Benzylic oligothioethers as ditopic ligands for Group 6 transition metal carbonyls

Article abstract of DOI:10.1039/a909313c

The co-ordination preferences of a family of novel thioethers based on (alkylsulfanylmethyl)benzene were examined. The alkyl chain length and the number and position of the thioether substituents were varied. The ligands were synthesized by coupling the alkanethiol to the appropriate benzyl bromide or via the reaction of benzyl mercaptans with bromoethane; Cs₂CO₃-DMF was employed as the base-solvent mixture. The molecular structure of hexakis(propylsulfanylmethyl)benzene (L3) and 1,2,4,5-tetrakis(propylsulfanylmethyl)benzene (L4) were obtained at room temperature. Both have a crystallographic centre of symmetry. In L3 the S-propyl substituents ("legs") alternate "a(bove)" and "b(elow)" the plane of the benzene ring, whereas in L4 the "legs" adopt an abba pattern. Several co-ordination modes of the ligands were observed. Bismetallated tetracarbonyl complexes where the ligand bridges two monometal Group 6 carbonyl fragments (M(CO)₄) were generated on reaction of [W(CO)₄(MeCN)₂] or [Mo(CO)₃(MeCN)₃] with the ligands L1 and L2. The molecular structures of the resulting complexes [{Mo(CO)₄}₂L] (L = L1 or L2 which are the pentyl analogues of L3 and L4 respectively) show that the conformations of the ligands change radically to accommodate the octahedral geometry about the metal centres. In all cases the metal atoms are chelated by "legs" positioned ortho to each other. Changing the stoichiometry of the reactions does not significantly influence the products. & The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a909313c

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Benzylic oligothioethers as ditopic ligands for Group 6 transition
metal carbonyls
Fiona K. Gormley, Julie Gronbach, Sylvia M. Draper* and Anthony P. Davis
Chemistry Department, University of Dublin, Trinity College, Dublin 2, Ireland.
E-mail: smdraper@tcd.ie
Received 30th June 1999, Accepted 25th November 1999
The co-ordination preferences of a family of novel thioethers based on (alkylsulfanylmethyl)benzene were examined.
The alkyl chain length and the number and position of the thioether substituents were varied. The ligands
were synthesized by coupling the alkanethiol to the appropriate benzyl bromide or via the reaction of benzyl
mercaptans with bromoethane; Cs2CO3–DMF was employed as the base–solvent mixture. The molecular structure
of hexakis(propylsulfanylmethyl)benzene (L3) and 1,2,4,5-tetrakis(propylsulfanylmethyl)benzene (L4) were obtained
at room temperature. Both have a crystallographic centre of symmetry. In L3 the S-propyl substituents (“legs”)
alternate “a(bove)” and “b(elow)” the plane of the benzene ring, whereas in L4 the “legs” adopt an abba pattern.
Several co-ordination modes of the ligands were observed. Bismetallated tetracarbonyl complexes where the ligand
bridges two monometal Group 6 carbonyl fragments (M(CO)4) were generated on reaction of [W(CO)4(MeCN)2] or
[Mo(CO)3(MeCN)3] with the ligands L1 and L2. The molecular structures of the resulting complexes [{Mo(CO)4}2L]
(L = L1 or L2 which are the pentyl analogues of L3 and L4 respectively) show that the conformations of the ligands
change radically to accommodate the octahedral geometry about the metal centres. In all cases the metal atoms are
chelated by “legs” positioned ortho to each other. Changing the stoichiometry of the reactions does not significantly
influence the products.
Introduction
Prior to the 1980s, relatively few thioether complexes had been
prepared in comparison to those of phosphines, arsines and
amines.1 The development of cyclic thioethers2 such as
[9]aneS3 and [12]aneS3 redressed this imbalance, though sub-
sequently it became clear that the macrocyclic effect of crown
thioethers was considerably less than for the analogous crown
ethers. The recent resurgence in acyclic polythioether chemistry
has resulted in reports of the synthesis of monometal com-
plexes3 and linear organometallic co-ordination polymers.4
In principle, thioether ligands possess unusual potential for
structural control in inorganic chemistry. On the one hand
divalent sulfur has a high affinity for a wide range of metallic
elements. On the other it is easily manipulated by synthetic
organic chemistry. Carbon–sulfur bonds are readily created
through electrophilic attack on thiolates, without creation of
the stereogenic centres which so complicate phosphine chem-
istry. Elaborate polysulfide ligands are readily conceived, and
are realistic targets for synthesis.
Herein we report some initial results from a programme on
the design, synthesis and study of extended non-macrocyclic
polythioether ligands. The ligands studied, mainly L1–L4 (see
Chart 1), are still quite simple but are interesting in that their
sulfur atoms are widely spaced and cannot co-ordinate simul-
taneously to a single metal atom. By design, they provide scope
for an expanding multidimensional framework to support a
variety of bridging metal atoms. The 1,3-bis(alkylsulfanyl-
methyl) substitution pattern present in L2 and L4 has previ-
ously appeared in orthopalladation reagents.4,5 However, in
the present work CH insertion is avoided and a different co-
ordination pattern is observed. As far as we are aware, the hexa-
(alkylsulfanylmethyl) pattern of L1 and L3 has no precedent in
transition metal chemistry; previous work on similar systems
concentrated on their host–guest properties6,7 or their use as a
support for polyoxygenated chains.8 Related ligand geometries
such as “star polysulfoxides”,9 tripodal tri/hexathiols10 and
Chart 1
“coelenterands”11 have recently been reported. The benzylic
methylene groups in L1 and L3 allow the S-donor atoms to
deviate from the planarity of the benzene ring, distinguishing
these ligands from earlier hexakis aromatic thioether systems
with direct S–Ar bonds.12,13
Thioethers have been treated with a large range of transition
metal cations but zerovalent metal fragments are more unusual.
In view of this, Group 6 transition metal carbonyls were used
as a starting point to investigate the co-ordinating preferences
J. Chem. Soc., Dalton Trans., 2000, 173–179
This journal is © The Royal Society of Chemistry 2000
173

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of these novel ligands. An advantage of preparing metal
carbonyl complexes is that they have an additional spectro-
scopic handle. IR gives an indication of the number of carbonyl
groups, geometry of the metal carbonyl fragment and the
nature of the metal environment(s). Some examples of struc-
turally characterised Group 6 metal thioether complexes
12
include: [Cr(CO)4L] (L = C6(SMe)6 or RS(CH2)nSR,14 n = 1
or 2), [{Mo(CO)4}2L] (L = 2,6,15,19-tetrathia[7.7]paracyclo-
phane)15 and [Mo(CO)3L] (L = [9]aneS3).16
Results and discussion
(a) Synthesis
The ligands L1–L6 were prepared via the coupling of each
alkanethiol to the appropriate benzyl bromides or in the case of
L7, L8 and L9 via the reaction of benzyl mercaptans with
bromoethane. The base–solvent mixture employed was Cs2CO3–
DMF as is also common for macrocyclisation reactions. This is
in contrast to the literature preparations for analogous systems
which use sodium alkoxides in ethanol and require reflux.5
The synthesis of Group 6 metal carbonyl complexes via
reflux of the hexacarbonyl with the appropriate ligand is well
documented. However more controlled reactions result from
the use of intermediates with labile ligands, such as [Mo(CO)4-
(MeCN)2] or [Cr(CO)3(C7H8)], where high temperatures are
not required.17 The literature procedures18 for the generation of
[M(CO)4(MeCN)2] were modified for M = Cr or W to include
an initial photolysis step because the reported thermal reactions
were found to be inefficient. As previously reported,19 even
lengthy reflux was found to give a significant amount of
[M(CO)5] (M = Cr) and unchanged [M(CO)6] (M = W).
Fig. 1 An ORTEX22 drawing of the structure of L3 (thermal
ellipsoids have been drawn at 40% probability level, hydrogen atoms
have been omitted for clarity).
The clean preparation of Cr(CO)5 complexes requires an
alternative route in which the labile ligand is an olefin, here
cyclooctene,20 and the solvent is non-polar. The presence of co-
ordinating solvents, such as MeCN or THF, compete with the
thioether for metal complexation.
Bismetallated tetracarbonyl complexes were readily formed
by stirring the acetonitrile intermediates [M(CO)4(MeCN)2] in
the presence of the ligands L1 and L2 (shown for L1 in
Scheme 1). Even starting from the tricarbonyl acetonitrile deriv-
Fig. 2 An ORTEX drawing of the structure of L4. Details as in Fig. 1.
ortho to each other co-ordinate to give stable metal complexes.
Reaction of the acetonitriles with ligands where the donors are
meta e.g. L5, L7 did not lead to stable complexes. This is attrib-
uted to the spatial positioning of the donors which are too
far apart (4.6 Å by molecular modelling) to chelate to a cis-
octahedral metal geometry. In the absence of a suitable chelate
ring, the metal fragment is not stable to the reaction conditions,
as seen from the reaction of [Mo(CO)3(MeCN)3] with two
equivalents of L9, which also failed to yield stable complexes.
Molybdenum complexes of the other ligands were successfully
synthesized and isolated yielding [{M(CO)4}2L3], [{M(CO)4}2-
L4], [Mo(CO)4L6] and [Mo(CO)4L8]; [Cr(CO)5L9] was syn-
thesized by coupling [Cr(CO)5(C8H14)] with L9 in pentane.
(b) Crystal structures
Data were collected on the propylsulfanyl ligands L3 and L4
(rather than the pentylsulfanyl L1 and L2) as these were solids
(not oils) at room temperature. Examination of the structure
of L3 shows that it has a crystallographic centre of symmetry.
The S-propyl substituents alternate “a(bove)” and “b(elow)” the
plane of the benzene ring in an abab pattern (as illustrated in
Fig. 1). This is the expected conformation based on reported
structures of other hexasubstituted benzenes5 and has been
attributed to the minimisation of steric interactions between
neighbouring “legs”. The structure of L4 (Fig. 2) also has a
centre of symmetry. In this case it is because the legs adopt
an abba pattern. Again this conformation minimises steric
constraints.
Scheme 1
ative [Mo(CO)3(MeCN)3] the tetracarbonyl [{Mo(CO)4}2L]
(L = L1 or L2) complexes were isolated. This is not without
precedent and has been reported to result from the release
of CO from the decomposition of some of the [Mo(CO)3-
(MeCN)3] intermediate.21
Changing the stoichiometry of the reactions does not signifi-
cantly influence the products. Excess of metal reagent with L1
does not give [{M(CO)4}3L1] and excess of ligand does not give
primarily [M(CO)4L1]. Only ligands with thioethers related
Upon complexation to two Mo(CO)4 fragments, the con-
formation of the ligands is radically changed to accommodate
174
J. Chem. Soc., Dalton Trans., 2000, 173–179

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Fig. 3 An ORTEX drawing of the structure of [{Mo(CO)4}2L2].
Details as in Fig. 1.
Fig. 5 An ORTEX drawing of the structure of [{Mo(CO)4}2L1].
Details as in Fig. 1. The three terminal C atoms of each pentyl group
have not been shown. The high disorder associated with these groups
meant that their thermal ellipsoids obscured the metal benzene skeleton.
Fig. 4 Space-filling diagram of the structure of [{Mo(CO)4}2L2]
(hydrogen atoms have been omitted for clarity) illustrating the orien-
tation of the carbonyl groups.
the octahedral geometry about the metal centre. In the simpler
derivative, [{Mo(CO)4}2L2] (Fig. 3) where L2 is the pentyl
analogue of L4, the “legs” are required to adopt an aabb con-
formation to chelate to the metal atoms. The metal bridges
“legs” positioned ortho to each other exclusively. The two sides
of the molecule, and hence the metal environments, are identi-
cal. The metal atoms are positioned above and below the plane
of the benzene ring, as required by the centre of symmetry
Fig. 6 Space-filling diagram of the structure of [{Mo(CO)4}2L1]
(hydrogen atoms have been omitted for clarity) illustrating the orien-
tation of the carbonyl groups.
¯
associated with P1. A unique carbonyl ligand from each metal
centre is positioned directly below the benzene ring at a distance
of 3.6 Å. This may be due to some π–π type interaction between
the benzene ring and π cloud of the carbonyl ligand or simply
a result of crystal packing. This carbonyl, C(16)–O(1), can be
viewed upon looking through the centre of the benzene ring
and has the parallel geometry required to maximise such an
interaction (Fig. 4).
The structure of [{Mo(CO)4}2L1] (Fig. 5), where L1 is the
pentyl analogue of L3, is more complicated. Independent of
reaction stoichiometry, only two out of a possible three
Mo(CO)4 fragments are co-ordinated. This is probably due to
the steric constraints that would be imposed by complete com-
plexation. The unco-ordinated legs play an important role in
determining the conformation of the complex. Situated para
relative to each other, they force the two metal centres to the
same side of the benzene ring. The new arrangement of the legs
is now aabaab. In contrast to [{Mo(CO)4}2L2], the two metal
carbonyl fragments are not crystallographically related either
by a centre of symmetry or a mirror plane. It is only possible for
one metal centre, Mo1, to direct a carbonyl ligand [C(24)–
O(24)] under the benzene ring for steric reasons. The other
tetracarbonyl fragment, Mo(2)(CO)4, “hangs” outside the
“bowl” generated by the four co-ordinated legs (Fig. 6).
In both molybdenum structures the Mo–S distances are con-
sistent with the literature (2.3–2.5 Å). The geometry about the
S atoms is pyramidal with one remaining lone pair. Unfortu-
nately due to poor crystal quality and the severe disorder of the
pentyl groups which could not be satisfactorily modelled, the
bond lengths and bond angles derived from the molecular
structure of [{Mo(CO)4}2L1] show large e.s.d. values and can-
not reliably be discussed in any detail.
NMR Spectra
For the “free” ligands it was noticed that 1H NMR signals shift
upfield with increasing distance from the benzene ring, i.e.
along the alkyl chain. However in the 13C NMR spectra this
sequence is interrupted with the benzyl CH2S being further
upfield than the SCH2R signals and in the pentyl derivatives the
SCH2CH2CH2R being further upfield than the SCH2CH2-
CH2R. This phenomenon is a common feature of the 13C NMR
spectra of both the ligands and the complexes.
1
In the H/13C NMR spectra of the complexes the downfield
shifts (generally 0.5/10 ppm) of SCH2R with respect to the
“free” ligand are most characteristic of complexation. In con-
J. Chem. Soc., Dalton Trans., 2000, 173–179
175

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Table 1 Crystal data and refinement details for L3, L4, [{Mo(CO)4}2L1] and [{Mo(CO)4}2L2]
L3
L4
[{Mo(CO)4}2L1]
[{Mo(CO)4}2L2]
Molecular formula
Crystal system
Space group
C30H54S6
Monoclinic
P21/c
C22H38S4
Triclinic
P1
C50H78Mo2O8S6
Monoclinic
P21/n
C38H54Mo2O8S4
Triclinic
P1
¯
¯
a/Å
b/Å
c/Å
α/Њ
β/Њ
γ/Њ
V/ÅЊ
Z
9.6291(8)
16.0389(8)
11.5569(11)
5.127(2)
9.294(2)
13.945(4)
104.866(2)
94.880(3)
100.868(2)
624.5(3)
1
0.385
1209
1147
0.0580
0.1449
16.660(2)
12.840(2)
28.207(3)
7.783(2)
11.458(1)
13.551(2)
72.341(9)
77.92(1)
79.18(2)
1115.9(3)
1
0.794
2972
2725
0.0269
0.0548
90.078(4)
98.71(1)
1784.8(2)
2
0.208
3029
2878
0.0448
0.1580
5965(2)
2
0.676
7588
7282
0.1184
0.2314
µ(Mo-Kα)/cmϪ1
Total no. reflections
Independent reflections
R (I > 2σ(I))
wR (I > 2σ(I))
trast the benzyl CH2S resonances do not shift as significantly in
the 1H NMR spectra on co-ordination and are less diagnostic.
At room temperature, unexpectedly complex coupling and
spectrometer operating in a FABϩ mode and NMR spectra
on Bruker MSL 300 and DPX 400 spectrometers operating
at 300.13 and 400.13 MHz for 1H and 75.47 and 100.61
MHz for 13C respectively. All NMR spectra were recorded
in CHCl3-d and referenced relative to SiMe4. Hexakis(bromo-
methyl)benzene,5 1,3,5-tris(sulfanylmethyl)benzene,23 1,2,3-
1
broadening of the benzyl signals in H NMR spectra of the
hexakis complexes [{Mo(CO)4}2L1/3] (but not the “free” lig-
ands) is observed. This type of effect has been reported for
uncomplexed hexasubstituted (polyether)(sulfanylmethyl)-
benzenes and was attributed to steric overcrowding.6 As
samples are warmed (35 ЊC) the benzyl regions sharpen to
give two singlets integrating for the “co-ordinated” protons
(H*Ј, for numbering scheme see diagram in Experimental
section) and unco-ordinated (H) protons. On cooling (Ϫ50 ЊC),
the benzyl region, although sharper, is a complex set of multi-
plets and spreads over a larger frequency range. In addition, the
triplet corresponding to “co-ordinated” H2* and H2Ј splits. No
significant temperature dependency is observed in 13C NMR
spectra.
tris(sulfanylmethyl)benzene,23
[Mo(CO)3(MeCN)3]18
and
[Cr(CO)5(C8H14)]20 were made following published methods.
Unless otherwise stated reagents were used as purchased and
without further purification.
Crystallography
Data were collected on an Enraf-Nonius CAD-4 diffractometer
(Mo-Kα, λ = 0.71073 Å radiation, graphite monochromator,
ω–2θ scan mode) at 20 ЊC. The crystal data and experimental
parameters are summarised in Table 1. The final cell parameters
were determined using the Celdim routine. It was not found
necessary to apply decay or absorption corrections.
The structures were solved by automatic direct methods
using SHELXS 8624 and refined by full-matrix least-squares
analysis on F2 with SHELXL 93.25 Apart from the structure
of [{Mo(CO)4}2L1], all the non-hydrogen atoms were refined
anisotropically. The hydrogen atoms which could not be located
from subsequent Fourier difference maps were added in calcu-
lated positions, “riding” on the parent C atom. Poor crystal
quality in the case of [{Mo(CO)4}2L1] meant that some of
the outlying C atoms of the alkyl chains could not be satis-
factorily located and required fixing. However the important
structural features, such as those of the phenyl backbone and
the local environments about both metal centres, were well
refined. Diagrams of the structures were drawn using ORTEX22
and SCHAKAL.26
Conclusion
The co-ordination of a series of (alkylsulfanylmethyl)benzene
ligands to Group 6 metal carbonyl fragments has been illus-
trated. The ligands are readily synthesized and bischelate to
octahedral metal centres. The benzyl CH2 introduces a degree
of flexibility allowing the ligands to rearrange so as to minimise
steric interactions both in the free and co-ordinated forms. Co-
ordination is exclusively via the ortho substituents on the ligand.
Chelation dominates so that only bischelated complexes are
isolated. The syntheses are ligand-directed in that irrespective
of the reaction stoichiometry two metal centres are bischelated.
This work has established that the number of metal centres
co-ordinated can be controlled by the number and position of
the thioether substituents on the benzene ring. Modification
of the ligand design should permit the synthesis of preorganised
ligands that will act as templates for the generation of metal
clusters. Work is ongoing but we have already shown the
versatile nature of thioethers as ligands in transition metal
chemistry.
CCDC reference number 186/1742.
Synthesis of the ligands
Hexakis(pentylsulfanylmethyl)benzene L1. Pentanethiol (0.50
g, 0.43 mL, 4.6 mmol) was added to a suspension of hexakis-
(bromomethyl)benzene (0.50 g, 0.77 mmol) and caesium carb-
onate (0.77 g, 2.4 mmol) in DMF (5 mL). The reaction was
allowed to proceed for 12 h at room temperature then HCl
(0.1 M, 25 mL) was added and extracted into diethyl ether
(2 × 25 mL). The combined diethyl ether layers were dried over
MgSO4 and the solvent was removed by a rotary evaporator.
The final traces of DMF were removed from the oily residue
by flash chromatography on silica (eluent hexane–ethyl acetate
10:1). The pure product was recovered as a colourless oil that
was soluble in most organic solvents (0.54 g, 93%) (Found: C,
65.0; H, 9.9. C7H13S requires C, 65.1; H, 10.0%). All analyses
were performed by the analytical service at University College
Dublin. δH(300 MHz) 4.04 (12 H, s, aryl CH2S), 2.63 (12 H, t,
Experimental
General
All syntheses involving transition metal compounds were
carried out under an argon atmosphere using standard Schlenk
techniques. Dry, oxygen-free solvents were used for reactions
but not for chromatographic separations, which were under-
taken in air. Acetonitrile, CH2Cl2 and DMF were distilled from
CaH2, THF and hexane from sodium–benzophenone; CHCl3-d
was vacuum distilled from molecular sieves. The IR spectra
were recorded on a Perkin-Elmer Paragon 2000 spectro-
photometer, mass spectra on a Micromass AutospecQ mass
176
J. Chem. Soc., Dalton Trans., 2000, 173–179

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J(HH) 7.6, CH2SCH2), 1.68 (12 H, qn, J(HH) 7.2, SCH2CH2),
1.36 (24 H, m, SCH2CH2CH2CH2) and 0.91 (18 H, t, J(HH)
7 Hz, Me). δC(300 MHz) 31.0 (aryl CH2S), 33.7 (CH2SCH2),
29.5 (SCH2CH2), 31.1 (SCH2CH2CH2), 22.3 (SCH2CH2CH2-
CH2), 14.0 (Me) and 135.8 (aryl).
J(HH) 7.5 Hz, H3b) and 7.17 (3 H, m, CHaryl). δC 33.2 (C2a), 28.6
(C1a), 27.0 (C1b), 25.7 (C2b), 14.4 (C3b), 14.1 (C3a), 129.0, 126.5
(CHaryl) and 133.0 (Cquat/aryl).
Compounds L2–L6 were synthesized via a similar procedure.
Their yields (based on 0.5 g starting bromide) and spectroscopic
data are reported below. The oils or oily solids L2, L4–L9 were
submitted for elemental analysis but solvent inclusion meant
that the results were not adequate for publication. In some cases
elemental analyses were successfully obtained for complexes
generated from the ligands ([{Mo(CO)4}2L3], [Mo(CO)4L8]
and [Cr(CO)5L9]).
Ethylsulfanylmethylbenzene L9. This was prepared as for L8
starting from phenylmethanethiol (0.5 g, 4 mmol), bromo-
ethane (0.44 g, 4 mmol) and caesium carbonate (1.3 g, 4 mmol).
The pure product was recovered as a colourless oil that was
soluble in most organic solvents (0.48 g, 78%). δH(400 MHz)
3.75 (2 H, s, aryl CH2S), 2.48 (2 H, q, J(HH) 5, CH2SCH2), 1.25
(3 H, t, J(HH) 7.5 Hz, Me) and 7.30 (5 H, m, CHaryl). δC 33.5
(aryl CH2S), 24.8 (CH2SCH2), 14.0 (Me), 138.2 (Cquat/aryl), 128.4,
128.0 and 126.4 (CHaryl).
1,2,4,5-Tetrakis(pentylsulfanylmethyl)benzene L2. Yield 0.52
g (96%). δH (300 MHz) 3.83 (8 H, s, aryl CH2S), 2.46 (8 H, t,
J(HH) 7.3, CH2SCH2), 1.57 (8 H, m, SCH2CH2), 1.32 (16 H, m,
SCH2CH2CH2CH2), 0.89 (12 H, t, J(HH) 7 Hz, Me) and 7.12
(2 H, s, CHaryl). δC 31.1 (aryl CH2S), 33.2 (CH2SCH2), 29.1
(SCH2CH2), 32.0 (SCH2CH2CH2), 22.3 (SCH2CH2CH2CH2),
14.0 (Me), 135.3 (Cquat/aryl) and 132.6 (CHaryl).
Synthesis of complexes
Hexakis(propylsulfanylmethyl)benzene L3. Yield 0.44 g (95%)
(Found: C, 59.6; H, 8.9. C5H9S requires C, 59.4; H, 8.7%).
δH(300 MHz) 4.04 (12 H, s, aryl CH2S), 2.62 (12 H, t, J(HH) 7.0,
CH2SCH2), 1.73 (m, 12 H, SCH2CH2) and 1.04 (t, 18 H, J = 7.2
Hz, Me). δC 30.9 (aryl CH2S), 35.8 (CH2SCH2), 22.9 (SCH2-
CH2), 13.5 (Me) and 135.8 (aryl).
Suitable elemental analyses could not be obtained for all the
metal complexes. This was due to difficulties in separating the
pure product from unchanged ligand: prolonged or repeated
column chromatography results in the degradation of the prod-
uct to metal residues that stick to the silica and “free” ligand
which travels at the same rate as the product. In these cases
mass spectra were obtained.
1,2,4,5-Tetrakis(propylsulfanylmethyl)benzene L4. Yield 0.43
g (91%). δH(300 MHz) 3.83 (8 H, s, aryl CH2S), 2.44 (8 H, t,
J(HH) 7.2, CH2SCH2), 1.61 (8 H, m, SCH2CH2), 0.96 (16 H,
t, J(HH) 7.5 Hz, Me) and 7.11 (2 H, s, CHaryl). δC 31.4
(aryl CH2S), 36.5 (CH2SCH2), 22.7 (SCH2CH2), 13.5 (Me),
135.3 (Cquat/aryl) and 132.7 (CHaryl).
ꢀ-Hexakis(pentylsulfanylmethyl)benzenebis(tetracarbonyl-
molybdenum) [{Mo(CO)4}2L1]. A solution of hexakis(pentyl-
sulfanylmethyl)benzene (0.25 g, 0.32 mmol) in THF (20 mL)
was added dropwise to a solution of [Mo(CO)3(MeCN)3] (0.30
g, 0.99 mmol) in THF (20 mL) at 0 ЊC. The resulting solution
gradually became brown and was allowed to stir for 12 h at
room temperature. Evaporation of the solvent under reduced
pressure gave a brown oil. Purification using column chromato-
graphy on silica (first eluent hexane–ethyl acetate 10:1,
second hexane–CH2Cl2 1:1) yielded a yellow solid which after
washing (hexane, 2 × 20 mL) was crystallised from hexane–
CH2Cl2 at Ϫ20 ЊC. Recrystallisation gave yellow crystals suit-
able for single crystal X-ray analysis (0.23 g, 60%) (Found:
C, 50.4; H, 6.2. C25H39MoO4S3 requires C, 50.4; H, 6.6%).
1,3-Bis(propylsulfanylmethyl)benzene L5. Yield 0.47 g (98%).
δH(400 MHz) 3.71 (4 H, s, aryl CH2S), 2.42 (4 H, t, J(HH) 7.0,
CH2SCH2), 1.61 (4 H, m, SCH2CH2), 0.98 (6 H, t, J(HH) 7.2 Hz,
Me) and 7.20 (4 H, m, CHaryl). δC 33.0 (aryl CH2S), 35.5
(CH2SCH2), 22.1 (SCH2CH2), 13.0 (Me), 138.4 (Cquat/aryl),
128.8, 128.0 and 126.9 (CHaryl).
1,2-Bis(propylsulfanylmethyl)benzene L6. Yield 0.47 g (98%).
δH(300 MHz) 3.91 (4 H, s, aryl CH2S), 2.48 (4 H, t, J(HH) 7.0,
CH2SCH2), 1.63 (4 H, m, SCH2CH2), 0.99 (6 H, t, J(HH) 7.2
Hz, Me), 7.21 and 7.20 (4 H, m, m, CHaryl). δC 33.2 (aryl CH2S),
33.7 (CH2SCH2), 22.3 (SCH2CH2), 13.0 (Me), 136.2 (Cquat/aryl),
130.0 and 126.7 (CHaryl).
ν˜
/cmϪ1(CO) (KBr disk) 2026w, 1949w, 1917s, 1890s and 1845m.
δH(300 MHz) 4.4–3.8 (12 H, br m, H1, H1*Ј), 2.99 (8 H, br t,
H2*Ј), 2.64 (4 H, t, J(HH) 7.2, H2), 1.86 (8 H, m, H3), 1.70
(4 H, m, H3), 1.44 (24 H, m, H4, H4*Ј, H5, H5*Ј) and 0.96
(18 H, t, J(HH) 6.0 Hz, H6, H6*Ј). δC 36.3, 36.0 (C1Ј, C1*), 44.2,
44.1 (C2Ј, C2*), 33.7 (C2), 31.1 (C4), 30.8, 30.7 (C1, C4*, C4Ј),
29.4 (C3), 28.4, 28.2 (C3Ј, C3*), 22.28, 22.33 (C5*, C5Ј, C5Ј),
13.9 (C6*, C6Ј, C6), 138.3 (C7), 135.4, 134.0 (C7Ј,C7*), 214.8,
215.1 (CO).
1,3,5-Tris(ethylsulfanylmethyl)benzene L7. Bromoethane (1.6
mL, 15 mmol) was added to a suspension of 1,3,5-tris(sulfanyl-
methyl)benzene (1 g, 4.6 mmol) and caesium carbonate (1.12 g,
3.4 mmol) in DMF (5 mL). The reaction was allowed to pro-
ceed for 12 h at room temperature, then HCl (0.1 M, 25 mL)
was added and extracted into diethyl ether (2 × 25 mL). The
combined diethyl ether layers were dried over MgSO4 and the
solvent was removed by a rotary evaporator. The final traces of
DMF were removed from the oily residue by flash chromato-
graphy on silica (eluent hexane–ethyl acetate 10:1). The pure
product was recovered as a colourless oil (1.20 g, 86%). δH(300
MHz) 3.68 (6 H, s, aryl CH2S), 2.43 (8 H, q, J(HH) 7.2,
CH2SCH2), 1.22 (9 H, t, J(HH) 7.5 Hz, Me) and 7.14 (3 H, s,
CHaryl). δC 33.1 (aryl CH2S), 22.0 (CH2SCH2), 12.9 (Me), 134.7
(Cquat/aryl) and 128.1 (CHaryl).
1,2,3-Tris(ethylsulfanylmethyl)benzene L8. By a similar pro-
cedure to that for L7 (1.35 g, 97%). δH(400 MHz) 4.10 (2 H, s,
H1a), 3.19 (4 H, s, H1b), 2.67 (2 H, q, J(HH) 7.4, H2a), 2.54 (4 H,
q, J(HH) 7.5, H2b), 1.38 (3 H, t, J(HH) 7.4, H3a), 1.29 (6 H, t,
The complexes [{Mo(CO)4}2L3], [{Mo(CO)4}2L2], [Mo-
(CO)4L6] and [Mo(CO)4L8] were made by a similar procedure.
Yields (based on 0.99 mmol [Mo(CO)3(MeCN)3]) and spectral
details are reported below.
J. Chem. Soc., Dalton Trans., 2000, 173–179
177

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ꢀ-Hexakis(propylsulfanylmethyl)benzene-bis(tetracarbonyl-
molybdenum) [{Mo(CO)4}2L3]. Yield 0.18 g (55%) (Found:
C, 47.3; H, 7.8. C19H27MoO4S2 requires C, 47.6; H, 8.2%).
(4 H, br t, J(HH) 7.2, H2), 1.86 (8 H, m, H3), 1.70 (4 H, m, H3),
1.44 (24 H, m, H4, H4*Ј, H5, H5*Ј) and 0.94 (18H, t, J(HH) 6.0
Hz, H6, H6*Ј). δC 35.22, 35.20 (C1Ј, C1*), 43.7, 43.6 (C2Ј, C2*),
33.6 (C2), 31.1 (C4), 30.9, 30.7 (C1, C4*, C4Ј), 29.4 (C3), 28.4, 28.2
(C3Ј, C3*), 22.29, 22.23 (C5*, C5Ј, C5Ј), 13.97 (C6*, C6Ј), 13.90 (C6),
137.9 (C7), 135.2, 133.6 (C7Ј,C7*), 224.3 and 224.5 (CO).
Preliminary crystallographic data were obtained on a suitable
crystal. The data were solved so as to confirm the metal and
sulfur arrangement. This was found to be isostructural with the
completely refined molybdenum analogue. The data were of
insufficient quality for further refinement: monoclinic, space
group, P21/c; Z = 2; a = 16.555(3), b = 12.710(2), c = 28.456(6)
Å; β = 100.525(2)Њ; V = 5887(2) Å3.
ν˜
/cmϪ1(CO) (CH2Cl2–hexane 1:1) 2026m, 1921s, 1901s and
1861s. δH(300 MHz) 4.4–3.8 (12 H, br m, H1, H1*Ј), 2.99 (8 H, br
t, H2*Ј), 2.64 (4 H, t, J(HH) 7.2, H2), 1.88 (8 H, m, H3*Ј), 1.72
(4 H, m, H3), 1.13 (18 H, td, J(HH) 6.0, 1.8, H4*Ј) and 1.06 (4 H,
t, J(HH) 6.0 Hz, H4). δC 36.0, 35.7 (C1Ј, C1*), 46.3, 46.2 (C2Ј,
C2*), 35.7 (C2), 30.7 (C1), 22.9 (C3), 22.03, 21.97 (C3Ј, C3*), 13.4,
13.3 (C4, C4*, C4Ј), 138.3 (Cquat), 135.5 and 134.0 (CHaryl).
ꢀ-1,2,4,5-Tetrakis(pentylsulfanylmethyl)benzene-bis(tetra-
carbonylmolybdenum) [{Mo(CO)4}2L2]. Yield 0.15 g (50%).
ν˜
/cmϪ1(CO) (CH2Cl2–hexane 1:1) 2026m, 1918s, 1900 (sh) and
1864m. δH(400 MHz) 3.83 (8 H, s, H1*), 2.87 (8 H, t, J(HH) 7.5,
H2*), 1.82 (8H, m, H3*), 1.44 (16 H, m, H4*, H5*), 0.96 (12 H, t,
J(HH) 7.0 Hz, H6*) and 1.44 (2 H, s, CHaryl). δC 37.0 (C1*),
42.9 (C2*), 28.1 (C3*), 30.6 (C4*), 22.3 (C5*), 14.0 (C6*), 133.8
(Cquat/aryl), 135.0 (CHaryl), 215.2 and 205.9 (CO). m/z 958 (Mϩ)
and 902 (Mϩ Ϫ 2CO).
Bis(acetonitrile)tetracarbonyltungsten(0). A suspension of
[W(CO)6] (0.60 g, 1.7 mmol) in acetonitrile (80 mL) was photo-
lysed for 3 h. The resulting yellow solution was brought to
reflux for 24 h, yielding, by IR analysis, predominantly the
tetracarbonyl product. ν˜
/cmϪ1(CO) (CH2Cl2) 2019w, 1976m,
1936s, 1937s, 1884 (sh) and 1839m.
ꢀ-Hexakis(pentylsulfanylmethyl)benzene-bis(tetracarbonyl-
tungsten) [{W(CO)4}2L1]. A solution of hexakis(pentylsulfanyl-
methyl)benzene (0.11 g, 0.14 mmol) in THF (20 mL) was added
dropwise to a solution of [W(CO)4(MeCN)2] (0.43 mmol) in
MeCN (20 mL) at 0 ЊC. The resulting yellow/orange solu-
tion gradually darkened and was allowed to stir for 12 h at
room temperature. Evaporation of the solvent under reduced
pressure gave a green/brown oil. Purification using column
chromatography on silica (hexane–CH2Cl2 1:1) followed by
washing in hexane (2 × 20 mL) yielded a yellow solid (0.12 g,
[1,2-Bis(propylsulfanylmethyl)benzene]tetracarbonylmolyb-
denum [Mo(CO)4L6]. Yield 0.34 g (80%). ν˜
/cmϪ1(CO) (CH2Cl2–
hexane 1:1) 2028m, 1920s, 1900s and 1860m. δH(400 MHz) 3.87
(4 H, s, H1*), 2.88 (4 H, t, J(HH) 7.5, H2*), 1.88 (4 H, m, H3*),
1.44 (6 H, m, J(HH) 7.3 Hz, H4), 7.36 and 7.22 (4 H, m, CHaryl).
δC 37.0 (C1*), 44.4 (C2*), 21.8 (C3*), 13.1 (C4*), 133.8 (Cquat/aryl),
130.9, 128.2 (CHaryl), 215.2 and 205.5 (CO). m/z 462 (Mϩ) and
434 (M Ϫ CO).
Tetracarbonyl[1,2,3-tris(ethylsulfanylmethyl)benzene]molyb-
denum [Mo(CO)4L8]. Yield 0.28 g (80%) (Found: C, 44.3;
63%). ν˜
/cmϪ1(CO) (KBr disk) 2026w, 1949w, 1917s, 1890s and
1845 (m). δH(300 MHz) 4.6–4.0 (12 H, br m, H1, H1*Ј), 3.14 (8 H,
t, H2*Ј), 2.66 (4 H, t, J(HH) 7.2, H2), 1.87 (8 H, m, H3), 1.72
(4 H, m, H3), 1.45 (24 H, m, H4, H4*Ј, H5, H5*Ј) and 0.99 (18 H,
m, J(HH) 6.0 Hz, H6, H6*Ј). δC 37.0 (C1Ј, C1*), 45.51, 45.45 (C2Ј,
C2*), 33.3 (C2), 30.6 (C4), 30.3, 30.2 (C1, C4*, C4Ј), 28.9 (C3), 28.1,
28.0 (C3Ј, C3*), 21.84, 21.79 (C5*, C5Ј, C5Ј), 13.5, 13.4 (C6*, C6Ј,
C6), 138.3 (C7), 135.4, 134.0 (C7Ј,C7*), 204.9 and 204.7 (CO). m/z
1367 (Mϩ) and 1071 (M Ϫ W(CO)4).
H, 4.4. C19H24MoO4S3 requires C, 44.8; H, 4.7%). ν˜
/cmϪ1(CO)
(CH2Cl2–hexane 1:1) 2026m, 1921s, 1901s and 1861s. δH(400
MHz) 4.19 (2 H, s, H1a*), 3.93, 3.91 (2 H, 2 H, s, s, H1b*, H1b),
3.02 (2 H, q, J(HH) 7.5, H2a*), 2.91 (2 H, q, J(HH) 7.5, H2b*),
2.53 (2 H, q, J(HH) 7.5, H2b), 1.52 (6 H, m, H3a*, H3b*), 1.29
(3 H, t, J(HH) 7.5, H3b), 7.26 (2 H, d, J(HH) 7.6, CHaryl(4/6)) and
7.11 (1 H, t, J(HH) 7.6 Hz, CHaryl(5)). δC 37.4 (C2a*), 36.8 (C1b*),
35.9 (C2b*), 34.0 (C1a*), 33.2 (C1b), 25.7 (C2b), 14.0 (C3b), 13.4,
13.3 (C3a*, C3b*), 138.0, 135.3, 132.1 (Cquat/aryl), 130.7, 129.8,
127.9 (CHaryl), 215.0 and 205.5 (CO).
ꢀ-Hexakis(propylsulfanylmethyl)benzene-bis(tetracarbonyl-
tungsten) [{W(CO)4}2L3]. This was prepared as for [{W(CO)4}2-
L1] starting from hexakis(propylsulfanylmethyl)benzene (85
mg, 0.14 mmol) and [W(CO)4(MeCN)2] (0.43 mmol) (0.14 g,
84%). ν˜
/cmϪ1(CO) (CH2Cl2–hexane 1:1) 2020m, 1939m, 1910s,
1921s, 1896s and 1865m. δH(300 MHz) 4.6–3.7 (12 H, br m, H1,
H1*Ј), 3.11 (8 H, br t, H2*Ј), 2.64 (4 H, t, J(HH) 7.2, H2), 1.87
(8 H, m, H3*Ј), 1.73 (4 H, m, H3), 1.16 (18 H, td, J(HH)
6.0, 1.8, H4*Ј) and 1.06 (8 H, t, J(HH) 6.0 Hz, H4). δC 37.3 (C1Ј,
C1*), 49.0, 47.8 (C2Ј, C2*), 35.7 (C2), 30.7 (C1), 22.8 (C3), 22.15,
22.22 (C3Ј, C3*), 13.5, 13.2 (C4, C4*, C4Ј), 138.5 (Cquat), 135.5,
134.0 (CHaryl), 205.4 and 205.2 (CO). m/z 1198 (Mϩ) and 902
(M Ϫ W(CO)4).
Bis(acetonitrile)tetracarbonylchromium(0). A suspension of
[Cr(CO)6] (0.60 g, 2.7 mmol) in acetonitrile (80 mL) was photo-
lysed for 3 h. The resulting yellow solution was brought to
reflux for 12 h, yielding, by IR analysis, predominantly the tetra-
carbonyl product. ν˜
/cmϪ1(CO) (CH2Cl2–hexane 1:1) 2017w,
Pentacarbonyl(ethylsulfanylmethylbenzene)chromium
1941w, 1906vs, 1988 (sh), 1841s and 1795m.
[Cr(CO)5L9]. A solution of ethylsulfanylmethylbenzene (50
mg, 0.33 mmol) in pentane (20 mL) was added dropwise to
[Cr(CO)5(C8H14)] (100 g, 0.33 mmol) at Ϫ60 ЊC. The solution
was allowed to warm to room temperature and purified by
column chromatography on silica (first eluent hexane, second
hexane–CH2Cl2 1:1). The pure product was recovered as an
oily solid, soluble in common organic solvents (90 mg, 80%)
(Found: C, 48.6; H, 3.4. C30H54CrO5S6 requires C, 48.8; H,
ꢀ-Hexakis(pentylsulfanylmethyl)benzene-bis(tetracarbonyl-
chromium) [{Cr(CO)4}2L1]. A solution of hexakis(pentyl-
sulfanylmethyl)benzene (0.18 g, 0.23 mmol) in THF (20 mL)
was added dropwise to a solution of [Cr(CO)4(MeCN)2] (0.68
mmol) in MeCN (20 mL) at 0 ЊC. The resulting yellow/orange
solution gradually darkened and was allowed to stir for 12 h at
room temperature. Evaporation of the solvent under reduced
pressure gave a green/brown oil. Purification using column
chromatography on silica (hexane–CH2Cl2 1:1) yielded a
yellow solid which was crystallised from hexane (0.18 g, 72%).
3.5%). ν˜
/cmϪ1(CO) (CH2Cl2–hexane 1:1) 2068w, 1943s and
1935 (sh). δH(400 MHz) 3.83 (2 H, s, aryl CH2S), 2.60 (2 H, q,
J(HH) 7.5, CH2SCH2), 1.30 (3 H, t, J(HH) 7.5 Hz, Me) and
7.35 (5 H, m, CHaryl). δC 45.0 (aryl CH2S), 32.7 (CH2SCH2), 12.0
(Me), 134.5 (Cquat/aryl), 128.8, 128.5, 127.9 (CHaryl), 220.6 and
214.5 (CO).
ν˜
/cmϪ1(CO) (hexane) 2020w, 1918w, 1898s and 1880s. δH(300
MHz) 4.3–3.7 (12 H, br m, H1, H1*Ј), 2.95 (8 H, br t, H2*Ј), 2.64
178
J. Chem. Soc., Dalton Trans., 2000, 173–179

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10 C. Walsdorff, W. Saak and S. Pohl, J. Chem. Soc., Dalton Trans.,
Acknowledgements
The authors thank FORBAIRT (Ireland) for financial support
(grant SC/93/202) and the Trinity Trust for a Postgraduate
Scholarship for F. K. G.
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Paper a909313c
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