ESR study of paramagnetic derivatives of sterically hindered di-o-quinone with the tetrathiafulvalene bridge

Article abstract of DOI:10.1007/s11172-010-0299-5

The paramagnetic derivatives of 4,4′,7,7′-tetra-tert-butyl-2, 2′-bis-1,3-benzodithiol-5,5′,6,6′-tetraone (1), viz., radical anion salts of the alkali metals (Li, Na, K) and cobaltocenium cations, chelated mono-o-semiquinone complexes with different metal fragments (Tl, TlMe ₂, SnPh₃, Mn(CO)₄, Mn(PPh₃)(CO) ₃), a number of copper(I) complexes with sterically hindered phosphines as well as binuclear heterometallic derivatives of triphenylantimony(V) o-semiquinone-catecholate with the analogous paramagnetic centers, were studied by ESR spectroscopy. The reaction of di-o-quinone 1 with sodium amalgam resulted in the formation of all reduced forms including quinone-semiquinone, disemiquinone, semiquinone-catecholate, and dicatecholate. A radical cation with the unpaired electron localized on the tetrathiafulvalene (TTF) fragment, which resulted from the oxidation of di-o-quinone 1, was detected by ESR spectroscopy.

Full text of DOI:10.1007/s11172-010-0299-5

Russian Chemical Bulletin, International Edition, Vol. 59, No. 9, pp. 1698—1706, September, 2010
1698
ESR study of paramagnetic derivatives of sterically hindered
diꢀoꢀquinone with the tetrathiafulvalene bridge
V. A. Kuropatov, S. V. Klementieva, A. I. Poddel´sky, V. K. Cherkasov, and G. A. Abakumov
G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhnii Novgorod, Russian Federation.
Fax: +7 (831) 462 7497. Eꢀmail: cherkasov@iomc.ras.ru
The paramagnetic derivatives of 4,4´,7,7´ꢀtetraꢀtertꢀbutylꢀ2,2´ꢀbisꢀ1,3ꢀbenzodithiolꢀ
5,5´,6,6´ꢀtetraone (1), viz., radical anion salts of the alkali metals (Li, Na, K) and cobaltoꢀ
cenium cations, chelated monoꢀoꢀsemiquinone complexes with different metal fragments
(Tl, TlMe2, SnPh3, Mn(CO)4, Mn(PPh3)(CO)3), a number of copper(I) complexes with steriꢀ
cally hindered phosphines as well as binuclear heterometallic derivatives of triphenylantimony(V)
oꢀsemiquinoneꢀcatecholate with the analogous paramagnetic centers, were studied by ESR specꢀ
troscopy. The reaction of diꢀoꢀquinone 1 with sodium amalgam resulted in the formation of all
reduced forms including quinoneꢀsemiquinone, disemiquinone, semiquinoneꢀcatecholate, and
dicatecholate. A radical cation with the unpaired electron localized on the tetrathiafulvalene
(TTF) fragment, which resulted from the oxidation of diꢀoꢀquinone 1, was detected by ESR
spectroscopy.
Key words: 4,4´,7,7´ꢀtetraꢀtertꢀbutylꢀ2,2´ꢀbisꢀ1,3ꢀbenzodithiolideneꢀ5,5´,6,6´ꢀtetraone,
tetrathiafulvalene, ESR spectroscopy, metal oꢀsemiquinone and catecholate complexes.
Search for the methods for the design of molecular
TTF•TCNQ22 (TCNQ is 4,4´,7,7´ꢀtetracyanoꢀpꢀquinꢀ
odimethane) possessing electrical conductivity, TTF and
its analogs are widely used as building blocks in the design
of organic conductors and superconductors.23,24 Thereꢀ
fore, combining redoxꢀactive fragments of different naꢀ
ture in one molecule offers prospects for the design of
multispin systems with controllable exchange, molecular
ferromagnetics, photoswitchable materials, and other
molecular devices.
electronic devices remains one of the main trends in the
modern materials science.1—3 The development of approꢀ
aches to the synthesis of new polyfunctional compounds
exhibiting electrical, magnetic, and photoactive properꢀ
ties is topical and interesting. Based on these compounds,
it is possible to design new materials, e.g., electroꢀ and
photoactive molecular magnetic materials.4—9
The coordination and organometallic compounds with
the redoxꢀactive ligands10 (primarily, oꢀquinones and their
Nꢀheteroanalogs) are promising for the design of such maꢀ
terials. oꢀQuinones can form radical anion salts, as well as
chelated semiquinone and catecholate complexes with all
transition and nontransition metals.11—14 Using diꢀoꢀ
quinones, one can prepare bisꢀ and polyderivatives with
the diꢀoꢀquinone ligand (in one of its reduced forms) as
the spacer between two metal centers. To date, a variety of
monoꢀ and binuclear metal complexes based on diꢀoꢀ
quinones with different bridges between the ligand cenꢀ
ters has been studied.15—20 However, in all known
examples, the bridge is not redoxꢀactive. The introduction
of a redoxꢀactive spacer, which can also undergo
a reversible oxidation, into the diꢀoꢀquinone molecule ofꢀ
fers additional opportunities for control of the channel
connecting the metal centers. The tetrathiafulvalene fragꢀ
ment (TTF) exhibits precisely these properties, viz., it can
be oxidized reversibly to the radical cation and dication.21
Since the discovery of the chargeꢀtransfer complex
Recently,25 in search for approaches to the design of
such systems, we have synthesized diꢀoꢀquinone 1 conꢀ
taining two sterically hindered oꢀquinone fragments coꢀ
valently bound to the TTF spacer and capable of chelate
binding to various metal centers. In the present work we
studied a number of paramagnetic metal complexes with
ligand 1 and its radical cations by ESR spectroscopy.
Oneꢀelectron reduction of 1 with alkali metals and
cobaltocene results in radical anion salts 2—5 whose ESR
spectral parameters are given in Table 1. Since there are
no protons and other magnetic nuclei in the quinone rings
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1652—1660, September, 2010.
1066ꢀ5285/10/5909ꢀ1698 © 2010 Springer Science+Business Media, Inc.

ESR study of quinone with tetrathiafulvalene
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 9, September, 2010
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Table 1. The parameters of the isotropic ESR spectra of the paramagnetic derivatives of diꢀoꢀquinone 1 in THF at
290 K
Complex*
gi
Ai(M)
Ai(31P)
mT
QꢀTTFꢀSQLi (2)
QꢀTTFꢀSQNa (3)
QꢀTTFꢀSQK (4)
QꢀTTFꢀSQCoCp2 (5)
Na2CatꢀTTFꢀSQNa (8)
QꢀTTFꢀSQTl (9)
QꢀTTFꢀSQTlMe2 (10)
QꢀTTFꢀSQSnPh3 (11)
2.0056
2.0062
2.0063
2.0052
2.0068
1.9998
2.0037
2.0048
2.0070
2.0069
2.0073
2.0063
2.0065
2.0049
2.0032
2.0050
2.0051
2.0003
2.0054
2.0060
2.0044
2.0065
2.0081
2.0086
0.050 (7Li)
0.037 (23Na)
—
—
—
—
—
—
—
—
—
1.65
2.04
1.87
0.13
1.48
—
3.15
—
—
—
1.43
—
2.60
—
—
—
0.033 (23Na)
5.24 (203Tl, 205Tl)
2.84 (203Tl, 205Tl)
0.86 (117Sn), 0.89 (119Sn)
1.01 (63Cu), 1.11 (65Cu)
1.28 (63Cu), 1.43 (65Cu)
1.09 (63Cu), 1.20 (65Cu)
0.22 (63Cu, 65Cu)
0.91 (63Cu), 1.00 (65Cu)
0.36 (55Mn)
QꢀTTFꢀSQCu(PPh3)2 (12)
QꢀTTFꢀSQCu(dppph) (13)
QꢀTTFꢀSQCu(dppfc) (14)
QꢀTTFꢀSQCuPBut2C6H4Phꢀo (15)
Ph3PCatꢀTTFꢀSQCu(PPh3)2 (16)
QꢀTTFꢀSQMn(CO)4 (18)
QꢀTTFꢀSQMn(CO)3(PPh3) (19)
Ph3SbCatꢀTTFꢀSQLi (21)
Ph3SbCatꢀTTFꢀSQNa (22)
Ph3SbCatꢀTTFꢀSQTl (23)
Ph3SbCatꢀTTFꢀSQCu(PPh3)2 (24)
Ph3SbCatꢀTTFꢀSQMn(CO)4 (25)
Ph3SbCatꢀTTFꢀSQMn(CO)3(PPh3) (26)
Ph3SbCatꢀTTFꢀSQSnPh3 (27)
Ph3SbCatꢀTTF•+ꢀCatSbPh3 (29)
0.88 (55Mn)
0.047 (7Li)
0.034 (23Na)
4.17 (203Tl, 205Tl)
0.88 (63Cu), 0.98 (65Cu)
0.22 (55Mn)
0.64 (55Mn)
0.48 (117Sn, 119Sn)
—
+
[Ph3SbCatꢀTTF• ꢀCatSbPh3][TCNQ•–]** (30)
—
—
* dppph is bis(diphenylphosphino)ꢀoꢀphenylene; dppfc is bis(diphenylphosphino)ferrocene.
** g(TCNQ•–) = 2.0040, A(4 H) = 0.042 mT, A(4 14N) = 0.145 mT.
and TTF fragment of the molecule of 1, except for the 13C
and 33S isotopes whose content is extremely low (1.108%
and 0.74%, respectively), the ESR spectra display the
hyperfine coupling (HFC) only with the nuclei of the magꢀ
netic isotopes of the corresponding metals. For example,
the ESR spectra of complexes 2 and 3 are quartets caused by
the HFC of the unpaired electron with the magnetic nuꢀ
clei 7Li (92.57%, I = 3/2, μN = 3.2560) and 23Na (100.0%,
I = 3/2, μN = 2.2161).26 Lithium semiquinolate can also
be obtained upon oneꢀelectron reduction of diꢀoꢀquinone
1 by metallic mercury in the presence of lithium chlorꢀ
ide.27,28 The ESR spectra of the free radical anions of
semiquinones 4 and 5 are singlets, because there is no
HFC of the unpaired electron with potassium and the
magnetic nuclei of the cobaltocenium cation, as in other
cases.18,19,29
Subsequent reduction of 1 with massive metals is comꢀ
plicated due to a low solubility of products. The use of
excess sodium amalgam leads to reduction of 1 to the diꢀ
amagnetic dicatecholate 6. In addition, each reduced form,
viz., quinoneꢀsemiquinone (3), disemiquinone (7), and
semiquinoneꢀcatecholate (8), can be prepared individualꢀ
ly by the reaction of 1 with one, two, and three equivalents
of sodium amalgam, respectively, or by the addition of the
corresponding amount of 1 to dicatecholate 6 (Scheme 1).
Compounds 3 and 6—8 were generated in situ to
study the ESR spectra of paramagnetic derivatives, as well
as these compounds were synthesized on the preparative
scale. Complexes 3 and 8 contain an odd number of elecꢀ
trons and the ESR spectra of solutions of these compounds
display intense ESR signals as quartets with the characteristic
splitting on the magnetic 23Na nuclei (Fig. 1, a and b).
For complex 8, the HFC constant is somewhat lower (see
Table 1). A weak ESR signal observed upon dissolution of
complex 7 in THF is the superposition of two quartets
with equal intensities (see Fig. 1, c), which are due to the
M = Li (2), Na (3), K (4), Cp2Co (5)

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a
Kuropatov et al.
c
1
2
3434
3435
3436
3437 |H|•104/T
b
3433
3434
3435
3436
3437 |H|•104/T
3433
3434
3435
3436 |H|•104/T
Fig. 1. The ESR spectra of complexes 3 (a), 8 (b), and 7 (c) in THF; spectrum c is the superposition of spectra a and b: 1 is the
experimental spectrum (290 K), 2 is the simulated spectrum.
presence of forms 3 and 8 in the solution. Their emergence
suggests partial disproportionation of the binuclear comꢀ
plex in the solution (Scheme 1). According to the ESR
data, the degree of disproportionation is at most 1%.
The sodium complexes 3 and 6—8 are stable in inert
atmosphere in solution and in the crystalline state; howꢀ
ever, they are extremely oxygenꢀ and moistureꢀsensitive
and rapidly oxidized to form the original ligand 1. The
monoꢀ and disemiquinolates 3 and 7, respectively, isolatꢀ
ed by recrystallization from the reaction mixture, are deepꢀ
colored fineꢀcrystalline substances, which are almost inꢀ
soluble in organic solvents, except for THF and MeOH.
Solutions of the complexes in THF have deep blue (3) and
green (7) color and are characterized by maxima at 685
and 990 nm, respectively, in the electronic absorption specꢀ
tra. The stretching frequencies of the carbonyl groups in
Scheme 1

ESR study of quinone with tetrathiafulvalene
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 9, September, 2010
1701
the IR spectrum of complex 3 are lower than those in the
ly, 1,2ꢀbis(diphenylphosphino)benzene and 1,1´ꢀbis(diꢀ
phenyldiphosphino)ferrocene, as well as the threeꢀcoorꢀ
dinate copper semiquinolate 15 with 2ꢀ[diꢀ(tertꢀbutyl)ꢀ
phosphino]biphenyl can also be prepared by the metatheꢀ
sis reaction of sodium or thallium semiquinolate with anꢀ
hydrous copper(I) chloride in the presence of neutral
ligands or by displacement of 3,6ꢀdi(tertꢀbutyl)ꢀ4,5ꢀ
dimethoxyꢀoꢀbenzoquinone from the corresponding copꢀ
per(I) complexes.30—34
spectrum of the starting compound 1 (1599 and 1647 cm–1
,
respectively).25 In the IR spectrum of 7, the correspondꢀ
ing stretching vibrations are observed in the region of
1350—1420 cm–1, which is typical of normal semiquinoꢀ
ne complexes.11—14
Compounds 8 and 6 corresponding to the higher deꢀ
gree of reduction of 1 are respectively brown and yellow
fineꢀcrystalline substances insoluble in organic solvents.
The deepꢀbrown precipitate of semiquinoneꢀcatecholate
8 makes the solution greenishꢀbrown. The formation of comꢀ
plex 8 occurs immediately upon reduction of a solution of
diꢀoꢀquinone 1 in THF with three equivalents of sodium
amalgam. Subsequent reduction to dicatecholate 6 is posꢀ
sible only when using an excess of sodium amalgam. The
C—O stretching vibration bands in the IR spectra of
the metal complexes 8 and 6 appear in the regions of
1150—1350 cm–1 and 1150—1250 cm–1, respectively,
which are typical of the oneꢀandꢀaꢀhalf order bond in the
semiquinone fragment and the ordinary bond in the cateꢀ
cholate.11—14
MLn = Tl (9), TlMe2 (10), SnPh3 (11)
Oneꢀelectron reduction of 1 with sodium amalgam reꢀ
sults in chelated thallium(I) semiquinolate (9), as indicatꢀ
ed by the appearance of a doublet ESR signal caused by
the HFC of the unpaired electron with the magnetic thalꢀ
lium isotopes (203Tl, 29.52%, I = 1/2, μN = 1.6222; 205Tl,
70.48%, I = 1/2, μN = 1.6382).26
Dimethylthallium semiquinolate 10 was prepared
in situ by the oxidative reaction of 1 with trimethylthalliꢀ
um at an equimolar reactant ratio. It also has a doublet
ESR spectrum; however, the splitting on the magnetic
isotopes 203,205Tl is smaller than that in the spectrum of
complex 9 (see Table 1). The splittings are typical of the
semiquinone complexes of triꢀ and monovalent thallium,
respectively.17,18
The ESR spectrum observed upon the reaction of 1
with hexaphenyldistannane is a singlet with satellites due
to the HFC of the unpaired electron with the magnetic
isotopes of tin (117Sn, 7.75%, I = 1/2, μN = 1.000; 119Sn,
8.60%, I = 1/2, μN = 1.046)26. This signal indicates the
formation of triphenyltin semiquinolate 11.
Diꢀoꢀquinone 1 can dissolve metallic copper in the
presence of phospines to form copper semiquinone comꢀ
plexes. The fourꢀcoordinate complexes of copper(I) 12—14
with triphenylphosphine, two bidentate phosphines, nameꢀ
The ESR spectra of complexes 12—14 can be exempliꢀ
fied by the spectrum of complex 13 (Fig. 2, a). The obꢀ
served hyperfine structure (HFS) of the spectrum reveals
the HFC of the unpaired electron with the magnetic
isotopes of one copper atom (63Cu, 69.09%, I = 3/2,
μN = 2.2206; 65Cu, 30.91%, I = 3/2, μN = 2.3790)26 and
two equivalent 31P phosphorus nuclei (100%, I = 1/2,
μ
N = 1.13160)26 (triplet 1 : 2 : 1). Large values of the conꢀ
stants of HFC with the copper and phosphorus nuclei (see
Table 1) suggest a pseudotetrahedral geometry of the coꢀ
ordination sphere.30—33 The isotropic ESR spectrum of
complex 15 is shown in Fig. 2, b. The splitting occurs on
one 31Р nucleus and on the magnetic isotopes of one copꢀ
per atom. The values of the HFC constants are much
smaller than in the spectra of complexes 12—14 (see
Table 1) and correspond to the values observed in the ESR
spectra of threeꢀcoordinate oꢀsemiquinone complexes of
copper with a planar trigonal geometry.34
The reactions of diꢀoꢀquinone 1 with two equivalents
of copper(I) 3,6ꢀdi(tertꢀbutyl)ꢀ4,5ꢀdimetoxyꢀoꢀbenzoꢀ
semiquinolates containing all the phosphines listed above,

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Russ.Chem.Bull., Int.Ed., Vol. 59, No. 9, September, 2010
a
Kuropatov et al.
1
2
3
3390
3410
3430
3450
|H|•104/T
b
3400
3420
3440
3460 |H|•104/T
Fig. 3. Change in the ESR spectrum upon reduction of 1 with
copper amalgam in the presence of PPh3 in THF: 1 is the ESR
spectrum of complex 12; 2 is the superposition of the ESR spectra
of complexes 12 and 16; 3 is the ESR spectrum of complex 16.
3430
3434
3438
3442 |H|•104/T
Fig. 2. The ESR spectra of complexes 13 (a) and 15 (b) in THF.
nes react with phosphines to form phospholane rings.31
The reaction of 1 with copper amalgam in the presence of
PPh3 is accompanied by this side reaction (Scheme 2). In
addition, complex 16 forms upon the reduction of phosꢀ
pholane 17 prepared by the reaction of 1 with PPh3 with
copper amalgam (see Scheme 2).31 The ESR spectrum of
compound 16 shows no splitting on the 31P magnetic isoꢀ
tope containing in the phospholane ring.
When a solution of 1 in THF mixed with Mn2(CO)10
was irradiated by the full spectrum of a HBO 50W/AC
lamp equipped with a focusing device (UV region), the
ESR spectrum appears as a sextet (Fig. 4, a) due to the
HFC of the unpaired electron with the 55Mn magnetic
isotope (100%, I = 5/2, μN = 3.4687);26 this suggests the
formation of the semiquinone complex 18 (Scheme 3).
The addition of PPh3 to the reaction mixture enables reꢀ
placement of one CO group in the apical position of this
complex to form the monophosphine derivative 19 (see
Scheme 3) whose ESR spectrum displays an additional
splitting on the magnetic 31Р nucleus (Fig. 4, b). At the
same time, the constant of HFC with the manganese nuꢀ
cleus also increases (see Table 1).
result in precipitation of green powders and no isotropic
ESR signals are observed. The solids thus formed are likeꢀ
ly the corresponding copper(I) complexes. This assumpꢀ
tion is substantiated by the fact that the addition of
equimolar amounts of diꢀoꢀquinone 1 to the compounds
obtained results in their complete dissolution and the apꢀ
pearance of intense ESR spectra of complexes 12—15.
Our attempt to obtain the binuclear copper(I) complex
by direct reduction of diꢀoꢀquinone 1 with copper amalꢀ
gam in the presence of PPh3 in a sealed tube with ESR
monitoring of the process led to observation of the new
initial signal of complex 12 (Fig. 3) and a new ESR specꢀ
trum of a copper(I) complex with lower constants of splitꢀ
ting on the magnetic nuclei of copper and phosphorus. As
the reaction proceeds, the intensity of the second specꢀ
trum increases stepwise while that of the first spectrum
decreases. The second spectrum belongs to the catecholꢀ
semiquinone complex 16 formed upon oxidative addition
of PPh3 to the free quinone ring in the monoꢀoꢀsemiꢀ
quinone complex 12 (Scheme 2). It is known that oꢀquinoꢀ
Scheme 2

ESR study of quinone with tetrathiafulvalene
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 9, September, 2010
1703
Scheme 3
A number of paramagnetic heteronuclear complexes
containing the threeꢀreduced form of ligand 1 was sucꢀ
cessfuly prepared by analogy with triphenylantimony(V)
6ꢀ(tertꢀbutyl)ꢀ4ꢀ[5ꢀ(tertꢀbutyl)ꢀ2ꢀmethylꢀ3,4ꢀdioxocycloꢀ
hexaꢀ1,5ꢀdienyl]ꢀ3ꢀmethylcatecholate.19 The oxidative
addition of triphenylantimony to 1 at an equimolar reacꢀ
tant ratio led to in situ formation of a diamagnetic quinoꢀ
neꢀcatecholate 20, from which the bimetallic complexes
21ꢀ27 were generated following Scheme 4; the parameters
of their isotropic ESR spectra are given in Table 1. The
patterns of the ESR spectra of all semiquinoneꢀcatechoꢀ
late derivatives is analogous to those of the monosemiꢀ
quinone complexes with the same magnetic centers. No
hyperfine coupling with the magnetic isotopes 121,123Sb is
observed. The distinctive features of the ESR spectra of all
the catecholꢀsemiquinone derivatives obtained including
the trisodium complex 8 and complex 16 having the phosꢀ
pholane ring are the smaller of the splittings on the magꢀ
netic centers compared to the ESR spectrum of the
monoreduced form of diꢀoꢀquinone 1 (see Table 1). It
appears that this is due to a lower contribution of the
metal orbitals to the molecular orbital of the complex that
contains the unpaired electron in the case of semiquinoꢀ
neꢀcatecholate.
It should be noted that the paramagnetic derivative 27
formed in the reaction with hexaphenyldistannane was
more stable than triphenyltin semiquinolate 11; its ESR
spectrum appeared as an intense singlet with satellites
(Fig. 5) caused by the HFC of the unpaired electron with
the magnetic isotopes of one tin atom remained unchanged
for long. A high lability of the monosemiquinone comꢀ
plex 11 can be related to the addition of yet one triphenylꢀ
tin fragment to the second quinone ring followed by
elimination of the phenyl groups to form diamagnetic
products.35
a
3426
3434
3442
3450 |H|•104/T
b
|H|•104/T
3400
3420
3440
3460
|H|•104/T
3432 3433 3434 3435 3436 3437
Fig. 4. The ESR spectra of complexes 18 (a) and 19 (b) in THF.
Fig. 5. The ESR spectrum of the binuclear complex 27 in THF.

1704
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 9, September, 2010
Kuropatov et al.
Scheme 4
Scheme 5
All examples listed above charaterize the coordinating
ability of diꢀoꢀquinone 1, which enables realization of all
possible reduced states to form the paramagnetic monoꢀ
semiquinone (2—5, 9—15, 18, and 19) and semiquinoneꢀ
catecholate (8, 16, and 21—27) derivatives, two different
doubly reduced forms (disemiquinone 7 and quinoneꢀcatꢀ
echolate 20), and the diamagnetic dicatecholate form of
the completely reduced sodium dicatecholate (6).
electron reduction of 28 with the silver and copper(II)
salts, as well as with molecular iodine resulted in the radiꢀ
cal cation 29 (Scheme 5) characterized by the singlet ESR
signal with the gꢀfactor (see Table 1) close to that of the
radical cation formed upon the oxidation of 1. The abꢀ
All attempts to oxidize diꢀoꢀquinone 1 at the TTF fragꢀ
ment both in the electrochemical cell and using different
chemical oxidizers (silver triflate, CuCl2, I2, Br2, H2O2)
resulted in the appearance of a singlet with g = 2.0080 in
the ESR spectrum. By analogy with the oxidation of diꢀpꢀ
quinone having the TTF fragment,36 this can be explained
by the formation of the corresponding radical cation. Howꢀ
ever, the intensity of this signal is extremely low. In addiꢀ
tion, the oxidized form was unstable and the signal disapꢀ
peared irreversibly within a few hours.
The oxidation of the diamagnetic chelated triphenyꢀ
lantimony dicatecholate 28 generated in situ allows quanꢀ
titative preparation of the radical cation derivatives. Oneꢀ
3430 3432 3434 3436 3438 3440 3442
|H|•104/T
Fig. 6. The ESR spectrum of the radical salt 30 in THF.

ESR study of quinone with tetrathiafulvalene
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 9, September, 2010
1705
sence of splitting on the magnetic isotopes 121,123Sb conꢀ
firms the fact that the unpaired electron in 29 is localized
just on the TTF fragment and no semiquinone derivatives
are produced in this case. The reaction of 28 with the
strong organic πꢀelectron acceptor TCNQ affords the radꢀ
ical salt 30 (see Scheme 5) whose ESR spectrum displays
the corresponding singlet signal of the radical cation and a
multiplet signal of the radical anion TCNQ– with the typꢀ
ical HFS (Fig. 6, see Table 1). The integrated intensities
of these signals are in a 1 : 1 ratio, which confirms the
formation of the stoichiometric compound 30.
metal complexes using hexane affords the powder samples in
90% yield.
Sodium semiquinoneꢀcatecholate (8). A solution of 1 (0.1178 g,
0.2 mmol) in THF (30 mL) was agitated with sodium amalgam
(0.0138 g, 0.6 mmol) until the solution color changed from violet
to greenishꢀbrown and a precipitate was formed. The resulted
slurry was decanted, separated from mercury metal, and washed
with THF to isolate the deepꢀbrown fineꢀcrystalline complex 8
(0.0921 g, 70%), which is insoluble in organic solvents. Found (%):
C, 54.82; H, 5.51; Na, 10.37; S, 19.18. C30H36Na3O4S4. Calꢀ
culated (%): C, 54.77; H, 5.52; Na, 10.48; S, 19.50. IR,
ν(C—О)/cm–1: 1349, 1227, 1181.
Sodium dicatecholate (6) was prepared analogously to comꢀ
plex 8. Sodium amalgam with an excess of metal (0.1840 g,
8 mmol) was used for the reduction of 1 (0.1178 g, 0.2 mmol).
Upon agitation, a solution became virtually colorless and a goldꢀ
en yellow precipitate formed. Complex 6 was separated by deꢀ
cantation from an excess of amalgam to isolate a yellow fineꢀ
crystalline substance (0.1158 g, 85%) insoluble in organic solꢀ
vents. Found (%): C, 53.13; H, 5.27; Na, 13.62; S, 18.50.
C30H36Na4O4S4. Calculated (%):C, 52.92; H, 5.33; Na, 13.51;
S, 18.84. IR, ν(C—О)/cm–1: 1229, 1184.
Complexes 3, 7, and 8 were obtained from compound 6
by the addition of diꢀoꢀquinone 1 (1.5, 1 or 0.5 equiv., respecꢀ
tively) to it.
Triphenylantimony monocatecholate 20 was synthesized
in situ in THF by oxidative addition of triphenylantimony to
diꢀoꢀquinone 1 (see Ref. 19) at a reactant ratio of 1 : 1. The
resulted blueꢀgreen solution was used for the preparation of the
semiquinoneꢀcatecholate complexes 21—27 according to the
previously described procedures.19
Triphenylantimony dicatecholate 28 was prepared accordꢀ
ing to the analogous procedure19 upon mixing of solutions of 1
and triphenylantimony in THF at a 1 : 2 molar ratio. The addiꢀ
tion of slight amounts of the oxidizing reagents to the resulted
diamagnetic solution led to the change in the solution color from
greenꢀyellow to deepꢀbrown and the ESR spectrum displayed an
intense singlet corresponding to the radical cation 29. Anhydrous
CuCl2, silver triflate, and I2 were used as the oxidizing agents.
The radical ion salt 30 was generated by addition of a soluꢀ
tion of TCNQ in THF to a solution of triphenylantimonic dicatꢀ
echolate 28 prepared in situ according to the procedure described
above. The ESR spectrum of the resulted brown solution disꢀ
played the signal typical of the radical cations and radical anions
contained in 30.
Experimental
ESR spectra were recorded on a Bruker EMX spectrometer.
Electronic absorption spectra were recorded on a PerkinꢀElmer
Lambda 25 spectrophotometer in an evacuated cell made of
molybdenum glass with an absorption layer thickness of 5 mm.
IR spectra were recorded on a FSMꢀ1201 FTꢀIR spectrometer.
Solvents were purified and dried according to conventional
procedures.37 Diꢀoꢀquinone 1 was synthesized according to the
previously described procedure.25 The samples of the paramagꢀ
netic derivatives 2—5, 9—15, 18, and 19 for ESR studies were
prepared in evacuated tubes in THF according to known proceꢀ
dures for the synthesis of semiquinone complexes.11—13 All proꢀ
cedures for the synthesis and isolation of the sodium complexes
3 and 6—8 were performed in vacuo or in argon atmosphere.
The semiquinoneꢀcatecholate complex 16 was generated in
THF solution by reduction of 1 with copper amalgam in the
presence of excess PPh3. The reaction was performed with conꢀ
tinuous stirring in a sealed tube. The initially emerged ESR sigꢀ
nal of the monosemiquinone complex 12 was transformed stepꢀ
wise to the signal of complex 16 with the phospholane ring. The
process completed within 5 days. The ESR signal of compound
16 was also recorded upon the addition of copper to a solution of
phospholane 17 prepared according to a known procedure.31
Sodium monosemiquinolate (3). A solution of diꢀoꢀquinone 1
(0.1178 g, 0.2 mmol) in THF (40 mL) was agitated with sodium
amalgam containing sodium (0.0046 g, 0.2 mmol) for a few minꢀ
utes. The resultant darkꢀblue solution was filtered off and conꢀ
centrated to 5 mL. After cooling to –20 °C, the darkꢀblue fineꢀ
crystalline complex 3 (0.0490 g, 40%) was isolated. The comꢀ
pound is insoluble in hydrocarbons, halogenated hydrocarbons,
Et2O, MeCN, and is partially soluble in MeOH. Found (%):
C, 59.11; H, 5.87; Na, 3.82; S, 20.85. C30H36NaO4S4. Calculatꢀ
The oxidation of 1 was performed using silver triflate, CuCl2,
I2, Br2 or a diluted solution of H2O2 in THF, CH2Cl2, and
MeCN. In all cases, the solution color remained violet and the
ESR signal (singlet, g = 2.0080) had low intensity and disapꢀ
peared for a few hours.
ed (%): C, 58.89; H, 5.93; Na, 3.76; S, 20.96. IR, ν(C—О)/cm–1
1599, 1406, 1359. EAS (THF), λmax/nm: 400 (ε 11000), 685
(ε 16000).
:
Sodium disemiquinolate (7) was obtained analogously. Sodiꢀ
um (0.0092, 0.4 mmol) was used for the reduction of 1 (0.1178 g,
0.2 mmol). Complex 7 (0.0381 g, 30%) was isolated as darkꢀ
green fine crystals from the green solution upon cooling. Comꢀ
pound 7 is insoluble in organic solvents, except for THF. Found
(%): C, 56.55; H, 5.77; Na, 7.28; S, 20.11. C30H36Na2O4S4.
Calculated (%): C, 56.76; H, 5.72; Na, 7.24; S, 20.20. IR,
ν(C—О)/cm–1: 1403, 1352. EAS (THF), λmax/nm: 390 (ε 25000),
990 (ε 13000).
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 10ꢀ03ꢀ00788
and 10ꢀ03ꢀ00921) and the Council for Grants at
the President of the Russian Federation (Program for Supꢀ
port of Leading Scientific Schools of the RF, Grant
NShꢀ7065.2010.3). This research work was performed as
a part of the Federal Target Progam "Academic and Teachꢀ
ing Staff of Innovative Russia" in 2009—2013 (GK P839
of May 25, 2010).
The low yields of complexes 3 and 7 are explained by
sufficiently high solubility in THF. Precipitation of the

1706
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Kuropatov et al.
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Received July 21, 2010