Synthesis, characterization, and properties of binuclear ruthenium complexes with dendritic side chains on their bridges

Article abstract of DOI:10.1016/j.ica.2011.01.075

Three binuclear ruthenium complexes with dendritic side chains, 1,4-[RuCl(CO)(PMe₃)₃CHCH]₂C₆H ₂-2,5-(G_n)₂ with G_n = G₀ (1), G₁ (2), and G₂

Full text of DOI:10.1016/j.ica.2011.01.075

Inorganica Chimica Acta 370 (2011) 286–291
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, characterization, and properties of binuclear ruthenium complexes
with dendritic side chains on their bridges
Xiang Hua Wu a,b, Jin Hua Liang a, Jiang Long Xia a, Jun Yin a, Shan Jin a, Guang-ao Yu a, Sheng Hua Liu a,
⇑
a Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, PR China
b College of Chemistry and Chemical Engineering, Yunan Normal University, Kunming 650092, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three binuclear ruthenium complexes with dendritic side chains, 1,4-[RuCl(CO)(PMe3)3CH@CH]2C6H2-
2,5-(Gn)2 with Gn = G0 (1), G1 (2), and G2 (3), have been synthesized by the reactions of the corresponding
diethynylaryls with the ruthenium hydride complex [RuHCl(CO)(PPh3)3] and subsequent ligand exchange
with PMe3. The complexes have been characterized by elemental analysis, NMR, and UV–Vis spectropho-
tometry. The structure of complex 1 has been determined by X-ray crystallography. Their electrochemical
properties have been investigated. Electrochemical studies in solution may imply that the two metal cen-
ters in complexes 1–3 have good electronic communications between each other. However, the electron
communication is not effectively enhanced with increasing generation of the dendrons in solution.
Ó 2011 Elsevier B.V. All rights reserved.
Received 14 December 2010
Accepted 22 January 2011
Available online 3 February 2011
Keywords:
Ruthenium complex
Dendrons
Electrochemistry
Structure
1. Introduction
as insulators and kinetically protect the bridges against side reac-
tions [35]. To further explore this shielding effect, a pseudo
Linear conjugated molecular wires are important for the explo-
ration of physical properties related to the delocalization of elec-
‘‘core–shell’’ design of organometallic molecular wires is proposed.
Herein, we report the preparation and characterization, together
with electrochemical investigations, of three binuclear ruthenium
complexes 1–3 with dendritic side chains to systematically evalu-
ate the influence of the ‘‘dendrimer effect’’ on intramolecular elec-
tron transfer.
p
trons and have also attracted attention for their potential
application in molecular electronics [1–6]. Among the many mole-
cules under investigation, conjugated oligomers are limited in
length to tens of nanometers because of their low solubility and
strong tendency to aggregate [7–11]. This makes it rather challeng-
ing to fabricate conjugated oligomeric molecular wires on a single-
molecular scale. To date, several intriguing strategies have been
developed to solve this problem, in which insulated molecular
wires have been designed through covalent or noncovalent ap-
proaches, and the conjugated oligomeric backbones have been
encapsulated by a protective sheath, such as by threading conju-
gated oligomers through cyclophanes [12–15], cyclodextrins
[16–19], and zeolites [20–23], by wrapping them in polymer heli-
ces [24–26,2,27], or by decorating them with dendritic side chains
[28–34], limiting inter-chain interactions, and enhancing the one-
dimensional nature of the transport properties. Although a consid-
erable number of insulated molecular wires have been reported,
such studies have been mainly focused on their synthesis, chemical
stability, and photoluminescence properties.
2. Experimental
2.1. Materials and methods
All manipulations were carried out at room temperature under
a nitrogen atmosphere using standard Schlenk techniques, unless
otherwise stated. Solvents were pre-dried, distilled and degassed
prior to use, except those for spectroscopic measurements, which
were of spectroscopic grade. The starting materials RuHCl
(CO)(PPh3)3 [36], 5-(bromomethyl)-1,3-bis{[4-(tert-butyl)benzyl]
oxy}benzene [37,38], 1,3-bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}
benzyl)oxy]-5-(bromomethyl)benzene [37,38], and 2,5-bis(2-
(trimethylsilyl)ethynyl)benzene-1,4-diol [39] were prepared by
the procedures described in literature methods. 1H, 13C{1H}, and
31P{1H} NMR spectra were collected on a Varian MERCURY Plus
400 spectrometer (400 MHz) or on a Varian MERCURY Plus 600
spectrometer (600 MHz). 1H, 13C{1H} NMR chemical shifts are rel-
ative to TMS, and 31P{1H} NMR chemical shifts are relative to 85%
H3PO4.
Previously, we reported that the introduction of long carbon
chains on the bridge enhances the electron communication be-
tween the two metal centers, whereby the long carbon chains act
⇑
Corresponding author. Tel.: +86 27 67867725.
E-mail address: chshliu@mail.ccnu.edu.cn (S.H. Liu).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.075

X.H. Wu et al. / Inorganica Chimica Acta 370 (2011) 286–291
287
Elemental analyses (C, H, N) were performed by Vario ElIII
Chnso. IR spectra were recorded on a Nicolet AVATAR 360 FT-
IR spectrophotometer using KBr disks. UV–Vis spectra were re-
corded on a PDA spectrophotometer by quartz cells with path
length of 1.0 cm. The electrochemical measurements were per-
formed on a CHI 660C potentiostat (CHI USA). A three-electrode
one-compartment cell was used to containing the solution of
the compound and supporting electrolyte in dry CH2Cl2. Deaer-
ation of the solution was achieved by argon bubbling through
the solution for about 10 min before measurement. The ligand
and electrolyte (Bu4NPF6) concentrations were typically 0.001
for 30 min to give a red solution. Then a 1 M THF solution of
PMe3 (4.0 mL, 4.0 mmol) was added to the red solution. The mix-
ture was stirred for another 20 h. The solution was filtered through
a column of Celite. The volume of the filtrate was reduced to ca.
2 mL under vacuum. Addition of hexane (30 mL) to the residue
produced a yellow solid, which was collected by filtration, washed
with hexane, and dried under vacuum. Yellow solid: 0.36 g, 65%.
Anal. Calc. for C52H90Cl2O4P6Ru2: C, 50.44; H, 7.33. Found: C,
50.65; H, 7.07%. 31P NMR (160 MHz, CDCl3):
d
À20.28 (t,
J = 21.1 Hz), À8.59 (d, J = 21.1 Hz). 1H NMR (400 MHz, CDCl3): d
1.32 (s, 18H, CH3), 1.40 (t, J = 3.2, 36H, PMe3), 1.49 (d, J = 6.8,
18H, PMe3), 5.06 (s, 4H, OCH2), 7.14–7.17 (m, 2H, Ph-CH@), 7.17
(s, 2H, Ph-H), 7.37 (d, J = 8.0 Hz, 4H, Ph-H), 7.53 (d, J = 8.0 Hz, 4H,
Ph-H), 7.91–7.07 (m, 2H, Ru-CH@). 13C NMR (150 MHz, CDCl3): d
16. 60 (t, J = 15.1 Hz, PMe3), 20.21 (d, J = 20.5 Hz, PMe3), 31.36,
34.42, 71.38, 110.27, 125.06, 126.92, 128.43, 128.73, 135.48,
163.05, 202.37 (CO). IR (KBr, cmÀ1): 1912 (CO), 1554, 1517, 1469,
1417 (C@C aryl, vinyl).
and 0.1 mol dmÀ3, respectively. A 500
lm diameter platinum
disc working electrode, a platinum wire counter electrode, and
an Ag|Ag+ reference electrode were used. The Ag|Ag+ reference
electrode contained an internal solution of 0.01 mol dmÀ3
AgNO3 in acetonitrile and was incorporated to the cell with a
salt bridge containing 0.1 mol dmÀ3 Bu4NPF6 in CH2Cl2. All elec-
trochemical experiments were carried out under ambient
conditions.
2.2.5. Preparation of complex [RuCl(CO)(PMe3)3]2(l-CH@CH–C6H2-
2.2. Syntheses
(OG1)2-2,5–CH@CH) (2)
The synthesis is similar to 1, with diethynylaryls 13 being re-
placed by diethynylaryls 14. Yellow solid: 0.36 g, 25%. Anal. Calc.
for C88H128Cl2O8P6Ru2: C, 59.62; H, 7.28. Found: C, 59.44; H,
7.62%. 31P NMR (160 MHz, CDCl3): d À20.26 (t, J = 21.1 Hz), À8.52
(d, J = 21.1 Hz). 1H NMR (400 MHz, CDCl3): d 1.33 (s, 36H, CH3),
1.36 (t, J = 3.2, 36H, PMe3), 1.45 (d, J = 6.8, 18H, PMe3), 5.01 (s,
8H, OCH2), 5.05 (s, 4H, OCH2), 6.51–6.57 (m, 2H, Ph-CH@), 6.86
(s, 4H, Ph-H), 7.11–7.16 (m, 4H, Ph-H), 7.36 (d, J = 8.4, 8H, Ph-H),
7.41 (d, J = 8.4, 8H, Ph-H), 7.92–7.99 (m, 2H, Ru-CH@). 13C NMR
2.2.1. Preparation of compound (CH„C–C6H2(OG0)2-2,5–C„CH) (13)
A THF solution (20 mL) of a mixture of G0–Br (0.52 g, 2.2 mmol),
2,5-trimethylsilylethynyl-1,4-hydroquinone (0.3 g, 1.0 mmol),
K2CO3 (0.84 g, 6.0 mmol), and 18-crown-6 ether (0.26 g, 1.0 mmol)
was refluxed under Ar overnight in the dark [39]. After removal of
the solvent in vacuo, dichloromethane was added to the residue
and extracted with brine and water. The organic phases were dried
with Na2SO4. The residue was purified by flash chromatography
(dichloromethane/petroleum ether, 10:1–5:1, v/v) to give 13
(0.34 g, 76%) as yellow solid. Anal. Calc. for C32H34O2: C, 85.29; H,
7.61. Found: C, 84.96; H, 7.45%. 1H NMR (400 MHz, CDCl3): d 1.32
(s, 18H, CH3), 3.36 (s, 2H, „CH), 5.07 (s, 4H, OCH2), 7.05 (s, 2H,
Ph-H), 7.39 (d, J = 1.2 Hz, 8H, Ph-H). 13C NMR (100 MHz, CDCl3): d
29.66, 34.32, 79.49, 113.42, 118.08, 125.07, 125.37, 126.56,
126.84, 133.34, 150.62, 153.68.
(150 MHz, CDCl3):
d 16.53 (t, J = 15.1 Hz, PMe3), 20.09 (d,
J = 20.5 Hz, PMe3), 31.27, 34.46, 69.66, 71.29, 101.19, 105.55,
109.99, 125.28, 127.49, 128.32, 129.08, 133.98, 140.73, 148.64,
150.65, 159.93,163.50, 202.24 (CO). IR (KBr, cmÀ1): 1917 (CO),
1596, 1554, 1457, 1415 (C@C aryl, vinyl).
2.2.6. Preparation of complex [RuCl(CO)(PMe3)3]2(l-CH@CH–C6H2-
(OG2)2-2,5–CH@CH) (3)
2.2.2. Preparation of compound (CH„C–C6H2(OG1)2-2,5–C„CH) (14)
Similar synthesis procedures in 13 were adopted to obtain a
yellow solid in 74% yield. Anal. Calc. for C68H74O6: C, 82.72; H,
7.55. Found: C, 82.25; H, 7.14%. 1H NMR (400 MHz, CDCl3): d 1.32
(s, 36H, CH3), 3.32 (s, 2H, „CH), 5.00 (s, 8H, OCH2), 5.04 (s, 4H,
OCH2), 6.56 (s, 2H, Ph-H), 6.72 (s, 4H, Ph-H), 7.01 (s, 2H, Ph-H),
7.36 (d, J = 8.4, 8H, Ph-H), 7.41 (d, J = 8.4, 8H, Ph-H). 13C NMR
(100 MHz, CDCl3): d 31.28, 34.52, 69.83, 70.84, 79.57, 83.09,
101.32, 105.45, 113.50, 118.10, 125.50, 127.58, 133.60, 150.99,
153.65, 160.13.
The synthesis is similar to 1, with diethynylaryls 13 being re-
placed by diethynylaryls 15. Yellow solid: 1.04 g, 81%. Anal. Calc.
for C160H210Cl2O16P6Ru2: C, 67.47; H, 7.43. Found: C, 67.64; H,
7.19%. 31P NMR (160 MHz, CDCl3): d À20.73 (t, J = 21.1 Hz), À8.66
(d, J = 21.1 Hz). 1H NMR (400 MHz, CDCl3): d 1.32 (s, 72H, CH3),
1.41 (t, J = 3.2, 36H, PMe3), 1.49 (d, J = 6.8, 18H, PMe3), 4.99 (s,
28H, OCH2), 6.49–6.51 (m, 2H, Ph-CH@), 6.62 (s, 6H,, Ph-H), 6,69
(s, 8H, Ph-H), 6.87 (s, 4H, Ph-H), 7.10 (s, 2H, Ph-H), 7.35 (d,
J = 8.0 Hz, 16H, Ph-H), 7.40 (d, J = 8.0 Hz, 16H, Ph-H), 7.94–7.96
(m, 2H, Ru-CH@). 13C NMR (150 MHz, CDCl3):
d 16.53 (t,
J = 15.1 Hz, PMe3), 20.02 (d, J = 20.5 Hz, PMe3), 31.26, 34.47,
69.83, 71.43, 101.18, 101.44, 105.66, 106.29, 110.16, 125.42,
127.56, 128.27, 129.21, 133.64, 139.40, 148.71, 150.91, 159.82,
160.71, 202.41 (CO). IR (KBr, cmÀ1): 1917 (CO), 1596, 1555, 1456,
1414 (C@C aryl, vinyl).
2.2.3. Preparation of compound (CH„C–C6H2(OG2)2-2,5–C„CH) (15)
Similar synthesis procedures in 13 were adopted to obtain a
yellow solid in 81% yield. Anal. Calc. for C140H154O14: C, 81.60;
H, 7.53. Found: C, 81.14; H, 7.27%. 1H NMR (400 MHz, CDCl3):
d 1.30 (s, 72H, CH3), 3.32 (s, 2H, „CH), 4.95 (s, 28H, OCH2),
6.57 (s, 6H, Ph-H), 6.68 (s, 8H, Ph-H), 6.97 (s, 4H, Ph-H), 7.14
(s, 2H, Ph-H), 7.35 (d, J = 8.4, 16H, Ph-H), 7.38 (d, J = 8.4, 16H,
2.3. Crystallographic analysis
Ph-H). 13C NMR (100 MHz, CDCl3):
d
31.25, 34.47, 69.78,
Crystals suitable for X-ray diffraction were grown from a dichlo-
romethane of solution 1 layered with hexane. A crystal with
approximate dimensions of 0.23 Â 0.12 Â 0.10 mm3 for 1 was
mounted on a glass fiber for diffraction experiment. Intensity data
70.67, 79.58, 83.21, 101.28, 105.50, 106.06, 113.36, 117.94,
125.44, 127.55, 129.22, 133.55, 139.01, 150.90, 153.55, 159.90,
160.09.
were collected on a Nonius Kappa CCD diffractometer with Mo K
a
2.2.4. Preparation of complex [RuCl(CO)(PMe3)3]2(
(OG0)2-2,5–CH@CH) (1)
l
-CH@CH–C6H2-
radiation (0.71073 Å) at room temperature. The structures were
solved by a combination of direct methods (SHELXS-97 [40]) and
Fourier difference techniques and refined by full-matrix least
squares (SHELXL-97 [41]). All non-H atoms were refined anisotropi-
cally. The hydrogen atoms were placed in the ideal positions and
To suspension of RuHCl(CO)(PPh3)3 (0.86 g, 0.9 mmol) in CH2Cl2
(30 mL) was slowly added solution of diethynylaryls 13
(0.50 mmol) in CH2Cl2 (10 mL). The reaction mixture was stirred
a

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X.H. Wu et al. / Inorganica Chimica Acta 370 (2011) 286–291
Table 1
Table 2
Crystal data, date collection, and refinement parameters for complex 1.
Selected bond lengths (Å) and angles (°) for complex 1.
Formula
Formula weight
T (K)
Crystal system
Space group
a (Å)
C53H92Cl4O4P6Ru2
1323.09
298(2)
monoclinic
P2(1)/c
9.81640(10)
11.41290(10)
30.9110(3)
90.00
C(11)–C(12)
C(12)–C(13)
C(10)–O(1)
C(15)–O(2)
C(12)–C(11)–Ru(1)
C(11)–C(12)–C(13)
C(12)–C(13)–C(15)
1.323(6)
1.473(6)
1.158(6)
1.397(5)
131.2(4)
128.0(4)
121.2(4)
C(16)–O(2)
C(16)–C(17)
C(20)–C(23)
Ru(1)–Cl(1)
C(13)–C(15)–O(2)
C(15)–O(2)–C(16)
O(2)–C(16)–C(17)
1.397(7)
1.503(7)
1.531(7)
2.4828(13)
119.0(4)
114.4(4)
109.5(5)
b (Å)
c (Å)
a
(°)
b (°)
90.5410(10)
90.00
3462.92(6)
4
1.350
0.0633, 7.1106
0.0639
c
(°)
3. Results and discussion
V (ÅÀ3
)
Z
3.1. Synthesis and characterization
Dcalc (g cmÀ3
a, b for Wa
Final R
)
The convergent synthesis of the shell of Fréchet-type aryl ether
dendrons Gn–Br is outlined in Scheme 1 [37,38]. Etherification of
methyl 3,5-dihydroxybenzoate (4) gave 6, and subsequent ester
reduction yielded alcohol 7, which was transformed into benzyl
bromide 8, the first-generation dendritic branch. A similar se-
quence provided the second-generation dendron 11. The substi-
tuted 1,4-diethynylbenzene derivatives 13–15 were synthesized
according to literature methods (Scheme 2), whereby different
generation dendrons (G0, G1, and G2) were attached to 2,5-bis[2-
(trimethylsilyl)ethynyl]benzene-1,4-diol (12) [39]. Reactions of
the diethynylaryls 13–15 with the ruthenium hydride complex
[RuHCl(CO)(PPh3)3] afforded the corresponding insertion products,
Rw
0.1491
0.0759
0.1584
1.165
R (all date)
Rw (all date)
Goodness-of-fit (GOF) on F2
Largest difference in peak and hole (e ÅÀ3
)
0.971, À0.633
W = 1/[r
2(Fo)2 + (aP)2 + bP], where P = (Fo2 + Fc2)/3.
a
refined as riding atoms. Further crystal data and details of the data
collection are summarized in Table 1. Selected bond distances and
angles are given in Table 2.
(G0-Br)
5
HO
OH
CH2Br
LiAlH4
O
O
O
O
THF
K2CO3/[18]-crown-6
THF
COOCH3
CH2OH
COOCH3
4
6
7
O
O
4/K2CO3
PBr3
O
O
O
O
ether
[18]-crown-6/THF
O
O
COOCH3
CH2Br
(G1-Br)
9
8
O
O
O
O
PBr3
ether
LiAlH4
THF
O
O
O
O
O
O
O
O
CH2OH
CH2Br
(G2-Br)
10
11
Scheme 1. Synthesis of aryl ether dendrons Gn–Br.

X.H. Wu et al. / Inorganica Chimica Acta 370 (2011) 286–291
289
OH
OGn
K2CO3/[18]-crown-6
TMS
TMS
+ GnBr
THF
HO
GnO
G0
G1
5
8
G0 13
G1 14
G2 15
12
G2 11
PMe3
Ru
PMe3
Cl
OC
GnO
1. RuHCl(CO)(PPh3)3
2. PMe3
PMe3
Ru
Cl
PMe3
OGn
Me3P
CO
PMe3
G0
G1
G2
1
2
3
Scheme 2. Synthesis of complexes 1, 2 and 3.
and subsequent ligand exchange with PMe3 gave complexes 1–3.
These complexes were characterized by NMR. The PMe3 ligands
in all of these bimetallic complexes are meridionally coordinated
to ruthenium, as indicated by an AM2 pattern in the 31P{1H} NMR
spectra.
ruthenium centers linked by
a
linear
l
-CH@CH–Ar–CH@CH
(Ar = C6H2(OG1)2-2,5) bridge. The molecular structure of 1 is cen-
trosymmetric and the two Ru centers are related by a pseudo-C2
rotation axis. The distance between the two metal centers is
11.857 Å, which is slightly shorter than those in [RuCl(CO)(P-
Me3)3]2(l-CH@CH–Ar–CH@CH)
(Ar = C6H2(OR)2-2,5;
R = CH3
11.919 Å, nC4H9 11.913 Å, nC8H17 11.906 Å) [8,14]. The carbon
atoms of the two CH@CH units and benzene ring are not copla-
nar, forming a dihedral angle of 17.25°, due to the steric hin-
drance. The two double bonds are in a trans configuration. The
overall geometry of complex 1 closely resembles those of the
3.2. Description of the structure
The molecular structure of complex 1 was confirmed by X-ray
diffraction study. The crystallographic details are given in Table
1. Selected bond distances and angles for complex 1 are pre-
sented in Table 2. The molecular structure of complex 1 is de-
picted in Fig. 1. As shown in Fig. 1, complex 1 contains two
bimetallic ruthenium complexes [RuCl(CO)(PMe3)3]2(l-CH@CH–
Ar–CH@CH) [35,42].
Fig. 1. Molecular structure of 1.

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X.H. Wu et al. / Inorganica Chimica Acta 370 (2011) 286–291
Table 3
1500
UV–Vis data for complexes 1–3 in
CH2Cl2.
Complex
Absorption, nm
(10À3 , MÀ1 cmÀ1
e
)
1000
500
0
1
1
2
3
350 (17.9)
350 (17.5)
350 (17.1)
2
3.3. Electronic absorption spectroscopy
To assess the influence of the dendritic side branches, the elec-
tronic properties of these three vinyl bimetallic complexes 1–3
have been investigated by UV–Vis spectrophotometry, and the re-
sults are summarized in Table 3. For these vinyl complexes, ener-
getic transitions are observed above 350 nm, which can be
3
-0.2
0.0
0.2
0.4
0.6
0.8
attributed to
p–
p⁄ ligand-centered transitions. This suggests that
Potential (V)
the incorporation of various dendrons does not induce changes in
the electronic structure of the conjugated 1,4-diethenylphenylene
core.
Fig. 2. Cyclic voltammograms (CV) of complexes 1, 2, and 3 in CH2Cl2/Bu4NPF6 at
= 0.1 V sÀ1
m
.
illustrate that the attached dendritic side chains is not effectively
enhance the electron communication between the two metal cen-
3.4. Electrochemistry
ters. The much smaller variation in
DE1/2 with generation in solu-
The redox behavior of the binuclear ruthenium complexes 1–3
in dichloromethane solutions has been investigated by cyclic vol-
tammetry and square-wave voltammetry techniques. The electro-
chemical data are presented in Table 4. In this case, the three
complexes undergo two consecutive one-electron oxidation pro-
cesses, giving rise to redox waves A and B (Table 4) in the potential
region from 0.10 to 0.49 V, corresponding to oxidation of Ru2II,II to
Ru2II,III and then of Ru2II,III to Ru2III,III. The first redox process of these
complexes is quasi-reversible, however these complexes undergo a
irreversible one-electron oxidation at moderately positive poten-
tial during the second redox process. Cyclic voltammograms (CV)
acquired for complexes 1–3 in dichloromethane solution are de-
picted in Fig. 2. The result may imply that the two metal centers
in complexes 1–3 have good electronic communications between
each other.
tion electrochemistry may be reduced by less than two reasons.
One is probably because the ‘‘shell’’ dendrimer is solvated, which
is similar to the results reported by Gorman and Smith [43]. The
other is that the carbon atoms of the two CH@CH units and ben-
zene ring are not coplanar, that is, highly branched geometry re-
sults in a non-conjugated part of the bridging ligand.
4. Conclusions
Three ‘‘core–shell’’ designed binuclear ruthenium vinyl com-
plexes 1–3 have been synthesized and characterized, and their
electrochemical properties have been investigated. Electro-
chemical studies in solution may imply that the two metal centers
in complexes 1–3 have good electronic communications between
each other; however, the electron communication is not effec-
tively enhanced with increasing generation of the dendrons in
solution.
As shown in Fig. 2 and Table 4, for complex 2, with two first-
generation groups attached to the 1,4-diethenylphenylene spacer
unit, the
DE1/2 value is 0.34 V, and the corresponding Kc value is
5.6 Â 105. Compared with the
DE1/2 (0.34 V) of complex 1, the
first-generation group attached to 1,4-diethenylphenylene is not
seen to be stronger with respect to electron communication be-
tween the two metal centers, with the DDE1/2 being about 0.0 V.
Acknowledgments
The authors acknowledge financial support from National Nat-
ural Science Foundation of China (Nos. 2072039, 20931006,
21072070, 21002086) and Program for Changjiang Scholars and
Innovative Research Team in University (No. IRT0953).
By comparison of the
the
DE1/2 values of complexes 2 and 3, in which
D
E1/2 values are 0.34 and 0.35 V, and the corresponding Kc val-
ues are 5.6 Â 105 and 8.2 Â 105, respectively (Table 4), these data
also illustrate that the electron communication is not effectively
enhanced with increasing dendrimer generation. The above results
Appendix A. Supplementary material
Table 4
CCDC 803493 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.
Electrochemical data for complexes 1–3a in CH2Cl2 solution.
b
c
Complex
E1/2 (A)
E1/2 (B)
D
E1/2
Kc
1
2
3
0.11
0.10
0.14
0.45
0.44
0.49
0.34
0.34
0.35
5.6 Â 105
5.6 Â 105
8.2 Â 105
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