Water-soluble copper(II) complexes with a sulfonic-functionalized arylhydrazone of β-diketone and their application in peroxidative allylic oxidation of cyclohexene

Article abstract of DOI:10.1002/ejic.201101361

The reaction of Cu^II acetate with the new sulfo-functionalized arylhydrazone of β-diketone 2-[2-(4,4-dimethyl-2,6-dioxocyclohexylidene) hydrazinyl]benzenesulfonic acid (H₂L, 1) in aqueous methanol solution led to the formation of the

Full text of DOI:10.1002/ejic.201101361

FULL PAPER
DOI: 10.1002/ejic.201101361
Water-Soluble Copper(II) Complexes with a Sulfonic-Functionalized
Arylhydrazone of β-Diketone and Their Application in Peroxidative Allylic
Oxidation of Cyclohexene
Archana Mizar,[a] M. Fátima C. Guedes da Silva,*[a,b] Maximilian N. Kopylovich,[a]
Sanghamitra Mukherjee,[a] Kamran T. Mahmudov,[a,c] and Armando J. L. Pombeiro*[a]
Keywords: Hydrazones / Ketones / Copper / Structure elucidation / Oxidation
The reaction of CuII acetate with the new sulfo-function-
clear [{Cu(κ2O,κN-L)(H2O)}2(κ-py)]·CH3OH (6) complexes
alized arylhydrazone of β-diketone 2-[2-(4,4-dimethyl-2,6-di- were obtained, respectively. The compounds were charac-
oxocyclohexylidene)hydrazinyl]benzenesulfonic acid (H2L,
1) in aqueous methanol solution led to the formation of the
2Dcoordinationpolymer{[Cu4(1κ2O,κN:2κO,κN-L)4(μ-OH2)2]·
H2O}n (2). However, when the reaction was peformed in the
presence of the N-containing species cyanoguanidine (cyg),
3,5-dimethyl-1H-pyrazole (dp), 2,2Ј-bipyridine (bpy) or pyr-
azine (py), the mononuclear (H3O+)2[Cu(κ2O,κN-L)2] (4), [Cu-
(κ2O,κN-L)(dp)2] (3) or [Cu(κ2O,κN-L)(κ2N-bpy)] (5) or dinu-
terized by elemental analysis, IR spectroscopy, single-crystal
X-ray diffraction analysis and, for 1, by 1H and 13C NMR
spectroscopy. The CuII complexes 2–6 act as catalyst precur-
sors for the selective peroxidative (with TBHP) allylic oxi-
dation of cyclohexene to cyclohex-2-enol (Cy-ol) and cy-
clohex-2-enone (Cy-one), formed in a Cy-one/Cy-ol ratio of
up to 9 with total yields of around 70% and TONs of up to
350.
aerobic oxidation of benzylic alcohols in aqueous media.
Incorporation of a hydrophilic polar (e.g., sulfo or arseno)
group into the ligand is one of the common ways to in-
crease the water solubility of its complexes. Moreover, such
a ligand can behave as a polydentate donor moiety, thus
supporting an extension of coordination arrays in the solid
state. In addition, it has been noted[4k] that particularly
stable complexes with two fused six-membered metalla-
cycles can be synthesized by taking advantage of the coor-
dination ability of an ortho substituent of the AHBD.
The use of a hetero-proligand (e.g. imidazole, cyano-
guanidine, ethylenediamine) in a CuII–AHBD can modu-
late, to some extent, the structure of the thus synthesized
complexes.[4k] The auxiliary species affects the complexation
process through coordination, template condensation or as
a proton attractor or spacer, thus allowing regulation of the
structures of the primary subunits as well as their supra-
molecular assemblies.[6] Hence, AHBDs and their com-
plexes can form interesting architectures involving mono-
meric, oligomeric or polymeric subunits.[2,4k] This structure
modulation is related to current topics of crystal engineer-
ing[7a] and molecular recognition[7b,7c] aiming at the design
of materials that may be used for compound storage[7d,7e]
Introduction
Arylhydrazones of β-diketones (hereafter denoted as
AHBDs) and their complexes have attracted considerable
attention due to their high synthetic potential in organic[1]
and inorganic[2] chemistry and their wide range of useful
properties. For example, AHBDs can find applications in
the design of functional materials attributed to smart hy-
drogen bonding,[3] photo-triggered structural switching,[4a]
self-assembled layers,[4b] liquid crystals,[4c] semiconduc-
tors,[4d,4e] ionophores,[4f] indicators,[4g] spectrophotometric
reagents for the determination of metal ions,[4h,4i] cata-
lysts,[2a,4j–4l] photoluminescent materials,[4m] optical re-
cording media[4n] and spin-coating films.[4o]
The water solubility of the AHBD compounds has par-
ticular importance for catalysis and other applications in
which water is used as solvent and/or reactant. For instance,
we have previously shown[5] that water-soluble CuII–AHBD
complexes are suitable catalysts for the TEMPO-mediated
[a] Centro de Química Estrutural, Complexo I, Instituto Superior
Técnico, Technical University of Lisbon,
Av. Rovisco Pais, 1049-001 Lisbon, Portugal
E-mail: pombeiro@ist.utl.pt
[b] Universidade Lusófona de Humanidades e Tecnologias, ULHT or chemical sensing.[7f]
Lisbon,
On the other hand, it has been shown[2a,4k,5] that CuII–
Campo Grande 376, 1749-024 Lisboa, Portugal
E-mail: fatima.guedes@ist.utl.pt
[c] 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/ejic.201101361.
AHBD complexes are valuable catalysts for some oxidation
processes, for example, the peroxidative oxidation reactions
of cyclohexane and alcohol. Moreover, the selective allylic
oxidation of alkenes, which preserves the C=C double bond
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M. F. C. Guedes da Silva, A. J. L. Pombeiro et al.
FULL PAPER
and allows further functionalization, is a very useful syn- complexes as catalysts or catalyst precursors for the selec-
thetic transformation that deserves further investigation to tive peroxidative allylic oxidation of cyclohexene to cy-
find new effective catalysts. Some copper complexes have clohex-2-enol and cyclohex-2-enone.
been found to catalyse such reactions,[8] but so far there
have been no report of the use of CuII–AHBD catalysts for
Results and Discussion
this purpose. Hence, it is worthwhile attempting to use
CuII–AHBD complexes as catalysts for this selective trans-
formation under mild conditions. The oxidation of cyclo-
hexene to cyclohex-2-enol and cyclohex-2-enone with tert-
butyl hydroperoxide (TBHP) (Scheme 1) was chosen as a
model reaction.
Synthesis and Characterization of 1 and Its Copper(II)
Complexes
The water-soluble AHBD 1 (Scheme 2) was synthesized
by a modified Japp–Klingemann reaction:[9a–9c] 2-sulfo-
phenyldiazonium chloride was treated with 5,5-dimethyl-
cyclohexane-1,3-dione in an ethanolic solution of sodium
hydroxide.[9d] 2-Sulfophenyldiazonium chloride was ob-
tained by diazotization of the corresponding substituted
aniline. AHBD 1 is highly soluble in polar solvents such as
water, DMF and DMSO, but almost insoluble in chloro-
form, dichloromethane and toluene. The presence of the
Scheme 1.
Thus, in this work we combine the above-mentioned ap- SO3H group is crucial for its solubility in water; the unfunc-
proaches to achieve our aims: 1) the synthesis of a new tionalized analogue of 1, with H instead of SO3H, is insolu-
water-soluble AHBD species bearing a sulfonic group, 2-[2- ble in water.[2a,4k]
(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl]benz-
The NMR spectrum of 1 in [D6]DMSO at room tem-
enesulfonic acid (H2L, 1), which contains an ortho-SO3H perature indicates that this compound exists in this solvent
moiety, and its application to the preparation of new water- in the hydrazone rather than the enol-azo or keto-azo
soluble CuII–AHBD complexes, 2) the design of diverse form.[2] The two resonances in the 13C NMR spectrum aris-
CuII–AHBD hetero-ligand-containing complexes of dif- ing from the carbonyl groups (see the Exp. Sect.) show that
ferent geometries and nuclearities and 3) the use of these one of these groups undergoes a shift due to hydrogen
Scheme 2. Reactions of CuII acetate with 1 in water in the presence and absence of auxiliary ligands (a H2O/CH3OH mixture was used
as solvent for the recrystallization).
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Water-Soluble Copper(II) Complexes
bonding with the hydrazone NH moiety. This is in accord
1
with the low-field H chemical shift (δ = 15.28 ppm) of the
hydrazone NH proton and is also consistent with the IR
data: IR bands for ν(C=O) and ν(C=O···H) appear at 1664
and 1630 cm–1, respectively, the latter being shifted on ac-
count of the hydrogen bond.[2–5] The ν(OH) and ν(NH)
bands at 3491 and 2954 cm–1, respectively, also support[2–5]
the existence of the hydrogen-bonded hydrazone structure
in the solid state. Moreover, the single-crystal X-ray analysis
of 1 (Figure 1) also shows that, in the solid phase, it exists
in the hydrazone form, although with electron delocaliza-
tion. The N1–N2 bond length of 1.255(6) Å is typical of a
double bond, whereas that of C6–N1 [1.421(7) Å] is repre-
sentative of a CAr–NH–N= moiety. However, the C7–N2
Figure 1. Molecular structure of 1 with atomic numbering scheme
and showing the intra- as well as the strongest intermolecular hy-
bond length of 1.324(7) Å is close to the value of a classic drogen-bonding interactions. Thermal ellipsoids are drawn at the
C
sp2–N bond (1.336 Å),[10] thus providing evidence for elec-
50% probability level. Selected bond lengths [Å] and angles [°]: N1–
N2 1.255(6), C6–N1 1.421(7), C7–N2 1.324(7), C12–O5 1.240(6),
C8–O4 1.238(6), C7–C8 1.490(6), C7–C12 1.463(8); N2–N1–C6
121.2(4), N1–N2–C7 121.5(5), C1–C6–N1 120.8(5). Selected hydro-
gen bonds {d(H···A) [Å], Є(DHA) [°]}: N1–H1···O3 2.47, 120.9;
N1–H1···O5 1.91, 133.3; C2–H2···O2 2.871(7), 106; C13–
H13C···O2 3.461(7), 150. Symmetry operation to generate equiva-
lent atoms: (i) 1.5 – x, –y, –½ + z.
tron delocalization over the OCCCO skeleton. Thus, the C–
O bond lengths of 1.238(6) and 1.240(6) Å are close to
those usually found in delocalized double bonds in carb-
oxylate anions.[10] Such delocalization is also the reason for
the weak πOCCCO···H14C interaction (centroid···H and Є
centroid···H14C–C14, 3.290 Å and 168.77°, respectively).
There are intramolecular hydrogen bonds in 1 (see Figure 1)
that strengthen the hydrazone form of the molecule and
influence its coplanarity. Indeed, molecule 1 is nearly
The reaction of Cu(CH3COO)2·H2O with 1 in water/
planar, as indicated by the very low angle (5.87°) between methanol in the absence or in the presence of 3,5-dimethyl-
the CC=O–C–CC=O-containing plane (hereafter denoted as 1H-pyrazole (dp), cyanoguanidine (cyg), 2,2Ј-bipyridine
plane C) and the plane of the aromatic ring (hereafter de- (bpy) or pyrazine (py) led to the CuII complexes {[Cu4-
noted as plane Ar). This parameter was selected as a way (1κ2O,κN:2κO,κN-L)4(μ-OH2)2]·H2O}n (2), [Cu(κ2O,κN-
of comparing the degree of coplanarity of molecule 1 and L)(dp)2] (3), (H3O+)2[Cu(κ2O,κN-L)2] (4), [Cu(κ2O,κN-
its ligating forms (see below and Table 1).
L)(κ2N-bpy)] (5) and [{Cu(κ2O,κN-L)(H2O)}2(κ-py)]·
Table 1. Comparison of selected features of compound 1 and complexes 2–6.
1
2
3
4
5
6
Organic moiety H2L (or L2–
N–N [Å]
)
1.255(6)
1.283(4)
1.295(4)
1.283(9)
|
1.275(3)
1.280(3)
1.283(6)
1.2810(18)
1.375(9)
Є plane C–plane Ar [°][a]
5.87
66.52(18) (Cu1)
21.3(3) (Cu2)
59.6(5) (Cu1)
61.5(5) (Cu2)
39.2(3) (Cu1)
44.19(19) (Cu2)
34.7(3)
57.4(1)
Surrounding of the copper atom
Cu–N [Å]
–
–
1.950(3)
|
2.448(3)
1.943(8)
|
2.092(8)
1.952(2)
1.968(2)
1.980(4)
|
2.037(4)
1.9767(13)
2.0235(13)
Cu–O [Å]
1.908(2)
|
1.966(6)
|
1.9486(19)
1.943(4)
2.255(4)
1.9240(11)
|
|
2.342(2)
2.140(6)
2.421(2)
2.1690(14)
Є O–Cu–X (X = O or N) [°]
Largest
Smallest
–
172.46(11) (Cu1)
73.89(10) (Cu2)
174.3(3) (Cu2)
86.7(3) (Cu2)
180.0
82.67(8) (Cu1)
172.1(2)
81.60(18)
171.22(5)
87.55(5)
τ parameter for five-
0.08 (Cu2)
0.67 (Cu1)
0.63 (Cu2)
–
0.21
0.07
coordinated Cu centre (τ5)[11]
Geometry
–
octahedral (Cu1)
trigonal bipyramidal
octahedral
square pyramidal square pyramidal
square pyramidal (Cu2)
[a] For identification of these planes, see text.
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CH3OH (6; Scheme 2), which were isolated and charac- (1κ2O,κN:2κO,κN-L)4(μ-OH2)2]·H2O}n (2; see Figure 2 and
terized by elemental analysis, IR spectroscopy and single- Supporting Information, Figure S1), which crystallized di-
crystal X-ray diffraction.
rectly from the reaction mixture as greenish-black crystals.
The reaction of CuII acetate hydrate with 1 in water The polymeric structure of 2 contains crystallographically
afforded a polymer with a tetranuclear core {[Cu4- imposed inversion centres in the heart of the Cu2O2 planes.
Figure 2. Molecular structure of compound 2 with atomic numbering scheme and showing the strongest intermolecular hydrogen-bonding
interactions. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths [Å] and angles [°]: N1–N2 1.283(4), N1–
Cu2 2.448(3), N2–Cu1 1.969(3), N3–N4 1.295(4), O1–Cu1 1.925(2); O1–Cu1–O11 171.46(10), O1–Cu1–N2 89.22(11), O11–Cu1–N2
93.14(11), O1–Cu1–O10 89.32(10), O11–Cu1–O10 87.26(10), N2–Cu1–O10 172.46(11). Selected hydrogen bonds {d(H···A) [Å],
Є(DHA) [°]}: O10–H10A···O13i 1.832(2), 147.41(16); O10–H1OB···O20 1.667(3), 175.53(17); O20–H20C···O23 1.957(3), 167.09(19); O20–
H20D···O23 1.991(3), 154.76(18). Symmetry operations to generate equivalent atoms: (i) –x, 1 – y, 1 – z; (ii) 1 – x, 1 – y, 1 – z; (iii) –1 –
x, –y, 1 – z; (iv) –1 + x, y, z; (v) –1 + x, –1 + y, z; (vi) 1 + x, 1 + y, z.
Figure 3. Molecular structure of compound 3 with atomic numbering scheme and showing the intra- as well as the strongest intermo-
lecular hydrogen-bonding interactions. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths [Å] and angles
[°]: N1–N2 1.288(9), N1–Cu1 1.946(7), N5–N6 1.373(9), N5–Cu1 1.984(8), N7–N8 1.383(9), N7–Cu1 2.084(7), O1–Cu1 2.138(6), O4–
Cu1 1.965(6); N1–Cu1–N5 172.7(3), O4–Cu1–N7 122.5(3), N5–Cu1–N7 94.2(3), O4–Cu1–O1 133.0(3). Selected hydrogen bonds {d(H···A)
[Å], Є(DHA) [°]}: N6–H6A···O5 2.45, 119.7; N8–H8···O2 2.00, 158.4; N10–H10···O10 2.37, 121.9; N12–H12···O9 1.98, 156.2. Symmetry
operations to generate equivalent atoms: (i) 1.5 – x, ½ + y, ½ – z; (ii) ½ – x, –½ + y, ½ – z.
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Water-Soluble Copper(II) Complexes
Figure 4. Molecular structure of the complex dianions of 4 with atomic numbering scheme. Thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths [Å] and angles [°]: N1–N2 1.275(3), C6–N1 1.433(4), C7–N2 1.366(4), N3–N4 1.280(3), N1–Cu1
1.968(2), O1–Cu1 1.954(2), O11–Cu1 2.421(2); N2–N1–C6 113.0(2), O1–Cu1–N1 87.46(9), O1–Cu1–O11 97.33(9), N1–Cu1–O11 84.66(8),
N1–N2–C7 120.2(2), N4–N3–C26 114.1(2). Symmetry operations to generate equivalent atoms: (i) 1 – x, –y, –z: (ii) –x, 1 – y, 1 – z.
The Cu1 cations form edge-sharing bi-octahedrons each
with two bridging aqua ligands, the two distorted octahedra
i
dividing the common Oaqua–Oaqua edge. The anionic L2–
ligand acts as a tridentate O,N,O ligand to Cu1 and, simul-
taneously, as a N,O ligand to the pentacoordinate Cu2.
Consequently, complex 2 is the first metal–AHDB complex
in which both nitrogen atoms of the hydrazone unit are ef-
fectively coordinated to a metal cation. Moreover, the
pentacoordinate L2– ligand displays the major distortion
found in these complexes, whereas the ligand coordinated
solely to Cu2 is considerably more planar, which is evi-
denced by the angle between the C and Ar planes [66.52(18)
and 21.3(3)°, respectively]. The complexes 3–6 (Figures 3,
4, 5 and 6) exhibit intermediate values ranging from 34.7(3)
to 61.5(5)°, which substantiates the twisting of the AHBD
ligand upon coordination.
Complexes 2 and 4–6 illustrate well the influence of the
co-ligand in the coordination mode of AHBD (due to its
different geometry, complex 3 is excluded from this dis-
cussion). Apparently, co-ligand imposed geometry constric-
tions oblige the Ocarbonyl and N atoms from the hydrazone
molecule to occupy equatorial positions and its Osulfonate
atom to occupy the apical site, as observed in structures 4
Figure 5. Molecular structure of complex 5 with atomic numbering
scheme. Thermal ellipsoids are drawn at the 50% probability level.
Selected bond lengths [Å] and angles [°]: C1–N1 1.437(7), C7–N2
1.357(7), N1–N2 1.283(6), N1–Cu1 1.980(4), N3–Cu1 2.037(4),
N4–Cu1 2.003(4), O1–Cu1 2.255(4), O4–Cu1 1.943(4); N1–Cu1–
N4 172.1(2), O4–Cu1–N3 159.26(17), N1–Cu1–N3 102.56(18), N4–
(with two AHBD ligands) and 5 (with 2,2Ј-bipyridine). In Cu1–N3 81.60(18), O4–Cu1–O1 104.86(15), N4–Cu1–O1
84.61(17), N3–Cu1–O1 93.59(16).
contrast, for 2 and 6, in which ligand constraints are less
evident, the Ocarbonyl, the N and the Osulfonate atoms of the
hydrazone occupy the equatorial positions.
donor. The copper cations adopt a distorted octahedral (2),
In complexes 2–6 (Figures 2–6), the ligand 1 presents two a trigonal bipyramid (3), a perfect octahedral (4) or a
different coordination modes and the copper ion features square pyramid (5 and 6) geometry. Addison and Reedijk
diverse coordination numbers and geometries. It is in the and co-workers[11] introduced a parameter (τ5) to describe
2D polymer 2 that the L2– moiety presents the most intri- the geometry of a five-coordinate metal system, which is
cate coordination mode sharing three oxygen and two nitro- determined by Equation (1) in which β and α are the largest
gen atoms with two copper cations in a 1κ2O,κN:2κO,κN angles involving the metal. By means of this simple crite-
manner. In the other complexes the ligand acts as a κ2O,κN rion, perfect square-pyramid or trigonal-bipyramid geome-
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M. F. C. Guedes da Silva, A. J. L. Pombeiro et al.
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Figure 6. Molecular structure of complex 6 with atomic numbering scheme. Thermal ellipsoids are drawn at the 50% probability level.
Selected bond lengths [Å] and angles [°]: N1–N2 1.2810(18), N1–Cu1 1.9767(13), N3–Cu1 2.0235(13), O4–Cu1 1.9240(11), O6–Cu1
2.1690(14); N2–N1–Cu1 127.12(10), O4–Cu1–O1 171.22(5), N1–Cu1–N3 166.79(5), O4–Cu1–N1 88.81(5), O4–Cu1–N3 87.61(5). Selected
hydrogen bonds {d(H···A) [Å], Є(DHA) [°]}: O6–H6A···O2 1.93, 168.5; O6–H6B···O20 2.05(2), 166(3); O20–H20···O5 2.03, 162.9. Symmetry
operations to generate equivalent atoms: (i) –x, –y,1 – z; (ii) –1 + x, –y, 1 – z; (iii) 1 – x, –y, 1 – z; (iv) –1 + x, y, z; (v) –1 + x, –1 + y, z.
tries should have τ5 values of 0 or 1, respectively. The τ5 pentacoordinate complex 5 (entry 8), a possible precursor
values for our complexes with a pentacoordinate copper of an eventual less sterically hindered active metal centre
centre are listed in Table 1. Complexes 2 and 6 have τ5 val- under the reaction conditions.
ues very close to zero (0.08 and 0.07, respectively), which
Table 2. Peroxidative oxidation of cyclohexene to cyclohex-2-enol
fit a square-pyramid geometry. Complex 3, with τ5 values
of 0.67 and 0.63, support the assignment of a distorted tri-
gonal-bipyramidal geometry. The value of τ5 for complex 5
(0.21) indicates its immediacy to the square-pyramidal ge-
ometry.
and cyclohex-2-enone.[a]
Entry
Catalyst
T [K]
Ketone/
alcohol[b] [%][c] (TOF)[e]
Yield TON[d]
1
2
3
4
5
6
7
8
2
2
3
3
4
4
5
5
298
328
298
328
298
328
298
328
298
1.1
6.7
4.0
5.7
9.0
3.5
4.0
9.0
–
10.1
–
4.0
–
15.2 30 (3.7)
66.3 330 (13.7)
15.0 30 (3.7)
65.2 325 (13.5)
20.2 40 (2.5)
53.4 265 (11.0)
24.8 50 (6.2)
70.3 350 (14.6)
τ5 = (β – α)/60°
(1)
The crystal lattices in 2, 3 and 6 are stabilized by me-
dium-to-strong intermolecular hydrogen-bonding interac-
tions (Figures 2, 3 and 6) between the free water molecule
and the sulfonate or bridging water molecules (2), the N
atom of the pyrazolyl and the O-sulfonate (3) and the free
methanol molecule and the coordinated water or sulfonate
moieties (6).
9[f]
10
11
12
13
14[g]
15[h]
16[i]
17[j]
6
6
–
–
328
44.9 225 (9.4)
blank
Cu(CH3COO)2
298 or 328
328
–
32.4
–
–
–
–
1
Cu–A
B
C
D
328
323
393
323
3.4
–
2.1
0.1
79
51
–
(18.2)
–
31
–
353
4
Catalytic Activity of 2–6 in Cyclohexene Oxidation
[a] Selected data are presented. Reaction conditions (unless stated
otherwise): C6H10 (2.0 mmol at 298 K and 5.0 mmol at 328 K),
MeCN (5 mL), catalyst precursor (0.01 mmol), TBHP (5 mmol
added as a 70% aqueous solution). The data in entries 14–17 are
taken from the literature and are included for comparative pur-
poses. [b] Product molar ratio. [c] Moles of products/100 mol of
Complexes 2–6 were tested as catalysts for the selective
mild peroxidative oxidation (with TBHP) of cyclohexene to
cyclohex-2-enol and cyclohex-2-enone (Scheme 1). The
amount of oxidant, reaction time and temperature were
varied to optimize the yields of the desired products C6H10. [d] Overall TON values (mol of products/mol of catalyst).
[e] TOF = TON/h (values are given in parentheses) at 298 and
(Table 2, Figures S2 and S3 in the Supporting Information).
328 K for reaction times of 8 and 24 h, respectively. [f] Products
are negligible. [g] Cu catalyst immobilized on modified silica, A =
The results show that it is possible to obtain a good molar
ratio (9–10) of the products (entries 5, 8 and 10) with yields
of up to around 70% and TONs of up to 350 (entry 8).
Increasing the temperature (from 298 to 328 K) led to im-
proved yields and TONs (Table 2, Figure S2 for catalyst 5)
and under similar conditions, at 328 K, the activities of all
the complexes are comparable (entries 2, 4, 6 and 8). Never-
N-(hydroxyphenyl)salicyldimine; ketone/epoxide = 19; see ref.[8a] [h]
B = calcined (Cr)MCM-48 (MCM-48 = molecular sieves). Alcohol
was not observed; ketone/epoxide = 5.0 and ketone/1,2-cyclohex-
anediol = 11; see ref.[8b] [i] Cu–MOF (metal–organic framework),
C = [Cu(BF4)2(OH2···bpy)(bpy)], bpy = 4,4Ј-bipyridine. Ketone/2-
cyclohexene hydroperoxide = 0.07 and ketone/epoxide = 2.9; see
ref.[8e] [j] D = α-titanium–Cu–arsenate/TBHP; ketone/epoxide =
theless, the highest yield and TON were achieved for the 0.05; see ref.[8f]
2310
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Eur. J. Inorg. Chem. 2012, 2305–2313

Water-Soluble Copper(II) Complexes
75.468 MHz for 1H and 13C NMR, respectively. The chemical shifts
are reported in ppm with tetramethylsilane as the internal refer-
ence. IR spectra (4000–400 cm–1) were recorded with a BIO-RAD
FTS 3000MX instrument in KBr pellets. CHN elemental analyses
were carried out at the Microanalytical Service of the Instituto Su-
perior Técnico. All the synthetic work was performed in air at room
temperature. Chromatographic analyses were undertaken by using
a Fisons Instruments GC 8000 series gas chromatograph with a
DB-624 (J&W) capillary column (FID detector) and the Jasco-Bor-
win v.1.50 software. The organic products were quantified by the
Another important factor in the performance of the sys-
tem concerns the relative amount of TBHP oxidant. An
increase in the peroxide-to-catalyst molar ratio results in an
increase in the yield (Figure S3 for catalyst 5), for example,
from around 57 to 70% (24 h reaction time) upon changing
the ratio from 0.5 to 1.5 at 328 K.
Many metal complexes have been used as catalysts or
catalyst precursors for the peroxidative oxidation of cyclo-
hexene in homogeneous and heterogeneous catalysis,[8] such
as those quoted in entries 14–17 of Table 2 for comparative internal standard method; calibration curves with estimated errors
are given in Figure S4.
purposes. Some Cu–Schiff base complexes can lead to a
higher yield (79%) of products (entry 14),[8a] whereas a
heterogeneous chromium species leads to a yield (51%; en-
try 15)[8b] that is lower than those (ca. 65–70%) we observed
for 2, 3 and 5. However, these catalysts show lower selectivi-
ties than our systems, leading to lower ketone/alcohol mo-
lar ratios and also to epoxide formation. Various products
were also observed when the Cu–MOF (metal–organic
framework) [Cu(BF4)2(OH2···bpy)(bpy)] (bpy = 4,4Ј-bipyr-
idine) and α-titanium–Cu–arsenate were used as catalysts,
the main ones being 2-cyclohexene hydroperoxide and the
epoxide, respectively (Table 2, entries 16 and 17).[8e,8f]
Therefore our complex 5 (Table 2, entry 8) is among the
best catalyst precursors for selective allylic cyclohexene oxi-
dation, which results in the preferred formation of the
ketone.
2-[2-(4,4-Dimethyl-2,6-dioxocyclohexylidene)hydrazinyl]benzene-
sulfonic Acid (1): Compound 1 was synthesized by a modified[9d]
Japp–Klingemann reaction[9a–9c] between the aromatic diazonium
salt of 2-sulfoaniline and 5,5-dimethylcyclohexane-1,3-dione in
water solution containing sodium hydroxide.
Diazotization: 2-Sulfoaniline (4.325 g, 25 mmol) was dissolved in
water (50 mL) and NaOH (0.50 g, 12.5 mmol) was added. The
solution was cooled in an ice bath to 273 K and NaNO2 (1.725 g,
25 mmol) was added. HCl (5.00 mL) was then added in 0.5 mL
portions over 1 h. The temperature of the mixture should not ex-
ceed 278 K.
Azocoupling: NaOH (1.00 g, 25 mmol) was added to a mixture of
5,5-dimethylcyclohexane-1,3-dione (3.50 g, 25 mmol) in ethanol
(50 mL). The solution was cooled in an ice bath to around 273 K
and a suspension of 2-sulfoaniline diazonium chloride (see above)
was added in three portions under vigorous stirring over 1 h. The
precipitated yellow product was filtered off, dried in air and recrys-
tallized from ethanol to give crystals of suitable quality for X-ray
analysis.
Conclusions
A new water-soluble AHBD functionalized with a sulf-
onic acid group has been synthesized and fully charac-
H2L1 (1): Yield: 77% (based on 5,5-dimethylcyclohexane-1,3-di-
one), yellow powder soluble in water, methanol, ethanol, acetone
1
terized by elemental analysis, IR, H and 13C NMR spec-
and insoluble in chloroform. IR (KBr): ν = 3491 (νOH), 2954
˜
(νNH), 1664 (νC=O), 1630 (νC=O···H), 1578 (νC=N) cm–1. 1H
NMR (300.130 MHz, [D6]DMSO, internal TMS): δ = 0.98 (3 H,
CH3), 1.02 (3 H, CH3), 2.56 (2 H, CH2), 2.60 (2 H, CH2), 7.17–
7.84 (4 H, Ar–H), 15.28 (1 H, NH) ppm. 13C{1H} NMR
(75.468 MHz, [D6]DMSO, internal TMS): δ = 28.1 (CH3), 30.3
(CH3), 46.0 (Cipso), 51.8 (CH2), 52.2 (CH2), 116.4 (Ar-H), 125.3
(Ar-H), 127.5 (Ar-H), 130.6 (Ar-H), 130.7 (Ar-SO3H), 136.1
(C=N), 138.4 (Ar-NH-N), 193.3 (C=O), 195.2 (C=O) ppm.
C14H16N2O5S (324): calcd. C 51.72, H 4.48, N 8.53; found C 51.84,
H 4.97, N 8.64.
troscopy and single-crystal X-ray analysis. It has been
shown that it acts as a versatile ligand, forming new water-
soluble CuII–AHBD complexes of different nuclearities and
diverse structures simply by treating copper acetate with
AHBD in the absence or presence of a coordinating N spe-
cies such as 3,5-dimethyl-1H-pyrazole, cyanoguanidine,
2,2Ј-bipyridine or pyrazine. Their structural diversity is re-
flected in the important roles played by AHBD and the
auxiliary ligands in the assembly of the resulting frame-
works. Thus, the tuneable synthesis of a variety of com-
plexes of different geometries and nuclearities by a simple
and convenient method has been achieved.
Synthesis of Copper(II) Complexes 2–6: Compound 1 (1 mmol) was
dissolved in water (30 mL) and then Cu(CH3COO)2·H2O (1 mmol)
and (in the cases of 3–6, 1 mmol of) 3,5-dimethyl-1H-pyrazole (dp),
cyanoguanidine (cyg), 2,2Ј-bipyridine (bpy) or pyrazine (py),
respectively, were added. The mixture was stirred at reflux for
15 min and left to slowly evaporate. After evaporation of the sol-
vent, the microcrystalline product was recrystallized from methanol
and water (2:1, v/v). All the complexes are soluble in water, meth-
The thus synthesized water-soluble CuII–AHBD com-
plexes can be used as efficient and selective catalysts for the
peroxidative oxidation of cyclohexene to cyclohex-2-enol
and cyclohex-2-enone under mild conditions to give good
yields and TONs. This approach deserves further explora-
tion in the search for other types of functionalized water- anol, ethanol and DMSO.
soluble AHBD ligands and metal ions.
2: Yield: 54% (based on Cu). IR (KBr): ν = 3536 (br. s, νOH),
˜
1674 (s) (νC=O), 1621 δ(OH, H2O), 1602 (s) (νC=N) cm–1.
C28H32Cu2N4O12S2 (807.8): calcd. C 41.63, H 3.99, N 7.54; found
C 41.32, H 3.73, N 7.46.
Experimental Section
Materials and Instrumentation: The 1H and 13C NMR spectra were
recorded at room temperature with a Bruker Avance II + 300 (Ul-
traShieldTM Magnet) spectrometer operating at 300.130 and
3: Yield: 63% (based on Cu). IR (KBr): ν = 2360 (br. s, νNH), 1637
˜
(s, νC=O), 1528 (s, νC=N) cm–1. C24H30CuN6O5S (578.1): calcd. C
49.86, H 5.23, N 14.54; found C 49.67, H 5.13, N 14.45.
Eur. J. Inorg. Chem. 2012, 2305–2313
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2311

M. F. C. Guedes da Silva, A. J. L. Pombeiro et al.
FULL PAPER
Table 3. Crystal data and structure refinement details for compounds 1–6.
1
2
3
4
5
6
Formula unit
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
Β [°]
γ [°]
C14H15N2O5S C28H32Cu2N4O12S2 C24H30CuN6O5S C28H28CuN4O10S2 C24H22CuN4O5S C34H44Cu2N6O14S2
323.34
orthorhombic triclinic
P212121
6.4413(2)
14.9502(5)
19.9725(6)
90.00
90.00
90.00
4
807.78
578.14
monoclinic
P21/n
19.480(2)
12.3303(14)
23.349(3)
90.00
112.211(5)
90.00
8
708.20
542.06
monoclinic
P21/c
11.0281(12)
27.196(3)
8.6830(9)
90.00
92.217(4)
90.00
951.95
triclinic
triclinic
¯
¯
¯
P1
P1
P1
11.2517(4)
11.3996(3)
13.4223(5)
113.166(3)
91.521(2)
101.5220(10)
2
10.0268(3)
12.5244(4)
16.2570(6)
69.3980(10)
80.837(2)
80.9000(10)
2
7.7982(2)
9.5126(2)
13.4944(3)
91.5850(10)
93.436(2)
101.1300(10)
1
Z
4
Volume [Å3]
Dc [gcm–3]
μ(Mo-Kα) [mm–1]
1923.33(11)
1.117
0.188
1540.30(9)
1.742
1.589
5192.2(11)
1.479
0.969
1875.05(11)
1.254
0.745
2602.2(5)
1.384
0.960
979.65(4)
1.614
1.267
Reflections collected 12817
22226
6314
0.0712
35389
9482
0.3189
18854
6823
0.0317
19701
5724
0.1470
0.0664, 0.1636
24151
6528
0.0379
0.0314, 0.0752
Unique reflections
Rint
4148
0.0592
Final R1,[a] wR2[b]
(IՆ2σ)
0.0916, 0.2459 0.0420, 0.0983
0.0763, 0.0937 0.0454, 0.1308
GOF on F2
1.078 1.015
0.886 1.058
0.838
0.983
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]} .
2
2 2
½
4: Yield: 61% (based on Cu). IR (KBr): ν = 3343 (br. s, νOH),
rium in the structure of 4, we believe the disordered water mole-
˜
1655 (s, νC=O), 1630 (δOH, H3O+), 1553 (s, νC=N) cm–1. cules are protonated.
C28H34CuN4O12S2 (746.26): calcd. C 45.06, H 4.59, N 7.51; found
C 45.01, H 4.52, N 7.54.
CCDC-850011 (for 1), -850012 (for 2), -850013 (for 3), -850014 (for
4), -850015 (for 5) and -850016 (for 6) 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.
5: Yield: 53% (based on Cu). IR (KBr): ν = 1637 (s, νC=O), 1601
˜
(s, νC=O), 1535 (s, νC=N) cm–1. C24H22CuN4O5S (542.1): calcd. C
53.18, H 4.09, N 10.34; found C 53.23, H 4.45, N 10.47.
Oxidation of Cyclohexene: The reaction mixtures were prepared as
follows: MeCN (5.0 mL), C6H10 (2.00–5.00 mmol) and TBHP
(70% solution in H2O, 2.50–7.50 mmol), in this order, were added
to complex 2–6 (0.010 mmol) in a reaction flask. The reaction mix-
ture was stirred for the required time, typically 8 h, at room tem-
perature (ca. 298 K) or for 24 h at 338 K in air. Then cyclooctane
(10 μL, as internal standard) and diethyl ether (2.0 mL, to extract
the substrate and the products from the reaction mixture) were
added. The resulting mixture was stirred for 15 min and then a
sample taken from the organic phase was analysed by GC. Blank
experiments were performed and confirmed that no cyclohexene
oxidation products were formed in the absence of the metal cata-
lyst.
6: Yield: 56% (based on Cu). IR (KBr): ν = 3220 (br. s, νOH),
˜
1658 (s, νC=O), 1632 (δOH, H2O), 1509 (s, νC=N) cm–1.
C33H40Cu2N6O13S2 (919.9): calcd. C 43.09, H 4.38, N 9.14; found
C 43.05, H 4.21, N 9.08.
X-ray Structure Determinations: X-ray quality single-crystals of
complexes 1–6 were immersed in cryo-oil, mounted in a Nylon loop
and measured at a temperature of 150 K (Table 3). Intensity data
were collected by using a Bruker AXS-KAPPA APEX II dif-
fractometer with graphite-monochromated Mo-Kα (λ = 0.71073)
radiation. Data were collected by using ω scans of 0.5° per frame
and a full sphere of data were obtained. Cell parameters were re-
trieved by using the Bruker SMART software and refined by using
Bruker SAINT[12a] on all the observed reflections. Absorption cor-
rections were applied by using the SADABS software.[12b] The
structures were solved by direct methods by using the SHELXS-97
package[12c] and refined with SHELXL-97.[12d] Calculations were
performed by using the WinGX System Version 1.80.03.[12b] All
hydrogen atoms were inserted at calculated positions. Least-squares
refinements with anisotropic thermal motion parameters for all the
non-hydrogen atoms and isotropic parameters for the remaining
atoms were employed. Disordered solvents were present in the
structures of complexes 1, 4 and 5. Because no obvious major site
occupations were found for those molecules, it was not possible to
model them. PLATON/SQUEEZE[12d] was used to correct the data
and potential volumes of 483.3 (for 1), 463.7 (for 4) and 434.0 (for
5) Å3 were found with, respectively, 217, 148 and 190 electrons per
unit cell worth of scattering. The electron counts suggest the pres-
ence of around two molecules of ethanol (for 1), around two mole-
cules of water (for 4) and around one molecule of methanol and
one molecule of water (for 5) per unit cell. The modified datasets
improved the R1 factor markedly. To accomplish charge equilib-
Supporting Information (see footnote on the first page of this arti-
cle): Packing diagrams of compound 2, effects of temperature and
TBHP/C6H10 molar ratio on the overall yield of cyclohex-2-enol
and cyclohex-2-enone, calibration curves for determination of cy-
clohexene-1-one and cylohexene-2-ol.
Acknowledgments
This work was partially supported by the Fundação do Ministério
de Ciência e Tecnologia (FCT) (project numbers PTDC/QUI-QUI/
102150/2008 and PEst-OE/QUI/UI0100/2011) and “Science” pro-
grams. The authors acknowledge the Portuguese NMR Network
for providing access to the NMR facility.
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Received: December 5, 2011
Published Online: March 14, 2012
Eur. J. Inorg. Chem. 2012, 2305–2313
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2313