Synthesis and reactivity of structurally analogous phenylimido and oxo complexes of rhenium(V) with N,N-dialkyl-N′-benzoylthioureas

Article abstract of DOI:10.1002/zaac.200800120

[ReOCl₃(PPh₃)₂] and [Re(NPh)Br ₃(PPh₃)₂] react at room temperature with equivalent amounts of N,N-dialkyl-N′-benzoylthioureas (HR ¹R²btu) in CH₂Cl₂ under formation of the rhenium(V) complexes [ReOCl₂(R¹R¹btu) (PPh₃)] and [Re(NPh)Br₂(R¹R²btu) (PPh³)], respectively. The products are structurally analogous with the oxygen atoms of the benzoylthioureas binding in trans positions to the oxo or phenylimido ligands. Prolonged reaction times result in the reduction of the oxo compound by the released PPh₃ and the formation of rhenium(III) complexes of the composition [ReCl₂(PPh₃) ₂(R¹R²btu)], while such a second reaction path is excluded for the phenylimido compound. Phenylimido species with more than one N,N-dialkyl-N′-benzoylthioureato ligand could not be isolated, even when a large excess of HR¹R²btu was used during the reaction.

Full text of DOI:10.1002/zaac.200800120

DOI: 10.1002/zaac.200800120
Synthesis and Reactivity of Structurally Analogous Phenylimido and Oxo
Complexes of Rhenium(V) with N,N-Dialkyl-NЈ-benzoylthioureas
Nguyen Hung Huy and Ulrich Abram*
Berlin, Institut für Chemie und Biochemie der Freien Universität
Received March 27th, 2008.
Abstract. [ReOCl3(PPh3)2] and [Re(NPh)Br3(PPh3)2] react at
room temperature with equivalent amounts of N,N-dialkyl-NЈ-
benzoylthioureas (HR1R2btu) in CH2Cl2 under formation
of the rhenium(V) complexes [ReOCl2(R1R1btu)(PPh3)] and
[Re(NPh)Br2(R1R2btu)(PPh3)], respectively. The products are
structurally analogous with the oxygen atoms of the benzoylthio-
ureas binding in trans positions to the oxo or phenylimido ligands.
Prolonged reaction times result in the reduction of the oxo com-
pound by the released PPh3 and the formation of rhenium(III)
complexes of the composition [ReCl2(PPh3)2(R1R2btu)], while such
a second reaction path is excluded for the phenylimido compound.
Phenylimido species with more than one N,N-dialkyl-NЈ-benzoyl-
thioureato ligand could not be isolated, even when a large excess
of HR1R2btu was used during the reaction.
Keywords: Rhenium; Benzoylthioureas; Oxo complexes; Phenylim-
ido complexes; Structure analysis
Introduction
[Re(NPh)Br2(R1R2btu)(PPh3)] together with the structural
data of analogous ReV oxo compound [ReOCl2(iPr2btu)-
(PPh3)], and compare the chemical behavior, spectroscopic
data and structures of the two classes of benzoylthiourea
complexes. Chart 1 illustrates the ligands which were used
throughout the experiments.
N,N-Dialkylbenzoylthioureas, HR1R2btu, are known to
form stable complexes with a large number of transition
metals [1]. In the majority of their structurally characterized
complexes they act as bidentate O,S-monoanionic ligands
[2]. Coordination as neutral, monodentate S-ligands can be
found in some AgI, AuI compounds and in a PtII complex
[3], while examples of transition metal complexes with ben-
zoylthioureas as bridging ligands are very rare [4, 5].
We are interested in complexes of technetium and
rhenium with benzoylthiourea ligands mainly due to the
flexibility of the periphery of their chelating system, which
allows the control of the lipophilicity of the complex and
gives access to bioconjugated rhenium and technetium com-
pounds. In a previous paper [6], we reported the compli-
cated pattern of reactions of benzoylthioureas with
[ReOCl3(PPh3)2], which is a common starting material for
the synthesis of rhenium(V) oxo complexes. In CH2Cl2,
such reactions give two different products: complexes of the
general formula [ReOCl2(R1R2btu)(PPh3)] (1), and/or ReIII
complexes of the composition [ReCl2(R1R2btu)(PPh3)2] (2).
The formation of the ReIII compounds is the result of re-
duction of ReV by released PPh3. We have now extended
these studies to the phenylimido core.
Chart 1 N,N-Dialkylbenzoylthioureas, HR1R2btu, used in this
work
Results and Discussion
The phenylimido and the oxo cores of rhenium(V) com-
plexes, [ReϭNPh]3ϩ and [ReϭO]3ϩ, are chemically very
similar [7]. This has been demonstrated by the synthesis of a
number of structurally analogous complexes, including the
triphenylphosphine complexes [ReOX3(PPh3)2] (X ϭ Cl,
Br) and [Re(NPh)X3(PPh3)2] (X ϭ Cl, Br, I). They are used
as common precursors in the synthesis of other ReV oxo
and ReV phenylimido complexes by ligand exchange reac-
tions [7, 8]. Reactions of N,N-dialkyl-NЈ-benzoylthioureas
with these two starting materials, however, show a slightly
different course of the reactions.
Here, we report the synthesis and molecular structures of
the ReV phenylimido complexes of the composition
[ReOCl3(PPh3)2] readily reacts with HiPr2btu at room
temperature in CH2Cl2 under formation of the yellow-green
main product [ReOCl2(iPr2btu)(PPh3)] (1a) and the deep-
red side product [ReCl2(iPr2btu)(PPh3)2] (2a). Deep-green
bis-chelates of the formula [ReOCl(R1R2btu)2] are formed,
when such reactions are performed in acetone using two
* Prof. Dr. Ulrich Abram
Freie Universität Berlin
Institut für Chemie und Biochemie
Fabeckstraße 34-36
D-14195 Berlin
E-mail: abram@chemie.fu-berlin.de
1560
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 634, 1560Ϫ1564

Phenylimido and Oxo Complexes of Rhenium(V) with N,N-Dialkyl-NЈ-benzoylthioureas
equivalents of the corresponding benzoylthioureas with the
addition of NEt3 as a supporting base (Scheme 1). The
spectroscopic data of the products have been published pre-
viously together with those of some other representatives
of oxorhenium(V) and rhenium(III) complexes with N,N-
dialkyl-NЈ-benzoylthioureas [6].
leased PPh3 to the oxo ligand with subsequent formation of
OPPh3 and reduction of the metal ion. This is certainly not
possible with the phenylimido species under study. An ad-
ditional stabilization of the higher oxidation state might be
given by the fact that the nitrogen atom is a stronger π
electron donator and a weaker electron acceptor than the
oxygen atom as has been discussed recently [9]. Experimen-
tal support for this discussion is given by 31P-NMR, which
shows the presence of a considerable amount of OPPh3 in
the reaction mixture of the oxo compounds, while only the
signals of the [Re(NPh)Br2(R1R2btu)(PPh3)] complexes and
released PPh3 could be detected in the spectra of reaction
mixtures of the phenylimido compounds. The use of an ex-
cess of HR1R2btu during the reactions did not result in the
formation of a further ligand exchange products with more
than one of the chelating ligand.
The infrared spectra of the imido compounds are very
similar to those of the oxo complexes. All exhibit strong
bands between 1470 and 1510 cmϪ1, but no absorptions in
the range between 1670 and 1690 cmϪ1, where the νCϭO
stretches typically appear in the spectra of the non-coordi-
nated benzoylthioureas [1]. This corresponds to a strong
bathochromic shift of approximately 200 cmϪ1 and indi-
cates chelate formation with a large degree of electron de-
localization within the chelate rings [2]. The absence of νNH
bands in the region of 3100 cmϪ1 indicates the expected de-
protonation of the ligands during complex formation. The
ReϭN vibrations can not be assigned unambiguously in the
IR spectra of 4b and 4c, while an intense band at 976 cmϪ1
can be assigned to the νReϭO stretch in the spectrum of 1a.
The FABϩ mass spectrum of the phenylimido complex 4b
shows an intense signal for the molecular ions at m/z ϭ
1032, while the the spectrum of the oxo compound 1a
Scheme 1
In contrast to the behavior of [ReOCl3(PPh3)2], the phe-
nylimido complex [Re(NPh)Cl3(PPh3)2] does not react in
CH2Cl2 or acetone with benzoylthioureas under ambient
conditions. Prolonged heating on reflux in CH2Cl2 and the
addition of NEt3 as a supporting base resulted in the grad-
ual consumption of [Re(NPh)Cl3(PPh3)2], but results in the
formation of intractable brown solutions. Unfortunately, all
our attempts to isolate crystalline product from the reac-
tions of this precursor failed.
More successful were reactions using another ReV
phenylimido precursor, [Re(NPh)Br3(PPh3)2]. The bromo
derivative is slightly better soluble and quickly reacts with
the corresponding benzoylthioureas in warm CH2Cl2 under
formation of [Re(NPh)Br2(Ph2btu)(PPh3)] (4b) and
[Re(NPh)Br2(Morphbtu)(PPh3)] (4c). The yellow-green
solids can be isolated in good yields from the yellow-green
solutions as the sole products (Scheme 2). No further re-
duction of the products was found. This comes not com-
pletely unexpected, since the formation of rhenium(III) side
products during ligand exchange reactions starting from
[ReOCl3(PPh3)2] is commonly explained by an attack of re-
is dominated by fragment peaks at m/z
ϭ
881
(M(NBA)Ϫ2Cl), 764 (M-ClϩH), 729 (M-2ClϩH) and 466
(M-2Cl-PPh3).
NMR spectra of the compounds 4b and 4c provide ad-
ditional evidence for the proposed composition and molec-
ular structure of the complexes. The spectra are charac-
terized by complex coupling patterns due to hindered ro-
tation around the CϪNR1R2 bonds. This has previously
been described for the uncoordinated N,N-dialkylben-
zoylthioureas and some of their metal complexes [10], and
leads to complex coupling patterns in the proton spectra as
in that of 4c. The CH2 protons show a complex array of
overlapping multiplets in the range between 3.8 and
4.7 ppm and only the 13C NMR spectra clearly show four
separated resonances of these CH2 groups at 48.79, 51.16
for (CH2-N) and 66.51, 67.38 ppm for (CH2O). The signals
of the CϭO carbon atoms in 4b and 4c appear in the region
of 190 ppm which well agrees with the corresponding
chemical shift detected in the 13C-NMR spectrum of 1a
(190.43 ppm).
The X ray structure studies confirm the analogous struc-
tures of 1a and 4b. Figure 1 and 2 depict the ORTEP dia-
grams of the molecules. Selected bond lengths and angles
are compared in Table 1. The rhenium atoms are found in
Scheme 2
Z. Anorg. Allg. Chem. 2008, 1560Ϫ1564
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1561

N. H. Huy, U. Abram
Figure 2 Ellipsoid representation [16] of the molecular structure
of [Re(NPh)Br2(PPh3)(Ph2btu)]. Hydrogen atoms are omitted for
clarity.
Figure 1 Ellipsoid representation [16] of the molecular structure
of [ReOCl2(PPh3)(iPr2btu)]. Hydrogen atoms are omitted for
clarity.
i
˚
Table 1 Selected bond lengths /A and angles /° in [ReOCl2(PPh3)( Pr2btu)] (1a) [Re(NPh)Br2(PPh3)(Ph2btu)] (4b)
1a
4b
1a
4b
Re1ϪO10 / N10
Re1ϪP1
Re1ϪCl1 / Br1
Re1ϪCl2 / Br2
Re1ϪS1
1.679(4)
2.471(1)
2.382(1)
2.405(1)
2.392(1)
2.068(3)
1.725(6)
2.422(2)
2.535(1)
2.605(1)
2.415(2)
2.064(4)
S1ϪC2
1.763(6)
1.325(7)
1.351(6)
1.313(7)
1.288(6)
1.749(6)
1.363(8)
1.316(9)
1.322(9)
1.283(8)
1.366(9)
C2ϪN6
C2ϪN3
N3ϪC4
C4ϪO5
N10ϪC61
Re1ϪO5
O10/N10ϪRe1ϪO5
O10/N10ϪRe1ϪCl1/Br1
O10/N10ϪRe1ϪS1
O10/N10ϪRe1ϪCl2/Br2
O10/N10ϪRe1ϪP1
Cl1/Br1ϪRe1ϪCl2/Br2
Cl1ϪRe1ϪP1
175.8(2)
101.7(2)
96.2(2)
97.6(2)
88.7(2)
86.7(1)
93.9(1)
90.6(1)
170.7(2)
102.8(2)
92.0(2)
90.1(2)
97.7(2)
88.6(1)
87.7(1)
90.5(1)
O5ϪRe1ϪCl1/Br1
O5ϪRe1ϪS1
O5ϪRe1ϪCl2/Br2
O5ϪRe1ϪP1
Cl1/Br1ϪRe1ϪS1
S1ϪRe1ϪP1
Cl2/Br2ϪRe1ϪP1
C61ϪN10Ϫ Re1
82.1(1)
80.1(1)
84.5(1)
89.1(1)
162.2(1)
86.9(1)
173.5(1)
83.1(1)
82.1(1)
82.8(1)
89.6(1)
165.1(1)
91.3(1)
171.9(1)
162.9(4)
S1ϪRe1ϪCl2
˚
distorted octahedral coordination environments in both
structures. The axial positions are occupied by the oxygen
atoms of the chelating ligands and the double bonded oxy-
gen or nitrogen atoms of the oxo or phenylimido ligands.
The equatorial planes are formed by the sulphur atoms of
the singly deprotonated benzoylthioureas, the phosphorus
atoms and the halogeno ligands, which are in cis arrange-
ment to each other. The rhenium atom is located above the
mean least-square plane formed by the equatorial donor
each for the atoms S1 in both compounds, 0.490(2) A in 1a
˚
and 0.433(3) A in 4b), a considerable delocalization of
π-electron density throughout the chelate rings is indicated
by the observed bond lengths. The respective values of the
CϪS and CϪO bonds are between those expected for
carbonϪsulphur and carbonϪoxygen single and double
bonds. All CϪN bond lengths including the C2ϪN6 bonds
are almost equal.
˚
atoms by 0.201 and 0.194 A in 1a and 4b, respectively,
towards the ReϭO and ReϭN double bonds. The ReϭO
bond length in 1a of 1.679(4) A is in the expected range
Experimental Section
˚
of a rheniumϪoxygen double bond [7], whereas the ReϭN
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. [ReOCl3(PPh3)2] [12] and
[Re(NPh)Cl3(PPh3)2] [13] were prepared by standard procedures.
The synthesis of benzoylthioureas was performed by the standard
procedure of Beyer et al. [14].
˚
distance of 1.725(6) A in 4b is slightly shorter with respect
to some other ReV phenylimido complexes having an oxy-
gen atom coordinated trans to a NPh2Ϫ ligand [11]. Despite
the fact that the chelate rings are not planar in both com-
pounds (main deviations from the planarity is indicated
1562
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 1560Ϫ1564

Phenylimido and Oxo Complexes of Rhenium(V) with N,N-Dialkyl-NЈ-benzoylthioureas
Table 2 X-ray structure data collection and refinement parameters.
[ReOCl2(PPh3)(iPr2btu)]
[Re(NPh)Br2(PPh3)(Ph2btu)]
Formula
C32H34Cl2N2O2PReS
798.74
monoclinic
9.911(1)
19.233(1)
16.768(1)
92.03(1)
3194.3(4)
P21/n
C44H35Br2N3OPReS
1030.80
monoclinic
12.208(1)
19.265(1)
17.257(1)
93.59(1)
4050.8(5)
P21/c
4
Mw /g molϪ1
Crystal system
˚
a/ A
˚
b/ A
˚
c/ A
β/ °
3
˚
V/ A
Space group
Z
4
Dcalc./g cmϪ3
1.661
4.119
1.690
5.101
μ/ mmϪ1
Absorption correction
Tmin/Tmax
No. of reflections
No. of independent/
R(int)
Numerical/integration
0.4327/0.6600
22445
Numerical/integration
0.2927/0.5224
19089
8558 / 0.0516
8559 / 0.0577
No. parameters
R1/wR2
GOF
370
478
0.0440 / 0.1009
0.913
0.0522 / 0.1281
1.020
Deposit reference number
CCDC 682101
CCDC 682102
Infrared spectra were recorded from KBr pellets on a Shimadzu
FT instrument in the range 400Ϫ4000 cmϪ1. FABϩ mass spectra
were recorded with a TSQ (Finnigan) instrument using a nitro-
benzyl alcohol matrix (results are given in the form: m/z, assign-
ment). Elemental analyses were determined using a Heraeus vario
EL elemental analyzer. NMR-spectra were taken at 25 °C with a
JEOL 400 MHz multinuclear spectrometer. The X-ray diffraction
data were collected on a STOE IPDS diffractometer with Mo Kα
radiation. The structures were solved by the Patterson method
using SHELXS-97 [15]. Subsequent Fourier-difference map analy-
ses yielded the positions of the non-hydrogen atoms. Refinement
was performed using SHELXL-97 [15]. The positions of hydrogen
atoms were calculated for idealized positions and treated with the
‘riding model‘ option of SHELXL-97. Crystal data and more
details of the data collections and refinements are contained in
Table 2. Additional information on the structure determinations
have been deposited at the Cambridge Crystallographic Data
Centre.
4b (R1 ؍ R2 ؍ Ph): Yield: 70 % (72 mg). Elemental analysis: Calcd.
for C44H35Br2N3OPSRe: C, 51.25; H, 3.40; N, 4.08; S, 3.11. Found:
C, 51.21; H, 3.08; N, 3.78; S, 3.08 %.
IR (KBr, cmϪ1): 3055(w), 1481(s), 1431(vs), 1400(vs), 1257(w), 1173(w),
1091(m), 1072(w), 1026(m), 999(w), 759(m), 694(s), 528(s). 1H-NMR
(CDCl3; ppm): 7.0Ϫ7.5 (m, 35H, Ph). 31P-NMR (CDCl3; ppm): 1.06 (s);
13C-NMR (CDCl3; ppm): 121Ϫ134 (Ph), 158.26 (ReϭN-CPh), 173.11(CϭS),
191.77(CϭO). FAB؉-MS (m/z): 1032, [M ϩ H]ϩ, 950, [MϪBr]ϩ, 941,
[MϪPhN]ϩ.
4c (R1, R2 ؍ Morph): Yield: 66 % (61 mg). Elemental analysis:
Calcd. for C36H33Br2N3OPSRe: C, 45.56; H, 3.48; N, 4.43; S, 3.37.
Found: C, 45.70; H, 3.41; N, 4.32; S, 3.41 %.
IR (KBr, cmϪ1): 3051(w), 2862(w), 1508(s), 1485(s), 1435(s), 1396(vs),
1261(m), 1211(m), 1176(w), 1091(m), 1064(w), 1026(m), 995(w), 750(w),
694(s), 524(s). 1H-NMR (CDCl3; ppm): 3.8Ϫ4.0 (m, 5H, CH2), 4.14 (m, 1H,
CH2), 4.77 (m, 2H, CH2), 7.1Ϫ7.7 (m, 25H, Ph). 31P-NMR (CDCl3; ppm):
1.88 (s); 13C-NMR (CDCl3; ppm): 48.79, 51.16 (CH2-N), 66.51, 67.38 (CH2-
O), 121Ϫ134 (Ph), 172.24(CϭS), 189.33(CϭO).
[ReOCl2(iPr2btu)(PPh3)] (1a). The compound was prepared from
[ReOCl3(PPh3)2] and HiPr2btu as described previously [6]. Single
crystals suitable for X-ray study were obtained by slow evaporation
of a CH2Cl2/MeCN solution.
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0.1 mmol) in 5 ml of CH2Cl2. The temperature of the mixture was
kept at 30 °C for 1h. During this time, the precursor complex com-
pletely dissolved and a clear yellow-green solution was obtained.
The solvent was removed under vacuum to dryness and the residue
was recrystallized from 3 ml acetone.
Z. Anorg. Allg. Chem. 2008, 1560Ϫ1564
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