Reduction of inner sulfonium salts, thioethers, and sulfones derived from closo-[B12H12]2- by lithium in methylamine: A new route to mercaptododecaborates

Article abstract of DOI:10.1021/ic0011011

Anions [Me₂SB₁₂H₁₁]^- (2) and [MeSB₁₂H₁₁]^2- (3) can be reduced by excess lithium in methylamine at -15 °C to yield [HSB₁₂H₁₁]^2- (1) after workup. Such behavior toward this reducing system is similar to that of alkyl aryl sulfides. The sulfone [MeSO₂B₁₂H₁₁]^2- (12) also yields 1 as a major boron product upon reduction, while alkyl aryl sulfones produce the corresponding arenes under the same conditions. Similarly, isomers of (Me₂S)₂B₁₂H₁₀ (4-6) are reduced by lithium in methylamine yielding dithiols [(HS)₂B₁₂H₁₀]^2- (7-9). The tetrabutylammonium salts of 1 and 7-9 are obtained in 80-90% yields and characterized by multinuclear NMR and mass spectrometry, the latter three compounds being isolated and characterized for the first time. The reduction reaction provides access to dithiols 7-9 for biological evaluation and use in synthesis. Thus, 2 and 4-6 can be easily converted to [R₂SB₁₂H₁₁]^- and (R₂S)₂B₁₂H₁₀ in a two-step reduction-alkylation procedure. 1,2-(Bn₂S)₂B₁₂H₁₀ (13) obtained by alkylation of the reduction product of 4 by benzyl chloride was characterized by single-crystal X-ray diffraction analysis. Crystal data for 1,2-(Bn₂S)₂B₁₂H₁₀·CD₃ CN: C2/c (No. 15), a = 13.666(1) A, b = 16.978(1) A, c = 14.667(1) A, β = 91.08(1)°, Z = 4.

Full text of DOI:10.1021/ic0011011

6094
Inorg. Chem. 2000, 39, 6094-6099
Reduction of Inner Sulfonium Salts, Thioethers, and Sulfones Derived from closo-[B12H12]2-
by Lithium in Methylamine: A New Route to Mercaptododecaborates
Roman G. Kultyshev, Shengming Liu, and Sheldon G. Shore*
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
ReceiVed October 3, 2000
Anions [Me2SB12H11]- (2) and [MeSB12H11]2- (3) can be reduced by excess lithium in methylamine at -15 °C
to yield [HSB12H11]2- (1) after workup. Such behavior toward this reducing system is similar to that of alkyl aryl
sulfides. The sulfone [MeSO2B12H11]2- (12) also yields 1 as a major boron product upon reduction, while alkyl
aryl sulfones produce the corresponding arenes under the same conditions. Similarly, isomers of (Me2S)2B12H10
(4-6) are reduced by lithium in methylamine yielding dithiols [(HS)2B12H10]2- (7-9). The tetrabutylammonium
salts of 1 and 7-9 are obtained in 80-90% yields and characterized by multinuclear NMR and mass spectrometry,
the latter three compounds being isolated and characterized for the first time. The reduction reaction provides
access to dithiols 7-9 for biological evaluation and use in synthesis. Thus, 2 and 4-6 can be easily converted
to [R2SB12H11]- and (R2S)2B12H10 in a two-step reduction-alkylation procedure. 1,2-(Bn2S)2B12H10 (13) obtained
by alkylation of the reduction product of 4 by benzyl chloride was characterized by single-crystal X-ray diffraction
analysis. Crystal data for 1,2-(Bn2S)2B12H10‚CD3CN: C2/c (No. 15), a ) 13.666(1) Å, b ) 16.978(1) Å,
c ) 14.667(1) Å, â ) 91.08(1)°, Z ) 4.
Introduction
(Me2S)2B12H10 (4-6),8,9 we found that they can be reduced to
the corresponding methyl thioethers by excess sodium or
potassium in liquid ammonia.10 These thioethers are stable
toward further cleavage to the corresponding thiolates and
methane, a rather surprising fact considering the behavior of
alkyl aryl sulfides, their organic counterparts.11 On the other
hand, Truce and co-workers12 reported that lithium in methy-
lamine reduces alkyl aryl sulfides to arylthiolates and alkanes,
while the corresponding sulfones are reduced to aromatic
hydrocarbons and alkylsulfinic acids (Scheme 1). Hoping to
develop a new method of synthesis of dodecaboranethiolates
as well as a method to remove a sulfur substituent from the
cage, we studied the reduction of the inner sulfonium salts of
dodecaborane and their derivatives by lithium in methylamine.
The results are reported herein.
A dodecaborate anion bearing a thiol group was first
synthesized by Muetterties and co-workers from the reaction
of [B12H12]2- with H2S.1 Since then, the product, [HSB12H11]2-
(1), also known as BSH, was found to be a promising agent for
boron neutron capture therapy (BNCT),2 which spurred the
development of new superior methods of its synthesis. Naka-
gawa and Nagai3 and Tolpin and co-workers4 used proton-
assisted nucleophilic substitution on [B12H12]2- with N-meth-
ylthiopyrrolidone and N-methylbenzothiazole-2-thione, respect-
ively, to obtain the intermediate thioethers which produced the
desired thiolate upon alkaline hydrolysis. Electrophilic substitu-
tion as a method of sulfur introduction on the cage was also
explored. Thus, Tolpin and co-workers4 showed that acetyl-
sulfenyl chloride reacts with [B12H12]2- yielding [HSB12H11]2-
,
and Brattsev and Morris5 used electrochemical oxidation of
thiourea to generate the suitable electrophile to produce
[(H2N)2CSB12H11]-, which afforded thiolate after hydrolysis.
On the other hand, dithiols received considerably less attention.
Their formation was observed in reactions of [B12H12]2- with
H2S1 and ClSC(O)CH3,4 and it was shown that they react with
5,5′-dithiobis(2-nitrobenzoic acid) to make mixed bis(disul-
fides).4 No salt of [(HS)2B12H10]2- either as a mixture of three
possible isomers (7-9) or as an individual isomer was isolated.6
Studying the basic chemistry of the inner sulfonium salts
derived from [B12H12]2-, [Me2SB12H11]- (2), and isomers of
Results and Discussion
Reduction of [MeSB12H11]2- (3) and [Me2SB12H11]- (2)
and Synthesis of Derivatives of 1. The tetramethylammonium
salt of thioether 3, prepared from sulfonium salt 2 by reaction
with NaSEt or sodium in liquid ammonia,10 is reduced to the
corresponding thiolate [SB12H11]3- by excess lithium in me-
thylamine (Scheme 2) as expected from the behavior of alkyl
aryl sulfides. Similarly, [Me3S][2] is directly reduced to the
above thiolate, apparently through the formation of intermediate
(1) Knoth, W. H.; Sauer, J. C.; England, D. C.; Hertler, W. R.; Muetterties,
E. L. J. Am. Chem. Soc. 1964, 86, 3973.
(2) Soloway, A. H.; Tjarks, W.; Barnum, B. A.; Rong, F.-G.; Barth, R.
F.; Codogni, I. M.; Wilson, J. G. Chem. ReV. 1998, 98, 1515.
(3) Nakagawa, T.; Nagai, T. Chem. Pharm. Bull. 1976, 24, 2934.
(4) Tolpin, E. I.; Wellum, G. R.; Berley, S. A. Inorg. Chem. 1978, 17,
2867.
(7) Knoth, W. H.; Sauer, J. C.; Miller, H. C.; Muetterties, E. L. J. Am.
Chem. Soc. 1964, 86, 115.
(8) Hamilton, E. J. M.; Jordan IV, G. T.; Meyers, E. A.; Shore, S. G.
Inorg. Chem. 1996, 35, 5335.
(9) Kultyshev, R. G.; Liu, J.; Meyers, E. A.; Shore, S. G. Inorg. Chem.
1999, 38, 4913.
(10) Kultyshev, R. G.; Liu, J.; Meyers, E. A.; Shore, S. G. Inorg. Chem.
2000, 39, 3333.
(11) Wardell, J. L. In The Chemistry Of The Thiol Group; Patai, S., Ed.;
Wiley: London, 1974; Part 1, pp 235-238.
(12) Truce, W. E.; Tate, D. P.; Burdge, D. N. J. Am. Chem. Soc. 1960, 82,
2872.
(5) Brattsev, V. A.; Morris, J. H. In AdVances in Neutron Capture Therapy;
Larsson, B., Crawford, J., Weinreich, R., Eds.; Elsevier: New York,
1997; Vol. II, pp 51-55.
(6) [1,10-(HS)2B10Cl8]2-, a closely related dimercaptane, was reported by
Muetterties et al.7 from the reaction of 1,10-(N2)2B10Cl8 with H2S.
10.1021/ic0011011 CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/29/2000

A New Route to Mercaptododecaborates
Inorganic Chemistry, Vol. 39, No. 26, 2000 6095
Scheme 1
Scheme 2
Scheme 3
thioether 3. Under these conditions the tetramethylammonium
and trimethylsulfonium cations are reduced as well providing
the lithium salt soluble in water and alcohols. Attempts to isolate
thiol 1 and dithiols 7-9 (see below) as their cesium salts in
good yields were unsatisfactory since they are relatively soluble
in water. Besides, Cs2[(HS)2B12H10], which was precipitated by
addition of CsCl to the aqueous acidified solution, was found
to contain some CsCl by mass spectrometry (ESI). Therefore
we used [n-Bu4N]Br for metathesis purposes. This also allowed
us to relate the integrals of the thiol protons to those of the
cation. The reduction reaction makes various derivatives,
[R2SB12H11]- and [RC(O)SB12H11]2-, easily accessible from 2.
For example, without isolation the reduction product was
alkylated by allyl bromide. The 1H NMR spectrum of the
isolated tetramethylammonium salt of [(C3H5)2SB12H11]- (10)
agreed with the one reported earlier by Gabel and co-workers.13
The isolated tetrabutylammonium salt of 1 was acylated by
benzoyl chloride yielding the corresponding S-acyl derivative
[C6H5C(O)SB12H11]2- (11), the tetramethylammonium salt of
the latter dianion being reported by the same authors.13
lithium in methylamine this sulfone yielded, unexpectedly, the
thiolate [SB12H11]3- as the main boron product instead of
[B12H12]2- (Scheme 3). The failure of the analogy in this case
might be attributed to the strength of the B(cage)-S bond. The
product of reduction was isolated as the tetramethylammonium
salt and reacted with methyl iodide, providing 2, which was
identified by its 11B{1H} NMR.8,10 Since the reduction of sulfone
12 led to the same boron product as the reduction of sulfide 3
and sulfonium salt 2, and sulfones are prepared from sulfides,
the reduction of sulfones was not pursued any further.
Reduction of Isomers of (Me2S)2B12H10 (4-6) and Alky-
lation of Products. The early failure to isolate a salt of
[(HS)2B12H10]2- was presumably due to a mixture of isomers
that formed.4 We expected that starting from a pure isomer of
(Me2S)2B12H10 (which are all available by chromatography
followed by recrystallization) one can obtain the corresponding
isomer of [(HS)2B12H10]2- through reduction by lithium in
methylamine. Indeed, reduction of each of the three isomers
followed by acidification and metathesis with [n-Bu4N]Br led
to the tetrabutylammonium salt of the corresponding dithiol in
80-90% yields; one example of these reactions is presented in
Scheme 4. In addition, all three reduction products were
alkylated by benzyl chloride in the presence of NaI as a
nucleophilic catalyst yielding the corresponding isomers of
(Bn2S)2B12H10 (13-15). Thus, isomers of (R2S)2B12H10 can be
prepared from 4-6 using the reduction by lithium in methyl-
Reduction of [MeSO2B12H11]2- (12). The boron-cage ana-
logue of the methyl phenyl sulfone was prepared by oxidation
of 3 by hydrogen peroxide in acetonitrile. Upon reduction by
(13) Gabel, D.; Moller, D.; Harfst, S.; Rosler, J.; Ketz, H. Inorg. Chem.
1993, 32, 2276.

6096 Inorganic Chemistry, Vol. 39, No. 26, 2000
Kultyshev et al.
Scheme 4
Table 1. Crystallographic Data for 1,2-(Bn2S)2B12H10‚CD3CN
(13‚CD3CN)
empirical formula
fw
space group
a, Å
b, Å
c, Å
C30H38D3NB12S2
612.55
C2/c
13.6655(10)
16.9782(10)
14.6673(10)
91.080(10)
3402.4(4)
4
â, deg
vol, Å3
Z
F (calcd), Mg m-3
cryst size, mm
temp, K
1.137
0.60 × 0.08 × 0.06
150(2)
radiation (λ, Å)
2θ limits, deg
µ, mm-1
0.71073
4.70-50.02
0.177
0.0528
0.1311
R1a [I > 2σ(I)]
wR2b (all data)
a R1 ) Σ||Fo| - |Fc||/Σ|Fo|. b wR2 ) {Σw(Fo2 - Fc2)2/Σw(Fo )2}1/2
.
2
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
1,2-(Bn2S)2B12H10‚CD3CN (13‚CD3CN)
Figure 1. The molecular structure of 1,2-(Bn2S)2B12H10‚CD3CN
showing the crystallographic numbering scheme. The solvent molecule
and hydrogen atoms are omitted for clarity.
Bond Lengths
S(1)-C(1)
S(1)-C(8)
S(1)-B(1)
B(5)-B(6)
B(5)-B(4)
B(5)-B(3)
B(4)-B(1)
1.820(3)
1.825(3)
1.906(3)
1.780(4)
1.783(4)
1.788(4)
1.760(4)
B(4)-B(3)
B(4)-B(2)
B(4)-B(6)
B(1)-B(2)
B(1)-B(6)
B(3)-B(2)
1.777(4)
1.795(4)
1.798(4)
1.751(4)
1.774(4)
1.779(4)
disulfide and further.14,15 In their attempt to isolate [(HS)2B12H10]2-
Tolpin and co-workers noticed that dithiols are similar in this
respect.4 Our results showed that the tetrabutylammonium salts
of 7-9 turned blue within 1 min after precipitation from acidic
aqueous solutions in air. The boron NMR spectra of these salts
contained extra peaks. On the other hand, the white solids
isolated under nitrogen turned blue slowly when exposed to air.
The NMR samples of the white solids in acetonitrile and DMF
showed new peaks upon standing in air and, if acidified with
HCl, produced intensely blue colored solutions. This behavior
is consistent with formation of disulfides upon oxidation by air
and their ability to generate thiol or thiyl radicals, similar to
that of 1.14
Angles
C(1)-S(1)-C(8)
C(1)-S(1)-B(1)
C(8)-S(1)-B(1)
C(2)-C(1)-S(1)
C(9)-C(8)-S(1)
B(6)-B(5)-B(4)
100.90(13) B(2)-B(4)-B(6) 108.1(2)
107.49(13) B(2)-B(1)-B(4)
61.48(17)
105.06(13) B(2)-B(1)-B(6) 111.2(2)
111.18(18) B(4)-B(1)-B(6)
61.17(17)
124.60(19)
124.6(2)
110.6(2)
60.61(17) B(4)-B(1)-S(1)
B(6)-B(1)-S(1)
B(2)-B(1)-S(1)
B(6)-B(5)-B(3) 108.1(2)
117.86(19)
B(4)-B(5)-B(3)
59.69(18) B(1)-B(6)-B(5) 106.0(2)
11B{1H} NMR Spectra of [HSB12H11]2- (1), Isomers of
[(HS)2B12H10]2- (7-9), [(C3H5)2SB12H11]- (10), and Isomers
of (Bn2S)2B12H10 (13-15). The spectra of 1 and 7-9 are very
similar to the corresponding spectra of [MeSB12H11]2- (3) and
isomers of [(MeS)2B12H10]2-, respectively, except that the
chemical shifts of the ipso-boron atoms in thiols are significantly
moved upfield, presumably, due to the lower electron-withdraw-
ing capacity of the SH substituent. Another difference is that
the spectra of 7 and 8 (both anions have C2V symmetry) look
almost identical (Figure 2), while those of 1,2- and 1,7-
[(MeS)2B12H10]2- can be distinguished easily because the signals
of B(3,6) and B(4,5,7,11) overlap in the spectrum of the former
anion.10 The assignment of the signals in all four spectra of
thiols is the same as for the corresponding spectra of the methyl
thioethers as it was shown by 11B-11B{1H} 2D COSY experi-
B(1)-B(4)-B(3) 105.9(2)
B(1)-B(4)-B(5) 106.4(2)
B(1)-B(6)-B(4)
B(5)-B(6)-B(4)
59.04(17)
59.76(17)
60.61(17)
60.00(18)
B(3)-B(4)-B(5)
B(1)-B(4)-B(2)
B(3)-B(4)-B(2)
60.31(18) B(4)-B(3)-B(2)
59.01(17) B(4)-B(3)-B(5)
59.76(18) B(2)-B(3)-B(5) 108.6(2)
B(1)-B(2)-B(3) 106.2(2)
59.79(17) B(1)-B(2)-B(4) 59.51(17)
59.63(18)
B(5)-B(4)-B(2) 108.2(2)
B(1)-B(4)-B(6)
B(3)-B(4)-B(6) 107.8(2)
B(3)-B(2)-B(4)
B(5)-B(4)-B(6)
59.63(17)
amine. 1,2-(Bn2S)2B12H10‚CD3CN (13‚CD3CN) was character-
ized by X-ray single-crystal diffraction. Tables 1 and 2 provide
the crystallographic data and selected bond lengths and angles,
respectively, for 13‚CD3CN. The molecular structure of 13
(Figure 1) is very similar to the previously reported structure
9
of 1,2-(Me2S)2B12H10 except that the sulfur-carbon bonds in
13 are 0.01-0.03 Å longer than those in 1,2-(Me2S)2B12H10.
Compound 13 possesses crystallographically imposed C2 sym-
metry in the solid state.
(14) Wellum, G. R.; Tolpin, E. I.; Soloway, A. H.; Kaczmarczyk, A. Inorg.
Chem. 1977, 16, 2120.
(15) Nagasawa, K.; Ikenishi, Y.; Nakagawa, Y. J. Organomet. Chem. 1990,
391, 139.
Oxidative Stability of Dithiols [(HS)2B12H10]2- (7-9).
Anion 1 is notorious for its tendency to undergo oxidation to

A New Route to Mercaptododecaborates
Inorganic Chemistry, Vol. 39, No. 26, 2000 6097
be seen in the spectra of 9 and 15. The methylene hydrogens in
10 and 13-15 are diastereotopic and give rise to a pair of
1
doublets in their H NMR spectra.
Conclusion
Reduction of the inner methylsulfonium salts, thioethers, and
sulfones derived from closo-[B12H12]2- by lithium in methyl-
amine produces the corresponding thiols. Thus, 1 and 7-9 can
be obtained essentially in a two-step synthesis involving
pyrolysis of BH3‚SMe2 followed by reduction of [Me3S][2] and
4-6, respectively. Even though in our hands the yield of [Me3S]-
[2] after the pyrolysis never exceeded 50%, the reaction
conditions are not optimized and the second step seems to
proceed qualitatively. This two-step procedure might have an
advantage over the previously known methods of synthesis of
1. It is certainly valuable for the synthesis of dithiols 7-9, which
are isolated in pure form and characterized for the first time,
making them available for biological evaluation and use in
synthesis. Alternatively, the reduction reaction can be used for
the synthesis of thiols in tandem with other known methods of
synthesizing inner sulfonium salts17 and thioethers18 of closo-
[B12H12]2-. Our preliminary studies have also shown that the
scope of the lithium reduction is not limited to closo-B12 system.
Figure 2. 11B{1H} NMR spectra (160.5 MHz) of [1,2-(HS)2B12H10]2-
(7) (a), [1,7-(HS)2B12H10]2- (8) (b), and [1,12-(HS)2B12H10]2- (9) (c)
in CD3CN (cation [n-Bu4N]+).
Thus, 1,10-(Me2S)2B10H8 was reduced to [1,10-(HS)2B10H8]2-
,
which was isolated as the tetrabutylammonium salt and char-
1
acterized by 11B and H NMR.19
ments for thiols 1, 7, and 8 (see the Supporting Information).
Thus, the SH substituent has nearly the same effect on the
unsubstituted boron atoms as the SMe does. Spectra of 10 and
13-15 are very similar to those of 2 and 4-6,10 respectively;
therefore we used the same assignments for their boron signals.
1H and 1H{11B} NMR Spectra of [HSB12H11]2- (1),
Isomers of [(HS)2B12H10]2- (7-9), and Isomers of (Bn2S)2-
B12H10 (13-15). Since we failed to locate any literature data
on the chemical shift of the thiol proton in 1, we were surprised
to find this signal upfield from TMS at -0.42 ppm in CD3CN
(the usual range for the aliphatic thiols is 1.2-1.6 ppm and
2.8-3.6 ppm for aromatic ones16). On the other hand, such a
low chemical shift correlates well with the observed low acidity
of dianion 1,13 which is below that of the organic thiols.
Similarly, the sulfhydryl protons of isomers of [(HS)2B12H10]2-
exhibit chemical shifts in the same region. These signals
disappear upon addition of several drops of D2O to NMR
samples and shaking because of the H-D exchange. The
chemical shift of the thiol protons in [(HS)2B12H10]2- depends
on the geometry of substitution, with the most upfield value
for the 1,12-isomer and the least upfield (but still negative) value
for the 1,2-isomer. The shielding of the thiol protons is in
agreement with the donation of the electron density from a cage
Experimental Section
General Data. [Me3S][2] and 4-6, prepared by pyrolysis of BH3‚
SMe2, were separated and purified as described earlier.9,10 BH3‚SMe2
complex with 5-10% excess dimethyl sulfide and lithium powder
(99.5%) were purchased from Aldrich Chemical Co. Methylamine was
purchased from Matheson Tri-Gas, Inc., and dried over sodium prior
to use. Chromatography was performed on Selecto silica gel (230-
430 mesh) purchased from Fisher Scientific. 11B and 1H NMR spectra
were obtained on a Bruker DRX-500 spectrometer at 160.5 and 500.1
MHz, respectively. Proton spectra were referenced to residual solvent
protons. Boron spectra were referenced externally to BF3‚OEt2 in C6D6
(δ ) 0.00 ppm). 13C NMR spectra were obtained on Bruker DRX-500
and DPX-400 spectrometers operating at 125.8 and 100.6 MHz,
respectively, and referenced to deuterated solvent peaks. The 1H NMR
data for [n-Bu4N]+ cation are only listed once for [n-Bu4N]2[1] and
omitted elsewhere. The mass spectra were recorded on the Micromass
QTOF electrospray mass spectrometer. The elemental analysis was
performed by Galbraith Laboratories, Inc.
X-ray Structure Determination. Single-crystal X-ray diffraction
data were collected on an Enraf-Nonius KappaCCD diffraction system,
which employs graphite-monochromated Mo KR radiation. A single
crystal of 1,2-(Bn2S)2B12H10‚CD3CN obtained by slow evaporation of
CD3CN from an NMR sample was mounted on the tip of a glass fiber
coated with Parabar. Data were collected at 150 K. Unit cell parameters
were obtained by indexing the peaks in the first 10 frames and refined
employing the whole data set. All frames were integrated and corrected
for Lorentz and polarization effects using DENZO.20 The structure was
solved by direct methods and refined using SHELXTL (difference
electron density calculations, full least-squares refinements).21 One
molecule of solvent, CD3CN, crystallizes with one molecule of 1,2-
to a sulfur atom, as we suggested before for [MeSB12H11]2-
,
[(MeS)2B12H10]2-, and [(MeS)(Me2S)B12H10]-.10 On the basis
of the values of the chemical shift, such donation is most
1
important in the case of 9 and least important for 7. H{11B}-
NMR spectra of the tetrabutylammonium salts of 1, 7, and 8
show the 5:1, 4:2:2, and 2:4:2 patterns, respectively, for the
boron-attached protons. The second signal of intensity 5 in the
spectrum of 1 is hidden under the triplet resulting from the
cation. The same is true for the third signal of intensity 2 in the
spectrum of 8. The third signal of intensity 2 in the spectrum
of 7 is covered by the triplet of quartets due to the cation. Two
signals of intensity 4 (one of them is an overlap of two signals)
and one of intensity 2 are found in the spectra of 13 and 14, in
agreement with their C2V symmetry. Only one B-H signal can
(17) Wright, J.; Kaczmarczyk, A. Inorg. Chem. 1973, 12, 1453.
(18) Knoth, W. H.; Sauer, J. C.; England, D. C.; Hertler, W. R.; Muetterties,
E. L. J. Am. Chem. Soc. 1964, 86, 3973.
(19) NMR data for [n-Bu4N]2[1,10-(HS)2B10H8]. 1H NMR (CD3CN): δ
0.32 (br s, 2H, SH). 1H{11B} NMR (CD3CN): δ 0.26 (br s, 8H, BH).
11B NMR (CD3CN): δ 3.6 (s, B(1,10)), -26.0 (d, JB-H ) 126 MHz,
B(2-9)).
(20) Otwinowsky, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology, Vol. 276:
Macromolecular Crystallography, part A; Carter, C. W., Jr., Sweet,
R. M., Eds.; Academic Press: New York, 1997; pp 307-326.
(21) SHELXTL (version 5.10), Bruker Analytical X-ray Systems, 1997.
(16) Silverstein, R. M.; Webster, F. X. Spectrometric Identification of
Organic Compounds; Wiley: New York, 1998; p 168.

6098 Inorganic Chemistry, Vol. 39, No. 26, 2000
Kultyshev et al.
(Bn2S)2B12H10. The solvent molecule is disordered. Its center carbon
resides on a 2-fold axis. The methyl group and nitrogen each occupy
two separate off axis sites. Each pair of sites is related by the 2-fold
axis. Occupancies of the sites are approximately 0.5.
130.2, 123.3, 56.3 (t, JC-N ) 4 Hz), 43.6. 11B NMR (CD3CN): δ -10.1
(s, B(1)), -13.5 (d, B(12)), -14.1 (d, B(7-11)), -15.5 (d, B(2-6)).
Preparation of [n-Bu4N]2[C6H5C(O)SB12H11] ([n-Bu4N]2[11]). This
compound was prepared according to the procedure of Gabel and co-
workers13 for the synthesis of [Me4N]2[11] except that [n-Bu4N]2[1]
was used as a starting material (0.4486 g, 0.681 mmol). The NMR
pure [n-Bu4N]2[11] was obtained after drying of the material precipitated
from ether under dynamic vacuum for 2 days at 80 °C (0.5195 g, 95%
Preparation of [n-Bu4N]2[HSB12H11] ([n-Bu4N]2[1]). Method A.
From [NMe4]2[MeSB12H11]. [NMe4]2[3] (0.2454 g, 0.730 mmol) was
placed in a 50 mL round-bottom flask with a 9 mm solv-seal joint
equipped with a stirbar. In a glovebox lithium powder (0.2122 g, 30.
57 mmol) was added and the flask was evacuated. Methylamine (25
mL) was condensed with liquid nitrogen, and the flask was warmed
up to -15 °C by being placed in a cold ethanol-dry ice bath. The
blue solution was stirred for 1 h at -15 ( 5 °C. Twice during this
time the solution was frozen, and the noncondensable gas was pumped
out. All volatiles were removed through a cold trap at -196 °C, and
the residue was brought into a glovebag under nitrogen and dissolved
in 30 mL of methanol to destroy excess lithium. The solvent was
removed on a flash evaporator followed by pumping on the vacuum
line through a cold trap. In the glovebag the residue was dissolved in
40 mL of distilled water, the pH was adjusted to about 1 with H2SO4
(1:1), and the solution was filtered into a 150 mL beaker. [n-Bu4N]Br
(0.6300 g, 1.956 mmol) was added to the filtrate, and the resulting
white precipitate was filtered off. It was washed with 30 mL of distilled
water followed by 30 mL of ether, scraped into a 50 mL round-bottom
flask with a 15 mm solv-seal joint, attached to the vacuum line, and
evacuated. The solid was kept under dynamic vacuum for 1.5 days at
70 °C (oil bath). The yield was 0.4068 g (81%).
1
yield). H NMR (CD3CN): δ 7.96 (dd, 2H, J ) 8.5; 1.3 Hz, C6H5),
7.45 (m, 1H, C6H5), 7.36 (m, 2H, C6H5). 13C{1H} NMR (CD3CN): δ
195.1, 142.7, 132.1, 128.9, 128.0, 59.4 (t, JC-N ) 4 Hz), 24.5, 20.4,
14.0. 11B NMR (CD3CN): δ -9.5 (s, B(1)), -14.1 (d, B(2-6)), -15.2
(d, B(7-12)).
Preparation of [NMe4]2[MeSO2B12H11] ([Me4N]2[12]). [Me3S][2]
(0.9274 g, 3.311 mmol) was converted into [Me4N]2[3] by reaction
with sodium ethanethiolate.10 The product was dissolved in 90 mL of
acetonitrile, and 0.90 mL of 30% H2O2 was added. After stirring at
room temperature for 42 h the 11B NMR spectrum of the reaction
mixture revealed that both sulfoxide and sulfone are present in an
approximately 1:1 ratio (chemical shifts -5.0 and -6.0 ppm, respec-
tively, for the ipso-boron atoms). Another portion of hydrogen peroxide
(0.45 mL) was added, and stirring was continued for an additional 27
h. At this point the sulfoxide-to-sulfone ratio was about 1:2. The third
portion of H2O2 (0.45 mL) was added, and reaction was carried on
until no sulfoxide could be detected by 11B NMR (67 h). Acetonitrile
was removed on the flash evaporator, and ether (80 mL) was added to
the oily residue in the flask. After trituration, white solid formed, which
was filtered off, washed with 30 mL of ether and 30 mL of pentane,
and dried under dynamic vacuum overnight at 95-100 °C. The yield
Method B. From [Me3S][Me2SB12H11]. [Me3S][2] (0.9075 g, 3.240
mmol) was placed in a 150 mL round-bottom flask with a 15 mm solv-
seal joint equipped with a stirbar. In the glovebox 0.5821 g (83.86
mmol) of lithium powder was added, the flask was evacuated, and 20
mL of methylamine was condensed by means of liquid nitrogen. Upon
warming up to -15 °C in the cold bath, vigorous gas evolution occurred
and the reaction mixture was cooled to -196 °C to pump out the
noncondensable gas. After stirring at -15 ( 5 °C for 30 min the mixture
was freeze-pumped again and stirred at the above temperature for
another 30 min. After removing volatiles through a cold trap, a residue
was brought into a glovebag under nitrogen and worked up similarly
to method A. [n-Bu4N]Br (2.60 g, 8.07 mmol) was used to precipitate
the dianion from acidified aqueous solution. After washing with water
and ether, the precipitate was placed into a 100 mL round-bottom flask
with a 15 mm solv-seal joint, and the flask was evacuated on the
vacuum line and kept under dynamic vacuum for 1.5 days at 60 °C;
1.9131 g of product was obtained (90% yield). The spectral charac-
teristics of the products obtained by the two methods were identical.
1H NMR (CD3CN): δ 3.09 (m, 16H, NCH2), 1.60 (m, 16H, NCH2CH2),
1.36 (tq, 16H, J ) 7.4; 7.4 Hz, NCH2CH2CH2), 0.97 (t, 24H, J ) 7.4
1
of [Me4N]2[12] from [Me3S][2] was 90% (1.0980 g). H NMR (CD3-
CN): δ 3.10 (s, 24H, NCH3), 2.55 (s, 3H, SO2CH3). 13C{1H} NMR
(CD3CN): δ 56.3 (t, JC-N ) 4 Hz), 45.7. 11B NMR (CD3CN): δ -6.0
(s, B(1)), - 14.8 (d, B(2-12)). Anal. Calcd: C, 29.36; H, 10.40; N,
7.61. Found: C, 29.55; H, 10.75; N, 7.46.
General Procedure for Preparation of [n-Bu4N]2[(HS)2B12H10].
An isomer of (Me2S)2B12H10 (0.5-2.2 mmol) was placed in a 50 or
100 mL round-bottom flask with a 9 or 15 mm solv-seal joint and a
stirbar, and lithium powder was added in the glovebox (typically the
molar ratio of borane to metal was about 1:30). The flask was evacuated,
and methylamine (20-25 mL) was condensed with liquid nitrogen.
Upon warming up to -15 °C in a cold ethanol-dry ice bath, vigorous
gas evolution took place, and the solution was frozen with liquid
nitrogen to pump out the noncondensable gas. During the 1 h period
of stirring at -15 ( 5 °C, the reaction mixture was freeze-pumped
additionally 2-3 times. After solvent removal through a cold trap, the
residue was dissolved carefully in methanol in a glovebag under
nitrogen. Most of the methanol was removed on a flash evaporator,
the residual solvent being removed on the vacuum line by pumping
through a cold trap. A white solid was dissolved in 20-30 mL of
distilled water in the glovebag, the pH of the solution was adjusted to
about 1 with H2SO4 (1:1), and the solution was filtered into a 150 mL
beaker followed by addition of solid [n-Bu4N]Br (ratio of borane to
salt about 1:2.6). The white precipitate was filtered off, washed with
30 mL of water and 30 mL of ether, placed in a 100 mL round-bottom
flask with a 15 mm solv-seal joint, and pumped on the vacuum line
with heating (70-80 °C) for 1.5-2 days. All salts have a good solubility
in methanol and acetonitrile.
1
Hz, NCH2CH2CH2CH2), -0.42 (br s, 1H, SH). H{11B} NMR (CD3-
CN): δ 1.20 (br s, 5H, BH), 0.79 (br s, 1H, BH). 11B NMR (CD3CN):
δ -8.8 (s, B(1)), -13.2 (d, JB-H ) 128 Hz, B(2-6)), -15.1 (d, JB-H
) 127 Hz, B(7-11)), -18.2 (d, JB-H ) 127 Hz, B(12)). MS (ESI):
11
calcd for C32H84N2 B12SNa, m/z ) 683.742; obsd, m/z ) 683.742 (M
+ Na)+.
Preparation of [Me4N][(C3H5)2SB12H11] ([Me4N][10]). [Me3S][2]
(0.2753 g, 0.983 mmol) was placed in a 50 mL round-bottom flask
with a 9 mm solv-seal joint and a stirbar. In the glovebox 0.2483 g
(35.8 mmol) of lithium wire (small chunks) was added, the flask was
evacuated, and 15 mL of methylamine was condensed by means of
liquid nitrogen. The reduction was carried out at -15 ( 5 °C for 30
min, the mixture being freeze-pumped twice during this time. After
solvent removal, EtOH (25 mL) was added carefully and the insoluble
residue was filtered off. When ethanol was removed from the filtrate,
acetonitrile (50 mL), water (10 mL), and 1 mL of allyl bromide were
added to the residue, and the mixture was refluxed under nitrogen for
1 h. The volatile materials were removed on a flash evaporator followed
by addition of water. Solid [Me4N]Cl was used to precipitate the anion.
The resulting solid was washed with 60 mL of ether and dried at 70
[n-Bu4N]2[1,2-(HS)2B12H10] ([n-Bu4N]2[7]). Starting from 0.1387
1
g of 4, 0.2936 g of the product was isolated (81% yield). H NMR
1
(CD3CN): δ -0.21 (br s, 2H, SH). H{11B} NMR (CD3CN): δ 1.24
(br s, 4H, BH), 1.19 (br s, 2H, BH), 0.86 (br s, 2H, BH). 11B NMR
(CD3CN): δ -8.3 (s, B(1,2)), -11.4 (d, JB-H ) 133 Hz, B(3,6)), -13.7
(d, JB-H ) 129 Hz, B(4,5,7,11)), -15.9 (d, JB-H ) 130 Hz, B(8,10)),
-17.6 (d, JB-H
) 129 Hz, B(9,12)). MS (ESI): calcd for
11
C32H84N210B2 B10S2Na, m/z ) 713.718; obsd, m/z ) 713.717 (M +
Na)+.
[n-Bu4N]2[1,7-(HS)2B12H10] ([n-Bu4N]2[8]). Starting from 0.5635
1
1
°C. Mass of the crude product was 0.2370 g (73% yield). H NMR
g of 5, 1.3316 g of the product was obtained (90% yield). H NMR
1
(CD3CN): δ 5.99-5.94 (m, 2H, CHdCH2), 5.45-5.35 (m, 4H, CHd
CH2), 3.70 (dd, 2H, J ) 13.6; 6.6 Hz, CHaHb), 3.54 (dd, 2H, J ) 13.6;
7.9 Hz, CHaHb), 3.08 (s, 12H, NCH3). 13C{1H} NMR (CD3CN): δ
(CD3CN): δ -0.38 (br s, 2H, SH). H{11B} NMR (CD3CN): δ 1.43
(br s, 2H, BH), 1.22 (br s, 4H, BH), 1.01 (br s, 2H, BH). 11B NMR
(CD3CN): δ -8.8 (s, B(1,7)), -11.5 (d, JB-H ) 132 Hz, B(2,3)), -13.3

A New Route to Mercaptododecaborates
Inorganic Chemistry, Vol. 39, No. 26, 2000 6099
(d, JB-H ) 130 Hz, B(4,6,8,11)), -15.2 (d, B(9,10)), -16.4 (d,
47.1. 11B NMR (CD2Cl2): δ -10.3 (s, B(1,2)), - 13.1 (d, B(9,12) and
11
B(5,12)). MS (ESI): calcd for C32H85N210B2 B10S2, m/z ) 691.734;
B(8,10)), -15.3 (d, JB-H ) 136 Hz, B(4,5,7,11)), -17.2 (d, JB-H )
obsd, m/z ) 691.731 (M + H)+.
135 Hz, B(3,6)). MS (ESI): calcd for C28H39 B12S2, m/z ) 571.361;
obsd, m/z ) 571.363 (M + H)+.
11
[n-Bu4N]2[1,12-(HS)2B12H10] ([n-Bu4N]2[9]). Starting from 0.4148
1
g of 6, 0.9944 g of the product was isolated (92% yield). H NMR
Preparation of 1,7-(Bn2S)2B12H10 (14). From 0.2506 g of 1,7-
(Me2S)2B12H10, 0.4052 g of 14 (75%) was isolated after chromatography
of the crude product (CH2Cl2-toluene, 1:1). The compound for
(CD3CN): δ -0.51 (br s, 2H, SH).1H{11B} NMR (CD3CN): δ 1.24
(br s, 10H, BH). 11B NMR (CD3CN): δ -10.6 (s, B(1,12)),
-13.2 (d, JB-H ) 128 Hz, B(2-11)). MS (ESI): calcd for
1
characterization was recrystallized from toluene. H NMR (CD2Cl2):
11
C32H84N210B2 B10S2Na, m/z ) 713.718; obsd, m/z ) 713.717 (M +
δ 7.31-7.26 (m, 12H, C6H5), 7.14-7.12 (m, 8H, C6H5), 4.48 (d, 4H,
Na)+.
J ) 13.7 Hz, CHaHb), 4.02 (d, 4H, J ) 13.6 Hz, CHaHb). H{11B}
1
General Procedure for Preparation of (Bn2S)2B12H10. An isomer
of (Me2S)2B12H10 (0.8-1.0 mmol) was placed in a 50 mL round-bottom
flask with a 9 mm solv-seal joint and a stirbar. In a drybox, lithium
wire cut into little pieces was added (molar ratio of borane to metal
was about 1:30). The flask was evacuated, and 10 mL of methylamine
was condensed by liquid nitrogen. Then the procedure was analogous
to the one used for the synthesis of [n-Bu4N]2[(HS)2B12H10], except
that ethanol (95%) was used to destroy excess lithium. The precipitate,
insoluble in ethanol, was filtered off and the solvent was removed on
a flash evaporator. Acetonitrile (50 mL) was added to the residue
followed by 1 mL of benzyl chloride and 0.25-0.30 g of sodium iodide,
and the resulting mixture was refluxed for 2-3.5 h under nitrogen.
The volatile materials were removed on the flash evaporator, the residue
was partitioned between CH2Cl2 and water, and the organic phase was
separated, dried with MgSO4 and filtered. After solvent removal the
crude product was chromatographed or recrystallized from an appropri-
ate solvent.
NMR (CD2Cl2): δ 1.80 (br s, 4H, BH), 1.74 (br s, 4H, BH), 1.58 (br
s, 2H, BH). 13C{1H} NMR (CD2Cl2): δ 131.8, 130.0, 129.4, 129.2,
46.9. 11B NMR (CD2Cl2): δ -9.3 (s, B(1,7)), -13.9 (d, B(9,10)), -14.7
(d, B(5,12)), -15.4 (d, B(4,6,8,11)), -16.6 (d, B(2,3)). MS (ESI): calcd
for C28H38 B12S2Na, m/z ) 593.343; obsd, m/z ) 593.346 (M + Na)+.
11
Preparation of 1,12-(Bn2S)2B12H10 (15). From 0.2638 g of 1,12-
(Me2S)2B12H10, 0.4101 g of 15 (72%) was isolated after recrystallization
1
of the crude product from acetonitrile-methanol. H NMR (CD2Cl2):
δ 7.30-7.24 (m, 12 H, C6H5), 7.12-7.10 (m, 8 H, C6H5), 4.48 (d, 4H,
1
JH-H ) 13.7 Hz, CHaHb), 4.00 (d, 4H, JH-H ) 13.7 Hz, CHaHb). H-
{11B} NMR (CD2Cl2): δ 1.73 (br s, 10H, BH). 13C{1H} NMR (CD2-
Cl2): δ 132.0, 130.0, 129.4, 129.1, 46.9. 11B NMR (CD2Cl2): δ -7.4
(s, B(1,12)), -15.4 (d, JB-H ) 137 Hz, B(2-11)). MS (ESI): calcd
for C28H38 B12S2Na, m/z ) 593.343; obsd, m/z ) 593.339 (M + Na)+.
11
Acknowledgment. This work was supported by the Petro-
leum Research Fund through Grant 31467-AC3.
Preparation of 1,2-(Bn2S)2B12H10 (13). Starting from 0.2210 g of
1,2-(Me2S)2B12H10, 0.2736 g of pure compound 13 (58%) was obtained
after recrystallization of the crude product from acetone. 1H NMR (CD2-
Cl2): δ 7.33-7.26 (m, 12H, C6H5), 7.05-7.03 (m, 8H, C6H5), 4.38 (d,
4H, J ) 13.6 Hz, CHaHb), 4.06 (d, 4H, J ) 13.6 Hz, CHaHb). 1H{11B}
NMR (CD2Cl2): δ 1.84 (br s, 4H, BH), 1.65 (br s, 2H, BH), 1.60 (br
s, 4H, BH). 13C{1H} NMR (CD2Cl2): δ 131.3, 130.2, 129.6, 129.5,
Supporting Information Available: Tables of crystallographic
data, positional parameters, bond lengths and bond angles, and
anisotropic thermal parameters and 11B-11B{1H} 2D COSY spectra.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC0011011