Thiol-Derivatized Porphyrins for Attachment to Electroactive Surfaces

Article abstract of DOI:10.1021/jo9911084

The attachment of porphyrin monomers and multiporphyrin arrays in controlled architectures on electroactive surfaces opens many opportunities for electrochemical studies. Toward this goal, we have developed routes for the preparation of thiol-derivatized porphyrin monomers and porphyrin building blocks that require minimal or no handling of free thiols. Routes to S-protected p-thiobenzaldehydes and m-(thiomethyl)benzaldehydes have been developed. Two sets of meso-substituted porphyrins with variation in electrochemical potentials have been prepared for vertical or horizontal orientation with respect to the electroactive surface. In one set, each porphyrin bears one S-protected p-thiophenyl unit and substituents at the three remaining meso-positions. In the other set each porphyrin possesses four S-protected m-(thiomethyl)phenyl units. Tuning the electrochemical potential in the former set has been achieved by variation of the meso substituents (mesityl, 2,4,6-trimethoxyphenyl, n-pentyl, pentafluorophenyl) and in the latter set by variation of the central metal (Zn, Cu, Co, Ag). Six thiol protecting groups [S-cyano, S-(N-ethylcarbamoyl), S-acetyl, S-(9-anthrylmethyl), S-(2,4-dinitrophenyl), S-pivaloyl] have been found to be compatible with porphyrin formation and metalation with zinc. The S-cyano, S-(N-ethylcarbamoyl), and S-acetyl groups undergo in situ cleavage and/or binding on a gold surface. Of these three, only the S-acetyl protecting group is compatible with the Pd-mediated iodo-ethyne coupling conditions for the preparation of multiporphyrin arrays. Three trans-substituted porphyrin building blocks have been prepared for the synthesis of multiporphyrin arrays that can be attached to an electroactive surface. One porphyrin has two mesityl, one p-iodophenyl, and one p-(S-acetylthio)phenyl substituent for vertical positioning, and two porphyrins each have two m-iodophenyl and two S-protected m-(thiomethyl)phenyl substituents for horizontal positioning. Altogether, 16 free base and 16 metalloporphyrins have been prepared. This work establishes the foundation for preparing diverse thiol-derivatized porphyrin monomers and building blocks.

Full text of DOI:10.1021/jo9911084

J . Org. Chem. 1999, 64, 8635-8647
8635
Th iol-Der iva tized P or p h yr in s for Atta ch m en t to Electr oa ctive
Su r fa ces
Daniel T. Gryko, Christian Clausen, and J onathan S. Lindsey*
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204
Received J uly 16, 1999
The attachment of porphyrin monomers and multiporphyrin arrays in controlled architectures on
electroactive surfaces opens many opportunities for electrochemical studies. Toward this goal, we
have developed routes for the preparation of thiol-derivatized porphyrin monomers and porphyrin
building blocks that require minimal or no handling of free thiols. Routes to S-protected
p-thiobenzaldehydes and m-(thiomethyl)benzaldehydes have been developed. Two sets of meso-
substituted porphyrins with variation in electrochemical potentials have been prepared for vertical
or horizontal orientation with respect to the electroactive surface. In one set, each porphyrin bears
one S-protected p-thiophenyl unit and substituents at the three remaining meso-positions. In the
other set each porphyrin possesses four S-protected m-(thiomethyl)phenyl units. Tuning the
electrochemical potential in the former set has been achieved by variation of the meso substituents
(mesityl, 2,4,6-trimethoxyphenyl, n-pentyl, pentafluorophenyl) and in the latter set by variation of
the central metal (Zn, Cu, Co, Ag). Six thiol protecting groups [S-cyano, S-(N-ethylcarbamoyl),
S-acetyl, S-(9-anthrylmethyl), S-(2,4-dinitrophenyl), S-pivaloyl] have been found to be compatible
with porphyrin formation and metalation with zinc. The S-cyano, S-(N-ethylcarbamoyl), and S-acetyl
groups undergo in situ cleavage and/or binding on a gold surface. Of these three, only the S-acetyl
protecting group is compatible with the Pd-mediated iodo-ethyne coupling conditions for the
preparation of multiporphyrin arrays. Three trans-substituted porphyrin building blocks have been
prepared for the synthesis of multiporphyrin arrays that can be attached to an electroactive surface.
One porphyrin has two mesityl, one p-iodophenyl, and one p-(S-acetylthio)phenyl substituent for
vertical positioning, and two porphyrins each have two m-iodophenyl and two S-protected
m-(thiomethyl)phenyl substituents for horizontal positioning. Altogether, 16 free base and 16
metalloporphyrins have been prepared. This work establishes the foundation for preparing diverse
thiol-derivatized porphyrin monomers and building blocks.
In tr od u ction
A large number of porphyrin monomers bearing thiols
have been prepared,4-14 and some have been attached to
gold electrodes.15,16 The prevalent synthetic route to
porphyrin thiols involves the derivatization of a substi-
tuted porphyrin with a thiol reagent or protected thiol
unit. Representative examples include the reaction of a
porphyrin-amine with an S-protected alkanethiol bear-
ing an acid chloride,11 reaction of a porphyrin-amine
with the disulfide of an ω-mercaptoalkanoic acid,7 reac-
tion of a porphyrin-bromide with thioacetate5,9 or thio-
As part of a program in molecular electronics, we
sought to attach porphyrin-based molecular devices to
an electroactive surface. The molecular devices of interest
range from simple monomeric porphyrins to multipor-
phyrin arrays such as optoelectronic gates1 and inte-
grated antenna-reaction center complexes.2 We sought
to be able to (1) attach monomeric porphyrins of varying
redox potentials in a vertical or horizontal arrangement
on the gold surface, (2) make attachments to specific
porphyrins in a multiporphyrin array, and (3) employ
linkers that afford facile electronic communication be-
tween the porphyrin and the electroactive surface. A
common approach for attaching organic molecules to an
electroactive surface such as gold involves the use of thiol
substituents. Indeed, the use of thiophenol linkers has
enabled rapid electron-transfer reactions between redox-
active substituents and a gold electrode.3
(4) Kuroda, Y.; Hiroshige, T.; Sera, T.; Shiroiwa, Y.; Tanaka, H.;
Ogoshi, H. J . Am. Chem. Soc. 1989, 111, 1912-1913.
(5) Hutchison, J . E.; Postlethwaite, T. A.; Murray, R. W. Langmuir
1993, 9, 3277-3283.
(6) Bradshaw, J . E.; Moghaddas, S.; Wilson, L. J . Gazz. Chim. Ital.
1994, 124, 159-162.
(7) Akiyama, T.; Imahori, H.; Sakata, Y. Chem. Lett. 1994, 1447-
1450.
(8) Chambrier, I.; Cook, M. J .; Russell, D. A. Synthesis 1995, 1283-
1286.
(9) Guo, L.-H.; McLendon, G.; Razafitrimo, H.; Gao, Y. J . Mater.
Chem. 1996, 6, 369-374.
(1) Wagner, R. W.; Lindsey, J . S.; Seth, J .; Palaniappan, V.; Bocian,
D. F. J . Am. Chem. Soc. 1996, 118, 3996-3997.
(2) Kuciauskas, D.; Liddell, P. A.; J ohnson, T. E.; Weghorn, S. J .;
Lindsey, J . S.; Moore, A. L.; Moore, T. A.; Gust, D. J . Am. Chem. Soc.
1999, 121, 8604-8614.
(3) (a) Sachs, S. B.; Dudek, S. P.; Hsung, R. P.; Sita, L. R.; Smalley,
J . F.; Newton, M. D.; Feldberg, S. W.; Chidsey, C. E. D. J . Am. Chem.
Soc. 1997, 119, 10563-10564. (b) Creager, S.; Yu, C. J .; Bamdad, C.;
O’Connor, S.; MacLean, T.; Lam, E.; Chong, Y.; Olsen, G. T.; Luo, J .;
Gozin, M.; Kayyem, J . F. J . Am. Chem. Soc. 1999, 121, 1059-1064.
(10) Shimazu, K.; Takechi, M.; Fujii, H.; Suzuki, M.; Saiki, H.;
Yoshimura, T.; Uosaki, K. Thin Solid Films 1996, 273, 250-253.
(11) Yuan, H.; Woo, L. K. J . Porphyrins Phthalocyanines 1997, 1,
189-200.
(12) Kondo, T.; Yanagida, M.; Nomura, S.; Ito, T.; Uosaki, K. J .
Electroanal. Chem. 1997, 438, 121-126.
(13) Wen, L.; Li, M.; Schlenoff, J . B. J . Am. Chem. Soc. 1997, 119,
7726-7733.
(14) Uosaki, K.; Kondo, T.; Zhang, X.-Q.; Yanagida, M. J . Am. Chem.
Soc. 1997, 119, 8367-8368.
10.1021/jo9911084 CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/22/1999

8636 J . Org. Chem., Vol. 64, No. 23, 1999
Gryko et al.
urea,13 or conversion of a phthalocyanine-alcohol to
the thiol via treatment of the mesylate with thiourea.8
In this manner, porphyrins bearing one to four thiols
have been prepared. Most of these structures have long
flexible hydrocarbon chains between the thiol and the
porphyrin. A complementary but rarely used route
involves introducing the thiol unit into the aldehyde
precursor of the porphyrin. One example of this strategy
involves the conversion of p-(methylthio)benzaldehyde to
the p-(methylthio)phenyl-substituted porphyrin, which
upon Pummerer rearrangement and cleavage afforded
the free thiol.6 The only other examples using this route
are described in communications where S-acetyl-deriva-
tized thiobenzaldehydes were converted to the corre-
sponding porphyrins, which upon alkaline hydrolysis
afforded the free thiols.4,10 Although undeveloped, this
latter route affords the opportunity to prepare porphyrins
bearing protected thiols without performing extensive
manipulations on the porphyrin. In general, the incor-
poration of sensitive, bulky, or elaborate substituents in
the aldehyde precursor rather than derivatizing the
porphyrin has proved to be a very valuable approach,
particularly in the synthesis of porphyrin building
blocks.17-19
thiol-derivatized porphyrin monomers requires the in-
troduction of the thiol moiety at the aldehyde stage. To
avoid the problems associated with disulfide formation,
the thiol is best handled in a protected form. Protecting
groups are anticipated to be essential in multiporphyrin
arrays bearing multiple thiol units. The development of
thiol protecting groups that are compatible with Pd-
mediated coupling reactions is an active area of re-
search.25 Recently Tour et al. reported that an S-acetylthio-
substituted phenylethynyl oligomer could be deprotected
in situ upon exposure to the gold surface.26 This feature
of in situ deprotection was very attractive to us as it
enabled handling of the free thiol to be avoided at any
stage of the synthesis after forming the protected alde-
hyde.
In this paper, we have explored a variety of thiol
protecting groups in order to identify those that are
compatible with porphyrin formation, porphyrin meta-
lation, and Pd-coupling, as well as undergo cleavage in
situ on a gold surface. The results concerning behavior
of various protecting groups on gold electrodes are
important for the design and synthesis of thiol-protected
molecular devices. One of our goals is to investigate the
fundamental electrochemical properties of porphyrins
with different redox potentials and with vertical or
horizontal organization on a gold surface. For vertical
orientation, we have prepared a family of porphyrins
where each porphyrin bears one S-protected p-thiophenyl
group and three electron-withdrawing or electron-releas-
ing substituents at the periphery to tune the electro-
chemical oxidation potential. For horizontal orientation,
a set of porphyrins has been prepared where each
porphyrin bears two or four S-protected m-(thiomethyl)-
phenyl groups and one of a variety of central metals for
tuning the electrochemical potential. Three porphyrin
building blocks have been prepared that bear S-protected
thiol groups and one or two iodo substituents. This study
provides the foundation for preparing diverse thiol-
derivatized porphyrin monomers with minimal handling
of free thiols.
We have developed porphyrin building blocks as part
of a modular route for synthesizing multiporphyrin
arrays.1,2,20-22 The porphyrin building blocks are em-
ployed in defined metalation states, bear substituents
that impart solubility, and have iodo and/or ethyne
groups as synthetic handles at the periphery. These
building blocks are then assembled in a stepwise manner
via Pd-coupling reactions to form the diarylethyne-linked
array.23,24 In keeping with this strategy, the synthesis of
(15) (a) Zak, J .; Yuan, H.; Ho, M.; Woo, K. L.; Porter, M. D. Langmuir
1993, 9, 2772-2774. (b) Postlethwaite, T. A.; Hutchison, J . E.;
Hathcock, K. W.; Murray, R. W. Langmuir 1995, 11, 4109-4116. (c)
Kondo, T.; Ito, T.; Nomura, S.; Uosaki, K. Thin Solid Films 1996, 284-
285, 652-655. (d) Simpson, T. R. E.; Cook, M. J .; Petty, M. C.; Thorpe,
S. C.; Russell, D. A. Analyst 1996, 121, 1501-1505. (e) Simpson, T. R.
E.; Revell, D. J .; Cook, M. J .; Russell, D. A. Langmuir 1997, 13, 460-
464. (f) Ishida, A.; Sakata, Y.; Majima, T. Chem. Lett. 1998, 267-268.
(g) Ishida, A.; Sakata, Y.; Majima, T. Chem. Commun. 1998, 57-58.
(h) Imahori, H.; Norieda, H.; Ozawa, S.; Ushida, K.; Yamada, H.;
Azuma, T.; Tamaki, K.; Sakata, Y. Langmuir 1998, 14, 5335-5338.
(i) Yanagida, M.; Kanai, T.; Zhang, X.-Q.; Kondo, T.; Uosaki, K. Bull.
Chem. Soc. J pn. 1998, 71, 2555-2559.
(16) Other sulfur-containing (nonthiol) moieties attached to
porphyrins for binding to gold include isothiocyanato,a methylthio-
phenyl,b,c and thiophened units. (a) Han, W.; Li, S.; Lindsay, S. M.;
Gust, D.; Moore, T. A.; Moore, A. L. Langmuir 1996, 12, 5742-5744.
(b) Akiyama, T.; Imahori, H.; Ajawakom, A.; Sakata, Y. Chem. Lett.
1996, 907-908. (c) Imahori, H.; Ozawa, S.; Ushida, K.; Takahashi,
M.; Azuma, T.; Ajavakom, A.; Akiyama, T.; Hasegawa, M.; Taniguchi,
S.; Okada, T.; Sakata, Y. Bull. Chem. Soc. J pn. 1999, 72, 485-502.
(d) Crossley, M. J .; Prashar, J . K. Tetrahedron Lett. 1997, 38, 6751-
6754.
(17) (a) 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. (b) Lindsey, J .
S. In The Porphyrin Handbook; Kadish, K. M., Smith, K., Guilard, R.,
Eds.; Academic Press: Burlington, MA, 1999, in press.
(18) Lindsey, J . S.; Prathapan, S.; J ohnson, T. E.; Wagner, R. W.
Tetrahedron 1994, 50, 8941-8968.
(19) Ravikanth, M.; Strachan, J .-P.; Li, F.; Lindsey, J . S. Tetrahe-
dron 1998, 54, 7721-7734.
(20) Wagner, R. W.; J ohnson, T. E.; Lindsey, J . S. J . Am. Chem.
Soc. 1996, 118, 11166-11180.
Resu lts a n d Discu ssion
Syn th esis of Ald eh yd es. Our initial synthetic strat-
egy toward monothiol (A3B) porphyrins for vertical
orientation started from 4-methylthiobenzaldehyde which
we planned to convert to 4-mercaptobenzaldehyde dim-
ethyl acetal (using the strategy of Young et al.27) and next
to the thiol-protected dimethyl acetals. The first step
involved conversion of the aldehyde group to its dimethyl
acetal under standard conditions. The sulfide obtained
was successfully converted to the sulfoxide in 95% yield
but treatment of the sulfoxide with TFAA led to polym-
erization rather than affording the free thiol (probably
because of cleavage of acetal and intermolecular thioac-
etalization). We overcame this problem by making two
improvements: (1) the dimethyl acetal was replaced by
a more bulky acetal protecting group at an earlier stage
of the synthesis, (2) milder conditions for the Pummerer
(21) Li, F.; Gentemann, S.; Kalsbeck, W. A.; Seth, J .; Lindsey, J . S.;
Holten, D.; Bocian, D. F. J . Mater. Chem. 1997, 7, 1245-1262.
(22) Li, J .; Ambroise, A.; Yang, S.-Y.; Diers, J . R.; Seth, J .; Wack,
C. R.; Bocian, D. F.; Holten, D.; Lindsey, J . S. J . Am. Chem. Soc. 1999,
121, 8927-8940.
(25) (a) Hsung, R. P.; Babcock, J . R.; Chidsey, C. E. D.; Sita, L. R.
Tetrahedron Lett. 1995, 26, 4525-4528. (b) Yu, C. J .; Chong, Y.;
Kayyem, J . F.; Gozin, M. J . Org. Chem. 1999, 64, 2070-2079.
(26) Tour, J . M.; J ones, L., II; Pearson, D. L.; Lamba, J . J . S.; Burgin,
T. P.; Whitesides, G. M.; Allara, D. L.; Parikh, A. N.; Atre, S. V. J .
Am. Chem. Soc. 1995, 117, 9529-9534.
(23) Wagner, R. W.; J ohnson, T. E.; Li, F.; Lindsey, J . S. J . Org.
Chem. 1995, 60, 5266-5273.
(24) Wagner, R. W.; Ciringh, Y.; Clausen, C.; Lindsey, J . S. Chem.
Mater., in press.
(27) Young, R. N.; Gauthier, J . Y.; Coombs, W. Tetrahedron Lett.
1984, 25, 1753-1756.

Porphyrins for Attachment to Electroactive Surfaces
J . Org. Chem., Vol. 64, No. 23, 1999 8637
Sch em e 1
Sch em e 2
Sch em e 3
rearrangement were employed.28 Thus, protection of the
formyl group with neopentyl glycol29 followed by oxidation
of the resulting acetal 1 smoothly afforded sulfoxide 2 in
86% overall yield (Scheme 1). Treatment of sulfoxide 2
with TFAA in the presence of 2,6-lutidine followed by
hydrolysis of the resulting intermediate furnished thiol
3. Compound 3 was transformed into the S-protected
acetals 4, 5, 6, and 7 using ethyl isocyanate,30 2,4-
dinitrofluorobenzene,31 9-chloromethylanthracene,32 and
pivaloyl chloride, respectively, in overall yields of 20-
65% from the sulfoxide 2 (Scheme 2). The acetal group
in 4, 5, 6, and 7 was selectively hydrolyzed prior to
formation of the corresponding porphyrin.
The S-acetyl-protected p-thiobenzaldehyde 8 was ob-
tained as shown in Scheme 3. S-Acetylthiobenzaldehyde
8 was initially prepared in a two-step one-flask proce-
dure. Cleavage of the methyl group of 4-(methylthio)-
benzaldehyde according to a general procedure33 followed
by trapping of the resulting thiolate anion with acetyl
chloride afforded the desired (S-acetylthio)benzaldehyde
8 in 55% yield. The moderate yield and tedious purifica-
tion of 8 prompted modification of this synthesis. Thus
transformation of acetal 1 into 9 according to a general
procedure34 followed by selective TFA-cleavage of the
acetal group afforded aldehyde 8 in 68% overall yield
(from acetal 1) without any chromatography.
tempts to improve the yield by replacement of DMF
with 1,3-dimethyl-2-imidazolidinone, increasing the tem-
perature, or prolonging the reaction time were unsuc-
cessful.
The thiocyanato-benzaldehyde 10 was prepared ac-
cording to a general procedure35 in 20% yield. All at-
(28) Sugihara, S.; Tanikaga, R.; Kaji, A. Synthesis 1978, 881.
(29) Rondestvedt, C. S. J r. J . Org. Chem. 1961, 26, 2247-2253.
(30) Ricci, A.; Danieli, R.; Pirazzini, G. J . Chem. Soc., Perkin Trans.
1 1977, 1069-1073.
(31) Vorozhtsov, N. N., J r.; Iakobson, G. G. Zh. Obshch. Chim. 1958,
28, 40-44, Engl. Transl. 1958, 28, 40-44.
(32) Kornblum, N.; Scott, A. J . Am. Chem. Soc. 1974, 96, 590-591.
(33) Tiecco, M.; Tingoli, M.; Testaferri, L.; Chianelli, D.; Maiolo, F.
Synthesis 1982, 478-480.
(34) Testaferri, L.; Tiecco, M.; Tingoli, M.; Chianelli, D.; Montanucci,
M. Synthesis 1983, 751-755.
(35) Suzuki, H.; Abe, H. Synth. Commun. 1996, 26, 3413-3419.
Our approach toward horizontally oriented porphyrins
required access to S-protected m-(methylthio)benzalde-

8638 J . Org. Chem., Vol. 64, No. 23, 1999
Gryko et al.
Sch em e 4
Sch em e 5
hydes. The commercially available m-(bromomethyl)-
benzonitrile was reduced with DiBAl-H to the corre-
sponding m-(bromomethyl)benzaldehyde.36 Substitution
of the bromide with potassium thiocyanate or potassium
thioacetate gave the respective thiocyanatobenzaldehyde
11 or thioacetatobenzaldehyde 12 in good yield (Scheme
4). It is noteworthy that the S-cyano and S-acetyl
protecting groups enabled the protected sulfur unit to be
incorporated in one step.
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-thiophenyl unit at one meso position. The
other three meso positions are available for placement
of electron-withdrawing or electron-releasing substitu-
ents. Such A3B-porphyrins were prepared using a two-
step, one-flask room-temperature synthesis of meso-
substituted porphyrins that is compatible with a variety
of precursor aldehydes including the ortho-disubstituted
benzaldehydes that yield facially encumbered porphy-
rins.17,37,38 A mixed-aldehyde condensation of mesitalde-
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 acetals 4-7 were hydrolyzed with trifluoroacetic
acid, and the resulting aldehydes 13-16 were used
directly without purification in the respective porphyrin
syntheses. Thus, aldehydes 8, 13, 14, 15, or 16 as well
as commercially available 4-(methylthio)benzaldehyde
afforded thiol-protected A3B-porphyrins (17-22) in ∼10%
yield (Scheme 5). The corresponding zinc chelates were
obtained by reaction with Zn(OAc)2‚2H2O without alter-
ing the thiol protecting groups. The similar use of the
S-acetyl porphyrin Zn -22. Both Zn -17 and Zn -22 exhib-
ited binding behavior on gold identical to that of the free
thiol containing porphyrin Zn -23.
p-thiocyanatobenzaldehyde 10 in
a mixed-aldehyde
condensation afforded a mixture of porphyrins that could
not be separated. This aldehyde was not examined
further.
Examination of the behavior of various thiol-protected
zinc porphyrins revealed that the S-(N-ethylcarbamoyl)
and S-acetyl groups easily cleaved in situ and the
resulting porphyrin product bound on the gold surface
(vide infra). We decided to confirm this result by also
cleaving the S-(N-ethylcarbamoyl) group in porphyrin
Zn -17 using basic conditions. Treatment of porphyrin Zn -
17 with sodium methoxide followed by acidic workup
gave monothiol porphyrin Zn -23, which was air-sensitive
and proved very difficult to purify to homogeneity (the
porphyrin disulfide was also present). The same reaction
performed with quenching by acetyl chloride afforded the
(36) Wagner, R. W.; J ohnson, T. E.; Lindsey, J . S. Tetrahedron 1997,
53, 6755-6790.
(37) Lindsey, J . S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.;
Marguerettaz, A. M. J . Org. Chem. 1987, 52, 827-836.
(38) Lindsey, J . S.; Wagner, R. W. J . Org. Chem. 1989, 54, 828-
836.

Porphyrins for Attachment to Electroactive Surfaces
J . Org. Chem., Vol. 64, No. 23, 1999 8639
Sch em e 6
Sch em e 7
The results of the gold-binding studies (vide infra)
prompted us to use the S-(N-ethylcarbamoyl)-protected
thiobenzaldehyde 13 in subsequent syntheses. Thus,
mixed aldehyde-pyrrole condensations of aldehyde 13
with 2,4,6-trimethoxybenzaldehyde, pentafluorobenzal-
dehyde, or n-hexanal yielded porphyrin 24, 25, or 26,
respectively (Scheme 6). Attempted conversion to the zinc
chelate gave the thiol-protected porphyrin Zn -24; how-
ever, the more forcing conditions required for metalation
of the tris(pentafluorophenyl)porphyrin and tri-n-pentyl-
substituted porphyrin resulted in cleavage of the S-(N-
ethylcarbamoyl) group, giving the free thiol-containing
porphyrins Zn -27 and Zn -28.
zinc-chelate Zn -29. The tetrathiocyanate porphyrin
bound on the gold surface in a horizontal orientation (vide
infra).
The investigation of porphyrins oriented in a horizontal
manner on an electroactive surface can be achieved by
the synthesis of porphyrins bearing a m-(mercaptometh-
yl)phenyl group at each of the four meso positions. We
attempted to repeat the synthesis of the unprotected 5,-
10,15,20-tetrakis[3-(mercaptomethyl)phenyl]porphy-
rin,13 but encountered solubility problems due to disulfide
formation. Because of the promising results with other
thiol protecting groups that resulted in cleavage and
binding directly on the gold surface, we decided to
synthesize two of the corresponding thiol-protected por-
phyrins.
The reaction of 11 with pyrrole at room tempera-
ture was performed using new mixed-acid catalysis
conditions (TFA + BF3‚OEt2) we have recently devel-
oped.39 This approach afforded the desired 5,10,15,20-
tetrakis[3-(thiocyanatomethyl)phenyl]porphyrin 29 in
18% yield. Metalation with zinc acetate afforded the
(39) Riggs, J . A.; Lindsey, J . S. Unpublished data.

8640 J . Org. Chem., Vol. 64, No. 23, 1999
Gryko et al.
Sch em e 8
Two routes were examined for the synthesis of 5,10,-
15,20-tetrakis[3-(S-acetylthiomethyl)phenyl]porphyrin
(30), as shown in Scheme 7. Substitution of all four
bromides in 5,10,15,20-tetrakis[3-(bromomethyl)phenyl)-
porphyrin13,40 with potassium thioacetate afforded 30 in
63% yield. Alternatively, reaction of aldehyde 12 with
pyrrole at room temperature using the mixed acid
catalysis conditions39 gave 30 in 32% yield.
A range of electrochemical potentials was achieved
with the horizontally oriented porphyrins by metalation
of 5,10,15,20-tetrakis[3-(S-acetylthiomethyl)phenyl]por-
phyrin (30) with various metal salts. Metalation of free
base porphyrin 30 with Zn(OAc)2‚2H2O, Co(OAc)2‚4H2O,
Cu(OAc)2‚H2O, or AgNO3/triethylamine gave the corre-
sponding metalloporphyrin (Zn -30, Co-30, Cu -30 or Ag-
30) without alteration of the S-acetyl protecting groups.
Driven by these positive results, we decided to syn-
thesize a porphyrin with only two groups for attachment
to the gold surface. Condensation of aldehyde 11 with
5-phenyldipyrromethane41 using BF3‚OEt2 in acetonitrile
to minimize scrambling42 gave the desired trans-porphy-
rin 31 in 7% yield. This product was accompanied by 10,-
15,20-triphenyl-5-[3-(thiocyanatomethyl)phenyl]porphy-
rin in 2% yield due to scrambling. Metalation of 31 with
zinc acetate afforded the zinc porphyrin Zn -31 in 59%
yield. Porphyrin Zn -31 also bound to the gold surface.
was performed by mixed aldehyde condensation of S-
acetyl-protected p-thiobenzaldehyde 9, p-iodobenzalde-
hyde, and 5-mesityldipyrromethane. The three expected
porphyrin products were separated by chromatography,
affording the desired trans-porphyrin 32 in 4.9% yield.
We next turned to the preparation of porphyrin build-
ing blocks for the synthesis of multiporphyrin arrays that
can be attached to an electroactive surface. Porphyrins
bearing iodophenyl groups are versatile synthetic units
for the preparation of a wide variety of multiporphyrin
arrays in linear,20 star,21 cyclic,22 and dendritic2 archi-
tectures. We prepared a porphyrin bearing one iodophe-
nyl group and one S-protected p-thiophenyl unit in a
trans orientation. This porphyrin can be used for vertical
organization via single-site attachment of a multipor-
phyrin array on an electroactive surface. The synthesis
We also prepared porphyrins bearing two m-iodophenyl
groups and two S-protected m-(thiomethyl)phenyl units
in a trans orientation. These porphyrins can be used for
horizontal organization via two-site attachment of a
multiporphyrin array on an electroactive surface. Thus,
the condensation of S-acetyl-protected benzaldehyde 12
and 5-(3-iodophenyl)dipyrromethane resulted in a small
amount of scrambling, as is typical with unhindered
dipyrromethanes.42 The desired trans-porphyrin 33 was
obtained by chromatography in 3% yield (Scheme 8).
Porphyrin 34 was prepared in a similar manner from the
thiocyanatobenzaldehyde 11 in 6% yield.
(40) Karaman, R.; Blasko´, A.; Almarsson, O¨ .; Arasasingham, R.;
Bruice, T. C. J . Am. Chem. Soc. 1992, 114, 4889-4898.
(41) (a) Lee, C.-H.; Lindsey, J . S. Tetrahedron 1994, 50, 11427-
11440. (b) Littler, B. J .; Miller, M. A.; Hung C.-H.; Wagner, R. W.;
O’Shea, D. F.; Boyle, P. D.; Lindsey, J . S. J . Org. Chem. 1999, 64,
1391-1396.
Ch a r a cter iza tion of P or p h yr in s. The protected-
thiol porphyrins were stable under routine handling. The
(42) Littler, B. J .; Ciringh, Y.; Lindsey, J . S. J . Org. Chem. 1999,
64, 2864-2872.

Porphyrins for Attachment to Electroactive Surfaces
J . Org. Chem., Vol. 64, No. 23, 1999 8641
1
Ta ble 1. Eva lu a tion of Th iol P r otectin g Gr ou p s
porphyrins were characterized by TLC, H NMR (with
the exception of the paramagnetic Co-30, Cu -30 and Ag-
30), LD-MS, FAB-MS, and UV/vis spectroscopy. Fluores-
cence emission and excitation spectroscopy were used to
confirm the completeness of the different metalation
procedures.
porphyrin metalation binding Pd-coupling
R
formationa
(Zn)b
on Auc
reactiond
3-(RSCH2)phenyl
S-cyano
S-acetyl
4-(RS)phenyl
S-acetyl
S-(N-ethylcarb-
amoyl)
S-cyano
S-(9-anthryl-
methyl)
S-(2,4-dinitro-
phenyl)
S-pivaloyl
yes
yes
yes
yes
yes
noe
yesf
yesg
Generally, the LD-MS spectrum of a porphyrin shows
the molecule ion peak M+ in high intensity with only little
fragmentation.43 However, some porphyrins with delicate
peripheral groups undergo characteristic and extensive
fragmentation upon LD-MS analysis. Of the six thiol
protecting groups examined, all but the 2,4-dinitrophenyl
group exhibited significant fragmentation. For example,
porphyrins with thiocyanate substituents show the loss
of the cyano and the thiocyanato groups, with the latter
exhibiting more intense peaks. If more than one thiocy-
anate group is present, fragmentation can occur for each
of these groups. Porphyrins with S-acetyl groups show
loss of both the acetyl (-COCH3) and the thioacetate
(-SCOCH3) groups. Such fragmentation can generally
occur for each thioacetate substituent. A further LD-MS
feature observed with thioacetate-derivatized porphyrins
involves the appearance of an (M + 15)+ peak. Because
this peak occurred in the LD-MS spectra of all porphyrins
with thioacetate substituents, which were synthesized via
different routes, and no other types of spectra show any
evidence for the presence of another species, this cannot
be an impurity but must be a laser photolysis artifact
involving the transfer of a methyl group. In each case,
the (M + 15)+ peak exhibited the same pattern of
fragmentation as observed for the parent molecule ion
(M+). The intensity of the (M + 15)+ peak is about 10%
of that of the M+ peak. In general, each protecting group
exhibited a characteristic fragmentation pattern and did
not interfere with identification of the porphyrin.
yes
yes
yes
yes
yesf
yesf
NEh
noi
yes
yes
yes
yes
yes
no
NEh
NEj
yes
yes
yes
yes
no
no
NEj
yesk
a
Porphyrin formation was assessed using the two-step one-flask
b
synthesis at or near room temperature. Metalation was per-
formed using zinc acetate in methanolic CHCl3 or CH2Cl2 at room
temperature. c Binding on gold was assessed by exposure of the
porphyrin solution to the gold surface followed by electrochemical
d
examination. Pd-coupling reactions were assessed by a screening
reaction in the presence of an appropriate S-protected thio-
benzaldehyde or acetal (as well as by the coupling of an iodo
porphyrin and an ethynyl porphyrin). e Examined using 11. f Cleav-
age of the protecting group and binding of the resulting thiol to
h
gold. g Examined using 12. Not examined due to results with the
i
same protecting group at the 3-position. Examined using 4 and
k
13. j Not examined due to lack of any binding on gold. Examined
using 7.
rin arrays, we developed a refined Pd-coupling method
that proceeds under mild conditions and is compatible
with diverse free base and metalloporphyrins.23,24 To
check if the various thiol protecting groups are compat-
ible with these conditions, screening experiments were
done. The Pd-coupling of zinc(II)-5-(p-ethynylphenyl)-
10,15,20-trimesitylporphyrin23 with zinc(II)-5-(p-iodophe-
nyl)-10,15,20-trimesitylporphyrin18 was examined in the
presence of an equimolar amount of an appropriate thiol-
protected aldehyde or acetal. The results were monitored
by analytical SEC (HPLC). These screening tests showed
that the S-cyano and the S-(N-ethylcarbamoyl) groups
are incompatible with the Pd-coupling conditions, while
the S-acetyl or S-pivaloyl groups did not interfere with
the Pd-coupling reaction. These results were confirmed
by Pd-coupling with a zinc porphyrin bearing two iodo
and two S-cyano groups (Zn -34), where no porphyrin
trimer was formed.45 Complexation of the nitrogen atoms
of the thiocyanates with Pd and formation of a precipitate
has been observed under different conditions.46 In con-
trast, the Pd-coupling of a porphyrin bearing two iodo
and two S-acetyl groups (Zn -33) afforded the expected
trimer in good yield.45 These results are summarized in
Table 1. The use of these and related porphyrin building
blocks in the synthesis of multiporphyrin arrays with
protected thiol groups at specific sites, and the electro-
chemical properties of the arrays on electroactive sur-
faces, will be reported in due course.
Beh a vior of th e P or p h yr in s on Gold . We surveyed
the behavior of the thiol-protected zinc chelates Zn -17-
Zn -22 on gold electrodes. These studies revealed that the
S-(N-ethylcarbamoyl) (Zn -17) and S-acetyl (Zn -22) groups
were easily cleaved on the gold surface, whereas the
S-(2,4-dinitrophenyl) (Zn -18), S-(9-anthrylmethyl) (Zn -
19), S-pivaloyl (Zn -20), and S-methyl (Zn -21) protecting
groups were not cleaved. For these groups where no
cleavage occurred, the thiol-protected porphyrins were
not bound to the gold surface. We found that Zn -17 (S-
(N-ethylcarbamoyl) protected), Zn -22 (S-acetyl pro-
tected), and Zn -23 (free thiol) afforded products that
bound to the gold surface identically. The thiocyanatom-
ethyl-derivatized porphyrins (Zn -29, Zn -31) bound to the
gold electrode, though in this case, our current data are
insufficient to determine whether the bound species is a
thiol (cleavage and binding) or a thiocyanate (binding
only). A full description of these studies, including results
from electrochemistry and surface spectroscopy, will be
published elsewhere.44 These results are in accord with
and extend the report of Tour et al. that the S-acetyl
group of various thiol-substituted arenes (not porphyrins)
is cleaved on the gold surface.26 These results are
summarized in Table 1.
Con clu sion s
The introduction of a protected thiol unit in an alde-
hyde enables the corresponding porphyrin to be prepared
without handling free porphyrin thiols. One set of por-
phyrins has been prepared for vertical organization via
Com p a tibility of th e P r otectin g Gr ou p s w ith P d -
Cou p lin g Rea ction s. For the synthesis of multiporphy-
(43) Srinivasan, N.; Haney, C. A.; Lindsey, J . S.; Zhang, W.; Chait,
B. T. J . Porphyrins Phthalocyanines 1999, 3, 283-291.
(44) Roth, K. M.; Gryko, D. T.; Clausen, C.; Lindsey, J . S.; Bocian,
D. F.; Kuhr, W. G. Manuscript in preparation.
(45) Clausen, C.; Lindsey, J . S. Manuscript in preparation.
(46) Davis, R. C.; Grinter, T. J .; Leaver, D.; O’Neil, R. M.; Thomson,
G. A. J . Chem. Soc., Perkin Trans. 1 1990, 2881-2887.

8642 J . Org. Chem., Vol. 64, No. 23, 1999
Gryko et al.
2.50 (s, 3H), 3.67 (AB/2, 2H, J ) 10.2 Hz), 3.79 (AB/2, 2H, J )
10.2 Hz), 5.25 (s, 1H), 7.30, (AA′BB′, 4H); 13C NMR δ 16.5,
22.6, 23.8, 30.9, 78.3, 102.1, 127.1, 127.4, 136.2, 140.0; EI-MS
m/z 238.1028 (M)+ (C13H18O2S requires 238.1028). Anal. Calcd
for C13H18O2S: C, 65.51; H, 7.61; S, 13.45; Found: C, 65.62;
H, 7.70; S, 13.55.
one linker, and a second set has been prepared for
horizontal organization via two or four linkers on an
electroactive surface. The S-(N-ethylcarbamoyl) protect-
ing group has been identified to undergo cleavage in situ
on gold electrodes, a phenomenon previously recognized
only for the S-acetyl group. The S-cyano group results
in binding (if not cleavage) on the gold surface. These
three protecting groups can be used in the synthesis of
monomeric porphyrins for attachment to an electroactive
surface. Conversely, the S-(9-anthrylmethyl), S-(2,4-
dinitrophenyl), and S-pivaloyl groups do not afford a
bound species upon exposure to gold. Among the groups
that do undergo cleavage, only the S-acetyl group is
compatible with the Pd-coupling reactions employed in
the synthesis of diarylethyne-linked multiporphyrin ar-
rays.
2-[4-(Me t h ylsu lfoxy)p h e n yl]-5,5-d im e t h yl-1,3-d iox-
a n e (2). A solution of acetal 1 (19 g, 80 mmol) in CH2Cl2 (150
mL) was cooled to -20 °C and stirred vigorously. Then a
solution of m-CPBA (31 g of 50-55% water suspension, 90
mmol) in CH2Cl2 (100 mL) was added dropwise over 1 h. The
mixture was stirred at 0 °C for an additional 1 h. Then Ca-
(OH)2 (11 g, 0.15 mmol) and Na2SO4 (20 g) were added, and
stirring was continued for 1 h. After filtration and evaporation,
the warm colorless oil was dissolved in CH2Cl2 (20 mL) and
hexanes was added, affording white crystals that were isolated
by filtration (14.6 g). The filtrate was evaporated, and the
residual oil was recrystallized, affording a second crop of white
crystals. The total yield was 19.6 g (97%): mp 116-117 °C;
1H NMR δ 0.77 (s, 3H), 1.24 (s, 3H), 2.65 (s, 3H), 3.62 (AB/2,
2H, J ) 11.1 Hz), 3.74 (AB/2, 2H, J ) 10.8 Hz), 5.40 (s, 1H),
7.6-7.7 (m, 4H); 13C NMR δ 22.5, 23.7, 30.9, 44.7, 78.3, 101.3,
124.0, 128.0, 142.2, 146.7; EI-MS obsd 254.0975, calcd exact
mass 254.0977 (C13H18O3S). Anal. Calcd for C13H18O3S: C,
61.39; H, 7.13; S, 12.61. Found: C, 61.29; H, 7.03; S, 12.70.
2-(4-Mer captoph en yl)-5,5-dim eth yl-1,3-dioxan e (3). Sul-
foxide 2 (7.62 g, 30.0 mmol) was dissolved in acetonitrile (120
mL). 2,6-Lutidine (10.8 mL, 93.0 mmol) was added, and the
mixture was cooled to -20 °C. To the resulting suspension was
added TFAA (12.7 mL, 90.0 mmol) dropwise, maintaining the
temperature below 0 °C. The precipitate disappeared, and the
mixture turned a lemon yellow. When the addition was
complete, the mixture was stirred at -10 to 0 °C for 1 h and
then allowed to warm to room temperature. All volatile
materials were evaporated at 30 °C. Next, a precooled (0 °C)
mixture of triethylamine (50 mL) and methanol (50 mL) was
added. After 30 min at room temperature, all volatile materials
were evaporated under reduced pressure at low temperature.
The residual yellow oil was dissolved in ethyl ether (70 mL)
and extracted with saturated NH4Cl (250 mL). The layers were
separated, and the organic layer was dried (Na2SO4) and
concentrated to dryness giving a yellow-orange oil (6.61 g, 98%
yield of crude material) of which ∼70% was the desired
compound (1H NMR analysis). The crude thiol was pure
enough for the next step. A small sample was oxidized to the
respective disulfide and characterized: mp 134-136 °C; 1H
NMR δ 0.80 (s, 3H), 1.28 (s, 3H), 3.63 (AB/2, 2H, J ) 10.2
Hz), 3.76 (AB/2, 2H, J ) 11.2 Hz), 5.36 (s, 1H), 7.43, 7.49
(AA′BB′, 4H); 13C NMR δ 16.5, 22.6, 23.7, 30.9, 78.3, 101.8,
127.6, 128.1, 138.2, 138.4; FAB-MS obsd 446.1574, calcd exact
mass 446.1586 (C24H30O4S2). Anal. Calcd for C24H30O4S2: C,
64.54; H, 6.77; S, 14.36. Found: C, 64.52; H, 6.70; S, 14.44.
2-[4-[S-(N-Eth ylca r ba m oyl)th io]p h en yl]-5,5-d im eth yl-
1,3-d ioxa n e (4). To the crude thiol 3 (6.60 g, 29.5 mmol) was
added ethyl isocyanate (2.33 mL, 29.5 mmol) followed by
phenylthiotrimethylsilane (0.568 mL, 3.00 mmol). The reaction
mixture was stirred for 3 h at room temperature. During this
time, the mixture gradually solidified to a pale yellow solid.
Then n-pentane (5 mL) was added, and the suspension was
filtered and washed thoroughly with n-pentane. The yellowish
crystals were dissolved in hot toluene, and hexanes was added.
After standing for a few hours at room temperature, off-white
crystals were collected (4.01 g, yield 45.2% from sulfoxide 2):
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) and HPLC-grade solvents
(acetonitrile, toluene) were used as received from Fisher.
Pyrrole was distilled from CaH2. All reported NMR spectra
were obtained at 300 MHz in CDCl3. UV-vis absorption and
fluorescence spectra were recorded in CH2Cl2 or toluene as
described previously.21,22 Flash chromatography was performed
on flash silica (Baker, 200-400 mesh) or alumina (Fisher, 80-
200 mesh). Mass spectra were obtained via laser desorption
(LD-MS) in the absence of an added matrix,47 fast atom
bombardment (FAB-MS, 10 ppm elemental compositional
accuracy for the porphyrins), or electron-impact mass spec-
trometry (EI-MS). Porphyrin metalation was monitored by
fluorescence excitation and emission spectroscopy.
Ch a r a cter iza tion of th e P or p h yr in s on Gold Elec-
tr od es. Glass slides with gold electrodes 75 µm in width were
stored under dry ethanol until use. The slides were dried with
a stream of nitrogen prior to exposure to a porphyrin solution.
Exposure of the porphyrin solution (0.1 mg/mL in absolute
ethanol) was performed at room temperature for several hours
(at which point no further change was observed in monolayer
properties). The slide was then rinsed with dry ethanol. The
gold electrode was then examined by cyclic voltammetry in
order to establish the presence of a self-assembled porphyrin
monolayer. This approach also enabled the extent of coverage
of the monolayer on the gold surface to be determined. Thiol-
derivatized porphyrins that do not bind to the gold surface do
not exhibit a characteristic electrochemical response. Control
compounds were provided by the p-(methylthio)phenyl sub-
stituted porphyrin Zn -21, which does not bind to the gold
electrode, and the analogous p-mercaptophenyl substituted
porphyrin Zn -23, which does bind to the gold electrode. (For
clarification of the conflicting results concerning formation of
self-assembled monolayers from thiols and sulfides, see J ung
et al.48) A detailed description of the fabrication of the gold
electrodes, deposition procedures, and electrochemical results
will be published elsewhere.44
2-[4-(Meth ylth io)p h en yl]-5,5-d im eth yl-1,3-d ioxa n e (1).
Samples of 4-(methylthio)benzaldehyde (20.0 mL, 150 mmol),
neopentyl glycol (16.0 g, 155 mmol), toluene (250 mL), and
p-toluenesulfonic acid (190 mg, 1.00 mmol) were placed in a
500 mL flask fitted with a Dean-Stark trap and a reflux
condenser. The mixture was refluxed cautiously until a sudden
exotherm ceased and then for an additional hour (total ∼1.5
h). The cooled mixture was washed with NaHCO3 solution and
with water. After drying with Na2SO4 and evaporation,
crystallization from hexanes afforded white crystals (33.1 g,
1
mp 117-118 °C; H NMR δ 0.81 (s, 3H), 1.08 (t, 3H, J ) 7.2
Hz), 1.29 (s, 3H), 3.2-3.3 (m, 2H), 3.67 (AB/2, 2H, J ) 10.8
Hz), 3.78 (AB/2, 2H, J ) 11.1 Hz), 5.42 (s, 1H), 5.57 (br s, 1H),
7.58 (br s, 4H); 13C NMR δ 15.5, 22.6, 23.7, 30.9, 37.2, 78.3,
101.5, 128.1, 130.0, 136.0, 140.7, 166.4; EI-MS obsd 295.1235,
calcd exact mass 295.1242 (C15H21NO3S). Anal. Calcd for
1
C
15H21NO3S: C, 60.99; H, 7.17; N, 4.74; S, 10.86. Found: C,
92.0%): mp 74-75 °C; H NMR δ 0.83 (s, 3H), 1.33 (s, 3H),
61.16; H, 7.05; N, 4.70; S, 11.02.
2-[4-[S-(2,4-Din itr op h en yl)th io]p h en yl]-5,5-d im eth yl-
1,3-d ioxa n e (5). Crude thiol 3 (1.00 g, 4.46 mmol) was mixed
with 2,4-dinitrofluorobenzene (830 mg, 4.46 mmol). After the
mixture was heated to 35 °C, cesium fluoride (1.35 g, 8.92
(47) Fenyo, D.; Chait, B. T.; J ohnson, T. E.; Lindsey, J . S. J .
Porphyrins Phthalocyanines 1997, 1, 93-99.
(48) J ung, C.; Dannenberger, O.; Xu, Y.; Buck, M.; Grunze, M.
Langmuir 1998, 14, 1103-1107.

Porphyrins for Attachment to Electroactive Surfaces
J . Org. Chem., Vol. 64, No. 23, 1999 8643
mmol) was added. The yellow mixture was stirred and heated
at 45 °C for 1 h. Next, toluene (10 mL) was added, and the
hot suspension was filtered to remove insoluble materials. The
filtrate was evaporated to dryness, giving an orange oil. The
crude product was chromatographed on silica (CH2Cl2/hexanes,
1:2), affording a yellow oil that finally was crystallized from
hot ethanol, affording yellow crystals (1.2 g, 63% from sulfoxide
2): mp 132-133 °C; 1H NMR δ 0.77 (s, 3H), 1.24 (s, 3H), 3.63
(AB/2, 2H, J ) 10.8 Hz), 3.74 (AB/2, 2H, J ) 11.1 Hz), 5.40 (s,
1H), 6.93 (d, 1H, J ) 8.7 Hz), 7.57 (AA′BB′, 4H), 8.00 (dd, 1H,
J ) 8.7 Hz, J ) 2.1 Hz), 8.99 (d, 1H, J ) 2.1 Hz); 13C NMR δ
22.4, 23.6, 30.9, 78.4, 101.2, 122.0, 127.5, 129.2, 129,6, 130.0,
136.4, 142.2, 144.9, 148.8; EI-MS obsd 390.0873, calcd exact
mass 390.0886 (C18H18N2O6S). Anal. Calcd for C18H18N2O6S:
C, 55.38; H, 4.65; N, 7.18; S, 8.21. Found: C, 55.50; H, 4.64;
N, 7.12; S, 8.30.
ethanol giving off-white crystals (1.05 g, 18.3%). Meth od II.
Acetal 9 (7.0 g, 0.027 mol) was suspended in water (4 mL),
and TFA (13 mL) was added. The resulting orange solution
was allowed to stand overnight and then poured into water
and extracted with toluene. The organic layer was washed
extensively with water, dried, and evaporated. The brown
residue was distilled under reduced pressure (120 °C, 0.01
mmHg) to obtain a light orange oil. After dissolution in
ethanol, addition of seed crystals and cooling afforded light
orange crystals. Careful evaporation of this suspension at room
temperature afforded 3.8 g (81%): mp 44-45 °C (lit.49 mp 46
1
°C); H NMR δ 2.44 (s, 3H), 7.56 (AA′BB′, 2H), 7.87 (AA′BB′,
2H), 10.00 (s, 1H); 13C NMR δ 31.2, 130.6, 135.2, 136.1, 137.1,
192.1, 192.9; EI-MS obsd 180.0252 (M)+, calcd exact mass
180.0245. Anal. Calcd for C9H8O2S: C, 59.98; H, 4.47; S, 17.79.
Found: C, 59.58; H, 4.52; S, 17.78.
2-[4-[S-(9-An t h r ylm et h yl)t h io]p h en yl]-5,5-d im et h yl-
1,3-d ioxa n e (6). Crude thiol 3 (1.15 g, 50.0 mmol) was
dissolved in methanol (10 mL). To this solution was added a
freshly prepared solution of sodium methoxide [from Na (117
mg, 50.0 mmol) and methanol (20 mL)]. After 15 min, the
mixture was evaporated to dryness and the orange solid was
dried under vacuum. Then the solid was dissolved in anhy-
drous DMF (15 mL) at room temperature and a solution of
9-chloromethylanthracene (1.13 g, 50.0 mmol) in DMF (10 mL)
was added. The reaction mixture was stirred at room temper-
ature for 72 h. The DMF was evaporated under reduced
pressure, and the resulting yellow oil was chromatographed
on alumina (hexanes/CH2Cl2). The resulting yellow crystals
were recrystallized from CH2Cl2/hexanes to afford 1.17 g of
the desired product (56.4% from sulfoxide 2): mp 158-159 °C;
1H NMR δ 0.84 (s, 3H), 1.37 (s, 3H), 3.69 (AB/2, 2H, J ) 10.8
Hz), 3.84 (AB/2, 2H, J ) 10.8 Hz), 5.01 (s, 2H), 5.44 (s, 1H),
7.4-7.6 (m, 8H), 8.01, 8.26 (AA′BB′, 4H), 8.42 (s, 1H); 13C NMR
δ 22.6, 23.8, 30.9, 32.7, 78.4, 102.0, 124.8, 125.8, 127.1, 127.6,
128.1, 128.5, 129.7, 129.9, 130.8, 132,2, 137.5, 139.3; FAB-MS
obsd 414.1653, calcd exact mass 414.1654 (C27H26O2S). Anal.
Calcd for C27H26O2S: C, 78.22; H, 6.32; S, 7.73. Found: C,
78.05; H, 6.24; S, 7.63.
2-[4-(S -P iva loylt h io)p h e n yl]-5,5-d im e t h yl-1,3-d iox-
a n e (7). Crude thiol 3 (2.24 g, 8.82 mmol) was dissolved in
CH2Cl2 (10 mL), and methanol (10 mL) was added. To this
solution was added a freshly prepared solution of sodium
methoxide [from Na (230 mg, 10.0 mmol) and methanol (5
mL)]. After 30 min, pivaloyl chloride (1.40 mL, 11.4 mmol) was
added, and the mixture was stirred for an additional 3 h at
room temperature. After evaporation of all volatile compo-
nents, the residual oil was chromatographed (silica, CH2Cl2),
affording a mixture of less polar compounds. The yellowish
oil was further purified using centrifugal preparative chro-
matography (silica, CH2Cl2/hexanes, 1:1) to afford a mixture
of the title compound and the corresponding disulfide. The
mixture was dissolved in CH2Cl2, and methanol was added.
Next, CH2Cl2 was flushed out with argon. The crystals were
filtered and dissolved in hot methanol and the mixture was
carefully cooled. After 30 min, crystals of the title compound
were collected (502 mg, 19.8% from sulfoxide 2): mp 115-
116 °C; 1H NMR δ 0.80 (s, 3H), 1.28 (s, 3H), 1.32 (s, 9H), 3.64
(AB/2, 2H, J ) 10.2 Hz), 3.77 (AB/2, 2H, J ) 10.2 Hz), 5.41 (s,
1H), 7.40, 7.55 (AA′BB′, 4H); 13C NMR δ 22.6, 23.7, 28.1, 30.9,
47.6, 78.3, 101.6, 127.5, 129.3, 135.4, 140.1. Anal. Calcd for
2-[4-(S-Acetylth io)ph en yl]-5,5-dim eth yl-1,3-dioxan e (9).
Sodium thiomethoxide (10.0 g, 0.143 mol) and acetal 1 (6.80
g, 29 mmol) were suspended in N,N-dimethylacetamide (125
mL), and the mixture was heated at 140 °C overnight. The
resulting orange, turbid solution was cooled and acetyl chloride
(10.2 mL, 0.143 mol) was added dropwise. The light orange
suspension was then poured into water and extracted with
ethyl ether. The ethereal layer was washed with water, dried,
and evaporated. The resulting oil was distilled under reduced
pressure (140-160 °C, 0.01 mmHg) to obtain light orange
1
crystals (7.0 g, 92%): mp 88-90 °C; H NMR δ 0.81 (s, 3H),
1.30 (s, 3H), 2.41 (s, 3H), 3.66 (AB/2, 2H, J ) 10.2 Hz), 3.79
(AB/2, 2H, J ) 10.2 Hz), 5.42 (s, 1H), 7.44, 7.58 (AA′BB′, 4H);
13C NMR δ 22.6, 23.8, 30.9, 30.9, 78.3, 101.6, 127.7, 129.2,
135.0, 140.5, 194.4; EI-MS obsd 266.0979 (M)+, calcd exact
mass 266.0977 (C14H18O3S).
4-Th iocya n a toben za ld eh yd e (10). Under an argon at-
mosphere, a mixture of 4-iodobenzaldehyde (232 mg, 1.00
mmol), KSCN (95.0 mg, 1.00 mmol), CuSCN (120 mg, 1.00
mmol), and DMF (7.5 mL) was heated with stirring in an oil
bath at 140 °C for 12 h. After cooling, the mixture was diluted
with toluene and water and then filtered through a Celite pad.
The aqueous phase was extracted with toluene, and the
organic fractions were combined and washed with water, dried,
and concentrated. The resulting dark oil was purified using
centrifugal preparative chromatography (silica, CH2Cl2/hex-
anes, 1:2) to obtain off-white crystals (33 mg, 20%): mp 82-
1
83 °C; H NMR δ 7.63, 7.92 (AA′BB′, 2H), 10.01 (s, 1H); 13C
NMR δ 109.4, 129.3, 131.6, 132.9, 191.3; EI-MS obsd 163.0092,
calcd exact mass 163.0092 (C8H5NOS). Anal. Calcd for C8H5-
NOS: C, 58.88; H, 3.09; N, 8.58; S, 19.65. Found: C, 58.85;
H, 2.99; N, 8.61; S, 19.68.
3-(Th iocya n a tom eth yl)ben za ld eh yd e (11). To a solution
of 3-(bromomethyl)benzaldehyde36 (300 mg, 1.5 mmol) in
methanol (5 mL) was added a solution of potassium thiocy-
anate (321 mg, 3.3 mmol) in methanol (4 mL) under stirring
at room temperature. After a few minutes, a precipitate
formed. The reaction was monitored by TLC and stopped by
adding water (20 mL) when no starting material was detect-
able. Ethyl ether (30 mL) was added, and the phases were
separated. The aqueous phase was washed twice with ethyl
ether (20 mL), and the combined organic phases were dried
(Na2SO4). Column chromatography over flash silica gel (ethyl
ether/hexanes, 1:2) gave 198 mg (74% yield) of a slightly yellow
oil that solidified upon standing at 0 °C. Recrystallization
(ethyl ether/hexanes) gave colorless crystals (mp 39 °C): IR
C
17H24O3S: C, 66.20; H, 7.84; S, 10.40. Found: C, 66.22; H,
1
7.92; S, 10.60.
(neat) ν˜ 3060, 2996, 2832, 2149, 1695, 1603; H NMR δ 4.22
4-(S-Acetylth io)ben za ld eh yd e (8). Meth od I. 4-(Meth-
ylthio)benzaldehyde (4.45 mL, 0.033 mol) and sodium thi-
omethoxide (10 g, 0.143 mol) were suspended in HMPA (100
mL), and the reaction mixture was heated with stirring at 100
°C for 18 h. The resulting brown suspension was cooled, and
acetyl chloride (10.2 mL, 0.143 mol) was added. After 2 h, the
resulting suspension was poured into water, and ethyl ether
was added. The ethereal layer was extracted with water three
times, dried, and evaporated. Next, chromatography was
performed (silica, CH2Cl2/hexanes, 1:1). A yellow oil was
collected containing the title compound with some impurities
(3.33 g, crude yield 55.5%). This oil was recrystallized from
(s, 2H), 7.55-7.69 (m, 2H), 7.86-7.93 (m, 2H), 10.04 (s, 1H);
13C NMR (APT) δ 32.7 (+), 111.4 (+), 129.6 (-), 129.8 (-), 130.1
(-), 134.6 (-), 135.7 (+), 136.8 (+), 191.4 (-); GC-MS (EI)
obsd 177, 149, 120, 119, 91. Anal. Calcd for C9H7NOS: C,
60.99; H, 3.98; N, 7.90; S, 18.09. Found: C, 60.75; H, 4.05; N,
7.86; S, 18.19.
3-(S-Acetylth iom eth yl)ben za ld eh yd e (12). To a solution
of 3-(bromomethyl)benzaldehyde36 (3.156 g, 15.9 mmol) in
(49) Zhdanov, Y. A.; Minkin, V. I.; Olekhnovich, L. P.; Malysheva,
E. N. Zh. Org. Khim. 1970, 6, 554-559, Engl. Transl. 1970, 6, 551-
555.

8644 J . Org. Chem., Vol. 64, No. 23, 1999
Gryko et al.
acetone (50 mL) was added potassium thioacetate (2.180 g,
19.1 mmol) under stirring at room temperature. Then the
mixture was refluxed. After a few minutes, a precipitate
formed. The reaction was monitored by TLC and cooled to room
temperature after 4 h when no starting material was detect-
able. Water (60 mL) was added, and the mixture was extracted
four times with ethyl ether (50 mL). The combined organic
phases were dried (Na2SO4). Column chromatography over
flash silica gel (ethyl ether/hexanes, 1:3) gave 2.736 g (89%
yield) of a yellow oil that darkened upon standing (nonetheless,
elementary analysis 7 weeks after exposure to air at room
temperature indicated a high level purity as listed below): IR
C2H6], 774.2 [M+ - COC(CH3)3]; FAB-MS obsd 856.4186, calcd
exact mass 856.4175 (C58H56N4OS); λabs (CH2Cl2) 419, 515, 548,
591, 646 nm.
5,10,15-Tr im esit yl-20-[4-(m et h ylt h io)p h en yl]p or p h y-
r in (21). The mixture was chromatographed on one silica
column (toluene/hexanes, 1:1) and then on a second silica
column (toluene/hexanes, 1:4). The title porphyrin comprised
the second purple band, affording 57 mg (10%): 1H NMR δ
-2.49 (s, 2H), 1.92 (s, 18H), 2.68 (s, 9H), 2.79 (s, 3H), 7.33 (s,
6H), 7.67, 8.18 (AA′BB′, 4H), 8.70 (s, 4H), 8.74 (d, 2H, J ) 5.1
Hz), 8.87 (d, 2H, J ) 5.1 Hz); LD-MS obsd 786.9; FAB-MS
obsd 786.3790, calcd exact mass 786.3756 (C54H50N4S); λabs
(CH2Cl2) 420, 515, 550, 592, 648 nm.
1
(neat) ν˜ 3062, 2835, 2732, 1694, 1603, 1588; H NMR δ 2.24
(s, 3H), 4.06 (s, 2H), 7.31-7.39 (m, 1H), 7.43-7.49 (m, 1H),
7.61-7.71 (m, 2H), 9.87 (s, 1H); 13C NMR (APT) δ ) 29.9 (-),
32.4 (+), 128.3 (-), 129.0 (-), 129.5 (-), 134.5 (-), 136.4 (+),
138.8 (+), 191.6 (-), 194.3 (+); GC-MS (EI) obsd 194, 152,
119, 91. Anal. Calcd for C10H10O2S, C, 61.83; H, 5.19; S, 16.51.
Found: C, 61.72; H, 5.25; S, 16.64.
5,10,15-Tr im esityl-20-[4-(S-a cetylth io)p h en yl]p or p h y-
r in (22). The mixture was chromatographed on a silica column
(toluene/hexanes, 1:1, then toluene). The title porphyrin
comprised the second purple band, affording 62 mg (10.5%):
1H NMR δ -2.46 (s, 2H), 1.94 (s, 18H), 2.66 (s, 3H), 2.70 (s,
9H), 7.35 (s, 6H), 7.88, 8.35 (AA′BB′, 4H), 8.73 (s, 4H), 8.79
(d, 2H, J ) 4.2 Hz), 8.89 (d, 2H, J ) 4.2 Hz); LD-MS obsd
815.7, 830.9 [M+ + 15]; 787.7 [M+ - CH3CO + 15], 773.7 [M+
- CH3CO]; FAB-MS obsd 814.3694, calcd exact mass 814.3705
(C55H50N4OS); λabs (CH2Cl2) 419, 515, 548, 591, 647 nm.
5,10,15-Tr is(2,4,6-tr im eth oxyp h en yl)-20-[4-[S-(N-eth yl-
ca r ba m oyl)th io]p h en yl]p or p h yr in (24). Purification was
performed by preparative centrifugal chromatography (silica,
CH2Cl2/methanol, 98:2). The title compound was obtained as
a 1:1 mixture with 5,10,15,20-tetrakis(2,4,6-trimethoxyphe-
nyl)porphyrin. The presence of the title compound was con-
firmed by mass spectrometry (LD-MS C56H53N5O10S calcd
average mass 987.4, obsd 988.6). This mixture was not purified
further but was used in the metalation reaction to prepare
Zn -24.
5,10,15-Tr is(2,3,4,5,6-p en t a flu or op h en yl)-20-[4-[S-(N-
eth ylca r ba m oyl)th io]p h en yl]p or p h yr in (25). The mixture
of porphyrins was chromatographed on a silica column (hex-
anes/CH2Cl2, 2:1). The title porphyrin comprised the second
purple band, affording 72 mg (10%): 1H NMR δ -2.74 (s, 2H),
1.32 (t, 3H, J ) 7.2 Hz), 3.5-3.6 (m, 2H), 5.67 (br s, 1H), 8.00,
8.32 (AA′BB′, 4H), 8.94 (d, 2H, J ) 5.1 Hz), 9.02 (s, 4H), 9.09
(d, 2H, J ) 4.2 Hz); LD-MS obsd 989.9, 918.7 [M+ - CONHEt];
FAB-MS obsd 987.1136, calcd exact mass 987.1149 (C47H20F15N5-
OS); λabs (CH2Cl2) 415, 509, 540, 584, 638 nm.
5,10,15-Tr i-n -p en tyl-20-[4-[S-(N-eth ylca r ba m oyl)th io]-
p h en yl]p or p h yr in (26). The free base was purified by
preparative centrifugal chromatography (silica/CH2Cl2/hex-
anes, 5:1) followed by column chromatography (silica/CH2Cl2/
toluene, 4:1). The title porphyrin comprised the second purple
band, affording 9 mg (4%): 1H NMR δ -2.62 (s, 2H), 1.00-
1.10 (m, 9H), 1.30-1.70 (m, 9H), 1.75-1.90 (m, 6H), 2.45-
2.70 (m, 6H), 3.50-3.62 (m, 4H), 4.90-5.10 (m, 6H), 5.63 (br
t, 1H, J ) 5.1 Hz), 7.98, 8.26 (AA′BB′, 4H), 8.85 (d, 2H, J )
4.2 Hz), 9.43 (d, 2H, J ) 5.1 Hz); 9.52-9.62 (m, 4H); LD-MS
obsd 700.7; FAB-MS obsd 699.3996, calcd exact mass 699.3971
(C44H53N5OS); λabs (CH2Cl2) 419, 519, 554, 598, 656 nm.
Gen er a l P r oced u r e for Zin c In ser tion . The porphyrin
(0.040 mmol) was dissolved in CH2Cl2 (15 mL), and a solution
of Zn(OAc)2‚2H2O (880 mg, 4.00 mmol) in methanol (15 mL)
was added. The reaction mixture was stirred overnight at room
temperature. After metalation was complete (TLC, fluores-
cence excitation spectroscopy), the reaction mixture was
washed with water and 10% NaHCO3, dried (Na2SO4), filtered,
and rotary evaporated to a purple solid. Purification was
achieved by chromatography on silica.
Zin c(II)-5,10,15-Tr im esityl-20-[4-[S-(N-eth ylcar bam oyl)-
t h io]p h en yl]p or p h yr in (Zn -17). Column chromatography
(silica, CH2Cl2) afforded 29 mg (75%): 1H NMR δ 1.30 (t, 3H,
J ) 7.5 Hz), 1.87 (s, 18H), 2.66 (s, 9H), 3.4-3.6 (m, 2H), 5.61
(br s, 1H), 7.31 (s, 6H), 7.93, 8.30 (AA′BB′, 4H), 8.74 (s, 4H),
8.80 (d, 2H, J ) 5.1 Hz), 8.88 (d, 2H, J ) 4.2 Hz); LD-MS obsd
906.7, 835.7 [M+ - CONHEt]; FAB-MS obsd 905.3098, calcd
exact mass 905.3106 (C56H51N5OSZn); λabs (CH2Cl2) 421, 549
nm.
Gen er a l P r oced u r e for Syn th esis of P or p h yr in s 17-
22 a n d 24-26. The acetal (4, 5, 6, or 7) (0.730 mmol) was
dissolved in CH2Cl2 (1 mL), and trifluoroacetic acid (2 mL) was
added. The mixture was stirred at room temperature over-
night. After evaporation of the reaction mixture to dryness,
the residue was redissolved in CHCl3 (40 mL). Alternatively,
aldehyde 8 or 4-(methylthio)benzaldehyde (0.730 mmol) was
added to CHCl3 (40 mL). Next, samples of the other aldehyde
(2.20 mmol), pyrrole (0.200 mL, 2.92 mmol), and BF3‚OEt2
(0.090 mL, 0.71 mmol) were added. The reaction mixture was
stirred at room temperature for 90 min. Then DDQ (500 mg,
2.20 mmol) was added, and the reaction mixture was gently
refluxed for 1 h. After cooling, the reaction mixture was passed
over a short silica column (CH2Cl2), affording porphyrins
usually free from dark pigments and quinone species. Further
purification details are described for each case as follows.
5,10,15-Tr im esityl-20-[4-[S-(N-eth ylcar bam oyl)th io]ph e-
n yl]p or p h yr in (17). The mixture of porphyrins was loaded
onto a silica column (toluene). The title porphyrin comprised
the second purple band, affording 72 mg (12%): 1H NMR δ
-2.47 (s, 2H), 1.32 (t, 3H, J ) 7.2 Hz), 1.94 (s, 18H), 2.69 (s,
9H), 3.4-3.6 (m, 2H), 5.65 (br s, 1H), 7.35 (s, 6H), 8.00, 8.33
(AA′BB′, 4H), 8.72 (s, 4H), 8.78 (d, 2H, J ) 4.2 Hz), 8.87 (d,
2H, J ) 4.2 Hz); LD-MS obsd 844.6 [M+], 773.1 [M+
-
CONHEt]; FAB-MS obsd 843.4019, calcd exact mass 843.3971
(C56H53N5OS); λabs (CH2Cl2) 419, 515, 548, 591 nm.
5,10,15-Tr im esityl-20-[4-[S-(2,4-din itr oph en yl)th io]ph e-
n yl]p or p h yr in (18). The mixture of porphyrins was purified
by preparative centrifugal chromatography (silica, toluene/
hexanes, 1:2). The title porphyrin comprised the second
purple band, affording 70 mg (10%): 1H NMR δ -2.44 (s, 2H),
1.95 (s, 18H), 2.71 (s, 9H), 7.30 (d, 1H, J ) 8.1 Hz), 7.37 (s,
6H), 7.60 (d, 1H, J ) 8.7 Hz), 8.00, 8.49 (AA′BB′, 4H), 8.75 (s,
4H), 8.8-9.0 (m, 4H), 9.30 (d, 1H, J ) 2.1 Hz); LD-MS obsd
938.0; FAB-MS obsd 938.3632, calcd exact mass 938.3614
(C59H50N6O4S); λabs (CH2Cl2) 419, 515, 549, 591, 646 nm.
5,10,15-Tr im esityl-20-[4-[S-(9-a n th r ylm eth yl)th io]p h e-
n yl]p or p h yr in (19). The mixture was chromatographed on
an alumina column (toluene/hexanes, 1:4). The resulting
mixture of porphyrins was purified by preparative centrifugal
chromatography (silica, toluene/hexanes, 1:3). The title por-
phyrin comprised the second purple band, affording 28 mg
(4.0%): 1H NMR δ -2.51 (s, 2H), 1.90 (s, 18H), 2.66 (s, 9H),
5.43 (s, 2H), 7.1-7.8 (m, 5H), 7.31 (s, 6H), 7.79, 8.52 (AA′BB′,
4H), 8.0-8.2 (m, 4H), 8.68 (s, 4H), 8.75 (d, 2H, J ) 4.5 Hz),
8.80 (d, 2H, J ) 4.5 Hz); LD-MS obsd 964.0, 787.4 [M+
-
C
14H8], 773.1 [M+ - C15H10]; FAB-MS obsd 962.4368, calcd
exact mass 962.4382 (C68H58N4S); λabs (CH2Cl2) 420, 515, 549,
593, 648 nm.
5,10,15-Tr im esit yl-20-[4-(S-p iva loylt h io)p h en yl]p or -
p h yr in (20). The mixture was chromatographed on a silica
column (toluene/hexanes, 1:1). The title porphyrin comprised
the second purple band, affording 68 mg (11%): 1H NMR δ
-2.49 (s, 2H), 1.52 (s, 9H), 1.92 (s, 18H), 2.68 (s, 9H), 7.35 (s,
6H), 7.83, 8.30 (AA′BB′, 4H), 8.70 (s, 4H), 8.75 (d, 2H, J ) 5.4
Zin c(II)-5,10,15-Tr im esityl-20-[4-[S-(2,4-din itr oph en yl)-
t h io]p h en yl]p or p h yr in (Zn -18). Column chromatography
Hz), 8.88 (d, 2H, J ) 5.4 Hz); LD-MS obsd 858.6, 831.5 [M+
-

Porphyrins for Attachment to Electroactive Surfaces
J . Org. Chem., Vol. 64, No. 23, 1999 8645
(silica, toluene/hexanes) afforded 34 mg (85%): 1H NMR δ 1.87
(s, 18H), 2.64 (s, 9H), 7.26 (d, 1H, J ) 9.0 Hz), 7.29 (s, 6H),
7.54 (d, 1H, J ) 9.0 Hz), 7.99, 8.44 (AA′BB′, 4H), 8.75 (s, 4H),
8.86 (AB, 4H, J ) 4.5 Hz), 9.23 (d, 1H, J ) 3.0 Hz); LD-MS
obsd 1000.3; FAB-MS obsd 1000.2726, calcd exact mass
1000.2749 (C59H48N6O4SZn); λabs (CH2Cl2) 422, 550 nm.
Zin c(II)-5,10,15-Tr im esityl-20-[4-[S-(9-a n th r ylm eth yl)-
th io]p h en yl]p or p h yr in (Zn -19). The product was purified
by preparative centrifugal chromatography (silica, hexanes/
CH2Cl2) 31 mg (74%): 1H NMR δ 1.85 (s, 9H), 1.88 (s, 9H),
2.65 (s, 9H), 5.36 (s, 2H), 7.1-8.5 (m, 19H), 8.72 (s, 2H), 8.73
J ) 4.5 Hz), 8.84 (s, 4H); LD-MS obsd 1052.7, 981.5 [M+
-
CONHEt]; FAB-MS obsd 1049.2666, calcd exact mass 1049.2648
(C56H51N5O10SZn); λabs (CH2Cl2) 423, 549 nm.
Zin c(II)-5,10,15-Tr is(2,3,4,5,6-p en ta flu or op h en yl)-20-
[4-m er ca p top h en yl]p or p h yr in (Zn -27). Refluxing a mix-
ture of porphyrin 25 and Zn(OAc)2‚2H2O for 8 h followed by
purification on silica (CH2Cl2) afforded 25 mg (63% yield): 1H
NMR δ 3.79 (s, 1H), 7.67, 8.09 (AA′BB′, 4H), 8.93 (d, 2H, J )
4.2 Hz), 9.00 (s, 4H), 9.09 (d, 2H, J ) 4.2 Hz); LD-MS obsd
975.4; FAB-MS obsd 977.9925, calcd exact mass 977.9913
(C44H13F15N4SZn); λabs (CH2Cl2) 416, 545 nm.
Zin c(II)-5,10,15-Tr i-n -p en tyl-20-[4-m er ca p top h en yl]-
p or p h yr in (Zn -28). The product was purified by column
chromatography (silica/CH2Cl2) followed by preparative cen-
trifugal chromatography (silica, hexanes/CH2Cl2, 1:9), afford-
ing 12 mg (44%): 1H NMR δ 0.80-1.40 (m, 12H), 1.50-1.70
(m, 6H), 1.75-1.95 (m, 6H), 2.40-2.60 (m, 6H), 4.70-4.90 (m,
6H), 8.17, 8.28 (AA′BB′, 4H), 8.95 (d, 2H, J ) 5.1 Hz), 9.35-
9.48 (d, 6H); LD-MS obsd 690.4, 633.1 [M+ - C4H9]; FAB-MS
obsd 690.2706, calcd exact mass 690.2735 (C41H46N4SZn); λabs
(CH2Cl2) 419, 554 nm.
(s, 2H), 8.8-9.0 (m, 4H); LD-MS obsd 1027.3, 850.0 [M+
-
C14H8], 834.9 [M+ - C15H10]; FAB-MS obsd 1024.3529, calcd
exact mass 1024.3517 (C68H56N4SZn); λabs (CH2Cl2) 421, 550
nm.
Zin c(II)-5,10,15-Tr im esityl-20-[4-(S-p iva loylth io)p h e-
n yl]p or p h yr in (Zn -20). The product was purified on a silica
column (toluene/hexanes, 1:1), affording 31 mg (85%): 1H NMR
δ 1.50 (s, 9H), 1.87 (s, 18H), 2.65 (s, 9H), 7.31 (s, 6H), 7.79,
8.29 (AA′BB′, 4H), 8.74 (s, 4H), 8.79 (d, 2H, J ) 4.2 Hz), 8.91
(d, 2H, J ) 4.2 Hz); LD-MS obsd 919.5, 891.4 [M+ - C2H6],
835.3 [M+ - COC(CH3)3]; FAB-MS obsd 918.3332, calcd exact
mass 918.3310 (C58H54N4OSZn); λabs (CH2Cl2) 422, 549 nm.
Zin c(II)-5,10,15-Tr im esityl-20-[4-(m eth ylth io)p h en yl]-
p or p h yr in (Zn -21). The mixture was chromatographed on a
silica column (toluene/hexanes, 1:1). The resulting mixture was
next chromatographed on a silica column (toluene/hexanes,
1:4). The title porphyrin comprised the second purple band,
affording 31 mg (90%): 1H NMR δ 1.84 (s, 18H), 2.63 (s, 9H),
2.74 (s, 3H),7.26 (s, 6H), 7.59, 8.13 (AA′BB′, 2H), 8.70 (s, 4H),
8.75 (d, 2H, J ) 5.1 Hz), 8.87 (d, 2H, J ) 5.1 Hz); LD-MS obsd
851.5; FAB-MS obsd 848.2913, calcd exact mass 848.2891
(C54H48N4SZn); λabs (CH2Cl2) 421, 550 nm.
Zin c(II)-5,10,15-Tr im esityl-20-[4-(S-a cetylth io)p h en yl]-
p or p h yr in (Zn -22). Meth od I. (From 22 by general zinc
insertion procedure). Purification by chromatography (silica,
toluene/CH2Cl2), yield 82%. Meth od II. Porphyrin Zn -17 (9.0
mg, 0.010 mmol) was dissolved in CH2Cl2 (20 mL), and the
solution was carefully flushed with argon. Next, a solution of
sodium methoxide [freshly prepared from sodium (23 mg, 1.0
mmol) and methanol (10 mL) under argon] was added. The
reaction mixture was stirred under argon at room temperature
for 1 h. Then, acetyl chloride (1 mmol, 0.7 mL) was added,
and the mixture was evaporated to dryness. The mixture of
porphyrins was dissolved in CH2Cl2 and chromatographed
(silica, hexanes/CH2Cl2) affording 6.3 mg (72%): 1H NMR δ
1.85 (s, 18H), 2.63 (s, 9H), 2.61 (s, 3H), 7.28 (s, 6H), 7.46, 8.07
(AA′BB′, 4H), 8.70 (s, 4H), 8.74 (d, 2H, J ) 5.1 Hz), 8.83 (d,
2H, J ) 5.1 Hz); LD-MS obsd 874.6; FAB-MS obsd 878.2983,
calcd exact mass 878.2997 (C55H50N4OSZn); λabs (CH2Cl2) 421,
550 nm.
Zin c(II)-5,10,15-Tr im esityl-20-[4-m er ca p toph en yl]por -
p h yr in (Zn -23). A sample of Zn -17 (9.0 mg, 0.010 mmol) was
dissolved in CH2Cl2 (20 mL) and the solution was carefully
flushed with argon. Next a solution of sodium methoxide
[freshly prepared from sodium (23 mg, 1 mmol) and methanol
(10 mL) under argon] was added. The reaction mixture was
stirred at room temperature for 1 h, HCl (0.2 mL, 5 M solution)
was added, and the mixture was evaporated to dryness. The
mixture of porphyrins was dissolved in CH2Cl2 and chromato-
graphed (silica, hexanes/CH2Cl2), affording 4.3 mg (51%): 1H
NMR δ 1.89 (s, 18H), 2.66 (s, 9H), 7.31 (s, 6H), 7.64, 8.22
(AA′BB′, 2H), 8.76 (s, 4H), 8.8-9.0 (m, 4H); LD-MS obsd 834.0;
FAB-MS obsd 834.2071, calcd exact mass 834.2735 (C53H46N4-
SZn); λabs (CH2Cl2) 421, 550 nm.
Zin c(II)-5,10,15-Tr is(2,4,6-tr im eth oxyp h en yl)-20-[4-[S-
(N-eth ylca r ba m oyl)th io]p h en yl]p or p h yr in (Zn -24). 30.0
mg of a mixture of the desired free base A3B-porphyrin and
the corresponding A4-porphyrin was metalated according to
the general procedure. The desired chelate was purified by
preparative centrifugal chromatography (silica, CH2Cl2/metha-
nol, 99:1), affording 10.0 mg (1.3% from acetal 4): 1H NMR
δ 1.27 (t, 3H, J ) 7.2 Hz), 3.4-3.6 (m, 2H), 3.49 (s, 18H),
4.09 (s, 9H), 5.57 (br t, 1H, J ) 5.1 Hz), 6.57 (s, 6H), 7.89,
8.26 (AA′BB′, 4H), 8.81 (d, 2H, J ) 4.5 Hz), 8.86 (d, 2H,
5,10,15,20-Tetr a k is[3-(th iocya n a tom eth yl)p h en yl]p or -
p h yr in (29). A solution of 11 (513 mg, 2.9 mmol) and pyrrole
(0.20 mL, 2.9 mmol) in CHCl3 (300 mL) was purged with argon
for 30 min. Under stirring at room temperature, BF3‚OEt2 (12
µL, 0.1 mmol) and TFA (180 µL, 2.3 mmol) were added in the
dark. Soon the solution turned yellow and later to dark red.
After 2 h, additional BF3‚OEt2 (90 µL, 0.7 mmol) was added.
After a further 2 h, triethylamine (500 µL, 3.6 mmol) and
o-tetrachlorobenzoquinone (583 mg, 2.4 mmol) were added, and
the mixture was refluxed for 1 h. The mixture was cooled to
room temperature, and the solvents were removed under
reduced pressure. Column chromatography over flash silica
gel (ethyl ether/hexanes, 3:1) gave 119 mg (18% yield) of a dark
1
purple solid: IR (neat) ν˜ 2953, 2917, 2846, 2152; H NMR δ
-2.84 (s, 2H), 4.44 (s, 8H), 7.76-7.85 (m, 8H), 8.18-8.25 (m,
8H), 8.88 (s, 8H); LD-MS obsd 898.0 [M+], 871.0 [M+ - CN],
839.9 [M+ - SCN], 781.9 [M+ - 2 SCN], 724.9 [M+ - 3 SCN],
666.7 [M+ - 4 SCN]; FAB-MS obsd 898.1797, calcd exact mass
898.1789 (C52H34N8S4); λabs (toluene) 420, 514, 549, 590, 646
nm.
Zin c(II)-5,10,15,20-Tet r a k is[3-(t h iocya n a t om et h yl)-
p h en yl]p or p h yr in (Zn -29). To a solution of 27 (84 mg, 93
µmol) in CHCl3 (50 mL) was added 5 mL of a methanolic
solution of Zn(OAc)2‚2H2O (250 mg, 1.1 mmol) with stirring
at room temperature in the dark. After completion of the
metalation, the mixture was washed with 10% NaHCO3
solution (20 mL) and water (20 mL), dried (Na2SO4), and
filtered. The solvents were removed under reduced pressure,
affording 71 mg (79% yield) of a dark purple solid. Recrystal-
lization (CH2Cl2/methanol) gave dark purple crystals: IR
(neat) ν˜ 2995, 2880, 2153, 1601; 1H NMR δ 4.44 (s, 8H), 7.77-
7.83 (m, 8H), 8.20-8.25 (m, 8H), 8.97 (s, 8H); LD-MS obsd
961.1 [M+], 903.0 [M+ - SCN], 845.0 [M+ - 2 SCN], 786.9 [M+
- 3 SCN], 727.9 [M+ - 4 SCN]; FAB-MS obsd 960.0959, calcd
exact mass 960.0924 (C52H32N8S4Zn); λabs (toluene) 422, 550,
589 nm; λem (toluene) 603, 652 nm.
5,10,15,20-Tetr a k is[3-(S-a cetylth iom eth yl)p h en yl]p or -
p h yr in (30). Meth od I. A solution of 5,10,15,20-tetrakis[3-
(bromomethyl)phenyl)porphyrin13,40 (102 µmol) and potassium
thioacetate (60 mg, 525 µmol) in THF (20 mL) was refluxed
in the dark. After 5 h, the mixture was cooled to room
temperature. Water (30 mL) was added, and the phases were
separated. The organic phase was washed with 5% NaHCO3
solution (40 mL) and dried (Na2SO4). Column chromatography
over flash silica gel with THF afforded a purple wax, which
was purified by refluxing in hexanes. The mixture was filtered,
and the residue was dissolved in CH2Cl2. The solvent was
removed under reduced pressure, affording 63 mg (63% yield)
of a purple solid. Meth od II. To a solution of aldehyde 12 (525
mg, 3.0 mmol), pyrrole (206 µL, 3.0 mmol), and TFA (185 µL,
2.4 mmol) in CH2Cl2 (300 mL) was added BF3‚OEt2 (13 µL,
0.1 mmol) with stirring at room temperature in the dark under
argon. The solution turned yellow and later dark red. After 3
h, DDQ (505 mg, 2.2 mmol) was added, and the mixture was

8646 J . Org. Chem., Vol. 64, No. 23, 1999
Gryko et al.
refluxed. After 1.5 h, the mixture was cooled to room temper-
ature, and the solvents were removed under reduced pressure.
Column chromatography over flash silica gel (ethyl ether/
hexanes, 1:1) was performed twice, affording 226 mg (32%
yield) of a purple solid: IR (neat) ν˜ 3423, 3318, 2963, 2926,
1690, 1600; 1H NMR δ -2.83 (s, 2H), 2.40 (s, 12H), 4.41 (s,
8H), 7.65-7.75 (m, 8H), 8.06-8.17 (m, 8H), 8.84 (s, 8H); LD-
MS obsd 982.4 [M+ + 15], 967.4 [M+], 925.3 [M+ - COCH3],
892.2 [M+ - SCOCH3], 850.0 [M+ - SCOCH3 - COCH3], 817.2
[M+ - 2 SCOCH3], 775.5 [M+ - 2 SCOCH3 - COCH3]; FAB-
MS obsd 966.2413, calcd exact mass 966.2402 (C56H46N4O4S4);
λabs (toluene) 421, 515, 550, 591, 648 nm.
10,20-Dip h en yl-5,15-bis[3-(th iocya n a tom eth yl)p h en yl]-
p or p h yr in (31). A mixture of 11 (316 mg, 1.8 mmol), 5-phe-
nyldipyrromethane (396 mg, 1.8 mmol), and NH4Cl (1.07 g,
20.0 mmol) in acetonitrile (200 mL) was purged with argon
for 30 min. Then BF3‚OEt2 (23 µL, 0.18 mmol) was added with
stirring at room temperature in the dark. Soon the solution
turned yellow and later dark red. After 6.5 h, DDQ (607 mg,
2.7 mmol) was added. After an additional 1 h, the reaction
was quenched with triethylamine (0.5 mL, 3.6 mmol). The
solvents were removed under reduced pressure. Purification
was done by column chromatography over two flash silica gel
columns with different solvent mixtures: (column 1) ethyl
ether/hexanes (3:1) and (column 2) CH2Cl2/hexanes (gradient,
start: 1:1). Two fractions of dark purple solids were obtained.
I: 12 mg 10,15,20-triphenyl-5-[3-(thiocyanatomethyl)phenyl]-
porphyrin (2% yield). II: 44 mg of the title compound (7%
Zin c(II)-5,10,15,20-Tet r a k is[3-(S-a cet ylt h iom et h yl)-
p h en yl]p or p h yr in (Zn -30). A solution of 30 (16.2 mg, 16.7
µmol) in CHCl3 (20 mL) was treated with 5 mL of a methanolic
solution of Zn(OAc)2‚2H2O (80.0 mg, 365 µmol) with stirring
at room temperature in the dark. After 2 h, the metalation
was completed, and water (40 mL) was added. The phases were
separated, and the organic layer was washed three times with
5% NaHCO3 and dried (Na2SO4). The solvents were removed
under reduced pressure. Column chromatography over flash
silica gel (CH2Cl2/hexanes, 4:1) gave the title compound as a
purple solid in quantitative yield: IR (neat) ν˜ 2922, 2849, 1690,
1
yield): IR (neat) ν˜ 2921, 2850, 2154, 1597; H NMR δ -2.81
(s, 2H), 4.57 (s, 4H), 7.71-7.83 (m, 11H), 8.17-8.25 (m, 8H),
8.84 (d, 4H, 3J ) 5.1 Hz), 8.88 (d, 4H); LD-MS obsd 757.4 [M+],
699.2 [M+ - SCN], 641.0 [M+ - 2 SCN]; FAB-MS obsd
756.2172, calcd exact mass 756.2130 (C48H32N6S2); λabs (tolu-
ene) 420, 514, 549, 590, 647 nm.
Zin c(II)-10,20-Dip h en yl-5,15-bis[3-(th iocya n a tom eth -
yl)p h en yl]p or p h yr in (Zn -31). A solution of 28 (38 mg, 50.2
µmol) in CH2Cl2 (30 mL) was treated with 5 mL of a methanolic
solution of Zn(OAc)2‚2H2O (140 mg, 0.64 mmol) with stirring
at room temperature in the dark. After completion of the
metalation, water (20 mL) was added, the phases were
separated and the organic layer was washed with 5% NaHCO3
solution (20 mL) and water (20 mL), dried (Na2SO4), and
filtered. The solvents were removed under reduced pressure.
Column chromatography over flash silica gel (CH2Cl2/hexanes,
5:1) gave 22 mg (53% yield) of a dark purple solid: IR (neat)
ν˜ 3049, 2924, 2853, 2154, 1598; 1H NMR δ 4.44 (s, 4H), 7.70-
1
1600; H NMR: δ 2.30 (s, 12H), 4.31 (s, 8H), 7.62-7.69 (m,
8H), 8.05-8.13 (m, 8H), 8.92 (s, 8H); LD-MS, obsd 1043.6 [M+
+ 15], 1028.8 [M+], 986.6 [M+ - COCH3], 954.7 [M+
-
SCOCH3], 911.3 [M+ - SCOCH3 - COCH3], 880.4 [M+ - 2
SCOCH3], 838.8 [M+ - 2 SCOCH3 - COCH3], 805.3 [M+ - 3
SCOCH3]; (C56H44N4O4S4Zn), FAB-MS obsd 1028.1560, calcd
exact mass 1028.1537 (C56H44N4O4S4Zn); λabs (toluene) 424,
550, 589 nm; λem (toluene) 597, 647 nm.
Coba lt(II)-5,10,15,20-Tetr a k is[3-(S-a cetylth iom eth yl)-
p h en yl]p or p h yr in (Co-30). A solution of 30 (14.2 mg, 14.7
µmol) in CHCl3 (20 mL) was treated with 5 mL of a methanolic
solution of Co(OAc)2‚4H2O (60.0 mg, 339 µmol) with stirring
at room temperature in the dark. After 5 h, additional Co-
(OAc)2‚4H2O (261.0 mg, 1.5 mmol) was added, and stirring was
continued. After 20 h, the metalation was completed and the
mixture was worked up in the general way. Column chroma-
tography over flash silica gel (CH2Cl2/hexanes, 5:1) gave the
title compound as an orange-purple solid in quantitative
yield: IR (neat) ν˜ 3037, 2955, 2924, 1693, 1601; LD-MS obsd
1038.4 [M+ + 15], 1023.4 [M+], 980.3 [M+ - COCH3], 948.3
[M+ - SCOCH3], 875.2 [M+ - 2 SCOCH3]; FAB-MS obsd
1023.1611, calcd exact mass 1023.1577 (C56H44N4O4S4Co); λabs
(toluene) 414, 529 nm.
Copper (II)-5,10,15,20-Tetr akis[3-(S-acetylth iom eth yl)-
p h en yl]p or p h yr in (Cu -30). A solution of 30 (14.0 mg, 14.5
µmol) in CHCl3 (20 mL) was treated with 5 mL of a methanolic
solution of Cu(OAc)2‚H2O (60.0 mg, 301 µmol) with stirring at
room temperature in the dark. After 2.5 h, the metalation was
completed, and the mixture was worked up in the general way.
Column chromatography over flash silica gel (CH2Cl2/hexanes,
5:1) gave 13.2 mg (89%) of the title compound as an orange-
purple solid: IR (neat) ν˜ 2922, 2851, 1691, 1600; LD-MS obsd
1043.3 [M+ + 15], 1028.3 [M+], 984.3 [M+ - COCH3], 953.2
[M+ - SCOCH3], 911.0 [M+ - SCOCH3 - COCH3], 878.1 [M+
- 2 SCOCH3]; FAB-MS obsd 1027.1570, calcd exact mass
1027.1541 (C56H44N4O4S4Cu), λabs (toluene) 419, 541 nm.
Silver (II)-5,10,15,20-Tetr a k is[3-(S-a cetylth iom eth yl)-
p h en yl]p or p h yr in (Ag-30). A solution of 30 (13.1 mg, 13.5
µmol) in CHCl3 (20 mL) was treated with 5 mL of a methanolic
solution of AgNO3 (50.0 mg, 294 µmol) with stirring at room
temperature in the dark. In 3 h a brown precipitation formed
and the solution turned green; upon adding triethylamine (0.5
mL) the mixture turned back to red. After an additional 2 h,
the metalation was completed and the mixture was worked
up in the general way. Column chromatography over flash
silica gel (CH2Cl2/hexanes, 4:1) gave 4.8 mg (33%) of the title
compound as a purple solid: IR (neat) ν˜ 2921, 2850, 1684; LD-
MS obsd 1086.5 [M+ + 15], 1071.5 [M+], 1028.4 [M+ - COCH3],
996.4 [M+ - SCOCH3], 954.3 [M+ - SCOCH3 - COCH3], 921.3
[M+ - 2 SCOCH3]; FAB-MS obsd 1071.1281, calcd exact mass
1071.1296 (C56H44N4O4S4Ag); λabs (toluene) 429, 543 nm.
3
7.90 (m, 11H), 8.16-8.28 (m, 8H), 8.93 (d, 4H, J ) 4.2 Hz),
8.98 (d, 4H); LD-MS obsd 819.6 [M+], 792.3 [M+ - CN], 761.5
[M+ - SCN], 703.3 [M+ - 2 SCN], 626.0 [M+ - 2 SCN - C6H5],
613.5 [M+ - 2 SCN - C7H7]; FAB-MS obsd 818.1275, calcd
exact mass 818.1265 (C48H30N6S2Zn); λabs (toluene) 424, 550,
590 nm; λem (toluene) 599, 647 nm.
5,15-Dim esityl-10-[4-iod op h en yl]-20-[4-(S-a cetylth io)-
p h en yl]p or p h yr in (32). Acetonitrile (500 mL) was degassed
with a stream of Ar for 10 min. Freshly ground NH4Cl (2.68
g, 50 mmol) was added, and the flask was placed in an ice-
bath and cooled under Ar. Samples of 5-mesityldipyrromethane
(1320 mg, 5.0 mmol), 4-iodobenzaldehyde (575 mg, 2.5 mmol),
and aldehyde 8 (450 mg, 2.5 mmol) were added, followed by
BF3‚OEt2 (0.63 mL, 0.5 mmol), and the mixture was stirred
at 0 °C under Ar. After 6 h, DDQ (1.70 g, 7.5 mmol) was added.
The ice bath was removed, and the mixture was stirred at room
temperature overnight. Removal of the solvents gave a black
solid that was filtered through a pad of silica and eluted with
toluene. Next, the mixture of porphyrins was chromatographed
on a silica column (toluene/hexanes 1:1, then toluene). The title
porphyrin comprised the second purple band, affording 109
mg (4.9%): 1H NMR δ -2.65 (s, 2H), 1.84 (s, 12H), 2.61 (s,
3H), 2.64 (s, 6H), 7.29 (s, 4H), 7.81, 8.08 (AA′BB′, 4H), 7.96,
8.27 (AA′BB′, 4H), 8.7-8.9 (m, 8H); LD-MS obsd 902.3, 917.4
[M+ + 15]; 860.1 [M+ - CH3CO]; 775.7 [M+ - I]; 734.5 [M+
-
CH3CO - I], FAB-MS obsd 898.2186, calcd exact mass
898.2202 (C52H43IN4OS); λabs (CH2Cl2) 419, 515, 549, 590, 646
nm.
10,20-Bis[3-(S-a cet ylt h iom et h yl)p h en yl]-5,15-b is-(3-
iod op h en yl)p or p h yr in (33). A mixture of aldehyde 12 (1.943
g, 10.0 mmol), 5-(3-iodophenyl)dipyrromethane (3.483 mg, 10.0
mmol), and NH4Cl (5.349 g, 100.0 mmol) in acetonitrile (1 L)
was purged with argon for 30 min and stirred in an ice bath
in the dark. Then BF3‚OEt2 (127 µL, 1.0 mmol) was added.
Soon the reaction mixture turned yellow and later dark red.
After 4.5 h, DDQ (3.406 g, 15.0 mmol) was added, and the ice-
bath was removed. After an additional hour, the reaction was
filtered through a pad of alumina and eluted with CH2Cl2. The
solvents were removed under reduced pressure, and the black
solid was dissolved in toluene (200 mL). DDQ (2.271 g, 10.0
mmol) was added, and the mixture was refluxed for 1 h. The

Porphyrins for Attachment to Electroactive Surfaces
J . Org. Chem., Vol. 64, No. 23, 1999 8647
mixture was cooled to room temperature, filtered through a
pad of alumina, and eluted with CH2Cl2. Purification by
column chromatography (silica, CH2Cl2/hexanes, 2:1) afforded
two fractions of dark brown purple solids, I, 112 mg of 10,20-
bis[3-(S-acetylthiomethyl)phenyl]-5,15-bis(3-iodophenyl)por-
phyrin (2% yield); II, 153 mg of the title compound (3% yield):
IR (neat) ν˜ 3316, 2923, 2852, 1691, 1583, 1554; 1H NMR δ
-2.87 (s, 2H), 2.41 (s, 6H), 4.42 (s, 4H), 7.45-7.53 (m, 2H),
7.66-7.76 (m, 4H), 8.07-8.22 (m, 8H), 8.59 (s, 2H), 8.82-8.89
(m, 8H); LD-MS obsd 1057.4 [M+ + 15], 1042.3 [M+], 999.2
[M+ - COCH3], 967.3 [M+ - SCOCH3], 916.2 [M+ - I], 892.0
[M+ - 2 COCH3], 874.1 [M+ - I - COCH3], 841.1 [M+ - I -
SCOCH3]; FAB-MS obsd 1042.0355, calcd exact mass 1042.0369
(C50H36I2N4O2S2); λabs (toluene) 421, 515, 550, 591, 647 nm.
10,20-Bis[3-(th iocya n a tom eth yl)p h en yl]-5,15-bis-(3-io-
d op h en yl)p or p h yr in (34). A mixture of 11 (1.056 g, 6.0
mmol), 5-(3-iodophenyl)dipyrromethane (2.075 mg, 6.0 mmol),
and NH4Cl (3.209 g, 60.0 mmol) in acetonitrile (600 mL) was
purged with argon for 30 min. Then BF3‚OEt2 (76 µL, 0.6
mmol) was added with stirring in the dark. Soon the mixture
turned yellow and later dark red. After 1 h, the mixture was
cooled in an ice bath for a further 5.5 h. Then DDQ (2.029 g,
8.9 mmol) was added, and stirring was continued for 30 min.
The mixture was warmed to room temperature, and the
solvents were removed under reduced pressure. Purification
by column chromatography with silica flash gel (first column
CH2Cl2/hexanes, 5:1; second column CHCl3; third column CH2-
Cl2/hexanes, 3:1-4:1) afforded 171 mg (6%) of the title
compound as a brown-purple solid: IR (neat) ν˜ 3306, 2921,
2846, 2152, 1584, 1560; 1H NMR δ -2.87 (s, 2H), 4.42 (s, 4H),
7.45-7.52 (m, 2H), 7.78-7.84 (m, 4H), 8.10-8.24 (m, 8H), 8.58
(s, 2H), 8.87 (s, 8H); LD-MS obsd 1010.7 [M+], 952.5 [M+
-
SCN], 993.3 [M+ - 2 SCN], 824.2 [M+ - SCN - I], 766.0 [M+
- 2 SCN - I], 688.7 [M+ - 2 SCN - I - Ph]; FAB-MS obsd
1008.0081, calcd exact mass 1008.0063 (C48H30I2N6S2); λabs
(toluene) 421, 515, 549, 591, 647 nm.
Ack n ow led gm en t. This work was supported by the
Office of Naval Research (N00014-99-1-0357). We thank
Professors David F. Bocian and Werner G. Kuhr (UC,
Riverside) for stimulating discussions as well as elec-
trochemical examination of the porphyrins on gold
electrodes. 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 Biotech-
nology Center and the NSF.
Su p p or tin g In for m a tion Ava ila ble: LD-MS spectra for
1
each porphyrin, H NMR spectra for all diamagnetic porphy-
rins, and 1H NMR and 13C NMR spectra for 9. This material
is available free of charge via the Internet at http://pubs.acs.org.
J O9911084