New organic picolylamine-type ligands and electrochemical study of their complexation with Cu(MeCN)4ClO4

Article abstract of DOI:10.1007/s11172-011-0044-8

A series of novel organic ligands with dipicolylamine and disulfide groups connected by polymethylene, alkylaryl, alkoxyaryl, or alkoxycarbonyl linker was synthesized. The electrochemical study by cyclic voltammetry was carried out for two synthesized lig

Full text of DOI:10.1007/s11172-011-0044-8

Russian Chemical Bulletin, International Edition, Vol. 60, No. 2, pp. 261—268, February, 2011
261
New organic picolylamineꢀtype ligands and electrochemical study
of their complexation with Cu(MeCN)4ClO4
A. G. Majouga, R. B. Romashkina, A. S. Kashaev, Е. К. Beloglazkina, А. А. Moiseeva, and N. V. Zyk
Department of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 939 4652. Eꢀmail: bel@org.chem.msu.ru
A series of novel organic ligands with dipicolylamine and disulfide groups connected by
polymethylene, alkylaryl, alkoxyaryl, or alkoxycarbonyl linker was synthesized. The electroꢀ
chemical study by cyclic voltammetry was carried out for two synthesized ligands, and the
formation of the complexes with Cu(MeCN)ClO4 in the solution or on the gold electrode
surface was established. The complex of CuI with 1,24ꢀbis[N,Nꢀbis(2ꢀpyridylmethyl)ꢀ
glycinoyloxy]ꢀ12,13ꢀdithiatetracosane chemisorbed on the Au electrode is capable of binding
molecular oxygen from solution.
Key words: dipicolylamines, disulfides, copper(I) complexes, chemisorption, gold, cyclic
voltammetry.
Copper complexes with nitrogenꢀcontaining ligands
can be used as lowꢀmolecularꢀweight models of enzymes
hemocyanine, tyrosinase, and catechol oxidases (see, e.g.,
Refs 1—5). These redox enzymes act as oxygen carriers
(hemocyanine6—8), catalyze the orthoꢀhydroxylation of
phenols to the corresponding pyrocatechols (tyrosinase7,9),
or the oxidation of pyrocatechols to oꢀquinones (catechol
oxidase9,10). Diꢀ and tripyridylalkylamines are presently
considered to be among the most promising models of
active centers of copperꢀcontaining oxygenases.1—5,11,12
The copper(I) complexes with these ligands have been synꢀ
thesized to date and show a high capability of binding
oxygen.11,12
plexes immobilized on the solid surface are described (see,
e.g., Refs 14—16).
In the present work, we describe the synthesis of novel
organic ligands containing the dipicolylamine and disulꢀ
fide groups. Such a combination of structural fragments
imparts to the molecules the ability to both form coordiꢀ
nation bonds of the nitrogen atoms of the amino groups
and to chemisorb on the gold surface with the formation
of the Au—S bond. The formation of the copper(I) comꢀ
plexes with such ligands, including those chemisorbed on
the Au electrode surface, and molecular oxygen binding by
the complex immobilized on the Au surface were studied.
Metal complex catalysts immobilized on the metallic
surface have several advantages for the use in catalysis.
The immobilization of a homogeneous catalyst on the surꢀ
face imparts practical advantages of heterogeneous catalyꢀ
sis to the performed reaction and retains advantages of
homogeneous catalytic reactions. A doubtless advantage
of immobilized catalysts is the easiness of catalyst separaꢀ
tion from reactants and reaction products and the simpliꢀ
fication of the procedure of their repeated use. It is imporꢀ
tant that catalysts with high molecular weight immobiꢀ
lized on the polymer or metal support are nonꢀtoxic and
safe and, hence, they are insoluble in water and organic
solvents (in some cases, this makes it possible to assign
these reactions to the area of "green chemistry").13 Selfꢀ
organized monolayers capable of binding metal ions are
formed upon adsorption of thiols and disulfides containꢀ
ing additional donor groups on the gold surface. The exꢀ
amples of performing catalytic reactions using metal comꢀ
Results and Discussion
Synthesis of the ligands. The general structure of the
target organic ligands is given below. All synthesized comꢀ
pounds contain the dipicolyl fragment connected with the
disulfide group by a linker being the polymethylene, alkylꢀ
aryl, alkoxyaryl, or alkoxycarbonyl group.
Two methods were used for the synthesis of the target liꢀ
gands with different linkers
(Scheme 1). One of the
methods is based on the
alkylation of dipicolylamine
(1) with alkyl halide (route
А), and another method is
based on the reductive amiꢀ
nation of the correspondꢀ
ing aldehyde with dipicolꢀ
ylamine 1 (route B).
Linker
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 255—262, February, 2011.
1066ꢀ5285/11/6002ꢀ261 © 2011 Springer Science+Business Media, Inc.

262
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 2, February, 2011
Majouga et al.
Scheme 1
tained, in turn, from 1,6ꢀdibromohexane and potassium
phthalimide according to the Garbriel method.
Scheme 3
RHal = BrC6H12Br, 4ꢀClCH2C6H4SMe, BrCH2COOH
RCHO = 4ꢀMeSC6H4CHO, [4ꢀHC(O)C6H4S]2,
[4ꢀHC(O)C6H4OC11H22S]2
Compound 2 containing the alkanediyl linker was synꢀ
thesized following route A (Scheme 2). First, the reaction
of dipicolylamine 1 with 1,6ꢀdibromohexane in the presꢀ
ence of BunLi at –70 °C afforded monobromide 3. A threeꢀ
fold excess of the alkylating reactant was used to obtained
the product of substitution of only one bromine atom in
α,ωꢀdibromoalkane. The nucleophilic substitution of the
sulfurꢀcontaining group for the second bromine was perꢀ
formed by the treatment with potassium thioacetate in
MeOH; when the reaction product is isolated, the primꢀ
arily formed thiol is oxidized with air oxygen to disulfide 2.
Scheme 2
Reagents and conditions: i. DMF; ii. (1) Na2S2O6, MeOH, H2O,
(2) I2; iii. NH2NH2•H2O, EtOH, 80 °C; iv. (1) KOH, EtOH,
(2) NaBH3CN, 2ꢀPyCHO, AcOH, MeOH.
Apart the ligands bearing the disulfide group, we synꢀ
thesized compound 7 containing the methylthio group
(Scheme 4). It is known that aryl alkyl sulfides, similarly
to thiols and disulfides, are capable of chemisorbing on
the Au surface to form selfꢀorganized monolayers, which
are usually less ordered and are formed with a lower rate
than alkanethiols and dialkyl disulfides.17 Compound 7
can be synthesized by two alternative routes (see Scheme 1).
The first route (see Scheme 4) is the condensation of
4ꢀmethylthiobenzaldehyde with dipicolylamine 1 in the
presence of sodium cyanoborohydride and produces comꢀ
pound 7 in 73% yield. The second route is the nucleophilic
substitution of the chlorine atom in 4ꢀmethylthiobenzyl
chloride under the action of 1 in the presence of potassium
carbonate. A higher yield (84%) of target product 7 is
achieved in the second case.
Reagents and conditions: i. BunLi, THF; ii. (1) AcSK, MeOH,
65 °C, (2) NH4Cl, H2O, O2 (air).
An alternative method of synthesis of ligand 2 (Scheme 3)
is the reductive amination of two equivalents of 2ꢀpyridineꢀ
carbaldehyde with diamino disulfide 4, which was obꢀ

Disulfide dipicolylamines
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 2, February, 2011
263
Scheme 4
Scheme 6
Reagents and conditions: i. 1, NaBH3CN, AcOH, MeOH; ii. 1,
K2CO3, DMF.
Ligand 8, being close in structure to compound 7 and
differing by the presence of the disulfide group instead of
the methylsulfide one, was synthesized in 78% yield by the
reaction of bis(4ꢀformylphenyl) disulfide with dipicolylꢀ
amine 1 in the presence of sodium cyanoborohydride
(Scheme 5).
Reagents and conditions: i. I2, MeOH; ii. 4ꢀHOC6H4CHO,
K2CO3, DMF; iii. 1, NaBH3CN, AcOH, MeOH.
Scheme 5
reaction with dibromide 10. Ligand 12 was synthesized in
88% yield at the second stage of the synthesis.
Scheme 7
Reagents and conditions: 1, NaBH3CN, AcOH, MeOH.
To obtain ligand 9 containing the aryloxyalkyl fragꢀ
ment as a linker, we used the sequence of reactions
(Scheme 6) including the synthesis of dibromo disulfide
10 by the oxidation of 11ꢀbromoꢀ1ꢀundecanethiol with
iodine, the alkylation of 4ꢀhydroxybenzaldehyde with
compound 10 in the presence of potassium carbonate in
DMF, and the subsequent condensation of obtained prodꢀ
uct 11 with dipicolylamine 1 in МеОН in the presence of
sodium cyanoborohydride.
The synthesis of ligand 12 bearing the ester group was
performed in two stages from dipicolylamine 1, bromoaceꢀ
tic acid, and dibromo disulfide 10 (Scheme 7). At the first
stage, dipicolylamine 1 was alkylated with bromoacetic
acid in the presence of potassium hydroxide. Isolated poꢀ
tassium salt 13 was used in the nucleophilic substitution
Reagents and conditions: i. 1, KOH, H2O; ii. 10, K2CO3, DMF.
Electrochemical properties of ligands 7 and 12 and their
complexes with СuI. The possibility of formation of coorꢀ

264
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 2, February, 2011
Majouga et al.
Table 1. Oxidation (EOx) and reduction (ERed) potentials of
Cu(MeCN)4ClO4, ligands 7 and 12, and their complexes with
Cu(MeCN)4ClO4 measured by the CV and RDE methods
(MeCN, 0.1 M Bu4NClO4, vs Ag/AgCl/KCl (sat.))
dination compounds with Сu(MeCN)4ClO4 by ligands 7
and 12, chemisorption of ligand 12 and its copperꢀconꢀ
taining complex on the Au electrode, and binding of moꢀ
lecular O2 by the latter in solution was studied by the
methods of cyclic voltammetry (CV) and rotating disk
electrode (RDE). The electrochemical oxidation and reꢀ
duction potentials measured vs Ag/AgCl/KCl (sat.) are
listed in Table 1.
The reduction of ligand 7 in MeCN proceeds as one
twoꢀelectron stage, while the oxidation proceeds in three
stages for the CV method and in two stages for the RDE
method with the current ratio 1 : 1.5, which indicates its
stepwise oxidation (see Table 1, Fig. 1).
The starting copper(I) salt, Сu(MeCN)4ClO4, on the
GC electrode in MeCN is oxidized quasiꢀreversibly at
Epa = 1.08 V and is reduced at Epс = –0.60 V (see Table 1).
The Cu0 complex formed upon the electroreduction of
Cu(MeCN)4ClO4 is restrictedly stable, which is confirmed
by the presence of the lowꢀintensity oxidation peak of
Cu0 → CuI (–0.46 V) and the peak of desorption of metalꢀ
lic copper from the electrode surface at –0.13 V in the
reverse scan of the CV curve. Note that at the Au electrode
the oxidation of Сu(MeCN)4ClO4 proceeds reversibly
(Epa/Epс = 1.04/0.97), whereas the reduction occurs with
the formation of metallic copper (Epс/Epа = –0.49/–0.20
(desorption).
Immediately after mixing solutions of ligand 7 and
Сu(MeCN)4ClO4 in a solution of МеCN, the peaks of
oxidation and reduction of the free salt disappear from the
CV curve (see Fig. 1) and the peaks of the complex appear.
The reversible oxidation peak of CuI → CuII for the comꢀ
plex is observed at Epa/Epс = 0.30/–0.23 V, i.e., a very
considerable shift of the potential to the cathodic region
(by 780 mV) compared to the oxidation of the salt is obꢀ
served. The potential of the reduction peak of CuI → Cu0
changes insignificantly (shift by 30 mV to the cathodic
Red
Red
Ox
Ox
Compound
Ep
E1/2
Ep
E1/2
GC electrode
–
Cu(MeCN)4ClO4
–0.60 –0.48
/–0.46
–0.13 a 0—
1.08 1.10
/0.92
—
0—
7
–2.51 –2.50 (2е) 0.94 0.99 (1е)
0—
0—
1.33 1.42
(1.5е)
0—
0—
1.60 0—
0.30 0.24
/0.23 b
–
7 + Cu(MeCN)4ClO4
–0.63 –0.65
/–0.52
–0.12 a –0.86
0— –1.62
–0.75 d 0—
0.80 1.47
1.60 0—
0.37 0—
0.74 0—
12 с
–1.51
–1.98
–2.31
0—
0—
0—
0—
0—
0—
0—
Au electrode
12 e
12 d
–0.73 d 0—
0.53 0—
0.95 0—
–1.46
–1.67
–0.93
–0.53
0—
0—
0—
0—
0—
0—
0.28 0—
0.25 0—
/0.14
– f
12 + Cu(MeCN)4ClO4
–0.98
–1.66
–1.76
/–0.60
0.23
/0.14
–0.51
–0.98
0.28
0—
0—
0—
0.92 0—
0—
0—
0.92 0—
– g
– h
12 + Cu(MeCN)4ClO4
0—
0.96 0—
0—
0—
0—
0—
0—
0—
0—
12 + Cu(MeCN)4ClO4
0.94 0—
/0.14
–0.88
0—
0— 0—
5 μA
Note. Ep are the cathodic peak potentials measured by the CV
method (200 mV s–1); the potentials of the peaks at reverse scans
of the CV curves are presented under slashes; E1/2 are the halfꢀ
wave potentials measured by the RDE method (2800 rpm); the
number of electrons transferred at each stage is given in parenꢀ
theses.
a Desorption potential.
b The initial potential is 0.7 V.
c Solution in DMF.
d Adsorption potential.
e In solution.
f In monolayer.
g In monolayer after purging with O2.
h In monolayer after removal of O2.
1.0
0
–1.0
–2.0
E/V
Fig. 1. Cyclic voltammograms (GC electrode, МеCN,
Bu4NClO4) of ligand 7 (dashed lines) and its complex with
Cu(MeCN)4ClO4 (solid lines); concentration 10–3 mol L–1. The
curve at the left was obtained by the anodic scan, and the curves
at the right are the cathodic scan.
region of potentials, see Table 1). As the starting salt, the
Cu0 complex formed in this process is restrictedly stable
(the lowꢀintensity oxidation peak of Cu0 → CuI at –0.52 V

Disulfide dipicolylamines
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 2, February, 2011
265
and the peak of desorption of Cu0 at –0.12 V are detected
on the reverse scan of the voltammetric curve).
a
The prolong O2 purging through a solution of the comꢀ
plex does not result in a change in the peak potentials of
the transitions CuI → CuII and CuI → Cu0 or the appearꢀ
ance of any new peaks in the CV curve. Evidently, this
complex does not react with oxygen under the experimenꢀ
tal conditions.
2 μA
Disulfide 12 has a very low solubility in MeCN and,
hence, its electrochemical behavior was studied in DMF,
where the peaks observed in the CV curves are most disꢀ
tinct. Compound 12 is oxidized in two stages, whereas its
reduction proceeds in three stages, the first of which
(–1.51 V) corresponds to the reduction of the S—S bond,
and the second stage (–1.98 V) corresponds to the reducꢀ
tion of the ester moiety.18 Note that the reduction of comꢀ
pound 12 in МеCN on the Au electrode is accompanied
by the formation of three peaks, the first of which is the
adsorption one and the second and third peaks correspond
to the reduction of the S—S bond and the ester group,
respectively, and the potentials are shifted to the anodic
region compared to the GC electrode (see Table 1, Fig. 2).
The chemisorption of disulfide 12 on the Au electrode
surface results in the disappearance of the adsorption preꢀ
peak at –0.75 V and the peak of S—S bond reduction in
the CV curve, whereas the reduction peak of the S—Au
bond appears at –0.93 V (see Table 1 and Refs 19—21).
The behavior of chemisorbed complex 12 with CuI in
МеCN was studied after the Au electrode was stored in
a solution of compound 12 in DMF (10–3 mol L–1) for 3 h.
In this case, according to the literature data, disulfide is
chemisorbed on the metal surface with the S—S bond
cleavage and the formation of the Au—S bond. Then the
electrode was consequently washed with DMF and МеCN
and placed in a solution of Сu(MeCN)4ClO4 in MeCN
for 6 h to form the coordination compound on the elecꢀ
trode surface.
b
1 μA
c
1 μA
The formation of chemisorbed complex 12 with
Сu(MeCN)4ClO4 is confirmed by the appearance in the
1
0
–1
E/V
Fig. 3. Cyclic voltammograms (MeCN, Bu4NClO4, monolayers
on the Au electrode) of the complex of ligand 12 with
Сu(MeCN)4ClO4 before (a) and after purging of the solution
with oxygen for 40 min (b) (the CV curve was detected for the
solution containing an excess of oxygen; therefore, after passing
a potential of ~0.6 V, a very intense peak of О2 reduction is
observed in the cathodic region) and after oxygen was removed
from the solution with argon for 40 min (c).
5 μA
CV curve of the oxidation CuI → CuII (Epа/Epс
=
= 0.25/0.14) and reduction CuI → Cu0 (Epс = –0.53 V)
peaks (Fig. 3, a).
1.0
0
–1.0
–2.0
E/V
After the electrochemical cell containing the Au elecꢀ
trode with the monolayer of the complex of ligand 12 with
CuI was purged with O2 for 40 min, the shape of the CV
Fig. 2. Cyclic voltammograms (МеCN, Bu4NClO4) of ligand 12
on the Au electrode in solution (dashed lines) and in the monoꢀ
layer (solid lines).

266
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 2, February, 2011
Majouga et al.
Nꢀ(6ꢀBromohexyl)ꢀN,Nꢀbis(2ꢀpyridylmethyl)amine (3).
A twoꢀnecked flask preꢀheated and then cooled to room temperꢀ
ature in an argon flow was filled with a solution of dipicolylꢀ
amine 1 (0.5 g, 2.5 mmol) in absolute THF (15 mL). The flask
was cooled to –70 °C, and a 1.6 М solution of nꢀbutyllithium in
hexane (1.73 mL, 2.8 mmol) was syringed. The reaction mixture
was stirred for 15 min at the same temperature, and then 1,6ꢀdiꢀ
bromohexane (1.5 g, 6.3 mmol) in absolute THF (5 mL) was
added. The resultant solution was stirred for 12 h, gradually
raising temperature to ambient. Water (20 mL) was added to the
solution, and organics was extracted with CH2Cl2 (3×20 mL).
The organic fractions were dried with anhydrous Na2SO4. The
solvent was evaporated under reduced pressure, and the product
was isolated by column chromatography on silica gel (petroleum
ether—ethyl acetate, 6 : 1). Compound 3 was obtained as a yelꢀ
low oil in a yield of 0.56 g (62%). 1H NMR (CDCl3), δ: 8.49
(d, 2 H, HC(6), HC(6´), Py, J = 4.9 Hz); 7.77 (td, 2 H, HC(4),
HC(4´), Py, J1 = 1.7 Hz, J2 = 7.7 Hz); 7.52 (d, 2 H, HC(3),
HC(3´), Py, J = 7.7 Hz); 7.25 (td, 2 H, HC(5), HC(5´), Py,
J1 = 1.5 Hz, J2 = 6.3 Hz); 3.75 (s, 4 H, CH2Py); 3.47 (t, 2 H,
CH2Br, J = 6.7 Hz); 2.46 (t, 2 H, CH2N, J = 7.1 Hz); 1.73
(m, 2 H, CH2); 1.48 (m, 2 H, CH2); 1.25 (m, 4 H, (CH2)2). MS,
m/z (Irel (%)): 362 (10%) [M]+.
6,6´ꢀDithiobis[N,Nꢀ(2ꢀpyridylmethyl)hexaneꢀ1ꢀamine] (2).
A. Potassium thioacetate (0.53 g, 4. 6 mmol) was added to
a solution of compound 3 (0.56 g, 1.6 mmol) in MeOH (25 mL).
The mixture was refluxed for 12 h and cooled to ~20 °C. A satuꢀ
rated solution of NH4Cl (30 mL) was added, and organics was
extracted with CH2Cl2 (3×20 mL). The organic fractions were
dried with Na2SO4, and the solvent was evaporated under reꢀ
duced pressure. Compound 2 was obtained as a yellow oil in
a yield of 0.43 g (86%). 1H NMR (CDCl3), δ: 8.49 (d, 2 H, HC(6),
HC(6´), Py, J = 4.5 Hz); 7.66 (td, 2 H, HC(4), HC(4´), Py,
J1 = 1.8 Hz, J2 = 7.8 Hz); 7.57 (d, 2 H, HC(3), HC(3´), Py,
J = 7.8 Hz); 7.16 (td, 2 H, HC(5), HC(5´), Py, J1 = 1.3 Hz,
J2 = 5.7 Hz); 3.91 (s, 4 H, CH2Py); 2.77 (t, 2 H, CH2S, J = 7.2 Hz);
2.62 (t, 2 H, CH2N, J = 6.7 Hz); 1.56 (m, 2 H, CH2); 1.40
(m, 2 H, CH2); 1.25 (m, 4 H, (CH2)2). MS, m/z (Irel (%)): 629
(12%) [M]+.
B. 2ꢀ(6ꢀBromohexyl)ꢀ1Hꢀisoindoleꢀ1,3(2H)ꢀdione (5).
A solution of 1,6ꢀdibromohexane (10 g, 43.2 mmol) in DMF
(5 mL) was added to a suspension of potassium phthalimide (1.94 g,
10.5 mmol) in DMF (10 mL). The reaction mixture was stirred
for 48 h. After reaction completion, water (5 mL) was added to
the mixture, and organics was extracted with CH2Cl2 (3×10 mL).
The combined organic extracts were washed with brine and waꢀ
ter and dried with anhydrous Na2SO4. The solvent was evapoꢀ
rated under reduced pressure. Compound 5 was obtained as
a white powder, m.p. 63 °C, in a yield of 2.5 g (78%). Found (%):
С, 53.96; H, 5.12; N, 4.35; Br, 25.53. С14H16BrNO2. Calculatꢀ
ed (%): С, 54.21; H, 5.20; N, 4.52; Br, 25.76. 1H NMR (CDCl3),
δ: 7.87 (d, 2 H, HC(3), HC(6), Ph, J = 5.4 Hz); 7.74 (d, 2 H,
HC(4), HC(5), Ph, J = 5.4 Hz); 3.71 (t, 2 H, CH2N, J = 7.3 Hz);
3.42 (t, 2 H, CH2Br, J = 6.8 Hz); 1.88 (m, 2 H, CH2); 1.72
(m, 2 H, CH2); 1.51 (m, 2 H, CH2); 1.40 (m, 2 H, CH2).
2,2´ꢀ[Dithiobis(hexaneꢀ1,6ꢀdiyl)]bis[1Hꢀisoindoleꢀ1,3(2H)ꢀ
dione] (6). A solution of sodium thiosulfate (0.5 g, 3.14 mmol)
was added to a solution of compound 3 (1 g, 3.2 mmol) in
a МеОН—water (1 : 1) mixture. The reaction mixture was reꢀ
fluxed for 24 h with stirring. Iodine was added to the resultant
solution under reflux until stable color appeared, and then the
changes dramatically: a cathodic peak corresponding to
the transition CuII → CuI (Epс = 0.23 V) appears. The
presence of this peak shows that, when binding with O2,
the copper in the composition of the complex is oxidized
to CuII. In addition, in the voltammetric curve, the reꢀ
duction peak of CuI → Cu0 is shifted to the anodic region
and a new peak appears at –0.18 V (see Fig. 3, b), which
probably corresponds to the reduction of the oxygenꢀconꢀ
taining moiety of the product.
When the cell is purged with argon for 40 min after the
formation of the oxygenꢀcontaining complex, the reducꢀ
tion peak of CuII → CuI (Epс = 0.28 V) is observed in
the CV curve (see Fig. 3, c) and the reduction peak of
CuI → Cu0 of the starting complex at –0.53 V is absent.
These data indirectly indicate that the oxidation with oxyꢀ
gen of the starting copperꢀcontaining complex of ligand
12 is irreversible under these conditions.
Thus, the electrochemical data confirm the possibility
of formation of the chemisorbed complex of ligand 12
with Сu(MeCN)4ClO4 on the Au electrode surface and
the binding of molecular oxygen by this complex. It seems
promising to study this complex as a catalyst of redox
reactions, first of all, phenol and pyrocatechol oxidation.
At the same time, according to the CV data, ligand 7
containing the methylthio group and benzyl linker, which
links the latter with the dipicolylamine fragment, forms
no complexes with CuI in a MeCN solution.
Experimental
The reaction course and individual character of products
were monitored by thin layer chromatography on an immobilized
silica gel layer (Silufol). 1Н and 13C NMR spectra were recorded
on a Bruker Avance instrument at 400 and 100 MHz, respectiveꢀ
ly. IR spectra were measured on a URꢀ20 instrument in Nujol,
and electronic spectra in the UV and visible regions were reꢀ
corded on a Hitachi Uꢀ2900 instrument. Mass spectra were obꢀ
tained on a Finnigan MAT 95 XL instrument (direct inlet, elecꢀ
tron impact, 70 eV).
A PIꢀ50ꢀ1.1 potentiostat switched to a PRꢀ8 programmer
was used for electrochemical studies. The working electrodes
were glassy carbon (GC) (d = 2 mm), platinum (d = 3 mm), and
gold (d = 2 mm) disks, the supporting electrolyte was a 0.1 М
solution of Bu4NClO4 in MeCN, the reference electrode was
Ag/AgCl/KCl (sat.), and a Pt plate served as an auxiliary elecꢀ
trode. The surface of working electrodes was polished with
an alumina powder with the particle size less than 10 μm (Sigꢀ
ma—Aldrich). For CV studies, the potential sweep rate was
200 mV s–1, and for the RDE method it was 20 mV s–1. The
potentials are presented with allowance for iRꢀcompensation.
All measurements were carried out under dry argon; and the
samples were dissolved in a beforehand deaerated solvent. The
number of transferred electrons in redox processes was deterꢀ
mined by comparing the limiting current of the wave in RDE
experiments with the current of oneꢀelectron oxidation of ferꢀ
rocene taken in an equal concentration.
11ꢀBromoꢀ1ꢀundecanethiol22 and bis(4ꢀformylphenyl) diꢀ
sulfide23 were synthesized following the known procedures.

Disulfide dipicolylamines
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 2, February, 2011
267
mixture was refluxed for 4 h. Sodium sulfite was added until the
solution decolorized to remove a iodine excess. The precipitate
formed was filtered off and purified by flash chromatography
(hexane—diethyl ether, 1 : 1). Compound 6 was obtained as
a white powder, m.p. 59 °C, in a yield of 0.79 g (94%). Found (%):
С, 63.87; H, 5.02; N, 5.12; S, 12.09. С28H32N2O4S2. Calculatꢀ
ed (%): С, 64.09; H, 6.15; N, 5.34; S, 12.22. 1H NMR (CDCl3),
δ: 7.83 (d, 2 H, HC(3), HC(6), Ph, J = 5.4 Hz); 7.70 (d, 2 H,
HC(4), HC(5), Ph, J = 5.4 Hz); 3.67 (t, 2 H, CH2N, J = 7.6 Hz);
2.64 (t, 2 H, CH2S, J = 7.1 Hz); 1.65 (m, 4 H, (CH2)2); 1.40
(m, 2 H, (CH2)2).
1,14ꢀDiammonioꢀ7,8ꢀdithiatetradecane dichloride (4).
A mixture of compound 6 (0.79 g, 1.5 mmol), hydrazine hydrate
(0.24 g, 4.8 mmol), and EtOH (10 mL) was refluxed for 1 h
under argon. After the starting compounds were completely disꢀ
solved, the formation of a colorless precipitate of the reaction
production was observed. The solvent was removed under reꢀ
duced pressure, and 1 М HCl (15 mL) was added to the residue.
The mixture was refluxed with stirring for 1 h. The solvent was
evaporated in vacuo, and EtOH (30 mL) was added to the resiꢀ
due. The undissolved precipitate was filtered off, and the prodꢀ
uct was precipitated from the filtrate with an Et2O—AcOEt (1 : 1)
mixture, filtered off, and recrystallized from an EtOH—Et2O—
AcOEt (1 : 2 : 2) mixture. Compound 4, m.p. 230 °C, was obꢀ
tained as a white powder in a yield of 0.45 g (88%). Found (%):
С, 42.51; H, 8.54; N, 8.12. С12H30Cl2N2S2. Calculated (%):
С, 42.72; H, 8.96; N, 8.30. 1H NMR (DMSOꢀd6), δ: 8.02 (s, 3 H,
NH3+); 2.75 (t, 2 H, CH2N, J = 6.6 Hz); 2.71 (t, 2 H, CH2S,
J = 7.7 Hz); 1.62 (m, 2 H, CH2); 1.56 (m, 2 H, CH2); 1.34
(m, 4 H, (CH2)2).
Compound 2. A solution of KOH (0.075 g, 1.3 mmol) in
EtOH was added to a solution of ammonium salt 4 (0.45 g,
1.3 mmol) in EtOH. The mixture was stirred for 15 min at room
temperature. A precipitate of KCl was filtered off, and the solꢀ
vent was removed under reduced pressure. The residue was disꢀ
solved in anhydrous dichloroethane (10 mL), and sodium triaceꢀ
toxyborohydride (0.83 g, 3.9 mmol) in dichloroethane (10 mL)
and pyridineꢀ2ꢀcarbaldehyde (0.31 g, 2.9 mmol) were added to
the resultant solution. The mixture was stirred for 18 h at ~20 °C,
a saturated solution of NaHCO3 (20 mL) was added, and organꢀ
ics was extracted with ethyl acetate (3×10 mL). The organic
fractions were dried with anhydrous Na2SO4, and the solvent
was evaporated under reduced pressure. Compound 2 was obꢀ
tained in a yield of 0.66 g (81%).
Nꢀ[4ꢀMethylthiobenzyl]ꢀN,Nꢀbis(2ꢀpyridylmethyl)amine (7).
A. A solution of dipicolylamine (1) (0.3 g, 1.5 mmol) in absolute
МеОН containing AcOH (0.13 g, 2 mmol) was added to a soluꢀ
tion of 4ꢀmethylbenzaldehyde (0.29 g, 1.9 mmol) in МеОН, and
then NaBH3CN (0.14 g, 2 mmol) was added by portion, avoidꢀ
ing warming of the reaction mixture. Then the mixture was stirred
for 24 h at ~20 °C under argon. Concentrated HСl was added to
pH 2, and the mixture was stirred for 1 h. The solvent was reꢀ
moved under reduced pressure, and the residue was dissolved in
water and washed with CH2Cl2. The aqueous phase was alkalꢀ
ized with a solution of NaHCO3 to pH 8, and organics was
extracted with CH2Cl2. The organic extracts were dried with
anhydrous Na2SO4, and the solvent was removed under reduced
pressure. Compound 7 was obtained as a yellow oil in a yield of
0.37 g (73%). 1H NMR (CDCl3), δ: 8.48 (d, 2 H, HC(6), HC(6´),
Py, J = 8.7 Hz); 7.58 (t, 2 H, HC(4), HC(4´), Py, J = 7.3 Hz);
7.52 (d, 2 H, HC(3), HC(3´), Py, J = 7.3 Hz); 7.28 (t, 2 H,
HC(5), HC(5´), Py, J = 8.7 Hz); 7.16 (d, 2 H, HC(2), HC(6),
Ph, J = 8.3 Hz); 7.08 (d, 2 H, HC(3), HC(5), Ph, J = 8.3 Hz);
3.93 (s, 4 H, CH2Py); 3.75 (s, 2 H, CH2Ph); 2.40 (s, 3 H, MeS).
MS, m/z (Irel (%)): 335 (12%) [M]+.
B. Potassium carbonate (0.41 g, 3 mmol) was added to
a solution of 4ꢀmethylthiobenzyl chloride (0.3 g, 1.7 mmol) and
dipicolylamine (1) (0.4 g, 2 mmol) in DMF (5 mL). The reacꢀ
tion mixture was stirred at room temperature for 48 h. After
reaction completion, water (3 mL) was added to the mixture,
and organics was extracted with CH2Cl2 (3×5 mL). The organic
extracts were dried with anhydrous Na2SO4, and the solvent was
evaporated under reduced pressure. Compound 7 was obtained
in a yield of 0.48 g (84%).
Bis(4ꢀ{[N,Nꢀbis(2ꢀpyridylmethyl)amino]methyl}phenyl) diꢀ
sulfide (8). A solution of dipicolylamine 1 (0.24 g, 1.2 mmol) in
absolute МеОН containing AcOH (0.23 g, 3.8 mmol) was added
to a solution of bis(4ꢀformylphenyl) disulfide (0.17 g, 0.6 mmol),
and then NaBH3CN (0.24 g, 3.8 mmol) was added by portions,
avoiding warming of the reaction mixture. The resultant mixture
was stirred for 24 h at ~20 °C under argon. Concentrated HCl
was added to pH 2, and the mixture was stirred for 1 h. The
solvent was evaporated under reduced pressure, and the residue
was dissolved in water and washed with CH2Cl2. The aqueous
phase was alkalized with NaHCO3 to pH 8 and extracted with
CH2Cl2. The organic extracts were dried with anhydrous
Na2SO4, and the solvent was evaporated under reduced presꢀ
sure. Compound 8 was obtained as a yellow oil in a yield of 0.3 g
(78%). 1H NMR (CDCl3), δ: 8.48 (d, 2 H, HC(6), HC(6´), Py,
J = 8.7 Hz); 7.58 (t, 2 H, HC(4), HC(4´), Py, J = 7.3 Hz); 7.52
(d, 2 H, HC(3), HC(3´), Py, J = 7.3 Hz); 7.28 (t, 2 H, HC(5),
HC(5´), Py, J = 8.7 Hz); 7.16 (d, 2 H, HC(2), HC(6), Ph,
J = 8.3 Hz); 7.08 (d, 2 H, HC(3), HC(5), Ph, J = 8.3 Hz); 3.87
(s, 4 H, CH2Py); 3.65 (s, 2 H, CH2Ph). MS, m/z (Irel (%)): 641
[M]+ (10%).
Bis(11ꢀbromoundecyl) disulfide (10). A solution of 11ꢀbroꢀ
moꢀ1ꢀundecanethiol (1.49 g, 5.6 mmol) in MeOH (15 mL) was
titrated with a 1 М solution of iodine in MeOH until the solution
turned light yellow and this color did not disappear for several
minutes. To remove a iodine excess, a small amount of sodium
sulfite was added to the mixture, which was stirred to dissolution.
The solution was cooled, and the precipitate that formed was filtered
off and washed with EtOH. Disulfide 10, m.p. 102—103 °C, was
obtained as white crystals in a yield of 1.34 g (90%). Found (%):
С, 50.05; H, 8.44; S, 12.34. C22H44S2Br2. Calculated (%):
1
С, 49.62; H, 8.27; S, 12.03. H NMR (CDCl3), δ: 3.43 (t, 2 Н,
СН2Br, J = 6.8 Hz); 2.70 (t, 2 Н, СН2S, J = 7.4 Hz); 1.87
(m, 2 Н, CH2); 1.69 (m, 2 Н, CH2); 1.42 (m, 2 Н, CH2); 1.31
(m, 12 Н, (СН2)6).
4,4´ꢀ[Dithiobis(undecaneꢀ11,1ꢀdiyloxy)]dibenzaldehyde (11).
Dibromide 10 (1.1 g, 2.05 mmol) was added to a suspension of
4ꢀhydroxybenzaldehyde (0.5 g, 4.1 mmol) and anhydrous poꢀ
tassium carbonate (0.68 g, 4.9 mmol) in absolute DMF (10 mL).
The reaction mixture was stirred for 18 h at 60 °C. The mixture
was cooled to ~20 °C, water (20 mL) was added, and organics
was extracted with CH2Cl2 (3×10 mL). The organic extracts
were washed with brine and dried with anhydrous Na2SO4.
The solvent was evaporated under reduced pressure. Comꢀ
pound 11 was obtained as a yellow oil in a yield of 1 g (79%).
1H NMR (CDCl3), δ: 9.85 (s, 1 H, CHO); 7.80 (d, 2 H,
HC(2), HC(6), Ph, J = 7.9 Hz); 6.96 (d, 2 H, HC(3), HC(5),
Ph, J = 7.9 Hz); 4.01 (t, 2 H, CH2O, J = 6.4 Hz); 2.66 (t, 2 H,

268
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 2, February, 2011
Majouga et al.
CH2S, J = 7.9 Hz); 1.79 (m, 2 H, CH2); 1.65 (m, 2 H, CH2);
1.43 (m, 2 H, CH2); 1.28 (m, 12 H, (CH2)6). MS, m/z (Irel (%)):
615 (13%) [M]+.
(t, 2 H, CH2S, J = 7.5 Hz); 1.62 (m, 4 H, (CH2)2); 1.27 (m, 14 H,
(CH2)7). MS, m/z (Irel (%)): 884 (11%) [M]+.
4,4´ꢀ[Dithiobis(undecaneꢀ11,1ꢀdiyloxy)]bis{[N,Nꢀbis(2ꢀpyrꢀ
idylmethyl)aminomethyl]benzene} (9). A solution of dipicolylꢀ
amine 1 (0.26 g, 1.3 mmol) in absolute МеОН containing AcOH
(0.31 g, 5 mmol) was added to a solution of dibenzaldehyde 11
(0.5 g, 0.8 mmol) in MeOH. Then NaBH3CN (0.31 g, 5 mmol)
was added by portions, avoiding warming of the resultant mixꢀ
ture. The reaction mixture was stirred for 24 h under argon atꢀ
mosphere at ~20 °C, concentrated HCl was added to pH 2, and
the mixture was stirred for 1 h. The solvent was evaporated unꢀ
der reduced pressure, and the residue was dissolved in water and
washed with CH2Cl2. The aqueous phase was alkalized to pH 8
by the addition of NaHCO3 and organics was extracted with
CH2Cl2. The organic extracts were dried with anhydrous
Na2SO4 and the solvent was evaporated under reduced pressure.
Compound 9 was obtained as a yellow oil in a yield of 0.45 g
(71%). 1H NMR (CDCl3), δ: 8.61 (d, 2 H, HC(6), HC(6´), Py,
J = 4.5 Hz); 7.78 (t, 2 H, HC(4), HC(4´), Py, J = 7.8 Hz); 7.52
(d, 2 H, HC(3), HC(3´), Py, J = 7.8 Hz); 7.43 (t, 2 H, HC(5),
HC(5´), Py, J = 5.7 Hz); 7.34 (d, 2 H, HC(2), HC(6), Ph,
J = 7.9 Hz); 6.90 (d, 2 H, HC(3), HC(5), Ph, J = 7.9 Hz); 4.25
(s, 4 H, CH2Py); 4.13 (s, 4 H, CH2Ph); 3.74 (t, 2 H, CH2O,
J = 6.9 Hz); 2.68 (t, 2 H, CH2S, J = 7.8 Hz); 1.76 (m, 2 H, CH2);
1.67 (m, 2 H, CH2); 1.44 (m, 2 H, CH2); 1.27 (m, 12 H, (CH2)6).
MS, m/z (Irel (%)): 981 (12%) [M]+.
References
1. L. Casella, E. Monzani, M. Gullotti, D. Cavagnino, G. Ceꢀ
rina, L. Santagostini, R. Ugo, Inorg. Chem., 1996, 35, 7516.
2. M. M. Rogic, T. R. Demmin, J. Am. Chem. Soc., 1978,
100, 5472.
3. D.ꢀH. Lee, N. N. Murthy, K. D. Karlin, Inorg. Chem., 1996,
35, 804.
4. N. Wei, N. N. Murthy, Z. Tyeklar, K. D. Karlin, Inorg.
Chem., 1994, 33, 1177.
5. Z. Tyeklar, R. R. Jacobson, N. Wei, N. N. Murthy, J. Zubieꢀ
ta, K. D. Karlin, J. Am. Chem. Soc., 1993, 115, 2677.
6. I. A. Koval, P. Gamez, C. Belle, K. Semeczi, J. Reedijk,
Chem. Soc. Rev., 2006, 35, 814.
7. P. Gamez, P. G. Aubel, W. L. Driessen, J. Reedijk, Chem.
Soc. Rev., 2001, 30, 376.
8. L. M. Mirica, X. Ottenwaelder, T. D. P. Stack, Chem. Rev.,
2004, 104, 1013.
9. E. I. Solomon, U. M. Sundaram, T. E. Machonkin, Chem.
Rev., 1996, 96, 2563.
10. E. I. Solomon, R. Sarangi, J. S. Woertink, A. J. Augustine,
J. Yoon, S. Ghosh, Acc. Chem. Res., 2007, 40, 581.
11. K. D. Karlin, S. Kaderli, A. D. Zuberbühler, Acc. Chem.
Res., 1997, 30, 139.
12. N. N. Murthy, М. MahroofꢀTahir, K. D. Karlin, Inorg.
Chem., 2001, 40, 628.
13. P. K. Dhal, B. B. De, S. Sivaram, J. Mol. Catal. A: Chem.,
2001, 177, 71.
14. T. Zak, H. Yuan, M. Ho, L. K. Woo, M. D. Porter, Langꢀ
muir, 1993, 9, 2772.
15. E. M. Gaigneaux, R. Maggi, Р. Ruiz, В. Delmon, J. Mol.
Catal. A: Chem., 1996, 109, 67.
16. B. Wentzel, S.ꢀM. Leinonen, S. Thomson, D. C. Sherringꢀ
ton, M. C. Feiters, R. J. M. Nolte, J. Chem. Soc., Perkin
Trans. 1, 2000, 3428.
17. A. Ulman, Chem. Rev., 1996, 96, 1533.
18. Organic Electrochemistry, Eds M. M. Baizer, H. Lund, Marꢀ
cel Dekker, New York, 1983, 1166 pp..
Potassium N,Nꢀbis(2ꢀpyridylmethyl)glycinate (13). Bromoꢀ
acetic acid (0.28 g, 2 mmol) and KOH (0.24 g, 4 mmol) were
added to a solution of dipicolylamine 1 (0.8 g, 2 mmol) in water
(20 mL). The mixture was stirred for 32 h under argon at ~20 °C
and organics was extracted with CH2Cl2 (3×10 mL). The organꢀ
ic extracts were dried with anhydrous Na2SO4, the solvent was
washed under reduced pressure, and the residue was washed
with MeCN. Compound 13 was obtained as a brown powder in
1
a yield of 0.56 g (92%). H NMR (DMSOꢀd6), δ: 8.45 (d, 2 H,
HC(6), HC(6´), Py, J = 4.9 Hz); 7.72 (td, 2 H, HC(4), HC(4´),
Py, J1 = 1.7 Hz, J2 = 7.7 Hz); 7.56 (d, 2 H, HC(3), HC(3´), Py,
J = 7.7 Hz); 7.21 (td, 2 H, HC(5), HC(5´), Py, J1 = 1.5 Hz,
J2 = 6.3 Hz); 3.88 (s, 4 H, CH2Py); 2.86 (s, 2 H, CH2CO). MS,
m/z (Irel (%)): 295 (9%) [M]+.
1,24ꢀBis[N,Nꢀbis(2ꢀpyridylmethyl)glycinoyloxy]ꢀ12,13ꢀdiꢀ
thiatetracosane (12). Potassium carbonate (0.41 g, 3 mmol) was
added to a solution of salt 13 (0.5 g, 1.7 mmol) and disulfide 10
(0.55 g, 1 mmol) in DMF (10 mL), and the reaction mixture was
stirred for 48 h at ~20 °C. Water (10 mL) was added and organics
was extracted with CH2Cl2 (3×10 mL). The organic extracts
were washed with brine and dried with anhydrous Na2SO4.
The solvent was removed under reduced pressure. Compound
12 was obtained as a beige oil in a yield of 0.66 g (88%). 1H NMR
(CDCl3), δ: 8.50 (d, 2 H, HC(6), HC(6´), Py, J = 5.8 Hz); 7.63
(td, 2 H, HC(4), HC(4´), Py, J1 = 1.9 Hz, J2 = 7.7 Hz); 7.55
(d, 2 H, HC(3), HC(3´), Py, J = 7.8 Hz); 7.13 (td, 2 H, HC(5),
HC(5´), Py, J1 = 1.4 Hz, J2 = 5.8 Hz); 4.07 (t, 2 H, CH2O,
J = 6.9 Hz); 3.78 (s, 4 H, CH2Py); 2.89 (s, 2 H, CH2CO); 2.65
19. H. Hagenström, M. A. Schneeweiss, D. M. Kolb, Langmuir,
1999, 15, 2435.
20. J. Zhang, Q. Chi, J. U. Nielsen, E. P. Friis, J. E. T. Andersꢀ
en, J. Ulstrup, Langmuir, 2000, 16, 7229.
21. F. Loglio, M. Schweizer, D. M. Kolb, Langmuir, 2003,
19, 830.
22. K. Fujita, M. Hara, H. Sasabe, W. Knoll, K. Tsuboi, K. Kaꢀ
jikawa, K. Seki, Y. Ouchi, Langmuir, 1998, 14, 7456.
23. H. S. Kasmai, S. G. Mischke, Synthesis, 1989, 763.
Received February 24, 2010;
in revised form October 25, 2010