Structural studies on diaryl selenide dihalides in solution: Molecular complex formation of substituted diphenyl selenides with bromine

Article abstract of DOI:10.1039/b108556e

Diaryl selenides that yield molecular complexes (MC) with bromine are prepared by modulating the effective electronegativity of the selenium atom and the steric environment around the atom in diphenyl selenide (1) with various substituents at the 2-, 3- and/or 4-positions. Halogen induced ¹H and ¹³C NMR chemical shifts of the diaryl selenides are examined. The chlorine and iodine adducts of the selenides are shown to be trigonal bipyramidal adducts (TB) and MC, respectively. In the case of bromine adducts, the structures of (3- and 4-YC₆H₄)₂SeBr₂ are demonstrated to be MC if Y is CN and NO₂, contrary to the general rule: they are TB if Y is less electron-withdrawing than the ethoxycarbonyl group. The CN and NO₂ groups increase the effective electronegativity of the Se atom in (3- and 4-YC₆H₄)₂Se and do not give TB with bromine. The four chloro groups at all meta-positions in 1 are also effective for MC formation. However, 3,5-(O₂N)₂C₆H₃SeBr₂Ph is TB. Ab initio MO calculations show that the structures of (3-O₂NC₆H₄)₂Se and 3,5-(O₂N)₂C₆H₃SePh are close to the C₂ and C _s symmetries, respectively, which reveals that the conformational change is also important when the structures of the bromine adducts are determined. The steric congestion must be more severe for TB formation than for MC formation. The structures of 2,6-Cl₂C₆H₃- SeBr₂C₆H₄Y-p (Y = H and Br) are MC, which shows that the steric effect of 2,6-Cl₂C₆H₃ group is effective for MC formation. (2-MeC₆H₄)₂SeBr₂ and (2-ClC₆H₄)₂SeBr₂ are TB and MC, respectively: the electronic effect of the Cl group must play an additional role in the MC formation since the bulkiness of the Me and Cl groups are expected to be similar. The bromine adduct of (2,4,6-Me₃C₆H₂)₂Se is also concluded to be MC: the steric effect of the four Me groups at the ortho-positions is large enough to give MC with bromine. The oxidation potentials (E_ox) of the diaryl selenides explain well the structures of the bromine adducts: the electronic effect is directly correlated with E_ox and the importance of the steric effect has been brought into sharp relief by E_ox. Results of MO calculations support the outline of the observations. The structural behavior of some halogen adducts such as 2,6-Cl₂C₆H₃SeCl₂C₆H ₄Y-p (TB: Y = H and Br) is also discussed in some detail.

Full text of DOI:10.1039/b108556e

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Structural studies on diaryl selenide dihalides in solution:
molecular complex formation of substituted diphenyl selenides
with bromine
2
Warô Nakanishi,*a Satoko Hayashia and Yoshiaki Kusuyamab
a Department of Material Science and Chemistry, Faculty of Systems Engineering,
Wakayama University, 930 Sakaedani, Wakayama 640-8510, Japan.
E-mail: nakanisi@sys.wakayama-u.ac.jp; Fax: ϩ81-73-457-8253; Tel: ϩ81-73-457-8252
b Department of Chemistry, Faculty of Education, Wakayama University, 930 Sakaedani,
Wakayama 640-8510, Japan
Received (in Cambridge, UK) 21st September 2001, Accepted 14th November 2001
First published as an Advance Article on the web 2nd January 2002
Diaryl selenides that yield molecular complexes (MC) with bromine are prepared by modulating the effective
electronegativity of the selenium atom and the steric environment around the atom in diphenyl selenide (1) with
various substituents at the 2-, 3- and/or 4-positions. Halogen induced 1H and 13C NMR chemical shifts of the diaryl
selenides are examined. The chlorine and iodine adducts of the selenides are shown to be trigonal bipyramidal
adducts (TB) and MC, respectively. In the case of bromine adducts, the structures of (3- and 4-YC6H4)2SeBr2
are demonstrated to be MC if Y is CN and NO2, contrary to the general rule: they are TB if Y is less electron-
withdrawing than the ethoxycarbonyl group. The CN and NO2 groups increase the effective electronegativity of the
Se atom in (3- and 4-YC6H4)2Se and do not give TB with bromine. The four chloro groups at all meta-positions in 1
are also effective for MC formation. However, 3,5-(O2N)2C6H3SeBr2Ph is TB. Ab initio MO calculations show that
the structures of (3-O2NC6H4)2Se and 3,5-(O2N)2C6H3SePh are close to the C2 and Cs symmetries, respectively, which
reveals that the conformational change is also important when the structures of the bromine adducts are determined.
The steric congestion must be more severe for TB formation than for MC formation. The structures of 2,6-Cl2C6H3-
SeBr2C6H4Y-p (Y = H and Br) are MC, which shows that the steric effect of 2,6-Cl2C6H3 group is effective for MC
formation. (2-MeC6H4)2SeBr2 and (2-ClC6H4)2SeBr2 are TB and MC, respectively: the electronic effect of the Cl
group must play an additional role in the MC formation since the bulkiness of the Me and Cl groups are expected to
be similar. The bromine adduct of (2,4,6-Me3C6H2)2Se is also concluded to be MC: the steric effect of the four Me
groups at the ortho-positions is large enough to give MC with bromine. The oxidation potentials (Eox) of the diaryl
selenides explain well the structures of the bromine adducts: the electronic effect is directly correlated with Eox and
the importance of the steric effect has been brought into sharp relief by Eox. Results of MO calculations support
the outline of the observations. The structural behavior of some halogen adducts such as 2,6-Cl2C6H3SeCl2C6H4Y-p
(TB: Y = H and Br) is also discussed in some detail.
is rather easily understood by the 3c–4e description.1,2,4
Introduction
Recently, the Z–X–X bond in RRЈZ–X–X (MC) has also been
It has been well established that diorganyl selenides such as
proposed to be suitable for analysis by the 3c–4e model.5
diphenyl selenide (1) react with bromine, as well as chlorine and
fluorine, to yield trigonal bipyramidal adducts (TB) with highly
Although the examples of MC are growing, the numbers are
not so many and the scope of the MC formation is not well
established yet relative to the case of the TB formation.
polar hypervalent bonds.1,2 On the other hand, diorganyl selen-
ides react with iodine to give molecular complexes (MC).1,2
Mulliken has proposed a theory for MC based on quantum
mechanics.3 A theory for TB with hypervalent three center–four
electron bonds (3c–4e) has also been proposed by Pimentel and
Musher.4a The 3c–4e description of the X–Z–X bond in TB has
been further developed by the preparation and characterization
of a variety of compounds with the TB structure1,2 and by
theoretical calculations.4 The structures of RZX2RЈ, where
Z = S, Se, Te and X = halogens etc., are studied in some detail, in
this line. Consequently, the character of the X–Z–X bond in TB
The MC formation is the result of charge transfer (CT),
within some limits, where electrons move from electron donors
262
J. Chem. Soc., Perkin Trans. 2, 2002, 262–270
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b108556e

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to acceptors in the complexes, RSeX2RЈ. If CT from Se to X is
large enough, TB adducts will form accompanied by the highly
polar 3c–4e hypervalent X–Se–X bond.2,4 The magnitude of CT
from RSeRЈ to X2 is roughly estimated by the electronegativity6
of Se (χ(Se)) and that of X (χ(X)). TB will form if χ(X) is larger
than χ(Se), while the adducts will be MC when χ(X) is less than
χ(Se) (general rule).2 The bromine adducts of selenides are
concluded to be TB based on the general rule. However, the
adducts change from TB to MC if the effective electronegativity
of Se (χeff(Se)) in RSeRЈ increases sufficiently by modulating the
electronic properties of the Se atom in the selenide. The adducts
will be MC when χeff(Se) is larger than χ(X).7 The steric conges-
tion8 is also important. It should be more severe for the TB
formation than for the MC formation, since an Se atom in TB is
four-coordinated whereas that in MC is three-coordinated.
Indeed, the electronic and steric factors play an important role
in stabilizing or destabilizing both TB and MC, but the magni-
tude must be larger for TB. This is our basic strategy to prepare
diaryl selenides, especially variously substituted 1, that yield
MC with bromine.9
modified to increase the effective electronegativity of the selen-
ium atom and/or to increase the bulkiness around the atom.
Here, we present the results of our investigations.
Results
Substituted diphenyl selenides (3–17), bearing various substitu-
ents at the 2-, 3- and/or 4-positions of 1, are prepared,6 together
with their chlorine, bromine and iodine adducts. The 1H and 13
C
NMR chemical shifts (δ(H) and δ(C), respectively) have been
measured. Aromatic carbons are numbered 1, 2, . . and 6,
except for the Ph groups in 1 and 3–5 and the p-BrC6H4 group
in 6, in which carbons are named i, o, m and p. Aromatic
protons are numbered or named the same as the carbons with
which they are directly bonded.
Table 1 shows the halogen induced δ(H) and δ(C) chemical
shifts of chlorine, bromine and iodine for 4-nitrophenyl phenyl
selenide (3), 3,5-dinitrophenyl phenyl selenide (4), 2,6-dichloro-
phenyl phenyl selenide (5) and 2,6-dichlorophenyl p-bromo-
phenyl selenide (6), together with δ(H) and δ(C) values of the
parent selenides. Table 2 collects the halogen induced chemical
shifts for (4-YC6H4)2SeX2 (Y = Cl (7), COOEt (8), CN (9), NO2
(10)), (3-YC6H4)2SeX2 (Y = Cl (11), CN (12), NO2 (13)) and
(3,5-Cl2C6H3)2SeX2 (14). Table 3 exhibits the halogen induced
chemical shift values for (2-YC6H4)2SeX2 (Y = Me (15), Cl (16))
and (2,4,6-Me3C6H2)2SeX2 (17). Table 4 shows oxidation poten-
tials (Eox) of some diaryl selenides,14 together with the struc-
tures of their halogen adducts. Results of MO calculations
performed using Gaussian 9415 and/or 9816 programs with
the B3LYP/6-311ϩG(2d,p) method are shown in Table 5.
Optimized structures of some selenides and the chlorine
adducts are shown in Fig. 1.
The criteria distinguishing MC from TB adducts of the halo-
gen adducts of aryl selenides in solutions based on the NMR
chemical shifts are well established not only by the experimental
results2b,10 but also by theoretical calculations.11 The MC form-
ation of some bromine adducts of aryl selenides are reported
based on the criteria; selenoxanthone,7 selenanthrene7 and
1-(phenylselanyl)-2-(phenyldibromoselanyl)benzene (2ؒBr2).11,12
The structure of 2ؒBr2 is TB. The tetrabromide, 1,2-(PhBr2-
Se)2C6H4 (2ؒ2Br2), is obtained in the reaction of 2ؒBr2 with
bromine. The structure of 2ؒ2Br2 is TB for one of the SeBr2
moieties and the other is MC, which is notated as (TB, MC).11,12
Since 2ؒBr2 is a 2-phenyl(dibromo)selanyl derivative of 1, it is
recognized that a derivative of 1 reacts with bromine to give
MC. The (TB, MC) formation of 2ؒ2Br2 led us to the follow-
ing working hypothesis: such substituted diphenyl selenides
can be prepared9 that yield MC with bromine if 1 is suit-
ably modulated electronically13 and/or sterically.8 The phenyl-
(dibromo)selanyl group in 2ؒBr2 acts not only as a very strong
electron-withdrawing group but also as a bulky group to the
selanyl group at the 2-position of the diphenyl selenide. The
electronic effect must increase the effective electronegativity of
the selenium atom.
Fig. 1 Structures of some diaryl selenides and the chlorine adducts
optimized with the B3LYP/6-311ϩG(2d,p) method.
Discussion
Structure of ArSeX2ArЈ (X ؍ Cl and I)
Before discussing the structures of diaryl selenide dibromides, it
is worthwhile clarifying the structures of chlorine and iodine
adducts of the selenides. The structures of the chlorine adducts
of 3–17 in Tables 1–3 are concluded to be all TB. Large down-
field shifts are observed for the C(1) (and C(i)) and C(4) (and
C(p)) in the formation of the adducts. The shift values are
ca. 10–12 and ca. 4–5 ppm, respectively, although the values are
In order to demonstrate the formation of MC in the reaction
of substituted diphenyl selenides with bromine, 1 is chemically
J. Chem. Soc., Perkin Trans. 2, 2002, 262–270
263

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Table 1 Halogen induced 1H and 13C NMR chemical shifts for 3–6 together with the chemical shifts of parent selenidesa, b
Compd
H(2)
H(o)
C(1)
C(2) (C(6))
C(3) (C(5))
C(4)
C(i)
C(o)
C(m)
C(p)
Structure
Selenide
3
7.35
0.00
0.85
0.86
0.00
8.36
0.00
0.82
0.88
0.00
7.60
0.00
0.37
0.42
0.00
7.68
0.00
0.48
0.47
0.06
7.36
0.00
1.17
0.01
0.02
0.00
7.34
0.00
1.01
0.01
0.00
143.1
0.0
5.7
129.6
0.0
1.7
3.2
0.2
129.1
0.0
1.4
3.1
0.0
141.7
0.0
Ϫ6.5 (Ϫ6.6)
Ϫ0.5
Ϫ1.4
0.0
141.8
0.0
Ϫ6.6 (Ϫ6.8)
Ϫ0.2
0.0
123.8
0.0
0.6
0.8
0.1
148.5
0.0
0.2
Ϫ0.5
0.1
128.3
0.0
1.8 (3.3)
0.2
0.6
0.1
128.5
0.0
1.8 (3.2)
0.1
0.0
146.1
0.0
3.0
2.5
0.2
116.1
0.0
5.3
5.3
0.1
130.5
0.0
1.8
0.4
1.2
0.1
130.9
0.0
1.6
0.1
127.1
0.0
14.6
9.5
Ϫ0.2
126.1
0.0
15.2
5.8
135.8
0.0
Ϫ3.5
Ϫ2.7
Ϫ0.3
135.9
0.0
Ϫ4.8
Ϫ3.7
Ϫ0.1
130.8
0.0
129.9
0.0
0.1
0.4
0.1
130.4
0.0
0.6
0.3
0.1
129.1
0.0
Ϫ0.2
0.2
0.5
0.1
132.3
0.0
Ϫ0.3
0.1
129.3
0.0
2.9
2.6
0.2
130.1
0.0
2.8
2.6
0.0
126.8
0.0
5.1
0.7
1.5
0.0
121.2
0.0
6.0
0.2
3ؒCl2
3ؒBr2
3ؒI2
4
TB
TB
MC
Selenide
1.9
Ϫ0.8
138.8
0.0
8.3
5.0
0.0
130.4
0.0
4ؒCl2
4ؒBr2
4ؒI2
5
TB
TB
MC
Selenide
Ϫ0.1
131.2
0.0
5ؒCl2
5ؒBr2
11.2
8.3
2.3
TB
MC
MC
MC
c
c
Ϫ0.1
Ϫ0.6
Ϫ0.1
132.6
0.0
2.1
0.0
d
5ؒ2Br2
Ϫ0.6
0.0
130.2
0.0
11.5
Ϫ0.2
0.0
Ϫ1.0
Ϫ0.1
132.1
0.0
8.1
Ϫ0.3
Ϫ0.1
5ؒI2
6
Selenide
6ؒCl2
6ؒ2Br2
6ؒI2
TB
MC
MC
0.1
0.0
0.0
0.0
a Chemical shifts of selenides (δ) are given relative to TMS and the halogen induced chemical shifts (∆δ) are measured with respect to their parent
selenides. b In CDCl3. c Not observed due to broadening. d At Ϫ30 ЊC.
Table 2 Halogen induced 1H and 13C NMR chemical shifts for 7–14 together with the parent selenidesa, b
Compd
H(2)
H(3)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
Structure
Selenide
7
7.34
7.26
0.00
0.25
0.22
0.03
7.94
0.00
0.23
0.17
0.00
7.56
0.00
0.28
0.00
0.01
8.16
0.00
0.26
0.00
0.00
128.9
0.0
11.5
7.8
Ϫ0.6
136.6
0.0
10.1
6.1
Ϫ0.5
136.5
0.0
10.6
Ϫ0.1
Ϫ0.1
138.8
0.0
134.2
0.0
Ϫ1.6
Ϫ0.7
Ϫ0.2
132.4
0.0
Ϫ1.2
Ϫ0.1
Ϫ0.1
133.1
0.0
Ϫ1.1
0.0
0.0
133.2
0.0
Ϫ0.6
0.0
Ϫ0.1
132.6
0.0
Ϫ1.6
Ϫ0.9
Ϫ0.1
136.0
0.0
Ϫ1.4
0.0
0.0
127.6
0.0
Ϫ1.2
0.1
0.0
130.9
0.0
Ϫ1.7
Ϫ0.1
0.0
129.5
0.0
0.4
0.8
0.2
130.3
0.0
0.3
0.5
0.1
132.8
0.0
0.4
0.0
0.0
124.5
0.0
0.4
0.0
0.0
135.0
0.0
0.4
0.7
0.1
113.9
0.0
0.6
0.1
0.0
148.6
0.0
Ϫ0.2
0.1
0.0
135.7
0.0
0.5
0.1
0.0
133.8
0.0
4.7
4.5
0.6
129.6
0.0
3.9
3.6
0.5
111.6
0.0
4.5
0.2
0.1
147.6
0.0
2.0
0.0
0.0
127.9
0.0
4.3
4.2
0.4
131.5
0.0
3.9
0.1
0.1
123.0
0.0
3.9
0.1
0.1
128.3
0.0
4.2
0.7
0.1
0.00
0.60
0.61
0.02
7.49
0.00
0.60
0.62
0.02
7.56
0.00
0.60
0.00
0.01
7.61
0.00
0.64
0.00
0.00
7.44
0.00
0.53
0.55
0.01
7.72
0.00
0.60
0.01
0.00
8.34
0.00
0.57
Ϫ0.01
Ϫ0.01
7.32
0.00
0.60
0.61
0.02
7ؒCl2
7ؒBr2
7ؒI2
8
TB
TB
MC
Selenide
8ؒCl2
8ؒBr2
8ؒI2
9
TB
TB
MC
Selenide
9ؒCl2
9ؒBr2
9ؒI2
TB
MC
MC
Selenide
10
10ؒCl2
10ؒBr2
10ؒI2
11
9.8
TB
MC
MC
Selenide
Ϫ0.1
Ϫ0.1
131.9
0.0
11.3
6.8
Ϫ0.5
131.5
0.0
12.3
Ϫ0.2
Ϫ0.2
131.6
0.0
12.5
0.0
Ϫ0.1
132.2
0.0
11.6
Ϫ0.2
Ϫ0.1
130.4
0.0
0.2
0.4
0.1
130.2
0.0
0.4
0.0
0.0
130.3
0.0
0.6
0.1
0.1
131.0
0.0
Ϫ1.7
Ϫ0.5
Ϫ0.1
137.2
0.0
Ϫ2.1
Ϫ0.1
0.0
138.8
0.0
11ؒCl2
11ؒBr2
11ؒI2
12
TB
TB
MC
Selenide
12ؒCl2
12ؒBr2
12ؒI2
13
TB
MC
MC
Selenide
13ؒCl2
13ؒBr2
13ؒI2
14
Ϫ2.4
Ϫ0.1
Ϫ0.1
TB
MC
MC
Selenide
14ؒCl2
14ؒBr2
14ؒI2
TB
MC
MC
a Chemical shifts of selenides (δ) are given relative to TMS and the halogen induced chemical shifts (∆δ) are measured with respect to their parent
selenides. b In CDCl3.
out of the ranges if the selenides are unsymmetrical such as 3–6
or if Y is strongly electron-withdrawing, such as 10. The iodine
adducts are all MC. The signals due to C(1) (and C(i)) and
C(4) (and C(p)) are shifted downfield and upfield, respectively.
The upfield shifts of ipso-carbons are characteristic of MC
formation. Since the MC adducts are in equilibrium with the
264
J. Chem. Soc., Perkin Trans. 2, 2002, 262–270

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Table 3 Halogen induced 1H and 13C NMR chemical shifts for 15–17 together with the parent selenidesa, b
Compd
H(2)
H(3)
H(6)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
Structure
Selenide
15
2.39c
7.17
0.00
0.23
0.22
0.03
7.18
0.00
0.28
0.05
0.00
6.82
0.00
0.18
0.00
7.23
0.00
0.56
0.55
0.02
7.39
0.00
0.64
0.05
0.04
131.2
0.0
11.1
3.5
Ϫ1.0
131.9
0.0
11.8
Ϫ0.9
Ϫ0.3
129.3
0.0
139.7
0.0
Ϫ1.8
Ϫ1.6
Ϫ0.2
132.6
0.0
Ϫ2.8
Ϫ0.1
0.0
141.2
0.0
130.1
0.0
1.0
1.7
0.4
135.0
0.0
1.8
0.4
0.1
128.8
0.0
Ϫ0.2
0.1
0.2
0.1
127.4
0.0
5.0
4.9
0.8
127.9
0.0
3.7
1.1
0.2
136.8
0.0
3.9
0.4
0.7
126.6
0.0
0.6
1.1
0.4
130.4
0.0
0.5
0.4
0.0
133.0
0.0
Ϫ1.5
Ϫ1.2
0.0
131.0
0.0
Ϫ2.3
Ϫ0.2
0.0
0.00c
0.46c
0.30c, d
0.01c
15ؒCl2
15ؒBr2
15ؒI2
16
TB
TB
MC
Selenide
16ؒCl2
16ؒBr2
16ؒI2
17
TB
MC
MC
Selenide
2.24c
0.00c
17ؒCl2
17ؒBr2
0.45c
10.3
Ϫ0.5
0.7
Ϫ1.2
Ϫ0.1
Ϫ0.2
0.1
TB
MC
Ϫ0.01c, e
17ؒI2
Ϫ0.01c
0.00
0.0
0.2
MC
a Chemical shifts of selenides (δ) are given relative to TMS and the halogen induced chemical shifts (∆δ) are measured with respect to their parent
selenides. b In CDCl3. c Methyl group. d At Ϫ30 ЊC. e At Ϫ20 ЊC.
Table 4 Oxidation potentials of ArSeArЈa together with the structures
of ArSeX2ArЈ (X = Cl, Br and I)
Structure of adduct
Selenide
X =
Cl
Br
I
Eox/V
Di-4-anisyl selenide
Di-4-tolyl selenide
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
TB
MC
MC
MC
MC
MC
MC
MC
MC
MC
MC
MC
MC
MC
MC
MC
1.65
1.81
1.86
2.00
2.00
2.08
2.18
2.19
2.22
2.23
2.27
(1.22)b
(1.32)b
(1.38)b
(1.44)b
(1.54)b, c
1
7
8
3
Scheme 1 Mechanism for the site exchange of the 2,6-dichlorophenyl
plane in 5ؒCl2 and 6ؒCl2. The conformers are shown by 18a and 18b and
an ionic species by 19.
4
12
9
13
10
(1.76)b
in 5ؒCl2 are observed as a very broad singlet at an ambient
NMR probe temperature of ca. 23 ЊC when measured at 300
MHz. The signals show a B2 pattern in AB2 at 45 ЊC. The
behaviour of 6ؒCl2 is very close to that of 5ؒCl2. No noticeable
differences are observed in the temperature and solvent
dependences (C6D6 vs. CDCl3) between 5ؒCl2 and 6ؒCl2. The
results are in accordance with a mechanism involving rotation
around the Se–C(1) bond. Rotation in an ionic species, such as
19, formed by Se–Cl bond scission, is unlikely (Scheme 1). The
contribution from the dissociation of 5ؒCl2 and 6ؒCl2 to the
components would also be negligible under these conditions.18
The rotation around the Se–C(1) bonds in 17ؒCl2 is also
expected to be restricted due to the steric hindrance of the four
methyl groups at all ortho-positions. However, only one set of
signals is observed for C(2) and C(3) (or C(6) and C(5)) as
shown in Table 3. These results show that the activation energy
of the rotation around the Se–C(1) bond in 17ؒCl2 is smaller
relative to that in 5ؒCl2. There are two posibilities for the
smaller activation energy in 17ؒCl2: one is the stabilization of
the transition state and the other is the destabilization of the
ground state. The latter is often observed in the rotational bar-
rier of very crowded molecules.19 While the Cl–Se–Cl bond in
17ؒCl2 could have greater stability than that of 5ؒCl2 due to the
electron-donating six methyl groups, the steric hindrance in
17ؒCl2 must be greater than that in 5ؒCl2. Therefore, it is more
plausible that the methyl groups at all ortho-positions in 17ؒCl2
destabilize the ground state.
15
17
5
TB
TB
TB
TB
TB
MC
MC
MC
MC
1.89
1.92
2.09
2.13
MC
MC
MC
16
a Oxidation potentials are given versus an Ag/AgI reference electrode
with the ferrocene redox pair as a standard, measured in MeCN con-
taining 0.1 M Et4NClO4 as a supporting electrolyte with a Pt electrode.
b Ref. 14. c The value for Se(C6H4COOH)2.
components, the magnitude of the observed shift values are
governed not only by the intrinsic chemical shifts of the MC
but also by the equilibrium (dissociation) constants of the
adducts (ArSeI2ArЈ).7,17
The NMR signals revealed some structural features of the
chlorine adducts. Both C(2) and C(3) (or C(6) and C(5)) signals
of 5ؒCl2 are observed as two types. Their chemical shifts, half-
width values and integrations do not change with excess chlor-
ine. The results show that the rotation of the 2,6-dichlorophenyl
plane in 5ؒCl2 around the Se–C(1) bond is restricted relative to
the NMR time scale, as shown by 18a and 18b in Scheme 1. The
plane must be locked almost perpendicular to the hypervalent
Cl–Se–Cl bond due to the bulkiness of the chlorine atoms at the
2,6-positions. Consequently, the phenyl ring is placed nearly
parallel to the hyprvalent bond, and it can rotate essentially
freely under the conditions. The structure around the Se atom
in 6ؒCl2 is similar to that in 5ؒCl2: the C(2) and C(3) (or C(6)
and C(5)) signals of the 2,6-dichlorophenyl group in 6ؒCl2 also
gave two sets of data.
Next, we discuss the magnitude of the chlorine induced
chemical shifts. The downfield shifts of C(1) and C(i) in 5ؒCl2
and 6ؒCl2 were 11.2–11.5 and 8.1–8.3 ppm, respectively, and
those of C(4) and C(p) were 1.6–1.8 and 5.1–6.0 ppm, respect-
ively. These results show that the downfield shifts of C(1) and
C(i) of aryl rings perpendicular to and parallel to the Cl–Se–Cl
Although the 13C NMR spectra gave little information on the
dynamic behaviour of 5ؒCl2 and 6ؒCl2, δ(H) values shed light on
this behaviour of the adducts. The δ(H(3)) and δ(H(5)) signals
J. Chem. Soc., Perkin Trans. 2, 2002, 262–270
265

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Table 5 Energies of ArSeArЈ, ArSeCl2ArЈ (TB) and ArSeBr2ArЈ (TB) together with Cl2, Br2 and 1ؒCl2 (MC), calculated with the B3LYP/
6-311ϩG(2d,p) methoda
X
Cl
Br
Null
E(au)
ArSeX2ArЈ
E(au)
∆E/kJ molϪ1 b
E(au)
∆E/kJ molϪ1 b
1ؒX2
Ϫ2864.9713
Ϫ2979.5316
Ϫ3069.5407
Ϫ3069.5428
Ϫ3274.1050
Ϫ3274.1090
Ϫ3784.2108
Ϫ3022.2764
Ϫ2864.9713
Ϫ3785.4266
Ϫ3899.9880
Ϫ3989.9919
Ϫ3989.9919
Ϫ4194.5522
Ϫ4194.5558
Ϫ4704.6527
Ϫ3942.7143
Ϫ3785.4031
96.3
99.2
85.8
74.8
74.8
74.1
61.2
50.7
34.7
Ϫ8013.2666
Ϫ8127.8283
50.3
53.6
40.8
4-MeOC6H4SeX2Ph
3-O2NC6H4SeX2Ph
3ؒX2
Ϫ8217.8317
c
4ؒX2
Ϫ8422.3917
Ϫ8422.3954
Ϫ8932.4924
27.8
27.2
14.6
2.6
10ؒX2
5ؒX2
(2,6-Me2C6H3)2SeX2
1ؒX2 (MC)
Ϫ8170.5535
c
a E(Cl2) = Ϫ920.4186 au and E(Br2) = Ϫ5148.2761 au. 1 au (atomic unit) = 1 hartree = 4.360 × 10Ϫ18 J. b ∆E = [E(ArSeArЈ) ϩ E(X2)] Ϫ E(ArSeX2ArЈ).
c Not optimized due to convergence failure in the SCF.
bond are ca. 11 and 8 ppm, respectively, while those of C(4) and
C(p) are less than 2 and 5–6 ppm, respectively. The chlorine
induced chemical shifts of the aryl C(1) and C(4) carbons
become larger and smaller when the π-orbitals of the aryl ring
are parallel to the Cl–Se–Cl bond, respectively. The average
values for carbons at the 1- and ipso-positions and 4- and
para-positions are estimated to be 9.7–9.8 and 3.4–3.8 ppm,
respectively. The observed chlorine induced chemical shifts for
the corresponding carbons in Tables 1–3 are close to or slightly
larger than the average values, except for C(4) of 10ؒCl2. The
smaller chlorine induced chemical shifts observed in 10ؒCl2
is the result of the saturation effect by the strong electron-
withdrawing nitro groups in the formation of the highly polar
ClδϪ–Seδϩ–Clδ– bond.
The chemical shift values of the ortho-carbons of aryl rings
perpendicular and parallel to the Cl–Se–Cl bond are Ϫ6.5 to
Ϫ6.8 and 2.1–3.2 ppm, respectively, whereas those of the
meta-carbons are 1.8–3.3 and Ϫ0.2 to Ϫ0.3 ppm, respectively,
as observed in 5ؒCl2 and 6ؒCl2. The average values for ortho-
and meta-carbons are estimated to be Ϫ1.6 to Ϫ2.4 and 0.7–1.6
ppm, respectively. Most of the chlorine induced chemical shifts
of the ortho- and meta-carbons are observed in these ranges.
The chlorine induced chemical shifts for the ortho-protons of
the phenyl and the p-bromophenyl groups in 5ؒCl2 and 6ؒCl2 are
ca. 1.2 ppm when they are nearly parallel to the Cl–Se–Cl bond.
Since the values for 5ؒBr2 are equal to those for 6ؒBr2, it is
evident that they are mainly governed by the anisotropic effect
of the hypervalent X–Se–X bonds, although the large electron-
withdrawing ability of the group cannot be ignored. Those for
the phenyl groups in ArSeX2Ar (X = Cl, Br) are 0.6–0.8 ppm as
shown in Tables 1–3, and are 0.5–0.7 times larger than those of
5ؒX2 and 6ؒX2 (X = Cl, Br).
when TB adducts are formed mainly by steric constraints. The
conformational change in the formation of TB must be respon-
sible for the unique Y dependence of the chlorine induced
chemical shifts.
The iodine induced δ(C(1)) and δ(C(i)) values in MC form-
ation also dramatically change depending on Y: the values for
3ؒI2 are Ϫ0.8 and Ϫ0.2 ppm, respectively, for example. It is
worthwhile commenting that the halogen induced chemical
shifts by chlorine and iodine are just the opposite in both sign
and magnitude. The conformational change that occurs in MC
formation is responsible for the phenomena. The position of
the Se atom in the sequence of the X–Y–Z 3c–4e bond must
also be important:5 the Se atom is located at the center of the
Cl–Se–Cl bond in 3ؒCl2 but is at the terminal position of the
Se–I–I bond in 3ؒI2.
Structure of ArSeBr2ArЈ
Electronic requirements for MC formation. The C(1) (and
C(i)) signals of the bromine adducts of 3, 4, 7, 8, 11 and 15,
among 3–17, are shifted downfield relative to those of the
parent selenides. The structures of these bromine adducts must
be TB. The electron-withdrawing ability of the two ethoxy-
carbonyl groups in 8 is not large enough for MC formation with
bromine: disubstituted diphenyl selenides13 at the 3,3Ј- or
4,4Ј-positions give TB adducts with bromine, if the electron-
withdrawing ability of the substituent is less than that of the
ethoxycarbonyl group.
The chlorine induced δ(C(1)) and δ(C(i)) chemical shift
values also change dramatically in TB formation depending on
the substituents Y in the substituted diphenyl selenides: the
values for 3ؒCl2 are 5.7 and 14.6 ppm, respectively, for example.
The importance of the conformational change from a selenide
to its adduct is supported by ab initio MO calculations per-
formed with the B3LYP/6-311ϩG(2d,p) method. The opti-
mized structures of some selenides and their chlorine adducts
are shown in Fig. 1 (for details, see MO Calculations section,
below). The conformation of selenides is affected greatly by the
electronic effect of Y. Although the conformation of sym-
metrical selenides is expected to be of C2 symmetry, that of the
unsymmetrical ones will be close to the Cs symmetry. The filled
p-type lone pair orbital of Se in ArSePh is parallel to the
π-orbitals of the Ar group, if Ar has an electron-withdrawing Y
substituent, but the lone pair orbital is parallel to the π-orbitals
of the Ph group if Y is electron-donating. The interactions
between the lone pair orbital and the π-orbitals will stabilize
the selenides in the predicted cases more than the inverse
cases. However, the structures will be close to C2 symmetry
On the other hand, upfield shifts were observed for C(1) (and
C(i)) in 5ؒBr2, 6ؒBr2, 9ؒBr2, 10ؒBr2, 12ؒBr2, 14ؒBr2, 16ؒBr2 and
17ؒBr2: The structures must be MC. That of 13ؒBr2 must also
be MC, although the upfield shifts are not explicitly recorded.
Diaryl selenides with cyano or nitro groups at the 3,3Ј- or 4,4Ј-
positions yield MC with bromine: the groups are sufficiently
electron-withdrawing for MC formation. The four chloro
groups at all the meta-positions in 14 are also effective for MC
formation with bromine.
Why are 10ؒBr2 and 13ؒBr2 MC, while 4ؒBr2 being TB? The
energy difference between the TB adduct and the components,
∆E, defined in the MO Calculations section, is evaluated to
be only slightly larger for 4ؒBr2 than for 10ؒBr2 by MO
calculations. A similar trend is also predicted for the chlorine
266
J. Chem. Soc., Perkin Trans. 2, 2002, 262–270

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adducts (see Table 5). Although the observed ∆E values are too
small to be supported by calculations, the two nitro groups in 4
do not give MC with bromine under the experimental condi-
tions. Since the two nitro groups in 4 are substituents of the
same phenyl ring, the electron-withdrawing effect of the nitro
groups would be saturated more strongly in 4 than in 10 and 13.
The conformation of 4 must also play an important role for
MC not to be given with bromine. The conformation of 4 is
very close to Cs symmetry but that of 4ؒCl2 is close to C2 sym-
metry (Fig. 1). That of 4ؒBr2 must also be close to C2 symmetry.
The electron-withdrawing ability of the 3,5-dinitrophenyl
group is a maximum in the Cs symmetry, as shown in 20, since
Two sets of signals are observed for the 2,4,6-Me3C6H2
groups in 17ؒBr2. The chemical shifts of 17ؒBr2 are very differ-
ent from those of 17ؒCl2 (TB) but they are similar to 17ؒI2
(MC). One signal for C(1) is shifted upfield by 0.5 ppm but
another (C(1Ј)) is shifted downfield by 0.7 ppm. The total
halogen induced chemical shift (Σδi(C)) has been proposed to
examine the structures of halogen adducts of aryl selenides in
solutions:11 Σδi(C) = δi(C(1)) ϩ 2δi(C(2)) ϩ 2δi(C(3)) ϩ δi(C(4)).
The 2Σδi(C) values for 17ؒX2, where X = Cl, Br and I, are 22.8,
1.3 and 1.4 ppm, respectively. Therefore, it is concluded that
17ؒBr2, as well as 17ؒI2, is MC, while 17ؒCl2 is TB, based on
above discussion.
Oxidation potentials of parent selenides
The n(pz)-orbital of the selenium atom in a diaryl selenide must
play an important role in TB formation, but the electron trans-
fer from HOMO to the σ*-orbital of a halogen occurs in the
initial stage of the reaction.20 The oxidation potentials (Eox) of
diaryl selenides correlate well with the energies of HOMO. The
HOMO has both the π-character of the aryl groups and the
n(pz)-character of the selenium atom in ArSeArЈ. Therefore, it
is expected to serve as a good measure to predict the structure
of the bromine adduct. The Eox values of some parent selenides
are given in Table 4. The Eox values of the 3- and 4-substituted
diphenyl selenides become larger as the electron-withdrawing
ability of the substituent(s) increases.14,21 As shown in Table 4,
the bromine adduct of a 3- or 4-substituted diphenyl selenide
will be MC when Eox is larger than 2.2 V under the conditions.
The borderline between the existence of the two structures
occurs with 4ؒBr2 (TB) and 12ؒBr2 (MC). However, Eox values
for 4 and 12 are essentially the same (2.18 V and 2.19 V, respect-
ively). This may be reflected in the conformational change of 4
in the reaction with bromine as discussed above.
The oxidation potentials of 1, di-4-tolyl selenide, 15 and 17
are 1.86, 1.81, 1.89 and 1.92 V, respectively. The value for di-4-
tolyl selenide is smaller than that of 1 due to the electron-
releasing effect of the methyl groups. However, the values of 15
and 17 are larger than that of 1, irrespective of the electron-
releasing group(s) in 15 and 17. This must come from the steric
effect exerted by the methyl groups at the 2-positions,8 which
prevents the cations produced from stabilizing by effective
solvation. A similar steric effect is also observed for the chloro
groups at the 2-positions in 5 and 16: the oxidation potentials
of 5 and 16 are larger than that of 7. Such steric effects must be
greater in TB formation than in MC formation. Although the
Eox values of 5, 16 and 17 are all less than 2.2 V, the structures
of the bromine adducts are all MC. These results clearly show
the importance of the steric effect of methyl and chloro groups
at the ortho-positions on the reaction of the selenides with
bromine.
the p-type orbitals of the nitro groups are parallel to the p-type
lone pair orbital of the Se atom. However, the effect is reduced
in the C2 symmetry. If the phenyl group can supply electrons to
the bromine atoms through the Se atom, the hypervalent
Br–Se–Br bond will be formed. The effect of the electron
donation in 4ؒBr2 (TB) will be larger for the C2 symmetry rela-
tive to the Cs symmetry (see 20 for the selenide part in 4ؒBr2).
On the other hand, the conformations of 10 and 10ؒCl2 (TB) are
predicted to be of C2 symmetry. Those of 13 and 13ؒCl2 (TB)
are also of C2 symmetry, although these are not shown in Fig. 1.
Indeed, the conformational changes around the Se atom
between 4 and 4ؒCl2 (TB) are large, but they are very small for
10 and 13. Such a delicate change in the conformation of 4
relative to 10 and 13 in the reaction with bromine makes 4ؒBr2
TB.
The steric effect on the structures of 5ؒBr2, 6ؒBr2, 15ؒBr2,
16ؒBr2 and 17ؒBr2 will be discussed in the next section.
Steric requirements for MC formation. The structures of
5ؒBr2, 6ؒBr2 and 16ؒBr2 are demonstrated to be MC whereas
those of 7ؒBr2, 11ؒBr2 and 15ؒBr2 are TB, judging from the
bromine induced C(1) (and C(i)) chemical shifts. Although
the two chloro groups at the 3,3Ј- and 4,4Ј-positions in 7 and 11
do not work effectively for the MC formation with bromine, the
groups at the 2,2Ј-positions in 5, 6 and 16 do effectively. These
results show that the steric effect is also important for MC
formation with bromine. Since the coordination number is four
for TB but is three for MC, the steric congestion must be more
severe for TB than for MC. On the other hand, 15ؒBr2 is TB:
MC formation of 16ؒBr2 compared with TB formation of
15ؒBr2 must be due to the difference in the electronic ability of
the two groups, since the bulkiness of the methyl and chloro
groups are similar.
MO Calculations
Table 5 shows the energies of 1, 3–5, 10, p-MeOC6H4SePh,
3-O2NC6H4SePh and (2,6-Me2C6H3)2Se, a model of 17,
together with the chlorine and bromine adducts of TB
structures, calculated by the B3LYP/6-311ϩG(2d,p) method.
Table 5 also contains the results of MO calculations for 1ؒCl2
(MC), and also for the Cl2 and Br2 adducts. The energy differ-
ences between the halogen adducts and the components are
also given in the Table (∆E = [(E(ArSeArЈ) ϩ E(X2)] Ϫ
E(ArSeX2ArЈ; X = Cl, Br)).
In the case of X = Cl, ∆E decreases in the order of
p-MeOC6H4SePh > 1 > 3-O2NC6H4SePh > 3, which is a reflec-
tion of the electron-withdrawing ability of the substituent. The
∆E values are almost equal for 3, 4 and 10. The decrease in ∆E
from 10 to (2,6-Me2C6H3)2Se via 5 is just the opposite to the
expectation based on the electron-withdrawing ability of the
substituents. This must be due to the steric effects of the chloro
and methyl groups at the ortho-positions. The trend in ∆E is
J. Chem. Soc., Perkin Trans. 2, 2002, 262–270
267

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more dramatic for X = Br. The ratios of ∆E(ArSeBr2ArЈ) :
∆E(ArSeCl2ArЈ) are about 0.53 for 1ؒX2 and p-MeOC6H4-
SeX2Ph, 0.37 for 3ؒX2, 4ؒX2 and 10ؒX2, 0.24 for 5ؒX2 and 0.06
for (2,6-Me2C6H3)2SeX2. The decrease in the ratio from 0.53 to
0.37 is a reflection of the smaller electron-accepting ability of
bromine relative to that of chlorine. The larger volume of
bromine relative to that of chlorine must mainly contribute
to the decrease from 0.37 to 0.06 via 0.24. The steric conges-
tion must be more severe for TB formation with bromine.22 The
results of MO calculations support the outline of the
observations.
δ 7.35 (d, J = 9.0 Hz, 2H), 7.32–7.76 (m, 5H), 8.04 (d, J = 9.0 Hz,
2H). Anal. Calcd. for C12H9NO2Se: C, 51.81; H, 3.26; N, 5.04%.
Found: C, 51.71; H, 3.29; N, 5.12%.
ꢀ4-4-Nitrophenyl(phenyl)dichloroselane (3ؒCl2). 1H NMR (300
MHz, CDCl3) δ 7.45–7.66 (m, 3H), 7.72–8.22 (m, 2H), 8.20 (d,
J = 9.4 Hz, 2H), 8.37 (d, J = 9.4 Hz, 2H). Anal. Calcd. for
C12H9Cl2NO2Se: C, 41.29; H, 2.60; N, 4.01%. Found: C, 41.25;
H, 2.81; N, 3.91%.
3,5-Dinitrophenyl phenyl selenide (4). Diphenyl diselenide
(1.50 g, 4.80 mmol) was reduced by NaBH4 (0.55 g, 14.42
mmol) in an aqueous THF under argon atmosphere and the
resulting selenolate anion was allowed to react with 3,5-dinitro-
benzenediazonium chloride (2.66 g, 11.53 mmol) at low tem-
perature. The reaction mixture was stirred at 4 ЊC for 1.5 h and
at 40 ЊC for 2 h. After usual work-up, the crude product was
purified by flush chromatography on a silica gel column con-
taining acidic and basic alumina eluted with hexane. Recrystal-
lization from ethanol gave 2.61 g of pure product as yellow
needles. Yield 84%, mp 101–102 ЊC. 1H NMR (300 MHz,
CDCl3) δ 7.31–7.82 (m, 5H), 8.36 (d, J = 2.0 Hz, 2H), 8.78 (t,
J = 2.1 Hz, 1H). Anal. Calcd. for C12H8N2O4Se: C, 44.60; H,
2.50; N, 8.67%. Found: C, 44.63; H, 2.53; N, 8.72%.
Conclusion
Typical examples of MC formation in the reaction of substi-
tuted diphenyl selenides with bromine are reported. This has
been clearly demonstrated by increasing the effective electro-
negativity of the Se atom and the steric hindrance around the
atom in diphenyl selenide (1) with various substituents at the 2-,
3- and/or 4-positions of the phenyl groups. Oxidation poten-
tials of diaryl selenides and ab initio MO calculations support
these observations. Diaryl selenide dibromides are in equi-
librium with their components.23 They also equilibrate between
the MC and TB structures if diaryl selenides are appropriately
designed.24 Studies on the halogen adducts of selenides bearing
more complex structures are in progress in our laboratory.
1
ꢀ4-3,5-Dinitrophenyl(phenyl)dichloroselane (4ؒCl2). H NMR
(300 MHz, CDCl3) δ 7.62–7.83 (m, 3H), 7.88–8.24 (m, 2H), 9.18
(br s, 2H), 9.18 (t, J = 2.0 Hz, 1H). Anal. Calcd. for
C12H8Cl2N2O4Se: C, 35.57; H, 2.05; N, 7.11%. Found: C, 35.74;
H, 2.06; N, 6.82%.
Experimental
General
Chemicals were used without further purification unless other-
wise noted. Solvents and reagents were purified by standard
methods as necessary. Melting points are uncorrected. 1H (300
MHz) and 13C (75 MHz) NMR spectra were recorded on a
2,6-Dichlorophenyl phenyl selenide (5). The synthetic pro-
cedure was similar to that of 4. Colorless prisms. Yield 68%, mp
53.5–54.5 ЊC. 1H NMR (300 MHz, CDCl3) δ 7.04–7.40 (m, 5H),
7.36 (br s, 2H), 7.50 (d, J = 4.8 Hz, 1H). Anal. Calcd. for
C12H8Cl2Se: C, 47.72; H, 2.67%. Found: C, 47.97; H, 2.72%.
1
JEOL JNM-AL 300 spectrometer and H (90 MHz) and 13C
(22.4 MHz) NMR spectra were recorded on a JEOL EX-90
spectrometer. The 1H and 13C chemical shifts are given in ppm
relative to those of internal CHCl3 slightly contaminated
in solution and CDCl3 as the solvent, respectively. Column
chromatography was performed on silica gel (Fuji Silysia BW-
300), acidic alumina and basic alumina (E. Merk). Flash col-
umn chromatography was performed with 300–400 mesh silica
gel, acidic alumina and basic alumina and analytical thin layer
chromatography was performed on precoated silica gel plates
(60F-254) with the systems (v/v) indicated.
ꢀ4-2,6-Dichlorophenyl(phenyl)dichloroselane
NMR (300 MHz, CDCl3) δ 7.32–7.74 (m, 6H), 8.34–8.62 (m,
2H). Anal. Calcd. for C12H8Cl4Se: C, 38.64; H, 2.16%. Found:
C, 38.88; H, 2.22%.
(5ؒCl2).
1H
2,6-Dichlorophenyl p-bromophenyl selenide (6). The synthetic
procedure was similar to that of 4. Colorless prisms. Yield 72%,
mp 109–110 ЊC. 1H NMR (300 MHz, CDCl3) δ 7.19 (d, J = 8.5
Hz, 2H), 7.25 (t, J = 8.0 Hz, 1H), 7.34 (d, J = 8.5 Hz, 2H), 7.41
(d, J = 7.7 Hz, 2H). Anal. Calcd. for C12H7BrCl2Se: C, 37.83; H,
1.85%. Found: C, 37.67; H, 1.75%.
Synthesis of compounds
Diphenyl diselenide25 and bis(p-bromophenyl) diselenide25
were prepared according to the methods in the literature or the
improved method.
ꢀ4-2,6-Dichlorophenyl( p-bromophenyl)dichloroselane (6ؒCl2).
1H NMR (300 MHz, CDCl3) δ 7.30–7.52 (m, 3H), 7.65 (d,
J = 9.0 Hz, 2H), 8.35 (d, J = 9.2 Hz, 2H). Anal. Calcd. for
C12H7BrCl4Se: C, 31.90; H, 1.56%. Found: C, 31.74; H, 1.65%.
Selenide dichlorides were prepared in the reaction of
selenides with chlorine or sulfuryl chloride in inert solvent such
as carbon tetrachloride, hexane, or dichloromethane. NMR
spectra of bromine and iodine adducts were measured for
mixtures of selenides with halogens at the given ratios.
Bis(4-chlorophenyl) selenide (7)26. Selenium powder (1.00 g,
12.66 mmol) was reduced by NaBH4 (1.44 g, 37.99 mmol) in
H2O under argon atmosphere and the resulting sodium dis-
elenate was allowed to react with 4-chlorobenzenediazonium
chloride (4.88 g, 27.86 mmol) at low temperature. The reaction
mixture was stirred at 4 ЊC for 1.5 h and at 40 ЊC for 2 h. After
the usual work-up, the crude product was purified by flash
chromatography on a silica gel column containing acidic and
basic alumina eluted with hexane. Recrystallization from
hexane gave 2.37 g pure product as colorless prisms. Yield 62%,
mp 96–97 ЊC. 1H NMR (300 MHz, CDCl3) δ 7.26 (d, J = 8.8 Hz,
4H), 7.34 (d, J = 8.8 Hz, 4H). Anal. Calcd. for C12H8Cl2Se: C,
47.72; H, 2.67%. Found: C, 47.88; H, 2.81%.
1
The physical properties, H NMR data and the results of
elementary analyses of 3–17 and their chlorine adducts are as
follows. Their 13C NMR data are shown in Tables 1–3.
4-Nitrophenyl phenyl selenide (3). Diphenyl diselenide (2.03 g,
6.50 mmol) was reduced by NaBH4 (0.74 g, 19.51 mmol) in
ethanol under argon atmosphere and the resulting selenate
anion was allowed to react with p-nitrochlorobenzene (2.05 g,
13.00 mmol) at low temperature. The reaction mixture was
refluxed for 2 h. After the usual work-up, the crude product was
purified by flash chromatography on a silica gel column con-
taining acidic and basic alumina eluted with hexane. Recrystal-
lization from ethanol gave 2.83 g pure product as yellow
ꢀ4-Bis(4-chlorophenyl)dichloroselane (7ؒCl2). H NMR (300
MHz, CDCl3) δ 7.51 (d, J = 9.0 Hz, 4H), 7.94 (d, J = 9.0 Hz,
1
1
needles. Yield 78%, mp 58 ЊC. H NMR (300 MHz, CDCl3)
268
J. Chem. Soc., Perkin Trans. 2, 2002, 262–270

View Article Online
1
4H). Anal. Calcd. for C12H8Cl4Se: C, 38.64; H, 2.16%. Found:
C, 38.58; H, 2.22%.
ꢀ4-Bis(3-nitrophenyl)dichloroselane (13ؒCl2). H NMR (300
MHz, CDCl3) δ 7.81 (t, J = 8.4 Hz, 2H), 8.37 (ddd, J = 0.7, 1.1
and 8.1 Hz, 2H), 8.48 (ddd, J = 0.9, 1.7 and 8.1 Hz, 2H), 8.91
(t, J = 2.0 Hz, 2H). Anal. Calcd. for C12H8Cl2N2O4Se: C, 36.57;
H, 2.05; N, 7.11%. Found: C, 36.71; H, 2.27; N, 7.15%.
Bis(4-ethoxycarbonylphenyl) selenide (8). The synthetic pro-
cedure was similar to that for 7. Colorless prisms. Yield 48%,
mp 48–49 ЊC. 1H NMR (300 MHz, CDCl3) δ 1.38 (t, J = 8.7 Hz,
6H), 4.37 (q, J = 8.6 Hz, 4H), 7.49 (d, J = 7.1 Hz, 4H), 7.94 (d,
J = 7.1 Hz, 4H). Anal. Calcd. for C18H18O4Se: C, 57.30; H,
4.81%. Found: C, 57.11; H, 4.69%.
Bis(3,5-dichlorophenyl) selenide (14). The synthetic procedure
was similar to that of 7. Colorless prisms. Yield 81%, mp 74–75
ЊC. H NMR (300 MHz, CDCl3) δ 7.25–7.43 (br s, 6H). Anal.
1
Calcd. for C12H6Cl4Se: C, 38.85; H, 1.63%. Found: C, 38.68; H,
1.68%.
ꢀ4-Bis(4-ethoxycarbonylphenyl)dichloroselane (8ؒCl2). 1H
NMR (300 MHz, CDCl3) δ 1.41 (t, J = 7.1 Hz, 6H), 4.43 (q,
J = 7.2 Hz, 4H), 8.17 (d, J = 9.2 Hz, 4H), 8.09 (d, J = 9.2 Hz,
4H). Anal. Calcd. for C18H18Cl2O4Se: C, 48.24; H, 4.05%.
Found: C, 48.06; H, 4.11%.
ꢀ4-Bis(3,5-dichlorophenyl)dichloroselane (14ؒCl2). 1H NMR
(300 MHz, CDCl3) δ 7.59 (t, J = 1.7 Hz, 2H), 7.92 (d, J = 1.7 Hz,
2H). Anal. Calcd. for C12H6Cl6Se: C, 32.62; H, 1.37%. Found:
C, 32.55; H, 1.19%.
Bis(4-cyanophenyl) selenide (9). The synthetic procedure was
similar to that of 7. Colorless needles. Yield 72%, mp 142–143
ЊC. 1H NMR (300 MHz, CDCl3) δ 7.56 (br s, 8H). Anal. Calcd.
for C14H8N2Se: C, 59.38; H, 2.85; N, 9.89%. Found: C, 59.61; H,
2.95; N, 9.84%.
Di-2-tolyl selenide (15). The synthetic procedure was similar
to that of 7. Colorless needles. Yield 59%, mp 61–62 ЊC. H
NMR (300 MHz, CDCl3) δ 2.39 (s, 6H), 7.00–7.31 (m, 8H).
Anal. Calcd. for C14H14Se: C, 64.37; H, 5.40%. Found: C, 64.22;
H, 5.55%.
1
ꢀ4-Bis(4-cyanophenyl)dichloroselane (9ؒCl2). 1H NMR (300
MHz, CDCl3) δ 7.84 (d, J = 8.9 Hz, 4H), 8.16 (d, J = 8.9 Hz,
4H). Anal. Calcd. for C14H8Cl2N2Se: C, 47.49; H, 2.28; N,
7.91%. Found: C, 47.62; H, 2.35; N, 8.11%.
1
ꢀ4-(Di-2-tolyl)dichloroselane (15ؒCl2). H NMR (300 MHz,
CDCl3) δ 2.85 (s, 6H), 7.28–7.55 (m, 6H), 7.74–8.04 (m, 2H).
Anal. Calcd. for C14H14Cl2Se: C, 50.63; H, 4.25%. Found: C,
5.52; H, 4.33%.
ꢀ4-Bis(4-nitrophenyl) selenide (10). The synthetic procedure
was similar to that of 7. Yellow needles. Yield 78%, mp 172–173
ЊC. 1H NMR (300 MHz, CDCl3) δ 7.61 (d, J = 8.9 Hz, 4H), 8.16
(d, J = 8.9 Hz, 4H). Anal. Calcd. for C12H8N2O4Se: C, 44.60; H,
2.50; N, 8.67%. Found: C, 44.74; H, 2.47; N, 8.54%.
Bis(2-chlorophenyl) selenide (16). The synthetic procedure
was similar to that of 7. Colorless needles. Yield 72%, mp 56–57
ЊC. 1H NMR (300 MHz, CDCl3) δ 7.01–7.41 (m, 6H), 7.41–7.62
(m, 2H). Anal. Calcd. for C12H8Cl2Se: C, 47.72; H, 2.67%.
Found: C, 47.65; H, 2.51%.
1
ꢀ4-Bis(4-nitrophenyl)dichloroselane (10ؒCl2). H NMR (300
1
ꢀ4-Bis(2-chlorophenyl)dichloroselane (16ؒCl2). H NMR (300
MHz, CDCl3) δ 8.25 (d, J = 9.5 Hz, 4H), 8.42 (d, J = 9.4 Hz,
4H). Calcd. for C12H8Cl2N2O4Se: C, 36.57; H, 2.05; N, 7.11%.
Found: C, 36.81; H, 2.17; N, 7.08%.
MHz, CDCl3) δ 7.37–7.73 (m, 6H), 7.83–8.20 (m, 2H). Anal.
Calcd. for C12H8Cl4Se: C, 38.64; H, 2.16%. Found: C, 38.51; H,
2.16%.
ꢀ4-Bis(2,4,6-trimethylphenyl) selenide (17). The synthetic
procedure was similar to that of 7. Colorless needles. Yield
76%, mp 105.5–106.0 ЊC. 1H NMR (300 MHz, CDCl3) δ 2.23 (s,
6H), 2.24 (s, 12H), 6.82 (s, 4H). Anal. Calcd. for C18H22Se: C,
68.13; H, 6.99%. Found: C, 67.94; H, 6.95%.
Bis(3-chlorophenyl) selenide (11). The synthetic procedure
was similar to that of 7. Colorless needless. Yield 69%, mp 108–
109 ЊC. H NMR (300 MHz, CDCl3) δ 6.9–7.6 (m, 8H). Anal.
Calcd. for C12H8Cl2Se: C, 47.72; H, 2.67. Found: C, 47.81; H,
2.61.
1
1
ꢀ4-Bis(3-chlorophenyl)dichloroselane (11ؒCl2). H NMR (300
ꢀ4-Bis(2,4,6-trimethylphenyl)dichloroselane
NMR (300 MHz, CDCl3) δ 2.32 (s, 6H), 2.69 (s, 12H), 7.00 (s,
4H). Anal. Calcd. for C18H22Cl2Se: C, 55.69; H, 5.71%. Found:
C, 55.88; H, 5.92%.
(17ؒCl2).
1H
MHz, CDCl3) δ 7.25–7.72 (m, 4H), 7.90 (d, J = 8.2 Hz, 2H),
7.97 (br s, 2H). Anal. Calcd. for C12H8Cl4Se: C, 38.64; H,
2.16%. Found: C, 38.71; H, 2.26%.
Bis(3-cyanophenyl) selenide (12). The synthetic procedure was
similar to that of 7. Colorless prisms. Yield 77%, mp 94.5–95.0
ЊC. 1H NMR (300 MHz, CDCl3) δ 7.43 (t, J = 8.8 Hz, 2H), 7.61
(d, J = 7.5 Hz, 2H), 7.69 (d, J = 7.5 Hz, 2H), 7.72 (s, 2H). Anal.
Calcd. for C14H8N2Se: C, 59.38; H, 2.85; N, 9.89%. Found: C,
59.08; H, 2.89; N, 9.74%.
Ab initio calculations
Ab initio MO calculations were performed with the B3LYP/
6-311ϩ(2d,p) method, using the Gaussian 9415 and 9815
programs.
Acknowledgements
1
ꢀ4-Bis(3-cyanophenyl)dichloroselane (12ؒCl2). H NMR (300
This work was partly supported by a Grant-in-Aid for Scientific
Research on Priority Areas (A) (Nos. 11120232, 11166246 and
12042259) from the Ministry of Education, Culture, Sports,
Science and Technology of Japan and by the Hayashi Memorial
Foundation for Female Natural Scientists.
MHz, CDCl3) δ 7.72 (t, J = 8.1 Hz, 2H), 7.89 (dt, J = 7.7 and 1.1
Hz, 2H), 8.26 (ddd, J = 1.1, 2.2 and 8.3 Hz, 2H), 8.32 (t, J = 1.3
Hz, 2H). Anal. Calcd. for C14H8Cl2N2Se: C, 47.49; H, 2.28; N,
7.91%. Found: C, 47.52; H, 2.25; N, 7.88%.
Bis(3-nitrophenyl) selenide (13). The synthetic procedure was
similar to that of 7. Yellow needles. Yield 77%, mp 112–113 ЊC.
1H NMR (300 MHz, CDCl3) δ 7.51 (t, J = 8.1 Hz, 2H), 7.79
(dt, J = 1.3 and 7.7 Hz, 2H), 8.18 (ddd, J = 0.9, 2.2 and 8.3 Hz,
2H), 8.34 (t, J = 1.9 Hz, 2H). Anal. Calcd. for C12H8N2O4Se:
C, 44.60; H, 2.50; N, 8.67%. Found: C, 44.54; H, 2.57; N,
8.64%.
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270
J. Chem. Soc., Perkin Trans. 2, 2002, 262–270