Chelated hydrazido(3-)rhenium(V) complexes: On the way to the nitrido-M(V) core (M = Tc, Re)

Article abstract of DOI:10.1021/ic0110979

Neutral and asymmetrical hydrazido(3-)rhenium(V) heterocomplexes of the type [Re(η²-L⁴)(Lⁿ)(PPh₃)] (η²-L⁴ = NNC(SCH₃)S; H₂L¹ = S-methyl β-N-((2-hydroxyphenyl)ethylidene)dithiocarbazate, 1, H₂L² = S-methyl β-N-((2-hydroxyphenyl)methylidene)dithiocarbazate, 2) are prepared via ligand-exchange reactions in ethanolic solutions starting from [Re^V(O)Cl₄]^- in the presence of PPh₃ or from [Re^V(O)Cl₃(PPh₃)₂]. The distorted octahedral coordination sphere of these compounds is saturated by a chelated hydrazido group, a facially ligated ONS Schiff base, and PPh₃. Reduction-substitution reactions starting from [NH₄][Re^VIIO₄] in acidic ethanolic mixtures containing PPh₃ and H₂Lⁿ (or its dithiocarbazic acid precursor H₃L⁴) produce another example of chelated hydrazido(3-) rhenium(V) derivative, namely [Re(η²-L⁴)Cl₂(PPh₃) ₂], 3. On the contrary, the N-methyl-substituted dithiocarbazic acid H₂L³ reacts with perrhenate to give the known nitrido complex [Re(N)Cl₂(PPh₃)₂]. Rhenium(V) complexes incorporating the robust η²-hydrazido moiety represent key intermediates helpful for the comprehension of the reaction pathway which generates nitridorhenium(V) species starting from oxo precursors. An essential requirement for the stabilization of such chelated hydrazido-Re(V) units is the triple deprotonation at the hydrazine nitrogens, thereby providing efficient π-electron circulation in the resulting five-membered ring. The thermal stability of these units is affected by the nature of the anchoring donor, thione sulfur ensuring stronger chelation than nitrogen and oxygen. The η²-hydrazido complexes are characterized by conventional physicochemical techniques, including the X-ray crystal structure determination of 1 and 3.

Full text of DOI:10.1021/ic0110979

Inorg. Chem. 2002, 41, 1591−1597
Chelated Hydrazido(3−)rhenium(V) Complexes: On the Way to the
Nitrido−M(V) Core (M ) Tc, Re)
Franck Me´vellec,† Nicolas Lepareur,† Alain Roucoux,† Nicolas Noiret,† Henri Patin,† Giuliano Bandoli,‡
,§
Marina Porchia,§ and Francesco Tisato*
Laboratoire de Chimie des Biomole´cules et des Syste`mes Organise´s, CNRS UMR 6052,
Ecole Nationale Supe´rieure de Chimie de Rennes (ENSCR), 35700 Rennes, France,
Dip. Scienze Farmaceutiche, UniVersita` di PadoVa, Via Marzolo 5, 35131 PadoVa, Italy, and
CNR-ICIS, Corso Stati Uniti 4, 35127 PadoVa, Italy
Received October 22, 2001
Neutral and asymmetrical hydrazido(3−)rhenium(V) heterocomplexes of the type [Re(η2-L4)(Ln)(PPh3)] (η2-L4 )
NNC(SCH )S; H L1 ) S-methyl â-N-((2-hydroxyphenyl)ethylidene)dithiocarbazate, 1, H L2 ) S-methyl â-N-((2-
3
2
2
hydroxyphenyl)methylidene)dithiocarbazate, 2) are prepared via ligand-exchange reactions in ethanolic solutions
starting from [ReV(O)Cl4]- in the presence of PPh3 or from [ReV(O)Cl3(PPh3)2]. The distorted octahedral coordination
sphere of these compounds is saturated by a chelated hydrazido group, a facially ligated ONS Schiff base, and
PPh3. Reduction−substitution reactions starting from [NH ][ReVIIO ] in acidic ethanolic mixtures containing PPh3
4
4
and H Ln (or its dithiocarbazic acid precursor H L4) produce another example of chelated hydrazido(3−) rhenium(V)
2
3
derivative, namely [Re(η2-L4)Cl2(PPh3)2], 3. On the contrary, the N-methyl-substituted dithiocarbazic acid H L3 reacts
2
with perrhenate to give the known nitrido complex [Re(N)Cl2(PPh3)2]. Rhenium(V) complexes incorporating the
robust η2-hydrazido moiety represent key intermediates helpful for the comprehension of the reaction pathway
which generates nitridorhenium(V) species starting from oxo precursors. An essential requirement for the stabilization
of such chelated hydrazido−Re(V) units is the triple deprotonation at the hydrazine nitrogens, thereby providing
efficient π-electron circulation in the resulting five-membered ring. The thermal stability of these units is affected
by the nature of the anchoring donor, thione sulfur ensuring stronger chelation than nitrogen and oxygen. The
η2-hydrazido complexes are characterized by conventional physicochemical techniques, including the X-ray crystal
structure determination of 1 and 3.
Introduction
on these two elements even more attractive. The advantage
of manipulating “cold” materials (the natural isotopic mixture
of 185Re and 187Re) instead of using a radioactive nuclide
(the soft â-emitter 99gTc; t1/2 ) 2.12 × 105 y, Eâ ) 292 keV)
makes common inorganic chemistry studies on rhenium
much easier to carry out. In fact, Re is often used as a
technetium surrogate to study the macroscopic chemistry of
potentially useful agents in nuclear medicine. However, while
analogies such as synthetic and general chemistry seem to
support this choice, a few important differences, lately
disclosed, concerning the redox behavior and kinetics of
substitution (rhenium species are more difficult to reduce to
lower oxidation states and kinetically more inert toward
substitution than technetium analogues),3 suggest to use the
chemical similarity of the two elements with some caution.
In the past two decades, the coordination chemistry of the
group 7 metals technetium and rhenium has known a period
of increasing investigation due to the widespread use of the
metastable isomer 99mTc (pure γ-emitter with ideal physical
properties for imaging: t1/2 ) 6 h, Eγ ) 140 keV) in
diagnostic nuclear medicine.1 The recent advent of diphos-
phonate agents based on the â-emitters 186Re (t1/2 ) 3.8 d,
Eâmax ) 1.07 MeV) and 188Re (t1/2 ) 0.7 d, Eâmax ) 2.11
MeV) as potential radiopharmaceuticals for the palliation of
pain in patients with metastatic bone cancer2 has made studies
* To whom correspondence should be addressed. E-mail: FRANCESCO.
TISATO@ICTR.PD.CNR.IT.
† Ecole Nationale Supe´rieure de Chimie de Rennes (ENSCR).
‡ Universita` di Padova.
§ CNR-ICIS.
(1) (a) Jurisson, S.; Lydon, J. D. Chem. ReV. 1999, 99, 2205. (b) Liu, S.;
(2) (a) Jurisson, S.; Berning, D.; Wei, J.; Dangshe, M. Chem. ReV. 1993,
93, 1137. (b) Reubi, J. C. J. Nucl. Med. 1995, 36, 1825.
Edwards, D. S. Chem. ReV. 1999, 99, 2235.
10.1021/ic0110979 CCC: $22.00 © 2002 American Chemical Society
Published on Web 02/26/2002
Inorganic Chemistry, Vol. 41, No. 6, 2002 1591

Me´vellec et al.
The design of improved radiopharmaceuticals depends on
the availability of both new ligand systems and new metal
containing fragments. Studies concerning the [M(O)]3+ core
have played a prevalent role in the chemistry of Tc(V) and
Re(V) since many of the radiopharmaceutical agents utilized
for clinical purposes show a polydentate ligand coordinated
to an oxo-metal core.1a,4 Recent developments based on the
incorporation of the nitrogen donor in the metal coordination
sphere have led to the synthesis of complexes containing
diazenido,5 imido,6 and nitrido7 cores. Particular emphasis
has been devoted to the latter [Tc(N)]2+ moiety, for which
a standard method of production at “noncarrier added” level
(nca) has been proposed.8 In this field, a new myocardial
imaging agent [99mTc(N)(NOEt)2] (NOEt ) N-ethyl-N-
ethoxydithiocarbamate) has been prepared and is now under
phase III clinical trials.9 Various hydrazines and substituted
hydrazines have been utilized as N3- source in the prepara-
tion of the nitrido-99mTc core at nca level starting from the
pertechnetate ion eluted from the commercially available
99Mo/99mTc generator. Among substituted hydrazines, S-
methyl â-N-((2-hydroxyphenyl)ethylidene)dithiocarbazate
(H2L1) and S-methyl â-N-((2-hydroxyphenyl)methylidene)-
dithiocarbazate (H2L2) and the related dithiocarbazate precur-
sors H2NN(CH3)C(dS)SCH3 (H2L3) and H2NNHC(dS)SCH3
(H3L4) have been used as prototype ligands not only as
potential source of nitrogen but also as suitable polydentate
ligands able to stabilize the [Tc(N)]2+ core both at macro-
scopic and nca levels.10 Despite extensive effort aiming at
the elucidation of the mechanism of formation of the nitrido
group starting from (poly)oxo precursors, no exhaustive
explanation has been produced so far. Some postulated
intermediate species bearing alternatively the oxo or the
nitrido group have been proposed in the case of technetium,
i.e. the five-coordinate [TcV(O)Cl(L2)],11 [TcV(N)(L2)-
(PPh3)],12 and [TcV(N)(L4)2]12 complexes and the anomalous
six-coordinate [TcIIICl2(HL2)(PPh3)2]11 one. Additional in-
vestigation with the third row congener has produced similar
five-coordinate [ReV(O)X(L1)] (X ) Cl or I)13 and the six-
coordinate phosphine-containing compounds [ReV(O)Cl(L1)-
(PPh3)] and [ReV(O)Cl(L1)(OPPh3)].14
In this study we report on the synthesis and characteriza-
tion of some hydrazido(3-) rhenium(V) species, namely [Re-
(η2-L4)(L1)(PPh3)], 1, [Re(η2-L4)(L2)(PPh3)], 2, and [Re(η2-
L4)Cl2(PPh3)2], 3, which are relevant for the comprehension
of the mechanism of formation of the nitrido core starting
from the high-valent perrhenate precursor. In this case we
have utilized profitably the differences between the two
elements. In particular, while the isolation of intermediate
hydrazido-Tc species is extremely difficult because the
kinetic of conversion of oxo-Tc into the corresponding
nitrido-Tc compounds is very fast, the slower kinetic of
substitution at the rhenium center, along with the careful
choice of properly designed substituted hydrazines, has
granted the isolation of stable intermediate (η2-hydrazido)-
rhenium species. Hence, a possible reaction pathway ongoing
from perrhenate to nitrido-Re(V) through intermediate
hydrazido-Re(V) derivatives is here proposed.
Experimental Section
Materials. Ethanol was distilled twice under dinitrogen over
magnesium turnings. Dichloromethane and petroleum ether (30-
60 °C) were distilled over calcium chloride. Perrhenate ammonium
salt was purchased from STREM Chemicals (Newberyport). Carbon
disulfide, hydrazine dihydrochloride, methyl iodide, triphenylphos-
phine, salicylaldehyde, and 2-hydroxyacetophenone are com-
mercially available from Aldrich (Saint Quentin Fallavier, France).
[NBu4][Re(O)Cl4] and [Re(O)Cl3(PPh3)2] starting materials,15 S-
methyl â-N-((2-hydroxyphenyl)ethylidene)dithiocarbazate (H2L1)
and S-methyl â-N-((2-hydroxyphenyl)methylidene)dithiocarbazate
(H2L2) Schiff base ligands,13 and the dithiocarbazic acid precursors
H2NNHC(dS)SCH3 (H3L4) and H2NN(CH3)C(dS)SCH3 (H2L3)16
were prepared according to literature methods.
(3) Deutsch, E. A.; Libson, K.; Vanderheyden, J.-L. In Technetium and
Rhenium in Chemistry and Nuclear Medicine 3; Nicolini, M., Bandoli,
G., Mazzi, U., Eds.; Raven Press: New York, 1990; p 13.
(4) (a) Schwochau, K. Technetium: Chemistry and Radiopharmaceutical
applications; Wiley-VCH: Weinheim, Germany, 2000. (b) Bandoli,
G.; Dolmella, A.; Porchia, M.; Refosco, F.; Tisato, F. Coord. Chem.
ReV. 2001, 214, 43-90, (c) Tisato, F.; Refosco, F.; Bandoli, G. Coord.
Chem. ReV. 1994, 135/136, 325.
Instrumentation. Carbon, hydrogen, and sulfur analysis were
performed by the ICSN (91198 Gif sur Yvette, France) on a model
1106 Carlo Erba elemental analyzer. IR spectra were obtained by
a Nicolet 205 instrument in KBr pellets (4000-500 cm-1). Mass
spectrometry was carried out by the CRMPO (37500 Rennes,
France) on a Zabspect TOF (Micromass) spectrometer (FAB+,
(5) (a) Archer, C. M.; Dilworth, J. R.; Jobanputra, P.; Thompson, R. M.;
McPartlin, M.; Povey, D. C.; Smith, G. W.; Kelly, J. D. Polyhedron
1990, 9, 1497. (b) Rossi, R.; Marchi, A.; Duatti, A.; Magon, L.;
Casellato, U.; Graziani, R. J. Chem. Soc., Dalton Trans. 1988, 1857.
(c) Dilworth, J. R.; Jobanputra, P.; Miller, J. R.; Parott, S. J.; Chen,
Q.; Zubieta, J. Polyhedron 1993, 12, 513. (d) Douglas, P. G.; Galbraith,
A. R.; Shaw, B. L. Transition Met. Chem. 1975, 1, 17.
(6) (a) Nicholson, T.; Davison, A.; Zubieta, J.; Chen, Q.; Jones, A. G.
Inorg. Chim. Acta 1995, 230, 205. (b) Nicholson, T.; Cook, J.; Davis,
W. M.; Davison, A.; Jones, A. G. Inorg. Chim. Acta 1994, 218, 97.
(c) Nicholson, T.; Storm, S. L.; Davis, W. M.; Davison, A.; Jones, A.
G. Inorg. Chim. Acta 1992, 196, 27.
(7) (a) Baldas, J.; Boas, J. F.; Bonnyman, J.; Williams, G. A. J. Chem.
Soc., Dalton Trans. 1984, 2395. (b) Baldas, J.; J. F.; Bonnyman, J.;
Williams, G. A. Inorg. Chem. 1986, 25, 150. (c) Abram, U.; Lorenz,
B. J.; Kaden, L.; Scheller, D.; Polyhedron 1988, 7, 285. (e) Archer,
C. M.; Dilworth, J. R.; Griffith, D. W.; McPartlin, M.; Kelly, J. D. J.
Chem. Soc., Dalton Trans. 1992, 183.
1
NBA matrix). All prepared compounds were characterized by H,
13C, and 31P NMR recorded with a Bruker ARX 400 at 400.13,
100.62, and 161.98 MHz, respectively. Chemical shift values are
1
referred to residual CHCl3 (7.26 ppm, H NMR; 77.1 ppm, 13C
NMR).
(11) Marchi, A.; Duatti, A.; Rossi, R.; Magon, L.; Pasqualini, R.; Bertolasi,
V.; Ferretti, V.; Gilli, G. J. Chem. Soc., Dalton Trans. 1988, 1743.
(12) Marchi, A.; Rossi, R.; Magon, L.; Duatti, A.; Pasqualini, R.; Ferretti,
V.; Bertolasi, V. J. Chem. Soc., Dalton Trans. 1988, 1743.
(13) Me´vellec, F.; Roucoux, A.; Noiret, N.; Patin, H.; Toupet, L. Polyhedron
1999, 18, 2537.
(14) Me´vellec, F.; Roucoux, A.; Noiret, N.; Patin, H. J. Chem. Soc., Dalton
Trans. 2001, in press.
(15) (a) Cotton, F. A.; Lippard, S. Inorg. Chem. 1966, 5, 9. (b) Lis, T.;
Jezowska-Trzebiatowska, B. Acta Crystallogr. 1977, B33, 1278.
(16) Ali, M. A.; Livingstone, S. E.; Phillips, D. J. Inorg. Chim. Acta 1972,
6, 11.
(8) Pasqualini, R.; Comazzi, V.; Bellande, E.; Duatti, A.; Marchi, A. Int.
J. Appl. Radiat. Isot. 1992, 43, 1329.
(9) (a) Duatti, A.; Uccelli, L. Trends Inorg. Chem. 1996, 4, 27-41. (b)
Duatti, A.; Bolzati, C.; Uccelli, L.; Zucchini, G. L. Transition Met.
Chem. 1997, 22, 313-314. (c) Pasqualini, R.; Duatti, A.; Bellande,
E.; Comazzi, V.; Brucato, V.; Hoffschir, D.; Fagret, D.; Comet, M. J.
Nucl. Med. 1994, 35, 334-341.
(10) Duatti, A.; Marchi, A.; Pasqualini, R. J. Chem. Soc., Dalton Trans.
1990, 3729.
1592 Inorganic Chemistry, Vol. 41, No. 6, 2002

Chelated Hydrazido(3-)rhenium(V) Complexes
Syntheses of Complexes. [Re(η2-L4)(L1)(PPh3)], 1. Method A.
To an ethanolic solution (20 mL) of [Re(O)Cl4][NBu4] (0.100 g,
0.17 mmol) were added dropwise H2L1 (0.082 g, 0.34 mmol) and
triphenylphosphine (0.180 g, 0.68 mmol) in ethanol (10 mL), and
the solution was stirred at room temperature for 7 days. The yellow
brown precipitate was filtered out, washed several times with
ethanol, and dried under reduced pressure. The resulting khaki
powder was dissolved in a mixture of dichloromethane/petroleum
ether (50/50; 10 mL). After 5 days at room temperature, dark
crystals of 1 were collected, washed with petroleum ether, and dried
under reduced pressure (0.064 g, yield ) 47%). Anal. Calcd (found)
for C30H29N4OPReS4: C, 44.71 (44.75); H, 3.50 (3.50); S, 15.91
(15.88). IR (KBr, cm-1): 1596 (m, νCdN), 1566 (m, νNdN), 1527
(m, νCdN), 1462 (m, νPPh ), 1433 (s, νPPh ), 1312 (m, νC-O), 1240
Table 1. Crystallographic Data for 1 and 3
1
3
formula
fw
C30H29N4OPS4Re
807.0
C30H29N4OPS4Re
900.8
monoclinic
Cc
17.514(4)
10.639(2)
20.106(4)
102.29(3)
3660(1)
4; 1.635
3.70
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/n (No. 14)
20.916(3)
10.236(4)
29.463(7)
92.33(2)
6303(3)
8; 1.701
4.20
â, deg
V, Å3
Z; Dcalcd, g cm-3
µ(Mo KR), cm-1
T, °C
20
23
λ(Mo KR), Å
0.710 69
27
8713
0.037
0.072
0.710 73
27
θ
max, deg
3
3
obsd reflcns (I > 2σ(I))
3879
0.045
0.114
1.089
(m), 1191 (s), 1094 (m, νPPh ), 1060 (m, νC-S), 992 (s, νC-S), 751
3
R1a
(m, νPPh ), 692 (s, νPPh ), 683 (m), 527 (s). FAB(+) (m/z): 807.0,
3
3
wR2b
GOFc
[M + H]+. 1H NMR (CDCl3, ppm): δ 2.36 (s, SCH3, 3H), 2.69 (s,
SCH3, 3H), 2.99 (s, CCH3, 3H), 6.46 (d, 3JHH ) 7.6 Hz, 1H), 6.94
(t, 3JHH ) 8.1 Hz, 1H), 7.28 (t, 3JHH ) 7.9 Hz, 1H), 7.40 (m, 9H),
0.979
a R1 ) Σ(|Fo| |Fc||)/Σ(|Fo|). b wR2 ) {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo)2]}1/2
.
c GOF ) {Σ[w(Fo Fc )2]/(n - p)}1/2 (n ) reflections; p ) parameters).
2 -
2
3
7.55 (m, 6H); 7.59 (d, JHH ) 8.1 Hz, 1H). 13C NMR (CDCl3,
ppm): δ 18.1, 18.3, and 18.5 (CH3), 119.1, 120.2, 126.0, and 133.7
(aromatic C), 128.2 (d, J ) 10 Hz), 130.6 (d, J ) 2 Hz), 132.7 (d,
J ) 41 Hz) and 134.5 (d, J ) 10 Hz) (PPh3-aromatic C), 164.1
(C-O), 166.5 (CH3CdN), 191.5 and 192.2 (CS2). 31P NMR
(CDCl3, ppm): δ 13.8 (s, Re-PPh3).
Method B. To an ethanolic solution (20 mL) of [Re(O)Cl3-
(PPh3)2] (1.0 g, 1.2 mmol) was added dropwise H2L1 (0.540 g, 2.4
mmol) in ethanol (10 mL), and the solution was stirred at room
temperature for 7 days. The yellow brown precipitate was filtered
out, washed several times with ethanol, and dried under reduced
pressure. The resulting khaki powder was dissolved in a mixture
of dichloromethane/petroleum ether (50/50; 10 mL) (0.490 g, yield
) 51%). Spectroscopic data are as above.
(m), 1093 (s, νPPh ), 1070 (s, νC-S), 1028 (w), 997 (m, νC-S), 967
3
(m), 749 (s, νPPh ); 693 (s, νPPh ), 519 (s), 506 (s). FAB(+) (m/z):
3
3
900.0, [M + H]+. 1H NMR (CDCl3, ppm): δ 2.25 (s, SCH3, 3H),
7.30-7.60 (30 H; PPh3). 13C NMR (CDCl3, ppm): δ 17.3 (SCH3),
128.0, 130.3, 131.5 and 134.6 (PPh3-aromatic C), 207.2 (CS2).
31P NMR (CDCl3, ppm): δ -6.2 (s, Re-PPh3).
Method B. To an ethanolic solution (5 mL) of [NH4][ReO4]
(0.100 g, 0.373 mmol) containing 1 mL of 12 M HCl were added
dropwise H3L4 (0.091 g, 0.746 mmol) and triphenylphosphine
(0.390 g, 1.491 mmol) in ethanol (30 mL), and the solution was
kept at 60 °C for 3 h. The resulting yellow green precipitate was
filtered off, washed several times with hot ethanol, and dried under
vacuum. (0.285 g, yield ) 85%). Spectroscopic data are as above.
[Re(N)Cl2(PPh3)2], 4. To an ethanolic solution (5 mL) of [NH4]-
[ReO4] (0.100 g, 0.373 mmol) containing 1 mL of 12 M HCl were
added dropwise H3L3 (0.102 g, 0.746 mmol) and triphenylphosphine
(0.390 g, 1.491 mmol) in ethanol (30 mL), and the solution was
kept at 60 °C for 3 h. The resulting red-brick precipitate was
collected by filtration, washed with ethanol, and dried under vacuum
(0.202 g, yield ) 68%). The spectroscopic data correspond to those
reported in the literature for complex 4.17
[Re(η2-L4)(L2)(PPh3)], 2. Compound 2 was prepared using the
same procedures above detailed for 1 (yield ) 48%). Anal. Calcd
(found) for C29H27N4OPReS4: C, 44.00 (43.85); H, 3.30 (3.60); S,
16.20 (16.36). IR (KBr, cm-1): 1599 (m, νCdN), 1579 (m, νNdN),
1537 (m, νCdN), 1479 (m, νPPh ), 1432 (s, νPPh ), 1309 (m, νC-O),
3
3
1274 (m), 1182 (s), 1100 (s, νPPh ), 1065 (m, νC-S), 996 (m, νC-S),
3
750 (s, νPPh ), 713 (s), 691 (s, νPPh ), 637 (s), 612 (s). FAB(+) (m/
3
3
1
z): 794, [M + H]+. H NMR (CDCl3, ppm): δ 2.39 (s, SCH3;
3H), 2.69 (s, SCH3; 3H), 6.57 (d, 3JHH ) 7.6 Hz, 1H), 6.98 (t, 3JHH
3
) 8.1 Hz, 1H), 7.04 (d, JHH ) 8.1 Hz, 1H), 7.40 (m, 9H), 7.56
X-ray Crystallographic Study. Single crystals of complexes 1
and 3 were grown by slow evaporation of a petroleum ether/
dichloromethane solutions. Pertinent crystallographic data and
structure refinement for both compounds are summarized in Table
1, and the relevant bond lengths and angles in Table 2. The data
sets of 1 and 3 were collected at room temperature on CAD4 Nonius
and Philips PW 1100 automatic diffractometers, respectively, with
graphite-monochromatized Mo KR radiation. The cell parameters
were obtained by fitting a set of 25 high-angle reflections. After
Lorentz, polarization, and absorption corrections (ψ-scan method),
the structures were solved using the SHELXS computer program18
and refined with SHELXL-9719 by the full-matrix least-squares
techniques based on F2. Atomic scattering factors were obtained
from the International Tables for X-ray Crystallography, and the
figures were performed with the ORTEP II program.20
(m, 6H); 7.99 (s, HCdN; 1H), 8.32 (d, J ) 8.1 Hz, 1H). 13C NMR
(CDCl3, ppm): δ 18.6 and 18.7 (SCH3), 118.0, 119.6, 119.7, 121.3
and 121.8 (aromatic C), 128.6 (d, J ) 10.1 Hz), 128.9 (d, J ) 12.1
Hz), 134.8 (d, J ) 10.1 Hz) and 136.4 (d, J ) 38 Hz) (PPh3-
aromatic C), 160.4 (C-O), 161.4 (HCdN), 193.2 and 198.4 (CS2).
31P NMR (CDCl3, ppm): δ 15.1 (s, Re-PPh3).
[Re(η2-L4)Cl2(PPh3)2], 3. Method A. To an ethanolic solution
(5 mL) of [NH4][ReO4] (0.100 g, 0.373 mmol) containing 1 mL of
12 M HCl were added dropwise H2L2 (0.169 g, 0.746 mmol) and
triphenylphosphine (0.390 g, 1.491 mmol) in ethanol (30 mL), and
the solution was kept at 60 °C for 3 h. The yellow green precipitate
was filtered out, washed several times with hot ethanol, and dried
under reduced pressure. The resulting olive-green powder was
dissolved in a mixture of dichloromethane/petroleum ether (50/50;
10 mL). After standing at room temperature for few days, green
crystals of 3 were collected, washed with petroleum ether, and dried
under reduced pressure (0.195 g, yield ) 76%). Anal. Calcd (found)
for C38H33Cl2N2P2ReS2: C, 50.70 (50.62); H, 3.70 (3.72); S, 7.10
(7.14). IR (KBr, cm-1): 1587 (w, νCdN), 1571 (w, νNdN), 1481 (s,
(17) Sullivan, P.; Brewer, J. C.; Gray, H. B. Inorg. Synth. 1992, 29, 146.
(18) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(19) Sheldrick, G. M. SHELX 97, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(20) Johnson, C. K. ORTEP II; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
ν
PPh ), 1433 (s, νPPh ), 1315 (m), 1286 (s), 1187 (m), 1157 (s), 1136
3
3
Inorganic Chemistry, Vol. 41, No. 6, 2002 1593

Me´vellec et al.
Scheme 1
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1 and 3
1
A
B
Re-S(1)
2.353(2)
2.538(2)
2.114(5)
1.764(5)
2.414(2)
2.002(4)
1.416(7)
1.311(6)
168.6(1)
79.3(1)
72.9(2)
159.5(1)
80.6(2)
154.9(2)
95.3(2)
2.348(2)
2.541(2)
2.103(5)
1.769(5)
2.426(2)
1.995(4)
1.426(6)
1.312(6)
170.1(1)
79.3(1)
72.8(2)
166.1(1)
81.1(2)
155.7(2)
94.8(2)
Re-S(3)
Re-N(1)
Re-N(3)
Re-P(1)
Re-O(1)
N(1)-N(2)
N(3)-N(4)
S(1)-Re-S(3)
S(1)-Re-N(1)
S(3)-Re-N(3)
N(1)-Re-P(1)
N(1)-Re-O(1)
N(3)-Re-O(1)
Re-S(1)-C(9)
Re-S(3)-C(11)
Re-N(1)-N(2)
Re-N(1)-C(7)
Re-N(3)-N(4)
Re-O(1)-C(1)
Scheme 2
94.9(2)
94.8(2)
116.9(4)
128.0(5)
143.3(4)
122.0(4)
117.3(3)
128.3(4)
143.5(4)
123.2(4)
3
Re-P(1)
Re-P(2)
Re-Cl(1)
Re-Cl(2)
2.513(6)
Cl(1)-Re-Cl(2)
P(1)-Re-P(2)
P(2)-Re-Cl(1)
P(1)-Re-Cl(2)
98.4(2)
2.451(6)
2.312(3)
2.422(3)
170.5(1)
90.7(2)
88.2(2)
dehyde with dithiocarbazic acid methyl ester (H3L4). These
potentially tridentate chelates as well as the related dithio-
carbazic acid precursors undergo a tautomeric equilibrium
in solution as shown in Scheme 1. Equimolar amounts of
H2Ln react with [Re(O)Cl4]- giving the five-coordinate [Re-
(O)Cl(Ln)] complexes,13 whereas the presence of triphen-
ylphosphine in the coordination sphere of the [Re(O)Cl3-
(PPh3)2] starting material induces the formation of the six-
coordinate mixed-ligand [Re(O)Cl(Ln)(PPh3)] complexes.14
On the contrary, excess of H2Ln react with monooxorhenium
precursors in the presence of triphenylphosphine to afford
the novel mixed hydrazido-Re(V) heterocomplexes [Re(η2-
L4)(Ln)(PPh3)], 1 and 2 (Scheme 2), in which the original
oxo group has been abstracted and replaced by a multiple
metal-nitrogen hydrazido bond.
Reaction of perrhenate with excess of H2Ln and triphen-
ylphosphine in acidic ethanolic solutions affords another
chelated hydrazido species, the six-coordinate green complex
[Re(η2-L4)Cl2(PPh3)2], 3. The same compound is obtained
by adopting similar reaction conditions but replacing the
Schiff base with the dithiocarbazic acid precursor H3L.4 It
is worth noting that the use of the N-methyl-substituted
hydrazine H2L3 instead of H3L4 does not give hydrazido-
Re(V) species under the conditions utilized above, the red-
brick nitrido complex [Re(N)Cl2(PPh3)2] being recovered as
the resulting product.
Characterization of Chelated Hydrazido-Re(V) Com-
plexes. Elemental analyses of complexes 1-4, as given in
the Experimental Section, are in good agreement with the
proposed formulations. Compounds 1-3 show the [MH]+
molecular ion peaks when subjected to FAB mass spectro-
scopy in the positive mode, with no significant fragmentation
in the three cases. The IR spectra of all of the complexes do
not show bands characteristic of the [RetO] stretching
vibration, while peaks attributable to coordinated triphen-
Figure 1. Two ligating modes of the η2-hydrazido moiety in [Re(η2-L4)-
Cl2(PPh3)2], 3.
A relevant anomaly was encountered in the refinement of 3.
Refinement of the non-hydrogen atoms converged with R ) 0.073,
and a Fourier-difference map at this stage revealed maxima in the
vicinity of the hydrazido ligand, indicating a second complete image
of the ligand. The orientation, position, and relative occupancy for
it were refined, along with the parameters of the other atoms. The
two alternative ligating modes (i and ii) (Figure 1) refined
satisfactorily with occupancies of ca. 0.5; no significant matrix
correlation was observed, and refinement converged at R ) 0.045.
Anisotropy was applied only to Re, Cl, and P atoms, and the phenyl
rings were treated as rigid idealized hexagons. The maximum
residual peak in the final difference map corresponded to 1.12 e
Å-3, 1.14 Å from rhenium.
Results
Synthesis of Chelated Hydrazido-Re(V) Complexes.
The Schiff base ligands H2L1 and H2L2 have been prepared
from condensation of 2-hydroxyacetophenone or salicylal-
1594 Inorganic Chemistry, Vol. 41, No. 6, 2002

Chelated Hydrazido(3-)rhenium(V) Complexes
Figure 3. ORTEP representation of [Re(η2-L4)Cl2(PPh3)2], 3. Ellipsoids
are drawn at the 40% probability level, and for clarity, only one liganting
mode is shown.
Figure 2. ORTEP view of molecules A and B of [Re(η2-L4)(L1)(PPh3)2],
1. Ellipsoids are drawn at the 40% probability level. Hydrogen atoms are
omitted for clarity, and the atom numbering scheme only for A is reported.
O(1)-RedN(3) and S(1)-Re-S(3) angles deviate signifi-
cantly from linearity (155.3(2) and 169.3(1)°, respectively),
and the η2-hydrazido N(3)-Re-S(3) bite angle is constrained
at 72.9(2)°. The Re atom is displaced by 0.11 Å from the
mean plane defined by N(1), S(1), S(3), and P(1), pointing
toward the imine N(3) atom. According to the different
coordination mode (facial vs meridional) and the increased
coordination number (6 vs 5), the metal-donor distances of
the tridentate Schiff base are slightly lengthened (by 0.05-
0.10 Å) in complex 1 compared to those exhibited by less
crowded [Re(O)I(L1)].14 The Re-N(1) distance of 2.109(5)
Å attests a single bond in contrast with the Re-N(3) bond
distance of 1.766(5) Å, which indicates strong multiple bond
character (vide infra). The five-membered chelate ring of
the η2-hydrazido moiety is essentially planar (perfectly planar
in A, deviation within 0.03 Å in B). Despite the scattered
bond angles (between 72.8 and 143.5°) the ring reaches the
planarity and the sum of the internal angles approaches 540°.
The hydrazido ring is perpendicular to the mean plane of
the other five-membered ring Re(1)N(1)N(2)C(9)S(1) and
to the six-membered one Re(1)N(1)C(7)C(6)C(1)O(1), di-
hedral angles being 90.8 and 95.5°, respectively.
For 3, the solution of the structure was relatively difficult
due to the two ligating modes of the hydrazido ligand (see
Experimental Section and Figure 1) and, consequently, only
the metrical data for the remaining portion of the complex
are quoted in Table 2. In any case, in both the orientations
i and ii, the five-membered ring is substantially planar with
the N-Re-S bite angle of 73(1)°. As outlined in Figure 3,
the coordination octahedron is somewhat distorted, as
evidenced by the dihedral angle between the triangular faces
Cl(1)P(1)N(1) and S(1)P(2)Cl(2) (16.3 and 18.0° in i and ii,
respectively).
ylphosphine appear around 1100 and 700 cm-1. Moreover,
the absence of significant bands over 3000 cm-1 in com-
plexes 1 and 2 indicates coordination of the Schiff base in
the classical tridentate fashion as dianionic SNO chelate,11,13
via charged phenolate oxygen, neutral imine nitrogen, and
charged thiolate sulfur.
Quite narrow profiles, characteristic of diamagnetic spe-
1
cies, are shown in H, 13C, and 31P spectra of complexes
1-3. Upon coordination the 31P phosphine signal moves
downfield from -5.0 ppm in the free ligand to 13.8 and 15.1
ppm in complexes 1 and 2, respectively. A singlet at -6.2
ppm is observed in complex 3 as well, indicating magnetic
equivalence of the two phosphine phosphorus. Proton and
carbon spectra of complexes 1 and 2 show peaks character-
istic of coordinated Schiff bases and triphenylphosphine.14
However, an extra proton signal attributable to a methyl
group and two dithiocarbazate carbon signals appear in the
spectra. These features are consistent with the coordination
of an additional ligand, which may be generated in situ by
the cleavage of the Schiff base carboimine function.
To confirm this hypothesis we have grown crystals of
complex 1 to perform the X-ray diffraction analysis. The
unique portion of the unit cell comprises two molecules (A
and B), and as illustrated in Figure 2, each neutral [Re(η2-
L4)(L1)(PPh3)] molecule displays a distorted octahedral
environment around the rhenium atom. Since A and B are
practically superimposable (rms of 0.08 Å when the fitting
is performed on the 13 atoms nearest to Re) in the discussion
the mean values for bond lengths and angles are reported.
An intact Schiff base ligand acts as classical tridentate donor
in a facial manner having the triphenylphosphine phosphorus
trans to its central imine nitrogen. The coordination is
completed by a chelated hydrazido-N,S fragment placing the
N(3) atom trans to the phenolate oxygen and the S(2) atom
trans to the thiolate sulfur. Major distortions from the ideal
octahedron arise from the chemical unequivalence of the
three chelate rings and from significant steric interactions
with the bulky triphenylphosphine molecule. Hence, the
Discussion
The determination of the metal oxidation state in hy-
drazido-type technetium and rhenium compounds is not
always straightforward,21 formal oxidation states from 1+
(21) Nicholson, T.; Davison, A.; Jones, A. Inorg. Chim. Acta 1990, 168,
227.
Inorganic Chemistry, Vol. 41, No. 6, 2002 1595

Me´vellec et al.
Chart 1
rhenium complex 3 always failed, even under drastic
conditions. In fact, after prolonged reflux in ethanol at pH
) 1 complex 3 was recovered intact (see route B of Scheme
3). Analogously, reaction with diethyldithiocarbamate sodium
salt (Na(dedc)), under the conditions utilized to convert the
chelated hydrazido complex [Re(η2-N,O-hydrazido)Cl2-
(PPh3)2] into the linear hydrazido [Re(η1-N-hydrazido)-
(dedc)2(PPh3)] species,28 gives complex 3 unmodified. It has
to be noted that chelated hydrazido [Re(η2-N,O-hydrazido)-
Cl2(PPh3)2]-type complexes represent ideal starting materials
to produce linear diazenido derivatives,30 confirming the
hemilability of N,O-chelated moieties. Similar hemilability,
followed by rapid N-N cleavage to yield the terminal [Tc-
(N)]2+ group under relatively mild conditions (refluxing
dichloromethane), was observed in the related [Tc(η2-N,N-
hydralazino)Cl2(PPh3)2] complex.23
to 5+ being reported.4b,c This uncertainty is mainly related
with the degree of protonation at the R and/or â nitrogens,
which, in turn, determines various M-NN- arrangements
and, eventually, the rich geometrical versatility of these
ligands. For example, as shown in Chart 1, (thiobenzoyl)-
hydrazine-type ligands may adopt the η2-diazene I, the η2-
hydrazido II, and the η1-diazenido coordination mode III,22
with the pertinent metal-nitrogen distances moving from
1.76 Å (form II) to 2.16 Å (form I).
The substitution inert complex 3 crumbles only by
removing the π-electron delocalization at the η2-S,N-hy-
drazido(3-) moiety, i.e by insertion of a methyl group at
the â-hydrazine nitrogen, as in H2L3. As depicted in route
A of Scheme 3, the chelated hydrazido adduct [Re(η2-hyd-
L3)Cl2(PPh3)2]+ may form, but it is rapidly converted through
N-N cleavage into [Re(N)Cl2(PPh3)2]. A similar behavior
was previously reported in related [Re(η2-N,S-thiosemicar-
bazido)Cl2(PPh3)2] compounds,31 in which a flipping proton
delocalized over the hydrazido ring partially removes
π-electron circulation, thereby promoting cleavage of the
N-N bond to give eventually the [Re(N)Cl2(PPh3)2] species.
On the basis of the above arguments, we can say that
perrhenate can be converted into nitrido-Re(V) species
through intermediate η2-hydrazido(3-) rhenium(V) deriva-
tives, according to the simplified reaction pathway depicted
in Scheme 4. Since the reduction of perrhenate operated by
tertiary phosphines in acid media is a consolidated route of
synthesis of monooxo-Re(V) compounds32 and these species
can be also converted into η2-hydrazido(3-)-Re(V) ones
by oxo abstraction operated by PPh3 or by condensation-
type reactions in absence of PPh3,33 monooxo-Re(V) deriva-
tives may also represent other intermediate species in the
process.
The mechanism underlying the conversion of hydrazido-
(3-) into nitridorhenium and technetium compounds has
been proposed by other authors.31,33 Imido-technetium ad-
ducts have been postulated,33 and imido-hydrazido(1-)-
rhenium derivatives have been isolated31 as intermediates in
the process. Thus, it is reasonable to apply the same reaction
pathway of Scheme 4 to the second-row congener techne-
tium. However, the faster kinetic of substitution at the
technetium center3 does not allow easy isolation of η2-
hydrazido(3-)-Tc(V) intermediate species, which quickly
rearrange to the more stable nitrido species. This drawback
at macroscopic level becomes an advantage at the nca level,
The disorder at the hydrazido moiety of complex 3 (vide
supra) does not allow one to use the structural parameters
for a comparison with those exhibited by similar compounds
of formula [M(η2-hydrazido)Cl2(PPh3)2] (M ) Tc, Re),23-25
cumulated in Table 3. However, the related complex 1
contains an identical not disordered η2-hydrazido group,
whose parameters can in turn be utilized for a detailed
correlation. Its multiple Re-N bond distance of 1.763(5) Å
falls in the narrow range exhibited by isosterical η2-
hydrazido(3-) compounds (Table 3). Although their chelated
moieties hold different anchoring donors (S or N or O), the
bite angles are homogeneous in the restricted 70-75° region
as well. In these compounds extended delocalization of the
electronic density is warranted by the planar five-membered
ring through the π-network system. Also η1-hydrazido(3-)
groups, frequently referred to as metal-diazenido units, show
multiple Tc-N bond distances in the identical 1.76-1.78 Å
narrow range26-29 (Table 3). The strict analogy in the M-N
bond distances along with the diamagnetism shown in
solution for both linear and chelated hydrazido(3-) com-
plexes are in agreement with the metal exhibiting a low-
spin d2 configuration typical of Tc(V) and Re(V) species.4
As previously mentioned, the chelated hydrazido(3-)
moiety in [M(η2-hydrazido)Cl2(PPh3)2] complexes can hold
different anchoring donors. The stability of the complexes
depends on the chelate donor set according to the series N,S
. N,N = N,O. In fact, attempts to open and/or cleave the
N-N group of the η2-S,N-hydrazido(3-) moiety of the
(22) (a) Fitz Roy, M. D.; Frederiksen, J. M.; Murray, K. S.; Snow, M. R.;
Inorg. Chem. 1985, 24, 3265. (b) Liu, S.; Zubieta, J. Polyhedron 1989,
8, 677. (c) Abrams, M. J.; Shaikh, S. N.; Zubieta, J. Inorg. Chim.
Acta 1990, 171, 133.
(23) Abrams, M. J.; Larsen, S. K.; Shaikh, S. N.; Zubieta, J. Inorg. Chim.
Acta 1991, 185, 7.
(24) Nicholson, T.; Zubieta, J. Polyhedron 1988, 7, 171.
(25) Refosco, F.; Tisato, F.; Moresco, A.; Bandoli, G. J. Chem. Soc., Dalton
Trans. 1995, 3475.
(26) Rose, D. J.; Maresca, K. P.; Nicholson, T.; Davison, A.; Jones, A.
G.; Babich, J.; Fischman, A.; Graham, W.; DeBord, J.; Zubieta, J.
Inorg. Chem. 1998, 37, 2701.
(27) Dilworth, J. R.; Jobanputra, P.; Thompson, R. M.; Povey, D. C.;
Archer, C. M.; Kelly, J. D. J. Chem. Soc., Dalton Trans. 1994, 1251.
(28) Dilworth, J. R.; Jobanputra, P.; Thompson, R. M.; Archer, C. M.; Kelly,
J. D.; Hiller, W. Z. Naturforsch. 1991, 46b, 449.
(30) Chatt, J.; Dilworth, J. R.; Leigh, G. J.; Gupta, V. D. J. Chem. Soc. A
1971, 2631.
(31) Dilworth, J. R.; Lewis, J. S.; Miller, J. R.; Zheng, Y. J. Chem. Soc.,
Dalton Trans. 1995, 1357.
(32) Rouschias, G. Chem. ReV. 1974, 74, 531.
(33) Nicholson, T.; Davison, A.; Jones, A. Inorg. Chim. Acta 1991, 187,
51.
(29) Rochon, F. D.; Melanson, R.; Kong, P. Inorg. Chem. 1995, 34, 2273.
1596 Inorganic Chemistry, Vol. 41, No. 6, 2002

Chelated Hydrazido(3-)rhenium(V) Complexes
Table 3. Relevant Structural Parameters for Selected η2-Hydrazido(3-)- and η1-Hydrazido(3-)-Containing Technetium and Rhenium Complexes
compd
M
η2-N-N--, Å
M
η2-X-C-, Å (X, anchor donor)
M
η1-N,N-R, Å
X-M-N, deg
ref
[Tc(η2-NkN)Cl2(PPh3)2]a
1.77(1)
1.77(1)
1.763(5)
1.780(7)
2.15(1) (N)
2.12(1) (O)
2.538(2) (S)
2.492(2) (P)
69.8(4)
71.0(5)
72.9(2)
75.2(2)
73(1)
23
[Re(η2-NkO)Cl2(PPh3)2]b
24
this work
25
this work
26
[Re(η2-NkS)(L1)(PPh3)], 1c
[Re(η2-NkP)Cl2(η2-PkNH)]d
[Re(η2-NkS)Cl2(PPh3)2], 3c
[Tc(η2-HNkN)(η1-NNR)(Sk N)(SR)]e
[Re(η2-HNkN)(η1-NNR)(SkN)(SR)]e
[Tc(η1-NNPh-Cl)(salen)(PPh3)]f
[Tc(η1-NNPh-Cl)(dmdc)2(PPh3)]g
[Tc(η1-NNPh)Br2(PMe2Ph)3]h
1.985(9)
1.956(6)
2.150(7) (N)
2.127(5) (N)
1.767(9)
1.766(6)
1.764(8)
1.763(3)
1.77(1)
74.5(4)
73.3(3)
26
27
28
29
b
c
d
e
a (η2-NkN) ) η2-hydralazine (C8H5N4). (η2-NkO) ) η2-acetylhydrazide. (η2-NkS) ) L4. (η2-NkP) ) η2-(2-diphenylphosphino)benzeneamide. (η2-
HNkN) ) η2-hydrazinonicotinamide; (η1-NNR) ) η1-hydrazinonicotinamide; (SkN) ) η2-pyridine-2-thiolate; (SR) ) η1-pyridine-2-thiolate. (η1-NNPh-
f
Cl) ) η1-p-Cl-phenyldiazenido; salen ) N,N′-ethylenebis(salicylideneimine). dmdc ) dimethyldithiocarbamate. (η1-NNPh) ) η1-phenyldiazenido.
g
h
Scheme 3
Scheme 4
(N,O-hydrazine) succinic acid in the kit formulation, initially
justified by experimental evidence only, has now a chemical
explanation. This study demonstrates that the use of N,S-
dithiocarbazic ligands favors the obtainment of substitution-
inert intermediates such as chelated hydrazido-Re(V) spe-
cies. In the case of technetium, similar adducts likely make
more difficult the clean formation of the [99mTc(N)] group.
On the contrary, the hemilability of the N,O-succinic chelate,
followed by rapid N-N cleavage, appears to be the key
factor for the easy formation of the [99mTc(N)] moiety starting
from pertechnetate.
Supporting Information Available: X-ray cystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org. Supplementary data for complexes
1 and 3 have been deposited at the Cambridge Crystallographic
Data Centre. Copies of this information are available free of charge
on request from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, U.K. (fax +44-1223-336033; e-mail deposit@ccdc.
cam.ac.uk or www.ccdc.cam.ac.uk), quoting the deposition numbers
CCDC 140023 and 172547 for complex 1 and 3, respectively.
promoting the clean formation of the [99mTc(N)] group. In
this connection, the substitution of the N,S-dithiocarbazic acid
(utilized in early preparations as the nitrogen source for the
formation of the [99mTc(N)] core at nca level) with the bis-
IC0110979
Inorganic Chemistry, Vol. 41, No. 6, 2002 1597