Cyclometallated, bis-terdentate iridium complexes as linearly expandable cores for the construction of multimetallic assemblies

Article abstract of DOI:10.1039/b821161b

Cyclometallated iridium complexes comprised of two terdentate cyclometallating ligands, of the form [Ir(NCN)(NNC)]⁺, have been explored for the preparation of multimetallic systems by palladium-catalysed cross-coupling reactions. An NNC-coordin

Full text of DOI:10.1039/b821161b

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www.rsc.org/dalton | Dalton Transactions
Cyclometallated, bis-terdentate iridium complexes as linearly expandable
cores for the construction of multimetallic assemblies†
Victoria L. Whittle and J. A. Gareth Williams*
Received 26th November 2008, Accepted 12th February 2009
First published as an Advance Article on the web 17th March 2009
DOI: 10.1039/b821161b
Cyclometallated iridium complexes comprised of two terdentate cyclometallating ligands, of the form
[Ir(NŸCŸN)(NŸNŸC)]+, have been explored for the preparation of multimetallic systems by
palladium-catalysed cross-coupling reactions. An NŸNŸC-coordinating ligand carrying a boronate ester
group has been prepared and complexed to iridium to give a boronic acid appended complex of this
type, 3. This complex has been subjected to cross-coupling with a bromo-substituted bis-terpyridyl
iridium complex to give a dinuclear iridium compound 6, in which one of the two iridium centres is
N6-coordinated and the other has an N4C2-coordination sphere. Meanwhile, a bromo-substituted
complex 4 has been coupled with a boronic acid-appended ruthenium complex, to give a dinuclear
heterometallic complex 8 that can be activated to a second coupling by in situ bromination, offering
access to a linear Ir–Ir–Ru trimetallic assembly 11. The electrochemical and luminescence properties of
these systems are investigated. In the case of 8 and 11, the behaviour can be rationalised in terms of a
supramolecular description: efficient energy transfer occurs from the Ir terminus to the Ru. In contrast,
for compound 6, an excited state with significant bridge character appears to play a key role in
determining the emission properties.
Pioneering work in the 1990s made use of bridging aromatic
Introduction
ligands (e.g. hexaazaphenanthrene and triazoles) to construct
Within the field of supramolecular photochemistry, a prevailing
heterometallic Ru/Ir assemblies, in which each metal was chelated
theme of research has been the question of how to construct
in a tris-bidentate fashion.13–15 Assemblies displaying energy
molecular assemblies in a controlled and efficient manner from
transfer from Ir to Ru or vice versa could be constructed, although
individual units, in such a way that the photophysical properties
the quantum efficiencies of systems based on pyrazine bridges, for
of the final assembly can be predicted reliably on the basis of
example, are compromised by severe non-radiative decay.15 More
the “building blocks” from which it is comprised. Indeed, one
of the definitions of the term “supramolecular photochemistry”,
as proposed by Balzani, relates to photoactive multi-component
recent studies have made use of bridging para-phenylene-bridged
bis-bipyridines of the form NŸN–(f)n–NŸN.16
The conventional approach to such (poly)aryl-bridged systems
systems held together by covalent bonds, where the components
involves the prior synthesis of multitopic ligands, followed by
have distinct spectroscopic and photophysical identities.1 Inter-
stepwise metal complexation.17 Although this strategy has led to a
component processes, such as long-range directional energy-
diverse range of complexes, it is frequently limited by incomplete
and/or electron-transfer and charge separation, can then fre-
control over the structure and composition of the final assembly.
quently be achieved through appropriate choice of units.2–4
A number of research teams have been developing a “building
Polypyridyl complexes of the transition metals Ru(II) and Ir(III)
block” approach to the formation of multimetallic assemblies,
are widely regarded as attractive components in such assemblies,
involving chemistry on suitably functionalised complexes.18–20 In
owing partly to their relatively long excited state lifetimes, which
our case, we have been exploring the utility of boronic acid-
allow energy- or electron-transfer to compete with usual deactiva-
appended complexes in Pd-catalysed cross-coupling reactions with
tion pathways, and to the relative ease with which their key pho-
halo-substituted complexes as a reliable route to heterometallic
tophysical properties—in particular, excited state energies—can
assemblies, and have constructed systems containing three or more
be controlled through ligand modification.5,6 Interest in iridium-
different types of tris-bidentate metal centres in this way.21,22
based complexes, in particular, is blossoming at present owing
to diverse applications.7 These include the use of mononuclear
Tris-bidentate complexes are intrinsically chiral (D3 or C2
symmetry with K and D enantiomers), which leads to mixtures
complexes as triplet-harvesting dopants in OLEDs,8,9 luminescent
of diastereomeric products when incorporated into multimetallic
probes for biological systems,10 photovoltaics,11 and photocata-
assemblies. The diastereomers may have different photophysical
lysts for water splitting.12 Further potential may be opened up
through incorporation into multimetallic systems.
properties, for example arising from different distances between
units. The cis-disposition of the cyclometallated carbon atoms in
[Ir(ppy)2(bpy)]+ complexes23 alleviates the problem to the extent
Department of Chemistry, University of Durham, Durham, UK DH1 3LE.
that linear assembly is assisted, for instance by substitution at
E-mail: j.a.g.williams@durham.ac.uk
the pyridyl 4-position of the ppy ligands, but does not remove
† Electronic supplementary information (ESI) available: Fig. S1–S5. See
DOI: 10.1039/b821161b
This journal is The Royal Society of Chemistry 2009
the chirality. An attractive alternative is the use of achiral D2d
Dalton Trans., 2009, 3929–3940 | 3929
©

bis-terdentate components, which are particularly appealing for
the construction of linear assemblies when elaborated at the
central position (e.g. the 4¢ of terpyridines).24–26 However, rather
fewer such complexes have been established to date, and they
sometimes have vastly inferior properties; e.g. the well known case
of [Ru(tpy)2]2+, which suffers from very rapid non-radiative decay
at room temperature (tem ~ 1 ns), in contrast to the desirable
properties of [Ru(bpy)3]2+ (tem ~ 1 ms).27
Our group has been investigating the chemistry and excited
state properties of iridium(III) complexes with terdentate ligands.26
Very recently, we described the preparation of iridium(III) com-
plexes comprising NŸCŸN and NŸNŸC-coordinating ligands, e.g.
1 (Fig. 1), which are bis-terdentate analogues of the well-known
class of complexes of the type [Ir(NŸC)2(NŸN)]+.28 The latter—
of which [Ir(ppy)2(bpy)]+ 2 (Fig. 1) is the archetypal example—
have attractive photophysical properties similar to those of
[Ru(bpy)3]2+.6,29,30 We found that, in contrast to [Ru(tpy)2]2+, these
desirable properties are retained—indeed sometimes augmented—
neopentylglycolate ester, the boronate product can be hydrolysed
readily to the corresponding boronic acid.
In the present work, we found that the NŸNŸC-coordinating
proligand 4-(p-bromophenyl)-6-(m-tolyl)bipyridine (mtbpyH–Br)
could be readily converted to the boronate ester deriva-
tive mtbpyH-f-B upon palladium-catalysed reaction with bis-
neopentylglycolato diboron (B2neo2) in the presence of potas-
sium acetate. This ligand was then used to prepare an
[Ir(NŸCŸN)(NŸNŸC)]+ complex, by reaction with the chloro
bridged dimer [Ir(dpyx)Cl(m-Cl)]2 (Scheme 1), which is in turn
generated by the cyclometallation of iridium to the dipyridylxylene
ligand, dpyxH.34,35 In our previous work, the introduction of the
NŸNŸC-coordinating ligand was achieved by reaction at high
temperature (refluxing ethylene glycol at 198 ◦C) for a short
period of time (30–60 min).28 However, the relatively weak and
labile nature of the C–B bond renders aryl boronates susceptible
to thermally activated hydrodeboronation, and the new ligand
did not tolerate complexation at such high temperatures. We
found that complexation could be achieved successfully, without
significant competing deboronation, by using a lower temperature
of 140 ◦C in conjunction with a longer reaction time of 3 h.
In a similar way, Collin et al. were able to achieve the selective
complexation of a terpyridine to Ir(tButpy)Cl3, in the presence of a
phenanthroline pendant, by reducing the temperature to 140 ◦C.36
The resulting orange bis-terdentate complex [Ir(dpyx)(mtbpyH-f-
B)]Cl 3 was converted to the hexafluorophosphate salt and purified
by column chromatography on silica, using CH2Cl2/MeOH as the
in the bis-terdentate systems (e.g. for 1, lmax = 632 nm, Ulum
=
0.023, tlum = 120 ns in MeCN at 298 K). We also demonstrated
that complexes of this type are amenable to extension with organic
groups, in a stepwise manner, by a sequence of successive cross-
coupling–bromination–cross-coupling reactions. In this contri-
bution, we explore the potential of such complexes as building
blocks in the construction of multimetallic assemblies using this
methodology.
1
eluant. H NMR spectroscopy and mass spectrometry revealed
Results and discussion
that the expected hydrolysis of the boronate ester occurred during
chromatography, and that the main component isolated, in high
yield, was the monomethyl ester, as shown in Scheme 1.
Synthesis
1. Boronate-ester substituted complex. In the first instance,
we sought to prepare an [Ir(NŸCŸN)(NŸNŸC)]+ complex incor-
porating boronic acid functionality. The boronic acid group is
widely used in palladium-catalysed cross-couplings, as originally
pioneered by Suzuki and now a central tool in synthetic organic
chemistry for aryl–aryl bond formation.31 The classical route
to aryl boronic acids involves conversion of haloaromatics to
aryl lithium derivatives, and treatment with trialkylborates. In
previous work on terpyridines and bipyridines, we found that this
method gave very poor results, whereas palladium-catalysed cross-
coupling with bis-boron esters such as bis(pinacolato)diboron gave
far superior yields of the boronate ester.32,33 In the case of the bis-
The alternative and potentially attractive method of prepar-
ing such a boronate ester-substituted complex in situ, i.e. by
carrying out a palladium-catalysed cross-coupling reaction on a
bromo substituted complex, was also investigated. The complex
[Ir(dpyx)(mtbpyH-f-Br)]+ 4 was treated with an excess of B2neo2
in the presence of Pd(dppf)Cl2 in DMSO solution, a medium
that offers solubilisation of both the complex and reactants.
However, none of the desired boronated complex was isolated, the
main product being identified as the hydro-debrominated complex
by 1H-NMR spectroscopy and mass spectrometry. Similarly,
attempts to boronate the NŸCŸN-coordinating ligand of [Ir(dpyx-
Br)(mtbpy-f-ph)]+ at the C4¢-position gave a mixture of unreacted
Fig. 1 The parent structures of complexes of the type [Ir(NŸCŸN)(NŸNŸC)]+ and [Ir(NŸC)2(NŸN)]+: Ir(dpyx)(phbpy)]+ 1 and [Ir(ppy)2(bpy)]+ 2, and the
structure of the biphenyl-appended complex 12 used as a model in interpreting the emission properties of the multimetallic compounds.
3930 | Dalton Trans., 2009, 3929–3940
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©

Scheme 1 Synthesis of boronic ester-appended NŸNŸC ligand and its use in the preparation of a boronic acid-substituted iridium(III) complex 3.
and hydrodebrominated complexes. We note that although such a
strategy in previous work on ruthenium(II) terpyridines did allow
conversion of [Ru(tpy)(tpy–Br)]2+ to [Ru(tpy){tpy–B(OH)2}]2+, the
yield was greatly inferior to that obtained by direct complexation
of the terpyridine boronate to ruthenium.32 Apparently, therefore,
hydrodehalogenation is promoted when the ligand is coordinated
to the metal ion.
generate the target complex [Ir(tpy)(m-tpy-f-f-mtbpy)Ir(dpyx)]4+,
6, which was isolated as an orange solid following anion ex-
change with KPF6(aq). Purification by column chromatography
was necessary to remove less polar species such as traces of
the hydrodebrominated and hydrodeboronated complexes. The
identity of 6 was confirmed by mass spectrometry and by a
combination of 1H–1H COSY and NOESY spectroscopy in
conjunction with the spectra of the corresponding monometallic
species.
2. Cross-coupling using the boronate-substituted complex. To
test the utility of the new boronate-substituted complex in the
preparation of a multimetallic derivative by cross-coupling, we
selected the reaction shown in Scheme 2, in which a coupling
was carried out with a bromo-substituted bis-terpyridyl complex.
This was chosen because the product would represent a structure
that would be especially difficult to prepare through conventional
methods involving the pre-synthesised bridging ligand. Thus,
although the bridging ligand itself would be accessible, the selective
complexation of the terpyridine terminus to the NŸNŸN-bound
iridium, and likewise the 6-tolylbipyridine unit to the NŸCŸN-
bound iridium, would be difficult—and probably impossible—to
achieve, and the synthesis would have to resort to purification of
a statistical mixture of products.
The complex [Ir(tpy)(tpy-f-Br)]3+ 5 was prepared by reaction of
Ir(tpy)Cl3 with p-(bromophenyl)terpyridine.37 The Suzuki cross-
coupling with 3 was carried out using the standard catalyst
Pd(PPh3)4 in the presence of sodium carbonate as the base. The
use of DMSO as the solvent—rarely used for cross-couplings
of organic compounds—was previously shown to facilitate the
dissolution of the charged reagents allowing reaction to proceed
readily.37 In the present instance, cross-coupling proceeded to
3. Stepwise linear elaboration of bis-terdentate Ir complex as a
route to linear multimetallic assemblies. The concept of stepwise
cross-couplings of haloaromatics in a controlled fashion relies
either on (i) different reactivities of halogen substituents in an
aromatic ring (e.g. 2,5-dibromopyridine can be cross-coupled first
at the 2 position and then at the 5 position owing to their relative
reactivities), or (ii) on being able to introduce a halogen atom under
mild conditions following the first cross-coupling. In a purely or-
ganic system, the second option is unusual, because of the forcing
conditions typically needed for halogenation of aromatics. We
previously demonstrated that bis-cyclometallated, tris-bidentate
complexes of the type [Ir(ppy)2(bpy)]+ 2 are susceptible to facile
electrophilic bromination of the cyclometallating phenyl rings,
which occurs selectively at the positions para to the metal ion.21
This remarkable reactivity, similar to that observed by Coudret
et al. for [Ru(bpy)2(ppy)]+,38 can be attributed to the increase
in the electron density in the phenyl rings that accompanies
cyclometallation.
In a similar manner, we found that treatment of 1 with NBS
in MeCN at RT leads to bromination of the NŸCŸN ligand at
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 3929–3940 | 3931
©

Scheme 2 Cross-coupling of a bis-terpyridyl iridium(III) complex 5 with the boronic-acid substituted complex 3 to generate the homodinuclear system
[Ir(tpy)(m-tpy-f-f-mtbpy)Ir(dpyx)]4+ 6.
the 4¢-position trans to the metal but—not surprisingly—also
at the equivalent position of the phenyl ring of the NŸNŸC ring.28
The modified complex [Ir(dpyx)(mtbpy-f-Br)]+ 4 (Scheme 3) was
selected for study, as it carries a methyl group at the latter
position, restricting the site of potential bromination to the
NŸCŸN ligand. It also carries a bromo substituent in the NŸNŸC
ligand from the outset, and is therefore an ideal candidate
for a sequence of cross-coupling–bromination–cross-coupling
(Scheme 3).
appended iridium complex [Ir(F2ppy)2(bpy-f-B)]2+ 10, leading
to the heterotrimetallic complex [Ir(F2ppy)2(m-bpy-f-dpyx)Ir(m-
mtbpy-f-f-bpy)Ru(bpy)2]4+ 11, isolated as an orange–red solid in
62% yield after anion exchange with KPF6(aq) and chromatographic
purification. The choice of constituent building blocks is discussed
in Section 5.
Naturally, the incorporation of the third metal complex and the
presence of 80 aromatic protons (70 inequivalent environments)
leads to a rather complicated 1H NMR spectrum. However,
notwithstanding some overlapping signals, most peaks could
Complex 4 was first subjected to cross-coupling with a
tris-bipyridyl ruthenium(II) complex appended with a boronic
acid group, [Ru(bpy)2(bpy-f-B)]2+ 7, using the standard con-
ditions {Pd(PPh3)4 catalyst, Na2CO3(aq) as base, DMSO sol-
vent at 80 ◦C}. The heterometallic dimer [Ir(dpyx)(m-mtbpy-
f-f-bpy)Ru(bpy)2]3+ 8 was isolated as an orange–red solid in
43% yield after ion exchange with KPF6(aq) and purification by
1
be assigned unambiguously with the aid of H–1H COSY and
NOESY spectra, 19F NMR, and the spectra of the constituent
building blocks (see Experimental section). Perhaps more defini-
tive proof of identity for such large assemblies is offered by
electrospray mass spectrometry, faciliated by the high net charge
-
leading to m/z peaks (z = 1–4) and adducts with n PF6 ions
1
column chromatography. The H NMR spectrum, assigned on
(n = 0–4). High resolution electrospray mass spectrometry showed
excellent correlation between the measured and theoretical masses
Dm < 1 ppm for z = 1). On the other hand, the large size of such
species means that several molecular formulae containing only the
atoms in the desired complex often closely match the measured
mass. Isotope peak matching provides additional and arguably
more conclusive and reliable support of structure. The isotope
peak matching for the trimetallic complex 11 is shown in Fig. S2
(see ESI†), showing the excellent match between experimental and
simulated spectra.
1
the basis of H–1H COSY and NOESY spectra and reference to
corresponding mononuclear complexes, is shown in Fig. S1 (see
ESI†). Bromination of the dimer, specifically at the 4¢-position
of the NŸCŸN ligand, was then accomplished by treatment with
NBS in MeCN at room temperature, followed by ion exchange
and washing of the product hexafluorophosphate salt with water
to remove N-hydrosuccinimide. The brominated complex 9 was
obtained in essentially quantitative yield. Now primed for a second
cross-coupling reaction, 9 was reacted with the boronic acid
3932 | Dalton Trans., 2009, 3929–3940
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©

Scheme 3 The cross-coupling–bromination–cross-coupling sequence used in the preparation of the trinuclear assembly [Ir(F2ppy)2(m-bpy-
f-dpyx)Ir(m-mtbpy-f-f-bpy)Ru(bpy)2]3+ 11 via the heterodinuclear complex [Ir(dpyx)(m-mtbpy-f-f-bpy)Ru(bpy)2]3+ 8.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 3929–3940 | 3933
©

4. Electrochemistry. Electrochemical studies of the multi-
metallic systems were carried out in acetonitrile solution at 298
3 K using Bu4NBF4 (0.1 M) as the supporting electrolyte. Results
are compiled in Table 1, together with those of pertinent mononu-
clear complexes that can be regarded as the constituent units
of the assemblies. The dinuclear iridium compound [Ir(tpy)(m-
tpy-f-f-mtbpy)Ir(dpyx)]4+ 6, which comprises a bis-terpyridyl
iridium centre and a doubly cyclometallated iridium ion, displays
reversible oxidation waves at 1.08 and 1.67 V. The first of these
is only a little higher than that displayed by the cyclometallated
monometallic complex 12 (the structure of 12 is shown in Fig. 1)28
suggesting that the first oxidation process occurs at this unit. The
second wave could be associated with a second oxidation at this
site or perhaps with the bridge. It seems unlikely to involve the
Ir(tpy)2 unit, given that the corresponding tricationic mononuclear
complexes do not normally display oxidation within accessible
windows.39 The first and second reduction processes observed are
probably associated with one of the terpyridyl units of the Ir(tpy)2
centre and with the bpy unit of the NŸNŸC ligand respectively, by
comparison with data for the respective mononuclear complexes
in Table 1. That the values in the multimetallic complexes differ
quite significantly from the respective building blocks does imply
that there is significant interaction between the metal centres by
communication through the biphenylene bridge.
dine units and terminal bipyridines respectively, are cathodically
shifted relative to the building blocks. The trimetallic assembly 11
similarly displays two oxidation and two reduction waves within
the region studied (-2.5 to + 2.0 V). Given that the monometallic
complex [Ir(F2ppy)2(bpy)]+ is oxidised at considerably higher
potentials than either 12 or [Ru(bpy)3]2+, it seems likely that the
oxidations are again associated with the bis-terdentate iridium and
ruthenium centres respectively. This interpretation is supported by
the report of De Cola and co-workers that a series of dinuclear
species of the type [Ir(F2ppy)2Ir(m-bpy-fn-bpy)Ru(bpy)2]3+ exhibit
only a ruthenium-based oxidation within this range.3 On the other
hand, the presence of five different NŸN-bipyridyl-based sites
within molecule 11 renders it difficult to make reliable assignments
about the site of reduction.
5. Electronic absorption and emission spectroscopy.
(i) Heterodinuclear
complex
[Ir(dpyx)(m-mtbpy-f-f-
bpy)Ru(bpy)2]3+ 8. The absorption spectrum of 8 in acetonitrile
solution at room temperature displays peaks characteristic of
the monometallic complexes of which it can be considered
to be comprised, namely [Ir(dpyx)(mtbpy-f-Ph)]+ 12 and
[Ru(bpy)2(bpy-Ph)]2+ (see Fig. S3 in ESI† and Table 1). Although
the overall profile is quite similar to the simulated spectrum
based on summation of these two components, it can be seen
that there is enhanced absorption in the region between 325–
400 nm, probably attributable to the bridging polyphenylene
unit. Similar observations have previously been reported for
[Ir(tpy)(m-tpy-f-f-bpy)Ru(bpy)2]5+ from our laboratory22 and for
the [Ir(F2ppy)2(m-bpy-fn-bpy)Ru(bpy)2]3+ complexes of De Cola
and co-workers,3 where absorption spectra were similar to those
of the sum of the monometallic components, in line with the
supramolecular description in terms of properties of constituent
units being retained.
The heterometallic dimer [Ir(dpyx)(m-mtbpy-f-f-bpy)Ru-
(bpy)2]3+ 8 displays reversible oxidation waves at 0.81 and 0.98 V.
One might tentatively attribute these to oxidation processes at
the Ir and Ru centres respectively, based on the data for the
monometallic species, although both oxidations are more facile
than anticipated on this basis, presumably reflecting the additional
stabilisation of the resultant higher positive charge through
delocalisation. In contrast, the reduction waves observed, which
could reasonably correspond to the phenylene-substituted bipyri-
Table 1 Ground state UV-visible absorption and electrochemical data for the multimetallic assemblies and for pertinent monometallic model complexes
in MeCN at 298 3 Ka
E1/2 / Vc (DE / mV) E1/2red / Vc (DE / mV) Absorbanceb lmax / nm (e/M-1cm-1)
ox
Compound
[Ir(tpy)(m-tpy-f-f-mtbpy)Ir(dpyx)]4+
6
1.08 (120)
-1.21 (150)
382 (62000), 354 (56000), 308 (96800),
280 (109000), 250 (116000)
1.67 (100)
—
-2.01 (110)
-0.81, -0.97
d
[Ir(tpy)(ttpy)]3+
372 (13200), 354 (18000), 340 (23300),
322 (29500), 310 (31900), 279 (43200),
251 (52000)
479 (1940), 412sh (13200), 375
(23200), 293 (60900)
[Ir(dpyx)(mtbpy-f-Ph)]+ 12
0.96 (90)
-1.54 (80)
-2.25 (90)
-1.67 (170)
[Ir(dpyx)(m-mtbpy-f-f-bpy)Ru(bpy)2]3+
8
0.81 (140)
451 (27600), 426 (30600), 373 (47600),
327 (71800), 288 (96400)
0.98 (160)
1.31f
-2.42 (70)
-1.34f
e
[Ru(bpy)2(bpy-Ph)]2+
454 (16900), 430 (14000), 399 (7030),
288 (84100), 253 (35000)
453 (27000), 426 (29900), 379 (50100),
288 (147000)
[Ir(F2ppy)2(m-bpy-f-dpyx)Ir(m-mtbpy-f-f-bpy)Ru(bpy)2]4+ 11 1.16 (140)
-1.54 (60)
1.31 (120)
-2.07 (120)
-1.29h
g
[Ir(F2ppy)2(bpy-Ph)]+
1.65h
446 (600), 417 (1300), 359 (7860), 333
(12100), 313 (23500), 300 (28100), 262
(49100)
-1.97h
a Complexes as their hexafluorophosphate salts at 10-3 M, using B4NBF4 (0.1 M) as the supporting inert electrolyte. b For bands > 250 nm. c DEox and
DEred are the peak-to-peak separation of the reversible oxidation and reduction processes respectively. d Data from ref. 39. e Data from ref. 22. f For
[Ru(bpy)3]2+ g Data from ref. 21. h For [Ir(F2ppy)2(bpy)]+, ref. 3.
.
3934 | Dalton Trans., 2009, 3929–3940
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©

Table 2 Luminescence data for the multimetallic systems 6, 8 and 11 together with data for relevant monometallic complexes for comparison. Data
refers to the complexes as their hexafluorophosphate salts in dilute solutions in MeCN at 298 3 K, except where stated otherwise
ꢀ
a
O2
Complex
l
max/nm Ulum ¥ 102 t/nsb
krc/104 s-1
0.08
knrc/105 s-1 kQ d/109 s-1
l
max/nme 77 K t/mse 77 K
[Ir(tpy)(m-tpy-f-f-mtbpy)Ir(dpyx)]4+
6
607
506
0.3
2.6
6.3
3200
(700)
5800
3.1
0.58
0.14
570, 597
490
3.4, 160
37
[Ir(tpy)(ttpy)]3+
1.1
4.2
f
(2300)
[Ir(dpyx)(mtbpy-f-Ph)]+ 12 g
636
630
150 (57) 42
63
5.7
1.6
553, 590
604, 644
4.0
4.9
[Ir(dpyx)(m-mtbpy-f-f-bpy)Ru(bpy)2]3+
8
12
1200
(260)
1300
(200)
1200
(220)
1400
(140)
10
6.9
6.4
47
7.3
7.0
7.7
2.4
[Ru(bpy)(bpy-Ph)]2+
627
632
539
9.0
7.7
2.2
2.0
3.4
—
—
5.1
—
h
[Ir(F2ppy)2(m-bpy-f-dpyx)-
614, 664
—
Ir(m-mtbpy-f-f-bpy)Ru(bpy)2]4+ 11
[Ir(F2ppy)2(bpy-Ph)]+
66
h
a Luminescence quantum yield measured using [Ru(bpy)3]Cl2 in H2O as the standard. b lex = 374 nm. c Radiative and non-radiative decay rate constants
estimated from t and Ulum values at 298 K. d Bimolecular rate constant for quenching by O2, estimated from t in degassed and aerated solutions, and
assuming [O2] = 1.9 mmol dm-3 at 1 atm air. e In an ether/isopentane/ethanol (2:2:1 v/v) glass. f Data from ref. 39. g Data from ref. 28. h Data from
ref. 22.
Upon excitation of 8 in degassed acetonitrile, a single structure-
less emission band centred at 630 nm was observed, irrespective
of the excitation wavelength (Fig. 2, Table 2). The excitation
spectrum registered at 630 nm matches closely the absorption
spectrum, and the luminescence decay follows mono-exponetial
kinetics, with a lifetime of 1.2 ms. These observations indicate
that the emission arises from a single excited state. The excited
state energies of the two constituent monometallic units would
be essentially identical (~15800 cm-1) based on the emission
data for the individual complexes [Ir(dpyx)(mtbpy-f-Ph)]+ 12
and [Ru(bpy)2(bpy-f-Ph)]2+. However, the observed luminescence
lifetime of 1.2 ms for 8 is much longer than that of the former
under the same conditions (t = 190 ns), whereas it is very similar
to that of the Ru complex (t = 1.3 ms). Thus, we conclude that
the emitting state is probably localised on the ruthenium moiety,
and that energy absorbed by the iridium unit is rapidly transferred
to this end of the molecule. Further support for this assignment
comes from the emission spectrum at 77 K, lmax = 604 and 644 nm
(Fig. 2), which contrasts with the substantially higher energy
spectrum displayed by 12 at this temperature, indicating that the
energy transfer to the ruthenium terminus must be fast also under
these conditions.
(ii) Trinuclear complex [Ir(F2ppy)2(m-bpy-f-dpyx)Ir(m-
mtbpy-f-f-bpy)Ru(bpy)2]3+ 11. The absorption, excitation and
emission spectra of the heterotrinuclear assembly 11 are shown
in Fig. 3. The choice of the [Ir(F2ppy)2(bpy-Ph)]+ unit to append
onto the dimetallic complex 8 was based on the known higher
excited state energy of this unit, a green emitter (~18900 cm-1).
The absorption spectrum of 11 is similar to that of the sum of
the constituent “building blocks” 8 and [Ir(F2ppy)2(bpy-Ph)]+,
indicating that the polyphenylene bridge formed between the two
iridium centres does not significantly influence the ground state
absorption. The steric influence of the flanking methyl groups of
the dpyx unit probably inhibits ground state delocalisation across
the bridge.
Fig. 3 Absorption, excitation (lem = 630 nm) and emission (lex = 410 nm)
spectra of [Ir(F2ppy)2-(m-bpy-f-dpyx)Ir(m-mtbpy-f-f-bpy)Ru(bpy)2]3+ 11
in MeCN at 298 K. The emission spectrum of [Ir(F2ppy)(bpy-Ph)]+ under
the same conditions is also shown.
Fig. 2 Absorption, excitation (lem = 630 nm) and emission (lex = 410 nm)
spectra of [Ir(dpyx)(m-mtbpy-f-f-bpy)Ru(bpy)2]3+ 8 in MeCN at 298 K.
The emission spectrum in an EPA glass at 77 K is also shown.
Excitation of 11 in MeCN at 298 K results in a single
structureless emission band centred at 632 nm, irrespective of
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 3929–3940 | 3935
©

the excitation wavelength in the range 275–500 nm. The emission
energy, lifetime of 1.2 ms and quantum yield of 0.077 are all similar
to those of [Ru(bpy)2(bpy-Ph)]+. Moreover, there is no evidence
of any detectable emission in the region around 530 nm, where
[Ir(F2ppy)2(bpy-Ph)]+ emits (Fig. 3), and the excitation spectrum
registered at 632 nm corresponds closely to the absorption profile.
Thus we conclude that there is essentially quantitative energy
transfer to the ruthenium terminus of the assembly, which then
emits. The approach of forming a trinuclear assembly from
constituent units of appropriate excited state energies thus allows
access to a linear “funnel” of energy to a single terminus of the
molecule. Although the emission in terms of the quantum yield is
not significantly improved compared to that of the tris-bipyridyl
runthenium(II) model complex, being limited by the same decay
processes, the quantity e ¥ Ulum, which takes into account both the
absorbance and emission, is improved.
with an excited state associated with the bridge, having lower
metal character to promote triplet decay. The structure on the
high-energy side of the emission band could then tentatively
be attributed to some emission from the [Ir(tpy)(tpy-f)] unit,
indicative of incomplete energy transfer to the lower state. We were
not able to obtain any convincing indication of a second, longer
decay component when monitoring the emission at the shorter
wavelengths associated with the structured bands, and the data
quality was hampered by the weakness of the emission. However,
we note that upon aeration of the solution, these higher-energy
bands become less apparent (Fig. 4), suggesting that they are
quenched more efficiently by O2 and hence may be characterised
by a longer lifetime. The more effective oxygen quenching of
the higher-energy emission bands is similar to that of other
iridium complexes recently reported to display dual emission.40
Unfortunately, the low emission intensity (Ulum = 3 ¥ 10-3 in
MeCN) hampered efforts to obtain good quality time-resolved
spectra, but the high-energy bands are undoubtedly resolved more
clearly at longer time intervals after excitation (Fig. S5, ESI†).
Changing from acetonitrile to water as the solvent for 6 was
found to have a dramatic influence on the emission (Fig. 5).
In pure water, the emission is an order of magnitude brighter
(Ulum = 1.4 ¥ 10-2) and a single structureless emission band is
observed. Strikingly, the luminescence lifetime is now much longer,
t = 75 ms. A similarly augmented lifetime on going from MeCN
to aqueous solution was previously observed for bis-terpyridyl
complexes appended with biphenyl tails, which we attributed to
modulation of the relative energies of the excited states such that a
p–p* state largely localised on the biphenyl tail becomes the lowest-
energy excited state.37,41 In the present instance, the corresponding
implication is that in H2O, the emission emanates from an excited
state associated largely with the bridge, with relatively little metal
character to promote radiative decay. The lack of vibrational
structure is not inconsistent with a ligand-centred assignment,
since the presence of a thermal distribution of conformers having
different torsion angles between the aryl rings will naturally
lead to a blurring-out of the spectrum, for example, as seen in
the effect of 4-aryl substituents on the emission of [Ir(tpy)2]3+
complexes.39,26,7
(iii) Binuclear
complex
[Ir(tpy)(m-tpy-f-f-mtbpy)Ir-
(dpyx)]4+ 6. Although the absorption spectrum of the
homodinuclear complex 6 shows some resemblance to the
sum of the spectra of its constituent monometallic units, the
absorption is enhanced throughout (see Fig. S4, ESI†). This
suggests a significant influence of the formation of the bridge.
Excitation of this complex in MeCN at room temperature
leads to weak emission centred at 607 nm, but with evidence
of some structured bands superimposed on the higher-energy
side of the main band (Fig. 4). In this system, the building
blocks [Ir(tpy)(ttpy)]3+ and [Ir(dpyx)(mtbpy-f-Ph)]+ 12 have
very different excited state energies, and the former displays a
structured spectrum in contrast to the structureless nature of the
latter. The lack of resemblance of the predominant emission band
of 6 to either of the constituent units suggests that the bridging
polyphenylene may be playing a significant role. The luminescence
decay kinetics at the emission maximum gave a lifetime of 3.2 ms,
much longer than that of 12 (150 ns). The quantum yield of
emission (Ulum = 2.5 ¥ 10-3) is much less than that of either the
terpyridyl or cyclometallated mononuclear complexes under the
same conditions, apparently due to a particularly small radiative
decay constant (Table 2). Such a small value would be consistent
Fig. 4 Absorption and emission spectra of [Ir(tpy)(tpy-f-f-mtbpy)Ir-
(dpyx)]4+ 6 in degassed MeCN at 298 K, together with the spectra of
[Ir(tpy)(ttpy)]3+ and 12 under the same conditions. The dashed line is the
emission spectrum in air-equilibrated solution.
Fig. 5 Absorption and emission spectra of [Ir(tpy)(tpy-f-f-mtbpy)Ir-
(dpyx)]4+ 6 in degassed H2O at 298 K (solid lines), and the emission
spectrum in air-equilibrated solution (dashed line).
3936 | Dalton Trans., 2009, 3929–3940
This journal is
The Royal Society of Chemistry 2009
©

Interestingly, the use of mixtures of MeCN/H2O leads to
intermediate values of t, which increase with the increasing
proportion of water (Fig. 6), even though the emission energy re-
mains essentially constant. Since, the emission intensity increases
concomitantly with the lifetime, the most likely explanation is that
non-radiative decay is progressively reduced as the proportion of
water increases.
key role in determining the emission properties. Overall, the results
demonstrate the versatility of this new class of iridium complex
and their potential in the design of linear multimetallics offering
unidirectional energy transfer.
Experimental
Proton and 13C NMR spectra, including NOESY and COSY,
were recorded on Varian 300, 400 or 500 MHz instruments.
Chemical shifts (d) are in ppm, referenced to residual protio-
solvent resonances, and coupling constants are in Hertz. Electron
ionisation (EI) mass spectra were recorded with a Micromass
AutoSpec spectrometer. Electrospray ionisation (ES) mass spectra
were acquired on a time-of-flight Micromass LCT spectrometer
with methanol or acetonitrile as the carrier solvent. All solvents
used in preparative work were at least Analar grade, and water
R
was purified using the Puriteꢀ system. Acetonitrile used for optical
spectroscopy was HPLC grade.
4-(p-Bromophenyl)-6-(m-tolyl)bipyridine
(mtbpyH-f-Br),28
1,3-di(2-pyridyl)-4,6-dimethyl-benzene (dpyxH),34 and bis(m-chlo-
ro)-bis[1,3-di(2-pyridyl)-4,6-dimethylbenzene-N,C2¢,N -iridium
chloride], [Ir(dpyx)2Cl(m-Cl)]2,34 were prepared as described pre-
viously. The complexes [Ir(tpy)(tpy-f-Br)]3+ 5,37 [Ir(dpyx)(mtbpy-
f-Br)]+ 4,28 [Ru(bpy)2(bpy-f-B)]2+ 7,22 and [Ir(F2ppy)2(bpy-f-B)]+
1022 were prepared according to procedures described in our
earlier work.
Fig. 6 Emission decays of the dinuclear complex 6 in the acetoni-
trile/water mixtures indicated; registered at 580 nm.
4¢-(p-neopentylglycolatoboron)-phenyl-6¢-(m-tolyl)-bipyridine:
mtbpyH-␾-B
Such a non-innocent bridge has also been noted in the
case of De Cola’s symmetric dinuclear complexes of the type
[{Ir(F2ppy)2}2(m-bpy-fn-bpy)]2+, where biexponential decay ki-
netics were attributed to an additional long component from
the bridge.42 Similarly, in symmetrical dimers of the type
[{Ir(dpyx)2}2(m-mtbpy-f-mtbpy)]2+, we observed biexponential
decay at 77 K, in which a long component of 70 ms was assigned
to a p–p* state of the bridging unit.
A mixture of mtbpyH-f-Br (0.10 g, 0.25 mmol), bis(neopen-
tylglycolato)diboron (0.68 g, 0.30 mmol) and potassium acetate
(0.068 g, 0.30 mmol) in DMSO (6 mL) was degassed by four
freeze–pump–thaw cycles. Pd(dppf)Cl2 (0.074 g, 0.075 mmol) was
added under◦a positive pressure of N2 and the reaction mixture
heated at 80 C, under a N2 atmosphere, for 16 h. The resultant
black solution was diluted with DCM (20 mL), washed with water
(5 ¥ 100 mL) and dried over sodium sulfate. The solvent was
then removed under reduced pressure and the product dried under
vacuum giving a brown/black solid (0.15 g). The product was used
without further purification.
1H-NMR (CDCl3, 500 MHz) d = 8.73–8.64 (2H, m, H3 and
H6), 8.63 (1H, s, H3¢), 8.02–7.93 (3H, m, H4¢¢ and Ha), 7.91 (1H, d,
3J = 8.0, H5¢), 7.85 (1H, t, 3J = 8.0, H4), 7.82–7.78 (3H, m, H2¢¢ and
Hb), 7.38 (1H, t, 3J = 7.5, H5¢¢), 7.32 (1H, t, 3J = 5.0, H5), 7.24 (1H,
d, 3J = 9.0, H6¢¢), 3.79 (4H, s, CH2), 2.48 (3H, s, CH3), 1.03 (6H,
s, CH3-Bneo). 13C-NMR (CDCl3, 126 MHz) d = 207.3 (C), 157.6
(C), 156.6 (C), 150.5 (C), 149.2 (C3), 140.9 (C), 139.7 (C), 138.7
(C), 138.6 (C), 137.2 (C4), 134.8 (Cb), 130.2 (C), 130.1 (C6¢¢), 128.9
(C5¢¢), 128.0 (C2¢¢), 127.9 (C), 126.6 (Ca), 124.5 (C4¢¢), 124.0 (C5),
121.9 (C6), 118.9 (C), 117.7 (C3¢), 72.6 (CH2), 21.9 (CH3-Bneo),
21.8 (CH3). MS (MALDI, DCTB matrix) m/z = 453.3 [M + H]+.
HRMS (ES+) m/z = 434.22672 [M + H]+; 434.22747 calculated
for [C28H2810BN2O2]+.
Conclusions
In summary, cyclometallated iridium complexes comprised
of two terdentate cyclometallating ligands, of the form
[Ir(NŸCŸN)(NŸNŸC)]+, have been used in the preparation of
multimetallic systems. Access to a complex of this type carrying a
boronic acid functional group allows palladium-catalysed cross-
coupling with complexes bearing halogens. Equally, a halogenated
complex can be coupled with a boronic acid-substituted complex.
Owing to the susceptibility of the cyclometallating ligand to
bromination under mild conditions at the central C4¢ of the
NŸCŸN ligand, a second cross-coupling can be carried out with
a third complex, offering stepwise generation of a linear A–B–
C assembly. The luminescence properties of the Ir–Ir–Ru system
indicate that it can be regarded as a supramolecular system:
the properties of the individual units are largely retained, and
excitation at any wavelength leads to exclusive emission from
the lower energy terminus, indicative of fast energy transfer. On
the other hand, for the system comprised of [Ir(NŸNŸN)2] and
[Ir(NŸCŸN)(NŸNŸC)] units linked together via the NŸCŸN ligand,
an excited state with significant bridge character seems to play a
[Ir(dpyx)(mtbpy-␾-B)]+ 3
A suspension of [Ir(dpyx)Cl(m-Cl)]2 (0.052 g, 0.050 mmol),
mtbpyH-f-B (0.076 g, 0.18 mmol) and silver triflate (0.051 g,
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 3929–3940 | 3937
©

0.20 mmol) in ethylene glycol (4 mL) was stirred at room
temperature under a N2 atmosphere for 1 h, before being heated
to 140 C for a further 3 h. After cooling to room temperature,
[Ir(dpyx)(l-mtbpy-␾-␾-bpy)Ru(bpy)2]3+
8
A mixture of [Ir(dpyx)(mtbpy-f-Br)]+ 5 (0.030 g, 0.030 mmol),
[Ru(bpy)2(bpy-f-B)]2+ (0.031 g, 0.030 mmol) and Na2CO3
(0.0095 g, 0.090 mmol in 100 mL water) in DMSO (5 mL) was
degassed by three freeze–pump–thaw cycles. Pd(PPh3)4 (0.0042 g,
0.0035 mmol) was added under a positive pressure of N2 and
the same reaction procedure employed as for 6. The crude
product was purified by flash column chromatography (silica,
acetonitrile/water/KNO3(aq), gradient elution from 100/0/0 to
89.0/10.8/0.4). Following evaporation of the solvent, the product
◦
the precipitated AgCl was collected by centrifuge and washed with
acetonitrile (2 ¥ 1 mL). The washings and filtrate were combined,
added to saturated aqueous KPF6 solution (25 mL) and the result-
ing orange precipitate collected by centrifuge, washed with water
(3 ¥ 5 mL) and dried under vacuum. Purification was achieved by
flash column chromatography (silica, DCM/methanol, gradient
elution from 100/0 to 93/7) to give the desired product as an
1
orange solid (0.087 g, 89%). H-NMR (d6-acetone, 400 MHz)
-
was ion exchanged to the PF6 salt to give the product as an
4
3
d = 9.07 (1H, d, J = 1.6, H3¢-NNC), 8.99 (1H, d, J = 8.0,
1
orange solid (0.024 g, 43%). H-NMR (CD3CN, 500 MHz) d =
H3-NNC), 8.90 (1H, d, J = 1.2, H5¢-NNC), 8.33 (2H, d, J =
4
3
3
8.86 (1H, s, H3¢-bpy-f), 8.77 (1H, d, J = 9.0, H3-bpy-f), 8.76
4.4, H3-NCN) 8.28 (2H, d, J = 8.0, Hb-NNC), 8.14 (1H, td,
3
(1H, s, H3¢-NNC), 8.68 (1H, s, H5¢-NNC), 8.65 (1H, d, J = 8.0,
3
3J = 7.6, J = 1.6, H4-NNC), 8.07 (2H, d, J = 8.4, Ha-NNC),
4
3
3
3
H3-NNC), 8.56 (4H, t, J = 9.0, H3-bpy) 8.31 (2H, d, J= 8.5,
7.96 (1H, s, H3¢¢-NNC), 7.85 (2H, ddd,, J = 8.4, 7.6, J = 1.6,
H4-NCN), 7.79 (2H, dd, 3J = 5.6, 4J = 1.2, H6¢¢-NNC), 7.69
(1H, dd, 3J = 5.6, 4J = 1.6, H6-NNC), 7.42 (1H, ddd, 3J =
3
4
3
Hb¢-bpy-f), 8.26 (2H, d, J = 8.5, H3-NCN), 8.15–8.07 (10H, m,
H4-bpy, H4-bpy-f, H6¢-bpy-f, Ha¢-bpy-f and Hb-NNC), 8.02 (1H,
3
3
t, J = 7.0, H4-NNC), 7.88 (1H, s, H3¢¢-NNC), 7.87 (1H, d, J =
7.6, 5.6, J = 1.2, H5-NNC), 7.23 (1H, s, H4¢-NCN), 6.96 (2H,
4
6.5, H6-bpy-f), 7.84–7.75 (9H, m, H4-NCN, H5¢-bpy-f, H6-bpy
ddd, J = 7.6, 5.6, J = 1.2, H5-NCN), 6.51 (1H, dd, J = 8.4,
4J = 1.2, H5¢¢-NNC), 5.84 (1H, d, 3J = 7.2, H6¢¢–NNC), 4.49
(3H, s, OMe) 2.99 (6H, s, CH3–NCN), 2.18 (3H, s, CH3-NNC).
MS (MALDI, DCTB matrix) m/z = 817.3 [Ir(dpydmb)(mtbpy-f-
B(OH)2]+, 831.3 [Ir(dpydmb)(mtbpy-f-B(OH)(OMe)]+ and 847.3
[Ir(dpydmb)(mtbpy-f-B(OMe)2]+. HRMS (ES+) m/z = 830.25034
[Ir(dpydmb)(mtbpy-f-B(OH)(OMe)]+; 830.25133 calculated for
[C42H3510B193IrN4O2]+. TLC (silica) Rf = 0.26 in DCM/methanol,
90/10. Mp > 250◦C.
3
4
3
3
and Ha-NNC), 7.59 (2H, d, J = 5.0, H6-NCN), 7.55 (1H, d,
3J = 5.5, H6-NNC), 7.49–7.44 (5H, m, H5-bpy and H5-bpy-f),
7.27 (1H, t, 3J = 7.0, H5-NNC), 7.21 (1H, s, H4¢-NCN), 6.88 (2H,
3
3
t, J = 6.5, H5-NCN), 6.56 (1H, d, J = 8.5, H5¢¢-NNC), 5.81
(1H, d, J = 8.0, H6¢¢-NNC), 2.96 (6H, s, CH3-NCN), 2.24 (3H,
3
s, CH3-NNC). MS (MALDI, DCTB matrix) m/z = 1707.3 [M +
PF6 ]+. HRMS (ES+) m/z = 777.15976 [M + PF6 ]2+/2; 777.15794
calculated for [C77H58F6191IrN10P96Ru]2+/2. TLC (silica) Rf = 0.59
in MeCN/H2O/KNO3(aq), 80/18/2. Mp > 250◦C.
-
-
[Ir(tpy)(l-tpy-␾-␾-mtbpy)Ir(dpyx)]4+
6
[Ir(dpyx-Br)(l-mtbpy-␾-␾-bpy)Ru(bpy)2]3+
9
A mixture of [Ir(dpydmb)(mtbpy-f-B(OH)(OMe)]+ 3 (0.030 g,
0.031 mmol), [Ir(tpy)(tpy-f-Br)]3+ 5 (0.039 g, 0.031 mmol) and
Na2CO3 (0.0099 g, 0.093 mmol in 100 mL water) in DMSO
(5 mL) was degassed by three freeze–pump–thaw cycles. Pd(PPh3)4
(0.0043 g, 0.0037 mmol) was added under a positive pressure of
N2 and the mixture heated for 24 h. The solution was added to an
aqueous solution of KPF6, and the resulting precipitate collected
by centrifuge and washed with water. Purification of the crude
product was achieved by flash column chromatography (silica,
acetonitrile/water/KNO3(aq), gradient elution from 100/0/0 to
78.0/20.7/1.3). Following evaporation of the solvent, the product
was ion exchanged to the PF6- salt to give the product as an orange
solid (0.011 g, 16%). 1H-NMR (CD3CN, 500 MHz) d = 9.21 (2H,
s, H3¢-tpy-f), 8.91 (2H, d, 3J = 8.0, H3¢-tpy), 8.84–8.79 (4H, m, H3-
tpy-f, H3¢-NNC and H4¢-tpy), 8.73 (1H, s, H5¢-NNC), 8.68 (1H, d,
A mixture of [Ir(dpyx)(m-mtbpy-f-f-bpy)Ru(bpy)2]3+ 8 (0.029 g,
0.029 mmol) and N-bromosuccinimide (0.0034 g, 0.019 mmol)
was stirred in acetonitrile (5 mL) for 18 h. The solution was then
added to saturated aqueous KPF6 solution (20 mL), forming a
precipitate which was collected by centrifugation, washed with
water (3 ¥ 2 mL) and dried under vacuum to give the product
as a red solid (0.036 g, 97%). 1H-NMR (CD3CN, 400 MHz) d =
8.86 (1H, s, H3¢-bpy-f), 8.77 (1H, d, 3J = 7.2, H3-bpy-f), 8.76 (1H,
3
s, H3¢-NNC), 8.69 (1H, s, H5¢-NNC), 8.65 (1H, d, J = 8.0, H3-
NNC), 8.56 (4H, t, 3J = 8.0, H3-bpy), 8.59–8.53 (4H, m, Hb¢-bpy-f
and H3-NCN), 8.17–8.06 (10H, m, H4-bpy, H4-bpy-f, H6¢-bpy-f,
3
Ha¢-bpy-f and Hb-NNC), 8.02 (1H, td, J = 6.8, 1.6 H4-NNC),
7.89–7.86 (2H, m, H3¢¢-NNC and H6-bpy-f), 7.85–7.76 (9H, m,
H4-NCN, H5¢-bpy-f, H6-bpy and Ha-NNC), 7.65 (2H, d, 3J = 6.0,
3
H6-NCN), 7.58 (1H, d, J = 4.8, H6-NNC), 7.50–7.43 (5H, m,
3
3J = 8.0, H3-NNC), 8.64 (2H, d, J = 8.0, H3-tpy), 8.45 (2H, d,
H5-bpy and H5-bpy-f), 7.27 (1H, t, 3J = 6.4, H5-NNC), 6.93 (2H,
td, 3J = 7.2, 4J = 1.2, H5-NCN), 6.57 (1H, d, 3J = 8.0, H5¢¢-NNC),
3
3J = 8.5, Ha-NNC), 8.38 (2H, d, J = 8.5, Hb¢-tpy-f), 8.33–8.24
(10H, m, H3-NCN, H4-tpy, H4-tpy-f, Ha¢-tpy-f and Hb-NNC),
8.04 (1H, t, 3J = 8.0, H4-NNC), 7.91 (1H, s, H3¢¢-NNC), 7.81–7.75
(4H, m, H4-NCN, H6-tpy and H6-tpy-f), 7.66–7.61 (4H, m, H6-
tpy, H6-tpy-f and H6-NCN), 7.59–7.51 (5H, m, H5-tpy, H5-tpy-f
3
5.83 (1H, d, J = 7.6, H6¢¢-NNC), 3.18 (6H, s, CH3-NCN), 2.24
(3H, s, CH3-NNC). MS (MALDI, DCTB matrix) m/z = 1758.3
[M + 2PF6 ]+. HRMS (ES+) m/z = 498.42015 [M]3+/3; 498.42025
-
calculated for [C77H5779Br191Ir193IrN10]3+/3. TLC (silica) Rf = 0.65
in MeCN/H2O/KNO3 (aq), 80/18/2. Mp > 250◦C.
3
and H6-NNC), 7.29 (1H, t, J = 6.0, H5-NNC), 7.22 (1H, s, H4¢-
NCN), 6.90 (2H, t, 3J = 6.0, H5-NCN), 6.58 (1H, d, 3J = 7.0, H5¢¢-
NNC), 5.83 (1H, d, 3J = 8.0, H6¢¢-NNC), 2.97 (6H, s, CH3–NCN),
2.26 (3H, s, CH3–NNC). MS (MALDI, DCTB matrix) m/z =
[Ir(F2ppy)2(l-bpy-␾-␾-dpyx)Ir(l-mtbpy-␾-␾-bpy)Ru(bpy)2]3+ 11
1939.4 [M + 3PF6 ]+. HRMS (ES+) m/z = 375.59682 [M]4+/4;
A
mixture of [Ir(dpyx-Br)(m-mtbpy-f-f-bpy)Ru(bpy)2]3+
9
-
375.59699 calculated for [C77H56191Ir2N10]4+/4. TLC (silica) Rf =
0.15 in MeCN/H2O/KNO3(aq), 80/18/2. Mp > 250◦C.
(0.030 g, 0.016 mmol), [Ir(ppy-F2)2(bpy-f-B)]+ (0.016 g,
0.016 mmol) and Na2CO3 (0.0051 g, 0.048 mmol in 100 mL water)
3938 | Dalton Trans., 2009, 3929–3940
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The Royal Society of Chemistry 2009
©

in DMSO (5 mL) was degassed by three freeze–pump–thaw cycles.
Pd(PPh3)4 (0.0022 g, 0.0019 mmol) was added under a positive
pressure of N2 and the same reaction procedure employed as for
6. The crude product was purified by flash column chromatog-
raphy (silica, acetonitrile/water/KNO3(aq), gradient elution from
100/0/0 to 89.0/10.8/0.4). Following evaporation of the solvent,
the product was ion exchanged to the PF6- salt to give the desired
product as an orange/red solid (0.028 g, 62%). 1H-NMR (CD3CN,
500 MHz) d = 8.95 (1H, s, H3¢-Ir-bpy-f), 8.87 (1H, s, H3¢-Ru-bpy-
to the vacuum manifold; final vapour pressure at 77 K was <
5 ¥ 10-2 mbar, as monitored using a Pirani gauge. Luminescence
quantum yields were determined using [Ru(bpy)3]Cl2 in air-
equilibrated aqueous solution (f = 0.02843) as the standard;
estimated uncertainty in f is 20% or better.
The luminescence lifetimes of the complexes were measured
by time-correlated single-photon counting, following excitation
at 374.0 nm with an EPL-375 pulsed-diode laser. The emitted
light was detected at 90◦ using a Peltier-cooled R928 PMT after
passage through a monochromator. The estimated uncertainty in
the quoted lifetimes is 10% or better. Bimolecular rate constants
for quenching by molecular oxygen, kQ, were determined from
the lifetimes in degassed and air-equilibrated solution, taking the
concentration of oxygen in CH2Cl2 at 0.21 atm O2 to be 2.2 mmol
dm-3.44
3
f), 8.84 (1H, d, J = 8.0, H3-Ir-bpy-f), 8.79 (1H, s, H3¢-NNC),
8.78 (1H, d, 3J = 10.0, H3-Ru-bpy-f), 8.71 (1H, s, H5¢-NNC), 8.68
3
3
(1H, d, J = 8.5, H3-NNC), 8.56 (4H, t, J = 9.0, H3-Ru-bpy),
8.40 (2H, t, 3J = 9.5, Hb¢-Ru-bpy-f), 8.34–8.25 (4H, m, H3-NCN,
H4-Ir-bpy-f and H5-Ir-bpy-f), 8.19–8.07 (15H, m, H4-Ru-bpy, H4-
Ru-bpy-f, H6-Ir-bpy-f, H6¢-Ru-bpy-f, Ha-Ir-bpy-f, Ha¢-Ru-bpy-f,
Hb-Ir-bpy-f and Hb-NNC), 8.05 (1H, t, 3J = 8.0, H4-NNC), 8.02–
7.96 (3H, m, H3-Ir-ppy and H5¢-Ir-bpy-f), 7.91 (1H, s, H3¢-NNC),
7.87 (1H, d, 3J = 5.5, H6-Ru-bpy-f), 7.85–7.74 (11H, m, H4-NCN,
H4-Ir-ppy, H5¢-Ru-bpy-f, H6-Ru-bpy and Ha-NNC), 7.70 (2H, d,
3J = 9.0, H6-Ir-ppy), 7.67–7.59 (4H, m, H6-NCN, H6-NNC and
H6¢-Ir-bpy-f), 7.50–7.44 (5H, m, H5-Ru-bpy and H5-Ru-bpy-f),
Acknowledgements
We thank EPSRC for a DTA studentship to V.L.W. and for
equipment purchased under grant EP/D500265/1, and Frontier
Scientific for supplying key starting materials.
3
7.33 (1H, t, iJ = 6.5, H5-NNC), 7.20–7.15 (2H, m, H5-Ir-ppy),
3
6.91 (2H, t, J = 6.5, H5-NCN), 6.82–6.74 (2H, m, H4¢-Ir-ppy),
References
3
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6.62 (1H, d, J = 8.0, H5¢¢-NNC), 5.95 (1H, d, J = 7.5, H6¢¢-
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2.27 (3H, s, CH3-NNC). 19F-NMR (CD3CN, 658 MHz) d = -73.0
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3940 | Dalton Trans., 2009, 3929–3940
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The Royal Society of Chemistry 2009
©