Rhenium(III) and technetium(III) complexes with 2-mercapto-1,3-azole ligands and X-ray crystal structures

Article abstract of DOI:10.1016/j.ica.2004.09.010

Reactions of labile precursors [MCl₃(PPh₃) ₂(CH₃CN)] (M = Re, Tc) with imidazole-2-thiol ligands give new trigonal bipyramidal complexes, while with benzothiazole-2-thiol and benzoxazole-2-thiol octahedral chelate compounds are obtained. Crystal structures of these metal(III) complexes are also discussed. Reactions of labile [MCl₃(PPh₃)₂(NCMe)] (M = Tc, Re) precursors with 1H-benzoimidazole-2-thiol (H₂L¹), 5-methyl-1H-benzoimidazole-2-thiol (H₂L²) and 1H-imidazole-2-thiol (H₂L³), in the presence of PPh ₃ and [AsPh₄]Cl gave a new series of trigonal bipyramidal M(III) complexes [AsPh₄]{[M(PPh₃)Cl(H₂L ^1-3)₃]Cl₃} (M = Re, 1-3; M = Tc, 4-6). The molecular structures of 1 and 3 were determined by X-ray diffraction. When the reactions were carried out with benzothiazole-2-thiol (HL⁴) and benzoxazole-2-thiol (HL⁵), neutral paramagnetic monosubstituted M(III) complexes [M(PPh₃)₂Cl₂(L^4,5)] (M = Re, 8, 9; M = Tc, 10, 11) were obtained. In these compounds, the central metal ions adopt an octahedral coordination geometry as authenticated by single crystal X-ray diffraction analysis of 8 and 11. Rhenium and technetium complexes 1, 4 and rhenium chelate compounds 8, 9 have been also synthesized by reduction of [MO₄]^- with PPh₃ and HCl in the presence of the appropriate ligand. All the complexes were characterized by elemental analyses, FTIR and NMR spectroscopy.

Full text of DOI:10.1016/j.ica.2004.09.010

Inorganica Chimica Acta 358 (2005) 352–362
www.elsevier.com/locate/ica
Rhenium(III) and technetium(III) complexes with
2-mercapto-1,3-azole ligands and X-ray crystal structures
a
a,
a,
c
Elena Marchesi , Andrea Marchi *, Lorenza Marvelli *, Maurizio Peruzzini ,
a
Michele Brugnati , Valerio Bertolasi
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
c
Istituto di Chimica dei Composti OrganoMetallici, ICCOM CNR, Via Madonna del Piano snc, Area di Ricerca del CNR, 50019,
Sesto Fiorentino, Italy
Received 29 July 2004; accepted 6 September 2004
Available online 22 October 2004
Abstract
Reactions of labile [MCl3(PPh3)2(NCMe)] (M = Tc, Re) precursors with 1H-benzoimidazole-2-thiol (H2L1), 5-methyl-1H-benzo-
imidazole-2-thiol (H2L2) and 1H-imidazole-2-thiol (H2L3), in the presence of PPh3 and [AsPh4]Cl gave a new series of trigonal bipy-
ramidal M(III) complexes [AsPh4]{[M(PPh3)Cl(H2L1–3)3]Cl3} (M = Re, 1–3; M = Tc, 4–6). The molecular structures of 1 and 3 were
determined by X-ray diffraction. When the reactions were carried out with benzothiazole-2-thiol (HL4) and benzoxazole-2-thiol
(HL5), neutral paramagnetic monosubstituted M(III) complexes [M(PPh3)2Cl2(L4,5)] (M = Re, 8, 9; M = Tc, 10, 11) were obtained.
In these compounds, the central metal ions adopt an octahedral coordination geometry as authenticated by single crystal X-ray dif-
fraction analysis of 8 and 11. Rhenium and technetium complexes 1, 4 and rhenium chelate compounds 8, 9 have been also synthe-
sized by reduction of [MO4]À with PPh3 and HCl in the presence of the appropriate ligand. All the complexes were characterized by
elemental analyses, FTIR and NMR spectroscopy.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Rhenium; Technetium; Thiolate complexes; Structures
1. Introduction
99mTc- and 186/188Re-based agents produced in very
low concentrations at nanomolar scale. This may be
achieved through the comparison of their chemical
and physical properties with those of the corresponding
compounds prepared at macroscopic scale with the
long-lived isotope 99Tc and with cold rhenium. In addi-
tion, rhenium and technetium belong to the same group
of the periodic table and therefore they may show simi-
lar chemical properties and rhenium may be often used
as a non-radioactive alternative to technetium. Chelates
which contain nitrogen and sulfur donor atoms such as
pyridine-2-thiolate ligands show an interesting coordi-
nation versatility and may give an important contribu-
tion as models for the development of diagnostic
The coordination chemistry of rhenium and techne-
tium is currently attracting much attention due to the
radionuclide-based application in radiopharmaceuticals.
99mTc is the radionuclide of choice for use in diagnostic
imaging due to its ideal physical properties (t1/2 = 6.02 h,
c-energy = 140 keV). Recently, 186/188Re have been
introduced in nuclear medicine as suitable b-emitting
radionuclides for the therapy of malignant and degener-
ative diseases [1,2]. The ultimate goal of these investiga-
tions is to elucidate the molecular structures of
*
Corresponding authors. Tel.: +39 0532 291128; fax: +39 0532
(
99mTc) or therapeutic (186/188Re) radiopharmaceuticals
[3].
240709.
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.2004.09.010

E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
353
Mercapto-1,3-azole ligands have an important role in
2. Experimental
industry and medicine [4–8] and an attractive feature is
their acidity, which could influence their chemical prop-
erties towards transition metal ions determining the
structure of the final complexes. These small molecules
exist as two tautomeric conformations exhibiting
thiol–thione isomerism involving –NH–C@S and –
N@C–SH groups in a thione–thiol equilibrium.
2.1. Materials and instrumentation
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 start-
ing compounds [MCl3(PPh3)2(NCMe)] [9,10] (M = Re,
Tc) were prepared according to the literature proce-
dures. Ligands 1H-benzoimidazole-2-thiol (H2L1),
5-methyl-1H-benzoimidazole-2-thiol (H2L2), 1H-imi-
dazole-2-thiol (H2L3), benzothiazole-2-thiol (HL4) and
benzoxazole-2-thiol (HL5) were purchased from Ald-
rich. Elemental analyses were performed using a Carlo
Erba Instruments model EA 1110; FT-IR spectra were
recorded in a range 4000–200 cmÀ1 on a Nicolet 510 P
FT-IR instrument in KBr, using a Spectra-Tech collec-
tor diffuse reflectance accessory. Proton spectra of
CDCl3 solutions of the compounds 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. Conductiv-
ities were obtained at sample concentrations of ca.
1 · 10À4 M in CH2Cl2 solutions at room temperature
with an Amel Model 134 conductivity meter.
H
N
X
N
SH
S
X
X = NH, O, S
Probably, only two atoms could act as bonding sites,
the sulfur exocyclic atom and the cyclic nitrogen atom.
Since the lone pairs on the oxygen or sulfur atoms in
HL4,5 are involved in the resonating structures of the
molecules, we may expect that they should have no
coordinating abilities.
At this regard and as part of our activity on rhenium
and technetium chemistry, we decided to investigate the
chemical behavior of ambidentate ligands such as 1H-
benzoimidazole-2-thiol (H2L1), 5-methyl-1H-benzoimi-
dazole-2-thiol (H2L2), 1H-imidazole-2-thiol (H2L3),
benzothiazole-2-thiol (HL4) and benzoxazole-2-thiol
(HL5) (see Scheme 1) in order to compare their reactivity
as a function of the different heteroatom in the five-
membered ring.
2.2. Synthesis of complexes [AsPh4]{[M(PPh3)Cl
(H2Ln)3]Cl3} (n = 1 to 3), (M = Re, 1–3; M = Tc, 4–
6) and [Ph3PC(Me)2CH2COMe][ReCl5(PPh3)] (7)
Accordingly, we have been examining the substitu-
tion reactions of Re(III) and Tc(III) precursors
[MCl3(PPh3)2(NCMe)] as well as reduction reactions
of [MO4]À anions with this class of ligands. We re-
port here the results of these reactions together with
X-ray crystal structures of some representative
complexes.
The synthetic procedure for the preparation of com-
plexes 1–6 was very similar. Complexes were prepared
by a substitution route from [MCl3(PPh3)2(NCMe)]
(Method A) and as an example, 1 and 4 by reduction
reaction from [MO4]À (Method B). Here, we describe
the synthesis of 1 and 4 in detail.
X
N
N
SH
SH
N
H
N
H
1
H L = 1H-benzoimidazole-2-thiol, X=H
3
2
H L = 1H-imidazole-2-thiol
2
2
H L = 5-methyl-1H-benzoimidazole-2-thiol, X=Me
2
N
N
SH
O
SH
S
4
5
HL = benzothiazole-2-thiol
HL = benzoxazole-2-thiol
Scheme 1.

354
E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
Method A. A solution of H2L1 (0.42 mmol) in MeOH
NMR (CDCl3, ppm): 14.3 (6H, s, NH), 7.9–6.9 (51H,
m, Ph, C6H3), 2.2 (9H, s, CH3); 31P NMR (CDCl3,
ppm): À3.0 (s).
(2 ml), PPh3 (0.56 mmol) as a solid and [AsPh4]Cl (0.14
mmol) dissolved in 3 ml of MeOH were added to a stir-
red orange suspension of [MCl3(PPh3)2(NCMe)] (0.14
mmol) in C6H6 (30 ml) kept under a nitrogen stream.
Addition of triphenylphosphine as well as nitrogen
atmosphere is required in order to minimise decomposi-
tion or oxidation of the labile M(III) precursors. The
mixture was refluxed for 30 min. Within 20 min of re-
flux, the solution became transparent giving a violet col-
or. The solvent was removed on a rotary evaporator and
the residue treated with CH2Cl2 and C6H6 to separate 1
and 4 as dark violet solids. The crude solid was washed
with hot benzene, acetone and finally dried with Et2O.
Conductivity measurements at sample concentrations
of ca. 1 · 10À4 M in CH2Cl2 solutions gave values in
the range 99–105 S cm2 molÀ1. Yields were determined
on starting materials.
2.2.3. [AsPh4]{[Re(PPh3)Cl(H2L3)3]Cl3 Æ 2H2O} (3)
Yield 70%. Anal. Calc. for C51H55N6AsCl4O2PReS3:
C, 46.6; H, 4.2; N, 6.4; S, 7.3. Found: C, 46.55; H,
4.15; N, 6.5; S, 7.35%. FTIR (KBr, cmÀ1): 3000–2500
1
m(N–HÁ Á ÁCl); 1580–1435 m(N–C–N), 1092 m(PPh3); H
NMR (CDCl3, ppm): 13.9 (6H, s, NH), 7.9–6.9 (41H,
m, Ph, C2H2), 1.7 (4H, s, H2O); 31P NMR (CDCl3,
ppm): À1.2 (s).
2.2.4. [AsPh4]{[Tc(PPh3)Cl(H2L1)3]Cl3} (4)
Yield 73%. Anal. Calc. for C63H53N6AsCl4PS3Tc: C,
56.6; H, 4.0; N, 6.3; S, 7.2. Found: C, 56.8; H, 4.1; N,
6.25; S, 7.3%. FTIR (KBr, cmÀ1): 3000–2500 m(N–
HÁ Á ÁCl); 1500–1440 m(N–C–N), 1081 m(PPh3); 1H
NMR (CDCl3, ppm): 14.3 (6H, s, N–H), 8.0–7.1 (47H,
m, Ph, C6H4).
Recrystallization of 1 and 3 from CH2Cl2–C6H6 (2:1
v/v) gave good quality crystals suitable for X-ray
analysis.
Method B. 356.7 mg (1.36 mmol) of PPh3, 71.2 mg
(0.17 mmol) of [AsPh4]Cl and 77.6 mg (0.51 mmol) of
H2L1 were dissolved in 3 ml of acetone. This solution
was added to a solution of KReO4 (50 mg, 0.17 mmol)
and 0.35 ml of HCl (37%) in 50 ml of acetone. Upon
mixing the solutions, the color became bright green.
The reaction mixture was stirred and refluxed for 2 h.
Solvents were stripped in vacuo until a violet solid pre-
cipitated. The complex 1 was separated by filtration,
washed three times with acetone and dried with Et2O
(yield 40%). An identical procedure was employed for
the preparation of 4 (yield 35%). In a second experi-
ment, in order to improve the yield of 1, the reaction
mixture was refluxed for 10 h. During this time the color
changed from green to brown. The volume of the reac-
tion mixture was reduced in vacuo and after few minutes
complex 1 precipitated in very poor yield (10%). It was
separated by filtration. The mother solution was allowed
to stand overnight at room temperature affording yel-
low-green suitable crystals for diffraction studies of
[Ph3PC(Me)2CH2COMe][ReCl5(PPh3)] (7). Yield 30%.
2.2.5. [AsPh4]{[Tc(PPh3)Cl(H2L2)3]Cl3} (5)
Yield 68%. Anal. Calc. for C66H59N6AsCl4PS3Tc: C,
57.5; H, 4.3; N, 6.1; S, 7.0. Found: C, 57.3; H, 4.3; N,
6.15; S, 7.1%. FTIR (KBr, cmÀ1): 3000–2500 m(N–
HÁ Á ÁCl), 1520–1470 m(N–C–N), 1085 m(PPh3); 1H
NMR (CDCl3, ppm): 14.1 (6H, s, N–H), 8.2–7.3 (44H,
m, Ph, C6H3); 2.9 (9H, s, CH3).
2.2.6. [AsPh4]{[Tc(PPh3)Cl(H2L3)3]Cl3 Æ 2H2O} (6)
Yield 70%. Anal. Calc. for C51H55N6AsCl4O2PS3Tc:
C, 50.0; H, 4.5; N, 6.8; S, 7.8. Found: C, 49.8; H,
4.45; N, 6.8; S, 7.75%. FTIR (KBr, cmÀ1): 3000–2500
1
m(N–HÁ Á ÁCl), 1576–1472 m(N–C–N), 1087 m(PPh3); H
NMR (CDCl3, ppm): 13.9 (6H, s, N–H), 7.1–6.9 (45H,
m, Ph, C2H2), 1.8 (4H, br s, H2O).
2.2.7. [Ph3PC(Me)2CH2COMe][ReCl5(PPh3)] (7)
Yield 30%; Anal. Calc. for C42H41Cl5OP2Re: C, 51.0;
H, 4.2. Found: C, 50.95; H, 4.2%. FTIR (KBr, cmÀ1):
1
1720 m(C@O), 1096 m(PPh3); H NMR (CDCl3, ppm):
19.7 (2H, s, PPh3), 10.9 (1H, t, PPh3), 8.77 (2H, s,
PPh3), 8.18 (1H, s, PPh3+), 7.9 (2H, s, PPh3+), 7.4 (2H,
m, PPh3+), 3.15 (3H, s, CH3), 2.15 (3H, s, CH3), 2.0
(3H, s, CH3), 1.8 (2H, d, CH2); 31P NMR (CDCl3,
ppm): 59.0 (br, s).
2.2.1. [AsPh4]{[Re(PPh3)Cl(H2L1)3]Cl3} (1)
Yield: 80%. Anal. Calc. for C63H53N6AsCl4PReS3: C,
53.0; H, 3.7; N, 5.9; S, 6.7. Found: C, 52.9; H, 3.6; N,
5.85; S, 6.6%. FTIR (KBr, cmÀ1): 3000–2500 m(N–
HÁ Á ÁCl), 1505–1436 m(N–C–N), 1095 m(PPh3); 1H
NMR (CDCl3, ppm): 14.45 (6H, s, NH), 7.86–7.08
(47H, m, Ph, C6H4); 31P NMR (CDCl3, ppm): À0.72 (s).
2.3. Synthesis of [M(PPh3)2Cl2(L4,5)] (M = Re, 8, 9;
M = Tc, 10, 11)
All rhenium(III) and technetium(III) chelate com-
plexes 8–11 were prepared using a common procedure
and very similar to that reported for 1–6.
Method A. For the synthesis of these compounds, the
more convenient stoichiometric ratio was 1:2 and addi-
tion of [AsPh4]Cl salt was not required. Within 1 h of
2.2.2. [AsPh4]{[Re(PPh3)Cl(H2L2)3]Cl3} (2)
Yield 70%. Anal. Calc. for C66H59N6AsCl4PReS3: C,
53.9; H, 4.2; N 5.7; S, 6.5. Found: C, 53.8; H, 4.1; N,
5.65; S, 6.45%. FTIR (KBr, cmÀ1): 3000–2500 m(N–
HÁ Á ÁCl), 1481–1434 m(N–C–N), 1092 m(PPh3); 1H

E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
355
reflux the solution turned from yellow-orange to red for
8–10 and magenta for 11. The reaction mixture was con-
centrated in vacuo and the residue treated with CH2Cl2
and MeOH. Slow evaporation of solvent provided crys-
tals of desired products. They were washed with MeOH
and dried with Et2O. Recrystallization from CH2Cl2–
MeOH (2:3 v/v) of 8 and 11 gave suitable crystal for
X-ray diffraction analysis. Yields were determined on
starting compounds.
Method B. For the synthesis of 8 and 9 starting from
KReO4, the procedure described for 1 was employed.
After a few minutes of mixing the two solutions, the [Re-
OCl3(PPh3)2] complex precipitated. Benzene (50 ml) was
added to the mixture and the solution was stirred and
refluxed for 2 h. During the first hour the yellow-green
color of the solution turned to orange-red. Solvents were
removed and the residue was dissolved in 2 ml of dichlo-
romethane. Addition of 3 ml of ethanol led to the for-
mation of microcrystals of 8 in 70% yield and 9 (50%),
respectively. Similar reactions carried out with pertechn-
etate gave a dark green powder. Repeated elemental
analyses of these compounds gave unacceptable results.
8.1–7.8 (12H, m, Ph), 7.5 (1H, d), 6.8 (1H, d), À4.1
(1H, t).
2.4. Crystal structure determinations
The crystal data for the five compounds 1, 3, 7, 8
and 11 were collected at room temperature using a
Nonius Kappa CCD diffractometer with graphite
monochromated Mo Ka radiation. The data sets were
integrated with the DENZO-SMN package [11] and cor-
rected for Lorentz, polarization and absorption effects
(
SORTAV) [12]. The structures were solved by direct
methods (SIR97) [13] and refined using full-matrix
least-squares with all non-hydrogen atoms anisotropic
and hydrogens included on calculated positions, riding
on their carrier atoms. In compound 1, the tetraph-
enylarsonium ion is disordered around a threefold
axis and a phenyl group was refined with three inde-
pendent orientations. In compound 3, a molecule of
ethylic alcohol was found disordered an around a
twofold axis and their atoms were refined with the
occupancy of 0.5. In compound 11, the ligand 1,3-
benzoxazole-2-thiol and the Cl2 atom are disordered
around the Cl1–Tc1Á Á ÁC2 axis. Accordingly, S1, N1,
C1, C2, O1 and Cl2 atoms were refined with two ori-
entations with the occupancy of 0.5. Furthemore, the
2.3.1. [Re(PPh3)2Cl2(L4)] (8)
Yield 70%. Anal. Calc. for C43H34NCl2P2ReS2: C,
54.4; H, 3.6; N, 1.5; S, 6.75. Found: C, 54.3; H, 3.65;
N, 1.55; S, 6.7%. FTIR (KBr, cmÀ1): 1482–1370 m(C–
N–C), 1090 m(PPh3); 1H NMR (CDCl3, ppm): 13.9–
13.7 (12H, m, Ph), 8.7–8.3 (18H, m, Ph), 7.1 (1H, t,
J = 7.6), 5.2 (1H, d, J = 7.6), 3.8 (1H, d, J = 7.6), 2.4
(1H, t, J = 7.6).
asymmetric unit includes also
triphenylphosphine.
a
molecule of
All calculations were performed using SHELXL-97
[14] and PARST [15] implemented in WINGX [16] system
of programs. The crystal data and refinement parame-
ters are summarized in Table 1.
2.3.2. [Re(PPh3)2Cl2(L5)] (9)
Yield 70%. Anal. Calc. for C43H34NCl2OP2ReS: C,
55.4; H, 3.7; N, 1.5; S, 3.4. Found: C, 55.5; H, 3.75;
N, 1.6; S, 3.5%. FTIR (KBr, cmÀ1): 1481–1430 m(C–
N–C), 1091 m(PPh3); 1H NMR (CDCl3, ppm): 13.6–
13.3 (12H, m, Ph), 8.5–8.1 (18H, m, Ph), 6.8 (1H, t,
J = 7.8), 3.45 (1H, d, J = 7.8), 1.3 (1H, d, J = 7.8), 0.2
(1H, t, J = 7.8).
3. Results and discussion
3.1. Synthesis and characterization of [AsPh4]{[M
(PPh3)Cl(H2L1–3)3]Cl3} (M = Re, 1–3; M = Tc, 4–6)
and [Ph3PC(Me)2CH2COMe][ReCl5(PPh3)] (7)
Reactions
of
the
labile
precursors
2.3.3. [Tc(PPh3)2Cl2(L4)] (10)
[MCl3(PPh3)2(NCMe)] (M = Re, Tc) with three equiva-
lents of H2L1–3 in refluxing C6H6–MeOH mixture in
the presence of an excess of PPh3 and [AsPh4]Cl salt un-
der a nitrogen atmosphere yielded violet products
[AsPh4]{[M(PPh3)Cl(H2L1–3)3]Cl3}
M = Tc, 4–6) in high yields and with a reaction time
of 30 min (Scheme 2a).
The violet rhenium and technetium complexes 1 and
4 could be synthesized from [MO4]À anions (M = Re,
Tc) in acetone, in the presence of triphenylphosphine
as reducing agent, in an acidified solution with a reac-
tion time of 2 h according to Scheme 2b. Yields (ca.
40%) were slightly lower than in the synthesis of 1 and
4 from the corresponding M(III) precursors. If the reac-
tion with KReO4 and H2L1 was refluxed for 10 h, yield
Yield 70%. Anal. Calc. for C43H34NCl2P2S2Tc: C,
59.8; H, 4.0; N, 1.6; S, 7.4. Found: C, 59.65; H, 3.9;
N, 1.65; S, 7.35%. FTIR (KBr, cmÀ1): 1482–1434 m(C–
N–C); 1091 m(PPh3); 1H NMR (CDCl3, ppm): 16.8–
16.5 (12H, m, Ph) 11.8 (1H, t), 10.3 (1H, d); 9.8–9.6
(6H, m, Ph), 8.1–7.6 (12H, m, Ph), 2.1 (1H, d), À11.6
(1H, t).
(M = Re,
1–3;
2.3.4. [Tc(PPh3)2Cl2(L5)] (11)
Yield 73%. Anal. Calc. for C43H34Cl2NOP2STc: C,
61.0; H, 4.1; N, 1.7; S, 3.8. Found: C, 61.15; H, 4.0;
N, 1.75; S, 3.85%. FTIR (KBr, cmÀ1): 1481–1434 m(C–
N–C); 1092 m(PPh3); 1H NMR (CDCl3, ppm): 16.8–
16.6 (12H, m, Ph). 13.1 (1H, t), 9.8–9.5 (6H, m, Ph),

356
E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
Table 1
Crystal data
Compound
Formula
1
3
7
8
11
(C39H33ClN6PReS3)2+ Æ
(C24H20As)+ Æ 3ClÀ
(C27H27ClN6PReS3)2+ Æ
(C24H20As)+3ClÀ Æ
2H2O1/2(C2H5OH)
1333.08
(C18H15Cl5PRe)À Æ
C43H34Cl2NP2ReS2
C43H34Cl2NOP2STc Æ
C18H15P
(C24H26OP)+
M
1424.18
cubic
Pa-3
987.14
monoclinic
P21/n
947.90
monoclinic
P21/n
1106.80
tsriclinic
System
Space group
monoclinic
C2/c
ꢀ
P1
˚
a (A)
23.3819(2)
23.3819(2)
23.3819(2)
90
21.6655(3)
18.4798(3)
30.0706(4)
90
9.9681(2)
19.1709(3)
22.0801(4)
90
11.8451(2)
14.9149(2)
21.7857(4)
90
11.2324(1)
14.2133(2)
17.1411(2)
84.453(1)
77.566(1)
89.917(1)
2659.3(1)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
106.034(1)
90
102.443(1)
90
98.604(1)
90
3
˚
U (A )
12783.2(2)
8
1.474
11571.1(3)
8
1.530
4120.3(1)
4
1.591
3805.5(1)
4
1.655
Z
Dc (g cmÀ3
)
1.382
5.43
l (cmÀ1
)
27.48
30.33
33.83
35.61
h
min–hmax (ꢁ)
3.1–27.5
4883
0.043
2.8–27.5
11872
0.057
3.1–28.0
9777
0.045
3.2–28.0
8949
0.058
2.9–28.0
12791
0.045
Unique reflections
Rint
Observed reflections
[I > 2r(I)]
3019
8722
7214
6403
10595
R (observed reflections)
wR (all reflections)
S
0.0481
0.1582
0.0454
0.1155
0.0343
0.0751
0.0455
0.1166
0.0537
0.1307
1.13
1.30; À0.70
1.03
0.81; À1.41
1.03
0.83; À1.60
1.09
1.37; À1.76
1.13
1.83; À0.55
À3
˚
Dqmax; Dqmin (e A
)
of 1 was very poor (ca. 10%) and a green-yellow product
7 (yield ca. 30%) was collected (Scheme 2b).
The chemistry of five coordinate complexes of rhe-
nium(III) and technetium(III) with mono- and polyden-
tate thiolate ligands is well documented [18–22]. The
first example of a structurally characterized trigonal
bipyramidal (tbp) rhenium(III) complex [Re(SAr)3(NC-
Me)(PPh3)] with monodentate arylthiolate ligands was
reported by Dilworth and co-workers [18a]. This com-
plex was obtained by reduction of the oxo-Re(V) com-
pound [ReO(SAr)4]À with PPh3 or by substitution
reaction of [ReCl3(PPh3)2(NCMe)] with the arylthiolate
anion. The same author reported an interesting tbp
Tc(III) complex [Tc(PPh3)(Smetetraz)3(NCMe)] (Sme-
tetraz = 2-mercapto-methyltetrazolate anion) together
with oxo-[TcO(Smetetraz)4]À and nitrido-[TcN(Smetet-
raz)4]2À complexes [18f]. In any case, no chelate com-
The complexes of both metals are air stable but they
decompose slowly in solution over a period of days. Fi-
nally, repeated attempts to obtain chelate complexes
with H2L1–3 by addition of a base or a proton sponge
to reaction mixture have been unsuccessful. All IR spec-
tra of complexes 1–6 exhibit a broad intense band in the
range 3000–2500 cmÀ1 due to the stretching vibrations
of the N–H groups involved in hydrogen bonds. The
medium intensity bands observed in the range 1600–
1400 cmÀ1 may be assigned to (N–C–N) ring. A medium
absorption peak at ca. 1090 cmÀ1 is characteristic of
PPh3 moiety. Proton NMR spectra, recorded in CDCl3
solution and at room temperature, of the metal com-
plexes 1–6 show a pattern typical of diamagnetic com-
pounds. A downfield shift of the N–H resonances with
respect to those of the uncoordinated ligands (d 13.9–
14.45 in 1–6, d 11.8–12.6 in H2L1-3) is in agreement with
the presence of N–HÁ Á ÁCl hydrogen bonds. Aromatic
protons do not undergo significant chemical shifts. Fi-
nally, a singlet observed at d 2.2 and at d 2.9 in the spec-
pounds
were
isolated.
Similarly,
analogous
technetium(III) complexes were obtained by reduction
of the corresponding oxo-technetium(V) complex
[TcO(tmbt)4]À (Htmbt = 2,3,5,6-tetramethylbenzeneth-
iol) with phosphines or alkyl isocyanides or, alterna-
tively by [TcCl6]2À [18b,c]. The thiolates are in
equatorial plane and the axial positions are occupied
by p-accepting ligands such as CO, MeCN, PR3 and
py. A series of tbp complexes of M(III) (M = Re, Tc)
containing tripodal tetra- or tridentate thiolate ligands,
XS3 (X = N, P) and XS2 (X = S, O) have been described
and structurally characterized [19–22]. In all these com-
plexes, the etheroatom X is always in axial site and sul-
fur atoms in equatorial positions of the trigonal
bipyramid. From these studies, it appears that the tbp
trum of 2 and 5 is attributed to methyl protons. The 31
P
NMR spectra of rhenium complexes 1–3 display a sin-
glet in negative region at d À0.72, 3.0 and À1.2 for the
coordinated PPh3 moiety of 1, 2 and 3, respectively.
Phosphorus NMR spectra of the corresponding techne-
tium complexes 4–6 show very broad profiles; such
behavior was previously attributed to the coupling of
31P nuclei with the quadrupolar 99Tc center [17].

E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
357
2+
X
X
HN
NH
Cl
NH
S
X
HN
S
M
HN
NH
S
PPh3
NCMe
PPh3
M
M= Re, X= H, 1; X= Me, 2
M= Tc, X= H, 4; X= Me, 5
Cl
1-3
3 eq. H L
2
Ph3P
Cl
C6H6/ MeOH
N2, ref
2+
Cl
HN
NH
Cl
M=Re, Tc
NH
S
HN
S
M
HN
NH
S
PPh3
M= Re, 3
M= Tc, 6
(a)
H2L1
[MO4] -
M= Re, 1
M= Tc, 4
HCl, AsPh4Cl,
PPh3, 2h
M=Re, Tc
Cl
C(O)Me
H2L1
Cl
Cl
Cl
[ReO4] -
1 +
Re
C
Me
PPh3
HCl, AsPh4Cl,
PPh3,10h
Me
Cl
PPh3
(b)
7
Scheme 2.
geometry is stabilized by thiolate anions and p-accepting
coligands. In particular, tripodal tetradentate ligands
XS3 enforce a tbp coordination geometry. The com-
pounds 1–6 were recrystallized from dichloromethane
and benzene and single-crystal X-ray structure analyses
of 1 and 3 showed that they possess a trigonal bipyram-
idal structure.
system and are arranged to form a sort of ‘‘calyx’’
around the coordinated Cl1 anion.
In both compounds, the Re–S(thiolate) distances in
˚
the range 2.23–2.26 A are significantly shorter than
Re–S ones in octahedral or bipyramidal trigonal com-
plexes of Re(V) and Re(III) with aryl-monothiolates,
˚
where the Re–S distances are in the range 2.28–2.32 A
ORTEP [23] views of complexes 1 and 3 are shown in
Figs. 1 and 2. Selected interatomic distances and angles
are given in Table 2 and hydrogen bond parameters in
Table 3.
[3e,24–28]. The lengthening of Re–Cl1 distances of
˚
˚
Re–Cl distance of 2.36 A [29] can be accounted in terms
of trans influence exerted by the triphenylphosphine
group.
The cationic complex 3 displays an analogous coordi-
nation geometry to that observed in 1. In this case, the
basal ligands are three 1H-imidazole-2-thiol molecules
linked in cycle by bifurcated hydrogen bonds involving
all the N–H moieties, three ClÀ anions and a water mol-
ecule. The second water molecule bridges two Cl ions,
Cl2 and Cl3, belonging to two different cyclic
arrangements.
2.473(1) and 2.465(1) A with respect to the standard
In compound 1, the overall geometry about the Re
atom of the cationic complex can be described as trig-
onal bipyramidal with the equatorial plane comprising
the three thiolate ligands and the apical positions occu-
pied by a Cl anion and a triphenylphosphine. The com-
plex is situated on a crystallographic threefolded axis.
The neutral 1H-benzimidazole-2-thiol ligands H2L1 are
linked to Re(III) atoms 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 three ligands are linked to each other
by means of a cyclic N–HÁ Á ÁClÁ Á ÁH–N hydrogen bond
Compound 7 was identified by X-ray analysis as the
paramagnetic Re(IV) complex [Ph3PC(Me)2CH2CO-
Me][ReCl5(PPh3)]. Details of analytical and spectro-

358
E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
Table 2
Selected bond distances (A) and angles (degrees) for compounds 1 and
˚
3
1
3
˚
Bond distances (A)
Re1–Cl1
Re1–P1
Re1–S1
Re1–S2
Re1–S3
S1–C1
2.473(1)
2.332(2)
2.245(2)
2.465(2)
2.326(2)
2.235(2)
2.250(1)
2.258(1)
1.767(6)
1.764(7)
1.760(6)
1.325(7)
1.330(8)
1.331(8)
1.329(8)
1.318(8)
1.336(8)
1.735(8)
S2–C4
S3–C7
N1–C1
N2–C1
1.333(10)
1.327(10)
N3–C4
N4–C4
N5–C7
N6–C7
Bond angles (ꢁ)
Cl1–Re1–P1
Cl1–Re1–S1
Cl1–Re1–S2
Cl1–Re1–S3
P1–Re1–S1
P1–Re1–S2
P1–Re1–S3
S1–Re1–S1
S1–Re1–S2
S1–Re1–S3
S2–Re1–S3
Re1–S1–C1
Re1–S2–C4
Re1–S3–C7
180
91.96(6)
178.83(5)
93.32(5)
92.52(5)
91.27(5)
87.71(5)
87.49(5)
87.74(5)
88.04(6)
120
Fig. 1. An ORTEP view of complex 1 showing thermal ellipsoids at
30% probability.
117.56(6)
118.99(6)
122.95(6)
111.7(2)
110.3(2)
109.2(2)
107.2(3)
Table 3
˚
Hydrogen bond parameters (A and ꢁ) for compounds 1 and 3
D–HÁ Á ÁA
D–H
HÁ Á ÁA
DÁ Á ÁA
D–HÁ Á ÁA
1
N1–HÁ Á ÁCl2 (y,z,x)
0.86a
0.86a
2.30
2.21
3.133(8)
3.042(8)
162
163
N2–HÁ Á ÁCl2
3
N1–HÁ Á ÁCl2
N2–HÁ Á ÁCl3
N3–HÁ Á ÁCl4
O1–HÁ Á ÁCl4
N4–HÁ Á ÁCl3
N5–HÁ Á ÁO1
N6–HÁ Á ÁCl2
O2–HÁ Á ÁCl2
O2–HÁ Á ÁCl3
(1/2 À x, 1/2 À y, Àz)
0.86a
0.86a
2.38
2.30
2.15
3.198(5)
3.102(5)
3.013(6)
3.104(5)
3.118(6)
2.725(7)
3.136(6)
3.109(7)
3.176(7)
159
155
177
0.86a
b
0.86a
0.86a
2.28
1.87
2.28
164
172
176
0.86a
b
b
a
Fig. 2. An ORTEP view of complex 3 showing thermal ellipsoids at
30% probabilit.
H calculated.
H not determined.
b
3 and selected bond distances and angles for the anion
are shown in Table 4. The crystal is isomorphous with
that containing technetium instead of rhenium. The an-
ion displays an approximate octahedral symmetry with
the values of bond distances and angles very similar to
those observed in technetium complex.
scopic data are reported in Section 2. This complex is
isostructural to the technetium analog reported by
Bandoli and co-workers [30] in a study concerning the
reactions of pertechnetate with triphenylphosphine. A
picture of ionic couple of compound 7 is given in Fig.

E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
359
PPh3
M
3 eq. HL4,5
Cl
Cl
S
X
[MCl3(PPh3)2(NCMe)]
M=Re, Tc
PPh3, N2
N
PPh3
X=S, 8, 10
X=O, 9, 11
HL4,5
[ReO4]-
[TcO4]-
8, 9
HCl, PPh3
HL4,5
uncharacterized
products
HCl, PPh3
Scheme 3.
pound 11. Apart from that, notable differences in
reactivity between the Re(III) and Tc(III) precursors
were not observed. Rhenium(III) chelate complexes 8
and 9 were also isolated in satisfactory yield (8, 70%;
9, 50%) from KReO4 in the same reaction conditions
of 1 (Scheme 3).
Fig. 3. An ORTEP view of the ionic couple of compound 7 showing
thermal ellipsoids at 30% probability.
On the contrary, we were unable to obtain the corre-
sponding technetium compounds; dark green uncharac-
terized materials were formed. The chelate compounds
8–11 are indefinitely stable as solids as well as in solu-
tion. The infrared spectra of the complexes
[M(PPh3)2Cl2(L4,5)] (M = Re, Tc) 8–11 do differ from
those discussed above due to the absence of hydrogen
bonds indicative of deprotonation of HL4,5 ligands. Pro-
ton NMR spectra of 8–11 show sharp proton signals
characteristic of paramagnetic complexes in agreement
with d4 octahedral configurations. Their paramagnetism
can be seen by chemical shifts of the phenyl protons of
PPh3 as well as by those of ligands. In addition, no sig-
nal is observed in 31P MNR spectra. Comparing rhe-
nium with the corresponding technetium complexes,
an analogous pattern may be observed in all spectra,
although the signals of the latter compounds spread in
a wider range with respect to the former and are not well
resolved. In particular, the phosphinic proton reso-
nances occur as two multiplets at d 8.1–8.7 and d
13.6–13.9 (ratio 3:2) for 8 and 9 and do not undergo a
significant chemical shift in comparison with those of
the rhenium(III) precursor (d 8.8 and d 13.9). In fact,
Re(III) complexes having PPh3 as ligand in an octahe-
dral arrangement exhibit aromatic proton signals in a
very similar range [31,32]. The spectra of 10 and 11 show
three multiplets at d 16.5–16.8, 9.5–9.8 and 7.6–8.1 in the
ratio 2:1:2, which are attributed to aromatic protons of
PPh3 in ortho, para and meta positions, respectively [33].
The NMR spectrum of [TcCl3(PPh3)2(NCMe)] shows
the same pattern at d 15.8, 10.0 and 7.8, respectively.
The four aromatic protons of ligands HL4,5 in 8–11 res-
onate as a triplet–doublet–doublet–triplet pattern of
equal intensity (see Section 2).
Table 4
˚
Selected bond distances (A) and angles (ꢁ) for compound 7
˚
Bond distances (A)
Re1–Cl1
Re1–Cl2
Re1–Cl3
2.371(1)
2.335(1)
2.361(1)
Re1–Cl4
Re1–Cl5
Re1–P1
2.319(1)
2.334(1)
2.550(1)
Bond angles (ꢁ)
Cl1–Re1–Cl2
Cl1–Re1–Cl3
Cl1–Re1–Cl4
Cl1–Re1–Cl5
Cl1–Re1–P1
Cl2–Re1–Cl3
Cl2–Re1–Cl4
Cl2–Re1–Cl5
89.06(3)
92.65(3)
90.12(4)
90.36(3)
177.95(3)
87.83(3)
179.19(3)
88.92(3)
Cl2–Re1–P1
Cl3–Re1–Cl4
Cl3–Re1–Cl5
Cl3–Re1–P1
Cl4–Re1–Cl5
Cl4–Re1–P1
Cl5–Re1–P1
92.18(3)
92.20(4)
175.53(3)
85.77(3)
91.09(4)
88.63(3)
91.29(3)
3.2. Synthesis and characterization of [M(PPh3)2-
Cl2(L4,5)] (M = Re, 8, 9; M = Tc, 10, 11)
Ligand exchange reactions carried out with HL4,5 in
similar experimental conditions of 1–6 afforded or-
ange-red [Re(PPh3)2Cl2(L4,5)] (8, 9), bright red
[Tc(PPh3)2Cl2(L4)] (10), and magenta [Tc(PPh3)2Cl2(L5)]
(11) derivatives, respectively (Scheme 3). Formation of
these products did not depend on ligand concentration.
If the reaction of [ReCl3(PPh3)2(NCMe)] with HL5 was
performed in air, a mixture of three species was ob-
tained. The first has been authenticated as 9 based on
IR and NMR spectroscopy. The others, one yellow
and one green, respectively, will be discussed elsewhere.
It is interesting to note that the corresponding techne-
tium(III) precursor led in any case to the chelate com-

360
E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
Table 5
From analytical data and spectroscopic measure-
˚
Selected bond distances (A) and angles (ꢁ) for compounds 8 and 11
ments, we may conclude that 8–11 are monosubstituted
octahedral M(III) complexes. The X-ray structure anal-
yses of 8 and 11 confirmed that the central metal atom is
in an octahedral environment. ORTEP view of complex
8 is shown in Fig. 4. Selected bond distances and angles
are given in Table 5. The octahedral Re(III) neutral
complex displays two triphenylphosphine, in trans posi-
tion, each other and the basal plane occupied by two Cl
atoms and the bidentate (N,S)-benzothiazole-2-thiolate
Compound 8
˚
Bond distances (A)
Re1–Cl1
Re1–Cl2
Re1–P1
Re1–P2
Re1–S1
2.388(2)
2.373(2)
2.464(2)
2.483(2)
2.442(2)
Re1–N1
S1–C1
N1–C1
N1–C7
S2–C1
2.118(6)
1.760(9)
1.378(9)
1.377(11)
1.714(8)
Bond angles (ꢁ)
Cl1–Re1–Cl2
Cl1–Re1–P1
Cl1–Re1–P2
Cl1–Re1–N1
Cl1–Re1–S1
Cl2–Re1–P1
Cl2–Re1–P2
Cl2–Re1–N1
Cl2–Re1–S1
102.51(6)
91.36(6)
90.36(6)
165.1(2)
96.08(6)
87.69(5)
86.60(5)
92.3(2)
P1–Re1–P2
P1–Re1–S1
P1–Re1–N1
P2–Re1–S1
P2–Re1–N1
S1–Re1–N1
C1–S1–Re1
C1–N1–Re1
174.27(5)
˚
anion. The Re1–S bond distance of 2.442(2) A is in
agreement with those observed in Re (N,S) pyridinethi-
olato derivatives, which displays values from 2.35 to
91.87(5)
89.9(2)
93.38(5)
89.9(2)
69.2(1)
79.2(2)
100.5(5)
˚
˚
2.53 A [3e,34,35]. The Re1–N1 distance of 2.118(6) A
is shorter than those observed in pyridinethiolate com-
pound, where the Re–N distances range from 2.14 to
˚
2.26 A. This shortening could be due to the narrow
161.40(6)
N1–Re1–S1 bite angle of 69.2(1)ꢁ.
Compound 11
In the complex 11 (Fig. 5), which is strictly analogous
to complex 8, the rhenium atom has been replaced by a
technetium one and the (N,S) bidentate benzothiazole-2-
thiolate ligand by a benzoxazole-2-thiolate one. As ex-
pected, the geometry is very similar to that of compound
8, even if the disordered S1, N1, C1, C2, O1 and Cl2
atoms around the Cl1–Tc1Á Á ÁC2 axis affect considerably
the accuracy of the relative bond distances and angles
(Table 5).
In conclusion, there is a notable difference among lig-
ands used in this work and aryl or alkyl thiolates previ-
ously reported. In fact, in the former the –SH fragment
is bound to a carbon atom of a heterocylic structure and
involved in a thione–thiol equilibrium, which determines
their chemical behavior together with the presence of a
different heteroatom (N, S, O). Complexes with H2L1–3
˚
Bond distances (A)
Tc1–Cl1
2.368(1)
Tc1–N1
S1–C1
2.101(7)
2.099(8)
1.770(22)
1.713(19)
1.330(11)
1.309(10)
1.387(9)
1.398(8)
1.352(9)
1.349(10)
Tc1–Cl2
Tc1–P1
Tc1–P2
Tc1–S1
2.384(17)
2.292(15)
2.478(1)
N1–C1
N1–C2
O1–C1
2.499(1)
2.555(15)
2.507(18)
˚
Bond angles (A)
Cl1–Tc1–Cl2
Cl1–Tc1–P1
Cl1–Tc1–P2
Cl1–Tc1–N1
Cl1–Tc1–S1
Cl2–Tc1–P1
Cl2–Tc1–P2
Cl2–Tc1–N1
Cl2–Tc1–S1
103.4(4)
99.1(5)
90.81(3)
P1–Tc1–P2
P1–Tc1–S1
P1–Tc1–N1
P2–Tc1–S1
P2–Tc1–N1
S1–Tc1–N1
C1–S1–Tc1
C1–N1–Tc1
177.14(4)
88.2(4)
92.1(4)
90.7(2)
90.3(2)
94.6(4)
85.6(4)
90.8(2)
90.4(2)
69.3(5)
87.1(4)
73.2(6)
75.4(7)
98.9(5)
99.8(5)
88.16(3)
167.8(2)
172.6(2)
98.6(5)
105.0(4)
87.3(4)
90.2(5)
90.4(4)
92.6(5)
88.8(5)
88.2(5)
157.6(5)
155.8(5)
contain three neutral thiolate ligands on the basal plane
and are very similar to the complex reported in the liter-
ature [18a–c,f]. The presence of sulfur or oxygen atom in
the place of nitrogen in HL4,5 induces their spontaneous
deprotonation and as a consequence they form classical
octahedral paramagnetic chelate species. The same
behavior is also observed in the reactions with KReO4,
although they were carried out in acidified solution.
Fig. 4. An ORTEP view of complex 8 showing thermal ellipsoids at
30% probability.

E. Marchesi et al. / Inorganica Chimica Acta 358 (2005) 352–362
361
ion Road, Cambridge CB2 1EZ, UK [fax: +441223-
336033, e-mail: deposit@ccdc.cam.ac.uk]
Acknowledgments
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.
References
[1] W.A. Volkert, T.J. Hoffman, Chem. Rev. 99 (1999) 2269.
[2] P.A. Schubiger, R. Alberto, A. Smith, Bioconjugate Chem. 7
(1996) 165.
Fig. 5. An ORTEP view of complex 11 showing thermal ellipsoids at
30% probability. The Cl2, S1, C1, N1 and O1 atoms, refined with two
independent orientations, are shown only in one position for the sake
of clarity.
[3] (a) H. Spies, T. Fietz, H.J. Pietzsch, B. Johanssen, P. Liebnitz, G.
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from reduction of pertechnetate.
(d) D.J. Rose, K.P. Maresca, T. Nicholson, A. Davison, A.G.
Jones, J. Babich, A. Fischman, W. Graham, J.R.D. De Bord, J.
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4. Conclusion
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The synthesis and structural characterization of a
new family of trigonal bipyramidal technetium(III)
and rhenium(III) complexes incorporating three mole-
cules of imidazole-2-thiolate ligands have been success-
fully achieved from substitution reactions on
[MCl3(PPh3)2(NCMe)]. These compounds have also
been obtained from reduction of [MO4]À anions
(M = Re, Tc) with PPh3. Benzothiazole-2-thiol and
benzoxazole-2-thiol ligands give rise to paramagnetic
octahedral chelate complexes of both metals which have
been structurally characterized. These results suggest
that the different chemical behavior between the two
classes of ligands may be attributed to the substitution
of the nitrogen atom in imidazoles by oxygen or sulfur
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5. Supplementary material
Crystallographic data (excluding structure factors)
have been deposited with the Cambridge Crystallo-
graphic Data Centre and allocated the deposition num-
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