Regioselective functionalization of tetrabromophenanthroline-ruthenium complexes

Article abstract of DOI:10.1002/ejic.200400163

Structural, photophysical and photochemical characterization and reactivity of a novel polypyridyl ruthenium complex based on 3,5,6,8- tetrabromophenanthroline are discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200400163

SHORT COMMUNICATION
Regioselective Functionalization of Tetrabromophenanthroline؊Ruthenium
Complexes
Sven Rau,*[a] Reinald Fischer,[a] Michael Jäger,[a] Bernhard Schäfer,[a] Susann Meyer,[b]
Günter Kreisel,[b] Helmar Görls,[a] Manfred Rudolf,[a] William Henry,[c] and
Johannes G. Vos[c]
Keywords: Ruthenium / Nucleophilic substitution / Phenanthroline
Structural, photophysical and photochemical characteriza- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
tion and reactivity of a novel polypyridyl ruthenium complex
Germany, 2004)
based on 3,5,6,8-tetrabromophenanthroline are discussed.
Signal storage at a molecular level is a great challenge for
chemistry.[1] The possibility of connecting different func-
tionalities selectively to one ligand of a metal complex may
open the route towards higher integrated molecular units
capable of processing various external stimuli in a predesig-
nated order. The implementation of this concept demands
ligands with a multitude of potential connecting groups
which can selectively be transformed.[2] 3-bromo- and 3,8-
dibromophenanthrolines have proved useful for the prep-
aration of mononuclear[3] and multiheteronuclear com-
plexes.[4] These systems have found applications ranging
from DNA photoprobes,[5] to metalloligands in catalysis.[6]
Figure 1. Improved preparation of 3,5,6,8-tetrabromophenanthro-
line (Br4phen)
line-based protons. 13C, HSQC, and HMBC spectroscopy
allows the complete assignment of all signals in the 1H- and
13C NMR spectra, which together with mass spectroscopy
suggests that Br4phen coordinates in a similar fashion as
the unsubstituted phenanthroline. The X-ray crystallo-
graphic characterization confirms this assumption, and as
seen from Table 1 shows no significant differences com-
pared with the parent complex [(tbbpy)2Ru(phen)]2ϩ, 2 (see
Supporting Information). The molecular structure is de-
picted in Figure 2.
A
very useful and well-established feature of these
bromophenanthrolineϪruthenium complexes is their sus-
ceptibility towards nucleophilic aromatic substitution.[7]
We have improved the bromination reaction of phen-
[8]
´
anthroline first published by Denes and Chira, which al-
lows for the selective formation of 3,5,6,8,-tetrabromophen-
anthroline (Br4phen) in a one-step multigram reaction, Fig-
ure 1.[8]
Br4phen readily forms a complex with [tbbpy]2RuCl2 re-
sulting in [(tbbpy)2Ru(Br4phen)]2ϩ
, 1. The structural
characterization using two-dimensional NMR spectroscopy
suggests that a symmetrical complex is formed as indicated
by the presence of only two signals for the four phenanthro-
˚
Table 1. Bond lengths (A) and angles (°)
1
2
RuϪN1
RuϪN2
RuϪN3
RuϪN4
RuϪN5
RuϪN6
C2ϪBr1
C5ϪBr2
2.046(5)
2.060(5)
2.064(5)
2.052(5)
2.047(5)
2.071(5)
1.891(6)
1.883(6)
2.055(4)
2.056(5)
2.053(4)
2.055(4)
2.060(4)
2.074(4)
[a]
Institut für Anorganische und Analytische Chemie, Friedrich-
Schiller-Universität,
07743 Jena, Germany
E-mail: Sven.Rau@uni-jena.de
[b]
Institut für Technische Chemie und Umweltchemie, Friedrich-
Schiller-Universität,
07743 Jena, Germany
Ϫ
Ϫ
[c]
National Centre for Sensor Research, School of Chemical
Sciences, Dublin City University,
N1ϪRuϪN2
N3ϪRuϪN4
N5ϪRuϪN6
79.27(19)
78.21(19)
78.25(19)
79.9(2)
77.88(16)
78.99(16)
Dublin 9, Ireland
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2004, 2001Ϫ2003
DOI: 10.1002/ejic.200400163
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2001

S. Rau et al.
SHORT COMMUNICATION
tochemical reactivity of 3 using ion exchange HPLC suggest
that Br2OMe2phen is very photolabile.
Experimental Section
All solvents used for spectroscopic measurements were of Uvasol
(Merck) grade. All other reagents were of HPLC grade. cis-
[Ru(tbbpy)2Cl2]·2H2O,[10] was prepared by standard procedures. All
reagents for synthesis, RuCl3·3H2O (Chempur), 1,10-phenanthro-
line (Aldrich) and all other materials were commercially available
and of reagent grade.
Figure 2. Regioselective nucleophilic substitution of 1 with NaOMe
leading to 3; molecular structure of 1; anions and hydrogen atoms
omitted, and the structural motif of 3 confirming the regioselec-
tive substitution
3,5,6,8-tetrabromophenanthroline (Br4phen): 1,10-phenanthroline
monohydrate (4.0 g, 20 mmol) was dissolved in SOCl2 (200 mL).
Freshly distilled Br2 (9.3 g, 120 mmol) was carefully added. This
mixture was refluxed for 31 h and cooled to room temperature, and
the bright yellow precipitate was filtered off (3,5,6,8,-tetrabromo-
phenanthroline). The precipitate was washed with aqueous NH3
until a colorless solution was obtained. The white solid was recrys-
Reaction of 1 with NaOMe at room temperature in meth-
anol leads to the selective formation of one product that
contains two bromine and two new methoxy functions, as
confirmed by ESI-MS. The fact that the positions of all the
1
1
bipyridine-based signals in the H NMR spectra did not
tallized from toluene. H NMR (CDCl3): δ ϭ 9.16 (2 H, d), 8.91
(2 H, d) ppm. 13C NMR (CDCl3): δ ϭ 122.0, 125.1, 129.6, 139.0,
143.6, 152.4 ppm. MS (DCI with H2O): 497 [M ϩ Hϩ] 417 (M Ϫ
Br ϩ Hϩ), 338 (M Ϫ Br2 ϩ Hϩ), 257 (Mϩ Ϫ Br3). Yield 5.22 g
(52% based on phen).
change, together with the presence of only one new signal
at δ ϭ 4.15 ppm for the methoxy function, suggests the for-
mation of a symmetrical species where substitution at the
phenanthroline moiety has taken place. The regioselective
formation of the 5,6-dibromo-3,8-dimethoxyphenanthro-
line ruthenium complex 3 could be confirmed by a struc-
tural motive depicted in Figure 2.
Synthesis of [(tbbpy)2Ru(Br4phen)](PF6)2 (1): 3,5,6,8-Tetrabromo-
1,10-phenanthroline (1.15 g, 2.32 mmol) and [(tbbpy)2RuCl2]
(1.5 g, 2.11 mmol) were refluxed in a mixture of ethanol (80 mL)
Photophysical investigation of compounds 1 to 3 suggests and H2O (20 mL) for 8 hours. The crude reaction mixture was fil-
tered, washed twice with ethanol/H2O (80:20), and the combined
filtrate was concentrated to the half volume. On addition of
NH4PF6 and stirring at room temperature for 1 hour, the crude
product precipitated. Recrystallization from acetone/water gave the
desired product. Crystals suitable for X-ray analysis were obtained
from acetone/water. 1H NMR ([D6]DMSO): δ ϭ 8.997 [4,7, 2 H, s
(lc)], 8.792 [3ЈЈ, 2 H, s (lc)], 8.788 [3Ј, 2 H, s (lc)], 8.055 [2,9, 2 H,
s (lc)], 7.599 [5ЈЈ, 2 H, d (lc)], 7.527 (6Ј,6ЈЈ, 4 H, m), 7.310 [5Ј, 2 H,
d (lc)], 1.391 [CH3(tert-butyl), 18 H, s], 1.362 [CH3(tert-butyl), 18
H, s] ppm. MS (Micro-ESI in CHCl3 ϩ methanol); m/z (relative
that tetrabromo substitution lowers the electron density of
the phenanthroline ligand considerably. The absorption and
emission wavelength of 1 are red-shifted relative to 2, see
Table 2. This finding correlates well with the data obtained
for the oxidation potential of RuII/III, which clearly shows
that the four bromine substituents significantly decrease the
electron density at the metal center (difference of 137 mV).
Introduction of the methoxy groups increases the electron
density, as expected.[9] The introduction of two methoxy
groups has a pronounced influence on the photophysical intensity) with matching isotope pattern: 1279 (100) (1 ϩ PF6),
1201 (34) (1 Ϫ Br ϩ PF6), 567 (51) (12ϩ). Crystal data for 1:
properties, and this is in agreement with an electron-donat-
ing substituent.
[C48H52Br4N6Ru]2ϩ·2 [PF6]Ϫ, M ϭ 1423.61 g molϪ1, bordeaux-red
prism, size 0.02 ϫ 0.02 ϫ 0.01 mm, tetragonalic, space group I41/
3
˚
˚
a, a ϭ b ϭ 32.5281(3), c ϭ 20.5151(4) A, V ϭ 21706.6(5) A , T ϭ
Ϫ90 °C, Z ϭ 16, ρcalcd. ϭ 1.742 g cmϪ3, µ (Mo-Kα) ϭ 33.74 cmϪ1
,
Table 2. Photophysical and electrochemical properties of complexes
1؊3 in acetonitrile
psi-scan, trans(min): 0.5565, trans(max): 0.7367, F(000) ϭ 11264,
20023 reflections in h(Ϫ42/42), k(Ϫ29/29), l(Ϫ19/26), measured in
the range 2.66° Յ Θ Յ 27.49°, completeness Θmax ϭ 99.8%, 12423
independent reflections.
Compound E1/2 ox in V (vs. Fc/Fcϩ) λmax in nm λem in nm
1
2
3
0.92
0.783
0.845
470
444
450
680
610
615
Synthesis of [(tbbpy)2Ru(phen)](PF6)2 (2): 1,10-phenanthroline
(0.018 g, 0.09 mmol) and [(tbbpy)2RuCl2] (0.06 g, 0.085 mmol) were
reacted and purified according to 1. Yield 96 mg (95%). Crystals
suitable for X-ray analysis were obtained from acetone/water. 1H
NMR ([D3]acetonitrile): δ ϭ 8.613 [4,7, 2 H, s (lc)], 8.504 [3Ј, 2 H,
s (lc)], 8.456 [3ЈЈ, 2 H, s (lc)], 8.299 (5,6, 2 H, s), 8.058 [2,9, 2 H, s
(lc)] 7.753 (3,8, 2 H, m), 7.705 (6Ј, 2 H, d), 7.463 [5Ј, 2 H, d (lc)],
7.405 (6ЈЈ, 2 H, d), 7.200 [5ЈЈ, 2 H, d (lc)], 1.437 [CH3(tert-butyl),
18 H, s], 1.322 [CH3(tert-butyl), 18 H, s] ppm. MS FAB in nba
m/z (relative intensity) with matching isotope pattern: 980 (22) (2
ϩ PF6); 834 (15) (2). Crystal data for 2: [C48H56N6Ru]2ϩ·2 [PF6]Ϫ·2
In conclusion, rutheniumpolypyridyl complexes based on
the ligand Br4phen are readily obtainable. Most import-
antly a regioselective nucleophilic substitution with NaOMe
at the 3,8-position is possible. It is evident from the conven-
tional reactivity of bromine-substituted aromatics that 1
and 3 are potentially very interesting synthons in itself,
opening the possibility to derivatise the previously not eas-
C3H6O, M ϭ 1224.15 g molϪ1, red-brown prism, size 0.12 ϫ 0.10
¯
ily accessible 5,6-position. Initial investigations on the pho- ϫ 0.09 mm, triclinic, space group P1, a ϭ 12.1999(7), b ϭ
2002
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 2001Ϫ2003

Functionalization of TetrabromophenanthrolineϪRuthenium Complexes
SHORT COMMUNICATION
˚
13.3243(7), c ϭ 18.989(1) A, α ϭ 76.854(2), β ϭ 74.819(3), γ ϭ of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or
3
˚
78.206(3)°, V ϭ 2866.3(3) A , T ϭ Ϫ90 °C, Z ϭ 2, ρcalcd. ϭ 1.418 from the Cambridge Crystallographic Data Centre, 12 Union
g cmϪ3, µ (Mo-Kα) ϭ 4.13 cmϪ1, psi-scan, trans(min): 0.9521,
trans(max): 0.9637, F(000) ϭ 1264, 19624 reflections in h(Ϫ15/15),
k(Ϫ17/14), l(Ϫ24/24), measured in the range 2.11° Յ Θ Յ 27.44°,
completeness Θmax ϭ 97.4%, 12753 independent reflections.
Road, Cambridge CB2 1EZ, UK; Fax: ϩ 44-1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk).
Acknowledgments
Synthesis of [(tbbpy)2Ru(OMe2Br2phen)](PF6)2 (3): 1 (200 mg,
0.14 mmol), was dissolved in a solution of freshly prepared NaOMe
(1 ⁾ in MeOH (100 mL). The solution was stirred for 6 h and H2O
(200 mL) was added. The pH of the solution was slowly adjusted
to 7 by adding dilute HCl. The resulting opaque orange solution
was extracted with CH2Cl2 until colorless, and the solvent was re-
moved from the combined organic phases. The precipitate was dis-
solved in a minimal amount of EtOH and concentrated aqueous
NH4PF6 added. The precipitate was recrystallized from acetone/
Financial support for this work from the Deutsche Forschungsge-
meinschaft SFB 436 and a grant to S.R. is gratefully acknowledged.
We would like to thank Prof. D. Walther for helpful discussions
and encouragement.
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1
water. Yield 170 mg (90%). H NMR ([D6]acetone): δ ϭ 8.879 [3Ј,
[3]
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[4]
2 H, s (lc)], 8.844 [3ЈЈ, 2 H, s (lc)], 8.174 [4,7, 2 H, s (lc)], 7.939 (6Ј,
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d (lc)], 7.397 [5ЈЈ, 2 H, d (lc)], 4.156 [CH3(OMe), 6 H, s], 1.428
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tern: 1181 (5) (3 ϩ PF6); 1035 (5) (3). Crystal data for 3:
C52H61Br2F12N6O2P2Ru, M ϭ 1304.72 g molϪ1, red prism, size
0.02 ϫ 0.02 ϫ 0.01 mm, monoclinic, space group P21/n, a ϭ
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[9]
The electrochemical investigation shows different currents for
oxidation and reduction of the ruthenium center of 3 suggest-
ing an involvement of the methoxy function as observed pre-
viously: L. O’Brien, M. Duati, S. Rau, A. L. Guckian, T. E.
Keyes, N. M. Boyle, A. Serr, H. Görls, J. G. Vos, Dalton Trans.
2004, 514.
˚
13.983(3), b ϭ 39.063(5), c ϭ 10.4711(15) A, β ϭ 100.945(13)°,
3
V ϭ 5615.4(17) A , T ϭ Ϫ153 °C, Z ϭ 4, ρcalcd. ϭ 1.543 g cmϪ3
,
˚
µ(Mo-Kα) ϭ 6.22 cmϪ1, F(000) ϭ 2654, 21731 reflections in h(Ϫ15/
13), k(Ϫ45/45), l(Ϫ12/12), measured in the range 1.52° Յ Θ Յ
14.56°, completeness Θmax ϭ 72.1%, 6903 independent reflections.
[10]
S. Rau, M. Ruben, T. Büttner, C. Temme, S. Dautz, H. Görls,
M. Rudolph, D. Walther, A. Brodkorb, M. Duati, C.
O’Connor, J. G. Vos, J. Chem. Soc., Dalton Trans. 2000, 3649.
Received February 27, 2004
CCDC-216455 and -216456 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free
Eur. J. Inorg. Chem. 2004, 2001Ϫ2003
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2003