Azobenzene-Appended Bis-Cyclometalated Iridium(III) Bipyridyl Complexes

Article abstract of DOI:10.1021/acs.organomet.5b00838

A new synthetic route toward photochromic azobenzene-appended bipyridyl ligands has been developed, and 20 new cationic iridium(III) bis-cyclometalated complexes containing up to four azobenzene fragments on their structure have been synthesized and characterized electronically and spectroscopically. These compounds incorporate photochromic azobenzene units in their neutral pyridyl ligands 1-5, and in four of them azobenzenes have been also introduced a posteriori on their phenylpyridyl ligands by palladium-catalyzed cross-coupling. UV-vis-monitored light-triggered trans-to-cis isomerization of the azobenzene-appended ligands revealed a strong inhibition of this process upon coordination to the d⁶-metal ion. TD-DTF calculations revealed that this inhibition could be a consequence of a metal to ligand charge transfer relaxation process.

Full text of DOI:10.1021/acs.organomet.5b00838

Article
pubs.acs.org/Organometallics
Azobenzene-Appended Bis-Cyclometalated Iridium(III) Bipyridyl
Complexes
†
́ ́
Ainara Telleria, Jorge Perez-Miqueo, Ainhoa Altube, Eva García-Lecina, Abel de Coz
ar,§,∥
†
‡
‡
,
†,∥
and Zoraida Freixa*
†
§
Department of Applied Chemistry, and Department of Organic Chemistry I, Faculty of Chemistry, University of the Basque
, Spain
Surfaces Division, IK4-CIDETEC, 20009, San Sebastian
Country (UPV-EHU), 20080, San Sebastian
‡
́
́
, Spain
IKERBASQUE, Basque Foundation for Science, 48013, Bilbao, Spain
S Supporting Information
∥
*
ABSTRACT: A new synthetic route toward photochromic azobenzene-
appended bipyridyl ligands has been developed, and 20 new cationic
iridium(III) bis-cyclometalated complexes containing up to four azoben-
zene fragments on their structure have been synthesized and characterized
electronically and spectroscopically. These compounds incorporate photo-
chromic azobenzene units in their neutral pyridyl ligands 1−5, and in four
of them azobenzenes have been also introduced a posteriori on their
phenylpyridyl ligands by palladium-catalyzed cross-coupling. UV−vis-
monitored light-triggered trans-to-cis isomerization of the azobenzene-
appended ligands revealed a strong inhibition of this process upon
6
coordination to the d -metal ion. TD-DTF calculations revealed that this
inhibition could be a consequence of a metal to ligand charge transfer
relaxation process.
INTRODUCTION
toward the construction of smart chemical systems and
■
5
molecular machines has been stated, and many examples
Cationic bis-cyclometalated iridium(III) complexes containing a
neutral polypyridyl ligand (i.e., 2,2′-bipyridine or phenanthro-
line) have been the subject of intense research due to the
combination of their photophysical properties together with a
good solubility in polar solvents. In general, these complexes
show intense phosphorescence at room temperature, due to the
strong spin−orbit coupling of the 5d iridium(III) ion, which
allows spin-forbidden phosphorescent transitions. [Early studies
on the luminescent nature of model [Ir(ppy) (bipy)] cations
revealed a dual emission that was justified as metal to ligand
6
already appear in the literature.
The incorporation of well-known molecular switches in the
ligands of several bis-cyclometalated iridium(III) complexes has
been addressed in the last years. Bis(thienyl)ethene (BTE)-based
ligands have been employed for the construction of photo-
7
7a−e
6
chromic emitters. In most of the cases,
the phosphorescence
of diarylethene-tethered bis-cyclometaled iridium(III) com-
pounds can be controlled by light-trigged cyclization of the
appended BTE units. Recently, in our group, we studied
azobenzene-containing iridium(III) tris-cyclometalated com-
+
2
charge transfer (MLCT) transitions to close-lying triplet states
8
59
plexes. In these compounds, the presence of azobenzene units
localized on the ppy and bipy ligands, respectively. ] For this
reason, one of the most promising applications of such
organometallic compounds is as phosphors in the construction
of light-emitting electrochemical cells (LECS). Beyond this one,
there is a myriad of other potential applications, i.e., sensitizers
on the ligands suppressed the phosphorescent properties of the
metal center. This inhibition was already observed in other
9
10
1
ruthenium(II) and iridium(III) azobipyridine derivatives, but
it could be eventually recovered by reduction of the azobenzene,
which permitted their use as sensors for reducing agents. [The
lack of luminescence has been attributed to the trapping of the
excited state in a low-energy azobenzene-localized MLCT state
2
for photocatalytic hydrogen generation, labeling compounds for
luminescence imaging in biomaterials for bioanalytical applica-
3
tions, and sensors for oxygen, anions, amino acids, alkali and
9
4
during its lifetime and its nonradiative deactivation. ] Unfortu-
heavy transition metal cations, etc. Considering the wide range
of applications, their combination with organic photochromic
units is an appealing task.
The fusion of the properties of transition metal complexes
together with the photochromism creates a new generation of
multifunctional metallic compounds able to react to an external
stimuli, the light. The importance of such hybrid materials
nately, the strong inhibition of photoisomerization of the
coordinated azobenzenes in our former examples prevented
the study of their potential use as photochromic emitters.
Received: July 17, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00838
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Azobenzene is probably the photochromic fragment most
frequently used for the construction of photochromic com-
Chart 1. Azobenzene-Containing Pyridine and 2,2′-
Bipyridine Ligands Used in This Work
1
1
pounds. Considering pyridine-based ligands, the most simple
representatives (4,4′-azopyridine and 4-phenylazopyridine) are
readily available, and many examples of their coordination
12
compounds are known. Surprisingly, in spite of the wide
number of coordination complexes based on 2,2′-bipyridyl
ligands, to the best of our knowledge, only the groups of
6
f
Wenger, Nishihara, and Otsuki published examples of
transition metal complexes of azobenzene-containing bipyr-
idines. As part of their intensive studies on azobenzene-appended
polypyridyl metallic complexes, the group of Nishihara
demonstrated that, in some cobalt-bipyridyl derivatives, the
extent of the azobenzene photoisomerization process was
determined by the electronic interaction between the metal
center and the azobenzene (influenced by the substitution
13
pattern) and the oxidation state of the metal. They also
constructed dynamic copper-bipyridyl coordination compounds
by combining the photochromism of azobenzene-bipyridines
with a redox-driven ligand exchange process, in a very elegant
,2′-bipyridine (three steps from 2,2′-bipyridine21−23) prompted
2
1
4−17
manner.
Finally, they were able to construct photo-
us to consider azobenzene-containing bipyridine ligands that
could be synthesized by more direct routes.
controlled tristable platinum compounds by combining
18,19
dithiolato and bipyridine azobenzene-containing ligands.
Otsuki et al. also described switchable bi- and tetranuclear
As an alternative strategy we considered the introduction of
the photochromic units by Suzuki cross-coupling starting from
the corresponding azobenzene boronic acids and 4,4′-dibromo-
9
,20
compounds bridged by azobis(bipyridyl) ligands.
These
ground-breaking examples reveal the potential of such multi-
functional hybrid systems.
2
,2′-bipyridine (Scheme 1).
As part of our ongoing research on azobenzene-containing
a
Scheme 1. Synthetic Route toward Ligands 3−5
8
cyclometalated iridium(III) complexes, we present here a new
high-yielding synthetic route toward light-sensitive azobenzene-
containing bipyridines, together with their cationic azobenzene-
appended iridium(III) bis-cyclometalated compounds. As
mentioned before, our initial studies on azobenzene-appended
tris-cyclometalated compounds already showed that azobenzene
photoisomerization was significantly inhibited upon coordina-
tion to the metal center. We wanted to study the photochromism
of related compounds in which the azobenzene was tethered to
the ancillary neutral bipyridyl ligand instead of appended to the
covalently bonded cyclometalated phenylpyridyl units.
RESULTS AND DISCUSSION
■
Ligand Syntheses. A few azobenzene-containing 2,2′-
6
f,13,21
bipyridines have already been reported.
The most
a
Conditions: (i) n-BuLi (1.1 equiv), Et O, −112 °C; B(OMe ) (1.1
2
3 3
common synthetic strategy consists of condensation of nitro-
sotoluene with the corresponding amino-2,2′-bipyridines.
Unfortunately, these are not readily accessible compounds.
Here we propose an alternative, high-yielding, synthetic route
toward both mono- and bis-azobenzene bipyridines, through
palladium-catalyzed Suzuki cross-coupling of 4,4′-dibromo-2,2′-
bipyridine with the corresponding azobenzene boronic acids
equiv), Et O, −112 °C; diluted H SO , 0 °C; (ii) 4,4′-dibromo-2,′2′-
2
2
4
bipyridine (0.3−1 equiv), Pd(PPh ) (1.6−5 mol %), toluene,
3
4
K CO (aq) (2 M, 0.5−1.7 mol %), 115 °C, 15 h.
2
3
[4-(Phenylazo)phenyl]boronic acid 6 and (E)-[3-
(phenylazo)phenyl]boronic acid 7 were obtained by reacting
an ethereal solution of the corresponding iodoazobenzene
sequentially with n-BuLi, trimethyl borate at −112 °C, and
(
Chart 1).
8
Initially, we attempted the synthesis of the most simple
diluted sulfuric acid at 0 °C.
azobenzene-containing bipyridine, 2,2′-bis(4-phenylazopyri-
Palladium-catalyzed cross-coupling of 4,4′-dibromo-2,2′-
dine) (1), through the coupling of a nitrosobenzene with an
bipyridine with [4-(phenylazo)phenyl]boronic acid 6 in
6
f,13,21
amino-bypyridine, as reported for related compounds.
To
toluene/H O, using a 1.6 mol % catalyst loading rendered a
2
test the synthetic procedure, we used it to obtain the already
described 4-phenylazopyridine, the monodentate ligand 2.
This compound was obtained as a dark orange microcrystalline
solid with a yield of 88%. When the same synthetic methodology
was used for the condensation of 4,4′-diamino-2,2′-bipyridine
and nitrosobenzene, ligand 1 was obtained with a lower yield
mixture of 4,4′-bis(p-azobenzene)-2,2′-bipyridine 3 and 4-(p-
azobenzene)-4′-bromo-2,2′-bipyridine 4 (yields 41% and 28%,
respectively). Both compounds could be easily separated due to
their different solubilities in all the solvents assayed. The reaction
mixture, a dark orange suspension, was filtered, and the solid
washed with CH Cl and acetone. Its reactivity (vide infra) and
12d
2
2
(
56%). This relatively low reactivity, together with the long
analytical evidence permitted us to identity this solid as ligand 3.
synthetic procedure needed to obtain the starting 4,4′-diamino-
The filtrate was washed with H O, and the organic phase was
2
B
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evaporated to dryness. The residue was purified by column
The meta-substituted 4,4′-bis(m-azobenzene)-2,2′-bipyridine
ligand 5 was obtained with a 71% yield following the same
synthetic procedure described above for ligand 3, but using [3-
(phenylazo)phenyl]boronic acid 7. In this case the monosub-
stitution product was not observed. Ligand 5 is soluble in
chromatography using CH Cl as initial eluent, which was
2
2
gradually changed to acetone. The first fraction eluted (R = 1)
f
was the unreacted 4,4′-dibromo-2,2′-bipyridine. A second
fraction (R = 0.8) was eluted. After solvent evaporation, it
f
1
resulted in a light orange solid. The integration and number of
conventional solvents and was fully characterized by H NMR,
1
13
signals observed in the H NMR spectrum of this product were
C NMR, EA, and ESI-MS. The spectroscopic data of this ligand
indicative of an asymmetrically 4,4′-disubstituted 2,2′-bipyridine.
compare well with those of a similar compound reported by
Nishihara.
1
13
13a
Full characterization ( H NMR, C NMR, ESI-MS, and EA)
confirmed that it was the monoazobenzene-containing ligand 4, a
product of partial cross-coupling, and an intermediate toward
ligand 3. When the reaction time was extended to 72 h, ligand 3
was obtained as the sole reaction product in quantitative yield. If
equimolar quantities of 4,4′-dibromo-2,2′-bipyridine and [4-
Syntheses of Iridium Complexes. Iridium(III) bis-cyclo-
metalated 2,2′-bipyridyl complexes were obtained following well-
established synthetic procedures. In general the cleavage of the
corresponding dimeric bis-cyclometalated iridium(III) chloride-
bridged complex [Ir(C−N) Cl] (C−N = cyclometalated
2
2
(
phenylazo)phenyl]boronic acid 6 were used, instead of the
expected monoazobenzene bipyridine 4, a mixture of 3 and 4
1:3 ratio) was obtained, even when the conversion of the
phenylpyridyl-type ligand) in the presence of a 2-fold excess of
2,2′-bipyridine in refluxing CH Cl /MeOH (2:1) rendered
2
2
+
(
cationic complexes of the type [Ir(C−N) (bipy)] with good
2
25
dibrominated substrate was only 51%. This result indicates that,
although it is possible to obtain ligand 3 as the only reaction
product, ligand 4 must always be extracted from a mixture of both
compounds. A related one-azobenzene-bound 2,2′-bipyridine
was synthesized by the group of Nishihara employing a seven-
yields (Scheme 2). This procedure was used for the synthesis of
cationic compounds derived from the azobenzene-containing
bipyridine ligands 1 and 3−5.
Initially, we followed the same synthetic procedure to obtain
cationic complexes A2, B2, and C2, containing two monodentate
azopyridine ligands 2 instead of a bipyridine. From this series,
complex A2 was obtained with very low yield (13%). When the
dimeric [Ir(Fppy) Cl] (Fppy = 3,5-difluoro-2-pyridylphenyl)
step route based on the Kro
̈
hnke pyridine synthesis, starting from
13
3-nitrobenzaldehyde. To the best of our knowledge, the
experimental details and global yield of such a reaction sequence
remain unpublished.
Ligand 3, obtained as a light orange powder that precipitates
from the reaction crude, presented a very low solubility (less than
2
2
was used, the expected compound B2 was obtained as a 2 to 1
1
mixture together with a new compound. The H NMR
spectroscopic pattern of the latter could be assigned to a
0
.1 mg/mL) in all the solvents assayed (alcohols, DMSO,
dissymmetric neutral complex of the type [Ir(Fppy) (2)] (B2′)
2
CHCl , CH Cl , or acetone), which hampered its character-
in which the azopyridyl ligand was not coordinating as a neutral
donor through the pyridine nitrogen, but acted as a monoanionic
3
2
2
ization by NMR spectroscopy. From a highly diluted solution in
CDCl , a single crystal was obtained, which was suitable for X-ray
C−N chelate, formed by C−H activation at one of the meta
3
azo
diffraction. The molecular structure of ligand 3 is presented in
Figure 1, together with selected angles and distances. Similar
positions of the pyridine (Scheme 3). This coordination mode,
resulting from the ortho-metalation of an aromatic metal-azo
compound, is extensively described in the literature for related
26
azobenzenes. Compound B2′ could be obtained as the only
reaction product when the ligand to metal ratio was lowered to
1
:1 (87% yield). When the synthesis of C2 was attempted, the
unreacted dimer [Ir(Brppy) Cl] (Brppy = 5-bromopyridyl-
2
2
phenyl) was recovered at the end of the reaction.
Although ligands 1 and 3−5 could also potentially coordinate
as monoanionic C−N chelates (even bridging two different
azo
Figure 1. ORTEP drawing for ligand 3 with ellipsoids at the 50%
probability level. Selected bond lengths [Å] and angles [deg]: N2−N3
iridium centers), their preferential coordination as bipyridyl five-
membered ring chelates prevents this side reaction from
occurring. This coordination mode, quite frequent when
1
.2581(18); C12−N3−N2 114.20(12); N3−N2−C9 113.60(12); N1−
C5−C5A−N1A 180.00(13).
26
azobenzene was used as ligand, has never been observed for
azobenzene-appended bipyridines.
In view of the lower reactivity of monodentate ligand 2
compared to chelating ligands 1 and 3−5, the use of a halide
abstractor (a silver salt) to drive the reaction toward the desired
compounds was attempted. The corresponding iridium dimer
and 4 equiv of the monodentate ligand 2 were refluxed in
acetone, using AgOTf as halide abstractor. Following this
procedure complexes A2, B2, and C2 were obtained with
reasonable yields (Scheme 3).
Complexes A−C were fully characterized by H NMR and C
NMR spectroscopies, elemental analysis, and HR-MS spectrom-
etry. As expected, in all the compounds the two nitrogen atoms of
the phenylpyridyl ligands occupy mutually trans positions.
distances and angles were observed in the published X-ray
13a,21
structures of related ligands.
It shows a flat structure, with
the two nitrogen atoms of each pyridyl fragment in an anti
disposition relative to the pyridyl−pyridyl C−C bond, as is
generally observed for 4,4′-disubstituted-2,2′-bipyridine ligand-
13a,21,24
s.
The planarity of the molecule confirms the extended π-
conjugation present in para-substituted azobenzenes already
21
1
13
described by other authors. Only the central ring (C6−C11)
slightly deviates from this plane (torsion angle 18.06°). This
planarity is reflected in the crystal packing. The molecules are
stacked in layers, alternating between two nearly perpendicular
orientations (78.31°) (see Figure S12, SI). In contrast, out-of-
plane disposition of the azobenzene groups (±27°) and loss of π-
conjugation were previously observed for a meta derivative,
Complexes derived from ligands 1−3 and 5 are C
-symmetric
2
in solution, as confirmed by the number of signals observed in the
1
13
H and C NMR spectra. Compounds A4, B4, and C4, derived
13a
analogous to ligand 5.
from 4-(p-azobenzene)-4′-bromo-2,2′-bipyridine ligand 4,
C
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Scheme 2. Synthetic Route toward Azobenzene-Containing
Scheme 3. Synthetic Route toward Azobenzene-Containing
Iridium Complexes B2′, A2, B2, and C2
a
Iridium Complexes A, B, and C with 2,2′-Bipyridine and
a
Ligands 1 and 3−5
a
Conditions: (i) 2 (2 equiv), CH Cl /MeOH (2:1), reflux 15 h; (ii)
2
2
AgOTf (3.5−4.6 equiv), acetone (56 °C, 2 h); (iii) 2 (4 equiv), NEt
3
(
8 equiv), acetone (56 °C, 15 h). Yields: A2 (50%), B2 (48%), C2
48%); B2′ (87%).
(
arrangements of the phenylpyridyl ligands around the metal (Λ
and Δ), the crystals were obtained as racemates. For C3 both
enantiomers were packed in a nonpatterned manner, which was
reflected in the X-ray structure as a disorder in the phenyl-
pyridine ligands (Figure S16, SI). In the case of A4, the crystal
packing showed an interaction between the two enantiomeric
forms of the compound through Br−N nonbonding interactions.
One counterion was contained in the space defined between a
pair of enantiomers, while another one was localized outside and
presented more disorder. For this structure some disorder was
also observed in the disposition of the azobenzene unit. Two
different arrangements with 50% probability each have been
detected (Figure S15, SI). The same type of crystallographic
disorder was previously reported for other azobenzene-
2
7
containing complexes. As expected, all the complexes
presented the azobenzene fragments in the thermodynamically
most stable E form. The N−N distances observed are similar to
the ones of the free ligand 3, which confirms the integrity of the
azo functionality. An examination of the dihedral angles of the
azoaromatic ligands in these complexes showed that in the case
of compounds B1 and A2 the ligand can be described as planar
a
Conditions: (i) 2 equiv of bipyridine, CH Cl /MeOH (2:1), reflux 15
2
2
(
with extended π-conjugation), but for derivatives A4 and C3 the
h; (ii) KPF . Yields: A1 (85%), B1 (88%), C1 (61%); A3 (95%), B3
6
twist between aromatic rings is in the range 30−40°. Similar
values were observed previously for azobenzene-containing
(
(
34%), C3 (34%); A4 (86%); B4 (87%); C4 (98%); A5 (75%); B5
85%); C5 (66%).
18,28
bipyridyl and terpyridyl complexes (see Table 1).
In order
to gain more insight into these structures, density functional
theory (DFT) calculations have been performed at the CAM-
B3LYP(PCM)/6-31+G*&LANL2DZ level of theory on B1, A2,
C3, and A4. The minimized geometries are in good agreement
with the experimental ones, as shown by the low RMS values
obtained (ca. 0.3−0.5, Table S2 in the SI). However, there is a
systematical deviation on the computed dihedral angle between
the phenyl rings directly connected to the azo moiety (namely,
α1 and α3). For B1 and A2, α1 and α3 values are slightly smaller
than the experimental ones. However, this difference is more
remarkable for compounds A4 and C3, where the computed
present rather complicated fully aromatic H NMR and 13C
NMR spectra. All the expected signals were observed although
they could not be unequivocally assigned. The molecular
structures of B1, A2, C3, and A4 were confirmed by X-ray
diffraction of crystalline samples (see Figure 2 and Table 1).
The molecular structures of the complexes confirmed the
octahedral coordination environment of the iridium center, with
the two nitrogen atoms of the phenylpyridyl ligands occupying
relative trans positions, as observed in solution (vide supra).
Although these compounds are chiral, due to the two possible
1
D
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Table 1. Most Relevant Angles and Distances Extracted from
Molecular Structures of Complexes A2, B1, C3, and A4,
a
Determined by X-ray Diffraction
N−N
N−N
α1
α2
α3
α4
α5
B1
A2
C3
A4
1.257
1.255
1.269
1.256
1.260
1.255
1.254
9.15
0.40
10.01
4.51
57.82
0.36
0.40
36.37
29.63
40.42
39.71
23.29
26.68
9.04
a
Distances are expressed in angstroms and angles in degrees.
planarity is a consequence of an overestimation of the
stabilization associated with an optimal extended π-conjugation.
Complexes of type C were intended to introduce photo-
chromic azobenzene fragments not only on the bipyridyl ligand
but also on the phenylpyridyl units. These compounds are
susceptible to a posteriori modification by palladium-catalyzed
cross-coupling with boronic acid derivatives. Compounds Cbipy,
C1−C3, and C5 were reacted with (E)-[4-(phenylazo)phenyl]-
boronic acid 6 to form complexes Dbipy, D1−D3, and D5 with
four azobenzene groups, with rather modest yields (Scheme 4).
[
Depending on their availability, [4-(phenylazo)phenyl]boronic
acid 6 was substituted by [4-(phenylazo)phenyl]boronic acid
Scheme 4. Synthetic Route toward Azobenzene-Containing
a
Iridium Complexes D with Ligands 1, 2, 3, and 5
Figure 2. ORTEP representation of the molecular structure of
compounds B1, A2, C3, and A4 according to X-ray diffraction.
Hydrogens and some labels have been omitted for clarity. Ellipsoids are
at 50% probability. Most relevant angles and distances are presented in
Table 1.
a
Synthesis of complexes D by Pd-catalyzed cross-coupling: (i) (E)-[4-
(phenylazo)phenyl]boronic acid 6 (2.4 equiv), solvent 2:1 THF/
Na CO (aq) (1 M), Pd(PPh ) (10 mol %), 80 °C, overnight. Yields:
Dbipy (10%), D1 (34%), D2 (14%); D3 (24%); D5 (26%).
2
3
3 4
E
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pinacol ester 6′ without any detrimental effect on the yield of the
reaction. [4-(Phenylazo)phenyl]boronic acid pinacol ester 6′
was synthesized via condensation of (4-aniline)boronic acid
pinacol ester with nitrosobenzene. ] The reaction was not
attempted on C4, as the product of this reaction would be D3
due to cross-coupling also through the bromine atom present in
the bipyridyl ligand.
showed, as expected, a molar absorption approximately double
that of ligand 2, and it was shifted to lower energy probably due
to the extended conjugation present in this molecule. When
looking at the same transition band for ligands 3 and 4, a clear
red-shift compared to that of azobenzene was observed,
consistent with the existence of extended conjugation between
the bipyridine and the azobenzene fragments, as observed in the
X-ray structure of ligand 3 (vide supra). Nearly no shift of this
band was observed for ligand 5 when compared to azobenzene,
which indicates a weak conjugation of both bipyridine and
azobenzene fragments in this ligand. These trends are in
agreement with those reported by Nishihara for related meta
49
UV−Vis Characterization. UV−vis absorption spectra in
CH CN solution of ligands 1−5 and their complexes A−D were
3
registered at room temperature. Selected absorption maxima and
their corresponding molar extinction coefficients are presented
in Table S1 (SI), together with those of related model
compounds. A representative example of the series of spectra
obtained is presented in Figure 3 (overlapped spectra of all the
ligands and complexes are compiled in the SI).
13
and para azobenzene-substituted bipyridine ligands.
In addition to the absorption bands attributed to the
azobenzene fragment, the spectra of complexes A−D showed
complex structures due to overlapping with the ones character-
+
istic of their [Ir(ppy) (bipy)] core. Cationic complexes of the
2
+
type [Ir(ppy) (bipy)] typically present intense absorption
2
bands in the UV region of the spectra (250−350 nm) (ε ≈
4
−1
−1
(
3−5) × 10 M cm ) assigned to symmetry-allowed singlet
1
LC π−π* transitions involving both the phenylpyridyl and the
bipyridyl ligands. At longer wavelengths (350−450 nm) 1 order
of magnitude weaker bands are observed, which are attributed to
transitions with mixed metal-to-ligand ( MLCT) and ligand-to-
ligand ( ILCT) charge transfer character.
1
1
30−32
Model com-
pounds of type Abipy−Dbipy, containing 2,2′-bipyridine as
neutral N−N chelate, have also been synthesized and
characterized for comparative purposes (see Figure S2 in the
SI). In the case of complexes A−D, containing azobenzene-
+
derived ligands 1−5, the bands due to the [Ir(ppy) (bipy)] core
2
were difficult to identify, obscured by the intense absorptions of
the azobenzene fragment, but they are responsible for the
complex structure of the spectra. In general, for these
compounds, the most intense band attributed to a LC π−π*
transition is shifted to lower energies when they are coordinated
1
to the metal, as already observed for related 4,4′-bisstyryl-2,2′-
33
bipyridyl Ir(III) complexes. This effect, attributed to a lowering
of the LUMO energy level upon coordination of the pyridyl ring,
was clearly observed in the case of ligands 1 and 2 (see Table S1
in the SI, Figure 3, and Figures S3 and S4 in the SI). For
derivatives of ligands 3−5, the observed shift on the position of
this absorption upon coordination did not follow any clear trend.
In the case of derivatives of ligands 3 and 4 this is probably due to
the long distance existing between the coordinating nitrogen
atoms of the bipyridine and the azobenzene fragment. For
derivatives of ligand 5 the lack of electronic conjugation between
both fragments (as observed by X-ray analysis of a related 4-meta-
Figure 3. UV−vis absorption spectra. Top: UV−vis absorption spectra
of complexes A with ligands 1−5. The model compound Abipy is also
shown for comparative purposes. Bottom: UV−vis absorption spectra of
ligand 1 and its iridium derivatives A−D.
13a
azobenzene-2,2′-bipyridine) could be responsible for it. For
derivatives D, also containing azobenzene groups in the
cyclometalated phenylpyridyl ligands, this absorption band is
clearly red-shifted compared to compounds A−C and closer to
the absorption of the free (2-azobenzene)pyridine azoppy ligand
(see Table S1 in the SI). This observation is in concordance with
Azobenzene and its derivatives present two types of low-lying
excited singlet states, nπ* (S ) and ππ* (S ), which is reflected in
1
2
8
their absorption spectra by a weak (symmetry forbidden), broad,
visible absorption at about 445 nm and a strong (symmetry
our former report on azoppy-Ir(III) derivatives.
As observed in previous works, the extinction coefficient at
λmax (azobenzene-centered π → π* transition) is proportional to
29
allowed) UV band around 315 nm, respectively. In accordance
with this general description, both free ligands and complexes
8
,13
the number of azobenzene fragments present in the molecule.
showed one intense band between 290 and 355 nm (λazo π→π*
and a weaker red-shifted band, between 430 and 513 nm
)
Photoisomerization Studies. Light-triggered azobenzene
trans-to-cis isomerization is a well-known process. It can be
reversed by irradiation at the appropriate light wavelength, which
also occurs spontaneously in the dark, because of the
(
(
λazo n→π*), confirming the presence of azobenzene fragments
Table S1 in the SI).
3
4,35
The absorption band attributed to a π → π* transition
observed for ligand 1 (a chelating analogue of two ligands 2)
thermodynamic stability of the trans isomer.
UV−vis
absorption spectroscopy permits monitoring these processes
F
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Article
due to the different intensity and small shift of the characteristic
absorption bands of the azobenzene in the E and Z form.
The capacity of the azobenzene unit to isomerize both in free
ligands and their complexes has been studied by UV−vis
absorption spectroscopy. Diluted CH CN solutions of all the
3
compounds were irradiated for 30 min at the wavelength of the
absorption previously attributed to the π → π* transition of the
azobenzene (see Table S1 in the SI), to confirm if the
isomerization process was active. Later on, the optimal
wavelength to maximize the population of the Z form in the
photostationary state (PSS) was calculated individually for each
36
compound, following Monkowius’ procedure (see Table 2).
Table 2. Kinetic Data for the Z → E Isomerization Process at
5
5 °C
Figure 4. UV−vis spectral changes during thermal cis-to-trans
a
k [s−1
−5
compound
λoptimal [nm]
]
τ1/2 [min]
isomerization of complex B3, 2.5 × 10 M solution in CH
3
CN (55
4.0 × 10−
4
4
5
5
5
°C), after 30 min irradiation at 343 nm and 30 min irradiation at 354 nm.
1
325
312
337
320
348
326
341
364
327
328
344
350
345
354
355
355
343
351
336
319
319
318
327
29
29
2
4.0 × 10−
9.0 × 10−
4
128
231
1155
−
5
5.0 × 10
A1
B1
C1
D1
A2
B2
C2
D2
A3
B3
C3
D3
A4
B4
C4
A5
B5
C5
D5
1.0 × 10−
6.0 × 10−
1.0 × 10
3.0 × 10−
6
4
4
1925
115
38
−
3.0 × 10−
9.0 × 10−
9.0 × 10−
4
6
5
4
5
5
5
4
4
5
5
5
5
38
1284
128
115
192
128
165
115
115
385
289
231
192
−
1.0 × 10
6.0 × 10−
9.0 × 10−
−
7.0 × 10
1.0 × 10−
−
1.0 × 10
3.0 × 10−
4.0 × 10−
5.0 × 10−
6.0 × 10−
a
Optimized light wavelength for the E → Z photoisomerization.
After irradiation at λoptimal for an additional 30 min, the reverse
process (Z → E isomerization) was monitored by UV−vis
8
absorption spectroscopy at 55 °C. The calculated first-order rate
constants (k) and half-life times (τ ) for this process are
1
/2
presented in Table 2, and a representative example is shown in
Figure 4.
Figure 5. UV−vis spectra (absorbance vs wavelength (nm)) before and
after irradiation of free ligands and derivatives A after 30 min irradiation
All the azobenzene-containing ligands studied (1−5)
presented, as expected, a substantial change in their electronic
absorption spectra upon irradiation at the appropriate light
wavelength. The predictable decrease in the intensity of the
absorption, attributed to the π → π* transition of the
azobenzene, together with a less evident increase in the intensity
of the less energetic n → π* transition band was observed.
Azophenylpyridine derivatives 1 and 2 presented 1 order of
magnitude faster Z → E isomerization compared to azobenzene
derivatives 4 and 5.
at λazo π→π* and 30 min irradiation at λoptimal. CH CN (55 °C).
3
6f,10,37
inhibit)
the kinetics of trans-to-cis photoisomerization of
azobenzene-containing bipyridines, which was tentatively
attributed to the existence of strong metal-to-ligand charge
transfer. In the examples presented here, although the isomer-
ization process was significantly inhibited for all the complexes,
according to the extent of the spectral change, it was more
effective for derivatives of ligands 3 and 4, which can be described
as para-azobenzene-2,2′-bipyridines. Instead it was nearly
suppressed for derivatives of ligands 1 and 2, in which the
azophenyl pyridyl is directly coordinated to the metal center.
Surprisingly, for derivatives of 5, in which the azobenzene is not
conjugated with the bipyridyl fragment, the extent of the
When the light-triggered E → Z isomerization of the
corresponding Ir(III) derivatives was studied, according to the
change in the UV−vis absorption spectra, the isomerization was
not as efficient as in the free ligands (see Figures 4 and 5). It is
13,8
well-known that metal coordination can affect
(or even
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Article
Table 3. Electrochemical Properties of the Ir Complexes
a
a
a
b
a
b
b
Ered (V)
Eox (V)
Eonsetred (V)
LUMO (eV)
Eonsetox (V)
HOMO (eV)
ΔE (eV)
A
−1.75
−1.70
−1.65
−1.03
−1.00
−1.00
−1.42
−1.47
−1.40
−1.43
−1.37
−1.40
−1.62
−1.60
−1.58
−1.24
−1.19
−1.20
1.02
1.21
1.33
1.02
1.22
1.34
1.02
1.10
1.36
1.02
1.28
1.38
1.02
1.23
1.35
1.05
1.26
1.42
−1.61
−1.56
−1.51
−0.92
−0.88
−0.88
−1.15
−1.20
−1.27
−1.30
−1.24
−1.25
−1.42
−1.40
−1.39
−1.07
−1.00
−1.01
−3.19
−3.24
−3.29
−3.88
−3.92
−3.92
−3.65
−3.60
−3.53
−3.50
−3.56
−3.55
−3.38
−3.40
−3.41
−3.73
−3.80
−3.79
0.9
−5.70
−5.88
−5.95
−5.72
−5.91
−6.04
−5.65
−5.74
−5.98
−5.68
−5.92
−6.02
−5.67
−5.80
−6.02
−5.75
−5.96
−6.08
2.51
2.64
2.66
1.84
1.99
2.12
2.00
2.14
2.45
2.18
2.36
2.47
2.29
2.40
2.61
2.02
2.16
2.29
C
1.08
1.15
0.92
1.11
1.24
0.85
0.94
1.18
0.88
1.12
1.22
0.87
1.00
1.22
0.95
1.16
1.28
B
A1
C1
B1
A3
C3
B3
A4
C4
B4
A5
C5
B5
A2
C2
B2
a
+
b
Potential values are reported versus Fc/Fc . HOMO and LUMO levels have been deduced by the equation EHOMO/ELUMO (eV) = −(4.8 + Eonset),
and ΔE has been obtained as the difference LUMO − HOMO.
+
photoisomerization is rather small (see Figure 5, and the SI).
This result is not in agreement with the observations of Nishihara
for meta- and para-substituted cobalt-azobipyridine complexes.
vs Fc/Fc and their first reduction peak potentials between −1.60
and −1.00 V. First of all, experimental data measured suggest that
the anodic peak potentials are not affected by the nature of the
ancillary bipyridyl ligand. Concerning the values of the cathodic
peak potentials, they are anodically shifted with respect to those
corresponding to [(ppy) Ir(bipy)]PF . This fact could be
attributed to the presence of the low-lying π* orbital of the
azobenzene-type ligands. According to the literature, azo groups
are electron-withdrawing in nature and trap electrons in the
metal-to-ligand charge transfer excited state. These observa-
tions are in agreement with the general description of the frontier
orbital for [Ir(ppy)(bipy)] complexes. It is generally accepted
that for such compounds the HOMO and HOMO−1 levels are
basically a mixture of metal (Ir-5d) and ppy ligand states, unlike
the LUMO, which is localized essentially at the bipy ancillary
13
In that case, as expected, light-triggered trans-to-cis isomerization
was more effective when meta azobipyridines were used. In that
case the effect was most evident for the Co(II) derivatives than in
the analogous Co(III) compounds, for which the photo-
isomerization was strongly inhibited. The rather small changes
in the UV−vis spectra observed upon irradiation in all the cases
studied here prevent an unambiguous comparison from being
made. In all cases the original spectra, assigned to the original
trans isomers, were recovered upon thermal cis-to-trans isomer-
ization, which evidenced the stability of the complexes during the
irradiation. Although we tried to corroborate these results by a
quantitative NMR spectroscopic analysis, it was not possible due
to the overlap of signals (all aromatic).
2
6
10
+
42
ligand.
Cyclic Voltammetry. The electrochemical properties of
azobenzene-containing iridium cationic complexes were studied
in anhydrous acetonitrile (ACN) solutions. The measured half-
wave potentials are summarized in Table 3. The HOMO and
LUMO levels of all complexes have been deduced by the
equation EHOMO/ELUMO (eV) = −(4.8 + Eonset), and ΔE has
been obtained as the difference LUMO − HOMO.
Comparing the values of the oxidation potentials measured for
the model compounds A, B, and C, it can be observed that the
presence of electron-withdrawing fluorine (1.33 V) and bromine
(1.21 V) substituents on the ppy ligands leads to an anodic shift
of the oxidation peak (1.02 V in the absence of halide ions). The
reduction wave is affected to a much lesser extent. Consequently,
fluorine-containing complexes show larger ΔE values than their
fluorine-free counterparts (see Figure 6 for a representative
example). This broadening of the HOMO−LUMO when
increasing the electron-withdrawing nature of the substituents
38
The obtained voltammograms (Figures S190−S194 in the SI)
and redox potential values were compared to those of reference
parent complexes Abipy−Cbipy containing 2,2′-bipyridyl as
ancillary ligand (Figure S195 in the SI). According to the
literature, within the potential window studied the voltammo-
grams of model complexes [Ir(ppy) (bipy)]PF (Abipy) and
42−44
on the ppy ligands, already argued for related compounds,
was systematically observed in all the series of compounds.
The cathodic shift of reduction peak potentials found for
derivatives of ligand 3 (−1.43 V for C3) compared to derivatives
of ligand 1 (−1.00 V for C1) indicates that the incorporation of
an additional benzene ring in the structure of the phenylpyridine
ligand shields the electron-withdrawing effect of the azo
2
6
[
Ir(Fppy)(bipy)]PF (Bbipy) exhibit a reversible reduction peak
6
assigned to the reduction of the bipyridyl ligand. They also
IV
III
present a reversible oxidation wave attributed to the Ir /Ir
3
9
redox couple. The obtained ΔE values are comparable to those
40
8
found in the literature for similar Ir complexes. As reported
before, the values of the redox potentials of iridium complexes
containing ppy derivatives depend on the electron-donating or
substituent. On the other hand, as can be observed, by
comparing derivatives of ligand 3 (−1.43 V for C3) and ligand 5
(−1.60 V for C5), the change on the position of the azo
substituent on the ring from para to meta increases the shielding
effect of the additional aromatic ring. Finally, derivatives of ligand
4 show a behavior very similar to that of derivatives of 3,
39,41
electron-withdrawing nature of their substituents.
The
azobenzene-containing complexes analyzed in this work exhibit
their main oxidation peak at potentials between 1.02 and 1.38 V
H
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Figure 6. Cyclovoltammograms (10− M, dry ACN) of A1, B1, and C1
3
containing 0.1 M TBAPF as the supporting electrolyte, at a scan rate of
6
−
1
1
00 mV s .
indicating that both bromine and azo substituents exert a similar
electron-withdrawing effect (−1.37 V for C4 and −1.43 V for
C3). This tendency was corroborated by means of time-
dependent (TD)-DFT calculations (vide infra).
Figure 7. Most relevant MO of ligands 1−4 associated with the vertical
excitations shown in Table S3. Occupied and unoccupied orbitals are
represented by red and blue or yellow and green surfaces, respectively.
Comparison of ligand 1 and ligand 2 permitted us to study the
chelate effect. In terms of electrochemical behavior, the
comparison of the results found for these two series of complexes
indicates that, as expected, the use of bidentate or monodentate
ancillary ligand hardly influences the anodic peak potentials,
more susceptible to changes in the ppy ligands, as discussed
above. Concerning the reduction peak potentials, the anodic shift
induced on the reference complex by the presence of an azo
group is less pronounced in derivatives of ligand 2 (−1.19 V for
C2) than in derivatives of 1 (−1.00 V for C1) compounds. This
behavior can be attributed to the lower rigidity of monodentate
in the simulated maximum is observed when extended
conjugation is present. Ligand 2 has the most energetic
absorption band (305 nm, 4.0 eV), and an increase of 7 nm in
the wavelength is found in its dimeric counterpart 1.
Introduction of two additional phenyl groups on the latter
(namely, ligand 3) implies an even higher reduction in the band
gap, and therefore an increase in the computed wavelength to
333 nm (3.71 eV). Noteworthy, comparing ligands 3 and 4, it can
be seen that the effect on the wavelength due to the bromine in
the 4′ position of the bipyridine moiety is similar to the presence
of an azobenzene at the same position, even though only
inductive and not extended conjugation can be addressed for the
former substituent.
45
ligands compared to bidentate ligands.
TD-DFT Calculations. A computational study within the
DFT framework was made in order to further analyze the
electronic properties of ligands 1−4 and their complexes A−C.
Simulations of the absorption spectra of previously optimized
s t r u c t u r e s a t t h e T D - C A M - B 3 L Y P ( P C M ) / 6 -
As far as complexes are considered, there is a bathochromic
shift on the computed wavelength associated with the
chromophores 1−4 band due to coordination to the metal.
These bands are assigned to the spin-allowed π → π* transitions,
which mainly correspond to an intraligand charge transfer
3
1+G*&LANL2DZ level of theory have been performed. This
computational method has been proven to give reliable results on
the study of vertical excitations of azobenzene-iridium
complexes. The data associated with the main transition
8
1
computed and HOMO−LUMO gaps of these compounds are
collected in Table S3 in the SI. Representations of the most
relevant molecular orbitals are depicted in Figures 7 and 8.
The optimized structures of ligands 2−4 present a planar trans
conformation on the azo and bipyridyl moieties, as observed
experimentally (Figure 1). Moreover, the simulated wavelength
values are similar to the experimental ones, thus pointing out the
reliability of the chosen computational method for this family of
compounds. The computed main absorption bands are mainly
associated with π → π* transitions (Figure 7). Actually, in the
case of ligands 1 and 2, the vertical excitations start from an
orbital allocated on the nitrogen atoms, with a lower participation
of the orbital delocalized in the aromatic system. On the contrary,
in conjugated ligands 3 and 4, all the orbitals involved in the
transitions are located in the latter π system. Focusing on the
structure of the ligands (Chart 1), a bathochromic displacement
( ILCT) centered on the functionalized azobenzene moieties
1
with no negligible participation of metal to ligand ( MLCT)
1
transitions. In the case of C3 and A−C4, this latter MLCT
becomes the most important process since the vertical excitation
involves an occupied orbital located on the [Ir(ppy) ] moiety
2
and an unoccupied orbital lying on the azobenzene ligands
(Figure 8).
Besides, TD-DFT calculations show the existence of less
energetic MLCT Ir(d)−π* bands (see the SI).The existence of
these low-energy MLCT bands could imply a fast depopulation
of the π* azo orbital after irradiation, thus inhibiting the
isomerization process (Figure 9)
On the other hand, within a set of complexes, a monotonic
increase of the computed wavelength was observed when
extended conjugation is present on the ligand structure. This
trend was also observed in the isolated ligands’ analysis (vide
I
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Figure 8. Most relevant MO associated with the vertical excitations of cations of complexes AC1−4.
supra). Moreover, for a given ligand, a dependence upon the
computed wavelength with the halogen substitution in the
phenylpyridyl moieties was found. In general, the presence of
fluorine in the structure (B set of complexes) implies a
bathochromic displacement of the band compared to their
nonfluorinated counterparts (A complexes), whereas the
presence of bromine in the phenylpyridyl ligands has a
hypsochromic effect (C complexes).
complexes with the same ligand are compared. In general, the
presence of electron-withdrawing groups on the [Ir(ppy)2]
moiety (compounds B and C) implies an increase in the gaps
compared to their nonhalogenated counterparts (compounds
A). Noteworthy, the effect on fluorinated compounds B is higher
than in the brominated ones (C), thus presenting the highest
ΔE
gaps. However, a general underestimation on the
HOMO−LUMO
HOMO−LUMO gap values was observed maybe as a
consequence of the small deviations on the planarity of ligands
in the computed structures (vide supra).
Finally, the HOMO−LUMO energetic gap (ΔEHOMO−LUMO)
of these complexes has been calculated at the M06L(PCM)/6-
3
3
1 + G * & L A N L 2 D Z / / C A M - B 3 L Y P ( P C M ) / 6 -
1+G*&LANL2DZ level. This highly parametrized method has
CONCLUSIONS
■
been proven to give accurate results on energy calculations by
A new synthetic route toward photochromic azobenzene-
bipyridyl ligands based on Suzuki cross-coupling of azoben-
zene-boronic acids with brominated bipyridines has been
developed. This strategy constitutes a clear advance compared
to formerly described methodologies, which required long and
low-yielding synthetic routes, and can be easily extended to other
types of ligands. When combined with a posteriori modification of
brominated azobenzene-containing complexes, new compounds
that incorporate up to four azobenzene fragments were obtained.
Following this methodology 20 new azobenzene-containing
iridium(III) complexes have been synthesized. Crystallographic
analysis of free ligands (based on our own results and related
proper consideration of dispersion effects on organometallic
4
7
complexes. In general, the highest occupied molecular orbital is
located in the [Ir(ppy) ] moiety, whereas the LUMO is placed
2
42
on the azobenzene ligands. Only in complexes B3 and B4 do
both orbitals lie on the azobenzene fragment (see Figure S196 in
the SI). Therefore, the conjugated structure of the ligands has a
small effect on the computed ΔE
values. Actually, for
HOMO−LUMO
a given set of compounds, the ΔE
gap increases
HOMO−LUMO
following the trend 1 < 2 < 3 < 4, where the lowest gap is
associated with complexes A−C1 instead of the ones with the
simpler ligand structure (namely, A−C2). The effect of the
[
Ir(ppy) ] moiety on these gaps was clearly pointed out if
2
J
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Article
of the existence of low energetic and highly probable MLCT
bands that allow the relaxation of π* azo excited states after
irradiation.
Transient absorption spectroscopic measurements to confirm
the nature of the excited states and the main transitions
responsible for the inhibition of both the phosphorescence and
the photochromism of these iridium-azobenzene complexes are
currently under development. Also, we are exploring the
potential use of these compounds as selective sensors for
10
reducing agents (such as sulfite or bisulfite), as well as the
construction of photochromic bipyridyl complexes of other
metal ions, and their use as phototunable catalysts.
EXPERIMENTAL SECTION
■
General Considerations. IrCl ·3H O, Pd(PPh ) , 2-phenylpyr-
3
2
3 4
idine, 2-(3,5-difluorophenyl)pyridine, 4,4′-dibromo-2,2′-bipyridine,
and other general chemicals were obtained from commercial sources
and used without further purification. 4-Azophenylboronic acid pinacol
4
9
50
51
52
ester 6′, [Ir(ppy) Cl] , [Ir(Fppy) Cl] , [Ir(Brppy) Cl] , 2-(4′-
2
2
2
2
2
2
5
3
12d
bromophenyl)pyridine, 4-phenylazopyridine, and 3-azophenylbor-
onic acid 7 were synthesized according to published methodologies. All
8
solvents were dried and purified by known procedures and freshly
distilled under nitrogen from appropriate drying agents prior to use. All
manipulations and reactions involving air- and/or moisture-sensitive
organometallic compounds were performed under an atmosphere of dry
nitrogen using standard Schlenk techniques.
All the calculations were performed with the GAUSSIAN09 suite of
5
4
programs. Optimization and TD-DFT simulation of the absorption
processes were carried by using the Coulombic-attenuating method
5
5
developed by Handy et al. named CAM-B3LYP with the standard 6-
5
6
3
1+G* and the Hay−Wadt core effective potential LANL2DZ basis
Figure 9. Schematic representation of the isomerization process of (A)
azobenzene and (B) a model azobenzene-iridium complex, based on refs
sets. Solvent effects were estimated using the polarizable continuum
model (PCM) within the self-consistent reaction field (SCRF)
approach. This method was successfully optimized for vertical
5
7
3
4 and 46, respectively.
5
8
excitations and excited states and was previously proven to give
8
reliable results on the calculation of iridium complexes.
examples from the bibliography) and representative examples of
their iridium complexes show some clear trends: considering free
ligands, the extended conjugation described for ligands 1−4 is
lost in the case of meta derivatives analogous to 5. Upon
coordination to the metal, there is a loss of conjugation in the
compounds when the pyridyl unit is not part of the chromophore
Characterization Methods. All electrochemical measurements
−3
were carried out in a sealed glass cell under a N atmosphere on 10
M
2
solutions of A−D in anhydrous ACN (containing 0.1 M TBAPF as the
6
−1
supporting electrolyte) at a scan rate of 100 mV s . The working
electrode was a glassy-carbon rod (5 mm diameter), and a Pt wire
encapsulated on a porous glass tube was used as counter electrode. The
potentials were controlled using a Metrohm Ag/AgCl reference
(
derivatives of ligands 3−5). Although this trend could not be
electrode. On the other hand the ferrocene/ferrocenium couple
reproduced by means of theoretical calculations, it was also
reflected in the electronic absorption spectra of such compounds.
In complex B2′, formed by ortho-metalation, the ligand acts as
a monoanionic C−N donor coordinating through a carbon of the
phenyl ring and one of the nitrogen atoms of the azobenzene, and
consequently the photoisomerization process of the azobenzene
is inhibited.
−3
(
+0.352 V vs Ag/AgCl) was used as the internal standard (10 M),
and all potentials are related to it. The measurements were performed
using a Bio-Logic VMP3 potentiostat-galvanostat.
UV−vis absorption measurements were performed with an Agilent
8453 diode-array spectrophotometer utilizing 10 mm cell-path quartz
cuvettes (110 QS).
Photoisomerization Studies. Measurements of thermal cis to trans
isomerization rates were performed using 10−40 μM solutions of ACN.
To maximize the initial population of Z derivatives on the photosta-
tionary state (PSS), the procedure described by Monkowius was
The analysis of the light-triggered photoisomerization and the
reverse process (induced thermally) has been studied for both
ligands and complexes. The results obtained show that, although
it is very effective in all the free ligands (according to the UV−vis
change observed), for iridium derivatives of ligands 1 and 2, in
which the coordinated pyridyl unit is part of the photochromic
fragment, and when the azobenzene is appended in the meta
position of the bipyridyl (derivatives of 5), the photoisomeriza-
tion is nearly suppressed, but when the substitution is on the para
position one or both of the bipyridyl units (ligands 3 and 4)
behave as slightly photochromic compounds with isomerization
rates comparable to those reported for other azobenzene-
42
followed: Using a Shimadzu RF-540 fluorimeter, a 3 mL portion of
each sample was irradiated at the corresponding λmax (associated with its
π−π* transition band) until no further change in the UV−vis absorption
spectra was observed. The λ of the maximum observed after subtracting
the first and last spectra of the series was considered as the optimal light
wavelength to promote the Z−E photoisomerization (λopt). Fresh
samples were irradiated at λ for 60 min and then placed in a UV−vis
opt
spectrophotometer. Their absorbance spectral changes were measured
as a function of time for 10 h. Temperature was maintained at 55 °C
controlled with an HP 89090A Peltier temperature control accessory.
Synthetic Procedures. [4-(Phenylazo)phenyl]boronic acid 6. The
starting 4-iodoazobenzene (1.5 g, 4.87 mmol) was azeotropically dried
8
,36,48
containing complexes.
TD-DFT calculations suggest that
the isomerization process of the azobenzene could be inhibited
upon coordination to the iridium(III) centers as a consequence
with toluene under a N atmosphere and dissolved in 40 mL of freshly
distilled THF. The solution was cooled to −100 °C, BuLi (3.5 mL, 37.15
2
K
DOI: 10.1021/acs.organomet.5b00838
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
mmol) was added, and the mixture was stirred for 30 min. The mixture
was added to a solution of trimethyl borate (0.6 mL, 5.38 mmol) in 5 mL
of freshly distilled THF at −100 °C. The reaction temperature was
gradually raised to room temperature, and the solution was stirred
overnight. A mixture of H SO /H O (1:10, 55 mL) was added at 0 °C.
toluene. K CO (12 mL, 2 M in H O) and Pd(PPh ) (0.08 g, 0.07
2
3
2
3 4
mmol) were added, and the mixture was degassed by N bubbling for 15
2
min. The reaction mixture was heated to 115 °C for 15 h. The resulting
mixture was cooled to room temperature, and the product was extracted
with CH Cl . The organic phase was dried with MgSO , and the solvent
2
4
2
2
2
4
The organic layer was separated, and the aqueous layer was extracted
was evaporated. The product was obtained as an orange solid. Yield:
71%1 .
with Et O. An aqueous NaOH solution was added to the combined
2
organic solution, and the aqueous layer was washed with Et O. A
H NMR (300 MHz, CDCl ): δ 8.89 (d, J = 1.2, 1H), 8.85 (d, J = 5.1,
2
3
mixture of H SO /H O (1:10, 100 mL) was added to the aqueous layer,
and an orange product precipitated. The product was purified by column
1H), 8.39 (pst, J = 1.7, 1H), 8.06 (dpst, J = 7.9, J = 1, 1H), 8.02 (brdd, J =
8.2, J = 1.8, 2H), 7.96 (dpst, J = 8.1, J = 1.1, 1H), 7.71 (m, 2H), 7.57 (m,
2
4
2
3H). 13C APT NMR (75 MHz, CDCl ): δ 156.71 (Cquat), 153.19
chromatography (silica gel, CH Cl ) and was obtained as an orange
2
2
3
solid. Yield: 20%.
(Cquat), 152.58 (Cquat), 149.80 (CH), 148.68 (Cquat), 139.38 (Cquat),
131.29 (CH), 129.82 (CH), 129.53 (CH), 129.15 (2CH), 123.25 (CH),
122.98 (2CH), 121.84 (CH), 121.77 (CH), 119.32 (CH). Anal. Calcd
1
H NMR (300 MHz, CDCl ): δ 8.27 (d, J = 8.1, 2H, (2 or 3)), 7.91 (d,
3
J = 8.3, 2H, (2 or 3)), 7.88 (d, J = 9.1, 2H, (6)), 7.50−7.39 (m, 3H, (7 +
13
8
)). C APT NMR (75 MHz, CDCl ): δ 154.85 (C ), 152.23 (C ),
for (C34H N ·H O): C, 76.39; H, 4.90; N, 15.72. Found: C, 75.92; H,
24 6 2
3
quat
quat
+
1
36.14 (2CH, (2 or 3)), 130.96 (CH, (8)), 128.68 (2CH, (7)), 122.66
4.42; N, 15.28. Exact mass: ESI-MS [C34H N + H] calcd m/z =
24 6
(
2CH, (6)), 121.79 (2CH, (2 or 3)) (carbon-bearing boron substituent
517.2141, found: m/z = 517.2146.
not observed). Anal. Calcd for (C H BN O ): C, 63.76; H, 4.91; N,
General Procedure for the Synthesis of Complexes A−C, bipy, 1,
12
11
2
2
1
2.39. Found: C, 64.61; H, 4.81; N, 12.30.
,2′-Bis(4-phenylazopyridine), 1. 4,4′-Diamino-2,2′-bipyridine
0.500 g, 2.68 mmol) was dissolved in 4 mL of NaOH (2 g/4 mL of
3−5, and B2′. One equivalent of the chloro-bridged iridium(III) dimer
2
and 2 equiv of the ligand were dissolved in a mixture of CH Cl /MeOH
2 2
2:1) and refluxed for 15 h. The products were purified by column
(
(
chromatography (silica gel, CH Cl ). When the unreacted iridium(III)
H O) and 2 mL of pyridine. The mixture was heated to 80 °C for 45 min,
2
2
2
dimer eluted, KPF was added on top of the column, and the polarity of
and nitrosobenzene (0.750 g, 7 mmol) was added. The reaction mixture
6
the eluent was gradually increased to 100% acetone to elute the
was heated to 80 °C for another 15 h. The resulting mixture was cooled
complexes together with the excess of KPF . The desired compounds
to room temperature. The solid was filtrated and washed with CH Cl2
6
2
were purified by filtration through a Celite pad in CH Cl .
and H O. The product was obtained as an orange solid. Yield: 56%.
2
2
2
1
[
Ir(Brppy) (2,2′-bipyridine)]PF , C-bipy. The product was obtained
H NMR (300 MHz, CDCl ): δ 8.96 (d, J = 5.2, 1H), 8.92 (d, J = 1.4,
2
6
3
1
as a yellow solid after precipitation with ether. Yield: 46%. H NMR (300
1
5
H), 8.07 (brd, J = 4.0, 1H), 8.05 (d, J = 2.2, 1H), 7.81 (dd, J = 1.9, J =
.2, 1H), 7.60 (m, 3H). 13C APT NMR (75 MHz, CDCl ): δ 158.52
6
MHz, acetone-d ): δ 8.89 (d, J = 8.2, 1H), 8.35 (ddd, J = 1.6, J = 7.9, J =
3
9
7
7
.4, 1H), 8.32 (d, J = 8.0, 1H), 8.20 (d, J = 5.4, 1H), 8.04 (ddd, J = 1.5, J =
.5, J = 9.0, 1H), 7.90 (m, 2H), 7.77 (ddd, J = 1.2, J = 7.0, J = 7.6, 1H),
.27 (m, 2H), 6.44 (d, J = 1.9, 1H). 13C APT NMR (75 MHz, acetone-
d6): δ 167.76 (Cquat), 157.25 (Cquat), 153.80 (Cquat), 152.19 (CH),
50.79 (CH), 144.69 (Cquat), 141.31 (CH), 140.54 (CH), 135.08 (CH),
(
Cquat), 157.74 (Cquat), 152.46 (Cquat), 150.76 (CH), 132.34 (CH),
29.26 (2CH), 123.48 (2CH), 116.44 (CH), 114.18 (CH). Anal. Calcd
for (C H N ): C, 72.51; H, 4.43; N, 23.06. Found: C, 72.12; H, 3.97;
1
2
2
16
6
+
N, 23.04. Exact mass: ESI-MS [C H N + H] calculate: m/z =
22
16
6
1
1
1
4
3
65.1515, found m/z = 365.1515.
,4-Bis(p-azobenzene)-2,2′-bipyridine, 3. 4,4′-Dibromo-2,2′-bipyr-
idine (0.6 g, 1.91 mmol) and [4-(phenylazo)phenyl]boronic acid 6
30.14 (CH), 128.08 (CH), 127.12 (CH), 126.34 (CH), 126.21 (Cquat),
4
25.63 (CH), 121.84 (CH). Anal. Calcd for (C H Br IrN PF ): C,
32 22
2
4
6
0.06; H, 2.31; N, 5.84. Found: C, 40.11; H, 2.45; N, 5.37. Exact mass:
(
1.43 g, 6.33 mmol) were dissolved in 35 mL of toluene. K CO (16 mL,
2 3
+
ESI-MS [C H Br IrN ] calcd m/z = 812.9840, found m/z =
2
M in H O) and Pd(PPh ) (0.12 g, 0.104 mmol) were added, and the
32 22
2
4
2
3 4
8
12.9813.
Ir(ppy) (1)]PF , A1. It was obtained as a dark red solid. Yield: 85%.
mixture was degassed by N bubbling for 15 min. The reaction mixture
2
[
was heated to 115 °C for 72 h. The resulting mixture was cooled to room
2
6
1
H NMR (300 MHz, acetone-d ): δ 9.39 (d, J = 1.5, 1H), 8.37 (d, J = 5.8,
temperature. The solid was filtrated and washed with CH Cl and
6
2
2
acetone. The product was obtained as an orange solid. Quantitative
1H), 8.30 (d, J = 8.0, 1H), 8.13−8.04 (m, 4H), 7.99 (t, J = 8.9, 2H), 7.73
yield. Anal. Calcd for (C H N ·CH Cl ): C, 69.89; H, 4.36; N, 13.97.
(m, 3H), 7.22 (pst, J = 6.4, 1H), 7.10 (pst, J = 7.2, 1H), 6.99 (pst, J = 7.6,
34
24
6
2
2
1H), 6.43 (d, J = 7.4, 1H). 13C APT NMR (75 MHz, acetone-d
): δ
6
Found: C, 70.03; H, 4.45; N, 14.25. Exact mass: ESI-MS [C H N +
3
4
24
6
+
H] calcd m/z = 517.2141, found m/z = 517.2147.
-(p-Azobenzene)-4′-bromo-2,2′-bipyridine, 4. Under a N atmos-
168.96 (Cquat), 160.13 (Cquat), 159.28 (Cquat), 153.77 (CH), 153.72
(Cquat), 151.39 (Cquat), 150.91 (CH), 145.41 (Cquat), 140.17 (CH),
135.16 (CH), 132.95 (CH), 131.80 (CH), 131.08 (2CH), 126.34 (CH),
125.08 (CH), 125.01 (2CH), 124.07 (CH), 121.85 (CH), 121.35 (CH),
4
2
phere, 4,4′-dibromo-2,2′-bipyridine (1.00 g, 3.18 mmol) and [4-
phenylazo)phenyl]boronic acid pinacol ester 6′ (0.98 g, 3.18 mmol)
were dissolved in 60 mL of toluene. K CO (27 mL, 2 M in H O) and
(
119.96 (CH). Anal. Calcd for (C44
11.09. Found: C, 52.14; H, 3.09; N, 10.71. Exact mass: ESI-MS
H32IrN PF ): C, 52.33; H, 3.19; N,
2
3
2
8 6
Pd(PPh ) (0.184 g, 0.159 mmol) were added, and the mixture was
3
4
+
degassed by N bubbling for 15 min. The reaction mixture was heated to
[C44
[Ir(Fppy)
H
32IrN
8
] calcd m/z = 865.2379, found m/z = 865.2408.
(1)]PF , B1. It was obtained as a dark red solid. Yield: 88%.
H NMR (300 MHz, acetone-d ): δ 9.43 (d, J = 1.8, 1H), 8.51 (d, J = 5.9,
2
1
15 °C for 15 h. The resulting mixture was cooled to room temperature,
2
6
1
and the orange solid (ligand 3) was removed by filtration. The product
was extracted from the filtrate with CH Cl . The organic phase was dried
6
1H), 8.47 (d, J = 8.4, 1H), 8.17 (d, J = 5.9, 1H), 8.10 (m, 4H), 7.74 (m,
3H), 7.31 (ddd, J = 1.3, J = 5.9, J = 7.3, 1H), 6.84 (ddd, J = 2.4, J = 9.4, J =
12.6, 1H), 5.89 (dd, J = 2.4, J = 8.6, 1H). 13C APT NMR (75 MHz,
2
2
with MgSO , and the solvent was evaporated. The product was purified
4
by column chromatography (silica gel, 100% CH Cl to 100% acetone),
2
2
and it was obtained as an orange solid. Yield: 38%.
acetone-d
6
): δ 165.08 (d, J = 6.7, Cquat), 164.95 (dd, J = 12.4, J = 253.5,
quat), 162.78 (dd, J = 12.5, J = 258.3, Cquat), 160.54 (s, Cquat), 159.11 (s,
quat), 155.44 (d, J = 6.5, Cquat), 154.22 (s, CH), 153.71 (s, Cquat), 151.46
1
H NMR (300 MHz, CDCl ): δ 8.80 (d, J = 5.1, 1H), 8.75 (dd, J = 1.7,
C
C
3
J = 8.8, 2H), 8.56 (d, J = 5.2, 1H), 8.09 (d, J = 8.5, 2H), 8.00 (dd, J = 1.8, J
=
4
8.3, 2H), 7.96 (d, J = 8.4, 2H), 7.66 (dd, J = 1.8, J = 5.0, 1H), 7.56 (m,
(s, CH), 141.27 (s, CH), 135.29 (s, CH), 131.10 (s, 2CH), 129.29 (s,
quat), 125.62 (s, CH), 125.08 (d, J = 19.2, CH), 125.06 (s, 2CH),
122.05 (s, CH), 120.31 (s, CH), 115.15 (d, J = 19.6, CH), 100.30 (t, J =
26.9, CH). Anal. Calcd for (C44 IrN PF ·CH Cl ): C, 46.32; H,
2.59; N, 9.60. Found: C, 46.19; H, 2.72; N, 9.46. Exact mass: ESI-MS
H). 13C APT NMR (75 MHz, CDCl ): δ 157.25 (Cquat), 155.44
C
3
(
1
(
Cquat), 152.90 (Cquat), 152.66 (Cquat), 149.84 (2CH), 148.49 (Cquat),
40.35 (Cquat), 134.03 (Cquat), 131.32 (CH), 129.14 (2CH), 127.95
2CH), 127.06 (CH), 124.74 (CH), 123.56 (2CH), 122.99 (2CH),
H
28
F
4
8
6
2
2
+
1
3
22.07 (CH), 119.24 (CH). Anal. Calcd for (C H BrN ): C, 63.63; H,
.64; N, 13.49. Found: C, 63.42; H, 3.62; N, 13.23. Exact mass: ESI-MS
[C44H
28
F
4
IrN
[Ir(Brppy) (1)]PF
H NMR (300 MHz, acetone-d
6
8
] calcd m/z = 937.2002, found m/z = 937.2034.
, C1. It was obtained as a dark red solid. Yield: 61%.
): δ 9.41 (d, J = 1.6, 1H), 8.45 (d, J = 5.8,
22
15
4
2
6
+
1
[
C H BrN + H] calcd m/z = 415.0558, found m/z = 415.0566.
2
2
15
4
4
,4′-Bis(m-azobenzene)-2,2′-bipyridine, 5. Under a N atmosphere,
1H), 8.35 (d, J = 8.0, 1H), 8.14−8.03 (m, 5H), 7.96 (d, J = 8.4, 1H), 7.73
2
4
,4′-dibromo-2,2′-bipyridine (0.436 g, 1.39 mmol) and [3-(phenylazo)-
phenyl]boronic acid 7 (0.785 g, 3.47 mmol) were dissolved in 26 mL of
(brd, J = 7.0, 3H), 7.33 (dd, J = 1.8, J = 8.3, 1H), 7.28 (d, J = 6.1, 1H),
6.49 (d, J = 1.9, 1H). 13C APT NMR (75 MHz, acetone-d ): δ 167.67
6
L
DOI: 10.1021/acs.organomet.5b00838
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
+
(
1
(
(
Cquat), 160.38 (Cquat), 159.20 (Cquat), 154.07 (CH), 153.72 (Cquat),
53.43 (Cquat), 151.17 (CH), 144.74 (Cquat), 140.72 (CH), 135.24
CH), 135.12 (CH), 131.10 (2CH), 128.17 (CH), 127.38 (CH), 126.30
Cquat), 125.79 (CH), 125.06 (2CH), 122.04 (CH), 121.95 (CH),
Exact mass: ESI-MS [C H Br IrN ] calcd m/z = 1173.1215, found
56 38 2 8
m/z = 1173.1235.
[Ir(ppy) (4)]PF , A4. It was obtained as a red solid. Yield: 86%. H
NMR (300 MHz, acetone-d ): δ 9.36 (s, 2H), 8.26 (brd, J = 8.5, 4H),
1
2
6
6
1
20.14 (CH). Anal. Calcd for (C H Br IrN PF ): C, 45.26; H, 2.59;
8.19 (d, J = 5.8, 1H), 8.12 (brd, J = 8.5, 3H), 8.06−7.91 (m, 10H), 7.63
(m, 3H), 7.22 (ddd, J = 1.4, J = 5.8, J = 7.6, 2H), 7.07 (ddd, J = 1.0, J = 7.3,
J = 12.8, 2H), 6.96 (ddd, J = 1.2, J = 7.3, J = 12.6, 2H), 6.41 (dd, J = 3.6, J
44
30
2
8
6
N, 9.60. Found: C, 45.22; H, 2.51; N, 9.47. Exact mass: ESI-MS
+
[
C H Br IrN ] calcd m/z = 1021.0589, found m/z = 1021.0573.
44 30 2 8
[
Ir(ppy) (2)], B2′. KPF was not added to the column, and filtration
= 7.4, 2H). 13C APT NMR (75 MHz, acetone-d ): δ 168.98 (Cquat),
2
6
6
through a Celite pad was not necessary. The product was obtained as an
orange solid. Yield: 87%. H NMR (300 MHz, CDCl ): δ 9.84 (dd, J =
168.94 (Cquat), 158.78 (Cquat), 156.97 (Cquat), 154.86 (Cquat), 153.88
(Cquat), 152.48 (CH), 152.30 (CH), 151.56 (Cquat), 151.31 (Cquat),
151.25 (Cquat), 150.87 (CH), 150.72 (CH), 145.42 (Cquat), 145.40
(Cquat), 140.12 (2CH), 139.28 (Cquat), 137.13 (Cquat), 133.22 (CH),
133.15 (CH), 132.93 (2CH), 131.76 (2CH), 130.74 (2CH), 130.13
(2CH), 129.88 (CH), 127.66 (CH), 126.31 (2CH), 125.07 (2CH),
124.84 (2CH), 124.25 (3CH), 123.95 (2CH), 121.30 (2CH). Anal.
Calcd for (C H BrIrN PF ): C, 49.82; H, 2.95; N, 7.92. Found: C,
1
3
1
5
2
.0, J = 5.8, 1H), 8.24 (d, J = 8.5, 1H), 8.07 (d, J = 8.3, 1H), 8.00 (d, J =
.7, 1H), 7.83 (dd, J = 1.6, J = 7.4, 2H), 7.75−7.62 (m, 2H), 7.56 (m,
H), 7.50−7.38 (m, 4H), 7.17 (t, J = 6.3, 1H), 6.98 (ddd, J = 1.0, J = 5.8, J
=
7.4, 1H), 6.34 (ddd, J = 2.4, J = 9.1, J = 11.8, 1H), 6.25 (ddd, J = 2.3, J =
9
1
1
.3, J = 12.4, 1H), 5.73 (dd, J = 2.4, J = 8.6, 1H), 5.52 (dd, J = 2.4, J = 8.7,
H). 13C APT NMR (75 MHz, CDCl ): δ 165.17 (d, J = 7.6, Cquat),
3
44 31
6
6
+
64.51 (d, J = 6.1, Cquat), 163.61 (dd, J = 12.9, J = 256.9, Cquat), 162.77
49.71; H, 3.10; N, 7.58. Exact mass: ESI-MS [C H BrIrN ] calcd m/z
44 31 6
(
dd, J = 12.6, J = 258.4, Cquat), 161.02 (dd, J = 12.9, J = 260.7, Cquat),
= 915.1423, found m/z = 915.1398.
[Ir(Fppy) (4)]PF , B4. The product was obtained as an orange solid
1
6
1
(
(
60.76 (dd, J = 12.9, J = 259.9, Cquat), 156.97 (s, 2Cquat), 154.13 (d, J =
.8, Cquat), 152.26 (s, Cquat), 151.12 (d, J = 6.8, Cquat), 150.93 (s, CH),
48.86 (s, CH), 138.06 (s, CH), 137.69 (s, CH), 133.19 (s, CH), 129.37
s, 3CH), 127.92 (s, Cquat), 127.79 (s, Cquat), 123.64 (s, 2CH), 123.36
d, J = 20.5, CH), 122.51 (s, CH), 122.47 (d, J = 19.8, CH), 122.05 (s,
2
6
1
after precipitation with ether. Yield: 87%. H NMR (300 MHz, acetone-
d6): δ 9.43 (brs, 2H), 8.44 (m, 2H), 8.33 (d, J = 5.8, 1H), 8.28 (brd, J =
8.8, 2H), 8.20 (dd, J = 1.8, J = 5.8, 1H), 8.17−8.07 (m, 7H), 8.01 (m,
3H), 7.65 (m, 3H), 7.31 (m, 2H), 6.82 (m, 2H), 5.87 (t, J = 2.6, 1H),
5.84 (t, J = 2.6, 1H). 13C APT NMR (75 MHz, acetone-d ): δ 165.10
CH), 118.15 (s, 2CH), 114.07 (d, J = 17.5, CH), 113.53 (d, J = 17.5,
CH), 97.90 (t, J = 27.0, 2CH). Anal. Calcd for (C H F IrN ·CH Cl ):
C, 48.63; H, 2.64; N, 8.34. Found: C, 48.97; H, 2.87; N, 8.21. Exact mass:
6
(brs, 2Cquat), 165.00 (dd, J = 12.2, J = 254.5, 2Cquat), 162.82 (dd, J = 12.5,
J = 257.3, 2Cquat), 158.54 (s, Cquat), 156.79 (s, Cquat), 155.62 (d, J = 6.3,
Cquat), 155.36 (d, J = 6.4, Cquat), 154.99 (s, Cquat), 153.88 (s, Cquat),
33
20
4
5
2
2
+
ESI-MS [C H F IrN + H] calcd m/z = 756.1362, found m/z =
33
20
4
5
7
56.1362.
Ir(ppy) (3)]PF , A3. The product was obtained as an orange solid
152.92 (s, CH), 152.70 (s, CH), 151.85 (s, Cquat), 151.41 (s, CH),
151.27 (s, CH), 141.23 (s, 2CH), 139.06 (s, Cquat), 137.82 (s, Cquat),
133.50 (s, CH), 133.27 (s, CH), 130.74 (s, 2CH), 130.16 (s, 3CH),
129.29 (s, 2Cquat), 127.97 (s, CH), 125.59 (s, 2CH), 125.04 (d, J = 22.5,
CH), 124.87 (s, 3CH), 124.72 (d, J = 20.8, CH), 124.24 (s, 2CH),
115.09 (d, J = 17.7, 2CH), 100.19 (t, J = 26.9, 2CH). Anal. Calcd for
[
2
6
1
after precipitation with ether. Yield: 95%. H NMR (300 MHz, acetone-
d ): δ 9.52 (d, J = 1.4, 1H), 8.35−8.22 (m, 4H), 8.16 (m, 3H), 8.07−7.96
6
(
(
6
1
m, 5H), 7.70−7.62 (m, 3H), 7.24 (ddd, J = 1.3, J = 6.0, J = 7.2, 1H), 7.11
ddd, J = 1.2, J = 7.4, J = 8.5, 1H), 7.00 (ddd, J = 1.3, J = 7.4, J = 8.7, 1H),
.45 (dd, J = 0.9, J = 7.5, 1H). 13C APT NMR (75 MHz, acetone-d ): δ
(C44H27BrF IrN PF ·CH COCH ): C, 47.40; H, 2.79; N, 7.06. Found:
6
4 6 6 3 3
C, 47.23; H, 2.88; N, 7.27. Exact mass: ESI-MS [C44H27BrF IrN ] calcd
4 6
+
69.25 (Cquat), 158.06 (Cquat), 154.86 (Cquat), 153.88 (Cquat), 152.24
(
1
1
CH), 151.98 (Cquat), 151.30 (Cquat), 150.66 (CH), 145.44 (Cquat),
40.15 (CH), 139.54 (Cquat), 133.23 (CH), 132.97 (CH), 131.76 (CH),
30.74 (2CH), 130.15 (2CH), 127.42 (CH), 126.33 (CH), 125.00
m/z = 987.1032, found m/z = 987.1014.
[Ir(Brppy)
(4)]PF
, C4. It was obtained as an orange solid. Yield: 98%.
): δ 9.40 (d, J = 1.7, 2H), 8.34 (m, 2H),
2
6
1
H NMR (300 MHz, acetone-d
6
(
CH), 124.85 (2CH), 124.22 (2CH), 124.13 (CH), 123.88 (CH),
8.27 (m, 3H), 8.18 (dd, J = 1.8, J = 5.9, 1H), 8.14 (brd, J = 8.7, 2H),
8.11−8.05 (m, 4H), 8.05−7.98 (m, 4H), 7.95 (dd, J = 5.7, J = 8.4, 2H),
7.69−7.62 (m, 3H), 7.35−7.25 (m, 4H), 6.46 (dd, J = 2.0, J = 3.1, 2H).
1
9
21.32 (CH). Anal. Calcd for (C H IrN PF ): C, 57.88; H, 3.47; N,
56 40 8 6
.64. Found: C, 58.02; H, 3.43; N, 9.41. Exact mass: ESI-MS
+
13
[
C H IrN ] calcd m/z = 1017.3005, found m/z = 1017.3030.
C APT NMR (75 MHz, acetone-d ): δ 167.71 (C ), 167.66 (C ),
5
6
40
8
6
quat
quat
[
Ir(Fppy) (3)]PF , B3. It was obtained as an orange solid. Yield: 34%.
158.66 (Cquat), 156.90 (Cquat), 154.94 (Cquat), 153.88 (Cquat), 153.59
(Cquat), 153.34 (Cquat), 152.77 (CH), 152.55 (CH), 151.64 (Cquat),
151.13 (CH), 150.97 (CH), 144.74 (Cquat), 144.72 (Cquat), 140.67
(2CH), 139.15 (Cquat), 137.58 (Cquat), 135.10 (CH), 135.07 (CH),
133.38 (CH), 133.25 (CH), 130.74 (2CH), 130.15 (2CH), 130.07
(CH), 128.13 (2CH), 127.87 (CH), 127.26 (2CH), 126.26 (2Cquat),
125.76 (2CH), 124.86 (2CH), 124.48 (CH), 124.25 (2CH), 121.90
(2CH). Anal. Calcd for (C H Br IrN PF ): C, 43.37; H, 2.40; N, 6.90.
2
6
1
H NMR (300 MHz, acetone-d ): δ 9.54 (s, 1H), 8.48 (brd, J = 9.5, 1H),
6
8
.35 (d, J = 5.8, 1H), 8.27 (brd, J = 8.8, 2H), 8.23−8.09 (m, 5H), 8.05−
7
6
.98 (m, 2H), 7.71−7.62 (m, 3H), 7.33 (ddd, J = 1.4, J = 5.8, J = 7.8, 1H),
13
.84 (ddd, J = 2.3, J = 9.3, J = 12.8, 1H), 5.90 (dd, J = 2.3, J = 8.5, 1H). C
APT NMR (75 MHz, acetone-d ): δ 165.22 (d, J = 6.8, Cquat), 164.96
6
(
1
dd, J = 12.8, J = 255.9, Cquat), 162.76 (dd, J = 12.8, J = 260.47, Cquat),
57.80 (s, Cquat), 156.08 (d, J = 6.8, Cquat), 154.93 (s, Cquat), 153.86 (s,
Cquat), 152.55 (s, CH), 151.88 (s, Cquat), 151.18 (s, CH), 141.18 (s, CH),
44
29
3
6
6
Found: C, 42.97; H, 2.83; N, 6.79. Exact mass: ESI-MS
+
1
1
1
39.33 (s, Cquat), 133.25 (s, CH), 130.73 (s, 2CH), 130.19 (s, 2CH),
29.30 (s, Cquat), 127.73 (s, CH), 125.57 (s, CH), 125.18 (s, CH),
24.85 (s, 2CH), 124.42 (s, CH), 124.22 (s, 2CH), 115.08 (d, J = 17.4,
[C H Br IrN ] calcd m/z = 1070.9607, found m/z = 1070.9579.
44
29
3
6
[Ir(ppy) (5)]PF , A5. It was obtained as an orange solid. Yield: 75%.
2
6
1
H NMR (300 MHz, acetone-d ): δ 9.55 (s, 1H), 8.48 (s, 1H), 8.32 (d, J
6
CH), 100.13 (t, J = 26.4, CH). Anal. Calcd for (C H F IrN PF ·
= 8.1, 1H), 8.26 (d, J = 5.8, 1H), 8.14 (m, 3H), 8.01 (m, 6H), 7.85 (pst, J
= 7.9, 1H), 7.63 (m, 2H), 7.24 (pst, J = 6.0, 1H), 7.11 (pst, J = 7.6, 1H),
6.99 (pst, J = 7.3, 1H), 6.46 (d, J = 7.4, 1H). C APT NMR (75 MHz,
5
6
36
4
8
6
CH COCH ): C, 54.84; H, 3.28; N, 8.67. Found: C, 55.24; H, 3.60; N,
3
3
+
13
8
.28. Exact mass: ESI-MS [C H F IrN ] calcd m/z = 1089.2628,
56
36
4
8
found m/z = 1089.2665.
acetone-d ): δ 173.48 (Cquat), 162.42 (Cquat), 158.89 (Cquat), 158.03
6
[
Ir(Brppy) (3)]PF , C3. It was obtained as an orange solid. Yield: 34%.
(Cquat), 156.55 (CH), 156.29 (Cquat), 156.06 (Cquat), 154.98 (CH),
149.76 (Cquat), 144.35 (CH), 143.00 (Cquat), 137.46 (CH), 137.28
(CH), 136.12 (CH), 136.07 (1C, CH), 135.82 (1C, CH), 135.04 (2C,
CH), 131.96 (1C, CH), 130.62 (CH), 129.40 (CH), 129.31 (CH),
128.71 (CH), 128.42 (2CH), 128.18 (CH), 128.09 (CH), 125.61 (CH).
Anal. Calcd for (C H IrN PF ): C, 57.88; H, 3.47; N, 9.64. Found: C,
2
6
1
H NMR (300 MHz, acetone-d ): δ 9.54 (d, J = 1.6, 1H), 8.38 (dd, J =
6
1
3
7
.2, J = 8.5, 1H), 8.32 (d, J = 5.8, 1H), 8.27 (brd, J = 8.8, 2H), 8.18 (m,
H), 8.09 (m, 2H), 8.02 (m, 2H), 7.98 (d, J = 8.4, 1H), 7.66 (m, 3H),
.33 (m, 2H), 6.51 (d, J = 2.0, 1H). 13C APT NMR (75 MHz, acetone-
d6): δ 167.88 (Cquat), 157.94 (Cquat), 154.93 (Cquat), 154.02 (Cquat),
53.88 (Cquat), 152.48 (CH), 151.68 (Cquat), 150.90 (CH), 144.76
Cquat), 140.64 (CH), 139.43 (Cquat), 135.14 (CH), 133.26 (CH),
30.74 (2CH), 130.17 (2CH), 128.16 (CH), 127.66 (CH), 127.20
CH), 126.31 (Cquat), 125.72 (CH), 124.86 (2CH), 124.30 (CH),
24.24 (2CH), 121.94 (CH). Anal. Calcd for (C H Br IrN PF ·
56
40
8
6
+
1
(
1
(
57.48; H, 3.61; N, 9.55. Exact mass: ESI-MS [C H IrN ] calcd m/z =
56 40 8
1017.3005, found m/z = 1017.2991.
[Ir(Fppy) (5)]PF , B5. It was obtained as a red solid. Yield: 85%. H
1
2
6
NMR (300 MHz, acetone-d ): δ 9.58 (d, J = 1.4, 1H), 8.48 (m, 2H), 8.37
6
1
(d, J = 5.8, 1H), 8.16 (m, 5H), 7.99 (d, J = 4.3, 1H), 7.97 (d, J = 2.1, 1H),
7.86 (pst, J = 7.9, 1H), 7.63 (m, 3H), 7.33 (pst, J = 6.6, 1H), 6.83 (ddd, J
56
38
2
8
6
CH Cl ): C, 48.73; H, 2.87; N, 7.98. Found: C, 48.94; H, 2.90; N, 8.12.
2
2
M
DOI: 10.1021/acs.organomet.5b00838
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
3
=
(
2.3, J = 9.4, J = 12.4, 1H), 5.92 (dd, J = 2.3, J = 8.6, 1H). C APT NMR
1H), 7.72−7.63 (m, 4H), 7.20 (dd, J = 1.9, J = 8.3, 1H), 6.59 (d, J = 1.9,
1H). 13C APT NMR (75 MHz, acetone-d ): δ 168.01 (2C ), 159.22
75 MHz, acetone-d ): δ 165.25 (d, J = 6.9, Cquat), 164.99 (dd, J = 12.5, J
6
6
quat
=
1
254.7, Cquat), 162.80 (dd, J = 12.91, J = 257.8, Cquat), 157.88 (s, Cquat),
56.18 (d, J = 6.3, Cquat), 154.57 (s, Cquat), 153.72 (s, Cquat), 152.57 (s,
CH), 152.36 (s, Cquat), 151.23 (s, CH), 141.19 (s, CH), 138.53 (s, Cquat),
(Cquat), 155.57 (2CH), 153.75 (Cquat), 151.25 (CH), 151.12 (Cquat),
144.86 (Cquat), 140.97 (CH), 135.54 (CH), 134.92 (CH), 130.98
(2CH), 127.58 (CH), 127.38 (CH), 125.93 (CH), 124.85 (2CH),
121.76 (CH), 120.37 (2CH). Anal. Calcd for (C H Br IrN PF ): C,
133.18 (s, CH), 131.88 (s, CH), 131.56 (s, CH), 130.75 (s, 2CH),
129.34 (s, Cquat), 127.98 (s, CH), 125.62 (s, CH), 125.35 (s, CH),
125.06 (d, J = 19.8, CH), 124.74 (s, CH), 124.14 (s, 2CH), 123.72 (s,
44
32
2
8
6
45.18; H, 2.76; N, 9.58. Found: C, 45.13; H, 2.68; N, 9.35. Exact mass:
+
ESI-MS [C H Br IrN ] calcd m/z = 1023.0746, found m/z =
44
32
2
8
CH), 115.13 (d, J = 16.1, CH), 100.13 (t, J = 27.0, CH). Anal. Calcd for
1023.0744.
(
5
C H F IrN PF ·CH COCH ): C, 54.84; H, 3.28; N, 8.67. Found: C,
[Ir(azoppy) (2,2′-bipyridine)]PF , D-bipy. [Ir(Brppy) (2,2′-
5
6
38
4
8
6
3
3
2
6
2
+
4.70; H, 3.29; N, 8.34. Exact mass: ESI-MS [C H F IrN ] calcd m/z
bipyridine)]PF (0.065 g, 0.068 mmol) and [4-(phenylazo)phenyl]-
56
36
4
8
6
=
1089.2628, found m/z = 1089.2600.
boronic acid 6 (0.036 g, 0.160 mmol) were dissolved in 4 mL of THF.
[
Ir(Brppy) (5)]PF , C5. It was obtained as an orange solid. Yield: 66%.
Na CO (1 M (aq), 2 mL) and Pd(PPh ) (0.0079 g, 0.0068 mmol)
2
6
2
3
3 4
1
H NMR (300 MHz, acetone-d ): δ 9.58 (d, J = 1.4, 1H), 8.49 (pst, J =
were added, and the solution was degassed by bubbling N for 15 min.
6
2
1
=
=
.7, 1H), 8.38 (brd, J = 8.8, 1H), 8.33 (d, J = 5.8, 1H), 8.20 (dd, J = 1.8, J
The reaction mixture was refluxed (80 °C) for 15 h. The resulting
mixture was cooled to room temperature, and the product was extracted
with CH Cl . The organic phase was dried with MgSO and filtered off,
5.8, 1H), 8.16 (brd, J = 5.4, 1H), 8.09 (m, 3H), 7.98 (m, 3H), 7.86 (t, J
7.9, 1H), 7.63 (m, 3H), 7.32 (m, 2H), 6.51 (d, J = 1.9, 1H). 13C APT
2
2
4
NMR (75 MHz, acetone-d ): δ 167.89 (Cquat), 158.01 (Cquat), 154.59
and the solvent was evaporated. The residue was purified by column
6
(
1
Cquat), 154.05 (Cquat), 153.72 (Cquat), 152.49 (CH), 152.14 (Cquat),
50.92 (CH), 144.77 (Cquat), 140.62 (CH), 138.59 (Cquat), 135.14
chromatography (silica gel, CH Cl ). To the fraction containing the
2
2
eluted complex was added 0.05 g of KPF , and the resulting solution was
6
(
(
(
CH), 133.19 (CH), 131.87 (CH), 131.51 (CH), 130.75 (2CH), 128.16
CH), 127.89 (CH), 127.20 (CH), 126.31 (Cquat), 125.72 (CH), 125.26
CH), 124.60 (CH), 124.12 (2CH), 123.75 (CH), 121.93 (CH). Anal.
filtered through a Celite pad. The title compound was obtained as an
orange solid. Yield: 10%.
1
H NMR (300 MHz, acetone-d ): δ 8.93 (d, J = 7.9, 1H), 8.42−8.33
6
Calcd for (C H Br IrN PF ): C, 50.96; H, 2.90; N, 8.49. Found: C,
5
z = 1173.1215, found m/z = 1173.1239.
(m, 3H), 8.11−8.01 (m, 3H), 7.98−7.89 (m, 4H), 7.79 (ddd, J = 1.1, J =
5.4, J = 7.4, 1H), 7.68−7.57 (m, 5H), 7.50 (dd, J = 1.9, J = 8.1, 1H), 7.28
(ddd, J = 1.3, J = 5.9, J = 7.3, 1H), 6.76 (d, J = 1.7, 1H). 13C APT NMR
56
38
2
8
6
+
1.12; H, 2.90; N, 8.10. Exact mass: ESI-MS [C H Br IrN ] calcd m/
56 38 2 8
General Procedure for the Synthesis of Complexes A2−C2. One
equivalent of the chloro-bridged iridium(III) dimer and 4.6 equiv of
AgOTf were dissolved in acetone and refluxed for 2 h. After cooling to
room temperature, AgCl was removed by centrifugation, and the
resulting solution was added over a 1 h refluxed suspension of 4 equiv of
(75 MHz, acetone-d ): δ 168.60 (Cquat), 157.43 (Cquat), 153.94 (Cquat),
6
153.00 (Cquat), 152.35 (CH), 152.28 (Cquat), 150.88 (CH), 145.61
(Cquat), 144.99 (Cquat), 142.59 (Cquat), 141.00 (CH), 140.20 (CH),
132.63 (CH), 130.97 (CH), 130.61 (2CH), 130.03 (CH), 128.93
(2CH), 126.79 (CH), 126.20 (CH), 125.21 (CH), 124.45 (2CH),
123.97 (2CH), 123.09 (CH), 121.70 (CH). Anal. Calcd for
(C H IrN PF ·CH COCH ): C, 57.88; H, 3.47; N, 9.64. Found: C,
4
-phenylazopyridine and NEt in acetone. The reaction mixture was
3
refluxed for 15 h. The products were purified by column
5
6
40
8
6
3
3
+
chromatography (silica gel, CH Cl ). When the unreacted iridium(III)
58.03; H, 3.68; N, 9.09. Exact mass: ESI-MS [C H IrN ] calcd m/z =
2
2
56 40 8
dimer eluted, KPF was added on top of the column, and the polarity of
the eluent was gradually increased to 100% acetone to elute the
1017.3005, found m/z = 1017.3036.
[Ir(azoppy) (1)]PF , D1. [Ir(Brppy) (1)]PF , C1 (0.150 g, 0.128
mmol), and [4-(phenylazo)phenyl]boronic acid 6 (0.07 g, 0.311 mmol)
6
2
6
2
6
complexes together with the excess of KPF . The desired compounds
6
were precipitated with ether after filtration through a Celite pad in
were dissolved in 5 mL of THF. Na CO (1 M (aq), 2.5 mL) and
2
3
CH Cl .
Pd(PPh ) (0.0148 g, 0.0128 mmol) were added, and the solution was
2
2
3 4
[
Ir(ppy) (2) ]PF , A2. It was obtained as an orange solid. Yield: 50%.
degassed by bubbling N for 15 min. The reaction mixture was refluxed
2
2
6
2
1
H NMR (300 MHz, acetone-d ): δ 9.11 (d, J = 5.3, 1H), 9.07 (brd, J =
(80 °C) for 15 h. The resulting mixture was cooled to room
6
6
7
7
.8, 2H), 8.20 (d, J = 7.6, 1H), 8.12 (ddd, J = 1.4, J = 7.4, J = 8.7, 1H),
.99 (brdd, J = 1.4, J = 8.1, 2H), 7.86 (brd, J = 6.7, 2H), 7.75 (m, 1H),
.68 (m, 3H), 7.59 (ddd, J = 1.5, J = 5.9, J = 7.4, 1H), 6.97 (m, 2H), 6.51
temperature, and the product was extracted with CH Cl . The organic
2
2
phase was dried with MgSO and filtered off, and the solvent was
4
evaporated. The residue was purified by column chromatography (silica
(
m, 1H). 13C APT NMR (75 MHz, acetone-d ): δ 169.33 (Cquat),
gel, CH Cl ). To the fraction containing the eluted complex was added
6
2
2
1
(
1
59.03 (Cquat), 155.47 (2CH), 153.76 (Cquat), 150.88 (CH), 149.03
Cquat), 145.58 (Cquat), 140.42 (CH), 134.85 (CH), 133.40 (CH),
31.72 (CH), 130.97 (2CH), 125.81 (CH), 125.18 (CH), 124.80
0.05 g of KPF , and the resulting solution was filtered through a Celite
6
pad. The title compound was obtained as a brown solid. Yield: 34%.
1
H NMR (300 MHz, DMSO-d ): δ 9.50 (s, 1H), 8.44 (d, J = 8.2, 1H),
6
(
(
2CH), 124.05 (CH), 121.18 (CH), 120.10 (2CH). Anal. Calcd for
8.28 (d, J = 5.9, 1H), 8.18−7.97 (m, 6H), 7.95−7.86 (m, 4H), 7.78−7.69
C H IrN PF ): C, 52.22; H, 3.39; N, 11.07. Found: C, 52.4; H, 2.95;
(m, 3H), 7.61 (brt, J = 6.7, 5H), 7.51 (d, J = 7.1, 1H), 7.30 (t, J = 6.4,
4
4
34
8
6
+
13
N, 11.33. Exact mass: ESI-MS [C H IrN ] calcd m/z = 867.2512,
1H), 6.57 (s, 1H). C APT NMR (75 MHz, DMSO-d ): δ 166.14
44
34
8
6
found m/z = 867.2520.
(Cquat), 158.35 (Cquat), 157.42 (Cquat), 152.25 (CH), 151.96 (Cquat),
151.89 (Cquat), 151.05 (Cquat), 150.61 (Cquat), 149.81 (CH), 144.18
(Cquat), 142.96 (Cquat), 140.25 (Cquat), 139.14 (CH), 133.86 (CH),
131.60 (CH), 129.88 (2CH), 129.49 (2CH), 128.81 (CH), 127.42
(2CH), 125.71 (CH), 124.34 (CH), 123.46 (2CH), 123.19 (2CH),
122.54 (2CH), 122.06 (CH), 121.75 (CH), 120.59 (CH), 119.18 (CH).
[
Ir(Fppy) (2) ]PF , B2. It was obtained as an orange solid. Yield: 48%.
2
2
6
1
H NMR (300 MHz, acetone-d ): δ 9.22 (d, J = 5.5, 1H), 9.09 (brd, J =
6
6
8
.7, 2H), 8.36 (d, J = 8.4, 1H), 8.22 (t, J = 7.8, 1H), 8.00 (brdd, J = 1.6, J =
.3, 2H), 7.91 (brd, J = 6.7, 2H), 7.68 (m, 4H), 6.71 (ddd, J = 2.3, J = 9.3,
13
J = 12.6, 1H), 6.01 (dd, J = 2.3, J = 8.5, 1H). C APT NMR (75 MHz,
acetone-d ): δ 165.32 (d, J = 7.1, Cquat), 164.57 (dd, J = 12.4, J = 254.2,
Anal. Calcd for (C68
H48IrN12PF ·CH COCH ): C, 59.70; H, 3.81; N,
6 3 3
6
Cquat), 162.06 (dd, J = 13.6, J = 257.5, Cquat), 159.31 (s, Cquat), 155.55 (s,
11.77. Found: C, 59.87; H, 4.04; N, 11.76. Exact mass: ESI-MS
+
2
1
1
2
CH), 153.76 (s, Cquat), 153.31 (d, J = 6.6, Cquat), 151.67 (s, CH),
41.53 (s, CH), 134.93 (s, CH), 130.98 (s, 2CH), 129.41 (s, Cquat),
25.80 (s, CH), 124.90 (d, J = 20.5, CH), 124.85 (s, 2CH), 120.49 (s,
CH), 115.82 (d, J = 18.0, CH), 100.32 (t, J = 27.1, CH). Anal. Calcd for
[C68H
48IrN12] calcd m/z = 1225.3754, found m/z = 1225.3784.
[Ir(azoppy) (2) ]PF , D2. [Ir(Brppy) (2) ]PF , C2 (0.120 g, 0.103
mmol), and [4-(phenylazo)phenyl]boronic acid pinacol ester 6′ (0.077
g, 0.250 mmol) were dissolved in 4 mL of THF. Na CO (1 M (aq), 2
mL) and Pd(PPh ) (0.012 g, 0.010 mmol) were added, and the solution
2
2
6
2
2
6
2
3
(
C H F IrN PF ·CH COCH ): C, 49.43; H, 3.18; N, 9.81. Found: C,
44 30 4 8 6 3 3
+
3 4
4
9.71; H, 3.02; N, 10.16. Exact mass: ESI-MS [C H F IrN ] calcd m/
was degassed by bubbling N for 15 min. The reaction mixture was
44
30
4
8
2
z = 939.2159, found m/z = 939.2178.
refluxed (80 °C) for 15 h. The resulting mixture was cooled to room
[
Ir(Brppy) (2) ]PF , C2. It was obtained as a dark orange solid. Yield:
temperature, and the product was extracted with CH Cl . The organic
2
2
6
2
2
1
4
8%. H NMR (300 MHz, acetone-d ): δ 9.14 (d, J = 5.8, 1H), 9.09 (brd,
phase was dried with MgSO and filtered off, and the solvent was
6
4
J = 6.7, 2H), 8.25 (d, J = 8.2, 1H), 8.17 (ddd, J = 1.4, J = 7.4, J = 8.7, 1H),
.00 (brdd, J = 1.4, J = 7.9, 2H), 7.89 (brd, J = 6.7, 2H), 7.75 (d, J = 8.4,
evaporated. The residue was purified by column chromatography (silica
8
gel, CH Cl ). To the fraction containing the eluted complex was added
2
2
N
DOI: 10.1021/acs.organomet.5b00838
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
0
.05 g of KPF , and the resulting solution was filtered through a Celite
Crystallographic information in the form of CIF files is also available
free from the Cambridge Crystallographic Data Centre: CCDC
1413074−1413078.
6
pad. The title compound was obtained as a dark red solid. Yield: 14%.
1
H NMR (300 MHz, acetone-d ): δ 9.28−9.20 (m, 2H), 8.28 (d, J =
6
7
7
.8, 1H), 8.17 (t, J = 8.1, 1H), 8.03−7.83 (m, 9H), 7.71−7.56 (m, 10H),
.34 (dd, J = 1.6, J = 8.2, 1H), 6.89 (d, J = 1.7, 1H). 13C APT NMR (75
ASSOCIATED CONTENT
Supporting Information
■
MHz, acetone-d ): δ 168.80 (Cquat), 159.08 (Cquat), 155.67 (CH),
6
*
S
1
53.95 (Cquat), 153.76 (Cquat), 153.03 (Cquat), 151.24 (CH), 149.69
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00838.
(
Cquat), 145.82(Cquat), 144.94 (Cquat), 142.62 (Cquat), 140.63 (CH),
1
1
34.86 (CH), 132.64 (CH), 131.47 (CH), 130.98 (2CH), 130.89 (CH),
30.62 (2CH), 129.03 (2CH), 126.33 (CH), 125.53 (CH), 124.82
(
1
5
2CH), 124.71 (CH), 124.45 (2CH), 124.00 (2CH), 123.37 (CH),
Details of UV−vis absorption spectra, X-ray analysis,
synthesis, photoisomerization studies, voltammograms,
and TD-DFT calculation (PDF)
21.61 (CH), 120.26 (CH). Anal. Calcd for (C H IrN PF ): C,
68 50 12 6
9.51; H, 3.67; N, 12.25. Found: C, 59.81; H, 3.40; N, 11.67. Exact mass:
+
ESI-MS [C H IrN ] calcd m/z = 1227.3911, found m/z =
1
6
8
50
12
Cartesian coordinates for the calculated compounds
227.3932.
Ir(azoppy) (3)]PF , D3. [Ir(Brppy) (3)]PF , C3 (0.150 g, 0.114
(XYZ)
[
2
6
2
6
Crystallographic data for 3 (CIF)
Crystallographic data for B1 (CIF)
Crystallographic data for A2 (CIF)
Crystallographic data for C3 (CIF)
Crystallographic data for A4 (CIF)
mmol), and [4-(phenylazo)phenyl]boronic acid pinacol ester 6′ (0.085
g, 0.276 mmol) were dissolved in 5 mL of THF. Na CO (1 M (aq), 2.5
2
3
mL) and Pd(PPh ) (0.013 g, 0.011 mmol) were added, and the solution
3
4
was degassed by bubbling N for 15 min. The reaction mixture was
2
refluxed (80 °C) for 15 h. The resulting mixture was cooled to room
temperature, and the product was extracted with CH Cl . The organic
2
2
phase was dried with MgSO and filtered off, and the solvent was
evaporated. The residue was purified by column chromatography (silica
4
AUTHOR INFORMATION
Corresponding Author
*E-mail: Zoraida_freixa@ehu.eus.
Notes
■
gel, CH Cl ). To the fraction containing the eluted complex was added
2
2
0
.05 g of KPF , and the resulting solution was filtered through a Celite
6
pad. The title compound was obtained as an orange solid. Yield: 24%.
1
H NMR (300 MHz, acetone-d ): δ 9.58 (s, 1H), 8.45 (t, J = 5.8, 2H),
6
The authors declare no competing financial interest.
8
.29 (d, J = 8.5, 2H), 8.24−8.09 (m, 7H), 8.04−7.99 (m, 2H), 7.98−7.92
(
m, 4H), 7.71 (m, 7H), 7.55 (dd, J = 1.8, J = 8.1, 1H), 7.34 (t, J = 6.8,
1
1
H), 6.83 (d, J = 1.7, 1H). 13C APT NMR (75 MHz, acetone-d ): δ
ACKNOWLEDGMENTS
6
■
68.69 (Cquat), 158.11 (Cquat), 154.89 (Cquat), 153.95 (Cquat), 153.88
This work was supported by MICINN (CTQ2011-23333),
SAIOTEK (S-PE13UN020), UPV-EHU (GIU13/06), and
Basque Government grant to J.P.-M. (BFI-2012-147MEC).
UPV-EHU Research Support Unit and SGI/IZO-SGIker are
acknowledged for technical assistance and generous allocation of
computational resources. We are indebted to Prof. V. V. Grushin,
whose comments inspired this work.
(
1
Cquat), 153.03 (Cquat), 152.61 (CH), 152.54 (Cquat), 151.41 (Cquat),
51.00 (CH), 145.70 (Cquat), 145.01 (Cquat), 142.67 (Cquat), 140.30
(
(
CH), 139.57 (Cquat), 133.26 (CH), 132.65 (CH), 131.01 (CH), 130.74
2CH), 130.62 (2CH), 130.14 (2CH), 129.98 (CH), 128.95 (2CH),
1
(
27.57 (CH), 126.87 (CH), 125.31 (CH), 124.86 (2CH), 124.49
2CH), 124.23 (2CH), 123.98 (2CH), 123.17 (CH), 121.79 (CH).
Anal. Calcd for (C H IrN PF ·H O): C, 62.37; H, 3.79; N, 10.91.
80
56
12
6
2
+
Found: C, 62.18; H, 3.62; N, 10.34. Exact mass: ESI-MS [C H IrN ]
80
56
12
calcd m/z = 1377.4380, found m/z = 1377.4351.
Ir(azoppy) (5)]PF , D5. [Ir(Brppy) (5)]PF , C5 (0.150 g, 0.114
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[
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.9, J = 7.3, 1H), 6.85 (d, J = 1.6, 1H). C APT NMR (75 MHz, acetone-
d6): δ 168.64 (Cquat), 158.14(Cquat), 154.57 (Cquat), 153.91 (Cquat),
53.72 (Cquat), 152.97 (Cquat), 152.53 (CH), 151.83 (Cquat), 151.31
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(
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1
40.27 (CH), 138.65 (Cquat), 133.18 (CH), 132.63 (CH), 131.84 (CH),
31.52 (CH), 131.01 (CH), 130.75 (2CH), 130.61 (2CH), 130.15
(
(
CH), 128.93 (2CH), 127.73 (CH), 126.87 (CH), 125.35 (CH), 125.19
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56
12
6
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0
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O
DOI: 10.1021/acs.organomet.5b00838
Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.5b00838
Organometallics XXXX, XXX, XXX−XXX