Green-emitting iridium(iii) complexes containing sulfanyl- or sulfone-functionalized cyclometallating 2-phenylpyridine ligands

Article abstract of DOI:10.1039/c3dt53626b

A series of [Ir(C^N)₂(bpy)][PF₆] complexes in which the cyclometallating ligands contain fluoro, sulfane or sulfone groups is reported. The conjugate acids of the C^N ligands in the complexes are 2-(4-fluorophenyl)pyridine (H1), 2-(4-methylsulfonylphenyl)pyridine (H3), 2-(4-^tbutylsulfanylphenyl)pyridine (H4), 2-(4- ^tbutylsulfonylphenyl)pyridine (H5), 2-(4- ⁿdodecylsulfanylphenyl)pyridine (H6), 2-(4- ⁿdodecylsulfonylphenyl)pyridine (H7). The single crystal structures of H3 and H5 are described. [Ir(C^N)₂(bpy)][PF₆] with C^N = 1, 3, 4, 5 and 7 were prepared from the appropriate [Ir₂(C^N) ₄Cl₂] dimer and bpy; the structure of [Ir ₂(3)₄Cl₂]·2CH₂Cl₂ was determined. [Ir(6)₂(bpy)][PF₆] was prepared by nucleophilic substitution starting from [Ir(1)₂(bpy)][PF ₆]. The [Ir(C^N)₂(bpy)][PF₆] complexes have been characterized by NMR, IR, absorption and emission spectroscopic and mass spectrometric methods. The single crystal structures of enantiomerically pure Δ-[Ir(1)₂(bpy)][PF₆] and of rac-4{[Ir(1) ₂(bpy)][PF₆]}·Et₂O·2CH ₂Cl₂ are described, and the differences in inter-cation packing in the structures compared. [Ir(1)₂(bpy)][PF₆], [Ir(4)₂(bpy)][PF₆] and [Ir(6)₂(bpy)][PF ₆] (fluoro and sulfane substituents) are yellow emitters (λmaxem between 557 and 577 nm), and the room temperature solution emission spectra are broad. The sulfone derivatives [Ir(3)₂(bpy)] [PF₆], [Ir(5)₂(bpy)][PF₆] and [Ir(7) ₂(bpy)][PF₆] are green emitters and the emission spectra are structured (λmaxem = 493 and 523 to 525 nm). High photoluminescence quantum yields (PLQYs) of 64-74% are observed for the sulfone complexes in degassed solutions. The emission lifetimes for the three complexes containing sulfone substituents are an order of magnitude longer (2.33 to 3.36 μs) than the remaining complexes (0.224 to 0.528 μs). Emission spectra of powdered solid samples have also been recorded; the broad emission bands have values of λmaxem in the range 532 to 558 nm, and PLQYs for the powdered compounds are substantially lower (≤23%) than in solution. Trends in the redox potentials for the [Ir(C^N)₂(bpy)][PF₆] complexes are in accord with the observed emission behaviour. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c3dt53626b

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Green-emitting iridium(III) complexes containing
sulfanyl- or sulfone-functionalized
cyclometallating 2-phenylpyridine ligands†
Cite this: Dalton Trans., 2014, 43,
5343
Edwin C. Constable,* Cathrin D. Ertl, Catherine E. Housecroft* and
Jennifer A. Zampese
A series of [Ir(C^N)2(bpy)][PF6] complexes in which the cyclometallating ligands contain fluoro, sulfane or
sulfone groups is reported. The conjugate acids of the C^N ligands in the complexes are 2-(4-fluoro-
phenyl)pyridine (H1), 2-(4-methylsulfonylphenyl)pyridine (H3), 2-(4-tbutylsulfanylphenyl)pyridine (H4),
2-(4-tbutylsulfonylphenyl)pyridine (H5), 2-(4-ndodecylsulfanylphenyl)pyridine (H6), 2-(4-ndodecylsulfo-
nylphenyl)pyridine (H7). The single crystal structures of H3 and H5 are described. [Ir(C^N)2(bpy)][PF6] with
C^N = 1, 3, 4, 5 and 7 were prepared from the appropriate [Ir2(C^N)4Cl2] dimer and bpy; the structure of
[Ir2(3)4Cl2]·2CH2Cl2 was determined. [Ir(6)2(bpy)][PF6] was prepared by nucleophilic substitution starting
from [Ir(1)2(bpy)][PF6]. The [Ir(C^N)2(bpy)][PF6] complexes have been characterized by NMR, IR, absorption
and emission spectroscopic and mass spectrometric methods. The single crystal structures of enantio-
merically pure Δ-[Ir(1)2(bpy)][PF6] and of rac-4{[Ir(1)2(bpy)][PF6]}·Et2O·2CH2Cl2 are described, and the
differences in inter-cation packing in the structures compared. [Ir(1)2(bpy)][PF6], [Ir(4)2(bpy)][PF6] and
max
[Ir(6)2(bpy)][PF6] (fluoro and sulfane substituents) are yellow emitters (λ
between 557 and 577 nm), and
em
the room temperature solution emission spectra are broad. The sulfone derivatives [Ir(3)2(bpy)][PF6],
max
[Ir(5)2(bpy)][PF6] and [Ir(7)2(bpy)][PF6] are green emitters and the emission spectra are structured (λ
=
em
493 and 523 to 525 nm). High photoluminescence quantum yields (PLQYs) of 64–74% are observed for
the sulfone complexes in degassed solutions. The emission lifetimes for the three complexes containing
sulfone substituents are an order of magnitude longer (2.33 to 3.36 μs) than the remaining complexes
(0.224 to 0.528 μs). Emission spectra of powdered solid samples have also been recorded; the broad
emission bands have values of λmemax in the range 532 to 558 nm, and PLQYs for the powdered compounds
are substantially lower (≤23%) than in solution. Trends in the redox potentials for the [Ir(C^N)2(bpy)][PF6]
complexes are in accord with the observed emission behaviour.
Received 25th December 2013,
Accepted 2nd February 2014
DOI: 10.1039/c3dt53626b
www.rsc.org/dalton
(Hdfppy), and to a lesser extent 2-(4-fluorophenyl)pyridine,
are regularly employed to achieve blue-shifted emissions in
Introduction
Iridium(III) [Ir(C^N)2(N^N)]+ complexes incorporating cyclo- [Ir(C^N)2(N^N)]+ complexes.1,5–7 Bolink, Frey and coworkers8
metallating (C^N) and N,N-chelating (N^N) ligands offer an adapt- have shown that the number (one or two) and positions of sub-
able family of emissive ionic materials for use in light-emitting stitution of fluorine substituents in 2-phenylpyridine (Hppy)
electrochemical cells (LECs).1–4 In [Ir(C^N)2(N^N)]+ cations, have little effect on the photophysical and electrochemical pro-
the localization of the HOMO and LUMO on the iridium/C^N perties of [Ir(C^N)2(4,4′-tBu2bpy)][PF6] complexes (4,4′-tBu2bpy =
domain and on the N^N ligands respectively, facilitates 4,4′-di-tert-butyl-2,2′-bipyridine). However, significantly for
manipulation of the HOMO–LUMO separation by judicious application in LECs, increasing the number of fluorine atoms
choice of ligand substituents. Stabilization of the HOMO has results in shorter lived LECs.
been achieved by introducing electron-withdrawing substitu-
Less well explored than the use of fluoro-substituents is the
ents onto the C^N ligands, and 2-(2,4-difluorophenyl)pyridine incorporation of SR, SOR and SO2R electron-withdrawing sub-
stituents, either for functionalization of the C^N9–13 or N^N
ligand.14 Among these earlier studies is the use of 1-(4-(methyl-
sulfonyl)phenyl)-1H-pyrazole (Hmsppz) as the cyclometallating
Department of Chemistry, University of Basel, Spitalstrasse 51, CH-4056 Basel,
Switzerland. E-mail: catherine.housecroft@unibas.ch
†CCDC 972690–972694. For crystallographic data in CIF or other electronic
ligand in a series of green emitting [Ir(msppz)2(N^N][PF6] com-
plexes which perform efficiently under bias in LECs.13 The
format see DOI: 10.1039/c3dt53626b
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Cp2Fe was used as internal reference and was added at the end
of each experiment.
Solution emission spectra were recorded in MeCN on a
Shimadzu 5301PC spectrofluorophotometer. Solution quantum
yields were measured using
a Hamamatsu absolute PL
quantum yield spectrometer C11347 Quantaurus_QY. Life-
times and emission spectra of powdered samples were
measured using a Hamamatsu Compact Fluorescence lifetime
Spectrometer C11367 Quantaurus-Tau.
Scheme 1 Structures of the conjugate acids of the C^N ligands with
labelling for NMR spectroscopic assignments.
Compound H1 was prepared as reported in the literature19
and the spectroscopic properties matched those reported.20,21
[Ir2(COD)2Cl2]22 (COD = cycloocta-1,5-diene) and [Ir2(1)4Cl2]6
were prepared according to literature methods. All solvents
were dried before use. Silica and alumina were purchased
from Fluka (silica gel 60, 0.040–0.063 mm and activated,
neutral aluminium oxide).
achievement of both high luminances and efficiencies under
low driving voltages13 suggest that sulfone-functionalized
cyclometallating ligands may be a viable alternative to the
more commonly employed fluoro-substituted C^N ligands.
We present here a systematic study of the effects of functio-
nalizing the cyclometallating Hppy ligand with increasingly
electron-withdrawing substituents in the 4-position of the
phenyl ring. Our aim was to apply the series of ligands shown
in Scheme 1. Since the influence of fluoro-substituents is
rather well understood, ligand H1 was chosen to provide the
benchmark complex [Ir(1)2(N^N)]+ to which to relate the pro-
perties of the sulfane and sulfone derivatized complexes. The
increase in electron-withdrawing properties on changing from
SMe and SO2Me in compounds H2 to H3 (Scheme 1) is
reflected in the different Hammett parameters (SMe, σm 0.15,
σp 0.00; SO2Me, σm 0.60, σp 0.72),15–17 and one of us has ob-
served that on going from [Ru(tpy)2]2+ to [Ru(4′-MeO2Stpy)2]2+
(tpy = 2,2′:6′,2″-terpyridine, 4′-MeO2Stpy = 4′-methylsulfonyl-
2,2′:6′,2″-terpyridine), the sulfone unit causes a switch from a
non-emissive complex in fluid solution to emissive behaviour
in MeCN solution.18 The pairs of ligands H4/H5 and H6/H7
were selected to investigate the added effects of introducing
bulky (tbutyl) and long-chain (dodecyl) thiol and sulfone
substituents.
Compound H2. Compound H2 has been previously
reported23 but the following procedure gives a higher yield.
Compound H1 (617 mg, 3.56 mmol) and an excess of NaSMe
(1.06 g, 14.3 mmol) were added to N-methyl-2-pyrrolidone
(NMP) (18 mL) in a microwave vial. The violet reaction mixture
was heated at 80 °C for 1 h in a microwave reactor to give a
dark brown suspension. This was poured into a mixture of
H2O and brine (3 : 1, 100 mL). The resulting yellow precipitate
was separated by filtration, dissolved in CH2Cl2 and dried over
Na2SO4. The solvent was removed under reduced pressure
to yield H2 as a yellow solid (0.665 g, 3.30 mmol, 92.7%). M.p.
1
59.5 °C. H NMR (500 MHz, CDCl3) δ/ppm 8.67 (ddd, J = 4.9,
1.9, 1.0 Hz, 1H, HB6), 7.93 (m, 2H, HA2), 7.76–7.67 (overlapping
m, 2H, HB3+B4), 7.34 (m, 2H, HA3), 7.21 (ddd, J = 7.3, 4.8,
1.4 Hz, 1H, HB5), 2.53 (s, 3H, HMe). 13C{1H} NMR (126 MHz,
CDCl3) δ/ppm 157.0 (CB2), 149.8 (CB6), 139.9 (CA4), 136.9 (CB4),
136.2 (CA1), 127.3 (CA2), 126.5 (CA3), 122.1 (CB5), 120.2 (CB3),
15.7 (CMe). IR (solid, ν/cm−1) 3086 (w), 3046 (w), 3002 (w), 2981 (w),
2919 (w), 1982 (w), 1910 (w), 1767 (w), 1661 (w), 1605 (w),
1583 (s), 1569 (s), 1552 (m), 1498 (w), 1458 (s), 1431 (s), 1399 (m),
1322 (w), 1296 (w), 1256 (w), 1227 (w), 1190 (m), 1154 (w),
1121 (w), 1098 (m), 1089 (m), 1057 (w), 1008 (m), 988 (m),
969 (w), 958 (m), 884 (w), 830 (m), 772 (s), 738 (s), 725 (m),
Experimental
General
A Biotage Initiator 8 reactor was used for syntheses under 708 (m), 675 (w), 636 (w), 616 (w), 569 (w), 544 (w), 484 (m),
microwave conditions.
461 (m). ESI-MS m/z 202.0 [M + H]+ (calc. 202.1). Found C 71.43,
1H and 13C spectra were recorded at 295 K on a Bruker H 5.57, N 6.75; C12H11NS requires C 71.60, H 5.51, N 6.96%.
Avance III-500 spectrometer; chemical shifts are referenced to Compound H3. Compound H2 (1.00 g, 4.97 mmol) and
residual solvent peaks with δ(TMS) = 0 ppm. Solution absorp- sodium tungstate dihydrate (819 mg, 2.48 mmol) were dis-
tion spectra were recorded on an Agilent 8453 spectro- solved in MeOH (35 mL). H2O2 (30%, 1.20 mL, 1.36 g) was
photometer, and FT-IR spectra on a Perkin Elmer Spectrum Two added and the mixture was stirred overnight at room tempera-
UATR instrument. Electrospray ionization (ESI) and MALDI- ture. The suspension was poured into a mixture of H2O and
TOF mass spectra were recorded on Bruker esquire 3000plus brine (3 : 1, 200 mL) and extracted with CH2Cl2 (3 × 100 mL).
and Bruker Daltronics Microflex mass spectrometers, respect- The combined organic phases were dried over Na2SO4 and the
ively. LC-ESI-MS employed a combination of Shimadzu (LC) solvent was removed under reduced pressure to yield H3 as
and Bruker AmaZon X instruments. Electrochemical measure- a white powder (1.14 g, 4.89 mmol, 98.4%). M.p. 134.5 °C.
ments were carried out using cyclic voltammetry and using a 1H NMR (500 MHz, CDCl3) δ/ppm 8.75 (ddd, J = 4.7, 1.8,
CH Instruments 900B potentiostat with glassy carbon working 1.0 Hz, 1H, HB6), 8.21 (m, 2H, HA2), 8.10–7.99 (m, 2H, HA3),
and platinum auxiliary electrodes; a silver wire was used as a 7.87–7.75 (m, 2H, HB3+B4), 7.34 (ddd, J = 7.0, 4.8, 1.6 Hz, 1H,
pseudo-reference electrode. Solvent was dry, purified MeCN HB5), 3.09 (s, 3H, HMe). 13C{1H} NMR (126 MHz, CDCl3) δ/ppm
and 0.1 M [nBu4N][PF6] was used as supporting electrolyte. 155.4 (CB2), 150.2 (CB6), 144.7 (CA1), 140.7 (CA4), 137.3 (CB4),
5344 | Dalton Trans., 2014, 43, 5343–5356
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128.0 (CA3), 127.9 (CA2), 123.5 (CB5), 121.3 (CB3), 44.7 (CMe). Found C 65.41, H 6.31, N 5.14; C15H17NO2S requires C 65.43,
IR (solid, ν/cm−1) 3000 (w), 2921 (w), 1586 (m), 1563 (w), H 6.22, N 5.09%.
1465 (m), 1435 (m), 1392 (w), 1314 (w), 1292 (s), 1185 (w),
Compound H6. NaH (60% suspension in mineral oil,
1146 (s), 1087 (m), 1030 (w), 1013 (w), 988 (w), 964 (m), 187 mg, 4.67 mmol) was suspended in DMF (6 mL) under N2.
848 (m), 789 (m), 776 (s), 750 (s), 677 (m), 636 (w), 616 (m), 1-Dodecanethiol (1.14 mL, 956 mg, 4.63 mmol) and then DMF
562 (m), 548 (s), 514 (s). ESI-MS m/z 234.0 [M + H]+ (calc. (4 mL) were added and the mixture was stirred for 10 min.
234.1). Found: C 62.03, H 4.95, N 6.29; C12H11NO2S requires H1 (400 mg, 2.31 mmol) was added with DMF (2 mL) and the
C 61.78, H 4.75, N 6.00%.
mixture was heated at 120 °C for 4 h. The yellow mixture was
Compound H4. NaH (60% suspension in mineral oil, allowed to cool to room temperature and was then poured into
235 mg, 5.88 mmol) was suspended in DMF (8 mL) under N2. water–brine (3 : 1, 50 mL). The resulting suspension was
2-Methyl-2-propanethiol (0.660 mL, 528 mg, 5.80 mmol) was stirred for 5 min and the precipitate was removed by filtration,
added leading to gas evolution and a white foam. After the washed with H2O, dried under vacuum and purified by
reaction mixture had been stirred for 10 min at room tempera- column chromatography (silica, n-hexane–EtOAc 6 : 1 by vol.
ture, H1 (501 mg, 2.89 mmol) was added with DMF (2 mL). changing to 2 : 1). H6 was isolated as a white solid (542 mg,
1
The mixture was heated at 120 °C for 24 h. The yellow-orange 1.52 mmol, 65.8%). M.p. 65.3 °C. H NMR (500 MHz, CDCl3)
solution was allowed to cool to room temperature and was δ/ppm 8.67 (ddd, J = 4.8, 1.8, 1.0 Hz, 1H, HB6), 7.91 (m, 2H,
then poured into water–brine (3 : 1, 50 mL). The resulting sus- HA2), 7.78–7.63 (overlapping m, 2H, HB3+B4), 7.39 (m, 2H, HA3),
pension was stirred for 5 min. The precipitate was separated 7.21 (ddd, J = 7.2, 4.8, 1.4 Hz, 1H, HB5), 2.97 (m, 2H, HSCH2),
by filtration, washed with H2O and dried under vacuum. H4 1.68 (m, 2H, HSCH2CH2), 1.43 (m, 2H, HSCH2CH2CH2), 1.35–1.12
was isolated as a pale brown solid (704 mg, 2.89 mmol, 100%). (overlapping m, 16H, HCH2), 0.88 (t, J = 6.9 Hz, 3H, HCH3).
1
M.p. 90.7 °C. H NMR (500 MHz, CDCl3) δ/ppm 8.70 (ddd, J = 13C{1H} NMR (126 MHz, CDCl3) δ/ppm 157.0 (CB2), 149.8 (CB6),
4.8, 1.9, 1.1 Hz, 1H, HB6), 7.95 (m, 2H, HA2), 7.82–7.70 (overlap- 138.7 (CA4), 136.9 (CB4), 136.7 (CA1), 128.6 (CA3), 127.3 (CA2),
ping m, 2H, HB3+B4), 7.64 (m, 2H, HA3), 7.26 (m, 1H, HB5), 1.32 122.1 (CB5), 120.3 (CB3), 33.3 (CSCH2), 32.1 (CCH2), 29.8 (2CCH2),
(s, 9H, HtBu). 13C{1H} NMR (126 MHz, CDCl3) δ/ppm 157.0 29.7 (2CCH2), 29.5 (CCH2), 29.3 (CCH2), 29.2 (CSCH2CH2), 29.0
(CB2), 149.9 (CB6), 139.8 (CA1), 137.9 (CA3), 137.0 (CB4), 133.9 (CSCH2CH2CH2), 22.8 (CCH2), 14.3 (CCH3). IR (solid, ν/cm−1) 3059
(CA4), 127.0 (CA2), 122.5 (CB5), 120.8 (CB3), 46.4 (CCtBu), 31.2 (w), 3003 (w), 2954 (m), 2917 (s), 2872 (m), 2850 (s), 1585 (s),
(CtBu); IR (solid, ν/cm−1) 1462 (m), 1429 (m), 1391 (w), 1571 (m), 1554 (w), 1496 (w), 1463 (s), 1432 (s), 1398 (w), 1379
1366 (m), 1305 (w), 1289 (w), 1259 (w), 1168 (m), 1152 (m), (m), 1297 (m), 1259 (w), 1242 (w), 1191 (w), 1153 (w), 1122 (w),
1098 (m), 1059 (w), 1031 (w), 1014 (m), 989 (m), 934 (w), 1100 (m), 1056 (w), 1009 (m), 988 (w), 834 (m), 768 (s), 734 (m),
899 (w), 844 (s), 780 (s), 748 (s), 725 (m), 682 (w), 633 (w), 720 (m), 708 (m), 636 (w), 616 (w), 548 (w), 513 (w), 488 (w),
618 (w), 579 (w), 560 (m), 520 (m), 491 (m). ESI-MS m/z 244.0 462 (m). MALDI-TOF MS (no matrix) m/z 355.7 [M]+ (calc.
[M + H]+ (calc. 244.1). Found C 74.04, H 7.01, N 5.64; required 355.2). Found C 77.75, H 9.76, N 4.05; C23H33NS requires C
for C15H17NS C 74.03, H 7.04, N 5.76%.
77.69, H 9.35, N 3.94%.
Compound H5. H4 (501 mg, 2.06 mmol) and sodium tung-
Compound H7. H6 (212 mg, 0.597 mmol) and sodium tung-
state dihydrate (352 mg, 1.07 mmol) were dissolved in MeOH state dihydrate (98.4 mg, 0.298 mmol) were suspended in
(13 mL). H2O2 (30%, 0.500 mL, 568 mg, 5.01 mmol) was added MeOH (15 mL). H2O2 (35%, 0.120 mL, 136 mg, 1.40 mmol)
and the suspension was stirred at room temperature for 20 h. was added and the mixture was stirred at room temperature
CH2Cl2 (100 mL) was then added and the white precipitate was overnight. Water (50 mL) was added and the suspension was
separated by filtration. The filtrate was washed with H2O stirred for 15 min, after which time the precipitate was separ-
(50 mL), the aqueous layer extracted with CH2Cl2 (100 mL) and ated by filtration. It was washed with H2O and dried under
the combined organic layers dried over Na2SO4. The solvent vacuum. H7 was isolated as
a white solid (207 mg,
1
was removed under reduced pressure and the residue was 0.534 mmol, 89.4%). M.p. 84.4 °C. H NMR (500 MHz, CDCl3)
purified by column chromatography (silica, CH2Cl2 with 1% δ/ppm 8.74 (ddd, J = 5.0, 1.3 Hz, 1H, HB6), 8.19 (m, 2H, HA2),
MeOH). H5 was isolated as
a
white powder (473 mg, 8.00 (m, 2H, HA3), 7.81 (m, 2H, HB3+B4), 7.33 (ddd, J = 6.7, 4.7,
1
1.72 mmol, 83.5%). M.p. 174.4 °C. H NMR (500 MHz, CDCl3) 1.6 Hz, 1H, HB5), 3.11 (m, 2H, HSO2CH2), 1.71 (m, 2H,
δ/ppm 8.75 (ddd, J = 4.7, 1.8, 1.1 Hz, 1H, HB6), 8.17 (m, 2H, HSO2CH2CH2), 1.35 (m, 2H, HSO2CH2CH2CH2), 1.31–1.18 (overlap-
HA2), 7.98 (m, 2H, HA3), 7.88–7.75 (overlapping m, 2H, HB3+B4), ping m, 16H, HCH2), 0.87 (t, J = 7.0 Hz, 3H, HCH3). 13C{1H}
7.33 (ddd, J = 6.7, 4.8, 1.7 Hz, 1H, HB5), 1.37 (s, 9H, HtBu). NMR (126 MHz, CDCl3) δ/ppm 155.5 (CB2), 150.2 (CB6), 144.6
13C{1H} NMR (126 MHz, CDCl3) δ/ppm 155.7 (CB2), 150.2 (CB6), (CA1), 139.3 (CA4), 137.2 (CB4), 128.7 (CA3), 127.8 (CA2), 123.5
144.5 (CA1), 137.3 (CB4), 135.5 (CA4), 131.1 (CA3), 127.3 (CA2), (CB5), 121.3 (CB3), 56.6 (CSO2CH2), 32.0 (CCH2), 29.72 (CCH2),
123.5 (CB5), 121.3 (CB3), 60.1 (CCtBu), 23.8 (CtBu). IR (solid, 29.69 (CCH2), 29.6 (CCH2), 29.5 (CCH2), 29.4 (CCH2), 29.2 (CCH2),
ν/cm−1) 2970 (w), 1586 (m), 1561 (w), 1463 (m), 1436 (w), 1395 (w), 28.4 (CSO2CH2CH2CH2), 22.9 (CSO2CH2CH2), 22.8 (CCH2), 14.3
1314 (w), 1287 (s), 1192 (w), 1159 (w), 1131 (s), 1113 (m), (CCH3). IR (solid, ν/cm−1) 2915 (m), 2848 (m), 1586 (w),
1079 (s), 1011 (m), 990 (w), 853 (m), 801 (w), 778 (s), 752 (w), 1562 (w), 1468 (m), 1436 (w), 1399 (w), 1301 (m), 1285 (m),
741 (w), 722 (m), 694 (s), 646 (s), 616 (m), 579 (s), 555 (m), 1271 (m), 1144 (s), 1099 (w), 1086 (m), 1027 (w), 1009 (w),
517 (m), 505 (m). ESI-MS m/z 276.0 [M + H]+ (calc. 276.1). 991 (w), 853 (w), 776 (s), 758 (m), 739 (m), 722 (w), 691 (s),
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635 (w), 621 (m), 606 (s), 557 (m), 528 (s), 496 (m). ESI-MS m/z 2-ethoxyethanol (3 mL) and H2O (1 mL) under N2. The mixture
388.2 [M + H]+ (calc. 388.2). Found C 71.30, H 8.79, N 3.77; was heated at reflux for 22 h. After cooling to room tempera-
C23H33NO2S requires C 71.27, H 8.58, N 3.61%.
ture, the mixture was poured into H2O (≈50 mL) and stirred at
[Ir2(3)4Cl2]. [Ir2(COD)2Cl2] (285 mg, 0.424 mmol) and H3 room temperature for a few min. The resulting suspension was
(395 mg, 1.69 mmol) were suspended in degassed 2-ethoxy- poured into brine (≈40 mL) and stirred again at room tempera-
ethanol and the mixture purged with argon. The suspension ture. The precipitate was removed by filtration, washed with
was heated at reflux overnight and was then allowed to cool to H2O, EtOH and Et2O and dried under vacuum. [Ir2(7)4Cl2] was
room temperature. The yellow precipitate was separated by fil- isolated as a yellow powder (216 mg, 0.108 mmol, 84.0%
tration, washed with H2O and EtOH, and dried under vacuum. crude) and was used without further purification. 1H NMR
[Ir2(3)4Cl2] was isolated as
a yellow powder (516 mg, (500 MHz, CDCl3) δ/ppm 9.23 (ddd, J = 5.7, 1.5, 0.6 Hz, 4H,
0.373 mmol, 88.0% crude) and was used without further puri- HB6), 8.04 (pseudo-dt, J = 8.4, 1.0 Hz, 4H, HB3), 7.94 (pseudo-td,
1
fication. H NMR (500 MHz, CDCl3) δ/ppm 9.21 (ddd, J = 5.8, J = 7.8, 1.6 Hz, 4H, HB4), 7.66 (d, J = 8.2 Hz, 4H, HA3), 7.31 (dd,
1.6, 0.7 Hz, 4H, HB6), 8.06 (ddd, J = 8.4, 1.4, 0.7 Hz, 4H, HB3), J = 8.1, 1.8 Hz, 4H, HA4), 6.99 (ddd, J = 7.3, 5.7, 1.5 Hz, 4H,
7.95 (ddd, J = 8.1, 7.5, 1.6 Hz, 4H, HB4), 7.68 (d, J = 8.2 Hz, 4H, HB5), 6.30 (d, J = 1.8 Hz, 4H, HA6), 2.74 (m, 8H, HSO2CH2), 1.43
HA3), 7.36 (dd, J = 8.1, 1.9 Hz, 4H, HA4), 7.01 (ddd, J = 7.3, 5.7, (m, 8H, HSO2CH2CH2), 1.33–1.05 (overlapping m, 72H, HMe),
1.4 Hz, 4H, HB5), 6.36 (d, J = 1.9 Hz, 4H, HA6), 2.75 (s, 12H, 0.88 ppm (t, J = 7.0 Hz, 12H, HMe). 13C{1H} NMR (126 MHz,
HMe). 13C{1H} NMR (126 MHz, CDCl3) δ/ppm 166.5 (CB2), 151.8 CDCl3) δ/ppm 166.6 (CB2), 151.8 (CB6), 149.0 (CA2), 144.7 (CA1/A5),
(CB6), 149.2 (CA2), 144.8 (CA1/A5), 139.8 (CA1/A5), 138.0 (CB4), 138.6 (CA5/A1), 137.9 (CB4), 128.9 (CA6), 124.3 (CB5), 124.2 (CA3),
128.1 (CA6), 124.4 (CB5), 124.3 (CA3), 121.0 (CA4), 120.6 (CB3), 121.6 (CA4), 120.5 (CB3), 56.2 (CSO2CH2), 32.1 (CCH2), 29.73
44.3 (CMe). ESI-MS m/z 657.1 [Ir(3)2]+ (calc. 657.1), 698.2 (CCH2), 29.72 (CCH2), 29.6 (CCH2), 29.5 (CCH2), 29.4 (CCH2), 29.2
[Ir(3)2(MeCN)]+ (calc. 698.1).
[Ir2(4)4Cl2]. Compound H4 (401 mg, 1.65 mmol) was dis- MALDI-TOF MS (no matrix) m/z 965.9 [Ir(7)2]+ (calc. 965.4).
solved in 2-ethoxyethanol (18 mL) in a vial and the solution [Ir(1)2(bpy)][PF6]. [Ir2(1)4Cl2] (350 mg, 0.306 mmol) and bpy
(CCH2), 28.3 (CCH2), 22.8 (CCH2), 22.5 (CSO2CH2CH2), 14.3 (CMe).
purged with N2. [Ir2(COD)2Cl2] (280 mg, 0.417 mmol) was (150 mg, 0.960 mmol) were suspended in MeOH (45 mL). The
added and the mixture heated at 110 °C for 1.5 h in a micro- mixture was heated at reflux overnight and then allowed to
wave reactor. The yellow precipitate was separated by filtration, cool to room temperature. After filtration, an excess of solid
washed with H2O and EtOH and dried under vacuum to yield NH4PF6 was added to the filtrate and the mixture was stirred
[Ir2(4)4Cl2] as a yellow solid (383 mg, 0.269 mmol, 64.5% for 1 h at room temperature. The yellow precipitate was separ-
crude). The compound was used without further purification. ated by filtration, washed with H2O and redissolved in CH2Cl2.
1H NMR (500 MHz, CDCl3) δ/ppm 9.29 (d, J = 5.5 Hz, 4H, HB6), The solution was dried over Na2SO4 and the solvent removed
7.89 (d, J = 8.0 Hz, 4H, HB3), 7.76 (pseudo-td, J = 7.8, 1.6 Hz, under reduced pressure. The yellow residue was purified by
4H, HB4), 7.42 (d, J = 8.0 Hz, 4H, HA3), 6.92 (dd, J = 7.9, 1.7 Hz, column chromatography (silica, CH2Cl2 changing to CH2Cl2–
4H, HA4), 6.78 (ddd, J = 7.3, 5.7, 1.5 Hz, 4H, HB5), 5.96 (d, J = 2% MeOH). [Ir(1)2(bpy)][PF6] was isolated as a yellow solid
1.6 Hz, 4H, HA6), 0.98 (s, 36H, HtBu). ESI-MS m/z 677.2 [Ir(4)2]+ (405 mg, 0.483 mmol, 78.9%). 1H NMR (500 MHz, CD3CN)
(calc. 677.2), 718.3 [Ir(4)2(MeCN)]+ (calc. 718.2).
δ/ppm 8.53 (pseudo-dt, J = 8.3, 1.0 Hz, 2H, HE3), 8.14 (pseudo-
[Ir2(5)4Cl2]. Compound H5 (151 mg, 0.548 mmol, 2.0 eq.) td, J = 8.0, 1.6 Hz, 2H, HE4), 8.01 (m, 4H, HB3+E6), 7.85 (m, 4H,
was suspended in 2-ethoxyethanol (3 mL) and H2O (1 mL) HA3+B4), 7.57 (ddd, J = 5.8, 1.5, 0.8 Hz, 2H, HB6), 7.51 (ddd, J =
under N2 atmosphere. IrCl3·nH2O (≈82% IrCl3, 99.2 mg, 7.7, 5.5, 1.2 Hz, 2H, HE5), 7.04 (ddd, J = 7.3, 5.8, 1.4 Hz, 2H,
1.0 eq.) was added and the suspension was heated at reflux for HB5), 6.81 (m, 2H, HA4), 5.89 (dd, JHF = 9.6 Hz, JHH = 2.6 Hz,
21 h. The mixture was allowed to cool to room temperature 2H, HA6). 13C{1H} NMR (126 MHz, CD3CN) δ/ppm 167.1 (CB2),
and then H2O was added. The precipitate was removed by fil- 164.6 (d, JCF = 253 Hz, CA5), 156.6 (CE2), 154.3 (d, JCF = 5.8 Hz,
tration and was washed with H2O to give [Ir2(5)4Cl2] as a yellow CA1), 151.8 (CE6), 150.1 (CB6), 141.4 (d, JCF = 2.1 Hz, CA2), 140.5
powder (101 mg, 0.0650 mmol, 48%). This was used without (CE4), 139.8 (CB4), 129.4 (CE5), 128.1 (dCF, J = 9.4 Hz, CA3), 125.7
further purification. 1H NMR (500 MHz, CDCl3) δ/ppm 9.30 (CE3), 124.5 (CB5), 121.0 (CB3), 118.3 (dCF, J = 17.7 Hz, CA6),
(ddd, J = 5.8, 1.5, 0.6 Hz, 4H, HB6), 8.03 (ddd, J = 8.3, 1.3, 110.5 (d, J = 23.3 Hz, CA4). IR (solid, ν/cm−1) 1594 (m),
0.6 Hz, 4H, HB3), 7.93 (td, J = 7.8, 1.5 Hz, 4H, HB4), 7.64 (d, J = 1568 (m), 1555 (m), 1482 (w), 1447 (m), 1434 (m), 1314 (w),
8.2 Hz, 4H, HA3), 7.30 (dd, J = 8.1, 1.7 Hz, 4H, HA4), 6.98 (ddd, 1262 (w), 1245 (w), 1187 (m), 1163 (w), 1032 (w), 833 (s), 766 (s),
J = 7.3, 5.7, 1.5 Hz, 4H, HB5), 6.21 (d, J = 1.8 Hz, 4H, HA6), 1.00 733 (m), 675 (w), 576 (m), 556 (s). UV/Vis (MeCN, 1.1 × 10−5
(s, 36H, HtBu). 13C{1H} NMR (126 MHz, CDCl3) δ/ppm 166.7 mol dm−3) λ/nm (ε/dm3 mol−1 cm−1) 251 (62 000), 264
(CB2), 151.8 (CB6), 148.9 (CA2), 143.8 (CA1/A5), 137.9 (CB4), 134.4 (60 000), 295 sh (33 000), 310 sh (2000), 395 sh (4300). Emis-
max
(CA5/A1), 131.6 (CA6), 124.13 (CB5), 124.07 (CA4), 123.5 (CA3), sion (MeCN, 1.1 × 10−5 mol dm−3, λexc = 269 nm) λ
=
em
120.5 (CB3), 59.7 (CCtBu), 23.5 (CtBu). ESI-MS m/z 741.2 [Ir(5)2]+ 557 nm. ESI-MS m/z 693.2 [M − PF6]+ (calc. 693.1). Found
(calc. 741.1), 782.1 [Ir(5)2(MeCN)]+ (calc. 782.2), 823.1 C 45.95, H 2.84, N 6.74; C32H22F8IrN4P requires C 45.88,
[Ir(5)2(MeCN)2]+ (calc. 823.2).
H 2.65, N 6.69%.
[Ir2(7)4Cl2]. IrCl3·nH2O (≈82% IrCl3, 93.5 mg, 0.257 mmol)
[Ir(3)2(bpy)][PF6]. [Ir2(3)4Cl2] (109 mg, 0.0574 mmol) and
was added to a suspension of H7 (200 mg, 0.516 mmol) in bpy (26.9 mg, 0.172 mmol) were suspended in MeOH (10 mL)
5346 | Dalton Trans., 2014, 43, 5343–5356
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and the mixture was heated at 120 °C in a microwave reactor (pseudo-dt, J = 5.8, 1.2 Hz, 2H, HB6), 7.51 (ddd, J = 7.5, 5.3,
for 1 h (15 bar). After cooling, an excess of solid NH4PF6 was 1.2 Hz, 2H, HE5), 7.13 (dd, J = 8.0, 1.7 Hz, 2H, HA4), 7.05 (ddd,
added to the yellow solution and the resulting suspension was J = 7.4, 5.8, 1.4 Hz, 2H, HB5), 6.30 (d, J = 1.7 Hz, 2H, HA6), 1.00
stirred for 15 min at room temperature. The yellow precipitate (s, 18H, HtBu). 13C{1H} NMR (126 MHz, CD3CN) δ/ppm 167.7
that formed was separated by filtration, was washed with (CB2), 156.7 (CE2), 151.8 (CE6), 150.9 (CA5), 150.3 (CB6), 145.2
MeOH and redissolved in CH2Cl2. The solvent was removed (CB6), 140.4 (CA2), 140.3 (CE4), 139.7 (CA6), 136.0 (CB4), 131.6
under reduced pressure and the product was purified by (CA1), 129.4 (CA4), 125.7 (CE3), 125.5 (CA3), 124.8 (CB5), 121.3
column chromatography (silica, CH2Cl2 changing to CH2Cl2– (CB3), 46.8 (CCtBu), 31.1 (CtBu). IR (solid, ν/cm−1) 2970 (w), 1607 (m),
4% MeOH). The major fraction was collected and solvent 1569 (m), 1472 (m), 1447 (m), 1425 (m), 1366 (m), 1313 (w),
removed under reduced pressure. The residue was suspended 1258 (w), 1162 (m), 1099 (w), 1062 (w), 875 (w), 834 (s), 778 (s),
in CH2Cl2 and the mixture sonicated and then filtered. 765 (s), 733 (m), 650 (w), 600 (w), 557 (s). UV/Vis (MeCN,
[Ir(3)2(bpy)][PF6] was isolated as a yellow solid (92.3 mg, 1.0 × 10−5 mol dm−3) λ/nm (ε/dm3 mol−1 cm−1) 261 (57 000),
1
0.0964 mmol, 84.0%). H NMR (500 MHz, CD3CN) δ/ppm 8.54 305 sh (35 000), 415 sh (4800). Emission (MeCN, 0.99 × 10−5
max
(pseudo-dt, J = 8.3, 1.1 Hz, 2H, HE3), 8.23 (pseudo-dt, J = 8.2, mol dm−3, λexc = 260 nm): λ
= 568 nm. ESI-MS m/z 833.5
em
1.1 Hz, 2H, HB3), 8.15 (pseudo-td, J = 8.0, 1.6 Hz, 2H, HE4), 8.02 [M − PF6]+ (calc. 833.2). Found C 48.96, H 4.35, N 5.70;
(d, J = 8.3 Hz, 2H, HA3), 7.98 (ddd, J = 8.0, 7.7, 1.5 Hz, 2H, HB4), C40H40F6IrN4PS2 requires C 49.12, H 4.12, N 5.73%.
7.95 (ddd, J = 5.4, 1.6, 0.8 Hz, 2H, HE6), 7.72 (ddd, J = 5.8, 1.5,
[Ir(5)2(bpy)][PF6]. [Ir2(5)4Cl2] (101 mg, 0.0650 mmol) and
0.7 Hz, 2H, HB6), 7.58 (dd, J = 8.3, 1.9 Hz, 2H, HA4), 7.51 (ddd, bpy (44.3 mg, 0.284 mmol) were suspended in MeOH (10 mL)
J = 7.7, 5.5, 1.2 Hz, 2H, HE5), 7.21 (ddd, J = 7.4, 5.8, 1.4 Hz, 2H, and the mixture was heated at reflux for 14 h. The solution was
HB5), 6.70 (d, J = 1.9 Hz, 2H, HA6), 2.89 (s, 6H, HMe). 13C{1H} left to cool to room temperature, and an excess of solid
NMR (126 MHz, CD3CN) δ/ppm 166.2 (CB2), 156.6 (CE2), 152.0 NH4PF6 was then added followed by enough H2O to precipitate
(CE6), 151.2 (CA1), 150.9 (CB6), 150.2 (CA2), 142.3 (CA5), 140.7 the product. The resulting suspension was stirred for 30 min.
(CE4), 140.3 (CB4), 129.6 (CA6+E5), 126.31 (CA3), 126.29 (CB5), The yellow precipitate was separated by filtration, washed with
125.8 (CE3), 122.6 (CA4), 122.6 (CB3), 44.3 (CMe). IR (solid, H2O and redissolved in CH2Cl2. After removal of the solvent
ν/cm−1) 2927 (w), 1608 (w), 1575 (w), 1475 (m), 1447 (w), 1430 (w), under reduced pressure, the residue was purified by column
1375 (w), 1294 (m), 1267 (w), 1144 (s), 1091 (m), 1062 (m), chromatography (silica, CH2Cl2 changing to CH2Cl2–2%
1030 (w), 957 (m), 892 (w), 838 (s), 808 (m), 782 (m), 753 (s), MeOH). [Ir(5)2(bpy)][PF6] was isolated as
a yellow solid
733 (m), 699 (m), 666 (w), 651 (w), 600 (w), 592 (w), 557 (s), (119 mg, 0.114 mmol, 87.7%). 1H NMR (500 MHz, CD3CN)
546 (s), 524 (m), 487 (s). UV/Vis (MeCN, 1.0 × 10−5 mol dm−3
)
δ/ppm 8.58 (dd, J = 8.2, 1.1 Hz, 2H, HE3), 8.22 (d, J = 8.0 Hz,
λ/nm (ε/dm3 mol−1 cm−1) 256 (58 000), 300 sh (30 000), 350 sh 2H, HB3), 8.17 (pseudo-td, J = 8.0, 1.5 Hz, 2H, HE4), 8.09 (m,
(7500), 390 (4900), 425 sh (3200). Emission (MeCN, 1.0 × 10−5 2H, HE6), 8.02–7.93 (overlapping m, 4H, HA3+B4), 7.71 (m, 2H,
max
mol dm−3, λexc = 262 nm) λ
= 493, 525 nm. ESI-MS m/z HB6), 7.51 (ddd, J = 6.9, 5.5, 1.2 Hz, 2H, HE5), 7.45 (dd, J = 8.2,
em
813.1 [M − PF6]+ (calc. 813.1). Found C 41.74, H 3.33, N 5.90; 1.8 Hz, 2H, HA4), 7.20 (ddd, J = 7.4, 5.8, 1.4 Hz, 2H, HB5), 6.50
C34H28F6IrN4O4PS2·H2O requires C 41.84, H 3.10, N 5.74%.
(d, J = 1.8 Hz, 2H, HA6), 0.93 (s, 18H, HtBu). 13C{1H} NMR
[Ir(4)2(bpy)][PF6]. [Ir2(4)4Cl2] (144 mg, 0.101 mmol) and bpy (126 MHz, CD3CN, 295 K) δ/ppm 166.2 (CB2), 156.6 (CE2), 152.3
(66.0 mg, 0.423 mmol) were suspended in MeOH (15 mL) and (CE6), 150.9 (CB6), 150.6 (CA1/A5), 150.1 (CA2), 140.8 (CE4), 140.4
the mixture was heated at reflux for 16 h. The orange solution (CB4), 135.9 (CA5/A1), 133.2 (CA6), 129.6 (CE5), 126.3 (CB5), 125.9
was allowed to cool to room temperature. An excess of solid (CE3), 125.5 (CA4), 125.4 (CA3), 122.5 (CB3), 60.3 (CCtBu), 23.5
NH4PF6 was added followed by enough H2O to precipitate the (CtBu). IR (solid, ν/cm−1) 2979 (w), 1607 (w), 1575 (w), 1475 (m),
product, and the resulting suspension was stirred for 10 min. 1448 (w), 1430 (w), 1373 (w), 1285 (m), 1193 (w), 1129 (s),
The yellow precipitate was separated by filtration, washed with 1082 (m), 836 (s), 806 (m), 781 (m), 764 (m), 730 (w), 710 (m),
H2O and MeOH and then redissolved in CH2Cl2. The solution 672 (m), 658 (m), 648 (m), 585 (m), 569 (m), 556 (s), 492 (m).
was dried over Na2SO4 and the solvent was then removed UV/Vis (MeCN, 0.99 × 10−5 mol dm−3) λ/nm (ε/dm3 mol−1
under reduced pressure. The residue was purified twice by cm−1) 257 (59 000), 295 sh (35 000), 391 (4700), 420 sh
column chromatography (silica, CH2Cl2 changing to CH2Cl2 (3400 dm3 mol−1 cm−1). Emission (MeCN, 0.99 × 10−5 mol
max
with 1% MeOH; alumina, CH2Cl2 changing to CH2Cl2–5% dm−3, λexc = 262 nm) λ
= 493, 523 nm. ESI-MS m/z 897.2
em
MeOH). The residue was dissolved in MeOH and an excess [M − PF6]+ (calc. 897.2). Found C 45.51, H 4.05, N 5.56;
of solid NH4PF6 followed by H2O were added. The resulting C40H40F6IrN4O4PS2·H2O requires C 45.32, H 3.99, N 5.29%.
suspension was stirred for 5 min, and the yellow precipitate
[Ir(6)2(bpy)][PF6]. 1-Dodecanethiol (0.060 mL, 50.4 mg,
was collected by filtration and redissolved in CH2Cl2. The solu- 0.249 mmol) was added to a suspension of NaH (60% in
tion was dried over Na2SO4 and the solvent was removed mineral oil, 10.0 mg, 0.250 mmol) in DMF (2 mL) under N2.
in vacuo. [Ir(4)2(bpy)][PF6] was isolated as a yellow solid The mixture was stirred at room temperature for 10 min.
(139 mg, 0.142 mmol, 70.3%). 1H NMR (500 MHz, CD3CN): [Ir(1)2(bpy)][PF6] (53.0 mg, 0.0633 mmol) was added to the
δ/ppm 8.54 (pseudo-dt, J = 8.2, 1.0 Hz, 2H, HE3), 8.15 (pseudo- reaction mixture; this was heated at 120 °C for 1.5 h. The dark
td, J = 7.9, 1.6 Hz, 2H, HE4), 8.07 (m, 4H, HB3+E6), 7.86 (ddd, J = brown mixture was allowed to cool to room temperature and
8.2, 7.6, 1.5 Hz, 2H, HB4), 7.72 (d, J = 8.0 Hz, 2H, HA3), 7.61 was then poured into a mixture of H2O and brine (3 : 1 by vol.,
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20 mL). The resulting suspension was stirred for 30 min at 23.4 (CCH2), 14.4 (CCH3). IR (solid, ν/cm−1) 2923 (m), 2853 (w),
room temperature. The brown-yellow precipitate was separated 1608 (w), 1576 (w), 1476 (m), 1448 (w), 1430 (w), 1375 (w),
by filtration and was washed with H2O. The solid was redis- 1294 (m), 1140 (s), 1090 (m), 1063 (w), 836 (s), 762 (s), 728 (m),
solved in CH2Cl2 and the solution dried over Na2SO4. Solvent 667 (m), 652 (w), 606 (m), 582 (w), 556 (s), 500 (m). UV/Vis
was removed in vacuo and the product was purified by column (MeCN, 1.0 × 10−5 mol dm−3) λ/nm (ε/dm3 mol−1 cm−1) 256
chromatography (silica, CH2Cl2 changing to CH2Cl2–2% (58 000), 310 sh (25 000), 350 sh (7900), 390 (5000), 420 sh
MeOH). [Ir(6)2(bpy)][PF6] was isolated as an orange solid (3700 dm3 mol−1 cm−1). Emission (MeCN, 1.0 × 10−5 mol
max
(56.1 mg, 0.0467 mmol, 73.8%). 1H NMR (500 MHz, CD3CN) dm−3, λexc = 262 nm) λ
= 493, 524 nm. ESI-MS m/z 1121.6
em
δ/ppm 8.54 (pseudo-dt, J = 8.3, 1.0 Hz, 2H, HE3), 8.15 (pseudo- [M − PF6]+ (calc. 1121.5). Found C 53.38, H 5.57, N 4.72;
td, J = 7.9, 1.6 Hz, 2H, HE4), 8.06 (m, 2H, HE6), 8.00 (pseudo-dt, C56H72F6IrN4O4PS2 requires C 53.11, H 5.73, N 4.42%.
J = 8.4, 1.1 Hz, 2H, HB3), 7.83 (m, 2H, HB4), 7.68 (d, J = 8.3 Hz,
2H, HA3), 7.58 (pseudo-dt, J = 5.9, 1.1 Hz, 2H, HB6), 7.53 (ddd,
Crystallography
J = 7.7, 5.4, 1.2 Hz, 2H, HE5), 7.00 (ddd, J = 7.3, 5.8, 1.4 Hz, 2H,
Data were collected on a Bruker-Nonius KappaAPEX diffracto-
HB5), 6.94 (dd, J = 8.2, 1.9 Hz, 2H, HA4), 6.09 (d, J = 1.9 Hz, 2H,
meter with data reduction, solution and refinement using the
HA6), 2.63 (m, 4H, HSCH2), 1.40 (m, 4H, HSCH2CH2), 1.35–1.16
(m, 36H, HCH2), 0.89 (t, J = 7.0 Hz, 6H, HCH3). 13C{1H} NMR
(126 MHz, CD3CN) δ/ppm 168.0 (CB2), 156.7 (CE2), 151.8
(CA1+E6), 150.1 (CB6), 141.6 (CA2), 141.5 (CA5), 140.3 (CE4), 139.4
(CB4), 129.4 (CE5), 128.7 (CA6), 126.1 (CA3), 125.6 (CE3), 123.9
(CB5), 122.0 (CA4), 120.5 (CB3), 32.6 (CCH2), 32.0 (CSCH2), 30.3
(2CCH2), 30.25 (CCH2), 30.2 (CCH2), 30.1 (CCH2), 29.9 (CCH2), 29.7
(CSCH2CH2), 29.4 (CCH2), 23.4 (CCH2), 14.4 (SCH3). IR (solid,
programs APEX224 and SHELXL97.25 ORTEP-type diagrams
and structure analysis used Mercury v. 3.0.26,27 Crystallo-
graphic data are given in Table 1.
Results and discussion
Ligand synthesis and characterization
ν/cm−1) 2922 (m), 2852 (m), 1606 (m), 1567 (m), 1537 (w), The fluoro compound H1 is a convenient precursor to each of
1472 (m), 1446 (m), 1423 (m), 1373 (w), 1315 (w), 1261 (w), H2, H4 and H6. The thiomethyl group in H2 is readily intro-
1244 (w), 1164 (w), 1095 (m), 1062 (w), 1030 (w), 876 (w), duced by treatment of H1 with NaSMe in NMP under micro-
835 (s), 791 (m), 769 (s), 732 (m), 650 (w), 639 (w), 556 (s), wave conditions. The 93% yield of H2 is superior to the 10%
520 (w). UV/Vis (MeCN, 0.99 × 10−5 mol dm−3) λ/nm (ε/dm3 obtained using the reported Ullmann coupling of 2-bromopyri-
mol−1 cm−1
)
251 (41 000), 310 (36 000), 400 sh (8200). dine and 4-bromothianisole.23 The synthesis of H4 was
max
Emission (MeCN, 0.99 × 10−5 mol dm−3, λexc = 252 nm) λ
=
adapted from that reported for the formation of 2(2-tbutylthio-
em
577 nm. ESI-MS m/z 1058.1 [M − PF6]+ calc. 1057.5. Found phenyl)pyridine,28 and H6 was prepared in a similar manner.
C 56.02, H 6.00, N 4.73; C56H72F6IrN4PS2 requires C 55.93, For each, the appropriate thiol was treated with NaH in DMF
H 6.04, N 4.66%.
to generate the corresponding thiolate to displace the fluoro
[Ir(7)2(bpy)][PF6]. [Ir2(7)4Cl2] (214 mg, 0.107 mmol) and bpy group from H1. Of the oxidation strategies tried for conversion
(50.1 mg, 0.321 mmol) were suspended in MeOH (15 mL) and of the thiols to corresponding sulfones, use of Na2WO4–
the mixture was heated at reflux for 2 d. After cooling to room H2O229 proved to be the most efficient.
temperature, the mixture was filtered. An excess of NH4PF6 fol-
Compounds H2–H8 were characterized by routine spectro-
lowed by H2O were added to the orange filtrate and the result- scopic methods, mass spectrometry and elemental analysis.
ing suspension was stirred for 5 min. The precipitate was The base peak in the electrospray mass spectrum of H2, H3,
collected by filtration, was washed with H2O and redissolved H4, H5 and H7 corresponded to the [M + H]+ with the isotopic
in CH2Cl2. Solvent was removed in vacuo and the residue distribution matching that calculated in each case. For H6, a
was purified twice by column chromatography (silica, CH2Cl2 parent ion (m/z 355.7) was observed in the MALDI-TOF mass
1
changing to CH2Cl2–1% MeOH; silica, CH2Cl2–1% MeOH). spectrum, but no [M + H]+ ion was detected in the ESI-MS. H
[Ir(7)2(bpy)][PF6] was isolated as a yellow solid (81.1 mg, and 13C NMR spectra were assigned using 2D methods (COSY,
1
0.0640 mmol, 30.0%). H NMR (500 MHz, CD3CN) δ/ppm 8.56 HMQC and HMBC) and were consistent with the structures
(pseudo-dt, J = 8.4, 1.0 Hz, 2H, HE3), 8.23 (pseudo-dt, J = 8.1, shown in Scheme 1.
0.9 Hz, 2H, HB3), 8.17 (pseudo-td, J = 7.9, 1.5 Hz, 2H, HE4),
Single crystals of H3 were grown by overlaying a CHCl3 solu-
8.04–7.96 (overlapping m, 6H, HA3+B4+E6), 7.71 (m, 2H, HB6), tion with hexanes, and of H5 by overlaying a CH2Cl2 solution
7.50 (m, 4H, HA4+E5), 7.21 (ddd, J = 7.5, 5.8, 1.4 Hz, 2H, HB5), with hexanes. The structures are shown in Fig. 1 and 2. Both
6.58 (d, J = 1.8 Hz, 2H, HA6), 2.87 (m, 4H, HSO2CH2), 1.40–1.01 compounds crystallize in the monoclinic space group C2/c.
(overlapping m, 40H, HCH2), 0.88 (t, J = 7.1 Hz, 6H, HCH3). Detailed analyses of the structures of a range of aryl–alkyl sul-
13C{1H} NMR (126 MHz, CD3CN) δ/ppm 166.2 (CB2), 156.6 fones30 and diaryl sulfones30,31 illustrate the formation both
(CE2), 152.1 (CE6), 151.1 (CA1/A5), 150.9 (CB6), 150.1 (CA2), 140.8 intra- and intermolecular CHaryl⋯OS hydrogen bonds. In H3,
(CE4), 140.4 (CB4), 140.3 (CA5/A1), 130.8 (CA6), 129.6 (CE5), 126.3 the O1–S1–C9–C10 and O2–S1–C9–C8 torsion angles are
(CB5), 126.2 (CA3), 125.9 (CE3), 123.2 (CA4), 122.5 (CB3), 56.3 −25.0(1) and 28.2(1)°, respectively, leading to intramolecular
(CSO2CH2), 32.6 (CCH2), 30.33 (CCH2), 30.32 (CCH2), 30.2 (CCH2), O1⋯H10a and O2⋯H8a contacts of 2.60 and 2.64 Å. In H5,
30.1 (CCH2), 30.0 (CCH2), 29.7 (CCH2), 28.6 (CCH2), 23.8 (CCH2), the corresponding angles (O1–S1–C9–C8 and O2–S1–C9–C10)
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Table 1 Crystallographic data
Compound
H3
H5
[Ir2(3)4Cl2]·2CH2Cl2 Δ-[Ir(1)2(bpy)][PF6] rac-4{[Ir(1)2(bpy)][PF6]}·Et2O·2CH2Cl2
Formula
Formula weight
C12H11NO2S
233.29
C15H17NO2S
275.37
C50H44Cl6Ir2N4O8S4 C32H22F2IrN4P
C134H102Cl4F32Ir4N16OP4
3594.88
1554.31
837.73
Crystal colour and habit Colourless block Colourless block Yellow plate
Yellow block
Trigonal
P3121
13.9523(9)
13.9523(9)
26.0654(17)
90
90
120
4394.3(6)
1.899
6
Yellow block
Triclinic
P1
Crystal system
Space group
a, b, c/Å
Monoclinic
C2/c
23.4437(15)
7.1763(5)
16.5008(11)
90
Monoclinic
C2/c
22.2664(12)
6.1121(4)
22.0876(11)
90
Orthorhombic
Pbca
22.0732(12)
21.3598(11)
23.0604(12)
90
ˉ
14.2353(6)
16.2890(7)
17.6451(7)
66.1650(10)
81.642(2)
67.3900(10)
3454.7(3)
1.728
α, β, γ/°
129.026(3)
90
2156.6(2)
1.437
110.398(2)
90
2817.5(3)
1.298
90
90
U/ Å3
10 872.5(10)
1.899
8
13.963 (M = Cu)
123
Dc/Mg m−3
Z
8
8
1
μ(M-Kα)/mm−1
T/K
0.282 (M = Mo)
123
2.019 (M = Mo)
296
10.083 (M = Cu)
123
9.298 (M = Cu)
296
Refln. collected (Rint
Unique refln.
)
30 251 (0.0269)
3021
7450 (0.0275)
2523
59 052 (0.1107)
9726
67 974 (0.0341)
5359
23 674 (0.0287)
11 699
Refln. for refinement
Parameters
Threshold
R1 (R1 all data)
wR2 (wR2 all data)
Goodness of fit
Flack parameter
CCDC deposition
2681
146
I > 2.0σ
0.0323 (0.0376)
0.0913 (0.0962)
1.057
2228
175
I > 2.0σ
0.0378 (0.0420)
0.1024 (0.1068)
1.080
6764
699
I > 2.0σ
0.0470 (0.0820)
0.1111 (0.1295)
1.008
5311
415
10 552
906
I > 2.0σ
0.0368 (0.0399)
0.1120 (0.1168)
1.036
—
972694
I > 2.0σ
0.0170 (0.0172)
0.0436 (0.0437)
1.098
0.007(2)
972693
—
972690
—
972692
—
972691
are −23.1(1) and 24.6(1)° with O1⋯H8a and O2⋯H10a separ-
ations of 2.57 and 2.64 Å. The dihedral angles between the
phenyl and pyridine rings are 17.7° in H3, and 37.7° in H5.
This marked difference is associated with face-to-face π-stack-
ing of phenyl and pyridine rings in H3 (but not in H5). Centro-
symmetric pairs of H3 molecules interact through a slipped
arrangement of aromatic rings (Fig. 3a) with an intercentroid
distance of 3.81 Å. The sulfone group engages in hydrogen-
bonded contacts to the methyl groups of two adjacent
molecules and the pyridine ring CH of a third molecule.
In contrast, a primary packing interaction in H5 involves
CHphenyl⋯Osulfone contacts resulting in the formation of
Fig. 1 ORTEP representation of the structure of H3 (ellipsoids plotted
at 40% probability level). Selected bond lengths and angles: S1–O2 =
1.4411(9), S1–O1 = 1.4434(10), S1–C12 = 1.7569(14), S1–C9 = 1.7575(11)
Å; O2–S1–O1
= 118.19(6), O2–S1–C12 = 108.03(7), O1–S1–C12 =
108.11(6), O2–S1–C9 = 109.20(6), O1–S1–C9 = 108.45(6), C12–S1–
C9 = 103.93(6)°.
t
ribbons of hydrogen-bonded molecules (Fig. 3b). The butyl
groups protrude along one side of the ribbon, and pairs of
adjacent ribbons associate through short CHbutyl⋯Npyridine
t
contacts (2.73 Å) giving an extended domain of butyl units
sandwiched between aromatic domains (Fig. 3c).
Synthesis and characterization of [Ir2(C^N)4Cl2] dimers
Complexes in the [Ir(ppy)2(N^N)]+ family are usually syn-
thesized by reaction between the N^N ligand and the chlorido-
bridged dimer [Ir2(ppy)4Cl2].32 Typically, this dimer is pre-
pared from the reaction of IrCl3·nH2O with Hppy.33,34 Although
[Ir2(1)4Cl2] (prepared by the latter method) has previously
been described,6 the remaining chlorido-bridged precursors
to the target complexes [Ir(C^N)2(bpy)]+ with C^N = 2 to 7
have not, to the best of our knowledge, been previously
reported.
Fig. 2 ORTEP representation of the structure of H5 (ellipsoids plotted
at 40% probability level). Selected bond distances and angles: S1–O2 =
1.4378(12), S1–O1
= 1.4402(12), S1–C12 = 1.8190(16), S1–C9 =
The reaction of IrCl3·nH2O with sulfones H5 and H7 pro-
ceeded smoothly under reflux in a mixture of 2-ethoxyethanol
and water (Scheme 2). The compounds [Ir2(5)4Cl2] and
1.7727(15) Å; O2–S1–O1 = 118.85(8), O2–S1–C9 = 107.48(7), O1–S1–
C9 = 107.03(7), O2–S1–C12 = 108.05(8), O1–S1–C12 = 107.50(8), C9–
S1–C12 = 107.46(7)°.
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1
[Ir2(7)4Cl2] were isolated as yellow solids. The H and 13C NMR
spectra of the complexes showed negligible impurities and the
compounds were used in the next step (see the next section)
without purification. The NMR spectra were assigned using
routine 2D methods and were in accord with the structures
shown in Scheme 2. For a MeOH solution of [Ir2(5)4Cl2], the
second most intense peak in the electrospray mass spectrum
came at m/z 741.2 and as assigned to the [Ir(5)2]+ ion. The base
peak at m/z 782.1 and a lower intensity peak at m/z 823.1 arose
from [Ir(5)2(MeCN)]+ and [Ir(5)2(MeCN)2]+, respectively; we
assume that the MeCN arises from the eluent in the LC
column of the LC-ESI-MS. The isotope distributions for each
peak matched the calculated patterns. MALDI-TOF mass spec-
trometry proved more amenable to observing a mass spectrum
of [Ir2(7)4Cl2], with the base peak at m/z 965.9 corresponding
to [Ir(7)2]+.
Attempts to prepare the dimers [Ir2(C^N)4Cl2] with C^N = 2,
3 or 4 from reactions of H2, H3 or H4 with IrCl3·nH2O were
unsuccessful. We therefore adopted an alternative strategy
which involves the reaction of the conjugate acid of the cyclo-
metalling ligand with [Ir2(COD)2Cl2].35 Unfortunately, reaction
of H2 with [Ir2(COD)2Cl2] gave an insoluble solid which could
not be characterized, and attempts to prepare and isolate
[Ir2(2)4Cl2] were abandoned. We note that the latter insoluble
material reacted with bpy in MeOH to give a mixture of pro-
ducts rather than a salt of the desired [Ir(2)2(bpy)]+.
The reaction of [Ir2(COD)2Cl2] with H3 and H4 (Scheme 2)
yielded [Ir2(3)4Cl2] and [Ir2(4)4Cl2] as yellow powders in good
1
yields. As judged by H NMR spectroscopy, the crude products
were pure enough to be used directly in the next step (see the
next section). The solution 1H and 13C NMR spectra of
[Ir2(3)4Cl2] were assigned by COSY, HMQC and HMBC
methods and were in accord with the structures in Scheme 2.
In contrast, [Ir2(4)4Cl2] is poorly soluble in most common
Fig. 3 (a) Face-to-face interactions between centrosymmetric pairs of
molecules of H3. (b) Ribbon formation through CHphenyl⋯Osulfone con-
tacts in H5. (c) Sandwiching of butyl (space-filling) units between aro-
t
matic domains in H5.
1
organic solvents. The H NMR spectrum was assigned using a
COSY spectrum and by comparison with those of the other
dimers, but the 1D 13C NMR spectrum and the 2D HMQC and
HMBC spectra were too poorly resolved to permit 13C NMR
data to be determined. The electrospray mass spectrum of an
MeOH solution of [Ir2(3)4Cl2] showed peaks at m/z 657.1 and
698.2 assigned to [Ir(3)2]+ and [Ir(3)2(MeCN)]+, respectively;
(the origin of the MeCN is explained above). Analogous peaks
were observed in the ESI mass spectrum of [Ir2(4)4Cl2].
The synthesis of [Ir2(6)4Cl2] could not be achieved by the
reaction of [Ir2(COD)2Cl2] with H6, and unreacted ligand
was recovered from the reaction mixture after 22 hours reflux
in 2-ethoxyethanol.
Despite the widespread synthetic use of [Ir2(C^N)4Cl2]
dimers, X-ray diffraction data for this family of complexes in
which C^N is (or is derived from) a 2-phenylpyridine ligand
remains sparse. A search of the Cambridge Structural Data-
base36 (CSD, v. 5.34 with November 2012, and February and
May 2103 updates) using Conquest v. 1.3526 generated only
nine hits,37–44 including the structures of the enantiomerically
pure Λ,Λ- and Δ,Δ-forms42 of [Ir2(ppy)4Cl2] as well as that of
the centrosymmetric Δ,Λ-form.41 In addition, we have recently
Scheme 2 Routes to the dimers [Ir2(C^N)4Cl2] with C^N = 3, 4, 5 and
7. Conditions: (i) 2-ethoxyethanol–H2O, reflux ≈22 h; (ii) 2-ethoxyetha-
nol; reflux overnight (for H3), or 110 °C, 1.5 h under microwave con-
ditions (for H4).
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is disordered and has been modelled over two sites of frac-
tional occupancies 0.62 and 0.38.
Synthesis and characterization of [Ir(C^N)2(bpy)][PF6]
complexes
Synthesis of the [Ir(C^N)2(bpy)][PF6] complexes was initially
approached using the established methodology32 of treating
the appropriate [Ir2(C^N)4Cl2] dimer with two equivalents of
bpy. This method was successful in five out of six cases
(Scheme 3a). [Ir(1)2(bpy)][PF6], [Ir(3)2(bpy)][PF6], [Ir(4)2(bpy)]-
[PF6] and [Ir(5)2(bpy)][PF6] were isolated in yields ranging from
70.3 to 87.7%. Purification of [Ir(4)2(bpy)][PF6] required a
series of chromatographic and precipitation steps (see Experi-
mental section), but a high yield was still obtained. Purifi-
cation of [Ir(7)2(bpy)][PF6] also required two chromatography
columns and the final yield was only 30.0%; unreacted dimer
was not recovered and the side products were not identified.
Since the dimer [Ir2(6)4Cl2] could not be prepared (see above),
we adopted a nucleophilic substitution approach to prepare
[Ir(6)2(bpy)][PF6] from [Ir(1)2(bpy)][PF6] (Scheme 3b). The
fluoro-derivative was treated with 1-dodecanethiol in the pres-
ence of sodium hydride and, after workup, [Ir(6)2(bpy)][PF6]
was obtained in 73.8% yield. We have recently demonstrated
that the presence of small amounts of chloride ion can have
significant negative impact on the performance of materials
in LECs, and all new compounds were shown to exhibit
no changes in their 1H NMR spectra upon the addition of
[nBu4N][PF6].46
Fig. 4 ORTEP representation of [Ir2(3)4Cl2] in [Ir2(3)4Cl2]·2CH2Cl2 (ellip-
soids plotted at 30% probability level and H atoms omitted). Important
bond parameters: Ir1–C19 = 1.984(8), Ir1–C7 = 1.988(8), Ir1–N1 = 2.050(7),
Ir1–N2 = 2.057(7), Ir1–Cl1 = 2.486(2), Ir1–Cl2 = 2.512(2), Ir2–C43 =
1.995(8), Ir2–C31 = 2.015(9), Ir2–N4 = 2.043(7), Ir2–N3 = 2.053(7), Ir2–
Cl2 = 2.503(2), Ir2–Cl1 = 2.504(2), S1–O3 = 1.404(9), S1–O4 = 1.441(8),
S1–C21 = 1.778(9), S1–C24 = 1.786(10), O1–S2 = 1.422(8), O2–S2 =
1.439(7) Å; Cl1–Ir1–Cl2 = 84.46(7), Cl2–Ir2–Cl1 = 84.30(6), C19–Ir1–N1
= 80.2(3), C7–Ir1–N2 = 80.9(3), C31–Ir2–N3 = 80.7(3), O3–S1–O4 =
117.5(5), O1–S2–O2 = 117.0(5), O6–S3–O5 = 119.7(5), O7–S4–O8 =
117.1(6)°.
reported the structure of [Ir2(dfppz)2(µ-Cl)2]·CH2Cl2 (Hdfppz =
1-(2,4-difluorophenyl)-1H-pyrazole).45
Single crystals
of
The base peak in the electrospray mass spectrum of each
[Ir(C^N)2(bpy)][PF6] complex consisted of a peak envelope
corresponding to [M − PF6]+ exhibiting the characteristic isoto-
pic distribution for iridium. The 1H and 13C NMR spectra of
each complex were consistent with a C2-symmetric cation.
Fig. 5 shows the 1H NMR spectrum of [Ir(5)2(bpy)][PF6] as a
representative example. Signals in the 1H and 13C NMR spectra
were assigned using a combination of COSY, HMQC and
HMBC methods. The 1H NMR signal for the tbutyl group
in [Ir(4)2(bpy)][PF6] appears at δ 1.00 ppm and shifts to lower
frequency (δ 0.93 ppm) in the analogous sulfone derivative
[Ir(5)2(bpy)][PF6]. The 13C NMR resonance for the primary
carbon atom in the tbutyl group shifts from δ 31.1 to 23.5 ppm
on going from [Ir(4)2(bpy)][PF6] to [Ir(5)2(bpy)][PF6], while the
S-attached 13C nucleus resonates at δ 46.8 and 60.3 ppm,
respectively, in the sulfane and sulfone complexes. In
[Ir(6)2(bpy)][PF6] and [Ir(7)2(bpy)][PF6], the SCH2 unit is charac-
terized by signals at δ(1H) 2.63 ppm and δ(13C) 32.0 ppm in the
sulfane and δ(1H) 2.87 ppm and δ(13C) 56.3 ppm in the
sulfone. Across the series of [Ir(C^N)2(bpy)][PF6] complexes,
the only bpy-proton signal to be noticeably affected is that
assigned to HE6 (see Scheme 3) since only this bpy proton is
directed towards the substituted phenyl ring. As expected,
signals arising from the phenyl-ring protons (HA3, HA4 and
HA6) undergo the most significant changes in chemical shift.
For each pair of sulfane and sulfone complexes, signals for
HA3, HA4 and HA6 all move to higher frequency (Δδ is in the
range 0.20 and 0.56 ppm). Signals for protons HA6 and HA4
[Ir2(3)4Cl2]·2CH2Cl2 were grown from a CH2Cl2 solution of the
complex overlaid with Et2O. The structure of the dimer is
shown in Fig. 4; each iridium atom is in an octahedral environ-
ment. The complex crystallizes in the orthorhombic space
group Pbca and the asymmetric unit contains the Λ,Λ-enantio-
mer with both the Λ,Λ- and Δ,Δ-forms present in the lattice.
As in other [Ir2(C^N)4Cl2] dimers and in mononuclear
[Ir(C^N)2(N^N)]+ cations, the two cyclometallated ligands are
arranged with the N-donors trans to one another at each
iridium centre. Bond parameters (cation to Fig. 4) are unexcep-
tional. The orientations of the four independent sulfone
groups with respect to the phenyl ring to which each is
attached fall into two categories. Two are twisted in a similar
manner to that in the free ligand H3 (see above) with torsion
angles of O1–S2–C9–C8 and O2–S2–C9–C10 = 30.9(9) and
−20.5(9)° and O5–S3–C33–C32 and O6–S3–C33–C34 = 31.4(9)
and −17.4(9)°. This arrangement gives rise to short CHphenyl
⋯
Osulfone contacts of 2.59 and 2.66 Å, and 2.56 and 2.62 Å,
respectively (two per sulfone group). In contrast, the sulfone
groups containing S1 and S4 are oriented such that the torsion
angles are O3–S1–C21–C22 and O4–S1–C21–C20 = −58.2(9)
and −3.3(9), and O7–S4–C45–C46 and O8–S4–C45–C44 = −53.8(9)
and −1.3(9)°. This leads to one CHphenyl⋯Osulfone contact
being more effective than the other (separations of 2.49 versus
2.99 Å, and 2.47 versus 2.96 Å). The CH2Cl2 solvate molecules
sit in pockets between pairs of cyclometallated ligands bound
to different iridium centres of the dimer. One CH2Cl2 molecule
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Fig. 5 500 MHz 1H NMR spectrum (295 K, CD3CN) of [Ir(5)2(bpy)][PF6];
see Scheme 3 for proton labelling. Scale: δ /ppm.
Fig. 6 ORTEP representation of the Δ-[Ir(1)2(bpy)]+ in Δ-[Ir(1)2(bpy)]-
[PF6] (ellipsoids plotted at 40% probability level and H atoms omitted).
Selected bond parameters: Ir1–C17 = 2.008(4), Ir1–C28 = 2.008(4), Ir1–
N3 = 2.048(3), Ir1–N4 = 2.054(3), Ir1–N1 = 2.130(3), Ir1–N2 = 2.141(3),
C19–F1 = 1.374(5), C30–F2 = 1.370(5) Å; N1–Ir1–N2 = 76.95(12), C17–
Ir1–N3 = 80.17(14), C28–Ir1–N4 = 80.77(14), N3–Ir1–N4 = 172.38(12),
C17–Ir1–N1 = 170.94(13), C28–Ir1–N2 = 172.58(13)°.
Scheme 3 Synthetic routes to the [Ir(C^N)2(N^N)][PF6] complexes. In
route (a), conditions: (i) bpy, MeOH at reflux or in microwave reactor,
n
120 °C; (ii) NH4PF6. In route (b), conditions: (iii) C12H25SH, NaH, DMF,
Enantiomerically pure Δ-[Ir(1)2(bpy)][PF6] crystallizes in the tri-
gonal space group P3121 and Fig. 6 shows the structure of the
Δ-[Ir(1)2(bpy)]+ cation. The octahedral environment of Ir1 with
trans-arrangement of the N donors (N3 and N4) of the cyclo-
120 °C. Atom labelling for NMR spectroscopic assignments is shown.
undergo the largest shifts to lower frequency in the fluoro- metallating ligands is as expected, and bond parameters
derivative, appearing at δ 5.89 and 6.81 ppm, respectively.
(see Fig. 6 caption) are typical. We note that the packing inter-
Single-crystal data were collected for [Ir(1)2(bpy)][PF6] actions are predominantly CH⋯F contacts involving the F
(crystals being grown from MeCN or CH2Cl2 solutions of the atoms of both the [PF6]− anions and the fluorophenyl rings.
complex overlaid with Et2O, respectively) and fortuitously There are no π-stacking interactions between arene rings of
resulted in the determination of the structures of adjacent cations. This is in contrast to those observed in rac-
Δ-[Ir(1)2(bpy)][PF6] and rac-4{[Ir(1)2(bpy)][PF6]}·Et2O·2CH2Cl2. [Ir(1)2(bpy)][PF6] described below.
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the asymmetric unit. Extensive CH⋯F contacts contribute to
the crystal packing. The CH2Cl2 solvent molecule is ordered,
and the Et2O molecule is half occupancy.
Photophysical properties
The solution electronic absorption spectra of [Ir(C^N)2(bpy)]-
[PF6] (C^N = 1, 3–7) are shown in Fig. 9. All are dominated by
intense high-energy bands which we assign to ligand-centred
(LC), spin-allowed π*←π or π*←n transitions. The origin of the
lower intensity and broader spectrum of [Ir(6)2(bpy)][PF6] is
not readily interpreted, but reproducibility with different
batches of compound was confirmed. All spectra extend into
the visible region, consistent with the yellow colour of the com-
pounds [Ir(C^N)2(bpy)][PF6] (C^N = 1, 3–5, 7) and orange
colour of [Ir(6)2(bpy)][PF6]. Absorptions at wavelengths in the
approximate range 350 to 450 nm are attributed to low inten-
sity 1MLCT and 1LLCT bands.1
Excitation of MeCN solutions of the complexes with λexc
varying between 269 and 300 for [Ir(1)2(bpy)][PF6], and
between 252 and 400 nm for the other complexes results in
the emission spectra shown in Fig. 10. The spectra are invar-
iant of chosen values of λexc in the above ranges with the excep-
tion of the appearance of the relevant harmonic band. The
complexes [Ir(1)2(bpy)][PF6], [Ir(4)2(bpy)][PF6] and [Ir(6)2(bpy)]-
[PF6] (i.e. fluoro and sulfane substituents on the C^N ligands)
are yellow emitters and the emission bands are broad and fea-
tureless. In contrast, [Ir(3)2(bpy)][PF6], [Ir(5)2(bpy)][PF6] and
[Ir(7)2(bpy)][PF6] are green emitters and the emission
spectra exhibit vibrational structure. The emitting state of
[Ir(C^N)2(N^N)]+ is the lowest energy triplet state which may
contain contributions from 3MLCT, 3LC and 3LLCT states.1 Sig-
nificant charge-transfer contributions lead to broad emission
bands, but when the CT contributions are small, structured
emissions are observed as is the case for the sulfone-
containing complexes [Ir(3)2(bpy)][PF6], [Ir(5)2(bpy)][PF6] and
[Ir(7)2(bpy)][PF6]. Table 2 summarizes the room temperature
solution photophysical properties of the complexes. Compared
Fig. 7 Face-to-face/edge-to-face embrace between the two indepen-
dent
Δ
and Λ-[Ir(1)2(bpy)]+ cations in rac-4{[Ir(1)2(bpy)][PF6]}·
Et2O·2CH2Cl2: (a) space-filling, and (b) showing relative orientations of
the fluorophenyl and pyridine rings involved in the face-to-face inter-
action and CH⋯π contacts (red hashed lines).
Fig. 8 Chain of alternating Δ- (red) and Λ- (blue) [Ir(1)2(bpy)]+ cations in
rac-4{[Ir(1)2(bpy)][PF6]}·Et2O·2CH2Cl2.
The racemate crystallizes as the solvate rac-4{[Ir(1)2(bpy)]-
ˉ
[PF6]}·Et2O·2CH2Cl2 in the triclinic space group P1. In terms
of bond parameters, the structure of each enantiomer of the
[Ir(1)2(bpy)]+ cation is similar to that of the Δ-[Ir(1)2(bpy)]+
cation described above and we focus only upon the packing
interactions. The asymmetric unit in 4{[Ir(1)2(bpy)][PF6]}·
Et2O·2CH2Cl2 contains two [Ir(1)2(bpy)]+ cations of opposite
handedness which engage in an embrace47 involving face-to-
face and edge-to-face π-interactions (Fig. 7). The face-to-face
contact is between a fluorophenyl ring and one pyridine ring
of a bpy ligand; the rings are slipped such that the F atom
lies partly over the pyridine π-system48,49 (Fig. 7b) and the
interplane angle is 12.4°. The centroid⋯centroid separation
of 4.24 Å lies towards the upper end of the typical range of
interactions involving pyridine rings.50 For the CH⋯π contacts
(one CHfluoroPh⋯πpy and one CHpy⋯πfluoroPh), the CH⋯cen-
troid distances are 2.59 and 3.03 Å. Face-to-face π-interactions
between crystallographically independent Δ- and Λ-[Ir(1)2-
(bpy)]+ cations extend beyond the single pair in the asymmetric
unit to generate chains that run parallel to the c-axis (Fig. 8).
The [PF6]− anions are ordered; atoms P2 and P3 reside on
inversion centres with half of each respective anion present in
Fig. 9 Absorption spectra of MeCN solutions of [Ir(C^N)2(bpy)][PF6] for
C^N = 1, 3, 4, 5, 6 and 7. See experimental section for concentrations.
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Fig. 11 Solid-state emission spectra of [Ir(C^N)2(bpy)][PF6] for C^N = 1
and 3–7. Excitation wavelengths: see Table 3.
Fig. 10 Solution emission spectra of [Ir(C^N)2(bpy)][PF6] for C^N = 1, 3,
4, 5, 6 and 7 (298 K, MeCN). See experimental section for solution con-
centrations. Excitation wavelengths: 300 nm (with 1) and 400 nm (with
3, 4, 5, 6 and 7). * = Harmonic at 600 nm.
Table 3 Solid-state photophysical properties of [Ir(C^N)2(bpy)][PF6]
(C^N = 1, 3–7)
Table 2 Solution photophysical properties of [Ir(C^N)2(bpy)][PF6] (C^N =
1, 3–7). PLQY measured in de-aerated MeCN; lifetimes measured in Complex
λmemax a/nm
λexc (for PLQY)/nm
PLQY/%
de-aerated MeCN under argon atmosphere
[Ir(1)2(bpy)][PF6]
547
532
553
535
558
537
269
262
260
262
252
262
23
Complex
λexc/nm
λmemax/nm
τ1/2 a/μs
PLQY/%
[Ir(3)2(bpy)][PF6]
[Ir(4)2(bpy)][PF6]
[Ir(5)2(bpy)][PF6]
[Ir(6)2(bpy)][PF6]
[Ir(7)2(bpy)][PF6]
6.6
4.9
15
2.6
4.2
[Ir(1)2(bpy)][PF6]
[Ir(3)2(bpy)][PF6]
[Ir(4)2(bpy)][PF6]
[Ir(5)2(bpy)][PF6]
[Ir(6)2(bpy)][PF6]
[Ir(7)2(bpy)][PF6]
269
262
260
262
252
262
557
493, 525
568
493, 523
577
493, 524
0.224
2.33
0.528
3.36
0.369
3.21
36
74
24
64
15
64
a λexc = 405 nm.
a λexc = 280 nm for complexes with 3, 5 and 7; 340 nm for complexes
with 1, 4 and 6.
steric bulk of the alkyl substituent may be detrimental to the
PLQY value. We note that if solution samples are not de-
aerated, the PLQY values are dramatically reduced to values of
between 2.6% for [Ir(6)2(bpy)][PF6] and 5.5% for [Ir(5)2(bpy)]-
to the parent complex [Ir(ppy)2(bpy)][PF6] which emits at [PF6], consistent with strong quenching of the phosphor-
585 nm (de-aerated MeCN, 298 K),51 [Ir(1)2(bpy)][PF6] shows an escence by oxygen.
emission at 557 nm, consistent with a lowering of the energy
The emission lifetimes for the six complexes in de-aerated
of the HOMO and widening of the HOMO–LUMO gap upon MeCN were measured under argon and are given in Table 2.
the introduction of the electron-withdrawing fluoro-groups. The longest lived emission (3.36 μs) is for [Ir(5)2(bpy)][PF6]; in
t
Replacement of F by BuS on going from [Ir(1)2(bpy)][PF6] to general, the complexes in which the cyclometallated ligand
[Ir(4)2(bpy)][PF6] results in an 11 nm red-shift in the emission, bears a sulfone substituent exhibit lifetimes that are an order
t
and a change from butyl to ndodecyl sulfane gives a further of magnitude longer than those containing fluoro or sulfane
9 nm red-shift. Both sulfane complexes are blue-shifted with group.
respect to [Ir(ppy)2(bpy)][PF6]. The three sulfone complexes
Fig. 11 illustrates the emission spectra of powdered
exhibit almost identical solution emission spectra (Fig. 10 samples of the complexes and emission maxima and PLQY
max
em
and Table 2) with λ
[Ir(ppy)2(bpy)][PF6].
blue-shifted by 92 nm with respect to values are given in Table 3. All emission bands are broad and
featureless. For the complexes containing the sulfane- or
The photoluminescence quantum yields (PLQY) and fluoro-substituted C^N ligands (4, 6 or 1), a blue shift in the
lifetimes (τ1/2) of the solution-state emissions should be emission is observed on going from solution to the solid state.
compared with values of 14% and 0.43 μs measured for For [Ir(3)2(bpy)][PF6], [Ir(5)2(bpy)][PF6] and [Ir(7)2(bpy)][PF6],
[Ir(ppy)2(bpy)][PF6] under analogous room temperature con- the solid-state emission maximum is red-shifted to ≈535 nm.
ditions.51 Substantial enhancement of the PLQY is observed With the exception of [Ir(1)2(bpy)][PF6] for which the solid-
for the most electron-withdrawing (F and SO2R) substituents state PLQY is 23% (λexc = 269 nm), PLQYs for powdered
(Table 2). The value of 74% for [Ir(3)2(bpy)][PF6] (SO2Me substi- samples are significantly lower than those obtained in de-
tuents) is particularly high, and it appears that increasing the aerated solution (compare Tables 2 and 3).
5354 | Dalton Trans., 2014, 43, 5343–5356
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Table 4 Cyclic voltammetric data with respect to Fc/Fc+ in MeCN solu-
tions with [tBu4N][PF6] as supporting electrolyte, and a scan rate of 0.1 V
s−1 (ir = irreversible; qr = quasi-reversible)
derivative [Ir(1)2(bpy)][PF6] since attempts to prepare the dimer
[Ir2(6)4Cl2] were unsuccessful.
The new complexes have been fully characterized by spec-
troscopic and mass spectrometric methods. The single crystal
structures of Δ-[Ir(1)2(bpy)][PF6] and of rac-4{[Ir(1)2(bpy)]-
[PF6]}·Et2O·2CH2Cl2 have been elucidated, along with the
structures of the free ligands H3 and H5, and of the dimer
[Ir2(3)4Cl2]·2CH2Cl2. The solution absorption spectra of the
complexes are dominated by ligand-centred transitions, with a
tail into the visible arising from low intensity 1MLCT and
1LLCT bands. The room temperature, solution emission
spectra of [Ir(1)2(bpy)][PF6], [Ir(4)2(bpy)][PF6] and [Ir(6)2(bpy)]-
[PF6] (fluoro and sulfane substituents) are broad and feature-
less, consistent with substantial CT contributions to the lowest
energy triplet (emitting) state. These complexes are all yellow
emitters with λmemax between 557 and 577 nm. In contrast, incor-
poration of the sulfone substituents into the cyclometallating
ligands results in [Ir(3)2(bpy)][PF6], [Ir(5)2(bpy)][PF6] and
Complex
Eo1/x2/V
Er1e/2d/V
ΔE1/2/V
[Ir(1)2(bpy)][PF6]
[Ir(3)2(bpy)][PF6]
[Ir(4)2(bpy)][PF6]
[Ir(5)2(bpy)][PF6]
[Ir(6)2(bpy)][PF6]
[Ir(7)2(bpy)][PF6]
+1.07qr
+1.18
−1.74, −2.41ir, −2.54
−1.72, −2.16, −2.61ir
−1.75, −2.48ir, −2.57ir
−1.73, −2.18, −2.43
−1.76, −2.55ir
2.81
2.90
2.79
2.92
2.79
2.96
+1.04ir
+1.19
+0.82ir
+1.25
−1.71, −2.16, −2.39
Electrochemistry
Each of the [Ir(C^N)2(bpy)][PF6] complexes (C^N = 1, 3–7) is
electrochemically active, and cyclic voltammetric data are
given in Table 4. Unless stated otherwise, the electrochemical
processes are reversible or near-reversible. Each fluoro or
sulfone derivative (C^N = 1, 3, 5, 7) exhibits an iridium-based
reversible or quasi-reversible oxidation process at more posi-
tive potential than [Ir(ppy)2(bpy)][PF6] (E
[Ir(7)2(bpy)][PF6] being green emitters which exhibit structured
ox
1/2
= +0.84 V versus
max
em
emissions (λ
= 493 and 523 to 525 nm), consistent with
internal Fc/Fc+),51 consistent with the introduction of strongly
electron-withdrawing substituents on the cyclometallated
ligands. Compounds [Ir(4)2(bpy)][PF6] and [Ir(6)2(bpy)][PF6]
also undergo irreversible oxidations at +1.04 and +0.82 V,
respectively, which we have not investigated in detail. Two or
only minor CT contributions to the lowest energy triplet
state. The solution PLQYs of the sulfone complexes are 74%
for [Ir(3)2(bpy)][PF6] and 64% for both [Ir(5)2(bpy)][PF6] and
[Ir(7)2(bpy)][PF6], but for powdered solid samples, these are
significantly lower (≤15%). The emission lifetimes for the
complexes containing sulfone substituents in the C^N ligands
(3, 5 and 7) are an order of magnitude longer (2.33 to 3.36 μs)
than the complexes in which the C^N ligand carries a fluoro
or sulfane unit (0.224 to 0.528 μs). We are currently screening
[Ir(3)2(bpy)][PF6], [Ir(5)2(bpy)][PF6] and [Ir(7)2(bpy)][PF6] and
related complexes in device configuration in LECs.
three ligand-based reductions are observed for each complex,
and the E
red
1/2
potentials in Table 4 compare with −1.77 and
−2.60 V for [Ir(ppy)2(bpy)][PF6].51 The LUMO is localized on
the bpy ligand,1 and the values of the reduction potentials are
consistent with the processes being bpy-based, being little
affected by the electronic changes made to the C^N ligand
across the series of compounds.
The electrochemical band gaps, ΔE1/2 (Table 4) are all
larger than the 2.61 V in [Ir(ppy)2(bpy)][PF6],51 consistent with
the lowering of the HOMO upon introducing electron-with-
drawing substituents into the C^N domain. As expected,
the largest band gaps are observed for the sulfone derivatives
(C^N = 3, 5, 7). The trends in Table 4 parallel those observed
in the solution emission spectra (Table 2). The slightly smaller
values of ΔE1/2 on going from fluoro to sulfane derivatives are
consistent with the observed red-shift in emission maxima,
while the increase in ΔE1/2 on going to sulfones [Ir(C^N)2(bpy)]-
[PF6] (C^N = 3, 5, 7) corresponds to the blue-shift in the emis-
sions compared to those of [Ir(C^N)2(bpy)][PF6] (C^N = 1, 4, 6).
Acknowledgements
We thank the Swiss National Science Foundation, the
European Research Council (Advanced Grant 267816 LiLo) and
the University of Basel for financial support.
Notes and references
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We have prepared a series of [Ir(C^N)2(bpy)][PF6] complexes in
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