Tricarbonyl complexes of rhenium(I) and technetium(I) with thiourea derivatives

Article abstract of DOI:10.1016/j.jorganchem.2004.03.017

fac-[M(CO)₃X₃]^2- complexes (M=Re, X=Br; M=Tc, X=Cl) react with thiourea derivatives under formation of stable rhenium(I) and technetium(I) complexes. The composition of the products can be controlled by the steric requirements of the ligands and their ability to form chelates.The products of reactions with tetramethylthiourea, Me₄tu (I), N,N-diethylthiocarbamoylbenzamidine, H₂Et₂ tcb (II), and morpholinylthiocarbamoylbenzamidine, H₂morphtcb (III), have been studied by X-ray crystallography showing that the products belong to three different structural types. A mononuclear complex of the composition fac-[Re(CO)₃Br(Me₄tu) ₂] has been isolated with tetramethylthiourea, whereas the thiocarbamoylbenzamidines deprotonate and act as N,S-chelating ligands. This results in the formation of a dimeric [Tc(CO)₃ (HEt₂tcb-N,S)]₂ complex with a central, almost square Tc₂S₂ unit and a monomeric compound of the composition [Tc(CO)₃(Hmorphtcb-N,S) (H₂morphtcb-S)]. The latter compound contains a neutral, S-bonded morpholinylthiocarbamoylbenzamidine in the unusual imine form in addition to a chelate-bonded Hmorphtcb^- ligand.

Full text of DOI:10.1016/j.jorganchem.2004.03.017

Journal of Organometallic Chemistry 689 (2004) 2066–2072
www.elsevier.com/locate/jorganchem
Tricarbonyl complexes of rhenium(I) and technetium(I) with
thiourea derivatives
*
Henrik Braband, Ulrich Abram
Institut fu€r Chemie, Freie Universit€at Berlin, Fabeckstr. 34-36, D-14195 Berlin, Germany
Received 9 December 2003; accepted 3 March 2004
Abstract
fac-[M(CO)3X3]2ꢀ complexes (M ¼ Re, X ¼ Br; M ¼ Tc, X ¼ Cl) react with thiourea derivatives under formation of stable rhe-
nium(I) and technetium(I) complexes. The composition of the products can be controlled by the steric requirements of the ligands
and their ability to form chelates. The products of reactions with tetramethylthiourea, Me4tu (I), N,N-diethylthiocarbamoylbenz-
amidine, H2Et2tcb (II), and morpholinylthiocarbamoylbenzamidine, H2morphtcb (III), have been studied by X-ray crystallography
showing that the products belong to three different structural types. A mononuclear complex of the composition fac-[Re
(CO)3Br(Me4tu)2] has been isolated with tetramethylthiourea, whereas the thiocarbamoylbenzamidines deprotonate and act as N,S-
chelating ligands. This results in the formation of a dimeric [Tc(CO)3(HEt2tcb-N,S)]2 complex with a central, almost square Tc2S2
unit and a monomeric compound of the composition [Tc(CO)3(Hmorphtcb-N,S)(H2morphtcb-S)]. The latter compound contains a
neutral, S-bonded morpholinylthiocarbamoylbenzamidine in the unusual imine form in addition to a chelate-bonded Hmorphtcbꢀ
ligand.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Rhenium; Technetium; Carbonyl; Thiourea; Crystal structure
1. Introduction
nium(I) and technetium(I) tricarbonyl complexes [11]. A
huge number of ligand exchange procedures have been
described and most of them are directed towards the
labelling of biomolecules and mainly deal with nitrogen
and oxygen donor atoms [12,13]. Comparably less is
known about ligand exchange reactions of [Re
(CO)3Br3]2ꢀ or [Tc(CO)3Cl3]2ꢀ with ligands having a
thione functionality [14]. Recently, it was shown that
thiourea and thiourea derivatives are able to replace the
bromo ligands in [Re(CO)3Br3]2ꢀ under mild conditions,
and a few complexes such as [Re(CO)3(tu)3]þ (tu ¼
thiourea), [Re(CO)3Br(HEt2btu)] (H2Et2btu ¼ N,N-di-
ethylbenzoylthiourea) and [Re(CO)3(HEt2tcb)]2 (H2Et2-
tcb ¼ N,N-diethylthiocarbamoylbenzamidine) could be
isolated and structurally characterized [15]. Continuing
this work, we studied the influence of substituents in the
periphery of the ligands on the structure of the products
and extended the work to technetium.
Radioactive nuclides of technetium and rhenium are
of considerable interest for nuclear medical purposes [1–
3]. 99mTc complexes (99mTc: pure c-emitter, Ec ¼ 140
keV, half-life T1=2 ¼ 6 h) are used in many standard
procedures in diagnostic nuclear medicine [2], while
rhenium compounds are under discussion for palliative
treatment of cancer and radioimmunotherapy [3–5]. A
new approach is the labelling of biomolecules with low-
valent organometallic rhenium compounds for radio-
immunotherapy [6,7] and their technetium analogues for
diagnostic purposes. The application of carbonyl com-
plexes became possible with the development of a low-
pressure synthesis of [M(CO)3X3]2ꢀ (M ¼ Tc, X ¼ Cl;
M ¼ Re, X ¼ Br) [8–10].
[M(CO)3X3]2ꢀ anions have been shown to be excel-
lent starting materials for the synthesis of further rhe-
Here, wedescribereactionsof [M(CO)3X3]2ꢀ complexes
(M ¼ Tc, X ¼ Cl; M ¼ Re, X ¼ Br) with tetramethylthiou-
rea, Me4tu (I), N,N-diethylthiocarbamoylbenzamidine,
* Corresponding author. Tel.: +493083854002; fax: +493083852676.
E-mail address: abram@chemie.fu-berlin.de (U. Abram).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.03.017

H. Braband, U. Abram / Journal of Organometallic Chemistry 689 (2004) 2066–2072
2067
H2Et2tcb (II) and N,N-morpholinylthiocarbamoyl-
benzamidine, H2morphtcb (III). All the ligands have
thiocarbonyl donor sites, which are able to coordinate
to metal ions. Ligands (II) and (III) can bind as
monodentate ligands or as chelators depending on the
metal [16,17].
about 5 ml. A yellow precipitate was formed upon
cooling, which was separated and recrystallized from
CH2Cl2/MeOH.
Yield: 25 mg (30% based on Tc). IR(KBr) (cmꢀ1):
m(CO) 2014, 1926, 1896; m(NH) 3338. 1H NMR (d,
CDCl3) (ppm): 8.01 (s, NH, 2H), 7.51 (m, phenyl, 10H),
3.84 (m due to hindered rotation, CH2, 8H), 1.29 (m due
to hindered rotation, CH3, 12H). 99Tc NMR (d, CDCl3)
(ppm): )1020 (s, Dm1=2 ¼ 4878 Hz).
O
N
N
N
N
N
N
S
S
S
NH2
NH2
2.1.3. [Tc(CO)3(Hmorphtcb-N,S)(H2morphtcb-S)]
[Et4N]2[Tc(CO)3Cl3] (55 mg, 0.1 mmol) and H2mor-
phtcb (125 mg, 0.5 mmol) were dissolved in 40 ml of
methanol and two drops Et3N were added. The mixture
was heated under reflux for 2 h and reduced in volume
to about 10 ml. Colourless crystals were deposited from
this solution within two days.
I
II
III
2. Experimental
2.1. Synthesis
Yield: 56 mg (83% based on Tc). IR(KBr) (cmꢀ1):
1
Caution. 99Tc is a weak b-emitter (Emax ¼ 292 keV,
T1=2 ¼ 2:12 ꢁ 105 s). Shielding is not necessary when
small amounts are used as applied for this investigation,
since the b-particles do not penetrate glass walls and
secondary X-rays (bremsstrahlung) only play a signifi-
cant role when larger amounts of 99Tc are used. How-
ever, special care in the manipulation of radioactive
materials is required to avoid contamination and
incorporation.
[Et4N]2[Tc(CO)3Cl3] was prepared from tetrabu-
tylammonium pertechnetate, BH3 ꢂ THF and [Et4N]Cl
under an atmosphere of CO [9]. [Et4N]2[Re(CO)3Br3]
was a donation of Professor Roger Alberto (University
of Zurich, Switzerland). H2Et2tcb and H2morphtcb
were synthesized following literature procedures [18].
Tetramethylthiourea was purchased commercially
(Aldrich) and used without further purification.
m(CO) 2018, 1914, 1903. H NMR (d, CDCl3) (ppm):
11.84 (s, NH, 2H), 10.44 (s, NH, 1H), 6.5–7.8 (m, phe-
nyl, 10H), 3.3–4.4 (m, morph, 16H). 99Tc NMR (d,
CDCl3) (ppm): )1132 (s, Dm1=2 ¼ 2598 Hz).
2.2. Physical measurements
Routine IR spectra were recorded as KBr discs on a 5
SXC Nicolet IR spectrometer with DTGS-detector.
FABþ mass spectra were recorded on an TSQ spec-
trometer (Finnigan) with xenon as primary beam gas.
The ion gun was operated at 8 kV and 100 lA; nitro-
1
benzylalcohol was used as matrix. The H NMR and
99Tc spectra were recorded in CDCl3 on a Jeol 400MHZ
spectrometer with TMS as internal standard. A 0.1 m
solution of K99TcO4 in D2O was used as standard for
the 99Tc spectra (d ¼ 0).
2.3. X-ray diffraction
2.1.1. [Re(CO)3(Me4tu)2Br]
[Et4N]2[Re(CO)3Br3] (77 mg, 0.1 mmol) was dis-
solved in 2 ml of water and Me4tu (47 mg, 0.35 mmol)
was added. After stirring at room temperature for 2 h,
the solvent was removed under vacuum. The residue was
recrystallized by slow evaporation of a CHCl3/iso-pro-
panol solution giving colourless needles.
Yield: 22 mg (36% based on Re). Anal. Calc. for
C13H24BrN4O3S2Re: C, 25.4; H, 3.9; N, 9.1; S,
10.4. Found: C, 24.1; H, 3.7; N, 8.1; S, 9.2%. IR(KBr)
(cmꢀ1): m(CO) 2010, 1886. FABþ ) MS: m=z 535 [Re
(CO)3(Me4tu)2]þ, 506 [Re(CO)2(Me4tu)2]þ, 373 [Re
(CO)2(Me4tu)]þ.
The X-ray data were collected on an Enraf Nonius
CAD 4 diffractometer at room temperature ([Tc(CO)3
(HEt2tcb-N,S)]2) or a Bruker SMART CCD 1000 device
([Tc(CO)3(Hmorphtcb-N,S)(H2morphtcb-S)] and [Re
(CO)3(Me4tu)2Br]) with Mo Ka radiation (k ¼ 0:71073
ꢀ
A). Standard procedures were applied for data reduction
[19], structure solution [20,21] and refinement [22]. All
non-hydrogen atoms were refined with anisotropic
thermal parameters. The hydrogen atom H(22) in
[Tc(CO)3(Hmorphtcb-N,S)(H2morphtcb-S)] and the
hydrogen atoms H(1) and H(21) in [Tc(CO)3(HEt2tcb-
N,S)]2 have been derived from the difference Fourier
maps and included in the structure-factor calculations.
All other hydrogen atoms were placed at calculated
positions and refined with the Ôriding modelÕ option of
SHELXL 97. One phenyl ring in [Tc(CO)3(Hmorphtcb-
N,S)(H2morphtcb-S)] is disordered and split positions
have been considered in the structure calculation
2.1.2. [Tc(CO)3(HEt2tcb-N,S)]2
[Et4N]2[Tc(CO)3Cl3] (55 mg, 0.1 mmol) and H2Et2tcb
(120 mg, 0.5 mmol) were dissolved in 50 ml of methanol
and two drops of Et3N were added. The mixture was
heated under reflux for 2 h and reduced in volume to

2068
H. Braband, U. Abram / Journal of Organometallic Chemistry 689 (2004) 2066–2072
Table 1
X-ray structure data collection and refinement data
[Re(CO)3Br(Me4tu)2] ꢂ CHCl3
C14H25BrCl3N4O3ReS2
[Tc(CO)3(HEt2tcb-N,S)]2
[Tc(CO)3(Hmorphtcb-N,S)(H2morphtcb-S)]
Formula
C30H32N6O6S2Tc2
832.74
C27H29N6O5S2Tc
679.68
Orthorhombic
8.659(5)
20.607(5)
32.427(5)
90
Molecular weight
Crystal system
733.96
Triclinic
9.669(5)
11.043(5)
12.773(5)
73.88(1)
71.91(1)
73.70(1)
1217(1)
P1
Triclinic
9.995(1)
10.523(2)
17.130(4)
100.75(2)
97.76(1)
92.97(1)
1748.4(6)
P1
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
V (A )
Space group
Z
90
90
3
ꢀ
5786(4)
Pbca
8
1.560
2
2.003
7.157
2
1.582
Dcalc (g cmꢀ3
l (mmꢀ1
Absorption correction
min=Tmax
)
)
0.959
None
0.690
None
SADABS
0.287/0.517
15,106
7343
T
–
8766
–
No. of reflections
No. independent
No. parameters
44,143
4932
412
7367
424
257
0.033/0.081
1.021
a
R1ðF Þ=wR2ðF2Þ
0.047/0.085
1.007
0.040/0.100
1.076
Goodness-of-Fit
CCDC deposit
CCDC-225725
2
CCDC-225726
CCDC-225727
a R1 ¼ jFo ꢀ Fcj=jFoj; wR2 ¼ ½wðFo2 ꢀ Fc2Þ =ðwFo2Þꢃꢀ1=2
.
applying a site occupation of 0.55/0.45. More informa-
tion on crystal data and structure refinement is sum-
marized in Table 1.
compound crystallizes as CHCl3 solvate. The structure
of the complex is shown in Fig. 1. Selected bond lengths
and angles are summarized in Table 2.
The rhenium atom is coordinated through a facial
arrangement of three carbonyl groups, two tetrame-
thylthiourea ligands and one bromo ligand in a slightly
distorted octahedral arrangement. The Re–C bond
3. Results and discussion
The reaction of [Re(CO)3Br3]2ꢀ with an excess of
tetramethylthiourea yields [Re(CO)3Br(Me4tu)2]. No
evidence could be found for the formation of the [Re
(CO)3(Me4tu)3]þ cation, whereas the tris-thiourea de-
rivative dominates when non-alkyl-substituted thiourea
is used in the same reaction [15].
ꢀ
length are between 1.894(4) and 1.920(5) A. The mean
ꢀ
value for the Re–S distances is 2.529 A. This is slightly
ꢀ
longer than in [ReO(Me4tu)4](PF6)3 (2.339(3) A) [24],
but in the same range as in [Re(CO)3(tu)3]þ and can be
[Re(CO)3Br(Me4tu)2] is readily soluble in CHCl3 or
CH2Cl2, but only slightly soluble in alcohols. The car-
bonyl part of the IR spectrum shows the typical pattern
for a facial arrangement of CO ligands and is similar to
the previously reported tricarbonylrhenium(I) thiourea
complexes such as the neutral [Re(CO)3Cl(tu)2] (2023,
1914 cmꢀ1 [23]) and the cationic [Re(CO)3(tu)3]þ (2020,
1918, 1888 cmꢀ1 [15]). The FABþ mass spectrum shows
no signal for the molecular ion of the neutral complex.
The base peak of the spectrum at m=z ¼ 535 can be
assigned to the [Re(CO)3(Me4tu)2]þ cation. Further
fragmentation proceeds by the subsequent loss of com-
plete ligands (m=z ¼ 506 [Re(CO)2(Me4tu)2]þ, 373
[Re(CO)2(Me4tu)]þ).
C3
C7
N3
C8
C2
N1
Br1
S2
S1
C1
N2
N4
C11
C4
C20
Re1
C9
C5
C10
C30
O10
O20
O30
Colourless plates suitable for X-ray diffraction could
be obtained from a CHCl3/iso-propanol solution. The
Fig. 1. Ellipsoid representation [19] of the molecular structure of
[Re(CO)3Br(Me4tu)2]. Thermal ellipsoids represent 50% probability.

H. Braband, U. Abram / Journal of Organometallic Chemistry 689 (2004) 2066–2072
2069
1H NMR spectrum shows the signals of the ethyl groups
to be split into multiplets due to hindered rotation. The
99Tc NMR spectrum gives one broad signal
(Dm1=2 ¼ 4878 Hz) at r ¼ ꢀ1020 ppm, which is in the
expected range for technetium(I) tricarbonyl complexes
with sulphur-containing ligands [12].
The compound crystallizes in the triclinic space group
P1 with two dimeric units per unit cell. The dimeric units
are generated by inversion symmetry with the centre of
inversion positioned in the centre of the almost square
Tc2S2 ring. The molecular structure of one of the two
symmetry-independent species is shown in Fig. 2. There
are no significant differences between the independent
molecule. Therefore, significant bond lengths and angles
of only one of the species are summarized in Table 3.
The coordination environments of the technetium
atoms are almost octahedral with facially bonded CO
ligands. A distorted planar arrangement can be found
for the six-membered chelate rings (maximum variation
Table 2
ꢀ
Selected bond lengths (A) and angles (°) in [Re(CO)3Br(Me4tu)2]
Bond lengths
Re1–C10
Re1–C20
Re1–C30
Re1–S1
1.920(5)
1.900(4)
1.894(4)
2.530(1)
2.540(1)
2.648(1)
C10–O10
C20–O20
C30–O30
S1–C1
1.137(6)
1.159(6)
1.164(5)
1.723(4)
1.726(4)
Re1–S2
Re1–Br1
S2–C6
Bond angles
C10–Re1–C20
C10–Re1–C30
C10–Re1–S1
C10–Re1–S2
C10–Re1–Br1
C20–Re1–C30
C20–Re1–S1
C20–Re1–S2
C20–Re1–Br1
89.1(2)
89.4(2)
172.4(1)
95.7(1)
90.4(1)
91.5(2)
94.0(2)
172.6(1)
89.7(1)
C30–Re1–S1
C30–Re1–S2
C30–Re1–Br1
S1–Re1–S2
97.5(2)
94.2(1)
178.7(1)
80.56(4)
82.60(4)
84.59(4)
111.9(2)
109.9(1)
S1–Re1–Br1
S2–Re1–Br1
Re1–S1–C1
Re1–S2–C6
explained by the strong structural trans influence of the
carbonyls.
ꢀ
from planarity: 0.227(2) A, r.m.s. 0.1632). All carbon–
nitrogen bonds of this chelate system are equal within
The C–Re–S angles are slightly larger than 90° which
reduces interactions between the methyl substituents of
the thiourea ligands and the carbonyl groups. Although
tetramethylthiourea is not extremely bulky and a
rhenium complex with four Me4tu ligands, [Re-
O(Me4tu)4]3þ has been isolated recently [24], the coor-
dination of three of these ligands in facial positions is
prevented. Attempts to force the coordination of a third
Me4tu ligand by the addition of an excess of Me4tu and
three equivalents of Ag(NO3) to the reaction mixture
were not successful.
N,N-Dialkylthiocarbamoylbenzamidines form che-
late complexes as singly deprotonated N,S-donor li-
gands with a large number of metals including rhenium
and technetium [17,25]. The six-membered chelate rings
of the corresponding rhenium(V) and technetium(V)
oxo and nitrido complexes are almost planar and show
an extended p-system with almost equal C–N bond
lengths [25].
ꢀ
0.06 A which suggests an extended p-system. This type
of coordination was observed previously for a number
of HR2tcbꢀ-chelates [16,17,25] and only a few excep-
tions have been reported where the ligands bind as
neutral, monodentate thiocarbamoylbenzamidines via
their thiourea functionality [26].
The reaction of [NEt4]2[Tc(CO)3Cl3] with the mor-
pholinyl-substituted thiocarbamoylbenzaminide, H2-
morphtcb (III), gives a neutral monomeric complex with
one chelating Hmorphtcbꢀ ligand and one non-deprot-
onated H2morphtcb ligand: [Tc(CO)3(Hmorphtcb-N,S)
(H2-morph-tcb-S)]. The carbonyl part of the IR spectrum
shows the typical CO-bands indicating the presence of the
{Tc(CO)3}þ core. One broad signal (Dm1=2 ¼ 2598 Hz) at
r ¼ ꢀ1132 ppm can be observed by 99Tc NMR.
Reactions of [NEt4]2[Tc(CO)3Cl3] with N,N-dial-
kylthiocarbamoylbenzamidines give complexes of dif-
ferent compositions depending on the alkyl groups
attached. With H2Et2tcb (II), a dimeric complex is
formed, where the N,N-diethylthiocarbamoylbenzami-
dine is singly deprotonated and acts as a bridging ligand
between two technetium atoms via its sulfur atom. This
co-ordination mode of the ligand has previously been
observed for the analogous rhenium complex [15].
[Tc(CO)3(HEt2tcb-N,S)]2 is air-stable as a solid and
in solution. The compound is readily soluble in CH2Cl2
or CHCl3 and slightly soluble in alcohols. It can be
obtained as yellow plates from CH2Cl2/MeOH solu-
tions. The carbonyl region of the IR spectrum gives
evidence for the facial coordination of the CO ligands.
They are slightly shifted to higher wavenumbers com-
pared with the values of [Re(CO)3(HEt2tcb-N,S)]2. The
’
Tc1
N3
’
S1
C2
S1
N2
O20
C20
C1
N1
Tc1
C30
C10
O10
O30
Fig. 2. Ellipsoid representation [19] of the molecular structure of one
symmetry-independent dimer of [Tc(CO)3(HEt4tcb-N,S)]2. Thermal
ellipsoids represent 30% probability.

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H. Braband, U. Abram / Journal of Organometallic Chemistry 689 (2004) 2066–2072
Table 3
Table 4
ꢀ
ꢀ
Selected bond lengths (A) and angles (°) in [Tc(CO)3(HEt2tcb-N,S)]2
Selected bond lengths (A) and angles (°) in [Tc(CO)3(Hmorphtcb-
N,S)(H2morphtcb-S)]
Bond lengths
Tc1–C10
Tc1–C20
Tc1–C30
Tc1–N1
Tc1–S1
1.872(6)
2.036(6)
1.891(6)
2.273(4)
2.440(1)
2.525(1)
S1–C2
C2–N2
N2–C1
N1–C1
N3–C4
N3–C6
1.880(5)
1.383(7)
1.316(6)
1.320(6)
1.536(8)
1.544(8)
Bond lengths
Tc1–C10
Tc1–C20
Tc1–C30
Tc1–N1
Tc1–S1
Tc1–S2
S1–C2
1.916(5)
1.890(5)
1.925(5)
2.157(3)
2.477(1)
2.527(2)
1.738(4)
1.353(5)
N2–C1
N1–C1
N3–C2
1.314(5)
1.271(5)
1.326(5)
1.697(4)
1.391(6)
1.409(6)
1.194(6)
1.49(2)
S2–C22
C22–N22
N22–C21
C21–N21
C21–C40
Tc1–S10
Bond angles
C10–Tc1–C20
C10–Tc1–N1
C10–Tc1–S10
C20–Tc1–N1
C20–Tc1–S10
C30–Tc1–S1
N1–Tc1–S1
S1–Tc1–S10
92.6(2)
90.0(2)
C10–Tc1–S1
C20–Tc1–C30
C20–Tc1–S1
C30–Tc1–N1
C30–Tc1–S10
N1–Tc1–S10
Tc1–S1–C2
S1–C2–N2
96.0(2)
88.0(2)
92.1(2)
C2–N2
173.6(2)
177.1(2)
91.5(2)
Bond angles
C10–Tc1–C20
C10–Tc1–N1
C10–Tc1–S2
C20–Tc1–N1
C20–Tc1–S2
C30–Tc1–S1
N1–Tc1–S1
S1–Tc1–S2
93.4(2)
99.3(2)
85.9(1)
85.5(2)
95.6(2)
C10–Tc1–C30
C10–Tc1–S1
C20–Tc1–C30
C20–Tc1–S1
C30–Tc1–N1
C30–Tc1–S2
N1–Tc1–S2
91.9(2)
89.8(1)
90.2(2)
89.8(1)
93.2(2)
93.1(2)
87.26(9)
102.0(1)
124.0(3)
127.4(4)
122.1(4)
123.3(4)
178.2(2)
86.4(1)
174.2(1)
176.4(2)
91.4(2)
104.1(1)
134.2(3)
123.7(5)
101.09(5)
78.91(5)
127.2(4)
137.2(4)
85.8(2)
C2–N2–C1
C1–N1–Tc1
C10–Tc1–C30
N2–C1–N1
Tc1–S1–Tc10
178.3(2)
86.83(8)
85.28(4)
126.5(4)
130.9(3)
111.4(2)
120.5(3)
Tc1–S1–C2
S1–C2–N2
C2–N2–C1
The values for a second, symmetry-independent molecule are
identical within the standard deviations.
C1–N1–Tc1
Tc1–S2–C22
S2–C22–N22
N2–C1–N1
N22–C21–N21
C22–N22–C21
Symmetry operation: 1 ꢀ x; 1 ꢀ y; 1 ꢀ z.
Colourless needles suitable for an X-ray structure
determination were obtained directly from the reaction
mixture. A representation of the structure of the com-
plex is shown in Fig. 3. Selected bond lengths and angles
are summarized in Table 4. The technetium atom has a
slightly distorted octahedral environment with three
facially coordinated carbonyls. The chelating ligand is
deprotonated and forms an almost planar chelate ring
with similar nitrogen–carbon bonds as in the
[Tc(CO)3(HEt2tcb-N,S)]2 dimer. The second thiocarba-
moylbenzamdine ligand acts as a neutral monodentate
ꢀ
electron donor. The Tc–S2 bond length of 2.527(2) A is
ꢀ
slightly longer than the Tc–S1 bond (2.477(1) A).
An interesting structural feature in [Tc(CO)3(H-
morphtcb-N,S)(H2morphtcb-S)] is the bond length sit-
uation in the non-deprotonated H2morptcb ligand. The
distances between N22–C21 and N22–C22 (1.409(6) and
ꢀ
1.391(6) A) are close to a single bond and the distance
ꢀ
between C(21)–N(21) (1.194(6) A) can be regarded as a
carbon–nitrogen double bond. This strongly indicates
that this ligand is coordinated as an imine (IV) despite
the nitrogen atom not directly contributing to the
complex formation. This tautomeric form is supported
by the formation of an intramolecular hydrogen bond
between the nitrogen atoms N22 and N1 (distances
N22–H22 0.83(4), H22ꢂ ꢂ ꢂN1 2.08(5), N22ꢂ ꢂ ꢂN1 2.893(5)
ꢀ
C1
N1
A, angle N22–H22–N1 163(4)°) and a weaker intermo-
lecular hydrogen bond between N21 and N30 (symmetry
N2
C21
operation 1:5 ꢀ x; 0:5 ꢀ y; z; distances N21–H21 0.77,
N22
N21
0
0
ꢀ
H21ꢂ ꢂ ꢂN3 2.69, N21ꢂ ꢂ ꢂN3 3.117(5) A; angle N21–H21–
N30 117°) and is, to the best of our knowledge, without
precedent in the chemistry of N,N-dialkylthiocarba-
moylbenzamidines [28].
O10
C10
O30
C30
C2
Tc1
N3
C22
S1
N23
O
S2
O
H
N
C20
O20
O1
N
N
H
N
S
N
O21
S
N
H
H
IV
Fig. 3. Ellipsoid representation [19] of the molecular structure of
[Tc(CO)3(Hmorphtcb-N,S)(H2morphtcb-S)]. Thermal ellipsoids rep-
resent 30% probability.
In [TcN(Hmorphtcb-N,S)2] and [TcO(Hmorphtcb-
N,S)2]Cl [25a] as in complexes with numerous other

H. Braband, U. Abram / Journal of Organometallic Chemistry 689 (2004) 2066–2072
2071
2-
Cl
Cl
Cl
Tc
CO
CO
CO
R
N
R
N
+
+
S
N
S
N
R = Et2N
R = morph
H
N
R
N
R
+ [Tc(CO)3Cl3]2-
CO
Tc
NH
Tc
CO
CO
S
S
CO
CO
NH
HN
N
CO
Tc
S
S
CO
CO
HN
R
R
CO
N
+ H2R2tcb
Scheme 1.
metals, the ligands coordinate either as bidentate,
monoanionic chelate ligands or as monodentate
S-bonded thioureas. The latter coordination mode is
found in [Ag(H2Et2tcb-S)2]þ [26], and the bond lengths
in the ligands are close to those in the non-coordinated
H2Et2tcb [27] and indicate the enamin form.
In the present study we could show that steric factors
as well as polarization effects due to the substituents in
the periphery of thiourea ligands can significantly in-
fluence the structure of the rhenium(I) and technetium(I)
tricarbonyl complexes.
[Tc(CO)3(Hmorphtcb-N,S)(H2morphtcb-S)] can be
regarded as an intermediate in the formation of the di-
meric complex. This has been verified by a 99Tc-NMR
experiment. When [Tc(CO)3(Hmorphtcb-N,S)(H2mor-
phtcb-S)] and [NEt4]2[Tc(CO)3Cl3] are heated under
reflux for a prolonged time, the signals of these com-
pounds at )1132 and )868 ppm slowly decrease and a
new signal appears at )1043 ppm which most probably
belongs to [Tc(CO)3(Hmorphtcb-N,S)]2 (cf. the chemi-
cal shift of [Tc(CO)3(HEt2tcb-N,S)]2 at )1020 ppm).
Unfortunately we have not yet been able to isolate
[Tc(CO)3(Hmorphtcb-N,S)]2 in pure from such mixtures
due to the formation of numerous decomposition
products in these solutions, but the CO frequencies
in the IR spectra and the 99Tc NMR signals strongly
indicate this course of the reaction. The reverse experi-
ment, the prolonged heating of [Tc(CO)3(HEt2tcb-
N,S)]2 with an excess of H2Et2tcb did not give any
evidence for the formation of [Tc(CO)3(HEt2tcb-N,
S)(H2Et2tcb-S)], and the dimeric technetium complex
could be recovered almost quantitatively (Scheme 1).
The reason for the different behaviour of the two N,N-
dialkylthiocarbamoylbenzamidines is not yet clear. We
assume that the formation of the imine form as a con-
sequence of the monodentate complex formation is
preferred with the morpholinyl-substituted ligand. The
rapid formation of the observed intramolecular hydro-
gen bond may then contribute to the stabilization of the
monomeric complex.
Acknowledgements
We thank the Hermann-Starck A.G. (Goslar) for
providing us with rhenium metal and Prof. W. Preetz
(Kiel) for a gift of NH4TcO4.
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