Heterospin biradicals based on new piperidineoxyl-substituted 3,6-di-tert-butyl-o-benzoquinone

Article abstract of DOI:10.1007/s11172-017-1934-1

A nucleophilic addition reaction of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (OH-TEMPO) to 3,6-di-tert-butyl-o-benzoquinone was used to obtain a new sterically hindered o-benzoquinone (1) containing 2,2,6,6-tetramethylpiperidineoxyl functional group, which was characterized by IR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction. A one-electron reduction of 1 with potassium and thallium is an efficient method for the generation of earlier unknown heterospin biradicals 5a and 5b, respectively, containing nitroxide and o-semiquinone radical centers. Analysis of the hyperfine structure of the ESR spectra of biradicals 5a and 5b in solution showed that they belong to the group of heterospin biradicals with strong (J >> a) and fast exchange interaction between the radical centers.

Full text of DOI:10.1007/s11172-017-1934-1

Russian Chemical Bulletin, International Edition, Vol. 66, No.9, pp. 1629—1635, September, 2017
1629
Heterospin biradicals based on new piperidineoxylꢀsubstituted
3,6ꢀdiꢀtertꢀbutylꢀoꢀbenzoquinone*
E. N. Egorova, N. O. Druzhkov, K. A. Kozhanov, A. V. Cherkasov, and V. K. Cherkasov
G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhny Novgorod, Russian Federation.
Fax: +7 (831) 462 7497. Eꢀmail: cherkasov@iomc.ras.ru
A nucleophilic addition reaction of 4ꢀhydroxyꢀ2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxyl (OHꢀ
TEMPO) to 3,6ꢀdiꢀtertꢀbutylꢀoꢀbenzoquinone was used to obtain a new sterically hindered
oꢀbenzoquinone (1) containing 2,2,6,6ꢀtetramethylpiperidineoxyl functional group, which
was characterized by IR spectroscopy, mass spectrometry, elemental analysis, and Xꢀray
diffraction. A oneꢀelectron reduction of 1 with potassium and thallium is an efficient method
for the generation of earlier unknown heterospin biradicals 5a and 5b, respectively, containꢀ
ing nitroxide and oꢀsemiquinone radical centers. Analysis of the hyperfine structure of the
ESR spectra of biradicals 5a and 5b in solution showed that they belong to the group of
heterospin biradicals with strong (J >> a) and fast exchange interaction between the radical
centers.
Key words: sterically hindered 2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxyl, synthesis, oneꢀelecꢀ
tron reduction, heterospin biradicals, generation.
One of the directions in the design of molecular magꢀ
nets is the search for new bifunctional paramagnetic
ligands to be used in the construction of multispin biꢀ and
polynuclear metal complexes, as well as coordination
polymers. Nitroxide (nitronylꢀnitroxide) and oꢀsemiꢀ
quinone derivatives are two most representative classes of
radical organic ligands. The works of the school of Acaꢀ
demician G. A. Abakumov made a great contribution to
the formation and development of the chemistry of metal
complexes with these radical ligands.1—4 To date, a large
number of 2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxylꢀderived
paramagnetic ligands have been synthesized, which, in
addition to the nitroxide magnetic center, also contain
a functional group providing additional coordination with
the metal.5—8
Biradical heterospin ligands simultaneously containꢀ
ing two magnetic centers of different nature are of particꢀ
ular interest as building blocks in the construction of
molecular magnets. The most promising is a combinaꢀ
tion in this ligand of nitroxide and oꢀsemiquinone radical
centers, both capable to form strong coordination bonds
with the metal center. There are known several examples
of oꢀsemiquinone ligands functionalized with a nitronylꢀ
nitroxide substituents, in which the radical substituent is
bonded to the aromatic system of the oꢀsemiquinone fragꢀ
ment either directly or through a conjugated bridge.9—15
The first examples of sterically hindered 3,5ꢀdiꢀtertꢀbutylꢀ
pyrocatechol and the corresponding oꢀbenzoquinone
functionalized with 2,2,6,6ꢀtetramethylpiperidineoxyl
fragment are described in the work.16 No 3,6ꢀdiꢀtertꢀ
butylꢀoꢀbenzoquinone derivatives with piperidineoxyl
substituents have been known to date.
The purpose of the present work is the synthesis of
sterically hindered 3,6ꢀdiꢀtertꢀbutylꢀsubstituted oꢀbenzoꢀ
quinone with a radical 2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀ
oxyl fragment at position 4 of the aromatic ring, which is
regarded as a starting reagent for obtaining heterospin
(containing different in nature centers) biradicals, and
study of their ESR spectra.
The functionalization of oꢀbenzoquinones allowing
variation of their redox properties can be accomplished by
nucleophilic addition of organoelement compounds,17,18
alcohols,19 primary and secondary amines,20,21 C—H
acids.22,23 The nucleophilic addition of alcohols to
oꢀquinones is carried out in acetonitrile with a catalytic
amount of potassium hydroxide and leads to the correꢀ
sponding alkoxyꢀsubstituted oꢀbenzoquinones as the final
reaction products.
The reaction of 3,6ꢀdiꢀtertꢀbutylꢀoꢀbenzoquinone
(3,6ꢀQ) with 2,2,6,6ꢀtetramethylꢀ4ꢀhydroxypiperidineꢀ
oxyl (OHꢀTEMPO) under such conditions leads to a mixture
of unidentified products. The search for the conditions for
the synthesis of the target alkoxyquinone showed that the
optimal version is carrying out the reaction of 3,6ꢀQ and
OHꢀTEMPO in decane at 110 °C for two hours (Scheme 1).
* Dedicated to Academician of the Russian Academy of Sciences
G. A. Abakumov on the occasion of his 80th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1629—1635, September, 2017.
1066ꢀ5285/17/6609ꢀ1629 © 2017 Springer Science+Business Media, Inc.

1630
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017
Egorova et al.
Scheme 1
i. Decane, 110 °C.
The target 4ꢀ(3,6ꢀdiꢀtertꢀbutylꢀ1,2ꢀdioxocyclohexaꢀ
3,5ꢀdienꢀ4ꢀyloxy)ꢀ2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxyl
(1) was isolated in the individual state as dark red crystals
after separation of the reaction mixture by column chroꢀ
matography (80% yield calculated on OHꢀTEMPO).
Apart from that, some other reaction products were idenꢀ
tified, namely, 3,6ꢀdiꢀtertꢀbutylꢀ4ꢀ[(1ꢀhydroxyꢀ2,2,6,6ꢀ
tetramethylpiperidinꢀ4ꢀyl)oxy]cyclohexaꢀ3,5ꢀdienꢀ1,2ꢀ
dione (2) (4ꢀalkoxyquinone with the protonated nitroxide)
in ∼5% yield calculated on OHꢀTEMPO, 3,6ꢀdiꢀtertꢀ
butylpyrocatechol (3), and 2´,4,5´,7ꢀtetraꢀtertꢀbutylꢀ3´ꢀ
hydroxyꢀ3a,7aꢀdihydrospiro[benzodioxylꢀ2,1´ꢀcyclohexaꢀ
[2,5]diene]ꢀ4´ꢀone (4) (the coupling product of the startꢀ
ing 3,6ꢀQ) in 8% yield calculated on OHꢀTEMPO. The
formation of pyrocatechol 3 is explained by the oxidation
of the primary product of nucleophilic addition (4ꢀalkoxyꢀ
pyrocatechol A) with the starting quinone 3,6ꢀQ, while
the reduction of the TEMPOꢀcontaining quinone 1 to
piperidinehydroxyquinone 2 becomes possible as any of
the pyrocatechols appear in the reaction mixture. Note
that product 2 readily undergoes oxidation to oꢀquinone
1 even with air oxygen. Running a solventꢀfree reaction
of 3,6ꢀQ with OHꢀTEMPO leads to the local overheating
of the mixture, which results in the increase in the conꢀ
tent of the side product 4 up to 15% calculated on the
starting OHꢀTEMPO and in the decrease in the yield of
the target (piperidineoxyl)oxyquinone 1.
The structure of new alkoxyquinone 1 was confirmed
by IR and ESR spectroscopy, as well as by mass spectroꢀ
metry and Xꢀray crystallography.
The IR spectrum of compound 1 exhibits vibrations in
the region of 1635 and 1678 cm–1 corresponding to the
C=O carbonyl bonds of oꢀquinone, as well as a characterꢀ
istic vibrational band of the N—O• group (1365 cm–1).24
Apart from that, a band at 1236 cm–1 corresponding to
the asymmetric stretching vibrations of the CH2O—
quinone ether group is present in the spectrum.
The isotropic ESR spectrum of functionalized
oꢀquinone 1 is typical of 2,2,6,6ꢀtetramethylꢀ4ꢀhydrꢀ
oxypiperidineoxyl derivatives25,26 and has a triplet patꢀ
tern (1 : 1 : 1) with gi = 2.0060 due to the hyperfine
coupling (HFC) with one nitrogen nucleus (14N, 99.64%,
I = 1, gN = 0.404), aN = 1.535 mT (Fig. 1). The hyperꢀ
fine structure (HFS) on the protons of the methyl and
the methylene groups (1H, 99.99%, I = 1/2, gN=5.586)
is not observed because of too broad line (∼0.18 mT),
considerably exceeding the value of the HFC constant
(aH < 0.05 mT).

Heterospin biradicals based on 3,6ꢀQꢀTEMPO
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017 1631
Table 1. Selected bond distances (d) and bond angles (ω) in
compound 1
Bond
d/Å
Angle
ω/deg
1
O(1)—C(1)
1.214(6)
1.221(3)
1.220(7)
1.223(3)
1.553(7)
1.565(4)
1.357(2)
1.459(2)
1.514(2)
1.515(2)
1.288(2)
1.495(2)
1.497(2)
O(1)—C(1)—C(2)
117.7(2)
118.0(5)
106.9(5)
117.6(2)
119.4(2)
108.7(2)
124.8(2)
115.7(2)
115.6(2)
O(2)—C(2)
C(1)—C(2)
C(1)—C(2)—O(2)
C(4)—O(3)—C(7)
C(8)—C(7)—C(15)
C(9)—N(1)—C(12)
C(9)—N(1)—O(4)
C(12)—N(1)—O(4)
C(4)—O(3)
O(3)—C(7)
C(7)—C(8)
C(7)—C(15)
N(1)—O(4)
N(1)—C(9)
N(1)—C(12)
1´
10 Oe
Fig. 1. Experimental (1)and simulated (1´) ESR spectra of
oꢀbenzoquinone 1 (THF, ∼20 °C).
positions. The geometry of the OCCO dicarbonyl fragꢀ
ment is distorted, however, the C=O (1.214(6)—1.223(3) Å)
and C—C bond distances (1.553(7)—1.565(4) Å) are comꢀ
parable with the analogous values in similar oꢀquinones.27
The O(1)—C(1)—C(2) and C(1)—C(2)—O(2) angles lie
in a wide range of values 106.9(5)—118.0(5)°. The OCCO
fragment in 1 is nonplanar (the O—C—C—O torsion
angles lie within 3.9(9)—10.8(3)°), but is distorted conꢀ
siderably less than in other 3,6ꢀtertꢀbutylꢀoꢀquinone deꢀ
rivatives with bulky substituents at positions 4 and 5 of
the oꢀquinone ring.28
The tetramethylpiperidineꢀ1ꢀoxyl substituent in molꢀ
ecule 1 is in the chair conformation characteristic of such
fragments29 and is arranged at an angle to the oꢀquinone
fragment (a dihedral angle between the mean planes of
the sixꢀmembered rings is equal to 66.69(9)°). The
N(1)…C(4) distance in 1 is 5.132(2) Å.
The mass spectrometry analysis showed that the mass
spectrum of oꢀquinone 1 contained a peak attributed to
the molecular ion with m/z = 390 (M+) and a peak of the
ion corresponding to the 4ꢀhydroxypiperidineoxyl fragꢀ
ment with m/z = 171. A similar examination of oꢀquinoꢀ
ne 2 showed the presence in its mass spectrum of a molecꢀ
ular ion peak with m/z = 391 (M+).
The molecular and crystal structure of 1 was also conꢀ
firmed by Xꢀray diffraction. An independent region of the
crystal cell contains one molecule of oꢀquinone 1 and one
THF molecule. The molecular structure of 1 is shown in
Fig. 2. Selected bond distances and bond angles in the
molecule are given in Table 1.
In molecule 1, the carbonyl fragments and the tertꢀ
butyl substituent at atom C(6) are disordered over two
In order to obtain heterospin biradicals, we studied
the reduction reaction of oꢀquinone 1 with metallic poꢀ
tassium (Scheme 2) and thallium (Scheme 3). The reacꢀ
tion of 1 with potassium metal in THF led to a gradual
transformation of the initial signal of 1 to a new triplet
(1 : 1 : 1) of doublets (1 : 1) with gi = 2.0055 (Fig. 3). The
hyperfine structure of the ESR spectrum is caused by the
interaction of the unpaired electron with one nitrogen
nucleus 14N (aN = 0.78 mT) and one hydrogen nucleus
(aH = 0.18 mT). The observed values of parameters of the
isotropic ESR spectrum of 5 are equal to half the HFC
constant values aN and aH in common nitroxide and
oꢀsemiquinone radicals, which corresponds to the case of
heterospin biradical with strong and fast (J >> a) exꢀ
change interaction between different in nature magnetic
centers.33
C(14)
C(13)
C(6)
O(4)
C(12)
C(15)
C(7)
C(5)
O(1)
C(10)
N(1)
C(9)
C(1)
C(2)
C(4)
O(3)
C(8)
C(11)
O(2)
C(3)
Similar heterospin biradicals are described in the litꢀ
erature, namely, tetramethylpiperidineꢀ1ꢀoxyl derivatives
containing a phenoxyl or a diphenylpicrylhydrazyl fragꢀ
ment along with the nitroxide one.33 Computer simulaꢀ
Fig. 2. Molecular structure of compound 1. Thermal ellipsoids
are given with 30% probability. Hydrogen atoms are omitted.

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Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017
Egorova et al.
Scheme 2
Scheme 3
tion34 was used to determine ESR parameters for the
nitroxide and semiquinone radical centers in biradical 5a:
decreases until it completely disappears, which correꢀ
sponds, most likely, to the formation of the final diamagꢀ
netic trianion 7a. The signal corresponding to the nitrꢀ
oxylꢀcatecholate complex 8, yet another possible reducꢀ
tion product of biradical 5a (Scheme 2), is not observed
in the ESR spectrum. From this, it can be concluded that
the reduction of the nitroxide group in the heterospin
biradical 5a proceeds more easily than the reduction of
the semiquinone one.
gi = 2.00645, aN = 1.555 mT and gi = 2.00455, aH
=
= 0.355 mT, respectively, at an exchange interaction
energy J > 3000 MHz.
Thus, the reduction of oꢀquinone 1 with metallic potasꢀ
sium leads to the formation of the heterospin biradical 2.
A further reduction of biradical 5 with metallic potasꢀ
sium led to almost complete disappearance of its ESR
spectrum and the appearance of a new signal, a doublet
HFS of which is associated with the HFC of the unpaired
electron with one hydrogen nucleus. The parameters of
the HFS of the observed ESR spectrum (Fig. 3, c) with
gi = 2.0047 and aH = 0.37 mT are typical of the radical
anions of 3,6ꢀdiꢀtertꢀbutylꢀoꢀbenzoquinone 4ꢀalkoxy deꢀ
rivatives and indicate the reduction in the second step of
the process of the nitroxide center of biradical 5a with the
formation of a monoradical oꢀsemiquinone derivative 6a.
Upon further reduction, the ESR signal of 6 gradually
A reduction of oꢀquinone 1 with thallium gave similar
results (Scheme 3).
Thus, the signal of the starting oꢀquinone 1 initially
undergoes transformation into the signal of biradical 5b,
the ESR spectrum of which is a doublet (1 : 1) of triplets
(1 : 1 : 1) of doublets (1 : 1) with gi = 2.0017 and the HFS
caused by the HFC with one thallium nucleus (205Tl, 70.5%,
I = 1/2, gN = 3.275, 203Tl, 29.5%, I = 1/2, gN = 3.245)
aTl = 2.59 mT, one nitrogen nucleus aN = 0.775 mT, and
one proton aH = 0.18 mT (Fig. 4, b). The presence of an

Heterospin biradicals based on 3,6ꢀQꢀTEMPO
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017 1633
a
b
a
b
b´
b´
10 Oe
c
c
Fig. 3. The ESR spectra of the products of the reaction of
oꢀquinone 1 with potassium (THF, ∼20 °C) at the beginning of
the reaction (a), 20 (b, b´) and 45 min after the beginning of
the reaction (c); b, b´ are the experimental and the simulated
spectra, respectively.
10 Oe
Fig. 4. The ESR spectra of the products of the reaction of
oꢀquinone 1 with thallium amalgam (THF, ∼20 °C) 5 (a),
10 (b, b´), and 50 min after the beginning of the reaction (c);
b, b´ are the experimental and the simulated spectra, respectively.
additional coupling on the magnetic isotopes of thallium
is associated with the formation of a chelate semiquinone
complex.3 As in the previous case, the ESR signal indiꢀ
cates the biradical nature of 5b with strong and fast exꢀ
change interaction (J > 3500 MHz) between two differꢀ
ent in nature radical centers: the nitroxide (gi = 2.00625,
aN = 1.50 mT) and the semiquinone (gi = 1.9975,
aTl = 5.19 mT, aH = 0.36 mT).
showed that they belong to the group of heterospin biradꢀ
icals with strong (J >> a) and fast exchange interaction
between the radical centers.
Experimental
Like in the case with potassium, further reaction leads
to the reduction of the nitroxide radical center with the
formation of thallium(I) oꢀsemiquinolate 6b. Its ESR
spectrum is typical of the thallium(I) oꢀsemiquinone
derivatives and is a doublet (1 : 1) of doublets (1 : 1) with
gi = 1.9974 caused by the HFC of the unpaired electron
with the magnetic isotopes of thallium 203Tl and 205Tl
(aTl = 5.03 mT) and one proton (aH = 0.375 mT) (see
Fig. 4, c). More deep reduction leads to the formation of
diamagnetic catecholate 7b and, therefore, to the disapꢀ
pearance of the ESR signal.
In conclusion, we have developed and implemented
a procedure for the synthesis of new sterically hindered
3,6ꢀdiꢀtertꢀbutylꢀoꢀbenzoquinone functionalized with
4ꢀhydroxyꢀ2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxyl 1. We
have shown that the oneꢀelectron reduction of compound 1
is an efficient method for the generation of earlier unꢀ
known heterospin biradicals 5a and 5b containing nitrꢀ
oxide and oꢀsemiquinone radical centers. Analysis of the
HFS of the ESR spectra of the biradicals in solution
IR spectra were recorded on a FSM 1201 IR Fourierꢀtransꢀ
form spectrometer (a suspension in Nujol), ESR spectra were
recorded on a Bruker ER 200 DSRC spectrometer equipped
with an ER 4105 DR double resonator and an ER 4111 VT
thermocontroller, diphenylpicrylhydrazyl was used as a stanꢀ
dard in the determination of the gꢀfactor values. Mass spectra
were recorded on a Polaris Q mass spectrometer. The energy of
the ionizing electrons 70 eV.
Xꢀray diffraction study of compound 1 was carried out on an
Agilent Xcalibur E diffractometer (MoKα radiation, λ = 0.71073 Å,
ωꢀscan technique, T = 120 K). The integration of experimental
array of intensities and the correction for absorption were carꢀ
ried out using the CrysAlis PRO software package.35 The strucꢀ
ture was solved by a direct method and refined by the fullꢀ
matrix leastꢀsquares method with respect to F2 in the anisoꢀ
hkl
tropic approximation for nonhydrogen atoms. All the hydrogen
atoms were placed in geometrically calculated positions and
refined isotropically. The calculations were made using the
SHELX software package.36
Crystallographic data, parameters of Xꢀray diffraction
experiment and refinement for compound 1 are as follows:

1634
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017
Egorova et al.
C23H36NO4•C4H8O, molecular weight 462.63, Pbca,
a = 22.0737(4) Å, b = 10.8741(2) Å, c = 22.1030(5) Å, α = β =
2. G. A. Razuvaev, V. D. Tikhonov, G. A. Abakumov, Bull.
Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.), 1970,
19, 1634.
= γ = 90°, V = 5305.4(2) Å3, Z = 8, dcalc = 1.158 mg m–3
,
μ = 0.078 mm–1, range of scanning 3.21—27.10°, 74242 reꢀ
flection were measured (5838 of them were independent,
Rint = 0.0481), GOOF(F2) = 1.014, R1 = 0.0604 (I > 2σ(I)),
R2 = 0.1806 (on all the data), the maximum and the miniꢀ
3. V. A. Muraev, G. A. Abakumov, G. A. Razuvayev, Dokl. Akad.
Nauk SSSR,1974, 217, 5, 1083 [Dokl. Chem. (Engl. Transl.),1974].
4. G. A. Abakumov, Zh. Ros. khim. oꢀva im. D. I. Mendeleyeva
[Russ. Mendeleyev Chem. J.], 1979, 156 (in Russian).
5. S. V. Larionov, J. Struct. Chem., 1983, 23, 594.
6. S. S. Eaton, Coord. Chem. Rev., 1978, 26, 20.
7. S. S. Eaton, G. R. Eaton, Coord. Chem. Rev., 1988, 83, 29.
8. A. V. Artem´ev, O. V. Vysotskaya, L. A. Oparina, A. S.
Bogomyakov, S. S. Khutsishvili, I. V. Sterkhova, V. I.
Ovcharenko, B.A. Trofimov, Polyhedron, 2016, 119, 293.
9. D. A. Shultz, S. H. Bodnar, K. E. Vostrikova, J. W. Kampf,
Inorg. Chem., 2000, 39, 6091.
10. E. Depperman, S. H. Bodnar, K. E. Vostrikova, D. A.
Shultz, M. L. Kirk, J. Am. Chem. Soc., 2001, 123, 3133.
11. D. Shultz, K. Vostrikova, S. Bodnar, H. Koo, M. Whangbo,
M. Kirk, E. Depperman, J. Kampf, J. Am. Chem. Soc.,
2003, 125, 1607.
12. M. L. Kirk, D. A. Shultz, E. C. Depperman, Polyhedron,
2005, 24, 2880.
13. D. A. Shultz, R. K. Kumar, S. BinꢀSalamon, M. L. Kirk,
Polyhedron, 2005, 24, 2876.
14. D. E. Stasiw, J. Zhang, G. Wang, R. Dangi, B. W. Stein,
D. A. Shultz, M. L. Kirk, L. Wojtas, R. D. Sommer, J. Am.
Chem. Soc., 2015, 137, 9222.
15. E. V. Tretyakov, S. E. Tolstikov, G. V. Romanenko, A. S.
Bogomyakov, V. K. Cherkasov, D. V. Stass, V. I. Ovcharenko,
Russ. Chem. Bull., 2011, 60, 2325.
16. N. O. Druzhkov, E. N. Egorova, M. V. Arsen´ev, E. V. Baraꢀ
nov, V. K. Cherkasov, Russ. Chem. Bull., 2016, 65, 2855.
17. G. A. Abakumov, V. K. Cherkasov, L. G. Abakumova,
N. O. Druzhkov, V. I. Nevodchikov, Yu. A. Kursky, N. P.
Makarenko, Metalloorgan. Khimiya, 1991, 925 [Organomet.
Chem. USSR (Engl. Transl.), 1991].
18. G. A. Abakumov, V. K. Cherkasov, L. G. Abakumova, V. I.
Nevodchikov, N. O. Druzhkov, N. P. Makarenko, Yu. A.
Kursky, J. Organometallic. Chem., 1995, 491, 127.
19. M. P. Shurygina, N. O. Druzhkov, M. V. Arsen´yev, M. P.
Bubnov, G. K. Fukin, S. A. Chesnokov, V. K. Cherkasov,
Zh. Org. Khim, 2011, 47, 490 [Russ. J. Org. Chem. (Engl. Transl.),
2011, 47].
20. G. A. Abakumov, V. K. Cherkasov, T. N. Kocherova, N. O.
Druzhkov, Yu. A. Kurskii, L. G. Abakumova, Russ. Chem.
Bull., 2006, 55, 1195.
21. G. A. Abakumov, V. K. Cherkasov, T. N. Kocherova, N. O.
Druzhkov, Yu. A. Kurskii, M. P. Bubnov, G. K. Fukin,
L. G. Abakumova, Russ. Chem. Bull., 2007, 56, 1849.
22. G. A. Abakumov, V. I. Nevodchikov, N. V. Zaitova, N. O.
Druzhkov, L. G. Abakumova, Yu. A. Kurskii, V. K. Cherkaꢀ
sov, Russ. Chem. Bull., 1997, 46, 2093.
mum of the residual electron density was 0.522/–0.546 e Å–3
.
The structure was deposited with the Cambridge Crystalloꢀ
graphic Data Center (CCDC 1557609) and is available at
ccdc.cam.ac.uk/structures.
3,6ꢀDiꢀtertꢀbutylꢀoꢀbenzoquinone was synthesized accordꢀ
ing to the known procedure.37 Solvents were dried and purified
according to the standard procedures.38 4ꢀHydroxyꢀ2,2,6,6ꢀ
tetramethylpiperidineꢀ1ꢀoxyl (OHꢀTEMPO) was commerꢀ
cially available from Aldrich. Column chromatography was perꢀ
formed on silokhrom Cꢀ120 (Reakhim), eluent light petroleum
ether—THF (50 : 1).
Reaction of 3,6ꢀdiꢀtertꢀbutylꢀoꢀbenzoquinone and 4ꢀhydroxyꢀ
2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxyl. 3,6ꢀDiꢀtertꢀbutylꢀoꢀbenzoꢀ
quinone (2.57 g, 11.6 mmol) was fused with 2,2,6,6ꢀtetramethꢀ
ylꢀ4ꢀhydroxypiperidineoxyl (1 g, 5.8 mmol) in the presence of
decane (2 mL) with heating in an oil bath at 110 °C for 2 h.
Then, the cake was washed with acetone and filtered from
2´,4,5´,7ꢀtetraꢀtertꢀbutylꢀ3´ꢀhydroxyꢀ3a,7aꢀdihydrospiro(benzoꢀ
1,3ꢀdioxolꢀ2,1´ꢀcyclohexa[2,5]diene)ꢀ4´ꢀone (4), a side prodꢀ
uct poorly soluble under these conditions. The mother liquor
was concentrated and separated by column chromatography.
Eluent light petroleum ether—THF (50 : 1).
According to the NMR spectroscopy data, the first yellow
band contained 3,6ꢀdiꢀtertꢀbutylpyrocatechol (3). Dark red
crystals of 4ꢀ(3,6ꢀdiꢀtertꢀbutylꢀ1,2ꢀdioxocyclohexaꢀ3,5ꢀdienꢀ4ꢀ
yloxy)ꢀ2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxyl (1) were isolated
from the second reddish brown band after removal of the eluent
and crystallization from diethyl ether. M.p. 173 °C. Found (%):
C, 70.92; H, 9.54. C23H36NO4. Calculated (%): C, 70.74; H,
9.29. m/z: 390.26 (M+). IR, ν/cm–1: 480 w, 552 w, 587 w, 601
w, 650 w, 681 m, 721 m, 739 m, 809 w, 830 w, 844 w, 877 m,
888 m, 912 m, 921 m, 938 m, 964 s, 978 s, 999 w, 1024 m, 1083 s,
1185 s, 1202 s, 1236 s (CH2O of quinone), 1300 s, 1314 s, 1365 s
(N—O·), 1396 m, 1417 m, 1543 s, 1625 s, 1635 s (C=O),
1678 s (C=O).
The mass spectrometry data showed that the third light
brown band contained 4ꢀalkoxyquinone with a protonated nitrꢀ
oxyl, 3,6ꢀdiꢀtertꢀbutylꢀ4ꢀ[(1ꢀhydroxyꢀ2,2,6,6ꢀtetramethylpipeꢀ
ridinꢀ4ꢀyl)oxy]cyclohexaꢀ3,5ꢀdieneꢀ1,2ꢀdione (2), which upon
evaporation of the eluent in air slowly oxidized to the target
oꢀquinone 1. Found (%): C, 70.76; H, 9.89. C23H37NO4. Calꢀ
culated (%): C, 70.55; H, 9.52. m/z: 391.27 (M+). 1H NMR, δ:
1.25 (s, 12 H, Me); 1.31 (s, 18 H, But); 2.01 and 2.07 (both d,
2 H each, CH2, J = 3.60 Hz). 13C NMR, δ: 29,0 (Me); 30.6
(C(CH3)3); 35.1 (C(CH3)3); 77 2 (C—CH2—C); 129.3; 149.2;
181,8 (C=O); 184.9 (C=O).
23. G. A. Abakumov, V. I. Nevodchikov, N. V. Zaitova, N. O.
Druzhkov, L. G. Abakumova, Yu. A. Kurskii, V. K. Cherkaꢀ
sov, Russ. Chem. Bull., 1997, 46, 337.
24. V. T. Kasumov, I. Uзar, A. Bulut, Y. Yerli, Solid State
Sciences, 2011, 13, 1852.
This work was financially supported by the Russian
Science Foundation (Project No. 14ꢀ13ꢀ01296ꢀP).
25. C. C. Whisnant, S. Ferguson, D. B. Chesnut, J. Phys. Chem.,
1974, 78, 1410.
References
26. J. J. Windle, Magnetic Resonance, 1981, 45, 432.
27. C. G. Pierpont, R.M. Buchanan, Coord. Chem. Rev., 1981,
38, 45.
1. G. A. Razuvayev, G. A. Abakumov, E. S. Klimov, Dokl. Akad.
Nauk SSSR, 1971, 201, 3, 624 [Dokl. Chem. (Engl. Transl.), 1971].

Heterospin biradicals based on 3,6ꢀQꢀTEMPO
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017 1635
28. G. K. Fukin, A. V. Cherkasov, M. P. Shurygina, N. O.
Druzhkov, V. A. Kuropatov, S. A. Chesnokov, G. A. Abakuꢀ
mov, Struct. Chem., 2010, 21, 607.
37. E. G. Rozantsev, V. D. Sholle, Organicheskaya khimiya
svobodnykh radikalov [Organic Chemistry of Free Radicals],
Khimiya, Moscow, 1973, 344 pp. (in Russian).
29. O. L. Lebelev, S. N. Kazarnovskii, J. Gen. Chem. USSR,
1960, 30, 1631.
30. E. G. Rozantsev, V. D. Sholle, Synthesis, 1971, 401.
31. W. R. Couet, Tetrahedron, 1985, 41, 1165.
32. V. D. Sen, V. A. Golubev, N. N. Efimova, Bull. Acad. Sci.
USSR, Div. Chem. Sci., 1982, 31, 53.
38. A. J. Gordon, R. A. Ford, The Chemist´s Companion.
A Handbook of Practical Data, Techniques, and References,
Wiley Interscience, New York, 1972.
39. M. P. Shurygina, N. O. Druzhkov, M. V. Arsen´ev, M. P.
Bubnov, G. K. Fukin, S. A. Chesnokov, V. K. Cherkasov,
Russ. J. Org. Chem., 2011, 47, 486.
33. R. W. Kreilick, Chem. Phys. Letters, 1968, 2, 277.
34. S. Stoll, A. Schweiger, J. Magn. Res., 2006, 178, 42.
35. Agilent, CrysAlis PRO, 2014, Agilent Technologies Ltd,
Yarnton, Oxfordshire, England.
36. G. M. Sheldrick, Acta Cryst., 2015, C71, 3.
Received June 22, 2017