Template syntheses of copper(II) complexes from arylhydrazones of malononitrile and their catalytic activity towards alcohol oxidations and the nitroaldol reaction: Hydrogen bond-assisted ligand liberation and E/Z isomerisation

Article abstract of DOI:10.1002/chem.201203254

A one-pot template condensation of 2-(2-(dicyanomethylene)hydrazinyl) benzenesulfonic acid (H₂L¹, 1) or 2-(2-(dicyanomethylene) hydrazinyl)benzoic acid (H₂L², 2) with methanol (a), ethylenediamine (b), ethanol (c) or water (d) on copper(II), led to a variety of metal complexes, that is, mononuclear [Cu(H₂O)₂(κ O¹,κN² L^1a] (3) and [Cu(H ₂O)(κO¹,κN³ L^1b)] (4), tetranuclear [Cu₄(1 κO¹,κN²:2 κO¹ L^2a)₃-(1 κO¹, κN²:2 κO² L^2a)] (5), [Cu ₂(H₂O)(1 κO¹, κN²:2 κO¹ L^2c)-(1 κO¹,1 κN ²:2 κO¹,2 κN¹- L ^2c)]₂ (6) and [Cu₂(H₂O) ₂(κO¹,κN²- L^1dd)-(1 κO¹,κN²:2 κO¹ L ^1dd)(μ-H₂O)]₂× 2 H₂O (7×2 H₂O), as well as polymer- ic [Cu(H₂O) (κO¹,1 κN²:2 κN¹ L ^1c)]_n (8) and [Cu(NH₂C₂H ₅)(κO¹,1 κN²:2 κN ¹L^2a)]_n (9). The ligands 2-SO ₃H-C₆H₄-(NH)N=C{(CN)[C(NH₂)-(= NCH₂CH₂NH₂)]} (H₂L^1b, 10), 2-CO₂H-C₆H₄-(NH)N={C(CN)[C(OCH ₃)-(=NH)]} (H₂L^2a, 11) and 2-SO ₃H-C₆H₄-(NH)N=C{C(=O)-(NH₂)} ₂ (H₂L^1dd, 12) were easily liberated upon respective treatment of 4, 5 and 7 with HCl, whereas the formation of cyclic zwitterionic amidine 2-(SO₃^-)-C₆H ₄-N=NC(-C=(NH⁺)CH₂CH₂NH)(=CNHCH ₂CH₂NH) (13) was observed when 1 was treated with ethylenediamine. The hydrogen bond-induced E/Z isomerization of the (HL ^1d)^- ligand occurs upon conversion of [{Na(H ₂O)₂(μ-H₂O)₂}(HL ^1d)]_n (14) to [Cu(H₂O)₆][HL ^1d]₂×2 H₂O (15) and [{CuNa(H ₂O)-(κN¹,1 κO²:2 κO ¹ L^1d)₂}K_0.5(μ-O) ₂]n×H₂O (16). The synthesized complexes 3-9 are catalyst precursors for both the selective oxidation of primary and secondary alcohols (to the corresponding carbonyl compounds) and the following diastereoselective nitroaldol (Henry) reaction, with typical yields of 80-99%. Copyright

Full text of DOI:10.1002/chem.201203254

DOI: 10.1002/chem.201203254
Template Syntheses of Copper(II) Complexes from Arylhydrazones of
Malononitrile and their Catalytic Activity towards Alcohol Oxidations and
the Nitroaldol Reaction: Hydrogen Bond-Assisted Ligand Liberation and
E/Z Isomerisation
Maximilian N. Kopylovich,*[a] Archana Mizar,[a] M. Fꢀtima C. Guedes da Silva,*[a, b]
Tatiana C. O. Mac Leod,[a] Kamran T. Mahmudov,[a, c] and Armando J. L. Pombeiro*[a]
Abstract: A one-pot template conden-
sation of 2-(2-(dicyanomethylene)hy-
drazinyl)benzenesulfonic acid (H2L1, 1)
or 2-(2-(dicyanomethylene)hydrazinyl)-
benzoic acid (H2L2, 2) with methanol
(a), ethylenediamine (b), ethanol (c) or
water (d) on copper(II), led to a varie-
ty of metal complexes, that is, mononu-
and
L2a)]n (9). The ligands 2-SO3H-C6H4-
(NH)N=C{(CN)[C(NH2)-(=NCH2CH2-
NH2)]} (H2L1b, 10), 2-CO2H-C6H4-
(NH)N={C(CN)[C(OCH3)-(=NH)]}
(H2L2a, 11) and 2-SO3H-C6H4-(NH)N=
C{C(=O)-(NH2)}2 (H2L1dd
12) were
[Cu
G
treated with ethylenediamine. The hy-
drogen bond-induced E/Z isomeriza-
tion of the (HL1d)ꢁ ligand occurs upon
AHCTUNGTRENNUNG
A
conversion of [{Na
(HL1d)]n
(14) to
[HL1d]2·2H2O (15) and [{CuNa
(kN1,1kO2:2kO1 L1d)2}K
0.5A(m-O)2]n·H2O
A
(m-H2O)2}-
(H2O)6]-
(H2O)-
N
ACHTUNGTRENNUNG
U
ACHTUNGTRENNUNG
CHTUNGTRENNUNG
easily liberated upon respective treat-
ment of 4, 5 and 7 with HCl, whereas
(16). The synthesized complexes 3–9
are catalyst precursors for both the se-
lective oxidation of primary and secon-
dary alcohols (to the corresponding
carbonyl compounds) and the following
diastereoselective nitroaldol (Henry)
reaction, with typical yields of 80–
99%.
clear [Cu
[Cu
(H2O)(kO1,kN3 L1b)] (4), tetranu-
clear [Cu4(1kO1,kN2:2kO1 L2a)3-(1kO1,
2A
kN2:2kO2 L2a)] (5), [Cu (H2O)(1kO1,
kN2:2kO1 L2c)-(1kO1,1kN2:2kO1,2kN1-
2A
L2c)]2 (6) and [Cu (H2O)2(kO1,kN2-
L1dd)-(1kO1,kN2:2kO1 L1dd
(m-H2O)]2·
2H2O (7·2H2O), as well as polymer-
ic [Cu
(H2O)(kO1,1kN2:2kN1 L1c)]n (8)
N
E
the formation of cyclic zwitterionic
ꢁ
ꢁ
ꢁ
ꢁ
amidine 2-(SO3 ) C6H4 N=NC
N
U
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
CTHUNGTRENNUNG
)ACHTUNGTRENNUNG
Keywords: alcohols · copper · isom-
AHCTUNGTRENGNeUN rization · Lewis acids · oxidation
ACHTUNGTRENNUNG
ꢁ
ꢁ
Introduction
offer attractive routes for the creation of new C C, C N,
[1]
ꢁ
ꢁ
C O, and C S bonds. In organic chemistry, generally the
nitrile group is mildly reactive, but coordination to a transi-
tion metal can significantly enhance the reactivity.[2] For ex-
ample, in Nature the nitrile hydrase and amidase enzymes
contain either a cobalt or iron co-factor, thus effectively cat-
alyzing the conversion of nitriles into amides.[3] A number of
metal-based catalysts assisting the hydrolysis of nitriles have
been reported,[4] and copper is also known to provide effec-
tive activation centers to cyano groups.[5]
The nitrile group has a widely recognized chemical versatili-
ty, and the numerous known additions to the C N moiety
ꢀ
[a] Dr. M. N. Kopylovich, Dr. A. Mizar, Dr. M. F. C. Guedes da Silva,
Dr. T. C. O. Mac Leod, Dr. K. T. Mahmudov, Prof. A. J. L. Pombeiro
Centro de Quꢀmica Estrutural, Complexo I
Instituto Superior Tꢁcnico
Technical University of Lisbon, Av. Rovisco Pais
1049–001 Lisbon (Portugal)
Additions to metal-coordinated nitriles mostly involve
protic nucleophiles such as amines, alcohols and water,[2]
and template syntheses can lead to a variety of new lig-
E-mail: kopylovich@yahoo.com
fatima.guedes@ist.utl.pt
pombeiro@ist.utl.pt
AHCTUNGTRENNUNG
ands.[5b–f] However, liberation of the formed new organics is
[b] Dr. M. F. C. Guedes da Silva
Universidade Lusꢂfona de Humanidades e Tecnologias
ULHT Lisbon, Campo Grande 376, 1749-024 Lisbon (Portugal)
usually not trivial and involves complicated treatment and/
or expensive reagents.[6] Stabilization of the formed lig
ACHTUNGTRENNUNG
[c] Dr. K. T. Mahmudov
in the free state constitutes another important task because
many of them easily hydrolyze or decompose.[7] Introduction
of a supporting group that forms a strong resonance-assisted
Baku State University, Department of Chemistry
Z. Xalilov Str. 23, Az 1148 Baku (Azerbaijan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203254. It includes Tables
listing crystallographic data, atomic coordinates, bond lengths and
bond angles, anisotropic displacement parameters, hydrogen coordi-
nates and isotropic displacement parameters, torsion angles and hy-
drogen bonds; X-ray crystallographic data for 3–9 and 13–16 in CIF
format, and packing diagrams of 3–9 and 13–16.
ꢁ
ꢁ
hydrogen bond (RAHB, X···H Y$Y···H X [X, Y=N, O, S,
etc.])[8] with the newly created (e.g., upon nucleophilic
attack) moiety could facilitate the product liberation and/or
its stabilization. RAHB systems have been applied for the
selective activation of a dinitrile or a carbon atom in the
588
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Chem. Eur. J. 2013, 19, 588 – 600

FULL PAPER
a position to a carbonyl, for enolization in keto–enol tauto-
merism, controlled crystal packing or formation of bistable
H bonds in functional molecular materials.[8,9] Nevertheless,
to our knowledge, the possibility to use RAHB for facile
ligand liberation has not yet been reported.
Scheme 2. a) Oxidation of alcohol, and b) nitroaldol reaction.
Chemically activated rotary switches and motors have
only recently been under investigation.[10,11] In particular,
E/Z isomerization around the C=N double bond in hydra-
zones[12] can proceed through rotation and inversion, making
them good candidates for the synthesis of molecular ma-
chines. The reported E/Z isomerization in hydrazones is
regulated by pH, coordination-coupled proton transfer or
solvation, but, to our knowledge, no application of the
RAHB system to control this process has been reported.
The preparation of unsymmetrical products from dini-
triles, for example, derivatives of malononitrile, is an impor-
tant task in synthetic chemistry.[13] RAHB can assist such a
synthesis,[9] whereas transition metals, in particular MnII,[14]
were also found to be quite effective in this respect. As a
result, template additions of ethylenediamine, azide, or
water to arylhydrazones of malononitrile (AHM, Scheme 1)
one-pot template synthesis of new CuII complexes derived
from AHM; 2) to liberate and characterize the new arylhy-
drazone ligands; 3) to study the E/Z isomerization of such li-
gands; 4) to apply, for the first time, RAHB for promoting
such a type of reaction; 5) to explore the catalytic activity of
the CuII complexes in consecutive alcohol oxidation and ni-
troaldol reaction.
Results and Discussion
As mentioned above, AHM are good potential candidates
for the convenient one-pot synthesis of complexes of differ-
ent nuclearity bearing different types of ligands derived
upon nucleophilic attack.[14] However, to facilitate the com-
plex formation, new ligand liberation and stabilization, a
supporting group (e.g., sulfonyl or carboxyl) can be intro-
duced in the proximity of a cyano group that undergoes nu-
cleophilic attack (Scheme 1). The coordinating ability of the
ꢁ
ꢁ
COOH or SO3H group facilitates the formation of the
complexes, with different structures and topologies depend-
ing on the used nucleophile (Scheme 3, route A).[21] Further-
more, the moiety formed upon nucleophilic attack can par-
ticipate in an intramolecular RAHB system, thus facilitating
the product liberation and stabilization (Scheme 3, route B).
Another very interesting aspect of the present study con-
cerns the E/Z isomerism of the synthesized hydrazone lig-
Scheme 1. Arylhydrazones of malononitrile (AHM) 1 and 2 considered
in this work.
were performed easily, producing a variety of new interest-
ing ligands with cyano, amidine, tetrazole, or pyrimidine
moieties combined in one molecule.[14] In most of these
cases, the products of the nucleophilic attack on only one
CN moiety are stabilized upon coordination, whereas the
other cyano group is left unreacted. Several attractive com-
plexes of different nuclearity were thus synthesized,[14] but
without liberation of the newly formed ligands.
AHCTUNGTREGaNNUN nds (Scheme 3, routes C, D, and E). These results are de-
tailed below.
To our knowledge, CuII complexes with ligands formed
upon template nucleophilic additions to AHM are not
known, in spite of their expected interesting features. In
fact, copper complexes with labile hydroxoACTHNUGRTENUNG(aqua) sites and a
NON coordination environment can biomimic some en-
zymes[15] and serve as catalyst for various reactions,[16] in-
cluding oxidation of primary and secondary alcohols to car-
bonyl compounds (the corresponding aldehydes and ke-
tones).[17] This is one of the most useful organic reactions
due to the synthetic versatility of the carbonyl group and,
ꢁ
for example, it can be used for C C bond formation by the
nitroaldol (Henry) reaction.[18–20] To find an effective sole
catalyst for both transformations (the carbonyl group forma-
Scheme 3. Template synthesis of new ligands, their RAHB-assisted libera-
ꢁ
tion and E/Z isomerization.
tion and the Henry C C coupling, Scheme 2) is a challenge
worth pursuing.
Thus, bearing in mind the above considerations, we fo-
cused this work on the following aims: 1) to perform simple
Syntheses of complexes: Due to the presence of the ortho-
ꢁ
COOH or SO3H group, the starting materials 1 and 2 have
Chem. Eur. J. 2013, 19, 588 – 600
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589

M. N. Kopylovich, M. F. C. Guedes da Silva, A. J. L. Pombeiro et al.
volved a combination of CuII acetate, 1 or 2 AHM and a
protic nucleophile such as an amine, water or an alcohol,
with conversion of a cyano to an amino/imino group
(Scheme 4). In most cases the second cyano group remains
unreacted due to stabilization of the product of one nucleo-
philic attack upon coordination to CuII. Mononuclear 3 and
4, tetranuclear 5–7, and polymeric 8 and 9 compounds are
formed (Scheme 4); the nuclearity and type of structure of
the formed complexes depend on AHM, the nucleophile
and conditions (solvents, temperature, and time) used for
the synthesis. The detailed description of the structures is
given below.
ꢁ
a resilient intramolecular N H···O RAHB linking one of
the oxygen atoms of the carboxyl or sulfonyl groups to the
hydrazone NH moiety (Scheme 1), thus hampering their co-
ordination. However, upon dissolution in a polar solvent
with proton-acceptor ability, such as methanol or water, the
RAHB can be weakened and a metal ion can enter into the
chelating OXCCN pocket (Scheme 3, route A). Neverthe-
less, in some cases, upon concentration of the solution, the
RAHB system regains its structure, driving out the metal
ion, and thus the mixture of the starting ligand and the
metal salt is restored in the solid phase.[20,21] In fact, a slow
evaporation of the mixture of CuACTHNUTRGNE(UNG NO3)2·2.5H2O with meth-
anolic or ethanolic solutions of 1 or 2 recovers the starting
materials.
To shift the overall process to the complex formation, one
should deprotonate the ligands; acetate is a weak base that
can serve for the purpose. Thus, the successful syntheses in-
Ligand liberation: Upon protonation, the formed ligands
can form stable intramolecular RAHB systems.[8] This can
be used for easy ligand liberation by acidification of the con-
centrated solution of the complexes with subsequent precipi-
Scheme 4. Template transformations of 1 and 2 on CuII matrix with formation of complexes 3–9.
590
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Chem. Eur. J. 2013, 19, 588 – 600

Template Syntheses of Copper(II) Complexes
FULL PAPER
tation of the formed organic salt. The approach was exem-
plified for the liberation of ligands 10–12 from the com-
plexes 4, 5, and 3, respectively (Scheme 5). Firstly, hydro-
extend the known examples of E$Z molecular switches to
the hydrazone ligands synthesized herein. Therefore, a com-
pound in the E configuration was prepared by joint dissolu-
tion of the sodium salt (14) of 1 and copper tetrafluorobo-
rate CuACTHNUGTREN(UNG BF4)2·xH2O in acetone/water (1:2, v/v) mixture. In
this case, one of the cyano groups is hydrolyzed to a carbox-
amide moiety and the salt 15 with hydrated copper(II)
cation is formed (Scheme 6, route 14!15). Both salts 14
Scheme 5. Ligand liberation and further organic transformations.
chloric acid (33% w/w) was added to the concentrated solu-
tions of 3–5 in methanol and then the reaction mixtures
were diluted with acetone, thus leading to the precipitation
of the organic salts 10–12, which were then filtered off,
washed several times with acetone and recrystallized, giving
the isolated products in 61–75% yields.
Scheme 6. Formation of E or Z isomers.
The organic products were fully characterized by conven-
tional methods, including X-ray single-crystal analysis (for
13, see below). The IR spectra of the compounds 10–12
and 15 possess one RAHB system; the positive charges of
Na+ and Cu2+ ions are neutralized by the deprotonated sul-
fonyl group. The anion of 15 is in the E configuration in re-
lation to the hydrazo C=N double bond, the hydrazone hy-
drogen with its +d charge tends to form a hydrogen bond
with the negatively charged oxygen atom of the sulfonic
group rather than with the formally neutral oxygen atom of
the amido moiety.
To form a Z isomer from 14, one should firstly destroy
the RAHB system by deprotonation and then introduce a
Lewis acid (e.g., a Cu2+ ion), which can accept the free elec-
tron pairs of the oxygen atoms from the sulfonyl and car-
ꢁ1
ꢀ
show n
N
spectively. The unreacted nitrile group is also confirmed by
13C NMR signals at d=109.1, 110.7, and 110.3 ppm for 10–
12, respectively. In accord with the elemental analysis, the
solid state compounds 10–12 exist as hydrochloride salts.
Similarly to the known interaction of ethylenediamine
(en) with malononitrile,[9,13] the reaction of en and AHM re-
sults in the formation of diimidazoline (route 1!13,
Scheme 5). In the case of 13, IR and NMR data confirm the
1
disappearance of both nitrile groups. The H and 13C NMR
spectra of 13 demonstrate that the imidazoline rings are not
ꢁ
ꢁ
similar, with N H···N and N H···O protons being observed
at d=10.57 and 11.74 ppm, in accord with the NHN and
NHO RAHB systems in the compound. In the 13C NMR
spectrum of 13, one C=C resonance is displayed at d=
boxyl CACTHGNUTERNU(NG NH2)=O groups, thus stabilizing the Z configura-
tion. Hence, a reaction of 14 with copper acetate and KOH
in acetone/water enables the polymeric complex 16 to be
isolated, in which the L1d ligand is in the Z configuration
(Scheme 6, route 14!16).
ꢁ
85.3 ppm, whereas the C N and C=N resonances occur at
d=155.4 and 159.5 ppm, respectively. In contrast to the
known pure organic reaction 1!13, the metal-mediated
transformation (route 4!10) enables the preparation of the
acyclic amidinium salt 10, which is unreachable with the or-
ganic synthesis. It should also be noted that the compound
10 can further be easily converted to the diimidazoline 13
by reacting with en (route 10!13).
Compounds 14–16 were characterized by elemental analy-
sis, IR spectroscopy and single-crystal X-ray diffraction. Ele-
mental analysis supports the formulation of 14–16, whereas
ꢀ
the IR spectrum of 14 reveals the presence of both C N vi-
brations at approximately 2219 and 2228 cmꢁ1, and the IR
spectra of 15 and 16 show only one nitrile at approximately
2211 and 2217 cmꢁ1, respectively. The n
ACHTUNGTRENNUNG
1679 cmꢁ1] and n
ACHTUNGTRENNUNG
E/Z Isomerization: The controllable E$Z transition around
a double bond in, for example, hydrazone compounds con-
stitutes a topic of current interest.[10–12] Thus, we decided to
dicate that, in the solid state, 15 and 16 are stabilized in the
carboxamide form, as also supported by X-ray data (see
below).
Chem. Eur. J. 2013, 19, 588 – 600
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591

M. N. Kopylovich, M. F. C. Guedes da Silva, A. J. L. Pombeiro et al.
In summary, herein we have achieved a RAHB-supported
isomerization of hydrazones (Scheme 7), which has several
distinctive differences in comparison with the previously re-
ported[10–12] pH, coordination-coupled proton transfer, or sol-
atom and an additional N- or O atom from the organic Ln
ligand is involved in the chelation, leading to two fused six-
membered rings. An extra five-membered metallacycle is
found in 4, and a four-membered one is recognized in 6 and
in 7 due to central Cu2O2 cores.
The sulfonyl-containing complexes 3 and 4 (Figure 1) are
mononuclear, complex 7 is tetranuclear and 8, as well as the
heterometallic 16, are polymeric. As a result of imposed ge-
Scheme 7. Control of the E or Z isomers through coordination-coupled
proton transfer or RAHB system.
vation-induced rotary switches. Thus, the protonation or de-
protonation–complexation of the E configuration by acid
and alkali with addition of the copper salt leads to the Z
form, being accompanied by a configurational change origi-
nating from the rotation around the C=N double bond. Due
to formation of two six-membered RAHB or coordination-
assisted cycles, the Z configuration happens to be the ther-
modynamically more stable one. The configuration and con-
formation of the system can be modulated by the sequence
at which the acid and base are added, leading to a switch to
rotate around the C=N double bond. This type of molecular
switch can have promising applications[10–12] and expands the
molecular tool-box potentially available for the construction
of advanced molecular devices.
Figure 1. X-ray molecular structures of complexes 3 (top) and 4 (bottom)
with atom numbering schemes. Ellipsoids are drawn at 50% probability.
Hydrogen bonds (Table S3, the Supporting Information) are shown
as dashed lines. Symmetry elements to generate equivalent atoms:
i) y,ꢁx+y,1ꢁz; ii) y,ꢁx+y,1ꢁz; iii) xꢁy,x,1ꢁz; iv) xꢁy,x,2ꢁz; v) 2/3ꢁx,1/
3ꢁy,1.3(3)ꢁz.
X-ray diffraction analyses: X-ray quality crystals of the com-
pounds were obtained upon slow evaporation of their meth-
anolic (3, 5, 9, 13), ethanolic (6, 8) or aqueous (4, 7, 14–16)
solutions, at room temperature. The crystallographic data
and processing parameters are summarized in the Support-
ing Information (Table S1) and a comparison of selected di-
mensions is presented in Table S2 (the Supporting Informa-
tion); these data will be considered in the discussion below.
Representative plots are displayed in the following Figures
and in Figures S1–S6 (the Supporting Information). Hydro-
gen-bond interactions are presented in Tables S3 and S4
(the Supporting Information).
ometry constrictions from the sulfonyl groups, the Ln ligands
present considerable distortions that may be assessed
(Table S2, the Supporting Information) not only by the Cu-
O-S-C torsion angles, in the 57.27–64.148 range, but also by
the twisting of the phenyl rings relative to the NNCC-con-
taining planes, which adopt values from 18.85 (in 16) to
55.798 (in 8).
The carboxylate-containing compounds 5 and 6 (Figure 2)
are tetranuclear and 9 is a polymer. In contrast with the
aforementioned compounds, the organic chelating groups
are considerably flat with the Cu-O-C-C torsion angles rang-
ing from 1.29 to 36.558; the twisting of the phenyl rings rela-
tive to the NNCC-containing planes assumes values as low
as 1.308 (in 5) exceptionally adopting 31.638 (in 9).
Description of the copper complexes 3–9 and 16: In 3–6, 8,
9, and 16 the Cu atoms are in square-pyramidal coordina-
[22]
tion environments, with t5 values in the 0.02–0.31 range
(Table S2, the Supporting Information). Yet, one of the
copper centers in 5 (Cu2) is in an almost perfect square-
planar location (t4 =0.07),[23] and in 7 the coordination
sphere of the metal atoms is octahedral. In every compound,
one N-hydrazone atom, a sulfonyl (or carboxyl) oxygen
In all the compounds the bond distances of 1.289(10)–
ꢁ
1.318(5) ꢄ for the N N hydrazone groups suggest their
ꢁ
double bond character. The Cu Nhydrazo bond distances
(average 1.961(5) ꢄ) are, in general, longer than the other
existing copper–nitrogen bonds (1.922(4) ꢄ), the exceptions
592
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Chem. Eur. J. 2013, 19, 588 – 600

Template Syntheses of Copper(II) Complexes
FULL PAPER
nated (to Cu1 and Cu3, respectively) O-carboxylate atoms.
The intramolecular interactions in 5 are weaker than those
found in 6, in which the NH groups also act as donors to the
non-coordinated O-carboxylate acceptor atoms; in this com-
pound the water molecules bound to copper establish
H bonds to the N-cyanide atoms of two vicinal molecules
and extend the structure to the second dimension. Com-
pound 7 (Figure 3), which presents four crystallization water
Figure 3. X-ray molecular structure of 7 with atom numbering schemes.
Ellipsoids are drawn at 50% probability. Symmetry elements to generate
equivalent atoms: i) 1ꢁx,ꢁy,1ꢁz.
molecules per unit cell, discloses the most intricate network
based on noncovalent interactions, as expressed by the
higher number of H bonds detected (Table S3, the Support-
ing Information). The water molecules are intercalated into
the layers of the metal complexes and are active as donors
to the O-sulfonate atom; O10 water molecules are also
donors to the bridging hydroxide groups and act as accept-
ors of amine N14 hydrogen atoms. Compound 7 bears the
strongest H bonds (intramolecular N13-H13B···N12, d-
Figure 2. X-ray molecular structures of complexes 5 (top) and 6 (bottom)
with atom numbering schemes. Ellipsoids are drawn at 50% probability.
Hydrogen bonds (Table S3, the Supporting Information) are shown as
dashed lines. Symmetry elements to generate equivalent atoms:
i) ꢁx,ꢁy,1ꢁz; ii) 1ꢁx,ꢁy,2ꢁz.
ꢁ
being the apical Cu Ncyano distances in 6 and in 8 ((2.911(5)
and 2.290(5) ꢄ, respectively).
U
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
ꢁ
The Cu O bond dimensions also differ, depending wheth-
Compounds 8 and 9 (Figure 4) are coordination polymers
derived from the linkage of the second N-cyano groups of
Ln to copper cations. Apart from the fact that 8 contains sul-
fonate groups and 9 carboxylate ones, the other clear differ-
er the oxygen atoms belong to the organic Ln groups or to
aqua or hydroxide bridging ligands. On the whole, the latter
ꢁ
is considerably longer, excluding 3 in which the basal Cu
Oaqua and the Cu Ometallacycle distances are almost equal
(1.991(3) and 2.000(3) ꢄ, respectively).
ꢁ
ꢁ
entiation between these polymers comes from the Cu
ꢁ
Ncyano C bond angles which are considerably higher in 8
The
shortest
intramolecular
Cu···Cu
distance
(153.5(3)8) as compared with 9 (123.1(2)8), leading to the
formation of chains with a zigzag shape in the former and a
wave-like type in the latter (Figure 4, Figure S5, the Sup-
porting Information). The chains are interconnected by
means of strong H-bond interactions involving the coordi-
nated water (in 8) or ethyl amine (in 9) molecules.
(3.1526(9) ꢄ) is found in the dimeric 6, whereas the longest
(7.836(1) ꢄ) occurs in 8. Concerning the intermolecular
metal–metal interaction, it ranges from 5.4153(9) [in 9] to
7.598(2) ꢄ [in 16].
As shown in the Figures, noncovalent interactions are
present, more or less extensively, in every compound. In 3
and 4 the coordinated water molecules act as strong H-
The molecular structure of 16 (Figure 5) features a differ-
ent type of polymer (Figure S7, the Supporting Information)
owing to the presence, in the asymmetric unit, of copper,
two alkali metals (Na and K) and two L1d ligands bridging
in the m-OS(O)O mode that simultaneously coordinate to
donors (d
ACHTUNGTRENNUNG
ꢁ
aACHTUNGTRENNUNG
oxygen atoms and to the non-coordinated N-cyanide of vici-
nal molecules, giving rise to interesting 2D motifs (Fig-
ure S1, the Supporting Information). In 5, the most intense
interactions are intramolecular and concern the coordinated
(to Cu2 and Cu4) NH groups that act as donors to coordi-
Cu and Na (or K). This results in {CuNaACTHNUTRGNEUNG
(m-L1d)2}2 nodes that
are doubly bound with {KO4} linkers showing the way to an
infinite 1D double chain. This double chain comprises cavi-
ties formed by repeating 20-membered -(KOSOCuOSO-
Chem. Eur. J. 2013, 19, 588 – 600
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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593

M. N. Kopylovich, M. F. C. Guedes da Silva, A. J. L. Pombeiro et al.
3.5383(3) and 3.834(3) ꢄ are the shortest centroid···centroid
contacts found for, respectively, the intramolecular contacts
involving the C11>C16/C31>C36 phenyls and the Cu1-hy-
drazometallacycle/C31>C36 phenyl ring; 3.471(3) ꢄ is the
shortest intermolecular interaction for the Cu2-hydrazome-
tallacycle/C41>C46 phenyl ring, interestingly the former
being longer than the latter. Also in 6, intermolecular inter-
actions of the same kind were detected and within the same
range, for example, 3.396(3) ꢄ for the Cu1-hydrazometalla-
cycle/C21>C26 phenyl and 3.527(3) ꢄ for the Cu2-hydrazo-
metallacycle/C11>C16 phenyl contacts. In 7, this parameter
is elongated (3.965(6) ꢄ) and concerns the phenyl rings
C11>C16 and C21>C26. In 8, 9 and 16, no such interac-
tions can be detected due to the peculiarities of the struc-
tures.
Description of structures 13–15: The asymmetric unit of 13
(Figure 6) comprises the zwiterionic amidine compound that
ꢁ
crystallized with one molecule of water. Predictably, the N
N bond distance of 1.2740(18) ꢄ in 13 is considerably short-
er than that found in the aforementioned copper complexes
(Table S2, the Supporting Information) or in compounds 14
and 15 (1.302(3) and 1.316(3) ꢄ, respectively), what may be
related to the fact that this group is neither protonated nor
metal coordinated. The crystal structures of 14 and 15 con-
sist of organic anionic moieties with, respectively, independ-
ent Na or Cu cationic centers with distorted octahedral ge-
ACHUTNGERNoNUG mCAHUTNGTRENNeGUN tries filled with water ligands. In 14 the cationic part is
associated by means of m-O10 and m-O20 (Figure 6) leading
to a 1D infinite chain running along the crystallographic
b axis that spreads to the second dimension by means of ex-
tensive H-bond interactions (Figure S6 and Table S4, the
Supporting Information). An interesting feature of 15 con-
sists in the extensive hydrogen bonding (Figure S6) that
arises from the coordinated water molecules; each of the
equatorial ones repeatedly acts as a double H-bond donor
to one vicinal organic group, whereas each of the apical
ones contacts with a non-coordinated water molecule and
another organic moiety. This results in the extensive inter-
linkage of every hexaaqua-CuII unit with six L1d groups and
two water molecules, thus leading to a 3D supramolecular
framework solely based on noncovalent contacts (Fig-
ure S6).
Catalytic activity studies: Alcohol oxidations: The synthe-
sized mono- (3), tetra- (6), and polymeric (8) complexes
were used as catalyst precursors for the oxidation of primary
and secondary alcohols to the corresponding carbonyl prod-
ucts with two different oxidants: TBHP (tert-butyl hydroper-
oxide) and air/TEMPO (TEMPO=2,2,6,6-tetramethylpiper-
idine-1-oxyl). The systems operate effectively for 1) the
aerobic TEMPO-mediated oxidation of benzyl alcohol to
benzaldehyde and 2) the peroxidative oxidation (by aqueous
TBHP) of benzyl alcohol to benzaldehyde (main product)
and benzoic acid (Scheme 2a, for the case of oxidation to al-
dehyde). In fact, both systems lead to overall yields up to
82% (based on alcohol) and similar yields are obtained
using copper complexes with different nuclearities (Table 1,
Figure 4. The asymmetric units of 8 [top: i) 1/2+x,2.5ꢁy,ꢁz; ii) 1+x,y,z;
iii) ꢁx,1/2+y,1/2ꢁz; iv) ꢁ1/2+x,2.5ꢁy,ꢁz; v) ꢁ1+x,y,z] and 9 [bottom:
i) 1/2+x,1/2ꢁy,z; ii) 1ꢁx,ꢁy,1/2+z; iii) 1ꢁx,ꢁy,ꢁ1/2+z; iv) ꢁ1/2+x,1/
2ꢁy,z] with atom numbering schemes. Ellipsoids are drawn at 50% prob-
ability. Hydrogen bonds (Table S3, the Supporting Information) are
shown as dashed lines.
NaO)2- rings. The Cu···Cu intrachain distance is of
5.450(1) ꢄ, whereas the interchain distance equals the crys-
tallographic a dimension. The chains are assembled by
medium-strong H-bond interactions between the amino (as
donors) and the cyano (as acceptors) groups thus expanding
the structure to the second dimension.
Intermolecular p···p stacking interactions could also be
found in these structures. Whereas in 3 these are very weak
(higher than 5 ꢄ), in 4 the strongest centroid···centroid con-
tact is of 4.260(2) ꢄ and involves the hydrazometallacyles of
vicinal molecules, therefore evidencing the expected (based
on bond distances) electronic delocalization in these rings.
Complex 5 shows a considerable array of intra- and intermo-
lecular p···p interactions, with some of their values suggest-
ing a perfect (face-to-face), or slightly offset, stack whose
values are accepted to fall in the 3.3–3.8 ꢄ range.[24] Indeed,
594
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Chem. Eur. J. 2013, 19, 588 – 600

Template Syntheses of Copper(II) Complexes
FULL PAPER
excellent yields (Table 2). The
results show that generally the
shorter is the cyclic alcohol
chain, the higher the yield
(Table 2, entries 1, 2 vs. 3, 4),
probably due to the steric hin-
drance in higher alcohols.
However, this effect was not
observed for the linear aliphat-
ic alcohols C5–C8 (Table 2, en-
tries 5–9). It appears that the
efficiency of oxidation is not
affected by the position of the
OH group in the aliphatic
chain of the substrate, as at-
tested by the similar yields of
2-hexanone, 3-hexanone, 2-oc-
tanone, and 3-octanone (71–
75%) detected in the oxida-
tions of the corresponding iso-
meric alcohols (Table 2, en-
tries 6–9).
Mechanistic aspects of alco-
hol oxidation were studied
using complex 6, benzyl alco-
hol as model substrate and the
oxidants 1) TEMPO/air and
Figure 5. X-ray molecular structure of 15 (top) and the asymmetric unit of 16 (bottom) with atom numbering
schemes. Ellipsoids are drawn at 50% probability.
entries 1–6). In the system TEMPO/air/Cu catalyst, the pre-
cursors 3, 6, and 8 exhibit remarkably high selectivity to-
wards the formation of benzaldehyde (>99%), whereas the
Cu/TBHP systems produce both benzaldehyde and benzoic
acid, with selectivities up to 85% for the aldehyde.
The optimization of the reaction conditions (reaction
time, amount of catalyst and solvent, Figures S8–S10, the
Supporting Information) was carried out in a model benzyl
alcohol/TEMPO/air system with complex 6 as the catalyst
precursor. The conversion increases along the time from 21
2) TBHP. The studied TEMPO-mediated aerobic oxidation
with 6 as catalyst precursor conceivably involves a similar
pathway to that previously proposed for other Cu/air/
TEMPO systems.[17,25] It includes the coordination of
TEMPO and the alcohol substrate to an active site of cata-
lyst, followed by the Cu-centered oxidative dehydrogenation
of alcohol through H-abstraction and one-electron oxida-
tion.[17,25] In fact, the adduct of TEMPO with a mononuclear
copper center [CuACTHNUTRGENNGU ACHTUGNTRENNUGN
(HL4)(TEMPO)]+ (m/z 499, 35%) was
detected in the ESI-MS(+) spectra of reaction solutions (di-
luted with MeOH) containing the catalyst precursor 6,
benzyl alcohol, water, and TEMPO. The mechanistic aspects
of the reaction with TBHP as oxidant are less clear at this
stage, since the ESI-MS(+) in that case reveals only a disso-
ciation of the tetranuclear copper complexes to mononu-
to 99%, after
1 or 48 h, respectively, for catalyst 6
(0.2 mol% vs. substrate), at 508C for 48 h (Figure S8). The
product yield also increases with the catalyst amount (Fig-
ure S9, the Supporting Information), whereas the effect of
the content of solvent (1:1 MeCN/aqueous solution of 0.1m
K2CO3) in the reaction mixture is more complex (Fig-
ure S10, the Supporting Information). The maximum yield
of benzaldehyde is observed for 5 mL of the solvent mixture
under the used experimental conditions. Further enhance-
ment of the content of solvent leads to a significant yield
drop, which conceivably can be associated to the concom-
clear [Cu
(HL4)]+ (m/z 343, 100%) and dinuclear [Cu2-
ACHTUNGTRENNUNG
A
CHTUNGTRENNUNG
of any TEMPO adduct.
Nitroaldol reaction: We have tested the catalytic activity of
the complexes 3, 6, or 8 for the nitroaldol (Henry) reaction
between an aldehyde and a nitroalkane to produce a b-ni-
troalkanol (Scheme 2b, Table 3, and Table 4). According to
ACHTUNGTRENNUNGitant reduction of the concentrations of reagents (alcohol,
catalyst, TEMPO).
1
The oxidation with air was not particularly effective for
secondary alcohols because low yields (ca. 15% for cyclic al-
cohols) were obtained. However, aiming at oxidizing this
particular class of alcohol substrates, we have tested a strat-
egy based on microwave (MW)-assisted oxidation with
TBHP as oxidant.[17] Thus, sec-alcohols were oxidized with
TBHP to the corresponding carbonyl compounds in good to
the H NMR analyses with 1,2-dimethoxyethane as internal
standard,[18,19a,20] the products of the reaction at room tem-
perature are mixtures of the b-nitroalkanol threo- and eryth-
ro diastereoisomers with an appreciable diastereoselectivity
for threo (which is unusual for this type of reaction) and
with yields up to 97% (based on the aldehyde).
Chem. Eur. J. 2013, 19, 588 – 600
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595

M. N. Kopylovich, M. F. C. Guedes da Silva, A. J. L. Pombeiro et al.
Table 2. Solvent-free oxidation of different secondary alcohols by the
6/TBHP/MW system.[a]
Entry
Substrate
Product
Yield
[%][b]
1
2
96.1
91.3
3
4
85.5
70.9
5
6
7
8
9
73.4
74.7
72.3
72.5
70.8
[a] Reaction conditions: substrate (5.0 mmol), Cu catalyst precursor 6
(5 mmol, 0.1 mol% vs. substrate), TBHP (10.0 mmol, 70% in H2O),
808C, MW irradiation (10 W power), 240 min. [b] Moles of product/100
moles of substrate.
screening the typical reaction parameters including solvent,
catalyst loading and nitroalkane. Among the studied solvent
conditions, methanol, solvent free (e.g., nitroethane
medium), acetonitrile, DMF, toluene and mixture of metha-
nol and water were the best choices for this reaction
(Table 3, entries 2 and 7–11). High yields and selectivities
were obtained even when amounts of catalyst as low as
0.30 mol% versus substrate were used (Table 3, entries 1–6).
The reactivities of the different nitro compounds followed
the order: nitromethaneꢂnitroethane>1-nitropropane
(Table 3, entries 2, 14, and 15).
The activities of the complexes 3, 6, and 8 (mononuclear,
tetranuclear, and polymeric, respectively) are comparable
under standard conditions using the same aldehyde as sub-
strate (e.g., product yields ca. 96%, for benzaldehyde,
Table 4, entries 1–3). However, the nature of substrate
greatly influences the yields and selectivities. The use of
para- or ortho-substituted aromatic aldehydes with nitro-
ethane disfavor the reaction (product yields were ca. 88 and
77%, respectively, Table 4, entries 4–9) probably due to
steric hindrance. The linear aliphatic aldehydes lead to high
yields (up to 95%, approaching 97% for the aromatic ones)
but to lower selectivities for the threo diasteroisomer than
the aromatic ones (Table 4, entries 10–15).
Figure 6. X-ray molecular structure of 13 [top: i) 1ꢁx,1ꢁy,ꢁz;
ii) 2ꢁx,1ꢁy,ꢁz; iii) 2ꢁx,ꢁy,1ꢁz; iv) 2ꢁx,1ꢁy,ꢁz] and the asymmetric unit
of 14 (bottom) with atom numbering schemes. Ellipsoids are drawn at
50% probability. Hydrogen bonds (Table S3, the Supporting Informa-
tion) are shown as dashed lines.
Table 1. Oxidation of benzyl alcohol with TEMPO/air[a] and TBHP[b] oxi-
dants, catalyzed by Cu-AHM-derived complexes.
Entry
Catalyst
Oxidant
Yield
[%][c]
Selectivity
[%][d]
1
2
3
4
5
6
3
3
6
6
8
8
TEMPO/air
TBHP
TEMPO/air
TBHP
TEMPO/air
TBHP
75.5
80.8
82.3
82.5
78.7
75.4
>99
85
>99
82
>99
84
[a] Reaction conditions: benzyl alcohol (3.0 mmol), Cu catalyst precursor
(3 mmol, 0.1 mol%), TEMPO (0.15 mmol, 5 mol%), in an aqueous solu-
tion of MeCN/0.1m K2CO3 (5.0 mL of 1:1, v/v), 508C, air (1.0 atm).
[b] Reaction conditions: benzyl alcohol (3.0 mmol), Cu catalyst precursor
(3 mmol, 0.1 mol%), TBHP (15 mmol), in an aqueous solution of MeCN/
0.1m K2CO3 (1:1 v/v, 5.0 mL) at 508C; mol% values are versus substrate.
[c] Overall yield of carbonyl products, that is, moles of products (benzal-
dehyde and benzoic acid)/100 moles of benzyl alcohol. [d] Selectivity [%]
towards benzaldehyde formation is equal to the molar amount of benzal-
dehyde/total molar amount of products ꢅ100.
The common high efficiency of the studied complexes is
consistent with the possible involvement of metallic com-
plexes with different nuclearities similarly to what was pro-
posed for the Zn-catalyzed reactions involving either mono-,
di- or polynuclear complexes.[19l,o,r,s,20] The mechanism of the
reaction is expected[20] to involve metal-assisted (upon coor-
dination): 1) deprotonation of the methylene group of nitro-
ethane (to give a nitronate species), and 2) activation of
To search for the optimal conditions, we studied the addi-
tion of nitroalkanes to benzaldehyde by using catalyst 6 and
596
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Template Syntheses of Copper(II) Complexes
FULL PAPER
tetra- and polymeric CuII complexes with amidine,
carboxamide, and iminoester ligands. Their struc-
ture and nuclearity are dependent on the substitu-
ents in the ortho position of the aromatic parts of
the AHM ligands, as well as on the nature of nu-
cleophiles and reaction conditions. The organic
part of the complexes can be easily recovered by
simple protonation, leading to compounds that are
difficult to prepare by conventional organic synthe-
sis. The unprecedented possibility of RAHB/coor-
dination controlled E$Z isomeric transition was
demonstrated for the prepared hydrazones.
By using the synthesized complexes as catalyst
precursors, primary and secondary alcohols were
oxidized into the corresponding carbonyl com-
pounds in good to excellent yields. The primary
benzyl alcohol was effectively oxidized to benzal-
dehyde in the cases of O2/TEMPO and TBHP sys-
tems, whereas secondary alcohols were better oxi-
dized to ketones with TBHP as oxidant under mi-
crowave irradiation. Furthermore, the same copper
complexes were shown to be effective catalyst pre-
cursors for the diastereoselective nitroaldol reac-
tion, converting carbonyl products, synthesized
from alcohols, by the above mentioned catalytic
oxidation, to b-nitroalkanols in high yields, with
Table 3. Nitroaldol reaction between benzaldehyde and nitroalkane with 6 as catalyst
precursor at different conditions.[a]
Entry Catalyst
Nitroalkane
t
Amount
Solvent
Yield Selectivity
[%][b] threo/
erythro[c]
[h] catalyst
[mol%]
1
2
3
4
5
6
6
6
6
6
6
6
nitroethane
nitroethane
nitroethane
nitroethane
nitroethane
nitroethane
24 0.15
24 0.30
24 0.45
24 0.60
24 0.75
24 1.12
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
78.8
96.5
93.5
95.8
96.5
96.4
80:20
87:13
84:16
82:18
84:16
85:15
7[d]
8
9
10
11
6
6
6
6
6
nitroethane
nitroethane
nitroethane
nitroethane
nitroethane
24 0.30
24 0.30
24 0.30
24 0.30
24 0.30
–
87.9
84.0
87.6
81.6
79:21
74:26
81:19
70:30
71:29
acetonitrile
DMF
toluene
MeOH+H2O 88.9
12[e]
13[e]
14
Cu
blank
6
6
G
48 0.30
MeOH
MeOH
MeOH
MeOH
–
–
98.8
47.6
–
–
–
48
–
15
24 0.30
66:34
[a] Reaction conditions: 0.15–1.12 mol% of catalyst precursor (typically 0.30 mol%),
methanol (2 mL), nitroethane (4 mmol) and aldehyde (1 mmol). [b] Determined by
1H NMR analysis with 1,2-dimethoxyethane as internal standard. [c] Calculated by
1H NMR spectroscopy. [d] Methanol (solvent)-free conditions, using nitroethane as
solvent (2 mL). [e] For comparative purposes.
Table 4. Nitroaldol reaction of various aldehydes and nitroethane using
3, 6 or, 8 as catalysts.[a]
predominance of the threo diastereoisomer. The possibility
to use a common catalyst precursor for both types of reac-
tions, as found in this work for Cu-AHM-derived complexes,
deserves to be further explored towards the direct single-pot
conversion of alcohols into b-nitroalkanols.
Entry
Substrate
Catalyst
Yield
[%][b]
Selectivity
threo/erythro[c]
1
2
3
4
5
6
3
6
8
3
6
8
96.2
96.5
96.5
78.5
78.0
76.1
80:20
87:13
85:15
87:13
88:12
85:15
Experimental Section
7
8
9
10
11
12
13
14
15
3
6
8
3
6
8
3
6
8
89.8
83.3
88.3
85.4
89.8
91.5
94.4
94.5
90.7
70:30
77:23
75:25
55:45
57:43
52:48
67:33
74:26
73:27
Materials and instrumentation: All the synthetic work was performed in
air and at room temperature. All the chemicals were obtained from com-
mercial sources (Aldrich) and used as received. Infrared spectra (4000–
400 cmꢁ1) were recorded on a BIO-RAD FTS 3000 MX instrument in
KBr pellets. 1D (1H, 13C{1H}) NMR spectra were recorded on Bruker
Advance II+ 300.13 (75.468 carbon-13) and 400.13 (100.61 carbon-13)
MHz (UltraShield Magnet) spectrometers at ambient temperature. C, H,
and N elemental analyses were carried out by the Microanalytical Service
of the Instituto Superior Tꢁcnico. Chromatographic analyses were under-
taken by using a Fisons Instruments GC 8000 series gas chromatograph
with a DB-624 (J&W) capillary column (FID detector) and the Jasco–
Borwin v.1.50 software. Electrospray mass spectra (ESI-MS) were run
with an ion-trap instrument (Varian 500-MS LC Ion Trap Mass Spec-
trometer) equipped with an electrospray ion source. For electrospray ion-
ization, the drying gas and flow rate were optimized according to the par-
ticular sample with a nebulizer pressure of 35 psi. Scanning was per-
formed from m/z 100 to 1200 in methanol solution. The compounds were
observed in the positive mode (capillary voltage=80–105 V).
CH3CH2CHO
CH3ACHTUNGTRENNUNG(CH2)4CHO
[a] Reaction conditions: catalyst 3, 6 or 8 (0.30 mol%), methanol (2 mL),
nitroethane (4 mmol) and aldehyde (1 mmol), reaction time: 24 h. [b] De-
termined by 1H NMR analysis with 1,2-dimethoxyethane as internal
1
standard. [c] Calculated by H NMR spectroscopic analysis.
ꢁ
benzaldehyde towards its electrophilic attack (with C C
coupling) to the nitronate. The CuII complexes bearing aryl-
hydrazones of methylene-active nitriles appear to be able to
provide suitable Lewis acids for the above activations.
Syntheses of copper(II) complexes
The syntheses and characterization of the AHM compounds 2-(2-(dicya-
nomethylene) hydrazinyl)benzenesulfonic acid (H2L1, 1) and 2-(2-(dicya-
nomethylene) hydrazinyl)benzoic acid (H2L2, 2; Scheme 3) were reported
earlier,[9,14] and hence will not be discussed.
Conclusion
Synthesis of 3: Method 1: 0.250 g (1.0 mmol) of 1 was dissolved in metha-
We have achieved simple and effective CuII-assisted tem-
plate transformations of AHM, which led to new mono-,
nol (25 mL), then 0.200 g (1.0 mmol) of Cu
ACHTNUGTRENN(UGN CH3COO)2·H2O was added.
The mixture was stirred under solvent reflux for 30 min and left for slow
Chem. Eur. J. 2013, 19, 588 – 600
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597

M. N. Kopylovich, M. F. C. Guedes da Silva, A. J. L. Pombeiro et al.
evaporation; the green crystals of the product started to form after ap-
proximately 4 d at room temperature; they were then filtered off and
dried in air.
elemental analysis calcd (%) for C13H15CuN5O3 (352.83): C, 44.25; H,
4.29; N, 19.85; found: C, 44.10; H, 4.21; N, 20.11.
Liberation and characterization of the ligands
Method 2: Compound 1 (0.250 g, 1.0 mmol) of was dissolved in methanol
(25 mL) and (2.0 mmol) KOH was added. The mixture was stirred and
the solvent heated at reflux for 5 min, then (0.233 g, 1.0 mmol) of Cu-
ACHTUNGTRENNUNG(NO3)2·2.5H2O were added, stirred 30 min and left for slow evaporation;
the green crystals of the product started to form after approximately 4 d
at room temperature, then they were then filtered off and dried in air.
Liberation of 10–12: Complex 4 (0.0372 g, 0.1 mmol) of was dissolved in
methanol (10 mL) and HCl (22 mL (0.2 mmol) 33% w/w) were added
and diluted with acetone (25 mL). The yellow compounds 10–12 precipi-
tated after 5 min, which were filtered off, washed several times with ace-
tone (3ꢅ25 mL), dried in air, and recrystallized from methanol.
Compound 10: Yield: 61% (based on 4). Yellow powder is soluble in
methanol, ethanol, acetonitrile, DMSO, and water. 1H NMR
(300.13 MHz, [D6]DMSO, 258C, TMS): d=7.21–7.69 (4H, Ar-H), 8.06–
8.15 (3NH), 9.48–9.56 (3NH), 13.12 ppm (1H, NH); 13C{1H} NMR
(75.468 MHz, [D6]DMSO, 258C, TMS): d=37.2 (2CH2), 102.9 (C=N),
Compound 3: Yield 70% (based on Cu). Green crystals are soluble in
ethanol, acetonitrile, DMSO and water. IR (KBr, selected bands): n˜ =
2220 (C N), 1618 cmꢁ1 (C=N); elemental analysis calcd for
ꢀ
C10H12CuN4O6S (379.84): C, 31.62; H, 3.18; N, 14.75; found: C, 31.73H,
3.15; N, 14.80.
ꢀ
109.1 (C N), 116.6 (Ar-H), 125.1 (Ar-SO3H), 127.5, 130.6 and 134.3 (Ar-
H), 136.2 (Ar-NH-N), 155.9 ppm (C=N). MS (ESI): m/z: 311 [M+
Synthesis of 4: 0.250 g (1.0 mmol) of 1 was dissolved in water (15 mL),
then (0.200 g, 1.0 mmol) of CuACTHNUTRGNE(UNG CH3COO)2·H2O and 0.06 mL (1.0 mmol)
ethylenediamine were added. The mixture was stirred and heated to
808C for 30 min and then left at room temperature for slow evaporation;
deep-green crystals of 4 suitable for X-rays started to form after approxi-
mately 5 d.
+
ꢁ
ꢀ
HꢁCl] ; IR (KBr, selected bands): n˜ =3091 (N H), 2222 (C N), 1675,
1625 cmꢁ1 (C=N); elemental analysis calcd (%) for C11H15ClN6O3S
(346.79): C, 38.10; H, 4.36; N, 24.23; found: C, 37.76; H, 4.36; N, 23.85.
Compound 11: Yield 75% (based on 5), yellow powder soluble in metha-
1
nol, ethanol, water. H NMR (300.13 MHz, [D6]DMSO, 258C, TMS): d=
3.05 (3H, OCH3), 12.70 (H, H2N=C), 7.15–8.17 (4H, Ar-H), 15.10 ppm
Compound 4: Yield 43% (based on Cu). Green crystalline compound is
(1H, NH); 13C{1H} NMR (75.468 MHz, [D6]DMSO, 258C, TMS): d=52.9
soluble in ethanol, methanol, acetonitrile, and water. IR (KBr, selected
ꢁ1
ꢀ
(OCH3), 107.7 (C=N), 110.7 (C N), 115.0, 115.1, 124.0 and 131.4 (Ar-H),
ꢀ
bands): n˜ =2977, 2927 and 2849 n
G
134.9 (Ar-COOH), 143.0 (Ar-NH-N), 160.6 (CH3OC=N), 169.4 ppm
(C=N); elemental analysis calcd (%) for C11H14CuN6O4S (389.88): C,
(ArC=O); IR (KBr, selected bands): n˜ =3213 (OH), 2986 (NH), 2217
33.89; H, 3.62; N, 21.56; found: C, 33.53; H, 3.40; N, 21.36.
ꢁ1
(C N), 1594 cm (C=N); MS (ESI): m/z: 247 [MꢁCl]+; elemental analy-
ꢀ
Synthesis of 5 and 6: 0.214 g (1.0 mmol) of 2 was dissolved in methanol
(25 mL; ethanol in the case of 6), then (0.233 g, 1.0 mmol) of Cu-
ACHTUNGTRENNUNG(CH3COO)2·H2O was added. The mixture was stirred in solvent heated
at reflux for 30 min and then left at room temperature for slow evapora-
tion; the green (dark-green 6) crystals of the product started to form
after approximately 4 d at room temperature; they were then filtered off
and dried in air.
sis calcd (%) for C11H11ClN4O3 (282.05): C, 46.74; H, 3.92; N, 19.82;
found: C, 46.12; H, 3.79; N, 19.76.
Compound 12: Yield 69% (based on 3), yellow powder soluble in metha-
1
nol, ethanol, water. H NMR (300.13 MHz, [D6]DMSO, 258C, TMS), d=
3.81 (3H, OCH3), 4.80 (H, HN=C), 6.94–7.65 (4H, Ar-H), 12.66 ppm
(1H, NH); 13C{1H} NMR (75.468 MHz, [D6]DMSO, 258C, TMS), 52.4
ꢀ
(OCH3), 105.3 (C=N), 110.3 (C N), 114.7, 123.9, 127.2 and 130.4 (Ar-H),
Compound 5: Yield 70% (based on Cu). Green crystals are soluble in
133.5 (Ar-SO3H), 136.3 (Ar-NH-N), 160.5 ppm (CH3OC=N); IR (KBr,
ethanol, acetonitrile, DMSO and water. IR (KBr, selected bands, cmꢁ1):
ꢁ1
ꢀ
selected bands): n˜ =2955 and 3018 (NH), 2213 (C N), 1535, 1594 cm
ꢁ1
ꢁ
ꢀ
n˜ =2922 and 2851 (N H), 2225 (C N), 1628 cm (C=O); elemental anal-
ysis calcd (%) for C44H32Cu4N16O12 (1231.0): C, 42.93; H, 2.62; N, 18.21;
found: C, 42.66; H, 3.11; N, 17.30.
(C=N); MS (ESI): m/z: 283 [MꢁCl]+; elemental analysis calcd (%) for
C10H11ClN4O4S (318.74): C, 37.68; H, 3.48; N, 17.58; found: C, 36.96; H,
3.30; N, 17.16.
Compound 6: Yield 75% (based on Cu). Dark-green crystals are soluble
in ethanol, acetonitrile, DMSO, and water. IR (KBr, selected bands): n˜ =
Synthesis of 13: (Scheme 4): Method 1: Compound 1 (0.25 g, 1 mmol)
was dissolved in methanol (or water, but it is better to use methanol) and
ethylenediamine (0.36 mL , 6 mmol) was added and the system stirred
with heating at reflux for 30 min. The solvent was then removed under
vacuum and the residue was dissolved in acetone, the precipitated yellow
compound was filtered off, washed with acetone, and dried in air. To
obtain crystals suitable for X-ray analysis, 13 was dissolved in methanol
and then left at room temperature for slow evaporation (ca. 4 d).
2218 (C N), 1618 cmꢁ1 (C=O); elemental analysis calcd (%) for
ꢀ
C48H44Cu4N16O14 (1323.15): C, 43.57; H, 3.35; N, 16.94; found: C, 44.33H,
3.76; N, 17.21.
Synthesis of 7 and 8: Compound 1 (0.250 g, 1.0 mmol) of was dissolved in
NH4OH (25 mL 0.1m; 25 mL ethanol for 8), then CuACHTUNGTRENUNG(CH3COO)2·H2O
(0.200 g, 1.0 mmol) of was added and the system heated to 808C (heated
at reflux for 8) for 30 min and left for slow evaporation. Deep green crys-
tals of the product started to form after approximately 5 d at room tem-
perature, which were then filtered off and dried in air.
Method 2: Compound 10 (0.35 g, 1 mmol) was dissolved in methanol
(25 mL) and ethylenediamine (0.12 mL, 2 mmol) was added. The reaction
mixture was stirred at room temperature for 30 min, and then the solvent
was removed under vacuum. The residue was then dissolved in acetone.
The yellow product was allowed to precipitate (for ca. 10 min), then fil-
tered off, washed with acetone, and dried in air. The yields of 13 by both
methods are comparable and close to 81%.
Compound 7: Yield 53% (based on Cu). Deep green crystalline com-
pound is soluble in ethanol, methanol, and water. IR (KBr, selected
ꢁ
ꢁ
bands): n˜ =3465, 3383 and 3321 (O H), 3251 (N H), 1628 (C=O),
1601 cmꢁ1 (C=N); elemental analysis calcd (%) for C36H50Cu4N16O30S4
(1571.33): C, 27.52; H, 3.34 N, 14.26; found: C, 27.43H, 3.16; N, 14.17.
Compound 13: Yield 81% (based on 1), yellow powder soluble in metha-
1
Compound 8: Yield 75% (based on Cu). Deep-green crystalline com-
nol, ethanol, water. H NMR (300.13 MHz, [D6]DMSO, 258C, TMS), d=
pound is soluble in ethanol, acetonitrile, DMSO, and water. IR (KBr, se-
3.92–4.02 (8H, CH2), 7.16–7.93 (4H, Ar-H), 10.57 (3H, 3NH), 11.74 (1H,
NH); 13C{1H} NMR (75.468 MHz, [D6]DMSO, 258C, TMS): d=44.2
(2CH2), 44.7 (2CH2), 85.3 (C=C), 108.9, 114.8, 124.5 and 127.8 (Ar-H),
129.6 (Ar-N=N), 130.4 (Ar-SO3H), 155.4 (C-N), 159.5 (C=N); IR (KBr,
selected bands): n˜ =2903, 2964, 3256 (NH), 1635, 1583, 1528 cmꢁ1 (C=N);
MS (ESI): m/z: 336 [MꢁH2O]; elemental analysis calcd (%) for
C13H18N6O4S (354.39): C, 44.06; H, 5.12; N, 23.71; found: C, 44.04; H,
4.99; N, 23.50.
lected bands): n˜ =3431 (O H), 2220 (C N), 1611, cmꢁ1 (C=N); elemental
analysis calcd (%) for C11H12CuN4O5S (375.98): C, 35.15; H, 3.22 N,
14.91; found: C, 34.93H, 3.16; N, 14.83.
ꢁ
ꢀ
Synthesis of 9: Compound 5 (1.231 g, 1.0 mmol) of was dissolved in meth-
anol (50 mL), then 0.24 mL (4.0 mmol) ethylamine was added and the
system stirred with solvent heated at reflux for 30 min. After approxi-
mately 4 d at room temperature, green crystals precipitated, which were
then filtered off and dried in air.
E/Z Rotational isomerization
Compound 9: Yield 88% (based on 5). Green crystalline compound is
Synthesis of 14: NaOH (0.40 mmol) was added to an acetone/water
(50 mL, 1:1, v/v) solution of 1 (0.20 mmol) and the mixture was stirred
and heated at ruflux for 30 min and then left at room temperature for
soluble in ethanol, acetonitrile, DMSO and water. IR (KBr, selected
ꢁ1
ꢁ
ꢀ
bands): n˜ =2970, 2952, and 2902 (N H), 2221 n
N
598
www.chemeurj.org
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 588 – 600

Template Syntheses of Copper(II) Complexes
FULL PAPER
slow solvent evaporation. Crystals suitable for X-ray diffraction analysis
were obtained after 2 d.
added to an aqueous solution of MeCN/0.1m K2CO3 (1:1 v/v, 5.0 mL).
2) TBHP: the alcohol (3.0 mmol), Cu catalyst precursor (3 mmol), and
TBHP (15 mmol) were added to MeCN/0.1m K2CO3 (5.0 mL of 1:1, v/v)
aqueous solution. The reaction solutions in all cases were vigorously stir-
red by using magnetic stirrers, and an oil bath was used to achieve the
desired reaction temperature. After the oxidation reaction, the reaction
mixtures were neutralized by 1m HCl, and then extracted with ethyl ace-
tate (10 mL). The organic phase was used for chromatographic analyses
by using acetophenone as the internal standard. Negligible reactions
were observed when TEMPO, TBHP, or the copper complex was not em-
ployed. For mechanistic studies, samples were withdrawn at specific time
intervals and analyses by ESI-MS. The ESI-MS equipped with an ion
spray source in positive ion mode detected species in the m/z range of
100 to 1000.
Compound 14: Yield 90% (based on 1), yellow-orange crystals are solu-
ble in methanol, ethanol and water. 1H NMR (300.13 MHz, [D6]DMSO,
258C, TMS): d=7.13–7.85 (4H, Ar-H), 13.25 ppm (1H, NH);
13C{1H} NMR (75.468 MHz, [D6]DMSO, 258C, TMS): d=87.1 (C=N),
ꢀ
110.0 (CN), 114.1 (C N), 115.6, 125.3, 127.3 and 131.3 (Ar-H), 134.2 (Ar-
SO3H), 136.2 (Ar-NH-N); IR (KBr, selected bands): n˜ = 3123 (OH), 3076
ꢁ1
ꢀ
(NH), 2219, 2228 (C N), 1591 cm (C=N); elemental analysis calcd (%)
for C9H13N4NaO7S (M=344.28): C, 31.40; H, 3.81; N, 16.27; found: C,
31.25; H, 3.75; N, 16.13.
Synthesis of 15: Compound 14 (0.0688 mg, 0.02 mmol) was dissolved in a
mixture of acetone/water (35 mL 1:2, v/v), then CuACTHNUTRGNE(UNG BF4)2·xH2O
(0.0474 mg, 0.02 mmol) was added. The mixture was stirred and heated
to 808C for 30 min, then left for slow evaporation at room temperature.
Yellow crystals of 15 suitable for X-ray analysis started to form after ap-
proximately 3 d.
Peroxidative oxidation of sec-alcohols using the microwave-assisted
method: In a typical experiment, the alcohol substrate (5.00 mmol),
TBHP (10.0 mmol) and catalyst precursor 6 (5 mmol, 0.1 mol% vs. sub-
strate) were introduced to a cylindrical Pyrex tube, which was then
placed in the focused microwave reactor. The system was stirred and irra-
diated for 240 min at 808C and 10 W. After the reaction, the mixture was
allowed to cool down. The reaction samples (after cooling to ambient
temperature) were treated with acetonitrile (5 mL) and benzaldehyde
(300 mL; internal standard) and analyzed by gas chromatography.
Compound 15: Yield 40% (based on Cu). Yellow crystalline compound
is soluble in ethanol, acetonitrile, DMSO, and water. IR (KBr, selected
ꢁ1
ꢀ
bands): n˜ =3122 (OH), 2851 (NH), 2211 (C N), 1723 (C=O), 1595 cm
(C=N); elemental analysis calcd (%) for C18H30CuN8O16S2 (742.15): C,
29.13; H, 4.07 N, 15.10; found: C, 29.08H, 4.55; N, 14.91.
Synthesis of 16: Compound 14 (0.0688 mg, 0.02 mmol) was dissolved in
acetone/water (35 mL, 1:2, v/v) mixture, then CuACTHNUTRGNE(UNG CH3COO)2·H2O
(0.0400 mg, 0.02 mmol) and KOH (0.0112 mg, 0.02 mmol) was added.
The mixture was stirred for 15 min, and the reaction mixture was left at
room temperature for slow evaporation.
Nitroaldol reaction of aldehyde and nitroalkane: A typical reaction was
carried out under air as follows: methanol (2 mL), nitroethane (4 mmol)
and aldehyde (1 mmol), in that order, were added to of catalyst precursor
(0.15–1.12 mol%, typically 0.30 mol%) contained in the reaction flask.
The reaction mixture was stirred for the required time at room tempera-
ture and air atmospheric pressure. After evaporation of the solvent, the
Compound 16: 48% (based on 14). IR (KBr, selected bands,): n˜ =3217
ꢁ1
ꢀ
(OH), 2949 (NH), 2217 (C N), 1679 (C=O), 1599 cm (C=N); elemental
1
residue was dissolved in [D6]DMSO and analyzed by H NMR. The yield
analysis calcd (%) C36H32Cu2KN16Na2O24S4 (M=1413.18): C, 30.60; H,
of b-nitroalkanol product (relatively to the aldehyde) was established
typically by taking into consideration the relative amounts of these com-
pounds, as given by 1H NMR and previously reported.[20] The adequacy
of this procedure was verified by repeating a number of the 1H NMR
analyses in the presence of 1,2-dimethoxyethane as internal standard,
added to the [D6]DMSO solution, what gave yields similar to those ob-
tained by the above method. Moreover, the internal standard method
also confirmed that no side products were formed. The ratio between the
threo- and erythro isomers was also determined by 1H NMR spectrosco-
py. In the 1H NMR spectra, the values of vicinal coupling constants (for
the b-nitroalkanol products) between the a-N-C-H and the a-O-C-H pro-
tons identify the isomers, being J=7–9 or 3.2–4 Hz for the threo- or er-
ythro isomers, respectively.[18k, 19a] Control reactions were carried out in
2.28 N, 15.86; found: C, 30.38; H, 2.15; N, 15.78.
X-ray structure determinations: Crystals were immersed in cryo-oil,
mounted in a Nylon loop and measured at a temperature of 150 K. Inten-
sity data were collected by using a Bruker AXS-KAPPA APEX II dif-
fractometer with graphite monochromatic MoKa (l 0.71073) radiation.
Data were collected using omega scans of 0.58 per frame and full sphere
of data were obtained. Cell parameters were retrieved using Bruker
SMART software and refined using Bruker SAINT[26] on all the observed
reflections. Absorption corrections were applied using SADABS.[26]
Structures were solved by direct methods by using the SHELXS-97 pack-
age[27] and refined with SHELXL-97.[27] Calculations were performed
using the WinGX System-Version 1.80.03.[28] All hydrogen atoms were in-
serted in calculated positions. Exceptions are the N3, N5, N6, and N8 hy-
drogen atoms in 13, which were located in the difference Fourier maps,
but were included in the refinement using the riding-model approxima-
tion and taken with coefficients 1.2-times larger than the respective pa-
rameters of the parent atoms. There were disordered solvents present in
the structures of complexes 3 and 4. Because no obvious major site occu-
pations were found for those molecules, it was not possible to model
them. PLATON/SQUEEZE[29] was used to correct the data and potential
volumes of 736.6 (3) and 107.7 (4) ꢄ3 were found with, respectively, 196
and 47 electrons per unit cells worth of scattering. The electron counts
suggest the presence of ca. one molecule of water per each of the unit
cells. Least-square refinements with anisotropic thermal motion parame-
ters for all the non-hydrogen atoms and isotropic for most of the remain-
ing atoms, were employed. Crystallographic and selected structural de-
tails are listed in the Supporting Information Tables S1 and S2, respec-
tively. CCDC-893916 (3), CCDC-893917 (4), CCDC-893918 (5), CCDC-
893919 (6), CCDC-893920 (7), CCDC-893921 (8), CCDC-893922
(9),CCDC-893923 (13), CCDC-893924 (14), CCDC-893925 (15) and
893926 (16) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
the absence of catalyst or in the presence of Cu
action between benzaldehyde and nitroethane takes place in the absence
of the metal complex, even in the presence of Cu(NO3)2.
ACHTUGNTRENUN(GN NO3)2. No nitroaldol re-
AHCTUNGTRENNUNG
Acknowledgements
This work has been partially supported by the Foundation for Science
and Technology (FCT; projects PTDC/QUI-QUI/102150/2008 and PEst-
OE/QUI/UI0100/2011), Portugal, and “Science” programs. A.M., K.T.M.,
and T.C.O.M.L. express gratitude to the FCT for their postdoctoral and
doctoral fellowships. M.N.K. is grateful to the FCT and IST for research
contracts within the CiÞncia 2008 scientific program. The authors thank
the Portuguese NMR Network (IST-UTL Centre) for providing access to
the NMR facility.
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Chem. Eur. J. 2013, 19, 588 – 600
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: September 12, 2012
Published online: November 23, 2012
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