Design, Synthesis, and Reactivity of Multidentate Ligands with Rhenium(I) and Rhenium(V) Cores

Article abstract of DOI:10.1002/ejic.201700632

Synthetic pathways to a range of potentially N₃O-tetradentate ligands designed to coordinate to rhenium cores, as well as their coordination behaviors towards different rhenium cores (oxidation states +I and +V) are investigated. Two functionalized N-{[1-(4-R)-1H-1,2,3-triazol-4-yl]methyl}-2-(pyridin-2-ylmethoxy)aniline derivatives L₁H (R = methyl acetate) and L₂H (R = 4-nitrophenyl) act exclusively as bidentate ligands and lead to the formation of mononuclear tricarbonylrhenium(I) complexes of the general formula [(LH)Re(CO)₃Cl] with L = L₁ or L₂. Both complexes are characterized by ¹H NMR and ¹³C NMR, FTIR spectroscopy, electrospray ionization mass spectrometry, and in the case of [(L₂H)Re(CO)₃Cl], single-crystal X-ray diffraction. The rhenium is coordinated by three carbonyl groups, a chlorine atom and two nitrogen atoms of a triazole group, and a nitrogen of the aniline ring of the ligand, respectively. A theoretical study shows complex [(L₂H)Re(CO)₃Cl] is the most stable structural isomer. In addition, the oxorhenium(V) complex [(L₃)ReO] is isolated and fully characterized after the reaction of the Re^V precursor [ReOCl₃(PPh₃)₂] with L₃H₃ [methyl 2-(4-{[2-(2-hydroxyphenylamino)-2-oxoethylamino]methyl}-1H-1,2,3-triazol-1-yl)acetate]. Its corresponding ^99mTc complex was achieved with a good radiochemical yield (> 90 %). The convenient synthesis of this ligand, coupled with its high affinity for [ReO]³⁺ and [^99mTcO]³⁺ cores, make it a promising chelator for biomedical applications.

Full text of DOI:10.1002/ejic.201700632

A Journal of
Accepted Article
Title: Design, synthesis and reactivity of multidentate ligands with
rhenium(I) and rhenium(V) cores
Authors: Jin Hui WANG, Romain Eychenne, Mariusz Wolff, Sonia
Ladeira, Nicolas Lepareur, and Eric Benoist
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201700632
Link to VoR: http://dx.doi.org/10.1002/ejic.201700632

European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Design, synthesis and reactivity of multidentate ligands with rhenium(I) and rhenium(V)
cores
a,b
a,b
c, *
d
Jin-Hui Wang , Romain Eychenne , Mariusz Wolff , Sonia Mallet-Ladeira , Nicolas
e
†a,b
Lepareur, Eric Benoist
aCNRS, Laboratoire de Synthèse et Physico-Chimie de Molécules d'Intérêt Biologique, SPCMIB, UMR 5068,
18, Route de Narbonne, F-31062 Toulouse Cedex 9, France,
1
bUniversité de Toulouse, UPS, Laboratoire de Synthèse et Physico-Chimie de Molécules d'Intérêt Biologique,
SPCMIB, UMR 5068, 118, Route de Narbonne, F-31062 Toulouse Cedex 9, France,
c
th
University of Silesia, Institute of Chemistry, Department of Crystallography, 9 Szkolna St., 40-006 Katowice,
Poland,
dInstitut de Chimie de Toulouse (FR 2599), 118 Route de Narbonne, Toulouse 31062 Cedex 09, France.
eCentre Eugène Marquis, Radiopharmacy/Nuclear Medicine Department, INSERM UMR-S 1241, 35042,
Rennes, France.
Abstract: Synthetic pathways to a range of potentially N O tetradentate ligands,
3
designed to coordinate rhenium cores as well as their coordination behaviours towards different
rhenium cores (oxidation states +I and +V) are investigated. Two functionalized N-((1-(4-R)-
1
H-1,2,3-triazol-4-yl)methyl)-2-(pyridin-2-ylmethoxy)aniline derivatives L
acetate) and L H (R = 4-nitrophenyl) act exclusively as bidentate ligands and lead to the
formation of mononuclear tricarbonylrhenium(I) complexes of general formula
1
H (R = methyl
2
1
13
[
(LH)Re(CO)
FT-IR spectroscopy, electrospray ionization mass spectrometry and in the case of
(L H)Re(CO) Cl] single crystal X-ray diffraction study. The rhenium is coordinated by the
three carbonyl groups, the chlorine and the two nitrogens of the triazole and the nitrogen of the
aniline ring of the ligand, respectively. Theoretical study shows complex [(L H)Re(CO) Cl] is
the most stable structural isomer. In addition, the oxorhenium(V) complex [(L )ReO] is isolated
and fully characterized after the reaction of the Re(V) precursor [ReOCl (PPh ] with L
methyl 2-(4-((2-(2-hydroxyphenylamino)-2-oxoethylamino)methyl)-1H-1,2,3-triazol-1-
yl)acetate). Its corresponding 99mTc-complex was achieved with a good radiochemical yield
3
Cl] with L = L
1
or L
2
. Both complexes are characterized by H and C NMR,
[
2
3
2
3
3
3
3
)
2
3
H
3
(
3
+
(
>90%). The convenient synthesis of this ligand coupled with its high affinity for [ReO] and
[99m
TcO] cores make it a promising chelator for biomedical applications.
3+
*
Present address: Johannes Kepler Universität Linz, Institut für Anorganische Chemie, Altenberger Straße 69,
040 Linz, Austria,
Corresponding author: benoist@chimie.ups-tlse.fr (E. Benoist)
4
†
1
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Keywords: Oxorhenium(V) complex, tricarbonylrhenium(I) complex, polydentate ligands, X-
ray crystals structure, DFT calculations.
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Introduction
Rhenium coordination chemistry has gained considerable attention in the last three decades.
This interest is mainly due to the large range of its oxidation states (eight different oxidation
states varying from –I to +VII) and consequently the ability to develop numerous chelating
systems to stabilize different rhenium cores, particularly +I, +III and +V oxidation states.
Another interest is the potential applications of the corresponding rhenium complexes as
1
2
3
catalysts or photocatalysts, imaging agents (luminescent probes and IR probes ) or
therapeutic probes (CORMs or 188Re-radiopharmaceuticals).4
The structure of Re-specific chelating systems is largely influenced by the oxidation states of
the rhenium atom and the nature of its metallic cores. While tridentate or bidentate ligands
including oxygen or N-heteroaromatic nitrogen donor atoms are preferable for the stabilization
]+
the Re(V) species mainly [ReO] and [ReN]
3+
2+
of the tricarbonylrhenium(I) core [Re(CO)
3
,
moieties, is preferably stabilized by tetradentate ligands combining sulfur, nitrogen, phosphorus
and to a lesser extent oxygen donor atoms. These considerations have drawn our attention and
that of other groups to the possibility of applying the Copper(I)-catalyzed Alkyne-Azide
Cycloaddition (CuAAC) to the synthesis of multidentate ligands for rhenium(I) cores (and
5
analogous technetium-99m cores as well). Its remarkable simplicity and efficiency combined
6
to the Click-to-Chelate approach developed by Schibli et al., has made it a powerful tool for
7
the conception of technetium(I) and rhenium(I) labelled radiopharmaceuticals. In contrast, up
to date, no example of an oxorhenium(V) radiocomplex based on a click ligand have been
reported. In addition, although coordination behaviours of chelators towards rhenium(I) and
8
rhenium(V) cores have been described, to our best knowledge, the development of a family of
chelating species able to lead to stable Re(I) and Re(V) complexes has been rarely explored.
We previously reported stable technetium-99m and rhenium-188 tricarbonyl complexes based
9
]+
O bifunctional chelating agents (BCAs), led us to
extend our studies to a series of potentially N O tetradentate ligands and to investigate the
coordination chemistry of their corresponding rhenium complexes in different oxidation states
+I and +V). In this present work, two synthetic strategies are reported for the preparation of
three new semi-rigid tetradentate ligands, as depicted in scheme 1. L H and L H act exclusively
as bidentate ligands and lead to the formation of mononuclear tricarbonylrhenium(I) complexes
of general formula [(LH)Re(CO) Cl] with LH = L H or L H, as confirmed by single crystal
on a semi-rigid click ligand. The excellent coordination capability towards the fac-[M(CO)
3
(
M = 99mTc or 188Re) moieties for tripodal N
2
3
(
1
2
3
1
2
X-ray diffraction study and DFT calculations. In contrast, the ligand L
3
H
3
acts as tetradentate
3
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
ligand and gave in high yield, its charge-neutral oxorhenium(V) and oxotechnetium(V)
complexes [(L
)MO] (M = Re or 99mTc).
3
Results and Discussion
Synthesis of the ligands and their corresponding rhenium complexes
As mentioned above, the goal of this work was to develop potentially tetradentate (N,O)-donor
9
BCAs based on a semi-rigid scaffold for rhenium cores (Scheme 1). Three new chelators, L
1
H,
L
2
H, L
3
H were synthesized either by introducing on the aromatic hydroxyl group a pyridine
3
coordinating arm (pathway A) or by the insertion of a glycine moiety between the aromatic and
triazole rings (pathway B).
The preparation of L
1
H and L H follows a five-steps procedure as shown in scheme 2. Briefly,
2
N-Boc-protected derivative (compound 1) of hydroxyaniline reacted under argon atmosphere
with 2-picolyl chloride hydrochloride in basic conditions to give 2 in 78% yield. N-alkylation
of compound 2 with propargyl bromide in the presence of sodium hydride yielded the protected
ligand 3. Subsequent treatment with an excess of trifluoroacetic acid resulted in cleavage of the
Boc group, yielding 4 (global yield of 42% starting from 2-hydroxyaniline). Then, ligands L
and L H are afforded by the triazole formed upon coupling of 4 with freshly prepared
azidomethylacetate or 4-azidonitrobenzene respectively, using classical click reaction
conditions (catalytic amount of Cu(OAc) .H O and sodium ascorbate in tBuOH/water
solution). Compound L H has also been prepared by conducting first the click reaction followed
by the N-Boc deprotection. In this pathway, a significantly lower yield was observed for the
CuAAC reaction (69% for 5 vs. 81% for L H), probably due to a steric hindrance generated by
the Boc group. Additionally, ESI-MS analysis revealed that no detectable coordination of
1
H
2
2
2
2
2
copper(I) species to L
1
H, L H and compound 4 was observed in the medium, during the click
2
chemistry step.
We also attempted to prepare an expanded analogue of L
carboxylate coordinating arm instead of a pyridine one, but were unable to obtain the desired
tetradentate ligand (see ESI part for detailed synthetic pathways). Regardless of the
1
H and L H by introducing a
2
N
2
O
2
approaches we tried, a ring closure side-reaction was always observed, yielding to a
benzoxazine derivative as a major product.
As depicted in Scheme 3, L
3
3
H was prepared in five steps with a global yield of 33%.
Compound 14 resulted from a conventional carbodiimide amide coupling of hydroxyaniline
4
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
and the activated ester 13, this latter compound being first prepared in two steps (N-alkylation
of N-Boc glycine with propargyl bromide followed by the activation of the carboxylic acid of
1
2 with NHS in the presence of DCC). Copper-catalyzed Huisgen [3+2] cyclodipolar addition
of 14 and methyl azidoacetate followed by N-Boc deprotection in acidic conditions yielded
L
3
H
3.
All the compounds were unambiguously identified by the common analytical techniques
including X-ray crystallographic analysis in the case of L H and L H. A representation of the
structures of L H and L H appears in Figure 1 and ESI part (Figure S1), respectively. As
1
2
1
2
expected, structural features are classical and compare well to bond distances and angles
observed for substituted triazoles, e.g. an azo character of the 1,2,3-triazole ring (Table 1).9,10
The synthesis of oxorhenium(V) complexes by the ligand-exchange reaction in warm methanol
1
1
of a slight excess of labile trans-[ReOCl
3
(PPh
3
)
2
] with L
1
H or L H (1.3:1 metal:ligand ratio)
2
in the presence of a methanolic sodium acetate solution as deprotonating agent surprisingly
failed, and only led to the recovery of the starting material. In contrast, using the same
procedure, L
Scheme 4). Unfortunately, attempts to obtain single crystals were unsuccessful.
In addition, two tricarbonylrhenium(I) complexes [(LH)Re(CO) Cl] (LH = L H or L
easily prepared from modest to good yields (60-80%) by the reaction of [Re(CO) Cl] with L
or L H in 1.15:1 molar ratio in the presence of Hünig's base in refluxing methanol. Complex
(L H)Re(CO) Cl] crystallised from acetone/acetonitrile solution by slow evaporation and
3
H
3
gave the corresponding oxorhenium complex [(L
3
)ReO], in modest yield
(
3
1
2
H) were
5
1
H
2
[
2
3
afforded yellow crystals suitable for X-ray analysis.
These three rhenium complexes are soluble in dichloromethane, chloroform, DMSO and
insoluble in water. They are stable in the solid state as well as in organic solvents and their
stability is not affected by the presence of air or moisture.
Tricarbonylrhenium(I) complexes: structural and computational studies
Infrared spectra of both complexes [(LH)Re(CO)
characteristic (CO) stretching bands at ca. 2024, 1910 and 1885 cm , attributed to the fac-
Re(CO)
]+ unit, as expected. More interestingly, ESI analysis in the positive mode generated
the parent peak [M+H] and/or the [M-Cl] ion, with the correct isotopic distribution patterns,
3
Cl] (LH = L
1
H or L
2
H) exhibited the
-1
[
3
+
+
indicating that L
1
H and L
2
H were coordinated to the metal center in a unexpected bidentate
fashion.
5
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
To elucidate this bidentate coordination mode, experimental and theoretical proton and carbon
NMR experiments were performed. Two coordination modes could be considered: bidentate
coordination through the two nitrogens of the triazole and the aromatic rings (Nta, NHarom.
coordination) or coordination through the oxygen atom and the nitrogen of the pyridine arm (O,
pyr.-coordination). In proton NMR, the signal of the triazole proton is significantly downfield
shifted (ca. 0.5 ppm) as compared to the metal free ligand, as highlighted in the Figure 2 for
(L H)Re(CO) Cl]. The same trend can also be observed for the protons of the methylene
group adjacent to the triazole unit. In addition, while no marked downfield shift was observed
for the signals of the four aromatic protons, the shapes of the multiplets for the ligand L H and
-
N
[
1
3
1
its corresponding rhenium complex are largely different. In contrast, the signals relative to the
pyridine protons are not affected by the metal complexation (Figure 2). These observations
suggest that our ligand L
1
H (and L H) is coordinated to the rhenium center in a (Nta, NHarom.)-
2
bidentate fashion.12
Theoretical proton and carbon NMR data are gathered in ESI part (Table S2a and Table S2b,
1
respectively). The calculated H NMR chemical shifts for [(L
2
H)Re(CO) Cl] are in good
3
1
agreement with the experimental H NMR data. Nevertheless, calculated proton NMR chemical
shifts for potential isomer 1 which corresponds to the rhenium(I) complex with a (O, Npyr.)-
bidentate fashion (Figure 3), were close to those calculated for [(L
2
H)Re(CO) Cl]. On the basis
3
of these computational data, it was difficult to definitively conclude in favor of a (Nta, NHarom.)-
bidentate coordination compared to a (O, Npyr.)-bidentate fashion. The coordination mode was
finally confirmed by X-ray diffraction analysis in the case of [(L
2
H)Re(CO) Cl].
3
X-ray diffraction study: Single crystals of [(L
2
H)Re(CO) Cl] were investigated by X-ray
3
diffraction. Figure 1 shows the ORTEP diagram of the complex [(L
2
H)Re(CO) Cl] and
3
selected parameters are listed in Table 1.
In [(L
2
H)Re(CO)
3
Cl], the ligand L H is coordinated to the rhenium atom in a bidentate N,N-
2
fashion through the nitrogen atom N(2)H of the secondary amine and triazole nitrogen atom
forming a five-membered chelate ring with the bite angle N(2)–Re(1)–N(3) of 75.8(2)°. The
five-membered chelate ring, [ReN(2)C(16)C(17)N(3)], adopts an envelope conformation, with
the C(16) atom deviating from the N(2)–Re–N(3)–C(17) plane by 0.304 Å. As expected, the
three carbonyl groups are bound to the rhenium(I) center in a facial arrangement. The sixth
position is occupied by the chlorido ligand. The octahedral coordination environment around
the metal center is distorted. The calculated octahedral distortion parameter (Σ) and the average
trigonal distortion angle (Θ), which define the degree of distortion from an ideal octahedron,
6
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
are equal to 5.53° and 4.33°, respectively. The Re–carbonyl bond distances, Re(1)–C(1) =
1
2
.916(10) Å, Re(1)–C(2) = 1.910(9) Å and Re(1)–C(3) = 1.923(8) Å, as well as Re(1)–Cl(1) =
.480(2) Å, are consistent which those found for other Re–tricarbonyl complexes containing
bidentate ligands.9b,10,12 The longest Re–C(3) bond distance is trans to the triazole ring. The
Re–N(3)ta bond distance (2.157(5) Å) is also comparable and significantly shorter than the
distance between the metal and the nitrogen atom of the secondary amine (Re–N(2)amine
=
2
3
2
.280(7) Å) as expected for the sp vs. sp hybridization of the nitrogen atoms, respectively.
(L H)Re(CO) Cl] crystallizes in the orthorhombic P2 space group with four molecules
per unit cell. The single crystal X-ray structure of [(L H)Re(CO) Cl] shows two types of
[
2
3
1
2
1 1
2
2
3
hydrogen bonding interaction (see ESI part, Table S3): stronger intramolecular hydrogen
bonding interactions of the type N—H•••O (2.647(8) Å) between the N(2)–H proton of the
secondary amine and O(4) atom as well as C—H•••O (2.737(10) Å) between the C(7)–H proton
of the 2-pyridyl group and O(4) atom on the same molecule and weaker intermolecular
hydrogen bonding interactions C—H•••O of methylene C(16)–H donors or 4-nitrophenyl
C(24)–H donors to carbonyl O(1) acceptors (ESI part, Figure S2A) and C—H•••O of methylene
C(9)-H donors or 2-pyridyl C(11)–H donors to nitro oxygen O(5) acceptors (ESI part, Figure
S2B). The weakest interactions involve also C—H•••Cl with Cl(1) atoms as acceptor groups
and methylene C(16)–H donors or triazole C(18)–H donors (ESI part, Figure S2C).
Besides C—H•••Cl interactions, two different types of slipped π–π stacking interactions
between N(3)N(4)N(5)C(17)C(18) and C(10)C(11)C(12)C(13)C(14)C(15) rings (symmetry
code: 1–x, 1/2+y, 1/2–z) [with a centroid-to-centroid distance of 3.681(4) Å and an interplanar
angle between the planes of these rings of 16.9(4)°] and between
C(10)C(11)C(12)C(13)C(14)C(15) and C(19)C(20)C(21)C(22)C(23)C(24) rings (symmetry
code: –x, –1/2+y, 1/2–z) [with a centroid-to-centroid distance of 4.081(4) Å and an interplanar
angle between the planes of these rings of 8.2(4)°] appear to be involved in the stabilization of
the crystal structure. Two CH−π interactions, the first one between C(5)–H and the 2-pyridyl
ring N(1)C(4)C(5)C(6)C(7)C(8) (symmetry code: 1/2+x, 3/2–y, –z) of the adjacent complex
(CH−centroid distance 2.81 Å), and the second one between C(9)–H and the 4-nitrophenyl ring
C(19)C(20)C(21)C(22)C(23)C(24) (symmetry code: 1–x, –1/2+y, 1/2–z) of the adjacent
complex (CH−centroid distance 2.80 Å) also stabilize the crystal structure.
Optimized structural geometries: DFT calculations were carried out on the potential structures
of tricarbonylrhenium(I) complexes based on L H as illustrated in Figure 3. Five different
2
isomers (bidentate, tridentate coordination, mer, fac isomers) were optimized with
7
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
B3LYP/LANDL2DZ.13,14 IR frequency spectra and the geometric parameters such as bond
lengths and bond angles as well as the calculated energy values of rhenium complexes are
reported in ESI part (Figure S3 and Tables S4-S6). The most stable isomer corresponds to the
complex [(L
2
H)Re(CO) Cl], in which the rhenium core is coordinated by the triazole ring and
3
the amino group of the aromatic moiety (fac-Nta,N coordination). The geometry obtained
theoretically is in good agreement with that obtained by X-ray crystallography. The isomer 1,
−
1
is found to be less stable than [(L
2
H)Re(CO) Cl] by 9.13 kcal mol . This energy difference at
3
room temperature indicates that this isomer can only exist as a minor product. Benny et al.
previously reported that in a multidentate ligand including pyridine and triazole rings, the
]+ core (M = 99mTc or Re) over the triazole. In
15
pyridine favored coordination to the [M(CO)
3
our case, the experimental and DFT findings showed that the binding strength of the (Nta
,
NHarom.)-bidentate pincer is stronger than that of the (Npyr, O )-bidentate one. Then, the
.
significant energy difference observed between isomers exhibiting a bidentate or a tridentate
coordination mode confirmed that the tridentate coordination mode could not be considered
with our ligands L
tricarbonylrhenium(I) complexes (isomers 2b, 3b) are less stable than analogous fac-ones
isomers 2a, 3a), as expected.
1
H and L H. In addition, DFT calculations showed mer-
2
(
Oxorhenium(V) complex: structural characterization and preliminary 99mTc-
radiolabelling
In the free ligand L
singlet at 3.41 ppm. After complexation with [ReOCl
doublets forming the pattern of two AB-spin systems at 4.77 and 5.17 ppm with geminal
coupling constants of approximately 18.0 Hz for [(L )ReO]. The same trend was observed for
3
H
3
, the methylene group next to the amide function appears as a unique
3
(PPh ], the singlet splits into two
3 2
)
3
the two protons close to the triazole ring. Upon complexation, they are non-equivalent and split
into two multiplets at 4.03 and 5.22 ppm. In addition, the signal for the corresponding triazole
proton is slightly shifted downfield by 0.23 ppm upon coordination. In carbon NMR, the most
distinguishing feature was the change in the chemical shift of the carbon atoms of the amide
group (188 ppm for the complex vs. 171 ppm for the ligand). The significant downfield shift
stems from the fact that, upon coordination to rhenium the electron density on the nitrogen of
the amide bond is less available to participate in resonance delocalization with the carbonyl
group. These NMR features are consistent with those reported for structurally related
1
6
oxorhenium(V) complexes. Negative-ion electrospray of the complex presents two prominent
ion peaks with an isotope distribution pattern consistent with the monomeric neutral complex.
8
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
-1
Then, the IR spectra showed an absorption at 959 cm indicating the presence of a rhenium-
oxo bond, as expected.
Considering that perrhenate anion 188ReO -
is more difficult to reduce than pertechnetate anion
4
99mTcO
-
combined with the high tendency of produced oxorhenium core [ ReO] to be
188
3+
4
reoxidized, a preliminary radiochemistry study was carried out with the analogous technetium-
9m core, [99mTcO] . The strict follow-up of the protocol of Martinage et al. allowed to get
3+
17
9
the expected 99mTcO-radiocomplex with a moderate yield of 70%. Different trials in order to
optimize this step -a higher temperature (50°C), a lower concentration (1 or 2 mg/mL) of
stannous chloride or a lower quantity of NaOH 0.1 M (< 140 µL)- showed a negative impact
on the radiochemical yield. Finally, better yields were obtained with a higher concentration of
stannous chloride (3 mg/mL) leading to the expected 99mTc-complex [(L
)99mTcO] in 90% yield
3
(see ESI part, Figure S4). Its chemical identity was confirmed by comparison of its HPLC
profile with that of the corresponding cold rhenium complex.
Conclusion
In summary, we synthesized a new series of potentially tetradentate semi-rigid ligands
including an aromatic ring and a triazole unit, by two distinct synthetic routes. The coordination
behaviours of L
unambiguously characterized by spectroscopic analyses as well as single crystal X-ray
diffraction for [(L H)Re(CO) Cl]. L H and L H exhibit an unexpected bidentate coordination
mode through the two nitrogens of the aromatic and triazole rings, respectively.
(LH)Re(CO) Cl] (L = L or L ) represents the most stable structural isomer as confirmed by
a DFT study. In addition, the mononuclear complex [(L )ReO] was isolated and fully
characterized after reaction of the Re(V) precursor [ReOCl
1
H and L
2
H ligands was investigated and fac-rhenium(I) complexes were
2
3
1
2
[
3
1
2
3
3
(PPh
3
2
) ] with L
3
H . The high
3
(V)
3+
99m
(V)
3+
affinity of the N O set toward cold [Re O] and [ Tc O] should be expected also for
3
[188
Re O] core, making this ligand a promising chelator for biomedical applications (as
(V)
3+
theranostic probes). 188Re-radiolabelling is under investigation.
Experimental section
General: All purchased chemicals were of the highest purity commercially available and used
1
13
without further purification. H and C spectra were recorded on a Bruker Avance 300 (75.5)
MHz or on a Bruker Avance DRX 500 (125) MHz spectrometer; chemical shifts are reported
9
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
in parts per million (ppm) relative to a residual solvent peak and coupling constants (J) are
given in Hertz (Hz). Multiplicities were recorded as s (singlet), br s (broad singlet), d (doublet),
t (triplet), q (quadruplet) … and m (multiplet). Electrospray (ESI) mass spectra were obtained
on a Q TRAP Applied Biosystems spectrometer and High-Resolution Mass Spectra (HRMS)
on an LCT Premier Waters spectrometer. DCI (CH
4
or NH
3
) mass spectra were obtained on a
DSQ II Thermo Fisher. Infrared spectra were recorded on a Perkin Elmer FTIR 1725
-1
spectrophotometer in the range 4000-400 cm .
Literature methods were used to prepare [ReOCl
1
1
18
3
(PPh ) ], methyl azidoacetate, and 4-
3
2
1
2
azidonitrobenzene (if azido compounds are potentially explosive intermediates, in our hands,
we never observed hazardous reactions for both azido intermediates). Preparation of N
2
O
tridentate ligand (compound A) and its intermediate 2-(prop-2-yn-1-ylamino)phenol (8) have
been described previously.9b
X-ray structure analysis: X-ray intensity data of compounds L
1
H, L H, and
2
[
(L H)Re(CO) Cl] were collected on a Bruker D8 VENTURE diffractometer and using
2
3
graphite monochromated Mo Kα radiation (λ = 0.71073 Å) at 193 K. The semi-empirical
absorption corrections were employed [SADABS, Program for data correction, Bruker-AXS].
Crystallographic data and refinement details are given in Table 1. The structures were solved
by direct methods and completed by subsequent difference-Fourier syntheses, and refined by
2
full matrix least squares procedures on F . All non-hydrogen atoms were refined with
anisotropic displacement coefficients. The hydrogen atoms bound to carbon atoms were placed
in calculated positions and treated as riding on their parent atoms with d(C—H) = 0.93 Å,
Uiso(H) = 1.2 Ueq(C) (aromatic); and d(C—H) = 0.96 Å, Uiso(H) = 1.5 Ueq(C) (methyl). The
methyl groups were allowed to rotate about their local threefold axis. The ShelX software
1
9
20
package within Olex2 were used for the calculations.
CCDC 1551602, 1551603 and 1551604 contain the supplementary crystallographic data for
compounds L
1
H, L
2
H, and [(L
2
H)Re(CO) Cl], respectively. These data can be obtained free
3
of charge from http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; tel: +44 (0)1223
3
36408; fax: +44 (0)1223 336033; or e-mail: deposit@ccdc.cam.ac.uk.
Computational studies: The GAUSSIAN09 program package 21 was used for all the
calculations with the aid of the ChemCraft visualization program. 22 The ground-state
geometries of complexes were fully optimized in gas-phase without any symmetry constraint
with the DFT method using the hybrid exchange-correlation B3LYP functional12,13 (See ESI
part for more details).
1
0
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Radiochemistry: 99mTc as carrier-free Na[99mTcO
] was obtained in physiological solution by
4
saline elution from a commercially available 99Mo/99mTc generator (Elumatic III, IBA
Molecular or Drytec, GE Healthcare). Activities were measured with a CRC-127R well-counter
(Capintec). The radiochemical purities (RCP) of the complex were determined by using a
Cyclone Storage Phosphor Imager (PerkinElmer) with the Packard Optiquant software. The
product was also characterized by HPLC (Thermo Fischer Scientific), on a Dionex Ultimate
3
000 instrument equipped with a diode array detector and a radiochromatographic fLumo
Berthold) detector piloted by the Chromeleon software. The chromatographic analytic system
employs a Thermo Accucore C18 100 x 3mm, 2.6 µm column with A = H O/0.1% TFA; B =
CH CN. The elution profile was a linear gradient 0-100% B in 30 min at the flow rate of 0.4
(
2
3
mL/min.
Syntheses
Pathway A, Pyridine coordinating arm
N-(tert-butoxycarbonyl)-2-aminophenol (1). A mixture of 2-aminophenol (1.09 g, 10
mmol) and di-tert-butyldicarbonate (4.37 g, 20 mmol) in THF (15 mL) was stirred at room
temperature overnight. After concentration under reduced pressure, the residue was purified by
column chromatography (silica gel, ethyl acetate/petroleum ether, v/v = 1/10) to afford 1 as a
1
light yellow solid (1.51 g, yield 72%). H NMR (300 MHz, CDCl
3
): δ 1.53 (s, 9H), 6.68 (br s,
1
H), 6.85 (td, J = 7.8, 1.7 Hz, 1H), 6.83-7.10 (m, 1H), 8.14 (br s, 1H).
tert-butyl 2-(pyridin-2-ylmethoxy)phenylcarbamate (2). To a solution of 1 (1.12 g,
.4 mmol) in CH CN (10 mL) were added under argon atmosphere, K CO (1.48 g, 10.7 mmol)
5
3
2
3
and 2-picolyl chloride hydrochloride (0.88 g, 5.4 mmol). The mixture was heated to reflux
overnight. The reaction was stopped by evaporation under vacuum. The residue was dissolved
in ethyl acetate (50 mL) and washed twice with H
2
O (30 mL) then brine (20 mL). The organic
layer was dried over anhydrous MgSO and the filtrate was concentrated under reduced
4
pressure. The residue was purified by column chromatography (silica gel, ethyl
1
acetate/petroleum ether, v/v = 1/2) to afford 2 as a yellow oil (1.23 g, yield 78%). H NMR (300
MHz, DMSO-d
7.8 Hz, 1H), 7.70-7.88 (m, 2H), 8.46 (s, 1H), 8.60-8.62 (m, 1H). NH
calcd for C17 , 301.1).
6
): δ 1.49 (s, 9H), 5.24 (s, 2H), 6.91-7.09 (m, 3H), 7.35-7.39 (m, 1H), 7.58 (d, J
=
3
-MS m/z 301.1 ([M+H]+
H
21
N
2
O
3
1
1
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
tert-butyl prop-2-ynyl(2-(pyridin-2-ylmethoxy)phenyl)carbamate (3). To a solution
of 2 (0.60 g, 2.0 mmol) in distilled DMF (20 mL) was added under argon atmosphere at 0ºC,
NaH (0.19 g, 8.0 mmol). The mixture was stirred at 0ºC for 30 min. Then propargyl bromide
solution (80 wt. % in toluene, 0.3 mL, 2.6 mmol) was added dropwise and stirred at room
temperature overnight. The reaction mixture was quenched with water (10 mL) and extracted
twice with ethyl acetate (50 mL). All the organic layers were combined, washed twice with
H
2
O (30 mL), brine (20 mL) and dried over anhydrous MgSO . The filtrate was concentrated
4
under reduced pressure and the residue was purified by column chromatography (silica gel,
1
ethyl acetate/petroleum ether, v/v = 1/2) to give 3 as a yellow oil (0.54 g, yield 81%). H NMR
(300 MHz, DMSO-d
6
): δ 1.19-1.46 (m, 9H), 3.14 (s, 1H), 4.21-4.30 (m, 1H), 4.51-4.55 (m, 1H),
5
1
.23 (s, 2H), 6.97-7.02 (m, 1H), 7.14-7.37 (m, 4H), 7.55 (d, J = 7.8 Hz, 1H), 7.85 (td, J = 7.7,
+
.6 Hz, 1H), 8.57-8.80 (m, 1H). NH
3
-MS m/z 339.1 ([M+H] calcd for C20
H
23
N
2
3
O , 339.2).
N-(prop-2-ynyl)-2-(pyridin-2-ylmethoxy)aniline (4) To a solution of 3 (0.32 g, 0.95
mmol) in CH Cl (10 mL) was added an excess of trifluoroacetic acid (3 mL, 40 mmol). The
2
2
reaction was stirred at 0ºC until the consumption of the starting material (2h, monitored by
TLC). After reaction, the mixture was evaporated to dry and purified by column
chromatography (silica gel, ethyl acetate/petroleum ether, v/v = 1/2) to give 4 as a brown oil
1
(
208 mg, yield 92%). H NMR (300 MHz, DMSO-d
6
): δ 3.06 (t, J = 2.4 Hz, 1H, CH), 3.99 (dd,
J = 6.4 Hz, J = 2.4 Hz, 2H, NCH
2
), 5.19 (s, 2H, OCH ), 5.48 (t, J = 6.4 Hz, 1H, NH), 6.61 (td,
2
J = 1.5 Hz, J = 7.8 Hz, 1H, HAr), 6.73 (dd, J = 1.5 Hz, J = 7.8 Hz, 1H, HAr), 6.86 (td, J = 1.2
Hz, J = 7.8 Hz, 1H, HAr), 6.93 (dd, J = 1.2 Hz, J = 7.8 Hz, 1H, HAr), 7.34-7.78 (m, 1H, Hpy),
7
.66 (d, J = 7.8 Hz, 1H, Hpy), 7.86 (td, J = 1.8 Hz, J = 7.8 Hz, 1H, Hpyr), 8.59-8.61 (m, 1H,
+
H
pyr). NH
3
-MS: m/z 239.0 ([M+H] calcd for C15
H
15
2
N O, 239.1).
methyl
yl)acetate (L H).
(140 mg, 0.59 mmol), methyl azidoacetate (88 mg, 0.76 mmol), copper(II) acetate
monohydrate (35 mg, 0.18 mmol) and sodium ascorbate (59 mg, 0.3 mmol) in t-BuOH/H
2-(4-((2-(pyridin-2-ylmethoxy)phenylamino)methyl)-1H-1,2,3-triazol-1-
1
4
2
O
(v/v = 1/1, 10 mL) were stirred at room temperature overnight. The mixture was partitioned
between ethyl acetate (25 mL) and saturated Na
2
EDTA solution (25 mL). The organic phase
. The filtrate was
was washed twice with water (20 mL) and dried over anhydrous MgSO
4
evaporated and purified by column chromatography (silica gel, ethyl acetate) to give L H as a
1
yellow solid (158 mg, yield 76%).
1
2
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European Journal of Inorganic Chemistry
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Suitable crystals of L
1
H for X-ray crystal structure determination were grown by slow
1
evaporation of an acetonitrile and dichloromethane mixture. H NMR (500 MHz, DMSO-d
6
):
CO),
.59 (t, J = 3.7 Hz, 1H, NH), 6.53 (td, J = 1.5 Hz, J = 7.5 Hz, 1H, HAr), 6.66 (dd, J = 1.5 Hz, J
δ 3.70 (s, 3H, OCH
3
), 4.44 (d, J = 3.7 Hz, 2H, NCH
2
), 5.18 (s, 2H, OCH
2
), 5.37 (s, 2H, CH
2
5
=
8.0 Hz, 1H, HAr), 6.77 (td, J = 1.5 Hz, J = 7.5 Hz, 1H, HAr), 6.93 (dd, J = 1.5 Hz, J = 8.0 Hz,
1
H, HAr), 7.33-7.36 (m, 1H, Hpy), 7.62 (dt, J = 1.5 Hz, J = 8.0 Hz, 1H, Hpy), 7.84 (td, J = 2.0
Hz, J = 8.0 Hz, 1H, Hpy), 7.95 (s, 1H, Hta), 8.57 (ddd, 2H, J = 1.0 Hz, J = 2.0 Hz, J = 3.0 Hz,
1
3
1
H, Hpy). C NMR (125 MHz, DMSO-d
6
) δ 38.9 (NCH
2
), 50.7 (CH
2
CO), 53.0 (OCH ), 71.1
3
(
OCH
2
), 110.5 (CHAr), 112.1 (CHAr), 116.4 (CHAr), 121.9 (CHpy), 122.0 (CHAr), 123.4 (CHpy),
1
1
24.6 (CHta), 137.4 (CHpy), 138.3 (C
q
), 145.7 (CqNH), 146.5 (Cq
O
), 149.5 (CHpy), 157.5 (Cq
N
),
+
68.2 (CO ester). ESI-HRMS: m/z 354.1559 ([M+H] calcd for C18
H
20
N O
5 3
, 354.1553).
N-((1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl)methyl)-2-(pyridin-2-
ylmethoxy)aniline (L H). Using same procedure than compound L H preparation, 4 (0.14 g,
.59 mmol), 1-azido-4-nitrobenzene (125 mg, 0.76 mmol), copper(II) acetate monohydrate (35
mg, 0.18 mmol) and sodium ascorbate (59 mg, 0.3 mmol) in t-BuOH/H O (v/v = 1/1, 10 mL)
2
1
0
2
gave, after purification by column chromatography (silica gel, ethyl acetate) L H as a yellow
2
solid (240 mg, yield 81%).
Alternative procedure for the preparation of L
tert-butyl (1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl)methyl)-(2-(pyridin-2-
ylmethoxy)phenyl)carbamate (5). Using same procedure than compound L H preparation, 3
0.43 g, 1.27 mmol), 1-azido-4-nitrobenzene (271 mg, 1.65 mmol), copper(II) acetate
monohydrate (76 mg, 0.38 mmol) and sodium ascorbate (128 mg, 0.64 mmol) in t-BuOH/H
2
H from compound 3
1
(
2
O
(v/v = 1/1, 20 mL) gave, after purification by column chromatography (silica gel, ethyl acetate),
1
5
1
7
8
as a yellow oil (440 mg, yield 69%). H NMR (300 MHz, CDCl
3
): δ 1.27 (s, 6H, N-Boc),
.42 (s, 3H, N-Boc), 4.95 (s, 2H, NCH ), 5.12 (s, 2H, OCH ), 6.88-6.92 (m, 2H, HAr), 7.10-
2
2
.20 (m, 3H, HAr), 7.34 (d, J = 7.8 Hz, 1H, Hpy), 7.61 (t, J = 7.5 Hz, 1H, Hpy), 7.88 (d, 2H, J =
.7 Hz, 2H, Hpy), 8.28-8.32 (m, 3H, HAr), 8.49 (br s, 1H, Hta). ESI-MS: m/z 503.3 ([M+H]+
+
calcd for C26
H
27
N
6
O
5
, 503.2); 403.2 ([M-Boc+2H] calcd for C21
H
19
N
6
O
3
, 403.2).
L
2
H. To a solution of 5 (0.42 g, 0.84 mmol) in CH
2
Cl
2
(20 mL) was added an excess of
trifluoroacetic acid (3 mL) at 0ºC. The reaction was stirred at room temperature for 2h. The
resulting mixture was concentrated to dry under reduced pressure and purified by column
chromatography (silica gel, ethyl acetate) to give L
2
H as a yellow solid (280 mg, yield 86%).
1
3
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European Journal of Inorganic Chemistry
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Suitable crystals of L
2
H for X-ray crystal structure determination were grown by slow
1
evaporation of an acetonitrile and dichloromethane mixture. H NMR (500 MHz, CDCl
3
): δ
4
7
7
.59 (s, 2H, NCH
2
), 5.20 (s, 2H, OCH ), 6.62-6.68 (m, 2H, HAr), 6.81-6.86 (m, 2H, HAr), 7.20-
2
.22 (m, 1H, Hpy), 7.45 (d, J = 7.5 Hz, 1H, Hpy), 7.68 (td, J = 1.5 Hz, J = 7.5 Hz, 1H, Hpy), 7.89-
1
3
.91 (m, 2H, HAr), 8.03 (s, 1H, Hta), 8.30-8.33 (m, 2H, HAr), 8.57 (d, J = 4.0 Hz, 1H, Hpy), C
) δ 39.7 (NHCH ), 71.3 (OCH ), 110.7 (CHAr), 111.8 (CHAr), 117.5
CHAr), 119.9 (CHta), 120.3 (CHAr), 121.6 (CHpy), 122.0 (CHAr), 122.9 (CHpy), 125.5 (CHAr),
NMR (125 MHz, CDCl
3
2
2
(
1
37.0 (CHpy), 137.6 (Cqta), 141.2 (CqAr), 145.9 (CqNO2), 147.0 (Cq
O
), 148.5 (CqNH), 149.3
+
(
CHpy), 157.5 (Cqpy). ESI-HRMS: m/z 403.1519 ([M+H] calcd for C21
H N
19 6
O
5
, 403.1513).
Pathway A’, carboxylate coordinating arm
See ESI part for the detailled syntheses of compounds 6-11
Pathway B
2
-(tert-butoxycarbonyl(prop-2-ynyl)amino)acetic acid (12). To a solution of N-Boc-
glycine (0.175 g, 1.0 mmol) in distilled DMF (10 mL) was added under argon atmosphere at
ºC, sodium hydride (0.096 g, 4 mmol) in two portions. After stirring 30 minutes, propargyl
0
bromide (0.18 mL, 1.7 mmol, 80% in toluene) was added dropwise. The resulting mixture was
stirred at room temperature overnight. The reaction was quenched with water, followed by
addition of 1 M HCl solution until the pH was 3. Then the mixture was extracted twice with
ethyl acetate (50 mL). All the organic layers were combined, washed twice with water (15 mL),
brine (15 mL) and dried over anhydrous MgSO . The filtrate was concentrated to give 12 as a
4
yellow oil (180 mg, yield 85%). The compound is used in the next step without further
1
purification. H NMR (300 MHz, CDCl
3
): δ 1.45 (s, 9H, Boc), 2.50 (t, J = 2.5 Hz, 1H, CH),
), 4.75 (d, J = 2.5 Hz, 2H, CH ). NH
-MS: m/z 214.1 ([M+H]+
, 214.1); 231.0 ([M+NH , 231.1).
]+ calcd for C10
3
.97 (d, J = 5.6 Hz, 2H, CH
2
2
3
calcd for C10
H
16NO
4
4
H
19
N
2
O
4
N-hydroxysuccinimidyl 2-(tert-butoxycarbonyl(prop-2-ynyl)amino)acetate (13).
To a solution of 12 (180 mg, 0.84 mmol) in CH Cl (10 mL) was added under argon atmosphere
2
2
at 0ºC, N-hydroxysuccinimide (146 mg, 1.27 mmol) and catalytic amount of
dimethylaminopyridine (10 mg, 0.08 mmol). Then dicyclohexylcarbodiimide (262 mg, 1.27
mmol) in CH
2
Cl (10 mL) was added dropwise. The reaction was stirred at 0ºC for another 45
2
minutes and at room temperature overnight. The resulting mixture was filtered and the filtrate
was washed with 0.5 M HCl, until the pH was 3, then brine (15 mL). The organic phase was
1
4
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
dried over anhydrous MgSO
4
, filtered and concentrated under evaporation. The residue was
dissolved in a minimum volume of ethyl acetate and placed at -20ºC to allow dicyclohexylurea
to precipitate. After filtration and concentration of the solution, 13 is obtained as a yellow solid
1
(
250 mg, yield 81%). H NMR (300 MHz, CDCl
3
): δ 1.48 (s, 9H, Boc), 2.33 (t, J = 2.4 Hz, 1H,
), 4.25 (d, J = 2.4 Hz, 2H, CH ), 4.39 (s, 2H, CH ). NH -MS: m/z 211.1
, 211.4).
CH), 2.85 (s, 4H, 2CH
2
2
2
3
+
(
[M-Boc+2H] calcd for C
9
H
11
N
2
O
4
tert-butyl 2-(2-hydroxyphenylamino)-2-oxoethyl(prop-2-ynyl)carbamate (14) To a
solution of 13 (380 mg, 1.2 mmol) and 2-aminophenol (158 mg, 1.45 mmol) in CH CN (10
3
mL) was added 4-dimethylaminopyridine (146 mg, 1.2 mmol). The mixture was heated to 60ºC
under argon overnight. After cooling to room temperature, the resulting solution was
concentrated to dryness and the residue was purified by column chromatography (silica gel,
ethyl acetate/petroleum ether, v/v = 1/2) to afford 14 as a pale white solid (280 mg, yield 77%).
1H NMR (300 MHz, CDCl
): δ 1.48 (s, 9H, Boc), 2.34 (s, 1H, CH), 4.13 (s, CH
), 4.20 (s, 2H,
3
2
+
CH ), 6.82-6.87 (m, 1H, HAr), 6.96-7.11 (m, 3H, HAr). NH
2
3
-MS: m/z 305.4 ([M+H] calcd for
+
C
16
H
21
N
2
O
4
, 305.1); 205.3 ([M-Boc+2H] calcd for C11
H
13
N
2
2
O , 205.1).
methyl
oxoethyl)amino)methyl)-1H-1,2,3-triazol-1-yl)acetate (15). Using same procedure than
compound L H preparation, 14 (0.28 g, 0.92 mmol), methyl azidoacetate (138 mg, 1.2 mmol),
copper (II) acetate (55 mg, 0.28 mmol) and sodium ascorbate (91 mg, 0.46 mmol) in t-
2-(4-((tert-butoxycarbonyl(2-(2-hydroxyphenylamino)-2-
1
BuOH/H
2
O (v/v = 1/1, 20 mL) gave after purification by column chromatography (silica gel,
1
ethyl acetate/petroleum ether, v/v = 2/1) 15 as a brown solid (289 mg, yield 75%). H NMR
(
300 MHz, CDCl
CH N), 5.14 (s, 2H, CH
H, Hta). NH -MS: m/z 420.5 ([M+H] calcd for C19
3
): δ 1.39 (s, 9H, Boc), 3.76 (s, 3H, OCH
3
), 4.13 (s, 2H, CH CO), 4.62 (s, 2H,
2
2
2
COO), 6.82-7.09 (m, 3H, HAr), 7.34 (d, J = 6.3 Hz, 1H, HAr), 7.65 (s,
+
1
3
H
26
N
5
6
O , 420.2).
methyl 2-(4-((2-(2-hydroxyphenylamino)-2-oxoethylamino)methyl)-1H-1,2,3-triazol-1-
yl)acetate (L ) To a solution of 15 (0.30 g, 0.72 mmol) in CH Cl (10 mL) was added an
3
H
3
2
2
excess of trifluoroacetic acid (3 mL, 40 mmol). The reaction was stirred at 0ºC until the
consumption of the starting material (2h, monitored by TLC). After reaction, the mixture was
evaporated to dry and purified by column chromatography (silica gel, ethanol/dichloromethane,
1
v/v = 1/10) to give L
3
H
3
as a brown oil (188 mg, yield 82%). H NMR (500 MHz, CDCl
3
): δ
3
.41 (s, 2H, CH CO), 3.74 (s, 3H, OCH
2
3
), 3.94 (s, 2H, CH
2
N), 5.11 (s, 2H, CH
2
COO), 6.82 (t,
1
5
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
J = 7.5 Hz, 1H, HAr), 6.95 (d, J = 8.0 Hz, 1H, HAr), 7.04 (t, J = 7.5 Hz, 1H, HAr), 7.33 (d, J =
1
3
8
.0 Hz, 1H, HAr), 7.60 (s, 1H, Hta). C NMR (125 MHz, CDCl
3
) δ (ppm) = 44.3 (NCH
2
), 50.7
(
(
CH COO), 51.6 (COCH ), 53.1 (OCH ), 118.6 (CHAr), 120.2 (CHAr), 121.9 (CHAr),123.6
2
2
3
CHta), 125.4 (CqNH), 126.5 (CHAr), 145.7 (Cqta), 148.2 (Cq
O
), 166.8 (CO ester), 171.2 (CO
+
amide); ESI-HRMS: m/z 320.1359 ([M+H] calcd for C14
H
18
N
5
O
4
, 320.1353).
Rhenium complexes preparation
[(L
1
H)Re(CO)
3
Cl]. A 10 mL methanolic solution of ligand L H (100 mg, 0.28 mmol),
1
[
Re(CO)
5
Cl] (118 mg, 0.33 mmol) and diisopropylethyl amine (40 mg, 0.31 mmol) were stirred
at 65ºC overnight. After cooling to room temperature, the solution was concentrated under
reduced pressure. The resulting residue was purified by column chromatography (silica gel,
1
ethyl acetate) to give a light yellow solid (102 mg, yield 80%). H NMR (300 MHz, CDCl
3
): δ
), 5.29 (t, J = 6.3 Hz,
CO), 6.56-6.61 (m, 1H, HAr), 6.72-6.78 (m, 1H, HAr), 6.87-6.94 (m,
H, HAr), 7.28-7.30 (m, 1H, Hpy), 7.47 (d, J = 7.8 Hz, 1H, Hpy), 7.75 (td, J = 1.0 Hz, J = 7.5 Hz,
H, Hpy), 8.02 (s, 1H, Hta), 8.60-8.62 (m, 1H, Hpy). 13C NMR (75 MHz, CDCl
) δ 41.7
), 52.3 (CH CO), 54.1 (OCH ), 71.7 (OCH ), 110.8 (CHAr), 112.4 (CHAr),
18.7(CHAr), 121.9 (CHpy), 122.3 (CHAr), 123.2 (CHpy), 128.4 (CHta), 136.5 (C ), 137.1 (CHpy),
46.2 (Cq ), 149.5 (CHpy), 152.9 (CqNH), 156.5 (Cq ), 164.3 (CO ester), 196.5, 197.2. 197.5
3
1
2
1
.86 (s, 3H, OCH
3
), 4.93 (d, J = 6.3 Hz, 2H, NCH
2
), 5.23 (s, 2H, OCH
2
H, NH), 5.49 (s, 2H, CH
2
3
(
NHCH
2
2
3
2
1
1
q
O
N
–
1
(
CO carbonyl). IR (ATR): ν(CO) = 2025, 1905, 1883, ν(C=O) = 1756 cm . ESI-HRMS: m/z
24.0903 ([M-Cl]+ calcd for C21 187Re, 624.0894). Anal. calcd (%) for
ReCl: C 38.27, H 2.91, N 10.63; found: C 38.54, H 2.98, N 11.02.
6
H
19
N
5
O
6
C
21
H
19
N
5
O
6
[
(L
2
H)Re(CO)
3
Cl]. Using the same protocol than above, 10 mL methanolic solution of ligand
Cl] (104 mg, 0.29 mmol) and diisopropylethyl amine (36
L
2
H (100 mg, 0.25 mmol), [Re(CO)
5
mg, 0.28 mmol) gave, after purification by column chromatography (silica gel, ethyl acetate),
a light yellow solid (100 mg, yield 60%).
Suitable crystals of [(L
2
H)Re(CO)
3
Cl] for X-ray crystal structure determination were grown
1
by slow evaporation of an acetonitrile and diethyl ether mixture. H NMR (500 MHz, CDCl
3
):
), 7.02-7.10 (m,
H, HAr), 7.15-7.18 (m, 1H, HAr), 7.21-7.25 (m, 2H, HAr, Hpy), 7.75-7.76 (m, 2H, Hpy), 8.03-
δ 4.39-4.43 (m, 1H, NCH
2
), 4.98-5.02 (m, 1H, NCH
2
), 5.31-5.44 (m, 2H, OCH
2
2
8
1
3
.05 (m, 2H, HAr), 8.20 (s, 1H, Hta), 8.47-8.50 (m, 2H, HAr), 8.59-8.60 (m, 1H, Hpy). C NMR
) δ 50.9 (NCH ), 72.1 (OCH ), 113.6 (CHAr), 118.3 (CHta), 120.4 (CHpy),
(125 MHz, CDCl
3
2
2
1
6
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
1
21.3 (CHAr), 122.2 (CHAr), 122.5 (CHpy), 123.2 (CHAr), 125.9 (CHAr), 127.0 (CHAr), 137.4
(
CHpy), 139.6 (CqNH), 148.1 (Cq ), 148.3 (CqNO2), 149.1(CHpy), 150.4 (Cqta), 155.6 (Cqpy),
O
–
1
1
91.7, 193.9, 195.7 (CO carbonyle). IR (ATR): ν(CO) = 2023, 1914, 1886 cm . ESI-HRMS:
+
187
+
m/z 709.0598 ([M+H] calcd for C24
187Re, 673.0845). Anal. calcd (%) for C24
found: C 40.97, H 2.35, N 11.59.
H
19
N
6
O
6
ReCl, 709.0607); 673.0836 ([M-Cl] calcd for
C
24
H
18
N
6
O
6
H
19
N
6
O
6
ReCl: C 40.65, H 2.70, N 11.85;
[(L
3
)ReO]. A 20 mL methanolic solution of ligand L
3
H
3
(200 mg, 0.63 mmol),
[
ReO(PPh
3
)
2
Cl ] (678 mg, 0.82 mmol) and sodium acetate (206 mg, 2.52 mmol) were stirred
3
at 65ºC overnight. After cooling to room temperature, the solution was concentrated under
reduced pressure. The resulting residue was purified by column chromatography (silica gel,
1
ethanol/dichloromethane, v/v = 1/10) to give a dark brown solid (210 mg, yield 64%). H NMR
(
500 MHz, CDCl
3
): δ 3.84 (s, 3H, OCH
CO), 5.17 (d, J = 18.0 Hz, 1H, CH
COO), 6.87 (t, J = 7.5 Hz, 1H, HAr), 6.95 (t, J = 7.5 Hz, 1H, HAr), 7.10 (d, J = 7.5 Hz, 1H,
3
), 4.03-4.07 (m, 1H, CH
2
N), 4.77 (d, J = 18.0 Hz, 1H,
CH
2
2
2
CO), 5.22-5.26 (m, 1H, CH
2
N), 5.41 (br s, 2H,
CH
1
3
H
Ar), 7.83 (s, 1H, Hta), 8.12 (dd, J = 1.0 Hz, J = 7.5 Hz, 1H, HAr). C NMR (125 MHz, CDCl
δ 53.9 (OCH ), 54.1 (CH CO), 64.5 (NCH ), 70.9 (COCH ), 115.7 (CHAr), 118.5 (CHAr), 120.4
CHAr), 124.2 (CHAr), 141.8 (Cq ), 159.3 (Cqta), 165.2 (CO ester), 169.0 (Cq ), 188.2 (CO
amide). IR (ATR): ν(C=O) = 1753 and 1667 cm , ν(Re=O) 959 cm . ESI-HRMS: m/z
3
)
3
2
2
2
(
N
O
–
1
–1
+
187
+
5
20.0631 ([M+H] calcd for C14
187ReNa, 542.0445). Anal. calcd (%) for C14
found: C 32.70, H 2.57, N 13.28.
H
15
N
5
O
5
Re, 520.0625); 542.0450 ([M+Na] calcd for
C
14
H
15
N
5
O
5
H
14
N
5
O
5
Re: C 32.43, H 2.72, N 13.51;
99mTc-radiolabelling of L
H
3
3
The generator eluate (200 µL, 40 MBq) was added to a mixture containing 40 µL of ligand
solution (1 mg/mL in ethanol), 70 µL of stannous chloride solution (3 mg/mL in water) and 140
µL of NaOH 0.1 M. After stirring 10 min at room temperature, the reaction was stopped by
adding 14 µL of HCl 1 M.
[
(L
3
)99mTcO]: Rf (silica, CH
2
Cl
2
/ethanol, 60:40) = 0.50; t = 11.41 min.
r
1
7
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European Journal of Inorganic Chemistry
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Figures and captions
Scheme 1. Design features of novel semi-rigid tetradentate ligands
Scheme 2. Pathway A, pyridine coordinating arm
Conditions (i) (Boc)
CH
overnight; (iv) trifluoroacetic acid, CH
azidoacetate, Cu(OAc) .H O, NaAsc., t-BuOH/H
2
O, THF, rt, overnight; (ii) 2-picolyl chloride hydrochloride, K
2
CO
3
,
3
CN, reflux, overnight; (iii) NaH, propargyl bromide, DMF, 0ºC to room temperature,
Cl , 0ºC, 2 h; (v) 4-azidonitrobenzene or methyl
O, rt, overnight.
2
2
2
2
2
1
8
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Scheme 3. Pathway B
Conditions (i) NaH, propargyl bromide, DMF, 0ºC to room temperature, overnight; (ii) NHS,
DCC, DMAP, CH
CH
overnight; (v) trifluoroacetic acid, CH
2
Cl
2
, 0ºC to room temperature, overnight; (iii) 2-aminophenol, DMAP,
.
3
CN, 60ºC, overnight; (iv) methyl azidoacetate, Cu(OAc)
2
H
2
O, NaAsc, t-BuOH/H O, rt,
2
2
Cl , 0ºC, 2 h
2
Scheme 4. Rhenium(I) and rhenium(V) complexation
1
9
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Figure 1. The molecular structures of ligand L
2
H and its rhenium(I) complex
[(L
2
H)Re(CO) Cl]. Displacement ellipsoids are drawn at 30% and 50% probability,
3
respectively.
Ligand L H
2
Complex [(L
2
H)Re(CO) Cl]
3
2
0
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Figure 2. Partial proton NMR spectra (300 MHz, CDCl
3
, 298 K) of compounds L H (bottom)
1
and [(L
1
H)Re(CO) Cl] (top)
3
2
1
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Figure 3. Optimized geometries of rhenium complexes based on L
coordination, mer, fac isomers) using B3LYP/LANL2DZ
2
H (bidentate, tridentate
Bidendate coordinating mode
[
(L
2
H)Re(CO)
3
Cl] (fac-Nta,N coordination)
Isomer 1 (fac-Npyr,O coordination)
Tridendate coordinating mode
Isomer 2a (fac-Npyr,N,O coordination)
Isomer 2b (mer-Npyr,N,O coordination)
Isomer 3a (fac-Nta,N,O coordination)
Isomer 3b (mer-Nta,N,O coordination)
2
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201700632
Table 1. Crystal data and structure refinement for L
1
H, L
2
H and [(L
2
H)Re(CO) Cl]
3
L
1
H
L
2
H
2
[(L H)Re(CO)
3
Cl]
Empirical formula
Formula weight
Temperature [K]
Wavelength [Å]
Crystal system
Space group
Unit cell dimensions [Å,]
C
18
H
19
N
5
O
3
C
21
H
18
N
6
O
3
C H18ClN O Re
24 6 6
353.38
193(2)
0.71073
orthorhombic
Pna2
a = 23.0933(13)
b = 5.3680(3)
c = 13.8595(7)
402.41
193(2)
0.71073
monoclinic
P2 /c
a = 10.5160(4)
b = 24.6454(10)
c = 7.7012(3)
β = 107.501(2)
1903.54(13)
4
708.10
193(2)
0.71073
orthorhombic
P2
a = 7.7223(7)
1
1
1 1 1
2 2
b = 10.7568(9)
c = 31.175(3)
Volume [Å3]
Z
1718.09(16)
4
2589.6(4)
4
Density (calculated) [Mg/m3]
Absorption coefficient [mm-1]
F(000)
1.366
0.096
744
1.404
0.098
840
1.816
4.847
1376
Crystal size [mm]
0.18×0.04×0.04
4.07 to 26.35
-28 ≤ h ≤ 28
0.20×0.10×0.04
2.89 to 29.57
-13 ≤ h ≤ 14
-33 ≤ k ≤ 34
-10 ≤ l ≤ 10
46691
0.08×0.08×0.01
3.23 to 25.03
-9 ≤ h ≤ 9
-8 ≤ k ≤ 12
-37 ≤ l ≤ 36
18252

range for data collection []
Index ranges
-
-
6 ≤ k ≤ 5
14 ≤ l ≤ 17
Reflections collected
9477
Independent reflections
Completeness to 2theta = 26.35 for L
Completeness to 2theta = 29.57 for L
2941 [R(int) = 0.0586]
94.2 %
5331 [R(int) = 0.0470]
4490 [R(int) = 0.0599]
1
H
H
2
99.7 %
98.8 %
Completeness to 2theta = 25.03 for [(L
2 3
H)Re(CO) Cl]
Min. and max. transm.
0.7454 and 0.6632
2941 / 2 / 240
1.026
0.7462 and 0.6968
5331 / 0 / 275
1.013
0.7454 and 0.6358
4490 / 1 / 347
1.060
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2(I)]
R1 = 0.0459
wR2 = 0.0943
R1 = 0.0751
wR2 = 0.1060
0.190 and -0.230
R1 = 0.0498
wR2 = 0.1172
R1 = 0.0811
wR2 = 0.1364
0.365 and -0.322
R1 = 0.0395
wR2 = 0.0707
R1 = 0.0512
wR2 = 0.0744
0.821 and -1.059
R indices (all data)
Largest diff. peak and hole [e Å-3]
2
3
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European Journal of Inorganic Chemistry
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Acknowledgments
J.-H. Wang thanks the Chinese Scholarship Council (CSC) for a Ph.D. funding. M. Wolff
acknowledges financial support from the Foundation for Polish Science (START 2014).
Calculations were carried out in Wroclaw Centre for Networking and Supercomputing, Poland
(http://www.wcss.pl). N. Lepareur acknowledges financial support from Labex IRON (Grant
no. ANR-11-LABX-0018).
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