One Scaffold, Many Possibilities – Copper(I)-Catalyzed Azide–Alkyne Cycloadditions, Strain-Promoted Azide–Alkyne Cycloadditions, and Maleimide–Thiol Coupling of Ruthenium(II) Polypyridyl Complexes

Article abstract of DOI:10.1002/ejic.201701126

The applicability of Ru^II polypyridyl complexes with appropriate functionalities as substrates for biorthogonal coupling reactions is investigated. In detail, copper(I)-catalyzed azide–alkyne cycloadditions (CuAAC), strain-promoted azide–alkyne

Full text of DOI:10.1002/ejic.201701126

A Journal of
Accepted Article
Title: One Scaffold, Many Possibilities: CuAAC, SPAAC and
Maleimide- Thiol Coupling of Ruthenium(II) Polypyridyl
Complexes
Authors: Anne Stumper, Martin Lämmle, Alexander Klaus Mengele,
Dieter Sorsche, and Sven Rau
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201701126
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European Journal of Inorganic Chemistry
10.1002/ejic.201701126
FULL PAPER
One Scaffold, Many Possibilities: CuAAC, SPAAC and Maleimide-
Thiol Coupling of Ruthenium(II) Polypyridyl Complexes
Anne Stumper, Martin Lämmle, Alexander K. Mengele, Dieter Sorsche and Sven Rau*
Abstract: The applicability of Ru(II) polypyridyl complexes with
appropriate functionalities as substrates for biorthogonal coupling
reactions is investigated. In detail, copper(I)-catalyzed azide-alkyne
cyclo-additions
(CuAAC),
strain-promoted
azide-alkyne
cycloadditions (SPAAC), and maleimide-thiol coupling of ruthenium
complexes are examined. The first examples of SPAAC where the
organic azide is provided by the metal complex are presented. All
chromophores belong to one easy-to-synthesize scaffold, which has
proven to be convenient for applications of metal chromophores. The
fundamental photophysical properties of the examined compounds do
not change with substitution, which is important for the design of
chromophore conjugates. Furthermore, limitations of CuAAC
reactions will be discussed with regard to copper impurities in the
products formed.
Introduction
Figure 1. Importance of the design: structural details resulting in sets of
possible isomers.
Providing possibilities to link functional molecular units is
essential for the generation of sophisticated supramolecular
architectures. Biological applications in particular are limited by
the choice of linkage given that bioorthogonal conditions have to
be applied. Click chemistry approaches such as the copper(I)-
catalyzed azide-alkyne cycloaddition (CuAAC) , strain promoted
azide-alkyne cycloaddition (SPAAC)[2] or maleimide-thiol
coupling[3] represent advantageous strategies for linkage of
avoided. The use of the strain-activated cyclo-octyne motif has
been shown to promote “click” chemistry without the need for a
catalyst, and hence, SPAAC depicts a valuable bioorthogonal
alternative. Commercially available cyclooctyne derivatives can
be employed for the functionalization of biomolecules[
hence focused our efforts on the development of ruthenium
photosensitizers with stable pending azide groups to undergo
SPAAC, which also provide the photophysical properties for a
potential PDT application. The reaction of cyclooctynes with
azides was observed already in 1967 and originates from the ring
strain within cyclooctyne.[
9–12]
[
1]
. We
sensitive
(bio)molecules
with
functional
units,
e.g.
[
4–6]
photosensitizers or other imaging agents,
and control of the
coupling is dependent on the corresponding functionalities. For
photodynamic therapy (PDT), one feasible approach is to couple
13,14]
To this end, however, the number
of Ru(II) chromophores with stable azide functionalities has been
limited.[ In order to prevent the formation of stereochemically
complex structures with respect to the chiral nature of
tris(bipyridine) ruthenium(II) complexes, we were further aiming
for a substitution pattern that would preserve the C symmetry of
2
the parent complexes. (Figure 1). The introduction of
selectivity mediating biomolecules to photosensitizers like Ru(II)
polypyridyl complexes.[7] Moreover, the choice of azide-alkyne
cycloadditions provides the advantage that the reacting groups
are not abundant in the body and therefore guarantees high
selectivity and control. CuAAC has proven useful for the
15]
development of novel drug systems as well as many other
applications.[
1,8]
dibenzocyclooctyne (DIBO) to Ru(II) and Ir(III) polypyridyl
Even though CuAAC is a chemically very
complexes[
16,17]
as well as SPAAC of an azide ligand on a Ru(II)
selective coupling method, the employment of cell toxic copper
ions for CuAAC reactions requires extensive purification and
limits the exploitation of the CuAAC for live cell studies and for
reactions where possible copper ion coordination has to be
core has recently been described in literature.[18] To the best of
our knowledge, no SPAAC of a Ru(II) polypyridyl complex offering
an azide group has been reported to date.
Additionally, our synthetic approach has proven convenient for
the facile introduction of a maleimide functionality suitable for
maleimide thiole “click” coupling. Among the amino acids, only
cysteine provides a thiol (-SH) functionality. Although they are
comparably less abundant in the body with respect to the other
amino acids, proteins often present distinct cysteines on their
accessible surface. Hence, maleimide-thiol coupling reactions[
can be used to link Ru(II) chromophores to proteins. The
cytotoxicity of several Ru(II)–arene complexes has been
A. Stumper, M. Lämmle, A. K. Mengele, D. Sorsche, S. Rau
Institute of Inorganic Chemistry, Materials and Catalysis
Ulm University
Albert-Einstein-Allee 11, 89081 Ulm, Germany
sven.rau@uni-ulm.de, http://www.uni-ulm.de/nawi/nawi-anorg1.html
3]
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
10.1002/ejic.201701126
FULL PAPER
Figure 2. Overview of the examined compounds; conversion of the nitro functionality to the amine on the chromophore core was not possible; reaction of 3a to yield
in a one-pot-synthesis was successful in 50% of the batches; the conversion from 7 to 8 and vice versa can be controlled easily.
8
previously examined.[19,20] Ru(II) and Ir(III) terpyridine complexes
were coupled to cytochrome c[21] and a Ru(II) polypyridine
chromophore was linked to different proteins via maleimide-thiol
coupling.[ Hence, providing a scaffold which is easily accessible
and undergoes a variety of reactions which can be employed for
linking biomolecules to chromophores is desirable. As a result of
our ongoing efforts to provide versatile new ligand frameworks for
the straightforward linkage of photoredox-active ruthenium
chromophores with functional biomolecules, we herein report the
development of functionalized imidazophenanthroline (ip)
scaffolds (Error! Reference source not found.), all resorting to the
easily accessible and versatile amine derivatives 3a,b. We show
CuAAC, SPAAC and maleimide-thiol reactions under biological
conditions as well as in organic solvents. Desirable photophysical
properties of the “click” precursors are shown to be retained upon
functionalization which is essential for the establishment of a
library of “clickable” chromophores.
symmetry (e.g. 4-R-bpy type ligands) would yield additional regio-
isomers (Figure 1).
22]
Synthesis of amine and azide precursor chromophores
Amine functionalized complex 3a, the corresponding azide 4a and
the performance of the CuAAC to yield 5a have previously been
reported.[24] However, we modified the syntheses and present
Results and Discussion
In order to ensure subsequent applicability, it is necessary to
devise strategies where the linking step, i.e. formation of the
triazole, does not alter the photochemical properties significantly.
The choice of the ip-phenyl ligand sphere preserves desired
properties as already described in literature covering the creation
of highly potent drug candidates and imaging agents.[4,7,23]
Intrinsic symmetry of the ip-phenyl ligand limits the number of
possible isomers to Δ/Λ-forms, whereas ligands showing lower
3
Figure 3. ATR-IR spectra of the azide species 4a and 4b with the typical N -
valence doublet.
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European Journal of Inorganic Chemistry
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FULL PAPER
here the lipophilic analogues 3b, 4b and 5b which feature
additional tert-butyl groups on the peripheral bipyridines. First,
moieties (black in Figure 4, d(phen-C-H∙∙∙Cl) = 3.707 Å, d(ph-C-
H∙∙∙Cl) = 3.634 Å). The ip ligand hence also appears completely
planar, showing no gauche-type repulsion between the ip and
phenyl moieties. This observation points to a surprisingly
ligand
2 is needed to generate the corresponding metal
complexes. In order to avoid possible metal contamination, we
abstained from using Pd/C for the reduction of the nitro group (1,
dominant H-bond interaction as related ruthenium complexes
show torsion angles between 14° and 38.5°.[
26]
Additional
crystal data in ESI) to the amine and used Na
2
S as a mild, fast
and cheap reduction agent with improved yield. We also tested
the direct reduction of the nitro functionality on the chromophore
implementing the same conditions but no conversion was
observable. Presumably, Na S is not strong enough in redox
2
potential to reduce the electron withdrawing nitro species on the
hydrogen bond interactions are established between the terminal
amine function and the second counter ion, with a somewhat
longer N∙∙∙Cl distance of 3.181(4) Å. This observation in the solid
state suggests that the multiple H-bond sites available in this
particular complex allow the formation of a neutral ion pair with
increased lipophilicity. This results in an overall charge of 0 for the
supramolecular assembly. Lipophilicity experiments were
performed with 3a and 3b (respectively Cl-salts). Thereby no
cationic chromophore core. Complexation reactions to obtain 3a
(
92%) and 3b (89%) were carried out in microwave reactions
following previously presented instructions using the
corresponding Ru(II) precursor ([Ru(4,4’-R-bpy) Cl ],
R=H or bu). Azides 4a (97%) and 4b (84%) were obtained in
excellent yields via diazotisation with NaNO and following
addition of NaN . Both azides show the typical doublet N -valence
2
2
partition coefficients could be obtained under commonly applied
t
[7]
[27]
experimental prodceedings.
For 3a no partition could be
2
obtained, as the compound remained completely within the
aqueous phase or did show the before-mentioned formation of a
solid. In contrast, 3b was completely migrating into the organic
phase, so that a highly significant effect of the tert-butyl
substitution can be ascertained. This effect is highly relevant for
the prospective design of molecular systems within a biological
environment as the solubility properties determine the latter
cellular uptake and accumulation characteristics.[
3
3
vibration band for phenyl azides[25] at 2095-2123 cm-1 in the IR
spectra (Figure 3). All compounds were fully characterized via
NMR spectroscopic techniques ( H, 13C (UDEFT), HMBC) as well
as HRMS. The fundamental photophysical properties were
determined via UV/Vis and emission spectroscopy. 3a is very well
soluble in water (153 mg/mL) but under addition of n-octanol to
the aqueous solution and shaking at 25°C over night to determine
partition coefficients, for some samples there was a decoloring of
the aqueous phase and a thin solid film on the glass wall of the
vessel was observed. Henceforth, no determination of partition
coefficients was possible. The solid-state structure of 3b shows
the two-fold positively charged complex as chloride salt. All
distances and angles regarding the coordination chemistry of the
tris-(bipyridine) ruthenium(II) fragment are in the expected range.
The anions both appear to establish hydrogen bonds with the ip
ligand (red in Figure 4Error! Reference source not found.). The
hydrogen bond between the imidazole amine function and one of
the chloride ions is rather short with d(N∙∙∙Cl)= 3.127(3) Å, and is
supported by additional short contact interactions with the
neighboring C-H groups of the phenanthroline and phenyl
1
28]
Figure 5. Solid-state structure of the Ru complex 5b (ellipsoids are drawn at
Figure 4. Mercury ball and stick representation of the molecular structure of
50% probability level, hydrogen atoms and counter ions were omitted for clarity);
3b, hydrogen bonds between the NH functionalities and the chloride counter
top: complex 5b in a hydrogen bonding network with two water molecules,
bottom: complex 5b interacting with two acetonitrile and one water molecule.
ions are depicted in red, supporting short contacts to CH moieties are depicted
in black, most hydrogen atoms were omitted for clarity.
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European Journal of Inorganic Chemistry
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FULL PAPER
Figure 6. (a) Synthesis
scheme for the SPAAC
reactions of 4a and 4b
1
with BCN-amine; (b) H-
NMR spectrum of 6a (Cl-
salt)
in
4
MeOH-d ,
aromatic region on the
top and signals of
aliphatic protons on the
bottom, solvent signal
was cut out for clarity
(
see Figure S10 for full
spectrum); (c) HRMS
MALDI-FT-ICR) signal
(
for 6a (PF
calculated
6
-salt) with
isotopic
pattern matching for the
+
+
molecular ion [M+H ] .
Copper (I) Catalyzed Azide Alkyne Cycloaddition (CuAAC)
and lipophilicity experiments
discussed above, a larger torsion angle of 18.92° (N18-C115-
C116-C117) was found between the ip sphere and the central
phenyl ring, which is clearly caused by the different hydrogen
bond framework. This is further corroborated by the fact that the
ip sphere as well as the triazole and the terminal phenyl ring are
virtually planar (torsion angle for N18-C115-N20-C122 is 5.41°
and 1.34° for C122-C123-C124-C125) whereas only the central
phenyl ring tilts out of this plane. Slow evaporation of a MeOH
solution of 3b yielded suitable crystals for XRD. Only one H-bond
interaction with a group of two water molecules at the N-H moiety
of the ip ligand was observed, which points to strong contribution
of hydrogen bonding patterns with regard to the formation of
different rotamers within one crystal structure. For both species
The CuAAC protocol is a powerful method to link different
moieties with each other to generate sophisticated molecular
systems. Conversion in CuAAC reactions with model compound
phenylacetylene to obtain 5a and 5b was performed with CuSO
4
5
H
2
O and sodium ascorbate. Formation of the product is readily
1
observed via H-NMR spectroscopy due to formation of a typical
singlet for the triazole proton (see Figure S3 and S4 in ESI). All
compounds were further characterized via HRMS (ESI/MALDI).
6
Crystals of 1 (see supporting information) and 5b (PF salt)
suitable for XRD were obtained by slow evaporation of the
solutions in DMSO and MeCN, respectively. The solid-state
structures in Figure 5 show the two-fold positively charged Ru
complex 5b exhibiting the 1,4-regioisomeric triazole group. Within
the asymmetric unit two different hydrogen bond motifs are found.
As depicted in Figure 5 (top), a hydrogen bonding pattern
between the N-H moiety of the ip sphere and two mutually linked
water molecules is established. This interaction leads to a
planarization of the ip framework with the phenyl moieties as
reflected by the torsion angle of 1.78° (N7-C52-C53-C58). The
triazole ring, as well as the terminal phenyl group, share one
common plane as the respective torsion angle (C59-C60-C61-
C66) is as small as 1.56°. Interestingly, the above described two
planarized spheres of the extended ligand are distorted to each
other as the torsion angle C55-C56-N9-N10 exhibits a value of
(3b, 5b) the triazole and terminal phenyl ring are coplanar, which
might point to a relatively strong conjugative coupling between
these moieties, overcompensating the repulsive gauche-type
interactions of the relevant H atoms.
For multiple reproductions of the CuAAC reactions
a
contamination with copper ions for different batches was
observed via HRMS (see Figure S9 in ESI). With regard to the
known cytotoxicity of copper ions this limits a potential application
[29]
of CuAAC derivatives of 4a,b for biological applications.
In
general, the yields for the CuAAC reaction are higher, when
utilizing stoichiometric equivalents of copper (2-4 eq), but copper
species were also detected when the amount of copper was
reduced (0.15 eq) with a loss in yield revealing unreacted educt
species. Some batches were still found to be contaminated with
copper ions after extensive purification. Pure batches were used
for further reactions and characterization. For batches showing
copper-containing fragments regarding mass spectrometry an
interesting, intensive absorbance band around 360 nm was
observed utilizing UV/Vis spectroscopy (see Figure S8 in ESI).
34.81°. The second hydrogen bonding network found in the
asymmetric unit Figure 5, bottom) consists of one acetonitrile
molecule bound via the N-H group of the ip ligand and one water
molecule, acting as a bridge between N22 of the triazole ring and
a
second acetonitrile molecule. Contrary to the structure
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European Journal of Inorganic Chemistry
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FULL PAPER
For these batches the common use of extraction with Na-ETDA
-
solution did not succeed. In future, precipitation with CN -ions
could be exploited. The corresponding 1H-NMR spectra were
interpretable which leads to the assumption that copper(I) ions are
the contaminant as Cu(II) would lead to a significant broadening
1
for the H-NMR signals due to its paramagnetism. Regarding the
contamination with metal ions, the choice of CuAAC should be
deliberated on. We assume the formation of a Ruthenium(II)-
Copper(I)-multinuclear species, where the copper ion might
coordinate triazole or imidazo-units. It is known that copper(I)
species similar in structure to our assumed species absorb within
the relevant wavelength region with significant absorption
coefficients.[30,31] These observations have to be examined in
more detail and are subject of ongoing studies.
Figure 7. Structural motif of 7 (ball-and-stick representation; most hydrogen
atoms were omitted for clarity).
Strain-promoted Azide Alkyne Cycloaddition (SPAAC)
Based on these observations we investigated alternative, metal-
free coupling concepts, and we present herein the first examples
for SPAAC reactions with Ru(II) polypyridyl complexes where the
azide functionality is provided by the chromophore. In order to
avoid the necessity of a metal-based catalyst, we utilized the
commercially available, strained cyclooctyne BCN-amine. A
s
further advantage of BCN is that its C symmetry prevents the
formation of complex regioisomers when linked to the chiral
chromophore precursors.[32] Additionally, BCN-amine depicts low
lipophilicity compared to other cyclooctyne derivatives. As the
application of SPAAC reactions is of interest for the generation of
molecular systems in general we employed two different Ru(II)
polypyridine
complexes
providing
different
solubility
characteristics. The SPAAC reaction to yield 6a was carried out
stirring 4a and BCN-amine in water for 18 h. For 6b a mixture of
MeCN and water was employed with respect to its increased
lipophilicity (Figure 6). Both SPAAC products were purified via
size exclusion chromatography and characterized via NMR
spectroscopy and HRMS. High resolution mass spectrometry
1
Figure 8. H-NMR spectra of open (a, 7) and closed (b, 8) form of the maleimide
3
in MeCN-d ; signals at the double bond ease characterization of the ring-closing
reaction via NMR spectroscopy.
set up[34] yield the desired closed maleimide either in excellent
yields or not at all. Therefore, the two-step way was preferred
later-on as it works reliably. The ring-closing reaction to obtain 8
was screened with modified literature conditions[33] (e.g.
elongated reaction time for complete conversion) of 7 to 8. It was
determined, that the ring-closing reaction is completed after three
hours and the most efficient way of work up is the direct
revealed expected signals for [M+H+]+ and [M–2Cl –H ] species
-
+ +
showing the typical isotopic pattern for ruthenium (Figure S14,
ESI). Screening of the reactions via NMR suggested quantitative
formation, however only moderate yields of the pure products
were obtained (27-40%) after size exclusion chromatography due
to the small scale these reactions have been carried out in.
However, to the best of our knowledge, no yields have been
6
precipitation from the reaction mixture as PF salt. More elongated
reaction times will lead to ring-opening due to the released water.
Compounds 7 and 8 were characterized in detail via NMR and IR
spectroscopic techniques, and HRMS. The 1H-NMR spectrum
provides direct information about the nature of the substitution, as
it reveals either two doublets or a singlet for the open and closed
form, respectively. The IR spectrum of 8 depicts a typical strong
C=O vibration band at 1716 cm . It is known, that maleimide
functionalities are reactive in protic environments, leading to ring-
opening reactions. We observed decomposition of about 40%
provided for other SPAAC reactions carried out with Ru(II)
chromophores in the literature[16]. A related Ir(III) based system
was reported via recrystallization[17]
.
Maleimide-Thiol Coupling
-
1
Displaying another metal-free click alternative we envisaged the
maleimide sulfide coupling reaction, since the respective
chromophore precursor 8 is readily accessible from 3a. The
amine functionality was converted to the open maleimide 7 using
maleic anhydride in a room temperature condensation reaction
providing quantitative yields. Successful reaction conditions were
modified according to literature which dealt with organic
maleimides.[ Surprisingly, when screening different reaction
conditions it was observed that reactions in a one-pot microwave
within
a
day in methanol solution, which precluded
chromatographic purification for 8 in protic solvents. The ring-
closing reaction can be repeated when decomposition is
observed and 8 is stable (weeks) in non-protic, dry solvents (e.g.
acetonitrile). Therefore, recrystallization protocols were
developed to yield 8 in sufficient purity for the next reaction.
33]
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European Journal of Inorganic Chemistry
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FULL PAPER
Single crystals of 7 suitable for X-ray diffractometry were obtained
via slow evaporation out of a MeOH solution of 8 as chloride salt.
The structural motif depicted in Figure 7 shows the complex 7
with a hydrolytic cleavage of the maleimide functionality forming
a ring-opened, hydrogen bonding stabilized carboxylic acid
moiety. All distances and angles regarding the coordination
chemistry of the pseudo-octahedral Ru-moiety are within the
expected range. The torsion angle between the ip motif and the
bridging phenyl moiety exhibits a very small value of 6.7°
indicating only minor gauche type interactions. Moreover, the
torsion angles in the ring-opened maleimide part cover rather
small values between 1.2° and 7.5° pointing to a fully conjugated
system, which is further supported by the short C-C distance
between C41 and C42 (1.276 Å) indicative of a substantial double
bond character. It is apparent from Figure 7 that H-bonding
interactions between the solvent and the N-H functionality of the
ip-ligand occur, whereas one of the two chloride counter ions
interacts with the hydrolytically generated amide N-H group of the
former maleimide moiety.
Figure 9. Exemplary absorbance of the series of Ru complexes 3a, 4a, 5a and
6a in MilliQ water.
To verify the potential of this functionality to serve as agent for the
2
spectroscopic properties of the [(bpy) Ru(ip-phenyl)]-type
complexes are not influenced by the substitution of the peripheral
phenyl moiety.
Table 1. Absorption and emission maxima in aqueous solution at
-5
concentrations of about c=10 mol/L.
LC
1MLCT
compounds
max,abs [nm]
max,abs [nm]
max,em [nm]
3
4
5
6
a
a
a
a
287
285.5
286
460
458.5
459.5
458
465.5
461
467.5
463
460
603.5
603
603.5
604
621
622
616.5
624
605
604
604
Figure 10. Reaction of 8 with 2-mercapto-ethanol to yield the coupling product
9; the reaction can be carried out in pure PBS or in PBS acetonitrile mixtures.
285
functionalization of proteins, we converted 8 with 2-mercapto-
ethanol as model thiol (Figure 9). Educt 8 was reprecipitated as
chloride salt for the reaction. The reaction was carried out at room
temperature in aqueous PBS buffer (pH=7.4). Upon addition of
the thiol to the PBS solution of 8 a darkening of the red solution
was observable and the reaction was completed after one hour,
indicated by the naked eye with a slight brightening of the red
color and as confirmed via NMR spectroscopy. The product was
purified via size exclusion chromatography and the conversion
was confirmed via NMR spectroscopy and HRMS. The reaction
can also be carried out in a PBS/acetonitrile mixture (1:1) utilizing
3b
287.5
285.5
287
285
286
4b
5b
6b
7
8
9
286
285
462
460
Conclusions
We present a series of Ru(II)polypyridyl complexes which can
undergo a variety of click reactions such as CuAAC, SPACC and
maleimide-thiol coupling. The utilized precursor compounds all
resort to the easy-to-synthesize compounds 3a and 3b. We here
present the first examples for SPAAC reactions where the organic
azide is provided by the metal chromophore. All compounds have
been characterized in detail and their fundamental photophysical
properties were determined. The introduced stable azide
functionalities can be converted in cycloaddition reactions under
biorthogonal (CuAAC, SPAAC) or highly selective conditions
6
the PF salt of 8.
Photophysical Characterization
For the straightforward introduction of chromophores into clicked
systems it is generally of paramount importance that such click-
motifs retain the photophysical properties of the former. Steady
state absorption and emission properties in aqueous solution
were determined for the ruthenium complexes and are
summarized in Table 1. As can be concluded with respect to the
virtually identical absorption and emission profiles, the ip scaffold
is indeed capable of preserving the photophysical properties of its
precursor chromophores upon click-substitution using either
(
maleimide-thiol coupling). Therefore, these complexes may be
employed for the functionalization of biomolecules enabling
various applications. Additionally, the reactions can also be
carried out in organic solvents which is important for the
establishment of molecular systems for other applications beyond
a biological background. We want to point out, that this scaffold
offers a variety of possible functionalizations without change in
CuAAC, SPAAC, or maleimide sulfide coupling, as no significant
shifts of LC and 1MLCT transitions can be observed. The
preliminary data show that the UV/Vis and emission
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European Journal of Inorganic Chemistry
10.1002/ejic.201701126
FULL PAPER
essential photophysical properties which can be exploited for the
prediction of characteristics of established conjugates. The carry-
off of copper ions is obviously a problem for the use of CuAAC
reactions with regard to biological applications, especially as the
contamination was varying from batch to batch. Therefore it is
highly interesting to provide efficient linking strategies for metal
complex conjugates avoiding contaminants like copper ions.
H
2
O (5 mL) and 3 drops of an aqueous KOH solution (1 plate dissolved in
15 mL H
2h at 180 W and changed the color from dark violet to red. The solvents
were rotary evaporated, the residue was dissolved in EtOH, Et O was
2
O) were added. The solution was reacted in the microwave for
2
added and red crystals precipitated. The red crystals were filtered off. Via
size exclusion chromatography (Sephadex©) in MeOH the desired
complex was isolated as a bright orange band. After the solvent was
removed via rotary evaporation the product was isolated as red crystals
(
92%, 414.5 mg, 571 μmol). 1H NMR (400.13 MHz, RT, MeOD-d
9.12 (d, J = 7.6 Hz, 2H), 8.71 (dd, J = 16.5, 7.9 Hz, 4H), 8.25 – 8.12 (m,
H), 8.11 – 8.00 (m, 6H), 7.94 (ddd, J = 5.6, 1.4, 0.7 Hz, 2H), 7.85 (dd, J
4
): δ =
Experimental Section
2
2
-(4-nitrophenyl)-1H-imidazo[4,5-f][1,10]-phenanthroline (1) was pre-
= 8.4, 5.3 Hz, 2H), 7.69–7.63 (m, 2H), 7.54 (ddd, J = 7.6, 5 .6, 1.3 Hz, 2H),
7.31 (ddd, J = 7.6, 5.7, 1.3 Hz, 2H), 6.90 – 6.81 (m, 2H) ppm. 13C-NMR
pared according to literature.[35] Other compounds were synthesized
utilizing optimized or alternate protocols presented below.
(101 MHz, RT, MeOD-d
4
): δ = 157.55, 157.38, 152.01, 150.66, 146.14,
1
38.15, 138.02, 134.87, 130.68, 127.85, 127.73, 127.42, 127.21, 126.37,
+
- +
Ligand Synthesis
124.55, 124.46 ppm. HRMS (MALDI-FT-ICR): 724.15194 [M-H -2Cl ]
(calculated: 724.15057).
2
-(4-nitrophenyl)-1H-imidazo[4,5-f][1,10]-phenanthroline (1): 4-Nitro-
benzaldehyde (1.25 g, 8.27 mmol) and phenanthroline-5,6-dione (1.68 g,
.00 mmol) were suspended in acetic acid (100%, 50 mL). Ammonium
[Bis(2,2-bipyridine)-(4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)-
8
phenyl-1-azido)-Ruthenium(II)] Cl
dissolved in 10 mL H O, 10mL MeCN and 0.45 mL 3 M HCl. NaNO
30μmol) dissolved in 0.45 mL H O was added and stirred for 10 min at
RT, then the reaction mixture was cooled to 0°C with an ice bath and NaN
36 mg, 550μmol) in 0.45 mL H O was added and stirred for further 10 min
at 0°C. Then it was allowed to come to RT and stirred for 3h. The reaction
mixture was neutralized with NH (25% in water) and the solvents were
2
(4a): 3a (200 mg, 275μmol) was
acetate (12 g) was added and the suspension was heated to 85°C to yield
a yellow solution. Upon heating to 120°C a thick yellow suspension was
observed which was refluxed for 2 h. The precipitate was filtered and
2
2
(23 mg,
3
2
3
washed with water to yield 1 (95%, 2.59 g, 7.6 mmol) as a bright yellow
(
2
1
solid. H NMR (400.13 MHz, DMSO-d
6
): δ= 9.53 (dd, J = 4.3, 1.8 Hz, 2H),
9
.43 (dd, J = 8.1, 1.7 Hz, 2H), 9.05 (d, J = 9.1 Hz, 2H), 8.97–8.94 (d, 2H),
.31 (dd, J = 8.1, 4.3 Hz, 2H) ppm. Crystal data for 1: C21 S,
/n, a =
3
8
5 3
H17 Cl N O
removed under reduced pressure. The residue was dissolved in EtOH and
the precipitated white salts were filtered off over a PTFE filter. Then the
-
1
M
r 1
= 419.47 g mol , white block, monoclinic, space group P2
7
=
=
1
.9969(2) Å, b = 16.9498(4) Å, c = 14.3417(4) Å, α = 90°, β= 90.503(2)°, γ
product was precipitated with Et
filtered via a glass frit (POR5). Via size exclusion chromatography
Sephadex©) in MeOH the desired complex was isolated as a bright red
2
O and n-hexane. The precipitate was
3
3
α
90°, V = 1917.28(9) Å , T = 150 K, Z = 4, ρcalcd. = 1.453 Mg/m , μ (Cu-K )
-
1
1.804 mm , F(000) = 872.0, altogether 9268 reflexes up to h(-9/9), k(-
(
1/21), l(-17/16) measured in the range of 15.346° ≤ Θ ≤ 148.978°,
band. After the solvent was removed via rotary evaporation the product
completeness Θmax = 99.7 %, 3884 independent reflections, Rint = 0.0220,
was received as dark red-brown crystals in a yield of 97% (202 mg, 269
2
0
0
73 parameters, 0 restraints, R1obs = 0.0429, wR2obs = 0.1183, R1all
=
1
μmol). H NMR (400.13 MHz, RT, MeOD-d
4
): δ=9.10 (d, J = 8.4 Hz, 2H),
.0458, wR2all = 0.1218, GOOF = 1.059, largest difference peak and hole:
8
7
2
.77 (dd, J = 14.2, 8.2 Hz, 4H), 8.28 – 8.15 (m, 4H), 8.15 – 8.05 (m, 4H),
-
3
.79/-0.46 e∙Å . CCDC 1573110 contains the supplementary
.97 (d, J = 5.7 Hz, 2H), 7.86 (dd, J = 8.3, 5.3 Hz, 2H), 7.76 (d, J = 5.5 Hz,
H), 7.64 – 7.50 (m, 2H), 7.45 – 7.28 (m, 2H), 7.06 (d, J = 8.6 Hz, 2H) ppm.
13C-NMR (101 MHz, RT, MeOD-d
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
4
): δ = 158.80, 158.60, 152.85, 152.80,
1
1
51.24, 143.98, 139.33, 139.19, 132.05, 129.71, 128.96, 128.88, 127.32,
27.21, 125.69, 125.62, 120.86 ppm. HRMS (MALDI-FT-ICR): 750.14197
4
-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)-phenyl-1-aniline (2): 2-
+
- +
[
3
M-H -2Cl ] (calculated: 750.14208). IR: ν =2095-2123 (s, doublet N -
stretching) cm-1.
(
4-nitrophenyl)-1H-imidazo-[4,5-f]-[1,10]-phenanthroline
(3.2 g,
9
.38 mmol) was suspended in 1,4-dioxane (76 mL) and heated to 80°C.
2 2
Na S was dissolved in water and heated to 80 °C. The warm Na S solution
[Bis(2,2-bipyridine)-(4-(1H-imidazo-4,5-f-1,10-phenanthroline-2-yl)-
was combined with the warm yellow suspension and heated to 80 °C for 4
h. The color changed instantaneously from orange to red and the solid was
dissolved completely. The dioxane was evaporated under precipitation of
the product. The solid was filtered off and washed respectively with water
2
phenyl-1-(1-H-1,2,3-triazolyl-4-phenyl)-Ruthenium(II)]Cl (5a): 57 mg
(
0.07mmol) of 4a and 10.5 mg (11 μl, 0.1mmol) of phenylacetylene were
dissolved in water. NaAsc (4 eq, 55 mg) and CuSO ·5 H O (2 eq, 34 mg)
were dissolved in 2 mL water respectively, added to the reaction mixture
and stirred overnight at rt. The product was precipitated as PF salt out of
the aqueous solution and filtered off over glass frit (POR4).
4
2
and Et
2
O. After drying the product was received as ochre colored solid in
6
1
a yield of 78% (2.3 g, 7.29 mmol). H NMR (400.13 MHz, RT, DMSO-d
6
):
a
δ = 8.90 (dd, 2 H), 8.87 (d, 2H), 8.01 (d, 2 H), 7.73 (dd, 2 H), 6.68 (d, 2H),
.42 (s, 2 H) ppm.
Reprecipitation to the Cl salt with TBACl in acetone and purification via
size exclusion chromatography (Sephadex©) in MeOH yielded the product
5
as a bright red-orange band. After removal of the solvent, the product was
isolated as red crystals in 95% yield (61 mg, 0.067 mmol). 1H-NMR
Ruthenium Complexes without tert-butyl groups
(
MeCN-d
J=8.4 Hz, 2H), 8.54 – 8.43 (m, 4H), 8.07 (s, 2H), 7.96 (d, J=9.9 Hz, 6H),
.87 (s, 2H), 7.76 (s, 2H), 7.63 (s, 4H), 7.51 (s, 2H), 7.42 (d, J=6.6 Hz, 4H),
3
, 400.13 MHz): δ=9.05 (d, J=8.5 Hz, 2H), 8.70 (s, 1H), 8.63 (d,
[
Bis(2,2'-bipyridine)-(4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)-
phenyl-1-aniline)-Ruthenium-(II)]Cl (3a): 300 mg (620 μmol)
(bpy) RuCl ] and 232 mg (746 mmol) of 2 were dissolved in EtOH (15 mL),
2
7
[
2
2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701126
FULL PAPER
7
1
1
.20 (s, 2H) ppm. 13C-NMR (101 MHz, MeCN-d
3
)=158.29, 158.00, 152.67,
R1all = 0.1690, wR2all = 0.4224, GOOF = 1.540, largest difference peak
-
3
48.82, 148.08, 145.44, 138.40, 138.23, 131.16, 129.92, 129.27, 128.66,
and hole: 1.66/-0.74 e∙Å .
28.28, 127.62, 126.48, 125.64, 124.99, 124.89, 121.33, 119.96 ppm.
+
- +
[Bis(2,2-bipyridine)-(4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)-
HRMS (MALDI-FT-ICR): 852.18794 [M-H -2Cl ] (calculated: 852.18802).
2
phenyl-1-(1-λ -pyrrole-2,5-dione)-Ruthenium(II)]
Cl
2
(closed
[Bis(2,2-bipyridine)-(4-(1H-imidazo-4,5-f-1,10-phenanthroline-2-yl)-
maleimide 8):
phenyl-1-(1H-1,2,3-triazolyl-4,5- ((1R,8S,Z)-bicyclo[6.1.0]non-4-en-9-
a) One pot synthesis from 3a (working 50% of batches): 70 mg
(0.07mmol) of 3a (PF salt) were dissolved in MeCN (1.5 mL) and 2 mL
yl)methyl (2-(2-(2-aminoethoxy)-ethoxy)-ethyl)-carbamate)-Rutheni-
6
um(II)]Cl
amount of H
-yn-9-yl-methyl-oxy-carbonyl]-1,8-diamino-3,6-dioxa-octane
2
(6a): 20.58mg (25.05μmol) of 4a were dissolved in a small
O. 8.1 mg (24.968μmol) N- [(1R, 8S, 9S) - Bicyclo[6.1.0]-non-
(BCN-
acetic anhydride. 8 mg (0.09mmol) of NaAc were added and the obtained
solution was refluxed (MW, 450 W) for 30 min. 8 was isolated via
precipitation from the reaction mixture with ether.
2
4
amine) was dissolved in an ethanol/water mixture and added subsequently.
A slight warming of the resulting solution was observed and it was stirred
b) Ring-closing reaction from 7 (works reliably): 60 mg (0.05mmol) of
6
7 (PF salt) were dissolved in MeCN (5 mL) and 6 mg (0.07mmol) of NaAc
for 18 h at rt. 60.2 mg (369.33μmol) NH
4
PF
6
dissolved in water were added
were added. The resulting solution was refluxed for 3 h and the product
was precipitated with diethylether from the reaction mixture. To avoid
decomposition the product was reprecipitated as Cl-salt and again
to precipitate the product. The solid was filtered via a syringe filter (nylon),
washed with water and dried (crude product yield: 85%). The product was
dissolved from the filter with MeCN and the solvent was evaporated.
Reprecipitation with TBACl yielded the Cl-salt of 6a which was purified via
size exclusion chromatography to remove the educt surplus. 6a was
6
reprecipitated to yield the PF salt, purification via chromatography would
have to be performed in non protic solvents to avoid a massive loss of yield
due to ring-opening. As the product is sensitive towards protic solvents it
should be dried intensively and should not be kept in protic solution for
long time. The product was obtained as red solid (45 mg, 76%, 0.04 mmol).
1
isolated as red solid in a moderate yield (7.6 mg, 6.631 μmol, 26.6%). H-
NMR (MeOD-d
4
, 500.13 MHz): δ=9.21 (d, J= 8.3 Hz, 2H), 8.76 (dd, J=15.9,
8
7
7
3
3
2
.3 Hz, 4H), 8.60 (d, J= 8.5 Hz, 2H), 8.14 (ddd, J= 32.6, 15.9, 8.0 Hz, 6H),
1H NMR (400.13 MHz, MeOD-d
4
): δ=9.00 (d, J = 8.3 Hz, 2H), 8.64 (dd, J
.96 (d, J= 5.5 Hz, 2H), 7.90 (dd, J= 8.3, 5.3 Hz, 2H), 7.73 (dd, J= 11.4,
.2 Hz, 4H), 7.61–7.52 (m, 2H), 7.40–7.29 (m, 2H), 4.27–4.08 (m, 2H),
.70 (dd, J= 13.3, 8.2 Hz, 6H), 3.55 (t, J= 5.4 Hz, 2H), 3.26–3.16 (m, 1H),
.16–3.05 (m, 3H), 3.03–2.92 (m, 1H), 2.89–2.77 (m, 1H), 2.36–2.18 (m,
H), 1.81–1.63 (m, 2H), 1.39–1.23 (m, 1H), 1.14 (s, 2H) ppm.13C-NMR
= 15.2, 8.2 Hz, 4H), 8.33 (d, J = 8.3 Hz, 2H), 8.17 (t, J = 7.9 Hz, 2H), 8.11
(d, J = 5.1 Hz, 2H), 8.06 (t, J = 7.9 Hz, 2H), 7.93 (d, J = 5.4 Hz, 2H), 7.83
(dd, J = 8.2, 5.1 Hz, 2H), 7.67 (dd, J = 15.4, 6.9 Hz, 4H), 7.56 – 7.50 (m,
2H), 7.36 – 7.25 (m, 2H), 7.05 (s, 2HMI) ppm. 13C NMR (101 MHz, MeOD-
d
4
): δ= 170.10, 157.55, 157.38, 152.53, 152.01, 150.66, 146.14, 138.15,
4
(101 MHz, MeOD-d ): δ=158.80, 158.61, 153.71, 153.28, 152.86, 152.79,
138.02, 134.87, 134.26, 130.68, 127.85, 127.73, 127.42, 127.21, 126.37,
-
1
1
1
7
2
51.90, 151.42, 147.23, 146.62, 146.45, 139.34, 139.21, 136.74, 132.15,
29.25, 128.97, 128.88, 127.89, 127.41, 125.69, 125.62, 71.38, 71.31,
1.10, 67.88, 63.62, 63.39, 41.54, 40.71, 26.46, 24.54, 23.77, 23.38,
1.16, 20.72, 19.16 ppm. HRMS (MALDI-FT-ICR): 1366.28849 [M+H+]+
124.55, 124.46, 123.94 ppm. IR(KBr): 1716 (C=O-valence) cm . HRMS
(MALDI-FT-ICR): 2045.2001 [2M-PF
]+ (calculated: 2045.18953),
950.11248 [M-PF
]+ (calculated: 950.11355), 804.14309 [M-2PF -H]+
(calculated: 804.14040).
6
6
6
(
calcd. 1366.28998), 1220.31673 [M–PF
6
-]+(calcd. 1220.31798).
Bis(2,2-bipyridine)-(4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)-
2
[Bis(2,2-bipyridine)-(4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)-
phenyl-1-(3-((2-hydroxyethyl)thio)-1-λ -pyrrolidine-2,5-dione))-
2
phenyl-1-((Z)-4-(λ -azanyl)-4-oxobut-2-enoic
acid))-Ruthenium(II)]
salt) were
2
Ruthenium (II)] Cl (9): 8 (30 mg, 0.03mmol) was dissolved in PBS
6
(PF )
2
(open maleimide 7): 84 mg (0.08mmol) of 3a (PF
6
(1.5 mL) and 2-mercapto-ethanol (3 μL, 0.04mmol) was added whereupon
dark red streaks appeared in the solution. The mixture was stirred at RT
for 1 h during which the red streaks vanished. The product was precipitated
with NH4PF6, filtered via a glass frit (POR5) and washed with diethylether.
It was reprecipitated to the Cl-salt with TBACl and the product was purified
twice by size exclusion chromatography (Sephadex©, MeOH) to yield 9 as
dissolved in MeCN (5 mL) and maleic anhydride. 8 mg (10 eq, 0.80mmol)
were added. The resulting solution was stirred at RT for 12 h. Product 7
was precipitated with diethylether from the reaction mixture, filtered off via
a POR3 glass frit and washed intensively with diethylether. The reaction
1
yielded 7 as a red solid (98%, 88 mg, 0.08 mmol). H NMR (400.13 MHz,
MeCN-d
3
): δ=12.36 (s, 1H, NHip), 9.62 (s, 1H, NHamide), 8.98 (d, J = 48.4
red solid (74%, 0.02mmol, 21 mg). 1H NMR (400.13 MHz, MeCN-d
3
):
Hz, 2H), 8.52 (dd, J = 16.2, 8.2 Hz, 4H), 8.31 (d, J = 8.6 Hz, 2H), 8.10 (t, J
δ=12.48 (s, 1H), 8.97 (s, 2H), 8.52 (dd, J = 16.2, 8.2 Hz, 4H), 8.37 (dd, J
= 8.3, 5.6 Hz, 1H), 8.21 (dd, J = 8.9, 2.1 Hz, 1H), 8.10 (t, J = 7.9 Hz, 2H),
8.05 – 7.96 (m, 4H), 7.92 (s, 1H), 7.89 – 7.73 (m, 5H), 7.59 (t, J = 5.0 Hz,
2H), 7.52 (d, J = 8.5 Hz, 1H), 7.45 (dd, J = 7.4, 6.1 Hz, 2H), 7.25 – 7.16
(m, 2H), 2.89 (m, 3H), 2.77 (m, 2H), 1.32 (m, 2H). HRMS (MALDI-FT-ICR):
=
5
7
1
3
2
2
7.9 Hz, 2H), 8.04 – 7.94 (m, 4H), 7.91 (d, J = 8.6 Hz, 2H), 7.85 (d, J =
.4 Hz, 2H), 7.76 (ddd, J = 10.7, 8.3, 5.3 Hz, 4H), 7.59 (d, J = 5.1 Hz, 2H),
.45 (t, J = 6.1 Hz, 2H), 7.21 (t, J = 6.5 Hz, 2H), 6.59 (d, J = 12.7 Hz,
H
openMI), 6.40 (d, J = 12.7 Hz, 1HopenMI) ppm. HRMS (MALDI-FT-ICR):
193.29621 [3M-PF
]+ (calcd. 3193.29054), 2081.21209 [2M–PF ]+(calcd.
081.21066), 968.12270 [M–PF
]+(calcd. 968.12297), 822.15048 [M–
-H ] (calcd. 822.15096). Crystal data for 7: C44 Ru,
= 918.16 g mol , red block, orthorhombic, space group Pbcn, a =
8.3662(10) Å, b = 15.9805(4) Å, c = 20.9099(6) Å, α = 90°, = 90.° γ =
1028.12559 [M-PF
6
]+ (calculated: 1028.12747). This reaction can also be
6
6
6
carried out with the PF
6
salt of 8 in a MeCN/PBS (1:1) mixture.
+
+
PF
6
9 4
H35 Cl1.78 N O
-
1
Ruthenium Complexes bearing tert-butyl groups
M
r
2
3
3
9
0°, V = 9478.6(5) Å , T = 149.95(10) K, Z = 8, ρcalcd. = 1.287 Mg/m , μ
[Bis(4,4’-di-tert-butyl-2,2'-bipyridine)-4-(1H-imidazo[4,5-f]-[1,10]-
-
1
(
Cu-K
α
) = 4.000 mm , F(000) = 3747.0, altogether 37069 reflexes up to
phenanthroline-2-yl)aniline-Ruthenium(II)]Cl
[(bpy*) RuCl ] and 283 mg (833 μmol) of 2 were dissolved in EtOH/H
(20 mL, 3:1) and 3 drops of an aqueous KOH solution (1 plate dissolved in
15 mL H O) were added. The solution was reacted in the microwave for
2
(3b): 454 mg (640 μmol)
h(-31/34), k(-12/19), l(-23/25) measured in the range of 15.096° ≤ Θ ≤
2
2
2
O
1
48.782°, completeness Θmax = 97 %, 9375 independent reflections, Rint
=
0
.0398, 561 parameters, 3 restraints, R1obs = 0.1358, wR2obs = 0.3927,
2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701126
FULL PAPER
(ESI): 488 [M-2Cl-]2+, 506 [M-Cl +H ] , 1011 [M-Cl ] . IR: ν=2095-2123 (s,
-
+ 2+
- +
2
h at 180 W and changed the color from dark violet to red. The solvents
-
1
were rotary evaporated, the residue was dissolved in EtOH, Et O was
2
3
doublet, N -stretching) cm .
added and red crystals precipitated. The red crystals were filtered off. Via
size exclusion chromatography (Sephadex©) in MeOH the desired
complex was isolated as a bright orange band. After the solvent was
removed via rotary evaporation the product was isolated as red crystals
[Bis(4,4’-di-tert-butyl-2,2-bipyridine)-(4-(1H-imidazo-4,5-f-1,10-
phenanthroline-2-yl)-1-H-1,2,3-triazolyl-4-phenyl)-Ruthenium(II)]Cl
2
(5b): 52 mg (0.04 mmol) of 4b (PF
eq) of phenylacetylene were dissolved in MeCN. NaAsc (8 eq, 62 mg) and
CuSO ·5 H O (4 eq, 39 mg) were dissolved in 2 mL water respectively,
6
salt) and 6 mg (6.5 μl, 0.06 mmol, 1.5
(
89%, 590.7 mg, 570 μmol). 1H NMR (400.13 MHz, RT, MeCN-d
.03 (d, J = 8.2 Hz, 2H), 8.51 (m,6), 8.30 (d, J = 8.8 Hz, 2H), 7.92-7.82 (m,
3
): δ =
9
6
6
1
=
1
3
–
H
4
2
H), 7.71 (d, J = 6.0 Hz, 2H), 7.64 (dd, J = 8.2, 5.2 Hz, 2H), 7.56 (d, J =
.1 Hz, 2H), 7.45 (dd, J = 6.0, 2.0 Hz, 2H), 7.26 (dd, J = 6.1, 1.9 Hz, 2H),
added to the reaction mixture and the emulsion was stirred rapidly
overnight at RT. The product was extracted with dichloromethane (DCM),
.42 (s, 18H), 1.31 (s, 18H). 13C-NMR (101 MHz, RT, MeOD-d
4
): δ [ppm]
2 4
dried over Na SO . Reprecipitation as Cl salt with TBACl and purification
164.48, 164.31, 158.54, 158.39, 154.02, 152.28, 152.15, 151.80, 147.44,
via size exclusion chromatography (Sephadex©) in MeOH yielded the
product as a bright orange band. After removal of the solvent, the product
was isolated as red crystals in good yield (77%, 42 mg, 0.03 mmol). 1
31.93, 130.30, 127.52, 126.27, 126.12, 124.10, 122.83, 122.75, 119.65,
-
6.69, 36.58, 30.65, 30.55. HRMS: (MALDI-FT-ICR): 948.40126 [M–2PF
6
H
H ] (calcd. 948.4010). MS (ESI): 474 [M-2Cl-]2+. Crystal data for 3b: C61
+
+
NMR (400.13 MHz, MeCN-d ): δ= 8.97 (d, J = 8.3 Hz, 2H), 8.74 (s, 1H),
3
-1
37 Cl
2
N12 Ru, M
r
= 1140.23 g mol , red prism, monoclinic, space group
8.51 (d, J = 18.5 Hz, 4H), 8.44 (d, J = 8.3 Hz, 2H), 8.08 (d, J = 7.8 Hz, 2H),
7.99 (d, J = 4.9 Hz, 2H), 7.94 (d, J = 7.4 Hz, 2H), 7.76 (dd, J = 18.4, 13.0
Hz, 2H), 7.71 (d, J = 5.9 Hz, 2H), 7.55 – 7.35 (m, 7H), 7.22 (d, J = 4.6 Hz,
P 2
1
/n, a = 14.43810(10) Å, b = 25.6586(2) Å, c = 15.6446(2) Å, α=
3
9
1.2930(10)°, V = 5794.25(10) Å , T = 150(2) K, Z = 4, ρcalcd. = 1.307 Mg/m3,
-
1
2H), 1.46 (s, 18H), 1.35 (s, 18H). 13C-NMR (101 MHz, MeCN-d
μ (Cu-K
α
) = 3.423 mm , F(000) = 2380, altogether 41016 reflexes up to
3
): δ [ppm]
h(-18/15), k(-32/30), l(-17/19) measured in the range of 7.463° ≤ Θ ≤
= 163.11, 162.88, 158.19, 157.87, 151.99, 151.91, 148.70, 147.17, 145.30,
139.03, 136.66, 133.37, 131.74, 130.73, 130.64, 129.98, 129.72, 129.23,
128.35, 128.02, 126.52, 125.39, 125.28, 122.25, 122.15, 121.23, 119.84,
36.28, 36.17, 30.51, 30.42. HRMS (MALDI -FT-ICR):1076.43889 [M–2
7
4.479°, completeness Θmax = 99.7 %, 11819 independent reflections, Rint
0.0342, 10349 reflections with F > 2 σ(F ), 648 parameters, 13 restraints,
=
0
0
R1obs = 0.0480, wR2obs = 0.01316, R1all = 0.0556, wR2all = 0.1373, GOOF
-
3
–H]+ (calcd. 1076.43842), 2297.84968 [2 M–3 PF
—
+ +
=
1.097, largest difference peak and hole: 1.404/-1.221 e∙Å . The position
PF
6
6
2 H ] ( calcd.
, M = 2952.79
of the amine function in the imidazole ring has been assigned with respect
to the hydrogen bond towards the chloride anion. Due to the considerable
disorder of solvent molecules, restraints were applied in order to fix their
respective geometry, i.e. in particular the DFIX for C-C distances (1.400
Å) and C≡N distances (1.050 Å), and DANG C-N (2.450 Å) in acetonitrile.
The solvent molecules were left isotropic. Protons at the amine function
were added using standard N-H distances (0.91 Å). CCDC 1520547
contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
2297.84156). Crystal data for 5b: C134
H
148
F
24
N
26
O
3
P
4
Ru
2
r
-
1
g mol , red block, triclinic, space group P-1, a = 16.1146(5) Å, b =
19.6835(6) Å, c = 23.6612(8) Å, α = 80.3508(15)°, β= 87.6796(16)°, γ =
69.9649(15)°, V = 6950.0(4) Å , T = 150.0 K, Z = 2, ρcalcd. = 1.411 Mg/m3,
3
-
1
α
μ (Mo-K ) = 0.357 mm , F(000) = 3044.0, altogether 120459 reflexes up
to h(-18/18), k(-23/23), l(-27/27) measured in the range of 4.234° ≤ 2Θ ≤
49.436°, completeness Θmax = 100 %, 23619 independent reflections, Rint
= 0.0628, 1850 parameters, 525 restraints, R1obs = 0.0773, wR2obs
=
0.2014, R1all = 0.1119, wR2all = 0.2397, GOOF = 1.054, largest difference
-
3
peak and hole: 1.65/-0.81 e∙Å . DFIX and ISOR restraints were used to fix
the geometry of disordered solvent molecules. CCDC 1573111 contains
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
[
Bis(4,4’-di-tert-butyl-2,2-bipyridine)-(4-(1H-imidazo-4,5-f-1,10-
phenanthroline-2-yl)azido)-Ruthenium(II)]Cl (4b): 3b (0.455 g,
O (7 ml), MeCN (7 ml) and
(15.8 mg, 0.229 mmol, 1.2
O (0.3 ml) was added. The red solution was stirred for
0 min. The solution was cooled to 0° C and NaN (25.0 mg, 0.385 mmol,
.0 eq.) dissolved in H O (0.3 ml) was added. The red solution was stirred
2
0
3
.45 mmol) was dissolved in a solution of H
2
M HCl (0.3 ml) and stirred for 20 min. NaNO
2
eq) dissolved in H
2
[Bis(4,4’-di-tert-butyl-2,2-bipyridine)-(4-(1H-imidazo-4,5-f-1,10-
1
2
3
phenanthroline-2-yl)-phenyl-1-(1H-1,2,3-triazolyl-4,5-
bicyclo[6.1.0]non-4-en-9-yl) methyl (2-(2-(2-aminoethoxy)ethoxy)-
ethyl)carbamate)-Ruthenium(II)]Cl (6b): 41.0 mg (32.41μmol) of 4b
(PF salt) were dissolved in a small amount of MeCN. 8.2 mg (25.276μmol)
((1R,8S,Z)-
2
at 0° C for 10 min and 2.5 h at room temperature (RT). The solution was
neutralized with ammonia solution (25 % in water. To the remaining red
2
6
solution aqueous NH
4
PF
6
was added. The precipitate was filtered off,
N- [(1R, 8S, 9S)-bicyclo[6.1.0]-non-4-yn-9-yl-methyl-oxy-carbonyl]-1,8-
diamino-3,6-dioxa-octane (BCN-amine) was dissolved in an ethanol and
added subsequently. A slight warming of the resulting solution was
observed and it was stirred for 16 h at rt. The solvent was removed and
the product was reprecipitated as Cl-salt (crude yield: 80%). The solid was
filtered via a syringe filter (PTFE), washed with diethylether and dried. The
product was dissolved from the filter with MeOH and purified via size
reprecipitated as Cl salt with TBACl and purified via size exclusion
chromatography (Sephadex©, MeOH) to receive the product as a red solid
(
84%, 0.398 g, 0.38 mmol). 1H NMR (400.13 MHz, RT, MeCN-d
2.13 (s, 1H), 9.06 (d, J = 8.2 Hz, 1H), 8.85 (d, J = 7.9 Hz, 1H), 8.50 (dd,
J = 18.9, 1.6 Hz, 4H), 8.29 (d, J = 8.8 Hz, 2H), 7.99 (d, J = 5.2 Hz, 2H),
3
): δ =
1
7
2
1
1
1
3
.79 (dd, J = 8.3, 5.3 Hz, 2H), 7.69 (d, J = 6.0 Hz, 2H), 7.46 (dd, J = 6.0,
.0 Hz, 4H), 7.33 (d, J = 8.8 Hz, 2H), 7.19 (d, J = 4.8 Hz, 2H), 1.45 (s, 18H),
.35 (s, 18H). 13C NMR (101 MHz, MeCN-d
exclusion chromatography (Sephadex©). 6b was isolated as red solid in a
1
3
): δ= 163.47, 163.34, 157.90,
moderate yield (13.80 mg (10.069μmol), 40%). H-NMR (MeOD-d
4
, 500.13
57.76, 152.70, 152.09, 151.93, 150.85, 146.71, 142.84, 130.85, 128.79,
26.79, 126.45, 125.57, 125.43, 122.41, 122.31, 120.42, 118.26, 36.26,
MHz): δ = 9.18 (d, J= 8.3 Hz, 2H), 8.77 (dd, J= 21.0, 1.8 Hz, 4H), 8.53 (dd,
J= 8.7, 2.3 Hz, 2H), 8.11 (dd, J= 5.3, 1.1 Hz, 2H), 7.93 –7.79 (m, 4H), 7.66
–7.56 (m, 6H), 7.39 (dd, J= 6.1, 1.6 Hz, 2H), 4.18 (d, J= 8.1 Hz, 2H), 3.78
–3.63 (m, 6H), 3.55 (t, J= 5.6 Hz, 2H), 3.35 (s, 2H), 3.26 –3.16 (m, 1H),
6.16, 30.42, 30.32 ppm. HRMS (MALDI-FT-ICR): 1120.36379, [M-PF
-]+ (calcd. 2385.69167), MS
6
-]+
(calcd. 1120.36347), 2385.69779 [2 M-PF
6
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European Journal of Inorganic Chemistry
10.1002/ejic.201701126
FULL PAPER
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Keywords: Ruthenium • click chemistry • CuAAC • SPAAC •
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European Journal of Inorganic Chemistry
10.1002/ejic.201701126
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Entry for the Table of Contents (Please choose one layout)
Layout 2:
FULL PAPER
Ruthenium; Click Chemistry
Anne Stumper, Martin Lämmle,
Alexander K. Mengele, Dieter Sorsche
and Sven Rau
Page No. – Page No.
A library of Ru(II) poylpyridine complexes is presented which allows the application
of different coupling reactions with potentially biologically active substrates.
Therefore precursor substrates for CuAAC, SPAAC and maleimide-thiol coupling are
generated and the feasibility of the click reactions is evaluated. All presented
precursor compounds resort to one easy-to-synthesize scaffold to retain essential
photophysical properties.
One Scaffold, Many Possibilities:
CuAAC, SPAAC and Maleimide-Thiol
Coupling of Ruthenium(II) Polypyridyl
Complexes
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