Aromatic selenoic,selenothioic,and diselenoic acid salts:isolation, characterization, and 77senmr spectra,together with theoretical elucidation

Article abstract of DOI:10.1246/bcsj.20140018

To systematically elucidate molecular and electronic structures of aromatic selenoic acid salts and their heavier congeners, they were synthesized by reacting selenoic, selenothioic, and diselenoic acid Se-[2-(trimethylsilyl) ethyl] esters with ammonium f

Full text of DOI:10.1246/bcsj.20140018

©
2014 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 87, No. 6, 677­692 (2014)
677
Selected Papers
Aromatic Selenoic, Selenothioic, and Diselenoic Acid Salts:
7
7
Isolation, Characterization, and Se NMR Spectra,
Together with Theoretical Elucidation
Toshiaki Murai,*1,2 Daisuke Nishi, Satoko Hayashi, and Waro Nakanishi*
1
3
3
1Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193
2JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012
3Department of Material Science and Chemistry, Faculty of Systems Engineering, Wakayama University,
930 Sakaedani, Wakayama 640-8510
Received January 22, 2014; E-mail: mtoshi@gifu-u.ac.jp, nakanisi@sys.wakayama-u.ac.jp
To systematically elucidate molecular and electronic structures of aromatic selenoic acid salts and their heavier
congeners, they were synthesized by reacting selenoic, selenothioic, and diselenoic acid Se-[2-(trimethylsilyl)ethyl] esters
with ammonium fluorides. The resulting salts were characterized by 13C and Se NMR spectra, and some of their
molecular structures were disclosed by X-ray analyses. These results were compared with spectroscopic properties and
molecular structures of selenoic and selenothioic acid Se-methyl esters. As a result, in the resonance hybrids of selenoic
and selenothioic acid ammonium salts, the resonance structures involving carbon­selenium double bonds also contribute
to the resonance hybrids, and the importance of these resonance structures appears to increase on going from selenoic to
selenothioic acid salts on the basis of the results of the coupling constants of carbon­selenium bonds and UV­visible
spectra. The results were well supported by the optimized structures and evaluated NMR parameters for the species.
77
Carboxylic acid and their salts are ubiquitous and comprise
swiftly as the heteroatom becomes heavier. However, the p­π
conjugation of the p(E)­π(C=C/Ar) type is demonstrated to
affect the fine structural details of the compounds, such as 1-
ArENap (A) and related ones, containing E for E = S, Se, and
several important central backbones in chemistry. Studies on
sulfur isologues such as thioic and dithioic acid and their salts
1
have also been continued for over 140 years. In fact, dithio-
1
2
benzoic acid potassium salt was reported as early as the mid-
Te, as well as O. Conjugated 6π ring systems containing
heteroatoms are also typical of p­π conjugation, of which
aromaticity is confirmed for the heavier congeners of benzene
C H M-Tbt (M = Si and Ge) (B) (Tbt: 2,4,6-tris[bis(trimethyl-
2
1
9th century. In turn, their heavier congeners, i.e., diselenoic
acid salts are ambiguous species, although the possibility of the
3
generation of their zinc salts was reported in 1970. In 2000,
5
5
1
3
Nakayama and co-workers synthesized the first example of
inner salts involving selenothio- and diselenocarboxy moieties
and reported their molecular structures, properties, and UV and
silyl)methyl]phenyl) and even dilithiotetraphenylplumbole
(C) (Chart 1).
1
4
On the other hand, 77Se NMR spectroscopy has been estab-
4
15­17
visible spectra. In 2002, diselenobenzoic acid ammonium salt
lished as a powerful tool to study selenium chemistry.
5
77
was structurally characterized for the first time by us. Before
Se NMR chemical shifts (¤(Se)) are sharply sensitive to the
1
8­22
this report, syntheses and characterization of selenothioic acid
structural changes in selenium compounds
and indirect
6
7
22
salts as well as their esters were separately developed. Unlike
carboxylic acid salts and their sulfur counterparts, a selenium
atom in selenium isologues is an NMR active nucleus giving
sharp signals due to I = 1/2 for 77Se. The combination of these
NMR data with theoretical elucidation provides broad per-
spective to the chemistry not only of selenium isologues of
carboxylic acid salts but also selenium-containing conjugated
nuclear spin­spin coupling constants containing Se [J(Se, X)]
also provide highly important information around the coupled
nuclei. Therefore, the NMR parameters are widely applied to
determine the structures and analyze the chemical bonds around
1
5­22
Se.
Indeed, relativistic effects should be considered to
2
3­28
calculate σ(Se),
but they are often evaluated under non-
relativistic conditions, since relative values of σ(Se) (¦σ(Se))
explain well the observed values, even if calculated under
8
9
systems such as selenoic acid, eneselenol, and phosphino-
1
0
11
29
selenoic acid derivatives, and their heavier congeners.
nonrelativistic conditions. J(Se, X) are evaluated under
The electronic structures of sulfur and selenium isologues of
carboxylic acid derivatives are closely related to how the p­π
conjugation operates effectively also in the heavier hetero-
atoms. Such p­π conjugation may be believed to decrease
nonrelativistic conditions in many cases, similarly to the case
of σ(Se).
t
Total absolute magnetic shielding tensors (σ ) are employed
t
to analyze ¤(Se) since σ can be predicted with satisfactory
Published on the web April 9, 2014; doi:10.1246/bcsj.20140018

6
78
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
Aromatic Selenoic, Selenothioic, and Diselenoic Acid Salts
H
E
Me
E2
E1
E2
E1
C1
C1
i
i
o
o'
o
o'
Y
A (E = S, Se,Te, and O)
Controlled by p(E)- (Ar) for Y of
acceptors, such as CN and NO .
I
II
2
1
2
(
E , E ) = (O, O), (O, S), (O, Se), (S, O), (S, S),
(
S, Se), (Se, O), (Se, S), and (Se, Se)
H
E
Y
Chart 2.
tions.41,42 Equation 6 explains the treatment. JFC(Se, X) usu-
1
A (E = S, Se, Te, and O)
1
1
Controlled by p(E)- (Nap) for Y of
ally contribute predominantly to J (Se, X), where J (Se, X)
originates when admixtures occur from only s-type atomic
orbitals in the upper states of the triplet states (T , T , T ,+) to
TL
FC
donors, such as OMe and NMe .
2
1
2
3
the ground state (S0).
SiMe3
t
d
p
· ¼ · þ ·
ð1Þ
ð2Þ
ð3Þ
ð4Þ
Tbt
M
Me Si
p
p
p
p
3
·
¼ ð· xx þ · yy þ · zzÞ=3
occ unocc p occ
SiMe3
·p ¼ ꢀi ꢀa
· i!a ¼ ꢀi · i
p
Tbt =
·d ¼ ꢀi · i
occ
d
SiMe3
·pzz;N ¼ ꢀð® e =2me Þꢀioccꢀaunoccð¾a ꢀ ¾iÞ
2
2
ꢀ1
o
(
M = Si and Ge) Me Si
3
ꢀ
3
^
^
SiMe3
ꢁ fh¼ jLzj¼ ih¼ jLz;NrN j¼ii
þ h¼ jLz;NrN j¼ ih¼ jLzj¼ ig
i
a
a
B
ꢀ3
^
^
ð5Þ
ð6Þ
i
a
a
n
i
n
n
n
n
JTL ¼ JDSO þ JPSO þ JSD þ JFC
For better understanding of the electronic structures around
chalcogen atoms of the species in question, absolute magnetic
Ph
Ph
1
shielding tensors of Se (σ(Se)) and J(Se, C) are calculated for
Ph Pb Ph
Li Li
benzoate anion derivatives I and methyl benzoate derivatives II
(
Chart 2), as models, after measurement of the NMR parame-
C
ters. Mechanisms for the origin of NMR chemical shifts and
indirect nuclear spin­spin coupling constants are elucidated,
Chart 1.
p
exemplified by I and II. It will be shown that σ (Se) and
t
d
1
t
1
precision. σ can be decomposed into diamagnetic (σ ) and
J (Se, C) contribute predominantly to σ (Se) and J (Se, C),
FC TL
p
p
paramagnetic (σ ) contributions under nonrelativistic condi-
respectively, in I and II. The origin of σ (Se) is explained
by decomposing it to the contribution from each occupied
molecular orbital (ψ ) and each ψ ¼ ψ transition. That of
tions, as shown in eq 1.3
0­32
The magnetic shielding tensors
consist of three components, which are shown exemplified by
i
i
a
p
p
1
σ in eq 2. As shown in eq 3, σ can be decomposed into the
contributions of the occupied orbitals or the orbital­orbital
JTL(Se, C) is similarly decomposed, however, the expression
based on molecular orbital theory seems somewhat more
complex.
3
3
transitions, since it is evaluated by the Coupled-Hartree­Fock
CPHF) method.34 σ is expressed simply as the sum of con-
tributions over the occupied orbitals (ψ ) as shown in eq 4.
While σ is evaluated accurately by the CPHF method and
decomposed by eq 3,35 we will mainly discuss σ with an
d
(
We report herein detailed studies of structures and properties
of aromatic selenoic, selenothioic, and diselenoic acid ammo-
nium salts. The studies are also extended to computational
i
p
p
77
approaches particularly focusing on the origin of Se NMR
3
6­40
approximated image derived from eq 5.
Namely, the origin
parameters of the salts and their esters.
p
of ¤(Se) are clarified by decomposing σ (Se) to the contribution
from each occupied molecular orbital (ψ ) and each ψ ¼ ψ
Results and Discussion
i
i
a
transition (ψ being vacant orbital) with the image of eq 5.
Generation of Aromatic Selenoic, Selenothioic, and
Diselenoic Acid Salts. For the generation of a series of acid
salts, selenoic acid Se-[2-(trimethylsilyl)ethyl] esters and their
heavier isologues 5­7 were chosen as starting materials. The
preparation of the desired esters 5­7 was achieved by reacting
aluminum 2-(trimethylsilyl)ethylselenolate generated in situ
from diselenide 1 and a series of chalcogenoic acid methyl
esters 2­4 (Table 1).
a
Indirect nuclear spin­spin coupling constants between Se and
X (J(Se, X)) are also analyzed for wide range of selenium
1
5,17,19a,41,42
n
compounds.
A calculated total value ( JTL) is
composed of the contributions from the diamagnetic spin­orbit
n
(
(
DSO) term ( J ), the paramagnetic spin­orbit (PSO) term
DSO
n
n
JPSO), the spin­dipolar (SD) term ( JSD), and the Fermi
contact (FC) term ( J ), under the nonrelativistic condi-
n
FC

T. Murai et al.
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
679
Table 1. Silylethylselanylation of Chalcogenoic Acid
Methyl Esters 2­4
and 7 with Me NF also gave the corresponding ammonium
salts 10 and 12 as green solids (Entries 4, 6, and 7).
4
a)
E
Among tetramethylammonium salts 8, 10, and 12, seleno-
benzoic acid salt 8a was the most labile and decomposed above
34 °C. The generation of tetrabutylammonium salts was also
successful by treating a THF solution of tetrabutylammonium
fluoride (Bu4NF) with the esters 5b, 6b, and 7b (Entries 2,
5, and 8). NMR spectra of the products clearly showed the
formation of the salts 7b, 9b, and 13b but the separation of
Ar
OMe
i-Bu AlH
E
2
2
–4
Me Si
3
Se
SiMe3
toluene
or xylene
2
Temp
Ar
Se
1
5
–7
0
°C
then rt
1
5 min
excess Bu NF from these salts was not successful. To confirm
4
Temp
°C
Time
/h
Yield
/%
the efficient generation of tetrabutylammonium salts, the meth-
ylation of 9b and 11b was carried out (eqs 7 and 8).
Entry Ester
E
Ar
Ph
4-PhC6H4
Ph
/
1
2
3
4
5
6
2a
2b
3a
3b
4a
4b
O
O
S
110
110
180
180
rt
5
6
5a 98
5b 93
+NBu4
–
Se
O
O
O
Bu NF
MeI
4
SiMe3
SiMe3
ð7Þ
Ar
Se
Ar
Ar
0 °C Ar
SeMe
0.5 6a 47
0.5 6b 74
3
THF
0 °C
1
h
5b
9b
14 76%
S
4-PhC6H4
3
h
Ar = 4-PhC H
6
4
Se Ph
Se 4-PhC6H4
7a 27
7b 43
+NBu4
–
Se
rt
22
S
S
S
Bu NF
MeI
0 °C Ar
4
ð8Þ
a) Reaction conditions: Diselenide 1 was reduced with
DIBAL-H in toluene. To this solution was added esters 2­4,
and the mixture was stirred.
Ar
Se
SeMe
15 94%
THF
0 °C
1
h
6b
11b
3
h
Ar = 4-PhC H
6
4
The reaction with methyl iodide for 1 h gave the desired
methyl esters 14 and 15 as colorless and red solids in 76 and
94% yields, respectively. In these reactions, the selenium atoms
in 9b and 11b were selectively methylated.
To evaluate the influence of the counter cations of the salts
on the spectroscopies, the preparation of alkaline metals salts
was attempted by reacting 5 and 6 with NaF and KF, but the
reaction did not take place at all. In contrast, the reaction of 5b
and 6b with KF in the presence of 18-crown-6 ether took place
under reflux in CH3CN to give the corresponding salts 9c and
Table 2. Desilylethylation of Esters with Ammonium
Fluoride
a)
E
MF
Se- +M
E
SiMe3
Ar
Se
Ar
5
–7 E = O, S, Se
8–13
Time
Yield
/%
Entry Ester E Ar
Solvent
CH3CN
MF
/h
1
2
3
4
5
6
7
8
5a
5b
5b
6a
6b
6b
O
O
O
S
S
S
Ph
5
2
3
3
Me4NF 8a 44
Bu4NF 9b 78
Me4NF 8b 83
Me4NF 10a 61
11c, respectively, although their solubility in THF and CHCl3
4-PhC6H4 THF
4-PhC6H4 CH3CN
Ph
4-PhC6H4 THF
4-PhC6H4 CH3CN
was very low, and they contained a small excess of crown ether
(
eq 9).
CH3CN
KF
0.5 Bu4NF 11b 61
M+
E
1
8-crown-
6 ether
E
3
1
2
Me4NF 10b 62
Me4NF 12a 59
Bu4NF 13b 41
–
9c E = O 56%
11c E = S 45%
Se
SiMe3
ð9Þ
7a Se Ph
7b Se 4-PhC6H4 CH3CN
THF
Ar
Se
Ar
CH CN
3
82 °C, 1h
Ar = 4-PhC H4
O
6
a) Reaction was carried with esters 5­7 and ammonium
fluoride (1­10 equiv).
5b E = O
O
O
6
b
E = S
M+ =
K+
O
O
O
The reaction with methyl esters 2 was carried out with
toluene as a solvent for 5­6 h to give the corresponding
products 5 as pale yellow solids (Entries 1 and 2), whereas the
reaction with thioic acid O-methyl esters 3 was complete within
Molecular Structures of Some of Esters and Ammonium
Salts. Molecular structures of some of products are disclosed
by X-ray analyses. ORTEP drawings of selenoic and seleno-
thioic acid esters 14 and 15 and selenoic and selenothioic acid,
0
.5 h in xylene to form the products 6 as reddish purple solids
Entries 3 and 4). In contrast, the preparation of diselenoic acid
esters 7 as green solids was carried out at room temperature
Entries 5 and 6). Otherwise, the decomposition of the formed
(
salts 8b¢CH CN are shown in Figures 1­3, respectively.
3
Representative bond lengths, angles, and dihedral angles are
listed in Table 3 along with data of reported diselenoic acid salt
(
5
esters 7 occurred at higher temperatures.
12a. In all cases, the selenocarboxy and selenothiocarboxy
The salts were then generated from the esters 5­7 by treating
with ammonium fluorides (Table 2). The reaction of selenoic
units adopt a trigonal-planar geometry. The bond length of C­
Se bond of 14 is the longest among two esters and two salts.
The replacement of the oxygen atom of 14 with a sulfur atom
shortened this bond length by ca. 0.035 ¡ as in 15. The bond
lengths of C­Se of the salt 8b are nearly equal to that of the
ester 15. Notably, the bond lengths of both C­Se bonds in 12a
are clearly shorter than that of the salt 8b. The values of
ca. 1.83 ¡ of C­Se bonds in 12a are within the range of C=Se
acid Se-esters 5 with tetramethylammonium fluoride (Me NF)
4
in CH3CN at 0 °C was complete within 5 h (Entries 1 and 3). To
the concentrated reaction mixture was added diethyl ether, and
the filtration of the resulting deposits with a glass filter gave the
corresponding tetramethylammonium salts 8 as yellow solids.
A similar treatment of selenothioic and diselenoic acid esters 6

6
80
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
Aromatic Selenoic, Selenothioic, and Diselenoic Acid Salts
bonds of reported selenoamides. In contrast, in all cases, the
bond lengths between selenocarbonyl carbon atoms and ipso-
carbon atoms are within the range of 1.497 « 0.020 ¡. Bond
angles of selenocarboxy groups, i.e., E1­C1­E2 of all esters
and salts are slightly greater than 120° probably because of
the steric repulsion among oxygen, sulfur, and selenium atoms.
The dihedral angle of the selenocarboxy plane and the aromatic
ring in 14 is 7°, whereas that in 8b is 17.7°. Further deviation
was found by replacing oxygen atoms of 14 and 8b with sulfur
and selenium atoms as in 15, and 12a, respectively. Similar
enlargements of bond angles and dihedral angles are also
C14
O
C2
4
3
reported in the case of thioic and dithioic acid salts.
Spectroscopic Properties. To elucidate the structures of
C1
Se
13
77
a series of the esters and salts in solutions, C and Se NMR
spectra and UV­vis spectra were measured (Table 4). The
results of the esters and the salts are shown in Tables 4 and 5,
C3
1
3
respectively. In C NMR spectra, the signals of the carbonyl
carbon atom of selenoic acid Se-esters 5 and 14 were observed
at about 195 ppm (Entries 1­3), whereas that of selenoic acid
O-ester 16 was at 222.4 ppm (Entry 7). In contrast, those of
selenothioic acid Se-esters 6 and 15 (Entries 4­6), and S-ester
17 (Entry 8) were nearly in the same regions which were
Figure 1. ORTEP representation of 14.
S
C14
Se
C1
C2
C1
C3
C2
O
Se
C
C3
N
N
Figure 2. ORTEP representation of 15.
Figure 3. ORTEP representation of 8b¢CH3CN.
Table 3. Selected Bond Lengths, Angles, and Dihedral Angles of Esters 14, 15, Salts 8b, and 12a
Se +NMe4
–
O
C14
CH3
S
C14
CH3
O
+NMe4
C2
C2
C2
C2
–
Se
C1
Se
C1
Se
C1
Se
C1
Ph
Ph
Ph
C3
C3
C3
C3
1
4
15
8b
12aa)
1
1
1
1
E = O
E = S
E = O
E = Se
2
2
2
2
E = Se
E = Se
E = Se
E = Se
Bond lengths/¡
C1­E1
C1­E2
C1­C2
1.205(6)
1.920(6)
1.503(7)
1.624(4)
1.885(4)
1.477(6)
1.225(6)
1.884(5)
1.516(6)
1.831(4)
1.828(4)
1.482(5)
Bond angles/degree
E1­C1­E2
E1­C1­C2
E2­C1­C2
C1­E2­C14
112.6(5)
122.2(6)
116.1(4)
96.7(3)
123.7(2)
124.3(6)
111.8(3)
101.3(2)
122.8(4)
118.2(4)
118.8(3)
124.3(2)
117.7(3)
118.0(3)
Dihedral angles/degree
E2­C1­C2­C3
E1­C1­E2­C14
6.9(7)
3.9(5)
31.1(5)
1.5(3)
17.7(14)
46.0(5)
a) Ref. 5.

T. Murai et al.
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
681
Table 4. Typical Spectroscopic Properties of Compounds 5­7 and 14­18a)
UV­vis
n­π*
13C NMR
77Se NMR
¤/ppm
1JC­Seb)
/Hz
Entry
Compd
Ar
¤/ppm
­
max/nm
O
5a
5b
Ph
195.8
195.2
581.8
581.4
150.6
150.2
340
1
2
4-PhC6H4
340
Ar
SeR
R = CH2CH2SiMe3
O
3
14
4-PhC6H4
194.4
443.6
147.2
340
Ar
Ar
SeMe
SeR
S
6a
6b
Ph
234.2
232.8
839.8
834.9
163.8
162.3
511
519
4
5
4-PhC6H4
R = CH2CH2SiMe3
S
6
7
15
16
4-PhC6H4
Ph
232.1
222.4
705.7
893.9
158.4
215.5
560
503
Ar
Ar
SeMe
OR
Se
R = CH2CH2SiMe3
Se
8
9
17
7b
18
Ph
233.3
235.4
236.2
1599.0
221.1
605
634
616
Ar
SR
R = CH2CH2SiMe3
8
91.5
171.1
222.3
Se
4-PhC6H4
Ph
1
755.3
Ar
SeR'
R = CH2CH2SiMe3
7
69.7
175.8
224.7
Se
1
0
1
786.8
Ar
SeMe
a) CDCl3 was used as a solvent for NMR spectra, whereas THF was used for UV spectra. b) The coupling
1
3
constants were determined in the C NMR spectra.
shifted to a lower field by about 10 ppm when compared with
that of 16. No critical difference of the chemical shifts among
selenothioic esters Se-esters 6 and 15, and S-ester 17, and
diselenoic acid esters 7b and 18 (Entries 9 and 10) was
20 ppm compared with those of the corresponding esters. As a
result, the signals of Se­C­E (E = S and Se) were observed at
lower than 250 ppm (Entries 6­12). Conversion of the esters 5
7
7
to the salts 8 shifted the signals in Se NMR spectra to higher
fields by more than 140 ppm, and they were observed at about
444 ppm (Entries 1­5). In contrast, the differences of the
chemical shifts of the signals due to selenothioic acid S-ester 17
and diselenoic acid ester 7b and those due to selenothioic and
diselenoic acid salts 10­13 were greater than the differences
between 5 and 8. Nonetheless, the signals of 10­13 were still
lower than 1200 ppm, which are in a region of carbon­selenium
double bonds, even if the salts generally involve two types of
resonance structures possessing not only the carbon­selenium
double bonds but also carbon­selenium single bonds. Notice-
able difference in the chemical shifts was not observed even
when the counter cations were replaced from ammonium to
potassium coordinated by the crown ether (Entries 5 and 10).
7
7
observed. In the Se NMR spectra, the signals of the Se-esters
­7, 14, 15, and 18 were highly dependent on the substituents
5
attached to the selenium atom. The replacement of C=O
groups in 5 and 14 with C=S and C=Se groups shifted the
signals of the selenium atoms of SeMe and SeCH CH SiMe to
2
2
3
lower fields by more than 250 ppm (Entries 1 and 2 vs. Entries
­6, 9, and 10). The signal of C=Se of selenoic acid O-ester 16
4
was at 893.9 ppm (Entry 7), whereas those of selenothioic S-
esters 17 and diselenoic acid esters 7b and 18 were at 1599 and
1
771 « 16 ppm (Entries 8­10). The coupling constants of the
carbon­selenium bonds are not influenced by the substituents
around the selenium atoms, but mainly depend on if it is a
single bond or a double bond. In fact, those of C­Se bonds
were 162 « 15 Hz (Entries 1­6, 9, and 10), and those of C=Se
were 220 « 5 Hz (Entries 7­10).
1
Similar tendency was further observed for the J coupling
constants between the carbon and selenium bonds. These
values are also depicted in Figure 4.
The coupling constants of the carbon­selenium single bonds
are at around 161 Hz as in the Se-esters 5b, 6b, and 7b whereas
those of the carbon­selenium double bonds are at around
It is also of great interest to compare the results of the esters
in Table 4 with those of the salts in Table 5. In the 1 C NMR
spectra, in all cases, the signals of seleno-, selenothio-, and
diselenocarboxy units were shifted to lower fields by about
3

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82
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
Aromatic Selenoic, Selenothioic, and Diselenoic Acid Salts
Table 5. Typical Spectroscopic Properties of Compounds 8­13a)
UV­visc)
n­π*
13C NMR
77Se NMR
¤/ppm
1JC­Seb)
/Hz
Entry
Compd
+NMe4
Ar
Ph
¤/ppm
­
max/nm
Se
8a
8b
9a
9b
211.7
211.1
210.6
210.1
437.9
444.2
442.9
450.6
187.2
®d)
341
355
353
370
1
2
–
4-PhC6H4
Ph
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
O
+NBu4
192.1
192.1
3
4
Se
–
4-PhC6H4
O
M+
Se
5
–
9ce)
4-PhC6H4
211.5
438.9
®d)
356
O
+NMe4
®d)
®d)
Se
10a
10b
11a
11b
Ph
257.8
256.3
254.3
253.4
1201.5
1203.0
1205.0
1208.9
595
589
587
560
6
7
–
4-PhC6H4
Ph
S
+NBu4
209.6
213.0
8
9
Se
–
4-PhC6H4
S
M+
Se
10
–
11ce)
12a
4-PhC6H4
Ph
253.1
259.3
254.7
1203.3
1433.3
1441.7
®d)
560
684
684
S
Se
+NMe4
11
–
213.5
213.5
Se
Se +NBu4
–
12
13b
4-PhC6H4
Se
a) THF-d8 was used as a solvent for tetrabutylammonium salt, whereas CD3CN was used for tetra-
methylammonium salts, 9c and 11c. b) The coupling constants were determined in the 13C NMR spectra.
c) THF was used as a solvent for UV visible spectra. d) Not determined. e) M = K•18-crown-6 ether.
Se
Se
O
O
+NBu4
4
-PhC H
SeR C H5
4-PhC H4
Se
4-PhC H
6 4
SeR
6
4
6
OR
6
7b
16
9b
5b
1JC=Se = 222.3 Hz 1JC=Se = 215.5 Hz
1JC-Se = 192.1 Hz
1JC-Se = 150.2 Hz
2
30
220
SR
210
200
Se
190
180
170
160
150
140
S
Se
+NBu4
4
-PhC H
SeR
4
-PhC H4
S
6 4
Ph
6
6
b
17
11b
1JC-Se = 162.3 Hz
Se
1JC-Se = 213.0 Hz
Se
1JC=Se = 221.1 Hz
+NBu4
4
-PhC H
SeR
4
-PhC H4
Se
6 4
6
7
b
1
3b
R = CH CH SiMe
3
1JC-Se = 171.1 Hz
2
2
1JC-Se = 213.5 Hz
Figure 4. 1J coupling constants (Hz) of C­Se and C=Se of a series of esters and salts.
2
20 Hz as in the esters with C=Se bonds 7b, 16, and 17.
and selenothioic acid salts, two resonance forms 8-III, 11-III
and 8-IV, 11-IV can be envisioned (eq 10). On the basis of the
chemical shifts and coupling constants shown above, the reso-
nance forms 8-III and 11-III possessing the carbon­selenium
double bonds are also contributed to the resonance hybrids 8
Notably, those of the salts 9b, 11b, and 13b are greater than
those of the Se-esters 5b, 6b, and 7b, in particular, those of the
salts 11b and 13b are observed at 213 Hz and are nearly the
same as that of 16. For the resonance hybrids of selenoic acid

T. Murai et al.
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
683
and 11 in spite of the fact that carbon­selenium double bonds
are less stable than carbon­oxygen and carbon­sulfur double
bonds. The resonance form 11-III appears to be more important
than that of 8-III. UV­vis spectra are informative on this point.
The absorptions of 8 probably due to n­π* transitions are blue-
shifted compared to that of the selenoic acid O-ester 16
cies are (global) minima, whereas those with (only) one
imaginary frequency correspond transition states (TS). Table 6
1
1
1
1
2
collects the distances of r(C ,C ), r(C ,E ), and r(C ,E ), the
i
1
1
1
2
1 1 2
angles of ¾C C E , ¾C C E , and ¾E C E , and the torsional
angle of º(C C C E ), together with their lowest frequencies
i
i
1
1
o
i
and the symmetry of the optimized structures. Figure 5 illus-
trates the optimized structures of I (S, Se: np), I (Se, Se: np),
II (O, Se: pl), and II (S, Se: np). Others are given in Figure S1
of the Supporting Information. Table 7 collects the energy
(Table 4, Entry 7 vs. Table 5, Entries 1­5, whereas those of 11
are nearly the same as those of the ester 15 possessing the
C=Se bond (Table 4, Entry 8 vs. Table 5, Entries 8­10). Inter-
estingly, the absorptions of 12a and 13b probably due to n­π*
transitions are red-shifted compared to those of diselenoic acid
esters 7b and 18 by more than 50 nm (Table 4, Entries 9 and 10
vs. Table 5, Entries 11 and 12.
1
2
differences between np and pl for I and II with E , E = S
and Se. Table 8 shows the energy differences in the opti-
2
2
mized structures between PhC(=O)E Me (II (O, E )) and
1
1
PhC(=E )OMe (II (E , O)).
1
1
1 2
As shown in Table 6, ¾C C E and ¾C C E are predicted to
be smaller for I (np) with (E , E ) = (S, S), (S, Se), and (Se,
Se), relative to the corresponding values in I (pl). However,
Se–
i
i
Se
Se
M+
E–
M+
1
2
M+
–
R
R
E
R
E
1
1 2
the inverse trend is predicted for ¾E C E . The results show
8
E = O
E = S
8-III
11-III
8-IV
11-IV
1 1 2
that the steric congestion between the C E E moiety and the
phenyl ortho-protons is substantially large in I (pl) and it is
released in I (np), which must be the reason for the minima of
1
1
ð10Þ
1
2
Therefore, the results of the chemical shifts, coupling
constants and UV­vis spectra of diselenoic acid salts 12 and
I (np) but the TS for I (pl) with (E , E ) = (S, S), (S, Se), and
(Se, Se). Such steric congestion seems not important if each
compound contains at least one oxygen atom. Similar trends
1
3 imply that both carbon­selenium bonds in these salts
1
2
possess double bond character.
are also predicted for II with (E , E ) = (S, S), (S, Se), (Se, S),
and (Se, Se), where II (np) are minima. It is worthwhile to
comment that the dihedral angle of the selenocarboxy plane
and the aromatic ring in 8b is observed to be 17.7°, although
the structure of I (O, Se) is predicted to be pl (º(C C C O) =
º(C C C Se) = 0.0°). The unsymmetric interaction due to the
o¤ i
Structural Feature of Anions and Esters.
Before
discussion of NMR parameters, it is appropriate to discuss
the structural features of the species, employed to evaluate the
parameters. Structural optimizations are performed on I and II
1
o
i
1
2
1
with E , E = O, S, and Se, models of 5­18, employing the 6-
11+G(3df,3pd) basis sets at the B3LYP level. The methyl
group in II is located similarly to the structures of 14 and 15
Figures 1 and 2, respectively). Plausible structures of I and
3
counter ion in 8b may give the observed nonplanar structure for
8b in the crystal, together with the crystal packing effect around
8b (Figure 3).
(
1
II will be planar (pl), perpendicular (pd), and nonplanar and
nonperpendicular (np) ones, which is intermediate between pl
How does the C=E character contribute to stabilize the
2
compounds, although the π contribution from C­E must also
1
1 2
and pd. The dihedral angles between the C E E and phenyl
planes are µ0° in pl, µ90° in pd, and around 45° in np, assum-
be important? The effect can be estimated in the isomers of II,
which is discussed, next. The energy difference between II (Se,
S: pl) and II (S, Se: pl) [= E (II (Se, S: pl)) ¹ E (II (S, Se: pl))]
1
1 2
ing the planarity of the C E E and phenyl planes. Scheme 1
explains the pl, pd, and np notation exemplified by I. The
requirements for the notation are rather strictly applied to pl
and pd, whereas they are not so to np. The pd structures are not
observed and not optimized in I and II.
¹
1
is predicted to be 0.3 kJ mol and that between II (Se, S: np)
¹
1
and II (S, Se: np) is ¹0.5 kJ mol , which are very small
(Table 7). The results demonstrate that the energy lowering
effect by the π-conjugation of ­C(=Se)­S­Me in II (Se, S) is
very close to that of ­C(=S)­Se­Me in II (S, Se), although the
π-conjugation between the groups and the phenyl group must
also be considered. The magnitudes of energy differences
Optimizations are started assuming the planar structures (pl).
Frequencies are all positive for I and II, when O is contained
1
2
for E and/or E . One imaginary frequency appears in pl of
1
2
¹1
1
I and II, if E , E = S and Se. The compounds with one
imaginary frequency were reoptimized starting with the tor-
sional angle (º(CoCiC E )) of around 45°. Reoptimized struc-
between np and pl in I and II are less than 5 kJ mol for (E ,
2
E ) = (S, S), (S, Se), (Se, S), and (Se, Se), as shown in Table 7.
1
1
On the other hand, the differences between II (S, O: pl) and II
(O, S: pl) and between II (Se, O: pl) and II (O, Se: pl) are
1
1
tures with all positive frequencies have the º(C C C E ) values
o
i
¹
1
of around 40°. Optimized structures with all positive frequen-
evaluated to be 56.2 and 62.2 kJ mol , respectively, which are
very large (Table 8). The extremely large stabilizing effect of
the C=O group must be responsible for the evaluation.
E2
–
E2–
A conformer, called II (Se, Se: np¤), would be important in
II (Se, Se), of which a methyl group is located upside the
phenyl group. The structure of II (Se, Se: np¤) is optimized and
illustrated in Figure 5. The structural parameters for II (Se, Se:
np¤) are shown in Table 6, for convenience of comparison.
The energy difference between II (Se, Se: np¤) and II (Se, Se:
E1
C
E2–
C
C
E1
E1
pl:
0°
pd:
90°
np:
45°
¹
1
Scheme 1. The pl, pd, and np notation, exemplified by
np) is estimated to be 16 kJ mol , as shown in Table 7. (Erel:
1
1
2¹
¹1
PhC E E (I).
E (np) ¹ E (pl) = ¹4.7 kJ mol and E (np¤) ¹ E (pl) = 11.4

6
84
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
Aromatic Selenoic, Selenothioic, and Diselenoic Acid Salts
Table 6. Optimized Distances, Angles, and Torsional Angles in I and II, Together with the Lowest Frequenciesa)
r(Ci,C1) r(C ,E ) r(C ,E ) ¾CiC1E1 ¾CiC1E2 ¾E C E º(CoCiC E )
1
1
1
2
1
1
2
1 1
¯1
/cm
1
2
(
E , E )
Symmetry
¹
1
/¡
/¡
/¡
/°
/°
/°
/°
I (O, O: pl)
I (O, S: pl)
I (O, Se: pl)
I (S, S: pl)
I (S, Se: pl)
I (Se, Se: pl)
I (S, S: np)
I (S, Se: np)
1.5520
1.5358
1.5298
1.5184
1.5113
1.5042
1.5051
1.4979
1.2509
1.2341
1.2263
1.6955
1.6823
1.8509
1.6928
1.6791
1.8453
1.2075
1.2088
1.2038
1.6461
1.8068
1.6459
1.6384
1.8068
1.7991
1.6429
1.6353
1.8020
1.7936
1.7931
1.2509
1.7281
1.9010
1.6955
1.8659
1.8509
1.6928
1.8607
1.8453
1.3483
1.7950
1.9650
1.3357
1.3288
1.7554
1.9234
1.7415
1.9077
1.7496
1.9158
1.7345
1.8990
1.8928
115.34
115.90
116.72
118.20
118.94
119.10
116.86
117.65
117.14
124.44
122.88
123.30
125.28
125.19
123.67
124.14
123.51
123.92
123.14
123.76
122.58
123.16
122.80
115.34
118.12
118.60
118.20
118.43
119.10
116.86
116.41
117.14
112.64
116.07
116.68
111.05
111.36
113.86
114.31
114.03
114.44
112.45
112.49
112.56
112.56
119.99
129.31
125.97
124.68
123.61
122.63
121.80
126.26
125.94
125.71
122.92
121.05
120.02
123.67
123.45
122.47
121.54
122.46
121.64
124.41
123.73
124.86
124.27
117.20
0.00
0.00
0.00
0.00
0.00
56.6
33.5
24.3
¹32.0
¹34.0
¹36.6
36.6
35.7
39.5
48.8
13.6
23.6
20.3
12.0
¹42.5
¹35.5
¹44.6
¹42.0
45.4
C2v
Cs
Cs
b)
C2v
b)
Cs
b)
0.00
C2v
c)
e)
d)
39.71
41.58
43.92
0.00
0.00
0.00
0.00
0.00
0.00
0.00
C1
C1
C2
Cs
Cs
Cs
I (Se, Se: np) 1.4909
II (O, O: pl)
II (O, S: pl)
II (O, Se: pl)
II (S, O: pl)
II (Se, O: pl)
II (S, S: pl)
II (S, Se: pl)
II (Se, S: pl)
1.4899
1.4939
1.4916
1.4837
1.4787
1.4892
1.4845
1.4846
b)
Cs
Cs
Cs
Cs
Cs
Cs
b)
b)
b)
b)
0.00
0.00
b)
II (Se, Se: pl) 1.4799
f)
g)
h)
i)
II (S, S: np)
II (S, Se: np)
II (Se, S: np)
II (Se, Se: np) 1.4754
II (Se, Se: np¤) 1.4719
1.4846
1.4801
1.4798
34.97
35.40
37.59
37.94
50.82
C1
C1
C1
C1
C1
43.6
47.3
46.3
44.0
j)
a) With the 6-311+G(3df,3pd) basis sets at the B3LYP level. b) Containing one imaginary frequency, of which motion
1
1
1
1 2
being the deformation of º(CoCiC E ) around the Ci­C bond. c) º(Co¤CiC E ) = 39.71°. d) Very close to C2.
1
2
1
2
1
2
1 2
e) º(Co¤CiC E ) = 42.64°. f) º(Co¤CiC E ) = 36.39°; º(CiC E CMe) = ¹176.61°. g) º(Co¤CiC E ) = 37.39°;
º(CiC E CMe) = ¹176.86°. h) º(Co¤CiC E ) = 38.32°; º(CiC E CMe) = ¹176.04°. i) º(Co¤CiC E ) = 39.21°;
º(CiC E CMe) = ¹176.26°. j) º(Co¤CiC E ) = 51.63°; º(CiC E CMe) = 16.09°.
1
2
1
2
1
2
1 2
1
2
1
2
1 2
Figure 5. Optimized structures of minima, illustrated for I and II.
¹
1
t
t
kJ mol ). The ratio of K = [II (Se, Se: np¤)]/[II (Se, Se: np)] is
values (= σ (Se: I or II) ¹ σ (Se: MeSeMe)) well reproduce
¹1
p
expected to be around 0.002 with the Erel value of 16 kJ mol
for II (Se, Se: np¤), relative to II (Se, Se: np).
NMR parameters and the origin are discussed next, employ-
¤(Se)obsd, although signs are inverse, where ¦σ (Se) obviously
contribute almost exclusively to ¦σ (Se).
Figure 6 shows the plot of ¤(Se)
II. ¦σ (Se) in I (np) and II (np) are predicted to be very close to
those in I (pl) and II (pl), respectively, except for Se in C=Se
of II (Se*, S) and II (Se*, Se), where each atom in question is
shown by *. The difference is less than 15 ppm but it is larger
than 100 ppm for the latter. The plots are analyzed assuming
the linear correlations with y = ax + b (a; correlation constant,
t
t
versus ¦σ (Se) for I and
obsd
1
t
ing the evaluated σ(Se) and J(Se, C) values.
Analysis of NMR Parameters. 77Se NMR parameters are
evaluated on the optimized structures of I and II containing Se,
given in Table 6, together with MeSeMe, although II (Se, Se:
44,45
np¤) is not considered for the estimation.
the σ (Se) values calculated under nonrelativistic conditions,
separated by σ (Se) and σ (Se) (cf: eq 1), together with the
observed values adjusted to the model compounds. The ¦σ (Se)
Table 9 shows
t
d
p
2
b; y-intercept, and R ; square of correlation coefficient). An
excellent linear correlation is obtained for ¤(Se)obsd versus
t

T. Murai et al.
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
685
Table 7. Evaluated Energies of the Planar (pl) and Nonplanar and Nonperpendicular (np) Structures for I and
1
2
a)
II with E , E = S and Se, Together with the Energy Differences
Erelb)
kJ mol
Erelb)
/kJ mol
Compound
E/au
Compound
E/au
¹1
¹1
/
I (S, S: pl)
¹1066.3624
¹1066.3634
¹3069.6949
¹3069.6952
¹5073.0262
¹5073.0279
0.0
¹2.6
0.0
¹0.8
0.0
II (S, S: pl)
¹1106.2222
¹1106.2234
¹3109.5499
¹3109.5513
¹3109.5498
¹3109.5515
¹5112.8770
¹5112.8788
¹5112.8727
0.0
¹3.2
0.0
¹3.7
0.0
¹4.5
0.0
¹4.7
11.4
I (S, S: np)
I (S, Se: pl)
I (S, Se: np)
I (Se, Se: pl)
I (Se, Se: np)
II (S, S: np)
II (S, Se: pl)
II (S, Se: np)
II (Se, S: pl)
II (Se, S: np)
II (Se, Se: pl)
II (Se, Se: np)
II (Se, Se: np¤)
¹4.5
a) With the 6-311+G(3df,3pd) basis sets at the B3LYP level. b) Erel = E (np or np¤) ¹ E (pl); Erel = E
pl) ¹ E (pl) is given as 0.0.
(
2
1
1
2
Table 8. Evaluated Energies of the Planar (pl) Structures for II (O, E ) and II (E , O) with E , E = S or
Se, Together with the Energy Differences
a)
1
2
b)
¹1
1
2
b)
¹1
II (E , E )
E/au
Erel /kJ mol
II (E , E )
E/au
Erel /kJ mol
II (O, S: pl)
II (S, O: pl)
¹783.2696
¹783.2482
as 0.0
56.2
II (O, Se: pl)
II (Se, O: pl)
¹2786.5983
¹2786.5746
1
as 0.0
62.2
2
a) With the 6-311+G(3df,3pd) basis sets at the B3LYP level. b) Erel = E (E , O) ¹ E (O, E ); Erel = E
2
2
(
O, E ) ¹ E (O, E ) is given as 0.0.
d
p
t
d
p
t
Table 9. Calculated σ (Se), σ (Se), and σ (Se) Values and the Relative Values from MeSeMe (¦σ (Se), ¦σ (Se), and ¦σ (Se)) in
a)
I and II, Together with ¤(Se)obsd Adjusted to the Model Compounds
σd(Se)
¦σ (Se)
d
σp(Se)
¦σ (Se)
p
σt(Se)
¦σ (Se)
t
Qn(Se)
¤(Se)obsd
Compound
MeSeMe
2992.2
3000.2
3000.9
3001.9
3002.8
3003.6
2989.9
2989.5
2991.9
2988.4
2990.8
2999.1
3000.2
3000.3
2999.6
2999.6
0.0
8.0
8.7
¹1440.1
¹1874.2
¹2821.7
¹2858.9
¹3094.0
¹3088.5
¹1861.6
¹2132.7
¹2148.0
¹2188.5
¹2205.2
¹2347.4
¹3088.7
¹3212.5
¹3255.9
¹3362.8
0.0
¹434.1
¹1381.6
¹1418.9
¹1653.9
¹1648.4
¹421.5
¹692.6
¹707.9
¹748.4
¹765.1
¹907.3
¹1648.6
¹1772.4
¹1815.8
¹1922.7
1552.1
1126.0
179.2
0.0
¹426.1
¹1372.9
¹1409.2
¹1643.3
¹1637.0
¹423.8
¹695.3
¹708.2
¹752.2
¹766.5
¹900.4
¹1640.6
¹1764.2
¹1808.4
¹1915.2
0.2394
¹0.5124
¹0.2768
¹0.2739
¹0.2169
¹0.2126
0.2291
0.3952
0.4138
0.4311
0.4515
¹0.0831
0.0150
0.0232
0.0442
0.0545
0.0
437.9
b)
I (O, Se*: pl)
I (S, Se*: pl)
I (S, Se*: np)
I (Se*, Se*: pl)
I (Se*, Se*: np)
II (O, Se*: pl)
II (S, Se*: pl)
II (S, Se*: np)
II (Se, Se*: pl)
II (Se, Se*: np)
II (Se*, O: pl)
II (Se*, S: pl)
II (Se*, S: np)
II (Se*, Se: pl)
II (Se*, Se: np)
1201.5
1201.5
1433.3
1433.3
444.0
710.6
710.6
769.7
769.7
9.7
142.9
10.6
11.4
¹2.3
¹2.7
¹0.3
¹3.8
¹1.4
6.9
8.0
8.1
7.4
7.4
¹91.2
¹84.9
1128.3
856.8
843.9
799.9
785.6
651.7
¹88.5
¹212.1
¹256.3
¹363.1
925.4
1630.5
1630.5
1786.8
1786.8
a) Calculated with STO-AOs (QZ4Pae) at the DFT (BLYP) level under the nonrelativistic conditions employing the optimized
structures corresponding to those in Table 6. b) Similar Qn(S) value of ¹0.4862 being predicted for I (O, S*: pl).
t
t
¦
σ (Se) in II (pl) with MeSeMe (¤(Se)
= ¹0.983¦σ (Se) +
so severe. Therefore, the results in Figure 6 is explained as
obsd
2
t
2
1.7 (R = 0.9995) in ppm; see Figure 6). Data for I (pl) and
follows: (a) ¦σ (Se) reproduced ¤(Se)
for I and II. (b)
obsd
1
2
t
I (np) with (E , E ) = (S, Se*) and (Se*, Se*) deviated from the
correlation. The differences in the conditions of the experi-
mental measurements and the calculations would be responsi-
ble for the deviation. The solvent effect in the former must be
large for the charged species, whereas the latter corresponds the
conditions of the isolated species in vacuum. Namely, the effect
of the negative charge in I would not be evaluated as in the
experimental measurements, although data for I (O, Se) are
on the line. The deviation of the data for II (np) seems not
¦σ (Se) for the SeMe group in II (np) seem not so different from
those for the corresponding II (pl), although the effect seems
larger for the C=Se group in II. And (c) the differences seem
small in I, however, the charge effect must be considered in I.
1
One may imagine that the structures of I and II with E ,
E = S and Se would be closer to the planar structures in solu-
2
tions than the nonplanar ones. However, the torsional angles of
I, II, and related species determined by X-ray crystallographic
analyses are close to those in Table 6. And the differences in

6
86
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
Aromatic Selenoic, Selenothioic, and Diselenoic Acid Salts
p(Se)
/ppm
(
/
Se)obsd
ppm
4
9
(
HOMO)
2
1
1
000
500
000
-
1500
II (Se*, Se)
II (Se*, S)
-1000
-500
0
I (Se*, Se*)
I (S, Se*)
45
II (Se*, O)
II (Se, Se*)
II (S, Se*)
40
5
18
5
00
0
II (O, Se*)
n in
n
I (O, Se*)
p
Figure 7. Contribution from each MO to σ (Se), exempli-
fied by II (Se*, O).
I (pl)
I (np)
MeSeMe
2
II (pl): y = 21.7 - 0.983x R = 0.9995
II (np)
-2000
-1500
-1000
-500
0
t
(
Se)/ppm
t
Figure 6. Plot of ¤(Se)obsd versus ¦σ (Se) for I and II.
¦
σt(Se) between np and pl are rather small. The results demon-
strate that ¤(Se)obsd are well explained based on the structures
optimized as minima for I and II shown in Table 6. Some
discrepancies between observed and calculated values must
arise from the solvent effect on the NMR chemical shifts in
solutions, relative to the calculated values, which correspond to
those of an isolated molecule in vacuum, together with some
errors in the calculation method. Nevertheless, the differences
between calculated and observed values are not so severe,
which enables us to explain the observed values on the basis of
the calculated ones.
p
Equation 5 implies that σ (Se) are mainly controlled by the
ꢀ3
three factors, the electron population terms, hrSe i, the recip-
¹
1
rocal orbital energy gaps, [(¾ ¹ ¾ ) ], and the orbital over-
a
i
3
6
lapping terms controlled by the angular momentum operators.
ꢀ3
The hrSe i terms can be estimated by the charge at Se evalu-
39
ated by natural population analysis (Qn(Se)). One may expect
¹
1
that the (¾ ¹ ¾ ) terms can be replaced by the (¾LUMO
¹
a
i
¹1
¾HOMO
)
gaps. However, it is usually difficult to find suitable
transitions in the electronic spectra for the NMR parameters,
since the values must be complex averages of the transi-
tions. The orbital overlapping terms controlled by the angular
momentum operators seem to be very important, however, it
would be difficult to evaluate the contributions. ¤(Se)obsd
should be explained based on the three factors. However,
p
Figure 8. Contributions of the transitions to σ (Se) (ppm)
from (ψ45 and ψ49) to (ψ50, ψ52, and/or ψ57) in II (Se*, O).
p
predominantly to σ (Se) of II (Se*, O) by 1525 ppm, which
correspond to 65% of σ (Se). ψ , ψ , and ψ contribute 9, 18,
and 5% to σ (Se), respectively. Contribution from the four
p
p
σ (Se) are evaluated as the mixed contributions of the three
4
8
45
40
p
factors. Therefore, it would be difficult to explain well ¤(Se)obsd
as a single function of Qn(Se) or observed ­max, although some
relations could be found for some limited types of compounds.
The orbital overlapping terms often operate strongly but they
are difficult to quantify. As a result, it makes the analysis more
p
MOs amounts to 97% to σ (Se) of II (Se*, O).
What vacant orbitals (ψ ) contribute to σp49(Se) in the
transitions from ψ49 (HOMO) to ψ ? σ 49(Se) was decomposed
into each transition. ψ of ψ (LUMO), ψ52 (LUMO+2), and
a
p
a
a
50
complex to evaluate ¤(Se)
separately by the factors. Instead,
ψ57 (LUMO+7) mainly contribute the transitions. Figure 8
draws the contributions from ψ49 (HOMO) to ψ50 (LUMO), ψ52
(LUMO+2), and ψ57 (LUMO+7), together with the ψ45 ¼ ψ50
transition, which also contributes substantially.
obsd
p
we tried to analyze σ (Se) separately by each molecular orbital
ψ ) and each ψ ¼ ψ transition, according to eq 3.
(
i
i
a
How does each ψ contribute to ¤(Se)obsd? The contribution
i
p
1
from ψ to σ (Se) is evaluated. Figure 7 shows the contribu-
The J(Se, C) values and the origin are discussed, next.
i
1
tion exemplified by II (Se*, O). HOMO of ψ49 contributes
The J(Se, C) values are also calculated for I and II, employing

T. Murai et al.
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
687
1
Table 10. Evaluated J(Se, C) Values and Components in I and II, Together with Observed Values
a)
Adjusted to the Model Compounds
Compound
1JTL(Se, C)
1JDSO
1JPSO
1JFC
1JSD
1J(Se, C)obsd
MeSeMe
¹92.6
¹240.7
¹257.2
¹255.7
¹270.4
¹268.1
¹174.6
¹185.7
¹187.3
¹195.1
¹196.3
¹267.4
¹271.6
¹275.7
¹278.4
¹280.4
0.1
0.1
0.1
0.1
0.2
0.2
0.1
0.1
0.1
0.2
0.2
0.1
0.1
0.1
0.2
0.2
8.0
¹41.0
¹59.2
¹58.4
¹65.2
¹63.8
¹31.6
¹38.1
¹39.1
¹40.5
¹41.4
¹57.3
¹65.1
¹65.4
¹68.1
¹68.9
¹113.0
¹202.8
¹200.6
¹199.7
¹206.6
¹206.1
¹146.5
¹149.3
¹149.6
¹154.9
¹155.0
¹223.0
¹218.8
¹222.0
¹223.0
¹223.3
12.3
3.0
2.5
2.3
1.2
1.6
3.4
1.6
1.3
62.0
187.2
209.6
209.6
213.5
213.5
147.6
159.9
159.9
175.8
175.8
211.6
223.5
223.5
224.7
224.7
I (O, Se*: pl)
I (S, Se*: pl)
I (S, Se*: np)
I (Se*, Se*: pl)
I (Se*, Se*: np)
II (O, Se*: pl)
II (S, Se*: pl)
II (S, Se*: np)
II (Se, Se*: pl)
II (Se, Se*: np)
II (Se*, O: pl)
II (Se*, S: pl)
II (Se*, S: np)
II (Se*, Se: pl)
II (Se*, Se: np)
0.1
¹0.1
12.8
12.2
11.6
12.5
11.6
a) Calculated with STO-AOs (QZ4Pae) at the DFT (BLYP) level under the nonrelativistic conditions
employing the optimized structures shown in Table 6.
1J(Se, C)obsd
Hz
in Figure 9 are also analyzed similarly to the case of ¤(Se)
obsd
/
t
versus ¦σ (Se) (Figure 6) (y = ax + b: a; correlation constant,
II (Se*, Se)
2
b; y-intercept, and R ; square of correlation coefficient). Both
II (Se*, S)
I (S, Se*)
2
I (Se*, Se*)
plots gave very good correlations (R = 0.996 for both), of
II (Se*, O)
which correlation constants (a values) are close to ¹1.00. The
a value for II (X, Se*) with MeSeMe is somewhat less than
¹1.00 (¹1.08), whereas that for II (Se*, X) and I (X, Se*) with
2
00
I (O, Se*)
II (Se, Se*)
II (S, Se*)
MeSeMe is somewhat larger than ¹1.00 (¹0.88). The dif-
1
ferences may come from the overestimation of J (Se, C)
II (O, Se*)
FC
calcd
for the C=Se moiety in I and II, relative to the case for the
1
C­Se moiety in II. The J (Se, C) values reproduced
calcd
Me
1
TL
well J(Se, C)obsd, although the calculated values are larger than
the observed by about 40 Hz in magnitudes, judging from the
b values. One often encounters such prediction, which seems to
be systematic in the calculation method employed here.
JFC(Se, C) contribute predominantly to JTL(Se, C) for I
and II ( J = 0.769 © J ¹ 7.4 (R = 0.968)), although not
pl of II (X, Se*) (X = S, Se)
1
00
2
:
y = –38.4 – 1.077x R = 0.996
np of II (X, Se*) (X = S, Se)
4
2
pl of I (X, Se*) and II (Se*, X) (X = S, Se)
MeSeMe
-100
2
1
1
:
y = –42.8 – 0.875x R = 0.996
np of I (X, Se*) and II (Se*, X) (X = S, Se)
1
1
2
FC
TL
1
-
300
-200
JTL(Se, C)calcd/Hz
shown by a figure. Consequently, JFC actually reproduce
J(Se, C)obsd, where the sign of J is negative. The J
1
1
1
1
FC
PSO
1
1
values of ¹30 to ¹70 Hz are predicted for I and II. This shows
Figure 9. Plots of J(Se, C)obsd versus JTL(Se, C)calcd for
I and II.
1
that the magnitudes of J(Se, C)
are governed mainly by the
obsd
exited triplet states but less by the exited singlet states in I and
1
II. It is worthwhile to comment that J
are proportional to
PSO
the optimized structures given in Table 6. The total values
the corresponding Se­C distances: A good linear correlation is
1
1
1
(
J (Se, C)), often denoted by J , were evaluated separated
obtained between J and the corresponding Se­C distances.
TL
TL
TL
1
1
1
1
1
by the contributions of J , J , J , and JSD, according
What is the origin of J(Se, C) in I and II? The origin is
DSO
PSO
FC
1
1
to eq 6. The results are shown in Table 10, together with the
observed values adjusted to the model compounds. Evaluated
values for np are substantially equal to the corresponding
values for pl.
elucidated employing J , since J predominantly contribute
FC FC
1
1
to J (µ77%). J are decomposed to the contribution from
TL
FC
each ψ . Figure 10 plots the contributions from ψ ­ψ in II
i
24
49
(Se*, O), where those from ψ ­ψ are very small in total
1
23
1
The observed values ( J(Se, C)obsd) were plotted versus
JTL(Se, C)calcd, together with the data of MeSeMe. Figure 9
(¹6.8 Hz), which corresponds to those from the inner orbitals.
Therefore, they are not shown in the Figure. The contributions
spread over ψ ­ψ . Those from ψ ­ψ and ψ ­ψ are
1
shows the results. The plots are analyzed as two groups: while
2
4
49
24
38
39
49
1
1
J(Se, C) for the C ­Se bonds in II (X, Se*) with MeSeMe
¹29.9 and ¹186.9 Hz, respectively, which amount to 13 and
Me
1
1
belong to one group, J(Se, C) for the C=Se bonds in II (Se*,
X) and I (X, Se*) with MeSeMe form another group. The plots
84% of J (¹223.0 Hz). The consideration led us to select ψ40
FC
(¹140.3 Hz: 63%) and ψ45 (¹43.0 Hz: 19%) as the substantial

6
88
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
Aromatic Selenoic, Selenothioic, and Diselenoic Acid Salts
1JFC(Se,C)
/Hz
3
2
1
00
00
00
0
2
9
2
6
2
4
4
9
(
HOMO)
4
5
3
0
-100
3
8
3
2
3
6
40
n in
n
1
Figure 10. Contributions from ψ24­ψ49 to JFC(Se, C) in II
Se*, O).
(
Figure 12. Illustration of ψ58, ψ62 (HOMO), and ψ63
LUMO) in II (Se*, Se).
(
between 2s(C) and 4s(Se) of triplet states whereas ψ40 and ψ45
do the bonding phase of the ground singlet state.
1
The ¤(Se)obsd and J(Se, C)
values are well analyzed by
obsd
the calculations, separately by the contribution from each ψ
a
p
1
and the ψ ¼ ψ transition, employing σ (Se) and J . For the
i
a
FC
1
better understanding of ¤(Se)obsd and J(Se, C)obsd, the origin
is further explained qualitatively exemplified by II (Se*, Se).
The pl structure is employed for the explanation to avoid the
complexity in the np structure.
The ¤(Se)obsd values for the C=Se* and C­SeMe* moieties in
II (Se, Se) are 1787 and 770 ppm, respectively. The former is
downfield from that of the latter by over 1000 ppm. On the
p
other hand, contributions from ψ (HOMO) to σ (Se: C=Se)
6
2
p
and ψ58 (HOMO¹4) to σ (Se: C­SeMe) in II (Se, Se: pl) are
2269 and ¹789 ppm, respectively. The values are well corre-
lated to the corresponding ¤(Se)obsd. The transitions of ψ62
(LUMO) and ψ58 ¼ ψ63 (LUMO) contribute much to
σ (Se) in II (Se*, Se: pl) and II (Se, Se*: pl), respectively.
Figure 12 shows ψ58 (HOMO¹4), ψ62 (HOMO), and ψ63
(LUMO) in II (Se, Se: pl). Characters of ψ , ψ , and ψ
¹
¼
ψ
6
3
p
1
Figure 11. Contributions of the transitions to JFC(Se, C)
Hz) from (ψ40 and ψ45) to (ψ55 and ψ57) in II (Se*, O).
5
8
62
63
(
are n (Se) constructed by 4s(Se) with 4p(Se) in the CSeC
s Me
plane, n (Se) constructed by 4p(Se) perpendicular to π(C=Se),
p
ψ for the contributions. Only s-type AOs at both C and Se of
and π* extended over the whole molecule, respectively. The
contribution from 4p(Se) in ψ62 at Se(=C) seems much larger
than that in ψ58 at SeMe, whereas ψ63 is a common orbital in the
both transitions from ψ58 and ψ62. Such characters in ψ58, ψ62,
i
1
the C=Se moiety contribute to J in II (Se*, O). HOMO of
FC
1
ψ49 contributes negligibly to J in II (Se*, O), which is
FC
reasonably understood, since π(C=Se) of ψ49 does not essen-
tially contain the s-character.
p
and ψ63 lead strongly σ (Se: C=Se) more downfield than the
1
p
How do the ψ ¼ ψ transitions contribute to J in II (Se*,
case of σ (Se: C­Se ) in II (Se, Se: pl).
i
a
FC
Me
1
O)? The contributions from ψ40 and ψ45 are decomposed to
those from the ψ40 ¼ ψ and ψ ¼ ψ transitions. The contri-
On the other hand, J(Se, C)
for the C=Se moiety of
obsd
225 Hz seems not so different from that for the C­SeMe moiety
a
45
a
butions are large for ψ of ψ and ψ57 in both transitions. The
of 176 Hz in II (Se, Se: pl). The results can be understood
a
55
1
total contributions from the four transitions are ¹121.9 Hz,
based on the mechanisms for J , contributing predominantly
FC
1
1
which amounts to 55% of J in II (Se*, O). Figure 11 shows
to J (around 80%). It seems more difficult to determine clear
FC
TL
the contributions from the ψ40 ¼ ψa and ψ45 ¼ ψa transitions
with ψ of ψ and ψ . The atomic 2s(C) and 4s(Se) orbitals
differences in the contributions of the 2s(C) and 4s(Se) atomic
orbitals between the C=Se and C­SeMe moieties of the σ- and
σ*-bonds, relative to the case of π(C=Se) and π(C­SeMe). This
a
55
57
must be contained in (ψ , ψ ) and (ψ , ψ ) of II (Se*, O).
4
0
45
55
57
1
1
JFC in II (Se*, O) originates through the mixing of ψ55 and ψ57
to ψ40 and ψ , where ψ and ψ57 have the antibonding phase
must result in the rather similar J for the C=Se and C­Se
TL
Me
1
1
moieties through J . However, the ratio in the J(Se, C)
45
55
FC
obsd

T. Murai et al.
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
689
values between the C=Se and C­SeMe moieties (225 Hz/176
for about 12 h. 4-Biphenylcarboxylic acid O-methyl ester,
1-naphthalenecarboxylic acid O-methyl ester. Xylene, benzoic
acid O-methyl ester, selenium powder, and methyl iodide were
purchased from Nacalai Tesque, Inc., and used without fur-
ther purification. Lawesson’s reagent, 2-(trimethylsilyl)ethanol,
tetrabutylammonium fluoride (in THF), tetramethylammonium
fluoride tetrahydrate were purchased from Aldrich Chemical
Co., Inc., and used without further purification. Diisobutyl-
aluminum hydride (DIBAL-H) 1.0 M toluene solution, 4-phen-
ylbenzenecarboxylic acid methyl ester were purchased from
Kanto Chemical Co., Inc., and used without further purifica-
tion. Silica Gel 60 (Kanto Chemical Co., Inc.) was used for
column chromatography.
2
2
Hz = 1.28) could be imaged on the basis of the sp (Se)­sp (C)
3
2
1
and sp (Se)­sp (C) bonds for the moieties. J
utes to make the differences smaller.
also contrib-
PSO
Conclusion
In summary, we have demonstrated synthetic procedures,
molecular structures, and spectroscopic properties of aromatic
selenoic, selenothioic, and diselenoic acid salts and theo-
retically elucidated their structures. All the salts were prepared
by reacting the esters with a 2-(trimethylsilyl)ethyl group with
ammonium fluoride. The resulting NMR spectra, UV­visible
spectra and X-ray analyses suggest the importance of the reso-
nance structures with carbon­selenium double bonds. The opti-
mized structures reproduced well the observed ones, although
the interaction between the anionic species and the counter ion
would shift the observed structure from the predicted one,
Calculation Method. The structure of each compound
4
6
was optimized with the 6-311+G(3df,3pd) basis sets with the
4
7
(6D,10F) system of the Gaussian 03 program package, under
nonrelativistic conditions. Optimizations were performed at
the DFT level of the Becke three-parameter hybrid functionals
together with the crystal packing effect. The ¤(Se)
and
obsd
1
48
J(Se, C)obsd values are also analyzed employing the calculated
values. The mechanisms or the origin for the values are also
elucidated based on the MO theory through decomposing the
with the Lee­Yang­Parr correlation functional (B3LYP). The
d
p
so
t
1
σ(Se) values of σ (Se), σ (Se), σ (Se), and σ (Se) and J(Se, C)
values were calculated under nonrelativistic conditions for each
4
9
contributions separately by each molecular orbital (ψ ) and each
compound. The ADF 2010 program was employed for the
calculations. The GIAO (gauge-independent atomic orbital)
i
ψi ¼ ψa transition.
3
4b,34e,34f,50
method
was applied to evaluate σ(Se) at the DFT
Experimental
level of the BLYP (the DFT-GIAO method). The Slater-type
basis sets of quadruple zeta all electrons with four polarization
functions (QZ4Pae: 4 © 1s, 3 © 2s, 4 © 2p, 3 © 3s, 3 © 3p,
4 © 3d, 4 © 4s, 4 © 4p, 2 © 4d, and 3 © 4f for Se) were
applied for the calculations, as implemented in the ADF
General.
Melting points were determined using a
Yanagimoto melting point apparatus and are uncorrected. The
IR spectra were obtained on a JASCO FT/IR 410 spectropho-
1
tometer. The H NMR spectra were recorded on a JEOL α-400
5
1
1
(
399.7 MHz) in CDCl . Chemical shifts of protons are reported
internal basis set library. The J(Se, C) values were obtained
similarly.
3
in ¤ values referred to tetramethylsilane as an internal standard,
and the following abbreviation are used; s: singlet, d: doublet,
Crystallographic data have been deposited with The
Cambridge Crystallographic Data Center: Deposition numbers
CCDC-981073, 981075, and 981076 for compounds 8b, 14,
and 15. Copies of the data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif (or from The Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge,
CB2 1EZ, U.K.; e-mail: data_request@ccdc.cam.ac.uk).
13
t: triplet, sex: sextet, m: multiplet, br: broad. The C (100.4
MHz) NMR spectra and the 77Se (76.2 MHz) NMR spectra
77
were measured on a spectrometer JEOL α-400. The Se chem-
ical shifts are expressed in ¤ values deshielded with respect to
Me Se as an external standard. All spectra were acquired in the
2
proton-decoupled mode; generally 0.05­0.30 mmol solutions in
CDCl3 (0.4 mL) were used. UV­visible spectra were measured
on a JASCO Ubest 55. Molar extinction coefficient (¾) was
calculated by Lambert­Beer’s law as follows: A = ¾¢l¢c (A:
absorptivity, l: thickness of solutions layer [cm], c: concen-
This research was supported by MEXT, Grants-in-Aid for
Scientific Research on Innovative Areas “Stimuli-responsive
Chemical Species for the Creation of Functional Molecules.”
¹
1
tration [mol L ]). The mass spectra (MS) were taken on a
SHIMADZU GCMS QP1000 or JEOL JMS-700 (EI mode).
High-resolution mass spectrometry (HRMS) and fast atomic
bombardment mass spectrometry (FAB-MS) were taken on a
JEOL JMS-700. Elemental analyses were carried out by the
Elemental Analysis Center of Kyoto University. Gel perme-
ation chromatography (GPC) was performed on a Japan
Analytical Industry LC-908 recycling preparative GPC coupled
to an RI indicator and UV detector (256 nm).
Supporting Information
The details of synthetic procedures of all the compounds in
Tables, their characterization, X-ray analyses of compounds 8b,
14, and 15 optimized structures with all positive frequencies for
I and II are provided. This material is available electronically
on J-STAGE.
References
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1
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2
Sulfur Chemistry, ed. by A. Senning, Georg Thieme Publischers,
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water under reduced pressure (150 °C/0.3 mmHg) with stirring
(

6
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Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
Aromatic Selenoic, Selenothioic, and Diselenoic Acid Salts
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44 Observed chemical shifts should correspond to the aver-
aged values of those of rotational isomers. The rotational isomers
1
1
around Ci­C in the Ar­C (E)E moiety must be important in I and
II. Two conformational isomers will be produced in this process.
Indeed, the population must concentrate in the two minima, but
they seem essentially identical from NMR chemical shifts. There-
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2
9
3
7
3
0
cussed in relation to the temperature dependence in ¤(Se). For the
1
1
2
pointed out for heavier atoms, the perturbation would be small for
the selenium nucleus: Ref. 24.
Ar­C (E )E Me moiety, similar discussion will be applied to the
1
conformers around Ci­C . The effect from the conformers around
2
3
1
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¹1
(Se, Se: np) by 16 kJ mol . Therefore, the prediction of σ(Se)
using most stable isomers would be rationalized in I and II.
45 In the case of the ionic species, the effect from the counter
ions is important. However, σ(Se) are often predicted using the
anionic parts of the species. Indeed, the precise prediction of σ(Se)
3
2
This decomposition includes a small degree of arbitrariness
due to the dependence on coordinate origin, though it is not
7
7
detrimental to our chemical analyses and insights into Se NMR
spectroscopy.
¹
¹
3
3
The transition from occupied orbitals (ψi) to unoccupied
seems difficult for HSe and RSe , since the effect of the charge
concentration at Se on σ(Se) is very severe. However, the charge
p
orbitals (ψa) mainly contributes to σ . However, that from occupied
orbitals (ψi) to occupied orbitals (ψj) sometimes plays an important
1
2¹
must delocalize on the whole molecule in PhCE E , together with
p
38
+
role in σ . Such typical cases are detected in the β effect.
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4
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¹1
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¹1
4
9
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