Addition and/or oxidation in the reaction of a tricobalt cluster with silver(I) salts: Synthesis, structure and solution properties of [Co3Cp3(μ3-CPh)2 {μ-Ag(X)}] (X=CF3CO2, NO3) and [Co3Cp3(μ3-CPh)2 {μ-Ag(NCMe)}]PF6

Article abstract of DOI:10.1016/j.jorganchem.2003.09.042

Reactions of the benzylidyne-capped tricobalt cluster [Co₃ Cp₃(μ₃-CPh)₂] (1) with various silver salts have been examined. The salts of weakly- or non-coordinating anions (e.g., BF₄^- and PF₆^-) oxidize 1 in CH₂Cl₂ to form its cationic radical, 1⁺. Reactions with salts of strongly coordinating anions (e.g., CF₃CO₂ ^- and NO₃^-) yield the silver(I) adducts of 1, [Co₃Cp₃(μ₃-CPh) ₂{μ-Ag(X)}] (for X=CF₃CO₂ ^-: 2 and NO₃^-: 3). Even with AgBF₄ or AgPF₆, the reaction in MeCN produces a silver(I) adduct, [Co₃Cp₃(μ₃-CPh) ₂{μ-Ag(NCMe)}]⁺ (4⁺). The Co₃Ag skeleton in the structures of 2, 3, and 4⁺ is similar in each compound. The Co-Co bond bridged by the Ag atom (for 2, Co-Co=2.4785(8) A?, for 3, Co-Co=2.4837(9) A?, and for 4⁺, Co-Co=2.4578(7) A?) is longer than the average Co-Co bond length in 1 where 〈Co-Co〉 _av=2.382(8) A?. The other Co-Co bonds in the compounds are slightly shorter than those in 1. The Co₂Ag triangle is not coplanar with the Co₃ triangle; the dihedral angles between these triangles for 2, 3 and 4⁺ are 162.7°, 157.7°, and 151.6°, respectively. Dissolution of 4PF₆ in CH₂Cl₂ leads to the formation of 1⁺ and the deposition of Ag metal. The ¹H NMR spectra of 2 and 3 in CD₂Cl₂ indicate that the AgX group moves over the three Co-Co bonds. The ESR spectra in frozen acetonitrile solutions of 2, 3, and 4PF₆ show the existence of a small amount of 1⁺, but the deposition of Ag metal was not observed.

Full text of DOI:10.1016/j.jorganchem.2003.09.042

Journal of Organometallic Chemistry 689 (2004) 146–153
www.elsevier.com/locate/jorganchem
Addition and/or oxidation in the reaction of a tricobalt cluster
with silver(I) salts: synthesis, structure and solution properties
of [Co3Cp3(l3-CPh)2{l-Ag(X)}] (X ¼ CF3CO2, NO3)
and [Co3Cp3(l3-CPh)2{l-Ag(NCMe)}]PF6
*
Masahiro Ebihara, Masami Iiba, Hiroaki Matsuoka, Chie Okuda, Takashi Kawamura
Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan
Received 21 August 2003; accepted 29 September 2003
Abstract
Reactions of the benzylidyne-capped tricobalt cluster [Co3Cp3(l3-CPh)2] (1) with various silver salts have been examined. The
salts of weakly- or non-coordinating anions (e.g., BF4ꢀ and PF6ꢀ) oxidize 1 in CH2Cl2 to form its cationic radical, 1þ. Reactions
with salts of strongly coordinating anions (e.g., CF3COꢀ2 and NO3ꢀ) yield the silver(I) adducts of 1, [Co3Cp3(l3-CPh)2{l-Ag(X)}]
(for X ¼ CF3COꢀ2 : 2 and NO3ꢀ: 3). Even with AgBF4 or AgPF6, the reaction in MeCN produces a silver(I) adduct, [Co3Cp3(l3-
CPh)2{l-Ag(NCMe)}]þ (4þ). The Co3Ag skeleton in the structures of 2, 3, and 4þ is similar in þeach compound. The Co–Co bond
ꢀ
ꢀ
ꢀ
bridged by the Ag atom (for 2, Co–Co ¼ 2.4785(8) A, for 3, Co–Co ¼ 2.4837(9) A, and for 4 , Co–Co ¼ 2.4578(7) A) is longer
ꢀ
than the average Co–Co bond length in 1 where hCo–Coiav ¼ 2.382(8) A. The other Co–Co bonds in the compounds are slightly
shorter than those in 1. The Co2Ag triangle is not coplanar with the Co3 triangle; the dihedral angles between these triangles for 2,
3 and 4þ are 162.7°, 157.7°, and 151.6°, respectively. Dissolution of 4PF6 in CH2Cl2 leads to the formation of 1þ and the de-
position of Ag metal. The 1H NMR spectra of 2 and 3 in CD2Cl2 indicate that the AgX group moves over the three Co–Co
bonds. The ESR spectra in frozen acetonitrile solutions of 2, 3, and 4PF6 show the existence of a small amount of 1þ, but the
deposition of Ag metal was not observed.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Trinuclear clusters; Silver complexes; Cobalt complexes; Metal–metal bonds; X-ray structure analyses
1. Introduction
M–Ag bonds are regarded as being intermediates in the
electron-transfer reaction between M and Agþ [3]. We
have investigated the electronic structures of Group 9
trinuclear clusters with l3-benzylidyne ligands,
[M3Cp3(l3-CPh)2] (where M ¼ Co or Rh) [4–6]. We at-
tempted to isolate the salts of 1þ by oxidizing 1 with
silver(I) salts. However, we obtained not only 1þ, but
also silver(I) adducts of 1, depending on the counter
anion and the solvent used. In this paper, we describe
the synthesis and X-ray structure of the silver(I) ad-
ducts: 2, 3, and 4PF6. The 1H NMR spectra of 2 and 3 in
dichloromethane indicate that the AgX moiety migrates
over the Co–Co bonds with moderate rates. In aceto-
nitrile solution of 2, 3, and 4PF6, there is an equilibrium
involving 1þ.
Silver(I) salts are one of the most popular reagents in
coordination chemistry. They are used for halogen ab-
straction and as an oxidant for compounds with low to
moderate oxidation potentials. These oxidation poten-
tials depend on the counter anions and solvents [1]. In
cluster chemistry, univalent Group 11 metal ions have
been used to synthesize higher-nuclearity clusters [2]. In
some cases, Group 11 metals bound to the metal–metal
bond, similar to a proton. Sometimes complexes with
* Corresponding author. Tel.: +81-58-293-2567; fax: +81-58-230-
1893.
E-mail address: kawamura@apchem.gifu-u.ac.jp (T. Kawamura).
0022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.09.042

M. Ebihara et al. / Journal of Organometallic Chemistry 689 (2004) 146–153
147
2. Experimental
temperature, the solution was filtered and evaporated to
dryness. LiPF6 (0.28 g, 1.8 mmol) in MeCN (20 ml) was
added to the residue, and the solution was stirred for 5
min. The brown solid obtained by evaporation was
washed with water, and recrystallized by slow diffusion
of diethylether into its MeCN solution. Yield: 0.060 g
(36%). Anal. Calc. for C31H28AgCo3F6NP: C, 44.11; H,
3.34; N, 1.66. Found: C, 44.21; H, 3.26; N, 1.59%.
2.1. General
Dichloromethane, n-hexane, and acetonitrile were
distilled over CaH2 before use, and the silver salts were
dried under vacuum before use. The starting material 1,
was synthesized using the literature method of Fritch
and Vollhardt [7], and purified by recrystallization from
n-hexane.
2.6. X-ray structure determination
2.2. Measurements
Crystals of 2 were obtained by slow evaporation from
a CH2Cl2/n-hexane solution. Complex 3 was crystallized
by slow diffusion of n-hexane into a CH2Cl2 solution.
Crystals of 4PF6 were obtained by vapor diffusion of
diethylether into an MeCN/diethylether solution. The
X-ray intensity data were collected on a Rigaku AFC7R
diffractometer employing graphite-monochromated Mo
1
The H and 13C NMR spectra were measured on a
ꢀ
JEOL a-400 spectrometer. Deuterated solvents over 4 A
molecular sieves that were degassed using several freeze–
pump–thaw cycles were transferred to J. Youngâ NMR
tubes before use on a vacuum line. The ESR data were
measured on a JEOL TE-200X ESR spectrometer. ESR
spectra were digitalized and integrated by using a Rad-
ical Research Win-RAD ESR Data analyzer.
ꢀ
Ka radiation (k ¼ 0.71069 A). The cell dimensions were
determined using the least-squares refinement of the
diffractometer angles for 25 automatically centered re-
flections. The scattering factors for the neutral atoms
were obtained from Cromer and Waber [8], using
anomalous dispersion [9]. The positions of the metal
atoms were determined by a direct method employing
the SHELXS 86 [10] package. The structures were ex-
panded using the DIRDIF [11] software, and refined
using a full matrix least-squares method by the teXsanâ
crystallographic software package [12]. An empirical
absorption correction based on six azimuthal scans was
applied for 2 [13]. An analytical absorption correction
[14] was applied for 3 and 4PF6. The final least-squares
cycle included non-hydrogen atoms, with the aniso-
tropic thermal parameters and hydrogen atoms main-
tained at fixed positions using isotropic thermal
parameters that were 1.2 times those of the connected
atoms. The crystal data and description of the structure
refinement are summarized in Table 1.
2.3. Preparation of [Co3Cp3(l3-CPh)2{l-Ag(O2CCF3)}]
(2)
AgO2CCF3 (0.15 g, 0.68 mmol) was added to a
CH2Cl2 solution (50 ml) of 1 (0.35 g, 0.64 mmol). After
stirring for 24 h, the solution was filtered and evapo-
rated to dryness. The resulting brown solid was washed
with n-hexane and recrystallized from CH2Cl2/n-hexane.
Yield: 0.40 g (82%). Anal. Calc. for C31H25AgCo3F3O2:
C, 48.28; H, 3.27. Found: C, 48.00; H, 3.21%. 1H NMR
(CD2Cl2, at )60 °C): d 4.76 (10H, s, AgCoCp), 4.96 (5H,
s, CoCp), 7.34 (2H, m, p-Ph), 7.40 (4H, m, m-Ph), 7.79
(4H, m, o-Ph).
2.4. Preparation of [Co3Cp3(l3-CPh)2{l-Ag(NO3)}]
(3)
AgNO3 (0.12 g, 0.71 mmol) was added to a CH2Cl2
solution (70 ml) of 1 (0.39 g, 0.71 mmol). After stirring
for 24 h at room temperature, the solution was filtered
and evaporated to dryness. The resulting brown solid
was washed with n-hexane and recrystallized from
CH2Cl2/n-hexane. Yield: 0.40 g (81%). Anal. Calc. for
C29H25AgCo3NO3: C, 48.36; H, 3.50; N 1.94. Found: C,
48.22; H, 3.32; N 1.99%. 1H NMR (CD2Cl2, at )20 °C):
d 4.76 (10H, s, AgCoCp), 4.99 (5H, s, CoCp), 7.36 (2H,
m, p-Ph), 7.42 (4H, m, m-Ph), 7.85 (4H, m, o-Ph).
3. Results and discussion
3.1. Reaction of 1 with silver(I) salts
The reaction of 1 with various silver(I) salts yields
two types of isolated product: the salts of the cationic
radical 1þ and the adducts of silver salts. In a previous
paper, we reported on the structure of 1ClO4 prepared
by the electrochemical oxidation of 1 [4]. This salt was
also isolated from the reaction of 1 with AgClO4 in
CH2Cl2. ESR spectra of solutions of 1 mixed with suf-
ficient amounts of other silver salts of weakly or non-
coordinating anions, e.g., PFꢀ6 , SbF6ꢀ, and BF4ꢀ, in
CH2Cl2 showed that 1þ is quantitatively formed. The
reaction of 1 with salts of strongly coordinating anions,
e.g., CF3COꢀ2 and NO3ꢀ, in CH2Cl2 does not show any
2.5. Preparation of [Co3Cp3(l3-CPh)2{l-Ag(NCMe)}]
PF6 (4PF6)
A CH2Cl2 solution (30 ml) of 1 (0.11 g, 0.20 mmol)
was added to an MeCN solution (30 ml) of AgBF4 (0.10
g, 0.51 mmol) with stirring. After 1 h of stirring at room

148
M. Ebihara et al. / Journal of Organometallic Chemistry 689 (2004) 146–153
Table 1
Crystal data and refinement description
2
3
4PF6
Chemical formula
Molecular weight
Crystal size (mm)
Space group
C31H25AgCo3F3O2
771.2
C29H25AgCo3NO3
720.19
C31H28AgCo3F6NP
844.20
0.35 ꢁ 0.30 ꢁ 0.30
P21=n (no. 14)
12.296(1)
17.607(1)
12.866(1)
91.351(7)
2784.9(3)
4
0.25 ꢁ 0.15 ꢁ 0.10
P21=c (no. 14)
8.730(2)
16.806(5)
17.248(3)
96.21(2)
2515.7(10)
4
0.66 ꢁ 0.17 ꢁ 0.09
P21=c (no. 14)
18.315(1)
8.790(2)
19.097(2)
95.922(6)
3058.0(7)
4
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
b (°)
V (A )
3
ꢀ
Z
d (calcd) (g cmꢀ3
)
1.839
2.495
1.901
2.742
1.833
2.341
l (mmꢀ1
)
T (°C)
2h limit (°)
Reflection measured
23
55
23
55
23
55
6919
6404
8600
5742
14969
7027
Reflection unique
Reflections with I > 2rðIÞ
4212
0.046, 0.104
1.45
3303
0.041, 0.100
1.47
4229
0.037, 0.086
1.32
a
R1, Rw
GOF
h
.
i
1=2
ꢀ
ꢁ
ꢀ
ꢁ
P
P
P
P
a R1 ¼ jjFoj ꢀ jFcjj= jFoj for reflections with I > 2rðIÞ, Rw
¼
w Fo2 ꢀ Fc2
w Fo2
for all data.
2
2
deposition of Ag metal, and X-ray structure analysis of
the products reveals that they are the silver salt adducts,
2 and 3. The cationic radical could not be isolated by
reaction in MeCN, even with AgBF4. The cationic Ag-
adduct 4þ was isolated as the PFꢀ6 salt by addition of
excess LiPF6 to the solution.
summarized in Table 2. The silver atom coordinated by
the oxygen atoms of the trifluoroacetate ion bridges
between two of the three cobalt atoms. The structure of
3 and 4PF6 are shown in Figs. 2 and 3, respectively, and
their selected bond distances and angles are listed in
Tables 3 and 4, respectively. The structure of 3 is quite
similar to that of 2. In the structure of 4PF6, the Agþ ion
is coordinated by a single MeCN molecule, and not by
the PFꢀ6 ions. The Ag atom in each structure is located
out of the Co3 plane with a dihedral angle of 151.6°–
162.7° between the Co3 and the Co2Ag planes.
3.2. X-ray structural analysis
Fig. 1 shows an ORTEP drawing of 2 including the
atom numbering. Selected bond distances and angles are
ꢀ
The Ag–Co bond lengths are 2.6150(7)–2.6572(6) A
in 2, 3 and 4þ, respectively. These are similar to those of
other complexes with Ag–Co bonds, e.g., 2.589(1)–
ꢀ
2.594(1) A in [{Co(CO)4}4(l-Ag)4] [15] and 2.600(2)–
F(1)
F(3)
ꢀ
2.724(2) A in [{Co(CNC6H3Me2)4}3Ag3] [16]. The
ꢀ
Co(Ag)–Co(Ag) distances (2.4785(8) A for 2, 2.4837(9)
þ
ꢀ
ꢀ
C(2)
C(1)
O(1)
A for 3, and 2.4578(7) A for 4 ) are elongated, and the
Co–Co(Ag) bonds are slightly shortened from the av-
erage Co–Co distance in the parent tricobalt cluster 1
C(31)
C(30)
Co(1)
Co(3)
ꢀ
(2.382(8) A) [4]. The elongation of the M–M bond by
F(2)
O(2)
Ag(1)
Co(2)
the addition of Group 11 metal ions to the M–M edge of
the trimetal clusters has also observed in [Ru3(CO)9(l3-
C2Bu){l-M0(PPh3)}] (where M0 ¼ Cu, Ag, and Au) [17],
in [Fe3(CO)9(l3-SPri){l-Au(PPh3)}] [18,19], and in
[Fe3(CO)9(l3-Te){l-Au(PPh3)}]ꢀ [20]. In all these clus-
ters, the M0-atom-bridged M–M bonds are elongated by
C(8)
C(9)
ꢀ
0.1–0.2 A, which are similar to those of the present Ag-
bridged complexes. For M3(l-M0) complexes (where
M ¼ Fe, Co, Ru, Os, and Ir; and M0 ¼ Cu, Ag, and Au)
the dihedral angles between the M3 and M2M0 triangles
are in the range of 110°–176° [17,19–22]. A complex with
two capping ligands, [CoFe2(CO)6(Cp)(l3-CO)(l3-
Fig. 1. ORTEP drawing of 2 with 30% probability. Hydrogen atoms
are omitted for clarity.

M. Ebihara et al. / Journal of Organometallic Chemistry 689 (2004) 146–153
149
Table 2
ꢀ
Selected bond distances (A) and bond and dihedral angles (°) of [Co3Cp3(l3-CPh)2{l-Ag(O2CCF3)}] (2)
Bond distances
Ag(1)–Co(1)
Ag(1)–Co(2)
Ag(1)–O(1)
Ag(1)–O(2)
Co(1)–Co(2)
Co(1)–Co(3)
Co(1)–C(1)
Co(1)–C(8)
Co(2)–Co(3)
2.6150(7)
2.6276(7)
2.351(4)
2.719(7)
2.4785(8)
2.3742(8)
1.868(4)
1.875(4)
2.3575(8)
Co(2)–C(1)
Co(2)–C(8)
Co(3)–C(1)
Co(3)–C(8)
O(1)–C(30)
O(2)–C(30)
C(1)–C(2)
C(8)–C(9)
1.890(4)
1.879(4)
1.870(4)
1.868(4)
1.210(7)
1.205(6)
1.467(6)
1.463(6)
Bond angles
Co(1)–Ag(1)–Co(2)
Ag(1)–Co(1)–Co(2)
Ag(1)–Co(2)–Co(1)
56.43(2)
62.04(2)
61.53(2)
Co(2)–Co(1)–Co(3)
Co(1)–Co(2)–Co(3)
Co(1)–Co(3)–Co(2)
58.08(2)
58.74(2)
63.17(2)
Dihedral anglesa
Plane 1
Co3
plane 2
Co2Ag
CpCo(2)
plane 1
CpCo(1)
CpCo(2)
plane 2
CpCo(3)
CpCo(3)
162.7
29.9
71.4
79.4
CpCo(1)
a CpCo(x) denotes the plane of the cyclopentadienyl ligand bonded to Co(x).
COMe){l-Au(PPh3)}], shows a dihedral angle value of
155.4° [22], which is similar to those of the current
complexes.
trifluoroacetate group in [Rh2Cp2(l-CO)(l-Ph2PCH2
PPh2){l-Ag(O2CCF3)}] is a bidentate ligand with Ag–O
ꢀ
distances of 2.522(9) A [23], which are close to the av-
In the structure of 2, the trifluoroacetate group is
non-symmetrically connected to the Ag atom, with the
ꢀ
two Ag–O distances being 2.351(4) and 2.719(7) A. The
erage Ag–O bond distances of 2. The nitrate ion in 3
chelates with the Ag atom. The difference between the
ꢀ
two Ag–O bond distances in 3 (DAgO ¼ 0.194 A) is
ꢀ
smaller than that observed in 2 (DAgO ¼ 0.368 A).
O(3)
N(1)
C(31)
O(2)
C(2)
C(30)
O(1)
N(1)
Ag(1)
C(1)
Ag(1)
Co(3)
Co(2)
C(8)
Co(1)
Co(2)
C(8)
C(9)
C(2)
C(1)
Co(1)
Co(3)
C(9)
Fig. 2. ORTEP drawing of 3 with 30% probability. Hydrogen atoms
are omitted for clarity.
Fig. 3. ORTEP drawing of 4PF6 with 30% probability. Hydrogen at-
oms are omitted for clarity.

150
M. Ebihara et al. / Journal of Organometallic Chemistry 689 (2004) 146–153
Table 3
ꢀ
Selected bond distances (A) and bond and dihedral angles (°) of [Co3Cp3(l3-CPh)2{l-Ag(NO3)}] (3)
Bond distances
Ag(1)–Co(1)
Ag(1)–Co(2)
Ag(1)–O(1)
Ag(1)–O(2)
Co(1)–Co(2)
Co(1)–Co(3)
Co(1)–C(1)
Co(1)–C(8)
Co(2)–Co(3)
2.6483(8)
2.6449(8)
2.374(5)
2.568(5)
2.4837(9)
2.3684(9)
1.881(5)
1.882(5)
2.3662(9)
Co(2)–C(1)
Co(2)–C(8)
Co(3)–C(1)
Co(3)–C(8)
O(1)–N(1)
O(2)–N(1)
O(3)–N(1)
C(1)–C(2)
C(8)–C(9)
1.893(5)
1.865(5)
1.891(5)
1.866(5)
1.229(7)
1.230(6)
1.227(6)
1.470(7)
1.478(7)
Bond angles
Co(1)–Ag(1)–Co(2)
Ag(1)–Co(1)–Co(2)
Ag(1)–Co(2)–Co(1)
55.97(2)
61.95(2)
62.08(2)
Co(2)–Co(1)–Co(3)
Co(1)–Co(2)–Co(3)
Co(1)–Co(3)–Co(2)
58.32(3)
58.40(3)
63.28(3)
Dihedral anglesa
Plane 1
Co3
plane 2
Co2Ag
CpCo(2)
plane 1
CpCo(1)
CpCo(2)
plane 2
CpCo(3)
CpCo(3)
157.7
30.1
76.9
74.3
CpCo(1)
a CpCo(x) denotes the plane of the cyclopentadienyl ligand bonded to Co(x).
3.3. Equilibrium of the Ag adducts in solution
Its frozen solution at 77 K showed a weak broad axially
symmetric ESR signal of g ¼ 2.22 and g ¼ 2.11. This g
?
k
The stabilities and the conversion to 1þ of the silver
adducts in solution depend strongly on the solvents.
tensor is the same as that of 1þ in MeCN with 0.1 M
nBu4NClO4 (M ¼ mol dmꢀ3) [4]. An MeCN solution of
2 showed the same ESR spectrum, but with slightly
weaker intensity. Comparison of integrated intensities of
ESR signals of 2 and 4PF6 in MeCN with that of 1þ in
MeCN containing 0.1 M nBu4NClO4 revealed that 1–2%
of 2 and 4PF6 converts to 1þ in MeCN solutions.
3.3.1. ESR study
Dissolution of 4PF6 in CD2Cl2 showed deposition of
Ag metal. A broad isotropic singlet ESR signal of
g ¼ 2.19 was observed at 77 K for the resulting solution.
It is the same as the signal of 1ClO4 in CH2Cl2 at 77 K
[4]. The integrated intensity of the signal indicates that
the silver adduct converted quantitatively to the cation
radical, 1þ. On the other hand, a CH2Cl2 solution of 2
showed neither deposition of Ag metal nor ESR signal.
Contrary to the behavior in CD2Cl2, complex 4PF6
dissolves into MeCN with no deposition of silver metal.
1
3.3.2. H NMR study in CD2Cl2
1
Fig. 4 shows the H NMR spectra of 2 (9 mM) in
CD2Cl2. At )60 °C, two singlet peaks assigned to the
cyclopentadienyl groups were observed at 4.76 ppm
(10H) and 4.99 ppm (5H). Their intensity ratio shows
that the former and the latter signals are due to the
Table 4
ꢀ
Selected bond distances (A) and bond and dihedral angles (°) of [Co3Cp3(l3-CPh)2{l-Ag(NCMe)}]PF6 (4PF6)
Bond distances
Ag(1)–Co(1)
Ag(1)–Co(2)
Ag(1)–N(1)
Co(1)–Co(2)
Co(1)–Co(3)
Co(1)–C(1)
Co(1)–C(8)
2.6572(6)
2.6330(6)
2.168(4)
2.4578(7)
2.3612(7)
1.891(4)
1.872(4)
Co(2)–Co(3)
Co(2)–C(1)
Co(2)–C(8)
Co(3)–C(1)
Co(3)–C(8)
C(1)–C(2)
2.3812(7)
1.891(4)
1.872(4)
1.873(4)
1.862(4)
1.481(5)
1.473(5)
C(8)–C(9)
Bond angles
Co(1)–Ag(1)–Co(2)
Ag(1)–Co(1)–Co(2)
Ag(1)–Co(2)–Co(1)
55.37(2)
61.82(2)
62.82(2)
Co(2)–Co(1)–Co(3)
Co(1)–Co(2)–Co(3)
Co(1)–Co(3)–Co(2)
59.18(2)
58.39(2)
62.43(2)
Dihedral anglesa
Plane 1
Co3
plane 2
Co2Ag
CpCo(2)
plane 1
CpCo(1)
CpCo(2)
plane 2
CpCo(3)
CpCo(3)
151.6
33.9
76.0
71.8
CpCo(1)
a CpCo(x) denotes the plane of the cyclopentadienyl ligand bonded to Co(x).

M. Ebihara et al. / Journal of Organometallic Chemistry 689 (2004) 146–153
151
Table 5
1H NMR chemical shift (ppm) for 2, 3, and 4PF6 in CD2Cl2 and
CD3CNa
Complex Temperature (°C) o-Ph m-Ph p-Ph Cp
In CD2Cl2
2
20
)60
)20
7.90 7.44
7.81 7.40
7.85 7.42
7.39
7.34
7.36
4.83
4.76, 4.99
4.76, 4.99
3
In CD3CN
2
20
)40
20
7.98 7.47
7.98 7.43
7.88 7.50
7.75 7.52
8.30 7.53
)7.77 9.67
7.27
7.35
7.20
7.07
7.43
4.62
4.71
4.55
4.44
4.46
3
4PF6
1b
20
20
b
1ClO4
20
)8.43 )5.72
a Concentration of the sample is 9–11 mM in CD2Cl2 and 5–7 mM in
CD3CN.
b Ref. [4].
4PF6 (5 mM) in CD3CN at 20 °C. In the Cp region,
there is a singlet peak at 4.44 ppm. The single peak of
the Cp ligands suggests that there is a rapid exchange
equilibrium between 1þ and 4þ. The peaks of the phenyl
protons exist as broad singlets for o-Ph (7.75 ppm) and
p-Ph (7.07 ppm), and as a relatively sharp triplet for m-
Ph protons (7.52 ppm). The broadening of the o-Ph and
p-Ph signals and the sharp signal of the m-Ph are also
due to rapid exchange reaction between 1þ and 4þ.
Signals of o-Ph, p-Ph, and m-Ph of 1þ are paramag-
netically shifted and have been observed at )7.77, )8.43,
and 9.67 ppm, respectively, at 20 °C [4]. The difference
of the chemical shift of the m-Ph proton between 1þ and
4þ is far smaller than those of the o-Ph and p-Ph peaks.
This is the origin of the line width differences between m-
Fig. 4. 1H NMR spectra of 2 in CD2Cl2 at: (a) 20 °C, (b) 0 °C, and (c)
)60 °C. The asterisk denotes CHDCl2.
Cp(CoAg) and Cp(Co) protons, respectively. With in-
creasing temperature, these peaks broaden (Fig. 4(b)),
and finally average into a broad singlet peak (Fig. 4(a)).
This result indicates that the bridging Ag atom is mov-
ing over the three Co–Co edges in CD2Cl2 intramolec-
ularly or intermolecularly. Similar fluxional behavior
has been observed in the protonated species of alkyli-
dyne-capped clusters [24–26]. The phenyl groups on the
capping carbon atoms of 2 are non-equivalent due to the
non-planar structure of the Co3Ag core in the crystal.
However, the two phenyl groups are equivalent in the
1H NMR spectrum, even at )60 °C. This should be so,
because the difference in their chemical shifts is smaller
than the rate of jumping of the Ag group between both
the sides of the Co3 plane. The chemical shifts of 3 in
CD2Cl2 are listed in Table 5 together with those of re-
lated complexes. A similar temperature dependence of
1
1
Ph and o- and p-Ph H signals. The H NMR and the
ESR spectra showed no detectable changes upon aging
of the 4PF6 solution. This suggests that the equilibrium
including 1þ is established in solution. Fig. 5(b) shows
1
the H NMR spectra was observed for 3.
1
3.3.3. H NMR study in CD3CN
When dissolved in CH2Cl2, 4PF6 converts quantita-
tively to 1þ with deposition of Ag0. However, the ESR
study in the previous section shows that a small portion
of the silver adduct dissolved in MeCN has converted to
the cationic radical, 1þ. To see the fate of the main
portion of 4PF6 dissolved in acetonitrile, we examine its
Fig. 5. 1H NMR spectra of: (a) 4PF6 and (b) 2 in CD3CN at 20 °C.
The concentrations of the complexes are 5 mM.
1
1H NMR. Fig. 5(a) shows the H NMR spectrum of

152
M. Ebihara et al. / Journal of Organometallic Chemistry 689 (2004) 146–153
Table 6
Qualitative summary of product or equilibrium mixture from the re-
5. Supplementary material
action of [Co3Cp3(l-Ph)2] (1) and silver salta
Crystallographic data (excluding structural factors)
for the structural analysis of 2, 3, and 4PF6 have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC Nos. 217788, 217789, and 217790. Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Ag salt
In CH2Cl2
In MeCN
AgPF6
AgClO4
AgBF4
1þ
[Co3Ag]þ + 1þ
AgO2CCF3
AgNO3
[Co3Ag]þ
[Co3Ag]þ + 1þ
a [Co3Ag]þ represents a Agþ adduct of 1.
the 1H NMR spectrum of 2 in CD3CN. The NMR
spectrum of 2 in CD3CN (Fig. 5(b)) differs from that of
4PF6 (Fig. 5(a)). This shows that the CF3COꢀ2 ion in 2
does not dissociate completely. If the CF3CO2 ligand
bound to the Ag atom of 2 were completely replaced by
MeCN, the NMR spectrum of 2 in acetonitrile must be
the same as that of 4PF6. When the temperature was
lowered to )40 °C, the Cp signal shifted to the lower
field and the peak width broadened. It means that the
rate of the exchange equilibrium including 2 and 1þ is
still rapid at this temperature. A CD3CN solution of 3
Acknowledgements
This work was supported by Grants-in-Aid for Sci-
entific Research from the Ministry of Education, Cul-
ture, Sports, Science and Technology of Japan.
References
[1] N.G. Connelly, W.E. Geiger, Chem. Rev. 96 (1996) 877.
[2] M. Ferrer, R. Reina, O. Rossell, M. Seco, Coord. Chem. Rev.
193–195 (1999) 619.
1
shows similar H NMR spectra to those of 2.
For the MeCN solutions of 2, 3, and 4PF6, deposition
of Ag metal was not observed, although the oxidation of
1 to its cationic radical was detected by ESR (vide su-
pra). Silver ion might be an only possible oxidant in the
solution. We suppose that a soluble Ag0 species is in-
cluded in the equilibrium in the MeCN solution.
Mononuclear silver(0) species should have one odd
electron. However, no such ESR signal was detected in
all the solutions of the Co3Ag complexes. A dinuclear
Ag0 complex with the S ¼ 0 spin state might be a pos-
sible candidate in the equilibrium.
[3] L. Song, W.C. Trogler, Angew. Chem., Int. Ed. Engl. 31 (1992)
770.
[4] M. Ebihara, M. Iiba, M. Kato, H. Minami, T. Kawamura, Inorg.
Chim. Acta, in press.
[5] M. Ebihara, M. Iiba, S. Higashi, N. Tsuzuki, T. Kawamura,
T.Morioka, S. Ozawa, T. Yamabe, H. Masuda, Polyhedron, in
press.
[6] S. Enoki, T. Kawamura, T. Yonezawa, Inorg. Chem. 22 (1983)
3821.
[7] J.R. Fritch, K.P.C. Vollhardt, Angew. Chem., Int. Ed. Engl. 19
(1980) 559.
[8] D.T. Cromer, J.T Waber, in: J.A. Ibers, W.C. Hamilton (Eds.),
International Tables for X-ray Crystallography, vol. IV, The
Kynoch Press, Birmingham, England, 1974, Table 2.2A.
[9] D.C. Creagh, W.J. McAuley, in: A.J.C. Wilson (Ed.), Interna-
tional Tables for X-ray Crystallography, vol. C, Kluwer Academic
Publishers, Boston, MA, 1992, p. 219, Table 4.2.6.8.
[10] G.M. Sheldrick, in: G.M. Sheldrick, C. Kruger, R. Goddard
(Eds.), Crystallographic Computing, vol. 3, Oxford University
Press, Oxford, 1985, p. 175.
4. Concluding remarks
The formation of two types of products (the cationic
radical 1þ and the Ag-adducts), depends on the reduc-
tion potential of the Agþ ion [1]. The oxidation potential
of 1 is )0.05 V versus Fcþ/Fc in CH2Cl2, and )0.06 V
versus Fcþ/Fc in MeCN [4]. In CH2Cl2, Agþ is a rela-
tively strong oxidizing reagent, whose reduction poten-
tial has been estimated as being 0.65 V versus Fcþ/Fc [1].
The Agþ reduction potential is expected to shift to a
negative value when CF3COꢀ2 or NO3ꢀ coordinates to
Agþ, and anion-coordinated Agþ cannot oxidize 1. The
Agþ ion in MeCN is a weaker oxidizing reagent than the
Agþ ion in CH2Cl2, since the Agþ ion is coordinated by
MeCN molecules. Although the formation of 1þ was
detected in MeCN, 1þ is only a minor component in the
equilibrium with the silver adduct. Observed reactions
of 1 with various silver(I) salts in CH2Cl2 and MeCN
are summarized qualitatively in Table 6.
[11] V. Parthasarathi, P.T. Beurskens, H.J.B. Slot, Acta Crystallogr. A
39 (1983) 860.
[12] teXsan: Crystal Structure Analysis Package 1.11, Molecular
Structure Corporation, Woodland, TX, 2000.
[13] A.C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystallogr. A
24 (1968) 351.
[14] J. de Meulenaer, H. Tompa, Acta Crystallogr. 19 (1965) 1014.
€
[15] P. Klufers, Z. Kristallogr. 166 (1984) 143.
[16] P.A. Leach, S.J. Geib, N.J. Cooper, Organometallics 11 (1992)
4367.
[17] T. Adatia, M. McPartlin, I.D. Salter, J. Chem. Soc., Dalton
Trans. (1988) 2889.
[18] A. Winter, L. Zsolnai, G. Huttner, Chem. Ber. 115 (1982) 1286.
[19] E. Delgado, E. Hernandez, O. Rossell, M. Seco, X. Solans,
J. Chem. Soc., Dalton Trans. (1993) 2191.
[20] L.C. Roof, D.M. Smith, G.W. Drake, W.T. Pennington, J.W.
Kolis, Inorg. Chem. 34 (1995) 337.

M. Ebihara et al. / Journal of Organometallic Chemistry 689 (2004) 146–153
153
[21] (a) B.F.G. Johnson, D.A. Kaner, J. Lewis, P.R. Raithby,
J. Organomet. Chem. 215 (1981) C33;
(n) R.A. Brice, S.C. Pearse, I.D. Salter, K. Henrick, J. Chem.
Soc., Dalton Trans. (1986) 2181;
(b) L.W. Bateman, M. Green, J.A.K. Howard, K.A. Mead, R.M.
Mills, I.D. Salter, F.G.A. Stone, P. Woodward, J. Chem. Soc.,
Chem. Commun. (1982) 773;
(o) A.J. Deeming, S. Donovan-Mtunzi, K. Hardcastle, J. Chem.
Soc., Dalton Trans. (1986) 543;
(p) L.J. Farrugia, Acta Crystallogr. C 42 (1986) 680;
(q) M. Ahlgren, T.T. Pakkanen, I. Tahvanainen, J. Organomet.
Chem. 323 (1987) 91;
(c) P. Braunstein, G. Predieri, A. Tiripicchio, E. Sappa, Inorg.
Chim. Acta 113 (1982) 1982;
(d) M. Green, K.A. Mead, R.M. Mills, I.D. Salter, F.G.A. Stone,
P. Woodward, J. Chem. Soc., Chem. Commun. (1982) 51;
(e) L.W. Bateman, M. Green, K.A. Mead, R.M. Mills, I.D.
Salter, F.G.A. Stone, P. Woodward, J. Chem. Soc., Dalton Trans.
(1983) 2599;
(r) C.E. Housecroft, B.F.G. Johns0on, J. Lewis, J.A. Lunniss,
S.M. Owen, P.R. Raithby, J. Organomet. Chem. 409 (1991)
271;
(s) M.I. Bruce, P.A. Humphrey, E. Horn, E.R.T. Tiekink,
B.W. Skelton, A.H. White, J. Organomet. Chem. 429 (1992)
207;
(f) M.I. Bruce, B.K. Nicholson, J. Organomet. Chem. 250 (1983)
627;
(t) J.T. Mague, C.L. Lloyd, Organometallics 11 (1992) 26;
(u) O. Rossell, M. Seco, R. Reina, M. Font-Bardia, X. Solans,
Organometallics 13 (1994) 2127;
(g) K. Burgess, B.F.G. Johnson, J. Lewis, P.R. Raithby, J. Chem.
Soc., Dalton Trans. (1983) 1661;
(h) K. Fischer, M. Muller, H. Vahrenkamp, Angew. Chem., Int.
Ed. Engl. 23 (1984) 140;
(v) C. Cathey, J. Lewis, P.R. Raithby, M.C.R.d. Arellano,
J. Chem. Soc., Dalton Trans. (1994) 3331;
(i) G. Lavigne, F. Papageorgiou, J.-J. Bonnet, Inorg. Chem. 23
(1984) 609;
(w) M.C. Comstock, T. Prussak-Wieckowska, S.R. Wilson, J.R.
Shapley, Organometallics 16 (1997) 4033.
(j) M.I. Bruce, O.B. Shawkataly, B.K. Nicholson, J. Organomet.
Chem. 286 (1985) 427;
[22] A.A. Aitchison, L.J. Farugia, Organometallics 5 (1986) 1103.
[23] G. Bruno, S. Lo Sciavo, E. Rotondo, P. Piraino, F. Faraone,
Organometallics 6 (1987) 2502.
(k) S. Attali, F. Dahan, R. Mathieu, J. Chem. Soc., Dalton Trans.
(1985) 2521;
[24] D.E. Van Horn, K.P.C. Vollhardt, J. Chem. Soc., Chem.
Commun. (1982) 203.
(l) M.I. Bruce, E. Horn, J.G. Matisons, M.R. Snow,
J. Organometal. Chem. 286 (1985) 271;
[25] K.P.C. Vollhardt, M. Wolfgruber, Angew. Chem., Int. Ed. Engl.
25 (1986) 929.
[26] H. Wadepohl, H. Pritzkow, Polyhedron 8 (1989) 1939.
(m) M.I. Bruce, M.L. Williams, J.M. Patrick, B.W. Skelton, A.H.
White, J. Chem. Soc., Dalton Trans. (1986) 2557;