Ru-TAP complexes with btz and pytz ligands: Novel candidates as photooxidizing agents

Article abstract of DOI:10.1039/c1dt10235d

Two ligands containing 1,2,3-triazole moieties 1 and 3 were easily prepared by a Cu^I-catalysed "click reaction" between commercially available (trimethylsilyl)alkynes and benzyl azide. These ligands were used in the synthesis of Ru(II) complexes with TAP ligands, i.e. [Ru(TAP) ₂btz]²⁺2 and [Ru(TAP)₂pytz]²⁺4. The electrochemical and photophysical properties of these complexes were investigated. The data show that both complexes should behave as highly oxidizing agents under illumination. However, complex 4 displays more attractive photophysical properties than complex 2 and constitutes thus a Ru-TAP compound that can be easily derivatized for photodamaging biomolecules.

Full text of DOI:10.1039/c1dt10235d

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PAPER
Ru-TAP complexes with btz and pytz ligands: novel candidates as
photooxidizing agents†
a
a
b
b
Alice Mattiuzzi, Ivan Jabin,* C e´ cile Moucheron* and Andr e´ e Kirsch-De Mesmaeker*
Received 11th February 2011, Accepted 28th April 2011
DOI: 10.1039/c1dt10235d
I
Two ligands containing 1,2,3-triazole moieties 1 and 3 were easily prepared by a Cu -catalysed “click
reaction” between commercially available (trimethylsilyl)alkynes and benzyl azide. These ligands were
2
+
2+
used in the synthesis of Ru(II) complexes with TAP ligands, i.e. [Ru(TAP)
2
btz] 2 and [Ru(TAP) pytz]
2
4. The electrochemical and photophysical properties of these complexes were investigated. The data
show that both complexes should behave as highly oxidizing agents under illumination. However,
complex 4 displays more attractive photophysical properties than complex 2 and constitutes thus a
Ru-TAP compound that can be easily derivatized for photodamaging biomolecules.
2
f
Introduction
their own sequence, in other words, they commit suicide. These
Ru conjugates can thus lead to interesting applications in gene
silencing. Despite these interesting photochemical properties, the
high hydrophilicity of the Ru(II) complexes or Ru-ODN prevents
their direct use in cellular biology. Indeed, the photoreactive TAP
metallic complexes are unable to penetrate the cell in order to reach
the cytoplasm or nucleus. Interestingly, Barton and co-workers
recently showed that complexes based on more hydrophobic
ligands such as the bathophenanthroline (diphenylphenanthro-
The photophysical and photochemical properties of the Ru(II)
polypyridyl complexes continue to attract much attention partic-
ularly for the development of various applications such as the
1
design of antenna systems for collecting light. In addition, some
Ru(II) polyazaaromatic complexes are characterized by a long-
lived visible luminescence very sensitive to the microenvironment.
Therefore they can be used as photoprobes of genetic material
2
and considered as potential drugs in anti-cancer therapy. In this
4
line) can easily penetrate the cell membranes. Another strategy
context, it has been shown that Ru(II) complexes containing at least
two highly p-deficient polyazaaromatic ligands such as 1,4,5,8-
tetraazaphenanthrene (TAP) or 1,4,5,8,9,12-hexaazatriphenylene
consists in functionalizing a ligand for tethering the resulting
complex on a vector to allow the cellular uptake. In our previous
2f ,2g
work,
the grafting of the complex via the phen ligand was not
(
HAT) are able to induce under illumination an electron transfer
straightforward. In our course of designing new Ru(II) complexes
3
process from a guanine residue of DNA to the excited complex.
This photo-induced electron transfer can give rise to the formation
of a covalent adduct between the Ru(II) complex and the guanine
2+
with a high oxidation power similar to that of [Ru(TAP) phen]
2
for damaging biomolecules, we were interested in the development
of a straightforward synthesis of bidentate N,N-ligands that can
be readily functionalized and replace the derivatized phen ligand.
For this, ligands containing 1,2,3-triazole moieties appeared as
valuable candidates. Indeed, these ligands can be easily obtained
through a Cu-catalyzed Huisgen 1,3-dipolar cycloaddition, the
so-called “click reaction”, between terminal alkyne and azide
(
G) base. These photo-adducts have been used for damaging DNA.
In this way, they inhibit the activity of the enzymes interacting
3f
with DNA templates. Moreover, deoxyribonucleotides (ODN)
derivatized via a phen ligand (phen = 1,10-phenanthroline) by a
2
+
[
Ru(TAP) phen] complex (Ru-ODN) can target their comple-
2
mentary sequence containing a G base. Thus, after hybridiza-
tion and illumination, they irreversibly photo-crosslink to the
5
reactants. Moreover, the coordination chemistry of 1,2,3-triazole
ring systems constitutes a recent topic of great interest. These
2f ,3f
DNA target.
Moreover if the target is not found during the
6
heterocycles were used in catalysis (with Cu, Pd, Zn) and
illumination, these Ru-ODN form a photo-adduct with a G of
7
99m
in radiolabelling of biomolecules (with
Tc, Re, Mo). The
tridentate ligand 2,6-bis(1,2,3-triazol-4-yl)pyridine forms stable
6
a,8
a
Cu(I), Ru(II), Fe(II) and Eu(III) complexes.
The bidentate
Laboratoire de Chimie Organique, Universit e´ libre de Bruxelles (U.L.B.),
ligand [1,2,3]triazolo[1,5-a]pyridine can lead to heteroleptic Ru(II)
complexes, while two other bidentate ligands 4,4¢-bis(1,2,3-
triazole) (btz) and 2-(1,2,3-triazol-4-yl)pyridine
) were used for the formation of heteroleptic or homoleptic
Ru(II) complexes. From a synthetic point of view, all these 1,2,3-
triazole based ligands are readily available. For example, Skoglund
Avenue F. D. Roosevelt 50, CP160/06, B-1050, Brussels, Belgium. E-mail:
ijabin@ulb.ac.be; Fax: +32-2650-2798
9
b
Service de Chimie Organique et Photochimie, Universit e´ libre de Bruxelles
10
10b,11
(pytz) (Fig.
(
U.L.B.), Avenue F. D. Roosevelt 50, CP160/08, B-1050, Brussels, Belgium.
1
E-mail: akirsch@ulb.ac.be, cmouche@ulb.ac.be; Fax: +32-2650-3018
†
Electronic supplementary information (ESI) available: Fig. SI1–SI12.
See DOI: 10.1039/c1dt10235d
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Results and discussion
Syntheses
The btz 1 and pytz 3 ligands were synthesized from commercially
available (trimethylsilyl)alkynes and benzyl azide (BnN ) through
a one-pot tandem deprotection/click reaction (Scheme 1). For
this, the protected alkynes were reacted with BnN in H O/t-
BuOH in presence of K CO and a catalytic amount of CuSO
The presence of K CO allows the in situ deprotection of the alkyne
reactants. It is noteworthy that a washing of the crude residue
with an aqueous NH OH solution (5%) was necessary in order to
3
1
0b
Fig. 1 The btz and pytz ligands.
3
2
2
3
4
.
2
3
has recently described a multistep one-pot methodology based
on click chemistry that leads to the btz and pytz ligands.
10b
4
remove the copper ion which was likely complexed to the obtained
ligand. Pure btz and pytz ligands 1 and 3 were obtained after flash
chromatography (FC) purification on silica gel in 72% and 78%
yield respectively.
In addition, thanks to the Cu-catalyzed Huisgen 1,3-dipolar
cycloaddition, 1,2,3-triazole based ligands functionalized with a
wide range of substituents are easily accessible. Thus, bidentate
1
1
,2,3-triazole ring systems seem to be promising alternatives to
,10-phenanthroline or 2,2¢-bipyridine (bpy) for the design of
The subsequent reaction of these ligands with [Ru(TAP) -
2
2
+
-
(
H
2
O)
2
] (NO
3
2
) in anhydrous DMF yielded a dark-red solution
readily functionalizable ligands devoted to the complexation of
which turned to brownish-orange. The complexes 2 and 4 were
obtained in 80% and 53% yields respectively either after FC
purification on silica gel (in the case of 2) or chromatography
on neutral alumina (in the case of 4). Both complexes are orange
solids, soluble in polar organic solvents and in water. The structure
transition metal ions.
Nevertheless, although 1,2,3-triazole ring systems would be
attractive for the tethering of Ru complexes, another condition
which has to be fulfilled by the resulting complex formed from the
Ru(TAP)
latter has to be higher than or equal to that of [Ru(TAP)
order to damage the biomolecules as explained above. Therefore
2
motif is the oxidation power of the excited state. This
12
2
+
of 2 and 4 has been confirmed by NMR spectroscopy.
2
phen] in
2
+
in this work, we report the synthesis of [Ru(TAP)
2
btz] and
Electrochemical data
2
+
[
Ru(TAP)
2
pytz] wherein btz = 1,1¢-dibenzyl-4,4¢-bi-1H-1,2,3-
triazolyl and pytz = 2-(1-benzyl-1H-1,2,3-triazol-4-yl)pyridine
and the evaluation of their photochemical and electrochemical
properties in view of their use with biological systems. Indeed
in this context, although these two complexes contain two TAP
ligands, it is difficult to predict whether a third ligand like btz or
pytz would improve or decrease their photooxidation power as
compared to a bpy or phen ligand.
The electrochemical behaviour of 2 and 4 was examined by cyclic
voltammetry in dry deoxygenated acetonitrile (for the reduction
of 4 in MeCN, see Fig. 2). The data, along with those of some
10b,13,14
reference complexes,
are collected in Table 1. Complexes 2
and 4 exhibit a reversible oxidation wave at +1.80 and +1.78 V
versus SCE respectively that correspond to the oxidation of the
Ru centre. In reduction, complexes 2 and 4 exhibit three reversible
2+
-)
2 3 2
2 and [Ru(TAP) pytz] (NO 4.
-)
2+
Scheme 1 Syntheses of [Ru(TAP)
2
btz] (NO
3
2
7
396 | Dalton Trans., 2011, 40, 7395–7402
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Table 1 Electrochemical data for complexes 2, 4 and reference complexes
Entry Complex Oxidation (V/SCE) Reduction (V/SCE)
c
E*red (V/SCE) lmax (eV)
2
+
-
a,13
1
2
3
4
5
6
7
8
[Ru(bpy)
3
] (PF
6
)
2
+1.28 (r)
+1.94 (r)
+1.70 (r)
+1.73 (r)
+1.35 (r)
+1.32 (r)
+1.80 (r)
+1.78 (r)
-1.35 (r, B), -1.54 (r, B), -1.79 (r, B)
+0.65
+2.00
+2.05
+1.93
+1.98
—
—
+2.03
+2.01
2
+
-
a,13
[Ru(TAP)
[Ru(TAP)
[Ru(TAP)
3
2
2
] (PF
bpy] (PF
6
)
2
-0.75 (r, T), -0.88 (r, T), -1.10 (r, T), -1.60 (r, T), -1.80 (r, T) +1.30
2+
-)
a,13
6
2
-0.83 (r, T), -1.01 (r, T), -1.56 (r, B), -1.72 (r, T)
-0.83 (r, T), -1.01 (r, T), -1.55 (r, P), -1.74 (r, T)
<-2.3
+1.10
+1.15
—
—
+1.24
+1.23
2+
-
a,14
phen] (Cl )
b,10b
2
2+
-
[Ru(btzR
1 3 2
) ] (Cl )
2+ -
b,10b
[Ru(pytzR
1
)
3
] (Cl )
2
-1.82
2
+
-)
3
a
[Ru(TAP)
[Ru(TAP)
2
btzR
2
] (NO
3
2
-)
2
2
-0.79 (r, T), -0.97 (r, T), -1.34 (r, T)
-0.78 (r, T), -0.97 (r, T), -1.50 (r, T), -1.75 (irr, T or pytz)
2
+
a
2
pytzR
2
] (NO
4
a
+
- a
+
- b
Redox potentials measured by cyclic voltammetry in MeCN, V versus SCE at room temperature, with 0.1 M Bu
4
N PF
6
or with 0.1 M TBA BF
4
as
b
c
supporting electrolyte and a Pt or a glassy carbon working electrode. The corresponding reduction potentials in the excited state (vs. SCE), as estimated
from the reduction potential in the ground state and the energy of the emission maximum in MeCN (E*red ª Ered + DElmax ). The reversibility and attribution
of the waves are given in parentheses. r = reversible; irr = irreversible;T = 1,4,5,8-tetraazaphenanthrene; B = 2,2¢-bipyridine; P = 1,10-phenanthroline; R =
1
hexyl-; R = benzyl-.
2
10b,11c
Table 1, entries 5 and 6).
The fourth reduction wave of
complex 4 could be also assigned to a fourth reduction of a TAP
ligand. However, such a fourth reduction wave should also be
observed for complex 2, which is not the case. Therefore, a fourth
addition of an electron on the pytz ligand in complex 4, although
2
+
occurring at a potential less negative than for [Ru(pytz) ] , might
3
not be totally excluded and could be due to the important
electron withdrawing effect of the two TAP ligands. The reduction
3
potentials of the excited MLCT state (E*red) have been estimated
in the same way as for the other Ru complexes, i.e. from the
reduction potential of the first reduction wave and the energy
of the emission maximum (Table 1). These latter values being
too small, it leads to oxidation powers of the excited state that
are under-estimated. Nevertheless, the E*red values for complex 2
(
+1.24 V) and 4 (+1.23 V) are even slightly more positive than
2
+
for [Ru(TAP) phen] (+1.15 V), i.e. the reference complex, which
could be applied in gene silencing.
2
2f
2
+
-)
Fig. 2 Reduction cyclic voltammogram of [Ru(TAP)
2
pytz] (NO
3
2
4 in
as
+
-
MeCN, V versus SCE at room temperature, with 0.1 M Bu
4
N PF
6
supporting electrolyte and a Pt working electrode.
Photophysical properties
waves and a fourth irreversible one for complex 4. The first two
The absorption data in acetonitrile and water for complexes 2,
12
waves can be attributed to the two TAP ligands, in comparison
4 and reference complexes are given in Table 2. The bands
of complexes 2 and 4 at wavelengths shorter than 270 nm
2
+
2+
with the reduction potentials of [Ru(TAP)
3
] , [Ru(TAP)
2
bpy]
2
+
2+
-
2+
and [Ru(TAP)
2
phen] (Table 1, entries 2–4). The third reduction
are similar to those of [Ru(btzR
1
)
3
] (Cl )
2
, [Ru(btzR
2
)
3
]
and
2
+
-
wave of complexes 2 and 4 can be assigned to a second reduction
of a TAP ligand because the reduction potentials are not negative
enough to account for the reduction of a btz or pytz ligand (around
[Ru(pytzR
1
)
3
] (Cl )
2
(Table 2, entries 4, 5, and 6). The most
bathochromic absorption bands around 450–460 nm in both
complexes 2 and 4 correspond most probably to MLCT transitions
2
+
2+
2+
2+
-
2.3 V/SCE for [Ru(btz)
3
]
and -1.82 V/SCE for [Ru(pytz)
3
] ,
Ru→TAP as compared to [Ru(TAP)
2
bpy] and [Ru(TAP) phen]
2
Table 2 Absorption data at 298 K in aerated solution for complexes 2, 4 and reference complexes
3
-1
-1
absorbance lmax, nm (e/10 M cm )
Entry
Complex
acetonitrile
water
2
+
-
13
1
2
3
4
5
6
7
8
[Ru(TAP)
[Ru(TAP)
[Ru(TAP)
3
2
2
] (Cl )
2
276, 408, 437
274, 412, 463
272, 412, 458
230, 301
237, 269, 382
222, 302
232, 275, 384, 452 (10.1)
232, 273, 403, 456 (9.7)
276, 408, 437 (13.0)
273, 412, 465 (12.8)
230, 272, 410, 466 (14.5)
—
—
2
+
-
13
bpy] (Cl )
2
-
2
+
14
phen] (Cl )
a,10b
2
2
+
-
[Ru(btzR
[Ru(pytzR
[Ru(btzR
1
)
1
3
] (Cl )
2
-
2
+
a,10b
)
3
2
] (Cl )
10a
2
+
-
2
)
3
] (Cl )
2
—
2
+
-)
3
[Ru(TAP)
[Ru(TAP)
2
btzR
pytzR
2
] (NO
3
2
-)
2
2
231, 278, 384, 455 (10.7)
232, 274, 406, 459 (10.3)
2
+
2
2
] (NO
4
a
Absorption data in MeOH; R
1
= hexyl-; R = benzyl-.
2
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a
Table 3 Emission data for complexes 2, 4 and reference complexes
acetonitrile
water
l
max
/
t
air
/
t
Ar
/
U
10
Ar
-
/
k
r(Ar)
3
/
10 s
k
nr(Ar)
/
l
max
/
t
air
/
t
Ar
/
U
10
Ar
-3
/
k
r(Ar)
3
/
10 s
k
nr(Ar)
/
3
-1
5
-1
-1
5
-1
Entry
Complex
nm
ns
ns
10 s
nm
ns
ns
10 s
2
+ 18
1
2
3
4
5
[Ru(TAP)
[Ru(TAP)
[Ru(TAP)
[Ru(TAP)
[Ru(TAP)
3
2
2
2
2
]
604
641
626
612
616
53
55
7
103
83
—
25
35
146
4
—
250
18
602
649
655
633
640
210
605
730
101
715
223
778
840
103
940
14
40
—
3
63
51
—
29
29
44
12
—
97
10
2
+
18
+ 14,15
bpy]
phen]
btz]
pytz]
660
760
40
1965
1800
40
174
—
1
2
2
+
2
4
2
+
385
536
19
27
a
Temperature: 298 K. The luminescence decays corresponding to the excited state lifetimes (t) were measured by SPC or pulsed laser. Estimated
experimental errors for the lifetimes: ~ 10%. The luminescence quantum yields U (approximate error <20%) were determined from the U values of
2+
[
Ru(bpy)
3
]
as reference. k
r
r
= U/t; knr = 1/t - k .
(
Table 2, entries 2 and 3) and on the basis of the reduction
with the case of numerous polypyridyl Ru complexes such as
2
+
2+13–15
potential data. Thus, these data indicate that, in absorption, the
novel complexes 2 and 4 behave similarly to [Ru(TAP)
and [Ru(TAP)
bathochromic absorption corresponding to the transition dp(Ru)–
p*(TAP). Such bathochromic MLCT transitions are not present in
[Ru(bpy)
3
]
or [Ru(TAP)
2
(bpy/phen)]
(Table 3, entries 2 and
2
+
2
bpy]
3) for which the excited state lifetime is usually shorter in water
than in acetonitrile because of the efficient vibrational deactivation
2
+
2
phen] in acetonitrile and water with the most
16
of the excited states by the O–H vibrators of water. In the present
case, a luminescence lifetime shorter in acetonitrile than in water is
typical of a control of t by another process than the radiationless
2
+
2+
2+
[
Ru(btzR
complexes, the LUMO corresponds to that of btzR
pytzR , much less stabilized than the LUMO of TAP according to
the reduction potential values.
1
)
3
] , [Ru(btzR
2
)
3
]
or in [Ru(pytzR
1
)
3
] since, in those
3
1
, btzR , and
2
deactivation of the MLCT to the ground state. Actually the
1
emission lifetime behaviour of complexes 2 and 4 is similar to
2
+
that of [Ru(TAP)
3
]
(Table 3, entry 1) for which it was clearly
13
3
The emission data for complexes 2, 4 and the reference
demonstrated that the MLCT state is easily activated at room
temperature to the MC state (Metal Centred), which does not emit
3
complexes are collected in Table 3 (for the spectra in MeCN, see
Fig. 3).
12
and causes an emission lifetime shortening. As this crossing to the
3
3
MC state is more efficient when the MLCT state is destabilized
3
and thus closer to the MC state in less polar solvent, this explains
the shortening of emission lifetime in acetonitrile in which the
thermal activation from the MLCT to the MC state controls
the lifetime. We should thus conclude that the new complexes 2
and 4 would present a photophysical mechanism similar to that of
3
3
2
+
[
Ru(TAP)
3
] . This would mean that the knr (argon) value should
3
include a term corresponding to this thermal activation to the MC
state and should be important. This is certainly true for complex
2
5
-1
5
-1
(knr = 250 10 s ) but for complex 4 the knr value (18 10 s ) is
not that important. There is also a striking feature for complex 2,
i.e. knr not only in acetonitrile but also in water is very high. This
could be attributed to the btz ligand itself. Indeed, because of the
17
presence of two five-membered rings, this ligand may not adopt
a planar geometry.
Thus, some distortion to an octahedral geometry should result,
increasing the radiationless deactivation in water. In order to test,
as concluded from the above considerations, whether complexes 2
and 4 would exhibit a photophysical behaviour in acetonitrile, sim-
2
+
-)
Fig. btz] (NO
3
Emission spectra of [Ru(TAP)
2
3
2
2 ( ) and
2+
-
[
Ru(TAP) pytz] (NO ) 4 (– –) in MeCN under argon.
2
3
2
2
+
ilar to that of [Ru(TAP) ] , i.e. would cross more or less easily to
3
3
3
2
+
the MC state from the MLCT state, we examined the behaviour
of the emission lifetime as a function of temperature (Fig. 4).
The emission maxima of [Ru(TAP)
2
btz] 2 and [Ru(TAP) -
2
2
+
3
pytz] 4 are similar and can be assigned to the MLCT emission
Ru-TAP as for [Ru(TAP) bpy/phen] . As usually observed, there
is a stabilization of the MLCT state in more polar solvents as
indicated by the bathochromic shift of emission from acetonitrile
to water (Table 3, entries 2–5).
3
2
+
It is quite clear that the MLCT state of complex 2 behaves
2
2
+
3
like [Ru(TAP) ] . Thus, from room temperature till ca. 260 K,
3
the lifetimes remain very short and constant because they are
controlled in this higher temperature domain, by the activation to
3
the MC state. At ca. 250 K, the lifetimes start increasing because
The luminescence lifetimes and the corresponding radiative (k )
r
3
3
the MLCT state reaches less easily the MC state. However, even at
and non radiative (knr) rate constants in acetonitrile and water as
determined from the quantum yields of emission, are also given in
Table 3. For both complexes 2 and 4, the emission lifetimes (under
air or argon) are longer in water than in acetonitrile. This contrasts
ca. 230 K, the lifetime has not yet reached a maximum value. This
2
+
contrasts with the behaviour of [Ru(TAP) phen] for which the
2
emission lifetime does not increase much from room temperature
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Steady state illumination
As it is well known that photodechelation takes place from the
3
MC state, we also examined the photodechelation of complexes
2
and 4 under steady state illumination as compared to that
2
+
2+
of [Ru(TAP)
3
]
and [Ru(TAP) phen] in the same experimental
2
conditions (Fig. 5).
Fig. 5A indicates that complex 2 exhibits a little photodechela-
2
+
tion even in water, as observed for [Ru(TAP) ] in water (Fig. 5B).
3
The products of dechelation correspond to the substitution of
-
one bidentate ligand by two monodentate ligands (Cl or H
2
O)
responsible for the bathochromic absorption around 500 nm.
3
2+
Thus the MLCT state of 2 and [Ru(TAP)
3
]
would indeed cross
3
over the MC state in addition to an important deactivation to
the ground state for 2. For complex 4 in water, the absorption
spectra do not change with the illumination time (Fig. 5C) as
2
+
for [Ru(TAP) phen] (Fig. 5D) which is quite photostable. These
2
Fig. 4 Luminescence lifetimes as a function of temperature. Diamonds:
2
+
2+
2
[
Ru(TAP)
2
btz] (2); circles: [Ru(TAP)
3
] ; triangles: [Ru(TAP)
2
pytz] (4);
observations correlate thus well with the data of Table 3 for water.
We also examined the photodechelation of the four complexes
2+
squares: [Ru(TAP)
2
phen] .
3
in acetonitrile (Fig. 6) in which the MLCT state is less stabilized,
3
thus closer in energy to the MC state. Fig. 6A and 6B show that
2
+
till the plateau value at ca. 275 K, meaning that in that case, quasi
the photodechelation of both complexes, 2 and [Ru(TAP) ] , is
3
for the whole temperature domain, the lifetime is not controlled
by a participation of the MC state. For complex 4, the data of Fig.
important. This is in excellent agreement with the temperature
3
3
dependence of their MLCT state lifetimes, as explained above.
-
4
indicate that its behaviour is intermediate to the two previous
In this case, the bidentate ligand is substituted again by Cl
cases: there is a more important increase of lifetime from room
and/or MeCN. For complex 2 (Fig. 6A), the absence of isosbestic
2
+
temperature till 255 K than for [Ru(TAP)
2
phen] but a plateau
point indicates that more than one dechelation product is formed.
2
+
value is reached from ca. 250 K. In conclusion, in acetonitrile the
Concerning complex 4 (Fig. 6C) and [Ru(TAP) phen] (Fig.
2
3
3
MLCT state of complex 4 can be activated to the MC state but
6D), it is clear that at room temperature, as concluded from
much less efficiently than for complex 2.
the emission lifetimes dependence on temperature, complex 4, in
2
+
-
-5
3 2
2, 6.2 10 M; (B) [Ru(TAP) ] (Cl )
, 4.5 10-5 M; (C)
2+
-
Fig. 5 Absorption spectra as a function of the illumination time, for (A) [Ru(TAP)
2
btz] (Cl )
2
2+
-
-5
2+
-
-5
[
Ru(TAP)
2
pytz] (Cl )
2
4, 6.6 10 M; (D) [Ru(TAP) phen] (Cl ) , 4.6 10 M, in H O, under argon.
2
2
2
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2
+
-
-5
3 2
2, 7.5 10 M; (B) [Ru(TAP) ] (Cl )
, 5.0 10-5 M; (C)
2+
-
Fig. 6 Absorption spectra as a function of the illumination time, for (A) [Ru(TAP)
2
btz] (Cl )
2
2+
-
-5
2+
-
-5
[
Ru(TAP)
2
pytz] (Cl )
2
4, 7.2 10 M; (D) [Ru(TAP) phen] (Cl ) , 5.1 10 M, in MeCN, under argon.
2
2
2
+
contrast to [Ru(TAP)
2
phen] , undergoes the loss of a ligand with
adopts a less distorted octahedral geometry than 2 as indicated by
the much smaller non radiative deactivation rate constant of 4.
In conclusion, the combination of one functionalized pytz
ligand with two TAP ligands in a ruthenium(II) complex makes
the resulting metallic compound an attractive photoreagent for
biomolecules and opens new horizons for applications with
biological systems.
substitution; in this case again, several dechelation products are
occurring.
Conclusion
As explained in the introduction, we have chosen to synthesize
2
+
2+
and study [Ru(TAP)
2
btz] 2 and [Ru(TAP)
2
pytz] 4 especially
because these complexes could fulfil two required conditions: (i)
they should be sufficiently oxidizing in their MLCT state to
3
Experimental section
extract an electron from components of biomolecules and give rise
to photo-adducts. Therefore, they should contain at least two TAP
ligands, provided that the third ligand does not change too much
the oxidizing power, (ii) they should be readily functionalizable.
The examination of their electrochemical and photophysical
behaviour constitutes thus an important prerequisite for their use
as conjugates or for tethering them on different vectors.
Interestingly, our results show that a simple change of a
spectator ligand (i.e. the phen by a btz or a pytz ligand) influences
greatly the resulting properties of the TAP-complex.
Instrumentation
1
13
The H NMR and C NMR spectra were recorded with a Bruker
Avance-300 instrument and a Bruker Varian Unity-600. Chemical
shifts are expressed in ppm. CDCl was filtered over a short
3
1
basic alumina column to remove traces of DCl. Most of the H
NMR spectra signals were attributed through 2D NMR analyses
(COSY, HSQC, HMBC). The electrospray mass spectra were
recorded with a Water Q-TOF 2 spectrometer (at the University
of Mons, Belgium). The emission spectra were recorded with a
Shimadzu RF-5301PC and the absorption spectra with a Perkin-
Elmer Lambda UV-Vis spectrophotometer. The determination of
the molar absorption coefficients was performed by weight and
absorption measurements. Cyclic voltammetry was carried out on
The electrochemical and emission data clearly show that both
complexes should behave as excellent oxidizing agents in their
3
MLCT states. Indeed, the oxidizing power under illumination is
2
+
even slightly better than that of [Ru(TAP) phen] . However, a
2
2
more detailed examination of the photophysical parameters that
characterize their luminescent excited states indicates that complex
a platinum disk working electrode (approximate area = 3 mm ),
in dried acetonitrile with tetrabutylammonium hexafluorophos-
-
1
4
with the pytz ligand should have the priority over compound 2
phate (0.1 mol L ) as supporting electrolyte. The potential of
the working electrode was controlled by an Autolab PGSTAT
100 (Eco Chemie B.V., Utrecht, The Netherlands) potentiostat
through a PC interface with a scan rate of 100 mV s between
-2 and +2 V versus SCE. The counter electrode was a platinum
disk and the reference electrode a Saturated Calomel Electrode
with the btz ligand. Indeed, the excited state lifetime of 4 is longer
than that of 2, which should favour the probability of quenching
by a reducing biomolecular agent in water. Moreover 4 is more
photostable than 2 at least in water. These advantages of complex
-
1
4
over 2 are due to the presence of the pytz ligand which probably
7
400 | Dalton Trans., 2011, 40, 7395–7402
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2
+
-)
(
SCE). All measurements were performed in a single compartment
[Ru(TAP)
2
btz] (NO
3
2
2. The bistriazole ligand 1 (21 mg,
2
+
-
cell. The emission lifetimes at room temperature were measured
by using the single-photon counting technique (SPC) with an
Edinburgh Instruments FL900 spectrometer (Edinburgh, U.K.)
equipped with a nitrogen-filled discharge lamp and a peltier-
cooled Hamamatsu R955s photomultiplier tube. The emission
decays were analyzed with the Edinburgh Instruments software
0.0728 mmol) and [Ru(TAP)
0.0801 mmol) were suspended in DMF (2 mL). The reaction
mixture was heated for 6 h at 100 C to yield a dark-red solution
which turned to brownish-orange. The reaction mixture was
concentrated under reduced pressure and the crude residue was
2
(H
2
O)
2
] (NO
3
)
2
(50 mg,
◦
purified by flash chromatography on silica gel (CH
2
2
Cl /MeOH;
(
version 3.0), based on nonlinear least-squares regressions using
8 : 2) to yield the starting material (8 mg) and the Ru-complex 2
Marquardt algorithms. The emission lifetimes in acetonitrile as
a function of temperature were measured by using the excitation
source of a frequency-tripled (355 nm) Nd:YAG Q-switched laser
as an orange solid (32 mg, 0.0353 mmol, 80% given the 61% of
conversion). m.p. 200 C (dec.); IR (KBr): 3053, 1498, 1355, 871,
◦
1
734; H NMR (300 MHz, CD
3
OD, 298 K): d(ppm) = 5.49 (d, 2H,
2
2
(
(
Continuum Inc.) coupled with an optical parametric oscillator
Continum Inc.) covering the wavelengths region 410–2300 nm
J = 14.7 Hz, NCH
(d, 4H, J = 6.3 Hz, HBn), 7.28–7.35 (m, 6H, HBn), 8.56 (d, 2H,
J = 2.7 Hz, HTAP ), 8.59 (d, 2H, J = 2.7 Hz, HTAP ), 8.64–8.66
(m, 6H, HTAP + Htriazole), 9.00 (d, 2H, J = 2.7 Hz, HTAP ), 9.20
2
), 5.56 (d, 2H, J = 14.4 Hz, NCH
2
), 7.12
3
3
3
with an average pulse energy of 15 mJ. The average pulse duration
was 5 ns. The grating Czerny–Turner monochromator (Spectra Pro
3
3
13
2
300i, Acton Research Corp.) was used for the spectral selection.
The steady state illuminations were performed with a Xe lamp
6
(d, 2H, J = 2.7 Hz, HTAP ); C NMR (75 MHz, d -DMSO, 298
K): d(ppm) = 54.8, 124.6, 127.9, 128.7, 128.8, 132.3, 133.9, 139.9,
(
500 W) Thermo Oriel with a KNO
2
(0.2 M) and H
2
O filters.
141.8, 142.3, 142.6, 144.0, 144.4, 148.9(8), 149.0(3), 149.9, 150.3;
2
+
HRMS (ESI-TOF) calcd for C38
91.0829.
28
H N14Ru (M ) 391.0832, found
3
Chemicals
2
-(1-benzyl-1H-1,2,3-triazol-4-yl)pyridine
3. 2-(trimethyl-
All the reactions were performed under an inert atmosphere.
Anhydrous DMF was obtained from Alfa Aesar. All the solvents
and reagents for the syntheses were at least reagent grade quality
and were used without further purification. The reaction mixtures
from the complexation with Ru(II) were protected from direct
light during the synthesis to prevent photochemical degradation.
Silica gel (230–400 mesh) was used for flash chromatography.
Neutral aluminium oxide was used for chromatography. The
solvents for photophysical measurements were of spectroscopic
grade and water was purified with a Millipore Milli-Q system.
silyl)ethynylpyridine (176 mg, 1.01 mmol) and benzyl azide
(
(
0
125 mL, 1.00 mmol) were dissolved in t-butanol (5 mL) and H
5 mL). CuSO (34 mg, 0.213 mmol), sodium ascorbate (79 mg,
.399 mmol) and K CO (136 mg, 0.986 mmol) were successively
added and the mixture was stirred vigorously for 24 h at room
temperature under inert atmosphere. CH Cl (10 mL) and an
aqueous NH OH solution (5%, 10 mL) were added to the reaction
mixture which was stirred for 30 min. The organic layer was
washed twice with an aqueous NH OH solution (5%, 2 ¥ 10 mL).
The combined aqueous layers were extracted with CH Cl (2 ¥
5 mL) and the combined organic layers were washed with H
3 ¥ 20 mL) until pH = 7 and then concentrated under reduced
pressure. The crude residue was purified by flash chromatography
on silica gel (CH Cl /MeOH; 95 : 5) to yield the compound 3 as
a white solid (187 mg, 0.793 mmol, 78%). H NMR (300 MHz,
2
O
4
2
3
2
2
4
4
2
2
2
+
-
Ru(TAP)
2
Cl
2
and [Ru(TAP)
2
(H
2
O)
2
] (NO
3
) were prepared fol-
2
1
(
2
O
19
lowing the procedures described in the literature. The syntheses
of ligands 1 and 3 were already described in the literature but
1
0a,11a
with different procedures than those given below.
For the
2
2
2
+
-
steady state illumination experiments, [Ru(TAP)
2
btz] (Cl )
2
was
1
obtained from complex 2 by anion exchange with a Dowex 1 ¥
4
CDCl
3
, 298 K): d(ppm) = 5.58 (s, 2H, NCH
2
), 7.20 (td, 1H, J = 1.5
4
2
+
-
8
, 100–200 mesh. Besides, [Ru(TAP)
2
pytz] (Cl ) was obtained
2
3
Hz, J = 5.5 Hz, Hpy), 7.31–7.41 (m, 5H, HBn), 7.76 (td, 1H, J =
.8 Hz, J = 7.8 Hz, Hpy), 8.04 (s, 1H, Htriazole), 8.18 (d, 1H, J =
.1 Hz, Hpy), 8.53 (d, 1H, J = 4.8 Hz, Hpy).
by purification of a small amount of complex 4 with a Sephadex
SPC25.
3
3
1
8
3
2
+
-)
4. The triazole-pyridine ligand 3
1
,1¢-dibenzyl-4,4¢-bi-1H-1,2,3-triazolyl 1. 1,4-bis(trimethyl-
[Ru(TAP)
2
pytz] (NO
3
2
2
+
-
silyl)-1,3-butadiyne (151 mg, 0.777 mmol) and benzyl azide
(26 mg, 0.110 mmol) and [Ru(TAP)
2
(H
2
O)
2
] (NO
3
2
) (77 mg,
(
(
0
7
200 mL, 1.60 mmol) were dissolved in t-butanol (7 mL) and H
7 mL). CuSO (48 mg, 0.301 mmol), sodium ascorbate (195 mg,
.985 mmol), K CO (211 mg, 1.53 mmol) and pyridine (600 mL,
.46 mmol) were successively added and the mixture was stirred
2
O
0.123 mmol) were suspended in DMF (2 mL). The reaction
mixture was heated for 5 h at 100 C to yield a dark-red solution
which turned to brownish-orange. The reaction mixture was
concentrated under reduced pressure and the crude residue was
◦
4
2
3
vigorously for 24 h at room temperature under inert atmosphere.
CH Cl (14 mL) and an aqueous NH OH solution (5%, 15 mL)
were added to the reaction mixture which was stirred for 30 min.
The organic layer was washed with an aqueous NH OH solution
5%, 2 ¥ 15 mL). The combined aqueous layers were extracted
with CH Cl (2 ¥ 20 mL) and the combined organic layers were
washed with H O (3 ¥ 30 mL) until pH = 7 and then concentrated
under reduced pressure. The crude residue was purified by flash
chromatography on silica gel (CH Cl /MeOH; 95 : 5) to yield the
compound 1 as a white solid (178 mg, 0.563 mmol, 72%). H
NMR (300 MHz, CDCl , 298 K): d(ppm) = 5.56 (s, 4H, NCH ),
.28–7.38 (m, 10H, HBn), 7.94 (s, 2H, Htriazole).
purified by chromatography on neutral alumina (CH
2
Cl /MeOH;
2
2
2
4
8 : 2) to yield the Ru-complex 4 as an orange solid (47 mg,
◦
0.0580 mmol, 53%). m.p. 197 C (dec); IR (KBr): 3033, 1529,
1
4
1340, 866, 734; H NMR (600 MHz, CD
3
OD, 298 K): d(ppm) = 5.55
2
2
(
(d, 1H, J = 14.4 Hz, NCH
7.19 (d, 2H, J = 7.2 Hz, HBn), 7.32 (m, 3H, HBn), 7.35–7.38 (m,
2
), 5.60 (d, 1H, J = 14.4 Hz, NCH
2
),
3
2
2
3
3
2
1H, Hpy), 7.79 (d, 1H, J = 5.4 Hz, Hpy), 8.11 (td, 1H, J = 7.8
4 3
Hz, J = 1.2 Hz, Hpy), 8.32 (d, 1H, J = 8.4 Hz, Hpy), 8.36 (m, 1H,
HTAP ), 8.53–8.55 (m, 2H, HTAP ), 8.59 (m, 1H, HTAP ), 8.61–8.70 (m,
2
2
1
3
4
4H, HTAP ), 8.94 (d, 1H, J = 3.0 Hz, HTAP ), 9.04 (d, 1H, J = 3.0 Hz,
TAP ), 9.10 (s, 1H, Htriazole), 9.19 (d, 1H, J = 3.0 Hz, HTAP ), 9.22
(d, 1H, J = 3.0 Hz, HTAP ); C NMR (150 MHz, CD
4
3
2
H
4
13
7
3
OD, 298 K):
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7395–7402 | 7401

View Article Online
d
1
1
(ppm) = 57.1, 124.6, 127.8, 127.9, 129.7, 130.2(6), 130.3(3), 133.9,
33.9(6), 134.0(5), 134.2, 134.6, 140.9, 143.7, 143.8, 144.3, 146.4,
46.7, 146.9, 147.0, 149.2, 149.6, 150.2, 150.4, 150.9, 151.8, 153.8;
4 C. A. Puckett and J. K. Barton, J. Am. Chem. Soc., 2007, 127, 46–47.
5
6
7
(a) H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem., Int.
Ed., 2001, 40, 2004–2021; (b) C. W. Tornoe, C. Christensen and M.
Meldal, J. Org. Chem., 2002, 67, 3057–3064; (c) V. V. Rostovtsev, L. G.
Green, V. V. Fokin and K. B. Sharpless, Angew. Chem., Int. Ed., 2002,
41, 2596–2599.
2
+
HRMS (ESI-TOF) calcd for C34
3
24
H N12Ru (M ) 351.0644, found
51.0651.
(a) T. R. Chan, R. Hilgraf, K. B. Sharpless and V. V. Fokin, Org. Lett.,
2
004, 6, 2853–2855; (b) B. Colasson, M. Save, P. Milko, D. Shr o¨ der and
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P6/27) and the FRFC-FNRS Belgium (Fonds National pour la
Recherche Scientifique) for financial support. A.M. is grateful to
the FNRS for a PhD grant.
1
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402 | Dalton Trans., 2011, 40, 7395–7402
This journal is © The Royal Society of Chemistry 2011