Synthesis of "Porphyrin-Linker-Thiol" Molecules with Diverse Linkers for Studies of Molecular-Based Information Storage

Article abstract of DOI:10.1021/jo000487u

The attachment of redox-active molecules such as porphyrins to an electroactive surface provides an attractive approach for electrically addressable molecular-based information storage. Porphyrins are readily attached to a gold surface via thiol linkers. The rate of electron transfer between the electroactive surface and the porphyrin is one of the key factors that dictates suitability for molecular-based memory storage. This rate depends on the type and length of the linker connecting the thiol unit to the porphyrin. We have developed different routes for the preparation of thiol-derivatized porphyrins with eight different linkers. Two sets of linkers explore the effects of linker length and conjugation, with one set comprising phenylethyne units and one set comprising alkyl units. One electron-deficient linker has four fluorine atoms attached directly to a thiophenyl unit. To facilitate the synthesis of the porphyrins, convenient routes have been developed to a wide range of aldehydes possessing a protected S-acetylthio group. An efficient synthesis of 1-(S-acetylthio)-4-iodobenzene also has been developed. A set of porphyrins, each bearing one S-acetyl-derivatized linker at one meso position and mesityl moieties at the three remaining meso positions, has been synthesized. Altogether seven new aldehydes, eight free base porphyrins and eight zinc porphyrins have been prepared. The zinc porphyrins bearing the different linkers all form self-assembled monolayers (SAMs) on gold via in situ cleavage of the S-acetyl protecting group. The SAM of each porphyrin is electrochemically robust and exhibits two reversible oxidation waves.

Full text of DOI:10.1021/jo000487u

J . Org. Chem. 2000, 65, 7345-7355
7345
Syn th esis of “P or p h yr in -Lin k er -Th iol” Molecu les w ith Diver se
Lin k er s for Stu d ies of Molecu la r -Ba sed In for m a tion Stor a ge
Daniel T. Gryko,† Christian Clausen,† Kristian M. Roth,‡ Narasaiah Dontha,‡
David F. Bocian,*,‡ Werner G. Kuhr,*,‡ and J onathan S. Lindsey*,†
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, and
Department of Chemistry, University of California, Riverside, California 92521-0403
jlindsey@ncsu.edu
Received March 30, 2000
The attachment of redox-active molecules such as porphyrins to an electroactive surface provides
an attractive approach for electrically addressable molecular-based information storage. Porphyrins
are readily attached to a gold surface via thiol linkers. The rate of electron transfer between the
electroactive surface and the porphyrin is one of the key factors that dictates suitability for
molecular-based memory storage. This rate depends on the type and length of the linker connecting
the thiol unit to the porphyrin. We have developed different routes for the preparation of thiol-
derivatized porphyrins with eight different linkers. Two sets of linkers explore the effects of linker
length and conjugation, with one set comprising phenylethyne units and one set comprising alkyl
units. One electron-deficient linker has four fluorine atoms attached directly to a thiophenyl unit.
To facilitate the synthesis of the porphyrins, convenient routes have been developed to a wide range
of aldehydes possessing a protected S-acetylthio group. An efficient synthesis of 1-(S-acetylthio)-
4-iodobenzene also has been developed. A set of porphyrins, each bearing one S-acetyl-derivatized
linker at one meso position and mesityl moieties at the three remaining meso positions, has been
synthesized. Altogether seven new aldehydes, eight free base porphyrins and eight zinc porphyrins
have been prepared. The zinc porphyrins bearing the different linkers all form self-assembled
monolayers (SAMs) on gold via in situ cleavage of the S-acetyl protecting group. The SAM of each
porphyrin is electrochemically robust and exhibits two reversible oxidation waves.
In tr od u ction
accessible oxidation states, the neutral state, monocation,
and dication. Porphyrins form stable radical cations and
dications and undergo reversible electrochemistry.2 (2)
The electrochemical potential of a porphyrin can be tuned
over a large range (>0.5 V) by choice of central metal3
and peripheral substituents.4 (3) The use of arrays
comprising multiple porphyrins (and other redox-active
moieties) with distinct oxidation potentials affords the
possibility of storing a large number of bits in a single
memory cell. (4) The methodology for synthesizing por-
phyrin monomers5 and multiporphyrin arrays,6 while far
from mature, has been developed sufficiently for explora-
We recently reported an approach for molecular-based
memory storage that employs a monolayer of redox-active
molecules attached to an electroactive surface.1 Informa-
tion is stored in the distinct oxidation states of the redox-
active molecules. Multiple bits of information can be
stored through the use of molecules or molecular arrays
that afford a set of distinct oxidation states. Writing and
reading information in the molecules is accomplished
electrically at room temperature under real-world condi-
tions. This molecular-based approach differs from the use
of semiconductor technology or disk drives for informa-
tion storage and is anticipated to provide a much higher
storage density.
This molecular-based information storage approach
has an absolute requirement for reversible electrochemi-
cal writing and reading processes. While information can
in principle be stored either in cationic or anionic states,
we have chosen to work with molecules that afford
reversible interconversion among neutral and cationic
states due to the greater stability of cations versus anions
under ambient conditions. Among the molecules consid-
ered for information storage, porphyrinic molecules stand
out for the following reasons. (1) Porphyrins provide three
(2) Felton, R. H. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. V, pp 53-126.
(3) Fuhrhop, J .-H.; Mauzerall, D. J . Am. Chem. Soc. 1969, 91, 4174-
4181.
(4) Yang, S. I.; Seth, J .; Strachan, J . P.; Gentemann, S.; Kim, D.;
Holten, D.; Lindsey, J . S.; Bocian, D. F. J . Porphyrins Phthalocyanines
1999, 3, 117-147.
(5) Lindsey, J . S. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2000; Vol.
1, pp 45-118.
(6) (a) Nakano, A.; Osuka, A.; Yamazaki, I.; Yamazaki, T.; Nish-
imura, Y. Angew. Chem., Int. Ed. Engl. 1998, 37, 3023-3027. (b)
Mongin, O.; Papamicae¨l, C.; Hoyler, N.; Gossauer, A. J . Org. Chem.
1998, 63, 5568-5580. (c) Burrell, A. K.; Officer, D. L. Synlett 1998,
1297-1307. (d) Mak, C. C.; Bampos, N.; Sanders, J . K. M. Angew.
Chem., Int. Ed. Engl. 1998, 37, 3020-3023. (e) Mak, C. C.; Pomeranc,
D.; Montalti, M.; Prodi, L.; Sanders, J . K. M. Chem. Commun. 1999,
1083-1084. (f) Li, J .; Ambroise, A.; Yang, S. I.; Diers, J . R.; Seth, J .;
Wack, C. R.; Bocian, D. F.; Holten, D.; Lindsey, J . S. J . Am. Chem.
Soc. 1999, 121, 8927-8940. (g) Li, J .; Lindsey, J . S. J . Org. Chem.
1999, 64, 9101-9108. (h) Sugiura, K.; Tanaka, H.; Matsumoto, T.;
Kawai, T.; Sakata, Y. Chem. Lett. 1999, 1193-1194. (i) Mongin, O.;
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8347-8350.
* To whom correspondence should be addressed. (D.F.B., W.G.K.)
E-mail: dbocian@ucrac1.ucr.edu, werner.kuhr@ucr.edu.
† North Carolina State University.
‡ University of California.
(1) Roth, K. M.; Dontha, N.; Dabke, R. B.; Gryko, D. T.; Clausen,
C.; Lindsey, J . S.; Bocian, D. F.; Kuhr, W. G. J . Vac. Sci. Technol. B
2000, 18, 2359-2364.
10.1021/jo000487u CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/23/2000

7346 J . Org. Chem., Vol. 65, No. 22, 2000
Gryko et al.
tion of the basic concepts in this approach toward
molecular information storage. No other class of mol-
ecules appears to offer such a rich set of possibilities for
information storage applications.
and lanthanide porphyrinic triple-decker sandwich com-
plexes,26 respectively, also for multibit information stor-
age.
The studies reported in this first paper build from the
methods we have previously described for the synthesis
of thiol-derivatized porphyrin monomers for studies of
molecular-based information storage.27 In this previous
work, porphyrins bearing one thiol group were designed
for vertical organization on a gold surface, while porphy-
rins bearing two or four thiol groups were designed for
horizontal arrangement on a gold surface. The redox
potentials were tuned through variation in the meso
substituents and/or the central metal. The different meso
substituents can also give rise to altered packing patterns
of the molecules in a self-assembled monolayer (SAM).
Thiol protecting groups were examined for compatibility
with the reactions for porphyrin formation, metal inser-
tion, Pd-mediated coupling to form multiporphyrin ar-
rays, and in situ deprotection on a gold surface. The
S-acetylthio protecting group gave the best overall results
(including in situ cleavage on gold) and has been used in
almost all of our subsequent work.
A host of scientific issues has emerged from consider-
ation of this basic concept of electrically addressable
molecular-based information storage. How is the rate of
writing and reading information affected by the nature
of the linker that attaches the redox-active molecule to
the surface? What molecular features (e.g., linker length
and composition, nature of the redox-active unit, 3-di-
mensional architecture) affect the retention of charge
necessary for information storage? What is the maximum
number of bits that can be stored in a molecular array?
Do different oxidation states in a given molecule exhibit
different charge retention properties?
To begin addressing the above-noted fundamental
scientific questions, we have synthesized several families
of porphyrinic molecules and examined the electrochemi-
cal behavior of the molecules self-assembled on gold via
the thiol unit. While there is a sizable literature concern-
ing self-assembled monolayers (SAMs) of thiol-deriva-
tized porphyrins on gold electrodes,7-22 families of such
porphyrins suitable for systematic studies have hereto-
fore not been available. Our studies of the thiol-deriva-
tized porphyrins are reported herein and in the four
accompanying papers. This first paper describes thiol-
derivatized porphyrins containing diverse linkers de-
signed to explore how the linker affects the rates of
writing and reading as well as duration of information
storage (i.e., retention). The second paper describes a set
of weakly coupled thiol-derivatized ferrocene-porphyrin
arrays for studies of multibit information storage with
different types of redox-active units.23 The third paper
describes weakly coupled multiporphyrin arrays for
multibit information storage.24 The fourth and fifth
papers describe tightly coupled multiporphyrin arrays25
The synthetic methodology described above is used
herein to prepare a set of porphyrins, each bearing one
thioacetate group and three mesityl groups. These mol-
ecules are designed for vertical organization on a gold
surface. The prototypical example, synthesized in our
previous work,27 incorporates a thiol-derivatized p-phen-
ylene unit (linker A, Chart 1). This molecule binds to a
gold electrode and exhibits facile electronic communica-
tion with the gold surface.1 The p,p′-diphenylethyne unit
(linker B) increases the distance of the porphyrin from
the gold surface, potentially slowing writing/reading
rates, though linkers of this type are known to provide
efficient hole transport.28 A similar structure with one
additional methylene unit (linker C) provides a test of
whether a conjugated connection (e.g., a direct thiophenyl
attachment) is essential. An electron-deficient p-phen-
ylene linker is provided by linker D. The effects of a
progressive increase in the alkyl character of the linker
can be examined by comparison of linkers A, E, F, G, and
H. Finally, an ethynylphenyl linker (I) is employed to
achieve direct conjugation to the porphyrin.29 A system-
atic investigation of these porphyrins as memory storage
entities will be reported elsewhere.
(7) Hutchison, J . E.; Postlethwaite, T. A.; Murray, R. W. Langmuir
1993, 9, 3277-3283.
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Electroanal. Chem. 1997, 438, 121-126.
Resu lts a n d Discu ssion
A large number of porphyrin monomers bearing free
thiols or S-acetyl-derivatized thiols have been prepar-
ed.7,9,12,14,22,27,30-36 The traditional method of synthesis
(15) Uosaki, K.; Kondo, T.; Zhang, X.-Q.; Yanagida, M. J . Am. Chem.
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212, 23-30.
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Electroanal. Chem. 1999, 473, 75-84.
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F.; Kuhr, W. G.; Lindsey, J . S. J . Org. Chem. 2000, 65, 7356-7362.
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F.; Kuhr, W. G.; Lindsey, J . S. J . Org. Chem. 2000, 65, 7363-7370.
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D. F.; Kuhr, W. G.; Lindsey, J . S. J . Org. Chem. 2000, 65, 7371-7378.
(26) Li, J .; Gryko, D.; Dabke, R. B.; Diers, J . R.; Bocian, D. F.; Kuhr,
W. G.; Lindsey, J . S. J . Org. Chem. 2000, 65, 7379-7390.
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64, 8635-8647.
(28) (a) Seth, J .; Palaniappan, V.; J ohnson, T. E.; Prathapan, S.;
Lindsey, J . S.; Bocian, D. F. J . Am. Chem. Soc. 1994, 116, 10578-
10592. (b) Seth, J .; Palaniappan, V.; Wagner, R. W.; J ohnson, T. E.;
Lindsey, J . S.; Bocian, D. F. J . Am. Chem. Soc. 1996, 118, 11194-
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1994, 124, 159-162.

Synthesis of “Porphyrin-Linker-Thiol” Molecules
J . Org. Chem., Vol. 65, No. 22, 2000 7347
Ch a r t 1
benzaldehydes, which are converted to the respective
porphyrin with the protecting group intact.22,27,30,36 The
advantages of introducing the S-acetylthio moiety at the
aldehyde stage are as follows. (1) Synthetic manipulation
of the porphyrins is minimized. (2) The polarity imparted
by the S-acetylthio moiety facilitates separation of the
desired porphyrin from a mixed aldehyde condensation.
(3) Purification of the mixture formed upon thiol intro-
duction is often more straightforward at the aldehyde
rather than the porphyrin stage. For those molecules
where the linker is constructed using a Pd-mediated
coupling reaction (e.g., diphenylethyne), the reaction
conditions for use with aldehydes (high concentration,
inclusion of CuI) afford superior results compared with
those with porphyrins.39 Thus, we have opted to introduce
the S-acetyl-protected thiol unit at the aldehyde stage
throughout this work.
Syn th esis of Ald eh yd es. The synthesis of aldehydes
possessing a thioacetate group required several different
approaches. Five of the aldehydes possess an alkanethiol
unit, and three contain an aryl thiol unit. The former are
usually obtained by straightforward reaction of an alkyl
halide and a thiol reagent (thioacetate, thiourea), while
the latter (S-protected or free thiol form) are often
obtained with more difficulty. The few known methods
for preparing aryl thiols, from aryl sulfides or aryl
halides, generally require harsh conditions. Thus, we
searched for other approaches for incorporating the
S-acetyl group in arenes. The S-acetyl group is compat-
ible with a variety of reaction conditions, including those
in porphyrin formation and Pd-mediated iodoethyne
couplings,27 but is labile in the presence of some bases
(e.g., triethylamine, alumina) if attached to an arene.
The structure of the aldehyde bearing linker B sug-
gested an obvious method of synthesis via Pd-coupling
of 4-iodobenzaldehyde with 1-(S-acetylthio)-4-ethynyl-
benzene (3) (Scheme 1). The synthesis of compound 3
requires 1-(S-acetylthio)-4-iodobenzene (1). We found that
the reported procedures40,41 for preparing 1 required
tedious purification. In searching for a more efficient
pathway to this key molecule, the selective transforma-
tion of 1-fluoro-4-iodobenzene into 1-(S-acetylthio)-4-
iodobenzene using conditions developed by Tiecco and co-
workers42 was attempted. However, we obtained an
inseparable mixture of products, regardless of the tem-
perature and the amount of MeSNa used. Sita and co-
workers converted pipsyl chloride (4-iodobenzenesulfonyl
chloride) to 1-iodo-4-mercaptobenzene.43 We adopted this
attractive route but with the use of the nonaqueous
conditions for reduction of sulfonyl chlorides recently
reported by Uchiro and Kobayashi,44 thereby obtaining
a much higher yield. Thus, pipsyl chloride was success-
fully reduced to 1-iodo-4-mercaptobenzene which upon
treatment in situ with acetyl chloride gave the desired
involves the derivatization of a substituted porphyrin
with a thiol reagent or protected thiol unit. The emer-
gence of mild conditions for preparing porphyrins has
made possible those strategies where sensitive or elabo-
rate substituents are incorporated in the aldehyde pre-
cursor to the porphyrin.5,37,38 This latter approach has
been explored using S-acetyl-protected thio-derivatized
(38) (a) Lindsey, J . S.; Prathapan, S.; J ohnson, T. E.; Wagner, R.
W. Tetrahedron 1994, 50, 8941-8968. (b) Ravikanth, M.; Strachan,
J .-P.; Li, F.; Lindsey, J . S. Tetrahedron 1998, 54, 7721-7734.
(39) Wagner, R. W.; Ciringh, Y.; Clausen, C.; Lindsey, J . S. Chem.
Mater. 1999, 11, 2974-2983.
(40) Pearson, D. L.; Tour, J . M. J . Org. Chem. 1997, 62, 1376-1387.
(41) Hsung, R. P.; Babcock, J . R.; Chidsey, C. E. D.; Sita, L. R.
Tetrahedron Lett. 1995, 26, 4525-4528.
(32) Yuan, H.; Woo, L. K. J . Porphyrins Phthalocyanines 1997, 1,
189-200.
(33) Wen, L.; Li, M.; Schlenoff, J . B. J . Am. Chem. Soc. 1997, 119,
7726-7733.
(34) Shaw, S. J .; Elgie, K. J .; Edwards, C.; Boyle, R. W. Tetrahedron
Lett. 1999, 40, 1595-1596.
(42) (a) Tiecco, M.; Tingoli, M.; Testaferri, L.; Chianelli, D.; Maiolo,
F. Synthesis 1982, 478-480. (b) Testaferri, L.; Tiecco, M.; Tingoli, M.;
Chianelli, D.; Montanucci, M. Synthesis 1983, 751-755.
(43) Hsung, R. P.; Chidsey, C. E. D.; Sita, L. R. Organometallics
1995, 14, 4808-4815.
(35) Shaw, S. J .; Edwards, C.; Boyle, R. W. Tetrahedron Lett. 1999,
40, 7585-7586.
(36) J agessar, R. C.; Tour, J . M. Org. Lett. 2000, 2, 111-113.
(37) Lindsey, J . S. In Modular Chemistry, Michl, J ., Ed., NATO ASI
Series C: Mathematical and Physical Sciences, Vol. 499, Kluwer
Academic Publishers: Dordrecht, 1997; pp 517-528.
(44) Uchiro, H.; Kobayashi, S. Tetrahedron Lett. 1999, 40, 3179-
3182.

7348 J . Org. Chem., Vol. 65, No. 22, 2000
Gryko et al.
Sch em e 1
Sch em e 2
1-(S-acetylthio)-4-iodobenzene (1, 85%) after straightfor-
ward chromatographic purification. The zinc chloride
formed in the first step is a likely catalyst of the acylation
in the second step. The iodobenzene 1 obtained in this
manner was successfully converted into the ethyne
derivative 3 using established procedures.40,41 The Pd-
mediated coupling of 3 and 4-iodobenzaldehyde smoothly
afforded aldehyde 4 in 90% yield. As noted by Sita and
co-workers,41 it is essential to use a hindered amine such
as N,N-diisopropylethylamine (DIEA) instead of triethy-
lamine to obtain satisfactory yields in all Pd-coupling
reactions involving the S-acetylthiophenyl group.
The synthesis of aldehyde 8 proceeded along a similar
strategy (Scheme 2). Treatment of 1-(bromomethyl)-4-
iodobenzene with thioacetate under very mild condi-
tions45 gave 5, which upon Pd-coupling with trimethyl-
silylacetylene afforded the building block bearing two
protecting groups (6). Deprotection of the TMS group in
6 gave 7, which upon Pd-mediated coupling with 4-iodo-
benzaldehyde furnished aldehyde 8. Each reaction in this
sequence afforded high yields.
the para position of pentafluorobenzenes is known to be
very reactive toward nucleophilic substitution. Indeed,
pentafluorophenyl-substituted porphyrins were recently
reported to undergo fluoro-substitution by alkanethi-
ols.34,35 Thus, treatment of pentafluorobenzaldehyde with
thioacetate (using conditions resembling those used in
the reaction of potassium thioacetate with benzyl halides)
resulted in disappearance of the substrate, and the only
product was a very polar substance which bound at the
origin upon TLC analysis (silica, CH2Cl2). We surmised
that the latter might be the anion of 2,3,5,6-tetrafluoro-
4-mercaptobenzaldehyde (formed by thioester cleavage
following nucleophilic substitution), and upon treatment
with acetyl chloride the desired aldehyde 9 was obtained
in 69% yield after chromatography.
The synthesis of aldehyde 10 was accomplished using
the strategy previously reported for 3-(S-acetylthiometh-
yl)benzaldehyde.27 Reduction of the commercially avail-
able 4-(bromomethyl)benzonitrile with DIBALH gave the
corresponding 4-(bromomethyl)benzaldehyde.33,46,47 Sub-
stitution of the bromide with potassium thioacetate gave
the desired S-acetyl-protected thiobenzaldehyde 10 in
good yield (eq 2).
The next target aldehyde was 4-(S-acetylthio)-2,3,5,6-
tetrafluorobenzaldehyde (9) (eq 1). The fluorine atom in
(45) Zheng, T.-C.; Burkart, M.; Richardson, D. E. Tetrahedron Lett.
1999, 40, 603-606.
(46) Bookser, B. C.; Bruice, T. C. J . Am. Chem. Soc. 1991, 113,
4208-4218.
(47) The reduction was performed according to the procedure for
the synthesis of 3-(bromomethyl)benzaldehyde. See: Wagner, R. W.;
J ohnson, T. E.; Lindsey, J . S. Tetrahedron 1997, 53, 6755-6790.

Synthesis of “Porphyrin-Linker-Thiol” Molecules
J . Org. Chem., Vol. 65, No. 22, 2000 7349
Sch em e 3
Aldehyde 11 was synthesized by radical addition48 of
thioacetic acid to 4-vinylbenzaldehyde49 (eq 3).
The homologous propyl aldehyde 15 was synthesized
starting from 4-bromobenzaldehyde (Scheme 3). Protec-
tion of the carbonyl group as the cyclic acetal 1250 and
conversion to the corresponding Grignard reagent fol-
lowed by addition of allyl bromide furnished intermediate
13. Radical addition of thioacetic acid afforded acetal 14,
which was easily hydrolyzed to the respective aldehyde
15 (overall yield 18% from 4-bromobenzaldehyde).
The aliphatic aldehyde 17 was accessed via the same
procedure used for aldehyde 10. Aldehyde 16 was pre-
pared by reduction of 7-bromoheptanitrile with 1 equiv
of DIBALH (∼50% yield) or by oxidation of 7-bromo-1-
heptanol with PCC (82% yield).51 Treatment of crude
aldehyde 16 with potassium thioacetate afforded alde-
hyde 17 as a yellow oil in 51% yield (eq 4).
It is noteworthy that in each strategy employed, the
S-acetyl protecting group and the sulfur atom were
incorporated in one step, or the thiol unit was protected
in situ with an acetyl group. In so doing, the handling of
free thiols was avoided while working with a wide range
of thiol-derivatized compounds.
Syn th esis of P or p h yr in s. The investigation of por-
phyrins oriented in a vertical manner on an electroactive
surface can be achieved by the synthesis of porphyrins
bearing a p-thioaryl or ω-thioalkyl unit at one meso
position. Such A3B-porphyrins were prepared by a mixed-
aldehyde condensation in a two-step, one-flask synthesis
procedure. The conditions for condensation of pyrrole and
mesitaldehyde require BF3-ethanol cocatalysis, with
optimal reaction occurring in the presence of increased
BF3-etherate concentration (but not ethanol) as the
concentrations of pyrrole and aldehyde are increased.52
Nonsterically hindered aldehydes also undergo condensa-
tion with pyrrole in the presence of BF3-ethanol coca-
talysis.5 A mixed-aldehyde condensation of mesitalde-
One approach for the synthesis of porphyrin 26 in-
volves the preparation of 3-[4-(S-acetylthio)phenyl]pro-
pynal followed by mixed-aldehyde condensation, rather
than attempting the Pd-mediated coupling of an iodo or
ethynyl porphyrin. Due to the instability of propynal, we
performed a Pd-coupling of commercially available pro-
piolaldehyde diethylacetal with 1-(S-acetylthio)-4-iodo-
benzene (1) (eq 5). The desired acetal 18 was obtained
in 64% yield.
(48) Lub, J .; Broer, D. J .; van den Broek, N. Liebigs Ann. Recueil
1997, 2281-2288.
(49) Vinyl benzaldehyde was synthesized by the procedure of Ren,
J .; Sakakibara, K.; Hirota, M. Bull. Chem. Soc. J pn. 1993, 66, 1897-
1902 with the following changes: The addition of DMF was performed
at a 38 mmol scale at 0 °C. Purification by column chromatography
(silica, Et2O/hexanes, 1:3) afforded 4-vinylbenzaldehyde in 60% yield.
(50) Hewlins, M. J . E.; J ackson, A. H.; Long, A.; Oliveira-Campos,
A.; Shannon, P. V. R. J . Chem. Res., Miniprint 1986, 8, 2645-2696.
(51) Enders, D.; Bartzen, D. Liebigs Ann. Chem. 1991, 569-574.
(52) Wagner, R. W.; Li, F.; Du, H.; Lindsey, J . S. Org. Proc. Res.
Dev. 1999, 3, 28-37.

7350 J . Org. Chem., Vol. 65, No. 22, 2000
Gryko et al.
Sch em e 4
Sch em e 5
difficulties in conversion to the porphyrin.5 The corre-
sponding zinc chelates Zn -19-Zn -26 were obtained by
reaction of the free base porphyrins 19-26 with
Zn(OAc)2‚2H2O (Chart 1). In each case, zinc insertion
occurred without altering the thiol protecting group.
Electr och em ica l Stu d ies. The electrochemical be-
havior of the Zn-porphyrins was investigated for samples
both in solution and self-assembled on gold. The solution
electrochemistry of each of the porphyrins is similar to
that previously reported for other aryl-substituted Zn-
porphyrins.2 In particular, each porphyrin exhibits two
reversible oxidation waves. The E1/2 values for all the
porphyrins in solution are similar to one another (E1/2(1)
∼0.58 V; E1/2(2) ∼0.86 V; versus Ag/Ag+; E1/2(FeCp2/
FeCp2+) ) 0.19 V), with the exception of Zn -21 and Zn -
26. The E1/2 values for Zn -21 are shifted ∼0.1 V more
positive due to fluorination of one of the porphyrin aryl
groups. The E1/2 values for Zn -26 are shifted ∼0.1 V more
negative due to the presence of the conjugating meso-
alkynyl group. The porphyrins bearing the different
linkers all form self-assembled monolayers (SAMs) on
gold via in situ cleavage of the S-acetyl protecting group.
The SAM of each of the porphyrins is electrochemically
robust and exhibits two reversible oxidation waves.
Representative fast-scan (100 V/s) cyclic voltammograms
of the Zn -20 SAM and Zn -23 SAM are shown in Figure
1. The voltammograms of the other Zn-porphyrins are
similar (not shown). As can be seen, the two oxidation
waves of the Zn-porphyrin SAMs are well resolved, as is
the case for the Zn-porphyrins in solution (not shown).
However, the two E1/2 values of the Zn -20 and Zn -23
SAM are each shifted ∼0.10-0.15 V more positive than
those observed in solution. This same behavior is ob-
served for the SAMs of the other Zn-porphyrins. The
positive shifts in redox potentials observed upon forma-
tion of the porphyrin SAMs are consistent with the
results of previous experiments on other electroactive
species (e.g., thiol-derivatized ferrocenes) on gold.53 Knowl-
edge of such shifts in potential is essential for the rational
hyde, a thiol-protected aldehyde, and pyrrole afforded a
mixture of porphyrins, from which the desired thiol-
protected A3B-porphyrin was obtained by chromatogra-
phy. The polarity imparted by the thioacetate group
facilitated separation of the mixture of free base porphy-
rins.
In this manner, aldehydes 4, 8-11, 15, and 17 were
converted to the thiol-protected A3B-porphyrins 19-25,
respectively, in yields of 7-22% (Scheme 4). It is note-
worthy that purification of most of the porphyrins was
achieved by silica pad filtration followed by one column
chromatography (or centrifugal preparative TLC) opera-
tion. This same approach was applied to acetal 18, but
the yield of the desired A3B porphyrin was only 0.8%
(Scheme 5). We attribute the low yield in part to the
competitive Michael reaction of pyrrole and the activated
alkyne. Ethynyl aldehydes are well-known to present

Synthesis of “Porphyrin-Linker-Thiol” Molecules
J . Org. Chem., Vol. 65, No. 22, 2000 7351
CA). Mass spectra were obtained via laser desorption (LD-MS)
in the absence of an added matrix,55 fast atom bombardment
(FAB-MS, 10 ppm elemental compositional accuracy for the
porphyrins), or electron-impact mass spectrometry (EI-MS).
ACS-grade chloroform (containing 0.75% ethanol) was used
in all porphyrin-forming reactions. Porphyrin metalation was
monitored by fluorescence emission and excitation spectro-
scopy. 4-Iodobenzaldehyde and 1-bromomethyl-4-iodobenzene
were obtained from Karl Industries, Ltd.
1-(S-Acetylth io)-4-iod oben zen e (1). Following a general
procedure,44 to a stirred suspension of zinc powder (3.80 g, 58.0
mmol) and dichlorodimethylsilane (7.00 mL, 58.0 mmol) in 1,2-
dichloroethane (126 mL) was added a solution of 4-iodoben-
zenesulfonyl chloride (5.00 g, 16.5 mmol) and N,N-dimethyl-
acetamide (4.60 mL, 50.0 mmol) in dichloroethane (126 mL).
The mixture was stirred at 75 °C for 2 h until the zinc powder
was no longer visible. The reaction mixture was cooled to 50
°C, and acetyl chloride (1.53 mL, 21.5 mmol) was added. After
15 min, the mixture was poured into water. The aqueous layer
was extracted with CH2Cl2, and the combined organic layers
were dried (Na2SO4), filtered, and evaporated. The colorless
oil thus obtained was chromatographed (silica, CH2Cl2/hex-
anes, 1:4) affording a colorless oil (3.93 g, 85%) that solidified
at -20 °C: mp 56-57 °C (lit.43 mp 54-55 °C); 1H NMR δ 2.42
(s, 3H), 7.12, 7.73 (AA′BB′, 2 × 2H); 13C NMR δ 31.0, 96.7,
128.4, 136.7, 139.0, 193.9. Anal. Calcd for C8H7IOS: C, 34.55;
H, 2.54; I, 45.63; S, 11.53. Found: C, 34.69; H, 2.59; I, 45.52;
S, 11.59.
F igu r e 1. Fast-scan (100 V/s) voltammetry of the Zn -20 SAM
(left panel) and the Zn -23 SAM (right panel).
design of molecular architectures for multibit information
storage.23-26
Con clu sion s
1-[4-(S-Acet ylt h io)p h en yl]-2-(4-for m ylp h en yl)a cet y-
len e (4). Samples of 4-iodobenzaldehyde (660 mg, 2.80 mmol),
340,41 (500 mg, 2.80 mmol), CuI (29 mg, 15 µmol), and
Pd(PPh3)2Cl2 (13 mg, 18 µmol) were placed in a Schlenk flask.
The flask was evacuated for 3 min then backflushed with argon
for 3 min. The process of evacuation and flushing was repeated
three times. The argon flow rate was increased, the threaded
stopcock was removed, and deaerated THF (5.0 mL) and DIEA
(5.0 mL) were added in succession by gastight syringe. The
threaded stopcock was replaced, the argon flow rate was
reduced, and the flask was immersed in an oil bath thermo-
stated at 40 °C. The reaction was stopped after 40 h. The
mixture was then filtered and evaporated. The resulting
orange-brown solid was chromatographed (silica, CH2Cl2/
hexanes, 2:3, then 1:1, then 3:2) to afford yellowish-white
crystals, which upon recrystallization (ethyl acetate/heptane)
afforded white crystals (707 mg, 90%): mp 128-129 °C (lit.36
The introduction of an S-acetyl-protected thiol unit in
an aldehyde enables the corresponding porphyrin to be
prepared without handling free porphyrin thiols. The
combination of a few simple strategies provided access
to a broad range of thiol-derivatized aldehydes. A set of
porphyrins has been prepared for vertical organization
via one linker on an electroactive surface. The S-acetyl
protecting group cleaves in situ when the porphyrin
contacts a gold surface. The porphyrins form SAMs that
exhibit robust, reversible electrochemistry. Collectively,
the studies indicated that all of the linker architectures
examined are potential candidates for molecular infor-
mation storage elements. This synthetic work now makes
possible a systematic examination of the effects of diverse
linker architectures on information storage properties,
including writing rate, reading rate, and information
retention. The results from such studies on linkers will
be incorporated with studies on multibit architectures
described in the companion papers23-26 in an effort to
design more sophisticated molecular information storage
systems.
1
mp 122-123 °C); H NMR δ 2.65 (s, 3H), 7.63, 7.79 (AA′BB′,
2 × 2H), 7.87, 8.07 (AA′BB′, 2 × 2H), 10.22 (s, 1H); 13C NMR
δ 31.2, 91.0, 93.5, 124.5, 129.9, 130.0, 130.5, 133.1, 133.2, 135.2,
136.5, 192.3, 194.1; FAB-MS obsd 280.0551, calcd exact mass
280.0558. Anal. Calcd for C17H12O2S: C, 72.83; H, 4.31; S,
11.44. Found: C, 72.66; H, 4.39; S, 11.52.
1-(S-Acetylth iom eth yl)-4-iod oben zen e (5). Following a
general procedure,45 potassium thioacetate (2.20 g, 19.3 mmol)
was added to a solution of 1-(bromomethyl)-4-iodobenzene (4.80
g, 16.2 mmol) in anhydrous N,N-dimethylacetamide (15 mL).
The mixture was stirred overnight at room temperature,
poured into water, and extracted with CH2Cl2. The combined
organic extracts were washed with water, dried (Na2SO4), and
evaporated. The resulting brown oil was distilled (90 °C, 0.005
mmHg) to give a pale-yellow oil that solidified after a few days
Exp er im en ta l Section
Gen er a l Met h od s. All chemicals obtained commercially
were used as received unless otherwise noted. Reagent-grade
solvents (CH2Cl2, CHCl3, hexanes, diethyl ether, acetone) and
HPLC-grade solvents (acetonitrile, toluene) were used as
received from Fisher. THF was distilled from sodium. Pyrrole
and triethylamine were each distilled from CaH2. All reported
NMR spectra were collected in CDCl3 (1H NMR at 300 MHz;
13C NMR at 75 MHz) unless noted otherwise. UV-vis absorp-
tion and fluorescence spectra were recorded in CH2Cl2 or
toluene as described previously.54 Melting points are uncor-
rected. Flash chromatography was performed on flash silica
(Baker, 200-400 mesh) or alumina (Fisher, 80-200 mesh).
Centrifugal preparative thin-layer chromatography was per-
formed using a Harrison Research Chromatotron (Palo Alto,
1
(4.68 g, 99%): mp 40-41 °C; H NMR δ 2.37 (s, 3H), 4.07 (s,
2H), 7.07, 7.64 (AA′BB′, 2 × 2H); 13C NMR δ 31.1, 33.6, 93.5,
131.6, 138.2, 138.4, 195.5; FAB-MS obsd 291.9425, calcd exact
mass 291.9419. Anal. Calcd for C9H9IOS: C, 37.00; H, 3.11; I,
43.44; S, 10.98. Found: C, 37.39; H, 3.13; I, 43.04; S, 11.26.
1-[4-(S-Acet ylt h iom et h yl)p h en yl)]-2-(t r im et h ylsilyl)-
a cetylen e (6). Following the procedure for 4, samples of 5
(2.92 g, 10.0 mmol), CuI (105 mg, 553 µmol), and Pd(PPh3)2-
Cl2 (46 mg, 66 µmol) were degassed, and then deaerated THF
(10.0 mL), DIEA (10.0 mL) and trimethylsilylacetylene (2.00
mL, 14.0 mmol) were added, and the reaction was carried out
(53) Creager, S. E.; Rowe, G. K. J . Electroanal. Chem. 1994, 370,
203-211.
(54) Li, F.; Gentemann, S.; Kalsbeck, W. A.; Seth, J .; Lindsey, J . S.;
Holten, D.; Bocian, D. F. J . Mater. Chem. 1997, 7, 1245-1262.
(55) Fenyo, D.; Chait, B. T.; J ohnson, T. E.; Lindsey, J . S. J .
Porphyrins Phthalocyanines 1997, 1, 93-99.

7352 J . Org. Chem., Vol. 65, No. 22, 2000
Gryko et al.
at 40 °C for 40 h. The mixture was then filtered and
evaporated. The resulting orange-brown solid was chromato-
graphed (silica, CH2Cl2/hexanes, 1:4, then 3:7) to afford a
slightly yellow oil that solidified upon standing at room
for 15 min. Then AIBN (20 mg) was added, and the mixture
was heated to 90 °C. After 2 h, more AIBN (160 mg) was added.
This was repeated after an additional 1 h. After 2 h, AIBN
(100 mg) was added again and the mixture was heated for an
additional 1 h. Then aqueous NaHCO3 (10%, 50 mL) was
added, and the phases were separated. The aqueous phase was
washed with diethyl ether, and the combined organic phases
were dried (Na2SO4). Purification by column chromatography
(silica, Et2O/hexanes, 1:3) gave an orange oil, which solidified
and darkened upon standing at -20 °C to give a black solid
(983 mg, 54%), which was pure enough for the next reaction.
A small sample was recrystallized from refluxing heptane to
afford colorless plates: mp 35 °C; IR (neat) ν˜ 3029, 2929, 2828,
1
temperature (2.40 g, 92%): mp 41-42 °C; H NMR δ 0.23 (s,
9H), 2.32 (s, 3H), 4.07 (s, 2H), 7.21, 7.36 (AA′BB′, 2 × 2H); 13
C
NMR δ 0.7, 31.0, 33.9, 95.1, 105.5, 122.8, 129.4, 132.8, 138.9,
195.4; FAB-MS obsd 262.0839, calcd exact mass 262.0848.
Anal. Calcd for C14H18SiOS: C, 64.07; H, 6.91; S, 12.22.
Found: C, 64.02; H, 6.99; S, 12.23.
1-[4-(S-Acetylth iom eth yl)p h en yl]a cetylen e (7). To a
solution of 6 (2.52 g, 9.60 mmol) in THF (30 mL) were added
acetic acid (0.2 mL) and acetic anhydride (0.2 mL). The mixture
was cooled to -20 °C, and a solution of Bu4NF (2.40 g, 9.60
mmol) in THF (20 mL) was added dropwise during 5 min. The
reaction mixture was kept at -20 °C for another 10 min and
then poured on a silica pad and eluted with CH2Cl2/hexanes
(1:1). The solvents were removed, and the residue was dis-
solved in CH2Cl2, dried (Na2SO4), and evaporated, affording a
yellowish oil (1.69 g, 92%): 1H NMR δ 2.13 (s, 3H), 2.88 (s,
1H), 3.88 (s, 2H), 7.02, 7.20 (AA′BB′, 2 × 2H); 13C NMR δ 30.8,
33.6, 83.8, 121.5, 129.3, 132.8, 139.0, 195.3; EI-MS obsd
190.0458, calcd exact mass 190.0452 (C11H10OS).
1
2737, 1699, 1606, 1578; H NMR δ 2.34 (s, 3H), 2.96 (t, J )
8.1 Hz, 2H), 3.15 (t, J ) 8.1 Hz, 2H), 7.40, 7.83 (AA′BB′, 2 ×
2H), 9.99 (s, 1H); 13C NMR (APT) δ 30.5 (+), 31.3 (-), 36.5
(+), 129.0 (-), 129.7 (-), 134.7 (+), 146.8 (+), 191.5 (-), 194.9
(+); GC-MS (EI) obsd 208. Anal. Calcd for C11H12O2S: C,
63.43; H, 5.81; S, 15.40. Found: C, 63.63; H, 5.90; S, 15.62.
2-(4-Br om op h en yl)-5,5-d im eth yl-1,3-d ioxa n e (12). The
following describes an improved procedure at three times
larger scale and in much shorter time compared with the
literature.50 4-Bromobenzaldehyde (3.00 g, 16.2 mmol), neo-
pentyl glycol (1.86 g, 17.9 mmol), and p-toluenesulfonic acid
(50 mg, 0.3 mmol) were dissolved in toluene (30 mL), and the
solution was refluxed for 3 h. Then the solution was cooled to
room temperature, washed with aqueous NaHCO3 (10%) and
water, and dried (Na2SO4). The solvent was evaporated, and
the oily residue was crystallized from hexanes, affording
colorless needles (2.81 g, 64%): 13C NMR (APT) δ 21.7 (-),
22.9 (-), 30.1 (+), 77.5 (+), 100.8 (-), 122.7 (+), 127.8 (-),
131.3 (-), 137.5 (+). Analytical data were consistent with the
literature.50
1-[4-(S-Acetylth iom eth yl)p h en yl]-2-(4-for m ylp h en yl)-
a cetylen e (8). Following the procedure for 4, samples of
4-iodobenzaldehyde (1.18 g, 5.00 mmol), 7 (950 mg, 5.00 mmol),
CuI (52 mg, 270 µmol), and Pd(PPh3)2Cl2 (23 mg, 33 µmol) were
reacted in the presence of THF (5.0 mL) and DIEA (5.0 mL)
at 40 °C for 40 h. The mixture was then filtered and
evaporated. The resulting orange-brown solid was chromato-
graphed (silica, CH2Cl2/hexanes, 2:3, 1:1, then 3:2) to afford
yellowish-white crystals. Recrystallization (ethyl acetate/hep-
1
tane) gave white crystals (1.30 g, 88%): mp 128-129 °C; H
NMR δ 2.49 (s, 3H), 4.07 (s, 2H), 7.25, 7.43 (AA′BB′, 2 × 2H),
7.59, 7.79 (AA′BB′, 2 × 2H), 9.95 (s, 1H); 13C NMR δ 30.9, 33.9,
89.5, 93.9, 122.1, 129.8, 130.1, 130.2, 132.7, 132.7, 136.1, 139.5,
192.0, 195.4; FAB-MS obsd 294.0717, calcd exact mass 294.0715.
Anal. Calcd for C18H14O2S: C, 73.44; H, 4.79; S, 10.89. Found:
C, 73.18; H, 4.82; S, 10.88.
2-(4-Allylp h en yl)-5,5-d im eth yl-1,3-d ioxa n e (13). A solu-
tion of 12 (2.05 g, 7.60 mmol) in THF (15 mL) was added
dropwise to magnesium powder (0.22 g, 9.1 mmol) under
argon. After the addition was completed, the mixture was
refluxed for 45 min. Then the mixture was cooled to room
temperature, and a solution of allyl bromide (720 µL, 8.30
mmol) in THF (10 mL) was added slowly. The mixture was
stirred for 4.5 h, quenched with saturated aqueous NH4Cl (25
mL), and extracted with diethyl ether. The combined organic
phases were washed with aqueous NaHCO3 (5%), brine, and
dried (Na2SO4). The solvent was removed, and the residue was
treated with hexanes and filtered. The filtrate was purified
by column chromatography (silica, Et2O/hexanes, 1:4), afford-
ing a light yellow oil (1.04 g, 59%): IR (neat) ν˜ 3077, 2955,
2904, 2846, 1639, 1619, 1517; 1H NMR δ 0.79 (s, 3H), 1.29 (s,
3H), 3.38 (d, J ) 6.6 Hz, 2H), 3.64 (d, J ) 11.0 Hz, 2H), 3.76
(d, J ) 11.0 Hz, 2H), 5.00-5.10 (m, 2H), 5.37 (s, 1H), 5.86-
6.01 (m, 1H), 7.19, 7.43 (AA′BB′, 2 × 2H); 13C NMR (APT) δ
21.7 (-), 22.9 (-), 30.0 (+), 39.8 (+), 77.5 (+), 101.5 (-), 115.6
(+), 126.1 (-), 128.4 (-), 136.3 (+), 137.2 (-), 140.5 (+); GC-
MS (EI) obsd 232. Anal. Calcd for C15H20O2: C, 77.55; H, 8.68.
Found: C, 77.52; H, 8.77.
2-[4-[3-(S-Acetylth io)p r op yl]p h en yl]-5,5-d im eth yl-1,3-
d ioxa n e (14). Following a general procedure,48 13 (845 mg,
3.60 mmol) and thioacetic acid (910 µL, 12.7 mmol) were
dissolved in toluene (20 mL), and the solution was purged with
argon for 15 min. Then AIBN (200 mg) was added, and the
mixture was heated to 90 °C. Over a period of 23 h, more AIBN
(1.10 g) was added in several portions. Then aqueous NaHCO3
(10%, 50 mL) was added, and the phases were separated. The
aqueous phase was extracted with diethyl ether, and the
combined organic phases were dried (Na2SO4). Purification by
column chromatography (silica, Et2O/hexanes, 1:4) gave an
orange oil, which solidified upon standing at -20 °C and was
recrystallized from pentane to give colorless needles (708 mg,
63%): mp 44 °C; IR (neat) ν˜ 2951, 2850, 1692, 1620, 1518; 1H
NMR δ 0.79 (s, 3H), 1.29 (s, 3H), 1.78-1.94 (m, 2H), 2.33 (s,
3H), 2.68 (t, J ) 7.3 Hz, 2H), 2.86 (t, J ) 7.3 Hz, 2H), 3.64 (d,
J ) 11.0 Hz, 2H), 3.76 (d, J ) 11.0 Hz, 2H), 5.37 (s, 1H), 7.18,
7.42 (AA′BB′, 2 × 2H); 13C NMR (APT) δ 21.6 (-), 22.8 (-),
28.1 (+), 29.9 (+), 30.4 (-), 30.8 (+), 34.3 (+), 77.3 (+), 101.4
(-), 126.0 (-), 128.1 (-), 136.1 (+), 141.5 (+), 195.3 (+); GC-
4-(S-Acetylth io)-2,3,5,6-tetr a flu or oben za ld eh yd e (9).
Potassium thioacetate (1.28 g, 11.2 mmol) was added to a
solution of pentafluorobenzaldehyde (1.24 mL, 10.2 mmol) in
anhydrous N,N-dimethylacetamide (20 mL). After an exotherm
subsided, the mixture was stirred at room temperature for 30
min. Acetyl chloride (1.60 mL, 22.4 mmol) was added, and the
mixture was stirred for another 30 min, then poured into water
and extracted thoroughly with diethyl ether. The combined
organic extracts were dried (Na2SO4) and evaporated to obtain
an orange oil, which was chromatographed (silica, CH2Cl2/
hexanes, 2:3) affording a pale-yellow solid. Recrystallization
from heptane gave white crystals (1.77 g, 69%): mp 86-87
°C; 1H NMR δ 2.53 (s, 3H), 10.30 (s, 1H); 13C NMR δ 30.9,
115.5, 117.2, 145.3, 148.7, 182.9, 187.9; FAB-MS obsd 252.9936,
calcd exact mass 252.9946. Anal. Calcd for C9H4F4O2S: C,
42.86; H, 1.60; S, 12.72. Found: C, 43.00; H, 1.71; S, 12.67.
4-(S-Acetylth iom eth yl)ben za ld eh yd e (10). To a solution
of 4-(bromomethyl)benzaldehyde43,46,47 (0.43 g, 2.2 mmol) in
acetone (10 mL) was added potassium thioacetate (280 mg,
2.5 mmol) under stirring at room temperature, and then the
mixture was refluxed. A precipitate formed after
a few
minutes. The reaction was monitored by TLC and cooled to
room temperature when no starting material was detectable
(3.5 h). Water (25 mL) was added, the mixture was extracted
with ethyl acetate, and column chromatography (silica, Et2O/
hexanes, 1:1) gave a brown oil (359 mg, 85%): IR (neat) ν˜ 3052,
1
2923, 2830, 2737, 1694, 1606, 1576; H NMR δ 2.36 (s, 3H),
4.15 (s, 2H), 7.45, 7.81 (AA′BB′, 2 × 2H), 9.97 (s, 1H); 13C NMR
(APT) δ 30.1 (-), 32.9 (+), 129.3 (-), 129.9 (-), 135.2 (+), 144.7
(+), 191.5 (-), 194.3 (+); GC-MS (EI) obsd 194. Anal. Calcd
for C10H10O2S: C, 61.83; H, 5.19; S, 16.51. Found: C, 61.97;
H, 5.20; S, 16.60.
4-[2-(S-Acetylth io)eth yl]ben za ld eh yd e (11). Following
a general procedure,48 4-vinylbenzaldehyde49 (1.15 g, 8.70
mmol) and thioacetic acid (2.20 mL, 30.8 mmol) were dissolved
in toluene (20 mL), and the solution was purged with argon

Synthesis of “Porphyrin-Linker-Thiol” Molecules
J . Org. Chem., Vol. 65, No. 22, 2000 7353
MS (EI) obsd 308. Anal. Calcd for C17H24O3S: C, 66.20; H, 7.84;
S, 10.40. Found: C, 66.19; H, 7.89; S, 10.54.
BF3‚OEt2 (90 µL, 0.71 mmol) were stirred in CHCl3 (40 mL)
for 1.5 h. The resulting mixture was treated with DDQ (500
mg, 2.20 mmol) in THF (10 mL) for 1 h. Filtration over a silica
pad (CH2Cl2) followed by preparative centrifugal chromatog-
raphy (silica, CH2Cl2/hexanes, 5:7) gave the title porphyrin as
the second purple band (96 mg, 14%): 1H NMR δ -2.53 (s,
2H), 1.85 (s, 18H), 2.35 (s, 3H), 2.59 (s, 9H), 4.13 (s, 2H), 7.26
(s, 6H), 7.31, 7.59 (AA′BB′, 2 × 2H), 7.90, 8.19 (AA′BB′, 2 ×
2H), 8.65 (s, 4H), 8.7-8.9 (m, 4H); LD-MS obsd 932.1; FAB-
MS obsd 928.4193, calcd exact mass 928.4175 (C64H56N4OS);
λabs (CH2Cl2) 420, 515, 548, 592, 648 nm.
5-[4-(S-Acetylth io)-2,3,5,6-tetr a flu or op h en yl]-10,15,20-
tr im esitylp or p h yr in (21). Following the general procedure
for 19, aldehyde 9 (184 mg, 0.730 mmol), mesitaldehyde (0.32
mL, 2.2 mmol), pyrrole (200 µL, 2.92 mmol), and BF3‚OEt2 (90
µL, 0.71 mmol) were stirred in CHCl3 (40 mL) for 1.5 h. The
resulting mixture was treated with DDQ (500 mg, 2.20 mmol)
in THF (10 mL) for 1 h. Filtration over a silica pad (CH2Cl2)
followed by preparative centrifugal chromatography (silica,
CH2Cl2/hexanes, 1:4) gave the title porphyrin as the second
purple band (46 mg, 7.1%): 1H NMR (THF-d8) δ -2.51 (s, 2H),
1.83 (s, 18H), 2.61 (s, 9H), 2.67 (s, 3H), 7.29 (s, 6H), 8.8-9.0
(m, 8H); LD-MS obsd 887.2; FAB-MS obsd 886.3364, calcd
exact mass 886.3328 (C55H46F4N4OS); λabs (CH2Cl2) 418, 513,
546, 588, 644 nm.
5-[4-(S-Acetylth iom eth yl)ph en yl]-10,15,20-tr im esitylpor -
p h yr in (22). Following the general procedure for 19, aldehyde
10 (148 mg, 0.76 mmol), mesitaldehyde (337 µL, 2.3 mmol),
pyrrole (211 µL, 3.0 mmol), and BF3‚OEt2 (94 µL, 0.74 mmol)
were stirred in CHCl3 (125 mL) for 3 h. The resulting mixture
was treated with DDQ (519 mg, 2.3 mmol) for 1 h. The mixture
was then filtered through a pad of silica (CH2Cl2) followed by
column chromatography (silica, CH2Cl2/hexanes, 1:3-1:1). The
title compound eluted as the second purple band (118 mg,
19%): IR (neat) ν˜ 3318, 2921, 2861, 1695, 1608, 1561; 1H NMR
δ -2.58 (s, 2H), 1.84 (s, 12H), 1.85 (s, 6H), 2.50 (s, 3H), 2.63
(s, 9H), 4.46 (s, 2H), 7.27 (s, 6H), 7.65, 8.12 (AA′BB′, 2 × 2H),
8.63 (brs, 4H), 8.67 (d, J ) 5.1 Hz, 2H), 8.77 (d, J ) 5.1 Hz,
2H); LD-MS obsd 829.0; FAB-MS obsd 828.3892, calcd exact
mass 828.3862 (C56H52N4OS); λabs (toluene) 420, 515, 548, 592,
649 nm.
5-[4-[2-(S-Acet ylt h io)et h yl]p h en yl]-10,15,20-t r im esi-
tylp or p h yr in (23). Following the general procedure for 19,
aldehyde 11 (98 mg, 0.47 mmol), mesitaldehyde (208 µL, 1.4
mmol), pyrrole (131 µL, 1.9 mmol), and BF3‚OEt2 (52 µL, 0.4
mmol) were stirred in CHCl3 (100 mL) for 3 h. The resulting
mixture was treated with DDQ (320 mg, 1.4 mmol) for 1.5 h.
The mixture was then filtered through a pad of silica (CH2-
Cl2) followed by column chromatography (silica, CH2Cl2/
hexanes, 1:1-3:2). The title compound comprised the second
purple band (69 mg, 17%): IR (neat) ν˜ 3319, 2920, 2861, 1694,
1608, 1561; 1H NMR δ -2.57 (s, 2H), 1.85 (s, 18H), 2.45 (s,
3H), 2.62 (s, 9H), 3.21 (t, J ) 8.1 Hz, 2H), 3.37-3.52 (m, 2H),
7.27 (s, 6H), 7.58, 8.13 (AA′BB′, 2 × 2H), 8.62 (s, 4H), 8.67 (d,
J ) 5.1 Hz, 2H), 8.77 (d, J ) 4.4 Hz, 2H); LD-MS 845.3; FAB-
MS obsd 842.4025, calcd exact mass 842.4018 (C57H54N4OS);
λabs (toluene) 420, 515, 548, 593, 650 nm.
4-[3-(S-Acetylth io)pr opyl]ben zaldeh yde (15). Compound
14 (525 mg, 1.70 mmol) was dissolved in CH2Cl2 (10 mL). TFA
(2.0 mL) was added together with a drop of water. The solution
was stirred for 15 h at room temperature. Then aqueous
NaHCO3 (5%, 35 mL) was added, and the phases were
separated. The organic phase was washed with aqueous
NaHCO3 (5%) and brine and dried (Na2SO4). The solvents were
removed, and the oily residue was purified by column chro-
matography (silica, Et2O/hexanes, 1:2), affording a yellow oil
(279 mg, 74%): IR (neat) ν˜ 3037, 2928, 2849, 2731, 1693, 1605;
1H NMR δ 1.88-1.99 (m, 2H), 2.35 (s, 3H), 2.78 (t, J ) 7.3 Hz,
2H), 2.89 (t, J ) 7.3 Hz, 2H), 7.35, 7.81 (AA′BB′, 2 × 2H), 9.98
(s, 1H); 13C NMR (APT) δ 28.1 (+), 30.4 (+), 34.7 (+), 128.8
(-), 129.7 (-), 134.4 (+), 148.3 (+), 191.6 (-), 195.2 (+); GC-
MS (EI) obsd 222; FAB-MS obsd 222.0709, calcd exact mass
222.0715 (C12H14O2S).
7-(S-Acetylth io)h ep ta n a l (17). To a solution of crude
7-bromoheptanal51 (3.32 g, 17.2 mmol) in acetone (50 mL) was
added potassium thioacetate (2.36 g, 21 mmol) under stirring
at room temperature. Then the mixture was refluxed, yielding
a precipitate after a few minutes. The reaction was monitored
by TLC and cooled to room temperature when no starting
material was detectable (4 h). Water (50 mL) was added, the
mixture was extracted with diethyl ether until the organic
phase was colorless, and the combined organic phases were
dried (Na2SO4) and evaporated. Distillation at 98 °C with a
water suction pump afforded a yellow oil (1.66 g, 51%; 42%
from 7-bromoheptanol): IR (neat) ν˜ 2938, 2857, 2721, 1725,
1
1694; H NMR δ 1.28-1.43 (m, 4H), 1.53-1.69 (m, 4H), 2.33
(s, 3H), 2.43 (dt, J ) 7.3 Hz, J ) 1.5 Hz, 2H), 2.86 (t, J ) 7.3
Hz, 2H), 9.77 (t, J ) 1.5 Hz, 1H); 13C NMR (APT) δ 21.6 (+),
28.1 (+), 28.3(+), 28.6 (+), 29.0 (+), 30.3 (-), 43.3 (+), 195.4
(+), 202.0 (-); GC-MS (EI) obsd 188; FAB-MS obsd 188.0862,
calcd 188.0871 (C9H16O2S).
1-[4-(S-Acet ylt h io)p h en yl]-2-(d iet h oxym et h yl)a cet yl-
en e (18). Following the procedure for 4, samples of 1 (500 mg,
1.80 mmol), CuI (19.0 mg, 100 µmol), and Pd(PPh3)2Cl2 (8.4
mg, 12 µmol) were deoxygenated, and then deaerated THF (5.0
mL), DIEA (5.0 mL), and propiolaldehyde diethyl acetal (258
µL, 1.80 mmol) were added and the reaction was carried out
at 40 °C for 40 h. The mixture was evaporated, and the
resulting orange-brown solid was chromatographed (silica,
CH2Cl2/hexanes, 1:1, then 7:3) to afford a pale yellow oil (319
mg, 64%): 1H NMR δ 1.27 (t, J ) 6.6 Hz, 6H), 2.40 (s, 3H),
3.5-4.0 (m, 4H), 5.49 (s, 1H), 7.36, 7.50 (AA′BB′, 2 × 2H); 13
C
NMR δ 15.8, 30.9, 61.7, 85.0, 86.8, 92.4, 123.7, 129.5, 133.1,
134.8, 193.7; FAB-MS obsd 278.0970, calcd exact mass 278.0977.
Anal. Calcd for C15H18O3S: C, 64.72; H, 6.52; S, 11.52. Found:
C, 64.45; H, 6.53; S, 11.34.
5-[4-[2-[4-(S-Acetylth io)p h en yl]eth yn yl]p h en yl]-10,15,-
20-tr im esitylp or p h yr in (19). Following a general procedure
for mixed-aldehyde condensations38 with mesitaldehyde,52
aldehyde 4 (204 mg, 0.730 mmol) was added to CHCl3 (40 mL,
containing 0.75% ethanol), followed by mesitaldehyde (0.32
mL, 2.2 mmol), pyrrole (200 µL, 2.92 mmol), and BF3‚OEt2 (90
µL, 0.71 mmol). The reaction mixture was stirred at room
temperature for 1.5 h. Then DDQ (500 mg, 2.20 mmol) in THF
(10 mL) was added. The resulting mixture was stirred at room
temperature for 1 h and then passed over a short silica column
(CH2Cl2/hexanes, 1:1) affording porphyrins free from dark
pigments and quinone species. The mixture of porphyrins was
purified by preparative centrifugal chromatography (silica,
CH2Cl2/hexanes, 5:7). The title porphyrin eluted as the second
purple band (78 mg, 12%): 1H NMR δ -2.40 (s, 2H), 1.99 (s,
18H), 2.57 (s, 3H), 2.73 (s, 9H), 7.40 (s, 6H), 7.58, 7.61 (AA′BB′,
2 × 2H), 8.04, 8.34 (AA′BB′, 2 × 2H), 8.78 (s, 4H), 8.8-9.0 (m,
4H); LD-MS obsd 917.2; FAB-MS obsd 914.4059, calcd exact
mass 914.4018 (C63H54N4OS); λabs (CH2Cl2) 420, 515, 550, 592,
646 nm.
5-[4-[3-(S-Acetylth io)p r op yl]p h en yl]-10,15,20-tr im esi-
tylp or p h yr in (24). Following the general procedure for 19,
aldehyde 15 (108 mg, 0.49 mmol), mesitaldehyde (215 µL, 1.5
mmol), pyrrole (135 µL, 1.9 mmol), and BF3‚OEt2 (54 µL, 0.4
mmol) were stirred in CHCl3 (100 mL) for 3.5 h. The resulting
mixture was treated with DDQ (331 mg, 1.5 mmol) for 1 h.
The mixture was then filtered through a pad of silica (CH2-
Cl2) followed by column chromatography (silica, CH2Cl2/
hexanes 3:2-2:1). The title compound comprised the second
purple band, which was triturated with methanol to give a
purple solid (41 mg, 10%): IR (neat) ν˜ 3322, 3102, 2920, 2852,
1693, 1612, 1559; 1H NMR δ -2.56 (s, 2H), 1.85 (s, 18H), 2.14-
2.25 (m, 2H), 2.41 (s, 3H), 2.61 (s, 9H), 3.02 (t, J ) 7.3 Hz,
2H), 3.37 (t, J ) 7.3 Hz, 2H), 7.27 (s, 6H), 7.53, 8.11 (AA′BB′,
2 × 2H), 8.63 (s, 4H), 8.67 (d, J ) 4.4 Hz, 2H), 8.79 (d, J ) 4.4
Hz, 2H); LD-MS obsd 858.4; FAB-MS obsd 856.4216, calcd
exact mass 856.4175 (C58H56N4OS); λabs (toluene) 420, 515, 548,
593, 649 nm.
5-[4-[2-[4-(S-Acetylth iom eth yl)ph en yl]eth yn yl]ph en yl]-
10,15,20-t r im esit ylp or p h yr in (20). Following the general
procedure for 19, aldehyde 8 (214 mg, 0.730 mmol), mesital-
dehyde (0.32 mL, 2.2 mmol), pyrrole (200 µL, 2.92 mmol), and

7354 J . Org. Chem., Vol. 65, No. 22, 2000
Gryko et al.
5-[6-(S-Acet ylt h io)h exyl]-10,15,20-t r im esit ylp or p h y-
r in (25). Following the general procedure for 19, aldehyde 17
(111 mg, 0.59 mmol), mesitaldehyde (261 µL, 1.8 mmol),
pyrrole (164 µL, 2.4 mmol), and BF3‚OEt2 (65 µL, 0.5 mmol)
were stirred in CHCl3 (100 mL) for 3 h. The resulting mixture
was treated with DDQ (401 mg, 1.8 mmol) for 1.5 h. The
mixture was then filtered through a pad of silica (CH2Cl2)
followed by two column chromatography procedures (silica,
CH2Cl2/hexanes, 1:1-3:2). The title compound eluted as the
second purple band and was purified by a further column
(silica, CH2Cl2/hexanes, 2:1) to afford a purple solid (105 mg,
22%): IR (neat) ν˜ 3317, 3107, 2922, 2856, 1691, 1609, 1562;
1H NMR δ -2.51 (s, 2H), 1.52-1.67 (m, 4H), 1.74-1.89 (m,
2H), 1.85 (s, 18H), 2.30 (s, 3H), 2.45-2.58 (m, 2H), 2.60 (s,
3H), 2.63 (s, 6H), 2.88 (t, J ) 6.6 Hz, 2H), 4.98 (t, J ) 8.1 Hz,
2H), 7.25 (s, 2H), 7.28 (s, 4H), 8.55-8.62 (m, 4H), 8.75 (d, J )
3.7 Hz, 2H), 8.40 (d, J ) 3.7 Hz, 2H); LD-MS obsd 825.2; FAB-
MS obsd 822.4355, calcd exact mass 822.4331 (C55H58N4OS);
λabs (toluene) 419, 516, 549, 594, 652 nm.
5-{2-[4-(S-Acetylth io)p h en yl]eth yn yl}-10,15,20-tr im esi-
tylp or p h yr in (26). Following the general procedure for 19,
acetal 18 (100 mg, 0.36 mmol), mesitaldehyde (0.16 mL, 1.1
mmol), pyrrole (100 µL, 1.46 mmol) and BF3‚OEt2 (45 µL, 0.35
mmol) were stirred in CHCl3 (20 mL) for 1.5 h. The resulting
mixture was treated with DDQ (250 mg, 1.10 mmol) in THF
(5 mL) for 1 h. Filtration over a silica pad (CH2Cl2) followed
by two preparative centrifugal chromatography procedures
(silica, CH2Cl2/hexanes, 1:3, then 1:1) gave the title porphyrin
as the second purple band (2.5 mg, 0.83%): 1H NMR δ -2.14
(s, 2H), 1.85 (s, 18H), 2.50 (s, 3H), 2.63 (s, 9H), 7.25 (s, 6H),
7.60, 8.03 (AA′BB′, 2 × 2H), 8.54 (s, 4H), 8.73 (m, 2H), 9.63
(m, 2H); LD-MS obsd 841.6; FAB-MS obsd 838.3737, calcd
exact mass 838.3705 (C57H50N4OS); λabs (CH2Cl2) 436, 534, 576,
611, 668 nm.
Gen er a l P r oced u r e for Zin c In ser tion . The porphyrin
was dissolved in CHCl3 or CH2Cl2, and a solution of Zn(OAc)2‚
2H2O in methanol was added. The reaction mixture was stirred
at room temperature. After metalation was complete (TLC,
fluorescence excitation spectroscopy), the reaction mixture was
washed with water, dried (Na2SO4), filtered and concentrated
to a purple solid. Purification was achieved by column chro-
matography on silica.
Zn (II)-5-[4-[2-[4-(S-Acetylth io)p h en yl]eth yn yl]p h en yl]-
10,15,20-tr im esitylp or p h yr in (Zn -19). A solution of por-
phyrin 19 (37 mg, 0.040 mmol) in CH2Cl2 (15 mL) was treated
with Zn(OAc)2‚2H2O (880 mg, 4.00 mmol) in methanol (15 mL),
and the mixture was stirred for 16 h. Column chromatography
(silica, CH2Cl2/hexanes, 1:1) afforded 35.6 mg (92%): 1H NMR
δ 1.85 (s, 18H), 2.48 (s, 3H), 2.64 (s, 9H), 7.27 (s, 6H), 7.48,
7.72 (AA′BB′, 2 × 2H), 7.92, 8.23 (AA′BB′, 2 × 2H), 8.70 (s,
4H), 8.70-8.90 (m, 4H); LD-MS obsd 979.8; FAB-MS obsd
976.3177, calcd exact mass 976.3153 (C63H52N4OSZn); λabs
(CH2Cl2) 422, 550 nm.
Zn (II)-5-[4-(S-Acet ylt h iom et h yl)p h en yl]-10,15,20-t r i-
m esitylp or p h yr in (Zn -22). A solution of porphyrin 22 (54.8
mg, 66.1 µmol) in CHCl3 (20 mL) was treated with Zn(OAc)2‚
2H2O (435 mg, 2.00 mmol) in methanol (5 mL), and the
mixture was stirred for 6 h. Excess Zn(OAc)2‚2H2O (290 mg,
1.3 mmol) was then added, and stirring was continued for 23
h. The organic phase was washed with aqueous NaHCO3 (5%).
Column chromatography (silica, CH2Cl2/hexanes, 1:1) afforded
a purple solid in quantitative yield: IR (neat) ν˜ 2922, 2853,
1
1663; H NMR δ 1.84 (s, 18H), 2.49 (s, 3H), 2.63 (s, 9H), 4.46
(s, 2H), 7.27 (s, 6H), 7.63, 8.14 (AA′BB′, 2 × 2H), 8.70 (brs,
4H), 8.74 (d, J ) 4.4 Hz, 1H), 8.75 (d, J ) 4.4 Hz, 1H), 8.84(5)
(d, J ) 4.4 Hz, 1H), 8.85(0) (d, J ) 4.4 Hz, 1H); LD-MS obsd
891.3; FAB-MS obsd 890.3035, calcd exact mass 890.2997
(C56H50N4OSZn); λabs (toluene) 423, 550 nm; λem (toluene) 593,
644 nm.
Zn (II)-5-[4-[2-(S-Acetylth io)eth yl]p h en yl]-10,15,20-tr i-
m esitylp or p h yr in (Zn -23). A solution of porphyrin 23 (48
mg, 57 µmol) in CHCl3 (20 mL) was treated with Zn(OAc)2‚
2H2O (1.25 g, 5.70 mmol) in methanol (5 mL), and the mixture
was stirred for 17 h. The organic phase was washed with
aqueous NaHCO3 (5%). Column chromatography (silica, CH2-
Cl2/hexanes, 3:1) afforded a purple solid in quantitative yield:
1
IR (neat) ν˜ 3096, 2910, 2849, 1646; H NMR δ 1.84 (s, 12H),
1.85 (s, 6H), 2.44 (s, 3H), 2.63 (s, 9H), 3.20 (t, J ) 7.3 Hz, 2H),
3.38-3.46 (m, 2H), 7.27 (s, 6H), 7.57, 8.14 (AA′BB′, 2 × 2H),
8.70 (s, 4H), 8.75 (d, J ) 4.4 Hz, 2H), 8.86 (d, J ) 4.4 Hz, 2H);
LD-MS obsd 906.4; FAB-MS obsd 904.3121, calcd exact mass
904.3153 (C57H52N4OSZn); λabs (toluene) 423, 550 nm; λem
(toluene) 593, 644 nm.
Zn (II)-5-[4-[3-(S-Acet ylt h io)p r op yl]p h en yl]-10,15,20-
tr im esitylp or p h yr in (Zn -24). A solution of porphyrin 24
(37.7 mg, 44 µmol) in CHCl3 (20 mL) was treated with Zn-
(OAc)2‚2H2O (965 mg, 4.40 mmol) in methanol (5 mL), and
the mixture was stirred for 5 h. The organic phase was washed
with aqueous NaHCO3 (5%) and dried (Na2SO4). Column
chromatography (silica, CH2Cl2/hexanes, 4:1) afforded a purple
solid in quantitative yield: IR (neat) ν˜ 3107, 2919, 2849, 1650;
1H NMR δ 1.84 (s, 12H), 1.85 (s, 6H), 2.13-2.26 (m, 2H), 2.40
(s, 3H), 2.63 (s, 9H), 3.03 (t, J ) 7.3 Hz, 2H), 3.11 (t, J ) 7.3
Hz, 2H), 7.27 (s, 6H), 7.53, 8.13 (AA′BB′, 2 × 2H), 8.69 (s, 4H),
8.74 (d, J ) 5.1 Hz, 2H), 8.86 (d, J ) 5.1 Hz, 2H); LD-MS obsd
921.8; FAB-MS obsd 918.3343, calcd exact mass 918.3310
(C58H54N4OSZn); λabs (toluene) 423, 550 nm; λem (toluene) 593,
644 nm.
Zn (II)-5-[6-(S-Acetylth io)h exyl]-10,15,20-tr im esitylp or -
p h yr in (Zn -25). A solution of porphyrin 25 (93 mg, 110 µmol)
in CHCl3 (25 mL) was treated with Zn(OAc)2‚2H2O (2.50 g,
11.4 mmol) in methanol (7 mL), and the mixture was stirred
for 18 h. The organic phase was washed with aqueous NaHCO3
(5%) and dried (Na2SO4). Column chromatography (silica, CH2-
Cl2/hexanes, 2:1) afforded a purple solid (85 mg, 85% yield):
IR (neat) ν˜ 3107, 2920, 2849, 1690, 1658, 1608; 1H NMR δ
1.55-1.67 (m, 4H), 1.78-1.89 (m, 2H), 1.83 (s, 18H), 2.20 (s,
3H), 2.5-2.7 (m, 11H), 2.83 (t, J ) 6.6 Hz, 2H), 5.02 (t, J )
8.1 Hz, 2H), 7.25 (s, 2H), 7.28 (s, 4H), 8.64 (d, J ) 5.1 Hz,
2H), 8.66 (d, J ) 5.1 Hz, 2H), 8.81 (d, J ) 4.4 Hz, 2H), 9.49 (d,
J ) 4.4 Hz, 2H); LD-MS obsd 887.7; FAB-MS obsd 884.3490,
calcd exact mass 884.3466 (C55H56N4OSZn); λabs (toluene) 423,
552 nm; λem (toluene) 593, 646 nm.
Zn (II)-5-[2-[4-(S-Acet ylt h io)p h en yl]et h yn yl]-10,15,20-
tr im esitylp or p h yr in (Zn -26). A solution of porphyrin 26 (2.5
mg, 2.9 µmol) in CH2Cl2 (5 mL) was treated with Zn(OAc)2‚
2H2O (64 mg, 29 µmol) in methanol (5 mL), and the mixture
was stirred for 16 h. Column chromatography (silica, CH2Cl2/
hexanes, 1:1) afforded 2.4 mg (92%): 1H NMR δ 1.85 (s, 18H),
2.50 (s, 3H), 2.62 (s, 9H), 7.29 (s, 6H), 7.60, 8.04 (AA′BB′, 2 ×
2H), 8.64 (m, 4H), 8.82 (m, 2H), 9.73 (m, 2H); LD-MS obsd
906.1; FAB-MS obsd 900.2825, calcd exact mass 900.2840
(C57H48N4OSZn); λabs (CH2Cl2) 440, 566, 611 nm.
Electr och em istr y. The solution electrochemical studies of
the Zn-porphyrins were performed using techniques and
instrumentation previously described.28 The solvent was CH2-
Cl2; tetrabutylammonium hexafluorophosphate (TBAH, 0.1 M)
(Aldrich, recrystallized three times from methanol and dried
Zn (II)- 5-[4-[2-[4-(S-Acetylth iom eth yl)p h en yl]eth yn yl]-
p h en yl]-10,15,20-tr im esitylp or p h yr in (Zn -20). A solution
of porphyrin 20 (37 mg, 0.040 mmol) in CH2Cl2 (15 mL) was
treated with Zn(OAc)2‚2H2O (880 mg, 4.00 mmol) in methanol
(15 mL), and the mixture was stirred for 16 h. Column
chromatography (silica, CH2Cl2/hexanes, 1:1) afforded 37.7 mg
(95%): 1H NMR (THF-d8) δ 1.86 (s, 18H), 2.34 (s, 3H), 2.60 (s,
9H), 4.18 (s, 2H), 7.29 (s, 6H), 7.38, 7.58 (AA′BB′, 2 × 2H),
7.88, 8.19 (AA′BB′, 2 × 2H), 8.63 (s, 4H), 8.6-8.8 (m, 4H); LD-
MS obsd 992.4; FAB-MS obsd 990.3280, calcd exact mass
990.3310 (C64H56N4OS); λabs (CH2Cl2) 422, 550 nm.
Zn (II)-5-[4-(S-Acet ylt h io)-2,3,5,6-t et r a flu or op h en yl]-
10,15,20-tr im esitylp or p h yr in (Zn -21). A solution of por-
phyrin 21 (35 mg, 0.040 mmol) in CH2Cl2 (15 mL) was treated
with Zn(OAc)2‚2H2O (880 mg, 4.00 mmol) in methanol (15 mL),
and the mixture was stirred for 16 h. Column chromatography
(silica, CH2Cl2/hexanes, 1:4) afforded 31.4 mg (83%): 1H NMR
(THF-d8) δ 1.87 (s, 18H), 2.66 (s, 9H), 2.71 (s, 3H), 7.30 (s,
6H), 8.7-9.0 (m, 8H); LD-MS obsd 953.5; FAB-MS obsd
948.2480, calcd exact mass 948.2463 (C55H44F4N4OSZn); λabs
(CH2Cl2) 421, 548 nm.

Synthesis of “Porphyrin-Linker-Thiol” Molecules
J . Org. Chem., Vol. 65, No. 22, 2000 7355
under vacuum at 110 °C) served as supporting electrolyte. The
potentials reported are vs Ag/Ag+; E1/2(FeCp2/FeCp2+) ) 0.19
V.
counter electrodes, respectively. The cyclic voltammograms
were recorded with an Ensman Instruments 400 potentiostat
at a rate of 100 V/s.
The SAM electrochemical studies of the Zn-porphyrins were
performed on 75-micron wide gold band electrodes formed via
E-beam evaporation (to a thickness of 100 nm) onto piranha-
solution-etched glass slides that had a 1 nm thick underlayer
of chromium. The electrochemical cell was constructed by
forming a 3-mm diameter poly(dimethylsiloxane) (PDMS) well
(∼3 mm deep) over the gold band. The Zn-porphyrins were
dissolved in absolute ethanol, and the solution (∼1 mM) was
added to the well and allowed to stand. Deposition times of
30 min were found to give the same quality cyclic voltammo-
grams as those obtained with much longer deposition times
(12 h). After soaking, the solvent was removed and the PDMS
well was rinsed with absolute ethanol followed by a final rise
with CH2Cl2. A small amount of CH2Cl2 containing 1 M TBAH
was then added to the PDMS well. Silver and platinum wires
were inserted into the well to serve as the reference and
Ack n ow led gm en t. This work was supported by the
DARPA Moletronics Programs, administered by the
ONR (N00014-99-1-0357). Mass spectra were obtained
at the Mass Spectrometry Laboratory for Biotechnology
at North Carolina State University. Partial funding for
the Facility was obtained from the North Carolina
Biotechnology Center and the NSF.
Su p p or tin g In for m a tion Ava ila ble: LD-MS and 1H
NMR spectra for all porphyrins; 1H NMR and 13C NMR spectra
for compounds 7, 15 and 17. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O000487U