Octahedral Fe(II) and Ru(II) complexes based on a new bis 1,10-phenanthroline ligand that imposes a well defined axis

Article abstract of DOI:10.1021/ja011250y

A bis-chelating ligand (L1), made of two 7-(p-anisyl)-1,10-phenanthroline (phen) subunits connected with a p-(CH₂)₂C₆H₄ (CH₂)₂ spacer through their 4 positions, has been prepared, using Skr

Full text of DOI:10.1021/ja011250y

J. Am. Chem. Soc. 2001, 123, 12215-12221
12215
Octahedral Fe(II) and Ru(II) Complexes Based on a New Bis
1,10-Phenanthroline Ligand That Imposes a Well Defined Axis
Didier Pomeranc, Vale´rie Heitz, Jean-Claude Chambron, and Jean-Pierre Sauvage*
Contribution from the Laboratoire de Chimie Organo-Mine´rale, UMR 7513 du CNRS,
UniVersite´ Louis Pasteur, Institut Le Bel, 4 rue Blaise Pascal, 67000 Strasbourg, France
ReceiVed May 21, 2001
Abstract: A bis-chelating ligand (L1), made of two 7-(p-anisyl)-1,10-phenanthroline (phen) subunits connected
with a p-(CH2)2C6H4(CH2)2 spacer through their 4 positions, has been prepared, using Skraup syntheses and
reaction of the anion of 4-methyl-7-anisyl-1,10-phenanthroline with R,R′-dibromo-p-xylene. Its Fe(II) complex,
[FeL1(dmbp)](PF6)2, was prepared in one step by reaction of L1 with [Fe(dmbp)3](PF6)2 (dmbp ) 4,4′-dimethyl-
2,2′-bipyridine). On the other hand, its Ru(II) complex, [RuL1(dmbp)](PF6)2, was prepared in two steps from
Ru(CH3CN)4Cl2 and L1, followed by reaction with dmbp. X-ray crystal structure analyses show that in the
two octahedral complexes, ligand L1 coils around the metal by coordination of the axial and two equatorial
positions. It defines a 21 Å long axis (O‚‚‚O distance) running through the central metal and the terminal
anisyl substituents. The complexes were also characterized by 1H NMR, mass spectrometry, cyclic voltammetry,
electronic absorption, and, in the case of Ru(II), fluorescence spectroscopy.
Introduction
geometry, the distance, and the electronic communication
between the different components.6 Linear and rigid bridges are
particularly well-adapted for obtaining long-lived charge-
separated states, because they best physically separate the
oxidized donor and reduced acceptor. Among the great variety
of chromophores that have been used as photosensitizers in
D-P-A triads, porphyrins,1,2 and ruthenium3,4 or osmium5
diimine complexes play a central role. Porphyrins have been
easily incorporated in linear systems through trans meso (1, 10)
positions, which define a C2 symmetry axis.1,2 Ru- or Os-
(terpy)22+ complexes (terpy ) 2,2′:6′,2′′-terpyridine) have been
used similarly, because 4′-substituted bis-terpy complexes have
a well-defined axis running through the 4′-position of each terpy
(Figure 1).4,5
The principles underlying photoinduced charge separation in
natural photosynthetic systems (bacterial reaction centers and
green plant photosystems I and II) have guided many research
groups in designing synthetic compounds able to perform
photoinduced charge separation at the molecular level, as
described in recent examples.1 One of these key principles is
fractionation of long-range electron transfer in discrete hopping
steps. It has led to the concept of triads such as the D-P-A
systems, in which D and A are electron-donor or -acceptor
components, respectively, with P being a photosensitizer
(electron-donor in the excited state).2-5 The bridge connecting
the two units is of crucial importance, because it controls the
The situation is very different for Ru(bipy)32+-based systems
in which no such axis can be found. As shown in Figure 2,
arrangement of two bipyridine ligands with donor and acceptor
moieties attached to each 4-position produces four stereoisomers,
with only one realizing the ideal situation of a linear arrangement
of D, the ruthenium chromophore, and A. In this latter case,
the donor and acceptor units are sitting along a coordination
axis of the complex (Figure 2c). Synthetic methods were
(1) Steinberg-Yfrach, G.; Liddell, P. A.; Hung, S.-C.; Moore, A. L.; Gust,
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10.1021/ja011250y CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/16/2001

12216 J. Am. Chem. Soc., Vol. 123, No. 49, 2001
Pomeranc et al.
photochemical isomerization is efficient, precluding any use of
pure isomers in photoinduced reactions.9 Therefore, using such
octahedral complexes for assembling donor-acceptor groups
in a linear fashion still remains a real challenge. It is also an
2+
important problem to solve, because Ru(bipy)3 is a better
chromophore than Ru(terpy)22+, with a relatively long-lived (µs)
MLCT state in the case of the former,10 while the latter is not
luminescent at room temperature, because of low-lying dd
states.11
This paper describes the synthesis of two new tetradentate
(bis-chelate) ligands L1 and L2 designed to confer a well-
defined axis when coordinated to metals with octahedral
coordination spheres. As a proof, complexes [RuL1(dmbp)]-
(PF6)2 (dmbp ) 4,4′-dimethyl-2,2′-bipyridine) and [FeL1(dmbp)]-
1
Figure 1. Porphyrin and [M(terpy)2]2+ chromophores contain a
“natural” axis (dotted line) along which electron-donor and electron-
acceptor groups can be poised. This ensures maximal spatial separation
between the electroactive components.
(PF6)2 have been prepared and characterized by H NMR and
mass spectrometry and their structures solved by single-crystal
X-ray analysis. Electrochemical, electronic absorption, and, for
the ruthenium complex, emission properties are also provided.
The [RuL1(dmbp)]2+ complex, in particular, is expected to
display increased photochemical stability toward isomerization
once the two phen subunits are linked by the appropriate spacer.
This is of great importance if it is to be used as the central
photosensitizer in linear D-P-A triad systems. A preliminary
account of the preparation and structural characterization of this
complex is given in ref 12.
Experimental Section
1
General. H NMR spectra were obtained on either Bruker AC200
(200 MHz) or AC300 (300 MHz) spectrometer. Chemical shifts in ppm
are referenced downfield from tetramethylsilane. Labels of the protons
of ligands L1 and L2 and their complexes are provided in Figure 4.
Mass spectral data were obtained on ZAB-HF (FAB) spectrometer.
UV-visible absorption spectra were recorded with a Kontron-Uvikon
860 spectrophotometer, and emission spectra were obtained with an
SLM-Aminco spectrofluorimeter. Cyclic voltammetry data were ob-
tained with an EG&G PAR potentiostat/galvanostat model 273A, using
a Pt disk or a homemade Hg/Au electrode to extend the range of
reduction potential available.
Materials. Starting materials were from commercial sources and
were used as received. THF was distilled from sodium/benzophenone
prior to use. Reactions performed under an atmosphere of argon used
standard Schlenk techniques. [Ru(CH3CN)4Cl2]13 was prepared accord-
ing to literature procedure.
X-ray Crystallography. Suitable single crystals of 4(C60H50N6O2-
Ru)‚PF6‚12CH2Cl2‚4C6H6‚4H2O ([RuL1(dmbp)](PF6)2) and 2(C60H50N6O2-
Fe)‚4PF6‚5CHCl3‚H2O ([FeL1(dmbp)](PF6)2) were obtained by slow
diffusion of ethyl acetate into CHCl3 solutions of the complex (Ru)
and evaporation of CHCl3 solutions (Fe) at room temperature.
Systematic searches in reciprocal spaces using a Nonius Kappa CCD
diffractometer showed that crystals of [RuL1(dmbp)](PF6)2 and
[FeL1(dmbp)](PF6)2 belong, respectively, to the monoclinic and triclinic
systems.
Quantitative data were obtained at -100 °C. All experimental
parameters used are given in the Supporting Information. The resulting
data sets were transferred to a DEC Alpha workstation, and for all
subsequent calculations, the Nonius OpenMoleN package14 was used.
Figure 2. Arrangements of two bipyridine ligands with electron-donor
and electron-acceptor moieties attached to each 4-position in the
octahedral coordination sphere of a transition metal cation. The ancillary
ligand is 2,2′-bipyridine (bipy).
developed for the controlled, sequential coordination of three
differently substituted bipyridine-like ligands to a ruthenium
center.7 However, these methods of preparation of mixed-ligand
complexes are not stereoselective, and careful separations are
required when the ligands are nonsymmetrical.8 Furthermore,
(9) (a) Porter, G. B.; Sparks, R. H. J. Photochem. 1980, 13, 123. (b)
Yamagishi, A.; Naing, K.; Goto, Y.; Taniguchi, M.; Takahashi, M. J. Chem.
Soc., Dalton Trans. 1994, 2085-2089. (c) Laemmel, A.-C. Ph.D. Thesis,
Louis Pasteur University, Strasbourg, 2000.
(10) Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.; von Zelewsky,
A. Coord. Chem. ReV. 1988, 84, 85-277.
(11) Lin, C. T.; Bottcher, W.; Chou, M.; Creutz, C.; Sutin, N. J. Am.
Chem. Soc. 1976, 98, 6536.
(12) Pomeranc, D.; Chambron, J.-C.; Heitz, V.; Sauvage, J.-P. C. R. Acad.
Sci. 2001, 4, 197-200.
(13) Hayoz, P.; von Zelewsky, A.; Stoeckli-Evans, H. J. Am. Chem. Soc.
1993, 115, 5111-5114.
(7) (a) Anderson, P. A.; Deacon, G. B.; Haarmann, V. H.; Keene, F. R.;
Meyer, T. J.; Reitsma, D. A.; Shelton, B. W.; Strouse, G. F.; Thomas, N.
C.; Treadway, J. A.; White, A. H. Inorg. Chem. 1995, 34, 6145. (b)
Treadway, J. A.; Meyer, T. J. Inorg. Chem. 1999, 38, 2267-2278. (c) Hesek,
D.; Inoue, Y.; Everitt, S. R. L.; Ishida, H.; Kunieda, M.; Drew, M. G. B.
Inorg. Chem. 2000, 39, 308-316.
(8) Rutherford, T. J.; Keene, F. R. Inorg. Chem. 1997, 36, 2872-2878.

Octahedral Fe(II) and Ru(II) Complexes
J. Am. Chem. Soc., Vol. 123, No. 49, 2001 12217
1
Table 1. Selected H NMR Data for Ligand L1 and Its Ru(II) and Fe(II) Complexes (Aromatic Protons)a
ligand L1
dmbp
compound
9
2
5
6
8
3
o
m
b1
b2
3′
5′
6′
L1
9.18
10.55
8.02
9.07
7.01
7.28
7.06
7.97
7.54
7.85
7.70
7.72
7.38
6.55
7.06
6.95
7.47
7.65
7.61
7.64
7.07
7.19
7.12
7.14
7.07
[RuL1Cl2]
7.94
8.12
8.14
8.18
8.28
8.29
6.53
6.58
6.53
6.20
6.25
6.24
[RuL1(dmbp)]2+
[FeL1(dmbp)]2+
8.23
8.28
7.21
7.22
8.02
7.71
7.72
a Chemical shifts in ppm downfield from TMS. Solvent: CDCl3.
The structures were solved using direct methods. Absorption
corrections are part of the scaling procedure of data reductions. After
refinement of the heavy atoms, difference Fourier maps revealed
maximas of residual electronic density close to the positions expected
for hydrogen atoms; they were introduced as fixed contributors in
structure factor calculations by their computed coordinates (C-H )
0.95 Å) and isotropic temperature factors such as B(H) ) 1.3 Beqv(C)
Å2 but not refined. For [RuL1(dmbp)](PF6)2, the PF6-,C6H6, and water
and, for [FeL1(dmbp)](PF6)2, the PF6-, CHCl3, and water protons were
omitted. Full least-squares refinements on /F/. A final difference map
revealed no significant maxima. The scattering factor coefficients and
anomalous dispersion coefficients come, respectively, from ref 15a and
b.
4-Methyl-7-anisyl-1,10-phenanthroline 6. Compound 4 (15 g, 0.095
mol) and arsenic pentaoxyde (43.9 g, 0.19 mmol) were dissolved in
o-phosphoric acid (100 mL) at 100 °C. Solid 5 (26.37 g, 0.133 mol)
was carefully added over a period of 30 min, without exceeding 120
°C. The mixture was heated to reflux at 140 °C for an additional hour.
After cooling, the solution was poured onto ice and its pH raised to
pH 8 with aqueous KOH, leading to the precipitation of large quantities
of a black viscous solid. The aqueous solution and the black residues
were repeatedly extracted with hot toluene. After evaporation of the
combined organic phases, a brown solid was obtained, which was
recrystallized from hot ethyl acetate to yield brown crystals of 6 (14.75
1
g, 52%). Mp: 154-155 °C. H NMR (300 MHz, CDCl3): δ 2.78 (s,
3H, CH3), 3.92 (s, 3H, OCH3), 7.08 (d, 2H, Hm, 3J ) 8.7 Hz), 7.48 (d,
2H, Ho, 3J ) 8.7 Hz), 7.50 (m, 2H, H3, H8), 7.93 (d, 1H, H5, 3J ) 9.4
Hz), 7.99 (d, 1H, H6, 3J ) 9.4 Hz), 9.05 (d, 1H, H2, 3J ) 4.5 Hz), 9.18
(d, 1H, H9, 3J ) 4.5 Hz). Anal. Calcd: C, 79.98%; H, 5.37%; N, 9.33%.
Found: C, 80.06%; H, 5.52%; N, 9.46%.
4-Methyl-8-nitroquinoline 3. Nitroaniline 2 (84.35 g, 0.61 mol)
and arsenic pentaoxide (80 g, 0.3 mol) were added to a mixture of
sulfuric acid (30 mL) and water (8 mL). The mixture was stirred
mechanically and heated to 100 °C. But-3-en-2-one 1 (50 mL, 0.61
mol) was then added slowly without exceeding 120 °C. The reaction
mixture was refluxed for two additional hours, during which the solution
turned black. After cooling, the solution was neutralized with aqueous
sodium hydroxide. A fraction of the resulting viscous black solid was
filtered under vacuum. Both the solid and the aqueous phase were
extracted with dichloromethane. The combined organic phases were
dried with magnesium sulfate. The orange solid obtained after evapora-
tion was chromatographed on silica, eluting with dichloromethane/
hexane (1:1), gradient to pure dichloromethane. The resulting solid was
recrystallized from ethanol to give pure orange crystals of 3 (64.15 g,
55%). Mp: 127 °C. 1H NMR (300 MHz, CDCl3): δ 2.76 (s, 3H, CH3),
7.38 (d, 1H, H3, 3J ) 4.3 Hz), 7.62 (dd, 1H, H6, 3J ) 7.7 Hz, 3J ) 7.7
Hz), 7.98 (dd, 1H, H5, 3J ) 8.0 Hz, 4J ) 1.3 Hz), 8.21 (dd, 1H, H7, 3J
L1. Diisopropylamine (0.1 mL) was dissolved in THF (2 mL) under
argon. n-Butyllithium (1.2 M, 0.6 mL) was added at 0 °C, and the
mixture was stirred at 0 °C for 1h. Compound 6 (0.200 g, 0.66 mmol)
was dissolved in THF (5 mL) under argon and transferred via cannula
at 0 °C to the freshly prepared LDA solution. The brown solution of
6 instantly turned dark green and was allowed to reach room
temperature (1 h). R,R′-Dibromo-p-xylene 7 (0.0879 g, 0.33 mmol)
was dissolved under argon in THF (2.5 mL) and transferred via cannula
to the reaction mixture at 0 °C. After reaction at room temperature
overnight, 10 drops of ethanol were added, and the brown solution
turned yellow. The solution was poured into water (100 mL), extracted
with dichloromethane, and washed with brine. The combined organic
phases were dried with magnesium sulfate, evaporated, and washed
with hot toluene to remove trace amounts of 6 to afford pure L1 (0.204
4
3
) 8.5 Hz, J ) 1.3 Hz), 8.91 (d, 1H, H2, J ) 4.4 Hz).
1
g, 88%) as a pale brown solid. Mp > 250 °C. H NMR (300 MHz,
4-Methyl-8-aminoquinoline 4. A solution of stannous chloride
dihydrate (58 g, 0.24 mol) in ethanol (70 mL) was added dropwise at
0 °C to a suspension of 3 (15 g, 0.08 mol) in ethanol (250 mL) and
refluxed for 1 h. After cooling, the solution was neutralized with
aqueous potassium hydroxyde and filtered under vacuum in order to
remove the solid stannic oxyde. The aqueous phase and the solid were
extracted with dichloromethane, yielding 4 as a black solid (12 g, 95%).
CDCl3): δ 3.06 (m, 4H, CH2), 3.38 (m, 4H, CH2), 3.90 (s, 6H, OCH3),
3
7.07 (m, 8H, Hm, Hb), 7.38 (d, 2H, H3, J ) 4.6 Hz), 7.47 (d, 4H, Ho,
3J ) 8.7 Hz), 7.54 (d, 2H, H8, 3J ) 4.6 Hz) 7.97 (s, 4H, H5, H6), 9.07
3
3
(d, 2H, H2, J ) 4.6 Hz), 9.18 (d, 2H, H9, J ) 4.6 Hz). FAB MS:
703.4 (M + H)+.
L2. Using the same procedure as for L1, 6 was reacted with freshly
prepared 1.4 M LDA and R,R′-dibromo-m-xylene 8 in THF. The crude
product was purified by preparative TLC (alumina), eluting with
dichloromethane/ethyl acetate/triethylamine (2:7:1) to yield L2 (100
1
Mp: 80 °C. H NMR (300 MHz, CDCl3): δ 2.66 (s, 3H, CH3), 4.75
(broad s, 2H, NH2), 6.91 (dd, 1H, H5, 3J ) 7.0 Hz, 4J ) 1.7 Hz), 7.20
3
3
(d, 1H, H3, J ) 4.3 Hz), 7.3 (m, 2H, H6, H7), 8.61 (d, 1H, H2, J )
1
4.5 Hz).
mg, 44%). H NMR (200 MHz, CDCl3): δ 3.03 (m, 4H, CH2), 3.32
p-(3-Chloropropan-1-one)-anisole 5. Aluminum trichloride (27.78
g, 0.208 mol) was suspended in a mixture of carbon disulfide (60 mL)
and anisole (20 mL). 1,3-Dichloropropanone (20 mL, 0.208 mol) was
added dropwise in 30 min. After 30 additional min of reaction at room
temperature, the solution was neutralized with aqueous sodium hy-
droxyde and extracted with dichloromethane. The combined organic
phases were washed with water, dried with magnesium sulfate, and
evaporated. The resulting solid was recrystallized from dichloromethane
yielding 5 (36 g, 87%) as a white solid. Mp: 63-64 °C. 1H NMR (300
MHz, CDCl3): δ 3.41 (t, 2H, CH2CO, 3J ) 6.9 Hz), 3.88 (s, 3H, OCH3),
3.94 (t, 2H, CH2Cl, 3J ) 6.9 Hz), 6.95 (d, 2H, ArH, 3J ) 8.9 Hz), 7.93
(d, 2H, ArH, 3J ) 8.9 Hz). Anal. calcd: C, 60.46%; H, 5.58%. Found:
C, 60.40%; H, 5.60%.
(m, 4H, CH2), 3.87 (s, 6H, OCH3), 7.05 (m, 8H, Hm, Hb), 7.31 (d, 2H,
H3, 3J ) 4.5 Hz), 7.44 (d, 4H, Ho, 3J ) 8.7 Hz), 7.49 (d, 2H, H8, 3J )
3
4.5 Hz), 7.92 (s, 4H, H5, H6), 9.05 (d, 2H, H2, J ) 5.0 Hz), 9.15 (d,
3
2H, H9, J ) 5.0 Hz).
[RuL1Cl2]. L1 (0.100 g, 0.142 mmol) was dissolved in 1,2-
dichloroethane (35 mL) under argon. Freshly prepared [Ru(CH3-
CN)4Cl2] (0.142 mmol) was dissolved in 1,2-dichloroethane (35 mL)
under argon. The two solutions were simultaneously added dropwise
to refluxing 1,2-dichloroethane (1.5 L) at a rate of 5 mL/h, using special
high dilution glassware and vigorous mechanical stirring. After the
addition, the dark violet mixture was refluxed for two additional hours,
evaporated, and flash chromatographed on silica, eluting with dichlo-
romethane/methanol (95:5), gradient to dichloromethane/methanol (90:
10), to yield [RuL1Cl2] (0.094 g, 65%) as a violet solid. 1H NMR (500
MHz, CDCl3): δ 2.8-4 (m, 8H, CH2), 3.98 (s, 6H, OCH3), 6.20 (d,
2H, Hb2, 3J ) 7.6 Hz), 6.53 (d, 2H, Hb1, 3J ) 8.5 Hz), 6.55 (d, 2H, H3,
3J ) 5.6 Hz), 7.01 (d, 2H, H2, 3J ) 5.5 Hz), 7.19 (d, 4H, Hm, 3J ) 8.6
Hz), 7.65 (d, 4H, Ho, 3J ) 8.6 Hz), 7.85 (d, 2H, H8, 3J ) 5.4 Hz), 7.94
(14) Nonius B. V. OpenMoleN, InteractiVe Structure Solution; Delft, The
Netherlands, 1997.
(15) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, 1974; Vol. IV. (a) Table
2.2b. (b) Table 2.3.1.

12218 J. Am. Chem. Soc., Vol. 123, No. 49, 2001
Pomeranc et al.
(d, 2H, H5, 3J ) 9.3 Hz), 8.18 (d, 2H, H6, 3J ) 9.3 Hz), 10.55 (d, 2H,
3
H9, J ) 5.4 Hz). FAB MS: 839.2 (M - Cl-)+, 874.2 (M+).
[RuL1(dmbp)](PF6)2. 4,4′-Dimethyl-2,2′-bipyridine (dmbp) (0.007
g, 0.038 mmol) was added to a suspension of [RuL1Cl2] (0.021 g, 0.024
mmol) in a mixture of ethanol (4 mL) and water (2 mL). The violet
reaction mixture rapidly turned orange-yellow upon heating and was
refluxed for 2 h. After cooling, a saturated aqueous solution of
potassium hexafluorophosphate (10 mL) was added, and ethanol was
evaporated. The resulting precipitate was filtered under vacuum and
chromatographed on silica, eluting with a gradient of acetonitrile/water/
saturated aqueous KNO3 from 100:1:1 to 100:18:2. The collected orange
fractions were combined and dissolved in acetone. An aqueous solution
of saturated potassium hexafluorophosphate (10 mL) was added and
acetone evaporated. Filtration under vacuum of the resulting precipitate
Figure 3. The three possible geometries expected for an octahedrally
coordinated metal bound to a bis-chelate ligand and their symmetry
point groups.
1
afforded [RuL1(dmbp)](PF6)2 (0.025 g, 80%) as an orange solid. H
NMR (400 MHz, CDCl3): δ 2.58 (s, 6H, CH3), 3.10 (m, 4H, CH2),
3
3.65 (m, 4H, CH2), 3.92 (s, 6H, OCH3), 6.25 (d, 2H, Hb2, J ) 9.6
3
3
Hz), 6.58 (d, 2H, Hb1, J ) 9.4 Hz), 7.06 (d, 2H, H3, J ) 5.5 Hz),
7.12 (d, 4H, Hm, 3J ) 8.7 Hz), 7.21 (d, 2H, H5′, 3J ) 4.6 Hz), 7.28 (d,
3
3
2H, H2, J ) 5.5 Hz), 7.61 (d, 4H, Ho, J ) 8.7 Hz), 7.70 (d, 2H, H8,
3J ) 5.5 Hz), 8.02 (m, 4H, H9 and H6′), 8.12 (d, 2H, H5, 3J ) 9.6 Hz),
3
8.23 (s, 2H, H3′), 8.28 (d, 2H, H6, J ) 9.4 Hz). FAB MS: 494.1 (M
- 2PF6 )
2+/2, 988.2 (M - 2PF6 + e-)+, 1133.2 (M - PF6-)+.
-
-
[Fe(dmbp)3](PF6)2. A solution of FeSO4‚(NH4)2SO4‚6H2O (0.638
g, 1.63 mmol) and 4,4′-dimethyl-2,2′-bipyridine (0.900 g, 4.78 mmol)
in ethanol/H2O (2:1) was heated at reflux for 30 min under argon.
Addition of aqueous KPF6 precipitated the desired complex. Further
purification involved dissolution in CH2Cl2 and washing with H2O. 1H
NMR (200 MHz, d6-acetone): 2.53 (s, 6H, CH3), 7.37 (dd, 6H, H5,5′, 3J
) 5.9 Hz, 4J ) 1 Hz), 7.48 (d, 6H, H6,6′, 3J ) 5.9 Hz), 8.68 (br s, 6H,
H3,3′).
[FeL1(dmbp)](PF6)2. [Fe(dmbp)3](PF6)2 (0.129 g, 0.142 mmol) was
dissolved in 50 mL of 1,2-dichloroethane under argon and transferred
via cannula to a refluxing solution of L1 (0.1 g, 0.142 mmol) in 50
mL of 1,2-dichloroethane under argon. After 24 h of reaction, the red-
violet solution was evaporated and chromatographed on silica, eluting
with acetonitrile/water/saturated aq KNO3 (100:3:1). The collected
fractions were combined and dissolved in acetonitrile. An aqueous
solution of saturated potassium hexafluorophosphate (20 mL) was added
and acetonitrile evaporated. Filtration under vacuum of the resulting
precipitate afforded [FeL1(dmbp)](PF6)2 (0.109 g, 75%) as a violet
solid. 1H NMR (300 MHz, CD2Cl2): δ 2.62 (s, 6H, CH3), 3.20 (m, 8H,
Figure 4. Chemical structures of bis-chelates L1 and L2 and complexes
[FeL1(dmbp)]2+ and [RuL1(dmbp)]2+. Sp is the symbol for spacer
moiety.
equatorial sites. Therefore, linear donor-acceptor systems can
be obtained by appropriate functionalization along the axial
positions, as discussed previously. Preventing unwanted complex
formation with C1 symmetry can be realized by an adequate
choice of the nature and length of the spacer linking the two
bidentate units of the tetradentate ligand. The optically active,
bipyridine-based “chiragen” ligands of von Zelewsky and co-
workers, which allow the enantioselective formation of C2-
symmetric Ru(II) complexes, turned out to be a good basis for
the design of the ligands of this study.13,17 1,10-Phenanthroline
moieties were chosen as chelate subunits. They are rigid and
can be functionalized on the 4 and 7 positions, which correspond
to the 4 and 4′ positions of 2,2′-bipyridine. We selected m- and
p-phenylene bridging moieties linked via CH2CH2 alkyl chains
to the 4-positions of two phenanthroline ligands, by analogy
with the “chiragen” ligands. Finally, anisyl substituents were
attached to the remaining 7-positions, to extend the coordination
axis upon complexation to a metal. The ligands L1 and L2 thus
designed and the structural formula of the Fe(II) and Ru(II)
complexes of L1 are represented in Figure 4.
3
4
CH2), 3.94 (s, 6H, OCH3), 6.27 (dd, 2H, Hb2, J ) 7.8 Hz, J ) 1.8
Hz), 6.57 (dd, 2H, Hb1, 3J ) 7.8 Hz, 4J ) 1.8 Hz), 6.84 (d, 2H, H3, 3J
3
3
) 5.5 Hz), 7.06 (d, 2H, H2, J ) 5.5 Hz), 7.18 (d, 4H, Hm, J ) 8.8
3
3
Hz), 7.18 (d, 2H, H5′, J ) 5.9 Hz), 7.60 (d, 2H, H6′, J ) 6.0 Hz),
3
3
7.64 (d, 4H, Ho, J ) 8.8 Hz), 7.68 (d, 2H, H8, J ) 5.5 Hz), 7.72 (d,
3
3
2H, H9, J ) 5.5 Hz), 8.23 (d, 2H, H5, J ) 9.6 Hz), 8.35 (d, 2H, H6,
3J ) 9.2 Hz), 8.36 (s, 2H, H3′). ES MS: 471.3 (M - 2PF6
)
2+/2.
-
Results and Discussion
1. Ligand Design and Synthesis. We reasoned that the linear
arrangement of Figure 2b could be favored over the other
geometries by using a bis-chelate ligand with an appropriate
spacer between the coordinating moieties. As shown in Figure
3, such a ligand can form complexes with three different
arrangements of the bis-chelate around the metal. The arrange-
ment with C2V symmetry has the four equatorial positions
coordinated by the ligand, and the remaining axial positions
are free for attachment of donor and acceptor components.
However, such a system has two drawbacks: (i) it is not
compatible with the [Ru(bipy)3]2+ stereochemistry, and (ii) the
four-coordinate square planar (SP-4) Ru(bipy)22+ chromophore
has been shown to decompose under light irradiation.16 In the
case of the configuration with C2 symmetry, the bis-chelate
ligand twists around the metal and occupies the axial and two
The preparation of intermediates 3, 4, and 6 from precursors
1, 2, and 5 is shown in Figure 5, and the synthesis of ligands
L1 and L2 is represented in Figure 6. The two ligands L1 and
(17) (a) Mu¨rner, H.; Belser, P.; von Zelewsky, A. J. Am. Chem. Soc.
1996, 118, 7989-7994. (b) Mamula, O.; von Zelewsky, A.; Bernardinelli,
G. Angew. Chem., Int. Ed. Engl. 1998, 37, 290-292. (c) von Zelewsky,
A.; Mamula, O. J. Chem. Soc., Dalton Trans. 2000, 219-231.
(16) Coe, B.; Friesen, D. A.; Thompson, D. W.; Meyer, T. J. Inorg. Chem.
1996, 35, 4275-4284.

Octahedral Fe(II) and Ru(II) Complexes
J. Am. Chem. Soc., Vol. 123, No. 49, 2001 12219
2. Preparation of the Iron(II) and Ruthenium(II) Com-
plexes. The chelating properties of ligand L1 were tested on
Ru(II) and Fe(II) (Figure 7). [RuL1(dmbp)](PF6)2 was prepared
in two steps. At first, reaction of freshly prepared [Ru(CH3-
CN)4Cl2] with stoichiometric amounts of L1 in refluxing 1,2-
dichloroethane, and in high dilution conditions, as described
by von Zelewsky and co-workers,17a afforded the intermediate
[RuL1Cl2] complex in 65% yield. [RuL1Cl2] was then reacted
with 1.6 equiv of dmbp in a 2:1 mixture of ethanol and water.
The crude product was purified by column chromatography after
anion exchange by treatment with KPF6. [RuL1(dmbp)](PF6)2
was obtained in 80% yield as an orange solid. The Fe(II)
complex was prepared by taking advantage of the lability of
the dmbp ligands in the [Fe(dmbp)3]2+ complex and the stronger
chelating properties of the tetradentate ligand L1 as compared
to two bidentate dmbp ligands. Thus, [Fe(dmbp)3](PF6)2 was
reacted with 1 equiv of L1 in refluxing 1,2-dichloroethane for
24 h. After anion exchange, chromatographic separation afforded
[FeL1(dmbp)](PF6)2 in 75% yield.
Figure 5. Precursors and synthetic route to phenanthroline intermediate
6.
3. X-ray Crystal Structures of [FeL1(dmbp)](PF6)2 and
[RuL1(dmbp)](PF6)2. [FeL1(dmbp)](PF6)2 crystallizes in the
triclinic P-1 space group with two molecules in the unit cell. A
view of the complex is shown in Figure 8. It shows nicely the
coiling of the bis-chelate ligand L1 around the Fe(II) center.
The metal adopts a pseudo-octahedral geometry with Fe-N
distances in the range 1.961(9)-1.976(9) Å and bite angles
within each chelate around 82°. All the chelates show some
deviation from planarity (torsional angles N-C-C-N), surpris-
ingly, to a lower extent (N(5)-C(54)-C(55)-N(6) ) -2.35-
(1.23)°) for dmbp than for the phen subunits of L1 (e.g., N(4)-
C(38)-C(33)-N(3) ) -7.45(1.32)°). In addition, the torsional
angle Fe-N(3)-C(33)-C(38) (9.25(1.11)°) of the part of the
phen ligand that is close to the bridge is higher than the angle
Fe-N(4)-C(38)-C(33) (1.93(1.11)°) of the part of the phen
ligand that is close to the anisyl substituent. The difference is
large enough to suggest that these deformations of the phen
subunits are imposed by the p-phenylene bridge. As a conse-
quence, the O(1)‚‚‚O(2) cation axes lie parallel to b, slightly
bent about Fe toward the bridge, with an O(1)‚‚‚Fe‚‚‚O(2) angle
deviating significantly from linearity (172.53(8)°). The O(1)‚‚‚
O(2) distance is 20.79(9) Å.
Within each consequent translation-generated cation column,
the complexes adopt a stairlike arrangement, with Fe‚‚‚Fe
distances of 12.63(9) Å. One of the anisyl substituents of a given
molecule is approximately parallel to the phenanthroline subunit
of its following neighbor, the closest contacts lying at the usual
aromatic interplanar distances. The driving force for the
columnar arrangement could be donor-acceptor interactions
between electron-releasing anisyl groups and electron-withdraw-
ing, Fe2+-complexed phen chelates.
Figure 6. Preparation of bis-chelates L1 and L2.
L2 were synthesized by the coupling of two substituted
phenanthrolines 6. This common precursor was constructed
using Skraup reactions, which turned out to be extremely useful
in the past for making variously substituted 1,10-phenanthro-
lines.18 At first, quinoline 3 was obtained in 55% yield by
reaction of o-nitroaniline 2 with but-3-en-2-one 1 in sulfuric
acid in the presence of arsenic pentaoxide. Reduction of 3 with
stannous chloride gave the amino derivative 4 in 95% yield.
Compound 4 was finally reacted with 5 in o-phosphoric acid
in the presence of arsenic pentaoxide to afford the desired
phenanthroline 6 in 52% yield after recrystallization.19 Ligands
L1 and L2 were prepared in a similar manner: deprotonation
of 6 with a solution of LDA was followed by reaction with 0.5
equiv of either R,R′-dibromo-p-xylene 7 or R,R′-dibromo-m-
xylene 8. L1 and L2 were obtained in 88% and 44% yields
after purification, respectively.
[RuL1(dmbp)](PF6)2 crystallizes in the monoclinic P121/c1
space group, with four molecules in the unit cell. The structure
of the molecule is very similar to that of the previous one, with
the axial and two equatorial positions occupied by the donor
atoms of L1, and the remaining equatorial positions occupied
by the dmbp ligand. Differences in the geometrical parameters
can be attributed to the larger size of the Ru2+ cation as
compared to Fe2+. The Ru-N distances range between 2.064(9)
and 2.074(9) Å, and as a consequence, the N-Ru-N bite angles
are slightly lower (78.50-79.23°). Deformations of the phen
subunits are also observed (torsional angles ranging between
7.6 and 10.6°), together with an increased bending of the O(1)‚‚‚
O(2) axis, with the O(1)‚‚‚Ru‚‚‚O(2) angle being 169.9(7)°,
probably because of the elongated Ru-N distances by com-
(18) Case, F. H. J. Chem. Soc. 1951, 1541-1545.
(19) Case, F. H.; Strohm, P. F. J. Org. Chem. 1962, 27, 1641-1643.

12220 J. Am. Chem. Soc., Vol. 123, No. 49, 2001
Pomeranc et al.
Figure 7. Preparation of the Ru(II) and Fe(II) complexes of L1.
Figure 9. View of the unit cell of [RuL1(dmbp)](PF6)2 down the a
axis. Thermal ellipsoids are given with 50% probability. Hydrogen
atoms are omitted for clarity.
Figure 8. X-ray crystal structure of the cation [FeL1(dmbp)]2+
.
Thermal ellipsoids are given with 50% probability. Hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and angles (deg)
are: Fe-N(1), 1.973(8); Fe-N(2), 1.972(9); Fe-N(3), 1.977(9); Fe-
N(4), 1.959(8); Fe-N(5), 1.967(9); Fe-N(6), 1.959(9); N(1)-Fe-N(4),
174.7(4); N(2)-Fe-N(5), 175.4(3); N(3)-Fe-N(6), 175.0(3); N(1)-
Fe-N(2), 82.3(3); N(2)-Fe-N(3), 85.8(4); N(3)-Fe-N(4), 82.5(4);
N(4)-Fe-N(5), 90.5(3); N(5)-Fe-N(6), 82.0(4); N(6)-Fe-N(1),
91.2(3). For the similar Ru analogue: Ru-N(1), 2.074(9); Ru-
N(2,3,5,6), 2.07(1); Ru-N(4), 2.064(9); N(1)-Ru-N(4), 172.5(4);
N(2)-Ru-N(5), 174.4(4); N(3)-Ru-N(6), 174.3(3); N(1)-Ru-N(2),
79.3(4); N(2)-Ru-N(3), 82.8(4); N(3)-Ru-N(4), 78.5(4); N(4)-Ru-
N(5), 88.2(4); N(5)-Ru-N(6), 78.5(4); N(6)-Ru-N(1), 91.2(4).
parison with the Fe-N bond lengths. The O(1)‚‚‚O(2) distance
increases slightly (21.04(8) Å) as compared to the Fe2+ complex
(20.79(9) Å).
1
Figure 10. 300 MHz H NMR spectra (low field region, CD2Cl2) of
(a) ligand L1 and (b) complex [RuL1(dmbp)]2+
.
A view of the unit cell is reproduced in Figure 9. Again,
with the long axes of the cations oriented quasiparallel to a,
unit translations generate obligate homochiral sequences of
cations in that dimension. Within each column, the molecules
are arranged as observed for the Fe(II) complex, with Ru‚‚‚Ru
distances of 12.92(9) Å between neighboring molecules.
It is interesting to note that the O(1)‚‚‚M‚‚‚O(2) molecular
axis that has been created at the molecular level is transposed,
in the crystal, to a privileged direction along which homochiral
molecules align themselves.
of the free ligand and [RuL1(dmbp)]2+ is shown in Figure 10.
L1 (C2V symmetry) shows the characteristic low field doublets
for protons ortho to the nitrogen atoms, at 9.07 ppm for H2 and
9.18 ppm for H9. Homotopic Hb1 and Hb2 of the p-phenylene
bridge appear as a singlet at 7.07 ppm. Coordination of L1 to
either of the two metal centers Fe(II) or Ru(II) produces chiral
complexes of C2 symmetry. As a consequence, Hb1 and Hb2
become diastereotopic and appear as a pair of doublets, which
makes these protons excellent probes for evidencing the chirality
of these complexes, as noted before.17b Upon Ru(II) coordination
(in [RuL1Cl2]), H9 is shifted downfield to 10.55 ppm (∆δ )
1.37), but H2 moves upfield to 7.01 ppm (∆δ ) -2.06) because
4. 1H NMR Spectroscopy. 1H NMR data relevant to L1 and
complexes [RuL1Cl2], [RuL1(dmbp)](PF6)2, and [FeL1(dmbp)]-
(PF6)2 are collected in Table 1, and a comparison of the spectra

Octahedral Fe(II) and Ru(II) Complexes
J. Am. Chem. Soc., Vol. 123, No. 49, 2001 12221
Table 2. Electrochemical and UV-Visible Absorption and Luminescence Data
λ
max, nm
λem, nm
b
b
compound
[Fe(dmbp)3]2+
redox potentialsa
(ꢀ × 10-4 M-1cm-1
)
(Φ em)
0.91 (30)
1.12 (80)
0.96 (80)
1.11 (80)
-1.47 (40)
-1.66 (80)
-1.67 (80)
-1.64 (110)c
-1.65 (70)
-1.57 (40)
-1.58 (40)
-1.89 (70)c
-1.90 (60)d
528(0.8)
-1.49 (90)
-1.46 (70)
-1.47 (80)
-1.40 (80)
-1.40 (100)
-1.45(70)c
-1.45(70)
[Ru(dmbp)3]2+
[FeL1(dmbp)]2+
[RuL1(dmbp)]2+
450(1.7)
618(0.06)e
-1.88 (100)d
-1.80 (100)c
-1.80 (100)d
531(1.20); 330(2.43)
457(2.96); 324(3.72)
615(0.25)
-1.61 (80)
(-1.84)d,f
a V vs SCE (∆Ep, mV); 0.1 mol/L tetrabutylammonium perchlorate in acetonitrile; sweep rate 100mV/s except (f) 500 mV/s. b Acetonitrile
solution. c Pt working electrode. d Au amalgam prepared by dipping a gold wire terminated with a φ ) 0.05 mm sphere into mercury. e According
to ref 21.
the deshielding effect of metal coordination on protons R to
the nitrogen atoms is counterbalanced by the shielding field of
the other phenanthroline moiety. Protons Hb1 and Hb2 also move
upfield to 6.55 ppm (∆δ ) -0.52) and 6.20 ppm (∆δ ) -0.87),
respectively, because the twist of the ligand places them in the
shielding field of the phenanthroline moieties. Coordination of
dmbp to the ruthenium center in [RuL1(dmbp)](PF6)2 shifts back
H9 upfield to 8.02 ppm, as this proton is experiencing now the
shielding field of the auxiliary ligand. Interestingly, H2 under-
goes an opposite effect, probably because of its location in the
deshielding field of the dmbp ligand. The spectrum of
[FeL1(dmbp)](PF6)2 is very similar to that of [RuL1(dmbp)]-
(PF6)2 except for the protons closest to the metal center (i.e.,
H2, H9, and H6′) which experience shieldings of 0.20-0.30 ppm.
This could be in relation to the smaller size of the Fe2+ cation
Conclusion
The preparation of a bis-chelating ligand (L1), made of two
1,10-phenanthroline subunits connected with a p-(CH2)2C6H4-
(CH2)2 spacer through their 4 positions, has been reported, as
well as the preparation of its complexes with Fe(II) and Ru(II).
X-ray crystal structure analyses show that in the two octahedral
complexes, ligand L1 coils around the metal by coordination
of the axial and two equatorial positions, thus defining an axis
running through its terminal anisyl substituents and the central
metal. In addition, fluorescence spectroscopy measurements
have demonstrated that [RuL1(dmbp)]2+ retains the luminophore
properties of Ru(II) tris-chelate analogues. Therefore, provided
that ligand L1 can be functionalized with electron-donor and
electron-acceptor groups at its extremities, the design strategy
described here will allow the stereoselective synthesis of
D-P-A triad systems based on the [Ru(bipy)3]2+ chromophore.
Furthermore, if the screw-shaped Fe or Ru complex is to be
used as the acyclic component of a [2]-rotaxane, the oxygen
atoms of the anisyl groups will be used to attach blocking
groups. Work along both of these lines is in progress and will
be reported soon.
by comparison with Ru2+
.
5. Electrochemistry, Electronic Absorption, and Lumi-
nescence Spectroscopy. Redox potentials from cyclic voltam-
metry and electronic spectroscopy data (absorption and lumi-
nescence) are collected in Table 2, together with those of
reference compounds. The values of the redox potentials of
[FeL1(dmbp)]2+ and [RuL1(dmbp)]2+ are very similar to those
measured for the references [Fe(dmbp)3]2+ and [Ru(dmbp)3]2+
respectively, indicating that the L1 bis-chelate behaves as two
independent, bipyridine-like ligands. As expected, the Ru3+
,
The crystallographic data (without the structure factors) for
the new structure described in this publication (Fe complex)
have been deposited as “supplementary publication no. CCDC-
161292” with the Cambridge Crystallographic Data Centre.
Copies of the data can be obtained, free of charge, from the
following address in Great Britain: The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ (Fax: int. code +(1223)-
336033. E-mail: deposit@ccdc.cam.ac.uk).
/
Ru2+ couple of [RuL1(dmbp)]2+ (1.11 V) is slightly anodically
shifted (150 mV) with respect to Fe3+/Fe2+ in [FeL1(dmbp)]2+
(0.96 V), whereas the reduction potentials are closer to each
other, probably because reduction is ligand-centered. For
example, the first reduction of [RuL1(dmbp)]2+ takes place at
-1.45 V (-1.40 V for [FeL1(dmbp)]2+).
Electronic absorption spectra show ligand-centered transitions
in the UV region and the expected MLCT transitions in the
visible at 531 nm for the Fe complex and 457 nm for the Ru
analogue. The value of the extinction coefficient of [RuL1-
(dmbp)]2+ (29 600 M-1cm-1) is close to those measured for
similar complexes with extended aromatic chelates, such as 4,7-
diphenyl-1,10-phenanthroline.10 Upon excitation in the MLCT
band at room temperature, [RuL1(dmbp)]2+ shows an intense
emission at 615 nm, about four times as much as the emission
of [Ru(bipy)3]2+ in the same conditions. Such a luminescence
enhancement, as previously observed for ruthenium(II) tris-
chelates of 4- and 4,7-diaryl-1,10-phenanthrolines,20-21 is an
essential feature for photosensitizer subunits.
Acknowledgment. This paper is dedicated to the memory
of John A. Osborn. We warmly thank Andre´ De Cian and
Nathalie Gruber for the determination of the X-ray crystal
structures, Roland Graff, Michelle Martigneaux, and Jean-Daniel
Sauer for the high field 1H NMR spectra, and Raymond Hueber
for the FAB mass spectra. We acknowledge the European
Commission for financial support and the French Ministry of
Education for a fellowship to D.P.
Supporting Information Available: Crystal data and the
refinement parameters for both structures. This material is
available free of charge via the Internet at http://pubs.acs.org.
(20) Alford, P. C.; Cook, M. J.; Lewis, A. P.; McAuliffe, G. S. G.; Skarda,
V.; Thomson, A. J.; Glasper, J. L.; Robbins, D. J. J. Chem. Soc., Perkin
Trans. 2 1985, 705-709.
(21) Mabrouk, P. A.; Wrighton, M. S. Inorg. Chem. 1986, 25, 526.
JA011250Y