Platinum(II) and copper(I) 1-(2-diphenylphosphino-1-naphthyl) isoquinoline complexes: Synthesis and phosphorescence at ambient conditions

Article abstract of DOI:10.1016/j.ica.2008.03.100

The compounds Pt(quinap)(CN)₂, Cu (quinap)₂⁺ and [Cu(quinap)I]₂ with quinap = 1-(2-diphenylphosphino-1-naphthyl)isoquinoline were synthesized. Quinap is a bidentate ligand which contains a isoquinoline and an ar

Full text of DOI:10.1016/j.ica.2008.03.100

Inorganica Chimica Acta 362 (2009) 226–228
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Platinum(II) and copper(I) 1-(2-diphenylphosphino-1-naphthyl) isoquinoline
complexes: Synthesis and phosphorescence at ambient conditions
*
Valeri Pawlowski, Horst Kunkely, Arnd Vogler
Institut für Anorganische Chemie, Universität Regensburg, D-93040 Regensburg, Germany
a r t i c l e i n f o
a b s t r a c t
The compounds Pt(quinap)(CN)2, CuðquinapÞþ and [Cu(quinap)I]2 with quinap = 1-(2-diphenylphos-
Article history:
2
Received 12 February 2008
Received in revised form 19 March 2008
Accepted 20 March 2008
phino-1-naphthyl)isoquinoline were synthesized. Quinap is a bidentate ligand which contains a isoquin-
oline and an arylphosphine group with CT acceptor properties. Accordingly, the Pt(II) and Cu(I) quinap
complexes are characterized by a phosphorescence originating from the lowest-energy MLCT triplets
with some IL admixture.
Available online 28 March 2008
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Luminescence
Phosphorescence
Platinum(II)
Copper(I)
1-(2-Diphenylphosphino-1-
naphthyl)isoquinoline
1. Introduction
in order to demonstrate the general benefit of this ligand for the
design of MLCT triplet emitters.
Applications of coordination compounds are often dependent
on ligands with desired properties. Transition metal complexes
which are phosphorescent at r.t. frequently rely on the presence
of low-energy MLCT states [1–3]. Suitable ligands should provide
low-energy empty p* orbitals and a large ligand field (LF) strength
in order to push up interfering LF states to higher energies. More-
over, it is also useful when ligands of this type are bidentate since
this increases the stability and decreases the structural flexibility
of the target complexes. The ligand 1-(2-diphenylphosphino-1-
naphthyl)isoquinoline (quinap) largely combines these requested
properties. The pyridine (or quinoline) moiety provides the CT
acceptor function [1–3] while the arylphosphine is a strong-field li-
gand owing to its large r-donor strength and p-accepting nature
[4]. For the same reason, phosphines are able to stabilize metals
in low oxidation states. Generally, such metals are reducing and
therefore are strong CT donors which are required for complexes
with low-energy MLCT states. For an initial confirmation of the ex-
pected behaviour we have previously reported the preparation and
optical properties of ReI(quinap)(CO)3Cl [5]. In addition to this
octahedral d6 complex, square-planar Pt(II) and tetrahedral Cu(I)
complexes are prototypes of d8 and d10 compounds with emitting
MLCT triplets [1–3]. We explored this possibility and selected
quinap complexes of Pt(II) and Cu(I) (Plate 1) for the present study
N
M = Pt(II), Cu(I)
M
PPh 2
2. Experimental
2.1. Materials
Solvents for preparations and spectroscopic measurements
were of spectrograde quality. The compounds Pt(CN)2, 1-(2-
diphenylphosphino-1-naphthyl)isoquinoline (quinap) and CuI
were commercially available from Strem Chemicals.
2.2. Pt(quinap)(CN)2 ꢀ 2.5 H2O
Finely powdered Pt(CN)2 (200 mg, 0.82 mmol) and quinap
(360 mg, 0.82 mmol) in 20 ml DMF were heated under reflux for
30 h. After cooling to r.t. the resulting suspension was filtered.
Upon addition of 150 ml ether to the filtrate an off-white precipi-
tate was formed. It was washed with ether and dried, yielding
120 mg (19%).
* Corresponding author. Tel.: +49 941 943 4716.
E-mail address: arnd.vogler@chemie.uni-regensburg.de (A. Vogler).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.03.100

V. Pawlowski et al. / Inorganica Chimica Acta 362 (2009) 226–228
227
Anal. Calc. for Pt(CN)2quinap ꢀ 2.5 H2O (755.64): C, 54.23;
H, 3.77; N, 5.67. Found: C, 54.17; H, 3.72; N, 5.74.
2.3. [Cu(quinap)I]2
CuI (91 mg, 0.48 mmol) was dissolved in 20 ml argon-saturated
CH3CN. Quinap (210 mg, 0.48 mmol) was added. The solution
turned yellow and yellow crystals separated. After stirring for 1 h
the precipitate was filtered off, washed with EtOH and ether, and
dried yielding 200 mg (66%).
Anal. Calc. for [Cu(quinap)I]2 (1259.88): C, 59.11; H, 3.52;
N, 2.22. Found: C, 58.95; H, 3.64; N, 2.22.
2.4. [Cu(quinap)2]PF6 ꢀ H2O
Quinap (264 mg, 0.6 mmol) was added to
a solution of
Fig. 2. Electronic emission spectrum (kexc = 350 nm) of solid Pt(quinap)(CN)2 at
room temperature, intensity in arbitrary units.
[Cu(CH3CN)4]PF6 (112 mg, 0.3 mmol) in 20 ml CH3CN. The mixture
was refluxed for 30 min under stirring. After removing the solvent
by vacuum evaporation the remaining residue was dissolved in
CH3OH. Solid impurities were filtered off. A mixture of ether/n-
hexane (1:1) was added to the solution. The yellow precipitate
was isolated by filtration, washed with n-hexane and dried over
silica gel yielding 260 mg (78%).
Anal. Calc. for [Cu(quinap)2]PF6 ꢀ H2O (1105.5): C, 67.36;
H, 4.19; N, 2.53. Found: C, 67.59; H, 4.32; N, 2.49.
2.5. Instrumentation
Absorption spectra were measured with an Uvikon 860 spectro-
photometer. Emission spectra were recorded on a Hitachi 850
spectrofluorometer equipped with a Hamamatsu 928 photomulti-
plier up to 900 nm. The luminescence spectra were corrected for
monochromator and photomultiplier efficiency variations.
Fig. 3. Electronic absorption and emission spectrum of [Cu(quinap)I]2 at room te-
M in CH3CN, 1-cm cell. Emission: solid,
kexc = 275 nm, intensity in arbitrary units.
mperature. Absorption: 3.05 ꢀ 10ꢂ5
3. Results
The compounds Pt(quinap)(CN)2, [Cu(quinap)2]PF6 and
[Cu(quinap)I]2 were synthesized in analogy to previous prepara-
tions of related complexes of the type Pt(1,2-diimine)(CN)2 [6],
Pt(diolefine)(CN)2 [7], Pt(bis-arylphosphine)(CN)2, [8], [Cu(bis-
arylphosphine)2]X [9] and [Cu(bis-arylphosphine)I]2 [9,10]. The
syntheses were carried out according to the following equations:
2370), 345 (sh, 3950), 326 (sh, 5600) and 288 (sh, 14000) nm.
The emission appears at 544 nm in CH2Cl2 and at kmax = 588 nm
in the solid state (Fig. 2). The emission spectrum in solution is
not concentration dependent. The quantum yield amounts to
approximately / = 10ꢂ4 at kexc = 380 nm.
The absorption spectrum of [Cu(quinap)2]PF6 in CH3CN and
[Cu(quinap)I]2 (Fig. 3) in CH3CN display bands at kmax = 324 (sh,
e = 13800 Mꢂ1 cmꢂ1), 310 (sh, 16300), 272 (sh, 38000) and 218
(168000) nm and kmax = 320 (sh, 19200), 310 (sh, 21800), 275
(sh, 39700) and 212 (68200) nm, respectively. The emission of
[Cu(quinap)2]PF6 at kmax = 650 nm and [Cu(quinap)I]2 (Fig. 3) at
kmax = 659 nm appears only in the solid state.
PtðCNÞ2 þ quinap ! PtðquinapÞðCNÞ2
½CuðCH3CNÞ4ꢁPF6 þ 2quinap ! ½CuðquinapÞ2ꢁPF6 þ 4CH3CN
2CuI þ 2quinap ! ½CuðquinapÞIꢁ2
ð1Þ
ð2Þ
ð3Þ
The electronic spectrum of Pt(quinap)(CN)2 in CH2Cl2 (Fig. 1)
shows absorptions at kmax = 441 (sh, e = 50 Mꢂ1 cmꢂ1), 365 (sh,
4. Discussion
Square-planar complexes of the type Pt(L–L)(CN)2 with L–
L = neutral bidentate ligand such as 1,2-diimines or bis-arylphos-
phines can be prepared by various procedures. However, according
to our own experience the best method simply involves the reac-
tion of Pt(CN)2 with L–L in a stoichiometric ratio [7,8]. This proce-
dure was also successful for obtaining Pt(quinap)(CN)2.
Tetrahedral cations of the type [CuI(L–L)2]+ with L–L = 1,2-dii-
mines [11,12] or bis-arylphosphines [9] as well as the neutral di-
mers [CuI(L–L)I]2, with L–L = bis-arylphosphines [9,10] have been
also previously synthesized. These dimers are known to contain
tetrahedral iodide-bridged CuI(L–L)I2 fragments. The preparation
of our target compounds [Cu(quinap)2]PF6 and [Cu(quinap)I]2
was achieved by similar procedures.
Fig. 1. Electronic spectra of Pt(quinap)(CN)2 in CH2Cl2 at room temperature, 1-cm
cell. Absorption: (a) 2.50 ꢀ 10ꢂ3 M, (b) 5.36 ꢀ 10ꢂ5 M. Emission: 5.36 ꢀ 10ꢂ5
(under argon, kexc = 380 nm).
M

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V. Pawlowski et al. / Inorganica Chimica Acta 362 (2009) 226–228
The lowest-energy electronic transitions of Pt(II) complexes
and emission spectra of both complexes are very similar the emis-
sion properties are certainly determined by the Cu(quinap) moiety.
It is suggested that in analogy to 1,2-diimine and arylphosphine
complexes the quinap complexes of Cu(I) emit also from MLCT
triplets.
with 1,2-diimine and bis-arylphosphine ligands are frequently of
the MLCT type [1–3,8]. Dependent on the particular ligand, IL ex-
cited states may be also involved [6,8]. The emission is a phospho-
rescence which in some cases appears only in the solid state.
Generally, the solid compounds may consist of columnar structure
with short Pt–Pt distances. These solids are frequently character-
ized by striking colours which are determined by metal-centered
transitions [13]. They occur at much longer wavelength than those
of the mononuclear components. Our target complex Pt(quin-
ap)(CN)2 does apparently not undergo such an aggregation in the
solid state or in solution as indicated by the similarity of the elec-
tronic spectra in dilute solution and in the solid state. The quinap
ligand seems to prevent a close approach of the complex molecules
perpendicular to the square-planar geometry. The longest-wave-
length absorption of Pt(quinap)(CN)2 at kmax = 441 nm (Fig. 1) is as-
signed to a spin-allowed mixed IL (quinap) and MLCT (Pt ?
quinap) transition. Shorter-wavelength bands may be of the IL
type. The emission of Pt(quinap)(CN)2 in solution at kmax = 544 nm
or in the solid state at kmax = 588 nm (Fig. 2) is suggested to origi-
nate from the lowest-energy MLCT/IL triplet in analogy to other
complexes of the general composition Pt(1,2-diimine)(CN)2 [6]
and Pt(bis-arylphosphine)(CN)2 [8].
5. Conclusion
Quinap combines the properties, in particular the CT acceptor
ability, of 1,2-diimines and arylphosphines in one ligand. Accord-
ingly, the new complexes Pt(quinap)(CN)2, CuðquinapÞþ2 and
[Cu(quinap)I]2 are characterized by lowest-energy MLCT triplets
which are emissive at ambient conditions.
Acknowledgement
Financial support by BASF is gratefully acknowledged.
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