Further molecular engineering of diruthenium-(2-anilinopyridinate) alkynyl compounds through ligand design

Article abstract of DOI:10.1016/j.jorganchem.2007.11.050

A modified ap ligand, 2-(3,5-dimethoxyanilino)pyridine (HDiMeOap) and its diruthenium compounds Ru₂(DiMeOap)₄Cl (1), Ru₂(DiMeOap)₄(C{triple bond, long}CC{triple bond, long}CSiMe₃) (2) and Ru₂(DiMeOap)₄(C{triple bond, long}CC{triple bond, long}CSiMe₃)₂ (3) were prepared and characterized. New compounds Ru₂(MeOap)₄(C{triple bond, long}CC{triple bond, long}CSiMe₃)_x (x = 1, 4; 2, 5; MeOap is 2-(3-methoxyanilino)pyridinate) were prepared from the previously reported Ru₂(MeOap)₄Cl. In addition, two related diruthenium compounds containing ferrocenyl acetylide ligand, Ru₂(MeOap)₄(C{triple bond, long}CFc) (6) and Ru₂(ap)₄(C{triple bond, long}CC{triple bond, long}CFc) (7), were synthesized. Molecular structures of compounds 1, 2, 6 and 7 were established using single crystal X-ray diffraction study.

Full text of DOI:10.1016/j.jorganchem.2007.11.050

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1656–1663
www.elsevier.com/locate/jorganchem
Further molecular engineering of diruthenium-(2-anilinopyridinate)
alkynyl compounds through ligand design
Bin Xi, Guo-Lin Xu, Jie-Wen Ying, Hong-Ling Han, Antoinette Cordova, Tong Ren *
Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA
Received 10 November 2007; received in revised form 27 November 2007; accepted 27 November 2007
Available online 4 December 2007
Dedicated to the memory of Professor Al Cotton, mentor, scholar and friend.
Abstract
A modified ap ligand, 2-(3,5-dimethoxyanilino)pyridine (HDiMeOap) and its diruthenium compounds Ru2(DiMeOap)4Cl (1),
Ru2(DiMeOap)4(C„CC„CSiMe3) (2) and Ru2(DiMeOap)4(C„CC„CSiMe3)2 (3) were prepared and characterized. New compounds
Ru2(MeOap)4(C„CC„CSiMe3)x (x = 1, 4; 2, 5; MeOap is 2-(3-methoxyanilino)pyridinate) were prepared from the previously reported
Ru2(MeOap)4Cl. In addition, two related diruthenium compounds containing ferrocenyl acetylide ligand, Ru2(MeOap)4(C„CFc) (6)
and Ru2(ap)4(C„CC„CFc) (7), were synthesized. Molecular structures of compounds 1, 2, 6 and 7 were established using single crystal
X-ray diffraction study.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Diruthenium; Modified ap ligands; Acetylide complexes; Molecular wires
1. Introduction
on Au surface revealed an improved molecular conductance
over –SC6H4(C„CC6H4)2S–, a conjugated organic mole-
cule of comparable length [10,11]. Despite these successes,
the exploration of longer wire-like Ru2(ap)4 compounds
has been hampered by the poor solubility in common
organic solvents [12]. Improved solubility of Ru2-alkynyl
building blocks may also enable their incorporation into
rigid rod polymers with interesting optoelectronic properties
[13]. Two ap-derivatives, 2-(3-methoxyanilino)pyridinate
(MeOap, Chart 1) and 2-(3-propoxyanilino)pyridinate were
prepared by us, but only a marginal improvement in solubil-
ity was achieved [14]. Described in this contribution are the
synthesis and characterization of a new ap-derivative,
namely 2-(3,5-dimethoxyanilino)pyridine (HDiMeOap,
Chart 1) and its Ru2-compounds including Ru2(Di-
MeOap)4Cl (1), Ru2(DiMeOap)4(C„CC„CSiMe3) (2)
and Ru2(DiMeOap)4(C„CC„CSiMe3)2 (3). Also reported
are the synthesis and characterization of related compounds
The chemistry of diruthenium paddlewheel species con-
taining axial alkynyl ligands began with the report of
Ru2(ap)4(C„CPh) (ap = 2-anilinopyridinate, Chart 1) by
Chakravarty and Cotton in 1986 [1]. Several families of diru-
thenium alkynyl compounds have since emerged including
those based on Ru2(DArF)4 (DArF = diarylformamidi-
nate) [2], Ru2(ap)4 and Ru2(Fxap)4 (Fxap = 2-(fluoro-
anilino)-pyridinate) [3–5] and Ru2(DMBA)4 (DMBA =
N,N0-dimethylbenzamidinate) [6]. Further studies of these
compounds demonstrated facile charge transfer along the
Ru2-alkynyl backbones [7–9], and a remarkably small atten-
uation factor (c) was deduced from the voltammetric and
spectroscopic data of the [Ru2(ap)4]2(l-C2n) family with n
ranging from 1 to 6 [8]. STM (scanning tunneling micros-
copy) study of Ru2(ap)4-r-[(C„CC6H4)2S] immobilized
Ru2(MeOap)4(C„CC„CSiMe3)
(4),
Ru2(MeOap)4
(C„CC„CSiMe3)2 (5), Ru2(MeOap)4(C„CFc) (6) and
Ru2(ap)4(C„CC„CFc) (7).
*
Corresponding author. Tel.: +1 765 494 5466; fax: +1 765 494 0239.
E-mail address: tren@purdue.edu (T. Ren).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.11.050

B. Xi et al. / Journal of Organometallic Chemistry 693 (2008) 1656–1663
1657
and display well resolved 1H NMR spectra. All compounds
reported herein yielded satisfactory combustion analysis
results.
OMe
OMe
N
H
N
N
N
N
H
N
MeO
H
2.2. Structural study
Hap
HMeOap
Chart 1.
HDiMeOap
Molecular structures of 1, 2, 6 and 7 were established
through single crystal X-ray diffraction studies. The struc-
tural plots of molecules 1, 2, 6 and 7 are shown in Figs. 1–4,
respectively, and the selected metric parameters are col-
lected in Table 1. Despite the crowding due to the MeO
substituents, the DiMeOap ligands in 1 adopt the so-called
(4,0) arrangement similar to Ru2(ap)4Cl [15], where all
pyridine nitrogens coordinate to the Ru(III) (Ru1), and
all aniline nitrogens coordinate to the other Ru (Ru2).
2. Results and discussion
2.1. Synthesis of HDiMeOap, Ru2(DiMeOap)4Cl and
Ru2(Xap)4(C2R)x (x = 1 or 2)
Ligand HDiMeOap was prepared from the reaction
between 2-bromopyridine and 3,5-dimethoxyaniline using
a procedure modified from that of HMeOap [14], and
1
was characterized with H NMR and mass spectroscopic
techniques. Similar to the preparation of Ru2(ap)4Cl [4],
Ru2(DiMeOap)4Cl (1) was obtained in satisfactory yield
from the reaction of Ru2(OAc)4Cl with 7 equiv. of HDi-
MeOap, and characterized with both the ESI-MS and com-
bustion analysis. Compound 1 has a room temperature
effective magnetic moment of 3.89 Bohr magneton, which
is consistent with the S = 3/2 ground state established early
for other Ru2(ap)4Cl type compounds [12].
The mono-alkynyl species, namely Ru2(DiMeOap)4-
(C„CC„CSiMe3) (2) Ru2(MeOap)4(C„CC„CSiMe3)
(4)
Ru2(MeOap)4(C„CFc)
(6),
and
Ru2(ap)4-
(C„CC„CFc) (7), were prepared in satisfactory yields
from the reaction of Ru2(Xap)4Cl with 1.5–2 equiv. of
LiC„CR (Scheme 1). Both of the bis-butadiynyl com-
pounds, Ru2(DiMeOap)4(C„CC„CSiMe3)2 (3) and
Ru2(MeOap)4(C„CC„CSiMe3)2 (5), were prepared from
the reaction of Ru2(Xap)4Cl with ca. 5 equiv of
LiC„CC„CSiMe3, which generally resulted in a mixture
of the expected bis-compound and the corresponding
mono-alkynyl species. Purification via silica column with
hexanes/ethyl acetate eluent afforded compounds 3/5 in
good yields. Alkynyl compounds supported by both MeOap
and DiMeOap ligands are generally more soluble in organic
solvents than the ap-based alkynyl analogs, and the
improved solubility enables more efficient column purifica-
tion and subsequent characterizations.
Fig. 1. Structural plot of compound 1 at 30% probability level. Hydrogen
atoms were omitted for clarity.
The effective magnetic moments of mono-alkynyl spe-
cies (2, 4 and 6) range from 3.91 to 4.11 Bohr magneton,
which are consistent with an S = 3/2 ground state. Com-
pound 7, on the other hand, exhibits a smaller effective
moment. This deviation is not well understood at the
moment. Both bis-alkynyl species 3 and 5 are diamagnetic
1.5 equiv LiC2R
Ru2(Xap)4Cl
Ru2(Xap)4(C2R) (60 - 70%)
Ru2(Xap)4(C2R)2 (60 - 70%)
5 equiv LiC2R
Fig. 2. Structural plot of compound 2 at 30% probability level. Hydrogen
Scheme 1. Preparation of Ru2(Xap)4(C2R)x (x = 1 and 2).
atoms were omitted for clarity.

1658
B. Xi et al. / Journal of Organometallic Chemistry 693 (2008) 1656–1663
˚
The Ru–Ru bond length in 1 is 2.2797(7) A, identical to
˚
that of Ru2(ap)4Cl (2.275(3) A) within the experimental
errors. Compound 1 was crystallized in the P4/n space
group and the Ru2–Ru1–Cl vector coincides with a crystal-
lographic 4-fold axis. There is a significant difference
˚
between two independent Ru–N bond lengths: 2.094(3) A
˚
for Ru1–N1 and 2.039(3) A for Ru2–N2. The difference
is attributed to the fact that the anilino nitrogen is a better
donor than the pyridino nitrogen.
The resemblance between molecule 2 and its precursor
molecule 1 is clear from Figs. 1 and 2. The notable differ-
ences include the displacement of the axial chloro ligand
in 1 by the butadiynyl ligand in 2 and the loss of crystallo-
graphic symmetry in the latter compound. The Ru–Ru
Fig. 3. Structural plot of molecule 6 at 30% probability level. Hydrogen
atoms were omitted for clarity.
˚
bond length in 2 (2.3245(6) A) is significantly elongated
from that of 1 because of the strong r-donating ability of
˚
the butadiynyl ligand. Both the Ru–C (2.089(6) A) and
˚
C„C (1.210(7) A) bond lengths agree well with those pre-
viously reported for Ru2(ap)4(C2R) type compounds
[12,16]. Structural similarity among mono-alkynyl com-
pounds 2, 6 and 7 is also apparent from the comparison
of Figs. 2–4 and geometric parameters listed in Table 1.
In addition, they have nearly identical Ru–Ru bond
lengths, indicating the comparable donor strengths of ap,
MeOap and DiMeOap ligands despite the difference in ani-
line ring substituents.
2.3. Electrochemistry and spectroscopy
Similar to the previously reported Ru2(ap)4Lx (x = 1 and
2) type compounds, compounds 1–7 exhibit rich redox activ-
ities and both the cyclic (CV) and differential pulse (DPV)
Fig. 4. Structural plot of molecule 7 at 30% probability level. Hydrogen
atoms were omitted for clarity.
Table 1
˚
Selected bond lengths (A) and angles (°) for compounds 1, 2, 6 and 7
1
2
6
7
Ru2–Ru1
Ru1–Cl
Ru1–N1
Ru2–N2
2.2797(7)
2.459(2)
2.094(3)
2.039(3)
Ru2–Ru1
Ru1–C1
Ru1–N1
Ru1–N3
Ru1–N5
Ru1–N7
Ru2–N2
Ru2–N4
Ru2–N6
Ru2–N8
C1–C2
2.3245(6)
2.089(6)
2.105(4)
2.086(4)
2.110(4)
2.099(5)
2.055(4)
2.025(4)
2.037(4)
2.030(4)
1.210(7)
1.367(8)
1.202(8)
2.3223(6)
2.110(5)
2.112(5)
2.097(5)
2.095(5)
2.087(4)
2.035(5)
2.044(4)
2.050(5)
2.040(4)
1.180(8)
2.3282(7)
2.090(6)
2.090(5)
2.126(5)
2.115(4)
2.102(5)
2.051(5)
2.043(5)
2.033(4)
2.036(5)
1.195(8)
1.402(8)
1.197(8)
C2–C3
C3–C4
Ru2–Ru1–Cl
Ru2–Ru1–N1
Ru1–Ru2–N2
180
87.43(6)
89.24(6)
Ru2–Ru1–C1
Ru2–Ru1–N1
Ru2–Ru1–N3
Ru2–Ru1–N5
Ru2–Ru1–N7
Ru1–Ru2–N2
Ru1–Ru2–N4
Ru1–Ru2–N6
Ru1–Ru2–N8
Ru1–C1–C2
179.21(15)
88.88(12)
88.30(12)
86.85(11)
87.25(13)
88.97(12)
88.78(11)
89.16(12)
89.87(13)
179.2(2)
178.04(17)
87.30(13)
87.12(13)
87.87(12)
88.58(12)
89.90(13)
89.94(13)
89.11(13)
89.06(12)
178.0(2)
178.49(19)
88.57(12)
87.20(12)
88.47(12)
88.35(12)
89.05(12)
90.20(12)
90.19(12)
89.64(12)
178.5(2)

B. Xi et al. / Journal of Organometallic Chemistry 693 (2008) 1656–1663
1659
voltammograms of compounds 1–3 and 6 are shown in
Fig. 5. The Ru2(II,III) species, namely compounds 1, 2, 4,
6 and 7, exhibit two reversible one-electron processes, an
oxidation (B) and a reduction (C) as designated in Scheme
2. Consistent with the electron richness at the Ru2 core,
the electrode potentials are most positive (anodic) for com-
pounds with axial chloro ligand and least positive (most
cathodic) for compounds with axial ethynyl ligand. Com-
pounds 6 and 7 are also unique in containing ferrocenyl
capped ethynyl (6) and butadiynyl (7) ligands. The Fc+/Fc
couples are observed at 0.65 and 0.71 V for compounds 6
and 7, respectively, and the difference in E1/2 reflects the elec-
tron-deficiency of butadiynyl compared to ethynyl. Both the
values and the trend of E1/2(Fc+/Fc) described herein are
consistent with those reported for trans-Fc(C„C)n-
[Ru2(DMBA)4]-(C„C)mFc (n, m = 1 and 2) [9].
of Ru2(ap)4(C„CC„CSiMe3)2, which displays a reversible
oxidation with E1/2 of 0.90 V [5]. The irreversible nature of
oxidations in 3 and 5 reflects, perhaps, the steric crowding
caused by the methoxy substitution of anilino-ring, which
drives the molecule to dissociate the butadiynyl ligand on
the anilino-side to release the stress on oxidation (Scheme
2). Corroborating this hypothesis, a wave (D) was observed
for 3 at Epc corresponding to the couple B of compound 2
and hence the presence of mono-butadiynyl species on the
backward sweep of compound 3.
All Ru2(ap)4 based compounds are deeply colored. The
Ru2(II,III) species exhibit two intense peaks in the visible
region, one at round 800 nm and the other around
450 nm. Upon the formation of bis-alkynyl compounds
(Ru2(III,III)), the absorption profile is altered and further
intensified, with peaks around 660 and 500 nm in the visible
region, and a very broad and intense peak around 1050 nm.
The latter feature, corresponding to a remarkably small
optical gap of 1.20 eV, is common among Ru2(III,III) com-
pounds supported by the ap-type ligands [12].
The bis-alkynyl Ru2(III,III) species, namely compounds
3 (Fig. 5) and 5, exhibit two reversible one-electron reduc-
tions (B and C) and an irreversible one-electron oxidation
(A). The latter feature is in stark contrast with the behavior
3. Conclusions
Results presented herein describe a significant improve-
ment in organic solubility of Ru2-alkynyl species through
the modification of ap ligand without compromising the
attractive structural and electronic properties of the origi-
nal Ru2(ap)4 compounds. These new Ru2 building blocks
may enable us to access both the Ru2–(C„C)2n–Ru2 type
compounds with n beyond 4 and Ru2–(C„C)m–Ru2
type compounds with m being odd based on the Glaser
type coupling reactions [8,17]. The improved solubility will
also facilitate the incorporation of Ru2-alkynyl species into
various device platforms, which offer new opportunities in
organometallics based molecular electronics [10,12,18].
4. Experimental
4.1. General
3,5-Dimethoxyaniline and 2-bromopyridine were pur-
chased from ACROS. n-BuLi was from Aldrich. 1,3-Bis(tri-
methylsilyl)butadiyne was from GFS. Ru2(OAc)4Cl [19],
Ru2(MeOap)4Cl [14], FcC„CH [20] and FcC„CC„CH
[21] were prepared using the literature reported procedures.
THF was distilled over Na/benzophenone under an N2
atmosphere prior to use. 1H spectra were recorded on a Var-
ian 300 NMR spectrometer, with chemical shifts (d) refer-
enced to the residual CHCl3 and the solvent CDCl3,
respectively. UV–Vis–NIR spectra were obtained in THF
with a JASCO V-670 UV–Vis–NIR spectrophotometer.
Magnetic susceptibility data were measured at 293 K with
a Johnson Matthey Mark-I magnetic susceptibility balance.
Cyclic voltammograms were recorded in 0.2 M (n-
Bu)4NPF6 solution (THF, N2-degassed) on a CHI620A vol-
tammetric analyzer with a glassy carbon working electrode
(diameter = 2 mm), a Pt-wire auxiliary electrode and a Ag/
Fig. 5. CV (solid) and DPV (gray) plots of compounds 1–3 and 6.
+ e-
+ e-
[Ru2-L]+
Ru2-L
[Ru2-L]-
+ e-
L = Cl, C2R
+ e-
B
C
- e-
[L-Ru2-L]+
- L
L-Ru2-L
[L-Ru2-L]-
[L-Ru2-L]2-
A
B
C
+ e-
D
[Ru2-L]+
[Ru2-L]
L = C4SiMe3
Scheme 2. Assignment of redox couples in compounds 1–7.

1660
B. Xi et al. / Journal of Organometallic Chemistry 693 (2008) 1656–1663
Table 2
Electrode potentials (V) of all observed redox couples in compounds 1–7
Epa (A)
E1/2 (B)
E1/2 (C)
E1/2 (Fc)
Eg/V
Ru2(mMeOap)4Cla
Ru2(DiMeOap)4Cl (1)
0.560
0.567
0.491
ꢀ0.760
ꢀ0.750
ꢀ0.717
ꢀ1.348
ꢀ0.716
ꢀ1.362
ꢀ0.886
ꢀ0.762
1.324
1.317
1.208
Ru2(DiMeOap)4(C4TMS) (2)
Ru2(DiMeOap)4(C4TMS)2 (3)
Ru2(MeOap)4(C4TMS) (4)
Ru2(MeOap)4(C4TMS)2 (5)
Ru2(MeOap)4(C2Fc) (6)
Ru2(ap)4(C4Fc) (7)
0.915
0.988
ꢀ0.244
0.500
1.216
ꢀ0.254
0.416
0.479
0.654
0.707
1.302
1.241
a
From Ref. [14].
AgCl reference electrode. The concentration of diruthenium
species is always 1.0 mM. The ferrocenium/ferrocene couple
was observed at 0.591 V (vs. Ag/AgCl) under experimental
conditions Table 2.
ture was slowly warmed to room temperature and stirred for
another hour to yield an off-white suspension. A portion of
the suspension (15 mL) was transferred to a flask containing
a THF solution (40 mL) of Ru2(DiMeOap)4Cl (0.538 g,
0.46 mmol). The solution color changed from green to
brown immediately, and the reaction mixture was stirred
for an hour. Removal of the solvents in vacuo yielded a
brown residue, which was purified on a silica column deac-
tivated by 10% Et3N in hexanes using a linear gradient of
eluents (hexanes/ethyl acetate, 90/10–60/10, v/v) to afford
analytically pure 2 (0.372 g, 65% based on Ru). Data for
2: Rf (THF/hexanes/Et3N = 10/30/1, v/v/v): 0.31. MS-ESI
(m/e, based on 101Ru): 1240 [M+]. Anal. Calc. for
C59H61N8O8SiRu2: C, 57.14; H, 4.92; N, 8.92. Found: C,
57.35; H, 5.09; N, 9.04%. UV–Vis, kmax (nm, e (Mꢀ1 cmꢀ1)):
785 (6610), 495 (8830). Electrochemistry (THF), E1/2/V,
DEp/V, ibackward/iforward: A, 0.491, 0.075, 0.949; B, ꢀ0.717,
0.052, 0.961. Magnetic (293 K): vg, 4.87 ꢁ 10ꢀ6 esu; vmol
(corr) 6.78 ꢁ 10ꢀ3 esu molꢀ1; leff = 3.99 lB.
4.2. Preparation of 2-(3,5-dimethoxyanilino)pyridine
(HDiMeOap)
A 50 mL Schlenk flask was charged with 3,5-dimethoxy-
aniline (5.1 g, 34 mmol) and 2-bromopyridine (2.6 g,
17 mmol) and heated at 140 °C for 20 h. The mixture was
neutralized with NaOH(aq), and then extracted with
CH2Cl2. After the solvent removal from the organic layer,
the residue was recrystallized from CH2Cl2/hexanes to
yield the ligand as an off-white solid (3.0 g, 77% based on
1
2-bromopyridine). Data for HDiMeOap: H NMR: 8.21
(d, 1H, aromatic), 7.53–6.17 (m, 6H, aromatic), 3.79 (s,
6H, OCH3); MS-ESI: 230 [M+]; UV–Vis, kmax (nm, e
(Mꢀ1 cmꢀ1)): 275 (33600), 256 (13300).
4.3. Preparation of Ru2(DiMeOap)4Cl (1)
4.5. Preparation of Ru2(DiMeOap)4(C4SiMe3)2 (3)
To a 100 mL round bottom flask was added Ru2(OAc)4Cl
(1.5 g, 2.5 mmol), HDiMeOap (4.3 g, 19 mmol), excess of
LiCl, and 60 mL toluene, and a Soxhlet extraction apparatus
with a K2CO3-filled glass thimble was mounted atop the
flask. The reaction solution was refluxed for 3 days with
K2CO3 changed daily. After solvent removal, the residue
was dissolved in CH2Cl2 and filtered. The filtrate was dried
and recrystallized from methanol to yield 1 as black powder
(2.6 g, 72% based on Ru). Data for 1: Rf (THF/hexanes/
Et3N = 10/30/1, v/v/v): 0.17. MS-ESI (m/e, based on
101Ru): 1155 [M+]. Anal. Calc. for C52H52N8O8Ru2: C,
54.10; H, 4.51; N, 9.71. Found: C, 54.12; H, 4.49; N,
9.79%. UV–Vis, kmax (nm, e (Mꢀ1 cmꢀ1)): 799 (7870), 452
To a 10 mL THF solution containing 0.37 mmol of
Me3SiC„CC„CSiMe3 was added 0.10 mL of n-BuLi
(2.5 M in hexanes) at liquid nitrogen temperature. The mix-
ture was slowly warmed to room temperature and stirred
for another hour to yield an off-white suspension. The sus-
pension was transferred to a flask containing a 30 mL THF
solution of Ru2(DiMeOap)4Cl (0.100 g, 0.086 mmol). The
solution color changed from dark green to brown immedi-
ately, and the reaction mixture was stirred for an hour.
Then the mixture was stirring in the air for another hour
to yield a blue-purple solution, which was filtered through
a silica gel pad (2 cm). Following the solvent removal, the
residue was purified on a silica column deactivated by 10%
Et3N in hexanes using a linear gradient of eluents (hexanes/
ethyl acetate, 90/10–60/10, v/v) to afford both compounds
3 and 2. Yields: 3, 0.072 g (62% based on Ru); 2, 0.025 g
(23% based on Ru); Data for 3: Rf (THF/hexanes/
Et3N = 10/30/1, v/v/v): 0.43. MS-ESI (m/e, based on
101Ru): 1361 [M+]. Anal. Calc. for C66H70N8O8Si2Ru2: C,
58.24; H, 5.15; N, 8.24. Found: C, 58.32; H, 5.22; N,
8.20%. 1H NMR: 9.04 (d, 4H, aromatic), 7.34–6.06 (m,
24H, aromatic), 3.46 (s, 24H, OCH3), 0.31 (s, 9H,
Si(CH3)3), 0.09 (s, 9H, Si(CH3)3). UV–Vis, kmax (nm, e
(6690); Electrochemistry (THF), E1/2/V, DEp/V, ibackward
/
iforward: A, 0.567, 0.064, 0.977; B, ꢀ0.750, 0.059, 0.997; Mag-
netic (293 K): vg, 4.94 ꢁ 10ꢀ6 esu;
10ꢀ3 esu molꢀ1; leff (293 K): 3.89 lB.
v
mol(corr) 6.44 ꢁ
4.4. Preparation of Ru2(DiMeOap)4(C4SiMe3) (2)
To a 20 mL THF solution containing 0.95 mmol of
Me3SiC„CC„CSiMe3 was added 0.38 mL of n-BuLi
(2.5 M in hexanes) at liquid nitrogen temperature. The mix-

B. Xi et al. / Journal of Organometallic Chemistry 693 (2008) 1656–1663
1661
(Mꢀ1 cmꢀ1)): 1049 (7310), 658 (11400), 499 (7780); Elec-
trochemistry (THF), E1/2/V, DEp/V, ibackward/iforward: A,
0.915 (Epa); B, ꢀ0.244, 0.070, 1.057; C, ꢀ1.348, 0.068,
0.810.
warmed to room temperature and stirred for another hour.
The suspension was transferred to a flask containing a
THF solution (40 mL) of Ru2(MeOap)4Cl (0.085 g,
0.08 mmol). The solution color changed from dark green
to red immediately, and the reaction mixture was stirred
for 30 min. After the removal of the solvents under vac-
uum, the residue was dissolved in THF and filtered through
a silica gel pad (2 cm). The product was further purified on
silica column eluted with a mixture of THF, hexanes and
Et3N (10/30/1, v/v/v) to give pure compound 6 (0.070 g,
72%). Data for 6: Rf (THF/hexanes/Et3N = 10/30/1, v/v/
v): 0.42. MS-ESI (m/e, based on 101Ru): 1210 [M+]. Anal.
Calc. for C60H53N8O4FeRu2, C, 59.65; H, 4.39; N, 9.28.
Found: C, 59.69; H, 4.44; N, 9.05%. UV–Vis, kmax (nm, e
(Mꢀ1 cmꢀ1)): 753 (5450), 473 (7850); Electrochemistry
(THF), E1/2/V, DEp/V, ibackward/iforward: A, 0.654, 0.072,
1.102; B, 0.416, 0.069, 0.715; C, ꢀ0.886, 0.071, 0.922.
Magnetic (293 K): vg, 5.34 ꢁ 10ꢀ6 esu; vmol(corr) 7.20 ꢁ
10ꢀ3 esu molꢀ1; leff = 4.11 lB.
4.6. Preparation of Ru2(MeOap)4(C4SiMe3) (4)
To a 10 mL THF solution containing 0.16 mmol of
Me3SiC„CC„CSiMe3 was added 0.06 mL of n-BuLi
(2.5 M in hexanes) at liquid nitrogen temperature. The mix-
ture was slowly warmed to room temperature and stirred
for another hour to yield an off-white suspension. A por-
tion of the suspension (6 mL) was transferred to a flask
containing a 30 mL THF solution of Ru2(MeOap)4Cl
(0.083 g, 0.08 mmol). The solution color changed from
green to brown immediately, and the reaction mixture
was stirred for an hour. Removal of the solvents in vacuo
yielded a brown residue, which was purified on a silica col-
umn using a linear gradient of eluents (hexanes/ethyl ace-
tate, 90/10–60/10, v/v) to afford pure 4 (0.055 g, 61%
based on Ru). Data for 4: Rf (THF/hexanes/Et3N = 10/
30/1, v/v/v): 0.44. MS-ESI (m/e, based on 101Ru): 1121
[M+]. UV–Vis, kmax (nm, e (Mꢀ1 cmꢀ1)): 770 (7540),
493 (10200). Electrochemistry (THF), E1/2/V, DEp/V,
ibackward/iforward: B, 0.500, 0.067, 0.939; C, ꢀ0.716, 0.057,
0.922. Magnetic (293 K): leff = 3.91 lB.
4.9. Preparation of Ru2(ap)4(C4Fc) (7)
To a 20 mL THF solution containing 0.37 mmol of
FcC4H was added 0.16 mL of n-BuLi (2.5 M in hexanes)
at liquid nitrogen temperature. The mixture was slowly
warmed to room temperature and stirred for another hour.
The suspension was transferred to a flask containing a
THF solution (40 mL) of Ru2(ap)4Cl (0.229 g, 0.25 mmol).
The solution color changed from dark green to red imme-
diately, and the reaction mixture was stirred for 30 min.
After the removal of the solvents under vacuum, the resi-
due was dissolved in THF and filtered through a silica
gel pad (2 cm). The product was further purified on silica
column with a mixture of THF, hexanes and Et3N (25/
100/1, v/v/v) to yield pure compound 7 (0.098 g, 35%).
Data for 7: Rf (THF/hexanes/Et3N = 10/30/1, v/v/v):
0.66. MS-ESI (m/e, based on 101Ru): 1112 [M+]. Anal.
Calc. for C58H45N8FeRu2 ꢂ 2H2O: C, 60.63; H, 4.27; N,
9.65. Found: C, 60.37; H, 4.70; N, 9.72%. UV–Vis, kmax
(nm, e (Mꢀ1 cmꢀ1)): 755 (7640), 473 (8260). Electrochemis-
try (THF), E1/2/V, DEp/V, ibackward/iforward: A, 0.707, 0.040,
0.280; B, 0.479, 0.060, 0.556; C, ꢀ0.762, 0.068, 0.923.
Magnetic (294 K): vg, 3.77 ꢁ 10ꢀ6 esu; vmol(corr) 4.95 ꢁ
10ꢀ3 esu molꢀ1; leff = 3.41 lB.
4.7. Preparation of Ru2(MeOap)4(C4SiMe3)2 (5)
To a 10 mL THF solution containing 0.30 mmol of
Me3SiC„CC„CSiMe3 was added 0.15 mL of n-BuLi
(2.5 M in hexanes) at liquid nitrogen temperature. The mix-
ture was slowly warmed to room temperature and stirred
for another hour to yield an off-white suspension. The sus-
pension was transferred to a flask containing a 40 mL THF
solution of Ru2(MeOap)4Cl (0.061 g, 0.058 mmol). After
30 min, the reaction mixture was opened in the air with
stirring for another hour to yield a blue-purple solution,
which was filtered through a silica gel pad (2 cm). After
the solvent removal, the residue was purified on a silica col-
umn with hexanes/ethyl acetate (90/10, v/v) to afford 5
(0.050 g, 69% based on Ru). Data for 5: Rf (THF/hex-
anes/Et3N = 10/30/1, v/v/v): 0.60. Anal. Calc. for
C62H62N8O4Si2Ru2 ꢂ H2O: C, 59.07; H, 5.08; N, 8.89.
1
Found: C, 59.05; H, 5.47; N, 8.41%. H NMR: 9.04 (s,
4H, aromatic), 7.25–6.02 (m, 24H, aromatic), 3.42 (s,
12H, OCH3), 0.29 (s, 9H, Si(CH3)3), 0.08 (s, 9H, Si(CH3)3).
4.10. Structure determination
Electrochemistry (THF), E1/2/V, DEp/V, ibackward/iforward
:
Single crystals were obtained by slow evaporation of
either a hexanes/THF solution (1, 6 and 7) or a hexanes/
ethyl acetate solution (2). X-ray intensity data of crystals
1, 2 and 6 were measured on a Bruker SMART1000
CCD X-ray diffractometer and those of 7 on a Nonius-
Kappa CCD X-ray diffractometer using Mo Ka
A, 0.988 (Epa); B, ꢀ0.254, 0.066, 1.019; C, ꢀ1.362, 0.087,
1.109. UV–Vis, kmax (nm, e (Mꢀ1 cmꢀ1)): 657 (11400),
486 (7270).
4.8. Preparation of Ru2(MeOap)4(C2Fc) (6)
˚
(k = 0.71073 A). Structures were solved and refined using
To a 40 mL THF solution containing 0.10 mmol of
FcC2H was added 0.05 mL of n-BuLi (2.5 M in hexanes)
at liquid nitrogen temperature. The mixture was slowly
the Bruker SHELXTLÓ (Version 5.1) software package. Posi-
tions of all non-hydrogen atoms were revealed by direct
method. The asymmetric unit of crystal 1 contains one-

1662
B. Xi et al. / Journal of Organometallic Chemistry 693 (2008) 1656–1663
Table 3
Crystal data for compounds 1, 2, 6 and 7
1 ꢂ 2THF
60H68ClN8O10Ru2
1106.57
P4/n
13.377(1)
13.377(1)
16.723(2)
(2)2 ꢂ EtOAc
C122H122N16O16Ru4
6 ꢂ THF
C64H61FeN8O5Ru2
1280.20
P21/n
17.397(1)
10.2286(6)
32.822(2)
7 ꢂ THF
C62H53FeN8ORu2
Formula
FW
C
2358.68
1184.15
ꢀ
ꢀ
Space group
P1
P1
˚
a (A)
13.956(1)
20.943(1)
22.34(1)
89.700(1)
73.637(1)
81.980(1)
6198.7(6)
2
10.125(2)
13.667(2)
19.620(3)
72.81(8)
78.83(8)
85.84(8)
2544.2(7)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
102.394(1)
3
˚
V (A )
2992.6(4)
2
1.441
0.613
5704.6(6)
4
1.491
0.832
Z
qcalc (g cmꢀ3
)
1.264
0.332
1.546
0.907
l (mmꢀ1
)
Crystal size (mm)
Unique reflections (Rint
Parameters refined
T (K)
0.35 ꢁ 0.27 ꢁ 0.06
2652 (0.029)
175
0.25 ꢁ 0.21 ꢁ 0.03
21579 (0.039)
1459
0.24 ꢁ 0.09 ꢁ 0.04
10012 (0.067)
700
0.25 ꢁ 0.19 ꢁ 0.05
10299 (0.095)
667
)
300
300
300
150
R, wR2 (I > 2r(I))
Goodness-of-fit on F2
0.035, 0.094
1.05
0.054, 0.110
1.01
0.052, 0.106
1.00
0.061, 0.128
1.04
quarter of the molecule, which is related to the rest of the
molecule via a crystallographic fourfold axis coinciding
with the Ru–Ru vector, and one-half of a THF molecule.
The asymmetric unit of crystal 2 contains two independent
diruthenium molecule and one ethyl acetate solvent. Each
of the asymmetric units of crystals 6 and 7 contains one
complete diruthenium molecule and a THF molecule. All
non-hydrogen atoms are anisotropic and the hydrogen
atoms were put in calculated positions and riding mode.
Each structure was refined to convergence by least squares
method on F2, SHELXL-93, incorporated in SHELXTL-PC V
5.03. Crystallographic data are given in Table 3.
K.-T. Wong, J.-M. Lehn, S.-M. Peng, G.-H. Lee, Chem. Commun.
(2000) 2259;
G. Xu, T. Ren, Inorg. Chem. 40 (2001) 2925;
J.-L. Zuo, E. Herdtweck, F.E. Kuhn, J. Chem. Soc., Dalton Trans.
¨
(2002) 1244;
G.-L. Xu, T. Ren, Organometallics 24 (2005) 2564;
G.-L. Xu, T. Ren, Inorg. Chem. 45 (2006) 10449.
[3] Y. Li, B. Han, K.M. Kadish, J.L. Bear, Inorg. Chem. 32 (1993)
4175;
J.L. Bear, Y.L. Li, B.C. Han, E. VanCaemelbecke, K.M. Kadish,
Inorg. Chem. 36 (1997) 5449;
T. Ren, Organometallics 21 (2002) 732;
G.-L. Xu, T. Ren, J. Organomet. Chem. 655 (2002) 239;
K.M. Kadish, T.D. Phan, L.-L. Wang, L. Giribabu, A. Thuriere,
J. Wellhoff, S. Huang, E.V. Caemelbecke, J.L. Bear, Inorg. Chem.
43 (2004) 4825;
G.-L. Xu, C.-Y. Wang, Y.-H. Ni, T.G. Goodson, T. Ren,
Organometallics 24 (2005) 3247;
5. Supplementary material
CCDC 666214, 666215, 666216 and 666217 contain 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.
S.K. Hurst, T. Ren, J. Organomet. Chem. 660 (2002) 1.
[4] G. Zou, J.C. Alvarez, T. Ren, J. Organomet. Chem. 596 (2000) 152.
[5] G.-L. Xu, T. Ren, Organometallics 20 (2001) 2400.
[6] G.-L. Xu, C. Campana, T. Ren, Inorg. Chem. 41 (2002) 3521;
S.K. Hurst, G.-L. Xu, T. Ren, Organometallics 22 (2003) 4118;
G.-L. Xu, C.G. Jablonski, T. Ren, J. Organomet. Chem. 683 (2003)
388;
Acknowledgement
J.-W. Ying, D.R. Sobransingh, G.-L. Xu, A.E. Kaifer, T. Ren,
Chem. Commun. (2005) 357;
J.-W. Ying, T. Ren, J. Organomet. Chem. 691 (2006) 4021;
J.-W. Ying, A. Cordova, T.Y. Ren, G.-L. Xu, T. Ren, Chem. Eur. J.
13 (2007) 6874.
This work is supported in part by the National Science
Foundation (Grant No. CHE 0715404) and Purdue
University.
[7] T. Ren, G. Zou, J.C. Alvarez, Chem. Commun. (2000) 1197;
Y. Shi, G.T. Yee, G. Wang, T. Ren, J. Am. Chem. Soc. 126 (2004)
10552.
References
[8] G.-L. Xu, G. Zou, Y.-H. Ni, M.C. DeRosa, R.J. Crutchley, T. Ren,
J. Am. Chem. Soc. 125 (2003) 10057.
[9] G.-L. Xu, M.C. DeRosa, R.J. Crutchley, T. Ren, J. Am. Chem. Soc.
126 (2004) 3728;
G.-L. Xu, R.J. Crutchley, M.C. DeRosa, Q.-J. Pan, H.-X. Zhang, X.
Wang, T. Ren, J. Am. Chem. Soc. 127 (2005) 13354.
[10] A.S. Blum, T. Ren, D.A. Parish, S.A. Trammell, M.H. Moore, J.G.
Kushmerick, G.-L. Xu, J.R. Deschamps, S.K. Pollack, R. Shashi-
dhar, J. Am. Chem. Soc. 127 (2005) 10010.
[1] A.R. Chakravarty, F.A. Cotton, Inorg. Chim. Acta 113 (1986) 19.
[2] J.L. Bear, B. Han, S. Huang, J. Am. Chem. Soc. 115 (1993) 1175;
J.L. Bear, B.C. Han, S.R. Huang, K.M. Kadish, Inorg. Chem. 35
(1996) 3012;
C. Lin, T. Ren, E.J. Valente, J.D. Zubkowski, Dalton Trans. (1998)
571;
C. Lin, T. Ren, E.J. Valente, J.D. Zubkowski, J. Organomet. Chem.
579 (1999) 114;

B. Xi et al. / Journal of Organometallic Chemistry 693 (2008) 1656–1663
1663
[11] T. Ren, D.A. Parish, G.-L. Xu, M.H. Moore, J.R. Deschamps, J.-W.
[18] F. Paul, C. Lapinte, Coord. Chem. Rev. 178–180 (1998) 431;
P.J. Low, Dalton Trans. (2005) 2821;
Ying, S.K. Pollack, T.L. Schull, R. Shashidhar, J. Organomet. Chem.
690 (2005) 4734.
[12] T. Ren, Organometallics 24 (2005) 4854.
S.A. Getty, C. Engtrakul, L. Wang, R. Liu, S.-H. Ke, H.U. Baranger,
W. Yang, M.S. Fuhrer, L.R. Sita, Phys. Rev. B 71 (2005) 241401(R);
B. Kim, J.M. Beebe, C. Olivier, S. Rigaut, D. Touchard, J.G.
Kushmerick, X.-Y. Zhu, C.D. Frisbie, J. Phys. Chem. C 111 (2007)
7521.
[13] W.-Y. Wong, C.-L. Ho, Coord. Chem. Rev. 250 (2006) 2627;
W.-Y. Wong, X.-Z. Wang, Z. He, A.B. Djurii, C.-T. Yip, K.-Y.
Cheung, H. Wang, C.S.K. Mak, W.-K. Chan, Nat. Mater. 6 (2007) 521.
[14] G.-L. Xu, A. Cordova, T. Ren, J. Cluster Sci. 15 (2004) 413.
[15] A.R. Chakravarty, F.A. Cotton, D.A. Tocher, Inorg. Chem. 24
(1985) 172.
[16] T. Ren, G.-L. Xu, Comment Inorg. Chem. 23 (2002) 355.
[17] P. Siemsen, R.C. Livingston, F. Diederich, Angew. Chem., Int. Ed.
39 (2000) 2632;
[19] T.A. Stephenson, G. Wilkinson, J. Inorg. Nuclear Chem. 28 (1966)
2285.
[20] G. Doisneau, G. Balavoine, T. Fillebeen-Khan, J. Organomet. Chem.
425 (1992) 113.
[21] Z. Yuan, G. Stringer, I.R. Jobe, D. Kreller, K. Scott, L. Koch, N.J.
Taylor, T.B. Marder, J. Organomet. Chem. 452 (1993) 115.
Q. Zheng, J.C. Bohling, T.B. Peters, A.C. Frisch, F. Hampel, J.A.
Gladysz, Chem. Eur. J. 12 (2006) 6486;
Q. Zheng, J.A. Gladysz, J. Am. Chem. Soc. 127 (2005) 10508.