The synthesis and photophysics of tris-heteroleptic cyclometalated iridium complexes

Article abstract of DOI:10.1039/c1dt10619h

Herein we report the synthesis and photophysical study of tris-heteroleptic complexes of the general formula IrLL′(acac), where L and L′ are two differently substituted 2-phenylpyridines (ppyH) and acacH is 2,4-pentanedione, using a combinatorial approach that could be employed for many ligand combinations. The tris-heteroleptic complexes and the analogous bis-heteroleptic complexes of the form IrL₂(acac) have been studied by a combination of absorption and photoluminescence spectroscopies in conjunction with modelling by DFT and TD-DFT to elucidate the nature and location of the excited state in the novel species.

Full text of DOI:10.1039/c1dt10619h

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An international journal of inorganic chemistry
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Volume 40 | Number 38 | 14 October 2011 | Pages 9621–9936
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COVER ARTICLE
Beeby et al.
The synthesis and photophysics of tris-heteroleptic
cyclometalated iridium complexes

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PAPER
The synthesis and photophysics of tris-heteroleptic cyclometalated iridium
complexes†
Robert M. Edkins,a Alisdair Wriglesworth,a,b Katharina Fucke,a Sylvia L. Bettingtona and Andrew Beeby*a
Received 11th April 2011, Accepted 7th June 2011
DOI: 10.1039/c1dt10619h
Herein we report the synthesis and photophysical study of tris-heteroleptic complexes of the general
formula IrLL¢(acac), where L and L¢ are two differently substituted 2-phenylpyridines (ppyH) and
acacH is 2,4-pentanedione, using a combinatorial approach that could be employed for many ligand
combinations. The tris-heteroleptic complexes and the analogous bis-heteroleptic complexes of the
form IrL2(acac) have been studied by a combination of absorption and photoluminescence
spectroscopies in conjunction with modelling by DFT and TD-DFT to elucidate the nature and
location of the excited state in the novel species.
the forcing conditions employed for this reaction, resulting in the
Introduction
formation of complex mixtures containing all permutations of
Over the past decade cyclometalated iridium complexes have
the two ligands. There has also been one report of the synthesis
attracted a great deal of attention, with numerous reports of
complexes that are highly emissive across the complete visible
of systems of the type IrLL¢L¢¢ as part of a mixture for a white
OLED (WOLED), but the pure tris-heteroleptic species was not
spectrum.1 This has been readily achieved through simple lig-
and modification, for example Ir(F2ppy)2(pic) (F2ppyH 2-(2¢,4¢-
difluorophenyl)pyridine, picH 2-picolinic acid), is a well known
blue emitter,2 whilst Ir(piq)3 (piqH 1-phenylisoquinoline) shows
strong red emission.3 The reason for this interest arose due to
their potential application as triplet state emitters in organic light
emitting diode (OLED) display technologies,4 whilst more recently
they have begun to arouse interest as biological imaging agents,5
sensors6 and as the light harvesting component of dye-sensitised
solar cells (DSSC).7 The key advantages of this class of material
are their large photoluminescence quantum yields (PLQY, UP)
and relatively short phosphorescent lifetimes coupled with high
photo-, electro- and thermal stability, and relative ease of emission
tunability.
isolated.9 Although heteroleptic complexes of the form IrL2A have
been known for more than a decade,10 to date there has been no
report of a complex of the type IrLL¢A.
In this work, we present a facile synthetic protocol to access
this previously unattainable group of complexes, along with a
photophysical study, backed up by molecular modelling. It is
known that the choice of A can influence the photophysical
properties of the complex, hence in this study we used acac- as the
ancillary ligand throughout. However, since the reaction of the
m-chlorodimer with the ancillary ligand is normally carried out
under mild conditions, the same methodology could be applied to
a number of other complexes.11
It is conceived that for use as imaging agents one ligand could
be utilised to control the photophysical properties, one to act as
site for functionalisation to targeting vectors and the third to
tune physical properties, such as solubility in biological media.
For OLED applications it also has the potential to facilitate the
synthesis of complexes with enhanced properties, for example
solubility.
Hitherto reported compounds can be divided into three main
categories by ligand composition: IrL3, IrL2L¢ and IrL2A, where
L and L¢ are different cyclometalating ligands and A is an
ancillary ligand, such as a bidentate diketone, commonly 2,4-
pentanedionate (acac-), pic- or a combination of two monodentate
ligands such as Cl- and PPh3. We have previously reported8 the
synthesis of complexes of the type IrL2L¢ by the reaction of ligand
L¢ with the m-chlorodimer, (IrL2Cl)2. However, in our experience
this method can lead to some scrambling of the ligands under
Results and Discussion
Synthesis
aDepartment of Chemistry, Durham University, South Road, Durham, UK,
DH1 3LE. E-mail: andrew.beeby@durham.ac.uk; Tel: +44 (0) 191 33 42023
Our approach is an adaption of the standard synthesis of
cyclometalated iridium complexes,12 based upon the formation
of the mixed m-chlorodimer in which IrCl3·3H2O is refluxed in
a mixture of water and 2-ethoxyethanol with two different cy-
clometalating ligands (Scheme 1). The crude product is subjected
to flash chromatography to remove traces of tris-cyclometalated
bDepartment of Chemistry, University of Nottingham, University Park,
Nottingham, NG7 2RD, UK
† Electronic supplementary information (ESI) available. CCDC reference
number 821508. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1dt10619h
9672 | Dalton Trans., 2011, 40, 9672–9678
This journal is
The Royal Society of Chemistry 2011
©

acid15 using Pd(PPh3)4 catalyst and NaOH(aq) base, followed by
phenylation at the 2-position of the unactivated pyridine ring
by reaction with phenyllithium in toluene. The work-up of this
reaction was simply exposure to air and the addition of water
with no further oxidising agent required to affect re-aromatisation
to the product. The phenylethynyl derivative, 2-(pep)pyH was
prepared by the Suzuki coupling of 4-phenylethynylbenzene
boronic acid with 2-bromopyridine.
Scheme 1 Synthesis of cyclometalated iridium complexes of the form
IrLL¢(acac).
The synthesis of the mixture of bimetallic intermediates, and
subsequent complexes, was facile and proceeded under the usual
conditions.16 These complexes could be separated on an analytical
and preparative scale by TLC and column chromatography
respectively. Excellent separation could be readily achieved under
TLC conditions and to illustrate this, Fig. 2 shows a TLC plate illu-
minated under ultraviolet light clearly showing the relatively large
difference in the Rf values of the final products. The individual
conditions used for the separation of compounds on a preparative
are provided in the ESI. Isolated complexes were characterised
by H, H–1H COSY and NOESY NMR experiments, through
which every 1H resonance could be unambiguously assigned (for
example see Fig. 3). Accurate mass mass-spectrometry and high
performance liquid chromatography (HPLC) were used to verify
the composition and purity of the sample.
complexes which are formed as by-products in the reaction, to
furnish only dimetallic species. These are present as a complex
mixture containing at least 7 combinations of ligands (L : L¢ ratios
of 4 : 0, 3 : 1, 2 : 2 (3 structural isomers), 1 : 3 and 0 : 4, without
consideration of the formation of diastereomers). This mixture is
reacted on with acetylacetone in basic 2-ethoxyethanol without
further purification yielding only three compounds, IrL2(acac),
IrL¢2(acac) and the coveted IrLL¢(acac) that can be separated by
column chromatography. For the photophysical studies presented
here the products were required to a high degree of purity, and
were isolated in yields of 7–11% based on the functionalised 2-
phenylpyridine ligand. Although this method is low yielding, it
is currently the only way to make this class of complex. We have
found that the product mixture can be biased in favour of the
desired compound by using an excess of one ligand over the other,
but no further optimisation of the procedure was attempted. It is
also possible to prepare the compounds using a one-pot method
in which the cyclometalating ligands are heated for 4 h with
IrCl3·3H2O in aqueous 2-ethoxyethanol followed by the addition
of acacH and K2CO3. After a further 30 min, the products were
isolated following the usual work-up.
1
1
The chosen examples were selected as cases where separation
might be anticipated to be challenging due to the similarity of the
ligands, in order to prove the viability of the method. The target
compounds contained a single 2-phenylpyridine (ppyH) ligand
and one substituted derivative as well as an acac- ancillary lig-
and. The substituted ligands 2-(4¢-phenylethynylphenyl)pyridine
(2-(pep)pyH), 2-(4¢-formylphenyl)pyridine (fppyH) and 2,4-
diphenylpyridine (dppyH) were used to give the products shown
in Fig. 1.
Fig. 2 TLC plate (SiO2, DCM : MeCN 5 : 1, UV (365 nm) illumination) of
(A) the crude mixture and (B–D) the separated fractions of Ir(ppy)2(acac),
Ir(fppy)(ppy)(acac) and Ir(fppy)2(acac) respectively. The latter fraction
includes additional material that remains at the baseline. The baseline and
solvent front are highlighted.
Single crystal X-ray diffraction of Ir(fppy)(ppy)(acac) con-
firmed the identity of the complex and its tris-heteroleptic
composition, Fig. 4. As is common with complexes of the form
IrL2(acac), the pyridine rings are mutually trans while the phenyl
rings are in a mutually cis configuration due to the large trans
influence of the formally anionic phenyl moieties. Complexes
of the type IrL2(acac) can usually be assigned as either cis or
trans pyridine from the NMR spectrum due to the presence of
equivalent protons on the cyclometalated ligands for the trans
isomer and inequivalent protons for the cis isomer. However in
the case of the tris-heteroleptic complex the different identity
of the two cyclometalated ligands meant that this could only be
confirmed by the X-ray structure. The metal–ligand bond lengths
Fig. 1 The three novel tris-heteroleptic complexes.
DppyH has been reported previously, having been synthesised
by various methods including reaction of phenyl magnesium bro-
mide and 4-phenylpyridine-N-oxide,13 PdCl2(PPh3)2/CuI catal-
ysed cyclisation of phenyl acetylene and an iodovinylimine14 or
Suzuki-Miyaura coupling of 2,4-dibromopyridine with phenyl-
boronic acid. In our work we synthesised it by a Suzuki-Miyaura
coupling of 4-bromopyridine hydrochloride and phenylboronic
˚
˚
(Ir–O (2.159(4) and 2.127(4) A), Ir–N (2.040(5) and 2.033(5) A)
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©

weaker trans influence of the aldehyde substituted phenyl ring
compared to that of the unsubstituted phenyl ring of ppy-. The
molecule packs as a head-to-tail p–p stacked dimer between the
-
˚
fppy ligands with a spacing of 3.4 A and is again typical in this
regard10 (see ESI Figure S1†).
Photophysics
Fig. 5–7 show the absorption, excitation and emission spectra
of the novel tris-heteroleptic complexes and Table 1 summarises
the photophysical data for all of the complexes studied. Fig. 8–
10 show the comparison of the emission spectra of the bis and
tris-heteroleptic complexes. In each example the emission spectra
are red-shifted with respect to the parent Ir(ppy)2(acac) and
this is attributed to the increased conjugation of the substituted
phenylpyridine ligands. Interestingly, the compounds showed a
marked difference in their solvatochromism and in the observed
phosphorescence lifetimes, UP and the calculated pure-radiative
lifetimes, t0. It is believed that the emission from this class
of complex is an admixture of metal to ligand charge transfer
(MLCT) and ligand centred (LC) transitions, with the dominant
component depending on the precise nature of the ligands and the
solvent conditions.
Fig. 3 Low field region of the1H NMR spectrum (400 MHz in acetone-d6)
of Ir(fppy)(ppy)(acac) with all resonances assigned, aided by NOESY and
COSY experiments. See inset for numbering system.
The phenylethynyl derivative, Ir(2-(pep)py)(ppy)(acac), exhibits
a structured emission spectrum which does not shift significantly
upon moving from cyclohexane to acetonitrile. This coupled with
its relatively long pure radiative lifetime of 10.0 and 9.1 ms in
toluene and acetonitrile respectively are indicative of a more ligand
centred transition.
A similar emission profile and long pure radiative lifetime are
observed from the bis-heteroleptic derivative Ir(2-(pep)py)2(acac).
These observations are evidence for the localisation of the
excitation upon the ligand that gives rise to the lowest energy
excited state, in this case the 2-(pep)py.
The tris-heteroleptic complex containing the dppy ligand
shows a small red-shift upon moving to a more polar solvent
environment. Furthermore, in a non-polar environment there is
some evidence of vibrational fine structure that is lost in the
more polar solvents. This complex has a comparatively short
pure radiative lifetime of 2.3 ms and, on the basis of these
observations, the emissive state is assigned as having mixed LC and
MLCT character, with the influence of the latter becoming more
Fig. 4 Molecular structure of Ir(ppy)(fppy)(acac), the first tris-heterolep-
tic cyclometalated iridium complex to be structurally characterised. Ele-
ment (colour): iridium (cyan), carbon (grey), nitrogen (blue), oxygen (red)
and hydrogen (white). Thermal ellipsoids are drawn at 65% probability.
Crystal data in footnote.17 See ESI for full structural details and CIF.†
˚
and Ir–C (1.996(6) and 1.988(6) A)) are in the typical ranges for
molecules of the type IrL2(acac). The difference in Ir–O bond
˚
lengths is small but significant (0.03 A) and arises due to the
Table 1 Spectroscopic data of bis and tris-heteroleptic Ir(III) cyclometalated complexes measured in degassed solvents at 298 K
d
Complex
labs (e)/nm (103 M-1 cm-1)a
l
em/nm
tP/msc
UP
t0/mse
CyHexb Toluene DCMb MeCN Toluene MeCN Toluene MeCN Toluene MeCN
Ir(ppy)2(acac)f
262, 306, 344, 372, 415, 476 512
520
585
550
550
590
520
600
560
550
620
522
603
565
548
623
1.6
1.8
1.0
2.6
1.3
2.1
0.9
1.2
2.9
0.3
0.46
0.04
0.33
0.22
0.02
0.42
0.12
0.42
0.23
0.11
3.5
45
3.3
12
5.0
7.5
2.9
13
Ir(fppy)2(acac)f,g
Ir(dppy)2(acac)f,g
Ir(2-(pep)py)2(acac)f,g
Ir(fppy)(ppy)(acac)
286, 307, 365, 413, 508
289, 354, 470, 501
288, 351, 392, 471
292 (38.9), 356 (6.4), 404
(4.0), 443 (2.8), 492 (2.0)
288 (31.9), 350 (11.4), 380
(7.6), 409 (5.0), 468 (2.9),
495 (2.0)
564
539
549
574
65
2.7
Ir(dppy)(ppy)(acac)
535
545
556
567
1.1
1.5
0.48
0.63
2.3
10
2.3
9.1
Ir(2-(pep)py)(ppy)(acac) 330 (35.1), 386 (6.2), 456
(3.6), 490 (2.7)
551
553
553
552
2.4
2.9
0.23
0.32
a Measured in cyclohexane; b CyHex = cyclohexane, DCM = dichloromethane; c Estimated error 5%; d Estimated error 10%; e Calculated using t0
tP.UT/UP and assuming UT = 1; f Extinction coefficient not measured; g Absorption spectrum measured in DCM due to low solubility in cyclohexane.
=
9674 | Dalton Trans., 2011, 40, 9672–9678
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Fig. 5 Normalised absorption, excitation (lem = 550 nm) and emission
(lex = 410 nm) spectra of Ir(2-(pep)py)(ppy)(acac). The absorption
spectrum is offset in intensity for clarity. All measurements were obtained
in degassed solvent at 298 K. CyHex is cyclohexane.
Fig.
8
A comparison of the emission spectra of the complex
Ir(2-(pep)py)(ppy)(acac) and the parent IrL2(acac) complexes in degassed
MeCN at 298 K (lex = 410 nm).
Fig. 6 Normalised absorption, excitation (lem = 570 nm) and emission
(lex = 410 nm) spectra of Ir(dppy)(ppy)(acac). The absorption spectrum is
offset in intensity for clarity. All measurements were obtained in degassed
solvent at 298 K. CyHex is cyclohexane.
Fig.
9
A comparison of the emission spectra of the complex
Ir(dppy)(ppy)(acac) and the parent IrL2(acac) complexes in degassed
MeCN at 298 K (lex = 410 nm).
Fig. 10
A comparison of the emission spectra of the complex
Fig. 7 Normalised absorption, excitation (lem = 619 nm) and emission
(lex = 525 nm) spectra of Ir(fppy)(ppy)(acac). The absorption spectrum is
offset in intensity for clarity. All measurements were obtained in degassed
solvent at 298 K. CyHex is cyclohexane.
Ir(fppy)(ppy)(acac) and the parent IrL2(acac) complexes in degassed
MeCN at 298 K (lex = 525 nm).
Finally, the aldehyde substituted complex Ir(fppy)(ppy)(acac)
exhibits a marked red-shift in its emission spectrum upon changing
to a more polar solvent, and the pure radiative lifetimes decrease
significantly. These observations are attributed to a change in the
nature of the excited state, from one that is rich in LC character in
significant in more polar solvents. Once again the spectroscopic
properties of the bis-heteroleptic complex, Ir(dppy)2(acac), are
similar to those of the tris-heteroleptic system.
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Table 2 CAM-B3LYP/6-31+G/LANL2DZ TD-DFT calculated lowest energy transitions for the IrL2(acac) and IrLL¢(acac) complexes
Compound
Triplet state
Excitationa
Energy/eV (l/nm)
Ir(ppy)2(acac)
Ir(fppy)2(acac)
Ir(dppy)2(acac)
Ir(2-(pep)py)2(acac)
T1
T2
T1
T2
T1
T2
T1
LUMO+1 ← HOMO
LUMO ← HOMO
2.67 (464)
2.68 (462)
2.37 (522)
2.38 (520)
2.35 (529)
2.35 (528)
2.29 (541)
LUMO ← HOMO
LUMO+1 ← HOMO
LUMO ← HOMO
LUMO+1 ← HOMO
LUMO+1 ← HOMO-1
LUMO ← HOMO
T2
LUMO+1 ← HOMO
LUMO ← HOMO-1
LUMO ← HOMO
2.29 (540)
Ir(fppy)(ppy)(acac)
T1
T2
2.36 (526)
2.69 (460)
LUMO+1 ← HOMO
LUMO+1 ← HOMO-2
LUMO ← HOMO
Ir(dppy)(ppy)(acac)
T1
T2
T1
2.64 (470)
2.68 (463)
2.29 (541)
LUMO+1 ← HOMO
LUMO ← HOMO-1
LUMO ← HOMO
Ir(2-(pep)py)(ppy)(acac)
T2
LUMO+1 ← HOMO
LUMO+1 ← HOMO-3
2.69 (461)
a Dominant component(s) of the transition.
a non-polar medium, to one that becomes more MLCT-like with
increasing solvent polarity.
Table 3 (overleaf) summarises the spatial extent of the HOMO,
LUMO and LUMO+1 orbitals for each of the complexes
prepared. For all complexes, of both the form IrL2(acac) and
IrLL¢(acac), the calculated HOMO is located primarily on the
iridium atom and the coordinating phenyl rings. This is in
agreement with previous work by Hay19 on related cyclometalated
Ir(III) complexes. In the case of the IrL2(acac) complexes, the
LUMO and the LUMO+1 are quasidegenerate and are equally dis-
tributed across both ligands. However, for complexes of the form
IrLL¢(acac) this quasidegeneracy of the LUMO and LUMO+1
levels is lifted and the LUMO is located on the functionalised ppy
ligand (i.e. fppy, dppy or 2-(pep)py).
Time-dependent DFT (TD-DFT) calculations were performed
at the CAM-B3LYP/6-31+G/LANL2DZ level in order to try to
establish the nature of the excited triplet states of the materials. The
CAM-B3LYP functional was chosen due to its better description
of states with charge-transfer character,20 which is crucial for an
accurate model of the cyclometalated iridium compounds where
MLCT is observed. Excitation energies calculated by TD-DFT
are shown in Table 2. Introduction of solvent to the calculations
using the polarisable continuum model (PCM) brings about little
change in the predicted absorption bands, (< 0.05 eV) which
appears to contradict the observed solvatochromism. The reason
for the large solvent effect is most likely due to a significant
structural/solvent reorganisation in the excited triplet state prior
to emission, which is difficult to predict using currently available
software packages. The TD-DFT method employed here describes
each individual excitation as involving contributions from many
occupied and unoccupied MOs and thus we report only the major
contribution(s) to the transition.
High quantum yields are desirable for the application of these
materials, in particular for OLEDs, sensing or imaging, with recent
reviews dedicated to methods for increasing this parameter.18
Interestingly the mixed ligand systems described here have similar
or higher quantum yields than the respective bis-heteroleptic
complexes, IrL2(acac), but retain a similar emission profile. The
complex Ir(dppy)(ppy)(acac) has PLQYs of 0.48 (toluene) and
0.63 (MeCN), which are significantly enhanced compared to
Ir(dppy)2(acac) which has values of 0.33 (toluene) and 0.42
(MeCN). We find that the radiative lifetimes of the complexes
are comparable; hence we conclude that the increases in PLQY
are due to a decrease in non-radiative decay pathways. This
may be due to the fact that in the asymmetric tris-heteroleptic
complexes the excited state is localised on a single ligand and
hence has a reduced number of vibrational states capable of non-
radiative deactivation of the excited state compared to the higher
symmetry bis-heteroleptic complex. There is the possibility that
these mixed systems offer an interesting method of enhancing
the photoluminescence quantum yield, whilst leaving the emission
spectrum state essentially unchanged.
Computational studies
In order to further understand the nature of the excited states
and the origins of the red-shift in terms of the modification
of the HOMO and LUMO energies, we carried out density
functional theory (DFT) calculations to model the electronic
structure of these complexes. The ground state geometries of the
tris-heteroleptic complexes and their IrL2(acac) analogues were
calculated using DFT at the B3LYP/6-31+G/LANL2DZ level of
theory in the manner described by Hay.19 For Ir(fppy)(ppy)(acac)
calculated bond lengths for Ir–N, Ir–C and Ir–O bonds all agreed
In all complexes the lowest energy excited state results mainly
from excitation from the HOMO to the LUMO, while the
second lowest energy transition is to the LUMO+1 level in all
cases. This is support for the hypothesis that the excitation is
primarily located on the energy cyclometalating ligand which gives
rise to the lowest energy excited state which in our examples
is the substituted phenylpyridine. Thus, it is this most readily
˚
within 0.07 A (3.2%) and with an average discrepancy of 1.5%,
with the experimentally determined X ray structure (see tabe S1 in
the ESI).
9676 | Dalton Trans., 2011, 40, 9672–9678
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©

Table 3 HOMO, LUMO and LUMO+1 orbital plots and energies of the novel tris-heteroleptic IrLL¢(acac) and parent IrL2(acac) complexes obtained
from DFT calculations at the B3LYP/6-31+G/LANL2DZ level. Hydrogen atoms have been omitted for clarity
Compound
HOMO EHOMO/eV
LUMO ELUMO /eV
LUMO+1 ELUMO+1 /eV
|EHOMO - ELUMO |/eV
Ir(ppy)2(acac)
3.47
Ir(dppy)2(acac)
3.19
Ir(dppy)(ppy)(acac)
3.20
Ir(fppy)2(acac)
3.14
Ir(fppy)(ppy)(acac)
3.05
Ir(2-(pep)py)2(acac)
3.27
Ir(2-(pep)py)(ppy)(acac)
3.24
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Dalton Trans., 2011, 40, 9672–9678 | 9677
©

reduced ligand which controls the emissive properties of the
complex.
This crude mixture was dissolved in 2-ethoxyethanol (15 ml) with
acetylacetone (0.1 ml, excess) and K2CO3 (100 mg) and heated to
65 ◦C for 1 h. Upon cooling to r.t., water (30 ml) was added giving
a yellow suspension, which was filtered, washed with water (2 ¥
5 ml), dissolved in DCM, dried over MgSO4 and reduced in vacuo
to leave an oily solid. This was triturated with hexane (3 ¥ 5 ml) to
remove excess acacH and reduced in vacuo to leave a solid which
was purified by column chromatography.
Conclusions
Complexes of the general form IrLL¢(acac) have been synthesised
and it is observed that they exhibit subtle differences in their
photophysics when compared to the related IrL2(acac) species. The
lowest energy ligand is found both experimentally and computa-
tionally to dominate the emission properties and we believe this
may allow exploitation of the remaining two ligands for ancillary
purposes. This class of cyclometalated iridium complex affords the
opportunity to have finer control over the photophysical properties
for a wide variety of applications.
Acknowledgements
R.M.E. wishes to thank Durham University for funding through
a Durham Doctoral Fellowship. K.F. and S.L.B. thank EPSRC
for funding. We thank Jack Strangward and James Milne for
experimental assistance. We also thank the referees for helpful
comments regarding the excited state dynamics of the complexes.
Experimental
For full details of materials and methods, consult the ESI.†
Notes and references
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the form IrL2(acac)
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IrCl3·3H2O (350 mg, 0.99 mmol) was dissolved in 2 : 1 2-
ethoxyethanol:water (15 ml) with L (2.2 eq.). The solution was
heated to 110 ◦C for 10 h. The reaction mixture was then allowed
to cool to r.t. and water (25 ml) added, affording a solid, which
was filtered, washed with water (2 ¥ 5 ml), dissolved in DCM
(30 ml), dried over MgSO4 and reduced in vacuo to leave a yellow-
brown or orange solid. Flash column chromatography on silica gel
(DCM with 1% EtOH) was used to remove fore-running fractions.
The crude material was dissolved in 2-ethoxyethanol (15 ml) with
acetylacetone (0.1 ml, excess) and K2CO3 (100 mg) and heated to
65 ◦C for 1 h. Upon cooling to r.t., water (30 ml) was added giving
a yellow suspension, which was filtered, washed with water (2 ¥
5 ml), dissolved in DCM, dried over MgSO4 and reduced in vacuo
to leave an oily solid. This was triturated with hexane (3 ¥ 5 ml) to
remove excess acacH and reduced in vacuo to leave a solid which
was purified by column chromatography.
12 S. Sprouse, K. A. King, P. J. Spellane and R. J. Watts, J. Am. Chem.
Soc., 1984, 106, 6647.
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15 C. Sicre, J.-L. Alonso-Go´mez and M. M. Cid, Tetrahedron, 2006, 62,
11063.
Typical procedure for the synthesis of tris-heteroleptic complexes
of the form Ir(ppy)L¢(acac)
IrCl3·3H2O (350 mg, 0.99 mmol) was dissolved in 2 : 1 2-
ethoxyethanol:water (15 ml) with 2-phenylpyridine (0.23 ml,
1.5 mmol) and L¢ (0.5 mmol). The solution was heated to 110 ◦C
for 10 h. The reaction mixture was cooled to r.t. and water (25 ml)
added, affording a solid, which was filtered, washed with water
(2 ¥ 5 ml), dissolved in DCM (30 ml), dried over MgSO4 and
reduced in vacuo to leave a yellow-brown or orange solid. Flash
column chromatography on silica gel (DCM with 1% EtOH) was
used to remove fore-running fractions from the mix of dimers.
16 S. Sprouse, K. A. King, P. J. Spellane and R. J. Watts, J. Am. Chem.
Soc., 1984, 22, 6647.
17 C28H23N2O3Ir, 627.68 g mol-1, crystal system monoclinic, space group
˚
˚
˚
P21/n, Z◦= 4, a = 11.4809(3) A, b = 9.6890(3) A, c = 20.4035(6) A, b =
3
˚
92.427(1) , V = 2267.6(1) A , temperature 120(2) K, 11 138 reflections
collected of which 3271 unique, Rint = 0.0399, Final R indices [I > 2s(I)]
R1 = 0.0289, wR2 = 0.0729.
1 8 Y. Yo u a n d S. Y. P a r k , Dalton Trans., 2009, 1267.
19 P. J. Hay, J. Phys. Chem. A, 2002, 106, 1634.
20 M. J. G. Peach, P. Benfield, T. Helgaker and D. J. Tozer, J. Chem. Phys.,
2008, 128, 044118.
9678 | Dalton Trans., 2011, 40, 9672–9678
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