A direct route to obtain manganese(III) complexes with a new class of asymmetrical Schiff base ligands

Article abstract of DOI:10.1039/b000235f

A new class of asymmetrically substituted Schiff base ligands has been synthesised incorporating hard amido donor atoms. The single crystal X-ray structure of one of these ligands, H₃-amsal, has been determined [H₃-amsal = 3-aza-4-(2

Full text of DOI:10.1039/b000235f

View Online / Journal Homepage / Table of Contents for this issue
A direct route to obtain manganese(III) complexes with a new class of
asymmetrical Schi† base ligands
Manuel R. Bermejo,*a Ana M. Gonzalez,a Matilde Fondo,a Ana Garc•a-Deibe,a Marcelino
Maneiro,a Jesus Sanmart•n,a Olga L. Hoyosb and Michael Watkinsonc
a Departamento de Qu•mica Inorganica, Facultad de Qu•mica, Universidad de Santiago de
Compostela, E-15706 Santiago de Compostela, Spain. E-mail: qimb45=uscmail.usc.es (M. R.
Bermejo)
b Departamento de Qu•mica, Universidad del Cauca, Popayan, Colombia
c Department of Chemistry, Queen Mary and W estÐeld College, L ondon, E1 4NS, UK
Received (in Montpellier, France) 3rd January 2000, Accepted 11th February 2000
A new class of asymmetrically substituted Schi† base ligands has been synthesised incorporating hard amido donor
atoms. The single crystal X-ray structure of one of these ligands, H -amsal, has been determined [H -amsal \ 3-
3
3
aza-4-(2-hydroxyphenyl)-N-(2-hydroxyphenyl)but-3-enamide]. The structure reveals the ligand to be suitable for use
as an equatorially co-ordinating ligand in octahedral complexes. A new route to obtaining manganese(III)
complexes of these ligands, with high yield and purity, has been designed. Complexes of the form MnIII(amsal-R)
(H O) (n \ 1È4) have been prepared by the electrochemical oxidation of a manganese anode in an acetonitrile
2
n
solution of the ligands. The compounds have been characterised by elemental analyses, IR and 1H NMR
spectroscopies, FAB mass spectrometry, magnetic measurements, K and cyclic voltammetry.
M
The co-ordination chemistry of manganese with a diverse
range of ligands remains an area of considerable interest. This
is not only because of the relevance that a number of model
manganese complexes have to biological systems,1 but also
due to the fascinating cluster compounds, which exhibit
unusual magnetic properties, and the elegant supramolecular
arrays that have been discovered.2 In addition to the interest
from this inorganic standpoint, there is also considerable
interest in the application of manganese complexes in organic
synthesis due to their potent catalytic properties, particularly
in the asymmetric epoxidation of certain oleÐns.3
Our interest in this area has centred for a considerable time
on the investigation of the co-ordination chemistry of man-
ganese with a range of symmetrical and asymmetrical Schi†
base ligands. There are principally two synthetic methods that
we have used in trying to prepare manganese(III) complexes of
these ligands. The Ðrst involves the classical aerobic oxidation
procedure of Boucher and Coe.4 Although we have had con-
siderable success with this methodology, there are frequently
intractable problems associated with this route, particularly
the formation of large quantities of insoluble materials when
poorly co-ordinating anions, such as perchlorate, are
employed. Furthermore, there are occasionally problems
associated with the integrity of the oxidation state in the
resultant complexes, depending on the nature of the substi-
tuents on the phenyl rings of the Schi† base ligand.5 The
second method, which is considerably less explored, involves
the synthesis of the complexes using an electrochemical cell in
which a manganese anode is oxidised with concomitant
cathodic reduction of the ligand. In contrast to the Boucher
methodology, this route generally gives very clean reactions
from which manganese(II) complexes are generally isolated.6
Occasionally we have isolated cationic manganese(III) species7
in which the complex anion results from the supporting elec-
trolyte; however, these examples are rare and the expected
oxidation level from this procedure is manganese(II).
manganese(III) complexes routinely and to investigate whether
higher oxidation states of manganese can be accessed via this
synthetic route, in view of the role that these higher oxidation
states play in natural systems, such as the oxygen evolving
complex of green plant photosynthesis and the putative
oxomanganese(V)salen species implicated in the JacobsenÈ
Katsuki epoxidation. Complexes of manganese in oxidation
states higher than (IV) are rare,8 particularly with biologically
relevant ligands. Okawa et al.9 reported the preparation of
what were assigned as manganese(IV) and (V) complexes using
amido donors to stabilise the high valent metal ion. However,
owing to the severe insolubility problems associated with
these complexes, no solution or single crystal data were pre-
sented. Irrefutable evidence of the isolation of manganese(V)
amido complexes has been provided by Collins and GordonÈ
Wylie,10 who have extensively characterised several species by
single crystal X-ray di†raction and solution 1H NMR. It is
thus clear that such ligands are capable of stabilising high oxi-
dation states.
In view of the diverse and interesting co-ordination chem-
istry we have previously encountered when we have employed
asymmetrical ligands, together with the potential of amido
donors to stabilise higher oxidation states of manganese, we
decided that it was of interest to incorporate an amido donor
into an asymmetrical Schi† base ligand and investigate
whether higher oxidation states of manganese could be acces-
sed using electrochemical synthetic methodology. We report
herein a preparative method to obtain Mn(III) complexes with
new asymmetrical Schi† bases in an easy way.
Results and discussion
Ligand synthesis
All of the new asymmetrical ligands reported in this study
have been prepared in an analogous manner as shown in
Scheme 1; their trivial names and structures are given in Fig.
1. The synthesis of all ligands involves three common steps.
The Ðrst step involves a conventional carbodiimide amide
We were keen to investigate the viability of the electro-
chemical methodology further for the preparation of new
DOI: 10.1039/b000235f
New J. Chem., 2000, 24, 235È241
235
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2000

View Online
employed as the precursor in the preparation of all of the new
ligands via conventional Schi† base condensation reactions
with commercially available salicylaldehydes. All of the new
ligands have been satisfactorily characterised by elemental
analysis 1H, 13C NMR and IR spectroscopies and mass spec-
trometry (see Experimental). We were keen to establish that
the ligands were capable of acting as tetradentate ligands
before embarking on a prelonged electrochemical synthesis
programme. Therefore, we decided that it was worthwhile to
attempt to crystallise one of the ligands to conÐrm that they
are conformationally compatible with the necessary tetra-
dentate co-ordination mode in an octahedral geometry.
Crystal structure of H -amsal
3
Yellow plate-like crystals of H -amsal, suitable for single
3
crystal X-ray di†raction studies, were obtained by slow evapo-
ration of an ethanol solution of the ligand. The crystal struc-
ture, with the atomic numbering scheme, is shown in Fig. 2.
Some selected bond lengths and angles, as well as potential
hydrogen bonds and bonding scheme, are listed in Table 1.
Scheme 1 Synthesis of the Schi† base ligands.
The crystal structure reveals that H -amsal exists as discrete
3
coupling11 of carbobenzyloxyglycine with 2-hydroxyaniline in
THF. As expected, this reaction proceeds in excellent yield
(see Experimental) and large quantities of amide 1 can be
readily prepared. There are many methods that have been
reported for the removal of the Z protecting group from
amine functionalities. We found the most convenient method
to be via sacriÐcial hydrogenation using cyclohexene and pal-
ladium on charcoal as catalyst.12 This methodology very
rapidly yielded the desired amine 2 in high yield, without the
need for any further puriÐcation. Amine 2 has then been
molecules. An intramolecular hydrogen bond exists between
the imine nitrogen atom N(2) and the phenolic oxygen atom
O(3) [O(3)É É ÉN(2) \ 2.615(4)
A and N(2)É É ÉH(3a)ÈO(3) \
147.7(3)¡]. These intramolecular hydrogen bonds are typical of
Schi† bases derived from salicylaldehydes.13
An additional bifurcated interaction also occurs between
the amido H atom H(1b) and O(1) and N(2), as indicated in
Table 1. SigniÐcant intermolecular interactions via hydrogen
bonds can also be observed between the phenolic oxygen
atom O(1) of one molecule and the amido oxygen atom O(2@)
of a neighbouring molecule [O(1)É É ÉO(2@) \ 2.662(3) A and
O(2@)É É ÉH(1a)ÈO(1) \ 177.7(3)¡]. Additional interactions can
Fig. 2 ORTEP plot of H -amsal. Atoms showing the atomic num-
3
Fig. 1 Structures of the Schi† base ligands.
bering scheme are represented by their 40% probability ellipsoids.
Table 1 Selected bond lengths (A) and angles (¡) for the ligand H -amsal
3
N(1)ÈC(6)
1.414(3)
1.342(3)
1.367(3)
1.355(4)
116.9(3)
129.6(2)
123.0(3)
124.2(3)
122.4(3)
119.1(3)
N(2)ÈC(8)
N(2)ÈC(9)
O(2)ÈC(7)
1.451(3)
1.268(4)
1.235(3)
N(1)ÈC(7)
O(1)ÈC(1)
O(3)ÈC(15)
N(1)ÈC(7)ÈC(8)
C(7)ÈN(1)ÈC(6)
N(2)ÈC(9)ÈC(10)
O(1)ÈC(1)ÈC(2)
O(2)ÈC(7)ÈN(1)
O(3)ÈC(15)ÈC(14)
C(1)ÈC(6)ÈN(1)
C(9)ÈN(2)ÈC(8)
N(2)ÈC(8)ÈC(7)
O(1)ÈC(1)ÈC(6)
O(2)ÈC(7)ÈC(8)
O(3)ÈC(15)ÈC(10)
115.3(2)
120.7(3)
114.1(2)
116.4(2)
120.7(2)
120.9(3)
Possible hydrogen bond scheme
DÈHÉ É ÉA
DÈH
HÉ É ÉA
DÉ É ÉA
DÈHÉ É ÉA
177.7(3)
109.6(2)
112.8(2)
147.7(3)
112.3(3)@
HÉ É ÉA*É É ÉA@
Sum (XZ)
O(1)ÈH(1a)É É ÉO(2)E1 a
N(1)ÈH(1b)É É ÉO(1)
N(1)ÈH(1b)É É ÉN(2)
O(3)ÈH(3a)É É ÉN(2)
O(3)ÈH(3a)É É ÉO(3)E2 a
0.820(3)
0.860(3)
0.860(3)
0.820(5)
0.820(5)
1.843(3)
2.189(3)
2.261(3)
1.885(4)
2.571(5)
2.662(3)
2.607(3)
2.713(3)
2.615(4)
2.980(5)
137.56(15)
99.63(18)
360.0(3)
359.6(5)
a Symmetry operations. E11/2 ] x, 3/2 [ y, [ 1/2 ] z; E2 [ x, 1 [ y, 2 [ z.
236
New J. Chem., 2000, 24, 235È241

View Online
solvents such as DMF and DMSO and appear to be stable in
the solid state and in solution.
also exist between neighbouring phenolic atoms through
H(3a).
Despite the mentioned intramolecular interactions and a
partial conjugation of the molecule, it is not planar, probably
due to the packing based on the intermolecular hydrogen
bonds. Thus, the angle formed by the two potentially chelate
planes [N(2)C(9)C(10)C(15)O(3) and O(1)C(1)C(6)N(1)] has a
value of 61.6(3)¡. If we consider that both amido and salycilal-
dehyde residues are rather planar, and that just a slight turn
around the N(2)ÈC(8) bond can provide a rather planar
spatial conformation, we can expect that this ligand should
easily act as a tetradentate donor in the equatorial plane
about an octahedral metal centre. Other bond lengths and
angles are typical and merit no further discussion.14h16
Elemental analyses (Table 2) of the complexes indicate that
the manganese complexes have the general stoichiometry
Mn(amsal-R)(H O) , suggesting that the complexes are
neutral manganese(III) species in which the ligand is tri-
deprotonated. This is supported by molar conductivity mea-
surements for the complexes in 10~3 M DMF solutions,
which are in the range 4.6È23.4 )~1 cm2 mol~1, indicating
the non-electrolyte nature of the complexes,18 which is com-
pletely consistent with this formulation.
All the fast atom bombardment (FAB) mass spectra show
peaks (Table 2) relating to fragments of the form [MnL]`,
indicating ligand co-ordination to the metal centre. Further-
more, some complexes exhibit peaks due to the fragment
2
n
[Mn L ]`, which could be tentatively attributed to the pres-
ence of dimeric species in the solid state.
2 2
Electrochemical synthesis of manganese complexes
All complexes exhibit very similar infrared spectral features.
Bands centred at ca. 3400 cm~1 can be assigned to a com-
bination of the l(OH) modes of co-ordinated and lattice
water. Strong bands attributable to l(CN) are evident; these
all show a shift of 3È48 cm~1 to lower energy from the free
ligand values indicative of co-ordination to manganese. In
addition, bands due to the amide I [l(CO)] mode undergo
positive shifts whereas the amide II [d(NH) ] l(CN)] mode
bands undergo negative shifts. This behaviour is compatible
with the participation of the amide nitrogen atom in the co-
ordination to the metal.19
In the light of the crystal structure of H -amsal it was clear
that the series of ligands were potentially trianionic Schi†
bases capable of co-ordinating in a tetradentate mode. We
therefore instigated a synthetic programme in which a man-
ganese anode was oxidised in an acetontitrile solution of the
3
ligand in the presence of
a small quantity of tetra-
ethylammonium perchlorate as a supporting electrolyte.17 It
soon became apparent that the electrochemical oxidation of
manganese in the presence of an acetonitrile solution of these
ligands presents a simple and efficient route to neutral
manganese(III) complexes of stoichiometry MnIII(amsal-R)
(H O) . This synthetic route allows the complexes to be iso-
The room temperature magnetic susceptibility data (in
Table 2) for these compounds is also consistent with the for-
mulation of the complexes as Mn(amsal-R)(H O) . All of the
2
n
lated in high yields and with high purity. Thus, this is the
most direct method we have found to obtain manganese(III)
compounds and it clearly improves on the results obtained by
using the Boucher procedure.
2
n
complexes exhibit room temperature magnetic moments close
to the spin-only value of 4.9 k expected for a magnetically
b
dilute octahedral high-spin d4 manganese(III) ion. The mag-
The electrochemical efficiency of the cell E was close to
f
netic behaviour has been studied in the temperature range
50È300 K and all complexes are found to obey the CurieÈ
Weiss law. This study shows little or no antiferromagnetic
interaction between close metal centres in the solid state. An
0.33 mol F~1, which is compatible with the following reaction
scheme:
Cathode: H -amsal-R ] 3 e~ ] 3/2 H (g) ] amsal-R3~
3
2
example is shown in Fig. 3 for the complex Mn(amsal)(H O).
Anode:
amsal-R3~ ] Mn ] Mn(amsal-R) ] 3 e~
2
The conclusion that can be drawn from these magnetic data is
The manganese complexes formed via this synthetic route are
brown or greenish brown powdery solids, which all melt at
over 300 ¡C. They are all obtained in high yields and are insol-
uble or sparingly soluble in water and common organic sol-
vents, and quite soluble in polar aprotic co-ordinating
that it is unlikely that there are strong associations between
manganese centres, implying that the complexes exist as either
monomers or as very weakly associated oligomers or poly-
mers.20 Unfortunately, our extensive e†orts to obtain crystals
suitable for single crystal X-ray di†raction studies, in order to
Table 2 Analytical and other data for the complexes
Analysis/%a
Redox potentialsc
Complex
C
H
N
FABb m/z
323.0
k
/k
E /V
E /V
eff
B
ox
red
Mn(amsal)(H O)
52.7(52.8)
48.1(47.9)
41.5(42.0)
46.2(46.6)
39.5(39.6)
44.2(44.0)
34.9(34.9)
39.5(39.7)
36.9(37.4)
4.2(4.0)
3.3(3.5)
3.0(3.3)
5.0(4.7)
3.5(3.7)
3.0(2.7)
2.1(2.5)
2.7(2.4)
2.3(2.7)
8.6(8.2)
7.5(7.5)
6.4(6.5)
6.3(6.4)
6.0(5.8)
7.3(6.9)
5.6(5.4)
6.5(6.2)
8.9(8.7)
4.7
5.1
5.1
5.3
5.1
5.3
5.3
5.0
5.2
0.782
È
2
È
È
[0.658
Mn(amsal-5Cl)(H O)
357.5
0.812
0.794
È
2
[0.622
È
Mn(amsal-5Br)(H O)
401.9(804.7)*
349.9
2
1.5
[0.440
0.760
È
0.768
[0.432
0.820
È
0.802
È
0.810
È
[0.600
Mn(amsal-3OEt)(H O)
È
2
4
[0.748
È
Mn(amsal-3OMe,5Br)(H O)
431.9(862.8)*
390.0
2
3
[0.600
Mn(amsal-3,5Cl)(H O)
È
2
[0.730
È
Mn(amsal-3,5Br)(H O)
479.8(959.6)*
436.6
2
2
[0.502
Mn(amsal-3Br,5Cl)(H O)
È
2
[0.664
È
[0.804
Mn(amsal-3Br,5NO )(H O)
447.0
0.782
[0.664
2
2
2
a Found (calculated). b Peaks correspond to [MnL]` except those marked with a *, which correspond to [Mn L ]`. c Potentials vs. SCE.
2 2
New J. Chem., 2000, 24, 235È241
237

View Online
1H NMR studies
Our Ðndings for these complexes are broadly consistent with
those of Pecoraro and co-workers21 and also with our own
results22,23 for Mn(III) complexes with related Schi† bases.
These data are presented in Table 3. The protons ortho to the
donor atoms of the Schi† base ligand, H3, H3@, H6 and H6@
(see Fig. 1) are not observed. Three or four resonances are
observed between [17.1 and [37.7 ppm, which we have
assigned, in accordance with PecoraroÏs observations and
other studies done by us,22,23 to the H4 and H5 protons of
the aldehyde and to H4@ and H5@ protons of the amine (see
Fig. 4). Most interestingly, we observe a resonance at ]36
ppm, which we can assign to the aliphatic protons in the
methylene bridge between the imine and amide nitrogen
atoms. This is in contrast to both our previous studies and
those of Pecoraro and co-workers. To the best of our know-
ledge, no signals of a methylene group adjacent to an atom
co-ordinated to the manganese(III) centre have previously been
observed. These data serve to substantiate the formation of
manganese(III) complexes, but they do not enable any further
deductions to be made as to the structural make-up of the
complexes or of any solution behaviour.
Fig. 3 Plots of
k
(K) and 1/s (>) vs. temperature for
eff
M
Mn(amsal)(H O).
2
establish the structural make-up of these complexes, have
been unsuccessful. Thus, we decided to investigate whether
paramagnetic 1H NMR of the complexes in solution could be
of utility in assigning their structures further.
Cyclic voltammetry studies
Table 3 1H NMR data for the complexes
Since one of the main driving forces behind this study was to
ascertain whether it was possible to stabilise higher oxidation
states of manganese with these ligands it was necessary to
investigate the electrochemical behaviour of the complexes.
Cyclic voltammograms of all of the complexes were obtained
as dimethylformamide solutions at slow scan rates of 0.02 V
s~1 over a potential range from ]1 to [1 V. The numerical
data are given in Table 2 and a typical voltammogram is
shown in Fig. 5.
Complex
H4
H5
H4@
H5@
Mn(amsal)(H O)
Mn(amsal-5Cl)(H O)
Mn(amsal-5Br)(H O)
Mn(amsal-3OMe,5Br)(H O)
[36.6 [26.2 [18.5
[17.3
[17.5
[17.5
[18.0
2
[37.7 naa
[37.7 na
[37.5 na
[22.3
[22.2
[23.7
2
2
1.5
2
3
a na, not applicable.
In general all voltammograms show an irreversible oxida-
tive process between 0.760 and 0.820 V, which we assign to the
oxidation of manganese(III) to manganese(IV). It is interesting
to note that the potentials of these processes are similar to
those found in manganese(III) complexes with the Schi† base
salpn and oxyanions.24 In the latter case, the stabilisation of
the manganese(IV) oxidation level is basically due to the pres-
ence of one additional basic oxyanion per manganese, which
provides another negative charge to the Mn ion. In our com-
plexes we do not have an additional basic ligand, but the pres-
ence of the amide nitrogen atoms must be responsible for the
easy stabilisation of the Mn(IV) in these systems.
A second redox wave, assigned to the Mn(II) % Mn(III)
process, is observed at negative potentials. Most of the
complexes su†er an irreversible reductive process
[Mn(III) ] Mn(II)] but some of them (see Table 2) present an
important rate of reversibility.
Fig. 4 1H NMR spectrum for the complex Mn(amsal-5Br)(H O)
.
2
1.5
In all cases the most signiÐcant wave is that corresponding
to the oxidation of manganese(III) to manganese(IV), suggest-
ing that the ligands readily stabilise higher oxidation states of
manganese, as previously found for ligands with amido
groups.9,10,25,26
Conclusion
A high yielding route to a new class of potentially trianionic
and tetradentate asymmetrical Schi† base ligands has been
developed. We have shown that the presence of an amido
donor in the asymmetrical ligand results in the easy oxidation
of a manganese anode in the presence of an acetonitrile solu-
tion of the ligands to manganese(III) rather than manganese(II).
It thus provides a new and simple way to prepare neutral
manganese(III) complexes. The structural characterisation of
the complexes indicates an octahedral environment around
the metal centre.27 Finally, cyclic voltammetry suggests that
these complexes can be readily oxidised and that they could
Fig. 5 Cyclic voltammogram for Mn(amsal-5Br)(H O)
at scan
2
1.5
rate of 0.02 V s~1.
238
New J. Chem., 2000, 24, 235È241

View Online
Table 4 Elemental analyses, mass spectrometry and melting points for the ligands
Analysis/%a
MS-EI
m/z
Ligand
C
H
N
Mp/¡C
H -amsal
66.2(66.7)
59.0(59.1)
51.3(51.6)
64.7(64.9)
50.7(50.7)
52.7(53.1)
41.8(42.1)
47.2(47.0)
44.5(44.7)
5.2(5.2)
4.4(4.3)
3.3(3.7)
5.9(5.7)
3.7(4.0)
3.3(3.5)
2.7(2.8)
3.1(3.1)
2.8(3.1)
10.4(10.4)
9.3(9.2)
8.0(8.0)
8.4(8.9)
7.7(7.4)
8.4(8.3)
6.9(6.5)
7.4(7.3)
10.9(10.7)
270.2
304.0
348.0
314.1
378.0
338.0
427.8
384.0
393.0
181
180
181
180
184
192
199
189
199
3
H -amsal-5Cl
3
H -amsal-5Br
3
H -amsal-3OEt
3
H -amsal-3OMe,5Br
3
H -amsal-3,5Cl
3
H -amsal-3,5Br
3
H -amsal-3Br,5Cl
3
H -amsal-3Br,5NO
3
2
a Found (calculated).
act as precursors to other high-valent compounds of man-
ganese. Investigations into chemical oxidation of these com-
plexes are currently underway.
ing of a graphite disc working electrode, a saturated calomel
reference electrode and a platinum auxiliary electrode. Volt-
ammograms were obtained from ca. 10~3 M dimethyl-
formamide solutions of the metal complexes containing 0.1 M
tetraethylammonium perchlorate as supporting electrolyte.
Experimental
Schi† base ligand preparation
Chemicals of the highest commercial grade available (Aldrich)
were used as received. Manganese metal (Ega Chemie) was
used as platelets and was cleaned of oxide in dilute hydro-
chloric acid prior to electrolysis.
Ligands were prepared according to a method in three steps
as shown in Scheme 1.
Synthesis
of
N-(2-hydroxyphenyl)-2-[(phenylmethoxy)-
solution of carbo-
carbonylamino]ethanamide (1). To
a
benzyloxyglycine (5.00 g, 23.90 mmol) in THF (100 cm3) were
added 2-hydroxyaniline (2.61 g, 23.90 mmol) and a slight
excess of N,N@-dicyclohexylcarbodiimide (5.30 g, 25.69 mmol).
This mixture was stirred at room temperature for 4 h. The
insoluble N,N@-dicyclohexylurea was removed by Ðltration
and the solvent replaced by ethyl acetate (100 cm3). The addi-
tion of petroleum ether 40È60 ¡C a†orded 6.46 g (90%) of the
amine 1. (Found: C, 64.1; H, 5.5; N, 9.4. Calcd. for
Physical measurements
Elemental analyses were performed on a Carlo Erba EA 1108
analyser. The NMR spectra were recorded on a Bruker
WM-250 spectrometer using DMSO-d as solvent. Infrared
6
spectra were recorded as KBr pellets on a Bio-Rad FTS 135
spectrophotometer in the range 4000È600 cm~1. Mass spec-
trometry (electronic impact) was performed on a Hewlett
Packard 5988A mass spectrometer whilst fast atom bombard-
ment (FAB) was done on a Micromass AutoSpec mass
spectrometer, employing m-nitrobenzyl alcohol as a matrix.
C
H
N O : C, 64.0; H, 5.4; N, 9.3). 1H NMR (DMSO-d ):
16 16
2
4
6
d 4.06 (d, 2H), 5.30 (s, 2H), 6.96 (m, 1H), 7.56 (m, 5H), 7.91 (t,
1H), 8.09 (d, 1H), 9.31 (s, 1 H), 10.09 (s, 1 H). 13C NMR
(DMSO-d ): d 44.7 (CH ÈNH), 65.9 (OÈCH ), 115.6È147.5
Magnetic susceptibility measurements in the 50È300
K
6
2
2
temperature range were obtained using a SQUID magneto-
meter operating at 5000 G. Room temperature magnetic
susceptibilities were measured using a Digital Measurement
(C ), 157.0 (HNÈCOÈO), 168.4 (HNÈCO). IR (KBr, cm~1):
arom
l(OH) 3392 (s), l(NH) 3270 and 3075 (s), l(amide I) 1677 (vs),
l(amide II) 1618 (s). Mp: 172 ¡C. Mass spectrometry (EI): m/z
system
MSB-MKI,
calibrated
using
tetrakis-
300.1.
(isothiocyanato)cobaltate(II). Conductivities were obtained at
25 ¡C from 10~3 M solutions in DMF on a WTW model
LF-3 instrument. Cyclic voltammetry was performed on an
EG&G PAR model 273 potentiostat, controlled by EG&G
PAR model 270 software, in conjunction with a three-
electrode cell, Ðtted with a purge gas inlet and outlet, consist-
Synthesis of 2-amino-N-(2-hydroxyphenyl)ethanamide (2). A
solution of 1 (2.00 g, 6.70 mmol) in ethanol (100 cm3) was
mixed with cyclohexene (5 cm3, in excess to the molar propor-
tion required) and 0.50 g of a commercial 10% PdÈC catalyst
(catalyst:susbstrate ratio 1 : 4 by weight).12 The mixture was
Table 5 1H and 13C NMR data for the ligands in DMSO-d
6
1H NMRa
13C NMR
Ligand
a
b
c
d
e
H
R
CH
C
CN
CO
R
arom
2
arom
H -amsal
10.14(br)
9.99(br)
9.95(br)
9.95(br)
9.47(s)
9.34(s)
9.38(s)
9.31(s)
4.68(s)
4.51(s)
4.53(s)
4.52(s)
8.80(s)
8.62(s)
8.63(s)
8.63(s)
12.90(br)
12.58(br)
12.63(br)
12.78(br)
6.91È8.12
6.80È7.95
6.89È7.96
6.75È7.95
62.0
59.0
60.0
57.4
115.8È160.4
115.8È157.9
115.8È158.8
115.7È150.2
167.5
165.8
166.3
166.0
168.2
167.4
168.0
168.5
3
H -amsal-5Cl
3
H -amsal-5Br
3
H -amsal-3OEt
4.06(q) OCH
66.0 OCH
3
2
2
1.33(t) CH
15.4 CH
3
3.82(s) CH
3
3
58.4 CH
3
H -amsal-3OMe,5Br
9.97(br)
9.97(br)
9.91(br)
9.88(br)
9.88(s)
9.35(s)
9.48(s)
9.55(s)
9.50(s)
9.68(s)
4.51(s)
4.67(s)
4.65(s)
4.67(s)
4.72(s)
8.58(s)
8.60(s)
8.60(s)
8.59(s)
8.80(s)
È
6.77È7.91
6.83È7.87
6.82È7.85
6.85È7.87
6.79È8.49
58.1
59.6
59.6
57.9
58.0
115.7È153.5
115.9È161.5
115.9È163.2
115.8È162.1
115.9È169.2
166.2
165.5
166.4
164.5
166.6
168.3
167.9
168.6
168.3
168.5
3
H -amsal-3,5Cl
14.29(br)
14.44(br)
14.40(br)
13.57(br)
3
H -amsal-3,5Br
3
H -amsal-3Br,5Cl
3
H -amsal-3Br,5NO
3
2
a See Fig. 1 for atom labelling
New J. Chem., 2000, 24, 235È241
239

View Online
Table 6 Selected IR bands (in cm~1) for the ligandsa
Ligand
l(OH)
l(NH)
l(amideI)
l(CN)
l(amideII)
H -amsal
3379s
3393s
3398s
3312m
3435m
3404s
3406m
3407m
3406m
3072s,br
3072s,br
3068s,br
3091s,br
3045m
3071m
3063m
È
1656vs
1656vs
1661vs
1650vs
1662s
1695vs
1693s
1635vs
1636vs
1633vs
1624s
1649vs
1662vs
1660vs
1662vs
1664vs
1615m
1616s
1616vs
1595m
1598m
1612m
1615s
3
H -amsal-5Cl
3
H -amsal-5Br
3
H -amsal-3OEt
3
H -amsal-3OMe,5Br
3
H -amsal-3,5Cl
3
H -amsal-3,5Br
3
H -amsal-3Br,5Cl
1694s
1693s
1614m
1604s
3
H -amsal-3Br,5NO
3098m
3
2
a Intensities are denoted by: vs very strong, s strong, m medium, br broad.
Table 7 Experimental conditions for the electrochemical synthesis (initial current 10.0 mA)
Compound
Time/h
Initial voltage/V
Am of Mn dissolved/mg
E
a/mol F~1
f
Mn(amsal)(H O)
Mn(amsal-5Cl)(H O)
Mn(amsal-5Br)(H O)
Mn(amsal-3OEt)(H O)
5.9
5.3
4.6
5.1
4.2
4.7
3.8
4.2
4.1
12.0
9.6
13.7
32.1
9.3
22.0
9.2
15.0
42.7
39.5
42.3
40.0
33.8
25.6
31.1
29.3
28.3
27.6
0.33
0.39
0.42
0.32
0.41
0.32
0.38
0.33
0.33
2
2
2
1, 5
2
4
Mn(amsal-3OMe,5Br)(H O)
2
Mn(amsal-3,5Cl)(H O)
2
3
Mn(amsal-3,5Br)(H O)
2
2
Mn(amsal-3Br,5Cl)(H O)
Mn(amsal-3Br,5NO )(H O)
2
2
2
2
a Electrochemical efficiency of the cell, deÐned as the amount of metal dissolved per Faraday of charge.
reÑuxed for 15 min, Ðltered from catalyst, the catalyst washed
with ethanol, and the combined Ðltrates evaporated under
reduced pressure to give the deprotected amine 2 (yield 1.05 g,
95%). (Found: C, 57.5; H, 6.2; N, 16.6. Calcd. for
C H N O : C, 57.8; H, 6.1; N, 16.9). 1H NMR (DMSO-d ):
acetonitrile (80 cm3), containing 20 mg of tetra-
ethylammonium perchlorate, was electrolysed for 3.8 h using a
current of 10 mA. During the electrolysis, nitrogen was
bubbled through the solution to ensure the presence of an
inert atmosphere. The brown solid obtained was washed with
diethyl ether and dried in vacuo.
8
10
2
2
6
d 3.26 (s, 2 H), 6.77 (m, 1H), 6.88 (s, 1H), 6.89 (s, 1H), 8.18 (d,
1H). 13C NMR (DMSO-d ): d 45.2 (CH ), 114.9È146.6 (C ),
6
2
arom
171.5 (CO). IR (KBr, cm~1): l(OH) 3431 (s), l(NH ) 3420 and
2
3252 (s), l(NH) 3083 (s, br), l(amide I) 1649 (vs), l(amide II)
1614 (s). Mp: 148 ¡C. Mass spectrometry (EI): m/z 166.0.
Crystallographic measurements. Crystal data and reÐnement
details are given in Table 8. Plate-like yellow crystals of H -
3
amsal were obtained by recrystallisation of the ligand from
Preparation of Schi† base ligands. All of the Schi† base
ligands were prepared in a standard manner by the reaction of
equimolecular quantities of the appropriate aldehyde and
ethanol. Data were collected using a Siemens SMART di†rac-
tometer
employing
graphite-monochromated
Mo-Ka
(j \ 0.710 73 A) radiation using u scans (2h \ 50.08¡). The
max
amine 2, which is typiÐed by the preparation of H -amsal. The
structure was solved by direct methods29 and reÐned by full
3
amine 2 (1.25 g, 7.53 mmol) and salicylaldehyde (0.80 cm3,
matrix least squares on F2.30 An absorption correction was
applied.31 All non-hydrogen atoms were reÐned anisotropi-
cally and hydrogen atoms were included in calculated posi-
tions using a riding model.
7.53 mmol) were dissolved in methanol (100 cm3) and the
solution was brought to reÑux. The volume of the solution
was reduced over a 3 h period to ca. 50 cm3, using a DeanÈ
Stark trap, and was then allowed to cool. The solid, which
precipitated, was collected by Ðltration, washed with diethyl
ether (3 cm3) and dried in vacuo. The purity of all ligands was
checked by elemental analysis (Table 4), 1H and 13C NMR
(Table 5), IR (Table 6) spectroscopy and mass spectrometry
(Table 4).
Table 8 Crystal data and details of reÐnement for ligand H -amsal
3
Formula
M
Crystal system
C
270.28
Monoclinic
H
N O
15 14
2
3
Space group
P2 /n
1
Synthesis of the complexes
a/A
b/A
c/A
b/¡
6.6655(2)
16.4067(5)
The compounds were all obtained using a standard electro-
chemical procedure as previously reported.28,17 The condi-
tions are given in Table 7. An acetonitrile solution of the
Schi† base ligand containing tetraethylammonium perchlor-
ate, as supporting electrolyte, was electrolysed using a plati-
num wire as the cathode and a manganese platelet as the
12.793 80(10)
94.307(2)¡
1395.16(6)
298(2)
U/A
Ž
3
T /K
Z
4
k/mm~1
0.091
2982
ReÑections collected
anode. The cell can be summarised as: Pt([) o (H -amsal-R)
No. unique reÑections
R
R@
2451 (R \ 0.0524)
3
int
] MeCN o Mn(]).
0.0584
The synthesis is typiÐed by the preparation of Mn(amsal-3,
5Br)(H O) : a suspension (0.2 g, 0.47 mmol) of the ligand in
0.1288
2
2
240
New J. Chem., 2000, 24, 235È241

View Online
18 W. I. Geary, Coord. Chem. Rev., 1971, 7, 81.
CCDC reference number 440/170. See http://www.rsc.org/
suppdata/nj/b0/b000235f/ for crystallographic Ðles in .cif
format.
19 (a) K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, John Wiley & Sons, New York, 5th
edn., 1997; (b) L. J. Bellamy, Advances in Infrared Group Fre-
quencies, Methuen & Co., London, 1st edn., 1969.
20 (a) N. Aurangzeb, C. E. Hulme, C. A. McAuli†e, R. G. Pritchard,
M. Watkinson, A. Garc•aÈDeibe, M. R. Bermejo and A. Sousa, J.
Chem. Soc., Chem. Commun., 1992, 1524; (b) A. Garc•aÈDeibe,
M. R. Bermejo, A. Sousa, C. A. McAuli†e, P. McGlynn, P. T.
Ndifon and R. G. Pritchard, J. Chem. Soc., Dalton T rans., 1993,
1605; (c) N. Aurangzeb, C. E. Hulme, C. A. McAuli†e, R. G. Prit-
chard, M. Watkinson, M. R. Bermejo and A. Sousa, J. Chem.
Soc., Chem. Commun., 1994, 2193; (d) C. E. Hulme, M. Watkin-
son, M. Haynes, R. G. Pritchard, C. A. McAuli†e, N. Jaiboon, B.
Beagley, A. Sousa, M. R. Bermejo and M. Fondo, J. Chem. Soc.,
Dalton T rans., 1997, 1805; (e) M. R. Bermejo, A. Sousa, A.
Garc•aÈDeibe, M. Maneiro, J. Sanmart•n and M. Fondo, Poly-
hedron, 1999, 15, 511.
Acknowledgements
We thank Xunta de Galicia (PGIDT99PXI20903B) for Ðnan-
cial support and a Predoctoral Grant to A.M.G.
References
1
V. L. Pecoraro, in Manganese Redox Enzymes, ed. V. L. Peco-
raro, VCH, New York, 1992.
2
D. M. J. Doble, C. H. Benison, A. J. Blake, D. Fenske, M. S.
Jackson, R. D. Kay, W.-S. Li and M. Schroder, Angew. Chem.,
Int. Ed. Engl., 1999, 38, 1915.
(a) R. A. Johnson, K. B. Sharpless and E. N. Jacobsen, in Cata-
lytic Asymmetric Synthesis, ed. I. Ojima, VCH, New York, 1993,
ch. 4; (b) J. Du Bois, J. Hong, E. M. Carreira and M. W. Day, J.
Am. Chem. Soc., 1996, 118, 915; (c) N. S. Finney, P. J. Pospisil
and E. N. Jacobsen, Angew. Chem., Int. Ed. Engl., 1997, 36, 1720;
(d) C. Linde and M. Arnold, Angew. Chem., Int. Ed. Engl., 1997,
36, 1723.
L. J. Boucher and C. G. Coe, Inorg. Chem., 1975, 14, 1289.
M. R. Bermejo, A. Castineiras, J. C. Garc•aÈMonteagudo, M.
Rey, A. Sousa, M. Watkinson, C. A. McAuli†e, R. G. Pritchard
and R. L. Beddoes, J. Chem. Soc., Dalton T rans., 1996, 2935.
(a) L. Luaces, M. R. Bermejo, J. A. Garc•aÈVazquez, J. Romero,
A. Sousa and and M. Watkinson, Polyhedron, 1996, 1375; (b) L.
Luaces, M. R. Bermejo, J. A. Garc•aÈVazquez, J. Romero, A.
Sousa, R. G. Pritchard and C. A. McAuli†e, Polyhedron, 1996,
3717.
3
21 J. A. Bonadies, M. J. Maroney and V. L. Pecoraro, Inorg. Chem.,
1989, 28, 2044.
22 M. R. Bermejo, M. Fondo, A., Garc•aÈDeibe, M. Rey, J.
Sanmart•n, A. Sousa and M. Watkinson, Polyhedron, 1996, 15,
4185.
23 A. M. Gonzalez, Ph.D. Thesis, University of Santiago de Com-
postela, 1999.
4
5
24 E. J. Larson and V. L. Pecoraro, J. Am. Chem. Soc., 1991, 113,
3810.
25 T. J. Collins, R. D. Powell, C. Slebodnick and E. S. U†elman, J.
Am. Chem. Soc., 1990, 112, 899.
26 K. Bertoncello, G. D. Fallon and K. S. Murray, Inorg. Chim.
Acta, 1990, 174, 57.
6
27 (a) A. Garc•aÈDeibe, A. Sousa, M. R. Bermejo, P. P. Mac Rory,
C. A. McAuli†e, R. G. Pritchard and M. Helliwell, J. Chem. Soc.,
Chem. Commun., 1991, 728; (b) R. G. Pritchard, C. A. McAuli†e,
R. V. Parish, A. A. J. Nabhan, F. M. Ashmawy, A. Garc•aÈDeibe,
A. Sousa and M. R. Bermejo, Acta Crystallogr., Sect. C, 1991, 47,
2453; (c) C. A. McAuli†e, R. G. Pritchard, A. Garc•aÈDeiba, A.
Sousa and M. R. Bermejo, Acta Crystallogr., Sect. C, 1992, 48,
364; (d) N. Aurangzeb, C. A. McAuli†e, R. G. Pritchard, M. Wat-
kinson, M. Bermejo, A. Garc•aÈDeibe and A. Sousa, Acta Crys-
tallogr., Sect. C, 1993, 49, 1945; (e) M. R. Bermejo, A.
Garc•aÈDeibe, J. Sanmart•n, A. Sousa, N. Aurangzeb, C. E.
Hulme, C. A. McAuli†e, R. G. Pritchard and M. Watkinson, J.
Chem. Soc., Chem. Commun., 1994, 645; ( f ) M. R. Bermejo, A.
Garc•aÈDeibe, M. Rey, J. Sanmart•n, A. Sousa, N. Aurangzeb,
C. E. Hulme, C. A. McAuli†e, R. G. Pritchard, M. Watkinson
and M. Helliwell, J. Chem. Soc., Dalton T rans., 1994, 1265; (g) N.
Aurangzeb, C. E. Hulme, C. A. McAuli†e, R. G. Pritchard, M.
Watkinson, M. R. Bermejo, A. Garc•aÈDeibe, M. Rey, J.
Sanmart•n and A. Sousa, J. Chem. Soc., Chem. Commun., 1994,
1153; (h) C. A. McAuli†e, A. Nabhan, R. G. Pritchard, M. Wat-
kinson, M. Bermejo and A. Sousa, Acta Crystallogr., Sect. C,
1994, 50, 1676; (i) M. Watkinson, M. Fondo, M. R. Bermejo, A.
Sousa, C. A. McAuli†e, R. G. Pritchard, N. Jaiboon, N. Aurang-
zeb and M. Naeem, J. Chem. Soc., Dalton T rans., 1999, 31.
28 C. Oldham and D. G. Tuck, J. Chem. Educ., 1982, 59, 420.
29 SHELXS86: G. M. Sheldrick, in Crystallographic Computing, eds.
G. M. Sheldrick, C. Krueger and R. Goddard, Oxford University
Press, Oxford, UK, 1985, p. 175.
7
8
C. A. McAuli†e, R. G. Pritchard, L. Luaces, J. A.
Garc•aÈVazquez, J. Romero, M. R. Bermejo and A. Sousa, Acta
Crystallogr., Sect. C, 1993, 49, 587.
(a) A. Danopoulos, G. Wilkinson, T. K. N. Sweet and M. B.
Hursthouse, J. Chem. Soc., Dalton T rans., 1994, 1037; (b) A.
Danopoulos, G. Wilkinson, T. K. N. Sweet and M. B. Hurs-
thouse, J. Chem. Soc., Dalton T rans., 1995, 205; (c) A. Dano-
poulos, G. Wilkinson, T. K. N. Sweet and M. B. Hursthouse, J.
Chem. Soc., Dalton T rans., 1995, 937; (c) J. Bendix, T.
Weyhermuller, E. Bill and K. Wieghardt, Angew. Chem., Int. Ed.
Engl., 1999, 38, 2766 and references therein.
9
M. Koikawa, H. Okawa and S. Kida, J. Chem. Soc., Dalton
T rans., 1988, 641.
10 T. J. Collins and S. W. GordonÈWylie, J. Am. Chem. Soc., 1989,
111, 4511.
11 J. C. Sheenan and G. P. Hess, J. Am. Chem. Soc., 1955, 77, 1067.
12 A. E. Jackson and R. A. W. Jonhstone, Synthesis, 1976, 685.
13 M. Gavranic, B. Kaitner and E. Mestrovic, J. Chem. Crystallogr.,
1996, 26, 23.
14 H.-K. Fun, K. Chinnakali, I. A. Razak, Z. Shen, J.-L. Zuo and
X.-Z. You, Acta Crystallogr., Sect. C, 1999, 55, 99.
15 Y. Elerman, A. Elmali, M. Kabak and I. Svoboda, Acta Crys-
talllogr., Sect. C, 1998, 54, 1701.
16 (a) J. Mah•a, M. A. Maestro, M. Vazquez, M. R. Bermejo, J.
Sanmart•n and M. Maneiro, Acta Crystallogr., Sect. C, 1999, 55,
1545; (b) J. Mah•a, M. A. Maestro, M. Vazquez, M. R. Bermejo,
A. M. Gonzalez and M. Maneiro, Acta Crystallogr., Sect. C, in
the press.
17 (a) M. R. Bermejo, M. Fondo, A. M. Gonzalez, O. L. Hoyos, A.
Sousa, C. A. McAuli†e, W. Hussain, R. Pritchard and V. M.
Novotorsev, J. Chem. Soc., Dalton T rans., 1999, 2211. (b) J.
Sanmart•n, M. R. Bermejo, A. M. Garc•aÈDeibe, O. Piro and
E. E. Castellano, Chem. Commun., 1999, 1953.
30 G. M. Sheldrick, Program for the ReÐnement of Crystal Struc-
tures, University of Gottingen, Gottingen, Germany, 1993.
31 G. M. Sheldrick, SADABS, an Empirical Absorption Correction
Program for Area Detector Data, University of Gottingen,
Gottingen, Germany, 1996.
Paper b000235f
New J. Chem., 2000, 24, 235È241
241