Molecular and crystal structures of Cp*M(S2N2) (M = Co, Rh, Ir) and related compounds

Article abstract of DOI:10.1002/ejic.200900541

Cp*Rh(S₂N₂) was prepared as a microcrystalline solid by using [S₄N₃]Cl in liquid ammonia or [nBu ₂Sn(S₂N₂)]₂. It was characterised by NMR, IR and Raman spectroscopy an

Full text of DOI:10.1002/ejic.200900541

FULL PAPER
DOI: 10.1002/ejic.200900541
Molecular and Crystal Structures of Cp*M(S2N2) (M = Co, Rh, Ir)
and Related Compounds
Vit Matuska,[a] Karla Tersago,[b] Petr Kilian,[a] Christian Van Alsenoy,[b] Frank Blockhuys,[b]
Alexandra M. Z. Slawin,[a] and J. Derek Woollins*[a]
Keywords: Metallacycles / Rhodium / Structure elucidation / Density functional calculations
Cp*Rh(S2N2) was prepared as a microcrystalline solid by
using [S4N3]Cl in liquid ammonia or [nBu2Sn(S2N2)]2. It was
characterised by NMR, IR and Raman spectroscopy and
mass spectrometry. Low-temperature crystal structures of
Cp*Co(S2N2) and Cp*Ir(S2N2) were determined. The experi-
mental characterisation of the Cp*M(S2N2) complexes was
complemented by calculated geometries and bond orders at
the DFT/B1B95 level of theory.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
1. Introduction
As a consequence of the fascinating discovery of the con-
ductive properties of (SN)x polymer, sulfur–nitrogen chem-
istry has registered a rapid development in all its areas since
1973.[1] As a part of that, inorganic sulfur–nitrogen rings
became so popular that even after three decades of research
the interest in them continues. The five-membered rings (di-
thiadiazoles) have attracted special attention mostly be-
cause of their ability to form radicals.[2] While dithiadia-
zoles have been investigated in detail,[2] metalladithiadia-
zoles have not received attention with similar intensity.
Moreover, only a small number of reports have been pub-
lished on 5,1,3,2,4-metalladithiadiazoles with a half-sand-
wich structure stabilised with cyclopentadienyl (Cp) or
pentamethylcyclopentadienyl (Cp*) ligands.[3–6] There were
several attempts to synthesise both Cp and Cp* metalla-
dithiadiazoles using various transition metals.[5] Unfortu-
nately, despite quite a wide range of commercially available
possible starting materials, only 5,1,3,2,4-metalladithiadia-
zoles containing group 9 metals could be prepared with
partial success. CpCo(S2N2) (1) was investigated in detail,
whereas the X-ray structure of Cp*Co(S2N2) (2) has not
been reported.[3–5] CpRh(S2N2) (3), Cp*Rh(S2N2) (4) and
CpIr(S2N2) (5) have not yet been synthesised and
Cp*Ir(S2N2) (6) thus remains the only prepared and fully
characterised iridium analogue (Figure 1).[6]
Figure 1. Structural formulae and numbering of the title com-
pounds. Formal bonding is displayed.
Quantum-chemical studies on metalladithiadiazoles con-
tinue to represent a challenge as the complexity of the cal-
culations increases dramatically with the growing number
of atoms/electrons involved and with the presence of heavier
elements such as phosphorus, sulfur and transition metals.
Thanks to the development of new approaches within den-
sity-functional theory (DFT) in the early 2000s, it has be-
come possible to study more advanced systems containing
heavier elements.[7–10] Since then, we focused our attention
on sulfur–nitrogen ring compounds and we found suitable
DFT methodologies which led to successful descriptions of
Roesky’s sulfoxide (S3N2O),[11] Roesky’s ketone [(S2N2)-
CO][12] and other ring compounds bearing the –SNSN–
fragment.[13] Experience from previous work combined with
the advantage of the use of hybrid functionals enabled us
to perform a detailed study on 1 with the emphasis on the
geometry of the molecule, its bonding, aromaticity, and re-
activity.[14]
In this article, we report the preparation and characteri-
sation of the missing 5-(η5-pentamethylcyclopentadienyl)-
5,1,3,2,4-rhodiadithiadiazole (4) alongside the low-tempera-
ture crystal structure of 2. The molecular structures of com-
pounds 2, 4 and 6, together with those of their non-penta-
methylated counterparts, are discussed in terms of calculated
(DFT/B1B95) gas-phase geometries and bond orders, and
are compared to the structures found in the solid state.
[a] University of St Andrews, School of Chemistry,
North Haugh, St Andrews, Fife, KY16 9ST, United Kingdom
[b] University of Antwerp, Department of Chemistry,
Universiteitsplein 1, B-2610 Wilrijk, Belgium
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900541.
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FULL PAPER
2. Results and Discussion
2.1. Syntheses of the Complexes
Complex 2 was prepared according to the published pro-
cedure from S4N4 and Cp*Co(CO)2 (Scheme 1).[4]
Scheme 3.
TLC analysis of the crude mixture suggested decomposi-
tion of 4 on both silica and alumina. However, small
amounts of pure 4 were obtained by a careful elution with
an acetone/toluene (1:2) mixture from a silica column. Both
Scheme 1.
The mechanism of the reaction is not completely under-
stood, but it was proposed that in the initial step S4N4 is
coordinated to the metal centre, which promotes cleavage
of S4N4 into S2N2. The next step is oxidative addition of
S2N2 to the metal.[15] In contrast to the CoI centre, the oxi-
dative addition of S2N2 to a RhI or IrI centre leads to for-
mation of insoluble precipitates, which are thought to be of
polymeric nature.[5] The method proved unsuitable also for
the synthesis of numerous other metalladithiadiazoles.[5] We
found that 4 can be prepared in two synthetic routes, but
its instability makes its purification and isolation difficult.
The reaction of [S4N3]Cl with liquid ammonia is a safe
and clean procedure, which has been used previously for
the preparation of a variety of five-membered metal–sulfur–
nitrogen rings.[16] The mechanism of this reaction and its
stoichiometry are complex and are not completely under-
stood to date. The [S4N3]Cl/NH3(l) system reacted with
[Cp*RhCl2]2 (Scheme 2) to give a beige/brown mixture of
1
the H and 13C NMR spectra were identical to the spectra
of 4 prepared by the liquid ammonia route. The ES+TOF
mass spectrum of pure 4 showed a single peak at m/z 330.99
([MH]+). To obtain better yields, we attempted separations
on silica, alumina, Bio-Beads together with dry and de-
gassed solvents. Although the yields were very small, we
were able to isolate 4 on every occasion, which demon-
strates the reproducibility of the preparation method.
Complex 6 was prepared by ligand exchange between
[Cp*IrCl2]2 and the tin reagent [nBu2Sn(S2N2)]2.[6] It is
noteworthy that for a successful synthesis of 6 the reactants
must be mixed in solutions. The published addition of solid
tin reagent in one portion to a solution of [Cp*IrCl2]2 leads
to the formation of a temporarily heterogeneous mixture,
in which [Cp*IrCl2]2 readily reacts with the gradually dis-
solving tin reagent to give complex 8 (Scheme 4).
1
solids, which produced a complex H NMR spectrum with
two dominant singlets at δ = 1.80 and 2.07 ppm.
Scheme 2.
Scheme 4.
The 13C NMR spectrum of the crude mixture contained
signals at 9.26 and 94.94 ppm accompanied by a weak sing-
let at δ = 8.70 ppm. The assignment of the signals was based
on an ES+TOF mass spectrum, which showed two peaks
corresponding to [Cp*Rh(S2N2H)]+ (330.95) and the deca-
methylrhodiocenium cation [Cp*RhCp*]+ (373.11). Given
the composition of the liquid ammonia reaction system, the
most probable decamethylrhodiocenium byproduct is
2.2. Molecular and Crystal Structures
Suitable crystals of 2 were obtained as purple plates by
recrystallization from a hot hexane solution. X-ray analysis
confirmed the structure of 2 as 5-(η5-pentamethylcyclopen-
tadienyl)-5,1,3,2,4-cobaltadithiadiazole. The Co(S2N2) ring
is planar and is perpendicular to the Cp* plane (Figure 2).
1
[Cp*RhCp*]Cl (7). A comparison of the recorded H and
13C NMR spectra of the crude mixture of solids and those
of 7 confirmed that the singlet at δ = 1.80 ppm (1H) and
the one at δ = 8.70 ppm (13C) can be assigned to 7, and
thus the signal at δ = 2.07 ppm (1H) and those at 9.26 and
94.94 ppm (13C) must belong to 4. We determined the struc-
ture of [Cp*RhCp*]Cl (7) and confirmed our assignment
of the observed NMR spectrum for this species.[17]
An alternative strategy for the synthesis of 4 is the trans-
metallation reaction between [nBu2Sn(S2N2)]2 and
[Cp*RhCl2]2, in a fashion similar to the preparation of 6
(Scheme 3).[6]
Figure 2. The crystal structure of 2.
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Cp*M(S2N2) (M = Co, Rh, Ir) and Related Compounds
The low-temperature X-ray structure of 6 is nearly iden- shorter than the Cp*–Ir(1) distance. This can be explained
tical to the structure measured at 293 K.[6] In the low-tem- by the presence of the two chlorine atoms on Ir(2), which
perature structure, the Ir–S and all N–S bond lengths ap- are withdrawing electron density from the metal centre forc-
pear slightly elongated, though the effect is modest. 2 and ing the Cp* ring to be situated closer to Ir(2).
6 show very similar crystal packing with stacking of mole-
Attempts to obtain crystals of 4 were unsuccessful.
cules illustrated in Figure 3. Intermolecular contacts be- Recrystallization by gas-phase diffusion of hexane into a
tween two NSN sulfur atoms were observed in the packing dichloromethane solution of 4 resulted only in deposition
of 6 (Figure 3), the distance (3.612 Å) being just on the edge of a thin red film on the walls of a sample vial suggesting
of the sum of van der Waals radii (3.60 Å).[20]
a low tendency of 4 to crystallise. Attempts to recrystallize
4 from a hot dichloromethane or toluene solution led to
the formation of black tarry globules as a result of heat
decomposition, while saturated toluene or dichloromethane
solutions of 4 stored at –20 °C over several weeks resulted
only in separation of powdery precipitates. Powder dif-
fractograms of several samples of 4 contained broad and
badly defined peaks rising only slightly from a noisy base-
line suggesting a microcrystalline substance with a very
small particle size. When recrystallized from non-predried
solvents (CH2Cl2/hexane), compound 4 hydrolysed into
compound 9, which formed rosettes of fragile red needles
at the bottom of the sample vial. The quality of the crystals
was below average even after several recrystallizations but
the X-ray structure could be solved. Compound 9 consists
of two Cp*Rh units bridged by a [S3N2]2– ligand and by the
terminal sulfur of a thiosulfate anion (Figure 5).[21] Metal
complexes bearing either [S3N2]2– or thiosulfate anion in a
bridging position are known but no rhodium analogues
have been reported.[22,23] Compound 9 also contains both
of these ligands in one molecule, which has not been ob-
served before.
Figure 3. The crystal packing of 6 with highlighted intermolecular
contacts.
The low-temperature single-crystal X-ray structure of 8
revealed cocrystallization of one molecule of nBu2SnCl2
and a disordered molecule of toluene (Figure 4). The mole-
cule of 8 consists of the Cp*Ir(S2N2) central unit, to which
the Cp*IrCl2 ligand is bound.
Figure 4. The X-ray structure of 8·nBu2SnCl2. Hydrogen atoms are
omitted for clarity.
The influence of the Cp*IrCl2 ligand on the Cp*Ir(S2N2)
moiety can be described by a comparison between 6 and
8. The surroundings of the Ir(1) centre in 8 are virtually
unaffected while the geometry of the (S2N2) unit changes
considerably. In 8, the angles at both nitrogen atoms be-
come wider and those at both sulfur atoms become more
acute. Particularly noteworthy is the angle at the donor ni-
Figure 5. The crystal structure of 9.
The molecule has approximate non-crystallographic Cs
trogen atom N(2) which opens by nearly 2°, and the angle symmetry. The Cp* rings in 9 are in an eclipsed position
at S(1) which closes by approximately 2.4°. The reduction and the distance between the two Rh atoms is 3.1347(17) Å
in the angle at S(1) is especially striking taking into account (Table S3 in Supporting Information). Both the [S3N2]2–
that the S(1) atom is formally bound by two double bonds ligand and the two S atoms of the thiosulfate anion lie in
in the Ir(S2N2) ring. The bond lengths of the Cp*Ir(S2N2) one plane that is parallel to the planes of the Cp* rings and
moiety in 8 do not change as considerably as the angles. It is bisecting the distance between them. The three Rh–S–Rh
is interesting to note that the Cp*–Ir(2) distance is 0.054 Å planes can be labelled according to the sulfur atoms as σ1,
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J. D. Woollins et al.
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σ3 and σ4 (Figure 6, a). The distribution of the planes is
influenced by steric hindrance of the bridging ligands. The
angles between σ1 and σ3, and between σ3 and σ4 are both
ca. 122.5°. The former is determined by the steric demands
of the [S3N2]2– ligand, the latter by the interference of the
[S2O3]2– anion with S(3) (Figure 6, b). There is no steric
hindrance between the planes σ4 and σ1 and thus the angle
between them is only 115.0°. The structure of the [S3N2]2–
ligand is analogous to that in the palladium compounds
prepared earlier.[22] The S(4)–S(5) distance in the bridging
thiosulfate anion is 2.163(5) Å which is in good agreement
with the values published for thiosulfate anions in
[Cp*2M2(µ-S2)(µ-S)(µ-SSO3)] (M = Cr, Mo).[23]
Figure 6. The central section of a molecule of 9 displayed by new-
man projection along the Rh(1)–Rh(2) axis (a) and a spacefill
model along the same axis showing the interference of O(1) and
S(3) (b); the front Cp* ring is omitted for clarity.
From both the experimental and computational results
several conclusions can be drawn about the influence of the
Cp/Cp* ligand and the metal centre on the structure and
bonding of CpM(S2N2) and Cp*M(S2N2). The solid-state
molecular geometry of 2 is similar to that of the Cp ana- Also, all bond lengths in the Co(S2N2) ring are approxi-
logue 1,[14] however, the overall size of a molecule of 2 ap- mately 0.05 Å longer in 2 than in 1 and the S–Co–N angle
pears to be larger than that of a molecule of 1 (Table 1).
is approximately 0.3° larger in 2 than in 1. The results of
The distance between the Cp* ring and the Co atom in the calculations (Table 1) suggest that this size increase is a
2 is 1.703(2) Å [cf. 1.662(2) Å between Cp and Co in 1].[14] crystal effect, as the calculated geometry of 2 is almost iden-
Table 1. Selected experimental and calculated bond lengths [Å] and angles [°] and Wiberg bond orders b of compounds 1–6.
1
3
5
X-ray[14]
DFT[a]
b
DFT[a]
b
DFT[a]
b
M(1)–N(1)
N(1)–S(1)
S(1)–N(2)
N(2)–S(2)
S(2)–M(1)
M(1)–C(1)
M(1)–C(2)
M(1)–C(3)
1.816(1)
1.556(1)
1.597(2)
1.657(2)
2.0764(6)
2.037(2)
2.042(2)
2.076(2)
2.065(2)
2.044(2)
1.662(2)
118.32(8)
112.04(7)
111.22(8)
107.40(5)
91.02(5)
1.792
1.558
1.600
1.646
2.102
–
–
–
–
–
1.649
119.9
110.7
112.2
106.6
90.5
0.72
1.49
1.25
1.19
0.79
0.23
0.27
0.23
0.23
0.27
–
1.931
1.562
1.594
1.648
2.215
–
–
–
–
–
1.810
120.0
112.0
114.0
107.4
86.6
0.74
1.48
1.26
1.18
0.81
0.24
0.29
0.24
0.24
0.29
–
1.933
1.573
1.592
1.651
2.216
–
–
–
–
–
1.815
120.3
111.6
114.0
107.7
86.3
0.81
1.42
1.28
1.16
0.87
0.27
0.34
0.27
0.27
0.34
–
M(1)–C(4)
M(1)–C(5)
Cp/Cp*–M(1)
M(1)–N(1)–S(1)
N(1)–S(1)–N(2)
S(1)–N(2)–S(2)
N(2)–S(2)–M(1)
S(2)–M(1)–N(1)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2
4
6
X-ray
DFT[a]
b
DFT[a]
b
X-ray
DFT[a]
b
M(1)–N(1)
N(1)–S(1)
S(1)–N(2)
N(2)–S(2)
S(2)–M(1)
M(1)–C(1)
M(1)–C(2)
M(1)–C(3)
1.8780(19)
1.594(2)
1.634(2)
1.718(2)
2.1371(7)
2.113(2)
2.108(2)
2.113(2)
2.126(2)
2.106(2)
1.703(2)
117.83(11)
112.75(11)
111.27(12)
106.86(8)
91.29(6)
1.801
1.559
1.596
1.657
2.106
–
–
–
–
–
1.634
119.2
111.4
112.3
106.2
90.9
0.66
1.48
1.27
1.16
0.74
0.23
0.27
0.23
0.23
0.27
–
1.944
1.561
1.589
1.660
2.228
–
–
–
–
–
1.792
119.4
112.8
114.2
106.8
86.8
0.69
1.47
1.28
1.15
0.77
0.24
0.30
0.24
0.24
0.30
–
1.963(3)
1.562(4)
1.583(4)
1.682(3)
2.1891(12)
2.201(4)
2.194(4)
2.177(4)
2.198(4)
2.192(4)
1.819(4)
118.59(19)
113.67(17)
112.7(2)
108.13(13)
86.94(11)
1.944
1.571
1.589
1.661
2.225
–
–
–
–
–
1.803
119.9
112.2
114.0
107.4
86.4
0.76
1.42
1.29
1.14
0.84
0.27
0.35
0.26
0.28
0.33
–
M(1)–C(4)
M(1)–C(5)
Cp/Cp*–M(1)
M(1)–N(1)–S(1)
N(1)–S(1)–N(2)
S(1)–N(2)–S(2)
N(2)–S(2)–M(1)
S(2)–M(1)–N(1)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
[a] Bond lengths and angles were calculated at DFT/B1B95/6-311+G*/def-TZPP/ecp level of theory.
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Cp*M(S2N2) (M = Co, Rh, Ir) and Related Compounds
tical to that of 1. The bond lengths in the Co(S2N2) ring tances between the metal centre and N(1) and S(2) ac-
differ by no more than 0.011 Å. The calculated Cp/Cp*–Co company a more acute angle. Analysis of the calculated
distances show an opposite trend to the experimental ones: geometrical data of 1, 3 and 5 brings further insight into
the Cp*–Co distance in 2 is shorter by 0.015 Å than the the influence of the metal. In the series 1Ǟ3Ǟ5 the elong-
Cp–Co distance in 1. The difference between these distances ation of the Cp–M, M–S(2) and M–N(1) bonds can be
is considerably smaller than between the two experimental clearly seen, as well as the reduction of the S(2)–M–N(1)
ones. The observation regarding the S–Co–N angle is also angle. In addition, the S(2)–N(2) and S(1)–N(1) bond
found in the calculated data, as the value in 2 is approxi- lengths increase slightly (by 0.005 and 0.015 Å, respectively)
mately 0.4° larger than in 1.
while the N(2)–S(1) distance becomes slightly shorter (by
Comparison of the calculated geometries of the rhodium 0.008 Å). As a result of this electron density reshuffling due
and complexes 3 and 4, for which no X-ray diffraction data to the change of the metal atom, the shortest S(1)–N(1)
exist, shows that the structures are very similar, in accord- bond has become longer while the medium N(2)–S(1) bond
ance with what was found for 1 and 2. The maximum differ- has become shorter. This is indicative of a slight increase in
ence in bond lengths in the heterocycle is just 0.013 Å and electron delocalisation in the heterocyclic ring when going
the Cp* ring sits closer to the rhodium atom than the Cp from cobalt to iridium. The Wiberg bond orders support
ring by 0.018 Å. The S–Rh–N angles differ by no more than this conclusion. In the direction from cobalt to iridium the
0.2°. When the iridium complexes 5 and 6 are compared, M–S(2) and M–N(1) bonds are slightly stronger. At the
similar conclusions can be drawn: the largest difference in same time, S(2)–N(2) and S(1)–N(1) become weaker, and
bond length in the heterocycle is 0.011 Å, the Cp* ring sits N(2)–S(1) becomes stronger. The M–S(2) and M–N(1)
closer to the iridium atom by 0.012 Å and the S–Ir–N bonds are generally somewhat weaker than the three sulfur–
angles are virtually identical.
nitrogen bonds.
The calculations revealed an increase of the ring-to-metal
distance when Cp* is replaced by Cp. This trend was further
investigated by means of Wiberg carbon–metal bond or-
ders, which are a measure of strength of the ring-metal
2.3. NMR Spectra
The NMR spectroscopic data of all the Cp* complexes
bond (Table 1). The differences between the bond order val- are summarised in Table 2. In the 1H NMR spectra, the five
ues of the corresponding Cp/Cp* pairs are negligible sug- methyl groups in the Cp*M(S2N2) complexes give singlets
gesting that such a ring replacement causes a very small that are significantly deshielded with respect to the signals
reduction in bonding.
of the starting materials, which enables a reliable identifica-
The experimental bond lengths and angles in 2 and 6 tion of the products in the reaction mixtures. The 1H NMR
reveal the influence of different van der Waals radii of the signals of the Cp* rings of the title complexes 2, 4 and 6
metal centres on the structure of the M(S2N2) rings show a trend of increased deshielding when going from Co
(Table 1). The bonds between the metal centre and N(1) to Ir.
and S(2) are considerably shorter in 2. The remaining bonds
In accord with expectations, the 13C NMR spectra of the
within the (S2N2) moiety are longer in 2 than in 6. The Cp* complexes showed two signals for every Cp* ring: one
differences in the bond lengths M–N(1) and M–S(2) are due to the CH3 groups and the other due to the aromatic
directly linked to the value of the angle S(2)–M–N(1). In 2, C5 ring. Since 103Rh has nuclear spin I = 1/2, the C5 signals
where the bonds coming from the metal centre are shorter, in the Rh complexes are split into doublets with small
the angle is more obtuse than in 6, where the longer dis- 103Rh-13C coupling constants.
Table 2. NMR spectroscopic data for complexes, 2, 4, 6, 7, 8 and 9.[a]
1H NMR
δ (ppm)
13C NMR
δ (ppm)
Assignment
Assignment
1J(103Rh–13C)
2
4
6
7
8
1.98
2.07
2.22
1.79
1.57
2.17
1.66
s, 15 H, 5ϫCH3
10.80
94.80
9.26
94.94
10.70
95.57
8.73
98.52
9.10
10.73
86.46
97.13
8.67
s, 5 C, 5ϫCH3
s, 5 C, C5
s, 5 C, 5ϫCH3
d, 5 C, C5
s, 5 C, 5ϫCH3
s, 5 C, C5
s, 10 C, 10ϫCH3
d, 10 C, 2ϫC5
s, 5 C, 5ϫCH3 (Cp*IrCl2)
s, 5 C, 5ϫCH3 [Cp*Ir(S2N2)]
s, 5 C, C5 (Cp*IrCl2)
s, 5 C, C5 [Cp*Ir(S2N2)]
s, 10 C, 10ϫCH3
d, 10 C, 2ϫC5
s, 15 H, 5ϫCH3
8.30 Hz
7.27 Hz
s, 15 H, 5ϫCH3
s, 15 H, 5ϫCH3
s, 15 H, 5ϫCH3 (Cp*IrCl2)[b]
s, 15 H, 5ϫCH3 [Cp*Ir(S2N2)]
s, 15 H, 5ϫCH3
9
99.56
7.27 Hz
1
[a] Spectra measured in CDCl3. The H NMR chemical shifts are calibrated to the peak of residual CHCl3 (δ = 7.26 ppm).[24]. [b] The
assignment of the spectra of 8 follows from the known chemical shifts for both [Cp*IrCl2]2 and Cp*Ir(S2N2).
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J. D. Woollins et al.
FULL PAPER
niques. Solvents were dried, purified and stored according to com-
mon procedures.[26] RhCl3·xH2O and IrCl3·xH2O were obtained on
loan from Johnson Matthey Plc. Compounds S4N4,[27] [S4N3]Cl,[28]
2.4. IR and Raman Spectroscopy
The majority of the IR bands are due to the Cp* moie-
ties. Spectra of all the compounds show characteristic C–H
stretches in the area 3000–2900 cm–1 and CH3 deformation
vibrations between 1460 and 1370 cm–1.
The IR frequencies in the spectrum of 2 matched well
with the published values.[4] The IR spectra of 4 closely
match with those of 2 and 6, which supports the existence
of the five-membered Rh(S2N2) ring in 4. The intense bands
at 724 (2) and 700 cm–1 (4, 6), and at 646 (4) and 635 cm–1
(2, 6) are the most characteristic modes observed also in a
number of other metalladithiadiazoles.[25]
It seems reasonable to assign the Raman lines at 919,
649, 426 and 403 cm–1 in the spectra of 4 to the Rh(S2N2)
ring vibrational modes. The wavenumbers correspond well
with those at 864, 639, 419 and 385 cm–1 found in the spec-
trum of 6. It is noteworthy that the lines in the spectrum of
6 are generally shifted towards lower wavenumbers.
[6]
Cp*Co(CO)2,[29] [Cp*RhCl2]2,[30] [Cp*IrCl2]2,[30] [nBu2Sn(S2N2)]2
and 2[4] were prepared according to published methods. Compound
6 was prepared by the published procedure but the reactants were
mixed in their CH2Cl2 solutions.[6] 1H and 13C NMR spectra were
recorded with a Jeol GSX 270 MHz spectrometer with δ referenced
to external tetramethylsilane. All 13C NMR spectra are proton-de-
coupled. 14N NMR spectra were recorded on a Bruker Avance II
400 spectrometer with δ referenced to external liquid ammonia.
Mass spectrometry was performed by the University of St Andrews
Mass Spectrometry Service and elemental analyses were performed
by the St Andrews University School of Chemistry Service. The
elemental analysis data could not be obtained with better accuracy
due to air-sensitivity of the compounds. IR spectra were recorded
as pressed KBr discs with a Perkin–Elmer 2000 FT/IR/Raman
spectrometer. Raman spectra of neat materials were recorded in
glass capillaries in the range 3500–100 cm–1 using the same spec-
trometer. Powder X-ray diffraction patterns were recorded with a
Stoe STADI/P diffractometer using Cu-Kα1 radiation.
X-ray Structure Determination: Crystal structure data were col-
lected at 93 K with a Rigaku MM007 confocal optics/Saturn CCD
3. Conclusion
diffractometer using Mo-Kα radiation (confocal optic,
λ =
We have prepared 5-(η5-pentamethylcyclopentadienyl)-
5,1,3,2,4-rhodiadithiadiazole (4) from [Cp*RhCl2]2 by two
reproducible methods. The first synthetic route uses the
[S4N3]Cl/NH3(l) reaction system, the other takes advantage
of the ligand exchange with the versatile tin reagent
[nBu2Sn(S2N2)]2. Compound 4 is a microcrystalline sub-
stance that does not crystallise into well-grown single crys-
tals or crystals of sufficient size to be investigated by pow-
0.71073 Å), and corrected for absorption. The structure was solved
by direct methods and refined by full-matrix least-squares methods
on F2 values of all data. Refinements were performed using
SHELXTL (Version 6.1, Bruker-AXS, Madison WI, USA, 2001).
The experimental details including the results of the refinement are
given in Table 3.
Purification of S4N4
CAUTION: S4N4 explodes upon mechanical or heat shock. Its ex-
plosiveness increases with the purity of the substance. Kevlar gloves
and visor should be used when manipulating with S4N4. Residues
of S4N4 were disposed of by decomposition with aqueous
NaOH.[31]
The crude S4N4/S8 mixture obtained from the dioxane extract[27]
contained a high amount of sulfur. A significant amount of sulfur
was removed by suspending the S4N4/S8 mixture in a sufficiently
small amount of dichloromethane and subsequent decanting of the
orange S4N4-rich solution. The solvent was removed (rotary evapo-
rator) and the S4N4-rich crude mixture was recrystallised from tolu-
ene. The purity of S4N4 was checked by TLC.
1
der X-ray diffraction. It was characterised by H and 13C
NMR spectroscopy, mass spectrometry, and its constitution
was supported by vibrational spectra. It is air-sensitive and
partially hydrolyses into 9, which contains the [S3N2]2– and
[S2O3]2– bridging ligands in one molecule.
The low-temperature crystal structure of 2 was deter-
mined. Comparison of the solid-state structures of both 1
and 2 showed insignificant differences between the two
molecules, and quantum chemical calculations suggested
that the larger size of the molecule of 2 is a result of crystal
effects.
Preparation of Cp*Rh(S2N2) (4): The [S4N3]Cl/NH3(l) method: gas-
eous ammonia (20–30 mL) was condensed into a predried three-
neck flask. [S4N3]Cl (51 mg, 0.247 mmol) was added in one por-
tion. The mixture turned red immediately and was stirred for
30 min at –78 °C. [Cp*RhCl2]2 (153 mg, 0.247 mmol) was added in
one portion and the mixture was warmed up to –33 °C. Once the
temperature was reached, the cooling bath in the ammonia con-
denser was regularly supplied with dry ice and the mixture was kept
under cold reflux for 2 h until the colour of the mixture changed
to dark purple with a slight greenish tint at the meniscus. After
that period, the ammonia was allowed to evaporate spontaneously
leaving a beige/brown mixture of solids. The mixture was put under
high vacuum for 15 min. to remove residual ammonia and after
reintroduction of nitrogen gas it was extracted with just one por-
tion of dry dichloromethane (10 mL). The extract was filtered
through a sinter, the solvent was removed and the compound dried
in high vacuum.
A thorough comparison of the calculated structures has
been carried out between the nonmethylated and methyl-
ated pairs of cyclopentadienylmetalladithiadiazoles. The
crystal structures of 1 and 2 reveal an increased ring-metal
distance in 2, while the calculated structures show an oppo-
site trend. The Wiberg bond order analysis demonstrated
that substitution of a Cp ring with a Cp* ring has a very
small effect on the bonding between the ring and the metal
centre. The calculations, supported by the low-temperature
X-ray structures of 1,[14] 2 and 6, indicate an increasing de-
gree of π-electron delocalisation in the M(S2N2) heterocycle
when going from Co to Ir.
4. Experimental Section
General: Unless otherwise stated, all reactions were carried under
Transmetallation with [nBu2Sn(S2N2)]2: The tin reagent (161 mg,
oxygen-free nitrogen using standard Schlenk and syringe tech-
0.247 mmol) was dissolved in dry dichloromethane (30 mL). A
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Eur. J. Inorg. Chem. 2009, 4483–4490

Cp*M(S2N2) (M = Co, Rh, Ir) and Related Compounds
Table 3. Crystallographic data for compounds 2, 6, 8·nBu2SnCl2 and 9·CH2Cl2.
Compound
2
6
8·nBu2SnCl2
9·CH2Cl2
Empirical formula
Formula weight
Temperature
Crystal colour, habit
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C10H15CoN2S2
286.29
93(2) K
purple plate
monoclinic
P21/n
8.1372(10)
13.1558(16)
12.9834(16)
90
104.008(7)
90
C10H15IrN2S2
419.56
93(2) K
orange plate
monoclinic
P21/n
7.856(3)
13.129(5)
12.860(13)
90
103.39(3)
90
C31.5H52Cl4Ir2N2S2Sn
1167.76
93(2) K
C21H32Cl2N2O3Rh2S5
797.51
93(2) K
red needle
monoclinic
P21/c
10.615(3)
23.415(6)
23.361(6)
90
90.089(4)
90
red prism
triclinic
¯
P1
10.1044(8)
12.1259(13)
16.8451(18)
78.220(8)
80.344(8)
77.688(9)
1957.3(3)
2
γ [°]
U [Å3]
1348.6(3)
4
1.410
1290.4(14)
4
2.160
5806(2)
8
1.825
Z
Dc [Mgm–3]
1.981
7.819
µ [mm–1]
1.554
10.641
1.708
F(000)
592
11599
2372
0.0342, 0.0864
0.401, –0.406
792
7725
2296
0.0217, 0.0416
1.051, –0.825
1118
12710
6883
0.0220, 0.0445
1.145, –1.017
3200
43104
9933
0.1107, 0.2688
3.386, –2.291
Measured reflections
Observed reflections
Final R1, ωR2[IϾ2σ(I)]
Largest diff. peak hole [eÅ–3]
solution of [Cp*RhCl2]2 (153 mg, 0.247 mmol) in dry dichloro-
methane (30 mL) was added dropwise and the mixture was stirred
for 6 h at room temperature. The solvent was evaporated, the crude
product was adsorbed on a small amount of silica and added to a
packed silica column (25ϫ2 cm). Unreacted starting material and
the byproduct were removed with toluene as a pale yellow band.
Elution with toluene/acetone (2:1) gave several similarly coloured
fractions which had to be analysed by 1H NMR so that the product
could be identified. The residues were washed with toluene/acetone
(1:1) but they contained only a small amount of very contaminated
product and were not worth re-purifying. Yield 6 mg (10%). Com-
pound decomposed (with blackening) without melting at 190 °C.
C10H15N2RhS2 (330.28): calcd. C 36.4, H 4.6, N 8.5; found C 36.4,
H 5.0, N 6.1. MS (ES+OF): m/z (%) = 330.99 (100) [MH]+. 1H
resulting structures were energy minima. All subsequent calcula-
tions of molecular properties were performed using the optimised
geometries. Wiberg bond orders were calculated using the NBO
3.1 program[39] as it is implemented in the Gaussian 03 program
package.
CCDC-736035 (for 2), -736036 (for 6), -736037 (for 7), -736038 (for
8), -736039 (for 9) contain the complete crystallographic data for
this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data centre, 12 Union Road, Cambridge CB2
1EZ, UK; Fax (+44) 1223-336-033; E-mail: deposit@ccdc.cam.
ac.uk.
Supporting Information (see also the footnote on the first page of
this article): X-ray structure of [Cp*RhCp*]Cl (7) (Figure S1), re-
finement data and list of selected bond lengths and angles for
[Cp*RhCp*]Cl (7) (Tables S1 and S2), list of selected bond lengths
and angles for Cp*Ir[S2N2(IrCl2Cp*)] (8) (Table S3) and list of se-
lected bond lengths and angles for Cp*Rh(µ-S3N2)(µ-S3O2)RhCp*
(9) (Table S4).
NMR (270 MHz, CDCl3, 25 °C): δ = 2.04 (s, 15 H, Cp*) ppm. 13
C
NMR (67.9 MHz, CDCl3, 25 °C): δ = 9.26 (s, 5 C, 5ϫCH3), 94.94
1
[d, J(103Rh-13C) = 8.30 Hz, 5 C, C5] ppm.
[Cp*RhCp*]Cl·H2O (7):[18] Yield 274 mg (67%). M.p. 182 °C.
C20H32ClORh (426.83): calcd. C 56.3, H 7.6; found C 57.3, H 7.6.
MS (ES+OF): m/z (%) = 373.05 (100) [Cp*RhCp*]+. 1H NMR
(270 MHz, CDCl3, 25 °C): δ = 1.77 (s, 30 H, 2Cp*) ppm. 13C NMR
(67.9 MHz, CDCl3, 25 °C): δ = 8.73 (s, 10 C, 10ϫCH3), 98.52 [d,
1J(103Rh-13C) = 7.27 Hz, 10 C, 2ϫC5] ppm.
Acknowledgments
We wish to thank the Engineering and Physical Sciences Research
Council (EPSRC) for funding (V. M.) and the University of Ant-
werp for access to the university’s computer cluster CalcUA. We
are grateful to Dr. Mikael P. Johansson for his assistance with the
choice of the basis sets and core potentials for the transition metal
atoms.
[Cp*Rh(µ-S3N2)(µ-S2O3)RhCp*] (8): Compound 8 decomposed
without melting at 210 °C (with blackening). C20H30N2O3Rh2S5
(712.60): calcd. C 33.7, H 4.2, N 3.9; found C 35.1, H 4.3, N 2.8.
MS (ES+OF): m/z (%) = 734.62 (100) [MNa]+, 712.70 (5) [MH]+.
1H NMR (270 MHz, CDCl3, 25 °C): δ = 1.65 (s, 30 H, 2ϫCp*)
ppm. 13C NMR (67.9 MHz, CDCl3, 25 °C): δ = 8.67 (s, 10 C,
1
10CH3), 99.55 [d, J(103Rh-13C) = 7.27 Hz, 10 C, 2ϫC5] ppm.
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Received: June 16, 2009
Published Online: September 10, 2009
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Eur. J. Inorg. Chem. 2009, 4483–4490