg University, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
E-mail: hashmi@hashmi.de
b
Chemistry Department, Faculty of Science, King Abdulaziz University (KAU), Jeddah 21589, Saudi Arabia
+
Crystallographic investigation.
Received: December 1, 2017; Revised: January 22, 2018; Published online: &&&, &&&&
Supporting information for this article is available on the WWW under https://doi.org/10.1002/adsc.201701526
Abstract: Highly strained hydrocarbons have always been a research target of high interest. Due to their
untypical electronic structure, they show interesting reactivity patterns and can easily be activated by p-
coordination to or insertion reactions with metal complexes. Herein we report the synthesis of a range of 3,3-
disubstituted cyclopropenylgold(I) complexes. The synthesis of such compounds with a metal, which usually
easily activate cyclopropenes is a double-edged sword. We found s-bound vinylic gold to generally have a
strong stabilizing effect in terms of ring strain. The complexes show a strong distortion, preactivating the
cyclopropenyls towards the ring-opening mode which thermally generates 1-aurated vinylcarbenes which is
reflected by a much faster conversion (E of 10 kcal/mol instead of 40 kcal/mol, the reaction proceeds at
a
temperatures as low as ꢀ208C instead of 2008C reported in the literature). In 3-phenyl-cyclopropenyl
complexes, these could be trapped intramolecularly to give indenylgold(I) complexes. The properties of these
highly strained complexes were investigated, utilizing a range of analytical and experimental procedures and
Kohn-Sham density functional theoretic methods.
Keywords: activation energy; rearrangement reactions; strained compounds; vinylgold complexes
1 Introduction
In 2008, Lee et al. discovered gold-catalyzed nucle-
ophilic addition reactions proceeding by a ring-open-
[
6]
Highly strained systems have always fascinated chem- ing of cyclopropenes and F u¨ rstner et al. investigated
ists all over the world. Although there is a set of useful the stoichiometric reaction of a cyclopropenone ketal
applications, the major motivation for working with with gold(I) species. In the same year, Shi and Zhu
the highly strained organic system is that they discovered cycloisomerisations of arylvinylcyclopro-
[
7]
[
8]
represent an artistic quest. Some of these molecules penes. Cyclopropenes then have received significant
[
1]
[9]
show exotic reactivity.
interest in gold(I) chemistry. As the activation leads
Cyclopropenes contain the smallest unsaturated to an intermediate represented by both carbocationic
carbocycle, leading to a ring strain energy of about (B) and metal-carbon double-bond (C) mesomeric
[1e,2]
55 kcal/mol.
Apart from cyclobutadiene, which is structures (Scheme 1), it represents a carbene gold(I)
further destabilized due to the antiaromatic nature of
its p-system, this is the highest destabilization reached
in monocyclic compounds. The strong s-character and
acidity of the olefinic CH bonds induce alkyne-like
[
3]
reactivity in cyclopropenes.
Upon p-activation, they readily undergo ring-open-
[4]
ing reactions. p-Acidic metal compounds, such as
[
5]
Ag(I) are known to activate cyclopropenes.
Scheme 1. Carbene gold(I) complexes from cyclopropenes.
Adv. Synth. Catal. 2018, 360, 1–13
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complex and enables a broad subsequent chemistry protodeauration. After this procedure, column chro-
[10]
(see Scheme 1).
matography on aluminum oxide succeeded and all
Bearing this in mind, our scientific curiosity complexes could be isolated in fair to very good yields
challenged us to investigate cyclopropenylgold(I) (see Scheme 3 and Table 1).
complexes. Cyclopropene derivatives are well known
+
to react vigorously with LAu species, as soon as the
compounds are given a chance of reacting via p-
[6]
coordination. Therefore, merging these units by
covalently connecting them in an act of “molecular
sadism” seemed to be a particularly interesting and
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[
11]
challenging target.
2 Results and Discussion
2.1 Synthesis of Cyclopropenylgold(I) Complexes
Cyclopropene substrates. To evaluate a range of
electronic effects on the structure of the target
complexes and their reactivity, we chose to investigate
cyclopropene derivatives with different substitution
patterns (see Scheme 2).
Scheme 3. Synthesis of (cyclopropenyl)gold(I) complexes 2.
Table 1. Isolated yields of (cyclopropenyl)gold(I) complexes
2
.
Entry
Cyclopropene
Ligand
Product
Yield
1
2
R
R
Scheme 2. The range of investigated cyclopropene deriva-
tives.
1
2
3
4
5
6
7
Me
Me
Ph
Me
Ph
Ph
1a
1b
1c
IPr
IPr*
IPr
IPr*
IPr*
IPr
2a
2a*
2b
2b*
2c*
2d
80%
61%
82%
89%
80%
Synthesis. We isolated eight gold complexes, i.e.
the complexes of the four used cyclopropenes with the
NHC ligands IPr (1,3-bis-(2,6-diisopropylphenyl)
imidazole-2-ylidene) and IPr* (1,3-bis(2,6-bis(diphe-
[a]
O(CH ) O 1d
64%[
2
3
a]
IPr*
2d*
73%
[a]
Upon reacting 1d deprotection took place. See Scheme 4.
nylmethyl)-4-methylphenyl)imidazol-2-ylidene).
In
one case, however, instant rearrangement could not be
avoided, which will be discussed later and which
(
)
In the case of 2d * neither the exclusion of Lewis
stresses how sensitive this chemistry is. An extensive or Brønstedt acidic drying agents or stationary phases
development of the procedure was carried out to for chromatography, elevated temperatures, nor air or
identify the optimal reaction conditions and purifica- water during the whole reaction and workup proce-
tion methods needed to prevent exposure of the dure enabled isolation of the protected products (see
products 2 to electrophilic species, for example, Au(I) Scheme 4). The 3-oxocyclopropenyl complexes are
cations. Such cationic gold species are capable of strongly favored due to aromatic stabilization, they
catalytically inducing ring-opening reactions, leading represent the very first organometallic compounds of
[
12]
to a complex mixture of decomposition products.
this type.
Lithiation of 1 with LDA proceeded smoothly
within 15 min. The gold(I) chloro complexes (LAuCl)
were added at ꢀ788C over the course of 1 h. After the
addition, the reaction mixtures were allowed to warm
up to 08C in order to ensure full conversion, then they
were quenched with water, again starting from ꢀ788C,
allowing to warm up to 5–108C. The organic layer was
separated and quickly dried with MgSO . Longer
exposure to water frequently led to decomposition of
the product by setting free cationic gold(I) species via
4
Scheme 4. Synthesis of (3-oxocyclopropenyl)gold(I) com-
plexes 2d * (see Table 1).
(
)
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1
Figure 1. H NMR spectrum of 2b (d -DCM, 300 MHz).
2
A range of synthetic attempts with triphenylphos- within days to weeks, we could not observe any
phine and (2,4-di-tert-butylphenyl)phosphite ligands stability issues with the complexes over the course of
either led to spontaneous decomposition even at low several months. However, direct sunlight or gentle
temperatures under oxygen- and moisture-free reac- ‘warming’ above 08C led to the observation of minor
tion conditions, or to very unstable products. The amounts of decomposition products over the course of
bulkier phosphine ligand XPhos (2-dicyclohexylphos- several weeks/months.
phino-2’,4’,6’-triisopropylbiphenyl) seemed to give
more stable complexes, yet they did neither survive show steric and electronic effects in the isolated
the cold precipitation procedures we subjected them complexes (see Figure 1). Complexes with 3,3-dime-
to nor warming up for chromatographic purifica- thylcyclopropen-1-yl
tion. The less sterically shielding NHC ligand IMes groups rotate freely, while the complexes of 3-methyl-
led to similar results.
1
NMR spectroscopy. The H NMR spectra nicely
and
cyclopropen-3-on-1-yl
[13]
3-phenycycloprop-1-yl and 3,3-diphenylcycloprop-1-yl
groups show a frozen rotation around the NHCꢀAu-
cyclopropene axis:
The iso-propyl signal of the IPr ligand of 2b
demonstrates this effect very clearly (see Figure 1, see
2
(
.2 Spectroscopic Investigation of Cyclopropenylgold
I) Complexes
General. We managed to obtain the complexes in high Figure 2 for atom numbers). Both the methyl doublet
1
purities, their connectivity could be confirmed by H and the methine septet give two slightly shifted signals.
1
3
NMR, C NMR, FT IR, and high-resolution mass The methyl groups in the proximity of the ligand are
spectra, as well as elemental analyses, and crystal shifted much more (d=1.24 ppm, d=1.26 ppm, at d=
structure analyses.
The gold complexes show drastically increased propenyl methyl group). Similar effects are visible in
stability in the solid state. Opposed to the cyclo- the C spectra (for 1b: C 128.1 ppm, C 22.7 ppm,
[
14]
1.24 ppm we also observed the signal of the cyclo-
1
3
1
3
propenes, which decompose at room temperature
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2.3 Molecular Structure in the Solid State
Crystallisation. We were able to grow and analyze
single crystals of every of the isolated cyclopropenyl-
gold(I) complexes 2. Usually, toluene or THF/n-
hexane mixtures worked best for this purpose. An
example is shown in Figure 2. A selection of bond
lengths and angles is compared in Table 2 (atom
numbering is shown in Figure 2).
Single crystal X-ray analyses. We observed strongly
stretched bond lengths of the CꢀC single bonds
adjacent to gold with an average bond length of
1
1
1
1
1
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1
1
2
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Figure 2. Solid state structure of complex 2b (thermal
ellipsoids are shown at 50% probability).
1
3
˚
(C ꢀC )=1.52 A for all complexes in Table 2 (com-
2
3
˚
pared to (C ꢀC )=1.40 A). Analogously, the angles of
the ring systems showed a rather high grade of
1
2
1
2
3
methyl-C 25.6 ppm, for 2b:
C
155.9 ppm,
C
asymmetry (average angle (C ꢀC ꢀC )=678; average
3
2 3 1 2 1 3
118.8 ppm, C 21.9 ppm, methyl-C 27.0 ppm).
angle (C ꢀC ꢀC )=538; average angle (C ꢀC ꢀC )=
Furthermore, strong electronic influences are visi- 608 for all complexes from Table 2). This distortion
ble in the NMR shifts of the complexes compared to results in gold being closer to a linear bond angle than
2
1
2
1
2
the hydrocarbons. While the aurated carbon is to 1208 sp angle for AuꢀC ꢀC ((AuꢀC ꢀC )=1558).
strongly deshielded (by 27.8 ppm), the other carbon The average experimental CꢀCꢀH angle from crystal
ring members and all hydrogen atoms experience structure analyses of 3-substituted and 3,3-disubsti-
2
[15]
significant shifts to high fields (see Scheme 5). C is tuted cyclopropenes is 149.28.
This hints at elec-
3
shifted to higher field by about 9.3 ppm, C by tronic interaction of gold with the p-system. The
0.8 ppm, the olefinic hydrogen by 0.51 ppm. The distortion of the ring system in some cases leads to
1
3
3
3
methyl group carbon is deshielded by 1.4 ppm, where- bond lengths C ꢀC even longer than usual sp -sp
˚
˚
as the bound hydrogen atoms are shielded (shift of single bonds (2b: 1.56 (13) A, 2b*: 1.65 (19) A, 2c*:
˚
0.37 ppm). This indicates the sigma-donating partic- 1.57 (6) A). These distortions indicate significant
ipation of gold in the ring’s electron density. This even participation of the aurated vinylcarbene mesomer
leads to the methyl and the methine group of the (E) of the aurated cyclopropene (D) structure even in
4
cyclopropene ring showing coupling ( J=0.8 Hz).
the ground state of the complexes (see Scheme 6).
1
13
Scheme 5. H NMR (red) and C NMR (blue) chemical
Scheme 6. Aurated cyclopropenes as quasi-carbenes with an
electronic structure close to the aurated carbenes.
shifts of 1b and 2b (d -DCM, 300 MHz/75 MHz) given in
2
ppm.
The aromatic nature of the cyclopropenone com-
The ring systems carrying the gold complexes seem plexes is nicely displayed by the bond lengths and
to be much more electron-rich than the ones of the angles in the ring systems. While the same distortion
corresponding hydrocarbons, leading to weakened trends are visible, the complexes 2d and 2d* are much
3
deshielding of the hydrogen atoms. While C experi- closer to an ideal equilateral triangle. Also in the gold
1
2
2
3
ences a high field shift upon auration, the methyl complex 2a the bond lengths C ꢀC and C ꢀC are
1
3
group is deshielded. The asymmetry of the system, as essentially the same, whereas the bond C ꢀC is
3
1
2
˚
2
3
˚
1
well as the appearance of a measurable coupling of strongly stretched (C ꢀC 1.33 A, C ꢀC 1.33 A, C ꢀC
˚
the methyl and the methine group, indicate vinyl- 1.47 A).
carbene-like character, leading to p-interaction be-
2
3
1
tween C and C of the cyclopropenyl system (C is the
aurated carbon atom). The aurated carbon is signifi-
2.4 Rearrangement to Indenyl Complexes
cantly shifted to low field, supporting this proposed Spontaneous rearrangement. During the attempted
structure.
synthesis of (IPr)(3,3-diphenylcyclopropenyl)gold(I)
2c a spontaneous rearrangement to an indenyl
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Table 2. Selected solid state bond lengths and angles from crystal structure analyses.
˚
[a]
[a]
[b]
[a]
Bond length [A]
2a
2a*
2b
2b*
2c*
2d
2d*
1
2
3
3
C ꢀC
1.34(3)
1.48(2)
1.32(3)
2.00(1)
2.007(7)
1.299(9)
1.535(9)
1.43(1)
1.978(7)
2.018(5)
1.30(2)
1.56(1)
1.48(1)
2.02(1)
2.020(7)
1.28(1)
1.65(2)
1.50(2)
1.991(1)
2.011(9)
1.279(6)
1.571(6)
1.491(6)
1.997(4)
2.021(4)
1.33(1)
1.42(1)
1.36(1)
2.009(8)
2.031(4)
1.23(1)
1.34(3)
1.39(3)
1.38(4)
2.02(2)
2.017(7)
1.23(4)
1
C ꢀC
2
C ꢀC
1
C ꢀAu
NHC
AuꢀC
3
C ꢀO
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
Angle [8]
2a
2a*
2b
2b*
2c*
2d
2d*
1
2
3
1
3
C ꢀC ꢀC
67(2)
57(1)
56(1)
155(3)
68.1(6)
51.8(4)
60.1(5)
156.5(6)
68(1)
450.5(9)
61(6)
72(1)
47.7(8)
60(1)
68.7(3)
49.3(3)
62.1(3)
156.5(4)
63.6(8)
57.5(8)
59.0.1(6)
152.9(9)
62(2)
58(2)
60(2)
152(2)
2
3
C ꢀC ꢀC
2
1
C ꢀC ꢀC
1
2
AuꢀC ꢀC
167(2)
158(1)
See Figure 2 for atom numbers. We numbered the other complexes analogously. Co-crystallized solvent molecules: 2a: one
molecule of THF; 2a*: two molecules of dichloromethane; 2c*: four molecules of THF; 2d: one molecule of chloroform; 2d*:
2
.5 molecules of THF.
[
[
a]
Average values of two occurring orientations of the cyclopropenyl domain. Errors were added quadratically.
Average values of two crystal structure analyses. Errors were added quadratically.
b]
Table 3. Observed rearrangements of cyclopropenyl to in-
denyl complexes.
structure 3c was observed. Even thoroughly purifying
under dry, aprotic, and apolar conditions at ꢀ208C
still lead to the indenyl complex (see Scheme 7 and
Table 3, entry 3). Extracted NMR samples directly
from the reaction would also show the indenyl
complex and a mixture of by-products. This hints at an
uncatalyzed carbene mechanism rather than a proton-
or gold-catalyzed one. Thermally the cyclopropene is
1
Entry R Reactand Product Time Conversion Yield
[
a]
1
2
Me 2b
Me 2b*
3b
3b*
3 d
4 d
5 d
100%
93%
100%
100%
[
a,b]
a,b]
c]
82%[
77%
[
3
4
Ph 1c
Ph 2c*
3c
3c*
spont. 100%
6 d 100%
61%
100%
[a]
[
16]
known to react at 2008C.
[a]
NMR scale experiments (10 mmol) of 2 heated to 908C in
dry d -THF (600 mL). Yield and conversion were deter-
8
mined relative to hexamethylbenzene as an internal
standard.
A single unidentified by-product seems to arise over the
course of the reaction, possibly the product of a double
bond migration.
Isolated yield after spontaneous rearrangement during
auration of 1c.
[
[
b]
c]
Scheme 7. Synthesis of (3-phenyl-1H-inden-1-yl)gold(I) com-
plexes 3. 3c was isolated directly after warming up the
reaction solution to r.t. during the synthesis attempt of 2c.
ing from the spontaneous formation of 3c, we tried to
induce a thermal rearrangement in other phenyl-
This indene complex proved to be unstable on both bearing cyclopropenyl complexes. Indeed, upon heat-
silica and alumina and would decompose in solution ing, we were able to induce analogous rearrangement
on air over the course of a few days even at ꢀ288C by reactions in the cyclopropenyl complexes 2b, 2b* and
a non-regioselective protodemetalation to indenes. 2c*. The ring opening direction is in accordance to the
This is in accord with a presumed sensitivity of stretched direction observed in crystal structure analy-
allylgold species, which quickly react with electro- ses of the cyclopropene complexes (see Scheme 7,
[17]
philes.
To avoid chromatographic procedures and elevated
Table 3, and Figure 3).
To further support our hypothesis, we conducted
temperatures, we purified 3c by Soxhlet extraction control experiments. Addition of IPrAuNTf (either
with n-pentane at 308C and 600 mbar. Following this 5 mol% and stoichiometric) both at room temperature
procedure, we were able to isolate the complex in high and 508C led to slow and highly unselective decom-
2
purity.
position reactions. So did the addition of colloidal
Thermal rearrangement. To investigate the hypoth- gold nanoparticles. Still, it is not possible to fully
esis of thermal rearrangement, a hypothesis originat-
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3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
adjacent phenyl group (see Scheme 8 and Table 4).
Only for 2b* we detected a subsequent rearrangement
of 3b* to an unidentified product.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
Figure 3. Solid state structure of complex 3c*.
Scheme 8. Proposed possible products of rearrangement
reactions of 2c.
exclude an in situ-generation of free gold(I) molecules
or gold(0) nanoparticles.
We were not able to observe the rearrangement of
our cyclopropenyl complexes to indenyls under con-
ditions similar to the ones used by Wang et al. for the
rearrangement of 1,3-diphenyl-substituted cyclopro-
pene derivatives to indenes. To retain comparability
Table 4. Net thermochemistry of the rearrangement to
different possible indenyl complexes 3.
[a]
[b]
[c]
Entry Reactand DE0
DH
DG
[kcal/mol] [kcal/mol] [kcal/mol]
1
2
3
4
2c
3c
3c’
3c’’
49.5
0.0
7.2
50.1
0.0
7.3
47.9
0.0
7.1
6.4
we stuck to IPrAuNTf , whereas Wang et al. employed
2
+
[9p]
[PPh Au(I)] cations.
In our hands with 5 mol%
3
IPrAuNTf (5 mmol in 0.5 mL CD Cl with 2 mol% or
6.9
7.0
2
2
2
5 mol% IPrAuNTf ) several days of stirring at r.t. in
2
B97D/SDD+f (Au), 6-31G** (other atoms) level of theory
with THF PCM at 298.15 K. Energies are referenced to the
ones calculated for 3c. Further information can be found in
the chapter “Computational investigation”.
DCM were needed for a full conversion of the starting
materials, but we did not find indene complexes.
[
18]
These results show a strong effect of steric and
electronic influences. Diphenyl-substituted complexes
reacted much faster, even spontaneous in the case of
3c. Steric hindrance of the bulkier IPr* ligand slowed
the reactions down significantly but led to high
selectivity. Especially the combination of the labile
3,3-diphenylcyclopropenyl group with the bulky IPr*
ligand led to a slow and clean conversion.
[
[
[
a]
b]
c]
Sum of electronic and zero-point energy,
Sum of electronic and thermal enthalpy,
Sum of electronic and thermal free energy.
This observation is in line with the pre-stretching
1
3
of the C ꢀC bond we discussed earlier. Gold pushes
Usually, facilitating the ring-opening of cyclopro- electron density into the cyclopropene ring system and
penes needs transition metal catalysts or light. Ther- interacts with the p-system in such a way that the
mal rearrangements are possible, but will need much double bond and the remote single bond are short-
higher temperatures for pure hydrocarbon cyclopro- ened and strengthened in comparison to the hydro-
[19]
penes (we also conducted control experiments with carbons.
1
1b and 1c, monitored by H NMR; in both cases even
The adjacent single bond, however, is weakened
after days at 1208C no rearrangement was detected; as and lengthened, giving rise to regioselective ring-
describe above in Table 3, aurated 1c, i.e. 3c, opening. We calculated (3-phenyl-1H-inden-1-yl)gold
rearranges at ꢀ208C). As indicated in a remarkable (I) 3c to be 7.2 kcal/mol more stable than the
way by the spectroscopic data discussed earlier, regioisomer (1-phenyl-1H-inden-1-yl)gold(I) 3c’ (see
auration dramatically pre-activates cyclopropenes. Table 5). By that, our calculations suggest that the
This allows for thermal rearrangements in very good products evolving from those reactions are also
to excellent yields and selectivity slowly at room thermodynamically favored.
temperature and faster at 908C. From the NMR
Protodeauration of indenyl complexes. On treat-
kinetics taken during conversions at 508C and 908C, ment with hydrochloric acid we observed a mixture of
the barriers can be estimated to be 9 kcal/mol (2c*), 1- and allylic substitution (see Scheme 9 and Table 5).
10 kcal/mol (2b), and 12 kcal/mol (2b*), which is 1/3 This indicates significant delocalisation of p-electrons
[
19]
or the values of the non-aurated compounds.
in the allylic system. These results are in accordance
Regioselectivity. We observed a selective ring- to our earlier observations and calculations of p-allyl
1
3
opening, exclusively breaking the C -C bond, fol- transition states in S /S ’-reactions of allylgold(I)
E
E
[
17]
lowed by insertion into an ortho-CꢀH bond of the intermediates. We will discuss further details later.
Adv. Synth. Catal. 2018, 360, 1–13
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Table 5. Protodeauration of indenyl complexes 3.
31G** (other atoms) level of theory, modelling their
physical properties, i.e. ring strain, hydration energy,
bond lengths and orders compared to other alkene
1
[a]
Entry
R
Reactand Products Yield
Ratio 4/5
[
21]
1
2
3
4
Me 3b
Me 3b*
4b/5b
4b*/5b*
4c/5c
85%
95%
97%
93%
7:1
2:1
8:1
6:1
systems and vinyl gold systems.
Ring strain and hydration energies. We employed a
homodesmotic approach to calculating ring strain
energies. This means the thermochemistry for the
hypothetical reaction of cyclopropene derivatives to
E-alkenes. As another way of understanding the ring
strain, we also calculated the thermochemistry for
hydration of the cyclopropenes, releasing energy
proportional to the amount of strain energy intro-
duced by the double bond. To gain deeper insight into
the interaction of gold with the cyclopropenyl double
bond, we also calculated ring strain energies for the
aurated cyclopropenes 2a–d and compared them to
Ph
3c
Ph
3c*
4c*/5c*
NMR scale experiments (10 mmol) with 1.5 eq. HNTf in d -
2
8
THF (600 mL) after 24 h.
[
a]
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
Full conversion was reached in all cases. Yield and
conversion were determined via integrals relative to
hexamethylbenzene as internal standard.
[
1e,22]
1a–d.
The (IPr)Au(I) fragment shows significant stabili-
zation of the cyclopropenes compared to the cyclo-
propenes (see Table 6). On average we calculated ca.
6 kcal/mol stabilization. Also, the hydration energy to
cyclopropenes is significantly reduced in the aurated
analogues. However, the possibility of interaction with
the p-system and planarity with the ring system seems
Scheme 9. Protodeauration reaction starting from indenyl
complexes 6.
To the best of our knowledge, this is the first to be crucial as we even observed an increase in ring
directly observed allylic substitution on an isolated strain energies for most of the hydrogenated com-
allylgold(I) complex. Such are often proposed as pounds. Only in 2a the aurated complex shows slightly
reasonable reaction pathway in catalyzes, but lacking less RSE. Steric hindrance overweighs stabilisation by
isolated allylgold(I) complexes, so far no direct proof donation of electron density to the ring system in the
[6,20]
was reported.
other cyclopropylgold(I) systems. This, in turn, ex-
plains the hydration enthalpies decreasing for the
[
23]
more sterically demanding cyclopropenes.
2.5 Computational Investigation
1
A comparative library of different C substituents
Methodology. The synthesized products 1a–d, 2a–d, on 3,3-dimethylcyclopropene was screened (see Ta-
3c and additional selected compounds were subject to ble S1).
extensive DFT studies at the B97D/SDD+f (Au), 6-
Table 6. Ring strain and hydrogenation energies of the synthesized (cyclopropenyl)gold(I) complexes compared to their
hydrogen analogues.
1
2
3
Entry
Compound
R
R
R
RSEc-propene
kcal/mol]
DEHydr.
[kcal/mol]
RSEc-propane
[kcal/mol]
[
1
2
3
4
5
6
7
8
1a
2a
1b
2b
1c
2c
1d
2d
Me
Me
Me
Me
Ph
Ph
O
Me
Me
Ph
Ph
Ph
Ph
H
AuIPr
H
AuIPr
H
AuIPr
H
49.50
42.37
50.02
43.57
49.24
43.49
37.61
32.66
ꢀ49.97
ꢀ37.88
ꢀ48.71
ꢀ33.15
ꢀ47.92
ꢀ32.95
ꢀ26.15
ꢀ16.87
25.43
24.85
25.48
29.70
27.20
31.68
36.67
41.85
O
AuIPr
B97D/SDD+f (Au), 6-31G** (other atoms) level of theory with THF PCM. All values given are zero-point energy corrected
electronic energy differences. The most stable isomers were used for the calculations, i.e. relaxed surface scans of the rotation
of phenyl groups and the IPr ligand were performed.
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Table 7. Calculated bond lengths [ A˚ ] (blue) and atom-atom overlap-weighted natural atomic orbital bond orders (red) of a
[a]
range of the reported compounds and a comparative library of other olefins.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
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5
5
B97D/SDD+f (Au), 6-31G** (other atoms) level of theory with THF PCM.
[
a]
Olefinic and allylic bonds are compared, as well as CꢀAu bond lengths and the CꢀH bond lengths which were replaced with
an (IPr)gold(I) fragment. The bond lengths attached to “IPrAu” fragments describe the bond length of the NHC-carbon to
gold.
RSE ðRÞ ¼ F > H ꢁ OMe > Me > Et ꢁ i-Pr > c-Pr >
Ph ꢁ AuP ðOMeÞ ꢁ AuIPr > AuPMe > t-Bu
orders increase. The cyclopropenyl complexes are
desymmetrised, preforming the adjacent allylcarbene
ring-opening mode.
3
3
We found (L)Au(I) fragments to have a stabilizing
effect similar to cyclopropyl and phenyl substituents.
While no significant differences were calculated for
different ligand systems, the trend suggests stronger p-
backbonding of the ligand to further improve the
For indenyl complexes, the same tendencies are
observed. Allylic auration shifts bonding electron
density towards the single bond, while the double
bond is strengthened if the substitution is applied in
vinylic position. Steric demand does not suffice to
overweigh the increased bond strengths in single
bonds. The bond length shortens due to the increased
bond strength in the case of allylic auration. This
stabilization. The Au(PMe) substituted cyclopropene
3
is slightly more stable than AuIPr, which itself is
slightly more stable than the Au(POMe) analogue.
3
Bond lengths and orders. We calculated bond supports the allylic character we observed upon
lengths and atom-atom overlap-weighted natural protodeauration.
atomic orbital bond orders for the used cyclopropenes,
for three phenylindene isomers and for a range of
3
Conclusions
other alkenes for comparison and the AuIPr substi-
[
24]
tuted analogues of all of them (see Table 7).
We successfully synthesized a library of seven (NHC)
Generally, gold stabilizes the adjacent carbon- cyclopropenylgold(I) complexes and were able to
carbon bonds, increasing their bond orders. Vinylic thoroughly investigate their structure in the solid and
substitution usually leads to minor lengthening of the liquid phase. Spectroscopic data and DFT calculations
neighboring carbon-carbon double bonds.
intriguingly show that cyclopropenes in vinylic gold
This reaffirms our findings from solid state struc- complexes are strongly pre-activated towards the ring-
tures. While the influence in the 3-oxocyclopropenyl opening mode along the adjacent single bond of
complex is marginal, other cyclopropene complexes cyclopropene.
experience a distortion. Due to steric demand in those
This enabled on-metal vinylcarbene chemistry
cases, the bond length increases slightly, still the bond without further activation at low temperatures, even
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leading to spontaneous rearrangement to an inden- (IPr*)(3,3-Dimethylcyclopropenyl)gold(I) 2a*
ylgold complex in one case. We were also able to
(
IPr*)(3,3-dimethylcyclopropenyl)gold(I) 2a* was prepared
activate all other phenyl-bearing complexes to show
the same reactivity by moderately heating them.
With a vinylic 1-aurated carbene center in this new
family of gold complexes, we generated the first of its
according to GP1, 247 mg (805 mmol) 1,1,3-tribromo-2,2-
dimethylcyclopropane in 6 mL Et O, 638 mL n-BuLi (2.5 M
in hexane) in 6 mL Et O and 185 mg (161 mmol) (IPr*)gold
2
2
(I) chloride in 20 mL dry THF were employed. Drying at
kind. We are looking forward to discovering direct UHV yielded 61% (116 mg, 98.5 mmol) of a colourless solid.
proof of this functional group and to investigate the
amazing possibilities, this functional group might
offer.
1
H NMR: (d -DCM, 500 MHz): d=1.13 (ps, 6H), 2.24 (s,
H), 5.32 (s, 4H), 5.80 (s, 2H), 6.85–6.87 (m, 8H), 6.91 (s,
H), 7.13–7.19 (m, 24H), 7.19-7.28 (m, 8H), 7.60 (s, 1H);
2
6
4
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
13
C
NMR: (d -DCM, 125 MHz): d=15.7 (s, 1C), 21.8 (q, 2C),
2
3
1.1 (q, 2C), 51.5 (d, 4C), 123.4 (d, 2C), 126.8 (d, 8C), 126.9
Experimental Section
(d, 8C), 128.7 (d, 8C), 128.7 (d, 8C), 129.7 (d, 8C), 130.3 (d,
General Procedure (GP1) for the Synthesis of
1C), 130.3 (d, 4C), 134.6 (s, 2C), 140.3 (s, 2C), 141.5 (s, 4C),
142.9 (s, 4C), 143.5 (s, 4C), 165.1 (s, 1C), 195.7 (s, 1C); IR: ~n
=3084, 3060,3027, 2958, 2920, 2844, 1952, 1889, 1811, 1601,
(NHC)(3,3-dimethylcyclopropenyl)gold(I) Complexes
(*)
2a
1
494, 1470, 1448, 1413, 1339, 1261, 1155, 1079, 1032, 944, 915,
A solution of 5 eqs. 1,1,3-tribromo-2,2-dimethylcyclopropane
in diethylether was slowly added under inert gas atmosphere
to a solution of 9.9 eqs. n-BuLi (2.5 M in hexane) in
diethylether at ꢀ788C. The mixture was stirred at this
temperature for 30 min, before it was allowed to warm up to
ꢀ108C and stirred an additional for an hour. The slightly
8
84, 831, 786, 764, 746, 701, 623, 607; HR-MS (ESI+):
+
+
C H AuN Na
[M+Na ]: calcd. 1199.4549, found
7
4
63
2
1
199.4571; X-ray crystal structure analysis can be found in
the Cambridge Structural Database: CCDC 1543944.
yellow mixture was cooled to ꢀ788C and a solution of 1 eq. General Procedure (GP2) for the Synthesis of
(NHC)gold(I) chloride in THF was added drop by drop via 3,3-disubstituted (NHC)(cyclopropenyl)gold(I)
(*)
syringe pump over 1 hour. To ensure full completion, the
mixture was stirred for one additional hour at the same
temperature. The reaction was quenched by addition of
Complexes 2b-d
2
eqs. n-butyllithium (2.5 M in hexane) was added to a stirred
solution of 2.3 eqs. diisopropylamine (DIPA) in THF at
788C. The solution was stirred for 15 min prior to adding a
1
00 mL water at ꢀ788C and the mixture was allowed to warm
ꢀ
up to 5–108C. The crude solution was dried over magnesium
sulfate. After removal of solvent, the crude product was
purified by flash column chromatography (neutral aluminum
oxide, 3:1 PE:DCM, if not noted otherwise).
solution of 2 eqs. cyclopropene in dry THF. After stirring the
solution for 15 min 1 eq. (NHC)gold(I) chloride in dry THF
(concentrations depend on the solubility of (NHC)gold(I)
chloride) was added drop by drop via syringe pump over 1 h.
To ensure full completion, the mixture was stirred for one
additional hour at the same temperature. The reaction was
quenched by addition of 100 mL water at ꢀ788C and the
mixture was allowed to warm up to 5–108C. The crude
solution was dried over magnesium sulphate. After removal
of solvent, the crude product was purified by flash column
chromatography (neutral aluminium oxide, 3:1 PE:DCM, if
not noted otherwise).
(
IPr)(3,3-Dimethylcyclopropenyl)gold(I) 2a
(
IPr)(3,3-dimethylcyclopropenyl)gold(I) 2a was prepared
according to GP1, 100 mg (524 mmol) 1,1,3-tribromo-2,2-
dimethylcyclopropane in 6 mL Et O, 199 mL (497 mmol) n-
2
BuLi (2.5 M in hexane) in 6 mL Et O and 300 mg (283 mmol)
2
(IPr)gold(I) chloride in 20 mL dry THF were employed.
Drying at UHV yielded 80% (169 mg, 259 mmol) of a
colourless solid.
1
(IPr)(3-Methyl-3-phenylcyclopropenyl)gold(I) 2b
H NMR: (d -DCM, 500 MHz): d=0.80 (pd, 6H), 1.23 (d,
2
3
3
3
J=6.9 Hz, 12H), 1.35 (d, J=6.9 Hz, 12H), 2.63 (sept, J=
(IPr)(3-methyl-3-phenylcyclopropenyl)gold(I) 2b was pre-
3
6.9 Hz, 4H), 7.19 (s, 2H), 7.21 (s, 1H), 7.33 (d, J=7.8 Hz,
4H), 7.52 (t, J=7.8 Hz, 2H);
125 MHz): d=15.1 (s, 1C), 24.1 (q, 4C), 24.6 (q, 4C), 29.2 (d,
4C), 30.5 (q, 2C), 123.5 (d, 2C), 124.3 (d, 4C), 129.1 (d, 1C),
1
(
1
1
(
pared according to GP2, 209 mg (1.61 mmol) 3-methyl-3-
phenylcycloprop-1-ene 1b in 5 mL THF, 248 mL (1.77 mmol)
DIPA in 5 mL THF, 612 mL (1.53 mmol) n-BuLi (2.5 M in
hexane) and 500 mg (851 mmol) (IPr)gold(I) chloride in
25 mL THF were employed. Drying at UHV yielded 82%
(473 mg, 661 mmol) of a colourless solid.
3
13
C NMR: (d -DCM,
2
30.6 (d, 2C), 134.9 (s, 2C), 146.3 (s, 4C), 164.9 (s, 1C), 195.8
s, 1C); IR: ~n =3160, 3130, 2964, 2924, 2870, 1639, 1593, 1558,
461, 1412, 1385, 1364, 1351, 1327, 1274, 1256, 1212, 1179,
104, 1061, 947, 848, 804, 760, 743, 702, 671, 641; HR-MS
1
3
H NMR: (d -DCM, 400 MHz): d=1.20 (pd, J=6.8 Hz,
2
3
3
+
+
12H), 1.24 (ps, 3H), 1.24 (d, J=6.8 Hz, 6H), 1.26 (d, J=
6
1
7.8 Hz, 2H), 7.29 (pdd, J=7.8 Hz, 2H), 7.51 (t, J=7.8 Hz,
2H); C NMR: (d -DCM, 100 MHz): d=21.9 (s, 1C), 24.2 (q,
ESI+): C H AuN Na [M+Na ]: calcd. 675.2984, found
32 43 2
3
3
.8 Hz, 6H), 2.58 (pdsep, J=6.8 Hz, 4H), 6.77 (q, J=0.8 Hz,
6
75.9866; EA: calcd: C (58.89%), H (6.64%), N (4.29%)
3
H), 6.86 (m, 3H), 7.01 (m, 2H), 7.18 (s, 2H), 7.27 (pdd, J=
found C (58.92%), H (6.80%) N(3.76%); X-ray crystal
structure analysis can be found in the Cambridge Structural
Database: CCDC 1543943.
3
3
13
2
4C), 24.5 (q, 2C), 24.5 (q, 2C), 27.0 (q, 1C), 29.2 (d, 4C),
1
18.8 (d, 1C), 122.5 (d, 1C), 123.5 (d, 2C), 124.4 (d, 2C),
Adv. Synth. Catal. 2018, 360, 1–13
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+
+
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3
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5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
124.4 (d, 2C), 126.1 (d, 2C), 127.1 (d, 2C), 130.7 (d, 2C),
34.8 (s, 2C), 146.3 (s, 2C), 146.3 (s, 2C), 155.7 (s, 1C), 155.9
s, 1C), 194.8 (s, 1C); IR: ~n =3077, 2963, 2926, 2866, 1660,
[M+H ] : calcd. 1301.5043, found 1301.5016; EA: calcd. C
(77.52%), H (5.19%), N (2.15%) found C (77.13%), H
(5.34%) N(1.86%); X-ray single crystal structure analysis can
be found in the Cambridge Structural Database: CCDC
1543947.
1
(
1
1
6
7
597, 1490, 1461, 1413, 1385, 1363, 1328, 1289, 1256, 1213,
180, 1118, 1106, 1060, 1027, 947, 901, 803, 758, 736, 698, 667,
+
+
39; HR-MS (ESI+): C H AuN Na [M+Na ]: calcd.
3
7
45
2
37.31405, found 737.31386; EA: calcd. C (62.18%), H
(3.92%), found (62.18%), (6.56%),
(
IPr)(3-oxocyclopropenyl)gold(I) 2d
(
6.35%),
N
C
H
N(3.65%); X-ray single crystal structure analysis can be
found in the Cambridge Structural Database: CCDC
(
IPr)(3-oxocyclopropenyl)gold(I) 2d was prepared according
to GP2, 19.6 mg (175 mmol) 4,8-dioxaspiro[2.5]oct-1-ene 1d
in 1 mL THF, 26.9 mL (192 mmol) DIPA in 1 mL THF,
6.3 mL (166 mmol) n-BuLi (2.5 M in hexane) and 54.2 mg
87.3 mmol) (IPr)gold(I) chloride in 10 mL dry THF were
employed. For column chromatography a solvent gradient
from 3:1 PE:DCM to pure DCM was used. Drying at UHV
yielded 64% (35.8 mg, 56.1 mmol) of a colorless solid.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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1543945.
6
(
(
IPr*)(3-Methyl-3-phenylcyclopropenyl)gold(I) 2b*
(
IPr*)(3-methyl-3-phenylcyclopropenyl)gold(I) 2b* was pre-
pared according to GP2, 68.2 mg (524 mmol) 3-methyl-3-
phenylcycloprop-1-ene 1b in 5 mL THF, 80.7 mL DIPA in
5 mL THF, 199 mL (498 mmol) n-BuLi (2.5 M in hexane) and
1
3
H NMR: (d -DCM, 500 MHz): d=1.24 (d, J=6.9 Hz, 12H),
2
3
3
1
2
(
(
.34 (d, J=6.9 Hz, 12H), 2.59 (sept, J=6.9 Hz, 4H), 7.24 (s,
3 3
300 mg (262 mmol) (IPr*)gold(I) chloride in 20 mL THF
H), 7.35 (d, J=7.78 Hz, 4H), 7.56 (t, J=7.78 Hz, 2H), 9.07
were employed. Drying at UHV yielded 89% (290 mg,
13
s, 1H); C NMR: (d -DCM, 125 MHz): d=24.1 (q, 4C), 24.6
2
234 mmol) of a colourless solid.
q, 4C), 29.3 (d, 4C), 124.2 (d, 2C), 124.6 (d, 4C), 131.1 (d,
1
H NMR: (d -DCM, 600 MHz): d=1.55 (s, 3H), 2.23 (s, 6H),
2C), 134.4 (s, 2C), 146.2 (s, 4C), 166.1 (d, 1C), 173.4 (s, 1C),
191.1 (s, 1C), 209.0 (s, 1C); IR: ~n =3071, 2963, 2927, 2869,
1779, 1594, 1554, 1460, 1417, 1385, 1364, 1351, 1330, 1293,
1258, 1217, 1181, 1119, 1060, 948, 937, 826, 804, 758, 706, 640;
2
5.35 (s, 2H), 5.38 (s, 2H), 5.82 (s, 2H), 6.84-6.91 (m, 12H),
1
3
7.01-7.20 (m, 38H); C NMR: (d -DCM, 150 MHz): d=21.9
2
(q, 2C), 22.2 (s, 1C), 27.3 (q, 1C), 51.4 (d, 2C), 51.5 (s, 2C),
+
+ +
1
1
1
1
1
20.0 (d, 1C), 122.6 (d, 1C), 123.5 (d, 2C), 126.2 (d, 4C),
26.8 (d, 2C), 127.0 (d, 2C), 127.2 (d, 4C), 128.6 (d, 4C),
28.7 (d, 4C), 128.7 (d, 8C), 129.7 (d, 4C), 129.7 (d, 4C),
30.1 (d, 4C), 130.2 (d, 4C), 130.3 (d, 2C), 130.3 (d, 2C),
34.5 (d, 2C), 140.3 (s, 2C), 141.4 (s, 2C), 141.5 (s, 2C), 143.0
HR-MS (ESI+): C H AuN NaO
[M+Na ] : calcd
30 37
2
661.2464, found 661.2480; X-ray single crystal structure
analysis can be found in the Cambridge Structural Database:
CCDC 1543948 and CCDC 1543949.
(
s, 4C), 143.3 (s, 2C), 143.3 (s, 2C), 154.7 (s, 1C), 156.3 (s, 1C),
(IPr*)(3-Oxocyclopropenyl)gold(I) 2d*
1
1
(
94.5 (s, 1C); IR: ~n =3059, 3025, 2922, 1745, 1598, 1493, 1471,
447, 1413, 1077, 1031+, 763, 697, 622, 606; HR-MS
(
IPr*)(3-oxocyclopropenyl)gold(I) 2d* was prepared accord-
ing to GP2, 19.6 mg (175 mmol) 4,8-dioxaspiro[2.5]oct-1-ene
d in 1 mL THF, 26.9 mL (192 mmol) DIPA in 1 mL THF,
6.3 mL (166 mmol) n-BuLi (2.5 M in hexane) and 100 mg
87.3 mmol) (IPr*)gold(I) chloride in 10 mL dry THF were
employed. For column chromatography a solvent gradient
from 3:1 PE:DCM to pure DCM was used. Drying at UHV
yielded 73% (74.0 mg, 63.6 mmol) of a colourless solid.
+
+
DART+): C H AuN
[M+H ] : calcd: 1239.4886,
7
9
66
2
found: 1239.48623; EA: calcd. C (76.56%), H (5.29%), N
(2.26%), found C (76.79%), H (5.06%) N (2.17%); X-ray
single crystal structure analysis can be found in the Cam-
bridge Structural Database: CCDC 1543946.
1
6
(
(
IPr*)(3,3-Diphenylcyclopropenyl)gold(I) 2c*
1
H NMR: (d -DCM, 500 MHz): d=2.26 (s, 1H), 5.30 (s, 4H),
.99 (s, 2H), 6.90–6.95 (m, 11H), 7.09–7.02 (m, 31H), 9.34 (s,
H); C NMR: (d -DCM, 125 MHz): d=21.9 (q, 2C), 51.6
d, 4C), 124.1 (d, 2C), 127.0 (d, 4C), 127.1 (d, 4C), 128.8 (d,
2
(IPr*)(3,3-diphenylcyclopropenyl)gold(I) 2c* was prepared
according to GP2, 100 mg (524 mmol) 3,3-diphenylcycloprop-
5
1
(
13
2
1-ene 1c in 5 mL THF, 80.7 mL DIPA in 5 mL THF, 199 mL
(
498 mmol) n-BuLi (2.5 M in hexane) and 300 mg (262 mmol)
1
6C), 129.7 (d, 8C), 130.1 (d, 8C), 130.6 (d, 4C), 134.0 (s, 2C),
(
IPr*)gold(I) chloride in 20 mL THF were employed. Drying
140.7 (s, 4C), 141.2 (s, 2C), 142.9 (s, 4C), 143.1 (s, 4C), 165.8
(s, 1C), 173.5 (s, 1C), 190.6 (s, 1C), 209.2 (s, 1C); IR: ~n =3168,
3109, 3061, 3026, 2919, 2293, 2185, 2105, 1949, 1885, 1779,
1598, 1556, 1493, 1470, 1447, 1417, 1339, 1292, 1268, 1220,
1185, 1152, 1077, 1030, 1002, 944, 913, 881, 851, 831, 783, 762,
744, 696, 629, 605; HR-MS (ESI+): C H AuN NaO [M+
Na ]: calcd. 1185.4029, found 1185.4081; X-ray single crystal
structure analysis can be found in the Cambridge Structural
Database: CCDC 1543950.
at UHV yielded 80% (272 mg, 209 mmol) of a colourless
solid.
1
H NMR: (d
-DCM, 600 MHz): d=2.25 (s, 6H), 5.29 (s, 2H),
2
5
1
.31 (s, 2H), 5.80 (s, 2H), 6.83-6.85 (m, 6H), 6.89-6.92 (m,
13
+
2H), 6.98-7.09 (m, 26H), 7.12-7.13 (m, 10), 7.28 (s, 1H);
C
72 57
2
+
NMR: (d -DCM, 150 MHz): d=21.9 (q, 2C), 32.5 (s, 1C),
2
51.5 (s, 4C), 117.3 (d, 1C), 123.6 (d, 2C), 123.9 (d, 2C), 126.7
(
d, 4C), 126.9 (d, 4C), 127.7 (d, 4C), 128.7 (d, 8C), 128.7 (d,
8
1
C), 128.9 (d, 4C), 129.7 (d, 8C), 130.1 (d, 8C), 130.3 (d, 4C),
34.4 (s, 2C), 140.3 (s, 2C), 141.5 (s, 4C), 143.1 (s, 8C), 152.8
(
s, 2C), 153.4 (s, 1C), 193.6 (s, 1C); IR: ~n =3058, 3025, 1946,
Conflicts of interest
There are no conflicts of interest to declare.
1
1
887, 1747, 1598, 1887, 1747, 1598, 1493, 1472, 1446, 1413,
+
077, 1031, 765, 697, 606; HR-MS (DART+): C H AuN
8
4
68
2
Adv. Synth. Catal. 2018, 360, 1–13
10
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
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Acknowledgements
[9] The topic was reviewed: a) A. Archambeau, F. Miege, J.
Cossy, C. Meyer, in: Chemistry of Organogold Com-
pounds, Pt. 2, Z. Rappoport, (Eds.: J. F. Liebmann, & I.
Marek), Wiley VCH, Chichester, 2014, Pt. 2, pp. 631–
699; b) F. Miege, C. Meyer, J. Cossy, Beilstein J. Org.
Chem. 2011, 7, 717; for studies on the topic see: c) X.
Cheng, L. Zhu, M. Lin, J. Chen, X. Huang, Chem.
Comm. 2017, 53, 3745; d) A. Archambeau, F. Miege, C.
Meyer, J. Cossy, Acc. Chem. Res. 2015, 48, 1021; e) Q.
Zhou, Y. Li, J. Am. Chem. Soc. 2014, 136, 1505; f) N. A.
Rajabi, M. J. Atashgah, R. BabaAhmadi, C. Hyland, A.
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Koh, D. Li, H. Hirao, P. W. H. Chan, J. Am. Chem. Soc.
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Jordan-Hore, G. M. Rosair, A.-L. Lee, J. Org. Chem.
2012, 77, 7633; i) M. S. Hadfield, L. J. L. Haeller, A.-L.
Lee, S. A. MacGregor, J. A. T. OꢄNeill, A. M. Watson,
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Meyer, J. Cossy, Chem. Eur. J. 2012, 18, 7810; ; k) M. S.
Hadfield, A.-L. Lee, Chem. Comm. 2011, 47, 1333;
l) P. C. Young, M. S. Hadfield, L. Arrowsmith, K. M.
MacLeod, R. J, Mudd, J. A. Jordan-Hore, A.-L. Lee,
Org. Lett. 2012, 14, 898; m) C. Li, Y. Zeng, H. Zhang, J.
Feng, Y. Zhang, J Wang, Angew. Chem., Int. Ed. 2010,
The authors would like to thank their finest mocha pot for
strongly supporting the performance of the team during this
study.
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[2]
used cyclopropenes: 148.98. Average of all CꢀC-H
angles of our computational data from all used non-
aurated 3,3-disubstituted cyclopropenes (see Table 7).
16] G. Snatzke, H. Langen, Chem. Ber. 1969, 102, 1865.
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ensure gold is capable of performing the rearrangement
in similar selectivities and reaction times without silver.
[
[
[
While PPh AuCl gave no reaction in their hands, they
3
reported good yields for 1:1 mixtures of PPh AuCl and
3
AgOTf, see reference 9p.
[19] MePh: conversion at 1808C, but no kinetics measured:
a) I. N. Domnin, R. R. Kostikov, A. de Meijere, Zh.
Org. Khim. 1983, 19, 2206; PhPh: conversion at 2008C
on the GC column, but no kinetics, see reference 16;
[
[
22] Further elaboration can be found in the supporting
information. See also reference 2c.
MeMe: from kinetics in the gas phase (GC): E =
a
1
56.1 kJ/mol at 195 to 2358C. 37.3 kcal/mol: b) R.
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[24] It is not feasible to compare the homodesmotic RSE of
cyclopropenone and cyclopropanone directly. The ho-
modesmotic approach to ring cleavage yields a con-
jugated p-system for cyclopropenone, which is absent in
the case of cyclopropanone.
1
987, 6, 424: g) N. D. Shapiro, F. D. Toste, J. Am. Chem.
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Adv. Synth. Catal. 2018, 360, 1–13
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ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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FULL PAPER
Cyclopropenylgold(I) Complexes as Aurated Carbenoids
or Quasi-Carbenes
Adv. Synth. Catal. 2018, 360, 1–13
F. F. Mulks, P. W. Antoni, F. Rominger, A. S. K. Hashmi*
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