Reaction of 1,2,3-selenadiazoles with boranes

Article abstract of DOI:10.1007/s10593-007-0036-7

The complex formation of 1,2,3-selenadiazoles with boron trifluoride etherate and phenyldichloroborane has been studied. The molecular structure of the5-ethoxycarbonyl-4-methyl-1,2,3-selenadiazole has been confirmed by X-ray analysis.

Full text of DOI:10.1007/s10593-007-0036-7

Chemistry of Heterocyclic Compounds, Vol. 43, No. 2, 2007
REACTION OF 1,2,3-SELENADIAZOLES WITH BORANES
P. Arsenyan, K. Oberte, and S. Belyakov
The complex formation of 1,2,3-selenadiazoles with boron trifluoride etherate and phenyldichloro-
borane has been studied. The molecular structure of the5-ethoxycarbonyl-4-methyl-1,2,3-selenadiazole
has been confirmed by X-ray analysis.
Keywords: boranes, 1,2,3-selenadiazoles, complexes, molecular structure.
The great interest of many investigators in 1,2,3-selenadiazole and its derivatives is due to the fact that
this compound plays a significant role in resolving many theoretical and practical questions in organic chemistry
[1]. Compounds containing a selenadiazole ring show an aromatic character and, very importantly, lose
molecules of nitrogen and selenium with ring opening to give both acyclic series and also novel heterocyclic
products [2, 3]. Hence they are promising subjects for the study of the mechanisms of certain reactions and the
synthesis of many practically interesting compounds [4]. In the thermolysis reactions of selenadiazoles with
elemental sulfur and selenium polysulfur and polyselenium cyclic systems are formed [5-7]. Various
selanylethylenes can be prepared by treatment of selenadiazoles with nucleophilic agents such as butyl lithium,
trialkylphosphites, mercaptans, disulfides etc. [8].
There is particular interest in an investigation of the molecular structure of 1,2,3-selenadiazoles because
few structures have been confirmed by X-ray analysis according to literature data [9-12].
The aim of this work is to study the reaction of 1,2,3-selenadiazoles with boron trifluoride etherate and
with phenyldichloroborane.
Formation of complexes with electron-deficient compounds is possible because the selenium atom has
unshared electron pairs. The reaction of boron trifluoride etherate and phenyldichloroborane with an equimolar
amount of 4-phenyl-1,2,3-selenadiazole (1) in dry benzene gives the stable complexes 2 and 3 in almost
11
quantitative yield. Both complexes are crystalline materials, sensitive to moisture. B NMR spectroscopic data
shows that the boron atom in the complexes is tetracoordinated.
Ph
Ph
Ph
N
N
N
BF3 . Et2O
PhBCl2
+
+
–
BF3
–
N
N
N
BCl2Ph
Se
Se
Se
3
2
1
__________________________________________________________________________________________
Latvian Institute of Organic Synthesis, Riga LV-1006; e-mail: pavel.arsenyan@lycos.com. Translated
from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 289-293, February, 2007. Original article submitted
February 6, 2006.
0009-3122/07/4302-0233©2007 Springer Science+Business Media, Inc.
233

Fig. 1. Molecular structure of the H-complex of compound 4 with phenylboric acid.
A mixture of products is formed in the reaction of 5-etoxycarbonyl-4-methyl-1,2,3-selenadiazole (4) with
boron trifluoride etherate. However, complex formation of compound 4 with phenyldichloroborane occurs smoothly
to form the single product 5. As a result of crystallization of the complex 5 from hexane the phenyldichloroborane
undergoes hydrolysis to phenylboric acid. The structure of the mixed crystal 6 was studied by X-ray analysis.
Ph
OH
H
B
O
Me
Me
Me
N
+
N
N
–
H2O
N
N
N
BPhCl2
Se
O
Se
Se
EtOOC
EtOOC
OEt
5
6
4
TABLE 1. Basic Interatomic Distances (l) and Valence Angles (ω)
in Structure 6
Bond
l, Å
Angle
ω, deg
1.860(3)
1.834(4)
1.273(4)
1.366(5)
1.369(5)
1.469(5)
1.482(5)
1.200(4)
1.337(4)
1.378(5)
1.346(5)
1.564(5)
86.2(2)
111.2(2)
118.2(3)
113.9(3)
110.5(3)
117.6(3)
123.5(3)
118.9(4)
Se(1)−N(2)
Se(1)−C(5)
N(2)−N(3)
N(3)−C(4)
C(4)−C(5)
C(4)−C(6)
C(5)−C(7)
C(7)−O(1)
C(7)−O(2)
B(1)−O(3)
B(1)−O(4)
B(1)−С(10)
N(2)−Se(1)−C(5)
Se(1)−N(2)−N(3)
N(2)−N(3)−C(4)
N(3)−C(4)−C(5)
C(4)−C(5)−Se(1)
O(3)−B(1)−C(10)
O(3)−B(1)−C(10)
O(4)−B(1)−C(10)
234

The molecular structure, atom numbering and thermal vibration ellipsoids for 6 is given in Fig. 1. The
length of the hydrogen bond between the hydroxyl H atom in the phenylboric acid and the carbonyl oxygen
atom in the selenadiazole is 2.790(4) Å. The unit cell contains two molecules of 5-ethoxycarbonyl-4-methyl-
1,2,3-selenadiazole 4 and two molecules of phenylboric acid (Z = 2). The basic bond lengths and valence angles
for structure 6 are given in Table 1.
The C(5)–Se(1) bond length is 1.834(4) Å which is less than the N(2)–Se(1) (1.860(3) Å) and the
C(5)–Se(1)–N(2) angle is 86.2(2)°. According to the X-ray analysis of other selenadiazoles [9-13] the C–
Se bond is also shorter than the N–Se. The N(2)–N(3) and C(4)–C(5) bonds are lengthened when compared with
standard values for N=N and C=C bonds [14] and this confirms the aromatic character of the selenadiazole ring.
Fig. 2. Molecular packing in the crystal structure of compound 6.
Figure 2 shows the projection of the packing of the molecules in the crystalline structure of 6 in the
crystallographic [1 0 0] direction. Besides the hydrogen bond discussed before for structure 6 it also possesses an
O(4)–H···O(3) hydrogen bond (Table 2). The lengths of the hydrogen bonds are somewhat longer than the mean
statistical value of 2.72 Å for an OH···O type bond [15]. The crystal structure forms centrosymmetric associates
of four molecules via hydrogen bonding.
TABLE 2. Hydrogen Bond Parameters in the Crystal Structure 6
H-bond length
D⋅⋅⋅A, Å
D⋅⋅⋅A
distance, Å
D–H⋅⋅⋅A,
angle, deg.
D–H⋅⋅⋅A bond
Atom A position
2.867(3)
2.790(3)
2.03
1.90
148
167
x, y, z
O(3)–H⋅⋅⋅O(1)
O(4)–H⋅⋅⋅O(3)
2−x, −y, −z
EXPERIMENTAL
13
11
77
1H, C, B, and Se NMR spectra were measured on a Varian Mercury-200 instrument (200, 50, 64,
and 39.7 MHz respectively) using DMSO-d6 as solvent with TMS internal standard and BF3·etherate (11B) and
SeO2 (77Se) external standards.
235

X-Ray analysis was carried out on monocrystals of 6 grown from hexane. The 6 crystals are assigned a
triclinic symmetry with the crystal lattice parameters: a = 7.4666(3), b = 10.0980(3), c = 11.1689(4) Å,
α = 107.750(2), β = 98.402(2), γ = 107.905(2)°, V = 735.97(5) Å3, F(000) = 344, µ = 2.563 mm-1, dcalc = 1.539
-
g/cm-3, Z = 2, space group P .
1
The intensities of 3389 independent reflections were measured on a Nonius KappaCCD automatic
diffractometer (molybdenum radiation with λ = 0.71073 Å, graphite monochromator) to 2θmax = 55°. In the
calculations 2106 reflections with I > 2σ (I) were used. The structure was solved by method [16]. Refinement
was carried out by least squares analysis in the full matrix anisotropic approximation using the SHELXL
program package [17]. The final difference factor was R = 0.0441.
Complex Formation of 1,2,3-selenadiazole with Boranes (General Method). A mixture of equimolar
amounts of the selenadiazole and borane was dissolved in dry benzene and stirred at room temperature for 1 h.
The complexes 2, 3, 5 precipitated from the reaction mixture after several days. The precipitate was then filtered
off and recrystallized from a mixture of benzene and hexane (1 : 5).
1
Complex of 4-Phenyl-1,2,3-selenadiazole with Boron Trifluoride (2). Mp 69-70°C. H NMR
spectrum, δ, ppm: 7.42-7.52 (3H, m), 8.03-8.08 (2H, m), 9.38 (1H, s). 13C NMR spectrum, δ, ppm: 127.3, 128.1,
1
128.4, 132.5, 135.0, 137.4. B NMR spectrum, δ, ppm: -4.78. Found, %: C 34.74; H 2.22; N 10.11.
C8H6BF3N2Se. Calculated, %: 34.70; H 2.18; N 10.12.
1
Complex of 4-Phenyl-1,2,3-selenadiazole with Phenyldichloroborane (3). Mp 91-92oC. H NMR
spectrum, δ, ppm: 7.42-7.60 (6H, m), 8.03-8.07 (2H, m), 8.23-8.27 (2H, m), 9.39 (1H, s). 13C NMR spectrum, δ,
ppm: 127.7, 128.0, 128.9, 129.1, 132.0, 132.7, 135.6, 137.0, 166.8. 11B NMR spectrum, δ, ppm: 29.48. 77Se
NMR spectrum, δ, ppm: 1569.9. Found, %: C 45.74; H 3.08; N 7.70. C14H11BCl2N2Se. Calculated, %: C 45.70;
H 3.01; N 7.61.
1
Complex of 5-ethoxycarbonyl-4-methyl-1,2,3-selenadiazole with Phenyldichloroborane (5). H
NMR spectrum, δ, ppm (J, Hz): 1.34 (3H, t, J = 4.0), 3.02 (3H, s), 4.35 (2H, q, J = 4.0), 7.43-7.73 (5H, m). 13C
NMR spectrum, δ, ppm: 14.1, 24.9, 62.6, 127.9, 131.0, 131.1, 132.5, 135.6, 162.3. 11B NMR spectrum, δ, ppm:
29.60. 77Se NMR spectrum, δ, ppm: 1574.6. Found, %: C 38.10; H 3.41; N 7.36. C12H13BCl2N2O2Se. Calculated,
%: C 38.14; H 3.47; N 7.41.
Preparation of the H-complex of 5-ethoxycarbonyl-4-phenyl-1,2,3-selenadiazole (4) with
Phenylboric Acid (6). Complex 5 was dissolved in hexane at room temperature and left to crystallize at 5°C.
After 2 days crystals of compound 6 were obtained. The spectroscopic data for compound 4, appearing in the H-
complex, has been reported in [18].
The authors express their sincere thanks to the Latvian Council of Science (grants 05.1757 and 05.1758)
for financial support.
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