Tridentate cyclometalated ruthenium(II) complexes of "click" ligand 1,3-Di(1,2,3-triazol-4-yl)benzene

Article abstract of DOI:10.1021/om200039j

A tridentate cyclometalating ligand, 1,3-di(1,2,3-triazol-4-yl)benzene (dtab), has been prepared and used for the syntheses of a number of cyclometalated Ru^II complexes. A comparison of the electrochemical and spectroscopic properties of cyclometalated complexes made from dtab or 1,3-di(2-pyridyl)benzene is presented as well.

Full text of DOI:10.1021/om200039j

ARTICLE
pubs.acs.org/Organometallics
Tridentate Cyclometalated Ruthenium(II) Complexes of “Click” Ligand
1,3-Di(1,2,3-triazol-4-yl)benzene
Wen-Wen Yang, Lei Wang, Yu-Wu Zhong,* and Jiannian Yao*
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy
of Sciences, Beijing 100190, People’s Republic of China
S Supporting Information
b
ABSTRACT: A tridentate cyclometalating ligand, 1,3-di(1,2,3-
triazol-4-yl)benzene (dtab), has been prepared and used for the
syntheses of a number of cyclometalated RuII complexes. A
comparison of the electrochemical and spectroscopic properties
of cyclometalated complexes made from dtab or 1,3-di(2-
pyridyl)benzene is presented as well.
’ INTRODUCTION
yields and has received a tremendous degree of recent attention.7
We are particularly interested in the application of this reaction to
coordination chemistry.8 It should be noted that a number of
1,2,3-triazole-containing ligands, such as 2,6-bis(1,2,3-triazol-4-
yl)pyridines,9 2-(1H-1,2,3-triazol-4-yl)-pyridine,10 and phenyl-
1H-1,2,3-triazoles,11 have been synthesized and reported to form
stable complexes with Ru, Ir, Re, etc. However, to the best of our
knowledge, 1,2,3-triazole-containing cyclometalated ruthenium
complexes have not been documented.
As outlined in Scheme 1, dtab ligands 2 and 3 were prepared
through the Cu-catalyzed 1,3-dipolar cycloaddition between 1,3-
diethynylbenzene and 1-butylazide or phenylazide in good yields
(see the Experimental Section for details). Subsequent reaction of
1 equiv of Ru(tpy)Cl3 with 2 or 3 in the presence of silver triflate
afforded cyclometalated RuII complexes 4 and 5 in 19% and 5%
yield, respectively. The lower yield for the formation of complex 5
is partly because ligand 3 has more coordination sites available due
tothe presence of two additional phenyl rings. Complex 4 could be
regio-exclusively brominated on the para position of the RuꢀC
bond to give complex 6.12 On the other hand, complex 8, with a
bromine substituent on the tpy ligand side, could be prepared from
the known compound 74a and the above-synthesized ligand 2.
In addition, complex 10, with a tolyl group on the tpy ligand,
was prepared in order to examine the influence of substituents on
the electronic properties of these complexes. All of these efforts
illustrated that multiple positions are available for structural
variations and modifications of the new cyclometalated complex
with a “click” ligand and brominated complexes 6 and 8 could be
Polyazine transition-metal complexes have been the subject of
intense research activities because of their distinguished electrochemi-
cal and photophysical properties.1 One of the mostly studied prototype
complexes is [Ru(tpy)2](PF6)2 (tpy = 2,20:60,200-terpyridine). This
complex can be readily incorporated into supramolecular architectures
with well-defined structures via the easy and reliable functionalization
at the 4 and 40-position of the tpy ligand.2 Recently, much attention
has been drawn to the studies of cyclometalated transition-metal
complexes.3 Compound 1 (Figure 1) is the simplest cyclometalated
versionof[Ru(tpy)2](PF6)2, withaRuꢀC bond present between the
metal center and the 1,3-di(2-pyridyl)benzene (dpb) ligand.1d The
anionic nature of the cyclometalating ligand significantly changes the
properties of these complexes, as compared to noncyclometalated
ones. It has been reported that cyclometalated complexes can greatly
enhance electronic coupling between metal centers in mixed-valence
systems and have high potential to be used as molecular wires.4
Besides, recent investigations have proved that cyclometalated ruthe-
nium complexes could be used as efficient sensitizers for solar cell
applications,5 and there is still large room for further improvement.
In this contribution, we report the synthesis and studies of
new tridentate cyclometalated RuII complexes derived from
1,3-di(1,2,3-triazol-4-yl)benzene (dtab), which could be accessed
via click chemistry.6 This complex exhibits similar electrochemical
and spectroscopic properties to complex 1, but with more positions
available for further elaboration and fine-tuning its properties.
’ RESULTS AND DISCUSSION
Huisgen 1,3-dipolar cycloaddition, one of the so-called click
reactions, could readily afford a 1,2,3-triazole ring system in high
Received: January 17, 2011
Published: March 22, 2011
r
2011 American Chemical Society
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Table 1. Electrochemical and Electronic Absorption Data of
Complexes Studied
a
a
E1/2
anodic
E1/2
cathodic
λmax nm c
ΔE (eV)b ε (ꢁ105 Mꢀ1 cmꢀ1
complex
)
4
þ0.53 ꢀ1.57
þ1.60 ꢀ1.95
þ0.58 ꢀ1.53
þ1.64 ꢀ1.89
þ0.59 ꢀ1.55
þ1.65 ꢀ1.97
þ0.56 ꢀ1.35, ꢀ1.58
þ1.66 ꢀ1.96
þ0.53 ꢀ1.53
þ1.55 ꢀ1.92
þ0.56 ꢀ1.51
þ1.60 ꢀ1.92
2.10
2.11
2.14
2.14
2.06
2.07
2.54
316(0.43), 367(0.14)
490(0.10), 537(0.077)
315(0.41), 378(0.21)
485(0.079), 524(0.07)
315(0.36), 366(0.12)
483(0.083), 529(0.066)
316(0.31), 369(0.13)
500(0.10), 548(0.065)
314(0.35), 366(0.17)
497(0.12), 541(0.098)
315(0.37), 372(0.086)
423(0.095), 499(0.14)
307(0.78), 475(0.17)
5
6
8
Figure 1. Chemical structures of cyclometalated ruthenium complexes.
The arrows point to the sites that can be easily functionalized.
10
1
Scheme 1. Synthesis of 2ꢀ10
[Ru(tpy)2]2þ þ1.32 ꢀ1.22, ꢀ1.46
a The potential is reported as the E1/2 value vs Ag/AgCl. b The
electrochemical energy gap is determined by the potential difference
c
between the first oxidation and first reduction wave. The absorption
spectra were recorded in acetonitrile.
Figure 2. Cyclic voltammograms of 4 (red line), 1 (black line), and
[Ru(tpy)2](PF6)2 (blue line) in acetonitrile containing 0.1 M Bu4N-
ClO4 as the supporting electrolyte at a scan rate of 100 mV/s. The
working electrode was glassy carbon, and the counter electrode was a
platinum wire.
used as basic building blocks for the construction of more complex
systems.
potential led to the appearance of an irreversible oxidation at
þ1.60 V (Figure S2 in the Supporting Information). This peak is
attributable to a RuIII/IV process or ligand-based decomposition.4,5
The first reduction wave of 4 occurs at ꢀ1.57 V, followed by
an irreversible reduction peak at ꢀ1.95 V. The first reversible
redox couple is assigned to the reduction of the tpy ligand,4,5 and
the second irreversible peak is probably due to the reduction
of the cyclometalating ligand. The electrochemical energy gap
The electronic properties of these complexes were studied by
electrochemical analysis (Table 1). The cyclic voltammetric (CV)
profile of cyclometalated ruthenium complex 4 is shown in
Figure 2, together with those of complex 1 and [Ru(tpy)2]
(PF6)2 for comparison. The RuII/III redox process of 4 occurs at
þ0.53 V vs Ag/AgCl. This is a typical value for a cyclometalated
RuII/III redox process.4,5 The anodic scan to a more positive
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complex 10 leads to the increase of absorption of the MLtpyCT
transition.
’ CONCLUSION
In summary, two new tridentate cyclometalating ligands, 2 and
3, were designed and synthesized through click chemistry. A
number of cyclometalated ruthenium complexes could be ac-
cessed from reactions of 2 or 3 with various tpy ligands with
different substituents. Electrochemical and spectroscopic studies
demonstrated that electronic properties of these complexes
could be fine-tuned by changing the substituents on either the
cyclometalating or noncyclometalating ligand sides. This pre-
liminary study confirms the effectiveness of the “click” com-
pound dtab as an alternative tridentate ligand to the commonly
used dpb ligand, but with distinctive favorable differences, such as
the simple approach to the “click” ligand and more available
positions for structural variations and modifications of the com-
plexes. We are currently working on the optimization of the
cyclometalation reaction conditions and the construction of
supromolecular coordination systems from these ligands and
complexes.
Figure 3. UV/vis absorption spectra of 4 (red line), 5 (olive line), 10
(magenta line), 1 (black line), and [Ru(tpy)2](PF6)2 (blue line) in
acetonitrile.
determined by the potential difference between the first oxidation
and reduction wave is 2.10 eV for complex 4. In comparison to 1,
both oxidation and reduction waves of complex 4 shift negatively
slightly. It should be noted that the electrochemical properties of
cyclometalated complexes are significantly different from those of
noncyclometalated complexes, such as [Ru(tpy)2]2þ (blue line in
Figure 2). This complex displays a Ru-based oxidation at þ1.32 V
vs Ag/AgCl and two reduction couples at ꢀ1.22 and ꢀ1.46 V.
The electrochemical behaviors of complexes 5 and 6 (Figures
S3 and S4) are similar to that of 4. However, the cathodic scan of
complex 8 exhibits an additional peak at ꢀ1.35 V (Figure S5),
which could be assigned to the reduction of bromide followed by
irreversible loss of bromine anion. In contrast, complex 6, with a
bromine substituent on the cyclometalating ligand side, does not
show this process. This fact is in accordance with the assignment
of the first cathodic process of complexes with a “click” ligand to
the reduction of the tpy ligand instead of the cyclometalating
ligand (dtab). The electrochemical properties of 10 also support
this assignment. The introduction of a tolyl group on the tpy
ligand in complex 10 results in a 40 mV positive shift of the first
cathodic wave as compared to complex 4, while their RuIII/IV
processes take place at exactly the same potential (þ0.53 V). The
presence of a tolyl group enhances the delocalization degree of
the tpy ligand and makes it easier to be reduced.13
’ EXPERIMENTAL SECTION
General Procedures. NMR spectra were recorded in the desig-
nated solvent on a Bruker Avance 400 M spectrometer. Spectra are
reported in ppm values from residual protons of deuterated solvent
for 1H NMR (δ 7.26 ppm for CDCl3 and 1.92 ppm for CD3CN) and
13C NMR (δ 77.00 ppm for CDCl3). MS data were obtained with a
Bruker Daltonics Inc. ApexII FT-ICR or Autoflex III MALDI-TOF
mass spectrometer. The matrix for MALDI-TOF measurements is 2,5-
dihydroxybenzoic acid or R-cyano-4-hydroxycinnamic acid. Microana-
lysis was carried out using a Flash EA 1112 or Carlo Erba 1106 analyzer
at the Institute of Chemistry, CAS.
Compound 2. To a solution of 345 mg (5.3 mmol) of sodium azide
in a mixture of water (14 mL) and methanol (7 mL) was added 685 mg
(5.0 mmol) of n-butyl bromide at room temperature. The resulting
mixture was heated at 95 °C for 24 h, during which time the bottom layer
of butyl bromide disappeared and a top layer of butyl azide appeared.
The butyl azide layer (3 mL) was subsequently isolated using a
separatory funnel and used in the next transformation without further
purification.
The UV/vis absorption spectra of the above compounds were
recorded and compared with those of 1 and [Ru(tpy)2](PF6)2
(Figure 3, Table 1, and Figure S7 in the Supporting Infor-
mation) to further probe their electronic properties. Complex
[Ru(tpy)2](PF6)2 shows two strong intraligand absorptions in
the UV region and a metal-to-ligand charge-transfer (MLCT)
transition at 475 nm (blue line).14 In comparison, the MLCT
absorptions of cyclometalated Ru complex 1 are bathochromically
shifted (499 nm), broadened, and slightly decreased in absorptivity
(black line). The absorptions of cyclometalated complexes 4ꢀ6, 8,
and 10 are significantly different from those of [Ru(tpy)2](PF6)2
and 1. In addition to the intraligand transitions below 340 nm, an
intense absorption band between 340 and 420 nm is evident. This
band is attributable to the metal to N∧C∧N ligand CT transitions
(MLNCNCT).3c,e In addition, the metal to tpy liand CT transitions
(MLtpyCT) around 490 nm exhibit distinct lower energyshoulders.
This feature has also been documented for cyclometalated Ru
complexes with an ester substituent on the tpy ligand.3c Complex 5,
with two lateral phenyl groups on the triazole rings, display a more
intense MLNCNCT transition than those of 4 and 10. On the other
hand, the introduction of a tolyl group to the tpy ligand side on
A mixture of 1,3-diethynylbenzene (1 mmol, 126 mg), butyl azide (8
mmol, 792 mg), sodium ascorbate (0.2 mmol, 39.6 mg), and CuSO4
3
5H2O (0.02 mmol, 5 mg) in a 1:1 mixture of EtOH and H2O (20 mL)
was stirred at room temperature for 24 h. After removal of solvents under
vacuum, the crude product was purified by column chromatography
(eluent: CH2Cl2/ethyl acetate, 10:1) to afford 2 as a white solid (99%).
1H NMR (400 MHz, CDCl3): δ 0.99 (t, J = 7.4 Hz, 6H), 1.40 (dd, J =
14.9, 7.4 Hz, 4H), 1.95 (m, 4H), 4.42 (t, J = 7.1 Hz, 4H), 7.49 (t, J = 7.7
Hz, 1H), 7.84 (t, J = 6.2, 7.8 Hz, 4H), 8.30 (s, 1H). 13C NMR (100 MHz,
CDCl3): δ 147.4, 131.3, 129.4, 125.3, 122.8, 119.7, 50.2, 32.3, 19.7, 13.5.
EI-HRMS: calcd for C18H24N6 324.2062, found 324.2066. Anal. Calcd
for C18H24N6: C, 66.64; H, 7.46; N, 25.90. Found: C, 66.66; H, 7.62;
N, 25.85.
Compound 3. To an ethanol/water mixture (20 mL, 7:3 ratio)
were added bromobenzene (0.84 mL, 8 mmol), N,N0-dimethylethyle-
nediamine (0.13 mL, 1.2 mmol), CuI (154 mg, 0.8 mmol), and sodium
L-ascorbate (80 mg, 0.4 mmol). The flask was then flushed with nitrogen,
followed by the addition of NaN3 (260 mg, 4 mmol). The reaction
mixture was heated to reflux for 3 h. After cooling to room temperature,
1,3-diethynylbenzene (0.13 mL, 1.0 mmol) was added into the slightly
yellow mixture. After stirring for another 24 h at room temperature, the
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solution was concentrated under reduced pressure. The residue was then
dissolved in 100 mL of dichloromethane. After filtration, the organic
solution was washed with water and dried over MgSO4. The product was
purified by flash column chromatography on silica gel (eluent: CH2Cl2/
ethyl acetate, 10:1) to afford the product as a white solid (344 mg, 95%).
1H NMR (400 MHz, CDCl3): δ 7.48 (d, J = 7.4 Hz, 2H), 7.58 (t, J = 7.5
Hz, 5H), 7.82 (d, J = 7.8 Hz, 4H), 7.94 (d, J = 7.6 Hz, 2H), 8.33 (s, 2H),
8.47 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 148.0, 137.0, 130.9,
129.8, 129.6, 128.8, 125.7, 123.1, 120.5, 117.9. Anal. Calcd for
C22H16N6: C, 72.51; H, 4.43; N, 23.06. Found: C, 72.09; H, 4.45;
N, 22.74.
Complex 4. To 15 mL of dry acetone were added Ru(tpy)Cl3 (78.1
mg, 0.2 mmol) and AgOTf (154.3 mg, 0.6 mmol), and the mixture was
refluxed for 2 h. After cooling to room temperature, the mixture was
filtered to remove unwanted precipitates, and the filtrate was concen-
trated to dryness. To the residue were added ligand 2 (48.8 mg, 0.15
mmol), DMF (5 mL), and t-BuOH (5 mL). The mixture was heated to
reflux for 24 h. After cooling to room temperature, the solvent was
removed under reduced pressure, and the residue was dissolved in the
proper amount of methanol. After addition of an excess of KPF6, the
resulting precipitate was collected by filtering and washing with water
and Et2O. The obtained solid was subjected to flash column chroma-
tography on silica gel (eluent: CH2Cl2/CH3CN, 10:1) to give 22.5 mg
of complex 4 (19%). 1H NMR (400 MHz, CDCl3): δ 0.71 (t, J = 7.2 Hz,
6H), 1.04 (m, 4H), 1.61 (m, 4H), 4.02 (t, J = 7.0 Hz, 4H), 6.88 (t, J = 6.3
Hz, 2H), 7.29 (m, 3H, overlapped), 7.63 (t, J = 7.6 Hz, 2H), 7.75 (s, 2H),
7.77 (d, J = 4.3 Hz, 2H), 8.10 (t, J = 7.4 Hz, 1H), 8.22 (d, J = 7.9 Hz, 2H),
8.46 (d, J = 8.2 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ 12.4, 18.8,
31.3, 50.8, 118.3, 120.2, 120.7, 121.3, 122.9, 126.2, 132.0, 134.8, 135.0,
154.2, 154.5, 158.8, 159.6. MALDI-MS: 658.2 for [M ꢀ PF6]þ. ESI-
HRMS: calcd for C33H34N9Ru 658.1978, found 658.1985. Anal. Calcd
Complex 8. To 10 mL of dry acetone were added Ru(tpy-Br)Cl3
(52 mg, 0.1 mmol) and AgOTf (77 mg, 0.3 mmol), and the mixture
was refluxed for 2 h. After cooling to room temperature, the mixture
were filtered to afford a purple-black solution, and the filtrate was
concentrated to dryness. To the residue were added ligand 2 (32 mg,
0.1 mmol), DMF (4 mL), and t-BuOH (8 mL). The mixture was
heated to reflux in a sealed tube for 24 h. After cooling to room
temperature, the solvent was removed under reduced pressure, and
the residue was dissolved in the proper amount of methanol. After
addition of an excess of KPF6, the resulting precipitate was collected
by filtering and washing with water and Et2O. The obtained solid was
subjected to flash column chromatography on silica gel (eluent:
CH2Cl2/CH3CN, 10:1) to give 5.4 mg of complex 8 (6%). 1H
NMR (400 MHz, CD3CN): δ 0.64 (t, J = 7.2 Hz, 6H), 0.92 (m,
4H), 1.53 (m, 4H), 4.02 (t, J = 6.7 Hz, 4H), 7.04 (t, J = 6.6 Hz, 2H),
7.30 (d, J = 5.6 Hz, 2H), 7.34 (t, J = 8.5 Hz, 1H, overlapped with the
peak at 7.30 ppm), 7.72 (t, J = 8.1 Hz, 2H), 7.82 (d, J = 7.5 Hz, 2H),
8.04 (s, 2H), 8.36 (d, J = 8.1 Hz, 2H), 8.83 (s, 2H). ESI-MS: 736.3 for
[M ꢀ PF6]þ, 658.4 for [M ꢀ PF6 ꢀ Br]þ. Anal. Calcd for
C33H33BrF6N9PRu H2O: C, 44.06; H, 3.92; N, 14.01. Found: C,
3
43.96; H, 3.80; N, 14.19.
Complex 10. To 10 mL of dry acetone were added Ru(ttpy)Cl3
(79.9 mg, 0.2 mmol) and AgOTf (120.3 mg, 0.6 mmol), and the mixture
was refluxed for 3 h. After cooling to room temperature, the mixture was
filtered to afford a purple-black solution, and the filtrate was concen-
trated to dryness. To the residue were added ligand 2 (34.2 mg, 0.1
mmol) and 10 mL of DMF, and the mixture was heated to reflux for 24 h.
After cooling to room temperature, the solvent was removed under
reduced pressure, and the residue was dissolved in the proper amount of
methanol. After addition of an excess of KPF6, the resulting precipitate
was collected by filtering and washing with water and Et2O. The
obtained solid was subjected to flash column chromatography on silica
gel (eluent: CH2Cl2/CH3CN, 10:1) to give 27.4 mg of complex 10
(31%). 1H NMR (400 MHz, CD3CN): δ 0.63 (t, J = 7.4 Hz, 6H), 0.92
(m, 4H), 1.53 (m, 4H), 2.49 (s, 3H), 4.02 (t, J = 7.1 Hz, 4H), 7.00 (t, J =
6.6 Hz, 2H), 7.28 (d, J = 5.5 Hz, 2H), 7.36 (s, 1H), 7.50 (d, J = 7.9 Hz,
2H), 7.70 (t, J = 7.8 Hz, 2H), 7.82 (d, J = 7.5 Hz, 2H), 8.05 (d, J = 6.3 Hz,
4H), 8.46 (d, J = 8.1 Hz, 2H), 8.84 (s, 2H). ESI-MS: 748.5 for [M ꢀ
PF6]þ. ESI-HRMS: calcd for C40H40N9Ru 748.2453, found 748.2443.
Anal. Calcd for C40H40F6N9PRu: C, 53.81; H, 4.52; N, 14.12. Found: C,
53.62; H, 4.54; N, 14.12.
for C33H34F6N9PRu H2O: C, 48.29; H, 4.42; N, 15.36. Found: C,
3
48.20; H, 4.31; N, 15.10.
Complex 5. To 10 mL of dry acetone were added Ru(tpy)Cl3 (44
mg, 0.1 mmol) and AgOTf (77 mg, 0.3 mmol), and the mixture was
refluxed for 3 h. After cooling to room temperature, the mixture were
filtered to afford a purple-black solution, and the filtrate was concen-
trated to dryness. To the residue were added ligand 3 (36 mg, 0.1 mmol),
DMF (5 mL), and t-BuOH (5 mL), and the mixture was refluxed in a
sealed tube for 24 h. After cooling to room temperature, the solvent was
removed under reduced pressure, and the residue was dissolved in the
proper amount of methanol. After addition of an excess of KPF6, the
resulting precipitate was collected by filtering and washing with water
and Et2O. The obtained solid was subjected to flash column chroma-
tography on silica gel (eluent: CH2Cl2/CH3CN, 15:1) to afford 4.3 mg
of complex 5 as a purple-black solid (5%). 1H NMR (400 MHz,
CD3CN): δ 7.05 (t, J = 6.4 Hz, 2H), 7.39 (d, J = 4.2 Hz, 5H), 7.44
(d, J = 4.2 Hz, 7H), 7.72 (t, J = 7.8 Hz, 3H), 7.94 (d, J = 7.4 Hz, 2H), 8.23
(t, J = 8.0 Hz, 1H), 8.38 (d, J = 8.0 Hz, 2H), 8.62 (d, J = 5.9 Hz, 3H), 8.65
(s, 1H). ESI-MS: 698.4 for [M ꢀ PF6]þ. HRESI-MS: calcd for
C37H26N9Ru 698.1360, found 698.1350. Anal. Calcd for
’ ASSOCIATED CONTENT
S
Supporting Information. CV profiles of cyclometalated
b
complexes and electronic absorption spectra of 6 and 8, and
NMR and MS spectra of new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
C37H26F6N9PRu CH3CN: C, 63.40; H, 3.96; N, 18.96. Found: C,
63.33; H, 4.09; N, 19.37.
’ AUTHOR INFORMATION
3
Corresponding Author
*E-mail: zhongyuwu@iccas.ac.cn (Y.-W.Z.), jnyao@iccas.ac.cn
(J.Y.).
Complex 6. Complex 4 (16.7 mg, 0.02 mmol) was treated with 1.1
equiv of N-bromosuccinimide (NBS, 5 mg) in CH3CN at room
temperature, and the reaction mixture was allowed to stir for 6 h. The
crude product was purified by column chromatography (CH2Cl2/
CH3CN, 10:1) on neutral Al2O3 to afford 6 as a purple-black solid
(11 mg, 63%). 1H NMR (400 MHz, CD3CN): δ 0.64 (t, J = 7.3 Hz, 6H),
0.94 (m, 4H), 1.53 (m, 4H), 4.03 (t, J = 7.1 Hz, 4H), 7.00 (t, J = 6.5 Hz,
2H), 7.26 (d, J = 4.6 Hz, 2H), 7.71 (t, J = 7.8 Hz, 2H), 7.97 (s, 2H), 8.17
(s, 2H), 8.19 (t, J = 8.1 Hz, 1H), 8.34 (d, J = 8.0 Hz, 2H), 8.60 (d, J = 8.0
Hz, 2H). ESI-MS: 738.5 for [M ꢀ PF6]þ, 662.5 for [M ꢀ PF6 ꢀ Br]þ.
ESI-HRMS: calcd for C33H33BrN9Ru 736.1081, found 736.1068.
’ ACKNOWLEDGMENT
We thank the National Natural Science Foundation of China
(No. 21002104), Institute of Chemistry, Chinese Academy
of Sciences (“100 Talent” Program), and 973 program
(2011CB932300) for funding support.
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