The evolution of reactive ligands in the catalysis of radical processes by copper complexes

Article abstract of DOI:10.1080/10426507.2011.582056

Two radical reactions (addition of CCl₄ to the double bond of oct-1-ene and oxidation of dodecane-1-thiol with air oxygen) catalyzed by copper complexes have been investigated. Various nitrogen-containing compounds (aliphatic and aromatic amines, aminoalcohols, aminoacids) were used as the ligands. In both cases, products of ligand transformation have been observed, products of the transformations have been identified by GLC-MS. In case of the CCl₄ addition, the reaction can be initiated by the either copper complex or the ligand. In case of the thiol coupling, the reaction proceeds as a conjugated oxidation of both the thiol and the ligand. A correlation between the donor ability of the ligand and its reactivity has been found. Copyright Taylor and Francis Group, LLC.

Full text of DOI:10.1080/10426507.2011.582056

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Phosphorus, Sulfur, and Silicon and the
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The Evolution of Reactive Ligands in the
Catalysis of Radical Processes by Copper
Complexes
I. G. Tarkhanova a , M. G. Gantman a & T. N. Rostovschikova a
a Department of Chemistry , M.V. Lomonosov Moscow State
University, 1 Leninskie Gory , Moscow , Russian Federation
Published online: 06 Dec 2011.
To cite this article: I. G. Tarkhanova , M. G. Gantman & T. N. Rostovschikova (2012) The Evolution of
Reactive Ligands in the Catalysis of Radical Processes by Copper Complexes, Phosphorus, Sulfur, and
Silicon and the Related Elements, 187:1, 88-100, DOI: 10.1080/10426507.2011.582056
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Phosphorus, Sulfur, and Silicon, 187:88–100, 2012
Copyright ꢀC M.V. Lomonosov Moscow State University
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.582056
THE EVOLUTION OF REACTIVE LIGANDS
IN THE CATALYSIS OF RADICAL PROCESSES
BY COPPER COMPLEXES
I. G. Tarkhanova, M. G. Gantman, and T. N. Rostovschikova
Department of Chemistry, M.V. Lomonosov Moscow State University, 1 Leninskie
Gory, Moscow, Russian Federation
GRAPHICAL ABSTRACT
Abstract Two radical reactions (addition of CCl4 to the double bond of oct-1-ene and oxi-
dation of dodecane-1-thiol with air oxygen) catalyzed by copper complexes have been investi-
gated. Various nitrogen-containing compounds (aliphatic and aromatic amines, aminoalcohols,
aminoacids) were used as the ligands. In both cases, products of ligand transformation have
been observed, products of the transformations have been identified by GLC-MS. In case of the
CCl4 addition, the reaction can be initiated by the either copper complex or the ligand. In case
of the thiol coupling, the reaction proceeds as a conjugated oxidation of both the thiol and the
ligand. A correlation between the donor ability of the ligand and its reactivity has been found.
Keywords Carbon tetrachloride; addition; oxidation; thiols; copper complexes; reaction mech-
anism
INTRODUCTION
Transition metal complexes are active initiators of various radical processes. These
processes include redox steps with participation of metal ions. So the reactions should be
sensitive to the nature of the ligand. However, the role of ligands in radical reactions has
Received 1 March 2011; accepted 4 April 2011.
This work was supported by RFBR, project #09-03-00128.
Address correspondence to M. G. Gantman, Department of Chemistry, M.V. Lomonosov Moscow State
University, 1 Leninskie Gory, Moscow 119991, Russian Federation. E-mail: mikhail.gantman@gmail.com
88

EVOLUTION OF REACTIVE LIGANDS IN THE CATALYSIS
89
not been adequately studied as yet. This work aims at determining the role and evolution
pathways of the ligands in the catalysis of radical reactions by copper complexes and
at estimating the relationship between the catalytic activity of copper complexes and the
reactivity of the ligands. Two reactions [Equations (1) and (2)] were chosen as model
processes: the addition of carbon tetrachloride to the double bond of oct-1-ene:
C6H13 − CH = CH2 + CCl4 → C6H13 − CHCl − CH2 − CCl3
(1)
and the oxidative coupling of thiols (the model thiols are dodecane-1-thiol (DT) and
pentane-1-thiol)
1
2 RSH + / O2 → RSSR + H O
(2)
2
2
The chosen reactions are typical examples of radical-chain [Equation (1)] and radical
[Equation (2)] processes. Both reactions are catalyzed by metal complexes and include a
redox stage giving rise to reactive intermediates of radical nature. It is known that radical
processes with participation of CCl4 include intermediate formation of trichloromethyl
radicals.1 The generally accepted mechanism of reaction (2) implies consecutive steps of
reduction of divalent copper with thiol and oxidation of Cu(I) with oxygen into the divalent
state.2
In the present work, the evolution of ligands was studied by the example of cop-
per(II) complexes of various composition containing ligands of three types: amino alcohols
3-(N-methylamino)-1-phenylpropan-1-ol (PMP) and 2-(N-methylamino)-1-phenylethanol
[(PME)], benzylamine (BA), and dimethylsulfoxide (DMSO). These ligands possess dif-
ferent redox properties and are capable of initiating radical processes.3 It was stated earlier
that the mentioned amino alcohols can initiate reaction (1). For thiol oxidation, ligands of
two types were chosen. DMSO was chosen as the oxidizing ligand, as its ability to oxidize
thiols is well known.4 As the reducing ligand, we chose BA, which has a structure similar
to PMP and PME.
RESULTS AND DISCUSSION
Reactions with CCl4
Complexes with PMP and PME show high activity in reaction (1) at temperatures
as low as 80 ◦C. 1,1,1,3-Tetrachlorononane is the major product. In addition to the major
product, allylic substitution products (mainly, 3-chlorooct-1-ene) were found, their total
yield being less than 3%. The amount of telomerization products was less than 1%. Data
on the activity of the complexes under investigation in comparison with the activity of the
previously studied analogous complexes with amino alcohols and amino acids, which were
active only at higher temperature, are given in Table 1. As can be seen from Table 1, the
activity of complexes with aromatic amino alcohols exceeds several fold the activity of
other complexes.
It is known that trichloromethyl radicals are formed as intermediates in the reactions
of CCl4 with alkenes.1 The ability of copper complexes with PMP to initiate the formation
of the above-mentioned species was proved by spin-trapping technique with the use of
MNP. In a solution of the copper complex with PMP (0.1 M) in CCl4 at room temperature,
trichloromethyl radical spin adducts with 2-methyl-2-nitrosopropane (MNP) were detected;

90
I. G. TARKHANOVA ET AL.
Table 1 The activity of catalysts in the CCl4 addition to oct-1-ene (turnover frequency, TOF [C8H16] = 0.64 M,
[CCl4] = 9.6 M, [Cu2+] = 0.015 M)
Catalyst
TOF (80 ◦С), mol/mol·h
TOF (130 ◦С), mol/mol·h
Cu-monoethanolamine5
Cu-diethylaminoethanol5
Cu-hydroxyproline5
Cu-serine5
0
0
0
0
8.4
7.2
4.8
5.9
Cu-PMP
Cu-PME
0.28
0.34
29.9
32.1
they appeared as a triplet of multiplets in the ESR spectrum (Figure 1) with the following
HFS constants aN = 11.9 G (triplet) and a = 2.3 G (multiplet).
However, the concentration of spin adducts was very low as compared with the
concentration of the complex, namely, 7 × 10−7 M. Such a content of free radicals in the
system can be accounted for by two independent reasons. The first reason is low reactivity
of the copper complex at room temperature. The second one is the fact that trichloromethyl
radicals form and react in the coordination sphere of the metal ion. To check which of
the reasons is valid, the products of Cu-PMP and Cu-PME complexes interaction with
CCl4 were analyzed by GC-MS. Also, solutions of the complexes in benzene as well as
solutions of the amino alcohols in CCl4 were kept under similar conditions. The products
that form in all the systems are summarized in Table 2. As can be seen from the table, the
products of reactions of free ligands and the copper complexes differ. In all cases where
CCl4 was used as the solvent, amino alcohols were oxidized to benzaldehyde even at room
temperature. Furthermore, there are polymeric nitrogen-containing products. Probably, they
were formed as a result of condensation of the amino alcohol with the formed aldehyde.
No low-molecular-weight chloro-containing compounds were found among the reaction
products of copper complexes with CCl4.
In contrast to copper-containing systems, the systems with amino alcohols contain
products of recombination and subsequent transformations of trichloromethyl radicals such
Figure 1 The ESR spectrum of the system, containing PMP, CCl4, and MNP. The concentrations were as follows
[PMP] = 0.1 M, [MNP] = 0.1 M, [CCl4] = 9.6 M, 25 ◦C (dark).

EVOLUTION OF REACTIVE LIGANDS IN THE CATALYSIS
91
Table 2 The major products of transformations of aromatic amino alcohols and copper complexes (0.015 M
solution of the initiator in CCl4 or benzene, the reaction time was 1 h at 100 ◦C or 24 h at room temperature)
Products
Reagent
Solvent
Temperature 100 ◦C
PhCHO
Room temperature
PhCHO
Cu-PMP
Cu-PMP
PMP
СCl4
C6H6
СCl4
PhCHO
–
CHCl3, CHCl CCl2,
CCl2 CCl2, PhCOCH3,
PhCOCl, PhCOCH CH2,
С2Cl6, CCl2 CCl2,
CHCl CCl2, PhCHO
O
CH3
N
OH
O
Cu-PME
Cu-PME
PME
СCl4
C6H6
СCl4
PhCHO
PhCHO
C2Cl6, CCl2 CCl-CCl CCl2,
PhCHO,
PhCHO
–
С2Cl6, CCl2 CCl2,
CHCl CCl2, PhCHO
as С2Cl6, CCl2 CCl2, CCl2 CCl–CCl CCl2 CHCl CCl2, and CHCl3. The reactions of
aromatic amino alcohols with haloalkanes were studied in detail previously.3 The fact that
no products of CCl4 transformations are produced in the presence of copper complexes
proves that trichloromethyl radicals remain in the copper coordination sphere and cannot
react with one another. At the same time, the ability of copper complexes to interact with
CCl4 and to form the trichloromethyl radicals even at room temperature is responsible for
the high activity of these compounds in the radical chain addition of CCl4 to the double
bond.
Oxidation of Thiols
Copper complexes were also tested in the DT oxidation in isooctane solution.
4 C12H25SH + O2 = 2 C12H25SSC12H25 + 2 H2O
It was found that complexes with the aromatic amino alcohols PMP and PME were
inactive in the process. This is apparently caused by the fact that Cu(II) in these complexes
cannot be reduced by DT. Indeed, the characteristic d-d transition band at 720 nm does
not disappear and the whole UV spectrum stays invariable upon the addition of DT to the
complexes.
However, the copper complex with the aromatic amine (BA) is active in thiol oxidation
[Equation (2)]. Air oxygen selectively oxidizes the thiol to the corresponding disulfide at
room temperature in the presence of this complex. In accordance with iodometric titration
data, H2O2 is the primary product of the oxygen reduction. The amount of H2O2 that forms
in the beginning of the reaction is comparable with the amount of the oxidized thiol. In a
standard solution of DT (5 × 10−2 M) in isooctane containing the copper complex with BA
(2 × 10−3 M) and a 10-fold excess of the ligand, the thiol consumption was 1.5 × 10−2

92
I. G. TARKHANOVA ET AL.
(h)
Figure 2 Kinetics of decrease in BA concentration (•) and pentane-1-thiol concentration (ꢀ) in the presence of
copper complex with BA (T = 25 ◦C, initial concentrations [thiol] = 5.3 М, [Cu] = 2 × 10−3 М, [PhCH2NH2] =
1.9 М).
M and the concentration of the formed hydrogen peroxide was 10−2 M. The activity of the
catalyst calculated on the basis of these data was 8.3 moles of thiol/(mole of copper hour).
However, the maximum conversion of DT was not very high, namely, 23 moles of thiol
per mole of copper. When the new portions of the ligand and the substrate were repeatedly
added to the reaction mixture, the conversion of thiol over 72 h increased to about 800 moles
of thiol per mole of copper. The effect of the additional amounts of ligand is attributable to
the fact that the catalytic thiol oxidation is accompanied by a process involving the ligand.
Since in the absence of thiol no consumption of amine was observed, we can state that
conjugated processes of both thiol and amine oxidation take place. Moreover, as can be
seen from Figure 2, an average of 1.3 moles of the thiol is consumed per mole of the amine.
The GC-MS data showed that the major product of BA transformations was ben-
zaldehyde (90%), the minor product was benzonitrile (5%), and also heavy products of
polymerization were found (5%). These products probably result from consecutive oxida-
tion of amine according to the following route (Scheme 1, water is formed as a result of
thiol or amine oxidation.).
⎡⎢⎣O⎤⎥⎦,− H O
⎡⎢⎣O⎤⎥⎦,− H O
2
2
PhCH2 NH2 ⎯⎯⎯⎯⎯⎯→PhCH = NH ⎯⎯⎯⎯⎯⎯→PhC ≡ N
↓ +H2O,− NH3
Ph −COH
Scheme 1

EVOLUTION OF REACTIVE LIGANDS IN THE CATALYSIS
93
Figure 3 The ESR spectrum of the system, containing copper chloride, amine (BA or cyclohexylamine), dode-
canethiol, and MNP. (1—ditertbutylnitroxide, 2—spin-adduct of MNP with hydrogen atom).
It is well known that amines can be oxidized via radical mechanism in the presence
of copper compounds but the process occurs only at high temperature.6 The oxidation
of amine becomes possible at room temperature only owing to the presence of thiol.
Radical intermediates of the conjugated oxidation of thiol and amine were studied by ESR
spectroscopy using the spin trapping technique by the example of the system DT–copper
complex with BA–excess of BA–isooctane–oxygen. As can be seen from Figure 3, in the
presence of the MNP trap, the spectrum exhibits two signals. The first one refers to di-tert-
butylnitroxide. The second one appears as a triplet of doublets. The triplet splitting constant
on the nitrogen atom aN = 14.3 G, the doublet constant aH = 11.3 G. This spectral pattern
and HFC values correspond to the spin adduct with hydrogen.
These adducts are described in the literature. They were observed in systems, con-
taining alkanethiol (propanethiol, octanethiol, or cysteine), hydrogenperoxide, and MNP.7
Taking into account both the ESR data and the data on the structures of products of amine
oxidation, one can assume that the oxidation of amine involves consecutive steps giving to
radical species as intermediates (Scheme 2).
+•
−
−
−
−
⎯⎯→
−
−
+•
•
•
+
⎯−⎯⎯→
−
−
•
−
−
⇔
−
=
−
⋅
•
•
+
→
−
+
•
• + −
→ −
−
+
Scheme 2

94
I. G. TARKHANOVA ET AL.
Thus, in this process, as in reaction (1) involving CCl4 considered above, the ligands
act as electron or hydrogen donors, participating in the activation of the oxidizing agent,
namely, CCl4 in reaction (1) and O2 in reaction (2). Reaction (2) was also used as an
example to study the ability of copper complexes with DMSO to activate thiols. It is well
known4 that in the absence of a metal ion, DMSO oxidizes thiols at temperatures above
120 ◦C to give the corresponding disulfides:
CH3S(O)CH3 + 2RSH → RSSR + (CH3)2S + H2O
The complex CuCl2(DMSO)2, like the complex with BA, catalyzes the oxidation
of DT even at room temperature. This is accompanied by consumption of both DT and
DMSO. An example of kinetic curves of the consumption of thiol and DMSO in the system
CuCl2–DMSO–pentanethiol is presented in Figure 4. The catalytic activity estimated from
these data was 10 moles of thiol per mole of copper per hour. The maximum conversion of
the substrate was comparable with that of the copper complex with BA and still it was not
very high, 26 moles of thiol per mole of copper.
As can be seen from the figure, the rate of substrate consumption exceeds the rate
of DMSO consumption. Taking into account the stoichiometry of the reaction, we can
suppose that in the presence of copper ions, thiol is oxidized by air oxygen together with
DMSO (molar ratio 2:1). To check this statement, the products that form in the system
CuCl2–DMSO–pentane-1-thiol in the absence of oxygen were studied. It was found that
in an isooctane solution (5 ml) of the DMSO copper complex (0.005 g), pentane-1-thiol
(0.2 wt% of the thiol sulfur) is oxidized at room temperature in the absence of oxygen (see
Table 3).
The consumption of thiol is equal to 2.5 0.5 moles per mole of the copper com-
plex. The oxidation of thiol is accompanied by the formation of dimethyl sulfide (DMS).
(h)
Figure 4 Kinetics of pentane-1-thiol (ꢀ) and DMSO (◦) consumption. [Cu(DMSO)2Cl2] = 0.087 М,
[C5H11SH] = 5.2 М, [DMSO] = 2.3 М, room temperature.

EVOLUTION OF REACTIVE LIGANDS IN THE CATALYSIS
95
Table 3 Change of the amount of pentane-1-thiol (moles) in isooctane solution under various conditions. The
Cu2+ amount is 10−5 moles in all samples
System components and reaction conditions
0 h
1 h
2 h
CuCl2
C5H11SH under vacuum
CuCl2(DMSO)2
C5H11SH under vacuum
CuCl2(DMSO)2
C5H11SH in air
1.5 × 10−4
1.5 × 10−4
1.5 × 10−4
1.3 × 10−4
1.05 × 10−4
0.3 × 10−4
1.3 × 10−4
1.05 × 10−4
0
According to published data,8 DMS was also found in the systems prepared by mixing
cuprous chloride with DMSO under vacuum. In the absence of copper ions under similar
conditions, the reaction does not proceed. If DT was mixed with CuCl2 in isooctane, the
thiol consumption was equal to the amount of copper, copper being reduced to the univalent
state. The obtained data can be summarized in the following scheme (Scheme 3).
+
→
+
+
+
+
→
+
+
Scheme 3
This scheme describes satisfactorily the stoichometry of the consumption of DMSO
while the reaction of thiol and the copper complex with DMSO proceeds (2 moles of
copper per mole of thiol). On the basis of the published data,8 we can assume that DMS
formed during the process is oxidized to DMSO by oxygen in the presence of Cu(II) ions
(Scheme 4).
+
+
+
+
→
[
⋅⋅⋅⋅
]
→
+•⋅⋅⋅⋅
+
+•⋅⋅⋅⋅
+
→
−
− ⋅⋅⋅⋅
⎯⎯⎯⎯→
+
+
+
+
+
Scheme 4
The given equations reflect the general pattern of the mechanism of thiol oxidation
with air oxygen in the presence of copper complex with DMSO. This mechanism assumes
consecutive reduction of copper ions with thiol followed by reoxidation of Cu(I) to the
divalent state with DMSO, DMS being formed during this process. Partial reoxidation of
DMS to DMSO with air oxygen in the presence of copper ions accounts for the catalytic
properties of the complex. The mentioned processes form catalytic cycle, which breaks
only because of low efficiency of DMS oxidation to DMSO. Consequently, DMSO copper
complexes show low durability of operation (TON ≤ 23).
Unlike BA, the addition of excess DMSO did not increase the efficiency of the
catalytic action of the system. As can be seen from Figure 5, the catalytic activity (or the
rate or durability or both) decreases after the addition of DMSO. This fact can be attributed
to low solubility of DMSO in isooctane and heterogenization of the system. The excess of
DMSO forms a separate phase, which contains the greater part of the metal complex. The

96
I. G. TARKHANOVA ET AL.
Figure 5 Catalytic activity of the DMSO copper complex versus the volume of added DMSO. Initial concentration
of complex 2 × 10−3 M, thiol concentration 5 × 10−2 M, 25 ◦C.
green-blue coloring of the copper-containing layer proves this assumption. At the same
time, the thiol most likely occurs in the isooctane layer. As a result of separation of the
catalyst and the reactant, the reaction rate appreciably decreases.
CONCLUSIONS
Thus, in the studied radical processes catalyzed by copper complexes, the ligands
undergo a number of transformations, which influence greatly the rate and the mechanism
of the process. As opposed to the generally accepted views, these transformations are
not always auxiliary and lead to the destruction of the catalyst. The considered examples
show that in some cases, these transformations are inherent components of the catalytic
cycle. In the reactions with participation of CCl4, copper complexes with strongly reducing
ligands are the most active catalysts. Ligands such as aromatic amino alcohols participate
in the radical chain initiation. An additional low-temperature pathway of generation of
trichloromethyl radicals appears (Scheme 5).
In the oxidation of thiols, two pathways are also possible. The reaction can follow
the classical mechanism, which assumes participation of the ligand only in the formation
of metal complex. This mechanism does not imply direct interaction between the ligand
and the substrate. On the contrary, active ligands act simultaneously as complexing agents
and reagents that react with either the oxidizing substrate, oxygen (in the case of BA), or
the reducing substrate, the thiol (in the case of DMSO) (see Scheme 6).
The joint action of the metal ion and the ligand increases the efficiency of the catalysis.

EVOLUTION OF REACTIVE LIGANDS IN THE CATALYSIS
97
Scheme 5
Scheme 6
EXPERIMENTAL PART
Сatalyst Synthesis
Copper(II) complexes were synthesized as described in ref. 9. The composition was
determined by complexometric titration of copper with a solution of EDTA and elemental
analysis.
The IR spectra were recorded on a Fourier Transform spectrometer in the 3500–
650 cm−1 range. Pellets (100 µm thick) were prepared with a hand press after grinding of
the studied substance and KBr in a 1:20 ratio in a jasper mortar.
The electronic spectra were measured at λ 200–800 nm on a Shimadzu UV-320
spectrometer in quartz cells (1 cm length) in a chlorobenzene solution.
The ESR spectra were recorded at 77 K on an X-range radiospectrometer (high-
frequency modulation 100 kHz) in a thin-walled ampoule of 4 mm diameter. The g-factor
was determined by simultaneous recording of the studied sample with hyperfine structure
components of Mn2+ resonance in MgO.
Copper(II) complex with BA was obtained by the reaction of an ethanolic solution
(25 mL) of copper(II) chloride dihydrate (0.5 g, 0.0037 mol) with BA (0.8 mL, 0.0074
mol). The precipitate was filtered off and dried in air.
The composition of the complex represented by elemental analysis (Сu, 13.4%; Cl,
14.0%; C, 55.2%; N, 9.5%; H, 6%) corresponds to the formula CuCl2(NH2CH2Ph)3. The
shape and the position of the N–H stretching band in the IR spectrum of the complex
changed with respect to that in the spectrum of pure BA. The symmetric vibration band
shifted from 3315 to 3293 cm−1 and the asymmetric band shifted from 3390 to 3320 cm−1
;
this is in good agreement with the literature data for analogous complexes (3328 and 3320
cm−1, respectively).10

98
I. G. TARKHANOVA ET AL.
Figure 6 The structure of DMSO copper complex.
◦
Copper(II) complex with DMSO was obtained in ethanol at 40 С. Copper(II)
chloride (0.5 g, 0.0037 mol) was dissolved in ethanol (3.5 mL). DMSO (0.7 mL, 0.009
mol) was added with stirring and heating. The precipitate was filtered off and dried in air.
The characteristics of the obtained copper complex with DMSO are in good agreement
with the literature data.11 Elemental analysis showed that the content of copper in the
substance is 22.0 wt%. This corresponds to CuCl2(DMSO)2. The electronic spectrum of
the compound contains a Cu(II) d-d transition band at 730 nm. However, only 2% of the
total amount of copper ions is manifested in the ESR spectrum. This indicates that the
complex has a polynuclear structure.
The S O and C–S stretching bands of DMSO molecules bound to the copper ion are
located at 980 and 726 cm−1, respectively, in the IR spectrum (in ref. 11, the same bands
were recorded at 987 and 727 cm−1). Thus, it can be stated that the ligand and the metal
ion are bound via oxygen and that the complex has the following structure Figure 6.
Copper(II) complexes with amino alcohols are soluble in ethanol; therefore, they
were obtained from CuCl in acetonitrile solution as described in ref. 12. To an acetonitrile
solution (25 mL) of CuCl (0.11 g, 0.001 mol), an equimolar amount of PMP (0.038 g) or
PME (0.035 g) was added. The formed copper(II) complexes were filtered off and dried in
air.
The results of complexometric titration and elemental analysis (24.0% Cu; 13.4%
Cl; 5.3% N; 6.1% O; 45.5% C; 5.7% H for PMP and 25.5% Cu; 14.2% Cl; 5.6% N; 6.3%
O; 42.8% C; 5.6% H for PME) prove that the composition of complexes is CuLCl (L is
PMP or PME). Published data on the geometry of copper complexes with ephedrine13 (a
structural analogue of the amino alcohols used) suggest the following structure for the
obtained complexes (Figure 7).
Reaction Studies
The reaction of oct-1-ene with ССl4 [Equation (1)] was carried out in the temperature
◦
◦
range of 80 C–130 C in sealed glass ampoules as described in ref. 13. The reaction
mixtures were prepared in a vacuum setup, CCl4 was used as the solvent ([CCl4] = 9.6 M),
the concentration of complexes was 0.015 M, [C8H16] = 0.63 M.

EVOLUTION OF REACTIVE LIGANDS IN THE CATALYSIS
99
Cooper complex with PMP
Cooper complex with PME
Figure 7 The structure of aromatic aminoalcohols complexes of copper.
The oxidation of thiols [Equation (2)] was carried out at room temperature and
normal pressure in a flat-bottom flask with intense stirring such that the reaction rate was
independent of the intensity of stirring. A standard solution of DT in isooctane was prepared
beforehand and placed into the flask together with the catalyst. The volume of the solution
was 25 mL. The initial content of thiol sulfur was 0.2 wt% (300 µL of dodecanethiol,
5 × 10−2 M), the concentration of copper complexes was 2 × 10−3 M (the sample weight
was 0.016 g in the case of BA and 0.011 g in the case of DMSO). To study the influence
of excess DMSO on the catalytic activity, different portions (10–100 µL) of DMSO were
added to the system. When the experiments were performed in the absence of oxygen, the
samples were prepared in a vacuum setup (air residual pressure ≤10−2 atm).
The content of thiols in the reaction mixture was characterized by the weight percent
of thiol sulfur. The amount of thiol sulfur was determined by potentiometric titration with a
solution of diamminesilver nitrate using an EA-2 silver sulfide electrode. A silver chloride
electrode was used as the reference electrode.14
The organic products formed upon BA and DMSO transformations were analyzed
by GLC-FID and GLC-MS (a Varian 3400 chromatograph with a HP-101 capillary column
(25 m long, inner diameter 0.2 mm, thickness of liquid phase layer 0.2 µm), a Finnigan
MAT ITD-700 ion trap as the mass-spectrometric detector).
Based on the data on the compositions of reaction mixtures versus process duration,
the catalytic activities were found as the ratios of the number of product moles formed
during 1 h to the number of copper moles (TOF).
MNP was used as the spin trap. The ESR spectra of spin adducts with MNP were
recorded in the dark. Typical samples for the investigation of reaction (1) contained CCl4
(0.05 mL), MNP (0.0015 g, 0.1 M), and the copper complex with PMP (0.0043 g, 0.1
M). The reaction was performed under vacuum. Reaction (2) was held at the atmospheric
pressure, typical sample had a following composition: copper(II) chloride (0.0006 g, 3.7 ×
10−3 M), BA (10 µL, 0.38 M), penatne-1-thiol (20 µL, 0.38 M), MNP (0.017 g, 0.38 M),
isooctane was used as a solvent (isooctane was added up to a volume of 0.5 mL).
REFERENCES
1. Bland, W. J.; Davis, R.; Durrant, J. L. A. J. Organomet. Chem. 1985, 280, 397-406.

100
I. G. TARKHANOVA ET AL.
2. Akopyants, Y. G.; Borisenkova, S. A.; Kaliya, O. L.; Derkacheva, V. M.; Lukyanets, E. A.
J. Mol. Cat. 1993, 83, 1-16.
3. Tarkhanova, I. G.; Gantman, M. G.; Chizhov, A. O.; Smirnov, V. V. Russ. Chem. Bull. 2006, 55,
1624-1631.
4. Oae, S. Organic Sulfur Chemistry: Structure and Mechanism; CRC Press: Boca Raton, 1991;
pp. 250-273.
5. Smirnov, V. V.; Tarkhanova, I. G.; Kokorin, A. I.; Gantman, M. G.; Tsvetkov, D. S. Kin. Cat.
2005, 46, 72-76.
6. Clifton, J. R.; Yoke, J. T. Inorg. Chem. 1968, 7, 39-45.
7. Triquigneaux, M.; Tuccio, B.; Charles, L. Anal. Met. 2010, 2, 694-700.
8. Ainscough, E. W.; Brodie, A. M.; Husbands, J. M.; Gainsford, G. J.; Gabe, E. J.; Curtis, N. F.
J. Chem. Soc., Dalton Trans. 1985, 151-158.
9. Tarkhanova, I. G.; Gantman, M. G.; Chizhov, A. O.; Smirnov, V. V. Reaction Kinetics, Mecha-
nisms and Catalysis 2010, 101, 267-278.
10. Hathaway, B. J. Comprehensive Coordination Chemistry: The Synthesis, Reactions, Properties
& Application of Coordination Compounds; G. Wilkinson, Ed.; (Pergamon Press: 1985; Vol. 5,
p. 577.
11. Gutmann, V.; Hubner, L. Monatsh. Chem. 1961, 92, 1261-1268.
12. Amano, Y.; Uno, T. J. Chem. Soc. Jpn. 1965, 86, 1087-1098.
13. Smirnov, V. V.; Tarkhanova, I. G.; Kokorin, A. I.; Pergushov, V. I.; Tsvetkov, D. S. Kin. Cat.
2005, 46, 65-71.
14. Engine Fuels. Methods of Thiolate Sulfur Determination by Potentiometric Titration. GOST
17323–71; (Moscow, 1980) pp. 12-18.