Silica- and polymer-supported platinum(II) polypyridyl complexes: Synthesis and application in photosensitized oxidation of alkenes

Article abstract of DOI:10.1039/b916488j

Square-planar polypyridine platinum(II) complexes have been introduced into a silica/polymer matrix by covalent ligand modification. The photophysical properties of the supported matrices are well retained as their model complexes, and the quantum yields for singlet oxygen (¹O₂) generation are comparable with that of TPP (tetraphenylporphyrin) under similar conditions. A preliminary application in photosensitized oxidation indicates the silica/polymer-supported matrices are promising, which can be reused without loss of reactivity by a simple filtration. Moreover, the polymer-supported matrix exhibits excellent compatibility in various solvents. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b916488j

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PAPER
www.rsc.org/dalton | Dalton Transactions
Silica- and polymer-supported platinum(II) polypyridyl complexes: synthesis
and application in photosensitized oxidation of alkenes†
Ke Feng,‡ Ming-Li Peng,‡ Deng-Hui Wang, Li-Ping Zhang, Chen-Ho Tung and Li-Zhu Wu*
Received 11th August 2009, Accepted 10th September 2009
First published as an Advance Article on the web 29th September 2009
DOI: 10.1039/b916488j
Square-planar polypyridine platinum(II) complexes have been introduced into a silica/polymer matrix
by covalent ligand modification. The photophysical properties of the supported matrices are well
retained as their model complexes, and the quantum yields for singlet oxygen (1O2) generation are
comparable with that of TPP (tetraphenylporphyrin) under similar conditions. A preliminary
application in photosensitized oxidation indicates the silica/polymer-supported matrices are promising,
which can be reused without loss of reactivity by a simple filtration. Moreover, the polymer-supported
matrix exhibits excellent compatibility in various solvents.
heterogenization include facilitation of catalyst separation from
Introduction
reaction mixtures and the simplification of methods for sensitizer
Molecular oxygen is one of the most important substances on
recycling. In the present work, we report the synthesis of silica- and
earth and is involved in many chemical, biological and medical
polystyrene-bound platinum(II) polypyridyl complexes and their
processes. The use of molecular oxygen in chemical production
application in photosensitized oxidation of alkenes. A preliminary
is very attractive in realizing economically and environmentally
result suggests that photosensitized oxidation can proceed well
benign processes. However, the reactivity of oxygen toward most
using silica- or polymer-supported platinum(II) complexes, and
the quantum yields for 1O2 generation are comparable with that of
TPP (tetraphenylporphyrin) under similar conditions. Moreover,
the matrices have a solvent compatibility and only a simple
filtration is needed for the recovery of the platinum(II) polypyridyl
complexes without the loss of reactivity.
organic molecules is inhibited by its spin restriction due to the
triplet ground-state of oxygen. In this regard, photosensitized
oxidation holds a special promise, where molecular oxygen can
be activated by the excited triplet state of the photosensitizer
through an energy transfer process that generates highly reactive
singlet oxygen (1O2). It is well known that singlet oxygen is a
versatile reagent for oxidation reactions including cycloaddition
reactions to afford endoperoxides, and ene reactions to produce
allylic hydroperoxides.1-5
Results and discussion
Preparation and characteristics of silica-supported matrix
Platinum(II) polypyridyl complexes are appealing from a pho-
tochemical perspective owing to visible light absorption and
the population of the triplet state.6-12 We and others found
that platinum(II) complexes are able to react with molecular
oxygen to generate 1O2 with a high quantum yield.13-15 In the
course of extending their applications, we demonstrated that upon
irradiation of light in the visible region platinum(II) polypyridyl
complexes can be used as sensitizers for photooxidation using
molecular oxygen.16-20 To further extend previous work, we expect
to immobilize platinum(II) complexes on silica and polymer
supporting matrices in order to make the synthesis, purification
and recycling of the photosensitized oxidation more straightfor-
ward. The covalent attachment of homogeneous catalysts to silica
or polymer supports has been studied widely as an attractive
strategy for extending the practical advantages of heterogeneous
catalysts to homogeneous systems.21-27 The potential benefits of
Triethoxysilane modified platinum(II) polypyridyl complex
Pt(tpy)S was synthesized via ligand modification, as shown in
Scheme 1a. The ancillary ligand N-(3-(triethoxysilyl)propyl)-
4-ethynylbenzamide was obtained by a peptide linkage be-
tween 4-ethynylbenzoic acid and (3-aminopropyl)-triethoxysilane,
which was then reacted with 4¢-(p-methyl-phenyl)-2,2¢:6¢,2¢¢-
terpyridine platium(II) chloride using CuI-catalyzed chloride-to-
alkyne metathesis under ultrasonic conditions to afford the target
molecule Pt(tpy)S.
Corresponding xerogel Pt(tpy)SG was made from Pt(tpy)S via a
sol-gel process (Scheme 1b).28-30 Typically, Pt(tpy)S and tetraethyl
orthosilicate (TEOS) were mixed together in a controllable initial
proportion, and in which acetic acid and water were used to
adjust the pH value to 5–6. The mixture was stirred at 40 ◦C
for enough time until there were sol particles formed in the
solution. Then the silica species condensed to link together
forming three-dimensional networks. Removal of solvent led to
the formation of bulky xerogel Pt(tpy)SG. After drying under
vacuum overnight, the xerogel was ground and rinsed by solvent
for further experiments.
Key Laboratory of Photochemical Conversion and Optoelectronic Materials,
Technical Institute of Physics and Chemistry, the Chinese Academy of
Sciences, Beijing, 100190, P. R. China. E-mail: lzwu@mail.ipc.ac.cn; Fax: 86
10 8254 3580; Tel: 86 10 8254 3580
† Electronic supplementary information (ESI) available: ESR spectra of
nitroxide radical generated by irradiation of the oxygen saturated TMP
solution in the presence of sensitizers. See DOI: 10.1039/b916488j
Complex Pt(tpy)S in acetonitrile solution exhibits intense
vibronic-structured absorption bands at 250–350 nm with extinc-
tion coefficients (e) of the order of 104 L mol-1 cm-1, and a less
‡ The two authors contributed equally.
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Scheme 1 The preparation of Pt(tpy)S and Pt(tpy)SG.
intense band at 400–500 nm with e of the order of 103 L mol-1 cm-1
Preparation and characteristics of polymer-supported matrix
shown in Table 1. The absorption spectra of Pt(tpy)S and the
model complex ModS were found to follow Beer’s Law below the
saturated concentration (ESI, Fig. S1†), suggesting no significant
complex aggregation occurred. With reference to previous work on
platinum(II) terpyridyl complexes,31 the absorption bands at l <
350 nm are assigned to the intraligand (IL) transition of terpyridyl
and acetylide ligand as well as the charge transfer transition
involved in the phenylacetylide moiety, while the absorption bands
at 425 and 453 nm are ascribed to dyz(Pt) → p*(tpy) and dxz(Pt)
→ p*(tpy) MLCT transitions. Pt(tpy)S is emissive at 592 nm with
a lifetime of 0.71 ms. The correlated luminescence quantum yield
(Uem) of 0.026 were determined by the optical dilute method32
using a degassed acetonitrile solution of [Ru(bpy)3]-(PF6)2 as
the reference (Uem = 0.062) (Table 1).33 The similar photophys-
ical properties of Pt(tpy)S and model complex ModS indicate
that the characteristics of platinum(II) polypyridyl complexes
can be well retained with the ancillary ligand modification of
triethoxysilane.
The polymer-supported platinum(II) polypyridyl complex
PolyPt(pbp)L was prepared by the prepolymerization of
MonoPt(pbp)Cl and styrene followed by a CuI-catalyzed chloride-
to-alkyne metathesis from phenylacetylide ligand to the metal
center of platinum(II) (Scheme 2a), which is soluble in various
solvents. The ligand of 4-vinylbenzyl 6-phenyl-2,2¢-bipyridine-4-
carboxylate was synthesized by an ester linkage between 6-penyl-
2,2¢-bipyridine-4-carboxylic acid and 4-vinylbenzyl chloride, and
then it was refluxed with K2PtCl4 in a mixture of acetonitrile
and water to produce a monomer complex MonoPt(pbp)Cl. Ini-
tiated by 2,2¢-azobisisobutyronitrile (AIBN),22,34-36 the monomer
complex MonoPt(pbp)Cl and styrene were polymerized to give
the polymer PolyPt(pbp)L. It is worth noting that the polymer-
supported platinum(II) polypyridyl complex PolyPt(pbp)L cannot
be prepared by the route shown in Scheme 2b. We originally
synthesized the monomer complex MonoPt(pbp)L for polymeriza-
tion. However, the reaction of MonoPt(pbp)L and styrene failed to
give any desired polymer PolyPt(pbp)L, suggesting the monomer
complex MonoPt(pbp)L may not be stable toward the radical-
induced polymerization by AIBN.
The diffusion reflectance UV-visible spectroscopy (UV-DRS) of
xerogel Pt(tpy)SG displays broad energy absorption bands ranging
from 250 to 500 nm, similar to that of Pt(tpy)S. The luminescent
profile of Pt(tpy)SG shows an emission with lmax at 607 nm,
and an excitation band at 453 nm (ESI, Fig. S2†). In addition,
xerogel Pt(tpy)SG is insoluble in normal solvents, thereby leading
to convenient separation of silica matrices from reactions.
The polymer of PolyPt(pbp)L exhibits an intense absorption
band around 350 nm assignable to the absorption of IL states, and
a moderately intense low-energy absorption band in the region
of 400–500 nm with two peaks at 459 and 488 nm, respectively,
Table 1 Photophysical characteristics of platinum(II) polypyridyl complexes at room temperature
Entry
l
abs /nm (e/103 L mol-1 cm-1)
l
em/nm
t/ms
Uem
Pt(tpy)Sa
ModSa
Pt(tpy)SG
PolyPt(pbp)Lc
ModPc
289 (48.9), 310 (25.9), 337 (19.2), 425 (8.31), 453 (7.18)
263 (47.0), 288 (40.2), 313 (24.6), 338 (21.9), 427 (8.17), 454 (7.29)
297, 341, 449b
286 (57.4), 348 (21.9), 380 (16.4), 459 (6.64), 488 (6.34)
256 (36.6), 283 (42.4), 347 (15.7), 376 (10.8), 458 (5.89), 484 (5.79)
592
606
607
636
622
0.71
1.03
—
0.25
0.30
0.026
0.046
—
0.030
0.030
a The solvent is acetonitrile. b UV-DRS measurement. c The solvent is dichloromethane. The concentration of the polymer PolyPt(pbp)L is based on the
amount of the functional group.
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Scheme 2 The preparation of PolyPt(pbp)L.
which are attributed to the absorption of typical MLCT states.37
The UV/Vis and emission spectra of PolyPt(pbp)L in CH2Cl2
are also shown in Fig. S3 (ESI†). The correlated maximum
emission peak wavelength is at 636 nm, and the luminescence
quantum yield is 0.030 and the lifetime is 0.25 ms. As shown in
Table 1, PolyPt(pbp)L and the model complex ModP38 have similar
photophysical characteristics.
compound of the body, involving in a variety of biological
processes. Some of its oxidation products possess potent cytotoxic
and antitumor activity.50 The oxidation of 7-dehydrocholesterol
is a mixture of [4+2] cycloaddition and ene reaction to produce
endoperoxide and hydroperoxides with the molar ratio of 3:1, in
line with the reported value of 16:5.51,52 The mass balance of all the
reactions studied in this work were greater than 95%. The yield
of photoproducts is based on the consumption of the starting
material, and the conversion of the substrates exceeding 90%.
As expected, the recycled use of the sensitizer-supported matri-
ces can be simply achieved by filtration. The polymer PolyPt(pbp)L
displays an excellent compatibility in various solvents, such as
dichloromethane, chloroform, ethyl acetate, DMF and so on.
Polar solvents, like methanol, can precipate PolyPt(pbp)L for
recycling. Dimethoxystilbene was chosen for repeat experiments.
The result shows that the silica/polymer-supported matrices are
robust enough and do not undergo any degradation after five
consecutive runs of the photosensitized reaction.
Photooxidation
It has been known that the emissive 3MLCT excited states
of platinum(II) complexes are responsible for singlet oxy-
gen (1O2) production.16,17 To assess the 1O2 generation abil-
ity of silica/polymer-supported platinum(II) complexes, 2,2,6,6-
tetramethylpiperidine (TMP) was used as a probe to react with 1O2
yielding stable free radical nitroxide (2,2,6,6-tetramethylpiperidine
oxide, TMPO), which can be easily detected by electron spin
resonance (ESR) spectroscopy.39,40 The signal of TMPO was
clearly monitored when an oxygen saturated solution of TMP and
silica/polymer-supported platinum(II) polypyridyl complexes was
irradiated by laser beams (ESI, Fig. S4-5†), indicating that 1O2 can
be generated efficiently in these systems. The quantum yields for
1O2 generation were determined by the 9,10-diphenylanthrancene
bleaching method41 to be 0.40 for insoluble silica Pt(tpy)SG and
0.79 for soluble polymer PolyPt(pbp)L;42 which are comparable
to that of TPP (0.56), a well-known photosensitizer under similar
conditions.43
Several different kinds of olefins were selected to conduct
the photosensitized oxidation including three types of singlet
oxygen reactions (Table 2).1 Electron rich stilbene and dimethoxys-
tilbene undergo a [2+2] cycloaddition,44,45 and the generated
endoperoxy intermediates quickly convert to the corresponding
phenylaldehyde and methyl benzoate. Cyclopentadiene and 1,3-
cyclohexadiene undergo [4+2] cycloaddition with 1O2 to yield
endoperoxides, which can be reduced by thiourea to give the
corresponding cis-cyclodiols,46 an important chemical for the syn-
thesis of prostaglandins.47 (1S,5S)-(-)-a-Pinene can take part in
an ene reaction48,49 to afford hydroperoxy intermediates exclusively.
Following reduction by triphenylphosphate, (1S,3S,5R)-(+)-trans-
3-hydroxypin-2(10)-ene [(+)-trans-pinocarveol] can be obtained
as a unique product. 7-Dehydrocholesterol is an endogenous
Conclusions
To summarize, we successfully introduced platinum(II)
polypyridyl complexes into silica- and polymer matrices by
covalent ligand modification. The photophysical properties of the
supported matrices are well retained as their model complexes,
and the quantum yields for singlet oxygen (1O2) generation
are comparable with that of TPP under similar conditions. A
preliminary application to photosensitized oxidation indicates
the silica/polymer-supported matrices are promising in all three
types of 1O2 reactions, only a simple filtration is needed for
the recovery of the platinum(II) polypyridyl complexes without
loss of reactivity. Moreover, polymer-supported matrices exhibit
excellent compatibility in various solvents and can be precipitated
from the reaction by adding polar solvents like methanol.
Experimental
Materials and instrumentation
6-Phenyl-2,2¢-bipyridine-4-carboxylic acid, 4¢-(p-methylphenyl)-
2,2¢:6¢,2¢¢-terpyridine platium(II) chloride and ModS were
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Table 2 Photosensitized oxidation of alkenes by 0.6 mol% Pt(tpy)SG and 2 mol% PolyPt(pbp)L in dichloromethane at room temperature
Yield (%)a
Substrate
Product
PhCHO
Irradiation time (h)
2
Pt(tpy)SG
PolyPt(pbp)L
~100b
~100b
PhCOOCH3
2
~100c
~100c
3
3
>95d,e
>95e
>95d,e
>95e
4
3
~100f
~100f
75, 25
76, 24
a Yields were calculated based on the consumption of the substrates. Concentration of the substrates was 5.0 ¥ 10-3 mol L-1. The catalysts’ ratio was based
on the amount of functional group. b Trace amount of cis-stilbene was also detected. c Trace amount of cis-DMOS was also detected. d Isolated yield.
e The products were obtained by reduction using thiourea. f The products were obtained by reduction using PPh3.
synthesized according to the literature methods.31,37,38 Other
reagents were purchased from commercial sources.
and concentrated. Silica gel column chromatography (petroleum
ether:ethyl acetate = 6:1) gave ethyl 4-ethynylbenzoate (1.5 g, 50%
yield) as yellow acicular crystals.
UV/vis spectra were measured by a Shimadzu UV-1601PC
Spectrophotometer. Fluorescence spectra were run on a Hitachi
F-4500. Luminescent decay profiles were obtained by Edinburgh
LP 920 using the third harmonic (355 nm) of a pulse Nd:YAG
laser as excitation source. The characteristics of the polymer were
determined by Waters 515 GPC with columns HP2 & HP3 &
HP4 (515 HPLC pump, 2410 RI detector). A gas chromatograph
(GC) was monitored on a Shimadzu GC-14B. ESR spectroscopic
experiments were carried out at room temperature (298 K) with a
Bruker ESP 300E spectrometer.
Ethyl 4-ethynylbenzoate (1.5 g, 8.6 mmol) was refluxed with
NaOH (0.4 g, 10 mmol) in a mixture of methanol and water
(30 ml, 1: 5) for 6 h; after the system was cooled down,
adequate hydrochloric acid was added until there was a white
precipitate formed, filtered solid was recrystallized by methanol,
4-ethynylbenzoic acid (1.1 g, 7.8 mmol, 90% yield) was obtained as
white schistous crystals. MS: m/z = 146 (M+). 1H NMR (CDCl3,
300 MHz) d: 8.06 (d, J = 8 Hz, 2H), 7.59 (d, J = 8 Hz, 2H), 3.27
(s, 1H); (CD3CN, 300 MHz) d: 8.10 (d, J = 8 Hz, 2H), 7.59 (d,
J = 8 Hz, 2H), 3.91 (s, 1H), 3.53 (b, 1H).
4-Ethynylbenzoic acid
Ethyl 4-iodobenzoate (3.40 ml, 20.0 mmol), Pd(PPh3)2Cl2
(50.0 mg, 0.071 mmol), CuI (75.7 mg, 0.40 mmol) and PPh3
(65.4 mg, 0.25 mmol) were dissolved in 60 ml solvent of triethy-
lamine and pyridine (1: 1), after degassing, 2-methylbut-3-yn-2-
ol (3.90 ml, 40 mmol) was added and the mixture was stirred
at room temperature for 2 h. The reaction was quenched by
the addition of adequate hydrochloric acid and extracted with
dichloromethane; the organic layer was washed with brine, dried
over MgSO4, and concentrated. The residue was purified by silica
gel column chromatography (petroleum ether:ethyl acetate = 6:1),
which furnished ethyl 4-(3-hydroxy-3-methylbut-1-ynyl)benzoate
(4.0 g, 87% yield) as yellow acicular crystals.
NaH (50%, 1.5 g, 31 mmol) was added to a stirred solu-
tion of ethyl 4-(3-hydroxy-3-methylbut-1-ynyl)benzoate (4.0 g,
17.3 mmol) in 200 ml benzene at 75 ◦C for 1 h, the mixture
was distilled slowly until about 50 ml liquid was remaining, the
residue was filtered, washed with ethyl acetate, dried over MgSO4,
N-(3-(triethoxysilyl)propyl)-4-ethynylbenzamide
4-Ethynylbenzoic acid (300 mg, 2.0 mmol) and SOCl2 (5 ml)
were refluxed in THF (20 ml) for 3 h, then the mixture was
vacuum distilled to eliminate solvent and excessive SOCl2. The
residue was dissolved into 20 ml anhydrous CH2Cl2, then another
20 ml CH2Cl2 solution of (3-aminopropyl)triethoxysilane (0.60 ml,
2.6 mmol) and 2 ml NEt3 was dropped in, with the reaction
process, there was white precipitate in the system. After filtration,
the residue was purified by silica gel column chromatography
(petroleum ether:ethyl acetate = 6:1), which furnished N-(3-
(triethoxysilyl)propyl)-4-ethynylbenzamide (420 mg, 1.2 mmol,
58% yield) as white acicular crystals. MS: m/z = 349 (M+). H
1
NMR (CDCl3, 400 MHz) d: 7.72 (d, J = 8 Hz, 2H), 7.53 (d, J =
8 Hz, 2H), 6.53 (b, 1H), 3.83 (q, J = 8 Hz, 6H), 3.46 (m, 2H), 3.18
(s, 1H), 1.76 (m, 2H), 1.24 (t, J = 8 Hz, 9H), 0.69 (t, J = 8 Hz,
2H).
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Pt(tpy)S
with a mixture of acetonitrile and water, which furnished
MonoPt(pbp)Cl (733 mg, 1.18 mmol, 90% yield) as a red solid.
The mixture of 4¢-(p-methylphenyl)-2,2¢:6¢,2¢¢-terpyridine
platium(II) chloride (58 mg, 0.098 mmol), N-(3-(triethoxysilyl)-
propyl)-4-ethynylbenzamide (44 mg, 0.125 mmol), 3 ml DMF
and 6 ml NEt3 was degassed under nitrogen for 15 min, after
6 mg CuI was added, the system was ultrasonicated for 8 h,
then 0.5 g NaClO4 was added, the system was ultrasonicated
for another hour. The reaction was stopped by the addition of
excessive ether, the formed precipitate was filtered, then rinsed
by water and ether, the residue was redissolved in acetonitrile,
adequate ether was added, the reformed precipitate was filtered
and dried, a red solid was obtained (77 mg, 0.080 mmol, 81%
yield). HRMS: calcd. for [C40H43N4O4Pt194Si]+ 865.2680, found
865.2669 (M+) (67%); calcd. for [C40H43N4O4Pt195Si]+ 866.2701,
found 866.2678 (M+) (100%); calcd. for [C40H43N4O4Pt196Si]+
867.2703, found 867.2698 (M+) (99%). 1HNMR (DMSO-d6,
400 MHz) d: 8.96 (d, J = 8 Hz, 2H), 8.89 (s, 2H), 8.72 (d, J =
8 Hz, 2H), 8.42 (m, 2H), 8.00 (d, J = 8 Hz, 2H), 7.78 (m, 4H),
7.41 (m, 4H), 3.73 (q, J = 7 Hz, 6H), 3.23 (t, J = 7 Hz, 2H), 2.45
(s, 3H), 1.57 (m, 2H), 1.12 (t, J = 8 Hz, 9H), 0.58 (t, J = 8 Hz,
2H). Anal. calcd. for C40H43ClN4O8PtSi·H2O: C, 48.80; H, 4.61;
N, 5.69. Found: C, 48.12; H, 4.24; N, 5.53.
1
FAB-MS: m/z = 621 (M+). HNMR (DMSO-d6, 400 MHz) d:
5.42 (d, J = 11 Hz, 1H), 5.59 (s, 2H), 6.00 (d, J = 18 Hz, 1H),
6.90 (dd, J = 18 and 12 Hz, 1H), 7.17 (t, J = 7 Hz, 1H), 7.25
(t, J = 7 Hz, 1H), 7.56 (d, J = 7 Hz, 1H), 7.69 (m, 4H), 7.73 (d,
J = 7 Hz, 1H), 8.03 (t, J = 7 Hz, 1H), 8.23 (s, 1H), 8.44 (t, J =
7 Hz, 1H), 8.51 (s, 1H), 8.75 (d, J = 8 Hz, 1H), 8.92 (d, J = 8 Hz,
1H). Anal. Calcd. for C26H19ClN2O2Pt: C, 50.21; H, 3.08; N, 4.50.
Found: C, 50.07; H, 3.24; N, 4.15.
MonoPt(pbp)L
The mixture of MonoPt(pbp)Cl (125 mg, 0.020 mmol, according to
the amount of the functional group Pt(bpy)Cl), phenyl acetylene
(4.0 ml, 0.036 mmol), 5 ml DMF and 10 ml NEt3 was degassed
under nitrogen for 15 min, after 6 mg CuI was added, the system
was kept in ultrasonic conditions for 8 h. The reaction was
quenched by the addition of adequate ether after the system cooled
down. The formed precipitate was filtered and rinsed by water
and ether, then redissolved in dichloromethane; after filtering, the
solution was concentrated to a suitable small volume, excessive
ether was added, the reformed precipitate was filtered and rinsed
by ether again, which furnished a salmon solid MonoPt(pbp)L
(112 mg, 82% yield). FAB-MS: m/z = 687 (M+). 1H NMR
(DMSO-d6, 400 MHz) d: 5.42 (d, J = 11 Hz, 1H), 5.59 (s, 2H),
6.00 (d, J = 18 Hz, 1H), 6.90 (dd, J = 18 and 12 Hz, 1H), 7.18 (t,
J = 7 Hz, 1H), 7.25 (t, J = 7 Hz, 1H), 7.33–7.51 (m, 4H), 7.68–
7.79 (m, 7H), 7.97 (m, 1H), 8.31 (m, 1H), 8.42 (m, 1H), 8.59 (m,
1H), 8.73 (d, J = 8 Hz, 1H), 9.04 (d, J = 8 Hz, 1H). Anal. Cacld.
for C34H24N2O2Pt: C, 59.39; H, 3.52; N, 4.07. Found: C, 59.27; H,
3.36; N, 3.88.
Pt(tpy)SG
Pt(tpy)S (1.35 mg, 1.40 mmol), TEOS (7.52 g, 36.1 mmol) and 3 ml
water were dissolved in 200 ml mixture of acetonitrile and acetone
(1: 3), 3 ml 36% acetic acid was added to the system to adjust the pH
to around 5, the mixture was stirred at 40 ◦C for 24 h, after re◦moval
of the solvent the bulk gel was dried under vacuum at 60 C for
24 h, the solid was ground entirely with a carnelian mortar, the
crude product was rinsed with acetonitrile and acetone, a slightly
yellow powder Pt(tpy)SG (2.30 g) was obtained after further
drying under vacuum overnight. With various initial proportions
of Pt(tpy)S vs TEOS, Pt(tpy)SG of different loading amounts were
obtained for further experiments.
PolyPt(pbp)Cl
MonoPt(pbp)Cl (108 mg, 0.173 mmol) and styrene (2.00 ml,
17.3 mmol) was dissolved in 30 ml anhydrous DMF, after
degassing for 15 min, AIBN (2,2¢-azobisisobutyronitrile, 48 mg,
0.29 mmol) was added and the mixture was stirred at 75 ◦C for 24 h.
The reaction was quenched by the addition of adequate methanol
after the system cooled down. The formed precipitate was filtered
and rinsed by methanol, then redissolved in dichloromethane, ex-
cessive methanol was added, the reformed precipitate was filtered
and rinsed by methanol again, which furnished PolyPt(pbp)Cl
(1.74 g, 90% yield) as a red solid. 1H NMR (CDCl3, 300 MHz) d:
1.40 (br, 2H), 1.85 (br, 1H), 6.65 (br, 2H), 7.05 (br, 3H), 8.60 (br,
minor). The characteristics of the polymer were determined by gel
permeation chromatography (GPC) calibrated with polystyrene
standards in THF. Mn: 5037, Mw: 14714, PDI: 2.92.
4-Vinylbenzyl 6-phenyl-2,2¢-bipyridine-4-carboxylate
The mixture of 6-phenyl-2,2¢-bipyridine-4-carboxylic acid
(510 mg, 1.85 mmol), 4-vinylbenzyl chloride (0.50 ml, 3.5 mmol),
3 ml DMF and 6 ml NEt3 was stirred at room temperature
for 24 h. The reaction was quenched by addition of exces-
sive water, the precipitate was filtered and purified by silica
gel column chromatography (petroleum ether:ethyl acetate =
6:1), which furnished 4-vinylbenzyl 6-phenyl-2,2¢-bipyridine-4-
carboxylate (647 mg, 1.65 mmol, 90% yield) as white schistous
1
crystals. MS: m/z = 392(M+). H NMR (CDCl3, 300 MHz) d:
5.28 (d, J = 11 Hz, 1H), 5.46 (s, 2H), 5.80 (d, J = 17 Hz, 1H), 6.76
(dd, J = 18 and 11 Hz, 1H), 7.51 (m, 8H), 7.96 (m, 1H), 8.20 (d,
J = 7 Hz, 2H), 8.39 (s, 1H), 8.66 (d, J = 8 Hz, 1H), 8.80 (d, J =
3 Hz, 1H), 8.99 (s, 1H).
PolyPt(pbp)L
The mixture of PolyPt(pbp)Cl (355 mg, 0.032 mmol, according
to the amount of functional group Pt(bpy)Cl), phenylacetylene
(4.0 ml, 0.036 mmol), 6 ml DMF and 10 ml NEt3 was degassed
under nitrogen for 15 min; the system was ultrasonicated for 8 h
after 10 mg CuI was added. The reaction was quenched by the
addition of adequate methanol after the system had cooled down.
The formed precipitate was filtered and rinsed by methanol, then
redissolved in dichloromethane, excessive methanol was added,
MonoPt(pbp)Cl
The mixture of 4-vinylbenzyl 6-phenyl-2,2¢-bipyridine-4-
carboxylate (520 mg, 1.32 mmol) and K2PtCl4 (550 mg,
1.32 mmol) was refluxed in a mixture of acetonitrile and water
(150 ml, 1: 1) for 48 h. The precipitate was filtered and rinsed
9798 | Dalton Trans., 2009, 9794–9799
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the reformed precipitate was filtered and rinsed by methanol again,
which furnished a salmon solid PolyPt(pbp)L (287 mg, 80% yield).
1H NMR (CDCl3, 300 MHz) d: 1.40 (br, 2H), 1.80 (br, 1H), 6.70
(br, 2H), 7.10 (br, 3H), 8.70 (br, minor). The characteristics of
the polymer were determined by gel permeation chromatography
calibrated with polystyrene standards in THF. Mn: 6720, Mw:
16370, PDI: 2.43.
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Photooxidation experiments
R
The sample in a Pyrexꢀ reactor was bubbled with oxygen during
irradiation. A 500 W high-pressure Hanovia Hg lamp was
employed as the light source; a quartz jacket with water circulation
was used to cool the lamp. A glass filter was used to cut off light
with a wavelength below 400 nm and guaranteed irradiation with
visible light. The products were monitored by GC, GC-MS and
1H-NMR.
Acknowledgements
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We are grateful for financial support from the National Natural
Science Foundation of China (Nos. 20732007, 20672122, 20973189
and 50973125), the Ministry of Science and Technology of
China (Nos. 2006CB806105, G2007CB808004, 2007CB936001,
and 2009CB220008), and the Bureau for Basic Research of the
Chinese Academy of Sciences.
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