Water-soluble cobalt(II) and copper(II) complexes of 3-(5-chloro-2-hydroxy- 3-sulfophenylhydrazo)pentane-2,4-dione as building blocks for 3D supramolecular networks and catalysts for TEMPO-mediated aerobic oxidation of benzylic alcohols

Article abstract of DOI:10.1002/ejic.201100348

A new water-soluble β-diketone azo derivative 3-(5-chloro-2-hydroxy-3- sulfophenylhydrazo)pentane-2,4-dione(H₃L, 1) was synthesized and found to be stable in DMSO solution and in the solid state in the hydrazo tautomeric form. Its water-soluble

Full text of DOI:10.1002/ejic.201100348

FULL PAPER
DOI: 10.1002/ejic.201100348
Water-Soluble Cobalt(II) and Copper(II) Complexes of 3-(5-Chloro-2-hydroxy-
3-sulfophenylhydrazo)pentane-2,4-dione as Building Blocks for 3D
Supramolecular Networks and Catalysts for TEMPO-Mediated Aerobic
Oxidation of Benzylic Alcohols
Maximilian N. Kopylovich,[a] Kamran T. Mahmudov,[a] Matti Haukka,[b] Paweł J. Figiel,[a]
Archana Mizar,[a] José A. L. da Silva,[a] and Armando J. L. Pombeiro*[a]
Keywords: Cobalt / Copper / Supramolecular Network / Homogeneous catalysis / Water-soluble catalyst / Oxidation /
Hydrogen bonds
A new water-soluble β-diketone azo derivative Ϫ 3-(5-
chloro-2-hydroxy-3-sulfophenylhydrazo)pentane-2,4-dione
(H3L, 1) Ϫ was synthesized and found to be stable in DMSO
solution and in the solid state in the hydrazo tautomeric form.
Its water-soluble complexes [Co(HL)(en)(H2O)]·4H2O (3) and
the zwitterionic [Cu(L)(Hen)(H2O)] (4), with buffering prop-
erties, were prepared by reaction of cobalt(II) and copper(II)
nitrates with the ethylenediammonium (H2en) salt of 1,
(H2en)(HL) (2). In the formation of 3 and 4, 1 is a chelating
ligand, and a crucial synthetic and structural role is played
by en, allowing the organization of water-soluble assemblies
and influencing the overall 3D supramolecular arrangement.
Compound 3 is the first cobalt complex with an azo deriva-
tive of a β-diketone. Complex 4 acts as catalyst precursor for
the aerobic TEMPO-mediated selective oxidation of benzylic
alcohols to the corresponding aldehydes in aqueous media.
studies[4] have shown that copper(II) complexes with func-
tionalized azo derivatives of β-diketones (ADBs), in par-
ticular ortho-hydroxy-substituted ADBs, are significantly
active in the aerobic oxidation of benzyl alcohols to alde-
hydes. Hence, we report our continued preparation of new
water-soluble ADB copper(II) and cobalt(II) complexes,
which contain sites for possible pH regulation properties, in
particular sulfo and amino groups, considered to be good
candidates to fulfil these goals.
From another perspective, ADBs and their complexes
can create interesting supramolecular architectures involv-
ing monomeric, oligomeric or polymeric subunits.[4,5] Ethyl-
enediamine (en) can further participate in this process
through template Schiff base condensation or as a proton-
rich attractor and spacer, allowing the regulation of the size
of channels or cavities within the H-bonded assemblies.[6]
In addition, the presence of proton acceptor and donor
sites within one molecule will result in a pH-tunable ar-
rangement (association), which is interesting for a wide
range of applications.[7] Hence, the complexes created with
these types of ligands can be used as promising new build-
ing blocks in various multicomponent supramolecular
architectures.
Introduction
Catalytic processes in aqueous media can require con-
strained active particles in the water phase, and the design
of homogeneous water-soluble catalysts usually involves the
use of a suitable ligand with a hydrophilic functionality.[1]
In most cases such a ligand can be obtained by attaching a
water-solubilizing group, e.g. a sulfonato or carboxylato
group. Another major challenge is the reversible tuning of
the acid–base properties of the catalyst, which can enhance
the activity/selectivity towards a certain product and/or re-
versibly change the hydrophilicity. In addition, since many
processes require a certain pH interval, a complex that,
apart from its main catalytic function, can maintain the pH
within a certain range (i.e. possessing buffer properties) is
needed. Thus, the synthesis of water-soluble complexes with
several pH-tunable sites for protonation–deprotonation is
of interest for new green catalytic processes.
One potentially interesting process is the selective oxi-
dation of alcohols by dioxygen or air[2] using a combination
of TEMPO radicals (2,2,6,6-tetramethylpiperidine-1-oxyl),
or its derivatives, with copper complexes.[3] Our preliminary
[a] Centro de Química Estrutural, Complexo I, Instituto Superior
Técnico, TU Lisbon,
Therefore, based on these considerations, this work has
been undertaken with the following aims: i) to synthesize
new water-soluble cobalt(II) and copper(II) complexes with
3-(5-chloro-2-hydroxy-3-sulfophenylhydrazo)pentane-2,4-di-
one (1, H3L), ii) to explore their potential as building blocks
in supramolecular hydrogen-bonded assemblies, and iii) to
Av. Rovisco Pais, 1049-001 Lisbon, Portugal
Fax: +351-218464455
E-mail: pombeiro@ist.utl.pt
[b] University of Eastern Finland, Department of Chemistry,
P. O. Box 111, 80101 Joensuu, Finland
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100348.
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apply these complexes as catalysts for the aerobic TEMPO-
It has been demonstrated[10] that in solution cobalt(II)
mediated selective oxidation of benzylic alcohols to the cor- ions interact with 1, but attempts to prepare complexes in
responding aldehydes.
the solid state by concentration of solutions of cobalt(II)
nitrate and 1 failed (this strategy was used for the prepara-
tion of some copper(II)–ADB complexes).[4] In fact, evapo-
ration of methanol, ethanol, DMF, water, and DMSO (or
their mixtures) solutions of cobalt salts with 1 gave only
mixtures of the starting materials, whereas, in the case of
copper(II) salts, amorphous powders of unidentified prod-
uct mixtures were obtained. To solve this problem, 1 was
deprotonated by addition of en and the salt (H2en)(HL) (2)
was used as the starting material for further reactions with
CoII and CuII nitrate salts to afford [Co(HL)(en)(H2O)]·
4H2O (3) (the first Co–ADB complex to be reported) and
[Cu(L)(Hen)(H2O)] (4), respectively (Scheme 1). The added
en conceivably weakens the hydrogen-bonded system in 1
(see below) and the reactivity of activated 1 increases, facili-
tating the N–H deprotonation and coordination to the
metal ion.
Results and Discussion
Synthesis, Spectroscopic and Crystallographic Investigation
of 1–4
The new water-soluble ligand 1 (see Scheme S1, Support-
ing Information) was synthesized by a modified meth-
od[8a–8c] by reacting 5-chloro-2-hydroxy-3-sulfophenyldiaz-
onium chloride and pentane-2,4-dione in a water solution
containing sodium hydroxide.[8d] 5-Chloro-2-hydroxy-3-sulfo-
phenyldiazonium chloride was obtained by diazotization of
the substituted aniline. Compound 1 is highly soluble in
polar solvents such as water, DMF, and DMSO, but almost
insoluble in chloroform, dichloromethane, and toluene. The
presence of the SO3H group is crucial for water solubility;
the analogue of 1 with H instead of this group is completely
insoluble in water.[9]
Alternatively, 3 and 4 can be prepared by 2 formed in
situ, upon neutralization of 1 with en in solution and subse-
quent addition of the cobalt(II) or the copper(II) salt. In
any case, the complex product can be isolated in the solid
state upon concentration of the reaction solution left to
evaporate slowly. Interestingly, the interaction of en with 1
does not provide a Schiff base, which is in contrast to its
reaction with β-diketones[11] and other ADBs,[4] possibly
due to electrostatic repulsion.
The NMR spectrum of 1 in [D6]DMSO at room tem-
perature indicates that this compound exists in this solvent
in the hydrazo rather than in the enol-azo or keto-azo form
(Scheme S2, Supporting Information). The two peaks of the
1
acetyl groups in the H and 13C NMR spectra (see Experi-
mental Section) indicate that one of these groups undergoes
a shift due to hydrogen bonding of the carbonyl moiety
with the hydrazo NH group. This is in agreement with the
low field chemical shift (δ =14.33 ppm) of the hydrazo NH
1
The H NMR spectrum of 2, compared with that of 1,
proton and is also consistent with IR data: the stretching shows the shift of the hydrazo NH proton from δ = 14.33
bands ν(C=O) and ν(C=O···H) are at 1677 and 1624 cm–1, to 15.20 ppm and the absence of the ortho-OH proton of 1
respectively, the latter being shifted on account of the H- (δ = 11.23 ppm), whereas in the 13C NMR spectrum the H-
bond.[4,5] The ν(OH) and ν(NH) bands at 3400 and bonded carbonyl group is shifted from δ = 196.5 to 172.4
3094 cm–1 also support the existence of the H-bonded hy- ppm. To study the structural features of 2 and find out
drazone structure in the solid state.[4,5] X-ray diffraction which tautomeric form is stabilized in the solid state after
analyses of analogues of 1, with different substituents, dem- deprotonation with en, single crystals of 2 were prepared
onstrate that they are stabilized in the hydrazo II rather by slow evaporation of its ethanol solution at room tem-
than in the hydrazo I form.[4]
perature. Compound 2 crystallizes in the triclinic space
Scheme 1. Synthesis of 2–4.
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Co(II) and Cu(II) Complexes in 3D Supramolecular Networks
group P1 with almost planar overall geometry of the anion tent with strong hydrogen bonding.[12,13] Thus, 3 is com-
¯
(Table S1 and S2). In accord with previous findings,[12] the bined in a 3D network with channels (Figure 2, b), in which
molecular structure of the anionic part of 2 contains an water molecules interconnect carbonyl oxygen atoms, oxy-
intramolecular six-membered hydrogen-bonded ring with a gen atoms of the anions, and other water molecules. In ac-
strong hydrogen bond (Figure 1), as suggested by the geo- cord with the geometry of the complexes, the channels in-
metric parameters (Table S3). This behavior is well de- corporating the coordinated water have a nearly quadratic
scribed by the intramolecular resonance assisted hydrogen cross section, whereas those containing hydrate water mole-
bond model, which relates to the synergistic mutual rein- cules have an elongated profile. There are abundant hydro-
forcement of intramolecular hydrogen bonding due to π- gen bonds (Table S3) as well as π···π stacking interactions
electron delocalization.[12a,12c,13] The geometry, the typical of 4.6228(4) Å which extend the 2D frameworks into a 3D
double bond length of C(7)–N(2) [1.345(2) Å] (Table S2, supramolecular architecture (Figure 2, b). Moreover, build-
Figure 1), and the formation of the intramolecular N–H···O ing blocks of 3 are associated in layers separated by water
hydrogen bond indicate that the hydrazone is the preferred molecules.
tautomeric form of the molecule.[4] However, the N(1)–N(2)
distance (1.290 Å) suggests a partial double bond character
for this bond and thus some degree of conjugation with the
aromatic ring.
Figure 1. Structure of 2 (ellipsoids are drawn at 50% probability).
Selected bond lengths [Å] and angles [°]: O(4)–C(6) 1.316(2), O(5)–
C(8) 1.241(2), O(6)–C(10) 1.229(2), N(2)–C(7) 1.345(2), N(1)–
H(1N) 0.8115, H(1N)···O(4) 2.23, H(1N)···O(5) 1.89, N(1)–H(1N)···
O(4) 2.634(5), N(1)–H(1N)···O(5) 2.529(4), N(4)–H(4N)···S(1)
3.5448(18), N(1)–H(1N)–O(4) 111.09, N(1)–H(1N)–O(5) 135.28.
The cobalt atom in 3 is six-coordinate (Figure 2, a). The
Co–O bond lengths range from 1.862(3) to 1.958(3) Å,
whereas the Co–N distances are within 1.857(3)–1.967(3) Å
(Table S2). The coordination environment of the cobalt is
best described as distorted octahedral (4 + 2) with en (N3)
and a water molecule (O7) coordinated in the axial posi-
tions. The cobalt atom belongs to (i) two fused five- and
six-membered metallacycles, Co1–O4–C6–C5–N6 and
Co1–O5–C8–C7–N5–N6 and (ii) the five-membered metall-
acycle Co1–N3–C12–C13–N4 (in this case both N atoms of
en are coordinated to cobalt, in contrast to 4). The sixth
coordination position is occupied by H2O. This coordinated
Figure 2. Structure of 3 (a) (ellipsoids are drawn at 50% prob-
ability) with packing diagram (b). Selected bond lengths [Å] and
angles [°]: Co(1)–O(4) 1.874(3), Co(1)–O(5) 1.862(3), Co(1)–O(7)
1.958(3), Co(1)–N(3) 1.926(3), Co(1)–N(4) 1.967(3), Co(1)–N(6)
1.857(3), N(6)–Co(1)–O(5) 93.34(13), N(6)–Co(1)–O(4) 86.72(12),
O(5)–Co(1)–O(4) 179.21(11), N(3)–Co(1)–O(7) 177.81(13), O(4)–
Co(1)–N(4) 88.99(13).
X-ray structural analysis of 4 shows that it crystallizes as
water molecule and one part of en are anti to each other a zwitterionic neutral mononuclear complex in the triclinic
¯
and involved in two hydrogen bonds with the noncoordi- space group P1, with the ADB ligand, the coordinated
nated water molecules. The average H2O···O, H2O···Cl, water, and Hen in the asymmetric unit (Figure 3, a,
H2O···S, and H2O···N distances of the hydrogen bonds in 3 Scheme 1). The coordination polyhedron of the Cu atom is
fall within the 2.655(4)–3.629(4) Å range (Table S3), consis- tetragonal pyramidal with the O(3) atom in the axial posi-
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A. J. L. Pombeiro et al.
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tion. ADB acts as a tridentate ligand by means of the de- H-bonds between the free carbonyl oxygen atom O7 and
protonated OH group in the ortho position (O1) of the aro- the protonated N4 atom of Hen, thus giving rise to supra-
matic part, of one of the nitrogen atoms (N1) of Hen, and molecular cationic chains (Figure 3, b). Hence, the proton-
one oxygen atom (O2) from a carbonyl group. The cop- ated N4 atom of en acts as an H-donor bridging to O4, O5,
per(II) atom belongs to two six- and five-membered fused O7, and S1 atoms of 4 in the neighboring unit (Table S3).
metallacycles. The Cu(1)–O(1) bond length of 1.941(2) Å On the other hand, intermolecular H-bonds between the
within the five-membered ring is shorter than that of the coordinated water molecules and carbonyl oxygen atom O2
Cu(1)–O(2) bond [1.953(2) Å]. An extensive interlinkage of or the sulfo group oxygen atoms O5, O6 of two vicinal mo-
neighboring 4 molecules takes place through intermolecular lecules lead to chains. Moreover, H-bonds are formed be-
tween the coordinated N3 atom of en and O(4)#4, O(6)#2,
and S(1)#2. Additionally, intermolecular π···π interactions
are observed between the C1–C6 phenyl ring and the Cu1–
N1–N2–C7–C10–O2 metallacycle (x + 1, y, z); the
centroid···centroid distance of 3.5280(1) Å and the angle be-
tween the planes, 6.73°, indicate a π···π interaction (Figure
S1).
Buffer Properties of 4
The zwitterionic nature of 4 can be used in applications
where pH-tunable or buffer properties of the system are
crucial for the optimal performance of a specific function
(e.g. in catalysis). An important characteristic of a zwitter-
ionic compound is its isoelectric point, which was deter-
mined as 4.96 for 4 (see Supporting Information for details,
Tables S4, S5), and its buffer zones lie in the weak acidic
region with pH close to pK2 = 6.84 (where K2 is the depro-
tonation constant of 4 concerning the H3N+ group of Hen)
and in the acid area with pH close to pK1 = 3.08 (where K1
concerns the deprotonation of the SO3H group). Interest-
ingly, possibly due to the formation of the zwitterion, the
detection limit for the analytical determination of cop-
per(II) with 2 (in the formation of 4) decreases in compari-
son to 1 and other similar reagents,[14] therefore, both the
sensitivity and selectivity are enhanced (Tables S6, S7).
Catalytic Activity of 3 and 4
Copper(II) complexes with N,N- and N,O-donor ligands
have been found to be efficient catalysts for the TEMPO-
mediated aerobic oxidation of benzylic alcohols in basic
aqueous media (Scheme 2).[4,15] The catalysts lead to more
efficient oxidation by promoting deprotonation of the
alcohol.[15] Thus, we have applied 4 and, for comparison,
3 to check their potential as catalysts for this reaction in
previously optimized reaction conditions.[4]
Figure 3. Structure of 4 (a) (ellipsoids are drawn at 50% prob-
ability) with packing diagram (b). Selected bond lengths [Å] and
angles [°]: Cu(1)–N(1) 1.928(3), Cu(1)–O(1) 1.941(2), Cu(1)–O(2)
1.953(2), Cu(1)–N(3) 2.002(3), Cu(1)–O(3) 2.3521(19), N(1)–
Cu(1)–O(1) 84.73(10), N(1)–Cu(1)–O(2) 89.09(9), N(1)–Cu(1)–O(3)
Scheme 2. Oxidation of benzyl alcohols using 3 and 4 as catalyst
87.63(8), N(3)–Cu(1)–O(3) 91.83(9), O(1)–Cu(1)–O(3) 89.40(8),
precursors.
O(1)–Cu(1)–N(3) 93.02(9), O(2)–Cu(1)–O(3) 99.53(8), N(4)–
H(4NA)···O(5)#4 2.852(3), N(4)–H(4NA)···O(4)#4 3.160(3), N(4)–
Aerobic oxidation of benzyl alcohol (1.5 mmol) in aque-
H(4NB)···O(4) 2.842(3), N(4)–H(4NA)···S(1)#4 3.582(2). Sym-
ous alkaline (0.1 m K2CO3) solution, in the presence of a
catalytic amount of 4 and TEMPO, gave benzaldehyde in
metry transformations used to generate equivalent atoms: #4 x –
1, y, z.
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Co(II) and Cu(II) Complexes in 3D Supramolecular Networks
Table 1. Aerobic oxidation of selected alcohols to the corresponding aldehydes.[a]
.
Run
Complex
Substrate
Product
Time [h]
Yield [%][b]
TON/TOF [h–1][c]
1
2
3
4
4
benzyl alcohol
benzyl alcohol
benzyl alcohol
benzyl alcohol
benzyl alcohol
benzyl alcohol
2-Me-benzyl alcohol
3-Me-benzyl alcohol
4-Me-benzyl alcohol
4-Cl-benzyl alcohol
benzyl alcohol
benzaldehyde
benzaldehyde
benzaldehyde
benzaldehyde
benzaldehyde
benzaldehyde
2-Me-benzaldehyde
3-Me-benzaldehyde
4-Me-benzaldehyde
4-Cl-benzaldehyde
benzaldehyde
6
18
6
68
98
Ͻ 1
4
3
2
74
88
97
98
20
68/11
98/5.4
1/0.2
4/0.2
3/0.1
4
3
3
22
22
22
18
18
18
18
6
5[d]
6[e]
7
4
4
2/0.1
4
74/4.1
88/4.9
97/5.4
98/5.4
20/3.3
8
9
10
11
4
4
4
Cu(NO3)2
[a] Conditions: 1.5 mmol of the substrate, 0.015 mmol (1 mol-%) of catalyst and 0.075 mmol (5 mol-%) of TEMPO in 5 mL of 0.1 m
K2CO3 aqueous solution, 80 °C, 1 atm. air. [b] Yields based on GC analyses, selectivity in all cases Ͼ 99%. [c] TON = mol of product/
mol of catalyst; TOF = TON/h. [d] Reaction without K2CO3. [e] Reaction without TEMPO.
68% yield after 6 h (Table 1, run 1), and extension of the conditions, 3D supramolecular networks are formed by 3
reaction time to 18 h significantly increased the yield (98%, and 4 through extensive intermolecular H-bonds. These fea-
run 3). The yields obtained with 3 were poor, even after tures should be accounted for in further exploration of the
22 h (runs 3 and 4). In agreement with previously reported rare intramolecular NH3+···–O3S interaction and H-bond-
observations,[4,15] we also found that the presence of base ing abilities of the ADB–en systems in crystal engineering
(K2CO3) as well as TEMPO is crucial to obtain high yields in aqueous media.
(see runs 5–6, without these reagents).
Moreover, the water-soluble zwitterionic 4 has buffering
Substituted benzylic alcohols can be also converted into properties and exhibits a good catalytic activity towards the
the corresponding aldehydes in moderate to good yields. aerobic TEMPO-mediated selective oxidation of benzylic
For example, oxidation of 2-, 3-, and 4-methylbenzyl alcohols to the corresponding aldehydes in aqueous basic
alcohol results in 74, 88, and 97% yield of the correspond- medium, which could be extended to other H-bonded ADB
ing aldehydes, respectively, revealing the steric effect of the systems and oxidation reactions, broadening their applica-
methyl substituent position (runs 7–9). 4-Chlorobenzyl tion in catalysis under green conditions, an underdeveloped
alcohol is also converted to 4-chlorobenzaldehyde in very field for supramolecular metal assemblies.
good yield (98%, run 10). With Cu(NO3)2 instead of 3 or
4, only 20% yield of benzaldehyde was achieved (run 11).
We expect that these catalytic systems follow the previously
Experimental Section
proposed mechanism,[4,15,16] which involves coordination of
RCH2OH (or deprotonated RCH2O–) and the TEMPO rad-
ical to the copper(II) center, hydrogen abstraction from the
α-carbon by TEMPO, and intramolecular electron transfer
from the resulting O-ligated radical RC·HO to CuII giving
RCHO and CuI, which is subsequently reoxidized to CuII.
Materials and Instrumentation: All chemicals were obtained from
commercial sources and used as received. The 1H and 13C NMR
spectra were recorded at ambient temperature with a Bruker
Avance II + 300 (UltraShieldTM Magnet) spectrometer operating
at 300.130 and 75.468 MHz for 1H and 13C NMR, respectively. The
chemical shifts are reported in ppm using tetramethylsilane as an
internal reference. IR spectra (4000–400 cm–1) were recorded with
a BIO-RAD FTS 3000MX instrument as KBr pellets. Carbon, hy-
drogen, and nitrogen elemental analyses were carried out by the
Microanalytical Service of the Instituto Superior Técnico. All the
synthetic work was performed in air and at room temperature.
Chromatographic analyses were performed with a Fisons Instru-
ments GC 8000 series gas chromatograph with a DB-624 (J&W)
capillary column (FID detector) and the Jasco-Borwin v.1.50 soft-
ware.
Conclusions
A new hydrazone compound 1 and its en salt 2 have been
synthesized and shown to be stable in solution and in the
solid state in the hydrazo form. The new pH-tunable water
soluble zwitterionic CuII complex 4 and the first example
of a CoII–ADB complex 3 (Scheme 1) with labile H2O li-
gands have been prepared and structurally characterized.
Thus, 1 has proved to be a chelating ligand for complex-
ation with CoII and CuII. The complexes also bear ethyl-
enediamine as a coligand, which plays a crucial structural
role in the organization of the water-soluble assemblies in-
fluencing the overall 3D supramolecular arrangement, de-
pending on the reaction conditions. These observations are
of significance for the design of self-assembled coordination
organic–inorganic materials[17] or smart functional materi-
Synthesis of H3L (1): Compound 1 was synthesized according to
the Japp–Klingemann reaction[8] from the corresponding diazo-
nium salt and pentane-2,4-dione.
Diazotization: 5-Chloro-2-hydroxy-3-sulfoaniline (0.025 mol) was
dissolved in water (50 mL) and crystalline NaOH (1.0 g) was
added. The solution was cooled to 0 °C and NaNO2 (0.025 mol)
was added followed by 33% HCl (25ϫ0.2 mL portions) over 1 h
with vigorous stirring. During the reaction, the temperature of the
mixture did not exceed +5 °C. A suspension of the unstable 5-
als attributed to tautomerism.[12a] For example, at given chloro-2-hydroxy-3-sulfophenyldiazonium chloride was obtained
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(Supporting Information, Scheme S1), which was used without pu-
rification for the next stage (see below).
(5:1, v/v) mixture; yield 47% (based on Cu). C13H19ClCuN4O7S
(474.4): calcd. C 32.98, H 3.83, N 11.84; found C 33.42, H 3.72, N
11.82. IR (KBr): ν = 3437 [ν(OH)], 3305 [ν(NH)], 3245 [ν(NH)],
˜
Azocoupling: NaOH (0.025 mol) was added to a mixture of pen-
tane-2,4-dione (0.025 mol) with water (50 mL). The solution was
cooled in an ice bath, and a suspension of 5-chloro-2-hydroxy-3-
sulfophenyldiazonium chloride (prepared as above) was added in
two equal portions with vigorous stirring for 1 h. The following
day, 3-(5-chloro-2-hydroxy-3-sulfophenylhydrazo)pentane-2,4-di-
one (H3L, 1) formed as a precipitate was collected by filtration,
recrystallized from methanol, and dried in air; yield 77% (based on
pentane-2,4-dione), dark brown powder, soluble in water, DMSO,
ethanol, and dimethylformamide and insoluble in acetone and
chloroform. C11H11ClN3O6S (334.73): calcd. C 39.47, H 3.31, N
3165 [ν(NH)], 3068 [ν(NH)], 1662 [ν(C=O)], 1638 [ν(C=O)], 750
[δ(CH, Ar)] cm–1.
X-ray Structure Determination: Crystals of 2–4 were immersed in
cryo-oil, mounted on a nylon loop, and measured at a temperature
of 100 K. The X-ray diffraction data were collected with a Bruker
AXS Smart ApexII Duo (for 2, 3) or a Nonius KappaCCD (for 4)
diffractometer using Mo-Kα radiation (λ = 0.710 73 Å). APEX2[18a]
(for 2, 3) or Denzo–Scalepack[18b,18c] (for 4) program packages were
used for cell refinements and data reductions. The structures were
solved by direct methods using the SHELXS-97[18d] program. A
semiempirical (for 3, 4) or numerical (for 2) absorption correction
(SADABS)[18e] was applied to the data. The unit cell of 2 contained
four water molecules of crystallization. Two of these molecules
were disordered and partially lost. The final structure model was
refined without the disordered water molecules. The contribution
of these molecules to the calculated structure factors was taken into
account using the SQUEEZE routine of PLATON.[18f] Because of
the missing water molecules, the intermolecular H-bonding net-
work in 2 is not realistic. The NH, NH2, NH3, and H2O hydrogen
atoms were located from the difference Fourier map but con-
strained to ride on their parent atom, with Uiso = 1.5 and Ueq
(parent atom). Other hydrogen atoms were positioned geometri-
cally and were also constrained to ride on their parent atoms, with
C–H bond length in the range 0.95–0.99 Å, and Uiso = 1.2–1.5Ueq
(parent atom). Crystallographic data and selected geometric pa-
rameters are listed in Tables S1–S3 (see Supporting Information).
8.37; found C 39.35, H 3.27, N 8.30. IR (KBr): ν = 3400 [ν(OH)],
˜
3094 [ν(NH)], 1677 [ν(C=O)], 1624 [ν(C=O···H)], 1588 [ν(C=N)],
732 [δ(CH, Ar)] cm–1. 1H NMR ([D6]DMSO): δ = 2.44 (s, 3 H,
CH3), 2.50 (s, 3 H, CH3 signals overlapped with the solvent peak),
7.23–7.92 (2 H, Ar–H), 11.23 (s, 1 H, OH), 14.33 (s, 1 H, NH)
ppm. 13C{1H} ([D6]DMSO): δ = 26.66 (CH3), 31.33 (CH3), 115.00
(Ar–H), 122.05 (Ar–H), 123.45 (Ar–Cl), 131.00 (Ar–NH–N),
132.57 (C=N), 134.32 (Ar–SO3 H), 141.24 (Ar–OH), 196.45 (C=O),
197.22 (C=O) ppm.
(H2en)(HL) (2): Compound 1 (335 mg, 0.001 mol) was dissolved in
ethanol (50 mL) and ethylenediamine (60 mg, 0.001 mol) was
added. The mixture was stirred for 8 h at 70 °C giving a red precipi-
tate of 2, which was collected by filtration and recrystallized from
ethanol to obtain crystals suitable for X-ray analysis. 2 is soluble
in water, methanol, ethanol, and DMSO. C13H19ClN4O6S (394.83):
calcd. C 39.55, H 4.85, N 14.19; found C 39.24, H 4.53, N 14.11.
CCDC-809721 (for 2), -809722 (for 3), and 809723 (for 4) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
IR (KBr): ν = 3926 [ν(NH)], 1652 [ν(C=O)], 1617 [ν(C=O···H)],
˜
1
1560 [ν(C=N)], 739 [δ(CH, Ar)] cm–1. H NMR ([D6]DMSO): δ =
2.42 (s, 3 H, CH3), 2.50 (s, 3 H, CH3), 2.95 (s, 4 H, CH2), 7.23–
7.42 (2 H, Ar–H), 15.20 (s, 1 H, NH). 13C{1H} ([D6]DMSO): δ =
28.61 (CH3), 30.71 (CH3), 48.39 (CH2), 49.24 (CH2), 114.54 (Ar–
H), 116.42 (Ar–H), 123.64 (Ar–Cl), 132.18 (Ar–NH–N), 132.94
Potentiometric Measurements: The apparatus, general conditions,
and methods of calculation are the same as those given in our pre-
vious work.[5c,8d] A mixture of 4 (23.7 mg,0.0500 mmol) and KCl
(372.7 mg, 5.00 mmol) in water (50 mL) was titrated potentio-
metrically against standard water solutions of 0.01 m HCl or 0.01 m
NaOH at 298 K.
–
(C=N), 134.12 (Ar–SO3 ), 151.10 (Ar-O-), 172.38 (C=O), 196.16
(C=O) ppm.
[Co(HL)(en)(H2O)]·4H2O (3). Method A: Compound 2 (790 mg,
0.002 mol) was dissolved in methanol (50 mL), Co(NO3)2·6H2O
(582 mg, 0.002 mol) was added, and the mixture was stirred for
5 min and left to stand.
Aerobic Oxidation of Alcohols in Aqueous Media: The reactions
were carried out in 50 mL round-bottom flasks equipped with con-
densers under air at atmospheric pressure. Typically, to an aqueous
solution of K2CO3 (5 mL, 0.1 m) were added alcohol (1.5 mmol),
catalyst (0.015 mmol, 1 mol-% vs. substrate), and TEMPO
(0.075 mmol, 5 mol-% vs. substrate). The reaction solutions were
vigorously stirred using magnetic stirrers, and an oil bath was used
to achieve the desired reaction temperature. After the oxidation
reaction, reaction mixtures were neutralized by 1 m HCl, and then
extracted into EtOAc (5 mL). The organic phase was used for chro-
matographic analyses using acetophenone as an internal standard.
Method B: En (120 mg,0.002 mol) was added to a methanol solu-
tion (50 mL) of 1 (670 mg, 0.002 mol) and the mixture was heated
to reflux for 10 min. Co(NO3)2·6H2O (582 mg) was added. In both
cases, brown crystals of 3 separated from the reaction mixture after
4 d at room temperature, which were collected by filtration and
dried in air; yield 41% (based on Co). C13H26ClCoN4O11S
(540.82): calcd. C 28.87, H 4.85, N 10.36; found C 28.75, H 4.94,
N 10.45. IR (KBr): ν = 3508 [ν(OH)], 3437 [ν(NH)], 3211 [ν(NH)],
˜
3102 [ν(NH)], 1652 [ν(C=O)], 1583 [ν(C=N)], 775 [δ(CH, Ar)] cm–1.
Supporting Information (see footnote on the first page of this arti-
cle): Synthesis and tautomeric equilibria, crystallographic data,
atomic coordinates, bond lengths, bond angles, hydrogen bonds,
the determination of the isoelectric point of 4, and the quantitative
determination of CuII with 1 and 2. X-ray crystallographic data for
2–4 in CIF format.
[Cu(L)(Hen)(H2O)] (4). Method A: Compound
2 (790 mg,
0.002 mol) was dissolved in methanol (50 mL), Cu(NO3)2·2.5H2O
(466 mg, 0.002 mol) was added, and the mixture was stirred for
5 min and left to stand.
Method B: En (120 mg, 0.002 mol) was added to a solution of 1
(670 mg, 0.002 mol) in methanol (50 mL). The mixture was heated
to reflux for 10 min before Cu(NO3)2·2.5H2O (466 mg, 0.002 mol)
was added with stirring. The mixture was left to stand. In both
cases the formation of a dark brown powder was observed after
4 d at room temperature. The powder was collected by filtration,
dried in air, and recrystallized from an acetone/dimethylformamide
Acknowledgments
This work has been partially supported by the Portuguese Founda-
tion for Science and Technology (FCT) and its PEst-OE/QUI/
4180
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 4175–4181

Co(II) and Cu(II) Complexes in 3D Supramolecular Networks
[12]
UI0100/2011 and “Science 2007” program. M. N. K., K. T. M.,
P. J. F., and A. M. express gratitude to the FCT for their postdoc
and doctoral fellowships. The authors gratefully acknowledge the
Portuguese NMR Network (IST-UTL Center) for providing access
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Received: March 31, 2011
Published Online: August 10, 2011
Eur. J. Inorg. Chem. 2011, 4175–4181
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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