Phosphinoselenothioic acids and their salts: Synthesis, characterization, and reaction with electrophiles

Article abstract of DOI:10.1021/jo050576c

Phosphinoselenothioic acid ammonium salts were synthesized in good yields by reacting phosphinoselenothioic acid S-[2-(trimethylsilyl)ethyl] esters with ammonium fluorides. Phosphinoselenothioic acid alkali metal salts were obtained as 18-crown-6 ether co

Full text of DOI:10.1021/jo050576c

Phosphinoselenothioic Acids and Their Salts: Synthesis,
Characterization, and Reaction with Electrophiles
Tsutomu Kimura, Toshiaki Murai,* Akihiro Miwa, Daisuke Kurachi,
Haruhisa Yoshikawa, and Shinzi Kato
Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193
mtoshi@cc.gifu-u.ac.jp
Received March 21, 2005
Phosphinoselenothioic acid ammonium salts were synthesized in good yields by reacting phosphi-
noselenothioic acid S-[2-(trimethylsilyl)ethyl] esters with ammonium fluorides. Phosphinosele-
nothioic acid alkali metal salts were obtained as 18-crown-6 ether complexes with high efficiency
by treating the esters with alkali metal fluorides and 18-crown-6 ether. The salts were stable under
air and soluble in water. The structures of the phosphinoselenothioic acid tetramethylammonium
salt and P-methylseleno-P-methylthiophosphonium triflate were determined by X-ray molecular
structure analyses. These salts exhibited monomeric structures, and the central phosphorus atoms
adopted tetrahedral structures. Alkylation of the ammonium salts selectively gave phosphinose-
lenothioic acid Se-alkyl esters, whereas acylation of the salts preferentially gave S-acyl products.
Protonation of the salts selectively gave the phosphinoselenothioic S-acid. The S-acid generated in
situ was reacted with R,â-unsaturated carbonyl compounds and cyclohexene oxide to give the
adducts. Molecular orbital calculations were carried out for the model compound H2P(Se)S- to
elucidate the electronic structure.
Introduction
The chemistry of phosphinic and phosphinothioic acids
and their salts I and II has been studied in great depth
(Figure 1). In contrast, much less attention has been paid
to their heavier isologues, i.e., phosphinoselenoic and
phosphinotelluroic acids and their salts III and VI, until
recently. The electronic properties of the salts III and
IV are of great interest from the viewpoint of the
chemistry of heavy-atom-containing conjugate systems.1
In addition, these salts are of great importance as key
starting materials for phosphinochalcogenoic acid esters2
FIGURE 1. Phosphinic acid salts and their heavier isologues.
and organometallic compounds containing chalcogen-
heavy atom bonds, which are used as single-source
precursors for semiconducting metal chalcogenides.3
Recently, phosphinoselenoic, phosphinodiselenoic, phos-
(3) For recent examples, see: (a) Park, J.-H.; Afzaal, M.; Helliwell,
M.; Malik, M. A.; O’Brien, P.; Raftery, J. Chem. Mater. 2003, 15, 4205.
(b) Crouch, D. J.; Hatton, P. M.; Helliwell, M.; O’Brien, P.; Raftery, J.
Dalton Trans. 2003, 2761. (c) Crouch, D. J.; O’Brien, P.; Malik, M. A.;
Skabara, P. J.; Wright, S. P. Chem. Commun. 2003, 1454. (d) Afzaal,
M.; Crouch, D.; Malik, M. A.; Motevalli, M.; O’Brien, P.; Park, J.-H. J.
Mater. Chem. 2003, 13, 639. (e) Waters, J.; Crouch, D.; Raftery, J.;
O’Brien, P. Chem. Mater. 2004, 16, 3289. (f) Afzaal, M.; Ellwood, K.;
Pickett, N. L.; O’Brien, P.; Raftery, J.; Waters, J. J. Mater. Chem. 2004,
14, 1310. (g) Afzaal, M.; Crouch, D.; Malik, M. A.; Motevalli, M.;
O’Brien, P.; Park, J.-H.; Woollins, J. D. Eur. J. Inorg. Chem. 2004,
171.
(1) (a) Bildstein, B.; Sladky, F. Phosphorus, Sulfur Silicon Relat.
Elem. 1990, 47, 341. (b) Ebert, K. H.; Cea-Olivares, R.; Garcia-
Montalvo, V.; Espinosa-Perez, G.; Estrada, M. R.; Novosad, J.; Woollins,
J. D. Z. Naturforsch., B: Chem. Sci. 1996, 51, 1145. (c) Murai, T.;
Kamoto, T.; Kato, S. J. Am. Chem. Soc. 2000, 122, 9850. (d) Niyomura,
O.; Sakai, K.; Murai, T.; Kato, S.; Yamaguchi, S.; Tamao, K. Chem.
Lett. 2001, 968. (e) Tani, K.; Murai, T.; Kato, S. J. Am. Chem. Soc.
2002, 124, 5960. (f) Hernandez-Arganis, M.; Hernandez-Ortega, S.;
Toscano, R. A.; Garcia-Montalvo, V.; Cea-Olivares, R. Chem. Commun.
2004, 310.
(2) Kimura, T.; Murai, T. J. Org. Chem. 2005, 70, 952.
10.1021/jo050576c CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/03/2005
J. Org. Chem. 2005, 70, 5611-5617
5611

Kimura et al.
TABLE 1. Synthesis of Phosphinoselenothioic Acid
Ammonium Salts
SCHEME 1
phinoselenotelluroic, and phosphinoditelluroic acid alkali
metal salts were synthesized and characterized by X-ray
molecular structure analyses.4 As phosphinoselenothioic
acids and their salts, diethylphosphinoselenothioic acid,
and sodium salt were synthesized for the first time in
1964,5 and the synthesis and properties of transition
metal complexes of the salts were reported in 1970s.6
However, there appears to have been no further progress
on the syntheses and properties of phosphinoselenothioic
acid and their salts III (E ) S).
yield
(%)c
entry
1
R
R4NF
2
1a
2a
3b
4b
1a
1d
1a
1d
Ph
Bu4NF
Bu4NF
Me4NF
Me4NF
2a
2b
2c
2d
93
94
90
92
t-Bu
Ph
t-Bu
a Phosphinoselenothioic acid S-esters 1 were reacted with
Bu4NF (1.1 equiv) in THF at 0 °C for 2 h. b Phosphinoselenothioic
acid S-esters 1 were reacted with Me4NF (1 equiv) in THF under
reflux for 1.5 h. c Isolated yields.
During our studies on phosphinoselenoic acid deriva-
tives,7 we developed an efficient synthesis of phosphi-
noselenothioic acid salts.8 We report here the details of
the synthesis, structure, spectroscopic properties, and
reactivity of phosphinoselenothioic acids and their salts.
Molecular orbital calculations for model compounds are
also reported.
TABLE 2. Synthesis of Phosphinoselenothioic Acid
Alkali Metal Salt 18-Crown-6 Ether Complexes
yield
(%)b
Results and Discussion
entry
1
R
MF
2
1
2
3
4
5
6
1d
1a
1b
1c
1d
1d
t-Bu
KF
2e
2f
94
87
92
92
94
91
Synthesis of Phosphinoselenothioic Acid Salts. To
obtain phosphinoselenothioic acid salts 2, we chose
phosphinoselenothioic acid S-[(2-trimethylsilyl)ethyl] es-
ters 1 as key precursors. The high affinity of the fluorine
atom toward the silicon atom may lead to the formation
of salts 2 with the elimination of ethylene and Me3SiF
from the esters 1 (Scheme 1).1
As expected, synthesis of phosphinoselenothioic acid
ammonium salts 2 was achieved by reacting the esters
1 with ammonium fluorides (Table 1). For example, P,P-
diphenylphosphinoselenothioic acid S-[(2-trimethylsilyl)-
ethyl] ester (1a) was reacted with Bu4NF in THF at 0 °C
for 2 h. The reaction mixture was poured onto water and
extracted with CH2Cl2. After the solvent was removed,
Et2O was added to the residue. Filtration of the resulting
precipitates gave P,P-diphenylphosphinoselenothioic acid
tetrabutylammonium salt (2a) in 93% yield (entry 1). A
similar reaction of P-tert-butyl-P-phenylphosphinosele-
nothioic acid S-ester (1d) with Bu4NF gave the corre-
sponding salt 2b in 94% yield (entry 2). The reaction of
the esters 1a and 1d with Me4NF also took place under
reflux in THF to give phosphinoselenothioic acid tetram-
Ph
RbF
RbF
RbF
RbF
CsF
2-MeOC6H4
i-Pr
t-Bu
t-Bu
2g
2h
2i
2j
a Phosphinoselenothioic acid S-esters 1 were reacted with MF
(2 equiv) and 18-crown-6 ether (1 equiv) in THF under reflux for
1.5 h. b Isolated yields.
ethylammonium salts 2c and 2d in excellent yields
(entries 3 and 4).
Next, the synthesis of alkali metal salts was examined
by reacting the esters 1 with alkali metal fluorides.
However, this reaction did not proceed at all, probably
because of the insolubility of alkali metal fluorides toward
THF. 18-Crown-6 ether was then used as an additive
(Table 2). When the ester 1d was reacted with potassium
fluoride in the presence of 1 equiv of 18-crown-6 ether,
phosphinoselenothioic acid potassium salt-18-crown-6
ether complex 2e was formed in 94% yield (entry 1). In
addition to potassium fluoride, rubidium fluoride and
cesium fluoride could be used as fluorine sources, and
phosphinoselenothioic acid rubidium and cesium salt 18-
crown-6 ether complexes 2i and 2j were obtained with
high efficiency (entries 5 and 6). The reaction of esters
with various alkyl and aryl substituents on the phospho-
rus atom 1a-d with rubidium fluoride and 18-crown-6
ether gave the corresponding rubidium salt 18-crown-6
ether complexes 2f-i in high yields (entries 2-5). The
salts 2 obtained were stable under air, and no appreciable
change was observed upon exposure to air for 1 week.
Notably, the salts 2 were soluble not only in organic
solvents such as CH2Cl2 and THF but also in water.
(4) (a) Pilkington, M. J.; Slawin, A. M. Z.; Williams, D. J.; Woollins,
J. D. Main Group Chem. 1995, 145. (b) Wang, F.; Polavarapu, P. L.;
Drabowicz, J.; Kielbasinski, P.; Potrzebowski, M. J.; Mikolajczyk, M.;
Wieczorek, M. W.; Majzner, W. W.; Lazewska, I. J. Phys. Chem. A.
2004, 108, 2072. (c) Davies, R. P.; Martinelli, M. G. Inorg. Chem. 2002,
41, 348. (d) Davies, R. P.; Martinelli, M. G.; Wheatley, A. E. H.; White,
A. J. P.; Williams, D. J. Eur. J. Inorg. Chem. 2003, 3409. (d) Davies,
R. P.; Francis, C. V.; Jurd, A. P. S.; Martinelli, M. G.; White, A. J. P.;
Williams, D. J. Inorg. Chem. 2004, 43, 4802.
(5) (a) Kuchen, W.; Knop, B. Angew. Chem. 1964, 76, 496. (b)
Kuchen, W.; Knop, B. Chem. Ber. 1966, 99, 1663.
(6) (a) Hertel, H.; Kuchen, W. Chem. Ber. 1971, 104, 1735. (b) Hertel,
H.; Kuchen, W. Chem. Ber. 1971, 104, 1740. (c) Christophliemk, P.;
Rao, V. V. K.; Tossidis, I.; Mueller, A. Chem. Ber. 1972, 105, 1736. (d)
Mueller, A.; Rao, V. V. K.; Christophliemk, P. J. Inorg. Nucl. Chem.
1972, 34, 345. (e) Esperås, S.; Husebye, S. Acta Chem. Scand. 1973,
27, 3355.
Spectroscopic Properties. The spectroscopic data for
a series of phosphinoselenothioic acid derivatives, i.e.,
phosphinoselenothioic acid S-alkyl ester 1d, tetrabuty-
lammonium salt 2b, P-methylseleno-P-methylthiophos-
phonium triflate 3, and phosphinoselenothioic acid Se-
(7) (a) Kimura, T.; Murai, T. Chem. Lett. 2004, 33, 878. (b) Kimura,
T.; Murai, T.; Mizuhata, N. Heteroat. Chem. 2005, 16, 185.
(8) Murai, T.; Kimura, T.; Miwa, A.; Kurachi, D.; Kato, S. Chem.
Lett. 2002, 914.
5612 J. Org. Chem., Vol. 70, No. 14, 2005

Phosphinoselenothioic Acids and Their Salts
TABLE 3. Selected NMR Spectroscopic Data of
Phosphinoselenothioic Acid Derivativesa
FIGURE 2. ORTEP drawing of phosphinoselenothioic acid
tetramethylammonium salt 2c with a thermal ellipsoid plot
(50% probability). Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å): P-E1, 2.110(2); P-E2, 2.042(2);
P-C1, 1.837(6); P-C2, 1.825(6). Selected bond angles and
torsion angles (deg): E1-P-E2, 116.40(9); E1-P-C1, 110.8-
(2); E1-P-C2, 107.1(2); E2-P-C1, 108.0(2); E2-P-C2, 112.0-
(3); C1-P-C2, 101.5(3); E1-P-C1-C3, 2.5(5); E2-P-C2-
C4, 7.7(6).
a Measured in CDCl3.
SCHEME 2
methyl ester Se-4b, are listed in Table 3. Phosphonium
salt 3 was prepared by alkylation of phosphinosele-
nothioic acid Se-methyl ester Se-4b with methyl triflate
(Scheme 2). In the 31P NMR spectra, the signals of the
esters 1d and Se-4b were observed at 86.1 and 88.3 ppm,
respectively. On the other hand, the signal of the am-
monium salt 2b was observed at a higher field than those
of the esters 1d and Se-4b by about 12 ppm. The signal
of the phosphonium salts 3 was shifted downfield by
about 10 ppm compared to those of the esters 1d and
Se-4b. In the 77Se NMR spectra, the signal of the salt
2b (-125.0 ppm) was observed midway between those
of S-ester 1d (-311.5 ppm) and Se-ester Se-4b (108.2
ppm). The signal of the phosphonium salt 3 (3.2 ppm)
was close to that of Se-ester Se-4b rather than that of
S-ester 1d. Coupling constants between the phosphorus
atom and selenium atom of the phosphinoselenothioic
acid derivatives decreased in the order S-ester 1d to
ammonium salt 2b, phosphonium salt 3, and Se-ester Se-
4b, and that of the ammonium salt 2b was closer to that
of S-ester 1d rather than that of Se-ester Se-4b. These
results suggested that the phosphorus-selenium bond
in the ammonium salt 2b possesses a double-bond
character to some extent.
Structures. The molecular structures of phosphinose-
lenothioic acid tetramethylammonium salt 2c and P-
methylseleno-P-methylthiophosphonium triflate 3 were
determined by X-ray molecular structure analyses (Fig-
ures 2 and 3). The position of the sulfur and selenium
atoms in 2c and 3 could not be determined because they
were disordered. The selenium or sulfur atom appears
at positions E1 or E2 as shown in Figures 2 and 3. These
molecules adopted a monomeric structure in the solid
state with a tetrahedral geometry about the phosphorus
atom, and no intermolecular interactions were observed.
In the ammonium salt 2c, each benzene ring was almost
coplanar with respect to the plane of the P-E group [E1-
P-C1-C3 ) 2.5(5)°, E2-P-C2-C4 ) 7.7(6)°]. There was
no interaction between the ammonium cation and the two
FIGURE 3. ORTEP drawing of P-methylseleno-P-methylth-
iophosphonium triflate 3 with a thermal ellipsoid plot (50%
probability). Two independent molecules were present in one
asymmetric unit, and one of them is shown. Triflate anion and
hydrogen atoms are omitted for clarity. Selected bond lengths
(Å): P-E1, 2.198(1); P-E2, 2.106(1); P-C1, 1.853(4); P-C2,
1.795(4); E1-C3, 1.901(5); E2-C4, 1.864(5). Selected bond
angles and torsion angles (deg): E1-P-E2, 112.76(5); E1-
P-C1, 112.8(1); E1-P-C2, 103.9(1); E2-P-C1, 105.4(1); E2-
P-C2, 112.5(1); C1-P-C2, 109.6(2); P-E1-C3, 100.6(2);
P-E2-C4, 98.9(2); C1-P-E2-C4, 178.0(2); C2-P-E1-C3,
-161.0(2).
chalcogen atoms of the phosphinoselenoylthio group.
Similarly, no interaction was observed for the triflate
anion and the phosphorus atom in 3.
Reaction with Electrophiles. Initially, phosphinose-
lenothioic acid ammonium salts 2 were reacted with alkyl
halides (Table 4). When the tetrabutylammonium salts
2a and 2b were treated with methyl iodide in THF,
phosphinoselenothioic acid Se-methyl esters Se-4a and
Se-4b were obtained in high yields (entries 1 and 2).
Phosphinoselenothioic acid S-methyl esters S-4a and
S-4b were not observed at all. Similarly, the reaction of
tetramethylammonium salt 2d with methyl iodide selec-
tively gave Se-methyl ester Se-4b in 93% yield (entry 3),
although the reaction of the salt 2a with methyl triflate
gave a mixture of phosphinoselenothioic acid S-ester S-4a
and Se-ester Se-4a in a ratio of 10:90 (entry 4). In the
reaction of the salt 2a with allyl bromide, phosphinose-
lenothioic acid Se-allyl ester Se-4c was formed with high
selectivity (entry 5).
J. Org. Chem, Vol. 70, No. 14, 2005 5613

Kimura et al.
TABLE 4. Reaction of Phosphinoselenothioic Acid Salts
with Alkyl Halidesa
yield
(%)b
entry
2
R
R′
R′′X
S-4/Se-4
ratio
1
2
3
4
5
2a Ph Bu MeI
2b t-Bu Bu MeI
2d t-Bu Me MeI
S-4a/Se-4a <1:>99 99
S-4b/Se-4b <1:>99 91
S-4b/Se-4b <1:>99 93
FIGURE 4. ORTEP drawing of Ph2P(Se)SC(O)C6H4Cl-4 S-5e
with thermal ellipsoid plot (50% probability). Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å): P-Se, 2.086-
(2); P-S, 2.150(2); P-C1, 1.821(6); P-C2, 1.815(6); S-C3,
1.829(6); C3-O, 1.217(7); O‚‚‚P, 3.05. Selected bond angles and
torsion angles (deg): Se-P-S, 117.02(8); Se-P-C1, 115.1-
(2); Se-P-C2, 113.9(2); S-P-C1, 95.1(2); S-P-C2, 107.6(2);
C1-P-C2, 106.1(3); P-S-C3, 106.1(3); S-C3-O, 121.7(4); O‚
‚‚P-C2, 152.4; Se-P-S-C3, -68.5(2); P-S-C3-O, 0.3(5);
O-C3-C4-C5, 1.4(9).
2a Ph Bu MeOTf
S-4a/Se-4a 10:90
99
2a Ph Bu CH2dCHCH2Br S-4c/Se-4c <1:>99 88
a Phosphinoselenothioic acid ammonium salts 2 were reacted
with R′′X (1 equiv) in THF at 0 °C for 1 h. b Isolated yields.
TABLE 5. Reaction of Phosphinoselenothioic Acid Salts
with Acyl Chloridesa
SCHEME 3
yield
entry
2
R
R′C(O)Cl
PhC(O)Cl
4-MeOC6H4C(O)Cl S-5b/Se-5b 83:17 42
S-5/Se-5
ratio (%)b
Finally, protonation of the salts 2 was carried out
(Scheme 3). Although the reaction of tetramethylammo-
nium salt 2c and 2d with trifluoroacetic acid did not
proceed at all, the reaction of the salts 2c and 2d with
HCl took place smoothly to give phosphinoselenothioic
acids 6a and 6b. Isolation of P,P-diphenylphosphinose-
lenothioic acid (6a) was not successful, but P-tert-butyl-
P-phenylphosphinoselenothioic acid (6b) was isolated in
92% yield. The coupling constant between the phosphorus
atom and the selenium atom of the acid 6b was 750 Hz
and was typical for a coupling constant of a PdSe double
bond. In addition, the S-H stretching frequency of the
acid 6b was observed at 2397 cm-1. On the basis of these
results, the isolated phosphinoselenothioic acid was
assigned not as Se-acid Se-6 but rather as S-acid S-6.
To our knowledge, this is the first identification of
phosphinoselenothioic S-acid, although the generation of
Se- or S-acids has been noted.5
The acid generated in situ was reacted with electro-
philes (Scheme 4).10 When the acid 6a was reacted with
methyl vinyl ketone, phosphinoselenothioic acid S- and
Se-3-oxobutyl esters S-7 and Se-7 were obtained in a
ratio of 6:94 in 77% yield. A similar reaction of the acid
6a with ethyl propiolate gave phosphinoselenothioic acid
S- and Se-alkenyl esters S-8 and Se-8 in a ratio of 7:93.
In this reaction, Z-isomers were selectively formed. The
acid 6a underwent ring-opening of cyclohexene oxide to
give a mixture of S- and Se-(2-hydoxycyclohexyl) esters
S-9 and Se-9 in a ratio of 39:61.
1
2
3
4
5
2a Ph
2a Ph
2a Ph
2b t-Bu 4-MeC6H4C(O)Cl
2a Ph 4-ClC6H4C(O)Cl
S-5a/Se-5a 87:13 60
4-MeC6H4C(O)Cl
S-5c/Se-5c 82:18 47
S-5d/Se-5d 90:10 41
S-5e/Se-5e 85:15 67
a Phosphinoselenothioic acid ammonium salts 2 (1 mmol) were
reacted with acyl chlorides (1 equiv) at 0 °C for 1 h. b Isolated
yields.
In contrast to the reaction with alkyl and allyl halides,
acylation of the salts 2 gave products in which acyl groups
were introduced to the sulfur atom of 2 (Table 5). When
the salt 2a was treated with benzoyl chloride, a mixture
of phosphinoselenothioic anhydrosulfide S-5a and anhy-
droselenide Se-5a was obtained in a ratio of 87:13 (entry
1). A similar reaction of the salts 2 with acyl chlorides
that had electron-donating and -withdrawing groups at
the para position of the benzene ring was also carried
out (entries 2-5).9 In all cases, phosphinoselenothioic
anhydrosulfides S-5b-S-5e were preferentially formed
in moderate yields.
The structure of phosphinoselenothioic anhydrosulfide
S-5e was determined by X-ray structure analysis for the
first time (Figure 4). The phosphorus atom adopted a
tetrahedral structure. The dihedral angle of Se-P-S-
C3 was -69°, and the carbonyl group was twisted with
respect to the P(Se)S group. The 4-chlorophenyl ring was
almost coplanar with respect to the plane of the C(O)S
group. The distance between the phosphorus atom and
the oxygen atom of the carbonyl group (3.05 Å) was
shorter than the sum of their van der Waals radii (3.3
Å).
Calculation. To elucidate the electronic structure of
phosphinoselenothioic acid salts 2, geometry optimization
and molecular orbital calculations for the model com-
pound H2P(Se)S- 2′ were performed at the RHF/6-31+G-
(9) The ratio of S-5 and Se-5 was determined by 31P NMR spectra
of the crude products. In acylation, starting materials were recovered
in ca. 40% yield along with the formation of S-5 and Se-5. The reaction
at higher temperatures gave complex mixtures due to decomposition
of the desired products. The products S-5 and Se-5 were labile upon
long-term exposure to water.
(10) Only the reaction of the acid with CH2N2 has been reported to
give mixtures of S-esters and Se-esters: (a) Mastryukova, T. A.;
Michalski, J.; Uryupin, A. B.; Skrzypczynski, Z.; Kabachnik, M. I. Zh.
Obshch. Khim. 1978, 48, 463. (b) Mastryukova, T. A.; Michalski, J.;
Uryupin, A. B.; Skrzypczynski, Z.; Kabachnik, M. I. Zh. Obshch. Khim.
1978, 48, 1447.
5614 J. Org. Chem., Vol. 70, No. 14, 2005

Phosphinoselenothioic Acids and Their Salts
SCHEME 4
SCHEME 5
atom and the selenium atom, but the HOMO of 2′ was
the largest at the selenium atom.
Thus, the reaction of phosphinoselenothioic acid salts
with electrophiles is kinetically favorable at the selenium
atom compared to the sulfur atom. Indeed, alkylation of
the salts 2 selectively gave Se-alkyl esters. Nevertheless,
acylation and protonation of the salts 2 preferentially
gave phosphinoselenothioic anhydrosulfides and phos-
phinoselenothioic S-acid, respectively. The results in
Table 5 may be due to the thermodynamic stability of
the products. Indeed, the reaction of diphenylphosphi-
noselenoic chloride with potassium 4-methylbenzenecar-
bothioate gave a mixture of anhydrosulfide S-5c and
anhydroselenide Se-5c in a ratio of 83:17 (Scheme 5).
This cleanly shows that S-5c is thermodynamically more
stable than Se-5c, but their energy difference may be less
than 1 kcal/mol.
TABLE 6. RHF/6-31+G(d)-Optimized Geometries and
Atomic Charges of Model Compounds 1′-4′
bond length (Å)
atomic charge
P
model compound
P-Se
P-S
Se
S
H2P(Se)SMe
H2P(Se)S-
1′ 2.103
2′ 2.163
2.092 -0.565 0.559
0.003
2.004 -0.831 0.501 -0.670
H2P+(SeMe)(SMe) 3′ 2.201
2.056 -0.100 0.742
1.955 -0.234 0.613 -0.453
0.145
H2P(S)SeMe
4′ 2.241
Furthermore, energy calculations for the model com-
pounds Me2P(Se)SC(O)H S-5′ and Me2P(S)SeC(O)H Se-
5′ at the RHF/6-31+G(d) level indicated that the anhy-
drosulfide S-5′ was more stable than the anhydroselenide
Se-5′ by 0.9 kcal/mol (Figure 5). This value is in good
agreement with those calculated on the basis of the
results in Table 5 (0.8-1.2 kcal/mol). Similarly, energy
calculations for the model compounds H2P(Se)SH S-6′
and H2P(S)SeH Se-6′ suggested that S-acid S-6′ was
more stable than Se-acid Se-6′ by 1.8 kcal/mol.
FIGURE 5. Model compounds.
The P-Se bond lengths calculated for the model
compounds decreased in the order of 4′ to 3′, 2′, and 1′.
The P-Se bond lengths were linearly correlated with the
coupling constant between the phosphorus atom and the
selenium atom of the phosphinoselenothioic acid deriva-
tives 1d, 2b, 3, and Se-4b (Figure 7).
FIGURE 6. MOLDEN plot of HOMO calculated for H2P(Se)S-.
In summary, we have demonstrated that phosphinose-
lenothioic acid ammonium salts and alkali metal salt 18-
crown-6 ether complexes can be efficiently synthesized
by reacting phosphinoselenothioic acid S-[(2-trimethyl-
silyl)ethyl] esters with ammonium fluorides or alkali
metal fluorides and 18-crown-6 ether. X-ray structure
analysis of the phosphinoselenothioic acid ammonium
(d) level with GAUSSIAN 9811 (Figure 5). For compari-
son, geometry optimizations of H2P(Se)SMe 1′, H2P+-
(SeMe)(SMe) 3′, and H2P(S)SeMe 4′ were also carried out.
Selected bond lengths and atomic charges are listed in
Table 6. The MO plot drawn by the program MOLDEN12
is shown in Figure 6.
As a result, the negative charge on the phosphinose-
lenoylthio group in 2′ was delocalized on both the sulfur
(11) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.,
Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.;
Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian 98, revision A.7; Gaussian, Inc.; Pittsburgh,
PA, 1998.
(12) Schaftenaar, G.; Noordik, J. H. J. Comput.-Aided Mol. Des.
2000, 14, 123.
FIGURE 7. Plot of JPSe against calculated P-Se bond lengths.
J. Org. Chem, Vol. 70, No. 14, 2005 5615

Kimura et al.
added to the reaction mixture, the insoluble parts were filtered,
and the filtrate was concentrated in vacuo. To the residue was
added Et2O (5 mL), and the mixture was stirred for 10 min.
The resulting precipitates were collected by filtration to give
0.333 g (90%) of 2c as a colorless solid. mp: 165-167 °C (dec).
1H NMR: δ 3.17 (s, 12H), 7.21-7.29 (m, 6H), 8.10-8.16 (m,
4H). 13C NMR: δ 56.1, 127.4 (d, JCP ) 11.5 Hz), 129.0, 130.9
(d, JCP ) 11.6 Hz), 143.7 (d, JCP ) 69.4 Hz). 31P NMR: δ 44.3
salt showed that the salt was monomeric and the central
phosphorus atom was tetrahedral. Alkylation of the salts
selectively gave phosphinoselenothioic acid Se-esters,
whereas acylation of the salts preferentially gave phos-
phinoselenothioic anhydrosulfides. The phosphinosele-
nothioic S-acids generated by the acidolysis of the salts
showed high reactivity toward R,â-unsaturated carbonyl
compounds and an oxirane.
(JPSe ) 616.3 Hz); 77Se NMR (DMSO-d6): δ -7.0 (d, JSeP
)
646.4 Hz).
General Procedure for the Synthesis of Phosphinose-
lenothioic Acid Alkali Metal Salt 18-Crown-6 Ether
Complexes 2e-j. A Representative Procedure for the
Synthesis of P-(1,1-Dimethylethyl)-P-phenylphosphi-
noselenothioic Acid Potassium Salt 18-Crown-6 Ether
Complex (2e). To a THF suspension (5 mL) of potassium
fluoride (0.116 g, 2.0 mmol) and 18-crown-6 ether (0.264 g,
1.0 mmol) was added P-(1,1-dimethylethyl)-P-phenylphosphi-
noselenothioic acid S-[2-(trimethylsilyl)ethyl] ester (1d) (0.377
g, 1.0 mmol) at room temperature. The mixture was stirred
under reflux for 1.5 h. After THF (20 mL) was added to the
reaction mixture, the insoluble parts were filtered, and the
filtrate was concentrated in vacuo. To the residue was added
Et2O (5 mL), and the mixture was stirred for 10 min. The
resulting precipitates were collected by filtration to give 0.544
Experimental Section
General Procedures. All reactions were carried out under
an argon atmosphere. Me4NF, KF, RbF, and CsF were dried
under reduced pressure at 120 °C for 5 h. The silica gel used
in column chromatography was silica gel 60 from a commercial
supplier.
General Procedure for the Synthesis of Phosphinose-
lenothioic Acid S-[2-(Trimethylsilyl)ethyl] Esters 1. A
Representative Procedure for the Synthesis of P,P-
Diphenylphosphinoselenothioic Acid S-[2-(Trimethyl-
silyl)ethyl] Ester (1a). To a THF solution (20 mL) of
2-(trimethylsilyl)ethanethiol (0.32 mL, 2.0 mmol) was added
BuLi (1.6 mol/L hexane solution, 1.25 mL, 2.0 mmol) at 0 °C,
and the mixture was stirred at that temperature for 10 min.
P,P-Diphenylphosphinoselenoic chloride (0.599 g, 2.0 mmol)
was then added at 0 °C, and the mixture was stirred at that
temperature for 1 h. The reaction mixture was poured onto
water and extracted with Et2O (20 mL). The organic layer was
dried over MgSO4 and concentrated in vacuo. The residue was
purified by column chromatography on silica gel using n-C6H14/
Et2O as an eluent to give 0.715 g (90%) of P,P-diphenylphos-
phinoselenothioic acid S-[2-(trimethylsilyl)ethyl] ester (1a) as
1
g (94%) of 2e as a colorless solid. mp: 220-222 °C (dec). H
NMR: δ 1.21 (d, JHP ) 17.1 Hz, 9H), 3.60 (s, 24H), 7.26-7.48
(m, 3H), 8.39-8.44 (m, 2H). 13C NMR: δ 25.4 (d, JCP ) 3.3
Hz), 37.8 (d, JCP ) 44.7 Hz), 70.0, 126.1 (d, JCP ) 11.6 Hz),
128.6, 133.7 (d, JCP ) 9.9 Hz), 138.4 (d, JCP ) 56.2 Hz). 31P
NMR: δ 74.8 (JPSe ) 607.4 Hz). 77Se NMR: δ -128.4 (d, JSeP
) 607.4 Hz). Anal. Calcd for C22H38KO6PSSe: C, 45.59; H, 6.61.
Found: C, 45.31; H, 6.56.
Synthesis of P-(1,1-Dimethylethyl)-P-methylseleno-P-
methylthio-P-phenylphosphonium Trifluoromethane-
sulfonate (3). To an Et2O solution (5 mL) of P-(1,1-dimeth-
ylethyl)-P-phenylphosphinoselenothioic acid Se-methyl ester
(Se-4b) (0.291 g, 1.0 mmol) was added methyl trifluoromethane-
sulfonate (113 µL, 1.0 mmol) at 0 °C. The mixture was stirred
at that temperature for 1 h. After the solvent was removed,
the residue was recrystallized from THF/Et2O to give 0.323 g
(71%) of 3 as a colorless solid. mp: 145-147 °C (dec). 1H
NMR: δ 1.40 (d, JHP ) 21.0 Hz, 9H), 2.55 (d, JHP ) 14.6 Hz,
3H), 2.57 (d, JHP ) 13.2 Hz, 3H), 7.75-7.91 (m, 5H). 13C
NMR: δ 9.2 (d, JCP ) 4.1 Hz), 14.9 (d, JCP ) 5.0 Hz), 25.7,
41.9 (d, JCP ) 29.0 Hz), 117.2 (d, JCP ) 62.9 Hz), 130.8 (d, JCP
) 12.4 Hz), 133.0 (d, JCP ) 9.1 Hz), 135.8 (d, JCP ) 3.3 Hz).
31P NMR: δ 97.6 (JPSe ) 491.5 Hz). 77Se NMR: δ 3.2 (d, JSeP
) 491.5 Hz). Anal. Calcd for C13H20F3O3PS2Se: C, 34.29; H,
4.43. Found: C, 34.12; H, 4.15.
General Procedure for the Reaction of Phosphinose-
lenothioic Acid Salts 2 with Alkyl Halides. A Represen-
tative Procedure for the Reaction of P,P-Diphenylphos-
phinoselenothioic Acid N,N,N-Tributylbutanaminium
Salt (2a) with Methyl Trifluoromethanesulfonate. To a
THF solution (5 mL) of P,P-diphenylphosphinoselenothioic acid
N,N,N-tributylbutanaminium salt (2a) (0.539 g, 1.0 mmol) was
added methyl trifluoromethanesulfonate (113 µL, 1.0 mmol)
at 0 °C, and the mixture was stirred at that temperature for
1 h. The reaction mixture was poured onto water and extracted
with Et2O (50 mL). The organic layer was dried over MgSO4,
filtered, and concentrated in vacuo. The residue was purified
by column chromatography on silica gel using n-C6H14/Et2O
as an eluent to give 0.308 g (99%) of a mixture of P,P-
diphenylphosphinoselenothioic acid S-methyl ester (S-4a) and
P,P-diphenylphosphinoselenothioic acid Se-methyl ester (Se-
4a) in a ratio of 10:90 as a colorless oil. S-4a: 31P NMR: δ
58.0 (JPSe ) 780.2 Hz). 77Se NMR: δ -225.6 (d, JSeP ) 780.2
Hz). Se-4a: A colorless oil. 1H NMR: δ 2.22 (d, JHP ) 18.0
Hz, 3H), 7.24-7.51 (m, 6H), 7.90-7.96 (m, 4H). 13C NMR: δ
7.4, 128.7 (d, JCP ) 12.4 Hz), 131.5 (d, JCP ) 3.3 Hz), 131.9 (d,
JCP ) 11.6 Hz), 134.3 (d, JCP ) 80.3 Hz). 31P NMR: δ 53.9
1
a colorless solid. mp: 65-67 °C (dec). H NMR: δ -0.03 (s,
9H), 0.87-0.93 (m, 2H), 2.89-3.00 (m, 2H), 7.40-7.49 (m, 6H),
7.89-7.96 (m, 4H). 13C NMR: δ -1.7, 18.6 (d, JCP ) 5.0 Hz),
30.6, 128.5 (d, JCP ) 13.2 Hz), 131.8 (d, JCP ) 3.3 Hz), 131.8
(d, JCP ) 11.6 Hz), 133.9 (d, JCP ) 76.1 Hz). 31P NMR: δ 54.0
(JPSe ) 774.2 Hz). 77Se NMR: δ -217.9 (d, JSeP ) 774.2 Hz).
MS (EI) m/z: 398 (M+). Anal. Calcd for C17H23PSSeSi: C,
51.37; H, 5.83. Found: C, 51.62; H, 5.88.
General Procedure for the Synthesis of Phosphinose-
lenothioic Acid N,N,N-Tributylbutanaminium Salts 2a
and 2b. A Representative Procedure for the Synthesis
of P,P-Diphenylphosphinoselenothioic Acid N,N,N-Tribu-
tylbutanaminium Salt (2a). To a THF solution (10 mL) of
P,P-diphenylphosphinoselenothioic acid S-[2-(trimethylsilyl)-
ethyl] ester (1a) (0.397 g, 1.0 mmol) was added Bu4NF (1.0
mol/L THF solution, 1.1 mL, 1.1 mmol) at 0 °C. The mixture
was stirred at that temperature for 2 h. The reaction mixture
was extracted with CH2Cl2 (50 mL), and the organic layer was
washed with water (50 mL × 3). The organic layer was dried
over MgSO4, filtered, and concentrated in vacuo. To the residue
was added Et2O (5 mL), and the mixture was stirred for 10
min. The resulting precipitates were collected by filtration to
give 0.499 g (93%) of 2a as a colorless solid. mp: 78-80 °C
(dec). 1H NMR: δ 0.94 (t, J ) 7.3 Hz, 12H), 1.30-1.39 (m,
8H), 1.52-1.59 (m, 8H), 3.20-3.23 (m, 8H), 7.18-7.27 (m, 6H),
8.15-8.21 (m, 4H). 13C NMR: δ 13.7, 19.7, 24.1, 58.7, 127.0
(d, JCP ) 11.6 Hz), 128.5 (d, JCP ) 3.3 Hz), 131.0 (d, JCP
)
)
11.6 Hz), 144.2 (d, JCP ) 66.2 Hz). 31P NMR: δ 44.8 (JPSe
631.5 Hz). 77Se NMR: δ -5.2 (d, JSeP ) 631.5 Hz). Anal. Calcd
for C28H46NPSSe: C, 62.43; H, 8.61. Found: C, 62.16; H, 8.86.
General Procedure for the Synthesis of Phosphinose-
lenothioic Acid N,N,N-Trimethylmethanaminium Salts
2c and 2d. A Representative Procedure for the Synthesis
of P,P-Diphenylphosphinoselenothioic Acid N,N,N-Tri-
methylmethanaminium Salt (2c). To a THF suspension (10
mL) of Me4NF (0.093 g, 1.0 mmol) was added P,P-diphe-
nylphosphinoselenothioic acid S-[2-(trimethylsilyl)ethyl] ester
(1a) (0.397 g, 1.0 mmol) at room temperature. The mixture
was stirred under reflux for 1.5 h. After THF (40 mL) was
5616 J. Org. Chem., Vol. 70, No. 14, 2005

Phosphinoselenothioic Acids and Their Salts
(JPSe ) 359.5 Hz). 77Se NMR: δ 209.3 (d, JSeP ) 359.5 Hz).
MS (EI) m/z: 312 (M+). Anal. Calcd for C13H13PSSe: C, 50.17;
H, 4.21. Found: C, 50.03; H, 4.03.
of P-(1,1-dimethylethyl)-P-phenylphosphinoselenothioic acid
N,N,N-trimethylmethanaminium salt (2d) (0.350 g, 1.0 mmol)
was added hydrogen chloride (1.0 mol/L Et2O solution, 1.0 mL,
1.0 mmol) at 0 °C. The mixture was stirred at that temperature
for 10 min. The insoluble parts were filtered. Removal of the
solvent from the filtrate under reduced pressure gave 0.255 g
(92%) of S-6b as a pale-yellow solid. mp: 58-60 °C (dec); IR
General Procedure for the Reaction of Phosphino-
selenothioic Acid Salts 2 with Acyl Chlorides. A Repre-
sentative Procedure for the Reaction of P,P-Diphenyl-
phosphinoselenothioic Acid N,N,N-Tributylbutanamin-
ium Salt (2a) with 4-Chlorobenzoyl Chloride. To a CH2-
Cl2 solution (5 mL) of P,P-diphenylphosphinoselenothioic acid
N,N,N-tributylbutanaminium salt (2a) (0.539 g, 1.0 mmol) was
added a CH2Cl2 solution (5 mL) of 4-chlorobenzoyl chloride
(0.263 g, 1.5 mmol) at 0 °C, and the mixture was stirred at
that temperature for 1 h. The reaction mixture was poured
onto water and extracted with CH2Cl2 (50 mL). The organic
layer was dried over MgSO4, filtered, and concentrated in
vacuo. The residue was recrystallized from CH2Cl2/hexane to
give 0.292 g (67%) of a mixture of 4-chlorobenzenecarbothioic
acid (anhydrosulfide) with phosphinoselenothioic acid (S-5e)
and 4-chlorobenzenecarboselenoic acid (anhydroselenide) with
phosphinoselenothioic acid (Se-5e) in a ratio of 85:15 as a pale-
yellow solid. IR (KBr): 1677 cm-1 (CdO). 1H NMR: δ 7.40 (d,
J ) 8.6 Hz, 2H), 7.47-7.54 (m, 6H), 7.85 (d, J ) 8.6 Hz, 2H),
7.99-8.05 (m, 4H). 13C NMR: δ 128.7 (d, JCP ) 13.7 Hz), 129.2,
129.6, 131.7 (d, JCP ) 47.3 Hz), 132.1 (d, JCP ) 12.2 Hz), 132.3
(d, JCP ) 3.4 Hz), 134.6, 141.2, 185.1 (d, JCP ) 3.4 Hz). 31P
NMR: δ 48.4 (JPSe ) 799.8 Hz, S-5e), 55.3 (JPSe ) 339.8 Hz,
Se-5e). 77Se NMR: δ -151.9 (d, JSeP ) 799.8 Hz, S-5e); 685.6
(d, JSeP ) 339.8 Hz, Se-5e). MS (EI) m/z: 436 (M+). HRMS
calcd for C19H14ClOPSSe: 435.9357. Found: 435.9360.
Synthesis of P-(1,1-Dimethylethyl)-P-phenylphosphi-
noselenothioic S-Acid (S-6b). To an Et2O suspension (5 mL)
1
(KBr): 2397 cm-1 (SH). H NMR: δ 1.26 (d, JHP ) 19.5 Hz,
9H), 2.45 (s, 1H), 7.46-7.54 (m, 3H), 8.04-8.11 (m, 2H). 13C
NMR: δ 24.8, 39.1 (d, JCP ) 39.7 Hz), 128.0 (d, JCP ) 11.6
Hz), 131.0 (d, JCP ) 62.9 Hz), 131.7, 133.1 (d, JCP ) 9.9 Hz).
31P NMR: δ 74.9 (JPSe ) 749.6 Hz). 77Se NMR: δ -161.4 (d,
JSeP ) 749.6 Hz). MS (EI) m/z: 278 (M+). HRMS calcd for
C10H15PSSe: 277.9797. Found: 277.9776.
Acknowledgment. This was supported by a Grant-
in-Aid for Scientific Research on Priority Area (No.
16033224, “Reaction Control of Dynamic Complexes”)
from the Ministry of Education, Culture, Sports, Science
and Technology of Japan.
Supporting Information Available: Spectroscopic and
1
analytical data for 1, 2, 4, 5, 7-9; copies of H and 13C NMR
spectra for compounds 2b-d, 5-9; tables of crystallographic
data including atomic positional and thermal parameters for
2c, 3, and S-5e; Z matrixes of optimized structures for 1′-6′.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JO050576C
J. Org. Chem, Vol. 70, No. 14, 2005 5617