C^C* cyclometalated platinum(II) NHC complexes with β-ketoimine ligands

Article abstract of DOI:10.1021/om401023f

C^C* cyclometalated platinum(II) NHC complexes with chelating acetylacetonate ligands have been recently shown to be an interesting class of phosphorescent emitters. We sought to clarify the role of the acetylacetonate ligand by replacing one of the coord

Full text of DOI:10.1021/om401023f

Article
pubs.acs.org/Organometallics
C∧C* Cyclometalated Platinum(II) NHC Complexes with β‑Ketoimine
Ligands
Alexander Tronnier,† Alexander Poethig,†,§ Eberhardt Herdtweck,‡ and Thomas Strassner*,†
†Physikalische Organische Chemie, Technische Universitat Dresden, 01069 Dresden, Germany
̈
‡Anorganische Chemie, TU Munchen, Lichtenbergstrasse 4, 85747 Garching, Germany
̈
S
* Supporting Information
ABSTRACT: C∧C* cyclometalated platinum(II) NHC complexes with chelating acetylacetonate ligands have been recently
shown to be an interesting class of phosphorescent emitters. We sought to clarify the role of the acetylacetonate ligand by
replacing one of the coordinating oxygen atoms in the auxiliary ligand with an NH group. This allowed us to study the effect on
the emission, and we found that the nature of the emission process changes significantly. We herein report the synthesis of novel
cyclometalated platinum(II) NHC complexes with the chelating β-ketoimine ligands (3Z)-4-amino-3-penten-2-one and (2Z)-3-
amino-1-phenyl-2-buten-1-one. Due to the unsymmetrical nature of the auxiliary ligands, two isomers were always formed, which
could be separated and characterized. Their photophysical properties as well as solid-state structures of representative members
of this new class of compounds are given. All new complexes emit in the blue to green region of the visible spectrum with
quantum yields as high as 74% at room temperature. The photophysical data of the isomers show significant differences. The new
1
compounds have been fully characterized by H and 13C as well as 2D NMR (COSY, HSQC, HMBC, NOESY) spectroscopy.
DFT calculations were used to determine differences between the respective isomers and to predict the emission wavelengths of
the synthesized complexes. We found the reason for the different properties in comparison to the acetylacetonate complexes to
be the smaller HOMO−LUMO gap.
ingly important over the past years, showing promising
quantum efficiencies of up to 100%.7−10 Especially, cyclo-
metalated heteroleptic Ir(III)11−13 and Pt(II)14,15 complexes of
the type [(C∧N)1−2M(O∧O)] (C∧N, 2-arylpyridinate or a
related ligand; O∧O, a β-diketonate ligand) have been studied
in detail due to their exceptional luminescence properties.16,17
In most cases the photophysical properties were improved by
changing the cyclometalating ligands. These cyclometalating
bidentate ligands are often derived from biphenyl,16,18,19 2-
phenylpyridine,16,17,20 a phenylazole such as phenylpyrazole
(ppz),9,17 or 2-phenylbenzimidazole,21 generating a five-
membered metallacycle.
INTRODUCTION
■
Development over the past decade in organic light-emitting
diodes (OLEDs) has brought about considerable progress in
electrooptical applications such as true-color flat-panel displays
and illumination devices with remarkably low energy
consumption.1−4 The previously used purely organic lumo-
phores have been replaced more and more by organometallic
compounds. Organometallic chemistry is taking a leading role
in the development of this technology, which has the potential
to save vast amounts of global energy in the field of domestic
lighting.5 With the utilization of organometallic phosphorescent
emitters the limit of quantum efficiency in classical fluorescent
devices (25%) can be overcome. Due to greater heavy-metal-
induced spin−orbit coupling (SOC) and the resulting
admixture of metal d orbitals to the frontier orbitals of the
complexes, intersystem crossing from the excited singlet state
to the phosphorescent triplet states is enhanced in most cases.6
Therefore, transition-metal complexes have become increas-
N-heterocyclic carbene (NHC) ligands are versatile ligands
that today often replace the more traditional phosphines.22
Although their development as an important class of ligands in
Received: October 21, 2013
Published: February 6, 2014
© 2014 American Chemical Society
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organometallic chemistry is quite considerable, their application
in emissive transition-metal complexes has been far less
investigated in comparison to arylpyridines. Cyclometalated
heteroleptic NHC platinum complexes of the general structure
[(C∧C*)Pt(O∧O)] were first mentioned in patents in
200623−25 and have been investigated since in more detail by
our group and others (Chart 1).26−30 As recently shown by us
Scheme 1. Synthesis of the NHC Precursors: Imidazoles 1−6
and the Corresponding Imidazolium Salts 7−12
Chart 1. The Very First (a) and General Motif (b) of C∧C*
a
Cyclometalated Platinum(II) NHC (Imidazole) Complexes
Scheme 2. Synthesis of the β-Ketoimine Ligands 13 and 14
a
R1 = 4-Me, OMe, Br, NO2, BMes2, H, 2,3-OC6H4, 5-BMes2; R2 =
CH3, CF3.
and described in the literature for cyclometalated platinum(II)
β-diketonate complexes of the type [(C∧N)Pt(O∧O)], the
photophysical properties of these complexes depend strongly
on the substitution pattern of the cyclometalating li-
gands.15,26,31 The ongoing investigations of ligand effects have
quite recently also included the auxiliary ligand. Therein
different β-diketones32,33 as well as β-ketoimines34−36 derived
from the common acetylacetonate have had a significant impact
on the photophysical behavior. The latter have also attracted
considerable interest in other research fields as ligands in
numerous metal complexes.37−39
suffer from one or more disadvantages such as unsatisfactory
yields, usage of ammonium salts, and the necessity of extractive
workups or distillation of the reaction mixture.43 Both ligands
exist in their ketoenamine form in solution, as determined by
1H NMR (9.70 and 10.23 ppm for HNHO, 5.24 ppm for NH),
as well as in the solid state (Figure 1). For 13 our results are in
agreement with previous reports.44
We set out to combine another auxiliary ligand with C∧C*
cyclometalated NHC platinum(II) complexes. Our goal was to
investigate the influence of β-ketoimine ligands in lieu of
acetylacetonate on the photoluminescence properties of
cyclometalated Pt(II) complexes in combination with known
NHC ligands. The focus was on stable emitters for the (deep)
blue region of the visible spectrum. Here we present the
synthesis and photophysical properties of a new class of
temperature- and air-stable Pt(II) complexes bearing N-
heterocyclic carbenes as cyclometalating C∧C* ligands and β-
ketoimines as auxiliary ligands. Density functional theory
(DFT) calculations have been used to investigate the frontier
molecular orbitals, energies, and geometries of the complexes.
Figure 1. ORTEP representations of the β-ketoimine ligands 13 and
14 in the solid state. Thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths (Å) for 13: O(1)−C(2),
1.253(2); N(1)−C(4), 1.321(2); C(2)−C(3), 1.418(3); C(3)−C(4),
1.379(3). Selected bond lengths (Å) and angles (deg) for 14: O(1)−
C(1), 1.2582(12); C(1)−C(8), 1.4107(15); C(8)−C(9), 1.3866(14);
N(1)−C(9), 1.3203(14); O(1)−C(1)−C(8), 123.50(9); C(8)−
C(9)−N(1), 123.03(10).
RESULTS AND DISCUSSION
■
Synthesis. The preparation of aryl- and methyl-function-
alized imidazolium salts as ligand precursors is well established
(Scheme 1).40 Imidazoles 1−5 were prepared in good yields via
Radziszewski ring closure synthesis from commercially available
substituted anilines. Imidazole 6 was prepared via a different
route:26 the bromination of dibenzofuran followed by an
Ullmann-type reaction with copper(I) oxide and imidazole. The
iodide salts 7−12 were obtained in very good yields after
reaction with methyl iodide in THF at elevated temperatures.
The β-ketoimine ligands 13 and 14 were readily obtained by
a condensation reaction of the corresponding commercially
available β-diketones acetylacetone and 1-phenyl-1,3-butane-
dione with ammonium carbamate (Scheme 2). These reaction
conditions were found to be superior to those for other
reactions such as the silica gel41 or K-10 montmorillonite42
catalyzed enamination of β-dicarbonyl compounds. These
Dichloro(1,5-cyclooctadiene)platinum(II) (Pt(COD)Cl2,
15) was chosen as the platinum(II) precursor to introduce
one NHC ligand after deprotonation with silver(I) oxide via
transmetalation at the metal center, blocking two coordination
sites.26 The intermediate, most probably a chloro-bridged
binuclear complex, was then reacted with the bidentate auxiliary
ligand in DMF in the next step without isolation, leading to a
mixture of the two possible isomers. We were able to separate
and purify them by column chromatography, albeit in quite
different yields. Complexes of the a type (16a−22a) with the
imine group opposite the carbene carbon atom (trans) were
obtained more readily, with yields ranging from 22 to 44%
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Scheme 3. Synthesis of the Cyclometalated NHC Complexes 16−22
Figure 2. COSY (left) and HMBC (right) spectra of 17a in CDCl3 at room temperature.
(Scheme 3). This is in agreement with quantum chemical DFT
calculations, which showed a thermodynamic preference of
4.8−6.7 kcal/mol in favor of the a isomers (see the Supporting
Information). The b isomers were obtained in yields of 5−16%,
with the exception of 22, where only traces of the second
isomer were observed in the 1H NMR. All complexes are stable
toward air and moisture at elevated temperatures and have
melting points higher than 170 °C.
The two β-ketoimines 4-amino-3-penten-2-one (13) and 3-
amino-1-phenyl-2-buten-1-one (14) were chosen as auxiliary
ligands. The former has a close resemblance to the
acetylacetonate ligand and allows a direct comparison with
complexes bearing the same NHC ligand.26 In the case of 14 a
phenyl group was incorporated into the ligand backbone. An
expansion of the π system normally leads to a red shift of the
emission and in some cases to increased quantum yields. For
platinum complexes it was furthermore reported that π-
conjugated chromophoric ligands with their π systems
somewhat remote from the metal center could exhibit
fluorescence. Because of its good solubility, we reacted the
imidazolium salt 11 with both auxiliary ligands, yielding
complexes 20a and 21a and the corresponding b isomers, to
study these effects in more detail.
NMR Characterization. The ketoenamine form of the two
1
free ligands 13 and 14 in solution was proven by H NMR
spectroscopy. In both cases two separate proton resonances for
a NH group were detected with the signal for the NHO proton
at lower field (9.70 and 10.23 ppm). The other resonance was
measured in a region typical for amines: 5.24 ppm for both 13
and 14.
The successful deprotonation of the NHC precursor and the
subsequent formation of a silver(I) complex intermediate was
verified by the disappearance of the imidazolium CH signal,
whereas during the formation of the cyclometalated platinum
complexes one doublet of the NHC aryl ring disappeared. The
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Figure 3. ORTEP representation of complexes 17b, 19b, and 20a. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths
(Å), angles (deg), and dihedral angles (deg) for 17b: Pt(1)−C(1), 1.956(3); Pt(1)−C(5), 1.995(2); Pt(1)−O(1), 2.0415(17); Pt(1)−N(3),
2.049(2); O(1)−Pt(1)−N(3), 88.97(8); C(1)−Pt(1)−C(5), 80.00(10); C(4)−N(1)−C(1)−Pt(1), −1.72(3). Selected bond lengths (Å), angles
(deg), and dihedral angles (deg) for 19b: Pt(1)−C(1), 1.961(10); Pt(1)−C(5), 1.991(8); Pt(1)−O(3), 2.048(6); Pt(1)−N(4), 2.051(6); O(3)−
Pt(1)−N(4), 89.0(3); C(1)−Pt(1)−C(5), 80.6(4); C(4)−N(1)−C(1)−Pt(1), 0.7(9). Selected bond lengths (Å), angles (deg), and dihedral angles
(deg) for 20a: Pt(1)−C(1), 1.973(4); Pt(1)−C(5), 1.997(4); Pt(1)−O(2) 2.072(3); Pt(1)−N(3), 2.026(4); O(2)−Pt(1)−N(3), 89.13(13);
C(1)−Pt(1)−C(5), 80.34(17); C(4)−N(1)−C(1)−Pt(1), 0.3(4).
Figure 4. ORTEP representation of complexes 18a,b. Thermal ellipsoids are drawn at the 50% probability level, and solvent molecules are omitted
for clarity. Selected bond lengths (Å), angles (deg), and dihedral angles (deg) for 18a: Pt(1)−C(1), 1.964(5); Pt(1)−C(5), 2.000(4); Pt(1)−O(1),
2.077(2); Pt(1)−N(3), 2.013(3); O(1)−Pt(1)−N(3), 89.20(12); C(1)−Pt(1)−C(5), 80.79(19); C(4)−N(1)−C(1)−Pt(1), −1.0(5). Selected
bond lengths (Å), angles (deg), and dihedral angles (deg) for 18b: Pt(1)−C(1), 1.929(6); Pt(1)−C(5), 1.987(6); Pt(1)−O(1), 2.037(4); Pt(1)−
N(3), 2.022(5); O(1)−Pt(1)−N(3), 89.42(19); C(1)−Pt(1)−C(5), 80.3(3); C(4)−N(1)−C(1)−Pt(1), −1.12(10).
signal for its neighboring hydrogen atom changed into a
characteristic PtCCH signal (pseudo-triplet).
To distinguish between the two isomers, NOESY experi-
ments were conducted for all a and b isomers. Using the very
characteristic signals of the NCH3 group and the pseudo-triplet
adjacent to the Pt−C bond (PtCCH), a coupling with the
proton of the NH group of the auxiliary ligand could be
observed. The a isomers were identified as the complexes with
the NH group directly opposite the PtCCH group, where no
coupling is observed for the NCH3 group.
All complexes were fully characterized by two-dimensional
1H and 13C NMR (COSY, HSQC, HMBC and NOESY)
spectroscopy to unambiguously assign all signals. Generally,
significant differences between the two isomers were found (see
the Supporting Information, Figures S1−S7). A characteristic
1
long-range H−195Pt coupling, resulting in the formation of a
Solid-State Structure Determination. To unambiguously
assign the three-dimensional structure of the two isomers and
to verify the expected square-planar coordination of the
platinum atom, single crystals suitable for X-ray diffraction
were obtained by slow evaporation of solvent from a saturated
dichloromethane solution of the complexes 17b, 18a,b, 19b,
20a, and 21a,b (Figures 3−5) and the β-ketoimine ligands 13
and 14 (Figure 1). Details of the solid-state structure
pseudo-triplet (JH,Pt = 21.0−31.3 Hz), was observed (signal 15,
Figure 2). For the b isomers this coupling constant is on
average 6 Hz smaller. The 13C carbene signal (NCN) was
observed at 160.6−162.9 ppm for the a isomers and at the
higher field of 150.0−152.8 ppm for the b isomers, indicating a
greater electron density at the carbene carbon atom with an
oxygen atom at the opposite coordination site. As an example,
the COSY and HMBC spectra of 17a are given in Figure 2.
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Figure 5. ORTEP representation of complexes 21a and 21b. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å),
angles (deg), and dihedral angles (deg) for 21a: Pt(1)−C(1), 1.980(7); Pt(1)−C(5), 1.998(7); Pt(1)−O(2) 2.058(4); Pt(1)−N(3), 2.023(5);
O(2)−Pt(1)−N(3), 89.3(2); C(1)−Pt(1)−C(5), 80.6(3); C(4)−N(1)−C(1)−Pt(1), 4.2(8); O(2)−C(15)−C(16)−C(17) −154.8(6). Selected
bond lengths (Å), angles (deg), and dihedral angles (deg) for 21b: Pt(1)−C(1), 1.951(4); Pt(1)−C(5), 2.000(4); Pt(1)−O(2) 2.049(2); Pt(1)−
N(3), 2.049(3); O(2)−Pt(1)−N(3), 89.70(11); C(1)−Pt(1)−C(5), 80.22(15); C(4)−N(1)−C(1)−Pt(1), 0.3(4); O(2)−C(15)−C(16)−C(17),
140.9(3).
determination are given in the Supporting Information (Tables
S1 and S2).
All solid-state structures show an almost perfectly square-
planar coordinated metal ion. The Pt−C bond lengths are
different, and the distance between the metal and the carbene
carbon atom C1 (1.93−1.98 Å) is shorter than the distance to
the cyclometalated carbon atom C5 (1.99−2.00 Å). The
planarity becomes even more obvious from the small dihedral
angles in the central five-membered ring with the platinum(II)
center. The C1−Pt1−C5 angle (about 80°) deviates signifi-
cantly from the perfect 90° angle, whereas the O−Pt1−N angle
of the ketoimine ligand (about 88°) is nearly ideal for a square-
planar coordination geometry. Similar angles and bond lengths
Figure 6. Absorption spectra of selected complexes in 100% films at
room temperature. Annotations in the legend are given in the same
order as the traces at 220 nm.
have been described before for other cyclometalated platinum-
(II) NHC complexes with β-diketonates.26,28−30,45
For all solid-state structures the platinum−carbene bond as
well as the platinum−oxygen bond is always slightly shorter for
the b isomers, while the Pt−N contact is longer in comparison
to the a isomers (Figures 4 and 5). All complexes form zigzag
patterns throughout the crystal with intermolecular Pt−Pt
distances ranging from 3.33 to 7.07 Å (see the Supporting
Information, Figures S8−S11).
yields and broad unstructured emission bands (see the
Supporting Information, Figure S19). The chloro-substituted
complexes 17a,b showed even higher quantum yields and a red-
shifted emission in comparison to the diluted samples in
poly(methyl methacrylate) (PMMA).
Photoluminescence Properties. To investigate the
potential application of the synthesized compounds as emitters
in phosphorescent organic light-emitting devices (PhOLEDs)
and to compare them to their acetylacetonate analogues,26 the
absorption and emission behavior of complexes 16−22 was
investigated (see the Supporting Information, Figures S12−
S18).46 To determine intermolecular interactions of the square-
planar Pt(II) compounds during the photoluminescence
process, efforts were made to create pure emitter films. In
some cases this was not successful due to early crystallization.
Figure 6 shows the absorption spectra of the 100% film
measurements.
The absorption spectra were also measured in doped PMMA
films (2 wt % complex). The spectra for the a isomers are given
in Figure 7. They display a different number of peaks starting
from the high-energy absorption below 250 nm and additional
peaks around 300 and 350 nm. Most complexes show the same
absorption behavior, where the high-energy peak can be
assigned to a spin-allowed 1π−π* transition within the
cyclometalated ligand, while the transitions at higher wave-
lengths can be attributed to d−π* metal to ligand charge-
transfer (MLCT) processes between the platinum metal atom
and the cyclometalated ligand. The b isomers show very similar
behavior, with only minor deviations in the low-energy region
(see the Supporting Information).
The strongest absorption peak is found below 250 nm for all
complexes. The transition with the highest energy can be
All complexes emit in the blue to green region of the visible
spectrum (Table 1, Figure 8) with maxima red-shifted by up to
33 nm (for the a isomers) in comparison to their acac
analogues26 (see the Supporting Information, Figure S20). A
comparison of the respective isomers reveals a good agreement,
1
attributed to the π−π* transition of the NHC ligand. Further
MLCT d−π* transitions are found at around 300 and 350 nm.
For complexes 21a,b these are found at even lower energies at
about 370 nm. All pure film samples showed very low quantum
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Figure 8. Normalized emission spectra of complexes 16a−22a at
room temperature (2 wt % in PMMA).
Figure 7. Normalized absorption spectra of complexes 16a−22a at
room temperature (2 wt % in PMMA). Annotations in the legend are
given in the same order as the traces in the insert.
although some b isomers are slightly red-shifted to higher
wavelengths. Generally the obtained b isomers show signifi-
cantly lower quantum yields than the corresponding a isomers
(Table 1).
Quantum Chemical Calculations. For geometry opti-
mization of the singlet ground states and triplet states of all
complexes the B3LYP functional was used together with a 6-
31G(d) basis set and an ECP for platinum. BP86/6-31G(d)
was used for the prediction of the emission wavelengths.
All complexes show a square-planar coordination and no
twisting of the ligands in the singlet ground state (see Figure 9).
Substitution at the cyclometalated phenyl ring has no
significant impact on the bonding situation around the metal
center. For both isomers the carbene−platinum bond is the
shortest contact and the bond trans to the cyclometalated ring
is always the longest. Both isomers show similar features at first
glance, but the H−N−C angle in the β-ketoimine is always
smaller for the b isomers (about 112°, vs >113° for a isomers),
hinting at a slightly stronger steric interaction with the methyl
group of the NHC ligand on the opposite side. Indeed, all a
isomers are calculated to be thermodynamically favored by
about 5 kcal/mol (Table S3, Supporting Information). This
Figure 9. Optimized structures of 19a (left) and 19b (right) in the
singlet ground state (B3LYP/6-31G(d)).
preference may also result from an O−H interaction between
the oxygen of the auxiliary ligand and a hydrogen atom from
the NHC ligand. While the O−H distance in the a isomers
(O−HCH2N) is found to be about 2.10 Å, for the b isomers
1
(O−HCarom) it increases to 2.47 Å. Experimentally, the H
NMR spectra confirm this observation, since the resonance of
the NMe group is shifted to lower field because of the O−H
interaction for the a isomers (see the Supporting Information,
Figure S1). However, the signal of the hydrogen atom next to
the C−Pt bond is significantly shifted to lower field for the b
isomers. Again no substantial influence of the substituents at
Table 1. Photoluminescence Data (2 wt % in PMMA, Room Temperature) of the Cyclometalated Complexes
a
b
c
d
e
f
g
λexc (nm)
CIE x;y
λem (nm)
ϕ
τo (μs)
kr (103 s−1
)
knr (103 s−1
)
16a
350
355
355
355
370
350
310
355
355
355
355
355
355
350
350
355
355
0.185;0.269
0.203;0.319
0.185;0.267
0.199;0.307
0.193;0.287
0.209;0.344
0.171;0.163
0.430;0.547
0.424;0.547
0.362;0.469
0.193;0.291
0.215;0.337
0.167;0.157
0.383;0.554
0.411;0.536
0.156;0.297
0.162;0.314
476
483
476
480
479
493
446
555
553
546
478
491
456
544
553
0.12
0.05
0.15
0.06
0.05
0.03
0.05
0.31
0.20
0.11
0.15
0.05
0.32
0.14
0.07
0.74
0.90
19.4
51.4
363.5
16b
17a
3.1
322.2
1900.0
17b
18a
18b
h
h
h
18(acac)
19a
85.1
23.1
37.3
91
11.7
43.2
26.8
9.0
248.7
96.2
19b
105.3
70.6
19(acac)
20a
51.2
19.5
111.7
20b
20(acac)
21a
24
26.9
38.6
56.5
25.9
243.1
21b
22a
464, 498
463, 497
19.3
23
51.9
39.9
18.4
4.7
h
22(acac)
a
b
c
d
e
Excitation wavelength. CIE coordinates at room temperature. Maximum emission wavelength. Quantum yield at λexc; N2 atmosphere. Decay
f
g
h
lifetimes (excited by laser pulses (355 nm, 1 ns)) given as τo = τv/ϕ. kr = ϕ/τv. knr = (1 − ϕ)/τv. Complexes with the same NHC ligand but with
an acac auxiliary ligand.26
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Figure 10. Optimized structures for 17a (left) and 17b (right) in the lowest triplet state as examples of changes in the ligand backbone upon
excitation (B3LYP/6-31G(d)).
the phenyl ring was found with complexes 19 (electron
withdrawing) and 20 (electron donating), showing almost the
same energy difference for the isomers.
EXPERIMENTAL SECTION
■
General Comments. Solvents of at least 99.5% purity were used
throughout this study. Dry solvents were obtained through standard
procedures and stored under argon over molecular sieves 4 Å.
Imidazoles 2−5 were prepared according to literature procedures.40,49
Imidazole 6 was not isolated and was used without further purification
for the synthesis of the imidazolium salt. The corresponding
imidazolium iodides 8−12 were prepared according to a previously
described procedure.26 The β-ketoimine ligands 13 and 14 were
prepared by a modified method derived from a known literature
procedure.43 Potassium tetrachloroplatinate(II) was obtained from
Pressure Chemicals Co. All other chemicals were obtained from
A recently developed method47 using BP86 to reliably
predict the emission wavelength of transition-metal complexes
allowed us to predict the emission maxima with good accuracy
(Table S4, Supporting Information). The largest deviation
between predicted and experimentally determined wavelength
was found for 20a at 34 nm. On average the deviation for all
complexes was found to be 9 nm.
Additionally, the frontier molecular orbitals and spin
densities were calculated for the a isomers (Figures S21 and
S22, Supporting Information). These calculations reveal that
the density for the excited state lies on the auxiliary ligands,
with the exception of complexes 19 and 22, which clearly show
NHC-centered emission properties.
Geometry optimizations for the T1 state showed significant
reorganization effects upon excitation for most complexes. As
expected, the optimized bond distances around the Pt center
increase slightly. With the exception of 19a,b and 22a,b this
was also accompanied by large changes in the angle of the
NHC−Pt−ketoimine backbone of up to 40° (Figure 10). This
twisting of the auxiliary ligand is not uncommon for planar
Pt(II) complexes with low to moderate quantum yields and is
often encountered with halide ligands48 as well as with acac
analogues with bromo and methoxy and without a substituent
at the cyclometalating ring.26 It is interesting to note that the
compounds with the least changes have shown the best
quantum yields in the photophysical experiments.
1
common suppliers and used without further purification. H NMR,
13C NMR, and 19F NMR spectra were recorded at 298 K. H NMR
1
and 13C NMR spectra were referenced internally using the resonances
of the solvent (1H 7.26 ppm and 13C 77.0 ppm for CDCl3; H 2.50
1
ppm and 13C 39.43 ppm for DMSO-d6). 19F NMR spectra were
referenced externally against trifluoromethylbenzene (F3CC6H5).
Shifts are given in ppm and coupling constants J in Hz. Elemental
analyses were performed by the microanalytical laboratory of our
institute. Some of the microanalytical data deviate, as the isomers were
hard to separate and purify (extensive flash chromatography), but we
succeeded and even got solid-state structures from some of the
separated compounds. The problem with these particular compounds
was that methylene chloride from the flash chromatography could not
be removed efficiently in vacuo (see the Supporting Information
Figures S3−S7). Even under high vacuum (10−5 mbar) not all traces of
the solvent could be removed. Heating of the colorful solids under
reduced pressure led to a color change and degradation (validated by
1H NMR).
The melting points have been determined using a standard system
and are not corrected. The photoluminescence of the complexes was
measured in thin PMMA films doped with 2 wt % emitter or in 100%
emitter films. The 2 wt % films were prepared by doctor-blading a
solution of emitter (2 mg/mL) in a 10 wt % PMMA solution in
dichloromethane on a substrate with a 60 μm doctor blade. The film
was dried, and the emission was measured under nitrogen. The
excitation was carried out at a wavelength of 355−370 nm (Xe lamp
with monochromator), and emission was detected with a calibrated
CCD spectrometer. The phosphorescence decay was measured by
excitation with pulses of a THG-NdYAG laser (355 nm, 1 ns) and
time-resolved photon counting by the multichannel scaling (MCS)
technique.
1-(4-Fluorophenyl)imidazole (1). An 11.1 g portion (0.1 mol) of
4-fluoroaniline in 50.0 mL of methanol was treated with 16.2 mL (0.1
mol) of glyoxal (30% aqueous) for 16 h at room temperature. After
this period a yellowish mixture was formed. Then 10.7 g (0.2 mol) of
ammonium chloride was added followed by 37% aqueous form-
aldehyde (16.0 mL, 0.2 mol). The mixture was diluted with methanol
(400.0 mL) and refluxed for 1 h before H3PO4 (14.0 mL, 85%) was
slowly added. The resulting mixture was then stirred at reflux for
another 8 h. After removal of the solvent, the dark residue was poured
onto ice (300 g). KOH solution (1 N) was used to adjust the pH value
to pH 9. The crude product was extracted with CH2Cl2, the combined
organic layers were dried over MgSO4 and filtered, and the solvent was
removed in vacuo. The product was subsequently purified by
CONCLUSION
■
We synthesized the first C∧C*-cyclometalated heteroleptic
platinum(II) complexes with different aryl-substituted NHC
ligands and β-ketoimine ligands. Only a small number of
examples of the recently introduced new class of platinum(II)
compounds with cyclometalated carbenes have previously been
reported, in general with symmetrical counter ligands such as
acetylacetonate (acac). These had the advantage that no
isomers were formed during the synthesis. Changing one of the
oxygens of the acac ligand to a NH group allowed us to study
the influence on the emission process. We therefore had to
accept that isomers are formed but succeeded in separating and
characterizing them individually. Solid-state structures of seven
complexes could be obtained, confirming a square-planar
geometry of the heteroleptic complexes. In comparison to the
corresponding acac complexes the quantum yields are lower,
but other photophysical properties such as the color
coordinates or especially the short decay lifetimes make them
very interesting compounds. Additionally a quantum yield of
74% for the dibenzofuran complex 22a is still impressive and
indicates that the complexes are a promising class of triplet
emitters for PhOLEDs. Experimentally determined photo-
physical data and the measured emission behavior agree very
well with predicted values obtained by DFT calculations.
1
distillation and obtained as a colorless oil (12.1 g, 75%). H NMR
(CDCl3, 300.13 MHz): δ 7.11 (s, 1H, NCHCHN), 7.18 (s, 1H,
NCHCHN), 7.25 (m, 2H, CHarom), 7.38 (m, 2H, CHarom), 7.79 (s, 1H,
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NCHN). 13C NMR (CDCl3, 75.475 MHz): δ 116.6 (d, JF,C = 23.0 Hz,
CHarom), 118.5 (NCHCHN), 123.4 (d, JF,C = 8.6 Hz, CHarom), 130.5
(NCHCHN), 133.5 (d, JF,C = 2.8 Hz, NCarom), 135.7 (NCHN), 161.0
(d, JF,C = 247.2 Hz, FCarom). 19F NMR (CDCl3, 282.4 MHz): δ
−114.0. Anal. Calcd for C9H7FN2: C, 66.66; H, 4.35; N, 17.27. Found:
C, 66.61; H, 4.34; N, 17.51.
1-(4-Fluorophenyl)-3-methylimidazolium Iodide (7). A sealed
tube was charged with 811 mg (5.0 mmol) of 1-(4-fluorophenyl)-
imidazole and 5 mL of THF. A 781 mg portion (5.5 mmol) of methyl
iodide was added, and the reaction mixture was stirred for 17 h at 100
°C. A yellowish precipitate formed, which was separated and washed
with THF and diethyl ether. Drying in vacuo gave a white solid as the
product (1.38 g, 91%). Mp: 168−170 °C. 1H NMR (DMSO-d6,
300.13 MHz): δ 3.95 (s, 3H, NCH3), 7.55 (t, J = 8.8 Hz, 2H, CHarom),
7.84 (dd, J1 = 4.6 Hz, J2 = 9.0 Hz, 2H, CHarom), 7.95 (s, 1H,
NCHCHN), 8.26 (s, 1H, NCHCHN), 9.73 (s, 1H, NCHN). 13C
NMR (DMSO-d6, 75.475 MHz): δ 36.1 (NCH3), 117.0 (d, JF,C = 23.6
atmosphere. After addition of 10 mL of 2-butanone and 299 mg (0.8
mmol) of dichloro(1,5-cyclooctadiene)platinum(II) the reaction
mixture was heated and refluxed for 16 h. The solvent was removed
and the residue dissolved in 20 mL of DMF. A 3.2 mmol portion of
the β-ketoimine and 359 mg (3.2 mmol) of potassium-tert-butanolate
were added. The mixture was then stirred for 16 h at room
temperature and for another 6 h at 100 °C under argon. After filtration
all volatiles were removed under reduced pressure and the residue
washed with water, followed by column chromatography with
dichloromethane as eluent, yielding the two separated isomers a and
b (silica gel KG60).
(SP-4-4)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-fluorophenyl)-3-
methylimidazol-2-ylidene-κC,κC′]platinum(II) (16a). A 243 mg (0.8
mmol) portion of 1-(4-fluorophenyl)-3-methylimidazolium iodide and
317 mg of 4-amino-3-penten-2-one were reacted, following the general
procedure described above. Isomer a was obtained as a light green
1
solid (115 mg, 31%). Mp: 215−218 °C. H NMR (CDCl3, 600.16
Hz, CHarom), 121.3 (NCHCHN), 124.2 (NCHCHN), 124.4 (d, JF,C
=
MHz): δ 1.97 (s, 3H, OCCH3), 2.07 (s, 3H, NCCH3), 4.13 (s, 3H,
NCH3), 5.09 (d, J = 2.3 Hz, 1H, CH), 6.71 (dt, J = 2.6 Hz, J = 8.5 Hz,
1H, CHarom), 6.78 (d, J = 1.8 Hz, 1H, NCHCHNCH3), 6.91 (dd, JH,H
9.1 Hz, NCCHarom), 131.2 (d, JF,C = 3.0 Hz, NCarom), 136.1 (NCHN),
162.1 (d, JF,C = 247.1 Hz, FCarom). Anal. Calcd for C10H10FIN2: C,
39.50; H, 3.31; N, 9.21. Found: C, 39.75; H, 3.21; N, 9.20.
= 8.4 Hz, JH,F = 4.8 Hz, 1H, CHarom), 7.00 (ddt, JH,H = 2.6 Hz, JH,F
=
4-Amino-3-penten-2-one (13). The β-ketoimine ligand was
9.7 Hz, JH,Pt = 31.8 Hz, 1H, PtCCHarom), 7.18 (d, J = 1.9 Hz, 1H,
NCHCHNCH3), 7.42 (s, 1H, PtNH). 13C NMR (CDCl3, 125.8
MHz): δ 26.9 (OCCH3), 28.3 (NCCH3), 34.7 (NCH3), 98.4 (CH),
108.6 (d, JC,F = 23.8 Hz, FCCHarom), 111.1 (d, JC,F = 8.9 Hz,
NCCHarom), 113.9 (NCHCHNCH3), 116.2 (d, JC,F = 19.9 Hz,
PtCCHarom), 121.2 (NCHCHNCH3), 126.9 (d, JC,F = 4.8 Hz, NCarom),
143.9 (PtCarom), 159.2 (d, JC,F = 244.1 Hz, FCarom), 160.8 (NCN),
163.4 (NCCH3), 176.9 (OCCH3). Anal. Calcd for C15H16FN3OPt: C,
38.46; H, 3.44; N, 8.97. Found: C, 38.57; H, 3.15; N, 8.63.
(SP-4-3)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-fluorophenyl)-3-
methylimidazol-2-ylidene-κC,κC′]platinum(II) (16b). A 243 mg (0.8
mmol) portion of 1-(4-fluorophenyl)-3-methylimidazolium iodide and
317 mg of 4-amino-3-penten-2-one were reacted, following the general
procedure described above. Isomer b was obtained as a light green
solid (20 mg, 5%). Mp: 241−244 °C. 1H NMR (CDCl3, 600.16
MHz): δ 2.00 (s, 3H, NCCH3), 2.09 (s, 3H, OCCH3), 3.83 (s, 3H,
obtained by the modification of a known literature procedure.43
A
10.02 g amount (100 mmol) of acetylacetone was dissolved in 100 mL
of methanol, and 7.81 g (100 mmol) of ammonium carbamate was
added at room temperature. The solution was stirred for 2 h before
evaporation of the solvent at reduced pressure. Further drying in vacuo
1
gave the colorless crystalline product (9.25 g, 93%). Mp: 31 °C. H
NMR (CDCl3, 300.13 MHz): δ 1.90 (s, 3H, NCCH3), 2.02 (s, 3H,
OCCH3), 5.02 (s, 1H, CH), 5.24 (s, 1H, O-HNH), 9.70 (s, 1H, O-
HNH). 13C NMR (CDCl3, 75.475 MHz): δ 22.2 (NCCH3), 29.2
(OCCH3), 95.7 (CH), 160.8 (CH3CNH2), 196.7 (CH3CO). Anal.
Calcd for C5H9NO: C, 60.58; H, 9.15; N, 14.13. Found: C, 60.35; H,
9.35; N, 13.95.
3-Amino-1-phenyl-2-buten-1-one (14). For the synthesis of the
second β-ketoimine ligand we also used the procedure described
above. To 10 mL of methanol were added in succession a 1.62 g (10
mmol) portion of 1-benzoylacetone and 0.78 g (10 mmol) of
ammonium carbamate, and the suspension was stirred for 24 h at
room temperature. The solvent was removed in vacuo and the residue
washed with diethyl ether to give the product as a white solid (1.21 g,
NCH3), 5.10 (d, J = 2.3 Hz, 1H, CH), 6.70 (m, 2H, CHarom
NCHCHNCH3), 6.88 (dd, JH,H = 8.4 Hz, JH,F = 4.5 Hz, 1H, CHarom),
7.15 (d, J = 2.1 Hz, 1H, NCHCHNCH3), 7.68 (m, JH,H = 2.8 Hz, JH,F
,
=
9.4 Hz, JH,Pt = 24.0 Hz, 2H, PtNH, PtCCHarom). 13C NMR (CDCl3,
125.8 MHz): δ 27.1 (OCCH3), 28.8 (NCCH3), 35.9 (NCH3), 98.3
(CH), 108.8 (d, JC,F = 25.1 Hz, FCCHarom), 110.3 (d, JC,F = 8.3 Hz,
NCCHarom), 114.1 (NCHCHNCH3), 117.9 (d, JC,F = 19.9 Hz,
PtCCHarom), 121.1 (NCHCHNCH3), 139.8 (d, JC,F = 5.3 Hz, NCarom),
142.8 (PtCarom), 150.3 (NCN), 160.2 (d, JC,F = 244.2 Hz, FCarom),
163.5 (NCCH3), 177.3 (OCCH3).
1
75%). Mp: 132−134 °C. H NMR (CDCl3, 300.13 MHz): δ 2.06 (s,
3H, NCCH3), 5.24 (s, 1H, O-HNH), 5.74 (s, 1H, CH), 7.42 (m, 3H,
CHarom), 7.88 (dd, J1 = 1.8 Hz, J2 = 7.8 Hz, 2H, CHarom), 10.23 (s, 1H,
O-HNH). 13C NMR (CDCl3, 75.475 MHz): δ 22.9 (NCCH3), 92.3
(CH), 127.1 (CHarom), 128.2 (CHarom), 130.8 (CHarom), 104.2
(CaromCO), 162.8 (CH3CNH2), 189.5 (PhCO). Anal. Calcd for
C10H11NO: C, 74.51; H, 6.88; N, 8.69. Found: C, 74.36; H, 7.22; N,
8.65.
(SP-4-4)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-chlorophenyl)-3-
methylimidazol-2-ylidene-κC,κC′]platinum(II) (17a). A 257 mg (0.8
mmol) portion of 1-(4-chlorophenyl)-3-methylimidazolium iodide and
317 mg of 4-amino-3-penten-2-one were reacted, following the general
procedure described above. Isomer a was obtained as a light green
Dichloro(1,5-cyclooctadiene)platinum (Pt(COD)Cl2, 15). The
published synthesis of dichloro(1,5-cyclooctadiene)platinum(II)50 was
modified in the following way: potassium tetrachloroplatinate
(K2PtCl4, 2.00 g, 4.8 mmol) was dissolved in a solution of 53.0 mL
of water and 63.0 mL of acetic acid. To the light red solution was
added 1.6 mL (1.36 g, 12.6 mmol) of 1,5-cyclooctadiene. The reaction
mixture was stirred rapidly and heated to 110 °C. Over 3 h the
solution became pale yellow and a white precipitate was formed. The
volume of the solution was reduced to about 20 mL by evaporation
under reduced pressure. The precipitate was collected and washed in
succession with small portions of water, ethanol, and diethyl ether.
The product was dried in vacuo to give white needles (1.71 g, 95%).
Dec pt: >230 °C. 1H NMR (DMSO-d6, 300.13 MHz): δ 2.25 (m, 4H,
CH2), 2.60 (m, 4H, CH2), 5.50 (t, JH,Pt = 33.0 Hz, 4H, CH). 13C NMR
(DMSO-d6, 75.475 MHz): δ 30.3 (CH2), 100.2 (t, JC,Pt = 76.0 Hz,
CH). Anal. Calcd for C8H12Cl2Pt: C, 25.68; H, 3.23. Found: C, 25.68;
H, 3.18.
1
solid (170 mg, 44%). Mp: 195−200 °C. H NMR (CDCl3, 500.1
MHz): δ 1.97 (s, 3H, OCCH3), 2.09 (s, 3H, NCCH3), 4.14 (s, 3H,
NCH3), 5.10 (d, J = 2.3 Hz, 1H, CH), 6.81 (d, J = 2.0 Hz, 1H,
NCHCHNCH3), 6.89 (d, J = 8.2 Hz, 1H, CHarom), 7.01 (dd, J1 = 2.1
Hz, J2 = 8.2 Hz, 1H, CHarom), 7.19 (d, J = 2.0 Hz, 1H,
NCHCHNCH3), 7.24 (dt, JH,H = 2.1 Hz, JH,Pt = 30.8 Hz, 1H,
PtCCHarom), 7.46 (s, 1H, PtNH). 13C NMR (CDCl3, 125.8 MHz): δ
26.9 (OCCH3), 28.3 (NCCH3), 34.8 (NCH3), 98.5 (CH), 111.4
(NCCHarom), 114.0 (NCHCHNCH3), 121.4 (NCHCHNCH3), 122.6
(ClCCHarom), 126.5 (NCarom), 128.8 (ClCarom), 129.3 (PtCCHarom),
146.4 (PtCarom), 161.4 (NCN), 163.5 (NCCH3), 176.9 (OCCH3).
Anal. Calcd for C15H16ClN3OPt: C, 37.16; H, 3.33; N, 8.67. Found: C,
37.30; H, 3.17; N, 8.65.
(SP-4-3)-(4-aminopent-3-en-2-one-κN,κO)[1-(4-chlorophenyl)-3-
methylimidazol-2-ylidene-κC,κC′]platinum(II) (17b). A 257 mg (0.8
mmol) portion of 1-(4-chlorophenyl)-3-methylimidazolium iodide and
317 mg of 4-amino-3-penten-2-one were reacted, following the general
procedure described above. Isomer b was obtained as a light green
Preparation of Platinum(II) Complexes. General Procedure.
A 0.8 mmol portion of the imidazolium salt and 93 mg (0.4 mmol) of
silver(I) oxide were dissolved in 20 mL of dry 1,4-dioxane, and the
mixture was stirred for 16 h at room temperature under an argon
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solid (60 mg, 15%). Mp: 210−215 °C. 1H NMR (CDCl3, 500.1
MHz): δ 2.00 (s, 3H, NCCH3), 2.10 (s, 3H, OCCH3), 3.83 (s, 3H,
NCH3), 5.10 (d, J = 2.3 Hz, 1H, CH), 6.72 (d, J = 2.1 Hz, 1H,
NCHCHNCH3), 6.85 (d, J = 8.2 Hz, 1H, CHarom), 7.00 (dd, J1 = 2.3
Hz, J2 = 8.2 Hz, 1H, CHarom), 7.15 (d, J = 2.1 Hz, 1H,
NCHCHNCH3), 7.68 (s, 1H, PtNH), 7.91 (dt, JH,H = 2.3 Hz, JH,Pt
= 24.0 Hz, 1H, PtCCHarom). 13C NMR (CDCl3, 125.8 MHz): δ 27.1
(OCCH3), 28.8 (NCCH3), 35.9 (NCH3), 98.3 (CH), 110.6
(NCCHarom), 114.1 (NCHCHNCH3), 121.3 (NCHCHNCH3),
122.6 (ClCCHarom), 129.7 (NCarom), 131.1 (PtCCHarom), 138.9
(PtCarom), 145.2 (ClCarom), 150.9 (NCN), 163.4 (NCCH3), 177.3
(OCCH3). Anal. Calcd for C15H16ClN3OPt: C, 37.16; H, 3.33; N,
8.67. Found: C, 37.06; H, 3.04; N, 8.83.
procedure described above. Isomer b was obtained as an orange solid
(35 mg, 8.5%). Dec pt: >230 °C. H NMR (CDCl3, 500.1 MHz): δ
1
2.06 (s, 3H, NCCH3), 2.17 (s, 3H, OCCH3), 3.90 (s, 3H, NCH3), 5.17
(d, J = 2.2 Hz, 1H, CH), 6.83 (d, J = 2.1 Hz, 1H, NCHCHNCH3),
7.01 (d, J = 8.5 Hz, 1H, CHarom), 7.27 (s, 1H, NCHCHNCH3), 7.71
(s, 1H, PtNH), 7.96 (dd, J1 = 2.5 Hz, J2 = 8.5 Hz, 1H, CHarom), 8.84
(dt, JH,H = 2.5 Hz, JH,Pt = 24.2 Hz, 1H, PtCCHarom). 13C NMR
(CDCl3, 125.8 MHz): δ 27.1 (OCCH3), 28.9 (NCCH3), 36.1
(NCH3), 98.5 (CH), 109.5 (NCCHarom), 114.6 (NCHCHNCH3),
120.1 (O2NCCHarom), 122.2 (NCHCHNCH3), 126.3 (PtCCHarom),
138.5 (NCarom), 144.5 (PtCarom), 152.8 (NCN), 164.5 (NCCH3),
177.8 (OCCH3). Anal. Calcd for C15H16N4O3Pt·0.2CH2Cl2: C, 35.63;
H, 3.23; N, 10.93. Found: C, 35.95; H, 2.74; N, 10.87.
(SP-4-4)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-methoxyphenyl)-
3-methylimidazol-2-ylidene-κC,κC′]platinum(II) (20a). A 253 mg
(0.8 mmol) portion of 1-(4-methoxyphenyl)-3-methylimidazolium
iodide and 317 mg of 4-amino-3-penten-2-one were reacted, following
the general procedure described above. Isomer a was obtained as a
(SP-4-4)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-bromophenyl)-3-
methylimidazol-2-ylidene-κC,κC′]platinum(II) (18a). A 292 mg (0.8
mmol) portion of 1-(4-bromophenyl)-3-methylimidazolium iodide
and 317 mg of 4-amino-3-penten-2-one were reacted, following the
general procedure described above. Isomer a was obtained as a light
1
1
yellow solid (148 mg, 37%). Mp: 171−173 °C. H NMR (CDCl3,
orange solid (172 mg, 41%). Mp: 208−211 °C. H NMR (CDCl3,
500.1 MHz): δ 1.95 (s, 3H, OCCH3), 2.02 (s, 3H, NCCH3), 3.81 (s,
3H, OCH3), 4.09 (s, 3H, NCH3), 5.06 (d, J = 2.3 Hz, 1H, CH), 6.53
(dd, J1 = 2.6 Hz, J2 = 8.4 Hz, 1H, CHarom), 6.74 (d, J = 2.0 Hz, 1H,
NCHCHNCH3), 6.87 (dt, JH,H = 3.5 Hz, JH,Pt = 31.3 Hz, 1H,
PtCCHarom), 6.89 (d, J = 6.7 Hz, 1H, CHarom), 7.14 (d, J = 2.0 Hz, 1H,
NCHCHNCH3), 7.48 (s, 1H, PtNH). 13C NMR (CDCl3, 125.8
MHz): δ 26.9 (OCCH3), 28.2 (NCCH3), 34.6 (NCH3), 55.5 (OCH3),
98.2 (CH), 105.7 (OCCHarom), 110.7 (NCCHarom), 113.8
(NCHCHNCH3), 116.9 (PtCCHarom), 120.9 (NCHCHNCH3),
125.5 (NCarom), 141.9 (PtCarom), 155.8 (CaromOCH3), 160.6 (NCN),
163.1 (NCCH3), 176.8 (OCCH3). Anal. Calcd for C16H19N3O2Pt·
0.2CH2Cl2: C, 39.12; H, 3.93; N, 8.45. Found: C, 39.43; H, 3.52; N,
8.26.
500.1 MHz): δ 1.97 (s, 3H, OCCH3), 2.09 (s, 3H, NCCH3), 4.14 (s,
3H, NCH3), 5.10 (d, J = 2.3 Hz, 1H, CH), 6.81 (d, J = 2.1 Hz, 1H,
NCHCHNCH3), 6.85 (d, J = 8.2 Hz, 1H, CHarom), 7.16 (dd, J1 = 2.0
Hz, J2 = 8.2 Hz, 1H, CHarom), 7.19 (d, J = 2.1 Hz, 1H,
NCHCHNCH3), 7.39 (dt, JH,H = 2.0 Hz, JH,Pt = 30.3 Hz, 1H,
PtCCHarom), 7.44 (s, 1H, PtNH). 13C NMR (CDCl3, 125.8 MHz): δ
26.9 (OCCH3), 28.3 (NCCH3), 34.7 (NCH3), 98.4 (CH), 111.9
(NCCHarom), 113.9 (NCHCHNCH3), 117.1 (NCarom), 121.4
(NCHCHNCH3), 125.5 (BrCCHarom), 127.1 (PtCarom), 132.0
(PtCCHarom), 146.8 (BrCarom), 161.4 (NCN), 163.5 (NCCH3),
176.8 (OCCH3). Anal. Calcd for C15H16BrN3OPt: C, 34.04; H,
3.05; N, 7.94. Found: C, 34.35; H, 3.35; N, 7.64.
(SP-4-3)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-bromophenyl)-3-
methylimidazol-2-ylidene-κC,κC′]platinum(II) (18b). A 292 mg (0.8
mmol) portion of 1-(4-bromophenyl)-3-methylimidazolium iodide
and 317 mg of 4-amino-3-penten-2-one were reacted, following the
general procedure described above. Isomer b was obtained as a light
(SP-4-3)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-methoxyphenyl)-
3-methylimidazol-2-ylidene-κC,κC′]platinum(II) (20b). A 253 mg
(0.8 mmol) portion of 1-(4-methoxyphenyl)-3-methylimidazolium
iodide and 317 mg of 4-amino-3-penten-2-one were reacted, following
the general procedure described above. Isomer b was obtained as a
yellow solid (63 mg, 16%). Mp: 185−188 °C. 1H NMR (CDCl3, 500.1
MHz): δ 1.99 (s, 3H, NCCH3), 2.08 (s, 3H, OCCH3), 3.83 (s, 3H,
NCH3), 3.87 (s, 3H, OCH3), 5.09 (d, J = 2.1 Hz, 1H, CH), 6.57 (dd,
J1 = 2.7 Hz, J2 = 8.4 Hz, 1H, CHarom), 6.70 (d, J = 2.0 Hz, 1H,
NCHCHNCH3), 6.87 (d, J = 8.3 Hz, 1H, CHarom), 7.15 (d, J = 2.0 Hz,
1H, NCHCHNCH3), 7.61 (dt, JH,H = 2.7 Hz, JH,Pt = 23.0 Hz, 1H,
PtCCHarom), 7.69 (s, 1H, PtNH). 13C NMR (CDCl3, 125.8 MHz): δ
27.1 (OCCH3), 28.9 (NCCH3), 35.9 (NCH3), 55.4 (OCH3), 98.2
(CH), 108.0 (OCCHa ro m ), 110.2 (NCCHa r o m ), 113.9
(NCHCHNCH3), 116.6 (PtCCHarom), 120.8 (NCHCHNCH3),
138.0 (NCarom), 140.6 (PtCarom), 150.0 (NCN), 156.6 (CaromOCH3),
163.3 (NCCH3), 177.1 (OCCH3). Anal. Calcd for C16H19N3O2Pt·0.2
CH2Cl2: C, 39.12; H, 3.93; N, 8.45. Found: C 39.24, H 3.79; N, 8.15.
(SP-4-4)-(3-Amino-1-phenylbut-2-en-1-one-κN,κO)[1-(4-methox-
yphenyl)-3-methylimidazol-2-ylidene-κC,κC′]platinum(II) (21a). A
253 mg (0.8 mmol) portion of 1-(4-methoxyphenyl)-3-methylimida-
zolium iodide and 516 mg of 3-amino-1-phenyl-2-buten-1-one were
reacted, following the general procedure described above. Isomer a
was obtained as an orange solid (159 mg, 37%). Mp: 207−209 °C. 1H
NMR (CDCl3, 500.1 MHz): δ 2.16 (s, 3H, NCCH3), 3.85 (s, 3H,
OCH3), 4.21 (s, 3H, NCH3), 5.68 (d, J = 2.2 Hz, 1H, CH), 6.57 (dd,
J1 = 2.5 Hz, J2 = 8.4 Hz, 1H, CHarom), 6.80 (d, J = 2.0 Hz, 1H,
NCHCHNCH3), 6.92 (t, JH,Pt = 29.7 Hz, 1H, PtCCHarom), 6.93 (d, J =
10.5 Hz, 1H, NCCHarom), 7.20 (d, J = 2.0 Hz, 1H, NCHCHNCH3),
7.41−7.34 (m, 3H, CHarom), 7.73 (s, 1H, PtNH), 7.83 (dd, J1 = 1.7 Hz,
J2 = 7.8 Hz, 2H, OCCCHarom). 13C NMR (CDCl3, 125.8 MHz): δ 28.8
(NCCH3), 35.1 (NCH3), 55.5 (OCH3), 97.3 (CH), 105.8
(OCCHarom), 110.8 (NCCHarom), 113.8 (NCHCHNCH3), 117.0
(PtCCHarom), 120.9 (NCHCHNCH3), 125.0 (NCarom), 126.6
(CHarom), 128.1 (CHarom), 129.0 (CHarom), 141.8 (PtCarom), 142.1
(OCCarom), 155.8 (CaromOCH3), 160.6 (NCN), 163.9 (NCCH3),
172.7 (OCCarom). Anal. Calcd for C21H21N3O2Pt: C, 46.49; H, 3.90;
N, 7.75. Found: C, 46.36; H, 3.79; N, 7.47.
1
orange solid (61 mg, 14%). Mp: 217−220 °C. H NMR (CDCl3,
500.1 MHz): δ 2.00 (s, 3H, NCCH3), 2.10 (s, 3H, OCCH3), 3.82 (s,
3H, NCH3), 5.10 (d, J = 2.3 Hz, 1H, CH), 6.71 (d, J = 2.1 Hz, 1H,
NCHCHNCH3), 6.80 (d, J = 8.2 Hz, 1H, CHarom), 7.17−7.14 (m, 2H,
NCHCHNCH3, CHarom), 7.67 (s, 1H, PtNH), 8.06 (dt, JH,H = 2.2 Hz,
JH,Pt = 23.8 Hz, 1H, PtCCHarom). 13C NMR (CDCl3, 125.8 MHz): δ
27.2 (OCCH3), 28.8 (NCCH3), 35.9 (NCH3), 98.3 (CH), 111.2
(NCCHarom), 114.1 (NCHCHNCH3), 118.3 (NCarom), 121.3
(NCHCHNCH3), 125.5 (BrCCHarom), 133.9 (PtCCHarom), 139.6
(PtCarom), 145.6 (BrCarom), 151.0 (NCN), 163.4 (NCCH3), 177.3
(OCCH3). Anal. Calcd for C15H16BrN3OPt: C, 34.04; H, 3.05; N,
7.94. Found: C, 33.93; H, 2.87; N, 7.67.
(SP-4-4)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-nitrophenyl)-3-
methylimidazol-2-ylidene-κC,κC′]platinum(II) (19a). A 265 mg (0.8
mmol) portion of 1-(4-nitrophenyl)-3-methylimidazolium iodide and
317 mg of 4-amino-3-penten-2-one were reacted, following the general
procedure described above. Isomer a was obtained as a red-orange
solid (151 mg, 38%). Dec pt: >275 °C. 1H NMR (CDCl3, 500.1
MHz): δ 2.01 (s, 3H, OCCH3), 2.15 (s, 3H, NCCH3), 4.18 (s, 3H,
NCH3), 5.15 (d, J = 2.3 Hz, 1H, CH), 6.88 (d, J = 2.1 Hz, 1H,
NCHCHNCH3), 7.04 (d, J = 8.6 Hz, 1H, CHarom), 7.29 (d, J = 2.1 Hz,
1H, NCHCHNCH3), 7.55 (s, 1H, PtNH), 7.98 (dd, J1 = 2.3 Hz, J2 =
8.6 Hz, 1H, CHarom), 8.20 (dt, JH,H = 2.3 Hz, JH,Pt = 31.1 Hz, 1H,
PtCCHarom). 13C NMR (CDCl3, 125.8 MHz): δ 26.8 (OCCH3), 28.3
(NCCH3), 34.9 (NCH3), 98.7 (CH), 110.2 (NCCHarom), 114.3
(NCHCHNCH3), 120.1 (O2NCCHarom), 122.4 (NCHCHNCH3),
124.2 (PtCCHarom), 126.1 (NCarom), 143.8 (PtCarom), 153.3
(NO2Carom), 162.9 (NCN), 164.0 (NCCH3), 177.0 (OCCH3). Anal.
Calcd for C15H16N4O3Pt: C, 36.37; H, 3.26; N, 11.31. Found: C,
36.48; H, 3.05; N, 11.01.
(SP-4-3)-(4-Aminopent-3-en-2-one-κN,κO)[1-(4-nitrophenyl)-3-
methylimidazol-2-ylidene-κC,κC′]platinum(II) (19b). A 265 mg (0.8
mmol) portion of 1-(4-nitrophenyl)-3-methylimidazolium iodide and
317 mg of 4-amino-3-penten-2-one were reacted, following the general
906
dx.doi.org/10.1021/om401023f | Organometallics 2014, 33, 898−908

Organometallics
Article
(SP-4-3)-(3-Amino-1-phenylbut-2-en-1-one-κN,κO)[1-(4-methox-
yphenyl)-3-methylimidazol-2-ylidene-κC,κC′]platinum(II) (21b). A
253 mg (0.8 mmol) portion of 1-(4-methoxyphenyl)-3-methylimida-
zolium iodide and 516 mg of 3-amino-1-phenyl-2-buten-1-one were
reacted, following the general procedure described above. Isomer b
Notes
The authors declare no competing financial interest.
§Anorganische Chemie, TU Munchen, Lichtenbergstrasse 4,
̈
85747 Garching, Germany.
1
was obtained as an orange solid (58 mg, 13%). Mp: 193−195 °C. H
ACKNOWLEDGMENTS
NMR (CDCl3, 500.1 MHz): δ 2.11 (s, 3H, NCCH3), 3.86 (s, 3H,
NCH3), 3.91 (s, 3H, OCH3), 5.77 (d, J = 2.1 Hz, 1H, CH), 6.60 (dd,
J1 = 2.7 Hz, J2 = 8.4 Hz, 1H, CHarom), 6.71 (d, J = 2.0 Hz, 1H,
NCHCHNCH3), 6.90 (d, J = 8.4 Hz, 1H, CHarom), 7.17 (d, J = 2.1 Hz,
1H, NCHCHNCH3), 7.46−7.37 (m, 3H, CHarom), 7.79 (dt, JH,H = 2.7
Hz, JH,Pt = 23.7 Hz, 1H, PtCCHarom), 7.96 (s, 1H, PtNH), 8.06 (dd, J1
= 2.1 Hz, J2 = 7.5 Hz, 2H, OCCCHarom). 13C NMR (CDCl3, 125.8
MHz): δ 29.5 (NCCH3) 35.9 (NCH3), 55.4 (OCH3), 96.5 (CH),
109.1 (OCCHarom), 110.5 (NCCHarom), 114.0 (NCHCHNCH3),
116.2 (PtCCHarom), 120.9 (NCHCHNCH3), 126.9 (CHarom), 128.2
(CHarom), 129.3 (CHarom), 138.1 (NCarom), 140.6 (PtCarom), 140.8
(OCCarom), 149.6 (NCN), 156.6 (CaromOCH3), 164.2 (NCCH3),
171.6 (OCCarom). Anal. Calcd for C21H21N3O2Pt·0.15CH2Cl2: C,
45.75; H, 3.87; N, 7.57. Found: C, 45.84; H, 3.95; N, 7.24.
■
We thank Dr. Fuchs (BASF), Dr. Wagenblast (BASF), and Dr.
Lennartz (BASF) for helpful discussions and photophysical
measurements. We also thank the ZIH for computation time at
their high-performance computing facility.
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AUTHOR INFORMATION
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Corresponding Author
*T.S.: e-mail, thomas.strassner@chemie.tu-dresden.de; tel, 49
351 46338571; fax, 49 351 46339679.
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dx.doi.org/10.1021/om401023f | Organometallics 2014, 33, 898−908