A cyclometallated ruthenium(II) complex with a sterically hindered ligand displaying a long-lived MLCT excited state

Article abstract of DOI:10.1039/a608175d

Two cyclometallated ruthenium(II) complexes incorporating mono- or di-substituted phenanthroline moieties are synthesized and characterized by single-crystal X-ray diffraction; the complex with a sterically hindered ligand displays a long-lived MLCT excited state.

Full text of DOI:10.1039/a608175d

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A cyclometallated ruthenium(ii) complex with a sterically hindered ligand
displaying a long-lived MLCT excited state
Jean-Paul Collin,a Robert Kayhanian,a Jean-Pierre Sauvage,a* Giuseppe Calogero,b Francesco Barigelletti,b
Andre´ De Cianc and Jean Fischerc
a Laboratoire de Chimie Organo-Mine´rale, UA 422 au CNRS, Institut de Chimie, Universite´ Louis Pasteur, 4 rue Blaise Pascal,
F-67070 Strasbourg, France
b Istituto FRAE-CNR, via P. Gobetti 101, 40129 Bologna, Italy
c Laboratoire de Cristallochimie et de Chimie Structurale, UA 424 au CNRS, Institut de Chimie, Universite´ Louis Pasteur, 4 rue
Blaise Pascal, F-67070 Strasbourg, France
Two cyclometallated ruthenium(II) complexes incorporating
mono- or di-substituted phenanthroline moieties are synthe-
sized and characterized by single-crystal X-ray diffraction;
the complex with a sterically hindered ligand displays a
long-lived MLCT excited state.
the phenanthroline ligand Hdtp or Hmap in refluxing acetic acid
in the presence of one drop of N-ethylmorpholine. Considering
that both cyclometallated (NNC) and the non-cyclometallated
(NN) products could be obtained with Hmap, it is not surprising,
in view of previous results11 that Hdtp leads exclusively to the
formation of the cyclometallated (NNC) compound. Sat-
isfactory analytical data have been obtained for these com-
plexes. Single crystals of 1 and 2 were obtained by slow
diffusion of benzene into an acetonitrile solution of each
compound. The structures of 1 and 2 were determined by single-
crystal X-ray diffraction† and the ORTEP diagrams are shown
in Fig. 1 and 2.
By comparing the X-ray structures of 1 and 2, it is clear that
the ruthenium(ii) coordination polyhedra are very similar,
except for one particular Ru–N distance. In fact, the bond
between the metal and the nitrogen atom ortho to the linkage
point of the tolyl group borne by the phenanthroline nucleus is
ca. 0.06 Å longer in 1 than in the unsubstituted compound 2.
This difference probably reflects the steric effect of the aromatic
group in the vicinity of the Ru coordination sphere, which is
also in agreement with the close proximity between the tolyl
group and the central pyridine ring of the ttpy chelate. This
stacking situation is likely to result in donor–acceptor inter-
actions involving the tolyl group (donor) and the Ru-bonded
central pyridine (acceptor). This would explain the very
different photophysical behaviour of 1 as compared to 2.
The electrochemical and spectroscopic data for 1 and 2 are
collected in Table 1.
Transition-metal complexes exhibiting luminescence from
metal-to-ligand charge transfer (MLCT) excited states have
been the subject of numerous studies.1 In this field, the d6
polypyridyl complexes of RuII,2 OsII3,4 and ReI5 form the major
class of such compounds. Recently, cyclometallated com-
plexes6,7 of d6 and d8 transition-metal ions have also shown
interesting photophysical properties. Since ruthenium terpyr-
idine type complexes are particularly suitable to build up
multicomponent systems,8 the search for compounds of this
type displaying long-lived MLCT excited states at room
temperature remains a stimulating challenge. Here, we describe
the synthesis, crystal structures and photophysical properties of
two luminescent cyclometallated ruthenium complexes. Inter-
estingly, the photophysical properties of the compounds can be
strongly modified by introducing small structural changes in the
cyclometallating ligand.
In the presently reported complexes, 4A-tolyl-2,2A:6A,6B-
terpyridine (ttpy) affords NNN coordination. It is associated
with the 1,10-phenanthroline ligand bearing different aromatic
substituents in the 2 and 9 positions and leading to NNC
coordination. The aromatic sustituents are two tolyl groups for
Hdtp9 and a p-anisyl group for Hmap10 (Scheme 1).
The deep purple complexes [Ru(ttpy)(dtp)]+ 1 and [Ru(ttpy)-
(map)]+ 2 were prepared by the reaction of [Ru(ttpy)Cl3] with
It is of note that whereas 2 is practically not luminescent in
acetonitrile at room temperature, 1 luminesces and displays a
+
R
N
N
N
N
N
H
N
N
H
N
Me
N
Me
N
Ru
N
N
MeO
Me
Me
ttpy
Hmap
Hdtp
Me
+
+
Me
R =
R′
N
N
N
N
[Ru(ttpy)(dtp)]+
1
Me
N
Ru
N
Me
N
Ru
N
N
N
Cl
Me
R′ =
MeO
[Ru(ttpy)(map)]+
2
[Ru(ttpy)(Hmap)Cl]+ 3
Scheme 1
Chem. Commun., 1997
775

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relatively long-lived excited state (t = 95 ns). In fact, 1 seems
to be one of the longest-lived12 terpy-type ruthenium(ii)
complexes.
Clearly, the electronic properties of both compounds 1 and 2
seem to be almost identical (Table 1). The remarkable effect of
the tolyl group onto the MLCT excited state lifetime of 1 could
be related to the steric protection of the metal and strong
rigidifying of the molecular edifice via p–p interaction with the
ttpy ligand of the complex.
This work has been supported by the CNRS (France) and by
CNR (Italy). We thank Patrice Staub for his technical
assistance.
Footnotes
* E-mail: sauvage@chimie.u-strasbg.fr
†
Crystal data: 1, purple crystals from benzene–acetonitrile.
2(C48H36F6N5PRu)·CH3CN, M = 1898.8, monoclinic, space group P21/n;
a = 21.196(6), b = 17.212(5), c = 11.312(3) Å, b = 95.40(2), U
C(18)
=
4103(3) Å3, Z 1.537 g cm23, m 41.337 cm21
= 2, Dc = = .
Ru
N(4)
N(3)
Measurements: Philips PW1100/16, q–2q flying step-scans, Cu-Ka
graphite-monochromated radiation (l = 1.5418 Å), T = 173 K. 5396
reflections (q = 3–54°), of which 4334 unique with I > 3s(I) were used for
structure solution (direct methods) and refinement (full-matrix least
squares); R = 0.081, Rw = 0.143. The C(20)–C(26) tolyl moiety adopts two
orientations (50/50); for one of them a MeCN solvent molecule is present.
Atoms C(25)–C(26) in both orientations were introduced as fixed
contributors with isotropic temperature factors allowed to vary during
refinement. All other non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were calculated and fixed in idealized positions [d(C–
H) = 0.95 Å, B(H) = 1.3 Bequiv for the carbon to which it was attached]
with the exception of C(20)–C(26) tolyl and CH3CN protons not introduced.
2, dark blue crystals from benzene–acetonitrile. C41H30F6N5OPRu,
M = 854.8; monoclinic, space group P21/n; a = 12.535(3), b = 16.512(4),
c = 18.334(5) Å, b = 107.86(2), U = 3611(3) Å3, Z = 4, Dc = 1.572
g cm23, m = 5.387 cm21. Measurements: Nonius MACH3, q–2q scans,
Mo-Ka graphite-monochromated radiation (l = 0.7107 Å), T = 283 K.
8376 reflections (q = 2–26°), of which 3664 unique with I > 3s(I) were
used for structure solution (direct methods) and refinement (full-matrix least
squares); R = 0.056, Rw = 0.076. The fluorine atoms of the PF62 anion are
disordered over two positions (50/50) and where assigned isotropic
temperature factors. All other non-hydrogen atoms were refined anisotrop-
ically and treated as above. For all computations, the Nonius MolEN/Vax
package was used.13
N(1)
N(2)
N(5)
C(20)
C(26)
Fig. 1 ORTEP view of the cationic part of 1 with partial labelling scheme.
Ellipso¨ıds are scaled to enclose 30% of the electronic density. One
orientation of the C(20)–C(26) tolyl moiety is shown. Hydrogen atoms are
omitted. Selected distances (Å) and angles (°): Ru–N(1) 2.010(2), Ru–N(2)
2.256(3), Ru–N(3) 2.031(3), Ru–N(4) 1.942(3), Ru–N(5) 2.052(2), Ru–
C(18) 2.037(4); N(1)–Ru–N(2) 76.6(1), N(1)–Ru–C(18) 78.3(1), N(1)–Ru–
N(2) 100.6(1), N(3)–Ru–N(4) 79.8(1), N(4)–Ru–C(18) 93.5(1), N(2)–Ru–
N(4) 111.5(1).
Atomic coordinates, bond lengths and angles, and thermal parameters
have been deposited at the Cambridge Crystallographic Data Centre
(CCDC). See Information for Authors, Issue No. 1. Any request to the
CCDC for this material should quote the full literature citation and the
reference number 182/389.
C(18)
Ru
N(4)
N(5)
N(3)
N(2)
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N(1)
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Table 1 Electrochemicala and spectroscopic datab
Redox potential;
V vs. SCE
Ru3+/2+
L0/12
l
abs/nm
l
em/nm
t/ns
F
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1
2
3
0.54
0.54
0.77
21.57
21.54
21.50
527
518
508
802
95
0.02
c
c
c
820
6.6
@1 3 1025
a
Cyclic voltammetry in MeCN solution (0.1 m NBun4BF4); Pt working
electrode. b MeCN solutions; room temperature; uncorrected luminescence
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Received in Basel, Switzerland, 4th December 1996; Com.
6/08175D
776
Chem. Commun., 1997