Reaction of 2-ethyl-1,3,2-bezoxaphospholine with calix[4]resorcinarenes

Article abstract of DOI:10.1023/A:1012365203479

By reaction of calix[4]resorcinarene with 2-ethyl-1,3,2-benzoxazaphospholine in 1 : 1 ratio we prepared a cavitand possessing one dioxaphosphocinic fragment on the upper circle of the molecule. Reaction of the same compounds in ether solution in 1 : 4 and 1 : 8 ratio according to the data of spectral methods leads initially to formation of addition product, the P-H phosphorane with composition 1 : 4. This compound is not stable and on keeping forms 2-oxo-2-ethyl-1,3,2-benzoxazaphospholine, spirophosphorane, o-aminophenol and phosphorylated calixarene. In the reaction of the aminoalkylated calixarene with 2-ethyl-1,3,2-benzoxaza-phospholine we isolated a compound possessing four hydrophoshonyl fragments on the upper circle of the calixarene matrix.

Full text of DOI:10.1023/A:1012365203479

Russian Journal of General Chemistry, Vol. 71, No. 3, 2001, pp. 389 395. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 3, 2001,
pp. 426 432.
Original Russian Text Copyright
2001 by Terent’eva, Nikolaeva, Burilov, Kharitonov, Popova, Pudovik, Litvinov, Gubaidullin, Konovalov.
Reaction of 2-Ethyl-1,3,2-bezoxaphospholine
with Calix[4]resorcinarenes
S. A. Terent’eva, I. L. Nikolaeva, A. R. Burilov,
D. I. Kharitonov, E. V. Popova, M. A. Pudovik,
I. A. Litvinov, A. T. Gubaidullin, A. I. Konovalov
Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center,
Russian Academy of Sciences, Kazan, Tatarstan, Russia
Received June 15, 2000
Abstract By reaction of calix[4]resorcinarene with 2-ethyl-1,3,2-benzoxazaphospholine in 1: 1 ratio we
prepared a cavitand possessing one dioxaphosphocinic fragment on the upper circle of the molecule. Reaction
of the same compounds in ether solution in 1: 4 and 1: 8 ratio according to the data of spectral methods leads
initially to formation of addition product, the P H phosphorane with composition 1: 4. This compound is not
stable and on keeping forms 2-oxo-2-ethyl-1,3,2-benzoxazaphospholine, spirophosphorane, o-aminophenol
and phosphorylated calixarene. In the reaction of the aminoalkylated calixarene with 2-ethyl-1,3,2-benzoxaza-
phospholine we isolated a compound possessing four hydrophoshonyl fragments on the upper circle of the
calixarene matrix.
Calixarenes and their derivatives with calyx-like
form that capable of bonding both organic molecules
and ions [1 4] attract enhanced attention of
explorers. The calix[4]resorcinarenes can be easily
modified by phosphorylation of their hydroxy groups
located on the upper circle of the molecule. As the
phosphorylating agents were mainly used tetracordi-
nated phosphorus acid chlorides; the complete phos-
phates (phosphonates and phosphinates) such obtained
as a rule do not capable of further transformations [5].
Further development of the chemistry of O-phospho-
rylated calixarenes, in our opinion, is connected with
insertion to the molecules of reactive phosphorus-
containing groups including those with a P H bond.
Involving of such objects to chemical transformations
can result in formation of complexing reagents which
contain simultaneously a macro ring (formation of
guest host type complexes) and chelating fragments,
as well as new container-type compounds with
unusual properties and so on.
H
NH
O
NH
PEt + ArOH
PEt
O
OAr
I
II
Taking this in account we hoped to prepare stable
cavitands by reaction of phospholine I with calix[4]-
resorcinarenes. We expected that the number of phos-
phorane fragments with a P H bond located on the
upper circle of the calixarene matrix would defined by
the ratio of the reagents.
Reaction of phospholine (I) and calixarene (III)
(R = C6H13) in equimolar amounts proceeds smoothly
in ethereal solution at cooling and leads to formation
of cavitand VI, which possess one dioxaphospho-
cynic fragment.
31P NMR spectrum of the reaction mixture shows
a signal of P H-phosphorane IV (
28.31 ppm,
1JPH 617.9 Hz), which, however, soonPdisappears and
strong singlet peak of the final reaction product
appears at P 189.5 ppm; the product was isolated and
characterized. Its elemental analysis corresponds to
the presence of one phosphorus atom in a molecule.
In its IR spectrum occurs strong absorption of phenol
Recently we first prepared a calixarene possessing
four hydrophosphoryl fragments on the upper circle
of the molecule [6]. The current investigation is aimed
at the attempted synthesis of earlier unknown P H-
phosphoranes on a calixarene matrix. Earlier [7] we
showed that at 20 C compound I easily adds to
phenols to form the stable phosphoranes with a P H
bond, capable of distillation in a vacuum without de-
composition.
hydoxy groups in the region of 3100 3300 cm . 31P
1
NMR spectrum of reaction mixture contains also
signals of 5-ethyl-1,6-dioxa-4,9-diaza-2,3,7,8-dibenzo-
5-phosphaspiro[4.4]nonane VII (
23.97 ppm) and
P
1070-3632/01/7103-0389$25.00 2001 MAIK Nauka/Interperiodica

390
TERENT’EVA et al.
Et
P
HO
OH
HO
O
H
OH
HO
HO
OH
OH
HO
HO
R
R
R
R
I +
R
R
R
R
OH
HO
OH
HO
OH
III
IV
Et
P
HO
NH
HO
O
HO
O
P Et
O
OH
HO
HO
HO
R
R
R
R
o-H2NC6H4OH
R
R
R
R
HO
OH
OH
HO
OH
HO
OH
V
VI
R = C6H13.
2-oxo-2-ethyl-1,3,2-benzoxazaphospholine VIII (
50.67 ppm). From the reaction mixture we isolated
o-aminophenol. Formation of compound VI probably
calixarene molecule probably impossible by steric
reasons. Second, occurrence of only one signal charac-
terizing hydrophosphorane fragments evidences in
P
proceeds according to the scheme above. Reaction of favor of formation of symmetrical molecule IX.
phospholine I with calixarene III involves only one
We studied in detail reaction of phospholine I with
hydroxy group and leads to P H-phosphorane IV. The
calixarene III in a 4:1 ratio. The reaction is exotermic
in ethereal solution, and the calixarene dissolves
quickly while the solutin becomes brick-red. From
31P data follows that like the case of the reagent ratio
latter compound exists in equilibrium with linear phos-
phonite V due to cleavage of endocyclic P O bond
[8]. Cyclization of the latter involving neighboring
phenolic hydroxy group leads to release of o-amino-
phenol molecule and formation of dioxaphosphocine
VI. Note that earlier attempts to introduce one phos-
phite (phosphonite, phosphinite) fragment to calixarene
molecule by traditional methods failed. Phosphoryla-
tion of calixarenes by the derivatives of P(III) acids,
e.g., hexaalkyltriaminophosphines, led to symmetri-
cally substituted cavitands regardless of the reagent
ratio [9].
8:1 adduct, P H-phosphorane IX, is formed instantly
1
after mixing (
28.38 ppm, JPH 617.7 Hz). How-
ever, in this caPse the signal of parent phospholine I
(
160 ppm) is not observed in the spectrum of the
soPlution. IR spectrum of crude product contains ab-
1
sorption bands of P H (2420 cm ) and N H
(3275 cm ) bonds, typical of the phosphoranes of
1
similar structure [7], as well as broad band of unused
1
O H bonds (3100 3400 cm ). On keeping, the re-
31P NMR spectrum of the reaction mixture of
phospholine I with calixarene III in 8:1 ratio in
ethereal solution, contained signals of equal intensity
action mixture becomes colorless and a precipitate
drops down, consisting of spirophosphorane VII (
P
23.77 ppm) and o-aminophenol. According to 31P
data, the filtrate after removing of the precipitate
contains minor amounts of the oxidation product of
the parent phospholine I, 2-ethyl-2-oxo-1,3,2-benz-
oxazaphospholine VIII ( 50.58 ppm) [10], 5-ethyl-
1,6-dioxa-4,9-diaza-2,3,7P,8-dibenzo-5-phosphaspiro-
of the parent phospholine I ( P 160 ppm) and addition
1
product, P H phosphorane IX (
28.38 ppm, JPH
617.7 Hz). The spectral data obtaiPned show, first, that
only four hydroxy groups enter to the reaction and
introduction of eight phosphorane fragments to the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 3 2001

REACTION OF 2-ETHYL-1,3,2-BEZOXAPHOSPHOLINE
391
H
P
NH
O
H
NH
HO
O
P
Et
O
Et
OH
O
R
R
4I + III
R
R
HO
O
H
P
NH
O
H
NH
O
OH
P
Et
O
Et
IX
[4.4]nonane VII (
23.77 ppm), and dioxaphos-
the reaction mixture with parent phospholine I. Earlier
we showed [11] that this process goes through inter-
mediate formation of P H-phosphorane X which
easily transforms to spirophosphorane VII eliminating
a molecule of hydrogen.
phocine ( 189.87P ppm).
P
Formation of spirophosphorane VII can be ex-
plained by reaction of o-aminophenol appearing in
H
Et
NH
NH
NH2
NH
O
H2N
I +
P
P
OH
H2
O
O
Et
O
X
VII
One cannot exclude also direct transformation of
phospholine I to spirophosphorane VII [12]. o-Amino-
phenol can be formed as a result of chemical trans-
formation on the upper circle of the calixarene matrix
with involvement of phosphorane P H fragment and
O
O
+
NH2
OH
NH3 EtPO
+ EtPOH
H
OH
H
neigboring hydroxy group (sf. V
VI transforma-
XI
XII
tion). Besides, the observed reactions are probably
involve water which is contained in the calixarene
molecular cavity. According to the published data,
such type calixarenes can contain from one to several
tens of bounded water molecules forming a complex
As follows from x-ray crystallography, of a crystal
compound XII has form of a salt, the anion cation
pair (Fig. 1). The o-aminophenol cation and ethyl-
phosphonate anion have ordinary structures. The P O
system of H-bonds with phenol hydroxyl [13]. Partici- bond lengths are equal within the experimental error
pating of water in the observed transformations is also
confirmed by formation in small amount of o-hydroxy-
phenylammonium hydroxyethylphosphinite XII, the
product of reaction of o-aminophenol with ethylphos-
phonite XI. Appearance of phosphonite XI in the re-
action mixture is probably a result of hydrolysis of
the formed in the reaction phosphorylated calixarenes
possessing one (compound VI) or several dioxaphos-
phocine fragments.
[average 1.505(3) ] and fall to the range between
bond lengths of double and single bonds. The P H
bond length is 1.21 . A feature of the crystal struc-
ture of XII is its system of hydrogen bonds. All three
hydrogen atoms of the protonated amino group and
the hydroxyl hydrogen are involved in hydrogen
bonding with the oxygen atoms of the phosphoryl
group. Therewith, the contactcs of P H group obey-
ing the criterion of hydrogen bonding have not been
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 3 2001

392
TERENT’EVA et al.
found. The H-bond parameters are as follows: (1) O1
bond net), parallel to the yz plane (Fig. 2.)
H O22 (x, y
1, z), O1 H 1.06, H O22 1.58,
O1 O22 2.643(3) , angle O1 H O22 178 ; (2) N2
H21 O22 (x, 3/2 y, 1/2 + z), N2 H21 1.01, H21
O22 1.81, N2 O22 2.797(3) , angle N2 H21 O22
164 ; (3) N2 H22 O21 (1 x, 1/2 + y, 1/2 z),
For extension of these studies, we involved calixa-
rene XIII which possess dimethylaminomethyl
fragments in ortho position to the hydroxy groups of
the benzene rings, in the reaction with phospholine
I We expected that the addition product, P H phos-
phorane XII will be much more stable due to intra-
molecular N P donor acceptor interaction. Examles
of stabilization of the such type phosphoranes were
published earlier [14, 15].
N2 H22 0.89, H22 O21 1.87, N2 O21 2.747(3)
,
angle N2 H22 O21 168 ; (4) N2 H23 O21, N2 H23
1.02, H23 O21 1.72, N2 O21 2.736(3) , angle N2
H23 O21 175 .
These H-bonds form in the crystal a layer (hydrogen
NMe2
H
P
NH
O
CH2
HO
O
Et
R
HO
OH
R
4
OH
HO
XIV
R
R
O
R
R
4I +
R
O
EtP
PEt
R
R
HO
O
HO
OH
H
OH
O
H
R
R
R
HO
OH
R
R
XIII
R
R
O
HO
O
O
PEt
O
OH
EtP
H
H
R
XV
R = C6H13, R = CH2NMe2.
31P NMR spectrum of ethereal solution of phos-
pholine I and calixarene XIII mixture (4:1 ratio)
directly after mixing of the reagents contains a group
activation of the water inside a cavity when tertiary
amine or dialkylaminomethyl group constructed a part
of calixarene matrix, like this case.
1
of signals, P, ppm: 25.64, JPH 496 Hz (hydrophos-
1
phonite XV), 28.34, JPH 618 Hz (P H phosphorane,
From the data obtained follows that introducing of
dimethylaminomethyl groups to the ortho position to
the hydroxy groups at benzene rings results in de-
crease in reactivity of calix[4]resorcinarenes with
phospholine I and makes possible hydrolysis of the
formed compounds with the intercavital water.
similar to compound IX), 50.18 (phospholine VIII),
188.22 (the calixarene including dioxaphosphocine
fragments). After 6-h boiling of the reaction mixture,
the final product XV was isolated ( P 25.30 ppm, 1JPH
496 Hz), which contained four hydrophoshonyl
fragments. Probably the formation of phosphonite XV
is a result of hydrolysis of intermediately formed phos-
phorus-containing compounds with a water from the
cavity. In the course of the study of properties of the
Reaction of phospholine I with calixarene XVI
(4:1 ratio) which has four hydroxy groups and four
oxazine fragments on the upper circle of its calyx
phosphorylated calixarenes we repeatedly noted proceeds much slower than with calixarene XIII.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 3 2001

REACTION OF 2-ETHYL-1,3,2-BEZOXAPHOSPHOLINE
393
Ph
N
Ph
N
H
NH
O
CH2
CH2
4I +
CH2
CH2
P
HO
O
O
O
Et
CHR
CHR
4
4
XVI
XVII
C6
C5
C22
C21
C4
C1
O1
C2
C3
P2
N2
O22
O21
Fig. 1. Geometry of the anion-cation oair in the crustal
of salt XII.
In first two hours the reaction, as follows from the
data of 31P NMR, was not found to occur at all. After
4 h, in the spectrum was registered, besides great
amount of parent phospholine (I), appearance of P H
1
phosphorane XVII (
27 ppm, JPH 617 Hz) (10%
of the total signal intePnsity), phospholine VIII (20%),
the product of oxidation of the parent compound, and
Fig. 2. Hydrogen bonding system in a crystal of salt XII.
Projection along 0x axis.
5% of spirophosphorane VII (
23 ppm). Further
P
keeping results in significant complication of the
picture. Note that change of methyl groups on the
lower circle of the molecule by hexyl influences
significantly the calixarene reactivity with phospho-
line I: instantly after mixing I the spectrum contains
equal in intensity signals of parent compound I and
the produt of its oxidation VIII.
EXPERIMENTAL
IR spectra were registered on a UR-20 spectrometer
1
in the 400 3600 cm range, compounds studied were
taken as suspensions in mineral oil. 31P NMR spectra
were registered on a Fourier NMR spectrometer
Bruker MSL-400, operating frequency 161.97 MHz,
external reference 85% H3PO4.
The data concerning calixarene properties publi-
shed to the moment do not allow argue explaining of
the obtained experimental results. Generally, the
features of reactivity of calix[4]resorcinarenes in a
great extent are defined by their association in solu-
tion and macroring conformation, the later depends
substantially on the length of the alkyl group on the
lower circle of the calyx.
X-ray structural investigation of salt XII.
Crystals of the salt XII, C6H8NO+ C2H6O2P , mp
155 C, monoclinic. At 20 C a = 11.3413(2), b =
7.673(3), c = 12.142(5)
;
= 101.038(5) , V =
3
1037(1) 3, dcalc = 1.30 g cm , Z = 4, steric group
P21/c.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 3 2001

394
TERENT’EVA et al.
Atomic coordinates and equivalent isotropic thermal
Atomic coordinates in the structure of XII are
listed in the table, geometry of cation-anion pair and
the system of hydrogen bonding in the crystal of XII
are shown in Figs. 1 and 2. All calculations were
conducted on a DEC Alpha Station-200 computer
with the MolEN [17] program package. Figures of
hydrogen bond system in the crystal and calculation
of intermolecular contacts were performed with
PLATON 98 [18] package.
3
3
parameters of nonhydrogen atoms B = 4/3
(ai aj)B(i, j)
i=1 j=1
(
(
2) and isotropic thermal factors of hydrogen atoms Biso
2) in XII
Atom
x
y
z
B
P2
0.34078(7) 0.2569(1)
0.40793(6) 2.39(1)
O1
0.3853(2)
0.4311(2)
0.3533(2)
0.3946(2)
0.2796(3)
0.2810(3)
0.1746(3)
0.0653(4)
0.0640(3)
0.1695(3)
0.3348(4)
0.2230(6)
0.370(5)
0.240(3)
0.178(3)
0.028(4)
0.007(4)
0.161(4)
0.395(3)
0.458(3)
0.404(4)
0.418(4)
0.32(2)
0.2025(3) 0.3436(2) 3.21(5)
0.3032(3) 0.3368(2)
5,11,17,26-tetrahexyl-3,7,9,13,15,19-hexahydr-
O21
O22
N2
3.32(5)
2.84(4)
2.20(5)
2.38(5)
2.14(5)
2.84(7)
3.91(8)
4.09(8)
3.43(7)
4.03(9)
7.2(1)
6(2)
2.9(7)
4.9(9)
6(1)
6.1(9)
4.9(9)
3.4(8)
2.9(7)
5.7(9)
6(1)
oxy-22,24-dioxa-23-phospha[19.3.3.14,2,5.16,10.112,16
1
.
18,26]hexacyclotriginta[1,3,6,8,12,14,18,20,10(29),
0.0783(3) 0.4605(2)
0.4398(4) 0.1777(2)
0.2506(5) 0.2817(2)
0.3689(4) 0.1939(2)
0.4189(5) 0.1254(3)
0.3550(5) 0.1436(3)
0.2439(6) 0.2306(3)
0.1911(5) 0.2998(3)
0.4175(5) 0.5123(3)
0.4089(8) 0.5605(4)
0.090(8)
0.268(4)
0.522(5)
0.390(6)
0.208(6)
0.111(5)
0.482(5)
0.372(4)
0.534(5)
0.413(6)
0.53(3)
16(28),26(27),25(30)]dodecaene (VI). 0.82 g of
calixarene II was mixed with a solution of 0.17 g of
phospholine I in 3 ml of anhydrous ether at 5 C. The
calixarene completely dissolved to form transparent
solution. After 8-h keeping 0.7 g (43%) of o-amino-
phenol was filtered off, mp 171 174 C. From the
filtrate, after removing of solvent in a vacuum
dropped crystals which were separated, washed with
ether and dried. Yield 0.3 g (34%) of compound VI,
mp 182 190 C. Found, %: C 68.32; H 9.11; P 3.94.
C54H75O8P. Calculated, %: C 68.02: H 8.84; P 3.51.
C1
C2
C3
C4
C5
C6
C21
C22
H1
0.390(4)
0.353(2)
0.063(3)
0.087(4)
0.243(3)
0.364(3)
0.099(3)
0.178(3)
0.238(3)
0.569(4)
0.48(1)
H2
H3
H4
Reaction of 2-ethyl-1,3,2-benzoxazaphospholine
I with calix[4]resorcinarene II (4:1). To 1.67 g of
phospholine I at cooling to 10 C was slowly added
a suspension of 2.06 g of calixarene II in 10 ml of
ether. The calixarene was completely dissolved, the
solvent became of brick-red color. During 5 h we
observed the solution decolorization, evolution of a
gas in small bubbles and dropping of a precipitate.
The solid part was fractionally recrystallized and the
following compounds were isolated: 0.12 g (11%) of
o-aminophenol, mp 174 C; 0.11 g (8%) of 5-ethyl-
1,6-dioxa-4,9-diaza-2,3,7,8-dibenzo-5-phosphaspiro-
[4.4]nonane VII, mp 121 123 C [11]; 0.10 g (5%) of
o-hydroxyphenylammonium hydroethylphosphonite
XII, mp 155 C. Found P, %: 15.03. C8H14NO3P.
Calculated P, %: 15.27.
H5
H6
H21
H22
H23
H211
H212
H221
H222
H223
5(7)
0.13(1)
0.39(1)
0.505(7)
0.606(5)
0.585(8)
19(3)
10(2)
19(3)
0.246(7)
0.21(1)
0.306(9)
0.49(1)
The cell parameters and intensities of 2395 reflec-
tions, of which 1607 characterized by I 3 (I),
were measured on an automatic four-circle Enraf
2,8,14,20-tetraethylpentacyclo[19.3.1.13,7.19,13
.
Nonius CAD-4 difractometer ( CuK radiation,
1
15,19]octacoza-1(25),3,5,7(28),9,11,13(27),15,17,
graphite monochromator, /2 scanning (
76.3 ).
No decrease in intensity occurred during the experi-
ment in three testing measurements. Absorption was
19(26),21,23-dodecaene-4,10,16,22-tetrahydroxy-
5,11,17,19-tetra(dimethylaminomethyl)-6,12,18,24-
tetra(ethylhydrophosphinat) (XV). a. A mixture of
0.8 g of phospholine I and 0.63 g of calixarene XIII
(8:1) in 5 ml of anhydrous ether was refluxed for 6 h.
We obtained 0.64 g (79%) of compound XV, mp
1
not accounted for ( Cu 22.0 cm ). The structure was
decoded by a direct method using SIR package [16]
and refined in isotropic and then in anisotropic ap-
proximations. All hydrogen atoms were revealed from
the electron density difference series and their contri-
butions to the structural amplitudes were accounted
for in the final step of the refinement with fixed posi-
tion and isotropic termal parameters. Final divergence
factors are R 0.044, RW 0.057 on 1110 independent
1
92 C. IR spectrum, , cm : 1250 (P=O), 1600
1
(aromatic ring), 3200 3400 (OH). H NMR spectrum
(CDCl3), , ppm(J, Hz): 0.89 t [12H, CH3 (CH2)4,
3JHH
6.9),
1.11
t
(12H,
CH3 CH2P),
1.20 1.38 m [32H, CH3 (CH2)4], 2.18 m (CH2 P),
2.38 s (24H, CH3 N), 2.58 2.64 s (8H, CH2 N),
reflections with F2
3 .
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 3 2001

REACTION OF 2-ETHYL-1,3,2-BEZOXAPHOSPHOLINE
1999, vol. 69, no. 3, pp. 512 513.
395
2.83 m (8H, CH2 CH), 4.18 4.24 m (4H, CH CH2),
7.13 with (4H, Hm-calix). 31P NMR spectrum, P, ppm
(J, Hz): 25.64 (1JPH 496). Found, %: C 63.34; H 8.13;
P 8.67. C72H120N4O12P4. Calculated, %: C 63.71; H
8.84; P 9.14.
7. Pudovik, M.A., Terent’eva, S.A., and Pudovik, A.N.,
Izv. Akad. Nauk SSSR, Ser. Khim., 1976, no. 8,
p. 1897.
8. Pudovik, M.A., Terent’eva, S.A., Mikhailov, Yu.B.,
and Pudovik, A.N., Zh. Obshch. Khim., 1982, vol. 52,
no. 6, pp. 1302 1307.
b. A mixture of 0.8 g of phospholine I and 1.26 g
of calixarene XIII (4:1) in 5 ml of anhydrous ether
was refluxed for 6 h. 1.3 g (81%) of compound XV
was isolated, mp 92 C. 31P NMR spectrum, P, ppm
(J, Hz): 25.36 (2JPH 494).
9. Burilov, A.R., Nikolaeva, I.L., Galimov, R.D., Pudo-
vik, M.A., and Reznik, V.S., Zh. Obshch. Khim., 1995,
vol. 65, no. 10, pp. 1745 1746.
10. Terent’eva, S.A., Pudovik, M.A., and Pudovik, A.N.,
Izv. Akad. Nauk SSSR, Ser. Khim., 1979, no. 5,
pp. 1152 1155.
ACKNOWLEDGMENTS
This work was performed with financial support of
Russian Foundation for Basic Research (grant no. 99-
03-32999) and DFG (grant no. 98-03-04105).
11. Pudovik, M.A., Terent’eva, S.A., and Pudovik, A.N.,
Dokl. Akad. Nauk SSSR, Ser. Khim., 1976, vol. 228,
no. 2, pp. 363 365.
12. Pudovik, M.A., Terent’eva, S.A., and Pudovik, A.N.,
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