The formation of tetrameric oxotechnetium(V) and oxorhenium(V) complexes by cyclisation of a potentially multidentate thiocarbohydrazide derivative

Article abstract of DOI:10.1016/j.inoche.2011.04.037

Tetrameric complexes of the composition [MO(L¹)]₄ (M = Tc, Re), where (L¹)^3- represents an asymmetric, trianionic cyclisation product with thiocarbamoylbenzamidinato and mercaptotriazolato donor sites, were form

Full text of DOI:10.1016/j.inoche.2011.04.037

Inorganic Chemistry Communications 14 (2011) 1262–1265
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
The formation of tetrameric oxotechnetium(V) and oxorhenium(V) complexes by
cyclisation of a potentially multidentate thiocarbohydrazide derivative
⁎
Dirk Hauenstein, Ulrich Abram
Freie Universität Berlin, Institute of Chemistry and Biochemistry, Fabeckstr. 34-36, D-14195 Berlin, Germany
a r t i c l e i n f o
a b s t r a c t
Tetrameric complexes of the composition [MO(L1)]4 (M=Tc, Re), where (L1)3– represents an asymmetric,
trianionic cyclisation product with thiocarbamoylbenzamidinato and mercaptotriazolato donor sites, were
formed during reactions of [TcOCl4]– or [ReOCl4]– with a potentially multidentate ligand derived from
thiocarbohydrazide and N-[N',N'-diethylamino(thiocarbonyl)]benzimidoyl chloride.
© 2011 Elsevier B.V. All rights reserved.
Article history:
Received 14 March 2011
Accepted 28 April 2011
Available online 13 May 2011
Keywords:
Technetium
Rhenium
Oxo complex
Cyclisation
X-ray structure
N-[(Dialkylamino)(thiocarbonyl)]benzamidines can readily be
prepared from N-[(dialkylamino)(thiocarbonyl)]benzimidoyl chlo-
rides and amines [1,2]. Recently, we extended the well-known
coordination chemistry of bidentate ligands of this type [3] to novel
tridentate N-[(dialkylamino)(thiocarbonyl)]benzamidines and studied
their coordination behavior towards oxorhenium(V) and oxotechne-
tium(V) cores [3–7]. This also includes benzamidines derived from 4,
4-dialkylthiosemicarbazides, which form surprisingly stable techne-
tium(V) and rhenium(V) complexes [5,7].
In the present communication, we extend our studies to a
thiocarbamoylbenzamidine, which has been derived from thiocarbohy-
drazide (H4L0), and its reaction products with common technetium(V)
and rhenium(V) precursors. H4L0 can readily be prepared as a yellow
solid from thiocarbohydrazide and N-[N′,N′-diethylamino (thiocarbo-
nyl)]benzimidoyl chloride according to Scheme 1. The identity of the
compound was proven by elemental analysis and its IR, NMR and mass
spectra [8].
goes along with an extended transfer of π-electron density between the
CN bonds of the ligand backbone in such compounds [3–7,11]. The
crystallization of the products succeeded either from an extremely
diluted CH2Cl2 solution (CH2Cl2 solvate of the rhenium complex) or
directly from two-phase reaction mixtures (solvent-free single crystals of
the Tc complex and aqua solvate of the Re compound) [10,11].
The results of the X-ray structural determinations [12,13] on [TcO-
(L1)]4, and the pseudopolymorphs [ReO(L1)]4 · H2O and [ReO(L1)]4
·
H2O · CH2Cl2 confirm theconclusions drawn from the IR spectra, but also
show that a more complicate ongoing reaction appeared during the
complex formation. The central {TcO}3+ or {ReO}3+ units form five- and
six-membered chelate rings with one half of the organic ligand, while a
ring closure is observed in the remaining part, which yields a
triazolethiolato unit. Fig. 1a shows an ellipsoid representation of the
asymmetric unit of the technetium complex, while Fig. 1b contains a
representation of the complete tetrameric compound. The rhenium
complex is isostructural and is therefore not depicted in this commu-
nication. Both compounds are tetramers and possess four subunits with
each five-coordinate oxotechnetium(V) or oxorhenium(V) cores, the
equatorialcoordination spheres of whichare occupied by theS,N,S donor
atom set of the organic ligand, while the remaining fourth position
accommodates the sulfur atom of the triazolthiolato moiety of an
adjacent asymmetric unit generated from cyclisation of the second half
of H4L0 during the complex formation.
H4L0 readily reacts with (NBu4)[TcOCl4] or (NBu4)[ReOCl4] under
formation of reddish brown, microcrystalline solids, which are almost
insoluble in common organic solvents (Scheme 2) [9,10]. Their low
solubility prevented mass and NMR spectroscopic studies. But the
infrared spectra of the complexes suggest coordination of the thiocarba-
moylbenzamidine units of the organic ligand by a strong shift of the CN
vibrations of H4L0 from 1643 cm−1 to 1531 (Tc complex) and 1539 cm−1
(rhenium compound), respectively. Such a bathochromic shift is
characteristic for thiocarbamoylbenzamidinato complexes and normally
The bonding situation inside the monomeric units is unexceptional
with TcO and ReO double bond lengths between 1.6 and 1.7 Å and
M―S and M―N bonds in the expected range (Table 1). A slight double
bond character may be discussed for the relatively short M―N5
bonds, which are 2.011(5)Å ([TcO(L1)]4) and 2.029(5)Å ([ReO(L1)]4).
Similar values are observed in rhenium and technetium complexes
⁎
Corresponding author.
E-mail address: abram@chemie.fu-berlin.de (U. Abram).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.04.037

D. Hauenstein, U. Abram / Inorganic Chemistry Communications 14 (2011) 1262–1265
1263
N
N
S
HN
H2N
Cl
S
NH
NH
NH
+ 2 NEt3
- 2 (HNEt3)Cl
S
S
+
N
2
NH
N
H2N
HN
N
S
N
H4L0
Scheme 1. Formation of H4L0.
with mixed thiocarbamoylbenzamidinate/thiosemicarbazide coordi-
nation spheres [5,7]. The metal atoms in the [MO(L1)]4 (M=Tc, Re)
complexes are situated above the mean planes formed by the donor
atoms of the equatorial coordination spheres by 0.741(2)Å (Tc
compound) and 0.721(2)Å (Re complex). Such values are normally
observed for five-coordinate oxotechnetium(V) and oxorhenium(V)
complexes and are commonly explained by the steric bulk of the double
bonded oxo ligand [14]. While the five-membered chelate rings are
almost planar withmaximum deviationsof 0.127(3)Å (Tc complex)and
0.126(4)Å (Re complex), the six-membered thiocarbamoylbenzamidi-
nate chelate rings show very strong deviations from planarity.
Nevertheless, the C―N bonds inside the rings are all between 1.31
and 1.38 Å, which supports a delocalization of the electron density
inside the chelate rings.
The formation of N-heterocyclic ring systems is an occasionally
observed reaction pattern in the coordination chemistry of thiosemi-
carbazones and related ligand systems and is normally related to a
metal-induced mechanism [15]. This is also highly probable for the
reaction under study, since prolonged heating of H4L0 in various
solvents does not show any evidence for the cyclisation observed in the
presence of the rhenium compound. A possible mechanism is given in
Scheme 3. As a consequence of the coordination of a {ReO}3+ core to one
side of H4L0, the nucleophilicity of the remaining hydrazinic nitrogen
atoms is increased, which results in a ring closure reaction and the
abstraction of diethylamine. The final formation of a tetrameric complex
is obtained by coordination of the mercaptotriazolato unit to the fourth
equatorial coordination site of an adjacent oxotechnetium unit.
Fig. 1. a) Ellipsoid representation of the asymmetric unit of the molecular structure of
[TcO(L1)]4 with the molecular labelling scheme. Structure determinations were done
with SHELX [16] b) Molecular structure of the tetrameric complex [TcO(L1)]4 [17].
N
N
N
N
N
N
S
N
N
N
N
S
S
N
N
N
S
M
HN
S
M
N
O
NH
O
S
CH2Cl2 / MeOH
S
4 (NBu4)[MOCl4]
M = Tc, Re
+
4
S
N
N
- 4 (NBu4)Cl, 8 HCl
- 4 (H2NEt2)Cl
N
N
NH
S
S
O
N
O
N
HN
N
M
S
M
S
S
S
N
N
S
N
N
N
N
N
N
N
N
H4L0
N
Scheme 2. Reaction of H4L0 with (NBu4)[MOCl4] complexes (M=Tc, Re).

1264
D. Hauenstein, U. Abram / Inorganic Chemistry Communications 14 (2011) 1262–1265
Table 1
Selected bond lengths (Å) and angles (°) in [TcO(L1)]4 and [ReO(L1)]4 · H2O.a)
[TcO(L1)]4/[ReO(L1)]4
.
[TcO(L1)]4/[ReO(L1)]4
Tc/Re―O10
Tc/Re―S1
Tc/Re―N5
Tc/Re―S8
Tc/Re―S36′
S1―C2
C2―N3
O10―Tc/Re―S8
O10―Tc/Re―N5
O10―Tc/Re―S1
O10―Tc/Re―S36′
Tc/Re―S8―C7
S8―C7―N6
C7―N6―N5
Tc/Re―N5―N6
Tc/Re―N5―C4
N5―C4―N3
1.639(5)/1.663(7)
2.304(2)/2.304(2)
2.011(5)/2.029(5)
2.287(2)/2.291(2)
2.361(2)/2.357(2)
1.743(7)/1.741(9)
1.348(9)/1.34(1)
114.6(2)/114.6(2)
103.5(2)/103.5(2)
113.8(2)/111.8(2)
105.3(2)/105.0(2)
97.3(2)/97.1(2)
124.9(5)/124.6(6)
111.0(5)/112.6(6)
123.4(4)/122.7(4)
121.4(4)/120.9(5)
123.0(6)/124.3(7)
N3―C4
C4―N5
N5―N6
N6―C7
C7―S8
1.314(9)/1.31(1)
1.386(8)/1.377(9)
1.419(7)/1.407(8)
1.277(8)/1.245(9)
1.744(7)/1.760(7)
1.734(6)/1.752(7)
C33―S36
C4―N3―C2
N3―C2―S1
125.8(6)/124.3(7)
1232.6(5)/124.1(7)
108.0(3)/108.1(3)
89.1(2)/89.4(2)
85.46(6)/85.93(7)
80.6(2)/80.2(2)
81.48(6)/82.25(7)
131.53(8)/133.59(9)
150.4(2)/150.8(2)
Tc/Re―S1―C2
S1―Tc/Re―N5
S1―Tc/Re―S36′
N5―Tc/Re―S8
S8―Tc/Re―S36′
S1―Tc―S8
N5―Tc―S36′
a)Intramolecular bond lengths and angles in the CH2Cl2 solvate of [ReO(L1)]4 do not significantly differ and are therefore not given separately.
Symmetry operation: (′) y−1, 1−x, 2−z.
H
+
H
N
δ
H
N
N
N
N
N
N
N
N
N
H
N
N
M
S
M
S
−
N
δ
N
S
S
S
O
S
O
N
N
− Et NH
2
+
− H
S
N
S
N
S
N
N N
N
N
N
N
S
N
N
N
M
M
NH
N
S
O
O
S
M = Tc, Re
Scheme 3. Proposed mechanism of the formation of the [MO(L1)]4 complexes.
[3] H.H. Nguyen, J. Grewe, J. Schroer, B. Kuhn, U. Abram, Inorg. Chem. 47 (2008) 5136
and references cited therein.
[4] J. Schroer, U. Abram, Polyhedron 28 (2009) 2277.
[5] H.H. Nguyen, P.I.S. Maia, V.M. Deflon, U. Abram, Inorg. Chem. 48 (2009) 25.
[6] H.H. Nguyen, V.M. Deflon, U. Abram, Eur. J. Inorg. Chem. (2009) 3179.
[7] H.H. Nguyen, J.J. Jegathesh, P.I. da, S. Maia, V.M. Deflon, R. Gust, S. Bergemann, U.
Abram, Inorg. Chem. 48 (2009) 9356.
All four oxo ligands direct to the center of the voids (distances
between neighboring metal atoms: 5.2671(2)Å (Tc complex) and
5.2945(2)Å (Re complex); distances between diagonal metal atoms:
7.2303(3)Å (Tc complex) and 7.2779(3)Å (Re complex)), which are
formed between the four metal atoms (Fig. 1b). Consequently, the
empty sixth coordination sides point to the outer sphere of the complex
and may be matter for the coordination of additional ligands. With a
careful selection of bifunctional linker ligands, the tetrameric com-
pound under study can be used as building blocks for supramolecular
assemblies.
[8] Synthesis of H4L0: Thiocarbohydrazide (278 mg, 2.6 mmol) and triethylamine (75 μL,
5.4 mmol) were dissolved in 15 ml dry THF and N-[N′,N′-diethyl(thiocarbonyl)]-
benzimidoyl chloride (1.31 g, 5.4 mmol) in 5 mL of the same solvent was slowly added.
The reaction mixture was stirred for 4 h at room temperature. The colourless solid
of (HNEt3)Cl, which was formed during this time, was filtered off and the solvent of
the filtrate was removed in vacuum. The remaining yellow oil was suspended in
diethylether and stored for 48 h at −18 °C, which resulted in the formation of a yellow
solid, which was carefully washed with diethylether and dried in vacuum. Yield: 1.01 g
(70%). Elemental analysis: Calc. for C25H34N8S3: C, 55.3; H, 6.3; N, 20.6; S, 17.7 %. Found:
C, 56.2; H, 6.3; N, 19.8; S, 17.0%. IR (KBr, νmax in cm−1): 3186 (w), 2974 (m), 1643 (m),
1566 (w), 1481 (s), 1346 (m), 1315 (m), 1265 (s), 1134 (m), 1072 (m), 907 (w), 841
(w), 772 (s), 691 (s). 1H NMR (δ, CDCl3): 1,14 (m, 6 H, CH3), 1.25 (m, 6 H, CH3), 3.06 (q,
4 H, CH2), 3.40 (m, 4 H, CH2), 7.2–8.0 (m, 10 H, arom.), 9.48 (s, 2 H, NH), 10.40 (s, 2 H,
Appendix A. Supplementary material
Supplementary data to this article can be found online at
doi:10.1016/j.inoche.2011.04.037.
NH). ESI+ MS: m/z: 543.215 [M+H]+, 565.197 [M+Na]+, 581.17 [M+K]+
.
[9] Synthesis of [TcO(L1)]4: (NBu4)[TcOCl4] (50 mg, 0.1 mmol) was dissolved in 4 ml
MeOH and H4L0 (59 mg, 0.1 mmol) was added in 4 ml MeOH. The mixture was
References
stirred at room temperature for 30 min. A very fine, sparingly soluble red
precipitate was formed during this time. The solid was dissolved in about 50 ml of
warm CH2Cl2, from which [TcO-(L1)]4 deposited upon cooling and slow
evaporation as red microcrystals. Yield: 57 mg (95%). Single-crystals of [TcO
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D. Hauenstein, U. Abram / Inorganic Chemistry Communications 14 (2011) 1262–1265
1265
(L1)]4 were grown by careful overlayering of a highly diluted CH2Cl2 solution of
(NBu4)[TcOCl4] with a solution of H4L0 in MeOH. Slow diffusion of the two
solutions gave a deposit of red crystals at the interface between the two layers.
The identity of this product with the bulk, which was prepared following the
procedure given above was proven by means of their IR spectra and elemental
analyses. Elemental analysis: Calc. for C84H80N28O4S12RTc4: Tc, 17.0 %. Found: Tc,
15.9%. IR (KBr, νmax in cm−1): 2974 (w), 1531 (s), 1443 (m), 1350 (s), 1254 (w),
1138 (w), 1096 (w), 1072 (w), 961 (m), 945 (m), 775 (w), 729 (m), 683 (m).
[10] Synthesis of [ReO(L1)]4: a) (NBu4)[ReOCl4] (59 mg, 0.1 mmol) and H4L0 (59 mg,
0.1 mmol) were dissolved in 2 ml MeOH and stirred at room temperature for
30 min. The deposited yellow-brown solid was filtered off and re-dissolved in a
large amount (approximately 200 ml) of CH2Cl2, from which [ReO(L1)]4
precipitated as orange-red small crystals. Yield: 63 mg (94%).b) [ReOCl3(PPh3)2]
(83 mg, 0.1 mmol) was suspended in 5 ml CH2Cl2 and H4L0 (59 mg, 0.1 mmol)
T
min =0.2784; Tmax =0.6275. Structure solution and refinement: SHELXS-97,
SHELXL-97 [16], R1=0.0495, wR2=0.1258, GooF=0.956, Flack −0.02(1), CCDC
deposit number: CCDC-815916.Crystal data for [ReO(L1)]4∙ H2O∙ CH2Cl2: orthorhom-
bic, space group P22121, a=14.124(1), b=19.076(1), c=20.398(1) Å, V=5495.8
(6) Å3, Z=2. STOE-IPDS, Mo Kα radiation (λ=0.71073 Å), T=200 K, 99363
reflections measured, 14879 independent, 647 parameters, μ=4.728 mm−1
,
absorption correction: integration, Tmin=0.2538; Tmax=0.6179. Structure solution
and refinement: SHELXS-97, SHELXL-97 [16], R1=0.0475, wR2=0.1255,
GooF=1.081, Flack 0.001(7), CCDC deposit number: CCDC-815917.
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was added.
A brownish solid was obtained after stirring for 1 h at room
temperature. Recrystallisation from about 200 ml CH2Cl2 gave an orange-red,
crystalline solid of [ReO(L1)]4 ∙ H2O∙ CH2Cl2. Yield: 65 mg (91%).Single crystals of
[ReO(L1)]4 ∙ H2O were obtained following the two-phase reaction described above
for the technetium compound. Elemental analysis: Calc. for C84H80N28O4S12Re4: C,
37.7; H, 3.0; N, 14.6; S, 14.4%. Found: C, 37.3; H, 2.7; N, 14.3; S, 14.1%. IR (KBr, νmax
in cm-1): 2974 (w), 1539 (s), 1443 (m), 1350 (s), 1254 (w), 1138 (w), 1096 (w),
1072 (w), 988 (m), 949 (m), 775 (w), 729 (m), 683 (m).
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(1), c=14.448(1) Å, V=5327.2(5) Å3, Z=2. STOE-IPDS, Mo Kα radiation
(λ=0.71073 Å), T=200 K, 21772 reflections measured, 7187 independent, 299
parameters, μ=0.802 mm−1, no absorption correction. Structure solution and
refinement: SHELXS-97, SHELXL-97 [16], R1=0.0525, wR2=0.1417, GooF=0.911,
Flack 0.03(6), CCDC deposit number: CCDC-815915.
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b=19.246(1), c=14.454(1) Å, V=5353.9(5) Å3, Z=2. STOE-IPDS, Mo Kα
radiation (λ=0.71073 Å), T=200 K, 48033 reflections measured, 7246 inde-
pendent, 308 parameters, μ=4.802 mm−1, absorption correction: integration,
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