Syntheses, structures, and electronic and optical properties of platinum(II) complexes of 1,3-bis(imino)benzene-derived pincer ligands

Article abstract of DOI:10.1021/om3003152

Six new Pt^II complexes of 5-substituted 1,3-bis(N-methylimino) benzene (bIBH)-derived ligands have been synthesized by direct reactions with K₂Pt^IICl₄ in glacial acetic acid. The ethenylene groups in the two sty

Full text of DOI:10.1021/om3003152

Article
pubs.acs.org/Organometallics
Syntheses, Structures, and Electronic and Optical Properties of
Platinum(II) Complexes of 1,3-Bis(imino)benzene-Derived Pincer
Ligands
Octavia A. Blackburn, Benjamin J. Coe,* Madeleine Helliwell, and James Raftery
School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
S
* Supporting Information
ABSTRACT: Six new PtII complexes of 5-substituted 1,3-bis(N-methylimino)benzene (bIBH)-derived ligands have been
synthesized by direct reactions with K2PtIICl4 in glacial acetic acid. The ethenylene groups in the two styryl-substituted
1
complexes undergo E−Z photoisomerization, as revealed by H NMR spectroscopy. The UV−vis spectra of the styryl-/aryl-
substituted complexes show intense high-energy bands due to ligand-based π → π* transitions and a number of weaker bands at
lower energies in the 300−500 nm region. Time-dependent density functional theory (TD-DFT) calculations indicate that the
latter absorptions have mixed intraligand π → π* and Pt(d) → π* metal-to-ligand charge-transfer (MLCT) character. Four of the
new complexes give vibronically structured emission profiles in fluid solution at room temperature. The luminescence quantum
yields and lifetimes in nondegassed dichloromethane are in the ranges 0.1−0.2% and 159−170 ns, respectively. In contrast, the
styryl-substituted complexes are nonemissive, due to excited-state quenching by E → Z isomerization. DFT indicates that the
emissive triplet state has mixed ligand-to-ligand charge-transfer and MLCT character, with a geometry distorted with respect to
the symmetric ground state. Single-crystal X-ray structures have been determined for two of the complexes, showing N−Pt−N
angles of ca. 159°. The complex of an unsubstituted bIB− ligand is deep red and forms columns with short Pt···Pt distances of ca.
3.55 Å, indicating weak intermetallic interactions.
INTRODUCTION
■
Among complexes of the heavy d-block metals, square-planar
platinum species have been investigated extensively, often due
to their luminescent behavior.1 Cyclometalated PtII complexes
are especially efficient light emitters, because their strong ligand
field destabilizes d−d excited states that otherwise can lead to
nonradiative deactivation.2 Complexes of symmetrical, NCN
Figure 1. General structures of Pt(bAB)X, Pt(bIB)X, and Pt(bPyB)X
complexes (R = alkyl/aryl; X = halide, etc.).
tridentate “pincer” cyclometalating ligands such as the
monoanions derived from 1,3-bis(amino)benzene (bABH),
1,3-bis(imino)benzene (bIBH), and 1,3-bis(2-pyridyl)benzene
allows control of the low-lying excited states.4 When X = a
(bPyBH) (Figure 1) offer great structural versatility, allowing
halide or pyridine and Z = 1,2-bis(4-pyridyl)ethane, emission
emanates from spin-forbidden d−d states. For X = 4-
phenylpyridine and Z = 4,4′-bipyridyl or (E)-1,2-bis(4-
pyridyl)ethylene, the emissive state has ligand-centered (LC)
3(π→π*) character, whereas Z = pyrazine gives intense
luminescence from a 3MLCT state. Pt(bPyB)Cl and its
tuning of electronic and optical properties.
Pt(bAB)X complexes have been studied extensively by van
Koten and co-workers, including some 4-styryl derivatives
which are luminescent in fluid solutions at room temperature
when substituted with a terminal strong electron donor or
acceptor.3 Unfunctionalized [Pt(bPipB)X]n+ (bPipBH = 1,3-
bis(piperidylmethyl)benzene; n = 0, 1) complexes and
[{Pt(bPipB)}2(μ-Z)]2+ bimetallics, explored by Connick and
colleagues, emit only in rigid media, although varying X/Z
Received: April 18, 2012
Published: July 17, 2012
© 2012 American Chemical Society
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Synthesis of 5-Bromoisophthalaldehyde (1). Isophthalalde-
hyde (2.00 g, 14.9 mmol) was dissolved in concentrated sulfuric acid
(10 mL) and heated to 60 °C. N-Bromosuccinimide (3.18 g, 17.9
mmol) was added portionwise over 15 min, and the solution was
heated at 60 °C for 3 h. The solution was poured onto ice, and the
white precipitate was filtered off. The solid was washed thoroughly
with water and hexane and then dried. Further purification was
effected by multiple recrystallizations from hexane/ethyl acetate. Yield:
0.80 g (25%). δH (400 MHz, CDCl3): 10.06 (2H, s, 2CHO), 8.30 (1H,
t, J = 1.4, C6H3), 8.26 (2H, d, J = 1.4, C6H3). ν(CO): 1690 st cm−1.
Anal. Calcd for C8H5BrO2: C, 45.1; H, 2.4. Found: C, 45.4; H, 2.3. m/
z (−ES): 213 ([M − H]−).
derivatives, studied by Williams and co-workers, emit especially
3
efficiently from states of mixed LC/3MLCT character in fluid
solutions, where the LUMOs are based on the π-accepting
pyridyl rings.2b,5
Previous studies with Pt(bIB)X complexes have focused
largely on catalytic properties,6 while their electronic/optical
properties have received little attention. Related species with
N-, P-, or S-based, typically saturated neutral electron donors
have provided a wealth of functional materials.7 A recent report
t
describes the incorporation of [Pt(bIB)CNR]+ (R = Bu, 2,6-
Me2C6H3) pincer units into a thiophene-based polymer and
changes in the ligand-to-metal charge-transfer (LMCT)
absorption behavior as a function of redox state.8 Cyclo-
platinated complexes of benzophenoneimine, a bidentate
relative of bIBH, are known to be luminescent in solution at
room temperature.9 Also, Kanbara and co-workers have
investigated the luminescence of PtII complexes of SCS-pincer
ligands analogous to bIBH, based on 1,3-bis(thiocarbamoyl)-
benzene, some of which show room-temperature solution
emission.10
The minor structural change of moving from saturated to
unsaturated nitrogen donors in replacing bAB− with bIB− lends
the pincer ligand some of the π-acceptor character of bPyB−.
We explore herein the effects of the imine functionalities on the
electronic and optical properties of Pt(bIB)Cl complexes in
relation to their analogues containing bAB−, bPyB−, and similar
ligands. The long-term aim of this work is to produce new PtII
chromophores showing dichroic luminescence. While purely
organic species displaying such behavior are relatively well-
known (often when dissolved in a liquid crystal medium),11
only a few related studies with metal complexes have been
reported.12 Notably, Wang et al. reported very recently a liquid
crystalline, dinuclear PtII complex that shows dichroic emission
from aligned films.12e In Pt(bIB) complexes, combining small R
groups with extended 4-substituents enhances shape aniso-
tropy, potentially affording dichroic properties. However,
because preliminary studies with our new complexes give no
evidence for dichroism, further discussion of this particular
theme is confined to the Supporting Information.
Synthesis of 1,3-Bis(N-methylimino)benzene (2H). Isophtha-
laldehyde (200 mg, 1.49 mmol) and methylamine (33 wt % in ethanol,
421 mg, 4.52 mmol) were combined in ethanol (10 mL) and heated
under reflux for 90 min. The solvent was evaporated to leave a pale
yellow oil (232 mg). The 1H NMR spectrum indicated negligible
monoaldehyde impurity, and this material was used immediately
without purification. δH (400 MHz, CDCl3): 8.29 (2H, q, J = 1.6,
3
4
CHN), 7.97 (1H, t, J = 1.6, C6H4), 7.77 (2H, dd, J = 7.7, J = 1.7,
C6H4), 7.44 (1H, t, J = 7.6, C6H4), 3.52 (6H, d, J = 1.7, 2Me). m/z
(+ES): 161 ([M + H]+), 183 ([M + Na]+).
Synthesis of 1-Bromo-3,5-bis(N-methylimino)benzene (3H).
This compound was prepared in a manner identical with that for 2H,
by using 1 (100 mg, 0.469 mmol) and methylamine (33 wt % in
ethanol, 133 mg, 1.43 mmol) to give a pale yellow oil (112 mg). The
1H NMR spectrum indicated ca. 1% of monoaldehyde impurity, and
this material was used immediately without purification. δH (400 MHz,
CDCl3): 8.22 (2H, q, J = 1.7, CHN), 7.92 (2H, d, J = 1.4, C6H3), 7.86
(1H, t, J = 1.4, C6H3), 3.52 (6H, d, J = 1.7, 2Me). m/z (+ES): 239 ([M
+ H]+), 261 ([M + Na]+).
Synthesis of 5-Styrylisophthalaldehyde (4). 1 (500 mg, 2.35
mmol), K3PO4 (698 mg, 3.29 mmol), and PdII(OAc)2 (5 mg, 0.022
mmol) were combined in an oven-dried Schlenk flask under a flow of
argon. Styrene (293 mg, 2.81 mmol) was dissolved in anhydrous DMF
(4 mL), and the solution was degassed with argon bubbling. The
solution was added to the solids, and the mixture was heated at 140 °C
for 24 h and then cooled to room temperature. The reaction mixture
was poured into water (25 mL) and extracted with ethyl acetate (3 ×
20 mL), and the combined organic extracts were washed with brine,
dried over MgSO4, and evaporated to give a yellow oil. This oil was
purified by silica gel column chromatography, with hexane/ethyl
acetate (96/4) as eluent, followed by reprecipitation from a
dichloromethane solution with hexane to give a pale yellow solid.
Yield: 124 mg (22%). δH (400 MHz, CDCl3): 10.14 (2H, s, CHO),
8.26 (2H, d, J = 1.5, C6H3), 8.24 (1H, t, J = 1.5, C6H3), 7.57−7.54
(2H, Ph), 7.43−7.38 (2H, Ph), 7.35−7.29 (2H, Ph + CH), 7.19 (1H,
d, J = 16.4, CH). ν(CO): 1686 st cm−1. Anal. Calcd for
C16H12O2·0.1H2O: C, 80.7; H, 5.2. Found: C, 80.7; H, 5.1. m/z
(+MALDI): 236 ([M]+). The retention of 0.1 equiv of H2O is
supported by thermogravimetric analyses.
Synthesis of 5-(4-Methoxystyryl)isophthalaldehyde (5). This
compound was prepared and purified in a manner identical with that
for 4, by using 1 (500 mg, 2.35 mmol), 4-methoxystyrene (378 mg,
2.82 mmol), K3PO4 (698 mg, 3.29 mmol), PdII(OAc)2 (5 mg, 0.022
mmol), and anhydrous DMF (4 mL) to give a pale yellow solid. Yield:
106 mg (17%). δH (400 MHz, CDCl3): 10.13 (2H, s, CHO), 8.23
(2H, d, J = 1.4, C6H3), 8.21 (1H, t, J = 1.4, C6H3), 7.50 (2H, d, J = 8.7,
C6H4), 7.27 (1H, d, J = 16.3, CH), 7.06 (1H, d, J = 16.3, CH), 6.94
(2H, d, J = 8.8, C6H4), 3.85 (3H, s, Me). ν(CO): 1686 st cm−1.
Anal. Calcd for C17H14O3: C, 76.7; H, 5.3. Found: C, 76.4; H, 5.1. m/z
(+MALDI): 266 ([M]+).
Synthesis of 5-Styryl-1,3-bis(N-methylimino)benzene (6H).
This compound was prepared in a manner identical with that for 2H,
by using 4 (45 mg, 0.189 mmol) and methylamine (33 wt % in
ethanol, 54 mg, 0.580 mmol) to give a pale yellow oil (50 mg). The 1H
NMR spectrum indicated ca. 3% of monoaldehyde impurity, and this
material was used immediately without purification. δH (500 MHz,
CDCl3): 8.33 (2H, q, J = 1.6, CHN), 7.96 (2H, d, J = 1.5, C6H3), 7.83
(1H, t, J = 1.4, C6H3), 7.52−7.50 (2H, Ph), 7.38−7.35 (2H, Ph),
EXPERIMENTAL SECTION
■
Materials and Procedures. The compound 4-(4-
pentylcyclohexyl)benzeneboronic acid was synthesized by a published
method.13 All other chemicals were used as supplied by Sigma Aldrich
or Alfa Aesar. Products were dried at room temperature overnight in a
vacuum desiccator (CaSO4) or by direct attachment to a high-vacuum
line for several hours prior to characterization.
General Physical Measurements. 1H NMR spectra were
recorded on Bruker UltraShield 500 or AV 400 spectrometers, and
all shifts are quoted with respect to TMS. The fine splitting of phenyl
ring AA′BB′ patterns is ignored, and the signals are reported as simple
“doublets”, with “J values” (in Hz) referring to the two most intense
peaks. Electrospray mass spectrometry was performed on a Micromass
Platform II instrument, and MALDI mass spectra were recorded on a
Shimadzu Axima Confidence instrument with dichloromethane as the
solvent. In cases where clusters of peaks are observed due to the
presence of various isotopes, the most intense peak is always quoted.
Elemental and thermogravimetric analyses were performed by the
Microanalytical Laboratory, University of Manchester. UV−vis spectra
were obtained by using a Shimadzu UV-2401 PC spectrometer, and IR
spectra were recorded with pure solids on a Varian Bio-Rad Excalibur
series spectrometer. Abbreviations: Cy = cyclohexyl; st = strong; s =
singlet; d = doublet; dd = doublet of doublets; t = triplet; q = quartet;
m = multiplet.
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7.29−7.24 (2H, Ph + CH), 7.14 (1H, d, J = 16.4, CH), 3.56 (6H, d, J
= 1.6, 2Me). m/z (ES+): 263 ([M + H]+), 285 ([M + Na]+).
Synthesis of 5-(4-Methoxystyryl)-1,3-bis(N-methylimino)-
benzene (7H). This compound was prepared in a manner identical
with that for 2H, by using 5 (22 mg, 0.083 mmol) and methylamine
(33 wt % in ethanol, 23 mg, 0.248 mmol) to give an off-white solid (20
mg). The 1H NMR spectrum indicated a negligible amount of
monoaldehyde impurity, and this material was used immediately
without purification. δH (400 MHz, CDCl3): 8.33 (2H, q, J = 1.6,
2CHN), 7.93 (2H, d, J = 1.6, C6H3), 7.80 (1H, t, J = 1.6, C6H3), 7.45
(2H, d, J = 8.8, C6H4), 7.21 (1H, d, J = 16.4, CH), 7.00 (1H, d, J =
16.3, CH), 6.91 (2H, d, J = 8.8, C6H4), 3.83 (3H, s, OMe), 3.55 (6H,
d, J = 1.6, 2NMe). m/z (+ES): 293 ([M + H]+), 315 ([M + Na]+).
Synthesis of 5-(4-Methoxyphenyl)isophthalaldehyde (8). 1
(400 mg, 1.88 mmol), 4-methoxyphenylboronic acid (314 mg, 2.07
mmol), PdII(OAc)2 (42 mg, 0.187 mmol), and Na2CO3 (498 mg, 4.70
mmol) were combined in a Schlenk flask under argon. Dimethoxy-
ethane (5 mL), THF (5 mL), and water (5 mL) were combined and
degassed with argon bubbling. The solvents were added to the solid
reagents, and the mixture was heated under reflux for 24 h. The cooled
solution was extracted with dichloromethane (2 × 30 mL), and the
combined organic extracts were washed with water and dried over
MgSO4. Purification was effected by silica gel column chromatography,
with hexane/ethyl acetate (95/5) as eluent, followed by reprecipitation
from a dichloromethane solution with hexane to give a white solid.
Yield: 165 mg (37%). δH (400 MHz, CDCl3): 10.15 (2H, s, CHO),
8.31 (2H, d, J = 1.5, C6H3), 8.28 (1H, t, J = 1.5, C6H3), 7.61 (2H, d, J
= 8.9, C6H4), 7.03 (2H, d, J = 8.9, C6H4), 3.87 (3H, s, Me). ν(CO):
1697 st cm−1. Anal. Calcd for C15H12O3: C, 75.0; H, 5.0. Found: C,
74.8; H, 4.9. m/z (+MALDI): 240 ([M]+).
Synthesis of 5-[4-(4-n-Pentylcyclohexyl)phenyl]-
isophthalaldehyde (9). This compound was prepared in a manner
identical with that for 8, by using 1 (353 mg, 1.66 mmol), 4-(4-n-
pentylcyclohexyl)benzeneboronic acid (500 mg, 1.82 mmol),
PdII(OAc)2 (37 mg, 0.165 mmol), and Na2CO3 (439 mg, 4.14
mmol). Purification was effected by silica gel column chromatography,
with hexane/ethyl acetate (98/2) as eluent, followed by reprecipitation
from a dichloromethane solution with hexane to give a white solid.
Yield: 215 mg (36%). δH (400 MHz, CDCl3): 10.17 (2H, s, 2CHO),
8.35 (2H, d, J = 1.5, C6H3), 8.31 (1H, t, J = 1.5, C6H3), 7.61 (2H, d, J
= 8.4, C6H4), 7.36 (2H, d, J = 8.4, C6H4), 2.54 (1H, tt, J = 12.0, J = 3.2,
CHCy), 1.97−1.86 (4H, m, 2CH2Cy), 1.56−1.43 (2H, m, CH2Cy),
1.38−1.20 (9H, C4H8 + CHCy), 1.14−1.02 (2H, m, CH2Cy), 0.90 (3H,
t, J = 7.2, Me). ν(CO): 1690 st cm−1. Anal. Calcd for C25H30O2: C,
82.8; H, 8.3. Found: C, 82.7; H, 8.4. m/z (+MALDI): 362 ([M]+).
Synthesis of 5-(4-Methoxyphenyl)-1,3-bis(N-methylimino)-
benzene (10H). This compound was prepared in a manner identical
with that for 2H, by using 8 (61 mg, 0.254 mmol) and methylamine
(33 wt % in ethanol, 72 mg, 0.762 mmol) to give a white solid (67
mg). The 1H NMR spectrum indicated a negligible amount of
monoaldehyde impurity, and this material was used immediately
without purification. δH (400 MHz, CDCl3): 8.36 (2H, q, J = 1.6,
2CHN), 8.00 (2H, d, J = 1.5, C6H3), 7.89 (1H, t, J = 1.5, C6H3), 7.61
(2H, d, J = 8.9, C6H4), 6.97 (2H, d, J = 8.9, C6H4), 3.85 (3H, s, OMe),
3.55 (6H, d, J = 1.6, 2Me). m/z (+ES): 267 ([M + H]+), 289 ([M +
Na]+).
Synthesis of [2,6-Bis(N-methylimino)phenyl]chloroplatinum
(PtCl(2), 12). 2H (100 mg, ca. 0.62 mmol) and K2PtIICl4 (236 mg,
0.569 mmol) were combined in glacial acetic acid (5 mL). The mixture
was degassed by argon bubbling and heated under reflux, under an
atmosphere of argon, for 48 h. On cooling, the precipitate was filtered
off and washed with dichloromethane. The reaction filtrate and
washings were evaporated and combined. The crude material was
purified by silica gel column chromatography, with dichloromethane/
ethyl acetate (95/5) as eluent, to give a red solid. Yield: 53 mg (24%).
δH (400 MHz, CDCl3): 8.27 (2H, (66%) q, JHH = 1.3, (34%) d, 3JPtH
=
143.3, CHN), 7.40 (2H, (66%) d, JHH = 7.7, (34%) dd, JHH = 7.8, 4JPtH
= 7.8, C6H3), 7.10 (1H, (66%) t, JHH = 7.7, (34%) dt, JHH = 7.5, 5JPtH
=
=
2.8, C6H3), 3.89 (6H, (66%) d, JHH = 1.4, (34%) dd, JHH = 1.4, 3JPtH
32.6, 2Me). Anal. Calcd for C10H11ClN2Pt: C, 30.8; H, 2.8; N, 7.2.
Found: C, 31.0; H, 2.4; N, 7.1. m/z (+MALDI): 353 ([M − Cl]+), 390
([M]+), 742 ([M2 − Cl]+). Diffraction-quality crystals were grown by
slow evaporation of a dichloromethane solution.
Synthesis of [4-Bromo-2,6-bis(N-methylimino)phenyl]-
chloroplatinum (PtCl(3), 13). This compound was prepared and
purified in a manner identical with that for 12, by using 3H (112 mg,
ca. 0.47 mmol) and K2PtIICl4 (177 mg, 0.426 mmol) in glacial acetic
acid (6 mL) to give an orange solid. Yield: 60 mg (30%). δH (400
3
MHz, CDCl3): 8.24 (2H, (66%) q, JHH = 1.5, (34%) d, JPtH = 143.7,
4
CHN), 7.53 (2H, (66%) s, (34%) d, JPtH = 7.4, C6H2), 3.89 (6H,
3
(66%) d, JHH = 1.4, (34%) dd, JHH = 1.4, JPtH = 31.5, 2Me). Anal.
Calcd for C10H10BrClN2Pt: C, 25.6; H, 2.2; N, 6.0. Found: C, 25.9; H,
1.8; N, 5.8. m/z (+MALDI): 468 ([M]+), 901 ([M2 − Cl]+).
Synthesis of [4-Styryl-2,6-bis(N-methylimino)phenyl]-
chloroplatinum (PtCl(6), 14). This compound was prepared and
purified in a manner similar to that for 12, by using 6H (50 mg, ca.
0.19 mmol) and K2PtIICl4 (72 mg, 0.173 mmol) in glacial acetic acid
(4 mL). The column was eluted with dichloromethane/ethyl acetate
(95/5) and a red/orange solid obtained. Yield: 58 mg (68%). The
reaction mixture and column were kept in the dark to obtain the pure
E isomer; the Z isomer was generated later by exposure of the NMR
solution to ambient light. δH3(400 MHz, CDCl3): E isomer, 8.31 (2H,
(66%) q, J = 1.4, (34%) d, JPtH = 143.3, CHN), 7.58 (2H, (66%) s,
(34%) d, 4JPtH = 7.5, C6H2), 7.53−7.48 (2H, Ph), 7.39−7.34 (2H, Ph),
7.31−7.27 (1H, Ph), 7.09 (1H, d, J = 16.3, CH), 7.03 (1H, d, J = 16.2,
3
CH), 3.91 (6H, (66%) d, J = 1.4, (34%) d, JPtH = 31.5, 2Me); Z
3
isomer, 8.16 (2H, (66%) q, J = 1.3, (34%) d, JPtH = 144.2, CHN),
4
7.30 (2H, (66%) s, (34%) d, JPtH = 7.5, C6H2), 7.25−7.19 (5H, Ph),
6.63 (1H, d, J = 12.1, CH), 6.48 (1H, d, J = 12.1, CH), 3.86 (6H,
3
(66%) d, J = 1.4, (34%) d, JPtH = 31.4, 2Me). Anal. Calcd for
C18H17ClN2Pt: C, 44.0; H, 3.5; N, 5.7. Found: C, 44.0; H, 3.4; N, 5.7.
m/z (+MALDI): 456 ([M − Cl]+). Diffraction-quality crystals were
grown by layering of hexane on a dichloromethane solution.
Synthesis of [4-(4-Methoxystyryl)-2,6-Bis(N-methylimino)-
phenyl]chloroplatinum (PtCl(7), 15). This compound was
prepared and purified in a manner similar to that for 12, by using
7H (49 mg, ca. 0.17 mmol) and K2PtIICl4 (63 mg, 0.152 mmol) in
glacial acetic acid (4 mL). The column was eluted with dichloro-
methane/ethyl acetate (95/5) and an orange solid obtained. Yield: 45
mg (57%). The reaction and column were kept in the dark to obtain
the pure E isomer; the Z isomer was generated later by exposure of the
NMR solution to ambient light. δH (400 MHz, CD2Cl2): E isomer,
3
Synthesis of 5-[4-(4-n-Pentylcyclohexyl)phenyl]-1,3-bis(N-
methylimino)benzene (11H). This compound was prepared in a
manner similar to that for 2H, by using 9 (140 mg, 0.386 mmol) and
methylamine (40 wt % aqueous, 90 mg, 1.16 mmol) in ethanol (20
8.32 (2H, (66%) q, J = 1.2, (34%) d, JPtH = 143.5, CHN), 7.60 (2H,
(66%) s, (34%) d, 4JPtH = 7.4, C6H2), 7.45 (2H, d, J = 8.9, C6H4), 7.06
(1H, d, J = 16.3, CH), 6.93 (1H d, J = 16.4, CH), 6.89 (2H, d, J = 8.8,
3
C6H4), 3.83 (6H, (66%) d, J = 1.4, (34%) d, JPtH = 31.7, 2Me), 3.81
1
(3H, s, OMe); Z isomer, 8.20 (2H, (66%) q, J = 1.3, (34%) d, 3JPtH
=
mL) to give a white solid. Yield: 150 mg (100%). H NMR spectra
4
indicated a negligible amount of monoaldehyde impurity, both initially
and after 6 months of storage. δH (400 MHz, CDCl3): 8.36 (2H, q, J =
1.6, 2CHN), 8.02 (2H, d, J = 1.5, C6H3), 7.93 (1H, t, J = 1.4, C6H3),
7.60 (2H, d, J = 8.3, C6H4), 7.28 (2H, d, J = 8.1, C6H4), 3.55 (6H, d, J
= 1.6, 2Me), 2.51 (1H, tt, J = 12.1, J = 3.2, CHCy), 1.97−1.82 (4H, m,
2CH2Cy), 1.55−1.42 (2H, m, CH2Cy), 1.38−1.20 (9H, C4H8 + CHCy),
1.13−1.00 (2H, m, CH2Cy), 0.90 (3H, t, J = 7.2, Me). Anal. Calcd for
C27H36N2: C, 83.5; H, 9.3; N, 7.2. Found: C, 83.3; H, 9.7; N, 7.2. m/z
(+ES): 389 ([M + H]+), 411 ([M + Na]+).
143.4, CHN), 7.35 (2H, (66%) s, (34%) d, JPtH = 7.6, C6H2), 7.16
(2H, d, J = 8.3, C6H4), 6.75 (2H, d, J = 8.8, C6H4), 6.56 (1H, d, J =
12.1, CH), 6.40 (1H, d, J = 12.0, CH), 3.79 (6H, (66%) d, J = 1.4,
3
(34%) d, JPtH = 32.8, 2Me), 3.76 (3H, s, OMe). Anal. Calcd for
C19H19ClN2OPt: C, 43.7; H, 3.7; N, 5.4. Found: C, 43.6; H, 3.6; N,
5.3. m/z (+MALDI): 522 ([M]+), 486 ([M − Cl]+), 1008 ([M2 −
Cl]+).
Synthesis of [4-(4-Methoxyphenyl)-2,6-bis(N-methylimino)-
phenyl]chloroplatinum (PtCl(10), 16). This compound was
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prepared and purified in a manner similar to that for 12, by using 10H
(67 mg, ca. 0.25 mmol) and K2PtIICl4 (96 mg, 0.231 mmol). The
column was eluted with dichloromethane/ethyl acetate (95/5) and an
orange solid obtained. Yield: 51 mg (45%). δH (400 MHz, CDCl3):
Table 1. Crystallographic Data and Refinement Details for
Complexes 12 and 14
12
14
3
8.31 (2H, (66%) q, J = 1.4, (34%) d, JPtH = 143.9, CHN), 7.58 (2H,
formula
C10H11ClN2Pt
389.75
C18H17ClN2Pt
491.88
(66%) s, (34%) d, 4JPtH = 7.3, C6H2), 7.44 (2H, d, J = 8.7, C6H43), 6.97
M
(2H, d, J = 8.7, C6H4), 3.90 (6H, (66%) d, J = 1.4, (34%) d, JPtH
=
cryst syst
monoclinic
P21/c
tetragonal
P41212
31.0, 2Me), 3.85 (3H, s, OMe). Anal. Calcd for C17H17ClN2OPt: C,
41.2; H, 3.5; N, 5.7. Found: C, 41.1; H, 3.2; N, 5.7. m/z (+MALDI):
460 ([M − Cl]+), 956 ([M2 − Cl]+).
space group
a/Å
9.6323(9)
16.5241(16)
6.7869(7)
90
10.0609(13)
10.0609(13)
31.897(6)
90
b/Å
Synthesis of {4-[4-(4-n-Pentylcyclohexyl)phenyl]-2,6-bis(N-
methylimino)phenyl}chloroplatinum (PtCl(11), 17). This com-
pound was prepared and purified in a manner similar to that for 12, by
using 11H (30 mg, ca. 0.08 mmol) and K2PtIICl4 (29 mg, 0.070 mmol)
in glacial acetic acid (3 mL). The column was eluted with
dichloromethane/ethyl acetate (99/1) and a yellow solid obtained.
Yield: 18 mg (42%). δH (400 MHz, CDCl3): 8.32 (2H, (66%) q, J =
c/Å
α/deg
β/deg
109.008(2)
90
90
γ/deg
U/Å3
90
1021.34
3228.6(8)
8
Z
4
4
1.4, (34%) d, 3JPtH = 144.0, CHN), 7.61 (2H, (66%) s, (34%) d, JPtH
T/K
μ/mm−1
100(2)
100(2)
= 6.7, C6H2), 7.44 (2H, d, J = 8.3, C6H4), 7.28 (2H, d, J = 8.2, C6H4),
3.91 (6H, (66%) d, J = 1.4, (34%) d, 3JPtH = 31.1, 2Me), 2.51 (1H, tt, J
= 12.3, J = 3.1, CHCy), 1.96−1.85 (4H, m, 2CH2Cy), 1.54−1.42 (2H,
m, CH2Cy), 1.37−1.20 (9H, C4H8 + CHCy), 1.13−1.01 (2H, m,
CH2Cy), 0.90 (3H, t, J = 7.2, Me). Anal. Calcd for C27H35ClN2Pt: C,
52.5; H, 5.7; N, 4.5. Found: C, 52.0; H, 5.7; N, 4.5. m/z (+MALDI):
618 ([M]+), 1201 ([M2 − Cl]+).
X-ray Crystallography. Crystal structures of the complexes 12
and 14 have been obtained. Data were collected on a Bruker APEX
CCD X-ray diffractometer by using Mo Kα radiation (λ = 0.710 73 Å)
and processed by using the Bruker SAINT14 and SADABS15 software
packages. The structures were solved by direct methods by using
SHELXS-9716 and refined by full-matrix least squares on all Fo2 data by
using SHELXL-97.17 All other calculations were carried out by using
the SHELXTL package.18 All non-hydrogen atoms were refined
anisotropically, and hydrogen atoms were included in idealized
positions by using the riding model, with thermal parameters 1.2
times those of aromatic parent carbon atoms and 1.5 times those of
methyl parent carbons. For 14, atoms C9 and C10 are disordered over
two sites with occupancies 0.590(15)/0.410(15); restraints were
applied to this group, and the absolute configuration was determined
by refining the Flack parameter. Crystallographic data and refinement
details are presented in Table 1.
13.958
8.854
cryst size/mm
appearance
0.16 × 0.15 × 0.03
amber plate
8727
0.30 × 0.20 × 0.20
orange prismatic
18 629
no. of rflns collected
no. of indep rflns (Rint)
no. of rflns with I > 2σ(I)
goodness of fit on F2
final R1, wR2 (I > 2σ(I))
final R1, wR2 (all data)
peak, hole/eÅ−3
2422 (0.0301)
2182
3315 (0.0591)
2982
1.034
1.165
0.0203, 0.0414
0.0248, 0.0424
0.963, −0.653
0.0341, 0.0646
0.0410, 0.0661
1.068, −1.112
triplet excited states of 12 was also performed, at the B3LYP/Def2-
SVP/SDD level, without a CPCM. The geometry of the lowest triplet
excited state was optimized at the same level. Frequency calculations of
the ground state S0 and the first triplet excited state T1 at the
appropriate geometries were performed to give the zero-point
corrections. Quasi-restricted orbitals (QROs)26 were generated for
T1 by using the geometry of the ground state and the ORCA suite of
programs.27 The UV−vis absorption spectra were simulated by using
the GaussSum program.28
Luminescence Measurements. Steady-state emission and
excitation spectra were determined by using a PerkinElmer LS50 B
fluorimeter operating in fluorescence mode. The spectra were
corrected for both the excitation source and the emission spectral
response. Luminescence quantum yields ϕlum were determined upon
350 nm excitation in nondegassed dichloromethane solutions relative
to quinine sulfate (1 M H2SO4), which has ϕlum = 0.58 at 293 K.19
Time-resolved luminescence measurements were recorded by using an
Edinburgh instruments mini-Tau system by time-correlated single-
photon counting using an EPL 405 ps pulsed diode laser as the
excitation source and a 100 nm bandpass interference filter (450−550
nm) to select the visible emission. Lifetimes τ were obtained by tail-fit
on the data obtained, and the quality of fit was judged by minimization
of reduced χ2 and residuals squared. The fits gave χ2 values of between
1.622 (for 12) and 1.007 (for 17). Fitting to a biexponential decay
provided no improvement in all cases, indicating that there is only one
emissive species on the nanosecond time scale. The respective
estimated experimental errors for the ϕlum and τ values are 20% and
10%.
Theoretical Studies. All DFT and TD-DFT calculations were
carried out by using the Gaussian 03 suite of programs.20 Structure
optimization of complexes 12, 14, and 16 were conducted at the
B3LYP21 level by using the SDD22 basis set and pseudopotential on Pt
and Def2-SVP23 on all other atoms. TD-DFT calculations at these
optimized geometries were conducted with a CPCM24 solvent model
(dichloromethane) at the same level, apart from 14, for which
MPW1PW9125 was used instead. The first 60 excited states were
calculated, covering wavelength ranges of 179−388 nm (12), 191−421
nm (14), and 193−423 nm (16). A TD-DFT calculation of the first 10
RESULTS AND DISCUSSION
■
Synthesis. Six new PtII pincer complexes (12−17) have
been synthesized, with various 4-substituents (Scheme 1). The
key intermediate 5-bromoisophthalaldehyde (1) was prepared
by a new and facile method, adapted from a literature
procedure.29 One-step, regioselective bromination of isophtha-
laldehyde, using N-bromosuccinimide (NBS) in sulfuric acid,
gave 1 in a moderate yield (25%) after recrystallization. The 1H
NMR spectrum of the crude material revealed a high yield of 1,
while the isolated yield reflected difficulties in removing minor
impurities. Previous syntheses of 1 include the reduction of
either dimethyl 5-bromoisophthalate or 5-bromoisophthalic
acid to 3,5-bis(hydroxymethyl)bromobenzene followed by
oxidation30 or lithiation of 1,3,5-tribromobenzene and then
reaction with DMF.31
5-Styrylisophthaladehydes (4 and 5) were accessed via Heck
reactions of 1 with styrene or 4-methoxystyrene, using a
PdII(OAc)2 catalyst,32 with isolated yields of ca. 20%. 5-Phenyl
derivatives (8, 9) were prepared by Suzuki−Miyaura couplings
of 1 with boronic acids, giving isolated yields of ca. 35%. The
elongating groups are intended to aid alignment within liquid
crystal matrices, especially the cyclohexylphenyl group (in 9),
which is a common mesogenic subunit.
The proligands (2H, 3H, 6H, 7H, 10H, and 11H) were
formed by reacting the isophthalaldehydes with methylamine in
ethanol under reflux. Most of these compounds are unstable
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a
Scheme 1. Syntheses of the NCN Pincer Proligands and Their PtII Complexes
a
Reagents and solvents: (a) NH2Me/ethanol; (b) K2PtIICl4/acetic acid.
toward hydrolysis to mono- and dialdehydes in the solid state
(or as oils), with 1H NMR spectra showing CHO signals after 2
days of exposure to a moist environment. Rapid filtration of
solutions through silica plugs results in extensive hydrolysis.
Therefore, these proligands were used immediately without
purification, with 1H NMR spectra of the crude materials
indicating only trace impurities. In contrast, a pure sample of
11H was obtained without purification, as confirmed by
elemental analyses. This sample showed no evidence of
hydrolysis after 6 months of storage under ambient conditions,
consistent with the increased hydrophobicity expected for 11H.
A previous report notes the susceptibility of (N-arylimino)-
benzene compounds toward hydrolysis in ethanol;33 greater
hydrolytic susceptibility of (N-methylimino)benzenes is antici-
pated due to increased basicity, which facilitates the formation
of an amine leaving group.
The new Pt pincer complexes 12−17 were synthesized by
direct cyclometalation of the proligands by reacting with
K2PtIICl4 in acetic acid for 2 days under reflux, as reported for
similar compounds by Fossey and Richards.6a These reactions
were regioselective, and no other complexes were produced.
Reactions attempted using PtIICl2(DMSO)2 or PtIICl2(EtCN)2
in solvents such as dichloromethane and methanol were
unsuccessful. Alternative strategies7 to direct metalation include
oxidative addition from halogenated starting materials,34
transmetalation,35 or the “ligand introduction route” recently
conceived by Takenaka et al.6d For relative ease of synthesis of
the relevant starting materials, direct metalation is preferred,
despite moderate reported yields. 12−17 were isolated in yields
of 24−68%, based on K2PtIICl4. Decreased solubility in acetic
acid of the more extended complexes 14−17 aids precipitation,
preventing further reactions with the solvent, and giving
relatively higher yields.
The new compounds were characterized by 1H NMR
spectroscopy and CHN elemental analyses. Satisfactory CHN
analyses of the proligands apart from 11H were elusive, due to
facile hydrolysis (see above). Compound 1 and all of the
proligands were characterized also by electrospray mass
spectrometry, while the MALDI technique proved superior
for the precursors 4, 5, 8, and 9. MALDI also gives good results
for the complexes, with the molecular ion being clearly
observed in most cases and [M2 − Cl]+ being common.
1H NMR Spectroscopy. All of the compounds give spectra
consistent with their structures in CDCl3 or CD2Cl2.
Converting the aldehyde precursors into imines causes the
methine singlet signal to shift upfield by ca. 1.8 ppm and
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Figure 2. E → Z isomerization of the ethenylene group in 15 upon exposure to ambient light monitored by 1H NMR spectroscopy in CD2Cl2 over
time intervals of ca. 2 h. All except the initial (red) trace are offset steadily to the left to improve clarity; apparent changes in the signal positions are
therefore not real.
become a quartet due to coupling to the methyl protons. The
Table 2. Photophysical Data for Complexes 12−17 in
aromatic signals of the attached rings also shift upfield slightly
Dichloromethane at 293 K
1
by ca. 0.3−0.4 ppm on imine formation. H NMR spectra
absorption λmax, nm (ε, 103
emission λmax
,
ϕlum
τ,
a
b
c
d
complex
M−1 cm−1)/Emax, eV
nm/Emax, eV
(×103)
ns
reveal that the ethenylene groups of aldehyde precursors 4 and
5 and proligands 6H and 7H are present in the E configuration
only, as indicated by coupling constants of ca. 16 Hz.
12
400 (4.1)/3.10
386 (4.4)/3.21
339 (4.3)/3.66
295 (6.1)/4.20
254 (16.3)/4.88
416 (4.1)/2.98
401 (3.8)/3.09
343 (3.4)/3.61
330 (3.4)/3.76
302 (4.6)/4.11
425 (5.8)/2.92
316 (38.9)/3.92
427 (5.8)/2.90
297 (31.0)/4.17
420 (4.4)/2.95
406 (4.1)/3.05
350 (4.2)/3.54
338 (4.2)/3.67
259 (42.7)/4.79
418 (4.8)/2.97
405 (4.6)/3.06
349 (4.6)/3.55
257 (46.7)/4.82
562/2.21
606/2.05
1.26
160
1
Complexation is confirmed in the H NMR spectra by the
e
662/1.87
loss of an aromatic signal and the presence of distinctive 195Pt
satellites straddling the imine methine signals (3JPtH = 143−144
Hz). The resolution of the quartet fine structure within these
satellites is poor, and the methine signals show only very slight
shifts on complexation (≤0.05 ppm). Pt satellites are also
observed for the N-methyl proton signals (3JPtH = 31−33 Hz)
and the remaining aromatic signals (4JPtH ≈ 7−8 Hz), with the
latter also shifting upfield by ca. 0.3−0.4 ppm on complexation,
indicating substantial increases in shielding.
13
564/2.20
609/2.04
1.41
165
e
664/1.87
14
15
16
f
f
E → Z photoisomerization of the ethenylene moieties in
1
complexes 14 and 15 is detected by H NMR spectroscopy.
When the complexes are prepared in the dark, they are isolated
as their E isomers almost exclusively. Representative spectra for
15 (Figure 2) show the appearance of new signals at higher
field upon exposure to ambient light, especially the ethenylene
doublets with J ≈ 12 Hz. Signal integration reveals that, after 20
h of exposure, ca. 67% of the sample is in the Z form.
Analogous behavior is observed for 14. E → Z isomerization in
PtII complexes of 4-styryl-2-phenylpyridine (sppy) has been
noted previously by Yin et al.36 and for the substituted
Pt(bAB)X complexes of van Koten and co-workers.3 It is
noteworthy that photoisomerization does not occur in the
precursors or proligands, being apparently stimulated by
platination. Previous reports of ethenylene photoisomerization
facilitated by the presence of heavy metals, particularly
rhenium, attribute the effect to intramolecular energy transfer
572/2.17
611/2.03
1.36
1.70
159
170
17
567/2.19
609/2.04
a
Solutions ca. 2 × 10−6−3 × 10−4 M. The ε values are the averages
from measurements made at three or four different concentrations
(with ε showing no significant concentration dependence). Emission
maxima on excitation at 400 nm. Luminescence quantum yields
b
c
determined relative to quinine sulfate in 1 M H2SO4 on 350 nm
d
excitation (ϕ = 0.58).19 Luminescence lifetime determined on 405
37
3
3
nm excitation with a picosecond pulsed diode laser, using a 450−550
from a MLCT to a LC state of the (E)-ethenylene moiety.
e
f
nm bandpass interference filter. Shoulder. Not observed.
Interest in this phenomenon is stimulated by the potential
utility of molecular photoswitches.
Electronic Spectroscopy. Both absorption and emission
spectra have been recorded for the new PtII complexes 12−17
in dichloromethane; the resulting data are shown in Table 2,
with representative spectra in Figures 3 and 4.
Absorption. The absorption spectra of 12−17 (Figure 3)
display two structured bands between 300 and 500 nm with
moderate ε values (ca. 3−6 × 103 M−1 cm−1), except for the
styryl derivatives 14 and 15, for which a more intense band
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(CT) transitions.4a PtII(bPyB)Cl complexes show low-energy
bands at 350−440 nm attributed to CT transitions, with weak
bands at lower energy still due to direct population of triplet
intraligand CT (3ILCT) states.5a,b Such spin-forbidden bands
have been reported also for other PtII complexes38a,c,d but are
not observed with 12−17.
Emission. Except for 14 and 15, the new complexes are
luminescent in fluid solution at room temperature (Table 2,
Figure 4a). The emission bands cover the region ca. 550−750
Figure 3. UV−vis absorption spectra in dichloromethane at 293 K of
12 (red), 13 (orange), 14 (green), 15 (light blue), 16 (dark blue), and
17 (purple), showing (a) entire spectra and (b) expansion of the low-
energy region.
obscures the higher energy part. The Emax value of the lowest
energy absorption decreases steadily as the 4-substituent
changes in the order H > Br > aryl > styryl. On the basis of
literature precedents, such low-energy bands are attributable to
Pt(d) → π* MLCT transitions,36,38 leading to the observed
yellow/orange colors.
Figure 4. (a) Emission and (b) excitation spectra in dichloromethane
at 293 K of 12 (red), 13 (green), 16 (blue), and 17 (magenta).
14 and 15 show intense absorptions (ε ≈ (3−4) × 104 M−1
cm−1) centered at ca. 300 nm, with quite different band shapes
probably due to differing proportions of Z and E isomers. The
analogous bAB− complexes show similarly intense bands at ca.
350 nm, attributed by DFT to have mixed ligand-based π → π*
and MLCT character, with none at lower energies.3,39 Styryl-
substituted phenylpyridine PtII complexes have two low-energy
bands at ca. 300−350 and 400 nm, thought to have π → π* and
MLCT origins, respectively.36 The intensity and position of the
300 nm bands of 14 and 15, and their absence in the other
complexes, indicate stilbene-based π → π* character, consistent
with the presence of an intense band at 294 nm in stilbene
itself.40 16 and 17 give similarly intense bands at ca. 250 nm
due to biphenyl-based π → π* transitions.
nm and show some vibrational fine structure with a spacing of
ca. 1100−1300 cm−1, indicating some ligand-based character.
The emission energies decrease slightly as the 4-substituent
changes in the order H > Br > C6H4CyC5H11 > C6H4OMe. For
the unsubstituted complex 12, the intensities of the apparent 0
→ 0 and 0 → 1 peaks are similar (I00/I01 ≈ 1), indicating
geometric differences between the ground and emissive excited
states. I00/I01 increases with the 4-substituent in the order H <
Br < aryl, indicating less structural change on excitation for the
more substituted complexes. The 0 → 2 transitions appear also
as shoulders in 12 and 13.
The excitation spectra (Figure 4b) broadly mirror the
absorption spectra (Figure 3), with the lowest energy band
being red-shifted for more substituted complexes, although the
relative intensities of the peaks do not correlate. The measured
ϕlum (0.1−0.2%) and τ values (159−170 ns) are indistinguish-
able for all of the complexes, the latter being consistent with
triplet-state emission. Such relatively small ϕlum and τ values
suggest effective excited-state quenching, which would be
expected to decrease significantly in degassed solutions.
Previously, Milum et al. presented the only UV−vis analysis
of PtII complexes of bIB− ligands, although their complexes
differ markedly from ours.8 The appearance of an intense band
at ca. 450 nm on complexation was ascribed to LMCT
absorption, but DFT calculations show that the responsible
transition is substantially thiophene-based. In the PtII(bAB)X
complexes investigated by Connick et al., halide coligands give
colorless solutions with the lowest energy absorption bands at
260−285 nm ascribed to MLCT transitions and long tails to
lower energy due to d−d and spin-forbidden charge-transfer
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The nonemissive solution-state behavior of 14 and 15 is
attributed to excited-state quenching by E → Z isomerization.
Such quenching has been noted for PtII sppy complexes,
although weak solution luminescence was observed.36 IrIII sppy
complexes show similar behavior, with the intensity restored on
hydrogenation of the ethenylene bond.41 The same kind of
photoisomerization decreases the radiative lifetimes of ReI
complexes.42
Table 3. Selected Interatomic Distances (Å) and Angles
(deg) for Complexes 12 and 14
12
14
Pt−C
Pt−N
1.897(3)
2.035(3)
2.039(3)
2.4179(8)
1.294(4)
1.293(4)
1.464(4)
1.456(4)
1.887(9)
2.048(7)
2.037(7)
2.393(2)
1.285(11)
1.291(11)
1.453(10)
1.437(11)
1.33(3)
Pt−Cl
CN
The room-temperature luminescence of 12, 13, 16, and 17 is
a marked improvement on the PtII(bAB)Cl complex inves-
3
C−N
tigated by Connick et al., the (d−d) luminescence of which is
completely quenched in solution.4 Notably, styryl-function-
alized PtII(bAB)Cl complexes are appreciably luminescent in
degassed solutions at room temperature, but with lifetimes
much shorter than those measured here (picosecond time
scale).3,39 The relevant excited states in these PtII(bAB)Cl
compounds have intramolecular charge-transfer nature at
mostly higher energies, and solution luminescence occurs
only when a strong electron donor/acceptor substituent is
present. The emissive behavior of 12, 13, 16, and 17 indicates
that the imine functionality introduces an excited state that is
less susceptible to deactivation than in analogous PtII(bAB)Cl
complexes and is different from those in the polar styryl
derivatives. In comparison with highly luminescent PtII(bPyB)
Cl complexes,5a,b 12, 13, 16, and 17 have similar emission
profiles, but ϕlum and τ are lower by several orders of
magnitude. If the emissions originate from similar states, their
decreased efficiencies could result from a weaker ligand field,
influenced by decreased rigidity and a less appropriate
geometry for the metal (see below), making deactivating d−d
states more accessible. The origins of the emission in the new
complexes are explored by using DFT calculations (see below).
Crystallography. Single-crystal X-ray structures have been
solved for complexes 12 and 14. Representations of their
molecular structures are given in Figures 5 and 8, crystal
packing diagrams in Figures 6, 7 and 9, and selected bond
distances and angles in Table 3.
CC
a
1.27(4)
N−Pt−C
N−Pt−Cl
79.48(13)
79.62(13)
98.90(8)
79.4(3)
79.8(3)
100.9(2)
99.9(2)
102.00(8)
159.10(12)
178.31(10)
N−Pt−N
C−Pt−Cl
159.2(3)
177.5(2)
118.6(16)
118.3(17)
b
C−C−C
a
114(2)
a
116(3)
c
C−C−C
107.2(13)
132.1(12)
105.4(11)
136.1(12)
140.0(14)
a
a
98.9(13)
a
a
102.4(14)
139.3(14)
a
b
Incorporating the disordered C9B and/or C10B atoms. Encompass-
c
ing the ethenylene unit. Incorporating two aromatic ring carbons and
one ethenylene carbon.
are essentially coplanar, and the methyl groups are eclipsed
with respect to the planar core. The chloride ligand is almost
coplanar with the core in 12 (deviation ca. 0.04 Å), while a
larger corresponding deviation (0.15 Å) is observed in 14. The
geometries at Pt are distorted square planar, with N−Pt−C
angles of ca. 79° and N−Pt−N angles of ca. 159° indicative of
ring strain in the five-membered chelates, as in other NCN-
pincer complexes. PtII(bAB)X44 and PtII(bPyB)X5b,45 com-
plexes are less strained, with respective N−Pt−N angles of ca.
164 and 161° due to longer C−N distances. The C−Pt−Cl
angle is almost 180° in both 12 and 14. In comparison with 12
and 14, the Pt−C distances are slightly longer in related
complexes with N-tBu,6a N-phenyl,6a or N-benzyl6e groups in
place of N-Me (1.915(6), 1.908(6), and 1.901(7) Å,
respectively), giving smaller N−Pt−N angles (157.2(2),
157.9(2), and 159.29°, respectively). The Pt−Cl distances in
The geometric parameters about the Pt core in 12 and 14 are
similar and resemble closely those in other PtII(bIB) complex-
es,6a,b,e,8,34,43 revealing only a very slight asymmetry between
the two sides of the molecules. The aryl rings and metallocycles
12 and 14 are as expected for NCN-pincer complexes. The Pt−
6b,e,8,34,43
N distances resemble those in other bIB−
and
45
bPyB−
complexes, while N-tBu complexes have slightly
longer Pt−N distances (2.08−2.10 Å),6a as do PtII(bAB)X
species.44
12 stacks in columns parallel with the c axis. Adjacent
complexes within each column are rotated mutually, giving a
Cl−Pt···Pt−Cl torsion of ca. 82.8° (Figure 6), and avoiding
close methyl contacts. The complexes are almost coplanar
(dihedral angle ca. 1.3°), with an interplanar spacing of ca. 3.4
Å. Within the columns, Pt ions form a zigzag chain with an
Figure 5. Representation of the molecular structure of 12 (50%
probability ellipsoids).
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halide or pseudohalide ligands between adjacent diimines may
accommodate weak intermolecular bonding between filled
anionic ligand orbitals and diimine π* orbitals. In 12, the
proximity of the chloride ligands and imine groups is
reminiscent of the α-diimine systems (Figure 6).
For 14 (Figure 8), the structure shows an (E)-ethenylene
moiety, despite crystallization from a mixture of isomers in the
Figure 6. Structure of 12 viewed approximately along the c axis,
showing the torsional relationship between adjacent complexes.
intermolecular Pt···Pt distance of 3.5469(4) Å and a Pt···Pt···Pt
angle of 146.17(1)° (Figure 7). Such “linear-chain” packing of
Figure 8. Representation of the molecular structure of 14 (50%
probability ellipsoids).
presence of light. The disorder observed is common in (E)-
stilbene (and (E)-azobenzene) compounds and occurs via a
pedal motion.51 The proportion of the minor orientation in
(E)-stilbene increases with temperature, with a maximum of ca.
20% at 373 K.51b The proportion of the minor orientation in 14
is considerably larger (at 100 K), implying a smaller energy
barrier between the two conformers. The dihedral angle
between the two phenyl rings in 14 is ca. 17.1°. The molecular
structure is similar to that of the nitro-substituted complex in
the study on related bAB− complexes,3 but the twisting is less
severe in 14. The four other structures obtained in that
previous study show distinctly bowed shapes.3 In contrast to
the case for 12, 14 does not form columnar stacks but packs
with a Cl−Pt···Pt−Cl torsion of ca. 108.7° for the closest
associated complexes (Figure 9).
Figure 7. Packing diagram of 12, showing the planarity of the complex
units, the columnar structure, and zigzag close contacts between Pt
atoms (dashed lines).
planar PtII complexes has been widely studied, due to
interesting consequent electronic/optical properties.46 The
van der Waals radius of Pt is ca. 1.7−1.8 Å,47 and weak
Pt···Pt interactions can occur at distances of up to 3.60 Å.46a
Although the Pt···Pt separation in 12 is longer than in most
reported linear-chain Pt complexes, interactions have been
invoked in complexes with similar distances.48 While solid-state
UV−vis spectra are required to confirm the presence of Pt···Pt
interactions in 12, its red color is indicative.49 For PtIICl2(2,2′-
bipyridyl)2, the red polymorph shows close Pt···Pt contacts
(3.45 Å),49a while the yellow form has a much larger separation
(4.44 Å).50 Solutions of 12 appear orange-yellow, and color
differences between solid and solution states are not observed
for the other complexes. Close Pt···Pt interactions in the latter
are inhibited by their 4-substituents; for example, the Pt···Pt
distance in 14 is 3.9621(5) Å (see below).
Figure 9. Packing diagram of complex 14 viewed approximately along
the b axis. Hydrogens and disordered atoms are omitted for clarity.
Theoretical Studies. In order to rationalize their
electronic/optical properties, TD-DFT calculations have been
performed on complexes 12, 14 (E isomer), and 16 by using
Gaussian 03.20
Structures. Selected optimized bond distances and angles are
given in Table 4. The three structures show very similar,
symmetrical coordination geometries. In comparison with the
In addition to intermetallic interactions and steric effects, the
solid-state structure is also probably influenced by interligand
interactions. In a series of linear-chain Pt α-diimines, Connick
et al. noted that complexes are rotated successively through
120−180° within the columns.49c Resultant sandwiching of
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Table 4. Selected Interatomic Distances (Å) and Angles
(deg) for the Optimized (B3LYP/Def2-SVP/SDD)
Structures of 12, 14, and 16
12
14
16
Pt−C
Pt−N
1.92
2.08
2.08
2.42
1.31
1.31
1.45
1.45
1.92
1.92
2.08
2.08
2.42
1.31
1.31
1.45
1.45
2.08
2.08
Pt−Cl
CN
2.42
1.31
1.30
C−N
1.45
1.45
CC
1.35
N−Pt−C
79.3
79.2
79.2
79.3
79.2
79.2
N−Pt−Cl
100.7
100.6
158.6
179.9
100.9
100.7
158.4
179.9
127.6
127.2
122.6
118.1
123.6
118.8
100.8
100.8
158.4
180.0
N−Pt−N
C−Pt−Cl
a
C−C−C
b
C−C−C
a
b
Encompassing the ethenylene unit. Incorporating two aromatic ring
carbons and one ethenylene carbon.
crystal structures of 12 and 14 (Table 3), the predicted bond
distances are generally slightly longer, but the angles are very
similar. Optimization of 14 gives a fully planar structure, unlike
in the crystal, while the dihedral angle between the phenyl rings
in 16 is ca. 39°.
Electronic Absorption. The computed and experimental
UV−vis spectra of 12, 14, and 16 are shown in Figure 10,
predicted transition energies in Table 5, and selected orbitals in
Figures 11−13. The predicted profiles match the measured
spectra reasonably well, but the λmax values differ somewhat.
For 12, the two low-energy bands above 300 nm originate
from five transitions, with the highest energy of these being the
most intense. These transitions correspond to excitations from
π orbitals based on the aryl and imine units as well as Pt(d)
Figure 10. TD-DFT calculated (blue) and experimental (green) UV−
vis spectra of (a) 12, (b) 14, and (c) 16. The ε axes refer to the
experimental data only, and the vertical axes of the calculated data are
scaled to match the main experimental absorptions. The oscillator
strength axes refer to the individual calculated transitions (red).
2
(HOMO-3 is dz ) and Cl(p) to bIB π* orbitals with some Pt(d)
contribution (Figure 11). Both of the involved LUMOs are
antibonding across the imine fragment. These results indicate
that the corresponding absorptions have mixed MLCT/ligand-
based π → π* character. Introducing the imine π* orbitals red-
shifts the lowest energy absorption significantly with respect to
the related bAB− complexes.
rings (Figure 13). However, the LUMO/LUMO+1 are directly
equivalent to those of 12, with no electron density on the
pendent ring. The observed red shifting of the lowest energy
absorption on 4-substitution is therefore mostly due to
destabilization of the HOMO. However, while TD-DFT does
yield an increase in the λmax of this band on moving from 12 to
16, the observed further increase on moving to 14 is not
predicted (Figures 3 and 10). The intense band at ca. 260 nm
in the recorded spectrum of 16 (Table 2 and Figure 3) is
predicted to encompass several transitions; the dominant one at
ΔE = 4.53 eV is of biphenyl π → π* nature largely, but with
significant contributions from Pt, Cl, and imine orbitals (Figure
13).
In 14, the lowest energy band (λmax ∼415 nm) comprises
HOMO → LUMO/LUMO+1 transitions. The HOMO is
similar to that of 12, but the bIB− π system also includes the
styryl portion (Figure 12). The LUMO/LUMO+1 are based
around only the PtNCN core and are again π antibonding with
respect to the imine fragment. The styryl substituent effects
substantial asymmetry in the LUMOs. TD-DFT reveals also
multiple transitions in the range 300−400 nm; the most intense
transition at ΔE = 3.76 eV is HOMO → LUMO+2, largely of
stilbenyl π → π* character, but with contributions from Pt, Cl,
and imine orbitals (Figure 12).
Electronic Emission. TD-DFT indicates that excitation to
the lowest energy excited state T1 of 12 has ΔE = 2.44 eV/508
nm (although fos for all S0 → Tn excitations are zero, correlating
In 16, the two low-energy bands have origins similar to those
in 12, except that some of the HOMOs spread across both aryl
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Table 5. Data from TD-DFT Calculations Based on B3LYP/
Def2-SVP/SDD Geometries of 12, 14, and 16
complex
ΔE (eV)
fos
major contribn
μ12 (D)
12
3.20
3.22
3.25
3.38
3.84
4.50
4.96
0.06
0.01
0.01
0.01
0.19
0.04
0.28
HOMO → LUMO
2.19
0.90
1.09
0.94
3.64
1.45
3.87
HOMO → LUMO+1
HOMO−3 → LUMO+1
HOMO−2 → LUMO+1
HOMO−2 → LUMO
HOMO−4 → LUMO+1
HOMO−6 → LUMO+1
HOMO−1 → LUMO+2
HOMO−6 → LUMO
HOMO−3 → LUMO+3
HOMO → LUMO+4
HOMO → LUMO
5.10
5.68
0.12
0.35
2.52
4.04
14
2.95
3.03
3.76
3.85
0.07
0.11
1.28
0.14
2.57
3.14
9.47
3.14
HOMO → LUMO+1
HOMO → LUMO+2
HOMO−4 → LUMO
HOMO−4 → LUMO+1
HOMO−3 → LUMO
HOMO−4 → LUMO+1
HOMO−3 → LUMO
HOMO−8 → LUMO
HOMO−8 → LUMO+1
HOMO−6 → LUMO
HOMO−8 → LUMO
HOMO−8 → LUMO+1
HOMO → LUMO
Figure 11. Contour surface diagrams of MOs involved in the low-
energy transitions of complex 12, excluding HOMO−3, which is
4.13
5.11
0.21
0.31
3.65
4.02
2
simply the dz orbital (isosurface value 0.03 au).
5.27
0.18
3.03
16
2.93
3.00
3.70
0.05
0.04
0.08
2.20
1.80
2.45
HOMO → LUMO+1
HOMO−4 → LUMO
HOMO−2 → LUMO+1
HOMO−4 → LUMO
HOMO−2 → LUMO+1
HOMO−6 → LUMO+1
HOMO → LUMO+2
HOMO−8 → LUMO+1
HOMO−1 → LUMO+4
HOMO−8 → LUMO
3.90
4.53
4.95
5.08
0.12
0.97
0.23
0.43
2.85
7.52
3.47
4.70
Figure 12. Contour surface diagrams of MOs involved in the major
electronic transitions of complex 14 (isosurface value 0.03 au).
with the observed absence of spin-forbidden absorption bands),
with major contributions from the transitions HOMO−2 →
LUMO and HOMO → LUMO+1 (orbitals shown in Figure
11). A geometry optimization of T1 induces substantial
asymmetry in the structure around the coordination site
(Figure 14). This result correlates with the observed emission
profile with I00 ≈ I01, indicating geometrical changes on
excitation, and the discrepancy between the calculated vertical
excitation and observed emission energies. The calculated
difference in total energies between S0 and T1 now becomes
2.26 eV (549 nm), while frequency calculations to factor in
zero-point corrections give the difference in energy between the
lowest vibrational levels (0 → 0) as 2.15 eV (577 nm). The
experimentally measured 0 → 0 emission at 2.21 eV (562 nm)
lies between these two computed values, since the frequency
calculations do not incorporate the effects of anharmonicity.
To describe the nature of T1, QROs26 were calculated with
triplet electronic configuration at the ground-state geometry:
i.e., before the excited state has relaxed to its asymmetric
geometry. The singly occupied QROs are shown in Figure 15.
SOMO2 resembles very closely the LUMO derived by DFT for
the ground-state singlet molecule, while SOMO1 includes
occupancy of a d orbital that is different from those in
HOMO−2 or HOMO (Figure 11). The TD-DFT results
indicate that T1 is formed by depopulation of Pt(d) and Cl(p)
and subsequent population of bIB− ligand π*: i.e., the emissive
state has mixed MLCT and ligand-to-ligand charge-transfer
(LLCT) character. The emissive states of organometallic PtII
complexes are often intermediate between MLCT and ligand-
based.52 On comparison of 12 with theoretical studies on
PtII(bPyB)Cl, the origins of T1 are qualitatively quite similar,
although the LUMO in the latter case is located mostly on the
pyridyls with only a small contribution from the aryl ring.5c For
PtII(bPyB)Cl, TD-DFT provides a reasonable description of T1,
since only a small geometrical change occurs on excitation due
to greater rigidity. The introduction of a low-energy π* orbital
including the imine groups (SOMO2) is the key to the different
photophysical behaviors of PtII(bIB)Cl and PtII(bAB)Cl
complexes.
CONCLUSION
■
Six new PtII NCN-pincer complexes of 1,3-bis(N-
methylimino)benzene-derived ligands with various 5-substitu-
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Article
Figure 15. Singly occupied QROs of complex 12 corresponding to the
first triplet excited state, calculated at the ground state geometry
(isosurface value 0.03 au).
complete quenching by E → Z isomerization. Luminescence
quantum yields and lifetimes are in the ranges 0.1−0.2% and
159−170 ns, respectively. DFT calculations indicate that the
emissive state is of mixed 3LLCT/3MLCT origin, and this state
has a distorted geometry with respect to the very symmetric
ground state. The photophysical properties of PtII(bIB)Cl and
PtII(bAB)Cl complexes differ largely due to the presence of a
low-energy π* orbital including the imine groups in the former.
Single-crystal X-ray structures of two of the complexes also
reveal a symmetric PtNCN core, with N−Pt−N angles of ca.
159°. The unsubstituted complex packs in columnar stacks with
short Pt···Pt distances of ca. 3.55 Å. Weak Pt···Pt interactions
are tentatively invoked on the basis of this short distance and
the deep red color associated with solid samples of this complex
only.
ASSOCIATED CONTENT
* Supporting Information
Figure 13. Contour surface diagrams of MOs involved in the major
electronic transitions of complex 16 (isosurface value 0.03 au).
■
S
CIF files giving crystallographic information for 12 and 14 and
text, tables, and figures giving details relating to dichroic
properties, Cartesian coordinates of theoretically optimized
geometries for complexes 12, 14, and 16, and lifetime data and
fits. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: b.coe@manchester.ac.uk.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank DyStar U.K. Ltd. and the University of Manchester
for support. We are grateful to Dr. M. G. Hutchings (DyStar)
for initiating this project and also to Dr. J. J. W. McDouall
(Manchester) for advice concerning the TD-DFT calculations.
Dr. L. S. Natrajan (Manchester) is thanked for assistance with
the luminescence measurements and Prof. S. Faulkner
(Oxford) for access to the equipment used to measure the
lifetimes.
Figure 14. DFT calculated geometry of the lowest energy excited state
T1 of 12, showing selected bond distances (Å).
1
ents have been synthesized by direct metalation. H NMR
spectroscopy reveals E → Z photoisomerization of the
ethenylene groups in the styryl-substituted complexes. UV−
vis spectra show intense high-energy π → π* bands in aryl and
styryl-substituted complexes, and a number of lower energy
transitions in the 300−500 nm region of mixed MLCT/ligand-
based π → π* origins, as indicated by TD-DFT calculations.
Most of the complexes display vibronically structured emission
profiles in nondegassed fluid solutions at room temperature,
but the styryl-substituted complexes are nonemissive due to
REFERENCES
■
(1) (a) Hissler, M.; McGarrah, J. E.; Connick, W. B.; Geiger, D. K.;
Cummings, S. D.; Eisenberg, R. Coord. Chem. Rev. 2000, 208, 115.
(b) Wong, K. M.-C.; Yam, V. W.-W. Coord. Chem. Rev. 2007, 251,
2477. (c) Williams, J. A. G. Top. Curr. Chem. 2007, 281, 205.
(d) Williams, J. A. G.; Develay, S.; Rochester, D. L.; Murphy, L. Coord.
Chem. Rev. 2008, 252, 2596.
(2) (a) Lai, S.-W.; Che, C.-M. Top. Curr. Chem. 2004, 241, 27.
(b) Williams, J. A. G. Chem. Soc. Rev. 2009, 38, 1783.
5318
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Organometallics
Article
(3) Batema, G. D.; van de Westelaken, K. T. L.; Guerra, J.; Lutz, M.;
Spek, A. L.; van Walree, C. A.; de Mello Donega, C.; Meijerink, A.; van
́
Klink, G. P. M.; van Koten, G. Eur. J. Inorg. Chem. 2007, 1422.
(4) (a) Jude, H.; Krause Bauer, J. A.; Connick, W. B. Inorg. Chem.
2002, 41, 2275. (b) Jude, H.; Krause Bauer, J. A.; Connick, W. B. Inorg.
Chem. 2004, 43, 725. (c) Jude, H.; Krause Bauer, J. A.; Connick, W. B.
Inorg. Chem. 2005, 44, 1211.
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision
C.02; Gaussian, Inc., Wallingford, CT, 2004.
(5) (a) Williams, J. A. G.; Beeby, A.; Davies, E. S.; Weinstein, J. A.;
Wilson, C. Inorg. Chem. 2003, 42, 8609. (b) Farley, S. J.; Rochester, D.
L.; Thompson, A. L.; Howard, J. A. K.; Williams, J. A. G. Inorg. Chem.
2005, 44, 9690. (c) Sotoyama, W.; Satoh, T.; Sato, H.; Matsuura, A.;
Sawatari, N. J. Phys. Chem. A 2005, 109, 9760.
(6) (a) Fossey, J. S.; Richards, C. J. Organometallics 2002, 21, 5259.
(b) Fossey, J. S.; Richards, C. J. Tetrahedron Lett. 2003, 44, 8773.
(c) Fossey, J. S.; Richards, C. J. Organometallics 2004, 23, 367.
(d) Takenaka, K.; Minakawa, M.; Uozumi, Y. J. Am. Chem. Soc. 2005,
127, 12273. (e) Fossey, J. S.; Russell, M. L.; Malik, K. M. A.; Richards,
C. J. J. Organomet. Chem. 2007, 692, 4843.
(21) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(22) Andrae, D.; Haußermann, U.; Dolg, M.; Stoll, H.; Preuß, H.
̈
Theor. Chim. Acta 1990, 77, 123.
(23) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297.
(24) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995.
(b) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. J. Comput. Chem.
2003, 24, 669.
(25) Adamo, C.; Barone, V. J. Chem. Phys. 1998, 108, 664.
(26) Neese, F. J. Am. Chem. Soc. 2006, 128, 10213.
(27) Neese, F. ORCA-an ab initio, Density Functional and Semi-
empirical Program Package (v. 2.6-35); Universitat Bonn, Bonn,
Germany, 2007.
(28) O’Boyle, N. M.; Tenderholt, A. L.; Langner, K. M. J. Comput.
Chem. 2008, 29, 839.
̈
(7) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40,
3750.
(8) Milum, K. M.; Kim, Y. N.; Holliday, B. J. Chem. Mater. 2010, 22,
2414.
(9) Scaffidi-Domianello, Y. Y.; Nazarov, A. A.; Haukka, M.; Galanski,
M.; Keppler, B. K.; Schneider, J.; Du, P.; Eisenberg, R.; Kukushkin, V.
Y. Inorg. Chem. 2007, 46, 4469.
(29) Rajesh, K.; Somasundaram, M.; Saiganesh, R.; Balasubramanian,
K. K. J. Org. Chem. 2007, 72, 5867.
(30) (a) Netzke, K.; Snatzke, G. Chem. Ber. 1989, 122, 1365.
(b) Brunner, H.; Janura, M.; Stefaniak, S. Synthesis 1998, 1742.
(c) Eryazici, I.; Newkome, G. R. New J. Chem. 2009, 33, 345.
(31) Matsuda, K.; Nakamura, N.; Takahashi, K.; Inoue, K.; Koga, N.;
Iwamura, H. J. Am. Chem. Soc. 1995, 117, 5550.
(32) Yao, Q.-W.; Kinney, E. P.; Yang, Z. J. Org. Chem. 2003, 68, 7528.
(33) Oakley, S. H.; Coogan, M. P.; Arthur, R. J. Organometallics 2007,
26, 2285.
(10) (a) Kanbara, T.; Okada, K.; Yamamoto, T.; Ogawa, H.; Inoue,
T. J. Organomet. Chem. 2004, 689, 1860. (b) Okamoto, K.; Kanbara,
T.; Yamamoto, T.; Wada, A. Organometallics 2006, 25, 4026.
(c) Okamoto, K.; Yamamoto, T.; Akita, M.; Wada, A.; Kanbara, T.
Organometallics 2009, 28, 3307.
(11) Selected examples: (a) Grabchev, I.; Moneva, I.; Wolarz, E.;
Bauman, D. Dyes Pigments 2003, 58, 1. (b) Matsui, M.; Suzuki, M.;
Mizuno, K.; Funabiki, K.; Okada, S.; Kobayashi, T.; Kadowaki, M. Liq.
Cryst. 2004, 31, 1463. (c) Pucci, D.; Tirelli, N.; Ruggeri, G.; Ciardelli,
F. Macromol. Chem. Phys. 2005, 206, 102. (d) Zhang, X.-L.;
Yamaguchi, R.; Moriyama, K.; Kadowaki, M.; Kobayashi, T.; Ishi-i,
T.; Thiemann, T.; Mataka, S. J. Mater. Chem. 2006, 16, 736. (e) Chen,
Z.-H.; Swager, T. M. Org. Lett. 2007, 9, 997.
(34) Hoogervorst, W. J.; Elsevier, C. J.; Lutz, M.; Spek, A. L.
Organometallics 2001, 20, 4437.
(35) (a) Grove, D. M.; van Koten, G.; Louwen, J. N.; Noltes, J. G.;
Spek, A. L.; Ubbels, H. J. C. J. Am. Chem. Soc. 1982, 104, 6609.
(b) Terheijden, J.; van Koten, G.; Muller, F.; Grove, D. M.; Vrieze, K.
J. Organomet. Chem. 1986, 315, 401.
(36) Yin, B.; Niemeyer, F.; Williams, J. A. G.; Jiang, J.; Boucekkine,
A.; Toupet, L.; Le Bozec, H.; Guerchais, V. Inorg. Chem. 2006, 45,
8584.
(37) (a) Wrighton, M.; Morse, D. L. J. Am. Chem. Soc. 1974, 96, 998.
(b) Schanze, K. S.; Lucia, L. A.; Cooper, M.; Walters, K. A.; Ji, H.-F.;
Sabina, O. J. Phys. Chem. A 1998, 102, 5577. (c) Yam, V. W.-W.; Yang,
Y.; Zhang, J.-X.; Chu, B. W.-K.; Zhu, N.-Y. Organometallics 2001, 20,
4911. (d) Polo, A. S.; Itokazu, M. K.; Frin, K. M.; de Toledo
Patrocínio, A. O.; Iha, N. Y. M. Coord. Chem. Rev. 2006, 250, 1669.
(38) (a) Craig, C. A.; Garces, F. O.; Watts, R. J.; Palmans, R.; Frank,
A. J. Coord. Chem. Rev. 1990, 97, 193. (b) Jolliet, P.; Gianini, M.; von
Zelewsky, A.; Bernardinelli, G.; Stoeckli-Evans, H. Inorg. Chem. 1996,
35, 4883. (c) Balashev, K. P.; Puzyk, M. V.; Kotlyar, V. S.; Kulikova, M.
V. Coord. Chem. Rev. 1997, 159, 109. (d) Lai, S.-W.; Chan, M. C.-W.;
Cheung, T.-C.; Peng, S.-M.; Che, C.-M. Inorg. Chem. 1999, 38, 4046.
(39) Batema, G. D.; Lutz, M.; Spek, A. L.; van Walree, C. A.; de
(12) (a) Yang, C. Y.; Srdanov, V.; Robinson, M. R.; Bazan, G. C.;
Heeger, A. J. Adv. Mater. 2002, 14, 980. (b) Galyametdinov, Y. G.;
Knyazev, A. A.; Dzhabarov, V. I.; Cardinaels, T.; Driesen, K.; Gorller-
̈
Walrand, C.; Binnemans, K. Adv. Mater. 2008, 20, 252. (c) Yan, D.-P.;
Lu, J.; Wei, M.; Ma, J.; Evans, D. G.; Duan, X. Chem. Commun. 2009,
6358. (d) Wang, Y.-F.; Liu, Y.; Luo, J.; Qi, H.-R.; Li, X.-S.; Nin, M.-J.;
Liu, M.; Shi, D.-Y.; Zhu, W.-G.; Cao, Y. Dalton Trans. 2011, 40, 5046.
(e) Wang, Y.-F.; Chen, Q.; Li, Y.-H; Liu, Y.; Tan, H.; Yu, J.-T.; Zhu,
M.-X.; Wu, H.-B.; Zhu, W.-G.; Cao, Y. J. Phys. Chem. C 2012, 116,
5908.
(13) Lee, J.-B.; Lee, H.-K.; Park, J.-C.; Kim, Y.-B. Mol. Cryst. Liq.
Cryst. 2005, 439, 161.
(14) SAINT (Version 6.45); Bruker AXS Inc., Madison, WI, 2003.
(15) SADABS (Version 2.10); Bruker AXS Inc., Madison, WI, 2003.
(16) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(17) Sheldrick, G. M. SHELXL 97, Program for Crystal Structure
Mello Donega,
́
C.; Meijerink, A.; Havenith, R. W. A.; Per
́
ez-Moreno,
Analysis (Release 97-2); University of Gottingen, Gottingen, Germany,
̈
̈
J.; Clays, K.; Buchel, M.; van Dijken, A.; Bryce, D. L.; van Klink, G. P.
M.; van Koten, G. Organometallics 2008, 27, 1690.
̈
1997.
(18) SHELXTL (Version 6.10), Bruker AXS Inc., Madison, WI, 2000.
(19) Eastman, J. W. Photochem. Photobiol. 1967, 6, 55.
(40) (a) Beale, R. N.; Roe, E. M. F. J. Chem. Soc. 1953, 2755.
́
(b) Beveridge, D. L.; Jaffe, H. H. J. Am. Chem. Soc. 1965, 87, 5340.
(41) Lepeltier, M.; Le Bozec, H.; Guerchais, V.; Lee, T. K.-M.; Lo, K.
K.-W. Organometallics 2005, 24, 6069.
(42) Yam, V. W.-W.; Lau, V. C.-Y.; Wu, L.-X. J. Chem. Soc., Dalton
Trans. 1998, 1461.
(43) Hoogervorst, W. J.; Koster, A. L.; Lutz, M.; Spek, A. L.; Elsevier,
C. J. Organometallics 2004, 23, 1161.
(44) (a) Albrecht, M.; Lutz, M.; Schreurs, A. M. M.; Lutz, E. T. H.;
(20) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, V. G.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Spek, A. L.; van Koten, G. J. Chem. Soc., Dalton Trans. 2000, 3797.
(b) Kocher, S.; Lutz, M.; Spek, A. L.; Prasad, R.; van Klink, G. P. M.;
̈
van Koten, G.; Lang, H. Inorg. Chim. Acta 2006, 359, 4454.
5319
dx.doi.org/10.1021/om3003152 | Organometallics 2012, 31, 5307−5320

Organometallics
Article
́
(45) Cardenas, D. J.; Echavarren, A. M.; Ramírez de Arellano, M. C.
Organometallics 1999, 18, 3337.
(46) For reviews see: (a) Thomas, T. W.; Underhill, A. E. Chem. Soc.
Rev. 1972, 1, 99. (b) Extended Linear Chain Compounds; Miller, J. S.,
Ed.; Plenum Press: New York, 1982; Vols. 1−3. (c) Houlding, V. H.;
Miskowski, V. M. Coord. Chem. Rev. 1991, 111, 145. (d) Anderson, B.
M.; Hurst, S. K. Eur. J. Inorg. Chem. 2009, 3041.
(47) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(48) (a) Chassot, L.; Muller, E.; von Zelewsky, A. Inorg. Chem. 1984,
̈
23, 4249. (b) Palmans, R.; MacQueen, D. B.; Pierpont, C. G.; Frank,
A. J. J. Am. Chem. Soc. 1996, 118, 12647.
(49) (a) Osborn, R. S.; Rogers, D. J. Chem. Soc., Dalton Trans. 1974,
1002. (b) Connick, W. B.; Henling, L. M.; Marsh, R. E.; Gray, H. B.
Inorg. Chem. 1996, 35, 6261. (c) Connick, W. B.; Schaefer, W. P.;
Marsh, R. E.; Gray, H. B. Inorg. Chem. 1997, 36, 913.
(50) Herber, R. H.; Croft, M.; Coyer, M. J.; Bilash, B.; Sahiner, A.
Inorg. Chem. 1994, 33, 2422.
(51) (a) Galli, S.; Mercandelli, P.; Sironi, A. J. Am. Chem. Soc. 1999,
121, 3767. (b) Harada, J.; Ogawa, K. J. Am. Chem. Soc. 2001, 123,
10884. (c) Harada, J.; Ogawa, K. J. Am. Chem. Soc. 2004, 126, 3539.
(d) Harada, J.; Ogawa, K. Chem. Soc. Rev. 2009, 38, 2244.
(52) (a) Yersin, H.; Donges, D. Top. Curr. Chem. 2001, 214, 81.
(b) Yersin, H. Top. Curr. Chem. 2004, 241, 1. (c) Rausch, A. F.;
Homeier, H. H. H.; Yersin, H. Top. Organomet. Chem. 2010, 29, 193.
5320
dx.doi.org/10.1021/om3003152 | Organometallics 2012, 31, 5307−5320