Synthesis, crystal structure, and conjugation properties of phenanthroline copper phosphine complexes

Article abstract of DOI:10.1016/j.ica.2012.09.028

Facial synthetic method of 4,7-position conjugation extended phenanthrolines and X-ray structure of copper phosphine phenanthroline complexe were reported. The crystal structures showed π-stacking and hydrogen bonding, and a small torsional angle between phen and phenylacetylene. These complexes exhibited strong conjugation dependant MLCT luminescence. The electronic and fluorescence spectra displayed a gradual red shift of the MLCT band as the conjugation increased. The presence of the phenyl groups reduced the energy of the π^∞ state in the d-π^∞ MLCT transition, allowing for the red shift. The electron-donating tri-isopropylsilyl (TIPS) groups on the ethynyl moiety increased the energy of the MLCT charge vector, allowing for the blue shift at the luminescence.

Full text of DOI:10.1016/j.ica.2012.09.028

Inorganica Chimica Acta 394 (2013) 710–714
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Note
Synthesis, crystal structure, and conjugation properties of phenanthroline
copper phosphine complexes
Hyungsock Suh a, , Dominick J. Casadonte Jr. b, Louisa Hope-Weeks b, Han-Je Kim c, Beomsik Kim a,
⇑
Taesun Chang a,
⇑
a Green Chemistry Research Division, KRICT (Korea Research Institute of Chemical Technology), Yuseong, Daejeon 305-600, Republic of Korea
b Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
c Department of Science Education, Kongju National University of Education, Bongwhang Dong, Gongju 314-711, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 June 2012
Received in revised form 6 August 2012
Accepted 11 September 2012
Available online 8 October 2012
Facial synthetic method of 4,7-position conjugation extended phenanthrolines and X-ray structure of
copper phosphine phenanthroline complexe were reported. The crystal structures showed
p-stacking
and hydrogen bonding, and a small torsional angle between phen and phenylacetylene. These complexes
exhibited strong conjugation dependant MLCT luminescence. The electronic and fluorescence spectra dis-
played a gradual red shift of the MLCT band as the conjugation increased. The presence of the phenyl
groups reduced the energy of the p⁄ state in the d–p⁄ MLCT transition, allowing for the red shift. The elec-
tron-donating tri-isopropylsilyl (TIPS) groups on the ethynyl moiety increased the energy of the MLCT
charge vector, allowing for the blue shift at the luminescence.
Keywords:
Phenanthroline
Mixed ligand diimine complex
Copper complex
MLCT
Ó 2012 Elsevier B.V. All rights reserved.
Luminescence
1. Introduction
Previously, one group made 4,40-diethynylbipyridine, but the
analogous substituted phen using the same reaction conditions
The mixed-ligand metal complexes with diimines were of cur-
rent interest for a wide variety of potential chemical and material
applications, including electroluminescence for organic light emit-
ting diode (OLED) [1], water splitting catalyst [2], luminescence
quenching material [3], strong solid luminescence material [4],
functional metal complexes [5], catalyst for organic synthesis [6],
magnetic materials [7], electron transfer regent [8], and light in-
duced hydrogen production [9].
could not give any desired products [10]. Another group success-
fully made 4,7-diphenylethynyl-3,8-dihexylphen [11]. The hexyl
groups were added to the phen to enhance the solubility, but this
method could not make the simple 4,7-diacetylide phen. Very
recently, one group synthesized 4,7-diethynyl phen using 4,7-
dicarbaldehydehyde phen [12]. But this precursor 4,7-dicarbalde-
hydehyde phen is too expensive to become a largely applicable
materials.
Among these complexes, copper-based complexes are draw
attention due to the low cost advantage [4]. However the emission
signals from charge-transfer (CT) excited states of copper(I) com-
plexes are typically weak and short-lived due to the lowest energy
CT state of a d10 system involves excitation from a metal–ligand d
orbital [3]. The mixed-ligand copper systems including phosphine,
however, looks promising because they exhibit strong lumines-
cence with long lifetimes in the solid or frozen solution state [4].
This stimulated us to prepare phen ligands with unique substitu-
tion patterns. The literatures revealed mostly the 2,9-position
substituted phen, but the 4 or 7 position substituted phen were
scarcely reported.
We devised the facial synthetic method of conjugated 4.7 posi-
tion for phen ligands by simple modified Sonogashira reaction, and
we prepared copper phosphine phenanthroline complexes to study
the conjugation varible luminescnece properties followed by struc-
tural confirmation with exact X-ray crystallography.
2. Experimental and results
Trial with 10 mol% of copper iodide co-catalyst and check the Pd
coupling reaction resulted in less than 30% yield. We found that the
reaction yield dramatically enhanced when we used a copper com-
plexed phen as a reactant. We envisaged that the copper (I) iodide
was first chelated to the nitrogen atoms on the phen, resulting in a
bis Cu(I) structure with changing the color immediately dark red.
The synthetic procedure was shown in Scheme 1. The chemicals
4,7-dichloro phen [13], triisopropylsilyl acetylene, palladium
⇑
Corresponding author. Fax: +82 42 860 7042.
E-mail addresses: hyungsuh@krict.re.kr (H. Suh), bskim@krict.re.kr (B. Kim),
tschang@krict.re.kr (T. Chang).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.09.028

H. Suh et al. / Inorganica Chimica Acta 394 (2013) 710–714
711
1) TIPS acetylene,
Pd(dppf)Cl2,
TIPS
TIPS
TIPS
TIPS
BF4
Cl
Cl
X
Cu(PPh3)4BF4,
Ethanol, Ether,
rt 24h
CuI, TEA, Benzene,
reflux 72h
N
N
2) KCN, H2O,
dichloromethane,
rt 30min
X
N
N
N
N
X=H
X=CH3
X
X
X
X
Cu
1 (X=H)
4 (X=CH3)
Ph3P
PPh3
7 (X=H)
10 (X=CH3)
TIPS
TIPS
Cu(PPh3)4BF4,
Ethanol, Ether,
rt 24h
TBAF, THF,
rt 30min
N
N
N
N
X
X
BF4
N
N
Cu
X
X
2 (X=H)
X
X
1 (X=H)
4 (X=CH3)
Ph3P
5 (X=CH3)
PPh3
8 (X=H)
11 (X=CH3)
1) Phenyl acetylene,
Pd(dppf)Cl2,
Cl
Cl
X
CuI, TEA, Benzene,
reflux 72h
N
N
2) KCN, H2O,
dichloromethane,
rt 30min
X
N
N
X
X=H
X=CH3
X
3 (X=H)
6 (X=CH3)
Cu(PPh3)4BF4, Ethanol,
Ether, rt 24h
N
N
BF4
X
X
Cu
Ph3P
PPh3
9 (X=H)
12 (X=CH3)
Scheme 1. Synthesis of conjugation extended phen and copper phosphine complexes.
catalyst (5 mol%), copper iodide (60 mol%), and triethylamine
(2 eq.) were suspended in benzene. This suspension was refluxed
72 h in an argon environment. After the reaction, the copper ion
was removed by potassium cyanide solution.
The copper phosphine complexes were synthesized by simple
stirring with copper phosphine tetrafluoroborate in ether solution.
The quality X-ray crystal were obtained via slow evaporation of
methanol solution. The X-ray structures of Cu(I) triphenylphos-
phine complex containing 4,7-disubstituted phenylethynyl substi-
tuent was shown in Fig. 1. The phenanthroline molecule was
visible absorption bands at 360–410 nm due to a metal-to-ligand
charge transfer (MLCT) transition. This displayed a gradual red
shift as the conjugation increases. The presence of the electron-
withdrawing (in a
p sense) phenyl groups reduced the energy of
the p⁄ state in the d–p⁄ MLCT transition. On the other hand, the
presence of the electron-donating triisopropylsilyl (TIPS) groups
on the ethynyl moiety increased the energy of the MLCT charge
vector.
The phenylethynyl-substituted phenanthroline showed two
MLCT bands. This might be due to the presence of additional
p-
planar due to the extended
p
-conjugation, but the large torsional
conjugation. Alternatively, it was described by previous study that
the two energy states stem from a staggered or eclipsed conforma-
tion between the phenyl ethynyl and the phenanthroline ring [12].
Fig. 3b showed the uncorrected solution-based emission for all
the 2,9 dimethyl substituted phen Cu(I) complexes. Substitution at
the 2 and 9 positions protected the Cu(I) metal center from Lewis
base solvents, which leaded vibration deactivation of the excited
state [14,15].
Table 1 indicated photophysical data for copper complexes. The
quantum yields and life times were increased compared to dmp
compound. This means extended conjugation enhance the lumines-
cence properties. A gradual red shift occured in the emission
maximum as the ligand conjugation was increased. The 4,7-diethynyl-
substituted Cu(I) complex was red-shifted by about 45 nm relative
to the dmp complex. The TIPS ethynylphen complex was slightly
blue-shifted (by about 3 nm) from the 4,7-diethynyl substituted
complex. This might be due to the electron-donating properties of
TIPS. The phenylethynyl-substituted complex was again red-shifted
(by about 12 nm, based on the lower energy transition) than the
angle (75°) between the phenylethynyl group and the phenanthro-
line was due to the packing force in the crystal lattice. It should be
noted that the triphenylphosphine ligand does not participate in
the
p stacking in the unit cell packing.
The coordination environment around the copper atom was
pseudo-tetrahedral (Fig. 2), which was the expected geometry for
the copper(I) oxidation state. The nitrogen-copper bond length
was 2.1 Å and the phosphorus-copper bond length was 2.3 Å. The
bond angle for N–Cu–N was 80° and the bond angle for P–Cu–P
was 122°. The BF4-centered hydrogen bonding was complex. Bond-
ing between fifteen different hydrogen centers occured. The BF4
was connected via hydrogen bonding to 3 phenylacetylenes, 3 tri-
phenylphosphines, 1 phenanthroline, and 1 methanol. It was nota-
ble that the hydrogen bond length between the methanol and the
BF4 was very short (2.0 and 2.2 Å), indicating that the BF4 hydrogen
bonding was very strong.
Fig. 3 showed the UV–Vis and photoluminescence spectra for all
the 2,9-dimethylsubstituted Cu(I) complexes. The spectra showed

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H. Suh et al. / Inorganica Chimica Acta 394 (2013) 710–714
Fig. 1. X-ray structures of compound 9, (a) asymmetric unit, (b) unit cell contents.
4,7-diethynyl substituted compound. The conjugation in this case
was extended by the phenyl group. The blue-shifted peak at
580 nm was perhaps due to an eclipsed form between the phenyl-
ethynyl and the phenanthroline ring caused by excitation into the
p⁄ manifold of the phenanthroline system, leading to possible rota-
tion about the ethynyl group (i.e., a TICT state) [16].
the coupling reaction. The copper phosphine phenanthroline com-
plexes were prepared and these showed strong luminescence. The
crystal structures indicated the presence of p-stacking and hydro-
gen bonding as a means to facilitate crystal growth, and a small
torsional angle for the phenyl groups when they were attached.
The conjugation-extended phenanthrolines were planar in shape
for an extended
p-conjugation and this planarity allowed for the
p-stacked network. The small torsional angles of the phenanthro-
3. Conclusion
lines were due to both hydrogen bonding and crystal packing
forces. The Cu(I) complexes exhibited a distinctive MLCT (metal-
to-ligand charge transfer) absorption band. The UV–VIS spectra
In summary, we developed efficient coupling of 4,7-position of
phenanthrolines by modifying the amount of copper iodide used in

H. Suh et al. / Inorganica Chimica Acta 394 (2013) 710–714
713
Fig. 3. (a) UV spectra of copper phen phosphine complexed compounds (10ꢁ5M in
dichloromethane); (b) PL spectra of copper phen phosphine complexed compounds
(excited at 400 nm, 10ꢁ5 M in dichloromethane).
Table 1
Photophysical data for copper complexes
Compounds
kmax (Abs), nm
kmax (Em) (nm)
Ua
sb
(ls)
Fig. 2. X-ray structures of compound 9, (a) copper centered coordination environ-
ment, (b) BF4 centered hydrogen bonding.
dmp
11
12
365
395
398
390
540
588
560
585
0.0014
0.0025
0.0019
0.0029
0.33
0.48
0.43
0.52
10
displayed a gradual red shift of the MLCT band as the conjugation
increased. The presence of the phenyl groups reduced the energy of
the p⁄ state in the d–p⁄ MLCT transition, allowing for the red shift.
On the other hand, the presence of the electron-donating tri-
isopropylsilyl (TIPS) groups on the ethynyl moiety increased the
energy of the MLCT charge vector.
a
Error 10%.
b
Fitted by single exponential, measured in argon bubbled dichloromethane at
room temperature. Emission maxima and yields were measured by excitation at
400 nm. Lifetimes were determined by pulsed excitation at 400 nm.
to obtain an ivory solid (compound 1, 0.36 g, 78%). 1H NMR
(300 MHz, CDCl3): 9.18(d, J = 4.5 Hz, 2H), 8.48(s, 2H), 7.80(d,
J = 4.5 Hz, 2H), 7.70(m, 4H), 7.45(m, 6H). 13C NMR (75 MHz, CDCl3):
149.83, 146.27, 131.98, 129.96, 129.51, 128.64, 128.37, 125.47,
125.02, 122.10, 99.21, 85.04. MS: 380.6(M, 100%).
Ten milligram (0.018 mmol) of compound 1 and 27 mg (1.2 eq.)
of Cu(PPh3)4BF4 (previously prepared by refluxing 4:1 M equiva-
lents of triphenylphosphine and one mole equivalent of CuBF4 in
ethanol for eight hours, followed by filtration and washing with
cold ethanol and ether) 16 were suspended in 20 mL of an ether/
ethanol (4:1 v/v) solution. The suspension was stirred overnight
at room temperature. The filtrate solution was evaporated and
purified by alumina column chromatography (dichloromethane
with a methanol gradient; the third of the four bands is the desired
product) to obtain a viscous liquid (compound 9, 15 mg, 67%). Ele-
4. Experimental section
Experimental Details. 0.30 g (1.2 mmol) of 4,7-dichloro-1,10-
phenanthroline, 0.27 g (2.2 eq.) of phenylacetylene, 0.05 g
(0.05 eq.) of (dppf)PdCl2nꢀCH2Cl2, 0.24 g (2 eq.) of triethylamine,
and 0.14 g (0.6 eq.) of copper iodide were suspended in 10 mL of
benzene. This suspension was refluxed for 72 h under argon.
10 mL of a 10% aqueous KCN solution and 10 mL dichloromethane
were then added and the resulting mixture was stirred for 30 min
at room temperature. The organic layer was extracted with 50 mL
of dichloromethane twice and washed with water three times. The
solvent was then evaporated and the solid was purified by alumina
column chromatography (dichloromethane and gradient with
methanol; the middle of the three bands is the desired product)

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H. Suh et al. / Inorganica Chimica Acta 394 (2013) 710–714
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We thanked the Ministry of Knowledge Economy of Korea for
supporting this work through the green house gas research pro-
gram (SI-1108).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2012.09.028.
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