A tert-butyl/cyano substituted (1,2,3,5-dithiadiazolyl)benzene and η2 π complexes with CpCr(CO)2

Article abstract of DOI:10.1016/j.jorganchem.2006.11.049

A rational synthesis for 5-tert-butyl-3-cyano-1-(1,2,3,5-dithiadiazolyl)benzene, which was first observed from thermal cleavage of the bis-dithiadiazolyl, has been developed. Voltammetry and electron paramagnetic resonance (EPR) spectra for this radical are reported and its X-ray structure is described. Despite the bulky ^tBu substituent, the cyano supramolecular synthon is still able to maintain links to a single neighbouring sulfur atom of the S₂ unit, as previously observed in cyano-substituted dithiadiazolyls. In the η² complex with CpCr(CO)₂, no such interactions are observed; the nitrile group forms a centrosymmetric dimer through weak contacts with the para H atom on the aryl ring of the partner molecule. This behaviour is contrasted to similar complexes of less bulky dithiadiazolyls, where intermolecular interactions are retained in the crystalline lattice.

Full text of DOI:10.1016/j.jorganchem.2006.11.049

Journal of Organometallic Chemistry 692 (2007) 2697–2704
www.elsevier.com/locate/jorganchem
A tert-butyl/cyano substituted (1,2,3,5-dithiadiazolyl)benzene
and g2 p complexes with CpCr(CO)2
q
a,
b,
b
b
Rene T. Boere *, Lai-Yoong Goh *, Chwee Ying Ang , Seah Ling Kuan ,
´
´
b
b
a
a
Hiu Fung Lau , Victor Wee Lin Ng , Tracey L. Roemmele , Sonja D. Seagrave
a
Department of Chemistry and Biochemistry, The University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4
b
Department of Chemistry, National University of Singapore, Kent Ridge 119260, Singapore
Received 13 October 2006; received in revised form 24 November 2006; accepted 24 November 2006
Available online 9 December 2006
Abstract
A rational synthesis for 5-tert-butyl-3-cyano-1-(1,2,3,5-dithiadiazolyl)benzene, which was first observed from thermal cleavage of the
bis-dithiadiazolyl, has been developed. Voltammetry and electron paramagnetic resonance (EPR) spectra for this radical are reported
t
and its X-ray structure is described. Despite the bulky Bu substituent, the cyano supramolecular synthon is still able to maintain links
to a single neighbouring sulfur atom of the S2 unit, as previously observed in cyano-substituted dithiadiazolyls. In the g2 complex with
CpCr(CO)2, no such interactions are observed; the nitrile group forms a centrosymmetric dimer through weak contacts with the para H
atom on the aryl ring of the partner molecule. This behaviour is contrasted to similar complexes of less bulky dithiadiazolyls, where inter-
molecular interactions are retained in the crystalline lattice.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Chromium–sulfur complexes; Main-group heterocycles; Free-radicals; EPR spectroscopy; Electrochemistry
1. Introduction
tion across S@N bonds (Scheme 2) [2]. The novelty in all of
these reactions is the suppression of oxidative addition
which normally results from the reaction of unsaturated
S–N bonds with low-valent transition metal complexes
[3]. We attribute the success of our method to the employ-
ment of radical coupling reactions under mild conditions.
Our strategy is an alternative to the recently reported use
of b-pyridyl groups in the building of multi-spin magnetic
complexes incorporating C,N,S radicals [4].
Previous studies on the reactivity of [CpCr(CO)3]2, 2,
towards polyatomic main group elements [5] or various
classes of organic substrates [6] containing P–P and S–S
bonds, have shown that the reactions were initiated by the
17-electron radical [CpCr(CO)3Æ] 2a, into which 2 readily
dissociates in solution (Chart 1) [7]. Thus, the resulting pri-
mary products, A, from dibenzothiazolyl disulfide [(C6H4)-
NSCS]2 [8], B, tetraalkylthiuram disulfanes (R2NC(S)S)2
[9], C, tetraalkyldiphosphine disulfide [10], D and E, diphe-
nyl dichalcogenide Ph2E2 (X = S, Se, Te) [11], F, thiophos-
phorus compounds bis(diphenylthiophosphinyl)disulfane
We have recently communicated the first bona fide
p-complexes of unsaturated electron-rich C,N,S heterocy-
les [1,2]. The reaction of two different 1,2,3,5-dithiadiazol-
yls, 1, with the radical released from [CpCr(CO)3]2, 2
(Cp = g5-C5H5) led to synthesis in ca. 50% yield of new
complexes with g2 coordination across S–S bonds, which
crystallize in either exo (3a) or endo (3b) isomeric forms
(Scheme 1) [1]. Reaction of two different 1,2,4,6-thiatriazi-
nyls (4a,b) with the same organometallic radical likewise
yielded new complexes with either g1, 5, or g2, 6, coordina-
q
´
´
This article is based on the oral presentation by Rene T. Boere
(Abstract 61) at the 11th International Symposium on Inorganic Ring
Systems, Oulu, Finland, July 30–August 4, 2006.
*
Corresponding authors. Tel.: +1 403 329 2045; fax: +1 403 329 2057
´
´
(Rene T. Boere); fax: +65 6779 1691 (Lai-Yoong Goh).
´
E-mail addresses: boere@uleth.ca (R.T. Boere), chmgohly@nus.edu.sg
(L.-Y. Goh).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.11.049

2698
R.T. Boere´ et al. / Journal of Organometallic Chemistry 692 (2007) 2697–2704
Scheme 1.
ductive molecular materials [14]. Substituent effects have
been extensively investigated, especially regarding the
effects of steric bulk and supra-molecular synthons on crys-
tal engineering. Recently dithiadiazolyls bearing the super-
bulky 2,4,6-tris(trifluoromethyl)phenyl substituent were
shown to posses structure-dependent paramagnetism in
the solid state [15]. We previously reported the formation
t
of a ‘‘double column’’ structure when the bulky Bu group
on a bis-dithiadiazolyl 7 influences packing (Scheme 3),
where the lipophilic organic group and the CN2S2 rings
segregate in the crystal lattice [16]. Cyano-functionalised
dithiadiazolyl rings have been favourite supramolecular
synthons because of the highly polar nature of the S–N
bond, leading to CNdꢀ ꢁ ꢁ ꢁ Sd+ interactions that favour
the formation of molecular sheets [17]. A number of other
shape-directing substituents have been investigated as
alternatives to CN for dithiadiazolyl lattice modification,
including halogens [18]. In this paper, we report full syn-
thetic, structural, and electrochemical details for a new
dithiadiazolyl incorporating both tert-butyl and cyano sub-
stituents, and contrast the effects of these orienting groups
on the structure of the parent radical dimer and its g2-
CpCr(CO)2 complex, the structure of which was reported
in a preliminary communication [1].
Scheme 2.
(Ph2P(S)S)2 [12], or the analogous bis(thiophosphoryl)-
disulfane [(RO)2P(S)S]2 (R = iPr) [13], are the inevitable
consequence of the coupling of 2 and organic sulfur- or
phosphorus-centered radicals, under conditions where ther-
mally induced radical cleavage of E–E bonds occurs.
The dithiadiazolyl free radicals, and their diamagnetic
dimers which are predominantly found in the solid-state,
have been the subject of intense research because of their
potential as spin-bearers for magnetic and electrically con-
Chart 1.

R.T. Boere´ et al. / Journal of Organometallic Chemistry 692 (2007) 2697–2704
2699
Scheme 3.
2. Results and discussion
2.1. Discovery of 5-tert-butyl-3-cyano-1-(1,2,3,5-
dithiadiazolyl)benzene, 8
The synthesis, solid-state structure, EPR spectra and
electrochemistry of 5-tert-butyl-1,3-bis-(1,2,3,5-dithiadiaz-
olyl)benzene 7 was reported some time ago [16]. During
the sublimation of 7 in a thermal gradient tube furnace
under dynamic vacuum, a secondary deposit of crystals
was obtained which were more volatile than the major
product. Mass spectroscopic evidence was consistent with
the structure 5-tert-butyl-3-cyano-1-(1,2,3,5-dithiadiaz-
olyl)benzene, 8, which presumably is formed as a result
of thermal cleavage of one of the two 1,2,3,5-dithiadiazolyl
groups (Scheme 3), thereby converting diradical 7 into
monoradical 8 with the elimination of [NSS]Å.
Scheme 4.
Both [SNS]Å [19] and [NSS]Å isomers have been produced
along with other nitrogen sulfides when a mixture of N and
S vapor was subjected to a microwave discharge and have
been unambiguously characterized by matrix infrared
spectroscopy [20]. Interestingly, upon irradiation with
near-ultraviolet light, the [NSS]Å species underwent isomer-
ization to the more symmetrical [SNS]Å isomer. This
observation is in line with results of ab initio molecular
orbital calculations [21] which showed that the C2v species
[SNS]Å (2A1) is about 80.3 kJ/mol lower in energy than the
Cs species [NSS]Å (2A0). More recently, [1,2,5]thiadiaz-
olo[3,4-c][1,2,5]thiadiazole has been used to generate
[SNS]Å, despite the rather complex re-organization of the
starting material that is required to form the product [22].
the majority of the co-produced Ph3SbCl2 could be frac-
tionally crystallized at ꢀ35 ꢁC, leaving 8 to slowly precipi-
tate at RT over several days from the remaining mother
liquor. Crude 8 is pyrophoric when dry, but the crystalline
material produced by vacuum sublimation can be handled
briefly in air.
2.3. EPR spectroscopy of 8
The EPR spectrum of a solution of 8 in CH2Cl2, pre-
pared in a sealed ‘‘T’’ cell under vacuum with rigorous
exclusion of air, was investigated over a range of subambi-
ent temperatures because it was observed that the lines at
RT were substantially broadened. At 253 K a sharp spec-
trum (Fig. 1) was obtained of the expected five-line pattern
for coupling to two equivalent 14N nuclei, with aN =
0.509 mT and a g value of 2.011. The aN value is typical
for dithiadiazolyl radicals; e.g. 7 at 250 K has aN =
0.510 mT.
We were able to obtain an excellent fit to the theoreti-
cally expected Lorentzian lineshape by fitting additional
hyperfine coupling to two ortho H atoms with equivalent
hfc constants of 0.024 mT using the program WinSim
[25]. Without this contribution, the spectrum requires
Gaussian admixture into the lineshape to achieve a good
fit. It is possible that modulation of the coupling to the ring
H atoms with rotation about the Aryl-CN2S2 bond on the
EPR timescale is responsible for the observed small tem-
perature dependence of the linewidth, an effect that is
2.2. Synthesis of 5-tert-butyl-3-cyano-1-(1,2,3,5-
dithiadiazolyl)benzene, 8
In contrast to the original, accidental production of 8,
we set out do design a rational synthesis of this heterocyclic
radical (Scheme 4). In our hands the fully silylated amidine,
which is normally the most versatile reagent for the prepa-
ration of the 1,2,3,5-dithiadiazolium chlorides [23], could
not be prepared from 5-tert-butyl-1,3-dicyanobenzene
[24]. However, the intermediate N-lithio carboximidamide
was found to be a suitable starting material for its prepara-
tion. The free-radical 8 turned out to be remarkably soluble
in acetonitrile, quite unlike the disubstituted analogue 7
which is extremely insoluble in this solvent. We found that

2700
R.T. Boere´ et al. / Journal of Organometallic Chemistry 692 (2007) 2697–2704
Fig. 2. Cyclic voltammogram of 8 plus internal ferrocene reference in
CH2Cl2/[nBu4N][PF6]; scan rate 0.1 V sꢀ1
.
a phenyldithiadiazole with a para CF3 group [27]. This is
consistent with Hammet parameters for meta cyano almost
identical to those for para CF3; evidently the much smaller
inductive effect of the meta tert-butyl group is swamped by
the larger influence of the cyano substituent. As is common
for 4-substituted 1,2,3,5-dithiadiazolyls, all remote substitu-
ent effects are small, consistent with a node at the carbon
atom of the five-membered ring in the SOMO of the free
radical [27]. The voltammetric behaviour, as the EPR also
suggests, reflects the dominance of the free radical rather
than its diamagnetic dimer in dilute solution in both
CH3CN and CH2Cl2 [27].
Fig. 1. EPR spectrum of 8. (a) Experimental spectrum at 253 K in CH2Cl2
at high dilution, g = 2.011; expansion at low- and high-field with very high
gain; arrows indicate 33S satellite peaks. (b) Computer simulation: 80%
Gaussian line-shape admixture; aN = 0.509 mT; aS = 0.63 mT.
approximately linear over the range 253–293 K (variation
of 0.7 nT/K).
The spectrum obtained at 253 K displayed a very high
signal-to-noise ratio which allowed for enlargement of the
intensity axis of this spectrum until the satellite peaks from
the 33S isotope at natural abundance (0.75%, I = 3/2)
become clearly visible (Fig. 1, inset). A good match was
obtained at aS = 0.630 mT. Preston and Sutcliffe measured
such a constant to be 0.62 mT in a single-crystal EPR study
of PhCN2S2 [26], in good agreement with the value
obtained here for 8. There is no reason to expect a large
substituent effect on the 33S hfc because none has been
observed for 14N hfc.
2.5. Crystal structure of 8
The crystal structure of 8 was reported in our prelimin-
ary communication, but the geometrical parameters were
not provided. A thermal ellipsoid plot is provided of the
molecular structure of 8 in Fig. 3. The tert-butyl group dis-
plays typical rotational disorder and was adequately mod-
elled using two full sets of methyl carbon atoms fixed at
half-occupancy, constrained to have similar bond lengths
to C9 and to have approximate isotropic temperature
coefficients.
2.4. Voltammetry of 8
The voltammetry of 8 has been investigated using both
cyclic- and Osteryoung square wave voltammetry (Table 1
and Fig. 2). Both the 0/+1 and the ꢀ1/0 redox processes
are essentially reversible, with Ea ꢀ Ec values of 97 and
66 mV, respectively, under conditions where the internal
reference ferrocene/ferrocenium couple displays 105 mV.
Platinum wire electrodes were employed as the working
and auxiliary and a platinum button as the pseudo reference
electrodes in an all-glass electrochemical cell operated under
vacuum [27]. The observed potentials of +0.658 V for the
0/+1 and ꢀ0.787 V for the ꢀ1/0 couples on the SCE scale
are almost identical to that measured by us previously for
The crystal structure of the new dithiadiazolyl radical 8
bears a resemblance to that of the bis radical 7 insofar as in
each case, the large out-of-plane tert-butyl group seems to
control the observed crystal architecture. In 8, as usual for
dithiadiazolyls, the thiazyl rings form discrete dimers, lead-
ing to a diamagnetic ground state, but they display a rare
example of the trans-cofacial arrangement (Fig. 4) [14a].
This motif has been reported previously in the structure
of 4-I–C6H4–CN2S2 [28] and in a 2,20-dimethylbiphenylene
(DMBP) bridged bisdithiadiazolyl [29].
Cyano groups have been extensively utilized as crystal
engineering building blocks in dithiadiazolyl chemistry
Table 1
Voltammetric data for the dithiadiazolylsa
Compound
E1/2/V
E1/2/V
E1/2/V
E1/2/V
Reference
CH3CN
‘‘Oxidation’’
+0.658
CH2Cl2
‘‘Oxidation’’
‘‘Reduction’’
ꢀ0.787
‘‘Reduction’’
8
7
a
This work
[16]
+0.61
ꢀ0.80
+0.78
ꢀ0.72
Measured at Pt wire or button electrodes in an all-glass cell operating under vacuum [27], employing a pseudo reference electrode and calibrated against
added Fc/Fc+ at +0.38 V vs. SCE in CH3CN and +0.48 V vs. SCE in CH2Cl2 [27b].

R.T. Boere´ et al. / Journal of Organometallic Chemistry 692 (2007) 2697–2704
2701
Fig. 3. Thermal elipsoid plot (Mercury) of the molecular structure of 8 as
˚
found in the crystal. Selected bond lengths (A) and angles (ꢁ): S1–S2
2.101(2), S1–N1 1.624(4), S2–N1 1.626(4), C1–N1 1.334(6), C1–N2
1.334(6), N3–C8 1.125(7), C1–C2 1.476(6), C2–C3 1.391(7), C3–C4
1.389(7), C4–C8 1.456(7), C4–C5 1.375(7), C5–C6 1.389(8), C6–C7
1.393(7), C7–C2 1.396(7), N1–S1–S2 93.8(2), S1–S2–N2 94.4(2), C1–N1–
S1 115.2(3), C1–N2–S2 114.6(3), C4–C8–N3 177.2(6).
Fig. 5. Lipophilic and stacked-ring regions in the crystal structure of 8.
The view is down horizontally oriented ab planes of the orthorhombic
lattice.
The specific structural motif of layers of lipophilic and
heterocyclic regions in a thiazyl crystal structure is, to
our knowledge, known elsewhere only in the case of ada-
mantyl-CN2S2 [30]. In the reported crystal structure of this
molecule, there are double layers of hydrocarbon groups
separated by interleaved layers of thiazyl rings. The lipo-
philic preference of the adamantyl groups seems to drive
the lattice geometry, and leads to rather unconventional
intermolecular interactions between the polar thiazyl
groups. This motif is thus highly reminiscent of that found
in 8 (see Fig. 5), with the difference that in the latter struc-
ture, the heterocyclic and the substituted phenyl rings are
interleaved.
Fig. 4. Intermolecular interactions in the crystal found for 8 include a
relatively-rare trans-cofacial dithiadiazolyl dimer (average S ꢁ ꢁ ꢁ N dis-
˚
tances are 3.09(1) A) as well as nitrile orienting links with CN ꢁ ꢁ ꢁ S1
˚
˚
contacts of 2.98(1) A. The CN ꢁ ꢁ ꢁ S2 distance is 3.37(1) A. The view is
down the c axis with the b axis horizontal.
[17]. In most of these structures, the nitrile nitrogen donor
atom coordinates to both sulfur acceptor atoms of
(another) dithiadiazolyl ring. In 8, this donating ability is
apparently incompatible with the steric demands of the
tert-butyl groups. Instead an asymmetric arrangement is
A slightly different, but related, packing behaviour is
observed in a DMBP bridged bisdithiadiazolyl (vide supra),
in which the methyl-substituted biphenylenes form lipo-
˚
found, with a short contact of 2.98(1) A between the nitrile
nitrogen N3 and sulfur S1 on a neighbouring thiazyl ring,
˚
ꢀ
and a longer distance of 3.37(1) A to S2. The latter corre-
philic zones parallel to the crystallographic f100g planes,
sponds more or less to the sum of the v.d. Waals radii of
these elements. This link results in an infinite flat ribbon
of molecules coordinated via the nitrile. As can be seen in
Fig. 4, the trans-cofacial dimerization, along with the CN
coordination, results in two ribbons running in opposite
directions along the b direction of the crystal lattice.
Between the dimeric [CN2S2]2 units are double layers of
the aryl ring. The resulting architecture provides a lamellar
structure with alternating layers of the tert-butyl groups
and aromatic nitrile/thiazyl ring layers parallel to the crys-
tallographic {001} planes (Fig. 5). The crystal packing
seems to be as much determined by the steric and lipophilic
preferences of the tert-butyl groups as by the Lewis base
interactions of the cyano groups. A similar effect was
observed in the crystal structure of the bisdithiadiazolyl
7, where the tert-butyl groups aggregate around fourfold
rotation axes to form long lipophilic columns [16].
and the CN2S2 rings form bilayers between these zones [29].
2.6. Crystal structure of 9
Radical 8 reacts with [CpCr(CO)3]2 to produce complex 9
(Scheme 3) [1]. The CpCr(CO)2 group is coordinated endo to
the thiazyl ring as in 3b, unlike the exo orientation obtained
in the solid-state structure of 3a [1]. In the crystal structure,
in contrast to the parent radical structure 8, the dithiadiaz-
olyl ring does not participate in any secondary contacts.
Instead two molecules of 9 form centrosymmetric dimers
˚
via duplicate C„N3 ꢁ ꢁ ꢁ H5–C contacts of 2.69(1) A, consis-
ꢀ
tent with P1 space symmetry (Fig. 6). Given the dominance
of nitrile-to-sulfur contacts in dithiadiazolyl structures men-
tioned above, it seems almost certain that the combined ste-
ric shielding of the meta tert-butyl and the CpCr(CO)2
groups serves to isolate the thiazyl rings from each other.

2702
R.T. Boere´ et al. / Journal of Organometallic Chemistry 692 (2007) 2697–2704
Fig. 8. Intermolecular contacts in the crystalline lattice of 3b. The short
Fig. 6. Nitrile to aromatic C–H dimer motif in the crystal structure of 9.
˚
contacts fall into two groups of 3.473 and 3.549 A. These distances are
˚
similar to, but slightly longer than the 3.385 and 3.521 A, observed in the
In other respects, the structure of 9 closely resembles that of
3a,b [1].
crystal structure of the free dithiadiazolyl dimer [27b].
The behaviour in this sterically congested complex may
be compared with those observed in the crystal lattices of
3a and 3b [1]. The short intermolecular contacts in 3a are
displayed in Fig. 7. This complex is quite remarkable in
that despite the large CpCr(CO)2 groups, the dithiadiazolyl
rings still manage to pack as side-by-side pairs. Such side-
ways interactions have been observed in numerous crystal
structures of dithiadiazolyl radical dimers. For example,
3. Conclusions
The bulky tert-butyl group does not hinder g2-coordina-
tion to CpCr(CO)2, and the structure of complex 9 is anal-
ogous to that of the less sterically-hindered analogues 3.
However, in the solid-state structure, in contrast to the free
dithiadiazolyl 8, complex 9 displays a crystal structure in
which the orienting influence of the cyano group towards
the thiazyl ring has been shut down. Only a C„N ꢁ ꢁ ꢁ ÆH–
C interaction remains to form weakly associated centrosym-
metric, isolated, pairs in the crystal lattice. By contrast, the
less sterically congested ligands in 3a and 3b show supramo-
lecular interactions in the crystalline lattices, which though
weakened by electronic and steric changes as a result of
complexation to CpCr(CO)2, are not eliminated.
The most significant observation of this work, however,
is that the potent thiophile [CpCr(CO)3]Å reacts with
1,2,3,5-dithiadiazolyl radicals or their dimers without rup-
turing S–S bonds, even though the resulting ‘‘oxidative
addition’’ products are known to dominate in the coordi-
nation compounds of thiazyl radicals. Investigations on
the generality of this principle for the reactivity of organo-
metallic radicals and unsaturated main-group ring com-
pounds are ongoing in our laboratories.
˚
in 1 (X = Cl), S ꢁ ꢁ ꢁ N contacts of 3.130 and 3.207 A were
reported [27b], while in several of the cyano-substituted
complexes mentioned above this motif also occurs, with
˚
S ꢁ ꢁ ꢁ N contacts ranging from 3.211 to 3.284 A [17a,17b].
As mentioned previously, other substituents have been
investigated as supramolecular synthons in dithiadiazolyls,
in particular halogens. In the crystal structure of 1 (X = Cl)
˚
[27b], short, somewhat asymmetric (3.385 and 3.521 A),
contacts are observed between the Cl atom and both sulfur
atoms of the heterocycle, although the interactions are not
strong enough to induce sheet-structures as commonly
observed for cyano complexes [17]. In the metal complex
3b similar intermolecular contacts are found (Fig. 8). The
interactions are to sulfur atoms on two different molecules,
perhaps because the Cr coordination partly blocks access
to the sulfur atoms, and their strength as indicated by dis-
˚
tances is slightly weaker (3.473 and 3.549 A). The interac-
tions in 3b lead to an infinite network connecting the
complexes via Cldꢀ ꢁ ꢁ ꢁ Sd+ interactions.
4. Experimental
4.1. General methods
5-tert-Butylisophthalic acid, sulfur dichloride, lithium
bis(trimethylsilyl)amide, n-butyllithium, thionyl chloride,
chlorotrimethylsilane, and triphenylantimony were all
obtained commercially (Aldrich). Sulfur dichloride was dis-
tilled before use. Lithium bis(trimethylsilyl)amide diethyl
etherate [23a], 5-tert-butyl-1,3-dicyanobenzene [24] and 5-
tert-butyl-1,3-bis-(1,2,3,5-dithiadiazolyl)benzene [16] were
prepared as described previously. NMR spectra (250 or
300 MHz) were referenced to the solvent (1H and 13C) or
to external H3PO4 (31P). EPR spectra were recorded on a
Bruker EMX 113 spectrometer operating in X band; temper-
ature was adjusted and controlled by the Bruker VT acces-
sory. All manipulations were conducted under exclusion of
the atmosphere by either vacuum or a nitrogen blanket.
Fig. 7. Intermolecular contacts in the crystalline lattice of 3a. Side-by-side
dimerization of the complexed 1,2,3,5-dithiadiazole ring occurs through
˚
N
dꢀ ꢁ ꢁ ꢁ Sd+ interaction at 3.104 A. Weaker van der Waals interactions link
˚
˚
the dimeric pairs through CH ꢁ ꢁ ꢁ N (2.722 A) and CO ꢁ ꢁ ꢁ S (3.210 A)
contacts.

R.T. Boere´ et al. / Journal of Organometallic Chemistry 692 (2007) 2697–2704
2703
4.2. Synthesis of 5-tert-butyl-3-cyano-1-(1,2,3,5-
dithiadiazolyl)benzene 8
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Solid 5-tert-butyl-1,3-dicyanobenzene (10.00 g, 54.3
mmol) and solid lithium bis(trimethylsilyl)amide diethyl
etherate (13.06 g, 54.1 mmol) were slurried in 100 mL
Acknowledgements
We thank the Natural Sciences and Engineering Re-
search Council (Canada) and the National University of
Singapore for financial support. T.L.R. acknowledges
NSERC for a PGS-D scholarship and the Alberta Ingenu-
ity Fund for a Doctoral Scholar award. The University of
Lethbridge Travel Fund and the Faculty of Arts and Sci-
ence helped to defray the costs of the delivery of the oral
form of this paper. R.T.B. thanks Dr. J.-P. Majoral of
LCC-Toulouse, France, for hospitality on a Sabbatical
leave where this paper was written.
1
anhydrous diethyl ether for 2 h. H NMR analysis of the
supernatant displayed a single peak (d ꢀ0.30 ppm refer-
enced to the ether methyl peak at 1.12 ppm) characteristic
of the lithiated amidine [23b]. Evaporation of volatiles left
a white solid N-lithio-5-tert-butyl-3-cyano-1-(1,3-bistrim-
ethylsilylcarboximidamide, which was taken up in 80 mL
CH3CN and reacted drop-wise with SCl2 (11.4 mL,
179 mmol) with vigorous stirring, whereupon the solution
was heated to reflux for 2 h. After cooling, orange dith-
iadiazolium chloride was filtered and dried in vacuo. The
salt was suspended in 25 mL of CH3CN and a solid-addi-
tion funnel containing Ph3Sb (10.1 g, 28.7 mmol) was
attached to the flask, the solvent deoxygenated 3· by
freeze–thaw cycles, whereupon the Ph3Sb was added. After
stirring a while, the resulting slurry was heated to reflux for
2 h, and then cooled to ꢀ35 ꢁC overnight. The precipitate
was largely Ph3SbCl2 (11.5 g dry); the dark filtrate was left
at RT for 2 d, and the black precipitate collected and dried.
The powder is extremely oxygen sensitive until it is purified
by sublimation in a three-zone tube furnace (24/45/120 ꢁC)
under dynamic vacuum, yielding black crystals of 8 (4.00 g,
28.2% yield based on nitrile). Analytical sample and crys-
tals suitable for X-ray crystallography obtained on re-sub-
limation. IR, Raman: m(C„N) = 2229 cmꢀ1, EI-MS: m/z
262 ([M]+, 100%), 247 ([MꢀCH3]+, 100%), 219 ([Mꢀ
4CO+1]+, 60%), 169 ([C11H9N2]+, 55%), 141 ([C11H9]+,
95%), 78 ([S2N]+, 82%).
References
[1] H.F. Lau, V.W.L. Ng, L.L. Koh, G.K. Tan, L.Y. Goh, T.L.
´
Roemmele, S.D. Seagrave, R.T. Boere, Angew. Chem. 118 (2006)
4610;
Angew. Chem. Int. Ed. 45 (2006) 4498.
´
[2] C.Y. Ang, R.T. Boere, L.Y. Goh, L.L. Koh, S.L. Juan, G.K. Tan,
X. Yu, Chem. Commun. (2006) 4735, doi:10.1039/b610089a.
[3] (a) J. Van Droogenbroeck, C. Van Alsenoy, S.M. Aucott, J.D.
Woollins, A.D. Hunter, F. Blockhuys, Organometallics 24 (2005)
1004;
(b) S.M. Aucott, P. Bhattacharyya, H.L. Milton, A.M.Z. Slawin,
J.D. Woollins, New J. Chem. 27 (2003) 1466;
(c) S.M. Aucott, A.M.Z. Slawin, J.D. Woollins, Can. J. Chem. 80
(2002) 1481;
(d) W.-K. Wong, C. Sun, W.-Y. Wong, D.W.J. Kwong, W.-T.
Wong, Eur. J. Inorg. Chem. (2000) 1045;
(e) A.J. Banister, I. May, J.M. Rawson, J.N.B. Smith, J. Organomet.
Chem. 550 (1998) 241;
(f) T. Chivers, F. Edelmann, Polyhedron 5 (1986) 1661.
[4] (a) M. Jennings, K.E. Preuss, J. Wu, Chem. Commun. (2006) 341;
(b) N.R.G. Hearns, K.E. Preuss, J.F. Richardson, S. Bin-Salamon, J.
Am. Chem. Soc. 126 (2004) 9942.
4.3. Electrochemistry
[5] (a) L.Y. Goh, Coord. Chem. Rev. 185–186 (1999) 257, and references
therein;
Voltammetry was performed in a previously described
all-glass electrochemical cell under vacuum [27]. CH3CN
was used as solvent, containing 7.62 · 10ꢀ3 M 9 and
9.6 · 10ꢀ2 M [nBu4N][PF6] as electrolyte. Ferrocene was
added at the end of the measurements as internal reference
to 5.2 · 10ꢀ3 M concentration. After verifying the solvent/
electrolyte background current, the analyte was added and
CV (scan rates 0.1–1.0 V sꢀ1) and OSV were measured
starting at the limit of detectability. No change was
observed in the essential characteristics of the system up
to the maximum concentration. Currents range from 1 to
600 lA from the lowest up to full concentration in OSV,
and from ꢂ1 to 450 lA for the anodic peak of the 0/+1
redox couple in CV.
(b) L.Y. Goh, W. Chen, R.C.S. Wong, Chem. Commun. (1999) 1481;
(c) L.Y. Goh, W. Chen, R.C.S. Wong, Organometallics 18 (1999)
306.
[6] Z. Weng, L.Y. Goh, Acc. Chem. Res. 37 (2004) 187, and references
therein.
[7] (a) R.D. Adams, D.E. Collins, F.A. Cotton, J. Am. Chem. Soc. 96
(1974) 749;
(b) T. Madach, H. Vahrenkamp, Z. Naturforsch. B 33b (1978) 1301;
(c) L.Y. Goh, M.J. D’Aniello Jr., S. Slater, E.L. Muetterties, I.
Tavanaiepour, M.I. Chang, M.F. Fredrich, V.W. Daz, Inorg. Chem.
18 (1979) 192–197;
(d) S.J. McLain, J. Am. Chem. Soc. 110 (1988) 643;
(e) M.C. Baird, Chem. Rev. 88 (1988) 1217;
(f) L.Y. Goh, Y.Y. Lim, J. Organomet. Chem. 402 (1991) 209;
(g) D.C. Woska, Y. Ni, B.B. Wayland, Inorg. Chem. 38 (1999) 4135.
[8] L.Y. Goh, Z. Weng, W.K. Leong, J.J. Vittal, J. Am. Chem. Soc. 124
(2002) 8804.
5. Supplementary material
[9] (a) L.Y. Goh, Z. Weng, W.K. Leong, P.H. Leung, Angew. Chem.
Int. Ed. 40 (2001) 3236;
CCDC 299596 contains the supplementary crystallo-
graphic data for 8. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Cen-
(b) L.Y. Goh, Z. Weng, W.K. Leong, P.H. Leung, Organometallics
21 (2002) 4398;
(c) L.Y. Goh, Z. Weng, T.S.A. Hor, W.K. Leong, Organometallics
21 (2002) 4408.

2704
R.T. Boere´ et al. / Journal of Organometallic Chemistry 692 (2007) 2697–2704
[10] L.Y. Goh, Z. Weng, W.K. Leong, J.J. Vittal, I. Haiduc, Organomet-
allics 21 (2002) 5287.
[11] (a) L.Y. Goh, M.S. Tay, T.C.W. Mak, R.-J. Wang, Organometallics
11 (1992) 1711;
(b) A.M.T. Bell, J.N.B. Smith, J.P. Attfield, J.M. Rawson, K.
Shankland, W.I.F. David, New J. Chem. (Nouv. J. Chim.) 23 (1999)
565;
(c) A.J. Banister, A.S. Batsanov, O.G. Dawe, P.L. Herbertson,
J.A.K. Howard, S. Lynn, I. May, J.N.B. Smith, J.M. Rawson, T.E.
Rogers, B.K. Tanner, G. Antorrena, F. Palacio, J. Chem. Soc.,
Dalton Trans. (1997) 2539;
(d) A.J. Banister, A.S. Batsanov, O.G. Dawe, P.L. Herbertson,
J.A.K. Howard, S. Lynn, I. May, J.N.B. Smith, J.M. Rawson, T.E.
Rogers, B.K. Tanner, G. Antorrena, F. Palacio, J. Chem. Soc.,
Dalton Trans. (1997) 2539.
(b) L.Y. Goh, M.S. Tay, Y.Y. Lim, T.C.W. Mak, Z.-Y. Zhou, J.
Chem. Soc., Dalton Trans. (1992) 1239;
(c) L.Y. Goh, M.S. Tay, W. Chen, Organometallics 13 (1994)
1813.
[12] L.Y. Goh, W.K. Leong, P.-H. Leung, Z. Weng, I. Haiduc, J.
Organomet. Chem. 607 (2000) 64.
[13] L.Y. Goh, Z. Weng, W.K. Leong, I. Haiduc, K.M. Lo, R.C.S.
Wong, J. Organomet. Chem. 631 (2001) 67.
[14] (a) J.M. Rawson, A. Alberola, A. Whalley, J. Mater. Chem. 16
(2006) 2560;
[19] T. Amano, T. Amano, in: Proceedings of the 44th Symposium on
Molecular Spectroscopy, June 12–16, 1989, Colombus, OH.
[20] P. Hassanzadeh, L. Andrews, J. Phys. Chem. 114 (1991) 83.
[21] Y. Yamaguchi, Y. Xie, R.S. Grev, H.F. Schaefer III, J. Chem. Phys.
92 (1990) 3683.
(b) J.M. Rawson, J. Luzon, F. Palacio, Coord. Chem. Rev. 249
(2005) 2631.
[15] A. Alberola, C.S. Clarke, D.A. Haynes, S.I. Pascu, J.M. Rawson,
Chem. Commun. (2005) 4726.
[22] M.T. Nguyen, R. Flamming, N. Goldberg, H. Schwarz, Chem. Phys.
Lett. 236 (1995) 201.
[16] R.A. Beekman, R.T. Boere´, K.H. Moock, M. Parvez, Can. J. Chem.
76 (1998) 85.
[23] (a) R.T. Boere´, R.G. Hicks, R.T. Oakley, Inorg. Synth. 21 (1997) 94;
´
(b) R.T. Boere, R.T. Oakley, R.W. Reed, J. Organomet. Chem. 331
[17] (a) A.W. Cordes, C.M. Chamchoumis, R.G. Hicks, R.T. Oakley,
K.M. Young, R.C. Haddon, Can. J. Chem. 70 (1992) 919;
(b) A.W. Cordes, R.C. Haddon, R.G. Hicks, R.T. Oakley, T.T.M.
Palstra, Inorg. Chem. 31 (1992) 1802;
(1987) 161.
[24] M.A. McCall, J.R. Caldwell, H.G. Moore, H.M. Beard, J. Macro-
mol. Sci. Chem. A3 (1969) 911.
[25] WINSIM 2002: D.R. Duling, J. Magn. Res., Ser. B 104 (1994) 105.
[26] F.L. Lee, K.F. Preston, A.J. Williams, L.H. Sutcliffe, A.J. Banister,
S.T. Wait, Magn. Reson. Chem. 27 (1989) 1161.
(c) G. Antorrena, S. Brownridge, T.S. Cameron, F. Palacio, S.
Parsons, J. Passmore, L.K. Thompson, F. Zarlaida, Can. J. Chem.
80 (2002) 1568;
´
[27] (a) R.T. Boere, T.L. Roemmele, Coord. Chem. Rev. 210 (2000) 369;
´
(d) A.W. Cordes, R.C. Haddon, R.G. Hicks, D.K. Kennepohl, R.T.
Oakley, T.T.M. Palstra, L.F. Schneemeyer, S.R. Scott, J.V. Waszc-
zak, Chem. Mater. 5 (1993) 820;
(b) R.T. Boere, K.H. Moock, M. Parvez, Z. Anorg. Allg. Chem. 620
(1994) 1589;
´
(c) R.T. Boere, K.H. Moock, J. Am. Chem. Soc. 117 (1995) 4755;
(e) A.J. Banister, N. Bricklebank, W. Clegg, M.R.J. Elsegood, C.I.
Gregory, I. Lavender, J.M. Rawson, B.K. Tanner, Chem. Commun.
(1995) 679;
(f) A.J. Banister, N. Bricklebank, I. Lavender, J.M. Rawson, C.I.
Gregory, B.K. Tanner, W. Clegg, M.R.J. Elsegood, F. Palacio,
Angew. Chem. Int. Ed. 35 (1996) 2533.
(d) K.H. Moock, M.H. Rock, J. Chem. Soc., Dalton Trans. (1993)
2459.
[28] N. Bricklebank, S. Hargreaves, S.E. Spey, Polyhedron 19 (2000)
1163.
[29] T.M. Barclay, A.W. Cordes, N.A. George, R.C. Haddon, M.E. Itkis,
R.T. Oakley, Chem. Commun. (1999) 2269.
[30] J.N. Bridson, S.B. Copp, M.J. Schriver, S. Zhu, M.J. Zaworotko,
Can. J. Chem. 72 (1994) 1143.
[18] (a) L. Beer, A.W. Cordes, D.J.T. Myles, R.T. Oakley, N.J. Taylor,
Cryst. Eng. Commun. (2000) 20;