Molecular batteries based on carbon - Carbon bond formation and cleavage in titanium and vanadium Schiff base complexes

Article abstract of DOI:10.1002/(SICI)1521-3765(19990201)5:2<708::AID-CHEM708>3.0.CO;2-I

The reduction of titanium(III) and vanadium(III) salophen complexes led to the reductive coupling of imino groups in the ligands, and thus to the formation of C-C-bonded dimers which released electrons on subsequent cleavage of the C-C bond. On reduction

Full text of DOI:10.1002/(SICI)1521-3765(19990201)5:2<708::AID-CHEM708>3.0.CO;2-I

FULL PAPER
Molecular Batteries Based on Carbon ± Carbon Bond Formation and
Cleavage in Titanium and Vanadium Schiff Base Complexes
[
a]
[a]
[a]
[b]
Federico Franceschi, Euro Solari, Carlo Floriani,* Marzio Rosi,
[
c]
[c]
Angiola Chiesi-Villa, and Corrado Rizzoli
Abstract: The reduction of titanium(iii)
and vanadium(iii) salophen complexes
led to the reductive coupling of imino
groups in the ligands, and thus to the
formation of C�C-bonded dimers which
together [Ti ´´´ Ti ˆ 2.518(1) Š in 6;
V´´´ Vˆ 2.393(1) Š in 7]. Complexes 3
and 4 reacted with 9,10-phenanthrene-
quinone to give [M(salophen)(9,10-
phen)] [M ˆ Ti (9), V (10)], using both
the electrons stored at the C�C bond
isolated from the reaction of 7 with O2.
The reaction became synthetically and
mechanistically interesting when organ-
ic azides were used as oxidizing agents:
reaction of 3 with PhN and Me SiN led
3
3
3
released electrons on subsequent cleav-
to the m-phenylimido dimers [Ti (salo-
2
III
age of the C�C bond. On reduction of
and those from the oxidation of M to
phen )(m-PhN)(thf) ] (17) and [Ti (salo-
2
2
2
IV
[
(
M(salophen)(Cl)(thf)] [M ˆ Ti (1), V
M . The reaction of 3 and 4 with O2
phen )(m-Me SiN)] (18), which was hy-
2 3
2)] with sodium metal in a 1:1 molar
yielded the oxometal(iv) complexes
drolyzed to the analogous m-oxo [{Ti2-
(salophen )(m-O)} ] (19). The reaction of
ratio the dimers [M (salophen )(thf) ]
[M(salophen)(O)] [M ˆ Ti (13),
V
2
2
2
2
2
[
M ˆ Ti (3), V (4)] formed, in which two
(11)] with a four-electron oxidation of
the starting dimers. The intermediate
oxovanadium(iii) complex [V(salo-
3 with Ph CN led to the phenylimido
3 3
salophen units are joined by a single
C�C bond. Further reduction resulted in
the introduction of an additional C�C
complex [Ti(salophen)(NCPh )] (20),
3
and
4 reacted with PhN3 to give
phen){m-O-Na(DME) }] (16), which
[V(salophen)(NPh)] (21). Extended
Hückel calculations enabled us to sub-
stantiate the electron-transfer process,
which never involves the C�C site as a
2
bridge between the two salophen units
can be subsequently oxidized to 11, was
and thus to the formation of [M (*salo-
2
phen *)(Na) (thf) ] [M ˆ Ti (6), V (7)],
2
2
6
Keywords: electron transfer ´ mo-
lecular devices ´ redox chemistry ´
Schiff bases ´ titanium ´ vanadium
in which *salophen * is a dinucleating,
reactive center; it only functions as an
electron reservoir.
2
octadentate, octaanionic ligand. In 6 and
7, the two metal centers are very close
Introduction
such as the formation or cleavage of bonds, and even more
rarely is this event reversible. A successful approach to this
field would provide the possibility of storing and releasing
electrons, a process which could be coupled to the variation in
the oxidation state of the metal and which would produce a
type of molecular battery.[
The redox chemistry of transition metal complexes containing
either macrocyclic or polydentate ligands essentially involves
variations in the oxidation state of the metal centers. The
metal-assisted redox chemistry of the macrocyclic or poly-
dentate ligand has been studied far less, coming into play only
when the delocalization of electrons or positive charges over a
p-delocalized system is concerned.[1] Very rarely does the
redox chemistry of the ligand have chemical consequences,
2]
We approached this goal by studying the redox chemistry of
transition metals bonded to tetradentate, highly p-delocalized
Schiff bases, and choose titanium(iii) and vanadium(iii) bound
to the salophen [N,N'-phenylenebis(salicylideneiminato) dia-
nion] ligand as model compounds. In such a chemical
environment, it is difficult to reduce titanium and vanadium
to lower oxidation states; thus the reduction affected the
ligand exclusively. This investigation led us to discover the
reductive coupling of imino groups across two monomeric
units, with the consequent formation of C�C bonds which
[
a] Prof. Dr. C. Floriani, Dr. E. Solari, F. Franceschi
Institut de Chimie Min e rale et Analytique, Universit e de Lausanne
BCH, CH-1015 Lausanne (Switzerland)
Fax : (‡ 41)21-6923905
E-mail: carlo.floriani@icma.unil.ch
[
[
b] Dr. Marzio Rosi
function as reversible reservoirs of two electrons. They can be
coupled or not with the metal, to function as long-range
electron-transfer agents. Some results in this field, with
Dipartimento di Chimica, Universit aÁ di Perugia (Italy)
c] Prof. Dr. A. Chiesi-Villa, Dr. C. Rizzoli
Dipartimento di Chimica, Universit aÁ di Parma (Italy)
7
08
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Chem. Eur. J. 1999, 5, No. 2

7
08±721
transition metals such as zirconium, cobalt,[4] nickel,[5] and
[
3]
[
2]
manganese, have already been reported, while the structure
of one of the vanadium complexes has been communicated.[
We report herein the synthesis, structure, and chemical
behavior of titanium(iii) and vanadium(iii) salophen com-
plexes reductively coupled to dimers and bridged by one or
two single C�C bonds. In contrast to work previously
6]
[
2±6]
reported
in this field, we were able to explore the reactivity
of the reduced species of the titanium and vanadium
compounds described here. In these reactions the electrons
stored at the C�C bond and in the metal atom can be
selectively used, either separately or all together, in the
reduction of O , quinones, and other substrates. An extended
2
Hückel analysis substantiated the hypothesis that the reduc-
Scheme 1. Synthesis of the starting compounds.
III
III
tion of Ti and V salophen complexes occurs with the
electron density stored at the carbon centers involved in the
C�C bridges across the two salophen units. The same
while the lower part consists of the corresponding chemical
equations. The starting materials 1 and 2 are drawn as two
overlapping, nonbonded, monomeric, cationic units. We have
calculations suggest that the first step in the transfer of the
electrons stored at the C�C bonds occurs with the oxidation of
�
the metal, followed by an electron withdrawal from nitrogen,
omitted the THF and Cl in the coordination sphere of the
and finally with the cleavage of the C�C bridge, which is never
metal. The one-electron reduction of 1 and 2 does not change
the oxidation state (‡3) of the metal. The chloride anion is
removed as NaCl, and one electron is introduced into each
monomer, resulting in a reductive coupling between two
imino groups and the formation of C�C bonded dimer.
involved directly as a reactive site.
Results and Discussion
Recrystallization of 4 in the presence of pyridine gave
crystals of [V (salophen )(Py )] (5) that were suitable for
Reductive coupling to produce C�C bonds across two metal ±
2
2
2
[7]
salophen units: The synthesis of the starting titanium(iii) and
X-ray analysis. The structural analysis of 5 (vide infra) shows,
however, that the C�C bond formation is accompanied by the
[
8]
vanadium(iii) Schiff base complexes was performed as
reported in Scheme 1, by reaction of the sodium salt of the
Schiff base, prepared in situ, with the corresponding metal(iii)
chloride. In the case of vanadium, there is an alternative
sharing of one of the oxygens of the Schiff base across the two
vanadium ions. The introduction of two further electrons into
the dimers 3 and 4 probably generates a diradical at the imino
groups and leads to a second C ± C coupling. Such a coupling is
accompanied by a change in the bonding mode of the
salophen skeleton, which can be visualized by rotating all
the oxygen arms in opposite directions, as can be followed
with the oxygen labeling employed in Scheme 2. At the same
time, each nitrogen atom bridges the two metal atoms. The
oxygen labeling in Scheme 2 shows that the two-electron
reduction of 1 and 2 not only results in the formation of a C�C
synthesis starting from the free Schiff base and VCl ´ 3thf in
3
the presence of tBu N (see Method B in the Experimental
3
Section). Complexes 1 and 2 have been fully characterized
8]
(
see Experimental Section), including an X-ray analysis of 2,[
which demonstrates the hexacoordination of the metal and
the planar arrangement of the salophen ligand.
Complexes 1 and 2 undergo stepwise reduction with sodium
metal in THF to 6 and 7, respectively. The sequence is shown
in Scheme 2, whose upper part presents the structural
consequences on the two salophen skeletons upon reduction,
bond, but also causes the exchange of the two salophen
skeletons between the two metal centers. The degree of
2+
2-
2-
2
1
2
1
1
2
1
O
O
N
N
O
O
O
N
N
O
1
O
O
2
O
O
O
O
N
N
N
O 2
N
N
O
O
N
N
+2e-
-2e-
+
2e-
2e-
M
M
M
M
M
M
M
M
M
M
-
2
'
1'
2'
N
1'
O
1'
N
N
1' O
O2'
1'
2'
N
N
O
2'
N
N
N
N
O
2
Na/THF
2
Na
2
[M(salophen)(Cl)(thf)]
M = Ti, 1
[M (salophen )(thf) ]
[M (*salophen *)(Na )(thf) ]
2
2
2
2
2
2
6
–
2NaCl
THF
M = Ti, 3
M = Ti, 6
M = V, 2
M = V, 4
M = V, 7
Py
[
V2(salophen2)(thf)2]
[V2(salophen2)(Py)2]
4
5
Scheme 2. The redox pathway showing the reversible formation and cleavage of C�C bonds. In the structural representation, THF and Cl� in the
coordination sphere of the metal have been omitted for the sake of clarity.
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709

C. Floriani et al.
FULL PAPER
coupling, that is the formation of one or of two C�C bonds,
between the two starting monomeric units is controlled by the
molar ratio between the metal and the reducing agent, which
is exactly 1:1 for 3 and 4 and 1:2 for 6 and 7. The second step in
the reduction process proceeds either intramolecularly, as
reported here for titanium and vanadium, or intermolecularly,
[
5]
as in the case of nickel, which yields a C�C-bridged polymer.
The choice between the two pathways is controlled by the
coordination sphere of the metal, which is pentacoordinate or
[
2]
II [5]
hexacoordinate in the case of Ti, V, and Mn, unlike Ni ,
which remains strictly planar tetracoordinate in such an
environment.
Complexes 3 ± 7 have been fully characterized; X-ray
structural analyses for 5 ± 7 have been carried out. Crystal
data are given in Table 1 and selected bond lengths and angles
in Table 2. The structure of 5 displays the main features given
in Scheme 2. Crystals suitable for X-ray analysis were
obtained from pyridine, which replaces thf in the coordination
sphere of the metal. The dimer shown in Figure 1 has a
crystallographically imposed C symmetry, with the twofold
axis running perpendicular to the C(7) ± C(7)' bond
Figure 1. ORTEP view of complex 5 (30% probability ellipsoids). The
prime denotes a transformation of � x, y, 0.5 � z.
2
(1.595(5) Š, Table 2). Vanadium has a distorted octahedral
coordination with the equatorial plane defined by the N O2
2
set of donor atoms from salophen, and the axial positions
filled by pyridine and the oxygen O(1)' of the adjacent
salophen. The N O core is planar, the deviations from
The major structural changes between 3/4 and 6 (Figure 2)/
7 (Figure 3) are depicted in Scheme 2.
The salophen moieties coupled by two C�C bonds [C(7) ±
2
2
planarity ranging from � 0.009(3) to 0.009(3) Š for N(1) and
N(2), respectively. As a consequence of the C�C bond
C(14)', 1.605(6) Š in 6 and 1.585(6) Š in 7] form the
centrosymmetric, dinucleating, octaanionic *salophen * li-
2
formation, the six-membered chelating ring involving C(7) is
folded along the C(7) ´´´ O(1) line; the dihedral angle between
the V(1)-N(1)-C(7)-O(1) and the O(1)-C(1)-C(6)-C(7) mean
planes is 40.7(2)8. The V± O and V± N distances are close to
gand, which has been drawn without the metal centers in
Figure 4. The two centrosymmetric metal atoms are bonded to
the opposite sides of the centrosymmetric N(4) planar core at
distances ranging from 2.120(4) to 2.135(2) Š in 6 and from
2.054(2) to 2.072(3) Š in 7. The coordination around each
metal is completed by two cis-arranged oxygens [O(1), O(2)
around Ti(1) or V(1)] (Figure 5). Referring to Figure 5, it
should be mentioned that i) the metal ion does not occupy the
center of the prism; the displacements from the three
faces O(1),O(2),N(1),N(2), O(1),O(2),N(1)',N(2)', and
[
8]
those found in 2, while the distances of vanadium to the
bridging oxygens are much longer [V(1)' ± O(1) 2.052(3);
V(1) ± O(1)' 2.055 Š]. The original salophen ligand has been
converted in the reduction, assisted by the metal, into the
dinucleating hexaanionic salophen , which holds the two
2
metal ions rather close [V(1) ´´´ V(1)' 3.099 Š].
Table 1. Crystallographic data for complexes 5 ± 7, 16, 19, and 20.
Complex
formula
5
6
7
16
19
20
C
50
H
38
N
6
O
4
V
2
´
C
68
H
84
N
4
Na
2
O
11Ti
2
´
C
64
H
76
N
4
Na
2
O
10
V
2
´
C
48
H
48
N
4
Na
2
O
10
V
2
C
80
H
56
N
8
O10Ti
4
´
39 29 3 2
C H N O Ti
3
C
4
H
8
O
2C
4
H
8
O
2C
4
H
8
O
7 8
2C H
a [Š]
b [Š]
c [Š]
a [8]
b [8]
15.742(1)
20.343(2)
17.262(2)
90
94.30(1)
90
12.971(5)
13.806(5)
12.527(5)
95.87(3)
115.91(2)
62.26(3)
1771.4(14)
1
21.275(2)
17.029(2)
19.552(2)
90
100.90(1)
90
12.026(2)
20.888(3)
9.641(1)
92.56(2)
106.98(2)
92.71(2)
2309.3(6)
1
12.502(2)
14.800(3)
11.190(2)
97.72(2)
108.16(2)
79.19(1)
1926.0(7)
2
9.528(1)
17.573(3)
18.534(3)
90
90
90
g [8]
V [Š ]
3
5512.4(9)
4
6955.7(13)
4
3103.3(8)
1
Z
M
r
1105.1
C2/c (No. 15)
22
0.71069
1.332
3.84
1419.4
P1 (No. 2)
� 135
1.5478
1.331
25.66
1353.4
C2/c (No. 15)
22
0.71069
1.292
3.31
988.8
P1 (No. 2)
� 135
1.54178
1.422
1665.3
P1 (No. 2)
� 135
1.54178
1.436
619.6
P2 2 2 (No. 19)
1 1 1
22
0.71069
1.326
3.09
Å
Å
Å
space group
T [8C]
l [Š]
calcd [gcm 3]
�
1
m [cm 1
�
]
41.26
39.78
transm. coeff.
R
0.907 ± 1.000
0.052
0.122
0.766 ± 1.000
0.070
0.208
0.968 ± 1.000
0.053
0.136
0.725 ± 1.000
0.054
0.161
0.744 ± 1.000
0.055
0.163
0.929 ± 1.000
0.060 [0.064]
0.120 [0.127]
[
a]
wR2[b]
a] R ˆ S j DF j /S j F
2
2
2
2 1/2
[
o
j based on the unique observed data [I > 2s(I)]. [b] wR2 ˆ [Sw j DF j /Sw j F
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
o
j ] calculated on the unique data with I > 0.
Chem. Eur. J. 1999, 5, No. 2
7
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Molecular Batteries
708±721
Table 2. Selected bond lengths [Š]and angles [8] for complexes 5 ± 7, 16, 19, and 20.
5[a]
6[b]
7[c]
16[d]
19[e]
20
Molecule Molecule
A
B
V(1) ± O(1) 2.052(3)
V(1) ± O(1)' 2.055(4)
V(1) ± O(2) 1.925(2)
V(1) ± N(1) 1.955(4)
V(1) ± N(2) 2.064(3)
V(1) ± N(3) 2.170(4)
N(1) ± C(7) 1.465(5)
N(2) ± C(14) 1.293(7)
C(7) ± C(7)' 1.595(5)
Ti(1) ± O(1) 2.050(3)
Ti(1) ± O(2) 2.052(3)
Ti(1) ± O(5) 2.363(3)
Ti(1) ± N(1) 2.135(3)
Ti(1) ± N(2) 2.132(4)
Ti(1) ± N(1)' 2.127(3)
Ti(1) ± N(2)' 2.120(4)
V(1) ± O(1) 1.999(2)
V(1) ± O(2) 1.993(2)
V(1) ± N(1) 2.054(3)
V(1) ± N(1)' 2.065(2)
V(1) ± N(2) 2.054(2)
V(1) ± N(2)' 2.072(3)
V(1) ± O(1) 1.954(3)
V(1) ± O(2) 1.930(4)
V(1) ± O(3) 1.617(4)
V(1) ± N(1) 2.036(4)
V(1) ± N(2) 1.994(4)
Ti(1) ± O(1)
Ti(1) ± O(2)
Ti(1) ± O(3)
Ti(1)B ± O(2)B'
Ti(1) ± N(1)
Ti(1) ± N(2)
N(1) ± C(7)
N(2) ± C(14)
1.832(5)
1.883(6)
1.787(4)
1.823(5)
2.035(5)
1.847(5)
2.144(5)
1.987(4)
2.153(6)
1.484(8)
Ti(1) ± O(1)
Ti(1) ± O(2)
Ti(1) ± N(1)
Ti(1) ± N(2)
Ti(1) ± N(3)
N(1) ± C(7)
N(2) ± C(14)
1.915(4)
1.902(4)
2.153(4)
2.151(4)
1.996(7)
2.147(6)
1.464(9)
1.686(4)
N(1) ± C(7)
1.350(7)
1.293(9)
N(1) ± C(7)
N(1) ± C(8)
1.470(5)
1.409(4)
N(2) ± C(14) 1.400(8)
Na(1) ± O(1) 2.309(4)
Na(1) ± O(2) 2.289(4)
Na(1') ± O(3) 2.284(4)
1.295(7)
N(1) ± C(7)
N(1) ± C(8)
1.458(7)
1.400(6)
1.315(11) 1.278(12) N(3) ± C(21)
1.469(6)
N(2) ± C(13) 1.407(5)
N(2) ± C(14) 1.462(5)
C(7) ± C(14)' 1.585(6)
C(7)A ± C(7)B 1.587(10)
Ti(1)-N(3)-C(21) 174.1(3)
N(2) ± C(13) 1.395(5)
N(2) ± C(14) 1.470(6)
C(7) ± C(14)' 1.605(6)
[
a] ' ˆ � x, y, 0.5 � z. [b] ' ˆ � x, 1 � y, � z. [c] ' ˆ 0.5 � x, 0.5 � y, � z. [d] ' ˆ � 1 � x, � y, 1 � z. [e] ' ˆ � x, 1 � y, 1 � z.
Figure 2. ORTEP view of complex 6 (50% probability ellipsoids). THF
Figure 4. Numbering scheme of the *salophen * ligand.
2
molecules are omitted for clarity. The prime denotes a transformation of
�
x, 1 � y, � z.
Figure 5. SCHAKAL drawing of the coordination polyhedra around
titanium and vanadium cations in complexes 6 and 7, respectively.
N(1),N(2),N(1)',N(2)' are 0.825(2), 0.364(1), and 1.259(1) for
6
, and 0.706(1), 0.495(1), and 1.196(1) Š for 7, respectively;
ii) the Ti(1) ± Ti(1)' separation is 2.518(1) and V(1) ± V(1)' is
.393(1) Š. Such a short metal ± metal distance is particularly
relevant in the explanation of the magnetic properties of 6 and
2
7
. The *salophen * ligand defines an approximately planar 12-
2
Figure 3. ORTEP view of complex 7 (30% probability ellipsoids). THF
molecules are omitted for clarity. The prime denotes a transformation of
membered ring (see Figure 4) (maximum deviation
0.5 � x, 0.5 � y, � z.
0.090(4) Š for N(1) in 6 and 0.103(4) Š for C(7)) which is
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711

C. Floriani et al.
FULL PAPER
almost coplanar with the two o-phenylenediamine rings
C(8) ´´´ C(13); the dihedral angle is 6.5(1)8 in 6 and 2.4(1)8
in 7. A better description of the macroring is that formed by
two nearly planar N(1),N(2),C(7),C(8),C(13),C(14) and
N(1)',N(2)',C(7)',C(8)',C(13)',C(14)' moieties [maximum dis-
placement 0.079(4) Š for C(14) in 6, and 0.085(4) for C(7) in
7] which are parallel from symmetry requirements and
separated by 0.153(8) in 6, and 0.065(7) Š in 7. The N O2
2
cores are almost perpendicular to the planar macroring
system [dihedral angle 88.0(1)8 in 6 and 73.1(1)8 in 7] and to
the C(8) ´´´ C(13) aromatic ring [dihedral angle 84.3(1)8 in 6
and 75.5(1)8 in 7]. The Ti�O, Ti�N, V�O, and V�N bond
lengths (Table 2) are close to those of titanium(iii) and
vanadium(iii) bonded to the Schiff base ligands previously
reported. The conformation of the ligands gives rise to cavities
which can accommodate two centrosymmetric sodium cati-
ons; each cation is bonded to the O(1) and O(2) oxygen atoms
of the same Schiff base (Figures S1 and S2 in the information
deposited at FIZ). Coordination around Na(1) is completed
by the O(3), O(4), O(5) oxygen atoms from three THF
molecules to give a distorted square pyramid. A further THF
molecule was found to be disordered about the inversion
center at 1 � x, � y, 1 � z in such a way as to provide a partial
sixth coordination site to two sodium cations which belong to
adjacent dimeric units, and which are symmetry-related by the
inversion center, in the case of 6.
At this stage we should comment on an important structural
parameter in 6 and 7, namely the very short metal ± metal
bond length. The metal ± metal separation, per se, seems to
suggest a direct metal ± metal interaction, though we are
aware that such a geometric proximity may be the conse-
quence of the constraint imposed by the very crowded
Figure 6. Magnetic properties of a) 6 and b) 7.
[
9]
2
+
2-
O 2
2
1
1
1
O
O
N
N
O
O
O
O
N
N
O
N
O
O
2
dinucleating *salophen * ligand. We expected that some
N
2
N
evidence for the existence of a metal ± metal interaction
would come from the analysis of the magnetic properties of 6
and 7 (Figure 6). The temperature dependence of the
magnetic moments of 3 and 4 are typical of antiferromagneti-
–2NaCl
+
M
M
M
M
M
M
2'
N
1'
O
1'
N
N
2'
N
N
2'
O
III
III
cally coupled Ti and V dimers, respectively. Effective
magnetic moments close to the expected values of 1.73 and
–2NaCl
2
[M(salophen)(Cl)(thf)] + [M2(*salophen2*)(Na2)(thf)6]
2 2 2
2 [M (salophen )(thf) ]
2.83 BM are observed at room temperature with a strong
M = Ti, 1
M = V, 2
M = Ti, 6
M = V, 7
M = Ti, 3
decrease as the temperature is lowered. Essentially diamag-
netic behavior is shown by 6 and 7, although the latter
compound shows a residual paramagnetism with a value of
almost 1 BM at room temperature. Such behavior can be
attributed to a high temperature-independent paramagnetism
M = V, 4
Scheme 3. The intermolecular electron transfer which occurs with cleav-
age and formation of the C�C bond.
electrons; iii) such an electron transfer can occur intermolec-
ularly. As far as the last point is concerned, we believe that the
reaction within the two complexes 1 and 6 or 2 and 7 is most
probably assisted by the alkali cations, which allow the two
species to come in contact by coordination to the same sodium
ions.[
(
TIP), probably as a result of the presence of a low-lying,
thermally nonpopulated, paramagnetic excited state.[
10]
Therefore, we remain with the hypothesis of a considerable
degree of metal ± metal single bond character in 6, and a
double bond in 7.
11]
The alternative synthesis of 3 and 4 led us to discover a
major property of the C�C bound Schiff base ligands: mixing
equimolar amounts of 1 and 6 or 2 and 7 in THF at room
temperature led to high yields of 3 and 4 as red-brown crystals
The C�C bond functioning as a two-electron reservoir: The
most attractive property of complexes 3 ± 7 is their tendency
to function as reducing agents. Depending on the oxidation
agent, both the electron stored at the C�C bond and/or the
(Scheme 3), through the same steps depicted in detail in
Scheme 2. The occurrence of such a reaction is significant in
many respects: i) the C�C bond formation and cleavage is
electrons available from the low oxidation state of the metal
can be made accessible. In Scheme 4 we report reactions in
which only the electrons stored at the C�C bond are used. In
reversible (see the reduction of 3 and 4 to 6 and 7, and reaction
in Scheme 3); ii) the C�C bond functions as a shuttle for two
7
12
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Molecular Batteries
708±721
Scheme 6. The deoxygenation of p-benzoquinone.
Scheme 4. The C�C bond functioning as an electron reservoir.
reactions represented in Schemes 5 and 6 we observed a four-
electron oxidation of the dimer; two electrons were supplied
by the cleavage of the C�C bond and two by the oxidation of
the reaction of 3 and 4 with benzyl chloride we observed the
formation of [Ti(salophen)Cl ] and 2 respectively, along with
2
III
IV
the two metal atoms (M !M ). The reactions of 3 and 4
with dioxygen (Scheme 7) emphasizes the major differences
between titanium and vanadium as a result of the difference in
toluene as a result of hydrogen abstraction from the solvent,
and 1,2-diphenylethane from the dimerization of the benzyl
‡
�
radical. The reaction of 4 with [Cp Fe] [BPh ] implies
2
4
the relative stability of the corresponding monomeric metal-
electron transfer only, without the formation of any chemical
13]
(
iv)oxo derivatives.[
[
12]
bond with the oxidized substrate in 8. The preferential use
of 3 and 4 rather than 6 and 7 as electron transfer agents is due
to their neutral form, since the identification of the reaction
products in the latter case requires the separation of the
titanium and vanadium derivatives from the sodium salts
derived from the reduction of the substrate.
In this context we examined the reaction of 3 ± 7 with
dioxygen and o- and p-quinones, which can be considered as
electronically equivalent. Quinones function primarily as two-
rather than four-electron oxidizing agents, and the reduced
form remains bonded to the metal without providing any oxo
species. In the reaction shown in Scheme 5, o-phenanthrene-
quinone was treated with 3 and 4 in THF solution. On
Scheme 7. The electron transfer from C�C bonds to dioxygen, mediated by
titanium and vanadium.
Both compounds absorb dioxygen in an O /dimer molar
2
Scheme 5. The two-electron transfer from the C�C bond to 9,10-phenan-
ratio of 1:1. The plausible peroxo species 12 undergoes a
different evolution, depending on the nature of the metal, to
give a stable monomeric oxometal(iv), 11 in the case of
vanadium, while in the case of titanium the derivative 13
polymerizes,[ usually to 14. It has to be mentioned that the
threnequinone.
refluxing the suspension we obtained the brown-red micro-
crystalline solids 9 and 10. They have been fully characterized,
including a preliminary X-ray analysis of 9 recrystallized from
DMSO. Although the atom connectivity is quite well defined,
the crystallographic structural data are so far very poor. The
reaction in Scheme 5 is a two-electron oxidation per mono-
meric fragment; one electron comes from the C�C bond and
14]
terminal oxotitanium(iv) moiety has only rarely been identi-
fied and structurally characterized.[
14±16]
In order to show that
6 and 7, which contain two C�C bonds, can be involved
equally well in redox processes, we treated 7 with dioxygen
(Scheme 8). The reaction proceeds with the very rapid
III
IV
the other from the oxidation of M to M . In fact, 9 is a
absorption of a mole of O , followed by slower absorption
2
1
diamagnetic titanium(iv) derivative, for which the H NMR
of a second mole per mole of starting material. The reaction
terminates with the formation of [VO(salophen)] (11) and
sodium peroxide. A plausible pathway can be drawn, based on
the isolation of the intermediate 16, which is intercepted when
the reaction is carried out with a limited amount of oxygen.
The first compound to form is probably the m-peroxo species
15, which still contains a C�C bond across the two Schiff base
spectrum has been recorded (see the Experimental Section),
and 10 is a vanadium(iv) derivative [meff ˆ 1.61 BM at 293 K].
The two-electron reduced form of 9,10-phenanthrenequinone
mimics the cis bonding mode of the peroxo species. The
reaction of 4 with p-benzoquinone (Scheme 6), which should
mimic dioxygen to give the trans-peroxo-type of species, led,
unexpectedly, to its unprecedented deoxygenation and thus to
the formation of the oxovanadium(iv) derivative 11. In the
units; this is presumably followed by the simultaneous
cleavage of the O�O and the C�C bonds. The reaction leads
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713

C. Floriani et al.
FULL PAPER
cation is provided by the O(1) and O(2) atoms from the Schiff
base and by the O(3)' oxo atom from the vanadyl fragment,
which are symmetry-related by the inversion center. Two
oxygen atoms from a DME molecule complete the coordina-
tion to produce a distorted trigonal bipyramid.
The reaction of 3 and 4 with organic azides, which are the
source of the nitrene PhN, which is electronically equivalent
to O, parallels the reaction with oxo-transfer reagents.[ Such
a reaction is not only mechanistically interesting with regard
to our work, but it is also a novel synthetic approach to
terminal and bridging metal ± amido derivatives.[
13]
13]
The results from the reaction of 3 with organic azides are
summarized in Scheme 9. A significant dependence on the R
substituent and the metal has been observed. The reaction of 3
Scheme 8. Reduction of dioxygen with electrons stored in the vanadium
molecular battery.
to the formation of a quite unusual oxovanadium(iii) complex
[
17]
dimer, 16, which can, eventually, absorb a further mole of
dioxygen to give the oxovanadium(iv) complex 11 and sodium
peroxide. The low yield of 16 is a consequence of the
sensitivity of 16 to oxygen.
Complex 16 consists of two crystallographically independ-
�
ent [VO(salophen)] anions, bridged in centrosymmetric
‡
dimers by two [Na(DME)] cations (Figure 7). Since the
crystals contain two independent dimers, the structural
Scheme 9. Formation of imido complexes of titanium with electrons stored
at the C�C bonds.
with PhN and Me SiN allowed the isolation of m-phenyl-
3
3
3
imido complexes 17 and 18, derived from the oxidation of
titanium(iii) to titanium(iv), while the C�C bridging bond
remained intact. These reactions provide evidence to support
the hypothesis that, in the initial step, the incoming substrate
binds and oxidizes the metal before drawing electrons from
the C�C bond reservoir. Both compounds have been fully
characterized. The low-quality X-ray structure of 17 and the
proposed bond connectivity is reported in the data deposited
at FIZ. In the case of 18, controlled hydrolysis gave a complex
which had retained the same skeleton, but in which the
phenylimido group is replaced by a bridging oxo ligand in 19,
which has been structurally characterized (vide infra). A
bridging bonding mode would be difficult in the case of
hindered substituents at the azide functionality; thus the
reaction probably follows a different pathway. Indeed, the
reaction of 3 with Ph CN resulted in the formation of the
Figure 7. ORTEP view of molecule 1 in complex 16 (50% probability
ellipsoids). The prime denotes a transformation of � 1 � x, � y, 1 � z.
parameters will be discussed only for the dimer containing
V(1). Vanadium has a square-pyramidal coordination, in
which the N O set of atoms from the salophen ligand defines
2
2
3
3
monomeric alkylimido 20 (Scheme 9).[ The formation of 20
requires both the oxidation of the metal and a concomitant
cleavage of the C�C bond. Its structure is discussed below.
18]
the base and the O(3) oxo oxygen atom is at the apex. The
metal is displaced from the mean basal plane by 2.205(4) Š,
with a V± O distance of 1.617(4) Š. As is usual in pentacoor-
dinated salophen ± metal complexes, the ligand assumes a
nearly planar conformation. Coordination around the sodium
According to the distinctive tendency of vanadium to
preferentially form terminal instead of bridging oxo or
7
14
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Molecular Batteries
708±721
phenylimido complexes, the latter type is a peculiarity of
O(3) vector forms a dihedral angle of 3.1(2)8 with the normal
titanium, the reaction of 4 with PhN led to the monomeric
3
to the N O2 core. Hexacoordination around Ti(1)B is
[
19]
2
phenylimido complex 21 (Scheme 10). This reaction paral-
lels that of 4 with PyO which gives the corresponding
oxovanadium(iv) complex 11 (Scheme 10).
provided by the donor atoms of the salophen ligand B,
namely the O(3) oxygen atom and the O(2)B' oxygen atoms
from the symmetry-related Schiff base. The metal atom is
displaced by 0.195(2) Š out of the equatorial plane towards
O(3). The Ti(1)A ´´´ Ti(1)B and Ti(1)B ´´´ Ti(1)B' separations
are 3.246(2) and 3.386(2) Š, respectively. The Ti�O(oxo)
bond length is longer for the hexacoordinate [Ti(1)B�O(3),
1
.847(5) Š] than for the pentacoordinate titanium
Ti(1)A�O(3), 1.787(4) Š]. The Ti�N bond lengths are short-
er for the negatively charged N(1) atom [mean value
.989(4) Š] than for the neutral N(2) atom [mean value
[
1
2
.150(3) Š] (Table 2). As a consequence of the C�C bond
formation, the six-membered chelation ring which involves
the C(7) carbon atoms is folded along the C(7) ´´´ O(1) line;
the dihedral angle between the Ti(1),N(1),C(7),O(1) and
O(1),C(1),C(6),C(7) mean planes is 21.0(3) and 17.7(3)8 for
the salophen ligands A and B, respectively.
Complex 20 consists of discrete [Ti(salophen){NC(Ph) }]
3
Scheme 10. Formation of vanadium(iv)-phenylimido and -oxo with elec-
trons stored both at the C�C bond and at the metal.
molecules (Figure 9). Titanium exhibits a square-pyramidal
coordination with the N and O donor atoms from the
salophen ligand at the base and the nitrogen atom from the
The structure of 19 consists of two neutral dimeric
[
{Ti(salophen)} (m-O)] units which both contain a C�C bond
2
between two iminic carbon atoms of the adjacent salophen
ligands (ligands A and B) [C(7)A ± C(7)B, 1.587(10) Š]. The
O(2) oxygen atom from the Schiff base B acts as a bridge
between the metal atoms of adjacent dimeric units to produce
the tetranuclear structure depicted in Figure 8. The tetramer
Figure 9. ORTEP view of complex 20 (30% probability ellipsoids).
imido ligand at the apex. The metal is displaced by 0.562(1) Š
from the nearly planar N O core (maximum displacements
2
2
ranging from � 0.014(4) to 0.014(4) Š). The line between Ti
and N(3) forms a dihedral angle of 5.8(1)8 with the normal to
the N O core. The Ti�N(3) bond length (1.686(4) Š) is in
2
2
good agreement with the values reported in the literature for
Figure 8. ORTEP view of complex 19 (30% probability ellipsoids). The
prime denotes a transformation of � x, 1 � y, 1 � z.
Ti�N(terminal nitrene) distances (e.g. 1.664(4) Š in dichloro-
(
tert-butylimido)(N,N,N',N'-tetramethylethylenediamine)tita-
nium and 1.681(7) Š in dichloro(tert-butylimido)(N,N'-diiso-
propylethylenediamine)titanium.[ The approximate linear-
ity of the Ti-N(3)-C(21) bond angle (174.1(3)8) is in agree-
ment with a Ti�N triple bond.
20]
possesses a crystallographically imposed C symmetry; the
i
inversion center lies at the center of gravity of the Ti(1)-
B,O(2)B,Ti(1)B',O(2)B' inner core. The coordination around
Ti(1)A is square-pyramidal, with the base defined by the
donor atoms of the salophen ligand A and the O(3) oxo
oxygen atom at the apex. The N O core is nearly planar, with
It should be emphasized that the reactions in Schemes 9 and
10 are a collection of two- and four-electron oxidations of the
dimers 3 and 4, and represent an interesting synthetic access
to bridging and terminal metal ± imido functionalities in
macrocyclic chemistry.[ In addition, these reactions provide
2
2
deviations from planarity ranging from � 0.012(6) to
21]
0.012(6) Š for N(1)A and N(2)A, respectively. The Ti(1)A ±
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715

C. Floriani et al.
FULL PAPER
very interesting information on the occurrence of the redox
reactions. It seems that the incoming reducible substrate binds
the metal, and the interconnected processes, namely the
oxidation of the metal, the formation of the metal ± nitrogen
double bond, and the cleavage of the carbon ± carbon bond,
occur as a cascade according to the sequence mentioned
above. Therefore, the removal of electrons from the metal,
then from the nitrogen will terminate with the cleavage of the
C�C bond. This hypothesis is in agreement with the obser-
vation that not one of the oxidation reactions reported
involves the C�C bond as a reactive site. We obtained
significant support for such a hypothesis from the extended
Hückel calculations carried out on the reduced species 6 and 7.
Extended Hückel analysis on titanium and vanadium Schiff
[
22, 23]
base complexes: Extended Hückel calculations
were
performed on the complexes [M(salophen)(Cl)(thf)] [M ˆ Ti,
2�
V] and [M (*salophen *)] , where *salophen * functions as a
2
2
2
dinucleating, octadentate, octaanionic ligand (see Figure 4),
in order to elucidate the nature of the reductive coupling of
imino groups that leads to C�C bonded dimers. Such a
reaction can be made reversible, so that the C�C bond
functions as a unit to store and release electrons and which
may be incorporated into rather complex structures. Our aim
is to understand the role played by the transition metal in the
redox process by means of an analysis of the electronic
structure of the oxidized and the reduced species. The
[
M(salophen)(Cl)(thf)] complex was simplified by replacing
thf with a water molecule, introduced in order to retain
hexacoordination around the metal center. The oxidized form
of the complexes has been investigated further by considering
Figure 10. Energy levels of [Ti(salophen)Cl ], [Ti(salophen)(Cl)(OH )],
and [{Ti(salophen)(Cl)} ].
2
2
2
IV
the M complex [M(salophen)(Cl) ] to be strictly related to
2
IV
[3]
the Zr system [Zr(salophen)(Cl) (thf)], as well as to the
2
dimer [{M(salophen)(Cl)} ], in which the two units interact
2
Table 3. Net charges (electronic units), obtained by Mulliken population
analysis, on the centers involved in the redox process of the titanium
complex.
through oxygen bridges in a fashion similar to that found
[
2]
experimentally for [{Mn(salophen)(Py)} ]. For the reduced
2
form of the complexes, we have considered only the species
Charge of Q(Ti)
the system
Q(N)
Q(C)
2�
[
M (*salophen *)] , which is directly related to the exper-
2
2
imental isolated system [M (*salophen *)(Na) (thf) ]. The
geometries, which were deduced from the available exper-
imental X-ray structures, were idealized to C2v symmetry for
2
2
2
6
[Ti(salophen)Cl
2
]
0
1.64
1.52
1.41
1.71
1.46
1.44
1.81
1.56
1.47
1.48
2.25
2.29
� 0.59
� 0.65
� 0.71
� 0.63
� 0.67
� 0.72
� 0.64
� 0.66
� 0.70
� 0.70
� 0.63
� 0.47
0.46
0.29
0.11
0.31
0.15
� 0.07
0.29
0.16
0.01
0.24
0.25
0.27
� 1
�
�
2
0
1
2
[Ti(salophen)(Cl)(OH )]
[
M(salophen)(Cl) ], C for [M(salophen)(Cl)(OH )], and C
2 s 2 i
2�
for the dimers [{M(salophen)(Cl)} ] and [M (*salophen *)] .
2
2
2
� 2
Let us start our analysis with [Ti(salophen)Cl ]. The
[{Ti(salophen)(Cl)}2]
0
2
IV
� 2
molecular orbitals of this Ti complex are reported in
�
4
Figure 10. The lowest unoccupied molecular orbital (LUMO)
*)]2
�
� 2
[Ti
2
(*salophen
2
is the 11b orbital, which is mainly CˆN p-antibonding in
1
0
character, with a strong polarization of the orbital towards the
carbon centers. The reduction of this system should therefore
imply a decrease of the carbon ± nitrogen bond order and an
acquisition of electron density, mainly by the carbon centers.
This is confirmed by the Mulliken population analysis
performed on the neutral and the reduced systems with a
fixed geometry; these results are reported in Table 3 as net
charges. The electron density increased by 0.12 e on Ti, 0.12 e
on N, and 0.34 e on C for a one-electron reduction and by
2
picture is more complicated because of the presence of
unpaired electrons. For [Ti(salophen)(Cl)(OH )] the 38a'
2
orbital is singly occupied. This orbital is mainly Ti d and CˆN
xz
p-antibonding in character, while the 31a'', which is the
LUMO, is essentially CˆN p-antibonding in character and is
polarized towards the carbon center. For [{Ti(salophen)(Cl)} ]
2
0.23 e on Ti, 0.24 e on N, and 0.70 e on C for a two-electron
the 64a and 64a orbitals are singly occupied and show a
u
g
reduction. A similar description applies also for [Ti(salo-
phen)(Cl)(OH )] and [{Ti(salophen)(Cl)} ], although here the
character similar to the 38a' orbital of [Ti(salophen)-
(Cl)(OH )], while the 65a and 65ag orbitals, which are
2
2
2
u
7
16
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Chem. Eur. J. 1999, 5, No. 2

Molecular Batteries
708±721
unoccupied, are essentially CˆN p-antibonding in character.
For these systems also, an increase in the electron density of
the carbon centers upon reduction is observed, though we
have an additional slight decrease in the oxidation state of the
metal. Indeed, from Table 3 we can see that the electron
density increases by 0.25 e on Ti, 0.08 e on N, and 0.32 e on C
for a one-electron reduction and by 0.27 e on Ti, 0.18 e on N,
and 0.76 e on C for a two-electron reduction for [Ti(salo-
phen)(Cl)(OH )]. For the dimer [{Ti(salophen)(Cl)} ] we
units, at least as long as the geometry does not change, while a
more pronounced oxidation strongly involves the nitrogen
centers. This is confirmed by the Mulliken population analysis
(Table 3): the electron density decreases overall by 1.54 e on
Ti (0.77 e for each metal center), 0.28 e on N, and 0.04 e on C
for a two-electron oxidation and by 1.62 e on Ti, 0.92 e on N,
and 0.12 e on C for a four-electron oxidation.
A similar description also applies for the analogous
vanadium complexes. In particular, as we can see from
Figure 12, which presents the molecular orbital diagram for
2
2
have to consider a two- and a four-electron reduction: in
Table 3 we notice that the overall increase in the electron
density is 0.50 e on Ti (0.25 e for each metal center), 0.08 e on
N, and 0.52 e on C for a two-electron reduction, and 0.68 e on
Ti, 0.24 e on N, and 1.12 e on C for a four-electron reduction.
2�
the [V (*salophen *)] complex, the orbitals describing the
2
2
C�C s bondings between the two salophen units, which are
the 59a and 59a orbitals, are more than 2 eV lower than the
g
u
energy of the HOMO in this system as well. The 60a and 60a
u
g
2�
The molecular orbitals of [Ti (*salophen *)] are reported
orbitals are mainly Np perpendicular to the N4 plane in
character, while the 61ag orbital describes the bonding
between the two vanadium atoms. The 61a and 62a orbitals,
2
2
in Figure 11, which also includes the interactions with the
u
g
which constitute the HOMO and the LUMO for the singlet
state, are very close in energy to vanadium d-orbitals. This
situation gives rise to an excited triplet state very close to the
singlet state, which is suggested to be the ground state from
the experimental magnetic behavior of [V (*salophen *)-
2
2
2�
(
Na) (thf) ]. The oxidation of the [V (*salophen *)] system
2
6
2
2
should therefore strongly affect the vanadium centers. This is
confirmed by the Mulliken population analysis performed on
2
�
[
V (*salophen *)] and its oxidized species at fixed geome-
2 2
try. The electron density decreased by 0.91 e on each
vanadium atom for the release of two electrons, and by
1.76 e for the release of four electrons, while the electron
densities on N and C remain almost unchanged.
*)]2 complex
�
Figure 11. Molecular orbital diagram for the [Ti
2
(*salophen
2
which depicts the interactions with the frontier orbitals of two
�
[
Ti(salophen)] units.
�
frontier orbitals of two [Ti(salophen)] units. The 59a and
g
5
9au orbitals describe the C�C s bonds between the two
salophen units, while the 60a and 60a are mainly composed
u
g
of Np orbitals perpendicular to the N4 plane. A small
delocalization of these orbitals towards the rings coplanar to
the N core is present. The 61a , which is the highest occupied
2�
Figure 12. Molecular orbital diagram for the [V (*salophen *)] complex
2
2
�
depicting the interactions with the frontier orbitals of two [V(salophen)]
units.
4
g
x2� y2
molecular orbital (HOMO), is mainly Ti d and binds the
two titanium atoms. Small Np components are present, which
also ascribe a weak Ti�N bonding character to this orbital.
Conclusions
The lowest unoccupied orbitals, 61a and 62a , are essentially
u
g
titanium d orbitals. Therefore, the oxidation of this system
implies, as a first step, the oxidation of the metal centers and
does not affect the C�C s bonds between the two salophen
This report deals with a rather unique investigation into the
chemical reduction of early transition metal ± Schiff base
complexes. This kind of experimental approach enabled us to
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717

C. Floriani et al.
FULL PAPER
discover: i) the possibility of investigating the reduction
pathways of p-delocalized ligands in the case of metals which
are difficult to reduce; ii) a novel mode of storing and
releasing electrons based on the reversible formation and
cleavage of C�C bonds; iii) C�C bonds which function as two-
Yield: 28.3 g (80%); anal. calcd for C28
.14; found: C 61.07, H 5.35, N 4.88.
Method B: Tributylamine (18.8 g, 100 mmol) was added to a solution of
salophen)H (12.84 g, 40.6 mmol) in THF (250 mL). The color turned from
yellow to brown after the addition of VCl ´ 3thf (14.5 g, 40.6 mmol). The
suspension was refluxed for 3 h and then allowed to stand at room
temperature for 1 h. The crystalline brown product was filtered, washed
with cooled THF (50 mL), and dried in a vacuum. Yield: 18.83 g (85%); IR
H
30ClN
2
O
4
V: C 61.71, H 5.55, N
5
(
2
3
electron reservoirs without being involved in the chemical
reactivity; iv) the metal-assisted long-range electron transfer
from the C�C bonds to incoming substrates; v) the introduc-
(
1
(
nujol): nÄ max ˆ 1602 (s), 1574 (s), 1532 (s), 1318 (m), 1256 (m), 1191 (m),
152 (m), 1032 (w), 924 (m), 868 (m), 814 (m), 758 (s), 622 (m), 538 (m), 497
tion (see the nitrene reactivity) of important functionalities by
the use of the electron-rich forms.
� 1
� 1
� 1
w) cm ; UV/Vis (THF): lmax (emax, m cm ) ˆ 308 (20400), 336 (17500),
388 (14100), 435 sh nm (8000); anal. found: C 61.45, H 5.31, N 5.11.
Synthesis of 3 ´ thf:
Method A: Sodium sand (386 mg, 16.8 mmol) was added to a dark blue
suspension of 1 ´ thf (9.09 g, 16.8 mmol) in THF (250 mL). This mixture was
stirred at room temperature for 3 days. Sodium chloride was filtered off and
the solvent was evaporated to dryness. The brown residue was then treated
Experimental Section
with Et
line product was collected. Yield: 5.69 g (78%); anal. calcd for C48
Ti : C 66.37, H 5.10, N 6.45; found: C 66.18, H 5.11, N 6.45.
2
O (150 mL) to give a suspension from which a brown microcrystal-
General procedure: All reactions were carried out in an atmosphere of
purified nitrogen. Solvents were dried and distilled before use by standard
methods. Infrared spectra were recorded with a Perkin ± Elmer FT1600
spectrophotometer, UV/Vis spectra were recorded with a Hewlett ± Pack-
ard 8452A diode array spectrophotometer, and NMR spectra were
recorded on a Bruker AC200 instrument. Phenyl azide was prepared
44 4 6
H N O -
2
Method B: 1 ´ thf (3.54 g, 6.53 mmol) was added to a brown solution of 6
(3.93 g, 3.27 mmol) in THF (500 mL). This mixture was stirred at room
temperature for 4 days. Sodium chloride was filtered off and the solvent
was evaporated to dryness. The residue was then treated with pentane
(150 mL), to give a suspension from which a brown product was collected
and dried in a vacuum. Yield: 4.9 g (86%); IR (nujol): nÄ max ˆ 1593 (m), 1544
(w), 1270 (s), 1190 (w), 1106 (m), 1081 (m), 1026 (m), 907 (m), 863 (m), 808
according to the reported procedure.[
24]
Magnetic susceptibility was
measured at 80 ± 300 K on a MPMS5 SQUID susceptometer (Quantum
Design) operating at a magnetic field strength of 3 kOe. Corrections were
applied for diamagnetism calculated from Pascal constants.
�
1
(
w), 753 (s), 639 (m), 553 (w) cm ; anal. found: C 66.51, H 5.42, N 6.73.
Synthesis of Ph
3 3 3 3
CN : NaN (6 g, 100 mmol) was suspended in CHCl
(
80 mL) in a three-necked flask equipped with a mechanical stirrer. The
Synthesis of 4:
suspension was cooled to � 58C in an ice ± salt bath, and then trifluoro-
Method A: Sodium sand (133 mg, 5.80 mmol) was added to a brown
suspension 2 ´ thf (3.16 g, 5.80 mmol) in THF (250 mL). This mixture was
stirred at room temperature for 3 days. Sodium chloride was filtered off and
the solvent was evaporated to dryness. The brown residue was then treated
acetic acid (28.6 g, 250 mmol) was added. After 10 min, triphenylmethanol
(
13 g, 50 mmol) was added to give a yellow slurry that slowly became white.
This mixture was kept at � 58C for 3.5 h, and was then allowed to reach
room temperature. The mixture was neutralized by the slow addition of an
aqueous solution of ammonia (12%, 36 mL) and then transferred to a
separation funnel. The organic layer was separated and the aqueous
with Et O (100 mL) resulting in a suspension from which a dark violet
2
microcrystalline product was collected and dried in a vacuum. Yield: 2.1 g
(83%); anal. calcd for C H N O V : C 65.91, H 5.07, N 6.41; found: C
48
44
4
6
2
solution extracted with fresh CHCl
extracts were then washed with water (50 mL), separated, dried over
MgSO , and filtered. The solvent was removed under vacuum to give a pale
3
(80 mL). The combined organic
65.10, H 5.40, N 6.89.
Method B: 2 ´ thf (6.22 g, 11.4 mmol) was added to a brown solution of 7
6.90 g, 5.71 mmol) in THF (500 mL). This mixture was stirred at room
temperature for 2 days. Sodium chloride was filtered off and the solvent
was evaporated to dryness. The brown residue was then treated with Et
200 mL) to give a suspension from which a dark violet microcrystalline
product was collected and dried in a vacuum. Yield: 3.5 g (70%); IR
4
(
yellow oil. Yield: 14.04 g (98%). As far as we found, this azide can be
1
handled without any particular precautions. H NMR (200 MHz, CDCl
3
,
2
O
2
98 K): d ˆ 7.34 (brs); IR (liquid film): nÄ max ˆ 2096 (s), 1955 (w), 1810 (w),
(
1732 (w), 1594 (w), 1486 (m), 1445 (s), 1252 (m), 1210 (w), 1084 (w), 1032
�
1
(
w), 943 (w), 898 (w), 760 (s), 715 (m), 696 (s), 667 (w), 626 (w) cm
Synthesis of 1 ´ thf: Sodium hydride (7.0 g, 292 mmol) was slowly added to a
yellow suspension of (salophen)H (42.4 g, 134 mmol) in THF (1100 mL).
This mixture was stirred at room temperature for 10 min, then refluxed for
h. The suspension was filtered and the yellow solid extracted with the
mother liquor to remove excess sodium hydride. To the resulting orange
solution was added TiCl ´ 3thf (49.6 g, 134 mmol) to give a deep blue
.
(
9
nujol): nÄ max ˆ 1600 (s), 1578 (m), 1528 (m), 1267 (m), 1144 (w), 1028 (w),
� 1
17 (w), 856 (w), 750 (s), 606 (w), 544 (m), 438 (w) cm ; UV/Vis (THF):
� 1
� 1
2
l
max (emax, m cm ) ˆ 294 sh (33400), 392 (16600), 548 nm (5920); anal.
found: C 64.99, H 5.77, N 6.18. Recrystallization from THF/Py produced
crystals of [Ti (salophen )(Py )] (5) which were suitable for X-ray analysis.
Synthesis of 6:
1
2
2
2
3
Method A: Sodium sand (0.418 g, 18.2 mmol) was added to a dark blue
suspension of 1 ´ thf (4.68 g, 8.64 mmol) in THF (250 mL). The color
immediately turned dark green and then slowly brown-red. The suspension
was stirred at room temperature for 30 min, then refluxed for 2 h. Sodium
suspension, which was then refluxed for 3 h. The product was filtered and
the solid extracted with the mother liquor from the filtration, which was
better than fresh solvent, in order to eliminate sodium chloride. The
suspension was reduced to half of its volume and the deep blue product
dried in a vacuum. Yield: 62 g (85%); IR (nujol): nÄ max ˆ 1597 (s), 1567 (s),
chloride was filtered off and the solution was concentrated to 30 mL. Et
70 mL) was added dropwise and the suspension was left to stand overnight
at room temperature. A brown crystalline product was collected and dried
2
O
(
1548 (w), 1525 (s), 1493 (m), 1430 (s), 1338 (m), 1321 (s), 1283 (m), 1257
(
(
(
m), 1231 (m), 1192 (s), 1152 (s), 1126 (m), 1062 (s), 1030 (s), 967 (m), 927
in a vacuum. Yield: 3.92 g (75%); anal. calcd for C64
63.89, H 6.37, N 4.66; found: C 63.23, H 5.71, N 4.84.
76 4 2 2
H N Na O10Ti : C
s), 878 (m), 818 (s), 788 (w), 755 (s), 664 (w), 625 (s), 601 (w), 587 (w), 558
�
1
m), 541 (s), 511 (w), 486 (s), 459 (m), 441 (w) cm ; anal. calcd for
Ti: C 62.06, H 5.58, N 5.17; found: C 61.89, H 5.27, N 5.28.
C
28
H
30ClN
2
O
4
Method B: Sodium sand (0.280 g, 12 mmol) was added to a brown
suspension of 3 (5.21 g, 6 mmol) in THF (300 mL). The mixture was stirred
for 2 days. The solution was concentrated to 30 mL before Et O (100 mL)
2
Synthesis of 2 ´ thf:
Method A: Sodium hydride (4.19 g, 175 mmol) was slowly added to a
was added dropwise. The suspension was left to stand overnight at room
temperature and the brown crystalline product was collected and dried in a
vacuum. Yield: 5.56 g (77%); IR (nujol): nÄ max ˆ 1586 (w), 1546 (w), 1255
yellow suspension of (salophen)H
and the mixture stirred at room temperature for 10 min, then refluxed for
h. The suspension was filtered and the yellow solid extracted with the
mother liquor in order to remove excess sodium hydride. To the resulting
orange solution was added VCl ´ 3thf (23.2 g, 64.8 mmol) to give a brown
2
(20.5 g, 64.8 mmol) in THF (500 mL)
1
(
(
s), 1147 (w), 1103 (w), 1045 (s), 895 (w), 845 (w), 753 (m), 730 (s), 639
w) cm ; anal. found: C 63.38, H 5.98, N 4.36;
�
1
3
Synthesis of 7:
suspension which was refluxed for 3 h. The product was extracted with the
mother liquor to eliminate sodium chloride. The suspension was reduced to
half of its volume and the brown product collected and dried in a vacuum.
Method A: Sodium sand (0.214 g, 9.33 mmol) was added to a brown
suspension of 2 ´ thf (2.31 g, 4.24 mmol) in THF (100 mL). This mixture was
7
18
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Chem. Eur. J. 1999, 5, No. 2

Molecular Batteries
708±721
539 (m), 500 (w) cm 1; anal. calcd for C38
�
H
N
O
5
V: C 70.70, H 4.68, N 4.34;
stirred at room temperature overnight and then refluxed for 3 h. Sodium
chloride was filtered off, the brown solution was reduced to half of its
30
2
found: C 70.78, H 4.73, N 4.14.
volume, Et
2 h. An amber microcrystalline solid was collected and dried in a vacuum.
Yield: 1.81 g(71%); anal. calcd for C64 Na : C 63.57, H 6.33, N
.63; found: C 63.16, H 6.91, N 4.95.
2
O (100 mL) was added, and the solution was then left at 08C for
Reaction of 4 with p-benzoquinone, synthesis of 11: Complex 4 (1.37 g,
.57 mmol) was added to an orange solution of p-benzoquinone (0.169 g,
.57 mmol) in THF (100 mL). The resulting dark green suspension was
1
1
1
H
76
N
4
2 10 2
O V
4
stirred for 20 min and then refluxed overnight. The solvent was evaporated
to dryness and the residue was treated with hexane (100 mL), collected, and
dried in a vacuum. Yield of 11 ´ thf: 1.15 g (80%); IR (nujol): nÄ max ˆ 1600
Method B: Sodium sand (184 mg, 8 mmol) was added to
a brown
suspension of 4 (3.5 g, 4 mmol) in THF (150 mL) and the mixture was
stirred for 2 days. The solvent was evaporated to dryness and the residue
(
(
4
s), 1578 (m), 1528 (m), 1267 (m), 1144 (w), 1028 (w), 917 (w), 856 (w), 750
�
1
s), 606 (w), 544 (m), 438 (w) cm ; anal. calcd for C24
.89, N 6.18; found: C 63.13, H 4.20, N 6.03.
22 2 4
H N O V: C 63.58, H
was treated with Et
2
O (100 mL), collected, and dried it in a vacuum. Yield:
1
.76 g (73%); IR (nujol): nÄ max ˆ 1589 (m), 1561 (w), 1282 (s), 1233 (m), 1105
�
1
(
w), 1085 (w), 1049 (s), 801 (w), 756 (s), 726 (s), 706 (m), 542 (w) cm ; UV/
Reaction of 3 with dioxygen, synthesis of 14: A solution of 3 (0.92 g,
1.06 mmol) in THF (100 mL) was exposed to dry oxygen. The color
changed from brown to dark red and a pale brown solid precipitated. Gas
Vis (THF): lmax (emax, m cm� 1) ˆ 286 (39400), 340 sh nm (21000); anal.
� 1
found: C 62.96, H 6.33, N 4.12.
volumetry showed that the solution absorbed 1.02 mmol of O
2
within
Reaction of 3 with PhCH
4.7 mmol) was added to a solution of 3 (1.46 g, 1.68 mmol) in THF
125 mL), the mixture was refluxed overnight, and allowed to cool to room
temperature. A brown microcrystalline solid precipitated. The solvent was
2
Cl: Freshly distilled benzyl chloride (4.39 g,
1
60 min. The solid was collected and dried in a vacuum. Yield: 0.71 g
3
(
(
(
(
88%); IR (nujol): nÄ max ˆ 1612 (s), 1583 (s), 1539 (s), 1444 (s), 1311 (s), 1189
m), 1140 (m), 1117 (w), 1033 (w), 922 (w), 872 (m), 817 (m), 750 (s), 623
�
1
m), 540 (m), 490 (w), 450 (w) cm ; anal. calcd for C20
14 2 3
H N O Ti: C 63.51,
evaporated to dryness and [Ti(salophen)Cl
2
] was then stirred in Et
2
O
H 3.73, N 7.41; found: C 62.71, H 3.98, N 6.73.
Reaction of 4 with dioxygen: A solution of 4 (1.18 g, 1.35 mmol) in THF
100 mL) was exposed to dry oxygen. The color changed from violet to dark
green. Gas volumetry showed that the solution absorbed 1.04 mmol of O
1
(
(
(
1
(
(
100 mL), filtered, and dried in a vacuum. Yield: 1.16 g (80%); H NMR
200 MHz, [D
m, 2H, Ar), 6.63 (m, 2H, Ar); IR (nujol): nÄ max ˆ 1594 (s), 1572 (s), 1544 (s),
294 (m), 1267 (s), 1235 (m), 1200 (m), 1150 (w), 1117 (w), 1033 (w), 967
w), 922 (m), 867 (m), 833 (s), 750 (s), 661 (s), 567 (w), 540 (m), 485 (m), 440
6
]acetone, 298 K): d ˆ 7.98 (s, 1H, CH), 7.02 (m, 2H, Ar), 6.91
(
2
within 129 min. The solvent was evaporated to dryness and was washed
with hexane (100 mL), the green product was collected and dried in a
vacuum. Yield of 11 ´ thf: 1 g (81%); anal. found: C 63.73, H 4.21, N 6.85.
For spectroscopic data vide supra.
�
1
w) cm ; anal. calcd for C20
5.81, H 3.73, N 6.28.
14 2 2 2
H N O Cl Ti: C 55.46, H 3.26, N 6.49; found: C
5
Reaction of 4 with PhCH
5.6 mmol) was added to a solution of 4 (1.25 g, 1.43 mmol) in THF
100 mL). The mixture was refluxed overnight and allowed to cool to room
2
Cl: Freshly distilled benzyl chloride (3.24 g,
Reaction of 7 with dioxygen: A solution of 7 (1.33 g, 1.1 mmol) in THF
2
(
(
100 mL) was exposed to dry oxygen. An immediate color change from
brown to wine-red was observed. Gas volumetry showed that the solution
absorbed 2.3 mmol of O . The solvent was evaporated to dryness and the
pale brown residue was suspended in doubly distilled water. The product
was obtained by filtration of the Na -containing solution and recrystal-
lization from CHCl . Yield of complex 11: 0.5 g (60%); anal. calcd for 11,
V: C 63.00, H 3.70, N 7.35; found: C 63.26, H 3.58, N 7.67. For
temperature. A brown microcrystalline solid precipitated. The solution was
concentrated to 2/3 of its initial volume, 2 ´ thf was collected and dried in a
vacuum. Yield: 1.36 g (87%); anal. found: C 61.83, H 5.28, N 5.07. For
spectroscopic data vide supra.
2
2
O
2
3
‡
�
Reaction of 4 with [(Cp)
2
Fe] [BPh
4
] , synthesis of 8: To a solution of 4
20 14 2 3
C H N O
(
[
1.17 g, 1.34 mmol) in THF (150 mL) at � 408C was added
spectroscopic data vide supra.
‡
�
(Cp) Fe] [BPh ] (2.17 g, 4.29 mmol) in one portion. The mixture was
2
4
Synthesis of 16: Complex 7 (2.3 g, 1.90 mmol) was dissolved in DME
allowed to slowly reach room temperature and a color change from violet
to dark-orange was observed. The solvent was evaporated to dryness and
the brown residue was suspended in hexane (150 mL). The orange solution
was discarded and the brown solid extracted in hot THF (100 mL). The
solvent was evaporated to dryness and the product was suspended in
hexane (100 mL), collected, and dried in a vacuum. Yield: 2 g (89%); IR
(
110 mL). The brown solution was exposed to a slow diffusion of O
until the color turned deep violet. The mixture was then allowed to stand at
58C for 3 days. The crystalline solid which formed was collected and
2
for 8 h,
�
analyzed. Yield: 220 mg (13%); IR (nujol): nÄ max ˆ 1606 (s), 1585 (s), 1536
(
(
(
m), 1481 (s), 1440 (s), 1322 (s), 1270 (s), 1172 (w), 1151 (m), 1128 (w), 1050
m), 949 (s), 920 (m), 865 (w), 801 (w), 746 (s), 732 (s), 627 (m), 610 (m), 569
w), 543 (m), 506 (w), 474 (w), 431 (w) cm ; anal. calcd for 16,
(
(
nujol): nÄ max ˆ 1945 (w), 1883 (w), 1821 (w), 1603 (s), 1533 (s), 1439 (s), 1304
� 1
m), 1282 (w), 1264 (w), 1238 (w), 1191 (w), 1151 (m), 1122 (w), 1104 (w),
44 44 4 2 10 2
C H N Na O V : C 65.00, H 5.45, N 6.32; found: C 64.73, H 5.11, N 6.88).
1
031 (w), 1016 (w), 965 (w), 922 (w), 864 (m), 813 (m), 754 (m), 729 (m), 700
Synthesis of 17: Phenyl azide (0.442 g, 3.71 mmol) was added to a solution
of 3 (1.61 g, 1.85 mmol) in THF (90 mL). The color immediately turned
dark red. The mixture was stirred overnight and then concentrated to
30 mL. n-Hexane (100 mL) was added dropwise and the product was
collected and dried in a vacuum. Yield: 1.35 g (76%). Crystals suitable for
X-ray analysis were grown in a toluene solution. 1H NMR (200 MHz,
�
1
(
s), 627 (m), 609 (m), 540 (m), 496 (w), 442 (w) cm ; anal. calcd for
V: C 75.72, H 5.99, N 3.33; found: C 75.33, H 6.18, N 3.04
52 2 4
C H50BN O
Synthesis of 9: Complex 3 (2.80 g, 3.22 mmol) was added to a solution of
,10-phenanthrenequinone (1.34 g, 6.45 mmol) in THF (250 mL). The
9
brown suspension was refluxed overnight and then concentrated to half of
its volume. Hexane (100 mL) was added, and the brown solid was then
CD
7.8 Hz, J
3
CN, 298 K): d ˆ 9.18 (s, 2H, CHˆN); 7.95 (m, 2H, Ar); 7.71 (dd, J
ˆ
o
1
filtered and dried in a vacuum. Yield: 3.10 g (75%); H NMR (200 MHz,
m
ˆ 1.5 Hz, 2H, Ar); 7.55 ± 7.45 (m, 4H, Ar); 7.09 ± 6.81 (m, 13H,
[
2
D
6
]DMSO, 298 K): d ˆ 9.53 (s, 1H, CHˆN); 8.49 (dd, J
.0 Hz, 1H, quin); 8.05 (m, 1H, Ar); 7.91 (dd, J
ˆ 6.8 Hz, J
quin); 7.75 (td, J ˆ 2.0 Hz, 1H, quin); 7.55 (m, 1H, Ar); 7.26
ˆ 6.8 Hz, J
m, 1H, Ar); 7.16 (t, J ˆ 6.8 Hz, 1H, quin); 7.04 (m, 2H, Ar); 6.85 (m, 1H,
o
ˆ 6.8 Hz, J
m
ˆ
Ar); 6.71 ± 6.36 (m, 8H, Ar); 5.85 (s, 2H, CH-N); 3.65 (m, 8H, THF); 1.8
(m, 8H, THF); IR (nujol): nÄ max ˆ 1600 (s), 1578 (s), 1533 (s), 1444 (s), 1306
(s), 1272 (s), 1144 (m), 1028 (w), 922 (w), 856 (m), 750 (s), 622 (m), 544
(w) cm ; anal. calcd for 17, C54H N O Ti : C 67.58, H 5.15, N 7.30; found: C
49 5 6 2
67.18, H 5.05, N 7.03.
o
m
ˆ 2.0 Hz, 1H,
o
m
�
1
(
Ar); 3.58 (m, 2H, THF); 1.75 (m, 2H, THF); IR (nujol): nÄ max ˆ 1608 (s),
1
1
7
4
580 (s), 1543 (s), 1489 (m), 1441 (s), 1334 (w), 1294 (s), 1281 (s), 1200 (w),
150 (m), 1123 (w), 1110 (w), 1059 (m), 1026 (m), 925 (w), 861 (m), 814 (m),
90 (w), 754 (s), 724 (w), 690 (w), 640 (s), 623 (m), 600 (s), 543 (m), 486 (m),
Synthesis of 18: Trimethylsilyl azide (0.53 g, 4.60 mmol) was added to a
suspension of 3 (2 g, 2.30 mmol) in THF (100 mL). The mixture was stirred
overnight, refluxed for 30 min, and then filtered and dried. The product was
washed with n-hexane (100 mL), collected, and dried in a vacuum. Yield:
1
�
1
30 2 5
52 (w), 412 (m) cm ; anal. calcd for C38H N O Ti: C 71.03, H 4.71, N 4.36;
found: C 70.29, H 4.63, N 4.28.
Synthesis of 10: Complex 4 (1.9 g, 2.17 mmol) was added to a solution of
,10-phenanthrenequinone (0.9 g, 4.34 mmol) in THF (150 mL). The
1
.17 g (63%); H NMR (200 MHz, C
6
D
6
, 298 K): d ˆ 8.36 (s, 2H, CHˆN),
); IR
nujol): nÄ max ˆ 1596 (s), 1575 (s), 1440 s), 1307 (m), 1280 (m), 1030 (w), 920
7
(
(
.40 ± 6.10 (m, 24H, Ar), 5.71 (s, 2H, CHˆN), � 0.19 (s, 9H, CH
3
9
�
1
w), 856 (w), 750 (s), 620 (m), 545 (w) cm
; anal. calcd for 18,
brown suspension was refluxed overnight and was then concentrated to
half of its volume. Hexane (100 mL) was added and the brown solid was
filtered and dried in a vacuum. Yield: 1 g (71%); meff (293 K) ˆ 1.61 BM; IR
43 37 5 4
C H N O
SiTi: C 63.63, H 4.59, N 8.63; found: C 63.08, H 4.51, N 8.57.
Synthesis of 19: Complex 18 (0.4 g, 0.493 mmol) was dissolved in wet
toluene (70 mL). The solution was stirred for 1 day and then allowed to
stand at � 28C for 2 days. A red-brown solid was collected and dried in a
(
(
nujol): nÄ max ˆ 1606 (s), 1572 (s), 1533 (s), 1439 (s), 1311 (s), 1256 (w), 1194
m), 1150 (s), 1028 (m), 922 (w), 850 (w), 806 (m), 750 (s), 722 (m), 622 (w),
Chem. Eur. J. 1999, 5, No. 2
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0947-6539/99/0502-0719 $ 17.50+.50/0
719

C. Floriani et al.
FULL PAPER
vacuum. Yield: 0.036 g (9.92%). Crystals suitable for X-ray analysis were
The final difference maps showed no peaks which had a chemical meaning
above the general background, except for a peak of 1.02 eŠ in 6 located
midway along the Ti(1)�N(2) bond.
The refinement of complexes 16 and 20 was straightforward.
1
� 3
grown in the mother liquor. H NMR (200 MHz, C
6
D
6
, 298 K): d ˆ 8.23 (s,
2
H, CHˆN), 7.52 ± 5.98 (m, 24H, Ar), 5.68 (s, 2H, CH-N); anal. calcd for
19, C40H
28
N
4
O
5
Ti : C 64.89, H 3.81, N 7.57; found: C 64.21, H 3.98, N 7.95.
2
Complex 5: The three THF solvent molecules of crystallization were
affected by severe disorder. The O(3), C(32) ± C(34) and O(4), C(35) ±
C(38) THF molecules were found to be statistically distributed over two
positions about an inversion center and a two-fold axis, respectively. The
atoms were therefore isotropically refined with a site occupation factor of
Synthesis of 20: Complex 3 (2.10 g, 2.42 mmol) was added to a solution of
triphenylmethyl azide (1.38 g, 4.83 mmol) in THF (150 mL). The solution
was stirred for 6 h, refluxed for 1 h, then allowed to reach room temper-
ature, and left to stand overnight which gave a precipitate. The solution was
concentrated to 20 mL and n-hexane (100 mL) was added dropwise. The
brown product was collected and dried in a vacuum. Yield: 2.03 g (67.8%).
0
.5. The O(5), C(39) ± C(42) THF molecule was distributed over four
positions about a two-fold axis. The best fit was obtained by splitting the
O(5) atom over two positions (A and B) and isotropically refining the
atoms with a site occupation factor of 0.75 for C(40), C(42) and 0.25 for
O(5)A, O(5)B, C(39), and C(41). During the refinement, the C�O and C�C
Crystals suitable for X-ray analysis were grown in a THF/Et
2
O solution.
1
H NMR (200 MHz, TDF, 298 K): d ˆ 8.99 (s, 2H, CHˆN), 7.83 (dd, 2H,
J
o
ˆ 6.35 Hz, J
m
ˆ 2.93 Hz, Ar salophen); 7.55 ± 7.40 (m, 6H, Ar salophen),
ˆ 6.35 Hz, J ˆ 2.93 Hz, Ar salophen), 7.08 (d, 2H, J ˆ
.30 Hz, Ar salophen), 6.90 ± 6.65 (m, 17H, Ar salophen ‡ Ph); IR (nujol):
7.37 (dd, 2H, J
o
m
bond lengths within the disordered THF solvent molecules were con-
strained to be 1.48(1) and 1.54(1) Š, respectively.
8
nÄ max ˆ 1601 (s), 1576 (s), 1534 (s), 1440 (s), 1315 (s), 1221 (s), 1191 (s), 1145
(
s), 1121 (m), 1076 (w), 1024 (w), 963 (w), 921 (w), 888 (w), 864 (w), 846 (w),
Complex 6: The C(31) carbon atom of a coordinated THF molecule
showed high thermal parameters which indicate the presence of disorder.
The atom was then split over two positions (A and B) and isotropically
refined with site occupation factors of 0.8 and 0.2, respectively. One THF
molecule was found to be statistically distributed over two positions about
an inversion center approximately sharing the C(33) atom and alternatively
coordinating the sodium cations of adjacent complexes. The best fit was
obtained by isotropically refining the O(6), C(34), and C(35) atoms with a
site occupation factor of 0.5 and anisotropically refining the C(33) atom.
The C(41) ± C(44) carbon atoms of the THF solvent molecule of
crystallization were found to be disordered over two positions (A and B)
and were isotropically refined with a site occupation factor of 0.5. During
the refinement, the C�O and C�C bond lengths involving the disordered
8
4
7
15 (m), 788 (w), 754 (s), 697 (s), 636 (m), 621 (m), 557 (w), 542 (s), 496 (m),
�
1
81 (w), 460 (w), 442 (w), 416 (m) cm ; anal. calcd for 20, C39
29 3 2
H N O Ti: C
5.61, H 4.72, N 6.78; found: C 75.34, H 4.81, N 6.93.
3
Reaction of 4 with PhN , synthesis of 21: Phenyl azide (0.332 g, 2.79 mmol)
was added to a solution of 4 (1.22 g, 1.39 mmol) in THF (100 mL). An
immediate color change from violet to brown was observed. The mixture
was stirred overnight and a microcrystalline solid separated. The solution
was concentrated to 40 mL and hexane (100 mL) was then added dropwise.
Then the product collected and dried in a vacuum. Yield: 1.18 g (80%); meff
(
1
9
295 K) ˆ 1.77 BM; IR (nujol): nÄ max ˆ 1605 (s), 1578 (s), 1534 (s), 1434 (s),
315 (s), 1257 (w), 1233 (w), 1187 (s), 1150 (s), 1126 (w), 1066 (w), 1029 (w),
96 (w), 969 (w), 923 (m), 899 (w), 859 (w), 809 (m), 788 (w), 752 (s), 685
THF solvent molecules were constrained to be 1.48(1) and 1.54(1) Š,
respectively.
(
(
m), 621 (m), 604 (m), 558 (m), 541 (s), 501 (m), 481 (m), 447 (w), 404
�
1
27 3 3
m) cm ; anal. calcd for 21, C30H N O V: C 68.18, H 5.15, N 7.95; found: C
Complex 7: The C(22), C(27), and C(28) carbon atoms of THF molecules
coordinated to the sodium cation showed high thermal parameters which
indicate the presence of disorder. The best fit was found by splitting the
atoms over two positions (A and B) and were isotropically refined with a
site occupation factor of 0.5. Additionally, ten independent residual peaks
were interpreted in terms of one THF solvent molecule of crystallization
disordered over two positions and isotropically refined with a site
occupation factor of 0.5. The position of the oxygen atom could not be
unambiguously determined.
68.17, H 4.68, N 8.72.
Reaction of
4
with pyridine-N-oxide: Pyridine-N-oxide (0.131 g,
1.38 mmol) was added to a violet solution of 4 (1.01 g, 1.15 mmol) in
THF (100 mL). The mixture was refluxed overnight to give a dark green
solution. The solvent was evaporated to dryness and the residue treated
with hexane (100 mL). The product was collected and dried in a vacuum.
Yield: of 11 ´ thf: 0.9 g (85%); anal. found: C 63.35, H 4.34, N 6.37. For
spectroscopic data vide supra.
Complex 19: The C(21) ± C(27) toluene solvent molecule of crystallization
was found to be statistically distributed over two positions (C and D) and
was isotropically refined with site occupation factors of 0.5. The disordered
aromatic rings were constrained to have a D6h symmetry.
X-ray crystallography for complexes 5 ± 7, 16, 19, and 20: Suitable crystals
were mounted in glass capillaries and sealed under nitrogen. The reduced
cells were obtained with the use of TRACER.[ Data for complexes 5 ± 7,
25]
16, and 19 were collected on a single-crystal diffractometer (Philips
Complex 20: Since the complex crystallizes in a polar space group, the
crystal chirality was tested by inverting the coordinates (x,y,z !x, � y, � z)
and refining to convergence again. The resulting R values quoted in
brackets in Table 1 indicated that the original choice should be considered
to be the correct one.
PW1100 for 5, 7, and Rigaku AFC6S for 6, 16, 19) at 295 K for 5, 7, 19 and
138 K for 6, 16. Data for complex 20 were collected on a KUMA CCD at
2
95 K. For intensities and background, individual reflection profiles were
[26]
analyzed.
The structure amplitudes were obtained after the usual
[27]
Lorentz and polarization corrections
established by the Wilson method. The crystal quality was tested by y-
and the absolute scale was
[28]
Further details of the crystal structure investigations may be obtained from
the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopolds-
hafen (Germany) (fax: (‡ 49)7247-808-606; e-mail: crysdata@fiz.karlsru-
he.de) on quoting the depository numbers CSD-410113 (5), 410114 (6),
410115 (7), 410116 (16), 410117 (17), 410118 (19), 410119 (20).
scans which showed that crystal absorption effects could be neglected
except for 6, 16, and 19. Data of complexes 6, 16, and 19 were then
29]
corrected for absorption by
a
semiempirical method.[
Anomalous
[
30b]
scattering corrections were included in all structure factor calculations.
Scattering factors for neutral atoms were taken from ref. [30a] for non-
hydrogen atoms and from ref. [31] for H.
Structure solutions were based on the observed reflections [I > 2s(I)]. The
structures were solved by the heavy-atom method starting from a three-
dimensional Patterson map.[ The least-square refinements were carried
Acknowledgments
32]
We thank the Fonds National Suisse de la Recherche Scientifique (Bern,
Switzerland, Grant No. 20-53'336.98) and Ciba Specialty Chemicals (Basel,
Switzerland) for financial support. Some earlier exploratory work by M.
Mazzanti is acknowledged.
2
out using the unique reflections with F > 0 by minimizing the function
2
2 [33]
2
2
2
2
Sw(DF ) .
The weighting scheme w ˆ 1/[s (F
o
) ‡ (aP) ] (P ˆ (F
o
‡
2
2
F
c
)/3), based on the counting statistics, was applied. In the last refinement
cycles a converged at 0.0585, 0.1430, 0.0820, 0.0728, 0.0571, and 0.0352 for 5,
, 7, 16, 19, and 20 respectively. Refinement was performed with full-matrix
6
least-squares, first isotropically, then anisotropically for all the non-H
atoms except for the disordered atoms. The hydrogen atoms, but not those
associated with the disordered carbon atoms, which were ignored, were
located from difference Fourier maps and introduced in the subsequent
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2
refinements as fixed contributions with isotropic Uꢁs fixed at 0.08 Š for 5,
7
, and 20 and 0.05 Š2 for 6, 16, and 19.
7
20
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Molecular Batteries
708±721
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Received: June 5, 1998 [F1193]
Chem. Eur. J. 1999, 5, No. 2
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0947-6539/99/0502-0721 $ 17.50+.50/0
721