Rhenium and technetium complexes with N,N-dialkyl-N′-benzoylthioureas

Article abstract of DOI:10.1021/ic070323x

N,N-Dialkyl-N′-benzoylthioureas, HR¹R²btu, react under single deprotonation and form air-stable chelate complexes with common rhenium or technetium complexes such as (NBu₄)[MOCl ₄] (M = Re, Tc) or [ReOCl₃(PPh₃)₂]. Compositions and molecular structures of the products are strongly dependent on the precursors used and the reaction conditions applied. Reactions with [ReOCl₃(PPh₃)₂] in CH₂Cl₂ give complexes of the general formula [ReOCl₂(R¹R ²btu)(PPh₃)] (3), with the benzoyl oxygen atom of the chelating benzoylthiourea being trans to the oxo ligand, and/or Re(III) complexes of the composition [ReCl₂(R¹R ²btu)(PPh₃)₂] (4) with the PPh₃ ligands in trans positions to each other. In polar solvents such as MeOH, EtOH or acetone, corresponding reactions without addition of a supporting base only result in intractable brown solutions, from which no crystalline complexes could be isolated. The addition of NEt₃, however, allows the isolation of the bis-chelates [ReOCl(R¹R²btu)₂] (1) in good yields. In this type of complex, one of the chelating R¹R ²btu^- ligands coordinates equatorially, while the second occupies the position trans to the oxo ligand with its oxygen atom. The latter compounds can also be prepared from (NBu₄)[ReOCl₄] in MeOH when no base is added, while the addition of NEt₃ results in the formation of [ReO(OMe)(R¹R²btu)₂] (5) complexes with the methoxo ligand trans to O^2-. Compounds of the type 5 can alternatively be prepared by heating 1 in MeOH with addition of NEt₃. A reversible conversion of 5 into oxo-bridged dimers of the composition [{ReO(R¹R¹btu)₂}₂O] (6) is observed in water-containing solvents. Starting from (NBu₄)[TcOCl ₄], a series of technetium complexes of the type [TcOCl(R ¹R²btu)₂] (2) could be prepared. The structures of such compounds are similar to those of the rhenium analogues 1: Reduction of 2 with PPh₃ in CH₂Cl₂ gives Tc(III) complexes of the composition [TcCl(R¹R²btu)₂(PPh ₃)] (7) having the chloro and PPh₃ ligands in cis positions. When this reaction is performed in the presence of excess chelating ligand, the Tc(III) tris-chelates [Tc(R¹R²btu) ₃] (8) are formed.

Full text of DOI:10.1021/ic070323x

Inorg. Chem. 2007, 46, 5310−5319
Rhenium and Technetium Complexes with
N,N-Dialkyl-N -benzoylthioureas
′
Nguyen Hung Huy and Ulrich Abram*
Institute of Chemistry and Biochemistry, Freie UniVersita¨t Berlin, Fabeckstrasse 34-36,
D-14195 Berlin, Germany
Received February 19, 2007
N,N-Dialkyl-N
′
-benzoylthioureas, HR1R2btu, react under single deprotonation and form air-stable chelate complexes
Re, Tc) or [ReOCl3(PPh3)2].
with common rhenium or technetium complexes such as (NBu4)[MOCl4] (M
)
Compositions and molecular structures of the products are strongly dependent on the precursors used and the
reaction conditions applied. Reactions with [ReOCl3(PPh3)2] in CH2Cl2 give complexes of the general formula
[ReOCl2(R1R2btu)(PPh3)] (3), with the benzoyl oxygen atom of the chelating benzoylthiourea being trans to the oxo
ligand, and/or Re(III) complexes of the composition [ReCl2(R1R2btu)(PPh3)2] (4) with the PPh3 ligands in trans
positions to each other. In polar solvents such as MeOH, EtOH or acetone, corresponding reactions without addition
of a supporting base only result in intractable brown solutions, from which no crystalline complexes could be
isolated. The addition of NEt3, however, allows the isolation of the bis-chelates [ReOCl(R1R2btu)2] (1) in good
yields. In this type of complex, one of the chelating R1R2btu- ligands coordinates equatorially, while the second
occupies the position trans to the oxo ligand with its oxygen atom. The latter compounds can also be prepared
from (NBu4)[ReOCl4] in MeOH when no base is added, while the addition of NEt3 results in the formation of
[ReO(OMe)(R1R2btu)2] (5) complexes with the methoxo ligand trans to O2-. Compounds of the type 5 can alternatively
be prepared by heating 1 in MeOH with addition of NEt3. A reversible conversion of 5 into oxo-bridged dimers of
the composition [{ }2O] (6) is observed in water-containing solvents. Starting from (NBu4)[TcOCl4],
ReO(R1R1btu)2
a series of technetium complexes of the type [TcOCl(R1R2btu)2] (2) could be prepared. The structures of such
compounds are similar to those of the rhenium analogues 1. Reduction of 2 with PPh3 in CH2Cl2 gives Tc(III)
complexes of the composition [TcCl(R1R2btu)2(PPh3)] (7) having the chloro and PPh3 ligands in cis positions. When
this reaction is performed in the presence of excess chelating ligand, the Tc(III) tris-chelates [Tc(R1R2btu)3] (8) are
formed.
Introduction
in some Ag(I) and Au(I) compounds and in a Pt(II) complex,3
while examples of transition metal complexes with ben-
zoylthioureas as bridging ligands are very rare.4,5 The
structural chemistry of square-planar bis-chelates of ben-
zoylthioureas with d8 or d9 ions such as Ni(II), Pd(II), Pt(II),
or Cu(II) is dominated by cis isomers,2c,6 and only a few
N,N-Dialkyl-N′-benzoylthioureas, HR1R2btu, are known to
form stable complexes with a large number of transition
metals.1 They are versatile ligands with various coordination
modes. In the majority of their structurally characterized
complexes, they act as bidentate O,S-monoanionic ligands.2
Coordination as neutral, monodentate S-ligands are found
(2) (a) Westra, A. N.; Bourne, S. A.; Esterhuysen, C.; Koch, K. R. Dalton
Trans. 2005, 2162. (b) Zhou, W.; Wen, Y.; Qiu, L.; Zhang, Y.; Yu,
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S.; Kirmse, R. Z. Anorg. Allg. Chem. 2004, 630, 1437. (d) Egan, T.
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* To whom correspondence should be addressed. E-mail: abram@
chemie.fu-berlin.de. Phone: (#49) 30 83854002. Fax: (#49) 30 83852676.
(1) (a) Beyer. L.; Hoyer, E.; Liebscher, J.; Hartmann, H. Z. Chem. 1981,
21, 228. (b) Koch, K. R. Coord. Chem. ReV. 2001, 216-217, 473. (c)
Beyer, L.; Hoyer, E.; Hennig, H.; Kirmse, R.; Hartmann, H.; Liebscher,
J. J. Prakt. Chem. 1975, 317, 829. (d) Schmidt, S.; Dietze, F.; Hoyer,
E. Z. Anorg. Allg. Chem. 1991, 603, 33. (e) Mohamadou, A.;
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5310 Inorganic Chemistry, Vol. 46, No. 13, 2007
10.1021/ic070323x CCC: $37.00
© 2007 American Chemical Society
Published on Web 05/08/2007

Rhenium and Technetium Complexes
crystal structures of trans-isomers have been elucidated.7
Photochemical cis/trans isomerization has been studied
recently on Pt(II) and Pd(II) complexes, showing that the
trans isomers are thermodynamically unstable and readily
re-form the cis compounds.8 Exclusively facial coordination
is observed for tris-chelates of benzoylthioureas with Ru(III),
Rh(III), and Co(III).9
Surprisingly less is known about rhenium and technetium
complexes with N,N-dialkyl-N′-benzoylthioureas. There are
only two structurally well characterized rhenium com-
pounds: the neutral oxorhenium(V) complex [ReOCl(Et2-
btu)2] (1c) and the tricarbonylrhenium(I) compound [Re-
(CO)3Br(HEt2btu)2] (9).10,11 The latter one is the only example
where chelate formation is observed with a neutral HR2btu
ligand. Only one early report describes an synthetic approach
to benzoylthioureato complexes of technetium by the reduc-
tion of pertechnetate in the presence of the ligands, and the
formation of neutral [Tc(R2btu)3] complexes was suggested
on the basis of spectroscopic data.12 This lack of knowledge
is particularly surprising in light of numerous thiourea
complexes of rhenium and technetium, which have been
studied extensively and found use as precursors for the
synthesis of low-valent Re and Tc complexes.13
Our interests in technetium and rhenium complexes with
benzoylthioureas mainly are due to the flexibility of this class
of ligands, which allows a variety of modifications in the
periphery of their chelating system. The compounds are
commonly prepared in a one-pot synthesis from benzoyl
chloride, (NH4)SCN, and (mainly secondary) amines (eq 1).
(4) (a) Che, D.-J.; Li, G.; Yao, X.-L.; Yu-Zhu; Zhou, D.-P. J. Chem. Soc.,
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(5) Kemp, G.; Roodt, A.; Purcell, W.; Koch, K. R. J. Chem. Soc., Dalton
Trans. 1997, 4481.
This approach allows substitutions at the phenyl ring of the
benzoyl unit as well as modifications of the amino site.
Particularly the latter one gives access to novel tripodal ligand
systems with functionalized amino substituents.
In the present Article, we study some basic reaction
patterns of the bidentate chelators with common rhenium
and technetium precursors such as [ReOCl3(PPh3)2] or
(NBu4)[MOCl4] complexes (M) Re, Tc) including the X-ray
structures of the products. Chart 1 illustrates the ligands
which were used throughout the experiments.
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Sanchez, A.; Manzano, J. L.; Monte, E.; Rodriguez-Fernandez, E.;
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Structures 2004, 219, 409. (d) Arslan, H.; Vanderveer, D.; Emen, F.;
Ku¨lcu¨, N. Z. Kristallogr.sNew Cryst. Struct. 2003, 218, 479. (e) Fitzl,
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Ku¨lcu¨, N.; Flo¨rke, U. Transition Met. Chem. (Dordrecht, Neth.) 2003,
28, 816. (i) Schro¨der, U.; Richter, R.; Anguio-Conejo, J.; Lino-
Pacheco, M.; Gullien, A. Z. Anorg. Allg. Chem. 2003, 629, 1081. (j)
Knuutila, P.; Knuutila, H.; Hennig, H.; Beyer, L. Acta Chem. Scand.
1982, A36, 541. (k) Dominguez, M.; Antico, E.; Aguirre, A.; Garcia-
Granda, S.; Salvado, V. Polyhedron 2002, 21, 1429. (l) Richter, R.;
Hartung, J.; Beyer, L.; Langer, V. Z. Anorg. Allg. Chem. 1993, 619,
1295. (m) Binzet, G.; Flo¨rke, U.; Ku¨lcu¨, N.; Arslan, H. Acta
Crystallogr. 2003, E59, m705. (n) Bailey, R. A.; Rothaupt, K. L.;
Kullnig, R. K. Inorg. Chim. Acta 1988, 147, 233. (o) Richter, R.;
Beyer, L.; Kaiser, J. Z. Anorg. Allg. Chem. 1980, 461, 67. (p) Bensch,
W.; Schuster M. Z. Kristallogr. 1995, 210, 68. (q) Hernandez, W.;
Spondine, E.; Munoz, J. C.; Beyer, L.; Schro¨der, U.; Ferreira, J.;
Pavani, M. Bioinorg. Chem. Appl. 2003, 1, 271. (r) Avsar, G.; Arslan,
H.; Haupt, H.-J.; Ku¨lcu¨, N. Turk. J. Chem. 2003, 27, 281. (s) Ku¨lcu¨,
N.; Flo¨rke, U.; Arslan, H. Turk. J. Chem. 2005, 29, 1. (t) Comejo, J.
A.; Ayala, K.; Richter, R.; Bohlig, H.; Hennig, L.; Beyer, L. Z. Anorg.
Allg. Chem. 2005, 631, 3030. (u) Hernandez, W.; Spodine, E.; Beyer,
L.; Schro¨der, U.; Richter, R.; Ferreira, J.; Pavani, M. Bioinorg. Chem.
Appl. 2005, 3, 299.
Experimental Section
Materials. All reagents used in this study were reagent grade
and were used without further purification. Solvents were dried
and used freshly distilled unless otherwise stated. (NBu4)[MOCl4]13i
and [ReOCl3(PPh3)2]14 were prepared by standard procedures. The
synthesis of HR1R2btu ligands was performed by the standard
procedure of Beyer et al.15
Radiation Precautions. 99Tc is a weak â--emitter. All manipu-
lations with this isotope were performed in a laboratory approved
for the handling of radioactive materials. Normal glassware provides
adequate protection against the low-energy â emission of the
technetium compounds. Secondary X-rays (bremsstrahlung) play
an important role only when larger amounts of 99Tc are used.
(7) (a) Koch, K. R.; du Toit, J.; Caira, M. R.; Sacht, C. J. Chem. Soc.,
Dalton Trans. 1994, 785. (b) Hernandez, W.; Spodine, E.; Vega, A.;
Richter, R.; Griebel, J.; Kirmse, R.; Schro¨der, U.; Beyer, L. Z. Anorg.
Allg. Chem. 2004, 630, 1381. (c) Arslan, H.; Flo¨rke, U.; Ku¨lcu¨, N.;
Emen, M. F. J. Coord. Chem. 2006, 59, 223.
(8) Hanekom, D.; McKenzie, J. M.; Derix, N. M.; Koch, K. R. Chem.
Commun. 2005, 767.
(9) (a) Sieler, J.; Richter, R.; Hoyer, E.; Beyer, L.; Lindqvist, O.; Anderson,
L. Z. Anorg. Allg. Chem. 1990, 580, 167. (b) Bensch, W.; Schuster,
M. Z. Anorg. Allg. Chem. 1992, 615, 93. (c) Bensch, W.; Schuster,
M. Z. Kristallogr. 1995, 210, 68. (d) Weiqun, Z.; Wen, Y.; Liqun,
X.; Xianchen, C. J. Inorg. Biochem. 2005, 99, 1314. (e) Weiqun, Z.;
Wen, Y.; Lihua, Q.; Yong, Z.; Zhengfeng, Y. J. Mol. Struct., 2005,
749, 89.
(12) Abram, U.; Abram, S. Z. Chem. 1983, 23, 228.
(13) (a) Abrams, M. J.; Davison, A.; Faggiani, R.; Jones, A. G.; Lock, C.
J. L. Inorg. Chem. 1984, 23, 3284. (b) Abrams, M. J.; Brenner, D.;
Davison, A.; Jones, A. G. Inorg. Chim. Acta 1983, 77, L127. (c) Otero,
L.; Benitez, J.; Gambino, D.; Kremer, E.; Baran, E. J.; Mombru, A.;
Suescun, L.; Mariezcurrena, R. Z. Anorg. Allg. Chem. 1999, 625, 1866.
(d) Gambino, D.; Benitez, J.; Otero, L.; Kremer, E.; Baran, E. J.; Piro,
O. E. Polyhedron, 1999, 18, 2099. (e) Rochon, F. D.; Melanson, R.;
Kong, P. C. Acta Crystallogr. 1990, C46, 571. (f) Gambino, D.; Otero,
L.; Kremer, E.; Piro, O. E.; Gastellano, E. E. Polyhedron 1997, 16,
2263. (g) Smith, J.; Purcell, W.; Lamprecht, G. J.; Roodt, A.
Polyhedron 1996, 15, 1389. (h) Rey, A.; Teran, M.; Kremer, C.;
Molina, S.; Gambino, D.; Kremer, E.; Leon, A. J. Radioanal. Nucl.
Chem. 1996, 214, 499. (i) Alberto, R.; Schibli, R.; Egli, A.; Schubiger,
P. A.; Herrmann, W. A.; Artus, G.; Abram, U.; Kaden, T. A. J.
Organomet. Chem. 1995, 217, 492.
(10) Dilworth, J. R.; Lewis, J. S.; Miller, J. R.; Zheng, Y. Polyhedron 1993,
12, 221.
(11) Abram, U.; Abram, S.; Alberto, R.; Schibli, R. Inorg. Chim. Acta 1996,
248, 193.
(14) Johnson, N. P.; Lock, C. J. L.; Wilkinson, G. Inorg. Synth. 1967, 145.
(15) Hartmann, H.; Beyer, L.; Hoyer, E. J. Prakt. Chem. 1978, 320, 647.
Inorganic Chemistry, Vol. 46, No. 13, 2007 5311

Huy and Abram
Data for 1c (R1 ) R2 ) Et). Yield: 30% (21 mg) for method
1; 91% (64 mg) for method 2. Anal. Calcd for C24H30ClN4O3S2-
Re: C, 40.70; H, 4.24; N, 7.91; S, 9.04%. Found: C, 40.31; H,
4.19; N, 7.56; S, 8.81%. IR (cm-1): 3055(w), 2977(w), 2931(w),
2870(w), 1496(vs), 1419(vs), 1358(vs), 1250(m), 1173(w), 1141(m),
1072(m), 980(s), 887(w), 825(w), 794(w), 702(s). 1H NMR (CDCl3;
δ, ppm): 1.27-1.31 (m, 6H, CH3), 1.39-1.46 (m, 6H, CH3), 3.78-
3.84 (m, 3H, CH2), 3.93-3.99 (m, 2H, CH2), 4.17-4.30 (m, 3H,
CH2), 6.92 (t, 2H, J ) 7.8 Hz, Ph, m-H), 7.36-7.45 (m, 6H, Ph),
8.36 (d, 2H, J ) 7.4 Hz, Ph, o-H). 13C NMR (CDCl3; δ, ppm):
13.13, 13.47, 13.59, and 13.67 (CH3), 46.79, 47.06, 47.56, and 47.84
(CH2), 127.49, 128.13, 129.44, 131.38, 131.79, 132.98, 134.40, and
134.94 (Ph), 171.63 (CdS), 174.04 (CdS), 183.06 (CdO), 190.80
(CdO).
Chart 1. N,N-Dialkyl-N′-benzoylthioureas Used in This Work
Infrared spectra were measured as KBr pellets on a Shimadzu
FTIR spectrometer between 400 and 4000 cm-1. FAB+ mass spectra
were recorded with a TSQ (Finnigan) instrument using a nitrobenzyl
alcohol matrix (results are given in the form: m/z, assignment).
Elemental analyses of carbon, hydrogen, nitrogen, and sulfur were
determined using a Heraeus vario EL elemental analyzer. The
technetium analyses were done by liquid scintillation counting.
NMR spectra were taken with a JEOL 400 MHz multinuclear
spectrometer.
[TcOCl(R1R2btu)2] (2). The technetium complexes were pre-
pared from (NBu4)[TcOCl4] by the procedure described above as
method 2 for their rhenium analogues.
Data for 2a (R1 ) R2 ) Ph). Yield: 70% (57 mg). Anal. Calcd
for C40H30ClN4O3S2Tc: Tc, 12.18%. Found: 12.0%. IR (cm-1):
3058(w), 1501(s), 1485(vs), 1450(vs), 1429(vs), 1389(vs), 1261(s),
1172(m), 1107(m), 1072(w), 1022(w), 956(s), 871(w), 798(m),
[ReOCl(R1R2btu)2] (1), Method 1. HR1R2btu (0.22 mmol) in
3 mL of acetone was added to a stirred suspension of [ReOCl3-
(PPh3)2] (83 mg, 0.1 mmol) in 3 mL of acetone. Three drops of
Et3N were added, and stirring was continued for 30 min at room
temperature, whereupon the precursor complex completely dissolved
and the color of the reaction mixture changed from yellow-green
to deep green. After the mixture was cooled to 0 °C, a colorless
precipitate of Et3N‚HCl was filtered off, and the solvent was
removed under reduced pressure. Released PPh3, excess ligand, and
small amounts of other, unidentified compounds were removed by
washing the resulting residue with 2 mL of cold acetone, and the
product remained as an analytically pure, green powder. The
separation of the complex can alternatively be done by column
chromatography. For this, the crude reaction mixture is loaded onto
a silica gel column. The first, yellow fraction of triphenylphosphine
and unidentified compounds is eluted with n-hexane/acetone (1/
1), while the second green fraction containing the complex is eluted
with acetone.
Method 2. A solution of (NBu4)[ReOCl4] (58 mg, 0.1 mmol) in
MeOH (2 mL) was added dropwise while stirring to a solution of
0.22 mmol of the ligand dissolved in 3 mL of MeOH. The color of
the solution immediately turned to deep green, and a green
precipitate deposited within 30 min. The green powder was filtered
off, washed with cold methanol, and recrystallized from CH2Cl2/
acetone.
Data for 1a (R1 ) R2 ) Ph). Yield: 45% (41 mg) for method
1; 78% (70 mg) for method 2. Anal. Calcd for C40H30ClN4O3S2-
Re: C, 53.35; H, 3.33; N, 6.22; S, 7.11%. Found: C, 53.01; H,
3.10; N, 6.14; S, 7.01%. IR (cm-1): 3040(w), 1485(vs), 1450(vs),
1427(vs), 1380(vs), 1261(m), 1172(m), 1107(w), 1072(w), 975(s),
871(w), 798(w), 756(m), 698(s). 1H NMR (CDCl3; δ, ppm): 7.3-
8.0 (m, Ph). 13C NMR (CDCl3; δ, ppm): 126-144 (Ph), 174.13
(CdS), 176.04 (CdS), 186.40 (CdO), 194.14 (CdO). FAB+ MS
(m/z): 865, [M - Cl]+.
1
756(m), 698(s). H NMR (CDCl3; δ, ppm): 8.06-7.09 (m, Ph).
Data for 2b (R1 ) Ph, R2 ) Me). Yield: 74% (51 mg). Anal.
Calcd for C30H26ClN4O3S2Tc: Tc, 14.37%. Found: 14.1%. IR
(cm-1): 3050(w), 1473(vs), 1423(vs), 1381(vs), 1269(m), 1174(w),
1
1107(w), 1072(w), 1022(w), 964(s), 898(m), 795(w), 698(s). H
NMR (CDCl3; δ, ppm): 3.8-4.1 (br, 6H, CH3), 7.1-8.0 (m, 20H,
Ph).
Single crystals suitable for X-ray diffraction were obtained by
slow evaporation of CH2Cl2/n-hexane solutions of the complexes.
[ReOCl2(PPh3)(R1R2btu)] (3) and [ReCl2(PPh3)2(R1R2btu)]
(4). Solid [ReOCl3(PPh3)2] (83 mg, 0.1 mmol) was added to a stirred
solution of HR1R1btu (0.2 mmol) in CH2Cl2 (5 mL). The mixture
was stirred at room temperature for 15 min. This resulted in a
complete dissolution of [ReOCl3(PPh3)2] and the formation of a
green solution. The solvent was removed under vacuum, and the
residue was redissolved in 3 mL of acetone. The green-yellow
solution slowly changed its color to orange-red. It contained a
mixture of the complexes 3 and 4.
In the case of HPh2btu, large yellow-orange crystals of 3a and
red plates of 4a (both types of X-ray quality) deposited together
from this solution upon standing for 2 days and were separated
mechanically.
Nitromethane (3 mL) was used for the crystallization of the
i-Pr2btu- chelates 3d and 4d. Large yellow-green plates of 3d
deposited from such solutions upon standing overnight at room
temperature, while small red crystals of 4d were obtained by slow
evaporation of the resulting filtrate in a refrigerator.
Yellow-green crystals of 3e (the morphbtu- derivative) were
isolated by slow evaporation of the acetone solution described
above. All attempts to isolate the corresponding compound 4e from
the remaining solution in crystalline form failed, and only oily,
impure products could be recovered.
Data for 1b (R1 ) Ph, R2 ) Me). Yield: 44% (34 mg) for
method 1; 93% (72 mg) for method 2. Anal. Calcd for C30H26-
ClN4O3S2Re: C, 46.41; H, 3.36; N, 7.22; S, 8.25%. Found: C,
46.33; H, 2.95; N, 7.21; S, 8.41%. IR (cm-1): 3035(w), 1473(vs),
1423(vs), 1377(vs), 1269(m), 1172(w), 1103(m), 1072(w), 984(s),
898(m), 798(w), 698(s), 547(s). 1H NMR (CDCl3; δ, ppm): 3.87,
3.91, 3.94, 3.96, 3.98, 4.02, 4.13 (7 singlets, 6H, CH3), 7.1-8.5
(m, 20H, Ph). 13C NMR (CDCl3; δ, ppm): 42.24 (CH3), 42.76
(CH3), 126-144 (Ph), 173.53 (CdS), 175.40 (CdS), 185.73
(CdO), 194.11 (CdO). FAB+ MS (m/z): 741, [M - Cl]+.
Single crystals suitable for X-ray analysis were obtained by slow
evaporation of CH2Cl2/acetone or CH2Cl2/n-hexane solutions.
Data for 3a (R1 ) R2 ) Ph). Yield: 26% (23 mg). Anal. Cald.
for C38H30Cl2N2O2PSRe: C, 52.64; H, 3.48; N, 3.23; S, 3.69%.
Found: C, 51.70; H, 3.35; N, 3.41; S, 3.82%. IR (cm-1): 3055(w),
1469(vs), 1439(s),1415(s) 1389(vs), 1272(w), 1095(m) 976(s),
748(m), 694(m), 529(m). 1H NMR (CDCl3; δ, ppm): 7.3-8.1 (m,
Ph). 13C NMR (CDCl3; δ, ppm): 126-137 (Ph), 172.01 (CdS),
191.23 (CdO). FAB+ MS (m/z): 948, [M(NBA) - 2Cl]+; 866,
[M]+; 831, [M - Cl]+.
Data for 4a (R1 ) R2 ) Ph). Yield: 41% (46 mg). Anal. Calcd
for C56H45Cl2N2OP2SRe: C, 60.42; H, 4.05; N, 2.52; S, 2.88%.
5312 Inorganic Chemistry, Vol. 46, No. 13, 2007

Rhenium and Technetium Complexes
Found: C, 59.13; H, 4.01; N, 2.39; S, 3.04%. IR (cm-1): 3059(m),
1481(s), 1465(s), 1434(vs), 1365(vs), 1261(m), 1091(m), 1026(w),
744(m), 694(vs), 513(vs). FAB+ MS (m/z): 850, [M - PPh3]+;
553, [ReLCl]+.
obtained by slow evaporation of a solution of 6c in CH2Cl2/MeCN.
Yield: 91% (31 mg). Anal. Calcd for C48H60N8O7S4Re2: C, 42.30;
H, 4.41; N, 8.23; S, 9.41%. Found: C, 42.12; H, 4.42; N, 8.30; S,
9.43%. IR (cm-1): 3054(w), 2977(w), 2924(w), 2870(w), 1497(vs),
1423(vs), 1354(s), 1250(m), 1204(m), 1168(w), 1138(m), 1076(w),
953(w), 934(w), 891(m), 725(s), 665(s), 547(w). 1H NMR (CDCl3;
δ, ppm): 1.27 (t, J ) 7.1 Hz, 6H, CH3), 1.28 (t, J ) 7.1 Hz, 6H,
CH3), 3.13 (q, J ) 6.8 Hz, 2H, CH2), 3.73-3.81 (m, 6H, CH2),
7.33 (t, J ) 7.5 Hz, 4H, Ph, m-H), 7.42 (t, J ) 7.3 Hz, 2H, Ph,
p-H), 8.25 (d, J ) 7.4 Hz, 4H, Ph, o-H). 13C NMR (CDCl3; δ,
ppm): 13.20, 13.36 (CH3), 45.74, 47.25 (CH2), 127.47, 130.65,
131.33, and 138.10 (Ph), 172.16 (CdS), 182.12 (CdO). FAB+ MS
(m/z): 1363, [M + H]+; 690, [ReO2L2 + H]+; 673, [ReOL2]+; 454,
[ReO2L]+.
[TcCl(PPh3)(Ph2btu)2] 7a. Compound 2a (40 mg, 0.05 mmol)
was dissolved in 5 mL of CH2Cl2, and PPh3 (26 mg, 0.1 mmol)
was added. The solution was stirred at room temperature for 3 h.
During this time, the color of the solution changed from yellow-
brown to deep red. The volume of the solvent was reduced to 2
mL, and 1 mL of MeOH was added. This final solution was slowly
evaporated at room temperature resulting in big red crystals of 7a,
which were suitable for X-ray diffraction. Yield: 64% (35 mg).
IR (cm-1): 3055(w), 1488(vs), 1435(vs), 1384(vs), 1311(vs),
1176(s), 1118(m), 1011(w), 748(m), 693(s).
[Tc(Ph2btu)3] 8a. HPh2btu (33 mg, 0.1 mmol) and PPh3 (26 mg,
0.1 mmol) were added to a solution of 2a (40 mg, 0.05 mmol) in
5 mL of CHCl3, and the mixture was stirred at room temperature
for 3 h. The color changed from yellow to deep red, and an almost
black solid was obtained after removal of the solvent in vacuum.
The residue was redissolved in a CH2Cl2/MeOH mixture (1/1), and
dark red crystals were deposited after slow evaporation of the
solvent. Yield: 75% (42 mg). Anal. Calcd for C61H49N6O4S3Tc:
Tc, 8.80%. Found: 7.8%. IR (cm-1): 3050(w), 1479(vs), 1419(vs),
1366(vs), 1257(s), 1172(w), 1111(w), 1072(w), 1026(w), 756(m),
698(s).
X-ray Crystallography. The intensities for the X-ray structure
determinations were collected on a STOE IPDS 2T instrument with
Mo KR radiation (λ ) 0.710 73 Å). Standard procedures were
applied for data reduction and absorption correction. Structure
solution and refinement were performed with SHELXS97 and
SHELXL97.16 Hydrogen atom positions were calculated for ideal-
ized positions. More details on data collections and structure
calculations are contained in Table 1.
Data for 3d (R1 ) R2 ) i-Pr). Yield: 55% (44 mg). Anal. Calcd
for C32H24Cl2N2O2PSRe: C, 48.11; H, 4.26; N, 3.51; S, 4.01%.
Found: C, 48.02; H, 4.05; N, 3.36; S, 4.15%. IR (cm-1): 3055(w),
2977(w), 2933(w), 1481(vs), 1435(vs), 1396(s), 1373(vs), 1307(m),
1265(m), 1145(m), 1096(s), 976(s), 752(s), 694(vs), 509(s). 1H
NMR (CDCl3; δ, ppm): 1.11-1.39 (m, 12H, Me), 3.64-3.70 (m,
2H, CH), 7.33-7.66 (m, 20H, Ph). 13C NMR (CDCl3; δ, ppm):
19.26, 19.96 (CH3), 67.75, 68.01 (CH), 127-134 (Ph), 170.27
(CdS), 190.43 (CdO). MS (m/z): 881, [M(NBA) - 2Cl]+; 764,
[M - Cl + H]+; 729, [M - 2Cl + H]+; 466, [ReOL]+.
Data for 4d (R1 ) R2) i-Pr). Yield: 18% (19 mg) Anal. Calcd
for C50H49Cl2N2OP2SRe: C, 57.46; H, 4.69; N, 2.68; S, 3.06%.
Found: C, 57.03; H, 4.31; N, 2.82; S, 3.34%. IR (cm-1): 3055(m),
2970(w), 2927(w), 1477(s), 1458(s), 1434(vs), 1400(s), 1373(s),
1338(s), 1261(m), 1195(w), 1149(m), 1091(m), 1026(w), 744(m),
694(vs), 516(vs). FAB+ MS (m/z): 1044, [M]+; 1009, [M - Cl]+;
782, [M - PPh3]+; 747, [M - Cl - PPh3]+; 712, [ReL(PPh3)]+;
450, [ReL]+.
Data for 3e (R1R2 ) Morph). Yield: 54% (42 mg). Anal. Calcd
for C30H28Cl2N2O3PSRe: C, 45.91; H, 3.57; N, 3.57; S, 4.08%.
Found: C, 46.00; H, 3.45; N, 3.47; S, 4.12%. IR (cm-1): 3055(w),
1
2923(w), 2862(w), 1481(vs), 972(s), 748(m), 694(s), 528(s). H
NMR (CDCl3; δ, ppm): 7.1-7.8 (m, 20H, Ph), 3.9-4.9 (m, 8H,
CH2). 13C NMR (CDCl3; δ, ppm): 49.68, 51.41, 67.00, 67.48 (CH2),
127-135 (Ph), 172.67 (CdS), 190.66 (CdO). FAB+ MS (m/z):
866, [M(NBA) - 2Cl]+; 784, [M]+; 749, [M - Cl]+; 714, [M -
2Cl]+.
[ReO(OMe)(Et2btu)2] 5c, Method 1. HEt2btu (52 mg, 0.22
mmol) dissolved in 3 mL of MeOH was added to a solution of
(NBu4)[ReOCl4] (58 mg, 0.1 mmol) in MeOH (2 mL). The color
of the solution immediately turned to deep green. After the addition
of three drops of Et3N and heating, the color of the reaction mixture
turned to red and a purple precipitate began to deposit. The mixture
was refluxed for 30 min then cooled to 0 °C. The product was
filtered off, washed with cold MeOH, and recrystallized from
CH2Cl2/MeOH. 5c can also be synthesized from [ReOCl3(PPh3)2]
applying the same reaction conditions.
Method 2. 1c (71 mg, 0.1 mmol) was suspended in 3 mL of
MeOH, and three drops of Et3N were added. The mixture was
heated on reflux for 15 min, whereupon its color changed from
green to red. After the mixture was cooled to 0 °C, a purple
precipitate of 5c was filtered off, washed with MeOH, and dried
under vacuum. Yield: 84% (59 mg) for method 1; 90% (63 mg)
for method 2. Anal. Calcd for C25H33N4O4S2Re: C, 42.70; H, 4.69;
N, 7.96; S, 9.10%. Found: C, 42.67; H, 4.68; N, 8.03; S, 9.23%.
IR (cm-1): 3053(w), 2977(m), 2931(m), 2808(m), 1512(vs),
1500(vs), 1419(vs), 1350(s), 1305(m), 1249(m), 1203(m), 1172(m),
1138(m), 1091(s), 941(s), 887(m), 713(s), 671(m), 493(m). 1H NMR
(CDCl3; δ, ppm): 1.34 (t, J ) 7.2 Hz, 6H, CH3), 1.28 (t, J ) 7.2
Hz, 6H, CH3), 3.17 (s, 3H, OCH3), 3.79-4.01(m, 8 H, CH2), 7.40-
746 (m, 6H, Ph, m-H and p-H), 8.41(d, J ) 6.5 Hz, 4H, Ph, o-H).
13C NMR (CDCl3; δ, ppm): 12.96, 13.19 (CH3), 46.38, 47.44
(CH2), 57.37(OCH3), 127.98, 130.23, 131.96, and 136.96 (Ph),
172.65(CdS), 180.32(CdO). FAB+ MS (m/z): 674, [M - OMe
+ H]+; 470, [M - L + H]+; 454, [ReO2L]+; 438, [ReOL]+.
[{ReO(Et2btu)2}2O] 6c. Compound 5e (35 mg, 0.05 mmol) was
dissolved in 5 mL of hot MeCN. The mixture was refluxed for 5
min and then slowly cooled to 0 °C. The product precipitated as
small green microcrystals. Single crystals of X-ray quality were
Additional information on the structure determinations have been
deposited with the Cambridge Crystallographic Data Centre.
Results and Discussion
Reactions between N,N-dialkyl-N′-benzoylthiourea ligands,
HR1R2btu, and the common rhenium(V) starting material
[ReOCl3(PPh3)2] proceed in different ways depending on the
solvents and the reaction conditions applied. In the absence
of a supporting base, [ReOCl3(PPh3)2] reacts with HR1R2btu
in MeOH and EtOH to form unattractive dark brown solids.
This result is in accordance with the findings of Dilworth et
al.,10 who were not able to isolate crystalline rhenium
complexes with HEt2btu when they started form this precur-
sor. In CH2Cl2 solutions of dialkylbenzoylthioureas, however,
the sparingly soluble [ReOCl3(PPh3)2] readily dissolves and
yellow-green solutions are formed, which contain mixtures
(16) Sheldrick, G. M. SHELXS-97 and SHELXL-97, programs for the
solution and refinement of crystal structures; University of Go¨ttin-
gen: Go¨ttingen, Germany, 1997.
Inorganic Chemistry, Vol. 46, No. 13, 2007 5313

Huy and Abram
of complexes [ReOCl2(PPh3)(R1R2btu)] (3) and [ReCl2-
(PPh3)2(R1R2btu)] (4) (eq 2). The formation of Re(III)
complexes as minor side-products of such reactions is not
unexpected and can be explained by the reduction of the
Re(V) oxo complexes by the released PPh3, which attacks
the oxo ligands under formation of triphenylphosphine oxide.
The presence of OPPh3 in the reaction mixture is confirmed
by its 31P NMR signal. The mechanism of the reduction was
first proposed by Rouschias and Wilkinson for the synthesis
of [ReCl3(MeCN)(PPh3)2]17 and more recently confirmed
during reactions of [ReOCl3(PPh3)2] with other systems.18
A dissociative mechanism with a trigonal-bipyramidal transi-
tion state is strongly suggested by the conformation of
complexes 4 with the PPh3 ligands in trans positions to each
other and with respect to the bulky ligands of 3.
Infrared spectra of complexes 3 and 4 exhibit strong bands
between 1400 and 1500 cm-1 but no absorptions in the range
between 1670 and 1690 cm-1, where the νCdO stretches
typically appear in the spectra of the noncoordinated ben-
zoylthioureas.1 This corresponds to a bathochromic shift of
more than 200 cm-1 and indicates chelate formation with a
large degree of electron delocalization within the chelate
rings as has been observed for other R1R2btu- chelates.2 The
absence of bands in the region of 3100 cm-1 indicates the
expected deprotonation of the ligands during complex
formation. Intense bands between 900 and 1000 cm-1, which
can be assigned to the RedO vibrations,19 confirm the
presence of oxo ligands in 3, while such bands are absent in
the spectra of the rhenium(III) complexes 4.
FAB+ mass spectra of complexes of type 3 show only
less intense signals of the molecular ions. They strongly tend
to combine with the matrix 4-nitrobenzylalcohol, and thus,
ions of the composition [M + NBA - 2Cl]+ represent peaks
of high intensity for these types of complexes. Spectra of
complexes 4 are more detailed and show peaks of the
molecular ions and fragments, which result from subsequent
loss of Cl- and PPh3.
(17) Rouschias, G.; Wilkinson, G. J. Chem. Soc. A 1967, 993.
(18) (a) Wei, L.; Babich, W.; Zubieta, J. Inorg. Chem. 2004, 43, 6445. (b)
Fortin, S.; Beauchamp, A. L. Inorg. Chem. 2001, 40, 105. (c) Banerjee,
S.; Bhattacharyya, S.; Dirghangi, B. K.; Menon, M.; Chakravorty, A.
Inorg. Chem. 2000, 39, 6. (d) Seymore, S. B.; Brown, S. N. Inorg.
Chem. 2000, 39, 325.
(19) Abram, U. Rhenium. In ComprehensiVe Coordination Chemistry II;
McCleverty, J. A., Mayer, T. J., Eds.; Elsevier: Amsterdam, The
Netherlands, 2003; Vol. 5, p 271.
5314 Inorganic Chemistry, Vol. 46, No. 13, 2007

Rhenium and Technetium Complexes
Figure 1. Molecular structure of [ReOCl2(PPh3)(morphbtu)] (3e). H atoms
have been omitted for clarity.
Figure 2. Molecular structure of [ReCl2(PPh3)2(Ph2btu)] (4a). H atoms
have been omitted for clarity.
Table 2. Selected Bond Lengths (Å) in [ReOCl2(PPh3)(morphbtu)] (3e)
and [ReCl2(PPh3)2(Ph2btu)] (4a)
is in the expected range of a rhenium-oxygen double bond.
A remarkable structural feature is the coordination of the
benzoylic oxygen atom trans to the oxo ligand. The Re-O5
bond is expectedly longer than Re-O10 but reflects some
double bond character, as has been observed previously for
a number of rhenium(V) complexes with oxo and alkoxo
ligands in the trans position.21 Markedly longer Re-OR
bonds are found when the alkoxo units are cis to the oxo
unit.22 Despite the fact that the chelate ring is not planar, a
considerable extent of π-electron density is indicated by the
observed bond lengths. The values of the C-S and C-O
bonds are between those expected for carbon-sulfur and
carbon-oxygen single and double bonds, and all C-N bonds
including the C2-N6 bond are almost equal.
A similar bonding situation is observed in the chelate ring
of the rhenium(III) complex 4a, but in contrast to 3e, the
C2-N6 bond contributes to the conjugated π-system to a
lesser extent and the chelate ring is almost planar with a
maximum deviation from planarity of 0.04 Å for atom S1.
Figure 2 depicts the molecular structure of 4a, and selected
bond lengths are contained in Table 2. The structure reveals
a distorted octahedral environment of the rhenium atom with
trans coordination of the bulky PPh3 ligands. No unusual
bond lengths are observed; the small differences to the
structure of 3e can be addressed by the different oxidation
states of the rhenium atoms and/or the influence of the trans
ligands.
3e
4a
3e
4a
Re1-O10
Re1-Cl2
Re1-O5
Re1-P2
C2-N3
1.689(2)
2.402(1)
2.069(2)
Re1-Cl1
Re1-S1
Re1-P1
S1-C2
C2-N6
C4-O5
2.379(1)
2.400(1)
2.464(1)
1.761(3)
1.323(4)
1.289(4)
2.389(1)
2.360(1)
2.486(1)
1.719(4)
1.364(4)
1.270(4)
2.385(1)
2.021(2)
2.467(1)
1.341(5)
1.328(4)
1.342(4)
1.315(4)
N3-C4
NMR spectra of complexes 3 provide additional evidence
for the proposed composition and molecular structure of the
complexes. The spectra are characterized by complex
coupling patterns due to hindered rotation around the
C-NR1R2 bonds. This has previously been described for the
uncoordinated N,N-dialkyl-N′-benzoylthioureas and some
metal complexes.6,15,20 A rotational barrier of ∆G ) 15.5
kcal/mol was determinded for HEt2btu,20c and an increase
of this parameter was detected as a consequence of complex
formation with Ni(II), Pd(II), or Co(II) ions.20b Usually, two
sets of signals are observed in 1H and 13C spectra of the Re
complexes under study. This may lead to complex coupling
patterns in the proton spectra as in that of 3d, where the
CH2 protons show a complex array of overlapping multiplets
in the range between 3.9 and 4.9 ppm, and only the 13C NMR
spectra clearly show four separated resonances of these CH2
groups at 49.68, 51.41 (CH2N) and 67.00, 67.48 ppm
(CH2O). 1H NMR spectra of the paramagnetic Re(III)
complexes exhibit broad lines and shall not be the subject
of discussion.
Figure 1 depicts the molecular structure of compound 3e
as a prototype for these types of complexes. Selected bond
lengths are given in Table 2. The rhenium atom exhibits a
distorted octahedral coordination geometry. Axial positions
are occupied by an oxo ligand and an oxygen atom of the
chelating ligand. The two chloro ligands of the equatorial
coordination sphere are in cis arrangement to each other,
and the rhenium atom is located 0.221 Å above the mean
least-square plane, which is formed from S1, Cl1, Cl2 and
P, toward the oxo ligand. The RedO distance of 1.689(2) Å
When acetone is used as the solvent and NEt3 is added as
a supporting base, reactions of [ReOCl3(PPh3)3] and an
excess of HR1R2btu ligands yield a second ligand exchange
product and reduction to Re(III) compounds can be sup-
pressed to a large extent. The different course of the reaction
is indicated by a change of the color of the reaction mixture
from pale yellow-green to deep green. Green solids can be
isolated upon concentration of such solutions, which consist
(21) (a) Abram, S.; Abram, U.; Schulz Lang, E.; Stra¨hle, J. Acta Crystallogr.
1995, C51, 1078 and references cited therein. (b) Paulo, A., Domingos,
A.; Marcalo, J.; Pires de Matos, A.; Santos, I. Inorg. Chem. 1995, 34,
2113. (c) Braband, H., Blatt, O.; Abram, U. Z. Anorg. Allg. Chem.
2006, 632, 2251.
(22) Hitchcock, P. B.; Lappert, M. F.; Pye, P. L. J. Chem. Soc., Dalton
Trans. 1978, 826.
(20) (a) Kleinpeter, E.; Beyer, L. J. Prakt. Chem. 1975, 317, 938. (b) Beyer,
L.; Behrendt, S.; Kleinpeter, E.; Borsdorf, R.; Hoyer, E. Z. Anorg.
Allg. Chem. 1977, 437, 282. (c) Behrendt, S.; Beyer, L.; Dietze, F.;
Kleinpeter, E.; Hoyer, E.; Ludwig, E.; Uhlemann, E. Inorg. Chim.
Acta 1980, 43, 141.
Inorganic Chemistry, Vol. 46, No. 13, 2007 5315

Huy and Abram
Scheme 1
of the bis-chelates [ReOCl(R1R2btu)2] (1), PPh3, some traces
of 3, and small amounts of dark unidentified side-products.
Purification can be done either by several recrystallizations
from acetone or by column chromatography using silica gel.
The yields of such reactions can be improved by using a
5-fold excess of the ligands and a prolonged reaction time.
A more facile approach to complexes of type 1 is the use of
(NBu4)[ReOCl4] as a precursor (Scheme 1). Such reactions
in methanol give 1 in excellent yields.
IR spectra of 1 show intense bands between 950 and 990
cm-1 which can be assigned to RedO vibrations. As
discussed for complexes of type 3 and 4, chelate coordination
of the R1R2btu- ligands results in a strong bathochromic shift
of the CdO bands, which appear in the spectra in the range
between 1400 and 1500 cm-1 and strongly overlap with CdC
and CdN bands.
The two sets of resonances of the CdO and CdS carbons
atoms in the 13C NMR spectra of 1 indicate that the two
organic ligands are magnetically inequivalent. The tentative
assignment of the CdS and CdO signals has been made
under the assumption that complex formation does not result
in dramatic changes of their chemical shifts with respect to
the positions where these signals appear in the spectra of
the uncoordinated benzoylthioureas. The proton NMR spectra
are complex due to hindered rotation. In the spectrum of
1b, which contains the asymmetric PhMebtu- ligands, seven
out of eight CH3 signals, which can be expected due the
possible Z,E isomerism of the ligands in such complexes,
are resolved. Two of them (3.87 and 3.96) dominate with a
relative intensity of approximately 60% and might be
assigned to the E,E isomer, which is also established in the
solid-state structure of the compound (Figure 3). The missing
eighth signal of minor intensity is most probably overlapped
by one of the others. The 13C signals of the less abundant
isomers could not be resolved from the noise of the spectrum.
Interestingly, the 1H NMR spectrum of the analogous
technetium compound 2b (vide infra) exhibits only one broad
methyl signal, indicating that the rotation barrier of the
C-NPhMe bond is lower in the technetium compound.
The molecular structure of 1b (Figure 3) confirms the
results of the spectroscopical studies showing the rhenium
atom in a distorted octahedral coordination environment with
inequivalent PhMebtu- ligands. One of them binds with its
oxygen atom trans to the oxo ligand, similar to the situation
in 3, while the second chelating ligands occupies two
equatorial coordination positions. This has significant effects
on the bond lengths and angles in the established chelate
rings. That of the equatorial ligand is slightly distorted with
a maximum deviation from the mean least-square plane of
the chelate ring of 0.205 Å for atom Cl2, while the sulfur
atom of the axial chelate ring is displaced from a mean least-
square plane formed by the atoms Re1, O5, C4, N3, C2,
and S2 by 0.367 Å. Selected bond lengths are summarized
in Table 3. The distribution of the electrons inside the chelate
rings is best described with an extended π-system. The C-N
bonds of the ring systems are very similar, and it is evident
that considerable π-electron density is transferred to the
exocyclic C2-N6 and C12-N16 bonds. This explains the
1
detection of E/Z isomers in the H NMR spectrum of the
compound.
Addition of a base such as NEt3 to a refluxing solution of
1c in MeOH causes an immediate color change from green
to red and a complex of the composition [ReO(OMe)(R1R2-
btu)2] (5c) is formed (Scheme 1). Structural analysis of the
resulting purple solid reveals that besides the exchange of
the chloro by a methoxy ligand, a rearrangement of the
chelating ligands is generated. They are both found in
equatorial positions in the product with the sulfur atoms cis
to each other, while MeO- is found trans to the oxo ligand.
Both chelate rings are almost planar in 5c, the molecular
structure of which is shown in Figure 4. The obvious ability
of ReO3+ cores to transfer electron density to alkoxo ligands
in the trans position and the higher degree of delocalized
electron density in the equatorial chelate rings seem to be
the driving forces of this ligand rearrangement. Several
examples of rhenium(V) oxo/alkoxo complexes have been
studied structurally before,21 and in all of these complexes
the Re-OR bond is shorter than expected for a Re-O single
5316 Inorganic Chemistry, Vol. 46, No. 13, 2007

Rhenium and Technetium Complexes
Figure 4. Molecular structure of [ReO(OMe)(Et2btu)2] (5c). H atoms have
been omitted for clarity.
Figure 3. Molecular structure of [ReOCl(PhMebtu)2] (1b). H atoms have
been omitted for clarity.
Table 3. Selected Bond Lengths (Å) in [ReOCl(PhMebtu)2] (1b)a and
[TcOCl(Ph2btu)2] (2a)
1b
2a
M1-O10
M1-Cl1
M1-S1
1.669(6)/1.657(6)
2.432(2)/2.421(2)
2.343(2)/2.345(2)
2.319(2)/2.341(2)
2.098(5)/2.138(5)
2.052(5)/2.052(5)
1.760(8)/1.752(8)
1.33(1)/1.33(1)
1.33(1)/1.35(1)
1.33(1)/1.32(1)
1.287(9)/1.280(9)
1.765(7)/1.748(8)
1.36(1)/1.33(1)
1.31(1)/1.33(1)
1.31(1)/1.29(1)
1.28(1)/1.285(9)
1.642(4)
2.437(2)
2.358(1)
2.323(2)
2.147(3)
2.043(3)
1.762(6)
1.320(7)
1.358(6)
1.364(6)
1.266(6)
1.750(5)
1.331(7)
1.352(7)
1.311(7)
1.285(6)
M1-S11
M1-O5
M1-O15
S1-C2
Figure 5. Molecular structure of [{ReO(Et2btu)2}2O] (6c). H atoms have
been omitted for clarity.
Table 4. Selected Bond Lengths (Å) in [ReO(OMe)(Et2btu)2] (5c) and
[{ReO(Et2btu)2}2O] (6c)
C2-N3
C2-N6
N3-C4
5c
6c
C4-O5
Re-O10/O20
1.699(5)
2.326(1)
2.321(1)
2.131(4)
2.129(3)
1.795(7)
1.703(7)/1.687(8)
2.340(3)/2.325(3)
2.334(3)/2.334(3)
2.089(6)/2.111(7)
2.101(6)/2.118(7)
S11-C12
C12-N13
C12-N16
N13-C14
C14-O15
Re-S1/S101
Re-S11/S111
Re-O5/O105
Re-O15/O115
Re1-O40
a Two crystallographically independent species.
Re1-O30 /Re11-O30
S1-C2/S101-C102
C2-N3/C102-N103
C2-N6/C102-N106
N3-C4/N103-C104
C4-O5/C104-O105
S11-C12/S111-C112
C12-N13/C112-N113
C12-N16/C112-N116
N13-C14/N113-C114
C14-O15/C114-O1115
1.897(6)/1.914(6)
1.742(9)/1.74(1)
1.36(1)/1.35(1)
1.33(1)/1.33(1)
1.31(1)/1.30(1)
1.26(1)/1.27(1)
1.768(9)/1.74(1)
1.33(1)/1.33(1)
1.33(1)/1.34(1)
1.32(1)/1.32(1)
1.27(1)/1.27(1)
1.745(6)
1.345(7)
1.346(7)
1.313(7)
1.262(6)
1.757(5)
1.351(7)
1.335(6)
1.296(7)
1.266(6)
bond. This is remarkable with respect to the oxo ligands in
the trans position, which should exert a considerable trans
influence and, thus, weaken these bonds instead of strengthen
them.
Nevertheless, the methoxo ligand in 5c is labile and can
readily be replaced by water, which finally yields to the
formation of the oxo-bridged dimer [{ReO(Et2btu)2}O] (6c).
Selected bond lengths of 5c and 6c are compared in Table
4. The dimeric complex is formed when 5c is dissolved in
CHCl3 or MeCN and a drop of water is added. This results
in an immediate change of the color from red to light green.
under common conditions. In most of the previous examples,
the formation of the dimeric species is preferred.25,26 Only
in some exceptional cases, the cleavage of the Re-O-Re
backbone of the {Re2O3}4+ core has been used to prepare
monomeric species, as in the synthesis of [ReO(OEt)Cl2-
(py)2] from [Re2O3Cl4(py)4].24
1
Signals of 6c are even observed during H NMR measure-
ments on 5c in CDCl3, when the solvent contains traces of
water. On the other hand, the reaction is perfectly reversible
and the green solution of 6c in CHCl3 suddenly turns to red
when a small amount of MeOH is added (Scheme 1). A
The RedO stretch in the IR spectrum of 6c is only weak,
which is in accord to previous reports,25 and a strong
1
corresponding H NMR in the CDCl3 experiment revealed
(23) Hansen, L.; Alessio, E.; Iwamoto, M.; Marzilli, P. A.; Marzilli, L. G.
Inorg. Chim. Acta 1995, 240, 413.
(24) Johnson, N. P.; Taha F. I. M.; Wilkinson, G. J. Chem. Soc. 1964,
2614.
(25) (a) Lawrence, A. B.; Paul, E. W.; Grant, N. H. Inorg. Chim. Acta
1997, 255, 149. (b) Benny, P. D.; Barnes, C. L.; Piekarski, P. M.;
Lydon, J. D.; Jurisson, S. S. Inorg. Chem. 2003, 42, 6519. (c) Gerber.
T. I. A.; Tshentu, Z. R.; Garcia-Granda, S.; Mayer, P. J. Coord. Chem.
2003, 56, 1093.
that after the addition of 15 equiv of MeOH, the resonances
of 6c completely disappeared and complex 5c is exclusively
present in such solutions. A dimerization most probably
occurs via formation of an intermediate hydroxo species,23,24
which has not been isolated in the present case. Remarkably,
the equilibrium between 5c and 6c is completely reversible
Inorganic Chemistry, Vol. 46, No. 13, 2007 5317

Huy and Abram
Figure 6. Molecular structure of [TcOCl(Ph2btu)2] (2a). H atoms have
been omitted for clarity.
Figure 8. Molecular structure of [Tc(Ph2btu)3] (8a). H atoms have been
omitted for clarity.
Table 5. Selected Bond Lengths (Å) in [TcCl(PPh3)(Ph2btu)2] (7a) and
[Tc(Ph2btu)3] (8a)
7a
8a
Tc-S1/S11/S21
Tc-O5/O15/O25
Tc-Cl
2.333(2)/2.360(2) 2.340(1)/2.352(1)/2.343(2)
2.044(5)/2.071(5) 2.049(3)/2.046(4)/2.048(4)
2.417(2)
Tc-P
2.428(2)
S1-C2/S11-C12/S21-C22
1.726(8)/1.723(8) 1.735(6)/1.738(6)/1.738(6)
C2-N3/C12-N13/C22-N23 1.323(9)/1.334(9) 1.329(7)/1.323(7)/1.337(8)
C2-N6 /C12-N16/C22-N26 1.383(7)/1.340(8) 1.370(7)/1.371(6)/1.355(7)
N3-C4/N13-C14/C23-C24 1.346(8)/1.319(9) 1.333(7)/1.327(6)/1.330(7)
C4-O5/C14-O15/C24-O25 1.257(7)/1.280(8) 1.266(6)/1.273(6)/1.278(6)
atoms of the chelate rings. This clearly indicates magnetic
equivalence of the Et2btu- ligands in these two compounds.
This is in accord with the structure of 5c and strongly
suggests a similar bonding situation in 6c.
Figure 7. Molecular structure of [TcCl(PPh3)(Ph2btu)2] (7a). H atoms have
been omitted for clarity.
Scheme 2
The spectroscopic results are confirmed by an X-ray
structural analysis. Figure 5 illustrates the molecular structure
of 6c, and selected bond lengths are contained in Table 4.
The Re-O-Re unit is almost linear (169.9(3)°), and the
corresponding bond lengths of 1.897(6) and 1.914(6) Å
indicate some double bond character as has been found
previously for other compounds with the {Re2O3}4+ core.19
Expectedly (with regard to the NMR results), all chelate rings
are almost planar with only negligible deviations (<0.155
Å) are observed.
The structural diversity of the obtained rhenium com-
pounds starting from common precursor complexes encour-
aged us to undertake similar experiments for technetium.
Unfortunately, the analogous PPh3 complex “[TcOCl3-
(PPh3)2]” does not exist due to the ready reduction of
{TcO}3+ centers by monodentate phosphines.27 Thus, reac-
(26) (a) Gerber. T. I. A.; Luzipo, D.; Mayer, P. J. Coord. Chem. 2005, 58,
1505. (b) Kurti, L.; Papagiannopoulou, D.; Papadopoulos, M.; Pirmet-
tis, I.; Raptopoulou, C. P.; Terzis, A.; Chiotellis, E.; Harmata, M.;
Kuntz, R. R.; Pandurangi, R. S. Inorg. Chem. 2003, 42, 2960. (c)
Benny, P. D.; Barnes, C. L.; Piekarski, P. M.; Lydon, J. D.; Jurisson,
S. S. Inorg. Chem. 2003, 42, 6519. (d) Tisato, F.; Refosco, F.; Mazzi,
U.; Bandoli, G.; Dolmella, A. Inorg. Chim. Acta 1989, 164, 127. (e)
Battistuzzi, G.; Bonamartini-Conradi, A.; Dallari, D.; Saladini, M.;
Battistuzzi, R. Polyhedron 1999, 18, 57.
absorption at 725 cm-1, which is assigned to the asymmetric
Re-O-Re stretch, dominates. Two sets of resonances are
1
observed for the ethyl residues in 5c and 6c in the H and
(27) Alberto, R. Technetium. In ComprehensiVe Coordination Chemistry
II; McCleverty, J. A., Mayer, T. J., Eds.; Elsevier: Amsterdam, The
Netherlands, 2003; Vol. 5, p 140.
13C NMR spectra due to the hindered rotation mentioned
above, while only one 13C signal is observed for the carbon
5318 Inorganic Chemistry, Vol. 46, No. 13, 2007

Rhenium and Technetium Complexes
Scheme 3
tions of (NBu4)[TcOCl4] with HR1R2btu ligands were studied
with methanol as the solvent. They give yellow-brown,
crystalline products of the composition [TcOCl(R1R2btu)2]
(2) in good yields (Scheme 2). The compounds are soluble
much better in MeOH than their rhenium analogues 1, and
only small amounts of solvent may be used to obtain the
products in good yields.
IR spectra of 2 exhibit the ν(TcdO) frequencies in the range
between 950 and 970 cm-1, and the spectral features
described above for 1, such as the strong bathochromic shift
of the CdO bands, also apply for the Tc compounds. The
same holds true for the main structural features of the solid-
state structures of the compounds. Figure 6 depicts the
molecular structure of 2a, and the corresponding bond lengths
are compared to those of 1b in Table 2. Again, two chelate
rings with different bonding characteristics are observed. An
almost planar equatorial chelate ring (maximum deviation
from the least-square plan of all atoms of the chelate ring
for atom Cl2: 0.201 Å) is accompanied by a strongly
distorted ring in the axial position.
The {TcO}3+ core is strongly oxidizing, and reactions of
2 with 2 equiv of PPh3 give technetium(III) complexes in
good yields even at room temperature. One equivalent of
the phosphine is used as a reducing agent, and the formed
OPPh3 can readily be detected by 31P NMR in the reaction
mixture. The second equivalent is used for coordination in
the resulting red [TcCl(PPh3)(R1R2btu)2] complexes (7). The
products are stable as solids and in solution. Figure 7 shows
the molecular structure of 7a. Selected bond lengths are
contained in Table 5. The coordination sphere of the metal
is best described as a distorted octahedron with trans angles
between 172.9(1) and 177.7(1)°. Triphenylphosphine coor-
dinates trans to the oxygen atom of one of the Ph2btu-
ligands. The chelate ring of this ligand is strongly distorted,
while the second one is almost planar. The sulfur atoms are
in the cis position to each other.
(8a) in good yields. The same products are formed in a one-
pot reaction starting from 2a, with 2 equiv of PPh3 and an
excess of HPh2btu. In both cases, addition of a base such as
Et3N supports deprotonation of the N,N-dialkyl-N′-ben-
zoylthiourea and, thus, the formation of the chelate complex.
An alternative synthesis of compounds of the type 8 has been
described previously starting directly from pertechnetate with
SnCl2 as a reducing agent.12 This procedure, however,
produced a mixture of compounds and a chromatographic
purification was necessary, while the present ligand exchange
approach gives 8 with high purity and in crystalline form.
Figure 8 illustrates the molecular structure of complex 8a.
It shows only minor deviations from idealized octahedral
geometry with trans angles in the range 174.4(1)-176.0(1)°.
The distorted octahedral geometry is defined by two sets of
three facially bound sulfur and oxygen atoms from three
Ph2btu- ligands. All chelate rings in 8a are almost planar.
The O-Tc-O bond angles fall in the range 84.5(2)-86.3(2)°
which is slightly smaller than the S-Tc-S bond angles
(90.4(1)-91.1(1)°). Similar patterns have been observed
previously for the tris-chelates fac-[Ru(Et2btu)3], fac-[Rh-
(Et2btu)3], fac-[Co(Et2btu)3], and fac-[Co(Morphbtu)3].9
Conclusions
N,N-Dialkyl-N′-benzoylthioureas are versatile ligands,
which form stable complexes with rhenium and technetium.
Irrespective of the oxidation states of the metals and/or the
cores, they act as monoanionic chelates (Scheme 3). The
bonding situation inside the chelate rings manifests a high
degree of delocalization of electron density, which also
includes the exocyclic C-N bonds. The composition of the
coordination sphere of the metal ions can be controlled by
the reaction conditions applied and by coligands such as
phosphines or alcoholates.
Supporting Information Available: X-ray crystallographic file,
in CIF format, for the compounds discussed. This material is
available free of charge via the Internet at http://pubs.acs.org.
The chloro and PPh3 ligands in the coordination sphere
of 7a are sufficiently labile to allow further ligand exchange.
Thus, the reaction of 7a with HPh2btu in a CH2Cl2/MeOH
mixture yields the dark red-brown tris-chelate [Tc(Ph2btu)3]
IC070323X
Inorganic Chemistry, Vol. 46, No. 13, 2007 5319