Dipyrrin based luminescent cyclometallated palladium and platinum complexes

Article abstract of DOI:10.1039/b908424j

A series of complexes based on the combination of cyclometallated palladium or platinum moieties with functionalized dipyrrin ligands bearing mesityl- or benzonitrile groups have been prepared and characterized both in the solid state and in solution; these compounds exhibit a characteristic dipyrrin-centered luminescence with an emission intensity modulated by the degree of rotational freedom of the aromatic group attached to the dipyrrin chelate. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b908424j

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PAPER
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Dipyrrin based luminescent cyclometallated palladium and platinum
complexes†
Catherine Bronner,a Ste´phane A. Baudron,*a Mir Wais Hosseini,*a Cristian A. Strassert,b,c Aure´lie Guenetb and
Luisa De Cola*b
Received 28th April 2009, Accepted 5th October 2009
First published as an Advance Article on the web 26th October 2009
DOI: 10.1039/b908424j
A series of complexes based on the combination of cyclometallated palladium or platinum moieties
with functionalized dipyrrin ligands bearing mesityl- or benzonitrile groups have been prepared and
characterized both in the solid state and in solution; these compounds exhibit a characteristic
dipyrrin-centered luminescence with an emission intensity modulated by the degree of rotational
freedom of the aromatic group attached to the dipyrrin chelate.
ZnII and octahedral InIII and GaIII complexes have been reported.7,8
In contrast, luminescent heteroleptic complexes of dpms have
Introduction
been much less investigated.9,10 Although the combination of
dpm with cyclometallated fragments to form such heteroleptic
species is pertinent, this remains almost unexplored.10 Indeed,
cyclometallated organometallic moieties such as [(Ppy)M]+ (Ppy =
2-phenylpyridine, M = PtII, PdII) (Scheme 1) offer two cis
available coordination sites and carry a single positive charge.
Furthermore, these fragments are known to be luminescent and,
in particular, phosphorescent as a result of their organometallic
nature and the presence of a heavy metal center.11–13 Thus, it
appeared interesting to prepare neutral complexes by combining
dpm with cyclometallated Pd and Pt moieties and to study
their structural and optical properties. We report herein on the
synthesis, structural and optical characterization of four new metal
complexes formulated (Ppy)M(dpm) with M = PtII and PdII and
dpm = 5-mesityldipyrrin, 1, and 5-(4-cyanophenyl)dipyrrin, 2
(Scheme 1). The mesityl derivative has been chosen as a model
owing to the known enhanced luminescence of its metal complexes
resulting from its restricted conformational freedom.7,8
The search for new emitting coordination compounds is a topic of
current interest.1 In particular, the modulation of the absorption,
emission wavelengths, the excited state lifetime and the quantum
yield is of prime importance. These parameters may be tuned
by the proper choice of the metal centre and the surrounding
ligands. In this respect, the dipyrrin backbone (dpm) (Scheme 1),2
known since the 1920s,3 but which has received a revived interest
with the synthesis of a,b-unsubstituted derivatives by Dolphin4
and Lindsey,4 is an appealing ligand. Indeed, it can be readily
functionalized at its 5 position (Scheme 1) by a variety of groups.
Furthermore, its deprotonated form acts as a monoanionic chelate
and forms complexes with a large variety of metal centers. These
features allow the design and synthesis of derivatives bearing a
secondary coordination site in addition to the bipyrrolic chelate.
Using these ligands, one can therefore envision the sequential
construction of heterometallic architectures.5,6 Finally, another
key feature associated with dpms is their propensity to generate lu-
minescent complexes. Recent examples of homoleptic tetrahedral
Results and discussion
Synthesis of the complexes
Compounds 5–8 were synthesized in 73-98% yield by the re-
action, in the presence of NEt3, of dipyrrins 114 and 214 with
15
either [(Ppy)Pd(OAc)]2 or [(Ppy)Pt(NCMe)2](SbF6) generated
Scheme 1 Schematic representation of the precursor, ligands and metal
complexes.
in situ upon reaction of two equivalents of AgSbF6 with
(Bu4N)[(Ppy)PtCl2]11 in MeCN (Scheme 2). Compounds 5 (77%),
6 (91%), 7 (98%) and 8 (73%) were isolated by column chro-
matography and are air-stable in the solid state for several days.
However, slow decomposition under light and in air was observed
by absorption spectroscopy and 1H NMR.
aLaboratoire de Chimie de Coordination Organique, UMR CNRS 7140,
Universite´ de Strasbourg, F-67000, Strasbourg, France. E-mail: sbaudron@
unistra.fr, hosseini@unistra.fr; Fax: +33 368851325; Tel: +33 368851323
bPhysikalisches Institut, Westfa¨lische Whilhems-Universita¨t Mu¨nster,
Mendelstrasse 7, D-48149, Mu¨nster, Germany. E-mail: decola@uni-
muenster.de
Structural investigations in the crystalline phase
cDutch Polymer Institute (DPI), P.O. Box 902, 5600, AX, Eindhoven, The
Netherlands
Single-crystals of complexes 5, 6 and 8 were obtained and
characterized by X-Ray diffraction (Fig. 1). Unfortunately, so far
only twin crystals of 7 have been obtained. However, preliminary
investigations indicate isomorphism between 5 and 7. Complex
† Electronic supplementary information (ESI) available: Emission and
excitation spectra at 77 K for compounds 6–8. CCDC reference numbers
729823–729825. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b908424j
180 | Dalton Trans., 2010, 39, 180–184
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The Royal Society of Chemistry 2010
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Table 1 Absorption and Emission Spectral Data at Room and Low Temperature of Complexes 5–8 in CH2Cl2
Absorption
max/nm (log e)
Emission
Emission 77 K
Complex
l
l/nm (rel. int.)
U
t/ms
l/nm (rel. int.)
t/ms
5
6
7
8
273 (4.21), 284 (4.22), 334 (3.94), 434 (4.02), 508 (4.27) 703 (1), 768 (0.56) 0.013 0.002
270 (4.48), 306 (4.24), 449 (4.19), 503 (4.32)
263 (4.27), 314 (3.93), 400 (3.78), 496 (4.63)
18
2
685 (1), 754 (0.56)
727 (1), 782 (0.91)
678 (1), 744 (0.34)
728 (1), 781 (0.46)
30
40
3
3
0.32 0.03
0.30 0.03
263 (4.40), 304 (4.20), 404 (3.78), 497 (4.58)
shows a distortion, albeit smaller, with a dihedral angle of 28.8◦
between the two pyrrolic units.
Rather interestingly, although the Pd complex 8 also crystallizes
in the monoclinic P21/n space group, it is not isostructural to
its Pt analog 6 (Fig. 1c). The geometry around the Pd center
deviates from square planar with each pyrrolic rings of the dipyrrin
lying either above or below the plane defined by Pd and the
Ppy ligand (dihedral angle of only 10.4◦ between the two five-
˚
membered rings). The Pd–C distance of 1.983(2) A is much
shorter than the three Pd–NPpy and Pd–Ndpm distances of 2.050(2),
˚
2.118(2), and 2.017(2) A respectively. As expected in the absence
of functionalization in the ortho positions of the aromatic moiety,
the dihedral angle between the peripheral benzonitrile and the
dipyrrin chelate is smaller for 6 and 8 (63.5 and 54.6◦ respectively)
than for 5 (vide supra).
Scheme 2 Synthetic route to complexes 5–8.
Absorption and emission properties
The photophysical data for complexes 5–8 in CH2Cl2, (fluid
solution at room temperature, and rigid matrix at 77 K) are
collected in Table 1. The absorption spectra of compounds 5–8 are
presented in Fig. 2. All four complexes feature strong absorption
bands between 460 and 500 nm, as previously reported for other
dpm metal complexes.2,7–9,14,16 These bands are attributed to a
p–p* transition of the dpm moiety. The metal dependence can
be observed by comparing the spectra of 5 and 6 with those of 7
and 8. In fact, while the band centered around 500 nm is present
for all the complexes, the one at 430 nm is only evident for the
compounds containing the Pt(II) ion. Such observation can be
attributed to a metal to ligand charge transfer transition which
Fig. 1 Crystal structures of Pt complexes 5 (a) and 6 (b), and Pd complex
8 (c). Hydrogen atoms have been omitted for clarity.
5 crystallizes in the orthorhombic space group P212121 with one
molecule in general position (Fig. 1a). To the best of our knowl-
edge, this represents the first crystal structure characterization of
a platinum complex incorporating the dpm ligand. The geometry
around the metal center is square planar with a Pt–C distance
˚
of 2.014(7) A and Pt–NPpy and Pt–Ndpm distances of 2.029(6),
˚
2.027(6) and 2.091(6) A respectively. Note however that the two
pyrrolic rings are not coplanar, showing a dihedral angle of 43.7◦.
Such a distortion of the ligand has been observed recently for a
heteroleptic CoIII complex.6 The mesityl moiety and the dipyrrin
chelate are almost perpendicular (dihedral angle 85.9◦) as a result
of the presence of the two methyl groups in ortho positions. The
packing does not feature any short Pt ◊ ◊ ◊ Pt distances. Complex
6 crystallizes in the monoclinic P21/n space group (Fig. 1b).
The geometry around the platinum center is similar to the one
˚
observed for 5 (Pt–C distance of 2.021(5) A and Pt–N distances
Fig. 2 Electronic absorption spectra in CH2Cl2 at room temperature of
complexes 5–8.
˚
of 2.027(4), 2.045(4) and 2.047(4) A). Again the dipyrrin chelate
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is enabled by the lower oxidation potential of Pt(II), if compared
with Pd(II).
Conclusions
Four cyclometallated Pd and Pt complexes coordinated simulta-
neously to a dipyrrin derivative and the 2-phenylpyridine ligand
have been synthesized and characterized. Within this series of
complexes, the Pt derivatives exhibit the highest luminescence.
As previously demonstrated, the limitation of rotational freedom,
imposed by the mesityl group, increases the emission intensity.
The development of novel functionalized dpm ligands with
hindered rotation and their combination with cyclometallated
complexes are currently under investigation. The elaboration of
heterometallic luminescent assemblies based on the use of the
secondary coordination sites on the dipyrrin moiety is also under
study.
The luminescence of complexes 5–8 is rather weak even at 77 K,
where all the complexes show two characteristic emission bands,
corresponding to progressive vibronic transitions from one single
electronic excited state. In fact, each pair of vibronic bands gives
rise to only one excitation spectrum, and displays the same excited
state lifetime (Fig. 3 and ESI†).
Experimental
Synthesis
Ligands 1 and 2 were prepared as described.14 The Pd and Pt
precursors, 3 and 4, were synthesised following the reported
procedures.11,15 All solvents were dried using standard procedures.
NMR chemical shifts are given in ppm and J values are given in
Hz.
Complex 5. To a solution of 3 (51 mg, 7.7 ¥ 10-5 mol) in MeCN
(4 mL), AgSbF6 (54 mg, 1.6 ¥ 10-4 mol) in MeCN (1 mL) was
added. This mixture was stirred overnight at room temperature.
The AgCl formed was filtered. The filtrate was then added to a
solution of 1 (22 mg, 8.4 ¥ 10-5 mol) in CHCl3 (3 mL). After
addition of an excess of NEt3, the solution was stirred at room
temperature for 5 h. Purification by column chromatography
(SiO2, CH2Cl2, Rf 0.94) afforded 5 (36 mg, 77%) as pure red powder
(Found: C, 56.87; H, 4.44; N, 6.58. C29H25N3Pt requires C, 57.04;
H, 4.13; N, 6.88%); dH (300 MHz, CD2Cl2) 2.11 (6H, s), 2.37 (3H,
s), 6.44 (1H, dd, J = 4.3, 1.6 Hz), 6.54 (1H, dd, J = 4.0, 1.6 Hz),
6.58 (1H, dd, J = 4.3, 1.3 Hz), 6.66 (1H, dd, J = 4.3, 1.1 Hz), 6.96
(2H, s), 7.14-7.24 (3H, m), 7.33 (1H, m), 7.62 (1H, m), 7.79-8.03
(4H, m) and 8.61-8.64 (1H, m); dC (75 MHz, CD2Cl2) 19.5, 20.8,
116.3, 116.9, 118.9, 121.2, 123.3, 123.4, 127.6, 128.5, 130.0, 130.3,
134.1, 134.7, 136.5, 137.1, 137.5, 138.1, 146.7, 147.0, 149.5, 149.9,
152.5 and 168.2; lmax (CH2Cl2)/nm 273 (log e 4.21), 284 (4.22),
334 (3.94), 434 (4.02) and 508 (4.27).
Fig. 3 Emission and excitation spectra of complex 5 in CH2Cl2 at 293
(solid line) and 77 K (dotted line).
The emission of the Pt complexes 5 and 6 is stronger than those
of their Pd analogues 7 and 8, implying that the Pd complexes
possess smaller radiative constants and higher non-radiative
deactivation rates. Indeed, the excited state lifetimes are two orders
of magnitude higher for Pt than for Pd (Table 1). This observation
can be explained by the out-of-plane distortion featured by the
Pd complexes (vide supra), leading to low-lying, metal-centered
d-d excited states that provide efficient non-radiative deactivation
pathways.
Complex 5 is the strongest emitter and its emission and
excitation spectra were investigated both at 77 K and room
temperature, as depicted in Fig. 3. The vibronic progression is
in this case better resolved, if compared with the other complexes
(compare Fig. 3 and ESI†). It is most likely related to the lack of
rotational freedom imposed by the methyl groups of the mesityl
moiety, which hinders its rotation with respect to the dpm chelate.
This feature has been also observed for Zn(1)2, Ga(1)3 and In(1)3
complexes.7,8
The rather low luminescence quantum yield, the emission
wavelength, the vibronic progression and the long excited state
lifetimes (even at room temperature in deareated solution) point
to a ligand centered excited triplet state localized on the dpm unit.
Moreover, the room temperature and 77 K emission spectra
present almost the same shape and energy range. Such an absence
of hypsochromic shifts confirms the lack of charge transfer
character in the excited state. Owing to the weakness of the
emission of 6–8, the quantum yield was not determined for these
compounds.
Complex 6. To a solution of 3 (54 mg, 8.1 ¥ 10-5 mol) in a
minimum of MeCN (4 mL), AgSbF6 (56 mg, 1.6 ¥ 10-4 mol)
in a minimum of MeCN (1 mL) was added. After stirring 3 h the
mixture at room temperature, AgCl was filtered and the filtrate was
added to a solution of 2 (20 mg, 8.1 ¥ 10-5 mol) in CHCl3 (4 mL).
Excess NEt3 was added and the solution turned immediately from
yellow to red. The solution was stirred at room temperature for
4 h. Solvents were removed under reduced pressure. Purification
by column chromatography (SiO2, CH2Cl2, Rf 0.71) afforded 6
(44 mg, 91%) as a red solid (Found: C, 54.44; H, 3.19; N, 9.11.
C27H18N4Pt requires C, 54.63; H, 3.05; N, 9.44%); dH (300 MHz,
CDCl3) 6.51 (1H, m), 6.59 (2H, m), 6.72 (1H, m), 7.13-7.35 (4H,
m), 7.58-7.67 (3H, m), 7.77 (3H, m), 7.89 (2H, m), 8.13 (1H, s)
and 8.58 (1H, d, J = 5.8 Hz); dC (75 MHz, CDCl3) 112.5, 117.4,
117.6, 118.5, 119.0, 121.2, 123.6, 123.7, 129.0, 131.0, 131.1, 131.2,
134.7, 135.9, 137.0, 138.1, 142.7, 144.7, 146.2, 148.2, 149.4, 150.8,
182 | Dalton Trans., 2010, 39, 180–184
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154.0 and 168.5; lmax (CH2Cl2)/nm 270 (log e 4.48), 306 (4.24),
449 (4.19) and 503 (4.32).
least-squares on F2 using SHELXL-97 with anisotropic thermal
parameters for all non hydrogen atoms. The hydrogen atoms were
introduced at calculated positions and not refined (riding model).
CCDC reference numbers 729823-729825.†
Red crystalline rods of 5 were grown by slow evaporation of an
acetone solution. Red crystalline plates of 6 were grown by slow
diffusion of pentane into a CHCl3 solution of the complex. Orange
crystalline plates of 8 were grown by slow diffusion of pentane into
a CHCl3 solution of the compound.
Complex 7. To a solution of 1 (40 mg, 1.5 ¥ 10-4 mol) in 3 mL
of CH2Cl2, 4 (49 mg, 7.7 ¥ 10-5 mol) in 4 mL of CH2Cl2 was
added. After addition of NEt3 in excess, the solution was stirred at
room temperature for 2 h. Purification by column chromatography
(Al2O3, CH2Cl2) afforded 7 (78 mg, 98%) as a red powder (Found:
C, 66.59; H, 4.91; N, 8.25. C29H25N3Pd requires C, 66.73; H, 4.83;
N, 8.05%); dH (300 MHz, CD2Cl2) 2.09 (6H, s), 2.35 (3H, s), 6.41-
6.56 (4H, m), 6.94 (2H, s), 7.13-7.23 (3H, m), 7.33-7.36 (1H, m),
7.54-7.57 (1H, m), 7.75-7.91 (4H, m) and 8.63-8.65 (1H, m); dC
(100 MHz, C6D6) 20.2, 21.2, 117.9, 118.0, 118.7, 121.1, 123.4,
124.3, 128.1, 129.5, 130.3, 130.3, 136.2, 137.1, 137.2, 137.4, 137.5,
137.9, 138.8, 146.7, 147.6, 149.3, 150.6, 154.0, 160.9 and 167.1;
lmax (CH2Cl2)/nm 263 (log e 4.27), 314 (3.93), 400 (3.78) and 496
(4.63).
Spectroscopic characterization
Suprasil quartz cells and spectrophotometric grade solvents were
employed. The measurements at low temperature (77 K) were
performed in quartz tubes inserted in a liquid-nitrogen-filled
quartz Dewar. UV/Vis spectra were recorded on Varian Cary 5000
double-beam UV/Vis/NIR spectrometer and baseline corrected.
Steady-state luminescence emission spectra were recorded on a
HORIBA Jobin-Yvon IBH FL-322 Fluorolog 3 spectrometer
equipped with a 450-W xenon arc lamp. Steady-state mea-
surements were performed using the Fluorolog 3 spectrometer
equipped with a cooled Hamamatsu R2658P PMT. Emission and
excitation spectra were corrected in all the cases for source intensity
(lamp and grating) and emission spectral response (detector
and grating) by standard correction curves. The lifetimes of the
complexes were recorded on the Fluorolog 3 spectrometer using
the FL-1040 phosphorescence module with a 70-W xenon flash
tube (full-width at half maximum FWHM =3 ms). The signals
were recorded on the TBX-4-X single-photon-counting detector
and collected with a multichannel scaling (MCS) card in the IBH
Data-Station Hub photon counting module, and data analysis
was performed using the commercially available DAS6 software
(HORIBA Jobin Yvon IBH). The goodness-of-fit was assessed by
minimizing the reduced chi squared function and visual inspection
of the weighted residuals. Luminescence quantum yields (Uem)
were measured on optically dilute solutions (absorbance value
lower than 0.1 at excitation wavelength). Quantum yields were de-
termined relative to those of [Ru(2,2¢-bipyridine)3]Cl2 (Uem=0.06
in degassed CH3CN).17
Complex 8. Precursor 4 (39 mg, 6.1 ¥ 10-5 mol) and 2 (30 mg,
1.2 ¥ 10-4 mol) were dissolved in CH2Cl2 (3 mL). After addition of
few drops of NEt3, the solution was stirred at room temperature
for 2 h. Solvents were removed under reduced pressure and the
complex washed with acetone affording 8 (44 mg, 73%) as a red
powder (Found: C, 63.39; H, 3.59; N, 11.23. C27H18N4Pd requires
C, 64.23; H, 3.59; N, 11.09%); dH (300 MHz, CD2Cl2) 6.53-6.67
(4H, m), 7.19-7.37 (4H, m), 7.61-7.71 (3H, m), 7.78-7.82 (2H, m),
7.87-7.89 (2H, m), 7.74-8.01 (2H, m) and 8.67 (1H, d, J = 5.7 Hz);
dC (75 MHz, CD2Cl2) 112.4, 117.5, 118.3, 118.6, 119.2, 122.0,
123.3, 124.4, 129.1, 130.9, 131.1, 131.3, 131.5, 136.2, 137.1, 138.1,
138.7, 143.7, 144.8, 146.4, 150.5, 150.8, 154.0, 159.1 and 166.6;
lmax (CH2Cl2)/nm 263 (log e 4.40), 304 (4.20), 404 (3.78) and 497
(4.58).
X-Ray crystallography
Data collection (Table 2) was carried out at 173 K on a Bruker
SMART CCD diffractometer with Mo Ka radiation. The struc-
tures were solved using SHELXS-97 and refined by full matrix
Table 2 Crystallographic data for compounds 5, 6 and 8
5
6
8
Acknowledgements
Formula
FW
C29H25N3Pt
610.62
C27H18N4Pt
593.54
Monoclinic
P21/n
7.2660(3)
12.5451(4)
22.3968(8)
90.177(2)
2041.52(13)
4
C27H18N4Pd
504.89
Monoclinic
P21/n
15.0039(3)
7.48110(10)
18.2111(3)
95.3430(10)
2035.24(6)
4
Support from the Universite´ de Strasbourg, the C.N.R.S., the In-
stitut Universitaire de France and the Ministe`re de l’Enseignement
Supe´rieur et de la Recherche (Ph. D. fellowship to C. B.) is
gratefully acknowledged. The work of C.A.S. forms part of the
research programme of the Dutch Polymer Institute (DPI), project
#628. The work of A.G. was supported by the European Com-
mission (EC) through the Human Potential Programme within the
6th framework programme (Marie Curie RTN NANOMATCH,
MRTN-CT-2006-035884).
Crystal system
Space group
Orthorhombic
P212121
7.8866(3)
14.9148(6)
19.3528(8)
—
2276.41(16)
4
173(2)
˚
a/A
˚
b/A
˚
c/A
b (◦)
3
˚
V/A
Z
T/K
173(2)
6.897
18358
173(2)
0.936
25659
m/mm-1
6.187
11628
Refls. coll.
Notes and references
Ind. refls. (R int)
R1 (I > 2s(I))a
wR2 (I > 2s(I))a
R1 (all data)a
wR2 (all data)a
GOF
4811 (0.0529)
0.0377
0.0615
0.0468
0.0669
4688 (0.0421)
0.0280
0.0670
0.0401
0.0911
5955 (0.0352)
0.0326
0.0883
0.0469
0.1093
1 Photofunctional Transition Metal Complexes, ed. V. W. W. Yam,
Structure and Bonding, Springer, Berlin, Heidelberg, 2007, vol. 123.
2 T. E. Wood and A. Thompson, Chem. Rev., 2007, 107, 1831–1861.
3 H. Fischer and M. Schubert, Ber. Dtsch. Chem. Ges., 1924, 57, 610–617.
4 C. Bru¨ckner, V. Karunaratne, S. J. Rettig and D. Dolphin, Can. J. Chem.,
1996, 74, 2182–2193; R. W. Wagner and J. S. Lindsey, Pure Appl. Chem.,
1996, 68, 1373–1380.
1.022
1.135
1.204
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| - |Fcꢀ/ |Fo|; wR2 = [ w(Fo - Fc2)2/ wFo
] .
2
4 1/2
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 180–184 | 183
©

View Online
5 S. R. Halper and S. M. Cohen, Inorg. Chem., 2005, 44, 486–488; D. L.
Murphy, M. R. Malachowski, C. F. Campana and S. M. Cohen, Chem.
Commun., 2005, 5506–5508; S. R. Halper, L. Do, J. R. Stork and S. M.
Cohen, J. Am. Chem. Soc., 2006, 128, 15255–15268; S. Garibay, J. R.
Stork, Z. Wang, S. M. Cohen and S. G. Telfer, Chem. Commun., 2007,
4881–4883.
6 D. Salazar-Mendoza, S. A. Baudron and M. W. Hosseini, Chem.
Commun., 2007, 2252–2254; D. Salazar-Mendoza, S. A. Baudron and
M. W. Hosseini, Inorg. Chem., 2008, 47, 766–768.
7 L. Yu, K. Muthukumaran, I. V. Sazanovich, K. Kirmaier, E. Hindin,
J. R. Diers, P. D. Boyle, D. F. Bocian, D. Holten and J. S. Lindsey, Inorg.
Chem., 2003, 42, 6629–6647; I. V. Sazanovich, K. Kirmaier, E. Hindin,
L. Yu, D. F. Bocian, J. S. Lindsey and D. Holten, J. Am. Chem. Soc.,
2004, 126, 2664–2665.
8 V. S. Thoi, J. R. Stork, D. Magde and S. M. Cohen, Inorg. Chem., 2006,
45, 10688–10697; J. R. Stork, V. S. Thoi and S. M. Cohen, Inorg. Chem.,
2007, 46, 11213–11223.
10 M. E. Thompson, C. Borek, K. Hanson, P. Djurovich, Y. Sun and S.
Forrest, U.S. Pat,. Appl. 2008/0061681 A1 Mar 13, 2008.
11 C. A. Craig, F. O. Garces, R. J. Watts, R. Palmans and A. J. Frank,
Coord. Chem. Rev., 1990, 97, 193–208.
12 J. A. G. Williams, Top. Curr. Chem., 2007, 281, 205–268.
13 F. Neve, in Palladacycles: Synthesis and Applications, ed. J. Dupont and
M. Pfeffer, Wiley-VCH, Weinheim, 2008, pp. 285–305.
14 K. Muthukumaran, S. H. H. Zaidi, L. Yu, P. Thamyongkit, M. E.
Calder, D. S. Sharada and J. S. Lindsey, J. Porphyrins Phthalocyanines,
2005, 9, 745–759; S. J. Vigmond, M. C. Chang, K. M. R. Kallury and
M. Thompson, Tetrahedron Lett., 1994, 35, 2455–2458; P. D. Rao, S.
Dhanalekshmi, B. J. Littler and J. S. Lindsey, J. Org. Chem., 2000, 65,
7323–7344.
15 E. C. Constable, A. M. W. Cargill Thompson, T. A. Leese, D. G. F.
Reese and D. A. Tocher, Inorg. Chim. Acta, 1991, 182, 93–100.
16 M. Bro¨ring, C. D. Brandt, J. Bley-Escrich and J. P. Gisselbrecht,
Eur. J. Inorg. Chem., 2002, 910–917; Q. Miao, J. -Y. Shin, B. O. Patrick
and D. Dolphin, Chem. Commun., 2009, 2541–2543.
9 S. J. Smalley, M. R. Waterland and S. G. Telfer, Inorg. Chem., 2009, 48,
13–15.
17 K. Nakamaru, Bull. Chem. Soc. Jpn., 1982, 55, 2697–2705.
184 | Dalton Trans., 2010, 39, 180–184
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