Fluorination of Cyclometalated Iridium β-Ketoiminate and β-Diketiminate Complexes: Extreme Redox Tuning and Ligand-Centered Excited States

Article abstract of DOI:10.1021/acs.organomet.6b00453

In this work we describe a series of bis-cyclometalated iridium complexes with ancillary β-ketoiminate (acNac) and β-diketiminate (NacNac) ligands, prepared by a general synthetic route. Fluorination of these ligands by introducing CF₃ substituents onto the ligand backbone and/or N-aryl substituent(s) leads to pronounced changes in the redox properties and photophysical properties. All of the complexes show a reversible Ir^IV/Ir^III redox couple that is sensitive to the degree of fluorination on the ancillary ligand. Introduction of CF₃ groups at the 3- and 5-positions of the N-aryl substituent shifts the potential positive by ca. 50-70 mV per CF₃ group, whereas fluorination of the acNac or NacNac backbone induces larger shifts of ca. 200-300 mV per CF₃ group. Fluorination of the NacNac backbone gives rise to substantially altered excited-state properties. Complexes with backbone CF₃ groups luminesce in the red and near-infrared regions out of an excited state that is predominately a π → π? NacNac-centered triplet state. A preponderance of evidence supports the assignment of this low-energy feature, including minimal dependence of this emission feature on the identity of the cyclometalating ligand, pronounced vibronic structure, and microsecond lifetimes. These results demonstrate that acNac and NacNac ancillary ligands can engender cyclometalated iridium complexes with desirable and readily tailorable redox and optical properties, motivating continued application of this important ligand class to the design of phosphorescent organometallic molecules.

Full text of DOI:10.1021/acs.organomet.6b00453

Article
pubs.acs.org/Organometallics
Fluorination of Cyclometalated Iridium β‑Ketoiminate and
β‑Diketiminate Complexes: Extreme Redox Tuning and Ligand-
Centered Excited States
Rosa A. Maya, Ayan Maity, and Thomas S. Teets*
Department of Chemistry, University of Houston, 3585 Cullen Boulevard, Room 112, Houston, Texas 77204-5003, United States
S
* Supporting Information
ABSTRACT: In this work we describe a series of bis-cyclo-
metalated iridium complexes with ancillary β-ketoiminate (acNac)
and β-diketiminate (NacNac) ligands, prepared by a general
synthetic route. Fluorination of these ligands by introducing CF3
substituents onto the ligand backbone and/or N-aryl substituent(s)
leads to pronounced changes in the redox properties and
photophysical properties. All of the complexes show a reversible
IrIV/IrIII redox couple that is sensitive to the degree of fluorination
on the ancillary ligand. Introduction of CF3 groups at the 3- and 5-
positions of the N-aryl substituent shifts the potential positive by
ca. 50−70 mV per CF3 group, whereas fluorination of the acNac or
NacNac backbone induces larger shifts of ca. 200−300 mV per CF3
group. Fluorination of the NacNac backbone gives rise to
substantially altered excited-state properties. Complexes with backbone CF3 groups luminesce in the red and near-infrared
regions out of an excited state that is predominately a π → π* NacNac-centered triplet state. A preponderance of evidence
supports the assignment of this low-energy feature, including minimal dependence of this emission feature on the identity of the
cyclometalating ligand, pronounced vibronic structure, and microsecond lifetimes. These results demonstrate that acNac and
NacNac ancillary ligands can engender cyclometalated iridium complexes with desirable and readily tailorable redox and optical
properties, motivating continued application of this important ligand class to the design of phosphorescent organometallic
molecules.
medical technologies.16 The design of red to near-infrared-
emitting cyclometalated iridium complexes remains a challenge,
owing to the intrinsically low quantum efficiencies of such
INTRODUCTION
■
Cyclometalated iridium(III) complexes have garnered much
acclaim for their photophysical properties, which include
efficient triplet emission and photoinduced electron transfer,
phosphors. Advances have been made primarily by incorporat-
ing elaborate conjugated functionalities into the C∧N
leading to widespread applications in OLEDs,1−4 bioimag-
ligand.4,16−21 Alternatively, it is possible to elicit low-energy
ing,5−8 and, in more recent years, photocatalysis.9−11
emission from a triplet state centered on the ancillary ligand;
Homoleptic complexes of the type Ir(C∧N)3 (C∧N is a
successful implementations of this strategy include tunable
cyclometalating ligand) are known and have received
considerable attention,10,12,13 but heteroleptic complexes of
emission into the red region with a pyridine-carboxylate family
of ancillary ligands22 and the observation of triplet dipyrrin-
the type [Ir(C∧N)2(LL′)]n (LL′ is a bidentate ligand or two
centered emission in a series of cyclometalated iridium dipyrrin
monodentate ligands) have also been developed extensively.
complexes.23
The triplet excited-state manifolds of these compounds are
complex and diverse and, depending on the structure of the
supporting ligands, can include contributions from ligand-
centered (LC) and metal-to-ligand charge transfer (MLCT)
Our group recently disclosed a suite of heteroleptic iridium
cyclometalates with nitrogen-containing β-ketoiminate (acNac)
and β-diketiminate (NacNac) ancillary ligands.24 Ligands of
this type have been utilized extensively in coordination
states, involving ligand π orbitals from either or both of the
chemistry25 and are especially prominent in polymerization
C∧N and LL′ ligands.1
catalysis26,27 and small-molecule activation chemistry,28−33 but
As such, tuning the electrochemical and photophysical
their potential as ancillary ligands for phosphorescent molecules
properties of these complexes for a specific application can be
brought on by alteration of either the C∧N ligand14 or the
had been previously unrecognized. One unexpected outcome
ancillary LL′ ligand(s).15 A recent area of focus has been the
from our study is that fluorination of the NacNac backbone in
design of near-infrared cyclometalated iridium emitters, which
are targeted for use in near-infrared organic light-emitting
diodes (OLEDs), desirable for certain sensing, display, and
Received: June 5, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
these complexes gives rise to structured luminescence at low
temperature that is dramatically red-shifted relative to the
unfluorinated variants, occurring in the red and near-infrared
regions. We tentatively assigned this unusual emission feature
to a triplet NacNac-centered excited state, on the basis of the
pronounced vibronic structure and the insensitivity of this
emission to the identity of the cyclometalating ligand, which
shows that NacNac ligands not only can act as ancillary ligands
for cyclometalated iridium phosphors but can themselves have
potentially interesting photophysical properties.
Chart 1
The use of NacNac ligands in the design of red- and near-
infrared-emitting photosensitizers is certainly attractive, owing
to their ease of synthesis from inexpensive, commercially
available precursors and the ability to add electronically
modifying substituents in different positions.34−37 In this
work, we further elaborate the distinct properties brought on
by incorporation of fluorinated acNac and NacNac ligands into
cyclometalated iridium complexes with 2-phenylpyridine (ppy)
and 2-phenylbenzothiazole (bt) supporting ligands. We show
that the electrochemical properties can be dramatically tuned
by addition of CF3 groups to various sites on the ancillary
ligand, with the magnitude of the potential shift dependent on
the site of substitution. In total, we are able to perturb the IrIV/
IrIII potential by >750 mV when six CF3 groups are added to
the NacNac ligand, demonstrating the pronounced effects that
CF3 groups can have on the electronic structures of otherwise
isostructural and isoelectronic complexes. By studying a wide
swathe of fluorinated acNac and NacNac ligands, we illustrate
that the low-energy, red to near-infrared emission occurs only
when the backbone of a NacNac ligand is fluorinated; these
features are absent in all acNac ligands or in NacNac ligands
where the CF3 groups are placed elsewhere. When the low-
energy emission is observed, we find that in addition to
showing pronounced vibronic structure it is long-lived (τ ≈
10−6 s), consistent with a triplet ligand-centered origin. The
results provide a much more thorough understanding of this
unprecedented NacNac-centered luminescence.
RESULTS
■
Synthesis of Complexes. Chart 1 outlines the nomencla-
ture and numbering scheme that will be utilized herein for the
series of bis-cyclometalated complexes we describe. Ancillary
ligand designations follow the format (N)acNacF#, where #
denotes the total number of fluorine atoms in the ligand and
the C∧N ligand is either ppy or bt. Except for NacNacF15 and
acNacF12, which are described here for the first time, the other
ancillary ligands have been utilized in other contexts.35−40
Syntheses of complexes 1−4, 11, and 12 were described
previously, and the 10 new complexes described here were
prepared following analogous methodology.24 Complexes with
no backbone CF3 substituents (1, 2, 5, 6, 11, and 12) were
prepared by room-temperature reaction of the dimers [Ir-
(C∧N)2(μ-Cl)]2 with two equivalents of the potassium salt of
the respective acNac or NacNac ligand in THF. For the
remaining complexes, which feature one or more backbone CF3
group, the lithium salt of the desired ancillary ligand was
substituted, and reactions were carried out in toluene at 90−
100 °C. All complexes were isolated as pure solids, as judged by
1H and 19F NMR and combustion analysis (see Experimental
Section and Figures S36−S59 in the Supporting Information).
Most of the new complexes, except 5 and 13, were
characterized by X-ray diffraction. Two representative struc-
tures, 10 and 16, are shown in Figure 1, with the rest deposited
Figure 1. X-ray crystal structures of 10 and 16. Hydrogen atoms and
solvate molecules are omitted. Ellipsoids are shown at the 50%
probability level. Carbon atoms of the ancillary NacNac (10) or acNac
(16) ligand are shown in black.
in the Supporting Information in Figures S1−S6. The
structures of the new compounds described here largely
resemble those previously reported.24 With a larger suite of
fluorinated ligands to compare, we can conclusively say that
fluorination has minimal structural impact. Ligands with
backbone CF3 substituents tend to show slightly longer Ir−N
B
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(NacNac) distances, but only by ca. 0.01−0.02 Å, and addition
of CF3 groups to the aryl rings induces no noticeable changes in
the bond distances. The structures of the NacNacF15 complexes
(7 and 8), which feature an asymmetric CF3/CH3 backbone,
are isostructural with their fully fluorinated NacNacF18
analogues (9 and 10), with the lone backbone CF3 group in
the former disordered over both positions. This crystallographic
disorder obfuscates any structural asymmetry brought on by the
unbalanced backbone substitution. Another feature of the
crystal structures is the nearly eclipsed orientation and close
approaches of the N-aryl groups and a nearby Ir-phenyl. This
structural motif is especially evident for the NacNac complexes;
with acNac ancillary ligands the smaller ligand size and absence
of a second N-aryl group allow the ligand to twist slightly,
which disrupts the eclipsed orientation of the two rings. Across
the NacNac structures the centroid-to-centroid distances
between the N-aryl rings and the adjacent Ir-phenyl range
between 3.395 and 3.986 Å, with seemingly no systematic
dependence on the extent of ligand fluorination. This close
aryl−aryl approach suggests hindered rotation of the N-aryl
substituent, which is born out in the room-temperature 19F
NMR spectra of complexes 5−10, 15, and 16, each showing
unique resonances for the CF3 groups at the 3- and 5-positions.
Electrochemistry. Cyclic voltammograms (CVs) for all
complexes share a common reversible IrIV/IrIII wave, the
potential of which depends on the ligand fluorination. Figure 2
Table 1. Summary of Electrochemical Data
a
complex
“LX” ligand
C∧N
(E1/2 vs Fc+/Fc)/V
1
NacNacF0
NacNacF0
NacNacF6
NacNacF6
NacNacF12
NacNacF12
NacNacF15
NacNacF15
NacNacF18
NacNacF18
acNacF0
ppy
bt
−0.07
+0.01
+0.44
+0.59
+0.18
+0.27
+0.46
+0.58
+0.71
+0.87
+0.25
+0.35
+0.62
+0.77
+0.71
+0.85
2
3
ppy
bt
4
5
ppy
bt
6
7
ppy
bt
8
9
ppy
bt
10
11
12
13
14
15
16
ppy
bt
acNacF0
acNacF6
acNacF6
acNacF12
acNacF12
ppy
bt
ppy
bt
a
Measured in acetonitrile, except complex 10, which was recorded in
dichloromethane. Glassy carbon working electrode, scan rate of 0.1 V/
s.
respectively, and these values shift to +0.18 V and +0.27 V in
NacNacF12 complexes 5 and 6. Similarly, comparison of
NacNacF6 complexes 3 and 4 (E1/2 = +0.44 V, +0.59 V) with
NacNacF18 complexes 9 and 10 (E1/2 = +0.71 V, +0.87 V)
reveals a similar trend. Thus, in the NacNac set of complexes
we see a consistent shift of +60−70 mV per CF3 group when
the 3- and 5-positions of both phenyl rings are substituted. For
acNac complexes, replacement of acNacF6 with acNacF12 causes
a 45 mV (13 → 15) or 60 mV (14 → 16) positive shift per
added CF3 group.
In contrast, the potentials are much more sensitive to
backbone fluorination. The best comparison is the NacNacF12
,
NacNacF15, and NacNacF18 set of complexes, which differ by
sequential replacement of CH3 groups with CF3 groups in the
NacNac backbone. The IrIV/IrIII potentials shift by +280 mV
(ppy) and +310 mV (bt) when the first CF3 group is added to
the backbone, and the second substitution yields additional
+250 mV (ppy) and +290 mV (bt) shifts. Thus, we see that the
potential shifts by about the same amount for each CF3 group
added, and the effect is about 4 times more potent (per CF3
group) than addition of CF3 groups to the aryl rings. The
acNac complexes are slightly less sensitive to backbone
fluorination, and in comparing acNacF0 complexes and acNacF6
complexes we see shifts of +180 mV (ppy) and +210 mV (bt)
per added CF3. Finally, we note that the “maximally
fluorinated” NacNacF18 (9 and 10) and acNacF12 (15 and 16)
complexes have remarkably similar potentials; substitution of
acNac for NacNac normally shifts the potential cathodically,
but the two additional CF3 groups in NacNacF18 compared to
acNacF12 perfectly counterbalance this effect.
Figure 2. Graphical depiction of the E1/2(IrIV/IrIII) values, determined
by cyclic voltammetry.
summarizes the IrIV/IrIII redox potentials for all of the
complexes described here, arranged by C∧N ligand (ppy and
bt) to clarify comparisons between the different ancillary
ligands. The data are summarized numerically in Table 1, and
overlaid CVs showing only the oxidation wave are depicted in
the Supporting Information, Figures S7 and S8. One trend that
holds true for all ancillary ligands is that the potential values for
bt complexes are between 80 and 160 mV positive of the ppy
analogues. Complexes with acNac ancillary ligands oxidize at
more positive potentials than their NacNac congeners at parity
of fluorination. For unfluorinated complexes the potential shifts
by 320 (ppy) and 340 mV (bt) upon replacing NacNac
(complexes 1 and 2) with acNac (complexes 11 and 12). The
backbone-fluorinated complexes with (N)acNacF6 ancillary
ligands (3/4 and 13/14) are less sensitive to this substitution,
differing by only 180 mV.
When comparing complexes with the same type of ancillary
ligand (acNac or NacNac), fluorination always induces an
anodic shift in the oxidation potential, although the magnitude
of the shift depends on the location of the CF3 substituent.
Addition of CF3 groups to the N-aryl group causes
comparatively small changes in the oxidation potential (all
potentials are referenced to ferrocene). The NacNacF0
complexes 1 and 2 oxidize at −0.07 V and +0.01 V,
Figures S9−S16 display full cyclic voltammograms for the
complexes described here. When sweeping cathodically, most
of the fluorinated complexes we describe here display complex
irreversible features that onset well before the expected C∧N-
centered reductions, which occur at ca. −2.2 to −2.4 V in
related complexes with unfluorinated ancillary ligands.14,15,24
This irreversible reduction also frequently results in additional
oxidation features on the return scan, which are particularly
evident for backbone-fluorinated complexes 3 and 4
(NacNacF6, Figure S10), 7 and 8 (NacNacF15, Figure S12), 9
C
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and 10 (NacNacF18, Figure S13), and 13 (acNacF6, Figure S15).
One exception to this trend is that acNacF12 complexes possess
reversible, one-electron reductions that occur at −1.81 V (15)
and −1.69 V (16), as shown in the full CVs displayed in Figure
S16. We tentatively assign this wave to a one-electron reduction
of the ancillary acNacF12 ligand, although it remains unclear
why only this particular ancillary ligand is reversibly reduced.
To better visualize the reduction features and how the onset
potentials depend on the ancillary ligand, Figures S17 and S18
show only the negative regions of the CVs for the ppy and bt
complexes, respectively. In general, backbone fluorination
anodically shifts the onset of reduction, which suggests the
presence of low-lying unoccupied orbitals in complexes with
backbone CF3 groups.
Optical Properties. Table 2 summarizes absorption and
emission data for all of the complexes here. On the basis of
Table 2. Summary of Emission Data, Recorded in Toluene
complex
emission 293 K (λ/nm)
emission 77 K (λ/nm)
1
565
615
522, 554 (sh)
590, 638, 691 (sh)
669, 737, 814
682, 755, 823 (sh)
509, 542
2
3
4
5
570
6
574, 612 (sh)
568, 604
Figure 3. Absorption, room-temperature emission, and 77 K emission
spectra of 5 (top) and 6 (bottom), recorded in toluene. The excitation
wavelength (λex) was 420 nm for the room-temperature spectra and
350 nm for the low-temperature spectra.
7
586, 636, 690 (sh)
600, 653, 716
677, 744, 815 (sh)
689, 762
8
9
10
11
12
563
505, 540
568, 609
554, 602, 655, 715 (sh)
spectra for complexes 5 and 6, shown in Figures S19 and S20,
bear good resemblance to the absorption spectra.
NacNac complexes with fluorinated backbones (3, 4, and 7−
10) exhibit entirely different emission behavior. Figure 4 shows
overlaid absorption and emission spectra for these complexes,
showing the impact the ancillary ligand has on the absorption
and emission spectra. In this subset of complexes, no emission
is observed at room temperature. However, at 77 K, emission
occurs in the red to near-infrared region of the spectrum,
showing pronounced vibronic structure with a spacing of ca.
1300−1400 cm−1 between adjacent bands. The free ligands
NacNacF#H are not luminescent and have similar absorption
maxima that show no systematic dependence on the extent of
fluorination (Figure S21). Similarly, the low-energy absorption
features of the iridium complexes with backbone-fluorinated
NacNac ancillary ligands vary minimally across the series. In
contrast, the position of this ligand-centered emission band
depends strongly on the extent of fluorination in the NacNac
backbone. Complexes with NacNacF15 (7 and 8) have maxima
at ca. 600 nm, which bathochromically shift by ∼2200 cm−1 (to
ca. 680 nm) when an additional CF3 group is added in the
NacNacF18 complexes. The position of this low-energy emission
feature is weakly responsive to N-aryl fluorination; comparison
of NacNacF6 complexes (3 and 4) with NacNacF18 complexes
(9 and 10) reveals a <300 cm−1 bathochromic shift in the latter.
Finally, we note that the emission bands are minimally
dependent on the identity of the C∧N ligand, with a consistent
∼300 cm−1 red-shift in bt complexes relative to ppy, when the
identity of the NacNac ligand is the same. Excitation spectra for
bt complexes 8 and 10 are shown in Figures S22 and S23.
Because of the low temperature and relatively high concen-
trations (ca. 5 × 10−5 M) for these samples, the excitation
absorption and emission properties, the complexes can be
divided into three categories: complexes with unfluorinated
backbones (1, 2, 5, 6, 11, and 12), NacNac complexes with
fluorinated backbones (3, 4, and 7−10), and acNac complexes
with fluorinated backbones (13−16). Complexes with un-
fluorinated backbones (1, 2, 5, 6, 11, and 12) luminesce at
room temperature and exhibit absorption and emission spectra
that are largely reminiscent of other neutral cyclometalated
iridium complexes.12,14 As we previously noted, the acNac- and
NacNac-substituted complexes include greater MLCT charac-
ter in their emissive excited states when compared to Ir(C∧N)3
and Ir(C∧N)2(acac) complexes, and the ppy complexes have
substantially lower quantum yields (Φ ≈ 0.01) when compared
to the bt complexes (Φ = 0.21 for NacNacF0 and 0.82 for
acNacF0).24 Addition of CF3 groups to the 3- and 5-positions of
the N-aryl groups minimally perturbs the optical properties of
the complexes, with the spectra for NacNacF12 complexes 5 and
6 shown in Figure 3. Absorption spectra display intense bands
at λ < 300 nm, with lower energy bands occurring near 400 nm
in both complexes. The room-temperature emission maximum
for 5, occurring at 570 nm, is virtually identical to the 565 nm
maximum observed for unfluorinated complex 1, and complex
5 likewise has a very low quantum yield (Φ = 0.0037 for 5,
0.013 for 1). The emission lifetimes for 1 (τ = 1.0 μs) and 5 (τ
= 1.4 μs) are also quite similar. The emission spectrum for bt
complex 6 (λem = 574 nm) is significantly hypsochromically
shifted relative to unfluorinated analogue 2 (λem = 615 nm), but
the lifetimes and quantum yields of 6 (τ = 0.57 μs, Φ = 0.30)
are very similar to those of 2 (τ = 0.61 μs, Φ = 0.21). Excitation
D
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
DISCUSSION
■
In this work we have presented a generalized synthesis of
cyclometalated iridium(III) complexes with fluorinated β-
ketoiminate and β-diketiminate ligands, systematically varying
the number of CF3 groups. Included in this study are five
ligands (NacNacF12, NacNacF15, NacNacF18, acNacF6, and
acNacF12), which expand upon our original set of bis-
cyclometalated iridium complexes with (N)acNac ancillary
ligands. While it may be possible to incorporate one additional
CF3 group onto the center (3-position) of the backbone as a
means of further perturbing the properties,41 one synthetic
limitation that presents itself is an inability to incorporate
substituents onto the 2- and 6-positions of the N-aryl.
Attempted synthesis of complexes using an analogue NacNacF6
that features 2,6-dimethylphenyl substituents led to mostly
unreacted starting material with no evidence for product
formation. This limitation is presumably caused by the crowded
environment for the N-aryl groups, revealed crystallographi-
cally, which prohibits incorporation of additional substituents
(CF3 or otherwise) ortho to the nitrogen. Analysis of the crystal
structures for the complexes we have characterized shows
almost no structural perturbation brought on by fluorination of
the ancillary acNac or NacNac ligands.
Bis-cyclometalated iridium complexes typically feature
ligand-based reduction waves and Ir-aryl-centered oxidations
in their cyclic voltammograms. We showed in our previous
report24 that the latter IrIV/IrIII potential is sensitive to the
incorporation of nitrogen donors into the ancillary ligand, with
the potential sequentially shifting ∼200−300 mV in the
cathodic direction as the ancillary ligand is altered from
acetylacetonate (acac)14 to acNac to NacNac. We observe a
substantial perturbation of the redox potentials when
fluorinating the ancillary ligands. Fluorination of the NacNac
backbone essentially undoes the effect of changing acac to
NacNac, such that the complexes Ir(C∧N)2(acac) and
Ir(C∧N)2(NacNacF6) have nearly identical IrIV/IrIII redox
potentials. By making appropriate comparisons between
ancillary ligands with differential fluorination, we find that
addition of CF3 groups to the ligand backbone is ca. 4× more
potent at influencing the IrIV/IrIII potential, as compared to the
addition of CF3 groups to the 3- and 5-positions of the N-aryl.
Many previous studies have looked at the effects of electron-
withdrawing groups, CF3 groups in particular, on the IrIV/IrIII
redox potentials in cyclometalated iridium(III) complexes.
Most of these previous reports focus on modifications to the
C∧N ligands. One of the earliest accounts on cyclometalated
iridium complexes by Watts and co-workers12 showed that
addition of a CF3 group to the phenyl ring’s 4-position in fac-
Ir(ppy)3 derivatives induced a 310 mV anodic shift in the IrIV/
IrIII potential, working out to 100 mV per CF3 group. Related
work has shown that addition of two CF3 groups to 2-
phenylpyridine (one at the 3-position of the phenyl and a
second at the 5-position of the pyridine) shifts the potential by
650 mV, which again corresponds to a shift of ∼100 mV per
CF3.42 Other groups have studied the addition of CF3 and
fluorine electron-withdrawing groups to ppy in bis-cyclo-
metalated complexes and likewise have shown shifts of no
more than 130 mV per added CF3, with the site of CF3
incorporation seemingly having little effect on the observed
shifts in potential.43−45 A few well-known studies have
examined the effects of adding CF3 substituents to ancillary
ligands in bis-cyclometalated complexes; two groups have
Figure 4. Overlaid absorption and emission spectra of backbone-
fluorinated NacNac complexes 3, 4, and 7−10. The absorption spectra
were collected at room temperature in THF solutions, whereas
emission spectra were collected at 77 K in frozen toluene glass, with
λex = 430 nm for 3, 4, 9, and 10, 350 nm for 7, and 340 nm for 8.
spectra do not perfectly overlay with the absorption spectra, but
qualitative agreement is observed.
Time-resolved emission spectra for the backbone-fluorinated
complexes were likewise recorded, and the results are
consistent with triplet luminescence in these complexes. We
had difficulty obtaining quantitatively reproducible results for
some of the complexes, owing to the low PMT sensitivity in the
red region. Nevertheless, we find lifetimes ranging between 0.4
and 0.8 μs for the NacNac complexes with two backbone CF3
groups (3, 4, 9, and 10). For NacNacF15 complexes 7 and 8
most of the signal occurs in the visible range, and a reliable fit of
the data was obtained. Consistent with the energy-gap law, for
these complexes the NacNac-centered emission band has a
longer lifetime of 2.9 μs (7) and 2.1 μs (8).
We also examined solvatochromic effects for the absorption
spectra of the NacNac complexes. Figures S24−S31 show
absorption spectra of 3−10 in both toluene and 2-propanol.
The low-energy absorption features for the backbone-
fluorinated complexes (3, 4, and 7−10) overlay perfectly.
The complex Ir(bt)2(NacNacF12) (6), which lacks backbone
fluorination, also shows minimal solvatochromism for the low-
energy absorption features, with a <5 nm hypsochromic shift
when changing from toluene to 2-propanol (Figure S27), but
the ppy analogue 5 exhibits a pronounced (>1600 cm−1) blue-
shift in its absorption spectrum when comparing toluene and 2-
propanol as solvents (Figure S26).
The complexes with fluorinated acNac ligands, 13−16, are
not luminescent at either room temperature or 77 K. The
absorption spectra for these complexes, shown in Figures S32−
S35, bear qualitative similarity to the fluorinated NacNac
complexes, albeit with less absorption in the visible range.
E
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
shown very minimal (60−80 mV) changes in the IrIV/IrIII
potential when substituting 2,2′-bipyridine ancillary ligands
with two CF3 groups in cationic complexes,46,47 and another
group has demonstrated that adding a CF3 group to a
quinoline-2-carboxylate ancillary ligand in a neutral complex
resulted in only a 60 mV shift in the redox potential.48 An
earlier work by Thompson and collaborators, while not
specifically investigating substituent effects, showed that
changing the ancillary ligand in a series of bis-cyclometalated
complexes could tune the oxidation potential over 800 mV,
although within their suite of neutral complexes the potentials
spanned a range of 410 mV. Thus, we think it is significant that
in our series of compounds described here the oxidation
potential is much more sensitive to trifluoromethylation of the
ancillary ligand backbone, shifting by ca. 250 to 300 mV per
CF3 group in the NacNac series. Furthermore, we can span a
large potential range within a homologous series of compounds
(same C∧N ligand, same ancillary ligand type). In the
Ir(ppy)2(NacNacF#) series, the potentials span a range of 780
mV (−0.07 V for NacNacF0, 0.71 V for NacNacF18). The range
is even larger for Ir(bt)2(NacNacF#) complexes, falling between
0.01 V for NacNacF0 and 0.87 V for NacNacF18, a difference of
860 mV. For the acNac series, with C∧N = ppy the range is 460
mV moving from acNacF0 to acNacF12, and for C∧N = bt the
corresponding range is 500 mV. These comparisons demon-
strate we can access a larger range of potentials with NacNac
ancillary ligands, and to our knowledge this redox tunability is
among the largest ever observed for a homologous series of
cyclometalated iridium(III) complexes.
The observation that the oxidation potential shifts anodically
with additional CF3 groups is unsurprising, even though the
magnitudes of the shifts are noteworthy. Perhaps more
unexpected is the effect of the CF3 groups on the optical
properties of the complexes. When CF3 groups are added to the
N-aryl substituent (complexes 5 and 6), the absorption and
emission spectra (Figure 3) are minimally perturbed from those
of the Ir(C∧N)2(NacNacF0) complexes (1 and 2)24 or from
other bis-cyclometalated heteroleptic complexes.2,14 The large
rigidochromic shift in the emission spectrum (Figure 3) and the
significant solvatochromism in the absorption spectrum (Figure
S26) both suggest augmented MLCT character in the low-
energy excited state of ppy complex 5 when compared to 6.
Nevertheless, the emission features for these complexes arise
from an excited-state manifold consisting of mixed 3MLCT and
3(π → π*) states involving the C∧N ligands, in line with
previously characterized complexes.2,14
cm−1 between successive emission maxima is consistent with a
vibronic structure originating from aromatic C−C vibrations.52
This feature, coupled with the relative insensitivity of the
emission bands to the identity of the C∧N ligand and the
microsecond lifetimes, is consistent with the assignment of
NacNac-centered triplet emission. Along the same lines as the
electrochemical properties, the emission maxima in this series
of complexes are much more sensitive to backbone fluorination
as opposed to fluorination of the N-aryl groups. NacNacF15
complexes 7 and 8, which feature only one backbone CF3
group, have emission maxima that differ by over 2000 cm−1
when compared to symmetrically fluorinated complexes with
two CF3 groups. In contrast, NacNacF6 complexes 3 and 4 and
NacNacF18 complexes 9 and 10, which differ with respect to N-
aryl fluorination, have emission spectra that are nearly identical.
These results show that in addition to the redox properties the
emission properties can be controlled by the extent of
fluorination in the ancillary ligand. The acNac complexes
with backbone CF3 groups (13−16) do not luminesce at all.
The lack of emission in these complexes, even from a C∧N-
centered excited state, suggests the presence of a low-energy,
nonluminescent acNac-centered state, although we cannot
conclusively prove that this is the origin of the nonradiative
decay of the excited state.
As a matter of clarification, we point out that in our previous
work, when we first described the low-energy emission in
complexes 3 and 4, we also noted a weaker emission band in
the 500−600 nm range, which we tentatively assigned as dual
emission from a C∧N-centered MLCT state.24 The compounds
we studied in this earlier work were of sufficient purity to give
satisfactory microanalysis and had no glaring issues with their
NMR spectra, but nonetheless we can now conclusively assign
this extra feature as arising from a minor but highly luminescent
impurity. In our subsequent studies presented here we have
found again that routine workup gives samples that are pure by
elemental analysis, but more rigorous purification of these
compounds, achieved by column chromatography, removes the
extra emission feature in the 500−600 nm range altogether.
CONCLUSIONS
■
We have presented here a thorough study of the effect of
fluorination on the electrochemical and optical properties of
cyclometalated iridium complexes with β-ketoiminate and β-
diketiminate ligands. The IrIV/IrIII redox potential can be tuned
over a wide range by introduction of CF3 groups, and within
the NacNac complexes the potentials shift by 780 mV (ppy) or
860 mV (bt) when unfluorinated NacNacF0 complexes are
compared to the NacNacF18 complexes, illustrating the
profound impact that fluorination has on the electronic
structure of these complexes. Systematic comparison of
different ligand structures reveals that the redox potentials are
much more sensitive to backbone fluorination than to
fluorination on the N-aryl substituent. Whereas fluorination
of the backbone of acNac ligands quenches luminescence
altogether, backbone fluorination of the NacNac ligand induces
dramatic changes in the excited-state properties. The
absorption spectra are not substantially perturbed, but the
low-temperature emission spectra display new features in the
red and near-infrared regions when one or two CF3 groups are
added to the backbone. These features are only observed in
complexes featuring backbone-fluorinated NacNac ligands, and
this observation coupled with the pronounced vibronic
In contrast, complexes with backbone CF3 groups (3, 4, and
7−10) exhibit entirely different emission properties. These
complexes are not luminescent at all at room temperature, and
the reasons for this poor efficiency are not immediately
obvious, although this is a common limitation for complexes
with low-energy excited states.16 It has also been shown that the
efficiency of triplet emission in related complexes depends
largely on the singlet−triplet energy gap, with a larger energy
gap leading to less efficient radiative decay.1,49−51 Although we
have not measured or computed the singlet−triplet gaps in
these complexes, we do observe a large apparent Stokes shift
(>ca. 7000 cm−1) between the low-energy absorption and
emission maxima, so we speculate that the singlet−triplet gap is
quite large and may contribute to the poor emission efficiency
at room temperature. The low-temperature emission in the red
and near-infrared region (Figure 4) is assigned to a NacNac-
3
centered (π → π*) excited state. The spacing of 1300−1400
F
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
were further purified by flash column chromatography. The
compounds were dissolved in a minimum amount of CH2Cl2 and
loaded onto a short (<20 cm) silica gel column. The column was
packed with hexane and eluted with a gradient Et2O/hexane eluent
under pressure. With increasing polarity of the eluent, the orange-red
band of the complex was collected as the major fraction at ca. 1:9
Et2O/hexane (v/v). Removal of the solvent under vacuum rendered an
orange-red product, which was washed with pentane. The NMR
spectra of 3−10 shown in the SI (Figures S36−S51) are for samples
purified in this manner. For complexes 5 and 6, the emission spectra
were unchanged after chromatographic purification. However, for
backbone-fluorinated complexes 7−10 chromatographic purification
removed a luminescent impurity that was present in the initially
isolated compounds. This minor impurity was undetectable by NMR
but gave rise to spurious emission in the 500−600 nm range at 77 K.
For acNac complexes 13−16, no emission was observed, so the
additional purification by chromatography was not performed.
structure and lifetimes between 0.4 and 2.9 μs points toward a
triplet excited state that is NacNac-centered.
These findings unveil a new application for fluorinated
NacNac ligands, which have become popular in small-molecule
activation35,53,54 and polymerization catalysis.36,55 These
ancillary ligands are arguably simpler to prepare and offer
more facile synthetic tunability than prior examples of ancillary
ligands that give rise to red and near-infrared emission
properties.16,23 Nevertheless, we acknowledge the current
limitation that our complexes exhibit these features only at
cryogenic temperatures, which obviates potential device
applications. We are targeting solutions to this limitation and
exploring whether other heavy transition metals, particularly
more abundant early transition metals, or different backbone
substituents besides CF3 can give rise to these desirable
properties that arise from NacNac-derived triplet excited states.
Physical Methods. NMR spectra were recorded at room
temperature using a JEOL ECA-400 or ECA-600 NMR spectrometer.
UV−vis absorption spectra were recorded in THF solutions in screw-
capped quartz cuvettes using an Agilent Cary 60 UV−vis
spectrophotometer or an Agilent Cary 8454 UV−vis diode array
spectrophotometer. Emission spectra were recorded using a Horiba
FluoroMax-4 spectrofluorometer, using appropriate long-pass filters to
exclude stray excitation light from detection. Samples for room-
temperature emission were housed in 1 cm quartz cuvettes with
septum-sealed screw caps, and samples for low-temperature emission
were contained in a custom quartz EPR tube with high-vacuum valve
and immersed in liquid nitrogen using a finger dewar. Emission
quantum yields were determined relative to a standard of
tetraphenylporphyrin in toluene, which has a reported fluorescence
quantum yield (ΦF) of 0.11.60 Luminescence lifetimes were measured
with a Horiba DeltaFlex Lifetime System, using 390 nm pulsed diode
excitation. Emission wavelengths were selected by using appropriate
long-pass filters, and the decay trace was fit using the instrument’s
analysis software. Cyclic voltammetry measurements were performed
with a CH Instruments 602E potentiostat interfaced with a nitrogen
glovebox via wire feedthroughs. Samples were dissolved in acetonitrile
or dichloromethane with 0.1 M TBAPF6 as a supporting electrolyte. A
3 mm diameter glassy carbon working electrode, a platinum wire
counter electrode, and a silver wire pseudoreference electrode were
used. Potentials were referenced to an internal standard of ferrocene.
Elemental analyses were performed by Midwest Microlab, LLC.
Preparation of NacNacF15. A 100 mL flask with a side arm and
Teflon cap was charged with solid PPh3 (6.03 g, 23.0 mmol). A
nitrogen atmosphere was established by repeated evacuation/backfill
cycles on the Schlenk line. The solid was dissolved in 40 mL of
anhydrous Et2O, at which point a solution of 3,5-bis(trifluoromethyl)-
phenyl azide (5.86 g, 23.0 mmol, 1.00 equiv) in 10 mL of Et2O was
added dropwise via cannula; the rate of addition was carefully
monitored to prevent excess frothing from release of N2. The pale
yellow solution was stirred under N2 for 18 h at room temperature
before removing the solvent in vacuo. The white solid was redissolved
in 35 mL of toluene, and 1,1,1-trifluoro-2,4-pentanedione (1.39 mL,
1.76 g, 11.5 mmol, 0.500 equiv) was added via syringe. The flask was
sealed and heated to 120 °C for 6 days. The solvent was removed via
rotary evaporation, and the crude product was filtered through a short
column of silica, eluting with 19:1 hexane/ethyl acetate to leave behind
the OPPh3 byproduct. After removing the solvent, the product was
further purified by silica gel flash chromatography, eluting with 9:1
hexane/ethyl acetate. Yield: 2.11 g (31.8%). 1H NMR (400 MHz,
C6D6) δ: 11.79 (s, 1H, NH), 7.50 (s, 1H, ArH), 7.47 (s, 1H, ArH),
7.31 (s, 2H, ArH), 6.91 (s, 2H, ArH), 5.21 (s, 1H, ArNC(CF3)CHC-
(CH3)NAr), 1.16 (s, 3H, CH3). 19F NMR (376 MHz, C6D6) δ:
−62.26 (s, 3F), −62.65 (s, 6F), −62.71 (s, 6F).
EXPERIMENTAL SECTION
■
Materials. Reactions were carried out in a nitrogen atmosphere;
reagents and solvents were measured in a glovebox operating at <1
ppm of O2 and H2O, whereas in most cases the workup and
purification could be executed on the benchtop in ambient
atmosphere. Starting materials and reagents were of commercial
origin and used without further purification, unless stated otherwise
below. Except for 2-propanol, which was used without further
purification, solvents for reactions, UV−vis absorption/emission
spectroscopy, and electrochemical measurements were dried by the
method of Grubbs,56 passing through dual alumina columns on a
commercial solvent purification system. Solvents used in the glovebox
were further dried by storage over 3 Å molecular sieves.
Tetrabutylammonium hexafluorophosphate (TBAPF6) was recrystal-
lized from hot ethanol, and ferrocene was sublimed at ambient
pressure before use in electrochemical experiments. CDCl3 for NMR
spectroscopy was stored over potassium carbonate and molecular
sieves to remove acidic impurities and moisture. NacNacF18H and 3,5-
bis(trifluoromethyl)phenyl azide were prepared by the method of
Sadighi et al.35 Caution: Organic azides present explosion hazards,
especially when heated. We omitted the recommended distillation step
when preparing the azide,35 instead using it without further
purification after extraction and solvent removal. We have not
encountered any issues with this compound in either of the procedures
described below. NacNacF12H was prepared by condensing 2,4-
pentanedione with 3,5-bis(trifluoromethyl)aniline in the presence of
tosic acid, similar to Budzelaar’s procedure.57 Spectral data for this
ligand matched that described previously.35 The ligand acNacF6H has
also been previously described,58 and in our hands this ligand was
isolated as a side product during the formation of NacNacF6H, which
occurs under similar conditions.36,37 The iridium precursors [Ir-
(C∧N)2(μ-Cl)]2 (C∧N = 2-phenylpyridine, 2-phenylbenzothiazole)
were prepared by the method of Nonoyama,59 refluxing IrCl3·xH2O
with ca. 2.1 equiv of the C∧N ligand in a 3:1 2-methoxyethanol/water
mixture. The iridium complexes Ir(C∧N)2(NacNacF0) (1: C∧N = ppy,
2: C∧N = bt), Ir(C∧N)2(NacNacF6) (3: C∧N = ppy; 4: C∧N = bt), and
Ir(C∧N)2(acNacF0) (11: C∧N = ppy; 12: C∧N = bt) were prepared as
described previously by our lab,24 except that for 3 and 4 additional
purification by column chromatography (silica gel stationary phase,
Et2O/hexane gradient eluent) was performed prior to recording
emission spectra (see below for more details). Lithium salts of the
NacNac and acNac ligands were prepared by treating the protonated
ligand with stoichiometric n-BuLi in hexane in a glovebox. The solid
was collected by filtration and used without further purification, except
for NacNacF15Li, which was extracted into Et2O and isolated as an
Et2O adduct. The potassium salt NacNacF12K was prepared by
reaction of NacNacF12H with benzylpotassium in diethyl ether. After
removing the solvent in vacuo, the solid was washed with hexane and
pentane and collected by vacuum filtration.
Preparation of acNacF12. Solid PPh3 (4.18 g, 15.9 mmol, 1.03
equiv) was added to a 100 mL flask with a side arm and Teflon cap,
which was evacuated and backfilled with nitrogen. The solid was
dissolved in 20 mL of anhydrous Et2O, and a solution of 3,5-
bis(trifluoromethyl)phenyl azide (3.95 g, 15.5 mmol, 1.00 equiv) in 5
For the synthetic procedures described below, purification as
described gave samples that were analytically pure. Complexes 3−10
G
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
mL of Et2O was added dropwise via cannula. The pale yellow solution
was stirred under N2 for 18 h at room temperature before removing
the solvent in vacuo. The white solid was taken up in 38 mL of
toluene, and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2.2 mL, 3.2 g,
15.5 mmol, 1.0 equiv) was added via syringe. The flask was sealed and
heated to 90 °C for 24 h. The solvent was removed via rotary
evaporation, and the crude product was purified by silica gel flash
chromatography, eluting with a gradient of ethyl acetate and hexane.
One pure fraction (0.54 g) was obtained, and a second fraction
required further purification by recrystallization from hexane, yielding
Anal. Calcd for C43H26F15IrN4: C, 48.00; H, 2.44; N, 5.21. Found: C,
47.37; H, 2.26,; N, 4.99.
Preparation of Ir(bt)2(NacNacF15) (8). Complex 8 was prepared
via the general method described for complex 7, using [Ir(bt)2(μ-Cl)]2
(49 mg, 0.038 mmol) and NacNacF15Li·Et2O (49 mg, 0.075 mmol, 2.0
equiv). We experienced difficulty separating a ca. 5% impurity of
NacNacF15H from this sample, by both recrystallization and
chromatography, but the free ligand impurity did not interfere with
subsequent electrochemical and optical spectroscopic measurements.
1
Yield: 59 mg (66%). H NMR (400 MHz, CDCl3) δ: 8.67 (d, J = 8.0
1
an additional 0.99 g. Combined yield: 1.53 g (23.5%). H NMR (400
Hz, 1H, ArH), 8.43 (d, J = 8.4 Hz, 1H, ArH), 8.05 (d, J = 7.2 Hz, 2H,
ArH), 7.71 (m, 2H, ArH), 7.62 (m, 2H, ArH), 6.97−7.07 (m, 5H,
ArH), 6.93 (s, 1H, ArH), 6.49 (t, J = 7.4 Hz, 1H, ArH), 6.45 (t, J = 7.6
Hz, 1H, ArH), 6.37 (t, J = 7.4 Hz, 1H, ArH), 6.32 (t, J = 7.2 Hz, 1H,
ArH), 5.80 (d, J = 7.2 Hz, 1H, ArH), 5.75 (d, J = 8.0 Hz, 1H, ArH),
5.67−5.73 (m, 2H, ArH), 5.47 (s, 1H, ArNC(CF3)CHC(CH3)NAr),
1.68 (s, 3H, CH3). 19F NMR (376 MHz, CDCl3) δ: −59.04 (s, 3F),
−62.64 (s, 3F), −62.68 (s, 3F), −62.74 (s, 3F), −63.00 (s, 3F). UV−
vis (THF): λ/nm (ε/M−1 cm−1) 271 (31 000), 314 (sh) (29 000), 324
(32 000), 409 (sh) (12 000), 421 (12 000). Anal. Calcd for
C47H26F15IrN4S2: C, 47.52; H, 2.21; N, 4.72. Found: C, 47.68; H,
2.21; N, 4.68.
MHz, C6D6) δ: 10.96 (br, s, 1H, NH), 7.45 (s, 1H, ArH), 6.79 (s, 2H,
ArH), 5.85 (s, 1H, ArNC(CF3)CHC(O)CF3). 19F NMR (376 MHz,
C6D6) δ: −62.67 (s, 6F), −63.62 (s, 3F), −77.16 (s, 3F).
Preparation of Ir(ppy)2(NacNacF12) (5). In the glovebox, solid
[Ir(ppy)2(μ-Cl)]2 (100 mg, 0.0933 mmol) was suspended in 2 mL of
THF in a scintillation vial. A solution of NacNacF12K (96 mg, 0.17
mmol, 1.8 equiv) in 2 mL of THF was added dropwise. The mixture
was stirred for 2 h at room temperature, after which the solvent was
removed in vacuo. The solid was extracted into 4 mL of toluene and
filtered through Celite. After removing the toluene in vacuo, the crude
product was washed with 1 mL of Et2O at −35 °C in the glovebox
freezer and then with 2 × 1 mL of pentane at room temperature before
drying in vacuo. Yield: 92 mg (52%). 1H NMR (600 MHz, CDCl3) δ:
9.10 (d, J = 6.0 Hz, 2H, ArH), 7.80 (t, J = 7.2 Hz, 2H, ArH), 7.63 (d, J
= 8.4 Hz, 2H, ArH), 7.32 (t, J = 6.3 Hz, 2H, ArH), 6.97−7.01 (m, 4H,
ArH), 6.83 (s, 2H, ArH), 6.41 (t, J = 7.2 Hz, 2H, ArH), 6.29 (t, J = 7.2
Hz, 2H, ArH), 5.74 (d, J = 7.2 Hz, 2H, ArH), 5.54 (s, 2H, ArH), 4.71
(s, 1H, ArNC(CH3)CHC(CH3)NAr), 1.60 (s, 6H, CH3). 19F NMR
(376 MHz, CDCl3) δ: −62.74 (s, 6F), −63.11 (s, 6F). UV−vis
(THF): λ/nm (ε/M−1 cm−1) 265 (45 000), 348 (15 000), 402
(14 000). Anal. Calcd for C43H29F12IrN4: C, 50.54; H, 2.86; N, 5.48.
Found: C, 50.49; H, 2.66; N, 5.41.
Preparation of Ir(ppy)2(NacNacF18) (9). Complex 9 was prepared
by the general method described for complex 7, using [Ir(ppy)2(μ-
Cl)]2 (110 mg, 0.103 mmol) and NacNacF18Li (132 mg, 0.207 mmol,
2.01 equiv). In this case the product was only sparingly soluble in
Et2O, and purification was achieved by washing with cold Et2O and
pentane. Yield: 143 mg (61.1%). 1H NMR (600 MHz, CDCl3) δ: 8.94
(d, J = 5.4 Hz, 2H, ArH), 7.92 (t, J = 7.2 Hz, 2H, ArH), 7.72 (d, J = 7.8
Hz, 2H, ArH), 7.43 (t, J = 6.0 Hz, 2H, ArH), 7.05 (s, 2H, ArH), 7.01
(d, J = 7.8 Hz, 2H, ArH), 6.85 (s, 2H, ArH), 6.46 (t, J = 7.5 Hz, 2H,
ArH), 6.32 (t, J = 7.2 Hz, 2H, ArH), 5.67 (s, 1H, ArNC(CF3)CHC-
(CF3)NAr), 5.60−5.63 (m, 4H, ArH). 19F NMR (565 MHz, CDCl3)
δ: −59.31 (s, 6F), −62.87 (s, 6F), −63.26 (s, 6F). UV−vis (THF): λ/
nm (ε/M−1 cm−1) 251 (41 000), 373 (9800), 418 (9200), 472 (sh)
(4900). Anal. Calcd for C43H23F18IrN4: C, 45.71; H, 2.05; N, 4.96.
Found: C, 45.42; H, 1.96; N, 4.88.
Preparation of Ir(bt)2(NacNacF12) (6). The title complex was
prepared analogously to complex 5, using [Ir(bt)2(μ-Cl)]2 (100 mg,
0.0771 mmol) and NacNacF12K (83 mg, 0.15 mmol, 1.9 equiv). Yield:
1
133 mg (78%). H NMR (400 MHz, CDCl3) δ: 8.63 (d, J = 8.0 Hz,
2H, ArH), 8.02 (d, J = 8.0 Hz, 2H, ArH), 7.68 (t, J = 7.0 Hz, 2H,
ArH), 7.58 (t, J = 7.0 Hz, 2H, ArH), 7.02 (d, J = 7.6 Hz, 2H, ArH),
6.99 (s, 2H, ArH), 6.94 (s, 2H, ArH), 6.44 (t, J = 7.4 Hz, 2H, ArH),
6.33 (t, J = 6.8 Hz, 2H, ArH), 5.85 (d, J = 7.6 Hz, 2H, ArH), 5.64 (s,
2H, ArH), 4.95 (s, 1H, ArNC(CH3)CHC(CH3)NAr), 1.62 (s, 6H,
CH3). 19F NMR (376 MHz, CDCl3) δ: −62.63 (s, 6F), −62.73 (s,
6F). UV−vis (THF): λ/nm (ε/M−1 cm−1) 273 (29 000), 312
(24 000), 323 (27 000), 409 (13 000), 494 (sh) (1200). Anal. Calcd
for C47H29F12IrN4S2: C, 49.78; H, 2.58; N, 4.94. Found: C, 49.77; H,
2.65; N, 4.79.
Preparation of Ir(bt)2(NacNacF18) (10). The title compound was
prepared via the general procedure described for complex 7, using
[Ir(bt)2(μ-Cl)]2 (100 mg, 0.0.0771 mmol) and NacNacF18Li (98 mg,
0.15 mmol, 2.0 equiv). Again, the product was purified by washing
1
with cold ether and pentane. Yield: 128 mg (66.8%). H NMR (600
MHz, CDCl3) δ: 8.45 (d, J = 8.4 Hz, 2H, ArH), 8.08 (d, J = 7.2 Hz,
2H, ArH), 7.76 (t, J = 7.8 Hz, 2H, ArH), 7.66 (t, J = 7.8 Hz, 2H, ArH),
7.03−7.06 (m, 4H, ArH), 6.98 (s, 2H, ArH), 6.49 (t, J = 7.2 Hz, 2H,
ArH), 6.36 (t, J = 7.5 Hz, 2H, ArH), 5.92 (s, 1H, ArNC(CF3)CHC-
(CF3)NAr), 5.73 (s, 2H, ArH), 5.69 (d, J = 7.2 Hz, 2H, ArH). 19F
NMR (565 MHz, CDCl3) δ: −59.48 (s, 6F), −62.82 (s, 6F), −62.94
(s, 6F). UV−vis (THF): λ/nm (ε/M−1 cm−1) 257 (44 000), 312 (sh)
(43 000), 323 (50 000), 405 (16 000), 431 (sh) (13 000). Anal. Calcd
for C47H23F18IrN4S2: C, 45.45; H, 1.87; N, 4.51. Found: C, 45.50; H,
1.79; N, 4.47.
Preparation of Ir(ppy)2(NacNacF15) (7). A general procedure was
followed for the preparation of all backbone-fluorinated complexes,
which is described in detail here. [Ir(ppy)2(μ-Cl)]2 (41 mg, 0.038
mmol) and NacNacF15Li·Et2O (49 mg, 0.075 mmol, 2.0 equiv) were
combined in 6 mL of toluene and sealed in a pressure vessel with a
Teflon screw cap. The mixture was heated at 90 °C for 24 h, giving a
red solution (in some cases small amounts of unreacted Ir(C∧N)
dimer are present). After cooling to room temperature the solution
was filtered through Celite and concentrated to dryness via rotary
evaporation. The solid was extracted into Et2O and filtered. The Et2O
was removed in vacuo, and the solid washed with pentane, giving the
Preparation of Ir(ppy)2(acNacF6) (13). This was prepared by the
general procedure described for complex 7, using [Ir(ppy)2(μ-Cl)]2
(100 mg, 0.0933 mmol) and acNacF6Li (54 mg, 0.19 mmol, 2.0 equiv).
The crude product was recrystallized from THF/pentane by vapor
1
diffusion, affording the product as 13·THF. Yield: 94 mg (57%). H
NMR (400 MHz, CDCl3) δ: 8.86 (d, J = 5.6 Hz, 1H, ArH), 8.62 (d, J
= 4.8 Hz, 1H, ArH), 7.80−7.94 (m, 2H, ArH), 7.74 (t, J = 7.6 Hz, 1H,
ArH), 7.54 (d, J = 7.6 Hz, 2H, ArH), 7.19−7.26 (m, 2H, ArH), 6.96
(d, J = 6.4 Hz, 1H, ArH), 6.83 (t, J = 7.6 Hz, 1H, ArH), 6.67 (m, 2H,
ArH), 6.51−6.57 (m, 3H, ArH), 6.45 (t, J = 7.2 Hz, 1H, ArH), 6.27 (d,
J = 7.6 Hz, 1H, ArH), 6.12 (d, J = 7.2 Hz, 1H, ArH), 5.99 (d, J = 8.0
Hz, 1H, ArH), 5.67 (s, 1H, PhNC(CF3)CHC(O)CH3), 5.36 (d, J =
6.8 Hz, 1H, ArH). 19F NMR (565 MHz, C6D6) δ: −60.67 (s, 3F),
−74.10 (s, 3F). UV−vis (THF): λ/nm (ε/M−1 cm−1) 262 (36 000),
295 (sh) (21 000), 348 (sh) (8600), 391 (sh) (6100), 425 (sh)
(4100). Anal. Calcd for C33H22F6IrN3O·THF: C, 51.99; H, 3.54; N,
4.92. Found: C, 51.82; H, 3.43; N, 4.86.
1
final product. Yield: 67 mg (83%). H NMR (400 MHz, CDCl3) δ:
9.03 (d, J = 6.0 Hz, 1H, ArH), 9.01 (d, J = 5.2 Hz, 1H, ArH), 7.86 (m,
2H, ArH), 7.70 (d, J = 8.4 Hz, 1H, ArH), 7.66 (d, J = 8.4 Hz, 1H,
ArH), 7.37 (m, 2H, ArH), 7.06 (s, 1H, ArH), 6.96−7.03 (m, 3H,
ArH), 6.86 (s, 1H, ArH), 6.83 (s, 1H, ArH), 6.44 (m, 2H, ArH), 6.33
(t, J = 7.4 Hz, 1H, ArH), 6.28 (t, J = 6.8 Hz, 1H, ArH), 5.67 (m, 2H,
ArH), 5.61 (s, 1H, ArH), 5.56 (s, 1H, ArH), 5.22 (s, 1H,
ArNC(CF3)CHC(CH3)NAr), 1.66 (s, 3H, CH3). 19F NMR (376
MHz, CDCl3) δ: −58.87 (s, 3F), −62.66 (s, 3F), −62.91 (s, 3F),
−63.10 (s, 3F), −63.19 (s, 3F). UV−vis (THF): λ/nm (ε/M−1 cm−1)
266 (51 000), 338 (sh) (17 000), 391 (14 000), 422 (sh) (11 000).
H
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Preparation of Ir(bt)2(acNacF6) (14). This was prepared by the
general procedure described for complex 7, using [Ir(bt)2(μ-Cl)]2 (27
mg, 0.021 mmol) and acNacF6Li (12 mg, 0.042 mmol, 2.0 equiv).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00453.
■
S
1
Yield: 28 mg (76%). H NMR (600 MHz, CDCl3) δ: 8.36 (d, J = 8.4
Hz, 1H, ArH), 8.07−8.12 (m, 2H, ArH), 7.98 (d, J = 7.2 Hz, 1H,
ArH), 7.91 (d, J = 8.4 Hz, 1H, ArH), 7.65 (d, J = 7.2 Hz, 1H, ArH),
7.48−7.58 (m, 4H, ArH), 7.07 (d, J = 7.2 Hz, 1H, ArH), 6.88 (t, J =
7.5 Hz, 1H, ArH), 6.78 (t, J = 7.5 Hz, 1H, ArH), 6.59−6.67 (m, 3H,
ArH), 6.46−6.55 (m, 2H, ArH), 6.31 (d, J = 7.8 Hz, 1H, ArH), 6.22
(d, J = 7.8 Hz, 1H, ArH), 5.61 (s, 1H, PhNC(CF3)CHC(O)CH3),
5.39 (d, J = 7.8 Hz, 1H, ArH). 19F NMR (565 MHz, C6D6) δ: −61.10
(s, 3F), −74.67 (s, 3F). UV−vis (THF): λ/nm (ε/M−1 cm−1) 273
(34 000), 315 (37 000), 324 (sh) (35 000), 378 (sh) (8700), 426
(6900), 453 (sh) (5500). Anal. Calcd for C37H22F6IrN3OS2: C, 49.66;
H, 2.48; N, 4.70. Found: C, 50.14; H, 2.64; N, 4.54.
Crystallographic data tables, crystal structure depictions
for 6−9, 14, and 15, cyclic voltammograms, additional
UV−vis absorption, excitation, and emission spectra, and
NMR spectra for all new compounds (PDF)
Crystallographic data (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: tteets@uh.edu.
Notes
■
Preparation of Ir(ppy)2(acNacF12) (15). The title compound was
prepared by the general procedure described for complex 7, using
[Ir(ppy)2(μ-Cl)]2 (100 mg, 0.0933 mmol) and acNacF12Li (71 mg,
0.17 mmol, 1.8 equiv). The crude product was purified by washing
The authors declare no competing financial interest.
1
with Et2O and pentane. Yield: 34 mg (22%). H NMR (400 MHz,
ACKNOWLEDGMENTS
CDCl3) δ: 8.78 (d, J = 6.0 Hz, 1H, ArH), 8.59 (d, J = 6.0 Hz, 1H,
ArH), 7.79−7.93 (m, 3H, ArH), 7.60 (d, J = 8.4 Hz, 1H, ArH), 7.55
(d, J = 7.6 Hz, 1H, ArH) 7.26−7.34 (m, 2H, ArH), 7.18 (s, 1H, ArH),
6.98 (d, J = 8.0 Hz, 1H, ArH), 6.85 (t, J = 7.6 Hz, 1H, ArH), 6.67−
6.73 (m, 2H, ArH), 6.54 (t, J = 7.6 Hz, 1H, ArH), 6.48 (t, J = 7.2 Hz,
1H, ArH), 6.08 (d, J = 7.2 Hz, 1H, ArH), 5.96 (d, J = 8.0 Hz, 1H,
■
We thank the University of Houston and the Welch
Foundation (grant no. E-1887) for funding. Acknowledgment
is made to the Donors of the American Chemical Society
Petroleum Research Fund for partial support of this research
(grant no. 54907-DNI3). R.A.M. acknowledges the University
of Houston’s SURF and PURS programs for undergraduate
research fellowships.
ArH), 5.75 (s, 1H, ArNC(CF3)CHC(O)CH3), 5.73 (s, 1H, ArH). 19
F
NMR (376 MHz, CDCl3) δ: −61.06 (s, 3F), −62.39 (s, 3F), −63.08
(s, 3F), −74.51 (s, 3F). UV−vis (THF): λ/nm (ε/M−1 cm−1) 257
(39 000), 272 (sh) (35 000), 291 (sh) (27 000), 350 (sh) (8900), 388
(sh) (7100), 424 (sh) (4400). Anal. Calcd for C35H20F12IrN3O: C,
45.76; H, 2.19; N, 4.57. Found: C, 45.91; H, 2.17; N, 4.56.
REFERENCES
■
(1) Highly Efficient OLEDs with Phosphorescent Materials; Yersin, H.,
Ed.; Wiley-VCH: Weinheim, 2008.
(2) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee,
H.-E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J.
Am. Chem. Soc. 2001, 123, 4304−4312.
(3) Nazeeruddin, M. K.; Humphry-Baker, R.; Berner, D.; Rivier, S.;
Zuppiroli, L.; Graetzel, M. J. Am. Chem. Soc. 2003, 125, 8790−8797.
(4) Tao, R.; Qiao, J.; Zhang, G.; Duan, L.; Wang, L.; Qiu, Y. J. Phys.
Chem. C 2012, 116, 11658−11664.
(5) Zhao, Q.; Huang, C.; Li, F. Chem. Soc. Rev. 2011, 40, 2508−2524.
(6) Baggaley, E.; Weinstein, J. A.; Williams, J. A. G. Coord. Chem. Rev.
2012, 256, 1762−1785.
Preparation of Ir(bt)2(acNacF12) (16). This complex was
prepared by the general method described for complex 7, using
[Ir(bt)2(μ-Cl)]2 (109 mg, 0.0854 mmol) and acNacF6Li (71 mg, 0.17
mmol, 2.0 equiv). The crude product was recrystallized by slow
1
cooling of a hot hexane solution. Yield: 27 mg (15%). H NMR (600
MHz, CDCl3) δ: 8.25 (d, J = 8.4 Hz, 1H, ArH), 8.01 (t, J = 8.4 Hz, 2H,
ArH), 7.94 (d, J = 7.2 Hz, 1H, ArH), 7.65 (d, J = 7.2 Hz, 1H, ArH),
7.51−7.62 (m, 4H, ArH), 7.30 (s, 1H, ArH), 7.12 (d, J = 7.6 Hz, 1H,
ArH), 6.96 (s, 1H, ArH), 6.90 (t, J = 7.5 Hz, 1H, ArH), 6.67 (t, J = 7.2
Hz, 2H, ArH), 6.56 (t, J = 7.5 Hz, 1H, ArH), 6.31 (d, J = 7.6 Hz, 1H,
ArH), 6.15 (d, J = 7.6 Hz, 1H, ArH), 5.84 (s, 1H, ArH), 5.71 (s, 1H,
ArNC(CF3)CHC(O)CH3). 19F NMR (565 MHz, CDCl3) δ: −61.33
(s, 3F), −62.13 (s, 3F), −62.63 (s, 3F), −74.98 (s, 3F). UV−vis
(THF): λ/nm (ε/M−1 cm−1) 261 (31 000), 316 (37 000), 323
(32 000), 380 (9200), 421 (7800), 448 (sh) (6300). Anal. Calcd for
C39H20F12IrN3OS2: C, 45.44; H, 1.96; N, 4.08. Found: C, 45.77; H,
2.08; N, 3.90.
X-ray Crystallography Procedures. Single crystals were grown
by vapor diffusion of pentane into concentrated THF solutions or by
slow evaporation of Et2O solutions. Crystals were mounted on a
Bruker Apex II three-circle diffractometer using Mo Kα radiation (λ =
0.710 73 Å). The data were collected at 123(2) K and processed and
refined within the APEXII software. Structures were solved by direct
methods in SHELXS and refined by standard difference Fourier
techniques in the program SHELXL.61 Hydrogen atoms were placed
in calculated positions using the standard riding model and refined
isotropically; all non-hydrogen atoms were refined anisotropically. All
of the structures except complex 14 contained at least one rotationally
disordered CF3 group, which were modeled as two-part disorders. The
structure of 16 also contained two crystallographically independent,
disordered diethyl ether solvate molecules. The crystals of complexes 7
and 8 were found to be isostructural with complexes 3 and 4,
respectively,24 with positional disorder between the backbone CF3 and
CH3 groups. Distance restraints (SADI) were used for all 1,2 and 1,3
distances within the disordered parts, and rigid bond restraints SIMU
and DELU were employed for the thermal displacement parameters.
Crystallographic details are summarized in Tables S1 and S2.
(7) Maity, A.; Choi, J.-S.; Teets, T. S.; Deligonul, N.; Berdis, A. J.;
Gray, T. G. Chem. - Eur. J. 2013, 19, 15924−15932.
(8) Lee, L. C.-C.; Lau, J. C.-W.; Liu, H.-W.; Lo, K. K.-W. Angew.
Chem., Int. Ed. 2016, 55, 1046−1049.
(9) Yoon, T. P.; Ischay, M. A.; Du, J. Nat. Chem. 2010, 2, 527−532.
(10) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev.
2013, 113, 5322−5363.
(11) Whang, D. R.; Sakai, K.; Park, S. Y. Angew. Chem., Int. Ed. 2013,
52, 11612−11615.
(12) Dedeian, K.; Djurovich, P. I.; Garces, F. O.; Carlson, G.; Watts,
R. J. Inorg. Chem. 1991, 30, 1685−1687.
(13) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. I.; Lamansky, S.;
Tsyba, I.; Ho, N. N.; Bau, R.; Thompson, M. E. J. Am. Chem. Soc.
2003, 125, 7377−7387.
(14) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.;
Kwong, R.; Tsyba, I.; Bortz, M.; Mui, B.; Bau, R.; Thompson, M. E.
Inorg. Chem. 2001, 40, 1704−1711.
(15) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Yousufuddin, M.; Ho, N.
N.; Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Inorg. Chem.
2005, 44, 1713−1727.
(16) Ho, C.-L.; Li, H.; Wong, W.-Y. J. Organomet. Chem. 2014, 751,
261−285.
(17) Qiao, J.; Duan, L.; Tang, L.; He, L.; Wang, L.; Qiu, Y. J. Mater.
Chem. 2009, 19, 6573−6580.
(18) Tao, R.; Qiao, J.; Zhang, G.; Duan, L.; Chen, C.; Wang, L.; Qiu,
Y. J. Mater. Chem. C 2013, 1, 6446−6454.
I
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(19) Zhou, G.; Wong, W.-Y.; Yao, B.; Xie, Z.; Wang, L. Angew. Chem.,
Int. Ed. 2007, 46, 1149−1151.
(20) Su, Y.-J.; Huang, H.-L.; Li, C.-L.; Chien, C.-H.; Tao, Y.-T.;
Chou, P.-T.; Datta, S.; Liu, R.-S. Adv. Mater. 2003, 15, 884−888.
(21) Williams, E. L.; Li, J.; Jabbour, G. E. Appl. Phys. Lett. 2006, 89,
83506-1−083506-3.
(22) You, Y.; Park, S. Y. J. Am. Chem. Soc. 2005, 127, 12438−12439.
(23) Hanson, K.; Tamayo, A.; Diev, V. V.; Whited, M. T.; Djurovich,
P. I.; Thompson, M. E. Inorg. Chem. 2010, 49, 6077−6084.
(24) Radwan, Y. K.; Maity, A.; Teets, T. S. Inorg. Chem. 2015, 54,
7122−7131.
(25) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002,
102, 3031−3066.
(26) Chamberlain, B. M.; Cheng, M.; Moore, D. R.; Ovitt, T. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 3229−
3238.
Metal and Rare Earth Compounds: Excited States, Transitions,
Interactions III; Springer: Berlin, Heidelberg, 2004; pp 1−26.
(52) Malkin, J. Photophysical and Photochemical Properties of Aromatic
Compounds; CRC: Boca Raton, 1992.
(53) Hong, S.; Hill, L. M. R.; Gupta, A. K.; Naab, B. D.; Gilroy, J. B.;
Hicks, R. G.; Cramer, C. J.; Tolman, W. B. Inorg. Chem. 2009, 48,
4514−4523.
(54) Chiong, H. A.; Daugulis, O. Organometallics 2006, 25, 4054−
4057.
(55) Kronast, A.; Reiter, M.; Altenbuchner, P. T.; Jandl, C.; Pothig,
̈
A.; Rieger, B. Organometallics 2016, 35, 681−685.
(56) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518−1520.
(57) Budzelaar, P. H. M.; Moonen, N. N. P.; Gelder, R. d.; Smits, J.
M. M.; Gal, A. W. Eur. J. Inorg. Chem. 2000, 2000, 753−769.
(58) Ye, W.-P.; Mu, H.-L.; Shi, X.-C.; Cheng, Y.-X.; Li, Y.-S. Dalton
Trans. 2009, 9452−9465.
(27) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc. 2002,
(59) Nonoyama, M. Bull. Chem. Soc. Jpn. 1974, 47, 767−768.
(60) Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31, 1−13.
(61) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112−122.
124, 2132−2133.
(28) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121,
7270−7271.
(29) Basuli, F.; Bailey, B. C.; Tomaszewski, J.; Huffman, J. C.;
Mindiola, D. J. J. Am. Chem. Soc. 2003, 125, 6052−6053.
(30) Kogut, E.; Wiencko, H. L.; Zhang, L.; Cordeau, D. E.; Warren,
T. H. J. Am. Chem. Soc. 2005, 127, 11248−11249.
(31) MacLeod, K. C.; Vinyard, D. J.; Holland, P. L. J. Am. Chem. Soc.
2014, 136, 10226−10229.
(32) Thompson, R.; Chen, C.-H.; Pink, M.; Wu, G.; Mindiola, D. J. J.
Am. Chem. Soc. 2014, 136, 8197−8200.
(33) Jang, E. S.; McMullin, C. L.; Kaß, M.; Meyer, K.; Cundari, T. R.;
̈
Warren, T. H. J. Am. Chem. Soc. 2014, 136, 10930−10940.
(34) Complexes of Bulky β-Diketiminate Ligands; Rauchfuss, T. B., Ed.;
Inorganic Syntheses; Wiley: New York, 2010; Vol. 35.
(35) Laitar, D. S.; Mathison, C. J. N.; Davis, W. M.; Sadighi, J. P.
Inorg. Chem. 2003, 42, 7354−7356.
(36) Tang, L.-M.; Duan, Y.-Q.; Li, X.-F.; Li, Y.-S. J. Organomet. Chem.
2006, 691, 2023−2030.
́
(37) Carey, D. T.; Cope-Eatough, E. K.; Vilaplana-Mafe, E.; Mair, F.
S.; Pritchard, R. G.; Warren, J. E.; Woods, R. J. Dalton Trans. 2003,
1083−1093.
(38) Kim, W.-K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1998, 17, 4541−4543.
(39) Martin, D. F.; Janusonis, G. A.; Martin, B. B. J. Am. Chem. Soc.
1961, 83, 73−75.
(40) Murashima, K.; Watanabe, T.; Kanegawa, S.; Yoshihara, D.;
Inagaki, Y.; Karasawa, S.; Koga, N. Inorg. Chem. 2012, 51, 4982−4993.
(41) Volkonsky, A. Y.; Rokhlin, E. M. J. Fluorine Chem. 1984, 26,
183−210.
(42) Grushin, V. V.; Herron, N.; LeCloux, D. D.; Marshall, W. J.;
Petrov, V. A.; Wang, Y. Chem. Commun. 2001, 1494−1495.
(43) Coppo, P.; Plummer, E. A.; De Cola, L. Chem. Commun. 2004,
1774−1775.
(44) Lowry, M. S.; Goldsmith, J. I.; Slinker, J. D.; Rohl, R.; Pascal, R.
A.; Malliaras, G. G.; Bernhard, S. Chem. Mater. 2005, 17, 5712−5719.
(45) Woo, H.; Cho, S.; Han, Y.; Chae, W.-S.; Ahn, D.-R.; You, Y.;
Nam, W. J. Am. Chem. Soc. 2013, 135, 4771−4787.
(46) Takizawa, S.; Shimada, K.; Sato, Y.; Murata, S. Inorg. Chem.
2014, 53, 2983−2995.
(47) Curtin, P. N.; Tinker, L. L.; Burgess, C. M.; Cline, E. D.;
Bernhard, S. Inorg. Chem. 2009, 48, 10498−10506.
(48) Zhou, Y.; Li, W.; Liu, Y.; Zeng, L.; Su, W.; Zhou, M. Dalton
Trans. 2012, 41, 9373−9381.
(49) Haneder, S.; Da Como, E.; Feldmann, J.; Lupton, J. M.;
Lennartz, C.; Erk, P.; Fuchs, E.; Molt, O.; Munster, I.; Schildknecht,
̈
C.; Wagenblast, G. Adv. Mater. 2008, 20, 3325−3330.
(50) Komada, Y.; Yamauchi, S.; Hirota, N. J. Phys. Chem. 1986, 90,
6425−6430.
(51) Yersin, H. Triplet Emitters for OLED Applications. Mechanisms
of Exciton Trapping and Control of Emission Properties. In Transition
J
DOI: 10.1021/acs.organomet.6b00453
Organometallics XXXX, XXX, XXX−XXX