Gold(I) complexes with multifunctional phosphane ligands: Synthesis and catalysis

Article abstract of DOI:10.1016/j.ica.2020.120218

Two novel gold(I) complexes with a phosphoguanidine ligand and with a novel cationic phosphane ligand have been prepared and structurally characterized. The phosphoguanidine ligand supports oxidative addition of biphenylene to the gold(I) centre, though the yield of the reaction is low. The phopshoguanidine gold(I) complexes is also able to efficiently catalyze the hydroamination of phenylacetylene with mesitylamine, whereas the gold(I) complex with the cationic phosphane ligand, due to its more electron-poor character, promotes the hydroarylation of ethyl propiolate with mesitylene.

Full text of DOI:10.1016/j.ica.2020.120218

Inorganica Chimica Acta 517 (2021) 120218
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Research paper
Gold(I) complexes with multifunctional phosphane ligands: Synthesis
and catalysis
,
,
,b
Andrea Biffisa *, Marco Barona, Cristina Tubaroa b, Marzio Rancanb, Lidia Armelaoa
,
Anatoliy Marchenkoc, Georgyi Koidanc, Anastasiia N. Hurievac, Aleksandr Kostyukc
a
`
Dipartimento di Scienze Chimiche, Universita di Padova, Via Marzolo 1, 35131 Padova, Italy
b Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE), National Research Council (CNR), Via F. Marzolo 1, 35131 Padova, Italy
c Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska 5, Kyiv-94 02660, Ukraine
A R T I C L E I N F O
A B S T R A C T
Two novel gold(I) complexes with a phosphoguanidine ligand and with a novel cationic phosphane ligand have
been prepared and structurally characterized. The phosphoguanidine ligand supports oxidative addition of
biphenylene to the gold(I) centre, though the yield of the reaction is low. The phopshoguanidine gold(I) com-
plexes is also able to efficiently catalyze the hydroamination of phenylacetylene with mesitylamine, whereas the
gold(I) complex with the cationic phosphane ligand, due to its more electron-poor character, promotes the
hydroarylation of ethyl propiolate with mesitylene.
Dedicated to Prof. Maurizio Peruzzini on the
occasion of his 65th birthday.
Keywords:
Gold
Phosphane
Oxidative addition
Hydroamination
Hydroarylation
Alkyne
1. Introduction
example by acting as a hydrogen bond acceptor [10–12]. Finally, gold(I)
can bind only to one Lewis-basic moiety of the ligand and interact with
The last decades have witnessed the steady development of a great
variety of heteroleptic polydentate ligands for transition metal com-
plexes [1–3], and more recently a growing number of applications of
these ligands to the preparation of coordination compounds of gold(III)
[4,5] and most notably gold(I) [6–15]. Two Lewis-basic moieties with
different characteristics on the same ligand can serve different purposes
in the context of gold(I) coordination chemistry. For example, since the
two coordination sites can bind to a gold(I) halide with different
strength, they can behave as hemilabile ligands, in which one of the
moieties is more strongly coordinated to the gold(I) centre whereas the
other one interacts more weakly; consequently, complexes with a dis-
torted trigonal planar coordination geometry can be prepared, which
often exhibit peculiar physico-chemical properties, such as a strong
luminescence [6]. Alternatively, a gold centre can bind only to one co-
ordination site of the ligand, whereas the other Lewis-basic moiety re-
mains pendant and can coordinate a second metal centre with different
characteristics [7–9], or it can direct and activate the attack of an
external reagent to a substrate precoordinated to the gold complex, for
the second one when it becomes oxidized to gold(III); at this point, the
ligand can coordinate in a chelating bidentate fashion, thereupon sta-
bilizing the complex. Following pioneering examples of Huang et al.
[13,14], a notable example of this behaviour has been quite recently
provided by Abdallah et al. with a gold(I) phosphane complex bearing a
pendant tertiary arylamino moiety, in which oxidative addition at gold
(I) is facilitated by chelate coordination of the amino moiety to the gold
(III) complex product [15].
In the context of this growing interest for gold(I) complexes with
heteroleptic polydentate ligands, we wish to report here on the prepa-
ration of gold(I) complexes with two novel multifunctional phosphane
ligands and on their properties, reactivity and preliminary evaluation as
catalysts for hydrofunctionalization reactions.
2. Results and discussion
We have considered two ligands in this study, namely 1 and 2
(Scheme 1). Ligand 1 is a phosphoguanidine ligand whose chelate
* Corresponding author.
E-mail address: andrea.biffis@unipd.it (A. Biffis).
https://doi.org/10.1016/j.ica.2020.120218
Received 3 November 2020; Received in revised form 13 December 2020; Accepted 17 December 2020
Available online 24 December 2020
0020-1693/© 2020 Elsevier B.V. All rights reserved.

A. Biffis et al.
Inorganica Chimica Acta 517 (2021) 120218
latter, 4b, obtained as prism-like, colourless crystals, crystallizes in the
monoclinic P21/n space group. The two structures present the same Au
complex but 4b contains also an acetonitrile molecule associated to each
complex unit. In both cases, a triflate anion is present in order to balance
the positively charged nitrogen atom of ligand 2. In both structures, the
Au coordination geometry is linear (P1-Au1-Cl1 of 173.82(5)◦ and
173.25(8)◦ for 4a and 4b, respectively) with Au1-P1 and Au1-Cl1 dis-
tances of 2.2301(14) Å and 2.2820(13) Å for 4a, and of 2.2286(19) Å
and 2.275(2) Å in 4b. The two coordination complex moieties are very
similar, as can be observed by their overlaid structures. The main dif-
ference is the relative orientation of the heterocycle unit, as can be seen
in Fig. 1d. In fact, looking along the N1-P1 bond, in 4a the heterocycle is
on the right of the Au1-Cl1 bond with a torsional angle of Cl1-Au1-P1-N1
171.2(7)◦. In 4b, the same angle is ꢀ 147.1(6)◦ and the heterocycle is on
the left of the Au1-Cl1 bond. Table 1 summarizes the main distances and
angles and Table 2 reports the main crystallographic and refinement
information for compounds 3, 4a and 4b.
Scheme 1. Phosphane ligands employed in this study.
From the crystal structure of complex 3, it is apparent that no
interaction is present between the gold(I) centre and the pendant imino
group of the ligand. In order to investigate the possibility to produce
chelate gold(III) complexes upon oxidation of gold and subsequent co-
ordination of the imino moiety, complex 3 was subjected to reaction
with several oxidants. We started by investigating reactions with Br2 or
PhICl2, which are commonly employed oxidants in the preparation of
gold(III) compounds from gold(I) precursors [25,26]. Treatment of
complex 3 with one equivalent of either of these reagents resulted
however in decomposition of the complex. In the case of PhICl2, analysis
of the 31P NMR and of the ESI-MS spectra of the reaction mixture
allowed to identify signals attributable to the free ligand and to a major
product (31P NMR δ 142.72, m/z 371.10) interpretable in terms of an
oxidized phosphorus species deriving from the ligand (PAd2Cl+2 in the
ESI-MS spectrum). Thus, PhICl2 seems to oxidize the phosphorus atom
together with the gold(I) centre, and consequently triggers complex
decomposition. Use of a milder oxidant such as Br2 provided no
improvement, and complex product mixtures were obtained , from
which it was not possible to identify any well-defined product.
complex with palladium(II) has been already investigated by our group
and found to be an active catalyst for alkyne hydroamination reactions
[16]. It belongs to a class of open chain, P,N 1,3-ligands, which com-
prises also 2-phosphanoimidazoles, 2-phosphanopyridines and phos-
phoamidines: examples of coordination chemistry of gold(I) with these
categories of ligands have been also published recently [17–20]. Ligand
2 is instead a novel example of cationic phosphane ligand deriving
directly from [1,2,4]triazolo[4,3-a]pyridine [21], whose coordination
chemistry has never been investigated before. It is an interesting po-
tential ligand: being cationic, the ligand can be expected to feature a
lower electron-donating capability, which may be useful for certain
applications (see below); examples of the successful application of gold
(I) complexes with cationic phosphane ligands to selected chemical re-
actions have been reported recently [22–24]. Furthermore, the presence
of the positive charge can possibly endow the complex with water sol-
–
ubility. Finally, the C H bond in 3-position of the heterocycle can be in
principle deprotonated giving rise to a carbene moiety; attempts to
deprotonate the free ligand actually have led up to now to decomposi-
tion [21], but deprotonation a gold(I) phosphane complex and/or in the
presence of metal centres able to promptly coordinate to the carbene
may result in stabilization of the carbene.
We then resolved to change the procedure and to consider even
weaker oxidants. Following the reaction protocol reported by Abdallah
◦
et al. [15], we reacted the complex at ꢀ 80 C with one equivalent of
AgSbF6 to remove the halide ligand, in the presence of organic mole-
cules, such as 4-iodoanisole or biphenylene, amenable to undergo
oxidative addition to gold(I) centres. In both cases extensive complex
decomposition with formation of colloidal gold was observed when the
reaction mixture was allowed to warm to room temperature, which is a
confirmation of the expected low stability of the gold(I) cationic com-
plex which forms upon chloride removal from 3. However, whereas with
iodoanisole no sign of progress of an oxidative addition was observed in
the reaction mixture, in the case of biphenylene definite evidence for the
formation of an oxidative addition product was clearly obtained from
the ESI-MS spectrum of the reaction mixture, in which a base peak at m/
z 853.33 corresponding to complex 5 (Scheme 3) was clearly observed.
Correspondingly, a new signal was also observed in the 31P NMR spec-
trum of the reaction mixture at 70.6 ppm, which is compatible with a
phosphane bound gold(III) cation [15]. Unfortunately, the yields of the
compound were invariably low and the reaction was not clean, with
several other lower molecular weight products being present in the re-
action mixture, as apparent from the 1H NMR. Consequently, it was not
possible up to now to isolate and further characterize complex 5 or a
derivative of it. We can conclude at the moment that ligand 1 is able to
some extent to facilitate oxidative addition to gold(I) upon formation of
a chelate complex, but that the rate of oxidative addition is much slower
compared to the aminophosphine ligand employed by Abdallah et al., to
the point that decomposition of the cationic gold(I) reagent derived from
3 becomes a serious competitive reaction. The reason for this different
behaviour is presumably the strained 4-membered chelate complex that
is formed with ligand 1.
Simple ligand exchange using [AuCl(SMe2)] as gold precursor in
dichloromethane at room temperature under light exclusion easily
provides gold(I) complexes 3 and 4, directly deriving from 1 and 2, in
good yield (Scheme 2). Recrystallization from acetonitrile/diethylether
provided crystals suitable for structure determination.
Complex 3 (Fig. 1a), crystallizes in the monoclinic P21/n space
group. The Au coordination geometry is linear (P1-Au1-Cl1 178.80(3)◦)
with Au1-P1 and Au1-Cl1 distances of 2.2473(5) Å and 2.2755(7) Å,
respectively. Crystallization of complex 4 under slightly different con-
ditions gave crystal structures 4a and 4b (Fig. 1b and 1c), respectively.
The former, 4a, crystallizes from a mixture of acetonitrile/diethylether
as needle-like colourless crystals in the triclinic P-1 space group. The
Scheme 2. Gold(I) complexes employed in this study.
2

A. Biffis et al.
Inorganica Chimica Acta 517 (2021) 120218
Fig. 1. ORTEP drawing of a) complex 3; b) and c) complex 4 in its crystallographic forms 4a and 4b, respectively; d) overlay of structures 4a (dark cyan) and 4b
(green). Ellipsoids are drawn at the 50% probability level. Hydrogen atoms were omitted for clarity. (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
The reactivity of complex 4 was instead briefly investigated relating
to the possibility to deprotonate the CH bond in 3-position on the het-
erocyclic ring to produce a carbene moiety. Several bases were
employed for the purpose, such as Na2CO3, NEt3 and NaOAc, in the
presence of metal complex precursors such as [AuCl(SMe2)], Pd(OAc)2
or [Pd2(allyl)2Cl2] that should promptly coordinate the newly generated
carbene and stabilize it. Unfortunately, all attempts invariably caused
decomposition of complex 4 with formation of colloidal gold, with a
decomposition rate depending on the employed base, and without any
evidence of formation of the free carbene or of metal complexes thereof.
Apparently, even starting from complex 4 it is not possible to form the
carbene or to intercept it under any of the conditions employed.
Finally, we turned to the preliminary evaluation of complexes 3 and
4 as catalysts [27–29]. The catalytic performance of the two complexes
in the hydroamination of alkynes [30] was considered first. Reaction of
phenylacetylene with mesitylamine was employed as standard reaction
(Scheme 4), for which there is considerable precedent in the literature
with several benchmark gold catalysts with which to critically compare
the recorded catalytic performance [31]. Complexes 3 and 4 were
activated by reaction with one equivalent of AgSbF6, which removes the
chloride ligand liberating the catalytically competent LAu+ or LAu2+
species, respectively. The reaction was carried out under neat conditions
using 0.4 mol% catalyst, according to a protocol recently developed in
our laboratories for dinuclear di-NHC gold(I) complexes as catalysts
[32]. The results are reported in Table 3.
reaction with this substrate reportedly requires a higher reaction tem-
perature (80 ◦C) which was not sustained by catalyst 3: catalyst
decomposition with formation of colloidal gold was invariably observed
alongside with the production of only traces of the hydroamination
product.
Surprisingly, complex 4 turned out instead to be inactive, at least
under the reaction conditions reported in Scheme 4. We speculated that
the solubility of complex 4 (which becomes dicationic once the chloride
ligand is removed) is limited in the neat reagents, and consequently we
repeated the test using as solvent the ionic liquid N-butyl-N’-methyl-
imidazolium triflimidate [bmim]NTf2. However, also in this solvent the
activity remained low TOF (TOFt=2h 3 hꢀ 1); a lower activity of complex
4 compared to 3 was in any case expected, since the cationic character of
–
the phosphane and the direct P N bond present in it render ligand 2 less
electron-donating than ligand 1, and consequently less able to promote
the rate determining step of the hydroamination process, which ac-
cording to the current knowledge is the protodeauration step liberating
the product after nucleophilic attack by the amine to the π-coordinated
alkyne [31]. On the other hand, it is interesting to remark that the yield
in the reaction with complex 4 appears to grow constantly with time,
which indicates a good stability of the catalytically competent species
even at longer reaction times.
The two complexes were also employed as catalysts in another
technologically relevant hydrofunctionalization reaction, namely the
hydroarylation of alkynes [36]. Gold(I) complexes in ionic liquids were
very recently found to be effective catalysts for this reaction under
The recorded catalytic activity with complex 3 (TOFt=2h 17 hꢀ 1
)
compares favourably with most gold complexes with phosphane ligands
reported in the literature [33], which under comparable reaction con-
ditions (low temperature, absence of acid promoters) generally exhibit
TOF values below 10 hꢀ 1. The recorded activity remains however
markedly lower than the best gold-phosphane catalysts reported to date
for this reaction, which are based on anionic or zwitterionic phosphanes
and can reach TOFs up to 102-103 hꢀ 1 [34,35]. The reaction was also
attempted with a secondary amine such as N-methylaniline. However,
Table 1
Main distances and angle in compounds 3, 4a and 4b.
3
4a
4b
Au1-P1 (Å)
Au1-Cl1 (Å)
P1-Au1-Cl1
2.2473(5)
2.2755(7)
178.80(3)◦
2.2301(14)
2.2820(13)
173.82(5)◦
2.2286(19)
2.275(2)
173.25(8)◦
3

A. Biffis et al.
Inorganica Chimica Acta 517 (2021) 120218
Table 2
Crystallographic and refinement data for compounds 3, 4a and 4b.
Compound
3
4a
4b
Empirical
formula
C
33H49AuClN2P
C15H23AuClF3N3O3PS C17H26AuClF3N4O3PS
Formula weight 737.13
Temperature/K 301(2)
645.81
686.86
293.8(3)
triclinic
296.4(3)
monoclinic
P21/n
Scheme 4. Gold catalyzed alkyne hydroamination investigated in this work.
Crystal system
Space group
a/Å
monoclinic
P21/n
P-1
10.0987(3)
24.0350(6)
13.5809(4)
90
7.8200(4)
12.2436(8)
12.3099(9)
99.752(6)
102.177(5)
96.831(5)
1120.72(12)
2
7.6524(3)
24.6403(11)
13.3334(8)
90
Table 3
b/Å
Catalytic performance of complexes 3 and 4 in alkyne hydroamination.
c/Å
Entry
Catalyst
Time (h)
Alkyne conv. (%)
Yield (%)
TON
◦
α/
β/◦
107.367(3)
90
102.703(5)
90
1
3
2
14
24
0
14
24
0
35
60
0
γ/◦
4
Volume/Å3
Z
3146.11(16)
4
2452.6(2)
4
2
3
4
2
4a
2
3
3
7
F(000)
Crystal size/
mm3
1488.0
624.0
1336.0
4
5
5
12
65
0.2 × 0.2 × 0.2
0.8 × 0.04 × 0.01
0.4 × 0.21 × 0.08
24
30
26
a
Reaction using the ionic liquid [bmim]NTf2 as solvent.
Radiation
MoK
0.71073)
4.554 to 65.522 5.326 to 58.652
α
(λ =
MoKα
(λ = 0.71073)
MoKα (λ = 0.71073)
2Θ range for
data
5.664 to 52.738
collection/◦
Reflections
collected
40,887
10,714
12,845
24,481
catalysis, since the rate determining step of the reaction is in this case
the external nucleophilic attack by the arene at the alkyne -coordinated
π
Independent
reflections
5245
4972
to gold [31]. Ligand 2 is expected to be less electron donating than
Data/restraints/ 10714/0/347
parameters
5245/18/259
1.005
4972/53/287
1.093
–
ligand 1 in consideration of its cationic nature and direct P N bond, and
also features a smaller steric bulk (Buried Volume 39.9%) hence it is not
surprising that complex 4 displays a higher catalytic activity than
complex 3. On the other hand, albeit catalyst 4 reaches similar TON
values compared to other gold-phosphane complexes reported in the
literature, its catalytic activity turns out to be somewhat lower under the
same reaction conditions (TOFt=1h 70 hꢀ 1 vs. 100–200 hꢀ 1) [37] and the
chemoselectivity towards the monosubstituted hydroarylation product
at complete alkyne conversion is also lower. Nevertheless, it seems from
the data in Table 2 that complex 4 is not rapidly deactivated under re-
action conditions, which may lend hope for a further improvement of
the efficiency of this catalytic system, for example by optimizing the
ligand substituents.
Goodness-of-fit 1.090
on F2
Final R indexes R1 = 0.0293,
R1 = 0.0367, wR2
0.0608
=
=
R1 = 0.0592, wR2
0.1511
=
=
[I>=2
σ
(I)]
wR2 = 0.0608
Final R indexes R1 = 0.0371,
R1 = 0.0553, wR2
0.0698
R1 = 0.0713, wR2
0.1610
[all data]
Largest diff.
peak/hole / e
Åꢀ 3
wR2 = 0.0634
0.92/-1.43
0.71/-1.18
1.94/-2.89
neutral conditions [37]. Preliminary tests run using ethyl propriolate
and mesitylene as reagents (Scheme 5) with catalysts 3 and 4 evidence,
in contrast to hydroamination, the complete inactivity of complex 3 for
the reaction. This lack of activity of complex 3 is quite unexpected, since
several other gold phosphane complexes, with weaker as well as stron-
ger electron-donating character, all display activity under the employed
reaction conditions [37]; the steric bulk of ligand 1, estimated upon
determining its Buried Volume (43.7%) [38], is also not significantly
larger than that of other successfully employed ligands [37]. At the
moment, we cannot provide an explanation for the observed inactivity
of complex 3. Complex 4 displays instead reasonable activity: the results
are reported in Table 4.
3. Conclusions
Ligands 1 and 2 readily form the corresponding mononuclear gold(I)
complexes 3 and 4. The resulting complexes display the expected reac-
tivity as catalysts in alkyne hydrofunctionalization reactions, with the
exception of complex 3 in the hydroarylation of ethyl propiolate with
mesitylene. Complex 3 also undergoes oxidative addition to the corre-
sponding gold(III) compound in the presence of biphenylene, albeit in
low yield, which demonstrates the potential usefulness of the pendant
amino group in stabilizing by coordination the oxidative addition
product. Finally, complex 4 does not seem to allow deprotonation of
position 3 of the ligand heterocycle with formation of a free carbene;
more work is needed here to individuate potential reaction partners and
According to the current mechanistic understanding of this reaction,
less electron donating ligands at gold should result in more efficient
Scheme 3. Oxidative addition of biphenylene to produce 5 and ESI-MS spectrum of the reaction mixture with the product signal at m/z 853.33.
4

A. Biffis et al.
Inorganica Chimica Acta 517 (2021) 120218
9.4 Hz 1H, CH), 9.48 (d, 1H, CH). 31P{1H} NMR (CD3CN): δ = 121.98.
13C{1H} NMR (CD3CN): δ = 29.0 (d, J = 7.2 Hz CH3), 42.7 (d, J = 19 Hz,
C), 113.8 (d, J = 4.5 Hz, CH), 121.8 (CH), 130.6 (CH), 140.26 (d, J = 3.6
Hz, C), 143.01 (CH). Elemental analysis calcd. for C15H23ClF3N3O3P-
SAu: C 27.90%, H 3.59% N 6.51%, S 4.97%; found: C 28.14%, H 3.46%,
N 6.36%, S 5.18%. ESI-MS (positive ions, CD3CN): m/z 496.01
[Mꢀ OTf-], 609.94 [Mꢀ Cl-], 1145.65 [2 Mꢀ OTf-].
Scheme 5. Gold catalyzed alkyne hydroarylation investigated in this work.
4.3. Oxidative addition of biphenylene to complex 3
The procedure was carried out according to [15]. In a Schlenk tube
AgSbF6 (7.9 mg, 23 mmol) was dissolved in CD2Cl2 (0.3 mL). In a small
round bottomed flask were added under an inert atmosphere complex 3
(17 mg, 23 mmol), biphenylene (35 mg, 0.23 mmol) and CD2Cl2 (0.3
mL). The Schlenk tube was subsequently placed in an ethanol/liquid N2
bath at ꢀ 80 ◦C and the solution in the round bottomed flask was
transferred into the Schlenk tube under an inert atmosphere. The reac-
tion mixture was left under stirring at ꢀ 80 ◦C for 30 min and was then
allowed to warm up to room temperature and left under stirring for 1
additional hour. A sample of the reaction solution was then directly
analyzed by NMR and ESI-MS.
conditions to indeed demonstrate the feasibility of such a deprotonation.
4. Experimental section
All manipulations were performed using standard Schlenk tech-
niques under an atmosphere of dry argon. Reagents and solvents were
commercially available as high-purity products and generally used as
received. The ligands 1 [16] and 2 [21] were prepared according to the
literature. A Bruker DRX 300 MHz (300.1 MHz for 1H; 121 MHz for 31P;
13
◦
75.5 MHz for C) was used for NMR experiments at 25 C; chemical
shifts (δ) are reported in units of parts per million (ppm) relative to the
residual solvent signals. ESI mass spectra were obtained by using a
Finnigan Thermo LCQ-Duo ESI mass spectrometer. Elemental analyses
were performed with a Thermo Scientific FLASH 2000 instrument at the
Department of Chemical Sciences of the University of Padova.
4.4. Hydroamination tests
General procedure. In a Schlenk tube equipped with a magnetic
stirring bar were placed 20 μmol Au complex and 20 μmol AgSbF6. The
tube was degassed and put under an inert atmosphere. 0.70 mL (5.0
mmol) mesitylamine and 0.55 mL (5.0 mmol) phenylacetylene were
then injected into the Schlenk tube. The flask was immediately placed in
an oil bath preheated at 40 ◦C and the reaction mixture was vigorously
stirred for 4 h. Conversions and yields were determined by 1H NMR on
0.1 mL samples of the reaction mixture diluted in CDCl3.
4.1. Synthesis of complex 3
In a three-necked, round bottomed flask were added under an inert
atmosphere ligand 1 (172 mg, 0.34 mmol) the gold(I) precursor [AuCl
(SMe2)] (100 mg, 0.34 mmol) and anhydrous dichloromethane (10 mL).
The reaction mixture was left under stirring overnight in the dark. The
solvent was subsequently evaporated to dryness and the resulting solid
was recrystallized from chloroform/ether. Yield 174 mg (69.6%).
1H NMR (CDCl3): δ = 1.20 (d, J = 6.9 Hz, 12H, CH3), 1.77 (bs, 12H,
Ad), 2.07 (bs, 6H, Ad), 2.27 (m, 6H, Ad), 2.42 (m, 6H, Ad), 4.45 (sept, J
= 6.9 Hz, 2H, CH), 6.83 (d, J = 7.5 Hz, 2H, Ph), 7.06 (t, J = 7.5 Hz, 1H,
4.5. Hydroarylation tests
General procedure. Mesitylene (0.35 mL, 2.3 mmol), the gold(I)
complex (12.5 µmol), AgSbF6 (4.6 mg, 13.4 µmol) and the ionic liquid 1-
butyl-3-metylimidazolium bis(trifluoromethansulfonyl)imide (0.75 mL,
2.6 mmol) were placed in a Schlenk tube previously evacuated and filled
with argon and stirred at room temperature for 5 min. Ethyl propiolate
(0.24 mL, 2.3 mmol) was subsequently added and the Schlenk tube was
immediately placed in an oil bath thermostated at 40 ◦C and vigorously
stirred at 40 ◦C for 24 h. Portions of the solution (0.1 mL) were drawn off
from the reaction mixture at intervals and analyzed by 1H NMR.
Ph), 7.35 (t, J = 7.8 Hz, 2H, Ph). 31P{1H} NMR (CDCl3): δ = 75.25. 13
C
{1H} NMR (CDCl3): δ = 24.0 (s, CH3), 28.9 (d, J = 10 Hz, CH2), 36.7 (d,
J = 1.2 Hz, CH2), 41.8 (d, J = 1.1 Hz, CH), 44.3 (d, J = 21 Hz, C), 52.4 (d,
J = 4.3 Hz, CH), 119.0 (s, CH), 123.2 (s, CH), 130.0 (s, CH), 149.5 (d, J
–
= 13 Hz, ipso-C), 155.7 (d, J = 82 Hz, C N). Elemental analysis calcd.
–
for C33H49N2PClAu: C 53.77%, H 6.70% N 3.80%; found: C 53.49%, H
6.60%, N 3.75%. ESI-MS (positive ions, CHCl3): m/z 1437.28 [2 Mꢀ Cl-],
1495.24 [2 M + Na+].
4.6. X-ray crystal structure determination
Data for compounds 3, 4a, and 4b were collected using an Oxford
Diffraction Gemini E diffractometer, equipped with a 2 K × 2 K EOS CCD
area detector and sealed–tube Enhance (Mo) and (Cu) X–ray sources.
Single crystals of the compounds were fastened on the top of a Linde-
4.2. Synthesis of complex 4
In a three-necked, round bottomed flask were added under an inert
atmosphere ligand 2 (140 mg, 0.34 mmol) the gold(I) precursor [AuCl
(SMe2)] (101 mg, 0.34 mmol) and anhydrous dichloromethane (10 mL).
The reaction mixture was left under stirring overnight in the dark. The
solvent was subsequently evaporated to dryness and the resulting solid
was recrystallized from acetonitrile/ether. Yield 150 mg (68.3%).
1H NMR (CD3CN): δ = 1.53 (d, J = 18 Hz 18H, CH3), 7.83 (t, J = 6.9
Hz 1H, CH), 8.44 (m, 1H, CH), 8.92 (d, J = 6.7 Hz 1H, CH), 9.16 (d, J =
mann glass capillary. Data were collected by means of the
ω
-scans
(λ =
technique using graphite-monochromated radiation and Mo K
α
0.71073) radiation. Detector distance was set at 45 mm. The diffraction
intensities were corrected for Lorentz/polarization effects as well as
with respect to absorption. Empirical multi-scan absorption corrections
using equivalent reflections were performed with the scaling algorithm
SCALE3 ABSPACK. Data reduction, finalization and cell refinement were
carried out through the CrysAlisPro software. Accurate unit cell pa-
rameters were obtained by least squares refinement of the angular set-
tings of strongest reflections, chosen from the whole experiment. The
structures were solved with Olex2 [39] by using ShelXT [40] structure
solution program by Intrinsic Phasing and refined with the ShelXL [41]
refinement package using least-squares minimization. In the last cycles
of refinement, non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included in calculated positions, and a riding
Table 4
Catalytic performance of complex 4 in alkyne hydroarylation.
Time(h)
Alkyne conv. (%)
TON
Selectivity (%)
6
7
8
1
35
70
66
61
42
22
22
23
12
17
35
3
62
124
200
17
>99
5

A. Biffis et al.
Inorganica Chimica Acta 517 (2021) 120218
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model was used for their refinement. Crystallographic data have been
deposited with the Cambridge Crystallographic Data Centre (CCDC
2040683–2040685).
´
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CRediT authorship contribution statement
[16] A. Marchenko, G. Koidan, A. Hurieva, A. Kostyuk, D. Franco, M. Baron, A. Biffis,
PdII Complexes with N-(Diadamantylphosphanyl)diaminocarbene and Related
Ligands: Synthesis and Catalytic Applications in Intermolecular Alkyne
Hydroaminations, Eur. J. Inorg. Chem. 2018 (5) (2018) 652–658, https://doi.org/
10.1002/ejic.201701342.
Andrea Biffis: Conceptualization, Methodology, Validation, Re-
sources, Supervision, Project administration. Marco Baron: Investiga-
tion, Validation. Cristina Tubaro: Validation. Marzio Rancan:
Investigation, Validation. Lidia Armelao: Resources. Anatoliy Mar-
chenko: Conceptualization. Georgyi Koidan: Investigation, Validation.
Anastasiia N. Hurieva: Investigation, Validation. Aleksandr Kostyuk:
Conceptualization, Methodology, Validation, Resources, Supervision,
Project administration.
[17] V.J. Catalano, S.J. Horner, Luminescent Gold(I) and Silver(I) Complexes of 2-
(Diphenylphosphino)-1-methylimidazole (dpim): Characterization of a Three-
Coordinate Au(I)ꢀ Ag(I) Dimer with a Short Metalꢀ Metal Separation, Inorg. Chem.
42 (2003) 8430–8438, https://doi.org/10.1021/ic030200m.
[18] C. Khin, A.S.K. Hashmi, F. Rominger, Gold(I) Complexes of P,N Ligands and Their
Catalytic Activity, Eur. J. Inorg. Chem. 2010 (7) (2010) 1063–1069, https://doi.
org/10.1002/ejic.200900964.
[19] C. Wetzel, P.C. Kunz, I. Thiel, B. Spingler, Gold(I) Catalysts with Bifunctional P, N
Ligands, Inorg. Chem. 50 (16) (2011) 7863–7870, https://doi.org/10.1021/
ic2011259.
Declaration of Competing Interest
[20] T. vanDijk, S. Burck, A.J. Rosenthal, M. Nieger, A.W. Ehlers, J.C. Slootweg,
K. Lammertsma, Synthesis and Coordination Chemistry of Iminophosphanes,
Chem. Eur. J. 21 (26) (2015) 9328–9331, https://doi.org/10.1002/
chem.201501126.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[21] A.P. Marchenko, H.N. Koidan, A.A. Kirilchuk, A.B. Rozhenko, A.A. Yurchenko, A.
N. Kostyuk, Investigation of N- and C-Phosphanylation of [1,2,4]Triazolo[4,3-a]
pyridines, Heteroatom Chem. 26 (4) (2015) 277–289, https://doi.org/10.1002/
hc.21258.
Acknowledgements
[22] X. Wang, Y. Wang, J. Zhang, X. Zhao, Y.e. Liu, The ionic mononuclear and
trinuclear Au(I)-complexes ligated by phosphine-functionalized ionic liquids:
Synthesis, characterization, and catalysis to hydration of phenylacetylene,
J. Organomet. Chem. 762 (2014) 40–47, https://doi.org/10.1016/j.
jorganchem.2014.04.005.
Partial support of this research through the CARIPARO Foundation
(Excellence Project « SELECT ») is gratefully acknowledged.
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7