Strongly coupled cyclometalated ruthenium-triarylamine hybrids: Tuning electrochemical properties, intervalence charge transfer, and spin distribution by substituent effects

Article abstract of DOI:10.1002/chem.201404549

Nine cyclometalated ruthenium complexes with a redox-active diphenylamine unit in the para position to the Ru-C bond were prepared. MeO, Me, and Cl substituents on the diphenylamine unit and three types of auxiliary li-gands-bis(N-methylbenzimidazolyl)pyridine (Mebip), 2,2′:6′,2′-terpyridine (tpy), and trimethyl-4,4′,4′-tricarboxy-late-2,2′:6′,2′-terpyridine (Me₃tctpy)-were used to vary the electronic properties of these complexes. The derivative with an MeO-substituted amine unit and Me₃tctpy ligand was studied by single-crystal X-ray analysis. All complexes display two well-separated redox waves in the potential region of + 0.1 to +1.0V versus Ag/AgCl, and the potential splitting ranges from 360 to 510 mV. Spectroelectrochemical measurements show that these complexes display electrochrom-ism at low potentials and intense near-infrared (NIR) absorptions. In the one-electron oxidized form, the complex with the Clsubstituted amine unit and Mebip ligand shows a moderate ligand-to-metal charge transfer at 800 nm. The other eight complexes show asymmetric, narrow, and intense intervalence charge-transfer transitions in the NIR region, which are independent of the polarity of the solvent. The Mebip-containing complexes display rhombic or broad isotropic EPR signals, whereas the other seven complexes show relatively narrow isotropic EPR signals. In addition, DFT and time-dependent DFT studies were performed to gain insights into the spin distributions and NIR absorptions.

Full text of DOI:10.1002/chem.201404549

DOI: 10.1002/chem.201404549
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&
Mixed-Valent Compounds
Strongly Coupled Cyclometalated Ruthenium–Triarylamine
Hybrids: Tuning Electrochemical Properties, Intervalence Charge
Transfer, and Spin Distribution by Substituent Effects
Chang-Jiang Yao, Hai-Jing Nie, Wen-Wen Yang, Jiang-Yang Shao, Jiannian Yao, and Yu-
Wu Zhong*[a]
Abstract: Nine cyclometalated ruthenium complexes with
a redox-active diphenylamine unit in the para position to
the RuꢀC bond were prepared. MeO, Me, and Cl substituents
on the diphenylamine unit and three types of auxiliary li-
urements show that these complexes display electrochrom-
ism at low potentials and intense near-infrared (NIR) absorp-
tions. In the one-electron oxidized form, the complex with
the Cl-substituted amine unit and Mebip ligand shows
a moderate ligand-to-metal charge transfer at 800 nm. The
other eight complexes show asymmetric, narrow, and in-
tense intervalence charge-transfer transitions in the NIR
region, which are independent of the polarity of the solvent.
The Mebip-containing complexes display rhombic or broad
isotropic EPR signals, whereas the other seven complexes
show relatively narrow isotropic EPR signals. In addition, DFT
and time-dependent DFT studies were performed to gain in-
sights into the spin distributions and NIR absorptions.
gands—bis(N-methylbenzimidazolyl)pyridine
(Mebip),
2,2’:6’,2’’-terpyridine (tpy), and trimethyl-4,4’,4’’-tricarboxy-
late-2,2’:6’,2’’-terpyridine (Me3tctpy)—were used to vary the
electronic properties of these complexes. The derivative with
an MeO-substituted amine unit and Me3tctpy ligand was
studied by single-crystal X-ray analysis. All complexes display
two well-separated redox waves in the potential region of
+0.1 to +1.0 V versus Ag/AgCl, and the potential splitting
ranges from 360 to 510 mV. Spectroelectrochemical meas-
Introduction
Beside fundamental electron-transfer studies, the recent re-
surgence in MV compounds is largely driven by the current
need for functional molecular materials for miniaturized elec-
tronic devices. MV compounds are well-known for their ap-
pealing optical, electronic, and magnetic properties. More im-
portantly, these properties are significantly dependent on the
redox states of the materials and the externally applied poten-
tials. This feature makes MV compounds particularly useful in
a wide range of optoelectronic applications, such as electro-
chromic devices,[6] molecular switches,[7] molecular conduc-
tance,[8] information storage,[9] two-photon absorption,[10] and
high-spin materials.[11]
Mixed-valent (MV) compounds[1] have been the subject of in-
tense research activities since the pioneering work of Creutz
and Taube on charge delocalization in diruthenium com-
plexes.[2] At the same time, the seminal work by Hush and
others laid the foundation of the electron-transfer theory of
MV compounds.[3] To date, MV chemistry has become a power-
ful means to examine the fundamental electron-transfer pro-
cess among redox-active components. By analyzing the inter-
valence charge-transfer (IVCT) transitions of MV compounds,
important electron-transfer parameters, such as reorganization
energy and electronic coupling parameter Vab, can be estimat-
ed. According to the classification of Robin and Day,[4] three
categories of MV compounds can be distinguished. In addition,
intermediate class II/III borderline systems have received much
attention.[5]
To become useful in the above-mentioned applications, MV
compounds should have strong charge delocalization, low
redox potentials, and wide structural diversity. We recently re-
ported that the combination of cyclometalated ruthenium and
triarylamine (complex 5(PF6)2, Scheme 1) gives rise to a redox-
asymmetric MV system with these desirable electronic proper-
ties.[12] The strong electronic coupling between ruthenium and
[a] C.-J. Yao,+ H.-J. Nie,+ W.-W. Yang, J.-Y. Shao, Prof. Dr. J. Yao,
Prof. Dr. Y.-W. Zhong
+/0
amine results in low RuIII/II and N
potentials with wide po-
C
tential separation and rich near-infrared (NIR) absorptions in
the MV state. Electropolymerized films of a related complex
show interesting NIR electrochromism with long retention
time.[13] We consider that, with respect to structurally symmet-
ric MV systems with either ruthenium complexes[14] or triaryla-
mines[15] as the redox sites, an asymmetric ruthenium–amine
hybrid would allow a wider structural diversity and property
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratory of Photochemistry
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190 (P. R. China)
E-mail: zhongyuwu@iccas.ac.cn
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201404549.
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Scheme 1. Synthesis of 4(PF6)–12(PF6) and chemical structures of model complexes 13(PF6)–15(PF6).
tuning by varying the substituents on the two components.[16]
In this context, a series of related complexes 4(PF6)–12(PF6)
with three different amine groups and three N,N,N-auxiliary li-
gands was prepared (Scheme 1). Methoxyl, methyl, and chloro
groups were used to tune the properties of the triarylamine
subunit. The tridentate ligands bis(N-methylbenzimidazolyl)pyr-
idine (Mebip),[17] 2,2’:6’,2’’-terpyridine (tpy), and trimethyl-
4,4’,4’’-tricarboxylate-2,2’:6’,2’’-terpyridine (Me3tctpy)[18] were
used to vary the properties of the ruthenium subcomponent.
This article presents experimental and computational studies
on these complexes by single-crystal X-ray crystallography,
electrochemistry, IVCT analysis, EPR spectroscopy, and DFT and
time-dependent (TDDFT) calculations. In addition, model com-
plexes 13(PF6)–15(PF6) without the amine substituent were
prepared for a comparison study.
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Results and Discussion
Synthesis and characterization
As outlined in Scheme 1, N,C,N-type amine ligands 1–3 were
synthesized in moderate yield by palladium-catalyzed CꢀN
coupling of 3,5-bis(pyrid-2-yl)bromobenzene[12] with 4,4’-dime-
thoxydiphenylamine, 4,4’-dimethyldiphenylamine, and 4,4’-di-
chlorodiphenylamine, respectively. Following the known proce-
dure for the synthesis of cyclometalated ruthenium com-
plexes,[19] the treatment of [(Mebip)RuCl3] (Mebip=bis(N-meth-
ylbenzimidazolyl)pyridine), [(tpy)RuCl3] (tpy=2,2’:6’,2’’-terpyri-
dine), and [(Me3tctpy)RuCl3] (Me3tctpy=trimethyl-4,4’,4’’-
tricarboxylate-2,2’:6’,2’’-terpyridine) with AgOTf, followed by re-
action with ligand 1, 2, or 3 under microwave heating and
anion exchange with KPF6, gave the desired complexes 4(PF6)–
12(PF6) in 34–65% yield. Complex 5(PF6)2 was isolated with
two anions, as was previously reported.[12] Other new com-
plexes were isolated with one anion. A short reaction time (mi-
crowave heating for 30 min) is preferred for the isolation of
the complexes with one anion. Complexes 13(PF6)[17] and
14(PF6)[20] were synthesized according to the known proce-
dures. Complex 15(PF6) was obtained from the reaction of 1,3-
bis(pyrid-2-yl)benzene with [(Me3tctpy)RuCl3].
Figure 1. Single-crystal X-ray structure of 6(PF6)·2CHCl3 with 30% probability
thermal ellipsoids. Anion, solvent, and H atoms are omitted for clarity. Se-
lected bond lengths [ꢁ] and angles [8]: RuꢀC32 1.981(4), RuꢀN1 2.059(3),
RuꢀN2 2.007(3), RuꢀN3 2.064(3), RuꢀN4 2.098(3), RuꢀN5 2.098(3), RuꢀN6
6.194, C32-Ru-N2 176.83(14), C32-Ru-N5 77.64(14), C32-Ru-N1 100.81(13), N1-
Ru-N5 91.73(12), N4-Ru-N5 155.04(12), N1-Ru-N3 156.63(12).
The new compounds were fully characterized by NMR spec-
troscopy, mass spectrometry, and microanalysis. Signals consis-
tent with the chemical structures of the above complexes
ꢀ
(after loss of the PF6 anion) were observed on their MALDI-
TOF mass spectra. Complexes with the Mebip or tpy ligand are
easily oxidized in solution. The presence of the resulting para-
magnetic impurities makes it difficult to obtain well-defined
1H NMR signals. However, we found that this issue could be
remedied by adding a small amount of aqueous hydrazine to
the deuterated solvent (see the NMR spectra in the Supporting
Information). The hydrazine is believed to reduce the small
amount of the oxidized paramagnetic species and ensure the
complex has a charge of 1+. We previously found that com-
plex 52+ can be fully converted to 5+ by aqueous hydrazine.[12]
A single crystal of 6(PF6) was obtained by slow diffusion of
hexane into a solution in CHCl3. The single-crystal X-ray struc-
ture is shown in Figure 1. The ruthenium ion has a distorted
octahedral configuration. The RuꢀC bond is 1.981 ꢁ in length,
which is slightly shorter than the RuꢀN bonds. The distance
between the redox-active Ru center and N6 is 6.194 ꢁ.
Figure 2. Anodic CVs of a)–c) 4(PF6)–12(PF6) and d) 1–3 and 13(PF6)–15(PF6)
in 0.1m Bu4NClO4/CH3CN.
Electrochemical studies
The electronic properties of these complexes were first studied
by electrochemical analysis (Figures 2 and 3, Table 1, and Fig-
ure S1 in the Supporting Information). In the anodic scan, com-
plexes 4(PF6)–12(PF6) all show two well-separated redox waves
in the range of +0.1 to +1.0 V versus Ag/AgCl, as shown by
the cyclic voltammograms (CVs) and differential pulse voltam-
mograms (DPVs) in Figures 2 and 3. By comparing complexes
4(PF6)–6(PF6) with the same amine substituent but different
N,N,N ligands, it is clear that both redox waves of each com-
plex shift to more positive potential as the N,N,N ligand be-
Figure 3. Anodic DPVs of 4(PF6)–12(PF6) in 0.1m Bu4NClO4/CH3CN.
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significantly increases from 4(PF6) to 7(PF6) and 10(PF6). This is
caused by the increasing redox asymmetry DG0 from 4(PF6) to
10(PF6), instead of increasing electronic coupling. The follow-
ing spectroscopic studies indeed showed that complex 102+
has the lowest degree of charge delocalization among the
nine complexes studied. For the compounds of the tpy and
Me3tctpy series, the variation of DE versus s is much smaller. In
these complexes, the effect of electronic coupling probably
Table 1. Electrochemical data in CH3CN.[a]
[c]
E1/2,anodic
DE[b]
KC
E1/2,cathodic
[V]
[V]
[mV]
1
+0.77
–
–
–
–
–
–
–
2
+0.95
–
3
+1.15
–
4(PF6)
5(PF6)
6(PF6)
7(PF6)
8(PF6)
9(PF6)
10(PF6)
11(PF6)
12(PF6)
13(PF6)
14(PF6)
15(PF6)
+0.20, +0.65
+0.27, +0.68
+0.40, +0.76
+0.27, +0.74
+0.33, +0.77
+0.50, +0.87
+0.33, +0.84
+0.42, +0.87
+0.54, +0.92
+0.43
450
410
360
470
440
370
510
450
380
–
4.2ꢂ107
8.9ꢂ106
1.3ꢂ106
9.2ꢂ107
2.9ꢂ107
1.9ꢂ106
4.4ꢂ108
4.2ꢂ107
2.8ꢂ106
–
ꢀ1.60
ꢀ1.50
plays a more important role in the DE values.
ꢀ1.07, ꢀ1.42
ꢀ1.57
+/0
C
Figure 2d shows the N
process of ligands 1–3 and the
ꢀ1.51
RuIII/II process of model complexes 13(PF6)–15(PF6). The poten-
tials of these processes can be varied effectively by changing
the substituent on the amine ligand (MeO, Me, or Cl) or the
N,N,N ligand (Mebip, tpy, or Me3tctpy).
ꢀ1.07, ꢀ1.42
ꢀ1.58
ꢀ1.50
ꢀ1.09, ꢀ1.44
ꢀ1.56
In the region of more positive potential, some irreversible
oxidations are present for all complexes (Supporting Informa-
tion, Figure S2), which are possibly due to the RuIV/III processes
or further oxidation of the aminium component. In the catho-
dic scan, complexes with Mebip or tpy show one redox wave,
whereas complexes with Me3tctpy show two waves. These
waves are attributed to the reduction events of these auxiliary
ligands.
+0.56
+0.74
–
–
–
–
ꢀ1.51
ꢀ1.11, ꢀ1.46
[a] The electrochemical potential is reported as the E1/2 value versus Ag/
AgCl. Potential versus ferrocene+/0 can be estimated by subtracting
0.45 V. [b] Potential splitting of the two anodic redox waves of 4(PF6)–
12(PF6). [c] Comproportionation constant, determined as 10(DE/59)
.
comes increasingly electron-deficient on going from Mebip to
tpy and Me3tctpy. Similar trends hold for the 7(PF6)–9(PF6) and
10(PF6)–12(PF6) series. On the other hand, in complexes 4(PF6),
7(PF6), and 10(PF6), with the same N,N,N ligand but different
amine substituents, changing the amine substituent from MeO
to Me and Cl also leads to a positive shift of both redox waves
of each complex. Again, similar trends are shown by the 5(PF6),
8(PF6), 11(PF6) and 6(PF6), 9(PF6), 12(PF6) series. Thus, changing
either the amine substituent or the N,N,N ligand causes both
redox potentials of any complex to shift significantly in the
same direction, which is suggestive of strong coupling be-
tween the amine segment and the ruthenium component. In
stark contrast, we previously reported that in a related weakly
coupled hybrid system,[21] in which the amine substituent and
the RuꢀC bond are located in the meta position of the cyclo-
metalated phenyl ring, only very small changes in the RuIII/II po-
tential was observed when the electronic nature of the amine
substituent was varied.
Spectroscopic studies
The electronic absorption spectra of complexes 4(PF6)–15(PF6)
are shown in Figure S3 of the Supporting Information. Com-
plexes 4(PF6), 7(PF6), and 10(PF6) with Mebip show similar ab-
sorption bands in the visible region. However, the absorptions
between 500 and 600 nm are distinctly expanded with respect
to 13(PF6) without the amine substituent (Supporting Informa-
tion, Figure S3a). The main absorption bands in the visible
region are largely assigned to the metal-to-ligand charge-trans-
fer (MLCT) transitions. The additional expanded shoulder
bands between 500 and 600 nm of 4(PF6), 7(PF6), and 10(PF6)
are a result of the intraligand charge-transfer (ILCT) transitions
from the amine group. This is discussed below with the aid of
TDDFT results. The situations for the series 5(PF6), 8(PF6),
11(PF6), 14(PF6) and 6(PF6), 9(PF6), 12(PF6), 15(PF6) are very simi-
lar (Supporting Information, Figure S3b and S3c), in that the
shape of the absorption band is largely dependent on the aux-
iliary ligand. The presence of the amine unit distinctly expands
the visible absorption. However, the substituent (MeO, Me, or
Cl) of the amine unit makes little difference to the shape and
intensity of the absorption.
The potential splitting DE between the two anodic redox
waves of 4(PF6)–12(PF6) is in the range of 360–510 mV. Accord-
ingly, the comproportionation constant KC for the equilibrium
[N-Ru]+ + [N-Ru]3+!2[N-Ru]2+ is estimated to be in the range
of 1.3ꢂ106 to 4.4ꢂ108. This means that the MV states of these
complexes have high thermodynamic stability against dispro-
portionation. Note that the DE values of asymmetric MV com-
pounds are more complicated than those of symmetric ana-
logues. They contain contributions from the electronic cou-
pling, the energy difference DG0 between the reactant and
product states of the electron-transfer process, the electrostatic
effect, and the inductive effect, among others.[22]
On stepwise oxidative electrolysis at a transparent indium
tin oxide (ITO)/glass electrode in CH3CN, complexes 4(PF6)–
12(PF6) all display reversible two-step electrochromism
(Figure 4). In the one-electron oxidized states (the MV state),
strong NIR absorptions were observed for complexes 42+–92+
,
112+, and 122+. These absorptions are attributed to the IVCT
transitions, and they decreased significantly on double oxida-
tion. In principle, these IVCT transition should completely dis-
appear if the complex is fully oxidized to have a charge of 3+.
However, the highly oxidized complexes (particularly 113+ and
123+) had poor solubility in the presence of the electrolyte,
and precipitates appeared on exhaustive electrolysis at high
Figure S1 in the Supporting Information shows the plots of
the potential splitting DE of 4(PF6)–12(PF6) versus the Ham-
mett constant s of the substituents on the diphenylamine unit
(MeO, Me, Cl). For the Mebip series compounds, the DE value
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Figure 4. Absorption spectral changes of 4+–12+ on electrolysis at ITO in 0.1m Bu4NClO4/CH3CN. The applied potentials are referenced to Ag/AgCl.
potentials. For complex 10(PF6), a moderate absorption band
at 800 nm appeared on single oxidation, and this new band
decreased a little on further oxidation. Theoretical calculations
suggest that the free spin of 102+ is largely localized on the
ruthenium component, and the absorption band at 800 is at-
tributed to the ligand-to-metal charge transfer (LMCT) transi-
tion.
complexes. When the complex has a charge of 3+, the ab-
sorption pattern is largely dependent on the amine substitu-
ent. For instance, complexes 43+–63+ with the methoxy-substi-
tuted amine group all show sharp and intense absorptions
around 700 nm, while multiple absorption bands (labs,max
around 640 nm) are observed for 73+–93+ with the methyl-
substituted amine group. For the Cl-containing complexes
103+–123+, the absorption maxima shift to a region of even
higher energy. The e values of the absorptions of 43+–123+ are
more or less underestimated, because some amounts of the
The absorption maxima labs,max and molar extinction coeffi-
cients e of these complexes with different total charges are
summarized in Table 2, together with those of the three model
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Table 2. Absorption data in CH3CN.[a]
labs,max [nm] (e [105 Mꢀ1 cmꢀ1])
4+
332 (0.36), 348 (0.40), 460 (0.10), 524 (0.17)
466 (0.14), 511 (0.14), 968 (0.108)
528 (0.13), 698 (0.37)
424 (0.090), 502 (0.14), 546 (0.13)
488 (0.12), 1048 (0.124)
42+
43+
5+
52+
53+
6+
558 (0.13), 689 (0.43)
323 (0.29), 339 (0.26), 420 (0.16), 507 (0.13), 583 (0.10)
516 (0.13), 697 (0.077), 1107 (0.126)
419 (0.11), 581 (0.12), 696 (0.31)
332 (0.39), 348 (0.43), 460 (0.11), 520 (0.19)
458 (0.11), 520 (0.12), 920 (0.087)
526 (0.15), 593 (0.17), 640 (0.23)
424 (0.083), 505 (0.14), 542 (0.13)
504 (0.11), 978 (0.055)
401 (0.10), 507 (0.11), 542 (0.11), 585 (0.12), 637 (0.15)
323 (0.28), 340 (0.24), 419 (0.16), 506 (0.11), 586 (0.091)
504 (0.13), 1024 (0.095)
416 (0.13), 507 (0.13), 590 (0.18), 640 (0.26)
332 (0.40), 348 (0.42), 461 (0.11), 520 (0.17)
452 (0.13), 800 (0.048)
62+
63+
7+
72+
73+
8+
82+
83+
9+
92+
93+
10+
102+
103+
11+
112+
113+
12+
122+
123+
13+
14+
15+
450 (0.15), 540 (0.12)
424 (0.083), 504 (0.15), 538 (0.14)
506 (0.11), 953 (0.091)
Figure 5. NIR transitions of 42+–122+ in CH3CN.
577 (0.17)
323 (0.37), 340 (0.31), 418 (0.19), 503 (0.14), 582 (0.11)
425 (0.14), 501 (0.15), 982 (0.127)
420 (0.16), 502 (0.15), 583 (0.14)
334 (0.29), 349 (0.39), 457 (0.115), 516 (0.17)
315 (0.37), 372 (0.086), 423 (0.095), 499 (0.14)
325 (0.20), 341 (0.22), 419 (0.19), 587 (0.092)
pendent of solvent polarity. The largest energy difference is
400 cmꢀ1 for complex 52+ between the IVCT bands in CH3NO2
with respect to that in DMF. This solvent effect suggests that
these complexes belong to the fully delocalized class III or the
borderline II/III systems. Note that the solvatochromic effects
of these complexes are much smaller than those of the previ-
ously reported bis-triarylamine MV systems. For instance, a
class III bis-triarylamine MV system bridged by 1,4-phenylene
has a solvatochromic effect of 860 cmꢀ1 in CH3CN versus
CH2Cl2.[23] In addition, a class II MV system bridged by para-
C6H4CꢁCC6H4 has a solvatochromic effect of 2170 cmꢀ1 in
CH3CN versus CH2Cl2.[24]
Figure 5 shows the NIR bands of 42+–122+ in CH3CN as
a function of the wavenumbers (u in cm-1). The variation of the
amine substituent and the auxiliary ligand makes a big differ-
ence to the shape, energy, and intensity of the IVCT transitions.
The IVCT parameters are summarized in Table 3 (complex 102+
[a] Complexes with a charge of 1+ were obtained according to Scheme 1
and the counteranions are PF6ꢀ. Complexes with a charges 2+ or 3+
were obtained by electrolysis, whereby ClO4 counteranions were intro-
ꢀ
duced from the electrolyte.
complexes were not fully oxidized and still had a charge of
2+, as discussed above.
Spectroelectrochemical measurements on these complexes
were also carried out in CH2Cl2, acetone, CH3NO2, and DMF. Fig-
ure S4 in the Supporting Information shows a comparison of
the NIR transitions of the one-electron oxidized forms 42+
–122+ in different solvents. The spectral shapes and energies
and the IVCT transitions of these complexes are virtually inde-
Table 3. Parameters for IVCT transitions.[a]
[f]
nmax
[cmꢀ1
emax
[mꢀ1 cmꢀ1
Dn1/2(exptl)
[cmꢀ1
Dn1/2(calcd)
[cmꢀ1
Dn1/2(high)
[cmꢀ1
Dn1/2(low)
[cmꢀ1
Dn1/2(high)
Dn1/2(low)
/
nmax/2
mge
Vab,II
[b]
[c]
[d]
[e]
]
]
]
]
]
]
[cmꢀ1
]
[D]
[cmꢀ1
]
42+
52+
62+
72+
82+
92+
112+
122+
10330
9540
9030
10870
10220
9770
10490
10180
10800
12400
12650
8700
5500
9500
3880
3540
3320
3320
3400
3430
2950
3200
3935
3796
3763
4045
3927
3960
3981
4054
4400
4420
3890
3680
3960
4230
3500
3720
3350
2670
2740
2960
2840
2630
2400
2690
1.32
1.66
1.42
1.24
1.39
1.61
1.46
1.38
5165
4770
4515
5365
5110
4885
5245
5090
5.4
5.9
5.0
4.7
3.6
4.8
4.6
5.6
1900
1920
1540
1740
1260
1600
1650
1950
9100
13000
[a] Based on the spectroelectrochemical results. [b] The experimentally observed width at half-height. [c] The theoretically predicted width at half-height,
as estimated by Dn1/2(calcd) =[2310(nmaxꢀDE)]1/2, where DE is the electrochemical potential splitting (in cmꢀ1). [d] Twice the band width at half-height of the
high-energy side. [e] Twice the band width at half-height of the low-energy side. [f] Vab values for class II compounds, calculated by (mgenmax)/eR.
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is not included, because only LMCT transitions were observed).
The energy nmax of the IVCT band varies in the range of 9030–
10870 cmꢀ1. The emax value varies in the range of 5500–
13000 cmꢀ1. The full width at half-height Dn1/2(exptl) is around
3000–4000 cmꢀ1. According to the Hush theory,[3] the predicted
band half-width Dn1/2(calcd) for the IVCT of asymmetric MV sys-
tems is [2310(nmaxꢀDG0)]1/2. The energy difference DG0 can be
estimated to an upper limit by the potential splitting DE (in
cmꢀ1).[16,25] Thus, the theoretical lower limits of Dn1/2(calcd) can be
estimated for these complexes, which are all slightly wider
than the Dn1/2(exptl) values. However, due to the strong rutheni-
um–amine coupling, a large portion of the DE value should
arise from the charge delocalization effect, and the exact DG0
value must be much smaller relative to DE. In this sense, the
observed Dn1/2 values should be much narrower with respect
to the theoretical values.
EPR analysis
The EPR signals of 42+–122+, obtained by chemical oxidation
with cerium ammonium nitrate (0.5 equiv oxidant was used in
order to prevent over-oxidation), are shown in Figure 6. All
measurements were performed at 77 K in frozen CH3CN. Com-
plexes 42+–62+ and 82+–122+ show isotropic signals with g
factors of 2.108, 2.086, 2.062, 2.095, 2.077, 1.131, 2.112, and
The IVCT bands of the above complexes are all asymmetric.
The ratios between the bandwidth of the high-energy side and
the low-energy side Dn1/2(high)/Dn1/2(low) lie in the range of 1.24–
1.66. The asymmetric shape, high intensity, narrow bandwidth,
and solvent effect of the IVCT bands suggest that these com-
plexes are very likely fully delocalized class III systems. The Vab
values for class III compounds Vab,III can be directly estimated as
nmax/2,[3] and the Vab,III values of the above complexes are in the
range of 4515–5365 cmꢀ1. Note that the use of “IVCT band” is
inappropriate for class III compounds, because the valence is
averaged in such compounds. A better term to describe the
nature of these NIR absorptions is charge-resonance transition.
Figure 6. EPR signals of 42+–122+
.
2.097, respectively. The EPR signal of 102+ is much broader
than those of the other complexes. Complex 72+ shows
a rhombic signal with g1, g2, and g3 values of 2.288, 2.116, and
1.943, respectively. The anisotropy Dg (=g1ꢀg3) and the aver-
ꢁ
ꢂ
ÂÀ
Áꢀ Ã
1
=
g21 þ g22 þ g23
3
are 0.345 and 2.120,
2
For comparison, the Vab values for class II compounds Vab,II
,
age g factor hgi
¼
estimated by mgenmax/eR, are provided in Table 3, where mge is
the transition dipole moment of the IVCT band and can be cal-
culated from the integrated absorbance of the IVCT band.[15a,m]
The diabatic electron transfer distance R is taken from the Ru–
N geometrical distance (6.1 ꢁ for all), and e is the elementary
charge. The Vab,II values of the above complexes are in the
range of 1260–1950 cmꢀ1. These values are much smaller than
the corresponding nmax/2 values. The Vab,II values may be under-
estimated, since the true electron-transfer distance is very
likely shorter than the Ru–N geometrical distance due to the
strong electron delocalization.
For redox-asymmetric MV systems, nmax is the sum of DG0
and the reorganization energy.[3,16] If the reorganization energy
is assumed to be constant for a series of structurally related
compounds and DG0 varies linearly as a function of DE, a good
linear relationship between nmax and DE would be expected.
Figure S5 in the Supporting Information shows plots of the
IVCT energies nmax versus the potential splitting DE of the
above complexes. In general, the IVCT energies increase with
increasing potential splitting, and the plot of nmax versus DE
could be fitted to a linear equation. However, the R2 value for
the linear equation is poor (0.7187). This may suggest that the
substituent effect has a significant impact on the electronic
properties of these MV complexes, which leads to a big varia-
tion of the reorganization and/or the DG0 values.
respectively. The rhombic EPR signal of 72+ and broad isotropic
signal of 102+ suggest that the ruthenium components of
these two complexes make significant contributions to the
free spins,[14,26] whereas the spins of the other seven complexes
are more biased toward the triarylamine segment.
DFT and TDDFT calculations
DFT and TDDFT calculations were performed to complement
the above experimental findings. The TDDFT results of 4+, 5+,
and 6+ are shown in Table S1 and Figures S6 and S7 in the
Supporting Information. Taking complex 4+ as an example, the
visible absorptions are mainly associated with the predicted S4,
S6, S8, S10, and S15 excitations. Among them, the S4, S8, and S15
excitations have dominant contributions from the HOMO!
LUMO+2, HOMO!LUMO+3, and HOMO!LUMO+4 transi-
tions. These transitions are mainly of ILCT character from the
amine unit to the cyclometalated ligand. The S6 and S10 excita-
tions are dominated by the MLCT transitions from HOMOꢀ1
and HOMOꢀ2. Similar ILCT and MLCT transitions were predict-
ed for 5+ and 6+ (Supporting Information, Table S1), and ac-
count for the slight expansion of the visible absorption of
these complexes with respect to those without the amine sub-
stituent (Supporting Information, Figure S3). Complexes 7+
–12+ are believed to have similar transitions, as they have very
similar absorption shapes with respect to the methoxy-contain-
ing series (4+–6+).
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bution from the N1 atom increas-
es from 0.238 to 0.257 and
0.278. The methyl-containing
series (72+–92+) and chloro-con-
taining series (102+–122+) show
similar trends.
A similar analysis can be ap-
plied to complexes with the
same auxiliary ligand but differ-
ent amine substituent. When the
substituent varies from MeO to
Me and Cl, the ruthenium contri-
bution of the Mebip-containing
series increases from 0.268 (42+
)
to 0.385 (72+) and 0.441 (102+),
and the contribution from the
N1 atom decreases from 0.238 to
0.197 and 0.159, respectively.
Again, a similar trend is present
for the tpy-containing series
(52+, 82+, and 112+) and chloro-
containing series (62+, 92+, and
122+).
The spin-population difference
can be reflected by the spin
ratio between the ruthenium ion
Figure 7. DFT-calculated Mulliken spin-density distributions of 42+–122+. See details in Table 4.
The geometries of the MV compounds 42+–122+ were opti-
mized by DFT calculations. It has been reported that class III
compounds show fully delocalized spin populations in polar
solvents.[27] Figure 7 and Table 4 show the spin-density distribu-
tions calculated by taking into account the solvent effect in
CH2Cl2. The electronic nature of the amine substituent and the
auxiliary ligand has a significant impact on the spin distribu-
tions. Taking the methoxy-containing series as an example, as
the auxiliary ligand becomes increasingly electron-deficient on
going from 42+ to 52+ and 62+, the ruthenium contribution
decreases from 0.268 to 0.220 and 0.160. Meanwhile the contri-
and the N1 atom, which varies in the range of 0.58 (62+) to
2.77 (102+). Complex 102+ has the largest Ru/N1 spin ratio,
which is significantly larger than those of the other complexes.
This supports the previous spectroscopic results that complex
102+ shows a weak LMCT band rather than a strong IVCT tran-
sition. The Mebip-containing complexes 72+ and 102+, which
show rhombic or broad isotropic EPR signals, have relatively
high Ru/N1 spin ratio. However, this rule is not strictly correct.
Complex 112+ also has a large Ru/N1 ratio, but has a narrow
isotropic EPR signal. Note that the spin is also rather delocal-
ized across the Ph1, Ph2, and Ph3 rings. In addition, DFT calcula-
tions are known to overestimate charge delocalization, and
these results should be taken with care.
Table 4. DFT-calculated Mulliken spin density (aꢀb) distribution.[a]
To rationalize the absorption spectra of the one-electron oxi-
dized compounds 42+–122+, TDDFT calculations were per-
formed on the above optimized structures. The predicted low-
energy doublet excitations are summarized in Table 5. Charge-
resonance transitions with strong oscillator strength were re-
produced for 42+–92+, 112+, and 122+. These transitions are all
associated with the spin transitions from the b highest occu-
pied spin orbital (HOSO) to the b LUSO (Figure 8 and Figure S8
in the Supporting Information). Other predicted transitions in
the NIR region have zero or negligible oscillator strength (Sup-
porting Information, Table S2).
The TDDFT results of 102+ are different from the others. The
predicted D3 excitation with oscillator strength of 0.4457 is re-
sponsible for the observed absorption band at 800 nm. This
excitation is dominated by the spin transition from b-HOSOꢀ1
to b-LUSO (right panel in Figure 8), which is mainly involved in
the LMCT transitions from the Mebip ligand to the ruthenium
ion. Figure S9 in the Supporting Information shows the plot of
42+
52+
62+
72+
82+
92+
102+ 112+ 122+
Ru
Ph3
N1
0.268 0.220 0.160 0.385 0.356 0.291 0.441 0.414 0.354
0.230 0.216 0.209 0.263 0.268 0.284 0.265 0.265 0.281
0.238 0.257 0.278 0.197 0.213 0.242 0.159 0.174 0.200
0.103 0.124 0.146 0.063 0.071 0.086 0.045 0.055 0.067
0.020 0.025 0.029 ꢀ0.003 ꢀ0.003 ꢀ0.004 0.004 0.005 0.007
0.104 0.125 0.146 0.062 0.070 0.085 0.046 0.055 0.067
0.020 0.025 0.029 ꢀ0.003 ꢀ0.003 ꢀ0.004 0.004 0.005 0.007
Ph1
X1
Ph2
X2
Ru/N1 1.13 0.86 0.58
1.95
1.67
1.20 2.77 2.38 1.77
[a] Method of calculation: UB3LYP/LANL2DZ/6-31G*/CPCM(solvent=
CH2Cl2).
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purities. However, the presence of small amount of aqueous
hydrazine successfully resolves this issue, and satisfactory NMR
spectra have been recorded for all new cyclometalated ruthe-
nium complexes studied herein. We believe that these two ex-
perimental techniques would be highly useful for the future
study and characterization of cyclometalated complexes.
Thirdly, this work demonstrates that, by combining organic
and inorganic redox sites, a library of structurally asymmetric
MV compounds can be easily expanded by changing the sub-
stituent or auxiliary ligand. With m types of amine substituents
and n types of auxiliary ligand at hand, a library of mꢂn two-
center compounds can be readily obtained. Such a method
would be very efficient for expanding structural diversity of re-
lated materials. Fourthly, the substituent effect has a significant
impact on the electrochemistry, IVCT transitions, and spin dis-
tributions of the resulting MV compounds. All nine com-
pounds, except 102+, show interesting electrochromism at low
potentials and with intense NIR absorptions. They belong to
the fully delocalized class III systems, according to the asym-
metric shape, high intensity, narrow bandwidth, and solvent
effect of the IVCT bands. Such compounds are highly useful as
information-storage media.[13] The variation of the redox poten-
tials and IVCT energies would allow us to make films with mul-
tistate electrochromism by copolymerization of two complexes
(e.g., complexes 5 and 11 with large potential difference),[29]
which will be the subject of future work. Finally, DFT and
TDDFT calculations were found to provide useful and comple-
mentary information on the spin populations and IVCT transi-
tions, and they are expected to attract increasing attention in
the study of MV compounds and transition-metal com-
plexes.[27,30]
Table 5. TDDFT-predicted doublet (D) excitations.[a]
Excitation
E [cmꢀ1
]
l [nm]
f
Major contribution
42+
D3
D3
D1
D3
D3
D3
D3
D3
D3
8979.4
8838.3
9030.2
9794.1
9457.7
9382.7
10264.3
9827.9
9565.0
1113.7
1131.4
1107.4
1021.0
1057.3
1065.8
974.3
0.4577
0.4680
0.4297
0.4408
0.4654
0.5116
0.4165
0.4457
0.5068
H(b)!L(b) (93%)
H(b)!L(b) (93%)
H(b)!L(b) (86%)
H(b)!L(b) (94%)
H(b)!L(b) (94%)
H(b)!L(b) (92%)
H-1(b)!L(b) (92%)
H(b)!L(b) (94%)
H(b)!L(b) (93%)
52+
62+
72+
82+
92+
102+
112+
122+
1017.5
1045.5
[a] The computational method was UB3LYP/LANL2DZ/6-31G*/CPCM/
CH2Cl2. f is the predicted oscillator strength. H=HOSO; L=LUSO.
Figure 8. Spin orbitals of a) 42+ and b) 102+ involved in the TDDFT results
shown in Table 5. Other spin orbitals are provided in Figure S6 in the Sup-
porting Information.
Experimental Section
Spectroscopic measurements
the calculated NIR absorption energies of 42+–122+ versus the
observed values. The trend in transition energies is basically re-
produced by the calculation.
Absorption spectra were recorded on a PE Lambda 750 UV/Vis/NIR
spectrophotometer at room temperature. Spectroelectrochemical
measurements were performed in a thin-layer cell (optical length=
0.2 cm), in which an ITO/glass working electrode (<10 W/square)
was set in the indicated solvent containing the compound to be
studied (cꢂ5ꢂ10ꢀ5 m) and 0.1m Bu4NClO4 as the supporting elec-
trolyte. A platinum wire and Ag/AgCl in saturated aqueous NaCl
were used as the counter electrode and reference electrode, re-
spectively. The cell was put into the spectrometer to monitor the
spectral change during electrolysis.
Conclusion
We have presented an experimental and theoretical study on
a series of strongly coupled cyclometalated ruthenium–triaryla-
mine hybrid compounds. We consider that the following infor-
mation is of high importance for the design and study of cy-
clometalated complexes, new MV systems, and electrochromic
molecular materials. Firstly, Me3tctpy seems to be a good auxil-
iary ligand for obtaining single crystals of cyclometalated com-
plexes. In addition to the ruthenium complex 6(PF6), we have
Electrochemical measurements
All electrochemical measurements were performed by using a CHI
660D potentiostat with one-compartment electrochemical cell
under an atmosphere of nitrogen. All measurements were carried
out in 0.1m Bu4NClO4 in indicated solvents at a scan rate of
100 mVsꢀ1. The glassy carbon working electrode had a diameter of
3 mm. The electrode was polished prior to use with 0.05 mm alumi-
na and rinsed thoroughly with water and acetone. A large-area
platinum wire coil was used as the counter electrode. All potentials
are referenced to an Ag/AgCl electrode in saturated aqueous NaCl
without regard for the liquid-junction potential. The potential
versus ferrocene+/0 can be estimated by subtracting 0.45 V.
recently reported
a
Me3tctpy-containing cyclometalated
osmium complex,[28] the structure of which has also been con-
firmed by single-crystal X-ray analysis. Cyclometalated com-
plexes are generally easily oxidized by oxygen, and the stability
can be enhanced by the electron-withdrawing Me3tctpy ligand.
Secondly, due to the stability issue of cyclometalated rutheni-
um complexes, it is sometimes difficult to obtain well-defined
NMR signals as a result of the presence of paramagnetic im-
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(m, 6H), 8.20 (s, 1H), 8.63 (d, J=6.3 Hz, 2H); 13C NMR (100 MHz,
CDCl3): d=20.8, 119.6, 121.0, 122.2, 122.4, 124.5, 130.0, 132.4,
136.8, 141.0, 145.4, 149.4, 149.5, 157.2; EI-MS (m/z): 427 for [M]+;
EI-HRMS: m/z calcd for C30H25N3: 427.2048; found: 427.2055.
X-ray crystallography
X-ray diffraction data were collected on a Rigaku Saturn 724 dif-
fractometer with a rotating anode (MoKa radiation, 0.71073 ꢁ) at
173 K. The structure was solved by the direct method by using
SHELXS-97[31] and refined with Olex.[32] Crystallographic data for
6(PF6)·2CHCl3: C53H43Cl6F6N6O8PRu, M=1350.67, triclinic, space
Synthesis of N,N-bis(p-chlorophenyl)-3,5-bis(pyrid-2-yl)aniline
(3): By using the same procedure for the synthesis of 2, ligand 3
was prepared from 3,5-bis(pyrid-2-yl)bromobenzene and bis(p-
¯
group P1, a=10.585(2), b=13.993(1), c=20.209(4) ꢁ; a=81.71(3),
a
white solid. 1H NMR
b=77.29(3), g=75.14(3)8; V=2810.1(10) ꢁ3; T=173 K; Z=2; final
R indices: R1=0.0664, wR2=0.1505, R indices (all data): R1=
0.0748, wR2=0.1573.
chlorophenyl)amine in 50% yield as
(400 MHz, CD3COCD3): d=7.14 (d, J=8.8 Hz 4H), 7.30 (t, J=5.8 Hz,
2H), 7.32 (d, J=8.8 Hz, 4H), 7.83 (t, J=7.7 Hz, 2H), 7.93 (s, 2H),
7.94 (d, J=9.2 Hz, 2H), 8.53 (s, 1H), 8.61 (d, J=4.4 Hz, 2H);
13C NMR (100 MHz, CD3COCD3): d=119.7, 119.8, 122.3, 122.8,
124.9, 127.2, 129.1, 136.5, 140.8, 145.9, 147.7, 149.1, 155.4; EI-MS:
m/z=467 [M]+; EI-HRMS: m/z calcd for C28H19Cl2N3: 467.0956;
found: 467.0962.
CCDC 996696 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
General procedure for the synthesis of ruthenium complexes
4(PF6), 6(PF6)–12(PF6), and 15(PF6): [(Mebip)RuCl3], [(tpy)RuCl3], or
[(Me3tctpy)RuCl3] (0.10 mmol) and AgOTf (0.33 mmol) were added
to 20 mL of dry acetone. The mixture was heated to reflux for 3 h.
One hour later, the mixture was filtered to remove the AgCl precip-
itate. The filtrate was concentrated to dryness. Ligand 1, 2, 3, or
1,3-di(pyrid-2-yl)benzene (0.11 mmol), DMF (10 mL), and tBuOH
(10 mL) were added to the residue. The resulting mixture was
heated to reflux under microwave heating (power=375 W) for
30 min. After cooling to room temperature, the solvent was re-
moved under reduced pressure. The residue was dissolved in 2 mL
of methanol, and an excess of aqueous KPF6 was added. The result-
ing precipitate was collected by filtration and washed with water
and Et2O. The crude solid was purified by chromatography on
silica gel (eluent: CH3CN/H2O/aq. KNO3 300/30/0.1), followed by
anion exchange with KPF6 to give the desired complexes as black
solids in 34–65% yield. Some of these complexes are easily oxi-
Computational methods
DFT calculations were carried out with the B3LYP exchange correla-
tion functional,[33] as implemented in the Gaussian 09 package.[34]
The electronic structures were optimized by using a general basis
set with the Los Alamos effective core potential LanL2DZ basis set
for Ru[35] and 6-31G* for other atoms.[36] The computations were
carried out with solvation effects taken into account by means of
the conductor polarizable continuum model (CPCM).[37] No symme-
try constraints were used in the optimization (nosymm keyword
was used). Frequency calculations were performed at the same
level of theory to ensure that the optimized geometries were local
minima. All orbitals were computed at an isovalue of 0.02 ebohrꢀ3
.
EPR measurements
EPR measurements were performed on a Bruker ELEXSYS E500-10/
12 spectrometer at 77 K in frozen CH3CN. The spectrometer fre-
quency was 9.7ꢂ109 Hz. The MV complex was obtained by chemi-
cal oxidation with 0.5 equiv cerium ammonium nitrate and used di-
rectly for the EPR measurement.
1
dized under ambient conditions. To obtain satisfactory H NMR sig-
nals, a small amount of aqueous hydrazine was added to the solu-
tion in [D6]acetone to remove the oxidized impurities (see the
NMR spectra in the Supporting Information).
Complex 4(PF6): Prepared from [(Mebip)RuCl3] and ligand 1 in
60% yield. H NMR (400 MHz, CD3COCD3): d=3.76 (s, 6H), 4.61 (s,
Synthesis
1
NMR spectra were recorded on a Bruker Avance 400 MHz spec-
trometer. Spectra are reported in parts per million (ppm) from re-
sidual proton signals of deuterated solvent. Mass data were ob-
tained with a Bruker Daltonics Inc. Apex II FT-ICR or Autoflex III
MALDI-TOF mass spectrometer. The matrix for MALDI-TOF mea-
surement was a-cyano-4-hydroxycinnamic acid. Microanalysis was
carried out on a Flash EA 1112 or Carlo Erba 1106 analyzer at the
Institute of Chemistry, Chinese Academy of Sciences. 3,5-Bis(pyrid-
2-yl)-bromobenzene,[12] ligand 1,[12] and complexes 5(PF6)2,[12]
13(PF6),[17] and 14(PF6)[20] were prepared according to the published
procedures.
6H), 6.38 (d, J=8.4 Hz, 2H), 6.58 (t, J=6.5 Hz, 2H), 7.01 (m, 6H),
7.16 (d, J=4.8 Hz, 2H), 7.30 (t, J=7.6 Hz, 2H), 7.34 (d, J=9.2 Hz,
4H), 7.46 (t, J=7.8 Hz, 2H), 7.60 (d, J=8.4 Hz, 2H), 8.04 (d, J=
8.0 Hz, 2H), 8.27 (s, 2H), 8.38 (t, J=8.2 Hz, 1H), 9.06 (d, J=8.0 Hz,
2H); MALDI-MS: m/z=899.0 [MꢀPF6]+; elemental analysis (%)
calcd for C51H41F6N8O2PRu·2H2O: C 56.72, H 4.20, N 10.38; found: C
56.63, H 4.03, N 10.37.
Complex 6(PF6): Prepared from [(Me3tctpy)RuCl3] and ligand 1 in
1
65% yield. H NMR (400 MHz, CD3COCD3): d=3.84 (s, 6H), 3.94 (s,
6H), 4.19 (s, 3H), 6.68 (m, 2H), 6.95–6.97 (m, 4H), 7.07 (d, J=
5.2 Hz, 2H), 7.24–7.25 (m, 4H), 7.64–7.72 (m, 6H), 8.16 (m, 4H),
9.25 (s, 2H), 9.65 (s, 2H); MALDI-MS: m/z=966.9 [MꢀPF6]+; ele-
mental analysis (%) calcd for C51H41F6N6O8PRu·H2O: C 54.21, H 3.84,
N 7.44; found: C 54.50, H 3.96, N 7.84.
Synthesis
of
N,N-Bis(p-tolyl)-3,5-bis(pyrid-2-yl)aniline
(2):
[Pd2(dba)3] (dba=trans,trans-dibenzylideneacetone; 0.02 mmol,
18.3 mg), 1,1’-bis(diphenylphosphino)ferrocene (dppf; 0.02 mmol,
11.1 mg), and NaOtBu (1.2 mmol, 115.3 mg) were added to a solu-
tion of 3,5-bis(pyrid-2-yl)bromobenzene (1.0 mmol, 323 mg) and di-
p-tolylamine (1.5 mmol, 296 mg) in 20 mL of dry toluene under N2
atmosphere. The mixture was bubbled with nitrogen for 10 min,
followed by heating to reflux for 24 h. After cooling to room tem-
perature, the solvent was removed under reduced pressure. The
residue was subjected to flash column chromatography on silica
gel (eluent: CH2Cl2/ethyl acetate/NH4OH 100/5/1) to afford 192 mg
of ligand 2 as a white solid in 45% yield. 1H NMR (400 MHz,
CDCl3): d=2.30 (s, 6H), 7.05 (s, 8H), 7.18–7.23 (m, 2H), 7.70–7.72
Complex 7(PF6): Prepared from [(Mebip)RuCl3] and ligand 2 in
1
34% yield. H NMR (400 MHz, CD3COCD3): d=2.35 (s, 6H), 4.61 (s,
6H), 6.39 (d, J=8.0 Hz, 2H), 6.59 (t, J=6.4 Hz, 2H), 7.00 (t, J=
7.8 Hz, 2H), 7.17 (d, J=5.2 Hz, 2H), 7.23 (d, J=8.4 Hz, 4H), 7.31 (m,
6H), 7.47 (t, J=7.7 Hz, 2H), 7.61 (d, J=8.4 Hz, 2H), 8.07 (d, J=
8.0 Hz, 2H), 8.29 (s, 2H), 8.39 (t, J=8.2 Hz, 1H), 9.07 (d, J=8.0 Hz,
2H); MALDI-MS: 867.2 [MꢀPF6]+; elemental analysis (%) calcd for
C51H41F6N8PRu: C 60.53, H 4.08, N 11.07; found: C 60.54, H 4.24, N
11.02.
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Complex 8(PF6): Prepared from [(tpy)RuCl3] and ligand 2 in 55%
yield. 1H NMR (400 MHz, CD3COCD3): d=2.32 (s, 6H), 6.74 (t, J=
6.4 Hz, 2H), 7.15 (m, 12H), 7.34 (d, J=5.2 Hz, 2H), 7.64 (t, J=
7.8 Hz, 2H), 7.84 (t, J=7.8 Hz, 2H), 8.17 (d, J=6.4 Hz, 2H), 8.18 (s,
2H), 8.39 (t, J=8.0 Hz, 1H), 8.69 (d, J=8.0 Hz, 2H), 9.02 (d, J=
8.0 Hz, 2H); MALDI-MS: m/z=761.2 [MꢀPF6]+; elemental analysis
(%) calcd for C45H35F6N6PRu·H2O: C 58.50, H 4.04, N 9.10; found: C
58.75, H 3.92, N 8.90.
Complex 9(PF6): Prepared from [(Me3tctpy)RuCl3] and ligand 2 in
1
52% yield. H NMR (400 MHz, CD3COCD3): d=2.34 (s, 6H), 3.94 (s,
6H), 4.19 (s, 3H), 6.69 (t, J=6.6 Hz, 2H), 7.09 (d, J=5.2 Hz, 2H),
7.16–7.22 (m, 8H), 7.63–7.72 (m, 6H), 8.19 (d, J=8.0 Hz, 2H), 8.21
(s, 2H), 9.25 (s, 2H), 9.66 (s, 2H); MALDI-MS: m/z=935.2 [MꢀPF6]+;
elemental analysis (%) calcd for C51H41F6N6O6PRu: C 56.72, H 3.83, N
7.78; found: C 56.48, H 4.01, N 7.82.
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Complex 10(PF6): Prepared from [(Mebip)RuCl3] and ligand 3 in
1
45% yield. H NMR (400 MHz, CD3COCD3): d=4.61 (s, 6H), 6.34 (d,
J=8.4 Hz, 2H), 6.61 (t, J=6.5 Hz, 2H), 7.02 (t, J=7.4 Hz, 2H), 7.20
(d, J=5.2 Hz, 2H), 7.30 (t, J=7.4 Hz, 2H), 7.46 (s, 7H), 7.48 (t, J=
8.0 Hz, 2H), 7.61 (d, J=8.4 Hz, 2H), 8.13 (d, J=8.4 Hz, 2H), 8.36 (s,
2H), 8.41 (t, J=8.2 Hz, 1H), 9.07 (d, J=8.4 Hz, 2H); MALDI-MS: m/
z=907.0 [MꢀPF6]+; elemental analysis (%) calcd for
C49H35Cl2F6N8PRu: C 55.90, H 3.35, N 10.64; found: C 55.70, H 3.52,
N 10.23.
Complex 11(PF6): Prepared from [(tpy)RuCl3] and ligand 3 in 63%
yield. 1H NMR (400 MHz, CD3COCD3): d=6.77 (t, J=6.2 Hz, 2H),
7.11–7.17 (m, 4H), 7.22 (d, J=5.4 Hz, 2H), 7.30–7.37 (m, 8H), 7.66
(t, J=7.7 Hz, 2H), 7.84 (t, J=7.8 Hz, 2H), 8.18 (s, 1H), 8.25 (d, J=
9.6 Hz, 2H), 8.26 (s, 1H), 8.40 (t, J=8.0 Hz, 1H), 8.70 (d, J=8.0 Hz,
2H), 9.03 (d, J=8.4 Hz, 2H); MALDI-MS: m/z=801.1 [MꢀPF6]+; ele-
mental analysis (%) calcd for C43H29Cl2F6N6PRu: C 54.56, H 3.09, N
8.88; found: C 54.60, H 3.33, N 8.91.
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Complex 12(PF6): Prepared from [(Me3tctpy)RuCl3] and ligand 3 in
1
42% yield. H NMR (400 MHz, CD3COCD3): d=3.94 (s, 6H), 4.20 (s,
3H), 6.72 (t, J=6.6 Hz, 2H), 7.13 (d, J=4.8 Hz, 2H), 7.33–7.39 (m,
8H), 7.65–7.71 (m, 6H), 8.28 (d, J=8.0 Hz, 2H), 8.31 (s, 2H), 9.26 (s,
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7.26; found: C 50.52, H 3.52, N 7.16.
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Complex 15(PF6): Prepared from [(Me3tctpy)RuCl3] and 1,3-bis(pyr-
1
id-2-yl)benzene in 40% yield. H NMR (400 MHz, CD3CN): d=3.89
(s, 6H), 4.18 (s, 3H), 6.59 (t, J=6.6 Hz, 2H), 6.82 (d, J=5.6 Hz, 2H),
7.42 (d, J=6.0 Hz, 2H), 7.48 (d, J=6.0 Hz, 2H), 7.53 (t, J=7.6 Hz,
1H), 7.61 (t, J=7.7 Hz, 2H), 8.14 (d, J=8.0 Hz, 2H), 8.28 (d, J=
7.6 Hz, 2H), 9.01 (s, 2H), 9.41 (s, 2H)); MALDI-MS: m/z=740.0
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Acknowledgements
We thank the National Natural Science Foundation of China
(grants 21271176, 91227104, 21472196, and 21221002), the Na-
tional Basic Research 973 Program of China (grant
2011CB932301), and the Strategic Priority Research Program of
the Chinese Academy of Sciences (grant XDB 12010400) for
funding support.
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Keywords: electrochemistry · charge transfer · mixed-valent
compounds · ruthenium · tridentate ligands
Chem. Eur. J. 2014, 20, 17466 – 17477
www.chemeurj.org
17476
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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Received: July 23, 2014
Published online on November 4, 2014
Chem. Eur. J. 2014, 20, 17466 – 17477
www.chemeurj.org
17477
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim