Efficient Access to 5-Bromo- and 5,6-Dibromophenanthroline Ligands

Article abstract of DOI:10.1002/ejic.201700548

Bromo-functionalized precursor molecules are essential for generating desired target compounds through cross-coupling reactions. Herein we show an improved synthetic route, feasible at low temperatures and affording high yields, to the ligands 5-bromo-1,10-phenanthroline (1) and 5,6-dibromo-1,10-phenanthroline (2). The corresponding ruthenium complexes, containing various equivalents of ligand 2, are easily accessible in high yields, including the analogue of tris-homoleptic [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridine), [Ru(2)₃]²⁺. X-ray diffraction analyses have provided detailed information on the structures of the ligands and their corresponding metal complexes. An investigation of the electrochemical properties has provided detailed information on the ³MLCT state localized on 2. We show the conversion of heteroleptic ruthenium complexes of these ligands in Suzuki cross-coupling reactions whereas the ligands did not undergo reaction under the same conditions.

Full text of DOI:10.1002/ejic.201700548

A Journal of
Accepted Article
Title: Efficient Access to 5- and 5,6- Dibromophenanthroline Ligands
Authors: Anne Stumper, Thomas David Pilz, Markus Schaub, Helmar
Görls, Dieter Sorsche, Katrin Peuntinger, Dirk Guldi, and
Sven Rau
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201700548
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10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
Efficient Access to 5- and 5,6- Dibromophenanthroline Ligands
Anne Stumper,[a] Thomas David Pilz,[b] Markus Schaub,[a] Helmar Görls,[b] Dieter Sorsche,[a] Katrin
Peuntinger,[c] Dirk Guldi[c] and Sven Rau*[a]
Abstract: Providing bromo functionalized precursor molecules is
essential to generate desired target compounds utilizing cross
coupling reactions. Here we show an improved synthetic route –
feasible at low temperatures and affording high yields - for the
ligands 5-bromo-1,10-phenanthroline (1) and 5,6-dibromo-1,10-
phenanthroline (2). Corresponding Ruthenium complexes providing
2 in varying numbers are easily accessible in high yields and the
based building blocks in order to improve the overall time and
substance efficiency of synthetic pathways towards functional
ligands and their Ru(II) complexes. Already in 1978 Dénes and
Chira presented
a synthetic strategy for multiple bromo
substituted 1,10-phenanthrolines.[ 7 ] Since then many groups
made use of those compounds and their properties albeit
modifying the synthetic conditions.[8-10] For example Tor et al.
used 3-bromo- or 3,8-dibromo substituted 1,10-phenanthrolines,
their corresponding alkyne substituted ligands and the Ru(II) and
Os(II) compounds[11] which are used for the design of hetero-
nuclear metal complexes via coupling reactions. 5,6-dibromo-
phenanthroline is used to build up a variety of compounds
bearing thioether functionalities or S,S- coordination sites[12-15] or
for the design of water oxidation catalysts,[16] whereas others
use alkyne substituted phenanthroline Ruthenium (II) complexes
for biological applications. Thereby, coupling was performed on
the ligand scaffold with subsequent complexation.[17] In 2008 the
group of Fujii presented Suzuki coupling on the chromophore
core of 5-bromo-phenanthroline Ru(II) complexes.[18] They used
common precursors like [(2,2’-bipyridine)2RuCl2] as well as
[(4,4’-dimethyl-2,2’-bipyridine)2RuCl2] and introduced ligands
such as 5-bromo-phenanthroline (Figure 1).
analogue to tris-homoleptic [Ru(bpy)3]2+ (bpy
= 2,2’-bipyridine),
[Ru(2)3]2+, is presented. Comparison of the X-ray diffraction analyses
provides detailed information about the structures of the ligands and
their corresponding metal complexes. The investigation of
electrochemical properties generated detailed information about the
3MLCT state localized on 2. We show conversion of heteroleptic
Ruthenium complexes of these ligands in Suzuki cross coupling
reactions whereas the ligands did not undergo Suzuki coupling
under the used conditions.
Introduction
In order to generate novel molecular systems chemists are
dependent on suitable possibilities to link different substrates
with one another. This is of great importance in a variety of
research fields like energy conversion or biomedical applications.
Compounds bearing bromo functionalities offer many suitable
reaction pathways like substitution reactions, cross coupling[1]
(Sonogashira,[2] Suzuki[3-5]) and elimination reactions to obtain
sophisticated molecules.
Therefore it is desirable to have access to suitably derivatised
bromo substituted building blocks. For example, a peptide
hormone Ru(II) polypyridyl conjugate functioning as selective
photodynamic therapeutic was generated using a synthetic
pathway including
a
bromo intermediate, 4-bromo-2,2’-
bipyridine.[6] In order to get to the bromo intermediate, however,
one has to carry out a multiplicity (partly inefficient) syntheses.
We hence investigated the possibility to use 1,10-phenanthroline
Figure 1. Complexes presented by the research groups Tor (top left),
Thummel and McFarland (top right) and Fujii (bottom).
[a]
A. Stumper, M.Schaub, 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
T. D. Pilz, H. Görls
Institute for Inorganic and Analytical Chemistry
Friedrich Schiller University Jena
August-Bebel-Straße 2, 07743 Jena, Germany
K. Peuntinger, D.Guldi
The yields for coupling reactions dropped significantly when
complexes were converted whose precursor molecules bore
substituted bipyridine units (yields: 53-54% (2,2’-bipyridine),
14-16% (4,4’-dimethyl-2,2’-bipyridine), 20% (4,4’-di-tertbutyl-
2,2’-bipyridine)).[18] Comparing the literature known synthetic
pathways of 4-bromo-2,2’-bipyridine[7] and 5-bromo-1,10-
phenanthroline[7,8,18] both expose disadvantages. As the
syntheses of 5-bromo- (1) and 5,6-dibromo-1,10-phenanthroline
(2) are single step reactions, this ligand system offers significant
time and resource profits compared to the bpy scaffold.
However, for 1 and 2 very harsh conditions have to be applied.
The reaction is carried out in pressure tubes at elevated
[b]
[c]
Institute of Chemistry and Pharmacy
Friedrich-Alexander-University Erlangen-Nuremberg
Egerlandstr. 3, 91058 Erlangen, Germany
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/ejic.201700548
European Journal of Inorganic Chemistry
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temperatures (>120°C) in oleum. Therefore, an optimization of
reaction protocols with milder conditions and high yields would
be desirable. We optimized the required ligand syntheses which
determine the yield and investigated the synthetic accessibility of
Ru(II) complexes bearing either 5-bromo- or 5,6-dibromo-
phenanthroline in varying numbers. Study of corresponding solid
state structures as well as photophysical and electrochemical
properties yielded crucial information on the effect of bromine
substitution. Furthermore we analyzed the feasibility of Suzuki
cross coupling utilizing these bromo functionalities. An overview
of the investigated compounds is depicted in Figure 2.
oleum (65%) at room temperature and normal pressure for 16 h
(1), and at 60 °C for 2 h (2), respectively (Figure 2). Thereby
elemental bromine is added in required equivalents to a solution
of phen in oleum. After completion of the reaction, extraction
with chloroform and recrystallization afforded pure compounds in
good yields of 70% for 1 and 93% for 2. Unreacted educt
phenanthroline can be easily removed via stirring in ether for 12
hours. The successful reaction can be determined by losing
signals for protons in 5- and 5,6-position in the 1H-NMR
spectrum. For 1 and 2 crystal structures (monoclinic, space
group P2(1)/n) could be obtained via slow evaporation of
chloroform solutions. The crystal lattice exhibits alternating
orientation of the phen scaffolds and aromatic -stacking can be
observed. (“-” in Table S1, example depicted in Figure S1,
ESI). The bromination had no significant effect on bond lengths
and angles of the phen scaffold (Table S1, ESI).
Figure 3. ORTEP representation of the molecular structures of 1 and 2;
coordination to chloroform via hydrogen bonds; ellipsoids were drawn at 50%
probability level.
Synthesis of Ruthenium chromophores
To understand the effects arising from the bromination of the
phen ligands the corresponding Ru(II) polypyridyl complexes
were synthesized bearing either 1 or 2 in their periphery.
Additionally, a series of Ru(II) polypyridyl complexes with
varying numbers of 2 according to the formula [(tbbpy)3-
nRu(2)m]2+ (with tbbpy= 4,4’-tert-butyl-2,2’-bipyridine and n = 0, 1,
2, m = 1, 2, 3) was prepared to verify the coordination of
multiple halogenated phen ligands towards Ru(II) chromophore
cores. It is known, that unequally halogenated tpphz derivatives
tend to show low coordination affinity mediated by the electron
withdrawing effect of these functional groups.[20,21]The synthesis
of heteroleptic Ruthenium polypyridine complexes of the type
[(tbbpy)2Ru(1/2)]2+ was performed using literature known
conditions[10]
and
yielded
[(tbbpy)2Ru(1)]2+
(3)
and
Figure 2. Schematic overview of investigated compounds and experiments.
[(tbbpy)2Ru(2)]2+ (4) in high yields (>90%) and purity (see Figure
4). Initial structural characterization was performed with various
NMR-spectroscopic methods as well as mass spectrometry.
Recrystallization in acetone/water or MeCN/water solutions
yielded appropriate single crystals for X-ray diffraction.
Results and Discussion
Bromination of 1,10-phenanthroline (phen)
We were able to develop an improved synthesis procedure for
5-bromo-1,10-phenanthroline (1) and for 5,6-dibromo-1,10-
phenanthroline (2). The literature known syntheses are carried
out in pressure tubes at elevated temperatures in oleum
(>120°C) with mostly low yields and time consuming work up
procedures.[7,8,18] The group of Eisenberg obtained the best yield
(90%) with 15% oleum in a pressure tube for 23 h at 135°C.[19]
We have established a new synthetic protocol protocol using
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10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
Figure 4. Solid state structures of 3 (left) and 4 (right); counter ions and
hydrogen atoms were omitted for clarity; ellipsoids were drawn at 60% level in
this ORTEP representation.
Figure 5. ORTEP representations of the molecular structures of precursor 9
(left) and resulting homologue 8 (right); counter ions and hydrogen atoms were
omitted for clarity; ellipsoids were drawn at 50% level.
The synthesis of the complexes comprising more than one
brominated ligand (8 and 10) required the preparation of the
[(2)2RuCl2] precursor derivative 9 (see Figure 2).
Reaction of the starting material [Ru(cod)Cl2]n[22] with 2 (2 eq) in
refluxing DMF under inert conditions and microwave irradiation
yielded in a blue, highly insoluble solid. After work up and
characterization of the product by 1H-NMR spectroscopy in
CD2Cl2 exhibited two sets of three signals. The low solubility in
various solvents made the product inaccessible for 13C-NMR
spectroscopy or mass spectrometry techniques. However, very
careful recrystallization from CH2Cl2 yielded black single crystals
suitable for X-ray diffraction (see Figure 5). Subsequent
preparation of [(tbbpy)Ru(2)2]2+ (8) succeeded by conversion of
Photophysical Characterization of Metal Complexes
At first glance, the absorption and emission properties of the two
series [(tbbpy)3-n Ru (2)n]2+ (n
=
0, 1, 2, 3) and
[(tbbpy)2Ru(phenBrm)]2+ (m = 0, 1, 2, 4) (the precursor 9 was
excluded) are typical for [Ru(bpy)3]2+ complexes. All substances
exhibit the characteristic singlet metal to ligand charge transfer
(1MLCT) absorption band ranging from 400 to 500 nm as well as
intense luminescence between 600 and 800 nm. A closer look
reveals an increase in molar extinction coefficients as a function
of the number n of 2 with values from ϵ (n=0)≈16000 Lmol-1cm-1 in
model compound [Ru(tbbpy)3]2+ to ϵ (n=3)≈19000 Lmol-1cm-1 in 10.
For acetonitrile and dichloromethane, the 1MLCT is
hysochromically shifted with increasing number of 2. This is
presumably due to the contribution of the bromo-substituted
phen-centered 1MLCT-absorption. A similar trend evolves when
inspecting the emission of the [(tbbpy)3-nRu(2)n]2+-series in
tbbpy and
9 in a microwave reaction utilizing literature
conditions.[24] For the detailed characterization of the product
NMR, MS and X-ray diffraction experiments were performed. To
obtain the tris-homoleptic derivative [Ru(2)3]2+ (10) three
equivalents of 2 in moist DMF were converted in a microwave
reaction chamber and after work up the red product was
characterized via NMR and MS techniques. This is pleasing as
previous attempts to convert the tetra-bromo derivative, 3,5,6,8-
acetonitrile. In particular,
a hypsochromically shifted and
intensified emission band is detected with increasing number of
phen ligands. Interestingly, the homoleptic model compound
[Ru(tbbpy)3]2+ shows an emission maximum at 614 nm and an
emission intensity which is in between 4, 8 and 10. Again, when
going from n = 1 to 3 a successive hypsochromical shift of the
emission maximum is discernable. In dichloromethane rather
than acetonitrile, the emission doubles in intensity and shifts
hypsochromically by 10 nm. For a better comparison of the
characteristic absorptions and emissions of 3 and 4, the data for
Br-phen, to yield
a tris-homoleptic chromophore did not
succeed.[9]
Comparing bond lengths and angles of the investigated Ru(II)
complexes resulted in high structural similarity (Table S2, ESI).
Free phen ligands compared to metal complexes did not show
significant changes in bond lengths and angles either and as a
result typical Ru-N1/N2 bond lengths (phen scaffold) and typical
Ru- N3/N4/N5/N6 bond lengths (bpy backbone) are observed,
which exactly match the known bond lengths of related
compounds.[8,20,23]
In contrast, cisoidal chloro complex 9 exhibits slightly shortened
Ru-N3 bond lengths which is in agreement with literature
concerning reference compound cis-[(tbbpy)2RuCl2].[24]
Obviously, 5-Bromo and -5,6-Dibromo-1,10-phenanthroline can
be utilized as conventional N,N’-chelating ligands for the
preparation of all kinds of [(tbbpy)nRu(2)m]2+ (n= 0, 1, 2; m = 1, 2,
reference
complexes
[(tbbpy)2Ru(phen)]2+
were taken from
and
the
[(tbbpy)2Ru(3,5,6,8-Br-phen)]2+
literature[8,10, 25 ] As such, all complexes in this series exhibit
absorption maxima around 450 nm with exception of
[(tbbpy)2Ru(3,5,6,8-Br-phen)]2+.
The
latter
shows
a
hypsochromically shifted absorption maximum at 441 nm. In
contrast, the emission behavior is only slightly changed with
increasing number of bromo functionalities comparing 3 and 4.
Emissions of these compounds are hypsochromically shifted
when compared to the reference [(tbbpy)2Ru(3,5,6,8-Br-phen)]2+
3) complexes. This result indicates that for
2 a more
conventional electronic properties may be expected in contrast
to 3,5,6,8-Br-phen since this ligand could not be employed for
similar reactions.
and
bathochromically
shifted
when
compared
to
[(tbbpy)2Ru(phen)]2+.
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10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
Table 1. UV/vis absorption and emission data of references, the series
[(tbbpy)3-nRu(phenBr2)n]2+ (n=0,1,2,3), [(tbbpy)2Ru(phenBrm)]2+ (m=0,1,2,4) and
Suzuki cross coupling products 5, 6 and 7.
lifetime, when compared to [(tbbpy)2Ru(phen)]2+ (211 ns). From
these results can be concluded that substitution of the phen
backbone with bromo substituents (-I/+M effect) exerts
a
3
compound
solvent
max,abs
εmax
max,em
remarkable influence on the MLCT excited state lifetime of the
corresponding Ru(II) complexes. Based on the emission data of
the [(tbbpy)3-nRu(2)n]2+ (n=1, 2, 3) series substitution of the 5,6-
positions only imperceptive influence on the excited state energy
is observable, while the effect of the substitution in the 3,8-
position is rather striking. The ordering of the lifetimes within this
series is similar to the ordering of the relative luminescence
intensities in dichloromethane. A direct correlation between short
lifetime intensities points to the lack of other deactivating
processes. Most notable is here the excited state quenching by
oxygen.
[nm] [L mol-1 cm-1] [nm]
[Ru(tbbpy)3]2+
DCM
MeCN
DCM
MeCN
DCM
464
458
455
454
440
440
16 000
17 900
19 000
16 000
18 000
19 000
607
614
602
610
638
657
[(tbbpy)2Ru(phen)]2+[8,20]
[(tbbpy)2Ru(3,8-Br-phen)]2+[20]
[(tbbpy)2Ru(3,5,6,8-Br-
phen)]2+[10,20]
DCM
MeCN
DCM
MeCN
MeCN
DCM
441
448
450
424
451
449
452
449
454
455
457
433
434
451
450
15 000
17 000
18 200
8 700
13 500
17 800
17 500
14 300
672
578
593
599
621
630
621
631
617
619
610
611
621
587
600
[Ru(phen)3]2+[10]
[Ru(3,8-Br-phen)3]2+[26]
3
MeCN
DCM
4
MeCN
MeCN
MeCN
MeCN
DCM
MeCN
DCM
MeCN
Table 2. Life times (τ) of Ruthenium complexes in DCM and MeCN.
5
6
7
8
compound
solvent
τaerated [ns]
τdeaerated [ns]
[Ru(tbbpy)3]2+
DCM
MeCN
DCM
MeCN
DCM
MeCN
DCM
MeCN
DCM
MeCN
DCM
MeCN
DCM
MeCN
DCM
248[28]
107[28]
460
150
272
211
452
139
438
140
591
100
573
196
353
247
609[28]
730[28]
20 500
22 200
19 000
18 200
[Ru(phen)3]2+[10]
10
[(tbbpy)2Ru(phen)]2+[9,27]
1423
3
4
1347
1336
2190
1380
[(tbbpy)2Ru(3,5,6,8-Br-phen)]2+[10,27]
8
10
MeCN
Electrochemical Characterization
Interpretation of luminescence data yielded the assumption that
functionalization in 5,6-position has less influence on the excited
state energy compared to 3,8-position substitution. Thus, the
electrochemical properties of [(tbbpy)3-nRu(2)n]2+ complexes (n =
0, 1, 2, 3) and [Ru(tbbpy)3]2+, 3, 4 and [(tbbpy)2Ru(3,5,6,8-Br-
phen)]2+ were determined and compared with literature[8,10]
(Table 3 ).
Figure 6. Exemplary UV/Vis and emission spectra of the standard complex
[Ru(tbbpy)3]2+, 3 and 4; measured in MeCN with same optical density at the
1MLCT transition.
Table 3. Selected redox potentials E1/2 [V] of presented Ruthenium complexes
and reference compounds; referenced vs. Fc/Fc+ in
a 0.1M solution of
Bu4NPF6 in dry acetonitrile under argon atmosphere; (LL)x: ligand centered
reduction.
E1/2(LL)3
[V]
E1/2(LL)2
[V]
E1/2(LL)1
[V]
E1/2(Ru2+/3+
)
Emission Decay Dynamics
Compound/
potential
[V]
[Ru(tbbpy)3]2+[28]
[(tbbpy)2Ru-
(phen)]2+[8,10]
[(tbbpy)2Ru(3,5,6,8
-Br-phen)]2+ [10]
3
-2.28
-2.23
-2.02
-1.99
-1.82
-1.80
0.73
0.78
3
The emission dynamics of the MLCT states of the complexes,
as determined in acetonitrile and dichloromethane by means of
time correlated single photon counting experiments (TCSPC)
corroborated the steady-state emission data (Table 2).
Generally, the lifetimes of 3 and 4 in aerated solutions of
dichloromethane (450 ns) are enhanced compared to those in
aerated acetonitrile solutions (140 ns). A different quencher
concentration and / or a different viscosity in the more polar
solvent might contribute to the differences. Nevertheless, in
aerated solvents the lifetimes slightly changed dependent on the
number of bromo substituents on the phen scaffold. Complexes
3 and 4 have a 40 ns longer lifetime, when compared to
[(tbbpy)2Ru(3,5,6,8-Br-phen)]2+ (100 ns), and a 50 ns shortened
-
-
-
0.92
0.83
0.85
-2.23
-2,32
-1.98
-2.00
-1.78
(-1.65, ir)
-1.79
(-1.68/
-1.58, ir)
-1.89
4
8
-2.27
-1.99
0.90
0.95
(-1.67 ir)
-1.54 (ir)
10
-2.18 (ir)
-1.79 (ir)
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10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
Interestingly, the series [(tbbpy)3-nRu(2)n]2+ (n=0, 1, 2, 3;
compounds [Ru(tbbpy)3]2+, 4, 8, 10) exhibited a shift of potentials
referring to the oxidation process centered on the metal center
(E1/2(Ru2+/3+)). Thereby increasing numbers of n of 2 afforded
higher potentials. Additionally, the complexes of this set (besides
n=3) show three quasi reversible reduction potentials which can
be assigned to the three ligand centered reductions ((LL)x). With
increasing number of bromo substituents the number of
irreversible reductions also rose which likely can be attributed to
reductions of bromine atoms under subsequent dehalogenation.
The other series [Ru(tbbpy)3]2+, 3, 4 and [(tbbpy)2Ru(3,5,6,8-Br-
phen)]2+ exhibited an analogous shift for the potential of the
metal centered oxidation (E1/2(Ru2+/3+)). Based on the available
data sets, the ground state redox properties of a general
compound A and the emission properties (one electron potential
according to the zero-zero excited state energy, E0-0) permits a
rough determination of the redox potentials of excited state
couples according to the adjacent equations:[29]
is irrespective of potential influences which result from other
ligands coordinating the metal ion. Thus, the 3MLCT-states
located on 2 account for the emitting excited states (KASHA’s
rule) in compounds with n=1, 2, 3 as they exhibit reduction
potentials about 0.16 eV lower in energy than the tbbpy centered
3MLCT-states. This is in agreement with the previous discussion
of the photophysical phenomena in terms of hypsochromically
shifted absorption and bathochromically shifted emission. The
analogous correlation for the set [(tbbpy)2Ru(phenBrm)]2+ (m=0, 1,
2, 4) is shown in Figure 8 and compares the influence of the
number of bromine atoms coupled to the phen backbone to the
introduced redox potentials.
E(A+/A*) ≈ E(A+/A) – E0-0
E(A*/A−) ≈ E(A/A−) + E0-0
Applying this for the series of Ruthenium complexes
[(tbbpy)3-nRu(2)n]2+ (n = 0, 1, 2, 3) yields an comparative energy
scheme (Figure 7). The excited state redox potential centered
on the ligand does not change and values of about -1.1 V are
obtained. For n = 1, 2, 3 the ground state metal centered redox
potential is shifted from 0.73 to 0.95 V with increasing number of
2. This effect is very interesting and has been applied by
Thummel et al in tuning water oxidation catalysis. The highest
activity was observed, when utilizing 2 (instead of phen or bpy)
as ligand for the photosensitizer unit.[16] This is in agreement
with our findings regarding the redox potentials of 2 compared to
tbbpy or phen.
Figure 8. Compilation of the 3MLCT excited state redox potentials of the that
can be tapped (oxidative quenching mechanism, E(A+/A*)), the ground state
redox potentials for the oxidation (E(A+/A)) and the emission energies (E0-0) of
the series [(tbbpy)2Ru(phenBrm)]2+ (m=1, 2, 4,) and [(tbbpy)2Ruphen]2+
.
Here, with increasing quantity of bromo substituents at the phen
scaffold higher ground state metal centered oxidation potentials
and a change in excited state oxidation potentials are observed. .
Multiple bromination of the phenanthroline ligand evidently
reduces the excited state reduction potential. This results in a
decreased energy for the phenBrm-centered 3MLCT leading to
emission when relapsing from the excited to the ground state.
Realizing this, the photochemical significance of the 5,6-position
becomes clearly evident for redox and luminescence properties
of corresponding Ruthenium chromophores.
Suzuki cross coupling of brominated complexes
In preliminary studies we investigated the suitability of the 5,6-
dibromophenanthroline scaffold to function as a substrate for
organometallic cross coupling reactions. For the free ligands no
reactivity in Suzuki coupling could be observed. We evaluated
the reactivity of [(tbbpy)2Ru(1)]2+ and [(tbbpy)2Ru(2)]2+ exemplary
in Suzuki cross coupling reactions to receive compounds 5, 6
and 7 (Figure 9). For the conversion of 3 with (4-acetylphenyl)
boronic acid a very good yield of 97% was achieved. Product 5
was characterized via mass spectrometry, NMR spectroscopy
and elemental analysis. Subsequently, we investigated if twofold
Suzuki reactions are possible on the chromophore core utilizing
4 as starting material. The reactions were carried out with
(4-acetylphenyl) boronic acid and (4-hydroxyphenyl) boronic
acid to yield 6 (68%) and 7 (45%), respectively. The achieved
yields for one and twofold Suzuki cross coupling reactions are
higher compared to literature data where yields dropped
Figure 7. Compilation of the 3MLCT excited state redox potentials that can be
tapped (oxidative quenching mechanism, E(A+/A*)), the ground state redox
potentials for the oxidation (E(A+/A)) and the emission energies (E0-0) of the
series [(tbbpy)3-nRu(2)n]2+ (n=0, 1, 2, 3).
Additionally, all compounds in this set (besides n=3) exhibited
three quasi reversible reduction potentials. They can be
assigned to the three reductions centered on the ligands,
respectively. Furthermore, a higher reduction potential (≈-0.16 V)
for the excited state is observed for n=0. In conclusion this
3
implies that the energy of the MLCT-state centered on ligand 2
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10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
drastically (14-20%) when utilizing precursors bearing
substituted (Me, tbbpy) ligands.[18] Characterization was
performed via NMR spectroscopy, mass spectrometry and via X-
ray diffraction (Figure 10).
Figure 11. Depiction of hydrogen bonds of interacting OH groups within the
solid state; counter ions, coordinated solvent and hydrogen atoms were
omitted for clarity; ellipsoids were drawn at 50% level.
1H-NMR spectra are informative to check if the coupling reaction
was successful. Exemplary shift of the protons in 4,4’ position
and appearance for phenyl protons in the aromatic region of the
spectrum are easy to follow. Exemplary depiction is given in
Figure 13.
Figure 9. Products of bromo substituted complexes converted with boronic
acids in Suzuki coupling; conditions: acetonitrile/water; 2M aqueous Na2CO3
solution; Pd(PPh3)2Cl2.
Figure 13. Aromatic region of the 1H-NMR spectra of educt 4 (top) and Suzuki
product 6 (bottom) in MeCN-d3 showing the shift for protons in 4- and 4’-
position (see ESI for description) and appearance of phenyl protons.
Comparison of complexes 6 and 7 with precursor complex 4
reveals high similarity in measured bond lengths and angles
(Compilation of selected bond lengths and angles is given in
Table S3, ESI). The torsion of the phenyl ring for 6 leads to an
almost orthogonal arrangement to the phen plane. Similar
arrangement is found for 7, were both phenyl rings are distorted
for 78.3(4)° and respectively 76.1(4)° out of the phen plane. For
7, two complexes are bridged via two water molecules.
Suzuki coupling products show absorption and luminescence
properties comparable to [Ru(tbbpy)3]2+. No bathochromic shift
was observed which could be explained with the twisting of the
substituted phenyl moieties possibly resulting in a reduced --
delocalization (see ESI).
Conclusions
Improved synthetic strategies for 5-bromo- and 5,6-dibromo-
phenanthroline using low temperatures (room temperature,
60°C), normal pressure and short reaction times (2-16 h) with
very good yields (70-93%) are presented. This provides access
to a brominated ligand system which may undergo a variety of
conversions. Henceforth, we prepared
a series of bromo
substituted Ru(II) complexes which generate a group of related
complexes where structure property relations can be established.
All complexes introduced are easily accessible in high yields. It
was possible to create a D3 symmetric homoleptic Ru(II)
complex which is terminated by six bromo functionalities. A
detailed characterization of the components via X-ray diffraction
provided important structural information. The comparison of the
photophysical and electrochemical properties of these
coordination compounds was performed and it could be shown,
that the energy of the 3MLCT-state centered on ligand 2 is
Figure 10. ORTEP representations of the molecular structures of 6 and 7,
counter ions and hydrogen atoms were omitted for clarity; ellipsoids were
drawn at 50% level.
Thereby typical hydrogen bond lengths of 1.936(3) Å are
observed between the hydrogen of the phenol moiety and an
oxygen atom of the water molecule. Also the O-O distances of
2.829(4) Å are common for similar Ru(II) polypyridyl complexes
which bear ligands like oxalamidines[30] or bibenzimidazoles.[31]
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
Supporting Information available: Crystallographic data (excluding
structure factors) has been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication CCDC-
1451528 for 1, CCDC-1451529 for 2, CCDC-1451530 for 3, CCDC-
1451531 for 4, CCDC-1451532 for 8, and CCDC-1451533 for 9. Copies
of the data can be obtained free of charge on application to CCDC, 12
independent of possible influences which result from other
ligands around the Ruthenium ion. Thus, the 3MLCT-states
localized on 2 represent the emitting excited states. It was
shown that the reactivity of bromo functionalities at the
phenanthroline in Suzuki cross coupling reactions scaffold can
be influenced by coordination of the corresponding ligand to a
metal center. Most interestingly, the free ligands showed no
reactivity in Suzuki coupling reactions, whereas the Ruthenium
bound 5-bromo- and 5,6-dibromophenanthrolines are facilely
substituted by different aromatic building blocks.
Union
Road,
Cambridge
CB2
1EZ,
UK
[E-
mail:
deposit@ccdc.cam.ac.uk].
Ligand syntheses
5-Bromo-1,10-phenanthroline (1): 30ml of fuming sulfuric acid (65%)
were added with cooling to 4.0 g (20.2 mmol) of 1,10-phenanthroline
hydrate. After the 1,10-phenanthroline was dissolved a slight excess of
bromine (0.6ml, 11.75mmol) was added to the solution in one portion.
Upon stirring for 3 hours at room temperature the reaction mixture turned
colorless due to the complete consumption of bromine. The reaction was
not stopped until 16 hours later by pouring the solution on 250ml on ice
and neutralization (pH=5) with ammonia. Extraction with small amounts
of chloroform and drying of combined organic phases over Na2SO4
yielded a crude product after removal of the solvent. Redissolving in
boiling toluene and hot filtration was used to remove impurities. A crude
Experimental Section
General
If not noted otherwise, all chemicals were commercially available and
used without further purification. The following chemicals were prepared
according to literature procedures: [Ru(tbbpy)2Cl2][8], [Ru(tbbpy)3][PF6]2
,
[8]
4,4’-ditertbutyl-2,2’-bipyridine [32,33], [Ru(cod)Cl2]n[22]. The NMR spectra
mixture of
1 and 2 with small traces of the starting material
were recorded on a Bruker AVANCE 400 MHz spectrometer, on a Jeol
phenanthroline was obtained. Purification by column chromatography did
not succeed. Starting material phenanthroline was removed by stirring in
EX-270 DELTA and on
a
Jeol EX-400 DELTA spectrometer
(270/400MHz), respectively. The chemical shifts δ are given in parts per
million relative to tetramethylsilane (TMS, δ=0 ppm) referenced internally
to the residual proton chemical shift in the deuterated solvent. Mass
spectra were recorded with a SSQ 710 spectrometer (Finnigan MAT).
ether for 12
h and subsequent collection of the solids. Slow
recrystallization from chloroform yielded the pure compound (1×CHCl3)
as colorless crystals in good yields (70%). 1H-NMR (CDCl3, 400MHz): δ =
9.1 (m, 2H(2/9)), 8.526 (dd, 1H(4), 3J = 8.4Hz, 4J = 1.6Hz), 8.034 (dd, 1H(7)
,
Electrospray ionization spectra were recorded with
(Thermoquest-Finnigan MAT). Steady state absorption spectra were
obtained using either Perkin Elmer Lambda2 UV/vis two-beam
a MAT 95 XL
3J = 8.1Hz, 4J = 1.6Hz), 7.979 (s, 1H(6)), 7.624 (dd, 1H(3), 3J = 8.3Hz, 3J =
4.4Hz), 7.520 (dd, 1H(8)
3J = 8.1Hz, 3J = 4.3Hz) ppm. 13C-NMR (CDCl3,
,
a
100MHz): δ = 150.89, 150.68, 146.65, 145.67, 135.89, 135.06, 145.09,
129.64, 128.80, 124.00, 123.64, 120.78 ppm. Crystals suitable for X-ray
spectrophotometer or a Jasco V-670 UV/Vis Spectrophotometer using a
width of 2 nm and a scan rate of 480 nm/min. All spectra were recorded
using a quartz glass cuvette of 10⋅10 mm. Steady state emission spectra
were recorded using a Jasco FP-6200 spectrofluorometer or a Jasco
Spectrofluorometer FP-8500 and a Horiba Jobin Yvon FluoroMax-3
spectrometer using a slitwidth of 2 nm for excitation and emission and an
integration time of 0.5 s. The studies were performed in a 10⋅10 mm
quartz glass cuvette. Electrochemical data were obtained by cyclic
voltammetry using a conventional single-compartment three-electrode
cell arrangement in combination with a potentiostate “AUTOLAB®, eco
chemie”. As auxiliary and reference electrode two Pt wires were used;
working electrode: glassy carbon. The measurements were carried out in
anhydrous and argon saturated acetonitrile. Tetrabutylammonium
hexafluorophosphate (c(TBAPF6)=0.1 M) was used as supporting
electrolyte at ambient temperature (20 (±5)°C). All potentials are
referenced to ferrocene/ferrocenium (E(Fc/Fc+) = 0.00V). Emission lifetimes
were determined via time correlated single photon counting (TCSPC) on a
Horiba Jobin Yvon FlouroLog-3 emission spectrometer with a Hamamatsu
MCP photomultiplier (R3809U-58). For excitation a laser diode (NanoLED-
405L, 403 nm, pulse width = 200 ps, maximum of repetition rate 100 kHz) was
used. All measurements were performed in a 10⋅10mm quartz glass cuvette.
Elemental analysis was performed on a Euro Vector Euro EA. Crystal
structure intensity data for the compounds were collected on a Nonius
Kappa CCD diffractometer using graphite-monochromated Mo-Kα
radiation. Data were corrected for Lorentz and polarization effects;
absorption was taken into account on a semi-empirical basis using
multiple-scans.[34,35, 36] The structures were solved by direct methods
(SHELXS[37]) and refined by full-matrix least squares techniques against
Fo2 (SHELXL-97[37]). All hydrogen atoms were included at calculated
positions with fixed thermal parameters. All non-hydrogen, non-
disordered atoms were refined anisotropically.[37] Crystallographic data
as well as structure solution and refinement details are summarized in
Table 4 (ESI). MERCURY was used for structure representations.[38]
diffraction
were
obtained
from
chloroform.
Crystal
data:
C12H7N2Br×CHCl3, Mr
=
378.47 g/mol, colorless crystal, size
0.065×0.065×0.05mm3, monoclinic, space group P21/n (No. 14), a =
6.9802(2), b = 20.3654(6), c = 9.8052(3) Å, α = 90.000, β = 92.768(2), γ
= 90.000°, V = 1392.23(7)Å3, T = -90(2)°C, Z = 4, ρcalcd. = 1.806 g/cm3,
μ(Mo-Kα) = 35.13 cm-1, F(000) = 744, 9838 reflections in h(-9/9), k(-25/26),
l(-12/10) measured in the range 2.00° ≤ Θ ≤ 27.48°, completeness Φmax
= 99.8%, 3182 independent reflections, Rint = 0.0449, 2576 reflections
with Fo > 4σ(Fo), 204 parameters, 0 restraints, Robs. = 0.0433, wR2
=
obs.
0.1016, Rall= 0.0583, wR2all= 0.1080, GOOF = 1.052, largest difference
peak and hole: 0.914/-0.486 e/Å3. Crystallographic data (excluding
structure factors) has been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication CCDC-
1451528.
5,6-Dibromo-1,10-phenanthroline (2): 30ml of fuming sulfuric acid
(65%) were added with cooling to 4.0
g (20.2 mmol) of 1,10-
phenanthroline hydrate. After the phenanthroline was completely
dissolved (2 hours) an excess of bromine 1.7ml (33.3 mmol) was added
to the solution. This mixture was heated to 60°C for two hours. This
mixture was poured onto 200 ml of ice after the reaction time. Upon
neutralization (pH=7) a precipitate formed, which was extracted with
chloroform. The combined organic layers were dried over Na2SO4 and
the solvent was removed under vacuum. Then the crude product was
dissolved in hot toluene, the insoluble dark impurities were filtered of and
the solvent was removed under vacuum. Purification was achieved by
recrystallization from chloroform. After drying at high-vacuum the pure
compound was obtained as white powder (93%). 1H-NMR (CDCl3,
400MHz): δ = 9.232 (dd, 2H(2/9),
3J = 4.4 Hz, 4J = 1.6 Hz), 8.778 (dd,
1H(4/7), 3J = 8.6Hz, 4J = 1.6Hz), 7.739 (dd, 1H(3/8), 3J = 8.6Hz, 3J = 4.4 Hz)
ppm. 13C-NMR (CDCl3, 100MHz): δ = 150.92 (2C(2/9)), 145.09 (2C(10a/10b)),
137.56 (2C(4a/6a), 128.74 (2C(4/7)), 125.27 (2C(5/6)), 124.60 (2C(3/8)) ppm.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
MS: 338 m/z (100%, M+). elemental analysis: calc.: C: 42.64%, H: 1.79%,
N: 8.29%, Br: 47.28% found: C: 37.95%, H: 2.71%, N: 8.22%, Br: 46.17%.
Crystals suitable for X-ray diffraction were obtained from chloroform.
Crystal data: C12H6N2 ×CHCl3, Mr = 2071.08 g/mol, colorless cuboid, size
0.05 × 0.05 × 0.04mm3, monoclinic, space group P21/n (No. 14), a =
11.7492(4), b = 11.7577(4), c = 12.3256(4) Å, α = 90.000, β = 118.106(2),
γ = 90.000°, V = 1501.92Å3, T = -90(2)°C, Z = 4, ρcalcd. = 2.023 g/cm3,
μ(Mo-Kα) = 5.920 cm-1, F(000) = 880, 10426 reflections in h(-15/15),
19983 reflections in h(-16/15), k(-18/16), l(-22/21) measured in the range
2.37° ≤ Θ ≤ 27.49°, completeness Φmax = 99.1%, 12387 independent
reflections, Rint
= 0.0376, 8826 reflections with Fo > 4σ(Fo), 699
parameters, 0 restraints, Robs. = 0.0605, wR2obs. = 0.1585, Rall = 0.0951,
wR2all = 0.1786, GOOF = 1.024, largest difference peak and hole: 2.767/-
1.715 e/Å3. Crystallographic data (excluding structure factors) has been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication CCDC-1451530.
k(-14/15), l(-16/15) measured in the range 2.55°
≤ Θ ≤ 27.505°,
completeness Φmax = 99.6%, 3429 independent reflections, Rint
=
[(tbbpy)2Ru(5,6-dibromo-1,10-phenanthroline)][PF6]2 (4): 300mg (423
μmol) of [Ru(tbbpy)2Cl2] and 143mg (423 μmol) 2 were reacted in the
microwave according to method C1 in 60ml of ethanol/water for 90
minutes. After cooling and removal of ethanol impurities were filtered off.
Then 415mg (2.54 mmol) NH4PF6 were added to precipitate the desired
product. Purification was achieved by recrystallization from
acetone/water by slow evaporation. This yielded also crystals suitable for
X-ray diffraction. Water was removed by dissolving the crude product in
dichloromethane and drying with Na2SO4 and removal of the precipitate
and solvent. The yield was 466mg (398 μmol, 90%) of pure 4 as red
powder. 1H-NMR (CD3CN, 400MHz): δ = 8.87 (dd, 2H(4/4’), 3J = 8.6Hz, 4J
= 1.2Hz), 8.50 (d, 2H(3-bpy), 4J = 1.8Hz), 8.45 (d, 2H(3’-bpy), 4J = 1.8Hz),
8.12 (dd, 2H(2/2’), 3J = 5.3Hz, 4J = 1.2Hz), 7.81 (dd, 2H(3/3’), 3J = 8.6Hz,
3J = 5.2Hz), 7.67 (d, 2H(6-bpy), 3J = 6.2Hz), 7.45 (dd, 2H(5-bpy), 3J = 6.1Hz,
4J = 2.0Hz), 7.32 (d, 2H(6’-bpy), 3J = 6.0Hz), 7.30 (dd, 2H(5’-bpy), 3J = 6.1Hz,
4J = 2.0Hz), 1.43 (s, 18H(t-Bu’)), 1.35 (s, 18H(t-Bu)) ppm. 13C-NMR (CD3CN,
100MHz): δ = 163.82 (2C(4-bpy)), 163.67 (2C(4’-bpy)), 157.95 (2C(2-bpy)),
157.69 (2C(2’-bpy)), 154.14 (2C(2/9)), 152.36 (2C(6’-bpy)), 152.02 (2C(6-bpy)),
148.68 (2C(10’/10”)), 138.08 (2C(4/7)), 131.96 (2C(4’/6’)), 128.31 (2C(3/8)),
127.22 (2C(5,6)), 125.67 (2C(5-bpy)), 125.44 (2C(5’-bpy)), 122.57 (2C(3-bpy)),
122.47 (C(3’-bpy)), 36.36 (2C(7’-bpy)), 36.27 (2C(7-bpy)), 30.50 (3C(8’-bpy)),
30.43 (3C(8-bpy)) ppm. MS: 1120.9 m/z (100%, [M-PF6]+), 1120.9 m/z
(10%, [M-PF6-Br]+). Crystals suitable for X-ray diffraction were obtained
0.0311, 3429 reflections with Fo > 4σ(Fo), 181 parameters, 0 restraints,
Robs. = 0.0311, wR2 obs. = 0.0702, Rall = 0.0532, wR2all = 0.0786, GOOF =
0.959, largest difference peak and hole: 0.572
/
-0.487 e/Å3.
Crystallographic data (excluding structure factors) has been deposited
with the Cambridge Crystallographic Data Centre as supplementary
publication CCDC-1451529.
Metal complex syntheses
Synthesis of [Ru(L)2(L’)]2+-type complexes (method C1): One
equivalent (∼ 50-300mg) of the cis-[Ru(tbbpy)2Cl2] compound and one
equivalent of the desired ligand were dissolved in 100ml of a mixture of
ethanol/water (4:1 / v:v).This mixture was refluxed in the microwave for
60-300 minutes with a power of 150W. Ethanol was removed after
cooling to precipitate impurities from the remaining aqueous solution.
After filtration,
9 equivalents of NH4PF6 were added. The formed
precipitate was collected after stirring for 30 minutes and was washed
with water several times. Purification was either achieved by
recrystallization from mixtures of acetone, acetonitrile or water, or by
column chromatography with mixtures of acetonitrile/sat. solution of
KNO3/water. To remove water from the product, it was dissolved in
dichloromethane, dried with Na2SO4 and filtered. After removal of the
solvent under vacuum pure product compound [Ru(L)2(L′)][PF6]2 was
obtained. Yield: (70-95%).
from acetone/water. Crystal data: [C48H54N6Br2Ru]2+[PF6]−
×
2
2CH3COCH3,Mr
=
1381.96 g/mol, red-orange crystal, size
0.04×0.04×0.04mm3, triclinic, space group P1¯ (No. 2), a = 10.5859(2), b
= 11.7274(3), c = 24.0080(7) Å, α = 90.444(1), β = 94.113(2), γ =
92.976(2)°, V = 2968.59(13)Å3, T = -90°C, Z = 2, ρcalcd. = 1.546 g/cm3,
μ(Mo-Kα) = 17.46 cm-1, F(000) = 1400, 20454 reflections in h(-13/13), k(-
[(tbbpy)2Ru(5-bromo-1,10-phenanthroline)][PF6]2 (3): According to
method C1, 664 mg (936 μmol) of [Ru(tbbpy)2Cl2] and 355 mg
(936 μmol) of 1 were reacted in the microwave for 90 minutes in 125ml of
ethanol/water. After cooling, ethanol was removed and precipitated
impurities were filtered off. Then 916 mg (5.62 mmol) NH4PF6 were
added and the formed precipitate was filtered collected and was washed
with water. Purification was achieved by recrystallization from
acetone/water by slow evaporation. This yielded also crystals suitable for
X-ray diffraction. After removal of water the pure 3 was obtained as red
powder. The yield is 1.07 g (898 μmol, 96%). 1H-NMR (CD3CN,
400MHz): δ = 8.79 (dd, 1H(4), 3J = 8.2Hz, 4J = 1.2Hz), 8.61 (s, 1H(6)), 8.51
15/14), l(-31/28) measured in the range 2.05°
≤ Θ ≤ 27.47°,
completeness Φmax = 98.1%, 13329 independent reflections, Rint
=
0.0362, 10002 reflections with Fo > 4σ(Fo), 728 parameters, 0 restraints,
Robs. = 0.0507, wR2obs. = 0.1164, Rall = 0.0797, wR2all = 0.1317, GOOF =
1.011, largest difference peak and hole: 1.029/-0.718 e/Å3.
Crystallographic data (excluding structure factors) has been deposited
with the Cambridge Crystallographic Data Centre as supplementary
publication CCDC-1451531.
(dd, 1H(7)
8.11 (dd, 1H(2)
1.2Hz), 7.83 (dd, 1H(3), 3J = 8.4Hz, 3J = 5.2Hz), 7.75 (dd,1H(8), 3J = 8.3Hz,
3J = 5.3Hz), 7.67 (dd, 2H(6-bpy) 3J = 6.0Hz, 3J = 3.0Hz), 7.45 (ddd, 2H(5-
bpy), 4J = 1.6Hz, 4J = 1.8Hz, 3J = 5.8Hz), 7.38 (dd, 2H(6’-bpy), 3J = 5.8Hz, 3J
= 4.2Hz), 7.21 (m, 2H(5’-bpy)), 1.43 (d, 18H(8’-bpy)
3J = 1.0Hz), 1.35 (s,
,
3J = 8.2Hz, 4J = 1.2Hz), 8.50 (m, 2H(3-bpy)), 8.46 (m, 2H(3’-bpy)),
3J = 4.8Hz, 4J = 0.8Hz), 8.07 (dd, 1H(9) 3J = 4.6Hz, 4J =
,
,
[(tbbpy)2Ru((4-(1,10-phenanthroline-5-yl)phenyl)ethan-1-one)][PF6]2
(5): Under Ar atmosphere 100 mg (0.08 mmol) of 3, 60 mg (0.37 mmol)
of 4-acetylphenylboronic acid and 10 mg (0.014 mmol) (Pd(PPh3)2Cl2
were dissolved in 50 ml degassed MeCN and 25 ml of a degassed 2 M
Na2CO3 solution. The solution was refluxed for 4 days and after cooling
to room temperature filtrated. Solvents were removed under reduced
pressure, the solid was dissolved in EtOH. The target compound was
precipitated with aqueous NH4PF6 solution, filtrated and washed
thoroughly with water and Et2O. Pure complex 5 could be received via
recrystallization by slow evaporation out of an acetone/water mixture.
The yield was 100 mg (82 μmol, 97%). 1H-NMR (CD3CN, 400 MHz): δ =
8.60 (dd, J = 8.3, 1.1 Hz, 1H), 8.52 (d, J = 1.9 Hz, 2H), 8.48 (d, J = 1.9
Hz, 2H), 8.43 (dd, J = 8.6, 1.1 Hz, 1H), 8.23 (s, 1H), 8.21 (d, J = 8.4 Hz,
2H), 8.08 (7, m, 2H), 7.80 – 7.66 (m, 6H), 7.50 – 7.41 (m, 4H), 7.23 (dd, J
= 7.9, 6.1, 2.0 Hz, 2H), 2.68 (s, 3H), 1.45 (s, 18H), 1.37 (s, 18H). MS
(FD; ethanol): m/z= 1082 [M-PF6]+, 468 [M-2PF6]2+. Elemental analysis
for C56H62F12N6OP2Ru: calc.: C: 54.86, H: 5.10, N: 6.85. found: C: 54.69,
H: 5.02, N: 6.55.
,
,
18H(8-bpy)) ppm. 13C-NMR (CD3CN, 100MHz): δ = 163,73 (2C(4-bpy)),
163,59 (2C(4’-bpy)), 158.05 (2C(2-bpy)), 157.76 (2C(2’-bpy)), 154.00 (1C(2)),
153.67 (1C(9)), 152.28 (2C(6’-bpy)), 152.06 (2C(6-bpy)), 149.73 (1C(10)),
148.45 (1C(1)), 137.05 (1C(4)), 136.52 (1C(7)), 132.08 (1C(6)), 131.89
(1C(5)), 131.44 (1C(4’)), 127.67 (1C(3)), 127.61 (1C(8)), 125.64 (2C(5-bpy)),
125.45 (2C(5’-bpy)), 122.72 (1C(5)), 122.53 (2C(3-bpy)), 122.44 (2 C(3’-bpy)),
36.36 (2C(7’-bpy)), 36.27 (2C(7-bpy)), 30.52 (3C(8’-bpy)), 30.44 (3C(8-bpy)) ppm.
Crystals suitable for X-ray diffraction were obtained from
acetonitrile/water. Crystal data: [C48H55N6BrRu]2+[PF6]− × 2CH3CN, Mr =
2
1269.01 g/mol, red-brown cuboid, size 0.06×0.06×0.05mm3, triclinic,
space group P1¯ (No. 2), a = 12.5680(3), b = 13.9694(4), c = 16.9912(4) Å,
α = 70.946(1), β = 75.702(1), γ = 89.332(2)°, V = 2724.56(12)Å3, T = -
90°C, Z = 2, ρcalcd. = 1.547 g/cm3, μ(Mo-Kα) = 11.65 cm-1, F(000) = 1292,
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
Ru, Mr = 1384.31 g mol-1, red hexagonal prism, crystal size 0.2158 x
0.1447 x 0.1353 mm3, triclinic, space group P -1, a = 11.8547(3) Å, b =
14.0372(4) Å, c = 20.8266(4) Å, α = 91.470(2)°, β= 91.017(2)°, γ =
107.516(2)°, V = 3302.73(15) Å3, T = 180(2) K, Z = 2, ρcalcd. = 1.392
Mg/m3, μ (Mo-Kα) = 0.370 mm-1, F(000) = 1432, altogether 39770
reflexes up to h(-14/14), k(-17/17), l(-25/26) measured in the range of
3.405° ≤ Θ ≤ 26.372° , completeness Θmax = 99.7 %, 13472 independent
reflections, Rint = 0.0482, 10349 reflections with Fo > 4 σ(Fo), 904
parameters, 7 restraints, R1obs = 0.0633, wR2obs = 0.1664, R1all = 0.0858,
wR2all = 0.1837, GOOF = 1.051, largest difference peak and hole: 1.132/-
0.678 e∙Å-3. OH distances in the single water molecule as well as C-C
and C-O distances of diethyl ether were fixed using the DFIX and DANG
commands. Short intermolecular distances reported in the checkcif report
correspond to the distortion of terminal methyl groups of diethyl ether.
CCDC 1518485 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.
[(tbbpy)2Ru((4,4‘-(1,10-phenanthroline-5,6-yl)-bis(phenylen-ethan-1-
one))][PF6]2 (6): Under Ar atmosphere 300 mg (0.24 mmol) 4, 77.87 mg
(0.48 mmol) of 4-acetylphenylboronic acid and 30 mg (0.042 mmol)
(Pd(PPh3)2Cl2 were dissolved in 50 ml degassed MeCN and 25 ml of a
degassed 2 M Na2CO3 solution. The solution was refluxed for 10 days
and after cooling to room temperature filtrated. Solvents were removed
under reduced pressure, the solid was dissolved in EtOH. The target
compound was precipitated with aqueous NH4PF6 solution, filtrated and
washed thoroughly with water and Et2O. Pure complex 6 could be
received via recrystallization by slow evaporation out of an acetone/water
mixture. The yield was 220 mg (16 μmol, 68%). 1H-NMR (CD3CN, 500
MHz): δ = 8.53 (d, J = 1.8 Hz, 2H), 8.49 (d, J = 1.8 Hz, 2H), 8.10 (dd, J =
5.2, 1.2 Hz, 2H), 7.99 (dd, J = 8.5, 1.2 Hz, 2H), 7.94 (dd, J = 8.0, 1.5 Hz,
2H), 7.93 (dd, J= 8.0, 1.5 Hz, 2H), 7.71 (d, J = 6.0 Hz, 2H), 7.65 (dd, J =
8.5, 5.2 Hz, 2H), 7.52 (d, J = 6.0 Hz, 2H), 7.47 (dd, J = 6.1, 2.1 Hz, 2H),
7.44 (dd, J = 8.0, 1.4 Hz, 2H), 7.38 (dd, J = 8.0, 1.4 Hz, 2H), 7.30 (dd, J =
6.0, 2.0 Hz, 2H), 2.56 (s, 6H), 1.45 (s, 18H), 1.40 (s, 18H). 13C-NMR
(CD3CN, 101 MHz): δ = 198.59 (2C), 163.52 (2C), 163.42 (2C), 157.92
(2C), 157.75 (2C), 153.02 (2C), 152.17 (2C), 151.92 (2C), 148.44 (2C),
141.49 (2C), 138.73 (2C), 137.53 (2C, 136.04 (2C), 132.00 (2C), 131.96
(2C), 131.58 (2C) , 129.01 (2C), 129.00 (2C), 127.03 (2C), 125.51 (2C),
125.33 (2C) , 122.45 (2C), 122.39 (2C), 36.24 (2C), 36.19 (2C), 30.39
(6C), 30.35 (6C),, 26.97 (2C). MS (HRM-ESI; acetonitrile): m/z= 1199 [M-
PF6]+, 528 [M-2PF6]2+. Elemental analysis for C64H68F12N6O2P2Rux1.25
H2O: calc.: C: 56.24, H: 5.20, N: 6.15. found: C: 56.27, H: 5.17, N: 5.89.
Crystal data: C66H71F12N7O2P2Ru, Mr=1385.30 g mol-1, red fragment,
crystal size 0.1558 x 0.1054 x 0.0746 mm3, triclinic, space group P -1, a
= 12.2062(3) Å, b = 15.1931(3) Å, c = 20.6095(5) Å, α = 102.6314(2)°, β=
99.352(2)°, γ = 103.924(2)°, V = 3525.33(15) Å3, T = 180(2) K, Z = 2,
ρcalcd. = 1.305 Mg/m3, μ (Cu-Kα) = 2.895 mm-1, F(000) = 1428, altogether
32893 reflexes up to h(-15/15), k(-18/13), l(-25/24) measured in the
range of 7.412° ≤ Θ ≤ 73.757° , completeness Θmax = 99.7 %, 13812
independent reflections, Rint = 0.0320, 13257 reflections with Fo > 4
σ(Fo), 812 parameters, 2 restraints, R1obs = 0.0481, wR2obs = 0.1351,
R1all = 0.0550, wR2all = 0.1390, GOOF = 1.057, largest difference peak
and hole: 1.047/-0.848 e∙Å-3. Residual electron densities could not be
fitted to a reasonable structure. The Platon SQUEEZE routine was
therefore applied. According to the respective residual electron count (81
e-) and the corresponding void shape clearly indicates the presence of
two molecules of heavily distorted acetonitrile. CCDC 1518486 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
[(tbbpy)Ru(5,6-dibromo-1,10-phenanthroline)2][PF6]2 (8): Following
method C1, 105mg (124 μmol) of 9 and 33,2mg (124 μmol) of tbbpy
were reacted in the microwave for 180 minutes in 100ml of ethanol/water.
After cooling, ethanol was removed and dark precipitated impurities were
filtered off. Then 121mg (720 μmol) of NH4PF6 were added and the
formed precipitate was collected and washed with water. Purification was
achieved by column chromatography using acetonitrile/water and
subsequent recrystallization from acetonitrile/water. Careful washing of
the obtained crystals with very small amounts of methylene chloride
yielded pure product. This yielded as well crystals suitable for X-ray
diffraction. After removal of water, pure 8 was obtained as red powder.
The yield was 17mg (12.5 μmol, 10%). 1H-NMR (CD3CN, 400MHz): δ =
8.93 (dd, 2H(4/4’), 3J = 8.8Hz, 4J = 0.8Hz), 8.83 (dd, 2H(4/4’), 3J = 7.6Hz, 4J
= 0.8Hz), 8.49 (d, 2H(3-bpy), 4J = 1.8Hz), 8.21 (dd, 2H(2/2’), 3J = 5.3Hz, 4J =
0.8Hz), 7.93 (dd, 2H(2/2’)
8.8Hz, 3J = 5.3Hz), 7.62 (dd, 2H(3/3’)
2H(6-bpy), 3J = 6.0Hz), 7.23 (dd, 2H(5-bpy)
,
3J = 5.2Hz, 4J = 0.8Hz), 7.87 (dd, 2H(3/3’)
3J = 7.6Hz, 3J = 5.2Hz), 7.48 (d,
3J = 6.1Hz, 4J = 2.0Hz), 1.37 (s,
,
3J =
,
,
18H(t-Bu)) ppm. 13C-NMR (CD3CN, 100MHz): δ = 164.14 (2C(4-bpy)), 157.82
(2C(2-bpy)), 154.81 (2C(2/9)), 154.53 (2C(2/9)), 152.68 (2C(6’-bpy)), 148.72
(2C(10’/10”)), 148.49 (2C(10’/10”)), 138.58 (2C(4/7)), 138.45 (2C(4/7)), 132.05
(2C(4’/6’)), 132.00 (2C(4’/6’)), 128.36 (2C(3/8)), 128.18 (2C(3/8)), 127.30
(2C(5,6)), 127.21 (2C(5,6)), 125.51 (2C(5-bpy)), 122.65 (2C(3-bpy)), 36.35 (2C(7-
bpy)), 30.47 (3C(8-bpy)) ppm. MS (ESI): 1190.5 m/z (100%, [M-PF6]+), 522.8
m/z (60%, [M-2PF6]2+). Crystals suitable for X-ray diffraction were
obtained from acetonitrile/water. Crystal data for 8: [C42H36N6Ru]2+[PF6]−
2
×CH3CN, Mr = 1376.47 g/mol, red-brown crystal, size 0.05 × 0.05 ×
0.04mm3, triclinic, space group P 1¯ (No. 2),
a = 12.0674(4), b =
13.6818(4), c = 16.1755(4) Å, α = 97.260(2), β = 93.727(2), γ =
98.202(2)°, V = 2612.73(13)Å3, T = -90(2)°C, Z = 2, ρcalcd. = 1.750 g/cm3,
μ(Mo-Kα) = 35.02 cm-1, F(000) = 1348, 19732 reflections in h(-15/15), k(-
[(tbbpy)2Ru((4,4‘-(1,10-phenanthroline-5,6-yl)-bis(phenol))][PF6]2 (7):
Under Ar atmosphere 150 mg (0.12 mmol) 4, 50 mg (0.36 mmol) of 4-
hydroxyphenylboronic acid and 20 mg (0.028 mmol) (Pd(PPh3)2Cl2 were
dissolved in 50 ml degassed MeCN and 25 ml of a degassed 2 M
17/17), l(-20/20) measured in the range 2.60°
≤ Θ ≤ 27.45°,
completeness Φmax = 99.3%, 11863 independent reflections, Rint
=
Na2CO3 solution. The solution was stirred for
7
days at room
0.0364, 8038 reflections with Fo > 4σ(Fo), 659 parameters, 0 restraints,
temperature. The solution was filtrated, solvents were removed under
reduced pressure and the solid was dissolved in a small amount of EtOH.
The target compound was precipitated with aqueous NH4PF6 solution,
filtrated and washed thoroughly with water and Et2O. Pure complex 7
could be received via recrystallization by slow evaporation out of an
acetone/water mixture. The yield was 0.07g ( 0.054 mmol, 45%). 1H-
NMR (CD3CN, 400 MHz): δ = 8.52 (d, J = 1.7 Hz, 2H), 8.49 (d, J = 2.0
Hz, 2H), 8.12 (dd, J = 8.5, 1.1 Hz, 2H), 8.03 (dd, J = 5.1, 1.1 Hz, 2 H),
7.71 (d, J = 5.9 Hz, 2H), 7.62 (dd, J = 8.5, 5.2 Hz, 2H), 7.53 – 7.41 (m,
4H), 7.27 (dd, J = 6.0, 2.0 Hz, 2H), 7.17 – 6.97 (m, 4H), 6.86 – 6.75 (m,
4H), 1.45 (s, 18H), 1.3 (s, 18H). MS (HRM-ESI; MeCN): m/z= 1147.3802
Robs. = 0.0545, wR2obs. = 0.1422, Rall = 0.0935, wR2all = 0.1618, GOOF =
1.032, largest difference peak and hole: 1.730
/
-0.919 e/Å3.
Crystallographic data (excluding structure factors) has been deposited
with the Cambridge Crystallographic Data Centre as supplementary
publication CCDC-1451532.
[Cl2Ru(5,6-dibromo-1,10-phenanthroline)2] (9): For this reaction, 280
mg (1.00mmol) of [Ru(COD)Cl2]n and 676 mg (2.00mmol) of 2 were
suspended in 50ml of dry DMF and heated for two hours at 150 W in the
microwave. After cooling, the solvent was removed. The remaining solid
was dissolved in a small amount of chloroform and heated to reflux very
short. Addition of ethanol and recrystallization in the cold yielded a black
precipitate. Removal of the side product 10 was achieved via extraction
of the methylene chloride solution with water and by column
[M-PF6]+,
501.2070
[M-2PF6]2+
.
Elemental
analysis
for
C64H68F12N6O2P2Rux0.25 C3H6O: calc.: C: 55.84, H: 5.05, N: 6.43.
measured: C: 55.77, H: 4.99, N: 6.50. Crystal data: C64 H76 F12 N6 O4 P2
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700548
European Journal of Inorganic Chemistry
FULL PAPER
chromatography with acetone/DMF. After removal of the solvent 400mg
(470 μmol) of a black and almost insoluble powder were obtained (yield =
[8] M. Hissler, W. B. Connick, D. K. Geiger, J. E. McGarrah, D. Lipa, R. J.
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Inorg.Chem. 2010, 49, 1307–1309.
47%). 1H-NMR (CD2Cl2, 400MHz): δ = 9.250 (d, 2H(2/9) 3J = 4.2Hz),
,
8.237 (d, 4H(4/7)
ppm. Crystals suitable for X-ray diffraction were obtained from
dichloromethane. Crystal data: [C24H12N4Cl2Br4Ru]×3CH2Cl2, Mr
, ,
3J = 8.4Hz), 7.687 (dd, 2H(2/9) 3J = 5.2Hz, 3J = 8.4Hz)
=
1101.76 g/mol, black crystal, size 0.06×0.06×0.03mm3, monoclinic,
space group C2/c (No. 15), a = 18.1042(8), b = 16.7210(13), c =
14.0302(9) Å, α = 90.000, β = 125.740(3), γ = 90.000°, V = 3447.4(4)A3,
T = -90°C, Z = 4, ρcalcd. = 2.123 g/cm3, μ(Mo-Kα) = 57.39 cm-1, F(000) =
2108, 11467 reflections in h(-23/22), k(-21/21), l(-14/18) measured in the
[14] L. K. Keniley Jr., N. Dupont, L. Ray, J. Ding, K. Kovnir, J. M. Hoyt, A.
Hauser, M. Shatruk Inorg. Chem., 2013, 52 (14), 8040–8052.
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Lochbrunner, W. W. Seidel Inorg.Chem. 2014, 53, 8859−8873.
range 1.93°
≤ Θ ≤ 27.46°, completeness Φmax = 99.5%, 3929
independent reflections, Rint = 0.0634, 2688 reflections with Fo > 4σ(Fo),
200 parameters, 0 restraints, Robs. = 0.0468, wR2
= 0.1075, Rall =
obs.
0.0834, wR2 = 0.1232, GOOF = 1.040, largest difference peak and
all
[16] L. Kohler, N. Kaveevivitchai, R. Zong, R. P. Thummel, Inorg. Chem.
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2014, 53, 912−921.
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Chem. Soc, 2013, 135, 17161−17
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Trans., 2008, 6709–6723.
[Ru(5,6-dibromo-1,10-phenanthroline)3][PF6]2 (10): For this reaction
131mg (468μmol) of [Ru(cod)Cl2]n and 474mg (1.40mmol) of 2 were
heated in a mixture of ethanol/water over night at reflux and afterwards
for two hours in the microwave (150W). After removal of the solvent and
the in water insoluble side products, NH4PF6 was added. Purification was
achieved using column chromatography in acetonitrile/water. Recrys-
tallization from acetonitrile gave the desired product in high purity. Yield:
17%, 109 mg, 31.2 μmol. 1H-NMR (CDCl3, 400MHz): δ = 8.876 (dd,
6H(4/7), 3J = 8.2Hz, 4J = 1.2Hz), 8.526 (dd, 1H(2/9), 3J = 5.6Hz, 4J = 1.2Hz),
[19] M. Hissler, W. B. Connick, D. K. Geiger, J. E. McGarrah, D. Lipa, R. J.
Lachicotte, R. Eisenberg, Inorg. Chem. 2000, 39, 447-457.
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Acta 357 (2004) 4496–4503.
8.034 (dd, 1H(3/8),
3J = 8.8Hz, 3J = 5.2Hz) ppm. 13C-NMR (CDCl3,
100MHz): δ = 155.14 (6C(4/7)), 148.49 (6C(10’/10”)), 138.80 (6C(2/9)), 131.99
(6C(4’/6’)), 128.21 (6C(3/7)), 127.21 (6C(5/6)) ppm. MS: (ESI) m/z = 1206.2
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Acknowledgements
We thank Ulm University (LGFG scholarship, A.S.) and the
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Keywords: Ruthenium • bromine • N ligands • cross coupling •
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10.1002/ejic.201700548
European Journal of Inorganic Chemistry
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Efficient Bromination
Improved syntheses for 5-bromo and
5,6-dibromo-1,10-phenanthroline are
presented. A series of corresponding
Ru(II) polypyridine complexes are
characterized in detail and converted
in Suzuki cross coupling reactions. A
detailed correlation is developed
between the number of bromine
substituents and photochemical and
Anne Stumper, Thomas David Pilz,
Markus Schaub, Helmar Görls, Dieter
Sorsche, Katrin Peuntinger, Dirk Guldi,
Sven Rau*
Page No. – Page No.
Efficient Access to 5- and 5,6-
Dibromophenanthroline Ligands
electrochemical
properties
of
ruthenium complexes.
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