Impact of constitutional isomers of (BMes2)phenylpyridine on structure, stability, phosphorescence, and lewis acidity of mononuclear and dinuclear Pt(II) complexes

Article abstract of DOI:10.1021/ic9007069

The impact of two constitutional isomers, 2-(4-BMes₂-Ph)- pyridine (p-B-ppy, 1) and 5-BMes₂-2-ph-pyridine (p-ppy-B, 2), as N, C-chelate ligands on the structures, stabilities, electronic and photophysical properties, and Lewis acidit

Full text of DOI:10.1021/ic9007069

7698 Inorg. Chem. 2009, 48, 7698–7713
DOI: 10.1021/ic9007069
Impact of Constitutional Isomers of (BMes2)phenylpyridine on Structure, Stability,
Phosphorescence, and Lewis Acidity of Mononuclear and Dinuclear Pt(II) Complexes
Ying-Li Rao and Suning Wang*
Department of Chemistry, Queen’s University, Kingston, Ontario, K7L 3N6, Canada
Received April 10, 2009
The impact of two constitutional isomers, 2-(4-BMes2-Ph)-pyridine (p-B-ppy, 1) and 5-BMes2-2-ph-pyridine (p-ppy-B,
2), as N,C-chelate ligands on the structures, stabilities, electronic and photophysical properties, and Lewis acidities of
Pt(II) complexes has been investigated. Six Pt(II) complexes, Pt(p-B-ppy)Ph(DMSO) (1a), Pt(p-B-ppy)Ph(py) (1b),
[Pt(p-B-ppy)Ph]2(4,40-bipy) (1c), Pt(p-ppy-B)Ph(DMSO) (2a), Pt(p-ppy-B)Ph(py) (2b), and [Pt(p-ppy-B)Ph]2(4,40-
bipy) (2c), have been synthesized and fully characterized. The structures of 1a, 1c, 2a, and 2c were established by
single-crystal X-ray diffraction analysis. All complexes adopt a cis geometry with the phenyl ligand being cis to the
phenyl ring of the ppy chelate. The dinuclear complexes 2a and 2c were found to exist in two isomeric forms in solution,
syn and anti, with respect to the relative orientation of the two BMes2 groups in the molecule. While all complexes are
stable in solution under ambient air, compound 2a was found to react with H2O slowly in solution and form complex
2a-OH, where one of the mesityl groups on the boron center was replaced by an OH group. This instability of 2a is
attributed to an internal dimethylsulfoxide-directed hydrolysis process via hydrogen bonds. The electron-accepting
ability of the free ligands and the complexes were examined by cyclic voltammetry, establishing that, for p-ppy-B, Pt(II)
chelation enhances the electron-accepting ability while, for p-B-ppy, Pt(II) chelation has little impact. All Pt(II)
complexes display oxygen-sensitive phosphorescence in solution at ambient temperature, dominated by B-ppy or ppy-
B centered π f π* transitions. The Lewis acidity of the complexes was examined by fluoride titration experiments
using UV-vis, phosphorescence, and NMR spectroscopic methods, establishing that the p-ppy-B complexes have
similar and strong binding constants while the p-B-ppy complexes have a much lower affinity toward F-, compared to
the free ligands. In the dinuclear complexes, weak electronic communication between the two Pt(II) units is evident in
1c but absent in 2c, attributable to the different steric interactions in the two molecules.
Introduction
and phosphorescent sensors for fluoride and cyanide ions;
and so forth.5,6 The synergic effect of metal-to-ligand charge
transfer (MLCT) and π(aryl)-B charge transfer has been
found to be responsible for many of the interesting properties
of the metal-containing triarylboron complexes. On the basis
of the binding modes, the majority of metal-containing
triarylboron compounds reported to date belong to two
categories: π complexes and σ complexes. The former has a
metal center bound to a π donor such as a cyclopentadienyl
Conjugated triarylboron compounds are known to display
unique photophysical and photochemical properties that
have enabled their various applications, such as their use in
emissive layers and charge-transport materials in organic
light-emitting diodes (OLEDs),1 nonlinear optics,2 and anion
sensors,3,4 which can be attributed mostly to the pπ-to-π*
conjugation through the vacant p orbital on the boron center.
It has been reported recently that inclusion of a metal ion in
the triarylboron compounds can lead to ambient temperature
phosphorescence; high Lewis acidity; visual, electrochemical,
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*To whom correspondence should be addressed. E-mail: wangs@chem.
queensu.ca.
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r
pubs.acs.org/IC
Published on Web 07/21/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7699
anion that is functionalized by a triarylboron center,6 while
the latter contains a metal ion that is bound to a σ donor such
as 2,20-bipy with a conjugated triarylboron group.5 Among
the σ complexes, in addition to N,N-chelate ligands,1e,5a-c
N,C-chelate complexes based on phenylpyridine (ppy)5d-f
or N-(2-py)-7-azaindole (NPA)5g functionalized by a BMes2
(Mes = mesityl) group have been reported. The ppy chelate
chromophore and its derivatives are most effective in produ-
cing highly emissive Ir(III) phosphorescent compounds.5d-f
Several Ir(III) complexes based on BMes2-functionalized ppy
(p-B-ppy, m-B-ppy) and the closely related 2-(p-BMes2-
phenyl)-quinoline (p-B-pq) molecule (Chart 1) have been
reported recently and used successfully either as a phosphor-
escent emitter in OLEDs or as a sensor for fluoride ions.5d-f
Notably, these previously reported ppy derivatives all have
the BMes2 group at the phenyl ring, instead of the pyridyl or
quinoline ring, perhaps due to the relatively easy functiona-
lization of the phenyl ring, compared to the pyridyl or
quinoline ring. We have reported recently that the direct
attachment of a BMes2 group to a pyridyl ring (e.g., 2,2-bipy)
can greatly enhance its Lewis acidity.5b,c Hence, the B-ppy
constitutional isomers with a BMes2 group attached on the
pyridyl ring, such as p-ppy-B shown in Chart 1, are worthy
candidates for investigation. On the basis of this considera-
tion, we have synthesized p-ppy-B and compared its proper-
ties to those of p-B-ppy. To examine the impact of the isomers
of p-B-ppy and p-ppy-B on the properties of the metal
complexes, we also synthesized a series of N,C-chelate Pt(II)
complexes based on these two ligands.
Chart 1
Pt(II) complexes are chosen because of their many poten-
tial applications such as vapochromic materials,7 photoche-
mical materials that convert light to chemical energy,8 and
emissive dopants in OLEDs.9 Unlike N,N-chelate Pt(II)
complexes of polypyridine ligands10 that display phosphor-
3
escence dominated by MLCT transition mixed with LC
(ligand-centered) transitions, N,C-chelate Pt(II) complexes
based on ppy and derivative ligands are known to display
mostly LC phosphorescence.9a Thus, the inclusion of the
3
BMes2 group on the ppy ligand would allow the direct
observation of its impact on MLCT transitions and the
possible enhancement of MLCT phosphorescence. To facil-
itate our investigation, Pt(II) complexes with different ancil-
lary ligands such as DMSO and pyridine were prepared and
examined. In addition, to examine the impact of the p-B-ppy
and p-ppy-B ligands on possible electronic communication
between two boron centers via a conjugated Pt2 unit, di-
nuclear Pt(II) complexes with 4,4-bipyridine as the bridging/
ancillary ligand were also prepared and investigated. The
anion binding ability of the new Pt(II) complexes was studied
through UV-vis, phosphorescence, and NMR spectroscopic
methods. The results of this comprehensive study are re-
ported herein.
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Experimental Section
All reactions were performed under N2 with standard
Schlenk techniques unless otherwise noted. All starting ma-
terials were purchased from Aldrich Chemical Company and
used without further purification. DMF, THF, Et2O, and
hexanes were purified using an Innovation Technology Com-
pany solvent purificationsystem. CH2Cl2 was freshlydistilled
over P2O5 prior to use. NMR spectra were recorded
on Bruker Avance 400 or 500 MHz spectrometers. High-
resolution mass spectra were obtained from a Waters/Micro-
massGC-TOF EI-MS spectrometer. Cyclicvoltammetrywas
performed using a BAS CV-50W analyzer with a scan rate of
100 mV/s to 1 V/s and a typical concentration of ∼0.003 M in
DMF using 0.10 M tetrabutylammonium hexafluoropho-
sphate (TBAP) as the supporting electrolyte. A conventional
three-compartment electrolyticcellconsistingofa Ptworking
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L. N.; Rheingold, A. L.; Jakle, F. J. Am. Chem. Soc. 2006, 128, 16554. (b)
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Parab, K.; Venkatasubbaiah, K.; Jakle, F. J. Am. Chem. Soc. 2006, 128, 12879.
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Chem.;Eur. J. 2007, 13, 5713. (f) Zhao, S. B.; Wucher, P.; Hudson, Z. M.;
McCormick, T. M.; Liu, X. Y.; Wang, S.; Feng, X. D.; Lu, Z. H. Organometallics
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2008, 27, 6446. (g) Zhou, G.; Baumgarten, M.; Mullen, K. J. Am. Chem. Soc.
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10670. (b) Sun, Y.; Ross, N.; Zhao, S. B.; Huszarik, K.; Jia, W. L.; Wang, R. Y.;
Wang, S. J. Am. Chem. Soc. 2007, 129, 7510. (c) Sun, Y.; Wang, S. Inorg. Chem.
2009, 48, 3755. (d) Zhou, G. J.; Ho, C. L.; Wong, W. Y.; Wang, Q.; Ma, D. G.;
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499. (e) You, Y. M.; Park, S. Y. Adv. Mater. 2008, 20, 3820. (f) Zhao, Q.; Li, F. Y.;
Liu, S. J.; Yu, M. X.; Liu, Z. Q.; Yi, T.; Huang, C. H. Inorg. Chem. 2008, 47, 9256.
(g) Zhao, S. B.; McCormick, T.; Wang, S. Inorg. Chem. 2007, 46, 10965.
(h) Hudson, Z. M.; Zhao, S. B.; Wang, S. Chem.;Eur. J. 2009, in press.
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Cummings, S. D.; Eisenberg, R. Coord. Chem. Rev. 2000, 208, 115. (b)
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4510.
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Bau, R.; Tompson, M. E. Inorg. Chem. 2002, 41, 3055. (b) Adamovich, V.;
Brooks, J.; Tamayo, A.; Alexander, A. M.; Djurovich, P. I.; D'Andrade, B. W.;
Adachi, C.; Forrest, S. R.; Tompson, M. E. New J. Chem. 2002, 26, 1171. (c) Lu,
W.; Mi, B. X.; Chan, M. C. W.; Hui, Z.; Che, C. M.; Zhu, N.; Lee, S. T. J. Am.
Chem. Soc. 2004, 126, 4958.
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R. H.; Jakle, F. Chem. Commun. 2007, 2154. (b) Venkatasubbaiah, K.;
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Pakkirisamy, T.; Lalancette, R. A.; Jakle, F. Dalton Trans. 2008, 4507. (c)
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7700 Inorganic Chemistry, Vol. 48, No. 16, 2009
Rao and Wang
electrode, a Pt auxiliary electrode, and a Ag/AgCl reference
electrode was employed using the ferrocene/ferrocenium
couple as the standard (E1/2 = 0.55 V in DMF). UV-vis
spectra were recorded on an Ocean Optics UV-visible spec-
trometer. Excitation and emission spectra were recorded on
a Photon Technologies International QuantaMaster model
C-60 spectrometer. Emission lifetimes were measured on a
Photon Technologies International Phosphorimeter (Time-
Master C-631F) equipped with a xenonflash lampand digital
emission photon multiplier tube using a band pathway of
5 nm for excitation and 2 nm for emission. [PtPh2(DMSO)2]
was synthesized according to a previous report.11
ether at -78 °C in the same manner as for the synthesis of 1.
Purification of the crude product by column chromatography
(CH2Cl2/hexane, 1:1) afforded 2 as a white solid in 46% yield.
1H NMR (400 MHz, CDCl3, 25 °C, δ, ppm): 8.75 (s, 1H),
8.12 (d, J=7.2 Hz; 2H), 7.84 (dd, J=8.0 Hz, J=1.6 Hz; 1H), 7.75
(d; J=8.0 Hz; 1H), 7.48 (m; 3H), 6.86 (s; 4H), 2.33 (s, 6H), 2.06
(s, 12H). 13C{1H}NMR (100 MHz, CDCl3, δ, ppm): 159.81,
157.51, 144.79, 141.06, 139.46, 139.25, 129.90, 129.10, 128.70,
127.50, 120.07, 116.91, 23.85, 21.53. HRMS calcd for C29H31BN
[M]þ: m/z 404.2549. Found: 404.2552.
Synthesis of Pt(p-B-ppy)Ph(DMSO), 1a. To a stirred THF
(20 mL) solution of [PtPh2(DMSO)2] (96 mg, 0.19 mmol) was
added p-B-ppy (80 mg, 0.20 mmol). The mixture was stirred at
50 °C for 6 h, and the solvent was removed under reduced
pressure. Yellow needle crystals of 1a were obtained from
hexane/CH2Cl2 (65% yield). 1H NMR (500 MHz, CD2Cl2,
25 °C, δ, ppm): 8.69 (d, J=5.5 Hz; 1H, py), 7.94 (m; 2H, py),
7.60 (d, J=7.5 Hz; 1H, py), 7.28 (m; 4H, Ph), 6.75 (m; 8H), 2.91
(s; 6H, Me-DMSO), 2.34 (s, 6H, p-Me-Mes), 1.93 (s, 12H, o-Me-
Mes). 13C{1H}NMR (100 MHz, CD2Cl2, δ, ppm): 165.16,
151.94, 151.85, 149.44, 146.62, 144.47, 140.56, 139.02, 138.34,
137.31, 133.22, 128.32, 128.08, 123.54, 122.82, 122.62, 119.87,
44.16, 23.43, 21.32. Anal. Calcd for C37H40BNOPtS: C, 59.04;
H, 5.36; N, 1.86. Found: C, 59.15; H, 5.43; N, 1.92.
Synthesis of 2-(4-Bromophenyl)-Pyridine. 2-(4-Bromophenyl)-
pyridine is a previously known compound.12 The procedure
described here for this molecule is different from the previously
reported one. To a stirred THF (30 mL) solution of 1 4-dibromo-
bezene (4 g, 16.9 mol) at -78 °C was added dropwise an n-BuLi
solution (1.6 M; 11.6 mL, 18.6 mol) over 2 min. The resulting
solution with white precipitates was stirred for 1 h at -78 °C, and
a B(OMe)3 solution (30 mmol, 3.3 mL) was then added. After
stirring at -78 °C for 1 h, the resulting transparent solution was
warmed to ambient temperature and stirred overnight. A satu-
rated NH4Cl solution (20 mL) was added. After extraction of the
aqueous layer with Et2O (2 ꢀ 30 mL), the organic layer was dried
with Na2SO4. After removal of the solvent, the residual
4-bromo-phenylboronic acid was used in next step without further
purification. A mixture of toluene (60 mL), ethanol (20 mL), and
water (20 mL) was stirred and purged by nitrogen for 1 h.
2-Bromopyridine (1.58 g, 10 mmol), 4-bromophenylboronic
acid (2.00 g, 10 mmol), Pd(PPh3)4 (0.31 g, 0.25 mmol), and
NaOH (2.5 g, 62.5 mmol) were added to the mixed solvents. The
mixture was stirred at room temperature for 2 days. The aqueous
layer was separated and extracted with CH2Cl2 (3 ꢀ 30 mL). The
combined organic layers were dried over Na2SO4, and the
solvents were evaporated under reduced pressure. Purification
of the crude product by column chromatography (CH2Cl2/
hexane, 1:1) afforded the product 2-(4-bromophenyl)-pyridine
as a white solid in 51% yield (0.68 g).
Synthesis of Pt(p-ppy-B)Ph(DMSO), 2a. To a stirred THF
(20 mL) solution of [PtPh2(DMSO)2] (96 mg, 0.19 mmol) was
added 5-BMes2-2-ph-py (80 mg, 0.20 mmol). The mixture was
stirred at 50 °C for 6 h, and the solvent was removed under
reduced pressure. Bright yellow needle crystals of 2a were
obtained from hexane/CH2Cl2 (60% yield) under nitrogen. 1H
NMR (500 MHz, CD2Cl2, 25 °C, δ, ppm): 9.57 (s; 1H, py), 7.94
(d, J = 8.0 Hz; 1H, py), 7.86 (d, J = 8.0 Hz; 1H, py), 7.71 (d, J =
7.5 Hz; 1H, py-Ph), 7.48 (d, satellite, J=8.0 Hz, JPt-H=66.0 Hz;
2H, o-ph), 7.09 (m; 3H, py-Ph), 7.01 (m; 2H, Ph), 6.90 (s; 4H,
Mes), 6.68 (d, satellite, J=7.5 Hz, JPt-H =65.0 Hz; 1H, Ph), 2.72
(s; 6H, Me-DMSO), 2.35 (s; 6H, o-Me-Mes), 2.10 (s, 12 H, p-Me-
Mes). 13C{1H}NMR (100 MHz, CD2Cl2, δ, ppm): 167.63,
159.15, 154.10, 146.34, 146.23, 146.06, 144.21, 139.83, 138.00,
137.84, 130.49, 128.77, 128.36, 125.24, 124.39, 123.19, 118.82,
44.07, 23.78, 21.37. Anal. Calcd for C37H40BNOPtS: C, 59.04;
H, 5.36; N, 1.86. Found: C, 59.44; H, 5.83; N, 1.81. The hexane
solvent molecule was removed by drying the sample under a
vacuum.
Synthesis of 2-(4-BMes2-Ph)-Pyridine (p-B-ppy, 1). To a
stirred THF solution of 2-(4-bromophenyl)-pyridine (0.60 g,
2.3 mmol) at -78 °C was added dropwise an n-BuLi solution
(1.60 M; 1.5 mL, 2.4 mmol) over 2 min. The resulting bright
yellow solution was stirred for 1 h at -78 °C; a solution of
dimesitylboron fluoride (0.75 g, 90%, 2.5 mmol) in Et2O was
then quickly added. The reaction mixture was kept at -78 °C
for another 1 h and allowed to reach ambient temperature. After
being stirred overnight and removal of the solvent, purification
of the crude product by column chromatography (CH2Cl2/
hexane, 2:1) afforded 1 as a white solid in 81% yield. 1H
NMR (400 MHz, CDCl3, 25 °C, δ, ppm): 8.73 (d, J=6.0 Hz;
1H), 8.99 (d, J = 8.0 Hz; 2H), 7.78 (m; 3H), 7.65 (d; J=8.4 Hz;
2H), 7.26 (dd; 1H), 6.85 (s; 4H), 2.34 (s, 6H), 2.05 (s, 12H).
13C{1H}NMR (100 MHz, CDCl3, δ, ppm): 157.53, 150.12,
146.78, 142.67, 142.06, 141.19, 139.05, 137.11, 137.05, 128.52,
126.73, 122.78, 121.32, 23.78, 21.55. HRMS calcd for C29H31BN
[M]þ: m/z 404.2549. Found: 404.2548.
Synthesis of PtPh[5-B(OH)(Mes)-2-Ph-py](DMSO), 2a-
OH. To a THF solution (10 mL) of 2a (20 mg, 0.027 mmol)
was added 5 mL of toluene. The solution was kept under air, and
the solvent was allowed to slowly evaporate at ambient tem-
perature. Yellow crystals of 2a-OH were obtained and isolated
after ∼20 days in ∼70% yield. 1H NMR (400 MHz, DMSO-d6,
25 °C, δ, ppm): 10.67 (s, 1H, B-OH), 9.83 (s; 1H, py), 8.06 (d,
J = 8.0 Hz; 1H, py), 7.95 (d, J=8.0 Hz; 1H, py), 7.77 (d, J=7.5
Hz; 1H, ph), 7.38 (d, satellites, J = 7.5 Hz, JPt-H = 65.0 Hz; 2H,
ph), 7.01 (m; 3H, ph, Py-ph), 6.89(m, 2H, Py-ph), 6.83 (s, 2H,
Mes), 6.50 (d, satellites, J=8.0 Hz, JPt-H=45.0 Hz; 1H, Py-ph),
2.53 (s, 6H, Me-DMSO), 2.26 (s; 3H, o-Me-Mes), 2.13 (s, 6 H,
p-Me-Mes). Anal. Calcd for C28H30BO2NPtS: C, 51.70; H, 4.65;
N, 2.15. Found: C, 50.87; H, 4.47; N, 2.08. (The toluene solvent
molecules escaped from the crystal lattice at ambient tempera-
ture.)
Synthesis of 5-BMes2-2-ph-Pyridine (p-ppy-B, 2). 3-Bromo-2-
ph-pyridine is a previously known molecule.13 The synthetic
method we employed is different from the literature procedure,
namely, via Suzuki coupling of phenylboronic acid and 2,
5-dibromopyridine at ambient temperature in a similar manner
as described for the synthesis of 2-(4-bromophenyl)-pyridine.
5-BMes2-2-Ph-pyridine was obtained by adding dimesitylboron
fluoride after lithiation of 3-bromo-2-ph-pyridine in diethyl
Synthesis of Pt(p-B-ppy)Ph(py), 1b. To a CH2Cl2 (2 mL)
solution of 1a (20 mg, 0.027 mmol) was added pyridine (3 μL,
0.037 mmol). Yellow powders of 1b were obtained after several
hours of standing at ambient temperature (90% yield). 1H NMR
(500 MHz, CD2Cl2, 25 °C, δ, ppm): 8.86 (dd, J=7.2 Hz, J=1.6
Hz; 2H, py), 7.87 (m; 3H, py, py-Ph), 7.70 (d, J=5.2 Hz; 1H,
py-Ph), 7.56 (d; J = 8.0 Hz; 1H, B-Ph), 7.46 (td; J = 6.0 Hz, J =
1.2 Hz; 2H, py), 7.29 (s, satellites, JPt-H = 45.0 Hz; 1H, B-Ph),
7.25 (dd, satellites, J=8.0 Hz, J=1.2 Hz; 2H, ph), 7.14 (dd,
J=7.6 Hz, J=1.2 Hz; 1H, B-Ph), 7.08 (td, J=7.6 Hz, J=1.2 Hz;
(11) Klein, A.; Schurr, T.; Knodler, A.; Gudat, D.; Klinkhammer,
K. W. K.; Jain, V.; Zalis, S.; Kaim, W. Organometallics 2005, 17, 4125.
(12) Ono, K.; Joho, M. Eur. J. Inorg. Chem. 2006, 3676.
(13) Prokopcova, H.; Kappe, C. O. J. Org. Chem. 2007, 72, 4440.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7701
Table 1. Crystal Data for 1a, 2a, 1c, 2c, and 2a-OH
compound
formula
fw
1a
2a
1c
2c
2a-OH
C
37H40NBOSPt
C37H40NBOSPt/0.5C6H14
C40H38N2BPt/ C3H6O
C40H38N2BPt
752.62
orthorhombic
Cmca
31.937(5)
11.0495(16)
21.821(3)
90
C28H30NBO2 SPt/2C7H8
834.76
752.66
orthorhombic
P212121
8.8185(11)
20.861(3)
35.238(5)
90
795.75
monoclinic
P21/c
16.465(3)
9.3894(18)
24.111(5)
90
103.167(2)
90
3629.6(12)
4
1.456
180
3.954
52.00
33583
7141
415
810.70
monoclinic
P21/n
17.8308(7)
8.5324(3)
24.2444(9)
90
crystal system
space group
triclinic
P1
˚
a, A
11.5949(12)
13.1194(17)
13.8204(14)
110.618(8)
102.690(7)
97.594(8)
1868.4(4)
2
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
90
90
105.149(2)
90
90
90
3
˚
V, A
Z
6482.5(14)
8
1.542
3560.4(2)
4
1.512
180
3.977
54.40
32681
7881
441
7700(2)
8
1.298
Dcalcd, g cm-3
T, K
1.484
180
3.847
54.60
14080
14080
421
180
4.423
54.36
72570
14278
774
180
3.670
54.34
μ, mm-1
2θmax, deg
reflns measured
reflns used
parameters
R [I > 2σ(I)]
36437
4358
289
a
R1
wR2
0.0448
0.0758
0.0388
0.0845
0.0566
0.0870
0.0729
0.1472
0.0552
0.1276
b
R (all data)
R1
wR2
GOF on F2
a
0.0676
0.0828
1.070
0.0537
0.0911
1.050
0.1525
0.1125
0.962
0.2651
0.2201
0.946
0.0848
0.1445
1.023
b
P
P
P
P
a R1 = |Fo| - |Fc|/ |Fo|. b wR2 = [ w[(Fo2 - Fc2)2]/ [w(Fo2)2]]1/2, w = 1/[σ2(Fo2) þ (0.075P)2], where P = [max(Fo2,0) þ 2Fc2]/3.
1H, B-Ph), 6.78 (s; 4H, H-Mes), 6.63 (m; 3H, Ph), 2.32 (s; 6H,
p-Me-Mes), 2.00 (s; 12H, o-Me-Mes). Anal. Calcd. for C40-
H39BN2Pt: C, 63.75; H, 5.22; N, 3.72. Found: C, 64.19; H, 5.01;
N, 3.62.
Synthesis of [Pt(p-ppy-B)Ph]2(4,40-bipy), 2c. To a CH2Cl2
solution (10 mL) of 2a (20 mg, 0.027 mmol) was slowly added
4,40-bipyridine (2.0 mg, 0.013 mmol) in CH2Cl2 (2 mL). A total
of 5 mL of hexane was layered on top. The mixture was kept
standing at ambient temperature. Yellow needle crystals of
Synthesis of Pt(p-ppy-B)Ph(py), 2b. To a CH2Cl2 (2 mL)
solution of 2a (20 mg, 0.027 mmol) was added pyridine (3 μL,
0.037 mmol). The mixture was kept standing for several hours.
After the removal of solvent and washing with hexanes, the
yellow powder of 2b was obtained in 90% yield. 1H NMR (500
MHz, CD2Cl2, 25 °C, δ, ppm): 8.68 (dd, J=7.5 Hz, J=1.5 Hz;
2H, py), 7.91 (dd, J=8.0 Hz, J=1.5 Hz; 1H, py-B), 7.84 (d,
J=8.0 Hz; 1H, py-B), 7.67 (d; J = 8.0 Hz; 1H, Ph-py), 7.58 (t,
J=8.0 Hz; 1H, py), 7.53 (s; 1H, py-B), 7.50 (dd, satellites, J=
8.0 Hz, J=1.0 Hz, JPt-H=65.0 Hz; 2H, Ph), 7.16 (t, J=8.0 Hz;
2H, py), 7.09 (td, J = 8.0 Hz, J = 1.0 Hz; 1H, Ph-py), 7.05 (dd,
J=8.0 Hz, J=1.5 Hz; 1H, Ph-py), 7.01 (m; 1H, Ph-py), 6.95 (t,
J=7.5 Hz; 2H, Ph), 6.86 (t, J = 7.5 Hz; 1H, Ph), 6.81 (s; 4H, H-
Mes), 2.35 (s; 6, p-Me-Mes), 1.99 (s; 12H, o-Me-Mes). 13C-
{1H}NMR (100 MHz, CD2Cl2, δ, ppm): 154.74, 151.07, 140.74,
139.38, 138.08, 136.88, 128.62, 127.04, 126.03, 124.64, 122.92,
121.94, 120.91, 119.00, 118.41, 23.47, 21.24. Anal. Calcd for
1
2c were obtained overnight (85% yield). H NMR (500 MHz,
CD2Cl2, 25 °C, δ, ppm): 8.86 (d, J=6.5 Hz; 2H, py), 7.92 (dd,
J=8.0 Hz, J=1.5 Hz; 1H, py-B), 7.87 (d, J=8.0 Hz; 1H, py-
B), 7.80 (s; 1H, py-B), 7.70 (d, J = 7.5 Hz; 1H, Ph-py), 7.52
(d, satellites, J=7.0 Hz, JPt-H=65.0 Hz; 2H, Ph), 7.28 (d, J=
6.5 Hz; 2H, py), 7.17 (d, satellites, J=7.5 Hz, JPt-H=42.0 Hz;
1H, Ph-py), 7.05 (m; 2H, 4, 5-Ph-py), 6.99 (t, J=7.5 Hz; 2H, Ph),
6.87 (t, J=7.5 Hz; 1H, Ph), 6.69 (s, 4H, H-Mes), 1.98 (s, 6H,
p-Me-Mes), 1.96 (s, 12H, o-Me-Mes). Anal. Calcd for C80-
H76B2N4Pt2 1/3CH2Cl2: C, 62.92; H, 5.04; N, 3.65. Found: C,
62.84; H, 5.27; N, 3.45.
3
X-Ray Diffraction Analysis. Single crystals of p-ppy-B (2) and
complexes 1a, 2a, 1c, 2c, and 2a-OH were mounted on glass
fibers for data collection. Data were collected on a Bruker Apex
II single-crystal X-ray diffractometer with graphite-monochro-
mated Mo KR radiation, operating at 50 kV and 30 mA and at
180 K. Data were processed on a PC with the aid of the Bruker
SHELXTL software package (version 5.10)14 and corrected for
absorption effects. No significant decay was observed in all
crystals except 2c. The crystals of 2c lose solvent rapidly when
removed from solution. Attempts were made to seal the crystal
along with the mother liquor in a capillary, but without success.
The best data set collected for 2c was obtained by mounting a
fresh crystal quickly to a glass fiber cooled to 180 K on the
goniometer head. A substantial loss of solvent molecules from
the crystal lattice was still evident, which is responsible for the
poor quality of the data collected for 2c and the low diffraction
intensity (only about 30% reflections have intensity greater than
2σ). None of the solvent molecules in the crystal lattice of 2c
could be located and modeled. Nonetheless, the key structural
features of molecule 2c were established. All structures were
solved by direct methods. Compound 2a contains 0.5 hexane per
C40H39BN2Pt DMSO: C, 60.65; H, 5.45; N, 3.37. Found: C,
3
60.82; H, 5.62; N, 3.28.
Synthesis of [Pt(p-B-ppy)Ph]2(4,40-bipy), 1c. To an acetone
solution (20 mL) of 1a (20 mg, 0.027 mmol) was slowly added
4,40-bipyridine (2.0 mg, 0.013 mmol) in acetone (2 mL). The
mixture was kept standing at ambient temperature, and the
solution was allowed to evaporate slowly. Orange crystals of 1c
were obtained after two days (90% yield). 1H NMR (500 MHz,
CD2Cl2, 25 °C, δ, ppm): 9.03 (d, J=5.0 Hz; 2H, py), 7.92 (m,
2H, 5, py-Ph), 7.77 (d, J=5.0 Hz; 1H, py-Ph), 7.72 (dd, J=
5.0 Hz, J = 1.5 Hz; 2H, py), 7.59 (d, J = 8.0 Hz; 1H, B-Ph), 7.29
(m, satellites; 3H, ph, B-Ph), 7.17 (dd, J=8.0 Hz, J=1.0 Hz; 1H,
B-Ph), 7.11 (td, J=7.0 Hz, J = 1.5 Hz; 1H, py-Ph), 6.80 (s, 4H,
H-Mes), 6.70 (t, J=7.5 Hz, 2H, Ph), 6.64 (t, J=7.5 Hz; 1H, Ph),
2.34 (s, 6H, p-Me-Mes), 2.01 (s, 12H, o-Me-Mes). Anal. Calcd
for C80H76B2N4Pt2: C, 63.83; H, 5.09; N, 3.72. Found: C, 63.21;
H, 5.24; N, 3.51. The acetone solvent molecules were removed
by drying the sample under a vacuum.
(14) SHELXTL, version 6.14; Bruker AXS: Madison, WI, 2003.

7702 Inorganic Chemistry, Vol. 48, No. 16, 2009
Rao and Wang
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for 1a, 2a, 1c, 2c, and 2a-OH
1a
2a-OH
Pt(1A)-C(12A)
2.008(8)
2.038(8)
2.120(6)
2.280(2)
2.013(7)
2.017(7)
2.136(6)
2.288(2)
92.2(3)
171.6(3)
79.4(3)
89.3(2)
175.3(2)
99.02(18)
90.1(3)
Pt(1)-C(12)
2.023(6)
2.051(6)
2.119(5)
2.2906(15)
1.331(9)
1.563(9)
1.585(9)
92.0(2)
Pt(1A)-C(1A)
Pt(1)-C(1)
Pt(1A)-N(1A)
Pt(1)-N(1)
Pt(1A)-S(1A)
Pt(1)-S(1)
Pt(1)-C(1)
B(1)-O(1)
Pt(1)-C(12)
B(1)-C(20)
Pt(1)-N(1)
B(1)-C(10)
Pt(1)-S(1)
C(12)-Pt(1)-C(1)
C(12)-Pt(1)-N(1)
C(1)-Pt(1)-N(1)
C(12)-Pt(1)-S(1)
C(1)-Pt(1)-S(1)
N(1)-Pt(1)-S(1)
O(1)-B(1)-C(20)
O(1)-B(1)-C(10)
C(20)-B(1)-C(10)
C(12A)-Pt(1A)-C(1A)
C(12A)-Pt(1A)-N(1A)
C(1A)-Pt(1A)-N(1A)
C(12A)-Pt(1A)-S(1A)
C(1A)-Pt(1A)-S(1A)
N(1A)-Pt(1A)-S(1A)
C(1)-Pt(1)-C(12)
C(1)-Pt(1)-N(1)
C(12)-Pt(1)-N(1)
C(1)-Pt(1)-S(1)
C(12)-Pt(1)-S(1)
N(1)-Pt(1)-S(1)
171.3(2)
79.7(2)
88.69(17)
177.78(16)
99.50(14)
124.0(5)
114.8(6)
121.2(6)
80.3(3)
170.3(3)
178.71(19)
90.1(2)
99.41(17)
2a
1c
Pt(1)-C(12)
2.010(5)
2.021(5)
2.121(4)
2.2888(14)
91.7(2)
171.22(19)
80.34(19)
88.79(16)
175.47(15)
99.48(12)
Pt(1)-C(1)
1.987(8)
1.997(9)
2.118(6)
2.124(7)
93.5(3)
177.7(3)
88.8(3)
80.3(3)
Pt(1)-C(1)
Pt(1)-C(12)
Pt(1)-N(1)
Pt(1)-S(1)
Pt(1)-N(2)
Pt(1)-N(1)
C(12)-Pt(1)-C(1)
C(12)-Pt(1)-N(1)
C(1)-Pt(1)-N(1)
C(12)-Pt(1)-S(1)
C(1)-Pt(1)-S(1)
N(1)-Pt(1)-S(1)
C(1)-Pt(1)-C(12)
C(1)-Pt(1)-N(2)
C(12)-Pt(1)-N(2)
C(1)-Pt(1)-N(1)
C(12)-Pt(1)-N(1)
N(2)-Pt(1)-N(1)
173.5(3)
97.4(3)
2c
Pt(1)-C(1)
Pt(1)-C(12)
Pt(1)-N(1)
Pt(1)-N(2)
N(1)-Pt(1)-C(1)
2.12(2)
1.993(18)
2.090(13)
1.990(19)
86.8(6)
N(2)-Pt(1)-C(12)
N(2)-Pt(1)-N(1)
C(12)-Pt(1)-N(1)
N(2)-Pt(1)-C(1)
C(12)-Pt(1)-C(1)
81.6(8)
96.9(7)
176.0(7)
171.2(10)
94.2(6)
complex in the lattice, while compounds 1c and 2a-OH contain
two acetone molecules and two toluene molecules per complex,
respectively, which were all modeled and refined successfully.
Most of the non-hydrogen atoms were refined anisotropically.
The positions of hydrogen atoms were calculated, and their
contributions in structural factor calculations were included.
For structure 2c, due to the sever disordering of the structure
and the lack of sufficient data, most of the carbon atoms were
refined isotropically. The crystal data of the complexes are given
in Table 1. Important bond lengths and angles for all of the
compounds are listed in Table 2. Data for p-ppy-B are provided
in the Supporting Information.
B)Ph(DMSO) (2a) were obtained readily by cyclometala-
tion reactions of PtPh2(DMSO)2 with ligands 1 and 2,
respectively, in THF at 50 °C. Because DMSO in 1a and
2a is a relatively weak donor, it can be replaced readily by
other donor ligands such as pyridine, leading to the
pyridine complexes Pt(p-B-ppy)Ph(py) (1b) and Pt(p-
ppy-B)Ph(py) (2b), respectively. Similarly, metal com-
plexes [Pt(p-B-ppy)]2(4,40-bipy) (1c) and [Pt(p-ppy-B)]2-
(4,40-bipy) (2c) were obtained by reacting 0.5 equiv of 4,40-
bipy with 1 equiv of 1a and 2a, respectively. The free
ligands and all Pt(II) complexes were fully characterized
by NMR, high-resolution mass spectrometry (HRMS),
or elemental analyses, and the structures of the metal
complexes are illustrated in Chart 2.
Results and Discussion
Syntheses. As shown in Scheme 1, the synthesis of p-B-
ppy (1) was achieved by Suzuki-Miyaura coupling of
4-bromophenylboronic acid with 2-bromopyridine, fol-
lowed by substitution of the bromo group with BMes2
in THF. This is a different procedure from the previously
reported one for compound 1 where Stille coupling
methods were used.5d Compound 2, p-ppy-B, was
achieved by Suzuki coupling of phenylboronic acid and
2,5-dibromopyridine, followed by substitution of the
bromo group with BMes2 in diethyl ether. The DMSO
complexes Pt(p-B-ppy)Ph(DMSO) (1a) and Pt(p-ppy-
Structures. The crystal structure of p-ppy-B was deter-
mined by single-crystal X-ray diffraction analysis and is
shown in Figure 1. The phenyl and the pyridyl planes are
off coplanarity by 23.6°. The structures of complexes 1a,
2a, 1c, and 2c were also established by single-crystal X-ray
diffraction analyses and are shown in Figures 2-5,
respectively.
1a, 2a, and 2a-OH. The crystal structures shown in
Figure 2 established unequivocally that the auxiliary
ligand DMSO in 1a and 2a is bound to the Pt(II) center
trans to the phenyl ring, not the pyridyl ring, of the ppy

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7703
Scheme 1
Reagents and conditions: a) 2-bromopyridine, Pd(PPh3)4, and NaOH, toluene, alcohol, and water (3:1:1), rt. 48 h; b) (i) n-BuLi, THF, -78 °C; (ii)
B(Mes)2F, -78 °C to rt, overnight; c) 2, 5-bromopyridine, Pd(PPh3)4, and NaOH, toluene, alcohol, and water (3:1:1), rt. 48 h; d) (i) n-BuLi, Et2O, -78 °C;
(ii) B(Mes)2F, -78 °C to rt, overnight.
Chart 2
Figure 1. The structure of p-ppy-B with 50% thermal ellipsoids.
In the asymmetric unit of 1a, there are two independent
molecules that form a stacked pair with a Pt-Pt separa-
tion distance of 4.906(1) A (see Supporting Information).
˚
The Pt-C, Pt-N, and Pt-S bond lengths and angles in
1a and 2a are similar. One common feature in
the structures of 1a and 2a is that the oxygen atom of
the DMSO ligand is oriented toward the ortho-H atom of
the pyridyl ring with the Co O and Ho O separation
chelate. NMR spectra confirmed that this cis isomer (the
two phenyl rings being cis to each other) is formed
exclusively for both 1a and 2a. This can be explained by
the well-established intramolecular C-H bond activation
mechanism on a Pt(II) center11 depicted for the formation
of complex 1a in Scheme 2. The greater trans effect
exerted by the phenyl ring of ppy in the five-coordinate
Pt(IV) intermediate leads to the regioselective reductive
elimination of the phenyl group trans to it along with
the H atom from the Pt(IV) center as a benzene molecule.
The subsequent DMSO coordination gives rise to
complex 1a. Similar regioselective cyclometalation reac-
tions involving a Pt(II) center have been observed pre-
viously.5h,15,16
3 3 3
3 3 3
˚
˚
distances being 2.98-3.04 A and 2.13-2.19 A, respec-
tively. The key difference between these two structures
is that in 1a the DMSO ligand is far away from the BMes2
group, while in 2a it is close to the BMes2 group. In fact,
the separation distance between O(1) and B(1) in 2a is
˚
˚
only 4.58(2) A, and that between O(1) and C(29) is 4.07 A.
There is also a notable difference in the stabilities of 1a
and 2a toward adventitious H2O molecules in solution.
Compound 1a is stable in solution under air for a long
period of time, while 2a undergoes slow decomposition
under air with nearly quantitative formation of a new
compound Pt[p-ppy-BMes(OH)]Ph(DMSO) (2a-OH),
which was fully characterized by NMR, elemental ana-
lysis, and single-crystal X-ray diffraction. The structure
of 2a-OH is shown in Figure 3.
(15) Zhao, S. B.; Wang, R. Y.; Wang, S. J. Am. Chem. Soc. 2007, 129,
3092.
(16) Yagyu, T.; Ohashi, J. I.; Maeda, M. Organometallics 2007, 26, 2383.
The Pt-ligand bond lengths and angles of 2a-OH are
similar to those of 1a and 2a. The B-O bond length of

7704 Inorganic Chemistry, Vol. 48, No. 16, 2009
Rao and Wang
Figure 2. The structures of 1a (left) and 2a (right) with 50% thermal ellipsoids and labeling schemes.
lysis process, as illustrated in Scheme 3. The greater Lewis
acidity and the close proximity to the DMSO ligand of the
BMes2 group in 2a, compared to that in 1a, are believed to
be responsible for the unusual decomposition of the ppy-
B ligand.
Interestingly, as shown in Figure 3, the molecule of
2a-OH forms a hydrogen-bond-linked dimer through
the DMSO oxygen atom and the hydroxo group in the
crystal lattice. Each of these dimers stacks with a neigh-
boring dimer with a Pt-Pt separation distance of 5.189-
˚
(1) A (see Supporting Information). Furthermore, com-
pound 2a-OH forms a highly porous crystal lattice that
hosts two toluene solvent molecules per complex
(Figure 3).
1c and 2c. As shown in Figures 4 and 5, complexes 1c
and 2c display a similar cis structure to those of 1a and 2a,
with the two pyridyl rings being cis to each other on the
same Pt(II) center. Hence, the replacement of the DMSO
ligand by 4,40-bipy does not alter the cis structure of the
complexes due to the strong trans effect of the phenyl
group. The N(1)-Pt(1)-C((12) (173.5(3)°) and N(2)-
Pt(1)-C(1) (177.7(3)°) angles in 1c are much less distorted
from linearity, compared to the corresponding S-Pt-C
bond angles in 1a and 2a. This may be attributed to the
greater steric interactions imposed by DMSO in 1a and
2a. The intramolecular Pt-Pt separation distance in 1c
˚
is 11.375(1) A, much longer than the shortest intermole-
˚
cular Pt-Pt distance, 8.532(1) A. The molecule of 1c
has a crystallographically imposed inversion center. The
two BMes2 groups have an anti configuration with a
˚
22.1 A separation distance between the two B atoms.
In solution, the syn configuration is also possible due
to the free rotation around the Pt-N (bipy) bond or
the C(20)-C(200) bond, which was in fact confirmed
Figure 3. Top: The hydrogen bonded dimer of 2a-OH. Bottom: Crys-
tal lattice packing diagram showing the toluene solvent molecules in the
lattice.
1
by variable-temperature H NMR that shows the pre-
sence of two isomers at ∼185 K (see Supporting In-
˚
1.331(9) A is much shorter than that of a typical B-O
formation).
˚
single bond (∼1.50-1.55 A, e.g., Ph2Bq, q = 8-hydroxy-
quinoline anion and derivatives),17 clearly supporting a
BdO double bond. When the water-free solution of 2a is
kept under nitrogen, 2a does not show any sign of
decomposition. Hence, we attributed the decomposition
of 2a to an internal DMSO-facilitated B-C bond hydro-
The molecule of 2c has a crystallographically imposed
inversion center and a mirror plane symmetry on which
the two Pt atoms and the entire bipy linker lie. As a
consequence of the mirror plane symmetry, the entire
molecule of 2c is disordered over the two sites related by
mirror plane reflection. Although we have been able to
model the disorder successfully, the quality of the struc-
ture data is poor due to both disordering and the poor
(17) Cui, Y.; Liu, Q. D.; Bai, D. R.; Jia, W. L.; Tao, Y.; Wang, S. Inorg.
Chem. 2005, 44, 601.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7705
Figure 4. The structure of 1c with 50% thermal ellipsoids and labeling schemes.
Figure 5. Left: The structure of2c with50% thermal ellipsoidsand labelingschemes. Hydrogenatomsareomitted. Right: A space-filling diagramshowing
the steric congestion in 2c.
Scheme 2
Scheme 3
quality of the diffraction data (see Experimental Section).
Because of the disordering, the structure of 2c in the solid
state could have either a syn or an anti configuration with
respect to the relative orientation of the two BMes2
groups, with the anti configuration of the two BMes2
groups being the less congested and, thus, the more
favored one. The separation distance of the two B atoms
˚
in the anti configuration shown in Figure 5 is 13.2 A, much

7706 Inorganic Chemistry, Vol. 48, No. 16, 2009
Rao and Wang
Figure 6. Variable-temperature 1H NMR spectra of the aromatic region of 2c in CD2Cl2.
Chart 3
shorter than that of 1c. Although the structures of 1b and
2b were not determined due to the lack of suitable crystals,
the coordination environments around the Pt center are
believed to be similar to those of 1c and 2c molecules.
To establish the structure of 2c in solution, we recorded
activation energy was estimated to be 38 kJ mol-1. The
relatively smaller barrier of 1c compared to that of 2c is
consistent with the more relaxed structure of 1c. Hence,
we have established that the two constitutional isomers of
B-ppy and ppy-B do have a distinct impact on the
structure of the Pt(II) complexes in solution and the solid
state.
Absorption Spectra. The absorption spectra of the
free liand p-B-ppy and p-ppy-B are shown in Figure 7
along with those of the Pt(II) complexes. The π to π*
absorption band of ppy-B (2) is slightly red-shifted (333
nm) compared to that of B-ppy (1; 329 nm). The Pt(II)
complexes of p-B-ppy and p-ppy-B display absorption
bands similar to those of the corresponding free ligand
and a new well-resolved MLCT band with moderate
intensity in the 380-500 nm region. Compared to the
free ligand, the π to π* absorption band is red-shifted, due
to the enhanced π conjugation via metal chelation. For
Pt(II) complexes, with the same auxiliary ligand, the
MLCT absorption band of the p-ppy-B complexes is
1
its variable-temperature H NMR spectra. As shown in
Figure 6, at ∼200 K in CD2Cl2, two sets of well-resolved
ortho-Ha peaks from the 4,40-bipy ligand were observed
in the 8.6-9.0 ppm region, which can be attributed to the
syn and anti isomers. Lowering the temperature further to
185 K causes the splitting of each peak into two, which
0
can be attributed to the Ha and Ha protons shown in
Chart 3. This can be explained by the C2 symmetry of
both isomers and the apparent lack of a mirror plane
symmetry, due to the strong steric interactions. The
activation barrier for the anti and syn configuration
interconversion of 2c was estimated to be 41 kJ mol-1
on the basis of the variable-temperature NMR data. For
1c, the syn and anti chemical shifts of the Ha protons are
still very broad and not fully resolved at 185 K, and the

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7707
Table 3. Electrochemical Dataa
compound p-B-ppy
E1/2red1 (V)
1a
1b
p-ppy-B
-2.12
2a
2b
-2.16
-2.10 -2.17
-1.96 -1.96
a All potentials are relative to FeCp20/þ, measured in DMF, using
NBu4PF6 as the electrolyte with scan rates of 100-1000 mV. [complex] =
∼0.003 M or less, [NBu4(PF6)] = 0.10 M.
sistent with our earlier reports.5b,c Both p-ppy-B Pt(II)
complexes 2a and 2b display a reduction potential of
-1.96 V, which is more positive than that of 2. However,
for the p-B-ppy Pt(II) complexes 1a and 1b, the impact of
Pt(II) chelation to the p-B-ppy ligand is either very small
or negligible, as shown by the potentials of complexes 1a
and 1b (1b has very poor solubility in DMF, which
resulted in the weak CV peak; -2.10 and -2.17 V,
respectively), indicating that metal binding to the N,
C-chelate is somewhat more effective in enhancing the
electron-accepting ability of the molecule when the
BMes2 group is on the py ring. This is also consistent
with our earlier finding on the Pt(II)-chelation-enhanced
electron-accepting ability of 7-azaindolyl-derivative N,C-
chelate ligands with BMes2 on the N-heterocyclic ring.5g
For complex 2b, a second reduction peak at -2.34 V is
also observed, which can be ascribed to the py ring
reduction.9a CV data of the dinuclear Pt(II) complexes
1c and 2c could not be obtained due to their poor
solubility in DMF.
Figure 7. UV-vis absorption spectra of free ligands and the Pt(II)
complexes recorded in CH2Cl2.
Luminescence. Under UV irradiation, p-B-ppy and p-
ppy-B both display blue luminescence in solution (CH2Cl2)
at ambient temperature, with λmax = 409 nm (Φ = 0.16) for
p-B-ppy and 412 nm (Φ = 0.01) for p-ppy-B. As shown in
Figure 9, the emission of p-B-ppy has a much stronger
dependence (e.g., λem = 376 nm in hexane, 425 nm in DMF)
on the solvent polarity than that of p-ppy-B (λem=409 nm in
hexane, 428 nm in DMF), indicating a more polarized
excited state than that of p-B-ppy.
In contrast to the free ligands, the emissions of the Pt(II)
complexes are all dominated by phosphorescence. The
luminescent data of the complexes are summarized in
Table 4. The ambient temperature emission spectra of the
complexes are shown in Figure 10. For a given ancillary
ligand, the emission maximum of the p-B-ppy complexes is
in general red-shifted by a few nanometers, compared to the
p-ppy-B complexes. This trend is opposite that of the
MLCT absorption band in the UV-vis spectra. For 1a
and 2a, well-resolved vibronic fine features are observed in
the emission spectra at ambient temperature, indicative of
ligand-centered emission. The emission red shift of the p-B-
ppy complexes relative to those of p-ppy-B can be therefore
attributed to the greater polarized excited state of the
former, as revealed by the free ligands. For 1b, 2b, 1c,
and 2c, the ambient temperature emission spectra are
broader than those of 1a and 2a and the vibronic fine
features are less obvious. However, at 77 K (Figure 11), the
emissionspectraofallPt(II) complexesdisplaywell-defined
vibrational features, supporting the position that ligand-
centered emission dominates in these complexes. The fact
that the emission maxima of the Pt(II) complexes show
little change with temperature also supports the position
that the emission is dominated by a 3LC excited state since
MLCT-dominated emission is known to have a greater
dependence on temperature.13 There is a notable shoulder
Figure 8. The CV diagrams for the free ligands and Pt(II) complexes
recorded in DMF.
red-shifted relative to that of p-B-ppy complexes, which is
in agreement with the fact that the pyridyl ring in con-
jugation with the boron center is more effective in low-
ering the π* energy level than the phenyl ring. The
extinction coefficients of the dinuclear complexes 1c and
2c are nearly twice those of the corresponding mono-
nuclear compounds 1b and 2b. For both p-B-ppy and
p-ppy-B series, the MLCT energy follows the order of
DMSO>4,40-bipy ≈py, supporting the position that the
electron-donating ability of the ligands to the Pt(II) center
follows the order DMSO<4,40-bipy ≈py.
Electrochemical Properties. The reduction potentials of
the free ligands and the Pt(II) metal complexes were
recorded by cyclic voltammetry (CV; DMF as the solvent,
NBu4PF6 as the electrolyte). As shown in Figure 8 and
Table 3, the reduction potential of p-ppy-B (2) (-2.12 V,
vs FeCp20/þ) is a little more positive than that of p-B-ppy
(1), -2.16 V, supporting the position that the pyridine
ring can enhance the electron-accepting ability of the
boron center more effectively than the phenyl ring, con-

7708 Inorganic Chemistry, Vol. 48, No. 16, 2009
Rao and Wang
Figure 9. The emission spectra of p-B-ppy and p-ppy-B in various solvents with λex=345 nm, concentration=∼1.0 ꢀ 10-5 M.
Table 4. Absorption and Luminescence Data
compound
abs, nm (ε, M-1 cm-1
)
λ
em, nm /τ, μsa (CH2Cl2, rt)
λem, nm /τ, μs (CH2Cl2, 77 K)
Φb (CH2Cl2, rt)
1, p-B-ppy
2, p-ppy-B
1a
326 (25 750)
329 (23 450)
344 (27 550)
392 (5400)
345 (24 500)
394 (8300)
343 (22 950)
411 (4050)
345 (26 850)
425 (7050)
409
412
515/14.7(1)
0.16
0.012
0.004
511/28.2(1)
501/40.2(1)
538/13.4(2)
525/14.0(1)
541/13.1(1)
530/12.5(1)
2a
1b
2b
1c
2c
509/24.1(1)
543/7.1(1)
534/8.1(1)
543/8.8(2)
535/7.1(1)
0.01
0.03
0.03
343 (47 300)
411 (13 300)
344 (56 600)
425 (15 400)
0.006
0.003
a The decay lifetime at rt for the Pt(II) complexes was measured under N2. b The quantum efficiency for the free ligands was obtained under air using 9,10-
diphenylanthracene as the standard. For the Pt(II) complexes, the quantum efficiency was measured under N2 using Ir(ppy)3 as the standard (Φ = 0.40).9a
peak in the emission spectrum of 1b at ∼485 nm at 298 K,
which is resolved with fine vibronic features at 77 K. This
peak is insensitive to oxygen and, thus, attributed to ligand-
based singlet emission.
For either p-B-ppy or p-ppy-B complexes, the emission
maxima of the 4,40-bipy and py complexes are similar but
about 30 nm red-shifted, compared to those of the corre-
sponding DMSO complexes. This trend is consistent with
that of the MLCT band observed in the UV-vis absorption
spectra. Hence, some MLCT contributions to the phosphor-
escent emission band are very likely. Compared to Pt(ppy)-
(acac) and its derivatives,9a the quantum efficiencies of
complexes 1a, 1b, 2a, and 2b are either much lower or
comparable. Although the diplatinum complexes 1c and 2c
have similar absorption and emission spectra to those of the
corresponding monoplatinum complexes 1b and 2b, their
emission quantum efficiency is however much lower than
that of the mononuclear complexes, which may be attributed
to intramolecular triplet-triplet quenching.
Molecular Orbital Calculations. To understand the
origin of the electronic transitions in the free ligands
and the metal complexes, DFT calculations for p-B-ppy
and p-ppy-B and their Pt(II) complexes 1b and 2b were
performed using the Gaussian 03 package with the
B3LYP/6-311þþG** basis set.18,19 The geometrical
parameters obtained for p-ppy-B, 1c, and 2c from X-ray
diffraction experiments were used as the starting point for
the geometry optimization of p-ppy-B, 1b, and 2b.
(18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; 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.; 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.2;
Gaussian, Inc.: Wallingford, CT, 2004.
The highest occupied molecular orbital (HOMO) and
lowest unoccupied molecular orbital (LUMO) diagrams
of p-B-ppy (1) and p-ppy-B (2) are shown in Figure 12.
The HOMO of 1 consists of contributions nearly exclu-
sively from the mesityls, while the LUMO is dominated
by the pπ orbital of the boron atom with significant
contributions from the pyridyl and phenyl ring. The
LUMO level of 2 closely resembles that of 1, but the
HOMO level has significant contributions from the pyr-
(19) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.;
Parr, R. G. Phys. Rev. B 1988, 37, 785. (c) Miehlich, B.; Savin, A.; Stoll, H.;
Preuss, H. Chem. Phys. Lett. 1989, 157, 200. (d) Hariharan, P. C.; Pople, J. A.
Theor. Chim. Acta 1973, 28, 213.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7709
Figure 10. Emission spectra of complexes in CH2Cl2, ∼1.0 ꢀ 10-5 M,
under N2 at 298 K.
Figure 13. HOMO and LUMO orbitals of 1b and 2b, plotted with a
0.015 isocontour value.
idyl ring, in addition to the mesityls. Hence, although the
lowest electronic transition for both 1 and 2 may be
described as charge transfer from mesityl to the B-ppy
or ppy-B unit, for 2, due to the direct conjugation of the
pyridyl ring with the B atom, its excited state is less
polarized than that of 1, thus explaining the greater
solvent-dependent emission of 1.
As shown in Figure 13, the HOMO of 1b is dominated
by the π orbitals of the phenyl group with some contribu-
tions from the Pt d orbitals. However, HOMO-1, which
is very close in energy to HOMO (0.001 hartree
difference), is a π orbital centered on the phenyl portion
of the ppy chelate with significant d orbital contributions
of the Pt(II) ion. The LUMO of 1b is a π* orbital
dominated by the B atom and the ppy chelate with
significant contributions from the py ligand. For 2b,
HOMO and HOMO-1 are nearly identical in energy
(0.0007 hartree difference), with HOMO being the
π orbital localized on the ppy ring and the Pt atom and
HOMO-1 being the phenyl π orbital with some Pt d
orbital contributions. The LUMO of 2b is a π* orbital
similar to that of 1b but with no significant contributions
from the py ligand. Hence, the lowest electronic transi-
tions in 1b and 2b likely involve both π f π* transitions
localized on the B-ppy chelate and interligand charge
transfer from phenyl to the B-ppy ligand, with MLCT
contributions in both transitions, in agreement with UV-
vis and luminescent data.
Figure 11. Emission spectra of complexes in CH2Cl2, ∼1.0 ꢀ 10-5 M,
under N2 at 77 K.
Lewis Acidity;Response to Fluoride Ions. Since triar-
ylboron groups such as B(Ar)Mes2 are well-known to
bind to fluoride ions with a high selectivity,3,4 we exam-
ined the Lewis acidity of the boron center in the Pt(II)
complexes by carrying out the fluoride titration experi-
ments in both absorption and luminescence modes.
p-B-ppy and p-ppy-B. As shown in Figure 14, upon the
addition of TBAF in CH2Cl2, the low-energy absorption
bands at 327 and 330 nm, respectively, in the spectra of
p-B-ppy (1) and p-ppy-B (2) are quenched and blue-
Figure 12. HOMO and LUMO orbitals of free ligands B-ppy and ppy-
B, plotted with a 0.015 isocontour value.

7710 Inorganic Chemistry, Vol. 48, No. 16, 2009
Rao and Wang
Figure 14. UV-vis (left) and fluorescent (right) spectral change of 1 (2.0 ꢀ 10-5 M) with the addition of NBu4F in CH2Cl2. Inset: Plots of A/Ao or I/Io vs
equiv of [F-] at λmax for both 1 and 2. The UV-vis and fluorescent titration spectra of 2 are provided in the Supporting Information.
Figure 15. The UV-vis spectral change of 1a (left) and 2a (right) (2.0 ꢀ 10-5 M) with the addition of NBu4F in CH2Cl2. Inset: A/A0 vs equiv [F-] plots at
345 nm for both 1a and 2a.
shifted. The saturation point is reached for both com-
pounds with ∼1.0 equiv of F- added, an indication that
both molecules bind to fluoride fairly strongly. None-
theless, the plots of A/Ao versus the equivalents of
F- added show clearly that the p-ppy-B has a somewhat
stronger binding toward F- than p-B-ppy, which is con-
sistent with its greater electron-accepting ability, as
established by the CV data, thus demonstrating that the
direct conjugation of a pyridyl ring with the BMes2 group
is more efficient in enhancing the Lewis acidity of the
boron center than the phenyl group. In the fluorescent
spectra, the emission band of both compounds undergoes
similar quenching with the addition of fluoride. Again,
the ppy-B molecule shows a slightly stronger binding with
fluoride than B-ppy does.
Pt(II) Complexes. Absorption Titration. Unlike the
free ligands, the response of the Pt(II) complexes 1a and
2a toward fluorides is quite different. As shown by the
UV-vis spectra in Figure 15, the addition of excess
TBAF (∼4 equiv) to the solution of 1a causes only a
20% decrease of the intense π to π* peak at 347 nm and
very little change of the MLCT band between 380 and 450
nm. In contrast, both π to π* and MLCT bands in 2a
experience about an 80% decrease of intensity and reach a
saturation point with ∼1 equiv of F-, indicating its strong
binding with fluorides. The same trend was also observed
between 1b and 2b and between 1c and 2c, as shown by the
titration spectra and the A/Ao versus equivalent [F-] plots
in Figures 16 and 17.
The binding constants of 1a and 1b with fluoride ions
were found to be 9ꢀ105 M-1 and 1ꢀ105 M-1, respec-
tively, which are about 100 times smaller than those of 2a
and 2b (∼107 M-1 to 108 M-1; see Supporting In-
formation). The weaker response of the p-B-ppy Pt(II)
complexes toward fluoride can be attributed to the weak-
er electron-accepting ability of the boron center in the
p-B-ppy complexes, relative to that of the p-ppy-B com-
plexes, as supported by the CV data. Compared to the
free p-B-ppy ligand (K = ∼6 ꢀ 107 M-1), the response of
1a, 1b, and 1c toward fluoride is much weaker, which can
be explained by steric factors. If both the ligand and the
complex show similar reduction potentials, the Lewis
acidity of the metal complexes would be lower than that
of the free ligand due to the greater steric interaction
imposed by the binding of fluoride in the complex, which
is the case for the p-B-ppy complexes.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7711
Figure 16. UV-vis spectral change of 1b and 2b (top, 2.0 ꢀ 10-5 M) and 1c and 2c (bottom, 1.0 ꢀ 10-5 M) with the addition of NBu4F in CH2Cl2.
ions shown in Figure 16. In contrast, the UV-vis spectral
change of 1b and 1c is notably different: for 1b, several
isosbestic points are present at 280-500 nm, while for 1c,
they are absent. Furthermore, the plots of A/Ao versus
[F-]/[Pt] for 1b and 1c shown in Figure 17 do not overlap,
with 1c showing somewhat greater response toward F-.
On the basis of these data, we can conclude that some
degree of electronic communication is present between
the two boron centers in 1c. The apparent lack of electro-
nic communications between the two Pt(II) units in 2c
is clearly caused by the strong steric interactions, which
is much reduced in 1c, making electronic communica-
tions between the two Pt(II) units via the bipy bridge
Figure 17. The plots of A/Ao vs [F-]/[Pt] at ∼340 nm for 1b, 2b, 1c,
possible in 1c.
Phosphorescent Titration. Due to the difficulty of car-
rying out phosphorescent titration in an oxygen-free
and 2c.
environment, the phosphorescent titration experiments
were performed for the py and the bipy complexes only.
The phosphorescent data provide qualitative information
concerning the impact of the fluoride ions on lumines-
cence, but they are not accurate in terms of stoichiometry
due to the difficulty of controlling concentrations when
preparing and transporting the sample for each addition
of fluoride in and out of a drybox. Nonetheless, the
titration data shown in Figure 18 illustrate that the
addition of fluoride shifts the emission peak to a shorter
wavelength for both 1b and 2b, with the emission color
changing from yellow-green to blue-green. The fluoride
adduct emission spectrum (λmax=489 nm) of 2b is similar
to that of Pt(ppy)L2 complexes reported by Tompson and
The difference between the mononuclear Pt(II) py
complex 2b and the corresponding dinuclear bipy com-
plex 2c is that the amount of F- needed to reach the
saturation point for 2c is about twice that for 2b due to the
presence of two boron acceptor centers. The plots of A/Ao
versus equivalent [F-] per Pt atom at 345 nm (Figure 17)
indicate that the two boron centers in 2c respond to
fluoride ions as they were two fully independent boron
units with binding strengths identical to that of the mono-
nuclear Pt(II) compound 2b, thus supporting the position
that there is little electronic communication between the
two boron centers in the dinuclear Pt(II) complexes. This
conclusion can also be reached by the essentially identical
change of the UV-vis spectra of 2b and 2c with fluoride

7712 Inorganic Chemistry, Vol. 48, No. 16, 2009
Rao and Wang
Figure 18. Phosphorescent emission spectral change of Pt(II) complexes 1b and 2b (top) and 1c and 2c (bottom) with the addition of NBu4F in CH2Cl2
under N2 at ambient temperature.
co-workers9a and is thus attributable to ppy-centered
emission. The fluoride addition switches the ppy-B-based
phosphorescence to ppy-based phosphorescence by
blocking the boron center. The fluoride adduct spectrum
of 1b is more complex, with contributions not only from
the ppy phosphorescence but also the ligand-based singlet
emission band. Nevertheless, the general trend of the
phosphorescent response of 1b and 2b toward fluoride
ions is similar to that of the N,C-chelate complex5h Pt(N,
C-BNPA)Ph(SMe2), reported recently by us.
The phosphorescent titration spectra of the dinuclear
complexes 1c and 2c display some unique features that are
not observed in 1b and 2b. For 1c, the emission spectrum
initially gains intensity greatly with the addition of fluor-
ide. Further addition of fluorides leads to the decrease of
emission intensity, and the final emission spectrum of the
fluoride adduct resembles that of the 1b fluoride adduct,
clearly due to the formation of the 2:1 adduct. The high-
energy emission band with distinct vibrational features in
the 1c fluoride adduct is attributed to 4,40-bipy (see 4,40-
bipy emission spectra in the Supporting Information).
The initial rise of the emission intensity of 1c with F- may
be explained by the formation of the 1:1 adduct which, if it
behaves like 1b, should have a much greater emission
efficiency than 1c, and thus, there should an enhancement
of the emission. The fluoride ions may be therefore
described as the “activator” for the emission of the 1:1
complex. This “activation” effect is only possible through
electronic communication between the two Pt(II) units in
the same molecule. The phosphorescent response of 1c
toward fluoride is therefore consistent with the UV-vis
titration data.
In contrast to 1c, which has a distinct emission spectral
change for the 1:1 and 2:1 adducts, the spectral change of
2c with fluoride resembles that of 2b; namely, the original
peak is quenched while the new ligand-centered emission
peak at ∼490 nm gains intensity. Compared to 2b, there is
an apparent two-stage change in the emission spectrum of
2c with fluoride, which may be attributed to the 1:1 and
2:1 adducts. In addition, there is a high-energy emission
band in the 400-480 nm region after the addition of
∼2 equiv of fluorides in the spectrum of 2c, which is not
observed in the fluoride adduct of 2b and is attributed to
the 4,40-bipy ligand. The phosphorescent titration results
of 2c indicate that the two Pt(II) units behave like two
independent monomer units, which is consistent with the
UV-vis titration data.
NMR Spectral Titration. To verify that the fluoride
ions are indeed bound to the boron center in the metal
complexes, we carried out NMR spectral titration experi-
1
ments for all complexes. The H NMR spectra of all
complexes undergo gradual change with the addition of
fluoride and become broad due to the equilibrium be-
tween bound and nonbound species (see Supporting

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7713
Table 5. 19F NMR Data of the Fluoride Adducts for All Complexes
or pyridyl, and perhaps as a consequence, both structures
A and B are observed. For p-B-ppy complexes, the phenyl
group is always on the same side as the BMes2 group,
which has a steric demand similar to that of py, and as a
result, regardless of the nature of the auxiliary ligand L,
only one 19F chemical shift is observed.
compound
1a
1b
1c
2a
2b
2c
19F, ppm
in CD2Cl2
-175.3 -175.8 -176.0 -176.9,
-177.7
-177.1 -177.0
Conclusions
Chart 4
This study has shown that the two constitutional isomers
of p-B-ppy and p-ppy-B have a distinct impact on the
structures, stabilities, and electronic and photophysical prop-
erties of the Pt(II) complexes. For p-B-ppy, Pt(II) chelation
does not alter the electron-accepting ability of B-ppy, com-
pared to the free neutral ligand. The increased steric interac-
tions in the Pt(II) complexes of p-B-ppy also significantly
diminish the Lewis acidity of the B center, as demonstrated
by the low binding strength of the Pt(II) complexes with
fluorides, relative to the free p-B-ppy. For p-ppy-B, Pt(II)
chelation does enhance its electron-accepting ability but does
not significantly change its Lewis acidity with fluoride due to
greater steric congestion in the complexes. Hence, we can
conclude that, for N,C-chelate ligands, it is most effective
with the boron moiety being directly conjugated with the
nitrogen heterocycle in order to enhance the electron-accept-
ing ability and Lewis acidity. The overall impact of metal
chelation with N,C-chelate ligands on the electron-accepting
ability and Lewis acidity of a triarylboron center is a balance
of both electronic and steric factors. In the dinuclear Pt(II)
complexes, weak electronic communication between the two
boron centers is possible in sterically less congested systems
such as 1c due to the greater π-conjugation of the B(III) and
Pt(II) centers with the 4,40-bipy linker (which can rotate freely
in solution in 1c). Lastly, the phosphorescent decay lifetimes
of the Pt(II) complexes p-B-ppy and p-ppy-B are all much
longer than those of Pt(ppy)(acac) and its derivatives, which
may be due to the stabilization of the excited state by the
BMes2 group or the influence of the phenyl ligand and the
auxiliary ligand. To fully establish the role of the boron center
in B-ppy and ppy-B ligands, it is necessary to synthesize Pt(p-
B-ppy)(acac) and Pt(p-ppy-B)(acac) complexes so that direct
comparison with Pt(ppy)(acac) can be made. This is currently
being investigated in our laboratory and will be reported in
due course.
Information). 19F NMR data (Table 5) are most infor-
mative. Our previous studies have shown that the chemi-
cal shift of F- bound to a B(Ar)Mes2 group appears typi-
cally at ∼-175 to -180 ppm. The 19F NMR data indeed
showed that all Pt(II) complexes except 2a display one
characteristic chemical shift at ∼-175 to -178 ppm
that grows in intensity with an increasing amount of
TBAF added (see Supporting Information), confirming
that the fluoride is indeed bound to the boron center.
The 19F chemical shift of a fluoride bound to a Pt
center usually appears in the region of -230 to -280
ppm, depending on the nature of other ligands and the
1
oxidation state of the Pt atom with distinct JPt-F cou-
F
pling satellites.20 The absence of any Pt-F signals in 19
NMR spectra of all Pt(II) complexes further confirmed
that the fluoride ion is bound to the boron center.
For the DMSO complex 2a, two fluoride chemical
shifts were observed at -176.9 ppm and -177.7 ppm
with nearly equal intensity in the fluoride adducts, in-
dicating the presence of isomers. The crystal structural
data of previously published fluoride adducts involving a
B(Ar)Mes2 group21 revealed that the two mesityl groups
in the adduct are oriented above and below the B-Ar
plane, respectively, to minimize steric interactions, and
the F atom lies approximately in the same plane with
B-Ar. As a consequence, if there is sufficient hindered
rotation around the B-C(Ar) bond due to the bulky
B(F)Mes2 group, two possible and distinct structures
for the fluoride adduct in the Pt(II) complexes can coexist
in solution, as depicted for the p-ppy-B complex in
Chart 4. For 2a, the auxiliary ligand DMSO is on the
same side as the B(F)Mes2 group in the fluoride adduct
and is much more sterically demanding than either phenyl
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada for financial
support and Dr. Rui-Yao Wang for his assistance in some
of the crystal structural work.
Supporting Information Available: UV-vis and fluorescent
titration spectra of p-ppy-B by TBAF; variable-temperature 1H
NMR data of 1c; emission spectra of 4,40-bipy in CH2Cl2;
determination of binding constants with fluoride ions; complete
1H NMR and 19F NMR titration spectra of all Pt(II) complexes
by TBAF; and complete crystal structural data of p-ppy-B, 1a,
2a, 1c, and 2c. This material is available free of charge via the
Internet at http://pubs.acs.org.
(20) (a) Cross, R. J.; Haupt, M.; Rycroft, D. S.; Winfield, J. M. J.
Organomet. Chem. 1999, 587, 195. (b) Jasim, S. A.; Perutz, R. N. J. Am.
Chem. Soc. 2000, 122, 8685. (c) Clark, H. C. S.; Fawcett, J.; Holloway, J. H.;
Hope, E. G.; Peck, L. A.; Russell, D. R. Dalton Trans. 1998, 1249.
(21) Zhao, S. B.; Wucher, P.; Hudson, Z. M.; McCormick, T. M.; Liu, X.
Y.; Wang, S.; Feng, X. D.; Lu, Z. H. Organometallics 2008, 27, 6446.