Intramolecular electron transfer in mixed-valence biferrocenium salts containing heteroatoms: Preparation, structure, and 57Fe m?ssbauer characteristics

Article abstract of DOI:10.1021/om970746e

A convenient new method is developed for the preparation of 1′,1?-disubstituted biferrocenes which can be oxidized with iodine to a new series of mixed-valence compounds. The X-ray structures of 1′,1?-dimethoxymethyl, 1′,1?-diethoxyl, 1′,1?-dimethyl, 1′,1?-dihydroxymethyl, 1′,1?-dibenzoyloxymethyl, 1′,1?-dimethylthio, and 1′,1?-diethylthio neutral biferrocenes and the mixed-valence 1′,1?-diethoxyl, 1′,1?-dimethyl, 1′,1?-dibenzoyloxymethyl, and 1′,1?-diphenylthio biferrocenium triiodide salts have been determined at 298 K. The rates of intramolecular electron transfer in these mixed-valence cations were estimated by variable-temperature ⁵⁷Fe M?ssbauer experiment.

Full text of DOI:10.1021/om970746e

5816
Organometallics 1997, 16, 5816-5825
In tr a m olecu la r Electr on Tr a n sfer in Mixed -Va len ce
Bifer r ocen iu m Sa lts Con ta in in g Heter oa tom s:
P r ep a r a tion , Str u ctu r e, a n d 57F e Mo1ssba u er
Ch a r a cter istics
Teng-Yuan Dong,*,1 Chung-Kay Chang,1 Shu-Hwei Lee,1 Long-Li Lai,1
Michael Yen-Nan Chiang,1 and Kuan-J iuh Lin2
Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan, and the
Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan
Received August 20, 1997X
A convenient new method is developed for the preparation of 1′,1′′′-disubstituted bifer-
rocenes which can be oxidized with iodine to a new series of mixed-valence compounds. The
X-ray structures of 1′,1′′′-dimethoxymethyl, 1′,1′′′-diethoxyl, 1′,1′′′-dimethyl, 1′,1′′′-dihy-
droxymethyl, 1′,1′′′-dibenzoyloxymethyl, 1′,1′′′-dimethylthio, and 1′,1′′′-diethylthio neutral
biferrocenes and the mixed-valence 1′,1′′′-diethoxyl, 1′,1′′′-dimethyl, 1′,1′′′-dibenzoyloxymethyl,
and 1′,1′′′-diphenylthio biferrocenium triiodide salts have been determined at 298 K. The
rates of intramolecular electron transfer in these mixed-valence cations were estimated by
variable-temperature 57Fe Mo¨ssbauer experiment.
Ch a r t 1
In tr od u ction
The study of intramolecular electron transfer in
mixed-valence complexes has enabled systematic and
creative investigation into the factors that affect rates
of electron transfer in solution redox processes, solid-
state materials, and biological electron-transfer chain.3-6
In the case of mixed-valence 1′,1′′′-disubstituted bifer-
rocenium triiodide salts (1; Chart 1), considerable
progress has been made in understanding the factors
that control the rate of intramolecular electron transfer
in the solid state.7-19 In the series of mixed-valence
biferrocenium cations (1), the rate of electron transfer
is influenced by various structural factors and lattice
dynamics,7-11 including the electronic and vibronic
coupling between two metal ions,12-15 the nature of the
counterion,16-18 and cation-anion interactions.19 How-
ever, owing to the methodological limitation in the
preparation of the neutral 1′,1′′′-disubstituted bifer-
rocene, not many biferrocenium triiodide salts have been
obtained for electron-transfer studies and the substit-
uents on the 1′,1′′′ position were mostly simple alkyl
groups, halide, or benzyl derivatives. No biferrocenium
triiodide salt containing heteroatoms or a heterocyclic
ring has ever been prepared.
X Abstract published in Advance ACS Abstracts, November 15, 1997.
(1) National Sun Yat-Sen University.
(2) Academia Sinica.
(3) Day, P. Int. Rev. Phys. Chem. 1981, 1, 149.
(4) Brown, D. Mixed-Valence Compounds, Theory and Applications
in Chemistry, Phyiscs, Geology and Biology; Reidel: Boston, MA, 1980.
(5) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.
(6) Richardson, D. E.; Taube, H. Coord. Chem. Rev. 1984, 60, 107.
(7) Cohn, M. J .; Dong, T.-Y.; Hendrickson, D. N.; Geib, S. J .;
Rheingold, A. L. J . Chem. Soc., Chem. Commun. 1985, 1095.
(8) Dong, T.-Y.; Hendrickson, D. N.; Iwai, K.; Cohn, M. J .; Rheingold,
A. L.; Sano, H.; Motoyama, S. J . Am. Chem. Soc. 1985, 107, 7996.
(9) Iijima, S.; Saida, R.; Motoyama, I.; Sano, H. Bull. Chem. Soc.
J pn. 1981, 54, 1375.
To study the influence of the electronic effects of the
substituent on the cyclopentadienyl (Cp) ring, we have
prepared a new series of 1′,1′′′-heterosubstituted bifer-
rocene and their corresponding biferrocenium triiodide
salts. We now show that there is a dramatic difference
in the electron-transfer rate for this new series of
biferrocenium salts. Furthermore, the preparation and
electrochemical measurements for neutral biferrocene
compounds are also presented.
(10) Nakashima, S.; Katada, M.; Motoyama, I.; Sano, H. Bull. Chem.
Soc. J pn. 1987, 60, 2253.
(11) Kai, M.; Katada, M.; Sano, H. Chem. Lett. 1988, 1523.
(12) Dong, T.-Y.; Lee, T. Y.; Lee, S. H.; Lee, G. H.; Peng, S. M.
Organometallics 1994, 13, 2337.
Resu lts a n d Discu ssion
(13) Dong, T.-Y.; Ke, T. J .; Peng, S. M.; Yeh, S. K. Inorg. Chem. 1989,
28, 2103.
(14) Dong, T.-Y.; Hwang, M. Y.; Wen, Y. S. J . Organomet. Chem.
1990, 391, 377.
(15) Dong, T.-Y.; Lee, T. Y.; Lin, H. M. J . Organomet. Chem. 1992,
427, 101.
(16) Dong, T.-Y.; Schei, C. C.; Hsu, T. L.; Lee, S. L.; Li, S. J . Inorg.
Chem. 1991, 30, 2457.
(17) Webb, R. J .; Geib, S. J .; Staley, D. L.; Rheingold, A. L.;
Hendrickson, D. N. J . Am. Chem. Soc. 1990, 112, 5031.
(18) Dong, T.-Y.; Kambara, T.; Hendrickson, D. N. J . Am. Chem.
Soc. 1986, 108, 5857.
Meth od ology. We attempted to develop an alterna-
tive method to synthesize 1′,1′′′-dibromobiferrocene,
which is an important precursor of 1′,1′′′-disubstituted
biferrocenes. A compound of 1′,1′′′-dibromobiferrocene
was previously prepared by the direct bromination of
ferrocene.20 Noteworthy is that 1′,1′′′-dibromobifer-
rocene is the minor product and the yield is quite low
(19) Kambara, T.; Hendrickson, D. N.; Dong, T.-Y.; Cohn, M. J . J .
Chem. Phys. 1987, 86, 2362.
(20) Kovar, R. F.; Rausch, M. D.; Rosenberg, H. Organomet. Chem.
Synth. 1971, 1, 173.
S0276-7333(97)00746-2 CCC: $14.00 © 1997 American Chemical Society

Mixed-Valence Biferrocenium Salts
Organometallics, Vol. 16, No. 26, 1997 5817
Ta ble 2. Exp er im en ta l a n d Cr ysta l Da ta for th e
X-r a y Str u ctu r es of Neu tr a l Bifer r ocen es
Sch em e 1
10
11
14a
C22H22
Fe2S2
462.22
monoclinic triclinic
14b
formula
C22H22
-
C36H30
Fe2O4
638.32
-
-
C24H26-
Fe2S2
490.27
Fe2O2
430.11
monoclinic triclinic
mol wt
cryst syst
space group
a, Å
b, Å
c, Å
Ta ble 1. Exp er im en ta l a n d Cr ysta l Da ta for th e
X-r a y Str u ctu r es of Neu tr a l Bifer r ocen es
P21/c
P1h
P21/n
8.372(2)
12.659(3)
P1h
14.669(2)
7.776(2)
15.627(3)
5.816(2)
8.355(1)
7.300(2)
12.226(4)
12.525(5)
101.25(3)
95.00(3)
90.88(2)
1.491
4
6
8
14.696(2) 9.403(2)
79.87(1)
formula
mol wt
cryst syst
space group
a, Å
C24H26Fe2O2
458.16
C24H26Fe2O2
458.16
monoclinic
P21/n
7.528(1)
14.682(1)
18.423(2)
C22H22Fe2
398.11
tetragonal
P41212
R, deg
â, deg
γ, deg
99.71(1)
87.83(2)
86.58(2)
1.511
701.4(3)
1
1.07
0.710 69
44.9
101.85(3)
orthorhombic
P212121
7.486(4)
16.430(4)
16.331(4)
97.36
1.515
2008.5(12)
4
1.44
0.710 69
49.9
0.032
0.033
F
calcd, g cm-3
1.626
1757.1(5)
4
1.66
0.710 69
1.574
975.3(4)
2
1.704
0.710 69
44.98
0.027
V, Å3
Z
1091.7(6)
2
1.527
0.710 69
44.86
0.038
7.604(2)
b, Å
c, Å
µ, mm-1
λ, Å
29.503(4)
â, deg
F
calcd, g cm-3
1.507
2019.6(4)
4
1.45
0.710 69
44.9
1.550
1705.8(7)
4
1.698
0.710 69
50.0
2θ limits, deg 45.0
V, Å3
a
Rf
0.028
0.036
0.034
0.035
b
Z
Rwf
µ, mm-1
λ, Å
wR2c
0.090
0.098
a
b
Rf ) ∑(||Fo| - |Fc||)/∑|Fo|. Rwf ) ∑[(w(Fo - Fc)2)/∑(wFo2)]1/2
.
2θ limits, deg
c wR2 ) [(∑w(Fo2 - Fc2)2)/(∑wFo2)2]1/2, where w ) 1/[σ2(Fo2) + (fp)2],
p ) (max(Fo2; 0) + 2Fc2)/3, and f ) 0.1000 for 14a and 0.1626 for
14b.
a
Rf
0.031
0.034
0.037
0.042
b
Rwf
a
b
Rf ) ∑(||Fo| - |Fc||)/∑|Fo|. Rwf ) ∑[(w(Fo - Fc)2)/∑(wFo2)]1/2
.
(4%, Scheme 1). We have found that 1′,1′′′-dibromobi-
ferrocene can be prepared easily by direct coupling of
1,1′-dibromoferrocene, using CuCN and oxygen as the
coupling reagent (Scheme 2). The yield was maintained
at 50% after work-up and recrystallization. Reaction
of 1′,1′′′-dibromobiferrocene with 2 equiv of butyllithium
in dry THF led to 1′,1′′′-dithiobiferrocene. The crude
1′,1′′′-dilithiobiferrocene without being isolated was in
situ treated with various electrophilic reagents, and the
Cp rings were, thus, functionalized with various sub-
stituents (Scheme 3).
In our previous paper,21,22 we reported a general
procedure to prepare 1′-substituted 1-bromoferrocene by
using the 1,1′-dibromoferrocene as a precursor. In the
past, 1′,1′′′-disubstituted biferrocenes, for example neu-
tral compounds of 1a -e, were prepared from the cor-
responding 1′-substituted 1-bromoferrocene, which was
prepared by the acylation of bromoferrocene in the
presence of AlCl3 followed by reduction.4 We found that
the monolithioferrocene can be prepared easily and
conveniently by adding stoichiometric amounts of n-
BuLi to a THF solution of 1,1′-dibromoferrocene. Crude
monolithioferrocene obtained in this way can be used
in further electrophilic substitution reactions. Our
method replaces the traditional Fridel-Crafts reaction
for preparing bromoferrocene derivatives. As shown in
Scheme 2, biferrocene 4 is synthesized by this alterna-
tive method.
F igu r e 1. ORTEP drawing of 4.
representative ORTEP drawing for 4 is shown in Figure
1. These neutral compounds exist in a trans conforma-
tion with the two iron ions on opposite sides of the
planar fulvalenide moiety observed for most bifer-
rocenes. The two Cp rings in the fulvalenide moiety are
crystallographically coplanar for compounds 8, 11, 14a ,
and 14b. In the case of 4, 6, and 10, the dihedral angles
between the two Cp rings in the fulvalenide moiety are
2.1(3)°, 3.9(2)°, and 1.6(2)°, respectively. In these
compounds, the substituents are located at the position
above the ring of the other sandwich, as seen in other
dialkyl biferrocenes.
Molecu la r Str u ctu r es of Neu tr a l Bifer r ocen es (4,
6, 8, 10, 11, a n d 14). Details of the X-ray crystal data
collections and unit-cell parameters of neutral bifer-
rocenes are given in Tables 1 and 2. Bond distances
and angles are given as supporting information. The
molecular structures of this series of neutral bifer-
rocenes are also given as Supporting Information. A
(21) Lai, L. L.; Dong, T.-Y. J . Chem. Soc., Chem. Commun. 1994,
2347.
(22) Dong, T.-Y.; Lai, L. L. J . Organomet. Chem. 1996, 509, 131.

5818 Organometallics, Vol. 16, No. 26, 1997
Dong et al.
Sch em e 2
Sch em e 3
As illustrated in Table 3, a direct comparison of the
average Fe-C, Fe-Cp ring, and Fe-fulvalenide (Fe-
ful) ligand distances is made. Inspection of the average
bond distance between the Fe atom and the five carbons
(Fe-C) of a given Cp ring and the average Fe-Cp
distance for a ferrocenyl moiety shows that these values
are closer to the corresponding value observed for
ferrocene23 (2.045 Å for Fe-C and 1.65 Å for Fe-Cp)
than the corresponding value observed for ferrocenium
cation24 (2.075 Å for Fe-C and 1.70 Å for Fe-Cp). The
average C-C bond length in the Cp rings in these
neutral compounds also agrees well with that in fer-
rocene (1.42 Å). In these compounds, the two least-
(23) Seiler, P.; Dunitz, J . D. Acta Crystallogr., Sect. B 1979, 35, 1068.
(24) Mammano, N. J .; Zalkin, A.; Landers, A.; Rheingold, A. L. Inorg.
Chem. 1977, 16, 297.

Mixed-Valence Biferrocenium Salts
Organometallics, Vol. 16, No. 26, 1997 5819
Ta ble 3. Com p a r ison of th e Atom ic Dista n ces (Å)
a n d An gles (d eg)
Ta ble 5. Selected Bon d Dista n ces (Å) a n d Bon d
An gle (d eg)
compd
Fe-Ca
Fe-Cpb Fe-fulc
tad
dae
saf
7
12
Neutral Biferrocene
Bond Distances
2.9255(7)
biferro- 2.052(3) 1.64(2)
cene
1.65(2)
1.2
0
16
I1-I2
2.9129(8)
2.749(1)
2.071(5)
2.047(5)
2.050(6)
2.062(7)
2.055(6)
2.072(6)
2.063(6)
2.057(6)
2.055(6)
2.074(6)
1.45(1)
1.433(8)
1.426(8)
1.408(9)
1.406(9)
1.396(9)
1.415(8)
1.407(9)
1.415(9)
1.405(9)
1.397(9)
I3-I3a
Fe-C1
Fe-C2
Fe-C3
Fe-C4
Fe-C5
Fe-C6
Fe-C7
Fe-C8
Fe-C9
Fe-C10
C1-C1b
C1-C2
C1-C5
C2-C3
C3-C4
C4-C5
C6-C7
C6-C10
C7-C8
C8-C9
C9-C10
4
2.042(6) 1.647(3) 1.647(4) 1.4(3) 2.1(3) 2.1(4)
1.646(3) 1.649(4) 1.7(3) 8.0(5)
2.043(4) 1.650(2) 1.650(2) 5.0(2) 3.9(2) 17.1(3)
1.656(2) 1.647(2) 2.2(2)
2.042(4) 1.651(4) 1.649(4) 3.3(2)
2.082(5)
2.057(5)
2.049(5)
2.044(5)
2.039(5)
2.132(5)
2.066(5)
2.031(5)
2.030(5)
2.081(5)
1.47(1)
1.428(7)
1.410(7)
1.408(7)
1.421(8)
1.403(7)
1.414(7)
1.414(7)
1.415(8)
1.402(8)
1.415(8)
6
8.6(3)
4.4(3)
8
10
0
2.044(4) 1.650(2) 1.650(2) 3.3(2) 1.6(2) 4.5(3)
1.652(2) 1.652(2) 1.9(2)
2.046(4) 1.649(2) 1.655(2) 1.8(2)
2.037(4) 1.643(5) 1.648(5) 1.5(5)
2.040(4) 1.642(4) 1.653(4) 1.9(2)
15.2(3)
6.6(3)
2.8(8)
1.0(2)
11
14a
14b
0
0
0
Mixed-Valence Biferrocenium
7
9
2.061(5) 1.682(5) 1.665(5) 5.7(3)
0
2.7(3)
2.07(1)g 1.674(7)g 1.703(7)g 4.8(6)g 6.8(6) 1.7(7)g
2.04(1)h 1.679(9)h 1.625(6)h 3.0(7)h
2.061(6) 1.675(5) 1.667(4) 2.5(4)
4.1(8)h
6.6(7)
12
15c
0
2.041(8)g 1.651(8)g 1.650(8)g 1.7(3)g 4.3(3) 2.1(3)g
2.081(8)h 1.698(8)h 1.704(8)h 4.6(3)h
3.0(3)h
a
b
Average Fe-C distance. The distance between the Fe atom
and the Cp ring. c The distance between the Fe and the fulvalenide
d
ligand. Dihedral angle between the Cp ring and the fulvalenide
ligand. e Dihedral angle between the two Cp rings in the fulvalen-
ide ligand. f Stagger angle between the Cp ring and the fulvalenide
Bond Angles
180.0
I2-I1-I2c
180.0
g
h
ligand. Associated with Fe1. Associated with Fe2.
C1b-C1-C2
C1b-C1-C5
C2-C1-C5
C1-C2-C3
C2-C3-C4
C3-C4-C5
C1-C5-C4
C7-C6-C10
C6-C7-C8
C7-C8-C9
C8-C9-C10
C6-C10-C9
125.8(5)
126.3(5)
107.5(4)
107.5(4)
108.6(5)
107.3(5)
109.1(4)
109.1(5)
106.5(5)
108.9(5)
108.3(5)
106.9(5)
126.5(7)
126.8(7)
106.5(5)
107.9(5)
108.5(6)
108.3(6)
108.8(6)
107.8(5)
108.1(5)
107.1(6)
109.2(6)
107.9(5)
Ta ble 4. Exp er im en ta l a n d Cr ysta l Da ta for th e
X-r a y Str u ctu r es of Mixed -Va len ce Bifer r ocen iu m
Tr iiod id es
7
9
12
15c
formula
C24H26
-
C22H22
-
C36H30
-
C32H26-
Fe2I3S2
967.05
triclinic
P1h
10.641(2)
10.623(2)
16.690(2)
89.78(1)
78.41(1)
60.23(1)
2.015
1594.0(5)
2
3.967
Fe2I3O2
838.84
Fe2I4
905.72
Fe2I5O4
1268.80
mol wt
cryst syst
space group
a, Å
b, Å
c, Å
triclinic
P1h
monoclinic triclinic
C2
P1h
7.352(2)
9.495(2)
10.472(2)
112.02(1)
99.92(1)
100.27(2)
2.165
15.010(2)
14.254(2)
13.715(4)
9.389(2)
11.168(2)
11.274(2)
61.63(1)
76.28(1)
65.97(1)
2.228
Symmetry equivalents: -x + 2, -y, -z + 1 for 12. b Symmetry
a
equivalents: -x + 2, -y + 1, -z + 1 for 7; -x + 2, -y + 1, -z for
12. c Symmetry equivalents: -x, -y, -z for 7 and 12.
R, deg
â, deg
γ, deg
120.13(1)
In the case of 7 and 12, the site symmetry imposed
on the mixed-valence cation obviously requires that both
iron centers of the cation are in equivalent positions.
In 7 and 12, the Fe-C distances are 2.061(5) and 2.061-
(6) Å, respectively. Each value is marginally larger than
that for the corresponding neutral biferrocene com-
pound. It lies midway between the 2.045 Å observed
for ferrocene23 and 2.075 Å observed for the ferrocenium
cation.24 The respective average Fe-Cp and Fe-ful
distances in 7 and 12 are 1.674(5) and 1.671(5) Å, which
are also larger than that for the corresponding neutral
biferrocene. Such an increase in the Fe-C and Fe-Cp
distances has been observed when ferrocenes are oxi-
dized to the corresponding ferrocenium ion.24 Further-
more, inspection of the Fe-Cp distances in 7 and 12
shows that these values also lie midway between the
value of 1.65 Å found for ferrocene23 and the value of
1.70 Å found for the ferrocenium ion.24 The dihedral
angles between the two least-squares Cp planes for a
given ferrocenyl moiety in 7 and 12 are 5.7(3)° and 2.5-
(4)°, respectively. The two Cp rings in each ferrocenyl
moiety in 7 and 12 are nearly eclipsed with average
staggering angles of 2.7(3)° and 6.6(7)°, respectively.
In the case of mixed-valence cations 9 and 15c, the
two ferrocenyl moieties are not equivalent. In 9, the
Fe1-C distance (2.07(1) Å) and the average Fe1-Cp
and Fe-ful distance (1.688 Å), which are larger than
F
calcd, g cm-3
2.370
2538.1(9)
4
V, Å3
Z
643.5(3)
1
948.6(3)
1
µ, mm-1
λ, Å
4.744
11.94
0.710 69
44.9
4.869
0.709 30
44.86
0.709 30
0.709 30
44.94
0.0364
2θ limits, deg 44.86
Rf
a
0.0243
0.025
0.024
0.0297
b
Rwf
wR2c
0.061
0.0702
0.0986
a
b
Rf ) ∑(||Fo| - |Fc||)/∑|Fo|. Rwf ) ∑[(w(Fo - Fc)2)/∑(wFo2)]1/2
.
c wR2 ) [(∑w(Fo2 - Fc2)2)/(∑wFo2)2]1/2, where w ) 1/[σ2(Fo2) + (fp)2],
p ) (max(Fo2; 0) + 2Fc2)/3, and f ) 0.0340 for 7, 0.0363 for 12, and
0.0499 for 15c.
squares planes of the Cp rings for a given ferrocenyl
moiety form a nearly parallel geometry, while these two
Cp rings are nearly eclipsed (see the ta and sa values
in Table 3).
Molecu la r Str u ctu r es of Mixed -Va len ce Bifer -
r ocen iu m Sa lts (7, 9, 12, a n d 15c). The experimental
and crystal data of the X-ray structures are collected
in Table 4. Collected in Tables 5 and 6 are selected bond
distances and angles. A direct comparison is also made
between these mixed-valence biferrocenium salts and
neutral biferrocenes (Table 3). Figures 2-5 show the
molecular structures and atomic labeling schemes for
the cation and anion. These mixed-valence compounds
also exist in a trans conformation.

5820 Organometallics, Vol. 16, No. 26, 1997
Dong et al.
Ta ble 6. Selected Bon d Dista n ce (Å) a n d Bon d
An gles (d eg)
9
15c
Bond Distances
3.010(2)
2.850(2)
3.394(2)
2.788(2)
2.128(9)
2.11(1)
2.08(1)
2.06(1)
2.06(1)
2.10(1)
2.05(1)
2.03(1)
2.03(1)
2.07(1)
2.030(9)
2.02(1)
2.03(1)
2.02(1)
2.04(1)
2.06(1)
2.04(1)
2.06(1)
2.07(1)
2.06(1)
1.41(2)
1.41(2)
1.48(1)
1.44(2)
1.41(2)
1.41(2)
1.43(2)
1.41(2)
1.41(2)
1.37(2)
1.40(2)
1.42(1)
1.43(2)
1.43(2)
1.44(2)
1.40(2)
1.41(2)
1.42(2)
1.38(2)
1.39(3)
1.40(2)
I1-I2
2.9326(9)
2.876(1)
I1-I3
I2-I4
I4-I4a
Fe1-C1
Fe1-C2
Fe1-C3
Fe1-C4
Fe1-C5
Fe1-C6
Fe1-C7
Fe1-C8
Fe1-C9
Fe1-C10
Fe2-C11
Fe2-C12
Fe2-C13
Fe2-C14
Fe2-C15
Fe2-C16
Fe2-C17
Fe2-C18
Fe2-C19
Fe2-C20
C1-C2
2.038(7)
2.046(8)
2.044(8)
2.033(7)
2.033(7)
2.024(8)
2.035(8)
2.053(7)
2.039(8)
2.050(8)
2.136(7)
2.089(8)
2.071(8)
2.057(8)
2.072(8)
2.142(8)
2.064(9)
2.043(8)
2.053(8)
2.086(8)
1.44(1)
1.41(1)
1.45(1)
1.39(1)
1.43(1)
1.39(1)
1.41(1)
1.43(1)
1.40(1)
1.40(1)
1.41(1)
1.41(1)
1.43(1)
1.42(1)
1.40(1)
1.40(1)
1.41(1)
1.42(1)
1.39(1)
1.40(1)
1.40(1)
C1-C5
C1-C11
C2-C3
C3-C4
F igu r e 2. ORTEP drawing of mixed-valence 7.
C4-C5
C6-C7
C6-C10
C7-C8
the corresponding values in ferrocene and neutral
biferrocene 8, indicate that the Fe1(Cp)2 metallocene
unit is in the Fe(III) oxidation state. However, in
comparison with ferrocene and the corresponding neu-
tral biferrocene 8, the Fe2-C distance (2.04(1) Å) and
the average Fe2-Cp and Fe-ful distance (1.652(8) Å)
indicate that the Fe2(Cp)2 metallocene unit is in the Fe-
(II) oxidation state. Similarly, making a comparison of
the Fe-C and Fe-Cp distances in 15c indicates that
Fe1 is in the Fe(II) oxidation state and Fe2 is in Fe(III)
oxidation state.
In 9 and 15c, the two Cp units in the fulvalenide
moiety are not crystallographically coplanar and the
dihedral angles between the two Cp units are 6.8(6)°
and 4.3(3)°, respectively. In both compounds (9 and
15c), the two least-squares planes of the Cp rings for a
given ferrocenyl moiety form a nearly parallel geometry
while the two Cp rings are nearly eclipsed.
C8-C9
C9-C10
C11-C12
C11-C15
C12-C13
C13-C14
C14-C15
C16-C17
C16-C20
C17-C18
C18-C19
C19-C20
Bond Angles
177.38(4)
96.15(3)
176.08(5)
108.5(9)
124(1)
I2-I1-I3
175.05(3)
I1-I2-I4
I2-I4-I4a
C2-C1-C5
107.6(7)
124.8(7)
127.6(7)
107.7(8)
108.2(7)
108.1(8)
108.4(8)
108.7(7)
107.4(8)
108.8(7)
109.2(7)
105.9(7)
126.0(7)
126.2(7)
107.3(7)
107.6(7)
108.7(7)
108.1(7)
108.2(7)
107.3(7)
108.6(8)
108.0(7)
108.5(7)
107.5(7)
C2-C1-C11
C5-C1-C11
C1-C2-C3
126(1)
108(1)
107(1)
109(1)
108(1)
107(1)
107(1)
109(1)
109(1)
108(1)
125(1)
124.5(9)
109.7(9)
107(1)
107(1)
109(1)
The triiodide anions in 7 and 12 are linear, and they
also show a symmetric structure. The I1-I2 distances
in 7 and 12 are 2.9255(7) and 2.9129(8) Å, respectively.
The solid-state structures of 7 and 12 are composed of
columns of biferrocenium cations and triiodide anions.
However, in 12, the polyiodide ions contain zigzag
C2-C3-C4
C3-C4-C5
C1-C5-C4
C7-C6-C10
C6-C7-C8
C7-C8-C9
C8-C9-C10
C6-C10-C9
C1-C11-C12
C1-C11-C15
C12-C11-C15
C11-C12-C13
C12-C13-C14
C13-C14-C15
C11-C15-C14
C17-C16-C20
C16-C17-C18
C17-C18-C19
C18-C19-C20
C16-C20-C19
-
chains of alternate I3 and I2 units. This well-estab-
lished polyiodide chain is also seen in structurally
characterized mixed-valence 1′,1′′′-bis(p-bromobenzyl)-
biferrocenium pentaiodide.25 This type of arrangement,
-
alternating I3 and I2, is quite common among the
pentaiodide salts. In 12, the bond length in the I2
molecule is 2.749(1) Å, significantly larger than the
value of 2.68 Å found in crystalline I2.26
106(1)
107(1)
108(1)
110(1)
108(1)
108(1)
(25) Dong, T.-Y.; Schei, C. C.; Hwang, M. Y.; Lee, T. Y.; Yeh, S. K.;
Wen, Y. S. Organometallics 1992, 11, 573.
(26) Kitaigorodskii, A. I.; Khotsyanova, T. L.; Struchkov, Y. T. Zh.
Fiz. Khim. 1953, 27, 780.
a
Symmetry equivalent: 1 - x, y, 2 - z for 9.

Mixed-Valence Biferrocenium Salts
Organometallics, Vol. 16, No. 26, 1997 5821
F igu r e 3. ORTEP drawing of mixed-valence 9.
F igu r e 4. ORTEP drawing of mixed-valence 12.
On the other hand, the triiodide anions in 9 and 15c
are essentially linear, and the I2-I1-I3 angles are
177.38(4)° and 175.05(3)°, respectively. However, the
triiodide anions in 9 and 15c have an asymmetric
structure with distances of I1-I2 ) 3.010(2) and 2.9226-
(9) Å and I1-I3 ) 2.850(2) and 2.876(1) Å, respectively.
In other words, the triiodide anion possesses I2-I-
character, where the I2 atom carries more negative
charge than the other terminal I3 atom. In 9, the
polyiodide ions also contain zigzag chains of alternating
to-peak separation between the resolved reduction and
oxidation wave maxima (∆ in Table 7) and a 1:1
relationship of the cathodic and anodic peak currents
(Ic/Ia in Table 7).
The effect of the substituent on the stability of the
ferrocenium cation is illustrated by the shift of the half-
wave potential (E1/2). The electron-donating groups
(-CH2OCH3, -OC2H5, -CH2OH, -SCH3, and -SC2H5)
stabilize the cation, lowering the half-wave potential,
while the electron-withdrawing groups (-CH2OCOC6H5
and -SC6H5) have the opposite effect.
-
I3 and I2 units. The bond length in the I2 molecule is
2.788(2) Å. The distance between neighboring iodine
atoms in I2 and I3- units (I2-I4 ) 3.394(2) Å) within a
chain indicates a significant interaction, in view of the
in-plane intermolecular distance of 3.50 Å found in
crystalline I2.26
From the value of ∆E1/2, the disproportionation equi-
librium constant K (eq 1) can be calculated. In eq 1,
K
\
[2,2] + [3,3]
(1)
Electr och em ica l Mea su r em en ts. Electrochemical
data for the neutral biferrocenes 4, 6, 8, 10, 11, and 14,
as well as those for some other relevant compounds, are
shown in Table 7. These binuclear biferrocenes all
undergo two successive reversible one-electron oxida-
tions to yield the mono- and then the dication. Elec-
trochemical reversibility is demonstrated by the peak-
the abbreviations [3,3], [2,3], and [2,2] denote the
dioxidized salt, the monooxidized salt, and the neutral
compound, respectively. The large value of K gives an
indication of the possibility of preparing the mixed-
valence biferrocenium salts. Except for the neutral
biferrocenes 10 and 13, mixed-valence compounds 5, 7,
9, 12, and 15 were prepared by oxidizing the corre-
sponding neutral biferrocenes with I2. The resulting
microcrystalline samples were recrystallized from a
(27) Nakashima, S.; Katada, M.; Motoyama, I.; Sano, H. Bull. Chem.
Soc. J pn. 1987, 60, 2253.

5822 Organometallics, Vol. 16, No. 26, 1997
Dong et al.
F igu r e 6. Variable-temperature 57Fe Mo¨ssbauer spectra
of 5.
Ta ble 8. Va r ia ble-Tem p er a tu r e 57F e Mo1ssba u er
F igu r e 5. ORTEP drawing of mixed-valence 15c.
Lea st-Squ a r es-F ittin g P a r a m eter s
a
Ta ble 7. Cyclic Volta m m etr y for Va r iou s
Bifer r ocen es
compd
T, K
∆EQ
δb
Γc
5
300
150
130
110
100
90
1.151
1.160
1.159
1.160
1.168
1.457
0.935
1.633
0.776
1.177
1.214
1.737
0.583
1.882
0.416
1.333
0.737
1.958
0.453
1.218
1.263
1.188
1.249
2.105
0.625
2.122
0.625
0.448
0.507
0.514
0.518
0.521
0.516
0.522
0.524
0.528
0.447
0.523
0.443
0.436
0.515
0.519
0.447
0.454
0.515
0.512
0.453
0.526
0.457
0.526
0.442
0.455
0.514
0.535
0.301, 0.313
0.389, 0.391
0.405, 0.403
0.438, 0.436
0.481, 0.483
0.465, 0.480
0.412, 0.412
0.422, 0.422
0.394, 0.403
0.338, 0.342
0.461. 0.458
0.301, 0.308
0.277, 0.278
0.288, 0.287
0.282, 0.283
0.518, 0.474
0.596, 0.520
0.347, 0.353
0.506, 0.434
0.299, 0.284
0.334, 0.320
0.383, 0.372
0.513, 0.501
0.247, 0.264
0.310, 0.270
0.247, 0.246
0.291, 0.287
a
d
compd
E1/2
,
V
∆E1/2,b V ∆,c mV Ic/Ia
K (×10-5
)
ferrocene
biferrocene
0.37
0.28
0.59
0.29
0.61
0.13
0.47
0.26
0.57
0.35
0.68
0.38
0.66
0.26
0.56
0.27
0.57
0.37
0.65
70
70
75
70
72
79
70
61
60
73
75
73
73
64
69
75
65
70
71
0.97
0.31
0.32
0.34
0.31
0.32
0.28
0.30
0.30
0.28
1.01
1.01
0.87
1.08
0.96
1.03
0.89
1.01
0.81
0.98
0.86
1.03
0.88
1.04
0.86
1.06
0.83
1.00
1.8
2.6
5.8
1.8
2.6
0.6
1.2
1.2
0.6
4
80
6
7
9
300
80
300
10
11
13
14a
14b
14c
80
300
80
12
15a
15b
15c
300
80
300
80
All half-wave potentials are referred to the Ag+/Ag electrode.
a
Peak separation between waves. c Peak-to-peak separation be-
b
300
d
tween the resolved reduction and oxidation wave maxima. Peak
current ratio between cathode and anode.
80
a
b
Quadrupole-splitting in mms-1
.
Isomer shift referenced to
CH2Cl2/hexane solution. The physical properties for
this series of new mixed-valence salts are described in
next section.
iron-foil in mms-1
squares-fitting program. The width for the line at a more positive
velocity is listed first for each doublet.
.
c Full width at half-height taken from the least-
Electr on Tr a n sfer in th e Solid Sta te. The rates
of intramolecular electron transfer in the solid state of
the mixed-valence cations 5, 7, 9, 12, and 15 were
estimated by variable-temperature 57Fe Mo¨ssbauer
spectroscopy (time scale ∼107 s-1). Typical 57Fe Mo¨ss-
bauer spectra of 5 are given in Figure 6. The various
absorption peaks in the Mo¨ssbauer spectra of these
compounds were fitted to Lorentzian lines. The result-
ing fitting parameters are collected in Table 8.
The rates of electron transfer in mixed-valence cations
5, 7, 9, 12, and 15 can be sensitively controlled by the
substituents. In this new series of mixed-valence
cations, three basic types of biferrocenium salts are
found. The cations of 9, 12, and 15c have localized
electronic structures at temperatures below 300 K
(electron-transfer rate < ∼107 s-1). On the other hand,
compounds 7, 15a , and 15b have delocalized electronic
structures (electron-transfer rate > ∼ 107 s-1) between
80 and 300 K. Compound 5 gives temperature-depend-
ent Mo¨ssbauer spectra (Figure 6).
In the case of 9, 12, and 15c, the features in all of
the 300 and 80 K spectra include two doublets, one with
a quadrupole splitting (∆EQ) ∼2 mm s-1 (Fe(II) site) and
the other with ∆EQ ) ∼0.5 mm s-1 (Fe(III) site). Both
doublets are fitted into a 1:1 area ratio. This pattern
of two doublets is expected for a biferrocenium cation
which is valence-trapped on the time scale of the
Mo¨ssbauer experiment (electron-transfer rate < ∼107
s-1).8 Furthermore, in 12, the Mo¨ssbauer behavior is

Mixed-Valence Biferrocenium Salts
Organometallics, Vol. 16, No. 26, 1997 5823
extracts were dried over MgSO4 and evaporated at reduced
pressure. The residue was recrystallized from methanol in a
refrigerator overnight (yield 45%). The compound thus pre-
pared is pure (identification with NMR and melting point)22
and can be used for further reaction. Further purification
could be carried out by chromatography, if necessary.
different from what is seen for 9 and 15c. The two
doublets, ∆EQ ) 1.333 and 0.737 mm s-1 at 300 K, just
move together. We believe that the decrease of ∆EQ in
the ferrocenyl doublet and the increase of ∆EQ in the
ferrocenium doublet are related to the magnitude of
electron-transfer rate in the cation. Thus, the rate of
electron transfer in 12 is greater than that in 9 or 15c.
It should be noted that the electron-transfer rate in
mixed-valence 1′,1′′′-dimethylbiferrocenium triiodide
was reported before.27 Sano et al. were able to prepare
a triiodide (I3-) salt of the mixed-valence cation of 1′,1′′′-
dimethylbiferrocenium. In our hands, attempts to
prepare a triiodide salt of the mixed-valence cation by
1′-(Meth oxym eth yl)-1-br om ofer r ocen e (3). At -30 °C,
n-BuLi (10 mmol) was added under nitrogen into a THF (40
mL) solution of dibromoferrocene (3.44 g, 10 mmol) and the
resulting solution was stirred for 30 min. Electrophilic reagent
ICH2OCH3 (10 mmol) was then added, and the solution was
further stirred at -30 °C for another 30 min. Water (40 mL)
was added, and the resulting mixture was extracted with ether
(40 mL × 2). The combined extracts were dried over MgSO4
and evaporated at reduced pressure. The residue was chro-
matographed on Al2O3. The first band eluted with hexane was
the starting material containing some impurities. Continued
elution with hexane:CH2Cl2 (4:1) gave elutes which yielded the
desired compound (69% yield). The properties of 3 are as
follows. 1H NMR (CDCl3, ppm): 3.30 (s, 3H, -CH3), 4.04 (t,
2H, Cp), 4.10 (s, 2H, -CH2), 4.19 (s, 4H, Cp), 4.34 (t, 2H, Cp).
MS: M+ at m/ z 308 and 310.
-
use of stoichiometric amounts of iodine resulted in a I4
salt (9). The Mo¨ssbauer spectrum of their compound,
taken at 298 K, also shows two quadrupole-split dou-
blets (∆EQ ) 1.74 and 0.56 mm s-1).
The Mo¨ssbauer results indicate that compounds 7,
15a , and 15b are delocalized on the Mo¨ssbauer time
scale above 80 K. Only a single “average-valence”
doublet (∆EQ ) ∼1.2 mm s-1) in each Mo¨ssbauer
spectrum is seen from 80 to 300 K.
In the case of 5, at temperatures below 90 K, there
are two doublets in each Mo¨ssbauer spectrum, one
representing the Fe(II) site and the other Fe(III) site.
An increase of temperature causes the two doublets to
move together, resulting in an “average-valence” doublet
at 100 K. At temperatures above 100 K, the spectrum
shows only a single quadrupole-split doublet which is
characteristic of a valence-detrapped cation (electron-
transfer rate > ∼107 s-1).
1′,1′′′-Bis(m eth oxym eth yl)bifer r ocen e (4). Compound 3
(2 mmol) was thoroughly mixed with activated Cu (5 g), and
the resulting mixture was heated at 120 °C (oil bath) for 22 h.
The solid was cooled to room temperature and then subjected
to the Soxhlet process with dichloromethane. The extract was
evaporated at reduced pressure, and the residue was chro-
matographed on Al2O3. Elution with hexane gave elutes
containing starting material and ferrocene. Continued elution
with dichloromethane:hexane (1:4) gave the desired bifer-
rocenes 4 (63% yield). 1H NMR (CDCl3, ppm): 3.21 (s, 6H,
-CH3), 3.96 (s, 4H, Cp), 3.98 (d, 4H, Cp), 4.01 (d, 4H, Cp),
4.17 (t, 4H, Cp), 4.30 (t, 4H, Cp). MS: M+ at m/ z 458. Mp:
101-102 °C.
1′,1′′′-Bis(eth oxyl)bifer r ocen e (6). Cuprous iodide (0.19
g, 1.0 mmol) and sodium ethoxide (0.272 g, 4.0 mmol) were
added under nitrogen into a 8 mL ethanol/DMF (3:5) solution
of dibromobiferrocene (0.528 g, 1.27 mmol). The resulting
solution was refluxed for 75 min. Water (10 mL) was added,
and the resulting mixture was extracted with CH2Cl2 (20 mL
× 3). The combined extracts were dried over MgSO4 and
evaporated at reduced pressure. The residue was chromato-
graphed on Al2O3 (activity III). Elution with hexane gave
elutes containing some impurities, which were discarded.
Continued elution with CH2Cl2:hexane (1:5) gave monosub-
stituted 1′-ethoxylbiferrocene (15% yield). The third band was
the desired compound 6 (21% yield). The physical properties
of 1′-ethoxylbiferrocene are as follows. 1H NMR (CDCl3,
ppm): 1.22 (t, 3H, -CH3), 3.68 (m, 4H, -CH2- and Cp), 3.94
(t, 2H, Cp), 4.01 (s, 5H, Cp), 4.20 (dt, 4H, Cp), 4.35 (t, 4H,
Cp). MS: M+ at m/ z 414. Mp: 124.0-124.3 °C. The physical
properties of 6 are as follows. 1H NMR (CDCl3, ppm): 1.23
(t, 6H, -CH3), 3.66 (m, 8H, -CH2- and Cp), 3.90 (d, 4H, Cp),
4.20 (t, 4H, Cp), 4.39 (t, 4H, Cp). MS: M+ at m/ z 458. Mp:
104.9-105.2 °C.
IR spectroscopy has also been applied to study the
rate of electron transfer. It has been shown that the
perpendicular C-H bending band is the best diagnosis
of the Fe oxidation state. This band is seen at 815 cm-1
for ferrocene and at 850 cm-1 for ferrocenium triiodide.8
A localized mixed-valence biferrocenium cation should
exhibit one C-H bending band for the Fe(II) ferrocenyl
moiety and one for the Fe(III) ferrocenium moiety.8
Infrared spectra were run on KBr pellets of the series
of biferrocenium cations. For 5, 7, 9, 12, and 15, there
are relatively strong bands at ∼818 and ∼840 cm-1 in
the perpendicular C-H bending region. It is clear that
the IR data conclusively indicate the presence of Fe(II)
and Fe(III) moieties.
Exp er im en ta l Section
Gen er a l In for m a tion . All manipulations involving air-
sensitive materials were carried out by using standard Schlenk
techniques under an atmosphere of N2. Chromatography was
performed on neutral alumina (Merck, activity II). Solvents
were dried as follows: benzene, hexane, ether, and THF
distilled from Na/benzophenone; CH2Cl2 and (CH3)2S2 distilled
from CaH2. 1,1′-Dibromoferrocene was prepared according to
the literature procedure.21
1′,1′′′-Dibr om obifer r ocen e (2). Dibromoferrocene (34.4 g,
0.11 mol) was placed in a freshly oven-dried three-necked flask
(500 mL) and dried under vacuum at 2 mmHg at 25 °C for 4
h. Dried THF (250 mL), followed by n-butyllithium (0.1 mol),
was added under nitrogen. The resulting solution was stirred
at -30 °C for 30 min, during which 1-bromo-1′-lithioferrocene
gradually precipitated. Solid CuCN (4.5 g, 50 mmol) was then
added, and the solution was stirred further at -30 °C for 10
min. At -78 °C, oxygen was bubbled continuously through
the solution for 4 h. The solution was then stirred at room
temperature for another 4 h. Water (200 mL) was added, and
the mixture was then extracted with CH2Cl2. The combined
Gen er al P r ocedu r e of 1′,1′′′-Disu bstitu ted Bifer r ocen es.
At -30 °C, 7.6 mL of n-BuLi (1.3 M in hexane) was added
under nitrogen to a THF (40 mL) solution of dibromobifer-
rocene (2.64 g, 5.0 mmol). The resulting solution was stirred
at -30 °C for 30 min. Various electrophilic reagents (10 mmol)
were then added, and the solution was stirred further at -30
°C for another 30 min. Water (40 mL) was added, and the
resulting mixture was extracted with CH2Cl2. The combined
extracts were dried over MgSO4 and evaporated at reduced
pressure. The residue was chromatographed on Al2O3. Elu-
tion with hexane:CH2Cl2 (5:1) gave the disubstituted bifer-
rocenes.
1′,1′′′-Bis(carbaldehyde)biferrocene (1.598 g, 75% yield) was
obtained with DMF (1 mL) as the electrophilic reagent. 1H

5824 Organometallics, Vol. 16, No. 26, 1997
Dong et al.
NMR (CDCl3, ppm): 4.33 (d, 4H, Cp), 4.41 (d, 4H, Cp), 4.45
(d, 4H, Cp), 4.60 (d, 4H, Cp), 9.73 (s, 2H, -CHO). MS: M+ at
m/ z 426.
H, 2.80. Found: C, 31.48; H, 2.93. Anal. Calcd for 15c (C32
26Fe2I3S2): C, 39.74; H, 2.71. Found: C, 38.80; H, 2.71.
P h ysica l Meth od s. 57Fe Mo¨ssbauer measurements were
-
H
1′,1′′′-Bis(phenylseleno)biferrocene (13, 47% yield) was ob-
tained with (C6H5)2Se2 as the electrophilic reagent. 1H NMR
(CDCl3, ppm): 4.14 (t, 4H, Cp), 4.20 (t, 4H, Cp), 4.30 (t, 4H,
Cp), 4.48 (t, 4H, Cp), 7.17 (m, 10H, -C6H5). MS: M+ at m/ z
682. Mp: 190.9-191.8 °C.
1′,1′′′-Bis(methylthio)biferrocene (14a , 24% yield) was ob-
tained with (CH3)2S2 as the electrophilic reagent. 1H NMR
(CDCl3, ppm): 2.23 (s, 6H, -CH3), 4.02 (t, 4H, Cp), 4.11 (t,
4H, Cp), 4.25 (t, 4H, Cp), 4.42 (t, 4H, Cp). MS: M+ at m/ z
462. Mp: 79.1-80.1 °C.
1′,1′′′-Bis(ethylthio)biferrocene (14b, 47% yield) was ob-
tained with (C2H5)2S2 as the electrophilic reagent. 1H NMR
(CDCl3, ppm): 1.14 (s, 6H, -CH3), 2.64 (q, 4H, -CH2-), 4.09
(t, 4H, Cp), 4.20 (t, 4H, Cp), 4.30 (t, 4H, Cp), 4.49 (t, 4H, Cp).
MS: M+ at m/ z 490. Mp: 69.3-70.5 °C.
1′,1′′′-Bis(phenylthio)biferrocene (14c, 65% yield) was ob-
tained with (C6H5)2S2 as the electrophilic reagent. 1H NMR
(CDCl3, ppm): 4.18 (t, 8H, Cp), 4.31 (t, 4H, Cp), 4.50 (t, 4H,
Cp), 7.03 (t, 6H, p- and m-benzyl), 7.15 (t, 4H, o-benzyl). MS:
M+ at m/ z 586. Mp: 191 °C (dec).
1′,1′′′-Dim eth ylbifer r ocen e (8). The reduction reaction
was carried out by carefully adding, with stirring, a small
portion of AlCl3 to a mixture of 1′,1′′′-bis(carbaldehyde)-
biferrocene and LiAlH4 in dry ether. After 30 min, the solution
became yellow, an excess of H2O was added to it, and the ether
layer was separated. The ether layer was washed with H2O
and dried over MgSO4. After evaporation of the solvent, the
crude product was chromatographed on Al2O3, eluting with
hexane. The first band was the desired compound (95% yield).
1H NMR (CDCl3, ppm): 1.75 (s, 6H, -CH3), 3.85 (s, 4H, Cp),
3.88 (s, 4H, Cp), 4.13 (d, 4H, Cp), 4.26 (d, 4H, Cp). MS: M+
at m/ z 398. Mp: 149-150 °C.
1′,1′′′-Bis(h yd oxym eth yl)bifer r ocen e (10). The reduc-
tion reaction of 1′,1′′′-bis(carbaldehyde)biferrocene was carried
out according the same procedure described above, except
using LiAlH4 as the reducing reagent. Purification was carried
out by recrystallizing from CH2Cl2. 1H NMR (CDCl3, ppm):
1.25 (s, 2H, -OH), 4.03 (d, 4H, Cp), 4.07 (d, 4H, Cp), 4.10 (d,
4H, -CH2-), 4.27 (d, 4H, Cp), 4.40 (d, 4H, Cp). MS: M+ at
m/ z 430. Mp: 148-149.5 °C.
1′,1′′′-Bis(ben zoyloxym eth yl)bifer r ocen e (11). To a 20
mL THF solution of 10 (0.1 g, 0.23 mmol) was added benzoyl
chloride (0.5 mmol). The resulting solution was stirred 1 min,
and then triethylamine was added. The mixture was placed
in a refrigerator overnight. The solution was extracted with
CH2Cl2 (20 mL × 3). The combined extracts were washed with
H2O, dried over MgSO4, and evaporated at reduced pressure.
The residue was chromatographed on Al2O3. Elution with
hexane:CH2Cl2 (1:2) gave the desired compound. 1H NMR
(CDCl3, ppm): 4.03 (t, 4H, Cp), 4.15 (t, 4H, Cp), 4.23 (t, 4H,
Cp), 4.39 (t, 4H, Cp), 4.87 (s, 4H, -CH2-), 7.40 (t, 4H,
m-benzyl), 7.52 (td, 2H, p-benzyl), 7.99 (s, 4H, o-benzyl). MS:
M+ at m/ z 638. Mp: 159 °C (dec).
Mixed -Va len ce Com p ou n d s 5, 7, 9, 12, a n d 15. Samples
of these mixed-valence compounds were prepared by adding
a benzene/hexane (1:1) solution containing a stoichiometric
amount of iodine to a solution of the corresponding biferrocene
at 0 °C. The corresponding biferrocene solution was prepared
by dissolving the biferrocene in a proper solvent (benzene/
hexane (1:1) for 4, 6, 8, and 11; hexane for 14a and 14b; CH2-
Cl2 for 14c). The resulting dark crystals were filtered and
made on a constant-velocity instrument which was previously
described.28 Velocity calibration was made using a 99.99%
pure 10-µm iron foil. Typical line widths for all three pairs of
iron foil lines fell in the range 0.24-0.27 mm s-1. Isomer shifts
are reported relative to iron foil at 300 K but are uncorrected
for temperature-dependent (second-order) Doppler effects. It
should be noted that the isomer shifts illustrated in the figures
are plotted as experimentally obtained. Tabulated data is
provided.
1H NMR spectra were run on a Varian VXR-300 spectrom-
eter. Mass spectra were obtained with a VG-BLOTECH-
QUATTRO 5022 system.
Electrochemical measurements were carried out with a BAS
100W system. Cyclic voltammetry was perform with a sta-
tionary glassy carbon working electrode, which was cleaned
after each run. These experiments were carried out with a 1
× 10-3 M solution of biferrocene in dry CH2Cl2/CH3CN (1:1)
containing 0.1 M (n-C4H9)4NPF6 as the supporting electrolyte.
The potentials quoted in this work are relative to a Ag/AgCl
electrode at 25 °C. Under these conditions, ferrocene shows
a reversible one-electron oxidation wave (E1/2 ) 0.37 V).
The single-crystal X-ray determinations of the compounds
were carried out on an Enraf-Nonius CAD4 diffractometer at
298 K. Absorption corrections were made with empirical ψ
rotation. A three-dimensional Patterson synthesis was used
to determine the heavy-atom positions, which phased the data
sufficiently well to permit location of the remaining non-
hydrogen atoms from Fourier synthesis. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were
calculated at ideal distances. The X-ray crystal data are
summarized in Tables 1, 2, and 4. Selected bond distances
and angles are given in Tables 5 and 6. Listings of the final
positional parameters for all atoms, and thermal parameters
of these compounds are given in the Supporting Information.
Str u ctu r e Deter m in a tion of 4. An orange crystal (0.1 ×
0.15 × 0.35 mm) was obtained when a layer of hexane was
allowed to slowly diffuse into a CH2Cl2 solution of 4. Cell
dimensions were obtained from 25 reflections with 17.78° <
2θ < 27.88°. The θ-2θ scan technique was used to record the
intensities for all reflections for which 1° < 2θ < 49.9°. Of
the 2030 unique reflections, there were 1598 reflections with
Fo > 2.0σ(Fo2), where σ(Fo2) was estimated from counting
statistics.
Str u ctu r e Deter m in a tion of 6. An orange crystal (0.31
× 0.10 × 0.22 mm) was obtained following the same procedure
as described for 4. Data were collected to a 2θ value of 44.9°.
The unit cell dimensions were obtained from 25 reflections
with 14.98° < 2θ < 30.54°. Of the 2636 unique reflections,
there were 1972 with Fo > 2.5σ(Fo2).
Str u ctu r e Deter m in a tion of 8. An orange crystal (0.16
× 0.20 × 0.22 mm) was obtained following the same procedure
as described for 4. The unit cell dimensions were obtained
from 25 reflections with 23.8° < 2θ < 33.9°. Of the 1783
unique reflections, there were 1424 with Fo > 3.0σ(Fo2).
Str u ctu r e Deter m in a tion of 10. An orange crystal (0.31
× 0.28 × 0.19 mm) was obtained following the same procedure
as described for 4. The unit cell dimensions were obtained
from 20 reflections with 15.06° < 2θ < 34.10°. Of the 2293
unique reflections, there were 1718 with Fo > 2.5σ(Fo2).
Str u ctu r e Deter m in a tion of 11. An orange crystal (0.13
× 0.64 × 0.32 mm) was obtained following the same procedure
as described for 4. Data were collected to a 2θ value of 44.9°.
The cell dimensions were obtained from 25 reflections with
2θ in the range 11.72-28.69°. Of the 1819 unique reflections,
there were 1405 with Fo > 2.5σ(Fo2).
washed repeatedly with cold hexane. Anal. Calcd for 5 (C24
-
H
26Fe2I3O2): C, 34.36; H, 3.12. Found: C, 33.79; H, 3.06. Anal.
Calcd for 7 (C24H26Fe2I3O3): C, 34.36; H, 3.12. Found: C,
34.21; H, 3.14. Anal. Calcd for 9 (C22H22Fe2I4): C, 29.17; H,
2.45. Found: C, 28.84; H, 2.49. Anal. Calcd for 12 (C36H30
-
Fe2I5O4): C, 33.97; H, 2.38. Found: C, 33.74; H, 2.50. Anal.
Calcd for 15a (C22H22Fe2I3S2): C, 31.35; H, 2.63. Found: C,
31.02; H, 2.64. Anal. Calcd for 15b (C24H26Fe2I7/2): C, 30.85;
(28) Dong, T.-Y.; Huang, C. H.; Chang, C. K.; Wen, Y. S.; Lee, S. L.;
Chen, J . A.; Yeh, W. Y.; Yeh, A. J . Am. Chem. Soc. 1993, 115, 6357.

Mixed-Valence Biferrocenium Salts
Organometallics, Vol. 16, No. 26, 1997 5825
Str u ctu r e Deter m in a tion of 14a . An orange crystal (0.26
× 0.20 × 0.20 mm) was obtained by slow evaporation from a
hexane solution of 14a . Data were collected to a 2θ value of
44.98°. The cell dimensions were obtained from 25 reflections
with 2θ in the range 19-27°. Of the 1362 unique reflections,
there were 1265 with Fo > 2.0σ(Fo2).
Str u ctu r e Deter m in a tion of 14b. An orange crystal (0.36
× 0.28 × 0.26 mm) was obtained following the same procedure
as described for 14a . Data were collected to a 2θ value of
44.86°. The cell dimensions were obtained from 25 reflections
with 2θ in the range 20-32°. Of the 2843 unique reflections,
there were 2550 with Fo > 2.0σ(Fo2).
procedure as described for 4. Data were collected to a 2θ value
of 44.86°. The cell dimensions were obtained from 25 reflec-
tions with 2θ in the range 16-25°. Of the 2457 unique
reflections, there were 1842 with Fo > 2.0σ(Fo2).
Str u ctu r e Deter m in a tion of 15c. A dark black crystal
(0.22 × 0.18 × 0.16 mm) was obtained following the same
procedure as described for 4. Data were collected to a 2θ value
of 44.94°. The cell dimensions were obtained from 25 reflec-
tions with 2θ in the range 11-21°. The data were also
corrected for absorption. Of the 4181 unique reflections, there
were 2717 with Fo > 2.0σ(Fo2).
Str u ctu r e Deter m in a tion of 7. A dark black crystal (0.32
× 0.24 × 0.20 mm) was obtained following the same procedure
as described for 4. Data were collected to a 2θ value of 44.86°.
The cell dimensions were obtained from 25 reflections with
2θ in the range 12-23°. Of the 1674 unique reflections, there
were 1336 with Fo > 2.0σ(Fo2).
Ack n ow led gm en ts are made to the National Science
Council (Grant No. NSC87-2113-M-110-010), Taiwan,
ROC, and Department of Chemistry at Sun Yat-Sen
University.
Str u ctu r e Deter m in a tion of 9. A dark black crystal (0.25
× 0.25 × 0.25 mm) was obtained following the same procedure
as described for 4. Data were collected to a 2θ value of 44.9°.
The cell dimensions were obtained from 25 reflections with
2θ in the range 14.56-30.84°. Of the 1737 unique reflections,
there were 1555 with Fo > 2.0σ(Fo2).
Str u ctu r e Deter m in a tion of 12. A dark black crystal
(0.24 × 0.20 × 0.20 mm) was obtained following the same
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters, bond distances and angles, and thermal param-
eters for 4, 6-12, 14a , 14b, and 15c, ORTEP drawings for 4,
6, 8, 10, 11, 14a , and 14b, and packing arrangements of 7, 9,
12, and 15c (44 pages). Ordering information is given on any
current masthead page.
OM970746E