Design and preparation of neutral substituted fluorene- and carbazole-based platinum(II)-acetylide complexes

Article abstract of DOI:10.1039/b702374j

Various combinations of mono- or diethynyl-substituted fluorene or carbazole building blocks were connected via a σ-bonded ethynyl linkage to ortho-metallated Pt(ii) fragments, giving rise to phosphorescent mono- and dinuclear complexes for which the solubility and extent of delocalization could be tuned by the chemistry on the acidic methylene position of the fluorene. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b702374j

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LETTER
www.rsc.org/njc | New Journal of Chemistry
Design and preparation of neutral substituted fluorene- and
carbazole-based platinum(II)–acetylide complexes
Julie Batcha Seneclauze,a Pascal Retailleaub and Raymond Ziessel*a
Received (in Montpellier, France) 14th February 2007, Accepted 23rd April 2007
First published as an Advance Article on the web 1st June 2007
DOI: 10.1039/b702374j
Various combinations of mono- or diethynyl-substituted fluorene
or carbazole building blocks were connected via a r-bonded
ethynyl linkage to ortho-metallated Pt(II) fragments, giving rise
to phosphorescent mono- and dinuclear complexes for which the
solubility and extent of delocalization could be tuned by the
chemistry on the acidic methylene position of the fluorene.
square-planar species seemed to us to offer intriguing possibi-
lities for extension of this chemistry.
Thus, as a part of our research program on the construction
of extended p-electronic systems, we attempted the develop-
ment of an efficient method for the synthesis of novel mono-
and binuclear Pt(II) complexes with electron-rich fluorene and
carbazole moieties. Ligands of this type are known, as are
Pt(II) complexes and polymers containing these species,16
although the introduction of neutral Pt(II) complexes of
ortho-metallated and tridentate ligands in conjunction with
fluorene and carbazole units has not been reported before to
the best of our knowledge. The key building blocks (Chart 1)
were prepared according to adapted literature procedures,
usually comprising four-synthetic steps involving: (i) bromina-
tion of the substrates; (ii) alkylation of the methylene (fluor-
ene) and nitrogen (carbazole) centres; (iii) alkynylation by
Sonogashira coupling; and (iv) deprotection.15,17
Much attention has been focused recently on alkyne-sub-
stituted molecular frameworks because they not only provide
useful models for intramolecular information transfer but also
have potential applications in materials science, including
polymer chemistry.1 Acetylide anions derived from terminal
alkynes are particularly useful for extending electronic con-
jugation2 as well as for tethering chromophores to transition
metals,3 boron centres4 and larger organic edifices.5 In these
regards, the chemistry of alkynyl–platinum(II) and –gold(I) has
received much recent attention.6,7
The preference of d8 Pt(II) to form square-planar species,
along with the linearity and pronounced electron density of
CRC bonds make the ‘‘Pt–CRC–’’ moiety, in particular, an
attractive and promising candidate for the design of lumines-
cent complexes with applications in fluid solution, thin films
and the solid state. It has been shown recently that some of
these complexes show liquid-crystalline and nonlinear optical
properties,8 electroluminescence,9 and singlet oxygen photo-
sensitization,10 and can be used in photocatalytic hydrogen
production,11 cation sensing,12 and conductance switches.13
The square-planar coordination geometry of Pt(II) in its com-
plexes of large aza-aromatic ligands makes such complexes
effective DNA intercalators and useful molecular probes for
biological macromolecules.14 Many alkynyl–platinum com-
plexes exhibit intriguing luminescent properties and polyimine
(phenanthroline, bipyridine, terpyridine and phenyl bipyridine)–
Pt(II) complexes incorporating s-alkynyl ligands, in particular,
are well-known for their rich photochemistry, forming a class
of luminophores that may find application in advanced elec-
tronic and light converting devices.9 In view of the fact that
fluorene and carbazole frameworks are easily transformable
and often used in OLEDs and polymeric materials,15 but are
yet to be found as systematically introduced components of
coordination complexes, the linking of these building blocks to
The mono- and dibromo starting materials were prepared
from fluorene and carbazole using stoichiometric amounts of
N-bromosuccinimide in CHCl3 at rt. Alkylation of 2-bromo-
fluorene and 2,7-dibromofluorene was achieved using CH3I,
C4H9Br or C12H25Br in a mixture of DMSO–H2O–NaOH,
with [Et3BzN]Cl as phase transfer catalyst (for 1a and 4a), or
with NaH in anhydrous DMF for 2a and 3a. Methylation of
3-bromocarbazole and 3,6-dibromocarbazole is also very effi-
cient using NaH and CH3I in anhydrous DMF at rt. The best
conditions for the synthesis of the ethynyl derivatives 1b to 6b
requires HCRCSiMe3, [Pd(PPh3)4] (5 mol% per Br), CuI
(10 mol% per Br), and piperidine as solvent at 80 1C. Removal
of the TMS group may be achieved using excess K2CO3 in
CH3OH–CH2Cl2 at rt.
To test the efficiency of cross-coupling of the mono-
ethynyl compounds 1c–3c and 5c, we targeted a neutral
[Pt(C4N4N)Cl] precursor prepared according to a known
procedure (C4N4N designates the deprotonated 6-phenyl-
a
´
Laboratoire de Chimie Moleculaire, Ecole de Chimie, Polymeres
´
`
´
´
Materiaux (ECPM), Universite Louis Pasteur (ULP), 25 rue
Becquerel, 67087 Strasbourg Cedex 02, France. E-mail:
ziessel@chimie.u-strasbg.fr
b Laboratoire de Cristallochimie, ICSN-CNRS, Baˆt 27-1 avenue de la
Terrasse, 91198 Gif-sur-Yvette Cedex, France
Chart 1
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Table 1 Selected data for the new Pt(II) complexes
Compound
Isolated yield (%)
n
CRC/cmꢁ1a
l
max/nm (e/Mꢁ1 cmꢁ1 b
)
l
em/nmc
7
8
9
95
82
80
76
60
67
38
46
51
60
2090
2091
2092
2097
2089
2093
2081
2093
2113
2095
446 (6300)
449 (7000)
465 (6700)
480 (5300)
444 (7600)
475 (10 000)
478 (5700)
484 (9900)
445 (5700)
468 (7700)
634
614
612
522
616
651
543
544
605
586
10
11
12
13
14
15
17
a
b
One drop of CH2Cl2 containing the sample was evaporated on a KBr disk. Averaged value determined from at least two different solutions of
c
non-degassed CH2Cl2 solution. Phosphorescence peak measured in non-degassed CH2Cl2 solution with an excitation wavelength corresponding
to the maximum of absorption.
2,20-bipyridine ligand).18 Cross-coupling with ethynyl-fluorene
and ethynyl-carbazole is effective (Table 1) in the presence of
catalytic amounts of CuI (8 mol%) in CH2Cl2 and triethyl-
amine (acid quencher) when conducted under strictly anaero-
bic conditions (Chart 2).
(Pt–N1 1.984 and 2.042; Pt–N2 1.993 and 2.119 A for 7 and
10). For compound 7, there is evidence of p–p stacking
involving aromatic ring plane separations B3.4 A. We con-
tend that the conjugation based on s–p interaction between
the Pt(II) and arylacetylide moieties confers high stability and
rigidity to this system.
Interestingly, mixing 2,7-diethynyl-9,9-dimethylfluorene 4c
or 3,6-diethynyl-9-methylcarbazole 6c with [Pt(C4N4N)Cl]
under similar conditions provides the neutral mononuclear
complexes 11 and 13 and no significant amounts of the
disubstituted analogues. After some experimentation with
the reaction mixture composition, the temperature and reac-
tion time, we succeeded in isolating the desired dinuclear Pt(II)
complexes 12 and 14 (Chart 3) in modest yields. We believe
that grafting the first metal to the diethynyl derivative de-
activates the remaining ethynyl group, rendering its binding
more difficult.
To test the efficiency of the copper-catalyzed cross-coupling
with a more polar alkyne substrate, we decided to prepare a
poly(ethylene glycol)-substituted fluorene derivative by
substitution of the methylene protons under phase transfer
conditions with [2-(2-{2-(2-bromoethoxy)ethoxy}ethoxy)-
ethoxy]methyl.19 Despite the strong polarity of the substituted
derivative, cross-coupling with HCRCSiMe3 was straightfor-
ward using [Pd(PPh3)4] (5 mol% per Br) and CuI (10 mol%
per Br), in hot piperidine. After removal of the TMS group
with K2CO3 in CH3OH–CH2Cl2, the resulting terminal alkyne
was linked to the neutral [Pt(C4N4N)Cl] precursor, leading to
the stable complex 15 (Chart 4).
The molecular structures of 7 and 10 were confirmed by
X-ray crystallography (Fig. 1). In both cases the Pt(C4N4N)-
acetylide fragment is square-planar whereas the dimethylfluor-
ene fragment is titled out of the plane by 761 (for 7), and the
methylcarbazole by 601 (for 10). This implies that p-orbitals of
the fluorene and carbazole are not engaged in favourable
overlap with the Pt core in the solid. Furthermore, the Pt–C,
CRC and C–aryl bond lengths are consistent with weak
Pt–alkynyl back-bonding. As would be expected for an
ortho-metallated ligand, the Pt–C bonds (Pt–C1 2.069 and
1.988 A for 7 and 10) lie in the expected range. Furthermore,
the central Pt–N bond is shorter than the peripheral one
The proton and carbon NMR spectra clearly show that the
aromatic protons of the fluorene and C4C4N ligand are well-
defined with 16 different multiplets and peaks for a strongly
deshielded single proton at 8.99 ppm (Fig. 2), likely attributed
to the proton b (see Chart 4). Interestingly, the protons (a) in
Chart 2
Chart 3
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Fig. 2 (a) Expanded proton NMR spectrum of 15 in CDCl3 (s),
integration 0.2, at 400.13 MHz. (b) Carbon NMR spectrum of 15 in
CDCl3 at 100.61 MHz. Inset is the expanded ethynyl region.
platinum-to-ligand charge transfer transition (MLCT) prob-
ably mixed with an alkynyl-to-C4N4N ligand-to-ligand
charge transfer character (LLCT).21 This band is found
around 445 nm in the mononuclear fluorene complexes, 7
and 11, whereas in the mononuclear carbazole derivatives, 10
and 13, it appears around 479 nm (Table 1). For the dinuclear
complexes 12 and 14, these broad bands are split and one band
is clearly shifted to the red and tails beyond 550 nm. This
bathochromic shift is probably induced by the increase of
electronic delocalization imported by the second Pt centre and
could be assigned to the contribution of the alkynyl–fluorene/–
carbazole to C4N4N ligand-to-ligand charge transfer. Excita-
tion of the fluorene complexes in fluid solution at 450 nm
results in red phosphorescence at 634 nm (f = 1%, t = 39 ꢂ
2 ns), 616 nm (f = 0.1%, t = 55 ꢂ 5 ns), and 651 nm (f =
0.2%, t = 1.5 ꢂ 0.5 ns), respectively for 7, 11 and 12 (Fig. 3b).
The weakness of the fluorescence of the carbazole derivatives
is possibly a consequence of intramolecular electron transfer
involving the tertiary amine of the carbazole subunit. As
anticipated from previous data obtained with ortho-metallated
ligands, the increase in charge density is responsible for the
decrease in excited state lifetimes due to the occurrence of non-
radiative deactivation pathways.
Fig. 1 ORTEP view of compound 7 (a) and 10 (b) (50% probability
displacement ellipsoids), with all hydrogen atoms removed for the sake
of clarity.
close proximity to the fluorene and oxygen atoms are diaster-
eotopic, leading to an AA0X pattern integrating for 2H around
2.8 ppm. The carbon NMR spectrum is in keeping with the
molecular structure, with two characteristic ethynyl carbon
resonances at 107.5 and 107.2 ppm (Fig. 2b).
Subsequently, we applied this synthetic protocol to the
preparation of more highly conjugated systems. The synthesis
of complex 17 was achieved in a three-step procedure invol-
ving: (i) deprotonation of 2-(trimethylsilylacetylene)fluorene
with LDA at ꢁ78 1C in THF followed by reaction with
benzophenone; (ii) removal of the TMS protecting group with
a base under polar conditions; and (iii) cross-coupling with
CuI as catalyst (Chart 5).
The electronic absorption spectra of all complexes in
CH2Cl2 solution at 298 K show intense multiple absorption
peaks in the range 250–600 nm (Fig. 3a). On the basis of earlier
studies of related compounds,20 the high-energy, structured
absorption bands are ascribed to p–p* transitions of the
C4N4N fluorene– and carbazole–alkynyl moieties. The low
energy absorption band in the visible region is assigned to a
In summary, a series of ortho-metallated platinum(II) acet-
ylide complexes bearing various appended moieties (fluorene
and carbazole) has been synthesized successfully, using a
rational protocol. High solubility in apolar or polar solvents
has been ensured by the use of alkyl substituents or a
Chart 4
Chart 5
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solution was stirred for 18 h at rt. The reaction mixture was
then evaporated to dryness under reduced pressure and the
crude oil purified by column chromatography (Al2O3,
CH2Cl2–MeOH (1%) as eluant) and recrystallized in a mixture
dichloromethane–methanol–cyclohexane to give 15 as a red
waxy solid (0.080 g, yield: 51%). 1H NMR (CDCl3, 400 MHz):
d = 8.99 (d, 1H, 3J = 5.0 Hz), 7.93–7.78 (7 line m, 3H),
7.65–7.49 (8 line m, 6H), 7.45–7.40 (4 line m, 2H), 7.34–7.21 (8
line m, 4H), 7.15 (t, 1H, 3J = 7.5 Hz), 7.00 (t, 1H, 3J =
7.5 Hz), 3.54–3.52 (11 line m, 12H), 3.49–3.46 (4 line m, 4H),
3
3.42 (t, 4H, J = 5.0 Hz), 3.32 (s, 6H), 3.25–3.22 (4 line m,
4H), 2.28–2.83 (5 line m, 2H), 2.79–2.73 (5 line m, 2H), 2.42 (t,
3
4H, J = 7.5 Hz); 13C{1H} NMR (CDCl3, 100 MHz): 165.4,
158.3, 154.7, 151.6, 149.3, 148.9, 147.2, 142.9, 141.0, 139.0,
138.9, 138.8, 137.9, 131.7, 128.5, 127.7, 127.2, 126.6, 124.7,
123.9, 123.4, 119.9, 119.8, 118.6, 107.4, 107.1, 70.9, 70.9, 70.8,
70.4, 67.5, 59.4, 51.3, 40.2, 27.3; UV-Vis (CH2Cl2) l nm (e,
Mꢁ1 cmꢁ1) = 445 (5700), 366 (12 900), 333 (41 700), 313
(35 000), 282 (33 200), 229 (39 800); IR (KBr): n = 3069 (w),
2924 (s), 2854 (s), 2113 (w, n CRC), 1729 (m), 1603 (m), 1452
(s), 1398 (w), 1291 (m), 1257 (m), 1043 (s), 1036 (s), 844 (w),
770 (m), 741 (m), 522 (w); ESI-MS m/z (nature of peak,
relative intensity): 997.2, 996.2, 995.2 ([M + H]+, 90, 100,
65), 451.2, 450.2, 449.1 ([M ꢁ fluo(C9H19O4)2–R–]+, 35);
anal. Calcd for C49H56N2O8Pt: C, 59.09; H, 5.67; N, 2.81.
Found: C, 58.72; H, 5.42; N, 2.57%.
Fig. 3 (a) Overlay of absorption spectra recorded for the fluorene
series in dichloromethane solution at rt. (b) Phosphorescence spectra
measured at rt, in dichloromethane in air, with an excitation wave-
length of 446 nm for 7, 444 nm for 11 and 475 nm for complex 12.
X-Ray crystallography
Crystal data for 7. C33H24N2Pt, M = 643.63, monoclinic,
space group P21/c, a = 7.2707(6) A, b = 12.3313(10) A, c =
28.699(2) A, b = 96.684(2)1, V= 2555.6(3) A3, Z = 4, l =
0.71073 A, Dc = 1.673 g cmꢁ3, m = 5.515 mmꢁ1, F(000) =
1256, T = 100(2) K. 31 394 measured reflections with 1.431 o
y o 31.001, 8052 unique Rint = 0.0423, and 7626 reflections
with [I 4 2s(I)], 327 variable parameters R1 = 0.0399 and
wR2 = 0.1001 refined on F2. CCDC reference number 644875.
For crystallographic data in CIF format see DOI: 10.1039/
b702374j
poly(ethylene glycol) chain grafted on the central fluorene
moiety. Additional reaction on this central fluorene position
allows the construction of a diphenylvinyl group, which
further extends the electron delocalization. X-Ray molecular
structures have revealed a non-coplanar arrangement of the
fluorene and carbazole entities with respect to the square-
planar platinum core. For the dinuclear complexes, the
absorption of the 3MLCT state exhibits a bathochromic shift,
which is more pronounced for the carbazole bridging unit.
This trend is confirmed with the diphenylvinyl fragment. In-
depth characterization of the photophysical and redox proper-
ties of these new complexes is currently in progress.
Crystal data for 10. C31H21N3Pt, M = 630.60, orthorhom-
bic, space group P212121, a = 7.301(5) A, b = 12.688(5) A,
c = 25.728(5) A, V= 2383.3(19) A3, Z = 4, l = 0.71069 A,
Dc = 1.757 g cmꢁ3, m = 5.913 mmꢁ1, F(000) = 1224, T =
293(2) K. 14 854 measured reflections with 1.581 o y o
25.431, 4276 unique Rint = 0.0425, and 3759 reflections with
[I 4 2s(I)], 317 variable parameters R1 = 0.0306 and wR2 =
0.0760 refined on F2. CCDC reference number 644876. For
crystallographic data in CIF format see DOI: 10.1039/
b702374j
The authors thank the CNRS, the Ministere de la Recherche
Scientifique and the ANR FCP-OLEDS N1-05-BLAN-0004-
01 for financial support. We are also indebted to Professor
Jack Harrowfield (ISIS Strasbourg) for commenting on the
manuscript prior to journal submission. We warmly thank Drs
Loıc Charbonniere and Franck Camerel for technical expertise
¨
and helpful discussions.
Experimental
References
Representative synthesis: compound 15
1 (a) R. E. Martin and F. Diederich, Angew. Chem., Int. Ed., 1999,
38, 1350; (b) J. M. Tour, Acc. Chem. Res., 2000, 33, 791; (c) U. H.
F. Bunz, Chem. Rev., 2000, 100, 1605; (d) U. H. F. Bunz, Acc.
Chem. Res., 2001, 34, 998.
2 (a) R. Ziessel, M. Hissler, A. El-ghayoury and A. Harriman,
Coord. Chem. Rev., 1998, 178–180, 1251; (b) A. Harriman and R.
Ziessel, Coord. Chem. Rev., 1998, 171, 331; (c) R. Ziessel, Synthesis,
1999, 1839.
A
mixture of (60-phenyl-2,20-bipyridine)chloroplatinum
(C4N4N)PtCl (0.090 g, 0.16 mmol) and 2-ethynyl-9,9-
[2-(2-{2-(2-ethoxy)ethoxy}ethoxy)ethoxy]fluorene (0.090 g,
0.19 mmol) in dichloromethane (15 ml) and triethylamine
(3 ml) was degassed by bubbling argon for 30 min. Then
CuI powder (8 mol% per Pt) was added as a solid and the
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3 J. Lewis, P. R. Raithby and W.-Y. Wong, J. Organomet. Chem.,
1998, 556, 219.
Kunai, H. Nakao, A. Adachi and K. Okita, Appl. Organomet.
Chem., 2001, 15, 604.
4 G. Ulrich, C. Goze, M. Guardigli, A. Roda and R. Ziessel, Angew.
Chem., Int. Ed., 2005, 44, 3694.
16 (a) W.-Y. Wong, G.-L. Lu, K.-H. Choi and J.-X. Shi, Macro-
molecules, 2002, 35, 3506; (b) L. Liu, W.-Y. Wong, S.-Y. Poon,
J.-X. Shi, K.-W. Cheah and Z. Lin, Chem. Mater., 2006, 18, 1369;
(c) V. W.-W. Yam, K. H.-Y. Chan, K. M.-C. Wong and B. W.-K.
Chu, Angew. Chem., Int. Ed., 2006, 45, 6169; (d) W.-Y. Wong,
Coord. Chem. Rev., 2005, 249, 971; (e) W.-Y. Wong and C.-L. Ho,
Coord. Chem. Rev., 2006, 250, 2627; (f) F. Montilla and R.
Mallavia, Adv. Funct. Mater., 2007, 17, 71; (g) L. Yang, J. K.
Feng, Y. Liao and A. M. Ren, Opt. Mater. (Amsterdam), 2007, 29,
642; (h) Z. W. Liu, M. Guan, Z. Q. Bian, D. B. Nie, Z. L. Gong, Z.
B. Li and C. H. Huang, Adv. Funct. Mater., 2006, 16, 1441; (i) H.
A. Al Attar, A. P. Monkman, M. Tavasli, S. Bettington and M. R.
Bryce, Appl. Phys. Lett., 2005, 86, 121101.
5 (a) K. Kobayashi and N. Kobayashi, J. Org. Chem., 2004, 69,
2487; (b) S. Eisler, A. D. Slepkov, E. Elliott, T. Luu, R. McDonald,
F. A. Hegmann and R. R. Tykwinski, J. Am. Chem. Soc., 2005,
127, 2666; (c) P. N. W. Baxter and R. Dali-Youcef, J. Org. Chem.,
2005, 70, 4935.
6 F. N. Castellano, I. E. Pomestchenko, E. Shikhova, F. Hua, M. L.
Muro and N. Rajapkse, Coord. Chem. Rev., 2006, 250, 1819.
7 (a) S.-K. Yip, E. C.-C. Cheng, L.-H. Yuan, N. Zhu and V. W.-W.
Yam, Angew. Chem., Int. Ed., 2004, 43, 4954; (b) V. W.-W. Yam,
K. M.-C. Wong, L.-L. Hung and N. Zhu, Angew. Chem., Int. Ed.,
2005, 44, 3107.
8 N. Tessler, G. J. Denton and R. H. Fried, Nature, 1996, 382,
695.
9 S.-C. Chan, M. C. W. Chan, Y. Wang, C.-M. Che, K.-K. Cheung
and N. Zhu, Chem.–Eur. J., 2001, 7, 4180.
10 Y. Yang, D. Zhang, L.-Z. Wu, B. Chen, L.-P. Zhang and C.-H.
Tung, J. Org. Chem., 2004, 69, 4788.
17 (a) G. A. Sotzing, J. L. Reddinger, A. R. Katritzky, J. Soloducho,
R. Musgrave, J. R. Reynolds and P. J. Steel, Chem. Mater., 1997,
9, 1578; (b) W.-Y. Wong, K.-H. Choi, G.-L. Lu, J.-X. Shi, P.-Y.
Lai, S.-M. Chan and Z. Lin, Organometallics, 2001, 20, 5446; (c)
X.-F. Yu, S. Lu, C. Ye, T. Li, T. Liu, S. Liu, Q. Fan, E.-Q. Chen
and W. Huang, Macromolecules, 2006, 39, 1364.
11 D. Zhang, L.-Z. Wu, L. Zhou, X. Han, Q.-Z. Yang, L.-P. Zhang
and C.-H. Tung, J. Am. Chem. Soc., 2004, 126, 3440.
12 V. W.-W. Yam, R. P.-L. Tang, K. M.-C. Wong and K.-K. Cheung,
Organometallics, 2001, 20, 4476.
13 Z. J. Donhauser, B. A. Mantooth, K. F. Kelly, L. A. Bumm, J. D.
Monnell, J. J. Stapleton, Jr, D. W. Price, A. M. Rawlett, D. L.
Allara, J. M. Tour and P. S. Weiss, Science, 2001, 292, 2303.
14 (a) G. Arena, L. Monsu Scolaro, R. F. Pasternack and R. Romeo,
Inorg. Chem., 1995, 34, 2994; (b) E. M. A. Ratilla, H. M. Brothers
and N. M. Kostic, J. Am. Chem. Soc., 1987, 109, 4592.
15 (a) K. R. J. Thomas, J. T. Lin, Y.-Y. Lin, C. Tsai and S.-S. Sun,
Organometallics, 2001, 20, 2262; (b) K. Sakamki, J. Ohshita, A.
18 S.-W. Lai, M. C.-W. Chan, T.-C. Cheung, S.-M. Peng and C.-M.
Che, Inorg. Chem., 1999, 38, 4046.
19 Preparation adapted from T. Shiyama, M. Furuya, A. Yamazaki,
T. Terada and A. Tanaka, Bioorg. Med. Chem., 2004, 12, 2831.
20 J. F. Michalec, S. A. Bejune, D. G. Cuttell, G. C. Summerton, J. A.
Gertenbach, J. S. Field, R. J. Haines and D. R. McMillin, Inorg.
Chem., 2001, 40, 2193.
21 (a) X. Zhou, H.-X. Zhang, Q.-J. Pan, B.-H. Xia and A.-C. Tang, J.
Phys. Chem. A, 2005, 109, 8809; (b) X.-J. Liu, J.-K. Feng, J. Meng,
Q.-J. Pan, A.-M. Ren, X. Zho and H.-X. Zhang, Eur. J. Inorg.
Chem., 2005, 1856; (c) F. Hua, S. Kinayyigit, J. R. Cable and F. N.
Castellano, Inorg. Chem., 2006, 45, 4304.
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