Mixed-ligand complexes of copper(I) with diimines and phosphines: Effective catalysts for the coupling of phenylacetylene with halobenzene

Article abstract of DOI:10.1016/j.poly.2009.09.021

New copper(I) mixed-ligand complexes 1-4 of the formula Cu(N-N)PR₃X, where N-N = 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′dimbpy) and PR₃ = tricyclohexylphosphine, tris(2-cyanoethyl)phosph

Full text of DOI:10.1016/j.poly.2009.09.021

Polyhedron 28 (2009) 4072–4076
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Mixed-ligand complexes of copper(I) with diimines and phosphines: Effective
catalysts for the coupling of phenylacetylene with halobenzene
Atif Fazal a, Sahar Al-Fayez b, Laila H. Abdel-Rahman b, Zaki S. Seddigi c, Abdul Rahman Al-Arfaj a,
Bassam El Ali a, Mohammad A. Dastageer d, Mohammad A. Gondal d, Mohammed Fettouhi a,
*
a Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
b Department of Chemistry, Science Girls College, Dammam 31113, Saudi Arabia
c Department of Chemistry, Umm Al-Qura University, Makkah, Saudi Arabia
d Department of Physics, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 July 2009
Accepted 16 September 2009
Available online 29 September 2009
New copper(I) mixed-ligand complexes 1–4 of the formula Cu(N–N)PR3X, where N–N =
1,10-phenanthroline (phen), 2,20-bipyridine (bpy), 5,50-dimethyl-2,20-bipyridine (5,50dimbpy) and
PR3 = tricyclohexylphosphine, tris(2-cyanoethyl)phosphine and isopropyldiphenylphosphine, have been
synthesized. The complexes were characterized by EA, IR, NMR and single crystal X-ray diffraction. The
solution fluorescence emission spectra were measured. The single crystal X-ray analysis showed that
the copper(I) ion is four-coordinate with a distorted tetrahedral geometry. The complexes catalyze
the formation of diphenylacetylene from the coupling of halobenzene with phenylacetylene. The com-
plex Cu(5,50-dimethylbpy)P(cyhexyl)3I showed the highest catalytic activity. At room temperature all
four complexes exhibit, in dichloromethane, emission maxima in the 329–344 nm range, corresponding
to intra-ligand excited states.
Keywords:
Copper(I) complexes
Crystal structures
Catalysis
Fluorescence
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
there is a need to develop new well defined and versatile solu-
ble catalysts that are active under milder conditions and less
Cross-coupling reactions to form C–C and C-heteroatom
bonds are of major importance in organic synthesis. While pal-
ladium-catalyzed reactions have seen important developments
[1–5], copper-catalyzed reactions remain more economically
attractive. The classical copper-based Ullman cross-coupling
chemistry [6,7] has many disadvantages such as the drastic
experimental conditions, requiring stoichiometric copper sys-
tems and affording rather moderate yields, in addition to the
sensitivity to the substrate substituents [8,9]. Mechanistic stud-
ies have revealed that soluble cuprous species are most likely
the active ones [10]. Recently, an increase of interest in cop-
per-based cross-coupling chemistry has taken place [11–16]
and versatile Cu(I)-based systems have been reported for C–C
and C–N bond formation to produce arylacetylenes and triaryl-
amines [17,18]. Most of the catalytic systems reported so far
are not well defined as they are generated in situ, based on
copper salts, ligands and additives. They require relatively
prolonged reaction times and convert effectively, among aryl
halides, only the most reactive aryl iodide substrates. Therefore
sensitive to the functional groups on the substrates.
Polypyridine metal complexes have been widely investigated
for their photophysical properties, with various potential appli-
cations such as electroluminescent devices and solar energy con-
version [19–21]. Complexes with higher quantum yields and
emission shifts towards the visible range are being targeted
[22,23]. Ru(II) complexes represent the most extensively investi-
gated family [19]. Despite the fact that copper-based complexes
are more attractive, both from a cost and a toxicity point of
view, they have been less studied than their ruthenium counter-
parts [24]. Due to the diversity of their excited states, mixed-li-
gand copper(I) complexes based on polypyridine and phosphine
ligands appear to have significant potential for photocatalytic
applications. However, only few reports exist in the literature,
including photochemical isomerization of norbornadiene to
quadricyclane [25], reduction of cobalt (III) complexes [26] and
reduction of methyl viologen [27]. As part of our interest in cop-
per(I) mixed-ligand complexes [28], we describe herein the
synthesis, spectroscopic characterization, X-ray structure and
the results of the catalytic activity of four new mixed-ligand
copper(I) complexes as versatile catalysts in the formation of
aryl-acetylene bonds. Results of solution emission studies are
also presented.
* Corresponding author. Tel.: +966 38602941; fax: +966 38604277.
E-mail address: fettouhi@kfupm.edu.sa (M. Fettouhi).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.09.021

A. Fazal et al. / Polyhedron 28 (2009) 4072–4076
4073
2.3. General procedure for the synthesis of complexes 1–4
2. Experimental section
The reaction mixture of the diimine (1.0 mmol), CuX (1.0 mmol)
and the phosphine (1.0 mmol) in 20.0 mL of dimethylformamide
was stirred at 60 °C for 6 h. The mixture was filtered and the fil-
trate left to evaporate for 3–4 weeks to afford yellow or orange
crystalline solids.
2.1. General information
The experiments were carried out under an atmosphere of
dried nitrogen using standard Schlenk techniques. Solvents were
purified by conventional procedures and freshly distilled before
use. All chemicals were purchased form Aldrich Chemicals. The
compounds halobenzene, phenylacetylene, CuX (X = Br, I), the dii-
mines and phosphines were used as received without further
purification. The melting points were recorded using a Büchi
510 melting point apparatus and are uncorrected. 1H NMR, 13C
NMR and 31P NMR were recorded on a JEOL LAMBDA 500 spec-
trometer using tetramethylsilane and 85% H3PO4 as internal and
external references respectively. Mass spectra were recorded on
GC–MS Varian Saturn 2000 spectrometer. IR spectra were re-
corded using a Perkin Elmer FTIR 16FPC spectrometer. Gas chro-
matograms were obtained using an HP 6890 Plus instrument.
Elemental analyses were carried out using a Perkin Elmer 2400
CHNS analyzer. UV–Vis spectra were obtained using a Perkin
Elmer Lambda EZ 210 spectrometer. Solution photoluminescence
measurements were carried out using a Shimadzu PF-5301 PC
spectrofluorometer in dichloromethane with concentrations of
2 ꢀ 10ꢁ4 M for 1, 3, 4 and 2.5 ꢀ 10ꢁ4 M for 2. Excitations were
at 290 nm for each of the compounds 1, 3 and 4 while compound
2 was excited at 300 nm.
2.3.1. Cu(Phen)P[(CH2)2CN]3I
Complex 1: yellow, yield. 68%, M.p. (°C): 235–236. Anal. Calc. for
C21H20CuIN5P: C, 44.73; H, 3.58; N, 12.42. Found: C, 44.14; H, 3.56;
N, 11.62%. IR (KBr, cmꢁ1): 3043s, 2911s, 2240s (
m
C„N), 1921w,
1586m, 1500m, 1416s, 1206m, 1050s, 949m, 839m, 753s, 509m,
458m. UV–Vis (DCM) k, nm (
, Mꢁ1 cmꢁ1): 269.0 (8360), 290.5 sh
e
(3390), 315.0 sh (1020), 383.0 (769). 1H NMR (r.t., DMSO-d6, d in
ppm): 9.25 (br. s, H2,9phen, 2H), 8.76 (br. s, H4,7phen, 2H), 8.21 (br.
s, H5,6phen, 2H), 8.05 (br. s, H3,8phen, 2H), 2.75–2.80 (m, PCH2, 6H),
2.13–2.17 (m, CH2CN, 6H). 31P NMR (r.t., DMSO-d6, 202.35 MHz):
ꢁ12.09.
2.3.2. Cu(bpy)P[(Ph)2(i-Pr)]Br
Complex 2: orange, yield. 60%, M.p. (°C): 176–177. Anal. Calc. for
C25H25CuBrN2P: C, 56.87; H, 4.78; N, 5.31. Found: C, 56.65; H, 4.78;
N, 5.74%. IR (KBr, cmꢁ1): 3773m, 3550s, 3004s, 2876s, 2760m,
2706m, 1975m, 1896m, 1818w, 1667w, 1577s, 1423s, 1298s,
1086s, 1001s, 753s, 661s, 470s. UV–Vis (DCM) k, nm (
e
, Mꢁ1
cmꢁ1): 288.5 (10 600), 387.5 (976). 1H NMR (r.t., DMSO-d6, d in
0
0
ppm): 8.70 (br. s, H6,6 bipy, 2H), 8.56 (br. s, H3,3 bipy, 2H), 8.14 (br.
2.2. X-ray structure determination
0
0
s, H4,4 bipy, 2H), 7.63 (br. s, H5,5 bipy, 2H), 7.40 (m, Ph, 10H), 2.77
(br. s, i-Pr, 1H), 0.81–0.86 (dd, i-Pr, 6H). 31P NMR (r.t., DMSO-d6,
202.35 MHz): 5.87.
Data were collected at 120 K on a Bruker-Axs Smart Apex dif-
fractometer using graphite monochromatized Mo K
a radiation
(k = 0.71073 Å). An empirical absorption correction was applied
using the SADABS program [29]. All structures were solved by direct
methods and subsequent Fourier difference techniques and refined
anisotropically for all non-hydrogen atoms by full-matrix least-
squares calculations on F2 using the SHELXTL package [30]. All hydro-
gen atoms, except for the hydration water molecule in 4, were in-
cluded at calculated positions using a riding model. Crystal data
and details of data collection and structure refinements are given
in Table 1. Further details are included in the Supporting
Information.
2.3.3. Cu(5,50-dimethylbpy)P[(cyhexyl)3]I
Complex 3: orange, yield. 62%, M.p. (°C): 180–181. Anal. Calc. for
C30H45CuIN2P: C, 54.99; H, 6.94; N, 4.28. Found: C, 55.50; H, 7.24;
N, 4.19%. IR (KBr, cmꢁ1): 3869m, 3784m, 3708m, 3494m, 3426m,
3341m, 3155m, 3023m, 2920s, 2849s, 2651m, 2372m, 1966w,
1664m, 1573m, 1446s, 1161m, 1001m, 840m, 730m, 474m. UV–
Vis (DCM) k, nm (
e
, Mꢁ1 cmꢁ1): 251.0 (9720), 303.0 (5540), 312.0
sh (5330), 429.5 (1870). 1H NMR (r.t., DMSO-d6, d in ppm): 8.56
0
0
0
(s, H6,6 Dimbipy, 2H), 8.41 (s, H3,3 Dimbipy, 2H), 7.97 (s, H4,4
,
Dimbipy
Table 1
Crystal and structure refinement data for 1–4.
Complex
1
2
3
4
Chemical formula
Formula weight
Space group (No.)
Temperature (K)
Radiation
C21H20CuIN5P
563.83
C2/c (15)
C25H25BrCuN2P
527.89
P2(1)/n (14)
C30H45CuIN2P
655.09
C27H29BrCuN2P.0.5(H2O)
564.95
C2/c (15)
120
ꢀ
P1 (2)
120
120
120
Vo Ka (k = 0.71073 Å)
qcalc (g cmꢁ3
a (Å)
)
1.725
1.515
1.457
1.422
24.844(2)
7.9571(7)
22.833(2)
90
105.831(1)
90
4342.6(7)
8
2.519
12.082(2)
13.512(2)
14.201(2)
90
93.566(2)
90
2313.9(5)
4
2.754
9.9791(7)
18.486(1)
18.536(1)
117.671(1)
96.773(1)
92.717(1)
2986.8(4)
4
21.126(3)
16.557(2)
17.851(3)
90
122.293(2)
90
5278.2(13)
8
2.421
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
l
(cmꢁ1
)
1.839
Reflections collected
Reflections unique (R(int))
18 504
5214 (0.0273)
4590
0.0258
0.0653
19 955
5505 (0.0218)
4940
0.0283
0.0723
26 522
13755 (0.0208)
11884
0.0339
0.0775
22 822
6289 (0.0497)
5129
0.0409
0.0949
Reflections observed (I > 2
r(I))
a
R1
b
wR2
a
R1
wR2 = {
=
R
(jFoj ꢁ jFcj)/
R
jFoj for (I > 2
r
(I)).
R
[w(F20 ꢁ F2c Þ ]/
R
[w(F20)2]}1/2 for all data.
b
2

4074
A. Fazal et al. / Polyhedron 28 (2009) 4072–4076
2H), 2.43 (s, CH3, 6H), 1.26–1.84 (m, c-hexyl, 33H). 31P NMR
(DMSO-d6, 202.35 MHz): ꢁ10.68.
2.3.4. Cu(5,50-dimethylbpy)P[(Ph)2(i-Pr)]Br. 0.5 H2O
Complex 4: yellow, yield. 66%, M.p. (°C): 170–171. Anal. Calc. for
C27H30CuBrN2O0.5P: C, 57.39; H, 5.36; N, 4.96. Found: C, 55.61; H,
5.13; N, 5.10%. IR (KBr, cmꢁ1): 3938m, 3771m, 3583m, 3419m,
3306m, 3233m, 3089m, 2813s, 2655s, 2531s, 2450s, 2240m,
1973m, 1838m, 1675m, 1572s, 1447s, 1239s, 1090m, 1031s,
835m, 694s, 513s. UV–Vis (DCM) k, nm (e
, Mꢁ1 cmꢁ1): 253.0
(15 600), 267.5 sh (13 300), 300.5 (10 900), 382.5 (1140). 1H
0
0
NMR (r.t., DMSO-d6, d in ppm): 8.41 (br. s, H6,6 ,3,3 Dimbipy, 4H),
0
7.90 (br. s, H4,4 Dimbipy, 2H), 7.40 (s, Ph, 10H), 2.75 (br. s, i-Pr, 1H),
2.33 (s, Dimbipy CH3, 6H), 0.79–0.84 (dd, i-Pr CH3, 6H). 31P NMR
(DMSO-d6, = 202.35 MHz): 6.09.
Fig. 2. Molecular structure of complex 2.
2.4. General procedure for the catalytic coupling of phenylacetylene
with halobenzene using catalysts 1–4
In a nitrogen-filled glove box, a Schlenk tube equipped with a
Teflon stirring bar, was charged with potassium carbonate
(2.00 mmol) and the catalyst (10.0 mol% with respect to phenyl-
acetylene), and was sealed with a rubber septum. The sealed
tube was taken out of the glove box and phenylacetylene
(2.50 mmol), iodobenzene (2.00 mmol) and toluene (15.0 mL)
were injected into the tube through the septum. The mixture
was then stirred at 115 °C for 24 h. The reaction mixture was
then cooled to room temperature and filtered to remove any
insoluble materials. The solvent was removed and the dry resi-
due was recrystallized from pentane giving the product as a
white solid.
M.p.: 62–63 °C. Anal.Calc. for C14H10: C, 94.33; H, 5.67. Found: C,
93.80; H, 6.02%. 1H NMR (500 MHz, DMSO-d6, d in ppm): 7.41–7.43
(m, 4H), 7.54–7.56 (m, 6H). 13C{1H} NMR (125.65 MHz, DMSO-d6, d
in ppm): 132.12, 130.81, 128.70, 123.20, 88.98.
X
N
Fig. 3. Molecular structure of complex 3.
PR1R2R3
Cu
N
N
+
CuX
DMF
6h, 60 oC
N
PR1R2R3
Scheme 1. Synthesis of complexes 1–4.
Fig. 1. Molecular structure of complex 1.
Fig. 4. Molecular structure of complex 4.

A. Fazal et al. / Polyhedron 28 (2009) 4072–4076
4075
Table 2
Selected bond lengths and bond angles for 1–4.
Complex 1
Complex 2
Complex 3
Complex 4
Cu1–N1
Cu1–N2
Cu1–P1
Cu1–I1
N2–Cu1–N1
N2–Cu1–P1
N1–Cu1–P1
N2–Cu1–I1
N1–Cu1–I1
P1–Cu1–I1
2.083(2)
2.051(2)
Cu1–N1
Cu1–N2
Cu1–P1
Cu1–Br1
N1–Cu1–N2
N1–Cu1–P1
N2–Cu1–P1
N1–Cu1–Br1
N2–Cu1–Br1
P1–Cu1–Br1
2.086(2)
2.095(2)
Cu1–N1
Cu1–N2
Cu1–P1
Cu1–I1
N1–Cu1–N2
N1–Cu1–P1
N2–Cu1–P1
N1–Cu1–I1
N2–Cu1–I1
P1–Cu1–I1
2.075(2)
2.076(2)
2.2033(8)
2.5999(4)
78.99(9)
112.84(6)
120.22(6)
99.63(6)
113.76(6)
120.57(2)
Cu1–N1
Cu1–N2
Cu1–P1
Cu1–Br1
N1–Cu1–N2
N1–Cu1–P1
N2–Cu1–P1
N1–Cu1–Br1
N2–Cu1–Br1
P1–Cu1–Br1
2.064(2)
2.069(2)
2.1817(6)
2.6427(4)
81.17(7)
132.71(5)
117.14(5)
106.28(5)
108.31(5)
107.66(2)
2.1967(5)
2.4395(4)
78.52(6)
117.93(5)
118.70(5)
102.95(5)
107.66(5)
122.16(2)
2.1792(8)
2.4933(5)
79.44(9)
123.36(6)
125.41(6)
104.89(6)
104.74(6)
113.34(2)
3.2. Molecular structures of complexes 1–4
The molecular structures of complexes 1–4 were further con-
firmed by single crystal X-ray analysis (Figs. 1–4). In the four
complexes, the copper(I) ion is four-coordinate with a distorted
tetrahedral geometry (Table 2). The bond lengths and bond angles
are in the same range as those reported for similar compounds
[28]. In complex 1, two of the three cyanoethyl groups adopt a
conformation close to the expected energetically favorable anti
conformation. The corresponding torsion angles are P1–C13–
C14–C15 = ꢁ167.44° and P1–C19–C20–C21 = 178.52°. The third
one has a less favorable synclinal conformation (P1–C16–C17–
C18 = ꢁ75.69°). Due to the rigidity of 1,10-phenanthroline, the
chelate bite angle is larger in 1 (81.17°) than for 2,20-bipyridine
and its derivative in compounds 2–4 (78.52–79.44°). In
compounds 2 and 4, the isopropyl group is anti to the bromo li-
gand with torsion angles C11–P1–Cu1–Br1 of 167.89° and C25–
P1–Cu1–Br1 of 172.96°, respectively. For these two compounds,
the electronic effect of the methyl substituent on the bipyridine
ligand is reflected on the Cu–N bond distances, which are shorter
in the 5,50-dimethylbipyridine-based complex and associated
with a longer Cu–Br bond distance. In compound 3, the cyclo-
hexyl groups adopt a chair conformation. In this case, the large
cone angle of the phosphine and its conformation induces a dis-
tortion that affects more significantly the bond angles P1–Cu1–
I1 and P1–Cu1–N2, 120.57° and 120.22°, respectively, in one of
the molecules of the asymmetric unit. Compound 4 crystallizes
as a hydrate and the bromo ligand is engaged in hydrogen bond-
ing with the water molecule.
Fig. 5. Emission spectra of 1–4 at room temperature in dichloromethane.
3. Results and discussion
3.1. Synthesis of the complexes
Complexes 1ꢁ4 were synthesized as shown in Scheme 1. The
reaction of stoichiometric amounts of the diimine and the phos-
phine with CuX in anhydrous dimethylformamide under reflux
afforded mononuclear complexes in 60–68% yields. Complexes
1, 2 and 4 are air stable while complex 3 decomposes after few
weeks in air. All the compounds were characterized by elemental
analysis, FT-IR, UV–Vis, 1H and 31P NMR spectroscopy. The 31P
NMR resonance shows a downfield shift in the range of 5.45–
12.46 ppm relative to the free ligands, supporting the fact that
the phosphorus atoms coordinate to the metal ion.
3.3. Catalysis
The four complexes were examined as catalysts for the coupling
of aryl halides with phenyl acetylene to give diphenylacetylene
using K2CO3 as a base in two different solvents, namely toluene
Table 3
Isolated yields of the reaction of aryl-halides with phenylacetylene in the presence of 10 mol% of 1–4.
x
10 mol % of complexes (1-4)
+
K2CO3 , (115 oC)
X
Catalyst
1
2
3
4
I
Br
Cl
69a
7
4
45b
25
14
66
6
3
55
28
5
95
23
6
75
43
28
73
16
6
59
39
22
a
In toluene.
In DMF.
b

4076
A. Fazal et al. / Polyhedron 28 (2009) 4072–4076
and dimethylformamide (Table 3). Good yields were obtained in
the case of iodobenzene. Complex 3 showed the highest activity.
Lower yields were obtained for bromo and chlorobenzene. Com-
pound 3 appears to be more active for the formation of diphenyl-
acetylene than the previously reported Cu(phen)(PPh3)Br
compound [17]. For iodobezene, the use of toluene as a solvent
gives higher yields than dimethylformamide, however the opposite
is observed for bromo and chlorobenzene.
CCDC Nos. 731100, 731102, 731101 and 731099 for 1, 2, 3 and 4,
respectively. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgments
We gratefully acknowledge the King Fahd University of Petro-
leum and Minerals, Dhahran, Saudi Arabia for financial support.
3.4. Absorption and emission studies in solution
The absorption and emission spectra were recored in dichloro-
methane at room temparature. By comparison to the diimine free
ligand absorption spectra, the following changes are observed
upon coordination. For the metal complexes, the weakly structured
and intense UV absorption bands (kmax = 250–315 nm), attributed
to intra-ligand transitions, are shifted to lower energies compared
to the free ligands. This shift is more pronounced in the 5,50-dim-
ethylbipyridine based complexes 3 and 4. A new broad band in
the 320–500 nm range, attributed to a metal to ligand charge
transfer (MLCT), appears.
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4. Conclusion
New copper(I) mixed-ligand complexes based on diimines and
phosphines have been synthesized and characterized. In the four
compounds, the copper(I) ion is four-coordinate with a distorted
tetrahedral geometry. The complexes catalyze the coupling of
halobenzene with phenylacetylene to form diphenylacetylene.
Good yields were obtained in the case of iodobenzene, while lower
yields were obtained for bromo and chlorobenzene. The complex
Cu(5,50-dimethylbpy)P(cyhexyl)3I showed the highest catalytic
activity. It is also more active than the previously reported Cu(neo-
cup)(PPh3)Br and Cu(Phen)(PPh3)Br catalysts. The photocatalytic
studies of these complexes are underway.
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5. Supplementary data
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic data Center with