Synthesis and structures of spiro-σ-complexes based on 2-(2-benzylaminophenyl)-5,6-dimethylbenzimidazole

Article abstract of DOI:10.1007/s11172-005-0075-0

The reactions of 2-(2-benzylaminophenyl)-5,6-dimethylbenzimidazole with electrophilic 8-chloro-5,7-dinitroquinoline and 7-chloro-4,6-dinitrobenzofuroxan afforded two new bipolar spiro-σ-complexes. The structure of the complex prepared by the latter reacti

Full text of DOI:10.1007/s11172-005-0075-0

Russian Chemical Bulletin, International Edition, Vol. 53, No. 9, pp. 2075—2079, September, 2004
2075
Synthesis and structures of spiroꢀσꢀcomplexes based on
2ꢀ(2ꢀbenzylaminophenyl)ꢀ5,6ꢀdimethylbenzimidazole*
P. G. Morozov,a S. V. Kurbatov,aꢀ F. M. Dolgushin,b M. Yu. Antipin,b and L. P. Olekhnovicha
aDepartment of Chemistry, Rostov State University,
7 ul. Zorge, 344090 RostovꢀonꢀDon, Russian Federation.
Fax: +7 (863 2) 64 5255. Eꢀmail: kurbatov@chimfak.rsu.ru
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: fedya@xray.ineos.ac.ru
The reactions of 2ꢀ(2ꢀbenzylaminophenyl)ꢀ5,6ꢀdimethylbenzimidazole with electrophilic
8ꢀchloroꢀ5,7ꢀdinitroquinoline and 7ꢀchloroꢀ4,6ꢀdinitrobenzofuroxan afforded two new bipoꢀ
lar spiroꢀσꢀcomplexes. The structure of the complex prepared by the latter reaction was
established by Xꢀray diffraction analysis. The activation parameters of the stereodynamic
rearrangement of quinoline spirane were determined by dynamic NMR spectroscopy.
Key words: 2ꢀ(2ꢀbenzylaminophenyl)ꢀ5,6ꢀdimethylbenzimidazole, 8ꢀchloroꢀ5,7ꢀdinitroꢀ
quinoline, 7ꢀchloroꢀ4,6ꢀdinitrobenzofuroxan, bipolar spiroꢀσꢀcomplex, rearrangement.
Scheme 1
Various bipolar spirocyclic σꢀcomplexes 1 have been
prepared earlier based on the tropolone ligands and have
been characterized in detail by Xꢀray diffraction analyꢀ
sis.1—6 It appeared that it is possible to synthesize such
compounds with highly variable structures of tautomeric
systems, and the spiroꢀσꢀcomplexes thus prepared serve
as models of transition states for nucleophilic aromatic
substitution reactions. These compounds can also exhibit
solvatochromic and thermochromic properties due to reꢀ
versible ringꢀchain rearrangements.6
For example, the kinetic and activation parameters
of the reversible cleavage—formation of the Cipso—R2
(Cipso—R3) bonds and degenerate R
S enantioꢀ
merization for a series of chiral spiranes 1 were deterꢀ
1
mined by dynamic H NMR spectroscopy.7—9
In the present study, we investigated new bipolar
spiroꢀσꢀcomplexes based on 2ꢀ(2ꢀbenzylaminopheꢀ
nyl)benzimidazole (2).
The reactions of ligand 2 with electrophilic 8ꢀchloꢀ
roꢀ5,7ꢀdinitroquinoline (3a) and superelectrophilic
7ꢀchloroꢀ4,6ꢀdinitrobenzofuroxan (3b)10 afforded bipoꢀ
lar spiroꢀσꢀcomplexes (4) (Scheme 2).
In the 1H NMR spectra of these compounds, the sigꢀ
nals for the protons of the electronꢀwithdrawing fragment
are substantially shifted upfield compared to the haloarene
reagent, which is indicative of an excess of electron denꢀ
sity on this fragment. The signals for the H(2″) and H(3″)
protons in the quinoline moiety of spirane 4a are characꢀ
terized by the largest shifts. Below are given the chemical
shifts of the protons of 8ꢀchloroꢀ5,7ꢀdinitroquinoline 3a,
* Results of the study were presented at the International Conꢀ
ference "Modern Trends in Organoelement and Polymer Chemisꢀ
try" dedicated to the 50th anniversary of the A. N. Nesmeyanov
Institute of Organoelement Compounds of the Russian Acadꢀ
emy of Sciences (May 30—June 4, 2004, Moscow).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1990—1994, September, 2004.
1066ꢀ5285/04/5309ꢀ2075 © 2004 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 9, September, 2004
Morozov et al.
Scheme 2
The signal for the protons of the CH2 group of the
diastereotopic benzyl substituent is transformed into an
AB quartet.
A reversible evolution of the signals for the protons of
the methylene and methyl groups into singlets is observed
on heating in the NMR spectra of a solution of comꢀ
pound 4a in DMSOꢀd6, which is evidence for the occurꢀ
rence of the ringꢀchain rearrangement (Scheme 3). The
kinetic and activation parameters extracted from analysis
of the temperature dependence of the line shapes of the
methyl and methylene indicator signals demonstrate that
the rearrangement 4a(R)
4a(S) can follow two paths.
One path involves the cleavage of the Cipso—N(7) bond
and torsional rotations about the benzimidazoꢀ
lyl—aminophenyl (T1) and quinolyl—N(5) (T2) bonds.
An alternative path involves the cleavage of the quinoꢀ
lyl—N(5) bond and rotations about the quinolyl—benzꢀ
imidazolyl (Т2) and benzimidazolyl—aminophenyl (T1)
bonds.
Heating of a solution of spirane 4b in DMSOꢀd6 up to
170 °C causes neither exchange broadening nor collapse
of indicator signals, which is characteristic of spirane 4a.
This fact indicates that the activation barrier of the ringꢀ
chain rearrangement sharply increases (see Scheme 3)
upon the replacement of dinitroquinoline with superꢀ
electrophilic12 dinitrobenzofuroxan.
Since data on the structures of bipolar spiroꢀσꢀcomꢀ
plexes based on 4,6ꢀdinitrobenzofuroxan are lacking
in the literature, we studied compound 4b by Xꢀray
diffraction analysis (Fig. 1). The benzimidazole and
quinazoline fragments of molecule 4b are virtually coꢀ
planar. These fragments are twisted with respect to
each other about the C(14)—C(15) bond by 175.1° (the
C(5)—C(15)—C(14)—N(12) torsion angle). The spiroꢀ
annelated dinitrobenzofuroxan fragment is almost orꢀ
thogonal to the tetracyclic benz[4,5]imidazo[1,2ꢀc]quinꢀ
azoline system (the dihedral angle between the
N(5)—C(6)—N(7) and C(6´)—C(6)—C(8´) planes
is 90.1°). Both nitro groups are coplanar with the benzoꢀ
furoxan moiety (the torsion angles are no larger than 3°).
Six bond angles in the spiro unit vary in a range
of 106.4—111.8°. The C(6´)—C(6)—C(8´) and
C(6´)—C(6)—N(5) angles have the smallest and largest
values (106.4° and 111.8°, respectively). The Nꢀbenzyl
substituent is twisted with respect to the quinazoline fragꢀ
ment by 83.4° so that its benzene ring is located in the
vicinity of the 6´ꢀnitro group (syn position) and is far
removed from the furoxan fragment (anti position). The
distances between the C(22) atom of the benzene ring of
the PhCH2 group and the N(6) and O(6´) atoms of the
nitro group are 3.23 and 3.21 Å, respectively (van der
Waals contacts). The dihedral angle between the planes of
the benzene rings of the benzyl and benzofuroxan fragꢀ
ments approximates 43°.
its ethylene glycolꢀderived anionic σꢀcomplex 5,11 and
spiro complex 4a.
The signal for the H(1) proton in the benzimidazole
fragment of spiro complexes 4a and 4b is shifted downfield
by 0.63 and 0.67 ppm, respectively, compared to the sigꢀ
nal in the spectrum of the starting ligand 2, which is
indicative of an electron deficiency. It should be noted
that the signals of two methyl groups, which are isochꢀ
ronic in ligand 2 due to free rotation about the benzꢀ
imidazolyl—phenyl bond and fast N(1)
N(3) proton
exchange, become anisochronic in spiroꢀσꢀcomplexes 4.

Synthesis and structure of spiroꢀσꢀcomplexes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 9, September, 2004
2077
Scheme 3
Fragment
k298/s–1
∆G≠
∆H≠
–∆S≠/e.u.
298
kcal mol–1
CH3
CH2
0.9
4.4
17.5
16.7
8
8.6
32
27
8022 independent reflections (Rint = 0.0459), which were used
in the structure solution and refinement. The structure was solved
by direct methods and refined by the fullꢀmatrix leastꢀsquares
method against F 2 with anisotropic thermal parameters for
nonhydrogen atoms. All hydrogen atoms were revealed from
difference electron density maps and refined isotropically. The
final reliability factors were R1 = 0.0544 (based on Fhkl for
Experimental
1
H NMR spectra were recorded on a Varian Unity 300 specꢀ
trometer (300 MHz). The rate constants of the ringꢀchain tauꢀ
tomeric rearrangement were determined with an accuracy
of 10% by computer simulation of the signal shapes for the
indicator protons (CH3 and CH2) and visual fitting to the line
shapes recorded at a particular temperature using the gNMR
V 4.1.0 program (Copyright © 1995—1998 IvorySoft). The actiꢀ
vation parameters were determined according to a standard proꢀ
cedure of linearization of lnk—1/Т with a regression coefficient
of no smaller than 0.98.
Xꢀray diffraction study. Single crystals of compound 4b were
grown by keeping its solution in DMSO in open air for one
month. Yellow needleꢀlike crystals of C28H21N7O6•2DMSO•
•H2O (M = 725.79) belong to the triclinic system, space
group Р1, at 110 K, a = 10.424(3), b = 10.694(3), c =
15.497(4) Å, α = 81.068(8), β = 78.292(8), γ = 82.492(7)°,
V = 1662.2(8) Å3, Z = 2, dcalc = 1.450 g cm–3. A total of
14616 reflections were collected on a Bruker SMART 1000 CCD
diffractometer at 110 K (MoꢀKα radiation, λ = 0.71073 Å,
ω scanning technique with a step of 0.3°, exposure time per
frame was 20 s, 2θmax = 56°) from a single crystal of dimensions
0.55×0.10×0.07 mm3. Merging of the equivalent reflections gave
3617 reflections with I > 2σ(I )), wR2 = 0.1230 (based on F 2
hkl
for all independent reflections), GOOF = 0.738, 599 parameters
were refined. All calculations were carried out using the
SHELXTL v.5 program package.13 The atomic coordinates for
the structure of compound 4b and the complete tables of the
bond lengths and bond angles were deposited with the Camꢀ
bridge Structural Database. Selected bond lengths and bond
angles are given in Tables 1 and 2, respectively.
2ꢀ(2ꢀBenzylaminophenyl)ꢀ5,6ꢀdimethylbenzimidazole (2).
2ꢀ(2ꢀAminophenyl)ꢀ5,6ꢀdimethylbenzimidazole14 (2.37 g,
0.01 mol) and anhydrous AcONa (0.82 g, 0.01 mol) were disꢀ
solved in MeOH (60 mL). Then PhCH2Cl (1.15 mL, 0.01 mol)
was added and the reaction mixture was refluxed for 15 h. The
solution was poured into water (100 mL) and kept for one day
until precipitation was completed. The reaction product was
filtered off, crystallized from CCl4, chromatographed on Al2O3
(CHCl3), and crystallized from CCl4. The yield was 1 g (30.5%).
M.p. 168—170 °C. Found (%): C, 80.83; H, 6.56; N, 12.95.
–

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 9, September, 2004
Morozov et al.
O(4´)
O(4)
C(19)
N(4)
C(18)
C(4´)
C(20)
N(3)
C(17)
C(5´)
C(9´´ )
C(21)
O(6)
C(6´)
C(8´)
O(2)
C(22)
C(4)
C(16)
N(5)
C(5)
N(6)
N(1)
O(1)
C(6)
C(9´)
C(8)
O(6´)
C(13)
N(7)
C(9)
C(14)
C(3)
C(2)
C(15)
C(10)
C(10´)
C(12)
N(12)
C(11)
C(1)
Fig. 1. Molecular structure of compound 4b.
Table 1. Selected bond lengths (d) in the structure of 4b
C22H21N3. Calculated (%): C, 80.70; H, 6.46; N, 12.83.
1H NMR (CDCl3), δ: 2.34 (s, 6 H, C(5)Me, C(6)Me); 4.55 (s,
2 H, CH2); 6.64 (dd, 1 H, H(5´), J = 7.3 Hz, J = 7.3 Hz); 6.71
(d, 1 H, H(3´), J = 8.4 Hz); 7.10—7.45 (m, 8 H, Ar); 7.49 (d,
1 H, H(6´), J = 7.8 Hz); 9.38 (br.s, 2 H, NH).
Bond
d/Å
Bond
d/Å
O(1)—N(1)
O(2)—N(3)
O(2)—N(1)
O(4)—N(4)
O(4´)—N(4)
O(6´)—N(6)
O(6)—N(6)
N(12)—C(14)
N(12)—C(12)
N(7)—C(14)
N(7)—C(13)
N(7)—C(6)
N(5)—C(5)
N(5)—C(16)
N(5)—C(6)
N(1)—C(8´)
N(3)—C(9″)
N(4)—C(4´)
N(6)—C(6´)
C(14)—C(15)
C(13)—C(8)
C(13)—C(12)
C(8)—C(9)
C(9)—C(10)
1.221(3)
1.413(5)
1.434(4)
1.240(3)
1.235(3)
1.241(3)
1.282(8)
1.333(3)
1.375(4)
1.339(3)
1.398(3)
1.478(3)
1.372(3)
1.457(3)
1.480(3)
1.327(4)
1.338(4)
1.410(4)
1.400(4)
1.416(4)
1.383(4)
1.390(4)
1.386(4)
1.415(4)
C(9)—C(9´)
C(10)—C(11)
C(10)—C(10´)
C(11)—C(12)
C(15)—C(1)
C(15)—C(5)
C(1)—C(2)
C(2)—C(3)
C(3)—C(4)
C(4)—C(5)
C(6)—C(8´)
C(6)—C(6´)
C(8´)—C(9″)
C(9″)—C(4´)
C(4´)—C(5´)
C(5´)—C(6´)
C(16)—C(17)
C(17)—C(22)
C(17)—C(18)
C(18)—C(19)
C(19)—C(20)
C(20)—C(21)
C(21)—C(22)
1.503(4)
1.369(4)
1.494(4)
1.398(4)
1.388(4)
1.410(4)
1.366(4)
1.386(4)
1.375(4)
1.402(4)
1.497(4)
1.503(4)
1.408(4)
1.417(4)
1.384(4)
1.377(4)
1.516(4)
1.382(4)
1.385(4)
1.366(4)
1.385(4)
1.375(4)
1.385(4)
5ꢀBenzylꢀ9,10ꢀdimethylꢀ5´,7´ꢀdinitroꢀ5,12ꢀdihydroꢀ6Hꢀ
spiro(benz[4,5]imidazo[1,2ꢀc]quinazolineꢀ6,8´ꢀquinoline) (4a).
Benzimidazole 2 (0.4 g, 1.22 mmol) and 8ꢀchloroꢀ5,7ꢀdinitroꢀ
quinoline (3a)11 (0.32 g, 1.22 mmol) were dissolved in MeCN
(7 mL). The reaction mixture was kept at room temperature for
7 days. The precipitate that formed was filtered off, suspended in
MeOH (5 mL), brought to reflux, and filtered without cooling.
The operation was repeated three times. Then the reaction prodꢀ
uct was dissolved in DMSO (20 mL) and poured into water
(120 mL). After 12 h, the precipitate that formed was filtered
off, twice washed with MeOH (5 mL), and once washed with
diethyl ether (5 mL). The yield was 0.19 g (57%). M.p. 278 °C
(with decomp.). Found (%): C, 68.54; H, 4.63; N, 15.61.
C31H24N6O4. Calculated (%): C, 68.37; H, 4.44; N, 15.43.
1H NMR (DMSOꢀd6), δ: 2.06 and 2.26 (both s, 3 H each,
C(9)Me, C(10)Me); 4.11 and 4.22 (both d, 1 H each, CH2, J =
18.1 Hz); 6.31 (s, 1 H, H(11)); 6.40 (d, 1 H, H(4), J = 8.6 Hz);
6.91 (dd, 1 H, H(2), J = 7.5 Hz, J = 7.5 Hz); 6.95—7.01 (m,
2 H, Ar)); 7.03—7.20 (m, 3 H, Ar); 7.30—7.40 (m, 2 H, H(3),
H(3´)); 7.53 (s, 1 H, H(8)); 8.12 (d, 1 H, H(1), J = 7.8 Hz); 8.21
(dd, 1 H, H(2´), J = 1.4 Hz, J = 4.4 Hz); 8.99—9.05 (m, 2 H,
H(4´), H(6´)).
5ꢀBenzylꢀ9,10ꢀdimethylꢀ4´,6´ꢀdinitroꢀ5,12ꢀdihydroꢀ6Hꢀ
spiro[(benz[4,5]imidazo[1,2ꢀc]quinazoline)ꢀ6,7´ꢀ(2,1,3ꢀbenzꢀ

Synthesis and structure of spiroꢀσꢀcomplexes
Table 2. Bond angles (ω) in the structure of 4b
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 9, September, 2004
2079
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 01ꢀ03ꢀ32550a
and 02ꢀ03ꢀ32562) and the Program "Russian Universiꢀ
ties — Basic Research" (Grant 05.01.013).
Angle
ω/deg Angle
ω/deg
N(3)—O(2)—N(1)
109.4(3) N(12)—C(12)—C(13)107.5(2)
C(14)—N(12)—C(12) 109.3(2) N(12)—C(12)—C(11)131.3(3)
C(14)—N(7)—C(13) 109.4(2) C(13)—C(12)—C(11)121.1(3)
C(14)—N(7)—C(6) 125.6(2) C(1)—C(15)—C(5) 120.8(3)
C(13)—N(7)—C(6) 124.6(2) C(1)—C(15)—C(14) 123.0(3)
C(5)—N(5)—C(16) 120.2(2) C(5)—C(15)—C(14) 116.2(3)
References
1. V. I. Minkin, L. P. Olekhnovich, and Yu. A. Zhdanov, Acc.
Chem. Res., 1981, 14, 210.
C(5)—N(5)—C(6)
125.6(2) C(2)—C(1)—C(15) 120.8(3)
2. L. P. Olekhnovich, N. G. Furmanova, V. I. Minkin, Yu. T.
Struchkov, O. E. Kompan, Z. N. Budarina, I. A. Yudilevich,
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C(16)—N(5)—C(6) 114.1(2) C(1)—C(2)—C(3)
O(1)—N(1)—C(8´) 131.7(3) C(4)—C(3)—C(2)
119.2(3)
121.1(3)
120.9(3)
121.6(2)
O(1)—N(1)—O(2)
122.8(3) C(3)—C(4)—C(5)
C(8´)—N(1)—O(2) 105.4(3) N(5)—C(5)—C(4)
C(9″)—N(3)—O(2) 105.0(3) N(5)—C(5)—C(15) 121.2(2)
O(4´)—N(4)—O(4) 123.3(2) C(4)—C(5)—C(15) 117.2(3)
O(4´)—N(4)—C(4´) 118.6(3) N(7)—C(6)—N(5) 108.6(2)
O(4)—N(4)—C(4´) 118.0(3) N(7)—C(6)—C(8´) 109.0(2)
O(6´)—N(6)—O(6) 119.5(4) N(5)—C(6)—C(8´) 109.9(2)
O(6´)—N(6)—C(6´) 120.6(3) N(7)—C(6)—C(6´) 111.1(2)
O(6)—N(6)—C(6´) 119.9(4) N(5)—C(6)—C(6´) 111.8(2)
N(12)—C(14)—N(7) 108.6(2) C(8´)—C(6)—C(6´) 106.3(2)
N(12)—C(14)—C(15) 128.7(3) N(1)—C(8´)—C(9″) 109.7(3)
N(7)—C(14)—C(15) 122.6(2) N(1)—C(8´)—C(6) 122.1(3)
C(8)—C(13)—C(12) 121.0(3) C(9″)—C(8´)—C(6) 128.0(3)
C(8)—C(13)—N(7) 133.8(3) N(3)—C(9″)—C(8´) 110.5(3)
C(12)—C(13)—N(7) 105.2(2) N(3)—C(9″)—C(4´) 131.2(3)
C(13)—C(8)—C(9) 118.1(3) C(8´)—C(9″)—C(4´) 118.3(3)
C(8)—C(9)—C(10) 120.7(3) C(5´)—C(4´)—N(4) 120.3(3)
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C(8)—C(9)—C(9´)
119.4(3) C(5´)—C(4´)—C(9″) 118.3(3)
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C(10)—C(9)—C(9´) 119.8(3) N(4)—C(4´)—C(9″) 121.4(3)
C(11)—C(10)—C(9) 120.8(3) C(6´)—C(5´)—C(4´) 123.2(3)
C(11)—C(10)—C(10´)119.5(3) C(5´)—C(6´)—N(6) 116.9(3)
C(19)—C(18)—C(17) 121.3(3) C(5´)—C(6´)—C(6) 125.2(3)
C(18)—C(19)—C(20) 119.7(3) N(6)—C(6´)—C(6) 117.9(3)
C(21)—C(20)—C(19) 120.0(3) N(5)—C(16)—C(17) 116.8(2)
C(20)—C(21)—C(22) 119.9(3) C(22)—C(17)—C(18)118.6(3)
C(17)—C(22)—C(21) 120.5(3) C(22)—C(17)—C(16)124.4(2)
C(9)—C(10)—C(10´) 119.7(3) C(18)—C(17)—C(16)117.0(3)
C(10)—C(11)—C(12) 118.2(3)
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oxadiazole)] 1´ꢀoxide (4b). Benzimidazole 2 (0.2 g, 0.61 mmol)
and 7ꢀchloroꢀ4,6ꢀdinitrobenzofuroxan 3b 15 (0.16 g, 0.61 mmol)
were dissolved in MeCN (5 mL). The reaction mixture was kept
at room temperature for 24 h. The precipitate that formed was
filtered off and purified analogously to compound 4a. The yield
was 0.1 g (60%). M.p. 256 °C (with decomp.). Found (%):
C, 61.12; H, 3.93; N, 17.94. C28H21N7O6. Calculated (%):
C, 60.98; H, 3.84; N, 17.78. 1H NMR (DMSOꢀd6), δ: 2.20 and
2.33 (both s, 3 H each, C(9)Me, C(10)Me); 4.46 and 4.65
(both d, 1 H each, CH2, J = 18.2 Hz); 6.47 (s, 1 H, H(11)); 6.79
(d, 1 H, H(4), J = 8.4 Hz); 7.01 (dd, 1 H, H(2), J = 7.5 Hz, J =
7.4 Hz); 7.08—7.27 (m, 5 H, Ar); 7.41 (dd, 1 H, H(3), J =7.4 Hz,
J =8.2 Hz); 7.54 (s, 1 H, H(8)); 8.16 (d, 1 H, H(1), J = 7.8 Hz);
9.01 (s, 1 H, H(5´)).
Received June 16, 2004;
in revised form September 14, 2004