Heterogeneous Catalytic Method for the Copper(II)-Catalysed Addition of H-Phosphinates and Secondary Phosphine Oxides to Phenylacetylene

Article abstract of DOI:10.1007/s10562-021-03694-6

Copper(II) on 4?? molecular sieve was found to be an efficient heterogeneous catalyst in the addition of different H-phosphinates and secondary phosphine oxides to phenylacetylene. All hydrophosphinylation reactions were completely regioselective, as only β-isomers were formed, and the E-alkenylphosphinates and E-alkenylphosphine oxides were synthesized in moderate to excellent yields. The catalyst could be reused multiple times in the reaction. Graphic Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-021-03694-6

Catalysis Letters
https://doi.org/10.1007/s10562-021-03694-6
Heterogeneous Catalytic Method for the Copper(II)‑Catalysed
Addition of H‑Phosphinates and Secondary Phosphine Oxides
to Phenylacetylene
Kinga Juhász1 · Bence Varga1 · Péter Bagi1 · Zoltán Hell1
Received: 9 April 2021 / Accepted: 4 June 2021
© The Author(s) 2021
Abstract
Copper(II) on 4 Å molecular sieve was found to be an efcient heterogeneous catalyst in the addition of diferent H-phosphi-
nates and secondary phosphine oxides to phenylacetylene. All hydrophosphinylation reactions were completely regioselective,
as only β-isomers were formed, and the E-alkenylphosphinates and E-alkenylphosphine oxides were synthesized in moderate
to excellent yields. The catalyst could be reused multiple times in the reaction.
Graphic Abstract
Keywords Hydrophosphinylation · Heterogeneous catalysis · Copper · Molecular sieve · Alkenylphosphine oxides
1 Introduction
[24–27], nickel [28, 29], palladium [20, 30–32] and rhodium
[19–21, 33, 34]. Microwave irradiation has also been used
to promote the addition of secondary phosphine oxides to
alkynes [35]. Han et al. elaborated the metal-free generation
of the alkenylphosphorus non-selective anti-Markovnikov
adducts under radical conditions [36]. Radical conditions
have also been applied for the selective synthesis of Z-alk-
enylphosphine oxides by Lei and co-workers [37]. Schmidt
et al. elaborated the hydrophosphinylation of alkynes under
mild conditions in the presence of a lanthanum-based N,N-
dimethylbenzylamine complex [38]. The earth abundant
cobaloxime was used to convert the H-phosphine oxide into
its reactive radical species under visible light irradiation
[39]. The metal-free hydrophosphorylation of ynamides was
achieved by the in situ generation of electrophilic phospho-
rus species to prepare β-aminovinylphosphine oxides [40].
Most of the metal-catalysed reactions mentioned
above used homogeneous catalysts for hydrophosphi-
nylations, consequently ligands played an important role
in the transformations. Only several among them were
Alkenylphosphine oxides represent a group of important
compounds in organic, medicinal and agricultural chemis-
try [1–4]. They are commonly used as building blocks in the
preparation of carbo- and heterocyclic compounds [5–8].
The olefnic bond can be modifed further to prepare various
phosphine ligands [9–12]. Alkenylphosphine oxide scafolds
can also be found in numerous biologically active products
or used as such compounds [13–16].
The synthesis of alkenylphosphine oxides usually
requires the presence of a transition metal in form of transi-
tion metal salts, complexes or the immobilized metals on
some kind of support [17–23]. The transition metals most
frequently used for the hydrophosphinylation are copper
* Zoltán Hell
hell.zoltan@vbk.bme.hu
1
Department of Organic Chemistry and Technology, Budapest
University of Technology and Economics, Műegyetem rkp.
3., Budapest 1111, Hungary
Vol.:(0123456789)
1 3

K. Juhász et al.
heterogeneous catalytic process, such as immobilized rho-
dium catalyst on MSC-41 support [17, 19] or immobilized
Rh, Pd, or Ni catalyst on polystyrene bound triphenylphos-
phane [20, 22]. A related reaction has also been described
using heterogeneous catalyst, Cu/Cu2O nanoparticles sup-
ported on Nb2O5, for the direct synthesis of alkynylphospho-
nates from alkynes and phosphite esters [41].
method. Prior to the adsorption measurement, the samples
were evacuated at 110 °C for 24 h [53].
LC-MS measurements were performed using an Agilent
1100 and Agilent 6130 LC-MS system in positive and nega-
tive electrospray mode. 1H, 13C and 31P NMR spectra were
made on BRUKER Avance-300 instrument using TMS as
an internal standard in CDCl3 for 1H and 13C NMR measure-
ments. 85% Solution of H3PO4 was the external reference for
31P NMR chemical shifts.
Reusability of the catalytic system and the separation of
product are the key concerns of the catalytic procedures. The
use of suitable heterogeneous catalysts may ease the separa-
tion and enable the recycling of the catalyst. Therefore, the
development of a heterogeneous catalytic method may be a
good alternative in hydrophosphinylation reactions.
In the last decades, our research group has been working
on the preparation of diferent supported metal catalysts. 4 Å
molecular sieves and mixed oxides served as solid supports
which were impregnated with transition metal salts such as
copper and nickel. Supported nickel catalyst showed good
activity in the Kumada-coupling [42]. The molecular sieves
supported copper(II) catalyst was used in the preparation
of propargylamines via A3-coupling [43] and the selective
1,4-addition of arylmagnesium compounds to chalcones
[44]. As copper [24–27] and nickel [28, 29] catalysts can be
used in homogeneous hydrophosphinylation reactions, we
thought that developing the heterogeneous version of such
P–C coupling reaction is an idea worth pursuing.
2.1 Preparation of the Catalysts
A suspension of 4 Å molecular sieves (2 g) in deionized
water (200 mL) containing the corresponding metallic
salt (CuCl2*2H2O, MnCl2*4H2O, NiCl2*6H2O) (0.34 g,
2 mmol) was stirred for 12 h at room temperature. The solid
was fltered, washed with deionized water (50 mL) and ace-
tone (20 mL), then dried in an oven at 120 °C for 1 h [43].
2.2 Characterization of the Cu(II)‑4A Catalyst
The copper content was 5.8 wt%, determined by ICP-OES,
which is in good correlation with the theoretical value (6.3
wt%). The original surface area of the molecular sieves (810
m2/g) dropped to 360 m2/g after the impregnation. During
the impregnation copper ions replaces the sodium ions in the
synthetic microporous sodium aluminosilicate. But because
of the microporous structure of 4A these ions take place on
the support’s surface. Surface analysis by scanning electron
microscope (SEM) showed that the zeolite crystals retained
their cubooctahedral form (Fig. 1). Energy-Dispersive X-ray
Spectroscopy (EDS) showed that copper evenly covered
the support’s surface. The size of the particles was in the
2.5–5 μm range [54].
Herein, we present our results achieved in the heterogene-
ous catalytic hydrophosphinylation of phenylacetylene in the
presence of a molecular sieve supported copper(II) catalyst
[Cu(II)-4A].
2 Experimental
Phenylacetylene, ethyl phenylphosphinate and diphenyl
phosphine oxide were purchased from Sigma Aldrich Ltd.
The reagents were used without further purifcation. The
solvents were purchased from Merck Chemicals Ltd., and
they were used without further purifcation.
Other H-phosphinates (1a–c) and secondary phosphine
oxides (4a–f) were synthesized as described in the literature
[45–52].
Thin layer chromatography (TLC) was performed on
Merck pre-coated Silica gel 60 F254 aluminium plates and
visualized by UV irradiation.
Column chromatography was performed on Silica gel 60
with a particle size of 0.063–0.200 mm supplied by Merck.
Surface area of 4A and Cu(II)-4A were measured to
investigate their changes after metal deposition. Specifc
surface areas of samples were measured by nitrogen adsorp-
tion and desorption at−196 °C with BET surface analyser
(Micromeritics Model TRISTAR 3000) using BET-BJH
Fig. 1 SEM image of the Cu(II)-4A catalyst [54]
1 3

Heterogeneous Catalytic Method for the Copper(II)-Catalysed Addition of H-Phosphinates…
TPR profle of the catalyst (Fig. 2) showed two peaks,
at about 200 °C and at 525 °C. The frst corresponds to the
reduction of Cu(II) to Cu(I), while the second to the reduc-
tion of Cu(I) to Cu(0), verifying the presence of Cu(II) on
the catalyst’s surface [53]. The measured values are in good
agreement with the published data; 155–270 °C for the frst,
while 360–600 °C for the second reduction step [55, 56].
1.97–2.05 (m, 1H), 6.49 (dd, J = 20.3, 17.4 Hz, 1H),
7.33–7.38 (m, 3H), 7.45–7.51 (m, 4H), 7.53 (d, J=8.1 Hz,
2H), 7.85 (dd, J = 12.2, 7.7 Hz, 2H). 13C NMR (CDCl3,
300 MHz) δ (ppm): 23.6, 25.2, 33.9, 74.9, 118.1, 119.2,
127.7, 128.8, 130.1, 131.4, 132.1, 147.4. 31P NMR
(202.4 MHz, CDCl3) δ (ppm): 29.6. ESI-MS: m/z: 327
(M+H)+.
(E)-1-Menthyloxylphenylphosphinyl-2-phenylethene (3c);
1H NMR (300 MHz, CDCl3) δ (ppm): 0.54 (d, J=6.8 Hz,
1H), 0.81 (d, J = 6.9 Hz, 3H), 0.85 (t, J = 7.3 Hz, 2H),
0.90 (d, J=6.9 Hz, 3H), 0.96 (d, J=7.0 Hz, 3H), 1.28 (q,
J=11.1, 10.7 Hz, 1H), 1.42 (dt, J=22.1, 11.2 Hz, 2H), 1.65
(q, J=15.9 Hz, 2H), 2.24 (m, 1H), 4,12–4.34 (m, 1H), 6.50
(dd, J=20.4, 17.4 Hz, 1H), 7.35 (d, J=7.6 Hz, 3H), 7.48
(dt, J=17.0, 9.0 Hz, 5H), 7.56 (dd, J=20.7, 17.7 Hz, 1H),
7.85 (dd, J=12.4, 7.5 Hz, 2H). 13C NMR (CDCl3, 300 MHz)
δ (ppm): 15.8, 21.2, 21.9, 22.8, 25.7, 31.5, 34.1, 43.7, 48.9,
117.9, 118.9, 127.7, 128.5, 128.8, 130.1, 131.1, 131.4,
131.9, 147.9. 31P NMR (202.4 MHz, CDCl3) δ (ppm): 29.1
(50%), 29.2 (50%). ESI-MS: m/z: 383 (M+H)+.
2.3 General Procedure for the Preparation
of Compounds 3a–c and 5a–f
The desired products were obtained by the reaction of the
corresponding H-phosphinate (1a–c, 1 mmol) or secondary
phosphine oxide (4a–f, 1 mmol) and phenylacetylene (2,
1 mmol) in DMSO (2 mL) in the presence of Cu(II)-4A cata-
lyst (0.1 g) under nitrogen atmosphere at 120 °C for 12 h.
After completion of the reaction the catalyst was fltered and
washed with EtOAc. Then, the reaction mixture was diluted
with H2O, and the aqueous phase was extracted with EtOAc.
The combined organic layers were dried over Na2SO4, and
the solvents were evaporated. The crude product was puri-
fed via column chromatography (silica gel, hexane:EtOAc
1:1).
(E)-1-Diphenylphosphinyl-2-phenylethene (5a) [26];
1H NMR (300 MHz, CDCl3) δ (ppm): 6.84 (dd, J = 22.3,
17.4 Hz, 1H), 7.36 (d, J = 6.3 Hz, 4H), 7.45–7.54 (m,
8H), 7.76 (dd, J = 11.9, 7.8 Hz, 4H). 13C NMR (CDCl3,
300 MHz) δ (ppm): 118.9, 119.7, 127.9, 128.1, 128.6,
2.3.1 Characterization of the Products
128.7, 128.8, 128.9, 130.2, 131.5, 131.6, 132.0, 147.8. 31
P
(E)-1-Ethoxylphenylphosphinyl-2-phenylethene (3a)
NMR (202.4 MHz, CDCl3) δ (ppm): 24.6. ESI-MS: m/z:
1
[26]; H NMR (300 MHz, CDCl3) δ (ppm): 1.35–1.38 (t,
305 (M+H)+.
J=6.9 Hz, 3H), 4.02–4.19 (m, 2H), 6.45–6.53 (dd, J=20.5,
17.4 Hz, 1H), 7.35 (s, 3H), 7.48–7.56 (m, 6H), 7.83–7.87
(dd, J=12.2, 7.5 Hz, 2H). 13C NMR (CDCl3, 300 MHz) δ
(ppm): 16.5, 60.9, 117.4, 118.5, 127.8, 128.7, 130.2, 131.4,
131.5, 132.3, 135.0, 147.9. 31P NMR (202.4 MHz, CDCl3)
δ (ppm): 31.4. ESI-MS: m/z: 273 (M+H)+.
(E)-1-(2-Methyoxyphenyl)phenylphosphinyl-2-pheny-
1
lethene (5b); H NMR (300 MHz, CDCl3) δ (ppm): 3.68
(s, 3H), 6.90 (dd, J = 8.3, 5.4 Hz, 1H), 7.05 (dd, J = 24.2,
17.5 Hz, 1H), 7.14 (m, 2H), 7.30–7.42 (m, 5H), 7.53 (m,
3H), 7.65–7.73 (m, 3H), 8.07 (dd, J = 13.2, 7.5 Hz, 1H).
13C NMR (CDCl3, 300 MHz) δ (ppm): 55.4, 118.8, 119.7,
121.2, 121.3, 127.7, 128.2, 128.3, 128.8, 129.7, 130.6,
130.7, 131.3, 134.0, 146.9. 31P NMR (202.4 MHz, CDCl3)
δ (ppm): 22.0. ESI-MS: m/z: 335 (M+H)+.
(E)-1-Cyclohexylphenylphosphinyl-2-phenylethene
1
(3b) [26]; H NMR (300 MHz, CDCl3) δ (ppm): 1.26 (d,
J = 9.5 Hz, 1H), 1.44–1.58 (m, 2H), 1.64 (dd, J = 13.1,
9.8 Hz, 3 H), 1.69–1.80 (m, 2H), 1.82–1.90 (m, 2H),
(E)-1-(2-Trifluoromethylphenyl)phenylphosphinyl-
1
2-phenylethene (5c); H NMR (300 MHz, CDCl3) δ
(ppm): 6.94–7.03 (dd, J = 25.2, 17.3 Hz, 1H), 7.36 (s,
3H), 7.42–7.43 (dd, J = 7.6, 2.9 Hz, 2H), 7.48–7.50 (m,
2H), 7.55–7.56 (m, 2H), 7.59–7.63 (dd, J = 12.9, 7.7 Hz,
2H), 7.69–7.71 (m, 1H), 7.72–7.74 (m, 1H), 7.77–7.80
(dd, J = 8.3, 4.1 Hz, 1H), 8.41–8.54 (dd, J = 13.6, 7.6 Hz,
1H).13C NMR (CDCl3, 300 MHz) δ (ppm): 117.7, 118.6,
121.9, 122.8, 124.9, 128.0, 128.6, 128.7, 129.0, 130.4,
130.8, 130.9, 132.0, 132.2, 132.6, 135.4, 149.5. 31P NMR
(202.4 MHz, CDCl3) δ (ppm): 24.0. ESI-MS: m/z: 373
(M+H)+.
(E)-1-(Biphenyl-2-yl)phenylphosphinyl-2-phenylethene
1
(5d); H NMR (300 MHz, CDCl3) δ (ppm): 6.19 (dd,
J = 25.1, 17.3 Hz, 1H); 7.10–7.13 (m, 2H), 7.14–7.17 (m,
Fig. 2 TPR profle of the Cu(II)-4A catalyst [53]
3H), 7.19–7.24 (m, 2H), 7.31 (s, 6H), 7.40–7.44 (m, 3H),
1 3

K. Juhász et al.
7.44–7.48 (m, 2H), 7.56 (t, 1H), 8.04 (dd, J=13.4, 7.8 Hz,
1H). 13C NMR (CDCl3, 300 MHz) δ (ppm): 118.6, 119.4,
126.9, 127.1, 127.5, 127.6, 128.2, 128.3, 128.6, 129.7,
129.9, 130.5, 130.7, 130.8, 131.2, 131.6, 133.3, 133.4,
140.7, 146.8. 31P NMR (202.4 MHz, CDCl3) δ (ppm):
23.7.ESI-MS: m/z: 381 (M+H)+.
catalysts. The reaction of ethyl phenylphosphinate (1a) and
phenylacetylene (2) was chosen for optimization purposes,
and the efect of the catalyst, solvent and the reaction time
1
was studied. H and 31P NMR spectroscopy and LC-MS
were used to follow the progress of the reaction during the
optimization study.
1
(E)-1-Butylphenylphosphinyl-2-phenylethene (5e); H
According to the literature copper and nickel, further
manganese catalysts were tested, all three on 4 Å molecular
sieve support. The catalysts were prepared in our research
group by the proven impregnation method of 4 Å molecu-
lar sieves with the corresponding metal salt in deionized
water, followed by fltration and drying [43]. Due to the
fact, that H-phosphinates and secondary phosphine oxides
are prone to oxidation in air at elevated temperatures, the
reactions were carried out under nitrogen atmosphere. The
results showed, that if the Cu(II)-4A catalyst was changed
to Mn(II)-4A or Ni(II)-4A the yields of 3a decreased sig-
nifcantly (Compare Table 1, Entries 1, 2 and 3). Thus, the
Cu(II)-4A catalyst was used for the further experiments.
Next the efect of four diferent solvents was studied. The
reaction temperature was set to 120 °C, unless the boiling
point of the corresponding solvent required lower tempera-
ture. The reaction time was 12 h. In DMSO and DMF the
desired product (3a) was prepared in moderate yields (52%
or 45%) (Table 1, Entries 3 and 6), but DMSO gave some-
what better results. In contrast, the reactions in 1,4-dioxane
and acetonitrile provided the product (3a) only in poor yields
(5% or 25%) (Table 1, Entries 4 and 5). Analysis of the crude
products revealed that complete conversion was not reached
NMR (300 MHz, CDCl3) δ (ppm): 0.89 (t, J=7.3 Hz, 3H),
1.43 (m, 2H), 1.51–1.71 (m, 2H), 2.00–2.14 (m, 2H), 6.62
(dd, J=23.8, 17.4 Hz, 1H), 7.35 (m, 2H), 7.46–7.54 (m, 6H),
7.73–7.83 (m, 3H). 13C NMR (CDCl3, 300 MHz) δ (ppm):
13.6, 23.5, 23.9, 30.1, 118.8, 119.6, 127.6, 128.7, 128.8,
129.9, 130.4, 131.6, 132.5, 146.8. 31P NMR (202.4 MHz,
CDCl3) δ (ppm): 31.0. ESI-MS: m/z: 285 (M+H)+.
(E)-1-Cyclohexylphenylphosphinyl-2-phenylethene (5f);
1H NMR (300 MHz, CDCl3) δ (ppm): 1.02–1.31 (m, 5 H),
1.60–1.89 (m, 6H), 6.68 (dd, J=24.6, 17.3, 1H), 7.30–7.42
(m, 4H), 7.46–7.56 (m, 5H), 7.76 (td, J=7.9, 3.8 Hz, 2H).
13C NMR (CDCl3, 300 MHz) δ (ppm): 24.8, 25.8, 26.2,
39.3, 116.9, 117.7, 127.6, 128.5, 128.8, 129.9, 130.7, 131.5,
132.4, 147.7. 31P NMR (202.4 MHz, CDCl3) δ (ppm): 33.6.
ESI-MS: m/z: 311 (M+H)+.
3 Results and Discussion
We studied the reaction of diferent H-phosphinates and
secondary phosphine oxides with phenylacetylene (2) in
the presence of molecular sieve supported transition metal
Table 1 Optimization of the reaction conditions in the reaction of ethyl phenylphosphinate (1a) and phenylacetylene (2)
Entry
Catalyst
Solvent
Time (h)
Temperature (°C)
Yield (%)b
1
2
3
4
5
6
7
8
Mn(II)-4A
Ni(II)-4A
Cu(II)-4A
Cu(II)-4A
Cu(II)-4A
Cu(II)-4A
Cu(II)-4A
Cu(II)-4A
DMSO
DMSO
DMSO
1,4-dioxane
MeCN
DMF
DMSO
DMSO
12
12
12
12
12
12
6
120
120
120
100
80
120
120
120
22
17
52
5
25
45
38
25
3
aReagents and conditions: ethyl phenylphosphinate (1 mmol), phenylacetylene (1 mmol), catalyst (0.1 g, 9 mol% Cu), DMSO (2 mL), 120 °C,
12 h
bIsolated yield
1 3

Heterogeneous Catalytic Method for the Copper(II)-Catalysed Addition of H-Phosphinates…
in these instances. A reason for the signifcantly lower con-
versions and yields could be the lower reaction temperature.
Therefore, the optimization of the catalysts was carried on
in DMSO at 120 °C.
the same reaction was carried out in the presence of 4 Å
molecular sieve. In both cases, no product formation could
be detected by spectroscopic methods, indicating that the
Cu(II) dispersed on the surface of the molecular sieve was
responsible for the catalytic transformation.
Finally, we examined, if the reaction time could be
reduced without any deterioration of the yields. Reducing
the reaction time to 3 h (Table 1, Entry 8), the yield was
also cut in half. With 6 h of reaction time (Table 1, Entry
7) a decrease in the yield was also observed. In both cases,
full conversion was not achieved, as unreacted ethyl phe-
nylphosphinate (1a) could be identifed in the 31P NMR
spectra of the crude product.
As the result of the optimization studies, the subse-
quent reactions investigating the substrate scope were car-
ried out in DMSO at 120 °C for 12 h in the presence of
the Cu(II)-4A catalyst under nitrogen atmosphere. After
the completion of the reaction, the catalyst was removed
by fltration, and the crude product obtained after extrac-
tion was purifed further by column chromatography. The
structure of the alkenylphosphinates (Tables 2 and 3)
was elucidated by NMR and MS spectroscopy. First, the
reaction of various H-phosphinates (1a–d) with phenyla-
cetylene (2) was examined. As a result of the optimization
In order to demonstrate the need for the catalyst, two con-
trol experiments were carried out. In one case, ethyl phe-
nylphosphinate (1a) and phenylacetylene (2) was heated in
DMSO at 120 °C for 12 h, and in a separate experiment
Table 2 Reaction of diferent H-phosphinates (1a–c) with phenylacetylene (2)
Entry
1
R
Product
Yield (%)b
52
Et 1a
2
3
cyclohexyl 1b
menthyl 1c
88
90
aReagents and conditions: H-phosphinate (1 mmol), phenylacetylene (1 mmol), catalyst (0.1 g, 9 mol% Cu), DMSO (2 mL), 120 °C, 12 h
bIsolated yield
1 3

K. Juhász et al.
Table 3 The addition of secondary phosphine oxides (4a–f) to phenylacetylene (2)
Entry
1
R
Product
Yield (%)b
50
Ph 4a
2
3
4
2-MeO-C6H4 4b
2-CF3- C6H4 4c
biphenyl-2-yl 4d
67
81
34
5
6
Bu 4e
65
87
cyclohexyl 4f
aReagents and conditions: phosphine oxide (1 mmol), phenylacetylene (1 mmol), catalyst (0.1 g, 9 mol% Cu), DMSO (2 mL), 120 °C, 12 h
bIsolated yield
1 3

Heterogeneous Catalytic Method for the Copper(II)-Catalysed Addition of H-Phosphinates…
studies the (E)-1-ethoxylphenylphosphinyl-2-phenylethene
(3a) was prepared with a yield of 52%, while in case of
the cyclohexyl and menthyl substituents the desired prod-
ucts (3b and 3c) were obtained in excellent yields (88% or
90%) (Table 2, Entries 2 and 3). It is noteworthy, that the
menthyl phenyl-H-phosphinate derived from (-)-menthol
was used as a 1:1 mixture of the (RP)- and (SP)-diastere-
omers. Thus, alkenylphosphinate 3c was obtained as a 1:1
mixture of two diastereomers. However, in the reaction of
tert-butyl phenylphosphinate (1d) the yield of the (E)-1-tert-
butoxylphenylphosphinyl-2-phenylethene was signifcantly
lower (< 5%), indicating that the increased steric bulk of
the tert-butoxy group hinders the reaction, which leads to
low conversion.
of alkynes in the presence of copper catalyst, yielding
the homo-coupled product (in this case 1,4-diphenyl-but-
1,3-diin) was not observed. This is in agreement with our
previous observations, that this Glaser-type side reaction
occurs only if a nitrogen-containing compound (mostly an
amine or an ammonium salt) is present in the reaction mix-
ture [see e.g. 43].
XRF studies showed that the no copper was found in the
crude product. The catalyst has been heated in DMSO, and
the catalyst was fltered out from the hot mixture. Based on
the XRF analysis, the fltrate did not contain copper either.
These results can verify the real heterogeneous catalytic
nature of the reaction. Similar results were observed gener-
ally in our previous experiments with metal-impregnated
molecular sieve catalysts, verifying that there is no leaching
of metal during these reactions.
Next, the addition of different secondary phosphine
oxides (4a–f) to phenylacetylene (2) was elaborated. Gen-
erally, the desired products (5a–f) were prepared in good
to excellent yields (50–87%). The only exception was the
biphenyl substituted product (5d), which phosphine oxide
was prepared only in a yield of 34% (Table 3, Entry 4). The
reason for this low yield can be attributed to the increased
steric hindrance of the given phenyl-(biphenyl-2-yl) phos-
phine oxide (4d), which is in accordance with the observa-
tions obtained in the reaction of phenylacetyene (2) with
the tert-butyl phenyl-H-phosphinate. Table 3 shows, that
1-diphenylphosphinyl-2-phenylethene (5a) could be pre-
pared in a yield of 50%, and the presence of small elec-
tron donating or withdrawing groups (OMe or CF3) in the
ortho position of the phenyl ring was also tolerated, as alk-
enylphosphine oxides 5b or 5c were prepared in yields of
67% or 81% (Table 3, Entries 2 and 3). Alkyl-arylphosphine
oxides, such as butyl- or cyclohexyl-phenylphosphine oxide
(4e or 4f) could also be coupled with phenylacetylene and
the desired product (5e and 5f) could be prepared in 65% and
87% yield (Table 3, Entries 5 and 6).
Based on our previous experiments, and in agreement
with the literature data [23, 34], a mechanism similar to the
metal catalysed cross-coupled reactions is assumed with
copper insertion and then elimination (Fig. 3).
The reusability or recyclability is an important prop-
erty of a heterogeneous catalyst. Thus, the reusability of
the Cu(II)-4A catalyst was tested in the reaction of ethyl
phenylphosphinate (1a) and phenylacetylene (2). After fltra-
tion from the reaction mixture the catalyst was washed with
ethyl acetate and dried at 120 °C for 1 h. Then the recovered
catalyst was used in a second experiment. The reusability
was tested in two successive runs, and it was found, that the
Cu(II)-4A catalyst can be reused one time without signif-
cant loss of activity (Table 4). In the third run, the yield of
All hydrophosphinylation reactions of phenylacetylene
(2) with various H-phosphinates (3) or secondary phosphine
oxides (4) were completely regioselective, as only the anti-
Markovnikov β-isomers were formed, and the corresponding
products (3 or 5) were isolated as sole (E) stereoisomers.
The addition of various phosphites, such as diethyl-, di(i-
propyl), dibutyl and diphenyl phosphite to phenylacetylene
(2) was also attempted under the standard conditions. How-
ever, the spectroscopic analysis of the reaction mixtures
showed that the desired dialkyl vinyl-phosphonates were
not formed.
There were no determinant by-product detected in the
reactions, but more or less tarry by-products were formed
which required the purifcation of the crude products by col-
umn chromatography. The stability of the given phosphorous
compound might afect the amount of this tarry material.
This can explain the lower yield obtained in some cases.
The side reaction, which may often occur in the reaction
Fig. 3 Proposed mechanism of the reaction
1 3

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phenylacetylene (2)
Entry Number Yield 3a (%)b
of uses
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1
2
3
1
2
3
52
50
49
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phenylacetylene (1 mmol), cata-
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products were obtained in moderate to excellent yields. The
catalyst could be reused at least in two more experiments
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Acknowledgements The research reported in this paper and carried out
at BME has been supported by the NRDI Fund (TKP2020 NC, Grant
No. BME-NC) based on the charter of bolster issued by the NRDI
Ofce under the auspices of the Ministry for Innovation and Technol-
ogy. B. V. acknowledges the fnancial support of the New National
Excellence Program of the Ministry of Human Capacities (Grant num-
ber: ÚNKP-20-3-II-BME-282).
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Funding Open access funding provided by Budapest University of
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Open Access This article is licensed under a Creative Commons Attri-
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copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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