An Unprecedented Family of Luminescent Iridium(III) Complexes Bearing a Six-Membered Chelated Tridentate C^N^C Ligand

Article abstract of DOI:10.1021/acs.inorgchem.7b00328

A new family consisting of three luminescent neutral Ir(III) complexes with the unprecedented [Ir(C^N^C)(N^N)Cl] architecture, where C^N^C is a bis(six-membered) chelating tridentate tripod ligand derived from 2-benzhydrylpyridine (bnpy) and N^N is 4,4′-di-tert-butyl-2,2′-bipyridine (dtBubpy), is reported. X-ray crystallography reveals an unexpected and unusual double C-H bond activation of the two distal nonconjugated phenyl rings of the bnpy coupled with a very short Ir-Cl bond trans to the pyridine of the bnpy ligand. Depending on the substitution on the bnpy ligand, phosphorescence, ranging from yellow to red, is observed in dichloromethane solution. A combined study using density functional theory (DFT) and time-dependent DFT (TD-DFT) corroborates the mixed charge-transfer nature of the related excited states.

Full text of DOI:10.1021/acs.inorgchem.7b00328

Article
pubs.acs.org/IC
An Unprecedented Family of Luminescent Iridium(III) Complexes
Bearing a Six-Membered Chelated Tridentate C^N^C Ligand
Claus Hierlinger,†,‡ Thierry Roisnel,† David B. Cordes,‡ Alexandra M. Z. Slawin,‡ Denis Jacquemin,*,§,∥
Veronique Guerchais,*,† and Eli Zysman-Colman*,‡
́
†Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite
France
́
de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex,
‡Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife, KY16 9ST, United
Kingdom
§UMR CNRS 6230, Universite
́ ̀
de Nantes, CEISAM, 2 rue de la Houssiniere, 44322 Nantes Cedex 3, France
∥Institut Universitaire de France, 1, Rue Descartes, 75005 Paris Cedex 5, France
S
* Supporting Information
ABSTRACT: A new family consisting of three luminescent
neutral Ir(III) complexes with the unprecedented [Ir(C^N^C)-
(N^N)Cl] architecture, where C^N^C is a bis(six-membered)
chelating tridentate tripod ligand derived from 2-benzhydryl-
pyridine (bnpy) and N^N is 4,4′-di-tert-butyl-2,2′-bipyridine
(dtBubpy), is reported. X-ray crystallography reveals an
unexpected and unusual double C−H bond activation of the
two distal nonconjugated phenyl rings of the bnpy coupled with
a very short Ir−Cl bond trans to the pyridine of the bnpy ligand.
Depending on the substitution on the bnpy ligand, phosphor-
escence, ranging from yellow to red, is observed in dichloro-
methane solution. A combined study using density functional
theory (DFT) and time-dependent DFT (TD-DFT) corrobo-
rates the mixed charge-transfer nature of the related excited states.
and 489 nm in dichloromethane).25 By contrast, Zhu et al.18
INTRODUCTION
■
reported in 2005 the iridium(III) complex [Ir(bis[2-(N-
carbazolyl)pyridinato-N,C3′)picolinate] ([Ir(cpy)2(pic)]) con-
taining a six-membered chelating framework where the ligand is
fully conjugated, leading to yellow luminescence in the
recrystallized solid state with λem = 538 nm (ΦPL = 5%).
In an ongoing effort in our group to develop charged blue-
emitting phosphors for solution-processed light-emitting
electrochemical cells (LEECs) and organic light emitting
diodes (OLEDs), we investigated the coordination of 2-
benzhydrylpyridine (bnpyH2) derivatives with Ir(III) in order
to access six-membered chelate complexes T1−T3 (Figure 1a).
Surprisingly, given the prior art, upon sequential treatment of
IrCl3·6H2O with bnpyH2 and then 4,4′-di-tert-butyl-2,2′-
bipyridine (dtBubpy) in a one-pot reaction,26 T1 was not
obtained. Instead, neutral complex [Ir(bnpy)(dtBubpy)Cl], 1,
was isolated. The formation of 1 arises from a highly unusual
double C−H bond activation27 of the bnpyH2 ligand, which
binds to the iridium in a tripodal fashion. Following a similar
synthetic protocol, analogues 2 and 3, functionalized with
either electron-donating tert-butyl or electron-withdrawing
Nearly all of the photoactive iridium(III) complexes that are
used as emitters in electroluminescent devices,1−6 as dyes in
solar cells,7−9 in nonlinear optics (NLO),10−12 as photoredox
catalysts,13,14 as solar fuels,15 and in bioimaging16,17 contain
conjugated five-membered chelated ligands, such as the
commonly used 2-phenylpyridine (ppyH), 2,2′-bipyridine
(bpy), acetylacetonate (acac), and picolinate (pic). Photoactive
iridium complexes containing a six-membered cyclometalating
chelate are very rare, and the few reported examples can be
categorized into two families of complexes: those containing
conjugated18−21 or nonconjugated22−24 bidentate cyclometalat-
ing ligands. For instance, in 2008, Song et al.22 obtained a
phosphorescent Ir(III) complex [Ir(dfb-pz)2(fptz)] (where
(dfb-pz)H = 2,4-difluorobenzyl-N-pyrazole and fptz = 3-
trifluoromethyl-5-(2-pyridyl)triazole) containing a nonconju-
gated N-benzylpyrazole ligand to form a six-membered chelated
framework. This complex is a blue emitter in dichloromethane
with λem = 437 and 460 nm (ΦPL = 10% and τe = 0.10 μs). The
methylene spacer of the cyclometalated ligand effectively
interrupts the π-conjugation to produce a significant blue
shift, compared to [Ir(dFppy)2(fptz)] (where dFppyH = 2-
(2,4-difluorophenyl)pyridine, which uses a five-membered ring
chelate C^N ligand and the same ancillary ligand (λem = 460
Received: February 7, 2017
© XXXX American Chemical Society
A
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Figure 1. (a) Scheme for the proposed synthesis of the initial targets (T1−T3) and the synthesis of complexes 1−3. (a, i) IrCl3·6H2O, 2-
ethoxyethanol/H2O (3:1), reflux, 19 h; (ii) dtBubpy, reflux, 6 h. (b) aq. NH4PF6. (b) Solid-state structures of 1−3. Thermal ellipsoids correspond to
a 50% probability level. Solvent molecules are omitted for clarity.
trifluoromethyl groups meta to the Ir−C bonds, were obtained.
To the best of our knowledge, this is the first report of an
iridium complex of the form [Ir(C^N^C)(N^N)Cl] and one in
which the tridentate bis-cyclometalated ligand is a tripod
featuring two six-membered metallacycles.28 Indeed, the
complex with the closest binding motif is [Ir(bppy)(bpy)Cl],29
where bppy is 2-([1,1′-biphenyl]-3-yl)pyridine. This previous
complex possesses a related [Ir(C^C^N)(N^N)Cl] structure,
but the bppy ligand coordinates to the iridium in the more
commonly observed planar five-membered chelate fashion. It is
ethoxyethanol/H2O (3:1) was refluxed. After 19 h, dtBubpy
4,4′-di-tert-butyl-2,2′-bipyridyl was added at once, and heating
was continued for 6 h to give the neutral complexes 1−3 as
solids in a one-pot synthesis26 in 45%, 51%, and 55% yield,
respectively (Figure 1a). Complexes 1−3 were characterized by
1H, 13C, and, for 3, 19F NMR spectroscopy; ESI-HR mass
spectra; elemental analysis; and melting point determination
(see Figures S21−S30 in the Supporting Information (SI) for
NMR and ESI-HR mass spectra).
Crystal Structures. Single crystals of sufficient quality of
1−3 were grown from CH2Cl2/Et2O at −18 °C. The structures
of 1−3 were determined by single-crystal X-ray diffraction
(Figure 1b, Table S1).39 All three complexes possess a distorted
octahedral geometry with the tridentate tripod ligand
coordinated to the iridium to form two six-membered chelated
rings. Both cyclometalating carbon atoms are trans to the
pyridine rings of the dtBubpy, and the pyridyl unit of the bnpy-
type ligands is trans to the chloride. This contrasts with the
configuration of the Ir−Cl bond in previously reported Ir(III)
complexes,29,31,32,36,37,40,41 where an Ir−C bond is trans to the
chloride ligand. For 1−3, the Ir−Cl bond [2.375(3) Å for 1,
2.3612(8) Å for 2, and 2.369(2) Å for 3] is in the same range as
that found for [Ir(tpy)(dmbpy)Cl]2+ (2.357 Å, where tpy =
2,2′:6′,2″-terpyridine and dmbpy = 4,4′-dimethyl-2,2′-bipyr-
idine)42 but is significantly shorter (by ca. 0.1 Å) than the Ir−Cl
bond in other cyclometalated tridentate Ir(III) com-
plexes.29,31,32,36,37,40,41 Given the short Ir−CC^N^C bonds
[2.048(13) and 2.064(6) Å for 1, 2.028(4) and 2.031(3) Å
for 2, and 2.017(7) and 2.027 Å for 3], this leads also to a
correspondingly shorter Ir−NC^N^C bond [2.055(11) Å for 1,
2.044(3) for 2, and 2.032(7) Å for 3] compared to the Ir−
a very poorly luminescent near-IR emitter in CH2Cl2 (λem
=
725 nm, ΦPL = 8.4 × 10−2%). Ir(III) complexes bearing
monocyclometalating planar tridentate bis(five-membered)
chelate ligands (e.g., N^N^C29 or N^C^N30−35) and a
cyclometalating bidentate ligand, C^N, have on the other
hand been more widely explored, while Kozhevnikov has
reported dinuclear Ir(III) complexes with a bridging ligand
featuring two N^C^N motifs.36,37
RESULTS AND DISCUSSION
■
Synthesis. Compounds L1, L2, and L3 (Scheme 1) were
synthesized in two steps via a Grignard reaction38 followed by a
reduction step38 and obtained as solids in good yields. A
mixture of the corresponding proligand and IrCl3·6H2O in 2-
Scheme 1. Synthesis of Intermediates A1−A3 and Target
a
Ligands L1−L3
N
dtBubpy bonds [2.158(10) and 2.159(11) Å for 1, 2.127(3) and
2.140(3) Å for 2, and 2.122(6) and 2.133(5) Å for 3]. The bite
angle of the N^N ligand is unremarkable at 75.60(4)° for 1,
75.85(12)° for 2, and 76.1(2)° for 3 and in line with cationic
Ir(III) complexes of the form [Ir(C^N)2(N^N)]+.43−47 Owing
to the presence of the six-membered chelates, the C−Ir−C
bond angle is significantly larger (85.60(5)° for 1, 85.65(15)°
for 2, and 84.(3) for 3) than the NdtBubpy−Ir−NdtBubpy bond
angle.
a
(a, 1) Mg, 1,2-dibromoethane, THF, N2, reflux, 4 h. (2) Methyl
picolinate, THF, 0 °C to r.t., 90 min; (b, 1) HOAc, 57% HI. (2)
NaOHaq., 0 °C to r.t.; (c, 1) PBr3, reflux, 2 h. (2) Zn, HOAc, (3)
NaOHaq., 0 °C to r.t.
B
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Electrochemical Properties. The electrochemical behav-
ior for 1−3 was evaluated by cyclic voltammetry (CV) and
differential pulse voltammetry (DPV) in deaerated CH2Cl2
solution at 298 K at a scan rate of 50 mV s−1 using Fc/Fc+ as
the internal reference and referenced with respect to SCE.48
The electrochemistry data can be found in Table 1, and the
from the bnpy-type ligand. Complex 2 displays a lower
oxidation potential (0.80 V) than 1 (0.87 V), both of which are
notably lower than [Ir(mesppy)2(dtBubpy)]PF6 (E1/2;ox. = 1.17
V in deaerated CH2Cl2, where mesppy is 2-phenyl-4-mesityl-
pyridinato).49 Conversely, 3 shows a significantly anodically
shifted oxidation potential at 1.14 V. The CVs of 1−3 show
irreversible reduction waves that are monoelectronic as inferred
from the respective DPVs. DFT calculations (Figure 3a)
Table 1. Luminescent and Electrochemical Properties of
Complexes 1−3
a
a
,
b
c
d
e
f
λem
ΦPL
τe
kr × 10−5 knr × 10−5 Epa
f
[nm]
[%]
[ns]
[s−1 [s−1
]
]
[V] Epc [V]
1
2
3
619
630
581
8
318
239
718
2.52
2.51
3.62
28.93
39.33
10.31
0.87
0.80
1.14
−1.82
−1.81
−1.62
6
26
a
λexc = 420 nm, recorded at 298 K in deaerated CH2Cl2 solution.
[Ru(bpy)3]PF6 in MeCN as reference (ΦPL = 1.8% in aerated MeCN
b
at 298 K).51 λexc = 378 nm. kr = ΦPL/τe. knr = [(1 − ΦPL)/τe].
c
d
e
f
Measurements were carried out in degassed CH2Cl2 at a scan rate of
50 mV s−1 with Fc/Fc+ used as the internal reference, and referenced
with respect to SCE (Fc/Fc+ = 0.46 V in CH2Cl2).48
voltammograms are shown in Figure 2. All complexes exhibit a
quasi-reversible single electron oxidation peak, which is
attributed to the Ir(III)/Ir(IV) redox couple with contributions
Figure 3. (a) Representation of the four frontier MOs of 1. (b) Side
and top views of the spin density distribution for the lowest triplet
state (T1) of 1.
indicate that both the HOMO and HOMO−1, which are close
in energy (see Figure S34 in the SI), involve the iridium and
chloride atoms and the two phenyl rings of the bnpy ligand.
The LUMO is almost exclusively localized on the dtBubpy
ligand, while the LUMO+1 is primarily on the pyridyl ring of
the bnpy ligand. Therefore, we conclude that the reduction is
based on the ancillary ligand. The reduction potentials of 1 and
2 are each found at −1.82 V, while the reduction wave of 3 at
−1.62 V is anodically shifted by 200 mV compared to 1 and 2.
All three complexes are significantly more difficult to reduce
than [Ir(mesppy)2(dtBubpy)]PF6 (E1/2;red. = −1.15 V), which
also shows an irreversible reduction in CH2Cl2.49
Photophysical Properties. The normalized UV−vis
absorption spectra of 1−3 recorded in CH2Cl2 at 298 K are
depicted in Figure 4 and the data summarized in Table S2 in
the SI. All complexes show similar absorption profiles. The
invariance of the intense high-energy (ε on the order of (1−
1.5) × 104 M−1 cm−1) absorption bands below 300 nm are
1
ascribed to π−π* ligand-centered (1LC) transitions localized
Figure 2. Cyclic voltammograms (in solid lines) and differential pulse
voltammetry (in dotted lines) carried out in degassed CH2Cl2 at a scan
rate of 50 mV s−1, with Fc/Fc+ as the internal reference, referenced to
SCE (0.46 V vs SCE).48
Figure 4. Normalized UV−vis absorption and photoluminescence
spectra of 1−3 in CH2Cl2 at 298 K.
C
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mL) was added dropwise. The reaction mixture was heated under
stirring and kept at reflux for 4 h, resulting in a color change of the
solution to gray. The reaction mixture was then cooled in an ice bath,
and a solution of methyl picolinate (7.50 mmol, 1.00 equiv) in THF
(40 mL) was added carefully. The mixture turned dark gray−black.
The solution was allowed to warm to room temperature and was
stirred for 90 min. The reaction mixture was quenched with aqueous
NH4Cl and extracted with Et2O. The combined organic layers were
dried over MgSO4, and the solvent was evaporated, leaving a residue,
which was purified over silica (10% EtOAc in petroleum ether as the
solvent). The desired fractions were combined, and the solvent was
evaporated, leaving the title compound.
Diphenyl(pyridin-2-yl)methanol A1. Compound A1 was prepared
according to the general procedure and was obtained as a colorless
solid (1.686 g, 6.45 mmol). Yield: 86%. Rf: 0.51 (10% EtOAc in
petroleum ether on silica). Mp: 103 °C. Litt.52: 102−103 °C. 1H NMR
(400 MHz, CDCl3): δ 8.60 (d, J = 4.7 Hz, 1H), 7.64 (td, J = 7.8, 1.8
Hz, 1H), 7.40−7.21 (m, 11H), 7.12 (d, J = 7.9 Hz, 1H), 6.28 (s, 1H).
13C NMR (101 MHz, CDCl3): δ 163.2, 147.7, 146.1, 136.4, 128.1,
127.9, 127.3, 122.9, 122.3, 80.8. HR-MS (FTMS+) [M + H]+
Calculated (C18H15NOH): 262.1226. Found: 262.1226. CHN Calcd
for C18H15NO: C, 82.73; H, 5.79; N, 5.36. Found: C, 82.68; H, 5.73;
N, 5.41. The compound characterization is in agreement with that
previously reported.53
on the dtBubpy ligand. Two moderately intense bands (ε on
the order of (3−5) × 103 M−1 cm−1) in the region of 340−360
nm and 390−405 nm are assigned to mixed charge-transfer
transitions with the former consisting of more metal-to-ligand/
ligand-to-ligand charge-transfer (1MLCT/1LLCT) character
while the latter, according to TD-DFT calculations, implicate
an intraligand CT (1ILCT) from the phenyl rings to the pyridyl
heterocycle of the bnpy-type ligand (see Figure S34 and Table
S3 in the SI). Weak bands (ε on the order of 103 M−1 cm−1)
with onsets between 470 and 510 nm and tailing to 580 nm are
1
attributed to a mixture of MLCT/1LLCT and spin-forbidden
3MLCT/3LLCT transitions involving the dtBubpy ligand.
Introduction of the tert-butyl groups in 2 results in a small
red-shift of the CT bands below 340 nm, whereas the
trifluoromethyl groups in 3 produce a significant blue-shift of
these bands, trends that are corroborated by TD-DFT
calculations (Figure S35 in the SI).
The normalized photoluminescence (PL) spectra of 1−3 in
degassed CH2Cl2 are shown in Figure 4, and the data are
summarized in Table 1. Upon photoexcitation at 420 nm, all
complexes show a broad and unstructured profile, indicative of
an emission with mixed CT character. In line with the trends
observed in the absorption spectra and the oxidation potentials
in the CVs, the emission maxima are 581, 619, and 630 nm for
3, 1, and 2, respectively. These emission maxima match very
closely to the vertical phosphorescence energies calculated by
spin-unrestricted DFT, which predicts emissions at 573, 613,
and 622 nm, respectively. The calculations reveal that the
emissive triplet state is localized on the iridium, chlorine, and
dtBubpy but does not include significant contributions from the
bnpy ligand (Figures 3b and S36 in the SI). The photo-
luminescence quantum yield (ΦPL) of 1 is 8%, which is lower
than that of the yellow-emitting [Ir(ppy)2(dtBubpy)]PF6 (ΦPL
= 64% in CH2Cl2, λem = 570 nm, where ppyH is 2-
phenylpyridine).50 The ΦPL of 2 is 6% while that of 3 is
26%. All three complexes show emission lifetimes, τe, in the
submicrosecond regime. The radiative rate constants, kr, for 1
and 2 are similar (2.52 vs 2.51 × 105 s−1, respectively).
However, 2 exhibits a significantly larger nonradiative rate
constant, knr (39.33 × 105 s−1), compared to 1 (28.93 × 105
s−1). Complex 3 possesses both the largest kr (3.62 × 105 s−1)
and the smallest knr values (10.31 × 105 s−1) in accordance with
the energy gap law.
Bis(4-(tert-butyl)phenyl)(pyridin-2-yl)methanol A2. Compound
A2 was prepared according to the general procedure and was obtained
as a colorless solid (1.994 g, 5.34 mmol). Yield: 71%. Rf: 0.39 (10%
54
1
EtOAc in petroleum ether on silica). Mp: 156 °C. Litt. : 156 °C. H
NMR (400 MHz, CDCl3): δ 8.58 (d, J = 3.2 Hz, 1H), 7.67−7.60 (m,
1H), 7.33−7.28 (m, 4H), 7.24−7.12 (m, 6H), 6.19 (s, 1H), 1.30 (s,
18H). 13C NMR (101 MHz, CDCl3): δ 163.8, 150.1, 147.7, 143.3,
136.4, 127.9, 124.9, 123.1, 122.3, 80.6, 34.6, 31.5. HR-MS (FTMS+)
[M + H]+ Calculated (C26H31NOH): 374.2478. Found: 374.2476.
CHN Calcd for C26H31NO: C, 83.60; H, 8.37; N, 3.75. Found: C,
83.45; H, 8.51; N, 3.88. The compound characterization is in
agreement with that previously reported.54
Pyridin-2-ylbis(4-(trifluoromethyl)phenyl)methanol A3. Com-
pound A3 was prepared according to the general procedure and was
obtained as a beige solid (1.893 g, 4.76 mmol). Yield: 64%. Rf: 0.26
1
(10% EtOAc in petroleum ether on silica). Mp: 164 °C. H NMR
(400 MHz, CDCl3): δ 8.64 (d, J = 7.4 Hz, 1H), 7.75−7.69 (m, 1H),
7.60 (s, 4H), 7.44 (s, 4H), 7.31 (d, J = 8.5 Hz, 1H), 7.13 (d, J = 9.7
Hz, 1H), 6.50 (s, 1H). 13C NMR (101 MHz, CDCl3): δ 161.5, 149.4,
148.2, 136.9, 130.4, 130.1, 129.7, 129.4, 128.5, 125.2, 125.1, 125.1,
125.1, 123.1, 122.7, 80.4, 77.4, 77.1, 76.7. 19F NMR (376 MHz,
CDCl3): δ −62.59. HR-MS (FTMS+) [M + H]+ Calculated
(C20H13F6NOH): 398.0974. Found: 398.0965. CHN Calcd for
C20H13F6NO: C, 60.46; H, 3.30; N, 3.53. Found: C, 60.51; H, 3.36;
N, 3.59.
CONCLUSIONS
2-Benzhydrylpyridine L1. A mixture of A1 (0.837 g, 3.21 mmol),
aqueous 57% HI (2.5 mL), and HOAc (13 mL) was heated to 100 °C
for 4 h. The resulting mixture was then cooled to 0 °C and basified to
pH 9 with an aqueous NaOH solution (2 M). Ethyl acetate (100 mL)
was added, and the mixture was washed successively with an aqueous
NaHSO3 solution and brine. The combined organic layers were dried
over MgSO4, and the solvent was evaporated. The residue was purified
over silica (10% EtOAc in petroleum ether as the solvent). The
desired fractions were combined and the solvent evaporated leaving a
beige solid (0.788 g, 3.21 mmol). Yield: 74%. Rf: 0.3 (10% EtOAc in
petroleum ether on silica). Mp: 95 °C. 1H NMR (400 MHz, CDCl3):
δ 8.64 (d, J = 4.1 Hz, 1H), 7.66−7.59 (m, 1H), 7.33 (t, J = 7.3 Hz,
4H), 7.24 (dd, J = 21.8, 7.2 Hz, 6H), 7.18−7.10 (m, 2H), 5.76 (s, 1H).
13C NMR (101 MHz, CDCl3): δ 163.2, 149.5, 142.7, 136.4, 129.4,
128.4, 126.5, 123.8, 121.4, 59.4. HR-MS (FTMS+) [M + H]+
Calculated (C18H15NH): 246.1277. Found: 246.1277. The compound
characterization is in agreement with that previously reported.55
2-(Bis(4-(tert-butyl)phenyl)methyl)pyridine L2. A mixture of the
A2 (0.900 g, 2.41 mmol), aqueous 57% HI (2.70 mL), and HOAc
(13.20 mL) was heated to 100 °C for 4 h. The resulting mixture was
then cooled to 0 °C and basified to pH 9 with an aqueous NaOH
■
In conclusion, a new family of luminescent iridium(III)
complexes bearing an unprecedented tripodal bis(six-mem-
bered) chelate tridentate ligand has been prepared through a
highly unusual double cyclometalation reaction. The emission
can be tuned through substitution on the cyclometalating aryl
rings. DFT calculations support a mixed charge-transfer
emission. Current efforts are focused on further modulating
the electronics through a combination of modifications of the
ancillary di-imine and the monodentate chloride ligands. This
unprecedented tripodal ligand opens new perspectives for the
design of tridentate Ir luminophores.
EXPERIMENTAL SECTION
■
General Procedure for Compound A1−A3. An oven-dried flask
was charged under a nitrogen atmosphere with magnesium turnings
(0.911 g, 37.50 mmol, 5 equiv) and THF (80 mL) followed by 2 mL
of 1,2-dibromoethane. After the observation of gas evolution, the
corresponding bromo derivative (22.50 mmol, 3 equiv) in THF (40
D
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solution (2 M). Ethyl acetate (100 mL) was added, and the mixture
was washed successively with an aqueous NaHSO3 solution and brine.
The combined organic layers were dried over MgSO4, and the solvent
was evaporated. The residue was purified over silica (10% EtOAc in
petroleum ether as the solvent). The desired fractions were combined
and the solvent evaporated, yielding the title compound as oil (0.655 g,
1.83 mmol). Yield: 76%. Rf: 0.33 (10% EtOAc in petroleum ether on
silica). 1H NMR (400 MHz, CDCl3): δ 8.62−8.56 (m, 1H), 7.62−7.56
(m, 1H), 7.31 (s, 4H), 7.10 (s, 6H), 5.62 (s, 1H), 1.29 (s, 18H). 13C
NMR (126 MHz, CDCl3): δ 163.8, 149.6, 149.2, 139.9, 136.5, 129.0,
125.4, 123.9, 121.4, 58.7, 34.5, 31.5. HR-MS (ASAP+) [M + H]+
Calculated (C26H31NH): 358.2535. Found: 358.2534.
as a yellow solid (0.096 g, 0.11 mmol). Yield: 55%. Mp: 324 °C
(decomp.). 1H NMR (400 MHz, CD2Cl2): δ 8.59 (d, J = 5.8 Hz, 2H),
8.44 (d, J = 2.0 Hz, 2H), 7.98 (d, J = 2.0 Hz, 2H), 7.62−7.48 (m, 4H),
7.37 (d, J = 7.7 Hz, 2H), 7.20−7.15 (m, 3H), 6.50 (ddd, J = 7.5, 5.9,
1.7 Hz, 1H), 5.46 (s, 1H), 1.51 (s, 18H). 13C NMR (126 MHz,
CD2Cl2): δ 163.5, 163.3, 157.3, 151.9, 151.1, 147.4, 142.2, 137.6,
134.7, 127.6, 126.7, 124.5, 124.3, 123.5, 123.4, 121.2, 119.4, 69.2, 36.0,
30.8. 19F NMR (376 MHz, CD2Cl2): δ −61.58. [M−Cl]+ Calculated
(C38H35F6IrN3): 840.2364. Found: 840.2379. CHN Calcd for
C38H35F6IrN3: C, 52.14; H, 4.03; N, 4.80. Found: C, 52.10; H, 4.16;
N, 4.74.
2-(Bis(4-(trifluoromethyl)phenyl)methyl)pyridine L3. A mixture of
A3 (0.500 g, 1.26 mmol, 1 equiv) and PBr3 (25 mL) was vigorously
stirred and heated and kept at 110 °C for 2 h. The mixture was then
cooled to r.t. and was carefully poured onto ice, and aqueous NaOH (2
M) was added until the pH was neutral. The organic layer was dried
over MgSO4, and the solvent was evaporated, leaving a residue which
was dissolved in acetic acid (50 mL). Then, zinc dust (0.799 g, 12.60
mmol, 10 equiv) was added. The mixture was stirred at r.t. After 1 h,
20 mL of water was carefully added, and aqueous NaOH (2 M) was
added until the pH was neutral. The organic layer was dried over
MgSO4, and the solvent was evaporated, leaving a residue which was
purified over silica (10% EtOAc in petroleum ether as the solvent).
The desired fractions were combined, and the solvent was evaporated,
leaving colorless oil (0.117 mg, 0.31 mmol). Yield: 24%. Rf: 0.55 (20%
EtOAc in petroleum ether on silica). 1H NMR (400 MHz, CDCl3): δ
8.63 (ddd, J = 4.9, 1.9, 0.9 Hz, 1H), 7.66 (td, J = 7.7, 1.9 Hz, 1H), 7.57
(d, J = 8.2 Hz, 4H), 7.30 (d, J = 8.1 Hz, 4H), 7.20 (ddd, J = 7.6, 4.8,
1.1 Hz, 1H), 7.10 (dt, J = 7.9, 1.1 Hz, 1H), 5.75 (s, 1H). 13C NMR
(126 MHz, CDCl3): δ 161.4, 150.1, 146.0, 137.0, 129.8, 129.3, 125.7,
125.3, 124.0, 122.2, 58.9. 19F NMR (376 MHz, CDCl3): δ −62.50.
HR-MS (FTMS+) [M + H]+ Calculated (C20H13F6NH): 382.1030.
Found: 382.1023.
General Procedure for the One-Pot Protocol. A mixture of the
corresponding ligand (1.2 equiv) and IrCl3·6H2O (1 equiv) in 2-
ethoxyethanol (15 mL) and H2O (5 mL) was heated under stirring to
125 °C. After 19 h, 4,4′-di-tert-butyl-2,2′-bipyridine (1.5 equiv) was
added, and heating was continued. After 6 h, the solvent was
evaporated, leaving a solid, which was filtered over silica (1% MeOH in
CH2Cl2). The desired fractions were combined, and the solvent was
evaporated, leaving a solid which was washed with diethyl ether. After
filtration, the desired complex was obtained as a solid.
[Ir(bnpy)(dtBubpy)Cl] (1). The general one-pot protocol using
0.114 g (0.38 mmol) of IrCl3·6H2O was followed, and 1 was obtained
as a red solid (0.127 g, 0.0.13 mmol). Yield: 45%. Mp: 320 °C
(decomp.). 1H NMR (400 MHz, CD2Cl2): δ 8.75 (d, J = 5.8 Hz, 2H),
8.42 (d, J = 1.7 Hz, 2H), 7.70 (dd, J = 7.3, 1.4 Hz, 2H), 7.53 (d, J = 7.5
Hz, 1H), 7.49 (dd, J = 5.9, 1.9 Hz, 3H), 7.24 (dd, J = 7.1, 1.6 Hz, 2H),
7.19 (d, J = 5.9 Hz, 1H), 6.90 (dtd, J = 26.4, 7.3, 1.5 Hz, 4H), 6.45−
6.39 (m, 1H), 5.28 (s, 1H), 1.50 (s, 18H). 13C NMR (126 MHz,
CD2Cl2): δ 165.4, 162.6, 157.4, 151.8, 151.3, 143.9, 141.4, 138.7,
137.0, 125.8, 124.0, 123.8, 123.4, 122.7, 122.1, 120.8, 69.7, 35.9, 30.8.
HR-MS (ASAP+) [M−Cl]+ Calculated (C36H37IrN3): 704.2618.
Found: 704.2618. CHN Calcd for C36H37ClIrN3·3/2 H2O: C, 56.42;
H, 5.26; N, 5.48. Found: C, 56.45; H, 5.24; N, 5.28.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b00328. The research data supporting this work can
be accessed at: http://dx.doi.org/10.17630/f6e8e203-82a9-
406b-977e-308da1021de1.
■
S
NMR and MS spectra for all precursors, C^N^C ligands
and complexes, supplementary crystallographic data,
supplementary electrochemical and photophysical data,
description of the DFT/TD-DFT protocol, and supple-
mentary DFT and TD-DFT computational results
(PDF)
X-ray crystallographic structures of 1−3, CCDC:
1519101−1519103 (CIF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: Denis.Jacquemin@univ-nantes.fr.
*E-mail: veronique.guerchais@univ-rennes1.fr.
*E-mail: eli.zysman-colman@st-andrews.ac.uk. Web: http://
www.zysman-colman.com.
■
ORCID
Denis Jacquemin: 0000-0002-4217-0708
Eli Zysman-Colman: 0000-0001-7183-6022
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
C.H. acknowledges the Reg
́
ion Bretagne, France for funding.
E.Z.-C. acknowledges the University of St. Andrews and
EPSRC (EP/M02105X/1) for financial support. We thank
Umicore AG for the gift of materials. We thank the EPSRC UK
National Mass Spectrometry Facility at Swansea University for
analytical services. T.R. thanks the FEDER funds for financial
support helping the acquisition of the D8Venture diffractom-
eter of ISCR. D.J. acknowledges the European Research
Council and the Region des Pays de la Loire for financial
́
[Ir(dtBubnpy)(dtBubpy)Cl] 2. The general one-pot protocol using
0.088 g (0.30 mmol) of IrCl3·6H2O was followed, and 2 was obtained
as a red solid (0.129 g, 0.15 mmol). Yield: 51%. Mp: 331 °C
(decomp.). 1H NMR (400 MHz, CD2Cl2): δ 8.79 (d, J = 5.9 Hz, 2H),
8.42 (d, J = 2.0 Hz, 2H), 7.80 (d, J = 2.1 Hz, 2H), 7.49−7.42 (m, 4H),
7.13 (d, J = 7.7 Hz, 3H), 6.89 (dd, J = 7.7, 2.1 Hz, 2H), 6.38 (ddd, J =
7.0, 5.9, 2.0 Hz, 1H), 5.22 (s, 1H), 1.51 (s, 18H), 1.32 (s, 18H). 13C
NMR (126 MHz, CD2Cl2): δ 166.0, 162.6, 157.5, 151.7, 151.3, 147.8,
141.1, 140.4, 136.8, 135.9, 123.7, 123.6, 122.7, 122.4, 120.8, 118.8,
68.6, 35.9, 34.9, 32.1, 30.9. [M−Cl]+ Calculated (C44H53IrN3)
816.3869. Found: 816.3867. CHN Calcd for C44H53ClIrN3: C,
62.06; H, 6.27; N, 4.93. Found: C, 61.96; H, 6.31; N, 5.02.
support in the framework of a Starting Grant (Marches
-278845) and the LUMOMAT RFI project, respectively. This
research used computational resources of (1) the GENCI-
CINES/IDRIS, (2) the CCIPL (Centre de Calcul Intensif des
Pays de Loire), (3) a local Troy cluster.
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