DOI: 10.1002/zaac.201100134 Syntheses and Structures of NitridorheniumV and NitridotechnetiumV Complexes with N,N-[Dialkylaminothiocarbonyl]-N'-2-hydroxyphenylbenzamidines Hung Huy Nguy
Trang 1DOI: 10.1002/zaac.201100134
Syntheses and Structures of Nitridorhenium(V) and Nitridotechnetium(V)
Complexes with
N,N-[(Dialkylamino)(thiocarbonyl)]-N'-(2-hydroxyphenyl)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-[(di-alkylamino)(thiocarbonyl)]-N'-(2-hydroxyphenyl)benzamidines (H2L1)
with formation of neutral, five-coordinate nitrido complexes of the
Introduction
Despite the fact that bidentate
N-[(dialkylamino)(thiocar-bonyl)]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]
surpris-ingly less is known about tridentate benzamidines Recently,
we have reported about such ligands (II), which can be
pre-pared by reactions of benzimidoyl chlorides with
functional-ized 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
ligands, preferably derivatives of thiosemicarbazides, reveal
promising cytotoxic properties against human MCF-7 breast
cancer cells.[4]
Particularly the coordination chemistry of rhenium and
tech-netium with
N-[(dialkylamino)(thiocarbonyl)]-N'-(2-hydroxy-* Dr N H Huy
E-Mail: nguyenhunghuy@hus.edu.vn
* Prof Dr U Abram
Fax: +49-30-838-2676
E-Mail: ulrich.abram@fu-berlin.de
[a] Inorganic Chemistry Department
Hanoi University of Science
19 Le Thanh Tong
Hanoi, Vietnam
[b] Institute of Chemistry and Biochemistry
Freie Universität Berlin
Fabeckstrasse 34–36
14195 Berlin, Germany
composition [MN(L1)(PPh3)] The products have distorted square-pyramidal coordination spheres with each a tridentate, double-deproto-nated benzamidine and a PPh3ligand in their basal planes
phenyl)benzamidines (H2L1) has been intensively studied Most of the isolated complexes with these ligands have rhenium(V) or oxotechnetium(V) cores Five-coordinate oxo-rhenium(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 com-plexes of rhenium and technetium, here we report the synthesis and molecular structures of nitridorhenium(V) and nitridotech-netium(V) complexes with ligands of the type H2L1.
Results and Discussion
[MNCl2(PPh3)2] compounds (M = Re, Tc) are common
start-ing materials for the synthesis of ReV and TcV nitrido com-plexes The compounds are sparingly soluble in organic sol-vents However, they slowly dissolve in stirred solutions of
H2L1 in CH2Cl2 at room temperature with formation of deep red solutions, from which red crystalline products of the
com-position [MN(L1)(PPh3)] (M = Re, Tc) can be isolated in high
yields The addition of a supporting base like Et3N accelerates the consumption of [ReNCl2(PPh3)2], whereas [TcNCl2(PPh3)2] is more labile than its analogous rhenium compound and readily reacts with the ligand without the addi-tion 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 stud-ied by common spectroscopic methods.
Infrared spectra of the complexes exhibit strong bathochro-mic shifts of the νC=Nstretches from the range between 1610 and 1620 cm–1 of the non-coordinated benzamidines to the
1510 cm–1region 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
Trang 2Nitridorhenium(V) and Nitridotechnetium(V) Complexes
Scheme 1 Reactions of [MNCl2(PPh3)2] (M = Re, Tc) with H2L1 The
addition of NEt3is only required for the rhenium compound (see text)
3350 cm–1and 3150 cm–1, in which the νNHand νOHstretches
are detected in the spectra of the uncoordinated H2L1, indicates
the expected double deprotonation of the ligands during
com-plex formation Absorption bands of medium intensity around
1065 cm–1are assigned to Re≡N and Tc≡N stretches.[7]
The NMR spectra of the complexes provide additional
evi-dence for the proposed composition and the molecular
struc-tures of the complexes A hindered rotation around the C–NR2
bonds results in magnetic inequivalence of the two residues R.
Thus, two triplet signals of the methyl groups in the –NEt2
residues are observed in the 1H NMR spectra of
[ReN(L1a)(PPh3)] and [TcN(L1a)(PPh3)] at room temperature.
However, the proton signals of the two methylene groups,
which should consequently be two quartet signals, appear as
four multiplet resonances including two overlapping signals
at 3.80 ppm and two well separated signals at 3.68 ppm and
4.17 ppm in the spectrum of the rhenium compound This
pat-tern of the methylene signals can be explained by the rigid
structure of the tertiary amine group, which makes the
methyl-ene protons magnetically inequivalent with respect to their
ax-ial and equatorax-ial positions The rigidity of morpholinyl moiety
of {L1b}2– in [ReN(L1b)(PPh3)] results in four broad singlet
signals at 3.59, 3.81, 3.96, and 4.32 ppm, which correspond to
two CH2–N protons and two CH2–O protons The signals of
four other protons appear as two overlapping broad singlet
sig-nals at 3.70 and 4.16 ppm Similar coupling patterns are
ob-served in the spectra of the corresponding technetium
com-plexes.
The13C NMR spectra of the complexes are easier to explain,
since their patterns are only influenced by hindered rotation
around the C–NR2bonds Consequently, two separated signals
for each CH2 and CH3 carbon atoms in the NEt2groups and/
or CH2–N and CH2–O atoms in the morpholinyl units appear.
The presence of triphenylphosphine ligands in the coordination
sphere of the products is confirmed by each one singlet signal
in their31P NMR spectra, appearing around 30.0 ppm for the
rhenium compounds and around 45 ppm for the technetium
complexes.
ESI+ mass spectra of the rhenium complexes show intense
signals corresponding to the expected [M + Na]+and [M + H]+
ions.
X-ray structure analyses were performed for [ReN(L1b)(PPh3)]
and [TcN(L1b)(PPh3)] Suitable single crystals were obtained by
slow evaporation of CH2Cl2/MeOH solutions of the compounds.
Figure 1 illustrates the molecular structure of the rhenium
com-plex Selected bond lengths and angles are presented in Table 1.
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 con-tained in Table 1.
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
[ReN(L1b)(PPh3)] [TcN(L1b)(PPh3)]
The metal atoms show distorted square-pyramidal coordina-tion spheres with the nitrido ligands in apical posicoordina-tions 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 com-plexes under study are better described with a
square-pyrami-dal 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 previ-ously 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
Trang 3H H Nguyen, T N Trieu, U Abram
ARTICLE
the rhenium complex and 0.544(2) Å for the technetium
com-pound 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
complete agreement with the typical bonding situation of
square-pyramidal ReVN and TcVN complexes.[8]
The Re–N10 and Tc–N10 distances of 1.645(6) and
1.619(5) Å are within the expected range of rhenium or
techne-tium–nitrogen triple bonds.[9]The six-membered chelate rings
are strongly distorted for both complexes, with main deviations
of 0.413(4) Å (rhenium complex) and 0.419(4) Å (technetium
complex) from the mean least-square planes each for the
nitro-gen atoms N5 Nevertheless, a considerable delocalization of
π-electron density is observed This is indicated by the C–S and
C–N bond lengths inside the chelate rings, which all fall within
the range between carbon–sulfur and carbon–nitrogen single
and double bonds This bond length equalization is even
extended to the C2–N6 bonds, which are significantly shorter
than expected for single bonds All the MO, MN and M–S
bonds are slightly longer than those in the corresponding oxo
complexes.[2,5]This can be understood by the larger steric bulk
of the M≡N triple bond, which results in larger
N≡MX(equatorial) angles and consequently in a somewhat less
effective overlap between the ligand and the d orbitals of the
metal ions Details have been discussed previously on a series
of oxo, nitrido and phenylimido compounds of technetium and
rhenium with 1,2-dicyanoethene-1,2-dithiolate.[10]
Conclusions
The ready synthesis and the stability of the nitrido complexes
under study and the promising biological properties of the
re-lated oxo compounds[2–4] recommend transition metal
com-plexes with ligands of the thiocarbamoylbenzamidine family
for further consideration with regard to medical and nuclear
medical applications Ongoing studies with tri- to pentadentate
ligands with peripheral coupling positions for biomolecules are
presently underway in our laboratories They also include
ni-trido complexes with the ligands discussed in this paper as
well as tetradentate systems derived from diamines.
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
un-less otherwise stated [ReNCl2(PPh3)2][11]and [TcNCl2(PPh3)2][12]were
prepared by standard procedures The synthesis of H2L1ligands 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
ioniza-tion mass spectra (ESI+MS) were measured with an Agilent 6210
ESI-TOF (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
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 X-rays (bremsstrahlung) play an important role only when larger amounts
of99Tc are used
Synthesis of [ReN(L1)(PPh3)]
Solid [ReNCl2(PPh3)2] (80 mg, 0.1 mmol) was added to a stirred solu-tion 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 This resulted in a complete dissolution of [ReNCl2(PPh3)2] and the formation of a red solution The solvent was removed under vacuum, and the residue was crystallized by slow evaporation of a CH2Cl2/ MeOH solution as red blocks The side products (HNEt3)Cl and PPh3
remain in the residual MeOH Alternatively, the crude reaction product can be washed twice with methanol before re-dissolution in CH2Cl2
for crystallization
Data for [ReN(L 1a )(PPh 3)] (R1= R2 = Et): Yield: 60 mg, 76 %
Ele-mental analysis Calcd for C36H34N4OPSRe: C, 54.88; H, 4.35; N,
7.11; S, 4.07 % Found: C, 54.78; H, 4.30; N, 7.07; S, 4.15 % IR:
ν = 3059 (w), 2978 (w), 2932 (w), 1512 (vs), 1492 (vs), 1477 (vs),
1439 (s), 1393 (m), 1354 (m), 1254 (vs), 1096 (m), 1065 (m), 1026 (w), 744 (m), 686 (s), 528 (s), 505 (m).1 H NMR (CDCl3): δ = 1.08 (t, J = 7.0 Hz, 3 H, CH3), 1.26 (t, J = 7.1 Hz, 3 H, CH3), 3.68 (m, 1
H, CH2), 3.80 (m, 2 H, CH2), 4.17 (m, 1 H, CH2), 6.27 (t, J = 7.6 Hz,
1 H, PhOH), 6.47 (d, J = 7.8 Hz, 1 H, PhOH), 6.62 (t, J = 7.0 Hz, 1
H, PhOH), 6.83 (d, J = 7.8 Hz, 1 H, PhOH), 7.26 (t, J = 7.3 Hz, 2 H,
Ph), 7.35 (m, 10 H, Ph + PPh3), 7.79 (m, 8 H, Ph + PPh3).13 C NMR
(CDCl3): δ = 12.8, 13.2 (CH3), 46.3, 47.7 (CH2), 117.0–135.8 (Caromatic), 141.3 (Caromatic–N), 162.1 (Caromatic–O), 166.8 (C=N), 171.6 (C = S).31 P NMR (CDCl3): δ = 29.6 (s) ESI+MS (m/z): 811, 100 %,
[M + Na]+; 789, 40 %, [M + H]+
Data for [ReN(L 1b )(PPh 3)] (NR1R2 = morph): Yield: 64 mg, 80 %.
Elemental analysis Calcd for C36H32N4O2PSRe: C, 53.92; H, 4.02; N,
6.99; S, 4.00 % Found: C, 53.87; H, 4.15; N, 7.10; S, 4.09 % IR: ν =
3051 (w), 2970 (w), 2905 (w), 2858 (w), 1507 (vs), 1477 (vs), 1435 (s), 1388 (s), 1357 (w), 1257 (s), 1219 (m), 1096 (m), 1068 (m), 1026 (m), 745 (m), 690 (s), 528 (s), 505 (m).1 H NMR (CDCl3): δ = 3.59
(br s, 1 H, NCH2), 3.70 (br s, 2 H, NCH2), 3.81 (br s, 1 H, NCH2), 3.96 (br s, 1 H, OCH2), 4.16 (br s, 2 H, OCH2), 4.32 (br s, 1 H, OCH2), 6.27 (t, J = 7.6 Hz, 1 H, PhOH), 6.49 (d, J = 7.8 Hz, 1 H, 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).13 C 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).31 P 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 de-scribed for their analogous rhenium complexes except that the precur-sor [TcNCl2(PPh3)2] was used and no NEt3was added
Data for [TcN(L 1a )(PPh 3)] (R1= R2 = Et): Yield: 59 mg, 84 %
Ele-mental analysis Calcd for C36H34N4OPSTc: Tc, 14.1 % Found: Tc,
14.1 % IR: ν = 3051 (w), 2970 (w), 2924 (w), 1504 (vs), 1477 (vs),
Trang 4Nitridorhenium(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–1.1 H
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).31 P NMR (CDCl3): δ = 45.4 (s).
Data for [TcN(L 1b )(PPh 3)] (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
(m), 1095 (m), 1060 (m), 1026 (m), 844 (m), 748 (s), 691 (s), 524 (s),
505 (m) cm–1 1 H NMR (400 MHz, CDCl3): δ = 3.61 (br s, 1 H,
NCH2), 3.70 (m, 2 H, NCH2), 3.76 (br s, 1 H, NCH2), 3.98 (br s, 1
H, OCH2), 4.05 (br m, 2 H, OCH2), 4.20 (br s, 1 H, OCH2), 6.22 (t,
J = 7.5 Hz, 1 H, PhOH), 6.38 (d, J = 7.8 Hz, 1 H, PhOH), 6.65 (t, J =
7.6 Hz, 1 H, PhOH), 6.79 (d, J = 7.8 Hz, 1 H, PhOH), 7.22 (t, J =
7.4 Hz, 2 H, Ph), 7.34 (m, 10 H, Ph + PPh3), 7.71 (m, 8 H, Ph +
PPh3).31P NMR (CDCl): δ = 44.6 (s).
X-ray Crystallography
The X-ray diffraction data were collected with a STOE IPDS
diffrac-tometer with Mo-Kαradiation The structures were solved by the
Pat-terson method using SHELXS-97.[13] Subsequent Fourier-difference
map analyses yielded the positions of the non-hydrogen atoms
Refine-ment was performed using SHELXL-97.[13]The positions of hydrogen
atoms were calculated for idealized positions and treated with the
‘rid-Table 2 Crystal data and refinement results.
[ReN(L1b)(PPh3)] [TcN(L1b)(PPh3)]
Formula C36H32N4O2PReS C36H32N4O2PSTc
Dcalcd./g·cm–3 1.671 1.485
No of independent /Rint 8499 / 0.1023 8518 / 0.1245
ing 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
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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Received: March 21, 2011 Published Online: June 6, 2011