9850
J. Am. Chem. Soc. 2000, 122, 9850-9851
The First Example of Ammonium Selenothioates:
Isolation and Characterization
Toshiaki Murai, Takeshi Kamoto, and Shinzi Kato*
Department of Chemistry, Faculty of Engineering
Gifu UniVersity, Yanagido, Gifu 501-1193, Japan
ReceiVed February 14, 2000
ReVised Manuscript ReceiVed August 2, 2000
Dithioic acids and their salts have been extensively studied
for over 50 years.1 In contrast, their selenium counterparts, i.e.,
selenothioic acids and their salts, have been totally ignored,2 but
are nonetheless fundamentally important classes of compounds
not only for the syntheses of a variety of selenothioates but also
for probing the electronic properties of heavy atom-containing
conjugate ions.3,4 Our recent studies in the area of heavy
chalcogenocarboxylic acids5a and their metal salts5b-e have
encouraged us to explore the synthesis of selenothioic acid salts,
and we report here the first successful isolation and characteriza-
tion of ammonium selenothioates.
Figure 1. ORTEP drawing of 2e. Hydrogen atoms are omitted for clarity.
The atoms Q1 and Q2 represent selenium or sulfur atom. Selected bond
lengths (Å): Q1-C1, 1.787(4); Q2-C1, 1.757(9); C1-C2, 1.486(5).
Selected bond angles (deg): Q1-C1-Q2, 126.4(2); Q1-C1-C2,
117.1(3), Q2-C1-C2 116.5(3).
Scheme 1
Selenothioic acid S-2-trimethylsilylethyl esters 16 were chosen
as a precursor of ammonium selenothioates. The high affinity of
a fluorine atom toward a silicon atom enabled us to obtain
ammonium salts 2 (Scheme 1). For example, the ester 1a was
treated with a THF solution of tetrabutylammonium fluoride for
3 h at 0 °C. The reaction mixture gradually turned from deep
purple to green. Upon subsequent concentration and washing of
the residue with hexane, this gave the desired ammonium
selenothioate 2a nearly quantitatively with a purity higher than
90% on the basis of NMR spectra (vide infra). To ensure the
efficient formation of ammonium selenothioate 2a, it was further
reacted with methyl iodide to give S- or Se-methyl selenothioate
3a and 4a (3a/4a ) 2/98) in 77% yield. Similar reactions of 1b-d
proceeded smoothly to form ammonium selenothioates 2b-d as
green to purple oils with high efficiency.7 The methylation of
(1) For reviews of dithioic acids and their salts, see: (a) Scheithauer, S.;
Mayer, R. In Topics in Sulfur Chemistry; Senning, A., Ed.; Georg Thieme
Publishers: Stuttgart, Germany, 1979; Vol. 4. (b) Mayer, R.; Scheithauer, S.
In Methoden der Organishen Chemie; Falbe, J., Ed.; Georg Thieme Verlag:
Stuttgart, Germany, 1985; Band E5, Teil 2, p 891. (c) Kato, S.; Murai T. In
Supplement B: The Chemistry of Acid DeriVatiVes; Patai, S., Ed.; John Wiley
& Sons: New York, 1992; Vol. 2, p 803. (d) Murai, T.; Kato, S. In
ComprehensiVe Organic Functional Group Transformations; Katritzky, A.
R., Meth-Cohn, O., Rees, C. W., Eds.; Pergamon: Oxford, U.K., 1995; Vol.
5, p 545.
(2) Very recently, Nakayama et al. have reported the formation of inner
salts involving selenothiocarboxylate and diselenocarboxylate groups; see: (a)
Nakayama, J.; Akiyama, I.; Sugihara, Y.; Nishio, T. J. Am. Chem. Soc. 1998,
120, 10027. (b) Nakayama, J.; Akiyama, I.; Sugihara, Y. Phosphorus Sulfur
and Silicon 1998, 136, 137, 138, 569.
(3) Several types of heavy atom-containing allylic anions have been
theoretically studied, see: (a) Gobbi, A.; Frenking, G. J. Am. Chem. Soc.
1994, 116, 9287. (b) Mo´, O.; Ya´nez, M.; Decouzon, M.; Gal, J.-F.; Maria,
P.-C.; Guillemin, J.-C. J. Am. Chem. Soc. 1999, 121, 4653.
(4) Increasing attention has been paid to theoretical studies on selenoic
acids and their heavy isologues; see: (a) Jemmis, E. D.; Giju, K. T.;
Leszczynski, J. J. Phys. Chem. A 1997, 101, 7389. (b) Remko, M.; Rode, B.
M. J. Phys. Chem. A. 1999, 103, 431. (c) Gonza´lez, A. I.; Mo´, O.; Ya´nez, M.
J. Phys. Chem. A. 1999, 103, 1662.
2b-d took place at their selenium atoms almost exclusively to
give esters 4 as deep blue oils in high yields. The use of
tetramethylammonium fluoride gave ammonium salts 2e-g as
green to purple solids.
The tetramethylammonium selenothioate 2e adopts a mono-
meric structure, as evidenced by X-ray crystallography,8,9 and its
molecular structure is shown in Figure 1. For 2e, two independent
molecules were present in one asymmetric unit and their average
data are shown. The selenothiocarboxyl unit in 2e has a
completely trigonal-planar geometry. The dihedral angle formed
by the selenothiocarboxyl unit and the phenyl plane is almost a
right angle (99.4(4)°).
The structure of 2 in solution was investigated by NMR
spectroscopy. The results are shown in Table 1 along with those
(5) (a) Kato, S.; Kawahara, Y.; Kageyama, H.; Yamada, R.; Niyomura,
O.; Murai, T.; Kanda, T. J. Am. Chem. Soc. 1996, 118, 1262. (b) Kawahara,
Y.; Kato, S.; Kanda, T.; Murai, T.; Ebihara, M. Bull. Chem. Soc. Jpn. 1995,
68, 3507. (c) Kato, S.; Kitaoka, N.; Niyomura, O.; Kitoh, Y.; Kanda, T.;
Ebihara, M. Inorg. Chem. 1999, 38, 496. (d) Niyomura, O.; Kato, S.; Kanda,
T. Inorg. Chem. 1999, 38, 507. (e) Kato, S.; Niyomura, O.; Nakaiida, S.;
Kawahara, Y.; Kanda, T.; Yamada, R.; Hori, S. Inorg. Chem. 1999, 38, 519
and references therein.
(6) The esters 1 were prepared according to the literature, see: (a) Murai,
T.; Ogino, Y.; Mizutani, T.; Kanda, T.; Kato, S. J. Org. Chem. 1995, 60,
2942. (b) Murai, T.; Takada, H.; Kakami, K.; Fujii, M.; Maeda, M.; Kato, S.
Tetrahedron 1997, 53, 12237.
(7) Although the ammonium selenothioates 2 were sensitive toward water
and oxygen, they were easily handled under an inert atmosphere at room
temperature.
(8) Crystal data of 2e: C12H19NSSe, FW ) 288.31, monoclinic, space group
P21/n, a ) 14.233(3) Å, b ) 9.036(5) Å, c ) 21.565(4) Å, â ) 92.92(2)°,
V ) 2769(1) Å3, Z ) 8, Dcalc ) 1.383 g‚cm-3, temperature 193 K, R ) 0.040,
Rw ) 0.034, 3671 reflections (I > 3σ(I)), 271 parameters.
(9) The position of the sulfur and selenium atoms is disordered. The
selenium or sulfur atom appeared at the position [Q(1)] or at the position
[Q(2)] shown in Figure 1. The occupancy of the selenium atom is 0.8 in [Q(1)]
and 0.2 in [Q(2)], respectively, and the reverse results are obtained for the
sulfur atom.
10.1021/ja000530v CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/22/2000