Thiolate derivatives of titanium(IV) and tantalum(V) as precursors to metal sulfides

Article abstract of DOI:10.1039/b104888k

Reaction of Ta(NMe₂)₅ with 10 equivalents of 2,6-Me₂C₆H₃SH in toluene resulted in the formation of bright red crystals of [Ta(SC₆H₃Me₂-2,6)₄(NMe ₂)] (1). The related reaction between Ti(NEt₂)₄ and 10 equivalents of Bu^tSH in toluene afforded a mixture of two complexes, [Ti(SBu^t)₄] (3) and [Ti(SBu^t)₃(NEt₂)] (4). X-Ray crystal structures of 1 and 4 have been determined. Vapour phase thin-film studies of compounds 1 and 3/4 revealed that 1 is not an effective tantalum sulfide precursor whereas 3/4 produced TiS₂.

Full text of DOI:10.1039/b104888k

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Thiolate derivatives of titanium(IV) and tantalum(V) as precursors
to metal sulfides
Claire J. Carmalt,*a Christopher W. Dinnage,a Ivan P. Parkin,a Andrew J. P. Whiteb and
David J. Williamsb
a Department of Chemistry, Christopher Ingold Laboratories, University College London,
20 Gordon Street, London, UK WC1H 0AJ. E-mail: c.j.carmalt@ucl.ac.uk
b Department of Chemistry, Imperial College of Science, Technology and Medicine,
South Kensington, London, UK SW7 2AY
Received 4th June 2001, Accepted 12th July 2001
First published as an Advance Article on the web 29th August 2001
Reaction of Ta(NMe2)5 with 10 equivalents of 2,6-Me2C6H3SH in toluene resulted in the formation of bright red
crystals of [Ta(SC6H3Me2-2,6)4(NMe2)] (1). The related reaction between Ti(NEt2)4 and 10 equivalents of ButSH in
toluene afforded a mixture of two complexes, [Ti(SBut)4] (3) and [Ti(SBut)3(NEt2)] (4). X-Ray crystal structures of 1
and 4 have been determined. Vapour phase thin-film studies of compounds 1 and 3/4 revealed that 1 is not an
effective tantalum sulfide precursor whereas 3/4 produced TiS2.
complexes reported herein extend the range of potential CVD
applications of these amido precursors.
Introduction
Heightened interest in thiolate derivatives of the early transi-
tion metals derives from their use as precursors to the techno-
logically important transition metal disulfides. Materials such
as titanium disulfide (TiS2) are of interest as high-temperature
lubricants, as hydrogenation catalysts and in high-energy
density batteries.1,2 In addition, transition metal disulfides
display a wide range of electronic properties from semiconduc-
tors (TiS2, MoS2) to superconductors (TaS2).3
Results and discussion
The reaction between Ta(NMe2)5 and 10 equivalents of
2,6-Me2C6H3SH in toluene at room temperature resulted, after
work up, in a 50% yield of bright red crystalline 1. Analytical
and spectroscopic data for 1 were consistent with the formation
of the neutral species [Ta(SC6H3Me2-2,6)4(NMe2)] rather
than that of the anticipated product [Ta(SC6H3Me2-2,6)5] 2
(Scheme 1).
We were interested in developing transition metal thiolate
derivatives for use as single-source precursors to metal sulfides.
Single-source precursors to TiS2 include [TiCl4(HSR)2] (R =
cyclohexyl or cyclopentyl)4 and [Ti(SBut)4].5,6 The homoleptic
thiolate [Ti(SBut)4] was initially reported to deposit thin films of
TiS via LPCVD (low pressure chemical vapour deposition).5
However, a more detailed study showed that LPCVD of
[Ti(SBut)4] produced thin films of TiS2 at 110–350 ЊC.6 We have
previously reported the synthesis and characterisation of
ionic titanium thiolates including [Et2NH2][Ti(SC6F5)4(NEt2)],7
[Et2NH2]3[Ti(SC6F5)5][SC6F5]2,7 and [Et2NH2][Ti2(SCH2Ph)9].8
Unfortunately, their low volatility precluded thin film growth by
CVD, although TiS2 could be produced via a thio ‘sol–gel’ pro-
cess.9 Other structurally characterised homoleptic titanium()
complexes containing unidentate thiolate ligands include
[Li(thf )4][Ti2(SPh)9],10 [Me2NH2][Ti2(SMe)9],11 [Ti3(SMe)12],11
[Ti(SC6HMe4-2,3,5,6)4]12 and [Et4N]2[Ti(SPh)6].13 The only
example of a structurally characterised neutral homoleptic
tantalum() thiolate is [Ta(SC6HMe4-2,3,5,6)5].11 In general,
homoleptic thiolate derivatives of the early transition metals
represent a class of compound that has only been studied to a
limited extent.14
In this contribution, we present the synthesis and X-ray
structural characterisation of two neutral thiolates [Ta(SC6-
H3Me2-2,6)4(NMe2)] and [Ti(SBut)3(NEt2)]. Vapour phase thin-
film experiments on the complexes are also described, enabling
assessments to be made of the potential of the compounds to
act as precursors to TaS2 and TiS2 thin films. Both [Ta(SC6-
H3Me2-2,6)4(NMe2)] and [Ti(SBut)3(NEt2)] were prepared via
the reaction of M(NR2)n (M = Ta, n = 5, R = Me; M = Ti, n = 4,
R = Et) with excess thiol (2,6-Me2C6H3SH or ButSH). Metal
dialkylamido complexes have been shown previously to act as
precursors to metal nitrides (e.g. TiN) and oxides.15,16 Thus, the
Scheme 1
A single crystal structure determination showed 1 to be the
incompletely thiolate-substituted complex illustrated in Fig. 1.
The complex has molecular C2 symmetry about the N–Ta bond
direction. The geometry at tantalum is distorted trigonal
bipyramidal, the equatorial plane [comprising Ta, N, S(3) and
S(4)] being co-planar to within 0.007 Å; the angles within the
equatorial plane are in the narrow range 119.04(6)–121.6(2)Њ
whereas that between the axial substituents is noticeably bent at
164.37(5)Њ (Table 1). As expected, the Ta–S distances to the
axial ligands [Ta–S(1) 2.427(2) Å, Ta–S(2) 2.428(2) Å] are longer
than those to their equatorial counterparts [Ta–S(3) 2.398(2)
Å, Ta–S(4) 2.389(2) Å], a differentiation that is not observed in
the homoleptic complex [Ta(SC6HMe4-2,3,5,6)5],12 where the
geometry is distorted slightly more towards square pyramidal
and the “axial” S–Ta–S angle is 156.7Њ. In this latter complex
the Ta–S distances range between 2.330 and 2.402 Å. In
[Ta(CHBut)(SC6H2Pri3-2,4,6)3(SEt2)],17 which has a distorted
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J. Chem. Soc., Dalton Trans., 2001, 2554–2558
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b104888k

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Table 1 Selected bond lengths (Å) and angles (Њ) for compound 1
Table 2 Selected bond lengths (Å) and angles (Њ) for compound 4
Ta–N
Ta–S(2)
Ta–S(4)
1.921(5)
2.428(2)
2.389(2)
Ta–S(1)
Ta–S(3)
2.427(2)
2.398(2)
Ti–N
Ti–S(2)
1.856(5)
2.302(2)
Ti–S(1)
Ti–S(3)
2.295(2)
2.283(2)
N–Ti–S(3)
115.5(2)
112.52(7)
101.16(7)
112.7(2)
121.2(2)
127.0(4)
N–Ti–S(1)
N–Ti–S(2)
S(1)–Ti–S(2)
C(5)–S(2)–Ti
C(15)–N–C(13)
C(13)–N–Ti
105.2(2)
110.06(14)
112.62(7)
114.6(2)
113.5(4)
119.2(3)
N–Ta–S(4)
119.4(2)
119.04(6)
81.40(6)
96.9(2)
80.37(6)
106.9(2)
115.7(2)
111.9(6)
122.1(5)
N–Ta–S(3)
N–Ta–S(1)
121.6(2)
98.5(2)
S(3)–Ti–S(1)
S(3)–Ti–S(2)
C(1)–S(1)–Ti
C(9)–S(3)–Ti
C(15)–N–Ti
S(4)–Ta–S(3)
S(4)–Ta–S(1)
N–Ta–S(2)
S(3)–Ta–S(2)
C(3)–S(1)–Ta
C(19)–S(3)–Ta
C(2)–N–C(1)
C(1)–N–Ta
S(3)–Ta–S(1)
S(4)–Ta–S(2)
S(1)–Ta–S(2)
C(11)–S(2)–Ta
C(27)–S(4)–Ta
C(2)–N–Ta
89.17(6)
93.49(6)
164.37(5)
109.2(2)
116.1(2)
125.9(5)
and ring D in a symmetry related counterpart (H ؒ ؒ ؒ π 2.90 Å,
C–H ؒ ؒ ؒ π 135Њ) to create loosely linked chains that extend in
the c direction.
Commenting more generally on compound 1, it is interesting
that even in the presence of excess thiol incomplete substitution
of all the dimethylamide ligands has occurred. We and others
have previously reported the results of reacting titanium tetra-
dialkylamides with excess thiols. Ionic compounds, such as
[R2NH2][Ti2(SRЈ)9] (R = RЈ = Me;11 R = Et, RЈ = CH2Ph8) and
[Et2NH2]3[Ti(SC6F5)5][SC6F5],7 have been isolated from the
aforementioned reactions and the compounds were structurally
characterised. In contrast, the complex [Ti(SBut)4] 3, has been
reported to result from the reaction of Ti(NR2)4 (R = Me or Et)
with excess ButSH.5,6 Earlier work indicated that the reaction of
excess thiol RЈSH (RЈ = Me, Et, Pri) with Ti(NR2)4 (R = Me
or Et) resulted in the formation of complexes of the type
[Ti(SRЈ)4(RЈSH)x(R2NH)y] (where x and y varied from 0.8 to
1.33).20 However, controlled addition of RЈSH to Ti(NMe2)4
afforded the partially substituted compounds [Ti(NMe2)4
-
Ϫ
x
(SRЈ)x] (where x = 1 or 2; RЈ = Et or Pri).20
We decided to investigate the reaction of Ti(NR2)4 with
ButSH in more detail for two reasons; (a) to attempt to isolate
X-ray quality crystals and (b) the importance of 3 as a single-
source precursor to TiS2. Accordingly, Ti(NEt2)4 was treated
with 10 equivalents of ButSH in toluene at room temperature.
An immediate colour change from orange to dark red was
observed and work-up of the reaction mixture yielded a dark
red oil. Crystallisation from hexanes solution resulted in the
isolation of a dark red crystalline material. Analytical and
spectroscopic data for these crystals are consistent with the
formation of a mixture of two complexes, namely [Ti(SBut)4] 3
and [Ti(SBut)3(NEt2)] 4 (Scheme 2). This is in contrast to the
Fig. 1 The molecular structure of 1.
trigonal bipyramidal geometry similar to that of 1 (the axial
ligands subtended an angle of 162.2Њ at tantalum), the three
equatorial Ta–S distances only range between 2.390 and 2.394
Å, values comparable to those observed in 1. Although the
axial ligands in 1 are bent away from the amide ligand [N–Ta–
S(1) 98.5(2)Њ, N–Ta–S(2) 96.9(2)Њ] the angles at these two sulfur
centres are noticeably contracted [106.9(2)Њ at S(1) and
109.2(2)Њ at S(2)] vis-a-vis those at their equatorial counterparts
[115.7(2)Њ at S(3) and 116.1(2)Њ at S(4)]. These deformations,
coupled with a positioning of ring A “over” C(1) and ring B
“under” C(2), permit the formation of a pair of weak intra-
molecular C–H ؒ ؒ ؒ π interactions between a hydrogen atom on
the C(1) and C(2) methyl groups and rings A and B respectively
[C(1)–H ؒ ؒ ؒ A, H ؒ ؒ ؒ π 3.06 Å, C–H ؒ ؒ ؒ π 124Њ; C(2)–H ؒ ؒ ؒ B,
H ؒ ؒ ؒ π 2.94 Å, C–H ؒ ؒ ؒ π 130Њ]. These interactions are accom-
panied by a small torsional twist (ca. 4Њ) about the Ta–N bond
such that C(1) and C(2) lie 0.06 and 0.12 Å “above” and
“below” the equatorial coordination plane in the directions of
rings A and B respectively. The Ta–N bond length of 1.921(5) Å
indicates a degree of multiple bond character, and this is
reflected in the near planar geometry at the nitrogen centre (the
nitrogen being only 0.026 Å out of the plane of its substitu-
Scheme 2
earlier reports that suggest only 3 is isolated from the reaction
of Ti(NEt2)4 with excess ButSH. An X-ray analysis of the red
crystalline material determined the structure of compound 4.
Unfortunately, X-ray quality crystals of 3 could not be isolated
from the mixture.
A single crystal structure determination revealed 4 also to
be an only partially thiolate substituted species (Fig. 2). The
geometry at titanium is distorted tetrahedral with angles in the
range 101.16(7)–115.5(2)Њ (Table 2). The Ti–S distances range
between 2.283(2) and 2.302(2) Å, values very similar to those
observed in, for example, [Ti(η5-NC4Me4)(SPh)3],21 where the
Ti–S distances range between 2.285 and 2.314 Å. The angles at
sulfur are 112.7(2), 114.6(2) and 121.2(2)Њ at S(1), S(2) and S(3)
respectively, the enlargement of the angle at S(3) reflecting a
possible steric conflict between its tert-butyl group and the
ents). This bond distance compares with a Ta᎐N double bond
᎐
length of 1.894 Å in [{Ta(SC6H3Pri2-2,6)3(thf )}2(µ-N2)],18 and
Ta–N single bonds of, for example, 1.949 Å in [TaCl(NSiMe3)-
19
{N(SiMe3)2}(µ-Cl)]2 and 2.024 Å in [Ta(OMe)(NSiMe3)-
{N(SiMe3)2}(µ-OMe)]2.19 The generally hydrophobic exterior
of the complex precludes any significant packing interactions,
though there is evidence for a weak intermolecular C–H ؒ ؒ ؒ π
contact between the C(13) hydrogen atom in one molecule
J. Chem. Soc., Dalton Trans., 2001, 2554–2558
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Fig. 2 The molecular structure of 4.
Fig. 3 TGA of 1 under N2.
diethylamino ligand. The geometry at nitrogen is trigonal
planar (the nitrogen lies only 0.052 Å out of the plane of its
substituents), and the Ti–N bond [1.856(5) Å] is fairly short,
but similar in length to those between titanium and the
dimethylamido ligands in [Ti(NMe2)2(OC6H2But3-2,4,6)2]22
[1.865 and 1.897 Å]. Interestingly, in this latter structure the
distortions from tetrahedral geometry are equally large cf. those
in 4, with the angles at titanium ranging between 98.6 and
116.7Њ. The outer surface of the complex is dominated by tert-
butyl and ethyl groups, and there are no intermolecular packing
interactions of note.
The structure of 4 is similar to that of 1 in the sense that one
amide ligand remains coordinated to the transition metal
centre. The formation of 4 is obviously a result of incomplete
substitution of all the amide ligands by the thiol. This is
surprising since an excess of thiol is present in the reaction
mixture. However, the reaction between Ti(NEt2)4 and excess
ButSH has been repeated a number of times. Analytical data
on a number of samples of the red crystalline material
isolated, reveals that the %N varies from 0.71 to 2.78. Thus,
even after repeated recrystallisation a small amount of nitrogen
1
is still present in the material. The H NMR data shows the
presence of Ti–NEt2 ligands in the mixture and so supports
the formation of 4. Overall, these results suggest that the
major product is compound 3, although no X-ray quality
crystals were obtained.
Fig. 4 TGA of 4 under N2.
In order to study the decomposition pathways of 1 and 3/4
thermal gravimetric analyses (TGA) were carried out. The
TGA results of 1 and 3/4 at 10 ЊC minϪ1 from 20 to 500 ЊC,
under N2, are shown in Figs. 3 and 4, respectively. The decom-
position of 1 has an onset temperature of 230 ЊC and is com-
pleted at 310 ЊC. The TGA of 1 shows a total weight loss of
67%, in good agreement with the calculated value of 68% for
the formation of TaS2. The decomposition of 3/4 is clean and
shows a weight loss of 67%. This behaviour indicates an
incomplete decomposition to TiS2 up to 500 ЊC (calculated
weight loss 72% from 3). However, since 3/4 is a mixture of
ill-defined proportions, an accurate interpretation of the TGA
results is not possible.
Vapour phase thin-film studies of 1 and 3/4 were investigated,
the details of which are described in the Experimental section.
In both instances a film was deposited on the inside of the hot
wall glass tube. Compound 1 produced a black film, whereas
3/4 deposited a dark purple film. The films were analysed by
EDAX/SEM and Raman spectroscopy. The EDAX data for the
film deposited from 1 showed a 2.5 : 1 ratio of Ta : S over a
number of spots. These data suggest that TaS2 has not been
isolated, which is in contrast to the TGA results. It is possible
that hydrolysis or oxidation of the films has occurred either
during or after deposition. However, significant breakthrough
of the excitation volume through the coating to the underlying
glass meant that accurate quantitative analysis was difficult.
The EDAX data for the film deposited from 3/4 showed a 1 : 2
ratio of Ti : S, over a number of spots, which is in good agree-
ment with the formation of TiS2. We have previously reported
the Raman pattern of bulk TiS2 prepared from a thio ‘sol–gel’
route.9 The Raman spectrum of the TiS2 film prepared here was
very similar to that obtained for bulk TiS2 with bands at 338
and 372 cmϪ1. A UV-Vis spectrum of the TiS2 film showed a
direct band gap of 1.9 eV. By Scanning Electron Microscopy
(SEM) the TiS2 film shows a ‘crazy paving’ island-growth
mechanism with an island size of 0.2 µm (Fig. 5). The tantalum
sulfide film grown from compound 1 shows a finer gain micro-
structure, by SEM, with a 0.1 µm island growth. Two reports on
the decomposition of 3 have been previously published, as
described in the introduction.5,6 Our results support the form-
ation of TiS2 from 3 (rather than TiS) and suggests that the
presence of compound 4 has little effect on the end material
obtained.
In summary, two novel thiolate complexes of tantalum()
and titanium(), namely [Ta(SC6H3Me2-2,6)4(NMe2)] and
[Ti(SBut)3(NEt2)] have been synthesised and structurally char-
acterised. Preliminary vapour phase thin-film studies indicate
that 3/4 can serve as a precursor to TiS2 whereas 1 did not
produce TaS2 under the same conditions. More detailed CVD
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J. Chem. Soc., Dalton Trans., 2001, 2554–2558

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(CH3)2C6H3], 39.7 (NCH3), 125.9, 137.9, 143.8 [s, 2,6-
(CH3)2C6H3].
[Ti(SBut)4] 3 and [Ti(SBut)3(NEt2)] 4. The compound ButSH
(1.90 cm3, 16.85 mmol) was added dropwise to an orange solu-
tion of Ti(NEt2)4 (0.60 cm3, 1.66 mmol) in toluene (20 cm3) at
room temperature. The solution turned dark red over a period
of 30 minutes and was allowed to stir for a further 2 h, after
which time the solvent was removed in vacuo. The resulting
dark red oil was redissolved in hexanes (15 cm3) and filtered
through Celite to give a dark red solution which was concen-
trated to a volume of approx. 5 cm3. Cooling of this solution to
Ϫ20 ЊC overnight afforded a mixture of 3 and 4. Single crystals
of 4, suitable for crystallography, were produced by fractional
crystallisation of a concentrated hexanes (2 cm3) solution of
this mixture. Calc. for C16H36S4Ti: C, 47.50; H, 8.97; N, 0. Calc.
for C16H37NS3Ti: C, 49.59; H, 9.62; N, 3.61. Found C, 47.70; H,
9.73; N, 2.78%. 1H NMR (CD2Cl2): δ 1.21 (t, NCH2CH3), 1.55
[s, SC(CH3)3], 1.64 [s, SC(CH3)3], 4.12 (q, NCH2CH3). 13C{1H}
NMR (CD2Cl2): δ 13.9 (NCH2CH3), 30.7 (NCH2CH3), 36.4
[SC(CH3)3], 36.6 [SC(CH3)3], 57.8 [SC(CH3)3], 59.2 [SC(CH3)3].
Fig. 5 SEM of the film produced by the decomposition of 3/4.
studies are currently being carried out and will be described in a
future publication.
Tube furnace reactions
A sample of compound 1 (0.3 g) was loaded into a glass
ampoule (40 cm length × 9 mm diameter) in the glovebox. The
ampoule was then placed in a furnace such that 30 cm was
inside the furnace and the end containing the sample protruded
by 4 cm. The ampoule was heated to a temperature of 450 ЊC
under dynamic vacuum, except for the section of the tube con-
taining the sample. The ampoule was slowly drawn into the
furnace over a period of a few minutes until 1 started to melt.
Once all of the compound had decomposed the furnace was
allowed to cool to room temperature. A black film resulted on
the inside wall of the ampoule where the tube was in the
furnace. The film was analysed by EDAX/SEM and Raman
spectroscopy. The same procedure was used to investigate the
decomposition of 3/4 which resulted in the formation of a
purple film.
Experimental
General procedures
All manipulations were performed under a dry, oxygen-free
dinitrogen atmosphere using standard Schlenk techniques or
in a Mbraun Unilab glove box. All solvents were distilled from
appropriate drying agents prior to use (sodium for toluene, thf
23
24
and hexanes; CaH2 for CH2Cl2). Ti(NEt2)4 and Ta(NMe2)5
were prepared by literature methods. All other reagents were
procured commercially from Aldrich and used without further
purification. Microanalytical data were obtained at University
College London (UCL).
Physical measurements
1H and 13C NMR spectra were recorded on Brüker AMX300 or
X-Ray crystallography
DRX500 spectrometers at UCL, referenced to CD2Cl2, which
Crystals of compound 1 were grown from CH2Cl2–hexanes
mixtures at room temperature whereas crystals of 4 were grown
from hexanes solution at Ϫ20 ЊC.
1
was degassed and dried over molecular sieves prior to use; H
and 13C chemical shifts are reported relative to SiMe4 (δ 0.00).
Mass spectra (CI) were run on a micromass ZABSE instru-
ment, and IR spectra on a Nicolet 205 instrument. EDAX/SEM
results were obtained on an Hitachi S570 instrument using the
KEVEX system. Raman spectra were acquired on a Renishaw
Raman System 1000 using a helium–neon laser of wavelength
632.8 nm. The Raman system was calibrated against the
emission lines of neon. TGA of the compounds were obtained
from the Thermal Methods Laboratory at Birkbeck college
(ULIRS). Melting points were obtained in sealed glass capillar-
ies under nitrogen and are uncorrected.
Crystal data for 1. C34H42NS4Ta, M = 773.9, tetragonal, I41/a
(no. 88), a = 32.088(7), c = 13.126(3) Å, V = 13515(6) Å3,
Z = 16, Dc = 1.521 g cmϪ3, µ(Mo-Kα) = 3.52 mmϪ1, T = 203 K,
orange-red blocks; 5949 independent measured reflections, F 2
refinement, R1 = 0.037, wR2 = 0.069, 4529 independent
observed absorption corrected reflections [|Fo| > 4σ(|Fo|),
2θ ≤ 50Њ], 362 parameters.
Crystal data for 4. C16H37NS3Ti, M = 387.6, orthorhombic,
Pbca (no. 61), a = 10.145(1), b = 15.861(4), c = 28.332(2) Å,
V = 4559(1) Å3, Z = 8, Dc = 1.129 g cmϪ3, µ(Cu-Kα) = 5.69
mmϪ1, T = 183 K, red blocks; 3351 independent measured
reflections, F 2 refinement, R1 = 0.057, wR2 = 0.137, 2199
independent observed absorption corrected reflections
[|Fo| > 4σ(|Fo|), 2θ ≤ 120Њ], 191 parameters.
CCDC reference numbers 165273 and 165274.
See http://www.rsc.org/suppdata/dt/b1/b104888k/ for crystal-
lographic data in CIF or other electronic format.
Preparations
[Ta(SC6H3Me2-2,6)4(NMe2)] 1. The dropwise addition of 2,6-
Me2C6H3SH (0.66 cm3, 4.98 mmol) to a pale yellow solution of
Ta(NMe2)5 (0.20 g, 0.499 mmol) in toluene (20 cm3) at room
temperature resulted in a colour change to dark orange-red.
The reaction mixture was allowed to stir for 2 h, after which the
solvent was removed in vacuo. The resulting dark red-orange oil
was redissolved in CH2Cl2 (15 cm3) and filtered through Celite.
A dark orange-red solution resulted and a hexanes overlayer (7
cm3) was added carefully. Solvent diffusion at room temper-
ature over a period of days produced bright red crystals of 1 in
a 50% yield. Calc. for C34H42NS4Ta: C, 52.77; H, 5.47; N, 1.81.
Found C, 52.0; H, 5.82; N, 2.15%. 1H NMR (CD2Cl2): δ 2.45 [s,
24H, 2,6-(CH3)2C6H3], 2.76 (s, 6H, NCH3), 6.78–7.18 [m, 12H,
2,6-(CH3)2C6H3]. 13C-{1H} NMR (CD2Cl2): δ 22.4 [s, 2,6-
Acknowledgements
We thank the EPSRC (GR/M11981) for financial support and a
studentship (C. W. D.). C. J. C. is also grateful to the Royal
Society for a Dorothy Hodgkin fellowship and research grant
and the London University Central Research Fund for
J. Chem. Soc., Dalton Trans., 2001, 2554–2558
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12 D. T. Corwin, J. F. Corning, S. A. Koch and M. Millar, Inorg. Chim.
Acta, 1995, 229, 335.
13 J. T. Kim, J. W. Park and S. M. Koo, Polyhedron, 2000, 19,
1139.
financial support. Dr Marianne Odlyha (ULIRS) is thanked for
the TGA reported herein. I. P. P. thanks the EPSRC for grant
GR/M82592 for purchase of the Renishaw Raman microscope.
14 D. W. Stephan and T. T. Nadasdi, Coord. Chem. Rev., 1996, 147,
147.
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