Five-membered arsenic-sulfur-nitrogen heterocycles, RAs(S2N 2) (R = Me, Et, iPr, tBu, Ph, Mes)

Article abstract of DOI:10.1021/ic1000107

A series of 5-alkyl/aryl-1,3λ⁴δ²,2,4,5- dithiadiazarsoles RAs(S₂N₂) (R = Me, Et, ⁱPr, ^tBu, Ph, Mes) were prepared by a ligand exchange between [ ⁿBu₂Sn(S₂N₂)]₂ and the corresponding organodihalogenoarsines RAsX₂ (X = Cl, I). All products were characterized by NMR, IR, and Raman spectroscopies and mass spectrometry. The crystal structures of the aryldithiadiazarsoles (R = Ph, Mes) were determined.

Full text of DOI:10.1021/ic1000107

3064 Inorg. Chem. 2010, 49, 3064–3069
DOI: 10.1021/ic1000107
Five-Membered Arsenic-Sulfur-Nitrogen Heterocycles, RAs(S2N2)
(R = Me, Et, iPr, tBu, Ph, Mes)
Vit Matuska, Alexandra M. Z. Slawin, and J. Derek Woollins*
Department of Chemistry University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, United Kingdom
Received January 3, 2010
A series of 5-alkyl/aryl-1,3λ4δ2,2,4,5-dithiadiazarsoles RAs(S2N2) (R = Me, Et, iPr, tBu, Ph, Mes) were prepared by a
ligand exchange between [nBu2Sn(S2N2)]2 and the corresponding organodihalogenoarsines RAsX2 (X = Cl, I). All
products were characterized by NMR, IR, and Raman spectroscopies and mass spectrometry. The crystal structures of
the aryldithiadiazarsoles (R = Ph, Mes) were determined.
1. Introduction
2. Experimental Section
The reaction between Me3SiNSNSiMe3 and MeAsCl2
leads to the formation of eight- or five-membered arsenic-
sulfur-nitrogen heterocycles. The outcome depends on the
stoichiometric ratio of the reactants.1,2 The eight-membered
ring can be converted into the five-membered one by reaction
with sulfur, though the yield is low (Scheme 1).1,2
While the eight-membered rings were thoroughly in-
vestigated,3-6 MeAs(S2N2) (1) has been the only known
five-membered As(S2N2) heterocycle for nearly 40 years. It
was formed in a low yield as an orange, air-sensitive, and
volatile liquid and was characterized by 1H NMR, IR, UV
spectroscopies and mass spectrometry.
Nowadays, a methodical research in this area is hindered
predominantly by complicated access to what used to be
commercially available starting materials. Here we report the
synthesis and characterization of a series of 1,3,2,4,5-dithia-
diazarsoles RAs(S2N2) (R = Me, Et (2), iPr (3), tBu (4), Ph
(5), Mes (6)). Single crystal X-ray structures of 5 and 6 were
determined and reactivity of 5 was briefly studied.
Materials. All reactions were carried out in an oxygen-free
nitrogen atmosphere using standard Schlenk and syringe tech-
niques. Dry solvents were used from the Solvent purification
system MB-SPS-800 (MBraun GmbH).
CH3I and C2H5I were purchased from Fluka, diethyl ether
solutions of iPrMgCl and tBuMgCl from Aldrich and 2-bromo-
mesitylene from Alfa-Aesar. AsCl3 was purchased from ABCR
and once used up, it was prepared according to the published
procedure.7 Phenylarsonic acid and As2O3 were obtained from
the departmental store. CH3AsI2,8 EtAsI2,8,9 iPrAsCl2,10
3,13
tBuAsCl2,11 PhAsCl2,12 and MesAsCl2
were prepared ac-
cording to published procedures. MesAsCl2 was used for further
synthesis in a crude form, that is, as a mixture of mesitylarsenic
chloride and bromide.3 Caution! Organodihalogenoarsines (esp.
PhAsCl2) are vessicants. Heavy rubber gloves should be worn
when working with these substances. Further details about the
syntheses of RAsX2 are presented in Supporting Information.
16
[nBu2Sn(S2N2)],14 Pt(COD)Cl2,15 Cp2Ti(CO)2 and Cp*Co-
(CO)217 were prepared according to literature procedures.
Instrumentation. All NMR spectra were recorded in CDCl3 at
298 K. 1H NMR spectra were recorded on a Jeol GSX spectro-
meter at the frequency of 270 MHz (compound 6 also on Bruker
*To whom correspondence should be addressed. E-mail: jdw3@
st-andrews.ac.uk. Fax: þ44.1334.463804.
(7) Pandey, S. K.; Steiner, A.; Roesky, H. W. Inorg. Synth. 1997, 31, 148–
150.
(8) Millar, I. T.; Heaney, H.; Heinekey, D. M.; Fernelius, W. C. Inorg.
Synth. 1960, 6, 113–115.
(9) McKenzie, A.; Wood, J. K. J. Chem. Soc. 1920, 117, 406–415.
(10) Dicarlo, R. L., Jr.;Shenai-Khatkhate, D. V.; Power, M. B.; Amamchyan,
A. Preparation of monoalkyl group 15 dihalides and dihydrides for use as chemical
vapor deposition precursors; Eur. Pat. Appl. No. EP1335416, 2003.
(11) Tzschach, A.; Deylig, W. Z. Anorg. Allg. Chem. 1965, 336, 36–41.
(12) Adams, E.; Jeter, D.; Cordes, A. W.; Kolis, J. W. Inorg. Chem. 1990,
29, 1500–1503.
(13) Vedejs, E.; Lee, N. J. Am. Chem. Soc. 1995, 117, 891–900.
(14) Aucott, S. M.; Slawin, A. M. Z.; Woollins, J. D. Can. J. Chem. 2002,
80, 1481–1487.
(1) Scherer, O. J.; Wies, R. Angew. Chem., Int. Ed. Engl. 1971, 10, 812–813.
(2) Scherer, O. J.; Wies, R. Angew. Chem., Int. Ed. Engl. 1972, 11, 529.
(3) Alcock, N. W.; Holt, E. M.; Kuyper, J.; Mayerle, J. J.; Street, G. B.
Inorg. Chem. 1979, 18, 2235–2239.
€
(4) (a) Gieren, A.; Betz, H.; Hubner, T.; Lamm, V.; Herberhold, M.;
Guldner, K. Z. Anorg. Allg. Chem. 1984, 513, 160–174. (b) Gieren, A.; H€ubner,
T.; Herberhold, M.; Guldner, K.; S€uss-Fink, G. Z. Anorg. Allg. Chem. 1987, 544,
ꢀ
137–148. (c) Herberhold, M.; Schamel, K.; Herrmann, G.; Gieren, A.; Ruiz-Perez,
C.; H€ubner, T. Z. Anorg. Allg. Chem. 1988, 562, 49–61. (d) Herberhold, M.;
Schamel, K. J. Organomet. Chem. 1988, 346, 13–22. (e) Herberhold, M.;
ꢀ
Guldner, K.; Gieren, A.; Ruiz-Perez, C.; H€ubner, T. Angew. Chem. 1987, 99,
81–82.
(5) Chivers, T.; Dhathathreyan, K. S.; Lensink, C.; Richardson, J. F.
Inorg. Chem. 1988, 27, 1570–1574.
(15) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem. Soc.
1976, 98, 6521–6528.
(16) Sikora, D. J.; Moriarty, K. J.; Rausch, M. D. Inorg. Synth. 1990, 28,
248–256.
(17) Frith, S. A.; Spencer, J. L. Inorg. Synth. 1990, 28, 273–280.
(6) (a) Spang, C.; Edelmann, F. T.; Noltemeyer, M.; Roesky, H. W.
Chem. Ber. 1989, 122, 1247–1254. (b) Edelmann, F.; Spang, C.; Noltemeyer, M.;
Sheldrick, G. M.; Keweloh, N.; Roesky, H. W. Z. Naturforsch. (B) 1987, 42,
1107–1109.
r
pubs.acs.org/IC
Published on Web 02/08/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 3065
Scheme 1
Table 1. Crystallographic Data for Compounds 5 and 6
5
6
empirical formula
formula weight
temperature
C6H5AsN2S2
244.16
93(2) K
yellow prism
triclinic
P1
5.046(2)
8.330(4)
10.155(6)
103.427(13)
91.802(15)
93.833(13)
413.8(4)
2
C9H11AsN2S2
286.24
93(2) K
red prism
monoclinic
P2(1)/c
14.367(6)
11.372(5)
13.911(5)
90
91.685(10)
90
2271.8(16)
8
1.674
crystal color, habit
crystal system
space group
˚
a (A)
˚
b (A)
˚
c (A)
Avance 500 at 500 MHz), with δ (ppm) referenced to external
tetramethylsilane and calibrated to the peak of residual CHCl3
(7.26 ppm).18 13C NMR spectra were recorded on a Jeol GSX
spectrometer at 67.9 MHz with δ referenced to external tetra-
methylsilane. All 13C NMR spectra are proton-decoupled. 14N
NMR spectra were recorded on Bruker Avance II 400 spectro-
meter at 28.9 MHz with δ referenced to external liquid ammonia.
Simulations of NMR spectra were performed using WIN-DAISY
module in Topspin 2.1 processing software (Bruker). IR spectra
were recorded as liquid films between CsI discs or as thin pressed
KBr discs on a Perkin-Elmer 2000 FT/IR/Raman spectrometer,
and Raman spectra were recorded in glass capillaries in the range
3500-100 cm-1 using the same spectrometer. Mass spectrometry
was performed by the University of St Andrews Mass Spectro-
metry Service, and elemental analyses were performed by the
St Andrews University School of Chemistry Service.
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
dcalc. (Mg m-3
)
1.960
4.541
240
2456
μ (mm-1
F(000)
measured reflections
)
3.322
1152
14163
4133 (0.1453)
0.0901, 0.2210
observed indt reflections (Rint
final R1, wR2 (I > 2σ(I))
˚
Largest diff. peak hole (e A
)
1367 (0.0313)
0.0477, 0.1047
0.883 and -1.042 0.854 and -0.750
-3
)
EtAs(S2N2) (2). Prepared from EtAsI2 (0.627 g, 1.75 mmol)
and [nBu2Sn(S2N2)]2 (0.572 g, 0.877 mmol) in the same way as 1
(vacuum distillation at 0.3 Torr, oil bath temperature 120 °C). 2
in the distillate was slightly contaminated with nBu2SnI2 and
was purified by silica column chromatography (25 ꢀ 1.5 cm).
The byproduct was removed by elution with hexane, and pure 2
was eluted by toluene. Removal of the solvent left 2 as an orange
oil which did not crystallize upon cooling. Yield 86 mg (25%).19
MS (CIþTOF): m/z 196.92 (100%) [MH]þ, 166.87 (65%)
[AsS2N2]þ, 149.94 (6%) [EtAsSN]þ, 136.92 (6%) [EtAsSH]þ,
117.96 (20%) [EtAsN]þ, 106.89 (13%) [AsS]þ, 104.97 (4%)
[EtAsH]þ. 1H NMR: ABX3 spin system: δ 0.99 (dd, 3H, CH3),
Cyclic voltammetry was performed using an EcoChemie
μAutolab apparatus controlled by GPES 4.2 software. The
three-electrode system consisted of a glass-embedded platinum
disk working electrode (area = 0.008 cm2), platinum wire
counter electrode, and Ag/AgCl reference electrode. Typically,
5 mM solutions of the analyte in dry CH3CN were placed in an
electrochemical cell of 10 mL capacity and were provided with
1.0 mmol of supporting electrolyte ([nBu4N][PF6]). A small
amount (0.2 mg) of solid ferrocene was added as internal
standard. The voltammograms were calibrated for the half-
wave potential of the ferrocene/ferrocenium couple E1/2 = 0 V.
Single crystal X-ray structure data were collected on Rigaku
MM007 Saturn or Mercury CCD diffractometers using Mo-
1.36 (m, 1H, H-A in CH2), 1.52 (m, 1H, H-B in CH2), JAB
=
13.42 Hz, JAX = 7.59 Hz, JBX = 7.78 Hz. 13C NMR: δ 6.5
(CH3), 32.5 (CH2). 14N NMR: δ 271.6 (AsN), 303.3 (SNS). IR
(cm-1, neat liquid between CsI discs): 1059, 931, 675, 611, 503,
370 (As(S2N2) ring vibr.); 1021 (ν C-C); 546, 522 (ν As-C).
Raman (cm-1): 1061, 932, 679, 612, 506, 367, 548, 523.
˚
KR radiation (confocal optic, λ=0.71073 A), and corrected for
i
iPrAs(S2N2) (3). PrAsCl2 (0.4 mL, 0.660 g, 3.50 mmol)
absorption (Table 1). The structures were solved by direct
methods and refined by full-matrix least-squares methods on
F2 values of all data. Refinements were performed using SHEL-
XTL (Version 6.1, Bruker-AXS, Madison WI, U.S.A., 2001).
Preparations. MeAs(S2N2) (1). MeAsI2 (370 mg, 1.08 mmol)
dissolved in CH2Cl2 (10 mL) was added dropwise at room tempera-
ture to a stirred solution of [nBu2Sn(S2N2)]2 (351 mg, 0.538 mmol)
in CH2Cl2 (10 mL). The color of the mixture changed from yellow
to orange, and no heat evolution was observed. The mixture was
gently refluxed for 3 h and after cooling to room temperature was
filtered through a sinter. The solvent was removed from the filtrate
to leave a dark red oil, which was distilled under vacuum (B14
microdistillation apparatus insulated with glass wool; 0.3 Torr, oil
bath temperature 90 °C). Pure 1 distilled as an orange/brown, air-
sensitive, volatile oil and was collected to a flask immersed in a small
acetone/dry ice cooling bath to avoid loss of the product to the
vacuum line cold trap. The distillation residue consisted of nBu2SnI2
(verified by 1H NMR) contaminated by unspecified impurities, and
was discarded. 1 did not crystallize upon cooling. Yield 54 mg
(30%). MS (EIþTOF): m/z 181.89 (18%) [M]þ, 166.87 (100%)
[AsS2N2]þ, 135.92 (8%) [MeAsSN]þ, 120.90 (10%) [AsSN]þ,
106.89 (10%) [AsS]þ, 89.94 (5%) [MeAs]þ, 74.92 (2%) [As]þ. 1H
NMR: δ 1.17 (s, 3H, CH3). 13C NMR: δ 24.5 (CH3). 14N NMR: δ
274.2 (AsN), 301.4 (SNS). IR (cm-1, neat liquid between CsI discs):
1054, 926, 677, 605, 503, 363 (As(S2N2) ring vibr.), 561 (ν As-C).
Raman (cm-1): 1057, 929, 679, 506, 562.
dissolved in CH2Cl2 (25 mL) was added dropwise at room
temperature to a stirred solution of [nBu2Sn(S2N2)]2 (1.14 g,
1.75 mmol) in CH2Cl2 (25 mL). The mixture was stirred at room
temperature overnight. The resulting cloudy orange reaction
mixture was reduced to a quarter of its original volume and was
filtered through a short glass pipet with a small Celite plug
directly onto a Bio-Beads S-X8 column (27 ꢀ 1.5 cm) soaked in
reagent grade CH2Cl2.20 Elution with CH2Cl2 (reagent grade)
n
removed impure Bu2SnCl2 as a yellowish band followed by a
broad orange band of the product. The orange fraction was
collected, reduced in volume (if necessary), and subjected twice
more to Bio-Beads size-exclusion chromatography. 3 was iso-
lated as an orange, volatile oil which did not crystallize upon
cooling. Yield 169 mg (23%). Anal. Calcd for C3H7AsS2N2: C,
17.1; H, 3.3; N, 13.3. Found: C, 16.8; H, 3.0; N, 13.3. MS
(EIþTOF): m/z 209.93 (8%) [M]þ, 166.87 (100%) [AsS2N2]þ,
120.90 (1%) [AsSN]þ, 89.93 (3%) [AsN]þ. 1H NMR: δ 0.942 (d,
3H, CH3), 0.960 (d, 3H, CH3), 1.62 (qqrt, 1H, CH), J = 7.16 Hz.
13C NMR: δ 15.1 (CH3), 15.7 (CH3), 38.2 (CH). 14N NMR: δ
272.3 (AsN), 303.4 (SNS). IR (cm-1, KBr disk): 1059, 932, 678,
(19) The microanalysis of 2 could not be performed because of technical
issues with the apparatus (the viscosity of the oil). Integrated 1H NMR
spectra of 2 can be found in high resolution in the Supporting Information.
(20) Bio-Beads tend to float, since their density is lower than that of
CH2Cl2. During the preparation of the column, the Bio-Beads/CH2Cl2 slurry
was stirred frequently to ensure good swelling of the beads. To prevent
floating of the packed column, a glass wool plug was put on top.
(18) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62,
7512–7515.

3066 Inorganic Chemistry, Vol. 49, No. 6, 2010
Matuska et al.
21
601, 505, 367 (As(S2N2) ring vibr.); 1156, 868 (ν C-C); 547 (ν
As-C). Raman (cm-1): 1060, 934, 680, 508, 367, 1158, 869, 549.
dithiadiazarsoles 1-6. [nBu2Sn(S2N2)]2 is a versatile rea-
gent,14,22 which, unlike Me3SiNSNSiMe3, is a stoichiometric
source of the [S2N2]2- ligand (eq 1).
t
tBuAs(S2N2) (4). Prepared from BuAsCl2 (400 mg, 1.97
mmol) and [nBu2Sn(S2N2)]2 (643 mg, 0.986 mmol) in the same
way as 3. 4 was obtained as an orange, volatile oil with charac-
teristic pungent onion-like odor. 4 did not crystallize at low
temperatures. Yield 88 mg (20%). Anal. Calcd for C4H9AsS2N2:
C, 21.4; H, 4.0;. Found: C, 22.0; H, 4.2 MS (EIþTOF): m/z
223.94 (5%) [M]þ, 166.86 (100%) [AsS2N2]þ, 120.90 (5%)
[AsSN]þ, 106.89 (3%) [AsS]þ, 91.95 (2%) [S2N2]þ, 57.07
1
t
(37%) [C4H9]þ. H NMR: δ 0.91 (s, 9H, Bu). 13C NMR: δ
23.3 (s, 3C, 3 ꢀ CH3), 41.4 (C-As). 14N NMR: δ 272.6 (AsN),
303.7 (SNS). IR (cm-1, KBr disk): 1060, 933, 679, 611, 507, 362
(As(S2N2) ring vibr.); 1203, 791 (ν C-C). Raman (cm-1): 1061,
935, 681, 616, 511, 366, 1204, 792, 518.
A facile cleavage of an Sn-N bond is well documented,23,24
and the reaction between Me3SnNSNSnMe3 and MeSiCl3,
which results in Si-N bond formation, indicates an easier
cleavage of an Sn-N bond. An additional driving force is
the propensity of tin to form bonds with halogens.
PhAs(S2N2) (5). PhAsCl2 (0.900 g, 4.0 mmol) dissolved in
CH2Cl2 (50 mL) was added at room temperature to a stirred
solution of [nBu2Sn(S2N2)]2 (1.32 g, 2.0 mmol) in CH2Cl2 (50
mL). The mixture was refluxed for 6 h. The solvent was
evaporated, and the residue was distilled under vacuum (0.3
Torr, oil bath temperature 110-113 °C, air condenser). The
In this work the tin reagent was allowed to react with
chloro-, bromo-, and iodoarsines with good results. The
reactions were not exothermic, proceeded smoothly under
mild conditions, and were accompanied by a color change.
The workup procedures were chosen on the basis of known
properties of the byproducts and 1. The relatively high
boiling points of nBu2SnX2 (X = Cl, Br, I) (Supporting
Information, Table S1) together with reported volatility and
thermal stability of 12 encouraged us to use vacuum distilla-
tion as means of products separation. Compounds 1 and 2
distilledprior tonBu2SnI2. 1 was obtained ingood purity, and
2 had to be purified by silica column chromatography. On the
contrary, 5 and 6 were isolated from the distillation residue
after nBu2SnCl2 had distilled off. Since compound 4 decom-
posed during vacuum distillation, we decided to make use of
the steric demand of the Pr and Bu groups and sepa-
rated both 3 and 4 by size-exclusion chromatography using
Bio-Beads. The dithiadiazarsoles 1-4 are volatile oils with a
characteristic onion-like odor. The odor of 4 is particularly
pungent. 5 and 6 were obtained as dense oils with less intense
odor. 5 solidified in a freezer overnight into a non-glassy solid
which was recrystallized from the melt. 6 crystallized at room
temperature in the course of two days, however, the quality of
the crystals was average. Attempted recrystallization from the
melt as well as gas phase diffusion of hexane into a CH2Cl2
solution of 6 did not yield well grown single crystals. We can
confirm the reported air-sensitivity of 1; however, we experi-
enced only moderate air-sensitivity of compounds 2-6. This
was exploited also in the preparative procedures, when these
compounds were purified by chromatographic methods using
not dry solvents. Nevertheless, all the title compounds should
be stored under an inert atmosphere.
n
orange distillate solidified into colorless needles of Bu2SnCl2
(verified by 1H NMR) contaminated with a small amount of an
orange oil, and was put aside. The orange/brown distillation
residue was dissolved in toluene and was added to a silica
column (25 ꢀ 2 cm). Elution with toluene separated sufficiently
n
the residual Bu2SnCl2 (at the front) from the product, which
was eluted as a yellow band. Evaporation of the solvent left an
orange oil, which solidified in a freezer overnight into a non-
glassy bulk. Repeated recrystallization from the melt led to
formation of well shaped yellow crystals of 5. The distillate
provided up to 10 mg of 5. Yield 0.568 g (51%). Mp 45-47 °C.
Anal. Calcd for C6H5AsS2N2: C, 29.5; H, 2.1; N, 11.5. Found: C,
29.6; H, 2.2; N, 10.9. MS (EIþTOF): m/z 243.90 (75%) [M]þ,
197.93 (100%) [PhAsSN]þ, 166.87 (40%) [AsS2N2]þ, 165.96
(62%) [PhAsN]þ, 106.90 (10%) [AsS]þ, 77.04 (5%) [C6H5]þ.
1H NMR: δ 7.27-7.41 (m, 5H, C6H5). 13C NMR: δ 129.2 (s, C3,
C5), 129.5 (s, C2,C6), 131.0 (C4), 146.4 (C1). 14N NMR: δ 269.2
(AsN), 304.8 (SNS). IR (cm-1, KBr disk): 1052, 932, 678, 602,
499, 361 (As(S2N2) ring vibr.); 995 (phenyl trigonal “breath-
ing”). Raman (cm-1): 1055, 931, 684, 505, 368, 999.
i
t
MesAs(S2N2) (6). Prepared from the mixture of mesitylarse-
nic chloride and bromide (1.97 g) and excess [nBu2Sn(S2N2)]2
(2.81 g, 4.32 mmol) in the same way as 5. The red/brown tarry
distillation residue was partially dissolved in a sufficiently small
amount of the mixture toluene/petroleum ether (1:4) and was
added to a silica column (27 ꢀ 2.5 cm). The same solvent system
was used as eluant. The early yellow and orange bands were dis-
carded, and the broad red band was collected. The solvents were
evaporated to leave 6 as dark red oil, which was evacuated for
1 h, then was stored under nitrogen and crystallized sponta-
neously when allowed to stand at room temperature for 2 days.
Yield 1.07 g (50%). Mp 46-48 °C. Anal. Calcd for C9H11-
AsS2N2: C, 37.8; H, 3.9; N, 9.8. Found: C, 37.3; H, 4.1; N, 9.4.
MS (EIþTOF): m/z 285.96 (65%) [M]þ, 239.98 (90%) [MesAs-
SN]þ, 208.01 (60%) [MesAsN]þ, 166.87 (35%) [AsS2N2]þ,
151.06 (85%) [MesS]þ, 119.08 (100%) [C9H11]þ. 1H NMR
(500 MHz): δ 2.25 (s, 3H, p-CH3), 2.45 (s, 6H, 2 ꢀ o-CH3),
6.82 (s, 2H, 2 ꢀ m-H). 13C NMR: δ 21.3 (p-CH3), 21.7 (s, 2 ꢀ
o-CH3), 130.5 (s, C3,C5), 140.8 (C1), 141.0 (C4), 141.9 (s, C2,
C6). 14N NMR: δ 265.9 (AsN), 309.8 (SNS). IR (cm-1, KBr
disk): 1057, 932, 681, 602, 494, 363 (As(S2N2) ring vibr.);
558 (Mes-ring “breathing”). Raman (cm-1): 1060, 932, 684,
607, 503, 369, 561.
1
The H NMR chemical shifts of RAs(S2N2) are shielded
with respect to the corresponding RAsX2 (Supporting In-
formation, Table S2). Thus, the course of the reactions could
be easily monitored. The identification of 2 and 3 was more
difficult, since their signals overlapped with the much more
intense ones of nBu2SnCl2.
A molecule of RAsX2 has a plane of symmetry and there-
fore the alkyl- and aryldihalogenoarsines give simple spectra
(Supporting Information, Table S2). The introduction of the
(21) [nBu2Sn(S2N2)]2 is an analogue of [Me2Sn(S2N2)]2 prepared by
Roesky and Wiezer (see ref 23). Both compounds form dimers in condensed
phases.
3. Results and Discussion
The ligand exchange between [nBu2Sn(S2N2)]2 and alkyl-
or aryldihalogenoarsines offers a simple synthetic route to
(22) Matuska, V.; Tersago, K.; Kilian, P.; Van Alsenoy, C.; Blockhuys,
F.; Slawin, A. M. Z.; Woollins, J. D. Eur. J. Inorg. Chem. 2009, 4483–4490.
(23) Roesky, H.; Wiezer, H. Angew. Chem., Int. Ed. Engl. 1973, 12, 674.
(24) Roesky, H. W.; Wiezer, H. Angew. Chem. 1974, 86, 130–131.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 3067
Figure 2. ORTEP32 drawing of the X-ray structure of
ellipsoids). Hydrogen atoms are omitted for clarity.
5 (50%
relatively high stability of the As(S2N2) ring, which gave base
peaks in the spectra of all the alkyldithiadiazarsoles.27 The
spectra of the aryldithiadiazarsoles 5 and 6 demonstrated the
stabilizing effect of the aromatic hydrocarbon on the mole-
cules of 5 and 6: the abundance of the molecular peaks was
more than 60% while the abundance of the As(S2N2) moiety
did not exceed 40%.
Figure 1. Simulated (A) and recorded (B) 1H NMR spectrum of EtAs-
(S2N2) (2).
(S2N2)2- moiety brings chirality to the molecules of RAs-
(S2N2), which could be observed in the NMR spectra. The 1H
NMR spectrum of 2 showed an ABX3 spin system consisting
of a doublet of doublet (CH3 group) and a more deshielded
complex multiplet (the two inequivalent protons in the CH2
group) (Figure 1). The chemical shifts and coupling constants
Irrespective of the organic residue, the vibrational spectra of
the dithiadiazarsoles 1-6 contained peaks at about 1050, 932,
680, 602, 500, and 365 cm-1. These peaks were observed in
none of the spectra of the starting materials and are most likely
due to the As(S2N2) ring vibrational modes (Supporting
Information, Tables S3-S8).28 The strong IR bands are those
at 1050, 680, 602, and 365 cm-1, the remaining peaks appear as
strong Raman lines. According to Scherer and Wies, the bands
at 1050 and 932 cm-1 are due to the NSN system.2 Further
assignment can be suggested by literature data: the stretching
frequencies of a cyclic S-N single bond are found between 780
1
are given in the Experimental Section. 3 gave a H NMR
spectrum containing two overlapping doublets (two inequi-
valent CH3 groups) and a quartet of quartet formed by
coupling of the CH signal by the two CH3 groups. The 13
C
NMR spectrum of 3 contained three signals, which is
expected for an iPr group with inequivalent CH3 groups. In
the 1H NMR spectrum of 6, the presence of a chiral center did
not result in anisochronicity of the diastereotopic ortho-Me
groups of the mesityl moiety. The spectrum was recorded at
both 270 and 500 MHz but all the proton signals appeared as
isochronic. Similarly, no anisochronicity was observed in the
13C NMR of 6.
and 670 cm
585 cm-1, and the As-S stretches in cyclic molecules and cages
range from 390 to 329 cm
-1 30,31 The deformation vibrations of
.
-1 25,26,29 The As-N stretch gives IR bands around
.
all the above-mentioned bonds are scattered over the remaining
low-frequency region. However, it should be noted that the
entire ring will most probably have its own vibrational motions,
similarly to, for example, the phenyl ring.28k,l
The X-ray structure of 5 is displayed in Figure 2. The central
motif of the molecule is the five-membered As(S2N2) ring,
All dithiadiazarsoles gave14N NMR spectra with two well-
defined peaks. The chemical shift differences (Δδ) between
these two peaks show an increasing trend from 1 to 6, that is,
with growing size of the organic group on arsenic. The Δδ
increase in the spectra of 6 with respect to 5 is particularly
noteworthy and can be explained by significant structural
differences of the two compounds as determined by X-ray
analysis. Since arsenic is a main group element and since the
14N NMR chemical shifts are similar to those measured for
Roesky’s ketone and sulfoxide,25,26 we assigned the lower
chemical shift to the arsenic-bound nitrogen and the higher
chemical shift to the SNS nitrogen.
(28) (a) Durig, J. R.; Jumper, C. F.; Willis, J. N., Jr. Appl. Spectrosc. 1971,
€
€
25, 218–225. (b) Ellermann, J.; Schossner, H.; Haag, A.; Schodel, H. J.
Organomet. Chem. 1974, 65, 33–49. (c) Revitt, D. M.; Sowerby, D. B. J. Chem.
Soc. A 1970, 1218–1222. (d) Durig, J. R.; Cheng, M.-S.; Harris, M. E.; Hizer, T. J.
J. Mol. Struct. 1989, 192, 47–62. (e) Klaboe, P. Spectrochim. Acta , Part A
1970, 26, 87–108. (f) Holmes, R. R.; Fild, M. Spectrochim. Acta , Part A 1971,
27, 1537–1547. (g) Evans, J. C.; Lo, G. Y.-S. J. Am. Chem. Soc. 1966, 88, 2118–
2122. (h) Bertie, J. E.; Sunder, S. Can. J. Chem. 1973, 51, 3344–3353. (i) Revitt,
D. M.; Sowerby, D. B. Spectrochim. Acta , Part A 1970, 26, 1581–1593.
(j) Schindlbauer, H.; Stenzenberger, H. Spectrochim. Acta , Part A 1970, 26,
1707–1712. (k) Herzberg, G. Molecular Spectra and Molecular Structure. Vol.
II, Infrared and Raman Spectra of Polyatomic Molecules; D. Van Nostrand
Company, Inc.: Princeton, NJ, 1945. (l) Whiffen, D. H. J. Chem. Soc. 1956,
1350–1356. (m) Kainz, B.; Schmidt, A. Spectrochim. Acta , Part A 1990, 46,
1361–1370.
Electron impact MS provided high quality spectra, in
which molecular peaks could be identified and fragmentation
paths followed. The m/z values and their assignments are
listed in the Experimental Section. The mass spectra suggest
(25) Tersago, K.; Van Droogenbroeck, J.; Van Alsenoy, C.; Herrebout,
W. A.; van der Veken, B. J.; Aucott, S. M.; Woollins, J. D.; Blockhuys, F.
Phys. Chem. Chem. Phys. 2004, 6, 5140–5144.
(29) (a) Nevitt, I.; Rzepa, H. S.; Woollins, J. D. Spectrochim. Acta , Part A
1989, 45, 367–369. (b) Turowski, A.; Appel, R.; Sawodny, W.; Molt, K. J. Mol.
Struct. 1978, 48, 313–323.
(26) Tersago, K.; Matuska, V.; Van Alsenoy, C.; Slawin, A. M. Z.;
Woollins, J. D.; Blockhuys, F. Dalton Trans. 2007, 4529–4535.
(27) For technical reasons chemical ionization was used for 2. The spectra
were of comparable quality with the EI spectra of the other compounds.
Thanks to the milder ionization method, 2 gave a spectrum with a [MH]þ
base peak and with the As(S2N2) fragment being the second most abundant
(65%).
(30) Davidson, G.; Phillips, S. Spectrochim. Acta , Part A 1979, 35, 141–
146.
(31) (a) Bues, W.; Somer, M.; Brockner, W. Z. Anorg. Allg. Chem. 1983,
499, 7–14. (b) Muniz-Miranda, M.; Sbrana, G.; Bonazzi, P.; Menchetti, S.; Pratesi,
G. Spectrochim. Acta , Part A 1996, 52, 1391–1401. (c) Davidson, G.; Ewer,
K. P. Spectrochim. Acta , Part A 1983, 39, 419–428.
(32) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.

3068 Inorganic Chemistry, Vol. 49, No. 6, 2010
Matuska et al.
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) of 5 and 6
5
6a
As(1)-N(1)
N(1)-S(1)
S(1)-N(2)
N(2)-S(2)
S(2)-As(1)
As(1)-C(1)
1.899(5)
1.540(5)
1.573(5)
1.671(5)
2.3028(19)
1.965(6)
1.927(7)
1.543(8)
1.563(7)
1.665(7)
2.315(3)
1.969(9)
(1.886(7))
(1.537(7))
(1.556(8))
(1.663(9))
(2.339(3))
(1.973(9))
As(1)-N(1)-S(1)
N(1)-S(1)-N(2)
S(1)-N(2)-S(2)
N(2)-S(2)-As(1)
S(2)-As(1)-N(1)
S(2)-As(1)-C(1)
N(1)-As(1)-C(1)
116.6(3)
115.1(3)
116.9(3)
100.23(18)
90.01(15)
101.07(17)
96.5(2)
114.7(4)
117.3(4)
116.9(5)
100.4(3)
90.6(2)
(118.5(4))
(114.7(4))
(117.8(5))
(100.0(3))
(88.9(2))
105.2(3)
103.3(3)
(106.9(2))
(103.4(3))
Figure 3. Stacking of molecules of 5 in the crystal.
a Values for two independent molecules in the asymmetric unit.
which is slightly puckered. The (S2N2) and S(2)-As(1)-N(1)
planes are inclined by 9.6°. Arsenic is situated approximately
˚
0.246 A above the least-squares plane of the (S2N2) moiety and
forms the vertex of a trigonal pyramid. The phenyl group is
attached to the As atom by an As-C single bond, which is
nearly perpendicular to the least-squares plane of the As(S2N2)
ring (the angle is 99.4°). The orientation of the phenyl group is
interesting in that it is in a periplanar arrangement with the
As(1)-S(2) bond; the dihedral angle between the phenyl ring
and the S(2)-As(1)-C(1) plane is only 11.8°.
Selected bond lengths and angles are listed in Table 2. The
˚
As(1)-S(2) bond is elongated (2.303(19) A) with respect to
the As-S single bond in As4S4 (2.243 A mean value).33 The
Figure 4. ORTEP32 drawing of the X-ray structure of
ellipsoids). Hydrogen atoms are omitted for clarity.
6 (50%
˚
elongation is, however, not too dramatic. Examples of longer
As-S single bonds were reported.34 Elongation of the bond
between the terminal sulfur of the (S2N2) moiety and the fifth
element bound to this moiety has been observed in other five-
membered main group sulfur-nitrogen heterocycles such as
Roesky’s ketone or Roesky’s sulfoxide.26,35
the N(2)-S(2) single bond is shortened. This slight bond
length equalization suggests some degree of π-electrons
delocalization in 5. The delocalization of π-electrons and
possible aromaticity of RAs(S2N2) are subjects of an ongoing
computational study.
The distribution of the bond angles in 5 is comparable to
other known five-membered sulfur-nitrogen rings. The most
open angles are found at the N atoms. Their mean value
together with that of the N(1)-S(1)-N(2) angle (116.7° and
115.1(3)°, respectively) is close to the optimum 120° expec-
ted for a trigonal planar coordination, which supports the
formal Lewis formula of 5. The S(2)-As(1)-N(1) right
angle corresponds well with the trend of inverse proportion-
ality between van der Waals’ radius of an atom and a bond
angle value at this atom in five-membered sulfur-nitrogen
rings.14,22,26,35,39
˚
The As(1)-N(1) bond length (1.899(5) A) is in a good
agreement with As-N single bonds found in eight-membered
As-N and As-S-N ring compounds.3,4,6,36 The length of
˚
the As(1)-C(1) bond is 1.965(6) A which is nearly identical to
the mean As-C bond length in arsenobenzene.37
The alternating sulfur and nitrogen atoms are connected
˚
by two shorter (1.540(5) and 1.573(5) A) and one longer
˚
(1.671(5) A) bonds. A comparison with Pauling’s values of
SdN double bonds38 justifies the formal description of 5 by a
Lewis formula with two double bonds coming from S(1).
However, the SdN bonds in 5 are longer than those in dithi-
atetrazadiarsocines and acyclic sulfurdiimides,3,4,6 whereas
The unit cell contains in total two molecules of 5, of which
only one forms the asymmetric unit. The surprising orienta-
tion of the phenyl ring seems to be fixed by a system of intra-
and intermolecular contacts within the crystal. Figure 3
shows stacking arrangement of the molecules with the S-
(33) Porter, E. J.; Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1972,
1347–1349.
(34) Burford, N.; Royan, B. W.; Whalen, J. M.; Richardson, J. F.;
Rogers, R. D. J. Chem. Soc., Chem. Commun. 1990, 1273–1275.
(35) Van Droogenbroeck, J.; Tersago, K.; Van Alsenoy, C.; Aucott,
S. M.; Milton, H. L.; Woollins, J. D.; Blockhuys, F. Eur. J. Inorg. Chem.
2004, 3798–3805.
(36) (a) Avtomonov, E. V.; Megges, K.; Li, X.; Lorberth, J.; Wocadlo, S.;
Massa, W.; Harms, K.; Churakov, A. V.; Howard, J. A. K. J. Organomet.
Chem. 1997, 544, 79–89. (b) Weiss, J.; Eisenhuth, W. Z. Anorg. Allg. Chem.
1967, 350, 9–17.
(37) (a) Kraft, M. Y.; Borodina, G. M.; Strel’tsova, I. N.; Struchkov,
Y. T. Dokl. Akad. Nauk SSSR 1960, 131, 1074–1076. (b) Hedberg, K.; Hughes,
E. W.; Waser, J. Acta Crystallogr. 1961, 14, 369–374.
˚
(1B)-S(2) and S(1)-S(2A) distances (3.614(5) A) being just
on the edge of the sum of van der Waals’ radii.
The molecular structure of 6 differs from that of 5. The
As(S2N2) ring in 6 is essentially planar, and the orientation of
the mesityl group also changes: its plane bisects the As(S2N2)
ring. The two planes are nearly perpendicular. One of the
ortho methyl groups is situated directly above the five-
membered ring (Figure 4).
(38) (a) Pauling, L. The Nature of the Chemical Bond and the Structure of
Molecules and Crystals: An Introduction to Modern Structural Chemistry,
3rd ed.; Cornell University Press: Ithaca, NY, 1960. (b) Schomaker, V.; Stevenson,
D. P. J. Am. Chem. Soc. 1941, 63, 37–40.
(39) (a) Weiss, J. Z. Anorg. Allg. Chem. 1966, 343, 315–322. (b) Martan, H.;
Weiss, J. Z. Anorg. Allg. Chem. 1984, 514, 107–114.

Article
Because of greater steric demand of the mesityl compared
Inorganic Chemistry, Vol. 49, No. 6, 2010 3069
voltammetry, which showed irreversible oxidation (Epa
=
to the phenyl group, the molecule of 6 is more “open” than
that of 5: the mesityl group is bound to arsenic with a wider
angle with respect to the least-squares plane of the As(S2N2)
ring (approximately 110° and 111° for the two independent
molecules).
1.08 V) and reduction (Epc = -1.71 V) at both slower and
faster scan rates (Supporting Information, Figure S3 and
Table S9).
4. Summary
The 5-alkyl/aryl-1,3λ4δ2,2,4,5-dithiadiazarsoles 1-6 were
prepared by an exchange reaction between RAsX2 and the
universal tin reagent [nBu2Sn(S2N2)]2. The compounds are
stable and with the exception of 1 only moderately air-
sensitive. The crystal structures of 5 and 6 revealed that the
As(S2N2) ring is relatively flexible with 5 containing a puck-
ered and 6 a planar As(S2N2) ring. A network of intra- and
intermolecular interactions fixes the molecular geometries of
5 and 6. Especially the geometry of 5 is interesting with a
Selected bond lengths and angles are listed in Table 2. The
bonding within the molecule can be formally described by a
Lewis formula with two double bonds coming from the NSN
sulfur atoms. The As-S, As-N, and As-C bonds are single
and are slightly longer than those in 5, which can be explained
as a consequence of the steric effect of the mesityl group and
its better electron-donating ability. The S-N bond lengths
can be regarded as intermediate between a single and a
double S-N bonds, and π-electrons delocalization can be
expected.
1
periplanar arrangement on the As-C bond. H and 13C
The unit cell contains eight molecules of 6, with two
crystallographically independent molecules in the asym-
metric unit. The five-membered rings in the asymmetric unit
are approximately coplanar but slipped so that the S(1)-N-
(1) bond lies over the S(12)-N(12) bond of the second
independent molecule (Supporting Information, Figure S2).
NMR spectra of 2 and 3 confirmed the presence of a chiral
arsenic center. The constitution of the title compounds was
further supported by 14N NMR, IR, and Raman spectro-
scopies.
The reactivity of compound 5 was investigated. Oxidation
and reduction of 5 leads to formation of unstable species, and
the tendency of 5 to serve as a donor of its lone pair of
electrons appears low.
˚
The S(1)-S(12) and N(1)-N(12) distances are 3.713(7) A
˚
and 3.952(8) A, respectively, which is beyond the sum of van
der Waals’ radii, and thus there are no contacts between the
two independent molecules. The molecules do not take up a
stacking arrangement, presumably since the bulky mesityl
group precludes an arrangement in closely packed layers.
Similarly to 5, the orientation of the mesityl group seems
strongly determinedby a number of intra- and intermolecular
interactions.
Acknowledgment. We wish to thank Dr Tomas Lebl for
help with NMR spectra simulations and Dr Joe Crayston
for advice during voltammetric measurements. This work
was carried out with the financial support of Engineering
and Physical Sciences Research Council (EPSRC), U.K.
Eight-membered AsSN rings are known to act as ligands
coordinated to a metal center via the lone pair of electrons on
arsenic.4-6 The reactions of 5 with Pt(COD)Cl2, Mo(CO)4-
(pip)2, and Cp2Ti(CO)2 resulted in formation of tarry mate-
rials or powders, which could not be worked up toward
crystallization. 5 reacted with Cp*Co(CO)2 to yield a small
amount of Cp*Co(S2N2) (proved by 1H and 13C NMR and
MS; see Supporting Information for details).22 Oxidation
and reduction of 5 was investigated by means of cyclic
Supporting Information Available: CIF files for compounds 5
and 6, comments on synthetic procedures for the RAsX2 starting
materials and for the reaction of 5 and Cp*Co(CO)2, 1H NMR
spectra of 2, melting and boiling points of Me3SiX and
nBu2SnX2 (X = F, Cl, Br, I), 1H and 13C NMR data of RAsX2,
selected IR and Raman wavenumbers of RAsX2 and 1-6, a
view of the asymmetric unit of 6, cyclic voltammogram of 5,
experimental values of Ep and Ip. This material is available free
of charge via the Internet at http://pubs.acs.org.