Synthesis, air stability, photobleaching, and DFT modeling of blue light emitting platinum CCC-N-heterocyclic carbene pincer complexes

Article abstract of DOI:10.1021/om200687w

The recently reported metalation/transmetalation route for the synthesis of CCC-bis(NHC) pincer ligand supported transition-metal complexes was extended to Pt. 2-(1,3-Bis(N-butylimidazol-2-ylidene)phenylene)(chloro)platinum(II) (1) and its bromo analogue 2 were synthesized and characterized. X-ray crystal structure determinations revealed complexes 1 and 2 to have distorted-square- planar configurations around the metal. Photophysical and thermal properties of these complexes are reported, and their extended photostability in air is discussed and contrasted. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) computations of the ground state and various low-lying excited states have revealed admixing of Pt 5d orbitals and the ligand π* orbitals for both the ground state and the low-lying excited states of complex 1, indicating the low-lying states to be a mixture of metal-to-ligand charge-transfer and ligand-centered transition (MLCT-LC). Somewhat surprisingly, the computed gas-phase geometry of the excited state of complex 1 had a significant distortion, mostly about the C_aryl-Pt-Cl angle. These complexes were congeners of materials for organic light emitting diodes (OLEDs).

Full text of DOI:10.1021/om200687w

Article
pubs.acs.org/Organometallics
Synthesis, Air Stability, Photobleaching, and DFT Modeling of
Blue Light Emitting Platinum CCC-N-Heterocyclic Carbene Pincer
Complexes
Xiaofei Zhang,† Ashley M. Wright,† Nathan J. DeYonker,‡ T. Keith Hollis,*,† Nathan I. Hammer,*,†
Charles Edwin Webster,*,‡ and Edward J. Valente§
†Department of Chemistry and Biochemistry, The University of Mississippi, University, Mississippi 38677, United States
‡Department of Chemistry, The University of Memphis, Memphis, Tennessee 38152, United States
§University of Portland Diffraction Facility, Department of Chemistry and Biochemistry, University of Portland, Portland,
Oregon 97203, United States
S
* Supporting Information
ABSTRACT: The recently reported metalation/transmetala-
tion route for the synthesis of CCC-bis(NHC) pincer ligand
supported transition-metal complexes was extended to Pt.
2-(1,3-Bis(N-butylimidazol-2-ylidene)phenylene)(chloro)-
platinum(II) (1) and its bromo analogue 2 were synthesized
and characterized. X-ray crystal structure determinations
revealed complexes 1 and 2 to have distorted-square-planar
configurations around the metal. Photophysical and thermal properties of these complexes are reported, and their extended
photostability in air is discussed and contrasted. Density functional theory (DFT) and time-dependent density functional theory
(TD-DFT) computations of the ground state and various low-lying excited states have revealed admixing of Pt 5d orbitals and
the ligand π* orbitals for both the ground state and the low-lying excited states of complex 1, indicating the low-lying states to be
a mixture of metal-to-ligand charge-transfer and ligand-centered transition (MLCT-LC). Somewhat surprisingly, the computed
gas-phase geometry of the excited state of complex 1 had a significant distortion, mostly about the Caryl−Pt−Cl angle. These
complexes were congeners of materials for organic light emitting diodes (OLEDs).
Pincer ligands have been one of the most widely investigated
and applied architectures in modern organometallic chem-
istry.19 The confluence of NHCs and pincer ligand chemistry
has seen much activity in recent years.20 The aryl-bridged
bis(NHC)-pincer ligands consist of four major classes, depending
on the atoms making the bonds to the metal and the linker
between the aryl and NHC groups (Scheme 1). The xylylene-
bridged C∧C∧C-NHC (type A)21 and 2,6-lutidinyl bridged
C∧N∧C-NHC (type C)20b,21c,22 pincer complexes are usually
found to have C2 symmetry due to the CH2 spacer. The
phenylene-bridged CCC-NHC (type B)23 and pyridylene-bridged
CNC-NHC (type D)20b,c,24 pincer complexes normally have
higher symmetry and adopt a C2v geometry. We introduced the
class of phenylene-bridged CCC-bis(NHC) pincer ligand
systems,23 and others have also begun exploring this architecture.25
The impact of molecular inorganic and organometallic
compounds in photonic applications has been growing rapidly.
Recent reports have illustrated their importance in develop-
ments for artificial photosynthesis,26 photocatalytic splitting of
water,27 solar cell applications,28 organic light-emitting diodes
(OLEDs),29 and photoluminescence.15a,h,30 A recent paper
detailed the pyridylene CNC-bis(NHC) pincer ligand Pt system
INTRODUCTION
■
The development of new molecular architectures to impart
desired physical and chemical properties has been an area of
highly active research. Specifically, stable carbenes have drawn
intense attention, in spite of their relatively short history.1 The
special stability of N-heterocyclic carbenes (NHCs) was
established with the first report of the X-ray crystallographically
determined molecular structure by Arduengo and co-work-
ers.1b,2 The dramatic importance of the nitrogen substituents
was further demonstrated when Alder and co-workers reported
the X-ray crystal structure of an acyclic diamido carbene.3
The applications of NHCs have blossomed since the 1991
report, and these compounds have been widely established as
strong ligands for transition metals.1c,4 Numerous applications
to catalytic organic transformations have been demonstrated,
including olefin metathesis,5 Pd cross-coupling reactions such
as the Heck,6 Suzuki−Miyaura,7 Negishi,8 Sonogashira,9 Buchwald−
Hartwig,7c,10 and many more.11 In addition, they have been demon-
strated to catalyze C−heteroatom bond forming reactions such as
C−N,10,12 C−Si,13 and C−O.14 Furthermore, their photophysical
properties have been explored for materials applications.15 Besides
serving as excellent ligands to transition metals, NHCs have been
demonstrated to be organocatalysts for the benzoin condensation,16
Stetter reaction,17 and more.18
Received: August 2, 2011
Published: February 9, 2012
© 2012 American Chemical Society
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1
bromo complex 2 was observed at 170.5 ppm with JPt−C
=
Scheme 1. Metal Complexes Derived from Aryl-Bridged
Bis(NHC)-Pincer Ligands
1166 Hz. The Pt-bound aryl carbon signal of 2 was observed at
134.0 ppm with JPt−C = 953 Hz. All chemical shifts and
1
coupling constants were similar to those previously reported for
Pt-NHC complexes.31,34 The ESI-MS of the Pt-Cl complex 1
revealed the molecular ion plus Na (575 Da). The molecular
ion was observed for the Pt-Br complex 2 (595 Da). The
experimental values for the CHN analyses of both complexes
were within an acceptable range.
X-ray-quality crystals of chloro complex 1 were obtained by
slow diffusion of Et2O into a CH2Cl2 solution. X-ray-quality
crystals of bromo complex 2 were observed after trans-
metalation and were collected from the reaction mixture.
ORTEP representations of the molecular structures of 1 and 2
are depicted in Figure 1.35 Selected bond distances and angles
and its photoluminescence.31 We report herein the development
and characterization of square-planar PtII CCC-NHC phenylene-
bridged pincer complexes 1 and 2 and their properties. To
understand the nature of the observed transitions, we describe
the application of theoretical methods (DFT) to explore the
geometric and electronic properties of the ground state and
excited state (both vertical and adiabatic transitions).
RESULT AND DISCUSSION
■
Synthesis and Characterization. The CCC-NHC pincer
ligand precursors were synthesized according to the liter-
ature.23,32 Simultaneous activation of the three C−H bonds of
the tridentate ligand was achieved through the well-established
basicity and electrophilicity of Zr(NMe2)4.23,33 A Pt(II) source
was added to the in situ prepared Zr reagent to achieve
transmetalation (Scheme 2). All reactions were carried out at
Scheme 2. Synthesis of CCCBu-NHC-PtII-X Complexes 1 and
2
Figure 1. ORTEP diagram (50% thermal ellipsoids) of CCCBu-NHC-
PtII-Cl (1) and CCCBu-NHC-PtII-Br (2). Hydrogen atoms are omitted
for clarity.
for complexes 1 and 2 are given in Table 1 and are consistent
with those for previously reported Pt(II) complexes.31,34a,36
The structural data for the pyridylene-bridged CNC analogue
have been listed for comparison.31 The structures of complexes
1 and 2 are similar. The Pt−Ccarbene bond distances in chloro
complex 1 (2.030(3) and 2.035(3) Å) and in bromo complex 2
(2.037(6) and 2.036(6) Å) fall into the range observed for
neutral and cationic Pt(II) pincer complexes.31,34a,36 Both complexes
display distorted-square-planar configurations at the metal center,
which has been commonly seen for four-coordinate Pt(II)
complexes.34a,36 The C7−PtII−X atoms are linear (1, 179.40(8)°;
2, 178.66(18)°). However, the C2−PtII−C13 angles were bent
(1, 157.44(11)°; 2, 157.3(2)°) due to ligand constraints.
It was possible to compare the metric data for Pt−Cl complex 1
to those for its pyridylene-bridged CNC analogue. The Pt−Caryl
bond length of complex 1 (1.941(3) Å) was slightly shorter
(∼0.025 Å) than the Pt−N bond length of the pyridylene-bridged
CNC complex, while the Pt−CNHC bonds of complex 1 were
about 0.06 Å longer.31 On comparison of the Pt−Cl bond
distances, a greater trans influence of the Caryl anionic ligand was
room temperature under an inert atmosphere. When trans-
metalation was complete, water was added, and excess Zr
reagent was decomposed and precipitated. The identity of each
1
complex was established by H and 13C NMR spectroscopy,
ESI-MS, and elemental analysis (see the Experimental Section).
1
Two of the primary observations in the H NMR spectra were
the disappearance of the imidazolium protons (11.27 ppm, 2H)
1
and an aryl H (8.96 ppm). The H NMR data of chloro
complex 1 and bromo complex 2 also indicated characteristic
long-range 195Pt−1H coupling. The NHC carbon signal of
1
chloro complex 1 was observed at 171.7 ppm with JPt−C
=
1168 Hz. The Pt-bound aryl carbon signal was observed at
1
133.8 ppm with JPt−C = 937 Hz. The NHC carbon signal of
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Table 1. Selected Bond Lengths and Angles of CCCBu-NHC-PtII-X Complexes 1 (X = Cl) and 2 (X = Br) and the CNCBu-NHC-PtII-Cl
Complex
bond lengths (Å)
bond angles (deg)
Pt−C2
Pt−C7
Pt−C13
Pt−X
C7−Pt−X
C2−Pt−C13
C7−Pt−C2
1
2
2.030(3)
2.037(6)
1.941(3)
1.955(6)
2.035(3)
2.036(6)
2.3997(7)
2.5028(8)
179.40(8)
157.44(11)
157.3(2)
78.58(11)
78.9(3)
178.67(18)
bond lengths (Å)
bond angles (deg)
Pt−C1
Pt−N1
Pt−C9
Pt−X
N1−Pt−Cl
C1−Pt−C9
N−Pt−C1
a
CNC
1.972(8)
1.968(5)
1.978(9)
2.278(2)
178.79(18)
158.1(3)
79.1(3)
a
Pyridylene-bridged CNC analogue with X = Cl. Data from ref 31.
notable in the longer bond length (2.3997(7) Å vs 2.278(2) Å,
Table 1). Other metric data for the two compounds were very similar.
Photophysical Studies. Complexes 1 and 2 were found to
emit blue light with UV stimulation. Their absorption and
emission data in MeOH solution have been included in Table 2
and Figure 2a. In MeOH solution, the UV absorption spectra of
Table 2. Photophysical Properties of CCCBu-NHC-PtII-X
Complexes 1 and 2 in MeOH Solution
λem/nm (rel
λabs/nm (ε/10−3 M−1 cm−1)
intens)
Φobs/% τ/μs
b
1
2
265 (22.9), 323 (3.3), 355 (5.7),
416 (0.12), 441 (0.08)
449 (100),
474 (63)
1.3
0.21
a
a
b
266 (24.0), 323 (3.5), 358 (6.2),
416 (0.13), 440 (0.08)
450 (100),
474 (77)
1.5
1.7
a
b
Irradiated with 360 nm light. Referenced to quinine sulfate.
complexes 1 and 2 were nearly identical. Both exhibited a major
absorption peak around 265 nm and minor peaks near 323 and
355 nm, which were ascribed as mixed metal to ligand charge
transfer and ligand centered (MLCT-LC) transitions.37 The
d−d transitions that lead to absorption peaks above 400 nm
with significant strength were consistent with a distorted-square-
planar configuration of each complex.38 The emission spectra of
complexes 1 and 2 were very similar, except for the ratio of major
peaks (Figure 2a). Observed solution quantum efficiencies were
1.3% for complex 1 and 1.5% for complex 2 (Table 2). Lifetimes
of excited states in methanol solutions were 210 ns for complex 1
and 1.7 μs for complex 2, which was comparable to those for
organometallic complexes with related structures.15a
Figure 2. Emission and absorption data of CCCBu-NHC-PtII-X
complexes 1 and 2 in (a) MeOH solution (the insert shows d−d
transitions) and (b) solid state at 298 K (irradiated at 355 nm).
In the solid state, the strong blue emission of complexes 1
and 2 varies only slightly (Figure 2b). While sharing λmax at
472 nm, complex 2 had a more intense shoulder peak at 455 nm,
which suggested a Pt to halogen interaction was involved in
the emission process. The emission curves extended to about
600 nm, but the sharp drop after the peak at ∼480 nm gave the
complexes a pure blue color. In comparison to the pyridine-
bridged analogue reported by Lee et al.,31 complexes 1 and 2
gave relatively narrow emission peaks (half peak width of
∼50 nm), and they were blue-shifted 100−150 nm. Decay of
the excited state of complexes 1 and 2 in the solid state exhibited
a biexponential pattern. The lifetimes of excited states of 1
(0.19 and 1.7 μs) and 2 (0.19 and 1.9 μs) are comparable to
those of other known organometallic complexes.15c,39 No differ-
ence in lifetime was observed between ambient and vacuum
(10−5 Torr) conditions for the solid state.
and differential scanning calorimetry (DSC). It was found that
the compounds melted at approximately 280 °C and remained
as supercooled liquids over a large temperature range. The 10%
weight loss temperatures (TΔ10%) were about 380 °C (see the
Supporting Information). Notably, complexes 1 and 2 evaporated
and deposited on the glass wall of the furnace. Spectroscopic
analysis of the residues (fluorescent, NMR, and ESI-MS) indicated
the compounds remained unchanged.
Photostability in Air. Previous studies on Pt NHC
complexes suggested that their emissions could be stable under
an inert atmosphere over an extended period of time.15c,40
Interestingly, the emissions of complexes 1 and 2 were found to
be stable even under an ambient atmosphere (room temperature
and 30−50% humidity). Time-resolved emission spectra of 1 and
2 are presented in Figure 3. The authentic blue λmax (472 nm) of
complexes 1 and 2 retained >97% intensity over 6 h of continuous
irradiation. The shape of the spectra remained unvaried during the
Thermophysical Studies. Thermal stability is crucial to
OLED emitter candidates. The thermal properties of complexes
1 and 2 were investigated by thermogravimetric analysis (TGA)
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more than half of its initial emission strength and a visible
darkening on the irradiated surface after only 1 h (Table 3). When
significant photobleaching (>10%) was observed under any
conditions, a control experiment was carried out to calibrate the
contribution to decomposition from other pathways. In the control
experiment, the initial emission spectrum A was collected and the
analyte was then kept under the same conditions with the radiation
beam blocked. After 1 h the irradiation was resumed and another
emission spectrum B was taken. The loss of emission intensity
between spectra A and B was ascribed to the sum of
decompositions through all other pathways. Since each spectrum
took ∼2 min to accumulate, a significant measurement-induced
photobleaching was observed for the less photostable analytes
(Figures S1 and S2, Supporting Information). An exponential
fitting based on the decay curve was applied to retrieve the
photobleaching during the initial 2 min irradiation. After 1 h in the
dark all compounds were found to undergo <1% decomposition,
which confirms a direct correlation between photobleaching and
loss of emission strength. On comparison of the pincer Pt(II)
complexes 1 and 2 and the four commercially available emitters,
these observations indicated that the Pt complexes were much more
photostable under an ambient atmosphere.
Figure 3. Time dependence of emission of solid-state 1 and 2 in air
over 6 h, irradiated at 355 nm.
Table 3. Solid-State Emission and Lifetime Data of CCCBu-
NHC-PtII-X Complexes 1 and 2 and Four Commercially
Available Emitters
b
remaining intens/%
τobs/μs
λem/nm (rel
a
intens/%)
in N2
in air
in air
in vac
1
445 (39)
472 (100)
502 (42)
99 (0.4)
0.19/1.7
0.19/1.7
Computational Studies. The pincer Pt(II) complexes
were modeled by DFT and TD-DFT methods to better understand
the observed photophysical properties.45 Previously, Halls and
Schlegel employed a somewhat similar approach to study the first
excited states of tris(8-hydroxyquinoline)aluminum(III) (Alq3).46
Additionally, Rocha, Martin, Batista, and co-workers successfully used
DFT/TD-DFT theoretical methods and experimental approaches to
study the electronic structure and spectroscopic properties of
ruthenium polypyridyl complexes.47 In our calculations the structure
of Pt-Cl complex 1 was simplified to structure 3 by replacing the two
butyl groups with methyl groups. The computationally predicted
ground-state geometry of 3 was in very good agreement with the
geometric results from the experimental X-ray crystallography of 1.
The rms deviation of the 20 heavy atoms was 0.047 Å.
2
455 (66)
472 (100)
502 (33)
97 (0.3)
0.19/1.9
0.19/1.9
c
e
Alq3
506 (100)
99 (0.2)
71 (4.6)
99 (1.8)
99 (0.3)
51 (3.8)
46 (3.0)
78 (1.8)
0.016
d
Ir(dfppy)3 499 (100)
Znq2
536 (100)
463 (100)
0.025
LBMQ
84 (5.6)
a
b
Irradiated at 355 nm (1.67 mW/cm2). λmax after 6 h of continuous
excitation. Data presented are an average of three measurements;
σ (standard deviation) values are included in parentheses. See ref 41,
data collected under nitrogen. After 1 h. See ref 43, data collected
under nitrogen.
c
d
e
measurements (Figure 3 and Table 3). These data indicated that
complexes 1 and 2 did not photobleach in air with UV irradiation.
The photostability test under N2 and ambient atmosphere
was also carried out on four commercially available emitters:
tris(8-hydroxyquinoline)aluminum (Alq3),29a,41 tris[2-(4,6-
difluorophenyl)pyridinato-C2,N]iridium(III) (Ir(dfppy)3),42
(8-hydroxyquinoline)zinc (Znq2),43 and lithium tetrakis(2-methyl-
8-hydroxyquinolinato)boron (LBMQ)44 (Scheme 3). Three of the
The absorbance and fluorescence spectra for CCCMe-NHC-
PtII-Cl (3) were computed using the optimized molecular
structure (Figure 4). The simulated absorption of structure 3
matched the experimental data of complex 1 in the energy
range (230−380 nm). However, the calculated emission
spectrum of the optimized planar excited-state geometry was
very different from the experimental result (compare Figure 2a
vs Figure 4 (×)), indicating that the planar excited state of the
molecule was not the major radiative state.
Scheme 3. Four Commercially Available Emitters
Further TD-DFT calculations revealed that although
CCCMe-NHC-PtII-Cl (3) adopts a distorted-square-planar
configuration at the ground state, constraining the first singlet
excited electronic state to the C2v point group symmetry
actually leads to a transition state. The imaginary vibrational
mode (ωe = 58.7i) corresponded to the Cl atom and the sides
of the two pincer ligand asymmetrically bending out of the C2v
plane. When performing a TD-DFT geometry optimization of
the first excited state in Cs symmetry, the Cl atom bent out of
emitters, Alq3, Znq2, and LBMQ, were found to be stable to
photoexcitation under nitrogen (no significant loss of emission
intensity after 6 h). Ir(dfppy)3 showed significant loss of intensity
of λmax (29%) after 6 h of photoexcitation under the same
conditions. When these commercially available complexes were
irradiated under ambient atmosphere, moderate to severe
photobleaching was observed. Ir(dfppy)3 exhibited a loss of
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Figure 4. Computed ground state absorbance (−) and C2v (planar)
excited state emission (×) of CCCMe-NHC-PtII-Cl (3).
Figure 6. Computed ground state absorbance (−) and optimized
Cs excited state emission (×) of CCCMe-NHC-PtII-Cl (3).
the observed one (Figure 2). S1 and the optimized Cs geometry
for the bent triplet excited state (T1) are quite similar.48 The
simulated spectrum suggested an emission from 380 to 510 nm
with three major peaks at 390, 445, and 490 nm. This result
matched the experimental data very well in the energy range
and in having three maxima. The simulated absorbance
spectrum is included in Figure 6. Compare the computed
emission spectra of the planar C2v and bent Cs structuresthe
computed emission spectrum of the planar structure has only a
small red shift, while the computed emission spectrum of the
distorted structure has a much larger red shift. In the bent Cs
excited state, the HOMO−LUMO transition loses almost all of
its intensity and moves to around 1200 nm (see the Supporting
Information). Also, in the bent Cs excited state, the first transi-
tion with appreciable intensity in the visible region was the third
computed singlet electronic excitation.
plane significantly (Caryl−Pt−Cl = 93°). HOMO and LUMO
diagrams (Kohn−Sham orbitals) of the planar ground state and
the optimized Cs-symmetric excited state are included in Figure 5.
In the ground state, significant admixture among the d orbitals of
Pt, the 3p orbital of Cl, and the ligand π orbital was observed in
both the HOMO and LUMO (Figure 5a,b). In the excited state,
the Cl atom bends out of the molecular plane along the Caryl
Pt−Cl axis, leading to Cs symmetry (Figure 5c−f). The molecular
orbitals are highly localized around the Pt and Cl atoms.
−
An emission spectrum was calculated on the basis of the
optimized Cs geometry for the bent singlet excited state (S1).
The S1 emission spectrum (Figure 6 (×)) was much closer to
Closer examination of molecular orbitals of CCCMe-NHC-PtII-
Cl (3) revealed a decrease in the HOMO−LUMO gap when the
Cl atom was distorted out of the molecular plane. A Walsh-like
diagram of the ground-state orbital energies versus constrained
Caryl−Pt−Cl angle at the TD-DFT S1 excited-state geometries is
included in Figure 7. This diagram demonstrates that the HOMO
Figure 7. Walsh-like diagram of the ground-state orbital energies at the
TD-DFT excited-state geometries.
is more destabilized than the LUMO is stabilized as the geometry
Figure 5. Molecular orbitals of the optimized ground state and
optimized excited state of complex CCCMe-NHC-PtII-Cl (3).
changes from the planar C2v structure to the bent Cs structure.49
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The solid was washed with water (2 × 1 mL), cold CH2Cl2 (2 × 1 mL),
and Et2O (3 × 3 mL) and was dried under vacuum, yielding a yellow
crystalline solid (0.13 g, 50%). X-ray-quality crystals were grown by
The energies in the Walsh-like diagram demonstrate the large red
shift in the emission spectrum; the geometric distortion
contributed to this red shift. In the Cs structure, there is a drastic
change in the HOMO shape, as ligand π character is removed
when the Caryl−Pt−Cl angle is bent away from 180°. The p orbital
of the chlorine, which has lone pair character (slightly antibonding)
in the planar structure, becomes strongly Pt−Cl antibonding (σ*)
in the Cs bent structure. In the LUMO, as the Caryl−Pt−Cl angle is
bent away from 180°, the bent chlorine retains much of the p lone
pair character but creates a small “divot” in the Pt−Cl π character.
In the bent structure, both the HOMO and the LUMO have a
large amount of nonbonding metal d orbital character. This unique
geometric change during the electronic transition may contribute
to the air stability and photostability of the complex.
1
slow diffusion of diethyl ether vapor into a CH2Cl2 solution of 1. H
NMR (CD2Cl2; 300.132 MHz): δ 7.40 (dd, 2H, J = 2.0 Hz, J = 9.0 Hz,
imid), 7.01 (dd, 2H, J = 2.0 Hz, J = 9.0 Hz, imid), 7.16 (t, 1H, J =
7.8 Hz, p-Ph), 6.93 (dd, 2H, J = 8.0 Hz, 4JPt−H = 16.1 Hz, m-Ph), 4.69
(t, 4H, J = 7.3 Hz, NCH2), 1.86 (quintet, 4H, J = 7.5 Hz), 1.45 (sextet,
4H, J = 7.7 Hz), 0.97 (t, 6H, J = 7.4 Hz). 13C NMR (d6-DMSO;
75.476 MHz, 350 K): δ 171.7 (1JPt−C = 1168 Hz), 144.1, 133.8 (1JPt−C
=
937 Hz), 123.3, 121.1, 115.7, 107.6, 47.7, 32.7, 18.8, 13.2. ESI-MS:
calcd for C20H25ClN4PtNa [M + Na] (m/z) 575 (100%), 574 (93%),
573 (74%), 576 (45%), 577 (42%); found 575 (100%), 574 (96%),
573 (78%), 576 (46%), 577 (43%). Anal. Calcd: C, 43.52; H, 4.57;
N, 10.15. Found: C, 43.19; H, 4.09; N, 9.90.
2-(1,3-Bis(N-butylimidazol-2-ylidene)phenylene)(bromo)-
platinum(II) (2). 1,3-Bis(1-butylimidazolium-3-yl)benzene dibro-
mide (0.48 g, 1.0 mmol), tetrakis(dimethylamino)zirconium (0.32 g,
1.2 mmol), and THF (10 mL) were stirred for 1 h at room temperature,
yielding a cloudy suspension. [Pt(COD)Br2] (0.463 g, 1.0 mmol) was
added, and the reaction mixture was stirred at room temperature for
8 h, yielding a cloudy yellow suspension. After standing for 10 min, a
yellow precipitate was observed with a clear reddish supernatant liquid.
The precipitate was collected and washed with toluene (3 × 3 mL),
yielding an analytically pure yellow solid (0.242 g, 52%). Some of the
CONCLUSION
■
The synthesis and characterization of the two novel CCC-NHC
pincer Pt(II) complexes 1 and 2 have been reported. They
display distorted-square-planar configurations, as expected for
d8 four-coordinated transition-metal compounds. Complexes 1
and 2 were found to emit bright blue light in the solid state
under UV irradiation with emissions that are stable under an
ambient atmosphere (O2 and H2O) for extended periods. At
the same time, they were found to be thermally stable under an
N2 atmosphere upon evaporation, which suggests that they
would be suitable for thermodeposition processing. Computa-
tional studies of the complexes illustrated the details of the
molecular orbitals and the electronic transitions involved in the
photophysical processes. Somewhat surprisingly, the computed
gas-phase geometry of the excited state of model 3 displays a
significant amount of geometric distortion, mostly about the
Caryl−Pt−Cl angle.
1
solid was directly used for X-ray crystallography. H NMR (CD2Cl2;
300.132 MHz): δ 7.40 (dd, 2H, J = 2.0 Hz, J = 9.0 Hz, imid), 7.01 (dd,
2H, J = 2.0 Hz, J = 9.0 Hz, imid), 7.18 (t, 1H, J = 7.8 Hz, p-Ph), 6.93
(dd, 2H, J = 8.0 Hz, 4JPt−H = 17.8 Hz, m-Ph), 4.76 (t, 4H, J = 7.3 Hz,
NCH2), 1.87 (quintet, 4H, J = 7.5 Hz), 1.45 (sextet, 4H, J = 7.7 Hz),
0.97 (t, 6H, J = 7.4 Hz). 13C NMR (d6-DMSO; 75.476 MHz, 350 K):
δ 170.5 (1JPt−C = 1166 Hz), 143.8, 134.0 (1JPt−C = 953 Hz), 122.8,
121.3, 115.4, 107.5, 48.3, 32.8, 18.6, 13.1. ESI-MS: calcd for
C20H25BrN4Pt [M+] (m/z) 595.1; found 595.0. Anal. Calcd: C,
40.28; H, 4.22; N, 9.39. Found: C, 40.10; H, 3.94; N, 9.30.
X-ray Crystallography. X-ray-quality crystals of 1 and 2 were
mounted atop fine glass fibers. Diffraction experiments were
performed on an Oxford Diffraction Systems Gemini S diffractometer
with Mo Kα radiation (λ = 0.710 73 Å) at 298 K. The structures were
solved and refined using the SHELX suite of programs.
Computational Details. Most of the presented theoretical
calculations were carried out using the Gaussian0951 implementation
of B3LYP (the B3 exchange functional52 and LYP correlation
functional)53 density functional theory (DFT),54 using the default
pruned fine grids for energies (75, 302), default pruned coarse grids
for gradients and Hessians (35, 110) (neither grid was pruned for
platinum), and nondefault SCF convergence for geometry optimiza-
tions (10−6). Excited states were geometry optimized using analytical
gradients55 with time-dependent density functional theory (TD-DFT)56
calculations. TD-DFT geometry optimizations were performed for the
first three excited singlet states. In most cases, 20 singlet excitations
were solved iteratively (TD(ROOT=X, NSTATES=20), where X was
the root number). However, in cases where during the optimization
the Davidson iterative solution of the excitations failed to converge,
40 singlet excitations were solved iteratively. Symmetry was disabled
during all excited-state geometry optimizations; however, the S1
geometry was optimized to have Cs symmetry. For TD-DFT optimi-
zations, the default convergence criteria for the energy (10−6) and
nondefault convergence criteria for the wave function (10−6) were
used. The Caryl−Pt−Cl angle was constrained (from the S1 optimized
angle of 93.31° to 180°) in a series of TD-DFT optimizations for the
first root. A Walsh-like diagram was constructed from the ground-
state orbital energies at the TD-DFT excited-state geometries. All
calculations were conducted with the same basis set combination. The
basis set for platinum was the Hay and Wadt basis set and effec-
tive core potential (ECP) combination (LanL2DZ)57 as modified by
Couty and Hall, where the two outermost p functions have been
replaced by a (41) split of the optimized platinum 6p functions.58 The
6-31G(d′) basis sets59 were used for all other atoms. Spherical harmonic d
functions were used throughout; i.e., there are five angular basis functions
EXPERIMENTAL SECTION
■
General Procedures. All starting materials were purchased from
Sigma-Aldrich, Fisher Scientific, or Strem. The reagents were used as
received unless otherwise mentioned. All solvents were dried and were
degassed by passing through a basic alumina column under Ar
protection.50 All reactions involving organometallic reagents were
carried out under a N2 or Ar atmosphere using standard glovebox and
Schlenk line techniques. NMR spectra were collected using a Bruker
Avance 300 or 500 spectrometer and were referenced to the residual
solvent peak (δ in ppm, J in Hz). Electrospray ionization mass spectra
were collected using a Waters Micromass ZQ mass spectrometer.
Elemental analyses were carried out by Columbia Analytical Service or
on a PerkinElmer 2400 Series II CHNS/O analyzer. UV−visible
absorption spectra were collected using a HP 8453 UV−visible system.
Emission spectra were collected using a PerkinElmer LS 55
fluorescence spectrometer. Photostability studies were carried out by
exposing the solid sample to 355 nm radiation. The light source was a
xenon lamp, and the detector was a photodiode array placed behind a
filter next to the sample chamber. Lifetime measurements were carried
out using 10 Hz pulsed 355 nm Nd:YAG laser output as the pumping
source and a photomultiplier tube as the detector. TGA/DSC data
were collected on PerkinElmer Pyris 1 TGA/DSC 4000, with nitrogen
flow at 20 mL/min and temperature gradient set at 20 °C/min.
2-(1,3-Bis(N-butylimidazol-2-ylidene)phenylene)(chloro)-
platinum(II) (1). 1,3-Bis(1-butylimidazolium-3-yl)benzene dichlo-
ride (0.20 g, 0.50 mmol), tetrakis(dimethylamino)zirconium (0.17 g,
0.63 mmol), and CH2Cl2 (∼4.0 mL) were combined. The mixture was
stirred for 1 h at room temperature to afford a red solution.
[Pt(COD)Cl2] (0.19 g, 0.50 mmol) was added, and the mixture was
stirred vigorously at room temperature for 6 h. The reaction mixture
was transferred to a round-bottom flask that contained 1 mL of
distilled water, and the precipitate was removed by filtration.
The filtrate was concentrated under vacuum to afford a yellow solid.
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Organometallics
Article
per d function. In all computations, the n-butyl group of the ligand was
trimmed to methyl. All structures were fully optimized, and frequency
calculations (analytical for DFT and numerical for TD-DFT) were
performed on all ground and select excited-state structures to ensure that
either a zeroth-order saddle point (a local minimum) or a first-order saddle
point was achieved. To analyze the electronic structure of the TD-DFT
excited states on roots with high oscillator strength, a natural transition
orbital (NTO) analysis60 was performed. The NTO analysis diagonalized
the transition density matrix and gave a representation of the electronic
excitation in terms of a single excited particle and empty hole. While the
ordering of the natural transition orbitals was slightly different from that of
the ground state molecular orbitals, the NTOs and MOs appeared to be
qualitatively similar. All molecular orbital plots represented in the article are
ground-state Kohn−Sham orbitals at either the ground-state or excited-
state geometries. The computed absorption spectrum was calculated from
the vertical transitions obtained from TD-DFT single-point calculations on
the optimized ground-state geometry. The geometry optimization from the
vertical excitation from the ground state produced a transition state
(verified by a numerical frequency calculation) that perturbed the
Caryl−Pt−Cl angle away from 180°. The computed emission spectrum
was calculated using the fully optimized, minimum-energy geometry of
the S1 excited state. The computationally derived absorption and emis-
sion spectra were simulated with an in-house Fortran program by con-
voluting61 the computed excitation energies and computed oscillator
strengths with a Gaussian line shape and a broadening of 20 nm.
In order to investigate the possibility that the observed emission
spectrum comes from the planar triplet excited state, we computed spectra
including spin−orbit coupling. PBE (the PBE exchange correction and
correlation correction62) density functional theory54 computations were
performed with the Amsterdam Density Functional program (ADF,
version 2008.01).63 ADF uses Slater-type orbital (STO) basis sets rather
than Gaussian-type orbitals (GTO) and contains a density fitting
procedure using auxiliary functions (fit functions) for the evaluation of
the Coulomb potential and molecular density. All reported ADF
calculations used gradient corrections to the LDA (local density
approximation) density functional energy during the SCF, utilized a
single-point grid accuracy factor (4.0), and used the default SCF
convergence (10−8). Relativistic effects were treated with the zeroth-order
regular approximation (ZORA)64 with the default sum of atoms potential
approximation (SAPA) potential.65 The frozen core approximation was
used. The basis set used in ADF calculations utilized the standard ADF
ZORA TZ2P basis sets for all atoms (an uncontracted triple-ζ STO basis
set with two polarization functions). ADF ZORA basis sets have been
optimized for use within ZORA relativistic calculations. Excitation
energies were computed with time-dependent density functional theory
(TD-DFT)66 with a Hamiltonian that includes spin−orbit coupling
(i.e., spin−orbit coupling is included self-consistently in the wave
function).67 All geometries used in ADF calculations were from
Gaussian 09 optimizations. A description of these results is included
in the Supporting Information. Molecular orbitals in Figure 5 were
visualized with JIMP 2.68
ACKNOWLEDGMENTS
■
We gratefully acknowledge the National Science Foundation
(NSF Grant Nos. CHE0911528, CHE0809732, CHE955550,
EPS0903787, MRI0421319, and MRI0618148), The University
of Mississippi, and The University of Memphis for financial
support and The University of Memphis High Performance
Computing Facility and Computational Research on Materials
Institute at the University of Memphis (CROMIUM) for
computing support. We thank Professor John M. Rimoldi,
Sarah Chajkowski, and Rob Smith for assistance with collecting
mass spectral data and elemental analyses, Professor Randy
Wadkins for assistance with quantum efficiency measurements,
Professor Jason Ritchie for assistance with DSC measurements,
and Professor Soumyajit Majumdar and Sindhuri Maddineni for
assistance with TGA measurements.
REFERENCES
■
(1) (a) Igau, A.; Grutzmacher, H.; Baceiredo, A.; Bertrand, G. J. Am.
Chem. Soc. 1988, 110, 6463−6466. (b) Arduengo, A. J. III; Harlow,
R. L.; Kline, M. J. Am. Chem. Soc. 1991, 113, 361−363. (c) Bourissou, D.;
Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. Rev. 2000, 100, 39−91.
(d) de Fremont, P.; Marion, N.; Nolan, S. P. Coord. Chem. Rev. 2009,
́
253, 862−892.
(2) (a) Arduengo, A. J.; Dias, H. V. R.; Harlow, R. L.; Kline, M. J. Am.
Chem. Soc. 1992, 114, 5530−5534. (b) Arduengo, A. J.; Goerlich, J. R.;
Marshall, W. J. J. Am. Chem. Soc. 1995, 117, 11027−11028.
(3) Alder, R. W.; Allen, P. R.; Murray, M.; Orpen, A. G. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1121−1123.
(4) (a) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev. 2004, 248,
2247−2273. (b) Cavallo, L.; Correa, A.; Costabile, C.; Jacobsen, H.
J. Organomet. Chem. 2005, 690, 5407−5413. (c) Scott, N. M.; Nolan,
S. P. Eur. J. Inorg. Chem. 2005, 1815−1828. (d) Lee, H. M.; Lee, C. C.;
Cheng, P. Y. Curr. Org. Chem. 2007, 11, 1491−1524. (e) Schuster, O.;
Yang, L.; Raubenheimer, H. G.; Albrecht, M. Chem. Rev. 2009, 109,
3445−3478. (f) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed.
2008, 47, 3122−3172. (g) Gil, W.; Trzeciak, A. M. Coord. Chem. Rev.
2011, 255, 473−483. (h) Jacobsen, H.; Correa, A.; Poater, A.;
Costabile, C.; Cavallo, L. Coord. Chem. Rev. 2009, 253, 687−703.
(5) (a) McReynolds, M. D.; Dougherty, J. M.; Hanson, P. R. Chem.
Rev. 2004, 104, 2239−2258. (b) Grubbs, R. H.; Miller, S. J.; Fu, G. C.
Acc. Chem. Res. 1995, 28, 446−452. (c) Monfette, S.; Fogg, D. E.
Chem. Rev. 2009, 109, 3783−3816. (d) Tallarico, J. A.; Randall, M. L.;
Snapper, M. L. Tetrahedron 1997, 53, 16511−16520. (e) Buchmeiser,
M. R. Chem. Rev. 2000, 100, 1565−1604. (f) Chatterjee, A. K.; Choi,
T.-L.; Sanders, D. P.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125,
11360−11370. (g) Connon, S. J.; Blechert, S. Angew. Chem., Int. Ed.
2003, 42, 1900−1923. (h) Lozano-Vila, A. M.; Monsaert, S.; Bajek, A.;
Verpoort, F. Chem. Rev. 2010, 110, 4865−4909.
(6) Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus, G. R. J.
Angew. Chem., Int. Ed. Engl. 1995, 34, 2371−2374.
(7) (a) Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F.
J. Am. Chem. Soc. 2004, 126, 15195−15201. (b) Huynh, H. V.; Han,
Y.; Ho, J. H. H.; Tan, G. K. Organometallics 2006, 25, 3267−3274.
(c) Marion, N.; Navarro, O.; Mei, J.; Stevens, E. D.; Scott, N. M.;
Nolan, S. P. J. Am. Chem. Soc. 2006, 128, 4101−4111.
(8) Valente, C.; Belowich, M. E.; Hadei, N.; Organ, M. G. Eur. J. Org.
Chem. 2010, 2010, 4343−4354.
(9) McGuinness, D. S.; Cavell, K. J. Organometallics 2000, 19, 741−
748.
(10) Broggi, J.; Clavier, H.; Nolan, S. P. Organometallics 2008, 27,
5525−5531.
(11) (a) Hillier, A. C.; Grasa, G. A.; Viciu, M. S.; Lee, H. M.; Yang,
C. L.; Nolan, S. P. J. Organomet. Chem. 2002, 653, 69−82.
(b) Samojłowicz, C.; Bieniek, M.; Grela, K. Chem. Rev. 2009, 109,
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures, tables, text, and CIF files giving TGA, DSC spectra,
and detailed crystallographic data for CCCBu-NHC-PtII-X com-
plexes 1 and 2, as well as Cartesian coordinates for opti-
mized geometries and detailed computed TD-DFT emission/
absorption spectra for CCCMe-NHC-PtII-Cl (3). This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: (662)915-7300. Tel: (662)915-5337. E-mail: hollis@
olemiss.edu (T.K.H.); nhammer@olemiss.edu (N.I.H.);
cewebstr@memphis.edu (C.E.W.).
́
3708−3742. (c) Díez-Gonzalez, S.; Marion, N.; Nolan, S. P. Chem.
Rev. 2009, 109, 3612−3676. (d) Nair, V.; Vellalath, S.; Babu, B. P.
Chem. Soc. Rev. 2008, 37, 2691−2698.
1670
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Organometallics
Article
(12) (a) Marion, N.; Ecarnot, E. C.; Navarro, O.; Amoroso, D.; Bell, A.;
(23) (a) Cho, J.; Hollis, T. K.; Helgert, T. R.; Valente, E. J. Chem.
Commun. 2008, 5001−5003. (b) Bauer, E. B.; Andavan, G. T. S.;
Hollis, T. K.; Rubio, R. J.; Cho, J.; Kuchenbeiser, G. R.; Helgert, T. R.;
Letko, C. S.; Tham, F. S. Org. Lett. 2008, 10, 1175−1178. (c) Rubio, R. J.;
Andavan, G. T. S.; Bauer, E. B.; Hollis, T. K.; Cho, J.; Tham, F. S.;
Donnadieu, B. J. Organomet. Chem. 2005, 690, 5353−5364. (d) Cho, J.;
Hollis, T. K.; Valente, E. J.; Trate, J. M. J. Organomet. Chem. 2011, 696,
373−377.
(24) (a) Pugh, D.; Boyle, A.; Danopoulos, A. A. Dalton Trans. 2008,
1087−1094. (b) Danopoulos, A. A.; Pugh, D.; Wright, J. A. Angew.
Chem., Int. Ed. 2008, 47, 9765−9767. (c) Loch, J. A.; Albrecht, M.;
Peris, E.; Mata, J.; Faller, J. W.; Crabtree, R. H. Organometallics 2002,
21, 700−706. (d) Poyatos, M.; Mata, J. A.; Falomir, E.; Crabtree,
R. H.; Peris, E. Organometallics 2003, 22, 1110−1114. (e) Danopoulos,
A. A.; Tsoureas, N.; Wright, J. A.; Light, M. E. Organometallics 2003,
23, 166−168. (f) McGuinness, D. S.; Gibson, V. C.; Steed, J. W.
Organometallics 2004, 23, 6288−6292. (g) Danopoulos, A. A.; Wright,
J. A.; Motherwell, W. B.; Ellwood, S. Organometallics 2004, 23, 4807−
4810. (h) Serra, D.; Cao, P.; Cabrera, J.; Padilla, R.; Rominger, F.;
Limbach, M. Organometallics 2011, 30, 1885−1895.
Nolan, S. P. J. Org. Chem. 2006, 71, 3816−3821. (b) Demir, S.;
̈
Ozdemir, I.; Çetinkaya, B.; Arslan, H.; VanDerveer, D. Polyhedron
2011, 30, 195−200.
(13) (a) Fujihara, T.; Obora, Y.; Tokunaga, M.; Sato, H.; Tsuji, Y.
Chem. Commun. 2005, 4526−4528. (b) Ohta, H.; Fujihara, T.; Tsuji,
Y. Dalton Trans. 2008, 379−385.
(14) Beletskaya, I. P.; Kashin, A. N.; Litvinov, A. E.; Tyurin, V. S.;
Valetsky, P. M.; van Koten, G. Organometallics 2006, 25, 154−158.
(15) (a) Au, V. K. M.; Wong, K. M. C.; Zhu, N. Y.; Yam, V. W. W.
J. Am. Chem. Soc. 2009, 131, 9076−9085. (b) Sajoto, T.; Djurovich,
P. I.; Tamayo, A.; Yousufuddin, M.; Bau, R.; Thompson, M. E.; Holmes,
R. J.; Forrest, S. R. Inorg. Chem. 2005, 44, 7992−8003. (c) Unger, Y.;
Zeller, A.; Ahrens, S.; Strassner, T. Chem. Commun. 2008, 3263−3265.
(d) Wu, Y.; Wu, S. X.; Li, H. B.; Geng, Y.; Su, Z. M. Dalton Trans. 2011,
40, 4480−4488. (e) Mizuhata, Y.; Sasamori, T.; Tokitoh, N. Chem. Rev.
2009, 109, 3479−3511. (f) Hindi, K. M.; Panzner, M. J.; Tessier, C. A.;
Cannon, C. L.; Youngs, W. J. Chem. Rev. 2009, 109, 3859−3884.
(g) Arnold, P. L.; Casely, I. J. Chem. Rev. 2009, 109, 3599−3611.
(h) Chi, Y.; Chou, P. T. Chem. Soc. Rev. 2010, 39, 638−655.
(16) (a) Stetter, H.; Ramsch, R. Y.; Kuhlmann, H. Synthesis 1976, 11,
̈
(25) (a) Chianese, A. R.; Mo, A.; Lampland, N. L.; Swartz, R. L.;
Bremer, P. T. Organometallics 2010, 29, 3019−3026. (b) Raynal, M.;
Pattacini, R.; Cazin, C. S. J.; Vallee, C.; Olivier-Bourbigou, H.;
Braunstein, P. Organometallics 2009, 28, 4028−4047.
733−735. (b) Henrique Teles, J.; Melder, J.-P.; Ebel, K.; Schneider, R.;
Gehrer, E.; Harder, W.; Brode, S.; Enders, D.; Breuer, K.; Raabe, G.
Helv. Chim. Acta 1996, 79, 61−83. (c) Matsumoto, T.; Yamamoto, H.;
Inoue, S. J. Am. Chem. Soc. 1984, 106, 4829−4832. (d) Matsumoto, T.;
Inoue, S. J. Chem. Soc., Chem. Commun. 1983, 171−172.
(26) (a) Moore, T. A.; Gust, D.; Mathis, P.; Mialocq, J. C.; Chachaty,
C.; Bensasson, R. V.; Land, E. J.; Doizi, D.; Liddell, P. A.; Lehman, W. R.;
Nemeth, G. A.; Moore, A. L. Nature 1984, 307, 630−632. (b) Gust, D.;
Moore, T. A.; Moore, A. L. Acc. Chem. Res. 2001, 34, 40−48.
(c) Chakraborty, S.; Wadas, T. J.; Hester, H.; Schmehl, R.; Eisenberg, R.
Inorg. Chem. 2005, 44, 6865−6878. (d) Wasielewski, M. R. Chem. Rev.
1992, 92, 435−461. (e) Hambourger, M.; Moore, G. F.; Kramer, D. M.;
Gust, D.; Moore, A. L.; Moore, T. A. Chem. Soc. Rev. 2009, 38, 25−35.
(27) (a) Archer, M. D.; Bolton, J. R. J. Phys. Chem. 1990, 94, 8028−
8036. (b) Borja, M.; Dutta, P. K. Nature 1993, 362, 43−45. (c) Bard,
A. J.; Fox, M. A. Acc. Chem. Res. 1995, 28, 141−145. (d) Jarosz, P.; Du,
P. W.; Schneider, J.; Lee, S. H.; McCamant, D.; Eisenberg, R. Inorg.
Chem. 2009, 48, 9653−9663. (e) Navarro, R. M.; Alvarez-Galvan,
M. C.; de la Mano, J. A. V.; Al-Zahrani, S. M.; Fierro, J. L. G. Energy
Environ. Sci. 2010, 3, 1865−1882. (f) Walter, M. G.; Warren, E. L.;
McKone, J. R.; Boettcher, S. W.; Mi, Q. X.; Santori, E. A.; Lewis, N. S.
Chem. Rev. 2010, 110, 6446−6473.
(28) (a) Becquerel, A.-E. C. R. Acad. Sci. Paris 1839, 9, 561.
(b) Mayo, E. I.; Kilsa, K.; Tirrell, T.; Djurovich, P. I.; Tamayo, A.;
Thompson, M. E.; Lewis, N. S.; Gray, H. B. Photochem. Photobiol. Sci.
2006, 5, 871−873. (c) Helgesen, M.; Sondergaard, R.; Krebs, F. C.
J. Mater. Chem. 2010, 20, 36−60.
(29) (a) Tang, C. W.; Vanslyke, S. A. Appl. Phys. Lett. 1987, 51, 913−
915. (b) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;
Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature 1990,
347, 539−541. (c) Bauer, R.; Finkenzeller, W. J.; Bogner, U.;
Thompson, M. E.; Yersin, H. Org. Electron. 2008, 9, 641−648.
(d) Finkenzeller, W. J.; Hofbeck, T.; Thompson, M. E.; Yersin, H. Inorg.
Chem. 2007, 46, 5076−5083. (e) Finkenzeller, W. J.; Thompson, M. E.;
Yersin, H. Chem. Phys. Lett. 2007, 444, 273−279. (f) Zhong, C. M.;
Duan, C. H.; Huang, F.; Wu, H. B.; Cao, Y. Chem. Mater. 2011, 23,
326−340.
(17) (a) Stetter, H. Angew. Chem., Int. Ed. Engl. 1976, 15, 639−647.
(b) Kerr, M. S.; Read de Alaniz, J.; Rovis, T. J. Am. Chem. Soc. 2002,
124, 10298−10299.
(18) (a) Enders, D.; Niemeier, O.; Henseler, A. Chem. Rev. 2007,
107, 5606−5655. (b) Powell, A. B.; Suzuki, Y.; Ueda, M.; Bielawski,
C. W.; Cowley, A. H. J. Am. Chem. Soc. 2011, 133, 5218−5220.
(c) Cesar, V.; Bellemin-Laponnaz, S.; Gade, L. H. Chem. Soc. Rev.
2004, 33, 619−636.
(19) (a) Crocker, C.; Errington, R. J.; McDonald, W. S.; Odell, K. J.;
Shaw, B. L.; Goodfellow, R. J. J. Chem. Soc., Chem. Commun. 1979,
498−499. (b) Morales-Morales, D.; Jensen, C. M.; The Chemistry of
Pincer Compounds; Elsevier: New York, 2007. (c) Jones, N. D.; Cavell,
R. G. J. Organomet. Chem. 2005, 690, 5485−5496. (d) Gagliardo, M.;
Snelders, D. J. M.; Chase, P. A.; Klein Gebbink, R. J. M.; van Klink,
G. P. M; van Koten, G. Angew. Chem., Int. Ed. 2007, 46, 8558−8573.
(e) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759−
1792.
(20) (a) Chen, J. C. C.; Lin, I. J. B. Dalton Trans. 2000, 839−840.
(b) Tulloch, A. A. D.; Danopoulos, A. A.; Tizzard, G. J.; Coles, S. J.;
Hursthouse, M. B.; Hay-Motherwell, R. S.; Motherwell, W. B. Chem.
Commun. 2001, 1270−1271. (c) Peris, E.; Loch, J. A.; Mata, J.;
Crabtree, R. H. Chem. Commun. 2001, 201−202. (d) Peris, E.;
Crabtree, R. H. Coord. Chem. Rev. 2004, 248, 2239−2246. (e) Peris, E.;
Crabtree Robert, H. In The Chemistry of Pincer Compounds; Morales-
Morales, D., Jensen, C. M., Eds.; Elsevier: New York, 2007, pp 107−
124. (f) Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009, 109,
3677−3707. (g) Pugh, D.; Danopoulos, A. A. Coord. Chem. Rev. 2007,
251, 610−641. (h) Corberan, R.; Mas-Marza, E.; Peris, E. Eur. J. Inorg.
Chem. 2009, 1700−1716. (i) Melaimi, M.; Soleilhavoup, M.; Bertrand,
G. Angew. Chem., Int. Ed. 2010, 49, 8810−8849.
(21) (a) Hahn, F. E.; Jahnke, M. C.; Pape, T. Organometallics 2007,
26, 150−154. (b) Danopoulos, A. A.; Tulloch, A. A. D.; Winston, S.;
Eastham, G.; Hursthouse, M. B. Dalton Trans. 2003, 1009−1015.
(c) Grundemann, S.; Albrecht, M.; Loch, J. A.; Faller, J. W.; Crabtree,
R. H. Organometallics 2001, 20, 5485−5488. (d) Schultz, K. M.;
Goldberg, K. I.; Gusev, D. G.; Heinekey, D. M. Organometallics 2011,
30, 1429−1437. (e) Lv, K.; Cui, D. Organometallics 2010, 29, 2987−
2993.
(22) (a) Hahn, F. E.; Jahnke, M. C.; Gomez-Benitez, V.; Morales-
Morales, D.; Pape, T. Organometallics 2005, 24, 6458−6463.
(b) Nielsen, D. J.; Cavell, K. J.; Skelton, B. W.; White, A. H. Inorg.
Chim. Acta 2002, 327, 116−125.
(30) (a) Moudam, O.; Rowan, B. C.; Alamiry, M.; Richardson, P.;
Richards, B. S.; Jones, A. C.; Robertson, N. Chem. Commun. 2009,
6649−6651. (b) Tam, A. Y.-Y.; Wong, K. M.-C.; Yam, V. W.-W. J. Am.
Chem. Soc. 2009, 131, 6253−6260.
(31) Lee, C. S.; Sabiah, S.; Wang, J. C.; Hwang, W. S.; Lin, I. J. B.
Organometallics 2010, 29, 286−289.
(32) Vargas, V. C.; Rubio, R. J.; Hollis, T. K.; Salcido, M. E. Org. Lett.
2003, 5, 4847−4849.
(33) Spencer, L. P.; Winston, S.; Fryzuk, M. D. Organometallics 2004,
23, 3372−3374.
(34) (a) Ahrens, S.; Strassner, T. Inorg. Chim. Acta 2006, 359, 4789−
4796. (b) Berthon-Gelloz, G.; Buisine, O.; Briere, J. F.; Michaud, G.;
1671
dx.doi.org/10.1021/om200687w | Organometallics 2012, 31, 1664−1672

Organometallics
Article
Sterin, S.; Mignani, G.; Tinant, B.; Declercq, J. P.; Chapon, D.;
Marko, I. E. J. Organomet. Chem. 2005, 690, 6156−6168.
(35) Farrugia, L. J. Appl. Crystallogr. 1997, 30, 565.
(60) Martin, R. L. J. Chem. Phys. 2003, 118, 4775−4777.
(61) Press, W. H. Numerical Recipes: The Art of Scientific Computing;
Cambridge University Press: London, 1992.
(36) (a) Vanderploeg, A.; Vankoten, G.; Vrieze, K.; Spek, A. L. Inorg.
Chem. 1982, 21, 2014−2026. (b) Fantasia, S.; Petersen, J. L.; Jacobsen,
H.; Cavallo, L.; Nolan, S. P. Organometallics 2007, 26, 5880−5889.
(37) Yersin, H.; Donges, D. In Transition Metal and Rare Earth
Compounds; Yersin, H., Ed.; Springer: Berlin/Heidelberg, Germany,
2001; Vol. 214, pp 81−186.
(62) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997,
78, 1396−1396. (b) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev.
Lett. 1996, 77, 3865−3868.
(63) (a) Guerra, C. F.; Snijders, J. G.; te Velde, G.; Baerends, E. J.
Theor. Chem. Acc. 1998, 99, 391−403. (b) Bickelhaupt, F. M.; Velde,
G. T.; Baerends, E. J.; Guerra, C. F.; Van Gisbergen, S. J. A.; Snijders,
J. G.; Ziegler, T. J. Comput. Chem. 2001, 22, 931−967. (c) Baerends, E. J.;
́
Autschbach, J.; Bashford, D.; Berces, A.; Bickelhaupt, F. M.; Bo, C.;
Boerrigter, P. M.; Cavallo, L.; Chong, D. P.; Deng, L.; Dickson, R. M.; Ellis,
D. E.; van Faassen, M.; Fan, L.; Fischer, T. H.; Fonseca Guerra, C.; Ghysels,
(38) Drago, R. S. Physical Methods in Chemistry; Saunders:
Philadelphia, PA, 1977.
(39) (a) Zhang, L. Y.; Li, B.; Shi, L. F.; Li, W. L. Opt. Mater. 2009, 31,
905−911. (b) Evans, R. C.; Douglas, P.; Winscom, C. J. Coord. Chem.
Rev. 2006, 250, 2093−2126. (c) Unger, Y.; Meyer, D.; Strassner, T.
Dalton Trans. 2010, 39, 4295−4301.
(40) Unger, Y.; Zeller, A.; Taige, M. A.; Strassner, T. Dalton Trans.
2009, 4786−4794.
A.; Giammona, A.; van Gisbergen, S. J. A.; Gotz, A. W.; Groeneveld, J. A.;
̈
Gritsenko, O. V.; Gruning, M.; Gusarov, S.; Harris, F. E.; van den Hoek, P.;
̈
Jacob, C. R.; Jacobsen, H.; Jensen, L.; Kaminski, J. W.; van Kessel, G.;
Kootstra, F.; Kovalenko, A.; Krykunov, M. V.; van Lenthe, E.; McCormack,
D. A.; Michalak, A.; Mitoraj, M.; Neugebauer, J.; Nicu, V. P.; Noodleman,
L.; Osinga, V. P.; Patchkovskii, S.; Philipsen, P. H. T.; Post, D.; Pye, C. C.;
Ravenek, W.; Rodríguez, J. I.; Ros, P.; Schipper, P. R. T.; Schreckenbach,
(41) (a) Walser, A. D.; Priestley, R.; Dorsinville, R. Synth. Met. 1999,
102, 1552−1553. (b) Martin, R. L.; Kress, J. D.; Campbell, I. H.;
Smith, D. L. Phys. Rev. B 2000, 61, 15804. (c) Colle, M.; Garditz, C.
Appl. Phys. Lett. 2004, 84, 3160−3162.
̀
G.; Seldenthuis, J. S.; Seth, M.; Snijders, J. G.; Sola, M.; Swart, M.;
Swerhone, D.; te Velde, G.; Vernooijs, P.; Versluis, L.; Visscher, L.; Visser,
O.; Wang, F.; Wesolowski, T. A.; van Wezenbeek, E. M.; Wiesenekker, G.;
Wolff, S. K.; Woo, T. K.; Yakovlev, A. L. ADF2008.01; SCM, Theoretical
Chemistry, Vrije Universiteit, Amsterdam, The Netherlands.
(42) Seo, J. H.; Kim, I. J.; Kim, Y. K.; Kim, Y. S. Thin Solid Films
2008, 516, 3614−3617.
(43) (a) Du, Y.; Fu, Y.; Shi, Y.; Lu, X.; Lu, C.; Su, Z. J. Solid State
̈
̈
Chem. 2009, 182, 1430−1437. (b) Kai, Y.; Morita, M.; Yasuoka, N.;
Kasai, N. Bull. Chem. Soc. Jpn. 1985, 58, 1631−1635.
(44) (a) Tao, X. T.; Suzuki, H.; Wada, T.; Miyata, S.; Sasabe, H.
J. Am. Chem. Soc. 1999, 121, 9447−9448. (b) Tao, X. T.; Suzuki, H.;
Wada, T.; Sasabe, H.; Miyata, S. Appl. Phys. Lett. 1999, 75, 1655−1657.
(c) Vinyard, D. J.; Richter, M. M. Dalton Trans. 2006, 4461−4464.
(45) Shi, L. L.; Li, T.; Zhao, S. S.; Li, H.; Su, Z. M. Theor. Chem. Acc.
2009, 124, 29−36.
(64) (a) Chang, C.; Pelissier, M.; Durand, P. Phys. Scr. 1986, 34,
394−404. (b) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem.
Phys. 1993, 99, 4597−4610. (c) van Lenthe, E.; Baerends, E. J.;
Snijders, J. G. J. Chem. Phys. 1994, 101, 9783−9792. (d) van Lenthe,
E.; van Leeuwen, R.; Baerends, E. J.; Snijders, J. G. Int. J. Quantum
Chem. 1996, 57, 281−293. (e) van Lenthe, E.; Ehlers, A.; Baerends,
E. J. J. Chem. Phys. 1999, 110, 8943−8953. (f) van Lenthe, E.; Snijders,
J. G.; Baerends, E. J. J. Chem. Phys. 1996, 105, 6505−6516.
(46) Halls, M. D.; Schlegel, H. B. Chem. Mater. 2001, 13, 2632−
2640.
(47) Jakubikova, E.; Chen, W.; Dattelbaum, D. M.; Rein, F. N.;
Rocha, R. C.; Martin, R. L.; Batista, E. R. Inorg. Chem. 2009, 48,
10720−10725.
(48) The bent T1 (triplet-ES Cs) species and the planar T1 (triplet-ES
C2v) species are very close in energy (0.8 kcal mol−1) but dissimilar in
geometry. The bent S1 (singlet-ES Cs) species and bent T1 species are
quite similar in geometry (rmsd = 0.134 Å for all atoms and 0.0457 Å
for all atoms other than chlorine) but are separated by 9.5 kcal mol−1.
The TD-DFT PBE-ZORA-SO computed spectra (see the Supporting
Information for further computational details) for both the bent S1 and
bent T1 match reasonably with the experimental observations in Figure
2a (see Figures S12 and S13 in the Supporting Information) and are in
qualitative agreement with the B3LYP computed spectra included in
Figures 4 and 6.
(49) We speculate that there is orbital crossing occurring of the
excited state orbitals, but we cannot prove that with the results from
TD-DFT calculations.
(50) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518−1520.
(51) Frisch, M. J. et al. Gaussian 09, Revision A.02; Gaussian, Inc.,
Wallingford, CT, 2009.
(65) Philipsen, P. H. T.; van Lenthe, E.; Snijders, J. G.; Baerends, E. J.
Phys. Rev. B 1997, 56, 13556−13562.
(66) (a) van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J.
Comput. Phys. Commun. 1999, 118, 119−138. (b) van Gisbergen, S. J. A.;
Kootstra, F.; Schipper, P. R. T.; Gritsenko, O. V.; Snijders, J. G.;
Baerends, E. J. Phys. Rev. A 1998, 57, 2556−2571. (c) Bauernschmitt, R.;
Ahlrichs, R. Chem. Phys. Lett. 1996, 256, 454−464. (d) Jamorski, C.;
Casida, M. E.; Salahub, D. R. J. Chem. Phys. 1996, 104, 5134−5147.
(e) van Gisbergen, S. J. A.; Groeneveld, J. A.; Rosa, A.; Snijders, J. G.;
Baerends, E. J. J. Phys. Chem. A 1999, 103, 6835−6844. (f) van
Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J. J. Chem. Phys. 1995,
103, 9347−9354. (g) Rosa, A.; Baerends, E. J.; van Gisbergen, S. J. A.;
van Lenthe, E.; Groeneveld, J. A.; Snijders, J. G. J. Am. Chem. Soc. 1999,
121, 10356−10365. (h) Casida, M. E.; Jamorski, C.; Casida, K. C.;
Salahub, D. R. J. Chem. Phys. 1998, 108, 4439−4449.
(67) Wang, F.; Ziegler, T.; van Lenthe, E.; van Gisbergen, S.;
Baerends, E. J. J. Chem. Phys. 2005, 122.
(68) Manson, J.; Webster, C. E.; Per
www.chem.tamu.edu/jimp2/index.html.
́
ez, L. M.; Hall, M. B.; http://
(52) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652.
(53) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(54) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: New York, 1989.
(55) (a) Furche, F.; Ahlrichs, R. J. Chem. Phys. 2002, 117, 7433−
7447. (b) Furche, F.; Ahlrichs, R. J. Chem. Phys. 2004, 121, 12772−
12773.
(56) Marques, M. A. L.; Gross, E. K. U. Annu. Rev. Phys. Chem. 2004,
55, 427−455.
(57) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299−310.
(58) Couty, M.; Hall, M. B. J. Comput. Chem. 1996, 17, 1359−1370.
(59) (a) Hehre, W. J.; Ditchfie., R; Pople, J. A. J. Chem. Phys. 1972,
56, 2257−2261. (b) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta
1973, 28, 213−222.
1672
dx.doi.org/10.1021/om200687w | Organometallics 2012, 31, 1664−1672