Synthesis of thioacetate-functionalized cobalt(II) porphyrins and their immobilization on gold surface - Characterization by X-ray photoelectron spectroscopy

Article abstract of DOI:10.1002/ejoc.200500656

Cobalt tetraarylporphyrins 1-Co and 2-Co with thioacetate-functionalized carbon chains on the aryl groups were synthesized. The cobalt porphyrin 2-Co was immobilized on a gold surface after deprotection of the S-acetyl group. The immobilized porphyrin was

Full text of DOI:10.1002/ejoc.200500656

FULL PAPER
DOI: 10.1002/ejoc.200500656
Synthesis of Thioacetate-Functionalized Cobalt(II) Porphyrins and Their
Immobilization on Gold Surface – Characterization by X-ray Photoelectron
Spectroscopy
Alida H. Éll,[a] Gábor Csjernyik,[a] Vincent F. Slagt,[a] Jan-E. Bäckvall,*[a] Simon Berner,[b]
Carla Puglia,*[c] Greger Ledung,[d] and Sven Oscarsson*[b,d]
Keywords: Functionalized porphyrin / Immobilization / Gold surface / Monolayers / Photoelectron Spectroscopy
Cobalt tetraarylporphyrins 1-Co and 2-Co with thioacetate-
functionalized carbon chains on the aryl groups were synthe-
sized. The cobalt porphyrin 2-Co was immobilized on a gold
surface after deprotection of the S-acetyl group. The immobi-
lized porphyrin was studied by X-ray Photoelectron Spec-
troscopy (XPS) and the results suggest that a complete mono-
layer of porphyrins is formed.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
Metal-catalyzed oxidation of organic compounds is a
continuously growing area of interest in organic chemistry
with many applications in industrial processes.[1] However,
there is an increased need for cleaner (“greener”) technol-
ogies, which are based on oxidation by molecular oxygen
or aqueous hydrogen peroxide. These oxidants are atom
economic and produce only water as the by-product. Direct
oxidation of organic substrates with these oxidants is usu-
ally inefficient and often proceeds in a non-selective man-
ner. However, in the presence of a suitable substrate-selec-
tive redox catalyst, like in nature,[2] combined with one or
several relaying redox-couples (electron-transfer mediators,
ETMs) the oxidation proceeds faster and in a selective man-
ner via the recycling of the components by O2 or H2O2
(Scheme 1).[3]
Scheme 1. Biomimetic oxidation involving electron-transfer media-
tor (ETM).
gen.[4a–d,4i–j,6] Based on the oxygen-activating properties of
the metalloporphyrins, mild biomimetic PdII-catalyzed oxi-
dations have also been developed.[6a] The most remarkable
feature of this system is that electrons from Pd0 are passed
through a benzoquinone-hydroquinone redox couple to the
oxidized form of the metal porphyrin (or to a related metal
macrocycle). The electron transfer between the hydroqui-
none and the oxidized form of the metal porphyrin is usu-
ally slow compared to the other electron transfer steps. A
solution to the latter problem was to employ a quinone-
functionalized porphyrin.[7] This, indeed, improved the rate
of the oxidation reaction, but still did not solve the problem
of oxidative dimerization. Moreover, metal porphyrins have
several disadvantages in these catalytic systems. They have
Macrocyclic metal complexes, in particular metallopor-
phyrins have attracted attention as biomimetic catalysts in
oxidation reactions.[4] Most oxidations with metalloporphy-
rins have been carried out with oxidants such as iodosoben-
zene,[4f–4h] periodide,[4e] hypochlorite[5] and molecular oxy-
[a] Department of Organic Chemistry, Arrhenius Laboratory,
Stockholm University,
10691 Stockholm, Sweden
E-mail: jeb@organ.su.se
[b] Department of Surface Biotechnology, Biomedical Center, low solubility in most organic solvents, they can readily di-
Uppsala University,
merize and they degrade in acidic media. In order to over-
Box 577, 75123 Uppsala, Sweden
come the problem of the deactivation, originating from the
homogeneous condition, we decided to study the surface-
immobilization of the metal porphyrin.
Porphyrins have been covalently bound to various kinds
of surfaces[8] such as silicon,[9] silica,[10] and polymers[11]
and gold[12] and they were also encapsulated in zeolites.[13]
The most intensively studied and successful existing meth-
E-mail: sven.oscarsson@ytbioteknik.uu.se
[c] Department of Physics, Uppsala University,
Box 524, 75120 Uppsala, Sweden
E-mail: carla.puglia@fysik.uu.se
[d] Department of Biology and Chemical Engineering, Mälardalen
University,
Box 325, 63105 Eskilstuna, Sweden
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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ods are based on the sulfur–gold linkages, and a large be metallated by standard procedures.[14k,15,16] In this paper,
number of porphyrin monomers bearing thiols have been we present both approaches towards S-acetyl functionalized
prepared.[14] In order to avoid the problems associated with cobalt() porphyrins containing four S-acetyl-protected lin-
disulfide formation the thiol is best handled in a protected kers (1-Co and 2-Co, Figure 1) and an efficient route to the
form.[15] It has been reported that S-acetyl, S-cyano, S-(N- formation of cobalt() porphyrin monolayers on gold sur-
ethylcarbamoyl) protecting groups undergo cleavage in-situ face. These nanostructured functional materials are of
on gold electrodes.[14k] In the present report we have pre- growing interest for the rational design and their use in elec-
pared thiol-functionalized cobalt porphyrins as their S-ace- tronic optical and biosensor applications.[17]
tyl-protected derivatives and studied their attachment to a
gold surface.
Results and Discussion
The prevalent synthetic routes to porphyrin thioacetates
Synthesis of Thioacetate-Functionalized Cobalt(II) Por-
phyrins: The first step towards the synthesis of the porphy-
rin of 1-Co was a palladium-catalyzed Sonogoshira coup-
ling between 4-bromobenzaldehyde, (3) and 5-chloro-1-pen-
tyne, yielding 4-(5-chloro-1-pentynyl)benzaldehyde (4) in
79% yield (Scheme 2). Attempts to use 4-chlorobenzalde-
hyde were unsuccessful and did not lead to the desired
product. The aldehyde 4 was protected as the acetal to pre-
vent side reactions in the subsequent steps. The alkyne func-
tionality was reduced via a RhCl(PPh3)3-catalyzed hydro-
genation to give a quantitative yield of 6. The thioacetate
was subsequently introduced via a nucleophilic displace-
ment of the chloride by KSAc to furnish 7 in 98% yield.
Deprotection of the acetal afforded the desired aldehyde 8
in 93% yield.
comprise the derivatization of the substituted porphyrins
with a suitable reagent to thioacetate unit.[14] Alternatively,
there are routes present in the literature where S-acetyl-deri-
vatized benzaldehyde-thiols were converted into the corre-
sponding porphyrins,[14] which upon alkaline hydrolysis af-
forded the free thiols. The S-acetyl-protected porphyrin can
The synthesis of the S-acetyl protected porphyrin 1 was
carried out according to the method developed by Lind-
sey[14k] (Scheme 3), in which trifluoro acetic acid was used
to catalyze the condensation of the freshly distilled pyrrole
with 8.
Two routes were examined for the synthesis of 2, as is
shown in Scheme 4. The first route involved the synthesis
thiol-aldehyde 11 followed by the acid-catalyzed condensa-
tion of 11 with pyrrole. The latter condensation resulted in
34% yield of S-acetyl-protected thiol-porphyrin 2.[14k] The
synthesis of 11 involved the reaction of 1,3-dibromopro-
pane with 3-hydroxybenzaldehyde (9) to give bromide 10,
followed by quantitative substitution of the bromide in 10
with potassium thioacetate, to produce 11 (Scheme 4).
Alternatively, porphyrin 2 was synthesized via porphyrin
12, which was obtained from aldehyde 10 and pyrrole in a
25% yield. Subsequent substitution of all four bromides in
12 with potassium thioacetate afforded 2 in 78% yield.
Figure 1. Thioacetate-functionalized cobalt() porphyrins for im-
mobilization on gold surface.
Scheme 2. Reagents and conditions: a. 5-chloro-1-pentyne, Pd(OAc)2, PPh3, NEt3, CuI, THF, room temp. overnight; b. ethylene glycol,
TsOH, benzene, reflux, 12 h; c. RhCl(PPh3)3, H2, benzene, room temp. 14 h; d. KSAc, reflux, 13 h, 56 °C; e. TsOH, acetone, H2O, reflux,
14 h.
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Thioacetate-Functionalized Co Porphyrins Immobilized on a Au Surface
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Preparations of 1-Co and 2-Co were conducted quantita-
tively by direct metallation of 1 and 2 with Co(OAc)2·4H2O
by standard literature procedure (Scheme 5).[14k]
X-ray Photoelectron Spectroscopy Study of the Immobi-
lized CoII Porphyrin Layers: Immobilized Co-porphyrin lay-
ers were prepared by acidic deprotection of 2-Co to give 13-
Co followed by the immobilization on a gold surface
(Scheme 6). The resulting porphyrin layers were studied by
means of X-ray Photoelectron Spectroscopy (XPS).
In Figure 2 (a) a survey photoelectron spectrum of the
bare Au surface obtained at a take off angle (TOA) of 10°
of the emitted photoelectrons is presented. No additional
contaminants besides residual carbon and oxygen could be
detected.
Scheme 3. Reagents and conditions: l. 1: pyrrole, TFA, DCM, room
temp., 1.5 h, 2: p-chloranil, reflux, 1 h.
Figure 2 (b) shows a survey spectrum at a TOA of 10°
for the deprotected 2-Co porphyrins 13-Co deposited on the
Au surface. The spectrum of the sample after molecular de-
position looks different, and shows additional features com-
pared to the spectrum of the bare Au surface. The new
peaks appearing in the spectrum can be related to the dif-
ferent atomic constituents of the molecule. The intensity ra-
tio in the spectrum for N, S and Co agrees, within the statis-
tical error with the molecular stoichiometry. Higher inten-
sity than expected is detected for carbon and oxygen.[18]
The slightly too high intensity of carbon can be explained
by the contamination of the bare Au surface and additional
air contamination of the molecular layer during mounting
the sample and introducing it into the load-lock chamber
of the XPS instrument. The same considerations can be ap-
plied to explain the too high intensity detected for oxygen,
i.e. it is very likely that oxygen adsorbs to the cobalt-center
of the 13-Co molecule. The high oxygen signal can also be
related to a not-completed deprotection of the 2-Co mole-
cules. However, the oxygen contamination makes it difficult
to give a quantitative estimation of the yield for the depro-
tection Scheme used.
The data shown in Figure 2 (b) corresponds to a deposi-
tion time in the order of 20 hours. For longer deposition
times the same results with non-increasing spectral intensity
were obtained. Consequently, saturation of the molecular
layer on the Au surface is reached, i.e. the growth stops
after an initial layer. The molecular coverage has been cal-
Scheme 4. Reagents and conditions: g. 1,3-diromopropane, NaOH,
H2O, room temp., 24 h; h. KSAc, THF, reflux, 16 h. i. 1: pyrrole,
TFA, DCM, room temp., 1.5 h, 2: p-chloranil, reflux 1 h; j. 1: pyr-
role, TFA, DCM, room temp., 1.5 h, 2: p-chloranil, reflux 1 h; k.
KSAc, THF, reflux 40 h.
Scheme 5. Reagents and conditions: k. Co(OAc)2·4H2O, DCM/MeOH, 4:1, reflux, 2 h.
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Scheme 6. Reagents and conditions: l. HCl(aq.), DMF, room temp.
Figure 3 illustrate the immobilization of the cobalt por-
phyrin 13-Co (deprotected Co-2) to the gold surface.
Conclusions
We have successfully prepared 1-Co and 2-Co in rela-
tively good overall yields, by acid-catalyzed condensation
of the corresponding S-acetyl-functionalized benzaldehydes
and pyrrole followed by direct metallation of the porphy-
rins. Moreover, an alternative route is presented for 2-Co
via the derivatization of the corresponding bromo-function-
alized porphyrin 12. After deprotection of the cobalt()
porphyrin 2-Co a complete porphyrin monolayer on Au
surface was formed, as indicated by the XPS results.
Experimental Section
General Procedures: 1H NMR and 13C NMR spectra were mea-
sured on a Varian Mercury (300 MHz or 400 MHz and at 75 MHz
or 100 MHz, respectively) in CDCl3 as solvent, if not otherwise
specified. Chemical shifts (δ values) are reported in ppm, using the
residual solvent peak in CDCl3 (δH = 7.26 and δC 77.0) as internal
standards, coupling constants (J) are given in Hz and without signs.
Flash column chromatography was performed by use of 60 Å (35–
70 µm) silica gel. MALDI mass spectra were obtained on a Finne-
gan-MAT GCQ four sector mass spectrometer using 3-nitrobenzyl
alcohol as matrix. UV/Vis spectra were recorded on a Varian Cary
50 spectrophotometer. XPS measurements have been performed in
Figure 2. a) Photoelectron spectrum obtained at a take off angle
(TOA) of 10° of the bare Au surface prior to molecular deposition.
The peaks corresponding to carbon and oxygen contamination are
marked. All other features in the spectrum are related to the Au
substrate. The most intensive photoemission line for Au is also
marked (Au4f). b) Photoelectron spectrum at a TOA of 10° of 13-
Co (deprotected 2-Co) on the Au surface. The different atomic con-
stituents of the molecule are present and marked in the spectrum.
culated using the XPS data. The result corresponds to the a Scienta ESCA 300 spectrometer using monochromized Al-Kα X-
rays with a photon energy of 1487 eV.
formation of a complete monolayer. These findings suggest
that a complete monolayer of porphyrins is formed in anal-
ogy to the results obtained for self-assembled monolayers
(SAM) on Au surfaces.[12a]
Materials: All reagents were purchased from commercial suppliers
and used without further purification. CH2Cl2, diisopropylethyl-
amine and triethylamine were distilled from CaH2. Pyrrole was dis-
Figure 3. Immobilization of cobalt porphyrin on a gold surface via sulfur tails.
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Thioacetate-Functionalized Co Porphyrins Immobilized on a Au Surface
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tilled prior to use. DMF was dried on CaH2 overnight then distilled
under vacuum prior to use.
3-(3-Formylphenoxy)propyl Bromide (10):[20] 3-Hydroxybenzalde-
hyde (9) (18.3 g, 150 mmol) was dissolved in a 75 mL aqueous solu-
tion of sodium hydroxide (150 mmol). After flushing with argon,
36.3 g (180 mmol) 1,3-dibromopropane was added and the reaction
mixture was stirred vigorously, over a 24-hour period under reflux.
The mixture was cooled, the layers were separated, and the aqueous
phase was extracted with dichloromethane (2×40 mL). The non-
aqueous layers were combined, washed with four 50 mL portions
of 2.0  aqueous sodium hydroxide, once with 50 mL 2.0  HCl,
and with two 50 mL portions of water. The organic layer was dried
(MgSO4) and concentrated. The product was purified by distil-
lation to give an analytically pure sample of 10 in a yield of 72%.
1H NMR (300 MHz): δ = 9.97 (s, 1 H), 7.45–7.38 (m, 3 H), 7.17
(m, 1 H), 4.16 (t, 2 H, J = 6.0 Hz), 3.60 (t, 2 H, J = 6.3 Hz), 2.34
(m, 2 H). 13C NMR (75.4 MHz): δ = 192.3, 159.5, 138.1, 130.3,
123.9, 122.1, 113.1, 65.8, 32.4, 30.0; m/z for C10H11BrO2 ([M]):
241.99 (calcd. 241.9942).
Polycrystalline gold films on Si(100) wafers were prepared by ther-
mal evaporation of a Cr adhesion layer (about 10 nm) followed by
thermal evaporation of about 150 nm of gold. These substrates
were cleaned in piranha solution [H2SO4:H2O2 30% (v/v), 2:1] and
rinsed with ultra pure water. Finally, the substrates were blow dried
with Ar. No additional contaminants could be detected in the XPS
besides a low amount of residual carbon and oxygen.
The smoothness of the clean surfaces was checked by atomic force
microscopy (AFM). Images with a scan range of 1 µm×1 µm were
taken at different spots on the surface in order to determine the
surface roughness. The resulting root mean square (RMS) is about
2.9 nm.
4-(5-Chloro-1-pentynyl)benzaldehyde (4): Triphenylphosphane
(280 mg, 1.06 mmol), Pd(OAc)2 (108 mg, 0.48 mmol), triethylamine
(4.4 mL, 31.3 mmol) and CuI (122 mg, 0.64 mmol) were dissolved
in 50 mL of THF under argon atmosphere. 4-Bromobenzaldehyde
(1.85 g, 10.0 mmol) was added via a syringe, followed by dropwise
addition of 5-chloro-1-pentyne (1.052 mL, 10.0 mmol). The reac-
tion mixture was stirred overnight at room temperature. The sol-
vent was removed under reduced pressure, and the residue was
purified by column chromatography (pentane/ethyl acetate, 85:15)
to give 1.64 g (79%) of 4. 1H NMR (300 MHz, CDCl3, 20 °C): δ =
2.07 (t, J = 7 Hz, 2 H), 2.64 (t, J = 7 Hz, 2 H), 3.70 (t, J = 6 Hz,
2 H), 7.51 (d, J = 8 Hz, 2 H), 7.80 (d, J = 9 Hz, 2 H), 9.97 (s, 1
H). 13C NMR (CDCl3, 20 °C): δ = 17.21, 31.42, 43.82, 81.18, 92.98,
129.73, 130.20, 132.36, 135.40, 191.65. Compound 4 was charac-
terized by comparison with spectroscopic data reported in ref.[19]
(ref.[19] reports 1H and 13C NMR in CD2Cl2, which are almost iden-
tical to those reported here).
Thioacetate 11: Bromide 10 (12.4 g, 51.2 mmol) and potassium
thioacetate (11.7 g 102.3 mmol) were dissolved in 100 mL of dry
THF and the mixture was refluxed for 16 hours. After cooling to
ambient temperature, the reaction mixture was filtered to remove
precipitates and the solvent of the filtrate was evaporated in vacuo.
The dark brown oil was dissolved in 75 mL diethyl ether and
washed twice with 75 mL of brine. The organic layer was dried
(MgSO4), filtered, and the solvent was evaporated in vacuo. The
product was purified by flash chromatography (silica, pentane/di-
1
ethyl ether, 4:1) to yield 12.0 g (98%) of thioacetate 11. H NMR
(300 MHz): δ = 9.96 (s, 1 H), 7.45–7.42 (m, 2 H), 7.37 (m, 1 H),
7.16 (m, 1 H), 4.06 (t, 2 H, J = 6.0 Hz), 3.06 (t, 2 H, J = 6.9 Hz),
2.33 (s, 3 H), 2.09 (m, 2 H). 13C NMR (75.4 MHz): δ = 195.8,
192.3, 159.6, 138.0, 130.3, 123.8, 122.1, 113.0, 66.7, 30.9, 29.4, 26.0;
m/z for C12H14O3S ([M]): 238.0669. (calcd. 238.0664).
2-[4-(5-Chloro-1-pentynyl)phenyl]-1,3-dioxolane (5): p-Toluenesul-
fonic acid monohydrate (151 mg, 0.80 mmol) was dissolved in
12 mL of benzene. Aldehyde 4 (1.64 g, 7.9 mmol) and ethylene
glycol (2.2 mL, 39.4 mmol) were added via syringe. The resulting
mixture was refluxed under Dean–Stark condition for 12 h. The
reaction mixture was washed three times with 15 mL of saturated
NaHCO3 solution. The organic phase was dried with K2CO3, and
the solvent was removed under reduced pressure to give 1.80 g
5,10,15,20-Tetrakis[4-(5-thioacetoxypentyl)phenyl]porphyrin
(1).
General Porphyrin Synthesis: Compound 7 (1074 mg, 3.65 mmol)
and p-toluenesulfonic acid monohydrate (138 mg, 0.73 mmol) were
dissolved in a mixture of 15 mL of acetone and 2.3 mL of H2O and
refluxed for 14 h. The solvent mixture was evaporated under re-
duced pressure and the solid residue was separated with column
chromatography with (pentane/ethyl acetate, 95:5), yielding 0.981 g
(93%) of 4-(5-thioacetoxypentyl)benzaldehyde (8). Aldehyde 8 was
used directly for the next step. Pyrrole (1.50 mL, 21.6 mmol) and
aldehyde 8 (5.4 mL, 21.6 mmol) were dissolved in 500 mL dichloro-
methane. Under argon atmosphere a solution of trifluoroacetic
acid (1.65 mL, 21.6 mmol) in 10 mL dichloromethane was slowly
added. The reaction mixture was stirred for 1.5 hours in the dark
under argon, during which time it turned dark purple. p-Chloranil
(3.98 g, 16.2 mmol) was added and the mixture was refluxed for
1 hour. After the mixture was cooled to ambient temperature, tri-
ethylamine (3.0 mL, 21.6 mmol) was added in order to neutralize
the solution. The reaction mixture was filtered and the volume re-
duced to approximately 50 mL. The product was purified using col-
umn chromatography (silica, CH2Cl2) to yield the porphyrin deriv-
ative 1 (1.92 g, 1.62 mmol, 30%). 1H NMR (300 MHz, CDCl3,
20 °C): δ = –2.73 (br. s, 2 H), 1.64 (m, 8 H), 1.77 (m, 8 H), 1.93
(m, 8 H), 2.38 (s, 12 H), 2.96 (t, J = 7 Hz, 8 H), 3.00 (t, J = 7 Hz,
8 H), 7.54 (d, J = 7 Hz, 8 H), 8.13 (d, J = 7 Hz, 8 H), 8.87 (s, 8
1
(95%) of 5. H NMR (300 MHz, CDCl3, 20 °C): δ = 2.06 (p, J =
7 Hz, 2 H), 2.61 (t, J = 7 Hz, 2 H), 3.71 (t, J = 6 Hz, 2 H), 4.00–
4.14 (m, 4 H), 5.79 (s, 1 H), 7.4 (s, 4 H). 13C NMR (CDCl3, 20 °C):
δ = 17.11, 31.65, 43.95, 65.53, 81.49, 88.90, 103.57, 124.67, 126.59,
131.81, 137.65.
2-[4-(5-Thioacetoxypentyl)phenyl]-1,3-dioxolane (7): Compound 5
(947 mg 3.78 mmol) and RhCl(PPh3)3 (70 mg, 0.075 mmol) were
dissolved under hydrogen atmosphere in 20 mL benzene. After 14 h
of stirring at room temperature the reaction was complete accord-
1
ing to H NMR spectra and the benzene was evaporated to give 6
as a solid, which was used in the subsequent step without further
characterization. The remaining solid 6 was dissolved in 70 mL of
acetone and potassium thioacetate (0.843 g, 7.4 mmol) was added
at once. The resulting mixture was refluxed for 13 h. The solid resi-
due was filtered off, followed by the evaporation of the acetone.
The remaining solid was dissolved in 400 mL diethyl ether and ex-
tracted with water (3×400 mL). The organic layer was dried with
Na2SO4 and the solvent was removed under vacuum to yield
H). m/z for C72H77N4O4S4 ([M]): 1191.27. UV (CH2Cl2): λabs
420, 516, 553, 599, 649 nm.
=
1
1.084 g (98%) of 7. H NMR (300 MHz, CDCl3, 20 °C): δ = 1.40
(m, 2 H), 1.62 (m, 4 H), 2.31 (s, 3 H), 2.68 (t, J = 7 Hz, 2 H), 2.85 5,10,15,20-Tetrakis[3-(3-thioacetoxypropoxy)phenyl]porphyrin (2):
(t, J = 7 Hz, 2 H), 7.32 (d, J = 8 Hz, 2 H), 7.79 (d, J = 8 Hz, 2 H), Prepared according to the general method from 11 (5.15 g,
9.97 (s, 1 H). 13C NMR (CDCl3, 20 °C): δ = 28.53, 29.13, 29.56, 21.6 mmol) and pyrrole (1.50 mL, 21.6 mmol) which afforded the
30.70, 30.86, 36.18, 129.29, 130.15, 134.72, 150.15, 192.20, 196.23.
porphyrin derivative 2 (2.3 g, 2.0 mmol, 34%). Alternatively, por-
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phyrin 12 (1.14 g, 0.981 mmol) and potassium thioacetate (671 mg,
5.88 mmol) were dissolved in 50 mL dry THF and the mixture was
refluxed for 40 hours. After cooling to ambient temperature, the
reaction mixture was filtered and the solvent was evaporated in
vacuo. The porphyrin was dissolved in 50 mL dichloromethane and
washed two times with 75 mL water. The organic layer was dried
with sodium sulfate, filtered and the evaporated to dryness. The
product was purified using column chromatography (silica, dichlo-
romethane) to yield porphyrin 2 (0.76 mmol, 0.87 g, 78%). 1H
NMR (300 MHz): δ = 8.92 (s, 8 H), 7.84 (d, 4 H, J = 7.8 Hz), 7.79
(s, 4 H), 7.65 (t, 4 H, J = 7.8 Hz), 7.33 (d, 4 H, J = 8.1 Hz), 4.22
(t, 8 H, J = 6.0 Hz), 3.14 (t, 8 H, J = 7.2 Hz), 2.32 (s, 12 H), 2.17
(m, 8 H), –2.78 (s, 2 H). 13C NMR (75.4 MHz): δ = 195.9, 157.4,
143.7, 132.2–130.7, 128.1, 127.8, 121.4, 120.1, 114.4, 66.7, 30.9,
29.7, 26.2. UV (CH2Cl2): λabs = 418, 514, 549, 589, 646 nm.
Acknowledgments
Financial support from the Swedish Foundation for Strategic Re-
search is gratefully acknowledged. We thank Prof. Ulrik Gelius and
Hans Lidbaum for assistance in the XPS measurements and for
helpful discussions.
[1] a) “Modern Oxidation Methods” (Ed. J. E. Bäckvall, Wiley-
VCH), 2004; b) G. W. Parshall, Homogeneuos Catalysis; Wiley-
Interscience: New York, 1980; c) R. A. Sheldon, J. K. Koichi,
Metal-Catalyzed Oxidation of Organic Compounds; Academic
Press: New York, 1981; d) M. Hudlický, Oxidation in Organic
Chemistry ACS Monograph 186; American Chemical Society:
Washington, DC, 1909.
[2] M. N. Huges, The Inorganic Chemistry of Biological Processes;
Wiley: Chichester, UK, 1981.
5,10,15,20-Tetrakis[3-(3-bromopropoxy)phenyl]porphyrin (12): Pre-
pared according to the general porphyrin synthesis from pyrrole
(1,50 mL, 21.6 mmol) and 10 (5,25 g, 21.6 mmol) to give 12 (1.55 g,
[3] G. Strukul, Catalytic Oxidations with Hydrogen Peroxide as
Oxidant, Kluwer: Dordrecht, The Netherlands, 1992.
[4] a) I. Tabushi, N. Koga, J. Am. Chem. Soc. 1979, 101, 6456–
6458; b) J. T. Groves, R. J. Quinn, J. Am. Chem. Soc. 1985, 107,
5790–5792; c) M. Perrée-Fauvet, A. Gaudemer, J. Chem. Soc.,
Chem. Commun. 1981, 874–875; d) D. Mansuy, M. Fontecave,
J.-F. Bartoli, J. Chem. Soc., Chem. Commun. 1983, 253–254; e)
J.-P. Renaud, J.-F. Battioni, D. Mansuy, J. Chem. Soc., Chem.
Commun. 1985, 888–889; f) J. T. Groves, W. J. Kruper, R. C.
Haushalter, J. Am. Chem. Soc. 1980, 102, 6375–6377; g) C. L.
Hill, B. C. Schardt, J. Am. Chem. Soc. 1980, 102, 6374–6375;
h) J. T. Groves, T. E. Nemo, R. S. Myers, J. Am. Chem. Soc.
1979, 101, 1032–1033; i) J.-E. Bäckvall, A. K. Awasthi, Z. D.
Renko, J. Am. Chem. Soc. 1987, 109, 4750–4752; j) J.-E.
Bäckvall, R. B. Hopkins, Tetrahedron Lett. 1988, 29, 2885–
2888.
[5] E. Guilmet, B. Meunier, Tetrahedron Lett. 1980, 21, 4449–4450.
[6] a) J.-E. Bäckvall, R. B. Hopkins, H. Grennberg, M. M. Mader,
A. K. Awasthi, J. Am. Chem. Soc. 1990, 112, 5160–5166; b) J.-
E. Bäckvall, R. L. Chowdhury, U. Karlsson, J. Chem. Soc.,
Chem. Commun. 1991, 473–475; c) G. Csjernyik, A. H. Éll, L.
Fadini, B. Pugin, J.-E. Bäckvall, J. Org. Chem. 2002, 67, 1657–
1662.
1
1.33 mmol, 25%). H NMR (300 MHz): δ = 8.90 (s, 8 H), 7.84 (d,
4 H, J = 7.8 Hz), 7.79 (s, 4 H), 7.65 (t, 4 H, J = 7.8 Hz), 7.34 (d,
4 H, J = 8.1 Hz), 4.30 (t, 8 H, J = 6.3 Hz), 3.68 (t, 8 H, J = 6.3 Hz),
2.41 (m, 8 H), –2.80 (s, 2 H). 13C NMR (75.4 MHz): δ = 157.3,
143.7, 131.8–130.5, 128.1, 127.8, 121.4, 120.0, 114.3, 65.8, 32.8,
30.2. UV (CH2Cl2): λabs = 419, 514, 551, 591, 646 nm.
5,10,15,20-Tetrakis[4-(5-thioacetoxypentyl)phenyl]porphyrincobalt-
(II) (1-Co). General Procedure: Porphyrin 1 (119 mg, 0.1 mmol) was
dissolved in 20 mL of a 4:1 mixture of CH2Cl2 and MeOH under
argon atmosphere. Co(OAc)2·4H2O (30.6 mg, 0.12 mmol) was
added and the resulting reaction mixture was refluxed for 2 h. The
formation of 1-Co was confirmed by UV spectroscopy. Yield:
112 mg, 98%. UV (CH2Cl2): λabs = 412, 530 nm.
5,10,15,20-Tetrakis[3-(3-thioacetoxypropoxy)phenyl]porphyrin-
cobalt(II) (2-Co): Prepared according to the general procedure from
114 mg (0.1 mmol) of porphyrin 2 and 30.6 mg (0.12 mmol) of Co-
(OAc)2·4H2O in 20 mL of 4:1 mixture of CH2Cl2 and MeOH to
give 117 mg (98%) of 2-Co. UV (CH2Cl2): λabs = 410, 529 nm.
[7] a) H. Grennberg, S. Faizon, J.-E. Bäckvall, Angew. Chem. 1993,
105, 269–271; Angew. Chem. Int. Ed. Engl. 1993, 32, 263–264;
b) H. Grennberg, J.-E. Bäckvall, J. Chem. Soc., Chem. Com-
mun. 1993, 1331–1332; c) R. C. Verboom, V. F. Slagt, J.-E.
Bäckvall, Chem. Commun. 2005, 1282–1284.
[8] R. A. Sheldon (Ed.), Metalloporphyrins in Catalytic Oxi-
dations, Marcel Dekker, New York, 1994.
Immobilization of 2-Co on a Gold Surface: The evaporated gold
substrates on Si wafers were cleaned in Piranha solution
[H2SO4:H2O2 (30% aq.), 2:1] and rinsed with ultra pure water prior
to molecular deposition. The Au surface was checked for remaining
contaminants by means of XPS. A solution of 0.5 m 2-Co in N,N-
dimethylformamide (DMF) was prepared. Deprotection of the S-
acetyl groups was performed by adding 40 molar excess of HCl.
After an initial reaction time in the order of 2 hours for the depro-
tection to take place, the Au surface was immersed in the molecular
solution for typically 20 hours. Then the sample was rinsed with
DMF, soaked for 10–20 minutes in DMF, rinsed again with DMF
and afterwards with ultra-pure water and finally blow dried in ar-
gon. The immobilization was confirmed by XPS.
[9] E. Pavlovic, A. P. Quist, U. Gelius, L. Nyholm, S. Oscarsson,
Langmuir 2003, 19, 4217–4221.
[10] a) P. Battioni, J. F. Bartoli, D. Mansuy, Y. S. Byun, T. G.
Traylor, J. Chem. Soc., Chem. Commun. 1991, 1051–1153; b)
F. L. Beneditoa, S. Nakagaki, A. A. Saczka, G. P. Peralta-Za-
morab, C. M. Macedo Costa, Appl. Catal. A 2003, 250, 1–11;
c) M. A. Schiavon, Y. Iamamoto, O. R. Nascimento, M. D.
Assis, J. Mol. Catal. A: Chem. 2001, 174, 213–222.
[11] a) B. Meunier, Chem. Rev. 1992, 92, 1411–1456; b) J. P.
Collman, X. M. Zhang, V. J. Lee, E. S. Uffelman, J. I. Brau-
man, Science 1993, 261, 1404–1408; c) D. Mansuy, Coord.
Chem. Rev. 1993, 125, 129–141; d) F. Bedioui, J. Devynick, C.
Bied-Charreton, Acc. Chem. Res. 1995, 28, 30–36; e) X.-Q. Yu,
J.-S. Huang, W.-Y. Yu, C.-M. Che, J. Am. Chem. Soc. 2000,
122, 5337–5342.
[12] a) A. Ulman, An Introduction to Ultrathin Organic Films: From
Langmuir-Blodgett to Self-Assembly; Academic Press: Boston,
MA, 1997; b) T. A. Postlethwaite, J. E. Hutchison, K. W.
Hathcock, R. W. Murray, Langmuir 1995, 11, 4109–4116; c) T.
Kondo, T. Ito, S. Nomura, K. Uosaki, Thin Solid Films 1996,
284–285, 652–655; d) T. R. E. Simpson, M. J. Cook, M. C.
Petty, S. C. Thorpe, D. A. Russell, Analyst 1996, 121, 1501–
1505; e) T. R. E. Simpson, D. J. Revell, M. J. Cook, D. A. Rus-
Surface Coverage Estimation by XPS: The coverage has been calcu-
lated by comparing the intensity of the N1s signal to the intensity
of the Au4f signal according to ref.[21] Standard cross sections have
been used for the calculation. The calculated coverage is 0.67 mol-
cules/nm2. This corresponds to an area of 150 Å2 per molecule.
This result fits very well to the size of a single porphyrin and corre-
sponds therefore to a full monolayer.
Supplementary Information (see footnote on the first page of this
1
article): General procedures. Copies of H and 13C NMR spectra
of compounds 1, 2, 5, 7, 10, 11, and 12. This material is available
free of charge via the Internet (http://www.eurjoc.org) or from the
author.
1198
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 1193–1199

Thioacetate-Functionalized Co Porphyrins Immobilized on a Au Surface
FULL PAPER
sell, Langmuir 1997, 13, 460–464; f) A. Ishida, Y. Sakata, T.
Majima, Chem. Lett. 1998, 267–269; g) A. Ishida, Y. Sakata,
8367–8368; m) R. C. Jagessar, J. M. Tour, Org. Lett. 2000, 2,
111–113.
T. Majima, Chem. Commun. 1998, 57–58; h) H. Imahori, H.
Norieda, S. Ozawa, K. Ushida, T. Yamada, T. Azuma, K. Ta-
maki, Y. Sakata, Langmuir 1998, 14, 5335–5338; i) M. Yanag-
ida, T. Kanai, X.-Q. Zhang, T. Kondo, K. Uosaki, Bull. Chem.
Soc. Jpn. 1998, 71, 2555–2559; j) J. Zak, H. Yuan, M. Ho, K. L.
Woo, M. D. Porter, Langmuir 1993, 9, 2772–2774; k) L. H. Du-
bois, R. G. Nuzzo, Annu. Rev. Phys. Chem. 1992, 43, 437–465;
l) A. Ulman, Chem. Rev. 1996, 96, 1533–1554; m) T. A. Eber-
spacher, J. P. Collman, C. E. D. Chidsey, D. L. Donohue, H.
Van Ryswyk, Langmuir 2003, 19, 3814–3821.
[15] a) J. S. Lindsey, S. Prathapan, T. E. Johnson, R. W. Wagner,
Tetrahedron 1994, 50, 8941–8968; b) M. Ravikanth, J.-P. Stra-
chan, F. Li, J. S. Lindsey, Tetrahedron 1998, 54, 7721–7734; c)
J. S. Lindsey, in The Porphyrin Handbook; (Eds.: Kadish,
K. M., Smith, K., Guilard, R.); Academic Press: Burlington,
MA, 1999.
[16] a) D. T. Gryko, C. Clausen, K. M. Roth, N. Dontha, D. F. Bo-
cian, W. G. Kuhr, J. S. Lindsey, J. Org. Chem. 2000, 65, 7345–
7355.
[17] a) E. Katz, I. Willner, Angew. Chem. Int. Ed. 2004, 43, 6042–
6108; b) C. M. Niemeyer, W. Burger, J. Peplies, Angew. Chem.
Int. Ed. 1998, 37, 2265–2268; c) C. M. Niemeyer, Angew. Chem.
Int. Ed. 2001, 40, 4128–4158; d) S. Mann, W. Shenton, M. Li,
S. Connolly, D. Fitzmaurice, Adv. Mater. 2000, 12, 147–150; e)
F. Caruso, Adv. Mater. 2001, 13, 11–22; f) S. G. Penn, L. He,
M. Natan, J. Curr. Opin. Chem. Biol. 2003, 7, 609–615; g) T. A.
Taton, Trends Biotechnol. 2002, 20, 277–279; h) Y. Xiao, F. Pa-
tolsky, E. Katz, J. F. Hainfeld, I. Willner, Science 2003, 299,
1877–1881.
[18] The XPS ratios were calculated with standard cross sections
and are normalized with the number of nitrogens in the mole-
cule): S/N = 1.3, C/N = 17.2, O/N = 2.6, Co/N = 0.18; real
ratios in the molecule: protected: S/N = 1, C/N = 16, O/N =
2, Co/N = 0.25; completely deprotected: S/N = 1, C/N = 14,
O/N = 1, Co/N = 0.25.
[13] a) K. J. Balkus Jr, A. K. Khanmamedova, K. M. Dixon, F. Be-
dioui, Appl. Catal A: General 1996, 143, 159–173; b) B.-Z.
Zhan, X.-Y. Li, Chem. Commun. 1998, 349–350; c) I. L. Vi-
ana Rosa, C. M. C. P. Manso, O. A. Serra, Y. Iamamoto, J.
Mol. Catal: Chem. 2000, 160, 199–208; d) X.-Q. Wang, S. Gao,
C.-S. Cao, L.-X. Yu, J.-F. Guo, X.-Z. Cao, J. Porphyrins
Phthalocyanines 1998, 2, 209–217; e) J. Wöltinger, J.-E.
Bäckvall, A. Zsigmond, Chem. Eur. J. 1999, 5, 1460–1467.
[14] a) Y. Kuroda, T. Hiroshige, T. Sera, Y. Shiroiwa, H. Tanaka,
H. Ogoshi, J. Am. Chem. Soc. 1989, 111, 1912–1913; b) J. E.
Hutchison, T. A. Postlethwaite, R. W. Murray, Langmuir 1993,
9, 3277–3283; c) J. E. Bradshaw, S. Moghaddas, L. Wilson, J.
Gazz. Chim. Ital. 1994, 124, 159–164; d) T. Akiyama, H. Im-
ahori, Y. Sakata, Chem. Lett. 1994, 1447–1449; e) I. Chambrier,
M. J. Cook, D. A. Russell, Synthesis 1995, 1283–1287; f) L.-H.
Guo, G. McLendon, H. Razafitrimo, Y. J. Gao, Mater. Chem.
1996, 6, 369–374; g) K. Shimazu, M. Takechi, H. Fujii, M.
Suzuki, H. Saiki, T. Yoshimura, K. Uosaki, Thin Solid Films
1996, 273, 250–253; h) H. Yuan, L. K. Woo, J. Porphyrins
[19] A. Fürstner, C. Mathes, Org. Lett. 2001, 3, 221–223.
[20] Similar procedure as: E. E. Schweizer, C. J. Berninger, D. M.
Crouse, R. A. Davis, R. Schepers Logothetis, J. Org. Chem.
1969, 34, 207–212.
Phthalocyanines 1997, 1, 189–200; i) T. Kondo, M. Yanagida, [21] D. D. Naumovic, “Surfaces of Noble Metals and Metal-on-
S. Nomura, T. Ito, K. J. Uosaki, Electroanal. Chem. 1997, 438,
121–126; j) L. Wen, M. Li, J. B. Schlenoff, J. Am. Chem. Soc.
1997, 119, 7726–7733; k) D. T. Gryko, C. Clausen, J. S. Lind-
sey, J. Org. Chem. 1999, 64, 8635–8647; l) K. Uosaki, T. Kondo,
X.-Q. Zhang, M. Yanagida, J. Am. Chem. Soc. 1997, 119,
Metal Systems Studied by Full-Hemispherical Photoelectron
Diffraction”, PhD Thesis, University of Fribourg (Switzer-
land), 1993.
Received: August 30, 2005
Published Online: December 19, 2005
Eur. J. Org. Chem. 2006, 1193–1199
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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