The synthesis and redox behaviors of binuclear ruthenocene derivatives bridged by an aromatic moiety

Article abstract of DOI:10.1016/S0022-328X(02)01407-9

2-Ruthenocenyl-4,4,5,5-tetramethyl-1,3-dioxa-2-borolane was prepared by the boration and the subsequent reaction with dilithium pinacolate as the starting material of the Suzuki-Miyaura coupling reaction. The dioxaborolane was heated with 1,4-dibromobenzene, 1,2-diiodobenzene, 4,4′-dibromobiphenyl, 1,4-dibromonaphthalene, and 2,6-dibromonaphthalene in the presence of (dppf)PdCl₂-aqueous NaOH in DME to give the corresponding bis(ruthenocenyl) derivatives in moderate yields. The reaction of the dioxaborolane with 2,2′-diiodobiphenyl and 1,8-diiodo-naphthalene in the presence of Pd(PPh₃)₄-Cs₂(CO)₃ in N,N-dimethylformamide (DMF) produced ruthenoceno[l]phenanthrene and ruthenocenyl[a]acenaphthylene in low yield, respectively. The result of the cyclic voltammetry suggests that there is weak electronic interaction between the two metal sites in the two-electron oxidized species of the binuclear ruthenocene derivatives with an aromatic bridge.

Full text of DOI:10.1016/S0022-328X(02)01407-9

Journal of Organometallic Chemistry 655 (2002) 23ꢀ30
/
www.elsevier.com/locate/jorganchem
The synthesis and redox behaviors of binuclear ruthenocene
derivatives bridged by an aromatic moiety
Masaru Sato *, Genta Maruyama, Atsushi Tanemura
Chemical Analysis Center, Saitama University, Urawa, Saitama 338-8570, Japan
Received 15 February 2002; received in revised form 14 March 2002; accepted 18 March 2002
Abstract
2-Ruthenocenyl-4,4,5,5-tetramethyl-1,3-dioxa-2-borolane was prepared by the boration and the subsequent reaction with
dilithium pinacolate as the starting material of the SuzukiꢀMiyaura coupling reaction. The dioxaborolane was heated with 1,4-
dibromobenzene, 1,2-diiodobenzene, 4,4?-dibromobiphenyl, 1,4-dibromonaphthalene, and 2,6-dibromonaphthalene in the presence
of (dppf)PdCl2ꢀaqueous NaOH in DME to give the corresponding bis(ruthenocenyl) derivatives in moderate yields. The reaction of
the dioxaborolane with 2,2?-diiodobiphenyl and 1,8-diiodo-naphthalene in the presence of Pd(PPh3)4ꢀCs2(CO)3 in N,N-
/
/
/
dimethylformamide (DMF) produced ruthenoceno[l]phenanthrene and ruthenocenyl[a]acenaphthylene in low yield, respectively.
The result of the cyclic voltammetry suggests that there is weak electronic interaction between the two metal sites in the two-electron
oxidized species of the binuclear ruthenocene derivatives with an aromatic bridge. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Dioxaborolane; SuzukiꢀMiyaura coupling reaction; Binuclear ruthenocene derivatives; Redox behavior
/
1. Introduction
The
valence-averaged
mixed-valence
complex,
[Ru2(C20H36N8)Cl4]ꢂ, was reported [10]. The oxidative
behavior of the binuclear ruthenium complexes is also
interesting. The oxidation of [1.1]ruthenocenophane led
Much attention is focused on bi- and multi-nuclear
transition-metal complexes with unsaturated bridges [1],
since electronic communication between the metal
centers should lead to unusual physical and chemical
properties. In particular, the chemistry of binuclear Ru
complexes has been investigated well from the viewpoint
of their interesting redox properties. Various binuclear
acetylide complexes are prepared: the ethynediyl com-
to the RuÃ
/Ru bond formation [11]. Biruthenocene gave
the fulvalene complex having a curious coordination
mode in the oxidation [12]. Bis(ruthenocenyl)ethenes
cause the structural rearrangement of the complexes
having a pentafulvadiene ligand in the 2-electron oxida-
tion [13]. The oxidative cleavage of the SÃ
/
S bond in
bis(ruthenocenyl)disulfide gave the cationic cyclopenta-
diene-1-thione complex [14]. We now report the synth-
esis and properties of the binuclear ruthenocene
derivatives bridged by an aromatic moiety.
plex, {Ru(CO)2(h-C5H5)}2(h-CÅ
diyl complex, {Ru(PPh3)2(h-C5H5)}2(h-CÅ
{Ru(CO)(PPh3)(dppf)}2(CÅCÃC6H4CÅC) [4], and
{trans-RuCl(PÃP)}2(CÅCRCÅC) (PÃPꢁdppm, dppe,
or dmpe; Rꢁ1,4-benzenediyl, 1,3-benzenediyl, 2,5-xy-
/
C) [2]; the butadiyne-
/C) [3],
/
/
/
/
/
/
/
/
/
lenediyl, 2,5-pyridinediyl, or 2,5-thiophenediyl) [5]. The
C5H5-bridged dimeric Ru complexes [6], the alkene-
bridged Ru complexes [7], the butadiynediyl bridged (b-
diketonato)Ru complex were also prepared [8]. The Ru
2. Results and discussion
2.1. Synthesis of ruthenocenyldioxaborolane
ethynediyl complex, {Ru(CO)2(h-C5H5)}2(h-CÅ
/
C), was
used in the preparation of the four-nuclear cluster [9].
The cross-coupling reaction is considered to be the
best choice for the preparation of binuclear ferrocene
derivatives [15], but a similar approach starting with
metal-functionalized ruthenocene has been little used.
As the only example, the cross-coupling reaction using
* Corresponding author. Fax: ꢂ
/
81-48-858-3707.
E-mail address: msato@cacs.saitama-u.ac.jp (M. Sato).
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 4 0 7 - 9

24
M. Sato et al. / Journal of Organometallic Chemistry 655 (2002) 23ꢀ30
/
Table 2
the in situ-prepared chlorozinc derivative was reported
in ruthenocene chemistry [16]. Recently, some halobor-
ane derivatives of ruthenocene were reported [17,18]. We
selected a dioxaborolane derivative of ruthenocene as
the starting material for the preparation of binuclear
ruthenocene derivatives. Ruthenocene was heated with
one equivalent of boron tribromide in hexane [8] and
subsequently treated with dilithium pinacolate in tetra-
hydrofuran (THF) at 0 8C to give 4,4,5,5-tetramethyl-2-
ruthenocenyl-1,3-dioxa-2-borolane (1) in 66% yield
(Scheme 1). This compound could be separated from
the starting material by deactivated alumina. When the
intermediate dibromoruthenocenylborane was treated
similarly with dilithium 2,3-butanediolate or bis(tri-
methylsiloxy)ethane, the formation of the corresponding
borolane derivatives in the reaction mixture was con-
˚
Selected bond distances (A) and bond angles (8) for 1
Bond distances
C(1)ÃB(1)
C(7)ÃO(1)
C(7)ÃC(9)
C(Cp)ÃC(Cp)
1.537(12)
2.344(9)
1.38(3)
B(1)ÃO(1)
C(7)ÃC(8)
Ru(1)ÃC(Cp)
1.364(16)
1.45(3)
2.176(av.)
1.428(av.)
Bond angles
C(1)ÃB(1)ÃO(1)
B(1)ÃC(1)ÃC(2)
C(7)ÃC(7)ÃO(1)
123.1(11)
125.9(8)
1106.0(6)
O(1)ÃB(1)ÃO(1)
B(1)ÃO(1)ÃC(7)
113.8(7)
107.1(7)
molecule, there is a symmetry plane bisecting the
borolane ring and the two Cp rings of the ruthenocene
nucleus through the B(1), C(1), and C(6) atoms. The Cp
rings of the ruthenocene nucleus are completely stag-
gered. There is a large disorder in the methyl groups
attached to the carbon atoms at 4,5-positions of the
1
firmed by H-NMR spectrum, but the product was not
isolated because of the easy protodeboration on Al2O3
or SiO2. The 1H-NMR spectrum of 1 showed the methyl
protons at d 1.28 (12H), the protons of unsubstituted
(cyclopentadienyl) Cp ring at d 4.53 and the protons of
substituted Cp ring at d 4.71 (2H) and 4.75 (2H). The
structure of 1 was confirmed by the single-crystal X-ray
diffraction. The crystallographic data is collected in
Table 1 and selected bond distances and angles in Table
2. The ORTEP view of 1 is shown in Fig. 1. In the
dioxaborolane ring. The BÃ
/
C bond distance [1.537(12)
A] is somewhat shorter than that observed in PhB(OH)2
˚
˚
(1.565 A) [19] and considerably longer than that in
˚
FcBBr2 [1.482(8) and 1.474(9) A] [20] which is consid-
ered to have a pronounced double bond character in the
C bond [17,18]. Another noticeable point in 1 is the
BÃ
/
coplanarity (2.378) between the plane of the dioxabor-
olane ring and the substituted Cp ring of ruthenocene
moiety. These may suggest the presence of the stabiliza-
tion due to the conjugation of the dioxaborolane ring
with ruthenocene.
Table 1
Crystallographic data for 1 and 8
1
8
2.2. Cross-coupling reaction
Molecular formula
Molecular weight
Crystal system
Space group
C
357.20
16H21BO2Ru
C20H14Ru
718.50
Orthorhombic
Pmnb
Orthorhombic
P212121
7.3260(2)
8.5590(3)
22.2240(8)
1393.52(8)
4
Ferroceneboronic acid [21] and its ester [22] were
reported to be a suitable starting material for the
˚
a (A)
10.701(2)
18.312(3)
7.908(1)
1549.7(4)
4
Suzukiꢀ
lides [23]. Compound 1 also carried successfully out the
cross-coupling with aromatic halides in a DMEꢀaqu-
/Miyaura coupling reaction with aromatic ha-
˚
b (A)
˚
c (A)
3
V (A )
˚
/
Z
eous NaOH mixture, using PdCl2(dppf) as catalyst, as
shown by Knapp and Rehahn [21]. Thus, the reaction of
1 with 1,4-dibromobenzene and 1,2-diiodobenzene af-
forded 1,4-bis(ruthenocenyl)benzene (2) and 1,2-
bis(ruthenocenyl)benzene (3) in 71 and 53% yields,
respectively (Scheme 2). Compound 3 was also obtained
from 1 and 1,2-diiodobenzene in 42% yield in the non-
aqueous conditions using Pd(PPh3)4 as catalyst in N,N-
dimethylformamide (DMF) [24]. 4,4?-Dibromobiphenyl
reacted with 1 to give 4,4?-bis(ruthenocenyl)biphenyl (4)
in 48% yield. The structure of these compounds was
identified by the 1H- and 13C-NMR spectra, mass
spectra, and elemental analysis. However, the cross-
coupling of 2,2?-dibromo- and 2,2?-diiodobiphenyl with
borolane 1 gave no desired product in the aqueous
conditions. The similar reaction of 1 with 2,2?-dibromo-
Dcalc (g cmꢃ3
Crystal size (mm)
)
1.531
0.62ꢄ0.34ꢄ0.18
1.694
0.35ꢄ0.08ꢄ0.08
˚
Radiation (l, A)
Reflection (hkl) limits
Moꢀ/Ka (0.71073) MoꢀKa (0.71073)
/
05h 513,
ꢃ235k 50,
05l 510
05h 57,
05k 510,
05l 57
2825
Total reflections measured 2137
Unique reflections
Linear absolute coeffi-
1707
9.891
2771
3.807
cients (cmꢃ1
Reflections used in L.S.
)
1682
120
2771
190
L.S. parameters
R
0.050
0.060
2.332
1.35
0.031
0.103
1.557
0.53
Rw
S
Maximum peak in final
ꢃ3
˚
Fourier map, e A
Minimum peak in final
ꢃ3
ꢃ0.87
ꢃ1.12
˚
Fourier map, e A
biphenyl using Pd(OAc)2ꢀP(o-biphenyl)(t-Bu)2 as a
catalyst [25], which was possible to carry out the
/

M. Sato et al. / Journal of Organometallic Chemistry 655 (2002) 23ꢀ
/
30
25
Fig. 1. ORTEP view of 1.
Suzukiꢀ
/
Miyaura coupling at room temperature, was
The cross-coupling reaction of 1 with sterically
hindered dihalo aromatics under non-aqueous condi-
tions using Pd(PPh3)4 led to a considerably different
result. The reaction of 1 with 2,2?-diiodobiphenyl in the
non-aqueous conditions using Pd(PPh3)4 as catalyst in
DMF [24] gave ruthenocene as a main product and a
mononuclear ruthenocene derivative, ruthenoce-
no[l]phenanthrene (7), in very low yield, but not desired
also unsuccessful. This may be probably because of the
increasing steric hindrance in 2,2?-dihalobiphenyl com-
pared with 4,4?-dihalobiphenyl. A similar steric retarda-
tion has been observed in the SuzukiꢀMiyaura coupling
/
reaction to form very hindered biphenyls from aryl
halides [26]. 1,4-Bis(ruthenocenyl)naphthalenes (5) and
2,6-bis(ruthenocenyl)naphthalenes (6) were obtained in
50 and 31% yields by reaction of 1 with the correspond-
ing dibromo derivatives under the conditions using
PdCl2(dppf) as catalyst, respectively. However, 1,8-
bis(ruthenocenyl)naphthalene was never produced in
the reaction of 1 with 1,8-diiodonaphthalene in similar
conditions. This is also due to a large steric hindrance in
the product. These results are in contrast to Negishi’s
coupling using ferrocenylzinc chloride which afforded
2,2?-bis(ferrocenyl)-biphenyl [27] and 1,8-bis(methallo-
cenyl)naphthalene [28].
binuclear
(Scheme 3). The structure of 7 can be assigned by the
complex,
2,2?-bis(ruthenocenyl)biphenyl
1
following spectral data: The H-NMR spectrum of 7
showed the substituted Cp-ring protons at d 4.84 (1H)
as a triplet and 5.60 (2H) as a doublet, meaning that the
Table 3
˚
Selected bond distances (A) and bond angles (8) for 8
Bond distances
Ru(1)ÃC(1)
Ru(1)ÃC(3)
Ru(1)ÃC(5)
C(1)ÃC(5)
2.207(5)
2.183(6)
2.198(6)
1.437(8)
1.432(9)
Ru(1)ÃC(2)
Ru(1)ÃC(4)
C(1)ÃC(2)
C(2)ÃC(3)
C(4)ÃC(5)
2.205(6)
2.191(5)
1.433(8)
1.429(7)
1.430(8)
1.40(av.)
1.459(8)
1.421(8)
1.370(9)
1.389(8)
1.36(1)
C(3)ÃC(4)
Fe(1)ÃC(C5H5)
C(1)ÃC(11)
C(11)ÃC(12)
C(12)ÃC(13)
C(14)ÃC(15)
C(15)ÃC(16)
C(17)ÃC(18)
C(19)ÃC(20)
2.186(av.) C(C5H5)ÃC(C5H5)
1.454(8)
1.380(8)
1.415(9)
1.427(9)
1.416(9)
C(5)ÃC(19)
C(11)ÃC(20)
C(13)ÃC(14)
C(15)ÃC(20)
C(16)ÃC(17)
1.411(10) C(18)ÃC(19)
1.438(8)
1.370(8)
Bond angles
C(1)ÃC(5)ÃC(19)
C(1)ÃC(11)ÃC(20)
C(11)ÃC(20)ÃC(19)
C(1)ÃC(5)ÃC(4)
C(18)ÃC(19)ÃC(20)
C(15)ÃC(20)ÃC(19)
108.4(5)
105.7(5)
111.8(5)
108.5(5)
117.7(6)
123.7(6)
C(5)ÃC(1)ÃC(11)
C(5)ÃC(19)ÃC(20)
C(2)ÃC(1)ÃC(5)
C(12)ÃC(11)ÃC(20)
C(11)ÃC(20)ÃC(15)
108.8(5)
105.2(5)
108.1(5)
118.1(6)
124.5(6)
Fig. 2. ORTEP view of 8.

26
M. Sato et al. / Journal of Organometallic Chemistry 655 (2002) 23ꢀ30
/
bis(ruthenocenyl)naphthalene. The structure of 8 was
confirmed by X-ray diffraction. The crystallographic
data of 8 are collected in Table 1 and the selected bond
distances and angles are collected in Table 3. The ORTEP
view of 8 is shown in Fig. 2. Two Cp rings of the
ruthenocene moiety adopt an eclipsed form. The ruthe-
nocene is fused with acenaphthylene at the 1,2-positions.
The plane of acenaphthylene is inclined by 128 to the
outer side of the Cp ring of ruthenocene. The CÃ
/
C (av.
˚
C bond distances (av. 2.197 A) of the
˚
1.432 A) and FeÃ
/
substituted Cp ring in the ruthenocene moiety are
similar to those of ruthenocene itself, indicating no
strain due to the fusion of acenaphthylene in the
ruthenocene moiety. The normal bond alternation
observed in the naphthalene ring of 8 means little strain
in the naphthalene ring, but the six-membered ring of
naphthalene is somewhat distorted because of the fusion
of a five-membered ring in the peri-positions [e.g.
C(12)Ã
/
C(11)Ã
/
C(20) 118.1(6)8 and C(11)Ã
/
C(20)Ã/C(15)
124.5(6)8].
2.3. Redox property
The cyclic voltammograms of compounds 1ꢀ
/
6 and
ruthenocene were measured in a solution of 0.1 M n-
Bu4NClO4 in CH2Cl2 at a glassy carbon (GC) electrode
and a sweep rate of 0.1 V sꢃ1. The oxidation and
reduction potentials are summarized in Table 4. Bi-
nuclear ruthenocene compounds, 2, 4, and 6, showed a
broad irreversible oxidation wave near 0.5 V and a
shoulder near 0.3 V, as exemplified in Fig. 3. The large
wave near 0.5 V is assigned to be due to the super-
Fig. 3. Cyclic voltammograms of 4 (upper) and 6 (lower).
Cp ring is di-substituted at 1,2-positions by the same
substituent. The aromatic ring protons appeared at d
7.42 (m, 4H), 7.86 (m, 2H), and 8.33 (m, 2H), indicating
a symmetrical substitution of the benzene ring. In
coincidence with this, the 13C-NMR spectrum of 7
gave only six aromatic carbon signals at d 123.42,
123.69, 125.61, 127.18, 129.35, and 133.10, along with
the ruthenocenyl ring carbon signals at d 65.49, 71.14,
71.44, and 85.17. The mass spectrum of 12 showed the
molecular ion at m/z 381. The reaction of 1 with 1,8-
diiodo-naphthalene in the similar non-aqueous condi-
tions also gave a mononuclear ruthenocene derivative,
ruthenoceno[a]acenaphthylene (8), in very low yield,
along with a large amount of ruthenocene, but no 1,8-
imposed two one-electron oxidation [Ru(II)ꢀ
/
Ru(III)
and Ru(III)ꢀRu(IV)] of two ruthenocenyl nuclei, in
/
comparison with that of ruthenocene. The latter
shoulder seems to be caused by the superimposed one-
electron oxidation [Ru(II)ꢀRu(III)] of two ruthenocenyl
/
nuclei, since 1,2-bis(ruthenocenyl)- and trans-1,2-di-
methyl-1,2-bis(ruthenocenyl)ethenes, in which a strong
electronic interaction between the metal sites was
observed in their two-electron oxidized species, exhib-
ited the two-electron redox wave at lower potential, 0.03
and 0.18 V, respectively [13]. The appearance of the two-
electron oxidation wave as a shoulder suggests that the
two-electron oxidized species of these compounds are
stable to some extent. That is, there would be probably a
little electronic communication through the aromatic
ring between two ruthenocenyl nuclei in the two-
electron oxidized species of 2, 4, and 6. On the other
hand, compounds, 3 and 5, showed no shoulder near 0.3
V, likely indicating no stabilization of the two-electron
oxidized species. In compound 3, the two ruthenocenyl
nuclei seem to be not coplanar with the benzene ring as a
result of the steric hindrance in the benzene ring ortho-
disubstituted by ruthenocene, similar to that shown in
the X-ray analysis of 1,2-bis(ferrocenyl)benzene [22].
Table 4
The oxidation potentials (V vs. FcHꢀ
/
FcHꢂ) of compounds 1ꢀ
6
/
Compound
Epa(1)
Epa(2)
RcH
0.53
0.55
0.46
0.52
0.43
0.49
0.42
1
2
3
4
5
6
0.42
0.32(sh)
0.28(sh)

M. Sato et al. / Journal of Organometallic Chemistry 655 (2002) 23ꢀ
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30
27
Also, the two substituted Cp rings in the ruthenocenyl
nuclei of 5 are not coplanar with the naphthalene ring
because of the steric hindrance by the peri-hydrogen
atom of naphthalene. As a result, the electronic com-
munication between the two ruthenocenyl nuclei in 3
and 5 may be greatly disturbed in the two-electron
oxidized species. Thus, the data obtained from the CV
In the case of 2,2?-diiodobiphenyl and 1,8-diiodo-
naphthalene, unusual products, ruthenoceno[l]phenan-
threne and ruthenoceno[a]acenaphthylene, were ob-
tained, although in low yields, respectively.
4. Experimental
(cyclic voltammetric) measurement of 2ꢀ6 may be able
/
to estimate the electronic interaction between the Ru
sites in the two-electron oxidized species of the binuclear
ruthenocenes bridged by aromatic moieties, if we can
assume that the magnitude of the oxidation wave near
0.3 V is parallel to that of the electronic interaction
between the metal sites. Thus, the electronic interaction
in the two-electron oxidized species of the naphthalene
derivative (6) is inferred to be somewhat larger than that
of benzene derivatives (2). The aromatics-bridged bir-
uthenocene derivatives showed weak electronic interac-
tion in the two-electron oxidized species as described
above, while a significant electronic interaction was
observed for the bis(ruthenocenyl)ethenes [13]. There-
fore, the former small interaction is probably because
the interaction between the metal sites is cross-conju-
gated with the aromaticity of the bridge in former
compounds. The fact that the electronic interaction in
the two-electron oxidized species of 6 is somewhat larger
than that of 2 probably may reflect the strength of
All reactions were carried out under an atmosphere of
N2 and/or Ar, and work-ups were performed without
precaution to exclude air. NMR spectra were recorded
on BRUKER AM400, ARX400, AC300P, or AC200 spectro-
meter. IR (KBr disc) spectra were recorded on Perkinꢀ
/
Elmer System 2000 spectrometer. CV was carried out by
using ALS 600 in 10ꢃ1 M solution of n-Bu4NClO4
(polarography grade, Nacalai tesque) in CH2Cl2. CV’s
cells were fitted with GC working electrode, Pt wire
counter electrode and Agꢀ
Agꢂ pseudo reference elec-
/
trode. The cyclic voltammograms were obtained at the
scan rate of 0.1 V sꢃ1 in the 10ꢃ3 M or saturated
solution of complexes. All potentials were represented
versus FcHꢀ
FcHꢂ, which were obtained by the sub-
sequent measurement of ferrocene at the same condi-
tions. THF was purified by distillation from the drying
/
agent, Naꢀbenzophenone. Ruthenocene was prepared
/
according to the literature [29]. Other reagents were used
as received from commercial suppliers.
aromaticity: benzeneꢀ
/
naphthalene.
4.1. 2-Ruthenocenyl-1,3-dioxa-2-borolane (1)
2.4. Chemical oxidation
To a suspension of ruthenocene (2.00 g, 8.65 mmol) in
hexane (65 ml) tribromoborane (10.4 ml, 10.4 mmol)
was drop-wise added under nitrogen. The mixture was
refluxed for 1 h. The resulting light brown solution was
cooled to room temperature and drop-wise added at
0 8C to a solution of dilithium pinacolate which was
prepared from pinacol (1.35 g, 11.4 mmol) and n-BuLi
(16.5 ml of 1.5 M solution in hexane, 25.2 mmol) in
THF (150 ml) at 0 8C. After stirring for 10 min at 0 8C,
the solvent was evaporated under vacuum. The residue
was dissolved in benzene (100 ml). The solution was
washed with saturated solution of NH4Cl in water and
then dried over MgSO4. After evaporation, the residue
was chromatographed on deactivated Al2O3 with 5%
The increased electronic interaction between the two
Ru sites may indicate the increased stability in the two-
electron oxidized species of the binuclear ruthenocenes.
So, compound 6, bridged by naphthalene at 2,6-
positions and exhibiting the largest shoulder near 0.3
V among the binuclear ruthenocenes bridged by aro-
matics, was oxidized with two equivalents of para-
benzoquinone and BF3×OEt2 in CH2Cl2 at 0 8C. The
/
resulting dark violet precipitate, which may be consid-
ered to be the two-electron oxidized species, was
obtained. However, it was unstable and gave no definite
1H-NMR signal when it was dissolved in CD3NO2 or
CD3CN.
H2O by elution of benzeneꢀEtOAc (1:1). Recrystalliza-
/
tion from hexane gave yellow crystals (2.04 g, 66%).
Melting point (m.p.) 144 8C. Found: C, 53.94; H,
5.96%. Anal. Calc. for C16H21O2BRu: C, 53.80; H,
5.93%. 1H-NMR (CDCl3): d 1.28 (s, 12H, CH3), 4.53 (s,
3. Conclusion
The binuclear ruthenocene derivatives bridged by
phenylene, biphenylene, and naphthalenylene were
synthesized using Suzukiꢀ
/
Miyaura cross-coupling reac-
tion of ruthenocenylꢀdioxaborolane, newly prepared.
/
The compounds showed no distinct oxidation wave at
lower potential in their cyclic voltammograms, indicat-
ing weak electronic communication between the two
ruthenocenyl nuclei in the two-electron oxidized species.
Scheme 1.

28
M. Sato et al. / Journal of Organometallic Chemistry 655 (2002) 23ꢀ30
/
5H, h-C5H5), 4.71 (t, 2H, Jꢁ
(t, 2H, Jꢁ
2 Hz, h-C5H4). 13C-NMR (CDCl3): d 24.59
(CH3), 70.57 (Cꢂ
/
2 Hz, h-C5H4), and 4.75
/
/
h-C5H4), 73.38 (h-C5H5), 74.97 (h-
C5H4), and 82.99 (ipso-h-C5H4).
4.2. 1,4-Bis(ruthenocenyl)benzene (2)
4.2.1. General procedure
A mixture of 1 (0.34 g, 0.96 mmol), 1,4-dibromoben-
zene (94 mg, 0.4 mmol), PdCl2(dppf) (11 mg, 0.013
mmol), 3 M aqueous solution of NaOH (3 ml), and
DME (3 ml) was heated for 48 h at 120 8C under Ar in
a sealed tube. After cooling, the mixture was dissolved in
CH2Cl2. The organic layer was separated, washed with
water, and then dried over MgSO4. After evaporation,
the residue was chromatographed on SiO2 by elution of
benzene to give yellow crystals, along with ruthenocene
(90 mg, 41%). The crystals were recrystallized from
Scheme 3.
4.4. 4,4?-Bis(ruthenocenyl)biphenyl (4)
This compound was prepared from 1 (0.36 g, 1.0
mmol) and 4,4?-dibromobiphenyl (125 mg, 0.40 mmol).
Pale yellow crystals (103 mg, 43%), m.p.ꢀ260 8C.
/
Found: C, 62.70; H, 4.21%. Anal. Calc. for
1
C32H26Ru2: C, 62.73; H, 4.28%. H-NMR (CDCl3): d
benzeneꢀ
71%), m.p.ꢀ
/
hexane to give pale yellow crystals (152 mg,
250 8C. Found: C, 58.54; H, 4.12%. Anal.
Calc. for C26H22Ru2: C, 58.20; H, 4.13%. MS (EI, 70
/
4.50 (s, 10H, h-C5H5), 4.68 (t, 4H, Jꢁ1.6 Hz, h-C5H4),
/
eV): m/z 536 [Mꢂ]. H-NMR (CDCl3): d 4.47 (s, 10H,
1
5.06 (t, 4H, Jꢁ1.6 Hz, h-C5H4), and 7.45 (m, 8H,
/
C12H8). 13C-NMR (CDCl3): d 69.57 (h-C5H4), 71.35 (h-
C5H5), 73.72 (h-C5H4), 93.34 (ipso-h-C5H4), 125.86
(C6H4), 132.37 (C6H4), and 136.37 (ipso-C6H4).
h-C5H5), 4.64 (t, 4H, Jꢁ
/
2 Hz, h-C5H4), 5.00 (t, 4H,
Jꢁ
/
2 Hz, h-C5H4), and 7.24 (s, 4H, C6H4). 13C-NMR
(CDCl3): d 69.37 (h-C5H4), 70.67 (h-C5H5), 71.39 (h-
C5H4), 90.23 (ipso-h-C5H4), 126.34 (C6H4) and 136.19
(ipso-C6H4).
4.5. 1,4-Bis(ruthenocenyl)naphthalene (5)
4.3. 1,2-Bis(ruthenocenyl)benzene (3)
This compound was prepared from 1 (0.36 g, 1.0
mmol) and 1,4-dibromonaphthalene (114 mg, 0.40
This compound was prepared from 1 (0.34 g, 0.96
mmol) and 1,2-diiodobenzene (132 mg, 0.4 mmol). The
mmol). Pale yellow crystals (115 mg, 50%), m.p. 200ꢀ
/
201 8C. Found: C, 61.32; H, 4.04%. Anal. Calc. for
C30H24Ru2: C, 61.42; H, 4.12%. H-NMR (CDCl3): d
1
product was recrystallized from CHCl3ꢀhexane. Pale
/
yellow crystals (112 mg, 53%), m.p. 224 8C (dec.).
Found: C, 53.26; H, 3.71%. Anal. Calc. for
C26H22Ru.2CHCl3: C, 53.38; H, 3.80%. 1H-NMR
4.63 (s, 10H, h-C5H5), 4.73 (t, 4H, Jꢁ
/
1.5 Hz, h-C5H4),
4.97 (t, 4H, Jꢁ
/
1.5 Hz, h-C5H4), 7.43 (m, 2H, 6,7-H),
7.60 (s, 2H, 2,3-H), and 8.50 (m, 2H, 5,8-H). 13C-NMR
(CDCl3): d 70.21 (h-C5H4), 71.55 (h-C5H5), 73.41 (h-
C5H4), 92.36 (ipso-h-C5H4), 125.00 (C10H6), 126.58
(C10H6), 128.56 (C10H6), 132.08 (q-C10H6), and 133.90
(q-C10H6).
(CDCl3): d 4.50 (s, 10H, h-C5H5), 4.52 (t, 4H, Jꢁ
Hz, h-C5H4), 4.60 (t, 4H, Jꢁ2 Hz, h-C5H4), 7.08 (q,
3 Hz, 2H, C6H4).
/
2
/
Jꢁ
/
3 Hz, 2H, C6H4), and 7.42 (q, Jꢁ
/
13C-NMR (CDCl3): d 69.57 (h-C5H4), 71.35 (h-C5H5),
73.72 (h-C5H4), 93.34 (ipso-h-C5H4), 125.86 (C6H4),
132.37 (C6H4), and 136.37 (ipso-C6H4).
4.6. 2,6-Bis(ruthenocenyl)naphthalene (6)
This compound was prepared from 1 (0.36 g, 1.0
mmol) and 2,6-dibromonaphthalene (114 mg, 0.40
mmol). Pale yellow crystals (68 mg, 29%), m.p. 200ꢀ
/
200.5 8C. Found: C, 61.24; H, 4.10%. Anal. Calc. for
C30H24Ru2: C, 61.42; H, 4.12%. H-NMR (CDCl3): d
1
4.48 (s, 10H, h-C5H5), 4.71 (t, 4H, Jꢁ
5.14 (t, 4H, Jꢁ1.5 Hz, h-C5H4), 7.37 (d, 2H, Jꢁ
Hz, 3,7-H), 7.62 (d, 2H, Jꢁ8.5 Hz, 4,8-H), and 7.88 (s,
/
1.5 Hz, h-C5H4),
/
/8.5
/
2H, 1,5-H). 13C-NMR (CDCl3): d 69.45 (h-C5H4), 70.98
(h-C5H4), 71.44 (h-C5H5), 90.09 (ipso-h-C5H4), 123.64
(C10H6), 126.04 (C10H6), 127.18 (C10H6), 132.17 (q-
C10H6), and 135.36 (q-C10H6).
Scheme 2.

M. Sato et al. / Journal of Organometallic Chemistry 655 (2002) 23ꢀ
/
30
29
4.7. Ruthenocenyl[l]phenanthrene (12)
the SIR 92 method in CRYSTAN-GM (software-package
for structure determination) for 1 and the SIR 92 in
MAXUS (software-package for structure determination)
for 8 and refined by full-matrix least-squares procedure.
Anisotropic refinements for non-hydrogen atom were
carried out. All the hydrogen atoms, partially located
from differential Fourier map, for complex 8 were
isotropically refined. In complex 1, no hydrogen was
located.
After a solution of 1 (0.26 g, 0.7 mmol), 2,2?-
diiodobiphenyl (122 mg, 0.3 mmol) in dimethylforma-
mide (2.5 ml) was bubbled with nitrogen for 20 min,
Pd(PPh3)4 (12 mg) and Cs2(CO)3 (0.23 g, 0.7 mmol)
were added, and the mixture was heated at 90 8C for 4 h
under Ar. The mixture was diluted with benzene (30 ml),
and the solution was washed with water (40 ml) twice
and then conc. aqueous LiCl (20 ml) twice. After being
dried with MgSO4, the solution was evaporated by
evaporator. The residue was chromatographed on SiO2
5. Supplementary material
by elution of hexaneꢀ
3%) as yellow crystals, along with ruthenocene (0.18 g,
80%). M.p. 183ꢀ
184 8 C. 1H-NMR (CDCl3, 400 MHz):
d 4.14 (s, 5H, h-C5H5), 4.84 (t, Jꢁ2.4 Hz, 1H, h-C5H4),
5.60 (d, Jꢁ
/benzene (3:1) to give 12 (11 mg,
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 178850 for complex 1 and
CCDC no. 178851 for complex 8. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
/
/
/
2.4 Hz, 2H, h-C5H4), 7.42 (m, 4H, 2,3,7,8-
H), 7.86 (m, 2H, 1,8-H), 8.33 (m, 2H, 4,5-H). 13C-NMR
(CDCl3, 100 MHz): d 65.49 (h-C5H4), 71.14 (h-C5H4),
71.44 (h-C5H5), 85.17 (ipso-h-C5H4), 123.42 (C12H8),
123.69 (C12H8), 125.61 (C12H8), 127.18 (C12H8), 129.35
(q-C12H8), 133.10 (q-C12H8). MS (EI, 75 eV): m/z 381
[Mꢂ].
UK (Fax: ꢂ44-1223-336033; e-mail: deposit@ccdc.ca-
/
m.ac.uk or www: http://www.ccdc.cam.ac.uk).
4.8. Ruthenoceno[a]acenaphthylene (13)
Acknowledgements
This compound was obtained from the reaction of 1
with 1,8-diiodonaphthalene under the same conditions
used in the reaction of 1 with 2,2?-diiodobiphenyl
described above. Yield: 13 mg (3%). Yellow needles.
The present work was supported by Grant-in Aid for
Science Research (No. 10640538) from the Ministry of
Education, Science and Culture of Japan.
M.p. 166ꢀ
Calc. for C20H14Ru: C, 67.59; H, 3.97%. 1H-NMR
(CDCl3, 400 MHz): d 4.30 (s, 5H, h-C5H5), 4.80 (t, Jꢁ
2.2 Hz, 1H, h-C5H4), 5.20 (d, Jꢁ2.2 Hz, 2H, h-C5H4),
7,36 (dd, Jꢁ7.0 and 8.1 Hz, 4H, 4,7-H), 7.50 (dd, Jꢁ
7.0 and 0.7 Hz, 2H, 3,8-H), 7.59 (dd, Jꢁ8.1 and 0.7 Hz,
/
167 8C. Found: C, 67.47; H, 3.88%. Anal.
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