Synthesis, Structure, Reactivity and Catalytic Implications of a Cationic, Acetylide-Bridged Trigold–JohnPhos Species

Article abstract of DOI:10.1002/chem.202000420

The cationic complex [(JohnPhos–Au)₃(acetylide)][SbF₆] (JohnPhos=(2-biphenyl)di-tert-butylphosphine, L1) has been characterised structurally and features an acetylide–trigold(I)–JohnPhos system; the trinuclear–acetylide unit, coordinated to the monodentate bulk phosphines, adopts an unprecedented μ,η¹,η²,η¹ coordination mode with an additional interaction between distal phenyl rings and gold centres. Other cationic σ,π-[(gold(I)L1)₂] complexes have also been isolated. The reaction of trimethylsilylacetylene with various alcohols (iPrOH, nBuOH, n-HexOH) catalysed by cationic [Au^IL1][SbF₆] complexes in CH₂Cl₂ at 50 °C led to the formation of acetaldehyde acetals with a high degree of chemo- and regioselectivity. The reaction mechanism was studied, and several organic and inorganic intermediates have been characterised. A comparative study with the analogous cationic [Cu^IL1][PF₆] complex revealed different behaviour; the copper metal is lost from the coordination sphere leading to the formation of cationic vinylphosphonium and copper nanoparticles. Additionally, a new catalytic approach for the formation of this high-value cationic vinylphosphonium has been established.

Full text of DOI:10.1002/chem.202000420

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Multinuclear Gold Complexes
Synthesis, Structure, Reactivity and Catalytic Implications of a
Cationic, Acetylide-Bridged Trigold–JohnPhos Species
Abdessamad Grirrane,*[a] Eleuterio ꢀlvarez,[b] Hermenegildo Garcꢁa,*[a] and Avelino Corma*[a]
Abstract: The cationic complex [(JohnPhos–Au)3(acetylide)]
[SbF6] (JohnPhos=(2-biphenyl)di-tert-butylphosphine, L1)
has been characterised structurally and features an acety-
lide–trigold(I)–JohnPhos system; the trinuclear–acetylide
unit, coordinated to the monodentate bulk phosphines,
adopts an unprecedented m,h1,h2,h1 coordination mode with
an additional interaction between distal phenyl rings and
gold centres. Other cationic s,p-[(gold(I)L1)2] complexes
have also been isolated. The reaction of trimethylsilylacetyle-
ne with various alcohols (iPrOH, nBuOH, n-HexOH) catalysed
by cationic [AuIL1][SbF6] complexes in CH2Cl2 at 508C led to
the formation of acetaldehyde acetals with a high degree of
chemo- and regioselectivity. The reaction mechanism was
studied, and several organic and inorganic intermediates
have been characterised. A comparative study with the anal-
ogous cationic [CuIL1][PF6] complex revealed different be-
haviour; the copper metal is lost from the coordination
sphere leading to the formation of cationic vinylphosphoni-
um and copper nanoparticles. Additionally, a new catalytic
approach for the formation of this high-value cationic vinyl-
phosphonium has been established.
Introduction
sumed to be formed via a highly reactive cationic p-gold(I)–
acetylide complex intermediate. It should be mentioned at this
point that the bulky Buchwald-type biarylphosphane ligand
(L1) is crucial for stabilising this kind of structure.[6,7] The ten-
dency for gold(I) species to form clusters has been
shown,[2d,5a,d,6,8] and the number of atoms in an AuI cluster has
been found to influence the stability, properties and catalytic
activity of these gold(I) complexes.
Cationic gold(I) complexes are known as efficient homogene-
ous catalysts.[1] Furthermore, alkynes are some of the most
commonly used substrates in gold-catalysed organic synthesis.
However, isolable gold–alkyne complexes are rare,[2] and the
nature of the intermediates involved in these reactions remains
uncertain.[3] Evidence that gold complexes of terminal alkynes
can evolve into polynuclear species has also been provi-
ded.[2d,4] Recently, the activation of terminal alkynes by AuI
complexes [L1Au][SbF6] (L1=JohnPhos, (2-biphenyl)di-tert-bu-
tylphosphine, A; Scheme 1) has been reported[5] and stable
fluxional cationic s,p-digold(I)–JohnPhos phenyl- and alkylace-
tylide complexes (B)[5a,6] have been synthesised (Scheme 1,
top). In addition, stable fluxional cationic s,p-digold(I)–John-
Phos acetylide complexes (C;[7] Scheme 1, bottom), prepared
when stoichiometric amounts of cationic [L1Au(NCMe)][SbF6]
complexes react with TMS-acetylene in dry CH2Cl2, have been
isolated and characterised. These digold complexes were as-
Continuing with this research aimed at the characterisation
and evaluation of the activity of polynuclear AuI complexes,
we report herein the incorporation of an additional JohnPhos–
Au+ cation into the HCꢀC triple bond of the s,p-acetylide in
complexes of the type C (Scheme 1), which resulted in a well-
defined trinuclear AuI complex.
[a] Dr. A. Grirrane, Prof. Dr. H. Garcꢀa, Prof. Dr. A. Corma
Instituto Universitario de Tecnologꢀa Quꢀmica CSIC-UPV
Universitat Politꢁcnica de Valꢁncia
Av. de los Naranjos s/n, 46022 Valencia (Spain)
E-mail: grirrane@itq.upv.es
hgarcia@qim.upv.es
acorma@itq.upv.es
[b] Dr. E. ꢂlvarez
Departamento de Quꢀmica Inorgꢃnica
Instituto de Investigaciones Quꢀmicas CSIC-US
Av. Amꢄrico Vespucio 49, 41092 Sevilla (Spain)
Supporting information and the ORCID identification number(s) for the au-
thor(s) of this article can be found under:
https://doi.org/10.1002/chem.202000420.
Scheme 1. Synthesis of the cationic s,p-digold(I) phenyl- and alkylacetylide
ligand L complexes B (top) and the cationic s,p-digold(I) acetylide ligand L
complexes C (bottom).
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which is attributable to the cationic [C48H58Au2BrP2]+ species,
Results and Discussion
the observed peak cluster showing good agreement with the
simulated isotopic distribution for the molecular formula
C48H58Au2BrP2 and the fragmentation pattern of the peak can
be easily rationalised on the basis of the structure of complex
2, confirming the elemental composition (see Figure S5). More-
over, the MS peaks recorded in negative-ion mode at 234.3
and 236.3 Da correspond to the two 121Sb and 123Sb isotopes
of the [SbF6]À counter anion (see Figure S5). In addition, the
HR-ESI-MS peak recorded in positive-ion mode at
1169.2377 amu is in good agreement with the corresponding
simulated mass of 1169.2528 amu (see Figure S6 for the iso-
topic distribution and single mass analysis).
With this goal, p-bromophenylacetylene was treated in the first
step with the gold(I)L1 complex 1 in CH2Cl2 at 508C for 30 h to
yield the isolable fluxional cationic [(s,p)(L1Au)2(m-bromophe-
nylacetylide)][SbF6] complex 2 (Scheme 2) in excellent yield
(92%) with the concomitant formation of HSbF6. In the second
step, an excess of the starting gold(I) complex 1 was added to
the cationic s,p-digold(I) complex 2 and allowed to react for
an additional 24 h (Scheme 2). However, under these condi-
tions, it was not possible to obtain the dicationic
[(s,p,p’)(L1Au)3(m-bromophenylacetylide)][SbF6]2 complex
3
(Scheme 2). It should be mentioned at this point that the
direct reaction of a stoichiometric (1:1) mixture of starting
gold(I) complex 1 and isolated s,p-digold(I) complex 2 also
failed to form any isolable product. In addition, no evidence
for the formation of any new species, including the target
[(s,p,p’)(L1Au)3(m-bromophenylacetylide)][SbF6]2 complex 3,
could be obtained when CH2Cl2/isopropanol (1:1) was used as
solvent instead of CH2Cl2. The failure to achieve the incorpora-
tion of an additional (L1Au)+ cation at the free p-coordination
position of the CꢀC triple bond of the [(s,p)(L1Au)2(m-bromo-
phenylacetylide)][SbF6] complex 2 (Scheme 2) can be explained
by electrostatic repulsion of the AuL moieties, or perhaps of
the electron density.
The solid-state structure of [(s,p)(L1Au)2(m-bromophenylace-
tylide)][SbF6] complex 2 was confirmed by single-crystal X-ray
diffraction analysis. An ORTEP diagram of 2 is shown in
Figure 1 (for the X-ray diffraction data, ORTEP view and crystal-
packing details, see Table S1 and Figure S7 in the Supporting
Information).
These results point to the difficulty in obtaining more than
dinucleation in gold complexes of the type A (Scheme 1)
under our reaction conditions. For this reason, the reactivity of
complexes of the type B (Scheme 1) was studied in the second
stage of this work. In our previous work,[7] we showed that a
stoichiometric mixture of trimethylsilylacetylene and gold(I)
complex 1 in CH2Cl2/isopropanol at 458C for 24 h leads, in
good yield, to the formation of the isolable fluxional cationic
s,p-digold(I)–acetylide complex 4 with concomitant formation
of the Me3SiSbF6 salt (Scheme 3, step i). It should be noted
that, even when the reaction time and temperature were in-
creased to 50 h and 608C, respectively, in the presence of an
excess of gold(I) complex 1, no evidence of any new gold(I)
species was obtained, except for the previously formed
The fluxional digold(I) complex 2 was fully characterised by
combustion elemental analysis and spectroscopy (see the Ex-
perimental Section as well as Figures S1–S6 in the Supporting
Information). The 1H, 31P, 13C and DEPT NMR spectra of 2 in
CD2Cl2 provide evidence that, under the reaction conditions,
the cationic [(s,p)(L1Au)2(m-bromophenylacetylide)][SbF6] com-
plex 2 is the only product formed in detectable amounts (see
Figures S1–S4). The 31P NMR spectrum shows the disappear-
ance of the signal corresponding to initial gold(I) complex 1 at
57.02 ppm (singlet) and the appearance of a new signal at
62.89 ppm (singlet) for 2 (see Figure S4). ESI-MS analysis of a
solution obtained after dissolving complex 2 in CH2Cl2 showed
an intense positive-ion MS peak at 1171.0 Da (see Figure S5),
Scheme 2. Synthesis of the cationic [(s,p)(L1Au)2(m-bromophenylacetylide)]
[SbF6] complex 2 (first step) and failure to obtain dicationic
[(s,p,p’)(L1Au)3(m-bromophenylacetylide)][SbF6]2 complex 3 (second step).
Figure 1. ORTEP diagram of cationic [(s,p)(L1Au)2(m-bromophenylacetylide)]
[SbF6] complex 2. Hydrogen atoms have been omitted for clarity. Thermal el-
lipsoids are set at the 30% probability level.
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[(s,p)(L1Au)2(m-acetylide)][SbF6] complex 4. Interestingly, when
CH2Cl2/isopropanol (1:1) was used instead of CH2Cl2 at 608C for
48 h, incorporation of an additional (L1Au)+ cation, replacing
the hydrogen atom present in the s-coordination position of
the CꢀC triple bond of [(s,p)(L1Au)2(m-acetylide)][SbF6] com-
plex 4, was observed, leading to the unusual cationic Au3 com-
plex 5 (Scheme 3). We suggest that alcohols as amphoteric sol-
vents could abstract the acidic proton present in the acetylide
HCꢀC fragment of complex 4 and the resulting anionic inter-
mediate nucleophilically attack the L1Au+ cation of complex 1.
In this way, due to the role of the alcohol, [(s,p,s’)(L1Au)3(m-
acetylide)][SbF6] complex 5 is produced with concomitant for-
mation of the strong Brønsted acid HSbF6 (Scheme 3, step ii).
Finally, no evidence for the formation of the tetragold
[(s,p)2(L1Au)4(m-acetylide)][SbF6]2 complex 6 (Scheme 3) could
be obtained, even when the reaction time was increased to
70 h. The failure to incorporate an additional L1Au+ cation at
the free p-coordination position of the CꢀC triple bond in the
[(s,p,s’)(L1Au)3(m-acetylide)][SbF6] complex 5 (Scheme 5) can
be explained by the steric hindrance at this position and the
low electron density of the CꢀC triple bond linked to three AuI
atoms.
ity of the three L1Au fragments (see Figure S9), as confirmed
by DEPT and HMQC NMR experiments (see Figures S10 and
S11). The ESI-MS of a solution obtained after dissolving com-
plex 5 in CH2Cl2 shows only one intense positive-ion MS peak
at 1509.5 Da (see Figure S13), which is attributable to the cat-
ionic [C62H81Au3P3]+ species. The observed peak cluster is in
good agreement with the simulated isotopic distribution for
the molecular formula C62H81Au3P3 (see Figure S13). The MS
peaks recorded in negative-ion mode at 234.7 and 236.6 Da
correspond to the two 121Sb and 123Sb isotopes of the [SbF6]À
counter anion (see Figure S13) and are also in good accord
with the simulated isotopic distribution for the molecular for-
mula SbF6 (see Figure S13). In addition, the HR-ESI-MS peak re-
corded in positive ion mode at 1509.4524 amu is in good
agreement with the corresponding simulated mass of
1509.4543 amu (see Figure S14 for the isotopic distribution of
this signal).
The single-crystal X-ray diffraction structure of the cationic
[(s,p,s’)(L1Au)3(m-acetylide)][SbF6] complex 5 is illustrated in
Figure 2 and shows that the acetylide bridge coordinates to
Au3 in a h1,h2,h1 fashion (for the X-ray diffraction data, ORTEP
view and crystal-packing details, see Table S2 and Figure S15).
To gain information on the chemical properties of complex
5, the catalysed nucleophilic addition of isopropanol to trime-
thylsilylacetylene was investigated, the evolution of the reac-
Trigold(I) complex 5 was fully characterised by combustion
elemental analysis and spectroscopy (see the Experimental
Section as well as Figures S8–S12 in the Supporting Informa-
tion). The 1H, 31P, 13C, DEPT and HQMC NMR spectra of 5 in
CD2Cl2 provide evidence for the formation of the cationic
[(s,p,s’)(L1Au)3(m-acetylide)][SbF6] complex 5 under the reac-
tion conditions (Scheme 3). Thus, the 31P NMR spectrum shows
the disappearance of the signal corresponding to initial gold(I)
complex 1 at 57.02 ppm and the appearance of a new signal
at 62.07 ppm for 5 (see Figure S12). The ethynediyl bridge in
the s,p,s’-acetylide complex 5 exhibits a unique 13C chemical
1
tion mixture being monitored by H and 31P NMR spectroscopy.
Special attention was paid to the signals supporting the inter-
mediacy of gold(I)–acetylide complexes 4 and 5. The spectro-
scopic study revealed the appearance of another four gold(I)
complexes 7–10 as intermediates during the formation of acet-
aldehyde diisopropyl acetal (11) as the final product of this cat-
alytic reaction (see Scheme 4). In these experiments, gold com-
plex 1 (3 mol%) was added to a mixture of TMS-acetylene
2
shift at 153.25 ppm (q, JCP =47.38 Hz) due to the fast fluxional-
Scheme 3. Synthesis of cationic digold(I) [(s,p)(L1Au)2(m-acetylide)][SbF6]
complex 4 (step i), cationic trigold(I) [(s,p,s)(L1Au)3(m-acetylide)][SbF6] com-
plex 5 (step ii) and failure to obtain tetragold [(s,p)2(L1Au)4(m-acetylide)]
[SbF6]2 complex 6 (step iii).
Figure 2. ORTEP diagram of cationic [(s,p,s’)(L1Au)3(m-acetylide)][SbF6] com-
plex 5. Hydrogen atoms have been omitted for clarity. The thermal ellipsoids
are set at the 30% probability level.
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(1 equiv) and isopropanol (10 equiv) at 508C in CD2Cl2
(Scheme 4). The 31P NMR spectrum recorded at 10 min reaction
time showed new peaks at 58.43 (58%), 61.94 (3%), 62.53
(10%), 64.88 (9%) and 67.88 ppm (5%) attributable, respective-
ly, to the cationic complexes isopropanol–gold(I)L1 9, s,p-di-
gold(I)L1–acetylide 4, [(s,p,s’)(L1Au)3(m-acetylide)][SbF6] 5, ace-
tylide–gold(I)L1 8 and (isopropyl vinyl ether)–gold(I)L1–acety-
lide 10 together with the peak corresponding to unreacted
complex 1 at 57.58 ppm (14%; see Figure S16 in the Support-
ing Information). After 30 min, the complexes 1 (1.5%), acety-
lide–gold(I)L1 8 (3%) and (isopropyl vinyl ether)–gold(I)L1–ace-
tylide 10 (0%) had almost completely disappeared, the per-
centage of digold(I)L1 4 (17%) and trigold(I)L1 5 (50%) in the
mixture had increased, and the percentage of isopropanol–
gold(I)L1 9 (19%) had decreased. The formation of 9% of tri-
methylsilylacetylide–gold(I)L1 complex 7, characterised by a
signal at 63.12 ppm (see Figure S17), was also observed. More-
over, the 1H NMR spectrum recorded after 30 min confirmed
the coexistence of complexes 4, 5 and 9 (see Figure S18). The
assignments of the gold(I) complexes based on the 31P NMR
signals were firmly supported by HR-ESI-MS analysis of the re-
action mixture. Positive-ion MS peaks at m/z=1015.3203 (4),
1509.4312 (5), 593.2222 (7), 521.1672 (8), 555.2205 (9) and
607.2404 (10) were recorded (see Figures S19–S24, respective-
ly). In addition to the exact mass in the HR-ESI-MS, the frag-
mentation patterns were also in complete accordance with the
structures of the gold(I) complexes 4, 5 and 7–10 (see Figur-
es S19–S24), thereby confirming the formation and composi-
tion of these gold(I) complexes as intermediates. High-resolu-
tion single-mass analysis of gold(I) intermediates 7 and 10
(Scheme 4) was performed with a tolerance of less than 5 ppm
(see Figures S19 and S22).
tion of the OH group of isopropanol; characterisation by GC-
MS, showed a peak at 132.1 Da (see Figure S26).
To expand the scope of cationic gold(I) complexes as cata-
lysts and in an attempt to confirm the general mechanism for
the addition of alcohols to acetylene, the more bulky cationic
L2gold(I) complex 12 and n-butanol were used as catalyst and
reagent, respectively, instead of cationic L1gold(I) complex 1
and isopropanol (Scheme 5). The course of the reaction was
also monitored by 31P NMR analysis of the reaction mixture,
looking for signals of gold(I) intermediates, including butanol
adduct 13 and acetylides 14 and 15 as monogold(I), digold(I)
and trigold(I) complexes, respectively. Thus, the 31P NMR spec-
trum recorded at 30 min reaction time revealed the total con-
sumption of the starting gold(I) complex 12, which should
appear at 55.64 ppm (see Figures S27 and S28 in the Support-
1
ing Information for the H and 31P NMR spectra of pure com-
plex 12). New peaks were observed at 56.67 (37%), 62.09
(51%) and 60.26 ppm (5%), attributable to cationic complexes
butanol–gold(I)L2 13, [(s,p)(L2Au)2(m-acetylide)][SbF6] 14, and
[(s,p,s)(L2Au)3(m-acetylide)][SbF6] 15, respectively (see Fig-
ure S29). Two additional 31P peaks at 65.85 (2%) and
56.13 ppm (4%) corresponding, respectively, to acetylide–
gold(I)L2 and acetal–gold(I)L2 (16) intermediates were also ob-
served (see Figure S29).
Evidence supporting the intermediacy of gold(I) complex 16
(Scheme 5), in which acetal 17 is coordinated to a AuI complex,
was provided by HR-ESI-MS of the reaction mixture showing
the presence of a positive-ion MS peak at m/z=795.4427,
which can be attributed to the cationic gold complex
[C39H67AuO2P]+ (see Figure S30 in the Supporting Information).
Release of acetaldehyde dibutyl acetal (17) as the final product
by ligand exchange with n-butanol or TMS-acetylene would
lead to the formation of gold complex 13 or 14/15, respective-
ly, ready to undergo a subsequent catalytic cycle (Scheme 5).
Assignment of this series of gold(I) complexes based on the
31P NMR signals was firmly supported by HR-ESI-MS analysis of
Regarding the reaction product, acetaldehyde diisopropyl
acetal (11) was obtained in excellent yield under mild condi-
tions without the need for acid additives (Scheme 4). It has
been reported in the literature that the addition of alcohols to
alkynes catalysed by gold(I) complexes generally requires a
Brønsted acid as co-catalyst.[1j] GC-MS analysis of 11 (C8H18O2)
dissolved in CH2Cl2 showed a peak at 146.10 Da, in agreement
with the molecular formula (see Figure S25 in the Supporting
Information).
In
addition,
(isopropyloxy)trimethylsilane
(C6H16OSi, Scheme 4) was also formed in this reaction by silyla-
Scheme 4. Synthesis of acetaldehyde diisopropyl acetal (11) catalysed by
cationic gold(I) complex 1 and structures of the AuI intermediates deter-
Scheme 5. Synthesis of acetaldehyde dibutyl acetal (17) catalysed by bulky
cationic gold(I) complex 12 and structures of the AuI intermediates deter-
1
1
mined by H and 31P NMR spectroscopy and HR-ESI-MS.
mined by H and 31P NMR spectroscopy and HR-ESI-MS.
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the reaction mixture. Positive-ion MS peaks at m/z=693.3687
(13À2H), 1267.5972 (14) and 1887.9171 (15) were observed
(see Figures S31–S33). The high-resolution single-mass analysis
of digold(I) intermediate complex 14 (Scheme 5) is presented
with a tolerance of less than 5 ppm in Figure S32.
the medium, in this case leading to the formation of 1-(chloro-
methoxy)hexane, HCl and the subsequent formation of the cat-
ionic chloro-bridged digold(I)L2 complex 18 as a less active
but more stable intermediate (Scheme 6). The 31P NMR spec-
trum of the reaction mixture in CD2Cl2 recorded at 5 h reaction
time provides evidence for the total consumption of the start-
ing gold(I) catalyst 12, with the formation of the cationic
[(s,p,s’)(L2Au)3(m-acetylide)][SbF6] complex 15 (55%), which ex-
hibits a signal at 60.22 ppm. Furthermore, the [(s,p)(L2Au)2(m-
acetylide)][SbF6] complex 14, characterised by a peak at
62.06 ppm, has been almost completely consumed (1%) and
the cationic hexanol–gold(I) adduct 19 appears at 59.11 ppm
(19%; see Figure S44 in the Supporting Information). Also, the
31P NMR spectrum shows the disappearance of the signal cor-
responding to the initial gold(I) complex 12 at 55.64 ppm and
the appearance of a new signal at 68.17 ppm (24%) arising
from the [(L2Au)2(m-Cl)][SbF6] complex 18 (Figure S44). It is
Acetaldehyde dibutyl acetal (17) was also obtained in excel-
lent yield (Scheme 5). GC-MS analysis of 17 (C10H22O2) dissolved
in CH2Cl2 showed a peak at 174.1 Da, in agreement with the
molecular formula (see Figure S34 in the Supporting Informa-
tion). In addition, (butoxy)trimethylsilane (Scheme 5) was also
characterised by GC-MS analysis, based on the peak at
146.1 Da, arising from the silylation of 1-butanol (see Fig-
ure S35).
It should be mentioned that a 3:1 mixture of trimethylsilyl-
acetylene and gold(I) complex 12 in CH2Cl2 at 508C for 30 h
led to the direct formation of the cationic s,p- (L2Au)2–acety-
lide complex 14 in good yield (91%). The digold(I) complex 14
was fully characterised on the basis of combustion elemental
analysis and spectroscopy (see the Experimental Section and
Figures S36–S42 in the Supporting Information). The 31P NMR
spectrum shows that the signal corresponding to the initial
gold(I) complex 12 at 55.64 ppm has shifted to 62.13 ppm due
to the formation of complex 14 (see Figure S40). The s,p-ace-
tylide complex 14 exhibits 13C chemical shifts at 140.18 (t,
2JCP =64.21 Hz) and 96.40 ppm (t, 2JCP =15.60 Hz; see Fig-
ure S37) corresponding to the C and CH moieties of the bridg-
ing ethynediyl (CꢀCH), respectively, as confirmed by DEPT and
HMQC NMR experiments (see Figures S38 and S39). The ESI-MS
of a solution obtained after dissolving complex 14 in CH2Cl2
showed only one intense positive-ion MS peak at 1267.4 Da
(see Figure S41), which is attributable to the cationic
[C60H91Au2P2]+ species. The observed peak cluster is in good
agreement with the simulated isotopic distribution for the mo-
lecular formula C60H91Au2P2. The fragmentation pattern of this
positive-ion MS peak shows an intense peak at 621.1 Da (see
Figure S41), which is attributable to the cationic L2Au+ frag-
ment [MÀSbF6ÀÀL2Au(CꢀCH)]+ (see Figure S41). On the other
hand, the negative-ion MS peaks recorded at 234.4 and
236.3 Da corresponding to the two 121Sb and 123Sb isotopes of
the [SbF6]À counter anion (see Figure S41) are in good accord
with the simulated isotopic distribution for the molecular for-
mula SbF6 (see Figure S41). The high-resolution single-mass
analysis of digold(I) intermediate complex 14 is presented with
a tolerance of less than 5 ppm in Figure S42 in the Supporting
Information.
Figure 3. ORTEP diagram of cationic [(s,p)(L2Au)2(m-acetylide)][SbF6] complex
14. Hydrogen atoms have been omitted for clarity. The thermal ellipsoids
are set at the 30% probability level.
The X-ray crystal structure of the cationic [(s,p)(L2Au)2(m-ace-
tylide)][SbF6] complex 14 is illustrated in Figure 3. As can be
seen, the acetylide bridge coordinates to Au2 in a h1,h2 fashion
(for the X-ray diffraction data, ORTEP view and crystal-packing
details, see Table S3 and Figure S43 in the Supporting Informa-
tion).
To verify the catalytic activity and thermal stability of gold(I)
catalyst 12, acetaldehyde dihexyl acetal (20) was synthesised
in the presence of 12 at 1108C instead of 508C using n-hexa-
nol as reagent (Scheme 6). It has been reported that when
CH2Cl2 is used as a solvent at high temperatures it can under-
go partial decomposition by reacting with alcohol present in
Scheme 6. Synthesis of acetaldehyde dihexyl acetal (20) using bulky cationic
gold(I) complex 12 as catalyst in CH2Cl2 at 1108C and structures of the AuI
1
intermediates determined by H and 31P NMR spectroscopy and HR-ESI-MS.
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likely that, at high reaction temperatures, partial deactivation
of gold(I) complex 12 occurs due to reaction with chloride ions
released into the medium (HCl), resulting in the formation of
the less active cationic chloro-bridged digold(I) complex 18. It
should be noted that, when the reaction was performed at
508C, no deactivation of the gold(I) catalyst was observed and
the solid catalyst could be recovered from the reaction mixture
and reused three times without losing activity and selectivity.
Furthermore, 1-(chloromethoxy)hexane (Scheme 6) was also
formed during this reaction through the partial condensation
of n-hexanol and CH2Cl2 and characterised by HR-ESI-MS analy-
sis (see Figure S45).
HR-ESI-MS analysis of the AuI catalyst recovered from CH2Cl2
showed the presence of
a
positive-ion MS peak at
1277.5754 Da (see Figure S46 in the Supporting Information),
which is attributable to the cationic chloro-bridged digold(I)
species [C58H90Au2ClP2]+ species derived from complex 18.[8e,9]
The observed peak cluster shows good agreement with the si-
mulated isotopic distribution for the molecular formula
C58H90Au2ClP2 (see Figure S46). The two additional intense posi-
tive-ion MS peaks at 721.3954 and 1887.8768 Da are attributa-
ble to the cationic monogold(I) hexanol adduct 19 and trigol-
d(I) [(s,p,s’)(L2Au)3(m-acetylide)][SbF6] complex 15, respectively.
The observed peak clusters show good agreement with the si-
mulated isotopic distributions for the molecular formulae of 19
and 15 (see Figures S47 and S48).
The cationic [(L2Au)2(m-Cl)][SbF6] complex 18 was also char-
acterised by single-crystal X-ray crystallography (Figure 4), the
data showing a chloride bridge coordinating the Au atoms (for
the X-ray diffraction data, ORTEP view and crystal-packing de-
tails, see Table S4 and Figure S49 in the Supporting Informa-
tion).
Figure 4. ORTEP diagram of cationic [(s,p)(L2Au)2(m-Cl)][SbF6] complex 18.
Hydrogen atoms have been omitted for clarity. The thermal ellipsoids are set
at the 30% probability level.
Cationic vinylphosphonium 22 was characterised on the
basis of combustion elemental analysis and spectroscopy (see
the Experimental Section and Figures S53–S58 in the Support-
1
ing Information). The H, 13C, DEPT, 31P and 19F NMR spectro-
scopic data of 22 in CD2Cl2 provide evidence that, under the
reaction conditions (Scheme 7), [(L1)(vinyl)][PF6] (22) is formed
as the final product with concomitant formation of Cu NPs as
a red solid precipitate. The 31P NMR spectrum shows the disap-
pearance of the two signals corresponding to the initial cop-
per(I) complex 21 at 32.49 (singlet) and À144.36 ppm (septu-
1
plet for the counter anion, J(PF)=710.42 Hz.) and the appear-
ance of two new signals, respectively, at 34.98 (singlet) and
À144.33 ppm (septuplet) with a relative peak area ratio of 1:1
1
Acetaldehyde dihexyl acetal (20) was also obtained in excel-
lent yield (96%) (Scheme 6). GC-MS analysis of 20 dissolved in
CH2Cl2 showed a peak at the m/z=230.2, in agreement with
the molecular formula (C14H30O2; see Figure S50 in the Support-
ing Information). Also, high-resolution single-mass analysis of
compound 20 was performed with a tolerance of less than
5 ppm; the value of 231.2323 amu< is in good agreement
with the molecular formula C14H30O2+H (231.2324 amu; see
Figure S51). In addition, (hexoxy)trimethylsilane (Scheme 6),
formed as a byproduct during this reaction, was characterised
by GC-MS, recording a peak at m/z=174.2, which corresponds
to the molecular formula C9H22OSi (see Figure S52).
(see Figure S56). The H NMR spectrum reveals in this case the
presence of two doublets for each of the tert-butyl methyl
groups of compound 22 at 1.23 and 1.47 ppm (see Figure S53).
Also, the 19F NMR spectrum shows a doublet corresponding to
the six fluorine atoms of the PF6 counter ion with a coupling
1
constant J(PF) of about 710.46 Hz (see Figure S57). The ESI-MS
of a solution obtained after dissolving compound 22 in CH2Cl2
shows only one intense positive-ion MS peak at 325.3 Da (see
Figure S58), which is attributable to the cationic species
[C22H30P]+. The observed peak cluster shows good agreement
with the simulated isotopic distribution for the molecular for-
mula C22H30P (see Figure S58). On the other hand, a negative-
ion MS peak corresponding to the [PF6]À counter anion was re-
corded at 144.8 Da (see Figure S58).
At this stage of the work, it was of interest to determine
whether the analogous cationic complex [L1CuI][PF6] (21)[10] be-
haved similarly to the AuI complexes in terms of its reactivity
with the CꢀC triple bond. Aimed at delineating the similarities
and differences between AuI and CuI complexes, [L1CuI][PF6]
complex 21 was mixed with trimethylsilylacetylene under the
reaction conditions employed for the AuI complexes
(Scheme 7). Interestingly, no evidence for the formation of any
CuI–acetylide complex was obtained. Moreover, completely dif-
ferent behaviour from that of the AuI complexes was observed.
In this case, cationic vinylphosphonium 22 was isolated in ex-
cellent yield (94%) along with copper nanoparticles (Cu NPs;
Scheme 7).
Scheme 7. Reaction of CuI complex 21 with trimethylsilylacetylene and for-
mation of Cu NPs and cationic vinylphosphonium 22.
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To unambiguously characterise compound 22, crystals suita-
ble for X-ray diffraction analysis were grown from the reaction
mixture after filtration of the red solid precipitate (Cu NPs).
Stable crystals of 22 were obtained under ambient conditions.
The structure of [(L1)(vinyl)][PF6] is illustrated in Figure 5 (for
the X-ray diffraction data, ORTEP view and crystal-packing de-
tails, see Table S5 and Figure S59 in the Supporting Informa-
tion). Furthermore, the red precipitate was collected, sonicated
in dichloromethane and then analysed by HR-TEM, dark-field
STEM, energy-dispersive X-ray spectroscopy and elemental
mapping (see Figures S60–S62). The dark-field STEM image is
presented in Figure 5. These analyses revealed the formation
of well-dispersed Cu NPs with a homogeneous particle size of
about 8 nm.
Conclusion
We have reported herein the isolation of cationic acetylide s,p-
digold(I) and s,p,s’-trigold(I) complexes that contain bulky
phosphine ligands. The di- and trigold complexes were charac-
terised by single-crystal X-ray diffraction, and their catalytic ac-
tivity determined in the double addition of alcohols to acety-
lenes to form acetaldehyde acetals. We propose that the bulk
of the phosphine ligands plays a role in the formation of the
cationic acetylide s,p-digold(I) and s,p,s’-trigold(I) complexes
based on the failure to observe tetragold complexes. Decom-
position of dichloromethane was observed at high tempera-
ture upon reaction with alcohol with the release of HCl and
subsequent formation of a less active cationic chloro-bridged
digold(I)-L2 complex. A comparative study with the analogous
cationic [L1CuI][PF6] complex showed remarkably different be-
haviour, with the decomposition of the complex and the loss
of copper metal from the coordination sphere of phosphorus
and the formation of a well-characterised cationic vinylphos-
phonium and copper nanoparticles. A new catalytic route for
the formation of vinylphosphonium has been established.
Experimental Section
The following experimental details are presented in the Supporting
Information. 1) The details of the preparation, isolation and full
characterisation of the new cationic gold(I) complexes 2, 5 and 14,
as well as the cationic vinylphosphonium 22, including the NMR
spectra, ESI- and HR-ESI-MS, combustion analysis and single-crystal
X-ray crystallography. 2) The details of the preparation, isolation
and characterisation of the acetaldehyde acetals 11, 17 and 20.
3) HR-ESI-MS and GC-MS data of the intermediate gold(I) com-
plexes 4, 5, 7–10, 13–16, 18 and 19. 4) The GC-MS data of (isopro-
pyloxy)-, (butoxy)- and (hexoxy)trimethylsilane. 5) The HR-ESI-MS
data of 1-(chloromethoxy)hexane. 6) The kinetic measurements de-
termined from NMR and HR-ESI-MS data.
Figure 5. ORTEP diagram of [(L1)(vinyl)][PF6] compound 22. Hydrogen atoms
have been omitted for clarity. The thermal ellipsoids are set at the 30%
probability level (left). Dark-field STEM image of the red precipitate of Cu
NPs (right).
Vinylphosphines are key building blocks that undergo ready
addition of various nucleophiles (amines,[11] phosphines,[12] car-
banions[13]) and other[14] reagents to afford functionalised phos-
phine derivatives, widely used as ligands for advanced cata-
lysts[15] and flame retardants[16] as well as for the synthesis of
conductive nanomaterials.[17] However, the synthetic route
shown in Scheme 7 and the methods reported in the literature
for their synthesis are laborious and require the use of stoi-
chiometric amounts of metals, which does not meet modern
environmental requirements.[18] Therefore, they cannot be con-
sidered as synthetically useful. For this reason, and considering
the importance of vinylphosphines, we have elaborated a new
catalytic strategy for the synthesis of vinylphosphonium 22 by
a facile, one-pot vinylation of tertiary phosphine L1. Mixing
[Cu(MeCN)4][PF6][19] as catalyst (5 mol%) with a stoichiometric
amount of L1 (1 equiv), TMS-acetylene (3 equiv) and NaPF6
(1 equiv) at 508C in CH2Cl2/isopropanol (1:1) led to the forma-
tion of vinylphosphonium 22 in 96% yield in 35 h (Scheme 8).
CCDC 1963453 (2), 1963454 (5), 1963451 (14), 1963452 (18) and
1963450 (22) contain the supplementary crystallographic data for
this paper. These data are provided free of charge by The Cam-
bridge Crystallographic Data Centre
All reactions were carried out under argon in solvents dried using
1
a Solvent Purification System (SPS). H NMR spectra were recorded
1
on a Bruker AV300 (300 MHz) spectrometer. The H chemical shifts
are reported in ppm using the solvent peak as internal standard
(CD2Cl2: 5.27 ppm). The data are reported as follows: Chemical
shift (multiplicity (s=singlet, d=doublet, dd=doublet of doublets,
t=triplet, q=quadruplet, sept=septuplet, m=multiplet), coupling
constants (Hz), assignment). The 13C chemical shifts were recorded
on a Bruker AV300 (300 MHz) spectrometer in ppm using the sol-
vent peak as internal standard (CD2Cl2: 53.84 ppm). The 31P and
19F NMR spectra were recorded on a Bruker 300 MHz spectrometer
and the 31P and 19F chemical shifts are reported in ppm. Gas chro-
matography (GC) was performed on a Varian 3900 instrument
equipped with a TRB-5MS column (5% phenyl, 95% polymethylsi-
loxane, 30 m, 0.25 mmꢃ0.25 mm, Teknokroma). GC-MS analyses
were performed on an Agilent spectrometer (5973N-6890N)
equipped with the same GC column and operated under the same
conditions. ESI-MS were acquired on an Agilent Esquire 6000 spec-
trometer. HR-ESI-MS were recorded on an Waters (XEVO QTOF MS)
spectrometer equipped with an ACQUIM UPLC BEH C18 column
Scheme 8. One-pot synthesis of cationic vinylphosphonium 22 using a CuI
catalyst.
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(1.7 mmꢃ2.1 mmꢃ100 mm) to obtain the exact mass of the com-
pounds. Elemental analyses were measured on a EuroEA Elemental
Analyser Eurovector. HR-TEM was performed with a JEOL JEM-
2100F microscope with the field emission gun operating at 200 kV
and the images were recorded using a GATAN Orius SC600A.
cold n-hexane and dried under vacuum (0.137 g, 91% yield).
1H NMR (300 MHz, CD2Cl2): d=7.95–7.75 (m, 2H; ArH), 7.60–7.45
(m, 4H; ArH), 7.20–7.09 (m, 2H; ArH), 7.06–6.90 (s, 4H; ArH), 2.86
(sept, 2H; iPrCH), 2.29 (sept, 4H; iPrCH), 1.47 (s, 1H; m-CꢀCH), 1.38
(s, 18H; tBu CH3), 1.32 (s, 18H; tBu CH3), 1.26 (d, 12H; iPrCH3), 1.16
(d, 12H; iPrCH3), 0.85 ppm (d, 12H; iPrCH3); 13C NMR (75 MHz,
CD2Cl2): d=150.02, 147.61, 140.18 (t; m-CꢀCH), 137.32, 137.24,
135.50, 135.38, 131.43, 128.68, 128.64, 128.07, 127.67, 127.57,
122.37, 96.40 (t; m-CꢀCH), 39.15, 38.83, 34.35, 31.66, 31.58, 31.21,
25.97, 25.30, 24.40, 23.51 ppm; DEPT-135 NMR (75 MHz, CD2Cl2, +
ve): d=135.49, 135.38, 131.45, 127.67, 127.57, 122.37, 34.35, 31.66,
31.57, 31.21, 25.98, 25.31, 24.41, 23.51 ppm; 31P NMR (CDCl3): d=
62.13 ppm (s, phosphine ligands); MS (ESI, +ve): m/z: 1267.4
[MÀSbF6À]+; MS (ESI, Àve): m/z: 234.4, 236.4 [SbF6]À; HRMS (ESI, +
ve): m/z calcd for [MÀSbF6À]+: 1267.5927; found: 1267.5972; ele-
mental analysis calcd (%) for C60H91Au2F6P2Sb: C 47.92, H 6.10;
found: C 47.89, H 6.08.
Isolation of cationic [(s,p)(L1Au)2(m-bromophenylacetylide)]
[SbF6] complex 2: A mixture of complex [Au(L1)(CH3CN)][SbF6] (1;
0.116 g, 0.15 mmol) and p-bromophenylacetylene (0.0543 g,
0.30 mmol) was dissolved in dichloromethane (2 mL). The solution
was stirred at 508C under argon atmosphere for 30 h. Then, the re-
sulting mixture was diluted with CH2Cl2 (2 mL), filtered and the su-
pernatant was covered carefully with a layer of n-hexane (1.5 mL).
A colourless crystalline material corresponding to complex 2, suita-
ble for single-crystal X-ray crystallography, was obtained upon
standing for 48 h at À308C. The crystals were collected by filtra-
tion, washed with n-hexane and dried under vacuum (0.195 g,
1
93% yield). H NMR (300 MHz, CD2Cl2): d=7.90–7.77 (m, 2H; ArH),
Isolation of cationic [(L1)(vinyl)][SbF6] compound 22
7.60–7.45 (m, 6H; ArH), 7.35–7.15 (m, 10H; ArH), 7.13–7.00 (m, 4H;
ArH), 1.39 (s, 18H; tBu CH3), 1.34 ppm (s, 18H; tBu CH3); 13C NMR
(75 MHz, CD2Cl2): d=149.74, 149.55, 143.25, 143.16, 134.43, 134.36,
134.33, 133.76, 133.66, 132.49, 131.59, 129.81, 129.49, 128.40,
128.00, 127.90, 125.78, 125.18, 124.95, 120.39, 38.56, 38.24, 31.32,
31.23 ppm; DEPT-135 NMR (75 MHz, CD2Cl2, +ve): d=134.43,
134.33, 133.76, 133.65, 132.49, 131.59, 129.81, 129.49, 128.41,
128.00, 127.91, 31.32, 31.23 ppm; 31P NMR (CD2Cl2): d=62.89 ppm
(s, phosphine ligands); MS (ESI, +ve): m/z: 1171.0 [MÀSbF6À]+; MS
(ESI, Àve): m/z: 234.3, 236.3 [SbF6]À; HRMS (ESI, +ve): m/z calcd for
[MÀSbF6À]+: 1169.2528; found: 1169.2377; elemental analysis calcd
(%) for C48H58Au2BrF6P2Sb: C 40.99, H 4.16; found: C 40.94, H 4.22.
Method A:
A mixture of complex [Cu(L1)(CH3CN)][PF6] (21;
0.0822 g, 0.15 mmol) and ethynyltrimethylsilane (0.0441 g,
0.45 mmol) was dissolved in dichloromethane/isopropanol (1:1,
2 mL). The solution was stirred at 608C under argon atmosphere
for 30 h. Then, the resulting mixture was diluted with CH2Cl2/iso-
propanol (1:1, 2 mL) and the suspension filtered to remove the red
solid precipitate (Cu NPs). A colourless crystalline material corre-
sponding to complex 22, suitable for single-crystal X-ray crystallog-
raphy, was obtained upon standing the supernatant for 30 h at RT.
The crystals were collected by filtration, washed with cold n-
hexane and dried under vacuum (0.065 g, 93% yield).
Isolation of cationic [(s,p,s)(L1Au)3(m-acetylide)][SbF6] complex
Method B: A mixture of phosphine L1 (0.0447 g, 0.15 mmol),
NaPF6 (0.026 g, 0.15 mmol), ethynyltrimethylsilane (0.0441 g,
0.45 mmol) and [Cu(CH3CN)4][PF6] (0.0028 g, 0.0075 mmol) as cata-
lyst (Cu/L1 ratio, 5 mol%) was suspended in CH2Cl2/CH3OH (1:1,
2 mL). The solution was stirred at 608C under argon atmosphere
for 35 h. Then, the resulting mixture was diluted with CH2Cl2/
CH3OH (1:1, 2 mL), filtered and the supernatant covered carefully
with a layer of n-hexane (1 mL). A colourless crystalline material
corresponding to compound 22, suitable for single-crystal X-ray
crystallography, was obtained upon standing the supernatant for
30 h at RT. The crystals were collected by filtration, washed with
cold n-hexane and dried under vacuum (0.067 g, 95% yield).
1H NMR (300 MHz, CD2Cl2): d=7.95–7.80 (m, 1H; ArH), 7.79–7.65
(m, 1H; vinyl-H), 7.60–740 (m, 4H; ArH), 7.37–7.08 (m, 4H; ArH),
5.94–5.65 (m, 1H; vinyl-H), 5.61–5.33 (m, 1H; vinyl-H), 1.47 (d, 9H;
tBu CH3), 1.23 ppm (d, 9H; tBu CH3); 13C NMR (75 MHz, CD2Cl2): d=
149.22, 140.55, 135.57 134.51, 134.22, 134.00, 132.18, 130.16,
129.72, 128.61, 128.34, 128.15, 117.04, 113.28, 37.68, 35.33, 30.64,
28.82 ppm; DEPT-135 NMR (75 MHz, CD2Cl2, +ve): d=134.51,
134.22, 134.00, 132.18, 130.16, 129.73, 128.61, 128.34, 128.15,
113.25, 30.64, 28.82 ppm; DEPT-135 NMR (75 MHz, CD2Cl2, Àve):
d=135.55 ppm; 31P NMR (CDCl3): d=62.13 (s, phosphine),
144.34 ppm (sept, PF6À); 19F NMR (CD2Cl2): d=73.14 ppm (d, PF6À);
MS (ESI, +ve): m/z: 325.3 [MÀPF6À]+; MS (ESI, Àve): m/z: 144.8
[PF6]À; elemental analysis calcd (%) for C22H30F6P2: C 56.17, H 6.43;
found: C 56.13, H 6.40.
5:
A mixture of complex [Au(L1)(CH3CN)][SbF6] (1; 0.077 g,
0.10 mmol) and ethynyltrimethylsilane (0.0294 g, 0.30 mmol) was
dissolved in dichloromethane/isopropanol (1:1, 2 mL). The solution
was stirred at 608C under argon atmosphere for 48 h. Then, the re-
sulting mixture was diluted with CH2Cl2/isopropanol (1:1, 2 mL). A
colourless crystalline material corresponding to complex 5, suitable
for single-crystal X-ray crystallography, was obtained upon stand-
ing for 30 h at RT. The crystals were collected by filtration, washed
with cold n-hexane and dried under vacuum (0.161 g, 92% yield).
1H NMR (300 MHz, CD2Cl2): d=7.92–7.78 (m, 3H; ArH), 7.59–7.43
(m, 7H; ArH), 7.38–7.15 (m, 12H; ArH), 7.12–7.00 (m, 5H; ArH), 1.40
(s, 9H; tBu CH3), 1.35 ppm (s, 9H; tBu CH3); 13C NMR (75 MHz,
CD2Cl2): d=153.25 (q; m-CꢀC-), 150.38, 150.19, 142.94, 142.86,
134.80, 134.78, 133.55, 133.45, 130.99, 130.97, 129.50, 129.44,
129.19, 128.34, 127.48, 127.40, 127.20, 126.65, 38.27, 37.97, 31.27,
31.18 ppm; DEPT-135 NMR (75 MHz, CD2Cl2, +ve): d=134.80,
134.78, 133.54, 133.44, 130.99, 130.96, 129.50, 129.44, 129.18,
128.34, 127.49, 127.40, 31.27, 31.18 ppm; 31P NMR (CD2Cl2): d=
62.07 ppm (s, phosphine ligands); MS (ESI, +ve): m/z: 1509.5
-
[MÀSbF6 ]+; MS (ESI, Àve): m/z: 234.7, 236.7 [SbF6]À; HRMS (ESI, +
ve): m/z calcd for [MÀSbF6À]+: 1509.4524; found: 1509.4543; ele-
mental analysis calcd (%) for C62H81Au3F6P3Sb: C 42.65, H 4.68;
found: C 42.63, H 4.70.
Isolation of cationic [(s,p)(L2Au)2(m-acetylide)][SbF6] complex 14:
A
mixture of complex [Au(L2)(CH3CN)][SbF6] (12; 0.0898 g,
0.10 mmol) and ethynyltrimethylsilane (0.0294 g, 0.30 mmol) was
dissolved in dichloromethane (2 mL). The solution was stirred at
608C under argon atmosphere for 65 h. Then, the resulting mixture
was diluted with CH2Cl2 (2 mL), filtered and the supernatant was
covered carefully with a layer of n-hexane (1.5 mL). A colourless
crystalline material corresponding to complex 14, suitable for
single-crystal X-ray crystallography, was formed upon standing for
48 h at À308C. The solid was collected by filtration, washed with
General procedure for the catalytic one-pot double addition of
alcohols to acetylene—preparation of acetaldehyde acetals 11,
17 and 20:
A mixture of isopropanol, butanol or hexanol
(2.5 mmol), respectively, with TMS-acetylene (0.25 mmol) and
gold(I) complex 1 or 12 (0.0075 mmol) as catalyst (Au/alkyne ratio,
3 mol%) was suspended in CH2Cl2 (1 mL), then the flask was evacu-
ated under vacuum and refilled with argon. The evacuation/refill-
ing cycle was repeated three times (pressure 3 bar). The mixture
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was stirred at 508C for the required time to obtain the maximum
yield of acetaldehyde acetals 11, 17 and 20 compounds (see
manuscript). Then, cold n-hexane was added to the reaction mix-
ture, the suspension was filtered and the solvents removed under
reduced pressure to provide the target acetaldehyde acetals as col-
ourless liquids in yields higher than 93% (see manuscript), The
purity and structures of the acetaldehyde acetals 11, 17 and 20
were confirmed by GC, GC-MS and HR-ESI-MS spectrometry analy-
sis. Compound 11: GC-MS: m/z: 146.1 [M]+. Compound 17: GC-MS:
m/z: 174.1 [M]+. Compound 20: GC-MS: m/z: 230.2 [M]+; HR-ESI-
MS: m/z calcd for [M+1]+: 231.2324; found: 231.2323.
Acknowledgements
Financial support by the Spanish Ministry of Economy and
Competitiveness (Severo Ochoa and RTI2018-89027-CO2-R1)
and the Generalitat Valenciana (Prometeo 2013–2014) is grate-
fully acknowledged.
Conflict of interest
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The authors declare no conflict of interest.
Keywords: acetals
·
gold
·
homogeneous catalysis
·
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Manuscript received: January 24, 2020
Version of record online: && &&, 0000
Chem. Eur. J. 2020, 26, 1 – 10
www.chemeurj.org
9
ꢂ 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
doi.org/10.1002/chem.202000420
Chemistry—A European Journal
FULL PAPER
&
Multinuclear Gold Complexes
A. Grirrane,* E. ꢂlvarez, H. Garcꢀa,*
A. Corma*
&& – &&
Synthesis, Structure, Reactivity and
Catalytic Implications of a Cationic,
Acetylide-Bridged Trigold–JohnPhos
Species
Multinuclear gold: A new family of tri-
AuI complexes have been characterised
as intermediates during the [AuIL][SbF6]
catalytic preparation of acetaldehyde
acetals. These well-characterised cation-
ic AuI intermediates lend support to the
proposed reaction mechanism. An anal-
ogous copper complex revealed differ-
ent behaviour, leading to a vinylphos-
phonium and copper nanoparticles.
&
&
Chem. Eur. J. 2020, 26, 1 – 10
www.chemeurj.org
10
ꢂ 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!