Rearrangement and co-ordination of 1-[(4-methylphenyl)sulfonamido]-2-[1- (2-pyridylmethylidene)amino] benzene

Article abstract of DOI:10.1039/a907731f

Two different compounds, L¹ {3-[ethoxy(2-pyridyl)methyl]-1-[(4- methylphenyl)sulfonyl]-2-(2-pyridyl)-2,3-dihydro-1H-benzo[d]imidazole} and L² {1-[(4-methylphenyl)sulfonyl]-2-(2-pyridyl)-2,3-dihydro-1H- benzo[d]imidazole} have been synthesised by the reaction of 2- pyridinecarboxaldehyde with N-tosyl-1,2-diaminobenzene. L¹ was crystallographically characterised. The interaction of L¹ with a nickel centre was checked. Electrochemical interaction of Ni with L¹ and N-(2- hydroxyphenyl)salicylidenimine (H₂L⁴) produces NiL¹L⁴·2H₂O 1. Its recrystallisation in dichloromethane leads to the isolation of single crystals of NiL³₂·0.75H₂O 2 (HL³ = 1-[(4-methylphenyl)sulfonamido]-2-[1- (2-pyridylmethylidene)amino]benzene), where L¹ underwent a rearrangement. In the reaction of L¹ with Ni and p-toluenesulfonic acid in an electrochemical cell, complex 2 is isolated as the bulk product. Nickel complexes have been characterised by elemental analysis, IR spectroscopy and magnetic measurements. The molecular structure of 2 has been determined by single X- ray diffraction studies.

Full text of DOI:10.1039/a907731f

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Rearrangement and co-ordination of 1-[(4-methylphenyl)-
sulfonamido]-2-[1-(2-pyridylmethylidene)amino]benzene
Manuel R. Bermejo,*a Antonio Sousa,*a Matilde Fondoa and Madeleine Helliwellb
a Departamento de Qu•mica Inorganica, Facultade de Qu•mica, Universidade de Santiago,
E-15706 Santiago de Compostela, Spain. E-mail: qimb45=uscmail.usc.es (M. R. Bermejo)
b Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL , UK
Received (in Montpellier, France) September 1999, Accepted 2nd November 1999
Two di†erent compounds, L1 M3-[ethoxy(2-pyridyl)methyl]-1-[(4-methylphenyl)sulfonyl]-2-(2-pyridyl)-2,3-dihydro-
1H-benzo[d]imidazoleN and L2 M1-[(4-methylphenyl)sulfonyl]-2-(2-pyridyl)-2,3-dihydro-1H-benzo[d]imidazoleN
have been synthesised by the reaction of 2-pyridinecarboxaldehyde with N-tosyl-1,2-diaminobenzene. L1 was
crystallographically characterised. The interaction of L1 with a nickel centre was checked. Electrochemical
interaction of Ni with L1 and N-(2-hydroxyphenyl)salicylidenimine (H L4) produces NiL1L4 É 2H O 1. Its
2
2
recrystallisation in dichloromethane leads to the isolation of single crystals of NiL3 É 0.75H O 2 (HL3 \
2
2
1-[(4-methylphenyl)sulfonamido]-2-[1-(2-pyridylmethylidene)amino]benzene), where L1 underwent a
rearrangement. In the reaction of L1 with Ni and p-toluenesulfonic acid in an electrochemical cell, complex 2 is
isolated as the bulk product. Nickel complexes have been characterised by elemental analysis, IR spectroscopy and
magnetic measurements. The molecular structure of 2 has been determined by single X-ray di†raction studies.
The co-ordination chemistry of Schi† base ligands has been
widely investigated. The interest in these ligands arose not
only from their versatility but also from their use for model-
ling the chemical environment in many metalloenzymes. The
construction of models that can lead to a better understanding
of their properties has attracted the attention of both bio-
chemists and inorganic chemists. Many metallobiosites are
formed by a metal atom surrounded by nitrogen atoms and
imine carbon atom by the tosyl protected amino group, fol-
lowed by an intermolecular nucleophilic attack on the carb-
onyl carbon of 2-pyridinecarboxaldehyde. The elimination of
the hydroxyl group would lead to the formation of water and
an intermediate containing, again, an imine group. The Ðnal
product L1 could be obtained from III, by nucleophilic attack
some of them, such as cofactor F , involve a nickel centre.
430
Thus, Schi† bases containing nitrogen donors could act as
versatile models of the active centre of these enzymes. In addi-
tion, nickel complexes with nitrogen donor atoms often show
interesting structural, electric and magnetic properties.1h6
Owing to our experience in the co-ordination chemistry of
symmetrical and asymmetrical Schi† base ligands,7,8 we
extended our studies to the investigation of potentially tri-
dentate asymmetrical Schi† bases containing N-donors.
Herein we report our attempts to obtain the Schi† base
1-[(4-methylphenyl)sulfonamido]-2-[1-(2-pyridylmethylidene)-
amino]benzene (HL3) and its reorganisation in solution to
yield two di†erent ligands, L1 and L2. The interaction of L1
with a nickel centre, under di†erent reaction conditions, has
also been investigated.
Results and discussion
N-Tosyl-1,2-diaminobenzene and 2-pyridinecarboxaldehyde
were mixed in di†erent ratios under various reaction condi-
tions (room temperature, reÑux, with or without traces of p-
toluenesulfonic acid) in an attempt to obtain 1-[(4-methyl-
phenyl)sulfonamido]-2-[1-(2-pyridylmethylidene)amino]ben-
zene, HL3. All e†orts were unfruitful and treatment of N-
tosyl-1,2-diaminobenzene with 2-pyridinecarboxaldehyde led
always to the isolation of two di†erent products (L1 and L2),
depending on the reaction solvent (Scheme 1). The products
can be formed through the reactions shown in Scheme 2.
The isolation of L2 seems to indicate that the reaction
begins with an intramolecular nucleophilic attack on the
Scheme 1 Reaction conditions (i absolute ethanol (99%), stir 5 h,
room temperature, (ii) ethanol (96%), stir 5 h, room temperature or
methanol, ethanol (96%) or chloroform, stir 3 h, reÑux. Labels for the
NMR spectra are also given.
New J. Chem., 2000, 24, 33È38
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2000
33

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Crystal structure of L1. The nature of L1 was determined by
single X-ray di†raction studies (Fig. 1). The experimental
details are given in Table 3 and main bond distances and
angles in Table 4.
All the angles and distances are in the range of those
expected for organic compounds containing a tosyl group8,9
and do not deserve further consideration. However, it is note-
worthy that the crystal structure shows that L1 has two tert-
iary carbon atoms, the compound being optically active.
IR spectroscopy. The IR spectra of L1 and L2 show a strong
band at ca. 1595 cm~1, assigned to l(CN ). Besides, a broad
py
and intense band at 3205 cm~1, due to the NH stretching
frequency,7b is observed for L2. No bands above 2500 cm~1
were detected for L1, indicating the absence of NH groups in
the molecule, as the crystal structure shows. Very strong
bands are observed at ca. 1340 and 1165 cm~1 for L1 and L2,
due to l(SO ) and l(SO ) , suggesting the presence of the
2 as
2 s
tosyl group in both cases, in agreement with previous
results.10
1H NMR and mass spectroscopy. L1 shows two doublets at
8.51 and 8.24 ppm, corresponding to two protons ortho to the
nitrogen atom of the pyridine ring, indicating the presence of
two pyridine moieties in the ligand. Two singlets at ca. 6 ppm
are assigned to two protons attached to two di†erent tertiary
carbon atoms.11 The spectrum shows a very complicated
multiplet (15 H), assigned to the aromatic protons, at 6.5È8
ppm. The ethyl chain of the ethoxy moiety gives two signals:
one at 0.58 ppm (t, 3H) and a second one at 2.38 ppm, which
appears as a multiplet as it is overlapped by the peak corre-
sponding to the methyl radical of the tosyl group.
The spectrum of L2 shows just one signal assigned to an
a-proton of the pyridine ring (8.56 ppm, d) and a multiplet for
the aromatic hydrogen atoms. The hydrogen on the tertiary
carbon atom occurs at 6.32 ppm and the methyl radical of the
tosyl group at 2.34 ppm. The signal of the NH proton was not
assigned because of overlap by the aromatic protons. No
singlets at ca. 8.5 ppm were detected so no imine groups are
present in L1 or L2.12
It is remarkable to note that the spectrum of L1 changes
with time: many new signals, most of them assigned to L2,
increase in intensity with time. This seems to indicate that L1
is unstable in solution and that many species are present. The
equilibrium between L1 and L2 is in agreement with the pro-
posed reaction scheme.
The mass spectra of L1 and L2 were recorded by the elec-
trospray technique. Peaks at 487 and 352 amu are assigned to
the molecular ions of L1 and L2, respectively.
Scheme 2 Proposed pathway for the formation of L1 and L2.
by the reaction solvent. Although all these products seem to
be in a dynamic equilibrium in solution, the displacement of
the reaction towards the formation of L1 could be explained
by the low solubility of the latter product in ethanol at room
temperature. This proposed reaction pathway is also consis-
tent with the isolation of L2 in an undried solvent: the higher
quantity of water would disfavour the formation of III, revert-
ing the equilibrium and producing L2 in yields high enough to
precipitate.
The stability and reactivity induced in these compounds by
the pyridine ring, directly bonded to the imine carbon atom, is
quite surprising. The related Schi† bases N-[(2-pyrrolyl)meth-
ylidene]-N@-tosylbenzene-1,2-diamine
and
2-tosylamino-
(2-pyridyl)aniline have been previously reported.7a,7c Both
were easily obtained by condensation of the corresponding
amine and aldehyde; the bases seem to be stable in solution
and no decomposition or rearrangement reactions were
reported for either of them.
Characterisation of L1 and L2
The products L1 and L2 were characterised by elemental
analyses, IR (Table 1) and 1H NMR (Table 2) spectroscopies.
A crystal structure determination on L1 conÐrmed the nature
of the compound.
Table 1 Elemental analyses and some physical properties of the ligands
Elemetal analysisa
IR spectroscopyb
Formula
Yield/%
Mp/¡C
%C
%H
%N
%S
l(NH)
l(CN
)
l(SO )
py
2
L1
L2
C
C
H
N O S
63.2
92.6
163È6
142È3
67.3 (66.7)
65.0 (65.0)
5.5 (5.3)
4.8 (4.8)
11.6 (11.5)
11.9 (12.0)
6.3 (6.6)
8.7 (9.1)
È
3205
1593
1595
1335, 1173
1349, 1165
27 26
H
4 3
N O S
19 17
3 2
a Found (calcd.). b In KBr, cm~1.
Table 2 Most signiÐcant 1H NMR peaks (ppm) and mass spectral data for the ligands
H ] H@
H ] H@
H
] NH
ÈCH
ÈCH a
ÈCH b
m/z
1
1
a
a
arom
2
3
3
L1
L2
6.06 (s,1H),
5.85 (s,1H)
6.32 (s,1H), [
8.51 (d,1H),
8.24 (d,1H)
8.56 (d,1H)
6.5È8 (m,15H)
2.38 (m,5H)a
2.39 (m,5H)a
0.58 (t,3H)
487
352
6.4È7.8 (m,12H)
È
2.34 (s,3H)
È
a Overlapping peaks.
34
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Table 3 Crystal data and structure reÐnement for L1 and 2.
L1
2
Empirical formula
Formula weight
Crystal system
Space group
C
486.58
Monoclinic
P2/1
2
H
N O S
C
H
N O
NiS
27 26
4
3
38 33.5
6
4.75
773.04
Trigonal
R3
Z
18
Temperature/K
296(2)
296(1)
27.512(4)
È
25.092(3)
90
90
120
16447(4)
2.257
7985
a/A
b/A
c/A
a/¡
8.7002(1)
10.0675(3)
14.1389(4)
90
91.217(1)
90
1238.14(5)
0.167
5226
b/¡
c/¡
U/A
Ž
3
l/mm~1
ReÑections collected
Independent reÑections
2494 (R \ 0.0537)
7557 (R \ 0.04)
int
int
Final R indices [I [ 2p(I)]
0.0767
0.070
w
R
indices (all data)
0.0884
0.049
w
Table 4 Selected bond distance (A) and angles (¡) for L1
SÈO1
1.422(8)
1.424(8)
1.648(6)
1.754(8)
1.421(11)
1.492(10)
1.382(12)
1.439(11)
105.7(4)
105.7(4)
108.8(5)
108.4(5)
107.7(3)
107.8(6)
121.8(6)
118.0(5)
119.9(4)
126.7(7)
109.2(7)
121.4(7)
110.6(7)
127.9(8)
131.0(9)
108.5(7)
N2ÈC27
1.461(10)
1.306(11)
1.348(14)
1.45(2)
SÈO2
N21ÈC26
SÈN1
N21ÈC22
SÈC6
C34ÈN35
N1ÈC16
N35ÈC36
1.41(2)
N1ÈC27
C37ÈO38
1.396(11)
1.418(12)
116.1(8)
125.2(11)
123.3(8)
115.7(7)
103.7(6)
112.8(6)
110.8(6)
117(2)
116.1(13)
122.7(11)
118.8(10)
112.3(7)
109.1(8)
112.2(8)
113.6(8)
109.7(11)
N2ÈC15
O38ÈC39
N2ÈC37
C26ÈN21ÈC22
C23ÈC22ÈN21
N21ÈC26ÈC25
N21ÈC26ÈC27
N2ÈC27ÈN1
N2ÈC27ÈC26
N1ÈC27ÈC26
C33ÈC34ÈN35
C34ÈN35ÈC36
C31ÈC36ÈN35
N35ÈC36ÈC37
O38ÈC37ÈN2
O38ÈC37ÈC36
N2ÈC37ÈC36
C39ÈO38ÈC37
O38ÈC39ÈC40
O1ÈSÈN1
O2ÈSÈN1
O1ÈSÈC6
O2ÈSÈC6
N1ÈSÈC6
C16ÈN1ÈC27
C16ÈN1ÈS
C27ÈN1ÈS
O1ÈSÈO2
C15ÈN2ÈC37
C15ÈN2ÈC27
C37ÈN2ÈC27
C16ÈC15ÈN2
C14ÈC15ÈN2
C11ÈC16ÈN1
C15ÈC16ÈN1
Fig. 1 An ORTEP view of the crystal structure of L1.
Characterisation of the nickel complexes
The unfruitful attempts to obtain HL3, with the isolation of
L1 (or L2), focussed our e†orts on the isolation of a nickel
complex containing L1.
purpose. The electrolysis of an acetonitrile solution containing
L1 and H L4, as described below, was done. Elemental
2
The electrochemical reaction of a nickel centre with L1 does
not seem to occur and the ligand L1 could be identiÐed as one
of the species after evaporation of the solution. Thus, an alter-
native method was tried.
analysis of the orange insoluble product isolated (Table 5)
seems to indicate that the compound obtained is NiL1L4 É 2
H O 1, although the evaporation of the mother waters of the
2
electrochemical synthesis yields NiL3 É 0.75H O 2, crystallo-
2
2
Once the structure of L1 was known, it was thought that its
size would prevent the co-ordination of more than one ligand
to the same metal centre. Besides, L1 has no acidic protons.
Thus, it should be necessary to react L1 with a nickel centre in
the presence of a ligand containing easily deprotonable
groups, which could balance the charge of the central atom, in
order to obtain a Ni(II) complex containing L1. A simple
graphically characterised. Attempts were made to determine
the structure of NiL1L4 É 2H O. However, its recrystallisation
2
in dichloromethane led, again, to the isolation of complex 2.
As a consequence of this unexpected result, we tried to sub-
stitute for ligand H L4 a weakly co-ordinating acid, which
2
could be easily deprotonated and balance the charge of the
nickel(II) cation, maybe by acting as a counter ion. The acid
used in this case was p-toluenesulfonic acid (p-TosH). Electro-
lysis of an acetonitrile solution containing L1 and p-TosH in a
potentially tridentate and dianionic Schi† base, such as H L4
2
[N-(2-hydroxyphenyl)salicylidenimine], was chosen for this
Table 5 Elemental analyses and some physical properties for the nickel complexes
Elemental analysisa
IR spectroscopyb
l(CN ) ] l(CN
Yield/%
Mp/¡C
%C
%H
%N
%S
)
l(OH)
k/BM
imine
py
1
2
37.6
30.5
[300
[300
60.4 (60.3)
58.8 (59.0)
5.3 (5.4)
4.1 (4.3)
8.7 (8.8)
10.8 (10.9)
4.0 (3.4)
8.1 (8.3)
1609, 1596
1592
3417
3477
3.1
3.1
a Found (calcd.). b In KBr, cm~1.
New J. Chem., 2000, 24, 33È38
35

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Table 6 Selected bond distances (A) and angles (¡) for 2
1 : 2 ratio was performed in the presence of a nickel anode.
Complex 2 was obtained after slow evaporation of the mother
waters. Thus, this seems to indicate that L1 is unstable in solu-
tion, as previously observed, and that the presence of a metal
centre accelerates the reorganisation process. Therefore, the
experimental Ðndings indicate that the best results that can be
achieved are the isolation of complexes containing [L3]~ as a
ligand.
With these considerations in mind, it was thought that, it
might be enough to catalyse the interaction of Ni and L1 with
a weak acid, in order to obtain complex 2. The electrochem-
ical interaction of Ni and L1, using traces of p-TosH, was
checked. It was observed that quick evaporation of the solu-
tion produces a copious product of unknown nature. When
the solution is left to stand and slowly evaporates, the isolated
product is compound 2. These data show that L1 rearranges
to HL3 in solution. However, the reorganisation is not instan-
taneous and thus, a quick precipitation leads to a mixture of
products, perhaps containing simultaneously derivatives of L1
and HL3, as well as other fragments of the reorganisation
process, which does not allow us to characterise the copious
material isolated. On the contrary a slow evaporation of the
solution allows L1 to rearrange in higher quantity. The most
insoluble product, in this case the nickel complex 2, precipi-
tates as a crystalline product and can be isolated with high
purity.
NiÈN1
2.090(5)
2.105(5)
2.025(5)
1.443(4)
1.584(5)
1.454(5)
1.597(5)
1.409(8)
1.271(8)
1.323(8)
1.383(8)
1.345(8)
78.6(2)
97.7(2)
92.7(2)
109.4(2)
93.7(2)
94.8(2)
77.9(2)
78.4(2)
106.7(3)
113.1(3)
NiÈN2
2.030(5)
2.146(5)
2.125(6)
1.444(4)
1.780(7)
1.456(5)
1.783(7)
1.401(8)
1.347(8)
1.398(8)
1.283(8)
1.317(8)
156.7(2)
108.5(2)
78.5(2)
169.5(2)
86.5(2)
92.3(2)
156.1(2)
116.1(3)
115.7(3)
109.1(3)
NiÈN3
NiÈN4
NiÈN5
NiÈN6
S1ÈO1
S1ÈO2
S1ÈN1
S1ÈC13
S2ÈO3
S2ÈO4
S2ÈN4
S2ÈC32
N1ÈC1
N2ÈC6
N2ÈC7
N3ÈC8
N3ÈC12
N5ÈC25
N6ÈC27
N1ÈNiÈN2
N1ÈNiÈN4
N1ÈNiÈN6
N2ÈNiÈN4
N2ÈNiÈN6
N3ÈNiÈN5
N4ÈNiÈN5
N5ÈNiÈN6
O1ÈS1ÈN1
O2ÈS1ÈN1
N4ÈC20
N5ÈC26
N6ÈC31
N1ÈNiÈN3
N1ÈNiÈN5
N2ÈNiÈN3
N2ÈNiÈN5
N3ÈNiÈN4
N3ÈNiÈN6
N4ÈNiÈN6
O1ÈS1ÈO2
O3ÈS2ÈO4
N1ÈS1ÈC13
NiÈN
imine
N2 \ 2.030(5) and NiÈN5 \ 2.025(5) A] remarkable di†er-
bond lengths are identical for both ligands [NiÈ
ences are observed in the NiÈN and NiÈN bond
amide
pyridine
lengths. These distances are signiÐcantly shorter for one of the
ligands [NiÈN1 \ 2.090(5) and NiÈN3 \ 2.105(5) A,
respectively] than for the second one [NiÈN4 \ 2.146(5) and
NiÈN6 \ 2.125(5) A, respectively]. In addition, the distance
Crystal structure of NiL3 Æ 0.75H O 2. The X-ray structure
2
2
of 2 is shown in Fig. 2. Experimental details are given in Table
3 and signiÐcant bond lengths and angles are listed in Table 6.
The unit cell contains 18 asymmetric units, accounting for the
large volume. The asymmetric unit contains, in addition to the
nickel complex, three disordered water fragments, with partial
occupancies.
NiÈN
is shorter than the distance NiÈN
for one of
amide
pyridine
the ligands while is longer for the other one. Thus, the
geometry of the complex can be considered as an octahedron
with a tetragonal distortion due to the elongation of the apical
bonds, with no interchangeable positions between both
ligands. In this polyhedron, one of the Schi† base ligands uses
its three donor atoms, N1, N2 and N3, to bind the Ni atom in
the equatorial plane and the second one uses the imine nitro-
gen atom, N5, to link the Ni centre in the equatorial plane
and the amide and pyridine nitrogen atoms, N4 and N6, to Ðll
the apical positions.
The structure of the Ni compound consists of a metal centre
surrounded by six nitrogen atoms corresponding to two Schi†
bases, which act as tridentate and monoanionic. The ligands
adopt
a mer conÐguration in the distorted octahedral
complex. It is remarkable, in spite of the adopted conÐgu-
ration, that both ligands are not equivalent. This is clearly
shown by a comparison of the NiÈN distances: while the
The NiÈN distances in the equatorial plane are quite similar
and shorter than those of the apical positions. All these dis-
tances are in the range of those expected for octahedral Ni
complexes containing N-donor ligands13,14 but are longer
than those found for tetrahedral15h17 and square planar7b,18
Ni compounds. This is a reÑection of the lower co-ordination
number in the related complexes.
The equatorial angles around the Ni atom in the distorted
octahedron vary from 77.9¡ to 108.5¡ and are quite di†erent
from the ideal value of 90¡. The interaxial angle N4ÈNiÈN6 of
156.1(2)¡ further reinforces the distortion from the ideal
geometry, which can be mainly attributed to the small bite
angles of the tridentate ligand. This observation is in agree-
ment with previous results, where chelate ligands induce a dis-
tortion from the ideal octahedral geometry.14,15,19
IR spectroscopy and magnetic measurements. The IR spec-
trum of complex 2 shows a strong and broad band at 1592
cm~1, assigned to l(CN
) ] l(CN
).13,14 A broad
pyridine imine
band at 3477 cm~1 is assigned to l(OH) from the water of
crystallisation. A comparison of the spectra of complexes 1
and 2 shows a clear di†erence. Complex 1 shows two strong
bands in the range 1590È1620 cm~1: a sharp and strong band
at 1596 cm~1 that can be assigned to l(CN
pyridine
present in the free ligand; a second strong band at 1609 cm~1,
) of L1,
assigned to l(CN ) of [L4]2~.
imine
The room temperature magnetic moments for the com-
plexes are 3.1 BM and are very close to the ideal value of 2.9
for magnetically diluted Ni(II) ions. The magnetic moment
value for 2 is in good agreement with the octahedral geometry
Fig. 2 An ORTEP view of the crystal structure of NiL3 É 0.75H O
2
2
2. Water solvent molecules have been omitted for clarity.
36
New J. Chem., 2000, 24, 33È38

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of the compounds, deduced from the X-ray results. However,
this value does not allow one to draw any unambiguous con-
clusions concerning the geometry of the chelate core in
complex 1.3 This only allows one to reject the square planar
geometry for the complex.
tetramethylammonium perchlorate, as supporting electrolyte,
was electrolysed for 2 h and 12 min with a current of 10 mA.
A small quantity of an insoluble orange solid of unknown
nature was isolated (ca. 0.06 mg). The mother waters were
reduced in volume (20 mL) and a second orange solid precipi-
tated. The product was Ðltered, washed with diethyl ether and
dried in air; the elemental analysis is in agreement with the
Conclusion
formulation NiL1L4 É 2H O 1 for the latter compound.
2
The reaction of N-Tosyl-1,2-diaminobenzene and 2-
pyridinecarboxaldehyde yields two di†erent optically active
organic compounds, L1 and L2, depending on the reaction
medium. However, the expected Schi† base, product of the
condensation of the amine and carbonyl reactants, could not
be isolated.
Recrystallisation of 1 in dichloromethane yielded small
crystals of NiL3 2 É 0.75H O 2.
2
2
NiL3 Æ 0.75H O 2. Complex 2 could be synthesized by two
2
2
other methods.
Method A: An acetonitrile solution (70 mL) of L1 (0.2 g,
0.41 mmol) and p-TosH (0.14 g, 0.82 mmol), containing about
10 mg of tetramethylammonium perchlorate as supporting
electrolyte, was electrolysed for 2 h and 12 min with a current
of 10 mA, as for 1. A small quantity (ca. 0.05 g) of an insoluble
product of unknown nature was Ðltered. The mother waters
were left to stand for one week. Slow evaporation of the solu-
tion yields small crystals, suitable for X-ray di†raction, of
NiL3 : 0.75H O 2.
The electrochemical interaction of L1 with nickel always
leads to the isolation of NiL3 É 0.75H O, obtained by reor-
2
2
ganisation of the ligand to the Schi† base (HL3) in solution.
Experimental
General
All solvents and 2-pyridinecarboxaldehyde are commercially
available and were used without further puriÐcation. Nickel
(Ega Chemie) was used as ca. 2 ] 2 cm2 plate. N-tosyl-1,2-
diaminobenzene was obtained as previously reported by
Malik and Sharma.20
2
2
Method B: An acetonitrile solution (70 mL) of L1 (0.2 g,
0.41 mmol) containing about 10 mg of tetramethylammonium
perchlorate, as supporting electrolyte, and 10 mg of p-
toluenesulfonic acid as catalyst, was electrolysed for 2 h and
12 min with a current of 10 mA, as for 1. The resultant garnet-
coloured solution was slowly evaporated and, after one week,
small crystals of NiL3 É 0.75H O 2 were recovered and dried
Elemental analyses were performed on a Carlo Erba EA
1108 analyser. NMR spectra were recorded on a Bruker
AC-300 spectrometer using DMSO-d as solvent. Infrared
6
spectra were recorded as KBr pellets on a Bio-Rad FTS 135
2
2
in air.
spectrophotometer in the range 4000È600 cm~1. Electrospray
mass spectra were obtained on a HewlettÈPackard LC/MS
spectrometer, in methanol as solvent. Room temperature
magnetic measurements were performed using a Digital Mea-
Crystallographic measurements
surement
tetrakis(isothiocyanato)cobaltate(II).
system
MSB-MKI,
calibrated
using
L . White crystals, suitable for single-crystal X-ray studies,
1
were obtained as previously described. Data were collected at
296 K with a CAD-4 di†ractometer, employing graphite-
monochromated Mo-Ka (j \ 0.710 73 A) radiation. The
structure was solved by direct methods21 and reÐned by full-
matrix least squares on F2. A semiempirical correction from
psi scans was applied. All non-hydrogen atoms were reÐned
anisotropically. Hydrogen atoms were included in the struc-
ture factor calculation in idealised positions. The aromatic
ring of the tosyl group (C1ÈC6) is disordered over two sites,
with partial occupancies of 0.5.
Syntheses
L1. To an absolute ethanol (99%) solution (75 mL) of N-
tosyl-1,2-diaminobenzene (0.524 g, 2 mmol) was added 2-
pyridinecarboxaldehyde (0.2 mL, 2.1 mmol). The mixture was
stirred for 5 h at room temperature until a white solid precipi-
tated. The solid was collected by Ðltration, washed with
diethyl ether (10 mL) and dried in air.
When the amine and aldehyde are mixed in a 1 : 2 molar
ratio in absolute ethanol, the same ligand is obtained. Crystals
of L1, suitable for X-ray di†raction studies, were obtained by
recrystallisation of the white powder in hot ethanol.
NiL3 Æ 0.75H O 2. Red needle crystals of 2 were obtained
2
2
as previously described and mounted on a glass Ðber. All mea-
surements were made at 296 K on a Rigaku AFC5R di†rac-
tometer, employing Cu-Ka (j \ 1.541 78 A) radiation and a
rotating anode generator, using the u [ 2h scan technique
L2. L2 could be synthesised by two di†erent methods.
Method A: To an ethanol (96%) solution (75 mL) of N-
tosyl-1,2-diaminobenzene (0.524 g, 2 mmol) was added 2-
pyridinecarboxaldehyde (0.2 mL, 2.1 mmol). The mixture was
stirred for 5 h at room temperature until a white solid precipi-
tated. The solid was Ðltered, washed with diethyl ether (10
mL) and dried in air.
Method B: To an ethanol (96%), chloroform or methanol
solution (100 mL) of N-tosyl-1,2-diaminobenzene (0.524 g, 2
mmol) was added 2-pyridinecarboxaldehyde (0.2 mL, 2.1
mmol). The resultant yellow solution was reÑuxed for 3 h,
removing the water with a Dean Stark. The solution was
reduced in volume (25 mL) and the solid collected by Ðltration
and dried in air.
(2h \ 159.4¡). The structure was solved by direct
max
methods,21 expanded using Fourier techniques22 and reÐned
by full-matrix least squares on F2. An absorption correction
was applied. Data were corrected for Lorentz and polarisation
e†ects. Non-hydrogen atoms were reÐned anisotropically,
except oxygen atoms of the disordered water fragment, which
were reÐned isotropically. Hydrogen atoms were included in
the structure factor calculation in idealised positions but not
reÐned. All calculations were performed using the TEXSAN
crystallographic software package.23
CCDC reference 440/155. See http://www.rsc.org/suppdata/
nj/a9/a907731f// for crystallographic Ðles of complex 2 in .cif
format.
NiL1L4 Æ 2H O 1. The compound was obtained using an
2
electrochemical procedure. The cell can be summarised as:
Pt o L1 ] H L4 ] MeCN o Ni . A platinum wire was used
Acknowledgements
(~)
2
(`)
as the cathode and a nickel plate as the anode.
An acetonitrile solution (70 mL) of L1 (0.2 g, 0.41 mmol)
The authors would like to thank Xunta de Galicia (Spain) for
Ðnancial support (XUGA/20903B 99).
and H L4 (0.09 g, 0.41 mmol), containing about 10 mg of
2
New J. Chem., 2000, 24, 33È38
37

View Article Online
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