Cyclopalladated complexes of perylene imine: Formation of acetato-bridged dinuclear complexes with 6,6- and 5,6-membered metallacycles

Article abstract of DOI:10.1021/om1010929

Perylene-3-carbaldehyde (1) was condensed with 4-ethylaniline to give 3-perilenylmetilen-4′-ethylaniline (2). The metalation reaction of 2 with palladium acetate, in toluene at 60 °C, produced a mixture of palladium complexes where the two major component

Full text of DOI:10.1021/om1010929

Organometallics 2011, 30, 1059–1066 1059
DOI: 10.1021/om1010929
Cyclopalladated Complexes of Perylene Imine: Formation of
Acetato-Bridged Dinuclear Complexes with 6,6- and 5,6-Membered
Metallacycles
ꢀ
Sergio Lentijo, Jesus A. Miguel,* and Pablo Espinet*
´
ꢀ
IU CINQUIMA Quımica Inorganica, Facultad de Ciencias, Universidad de Valladolid, 47071 Valladolid, Spain
Received November 19, 2010
Perylene-3-carbaldehyde (1) was condensed with 4-ethylaniline to give 3-perilenylmetilen-40-ethylani-
line (2). The metalation reaction of 2 with palladium acetate, in toluene at 60 °C, produced a mixture of
palladium complexes where the two major components, 3 and 4, have been characterized as acetate-
bridged dimers. Complex 3is made of two identical six-membered endo cyclometalated Pd(C∧N) moieties,
in which the palladium is bound to the peri site with anti arrangement. Compound 4 is the first example
combining six- and five-membered metallacycles in a dinuclear compound and adopts an unusual syn
arrangement of metal ligands. The X-ray structures of 3 and 4 show π-π stacking of perylenyl rings,
intermolecular for 3 and intramolecular for 4. The intramolecular π-π stacking in 4 has a detrimental
effect on luminescence. The imine 2 and all the palladium complexes exhibit fluorescence associated with
the perylene fragment, with emission quantum yields, in solution at room temperature, in the range
0.04-0.13 (and emission lifetimes ∼5 ns). The similarity of the luminescence spectral pattern of the imine
and their metalated complexes to that of perylene, although red-shifted, strongly suggests a perylene-
dominated intraligand π-π* emissive state, metal-perturbed by interaction of the palladium fragment.
Introduction
perylene and perylene monoimide, with Pt σ-bonded directly
to the perylene core,20 and have found that the coordination of
Pt has only a moderate quenching effect on the fluorescence
Cyclopalladated compounds, particularly those involving
benzene derivatives, have been widely studied for their appli-
cation in synthesis, catalysis, photochemistry, metallomesogen
chemistry, asymmetric synthesis, resolution of racemic ligands,
and other fields.1,2 The cyclometalation of N-donor ligands
involving fused ring has been less explored and poses the
question of regioselectivity of the orthometalation, due to
the presence of nonequivalent metalation positions. There
are a few reports on ligands based on two or three fused rings
with one or two nonequivalent metalation sites, leading to five-
or six-membered metallacycles,3 but not on higher polyaro-
matic systems, such as perylene, which are of interest for their
remarkable electro-optical properties.4-6 Perylene derivatives
have been used in photovoltaic cells,7 xerography,8 optical
switches,9 organic electronic devices such as organic light-
emitting diodes (OLED),10 laser dyes,11 and fluorescent
collectors,12 as tracers in fluorescence analytical assays,13 for
charge transport in Langmuir-Blodgett films,14 for liquid
crystals with special spectral properties,15 as fluorescent label-
ing reagents, or as fluorescent chemosensors,16 and recently,
providing highly fluorescent J-aggregates.17
(1) (a) Palladacycles; Dupont, J., Pfeffer, M., Eds.; Wiley-VCH:
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dated compounds see: (a) Slagt, M. Q.; Rodrıguez, G.; Grutters,
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Complexes have been reported where the metal center is
coordinated to a ligand that contains the perylene core18 or is
π-bonded to the perylene core.19 In contrast, perylene-contain-
ing transition metal compounds with a direct σ-bond of the
metal to the aromatic perylene core have been little studied. We
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*To whom correspondence should be addressed. E-mail espinet@
qi.uva.es.
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2011 American Chemical Society
Published on Web 01/18/2011
pubs.acs.org/Organometallics

1060 Organometallics, Vol. 30, No. 5, 2011
Lentijo et al.
(the organoplatinum derivatives kept 70-80% of the fluores-
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Article
Organometallics, Vol. 30, No. 5, 2011 1061
Figure 1. Metalation sites for the 3-substituted perylene.
Scheme 1
Figure 2. Possible isomers (enantiomers are not shown) de-
pending on the combination of ring size and coordination
isomerism. The number of members of the cyclometalated rings
is indicated inside each ring.
of the imine (see Figure 4). The structures of 3-anti and 4-syn
were further supported by X-ray diffraction studies (see later).
The formation of 3 or 4 is irreversible, and the isomers are
inert toward isomerization. Thus, heating 3 in toluene solution
does not produce any 4. However, some control of the direc-
tion of metalation can be achieved changing the reaction
conditions, as shown in synthetic experiments checked by
NMR. Thus, in THF at 30 °C for 48 h the molar ratio obtained
is 3:4 ≈ 1:1, and in THF at 50 °C for 24 h, 4 is obtained quite
preferently (molar ratio 3:4 ≈ 1:10). In both solvents the
metalation to six-membered cycles is more favorable, although
in the latter conditions the difference is small.27 It is remarkable
that all the five-membered moieties formed in the metalation
are found in the form of 6,5-dimers (besides 6,6-dimers
accounting for the excess of six-membered moieties in the
product), while no 5,5-dimers are observed. This suggests that
the combination 2 ꢀ (6,5) in a dimer is far more favorable than
the nonobserved (5,5) plus the corresponding (6,6).
temperature, to give 2 in good yield (Scheme 1). In the NMR
spectrum of 2, the signal of the imine proton (HCdN) appears
at rather low-field shift (9.08 ppm), showing the deshielding
induced by the perylenyl group. The orthopalladation reaction
of 2 with palladium acetate, in toluene at 60 °C for 2 h,
produced a deep purple suspension consisting of a mixture
of palladium complexes (Scheme 1). The two major compo-
nents, 3 and 4, could be separated in toluene (see Experimental
Section) and are acetate-bridged dimers. Complex 3, more
soluble in toluene, is made of two identical six-membered endo
cyclometalated Pd(C∧N) moieties, in which the palladium is
bound to the peri site. Compound 4 is a mixture of two isomers
(syn and anti) of a structure containing one six-membered and
one five-membered endo metallacycle. The separation of the
two isomers of 4 by recrystallization or chromatography
techniques was not possible.
X-ray Diffraction Crystal Structures. X-ray quality crystals
could be obtained for the dimers. Their molecular structures
were determined by single-crystal X-ray diffraction methods
and are shown in Figure 5. Selected bond lengths and angles
are collected in Table 1.
For complex 3 the crystal structure shows two six-membered
endo palladacycles (Figure 2). Reports of other X-ray structures
with six-membered palladacycles are scarce: a few complexes
derived from Schiff bases, with the ligand coordinated through
a CH2 (sp3) carbon, and only one complex that contains a
metalated aromatic (sp2) carbon atom, found in an endocyclic
six-membered cyclopalladated imine derived from anthracene.1
In the structure reported here, the dimeric molecules pack in
pairs via π-π stacking of two perylene rings, making none-
quivalent the two Pd atoms of each dimer. The plane-to-plane
The source of isomerism in these dinuclear complexes is the
fact that acetato bridges force the molecule into nonplanar
open-book (or butterfly) structures with syn or anti arrange-
ments depending on the arrangement of the imine moieties in
1
the dimer (Figure 2). The H NMR spectra of the crude
product initially isolated confirmed the presence of a single
isomer of 3, the anti isomer, and two isomers of 4 in approxi-
mately 4:1 syn:anti ratio (see Figure 3). As expected, the
spectrum of 3 displays one singlet for the two acetate groups
at 1.35 ppm and one ethyl group, whereas for 4 two signals for
the acetates (1:1) and two ethyl groups (1:1) are observed for
each of the two isomers. Therefore there are two singlets at 2.39
and 1.30 ppm corresponding to the two acetates of the 4-syn
isomer and two singlets at 1.68 and 1.52 ppm belonging to the
acetate group of the 4-anti isomer. The very different chemical
shift of the two acetate groups in 4-syn is due to the anisotropic
shielding induced on one of them by the close EtC6H4 groups
˚
stacking distance is 3.511 A. The coordination around Pd(1)
and around Pd(2) is essentially planar, as also are the π-π
stacked perylenes, but both are not coplanar. Both pallada-
cycles adopt an envelope-like conformation. Five of the six ring
atoms are almost coplanar, while the Pd atom is situated out of
˚
˚
the plane (0.3955 A for Pd(1) and 0.5709 A for Pd(2)).
(27) The proportion of 6- and 5-metallacycles formed would afford
approximate metalation rates of 9:1 in toluene at 60 °C and 6:5 in THF at
50 °C.

1062 Organometallics, Vol. 30, No. 5, 2011
Lentijo et al.
Figure 3. 1H NMR spectra (aliphatic zone) of 3 (top) and 4 (bottom).
In contrast, there is a much bigger distortion in the two
perylene fragments not involved in stacking, so that the
perylene is far from planar, particularly in the “naphthalene”
moiety bonded to Pd(1). A more detailed quantitative descrip-
tion is given in the Supporting Information.
For compound 4-syn the X-ray structure unambiguously
confirms two unusual features. First of all, the molecule
contains two dissimilar Pd(C∧N) moieties corresponding to
both possibilities of metalation: a perylene imine metalated at
the ortho-C(2) to yield a five-membered endo metallacycle
and another metalated at the peri-C(4) position, giving a six-
membered endo metallacycle. Moreover, the two imines adopt
a syn arrangement.28 The Pd(2) atom, with a five-membered
metallacycle, shows a slightly distorted square-planar geometry
(the maximum deviation is represented by the angle C(32)-Pd-
(2)-N(2) of 81.1° and the angle N(2)-Pd(2)-O(4) of 97.06°)
and is approximately coplanar with the perylene fragment
(dihedral angle between them, 3.06°). The other palladium
atom, Pd(1), is bound to C(7) (the peri position perylene
fragment), to N(1) of the imine group, and to O(1) and O(3)
of two different acetate groups. The coordination around the
Pd(1) is essentially planar, and the coordination angles are close
to the 90°. The conformation of the six-membered metallacycle
(28) To the best of our knowledge, only one example has been
ꢀ
reported of a syn disposition of the metalated imine ligands: Fernandez,
A.; Vazquez-Garcıa, V.; Fernandez, J. J.; Lopez-Torres, M.; Suarez, A.;
ꢀ
ꢀ
ꢀ
ꢀ
Castro-Juiz, S.; Vila, J. M. Eur. J. Inorg. Chem. 2002, 2389.

Article
Organometallics, Vol. 30, No. 5, 2011 1063
˚
Table 1. Selected Interatomic Distances (A) and Angles (deg) for
the Complexes 3-anti and 4-syn
3-anti
4-syn
Pd(1)-C(7)
1.980(6)
1.997(4)
2.068(4)
2.144(4)
1.972(6)
1.985(5)
2.048(4)
2.152(4)
1.962(5)
Pd(1)-N(1)
Pd(1)-O(1)
Pd(1)-O(3)
Pd(2)-C(32)
Pd(2)-C(37)
1.964(6)
2.003(5)
2.060(4)
2.143(4)
2.923
Pd(2)-N(2)
2.031(5)
2.055(4)
2.123(4)
2.907
Pd(2)-O(2)
Pd(2)-O(4)
Pd(1)-Pd(2)
C(7)-Pd(1)-N(1)
C(7)-Pd(1)-O(1)
N(1)-Pd(1)-O(1)
C(7)-Pd(1)-O(3)
N(1)-Pd(1)-O(3)
O(1)-Pd(1)-O(3)
C(32)-Pd(2)-N(2)
C(37)-Pd(2)-N(2)
C(32)-Pd(2)-O(2)
C(37)-Pd(2)-O(2)
N(2)-Pd(2)-O(2)
C(32)-Pd(2)-O(4)
C(37)-Pd(2)-O(4)
N(2)-Pd(2)-O(4)
O(2)-Pd(2)-O(4)
91.4(2)
91.0(2)
92.34(19)
174.77(17)
177.44(19)
90.81(17)
85.41(16)
91.19(19)
174.68(17)
174.89(18)
91.26(18)
86.98(17)
81.1(2)
Figure 4. Anisotropic shielding of one of two acetate groups in
4-syn by the close EtC6H4 groups of the imine.
91.6(2)
92.8(2)
90.5(2)
177.44(18)
172.84
176.32(19)
175.9(2)
92.40(17)
85.47(16)
97.06(18)
88.77(17)
Figure 6. X-ray packing view of complex 3 showing intermole-
cular π-stacking of the perylene groups.
Figure 5. ORTEPs of the crystal structures of 3-anti and 4-syn.
The ellipsoids are shown at 30% probability (H atoms are
omitted for clarity).
is as expected for a six-membered ring (see above). The Pd atom
˚
is situated 0.6741 A out of the plane C(1)-C(6)-C(7)-C-
Figure 7. Intramolecular π-stacking of the perylene groups in
4-syn.
(21)-N(1). In spite of these differences, the two perylene
fragments display fairly good π-π stacking. The angle between
˚
˚
the planes is 1.6°, and the average stacking separation is 3.48 A
(Figure 7).
2.048-2.068 A for bonds trans to N and in the range
˚
2.123-2.152 A for bonds trans to C, as expected from their
dissimilar trans influences.
As for other features found in the structures of 3 and 4,
˚
they are quite normal. The Pd-Pd distances are 2.923 A in 3
and 2.907 A in 4, both within the range observed in similar
The fact that complex 4-syn is the first example of a six-
and five-membered metallacycle in a dinuclear compound,
and combining this with an unusual syn arrangement of
metal ligands, suggests that this might not be by chance. It
˚
structures containing bridging acetate groups. The Pd-O
bond lengths to the acetate groups are in the range

1064 Organometallics, Vol. 30, No. 5, 2011
Lentijo et al.
Table 2. UV-Visible Absorption and Emission Data for Perylene-3-carbaldehyde (1), the Imine 2, and Their Palladium Complexes 3 and 4,
in Chloroform at 298 K
compd
λ (nm) (10-3 ε)/dm3 mol-1 cm-1
λex /nm
λem/nm
Φa
τb/ns
1
2
3
4
240 (26), 263 (30.6), 425 (15), 449 (24), 476 (26.4)
467
447
516, 551
526, 542
516, 553
510
588, 634
586, 634
0.53
0.13
0.09
0.04
243 (34.5), 263 (51.6), 425 (17), 449 (33.8), 477 (33.8)
241 (65.2), 276 (39.1), 359 (16.6), 487 (21,1), 519 (34.3), 553 (34.9)
243 (62.6), 361 (14.4), 492 (26.6), 522 (38.4), 557 (31.6)
5.29
0.87 (94.9) 3.37 (5.1)
0.95 (78.9) 8.31 (21.1)
a Quantum yield. b Fluorescence lifetimes. Decays were biexponential; numbers in parentheses indicate the relative amplitude of components.
Figure 9. Emission spectra recorded in CHCl3 solution (10-5 M)
Figure 8. Absorption spectra, recorded in CHCl3 solution
(∼10-5 M) at room temperature, for perylene-3-carbaldehyde
at room temperature.
(1) and imine 2 and their dinuclear palladium complexes 3 and 4.
the free imine, showing that when palladium is σ-bonded to the
looks that the combination of the slight flexibility of the six-
perylene fragment, a noticeable perturbation in the electronic
membered metallacycle with the rigidity of the five-mem-
spectrum of the perylene imine occurs, due to the interaction
bered metallacycle strongly favors a good a π-π stacking
between the Pd orbitals and the perylene π-system. It is
with additional stabilization of the molecule, which in part
noticeable that the relative peak intensity of the dinuclear
compensates the usual preference for the anti arrangement
complex 4 is different from that of complex 3. The absorption
found in the other products of the reaction. Thus, for the 6,6
maximum of 4 is at 522 nm, which is blue-shifted relative to
complexes only the anti arrangement is observed; for the 6,5
that of 3 (absorption maximum at 553 nm). This intensity
complexes, both syn and anti are formed, but the syn is the
change can be attributed to the formation of a face-to-face
major isomer (4:1).
stacked perylene fragment.29 Another difference observed
Photophysical Studies. a. UV-Vis Absorption Spectra.
upon complexation is the appearance of weak absorptions in
The UV-vis absorption and emission spectra of the aldehyde,
the range 335-380 nm, with extinction coefficients of 14.4 ꢀ
imine, and palladium(II) complexes of dilute solutions in
103 M-1 (for4) and 16.6 ꢀ 103 M-1 (for3), tentativelyassigned
chloroform (c ≈ 10-5 M) are summarized in Table 2. On the
to intraligand π-π* transitions.
other hand, the absorption spectra of 3 and 4 are compared
Moreover, the lowest energy bands of 3 are only slightly
with those of perylene-3-carbaldehyde (1) and perylene
sensitive to solvent polarity, as they are red-shifted by less than
imine (2) in Figure 2. By similarity to the absorption bands
200 cm-1 upon changing the solvent from toluene to chloro-
of the free imine ligand, the high-energy absorption bands
form (see Figure S3 in the Supporting Information). This
at 250-300 nm are tentatively assigned to the intraligand
behavior suggests that these bands are most probably linked
transitions. In the palladium complexes the low-energy bands
to electronic π-π* transitions within the ligand, rather than to
exhibit red shifts most likely associated with the disturbance
charge transfers.
of the π-π* transitions by the metal and appear at about
b. Luminescence Spectra. The luminescence spectra of the
540 nm.
perylene-3-carbaldehyde (1), perylene imine (2), and the
The UV-vis spectra of perylene-3-carbaldehyde (1) and
palladium complexes at room temperature in chloroform
imine 2 (Figure 8) are very similar, with two intense absorp-
are listed in Table 2. All complexes exhibit luminescence in
tions assigned to perylene π-π* transitions, namely, a first
solution (which is unusual for Pd complexes) and display
band in the ultraviolet in the range 230-320 nm with two
emission bands with scarcely defined vibronic structures in
maxima at 240 and 263 nm and a second band in the visible
the range 550-700 nm (see Figure 9), which can be correlated
region in the range 380-530 nm with one shoulder and two
to those well-defined for perylene at about 425-525 nm and
peaks at 425, 449, and 476 nm, respectively. These lowest
also scarcely defined for 1 and 2 at about 450-625 nm. The
energy bands have similar band shapes that resemble the
structurally similar luminescence spectra of all these cyclo-
spectrum of perylene (a vibronic structure with a vibrational
metalated complexes strongly suggest a ligand-dominated
spacing of ∼1300 cm-1 due to the stretching frequency of the
emissive state, which can be assigned as intraligand π-π*
CdC bond of the aromatic systems), with a moderate red
transitions disturbed by the metal. On the basis of similar
shift of ca. 1800 cm-1 relative to perylene.
Stokes shifts from absorption to emission for 2 and for the
Similar absorption patterns are observed in the dinuclear
complexes 3 and 4, supporting that the perylene imine chro-
mophore is largely responsible for the structured π-π* transi-
(29) (a) Han, J.; Wang, W.; Li, A. D. Q. J. Am. Chem. Soc. 2006, 128,
672. (b) Wang, Y.; Chen, H.; Wu, H.; Li, X.; Weng, Y. J. Am. Chem. Soc.
tions between 435-590 nm. The lowest energy bands are
2009, 131, 30. (c) Giaimo, G. M.; Lockard, J. V.; Sinks, L. E.; Scott, A. M.;
significantly red-shifted about 2900 cm-1 relative to those of
Wilson, T. M.; Wasielewski, M. R. J. Phys. Chem. A 2008, 112, 2322–2330.

Article
Organometallics, Vol. 30, No. 5, 2011 1065
complexes (less than 1000 cm-1), the luminescence observed
can be assigned to π-π* fluorescence, which is supported by
the fact that the emission properties remain unchanged in the
presence of air, and further confirmed by their emission
lifetimes (in the range 0.8-9 ns; see Table 2).
exhibit fluorescence associated with the perylene system in
solution at room temperature. The intramolecular π-π inter-
actions observed for 4-syn, which persist in solution, explain
the difference between the absorption spectra of 3 and 4 and
the lower emission quantum yields for 4.
Study of Quantum Yields. The emission quantum yields, Φ,
for 1-4, measured in dichloromethane at room temperature,
are in the range 0.04-0.53 (Table 2). The fluorescence quan-
tum yields of 1 and 2 were determined relative to perylene in
methanol (Φfl = 0.92), using an excitation wavelength 434 nm.
The palladated complexes were determined using cresyl violet
in methanol (Φfl=0.54), with an excitation wavelength of
540 nm.
The fluorescence quantum yields of the perylene-3-carbal-
dehyde (1) (0.53) is smaller than that of perylene and similar to
3-aminoperylene.30 The fluorescence intensity of the imine 2 is
significantly lower (0.13) than the emission of the perylene
moiety, probably because the fluorescence of the perylene
moiety is quenched by a photoinduced intramolecular electron
transfer (PET) process.31 For the cyclopalladated complexes 3
and 4 the emission quantum yield is somewhat lower than for
the imine precursor, but still on the same order of magnitude,
which for Pd complexes is notably high. The Pd quenching
effect is lower than usual probably because the interaction of
Pd with the perylene is mainly a σ interaction involving the 4dz
orbital of Pd, with very little π component. Due to the high
stabilization of the d orbitals at the end of the transition metal
series,32 the π back-bonding component of this bond, which
should involve donation from the π orbitals of Pd to the π*
orbitals of the aryl, is expected to be small. The same effect has
been observed in related Pd23 and Pt systems.20
Experimental Section
Materials and General Methods. All reactions were carried out
under dry nitrogen. The solvents were purified according to
standard procedures. C, H, N analyses were carried out on a
Perkin-Elmer 2400 microanalyzer. IR spectra (cm-1) were re-
1
corded on a Perkin-Elmer FT-1720X spectrometer. H NMR
spectra were recorded on Bruker AC 300 or Bruker 400 MHz
spectrophotometers in CDCl3, with chemical shifts referred to
TMS. UV-vis absorption spectra were obtained on a Shimadzu
UV-1603 spectrophotometer, in chloroform solution (1 ꢀ
10-5 M). Luminescence data were recorded on a Perkin-Elmer
LS-luminescence spectrometer, in CHCl3 (1 ꢀ 10-5 M). Lumines-
cence quantum yields were obtained at room temperature using
the optically dilute method (A < 0.1) in degassed dichloro-
methane (quantum yield standards were perylene in methanol
(Φfl = 0.92)33 and violet of cresyl violet in ethanol (Φfl = 0.54)34
and using an excitation wavelength of 434 and 540 nm, respec-
tively, in dichloromethane). The emission lifetime measure-
ments were carried out with a Lifespec-red picosecond fluor-
escence lifetime spectrometer from Edinburgh Instruments.
As excitation sources two diode lasers, with 405 and 470 nm
nominal wavelengths, were used. The first wavelength (405 nm)
has a pulse width of 88.5 ps, with a typical average power of
0.40 mW. The second wavelength (470 nm) has a pulse width of
97.2 ps, and its typical average power is 0.15 mW. The pulse period
is 1 μs, and the pulse repetition frequency is 10 MHz. The mono-
chromator slit is 2 nm. The instrument response measure at hwhm
(half-width at half-maximum) was below 350 ps. The technique
used is “time-correlated single-photon counting” (TCSPC).
Preparation of Perylene-3-carbaldehyde (1). This compound
was synthesized by following the procedure reported before.26
UV-vis (CHCl3) λmax (nm) (10-3ε)/(M-1 cm-1) = 240 (26), 263
(30.6), 449 (24), 476 (26.4). Fluorescence emission (CHCl3, λexc
= 467 nm) λem = 516 nm, 553 nm.
The difference between the emission quantum yields for 3
(φfluo = 0.09) and 4 (φfluo = 0.04) is remarkable and can be
related to their structure, since the two aromatic rings of
perylene in 4 have an intramolecular π-π stacking inter-
action between them, which induces a loss of luminescence
intensity,28b-c not observed in 3, where the anti arrangement of
the imines prevents that interaction.
Preparation of 3-Perilenylmetilen-40-ethylaniline (2). To a
mixture of perylene-3-carbaldehyde (1) (0.439 g, 1.56 mmol) in
toluene (70 mL) under a nitrogen atmosphere were added 4-ethy-
laniline (0.23 mL, 1.85 mmol), zeoliths, and a small crystal of
monohydrated p-toluensulfonic acid. The orange mixture was
stirred in the dark at room temperature overnight, then filtered
through a Kieselguhr filter, and orange crystals were obtained by
cooling the toluene solution (0.400 g, 67%) at -20 °C. Anal. Calcd
for C29H21N (383.49): C, 90.82; H, 5.51; N 3.65. Found: C, 90.50;
H, 5.45; N, 3.55. 1H NMR (300.13 MHz, CDCl3): δ 9.08 (s, 1H,
HCdN), 8.90 (d, J= 8.3 Hz, 1H), 8.31-8.25 (m, 4H), 8.12 (d, J=
7.9 Hz, 1H), 7.74 (t, J = 8.3 Hz, 2H), 7.64 (t, J = 7.9 Hz, 1H), 7.53
(t, J = 8.3 Hz, 2H), 7.28 (s, AA0BB0 system, 4H, C6H4), 2.72 (q,
J = 7.9 Hz, 2H, CH2CH3), 1.30 (t, J = 7.9 Hz, 3H, CH2CH3).
UV-vis (CHCl3) λmax (nm) (10-3ε)/ (M-1 cm-1) = 243 (34.5),
263 (51.6), 449 (33.8), 477 (33.8). Fluorescence emission (CHCl3,
Conclusions
The metalation of 3-perilenylmetilen-40-ethylaniline with
palladium acetate shows preference for the peri position with
respect to the imine group, giving six-membered metallacycles,
but metalation at the ortho position, giving five-membered
metallacycles, also occurs. The combination of 5,5-metalla-
cycles into dimers is not observed: all the five-membered
moieties make part of the 6,5-dimers, suggesting that this
combination in the dimer is energetically favored. The struc-
ture of the major isomer of 4, 4-syn, compared to that of 3,
suggests that the combination 6,5 into acetato-bridged dimers
might increase the intramolecular π-π interactions and also
reduce slightly the Pd-Pd distance. In contrast with the
majority of palladium complexes reported so far, which
usually emit only at low temperatures, complexes 3 and 4
λexc = 447 nm) λem = 510 nm.
Preparation of 3 and 4. A mixture of 2 (0.370 g, 0.96 mmol) and
Pd3(OAc)6 (0.196 g, 0.87 mmol) in toluene (20 mL) was stirred
under a nitrogen atmosphere at 60 °C for 2 h. The reaction mixture
was cooled to room temperature, and the two compounds could
be separated (3 is in the solution and 4 is insoluble).
(30) Mohammed, O. F.; Vauthey, E. Chem. Phys. Lett. 2010, 487,
246.
(31) (a) De Silva, A. P.; Rupasinghe, R. A. D. D. Chem. Commun.
1985, 1669. (b) de Silva, B. P.; Lgunaratne, H. Q. N.; Gunnlangsson, T. L.;
Unzley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. Rev.
The purple filtrate solution was evaporated, and the final
residue was washed with diethyl ether (4 ꢀ 10 mL) and acetone
ꢀ~
ꢀ
1997, 97, 1515. (c) Martínez-Manez, R.; Sancenon, F. Chem. Rev. 2003, 103,
4419.
(33) Montalti, M.; Credi, A.; Prodi, L.; Gandolfini, M. T. Handbook
of Photochemistry, 3rd ed.; CRC Press LLC: Boca Raton, FL, 2005.
(34) Magde, D.; Brannon, J. H.; Cremers, T. L.; Olmsted, J. J. Phys.
Chem. 1979, 83, 696.
(32) Anderson, G. K. In Comprehensive Organometallic Chemistry II;
Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Pergamon: Oxford, U.K.,
1995; Vol. 9, p 445.

1066 Organometallics, Vol. 30, No. 5, 2011
Lentijo et al.
(2 ꢀ 5 mL). The residue was dried under vacuum to obtain
compound 3 as a dark purple solid (0.197 g, 41%). Anal. Calcd
for C62H48N2O4Pd2 (1097.91): C, 67.71; H, 4.58; N 2.55. Found:
C, 67.07; H, 4.10; N 2.48. 1H NMR (400 MHz, CDCl3): δ 8.45
(d, J = 7.9 Hz, 2H), 8.33-8.26 (m, 4H), 7.99 (d, J = 8.3 Hz, 2H),
7.90, 6.75 (AA0BB0 system, J = 8.1 Hz, 8H), 7.78 (d, J = 7.9 Hz,
2H), 7.65 (m, 4H), 7.07-7.03 (m, 6H), 6.67 (d, J = 7.9 Hz, 2H),
2.60 (q, J = 7.5 Hz, 4H, CH2CH3), 1.35 (s, 6H, CH3), 1.20 (t,
J = 7.5 Hz, 6H, CH2CH3). Fluorescence emission (CHCl3,
diffusion of hexane into a THF solution of the crude products at
room temperature. Crystals from 4 were grown from slow diffu-
sion of Et2O into a dichloromethane solution of the product
at -20 °C. Data were taken on a Bruker AXS SMART 1000
CCD diffractometer, using φ and ω scans, Mo KR radiation (λ =
˚
0.71073 A), a graphite monochromator, and T = 298 K. Raw
frame datawereintegrated with the SAINT35 program. Structures
were solved by direct methods with SHELXTL.36 Semiempirical
absorption correction was made with SADABS.37 All non-hydro-
gen atoms were refined anisotropically. Hydrogen atoms were set
in calculated positions and refined as riding atoms, with a
common thermal parameter. All calculations were made with
SHELXTL. In the structures of compounds 3 and 4 there is an
incipient disorder in the ethyl groups of the imine ligands that
could not be satisfactory modeled. Compound 3 crystallized
with two molecules of disordered THF. Crystallographic data
(excluding structure factors) for the structures reported in this
paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publications with the following
deposition numbers: CCDC 797245 and 797246 for complexes 3
and 4, respectively. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif. A table with the X-ray structure data is
provided in the SI.
λ
exc = 516, 551 nm) λem = 588 nm, 634 nm. UV-vis (CHCl3)
λmax (nm) (10-3ε)/(M-1 cm-1) = 241 (65.2), 276 (39.1), 359
(16.6), 519 (34.3), 553 (34.9).
The precipitate was collected by filtration, washed with toluene
(2 ꢀ 3 mL), and dried under vacuum to obtain compound 4 as a
mixture of isomers syn/anti with ratio 4:1 (0.150 g, 31%). Anal.
Calcd for C62H48N2O4Pd2 (1097.91): C, 67.71; H, 4.58; N, 2.55.
Found: C, 67.43; H, 4.40; N, 2.35. 1H NMR (400 MHz, CDCl3)
syn þ anti isomers: δ 8.5-8.2 m, 8.0-7.3 m 7.1-6.3 m. (The
aromatic signals for 4 are too complex to be reported in detail.
This part of the spectrum is given in the SI, as Figure S1.)
syn isomer: δ 2.85 (q, J = 7.5 Hz, 2 H, CH2CH3), 2.58 (q, J =
7.8 Hz, 2H, CH2CH3), 2.39 (s, 3H, CH3), 1.44 (t, J = 7.5 Hz, 3H,
CH2CH3), 1.30 (s, 3H, CH3), 1.18 (t, J = 7.5 Hz, 3H, CH2CH3);
anti isomer: δ 2.60 (q, J = 7.5 Hz, 2H, CH2CH3), 2.50 (q, J = 7.8
Hz, 2H, CH2CH3), 1.68 (s, 3H, CH3), 1.52 (s, 3H, CH3), 1.21 (t,
J = 7.6 Hz, 3H, CH2CH3), 1.11 (t, J = 7.6 Hz, 3H, CH2CH3).
UV-vis (CHCl3) λmax (nm) (10-3ε)/(M-1 cm-1) = 243 (62.6),
361 (14.4), 522 (38.4), 553 (30.1). Fluorescence emission (CHCl3,
ꢀ
Acknowledgment. We thank the Spanish Comision
Interministerial de Ciencia y Tecnologıa (CTQ2008-03954/
BQU and MAT2008-06522-C02-02), INTECAT Consoli-
der Ingenio 2010 (CSD2006-0003), and the Junta de
ꢀ
Castilla y Leon (Project VA012A08 and GR169) for finan-
cial support.
λexc = 516, 551 nm): λem = 588 nm, 634 nm.
X-ray Crystal Structure Analysis. Single crystals of 3 2THF
3
suitable for X-ray diffraction studies were obtained from slow
1
Supporting Information Available: H NMR spectra (aromatic
(35) SAINTþ. SAX area detector integration program, Version 6.02;
Bruker AXS, Inc.: Madison, WI, 1999.
(36) Sheldrick, G. M. SHELXTL, An integrated system for solving,
refining, and displaying crystal structures from diffraction data, Version
5.1; Bruker AXS, Inc.: Madison, WI, 1998.
zone) of 3 and 4, Table S1 with X-ray structure data, a more
detailed quantitative description of the crystal structures of 3 and
4, absorption spectra of 3 in different solvents, and emission
spectra of 3. This material is available free of charge via the
Internet at http://pubs.acs.org.
(37) Sheldrick, G. M. SADABS, Empirical Absorption Correction
€
€
Program; University of Gottingen: Gottingen, Germany, 1997.