Redox-associated η1 to η2 conversion of disulfide ligands in dinuclear ruthenium complexes

Article abstract of DOI:10.1021/ic000392a

Disulfide-bridged dinuclear ruthenium complexes [{Ru(MeCN)(P(OMe)₃)₂}₂(μ-X) (μ,η²-S₂)][ZnX₃(MeCN)] (X = Cl (2), Br (4)), [{Ru(MeCN)(P(OMe)₃)₂}₂ (μ-Cl)₂(μ,η¹-S₂)] (CF₃SO₃) (5), [{Ru(MeCN)(P(OMe)₃)₂}₂ (μ-Cl)-(μ,η²-S₂)](BF₄) (6), and [{Ru(MeCN) ₂(P(OMe)₃)₂}₂(μ-Cl) (μ,η¹-S₂)] (CF₃SO₃)₃ (7) were synthesized, and the crystal structures of 2 and 4 were determined. Crystal data: 2, triclinic, P1, α = 15.921(4) A, b = 17.484(4) A, c = 8.774(2) A, α = 103.14(2)°, β = 102.30(2)°, γ = 109.68(2)°, V = 2124(1) A³, Z: 2, R (R_w) = 0.055 (0.074); 4, triclinic, P1, α = 15.943(4) A, b = 17.703(4) A, c = 8.883(1) A, α = 102.96(2)°, β = 102.02(2)°, γ = 109.10(2)°, V = 2198.4(9) A³, Z = 2, R (R_w) = 0.048 (0.067). Complexes 2 and 4 were obtained by reduction of the disulfide-bridged ruthenium complexes [{RuX(P(OMe)₃)₂}₂ (μ-X)₂(μ,η¹-S₂)] (X = Cl (1), Br (3)) with zinc, respectively. Complex 5 was synthesized by oxidation of 2 with AgCF₃SO₃. Through these redox steps, the coordination mode of the disulfide ligand was converted from μ,η¹ in 1 and 3 to μ,η² in 2 and 4 and further reverted to μ,η¹ in 5. Electrochemical studies of 6 indicated that similar conversion of the coordination mode occurs also in electrochemical redox reactions.

Full text of DOI:10.1021/ic000392a

2234
Inorg. Chem. 2001, 40, 2234-2239
Redox-Associated η1 to η2 Conversion of Disulfide Ligands in Dinuclear Ruthenium
Complexes
Kumiko Yoshioka, Hayato Kikuchi, Jun Mizutani,† and Kazuko Matsumoto*
Department of Chemistry and Advanced Research Institute for Science and Engineering,
Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan, and Japan Science and
Technology Corporation, Kawaguchi, Saitama 332-0012, Japan
ReceiVed April 14, 2000
Disulfide-bridged dinuclear ruthenium complexes [{Ru(MeCN)(P(OMe)3)2}2(µ-X)(µ,η2-S2)][ZnX3(MeCN)] (X
) Cl (2), Br (4)), [{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)2(µ,η1-S2)](CF3SO3) (5), [{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)-
(µ,η2-S2)](BF4) (6), and [{Ru(MeCN)2(P(OMe)3)2}2(µ-Cl)(µ,η1-S2)](CF3SO3)3 (7) were synthesized, and the crystal
structures of 2 and 4 were determined. Crystal data: 2, triclinic, P1h, a ) 15.921(4) Å, b ) 17.484(4) Å, c )
8.774(2) Å, R ) 103.14(2)°, â ) 102.30(2)°, γ ) 109.68(2)°, V ) 2124(1) Å3, Z ) 2, R (Rw) ) 0.055 (0.074);
4, triclinic, P1h, a ) 15.943(4) Å, b ) 17.703(4) Å, c ) 8.883(1) Å, R ) 102.96(2)°, â ) 102.02(2)°, γ )
109.10(2)°, V ) 2198.4(9) Å3, Z ) 2, R (Rw) ) 0.048 (0.067). Complexes 2 and 4 were obtained by reduction
of the disulfide-bridged ruthenium complexes [{RuX(P(OMe)3)2}2(µ-X)2(µ,η1-S2)] (X ) Cl (1), Br (3)) with
zinc, respectively. Complex 5 was synthesized by oxidation of 2 with AgCF3SO3. Through these redox steps, the
coordination mode of the disulfide ligand was converted from µ,η1 in 1 and 3 to µ,η2 in 2 and 4 and further
reverted to µ,η1 in 5. Electrochemical studies of 6 indicated that similar conversion of the coordination mode
occurs also in electrochemical redox reactions.
Introduction
hexanuclear cluster complex [Na2RuII (P(OMe)3)4(µ-Cl)4(µ4-
4
Cl)2(µ,η2-S2)2(µ-P(OMe)3-P,O)4]‚THF, in which the coordina-
tion mode of the disulfide ligand is converted from µ,η1 to µ,η2.6
In the present study, chemical and electrochemical redox
reactions of the disulfide-bridged dinuclear ruthenium complexes
were studied in pursuit of a more general view for such redox-
associated behavior of disulfide ligands.
Transition-metal complexes with inorganic sulfide ligands
have been widely investigated in relevance to bioinorganic and
industrial chemistry.1 Although most of the reactivities involved
in these fields utilize a monosulfide ligand, the disulfide ligand
is also noteworthy because of its strong π-donating nature, which
remarkably decreases the redox potential of the coordinated
metals.2 It is reported that disulfur ligands bridging two metal
atoms have three possible coordination modes: (η1, η1), (η1,
η2), and (η2, η2).3 It is also known that in several examples,
conversion of the coordination modes takes place on redox or
other reactions of the metals. For example, addition of F3Ct
CF3 to (CpV)2(µ-S)2(µ:η1,η1-S2) gives (CpV)2{µ-(CF3)2C2S2}-
(µ:η2,η2-S2),4 and chemical or electrochemical oxidation of
(Cp*Fe)2(µ-η1,η1-S2)(µ-η2,η2-S2) converts the η1,η1 ligand into
the η2,η2 one.5 In our recent study, reduction of [{RuIIICl-
(P(OMe)3)2}(µ-Cl)2(µ,η1-S2)] (1) by sodium metal affords a
Experimental Section
Materials and Methods. Complex [{RuCl(P(OMe)3)2}2(µ-Cl)2(µ,η1-
S2)] (1) was prepared according to the literature.7 All manipulations
were carried out under a nitrogen atmosphere in a drybox (oxygen less
than 0.03 ppm (v/v), dew point lower than -60 °C). Dichloromethane,
diethyl ether, and acetonitrile of low-water-content grade (water less
than 0.003%, 0.005%, and 0.005%, respectively, Kanto Chemical Co.,
Inc.) were used as purchased without purification. The UV-vis spectra
were recorded on a Shimazu UV-3101PC spectrometer, and the NMR
spectra were recorded on JEOL EX-270 and JEOL Lambda-270
spectrometers. The 31P chemical shifts were externally referenced to
P(OMe)3 in (CD3)2CO at 140.0 ppm. The ESR spectrum was recorded
on a JEOL RE-2XG spectrometer, and the FAB-MS spectra were
recorded on a JEOL JMS-HX110 spectrometer. The cyclic voltammo-
grams were measured by using a BAS CV-50W potentiometer with a
Pt working electrode, a Pt wire auxiliary electrode, and an Ag/Ag+
reference electrode separated from the sample solution via Bu4NBF4/
MeCN solution. The reference electrode was calibrated to Fe(C5H5)2/
Fe(C5H5)2+. The Bu4NBF4 used as the supporting electrolyte was
recrystallized from ethyl acetate. The molecular orbitals were calculated
by using ZINDO in the CaChe software.
* To whom correspondence should be addressed. Address: Department
of Chemistry, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan.
† Current address: School of Science, The University of Tokyo,
Bunkyo-ku, Tokyo 113-0033, Japan.
(1) (a) Mu¨ller, A.; Diemann, E. AdV. Inorg. Chem. 1987, 31, 89. (b) Stiefel,
E. I.; Chianelli, R. R. In Nitrogen Fixation: The Chemical-
Biochemical-Genetic Interface; Mu¨ller, A., Newton, W. E., Eds.;
Plenum Press: New York, 1983; p 341. (c) Rakowskii DuBois, M.
Chem. ReV., 1989, 89, 1. (d) Newton, W. E. In Sulfur: Its Significance
for Chemistry, for the Geo-, Bio- and Cosmosphere and Technology;
Mu¨ller, A., Kreb, B., Eds.; Elsevier: Amsterdam, 1984; p 409. (e)
Stiefel, E. I. In Transition Metal Sulfur Chemistry; Stiefel, E. I.,
Matsumoto, K., Eds.; ACS Symposium Series 653; American Chemi-
cal Society: Washington, DC, 1996; Chapter 1.
(5) (a) Brunner, H.; Merz, A.; Pfauntsch, J.; Serhadli, O.; Wachter, J.;
Ziegler, M. L. Inorg. Chem. 1988, 27, 2055. (b) Inomata, S.; Tobita,
H.; Ogino, H. Inorg. Chem. 1991, 30, 3039.
(2) Amarasekera, J.; Rauchfuss, T. B.; Wilson, S. R. Inorg. Chem. 1987,
26, 3328.
(3) Mu¨ller, A.; Jaegermann, W.; Enemark, J. H. Coord. Chem. ReV. 1982,
(6) Matsumoto, K.; Sano, Y. Inorg. Chem. 1997, 36, 4405.
(7) (a) Matsumoto, T.; Matsumoto, K. Chem. Lett. 1992, 559. (b)
Matsumoto, K.; Matsumoto, T.; Kawano, M.; Ohnuki, H.; Shichi, Y.;
Nishiide, T.; Sato, T. J. Am. Chem. Soc. 1996, 118, 2597.
46, 245.
(4) Bolinger, C. M.; Rauchfuss, T. B.; Rheingold, A. L. J. Am. Chem.
Soc. 1983, 105, 6321.
10.1021/ic000392a CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/31/2001

Conversion of Disulfide Ligands
Inorganic Chemistry, Vol. 40, No. 10, 2001 2235
[{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)(µ,η2-S2)][ZnCl3(MeCN)] (2). A
suspension of 1 (250 mg, 0.28 mmol) and zinc powder (750 mg, 11.5
mmol) in 10 mL of acetonitrile was stirred at room temperature for 24
h. After removal of the excess zinc by filtration, the filtrate was
concentrated to 3 mL under reduced pressure and 7 mL of diethyl ether
was added. Yellow crystals of 2 were obtained in 1 d (yield: 204 mg,
65%). Anal. Calcd for C18H45N3O12Cl4P4S2ZnRu2: C, 19.78; H, 4.15;
Scheme 1
1
N, 3.85. Found: C, 19.77; H, 4.41; N, 3.85. H NMR (CD2Cl2): δ
3
3
3.75 (d, JP-H ) 11.6 Hz), 3.61 (d, JP-H ) 11.6 Hz), 2.47 (s), 1.98
(s). 31P{1H} NMR (CD2Cl2): δ 148.7 (d, JP-P ) 67.1 Hz), 137.9 (d,
2
2JP-P ) 67.1 Hz). UV-vis (MeCN): λmax 379 nm (ꢀ ) 1.4 × 103 M-1
cm-1). FAB-MS (positive, NBA ()nitrobenzyl alcohol)): m/e 880
(M+), 798 (M+ - 2MeCN), 674 (M+ - 2MeCN - P(OMe)3).
[{RuBr(P(OMe)3)2}2(µ-Br)2(µ,η1-S2)] (3). To a methanol solution
(1.0 L) of 4.0 g (15.3 mmol) of RuCl3‚3H2O was added 96.3 g of LiBr‚
H2O (0.92 mol). After the mixture was refluxed for 24 h, PPh3 (24.0
g, 91.5 mmol) was added, and the solution was refluxed for 5 h. The
resulting brown solid of RuBr2(PPh3)3 was collected and washed with
methanol (yield: 11.4 g, 74% based on RuCl3‚3H2O). The solid was
dissolved in 1.2 L of hexane, to which 20 mL (169 mmol) of P(OMe)3
was added, and the mixture was refluxed for 2 h. Orange crystals of
trans-RuBr2(P(OMe)3)4 were obtained by cooling the reaction solution
(yield: 5.76 g, 76% based on RuBr2(PPh3)3). The isolated crystals and
0.76 g of elemental sulfur (22.8 mmol) were treated in 200 mL of
dichloromethane at room temperature for 24 h. In the course of the
reaction, the solution turned from reddish yellow to violet. Condensation
of the reaction solution to a half and slow introduction of diethyl ether
vapor gave violet needle crystals of 3 (yield: 2.88 g, 70% based on
trans-RuBr2(P(OMe)3)4). Anal. Calcd for C12H36O12P4Br4S2Ru2: C,
13.32; H, 3.35. Found: C, 13.71; H, 3.44. UV-vis (CH2Cl2): λmax
499 nm (ꢀ ) 2.6 × 103 M-1 cm-1), 751 nm (ꢀ ) 7.4 × 103 M-1 cm-1).
31P{1H} NMR(CD2Cl2): δ 120.3. The cyclic voltammogram of 3 in
MeCN containing 0.1 M Bu4NBF4 showed two reversible waves at
E1/2 ) 0.99 and -0.51 V vs Ag/Ag+. Single-crystal X-ray analysis of
3 confirmed that the structure was topologically the same as that of 1
(see the Supporting Information for the structure).
[{Ru(MeCN)2(P(OMe)3)2}2(µ-Cl)(µ,η1-S2)](CF3SO3)3 (7). To an
acetonitrile solution (2 mL) of 1 (90 mg, 0.1 mmol) was added Me3-
SiO3SCF3 (0.1 mL, 0.55 mmol), and the mixture was stirred at room
temperature for 3 h. The solution was concentrated to 1 mL under
reduced pressure, and 10 mL of diethyl ether was added to give a blue-
green powder of 7, which was washed with diethyl ether three times
and was dried under vacuum (yield: 94 mg, 85%). Anal. Calcd for
C23H48N4F9O21ClP4S5Ru2: C, 19.60; H, 3.43; N, 3.98. Found: C, 19.65;
1
3
H, 3.18; N, 3.67. H NMR (CD3CN): δ 4.02 (d, JP-H ) 11.2 Hz),
4.00 (d, 3JP-H ) 11.2 Hz), 3.67 (d, 3JP-H ) 11.2 Hz), 3.65 (d, 3JP-H
11.2 Hz), 2.73 (s), 2.15 (s). 31P{1H} NMR (CD3CN): δ 117.6 (d, 2JP-P
)
2
2
) 67.8 Hz), 117.2 (d, JP-P ) 69.8 Hz), 112.9 (d, JP-P ) 67.8 Hz),
2
110.6 (d, JP-P ) 69.8 Hz). UV-vis (MeCN): λmax 412 (ꢀ ) 2.8 ×
103 M-1 cm-1), 621 (ꢀ ) 1.3 × 104 M-1 cm-1) nm.
X-ray Structure Determination. Crystals of 2, 3, and 4 were
attached to thin glass rods and mounted on a Rigaku AFC-7R four-
circle diffractometer equipped with a rotating anode X-ray generator
(Mo KR, λ ) 0.7107 Å, monochromated with a graphite crystal). The
intensity data for 2 and 4 were measured at -50 °C, while those for 3
were measured at -10 °C. Three standard reflections were monitored
every 150 reflections, and no decay was observed. An empirical
absorption correction based on ψ-scan8 was applied. The initial phases
were obtained by direct methods (SIR929 for 2, and SHELXS8610 for
3 and 4), and the structures were refined by using least-squares
techniques and difference Fourier syntheses. All the calculations were
performed using a teXsan11 software package. The crystallographic
parameters are shown in Table 1.
[{Ru(MeCN)(P(OMe)3)2}2(µ-Br)(µ,η2-S2)][ZnBr3(MeCN)] (4). The
compound was prepared in a similar way as for 2 by using 3 instead
of 1 (yield: 65%). Anal. Calcd for C18H45N3O12Br4P4S2ZnRu2: C,
17.01; H, 3.57; N, 3.31. Found: C, 17.11; H, 3.30; N, 3.06. 1H NMR
3
3
(CD2Cl2): δ 3.75 (d, JP-H ) 11.5 Hz), 3.62 (d, JP-H ) 11.5 Hz),
2.46 (s), 2.00 (s). 31P{1H} NMR (CD2Cl2): δ 149.5 (d, JP-P ) 63.7
2
Hz), 136.8 (d, 2JP-P ) 63.7 Hz). UV-vis (MeCN): λmax 384 nm (ꢀ )
1.4 × 103 M-1 cm-1). FAB-MS (positive, NBA): m/e 925 (M+), 843
(M+ - 2MeCN), 718 (M+ - 2MeCN - P(OMe)3).
Results and Discussion
[{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)2(µ,η1-S2)](CF3SO3) (5). To a
dichloromethane solution (10 mL) of 2 (250 mg, 0.23 mmol) was added
AgCF3SO3 (177 mg, 0.69 mmol), and the mixture was stirred at 0 °C
for 24 h. The resulting silver metal and AgCl were removed by filtration,
and the filtrate was concentrated to 5 mL under reduced pressure.
Addition of 7 mL of diethyl ether afforded dark-green crystals of 5 in
1 d (yield: 161 mg, 68%). Anal. Calcd for C17H42N2O15F3Cl2P4S3Ru2:
C, 19.18; H, 3.98; N, 2.63; S, 9.04; Cl, 6.66. Found: C, 19.03; H,
3.88; N, 2.73; S, 8.97; Cl, 6.39. ESR (MeCN, room temperature): g )
2.050 (X-band, with a symmetrical pair of shoulders at g ) 2.039 and
2.061). UV-vis (MeCN): λmax 314 (ꢀ ) 2.6 × 103 M-1 cm-1), 394 (ꢀ
) 1.4 × 103 M-1 cm-1), 432 (ꢀ ) 9.1 × 102 M-1 cm-1), 695 (ꢀ ) 4.2
Syntheses and Structures of the η2 Complexes 2 and 4.
Addition of excess amount of zinc powder to the RuIIIRuIII
complex [{RuCl(P(OMe)3)2}2(µ-Cl)2(µ,η1-S2)] (1) in acetonitrile
led to abstraction of the two terminal and one bridging chloride
ligands in 1, giving the RuIIRuII cation [{Ru(MeCN)(P(OMe)3)2}2-
(µ-Cl)(µ,η2-S2)]+ (the cation of 2), and the abstracted chloride
and zinc ions formed an anion, [ZnCl3(MeCN)]- (the anion of
2). During the reaction, the ruthenium was reduced from +3 to
+2 (Scheme 1).
The structure of 2 was determined by single-crystal X-ray
structure analysis. A drawing of the cation of 2 is shown in
Figure 1, and the selected bond distances are listed in Table 2.
In the cation, two Ru(MeCN)(P(OMe)3)2 moieties are connected
to each other by one chloride and one disulfide bridge. The
coordination environment of the ruthenium atoms is virtually
× 103 M-1 cm-1) nm. FAB-MS (positive, NBA): m/e 983 (M+
-
2MeCN + CF3SO3), 874 (M+ - MeCN), 834 (M+ - 2MeCN), 800
(M+ - 2MeCN - P(OMe)3), 674 (M+ - 2MeCN - P(OMe)3 - Cl),
585 (M+ - 2MeCN - 2P(OMe)3).
[{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)(µ,η2-S2)](BF4) (6). Compound 2
(250 mg, 0.23 mmol) and Et4NBF4 (50 mg, 0.23 mmol) were treated
in 10 mL of dichloromethane for 1 min. After the solution was
concentrated under reduced pressure to 4 mL, the resulting white
precipitate was removed by filtration. To the filtrate was added 2 mL
of dichloromethane, and gradual introduction of diethyl ether vapor
into the solution afforded yellow crystals of 6 (yield: 80 mg, 36%).
Anal. Calcd for C16H42N8BF4O12ClP4S2Ru2: C, 19.87; H, 4.38; N, 2.90.
Found: C, 20.15; H, 4.44; N, 2.88.
(8) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, 24, 351.
(9) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1993, 26, 343.
(10) Sheldrick, G. M. SHELXS86, a program for crystal structure deter-
mination; University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(11) teXsan, Crystal Structure Analysis Package; Molecular Structure
Corporation: Houston, TX, 1985-1992.

2236 Inorganic Chemistry, Vol. 40, No. 10, 2001
Yoshioka et al.
Table 1. Crystallographic Parameters of 2, 3, and 4
2
3
4
chemical formula
fw
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
C18H45N3O12Cl4P4S2ZnRu2
C12H36O12Br4P4S2Ru2
1082.19
triclinic
P1h (No. 2)
16.888(4)
23.093(6)
8.779(2)
96.52(3)
101.76(2)
90.64(2)
3328(1)
4
C18H45N3O12Br4P4S2ZnRu2
1270.72
triclinic
P1h (No. 2)
15.943(4)
17.703(4)
8.883(1)
102.96(2)
102.02(2)
109.10(2)
2198.4(9)
1092.91
triclinic
P1h (No. 2)
15.921(4)
17.484(4)
8.774(2)
103.14(2)
102.30(2)
109.68(2)
2124(1)
2
Z
2
F
calcd/g cm-3
1.708
18.11
10 118
9762
2.160
60.88
15 822
15 299
1.920
51.54
6914
6611
µ/cm-1
measd reflns
unique reflns
obsd reflns
no. params
weighting scheme
Ra
7195 (I > 2.0 σ(I))
4113 (I > 5.0 σ(I))
4093 (I > 1.5 σ(I))
433
645
433
w ) 1/σ2(Fo) + 0.00034|Fo|
0.055
w ) 1/σ2(Fo)
0.041
w ) 1/σ2(Fo) + 0.00194|Fo|
2
2
0.048
0.067
1.14
b
Rw
0.074
2.00
1.03
0.021
0.057
1.22
0.64
0.69
Sc
∆Fmax d/e- Å-3
0.88
0.002
∆/σ e
2
a R ) ∑(|Fo| - |Fc|)/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
c S ) ∑w(|Fo| - |Fc|)2/(Nobsd - Nparam). d Maximum residual electron density
in the final difference Fourier map. e Maximum shift/error in the final cycle.
Figure 2. ORTEP drawing of the anion of [{Ru(MeCN)(P(OMe)3)2}2-
(µ-Cl)(µ,η2-S2)][ZnCl3(MeCN)] (2) at the 50% probability level.
Figure 1. ORTEP drawing of the cation of [{Ru(MeCN)(P(OMe)3)2}2-
(µ-Cl)(µ,η2-S2)][ZnCl3(MeCN)] (2) at the 50% probability level.
in 2 is 2.055(3) Å, which is 0.08 Å longer than that in 1. The
interatomic distance between the two Ru atoms in 2 is ca. 0.13
Å shorter than that in 1. The structure of the [ZnCl3(MeCN)]-
anion was determined crystallographically for the first time
(Figure 2). The average distance of the Zn-Cl bonds is ca. 2.24
Å, and the distance of the Zn-N bond is 2.062(8) Å. The Zn
atom has a virtually tetrahedral coordination environment (the
angles around the Zn atom range from 100.8(3)° to 116.3(1)°).
The bromide analogue of 2, [{Ru(MeCN)(P(OMe)3)2}2(µ-Br)-
(µ,η2-S2)][ZnBr3(MeCN)] (4), was prepared by using 3 instead
of 1. The structure of 4 is the same as that of 2. The halogen-
metal bond distances in 4 are ca. 0.12 Å longer than the
corresponding ones in the chloride complex 2, while all other
distances are not significantly different between the two.
Redox-induced conversion of the coordination mode of a
disulfide ligand is reported by Brunner et al.5a and Inomata et
al.5b In their studies, chemical and electrochemical two-electron
oxidation of [Cp*2Fe2(µ,η1-S2)(µ,η2-S2)] (Cp* ) 1,2,3,4,5-
pentamethylcyclopentadienyl) rotates the µ,η1-S2 into µ,η2-S2,
which is explained in terms of the 18-electron rule; removal of
the electrons on oxidation is compensated by the increased
hapticity of the disulfide ligand to satisfy the 18-electron rule
in both reduced and oxidized forms.5 In contrast, the present
Table 2. Selected Bond Distances (Å) of 2 and 4
2 (X ) Cl)
4 (X ) Br)
Ru1-S1
Ru1-S2
Ru2-S1
Ru2-S2
Ru1-X1
Ru2-X1
Ru1-P1
Ru1-P2
Ru2-P3
Ru2-P4
Ru1-N1
Ru2-N2
S1-S2
2.348(2)
2.491(2)
2.490(2)
2.345(2)
2.492(2)
2.503(2)
2.215(2)
2.200(2)
2.216(2)
2.218(2)
2.049(6)
2.043(6)
2.055(3)
2.228(3)
2.253(3)
2.227(3)
2.062(8)
2.355(3)
2.501(3)
2.490(3)
2.355(3)
2.612(2)
2.623(1)
2.226(3)
2.206(3)
2.229(3)
2.216(3)
2.033(10)
2.03(1)
2.057(4)
2.372(2)
2.372(2)
2.362(3)
2.04(1)
Zn-X2
Zn-X3
Zn-X4
Zn-N3
octahedral. The disulfide ligand, which bridged the two ruthe-
nium atoms in a µ,η1:η1 mode in the starting complex 1, is now
in the µ,η2:η2 coordination mode in 2. Thus, through the
reduction, the disulfide bridge rotates by 90°. The S-S distance

Conversion of Disulfide Ligands
Inorganic Chemistry, Vol. 40, No. 10, 2001 2237
Scheme 2
conversion from µ,η1 to µ,η2 occurs not on oxidation but on
reduction, and the products 2 and 4 do not obey the 18-electron
rule. Bolinger et al. reported the conversion of the µ,η1-S2 ligand
in (iPrCp)2V2(µ-S)2(µ,η1-S2) into the µ,η2 one accompanied by
dithiolene ligand formation by addition of hexafluoro-2-butyne
to the two µ-S ligands.12 It is rationalized as follows. Addition
of the alkyne-forming dithiolene ligand decreases the electron
density on the vanadium atoms, which is compensated by the
conversion of the S2 ligand by use of the higher σ-donating
nature of µ,η1-S2 compared with that of µ,η2-S2. This scheme
also seems to be our case because the oxidized RuIIIRuIII species
has the η1 form and the reduced RuIIRuII one has the η2 form.
As another explanation of the conversion, we carried out
qualitative molecular orbital calculations of 1 and 2 (Scheme
2). The LUMO of 1 has a Ru-S π-antibonding nature. Thus,
the reduction of 1 destabilizes the Ru-S-S-Ru geometry.
However, the reduced complex will be stabilized if the disulfide
ligand rotates by 90° because in this orientation the signs of
the atomic orbitals on the ruthenium and sulfur atoms fit with
each other and the molecular orbital will be bonding. Actually,
in the calculations of 2 having the η2-disulfide ligand, the
HOMO-9 corresponds to a σ-bonding interaction between the
ruthenium and the sulfur atoms. Thus, it is reasonable that
addition of electrons to the antibonding LUMO in 1 promotes
the conversion from η1 to η2, leading to the formation of 2.
Synthesis of the η1 Complex 5. Reaction of 3 equiv of
AgCF3SO3 with 2 led to the transfer of one of the chloride
ligands in [ZnCl3(MeCN)]- to the bridging position between
the two ruthenium atoms, together with one-electron oxidation,
to give the RuIIRuIII complex [{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)2-
(µ,η1-S2)](CF3SO3) (5) (Scheme 1). We have previously syn-
thesized 5 by the reaction of [{RuCl(P(OMe)3)2}2(µ-Cl)2(µ,η1-
S2)] with sodium metal, and the η1 nature of the disulfide ligand
has been confirmed crystallographically.13 Thus, in the present
reaction, one-electron oxidation of the η2 complex 2 led to the
conversion of the coordination mode of the disulfide ligand into
η1 again.
Figure 3. Cyclic voltammograms of [{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)-
(µ,η2-S2)](BF4) (6) at sweep rate of 50 mV/s.
Figure 4. Cyclic voltammograms of [{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)-
(µ,η2-S2)](BF4) (6) at sweep rate from 0.1 to 10 V/s.
Electrochemical Behavior of the η2 Complex. Conversion
of the disulfide coordination mode was examined with cyclic
voltammetry to see whether the disulfide ligand behaves
similarly to the chemical redox reactions. To avoid any possible
complexity of the electrochemical reaction expected for
appeared at ca. 0.5 V, which then grew and shifted to ca. 0.6 V
on further increase of the sweep rate with a concomitant decrease
of the wave a + b. Contrary to this change of the oxidation
wave, the reduction waves stayed almost unchanged. On further
increase of the sweep rate, i.e., at or above 4 V/s, another
reduction wave (d) grew at ca. 0.2 V. These facts suggest that
although several different oxidation processes proceed at the
increased sweep rate, the final oxidation product is always the
same because the reduction waves remain almost unchanged at
any sweep rate. When the sweep rate was decreased from 50 to
5 mV/s (Figure 5), the reduction wave g at -0.69 V gradually
disappeared and a new small wave f grew at ca. -0.25 V. At
the same time, the oxidation wave a + b was gradually separated
into two waves, a and b.
[ZnCl3(MeCN)]- in 2, the anion was substituted by BF4 and
-
[{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)(µ,η2-S2)](BF4) (6) was used
for the following measurement.
The cyclic voltammogram of 6 measured in MeCN at a sweep
rate of 50 mV/s is shown in Figure 3. In the first anodic sweep,
an oxidation wave (a + b) was observed at 0.07 V (all the
potentials are referenced to Fe(C5H5)2/Fe(C5H5)2+), whereas in
the following cathodic sweep, two smaller reduction waves
appeared at 0.01 V (e) and -0.69 V (g). When the sweep rate
was increased to 0.5 V/s (Figure 4), another oxidation peak c
(12) Bolinger, C. M.; Rauchfuss, T. B.; Rheingold, A. L. J. Am. Chem.
Soc. 1983, 105, 6321.
(13) Sano, Y. Master Thesis, Waseda University, Tokyo, Japan, 1995.
The above voltammograms suggest the following electro-
chemical behavior of 6 (Scheme 3). At sweep rates lower than

2238 Inorganic Chemistry, Vol. 40, No. 10, 2001
Yoshioka et al.
Scheme 4
in parallel. At sweep rate of 10 V/s, the oxidation proceeds via
two routes, A+ f A2+ f B2+ f B3+ and A+ f A2+ f A3+
.
In the latter route, a portion of the final product A3+ is rapidly
converted to B3+, and therefore, the reverse cathodic sweep starts
with the mixture of A3+ and B3+. The reduction of A3+ is via
either A3+ f A2+ f A+ or A3+ f A2+ f B2+ f B+ f A+,
and the reduction of B3+ is via B3+ f B2+ f B+ f A+. The
fact that the wave g is slightly larger than e at a sweep rate of
10 V/s indicates that the two reduction routes A3+ f A2+
B2+ and B3+ f B2+ merge at the process g.
f
Figure 5. Cyclic voltammograms of [{Ru(MeCN)(P(OMe)3)2}2(µ-Cl)-
(µ,η2-S2)](BF4) (6) at sweep rate from 5 to 30 mV/s.
At sweep rates lower than 50 mV/s (Figure 5), waves a and
b correspond to processes a and b in Scheme 3, respectively,
and the broad cathodic wave at f corresponds to the reverse
reaction of process a, i.e., A2+ f A+. This shows that at very
slow sweep rates, rearrangement of B2+ to A2+ can proceed to
Scheme 3
some extent, and therefore, the reduction routes B3+ f B2+
f
A2+ f A+ and B3+ f B2+ f B+ f A+ proceed in parallel.
The fact that wave g decreases as wave f becomes more
discernible supports the above assignment.
Apparently, the conversion between A2+ and B2+ is reversible
and the conversion rate from A2+ to B2+ is rapid, while the
reverse reaction is very slow. At medium to rapid sweep rates,
B
2+ is further reduced to B+ before B2+ isomerizes to A2+. This
is the reason for the disappearance of wave g at very low sweep
rates.
Since no direct evidence is yet obtained for the structures of
the intermediates A2+ and B2+, it is also possible that either or
both of these intermediates have the disulfide ligand in the
unsymmetric η1,η2 mode. But this is less possible because the
redox steps a-g are apparently much more rapid than the
isomerization processes, and therefore, it is more probable to
assign the structures of A2+ and B2+ as those in Scheme 3.
1 V/s, A+ is one-electron-oxidized to A2+ (process a), which is
followed by the rearrangement of the disulfide ligand from η2
to η1, giving B2+. The species B2+ is further oxidized to B3+
(process b) at almost the same potential as that of process a.
This process from A+ to B3+ is an ECE process.14 At higher
sweep rates, oxidation of A+ to A3+ becomes conspicuous via
processes a and c, and A3+ thus formed undergoes disulfide
rearrangement to give B3+. While this process is dominant at
higher sweep rates, the same process (wave c) is still observed
as a minor path even at a sweep rate as low as 30 mV/s. Since
the sweep rate is so high, process c takes place before the
rearrangement from A2+ to B2+ occurs.
In the cathodic sweep, the reduction wave e at ca. 0.0 V
corresponds to the reduction of B3+ to B2+ (process e), and the
reduction wave g at ca. -0.7 V is the reduction of B2+ to B+
(process g). Conversion of the disulfide ligand in B+ from η1
to η2 recovers the starting species A+. On increase of the sweep
rate, a broad wave d appears at ca. 0.2 V, which corresponds to
the reduction of A3+ to A2+. This wave at ca. 0.2 V appears
because at these high sweep rates, conversion of A3+ to B3+
does not proceed completely and reduction of A3+ takes place
To confirm the existence of B3+ in the electrochemical
process, B3+(CF3SO3)-3 (7) was chemically prepared by removal
of three chlorides from 1 by using Me3SiO3SCF3 (Scheme 4),
and cyclic voltammetry measurements were taken. The voltam-
mogram of 7 was almost the same with that of 6, which supports
the above electrochemical scheme. To further confirm the
process in Scheme 3, bulk electrolysis of 6 was carried out at
0.5 V. Although it had been expected that 2 F/mol would be
consumed in the bulk electrolysis, less than 1 F/mol was
consumed even after 3 h. The ESR spectrum (g ) 2.05) and
the UV-vis spectrum (λmax ) 703 nm) of the resulting solution
suggested that [{Ru(MeCN)(P(OMe)3)2}(µ-Cl)2(µ,η1-S2)]+ (5)
is formed instead of the expected species B3+ in solution. This
observation can be rationalized as follows (Scheme 5). After
the formation of a small amount of B3+ (RuIIIRuIII) by the
electrolysis, B3+ reacts with remaining 6 (A+(BF4)-, RuIIRuII),
giving the previously reported complexes [{Ru(MeCN)-
(P(OMe)3)2}(µ-Cl)2(µ,η1-S2)]+ (5, RuIIRuIII) and [{Ru(MeCN)3-
(P(OMe)3)2}(µ,η1-S2)]3+ (8, RuIIRuIII).7b The cyclic voltammo-
gram of a 1:1 mixture solution of 6 (A+(BF4)-) and 7
(B3+(CF3SO3)-3) was similar to that of the bulk electrolysis
solution. Because there was no indication of the existence of 5
(14) (a) Heinze, J. Angew. Chem., Int. Ed. Engl. 1984, 23, 831. (b) Bard,
A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and
Applications; Wiley: New York, 1980; Chapter 11.

Conversion of Disulfide Ligands
Inorganic Chemistry, Vol. 40, No. 10, 2001 2239
Scheme 5
The whole electrochemical behavior indicates that the RuII-
RuII species (A+) prefers the η2 structure and that the RuIIIRuIII
species (B3+) prefers the η1 one. For the RuIIRuIII species, A2+
and B2+ convert to each other, and there is an equilibrium
between them. This tendency in the coordination mode of the
disulfide ligand is in accordance with the results of the chemical
redox reactions in which the RuIIRuII species prefers the η2 mode
and the RuIIIRuIII species the η1 one.
Acknowledgment. We are grateful to the financial support
by CREST (Core Research for Evolutional Science and Tech-
nology) of the Japan Science and Technology Corporation.
Supporting Information Available: An X-ray crystallographic file
for the structure determination of 3 and X-ray crystallographic files in
CIF format for the structure determinations of 2 and 4. This material
is available free of charge via the Internet at http://pubs.acs.org.
or 8 in the cyclic voltammogram of 6 (vide supra), the above
reaction between 6 and 7 must be slow compared to the potential
sweep rates.
IC000392A