Inter-element linkage in 1,2- and 1,4-bis(arylselanyl)benzenes with halogens

Article abstract of DOI:10.1016/S0022-328X(00)00452-6

The criteria to distinguish the structure of halogen adducts of aryl chalcogenides in solutions based on the NMR chemical shifts are confirmed by ab initio molecular orbitals (MO) calculations based on the gauge-including atomic orbitals (GIAO) theory. The criteria are applied to determine the structure of halogen adducts of 1,2-bis(phenylselanyl)benzene (1), 1,4-bis(phenylselanyl)benzene (2), and 1,4-bis(p-tert-butylphenylselanyl)benzene (3) (1·nX₂, 2·nX₂, and 3·nX₂, respectively: n = 1 and 2 and X = Cl, Br, and I) in CDCl₃. The structure of 1·Br₂ is demonstrated to be trigonal bipyramidal (TB) not only in the solution but also in crystals. The TB formation of 1·Br₂ is just the opposite of the MC (molecular complexes) formation of selenanthrene with bromine in the solution. The driving force for the TB and MC formation is discussed based on the structure of the parent selenides. The structure of 2·2X₂ and 3·2X₂ is (TB, TB) for X = Cl and Br and (MC, MC) for X = I. On the other hand, the structure of 1·2Br₂ is revealed to be TB at one SeBr₂ moiety but MC for the other SeBr₂ group, which is described as (TB, MC). The bromine exchange is observed in 1·2Br₂ in the conditions of NMR measurements. The rate of bromine exchange becomes sharp as excess bromine is added to the 1·2Br₂ solution, which shows that the structural (TB, MC) ? (MC, TB) site exchange in 1·2Br₂ is accelerated by the excess bromine and/or its derivatives. Ab initio MO calculations are performed on the adducts to understand their structural features and on the proposed intermediate to confirm the mechanism.

Full text of DOI:10.1016/S0022-328X(00)00452-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 611 (2000) 178–189
Inter-element linkage in 1,2- and 1,4-bis(arylselanyl)benzenes with
halogens
Waroˆ Nakanishi *, Satoko Hayashi
Department of Material Science and Chemistry, Faculty of Systems Engineering, Wakayama Uni6ersity, 930 Sakaedani,
Wakayama 640–8510, Japan
Received 29 February 2000; received in revised form 20 April 2000; accepted 20 April 2000
Abstract
The criteria to distinguish the structure of halogen adducts of aryl chalcogenides in solutions based on the NMR chemical shifts
are confirmed by ab initio molecular orbitals (MO) calculations based on the gauge-including atomic orbitals (GIAO) theory. The
criteria are applied to determine the structure of halogen adducts of 1,2-bis(phenylselanyl)benzene (1), 1,4-bis(phenylse-
lanyl)benzene (2), and 1,4-bis(p-tert-butylphenylselanyl)benzene (3) (1·nX2, 2·nX2, and 3·nX2, respectively: n=1 and 2 and
X=Cl, Br, and I) in CDCl3. The structure of 1·Br2 is demonstrated to be trigonal bipyramidal (TB) not only in the solution but
also in crystals. The TB formation of 1·Br2 is just the opposite of the MC (molecular complexes) formation of selenanthrene with
bromine in the solution. The driving force for the TB and MC formation is discussed based on the structure of the parent
selenides. The structure of 2·2X2 and 3·2X2 is (TB, TB) for X=Cl and Br and (MC, MC) for X=I. On the other hand, the
structure of 1·2Br2 is revealed to be TB at one SeBr2 moiety but MC for the other SeBr2 group, which is described as (TB, MC).
The bromine exchange is observed in 1·2Br2 in the conditions of NMR measurements. The rate of bromine exchange becomes
sharp as excess bromine is added to the 1·2Br2 solution, which shows that the structural (TB, MC)?(MC, TB) site exchange in
1·2Br2 is accelerated by the excess bromine and/or its derivatives. Ab initio MO calculations are performed on the adducts to
understand their structural features and on the proposed intermediate to confirm the mechanism. © 2000 Elsevier Science S.A. All
rights reserved.
Keywords: Bis(arylselanyl)benzene; Halogen adducts; X-ray crystallographic analysis; Ab initio MO calculations; TB, MC
1. Introduction
to be located at distances less than the sum of van der
Waals radii in organic compounds, nonbonded interac-
tions will take place between the selenium atoms. The
interactions between their lone pairs are usually repul-
sive since they are characterized by the two center–four
electron interactions (2c–4e) with severe exchange re-
pulsion [2a]. However, some interactions containing
those of lone pairs with s*(SeꢀC) orbitals with the
3c–4e character can be attractive [2b]. This type of
interaction works in the inter-element linkage of chalco-
genides with halogens. Namely, novel structures, prop-
erties, and new types of chemical bonds are to be found
in multi-element organic compounds such as bromine
adducts of selenides [2c] (Plate 1).
Organic chalcogen compounds are well known to
show versatile reactivities, and afford many structurally
interesting compounds [1]. Among such chalcogen com-
pounds, we have been interested in halogen adducts of
aryl selenides, especially in bromine adducts of aryl
selenides bearing plural selenium atoms closely placed
in space [2]. If two or more selenium atoms are forced
Plate 1.
The s*-orbitals of halogens have been well estab-
lished to accept n-electrons of chalcogenides such as
selenides [3–5]. Molecular compounds [3] or molecular
complexes (MC) will be formed, when the electron
* Corresponding author. Tel.: +81-73-4578252, fax: +81-73-
4578253/8272.
E-mail address: nakanisi@sys.wakayama-u.ac.jp (W. Nakanishi).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00452-6

W. Nakanishi, S. Hayashi / Journal of Organometallic Chemistry 611 (2000) 178–189
179
The structure of halogen adducts of 1 (1·nX2) is deter-
mined in solutions based on the criteria. The TB and MC
notation is used for 1-(ArASeX2)C6H4(BSeAr)-2, if the
structure around ASeX2 is TB and MC, respectively. The
(TB, TB) and (MC, MC) notation is adopted for 1-
(ArASeX2)C6H4(BSeX2Ar)-2, if the structures around
ASeX2 and BSeX2 are both TB and both MC, respectively.
Plate 2.
transfer from a chalcogenide to a halogen is small. If the
electron transfer becomes larger, the halogen molecule
can no longer exist as a halogen molecule, resulting in the
formation of trigonal bipyramidal (TB) adducts with the
highly polar 3c–4e hypervalent bond, Xd− –Zd+ꢀXd−
[6]. The ZꢀXꢀX bonds in MC are shown to be analyzed
with the 3c–4e model [7]. The magnitude of the electron
transfer can be estimated by the electronegativity [8] of el-
ements: TB are formed if the electronegativity of halo-
gens (X) is larger than that of chalcogens (Z), while MC
are formed when  is less than  (general rule)
A
The (TB, MC) notation is used when one of SeX2 and
BSeX2 moieties is TB but the other is MC (Plate 2).
After establishment of the structure of 1·Br2 (Eq. (1)),
the structure for the 1:2 adduct with bromine, 1·2Br2, is
examined. That of 1:2 adducts of 1,4-bis(phenylse-
lanyl)benzene (2) and 1,4-bis(p-tert-butylphenylse-
lanyl)benzene (3) with halogens is also investigated as the
reference compounds. The structural (TB, MC) = (MC,
TB) site exchange is observed in 1·2Br2, together with the
bromine migration in 1·Br2. We present the results of in-
vestigations containing the molecular orbitals (MO) cal-
culations performed on the adducts to understand the
structural feature and on the proposed intermediate to
confirm the mechanism.
X
Z
[1c,1d,9,10].
We have proposed criteria of the experimental rule dis-
tinguishing MC from TB for halogen adducts of aryl
chalcogenides based on the NMR chemical shifts (l) [9–
11]. It is more useful if the criteria are demonstrated
based on the theoretical background. Recently the mag-
netic shielding tensor calculated with the gauge-including
atomic orbitals (GIAO) theory for the carbon nucleus
[12–14], together with 77Se nucleus [15–18], is shown to
be reliable. This encouraged us to calculate the GIAO
2. Results and discussion
2.1. Structure of halogen adducts of 1–3 in solution
1
magnetic shielding tensor for H, 13C, and 77Se nucleus
Table 1 shows the halogen induced l(H), l(C), and
l(Se) values (li(H), li(C), and li(Se), respectively) of 1,2-
bis(phenylselanyl)benzene (1), together with the l values
of 1. Table 2 exhibits the values for 1,4-bis(phenylse-
lanyl)benzene (2) and 1,4-bis(p-tert-butylphenylse-
lanyl)benzene (3), together with l for the parent
selenides. The l(C) values are not determined for 2·2Br2
due to its low solubility in CDCl3.
Before discussion of the structure of 1·nX2 (X=Cl, Br,
I), we first examine the structure of 2·2X2 and 3·2X2.
The li(H), li(C), and/or li(Se) values of the phenyl
and p-tert-butylphenyl groups are very close to those
in PhSeX2Ph (X=Cl, Br, I) (see also Table 6). The addi-
tivity of the values in the central benzene ring is very
good: li(H2) and li(C1) in 2·2X2 and 3·2X2 (X=Cl, Br)
are well evaluated by (li(Ho) and li(Hm)) and (li(Ci)
and li(Cp)), respectively. The results clearly show that
the structure of 2·2X2 and 3·2X2 (X=Cl, Br) is (TB, TB)
in the solution. The structure of 3·Cl2 must be TB with
a selenide Se atom at its p-position. That of 2·2I2 and
3·2I2 is (MC, MC) since li(Ci) are negative, although the
equilibrium with the components must be considered
(Plate 3).
(s(X): X=H, C, and Se) to confirm the criteria based on
the theoretical background. After establishment of the
criteria not only experimentally but also theoretically (see
Appendix A), the criteria are applied to determine the
structure of halogen adducts of aryl selenides bearing
plural selenium atoms closely placed in space.
1,2-Bis(phenylselanyl)benzene (1) is chosen as a model
compound, which corresponds to a bis-selenide where
one of the SeꢀC bonds in selenanthrene is cleaved [19].
Selenanthrene itself is demonstrated to give MC with
bromine in solutions [20]: its rigid roof structure prevents
the formation of TB with bromine. Therefore, the struc-
ture of 1·Br2 is also of interest. If the reason for the MC
formation of selenanthrene with bromine is really its rigid
roof structure, 1 should give TB with bromine since 1 is
free from the rigidity.
After establishment of the (TB, TB) structure for 2·2X2
and 3·2X2 (X=Cl, Br), the next extension of our study
is to examine the structure of 1·X2 and 1·2X2 (X=Cl,
Br, I). The 1H- and 13C-NMR signals of 1·Cl2
(1)

Table 1
The li(H), li(C), and li(Se) values of 1, together with the l values a,b
c
Compound
H-3
H-6
H-4
H-5
H-o
H-o%
H-m
H-m%
H-p
H-p%
C-1
C-2
C-3
C-6
C-4
C-5
C-i
C-i%
C-o
C-o%
C-m
C-m%
C-p
C-p%
Se
Se
Structure
Selenide
1
7.07
0.00
0.59
0.31
0.85
0.54
0.56
0.58
0.06
0.10
7.20
0.00
0.35
0.19
0.40
0.17
0.20
0.23
0.05
0.09
7.52
0.00
0.84
0.14
0.70
0.50
0.50
0.49
0.02
0.03
7.32
0.00
0.30
−0.01
0.26
0.12
0.12
0.12
0.03
0.05
7.32
0.00
0.29
−0.03
0.24
0.11
0.14
0.14
0.02
0.04
135.9
0.0
15.7
−3.3
133.0
0.0
4.7
−3.3
2.0
0.7
0.6
0.7
0.3
0.5
127.9
0.0
4.0
0.3
4.1
2.1
2.3
2.4
0.5
0.8
130.7
0.0
8.2
1.2
12.7
3.4
3.0
2.9
−0.6
−1.0
134.0
0.0
−0.4
−0.4
−1.5
0.3
0.2
0.1
−0.3
−0.4
129.5
0.0
0.2
0.1
0.2
0.2
0.3
0.4
0.2
0.4
127.9
0.0
4.2
0.1
4.2
3.0
3.3
3.5
0.9
1.3
424.1
/
0.0
160.6
8.5
173.4
150, 13
d
1·Cl2
TB
Selenide
(TB,TB)
TB
(TB,MC)
(TB,MC)
MC
1·2Cl2
11.0
e
f
1·Br2
g
h
1·2Br2 i
4.4
4.2
−0.5
−0.9
1·3Br2
1·I2
75
6.3
10.1
1·2I2
(MC,MC)
a The l(H) and l(C) values (ppm) are given from TMS and l(Se) from MeSeMe.
b In CDCl3.
c Carbons adjacent to the selenium atom without halogens are numbered as C-2 and C-i% for 1·Cl2.
d Assignments are partly tentative even after SEL mode measurements.
611
e Although the signals separation was not complete, two sets of broad signals were observed at low temperature.
f Not observed due to broadening.
(
g The signals were broad (l1/2=1–4 Hz) at −60°C in CD2Cl2.
h Very broad.
178
i Three molar bromine was added to the solution of 1.
189

Table 2
The li(H), li(C), and li(Se) values of 2 and 3, together with their l values a,b
Compound
H-2
H-3
H-o
H-o%
H-m
H-m%
H-p
H-p%
C-t
C-t%
C-Me
C-Me%
C-1
C-4
C-2
C-3
C-i
C-i%
C-o
C-o%
C-m
C-m%
C-p
C-p%
Se
Se%
Structure
Selenide
/
2
7.31
0.00
0.87
0.84
0.01
7.28
0.00
0.52
0.13
0.88
0.82
0.05
7.48
0.00
0.58
0.57 c
0.04
7.42
0.00
0.48
0.10
0.55
0.56
0.07
7.28
0.00
0.33
0.25 c
0.04
7.31
0.00
0.27
0.05
0.28
0.24
0.06
7.29
0.00
130.6
0.0
133.4
0.0
130.5
0.0
11.6
133.3
0.0
129.4
0.0
127.6
0.0
2·2Cl2
2·2Br2
2·2I2
3
0.30
16.0
−1.0
−2.0
0.7
4.6
(TB,TB)
(TB,TB)
(MC,MC)
Selenide
0.24 c
0.02
c
d
d
d
d
d
d
0.5
130.8
0.0
9.5
7.8
15.8
11.9
0.5
0.1
133.5
0.0
−3.4
2.4
−1.3
−0.3
0.0
−1.5
126.6
0.0
12.8
−3.0
11.5
6.6
−0.6
132.8
0.0
−1.7
−1.1
−1.6
−0.2
−0.5
0.5
126.5
0.0
0.6
0.4
0.7
1.0
0.5
1.3
151.2
0.0
4.4
1.5
4.9
4.8
1.4
1.30 e
0.00 e
0.04 e
0.04 e
0.07 e
0.07 e
0.02 e
34.6
0.0
0.5
0.2
0.6
0.7
0.2
31.3
0.0
410.2
0.0
181.9
18.5
166.3
133.1
14.5
3·Cl2
−0.2
−0.1
−0.3
−0.2
−0.1
(TB)
Selenide
(TB,TB)
(TB,TB)
(MC,MC)
3·2Cl2
3·2Br2
3·2I2
−1.6
611
a The l(H) and d(C) values (ppm) are given from TMS and l(Se) from MeSeMe.
b In CDCl3.
(
c Broad due to equilibrium with the components.
d Not observed due to low solubility and low sensitivity.
e Values for p-t-butyl protons.
178
189

182
W. Nakanishi, S. Hayashi / Journal of Organometallic Chemistry 611 (2000) 178–189
dependent (see Table 6). The li(Ci) and li(Co) values of
the phenyl groups in 1·Br2 are very close to those of the
half values in PhSeBr2Ph. The observations strongly
suggest that the structure of 1·Br2 is TB with the
relatively fast bromine migration between the two Se
atoms. While the li(C4), li(C5), li(Cp), and li(Cp%
)
values of 1·nBr2 increase in the order n=1, 2, and 3,
the li(C1), li(C2), li(Ci), and li(Ci%) values become
smaller in this order, although li(C1) and li(C2) are not
determined for n=1. These results are in accordance
with the (TB, MC) structure for 1·2Br2 accompanied by
the substantial equilibrium with 1·Br2 (TB) and
bromine.
In order to examine the structure of 1·Br2 and 1·2Br2
in solutions more clearly, we propose a total li(C)
value for a Ph group (S li(C)) in ArSeX2Ph: S li(C)=
li(Ci)+2li(Co)+2li(Cm)+li(Cp). The 2S li(C) val-
ues for ArSePh (1–3 and PhSePh) are collected in
Table 3. The values clearly show that the (TB, TB)
formation causes 25–30 ppm irrespective of halogens,
where TB of PhSeX2Ph is regarded as (TB, TB). Those
for the MC formation are negligible.
The 2S li(C) values for 1·Cl2, 1·Br2, and 1·I2 are
12.7, 14.8, and 0.2 ppm, respectively. The value for
1·Br2 is very close to that for 1·Cl2 and to a half value
for the (TB, TB) formation, which is taken as evidence
for the TB structure of 1·Cl2 and 1·Br2. The TB struc-
ture of 1·Br2 reveals the reason for selenanthrene react-
ing with bromine to give an MC in solutions: the rigid
roof structure of the selenanthrene prevents the forma-
tion of the planar structure necessary for the TB forma-
tion. The 2S li(C) values for 1·2Cl2, 1·2Br2, and 1·2I2
are 28.6, 14.6, and 0.6 ppm, respectively. The (TB, TB)
and (MC, MC) structure is well demonstrated for
1·2Cl2 and 1·2I2, respectively. The 2S li(C) value of
14.6 ppm for 1·2Br2, together with that of 14.4 ppm for
1·3Br2, is clear evidence for the (TB, MC) structure of
1·2Br2 equilibrating with the components.
Plate 3.
consist of two sets: one corresponds to those of PhSeCl2
groups in PhSeCl2Ph and the other appears close to
those of PhSe groups in PhSePh. The appearance of the
two sets of signals show that the chlorine migration in
1·Cl2 must be much slower relative to the NMR time
scale under the conditions of measurements. Therefore,
the structure of 1·Cl2 is concluded to be TB for the
SeCl2 moiety. The li(C1) and li(Ci) values of 1·Cl2 were
larger and smaller compared with those observed in
PhSeCl2Ph, respectively. This may be due to the
through-bond and through-space interactions between
the two selanyl groups, together with the conforma-
tional change before and after the formation of 1·Cl2.
Since the li values of the two PhSeCl2 groups in 1·2Cl2
are very close to those in PhSeCl2Ph, the structure of
1·2Cl2 is concluded to be (TB, TB).
The li(C1), li(C2), li(Ci), and li(Ci%) values are all
negative, whereas li(C4), li(C5), li(Cp), and li(Cp%) are
all positive for 1·I2 and 1·2I2. The magnitudes become
larger when 1·I2 goes to 1·2I2. These results show that
the structure of 1·I2 and 1·2I2 are MC and (MC, MC),
respectively, although the rapid equilibrium with the
components must also be considered.
The signals of two phenyl groups in 1·Br2 are ob-
served as a set with some broad ones: l(C1) and l(C2)
are not determined since the signals were very broad.
The l(C) values in 1·Br2 were close to the averaged
ones of the corresponding carbons in 1·Cl2, except for
Ci and Co. The l(Ci) and l(Co) are both halogen
The (TB, MC) structure of 1·2Br2 is the first observa-
tion of the MC structure for the bromine adduct of a
substituted diphenyl selenide, to the best of our knowl-
edge. The electron withdrawing ability of the PhSeBr2
Table 3
The 2S li(C) values in 1·nX2, 2·nX2, 3·nX2, and PhSeX2Ph a,b
c
1·nX2
2·nX2
3·nX2
PhSeX2Ph
Cl
n
Cl
Br d
I
Cl
Br
I
Cl
Br
I
Br
I
1
2
12.7
28.6
14.8
14.6
0.2
0.6
12.1
29.2
12 e f
26.0
−0.4 e
−0.4
27.2
−0.8
26.8
25.0
0.2
a S li(C)=li(Ci)+2li(Co)+2li(Cm)+li(Cp).
b In ppm.
c Classified as n=2.
d 14.4 for n=3.
e Not shown in Table 2.
f Based on broad signals.

W. Nakanishi, S. Hayashi / Journal of Organometallic Chemistry 611 (2000) 178–189
183
Table 4
Selected crystal data and structure analysis results for 1·Br2
2.2. Structure of 1·Br2 studied by X-ray
crystallographic analysis
Formula
C19H16Br2Se2Cl2
The structure of 1·Br2 is determined by X-ray crystal-
lographic analysis. Tables 4 and 5 display the crystal
data and selected bond lengths, angles, and torsional
angles, respectively. Fig. 1 shows the structure of 1·Br2,
which demonstrates its TB structure also in crystals.
The Se(1)ꢀC(7) bond is almost on the plane of the
central benzene ring (ÚC(2)C(1)Se(1)C(7)=169.4(5)°)
and the two SeꢀBr bonds are almost perpendicular to
the plane (ÚC(2)C(1)Se(1)Br(1)= −77.5(4)° and
ÚC(2)C(1)Se(1)Br(2)=97.8(4)°). The torsional angle
for C(1)C(2)Se(2)C(13) is 130.5(5)°. The feature of the
structure is discussed in the forthcoming section.
Formula weight
Crystal system
Space group
632.97
Triclinic
P-1(c2)
11.326(2)
11.525(2)
9.863(2)
113.04(1)
105.16(1)
63.831(8)
1057.2(4)
2
1.988
3198
226
604.00
111.22
0.066
,
a (A)
,
b (A)
,
c (A)
h (°)
i (°)
g (°)
3
,
V (A )
Z
Dcalc (g cm–3
)
No. of observations
No. of variables
F000
m(Cu–Ka) (cm–1
)
2.3. Bromine migration and site exchange in 1·Br2 and
1·2Br2
R
Rw
0.099
Goodness-of-fit
1.13
We next discuss the bromine migration in 1·Br2 and
the site exchange in 1·2Br2. The NMR signals of 1 are
of course very sharp in CDCl3 due to its quick molecu-
lar motion relative to the NMR time scale. The signals
become broad as bromine is added to the solution until
(TB) group must be very large and the bulkiness of the
group toward the group at the 2-position must be very
severe. Both electronic and steric effects of the PhSeBr2
(TB) group should operate to prevent the formation of
TB in the reaction of 1-PhSeBr2(TB)C6H4SePh-2 (1·Br2)
with bromine. The results show that reactivities of
organoselenium compounds can be controlled by chem-
ically modulating the effective electronegativity of the
selenium atom in a given selenide and/or by changing
bulkiness around the selenium atom of the compound
[10,20,21].
1
n in 1·nBr2 is about unity. However, the H and 13C
signals become sharp again if more bromine is added to
the 1·Br2 solution: the signals are substantially sharp
when n=ca. 3 [22]. The bromine migration and the site
exchange are shown in Eqs. (2) and (3), respectively.
(2)
Table 5
Selected interatomic distances, angles, and torsional angles of 1·Br2
,
Interatomic distances (A)
Se(1)ꢀC(1)
Se(1)ꢀC(7)
Se(1)ꢀBr(1)
Se(1)ꢀBr(2)
Se(1)ꢀSe(2)
1.944(6)
1.959(7)
2.5193(9)
2.6084(9)
3.240(1)
Se(2)ꢀC(2)
Se(2)ꢀC(13)
Se(2)ꢀBr(1)
Se(2)ꢀBr(2)
C(1)ꢀC(2)
1.920(7)
1.940(7)
3.613(1)
4.382(1)
1.40(1)
Bond angles (°)
C(1)ꢀSe(1)ꢀC(7)
Br(1)ꢀSe(1)ꢀBr(2)
C(1)ꢀSe(1)ꢀBr(1)
C(1)ꢀSe(1)ꢀBr(2)
C(2)ꢀC(1)ꢀSe(1)
102.9(3)
172.91(4)
89.9(2)
87.8(2)
115.1(4)
C(2)ꢀSe(2)ꢀC(13)
Br(2)ꢀSe(2)ꢀC(13)
Se(2)ꢀC(2)ꢀC(1)
C(7)ꢀSe(1)ꢀSe(2)
96.7(3)
91.7(2)
121.8(5)
162.2(2)
Torsional angles (°)
C(1)ꢀSe(1)ꢀC(7)ꢀC(8)
C(2)ꢀC(1)ꢀSe(1)ꢀC(7)
C(2)ꢀC(1)ꢀSe(1)ꢀBr(1)
C(2)ꢀC(1)ꢀSe(1)ꢀBr(2)
−47.4(6)
169.4(5)
−75.5(4)
97.8(4)
C(2)ꢀSe(2)ꢀC(13)ꢀC(14)
C(1)ꢀC(2)ꢀSe(2)ꢀC(13)
Se(1)ꢀC(1)ꢀC(2)ꢀSe(2)
−59.5(6)
130.5(5)
−1.1(6)

184
W. Nakanishi, S. Hayashi / Journal of Organometallic Chemistry 611 (2000) 178–189
Fig. 1. Structure of 1·Br2.
bridging bromine atom in organic chalcogen compounds
is reported for C6H10Br6Te2 [24]. The intermediacy of
1·Br−5 is further examined based on the MO calculations.
2.4. Examination based on ab initio MO calculations
(3)
Ab initio MO calculations are performed on 1 and
1·Br2 (TB) with the HF/6-311+G(d,p) method using the
Gaussian 94 program [25]. Fig. 2 shows the results. The
observed structure of 1·Br2 is well reproduced in the cal-
culations. In order to clarify the structural and mecha-
nistic future of 1·nBr2, model calculations are also
performed on 1,2-bis(methylselanyl)ethene (4), 4·Br2
(TB), 4·2Br2 (TB,MC), and 4·Br−5 with the B3LYP/6-
311+G(d,p) method [26]. Fig. 2 also contains the re-
sults. The nonbonded Se(2)···Se(1)–C 3c–4e interactions
are strongly suggested in 1 and 1·Br2, which are stabi-
lized by the electron donor–acceptor interaction, since
the atoms in the observed and/or the calculated struc-
tures are almost on the plane of central benzene. The tor-
sional angle of C1C2Se2Ci of 108–130° also supports the
interaction. The optimized structures of 4 and 4·Br2 (TB)
are close to those of 1 and 1·Br2 (TB), respectively, ex-
cept for the torsional angles between C1C2Se2Ci and
C1C2Se2CMe. The angles of the former are substantially
larger than those of the latter in magnitude.
The bromine migration will occur between the two Se
atoms intramolecularly in 1·Br2 (Eq. (2)), but the inter-
molecular process may also be via dissociation–recom-
bination process of the components. The intramolecular
process seems only marginally faster than the inter-
molecular one: the bromine migration in 1·Br2 is not sig-
nificantly faster than that in 2·Br2 and 3·Br2 [23]. The
signals of the former become sharper as 1·2Br2 (TB, MC)
is formed with the addition of bromine to the 1·Br2 solu-
tion. The site exchange would be facilitated by free
bromine in the solvent. It is natural to assume that the
intramolecular exchange process is accelerated by
adding bromine.
(4)
The key intermediate 1·Br−5 is proposed to be pro-
duced in the reaction of 1·2Br2 (TB, MC) with Br−3 . A
model anion 4·Br−5 is calculated to be the Cs symmetry
and its frequencies are predicted to all be positive by
the frequency analysis. The total energy of 4·Br−5 with
Br2 is evaluated to be not so different from that of 4·2Br2
(TB, MC) with Br−3 : DH=H(4·Br5−)+H(Br2)−
H(4·2Br2)−H(Br−3 )=0.0117 au (30.7 kJ mol−1). The
results are in accordance with the mechanism proposed
in Eq. (4) and demonstrate that the anion is likely to ex-
ist in solutions.
We propose a mechanism of the facile site exchange
between (TB, MC) and (MC, TB) in 1·2Br2, which is
shown in Eq. (4). The reaction proceeds along with a key
intermediate, 1·Br−5 . The anion may be produced in the
reaction of 1·2Br2 with a tribromide ion, for example:
Br− is added to 1·2Br2 in this reaction. The proposed in-
termediate contains a bridging bromine atom. Such a

W. Nakanishi, S. Hayashi / Journal of Organometallic Chemistry 611 (2000) 178–189
185
3.2. Synthesis of 1,4-bis(phenylselanyl)benzene (2)
3. Experimental
1H (400 MHz), 13C (100 MHz), and 77Se (76 MHz)
NMR spectra were recorded on a JEOL JNM-LA 400
Diphenyldiselenide (5.0 g; 16.0 mmol) was reduced by
NaBH4 (1.33 g; 35.2 mmol) in ethanol (50 ml) under an
argon atmosphere. After a few minutes, DMF (60 ml)
was substituted forethanol. Then dibromobenzene (3.4
g; 14.4 mmol) and Cu2O (5.0 g; 35.0 mmol) were added.
After a usual workup, the solid was purified by Silica Gel
column chromatography containing basic alumina to
give 2 (colorless needles; 3.98 g; 64% yield): m.p. 100–
101°C; NMR is in Table 2. Anal. Calc. for C18H14Se2: C,
55.69; H, 3.64. Found: C, 55.62; H, 3.65%.
1
spectrometer. The H, 13C, and 77Se chemical shifts are
given in ppm relative to those of internal CHCl3 slightly
contaminated in the solution, CDCl3 as the solvent, and
external MeSeMe, respectively. Chemicals were used
without further purification unless otherwise noted. Sol-
vents were purified by standard methods. Melting points
were measured with a Yanako-MP apparatus and uncor-
rected. Column chromatography was performed on sil-
ica gel (Fuji Silysia BW-300), acidic alumina and basic
alumina (E. Merck).
3.3. Synthesis of
1,4-bis(p-tert-butylphenylselanyl)benzene (3)
3.1. Synthesis of 1,2-bis(phenylselanyl)benzene (1) [27]
Bis(p-tert-butylphenyl)diselenide (3.0 g; 7.1 mmol)
was reduced by NaBH4 (0.59 g; 15.6 mmol) in ethanol
(30 ml) under an argon atmosphere. After a few minutes,
DMF (60 ml) was substituted for ethanol. Then dibro-
mobenzene (1.33 g; 5.64 mmol) and Cu2O (2.22 g; 15.5
mmol) were added. After a usual workup, the solid
was purified by Silica Gel column chromatography con-
taining basic alumina to give 3 (colorless needles; 1.75 g;
62% yield): m.p. 87–88°C; NMR is in Table 2. Anal.
Calc. for C26H30Se2: C, 62.40; H, 6.04. Found: C, 62.10;
H, 6.03%.
A mixture of diphenyliodonium-2-carbonylate [28]
(6.0 g; 78.8 mmol) and diphenyl diselenide (4.1 g; 13.1
mmol) in o-dichlorobenzene (40 ml) was refluxed at
180°C for 2 h under an argon atmosphere. The removal
of the solvent under reduced pressure was given the im-
pure orange oil. The oil was purified by Silica Gel
column chromatography containing basic alumina to
give 1 (a colorless oil; 4.0 g; 78% yield); NMR is in Table
1.
Fig. 2. Optimized structures for 1 and 1·Br2 with the HF/6-311+G(d, p) method and those for 4, 4·Br2, 4·2Br2, and 4·Br−5 with the
B3LYP/6-311+G(d,p) method. Total energies for Br2 are −5144.7265 and −5148.2849 au with HF/6-311+G(d, p) and B3LYP/6-311+G(d,
p) methods, respectively. The energy for Br−3 is evaluated to be −7722.5754 au with the latter method.

186
W. Nakanishi, S. Hayashi / Journal of Organometallic Chemistry 611 (2000) 178–189
3.4. Synthesis of 1,2-bis(phenylselanyl)benzene
dichloride (1·Cl2)
3.11. Synthesis of 1,4-bis(phenylselanyl)benzene
tetrabromide (2·2Br2)
Chlorine adducts were precipitated when sulfuranyl
chloride was introduced to a selenide solution in usual
solvents, hexane and chloroform (chloroform-d), after
the concentration became substantially larger than the
solubility. 1·Cl2 (colorless needles; 88% yield): m.p.
119°C; NMR is in Table 1. Anal. Calc. for
C18H14Cl2Se2: C, 47.09; H, 3.07. Found: C, 47.22; H,
3.10%.
Red crystals: NMR is in Table 2. Anal. Calc. for
C18H14Br4Se2: C, 30.54; H, 1.99. Found: C, 30.72; H,
1.98%.
3.12. X-ray crystal structure analysis of 1·Br2
The single crystals were obtained via slow evapora-
tion of chloroform and dichloromethane solutions. One
of the crystals which were suitable was subjected to
X-ray crystallographic analysis. All measurements were
made on a Rigaku RAXIS imaging plate with a detec-
tor with graphite monochromated Cu–Ka radiation
3.5. Synthesis of 1,2-bis(phenylselanyl)benzene
tetrachloride (1·2Cl2)
,
(u=1.54178 A).
Pale yellow crystals: m.p. 198–200°C (Lit. m.p. 196–
200°C) [27]; NMR is in Table 1.
The data were collected at a temperature of −709
1°C to a maximum 2q value of 136.5°. A total of 21
6.0° oscillation images were collected, each being ex-
posed for 20 min. The crystal-to-detector distance was
105.00 mm. The detector swing angle was 0.00°. Read-
out was performed in the 0.100 mm pixel mode.
The structure of 1·Br2 was solved by direct methods,
SIR92 [29], and expanded using Fourier techniques,
DIRDIF94 [30]. All the non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were included
but not refined. The final cycle of full-matrix least-
squares refinement was based on a total of 6413 reflec-
tions with 3198 observed reflections (I\1.50|(I)).
Crystallographic details are listed in Table 4.
3.6. Synthesis of 1,2-bis(phenylselanyl)benzene
dibromide (1·Br2)
Orange crystals: m.p. 107°C. NMR is in Table 1.
Anal. Calc. for C18H14Br2Se2: C, 39.45; H, 2.58. Found:
C, 39.51; H, 2.54%.
3.7. Synthesis of 1,2-bis(phenylselanyl)benzene
tetrabromide (1·2Br2)
Red crystals: m.p. 77°C. NMR is in Table 1. Anal.
Calc. for C36H28Br10Se4: C, 27.44; H, 1.80. Found: C,
27.44; H, 1.78%.
3.13. Ab initio MO calculations
Ab initio molecular orbital calculations were per-
formed on Origin computer using Gaussian 94 program
[25] with 6-311+G(2d,p), 6-311+G(d,p) and 3-21G*
basis sets at the DFT (B3LYP level). The calculations
at the HF level were also carried out.
3.8. Synthesis of 1,4-bis(phenylselanyl)benzene
dichloride (2·Cl2)
Colorless needles: NMR is in Table 2. Anal. Calc. for
C18H14Cl2Se2: C, 47.09; H, 3.07. Found: C, 47.32; H,
3.15%.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC 143534 for 1·Br2. Copies of this
information may be obtained free of charge from: The
Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
3.9. Synthesis of 1,4-bis(phenylselanyl)benzene
tetrachloride (2·2Cl2)
Pale yellow crystals: NMR is in Table 2. Anal. Calc.
for C18H14Cl2Se2: C, 47.09; H, 3.07. Found: C, 47.26;
H, 3.11%.
3.10. Synthesis of 1,4-bis(phenylselanyl)benzene
dibromide (2·Br2)
Acknowledgements
Orange crystals: NMR is in Table 2. Anal. Calc. for
C18H14Br2Se2: C, 39.45; H, 2.58. Found: C, 39.70; H,
2.60%.
This work was supported by a Grant-in-Aid for
Scientific Research on Priority Areas (A) (Nos.
09239232, 10133234, 11120232, and 11166246) from

Table 6
Calculated li(H), li(C), and li(Se) values for PhSeH and PhSeMe and the observed values for PhSeMe and PhSePh, together with the l values of the parent selenides
Compound
H(Me)
C(Me)
H-2
H-2%
H-3
H-3%
H-4
C-1
C-2
C-2%
C-3
C-3%
C-4
Se
Structure
Selenide
a
Calculated 6alues for PhSeH and PhSeMe with the B3LYP/6-311+G(2d,p) method
PhSeH
3.71
0.00
4.81
3.54
0.83
1.20
2.13
0.00
1.33
1.32
0.14
0.17
7.43
0.00
0.31
0.30
0.07
0.29
7.50
0.00
0.37
0.35
0.27
0.29
7.40
0.00
0.47
0.47
0.03
0.76
6.20
0.00
1.65
1.60
2.18
2.20
7.44
0.00
0.30
0.32
0.18
0.15
7.44
0.00
0.32
0.32
0.16
0.17
7.39
0.00
0.37
0.39
0.16
0.32
7.53
0.00
0.25
0.25
0.27
0.27
7.30
0.00
0.51
0.52
0.25
0.39
7.30
0.00
0.50
0.50
0.44
0.45
148.4
0.0
6.1
131.7
0.0
−0.4
0.7
1.0
6.7
132.0
0.0
1.5
2.4
6.3
133.9
0.0
2.4
3.6
1.0
6.6
128.0
0.0
−0.3
0.8
10.9
11.2
133.7
0.0
1.5
1.8
1.1
0.6
133.0
0.0
2.0
2.1
134.1
0.0
2.0
2.2
1.0
0.8
134.0
0.0
1.1
1.3
128.9
0.0
7.3
7.4
3.6
6.0
128.1
0.0
8.1
8.1
80.7
0.0
PhSeCl2H
PhSeBr2H
PhSeBr2H
PhSeBr2H
PhSeMe
151.2
36.7
97.8
54.7
165.3
0.0
232.6
153.4
169.3
155.0
TB
4.5
TB
−4.4
−10.9
153.7
0.0
3.7
1.9
MC b
MC
15.1
0.0
36.6
35.2
15.3
16.1
Selenide
/
PhSeCl2Me
PhSeBr2Me
PhSeCl2Me
PhSeBr2Me
TB
TB
MC
MC
−7.6
−8.1
0.5
0.7
1.4
1.5
7.3
7.5
6.5
Obser6ed 6alues
PhSeMe
2.36
0.00
1.57
1.56
0.27
0.42
7.2
0.0
38.5
36.4
5.0
7.42
0.00
0.54
0.50
0.10
0.15
7.47
0.00
0.56
0.59
0.03
0.08
7.26
0.00
0.31
0.31
0.09
0.13
7.26
0.00
0.31
0.27
0.05
0.13
7.21
0.00
0.36
0.33
0.14
0.21
7.27
0.00
0.29
0.31
0.03
0.08
131.7
0.0
9.3
130.2
0.0
−1.7
−1.1
0.2
0.4
132.9
0.0
−1.7
−0.5
−0.3
−0.6
128.8
0.0
1.1
1.4
0.6
1.0
129.9
0.0
0.5
0.6
125.9
0.0
5.8
5.7
1.9
3.4
127.2
0.0
4.4
4.4
207.1
0.0
Selenide
PhSeCl2Me
PhSeBr2Me
PhSeI2Me
[PhSeI2Me]
PhSePh
284.5 c
226.8 c
44.7 d
67
TB
TB
MC
[MC]
Selenide
6.4
−2.0
−3.6
131.1
0.0
11.4
7.9
9.1
423.0
0.0
611
PhSeCl2Ph
PhSeBr2Ph
PhSeI2Ph
160.7 e
120.0 f
6.8 g
17
TB
TB
MC
[MC]
)
−1.0
−1.9
0.3
0.6
1.1
2.1
[PhSeI2Ph]
178
a The s(Se) value for MeSeMe and s(C) and s(H) for TMS were 1952.3, 181.9, and 30.99, respectively.
189
b The torsional angle of CoCiSeH was assumed to be 0.00°.
c w1/2=5 Hz.
d w1/2=8 Hz.
e w1/2=4 Hz.
f w1/2=80 Hz.
g w1/2=2 Hz.

188
W. Nakanishi, S. Hayashi / Journal of Organometallic Chemistry 611 (2000) 178–189
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[11] The criteria are summarized as follows. (1) Large downfield
shifts of ipso and para carbons of aryl groups are observed in the
TB formation relative to those of the parent selenides: the former
depends on the electronegativity of halogens, whereas the latter
is almost independent of them. (2) The signal of para carbon
shifts downfield, whereas the ipso carbon goes upfield in the
formation of MC: the shift values are often small but the values
must be moderate if the equilibrium between the MC and its
components are taken into account. (3) Very large downfield
shifts are observed for 77Se-NMR signals in the TB formation,
whereas the values are small in the formation of MC. (4) Large
downfield shift of the ortho protons in the TB formation are also
useful.
[12] (a) J.R. Cheeseman, G.W. Trucks, T.A. Keith, M.J. Frisch, J.
Chem. Phys. 104 (1996) 5497. (b) D.M. Grant, R.K. Harris, in:
P. Pulay, J.F. Hinton (Eds.), Encyclopedia of Nuclear Magnetic
Resonance, Wiley, New York, 7 (1996) 4434. (c) D.A. Forsyth,
A.B. Sebag, J. Am. Chem. Soc. 119 (1997) 9483. (d) G.A. Olah,
T. Shamma, A. Burrichter, G. Rasul, G.K.S. Prakash, J. Am.
Chem. Soc. 119 (1997) 12923, 12929.
Appendix A
The criteria of the experimental rule distinguishing
MC from TB of ArSeX2R in solutions are confirmed by
the ab initio MO calculations using the Gaussian 94
program [25] with the B3LYP/6-311G+(2d,p) method
[31] based on the GIAO theory. The GIAO magnetic
shielding tensors of H, 13C, and 77Se nucleus (s(X):
1
X=H, C, and Se) are calculated on the TB and MC
structure for PhSeX2H and PhSeX2Me (X=Cl, Br, or
null). Calculations are also performed for PhSeBr2H
(MC) assuming the planar structure for PhSeH. The
results are collected in Table 6.
The criteria are well supported by the MO calcula-
tions especially for those of li(C) [32]. One must be
careful when the criteria concerning the li(Se) are
employed to determine the structure of halogen adducts
aryl selenides, since the small positive li(Se) values
would not mean the formation of MC in some cases. It
might be the reflection of the equilibrium between TB
and its components. The upfield shifts of the ipso
carbons of aryl groups are safely applied to determine
the MC formation of the adducts.
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[22] The 77Se signals are very broad when n=2, which is due to a
large difference in resonance energies in Hz between Se(IV) and
Se(II) (and/or S(III)) signals.
[26] Ab initio MO calculations are also performed on 1,2-bis-
(methylselanyl)benzene (5) and its bromine adducts, 5·Br2 (TB),
5·2Br2 (TB,MC), and 5·Br−5 , by the B3LYP/6-311+G(d,p) and/
or B3LYP/3-21G* method. The results are essentially the same
as those for 1 and 4 and their adducts. Some local minima are
optimized for 1, 4, and 5 and their adducts. The most stable ones
are shown in the Figure.
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University of Nijmegen, The Netherlands, 1994.
[23] While the Ci signals are broad singlet for 1·Br2, they are broad
doublet in 3·Br2, for example.
[24] The structure is di-m-bromo-m-1,2-cyclohexylenetetrabromoditel-
lurium: A.C. Hazell, Acta Chem. Scand. 26 1510 (1972).
[25] Gaussian 94, Revision D.4; M.J. Frisch, G.W. Trucks, H.B.
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[31] Similar results are obtained with B3LYP/6-311G+(d,p), HF/6-
311G+(2d,p)
and
HF/6-311G+(2d,p)//B3LYP/6-311G+
(2d,p) methods.
[32] Although the MO calculations demonstrate that the criteria are
effective for ArSeX2R (TB and MC) where R=H and Me and
X=Cl and Br, the results must be applicable for various
ArSeX2R (TB and MC). The experimental criteria are estab-
lished on ArZX2R (TB) where (Z,X)=(Se,Cl), (Se, Br), (Te, F),
(Te,Cl), (Te,Br), and (Te,I) and on ArZX2R (MC) where
(Z,X)=(S,Br), (S, I), and (Se,I).
.