Synthesis and photophysical properties of bipyridine-extended dithienophosphole chromophores for transition metal complexation

Article abstract of DOI:10.1021/om100421w

The synthesis and photophysical properties of a series of 5-(2,2′-bipyridyl)acetylene-extended dithieno[3,2-b:2′,3′-d] phospholes involving one and two of the latter units are reported. Their molecular scaffolds were found to show limited solubility that could, however, be addressed with the installation of solubilizing groups at the bipyridine unit or the dithienophosphole scaffold, respectively. The photoluminescence features of the new π-conjugated oligomers could be manipulated through complexation to a variety transition metal species (Zn, Pt, and Ru), resulting in polarizable systems with intramolecular charge transfer and/or phosphorescence features, or redox-switching.

Full text of DOI:10.1021/om100421w

Organometallics 2010, 29, 3289–3297 3289
DOI: 10.1021/om100421w
Synthesis and Photophysical Properties of Bipyridine-Extended
Dithienophosphole Chromophores for Transition Metal Complexation
Dong Ren Bai and Thomas Baumgartner*
Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
Received May 4, 2010
The synthesis and photophysical properties of a series of 5-(2,20-bipyridyl)acetylene-extended dithieno-
[3,2-b:20,30-d]phospholes involving one and two of the latter units are reported. Their molecular scaffolds
were found to show limited solubility that could, however, be addressed with the installation of solubilizing
groups at the bipyridine unit or the dithienophosphole scaffold, respectively. The photoluminescence
features of the new π-conjugated oligomers could be manipulated through complexation to a variety
transition metal species (Zn, Pt, and Ru), resulting in polarizable systems with intramolecular charge
transfer and/or phosphorescence features, or redox-switching.
Introduction
tures for the materials as a whole. We were able to illustrate
the benefits of using organophosphorus components in π-
conjugated materials by means of the dithieno[3,2-b:20,30-d ]-
phosphole moiety (I, Chart 1), which we have introduced in this
context several years ago.5 This unit exhibits some useful
photophysical properties (high quantum efficiency, easy color
fine-tuning) and provides flexible options toward derivatiza-
tion, which makes it an excellent chromophore for a variety of
applications.6
To further enhance the electronic properties and the
resulting performance of π-conjugated materials in opto-
electronic applications, researchers have recently also started
to combine the excellent photophysical (light-harvesting as
well as emission) properties of organic chromophores with
those of transition metal complexes to access materials that
exhibit beneficial photoinduced energy/electron transfer
processes that may be useful for solar energy conversion or
light-emitting processes.7
The development of organic π-conjugated materials is a
flourishing field of research, particularly with a view to utilizing
these materials as chromophores and/or light-harvesting build-
ing blocks for optoelectronics such as organic light-emitting
diodes or organic photovoltaics.1 Since a large variety of purely
organic materials have already proven their great value for such
applications, the use of organo-main group components has re-
cently provided a new angle toward π-conjugated materials.2-4
The chemical and electronic nature of the main group compo-
nent provides some intriguing features that create a variety of
tuning possibilities that are not accessible in such simplicity with
purely organic systems. Particularly organoboron,2 -silicon,3
and -phosphorus4 compounds have thus attracted an increasing
amount of attention in this context. The main group functional
groups allow for effective overlap of their orbitals (B: p; Si, P: σ*)
with the π-conjugated framework (π, π*), thus creating some
peculiar electronics and overall enhanced photophysical fea-
As part of our ongoing metal chelation-based supramole-
cular investigations, our initial study combining the excellent
photophysical properties of dithienophospholes with transi-
tion metal moieties allowed us to furnish the dithienophos-
phole scaffold with terpyridine (tpy) moieties to create highly
luminescent ligands (II) that were complexed with transition
*To whom correspondence should be addressed. E-mail: Thomas.
baumgartner@ucalgary.ca.
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Devices; M€ullen, K.; Scherf, U., Eds.; Wiley-VCH: Weinheim, 2006. (c)
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(2) (a) Bosdet, M. J. D.; Piers, W. E. Can. J. Chem. 2009, 87, 8. (b)
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125, 13662. (b) Xu, C.; Wakamiya, A.; Yamaguchi, S. J. Am. Chem. Soc.
2005, 127, 1638. (c) Mouri, K.; Wakamiya, A.; Yamada, H.; Kajiwara, T.;
Yamaguchi, S. Org. Lett. 2007, 9, 93. (d) Biaso, F.; Geoffroy, M.; Canadell,
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Krueger, R. A.; Baumgartner, T. J. Polym. Sci., Part A: Polym. Chem. 2008, 46,
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r
2010 American Chemical Society
Published on Web 06/30/2010 pubs.acs.org/Organometallics

3290 Organometallics, Vol. 29, No. 15, 2010
Bai and Baumgartner
Chart 1
Scheme 2. Synthesis of the Solubilized 50-Bipyridine Acetylene 7
Scheme 3. Synthesis of the Solubilized Chromophores 8 and 10
Scheme 1. Synthesis of Bipyridine-Functionalized Dithieno-
phospholes 2 and 3
metal species.8 In this contribution we now report our structure-
property studies of dithienophosphole-functionalized 2,20-bipyr-
idines (bpy) and their behavior upon metal complexation. Our
studies include the synthesis and photophysical characterization
of bipyridines with one or two dithienophosphole moieties, as
In order to address the solubility issue, we then decided to
furnish the 50-position of the bpy-acetylene with a trimethylsilyl
group for the monodithienophoshole system and the 6-position
of the dithienophosphole scaffold with an octyl moiety for the
bis(dithienophosphole) system. As shown in Scheme 2, the access
to the 50-trimethylsilyl-bpy-acetylene (7) involves a four-step
process. First, 2-bromo-5-trimethylsilylpyridine (4) was con-
verted into its 2-tributyltin counterpart (5) before undergoing
Stille coupling with 2,5-dibromopyridine. The resulting 5-bromo-
50-trimethylsilyl-2,20-bipyridine (6) was then reacted with tri-
methylsilylacetylene to afford 5-ethynyl-50-trimethylsilyl-2,20-bi-
pyridine (7) after deprotection; the choice of deprotection agent
was found to have a strong influence on the conversion efficiency
with K2CO3, giving 91% versus 30% by KF. The necessary
2-bromo-6-octyl-dithienophosphole (9) for the synthesis of the
bis(dithienophosphole) oligomer was reported as part of our
initial study involving the tpy-functionalized systems.8
The solubility-enhanced bpy-functionalized dithienophos-
pholes 8 and 10 (Scheme 3) were then conveniently accessed after
48 h via Heck-Cassar-Sonogashira cross-coupling, in a typi-
cal protocol involving [Pd(PPh3)2Cl2], CuI, and diisopropyl-
amine in THF at room temperature. The similar 31P NMR reso-
nances of δ= 19.4 and 19.7 ppm for 8 and 10, respectively,
correlate well with that of the tpy analogue IIb (Chart 1)8 and
the nonsolubilized species 2(δ=18.7 ppm) and 3(δ=19.1 ppm),
supporting a “pyridinyl”-acetylene-functionalized dithieno-
phosphole core. The 1H and 13C NMR data are also consistent
well as complexation of these π-conjugated oligomers to Zn2þ
,
Pt2þ, and Ru2þ species in order to investigate the electronic
effects of the transition metal species.
Results and Discussion
Synthesis and Characterization of Bipyridine-Functional-
ized Dithienophospholes. Following our previously pub-
lished procedures for the attachment of the tpy functionality
to the 2(6)-position of the dithienophosphole scaffold,8 the
(bpy)-capped dithienophosphole (2) and the bis(dithienophos-
phole)-capped bpy derivative (3) were successfully synthesized
via catalytic Heck-Cassar-Sonogashira cross-coupling proto-
col between 2-iodo-dithienophosphole oxide (1) and 5-bpy-
acetylene/5,50-bpy-diacetylene in moderate yields (Scheme 1).
However, these bpy derivatives were found to possess very
poor solubility in common organic solvents; the products
actually precipitated from the THF reaction mixture, which
prevented any further functionalization, such as metal com-
plexation, and limited their comprehensive characterization
to photophysical studies.
(8) Bai, D. R.; Romero-Nieto, C.; Baumgartner, T. Dalton Trans.
2010, 39, 1250.

Article
Organometallics, Vol. 29, No. 15, 2010 3291
Table 1. Photophysical and Computational Data of the Ligands 2, 3, 8, and 10 and the Complexes 11-1510
d
compound
λ
max [nm]a
λ
abs [nm]b
λ
em [nm]c
φPL
HOMO [eV]e
LUMO [eV]e
HOMO-LUMO gap [eV]e
opt band gap [eV] f
2
3
8
10
11
12
13
14
15
404
401
424
405
433
424
460
483
474
483
491
506
600
0.06
0.20
0.08
0.12
-5.49
-5.38
-5.47
-5.31
-2.33
-2.55
-2.32
-2.45
3.16
2.83
3.15
2.86
2.72
2.59
2.67
2.61
2.59
2.30
2.53
2.27
2.21
417, 440(sh)
402
424
422
460
425, 460(sh)
477, 503(sh)
448
-6.03
-5.89
-3.53
-3.53
2.50
2.36
a UV-vis in CH2Cl2. b λmax for excitation in CH2Cl2. c λmax for emission in CH2Cl2. d Relative to fluorescein (2 M H2SO4 soultion). e B3LYP/6-31G(d)
or B3LYP/LanL2DZ level of theory. f Obtained from the low-energy absorption onset of the UV-vis spectra.
with the targeted structures for 8 and 10 (2 and 3). All four
oligomers show maximum wavelengths of absorption at the
blue edge of the optical spectrum (λmax = 402-424 nm) with
emission in the blue-green region (λem = 474-491 nm). The
photoluminescence data reported in Table 1 of all four ligands in
solution reflect the extent of π-conjugation, with the bis-
(dithienophosphole) systems showing absorption values red-
shifted from those of the monodithienophosphole systems (see
Figure 1). Although the occurrence of a vibronic sideband/
shoulder implies a more rigid molecular scaffold in 3, its emis-
sion features do not follow the same trend, showing a surprising
blue shift of emission when compared to 2 and 8.
The observed values of the extended systems 3 and 10 are,
however, comparable to those of somewhat related, π-conju-
gated oligomers with two dithienophosphole end-caps that we
have reported recently.9 The octyl group in 10 has a similar
effect on the photophysical properties to that in the tpy-
functionalized monodithienophosphole (IIa,b), showing a red
shift of Δλmax=8 nm and Δλem=17 nm upon alkylation (cf. IIa,
b:Δλmax=13 nm and Δλem=17 nm). The photophysical data of
8, on the other hand, do not show any notable shift compared
to those of 2. Surprisingly however, the photoluminescence
quantum yields for all four extended π-conjugated materials are
only low to moderate (φPL = 0.06-0.20), which is in stark
contrast to the corresponding tpy-system, with quantum yields
between φPL=0.55 and 0.79.8 The values are, however, in line
with those of a bis(dithienophosphole)-capped oligomer with
4,40-biphenyl linker (cf. φPL = 0.21).9
For a better understanding of the electronic and lumines-
cence properties of the π-conjugated oligomers 2, 3, 8, and
100,10 DFT calculations were carried out at the B3LYP/6-
31G(d) level of theory.11 As shown in the frontier orbitals
(9) Durben, S.; Linder, T.; Baumgartner, T. New J. Chem. 2010, 34,
doi: 10.1039/c0nj00026d.
(10) The octyl group has been replaced with a methyl substituent to
shorten the DFT calculation times. To account for this truncation,
corresponding molecules are labeled 100, 120, and 140.
(11) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.;
Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
Figure 1. Optical spectra (top: absorption; middle: excitation;
bottom: emission) of the bpy-dithienophospholes 2, 3, 8, and 10.
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,
Revision E.01; Gaussian Inc.: Wallingford, CT, 2007.
(HOMO and LUMO) of 2 (Figure 2), the bpy group adopts a
twisted syn-conformation. Although obviously in conjuga-
tion with the main framework, the peripheral pyridyl ring

3292 Organometallics, Vol. 29, No. 15, 2010
Bai and Baumgartner
Figure 2. Frontier orbitals of compounds 2, 3, 8, and 100 (B3LYP/6-31G(d) level of theory).
contributes only to a minor extent to the π-conjugation,
resulting in a HOMO-LUMO gap of E = 3.16 eV.
observed low quantum yields, by increasing the probability
for nonradiative relaxation pathways.12
By comparison, 3 exhibits a similar frontier orbital profile
to that of 2 (Figure 2). However, the HOMO-LUMO gap is
reduced by 0.35 eV (E = 2.83 eV), due to the greater degree of
conjugation involving the second dithienophosphole unit. In
either case, the lowest electronic transition can be described as
a π-π* transition extended over the terminal dithienophos-
phole(s), the triple bond(s), and the central bipyridine ring(s).
The DFT calculation results also confirmed the inclusion of a
triple bond as a good π-spacer to ensure effective electronic
coupling between the dithienophosphole and bpy units. At-
tachment of a trimethylsilyl group to the bpy unit in 8 (E =
3.15 eV) and octyl functionalization10 of a dithienophosphole
ring in 100 (E = 2.86 eV), respectively, revealed an only mini-
mal effect on the HOMO/LUMO energy levels (ΔE(2,8) =
0.01 eV, ΔE(3,100) = 0.03 eV; Table 1). Although the absolute
values for the calculated HOMO-LUMO gaps for 2, 3, 8, and
100 are slightly different from the optical band gaps obtained
through UV spectroscopy (low-energy absorption edge), their
trends are in excellent agreement with the experimental values.
It should be noted in this context that only 3 shows a fully
coplanar anti-conformation of the bipyridine unit, whereas
the other three compounds were minimized to structures
with twisted syn-arrangement. Due to the similar absolute
HOMO-LUMO gap values for 3 and 100, it is therefore
plausible that the activation barrier for rotation is low and
both conformations represent equivalent minima. Conse-
quently, the twisting of the bipyridine unit could explain the
Synthesis and Characterization of Metal Complexes. To
investigate if the photophysical properties of the new bpy-
functionalized dithienophospholes can be further tuned
through metal coordination, we have synthesized a series
of transition metal complexes with the solubilized ligands 8
and 10. To account for mainly geometric parameter changes
to the scaffold, we have targeted the corresponding Zn2+
complexes, whereas the targeted Pt2+ and Ru2+ complexes
were expected to allow for the introduction of additional
features, such as energy transfer, phosphorescence, or redox
switching.7 With the two solubilized bpy-dithienophos-
pholes in hand, the synthesis of the corresponding complexes
was relatively straightforward (Scheme 4).
The Zn2+ complexes 11 and 12 with tetrahedral geometry
around Zn2+ were readily synthesized by the reaction of
ZnCl2 and the corresponding bpy ligand at room tempera-
ture in dichloromethane. The reactions proceeded very fast,
as evidenced by the immediate color and fluorescence change
upon addition of ZnCl2.
The observed red shifts in the absorption (see Figure 3)
and emission features of 11 and 12 can generally be rationa-
lized in terms of planarization of the molecular scaffold upon
binding to ZnCl2.8 Whereas the effect is less pronounced in
the monodithienophosphole complex 11 (Δλmax = 20 nm;
(12) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3rd ed.;
Springer: New York, 2006.

Article
Organometallics, Vol. 29, No. 15, 2010 3293
Scheme 4. Synthesis of Complexes 11-15
probability of ICT. The latter data are comparable with
those of the related tpy-monodithienophosphole (IIb) and
its Zn complex (Δλabs=29 nm; Δλem=25 nm; Δν=3935 f
3422 cm-1) and support the planarization/rigidification as
the main contributor to the shifted photophysics in 11.8 To
confirm the ICT and the DAD architecture for 12, we have
performed DFT calculations10 at the B3LYP/LanL2DZ
level of theory11 that support the Zn-bpy subunit as an accep-
tor moiety. The LUMO has an increased electron density at
this central component (Figure 4), whereas the HOMO
evenly stretches over the whole molecular scaffold of the
ligand, however, without notable participation of the ZnCl2
moiety.
An ICT in dichloromethane was further supported by the
solvatochromism that 12 exhibits. In contrast to the photolu-
minescence data in dichloromethane, excitation and emission
wavelengths experience a dramatic blue shift in polar donor
solvents such as acetone, dioxane, and DMSO (Figure 5). This
can be rationalized in terms of dielectric solvent interactions
with the Zn center,12,14 effectively reducing its acceptor character
within the molecular scaffold of 12, and therefore, suppressing
the ICT. In fact, the values observed in these donor solvents
(cf. λabs=434-449 nm; λem=496-511 nm) correlate very well
with those of the other related Zn complexes of dithienophos-
pholes reported herein and earlier.8 Remarkably, the Stokes
shifts of Δν=2700-2880 cm-1 also reflect the donor strength
of the solvent used, with the strongest donor (DMSO) resulting
in the smallest Stokes shift (Table 2). The blue shift is also
observed in the UV spectrum of 12 (cf. CH2Cl2: λmax = 460 nm;
acetone: λmax = 423 nm).
Figure 3. Normalized absorption spectra of the complexes
11-15 in CH2Cl2.
Δλem=21 nm), a surprisingly dramatic change is observed
for the extended system 12, particularly for its emission
(Δλmax=37 nm; Δλem=109 nm). In addition to the simple
planarization, Zn complexation also appears to introduce
additional electronic features in this latter case. Considering
the electronics of the Zn-bpy moiety and the dithienophos-
phole oxides, a donor-acceptor-donor (DAD) architecture
likely applies to 12 that allows for ligand-based intramole-
cular charge transfer (ICT) processes upon excitation/
relaxation.12,13 Typical ICT consists of charge redistribution
from the donor to acceptor unit upon excitation. The in-
herent increase of the Stokes shift upon complexation of 10
to 12 (Δν=2728 f 3241 cm-1) supports a polarized structure
in the excited state of 12. On the contrary, the excited state of
complex 11 appears to be of lower polarity than that of the
free ligand 8 (Δν = 4073 f 3822 cm-1), likely due to the
peripheral location of the Zn-acceptor species, reducing the
Pt complexation was successfully performed by stirring 8
or 10 with K2PtCl4 in a mixture of dichloromethane/H2O/
DMSO at room temperature, respectively, and could be
followed by the gradual loss of fluorescence upon excitation
with a hand-held UV lamp (at 366 nm). This solvent combi-
nation is the key to the successful Pt complex formation, as
(13) Valeur, B. Molecular Fluorescence, Principles and Applications;
Wiley-VCH: Weinheim, 2002.
(14) Caspar, J. V.; Meyer, T. J. J. Am. Chem. Soc. 1983, 105, 5583.

3294 Organometallics, Vol. 29, No. 15, 2010
Bai and Baumgartner
Figure 4. Frontier orbitals (B3LYP/LanL2DZ level of theory) for complexes 120 (left) and 140 (right).10,11
Table 2. Fluorescence Data of Complex 12 in Different Solvents
solvent
λ
abs [nm]a
λ
em [nm]b
Δν [cm-1
]
dichloromethane
acetone
dioxane
503
434
446
449
601
496
508
511
3241
2880
2737
2702
DMSO
a λmax for excitation. b λmax for emission.
the appropriate solvent mixture, both square-planar com-
plexes 13 and 14 could be isolated in moderate to good yields
as yellow and orange powders after aqueous workup, respec-
tively. The UV-vis absorption spectra of both complexes
(Figure 3) exhibit red-shifted values for the π-π* transi-
tions at λmax=425 nm for 13 and λmax=477 nm for 14 (cf.
8: λmax=402 nm, 10: λmax=424 nm), which are in line with the
planarization of the main scaffold similar to the Zn species 11
and 12. In addition to the π-π* transition, both Pt complexes
also exhibit shoulders at λmax = 460 nm for 13 and λmax = 503
nmfor14, respectively, thatcanbe assignedasmetal-to-ligand
charge transfer (MLCT) bands.15 The latter is comparable to
the observations with the related tpy-dithienophosphole PtCl2
complex of IIb (cf. λmax(MCLT) = 490 nm).8 As mentioned,
the fluorescence of the complexation reaction mixtures gradu-
ally decreases upon formation of 13 and 14, suggesting the
potential occurrence of phosphorescence. We have therefore
representatively looked into time-dependent photolumine-
scence measurements of the extended complex 14. The observed
relaxation decay for 14 in solution at room temperature could
satisfactorily be fitted for a dual lifetime at τ1 = 0.2 μs (74%)
and τ2 = 15.43 μs (26%). The absolute values and probabilities
suggest that the shorter component arises from a phosphores-
cence process involving a DAD architecture, whereas the long
component appears to involve a Pt-based phosphorescence
process that possibly arises from aggregates.15 The ICT process
is also supported by the frontier orbitals of 14, which confirm
the contribution from the Pt center in the mostly ligand-centered
HOMO and LUMO (Figure 4).
Figure 5. Normalized optical spectra of 12 in different solvents
(top: excitation, bottom: emission).
the commonly used EtOH/H2O combination,15 even at re-
fluxing temperatures, was found to be ineffective, with strong
fluorescence remaining after refluxing overnight; most of the
respective free ligand was recovered after workup. By using
Reaction between the extended bis(dithienophosphole) 10
and Ru(bpy)2Cl2 in refluxing ethanol produced a mixture of
the desired ruthenium complex together with a significant
amount of unreacted 10, as monitored by 1H and 31P NMR.
Replacing ethanol with 2-methoxyethanol was found to
result in a more complete formation of the [Ru(bpy)2(10)]
Cl2 complex, which is believed to be due to the higher boiling
(15) (a) Sun, Y.; Wang, S. Inorg. Chem. 2009, 48, 3755. (b) Castellano,
F. N.; Pomestchenko, I. E.; Shikhova, E.; Hua, F.; Muro, M. L.; Rajapakse, N.
Coord. Chem. Rev. 2006, 250, 1819. (c) Lu, W.; Mi, B.-X.; Chan, M. C. W.;
Hui, Z.; Che, C.-M.; Zhu, N.; Lee, S.-T. J. Am. Chem. Soc. 2004, 126, 4958.
(d) Whittle, C. E.; Weinstein, J. A.; George, M. W.; Schanze, K. S. Inorg.
Chem. 2001, 40, 4053.

Article
Organometallics, Vol. 29, No. 15, 2010 3295
Scheme 5. Synthesis of the bpy-Functionalized Pt Complex 16
transition metal centers in the molecular scaffold. Our studies
have indicated that the resulting mono- and bis(dithieno-
phosphole) bipyridines exhibit reduced solubility. However,
satisfactory solubility features can efficiently be achieved by
functionalizing either the bipyridine moiety with a trimethyl-
silyl group in the 50-positon or the dithienophosphole scaffold
with an octyl group in the 6-position. The resulting extended
bipyridine ligands show moderate photoluminescence fea-
tures that can be tuned further by the incorporation of a Zn,
Pt, or Ru metal center. The bis(dithienophosphole) complexes
of Zn2þ and Pt2þ, in particular, show some intriguing photo-
physical features that arise (a) from donor-acceptor-donor
architectures and (b) from the access to triplet excited states
(for Pt) that open up phosphorescence relaxation pathways;
the Ru2þ complex 15 was found to provide for stable redox
switching between Ru2þ/3þ. The extended Pt-bis(dithieno-
phosphole) complex 14 was used to access a further extended
molecular scaffold for multimetallic arrays, which was, how-
ever, found to be unstable in solution over extended periods
of time, releasing the uncomplexed bis(dithienophosphole)
ligand 10, likely due to steric overcrowding.
point of 2-methoxyethanol over ethanol. Complex 15 was
obtained through anion exchange with KPF6 in aqueous solu-
tion. The dark red complex 15 could be characterized by means
of 1H and31P NMR spectroscopy, as well as mass spectrometry.
Complex 15 was also subjected to cyclic voltammetry studies.
Building upon the observations presented herein, we are
currently addressing further bis(dithienophosphole) systems
that involve cyclometalating complexation sites for the central
transition metal unit. In addition, we are also exploring the
possibility of generating supramolecular assemblies that involve
more than one bis(dithienophosphole) ligand. The results of
these studies will be reported elsewhere in due course.
The characteristic reversible Ru2+/3+ redox couple at E1/2
=
1.43 V (vs Ag/AgCl) in acetonitrile clearly confirmed the pre-
sence of a (bpy)3Ru2+ environment for 15 and the successful
complexation of 10.16 The observed UV-vis absorption wave-
length of λmax = 448 nm is in line with the other complexes of 10
reported herein (Figure 3). A corresponding MLCT process, on
the other hand, could not unambiguously be identified, due to
the broad absorption profile of 15.
Experimental Section
Further Modification of a Pt Complex. Complex 14 was
envisioned to be an excellent building block for heteropoly-
nuclear arrays with potentially dual luminescence features. It is
well known in the literature that the chlorides at Pt can easily be
replaced with acetylides.15,17 When the acetylides are appended
with additional bipyridine units, the whole molecular scaffold
could potentially be further complexed with, for example, lan-
thanide moieties, allowing the extended (bpy)Pt-bisacetylide
moieties to act as sensitizers for lanthanide luminescence.17 In
an attempt to access a similar scaffold, functionalization of 14
with bpy-4-acetylene was carried out by Cu(I)-catalyzed sub-
stitution reaction in refluxing dichloromethane solvent in the
presence of diisopropylamine. Although 16 could be obtained
as dark orange powder in modest yield that allowed for charac-
terization by heteronuclear NMR spectroscopy and high-
resolution mass spectrometry, the bpy-functionalized Pt com-
plex was found to be unstable in solution. It decomposes into the
uncomplexed 10, which could be confirmed by the occurrence of
yellow fluorescence, as well as NMR spectroscopy.18 The inst-
ability of 16 unfortunately precluded any further characteriza-
tion and complexation.
General Procedures. Reactions were carried out in dry glass-
ware and under an inert atmosphere of purified nitrogen using
Schlenk techniques. Solvents were dried using an MBraun solvent
purification system. n-BuLi (2.5 M in hexane), 2,5-dibromopyr-
idine, K2PtCl4, ZnCl2 (0.1 M in THF), [Pd(PPh3)4] CuI, and
[Pd(PPh3)2Cl2] were used as received. Diisopropylamine, tributyltin
chloride, and trimethylsilyl acetylene were freshly distilled prior to
use. 2-Iododithieno[3,2-b:20,30-d]phosphole oxide (1),8 5-ethynyl-
2,20-bipyridine,19 5,50-diethynyl-2,20-bipyridine,19 2-bromo-5-tri-
methylsilylpyridine (4),16 2-bromo-6-octyldithieno[3,2-b:20,30-d]-
phosphole oxide (9),8 and Ru(bpy)2Cl220 were prepared by litera-
ture methods. 1H, 13C{1H}, and 31P{1H} NMR spectra were
recorded on a Bruker Avance-II 400 spectrometer. Chemical shifts
were referenced to external 85% H3PO4 (31P) and TMS (1H, 13C). It
should be mentioned in this context that due to their reduced
solubility, no satisfactory 13C NMR data could be obtained for the
transition metal complexes 11-16. Mass spectra were run on a
Finnigan SSQ 7000 spectrometer, or a Bruker Daltonics AutoFlex
III system. Optical spectroscopy experiments were recorded in a
dichloromethane solution using a Jasco FP-6600 spectrofluoro-
meter and UV-vis NIR Cary 5000 spectrophotometer. Electroche-
mical studies were performed on an Autolab PGSTAT302 instru-
ment with a Pt rod as working electrode, Pt wire as counter elec-
trode, and AG/AgCl/KCl3M as reference electrode; supporting
electrolyte was NBu4PF6; scan rate was 100 mV s-1. Theoretical
calculations have been carried out at the B3LYP/6-31G(d) (2, 3, 8,
100) and B3LYP/LanL2DZ (120, 140) level by using the GAUSS-
IAN 03 suite of programs.13 The geometries were fully optimized,
and at the resulting structures second derivatives were calculated.
Synthesis of Compound 2. 2-Iododithieno[3,2-b:20,30-d ]phos-
phole oxide (0.36 mmol, 150 mg), 5-ethynyl-2,20-bipyridine
Conclusion
In conclusion, we were able to successfully functionalize the
dithienophosphole unit with bipyridine mono- and bisacety-
lenegroups, whichallowed for the additionalincorporation of
(16) Stange, A. F.; Tokura, S.; Kira, M. J. Organomet. Chem. 2000,
612, 117.
(17) (a) Chen, Z.-N.; Fan, Y.; Ni, J. Dalton Trans. 2008, 573. (b) Muro,
M. L.; Rachford, A. A.; Wang, X.; Castellano, F. N. Top. Organomet. Chem.
2010, 29, 159.
(19) Grosshenny, V.; Romero, F. M.; Ziessel, R. J. Org. Chem. 1997,
62, 1491.
(20) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Inorg. Chem. 1978, 17,
(18) A pure sample of 10 could be isolated from the reaction mixture
by means of preparative thin-layer chromatography.
3334.

3296 Organometallics, Vol. 29, No. 15, 2010
Bai and Baumgartner
(0.4 mmol, 72 mg), [Pd(PPh3)4] (22 mg), diisopropylamine
(3 mL), and THF (15 mL) were heated at 80 °C for 72 h under
nitrogen. After cooling to ambient temperature, the precipitate
was filtered and dissolved in an excess amount of CHCl3. The
solution was then washed with aqueous KOH solution and
water. The organic layer was separated and dried over MgSO4,
and the solvents were evaporated under reduced pressure to
afford a yellow solid of 2 in 45% yield (0.076 g). 31P{1H} NMR
(162 MHz, CD2Cl2): δ 18.7 ppm. 1H NMR (400 MHz, CDCl3):
δ 8.79 (dd, J = 2.0, 0.8 Hz, 1H), 8.70 (d, J = 4.0 Hz, 1H), 8.44 (d,
J = 8.0 Hz, 2H), 7.92 (dd, J = 8.0, 2.0 Hz, 1H), 7.84 (dt, J = 2.0
Hz, 1H), 7.79-7.73 (m, 2H), 7.60-7.58 (m, 1H), 7.49-7.46 (m,
2H), 7.39-7.34 (m, 3H), 7.23 (dd, J = 4.8, 2.4 Hz, 1H) ppm.
13C{1H} NMR (100 MHz, CDCl3): δ 155.50 (J = 8.0 Hz),
151.39, 149.34, 146.45 (J = 23 Hz), 145.45 (J = 25 Hz), 139.60
(J = 93 Hz), 139.34, 138.60 (J = 93 Hz), 136.99, 132.80 (J =
3.0 Hz), 130.95 (J = 14 Hz), 130.87 (J = 12 Hz), 129.33 (J = 35
Hz), 128.43, 126.32 (J = 14 Hz), 125.98 (J = 17 Hz), 92.83,
85.81 ppm. HRMS: m/z 466.0365 ([M]þ, calcd 466.0363).
Synthesis of Compound 3. 2-Iododithieno[3,2-b:20,30-d ]phos-
phole oxide (0.9 mmol, 350 mg), 5,50-diethynyl-2,20-bipyridine
(0.36 mmol, 73 mg), [Pd(PPh3)4] (70 mg), diisopropylamine (10
mL), and THF (25 mL) were heated at 80 °C for 90 h under
nitrogen. After cooling to ambient temperature, the precipitate
was filtered and washed with plenty of ether and dried over
MgSO4, and the solvents were evaporated under reduced pres-
sure to afford a reddish solid of 3 in 15% yield (0.042 g). 31P{1H}
(80 mg), diisopropylamine (9 mL), and THF (50 mL) were
stirred at room temperature for 48 h under nitrogen. The solvent
was removed, and the residue was dissolved in pentane. The pre-
cipitate was filtered, the mother liquid was dried over MgSO4,
and the solvents were evaporated under reduced pressure to
afford the product as a pale white solid in 86% yield (0.70 g).
1H NMR (400 MHz, CDCl3): δ 8.75 (m, 2H, bpy), 8.37
(t, J = 8.0 Hz, 2H, bpy), 7.93 (dd, J = 8.0, 2.0 Hz, 1H,bpy), 7.87
(dd, J = 8.0, 2.0 Hz, 1H, bpy), 0.35 (s, 9H), 0.30 (s, 9H) ppm.
13C{1H} NMR (100 MHz, CDCl3): δ 155.45, 155.13, 153.42,
152.05, 142.09, 139.74, 135.68, 120.54, 120.12, 101.91, 99.08,
-0.13, -1.32 ppm. HRMS: m/z 324.1463 ([M]þ, calcd 324.1478).
Synthesis of 5-Ethynyl-50-(trimethylsilyl)-2,20-bipyridine (7).
To a stirred solution of 5-(trimethylsilyl)-50-((trimethylsilyl)-
ethynyl)-2,20-bipyridine (0.3 mmol, 100 mg) in MeOH/THF
(10/10 mL) was added KF (60 mg) as a solid. After overnight
stirring, the solvent was removed to give a crude product, which
was further purified by flash chromatography (pentane). Yield:
70 mg (95%). 1H NMR (400 MHz, CDCl3): δ 8.78 (m, 2H, bpy),
8.38 (dd, J = 20, 8.0 Hz, 2H, bpy), 7.93 (m, 2H, bpy), 3.30 (s,
1H), 0.35 (s, 9H). 13C{1H} NMR (100 MHz, CDCl3): δ 155.52,
155.26, 153.38, 152.17, 142.06, 139.88, 135.73, 120.51, 120.18,
119.05, 81.34, 80.75, -1.35 ppm. HRMS: m/z 252.1077 ([M]þ,
calcd 252.1083).
Synthesis of Compound 8. 2-Iododithieno[3,2-b:20,30-d ]phos-
phole oxide (1) (0.79 mmol, 328 mg), compound 7 (0.8 mmol,
200 mg), [Pd(PPh3)4] (80 mg), diisopropylamine (12 mL), and
THF (40 mL) were heated at 80 °C for 90 h under nitrogen. After
cooling to ambient temperature, the solvent was removed under
vacuum and extracted with CH2Cl2. The organic phase was
combined and dried over MgSO4. The crude was subjected to
preparative TLC (ethyl acetate) to afford a reddish solid of 8 in
62% yield (0.260 g). 31P{1H} NMR (162 MHz, CD2Cl2): δ 19.4
ppm. 1H NMR (400 MHz, CDCl3): δ 8.77 (d, J = 2.0 Hz, 1H),
8.44 (d, J = 8.0 Hz, 1H), 7.91 (dd, J = 8.0, 2.0 Hz, 1H), 7.84 (dt,
J = 2.0 Hz, 1H), 7.79-7.73 (m, 2H), 7.60-7.58 (m, 2H), 7.49-
7.46 (m, 2H), 7.39-7.34 (m, 3H), 7.23 (dd, J = 4.8, 2.4 Hz, 1H),
0.35 (s, 9H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 155.07,
154.97, 153.16, 151.42, 146.42 (J = 23 Hz), 145.40 (J = 24
Hz), 142.49, 139.90 (J=74 Hz), 139.14, 138.43, 136.12, 132.71
(J=2.8 Hz), 132.09 (J=10 Hz), 130.84 (J = 12 Hz), 129.46 (J=
15 Hz), 129.11 (J=108 Hz), 129.01 (J=13 Hz), 128.48 (J=12
Hz), 126.25 (J=15 Hz), 125.87 (J = 17 Hz), 120.59 (J = 28 Hz),
119.41, 92.76, 85.96, -1.35 ppm. HRMS: m/z 538.0764 ([M]þ,
calcd 538.0759).
Synthesis of Compound 10. Dithieno[3,2-b:20,30-d ]phosphole
oxide (9) (0.9 mmol, 350 mg), 5,50-diethynyl-2,20-bipyridine
(0.36 mmol, 73 mg), [Pd(PPh3)4] (70 mg), diisopropylamine
(10 mL), and THF (25 mL) were heated at 80 °C for 72 h under
nitrogen. After cooling to ambient temperature, the solvent was
removed under vacuum, and the residue was extracted with
CH2Cl2. The organic phase was collected and dried over
MgSO4. After evaporation of the solvent, the product was
further purified by washing with cold diethyl ether to afford a
reddish solid of 10 in 79% yield (0.340 g). 31P{1H} NMR (162
MHz, CD2Cl2): δ 19.7 ppm. 1H NMR (400 MHz, CDCl3): δ 8.78
(d, J = 1.6 Hz, 2H, bpy), 8.44 (d, J = 8.0 Hz, 2H, bpy), 7.91 (dd,
J = 8.0, 2.0 Hz, 2H, bpy), 7.76 (m, 4H), 7.55 (m, 2H), 7.47 (m,
4H), 7.33 (d, J = 2.8 Hz, 2H), 6.88 (s, 2H), 2.82 (t, J = 7.2 Hz,
4H), 1.68 (m, 4H), 1.28 (m, 20H), 0,.89 (t, J = 4.4 Hz, 6H) ppm.
13C{1H} NMR (100 MHz, CDCl3): δ 154.33, 152.06 (J = 16
Hz), 151.45, 147.39 (J=25 Hz), 142.64 (J=28 Hz), 139.47 (J=
112 Hz), 139.06, 137.69 (J = 113 Hz), 132.65, 131.03 (J = 19
Hz), 130.88 (J = 11 Hz), 129.53 (J = 92 Hz), 129.00 (J = 14 Hz),
124.85 (J=19 Hz), 122.92 (J=15 Hz), 120.70, 119.74, 92.44,
86.52, 31.81, 31.47, 30.51, 29.24, 29.15, 28.96, 22.65, 14.09 ppm.
HRMS: m/z 1001.2622 ([M]þ, calcd 1001.2638).
1
NMR (162 MHz, CD2Cl2): δ 19.1 ppm. H NMR (400 MHz,
CDCl3): δ 8.79 (d, J = 2.0 Hz, 1H, bpy), 8.47 (dd, J = 8.0, 3.2
Hz, 1H, bpy), 7.93 (dd, J = 8.0, 2.0 Hz, 1H,bpy), 7.79 (m, 2H,
bpy), 7.58 (m, 1H), 7.53 (m, 2H), 7.37 (m, 2H), 7.22 (dd, J = 4.8,
2.4 Hz, 2H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 154.34,
151.45, 146.52 (J = 22 Hz), 145.37 (J = 24 Hz), 139.95 (J = 75
Hz), 138.83 (J = 73 Hz), 138.47, 132.72, 131.07 (J = 14 Hz),
130.84 (J = 22 Hz), 129.53 (J = 15 Hz), 129.09 (J = 109 Hz),
129.03 (J = 13 Hz), 126.26 (J = 14 Hz), 125.77 (J = 17 Hz),
120.72, 119.64, 92.72, 86.28 ppm. HRMS: m/z 776.0012 ([M]þ,
calcd 776.0039).
Synthesis of 2-(Tributylstannyl)-5-(trimethylsilyl)pyridine (5).
To a solution of n-BuLi (2.5 M, 5.5 mL) diluted with dry Et2O
(6 mL) was added a solution of 2-bromo-5-(trimethylsilyl)pyridine
(4) in dry ether (13 mL) at -78 °C. The mixture was stirred for 1 h
at -78 °C before a solution of tributyltin chloride was added
dropwise. The reaction was allowed to reach room temperature
and left stirring overnight. The reaction was quenched with
saturated NH4Cl solution, and the organic layer was washed
with H2O. The organic phase was then dried with MgSO4 and
evaporated to afford a yellow oil in 95% yield (5.6 g). 1H NMR
(400 MHz, CDCl3): δ 8.82 (s, 1H, py), 7.59 (dd, J = 7.2, 2.0 Hz,
1H, py), 7.38 (dd, J = 7.2, 1.2 Hz, 1H, py), 1.57 (m, 6H), 1.34 (m,
6H), 1.12 (m, 6H), 0.89 (m, 9H), 0.29 (s, 9H, TMS) ppm.
13C{1H} NMR (100 MHz, CDCl3): δ 174.24, 154.36, 138.18,
132.58, 131.96, 29.18, 27.08, 13.69. 9.72, -1.50 ppm. HRMS:
m/z 426.1630 ([M - CH3]þ, calcd 426.1639).
Synthesis of 5-Bromo-50-(trimethylsilyl)-2,20-bipyridine (6).
Compound 5 (6.3 mmol, 780 mg), 2,5-dibromopyridine (6.0
mmol, 1.466 g), [Pd(PPh3)4] (80 mg), and toluene (50 mL) were
heated at 110 °C for 72 h under nitrogen. After cooling to
ambient temperature, the solvent was removed and the residue
was subjected to column chromatography (ethyl acetate/hex-
ane, 1:4). The first fraction was collected and run through a KF/
1
Celite mixture to afford a light yellow solid (1.5 g, 77%). H
NMR (400 MHz, CDCl3): δ 8.74 (m, 2H, bpy), 8.33 (m, 2H,
bpy), 7.93 (m, 2H,bpy), 0.35 (s, 9H) ppm. 13C{1H} NMR
(100 MHz, CDCl3): δ 155.16, 154.79, 153.39, 150.19, 142.14,
139.42, 135.71, 122.27, 121.08, 120.09, -1.34 ppm. HRMS: m/z
306.0181 ([M]þ, calcd 306.0188).
Synthesis of 5-(Trimethylsilyl)-50-((trimethylsilyl)ethynyl)-
2,20-bipyridine. Compound 6 (2.5 mmol, 770 mg), trimethylsilyl
acetylene (2.7 mmol, 0.83 mL), [Pd(PPh3)2Cl2] (186 mg), CuI
Synthesis of Zn(8)Cl2 (11). To a solution of compound 8
(25 mg, 0.025 mmol) in CH2Cl2 (6 mL) was added a THF solu-
tion of ZnCl2 (0.5M, 0.06 mL). The solution immediately turned

Article
Organometallics, Vol. 29, No. 15, 2010 3297
orange and was stirred overnight. The solvent was removed
under vacuum and then washed with cold ether to afford pure 11
in 59% yield (10 mg). 31P{1H} NMR (162 MHz, DMSO-d6): δ
17.15 ppm. 1H NMR (400 MHz, DMSO-d6): δ 8.89 (1H), 8.83
(1H), 8.52 (1H), 8.45 (1H), 8.19 (m, 2H), 7.81 (m, 2H), 7.72 (m,
2H), 7.63 (m, 1H), 7.53 (m, 2H), 7.44 (m, 1H), 0.34 (s, 9H) ppm.
HRMS: m/z 638.97092 ([M - Cl]þ, calcd 638.97071).
2H), 8.00 (d, J=7.6 Hz, 2H), 7.72 (m, 4H), 7.57 (m, 2H), 7.47 (m,
4H), 7.37 (d, J = 2.4 Hz, 2H), 6.82 (s, 1H), 2.80 (m, 4H), 1.60 (m,
4H), 1.28 (m, 20H), 0.89 (m, 6H) ppm. HRMS: m/z 1289.14061
([M þ Na]þ, calcd 1289.14555).
Synthesis of Ru(10)bpy2(PF6)2 (15). Compound 10 (50 mg,
0.05 mmol) and Ru(bpy)2Cl2 (60 mg, 0.12 mmol) were heated to
125 °C overnight. After the mixture cooled, an aqueous solution
of KPF6 (200 mg) was added. The solution was stirred for 2
days. The solvent was removed under vacuum, and the residue
was extracted with CH2Cl2 and dried over MgSO4. After the
evaporation of the solvent, the residue was washed with diethyl
ether to afford a dark red powder of 15 in 47% yield (40 mg).
31P{1H} NMR (162 MHz, CD3CN): δ 17.30, -143.68 (sept)
Synthesis of Zn(10)Cl2 (12). To a solution of 10 (25 mg, 0.025
mmol) in CH2Cl2 (6 mL) was added a THF solution of ZnCl2
(0.5 M, 0.06 mL). The solution immediately turned orange and
was stirred overnight. The solvent was removed under vacuum
and then washed with cold ether to afford pure 12 in 54% yield
(15 mg). 31P{1H} NMR (162 MHz, DMSO-d6): δ 17.64 ppm. 1H
NMR (400 MHz, DMSO-d6): δ 8.88 (s, 2H), 8,44 (d, 2H), 8.15
(d, 2H), 7.79 (2H), 7.68 (m, 4H), 7.63 (m, 2H), 7.54 (m, 4H), 7.19
(s, 2H), 2.85 (m, 4H), 1.65 (m, 4H), 1.23 (m, 20H), 0.84 (m, 6H)
ppm. HRMS: m/z 1101.15417 ([M - Cl]þ, calcd 1101.15019).
Synthesis of Pt(8)Cl2 (13). To a stirred solution of K2PtCl4 (38
mg, 0.09 mmol) in a mixed solvent of H2O (10 mL) and DMSO
(0.5 mL) was added 8 (40 mg, 0.07 mmol) in CH2Cl2 (5 mL). The
mixture was stirred at room temperature overnight. The organic
phase was separated and dried over MgSO4. After the evapora-
tion of solvent, the residue was washed by cold diethyl ether
to afford a light yellow powder of 13 in 50% yield (28 mg).
31P{1H} NMR (162 MHz, CD2Cl2): δ 18.85 ppm. 1H NMR (400
MHz, CDCl3): δ 9.66 (m, 2H), 8.22 (dd, J = 8.0, 1.6 Hz, 1H),
8.16 (dd, J = 8.0, 1.6 Hz, 1H), 8.40 (d, J = 8.0 Hz, 2H, bpy), 7.95
(dt, J = 8.0, 2.0 Hz, 4H,bpy), 7.78 (m, 2H), 7.61 (m, 1H), 7.50
(m, 2H), 7.40 (d, J = 2.4 Hz, 2H), 7.18 (dd, J = 2.4, 4.8 Hz, 1H),
0.40 (s, 9H) ppm. HRMS: m/z 826.96737 ([M þ Na]þ, calcd
826.966263).
1
ppm. H NMR (400 MHz, CD3CN): δ 8.49 (m, 6H), 8.11 (m,
8H), 7.79 (m, 4H), 7.69 (m, 8H), 7.43 (m, 8H), 6.97 (s, 2H), 2.86
(m, 4H), 1.68 (m, 4H), 1.28 (m, 20H), 0.89 (m, 6H) ppm. HRMS:
m/z 1414.29816 ([M - 2PF6]þ, calcd 1414.29747).
Synthesis of Pt(10)(4-ethynyl-bpy)2 (16). Compound 14 (145
mg, 0.141 mmol), 5-ethynyl-2,20-bipyridine (83 mg, 0.461
mmol), and CuI (30 mg) were dissolved in CH2Cl2 (12 mL)
and diisopropylamine (3 mL) and refluxed for 4 days. The
organic phase was separated and dried over MgSO4. After the
evaporation of solvent, the residue was washed by cold diethyl
ether first and then cold ethyl acetate to afford a dark orange
powder of 16 in 14% yield (30 mg). 31P{1H} NMR (162 MHz,
CD2Cl2): δ 19.21 ppm. 1H NMR (400 MHz, CD2Cl2): 9.88 (1H),
8.91 (2H), 8.68 (2H), 8.45 (2H), 8.39 (2H), 8.17 (2H), 7.97 (4H),
7.86 (4H), 7.72 (4H), 7.53 (2H), 7.41 (6H), 6.86 (s, 1H), 2.81 (m,
4H), 1.60 (m, 4H), 1.26 (m, 20H), 0.89 (m, 6H) ppm. HRMS: m/z
1555.34479 ([M þ H]þ, calcd 1555.34984).
Synthesis of Pt(10)Cl2 (14). To a stirred solution of K2PtCl4
(25 mg, 0.06 mmol) in a mixed solvent of H2O (10 mL) and
DMSO (0.5 mL) was added 10 (50 mg, 0.05 mmol) in CH2Cl2 (10
mL). The mixture was stirred at room temperature overnight.
The organic phase was separated and dried over MgSO4. After
the evaporation of solvent, the residue was washed by cold
diethyl ether to afford a dark orange powder of 14 in 66% yield
(50 mg). 31P{1H} NMR (162 MHz, CD2Cl2): δ 19.25 ppm. 1H
NMR (400 MHz, CD2Cl2): 9.69 (s, 2H), 8.17 (d, J = 9.2 Hz,
Acknowledgment. Financial support by the Natural
Sciences and Engineering Research Council (NSERC)
of Canada and by the Canada Foundation for Innovation
(CFI) is gratefully acknowledged. T.B. also thanks Al-
berta Ingenuity now Part of Alberta Innovates - Technol-
ogy Futures for a New Faculty Award. We thank Paolo
Bomben for his support with the phosphorescence life-
time measurements.