Synthesis and characterisation of rhenium dithiocarbamate complexes. Crystal structures of [ReO{O(OH)C6H4}(S2CNEt2) 2], [Re{PPh2(C6H4S-2)}2(S 2CNEt2)]·Me2CO and [ReO{PPh(C6H4S-2)2}(S2CNEt 2)]

Article abstract of DOI:10.1039/a702935g

The reaction of [Re₂O₃(S₂CNEt₂)₄] with catechol in acetone yielded the dark orange complex [ReO{O(OH)C₆H₄}(S₂CNEt₂) ₂] 1. The crystal structure shows a distorted-octahedral geometry with the oxo group trans to the monodentate catecholate ligand. The Re-O (catechol) bond length is typical of a Re-O single bond and implies little trans influence of the oxo ligand. Reaction of [Re₂O₃(S₂CNEt₂)₄] with 1,4-dihydroxybenzene yielded the red-brown dimer [{ReO(S₂CNEt₂)₂}₂(C ₆H₄O₂-1,4)] 2, in which the dianionic ligand bridges two rhenium centres. With 2-amino-4-methylphenol [ReO(OC₆H₃NH₂-2-Me-4)(S₂CNEt ₂)₂] 3 was obtained containing the ligand co-ordinated in a monodentate mode. Reaction of [Re₂O₃(S₂CNEt₂)₄] with dithiolate proligands such as ethane-1,2-dithiol yielded [NEt₂H₂][ReOL₂], L = C₂H₄S₂-1,2 4, C₆H₄S₂-1,2 5 or MeC₆H₃S₂-3,4 6, where degradation of the dithiocarbamate ligands to form the diethylammonium counter ion occurs. Reaction of 1 with bidentate phosphines yielded green complexes of the general formula [Re(S₂CNEt₂)₂L][BPh₄], where L = Me₂PCH₂CH₂PMe₂ 7 or Ph₂PCH₂CH₂PPh₂ 8. These reactions can be contrasted to the inactivity of these phosphine ligands towards [Re₂O₃(S₂CNEt₂)₄]. The reaction of [Re₂O₃(S₂CNEt₂)₄] with the bidentate phosphinothiolate proligand PPh₂(C₆H₄SH-2) in acetone at room temperature yielded the red-orange rhenium(III) complex [Re{PPh₂(C₆H₄S-2)}₂(S ₂CNEt₂)]·Me₂CO 9. The crystal structure revealed a distorted-octahedral geometry. The sulfur donors of the phosphinothiolate ligands adopt a cis configuration. Reaction of [Re₂O₃(S₂CNEt₂)₄] with the tridentate phosphinothiolate proligand PPh(C₆H₄SH-2)₂ proceeded at room temperature to yield the red rhenium(V) complex [ReO{PPh(C₆H₄S-2)₂}(S₂CNEt ₂)] 10. Its crystal structure shows a distorted-octahedral geometry. Reaction of [Re₂O₃(S₂CNEt₂)₄] with SiMe₃Cl yielded the new rhenium(V) precursor [ReCl₂(S₂CNEt₂)₂][BPh₄] 11 which permits investigation into rhenium dithiocarbamate chemistry without an oxo core.

Full text of DOI:10.1039/a702935g

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Synthesis and characterisation of rhenium dithiocarbamate
complexes. Crystal structures of [ReO{O(OH)C6H4}(S2CNEt2)2],
[Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒMe2CO and [ReO{PPh-
(C6H4S-2)2}(S2CNEt2)]
Jonathan R. Dilworth, D. Vaughan Griffiths, Suzanne J. Parrott and Yifan Zheng
Department of Biological and Chemical Sciences, Central Campus, University of Essex,
Wivenhoe Park, Colchester, UK CO4 3SQ
The reaction of [Re2O3(S2CNEt2)4] with catechol in acetone yielded the dark orange complex
[ReO{O(OH)C6H4}(S2CNEt2)2] 1. The crystal structure shows a distorted-octahedral geometry with the oxo group
trans to the monodentate catecholate ligand. The Re᎐O (catechol) bond length is typical of a Re᎐O single bond
and implies little trans influence of the oxo ligand. Reaction of [Re2O3(S2CNEt2)4] with 1,4-dihydroxybenzene
yielded the red-brown dimer [{ReO(S2CNEt2)2}2(C6H4O2-1,4)] 2, in which the dianionic ligand bridges two
rhenium centres. With 2-amino-4-methylphenol [ReO(OC6H3NH2-2-Me-4)(S2CNEt2)2] 3 was obtained containing
the ligand co-ordinated in a monodentate mode. Reaction of [Re2O3(S2CNEt2)4] with dithiolate proligands such
as ethane-1,2-dithiol yielded [NEt2H2][ReOL2], L = C2H4S2-1,2 4, C6H4S2-1,2 5 or MeC6H3S2-3,4 6, where
degradation of the dithiocarbamate ligands to form the diethylammonium counter ion occurs. Reaction of 1
with bidentate phosphines yielded green complexes of the general formula [Re(S2CNEt2)2L][BPh4], where
L = Me2PCH2CH2PMe2 7 or Ph2PCH2CH2PPh2 8. These reactions can be contrasted to the inactivity of
these phosphine ligands towards [Re2O3(S2CNEt2)4]. The reaction of [Re2O3(S2CNEt2)4] with the bidentate
phosphinothiolate proligand PPh2(C6H4SH-2) in acetone at room temperature yielded the red-orange rhenium()
complex [Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒMe2CO 9. The crystal structure revealed a distorted-octahedral
geometry. The sulfur donors of the phosphinothiolate ligands adopt a cis configuration. Reaction of
[Re2O3(S2CNEt2)4] with the tridentate phosphinothiolate proligand PPh(C6H4SH-2)2 proceeded at room
temperature to yield the red rhenium() complex [ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10. Its crystal structure shows
a distorted-octahedral geometry. Reaction of [Re2O3(S2CNEt2)4] with SiMe3Cl yielded the new rhenium()
precursor [ReCl2(S2CNEt2)2][BPh4] 11 which permits investigation into rhenium dithiocarbamate chemistry
without an oxo core.
The dithiocarbamate core, M᎐S2CNR2, could prove to be of
great synthetic utility in radiopharmacology as a wide variety
of organic substituents can be incorporated in the stable biden-
tate ligand. This allows the chemical ‘fine-tuning’ of the bio-
logical properties of the complex by variation of the organic
substituent R, and this can be carried out independently of the
other ligands on the metal. Also variation of coligands has
an effect on the biodistribution of the metal complex. Here we
report our attempts to synthesize rhenium dithiocarbamate
complexes with a variety of coligands to explore the chemistry
of the rhenium–dithiocarbamate core. We are interested in the
chemistry of rhenium and technetium dithiocarbamate com-
plexes for their potential use as radiopharmaceuticals for
imaging and therapy by using the 99mTc and 186/188Re radio-
nuclides. The chemistry of the rhenium–dithiocarbamate core
complements on-going work into the chemistry of the
technetium-99m–dithiocarbamate core.1
1,2-diol] and isoprotenerol [4-{1-hydroxy-2-[(1-methylethyl)-
amino]ethyl}-benzene-1,2-diol] which act as neurotransmitters
in the brain and nervous system. On co-ordination catechol
more commonly binds as a bidentate ligand, however there
are examples of monodentate catecholate complexes and the
first structures were determined by Heistand II et al.3 A more
recent example is of the niobium() porphyrin complex [Nb-
(tpp){O(OH)C6H4}(O2C6H4)]4 which was found to contain
both types of co-ordination geometries (tpp represents the
5,10,15,20-tetraphenylporphyrin dianion). The co-ordination
chemistry of bidentate phosphinothiolate ligands such as
PPh2(C6H4SH-2) has been explored to some extent 5 but that of
the potentially tridentate ligands such as PPh(C6H4SH-2)2 has
been less studied. Structures which have been determined of the
complexes of these mixed-donor tridentate ligands include
[Re{PPh(C6H4S-2)2}2]6 and [Mo(NNPh2){PPh(C6H4S-2)2}2].7
Here we report an investigation into the reaction of the
‘Re(S2CNEt2)’ core with a range of mono-, bi and tri-dentate
ligands including catechol, PPh2(C6H4SH-2) and PPh(C6H4SH-
2)2. Catechol complexes are well known for most of the tran-
sition elements including iron, molybdenum, osmium, man-
ganese and chromium.2 Catechol and catecholate ligands are
of interest due to their significance in certain biological systems
as their inherent redox activity plays a central role in inter-
molecular electron-transfer reactions. Biological applications
of catechol include incorporation in iron-sequestering agents
(siderophores) and also use as biogenic amines such as the
catecholamines adrenaline {4-[1-hydroxy-2-(methylamino)-
ethyl]benzene-1,2-diol}, dopamine [4-(2-aminoethyl)-benzene-
Results and Discussion
Preparation and properties of the dithiocarbamate complexes
The rhenium() precursor [Re2O3(S2CNEt2)4] reacts readily
with catechol in acetone under reflux to yield the orange, air-
stable rhenium() complex [ReO{O(OH)C6H4}(S2CNEt2)2] 1
1
in near-quantitative yield. The H NMR spectrum displays a
complex series of resonances in the range δ 6.5–6.7 attributable
to the phenyl protons of the catecholate ligand. The unexpected
co-ordination of catechol as a monodentate ligand was con-
firmed by the observation of the resonance due to the OH pro-
ton at δ 5.8 and a band in the infrared spectrum at 3489 cmϪ1
due to ν(O᎐H). Confirmation of this co-ordination is provided
J. Chem. Soc., Dalton Trans., 1997, Pages 2931–2936
2931

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by the shift of ν(CC), due to the ring stretch between C(1) and
C(2) of the catecholate ring, from 1620 cmϪ1 for the free cate-
chol8 to 1471 cmϪ1 for the complex. This shift to lower energy
is due to the deprotonation and co-ordination of one of the
oxygen donors. Also present at 1271 cmϪ1 is a band which can
be attributed to ν(C᎐O) of the co-ordinated catecholato anion
and indicates that the ligand had no semiquinone character for
which the ν(C᎐O) would occur around 1500 cmϪ1.9 A sharp
band at 969 cmϪ1 was observed which is typical of ν(Re᎐O).10 In
᎐
the 1H NMR spectrum the resonances due to the ethyl protons
of the dithiocarbamate ligand are present as a triplet at δ 1.3
and as a quartet at δ 3.8 due to the CH3 and CH2 protons
respectively, which confirms the presence of equivalent dithio-
carbamate ligands. The red-brown dimeric species [{ReO-
(S2CNEt2)2}2(C6H4O2-1,4)] 2 is formed by the reaction of
[Re2O3(S2CNEt2)4] with 1,4-dihydroxybenzene. The complex is
sparingly soluble in most solvents with the dianionic ligand
bridging the two rhenium metal centres. The presence of a
strong absorption due to ν(C᎐O) at 1248 cmϪ1 and absence of
any bands assignable to ν(OH) confirmed the ligand had com-
pletely deprotonated and had no semiquinone character con-
Fig. 1 Perspective view of [ReO{O(OH)C6H4}(S2CNEt2)2] 1 showing
the atom labelling scheme
1
firming a formal rhenium() oxidation state. The H NMR
Table 1 Selected bond lengths (Å) and angles (Њ) for [ReO{O(OH)-
C6H4}(S2CNEt2)2] 1
spectrum of complex 2 shows the retention of the dithiocar-
bamate ligand with the resonances due to the CH3 and CH2
protons present as a triplet at δ 1.3 and a quartet at δ 3.8
respectively. The resonances due to the aromatic protons of the
dianionic ligand were present as a multiplet between δ 6.5 and
6.7. Room-temperature reaction of [Re2O3(S2CNEt2)4] with 1,2-
dithiolate ligands yielded orange anionic complexes of the type
[NEt2H2][ReOL2], where L = C2H4S2-1,2 4, C6H4S2-1,2 5 or
MeC6H3S2-3,4 6. The crystal structure determination of 4 was
undertaken and confirmed a square-based pyramidal arrange-
ment of ligands surrounding the central rhenium centre. The
structure is analogous to [PPh4][ReO(S2C2H4)2] which has pre-
viously been determined.11 The [NEt2H2]ϩ cation results from
Re᎐O(1)
Re᎐O(2)
Re᎐S(3)
Re᎐S(2)
Re᎐S(1)
1.666(6)
1.969(5)
2.411(2)
2.425(2)
2.434(2)
Re᎐S(4)
2.444(2)
4.462(6)
1.338(8)
1.356(10)
Re ؒ ؒ ؒ O(3)
O(2)᎐C(31)
O(3)᎐C(36)
O(1)᎐Re᎐O(2)
O(1)᎐Re᎐S(3)
O(2)᎐Re᎐S(3)
O(1)᎐Re᎐S(2)
O(2)᎐Re᎐S(2)
S(3)᎐Re᎐S(2)
O(1)᎐Re᎐S(1)
O(2)᎐Re᎐S(1)
175.4(2)
97.1(2)
86.1(2)
96.8(2)
85.4(2)
105.97(7)
90.8(2)
86.1(2)
S(3)᎐Re᎐S(1)
S(2)᎐Re᎐S(1)
O(1)᎐Re᎐S(4)
O(2)᎐Re᎐S(4)
S(3)᎐Re᎐S(4)
S(2)᎐Re᎐S(4)
S(1)᎐Re᎐S(4)
C(31)᎐O(2)᎐Re
172.05(7)
72.37(7)
91.7(2)
86.1(2)
72.30(7)
171.48(7)
108.15(7)
146.5(5)
Ϫ
the decomposition of Et2NCS2 and similar reactions have
been observed previously during the reaction of sodium diethyl-
dithiocarbamate with metal complexes.12 The resonance due to
the NH protons was present at δ 6.1 and could be removed by
H/D exchange by shaking with D2O. These reactions with the
1,2-dithiolate ligands can be contrasted with the behaviour of
the parent monodentate ligands, phenol and benzenethiol, with
[Re2O3(S2CNEt2)4] where no reaction was found to occur even
in the presence of base and the use of forcing reaction condi-
tions. The terminal oxo core was found to be retained in all
due to the aromatic protons were found as a multiplet between
δ 7.1 and 7.9. The single phosphorus environment was con-
firmed by the singlet observed in the 31P-{1H} NMR spectrum
at δ 20.2. This reaction can be contrasted to the formation of
[ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10 which was obtained from
the reaction of [Re2O3(S2CNEt2)4] and the tridentate proligand
PPh(C6H4SH-2)2. In complex 10 the oxo ligand was retained
which was confirmed by the strong absorption observed in the
infrared spectrum at 941 cmϪ1 due to the stretching frequency
three complexes and the absorption due to ν(Re᎐O) was identi-
᎐
fied in the infrared spectrum as strong bands at 954, 948 and
of the Re᎐O bond. The 1H NMR spectrum was unremarkable
᎐
923 cmϪ1 for complexes 4, 5 and 6.
except for the observation of complex multiplets between δ 3.7–
4.1 and 1.4–1.5 which were assigned as the methylene and
methyl protons of ethyl groups in inequivalent environments.
The 31P-{1H} NMR spectrum shows the expected singlet at
δ 47.7 due to the co-ordinated phosphine. The new dithiocarb-
amate precursor [ReCl2(S2CNEt2)2][BPh4] 11 was prepared in
high yield by the room-temperature reaction of the oxo precur-
sor with SiMe3Cl. The resonances from the methyl and methy-
lene protons from the co-ordinated dithiocarbamates were
present as a triplet at δ 1.5 and a quartet at δ 3.9 respectively
indicating equivalence of the dithiocarbamate ethyl groups. The
aromatic protons from the counter ion were present as a multi-
plet between δ 6.9 and 7.5. The new precursor will allow a route
into rhenium dithiocarbamate chemistry without involvement
of an oxo core.
The complex [ReO{O(OH)C6H4}(S2CNEt2)2] reacts readily
with bidentate phosphines in boiling acetone to yield green
complexes of general formula [Re(S2CNEt2)2L][BPh4] where
L = Me2PCH2CH2PMe2 (dmpe) 7 or Ph2PCH2CH2PPh2 (dppe)
8. In contrast, no reaction was found to occur between the
phosphines and the dimeric precursor [Re2O3(S2CNEt2)4]. The
1
IR spectrum confirmed the absence of ν(Re᎐O) and the H
᎐
NMR spectra gave the expected resonances assigned to the
ethyl protons of the dithiocarbamate ligand and to the protons
of the co-ordinated bidentate phosphine. The 31P-{1H} NMR
spectra of 7 and 8 gave rise to the expected singlets at δ 44.5 and
12.4 due to the equivalent phosphorus donors in both com-
plexes. The FAB mass spectra show ions at m/z = 632 and 881
respectively with the appropriate isotope distribution.
The orange-red rhenium() complex [Re{PPh2(C6H4S-2}2-
(S2CNEt2)]ؒMe2CO 9 was prepared from the overnight room-
temperature reaction of [Re2O3(S2CNEt2)4] with the phosphino-
thiolate proligand PPh2(C6H4SH-2). The terminal oxo ligand
had been replaced by the bidentate phosphine/thiolate ligand.
Crystal and molecular structures of [ReO{O(OH)C6H4}-
(S2CNEt2)2] 1, [Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒMe2CO 9 and
[ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10
1
The H NMR spectrum shows the resonances due to the pro-
A representation of the structure of complex 1 is shown in Fig.
1 along with the associated atom numbering scheme. Selected
bond lengths and angles are given in Table 1. The overall geom-
tons of the dithiocarbamate ligands at δ 0.6 due to the methyl
protons and δ 2.9 due to the methylene protons. The resonances
2932
J. Chem. Soc., Dalton Trans., 1997, Pages 2931–2936

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Fig. 2 Perspective view of [Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒMe2CO 9
showing the atom labelling scheme
Fig. 3 Perspective view of [ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10 show-
ing the atom labelling scheme
Table 2 Selected bond lengths (Å) and angles (Њ) for [Re{PPh2-
(C6H4S-2)}2(S2CNEt2)]ؒMe2CO 9
Table 3 Selected bond lengths (Å) and angles (Њ) for [ReO{PPh-
(C6H4S-2)2}(S2CNEt2)] 10
Re᎐S(2)
Re᎐S(1)
Re᎐P(2)
Re᎐P(1)
Re᎐S(4)
2.265(2)
2.265(2)
2.371(3)
2.376(3)
2.496(2)
Re᎐S(3)
S(3)᎐C(1)
S(4)᎐C(1)
N᎐C(1)
2.502(2)
1.723(9)
1.714(9)
1.318(13)
Re᎐O(1)
Re᎐S(1)
Re᎐S(4)
Re᎐P(1)
1.679(4)
2.326(2)
2.378(2)
2.3847(14)
Re᎐S(3)
Re᎐S(2)
S(3)᎐C(1)
S(4)᎐C(1)
2.430(2)
2.624(2)
1.725(6)
1.746(6)
O(1)᎐Re᎐S(1)
O(1)᎐Re᎐S(4)
S(1)᎐Re᎐S(4)
O(1)᎐Re᎐P(1)
S(1)᎐Re᎐P(1)
S(4)᎐Re᎐P(1)
O(1)᎐Re᎐S(3)
S(1)᎐Re᎐S(3)
103.4(2)
108.5(2)
91.97(5)
93.2(2)
86.07(5)
157.97(6)
96.7(2)
S(4)᎐Re᎐S(3)
P(1)᎐Re᎐S(3)
O(1)᎐Re᎐S(2)
S(1)᎐Re᎐S(2)
S(4)᎐Re᎐S(2)
P(1)᎐Re᎐S(2)
S(3)᎐Re᎐S(2)
72.70(5)
102.07(5)
162.7(2)
81.74(5)
87.50(5)
70.49(5)
81.66(5)
S(2)᎐Re᎐S(1)
S(2)᎐Re᎐P(2)
S(1)᎐Re᎐P(2)
S(2)᎐Re᎐P(1)
S(1)᎐Re᎐P(1)
P(2)᎐Re᎐P(1)
S(2)᎐Re᎐S(4)
S(1)᎐Re᎐S(4)
116.88(9)
85.99(9)
93.48(9)
94.14(9)
85.78(9)
179.22(8)
86.57(8)
156.40(9)
P(2)᎐Re᎐S(4)
P(1)᎐Re᎐S(4)
S(2)᎐Re᎐S(3)
S(1)᎐Re᎐S(3)
P(2)᎐Re᎐S(3)
P(1)᎐Re᎐S(3)
S(4)᎐Re᎐S(3)
85.15(9)
95.63(9)
155.26(8)
87.71(8)
95.63(8)
84.58(8)
69.03(8)
157.82(6)
are the result of the bite angles of the bidentate ligands,
S(1)᎐Re᎐P(1) 85.78(9), S(2)᎐Re᎐P(2) 85.99(9)Њ, with the largest
distortion arising from the small bite angle of the dithiocarb-
amate ligand S(3)᎐Re᎐S(4) 69.03(8)Њ. The sulfur donors of the
phosphinothiolate ligands are in a cis configuration along with
the dithiocarbamate sulfurs resulting in one plane being com-
prised of only sulfur donors. There is significant opening up of
the S(1)᎐Re᎐S(2) angle to 116.88(9)Њ which was also observed in
the structure of [Re{PPh2(C6H4S-2)}3] where the corresponding
angle was determined to be 113.0(2)Њ. The most likely explan-
ation is electronic repulsion between the two negatively charged
thiol groups. The Re᎐S and Re᎐P distances are typical of those
found in rhenium() complexes.15
The structure of [ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10 is
shown in Fig. 3 and selected bond distances and angles are
shown in Table 3. The overall geometry about the central rhe-
nium atom is best described as distorted octahedral with the tri-
dentate ligand, PPh(C6H4S-2)2, bound in a facial co-ordination.
The oxo group is trans to a sulfur of the phosphinothiolate
ligand. The principal distortions arise from the small bite angles
of the polydentate ligands, S(3)᎐Re᎐S(4) 72.70(5)Њ in the dithio-
carbamate ligand, and due to the constraints of the P᎐C᎐C᎐S
chelate rings the S᎐Re᎐P bond angles are significantly reduced
from the ideal octahedral values of 90Њ to 86.07(5) and
70.49(5)Њ. The Re᎐S(2) bond shows significant lengthening due
to the trans influence of the oxo group, 2.624(2) Å, as compared
with the more usual bond length of 2.326(2) Å for Re᎐S(1). The
Re᎐S and Re᎐P distances are unremarkable and are similar to
those found for complexes of phosphinothiolate ligands.6
etry about the central rhenium atom is distorted octahedral
with the principal distortions coming from the relatively small
bite angles of the chelated dithiocarbamate ligands, S(1)᎐
Re᎐S(2) 72.37(7) and S(3)᎐Re᎐S(4) 72.30(7)Њ. The four sulfur
donors occupy the equatorial plane of the octahedron with the
two oxygen donors occupying the remaining sites. The most
surprising feature of the structure is the monodentate binding
of the potentially bidentate catechol ligand. The Re᎐O (cate-
cholate) distance of 1.969(5) Å shows no pronounced lengthen-
ing as a consequence of the trans influence of the oxo group.
This bond length can be compared with those found for
[ReO2(O2C6H4)2]Ϫ where the Re᎐O (catecholate) distances are
1.952(6) and 2.031(7) Å for the bond cis and trans to the oxo
core respectively and with 1.96(1) Å found in the cis catecholate
complex [ReO(O2C6H4)2]Ϫ.13 The C᎐O distance of C(31)᎐O(2)
1.338(8) Å is consistent with the presence of an anionic cate-
cholato ligand rather than the presence of the semiquinone or
benzoquinone forms.4 The Re᎐O (catechol) distance trans to the
oxo ligand is typical of an Re᎐O single bond 14 and implies little
bond lengthening due to the trans influence. The presence of the
unligated OH group is confirmed by the slightly longer C(36)᎐
O(3) bond [1.356(10) Å] and the Re ؒ ؒ ؒ O(3) distance of 4.462(6)
Å also supports the non-bonding of the hydroxyl group.
A representation of the structure of [Re{PPh2(C6H4S-2)}2-
(S2CNEt2)]ؒMe2CO 9 is shown in Fig. 2 together with the atom-
labelling scheme and selected bond lengths and angles are
shown in Table 2. The geometry about the rhenium is best
described as distorted octahedral. The principal distortions
J. Chem. Soc., Dalton Trans., 1997, Pages 2931–2936
2933

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Table 4 Cyclic voltammetric data for complexes 9 and 10
Complex Process ipa/ipc Epa */V Epc */V Ep/mV E /V
₁
₂
9
Oxidation 1 1.03
Oxidation 2 1.10
ϩ0.61
ϩ0.93
ϩ1.37
Ϫ1.02
ϩ1.39
Ϫ0.74
Ϫ1.39
Ϫ1.63
ϩ0.69
ϩ1.05
—
Ϫ1.08
—
Ϫ0.81
—
—
71
120
—
63
—
72
—
—
ϩ0.65
ϩ0.99
—
Ϫ1.05
—
Ϫ0.78
—
—
Oxidation 3
Reduction
Oxidation
—
0.96
—
10
Reduction 1 1.06
Reduction 2
Reduction 3
—
—
* All potentials are quoted relative to the ferrocenium–ferrocene couple
taken as 0.0 V. Ferrocene was added to the cell for each measurement.
Scan rate 0.2 V sϪ1
.
yielded complexes of the general type [NEt2H2][ReOL2], where
L = C2H4S2-1,2 4, C6H4S2-1,2 5 and MeC6H3S2-3,4 6. Degrad-
ation of the dithiocarbamate ligand by the thiolate ligands is
the source of the counter ion. The dimeric oxo-bridged pre-
cursor was found to be unreactive towards both mono- and
bi-dentate phosphines. Complexes such as [Re(S2CNEt2)2L]-
[BPh4], where L = dmpe 7 or dppe 8, could only be prepared
from the reaction of the catecholate complex [ReO{O(OH)-
C6H4}(S2CNEt2)2] 1 with these ligands. The mixed phosphine–
thiolate complexes [Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒMe2CO 9
and [ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10 could be prepared in
high yield from the room-temperature reaction of [Re2O3-
(S2CNEt2)4] with the mono- and bi-dentate ligands respec-
tively. The new rhenium dithiocarbamate precursor [ReCl2-
(S2CNEt2)2][BPh4] 11 was prepared in high yield and will
allow a route into rhenium dithiocarbamate chemistry without
involvement of the oxo core.
Experimental
All manipulations were carried out under an inert atmosphere
of dry dinitrogen gas using conventional Schlenk techniques
and all solvents were freshly distilled from appropriate drying
agents prior to use. Elemental analyses were performed by S.
Hodder and S. Ridgeway at the University of Essex or Medac
Ltd., University of Brunel. Infrared spectra were measured in
the range 200–4000 cmϪ1 as Nujol mulls (KBr plates) on a
Perkin-Elmer 1600 Series FTIR spectrophotometer, 1H and
31P-{1H} NMR using a JEOL EX270 MHz instrument. Fast
atom bombardment mass spectra (3-nitrobenzyl alcohol as
matrix) were recorded at the University of Essex, by E. Potter,
on a MS 50 instrument or by the EPSRC at the University of
Swansea facility. The electrochemical measurements were
recorded in dichloromethane solution at a platinum-wire work-
ing electrode and silver-wire pseudo-reference electrode with
Fig. 4 Cyclic voltammograms for [Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒ
Me2CO 9 (a) and [ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10 (b) recorded at
room temperature in CH2Cl2 at a platinum-wire auxiliary electrode and
silver-wire pseudo-reference electrode
Electrochemistry of [Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒMe2CO 9
and [ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10
The cyclic voltammetry data for complexes 9 and 10 are sum-
marised in Table 4. The complex [Re{PPh2(C6H4S-2)}2(S2-
CNEt2)]ؒMe2CO 9, Fig. 4(a), shows two reversible and one
irreversible oxidation which could be accounted for by the
reversible oxidation of the rhenium() complex to ReIV and
ReV and an irreversible oxidation to ReVI. The first oxidation
was a simple reversible one-electron process whilst the second
reversible oxidation appeared to have slow electron transfer.
The electrochemical behaviour of the complex during reduction
0.2  [NBun ][BF4] as the supporting electrolyte. Potentials are
4
quoted relative to the ferrocene–ferrocenium couple, which was
taken as 0.0 V. All other materials and reagents were obtained
commercially (Aldrich, Fisons) and used without further
purification. The compounds [Re2O3(S2CNEt2)4],16 PPh2-
showed
a reversible one-electron transfer. The complex
[ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10, Fig. 4(b), shows an
irreversible oxidation which can be accounted for by an oxid-
ation of ReV to ReVI. On the negative sweep one reversible
and two irreversible reductions were identified. The reversible
reduction, ReV to ReIV, exhibited an ideal one-electron transfer.
The two reversible reductions involve conversion of ReIV into
ReIII and a further reduction to ReII.
17
(C6H4SH-2)17 and PPh(C6H4SH-2)2 were prepared using
published procedures.
Preparation of the complexes
[ReO{O(OH)C6H4}(S2CNEt2)2] 1. The complex [Re2O3(S2C-
NEt2)4] (0.31 g, 0.31 mmol) and C6H4(OH)2-1,2 (0.30 g, 2.72
mmol) were heated under reflux in acetone (20 cm3) for 30 min.
A deep orange-brown solution and a dark orange crystalline
solid were formed on completion of the reaction. The solid was
filtered off, washed with Et2O and dried under vacuum. Yield
0.17 g, 94%. Recrystallisation from acetone–Et2O afforded dark
orange prisms. IR (KBr): ν(C᎐O) 1271s, ν(O᎐H) 3489w, ν(C᎐S)
Conclusion
We have described the syntheses and properties of some new
rhenium dithiocarbamato-complexes. The complex [ReO{O-
(OH)C6H4}(S2CNEt2)2] 1 represents a relatively rare example
of a complex containing a monodentate catecholate ligand.
Reaction with the analogous bidentate ligands unexpectedly
761s and ν(Re᎐O) 969s cmϪ1. 1H NMR (CDCl3): δ 1.3 (t, 12 H,
᎐
CH3), 3.8 (q, 8 H, CH2), 5.8 (s, 1 H, OH) and 6.5–6.7 (m, 4 H,
2934
J. Chem. Soc., Dalton Trans., 1997, Pages 2931–2936

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aromatic). 13C-{1H} NMR (CDCl3): δ 12.6 (CH3), 46.1 (CH2),
114.5, 118.1, 118.5, 120.0, 148.8, 149.0 (ring) and 235.6 (CS)
(Found: C, 31.6; H, 4.1; N, 4.6. C16H25N2O3ReS4 requires C,
31.6; H, 4.1; N, 4.6%). FAB mass spectrum: m/z, 499 {100%,
[ReO(S2CNEt2)2]ϩ}.
cm3) for 2 h. The dark orange suspension yielded a green solu-
tion on completion of the reaction. The solvent was removed
under vacuum and the resulting oil taken up in methanol (10
cm3). Immediately on addition of NaBPh4 (0.13 g, 0.38 mmol) a
green precipitate was formed which was filtered off and washed
with Et2O. Yield 0.27 g, 69%. IR (KBr): ν(CN) 1543m cmϪ1. 1H
NMR (CDCl3): δ 1.3 (2 s, 12 H, CH3), 1.5 (t, 12 H, CH3), 2.0
(m, 8 H, CH2) 3.6 (m, 8 H, CH2) and 7.1–7.4 (m, 20 H, aro-
matic). 31P-{1H} NMR (CDCl3): δ 44.5 (s) (Found: C, 50.4; H,
6.0; N, 2.9. C40H56BN2P2ReS4 requires C, 50.4; H, 5.9; N, 2.9%).
FAB mass spectrum: m/z, 632 {100, [Re(S2CNEt2)2(dmpe)]ϩ}
and 482 {100%, [Re(S2CNEt2)2]ϩ}.
[{ReO(S2CNEt2)2}2(C6H4O2-1,4)] 2. The complex [Re2O3-
(S2CNEt2)4] (0.30 g, 0.30 mmol), C6H4(OH)2-1,4 (0.33 g, 0.30
mmol) and NEt3 (0.41 cm3, 0.30 mmol) were heated under
reflux in acetone (20 cm3) for 1 h. The dark yellow-green suspen-
sion yielded a red-brown solid on completion of the reaction.
The solid was filtered off and washed with Et2O. Yield 0.23 g,
70%. IR (KBr): ν(C᎐O) 1248 and ν(Re᎐O) 960s cmϪ1. 1H NMR
᎐
(CDCl3): δ 1.3 (t, 12 H, CH3), 1.4 (t, 12 H, CH3), 3.8 (q, 16 H,
CH2), 6.5 (d, 2 H, aromatic) and 6.7 (d, 2 H, aromatic) (Found:
C, 28.3; H, 4.1; N, 4.9. C26H44N4O4ReS8 requires C, 28.2; H, 4.0;
N, 5.1%). FAB mass spectrum: m/z, 605 {50, [ReO(OC6H4O)-
(S2CNEt2)2]ϩ} and 499 {100%, [ReO(S2CNEt2)2]ϩ}.
[Re(S2CNEt2)2(dppe)][BPh4] 8. The complex [ReO{O(OH)-
(C6H4)}(S2CNEt2)2] (0.30 g, 0.49 mmol) and Ph2P(CH2)2PPh2
(0.98 g, 2.46 mmol) were heated under reflux in acetone (20
cm3) for 2 h. The dark orange suspension yielded a green solu-
tion on completion of the reaction. The solvent was removed
under vacuum and the resulting oil taken up in methanol (10
cm3). Immediately on addition of NaBPh4 (0.15 g, 0.44 mmol) a
green precipitate was formed which was filtered off and washed
with Et2O. Yield 0.49 g, 84%. IR (KBr): 1518 ν(CN) and ν(C᎐S)
746s cmϪ1. 1H NMR (CDCl3): δ 1.3 (t, 12 H, CH3), 1.7 (m, 2 H,
CH2), 3.5 (q, 8 H, CH2) and 6.9–7.9 (m, 20 H, aromatic). 31P-
{1H} NMR (CDCl3): δ 12.4 (s) (Found: C, 59.9; H, 5.4; N, 2.3.
C60H64BN2P2ReS4 requires C, 60.0; H, 5.4; N, 2.3%). FAB mass
spectrum: m/z, 881 {100%, [Re(S2CNEt2)2(dppe)]ϩ}.
[ReO(OC6H3NH2-2-Me-4)(S2CNEt2)2] 3. The complex
[Re2O3(S2CNEt2)4] (0.46 g, 0.45 mmol) and 2-amino-4-
methylphenol (0.29 g, 2.35 mmol) were heated under reflux in
acetone (20 cm3) for 1 h. The dark yellow-green suspension
yielded a dark orange solution which was filtered and the
solvent removed under vacuum to yield a dark orange oil.
Recrystallisation from CH2Cl2–Et2O yielded a dark orange
microcrystalline powder. Yield 0.19 g, 68%. IR (KBr): ν(C᎐S)
674s, ν(N᎐H) 3365w, 3468w and ν(Re᎐O) 964s cmϪ1. 1H NMR
᎐
(CDCl3): δ 1.3 (t, 12 H, CH3), 2.1 (s, 3 H, CH3), 3.1 (br s, 2 H,
NH), 3.8 (q, 8 H, CH2), 6.3, 6.7 (d, 2 H, aromatic) and 6.4 (s,
1 H, aromatic) (Found: C, 33.2; H, 4.6; N, 6.7. C17H28N3O2ReS4
requires C, 32.9; H, 4.6; N, 6.8%).
[Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒMe2CO 9. The complex
[Re2O3(S2CNEt2)4] (0.30 g, 0.30 mmol) and PPh2(C6H4SH-2)
(0.46 g, 1.57 mmol) were stirred at room temperature overnight
in acetone (20 cm3). A red-orange solid was formed on comple-
tion of the reaction. The solid was filtered off, washed with
Et2O and dried under vacuum. Yield 0.27 g, 90%. Recrystallis-
ation from acetone–Et2O afforded red-orange prisms. IR (KBr):
[NEt2H2][ReO(C2H4S2-1,2)2] 4. The complex [Re2O3(S2C-
NEt2)4] (0.30 g, 0.30 mmol) and C2H4(SH)2-1,2 (0.20 ml, 2.12
mmol) were stirred at room temperature for 1 h in acetone (20
cm3). The green suspension yielded an orange solution on com-
pletion of the reaction. The solution was filtered and the solv-
ent removed under vacuum which yielded an orange solid
which was filtered off and washed with Et2O. Cubic crystals
were obtained from slow evaporation of a solution of the com-
1
1708w cmϪ1. H NMR (CDCl3): δ 0.6 (t, 12 H, CH3), 2.9 (q,
8 H, CH2) and 7.1–7.9 (m, 28 H, aromatic). 31P-{1H} NMR
(CDCl3): δ 20.2 (s) (Found: C, 53.9; H, 4.4; N, 1.4. C44H44NO-
P2ReS4 requires C, 54.0; H, 4.5; N, 1.4%). FAB mass spectrum:
m/z, 917 {100%, [Re{PPh2(C6H4S-2)}2(S2CNEt2)]ϩ}.
plex in CH2Cl2. Yield 0.11 g, 78%. IR (KBr): ν(C᎐S) 772m,
1
ν(Re᎐O) 954s and ν(N᎐H) 3444w cmϪ1. H NMR (CDCl3): δ
᎐
[ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10. The complex [Re2O3-
(S2CNEt2)4] (0.31 g, 0.31 mmol) and PPh(C6H4SH-2)2 (0.30 g,
2.72 mmol) were stirred in acetone (20 cm3) for 30 min at room
temperature. A deep orange-brown solution and a dark orange
crystalline solid was formed on completion of the reaction. The
solid was filtered off, washed with Et2O and dried under vac-
uum. Yield 0.17 g, 94%. Recrystallisation from acetone–Et2O
1.2 (t, 6 H, CH3), 2.6, 2.73 (2 s, 8 H, CH2), 3.0 (q, 4 H, CH2) and
6.1 (m, 2 H, NH) (Found: C, 20.9; H, 4.4; N, 3.1. C8H20NOReS4
requires C, 20.9; H, 4.4; N, 3.0%).
[NEt2H2][ReO(C6H4S2-1,2)2] 5. As for complex 4, with
[Re2O3(S2CNEt2)4] (0.33 g, 0.33 mmol) and C6H4(SH)2-1,2 (0.50
cm3, 4.34 mmol). Yield 0.18 g, 86%. IR (KBr): ν(C᎐S) 746s,
afforded dark orange prisms. IR (KBr): ν(C᎐S) and ν(Re᎐O)
᎐
ν(N᎐H) 3440w and ν(Re᎐O) 948s cmϪ1. 1H NMR (CD3OCD3):
1
941s cmϪ1. H NMR (CDCl3): δ 1.4 (t, 12 H, CH3), 3.7–4.1 (q,
᎐
δ 1.3 (t, 6 H, CH3), 3.1 (q, 4 H, CH2), 6.1 (s, 2 H, NH) and 6.7–
7.8 (m, 8 H, aromatic). 13C-{1H} NMR (CD3OCD3): δ 11.6
(CH3), 43.5 (CH2), 123.1, 124.7, 128.3, 129.9, 152.7 (ring) and
237.2 (CS) (Found: C, 34.4; H, 3.6; N, 2.5. C16H20NOReS4
requires C, 34.5; H, 3.6; N, 2.5%). FAB mass spectrum: m/z, 483
{20, [ReO(S2C6H4)2]ϩ} and 465 {35%, [Re(S2C6H4)2]ϩ}.
8 H, CH2) and 7.0–8.0 (m, 13 H, aromatic). 31P-{1H} NMR
(CDCl3): δ 47.7 (s) (Found: C, 40.9; H, 3.5; N, 2.1. C23H23NO-
PReS4 requires C, 40.9; H, 3.4; N, 2.1%). FAB mass spectrum:
m/z, 595 {100%, [ReO{P(C6H4S-2)2}(S2CNEt2)]}.
[ReCl2(S2CNEt2)2][BPh4] 11. The complex [Re2O3(S2-
CNEt2)4] (0.13 g, 0.13 mmol) and SiMe3Cl (0.1 cm3, 0.79 mmol)
were stirred in methanol (10 cm3) for 20 min at room tempera-
ture. The green-brown suspension yielded a green solution on
completion of the reaction. The solvent was removed under
vacuum and addition of Et2O yielded a green precipitate, the
chloride salt, which was filtered off and washed with Et2O. The
precipitate was then dissolved in methanol (5 cm3) and NaBPh4
(0.04 g, 0.12 mmol) was added which resulted in the immediate
precipitation of an orange solid. Yield 0.09 g, 82%. IR (KBr):
ν(C᎐S) 705s cmϪ1. 1H NMR (CDCl3): δ 1.5 (t, 12 H, CH3), 3.8,
4.0 (q, 8 H, CH2) and 6.9–7.5 (m, 20 H, aromatic) (Found: C,
46.7; H, 4.8; N, 3.1. C34H40BCl2N2ReS4 requires C, 46.8; H, 4.6;
N, 3.2%).
[NEt2H2][ReO(MeC6H3S2-3,4)2] 6. As for complex 4, with
[Re2O3(S2CNEt2)4] (0.30 g, 0.30 mmol) and MeC6H3(SH)2-3,4
(0.23 cm3, 2.17 mmol). Yield 0.14 g, 78%. IR (KBr): ν(C᎐S)
770w, ν(Re᎐O) 923s and ν(NH) 3390w cmϪ1 1H NMR
.
᎐
(CDCl3): δ 0.9 (t, 6 H, CH3), 2.3 (s, 6 H, CH3), 2.5 (q, 4 H, CH2),
3.0 (br, 2 H, NH) and 6.8–7.7 (m, 6 H, aromatic) (Found: C,
37.2; H, 4.2; N, 2.5. C18H24NOReS4 requires C, 36.9; H, 4.1;
N, 2.4%). FAB mass spectrum: m/z, 511 {20%, [ReO(S2C6H3-
CH3)2]ϩ}.
[Re(S2CNEt2)2(dmpe)][BPh4] 7. The complex [ReO{O(OH)-
(C6H4)}(S2CNEt2)2] (0.25 g, 0.41 mmol) and Me2P(CH2)2PMe2
(0.71 cm3, 4.73 mmol) were heated under reflux in acetone (20
J. Chem. Soc., Dalton Trans., 1997, Pages 2931–2936
2935

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Table
5
Crystallographic data for complexes for [ReO{O(OH)C6H4}(S2CNEt2)2] 1, [Re{PPh2(C6H4S-2)}2(S2CNEt2)]ؒMe2CO 9 and
[ReO{PPh(C6H4S-2)2}(S2CNEt2)] 10
1
9
10
Formula
M
C16H25N2O3ReS4
607.82
C44H44NOP2ReS4
979.18
C23H23NOPReS4
674.83
Crystal size/mm
a/Å
b/Å
c/Å
α/Њ
β/Њ
0.50 × 0.50 × 0.25
10.092(3)
10.325(2)
12.144(2)
80.69(1)
74.05(2)
62.71(2)
1080.3(4)
1.869
0.35 × 0.39 × 0.21
12.572(2)
13.774(6)
14.366(3)
103.98(2)
97.880(10)
115.39(2)
2097.1(11)
1.551
0.52 × 0.50 × 0.20
9.0340(7)
9.8391(5)
14.365(2)
101.503(6)
102.875(8)
93.653(6)
1211.9(2)
1.849
γ/Њ
U/Å3
Dc/g cmϪ3
Reflections collected
3995
7644
4448
Unique data
3764
7322
4259
Observed reflections
3590
6486
4084
[Fo у 3σ(Fo)]
h, k, l Ranges
Ϫ10 to 11, 0–12, Ϫ14 to 14
Ϫ14 to 14, Ϫ15 to 15, 0–16
Ϫ10 to 10, Ϫ11 to 11, 0–17
θ Range for data/Њ
F(000)
1.75–24.98
596
1.52–25.01
984
2.13–25.00
660
Rint
0.0424
0.1546
0.0187
µ(Mo-Kα)
6.029
3.208
5.441
Absorption correction factors
R1
0.642–0.997
0.0448
0.37–1.000
0.0726
0.799–0.999
0.0303
wR2
0.1186
2.53, Ϫ3.00
0.2028
4.18, Ϫ3.67
0.0909
2.66, Ϫ1.50
Largest difference peak and hole/e ÅϪ3
Details in common: intensity data collected on a Enraf-Nonius CAD4 diffractometer 20 with monochromated Mo-Kα radiation (λ = 0.710 73 Å) in
2
2
2
¯
the scan mode ω–2θ at 293(2)K; plate crystal; triclinic, space group P1; Z = 2. Weighting schemes used: w = 1/[σ (Fo) ϩ (XP) ϩ YP], where
X = 0.0961, Y = 2.2605 for complex 1, X = 0.1746, Y = 7.2905 for 9 and X = 0.0492, Y = 4.4767 for 10 and P = [max(Fo2 ϩ 2Fc )]/3; R1 = Σ|Fo Ϫ Fc|/Fo
2
¹
2
2
and wR2 = [Σw(Fo2 Ϫ Fc )2/Σw(Fo )2]².
6 J. R. Dilworth, A. J. Hutson, J. S. Lewis, J. R. Miller, Y. Zheng,
Q. Chen and J. A. Zubieta, J. Chem. Soc., Dalton Trans., 1996, 1093.
7 E. Block, M. Gernon, H. Kang, G. Ofori-Okai and J. Zubieta,
Inorg. Chem., 1991, 30, 1736.
X-Ray crystallography
Structures 1, 9 and 10 were solved by direct methods18 and
refined on Fo2 by full-matrix least squares19 using all unique Fo
2
8 T. Osa and T. Kuwana, Electroanal. Chem., 1969, 22, 389.
9 S. Battacharya and C. G. Pierpont, Inorg. Chem., 1992, 31, 35.
10 W. A. Nugent and J. M. Mayer, Metal–Ligand Multiple Bonds,
Wiley-Interscience, New York, 1988.
11 P. J. Blower, J. R. Dilworth, J. P. Hutchinson, T. Nicholson and
J. A. Zubieta, J. Chem. Soc., Dalton Trans., 1986, 1339.
12 U. Abram and B. Lorentz, Z. Naturforsch, Teil B, 1993, 48, 771.
13 J. R. Dilworth, S. A. Ibrahim, S. R. Khan, M. B. Hursthouse and
A. A. Karaulov, Polyhedron, 1990, 9, 1323.
14 M. T. Ahmet, C. Lu, J. R. Dilworth, J. R. Miller, Y. Zheng,
D. E. Hibbs, M. B. Hursthouse and K. M. A. Malik, J. Chem. Soc.,
Dalton Trans., 1995, 3143.
15 L. Chang, S. Aizawa, M. J. Heeg and E. Deutsch, Inorg. Chem.,
1991, 30, 4920.
data corrected for Lorentz polarisation factors. An absorption
correction was applied using ψ scans of nine reflections with the
χ angle range 85–95Њ.20 The hydrogen atoms were included in
idealised positions with Uiso free to refine. The experimental
details of the data collections and structure solutions are sum-
marised in Table 5. The program ZORTEP was used to repre-
sent the structures.21
CCDC reference number 186/602.
Acknowledgements
We thank the Association for International Cancer Research
for funding and we gratefully acknowledge the Hermann Starck
Company, Germany for their generous gift of rhenium metal.
16 J. F. Rowbottom and G. Wilkinson, J. Chem. Soc., Dalton Trans.,
1972, 826.
17 E. Block, G. Ofori-Okai and J. Zubieta, J. Am. Chem. Soc., 1989,
111, 2327; E. Block, V. Eswarakrishnan, M. Gernon, G. Ofori-Okai,
C. Saha, K. Tang and J. Zubieta, J. Am. Chem. Soc., 1989, 111, 658.
18 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
19 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure
Refinement, University of Göttingen, 1993.
20 CAD-4 Software, Version 5.0, Enraf-Nonius, Delft, 1989.
21 L. Zsoluai, ZORTEP, An ellipoid representation program, Uni-
versity of Heidelberg, 1994.
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Received 29th April 1997; Paper 7/02935G
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