Reactivity of [M=O]3+ (M = Tc, Re) core towards 2-mercapto-1,3-azole ligands. Formation of a new organometallic complex of Re(IV) and X-ray crystal structures

Article abstract of DOI:10.1016/j.ica.2004.09.012

Reactions of [MOCl₄]^- anion (M = Re, Tc) with imidazole-2-thiol ligands H₂Lⁿ give bi- and tetra-substituted complexes [MOCl₂(H₂L)₂ (H₂O)]⁺ and [MO(H₂L)₄]³⁺. An organometallic species is formed from reaction of [ReOCl ₃(PPh₃)₂] and benzoxazole-2-thiol ligand HL⁵ by a desulfurization process. Imidazole-2-thiol derivatives H₂L^1-3 (H₂L¹ = 1H-benzoimidazole-2- thiol, H₂L² = 5-methyl-1H-benzoimidazole-2-thiol, and H₂L³ = 1H-imidazole-2-thiol) act as neutral monodentate ligands in a number of technetium and rhenium complexes. Disubstituted M(V) (M = Tc, Re) complexes of the type [AsPh₄]{[MOCl₂(H ₂Lⁿ)₂(H₂O)]Cl₂} are formed when [MOCl₄]^- react with H₂L ^1-3 in 1:2 stoichiometric ratio. Single crystal X-ray structure determinations were carried out on [AsPh₄]{[TcOCl₂(H ₂L¹)₂(H₂O)]Cl₂}. The coordination sphere is pseudo-octahedral in which the sulfur atoms of two ligands sit in the equatorial plane and a water molecule is in trans to the TcO multiple bond. All the complexes react with an excess of the corresponding ligand to form tetrasubstituted cationic species {[MO(H₂L ⁿ)₄]Cl₃}. These complexes can be also isolated by reaction of [MOCl₄]^- with an excess of ligand. No complex is obtained with benzothiazole-2-thiol (HL⁴) and benzoxazole-2-thiol (HL⁵). Ligand exchange reactions of [ReOCl ₃(PPh₃)₂] with HL^4,5 have also been investigated. Treating the oxo-precursor with HL⁴ no product is isolated, while with HL⁵ the chelate oxo-compound [ReOCl ₂(L⁵)(PPh₃)] is formed as two isomers. An interesting organometallic complex of Re(IV) [ReCl₃(L ⁵*)(PPh₃)₂] is obtained when a slight excess of HL⁵ reacts with [ReOCl₃(PPh₃) ₂] in refluxing benzene solution and in air. Geometry about the Re atom is approximately octahedral in which the equatorial plane contains three Cl atoms and the carbon atom of the benzoxazole ligand anion, the apical positions are occupied by two PPh₃. The reaction with O-ethyl S-hydrogen p-tolyl carbonothioimidate HL⁶ which contains the same heteroatoms of HL⁵ does not form an organometallic species, but forms the chelate oxo-Re(V) complex [ReOCl₂(L⁶)(PPh₃)]. The solid-state structure has been authenticated by X-ray crystallography.

Full text of DOI:10.1016/j.ica.2004.09.012

Inorganica Chimica Acta 358 (2005) 363–375
www.elsevier.com/locate/ica
Reactivity of [M@O]3+ (M = Tc, Re) core towards
2-mercapto-1,3-azole ligands. Formation of a new
organometallic complex of Re(IV) and X-ray crystal structures
a
a
a,
a
Michele Brugnati , Elena Marchesi , Andrea Marchi *, Lorenza Marvelli ,
b
Valerio Bertolasi , Valeria Ferretti
b
a
`
Laboratorio di Chimica Inorganica e Nucleare, Dipartimento di Chimica, Universita di Ferrara, via L. Borsari 46, 44100 Ferrara, Italy
b
`
Centro di Strutturistica Diffrattometrica, Dipartimento di Chimica, Universita di Ferrara, via L. Borsari 46, 44100 Ferrara, Italy
Received 29 July 2004; accepted 6 September 2004
Available online 22 October 2004
Abstract
Imidazole-2-thiol derivatives H2L1–3 (H2L1 = 1H-benzoimidazole-2-thiol, H2L2 = 5-methyl-1H-benzoimidazole-2-thiol, and
H2L3 = 1H-imidazole-2-thiol) act as neutral monodentate ligands in a number of technetium and rhenium complexes. Disubstituted
M(V) (M = Tc, Re) complexes of the type [AsPh4]{[MOCl2(H2Ln)2(H2O)]Cl2} are formed when [MOCl4]ꢀ react with H2L1–3 in 1:2
stoichiometric ratio. Single crystal X-ray structure determinations were carried out on [AsPh4]{[TcOCl2(H2L1)2(H2O)]Cl2}. The
coordination sphere is pseudo-octahedral in which the sulfur atoms of two ligands sit in the equatorial plane and a water molecule
is in trans to the Tc@O multiple bond. All the complexes react with an excess of the corresponding ligand to form tetrasubstituted
cationic species {[MO(H2Ln)4]Cl3}. These complexes can be also isolated by reaction of [MOCl4]ꢀ with an excess of ligand. No com-
plex is obtained with benzothiazole-2-thiol (HL4) and benzoxazole-2-thiol (HL5). Ligand exchange reactions of [ReOCl3(PPh3)2]
with HL4,5 have also been investigated. Treating the oxo-precursor with HL4 no product is isolated, while with HL5 the chelate
5
5
*
oxo-compound [ReOCl2(L )(PPh3)] is formed as two isomers. An interesting organometallic complex of Re(IV) [ReCl3(L )(PPh3)2]
is obtained when a slight excess of HL5 reacts with [ReOCl3(PPh3)2] in refluxing benzene solution and in air. Geometry about the Re
atom is approximately octahedral in which the equatorial plane contains three Cl atoms and the carbon atom of the benzoxazole
ligand anion, the apical positions are occupied by two PPh3. The reaction with O-ethyl S-hydrogen p-tolyl carbonothioimidate HL6
which contains the same heteroatoms of HL5 does not form an organometallic species, but forms the chelate oxo-Re(V) complex
[ReOCl2(L6)(PPh3)]. The solid-state structure has been authenticated by X-ray crystallography.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Rhenium/technetium/thiolate complexes/structures
1. Introduction
99mTc radionuclide (c-emitter, Emax = 140 keV, t1/2 = 6
h) [1,2]. Moreover, its availability from 99Mo/99mTc gen-
erator system [3] makes the technetium compounds ideal
for imaging in nuclear medicine practice. Both isotopes
of rhenium (186Re, Emax = 1.1 MeV, t1/2 = 90.64 h;
188Re, Emax = 2.1 MeV, t1/2 = 17 h) are b-emitters and
are suitable candidates for therapeutic applications by
means of b-irradiation in radiotherapy. In particular,
It is well known that the interest in coordination
chemistry of technetium derives from its applications
in radiodiagnosis due to optimal nuclear properties of
*
Corresponding author. Tel.: +39 0532 291128; fax: +39 0532
240709.
availability of
a
188W/188Re generator [4] makes
E-mail address: mg1@unife.it (A. Marchi).
0020-1693/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.09.012

364
M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
rhenium-188 the more promising choice for the develop-
ment of radiopharmaceuticals for use in cancer therapy
[5]. Technetium and rhenium possess a very rich chemis-
try because they display oxidation states ranging from
ꢀ1 to + 7 and coordinate to a great variety of ligands
showing various coordination geometries. This versatil-
ity is stressed in particular cores which have been studied
for developing new potential radiopharmaceuticals.
These are metal(V)-oxo [M@O]3+ [1–3,6–13] and -nitr-
uous field of study in bioinorganic chemistry and many
metal complexes containing this class of ligands have
been reported [42–48]. Recently, Romerosa et al. [49–
51] have reported a series of palladium and platinum
complexes of several 8-thio-purine derivatives (8-
TTH2) in order to study their coordination chemistry.
These thiopurines possess both N7H and SH groups,
which may be deprotonated leading to potential biani-
onic bidentate ligands.
O
O
O
H
H
Me
O
5
4
N
Me
O
Me
O
6
N
N
N
N
N
7
1
N
N
8
S
SH
SH
2
9
N
3
N
N
N
H
H
Me
Me
Me
8-(Thio)-theophilline (8TTH )
2
ido [M@N]2+[14–16], metal(III)-hydrazino [MNNR]n+
[17,18] and more recently, metal(I)-carbonyl fac-
[M(CO)3]+ [19–23] cores. Since the chemical species
eluted from radionuclide generator is the [MO4]ꢀ anion,
the studies have been focused on oxo-metal(V) com-
plexes containing the [M@O]3+ fragment which is read-
ily obtained by facile reduction of permetalate. In this
oxidation state, the corresponding compounds are five-
or six-coordinate species showing square pyramidal,
trigonal bipyramidal and octahedral geometries. The
majority of oxo-metal(V) complexes are represented by
compounds which contain tetradentate ligands such as
diaminedithiols or diamidedithiols (N2S2) [24–33], poly-
dentate Schiff bases [34–36] which stabilize the [M@O]3+
core. The so-called ‘‘3 + 1’’ system (a tridentate dithiol
HSXSH, X@S, O, NR; and monodentate thiol ligands
R-SH) was developed in order to prepare complexes of
general formula [MO(SXS)(RS)] [37,38]. These com-
pounds were found relatively unstable in vitro and in
vivo. Recently, the ‘‘3 + 2’’ approach [39], which con-
sists of a tridentate and bidentate ligand set, gives rise
to more stable oxometal complexes because they are
characterized by 18 electron structures compared to 16
electron structures of ‘‘3 + 1’’ oxo-compounds.
Purine bases are the principal constituents of nucleic
acid derivatives. Natural purines such as caffeine and
theophilline possess pharmacological activity (stimulant,
cardiotonic, diuretic); some thiopurines (6-thioguanine,
mercaptopurine) or more functionalized purines are em-
ployed and investigated for the treatment of leukemia
and used for their antiviral activity [40,41]. Purine deriv-
atives exhibit a variety of donor groups and conse-
quently represent an interesting class of ligands
towards a wide range of metal ions. Interaction among
metal ions and purine bases is an important and contin-
In view of all this and as a continuation of our studies
on coordination chemistry of technetium and rhenium,
it was useful to select simplified and commercially avail-
able model molecules which may mimic the reactivity of
8-TTH2 towards these metal ions. Recently, we have
investigated the reactivity of imidazole-2-thiol deriva-
tives with Tc(III) and Re(III) precursors to produce
new trigonal bipyramidal complexes in which ligands
are bound through the neutral sulfur atom. Moreover,
benzothiazole-2-thiol and benzoxazole-2-thiol ligands
in which a nitrogen atom is replaced by an oxygen and
sulfur showed a different reactivity giving octahedral
chelate complexes [52]. Our aim was to study the chem-
ical properties of these ligands (Scheme 1) towards the
[M@O]3+ core (M = Re, Tc). In this paper, we describe
the synthesis and characterization of oxo-complexes of
both metals. In addition, the X-ray crystal structures
of some representative compounds are also discussed.
2. Experimental
2.1. Materials and instrumentations
Caution! 99Tc is a weak b-emitter (Eb = 0.292 MeV,
t1/2 = 2.12 · 105 years). All manipulations were carried
out in a laboratory approved for low-level radioactivity.
Unless otherwise noted, all chemicals were of reagent
grade and used without further purification. The starting
compounds, [AsPh4][MOCl4] (M = Re, Tc) [53–56] and
[ReOCl3(PPh3)2] [57,58], were prepared according to the
literature procedures. Ligands 1H-benzoimidazole-2-
thiol
(H2L1),
5-methyl-1H-benzoimidazole-2-thiol
(H2L2), 1H-imidazole-2-thiol (H2L3), benzothiazole-2-
thiol (HL4), benzoxazole-2-thiol (HL5) and 4-methyl-

M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
365
N
X
N
N
S
SH
SH
SH
N
N
H
H
X=H, H2L1=1H-benzoimidazole-2-thiol
X=Me, H2L2=5-methyl-1H-benzoimidazole-2-thiol
H2L3=1H-imidazole-2-thiol
HL4=benzothiazole-2-thiol
OC2H5
N
H3C
N
C
SH
SH
O
HL5=benzoxazole-2-thiol
HL6=O-Ethyl S-hydrogen p-tolyl
carbonothioimidate
Scheme 1.
phenylisothiocianate were purchased from Aldrich.
Elemental analyses were performed using a Carlo Erba
Instruments model EA 1110; FT-IR spectra were re-
corded in a range 4000–200 cmꢀ1 on a Nicolet 510 P
FT-IR instrument in KBr using a Spectra-Tech collector
diffuse reflectance accessory. Proton spectra of CDCl3,
CD2Cl2, CD3OD, and (CD3)2CO solutions of the com-
pounds were examined on a Bruker AM 200 spectrometer
with SiMe4 as internal standard, 31P{1H} NMR on the
same instrument with a 85% H3PO4 solution as external
standard. Conductivities were obtained at sample concen-
trations of ca. 1 · 10ꢀ4 M in CH2Cl2 solutions at room
temperature with an Amel Model 134 conductivity meter.
6.45%. FTIR (KBr, cmꢀ1): 3000–2500 m(N–H ꢁ ꢁ ꢁ Cl);
1518–1441 m(N–C–N); 1081 and 997 (AsPh4+); 997
m(Tc@O); 1H NMR [(CD3)2CO, ppm]: 2.4 (6H, s,
CH3); 7.0–7.4 (6H, m, Ph); 7.7–8.1 (20H m, Ph).
[AsPh4]{[TcOCl2(H2L3)2(H2O)]Cl2} (3). Yield
55%; Calc. for C30H30N4AsCl4O2S2Tc: C, 42.0; H, 3.5;
N, 6.5; S, 7.5; Found: C, 41.9; H, 3.55; N, 6.5; S,
7.4%. FTIR (KBr, cmꢀ1): 3000–2500 (N–H Æ Cl); 1775–
1430 m(N–C–N); 1081 and 997 m(AsPh4+); 997 m(Tc@O);
1H NMR [(CD3)2CO, ppm]: 7.6 (4H, s, CH@CH); 8.1–
8.3 (20H, m, Ph).
[AsPh4]{[ReOCl (H2L1) (H2O)]Cl2} (4). Yield
2
2
70%; Calc. for C38H34N4 AsCl4O2ReS2: C, 43.6; H,
3.2; N, 5.35; S, 6.7%; Found: C, 43.5; H, 3.15; N, 5.3;
S, 6.75%. FTIR (KBr, cmꢀ1): 3000–2500 m(N–H Æ Cl);
1508–1450 m(N–C–N); 1081 and 998 m(AsPh4+); 998
2.2. Synthesis of [AsPh4]{[MOCl2(H2Ln)2(H2O)]Cl2}
(n = 1–3) (M = Tc, 1–3; M = Re, 4–6)
1
(Re@O); H NMR [(CD3)2CO, ppm]: 7.2–7.3 (8H, m,
The complexes 1–6 were prepared using the same syn-
thetic procedure described, in detail, for 1. The solid lig-
and H2L1 (34.2 mg; 0.228 mmol) was added to a stirred
solution of [AsPh4][TcOCl4] (73 mg; 0.114 mmol) in ace-
tone (30 ml) and the mixture was refluxed for 1 h. The
resulting green solution was concentrated in vacuo, the
crude solid was washed with acetone and dried with
Et2O. Conductivity measurements at sample concentra-
tions of ca. 1 · 10ꢀ4 M in MeOH solutions gave values
in the range 105–114 S cm2 molꢀ1. Yields were based on
starting complexes. Recrystallization of 1 from hot
Me2CO and MeOH (3:1 v/v) gave suitable crystals for
X-ray diffraction analysis.
Ph); 7.9–8.1 (20H, m, Ph).
[AsPh4]{[ReOCl2(H2L2)2(H2O)]Cl2} (5). Yield
60%; Calc. for C40H38N4 AsCl4O2ReS2: C, 44.7;H, 3.6;
N, 5.2; S, 6.0; Found: C, 44.65; H, 3.5; N, 5.15; S,
5.9%. FTIR (KBr, cmꢀ1): 3000–2500 m(N–H ꢁ ꢁ ꢁ Cl);
1518–1441 m(N–C–N); 1081 and 998 (AsPh4+); 998
m(Re@O); 1H NMR [(CD3)2CO, ppm]: 2.4 (6H, s,
CH3); 7.1–7.3 (6H, m, Ph); 7.9–8.1 (20H, m, Ph).
[AsPh4]{[ReOCl2(H2L3)2(H2O)]Cl2} (6). Yield
65%; Calc. for C30H30N4 AsCl4O2ReS2: C, 38.1; H,
3.2; N, 5.9; S, 6.7; Found: C, 38.0; H, 3.15; N, 5.8; S,
6.75%. FTIR (KBr, cmꢀ1): 3000–2500 m(N–H Æ Cl);
1776–1430 m(N–C–N); 1081 and 998 m(AsPh4+); 999
m(Re@O); 1H NMR [(CD3)2CO, ppm]: 7.6 (4H, s,
CH@CH); 8.1–8.3 (20H, m, Ph).
[AsPh4]{[TcOCl2(H2L1)2(H2O)]Cl2} (1). Yield
60%; Calc. for C38H34N4AsCl4O2S2Tc: C, 47.6; H, 3.6;
N, 5.85; S, 6.7; Found: C, 47.5; H, 3.5; N, 5.8; S,
6.75%. FTIR (KBr, cmꢀ1): 3000–2500 m(N–H ꢁ ꢁ ꢁ Cl);
1505–1356 m(N–C–N); 1081 and 996 (AsPh4+); 997
2.3. Synthesis of {[MO(H2Ln)4]Cl3} Æ 3H2O (n = 1–3)
(M = Tc, 7–9; M = Re, 10–12)
1
m(Tc@O); H NMR [(CD3)2CO, ppm]: 7.25–7.35 (8H,
m, Ph); 8.0–8.3 (20H, m, Ph).
These complexes were prepared by the same general
procedure based on the reaction of [AsPh4][MOCl4]
(method A), or [AsPh4]{[MOCl2(H2Ln)2(H2O)]Cl2}
(n = 1–3) (M = Tc, 1–3; M = Re, 4–6) (method B), with
[AsPh4]{[TcOCl2(H2L2)2(H2O)Cl2]} (2). Yield
58%; Calc. for C40H38N4AsCl4O2S2Tc: C, 48.7; H, 3.9;
N, 5.7; S, 6.5; Found: C, 48.65; H, 4.0; N, 5.7; S,

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M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
an excess of H2Ln. Details are given below for a repre-
sentative case. The compound 7 has also been synthe-
sized by reacting [NH4][TcO4] with H2L1 (method C).
Method A. To a solution of [AsPh4][TcOCl4] (50 mg;
0.078 mmol) in 30 ml of CH2Cl2, solid ligand H2L1 (70
mg; 0.47 mmol) was added and the resulting mixture
was stirred magnetically for 15 min at room tempera-
ture. During this time 7 separated out as a red powder.
The solution was filtered out and the solid was washed
with CH2Cl2 and dried with Et2O. For the synthesis of
rhenium complexes 10–12, the reactions were carried
out in CH2Cl2–MeOH mixture (30 ml; 1:1 v/v). The sol-
vent was removed under reduced pressure and the
crude solid was recrystallized from MeOH–CH2Cl2
(1:2 v/v).
{[ReO(H2L2)4]Cl3} Æ 3 H2O (11). Yield 85%; Calc.
for C32H38N8Cl3O4ReS4: C, 37.6; H, 3.7; N, 10.9; S,
12.5; Found: C, 37.5; H, 3.65; N, 10.8; S, 12.6%. FTIR
(KBr, cmꢀ1): 3000–2500 m(N–H ꢁ ꢁ ꢁ Cl); 1452–1430 m(N–
C–N); 970 m(Re@O); 1H NMR (CD3OD, ppm): 3.3
(12H, s, CH3); 7.5–7.9 (12H, m, Ph).
{[ReO(H2L3)4]Cl3} Æ 3H2O (12). Yield 89%; Calc.
for C12H22N8Cl3O4ReS4: C, 18.85; H, 2.9; N, 14.7; S,
16.8; Found: C, 18.8; H, 2.85; N, 14.5; S, 16.9%. FTIR
(KBr, cmꢀ1):3000–2500 m(N–H ꢁ ꢁ ꢁ Cl); 1585–1480 m(N–
C–N); 980 m(Re@O); 1H NMR (CD3OD, ppm): 6.9–
7.4 (8H, m, Ph).
2.4. Synthesis of [ReOCl2(L5)(PPh3)] (13a, b)
Method B. To a solution of [AsPh4]{[TcOCl2(H2
L1)2(H2O)]Cl2} (60 mg; 0.062 mmol) in CH2Cl2–Me2CO
(1:1 v/v, 30 ml) solid ligand H2L1 (55.8 mg; 0.37 mmol)
was added. Within 15 min at room temperature the mix-
ture turned from yellow-green to red and a red precipi-
tate of 7 formed. It was collected by filtration, washed
with CH2Cl2 and dried with Et2O. Also in this case for
the synthesis of rhenium complexes the reactions were
carried out in CH2Cl2–MeOH (30 ml; 1:1 v/v).
To a solution of [ReOCl3(PPh3)2] (200 mg; 0.24 mmol)
in C6H6 (50 ml) kept under a nitrogen stream, solid HL5
(96.6 mg; 0.60 mmol) was added. The reaction mixture
was stirred and refluxed for 3 h and it was accomplished
by a color change from yellow-green to dark-green. The
solvent was removed under reduced pressure and the res-
idue rinsed several times with CH2Cl2 until an emerald
green powder was obtained. The crude solid was recrys-
tallized from CH2Cl2–MeOH (2:1 v/v, 10 ml) to give a
mixture of green microcrystals of 13a, b.
[ReOCl2(L5)(PPh3)] (13a, b). Yield 80%; Calc. for
C25H19NCl2O2PReS: C, 43.0; H, 2.7; N, 2.0; S, 4.6%;
Found: C, 42.8; H, 2.65; N, 1.95; S, 4.7%. FTIR (KBr,
cmꢀ1): 1484–1405 m(N–C–N); 1095 m(PPh3); 968, 942
(Re@O); 1H NMR (CD2Cl2, ppm): 6.9–8.2 (19H, m,
Ph); 31P NMR (CD2Cl2, ppm): ꢀ3.0 (s); ꢀ11.0 (s).
Method C. The [NH4][TcO4] salt (50mg; 0.27 mmol)
and solid H2L1 (2.2 mmol) were dissolved in acetone
(30 ml). To the colorless solution, some drops of a mix-
ture of HCl–acetone (1:1 v/v) were added under stirring
until it became yellow-orange. The resulting solution
was heated under reflux for 30 min. The solvent was re-
moved on a rotary evaporator and the red-orange com-
pound 7 was washed with CH2Cl2 and dried with Et2O.
{[TcO(H2L1)4]Cl3} Æ 3 H2O (7). Yield 88%; Calc.
for C28H30N8Cl3O4S4Tc: C, 38.4; H, 3.45; N, 12.8; S,
14.6; Found: C, 38.2; H, 3.4; N, 12.75; S, 14.5%. FTIR
(KBr, cmꢀ1): 3000–2500 m(N–H ꢁ ꢁ ꢁ Cl); 1513–1468 m(N–
5
2.5. Synthesis of [ReCl3(L )(PPh3)2] (14)
*
1
C–N); 974 m(Tc@O); H NMR (CD3OD, ppm): 7.2–7.4
[ReOCl3(PPh3)2] (200 mg; 0.24 mmol) was dissolved
in C6H6 (30 ml) and solid HL5 (90 mg; 0.60 mmol)
was added. The reaction mixture was stirred for 1 h in
air. During this time the yellow-green solution rapidly
changed to dark green and finally to dark red. The solu-
tion was evaporated under vacuum and the residue
rinsed several times with CH2Cl2–EtOH until a red pow-
der was obtained. The solid was washed repeatedly with
Me2CO until a lemon yellow powder was separated and
dried with Et2O. Recrystallization of the crude product
14 from CH2Cl2-1-butanol (1:1 v/v) gave suitable crys-
tals for X-ray diffraction analysis. Yield was determined
on starting compound.
(16H, m, Ph).
{[TcO(H2L2)4]Cl3} Æ 3H2O (8). Yield 84%; Calc.
for C32H38N8Cl3O4S4Tc: C, 41.2; H, 4.1; N, 12.0; S,
13.7; Found: C, 41.25; H, 4.05; N, 11.95; S, 13.6%.
FTIR (KBr, cmꢀ1): 3000–2500 m(N–H ꢁ ꢁ ꢁ Cl); 1615–
1380 m (N–C–N); 970 m(Tc@O); 1H NMR (CD3OD,
ppm): 2.6 (12H, s, CH3); 7.2–7.6 (12H, m, Ph).
{[TcO(H2L3)4]Cl3} Æ 3H2O (9). Yield 87%; Calc.
for C12H22N8Cl3O4S4Tc: C, 21.3; H, 3.3; N, 16.6; S,
18.95%; Found: C, 21.4; H, 3.25; N, 16.6; S, 18.9%.
FTIR (KBr, cmꢀ1): 3000–2500 m(N–H ꢁ ꢁ ꢁ Cl); 1585–
1476 m(N–C–N); 980 m(Tc@O); 1H NMR (CD3OD,
ppm): 7.1–7.3 (8H, m, Ph).
5
*
[ReCl3(L )(PPh3)2] (14). Yield 60%; Calc. for
C43H34NCl3OP2Re: C, 55.2; H, 3.65; N, 1.5; Found:
C, 55.3; H, 3.7; N, 1.5%. FTIR (KBr, cmꢀ1): 1582–
1405 m(N–C–N); 1095 m(PPh3); 1H NMR (CD2Cl2,
ppm): 8.9 (18H, m, PPh3); 10.2 (1H, t, J = 12.2, CH);
10.75 (1H, d, J = 12.2, CH); 11.1 (1H, d, J = 12.2,
CH); 11.8 (1H, t, J = 12.2, CH); 15.8 (12H, m, PPh3).
{[ReO(H2L1)4]Cl3} Æ 3H2O (10). Yield 80%; Calc.
for C28H30N8Cl3O4ReS4: C, 34.9; H, 3.1; N, 11.6; S,
13.3; Found: C, 34.8; H, 3.0; N, 11.5; S, 13.4%. FTIR
(KBr, cmꢀ1): 3000–2500 m(N–H ꢁ ꢁ ꢁ Cl); 1499–1420
m(N–C–N); 974 m(Re@O); 1H NMR (CD3OD, ppm):
7.3–7.8 (16H, m, Ph).

M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
367
2.6. Synthesis of O-ethyl S-hydrogen p-tolyl carbon-
othioimidate, HL6
included on calculated positions, riding on their carrier
atoms. The crystal of compound 1 includes a tetraph-
enylarsonium ion and a benzene molecule which are dis-
ordered around mirror planes. The crystal of compound
14 contains a disordered solvent molecule of MeOH, per
octahedral complex, which was refined over two inde-
pendent positions with occupancy 0.5, and a disordered
molecule of benzene.
A solution of 4-methyl-phenylisothiocianate (5 g; 33
mmol) in EtOH (95%) was refluxed under stirring for
one week. The HL6 ligand separated out as a white pow-
der. The solution was filtered out and the solid was dried
with n-hexane.
Yield 80%; Calc. for C10H13NOS: C, 61.5; H, 6.7; N,
7.2; S, 16.4; Found: C, 61.35; H, 6.6; N, 7.1; S, 16.55%.
FTIR (KBr, cmꢀ1): 1595 m(CN); 1H NMR (CDCl3,
ppm): 1.4 (3H, t, J = 6.9, CH3); 2.3 (3H, s, CH3) 4.6
(2H, q, J = 6.9, CH2); 7.2 (2H, d, J = 7.6, Ph); 7.3(2H,
d, J = 7.6, Ph); 8.6 (1H, s, SH).
All calculations were performed using SHELXL-97
[62] and PARST [63] implemented in WINGX [64] system
of programs. The crystal data and refinement parame-
ters are summarized in Table 1.
2.7. Synthesis of [ReOCl2(L6)(PPh3)] (15)
3. Results and discussion
3.1. Synthesis of O-ethyl S-hydrogen p-tolyl carbono-
thioimidate, HL6
Method A. A solution of [ReOCl3(PPh3)2] (200 mg;
0.24 mmol) and HL6 (93 mg; 0.48 mmol) was refluxed
for 3 h in 50 ml of C6H6. The solution turned from yel-
low-green to bright green. The reaction mixture was
concentrated under reduced pressure and the emerald
green residue of 15 was washed with C6H6 and dried
with Et2O.
Method B. To a solution of [ReOCl3(PPh3)2] (200 mg;
0.24 mmol) in C6H6 (50 ml), solid 4-methyl-phenyliso-
thiocianate (0.48 mmol) and EtOH (10 ml) were added.
The reaction mixture was heated under reflux and stir-
red for 3 h. During this time the yellow-green solution
changed to bright green. The solution was evaporated
under vacuum, the green microcrystals washed with
C6H6 and dried with Et2O. Recrystallization of the
product 15 from CH2Cl2-Me2CO (1:1 v/v) gave suitable
crystals for X-ray diffraction analysis. Yield was deter-
mined on starting materials.
[ReOCl2(L6)(PPh3)] (15). Yield 80%; Calc. for
C28H27NCl2O2PreS: C, 46.0; H, 3.7; N, 1.9; S, 4.3%;
Found: C, 45.8; H, 3.65; N, 1.85; S, 4.35%. FTIR
(KBr, cmꢀ1): 1514–1434 m(N–C–N); 1095 m(PPh3); 985
m(Re@O); 1H NMR (CD2Cl2, ppm): 1.4 (3H, t,
J = 6.9, CH3); 2.3 (3H, s, CH3); 4.6 (2H, q, J = 6.9,
CH2); 7.2 (2H, d, J = 7.6, Ph); 7.3 (2H, d, J = 7.6, Ph);
7.4–7.5 (9H, m, PPh3); 7.7–7.9 (6H, m, PPh3); 31P
NMR (CD2Cl2, ppm): ꢀ16.0 (s).
The ligand was synthesized by reaction of 4-methyl-
phenylisothiocianate in EtOH under reflux for one
week. It was characterized by elemental analysis and
FTIR and 1H NMR spectra. The ligand is stable in
the solid state for several months.
3.2. Synthesis and characterization of complexes
3.2.1. Oxotechnetium(V) and oxorhenium(V) complexes
[AsPh4]{[MOCl2(H2Ln)2(H2O)]Cl2} (n = 1–3) (M = Tc,
1–3; M = Re, 4–6)
The tetrachloro-oxometalate(V) anions [MOCl4]ꢀ
(M = Tc, Re) are good starting materials for the prepa-
ration of metal(V) complexes. They reacted rapidly and
under mild conditions with H2Ln ligands (n = 1–3) in a
1:2 molar ratio to form stable, light green complexes
[AsPh4]{[MOCl2(H2Ln)2(H2O)]Cl2}(M = Tc, 1–3; M =
Re, 4–6) Scheme 2. Appreciable differences in the reac-
tivity of the two oxometal precursors were not observed.
These oxo-metal(V) compounds were fully characterized
by elemental analysis, NMR and FTIR spectroscopy
which are in agreement with the proposed formulations.
They are air stable in both the solid state and solution.
1
The H NMR spectra recorded in (CD3)2CO at room
temperature present, for the protons of tetraphenylarso-
nium cation and for those of ligands, patterns consistent
with oxo-metal(V) diamagnetic species (details are re-
ported in Section 2). The presence of the M@O fragment
is confirmed by a strong adsorption band in IR spectra
at ca. 1000 cmꢀ1, although it may be superimposed with
that of [AsPh4] moiety. This value is at high side of the
range 900–1000 cmꢀ1 usually observed for oxo-group in
square-pyramidal complexes with ligands which possess
r- and p-donating properties [65–69]. In our previous
study concerning the Tc@Ooxo distances in complexes
2.8. Crystal structure determinations
The crystal data for the three compounds 1, 14 and 15
were collected at room temperature using a Nonius
Kappa CCD diffractometer with graphite-monochro-
mated Mo Ka radiation. The data sets were integrated
with the Denzo-SMN package [59] and corrected for
Lorentz, polarization and absorption effects (SORTAV)
[60]. The structures were solved by direct methods
(SIR97) [61] and refined using full-matrix least-squares
with all non-hydrogen atoms anisotropic and hydrogens
containing
the
Ooxo@Tc–Otrans
fragment,
we

368
M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
Table 1
Crystal data
Compound
Formula
1
14
15
(C14H14Cl2N4O2S2Tc)+ Æ
C43H34Cl3NOP2Re Æ
CH3OH Æ C6H6
1045.35
orthorhombic
P212121
15.0478(1)
17.3614(2)
18.2735(2)
90
C28H27Cl2N2OPReS
(C24H20As)+ Æ 2Clꢀ Æ C6H6
Molecular weight
System
Space group
1035.64
orthorhombic
Cmc21
13.1769(2)
28.4984(4)
13.8973(2)
90
729.64
triclinic
ꢀ
P1
˚
a (A)
10.0298(2)
11.4029(3)
13.0002(4)
77.757(1)
79.684(1)
86.521(1)
1429.12(6)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
90
90
3
˚
U (A )
5218.7(1)
4
1.318
4473.97(8)
4
1.454
Z
Dcalc (g cmꢀ3
)
1.696
45.93
l (cmꢀ1
min–hmax (ꢁ)
Unique reflections
)
12.26
28.19
h
4.2–28.0
6226
0.044
2.9–28.0
11486
0.051
3.2–28.0
6610
0.062
Rint
Observed reflections [I > 2r(I)]
R (observed reflections)
wR (all reflections)
S
5715
10224
0.0407
5768
0.0438
0.0543
0.1547
1.09
0.1230
1.20
0.1115
1.04
ꢀ3
˚
Dqmax; Dqmin (e A
)
0.76; ꢀ0.59
0.92; ꢀ1.14
1.88; ꢀ0.93
demonstrated that when the trans ligand is alcoholate
ROꢀ anion, a very strong Lewis base, the Tc@Ooxo dis-
tance is long and the Tc–Otrans distance is very short
[70]. Coordination of a weaker donor in trans to
Tc@Ooxo causes a decreasing of the Tc@Ooxo distance
which assumes a triple bond character. The short bond
(H2O)]Cl2}, where a water molecule is in trans position
to the M@O group. These observations suggest that
the ligand coordinates to the metal through the neutral
sulfur atom and behaves as a monodentate donor
according to the presence of m(N–H ꢁ ꢁ ꢁ Cl) bands in
IR spectra. In the case of [AsPh4]{[TcOCl2(H2L1)2(-
H2O)]Cl2} (1), suitable crystals for X-ray diffraction
study were grown from methanol–acetone mixture. As
distance is reflected in a high value of the m(Tc@Ooxo
)
stretching. On the basis of analytical data together with
spectroscopic measurements, we may consider these spe-
cies as octahedral complexes [AsPh4]{[MOCl2(H2Ln)2
˚
expected, the Tc@O distance is very short (1.639 A)
˚
and the Tc–OH2 distance is relatively long (1.321 A).
+1
HN
O
H2L1-3 1:2
S
Cl
NH
M= Tc; H2L1, 1; H2L2, 2; H2L3, 3
M= Re; H2L1, 4; H2L2, 5; H2L3, 6
M
Me2CO, ∆
HN
Cl
S
OH2
NH
-1
O
M
H2L1-3 exc.
Cl
Cl
Cl
Cl
CH2Cl2-Me2CO, r.t.
NH
+3
M= Tc, Re
HN
O
M
S
S
H2L1-3 exc.
CH2Cl2, r.t.
NH
NH
H2L1 exc.; HCl
HN
-
3Cl-
[MO ]
4
Me2CO, ∆
S
HN
S
M= Tc
HN
NH
M= Tc; H2L1, 7; H2L2, 8; H2L3, 9
M= Re; H2L1, 10; H2L2, 11; H2L3, 12
Scheme 2.

M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
369
Table 2
Selected bond distances and angles (A and degree) and hydrogen bond
parameters for compound 1
A selected list of bond distances and angles is given in
Table 2 and ORTEP drawing is shown in Figs. 1(a)
and (b).
˚
Tc1–Cl1
Tc1–Cl2
Tc1–S1
Tc1–O1
Tc1–O2
S1–C1
2.355(2)
2.367(2)
2.381(1)
1.635(5)
2.323(4)
1.729(4)
C1–N1
C1–N2
N1–C2
N2–C7
C2–C7
1.328(6)
1.337(6)
1.391(6)
1.385(6)
1.381(7)
3.2.2. Oxotechnetium(V) and oxorhenium(V) complexes
{[MO(H2Ln)4]Cl3} Æ 3H2O (n = 1–3) (M = Tc, 7–9;
M = Re, 10–12)
The formation of red complexes {[TcO(H2Ln)4]-
Cl3} Æ 3H2O 7–9 from [AsPh4][TcOCl4] and an excess
of ligand H2L1–3 occurs quickly, in high yield and at
room temperature. The corresponding oxo-rhenium
analogs 10–12 required the presence of methanol in
the reaction mixture. The complexes 7–9 and 10–12
could also be obtained from reaction of 1–6 with an ex-
cess of the appropriate ligand. It was observed that the
formation of the corresponding rhenium compounds oc-
curred only if assisted by alcohol. Moreover, in order to
evaluate the possibility to form oxo-technetium com-
pounds starting from pertechnetate ion, a reaction in
acetone with HCl as reducing agent was performed with
H2L1 (Scheme 2). The red product was identified by a
comparison of analytical and spectroscopic data with
those of 7. In similar reaction conditions, no product
was recovered starting from perrhenate anion, because
Cl1–Tc1–Cl2
Cl1–Tc1–S1
Cl1–Tc1–O1
Cl1–Tc1–O2
Cl2–Tc1–S1
Cl2–Tc1–O1
Cl2–Tc1–O2
S1–Tc1–S10
162.33(6)
93.39(3)
98.6(2)
S1–Tc1–O1
S1–Tc1–O2
O1–Tc1–O2
Tc1–S1–C1
N1–C1–N2
C1–N1–C2
C1–N2–C7
99.60(3)
80.40(3)
180
81.4(1)
106.5(1)
108.7(4)
109.3(4)
109.1(4)
83.67(3)
99.1(2)
80.9(1)
158.43(4)
Hydrogen bonds
D–H
O2–H
Dꢁ ꢁ ꢁA
Hꢁ ꢁ ꢁA
Hꢁ ꢁ ꢁCl3
2.49
D–Hꢁ ꢁ ꢁA
O2–Hꢁ ꢁ ꢁCl3
157
O2ꢁ ꢁ ꢁCl3
0.82
N2–H
3.258(3)
N2ꢁ ꢁ ꢁCl3
Hꢁ ꢁ ꢁCl3
2.21
N2–Hꢁ ꢁ ꢁCl3
169
0.86
N1–H
3.059(4)
N1ꢁ ꢁ ꢁCl3 (1/2 ꢀ x,
1/2 ꢀ y,1/2 + z)
3.087(4)
Hꢁ ꢁ ꢁCl3
N1–Hꢁ ꢁ ꢁCl3
0.86
2.27
157
Fig. 1. (a) An ORTEP view of complex 1 showing thermal ellipsoids at 30% probability. (b) Hydrogen bond network in crystal of compound 1.

370
M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
rhenium is more difficult to reduce than is its technetium
analog. A complete reaction pathway is reported in
Scheme 2.
described, studies with heterocyclic thiols are rare
[73,74]. Moreover, mononuclear and dinuclear
oxorhenium(V) complexes such as [ReOLCl3(OH2)],
[ReOL2Cl(OH2)3]Cl3, [ReOLCl(OH2)3]Cl2, [Re2O3L2-
Cl4] Æ 2H2O and [Re2O2L3Cl6] Æ 2H2O obtained from
the reaction of 1H-benzoimidazole-2-thiol (H2L1) with
H2[ReOCl5] were reported by Mashaly [75,76]. These
compounds were characterized on the basis of molar
conductivity, IR and electronic spectroscopies and mag-
netic measurements.
All of these new oxo-complexes are stable in the solid
state but they slowly decompose in solution. Repeated
attempts to obtain crystals suitable for X-ray analysis al-
ways failed. Elemental analyses (see Section 2) are in
good agreement with the proposed formulations. In
the IR spectra, all of the oxo-M(V) complexes exhibit
an absorption typical of the [M@O] multiple bond at
ca. 970–980 cmꢀ1. These M@O stretching values are
comparable with those observed for other square
pyramidal oxo-species of technetium and rhenium [65–
3.2.3. Reactivity of [ReOCl3(PPh3)2]. Synthesis and
characterization of [ReOCl2(L5)(PPh3)] (13a, b)
Since our aim was to study the reactivity of the lig-
ands mentioned above towards oxo-rhenium precursors,
we performed some experiments with [ReOCl3(PPh3)2].
Reactions carried out with H2L1–3 ligands did not lead
to products which could be characterized because a
decomposition process occurred. In the presence of an
excess of triphenylphosphine, the oxo-precursor reacted
to give diamagnetic, violet compounds which were iden-
tified as trigonal bipyramidal Re(III) complexes
{[Re(PPh3)Cl(H2 L1–3)3]Cl3}ꢀ. When the same reactions
were carried out with HL4,5 under a nitrogen atmos-
1
69]. The H NMR spectra in CD3OD of complexes 7-
12 are comparable and present a pattern characteristic
of diamagnetic species in solution. In fact, they display
multiplets of the aromatic protons of the ligands at d
7.0–7.8. An additional resonance at d 2.6 and at d 3.3
in the spectrum of 8 and 11, respectively, is attributed
to methyl protons of H2L2. Finally, NMR spectra reveal
the absence of aromatic protons of the [AsPh4]+ group.
Although X-ray structure could not be determined, we
can hypothesize from the experimental data that these
compounds possess a ‘‘umbrella-shaped’’ square pyram-
idal geometry in which four neutral monodentate lig-
ands are on the basal plane and the oxo-oxygen atom
at the apical position. Oxo-technetium(V) and rhe-
nium(V) complexes with monothiolate ligands such as
[MO(ArS)4]ꢀ have been reported [71,72]. In all these
complexes, ligands are coordinated in monoanionic
manner through the sulfur atom. Although technetium
and rhenium complexes with aromatic thiols have been
phere,
paramagnetic
chelate
complexes
[Re-
III(PPh3)2Cl2(L4,5)] were formed (Scheme 3). These
complexes were obtained from the Re(III) precursor
[ReCl3(PPh3)2(NCMe)] and have been previously re-
ported [52]. Treating [ReOCl3(PPh3)2] with an excess
of HL5 in refluxing benzene and under a nitrogen
stream, a green oxo-derivative [ReOCl2(L5)(PPh3)] 13
was obtained. It is air stable in both solution and solid
1-3
H L
2
O
4, 5
1-3
Ph P
3
Cl
HL , PPh , N
2
H L , PPh
2
2
2
Re
Cl
PPh
3
Cl
5
C H , ∆, 3h
HL , N
6
6
2
4, 5
5
1-3
-
Re(PPh ) Cl (L
)
3 2
2
ReOCl (L )(PPh )
{[Re(PPh )Cl(H L ) ]Cl }
2
3
3
2
3
3
13a, 13b
+
14
5
HL , air
PPh
3
4, 5
1-3
Cl
Cl
NCCH
3
HL
,
N
H L
2
2
Re
Cl
PPh
3
Scheme 3.

M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
371
state. In this complex, the ligand classically acts as a
monoanionic bidentate chelate NSꢀ replacing a Clꢀ an-
ion and a PPh3 group. The proposed formulation is in
accord with elemental analysis and spectroscopic meas-
urements. The infrared spectrum showed two medium
absorption bands at 968 and 942 cmꢀ1 attributed to
m(Re@O) stretching vibration. These values are in the
usual range observed in six coordinate oxo-Re(V) com-
plexes but they are indicative of the presence of two spe-
cies 13a, 13b in which a different heteroatom is in trans
position to Re@O multiple bond. The 1H and 31P NMR
spectra were consistent with diamagnetic monosubsti-
tuted compounds. Proton NMR spectrum showed
multiplets of aromatic protons of PPh3 and ligand at d
8.2–6.9. Moreover, 31P NMR spectrum displayed two
singlets at d ꢀ3.0 and ꢀ11.0 for the coordinate PPh3
moiety (arbitrarily: 13a major, 13b minor; molar ratio,
based on 31P NMR integration, ca. 3:2). Formation of
13a and 13b was monitored by 31P NMR spectroscopy.
At first, there was a singlet of coordinated PPh3 of [Re-
OCl3(PPh3)2] at d ꢀ18.6. After 15 min, this signal de-
creased and three singlets at d ꢀ4.8 (uncoordinated
PPh3), d ꢀ3.0 and d ꢀ11.0 (13a and 13b) began to ap-
pear. Finally, the signal of the oxo-precursor completely
disappeared. Furthermore, in order to verify the pres-
ence of two different complexes, we collected 31P
NMR spectrum over a range of temperatures from 25
to 55 ꢁC, but the two signals remained unchanged. From
these observations, it is reasonable to assume as the
most likely structures for 13 that are reported below:
All attempts to obtain only one of the two complexes
or alternatively to separate them have been useless.
Alternatively and following a similar procedure, com-
plexes 13a, 13b could be also obtained in good yields
from [ReCl3(PPh3)2(NCMe)] when the reaction was con-
ducted in air. Moreover, the formation of a new yellow
product 14 in very low amount (ca. 10%) was observed.
Afterwards, this complex was synthesized and fully
characterized (see below). Finally, we were unable to
isolate and characterize analogous complexes with
HL4 ligand. All these reactions are depicted in Scheme 3.
5
*
3.2.4. Synthesis and characterization of [ReCl3(L )-
(PPh3)2] (14) and [ReOCl2(L6)(PPh3)] (15)
In order to provide a more convenient route to obtain
this new yellow product 14, some reactions were per-
formed with HL5. When a slight excess of ligand reacted
with [ReOCl3(PPh3)2] in refluxing benzene solution and
in air, only the yellow complex could be recovered in
good yield (Scheme 4).
Surprisingly, elemental analysis indicated the absence
of sulfur in the complex and in IR spectrum the typical
absorption band of Re@O multiple bond was absent.
Furthermore, proton MNR spectrum displayed a char-
acteristic pattern of a paramagnetic compound. In fact,
it exhibited two sets of aromatic signals arising from the
six phenyl groups of PPh3 at d 15.8 and 8.9 and a further
set of two doublets and two triplets at d 11.8 (t), 11.1 (d),
10.75 (d) and 10.2 (t) of the aromatic protons of ligand.
All of these resonances were unequivocally attributed on
1
the basis of 2D H COSY experiment (Fig. 2).
O
O
On the basis of analytical data together with spectro-
scopic measurements, we hypothesized this compound
as a neutral octahedral complex containing two PPh3
Ph3P
Cl
S
N
Ph3P
Cl
Cl
S
Re
Re
N
O
5
5
*
moieties and a fragment derived from HL , (HL ), as
a result of a desulfurization process and the central me-
tal ion in a different oxidation state. In any case, we were
unable to give an appropriate formulation. Fortunately,
crystals grew from dichloromethane and 1-butanol and
Cl
O
13a
13b
PPh3
5
Cl
Cl
Cl
HL , air
N
Re
14
C H ,∆, 1h
6
6
O
PPh3
O
O
6
Cl
S
Cl
Ph3P
PPh3
Cl
HL , air
OEt
Re
15
Re
C H , ∆, 3h
6
6
Ph3P
N
Cl
Cl
Me
4-MeC H N=C=S, EtOH
6
4
C H , ∆, 3h
6
6
Scheme 4.

372
M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
Fig. 2. Section of 1H COSY spectrum of 14 (CD2Cl2).
the solid-state structure could be determined by X-ray
diffraction methods (Fig. 3). This analysis confirmed
the identity of 14 as a Re(IV)-carbene complex
oxidation states is rare and is reported by Hahn [79].
In these reactions, 2-(trimethylsiloxy)phenyl isocyanide
ligand underwent a nucleophilic attack and a dicarbene
5
*
[ReCl3(L )(PPh3)2].
complex
[ReOCl3(NH–C–O)2]
(NH–C–O = 1,2-
To our knowledge, formation of carbene complexes
by a desulfurization process induced by an oxo-complex
of rhenium is not documented, although oxo-rhenium
complexes have been studied as catalysts in desulfuriza-
tion of thiiranes and in oxidation of thiols [77,78]. For-
mation of carbene complexes of rhenium in high
dihydrobenzoxazol-2-ylidene) was identified and struc-
turally characterized. It is worthy to note that with
HL4, formation of organometallic species was never ob-
served. In the reaction reported here, a redox process
took place; probably, the oxidation of S2ꢀ is accom-
plished by reduction of rhenium from +5 to +4 oxida-
tion state. Ligand HL6 was synthesized in order to
hypothesize a plausible mechanism of this process. It
contains the same heteroatoms of HL5 but in a linear
structure. The reaction between ligand and oxo-Re(V)
precursor was carried out in the same reaction condi-
tions for the synthesis of 14. To our disappointment, a
green chelate NSꢀ oxo-complex [ReOCl2(L6)(PPh3)]
(15) was recovered. It is interesting to note that 15 could
be formed from the reaction between [ReOCl3(PPh3)2]
and 4-methyl-phenylisothiocianate in the presence of
EtOH. Probably, ligand is formed in situ, thus the syn-
thesis of ligand is not required (Scheme 4).
Complex 15 was characterized by elemental analysis,
and IR and NMR spectroscopy which were in good
agreement with the proposed formulation. The complex
exhibits the distinctive Re@O stretching vibration at 985
cmꢀ1 and 31P NMR spectrum showed a singlet at d
ꢀ16.0. Details are reported in Section 2. These results
are in agreement with an octahedral, diamagnetic com-
pound as confirmed by X-ray crystallographic analysis
(Fig. 4).
Fig. 3. An ORTEP view of complex 14 showing thermal ellipsoids at
30% probability.

M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
373
Table 4
Selected bond distances and angles (A and degree) for compound 15
˚
Re1–Cl1
Re1–Cl2
Re1–S1
Re1–P1
Re1–O1
2.439(2)
2.384(2)
2.406(2)
2.493(1)
1.676(4)
Re1–N1
C1–S1
2.079(5)
1.743(6)
1.299(8)
1.318(9)
1.430(7)
C1–O2
C1–N1
N1–C4
Cl1–Re1–Cl2
Cl1–Re1–S1
Cl1–Re1–P1
Cl1–Re1–O1
Cl1–Re1–N1
Cl2–Re1–S1
Cl2–Re1–P1
Cl2–Re1–O1
Cl2–Re1–N1
85.17(6)
84.38(6)
81.51(6)
169.1(2)
87.9(1)
S1–Re1–P1
S1–Re1–O1
S1–Re1–N1
P1–Re1–O1
P1–Re1–N1
O1–Re1–N1
Re1–S1–C1
Re1–N1–C1
102.49(5)
97.3(2)
68.3(1)
87.6(2)
166.8(1)
102.7(2)
78.8(2)
159.25(6)
93.62(5)
96.3(2)
101.9(4)
93.4(1)
Fig. 4. An ORTEP view of complex 15 showing thermal ellipsoids at
30% probability.
gen atoms, from the mean plane passing through the
Cl1, Cl2 and S1 atoms. The multiple Tc1@O1 bond
length of 1.635(5) A is slightly shorter than Re@O mul-
tiple bond in 15 (see below) and is in accordance with
many other structural determinations. The Tc–
˚
In conclusion, we are unable to give an explanation
of this desulfurization process, but it only occurs when
the reaction between the oxo-Re(V) precursor and
HL5 is carried out in air.
˚
O2(water) lengthening of 2.323(4) A can be ascribed to
the strong trans influence exerted by the oxo group
[70]. The neutral 1H-benzoimidazole-2-thiol ligands, in
mutual trans position, are in cisoid orientation and are
linked to the Tc(V) atom in a tautomeric zwitterionic
form with the negative charge on the sulfur atom and
the positive charge delocalized on the H–N1–C1–N2–
H moiety. The cationic complexes and Cl3 anions form
a network of hydrogen bonds (Fig. 1(b)), where each
chloride anion accepts three hydrogen bonds donated
by both N–H groups of imidazole ring and by water
molecule.
In compound 14, the overall geometry about the Re
atom of the Re(IV) complex is approximately octahe-
dral with the equatorial plane comprising three Cl atoms
and the carbon atom of the benzoxazole ligand anion
and the apical positions occupied by two triphenylphos-
phines. The organic ligand is planar and is situated on
3.3. Crystal structures
ORTEP [80] views of complexes 1, 14 and 15 are
shown in Figs. 1, 3 and 4. Selected interatomic distances
and angles are given in Tables 2–4.
Compound 1 is a Tc(V)-oxo cationic complex where
the coordination environment around Tc can be de-
scribed as a distorted octahedron. The Tc1, O1, O2,
Cl1 and Cl2 atoms are situated on a mirror m crystallo-
graphic plane. If the axial positions are defined to be
those of the Tc-oxo and the trans water molecule, the
equatorial positions are occupied by two Cl atoms and
two sulfur atoms belonging to two 1H-benzoimidaz-
ole-2-thiol ligands. As observed in all Tc(V)-oxo com-
plexes, the oxo group induces an octahedral distortion
˚
where Tc1 is displayed by 0.3626(4) A, toward the oxy-
˚
the equatorial plane forming an angle of only 0.6(1) A
with the mean plane passing through Cl1, Cl2, Cl3
and C1 atoms. The Re–Cl2 bond distance of 2.469(2)
˚
A is much longer than those of Re–Cl1 and Re–Cl3 of
˚
2.328(2) and 2.364(2) A, which are typical for Re–Cl
bonds in trans position to each other [81], because of
strong trans effect exerted by Re1–C1 bond which dis-
˚
plays the distance of 2.080(6) A in accordance with
Re–C simple bond distance [82].
Table 3
Selected bond distances and angles (A and degree) for compound 14
˚
Re1–Cl1
Re1–Cl2
Re1–Cl3
Re1–P1
Re1–P2
Re1–C1
2.328(2)
2.469(2)
2.364(2)
2.484(2)
2.484(2)
2.080(6)
C1–N1
C1–O1
N1–C3
C2–O1
C2–C3
1.344(8)
1.358(8)
1.381(8)
1.392(8)
1.372(9)
Cl1–Re1–Cl2
Cl1–Re1–Cl3
Cl1–Re1–P1
Cl1–Re1–P2
Cl1–Re1–C1
Cl2–Re1–Cl3
Cl2–Re1–P1
Cl2–Re1–P2
Cl2–Re1–C1
91.13(6)
173.24(6)
91.50(6)
91.83(6)
87.2(2)
Cl3–Re1–P1
Cl3–Re1–P2
Cl3–Re1–C1
P1–Re1–P2
P1–Re1–C1
P2–Re1–C1
Re1–C1–N1
Re1–C1–O1
N1–C1–O1
89.01(6)
87.79(6)
86.0(2)
Compound 15 is a Re(V)-oxo complex whose struc-
ture exhibits distorted geometry about the Re center.
The equatorial basal plane contains a Cl atom, a triphe-
nylphosphine molecule, and a S-thiolate and N-imido
atoms belonging to a bidentate imido thiocarbonate an-
176.54(5)
90.9(2)
90.2(2)
95.62(6)
89.15(6)
89.83(6)
178.4(2)
˚
123.4(5)
128.1(4)
108.5(5)
ion. The Re1@O1 multiple bond of 1.676(4) A is in
agreement with many other Re(V)-oxo complexes giving
rise to a distortion of the octahedral geometry produced

374
M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
[15] U. Abram, M. Braun, S. Abram, R. Kirmse, A. Voight, J. Chem.
Soc., Dalton Trans. (1998) 231.
by the steric requirements of the oxo-group shown by
˚
the displacement of 0.2339(2) A towards O1 of the
Re1 from the mean plane passing through N1, P1, Cl1
and Cl2. The lengthening of Re1–Cl1 bond of 2.438(2)
˚
A can be accounted in terms of trans influence exerted
by the oxo group. The Re-S(thiolate) distance of
[16] T.I.A. Gerber, J. Bruwer, G. Bandoli, J. Perils, J.G.H. du Preez,
J. Chem. Soc., Dalton Trans. (1995) 2189.
[17] S. Liu, S. Edwards, A.R. Harris, S.J. Hemingway, J.A. Barret,
Inorg. Chem. 38 (1999) 1326.
[18] D.J. Rose, K.P. Maresca, T. Nicholson, A. Davison, A.G. Jones,
J. Babich, A. Fischman, W. Graham, J.R.D. DeBord, J. Zubieta,
Inorg. Chem. 37 (1998) 2701.
˚
˚
2.406(2) A is in agreement with that of 2.389(4) A ob-
served in a Re-oxo octahedral complex, where the sulfur
is in trans position to a Cl atom [83].
[19] X. Chen, F.J. Femia, J.W. Babich, J. Zubieta, Inorg. Chem. 40
(2001) 2769.
[20] R. Waibel, R. Alberto, J. Willude, R. Finnern, R. Schibli, A.
Stichelberger, A. Egli, U. Abram, J.-P. Mack, A. Pluchthun, P.A.
Schubiger, Nat. Biotechnol. 17 (1999) 897.
4. Supplementary material
[21] R. Alberto, R. Schibli, P.A. Schubiger, J. Am. Chem. Soc. 121
(1999) 6076.
[22] R. Alberto, R. Schibli, A. Egli, P.A. Schubiger, J. Am. Chem.
Soc. 120 (1998) 7987.
Crystallographic data (excluding structure factors)
have been deposited with the Cambridge Crystallo-
graphic Data Centre and allocated the deposition num-
bers CCDC 245657–245659. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/re-
trieving.html or on application to CCDC, Union Road,
Cambridge CB2 1EZ, UK [fax: (+44)1223 336033, mail-
to:e-mail: deposit@ccdc.cam.ac.uk].
[23] R. Alberto, R. Schibli, D. Angst, P.A. Schubiger, U. Abram, S.
Abram, T.A. Kaden, Transition Met. Chem. 22 (1997) 597.
[24] S.Z. Lever, K.E. Baidoo, A. Mahmood, Inorg. Chim. Acta 176
(1990) 184.
[25] H.G. Kung, Y.Z. Guo, C.C. Yu, J. Billings, V. Subramanyam, J.
Calabrese, J. Med. Chem. 32 (1988) 433.
[26] S.M.N. Efange, H.F. Kung, J.J. Billings, M. Blau, J. Med. Chem.
31 (1988) 1043.
[27] L. Epps, H.D. Burns, S.Z. Lever, H.W. Goldfarb, H.N. Wagner,
Appl. Radiat. Isot. 38 (1987) 661.
[28] S.Z. Lever, H.D. Burns, T.M. Kervitsky, H.W. Goldfarb, D.V.
Woo, D.F. Wong, L.A. Epps, A.V. Kramer, H.N. Wagner, J.
Nucl. Med. 28 (1985) 1287.
Acknowledgments
[29] A. Davison, A. Jones, C. Orving, M. Sohn, Inorg. Chem. 20
(1981) 1629.
This work was supported by Italian MURST in the
frame of the project ‘‘Pharmacological and Diagnostic
Properties of Metal Complexes’’ (coordinator Prof. G.
Natile). We are grateful to Dr. P. Bergamini for record-
ing NMR spectra. We thank Mr. M. Fratta for technical
assistance and elemental analyses.
[30] C. Costello, J. Brodack, A. Davison, D.L. Johnson, S. Kasina,
A.R. Fritzberg, J. Nucl. Med. 24 (1983) 353.
[31] A.R. Fritzberg, W.C. Klingensmith, W.P. Whitney, C.C. Kuni, J.
Nucl. Med. 22 (1981) 258.
[32] A.R. Fritzberg, S. Kasina, D. Eshima, D.L. Johnson, J. Nucl.
Med. 27 (1986) 111.
[33] G. Grummon, R. Rajagopalan, G.J. Palenik, A.F. Kosiol, D.L.
Nosco, Inorg. Chem. 34 (1995) 1764.
[34] A. Marchi, R. Rossi, L. Magon, A. Duatti, R. Pasqualini, V.
Ferretti, V. Bertolasi, J. Chem. Soc., Dalton Trans. (1988)
1411.
References
[1] S. Jurisson, J.D. Lydon, Chem. Rev. 99 (1999) 2205.
[2] S. Liu, D.S. Edwards, Chem. Rev. 99 (1999) 2235.
[3] J. Steigman, W.C. Eckelman, The Chemistry of Technetium in
Medicine, Nuclear Science Publications NAS-NS-3204, National
Academy Press, Washington, DC, 1992.
[35] J.G.H. DuPreez, T.I.A. Gerber, O. Knoesen, Inorg. Chim. Acta
130 (1987) 9.
[36] G. Bandoli, U. Mazzi, B.E. Wilcox, S. Jurisson, E. Deutsch,
Inorg. Chim. Acta 95 (1984) 217.
[37] F.J. Femia, X. Chen, K.P. Maresca, T.M. Shoup, J.W. Babich, J.
Zubieta, Inorg. Chim. Acta 306 (2000) 30.
[4] J.L. Vanderheyden, A.R. Fritzberg, T.N. Rao, S. Kasina, A.
Srinivasan, J.M. Reno, A.C. Morgan, J. Nucl. Med. 28 (1987)
656.
[38] X. Chen, F.J. Femia, J.W. Babich, J. Zubieta, Inorg. Chim. Acta
307 (2000) 154.
[5] P.A. Schubiger, R. Alberto, A. Smith, Bioconjug. Chem. 7 (1996)
165.
[39] X. Chen, F.J. Femia, J.W. Babich, J. Zubieta, Inorg. Chim. Acta
316 (2001) 33, references herein.
[6] E. Prats, F. Aisa, M.D. Abos, L. Villavieja, F. Garcia-Lopez,
M.J. Asenjo, P. Razola, J. Banzo, J. Nucl. Med. 40 (1999) 296.
[7] J.R. Dilworth, S.J. Parrot, Chem. Soc. Rev. 27 (1998) 43.
[8] R.K. Hom, J.A. Katzenllenbogen, Nucl. Med. Biol. 24 (1997) 485.
[9] S. Liu, D.S. Edwards, Bioconjug. Chem. 8 (1997) 621.
[10] K. Schwochan, Angew. Chem., Int. Ed. Engl. 33 (1994) 2258.
[11] S. Jurisson, D. Berning, W. Jia, D. Ma, Chem. Rev. 93 (1993)
1137.
[40] A. Gilman, J. Hardman, L. Limbird, in: A. Goodman, B.
Gilmans (Eds.), The Pharmacological Basis of Therapeutics,
10th ed., McGraw-Hill, New York, 2001.
[41] A.A. Johnson, A.S. Ray, J. Hanes, Z. Suo, J.M. Colacino, K.S.
Anderson, K.A. Johnson, J. Biol. Chem. 276 (2001) 40847.
´
[42] A. Romerosa, C. Lopez-Magan˜a, S. Man˜as, M. Saoud, A.E.
Goeta, Inorg. Chim. Acta 353 (2003) 145.
[43] R. Cini, M. Corsini, A. Cavaglioni, Inorg. Chem. 39 (2000) 5874.
[44] F.-C. Zhu, H.W. Schmalle, B. Fischer, E. Dubler, Inorg. Chem.
37 (1998) 1161.
[12] W. Volkert, E.A. Deutsch, Adv. Met. Med. 1 (1993) 115.
[13] A. Verbruggen, Eur. J. Nucl. Med. 17 (1990) 346.
[14] C. Bolzati, A. Boschi, L. Uccelli, E. Malago, G. Bandoli, F.
Tisato, F. Refosco, R. Pasqualini, A. Duatti, Inorg. Chem. (1999)
4479.
[45] A. Cavaglioni, R. Cini, J. Chem. Soc., Dalton Trans. (1997) 1149.
[46] R. Cini, R. Bozzi, A. Karaulov, M.B. Hursthouse, A.M. Calafat,
L.G. Marzilli, J. Chem. Soc., Chem. Commun. (1993) 899.

M. Brugnati et al. / Inorganica Chimica Acta 358 (2005) 363–375
375
´
[65] F. Mevellec, A. Roucoux, N. Noiret, H. Patin, J. Chem. Soc.,
Dalton Trans. (2001) 3603.
[47] L. Cavallo, R. Cini, J. Kobe, L.G. Marzilli, G. Natile, J. Chem.
Soc., Dalton Trans. (1991) 1867.
´
´
[48] E. Colacio, A. Romerosa, J. Ruiz, P. Roman, J.M. Gutierrez-
Zorilla, M. Martinez-Ripoll, J. Chem. Soc., Dalton Trans. (1989)
2323.
[66] A. Marchi, L. Marvelli, M. Cattabriga, R. Rossi, M. Neves, V.
Bertolasi, V. Ferretti, J. Chem. Soc., Dalton Trans. (1999) 1937.
[67] M. Cattabriga, A. Marchi, L. Marvelli, R. Rossi, G. Vertuani, R.
Pecoraro, A. Scatturin, V. Bertolasi, V. Ferretti, J. Chem. Soc.,
Dalton Trans. (1998) 1453.
[49] A. Romerosa, P. Bergamini, V. Bertolasi, A. Canella, M.
Cattabriga, R. Gavioli, S. Man˜as, N. Mantovani, L. Pellicani,
Inorg. Chem. 43 (2004) 905.
[68] F. Tisato, F. Refosco, A. Moresco, G. Bandoli, U. Mazzi, M.
Nicolini, J. Chem. Soc., Dalton Trans. (1990) 2225.
[69] N. Rao, D. Adhilkesavalu, A. Kamerman, A.R. Fritzberg, J. Am.
Chem. Soc. 112 (1990) 5798.
´
[50] A. Romerosa, C. Lopez-Magan˜a, A.E. Goeta, S. Man˜as, M.
Saoud, F.B. Benabdelouahab, F. El Guemmout, Inorg. Chim.
Acta 353 (2003) 99.
´
[51] A. Romerosa, C. Lopez-Magan˜a, M. Saoud, S. Man˜as, E.
[70] A. Duatti, A. Marchi, L. Magon, E. Deutsch, V. Bertolasi, G.
Gilli, Inorg. Chem. 26 (1987) 2182.
´
Colacio, J. Suarez-Varela, Inorg. Chim. Acta 353 (2003) 99.
[52] E. Marchesi, A. Marchi, L. Marvelli, M. Peruzzini, M. Brugnati,
V. Bertolasi, Inorg. Chim. Acta (in press).
[71] A. Davison, N. De Vries, J. Dewan, A. Jones, Inorg. Chim. Acta
120 (1986) L15.
[53] R.W. Thomas, M.J. Heeg, R.C. Helder, E. Deutsch, Inorg.
Chem. 24 (1985) 1472.
[72] J.R. Dilworth, B.D. Neaves, J.P. Hutchinson, J.A. Zubieta,
Inorg. Chim. Acta 65 (1982) L223.
[54] A. Davison, C. Orvig, H.S. Trop, M. Shon, B. DePamphilis,
A.G. Jones, Inorg. Chem. 19 (1980) 1988.
[73] U. Abram, J.R. Dilworth, Z. Anorg. Allg. Chem. 625 (1999)
609.
[55] F.A. Cotton, A. Davison, V.W. Day, L.D. Gage, H.S. Trop,
Inorg. Chem. 18 (1979) 3024.
[74] C.D. Bush, T.A. Harmor, W. Hussain, C.J. Jones, J.A. McClev-
erty, A.S. Rothin, Acta Crystallogr., Sect. C 43 (1987) 2088.
[75] M.M. Mashaly, M. El-Behairy, S.M.E. Khalil, J. Chim. Chem.
Soc. 46 (1999) 563.
[56] T. Lis, B. Jezowoska-Trzebiatowoska, Acta Crysallogr., Sect. B
33 (1977) 1248.
[57] N.P. Johnson, C.J.L. Lock, G. Wilkinson, Inorg. Synth. 9 (1967)
145.
[76] M.M. Mashaly, Synth. React. Inorg. Met. Org. Chem. 26 (2)
(1996) 211.
[58] J. Chatt, G.A. Rowe, J. Chem. Soc. (1962) 4019.
[59] Z. Otwinowski, W. Minor, in: C.W. Carter, R.M. Sweet (Eds.),
Methods in Enzymology, vol. 276, Academic Press, London,
1997, p. 307, Part A.
[77] J. Jacob, J.H. Espenson, Chem. Commun. (1999) 1003.
[78] J.B. Arterburn, M.C. Perry, S.L. Nelson, B.R. Dible, M.S.
Holguin, J. Am. Chem. Soc. 119 (1997) 9309.
[79] F.E. Ekkehardt, L. Imhof, Organometallics 16 (1997) 763.
[80] M.N. Burdett, C.K. Johnson, ORTEP III, Report ORNL-6895,
Oak Ridge National Laboratory, Oak Ridge, TN, 1996.
[81] A.G. Orpen, M.J. Quayle, J. Chem. Soc., Dalton Trans. (2001)
1601.
[60] R.H. Blessing, Acta Crystallogr., Sect A 51 (1995) 33.
[61] Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giac-
ovazzo, A. Guagliardi, A.G. Moliterni, G. Polidori, R. Spagna,
SIR97, J. Appl. Crystallogr. 32 (1999) 115.
[62] G.M. Sheldrick, SHELX-97, Program for Crystal Structure Refine-
ment, University of Gottingen, Germany, 1997.
[63] M. Nardelli, J. Appl. Crystallogr. 28 (1995) 659.
[64] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[82] A.G. Orpen, L. Brammer, F.H. Allen, O. Kennard, D.G. Watson,
R. Taylor, J. Chem. Soc., Dalton Trans. (1999) S1.
[83] G. Battistuzzi, M. Cannio, M. Saladini, R. Battistuzzi, Inorg.
Chim. Acta 320 (2001) 178.