Generation of ClCNS, ClNCS and NCCNS
FULL PAPER
diation was expected to decompose nitrile sulfides, but iden-
tification of NCCNS seemed to be feasible at the beginning
of the irradiation. IR spectra recorded during the irradiation
are shown in Figure 6 and Figure S9 of the Supporting Infor-
mation, and main decomposition routes are summarised in
Scheme 5. The major IR bands in the spectra can be unam-
bromine or iodine is generally more favourable than that of
chlorine, 3,4-dibromo-1,2,5-thiadiazole and 3,4-diiodo-1,2,5-
thiadiazole are expected to be better precursors for NCCNS
than 3,4-dichloro-1,2,5-thiadiazole. These precursors are still
unknown, but we have initiated research on synthetic routes
to these compounds. Identification of the first halogen iso-
thiocyanate, ClNCS may open the door to future discovery
of the entire halogen isothiocyanate family.
Experimental Section
3
,4-Dichloro-1,2,5-thiadiazole and 3,5-dichloro-1,2,4-thiadiazole were
Scheme 5. Decomposition pathways of 3,4-dicyano-1,2,5-thiadiazole.
[
25]
commercial products (Aldrich). 3-Chloro-1,2,5-thiadiazole, 3-chloro-4-
fluoro-1,2,5-thiadiazole
[
26,27]
[28]
and 3,4-dicyano-1,2,5-thiadiazole were syn-
thesised according to known literature methods from a-aminoacetonitrile
bisulfate and disulfur dichloride, from 3,4-dichloro-1,2,5-thiadiazole and
potassium fluoride and from diaminomaleonitrile and thionyl chloride,
respectively. Starting materials were commercial products (Aldrich). The
purity of precursors was checked by NMR and IR spectroscopy.
biguously assigned to NCCNS, NCCN, NCNCS and NCNC.
NCCN and NCNC are the expected photodecomposition
products of NCCNS and NCNCS, respectively, and the in-
tensity of their IR bands increased continuously during irra-
diation, in agreement with the photoinstability of NCCNS
and NCNCS at the applied wavelength.
[29]
The matrix isolation setup has been described in detail elsewhere. The
degassed thiadiazole precursors were premixed with argon (Messer,
purity 99.9997%) in 1:1000 molar ratio on a glass vacuum line. The gas
mixtures were deposited onto a CsI window at 8–10 K for IR and onto
a quartz window at 12–14 K for UV spectroscopic measurements. The
S2 chemiluminescence: After finishing the experiments and
warming the matrix, we observed very bright and blue
chemiluminescence. A photograph of the blue emission is
shown in Figure S10 of the supporting material. Light emis-
sion started above about 20 K, and increasing the tempera-
ture increased the intensity of the emitted light. The record-
ed emission spectrum was identical with that obtained after
the photodecomposition of 3,4-dimethyl-1,2,5-thiadiazole
3
À1
flow rate was about 1.2 and 0.3 cm min for IR and UV measurements,
respectively. The CsI and quartz windows were mounted on a cold head
cooled by a CTI Cryogenics Model 21 closed-cycle refrigerator. The tem-
perature of the cold head was controlled by a Lake Shore 321 thermostat
equipped with a silicon diode thermometer. A Cathodeon HPK 125 W
high-pressure mercury lamp and a Oriel 66057 xenon lamp were used as
photolysis sources. The deposited matrix was irradiated through a quartz
window and an interference filter (254 nm filter for Hg lamp and 280 nm
filter for Xe lamp). The interference filters had full width at half-heights
of 10 and 25 nm at 254 and 280 nm, respectively. For broad-band UV
under similar conditions and assigned to the emission of S
in our previous work. The blue emission is thus similarly
2
[7]
(
BBUV) photolysis the mercury or xenon lamp was used without any
filter.
assigned to S , which indicates that triplet sulfur atoms react
2
Infrared spectra were recorded on a Bruker IFS 28 FTIR spectrometer
equipped with a KBr beam splitter and a DTGS detector. A total of 250–
with each other on warming the matrix, and S species form
2
in the electronically excited state.
À1
À1
1
000 scans were accumulated at 1 cm resolution in the 400–4000 cm
spectral window. Happ–Genzel apodisation function, Metz phase correc-
À1
tion with a phase resolution of 32 cm and a zero filling factor of 4 were
applied.
Conclusions
Absorption UV spectra were recorded on a Varian Cary3E spectrometer
À1
with 5 nmmin scan rate, 0.333 nm step size and 1 nm spectral band
The photodecomposition of five thiadiazole derivatives has
been studied in cryogenic argon matrix, and ClCNS,
NCCNS and ClNCS have been identified as new compounds
by IR and UV spectroscopy. All of these compounds have
been structurally characterised by quantum chemical meth-
ods. The molecular frame of nitrile sulfides is confirmed as
linear, and that of ClNCS as trans-bent. ClCNS, NCCNS
and ClNCS are photolabile, and selection of the proper
wavelength for photodecomposition of thiadiazole precur-
sors and for the generation of ClCNS and NCCNS is of cru-
cial importance. Although ClCNS decomposes at 254 nm,
the decomposition is slow enough to support generation of
this species at this wavelength for application in solution re-
actions. The application of 3-chloro-1,2,5-thiadiazole seems
to be especially promising due to the relatively fast decom-
position and relatively good yield of ClCNS. Unexpected
formation of NCCNS from 3,4-dichloro-1,2,5-thiadiazole
width. Data were collected in the 190–400 nm spectral region.
Quantum chemical calculations were performed with the Gaussian 09
and ACES II program packages.
monic vibrational frequencies were calculated by using the B3LYP and
CCSD(T) methods and the aug-cc-pV
vibrational corrections, within the framework of second-order vibrational
perturbation theory,
The core electrons were not correlated (frozen core) in the calculations.
Singlet excitation energies and oscillator strengths were calculated apply-
ing the TD-B3LYP and SAC-CI methods.
[30,31]
Equilibrium geometries and har-
[
32]
[
33]
[34]
ACHTUNGTNERNUNG( T+d)Z basis set. Anharmonic
[
35]
were obtained at the CCSD(T)/cc-pVTZ level.
[
36]
[37]
For characterisation of the normal vibration modes of ClCNS and
NCCNS, the potential-energy distribution (PED), which provides a mea-
sure of the internal coordinate contributions, was determined by using
[
38]
the BMAT program.
was observed, likely by Cl elimination. Since elimination of
2
Chem. Eur. J. 2013, 19, 17201 – 17208
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
17207