Cyclopalladated complexes of perylene imine: Mononuclear complexes with five- or six-membered metallacycles

Article abstract of DOI:10.1039/c1dt10598a

Mononuclear palladium complexes [Pd(CN)L₂] (HCN = 3-C ₂₀H₁₁CHNC₆H₄-p-C₂H ₅) have been prepared with Pd bound to the peri site or to the ortho site of the perylenyl fragment. Thes

Full text of DOI:10.1039/c1dt10598a

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PAPER
Cyclopalladated complexes of perylene imine: mononuclear complexes with
five- or six-membered metallacycles†
Sergio Lentijo, Jesu´s A. Miguel* and Pablo Espinet*
Received 7th April 2011, Accepted 19th May 2011
DOI: 10.1039/c1dt10598a
Mononuclear palladium complexes [Pd(CŸN)L2] (HCŸN = 3-C20H11CH NC6H4-p-C2H5) have been
prepared with Pd bound to the peri site or to the ortho site of the perylenyl fragment. These metallations
correspond, respectively to six-membered (L2 = S2COMe (3); acac (4); Cl, PMe3 (5); Cl, PPh3 (6);
S2CNEt2 (7)) or five-membered (L2 = S2COMe (8); acac (9)) isomeric palladacyclic compounds. The
X-ray structures of 3, 5, 7 and 8 show that the perylenyl fragment remains essentially flat for 3, 7 and 8
and twisted for 5. Intermolecular p–p stacking of perylenyl rings is observed only for 7. All palladium
complexes exhibit fluorescence associated to the perylene fragments, with emission quantum yields (in
solution at room temperature) in the range 0.01–0.12 (compared to 0.13 for the free imine), and
emission lifetimes ~ 1 ns. The complexes with five-membered palladacycles show lower quantum yields
than their six-membered analogs. The similarity in shape of the luminescence spectra of these metallated
complexes with perylene, although red-shifted, strongly suggests a perylene-dominated intraligand p–p*
emissive state, metal-perturbed by interaction of the perylene orbitals with the palladium fragment.
Introduction
Palladacyclic complexes have been widely studied for their
applications.1,2 In this article we are concerned with cy-
clopalladated compounds derived from polyaromatic systems,
such as perylene, which could offer remarkable electro-optical
properties.3–5 Only two perylene complexes of Pd had been
reported until recently, and these are not cyclopalladated com-
pounds. They contain Pd directly attached to the 1,7 aromatic
positions of a perylene diimide and were obtained by Rybtchin-
ski’s group by oxidative addition of the appropriate perylenyl
halide to Pd(0).6 The cyclopalladation reaction should offer
a good opportunity to extend the family of Pd derivatives
bearing perylene fragments.1 In effect, recently we showed that
the dimeric complexes 1 and 2 could be synthesized by react-
Scheme 1
ing 3-perylenylmethylen-4¢-ethylaniline with palladium acetate
(Scheme 1).7
As expected, the perylene imine and the two palladium com-
and five-membered metallacycles in the dinuclear molecule, and
plexes exhibited fluorescence associated to the perylene fragment.
adopts an unusual syn arrangement of the ligands. The different
The complexes were characterized by X-ray diffraction methods.
sizes of the palladacycles involved in 1 and 2 arise from competitive
Complex 1 is made of two identical six-membered endo cyclomet-
metallation at the ortho and peri positions of 3-perilenylmethylen-
allated Pd(CŸN) moieties, in which the palladium is bound to the
4¢-ethylaniline (Fig. 1).
peri site with an anti arrangement. Compound 2 combines six-
Another remarkable feature of the X-ray structures of 1 and
2 is the observation of p–p stacking of perylenyl rings, which is
intermolecular for 1 and intramolecular for 2. Apparently the
intramolecular p–p stacking in 2 has a detrimental effect on
luminescence, so that the emission quantum yields are Ufl = 0.09
for 1, and Ufl = 0.04 for 2). However, since the possible dinuclear
complex containing two five-membered cyclopalladated halves
was not observed, there was no reference to estimate whether the
IU CINQUIMA Qu´ımica Inorga´nica, Facultad de Ciencias, Universidad de
Valladolid, 47071, Valladolid, Spain. E-mail: espinet@qi.uva.es
† Electronic supplementary information (ESI) available: 1H NMR spectra
(aromatic zone) of 3 and 8. Absorption and emission spectra of 7 in
different solvents. CCDC reference numbers 818347–818350. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1dt10598a
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the protons coupled to phosphorus of trimethylphosphine, and
very complicated aromatic resonances for 6, which has more
aromatic hydrogen atoms overlapping in the same region. The
1
31P{ H} NMR spectra in CDCl3 showed a singlet at -5.0 for 5,
and 35.9 ppm for 6.
The diethyldithiocarbamate complex 7 was prepared by reaction
of 1 with excess of sodium diethyldithiocarbamate (1 : 3 molar
ratio) in a mixture of dichloromethane/acetone = 1 : 1 at room
temperature. The 1H NMR spectrum of 7 shows a singlet at
8.37 ppm, assigned to the iminic proton, and two quadruplets
at 3.72 and 2.73 ppm as well as two triplets at 1.31 and 1.29 ppm,
corresponding to the two non-equivalent ethyl groups of the
diethyldithiocarbamate ligand.
Fig. 1 Metallation sites in 3-perilenylmethylen-4¢-ethylaniline.
difference in quantum yields was due to the stacking or whether
the luminescence was also influenced by the participation of one
five-membered, instead of a six-membered, palladacycle in 2.
This possible influence might be observed easily by comparing
five-membered with six-membered mononuclear derivatives. Our
dimeric systems offer the rare opportunity to produce pairs of ring-
size isomers. Thus, we report here the synthesis of either five- or
six-membered mononuclear cyclopalladated perylenyl complexes,
obtained by splitting of the dinuclear complexes 1 and 2, and study
their optical properties.
Starting from the minor isomer 2, similar reactions as for 1
are expected to produce 1 : 1 mixtures of the corresponding six-
membered and five-membered complexes (Scheme 3). In effect,
the reaction of complex 2 with a solution of KOH in methanol
(1 M) and CS2 in dichloromethane afforded a 1 : 1 mixture of
isomers 3 and 8. The two compounds 3 and 8 could be separated by
crystallization in dichloromethane/toluene at -20 ◦C, whereupon
isomer 8, was more insoluble, which contains a five-membered
palladacycle, and precipitated as a red solid, while 3 remained
in solution with traces of 8. Thus we have in our hands pure 8,
obtained from 2, and pure 3, obtained from 1. Comparison of
Results and discussion
Compounds 3–6, containing six-membered palladacycles, were
synthesized starting from the corresponding acetato-bridged
complexes 1 and 2 as shown in Scheme 2. Thus, reaction of
the dinuclear complex 1 with a solution of KOH in methanol
(1 M) and CS2 in dichloromethane at room temperature led to
displacement of the bridging acetato ligand by xanthate, and
afforded the mononuclear complex 3 as a red solid. Similarly,
the treatment of the dinuclear complex 1, in dichloromethane at
room temperature, with a slight excess of K(acac) (obtained in situ
by reaction of acetylacetone and a solution of KOH in methanol
1 M) provided the acetylacetonate complex 4 as a purple solid.
1
the H NMR spectra of 3 and 8 shows a significantly different
appearance of the aromatic resonances (see Fig. S1 in the ESI†).
The chemical shifts shown by the iminic protons (8.40 for 3 and
8.88 ppm for 8) and the OCH3 groups (4.10 for 3 and 4.28 ppm
for 8) reveal deshielding in the signals of the five-membered
metallacyclic compound 8, as compared with 3.
Scheme 3 i) KOH + MeOH, CS2; ii) K(acac).
Treatment of the dinuclear complex 2, in dichloromethane
at room temperature, with a slight excess of K(acac) provided
a mixture of the two isomers 4 and 9. Recrystallization in
dichloromethane/toluene produced the precipitation of 9, while 4
remained in solution with traces of 9. Again, we have pure samples
1
of 4, obtained from 1, and 9, obtained from 2. The H NMR
Scheme 2 i) KOH + MeOH, CS2; ii) K(acac); iii) LiCl, PR3; iv)
spectrum of 4 in CDCl3 showed a singlet at 8.34 ppm, assigned
to the iminic proton, one singlet at 5.28 ppm corresponding to
Cg -H, and two singlets at 1.54 and 1.52 ppm for the two non-
equivalent methyl groups of the acetylacetonate ligand. Similar to
the xanthate complexes, a shielding is observed for these protons
in the six-membered metallacycle complex compared to the values
in the five-membered metallacycle compound 9 (8.79 ppm for the
iminic proton and 5.44, 2.26 and 1.95 ppm for the acac ligand).
In other words, the deshielding induced by the perylenyl group on
the other ligands attached to Pd is larger when the palladium
NaS2CNEt2.
The metathesis reaction of 1 with two equivalents of LiCl and
subsequent addition of either PMe3 or PPh3 in THF at room
temperature led to the formation of the mononuclear complexes
5 and 6 respectively, as purple solids. A ligand arrangement
with the phosphorous atom trans to the iminic nitrogens is
proposed in agreement with the trans influences of the ligands.8
The 1H NMR spectrum of compound 5 shows a doublet at
1.46 ppm with a coupling constant JP-H = 10.8 Hz, assigned to
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is bonded to the perylene core in an ortho-(2) position (five-
membered metallacycle).
For the reactions that should produce the five-membered
isomers of 5–7, the higher and more similar the solubility of the
complexes precluded separation of the isomers.
Crystal structures
X-ray quality crystals of complexes 3, 5, 7 and 8 allowed for the
determination of their molecular structures by single-crystal X-ray
diffraction methods. These are shown in Fig. 2.
The crystal structures in all cases confirm the existence of the
Pd(CŸN) moieties proposed in Scheme 1. In the mononuclear
complexes 3, 5, 7 the palladium atom is metallated at the peri-C(4)
position, forming a six-membered endo metallacycle. Apart from
the recently published binuclear complexes 1 and 2,7 reports of
other X-ray structures with six-membered palladacycles derived
from Schiff bases are very scarce, and in most of them the
metallated carbon is sp3, in a CH2 group. Only one previous case
contains a metallated aromatic (sp2) carbon atom, included in
an endocyclic six-membered cyclopalladated imine derived from
anthracene.9 For complex 8 the crystal structure shows metallation
of the other site available in the perylene imine, the ortho carbon
C(2), yielding a five-membered endo metallacycle. This allows us
to compare the structural differences in isomers 3 and 8.
The six-membered palladacycles of 3, 5 and 7 adopt an
envelope-like conformation very similar to that found in the six-
membered palladacycles of 1.7 Five of the six ring atoms are
almost coplanar, while the Pd atom is out of the plane C(1)–
˚
˚
˚
C(6)–C(7)–C21)–N(1) (0.323 A for 3, 0.802 A for 5, and 0.388 A
for 7). In contrast, the five-membered metallacycle of 8 is, as
expected, almost planar (mean deviations from the least-squares of
˚
0.0479 A) and approximately coplanar with the perylene fragment
(dihedral angle between them, 7.56◦).
Selected bond lengths and angles in compounds 3, 5, 7 and 8
are collected in Table 1. The Pd–S bond lengths in the xanthate or
˚
carbamate complexes 3, 6 or 8 are in the range 2.300–2.320 A for
˚
bonds trans to N, and in the range 2.412–2.434 A for bonds trans
to C, reflecting the dissimilar trans influences of N- and C-donors.
In the xanthate derivatives 3 and 8 the palladium atom is bonded
in a distorted square planar geometry (the maximum deviation
is represented by the bite angle at the xanthate ligand S–Pd–S
(73.80(3)◦ for 3 and 74.56(6)◦ for 8). The perylene fragments are
essentially planar in both complexes (the dihedral angle of the two
“naphthalene” moieties forming the perylene fragment is 2.90◦
and 0.84◦, respectively) and makes angles of 16.13◦ and 10.64◦ to
the coordination plane of palladium, in 3 and 8 respectively. The
angle N–Pd–C is 92.47◦ for 3 and only 80.77◦ for 8.
Fig. 2 ORTEPs of the crystal structures of 3, 5, 7, and 8. The ellipsoids
are shown at 30% probability (H atoms omitted for clarity).
The effect of the ring size on the Pd–C bond length can be
compared (free of the different trans influences of other ligands)
in the xanthate complexes 3 and 8. This distance is apparently
shorter for 8, where the Pd atom is bound to C(2) (the ortho
position of the perylene fragment), than for 3, where the bond is
to C(7) (the peri position).10 On the contrary, the Pd–N bond is
shorter for 3 than for 8.
In the crystal structure of the chloro-phosphine derivative 5,
the palladium atom is bonded to the iminic nitrogen, to C(7) (the
peri position of perylene), to a Cl ligand, and to P(1) of PMe3.
Although the coordination angles are closer to the ideal value of
90◦ than those of 3 and 8, the square planar coordination around
the Pd(1) is still rather distorted from planarity [N(1)–C(7)–Pd(1)–
˚
Cl(1)–P(1): plane 1 mean deviation of 0.1412 A] and the nitrogen
˚
atom is situated 0.4464 A out of the average plane, apparently
due to steric hindrance of the phosphine with the perylene group.
Moreover, the angle between the coordination plane of palladium
and the average plane of perylene is 44.3◦ (much larger than in
3 or 8). The perylene fragment is far from planar, particularly
in the “naphthalene” moiety bonded to Pd(1) with a dihedral
angle of 8.87◦ between the two rings of the “naphthalene” and
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◦
˚
Table 1 Selected interatomic distances (A) and angles ( ) for the com-
plexes 3, 5, 7 and 8
3
5
7
8
Pd(1)–C(7)
Pd(1)–C(2)
Pd(1)–N(1)
2.016(2)
2.019(2)
1.990(6)
2.018(3)
2.035(2)
2.001(5)
2.047(4)
2.084(5)
Pd(1)–P(1)
Pd(1)–Cl(1)
2.2566(18)
2.3966(19)
Pd(1)–S(1)
Pd(1)–S(2)
2.3197(8)
2.4341(7)
92.47(10) 89.8(2)
92.94(16)
2.3027(11)
2.4128(11)
91.63(10)
2.3003(17)
2.4193(16)
C(7)–Pd(1)–N(1)
C(7)–Pd(1)–P(1)
N(1)–Pd(1)–P(1)
C(7)–Pd(1)–Cl(1)
N(7)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
C(21)–N(1)–Pd(1)
C(22)–N(1)–Pd(1)
C(7)–Pd(1)–S(1)
C(7)–Pd(1)–S(2)
N(1)–Pd(1)–S(2)
N(1)–Pd(1)–S(1)
S(1)–Pd(1)–S(2)
C(31)–S(1)–Pd(1)
C(31)–S(2)–Pd(1)
C(2)–Pd(1)–N(1)
C(2)–Pd(1)–S(1)
C(2)–Pd(1)–S(2)
165.68(14)
172.97(17)
92.99(14)
85.96(7)
125.6(10) 119.7(4)
124.27(18)
117.49(17)
95.69(8)
169.93(8)
98.40(7)
171.34(7)
74.24(4)
88.30(11)
85.01(11)
113.8(3)
126.1(3)
99.60(17)
172.53(16)
104.96(12)
178.64(13)
74.56(6)
86.4(2)
82.6(2)
80.77(19)
99.61(16)
172.58(16)
118.1(9)
96.19(8)
169.90(8)
97.45(6)
170.74(6)
73.80(3)
86.61(11)
83.42(10)
122.6(4)
Fig. 4 Absorption spectra recorded in CHCl3 solution (~10-5 M) at room
temperature. (top) Perylene, imine, and complexes 5, 6 and 7. (bottom)
Xanthate complexes 3 and 8 and acetylacetonate complexes 4 and 9.
of the [Pd(CŸN)L2] group on the photophysical properties of the
perylene.
8.73◦ between the two “naphthalene” groups forming the perylene.
By its similarity to the absorption bands of the free imine ligand,
the high-energy absorption bands at 250–300 nm (not shown in
the figure) are tentatively assigned as intraligand transitions. The
visible absorption of perylene is a band with vibronic structure
covering the range 350–450 nm. This band undergoes red-shift in
the imine (380–520 nm), and more marked in the complexes 3–9
(430–600 nm), maintaining some vibronic structure. This vibronic
structure, with a vibrational spacing of ~1200 cm-1, is related to
the stretching n(C C) frequency of the polyaromatic system.
The red-shift of the complexes relative to the imine, observed
for the six-membered metallacycle derivatives, shows the following
order: 5 Cl, PMe3 (2550 cm-1) < 3 xanthate (2700 cm-1) < 6 Cl,
PPh3 (2800 cm-1) ~ 7 carbamate < 4 acac (2880 cm-1). These
red-shifts are larger than in the case of the perylenyl complexes
containing a Pt(PEt3)2X group,12 but the influence of the ligands
on palladium is small. Moreover, the absorptions show very small
solvent dependence; for example, when the solvent is changed from
toluene to DMF, the lowest energy bands of 7 are red-shifted by
less than 400 cm-1 (see Fig. S2 in the ESI†). This behavior suggests
that these bands are most probably intraligand p–p* transitions,
rather than charge transfers.
˚
The Pd–Cl bond length is 2.396(19) A, which is somewhat larger
than those found in most similar metallacycles with palladium,11
reflecting the large trans influence of the perylenyl group.
Finally, in the diethyldithiocarbamate derivative 7 the observed
bond distances and angles around palladium are, as expected,
very similar to those found in the xanthate derivative 3. However,
the perylene is now far from planar with a dihedral angle
of 7.70◦ between the two “naphthalene” moieties forming the
perylene. Moreover, the molecules crystallize in pairs via partial
p–p stacking of the perylenyl rings (see Fig. 3) with a stacking
˚
distance of 3.451 A. This is in contrast with the structures of 3 and
8, where all the molecules essentially appear as individual objects
with no p–p stacking of perylenyl rings.
It can be noted that the spectral absorption patterns of the five-
membered palladacyclic complexes differ from those of the six-
membered palladacyclic complexes, enough as to be recognized.
Thus, the relative peak intensity and the vibronic structure for
six-membered palladacycles (complexes 3 and 4) is more similar
to that of perylene, with increasing intensity of the vibronic
bands as we move to higher l values. The complexes with five-
membered metallacycles show a less defined vibronic structure,
with only two observable maxima, and less intensity for the one
at lower energy (Fig. 4, bottom), in contrast with the order of
intensity observed in the six-membered palladacyclic complexes.
Moreover, the six-membered metallacyclic derivatives produce
larger red-shifts than the five-membered palladacycles: in the
Fig. 3 Intermolecular p–p stacking of the perylene groups in 7.
Photophysical studies
a) UV–Vis absorption spectra. The UV–Vis absorption and
emission spectra of dilute solutions in chloroform (c ~ 10-5 M) of
the palladium(II) complexes are summarized in Table 2. On the
other hand, the absorption spectra of perylene and its imine are
compared with those of complexes 3–9 in Fig. 4 to see the influence
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Table 2 UV–Vis absorption and emission data for the palladium complexes 3–9, in chloroform at 298 K
a
b
Compound
l (nm) (10-3 e)/dm3 mol-1 cm-1
lex/nm
l
em/nm
Ufl
t /ns
3
4
5
6
7
8
9
241 (56.9), 276 (59.1), 355 (14.4), 477 (18.4), 512 (29.2), 547 (35.1)
240 (59.6), 276 (59.1), 355 (14.4), 517 (28.9), 553 (35.3)
241 (51.1), 275 (40.4), 356 (11.1), 509 (28.2), 543 (32.6)
240 (60.1), 358 (10.6), 473 (15.7), 515 (25.4), 551 (29.2)
242 (47.3), 277 (64.6), 355 (12.4), 480 (14.9), 514 (28.7), 551 (35.2)
272 (72.2), 273 (35.6), 274 (64.2), 520 (29.3), 545 (28.4)
247 (60.8), 273 (40.6), 509 (29.6), 535 (28.4)
510, 545
517, 552
508, 542
517, 551
514, 551
509, 528
509
587, 640
591, 640
587, 640
596, 640
590, 640
591, 642
578, 626
0.12
0.08
0.01
0.01
0.03
0.09
0.04
0.77 (95.6), 2.89 (4,4)
0.51 (93.7), 4.12 (6.3)
0.49 (40.7), 3.44 (59.3)
0.54 (58.2), 3.23 (41.8)
0.31 (93.9), 3.67 (6.1)
0.67 (91.4), 3.75 (8.6)
0.47 (94.7), 2.76 (5.3)
a Quantum yield. b Fluorescence lifetimes. Decays were biexponential; numbers in parentheses indicate the relative amplitude of components.
xanthate complexes 2615 cm-1 for 8 < 2700 cm-1 for 3; in the
acetylacetonate derivatives 2270 cm-1 for 9 < 2880 cm-1 for 4.
unchanged in the presence of air, and was further confirmed
with the measurement of their emission lifetimes, which were in
the range 0.3–9 ns (Table 2). Complexes 3–9 show biexponential
decay with one major component of about 0.5 ns and another
substantially longer of about 3.5 ns, which may arise from the
existence of two different excited-state species.
The red-shifts observed, relative to perylene imine, of 2300–
2800 cm-1, show only a small dependence on the different ligands
around the palladium: 9 (2300 cm-1) < 3 ~ 5 (2570 cm-1) < 7
(2660 cm-1) < 4 ~ 6 (2690 cm-1) < 8 (2830 cm-1). The five-membered
complexes 8 and 9 are less red-shifted than the six-membered
compounds 3 and 9, respectively, as expected from the fact that
the fluorescence spectra should be mirror images of the absorption
spectra.
b) Luminescence spectra. The luminescence spectra of the
palladium complexes at room temperature in chloroform are listed
in Table 2. All complexes exhibit luminescence in solution (which
is unusual for Pd complexes) and display emission bands with
scarcely defined vibronic structures in the range 550–700 nm (see
Fig. 5), which can be correlated to those well defined for perylene
at about 425–525 nm and scarcely defined for imine at about 450–
625 nm.
The nearly identical emission spectra of 7 in different solvents
(acetonitrile, DMF, chloroform and toluene) at room temperature
(Fig. S3 in the ESI†), indicates that the fluorescence of the imine
derivatives is hardly sensitive to the polarity of the solvent.
Study of quantum yields
The fluorescence intensity of the perylene imine ligand is sig-
nificantly lower (Ufl = 0.13)7 than that of the perylene (Ufl
=
0.92),13 probably because the fluorescence of the perylene moiety
is quenched by a photoinduced intramolecular electron transfer
(PET) process.14 The emission quantum yields, of the palladated
complexes 3–9 measured in dichloromethane at room temperature,
were determined using as reference cresyl violet in methanol (Ufl =
0.54), with an excitation wavelength of 540 nm, and were in
the range 0.01–0.12 (Table 2). This is somewhat lower for the
complexes than for the imine precursor but still in the same order
of magnitude, which for Pd complexes is notably high, except
for the complexes with phosphines (0.01; these complexes have
the shortest Pd–C(perylene) bonds). The differences in emission
quantum yields when comparing six-membered palladacycles ver-
sus five-membered palladacycles, is remarkable. For the isomeric
pairs available for comparison, the quantum yields in the xanthate
complexes 3 (Ufl = 0.12) and 8 (Ufl = 0.09), in the acetylacetonate
complexes 4 (Ufl = 0.08) and 9 (Ufl = 0.04), are higher in
each case for the complex with the six-membered palladacycle,
suggesting a dependence of the quantum yield on the structure.
In view of the apparently larger C–Pd bond found for the six-
membered palladacycle 3 compared to the five-membered 8, its
higher quantum yield might be due to the lower interaction of the
perylenyl p-orbitals with Pd. In the parent dimers 1 (Ufl = 0.09)
and 2 (Ufl = 0.04), 1 has two six-membered moieties and 2 only
one, which might contribute in part to a higher quantum yield
Fig. 5 Emission spectra recorded in CHCl3 solution (10-5 M) at room
temperature. (top) Perylene, imine, and complexes 5, 6 and 7. (bottom)
Xanthate complexes 3 and 8 and acetylacetonate complexes 4 and 9.
The similarity of the overall luminescence spectra of these cy-
clometallated complexes with the perylene imine strongly suggests
a ligand-dominated emissive state that can be assigned to the
intraligand p–p* transitions disturbed by the metal. On the basis
of the similar Stokes shifts between absorption and emission for
the imine and for their complexes (less than 1000 cm-1 in all cases)
the luminescence observed can be assigned to p–p* fluorescence.
This was supported by the fact that the emission properties remain
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for 1, in addition to the fact that 2 shows p–p stacking, which is
detrimental for luminescence, and 1 does not.
at room temperature, then the solvent was evaporated in vacuum.
The residue was redissolved in dichloromethane, and the cloudy
solution was filtered through a Kieselguhr filter. Complex 3 was
precipitated by the addition of diethyl ether (10 mL) as a red solid
(0.075 g, 86%). Anal. Calc. for C31H23NOPdS2: C, 62.47; H, 3.89;
Conclusions
1
In contrast with the majority of palladium complexes reported
so far, which usually emit only at low temperatures, complexes
3–9 exhibit fluorescence associated with the perylene system
in solution at room temperature. The 3-perilenylmethylen-4¢-
ethylaniline ligand offers different bonding modes to palladium(II)
because of the two metallation sites of the 3-substituded perylene,
and the two types of mononuclear metallacyclic complexes (five-
or six-membered) induce somewhat different perturbations in the
original electronic spectrum and in the relative peak-intensity of
the low energy (visible) bands of the imine. As for the quantum
yields, these also depend on the ancillary ligands, but the com-
plexes based on five-membered palladacycles show systematically
lower quantum yields than their six-membered analogs. This
suggests that the lower quantum yield found in the six + five
dimer 2, compared to the six + six dimer 1, might be attributed to
the size of the metallacycle, as well as by the p–p stacking.
N, 2.35. Found: C, 62.29; H, 3.92; N, 2.03. H NMR (CDCl3,
300.13 MHz): d 8.40 (s, 1H, HC N), 8.32–8.27 (m, 3H), 8.15 (d,
J = 8.3 Hz, 1H), 7.84–7.79 (m, 3H), 7.71 (d, J = 7.9 Hz, 1H), 7.55
(t, J = 7.9 Hz, 1H), 7.54 (t, J = 7.9 Hz, 1H), 7.34, 7.27 (AA¢BB¢
system, J = 8.3 Hz, 4H), 4.1 (s, 3H, OCH3), 2.72 (q, J = 7.5 Hz,
2H, CH2CH3), 1.29 (t, J = 7.9, 3H, CH2CH3) ppm. Fluorescence
emission (CHCl3, lexc = 510, 545 nm) lem = 516 nm, 553 nm. UV–
Vis (CHCl3) lmax (nm) (10-3 e)/(M-1 cm-1) = 241 (56.9), 276 (59.1),
355 (14.4), 477 (18.4), 512 (29.2), 547 (35.1).
[Pd(CŸN)(acac)]-six-membered (4). To a solution of 1 (0.080 g,
0.07 mmol) in dichloromethane (10 mL) was added a solution of
KOH in methanol (0.44 mL, 0.22 mmol, 0.5 M) and acetylacetone
(0.022 mL, 0.219 mmol). The solution was stirred 2 h at room
temperature, then the solvent was evaporated to dryness. The
residue was redissolved in dichloromethane, and the cloudy
solution was filtered through a Kieselguhr filter. Complex 4 was
precipitated by the addition of diethyl ether (10 mL) as a purple
solid (0.070 g, 82%). Anal. Calc. for C34H27NO2Pd: C, 69.45; H,
4.63; N, 2.38. Found: C 69.14, H 4.32, N 2.13. 1H NMR (CDCl3,
300.13 MHz): d 8.34 (s, 1H, HC N), 8.30–8.21 (m, 5H), 7.79–
7.67 (m, 3H), 7.54 (t, J = 7.9 Hz, 1H), 7.53 (t, J = 7.9 Hz, 1H),
7.39, 7.23 (AA¢BB¢ system, J = 8.3 Hz, 4H), 5.28 (s, 1H), 2.70
(q, J = 7.5 Hz, 2H, CH2CH3), 1.54 (s, 3H), 1.52 (s, 3H), 1.25 (t,
Experimental
Materials and general methods
All reactions were carried out under dry nitrogen. The solvents
were purified according to standard procedures. Literature meth-
ods were used to prepare 1 and 2.7 C, H, N analyses were carried
out on a Perkin-Elmer 2400 microanalyzer. IR spectra (cm-1)
were recorded on a Perkin-Elmer FT-1720X spectrometer. 1H and
31P NMR spectra were recorded on Bruker AC 300 or Bruker
400 MHz spectrophotometers in CDCl3, with chemical shifts
referred to TMS and 85% H3PO4, respectively. UV–Vis absorption
spectra were obtained on a Shimadzu UV-1603 spectrophotome-
ter, in chloroform solution (1 ¥ 10-5 M). Luminescence data were
recorded on a Perkin-Elmer LS-luminescence spectrometer, in
CHCl3 (1 ¥ 10-5 M). Luminescence quantum yields were obtained
at room temperature using the optically dilute method (A < 0.1)
in degassed dichloromethane (quantum yields standard was cresyl
violet in ethanol (Ufl = 0.54)15 and using an excitation wavelength of
510 nm. The emission lifetime measurements were carried out with
a Lifespec-red picosecond fluorescence 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) had a pulse width of 88.5 ps, with a typical
average power of 0.40 mW. The second wavelength (470 nm) had a
pulse width of 97.2 ps, and its typical average power was 0.15 mW.
The pulse period was 1 ms and the pulse repetition frequency
was 10 MHz. The monocromator slit was 2 nm. The instrument
response measure at the HWHM (half with a high maximum) was
below 350 ps. The technique used was “Time Correlated Single
Photon Counting” (TCSPC).
J = 7.5, 3H, CH2CH3) ppm. Fluorescence emission (CHCl3, lexc
=
517, 552 nm) lem = 591 nm, 640 nm. UV–Vis (CHCl3) lmax (nm)
(10-3 e)/(M-1 cm-1) = 240 (59.6), 276 (59.1), 355 (14.4), 517 (28.9),
553 (35.3).
[Pd(CŸN)Cl(PMe3)]-six-membered (5). To a solution of 1
(0.020 g, 0.018 mmol) in THF (6 mL) was added LiCl (4 mg,
0.094 mmol) and a solution of PMe3 in THF (0.054 mL,
0.054 mmol, 1 M). The red solution was stirred 5 h at room
temperature, then the solvent was distilled off and the red residue
was redissolved in dichloromethane, and the cloudy solution was
filtered through a Kieselguhr filter. Complex 5 was precipitated
by the addition of diethyl ether (14 mL) as a red solid (0.018 g,
82%). Anal. Calc. for C32H29ClNPPd.CH2Cl2: C, 57.83; H, 4.56;
1
N, 2.04. Found: C, 57.65; H, 4.41; N, 1.87. H NMR (CDCl3,
300.13 MHz): d 8.38–8.33 (m, 3H), 8.26 (d, J = 7.8 Hz, 1H), 8.11
(d, J = 7.8 Hz, 1H), 7.96–7.88 (m, 2H), 7.81 (d, J = 7.8 Hz, 2H), 7.63
(d, J = 7.6 Hz, 1H), 7.61 (d, J = 7.7 Hz, 1H), 7.51, 7.35 (AA¢BB¢
system, J = 8.3 Hz, 4H), 2.80 (q, J = 7.8 Hz, 2H, CH2CH3), 1.46
(d, JP-H = 10.7 Hz, 9H), 1.36 (t, J = 7.8, 3H, CH2CH3) ppm. 31P
NMR (CDCl3): d = -5 (s) ppm. Fluorescence emission (CHCl3,
lexc = 508, 542 nm) lem = 587 nm, 640 nm. UV–Vis (CHCl3) lmax
(nm) (10-3e)/(M-1 cm-1) = 241 (51.1), 275 (40.4), 356 (11.1), 509
(28.2), 543 (32.6).
[Pd(CŸN)Cl(PPh3)]-six-membered (6). To a solution of 1
(0.050 g, 0.045 mmol) in THF (15 mL) was added LiCl (9 mg,
(0.212 mmol) and PPh3 (0.024 g, 0.090 mmol). The purple solution
was stirred during 5 h at room temperature, after which the solvent
was evaporated to dryness. The purple residue was redissolved in
dichloromethane, and the cloudy solution was filtered through a
Synthesis of the complexes
[Pd(CŸN)(S2COMe)]-six-membered (3).
(0.080 g, 0.07 mmol) in dichloromethane (10 mL) was treated
with a solution of KOH in methanol (0.44 mL, 0.22 mmol, 0.5 M)
and CS2 (0.13 mL, 2.19 mmol). The red solution was stirred 2 h
A solution of 1
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Dalton Trans., 2011, 40, 7602–7609 | 7607
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Table 3 Crystal data and structure refinements for 3, 5, 7 and 8
Compound
3
5·CH2Cl2
7
8
Empirical formula
Formula weight
Temperature (K)
C31H23NOPdS2
596.02
293(2)
0.71073
Orthorhombic
P2(1)2(1)2(1)
8.0423(3)
8.6606(3)
36.0862(9)
90
C33H31Cl3NPPd
685.31
298(2)
0.71073
Triclinic
P-1
8.2882(15)
13.595(2)
13.810(2)
100.691(3)
97.530(3)
95.454(4)
1504.5(5)
2
C34H30N2PdS2
637.12
293(2)
0.71073
Triclinic
P-1
8.860(4)
11.554(6)
14.640(7)
71.054(8)
87.763(9)
84.421(9)
1410.6(12)
2
C31H23NOPdS2
596.02
293(2)
0.71073
Triclinic
P-1
7.834(3)
10.954(4)
15.586(5)
94.315(6)
103.724(6)
106.064(6)
1234.3(7)
2
˚
Wavelength (A)
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (◦)
b (◦)
g (◦)
90
90
3
˚
V (A )
2513.43(13)
4
1.575
0.931
1208
Z
Dcalc (g cm-3)
1.513
0.960
696
1.500
0.833
652
1.604
0.947
602
Absorpt. coefficient (mm-1)
F(000)
Crystal size (mm)
Theta range for data collection
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission factor
Data/restraints/parameters
Goodness-of-fit on F2
R1 [I > 2s(I)]
0.61 ¥ 0.34 ¥ 0.13
2.90 to 26.37
8744
0.23 ¥ 0.10 ¥ 0.05
1.52 to 26.42
13166
0.31 ¥ 0.25 ¥ 0.09
1.47 to 26.42
12335
0.20 ¥ 0.12 ¥ 0.02
1.36 to 26.47
10784
4872
6117
5732
5044
Analytical
0.873 and 0.667
4872/0/327
0.997
0.0255
0.0496
Multi-scan
1.000 and 0.81327
6117/0/356
1.000
0.0544
0.1628
Multi-scan
1.000 and 0.80299
5732/0/355
1.077
0.0315
0.0854
Multi-scan
1.000 and 0.70583
5044/0/327
1.039
0.0450
0.1294
wR2 (all data)
Kieselguhr filter. Complex 6 was precipitated by the addition of
diethyl ether (10 mL) as a purple solid (0.040 g, 59%). Anal. Calc.
for C47H35ClNPPd: C, 71.76; H, 4.48; N, 1.78. Found: C, 71.57;
[Pd(CŸN)(S2COMe)]-five-membered (8). The same approach
described for the synthesis of 3 was followed to prepare 8, but
using complex 2 as starting product. Complex 8 was obtained in
dichloromethane/toluene (5 : 7, 12 mL) at -20 ◦C, collected by
filtration, washed with toluene (2 ¥ 2 mL) and dried in vacuum to
obtain the compound as a red solid. Yield: (0.015 g, 27%). Anal.
Calc. for C31H23NOPdS2: C, 62.47; H, 3.89; N, 2.35. Found: C,
1
H, 4.29; N, 1.57. H NMR (CDCl3, 300.13 MHz): d 8.33–8.29
(m, 2H), 8.18 (d, J = 8.1 Hz, 2H), 7.80–7.74 (m, 3H), 7.67 (d,
J = 7.8 Hz, 2H), 7.57–7.49 (m, 9H), 7.43 (t, J = 7.8 Hz, 1H),
7.3–7.14 (m, 11H), 7.02 (d, J = 8.1 Hz, 2H), 2.66 (q, J = 7.8 Hz,
2H, CH2CH3), 1.24 (t, J = 7.8, 3H, CH2CH3) ppm. 31P NMR
1
62.35; H, 3.80; N, 2.13. H NMR (CDCl3, 300.13 MHz): d 8.88
(CDCl3): d = 35.86 (s) ppm. Fluorescence emission (CHCl3, lexc
=
(s, 1H, HC N), 8.27 (d, J = 7.9 Hz, 1H), 8.20 (d, J = 7.5 Hz,
1H), 8.11 (d, J = 7.5, 1H), 7.99 (s, H1), 7.93 (d, J = 8.3 Hz, 1H),
7.71 (t, J = 7.9 Hz, 2H), 7.52–7.43 (m, 3H), 7.39, 7.28 (AA¢BB¢
system, J = 8.3 Hz, 4H), 4.28 (s, 3H, OCH3), 2.71 (q, J = 7.5 Hz,
2H, CH2CH3), 1.29 (t, J = 7.9, 3H, CH2CH3) ppm. Fluorescence
emission (CHCl3, lexc = 509, 528 nm) lem = 591 nm, 642 nm. UV–
Vis (CHCl3) lmax (nm) (10-3 e)/(M-1 cm-1) = 242 (72.2), 273 (35.6),
274 (64.2), 520 (29.3), 545 (28.4).
517, 551 nm) lem = 596 nm, 640 nm. UV–Vis (CHCl3) lmax (nm)
(10-3 e)/(M-1 cm-1) = 240 (60.1), 358 (10.6), 473 (15.7), 515 (25.4),
551 (29.2).
[Pd(CŸN)(S2CNEt2)]-six-membered (7). Sodium diethyldithio-
carbamate trihydrate (0.049 g, 0.219 mmol) was added to a
solution of 1 (0.080 g, 0.073 mmol) in dichloromethane/acetone
(1 : 1, 18 mL). The mixture was stirred 12 h at room temperature,
then the solvent was distilled off, and the purple residue was
redissolved in dichloromethane, and the cloudy solution was
filtered through a Kieselguhr filter. Complex 7 was precipitated
by the addition of diethyl ether (15 mL) as a purple solid (0.067 g,
72%). Anal. Calc. for C34H30N2PdS2: C, 64.09; H, 4.75; N, 4.40.
Found: C, 63.71; H, 4.76; N, 4.20. 1H NMR (CDCl3, 300.13 MHz):
d 8.38 (s, 1H, HC N), 8.28–8.22 (m, 3H), 8.13 (d, J = 7.9 Hz,
1H), 7.83 (d, J = 7.9 Hz, 1H), 7.76 (d, J = 7.9 Hz, 1H), 7.75 (d,
J = 7.9 Hz, 1H), 7.66 (d, J = 7.9 Hz, 1H), 7.51 (t, J = 7.9 Hz, 2H),
7.34, 7.27 (AA¢BB¢ system, J = 8.3 Hz, 4H), 3.83 (q, J = 7.1 Hz,
2H, NCH2CH3), 3.72 (q, J = 7.1 Hz, 2H, NCH2CH3), 2.73 (q, J =
7.5 Hz, 2H, CH2CH3), 1.31 (t, J = 7.1, 3H, NCH2CH3), 1.29 (t,
J = 7.1, 3H, NCH2CH3), 1.19 (t, J = 7.5 Hz, 3H, CH2CH3) ppm.
Fluorescence emission (CHCl3, lexc = 514, 551 nm) lem = 590 nm,
640 nm. UV–Vis (CHCl3) lmax (nm) (10-3 e)/(M-1 cm-1) = 242
(47.3), 277 (64.6), 355 (12.4), 480 (14.9), 514 (28.7), 551 (35.2).
[Pd(CŸN)(acac)]-five-membered (9). This complex was pre-
pared in a similar manner to 4 using 2 as starting compound.
Complex 9 is insoluble in dichloromethane/toluene (5 : 7,12 mL)
at -20 ◦C, and was collected by filtration, washed with toluene
(2 ¥ 2 mL) and dried in vacuum to obtain the compound as a red
solid. Yield: 0.020 g, 37%. Anal. Calc. for C34H27NO2Pd: C, 69.45;
1
H, 4.63; N, 2.38. Found: C, 69.15; H, 4.42; N, 2.18. H NMR
(CDCl3, 300.13 MHz): d 8.79 (s, 1H, HC N), 8.62 (s, 1H, H1),
8.42 (d, J = 7.1 Hz, 1H), 8.24 (d, J = 7.5 Hz, 1H), 8.16 (d, J =
7.5 Hz, 1H), 7.91 (d, J = 7.9 Hz, 1H), 7.74 (t, J = 7.9 Hz, 2H),
7.60–7.45 (m, 3H), 7.47, 7.28 (AA¢BB¢ system, J = 8.3 Hz, 4H),
5.44 (s, 1H), 2.72 (q, J = 7.5 Hz, 2H, CH2CH3), 2.26 (s, 3H), 1.95 (s,
3H), 1.30 (t, J = 7.47, 3H, CH2CH3) ppm. Fluorescence emission
(CHCl3, lexc = 509 nm) lem = 578 nm, 626 nm. UV–Vis (CHCl3)
lmax (nm) (10-3 e)/(M-1 cm-1) = 247 (60.8), 273 (40.6), 509 (29.6),
535 (28.4).
7608 | Dalton Trans., 2011, 40, 7602–7609
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X-ray crystal structure analysis
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10 We are aware that the application of 3 times the esd values, taking
the deviation as positive for one atom and as negative for the other,
makes these differences in distance, strictly speaking, non-significant.
In terms of probability, what the esd values indicate is that we do not
have the certainty that the distances are unequal. However, in favor of
considering them probably different it can be argued that, from another
point of view, these esd values also indicate a high probability (perhaps
more than 70%) that these distances are really different and in the
short/long order indicated by the experimental values. For this reason,
in the text we refer to these distances as “apparently” different and
the effects observed are only suggested to be influenced in part by this
difference in distance, assuming that it is real.
11 (a) J. M. Vila, G. Alberdi, M. T. Pereira, M. Marin˜o, A. Ferna´ndez, M.
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F. Rominger and I. M. McDonald, Organometallics, 2005, 24, 5665;
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Single crystals of 3, 5·CH2Cl2, 7 and 8 suitable for X-ray
diffraction studies were obtained from slow diffusion of Et2O into
a dichloromethane solution of the products at -20 ◦C. Crystals
were mounted in glass fibers, and diffraction measurements were
made using a Bruker SMART CCD and Varian Supernova area-
16
˚
detector diffractometers with Mo-Ka radiation (l = 0.71073 A).
Intensities were integ◦rated from several series of exposures, each
exposure covering 0.3 in w, the total data set being a hemisphere.17
Absorption corrections were applied, based on multiple and
symmetry-equivalent measurements.18 The structures were solved
by direct methods and refined by least squares on weighted F2
values for all reflections (see Table 3).19 All non-hydrogen atoms
were assigned anisotropic displacement parameters and refined
without positional constraints. All the hydrogen atoms, including
those involved in hydrogen bonding, were calculated with a riding
model. Complex neutral-atom scattering factors were used.20 In
the structure of compound 5 the methyl groups of the PMe3
ligand were affected by incipient disorder, which despite repeated
attempts could not be successfully modeled. Crystallographic data
(excluding structure factors) for the structures reported in this
paper have CCDC reference numbers 818347 for 3, 818344 for 5,
818347 for 7, and 818350 for 8.
Acknowledgements
We thank the Spanish Comisio´n Interministerial de Ciencia y Tec-
nolog´ıa (CTQ2008-03954/BQU, INTECAT Consolider Ingenio
2010 (CSD2006-0003), and the Junta de Castilla y Leo´n (Project
VA248A11-2) for financial support.
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(b) CrysAlisPro, Oxford Diffraction Ltd., Version 1.171.33.48.
19 SHELXTL program system version 5.1, Bruker Analytical X-ray
Instruments Inc., Madison, WI, 1998.
20 International Tables for Crystallography, Kluwer, Dordrecht, 1992,
vol. C.
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7602–7609 | 7609
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