Synthesis and structural studies on thioimides, R2CNSR and sulfur diimides, R2CNSNCR2

Article abstract of DOI:10.1039/c2dt32878j

Reaction of Ph₂CO and py₂CO with Li[N(SiMe ₃)₂] and ArSCl (Ar = 2-O₂NC₆H ₄, 2,4-(O₂N)₂C₆H₃) yielded Ph₂CNSAr (1a and 1b respectively) and py₂CNSAr (2a and 2b respectively). Reaction of fluorenone, C₁₂H₈CO with Li[N(SiMe₃)₂] and ArSCl under similar conditions afforded C₁₂H₈CNSAr (3a and 3b respectively). Whilst reaction of fluorenone with Li[N(SiMe₃)₂] and SCl ₂ in a 2:2:1 ratio afforded the sulfur-diimide, C₁₂H ₈CNSNCC₁₂H₈ (4), reaction of py₂CO with Li[N(SiMe₃)₂] and SCl₂ under similar conditions afforded the thiazyl heterocycle [py₂CNS]Cl (5) via intramolecular coordination. The structures of 1a, 1b, 2a, 2b, 3a, 3b and 4 are determined by X-ray diffraction. In the case of 4, bond lengths and DFT studies reveal greater π-delocalisation than in 1-3.

Full text of DOI:10.1039/c2dt32878j

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Synthesis and structural studies on thioimides,
R2CvNSR and sulfur diimides, R2CvNSNvCR2†
Cite this: Dalton Trans., 2013, 42, 3888
Rebecca L. Melen,‡* Dana J. Eisler, Rachel A. Hewitt and Jeremy M. Rawson§*
Reaction of Ph2CvO and py2CvO with Li[N(SiMe3)2] and ArSCl (Ar = 2-O2NC6H4, 2,4-(O2N)2C6H3)
yielded Ph2CvNSAr (1a and 1b respectively) and py2CvNSAr (2a and 2b respectively). Reaction of fluore-
none, C12H8CvO with Li[N(SiMe3)2] and ArSCl under similar conditions afforded C12H8CNSAr (3a and 3b
respectively). Whilst reaction of fluorenone with Li[N(SiMe3)2] and SCl2 in a 2 : 2 : 1 ratio afforded the
sulfur-diimide, C12H8CNSNCC12H8 (4), reaction of py2CvO with Li[N(SiMe3)2] and SCl2 under similar con-
ditions afforded the thiazyl heterocycle [py2CNS]Cl (5) via intramolecular coordination. The structures of
1a, 1b, 2a, 2b, 3a, 3b and 4 are determined by X-ray diffraction. In the case of 4, bond lengths and DFT
studies reveal greater π-delocalisation than in 1–3.
Received 1st December 2012,
Accepted 26th December 2012
DOI: 10.1039/c2dt32878j
www.rsc.org/dalton
Introduction
The discovery1,2 of the conducting and superconducting prop-
erties of (SN)x in 1973 generated a surge in interest in the physi-
cal properties of S/N compounds and, in particular, attempts
to include C in the polymer backbone led to the blossoming of
several new areas of C/N/S heterocycles.3 With a few excep-
tions,4 the incorporation of C into the polymer backbone has
proved largely unsuccessful; few C/N/S containing polymers
have been prepared and typically exhibit semi-conducting be-
haviour,4 presumably due to mismatch in the energies of the
thiazyl and phenylene π-systems. Whilst metallo-C/N/S conju-
gated polymers have also been proposed,5 the introduction of
metal binding groups has not been widely explored.6 The elec-
tronegative nature of the thiazyl chain, coupled with the poten-
tial for the S and particularly N lone pairs to become involved
in bonding, has led to metal-binding via the thiazyl chain in a
range of sulfur-diimides.7 Recent studies on the dipyridyl
thioimide, py2CvNSAr (2b), revealed that whilst the ligand
appears air and moisture stable, the presence of a Lewis acidic
metal centre catalyses the hydrolysis of the thioimide group
affording dipyridyl-ketone derivatives.6 A number of thiazyl
Scheme 1
chains RSxNyR have been prepared which can be considered as
fragments of (SN)x and reveal an increasing red-shift for longer
thiazyl chains associated with a reduced HOMO–LUMO gap as
the band structure evolves.5
However conjugation through the organic spacer and/or
metallo-centre continues to be a primary problem if such
C/N/S polymers are to exhibit enhanced conductivity or
efficient electronic communication in a similar manner to con-
jugated hydrocarbons.8 In the current study we probe the
structures of a series of short-chain S/N oligomers (1–4,
Scheme 1) and examine the energy (mis)match between the
energetics of the π-manifold of the S/N unit and that of the
organic substrate in order to evaluate the degree to which mis-
match in orbital energetics affects conjugation between the
thiazyl chain and organic terminal groups.
Department of Chemistry, The University of Cambridge, Lensfield Road, Cambridge,
CB2 1EW, UK. E-mail: rmelen@chem.utoronto.ca, mrawson@uwindsor.ca
†CCDC 913178–913183. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt32878j
‡Current address: Department of Chemistry, The University of Toronto, 80
St. George Street, Toronto, ON, Canada M5S 3H6.
§Current address: Department of Chemistry and Biochemistry, The University of
Windsor, 401 Sunset Avenue, Windsor, ON, Canada N9B 3P4.
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Synthesis of 2-O2NC6H4SNvCpy2 (2a). A solution of dipyri-
dyl ketone (0.50 g, 2.71 mmol) in ether (15 mL) was added to a
solution of Li[N(SiMe3)2] (0.45 g, 2.69 mmol) in ether (15 mL).
Experimental
General experimental
Unless otherwise stated, all reactions and manipulations were The resultant orange solution was stirred for 16 h at room
carried out under an atmosphere of dry nitrogen using stan- temperature. Me3SiCl (0.36 mL, 2.85 mmol) was added and the
dard Schlenk techniques and a glove box (Saffron Scientific). solution stirred for a further 3 h at room temperature. The
All solvents were dried and freshly distilled prior to use. solvent was removed in vacuo and the residue redissolved in
Li[N(SiMe3)2], benzophenone, fluorenone, Me3SiCl, and 2,4- CH2Cl2 (20 mL) and a solution of 2-O2NC6H4SCl (0.56 g,
(O2N)2C6H3SCl (Aldrich) were used as received. 2-O2NC6H4SCl 2.95 mmol) in CH2Cl2 (10 mL) added to afford a yellow suspen-
(Alfa Aesar) was used as received whilst SCl2 was prepared by sion which was stirred for a further 18 h. The solution was fil-
chlorination of S2Cl2 using an Fe catalyst.9
tered to afford an orange solid (0.58 g, 1.72 mmol, 64%) which
NMR spectra were recorded on a Bruker Avance DRX500 was recrystallised by slow evaporation of a saturated DMF solu-
Dual Cryoprobe or Bruker Avance DPX400 QNP probe. UV/vis tion to yield orange crystals of 2a suitable for X-ray analysis.
spectra were recorded on a Perkin-Elmer UV/vis lambda 12
Anal. Calc. for C17H12N4O2S: C 60.1, H 3.6, N 16.7%; Obs. C
spectrophotometer using UV Winlab software. Carbon, hydro- 58.5, H 3.6, N 15.8%; 1H NMR (400 MHz, d7-DMF): 8.96 (d,
gen and nitrogen analyses were carried out on an Exeter 4.4 Hz, 1H), 8.74 (s, 1H), 8.71 (d, 1.2 Hz, 1H), 8.33 (m, 1H),
CE-440 elemental analyser.
8.17 (d, 8.0 Hz, 1H), 7.92 (m, 1H), 7.90 (m, 1H), 7.88 (t, 1.2 Hz,
1H), 7.66 (d, 8.0 Hz, 1H), 7.40 (m, 1H), 7.37–1.39 (m, 2H);
+EI-MS m/z 337.08 (M+).
Synthesis
Synthesis of 2,4-(O2N)2C6H3SNvCpy2 (2b). This was pre-
Synthesis of 2-O2NC6H4SNvCPh2 (1a). A solution of benzo- pared in a similar manner to 2a, to afford 2b as a yellow solid
phenone (1.00 g, 5.49 mmol) in toluene (20 mL) was added (0.56 g, 1.47 mmol, 54%) which could be recrystallised by slow
dropwise to a solution of Li[N(SiMe3)2] (0.92 g, 5.49 mmol) in evaporation of a saturated DMF solution to yield orange crys-
toluene (20 mL). The resultant yellow mixture was stirred for tals of 2b suitable for X-ray analysis.
18 h at 70 °C then cooled to 50 °C and Me3SiCl (0.70 mL,
Anal. Calc. for C17H11N5O4S: C 53.54, H 2.90, N 18.36%;
1
5.49 mmol) added and stirred for a further 2 h at 50 °C. The Obs. C 50.77, H 2.69, N 17.68%; H NMR (400 MHz, d7-DMF):
resultant mixture was cooled to room temperature and a solu- 9.10 (d, 8.8 Hz, 1H), 9.03 (d, 2.4 Hz), 8.97 (dt, 5.2 Hz, 1.2 Hz,
tion of 2-O2NC6H4SCl (1.04 g, 5.49 mmol) in toluene (20 mL) 1H), 8.73 (dd, 9.2 Hz, 2.4 Hz, 1H), 8.6 (m, 1H), 8.40 (dt, 8 Hz,
was added dropwise to afford a yellow precipitate. The resul- 1.2 Hz, 1H), 8.08 (m, 2H), 7.77 (dt, 8 Hz, 1.2 Hz, 1H), 7.58–7.66
tant suspension was stirred for 14 h, filtered to remove an off- (m, 2H); +EI-MS m/z 382.06 (M+).
white solid (LiCl). The yellow solution was concentrated
in vacuo and stored at 0 °C to yield orange crystals of 1a in an identical fashion to 1a. The resultant solid (1.46 g) was
(0.73 g, 2.17 mmol, 40%) suitable for X-ray analysis. isolated by filtration, redissolved in CH2Cl2, filtered through
Synthesis of 2-O2NC6H4SNvCC12H8 (3a). This was prepared
Anal. Calc. for C19H14N2O2S: C 68.24, H 4.22, N 8.38%; Obs. Celite and concentrated in vacuo. Storage at −10 °C for 24 h
C 67.61, H 4.34, N 8.23%; 1H NMR (400 MHz, CDCl3): 8.81 (dd, afforded yellow needles of 3a (0.55 g, 1.64 mmol, 30%) suitable
8 Hz, 1 Hz, 1H), 8.32 (dd, 8 Hz, 1 Hz, 1H), 7.79 (m, 1H), 7.72 for X-ray diffraction.
(m, 2H), 7.58 (m, 3H), 7.47–7.40 (m, 5H), 7.35 (m, 1H); 13C
Anal. Calc. for C19H12N2O2S: C 68.66, H 3.64, N 8.43%; Obs.
NMR (500 MHz, CDCl3): 166.87, 142.65, 141.23, 138.95, 137.58, C 68.16, H 3.66, N 8.28%; 1H NMR (400 MHz, CDCl3): 8.86 (dd,
137.07, 133.99, 132.40, 130.37, 130.05, 129.70, 129.02, 128.34, 8 Hz, 1 Hz, 1H), 8.40 (m, 1H), 8.38 (dd, 8 Hz, 1 Hz, 1H), 7.90
128.26, 128.24, 127.45, 126.34, 125.45, 124.94; UV/vis (λmax
CHCl3): 416 nm, ε = 1.07 × 104 mol−1 L cm−1
,
(m, 1H), 7.84 (m, 1H), 7.71 (m, 1H), 7.63 (m, 1H), 7.52 (m, 1H),
.
7.50–7.40 (m, 3H), 7.36 (m, 1H); 13C NMR (500 MHz, CDCl3):
Synthesis of 2,4-(O2N)2C6H3SNvCPh2 (1b). This was pre- 160.92, 142.67, 140.55, 140.22, 137.61, 134.16, 132.68, 131.59,
pared in a similar manner to 1a. However the resultant orange 130.84, 128.40, 128.37, 128.26, 125.66, 125.54, 125.34, 122.24,
precipitate generated after addition of 2,4-(O2N)2C6H3SCl was 120.33, 119.78; UV/vis (λmax, CHCl3): 406 nm, ε = 7.76 ×
stirred for 18 h, filtered off and redissolved in CH2Cl2, filtered 103 mol−1 L cm−1
through Celite and the resultant solution concentrated
in vacuo and stored at −20 °C to afford 1b as orange crystals pared in a similar manner to 3a, to afford 3b as a yellow solid
(0.73 g, 1.92 mmol, 35%). (1.99 g) was isolated by filtration and washed with ether (2 ×
.
Synthesis of 2,4-(O2N)2C6H3SNvCC12H8 (3b). This was pre-
Anal. Calc. for C19H13N3O4S: C 60.15, H 3.45, N 11.08%; 10 mL). Compound 3b had very low solubility in common
Obs. C 59.48, H 3.48, N 10.89%; 1H NMR (500 MHz, CDCl3): organic solvents, hampering purification. However small quan-
9.13 (d, 2 Hz, 1H), 9.00 (d, 9 Hz, 1H), 8.54 (dd, 9 Hz, 2 Hz, 1H), tities of 3b (0.18 g, 0.48 mmol, 9%) were obtained by filtering
7.68 (m, 2H), 7.57 (m, 3H), 7.49 (m, 1H), 7.42 (m, 2H), 7.37 (m, a saturated dichloromethane solution through Celite, followed
2H); 13C NMR (500 MHz, CDCl3): 169.50, 149.11, 144.37, by slow evaporation of the resultant solution.
141.77, 138.41, 136.59, 131.11, 130.16, 129.17, 128.52, 127.44,
Anal. Calc. for C19H11N3O4S: C 60.47, H 2.94, N 11.13%;
127.36, 127.25, 121.24; UV/vis (λmax, CHCl3): 398 nm, ε = 1.10 × Obs. C 60.47, H 3.32, N 10.17%; 1H NMR (400 MHz, CDCl3):
104 mol−1 L cm−1
.
9.20 (d, 2 Hz, 1H), 9.06 (d, 9 Hz, 1H), 8.58 (dd, 9 Hz, 2 Hz, 1H),
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8.32 (m, 1H), 7.86 (m, 1H), 7.68–7.42 (m, 5H), 7.27 (m, 1H); DFT calculations
13C NMR (500 MHz, CDCl3): 144.41, 134.66, 134.12, 132.35,
131.65, 129.05, 128.57, 128.53, 128.41, 127.42, 126.54, 124.31,
Single point DFT studies were undertaken on the molecular
geometries of 1–4 using the B3LYP functional and 6-31G basis
set within GAMESS-UK.11
122.55, 120.61, 120.27, 120.00; UV/vis (λmax, CHCl3): 408 nm,
ε = 7.10 × 103 mol−1 L cm−1
.
Synthesis of C12H8CvNSNvCC12H8 (4). A solution of fluor-
enone (1.00 g, 5.55 mmol) in toluene (30 mL) was added drop-
wise to a solution of Li[N(SiMe3)2] (0.93 g, 5.55 mmol) in
toluene (30 mL) and the resultant yellow mixture stirred for
18 h at 70 °C. The solution was cooled to 50 °C and Me3SiCl
(0.70 mL, 5.55 mmol) added and the mixture stirred for a
further 2 h at 50 °C. The solution was cooled to room tempera-
ture and SCl2 (0.18 mL, 2.78 mmol) was added dropwise
forming an immediate yellow-orange precipitate. The resultant
suspension was stirred for a further 18 h, the solvent removed
to yield 4 (0.95 g). 4 was recrystallised as a CH2Cl2 solvate by
dissolving in CH2Cl2, filtering through Celite, followed by slow
evaporation of the resultant solution (0.57 g, 1.46 mmol, 53%).
Anal. Calc. for C26H16N2S·1/2CH2Cl2: C 73.86, H 3.97,
Results and discussion
The stoichiometric reaction of ketones with Li[N(SiMe3)2] is a
well-established route to the generation of silyl-ketimines
(A).12 We found that derivatives of A (R,R = Ph, Ph; py, py; and
fluorenone) generated in situ from the corresponding ketone
react with aryl sulfenyl chlorides, ArSCl to afford the thio-
imines 1a–3a (Ar
= 2-O2NC6H4) and 1b–3b (Ar = 2,4-
1
1
(O2N)2C6H3) (Scheme 2). Solution H NMR studies and 2D H
COSY spectra reveal that the R groups (R = Ph or py) are chemi-
cally distinct, indicative of hindered rotation about the CvN
bond in solution.
Compounds 1–3 could typically be recrystallised from
CH2Cl2 in the case of 1a, 1b, 3a and 3b or DMF for 2a and 2b
as yellow-orange solids.
1
N 6.50%; Obs. C 73.13, H 4.09, N 6.28%; H NMR (400 MHz,
CDCl3): 8.74 (d, 8 Hz, 2H), 7.98 (m, 4H), 7.69 (m, 4H), 7.58
(m, 2H), 7.49 (d, 8 Hz, 2H), 7.38 (m, 2H).
Crystallography
Single crystal X-ray diffraction analyses were performed on a
Nonius Kappa CCD diffractometer using Mo-Kα radiation and
an Oxford Cryosystems cryostream cooling device which main-
tained the temperature at 180(2) K. Data were processed using
COLLECT and SCALEPACK and structure solution and refine-
ment undertaken using SHELXTL and structures visualised
using Mercury 3.0.10 Crystallographic data are presented in
Table 1 and the structural data are available in electronic
format (see ESI†) or free of charge from the CCDC (CCDC
deposit numbers 913178–913183).
Scheme 2
Table 1 Single crystal data for compounds 1–4
Compound
1a
1b
2a
2b
3a
3b
4
Empirical formula
Crystal system
Space group
C19H14N2O2S
Monoclinic
P21/c
C19H13N3O4S
Monoclinic
P21/c
C17H12N4O2S
Triclinic
P1
C17H11N5O4S
Monoclinic
C2/c
C19H12N2O2S
Triclinic
P1
C19H11N3O4S
Monoclinic
P21/c
C26.5H17N2SCl
Orthorhombic
Pbcn
ˉ
ˉ
a/Å
b/Å
c/Å
α/°
12.2213(5)
12.5273(5)
11.9600(4)
90
119.087(1)
90
14.9965(4)
7.2996(2)
16.0914(4)
90
106.510(2)
90
8.8032(2)
11.8517(2)
16.3949(4)
74.4123(9)
76.190(1)
71.295(1)
1538.63(6)
4
18.4166(3)
6.4849(1)
27.9654(6)
90
100.4673(7)
90
7.3115(2)
9.4716(3)
12.3682(4)
101.868(1)
98.333(2)
112.163(2)
752.52(4)
2
13.1797(4)
7.9049(2)
15.5730(5)
90
93.866(1)
90
26.921(5)
7.7572(16)
19.322(4)
90
90
90
β/°
γ/°
V/Å3
1600.1(1)
4
1688.88(8)
4
3284.3(11)
8
1618.77(8)
4
4035.1(14)
8
Z
T/K
180(2)
1.388
15 888
3661
0.0395
0.0465
0.1201
1.023
180(2)
1.492
12 806
3868
0.0558
0.0453
0.1096
1.017
180(2)
1.452
16 668
6018
0.0409
0.0501
0.1291
0.930
180(2)
1.543
14 171
3728
0.0561
0.0406
0.0967
1.058
180(2)
1.467
7512
3072
0.0483
0.0452
0.1096
1.028
180(2)
1.548
9120
3702
0.0419
0.0405
0.1050
1.086
180(2)
1.419
33 865
3557
0.0601
0.0437
0.1110
1.045
Dc/g cm−3
Total data
Unique data
Rint
R1[F2 > 2σ(F2)]
wR2 (all data)
GoF
ρmin/ρmax/e Å−3
CCDC code
+0.246/−0.186
CCDC 913178
+0.296/−0.439
CCDC 913179
+0.224/−0.341
CCDC 913180
+0.200/−0.345
+0.359/−0.326
CCDC 913181
+0.248/−0.279
CCDC 913182
+0.555/−0.359
CCDC 913183
CCDC 69166917
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Structural studies on 1–3
With the exception of 2a which crystallises with two molecules
in the asymmetric unit, all compounds have Z′ = 1. The struc-
tures are presented in Fig. 1, 2 and 4.
Structures of 1a and 1b
The structure of 1a exhibited significant molecular disorder
which was refined with a 0.92 : 0.08 ratio of site occupancies.
Whilst the major component was refined freely, constraints
were applied to the minor component. In the structural discus-
sion which follows only the major component is considered.
Both 1a and 1b crystallise in the monoclinic space group P21/c
with one molecule in the asymmetric unit. In both cases one
of the two phenyl rings is near coplanar with the CNS bridge
(θ1 = 8.04 and 20.93° for 1a and 1b respectively) and the CNS
linker is nearly coplanar with the nitro-phenyl substituent (ϕ =
9.25 and 10.71°), permitting some degree of π-delocalisation
across the molecule. The second phenyl ring is rotated out of
the plane (θ2 = 81.90 and 52.94°). The C–N bond length
(average 1.294 Å) is consistent with a conventional CvN
double bond (1.27 Å).13 Similarly the N–S bond length (average
1.691 Å) is comparable with other N–S single bonds
(1.62–1.74 Å in Sx(NH)8−x rings).14
These observations are consistent with the dominant Lewis
structure shown in Scheme 2. There are few structural
Fig. 2 One of the two crystallographically independent molecules of 2a (top)
and the asymmetric unit of 2b (bottom) with atom labelling scheme. Thermal
ellipsoids drawn at 50% probability.
examples of Ar2CvNSAr reported in the literature. The closest
derivative is Ph2CvNSC6H4Me-p (dS–N = 1.6901(2) Å, dC–N
1.2944(1) Å),15 although several variants based on benzoqui-
nones have been reported16 (dS–N = 1.650(3)–1.667(3) Å, dC–N
=
=
1.302(4)–1.318(5) Å) and whose structural parameters indicate
slightly more delocalised bonding.
Structures of 2a and 2b
We previously reported17 the structure of 2b but it is included
in here for comparison with 2a as well as derivatives of 1 and
3. Unlike 1a, 1b and 2b, the crystal structure of 2a contains two
molecules in the asymmetric unit. Nevertheless the molecular
geometry of 2a is similar to 1a, 1b and 2b and selected geo-
metric parameters for both 2a and 2b are presented in Table 2.
As with 1a and 1b both derivatives of 2 reflect near planarity of
one of the pyridyl rings with both the CNS bridge and the
nitro-phenyl substituent whilst the second pyridyl group is
rotated significantly out of the plane (Fig. 2). The marked vari-
ation in angles between the two crystallographically indepen-
dent molecules for 2a suggests a relative low energy barrier to
perturb these rings by up to 20° from planarity. The inclusion
of the pyridyl group provides a potential hydrogen-bond accep-
tor centre and the solid state structure of 2a reveals a near-
planar centrosymmetric tetrameric array in which the central
two molecules are linked via a pair of C–H⋯O contacts
(dC⋯O = 3.412(5) Å) between the pyridyl ring and the nitro
Fig. 1 Asymmetric unit of 1a (top) and 1b (bottom) with atom labelling
scheme. Thermal ellipsoids drawn at 50% probability.
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Table 2 Geometric parameters for compounds 1–4
Compound
1a
1b
2a
2b
3a
3b
4
Bond length/Å
C(1)–N(1)
1.293(3)
1.693(2)
1.764(3)
1.295(3)
1.689(2)
1.755(2)
1.287(4)
1.290(4)
1.686(2)
1.687(2)
1.770(3)
1.768(3)
1.291(2)
1.680(2)
1.772(1)
1.292(3)
1.674(2)
1.768(3)
1.298(2)
1.682(1)
1.755(2)
1.304(3)
1.300(3)
1.655(2)
1.657(2)
—
N(1)–S(1)
S(1)–C()
Bond angle/°
C(1)N(1)S(1)
117.2(2)
98.08(9)
119.1(2)
98.58(9)
119.8(2)
119.3(2)
97.4(1)
123.0(1)
96.48(7)
120.9(2)
97.9(1)
117.0(1)
120.9(2)
120.6(2)
97.00(9)
N(1)S(1)C()
100.17(7)
97.4(1)
θ1/°
θ2/°
ϕ/°
8.04
81.90
9.25
20.93
52.94
10.71
15.38, 3.45
52.02, 64.26
19.71, 0.70
19.42
30.66
11.85
3.60
—
3.76
2.18
—
2.45
3.03
—
3.20
θ1 and θ2 refer to the twist angles between the CNS plane and the ring plane of the substituent at C, whereas ϕ1 refers to the angle made between
the CNS plane and the mean plane of the aryl ring substituent at S.
Fig. 3 Molecular packing of 2a (top) and 2b (bottom) in the solid state,
emphasising CH⋯N and C–H⋯O hydrogen-bonding motifs.
group and the outer pair of molecules in the tetrameric unit
are linked via a set of C–H⋯Npy contacts (dC⋯N = 3.368(5)–
3.451(5) Å) (Fig. 3). The pyridyl ring which is rotated out of the
molecular plane is also involved in N⋯H–C hydrogen bonding
(dC⋯N = 3.522(3) Å).
Structures of 3a and 3b
In both 1 and 2 the presence of two R substituents led to
rotation of one substituent (Ph or py) out of the molecular
plane. Use of the fluorenone derivative constrains the C-termi-
nal end to planarity. Indeed the structures of both 3a and 3b
Fig. 4 Asymmetric unit of 3a (top) and 3b (bottom) with atom labelling
are completely planar within 4° (Fig. 4). The bond lengths and
angles associated with the CNS linkage are otherwise the same
as those observed in 1 and 2 within experimental error.
scheme. Thermal ellipsoids drawn at 50% probability.
In order to extend this methodology further we reacted
fluorenone with Li[N(SiMe3)2] and then half an equivalent of
SCl2 to couple two fluorenone units via an NSN linker, leading
to a more conjugated system. Notably attempts to make the
related variant py2CvNSNvCpy2 from py2CvNSiMe3 and SCl2
under identical conditions proved unsuccessful, affording just
[py2CNS]Cl (5) in good yield as a white precipitate rather than
The presence of the nitro-substituent appears to favour a
lamellar packing arrangement with C–H⋯O contacts between
molecules (dC⋯O = 3.330(3)–3.332(3) Å) in 3a (Fig. 5). In 3b a
bifurcated C–H⋯O2N contacts generates chains parallel to the
crystallographic a-axis (dC⋯O = 3.413(2)–3.576(2) Å) (Fig. 5).
The additional nitro-group generates additional C–H⋯O con-
tacts out of the molecular plane (dC⋯O = 3.154(2)–3.588(2) Å).
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Fig. 6 Molecular structure of 4 with atom labelling scheme. Thermal ellipsoids
drawn at 50% probability.
Fig. 5 Molecular packing of 3a (top) and 3b (bottom) in the solid state.
Scheme 4
Scheme 3
4 and 6 are consistent with a SII centre whereas other sulfur
t
diimides such as BuNSNtBu (dS–N = 1.5282(4)–1.5455(6) reveal
substantially shorter N–S bonds consistent with a SIV geome-
try, tBuNvSvNtBu.19
the typical yellow-orange colour associated with the conjugated
thiazyl chains such as 1–4. In 5 the pyridyl substituent under-
goes an intramolecular coordination to the S–Cl unit forming
a fused N-bridgehead bicyclic thiadiazolium ring (Scheme 3).14
DFT studies
In order to probe the degree of delocalisation in 1–4, a series
of DFT calculations were undertaken. The frontier orbitals of
Structure of 4
Compound 4 crystallises in the orthorhombic space group 1–2 exhibit similar features in that the HOMO appears to be a
Pbcn with one molecule of 4 and a half molecule of CH2Cl2 in delocalised π-MO across the whole framework, excluding the
the asymmetric unit. The molecule is, within 3.5°, perfectly aryl substituent at C which is rotated out of the molecular
planar (Fig. 6). The more extended π-conjugation in 4 is plane whilst the LUMO is predominantly localised on the
reflected in a shortening of the S–N bond (mean 1.656(2) Å, cf. S-aryl group [Fig. 7 (top)]. Thus HOMO–LUMO transitions are
1.674(2)–1.693(2) Å in 1–3) consistent with some gain in mul- consistent with movement of electron density across the mole-
tiple bond character. There is also an apparent lengthening of cule (from C-terminal to S-terminal). When the pendant aryl
the corresponding C–N bonds (mean 1.302(3) Å, cf. 1.287(4)– ring is forced into conjugation (3a and 3b) then the system
1.298(2) Å in 1–3), though these latter changes are well within becomes further delocalised. The HOMO and LUMO of 3b in
3 esd’s. A search of the CSD revealed only one other example particular suggest marked changes in electron distribution
of formula R2CNSNCR2, Ph2CNSNCPh2 (6) (Scheme 4) which associated with the HOMO–LUMO transition [Fig. 7 (bottom)].
can be derived from the silylketimine A (R = Ph) according to Gas phase calculations of the HOMO–LUMO gap (ΔE) reveal
Scheme 2.18 In the latter case one phenyl group at each end of that inclusion of an extra nitro group reduces ΔE by ca. 0.1 eV
the molecule is coplanar with the central CNSNC unit, with (for both 1a/1b and 3a/3b). Whilst the nitro group lowers both
the two remaining phenyl rings rotated out of the plane in an the energy of the HOMO and LUMO, it is the LUMO energy
analogous fashion to 1a. In addition both the N–S bond which is more affected. Enforcing complete π-conjugation of
lengths (1.6741(7)–1.6765(4) Å) and C–N bond lengths (1.2853(3)– the substituents at C (compare 1a/3a and 1b/3b) also leads to a
1.2888(4) Å) in 6 appear more akin to those in 1–3, suggesting lowering of ΔE by ca. 0.1 eV. Further TD-DFT studies are in
more increased conjugation in 4. Notably the bond lengths in progress to probe the spectroscopic properties in more detail.
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Fig. 7 Frontier molecular orbitals for 1a (top) and 3b (bottom).
Conclusions
A series of thioketimides 1–3 have been prepared and charac-
terised in both solution and the solid state. Solution NMR
measurements reflect hindered rotation around the CvN
bond and X-ray studies reveal extended conjugation between
terminal aryl groups through the CNS linker. The degree of
delocalisation is sensitive to the nature of the capping groups;
for 1a the HOMO is extensively delocalised over both terminal
groups whereas the LUMO is thiolate based. Conversely for 3
the HOMO is fluorenone based and the LUMO predominantly
thiolate based. In both cases HOMO–LUMO transitions are
expected to lead to electron transport across the molecule. The
symmetric variant 4 provides a rare example of a bis-sulfur-
diimide featuring SII but the propensity for intramolecular
coordination inhibits formation of the corresponding poten-
tial bis-chelate, py2CvNSNvCpy2. Further studies on more
extended thiazyl chains are underway and will be the subject
of future reports.
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Acknowledgements
We would like to thank EPSRC (JMR) and NSERC (DJE) for
financial support.
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