Ruthenium-amine electronic coupling bridged through phen-1,3-diyl versus phen-1,4-diyl: Reverse of the charge transfer direction

Article abstract of DOI:10.1021/om400519b

Three tris-bidentate cyclometalated ruthenium complexes with a di(p-anisyl)amino [5(PF₆)], di(p-tolyl)amino [6(PF₆)], or di(p-chlorophenyl)amino [7(PF₆)] substituent on the cyclometalating phenyl ring have been prepared, where the amine nitrogen is in the meta position to the cyclometalated site (bridged through the phen-1,3-diyl unit). The structure of 6(PF₆) has been confirmed by single-crystal X-ray diffraction analysis. Two consecutive redox waves are evident at +0.48 and +0.87 V versus Ag/AgCl for 5(PF₆), +0.51 and +1.02 V for 6(PF ₆), and +0.53 and +1.18 V for 7(PF₆), respectively. The first wave is assigned to the Ru(II/III) process, and the second wave is attributed to the N(0/+) process. After one-electron oxidation using SbCl ₅, these complexes display distinct absorptions in the near-infrared region, which are assigned to the nitrogen-to-ruthenium intervalence charge-transfer (ICVT) transitions. The energies of the IVCT transitions vary linearly versus the potential splitting of the Ru(II/III) and N(0/+) process. The charge-transfer direction in these complexes is reversed with respect to a previously reported ruthenium-amine system where the amine nitrogen is in the para position to the cyclometalated site (bridged through the phen-1,4-diyl unit).

Full text of DOI:10.1021/om400519b

Article
pubs.acs.org/Organometallics
Ruthenium-Amine Electronic Coupling Bridged through Phen-1,3-
diyl Versus Phen-1,4-diyl: Reverse of the Charge Transfer Direction
Jian-Hong Tang,†,‡ Si-Hai Wu,† Jiang-Yang Shao,† Hai-Jing Nie,† and Yu-Wu Zhong*,†
†Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, China
‡College of Chemistry, Xiangtan University, Xiangtan 411105, China
S
* Supporting Information
ABSTRACT: Three tris-bidentate cyclometalated ruthenium
complexes with a di(p-anisyl)amino [5(PF6)], di(p-tolyl)-
amino [6(PF6)], or di(p-chlorophenyl)amino [7(PF6)]
substituent on the cyclometalating phenyl ring have been
prepared, where the amine nitrogen is in the meta position to
the cyclometalated site (bridged through the phen-1,3-diyl
unit). The structure of 6(PF6) has been confirmed by single-
crystal X-ray diffraction analysis. Two consecutive redox waves
are evident at +0.48 and +0.87 V versus Ag/AgCl for 5(PF6), +0.51 and +1.02 V for 6(PF6), and +0.53 and +1.18 V for 7(PF6),
respectively. The first wave is assigned to the Ru(II/III) process, and the second wave is attributed to the N(0/+) process. After
one-electron oxidation using SbCl5, these complexes display distinct absorptions in the near-infrared region, which are assigned
to the nitrogen-to-ruthenium intervalence charge-transfer (ICVT) transitions. The energies of the IVCT transitions vary linearly
versus the potential splitting of the Ru(II/III) and N(0/+) process. The charge-transfer direction in these complexes is reversed
with respect to a previously reported ruthenium−amine system where the amine nitrogen is in the para position to the
cyclometalated site (bridged through the phen-1,4-diyl unit).
component to the dithiolene unit.7 In the studies of electron
transfer between a [Ru(NNN)(NCN)]-type cyclometalated
ruthenium and ferrocene, we previously found that the charge
INTRODUCTION
■
The study of electron-transfer in mix−valence (MV) systems
[M1−BL−M2]n (BL = bridging ligand) has been the focus of
transfer direction was different when the ferrocene unit was
many research activities.1 The charge-bearing sites M1 and M2
attached on the NNN ligand versus NCN ligand.8 These
can either be an organometallic2 or a purely organic unit3 with
materials have implications for the design of new charge
well-defined redox processes. By analyzing the intervalence
charge-transfer (IVCT) transition in the near-infrared (NIR)
region, useful information, such as reorganization energy (λ),
electronic coupling parameter (Vab), and degree of charge
transfer systems and molecular switches.4
Triarylamines show one-electron oxidation processes cen-
tered on nitrogen (N0/+) and are extensively used in symmetric
organic MV systems.9 Cyclometalated ruthenium complexes
delocalization, can be accessed.1−3 This information is of
with an anionic carbon ligand possess RuII/III processes at
fundamental importance for the understanding of the electron
relatively low potentials with respect to noncyclometalated
transfer process occurring in natural systems and the design of
ruthenium complexes.10 Their uses in symmetric bisruthenium
molecular materials for electronics and optoelectronics.4
systems have been well-documented.11 We previously reported
When M1 = M2, the two-state Marcus−Hush theory5
a hybrid of triarylamine and cyclometalated ruthenium, where
predicts the energy of the IVCT band Eop = λ. In the case of
the redox asymmetric system (M1 ≠ M2), an additional term
the amine nitrogen is in the para position to the cyclometalated
site (bridged through phenyl-1,4-diyl) (see Figure 1).12 The
ΔG0, the energy difference between the ground state and
charge-separated state, is needed, namely, Eop = λ + ΔG0. The
odd electron is quite delocalized but more biased at the
triarylamine site, according to electrochemical, spectroscopic,
electronic paramagnetic resonance (EPR), and density func-
variation of the electronic nature of donor and/or acceptor will
change ΔG0, and consequently Eop. The examination of the
tional theory (DFT) results. This complex shows narrow and
influence of different substituents on the IVCT band and
intense Ru → N+ IVCT transitions at 1050 nm in the MV state.
electron transfer parameters bears much interest in MV
chemistry.6
In this contribution, we present the synthesis and electron
transfer studies of complexes 5(PF6)−7(PF6) (Scheme 1),
where the amine nitrogen is in the meta position to the
One topic of current interest is the reverse of the charge
transfer direction in systems with donor and acceptor of similar
redox potentials. For instance, Nishihara and co-workers
reported that the charge transfer direction in ferrocene−
dithiolene hybrids can be reversed by attaching a platinum
Received: June 6, 2013
Published: August 15, 2013
© 2013 American Chemical Society
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Figure 1. Ruthenium−amine hybrid.
Scheme 1. Synthesis of 5(PF6)−7(PF6)
Figure 2. Thermal ellipsoid plot of the single-crystal structure of
6(PF6)(CHCl3) with 30% probability. Hydrogen atoms, solvent, and
anion are omitted for clarity. Atom color code: carbon, gray; nitrogen,
blue; ruthenium, magenta. Selected bond length and angle: Ru1−C1,
2.04 Å; C2−N6, 1.43 Å; Ru1−N1, 2.05 Å; Ru1−N2, 2.05 Å; Ru1−N3,
2.15 Å; Ru1−N4, 2.07 Å; Ru1−N5, 2.10 Å; ∠C1−Ru1−N5 = 79.3°;
∠N5−Ru1−N3 = 95.4°.
Electrochemical Studies. Figure 3 (panels a and b) shows
the cyclic voltammograms (CVs) and differential pulse
cyclometalated site (bridged through phenyl-1,3-diyl) and a
reversed charge transfer from N to Ru is realized (after one-
electron oxidation).
RESULTS AND DISCUSSION
■
Syntheses and Single-Crystal Structure. Complexes
5(PF6)−7(PF6) were prepared as outlined in Scheme 1. The
Stille coupling between 1,4-dibromobenzene and 2-
(tributylstannyl)pyridine gave 2-(4-bromophenyl)pyridine in
57% yield.13 Ligands 2−4 were synthesized from the palladium-
catalyzed C−N coupling14 between 2-(4-bromophenyl)-
pyridine and corresponding diphenylamine derivatives. The
MeO, Me, and Cl substituents on the ligand were selected to
vary the redox potential of the amine site. The reaction of 2−4
with [Ru(p-cymene)Cl2]2 in the presence of KPF6 and NaOH
gave a ruthenium intermediate, which was complexed with 2,2′-
bipyridine (bpy) to afford 5(PF6)−7(PF6) in moderate yields.
Similar procedures have been used for the synthesis of
cyclometalated ruthenium complexes.15 The MALDI mass
spectra of 5(PF6)−7(PF6) show signals corresponding to the
losses of the PF6 anion (795.2, 763.3, and 803.0, respectively).
The 13C NMR signal around at 195 ppm is assigned to the
carbon atom connected to the ruthenium ion.
A single crystal of 6(PF6)(CHCl3) was obtained by diffusion
of petroleum ether into a solution in CHCl3.16 The thermal
ellipsoid plot of the X-ray structure is displayed in Figure 2. The
ruthenium ion has a [(NN)2(CN)]-type tris-bidentate
coodination geometry. The Ru1−C1 bond has a length of
2.04 Å. The Ru1−N3 bond opposite to the Ru1−C1 bond has
a length of 2.15 Å. Other Ru−N bonds are in the range of
2.05−2.10 Å. Similar geometrical distances have been reported
for cyclometalated ruthenium complexes.17
Figure 3. (a) DPVs and (b) CVs of 5(PF6) (black curves), 6(PF6)
(red curves), and 7(PF6) (blue curves) in CH2Cl2. (c) CVs of 2 (black
curves), 3 (red curves), and 4 (blue curves) in CH2Cl2.
voltammograms (DPVs) of 5(PF6)−7(PF6) versus Ag/AgCl.
All complexes display two well-defined redox processes. The
first series waves are at +0.48, +0.51, and +0.53 V for 5(PF6)−
7(PF6), respectively. The second series waves are at +0.87,
+1.02, and +1.18 V, respectively. The potential differences
between the anodic and cathodic peaks of all redox couples in
Figure 3b are in the range of 70−95 mV. This difference is
slightly bigger than that of a typical diffusion-controlled one-
electron Nernstian wave (59 mV). In consideration of the fact
that complex [Ru(bpy)2(ppy)](PF6) [ppy is the 2-deproto-
nated form of (pyrid-2-yl)benzene] has a RuII/III potential of
+0.70 V versus NHE (around +0.50 V vs Ag/AgCl)18 and
compounds 2−4 have the N0/+ potential of +0.74, +0.90, and
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+1.10 V, respectively (Figure 3c), it would be safe to conclude
that the RuII/III process occurs prior to the N0/+ process for
5(PF6)−7(PF6). This is in stark contrast with the previously
reported complex 1(PF6)2, where the RuII/III process occurs
after the N0/+ process.12 The potential difference ΔE between
the RuII/III process and N0/+ process is 390, 510, and 650 mV
for 5(PF6)−7(PF6), respectively. The comproportionation
The IVCT bands of 52+−72+ are moderate and broad. They
are assigned to the Robin-Day class II systems.2,3 The coupling
parameter Vab was estimated to be about 500 cm−1 for three
complexes, according to the Hush formula5 Vab = 0.0206 ×
(εmaxνmaxΔν1/2)
1/2/(rab), where νmax = Eop in cm−1, Δν1/2 is the
bandwidth at half-height after Guassin-fitting, and rab is taken to
be the Ru−N distance from the crystallographic data (5.52 Å).
It should be pointed out that no distinct emission has been
observed for complexes 5(PF6)−7(PF6) in CH2Cl2 solution at
room temperature. Previous studies showed that the emission
of conventional polypyridyl ruthenium complexes with a Ru−C
bond is very weak.18
constant Kc for the equation RuII−N0 + RuIII−N+
→
2(RuIII−N0) of these three complexes is calculated to be 4.1
× 106, 4.4 × 108, and 10.4 × 1010, respectively. These results are
summarized in Table 1.
a
DFT Studies. No distinct EPR signal has been observed for
5(PF6)−7(PF6) after one-electron oxidation using SbCl5. This
may be caused by the fast spin relaxation of the ruthenium ion.
The geometry of the closed-shell complex 6+ was optimized
using the B3LYP, B3PW91, MPW1PW91, or PBE1PBE
functionals (see details in the Experimental Section). However,
all calculations led to the highest occupied molecular orbital
(HOMO) dominated by the triarylamine unit (Figure S2 of the
Supporting Information), which is separated from the HOMO-
1 with over 0.5 eV. In addition, the DFT-predicted spin-density
of the open-shell state 62+ using the B3LYP functional is also
mainly distributed among the triarylamine component (Figure
S3 of the Supporting Information). These theoretical results
suggest that the triarylamine component in 62+ will be first
oxidized. However, the above electrochemical and spectro-
scopic experimental findings strongly suggest that the
ruthenium component in 5(PF6)−7(PF6) is first oxidized.
This means that the current DFT method is not suitable for
predicting the electronic structures of these complexes.
However, the discrepancy between theoretical and experimen-
tal results may be caused by the overestimation of
delocalization by DFT methods.
Table 1. Electrochemical Data
b
c
compound
1(PF6)2
E1 (V) E2 (V) ΔE (mV)
Kc
0.27
0.74
0.90
1.10
0.48
0.51
0.53
0.50
0.68
−
−
410
−
−
8.9 × 106
2
−
−
−
3
4
−
−
5(PF6)
0.87
1.02
1.18
−
390
510
650
−
4.1 × 106
4.4 × 108
10.4 × 1010
−
6(PF6)
7(PF6)
d
[Ru(bpy)2(ppy)](PF6)
a
Potentials were reported vs Ag/AgCl. Potentials versus ferrocene0/+
b
c
can be estimated by subtracting 0.45 V. ΔE = E2 − E1. Kc = 10(ΔE/59)
.
d
See ref 18.
Because complexes 5(PF6)−7(PF6) have substituents with
significantly different electronic nature on the amine
component, the energetic asymmetry ΔG0 must be different
for three compounds, which results in the big difference of the
above ΔE values.
Spectroscopic Studies. To probe the electron transfer
process of 5(PF6)−7(PF6), their absorption spectral changes
were monitored upon single (one-electron) and double (the
second one-electron) oxidation with SbCl5 in CH2Cl2 (Figure
4).6,9,11 During these two-step processes, 5(PF6)−7(PF6)
exhibited similar spectral changes. In the single oxidation
step, the absorption bands in the visible region decreased
significantly, and a broad transition in the NIR region appeared.
The latter band is assigned to the N → Ru IVCT transition, and
it disappeared in the double oxidation step. The intense peak
around 800 nm in Figure 4 (panels b, d, and f) is due to the
N•+-localized transition, which has previously observed in one-
electron-oxidized form of triarylamines.9,19 This, in turn,
supports that the second oxidation step of 5(PF6)−7(PF6) is
associated with the N0/+ process. The appearance and
disappearance of the IVCT band was also evidenced during
spectroelectrochemical measurements (Figure S1 of the
Supporting Information).
The substituents on the amine component has a dramatic
impact on the energy (Eop) and band shape of the IVCT band
of 52+−72+ (Figure 5 and Table 2). For example, the IVCT
band of 72+ is around 400 nm blue shifted with respect to that
of 52+, and the former is much narrower relative to the latter.
Such an effect clearly arises from the increased redox
asymmetry of 72+ versus 52+, as reflected by their different
ΔE values. A plot of Eop versus the redox splitting ΔE is
approximately linear (Figure 5b). Such a correlation has
previously been found in redox asymmetric MV systems,20
indicating that the optical electron transfer has a common λ,
and the IVCT band varies almost exclusively with ΔE.
CONCLUSION
■
In summary, the charge transfer direction in the cyclometalated
ruthenium−amine MV system was reversed by changing the
para position of two redox sites to the meta position. The
IVCT energy and shape can be tuned by substituents on the
amine component. This information is of interest and
importance for the design and synthesis of new asymmetric
MV systems.
EXPERIMENTAL SECTION
■
Synthesis. NMR spectra were recorded in the designated solvent
on Bruker Avance 400 MHz spectrometer. Spectra are reported in
ppm values from residual protons of deuterated solvent. Mass data
were obtained with a Bruker Daltonics Inc. Apex II FT-ICR or
Autoflex III MALDI-TOF mass spectrometer. The matrix for MALDI-
TOF measurement is α-cyano-4-hydroxycinnamic acid. Microanalysis
was carried out using Flash EA 1112 or Carlo Erba 1106 analyzer at
the Institute of Chemistry, Chinese Academy of Sciences.
2-(4-Bromophenyl)pyridine. This compound was prepared
according to a known procedure.13 To a solution of 1,4-
dibromobenzene (2.0 mmol, 472 mg) and 2-(tributylstannyl)pyridine
(2.0 mmol, 736 mg) in 15 mL of dry toluene were added
Pd(PPh3)2Cl2 (0.080 mmol, 56.2 mg) and LiCl (16.0 mmol, 678
mg). The mixture was bubbled with nitrogen for 15 min and heated at
110 °C for 10 h. The solvent was removed under reduced pressure.
The residue was subjected to column chromatography on silica gel
(eluent: CH2Cl2/petroleum ether, 2/1) to afford 269 mg of 2-(4-
1
bromophenyl)pyridine as a white solid in 57% yield. H NMR (400
MHz, CDCl3): δ 7.25 (overlapped with solvent residual, 1H), 7.61 (d,
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Figure 4. Electronic absorption spectral changes of (a and b) 5(PF6), (c and d) 6(PF6), and (e and f) 7(PF6) in CH2Cl2 upon (a, c, and e) single and
(b, d, and f) double oxidation with SbCl5. Symbol *: artifacts.
J = 8.4 Hz, 2H), 7.61 (d, J = 8.4 Hz, 2H), 7.66−7.70 (m, overlapped,
2H), 8.68 (d, J = 4.8 Hz, 1H).
1H NMR (400 MHz, CDCl3): δ 2.33 (s, 6H), 7.05−7.12 (m,
overlapped, 10H), 7.15−7.20 (m, 1H), 7.63 (m, overlapped, 2H), 7.83
(d, J = 8.8 Hz, 2H), 8.64 (d, J = 4.4 Hz, 1H). 13C NMR (400 MHz,
CDCl3): δ 20.87, 119.74, 121.28, 121.99, 124.99, 127.58, 129.96,
132.16, 132.93, 136.59, 145.01, 149.08, 149.56, 157.20. EI-HRMS (m/
z) calcd for C25H22N2: 350.1783; found: 350.1788.
2-[4-(Di-p-anisylamino)phenyl]pyridine (2). To a solution of 2-
(4-bromophenyl)pyridine (1.0 mmol, 234 mg) and 4,4′-dimethox-
ydiphenylamine (1.5 mmol, 344 mg) in 15 mL of dry toluene were
added Pd2 (dba)3 (0.050 mmol, 45.8 mg), 1,1′-bis-
(diphenylphosphino)ferrocene (dppf, 0.050 mmol, 27.7 mg) and
NaOtBu (1.2 mmol, 115.3 mg). The mixture was bubbled with
nitrogen for 10 min and then heated at 110 °C for 30 h. The solvent
was removed under reduced pressure. The residue was subjected to
column chromatography on silica gel (eluent: ethyl acetate/petroleum
2-[4-(Di-p-chlorophenylamino)phenyl]pyridine (4). To a
solution of 2-(4-bromophenyl)pyridine (1.0 mmol, 234 mg) and
bis(4-chlorophenyl)amine (1.5 mmol, 357 mg) in 15 mL of dry
toluene were added Pd2(dba)3 (0.050 mmol, 45.8 mg), dppf (0.050
mmol, 27.7 mg), and NaOtBu (1.2 mmol, 115.3 mg). The mixture was
bubbled with nitrogen for 10 min and then heated at 110 °C for 30 h.
The solvent was removed under reduced pressure. The residue was
subjected to column chromatography on silica gel (eluent: petroleum
ether/CH2Cl2, 1/2) to afford 171 mg of 4 as a yellow solid in 44%
1
ether, 8/1) to afford 119 mg of 2 as a yellow solid in 46% yield. H
NMR (400 MHz, CDCl3): δ 3.81 (s, 6H), 6.85 (d, J = 8.8 Hz, 4H),
6.99 (d, J = 8.8 Hz, 2H), 7.09 (d, J = 8.8 Hz, 4H), 7.15 (t, J = 6.0 Hz,
1H), 7.62−7.76 (m, overlapped, 2H), 7.81 (d, J = 8.8 Hz, 2H), 8.63
(d, J = 4.4 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 55.50, 114.75,
119.58, 120.10, 121.13, 126.86, 127.55, 131.10, 136.59, 140.62, 149.49,
149.59, 156.10, 157.22. EI-HRMS (m/z) calcd for C25H22N2O2:
382.1681; found: 382.1687.
2-(4-(Di-p-tolylamino)phenyl)pyridine (3). To a solution of 2-
(4-bromophenyl)pyridine (1.0 mmol, 234 mg) and di-p-tolylamine
(1.5 mmol, 296 mg) in 15 mL of dry toluene were added Pd2(dba)3
(0.050 mmol, 45.8 mg), dppf (0.050 mmol, 27.7 mg), and NaOtBu
(1.2 mmol, 115.3 mg). The mixture was bubbled with nitrogen for 10
min and then heated at 110 °C for 30 h. The solvent was removed
under reduced pressure. The residue was subjected to column
chromatography on silica gel (eluent: petroleum ether/CH2Cl2/ethyl
acetate, 15/15/2) to afford 182 mg of 3 as a yellow solid in 52% yield.
1
yield. H NMR (400 MHz, CDCl3): δ 7.04 (d, J = 8.4 Hz, 4H), 7.12
(d, J = 8.4 Hz, 2H), 7.18−7.30 (m, overlapped, 5H), 7.67−7.76 (m,
overlapped, 2H), 7.89 (d, J = 8.8 Hz, 2H), 8.66 (d, J = 4.8 Hz, 1H).
13C NMR (400 MHz, CDCl3): δ 119.96, 121.75, 123.65, 125.58,
128.04, 128.44, 129.56, 134.16, 136.72, 145.77, 147.85, 149.69, 156.75.
EI-HRMS (m/z) calcd for C23H16Cl2N2: 390.0691; found: 390.0695.
Synthesis of Complex 5(PF6). To a suspension of [Ru(p-
cymene)Cl2]2 (0.060 mmol, 36.7 mg), KPF6 (0.20 mmol, 37.2 mg),
and crushed NaOH (0.10 mmol, 4.0 mg) in 10 mL of dry CH3CN was
added ligand 2 (0.10 mmol, 38.2 mg). The resulting mixture was
stirred at 55 °C for 15 h under a nitrogen atmosphere. The solvent was
removed under reduced pressure. The residue was subjected to flash
column chromatography on neutral Al2O3 (CH2Cl2/CH3CN, 20/1).
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give an intermediate as a yellow solid. To this intermediate were added
2,2′-bipyridine (0.25 mmol, 39.1 mg) and 10 mL dry DMF. The
resulting mixture was stirred at 130 °C for 5 h under nitrogen
atmosphere. The solvent was removed under reduced pressure. The
residue was purified by flash column chromatography on silica gel
(ethyl acetate/acetone/H2O, 8/8/3) to give 41 mg of 6(PF6) as a
deep red solid in 45% yield. 1H NMR (400 MHz, CD3CN): δ 2.31 (s,
6H), 5.70 (d, J = 2.4 Hz, 1H), 6.39 (dd, J = 8.4, 2.4 Hz, 1H), 6.75 (d, J
= 8.4 Hz, 4H), 6.80 (t, J = 6.0 Hz, 1H), 6.91 (t, J = 6.4 Hz, 1H), 7.02
(d, J = 8.4 Hz, 4H), 7.24 (t, J = 6.4 Hz, 1H), 7.29 (t, J = 6.0 Hz, 1H),
7.39 (t, J = 6.4 Hz, 1H), 7.40−7.52 (m, overlapped, 3H), 7.58 (t, J =
6.4 Hz, 1H), 7.60 (d, J = 8.4 Hz, 1H), 7.79−7.85 (m, overlapped, 3H),
7.88 (d, J = 5.6 Hz, 1H), 7.91 (d, J = 5.6 Hz, 1H), 7.98 (t, J = 8.0 Hz,
1H), 8.04 (d, J = 8.0 Hz, 1H), 8.19 (d, J = 5.2 Hz, 1H), 8.27 (d, J = 8.0
Hz, 1H), 8.37 (d, J = 8.4 Hz, 1H), 8.44 (d, J = 8.0 Hz, 1H). 13C NMR
(100 MHz, CD3CN): δ 20.46, 118.49, 119.06, 121.50, 122.38, 123.26,
123.37, 123.69, 123.90, 125.93, 126.45, 126.45, 126.78, 127.50, 130.32,
133.58, 133.60, 134.15, 135.37, 135.91, 136.14, 136.75, 136.84, 145.29,
148.33, 149.95, 150.16, 150.47, 150.83, 154.68, 155.71, 157.16, 157.37,
158.29, 167.23, 193.50. MALDI-MS (m/z): 763.3 for [M − PF6]+.
Anal. Calcd for C45H37F6N6PRu: C, 59.53; H, 4.11; N, 9.26; found: C,
59.18; H, 4.19; N, 9.11.
Synthesis of Complex 7(PF6). To a suspension of [Ru(p-
cymene)Cl2]2 (0.060 mmol, 36.7 mg), KPF6 (0.20 mmol, 37.2 mg),
and crushed NaOH (0.10 mmol, 4.0 mg) in 10 mL dry CH3CN was
added ligand 4 (0.10 mmol, 39.0 mg). The resulting mixture was
stirred at 55 °C for 15 h under a nitrogen atmosphere. The solvent was
then removed under reduced pressure. The residue was subjected to
flash column chromatography on neutral Al2O3 (CH2Cl2/CH3CN,
10/1). The yellow band was collected, and the solvent was removed to
give an intermediate as a yellow solid. To this intermediate were added
2,2’-bipyridine (0.25 mmol, 39.1 mg) and 10 mL dry DMF. The
resulting mixture was stirred at 130 °C for 5 h under a nitrogen
atmosphere. The solvent was removed under reduced pressure. The
residue was purified by flash column chromatography on silica gel
(ethyl acetate/acetone/H2O, 15/15/1) to give 45 mg of 7(PF6) as a
deep red solid in 48% yield. 1H NMR (400 MHz, CD3CN): δ 5.70 (d,
J = 2.4 Hz, 1H), 6.53 (dd, J = 8.4, 2.4 Hz, 1H), 6.80−6.90 (m,
overlapped, 5H), 6.96 (t, J = 6.4 Hz, 1H), 7.20 (d, J = 8.8 Hz, 4H),
7.25−7.30 (m, 2H), 7.40 (t, J = 6.4 Hz, 1H), 7.49 (t, J = 4.8 Hz, 2H),
7.56−7.62 (m, 2H), 7.67 (d, J = 8.4 Hz, 1H), 7.80−7.90 (m, 4H), 7.91
(d, J = 5.2 Hz, 1H), 7.97 (t, J = 8.0 Hz, 1H), 8.06 (d, J = 8.0 Hz, 1H),
8.16 (d, J = 6.0 Hz, 1H), 8.26 (d, J = 8.0 Hz, 1H), 8.38 (d, J = 8.0 Hz,
1H), 8.45 (d, J = 8.4 Hz, 1H). 13C NMR (100 MHz, CD3CN): δ
115.28, 118.79, 122.00, 123.31, 123.37, 123.73, 123.95, 125.17, 126.53,
126.61, 126.71, 126.81, 127.49, 128.25, 128.52, 129.75, 133.70, 134.25,
135.49, 136.14, 136.84, 140.58, 146.42, 147.46, 149.77, 150.28, 150.65,
150.74, 154.60, 155.62, 157.16, 157.21, 158.18, 167.19, 195.34.
MALDI-MS (m/z): 803.0 for [M − PF6]+. Anal. Calcd for
C43H31Cl2F6N6PRu: C, 54.44; H, 3.29; N, 8.86; found: C, 54.62; H,
3.54; N, 8.40.
Figure 5. (a) Observed and Gaussian-simulated IVCT transitions of
5
2+ (black curves), 62+ (red curves), and 72+ (blue curves) as a function
of wavenumbers. Symbol *: artifacts. (b) Linear fit of Eop vs ΔE. R2 =
0.93997.
The yellow band was collected, and the solvent was removed to give
an intermediate as a yellow solid. To this intermediate were added
2,2′-bipyridine (bpy, 0.25 mmol, 39.1 mg) and 10 mL of distilled
DMF. The resulting mixture was stirred at 130 °C for 5 h under
nitrogen atmosphere. The solvent was removed under reduced
pressure and the residue was purified by flash column chromatography
on silica gel (ethyl acetate/acetone/H2O, 15/15/1) to give 47 mg of
5(PF6) as a deep red solid in 51% yield. 1H NMR (400 MHz,
CD3CN): δ 3.79 (s, 6H), 5.62 (d, J = 2.4 Hz, 1H), 6.30 (dd, J = 8.8,
2.4 Hz, 1H), 6.70−6.85 (m, overlapped, 9H), 6.90 (t, J = 6.4 Hz, 1H),
7.20−7.30 (m, 2H), 7.35−7.45 (m, 2H), 7.45−7.55 (m, 2H), 7.57 (d, J
= 8.4 Hz, 2H), 7.75 (d, J = 8.4 Hz, 1H), 7.81 (t, J = 8.0 Hz, 2H), 7.89
(d, J = 5.2 Hz, 2H), 7.95 (t, J = 8.0 Hz, 1H), 8.06 (d, J = 8.0 Hz, 1H),
8.18 (d, J = 5.6 Hz, 1H), 8.27 (d, J = 8.0 Hz, 1H), 8.36 (d, J = 8.4 Hz,
1H), 8.43 (d, J = 8.4 Hz, 1H). 13C NMR (100 MHz, CD3CN): δ
56.11, 112.45, 115.48, 121.47, 123.83, 124.20, 124.40, 124.83, 125.51,
126.85, 127.08, 127.83, 128.32, 134.02, 134.39, 136.72, 136.29, 137.11,
137.85, 141.09, 149.66, 150.06, 150.48, 150.81, 150.48, 150.81, 151.06,
154.87, 156.05, 157.16, 157.64, 158.60, 167.93, 195.00. MALDI-MS
(m/z): 795.2 for [M − PF6]+. Anal. Calcd for C45H37F6N6O2PRu: C,
57.51; H, 3.97; N, 8.94; found: C, 57.46; H, 4.19; N, 8.68.
Spectroscopic Measurement. UV−vis/NIR spectra were
recorded using a PE Lambda 750 UV−vis/NIR spectrophotometer.
Oxidative spectroelectrochemistry was performed in a thin-layer cell
(optical length 0.2 cm), in which an ITO glass electrode was set in the
indicated solvent containing the compound to be studied (the
concentration is around 1 × 10−4 M) and 0.1 M Bu4NClO4 as the
supporting electrolyte. A platinum wire and Ag/AgCl in saturated
aqueous NaCl solution was used as a counter electrode and a reference
Synthesis of Complex 6(PF6). To a suspension of [Ru(p-
cymene)Cl2]2 (0.060 mmol, 36.7 mg), KPF6 (0.20 mmol, 37.2 mg),
and crushed NaOH (0.10 mmol, 4.0 mg) in 10 mL of dry CH3CN was
added ligand 3 (0.10 mmol, 35.1 mg). The resulting mixture was
stirred at 55 °C for 15 h under a nitrogen atmosphere. The solvent was
then removed under reduced pressure. The residue was subjected to
flash column chromatography on neutral Al2O3 (CH2Cl2/CH3CN,
10/1). The yellow band was collected, and the solvent was removed to
a
Table 2. Parameters of the NIR Transitions
b
Eop (cm−1
)
Eop (eV)
Δν1/2 (cm−1
)
εmax (M−1cm−1
)
Vab (cm−1
)
c
12+
52+
62+
72+
9520
4390
4680
5420
1.20
0.54
0.58
0.67
3640
2880
2300
1940
20000
1500
1700
1840
2760
510
500
520
a
b
c
52+ − 72+ were obtained from chemical oxidation with SbCl5 in CH2Cl2. Calculated from the Hush formula. See ref 12.
4568
dx.doi.org/10.1021/om400519b | Organometallics 2013, 32, 4564−4570

Organometallics
Article
electrode, respectively. The cell was put into the spectrophotometer to
monitor spectral changes during electrolysis.
(6) (a) Ratera, I.; Sporer, C.; Ruiz-Molina, D.; Ventosa, N.;
Baggerman, J.; Brouwer, A. M.; Rovira, C.; Veciana, J. J. Am. Chem.
Soc. 2007, 129, 6117. (b) Glover, S. D.; Kubiak, C. P. J. Am. Chem. Soc.
2011, 133, 8721.
(7) Kusamoto, T.; Takada, K.; Sakamoto, R.; Kume, S.; Nishihara, H.
Inorg. Chem. 2012, 51, 12102.
(8) (a) Wu, S.-H.; Shen, J.-J.; Yao, J.; Zhong, Y.-W. Chem. Asian J.
2013, 8, 138. (b) Wu, S.-H.; Shao, J.-Y.; Kang, H.-W.; Yao, J.; Zhong,
Y.-W. Chem. Asian J. 10.1002/asia.201300739.
Electrochemical Measurement. All CV measurements were
taken using a CHI 620D potentiostat with a one-compartment
electrochemical cell under an atmosphere of nitrogen. All measure-
ments were carried out in denoted solvents containing 0.1 M
nBu4NClO4 as the supporting electrolyte at a scan rate of 100 mV/s.
The working electrode was a glassy carbon with a diameter of 3 mm.
The electrode was polished prior to use with 0.05 μm alumina and
rinsed thoroughly with water and acetone. A large area platinum wire
coil was used as the counter electrode. All potentials are referenced to
Ag/AgCl electrode in saturated aqueous NaCl without regard for the
liquid junction potential. Potentials versus ferrocene0/+ can be deduced
by subtracting 0.45 V.
X-ray Crystallography. The X-ray diffraction data were collected
using a Rigaku Saturn 724 diffractometer on a rotating anode (Mo K
radiation, 0.71073 Å) at 173 K. The structure was solved by the direct
method using SHELXS-9721 and refined with Olex2.22 The structure
graphic shown in Figure 2 was generated using Olex2.
Computational Methods. DFT and TDDFT calculations are
carried out using the B3LYP,23 B3PW91,24 MPW1PW91,25 or
PBE1PBE26 exchange correlation functional and implemented in
Gaussian 03.27 The electronic structures of complexes were
determined using a general basis set with the Los Alamos effective
core potential LanL2DZ basis set for ruthenium and 6-31G* for other
atoms.28 Solvent effects (CH2Cl2) are included in all calculations with
the conductor-like polarizable continuum model (CPCM).29 All
orbitals have been computed at an isovalue of 0.02 e/bohr.3
(9) (a) Lambert, C.; Noll, G. J. Am. Chem. Soc. 1999, 121, 8434.
̈
(b) Lambert, C.; Noll, G.; Schelter, J. Nat. Mater. 2002, 1, 69.
̈
(c) Jones, S. C.; Coropceanu, V.; Barlow, S.; Kinnibrugh, T.;
́
Timofeeva, T.; Bredas, J.-L.; Marder, S. R. J. Am. Chem. Soc. 2004,
126, 11782. (d) Chang, C.-C.; Yueh, H.; Chen, C.-T. Org. Lett. 2011,
13, 2702.
(10) Djukic, J.-P.; Sortais, J.-B.; Barloy, L.; Pfeffer, M. Eur. J. Inorg.
Chem. 2009, 817.
(11) (a) Patoux, C.; Launay, J.-P.; Beley, M.; Chodorowski-Kimmers,
S.; Collin, J.-P.; James, S.; Sauvage, J.-P. J. Am. Chem. Soc. 1998, 120,
3717. (b) Fraysse, S.; Coudret, C.; Launay, J.-P. J. Am. Chem. Soc.
2003, 125, 5880. (c) Wadman, S. H.; Havenith, R. W. A.; Hartl, F.;
Lutz, M.; Spek, A. L.; van Klink, G. P. M.; van Koten, G. Inorg. Chem.
2009, 48, 5685.
(12) Yao, C.-J.; Zheng, R.-H.; Shi, Q.; Zhong, Y.-W.; Yao, J. Chem.
Commun. 2012, 48, 5680.
(13) Zhou, G.; He, Y.; Dang, J.; Zhao, X.; Yao, B.; Xie, Z.; Wang, L.;
Wong. Chem. Asian J. 2010, 5, 2405.
(14) Yang, J.-S.; Lin, Y.-H.; Yang, C.-S. Org. Lett. 2002, 4, 777.
(15) Bomben, P. G.; Koivisto, B.; Berlinguette, C. P. Inorg. Chem.
2010, 49, 4960.
ASSOCIATED CONTENT
* Supporting Information
■
(16) Crystallographic data for 6(PF6)(CHCl3): C46H38Cl3F6N6PRu,
S
M = 1027.21, triclinic, space group P1, a = 13.765(4), b = 14.046(4), c
̅
Crystallographic data of 6(PF6)(CHCl3) in CIF format,
absorption spectral changes of 5(PF6)−7(PF6) during elec-
trolysis, DFT calculations results, and NMR and mass spectra
of new compounds. This material is available free of charge via
the Internet at http://pubs.acs.org.
= 14.086(4) Å, α = 84.100(10)°, β = 77.970(10)°, γ = 82.130(9)°, U =
2630.8(12) Å3, T = 173 K, Z = 2, radiation type Mo Kα, radiation
́
wavelength 0.71073 Å, final R indices R1 = 0.0931, wR2 = 0.2301, R
indices (all data) R1 = 0.1245, wR2 = 0.2522.
(17) Zhang, Y.-M.; Shao, J.-Y.; Yao, C.-J.; Zhong, Y.-W. Dalton Trans.
2012, 41, 9280.
(18) Bomben, P. G.; Robson, K. C. D.; Sedach, P. A.; Berlinguette, C.
P. Inorg. Chem. 2009, 48, 9631.
(19) Sreenath, K.; Thomas, T. G.; Gopidas, K. R. Org. Lett. 2011, 13,
1134.
(20) (a) Chang, J. P.; Fung, E. Y.; Curtis, J. C. Inorg. Chem. 1986, 25,
4233. (b) Chen, Y. J.; Kao, C.-H.; Lin, S, J.; Tai, C.-C.; Kwan, K. S.
Inorg. Chem. 2000, 39, 189. (c) Lambert, C.; Noll, G. J. Chem. Soc.,
Perkin Trans. 2 2002, 2039.
(21) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(22) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.;
Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339.
AUTHOR INFORMATION
Corresponding Author
*Email: zhongyuwu@iccas.ac.cn.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work is supported by the National Natural Science
Foundation of China (Grants 21271176, 91227104, 21002104,
and 212210017), the National Basic Research 973 program of
China (Grant 2011CB932301), and the Institute of Chemistry,
Chinese Academy of Sciences (“100 Talent Program” and
Grant CMS-PY-201230).
(23) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(24) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(25) Adamo, C.; Barone, V. J. Chem. Phys. 1998, 108, 664.
(26) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158.
(27) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, Jr. T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
REFERENCES
■
(1) (a) Creutz, C.; Taube, H. J. Am. Chem. Soc. 1969, 91, 3988.
(b) D’Alessandro, D. M.; Keene, F. R. Chem. Rev. 2006, 106, 2270.
(c) Kaim, W.; Lahiri, G. K. Angew. Chem., Int. Ed. 2007, 46, 1778.
(d) Chisholm, M. H.; Lear, B. J. Chem. Soc. Rev. 2011, 40, 5254.
(2) (a) Aguirre-Etcheverry, P.; O’Hare, D. Chem. Rev. 2010, 110,
4839. (b) Low, P. J. Coord. Chem. Rev. 2013, 257, 1507.
(3) (a) Hankache, J.; Wenger, O. S. Chem. Rev. 2011, 111, 5138.
(b) Heckmann, S.; Lambert, C. Angew. Chem., Int. Ed. 2012, 51, 326.
(c) Nelsen, S. E. Chem.Eur. J. 2000, 6, 581.
(4) (a) Paul, F.; Lapinte, C. Coord. Chem. Rev. 1998, 178, 431.
(b) Low, P. J. Dalton Trans. 2005, 2821. (c) Akita, M.; Koike, T.
Dalton Trans. 2008, 3523.
(5) (a) Hush, N. S. Coord. Chem. Rev. 1985, 64, 135. (b) Hush, N. S.
Prog. Inorg. Chem. 1967, 8, 391.
4569
dx.doi.org/10.1021/om400519b | Organometallics 2013, 32, 4564−4570

Organometallics
Article
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision
E.01; Gaussian Inc.: Pittsburgh PA, 2007.
(28) (a) Dunning, T. H.; Hay, P. J. In Modern Theoretical Chemistry;
Schaefer, H. F., Ed.; Plenum: New York, 1976; Vol. 3, p 1. (b) Hay, P.
J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (c) Wadt, W. R.; Hay, P.
J. J. Chem. Phys. 1985, 82, 284. (d) Hay, P. J.; Wadt, W. R. J. Chem.
Phys. 1985, 82, 299.
(29) (a) Klamt, A.; Schuurmann, G. J. Chem. Soc., Perkin Trans. 2
̈
̈
1993, 799. (b) Andzelm, J.; Kolmel, C.; Klamt, A. J. Chem. Phys. 1995,
̈
103, 9312. (c) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995.
(d) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. J. Comput. Chem.
2003, 24, 669.
4570
dx.doi.org/10.1021/om400519b | Organometallics 2013, 32, 4564−4570