A rigid molecular scaffold affixing a (polypyridine)ruthenium(II)- and a nickel(II)-containing complex: Spectroscopic evidence for a weakly coupled bichromophoric system

Article abstract of DOI:10.1002/ejic.200200561

The synthesis of DppztBuSalH₂ (7), a rigid conjugated ditopic ligand containing a Dppz (dipyrido[3,2-a:2′,3′-c]phenazine) skeleton and a salophen-type chelate, is reported. The complexes DppztBuSalNi (10), [Ru(bpy)₂(DppztBuSalH₂)]²⁺ (11), and [Ru(bpy)₂(DppztBuSalNi)]²⁺ (12) have been prepared and characterised using common spectroscopic methods. Electrochemical, UV/Vis spectroelectrochemical and EPR studies were conducted on compounds 7, 10, 11, and 12. The singly reduced radical forms of 7 and 10 can be generated electrochemically, with the lone electron located on the low-lying phenazine π*-molecular orbital. Complexes 11 and 12 show several reduction waves and electronic and EPR data obtained for the electrogenerated singly reduced species show them to be closely related to the radical species 7^.- and 10^.-, respectively. The presence of nickel(II) in compound 12 renders the addition of the second electron on the phenazine group reversible. Both 11 and 12 show common features on the cathodic side of their cyclic voltammograms, with reversible one-electron ruthenium-centred oxidation. An additional low-potential reversible oxidation wave is observed for 12, and this is ascribed to oxidation of the nickel(II) ion. The combined spectroscopic data best describe the ruthenium-containing complexes as weakly coupled bichromophoric systems. Photophysical studies attest to the formation of a charge-separated state for 11, whereas a strong quenching is detected for 12. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200200561

FULL PAPER
A Rigid Molecular Scaffold Affixing a (Polypyridine)ruthenium(II)- and a
Nickel(II)-Containing Complex: Spectroscopic Evidence for a Weakly Coupled
Bichromophoric System
[a]
[a]
[a]
[a]
`
´ `
Yann Pellegrin, Katja E. Berg, Genevieve Blondin, Elodie Anxolabehere-Mallart,
Winfried Leibl,[b] and Ally Aukauloo*[a]
Keywords: Ruthenium / Nickel / Polynuclear complexes / Rigid heteroditopic ligands / Redox chemistry / Photophysical
studies
The synthesis of DppztBuSalH2 (7), a rigid conjugated ditopic
ligand containing a Dppz (dipyrido[3,2-a:2Ј,3Ј-c]phenazine)
skeleton and a salophen-type chelate, is reported. The com-
10·−, respectively. The presence of nickel(II) in compound 12
renders the addition of the second electron on the phenazine
group reversible. Both 11 and 12 show common features on
plexes DppztBuSalNi (10), [Ru(bpy)2(DppztBuSalH2)]2+ (11), the cathodic side of their cyclic voltammograms, with revers-
and [Ru(bpy)2(DppztBuSalNi)]2+ (12) have been prepared
and characterised using common spectroscopic methods. low-potential reversible-oxidation wave is observed for 12,
ible one-electron ruthenium-centred oxidation. An additional
Electrochemical, UV/Vis spectroelectrochemical and EPR
studies were conducted on compounds 7, 10, 11, and 12. The
singly reduced radical forms of 7 and 10 can be generated
electrochemically, with the lone electron located on the low-
lying phenazine π*-molecular orbital. Complexes 11 and 12
show several reduction waves and electronic and EPR data
obtained for the electrogenerated singly reduced species
show them to be closely related to the radical species 7·− and
and this is ascribed to oxidation of the nickel(II) ion. The com-
bined spectroscopic data best describe the ruthenium-con-
taining complexes as weakly coupled bichromophoric sys-
tems. Photophysical studies attest to the formation of a
charge-separated state for 11, whereas a strong quenching is
detected for 12.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
(MLCT) bands of [Ru(bpy)32ϩ]; excitation of this complex
at wavelengths corresponding to these bands leads to the
Ruthenium complexes such as [Ru(bpy)32ϩ], which con- formation of the lowest-energy excited state corresponding
tain α,αЈ-diimine ligands, have repeatedly intrigued chemists to [RuIII(bpy)·Ϫ(bpy)2]2ϩ [5]
This energetic excited state has
.
due to their unique photophysical properties.[1] These lum- been exploited to serve both as an electron-transfer reduct-
ophores have been widely used in studies of photochem- ant and an oxidant.[6] In this respect, research on mixed-
ically or electrochemically induced multielectron or energy metal dimetallic systems containing both ruthenium and a
transfers.[2] More recently, a wide variety of complexes bear- first-row transition metal ion was triggered due to their po-
ing the Ru(bpy)32ϩ unit have been designed with the aim of tential in the study of electron transfer[7] and in the develop-
devising a new class of anion and cation sensors.[3] In such ment of novel photocatalysts.[8] At the forefront of this re-
‘‘molecular reconnaissance machines’’ the response is trig- search is the design of suitable ligands capable of coordinat-
gered by a modification of the luminescence and/or electro- ing the ruthenium centre and the transition metal ion. A
chemical properties of the photoactive core in the presence great number of homoditopic ligands and complexes ther-
of the substrate. Molecular switches using this lumophore eof have been synthesised, and electron and energy transfers
take advantage of this fundamental characteristic of the have been studied in relation to the chemical nature of the
[Ru(bpy)32ϩ] core.[4] In general, the recent extensive devel- complexes and the intermetallic separation provided by the
opments in the area of inorganic photochemistry can be spacer.[9] The 2,2Ј-bipyridine ligand has been extensively
credited to the well-known metal-to-ligand charge transfer used as the starting point in the synthesis of a considerable
number of functionalised heterotopic ligands.[10] In most
[a]
´
Laboratoire de Chimie Inorganique, UMR 8613, Universite de
cases however, bipyridine is covalently linked to an ancillary
ligand by a flexible arm. In such systems, the distance be-
tween, and the orientation of, the electron donor and ac-
ceptor, parameters which are essential in electron transfer
studies, are not known precisely.[11] In addition, it has been
shown that photophysical properties are a function of the
Paris-Sud,
91405 Orsay, France
E-mail: aukauloo@icmo.u-psud.fr
[b]
´
´
ˆ
Service de Bioenergetique, CEA Saclay,Bat. 532,
91191 Gif-sur- Yvette CEDEX, France
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
1900
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200200561
Eur. J. Inorg. Chem. 2003, 1900Ϫ1910

A Rigid Molecular Scaffold
FULL PAPER
position of the pendant ligand on the bipyridine moiety.[12]
With these considerations in mind, we have devoted our
attention to the synthesis of rigid conjugated hybrid ligands
capable of holding the two protagonist metal ions with
known intermetallic distances.[13] We report here the syn-
thesis of the novel heteroditopic ligand DppztBuSalH2 (7)
based on the Dppz[14] (dipyrido[3,2-a:2Ј,3Ј-c]phenazine)
skeleton which contains a salophen-type cavity. This ligand
can be viewed as a fused ring system of bipyridine, phena-
zine and salophen.
Scheme 1. Synthetic route for the preparation of the ligand
DppztBuSalH2 (7); conditions: (i) reflux in MeOH; (ii) concd.
H2SO4, room temp., Na2CO3; (iii) reflux in EtOH/HC(OEt)3
The coordinating ability of 7 is demonstrated by the step-
wise metallation of both anchoring sites leading to a new
ruthenium/nickel complex. Electrochemical studies coupled
with UV/Vis/NIR and EPR techniques have been used to
elucidate the redox behaviour and nature of the electro-
cation was necessary prior to use. Bearing in mind the solu-
bility problems encountered with rigid conjugated systems,
we intentionally synthesised the corresponding Schiff base
by condensation of 2 equiv. of 3,5-di-tert-butylsalicylal-
dehyde in the presence of triethyl orthoformate in boiling
ethanol. Selective metallation (Scheme 2) of the different
coordinating sites of 7 was achieved by initially coordi-
generated
species
derived
from
(11)
the
and
complexes
[Ru(bpy)2-
[Ru(bpy)2(DppztBuSalH2)]2ϩ
(DppztBuSalNi)]2ϩ (12). These results have been corrobor-
ated by comparative studies carried out on the unmetallated
ligand 7 and the mononuclear nickel() complex [DppztBu-
SalNi] (10), in which the phenanthroline end of the ligand
is metal-free. The synthesis of this latter complex and the
study of its electronic properties were necessary in order to
shed light on the actual contribution of each chromophore
in the dinuclear ruthenium/nickel complex. The results of
these studies suggest a weakly coupled bichromophoric
complex, and that the ligand participates actively in the
electrochemical processes of the mono- and dinuclear com-
pounds. Finally, results from preliminary photophysical
studies are given.
Results and Discussion
Synthesis
The synthetic pathway for 7 is shown in Scheme 1. Con-
densation of phendione 1 with 1,2-diamino-4,5-bis(p-tosyl-
amino)benzene (2) in refluxing methanol gave 5 in quanti-
tative yield. Deprotection of the tosyl groups was carried
out in concentrated sulfuric acid to give 6 in near quantita-
tive yield. Our synthetic approach leading to 6 differs from
Scheme 2. Selective metallation of DppztBuSalH2; (i) reflux in
MeOH, NH4PF6 (aq); (ii) Ni(acetate)2·4H2O reflux in MeOH,
the one described by Lehn et al[20] in that no further purifi- NH4PF6 (aq)
Eur. J. Inorg. Chem. 2003, 1900Ϫ1910
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A. Aukauloo et al.
FULL PAPER
nating the phenanthroline end to [Ru(bpy)2]2ϩ
.
Infrared Spectra
The salophen cavity of the resulting complex
[Ru(bpy)2(DppztBuSalH2)2ϩ] (11) was easily metallated
using nickel() acetate according to usual procedures.[36]
Compounds 11 and 12 were purified for photophysical
measurements, by chromatography on a neutral alumina
column using dichloromethane/methanol (95:5 and 90:10,
respectively) as eluents, and the desired compounds were
collected as the first major fraction in both cases.
The sequential binding of the different metal ions was
also monitored by infrared spectroscopy. Coordination of
ruthenium was characterised by aliphatic CϪH vibrations
of the tert-butyl groups in the region of 2950 cmϪ1, together
with intense absorption bands at about 1585Ϫ1610 cmϪ1
corresponding to the imino CϭN stretch. Nickel() inser-
tion to yield 12 was indicated by a red shift of about 30
cmϪ1 for the band of the imino groups.[24]
The synthetic pathway for 7 is shown in Scheme 1.
A different synthetic strategy was required to prepare
[DppztBuSalNi] (10), the complex containing NiII in the
salophenic cavity (see Scheme 3). Direct complexation of
the salophenic cavity was discarded as it results in the for-
mation of polynuclear NiII complexes and purification of
the mixture was arduous and gave only low yields. As an
alternative we used the well-known template synthesis to
prepare the NiII complex 8 in almost quantitative yield.[21]
Reduction of the nitro groups was carried out under hydro-
gen in the presence of Pd/C as catalyst. Complex 10 was
synthesised in good yield following the condensation of the
diamino derivative 9 with phendione 1 in refluxing meth-
anol.
Mass Spectrometry
Mass spectra of the ruthenium complexes 11 and 12 were
obtained by Electrospray Ionisation Mass Spectrometry.
Parent ion peaks minus one or two accompanying anions
were detected. In both cases, the doubly charged species
appeared as the major peak. The experimental and the
simulated spectra for the doubly charged complex [12 Ϫ 2
PF6]2ϩ are given in Figure 1.
UV/Vis Spectroscopy
The absorption spectra of 7, 10, 11 and 12 in CH2Cl2 are
shown in Figure 2, and the absorption maxima together
with their extinction coefficients given in Table 1. Figure 2
1H NMR Spectra
1H NMR spectroscopy was used to monitor the stepwise (a) shows the electronic perturbation that occurs upon met-
metallation of 7. Attachment of the NϪN chelating site of allation of the salophenic N2O2 cavity of 7 with NiII. Strong
the phenanthroline end to the diamagnetic RuII showed, as π-π* transitions at 310 and 430 nm characterise the ex-
expected, a downfield shift of the phenanthroline protons tended delocalised π-system of the DppztBuSalH2 skeleton.
and certain bipyridine protons.[22Ϫ23] This phenomenon was Spectral modifications for the mononuclear NiII complex
even more pronounced when the NiII ion was bound in the are noticed in both the high- and low-energy regions com-
tetracoordinating salophen cavity, with a downfield shift of pared to the free ligand. The prominent feature is the
as much as δ ϭ 0.95 ppm for the signal of the imine hydro- MLCT band at 500 nm typical of NiϪsalophen complexes.
gen atoms. Evidence for the coordination of nickel() to the The dissymmetric nature of this band may suggest the pres-
salophen cavity was also obtained from 1H NMR spec- ence of π-π* intra-ligand transitions which undergo a ba-
troscopy, with loss of the signal from the phenol protons.
thochromic shift relative to that of the free ligand. This shift
Scheme 3. Synthetic steps for DppztBuSalNi (10); (i) NiCl2·6H2O, reflux in dry ethanol/HC(OEt)3; (ii) H2 40 atm, Pd/C in MeOH;
(iii) reflux in MeOH
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A Rigid Molecular Scaffold
FULL PAPER
Figure 2. Absorption spectra in CH2Cl2; a) DppztBuSalH2 (7)
(solid line) and DppztBuSalNi (10) (dotted line); b) spectra of
[Ru(bpy)2DppztBuSalH2]2ϩ
(11)
(solid
line)
and
[Ru(bpy)2DppztBuSalNi]2ϩ (12) (dotted line)
Figure 1. ESI-MS of [Ru(bpy)2DppztBuSalNi]2ϩ (12); (a) exper-
pled from the metal t2g-type orbitals[26] due to the nearly
non-existent orbital contribution from the nitrogen atoms
of the coordinating imino groups. Hence, the optical
properties of 11 suggest a bichromophoric character for the
complex. Metallation of the salophen cavity with NiII in-
duces a significant change in the appearance of the elec-
tronic absorption spectrum as shown in Figure 2 (b). The
position and intensity of the π-π* transitions due to the
bpy moieties are almost unaffected. A series of three bands
between 320 and 380 nm, probably originating from intra-
ligand π-π* transitions together with charge transfer tran-
sitions from NiII to the ligand, is observed. This expla-
nation is supported by the observation of these bands in
the spectrum of complex 10. Ruthenium charge transfer
transitions towards π*-orbitals of the ligands are detected
as a shoulder at 460 nm on a more intense MLCT band
from the salophenϪNi part of the dinuclear Ru/Ni complex
12. The observation of a weak band at ca. 620 nm, charac-
teristic of a d-d transition for a d8 square-planar NiII com-
plex, provides further evidence for metallation of the sal-
ophen cavity.
imental and (b) simulated spectrum
can be attributed to a diminution of the HOMOϪLUMO
gap upon metallation. The weak absorption band observed
at the base of the MLCT transition at 620 nm corresponds
to a d-d transition for NiII sitting in a square-planar coordi-
nation site.[25]
UV/Vis spectra of 11 and 12 are depicted in Figure 2 (b).
The electronic absorption spectrum of 11 contains spectral
features due to both [Ru(bpy)3]2ϩ and DppztBuSalH2. Two
intense bands are observed at higher energy, one for the
usual intense spin-allowed ligand-centred transitions of the
bpy ligands at 290 nm characteristic of (polypyridine)-
ruthenium complexes[1,5] and a band at 325 nm attributed to
intra-ligand transitions of 7. A broad, asymmetric absorp-
tion band extending from 390 to 550 nm is accounted for by
the superposition of low-energy π-π* intra-DppztBuSalH2-
ligand transitions and an admixture of dπ(Ru)-π*(bpy) to-
gether with dπ(Ru)-π* (bpyЈ) (where bpyЈ denotes the bi-
pyridine moiety of the ligand 7) MLCT transitions. This
agrees with previous findings for (polypyridine)rutheniu-
m() complexes containing extended delocalised π-systems,
where it has been shown that the low-lying orbitals confined
Spectroelectrochemical Properties and EPR Spectroscopy
Electrochemical studies on [Ru(diimine)32ϩ] complexes
on the central part of the rigid aromatic ligand are decou- are widely used to characterise the π*-orbital energies of
Table 1. UV/Vis/NIR data for DppztBuSalH2 (7), DppztBuSalNi (10), [Ru(bpy)2DppztBuSalH2]2ϩ (11) and [Ru(bpy)2DppztBuSalNi]2ϩ
(12)
λ [nm] (ε [10Ϫ3 L·molϪ1·cmϪ1])
DppztBuSalH2 (7)
250 (38.4)
245 (54.6)
240 (94.4)
245 (116)
260 (38.7)
265 (55.7)
290 (145)
290 (172)
265 sh
330 (49)
325 sh
310 (36.3)
340 (48.8)
445 (63.1)
340 (85.1)
325 (39.1)
375 (28.6)
465 sh
345 sh
430 sh
430 (35.8)
500 (42.8)
DppztBuSalNi (10)
[Ru(bpy)2(DppztBuSalH2)]2ϩ (11)
[Ru(bpy)2(DppztBuSalNi)]2ϩ (12)
320 (99.1)
380 (68.6)
455 sh
535 (97.3)
620 sh
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A. Aukauloo et al.
FULL PAPER
Table 2. Half-wave potentials E for the oxidation (niE) and the reduction (nE) of DppztBuSalH2 (7), [DppztBuSalNi] (10),
[Ru(bpy)2DppztBuSalH2]2ϩ (11) and [Ru(bpy)2DppztBuSalNi]2ϩ (12) (from cyclic voltammetry at 100 mV/s; E ϭ 1/2(Epa ϩ Epc) in V
vs. SCE in the presence of TBAClO4)
VE
IVE
IIIE
IIE
IE
iE
iiE
iiiE
DppztBuSalH2 (7)[a]
Ϫ1.40[b]
Ϫ1.43[b]
Ϫ1.45
Ϫ1.11
Ϫ0.99
Ϫ0.88
Ϫ0.81
ϩ1.18
ϩ1.13
ϩ1.26[c]
ϩ1.07
ϩ1.29[c]
ϩ1.58[c]
[DppztBuSalNi] (10)[a]
[Ru(bpy)2(DppztBuSalH2)]2ϩ (11)[d]
[Ru(bpy)2(DppztBuSalNi)]2ϩ (12)[d]
Ϫ2.0[b]
Ϫ1.64
Ϫ1.63
Ϫ1.44
ϩ1.43[e]
ϩ1.29[c]
Ϫ1.88[b]
Ϫ1.27
ϩ1.42[e]
[a]
[b]
[c]
[d]
Measured in dichloromethane. Measured in acetonitrile. Partly irreversible step, cathodic peak given. Irreversible step, anodic
[e]
peac given. Adsorption and desorption phenomena observed under our experimental conditions, anodic peak given.
Table 3. UV/Vis/NIR data for the electrogenerated species (from spectroelectrochemistry)
λ [nm] (ε [10Ϫ3 L·molϪ1·mϪ1])
·Ϫ
DppztBuSalH2 (7·؊
)
300 (32.5) 381 (32.4) 455 (18.1) 545 sh
308 (36.3) 326 (35.8) 372 (42.4) 390 sh
245 (95.4) 291 (145) 382 (73.8) 470 (56.2) 550 sh 750 (14.7) 880 sh
244 (135) 289 (169) 353 (79) 388 (82.3) 475 sh 515 (80) 622 sh
750 sh 840 (10)
490 sh 517 (38.1) 613 (10.5) 820 sh 917 (17.1)
[DppztBuSalNi]·Ϫ (10·؊
[Ru(bpy)2(DppztBuSalH2)].ϩ (11·؉
[Ru(bpy)2(DppztBuSalNi)]·ϩ (12·؉
)
)
)
800 sh 865 (23.4)
the ligands linked to RuII. In addition, the redox potential cyclic voltammetry (CV) and these data are summarised in
of the RuIII/II metal centre gives, in general, a clear indi- Table 2. Electronic data for the electrochemically generated
cation of the nature of the interaction with the coordinated species are given in Table 3. In what follows, we analyse
ligands. Furthermore, electrochemical data coupled with the electrochemical behaviour of 7 and 10 and discuss the
other spectroscopic information are currently used to spectroscopic characterisation of the electrogenerated spec-
rationalise the modifications in the absorption and emission ies. These results are then correlated to the RuII-contain-
spectra of [Ru(diimine)32ϩ] derivatives.[1b,14c,27] The electro- ing complexes.
chemical properties of 7, 10, 11 and 12 were investigated by
Ligand DppztBuSalH2 (7) and Complex [DppztBuSalNi]
(10)
The cyclic voltammograms of the free ligand 7 and its
NiII complex 10 are shown in Figure 3 (a). Owing to the
poor solubility of these species in acetonitrile, cyclic vol-
tammograms of 7 and 10 were run in dry dichloromethane.
Two waves are observed upon reduction of 7, one reversible
and a second quasi-irreversible at Ϫ1.1 and Ϫ1.39 V vs.
SCE, respectively. The reversible one-electron reduction
wave at Ϫ1.1 V falls in the range of potentials typical for
phenazine-containing moieties.[27] No reversible waves are
observed upon oxidation, even when scanning up to ϩ1.7
V. However, two consecutive poorly resolved waves at ϩ1.18
and ϩ1.29 V vs. SCE are attributed to oxidation of the
phenol groups. Compared to the first reduction of Dppz,
an anodic shift of about 100 mV indicates the uptake of the
first electron by the ‘‘modified’’ phenazine framework
which contains imino π-accepting groups. The second elec-
tron addition occurs at a more positive potential than that
of Dppz [Ϫ1.4 vs. Ϫ2.0 V (SCE), respectively]. The fact that
salophen lacks a reduction wave within this potential range
clearly implies that this electron-transfer process involves
Figure 3. Cyclic voltammograms in CH2Cl2 (10Ϫ3  solutions,
the phenazine part of the ligand. As reported earlier, the
doubly reduced form of the Dppz ligand leads to a con-
siderable increase in charge at the nitrogen atoms, thus en-
hancing its protonation aptitude. In the case of 7, the same
phenomenon will be occurring and this explains the flat-
room temperature, sweep rate 100 mV·sϪ1, Ag/AgClO4 electrode as
reference, 0.1  TBAClO4 as supporting electrolyte); a) DppztBuS-
alH2 (7) (dotted line) and DppztBuSalNi (10) (solid line); b)
[Ru(bpy)2DppztBuSalH2]2ϩ
(11)
(solid
line)
and
[Ru(bpy)2DppztBuSalNi]2ϩ (12) (dotted line)
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Eur. J. Inorg. Chem. 2003, 1900Ϫ1910

A Rigid Molecular Scaffold
FULL PAPER
tened nature of the corresponding anodic peak.[28] Redox electrochemical study, showing the reversible nature of this
properties of 10 are illustrated in Figure 3 (a, solid line); in electron-transfer process under our experimental con-
comparison to 7 only minor changes are observed upon ditions. The singly reduced species was also generated by a
reduction. A shift of about 120 mV towards less negative controlled potential bulk electrolysis at Ϫ30 °C. The EPR
potential is noticed for the first reversible reduction wave. spectrum of the electrolysed solution showed an isotropic
The increased ease of reduction of the nickel() complex signal at g ϭ 2.007, indicating the presence of an organic
confirms the lowering in energy of the ligand LUMO upon radical species with a peak to trough line width of 0.75 mT.
metallation. In contrast to the ligand, a reversible oxidation In contrast to the paramagnetic singly reduced Dppz spec-
wave is observed at ϩ1.13 V vs. SCE, which is attributed to ies, where well-resolved EPR signals have been observed,[27]
the formation of a nickel() complex. Such a potential is the smooth EPR signal registered for 7·؊ confirms the de-
consistent with the NiIII/II redox couple of NiϪsalophen.[29] localisation of the electron on a more delocalised π-system,
Spectroelectrochemical studies were carried out to inves- hence resulting in the interaction of the single electron with
tigate the stability and the spectroscopic signatures of elec- a larger number of nuclear spins.
troreduced 7 and 10 after the first reduction wave. UV/Vis/
The spectroelectrochemical behaviour of 10 was moni-
NIR spectral changes of 7 and 10 were monitored at room tored using identical techniques as for 7. The changes in the
temperature by using a thin-layer cell in dry dichlorometh- electronic spectrum of 10 upon the addition of one electron
ane in the presence of 0.1  TBAPF6 at Ϫ1.2 and Ϫ1.0 V, are similar to those of 7, at least in the low-energy region.
respectively. The electronic response of 7 is strongly modi- However, the maxima of these broad bands are shifted to
fied upon addition of the first electron, as shown in Fig- lower wavenumbers (ca. 1040 cmϪ1) indicating a smaller en-
ure 4 (a). New high-intensity broad bands spanning the ergy difference between the HOMO and LUMO when NiII
range 600Ϫ950 nm and another broad band at 380 nm are is inserted into the N2O2 coordinating cavity. These absorp-
observed. These new spectral features are also found for tion bands resemble those observed for the monoanion rad-
singly reduced phenazine-containing compounds.[27] The ical of 7 which favours localisation of the added electron on
double-hump band observed for DppzϪ (547 and 570 nm) the phenazine part of the metallo complex. No substantial
is shifted to lower energy for 7·؊ with the maxima at 765 change in the d-d transition of the NiII centre at 620 nm
and 840 nm, indicating that the unpaired electron is local- is observed, but this band becomes more apparent in the
ised on a more extended π-system.
electrolysed species. The one-electron process for this re-
duction wave was confirmed by bulk electrolysis at a con-
trolled potential, and a reverse cyclic voltammogram on the
electrolysed solution indicates the presence of only one
species at the same potential as the initial complex. The
frozen solution EPR spectrum of the electrolysed com-
pound is shown in Figure 5. The signal is slightly aniso-
tropic and is best simulated with values of gЌ ϭ 2.0055 and
g// ϭ 2.0012. This weak anisotropy can be explained by a
partial delocalisation of the lone electron in a dπ-type or-
bital of the nickel centre.[30] The lack of hyperfine coupling
is most probably due to extensive overlap of a large number
of signals with small EPR coupling constants, resulting
from interaction with neighbouring atoms.
Figure 4. Electronic absorption spectra upon electrolysis at con-
trolled potential in CH2Cl2 (10Ϫ3  solutions, room temperature,
SCE as reference, 0.1  TBAClO4 as supporting electrolyte); a)
DppztBuSalH2 (7) upon reduction at Ϫ1.3 V/SCE; b)
[Ru(bpy)2DppztBuSalNi]2ϩ (12) upon reduction at Ϫ 0.96 V/SCE
The complete recovery of the initial spectrum upon reoxi-
dation, together with the observation of several isosbestic
points (265, 350, 405 and 450 nm), confirmed the presence
of only two species in equilibrium at all times during the
Figure 5. EPR spectra of [DppztBuSalNi]·Ϫ (10·؊) at 100 K after
bulk electrolysis at Ϫ1.2 V vs. SCE in dry dichloromethane and
TBAClO4 as supporting electrolyte
Eur. J. Inorg. Chem. 2003, 1900Ϫ1910
www.eurjic.org
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1905

A. Aukauloo et al.
FULL PAPER
Singly Reduced Forms of [Ru(bpy)2DppztBuSalH2]2؉ (11)
and [Ru(bpy)2DppztBuSalNi]2؉ (12)
[Ru(bpy)2DppztBuSalH2]2؉ and [Ru(bpy)2DppztBuSalNi]2؉
Complexes
The first reduction potential for 11 occurs at Ϫ0.99 V
Electrochemical properties of the ruthenium-containing
complexes have been studied in both dichloromethane and
acetonitrile in the presence of 0.1  TBAP as supporting
electrolyte, and the corresponding data are given in Table 2.
Electrochemical studies of [Ru(diimine)32ϩ] complexes are
indeed crucial in evaluating the relative energy of the ligand
π*-orbitals, especially for heteroleptic complexes, and also
the nature of the interactions of the ligands with the metal
centre. The first reductive process for the metal complex is
often informative regarding the energy levels of the π*-or-
bitals of the ligands linked to the ruthenium() ion, whereas
the first oxidation process is indicative of the metal t2g-or-
bital energy. However, this is only true if the processes of
reduction and oxidation are as in Equations 1 and 2, respec-
tively.[31]
which is very close to that of the free ligand under the same
I
conditions (Ϫ1.11 V) [IE(complex) Ϫ E(ligand) ϭ 0.12
V].[26,27] This implies that the coordination of ligand 7 to
the RuII ion has little influence on the uptake of the first
electron. Another way to describe this result is to consider
that the singly occupied molecular orbital (SOMO) is devel-
oped mainly on the phenazine together with the bis(salicyli-
dene)diimine framework. Moreover, the displacement of
this wave to a more positive potential can be related to the
dipositive charge of the complex of ligand 7. Spectroelectro-
chemically, the uptake of the first electron is characterised
by the growth of intense bands in the region of 600 to
950 nm and at 380 nm, attributable to the coordinated
DppztBuSalH2. Similarly to 7, a fall in intensity of the π-
π* intra-ligand charge-transfer transitions at 325 and
440 nm for 11 also underpins the proposed site of re-
duction. In addition, no alteration in either the RuII to bpy
MLCT transitions at about 460 nm or the internal tran-
sition of the bound bpy ligands in their neutral form at
290 nm is observed, thus providing further evidence for the
reduction site.[32]
[MIIL3]2ϩ ϩ eϪ Ǟ [MIIL2(L·Ϫ)]ϩ
[MIIL3]2ϩ Ǟ [MIIIL3]3ϩ ϩ eϪ
(1)
(2)
EPR of a frozen solution of the singly reduced complex
Cyclic voltammograms of 11 and 12 are given in Figure 3 11·؉ generated electrochemically showed an isotropic signal
(b). The electrochemical behaviours of 11 and 12 may be with a g factor of 2.007. The negligible change in the ob-
regarded as the superposition of each of 7 and 10 together served g values for the free ligand 7·؊ and the ruthenium
with the [Ru(bpy)32ϩ] chromophore, respectively. On the ca- complex 11·؉ reflects the feeble interaction of the unpaired
thodic side of the CV of 11, both reduction waves for the electron with the metal ion. It should be noted that the
ligands are observed at Ϫ0.89 and Ϫ1.3 V vs. SCE, fol- observed g values for other [Ru(bpy)2(L·Ϫ)]2ϩ species, where
lowed by the sequential addition of one electron to the bi- L is a diimine-type ligand, deviate markedly from the g
pyridine co-ligands. The oxidation wave for the RuIII/II cou- value of the metal-free ligand anion radical; this is mainly
ple is observed at ϩ1.4 V vs. SCE and is probably masking due to a strong interaction of the unpaired electron with
the oxidation wave for the phenol groups. The fact that the the RuII ion.[33] Thus, the EPR spectrum of 11·؉ is consist-
oxidation potential for the RuII ion remains unchanged ent with the single electron being confined to a molecular
when compared to [Ru(bpy)32ϩ] supports the idea that the orbital located predominantly on part of the ligand skel-
phenazine moiety together with the bis(salicylidene)diimine eton, with a weak contribution from the RuII centre and
groups have very little electronic influence on the metal cen- the ligating diimine part of the corresponding ligand. As
tre. One can thus envision [Ru(bpy)2DppztBuSalH2]2ϩ as observed in the case of the radical species of the free ligand,
consisting of two chromophores with little electronic com- no hyperfine structure is observed for 11·؉, probably for the
munication between them. Complex 12 displays similar same reason as mentioned above.
electrochemical behaviour; an almost identical pattern is
observed on the cathodic part of the CV while on oxidation,
a reversible wave is observed at ϩ1.07 V vs. SCE followed
by another wave at 1.42 V vs. SCE corresponding to oxi-
dation of the phenol group, which is detected as a shoulder
on the oxidation wave for the RuIII/II couple. It should be
noted that, when scanning up to 1.8 and 1.7 V for 11 and
12, respectively, we observed irreversible cathodic waves at
0.28 V for 11 and 0.37, 0.70 and 0.86 V for compound 12.
These waves probably originate from chemically altered
species as no such waves are present when scanning to a
potential just beyond the RuIII/II couple. The intensities of
the corresponding waves for the RuIII/II couple suggest that
adsorption and desorption phenomena are taking place at
the surface of the vitreous carbon electrodes.
The electrochemical response of 12 in acetonitrile is given
in Figure 3 (b). Five reversible one-electron reduction waves
at room temperature are observed in the potential range
scanned. Of particular interest is the approximately 200 mV
shift of the first reduction wave to more positive potential
relative to 11 and 10. Such a shift of the redox potential
clearly denotes the stabilisation of the LUMO predomi-
nantly localised on the phenazine skeleton of the spacer li-
gand 7.[34] The change in the electronic spectrum of 12 upon
addition of one electron is shown in Figure 4 (b). The singly
reduced species is characterised by the same bands in the
low-energy region as those already observed for compounds
7, 10 and 11 for the same electron transfer process. The
spectral modification of 12 is closely related to that of 10,
again confirming the same position for the unpaired elec-
1906
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Eur. J. Inorg. Chem. 2003, 1900Ϫ1910

A Rigid Molecular Scaffold
FULL PAPER
tron of the heterodimetallic complex. No appreciable alter- tuplet at higher magnetic field is the fingerprint of a six-
ation of the π-π* transition of the chelated bipyridine moi- coordinate NiIII species, with two pyridine rings in axial
eties at 290 nm is observed, and the RuII-to-ligand charge- positions and an axial repartition of the spin density on the
transfer transitions at 460 nm are present as shoulders on NiIII centre.
the pronounced MLCT transitions of the NiϪsalophen
chromophore. Decisive spectroscopic characterisation of
the first reduction process comes from the EPR spectrum
of an electrolysed solution of 12. An isotropic signal with a
g factor of 2.013 and a line-to-line width of 0.75 mT typical
of a radical species was detected. Here too, no hyperfine
coupling is apparent. An interesting feature in the CV of 12
is the presence of a second reversible wave at Ϫ1.27 V (in
acetonitrile vs. SCE). While no apparent shift has been de-
tected for the second wave of 7 upon metallation of only
one end of the heterotopic ligand (i.e. for compounds 10
and 11), a marked displacement of about 260 mV to more
anodic potential is observed in the case of the dimetallic
complex. The more reversible nature of the uptake of the
second electron on the bridging ligand reflects the gain in
stability of the doubly reduced species in the case where
both ends of the ligand contain a divalent ion.
Figure 6. EPR spectrum of [Ru(bpy)2DppztBuSalNi]3ϩ (123ϩ) at
15 K, generated by electrolysis at 1.11 V/SCE in dry degassed
acetonitrile and 0.1  TBAClO4 as supporting salt in the presence
of pyridine (solid line); the dotted line shows the simulated spec-
trum
Singly Oxidised Form of 12
The RuII/NiII complex exhibits three oxidation waves in
the positive potential region at ϩ1.07, ϩ1.29 and ϩ1.42 V
vs. SCE, respectively. When compared to the first oxidation
process of 10, where only the salophen cavity is occupied
by NiII, a small cathodic shift of ca. 60 mV is noted. The
observed potential falls within the range expected for the
NiIII/II couple of a salophen-type complex. Even the small
shift observed for 12 is surprising, as a more positive poten-
tial for the oxidation of the NiII centre would be expected
for this dicationic complex.[29] We tentatively rationalise this
observation by noting the more π-accepting character of
the bridging ligand when both extremities of the latter are
metallated. Hence, a stronger ligand field is exerted on the
NiII centre, thereby enhancing its propensity to oxidise. Few
changes were observed spectroelectrochemically upon the
removal of the first electron. The frozen-solution X-band
EPR spectrum of the electrochemically generated RuII/NiIII
complex at 15 K shows a rhombic symmetry, with a large g
tensor anisotropy (gx ϭ 2.289, gy ϭ 2.232, gz ϭ 2.022),
which is commonly observed for NiIII complexes in sal-
ophen-type environments.[29] Upon addition of degassed
pyridine to the electrolysed solution and subsequent freez-
ing, we obtained the EPR spectrum shown in Figure 6. The
new adduct still exhibits a rhombic-type spectrum with
superhyperfine couplings in all g regions. The best agree-
ment between the experimental spectrum and the simulated
Preliminary Photophysical Studies
Upon excitation of the mononuclear ruthenium complex
11 at 532 nm (MLCT RuIIǞbipyridine moiety) in degassed
ethanol at room temperature, fluorescence emission was ob-
served around 610 nm. The observed fluorescence lifetime
(minor of 40 ps is much shorter than that of [Ru(bpy)32ϩ],
which indicates rapid quenching of the excited state. Time-
resolved absorption spectroscopy revealed that the transient
species generated by photoexcitation at 532 nm displays an
absorption at around 820 nm, a wavelength similar to that
of the electrochemically singly reduced [Ru(bpy)2-
(DppztBusalH2·Ϫ)]2ϩ species (Figure 4, a). This is a strong
indication that the quenching of the excited state is due to
internal photoinduced electron transfer, probably forming
·Ϫ 2ϩ
the charge-separated state RuIII(bpy)2(DppztBusalH2
) .
The lifetime observed for this transient species was about
400 ns. In contrast, the dinuclear complex 12 exhibits a very
efficient quenching of the excited state which is not ac-
companied by absorption changes in the near infrared. The
most likely explanation is that fast energy transfer to the
NiII ion occurs in this complex where the excited state is
efficiently quenched before internal charge separation can
occur. We are currently investigating the photophysical
behaviour of 10 and 12 in more detail.
one was obtained using the following parameters: gx
ϭ
,
2.1986, gy ϭ 2.1645, gz ϭ 2.0265; Ax ϭ 16.34 ϫ 10Ϫ4 cmϪ1
Ay ϭ 16.10 ϫ 10Ϫ4 cmϪ1, Az ϭ 20.43 ϫ 10Ϫ4 cmϪ1. Simu-
lation was realised using a Gaussian profile and line widths
of 0.8, 0.7 and 0.6 mT for the x, y and z peaks, respectively.
In addition, a signal at g ϭ 2.0038 was detected, and attri-
Conclusion
Based on the X-ray structure of 10[35] an approximate
buted to the phenoxyl radical generated during the elec- distance of 12.5 A between the Ru and NiII ions is ex-
trolysis, due to the close proximity of the two oxidation pected. This separation thus falls within the desired dis-
waves (NiIII/NiII and PhO·ϩ/PhO). The well-resolved quin- tance for electron or energy transfer studies in these model
II
˚
Eur. J. Inorg. Chem. 2003, 1900Ϫ1910
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1907

A. Aukauloo et al.
FULL PAPER
Synthesis of 11,12-Bis(p-tosylamino)dipyrido[3,2-a:2Ј,3Ј-c]phenazine
(5): 1,2-diamino-4,5-bis(p-tosylamino)benzene (2) (2.23 g, 5 mmol)
was added to a suspension of phendione (1) (1.55 g, 5 mmol) in
methanol (50 mL) , and the mixture was refluxed for 1 h. The hot
suspension was filtered while hot to give a beige solid which was
washed with cold methanol and dried under vacuum. Yield: 2.92 g
(94%). IR: ν˜ ϭ 3436 (NϪH), 3034, 2820 (CϪH), 1619 (CϭN), 1580
complexes. Spectroelectrochemical studies suggest a weak
electronic coupling between the different chromophores in
our system, a prerequisite in the design of supramolecular
systems containing a photoactive site. We believe that our
approach to building novel heteroditopic ligands will be a
source of inspiration for the synthesis of novel ancillary li-
gands on anchoring molecules such as phenanthroline.
1
(CϭN) cmϪ1. H NMR ([D6]DMSO): δ ϭ 9.48 (d, 2 H), 9.16 (d,
2 H), 7.93 (dd, 2 H), 7.86 (s, 2 H), 7.78 (d, 2 H), 7.36 (d, 2 H), 2.28
(s, 6 H) ppm. C32H24N6O4S2 (620.7): calcd. C 61.92, H 3.90, N
13.54; found C 61.88, H 3.82, N 13.42.
Experimental Section
Synthesis of 11,12-Diaminodipyrido[3,2-a:2Ј,3Јc]phenazine (6): De-
protection of the tosyl group was achieved by treating 5 (1.24 g,
2 mmol) with concentrated sulfuric acid (10 mL) at room tempera-
ture for 4 h. The deep violet solution was then added dropwise to
ice-cold water and the brown solid was filtered off. After treatment
with a concentrated solution of sodium carbonate (20 mL), the yel-
low solid was collected by filtration and washed with the minimum
amount of water. The compound was then dried under vacuum.
General: Electrochemical measurements were performed with an
EGG PAR (model 273A) electrochemical workstation. The sol-
vents were distilled under nitrogen in the presence of dry calcium
chloride and the solution [1 mmol·LϪ1 for complexes and ligand
and 0.1 mol·LϪ1 of tetrabutylammonium perchlorate (TBAClO4)]
introduced within an argon-purged heart-shaped cell. Cyclic vol-
tammetry was performed using a glassy carbon electrode (3 mm in
diameter) as the working electrode, a platinum grid as the counter
electrode and an Ag/AgClO4 (0.01 ) electrode in acetonitrile as
the reference (Eref ϭ 0.3 V/ECS). Electrolyses were carried out at
controlled potentials in a three-electrode cell, using a platinum
gauze as the working electrode, a platinum grid as the counter elec-
trode and an Ag/AgClO4 (0.01 ) electrode in acetonitrile as the
reference. Low-temperature electrolyses were run using 0.2  TBA-
ClO4. UV/Vis/NIR spectra were obtained using 1-cm quartz cells
with a Varian Cary 5E spectrophotometer (200Ϫ1500 nm). Spec-
troelectrochemical data were obtained by a combination of a three-
electrode thin cell (0.5 mm) mounted in a UV/Vis/NIR spectropho-
tometer. IR spectra were obtained with a PerkinϪElmer 1000 spec-
trometer, using KBr matrix pellets. NMR spectra were obtained
using Bruker AC 200 (200 MHz) and AC 250 (250 MHz) spec-
trometers. The solvents used were CDCl3 or [D6]DMSO. EPR spec-
tra were recorded with an X-band Elexsys (Bruker) spectrometer
at 15, 77 or 100 K. Elemental analyses were carried out at the Ser-
vices de Microanalyse, ICSN-CNRS, Gif-sur-Yvette. Mass spectra
were recorded with a Finnigan Mat Mat95S in a BE configuration
at low resolution. Flash-absorption and fluorescence transients
were measured with setups of local design. All measurements were
taken at 296 K. For absorption transients the measuring light was
provided by a 150-W tungsten-halogen lamp, and the wavelength
was selected with interference filters placed before and after the 10
ϫ 1 mm sealed cuvette containing the sample. The sample was ex-
cited at 90° to the measuring beam by a flash from a frequency-
doubled Nd:YAG laser (532 nm, duration 5 ns, ca. 2 mJ/cm2; Sure-
light, Continuum). Absorbance changes were detected with a sili-
con photodiode and signals were amplified by a wideband pre-
amplifier (model 5185, EG&G) before they were recorded by a digi-
tal oscilloscope (TDS, 744A, Tektronix). For fluorescence transi-
1
Yield: 0.54 g (86%). IR: ν˜ ϭ 3390 (NϪH), 1630 (CϭN) cmϪ1. H
NMR ([D6]DMSO): δ ϭ 7.84 (d, 2 H), 7.63 (d, 2 H), 7.27 (dd, 2
H), 7.15 (s, 2 H), 6.33 (s, 4 H) ppm. C18H12N6 (312.33): calcd. C
69.22, H 3.87, N 26.91; found C 69.17, H 4.01, N 26.75.
Synthesis of DppztBuSalH2 (7): The diamino derivative 6 (94 mg,
0.3 mmol) and 3,5-di-tert-butylsalicylaldehyde (3) (188 mg,
0.8 mmol) were suspended in dry ethanol (30 mL) together with a
few drops of triethyl orthoformate. The mixture was heated under
reflux for 2 h and the yellow precipitate was separated by filtration.
The solid was washed with diethyl ether and dried under vacuum.
Yield: 192 mg (86%). IR: ν˜ ϭ 2950Ϫ2905 (CϪH, aliph), 1610 (Cϭ
N) cmϪ1.1H NMR (CDCl3): δ ϭ 13.26 (s, 2 H), 9.63 (dd, 2 H),
9.30 (dd, 2 H), 8.93 (s, 2 H), 8.07 (s, 2 H), 7.82 (dd, 2 H), 7.54 (d,
2 H), 7.35 (d, 2 H), 1.48 (s, 18 H), 1.37 (s, 18 H) ppm. C48H52N6O2
(744.97): calcd. C 77.39, H 7.04, N 11.28; found C 77.12, H 7.17,
N 11.36.
Synthesis of [DNtBuSalNi] (8): A solution of NiCl2·6H2O (0.480 g,
2 mmol) in ethanol (10 mL) was added to a solution containing
4,5-diamino-1,2-dinitrobenzene (4) (396 mg, 2 mmol) and 3,5-di-
tert-butylsalicylaldehyde (3) (936 mg, 4 mmol) in ethanol (100 mL).
The resulting mixture was then heated to reflux with constant stir-
ring for 2 h. The dark precipitate was then filtered off, washed with
ethanol and dried under vacuum. Yield: 1.1 g (80%). IR (KBr): ν˜ ϭ
1
2955 (aliphatic CH), 1619 (CϭN), 1358 and 1338 cmϪ1 (NO2). H
NMR (CDCl3): δ ϭ 8.23 (s, 2 H), 8.21 (s, 2 H), 7.48 (d, 2 H), 7.14
(d, 2 H), 1.43 (s, 9 H), 1.30 (s, 9 H) ppm. C36H46N4NiO7·H2O
(705.47): calcd. C 61.29, H 6.57, N 7.94; found C 60.96, H 6.62,
N 7.89.
ents, excitation was achieved by a flash from a frequency-doubled Synthesis of [DAtBuSalNi) (9): A slurry of compound 8 (690 mg,
picosecond Nd:YAG laser (532 nm, duration 25 ps, ca. 300 µJ/cm2;
Continuum). The detection wavelength was selected by an inter-
1 mmol) and Pd/C (10%, 100 mg) in dry THF was maintained un-
der hydrogen (40 bar) with stirring for 12 h. The mixture was fil-
ference filter centred at 610 nm and signals were detected with a tered through a bed of Celite and then washed twice with THF (2
microchannel plate photomultiplier tube (R2566 U, Hamamatsu)
and a 7-GHz digitising oscilloscope (IN7000, Intertechnique). Ru-
ϫ 40 mL). The solvents were removed under reduced pressure and
the red solid was sonicated in cold methanol (10 mL). The residue
thenium trichloride was purchased from the Aldrich Chemical was filtered off, washed with the minimum amount of methanol
Company. 2,2Ј-Bipyridine (bpy) and 1,10-phenanthroline (phen)
were obtained from the Janssen Chemical Company. 1,10-Phen-
anthroline-5,6-dione (phendione, 1),[15] 1,2-diamino-4,5-bis(p-tolu-
and dried under vacuum. Yield: 440 mg. (70%). IR (KBr): ν˜ ϭ 3330
(NH), 2950 (aliphatic CH), 1614Ϫ1596 cmϪ1 (CϭN). 1H NMR
(CDCl3): δ ϭ 7.88 (s, 2 H), 7.34 (d, 2 H), 7.02 (d, 2 H), 6.95 (s, 2
enesulfamido)benzene (2),[16] 3,5-di-tert-butylsalicylaldehyde (3),[17] H), 3.49 (s, 4 H), 1.43 (s, 9 H), 1.37 (s, 9 H) ppm. C36H48N4NiO2
4,5-diamino-1,2-dinitrobenzene (4),[18] and [Ru(bpy)2Cl2][19] were
synthesised as described in the literature.
(627.49): calcd. C 68.91, H 7.71, N 8.93; found C 69.16, H 7.84,
N 8.77.
1908
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Eur. J. Inorg. Chem. 2003, 1900Ϫ1910

A Rigid Molecular Scaffold
FULL PAPER
Synthesis of DppztBuSalNi (10): A slurry of compound 9 (628 mg,
1 mmol) in methanol (30 mL) was added dropwise to a refluxing
solution of phendione (1) (210 mg, 1 mmol) in methanol (20 mL)
with constant stirring. After the addition was complete, the mixture
was heated to reflux for 2 h, whereby a red solid formed. The hot
mixture was filtered and the solid was washed with methanol and
dried under vacuum. Yield: 680 mg (85%). IR (KBr): ν˜ ϭ 3330
(NH), 2950 (aliphatic CH), 1614Ϫ1596 cmϪ1 (CϭN). 1H NMR
(CDCl3): δ ϭ 9.49 (dd, 2 H), 9.22 (dd, 2 H), 8.39 (s, 4 H),7.68 (dd,
2 H), 7.45 (d, 2 H), 7.14 (d, 2 H), 1.46 (s, 9 H), 1.34 (s, 9 H) ppm.
C48H50N6NiO2·0.5CH2Cl2 (844.1): calcd. C 69.01, H 6.09, N 9.96;
found C 68.90, H 6.15, N 9.82.
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[Ru(bpy)2Cl2]·2H2O (52 mg, 0.1 mmol) and AgNO3 (34 mg,
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stirred magnetically for 2 h under argon and a white precipitate of
AgCl was filtered off. DppztBuSalH2 (7) (74 mg, 0.1 mmol) was
added to the clear red solution followed by a few drops of triethyl
orthoformate. The reaction mixture was heated to reflux under ar-
gon with constant stirring for 2 h. The reddish solution was filtered
to remove any insoluble material and then concentrated in a rotary
evaporator. An orange solid was precipitated upon addition of a
concentrated aqueous solution of NH4PF6. The precipitate was col-
lected by filtration and washed with diethyl ether. Yield: 70 mg
(47%). A pure sample of 11 for photophysical measurements was
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δ ϭ 13.48 (s, 2 H), 9.57 (d, 2 H), 9.33 (s, 2 H), 8.88 (m, 4 H), 8.49
(s, 2 H), 8.23 (m, 4 H), 8.14 (m, 2 H), 8.05 (m, 2 H), 7.83 (m, 2
H), 7.78 (m, 2 H), 7.67 (s, 2 H), 7.60 (m, 2 H), 7.48 (s, 2 H), 7.39
(m, 2 H), 1.41 (s, 18 H), 1.33 (s, 18 H) ppm. ES-MS: m/z ϭ 579.2
[11]. C68H68F12N10O2P2Ru·0.33NaPF6 (1504.35): calcd. C 54.29, H
4.56, N 9.31; found C 54.3, H 4.7, N 9.35.
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Synthesis of [Ru(bpy)2(DppztBusalNi)](PF6)2 (12): Metallation of
the salophen cavity was carried out following established pro-
cedures. Ni(acetate)2·4H2O (6 mg, 0.24 mmol) was added to com-
pound 11 (58 mg, 0.2 mmol) dissolved in methanol (20 mL) and
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solid was filtered off, washed with water and dried under vacuum.
Yield: 26 mg (85%). A pure sample of 12 for photophysical meas-
urements was obtained by chromatography on neutral alumina
using a mixture of dichloromethane/methanol (90:10) (Rf ϭ 0.61).
IR: ν˜ ϭ 2950Ϫ2905 (CϪH, aliph), 1605Ϫ1640 (CϭN), 845 cmϪ1
(PF6). 1H NMR ([D6]DMSO): δ ϭ 9.52 (d, 2 H), 9.33 (s, 2 H), 9.19
(s, 2 H), 8.88 (dd, 4 H), 8.22 (m, 4 H), 8.14 (m, 2 H), 8.06 (dd, 2
H), 7.82 (d, 2 H), 7.77 (d, 2 H), 7.64 (d, 2 H), 7.60 (m, 2 H), 7.41
(d, 2 H), 7.39 (m, 2 H), 1.41 (s, 18 H), 1.32 (s, 18 H) ppm. ES-
MS: m/z ϭ 607.2 [12]. C68H66F12N10NiO2P2Ru (1505.01): calcd. C
54.27, H 4.42, N 9.31; found C 54.05, H 4.31, N 9.29.
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The authors wish to thank Professor Jean-Jacques Girerd for fruit-
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gramme Energie, PRI4) and the CEA for the LRC project (LRC-
CEA no. 33V). K. B. wishes to acknowledge the European TMR
program and STINT (The Swedish Foundation for International
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