Ionization of gold (γ-methoxy)vinyl complexes generates reactive gold vinyl carbene complexes

Article abstract of DOI:10.1039/c9sc01574d

Cationic gold vinyl carbene/allylic cation complexes of the form (E)-[(L)AuC(H)C(H)CAr₂]⁺ OTf^- {L = IPr, Ar = Ph [(E)-5a], L = IPr, Ar = 4-C₆H₄OMe [(E)-5b], L = P(t-Bu)₂o-biphenyl, Ar = 4-C₆H₄OMe [(E)-5c]} were generated in solution via Lewis acid-mediated ionization of the corresponding gold (γ-methoxy)vinyl complexes (E)-(L)AuC(H)C(H)C(OMe)Ar₂ at or below -95 °C. Complexes (E)-5b and (E)-5c were fully characterized in solution employing multinuclear NMR spectroscopy, which established the predominant contribution of the aurated allylic cation resonance structure and the significant distribution of positive charge into the γ-anisyl rings. Complex (E)-5b reacted rapidly at -95 °C with neutral two-electron, hydride, and oxygen atom donors exclusively at the C1 position of the vinyl carbene moiety and with p-methoxystyrene to form the corresponding vinylcyclopropane. In the absence of nucleophile (E)-5a decomposed predominantly via intermolecular carbene dimerization whereas formation of 1-aryl-5-methoxy indene upon ionization of (Z)-(IPr)AuC(H)C(H)C(OMe)(4-C₆H₄OMe)₂ [(Z)-6b] implicated an intramolecular Friedel-Crafts or electrocyclic Nazarov pathway for the decomposition of the unobserved vinyl carbene complex (Z)-[(IPr)AuC(H)C(H)C(4-C₆H₄OMe)₂]⁺ OTf^- [(Z)-5b].

Full text of DOI:10.1039/c9sc01574d

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ARTICLE
Ionization of Gold (-Methoxy)vinyl Complexes Generates
Reactive Gold Vinyl Carbene Complexes
Nana Kim and Ross A. Widenhoefer*
Received 00th January 20xx,
Accepted 00th January 20xx
Cationic gold vinyl carbene/allylic cation complexes of the form (E)-[(L)AuC(H)C(H)CAr2]+ OTf– {L = IPr, Ar = Ph [(E)-5a], L =
IPr, Ar = 4-C6H4OMe [(E)-5b], L = P(t-Bu)2o-biphenyl, Ar = 4-C6H4OMe [(E)-5c]} were generated in solution via Lewis acid-
mediated ionization of the corresponding gold (-methoxy)vinyl complexes (E)-(L)AuC(H)C(H)C(OMe)Ar2 at or below –95 °C.
Complexes (E)-5b and (E)-5c were fully characterized in solution employing multinuclear NMR spectroscopy, which
established the predominant contribution of the aurated allylic cation resonance structure and the significant distribution
of positive charge into the -anisyl rings. Complex (E)-5b reacted rapidly at –95 °C with neutral two-electron, hydride, and
oxygen atom donors exclusively at the C1 position of the vinyl carbene moiety and with p-methoxystyrene to form the
corresponding vinylcyclopropane. In the absence of nucleophile (E)-5a decomposed predominantly via intermolecular
carbene dimerization whereas formation of 1-aryl-5-methoxy indene upon ionization of (Z)-(IPr)AuC(H)C(H)C(OMe)(4-
C6H4OMe)2 [(Z)-6b] implicated an intramolecular Friedel-Crafts or electrocyclic Nazarov pathway for the decomposition of
the unobserved vinyl carbene complex (Z)-[(IPr)AuC(H)C(H)C(4-C6H4OMe)2]+ OTf– [(Z)-5b].
DOI: 10.1039/x0xx00000x
Introduction
Cationic gold carbene complexes have been invoked as
intermediates in diverse range of gold(I)-catalyzed
a
transformations1-3 and, for this reason, considerable effort has
been directed toward understanding the structure and
reactivity of these complexes.4 A particularly important subset
of the reactive gold carbene complexes is the gold vinyl
carbene/allylic cation complexes, with the potential for both
the delocalization of positive charge on the Au, C1, and/or C3
atoms and diverse reaction pathways (Figure 1). Cationic gold
vinyl carbene complexes have been invoked as intermediates in
range of gold-catalyzed transformations employing
cyclopropenes,5-8 propargyl carboxylates,9,10 propargyl ethers,11
enynes,12 ene-allenes,13 vinyl diazo compounds,14 and
norcaradienes as vinyl carbene precursors.15
Figure 2. Gold vinyl carbene/allylic cation complexes possessing -conjugated
oxygen atoms, depicted in the form of the predominant oxonium resonance
contributor.
Notwithstanding the insight provided through the
computational analysis of Toste and Goddard,16 information
regarding the structure and reactivity of cationic gold vinyl
carbene complexes is scarce, owing in large part to the absence
of suitable model complexes for interrogation.4 Only three
cationic gold vinyl carbene/allylic cation complexes (1 - 3) have
been characterized, each of which contains either a C1 or
multiple C3 oxygen atoms (Figure 2).17,18 As such, neither the
electronic structure nor reactivity of complexes 1-3 is likely to
mimic that of the reactive vinyl carbenes generated under
gold(I) catalysis.1-3,5-15 Indeed, well defined, two-coordinate
gold carbene complexes that display reactivity analogous to
their catalytic counterparts, gold to alkene carbene transfer in
particular, are exceedingly rare.19,20 Although weakly-stabilized
vinyl carbene complexes are known for a range of transition
metals,21 the properties of cationic gold(I), including high d-
electron count, electronegativity22 and poor d   back
bonding,4 likely render the electronic structure and reactivity of
cationic gold vinyl carbene complexes distinct from these
related complexes.
Figure 1. Potential resonance contributors and composite representation of an
unstabilized gold vinyl carbene/allylic cation complex.
a. French Family Science Center, Duke University, Durham, North Carolina, USA.
Electronic Supplementary Information (ESI) available: Experimental procedures,
characterization data, and scans of NMR spectra. See DOI: 10.1039/x0xx00000x
We have recently reported the synthesis of the cationic, two
coordinate gold(I) diphenylallenylidene complex 4 and related
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Table 1. Selected NMR data for gold vinyl carbene complexesV(ieEw)-5A.rticleVOanlulinees
DOI: 10.1039/C9SC01574D
reported in ppm; J values reported in Hz.
a
b
c
(E)-5a
(E)-5b
(E)-5c
10.83
8.18
9.51
7.71
243.7
8.89
7.83
252.3
H1
H2
C1
––
––
146.9
185.7
17.8
48
C2
C3
J
148.2
185.6
Scheme 1. Synthesis of gold allenylidene complex 4 (IPr = 1,3-bis(2,6-bis-
(diisopropylphenyl)imidazol-2-ylidene).
––
17.5
17.4
––
H1,H2
J
C1C2
––
––
complexes, generated via the Lewis acid-mediated ionization of
the corresponding gold (-methoxy)acetylide complexes
(Scheme 1),23,24 and which represent rare examples of cationic
gold carbene complexes lacking -conjugated heteroatoms.25,26
The efficiency and facility of the -ionization process suggested
that a similar approach might provide access to particularly
reactive gold vinyl carbene/allylic cation complexes. Indeed,
here we report that ionization of gold (-methoxy-,-
diaryl)vinyl complexes generates cationic, two-coordinate gold
vinyl carbene complexes that react rapidly at –95 °C with a
range of nucleophiles, including alkenes, and that decompose in
the absence of nucleophile via inter- or intramolecular
pathways. The spectroscopy of these complexes points to
strong contribution of the aurated allylic cation resonance form
and stabilization by the -aryl groups.
J
48
––
C2C3
a –110 °C in CDFCl2/CD2Cl2. b –95 °C in CD2Cl2. c –90 °C in CD2Cl2.
bright orange/red solution that became colorless over the
course of ~10 s. 1H NMR analysis of the resulting solution at –
95 °C revealed formation of trimethylsilyl methyl ether
(TMSOMe) in 92 ± 5% yield, which established that efficient
ionization of (E)-6a had occurred, but no resonances were
1
observed that could be attributed to (E)-5a. Rather H NMR
analysis revealed formation of a ~11:1 mixture of (E)- and (Z)-
1,1,6,6-tetraphenylhexa-1,3,5-triene in 70% combined yield,
presumably generated via homocoupling of the vinyl carbene
groups of (E)-5a (Scheme 2).20,29 In an effort to directly observe
vinyl carbene (E)-5a, a solution of (E)-6a was treated with
TMSOTf at –110 °C in CDFCl2/CD2Cl2 and analysed immediately
by 1H NMR spectroscopy. The resulting spectrum was
broadened and largely uninterpretable, but displayed a pair of
mutually-coupled doublets at  10.83 and 8.18 (J = 17.5 Hz),
assigned to the C1 and C2 vinylic protons, respectively, of (E)-5a
(Table 1).
In an effort to enhance the stability of the gold vinyl
carbene/allylic cation complex to allow more rigorous
spectroscopic interrogation and reactivity analysis, we turned
our attention to the gold -bis(anisyl)vinyl carbene/allylic
cation complex (E)-[(IPr)AuC(H)C(H)C(4-C6H4OMe)2]+ OTf– [(E)-
5b]. To this end, ionization of gold vinyl complex (E)-6b in CD2Cl2
at –95 °C led to immediate (<1 min) formation of the bright red-
orange solution of (E)-5b in 96 ± 5% yield (1H NMR), which
persisted indefinitely at this temperature (Scheme 3). In a
similar manner, ionization of the phosphine-supported gold
vinyl complex (E)-6c at –95 °C led to formation of (E)-5c in 95%
yield (1H NMR; Scheme 3), which darkened noticeably over the
course of several hours at –95 °C.
Results and Discussion
Guided by our investigation of cationic gold allenylidene
complexes,23
(diphenyl)vinylcarbene/allylic
we
targeted
cation
the
gold
complex
-
(E)-
[(IPr)AuC(H)C(H)CPh2]+ OTf– [(E)-5a] for initial investigation
(Scheme 2). The requisite gold (-diphenyl)vinyl complex (E)-
(IPr)AuC(H)=C(H)C(OMe)Ph2 [(E)-6a] was synthesized in two
steps from propargylic ether 7a via zirconium-catalyzed
hydroboration27 followed by transmetallation of the resulting
boronic ester (E)-8a with (IPr)AuCl (Scheme 2).28 Treatment of
(E)-6a with trimethylsilyl trifluoromethanesulfonate (TMSOTf)
in CD2Cl2 at –95 °C led to immediate (<1 min) formation of a
Complexes (E)-5b and (E)-5c were fully characterized by
NMR spectroscopy at or below –85 °C (Table 1). For example,
the 13C NMR spectrum of (E)-5b displayed downfield resonances
at  243.7, 146.9, and 185.7 assigned to the C1, C2, and C3
carbon atoms, respectively, of the vinyl carbene/allylic cation
Scheme 2. Synthesis and thermal decomposition of gold vinyl carbene/allylic
cation complex (E)-5a.
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(Z)-5b.¶ To this end, the gold vinyl complex (Z)-6b was
View Article Online
DOI: 10.1039/C9SC01574D
synthesized in two steps
Scheme 3. Syntheses of gold vinyl carbene/allylic cation complexes (E)-5b and (E)-
5c.
Figure 4. Resonance structures D representing delocalization of positive charge
onto the -anisyl rings of (E)-5b.
Figure 3. Fluxional behaviour of (E)-5b.
1
1
moiety. These resonances as well as JC1C2 and JC2C3 were
unambiguously assigned via 13C NMR analysis of the
corresponding
13C-labelled
isotopomer
(E)-
[(IPr)Au13C(H)13C(H)C(4-C6H4OMe)2]+ OTf– [(E)-5b-13C2]. The 13
C
NMR spectrum of (E)-5b also displayed a pair of downfield
resonances at  168.3 and 167.6 assigned to the chemically
inequivalent methoxy-bound aromatic carbon atoms. These
resonances were shifted significantly downfield relative to
those of neutral (E)-6b ( 140), which points to the significant
delocalization of positive charge onto the -anisyl rings of (E)-
5b.30
Scheme 4. Generation and decomposition of gold vinyl carbene/allylic cation
complex (Z)-5b.
1
The H NMR spectrum of (E)-5b at –95 °C displayed two
mutually-coupled doublets at  9.51 and 7.71 (J = 17.8 Hz)
assigned to the C1 and C2 protons, respectively, and a pair of
singlets at  3.89 and 3.96 assigned to the chemically
inequivalent aryl methoxy protons. As the temperature was
raised, the methoxy resonances broadened and coalesced at –
42 °C, albeit with significant decomposition, which provided an
energy barrier of G‡231K = 10.5 kcal/mol for interconversion of
the anisyl groups of (E)-5b (Figure 3). Both the facile rotation
about the C2–C3 bond of (E)-5b and the significant
delocalization of positive charge onto the -anisyl rings of (E)-5b
point to the predominant contribution resonance structures D
to the electronic structure of (E)-5b (Figure 4), which is likewise
consistent with the significantly greater thermal stability of (E)-
5b relative to (E)-5a.
Warming a solution of (E)-5b at –40 °C (t1/2 = 35 min) or (E)-
5c at –60 °C (t1/2  10 min) led to decomposition to form
unidentified mixtures of products that included neither the
products of intramolecular Friedel-Crafts alkylation nor carbene
dimerization as determined by GCMS and LCMS analysis. We
were somewhat surprised by the absence of Friedel-
Crafts/Nazarov reactivity for complexes (E)-5, which is well
documented for 1-aryl allylic cations31,32 and which is directly
implicated in the gold(I)-catalyzed ring-opening of aryl
cyclopropenes.5,6 We reasoned that the less stable gold Z-vinyl
carbene complexes, which are generated as the kinetic
products of cyclopropene ring opening,33 might be more
susceptible toward intramolecular cyclization processes than
are the E-vinyl carbene complexes. To evaluate this hypothesis,
we sought the independent synthesis of vinyl carbene complex
from propargyl ether 7b via rhodium-catalyzed, anti-selective
hydroboration34 followed by transmetallation of boronic ester
(Z)-8b (Scheme 4).
Ionization of (Z)-6b with TMSOTf at –95 °C formed a pale
1
orange solution that displayed no resonances in the H NMR
spectrum that could be attributed to vinyl carbene complex (Z)-
5b.§ Rather, warming this solution above –50 °C led to
formation of the 1-aryl-5-methoxy indene 9 in 58% yield (1H
NMR; Scheme 4). Because 1-aryl indenes are less stable than
are the isomeric 3-aryl indenes,35 9 must be formed kinetically,
which points to a mechanism for the conversion of (Z)-5b to 9
involving intramolecular Friedel-Crafts alkylation or
electrocyclic Nazarov-type cyclization followed by selective
protonation of the -position of gold allyl intermediate II
through an SE’ pathway (Scheme 5). Interestingly, (3-phenyl-
1H-inden-1-yl)gold(I) complexes very similar to intermediate II
have been recently isolated via thermal rearrangement of
neutral 3,3-diphenylcycloprop-1-en-1-yl)gold(I)complexes and
were shown to undergo protodeauration with HCl
predominantly through an SE’ pathway.36,37 The facility of the
intramolecular Friedel-Crafts/Nazarov reaction of (Z)-5b and
the failure to form 9 in the decomposition of (E)-5b therefore
suggests that the energy barrier for E/Z isomerization of (E)-5b
exceeds that of the lowest energy decomposition pathway
available to (E)-5b (G‡  16 kcal/mol).
Nucleophilic trapping of a cationic gold vinyl carbene
complex represents one of the most common terminating steps
of catalytic transformations involving these intermediates.5,7,8
In
a similar manner, treatment of (E)-5b with either
tetrahydrothiophene (THT) or pyridine at –95 °C in CD2Cl2 led to
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immediate (< 1 min) disappearance of the distinctive red color
to form pale yellow solutions of the gold allyl carbenoid
complexes 10 and 11, respectively, in >90% yield (1H NMR;
View Article Online
DOI: 10.1039/C9SC01574D
Scheme 5. Proposed mechanism of the conversion of (Z)-5b to 9.
Figure 4. ORTEP diagram of 11. One of two crystallographically independent
molecules is depicted with ellipsoids shown at the 50% probability level with
counterion and hydrogen atoms omitted for clarity. Selected bond distances (Å)
and bond angles (deg) for 11: Au–C1 = 2.005(4), Au–C28 = 2.067(5), C28–C29 =
1.495(5), C29–C30 = 1.343(7), C28–N3 = 1.515(6), C30–C36 = 1.501(8), C30–C43 =
1.55(1), C1–Au–C28 = 177.4(2), Au–C28–C29 =115.6(3), Au–C28–N3 = 107.8(3),
N3–C28–C29 = 108.3(4), C28–C29–C30 = 125.5(5), C29–C30–C43 = 126.1(9), C29–
C30–C36 = 121.6(5), C36–C30–C43 = 112.0(9).
Scheme 6. Reactions of (E)-5b with THT and pyridine and interconversion of 10
and 11. Yields determined by 1H NMR spectroscopy versus internal standard.
Scheme 6). These complexes were characterized in solution,
and in the case of 11, by X-ray crystallography (Figure 4). For
example, selective attack of THT at the C1 vinyl carbene carbon
atom of (E)-5b was established by a pair of mutually-coupled
doublets at  3.22 and 5.60 (J = 11.5 Hz) assigned to the aliphatic
C1 and vinylic C2 protons, respectively of 10. In the solid state,
11 adopts a slightly distorted linear conformation (C1–Au–C28
= 177°) with the C1 allylic carbon atom adopting a distorted sp3
geometry with a larger Au–C28–C29 angle (115°) and smaller
Au–C28–N3 and N3–C28–C29 angles (108°) (Figure 4).
Treatment of 10 (15 mM) with pyridine (1 equiv) at 0 °C for 2 h
led to formation of an equilibrium 1.25:1 mixture of 11:10 (Keq
= 1.8 ± 0.1; Scheme 6). Kinetic analysis of the conversion of 10
to 11 established first-order approach to equilibrium through
2.5 half-lives with forward and reverse rate constants kf = 4.1 ±
0.9  10–4 s–1 and kr = 2.3 ± 0.5  10–4 s–1. The first-order kinetic
Scheme 7. Reactions of (E)-5b with 4-picoline-N-oxide and HSiEt3. Yields determined by
1H NMR spectroscopy versus internal standard.
of 3-arylcinnamaldehyde 12 in 88% yield and the 4-picoline gold
complex [(IPr)Au(4-pic)]+ OTf– in quantitative yield (Scheme 7).
This outcome is consistent with selective oxygen atom transfer
to the C1 carbon atom of the vinyl carbene moiety of (E)-5b
followed by elimination from the unobserved -oxopyridinium
intermediate III. Related to this, treatment of (E)-5b with
triethylsilane at –95 °C led to immediate (< 1 min) and selective
formation of the cationic gold -allyl silane complex 13,
presumably via hydride addition to the C1 position of (E)-5b
followed by silyldeauration of the resulting gold allyl
intermediate through an SE pathway.40 Warming this solution
above –40 °C led to decomplexation and formation of allylic
silane 14 in quantitative yield. Both the reaction of (E)-5b with
DSiEt3 and the reaction of the deuterated isotopomer (E)-5b-d1
with HSiEt3 at –95 °C led selective incorporation of deuterium
into the allylic position to form 13-d1 as a ~1:1 mixture of
behaviour points to
a dissociative mechanism for the
interconversion of 10 and 11 involving free (E)-5b.
Oxygen atom transfer to the C1 position of a gold vinyl
carbene intermediate has been invoked in the gold-catalyzed
reactions of cyclopropenes with diphenylsulfoxide.7,38,39 In a
similar manner, treatment of (E)-5b with 4-picoline N-oxide (4-
PNO) (1.9 equiv) in CD2Cl2 at –95 °C for ~1 min led to formation
diastereomeric isotopomers, pointing to
deauration/complexation process (Scheme 8).
a
stepwise
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Despite the dearth of examples of stoichiometric gold to the -anisyl groups. Indeed, the significantly greatVeierwsAtartibclieliOtynlionef
alkene carbene transfer19,20 perhaps no process is more closely the -bis(anisyl) vinyl carbene complexD(OEI):-150b.10re39la/Cti9vSeC0to157th4De
associated with the reactive gold carbene complexes, including -diphenyl vinyl carbene complex (E)-5a points to the
vinyl carbene complexes, generated as catalytic importance of the p-methoxy groups in the stabilization of (E)-
intermediates.1,2 It is therefore significant that vinyl carbene 5b.41 Complex (E)-5b reacted rapidly at –95 °C with neutral two-
complex (E)-5b underwent facile gold to alkene carbene electron, hydride, and oxygen atom donors exclusively at the C1
transfer with p-methoxystyrene. For example, treatment of (E)- position of the vinyl carbene/allylic cation moiety and with p-
methoxystyrene to form vinyl cyclopropane.
These
transformations are close or direct analogues to processes
attributed to gold vinyl carbene intermediates generated under
catalytic conditions.1-3,5-15
Two distinct pathways for
decomposition of these gold vinyl carbene complexes in the
absence of nucleophile were identified; complex (E)-5a
decomposed predominantly via intermolecular carbene
homocoupling whereas formation of indene 9 upon ionization
of (Z)-6b directly implicated an intramolecular Friedel-Crafts or
electrocyclic Nazarov pathway for the decomposition of the
unobserved vinyl carbene complex (Z)-5b.
Scheme 8. Reaction of (E)-5b with DSiEt3 and reaction (E)-5b-d1 with HSiEt3.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We thank the NSF (CHE-1213957) for support of this research.
X-ray crystallography measurements were made by Dr. Roger
Sommer in the Molecular Education, Technology, and Research
Innovation Center (METRIC) at NC State University.
Scheme 9. Reaction of (E)-5b with p-methoxystyrene and independent synthesis
of -(vinyl cyclopropane) complex 15.
Notes and references
5b with p-methoxystyrene (3 equiv) at –95 °C led to immediate
(<3 min) consumption of (E)-5b to form the gold -vinyl
cyclopropane complex 15 (Scheme 9). Although 1H NMR
analysis of this solution at –95 °C was complicated by the
presence of free p-methoxystyrene and byproducts, a doublet
was observed at  4.99 (J = 10.2 Hz), assigned to the vinyl proton
of 15, which corresponded to a 75% yield of 15 from (E)-5b
(Scheme 9). Warming this solution of 15 above –40 °C led to
decomplexation to form free vinyl cyclopropane 16 in 67% NMR
yield from (E)-5b as a ~3:1 mixture of cis/trans isomers (Scheme
9). Assignment of the  4.99 resonance to the vinyl proton of
15 was confirmed by independent synthesis of 15 from reaction
of 16 (cis/trans = 3:1) with a mixture of (IPr)AuCl and AgSbF6 in
CD2Cl2 at –80 °C.§§
¶) Fürstner has previously reported that attempted synthesis of the
PCy3-analog of (Z)-5a via reaction of 1,1-diphenylcyclopropene with
(PCy3)PAuNTf2 led instead to rapid oligomerization of the
cyclopropene.19 In our hands, attempted synthesis of (Z)-5b via
reaction of 1,1-(bisanisyl)cyclopropene with either (IPr)AuOTf or
(IPr)AuCl/AgSbF6 produced a similar outcome.
§) Two discrete intermediates were detected by 1H NMR
spectroscopy over the temperature range –95 to –30 °C. However,
broadening, overlapping resonances, and the dearth of potentially
diagnostic resonances precluded extraction of any meaningful
information from these data.
§§) Reaction of 16 (cis/trans = 3:1, 3 equiv) with a 1:1 mixture of
(IPr)AuCl and AgSbF6 in CD2Cl2 at –80 °C generated a single resonance
[ 4.99 (br d, J = 10.2 Hz)] that could be attributed to 15 and which
constituted ~25% of the reaction mixture, the remainder being free
1
16. This suggests that either (1) the vinylic H resonances for the
various diastereomers of 15 are coincidental or (2) only a single
diastereomer of 15 is formed in detectable concentrations from this
reaction. Therefore, the 75% yield determined for the conversion of
(E)-5b to 15 (determined by integrating the  4.99 resonance relative
to internal standard) represents a lower limit for the yield of 15
formed from (E)-5b and the 67% yield determined for 16
(determined by integrating the vinylic resonances of cis- and trans-
16 relative to internal standard after warming to room temperature
and filtering through silica gel) points to decomposition of 16 under
reaction conditions, which was confirmed experimentally.
Treatment of (E)-5b with 1-(p-methoxyphenyl)-1,3-butadiene at –95
Conclusions
We have generated highly reactive gold vinyl carbene/allylic
cation complexes via low-temperature ionization of gold -
methoxy-(-diaryl)vinyl complexes. Spectroscopic analysis of
vinyl carbene/allylic cation complex (E)-5b established the
predominant contribution of the aurated allylic cation canonical
form to the electronic structure of the vinyl carbene complex (C;
Figure 1) with significant delocalization of positive charge into
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°C led to immediate consumption of (E)-5b but produced no products
that could be attributed to either cyclopropanation or [4+3]
cycloaddition.
López, Organometallics, 2014, 33, 5924-5927; (c) D. Zhang,
View Article Online
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ARTICLE
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DOI: 10.1039/C9SC01574D
Highly reactive cationic gold vinyl carbene/allylic cation complexes are generated in solution via
-ionization of gold vinyl complexes.