ARTICLE
DOI: 10.1002/zaac.201100134

Syntheses and Structures of Nitridorhenium(V) and Nitridotechnetium(V)
Complexes with N,N-[(Dialkylamino)(thiocarbonyl)]-N'-(2hydroxyphenyl)benzamidines
Hung Huy Nguyen,*[a] Thi Nguyet Trieu,[a] and Ulrich Abram*[b]
Keywords: Rhenium; Technetium; Tridentate benzamidine; Nitrido complexes; Structure analysis
Abstract. [MNCl2(PPh3)2] complexes (M = Re, Tc) react with N-[(dialkylamino)(thiocarbonyl)]-N'-(2-hydroxyphenyl)benzamidines (H2L1)
with formation of neutral, five-coordinate nitrido complexes of the

composition [MN(L1)(PPh3)]. The products have distorted squarepyramidal coordination spheres with each a tridentate, double-deprotonated benzamidine and a PPh3 ligand in their basal planes.

Introduction

phenyl)benzamidines (H2L1) has been intensively studied.
Most of the isolated complexes with these ligands have oxorhenium(V) or oxotechnetium(V) cores. Five-coordinate oxorhenium(V) and oxotechnetium (V) complexes,[2] as well as
cis methoxo compounds,[5] ‘3+2’ mixed-ligand complexes,[6]
and dimeric oxorhenium(V) complexes[5] were isolated and
structurally characterized. Only one exceptional compound is
an octahedral technetium(III) complex.[2] In continuation of
our systematic studies on thiocarbamoylbenzamidinato complexes of rhenium and technetium, here we report the synthesis
and molecular structures of nitridorhenium(V) and nitridotechnetium(V) complexes with ligands of the type H2L1.

Despite the fact that bidentate N-[(dialkylamino)(thiocarbonyl)]benzamidines (I) are well known chelators and a large
number of their complexes with many transition metal ions,
such as Ni2+, Pd2+, Pt2+, Co3+, Cu2+, Ag+, and Au+ have been
extensively studied during the last three decades,[1] surprisingly less is known about tridentate benzamidines. Recently,
we have reported about such ligands (II), which can be prepared by reactions of benzimidoyl chlorides with functionalized primary amines.[2] These ligand systems allow a variety
of modifications in the periphery of their chelating system,
which tune their properties and also give access to amino acid
derivatives and bioconjugation.[3] Some complexes of the new

[TcNCl2(PPh3)2] is more labile than its analogous rhenium
compound and readily reacts with the ligand without the addition of a base (Scheme 1). The complexes are readily soluble
in polar organic solvents such as CHCl3 or THF. They are
stable as solids as well in solution. Their structures were studied by common spectroscopic methods.
Infrared spectra of the complexes exhibit strong bathochromic shifts of the νC=N stretches from the range between 1610
and 1620 cm–1 of the non-coordinated benzamidines to the
1510 cm–1 region. This indicates chelate formation with a large
degree of π-electron delocalization within the chelate rings and
has been observed before for the corresponding oxo
complexes.[2] The absence of absorptions in the regions around

© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Nitridorhenium(V) and Nitridotechnetium(V) Complexes

The structure of [TcN(L1b)(PPh3)] is virtually identical. Thus,
no extra Figure is presented for the technetium compound. The
corresponding bond lengths and angles, however, are also contained in Table 1.

Scheme 1. Reactions of [MNCl2(PPh3)2] (M = Re, Tc) with H2L1. The
addition of NEt3 is only required for the rhenium compound (see text).

3350 cm–1 and 3150 cm–1, in which the νNH and νOH stretches
are detected in the spectra of the uncoordinated H2L1, indicates
the expected double deprotonation of the ligands during complex formation. Absorption bands of medium intensity around
1065 cm–1 are assigned to Re≡N and Tc≡N stretches.[7]
The NMR spectra of the complexes provide additional evidence for the proposed composition and the molecular structures of the complexes. A hindered rotation around the C–NR2

Figure 1 illustrates the molecular structure of the rhenium complex. Selected bond lengths and angles are presented in Table 1.
Z. Anorg. Allg. Chem. 2011, 1330–1333

Figure 1. Ellipsoid representation of the molecular structure of
[ReN(L1b)(PPh3)]. Hydrogen atoms are omitted for clarity. Thermal
ellipsoids represent 50 per cent probability.

Table 1. Selected bond lengths /Å and angles /° in [MN(L1b)(PPh3)]
(M = Re, Tc) complexes The atomic labeling scheme of Figure 1 is
also applied for the technetium complex.

M–N10
M–P
M–S1
M–N5
M–O57
S1–C2
C2–N3
N3–C4
C4–N5
C2–N6
N10–M–P
N10–M–S1
N10–M–N5
N10–M–O57
P–M–N5
O57–M–S1

[ReN(L1b)(PPh3)]


104.9(2)
107.7(2)
112.0(2)
157.9(1)
143.0(1)

The metal atoms show distorted square-pyramidal coordination spheres with the nitrido ligands in apical positions. Such
an assignment of the molecular geometry is supported by the
corresponding τ values of 0.25 (technetium compound) and
0.24 (rhenium complex). They clearly indicate that the complexes under study are better described with a square-pyramidal coordination sphere (τ = 0) than as trigonal bipyramids (τ =
1). The thiocarbamoylbenzamidines coordinate meridional to
the metal atoms as tridentate dianionic ligands as in their previously reported oxo complexes. The remaining positions in the
basal planes of the square pyramids are occupied each by a
triphenylphosphine ligand. The metal atoms lie above the
equatorial planes towards the nitrido ligands by 0.528(2) Å for

© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.zaac.wiley-vch.de

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ARTICLE

H. H. Nguyen, T. N. Trieu, U. Abram

the rhenium complex and 0.544(2) Å for the technetium compound. The N10–Re–X angles (X = equatorial donor atom) fall
in the range between 92.6 and 111.5°, the corresponding N10–
Tc–X angles are between 93.3 and 112.0°. These values are in


Experimental Section
Materials and Measurements
All reagents used in this study were reagent grade and used without
further purification. Solvents were dried and used freshly distilled unless otherwise stated. [ReNCl2(PPh3)2][11] and [TcNCl2(PPh3)2][12] were
prepared by standard procedures. The synthesis of H2L1 ligands were
described in a previous paper.[2]
Infrared spectra were recorded from KBr pellets with a Shimadzu FT
instrument in the range 400–4000 cm–1. Positive electrospray ionization mass spectra (ESI+ MS) were measured with an Agilent 6210 ESITOF (Agilent Technologies) (results are given in the form: m/z, %
based peak, assignment). Elemental analyses were determined using
a Heraeus vario EL elemental analyzer. The technetium content was
determined by liquid scintillation measurements. NMR spectra were
taken at 25 °C with a JEOL 400 MHz multinuclear spectrometer.

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Radiation Precautions
99

Tc is a weak β- emitter. All manipulations with this isotope were
performed in a laboratory approved for the handling of radioactive
materials. Normal glassware provides adequate protection against the
low-energy β- emission of the technetium compounds. Secondary Xrays (bremsstrahlung) play an important role only when larger amounts
of 99Tc are used.

Synthesis of [ReN(L1)(PPh3)]
Solid [ReNCl2(PPh3)2] (80 mg, 0.1 mmol) was added to a stirred solution of H2L1 (0.1 mmol) in CH2Cl2 (5 mL). The mixture was stirred
at room temperature for 15 min and then 3 drops of Et3N were added.

PhOH), 6.64 (t, J = 7.6 Hz, 1 H, PhOH), 6.84 (d, J = 7.9 Hz, 1 H,
PhOH), 7.27 (t, J = 7.3 Hz, 2 H, Ph), 7.37 (m, 10 H, Ph + PPh3), 7.77
(m, 8 H, Ph +PPh3). 13C NMR (CDCl3): δ = 48.8, 49.7 (NCH2), 66.7,
66.9 (OCH2), 117.2–135.7 (Caromatic), 140.9 (Caromatic–N), 163.0
(Caromatic–O), 167.1 (C=N), 171.3 (C = S). 31P NMR (CDCl3): δ = 28.8
(s). ESI+ MS (m/z): 825, 100 %, [M + Na]+; 803, 40 %, [M + H]+.

Synthesis of [TcN(L1)(PPh3)].
The technetium complexes were prepared following the procedure described for their analogous rhenium complexes except that the precursor [TcNCl2(PPh3)2] was used and no NEt3 was added.
Data for [TcN(L1a)(PPh3)] (R1 = R2 = Et): Yield: 59 mg, 84 %. Elemental analysis. Calcd. for C36H34N4OPSTc: Tc, 14.1 %. Found: Tc,
14.1 %. IR: ν = 3051 (w), 2970 (w), 2924 (w), 1504 (vs), 1477 (vs),

© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Nitridorhenium(V) and Nitridotechnetium(V) Complexes
1434 (s), 1396 (m), 1350 (m), 1307 (m), 1258 (vs), 1095 (m), 1057
(m), 1026 (w), 798 (m), 741 (m), 690 (s), 528 (s), 497 (m) cm–1. 1H
NMR (CDCl3): δ = 1.09 (t, J = 7.1 Hz, 3 H, CH3), 1.26 (t, J = 7.1 Hz,
3 H, CH3), 3.67 (m, 1 H, CH2), 3.75 (m, 2 H, CH2), 4.00 (m, 1 H,
CH2), 6.23 (t, J = 7.5 Hz, 1 H, PhOH), 6.37 (d, J = 7.7 Hz, 1 H,
PhOH), 6.63 (t, J = 7.1 Hz, 1 H, PhOH), 6.79 (d, J = 7.8 Hz, 1 H,
PhOH), 7.26 (t, J = 7.4 Hz, 2 H, Ph), 7.30 (m, 10 H, Ph + PPh3), 7.73
(m, 8 H, Ph + PPh3). 31P NMR (CDCl3): δ = 45.4 (s).
Data for [TcN(L1b)(PPh3)] (NR1R2 = morph): Yield: 63 mg, 89 %.
Elemental analysis. Calcd. for C36H32N4O2PSTc: Tc, 13.8 %. Found:
Tc, 13.9 %. IR: ν = 3051 (w), 2970 (w), 2909 (w), 2843 (w), 1498
(vs), 1477 (vs), 1431 (s), 1400 (s), 1357 (w), 1312 (m), 1265 (s), 1215

No. of reflections
No. of independent /Rint
No. parameters
R1/wR2
GOF
Deposit reference number

[ReN(L1b)(PPh3)]

[TcN(L1b)(PPh3)]

C36H32N4O2PReS
801.89
triclinic
9.473(1)
11.650(1)
15.423(1)
95.04(1)
95.96(1)
108.32(1)
1593.9(2)
P1¯
2
1.671
3.968
17391
8499 / 0.1023
406
0.0422 / 0.0901
0.937

Acknowledgement
We thank the Deutscher Akademischer Austauschdienst (DAAD) for
generous support. H. H. Nguyen is additionally grateful to Vietnam’s
National Foundation for Science and Technology Development for the
financial support through project 104.02–2010.31.

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