An efficient and recyclable silica-supported carbene-Cu(II) catalyst for the oxidative coupling reaction of terminal alkynes with H-phosphonates under base-free reaction conditions

Article abstract of DOI:10.1002/aoc.1847

The oxidative coupling reactions of terminal alkynes with H-phosphonates were explored using SiO₂-NHC Cu(II) (5.0 mol%) as catalyst at room temperature under base-free reaction conditions. The reactions of a variety of terminal alkynes with H-p

Full text of DOI:10.1002/aoc.1847

Full Paper
Received: 16 April 2011
Revised: 17 August 2011
Accepted: 12 September 2011
Published online in Wiley Online Library: 11 October 2011
(wileyonlinelibrary.com) DOI 10.1002/aoc.1847
An efficient and recyclable silica-supported
carbene–Cu(II) catalyst for the oxidative
coupling reaction of terminal alkynes
with H-phosphonates under base-free
reaction conditions
Ping Liua, Jin Yanga, Pinhua Lia and Lei Wanga,b*
The oxidative coupling reactions of terminal alkynes with H-phosphonates were explored using SiO2ÀNHCÀCu(II)
(5.0 mol%) as catalyst at room temperature under base-free reaction conditions. The reactions of a variety of terminal
alkynes with H-phosphonates generated the corresponding alkynylphosphonate products in good to excellent yields.
In addition, SiO2ÀNHCÀCu(II) could be recovered and recycled for six consecutive trials without significant loss of its
reactivity. Copyright © 2011 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: NHCÀCu(II); terminal alkynes; H-phosphonates; recyclibility; silica-supported catalyst
metathesis,[8] oligomerization and polymerization of alkenes,[9] have
been studied widely. The most successful application at present
Introduction
Alkynylphosphonates, as important topical phosphorus element
scaffolds for the construction of structurally sophisticated phosphorus
compounds, are broadly found in bioactive natural products and
therapeutic molecules.[1] Therefore, considerable effort has been
made to develop efficient strategies for preparing them. In general,
reaction of (RO)2P(O)Cl with Li or Mg acetylene is one of the most
common and efficient methods for the synthesis of alkynylphospho-
nates, but it suffers from the use of hazardous chemicals and lack of
functionality tolerance.[2] Recently, Zhao et al. described a practical
copper-catalyzed aerobic oxidative coupling of terminal alkynes with
H-phosphonates to generate the corresponding alkynylphosphonate
products.[3] The reaction represents a novel and efficient strategy for
the synthesis of alkynylphosphonates using transition metal-catalyzed
oxidative C–P cross-coupling. Although the reaction materials, termi-
nal alkynes and H-phosphonates are commercially available, base is
still necessary. To eliminate the base used in the reaction, the search
for an efficient and practical catalytic system remains a challenge.
Transition metal complexes of N-heterocyclic carbenes (NHCs)
have attracted great interest because the strongly s-donating
NHCs offer a good opportunity to tune the reactivity and selectivity
of transition metal catalysts.[4] Their ability to strongly coordinate
to the metal center allows for the formation of stable metal species
facilitating catalyst design efforts.
appears to be the use of palladium complexes of NHC as ligands
in CÀC and CÀheteroatom cross-coupling reactions. In contrast,
although the first NHCÀCu(I) complex was reported in 1993 by
Arduengo et al.,[10] the chemistry of NHCÀCu(I) and NHCÀCu(II)
complexes has been relatively less studied compared with other
coinage metals and NHC. The investigation and application of
NHCÀCu(II) complexes remain relatively rare. The first NHCÀCu(II)
complex, which was presumably formed through addition of free
NHC to a Cu(II) source in the catalyzed conjugate addition of ZnEt2
to enones, was reported by Fraser and Woodward.[11] Yun reported
the NHCÀCu(II) complex, (IPr)Cu(II)(OAc)2 (IPr= 1,3-bis(2,6-diisopro-
pylphenyl)-imidazol-2-ylidene) as an efficient pre-catalyst for the
1,2- and 1,4-reduction of carbonyl compounds under hydrosilyla-
tion reaction conditions.[12]
N-Heterocyclic carbenes (NHCs) have proven to be excellent
supporting ligands in transition metal-mediated reactions.[13] For
the reaction of Cu-catalyzed oxidative coupling of terminal alkynes
with H-phosphonates, Cu species have been proposed to be respon-
sible for the formation of a copper acetylide intermediate, which is
then reacted with H-phosphonates to give the oxidative coupling
*
Correspondence to: Lei Wang, Department of Chemistry, Huaibei Normal
University, Huaibei, Anhui 235000, People's Republic of China. E-mail:
leiwang@hbcnc.edu.cn
Since the first stable N-heterocyclic carbene (NHC) isolated by
Arduengo et al. in 1991, NHCs have emerged as a class of ligands
in metal-mediated reactions due to their strong s-donor properties
compared with phosphine ligands, thereby enhancing the stability
of NHC complexes toward heat and moisture.[5] A large number of
NHC complexes of precious metals have been prepared and charac-
terized. Their catalytic applications in various organic transforma-
tions, including CÀC bond and CÀN bond formations,[6,7] olefin
a Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000,
People's Republic of China
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of
Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People's
Republic of China
Appl. Organometal. Chem. 2011, 25, 830–835
Copyright © 2011 John Wiley & Sons, Ltd.

An efficient and recyclable silica-supported carbene–Cu(II) catalyst
product based on previous studies.[3] We envisioned NHCÀCu(I) and
NHCÀCu(II) complexes working as efficient and convenient pre-
catalysts for the oxidative cross-coupling of terminal alkynes with
H-phosphonates. Indeed, copper-catalyzed oxidative coupling
reactions of terminal alkynes with various substrates, such as poly-
fluoroarenes, amides, ureas, N-alkyl-arylsulfonamides, heterocycles
and aldehyde–amine, have been documented in the literature.[14]
Although homogeneous catalysts have many advantages, they
are difficult to recover and reuse. Furthermore, residual catalyst metal
along with the products could induce serious problems in the syn-
thesis of bioactive and functional substrates. It could not be used in
large-scale synthesis, particularly on environmental and economic
concerns. However, immobilization of transition metal complexes
onto solid supports is one way to make such catalysis practical. The
use of silica substrates for catalysis has attracted a surge of interest
due to their superior mechanical and thermal stability, excellent
recyclability and convenient separation.[15]
In previous work, we found that polystyrene or SiO2-supported–
NHC complexes are highly effective for cyclo-addition and cou-
pling reactions.[16] Herein, we wish to report an efficient CÀP bond
oxidative cross-coupling reaction of terminal alkynes with H-
phosphonates catalyzed by a reusable silica immobilized NHCÀCu
(II) catalyst. It is noteworthy that SiO2ÀNHCÀCu(II) catalyst could
catalyze aerobic oxidative CÀP cross-coupling reaction of terminal
alkynes with H-phosphonates in the absence of any base. In addi-
tion, SiO2ÀNHCÀCu(II) catalyst could be reused at least six times
without significant loss of its catalytic activity (Scheme 1).
spectra were collected at 400 MHz using a 6000 Hz spectral width,
a relaxation delay of 3.5 s, a pulse width of 38ꢀ, 30 k data points,
and residual CDCl3 (7.26 ppm) as an internal reference. 13 C NMR
spectra were collected at 100 MHz using a 25 000 Hz spectra
width, a relaxation delay of 1.5 s, 75 k data points, a pulse width
of 40ꢀ, and residual CDCl3 (77.00 ppm) as the internal reference.
The C, H, and N analyses were performed with a Vario El III
Elementar. The Cu content was determined by an atomic absorp-
tion spectroscopy analysis (Z-5000, Hitachi). Products were
purified by flash column chromatography on 200–400 mesh silica
gel, SiO2. The chemicals were purchased from commercial suppli-
ers (Aldrich, USA and Shanghai Chemical Company, China) and
were used without purification prior to use. All the reactions were
carried out under an air atmosphere, and commercially obtained
materials were used without further purification. The benzyl chlo-
ride functionalized silica, silica-supported ionic liquid 1a, 1b, and
1c were prepared according to the literature.[14a] The loading of
the silica-supported ionic liquid 1a, 1b, and 1c were quantified
by CHN microanalysis based on the N content and found to be
1.10 mmol gÀ1, 0.81 mmol gÀ1, and 0.87 mmol gÀ1 respectively.
Preparation of SiO2ÀNHCÀCu(II) Catalyst 2a
In an oven-dried Schlenk flask, freshly prepared silica-supported
ionic liquid 1a (1.0 g), t-BuONa (0.096 g, 1.0 mmol), Cu(OAc)2
(0.181 g, 1.0 mmol) and toluene (5.0 ml) were added. The result-
ing suspension was stirred at room temperature for 12 h. Then
the solution was filtered, and the solid was washed with toluene
(3.0 ml), methanol (3.0 ml), acetone (3.0 ml), and dried under vac-
uum at 60 ꢀC for 12 h. SiO2ÀNHCÀCu(II) catalyst 2a was obtained
as a green powder (1.09 g). The copper content of 2a was found
to be 1.00 mmol gÀ1 based on atomic absorption spectroscopy
(AAS) analysis. IR (KBr): 3451, 3110, 2963, 2913, 1603, 1540,
Experimental
Materials and Methods
All 1H and 13 C NMR studies were performed in CDCl3 and
recorded on a Bruker Avance NMR 400 spectrometer. 1H NMR
1480, 1378, 1226, 1097, 1043, 930, 852, 750 cmÀ1
.
OH
OH
OH
O
Cl3Si
CH2Cl
N
N
R
Silica
Silica
Silica
O Si
O
CH Cl
2
Toluene, 80 °C
Toluene, 120 C
O
O
t
Cu(OAc)2, -BuONa
O Si
O
Silica
O Si
O
THF, rt
N
N
HCl
N
R
N
AcO Cu
R
1
1a
: R = 2,4,6−(CH3)3C6H2
OAc
2
1b
: R = C6H5CH2
2a
2b
2c
: R = 2,4,6−(CH3)3C6H2
1c
: R = C6H5
CuI
-BuONa
THF
rt
t
: R = C6H5CH2
: R = C6H5
O
Silica
O Si
O
N
N
R
Cu
I
3
: R = 2,4,6−(CH3)3C6H2
Scheme 1. Preparation of SiO2ÀNHCÀCu(II) and SiO2ÀNHCÀCu(I) catalysts
Appl. Organometal. Chem. 2011, 25, 830–835
Copyright © 2011 John Wiley & Sons, Ltd.
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P. Liu et al.
Preparation of SiO2ÀNHCÀCu(II) Catalyst 2b
8.19. HRMS (ESI): calc. for C16H23PO3 [M]+ 294.1384; found
294.1382.
The synthesis of 2b was similar to that of 2a, except that
silica-supported ionic liquid 1b (1.0 g) was used instead of
1a. SiO2–NHC–Cu(II) catalyst 2b was obtained as a green
powder (1.05 g). The copper content of 2b was found to
be 0.78 mmol gÀ1 based on AAS analysis. IR (KBr): 3301,
3150, 3066, 2965, 2872, 2826, 2748, 1717, 1595, 1537, 1443,
[Diethyl(4-bromphenyl)ethynyl]phosphonate (6 g): yellow oil.
1H NMR (400 MHz, CDCl3): d = 7.52 (d, J = 8.4 Hz, 2H, ArÀH), 7.42
(d, J = 8.4 Hz, 2H, ArÀH), 4.25–4.21 (m, 4H, ÀCH2CH3), 1.42 (t,
J = 7.2 Hz, 6H, ÀCH2CH3). 13 C NMR (100 MHz, CDCl3): d = 133.9
(d, JCÀP = 2.5 Hz), 131.9, 125.5, 118.4 (d, JCÀP = 5.6 Hz), 97.7 (d,
J
CÀP = 52.7 Hz), 79.6 (d, JCÀP = 297.5 Hz), 63.3 (d, JCÀP = 5.5 Hz),
1336, 1261, 1200, 1108, 1058, 942, 809, 764 cmÀ1
.
16.0 (d, JCÀP = 7.0Hz). Elemental analysis: calc. for C12H14BrPO3 C,
45.45; H, 4.45; found C, 45.15; H, 4.68. HRMS (ESI): calc. for
C12H14BrPO3 [M]+ 315.9867; found 315.9868.
Preparation of SiO2ÀNHCÀCu(II) Catalyst 2c
[Diethyl(2-bromophenyl)ethynyl]phosphonate (6i): yellow oil.
1H NMR (400 MHz, CDCl3): d = 7.64–7.58 (m, 2H, ArÀH), 7.34–7.30
(m, 2H, ArÀH), 4.31–4.23 (m, 4H, ÀCH2CH3), 1.42 (t, J = 6.8Hz,
6H, ÀCH2CH3). 13 C NMR (100 MHz, CDCl3): d = 134.5 (d, JC=P = 2.5
Hz), 132.7, 131.7, 127.2, 126.1 (d, JCÀP = 2.8 Hz), 122.2, 97.9 (d,
JCÀP = 52.6 Hz), 63.5 (d, JCÀP = 5.6 Hz), 16.1 (d, JCÀP = 7.1 Hz). Ele-
mental analysis: calc. for C12H14BrPO3 C, 45.45; H, 4.45; found C,
45.28; H, 4.72. HRMS (ESI): calc. for C12H14BrPO3 [M]+ 315.9867;
found 315.9862.
The synthesis of 2c was similar to that of 2a, except that silica-
supported ionic liquid 1c (1.0 g) was used instead of 1a.
SiO2ÀNHCÀCu(II) catalyst 2c was obtained as a green powder
(1.07 g). The copper content of 2c was found to be 0.83 mmol gÀ1
based on atomic absorption spectroscopy AAS analysis. IR (KBr):
3447, 3149, 3074, 2965, 2871, 1596, 1547, 1488, 1448, 1228,
1201, 853, 756, 720 cmÀ1
.
Preparation of SiO2ÀNHCÀCu(I) catalyst 3
The synthesis of 3 was similar to that of 2a, except that CuI
(0.190 g, 1.0 mmol) was used instead of Cu(OAc)2 (0.181 g,
1.0 mmol). SiO2ÀNHCÀCu(I) catalyst 3 was obtained as a gray
powder (1.14 g). The copper content of 3 was found to be
0.87 mmol gÀ1 based on AAS. IR (KBr): 3474, 2963, 2916, 1536,
Results and Discussion
In our initial screening experiments, the oxidative CÀP cross-
coupling reaction of terminal alkyne with H-phosphonate was
catalyzed by SiO2ÀNHCÀCu(II) (2a) (Table 1, entry 1). The reac-
tion of phenylacetylene with diethyl hydrogen phosphate (model
reaction) was carried out in the presence of 5.0 mol% 2a at room
temperature for 24 h. The formation of diethyl phenylethynylpho-
sphonate was confirmed by 1H and 13 C NMR spectroscopic anal-
ysis of the obtained product. To our surprise, the model reaction
was completed in the presence of SiO2ÀNHCÀCu(II) complex, 2a
as catalyst without base, and the isolated yield of the product
was observed to be 90% (with 3.21 of standard deviation)
(Table 1, entry 1). In a similar manner, SiO2ÀNHCÀCu(I) 3 was also
found to be effective for the reaction, and a comparable product
yield to that of SiO2ÀNHCÀCu(II) 2b, and 2c was obtained, infe-
rior to that of SiO2ÀNHCÀCu(II) 2a as catalyst (Table 1, entries
2–4). The influence of the substituted group of NHC in
SiO2ÀNHCÀCu(II) complexes on their catalytic activity for the
model reaction was found to be 2,4,6-(CH3)3C6H2 (2a) > C6H5CH2
(2b) > C6H5 (2c) (Table 1, entries 1–3). It is obvious that the cata-
lytic activity of SiO2ÀNHCÀCu(II) complexes decreases for the
oxidative-coupling reaction along with the steric hindrance of sub-
stituted group decreases. From Table 1, it is evident that 2a is the
best catalyst for this coupling reaction.
The effect of copper salt on the model reaction in the absence
of N-heterocyclic carbene (NHC) was also investigated. When the
model reaction was catalyzed by Cu(OAc)2 without ligand and
base, 55% yield (with 2.43 of standard deviation) of the desired
oxidative-coupling product was isolated (Table 1, entry 5). How-
ever, additional K2CO3 as base did not improve the yield of
desired product, but decreased the yield of the product (Table 1,
entry 6). When CuI was used as catalyst in the model reaction,
81% (with 1.97 of standard deviation) and 80% (with 2.58 of stan-
dard deviation) yields of the coupling products were isolated in
the presence of K2CO3 and Et3N as bases in the reaction, respec-
tively, similar to the results reported in the literature[3] (Table 1,
entries 8 and 9). Unfortunately, only trace amounts of desired
product were detected when the reaction was carried out in
the presence of CuI as catalyst without base (Table 1, entry 7).
1462, 1398, 1336, 1110, 1069, 947, 808, 757 cmÀ1
.
General Procedure for the Reaction of Terminal Alkynes with
H-Phosphonates
An oven-dried round-bottomed flask was charged with SiO2À
NHCÀCu(II) catalyst 2a (50 mg, 0.05 mmol), terminal alkyne
(1.0 mmol), H-phosphonate (1.2 mmol) and dimethyl sulfoxide
(DMSO) (2.0 ml). The mixture was stirred at room temperature
for 24 h under air. The progress of the reaction was monitored
by thin-layer chromatography. On completion of the reaction,
the mixture was filtered, and the solution was concentrated
under reduced pressure and purified by column chroma-
tography on silica gel (hexane:EtOAc = 3:1) to afford the pure
alkynylphosphonate.
Diethyl[(phenyl)ethynyl]phosphonate (6a),[3] diethyl[(4-methyl-
phenyl)ethynyl]phosphonate (6b),[17] diethyl[(4-methoxylphenyl)
ethynyl]phosphonate (6 d),[17] diethyl[(4-fluorophenyl)ethynyl]
phosphonate (6e),[18] [diethyl(4-chlorophenyl)ethynyl]phosphonate
(6f),[19] diethyl[(3-aminophenyl)ethynyl]phosphonate (6 h),[17]
diethyl[(4-phenylphenyl)ethynyl]phosphonate (6j),[18] diethyl
(3-pyridinylethynyl)phosphonate (6 k),[20] di(isopropyl)[(phe-
nyl)ethynyl]phosphonate (6 l),[3] diethyl-1-heptynylphosphonate
(6 m),[21] diethyl-1-hexynylphosphonate (6n),[17] diethyl-3-(ben-
zyloxy)-1-propynylphosphonate (6o),[22] and diethyl(ethoxycarbonyl)
phosphonate (6p),[23] have been characterized by comparing their
1H and 13 C spectral data (see Supporting Information) with those
reported in the literature.
Diethyl[(4-tert-butylphenyl)ethynyl]phosphonate (6c): yellow oil.
1H NMR (400MHz, CDCl3): d = 7.52–7.50 (m, 2H, ArÀH), 7.40 (d,
J =8.8 Hz, 2H, ArÀH), 4.27–4.19 (m, 4H, ÀCH2CH3), 1.41 (t,
t
J = 6.8 Hz, 6H, ÀCH2CH3), 1.32 (s, 9H, BuÀAr). 13 C NMR (100 MHz,
CDCl3): d = 154.3, 132.4 (d, JCÀP = 2.5 Hz), 125.5, 116.3 (d, JCÀP = 5.6
Hz), 99.5 (d, JCÀP = 53.0 Hz), 77.6 (d, JCÀP = 298.8 Hz), 63.1 (d, JCÀP
=
5.5 Hz), 35.0, 30.9 (d, JCÀP = 6.7 Hz), 16.0 (d, JCÀP = 7.0Hz). Elemental
analysis: calc. for C16H23PO3 C, 65.29; H, 7.88; found C, 65.05; H,
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Copyright © 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 830–835

An efficient and recyclable silica-supported carbene–Cu(II) catalyst
Table 1. Effect of catalyst and solvent on the oxidative CÀP cross-coupling of terminal alkyne with H-phosphonatea
Cu catalyst
PO(OEt)2
H(O)P(OEt)2
Catalyst
Solvent, air
Entry
Solvent
Yieldb (%)/SD
1
2a
2b
2c
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
90/3.21
69/2.65
61/4.17
65/1.78
55/2.43
29c/3.01
Trace
81c/1.97
80d/2.58
91/2.96
89c/3.01
83/2.54
80c/2.17
0
2
3
4
2d
5
Cu(OAc)2
Cu(OAc)2
CuI
6
7
8
CuI
9
CuI
e
e
10
11
12
13
14
15
16
17
(IPr)Cu(OAc)2
(IPr)Cu(OAc)2
(IPr)CuIe
(IPr)CuIe
2a
2a
THF
0
2a
Toluene
Methanol
0
2a
0
aReaction conditions: Cu catalyst (containing Cu 0.05 mmol), phenylacetylene (1.0mmol), diethyl hydrogen phosphate (1.2mmol) was carried out in
solvent (2.0ml) at room temperature for 24 h under air.
bIsolated yield and standard deviation (SD) obtained from three times.
cIn the presence of K2CO3 as base.
dIn the presence of Et3N as base.
eIPr = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene).
Furthermore, the oxidative CÀP cross-coupling reactions of termi-
nal alkyne with H-phosphonate catalyzed by the NHCÀCu(I)/(II)
complexes under homogeneous conditions were also investigated.
It was found that the coupling reaction could be finished under
homogeneous conditions in the present or absence of base, which
gives the desired product in good yield (Table 1, entries 10–13).
Finally, SiO2ÀNHCÀCu(II) 2a was selected as catalyst for the follow-
ing reaction without additional base considering the highly effi-
cient and recyclable catalyst used, and environment friendliness.
The effects of solvents on the model reaction were also exam-
ined in the presence of SiO2ÀNHCÀCu(II) 2a as catalyst. The use
of DMSO as solvent gave the best results among the solvents in-
cluding DMF, THF, toluene, and methanol. It is important to note
that no desired cross-coupling product was isolated when the
reaction was carried out in DMF, THF, toluene, or methanol
(Table 1, entries 14–17). A similar solvent effect was also observed
in the literature.[3,24] With respect to the effective catalyst loading,
5.0 mol% SiO2ÀNHCÀCu(II) 2a was found to be optimal. When
less than 5.0 mol% of SiO2ÀNHCÀCu(II) 2a was used, the reaction
did not go to completion. However, no significant improvements
were observed with more 5.0 mol% SiO2ÀNHCÀCu(II) 2a used in
the reaction.
generate the corresponding functionalized alkynylphosphonates
in good yields (Table 2, entries 1–10). It is worth noting that the
oxidative cross-coupling of terminal alkynes with H-phosphonate
is relatively insensitive to the electronic characteristics of a sub-
stituent as well as its location in the aromatic terminal alkyne,
and led to good yields.[3]
Most important, we also find that aliphatic alkynes, such as
1-hexyne and 1-heptyne, will also undergo oxidative carbon–
phosphorus bond cross-coupling smoothly with excellent yields.
It is superior to terminal aromatic alkynes used as substrates
(Table 2, entries 13 and 14 vs. entries 1–10). Fortunately, ethyl
propiolate and 3-(benzyloxy)-1-propyne also gave high yields of
oxidative-coupling products with diethyl hydrogen phosphate
(Table 2, entries 15 and 16). The scope of this reaction was
extended to heteroaryl alkynes, such as 3-ethynylpyridine, with
good results also obtained (Table 2, entry 11). Besides diethyl
hydrogen phosphate, the H-phosphonate diisopropyl hydrogen
phosphate was also used as reaction partner with phenylacety-
lene, and the result indicated that 91% yield of the corresponding
di(isopropyl)-phenylethynylphosphonate 6 l was isolated under
the present reaction conditions (Table 2, entry 12).
The recyclability and reusability of SiO2ÀNHCÀCu(II) catalyst
2a was also investigated. After the reaction, the catalyst 2a was
separated by simple filtration and washed. After drying, it could
be reused directly without further purification. The recovered cat-
alyst was used in the next run and almost consistent activity was
observed for six consecutive cycles (Table 3). Meanwhile, copper
leaching in SiO2ÀNHCÀCu(II) catalyst 2a was determined. AAS
analysis of the clear filtrates obtained by filtration after the reaction
indicated that Cu content was <0.3 ppm.
Under the optimized reaction conditions, the oxidative C=P
cross-coupling reaction of substituted phenylacetylenes with
H-phosphonates compounds was then investigated using 2a as
the catalyst. The results are summarized in Table 2. Various sub-
stituted phenylacetylene derivatives bearing either electron-
donating or electron-withdrawing functional groups, such as Cl,
Br, CH3, OCH3, C6H5, tert-C4H9 and NH2, on the phenyl rings could
be reacted with diethyl hydrogen phosphate smoothly to
Appl. Organometal. Chem. 2011, 25, 830–835
Copyright © 2011 John Wiley & Sons, Ltd.
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P. Liu et al.
Table 2. SiO2ÀNHCÀCu(II)-catalyzed oxidative coupling of terminal alkynes with H-phosphonatesa
SiO2-NHC-CuII (2a)
PO(OR1)2
HPO(OR1)2
H
+
R
R
DMSO, air
5
6
4
Entry
1
Product
Yieldb (%)/SD
90/3.21
PO(OEt)2
6a
2
3
4
5
6
7
73/1.56
82/2.63
78/4.21
68/4.31
70/4.13
76/3.25
PO(OEt)2
PO(OEt)2
6b
6c
6d
H3CO
F
PO(OEt)2
PO(OEt)2
PO(OEt)2
PO(OEt)2
6e
6f
6g
Cl
Br
8
9
80/3.86
75/2.75
PO(OEt)2
PO(OEt)2
6h
H2N
6i
Br
N
10
11
81/1.19
77/3.47
PO(OEt)2
6j
PO(OEt)2
6k
12
13
91/1.26
PO(Oi-Pr)2
PO(OEt)2
PO(OEt)2
6l
96c/2.57
6m
6n
14
15
95c/2.76
95c/3.58
PO(OEt)2
PO(OEt)2
6o
O
16
87/2.27
C2H5O2C
6p
aReaction conditions: SiO2ÀNHCÀCu(II) 2a (50 mg, containing Cu 0.05 mmol, 5mol%), terminal alkyne (1.0mmol), and H-phosphonate (1.2mmol) was
carried out in DMSO (2.0ml) at room temperature for 24 h under air.
bIsolated yield and standard deviation (SD) obtained from three times.
cReaction for 12 h.
recycled by filtration and reused six times without apparent loss
of catalytic activity. Thus this method constitutes an economical
Conclusions
The efficient and recyclable silica-supported carbeneÀCu(II) com-
and environmentally benign process for the synthesis of alkynyl-
phosphonate compounds.
plex SiO2ÀNHCÀCu(II) 2a as catalyst for aerobic oxidative cou-
pling of terminal alkynes with H-phosphonates in the absence
of any base at room temperature has been developed. The reac-
tions of a variety of terminal alkynes with H-phosphonates gener-
SUPPORTING INFORMATION
ated the corresponding alkynylphosphonate products in good
to excellent yields. In addition, SiO2ÀNHCÀCu(II) 2a could be
Supporting information may be found in the online version of
this article.
wileyonlinelibrary.com/journal/aoc
Copyright © 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 830–835

An efficient and recyclable silica-supported carbene–Cu(II) catalyst
Table 3. Successive trials using recoverable SiO2ÀNHCÀCu(II) catalysta
Reused
SiO2-NHC-CuII (2a)
Ph
H
+
Ph
HPO(OEt)2
PO(OEt)2
DMSO, air
Trial
Yieldb(%)/SD
Trial
Yieldb (%)/SD
1
2
3
90/2.37
89/2.69
88/2.54
4
5
6
87/2.42
85/3.47
83/3.97
aReaction conditions: SiO2ÀNHCÀCu(II) 2a (50mg, containing Cu 0.05mmol), phenylacetylene (1.0mmol), and diethyl hydrogen phosphate (1.2mmol)
was carried out in DMSO (2.0ml) at room temperature for 24 h under air.
bIsolated yield and standard deviation (SD) obtained from three times.
[9] a) E. F. Connor, G. W. Nyce, M. Myers, A. Mock, J. L. Hedrick, J. Am.
Acknowledgements
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Am. Chem. Soc. 2007, 129, 5832.
We gratefully acknowledge financial support by the National Nat-
ural Science Foundation of China (No. 20972057) and the Natural
Science Foundation of Anhui Province (No. 090416223).
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