Synthesis of stannyl porphyrins and porphyrin dimers via stille coupling and their 119Sn NMR and fluorescence properties

Article abstract of DOI:10.1021/jo901535c

(Graph Presented) Free base stannyl porphyrins and free base porphyrin dimers have been successfully synthesized via copper-free Stille coupling in 21-67%yields. This approach provides an access to stannyl porphyrin synthons that were previously unavailable. Moreover, variation of the reaction conditions selectively provides access to either stannyl porphyrins or porphyrin dimers. Full ^119/117Sn NMR analysis was used for characterization of the stannyl porphyrins and detailed ¹¹⁹Sn-¹H-¹³C NMR analyses were carried out on a series of the starting tin reagents and the stannyl porphyrins. These investigations indicate that significant structural information can be gathered by use of commonly known NMR techniques. Photophysical properties of the novel porphyrins prepared including absorption, emission, and fluorescence lifetimes were investigated. The stannyl porphyrins emitted in the visible region, and in all cases large Stokes shifts were observed. The emission intensities of the stannyl porphyrins were 100-fold higher than those of the starting bromoporphyrins. Measured fluorescence lifetime (S₀→S₁) of the stannyl and dimeric porphyrins were in the 7.7-12 ns region.

Full text of DOI:10.1021/jo901535c

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Synthesis of Stannyl Porphyrins and Porphyrin Dimers via Stille Coupling
and Their 119Sn NMR and Fluorescence Properties
Natalia N. Sergeeva,† Angela Scala,†,‡ Muntaz A. Bakar,† Grainne O’Riordan,†
John O’Brien,† Giovanni Grassi,‡ and Mathias O. Senge*,†,§
†School of Chemistry, SFI Tetrapyrrole Laboratory, Trinity College Dublin, Dublin 2, Ireland,
‡Dipartimento di Chimica Organica e Biologica, Universitaꢀ, Vill.S.Agata, 98166 Messina, Italy, and
§Medicinal Chemistry, Institute of Molecular Medicine, Trinity Centre for Health Sciences,
Trinity College Dublin, St James’s Hospital, Dublin 8, Ireland
sengem@tcd.ie
Received July 16, 2009
Free base stannyl porphyrins and free base porphyrin dimers have been successfully synthesized via
copper-free Stille coupling in 21-67% yields. This approach provides an access to stannyl porphyrin
synthons that were previously unavailable. Moreover, variation of the reaction conditions selectively
provides access to either stannyl porphyrins or porphyrin dimers. Full 119/117Sn NMR analysis was
used for characterization of the stannyl porphyrins and detailed 119Sn-1H-13C NMR analyses were
carried out on a series of the starting tin reagents and the stannyl porphyrins. These investigations
indicate that significant structural information can be gathered by use of commonly known NMR
techniques. Photophysical properties of the novel porphyrins prepared including absorption,
emission, and fluorescence lifetimes were investigated. The stannyl porphyrins emitted in the visible
region, and in all cases large Stokes shifts were observed. The emission intensities of the stannyl
porphyrins were 100-fold higher than those of the starting bromoporphyrins. Measured fluorescence
lifetime (S0fS1) of the stannyl and dimeric porphyrins were in the 7.7-12 ns region.
Introduction
approach to the synthesis of novel materials, including tin
reagents and coupling products.2 Tin compounds can be
easily prepared starting from the corresponding bromides
and can then be used for C-C bond formation in the
presence of a catalyst.3 Moreover, the precursors are com-
mercially available, and the tin reagents are cheap to make
Metal-catalyzed coupling reactions are an attractive syn-
thetic tool for C-C bond formation and are used for
modification of various organic molecules, especially hetero-
cycles. Organotin compounds have found wide agricultural
and industrial applications.1 Recent studies have shown their
potential use as antifungal agents and their relatively high in
vitro antitumor activity. Stille coupling represents a simple
(2) (a) Milstein, D.; Stille, J. K. J. Am. Chem. Soc. 1978, 100, 3636–3638.
(b) Stille, J. K. Angew. Chem., Int. Ed. 1986, 25, 508–524. (c) Farina, V.; Roth,
G. P. In Advances in Metal-Organic Chemistry; Liebeskind, L. S., Ed.; JAI Press:
Greenwich, 1996; Vol. 5, p 1. (d) Farina, V.; Krishnamurthy, V.; Scott, W. J. Org.
React. 1997, 50, 1–652. (e) Mitchell, T. N. In Metal-Catalyzed Cross-Coupling
Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH: New York, 1998; Chapter
4. (f) Amatore, C.; Bahsoun, A. A.; Jutand, A.; Meyer, G.; Ntepe, A. N.; Ricard, L.
J. Am. Chem. Soc. 2003, 125, 4212–4222.
(1) (a) Organotin Chemistry, Davies, A. G., Ed.; VCH: Weinheim, 2004. (b)
Harrison, P. G. Chemistry of Tin; Chapman and Hall: New York, 1989. For
example, see: (c) Molloy, K. C. Adv. Organometal. Chem. 1991, 33, 171–234. (d)
Smith, A. C.; Rochow, E. G. J. Am. Chem. Soc. 1953, 75, 4105–4106.
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Published on Web 08/18/2009
DOI: 10.1021/jo901535c
r
2009 American Chemical Society

Sergeeva et al.
JOCArticle
compared to the related boronates widely utilized for Suzuki
coupling.4 In addition, tin has three NMR active nuclei (spin
1/2) with relatively high natural isotope abundance of 115Sn
(0.34%), 117Sn (7.68%), and 119Sn (8.59%); they give a
narrow signal over a wide NMR scale. Every type of tin
compound has its characteristic chemical shift range, and
these unique isotope properties can be used to study the
organotin compounds.5
SCHEME 1. Preparation of Mono- and Bis-tin Reagents 2 and 4
Porphyrins are naturally occurring pigments with a vari-
ety of applications in emerging areas of modern science:
optoelectronics and nanotechnology as sensors and storage
devices, as photocatalysts in green chemistry, and as photo-
dynamic therapy agents for cancer treatments in medicine, to
name a few.6-8 These and many other possible applications
require the development of new and more efficient methods
to modify the porphyrin core to yield macrocycles with novel
and improved physicochemical properties. The Stille reac-
tion has been used in porphyrin chemistry to introduce some
functional groups into the macrocycle.9 However, the litera-
ture only reports examples associated with C-C bond for-
mations starting from porphyrin bromides and the non-
porphyrin tin counterparts.
The synthesis of porphyrin dimers is often performed via
metal catalyzed reactions, e.g., Suzuki or Sonogashira cou-
pling.10 Only a few examples have been reported so far for the
synthesis of porphyrin dimers11 and functional polymers12
using a Stille approach. Moreover, to protect the porphyrin
core from undesired metalation by copper (from CuI often
used as a co-catalyst to increase the reaction rate2b,c or to
improve the solubility of the starting porphyrins) the synth-
esis generally requires prior porphyrin metalation, prefer-
ably with zinc, that later has to be removed from a coupling
product if necessary.
At present, there is no universal procedure for Stille
coupling reactions of porphyrins in terms of the reaction
conditions. Reported protocols employ a variety of solvents,
catalysts, and additives for the reactions.1cHere we present
results aimed at the development of a novel synthetic
approach for the synthesis of free base stannyl porphyrins
that can be used as coupling partners in Stille reactions.
Depending on the reaction conditions either stannyl or
dimeric porphyrins can be prepared and their physicochem-
ical properties investigated.
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Chem. 2007, 72, 5414–5417. (c) Horn, S.; Cundell, B.; Senge, M. O. Tetra-
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Results and Discussion
1. Synthesis of Stannyl Porphyrins and Porphyrin Dimers.
The mono- and bis-tin aromatic compounds 2 and 4 can
be conveniently synthesized on a large scale via organo-
lithium reactions starting from commercially available
mono- or dibromoarenes 1 and 3 and tri(n-butyl)tin chloride
(Scheme 1).
Generally, the reactions were carried out with an excess of
tBuLi (2.5 equiv for mono and 4 equiv for dibromides) at
-90 to -100 °C followed by addition of tri(n-butyl)tin
chloride at -50 °C. The reaction of 1-bromonaphthalene
gave the tin compound 2a in 94% yield. 9-Bromoanthracene
reacted in a similar manner to give the compound 2b in 75%
yield. However, attempts to synthesized the 9,10-bis-tin
anthracene starting from the corresponding dibromide re-
sulted in the formation of anthracene in 71%. Nevertheless,
the 1,4- and 1,3-bis-tin substituted compounds 4a and 4b
were prepared in 54% and 63% yield, respectively.
The porphyrin bromides 6-9 are thermally stable and
easily accessible molecules.4 They readily reacted with the
corresponding tin reagents 2, 4, and 5 forming the stannyl
porphyrins 10-16 in up to 60% yield. Moreover, the por-
phyrin free bases can be used under these reaction conditions
and no palladium insertion was observed during these
(11) (a) Linke-Schaetzel, M.; Anson, C. E.; Powell, A. K.; Buth, G.;
Palomares, E.; Durrant, J. D.; Balaban, T. S.; Lehn, J. M. Chem.;Eur. J.
2006, 12, 1931–1940. (b) Frampton, M. J.; Akdas, H.; Cowley, A. R.; Rogers,
J. E.; Slagle, J. E.; Fleitz, P. A.; Drobizhev, M.; Rebane, A.; Anderson, H. L.
Org. Lett. 2005, 7, 5365–5368.
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Bo, Z. Macromolecules 2008, 41, 6895–6902. (b) Bao, Z.; Chan, W. K.; Yu, L.
J. Am. Chem. Soc. 1995, 117, 12426–12435.
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SCHEME 2. Synthesis of Stannyl Porphyrins 10-16
SCHEME 3. Formation of Porphyrin 18
transformations for the whole series. The reactions exclu-
sively gave tin products, when 2 (for monosubstitution) or 4
(for bisproducts) equiv of the tin compounds was used. No
dimer formation was detected. Generally, these reactions
proceeded under formation of the desired products only, and
in the case of lower yields the starting materials were
recovered. Noteworthy, conditions involving CsF and CuI
in most cases resulted in complex mixtures with a very low
yield of the tin adducts. Importantly, purification of all tin
complexes has to be carried on aluminum oxide; use of silica
gel causes a rapid hydrolysis of the stannyl groups. 5-Bromo-
SCHEME 4. Conversion of 20 into 21
10,20-diphenylporphyrin
6 reacted with 1,3-bis(tri-n-
butylstannyl)benzene 4b and 5 to give compounds 11 and
10 (Scheme 2).
This approach can also be used for modification of the β-
positions of porphyrins; e.g., 2-bromo-5,10,15,20-tetraphe-
nylporphyrin 7 was converted into the tin compound 12 in
30% yield. 5-Bromo-10,15,20-triphenylporphyrin 8 and 5
provided compound 13 in 60% yield. Alternatively, this
method can also be used for the synthesis of the dinaphtha-
lene 14 (50%) via a reaction of 5,15-dibromo-10,20-diphe-
nylporphyrin 9 with 2a. The reaction of 9 with 1,4-bis(tri-n-
butylstannyl)benzene 4a provided an entry to the bisstannyl
porphyrin 15, however, only as a minor product. In this case,
the product 15 turned out to be thermosensitive, and a partial
hydrolysis of 15 led to compound 16 as the major product.
These adducts 15 and 16 were isolated in 28% and 53% yield,
respectively, with an overall yield of 81%.
Another example for the temperature sensitivity was
demonstrated by the reaction of 5,10-bis(4-bromophenyl)-
porphyrin 17 with 4a. Here, curiously, the product of a
double insertion 18 was isolated (Scheme 3). This reaction
was repeated several times under slightly different conditions
(90-110 °C); however, in all cases porphyrin 18 was formed
(62-67%).
5-(4-Bromophenyl)-2,4,7,8,12,13,17,18-octaethylporphyrin
19, prepared from 2,3,7,8,12,13,17,18-octaethylporphyrin and
4-bromophenyllithium,13 was used for the synthesis of com-
pound 20. Porphyrin 20 (77%), isolated and purified on
aluminum oxide, can also be hydrolyzed to 21 on silica gel
(Scheme 4).
This methodology can be further extended and used for
the synthesis of porphyrin dimers. This was achieved simply
by reducing the number of tin reagent equivalents to 0.5
equiv. The reaction mixtures were purified on silica to give
the compounds 22-24 in 21-50% yield (Scheme 5).
Porphyrin 19 was treated with 4a to give the dimer 22
(21%). The reaction of compound 6 with 4b resulted in the
formation of 24 in 28% yield. Because of the low solubility of
22 and 24 they could only be isolated in 21% and 28% yields,
respectively. Surprisingly, zinc porphyrins did not undergo
any transformations under these conditions. Neither dimer
nor stannyl porphyrin formation was observed. However, 5-
bromo-10,15,20-triphenylporphyrinatonickel reacted with
4a to give 23 in 50% yield.
2. 119Sn NMR Studies. According to the literature, tin
NMR studies were only carried out for a series of
(porphyrinato)tin(IV) complexes with axial ligation at tin-
(IV) to investigate their axial ligation properties.14 119Sn
(8.59%) with a nuclear spin of 1/2 gives a narrow signal
and is slightly more sensitive than 117Sn or 115Sn. Thus, in our
studies of the organotin compounds synthesized, main atten-
tion was given to 119Sn NMR studies; in some cases for a
better clarity 117Sn analysis was performed as well. The tin
reagents 2, 4, and 5 and the stannyl porphyrins 10-12, 15, 16,
18, and 20 exhibit resonances in the approximate range of δ
-35 to -65 ppm compared to the starting compound
(14) (a) Brotherhood, P. R.; Luck, I. J.; Crossley, M. J. Magn. Reson.
Chem. 2009, 47, 257–262. (b) Deeb, R. S.; Peyton, D. H. Biochemistry 1992,
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3733. (d) Hawley, J. C.; Bampos, N.; Sanders, J. K. M. Chem.;Eur. J. 2003,
9, 5211–5222.
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1107–1109. (b) Senge, M. O.; Kalisch, W. W.; Bischoff, I. Chem.;Eur. J.
2000, 6, 2721–2738. (c) Senge, M. O.; Bischoff, I. Eur. J. Org. Chem. 2001,
1735–1751.
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SCHEME 5. Porphyrin Dimers 22-24 Prepared via Stille Coupling
nBu3SnCl with a chemical shift of 144.9 ppm.15 The data for
the proton decoupled 119Sn NMR are summarized in Table 1
and illustrated in Figure 1.
TABLE 1. 119Sn NMR Data for the Tin Reagents 2, 4, and 5 and
Stannyl Porphyrins 10-12, 15, 16, 18, and 21
reagent
nBu3SnCl
119Sn
porphyrin
119Sn
The 119Sn NMR resonances of the organostannanes can
be correlated with the substitution pattern at the tin atom.
Thus, visible changes in the chemical shifts are observed in
the case of the double bond pattern of 5 compared to
aromatic substituents for the 2 and further for 4. In all cases,
resonances for the tin atoms of the porphyrins appear
slightly downfield from their tin reagents.
144.9
-39.7
-49.8
-43.9
-43.3
-63.3
10
12
15
16
18
20
-45.1
-41.0
-40.6
-40.5
-40.9
-43.7
2a
2b
4a
4b
5
Tin NMR remains the main tool for the structure deter-
minations of organotin compounds (e.g., substitution pat-
tern on tin, coordination number, influence of solvent)
depending on the Sn chemical shifts.5a,16 Despite 117/119Sn
NMR literature data available,5,16-19 there is still a lack of
information describing in detail proton-tin spin-spin inter-
actions for systems in which two pairs of H and Sn nuclei
(H1/Sn1 and H2/Sn2, respectively) correlate to one another
by a number of nJ(1H-117/119Sn) couplings. Bearing the same
spins, 117Sn and 119Sn are also present in almost equal
isotopic ratios that complicate the matter. Additionally, a
quite insignificant isotope shift and a small difference in
J values are observed for the 117Sn and 119Sn nuclei. Thus,
there are only a few papers discussing in details an influence
1
n
of tin NMR active nuclei on H NMR J(119Sn-1H) cou-
pling constants.18,19
FIGURE 1. Proton decoupled 119Sn NMR spectra for the porphyr-
ins 10, 12, 16, 18, and 20.
For the symmetric olefin 5 with the two sets of the satellite
signals centered with a major (H,H)-singlet (6.96 ppm), a
J value for (117/119Sn-1H) was determined to be ca. 106 Hz
(Figure 2A).
for (117Sn-1H) in accordance with those reported for nBu4Sn
in the literature.18 Figure 2C presents 1H (for simplicity, only
the resonance at 7.28 ppm (Hx) is shown) and proton
coupled 119Sn spectra. In this case a number of the spin-spin
coupling systems can be considered as three separate reso-
nances centered around 7.28 ppm20 of 1H NMR with a
difference of ∼2 Hz (usually invisible nJ(115Sn-1H) cou-
plings satellites are suppressed19c): (i) protons attached to
non-NMR-active tin (80%; (ii) protons attached to NMR
In nBu3Sn the (Sn,H) spin-spin couplings are calculated
to be around 54 Hz for (119Sn-1H) (Figure 2B) and ∼52 Hz
(15) For all 119Sn NMR, nBu4Sn was used as external reference com-
pounds.
(16) (a) Davies, A. G.; Harrison, P. G.; Kennedy, J. D.; Mitchell, T. N.;
Puddephatt, R. J.; McFarlane, W J. Chem. Soc. C 1969, 1136–1141. (b)
Geissler, H.; Radeglia, R.; Kriegsma, H. J. Organomet. Chem. 1968, 15, 349–
357.
(17) Wrackmeyer, B. In Advanced Applications of NMR to Organometal-
lic Chemistry; Gielen, M., Willem, R., Wrackmeyer, B., Eds.; Wiley: Chiche-
ster, 1996; Chapter 4, p 87.
(18) (a) Holmes, J. R.; Kaesz, H. D. J. Am. Chem. Soc. 1961, 83, 3903–
3904. (b) Burke, J. J.; Lauterbur, P. C. J. Am. Chem. Soc. 1961, 83, 326–331.
(19) (a) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 1985, 16, 73–186.
(b) Petrosyan, V. S. Prog. NMR Spectrosc. 1977, 11, 115–148. (c) Martins, J.
C.; Biesemans, M.; Willem, R. Prog. NMR Spectrosc. 2000, 36, 271–322.
1
active tin, i.e., H-119Sn; (iii) protons attached to NMR-
1
active tin, i.e., H-117Sn. In the first case, the signal is a
doublet with J ≈ 19.3 Hz for trans spin-spin (H,H) coupling.
(20) The exact position of the dominant resonance depends on concen-
tration of the sample and the deuterated solvent CDCl3or CD2Cl2 and the
temperature of the probe for 400 MHz (296 K) and 600 MHz (300 K).
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FIGURE 2. Proton coupled 119Sn (149.3 MHz) and 1H (400 MHz) NMR spectra in CD2Cl2: (A) 119Sn, 1H for 5; (B) 119Sn spectrum of the
external reference compound nBu3Sn; (C) 1H (for Hx) and 119Sn for the porphyrin 10.
FIGURE 3. 2D (H,H) TOCSY (600 MHz, CDCl3): (A) double bond Hx and Hy, aromatic and porphyrin Hs [7-9 ppm]; (B) 1H, 119Sn HSQC
spectra for 10.
In the other two cases, the signal is double doublet, which is a
(Sn,H) spin coupling of 71.5 Hz and a (H,H) spin coupling of
19.3 Hz (Figure 3A).21
The J value can also be estimated for the alkyl chains of the
-SnBu3 as 8.2 Hz for the (H,H) of Sn(CH2Pr)3 and ca. 50 Hz
for (117/119Sn-1H) spin-spin couplings. This is in accor-
dance with the data for Bu4Sn. Thus, the complexity of the
proton coupled 119Sn NMR spectrum of the compound 10
can be explained as a number of the spin-spin coupling
contributions originating from ddtr (Figure 2C).
A determination of the position and the values of nJ in 13
C
reveals two interesting features. The isotopic difference on
the order of ∼2 Hz in 1H NMR is also preserved in the 13
C
(21) These experimental results are in accordance with theories proposed
in the literature: “the schematic representation of the outcome of a 1H-119Sn
HMQC-NMR experiment performed on a fictitious organotin compound in
which two pairs of 1H and 119Sn nuclei, respectively, H1/Sn1 and H2/Sn2, are
mutually correlated to one another by a nJ(1H-119Sn) scalar coupling. It is
assumed that proton H1 appears as a 1H singlet and proton H2 displays a
nJ(1H-1H) doublet in the standard proton spectrum”.19c
NMR, and a strong upfield shift for -Sn(CH2Pr)3 (10.2 ppm,
the first 13C resonance signal) that was confirmed by DEPT
and HSQC (similar results were found for the compound 5 as
well) was found. It is known that J coupling constants
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TABLE 2. Photophysical Data of Compounds 10, 11, 15, 16, 18, 20, 22, 24, and Foscan in THFa
entry
absorption λmax/nm [log(ε)]
excitation λex/nm
emission at 298 K λem/nm (τf, ns)
Foscan
10
11
15
16
373 (5.0), 408 (5.4), 419 (5.4), 516 (4.7), 541 (4.7), 600 (4.6), 652 (4.9)
415 (5.6), 511 (4.8), 547 (4.7), 592 (4.7), 645 (4.6)
412 (5.4), 440 (5.1), 509 (4.6), 545 (4.5), 585 (4.5), 643 (4.6)
417 (5.4), 427 (5.4), 515 (4.7), 550 (4.7), 593 (4.6), 654 (4.6)
417 (5.3), 427 (5.4), 516 (4.7), 551 (4.6), 593 (4.5), 648 (4.5)
408 (5.9), 501 (4.9), 536 (7.8), 578 (4.8), 642 (4.7)
406 (5.5), 502 (4.8), 533 (4.7), 577 (4.7), 630 (4.6)
407 (5.5), 502 (4.8), 535 (4.6), 549 (4.6), 577 (4.6), 626 (4.5)
408 (5.8), 420 (5.7), 508 (4.9), 540(4.7), 584 (4.7), 640 (4.5)
373
415
412
417, 427
417, 427
408
405
406
655 (8.8)
653, 721 (7.7 ( 0.1)
643, 709 (10.1 ( 0.1)
652, 720 (10.6 ( 0.1)
652, 722 (9.5 ( 0.1)
637, 702 (10.3 ( 0.2)
629, 697 (10.7 ( 0.1)
630, 698 (12 ( 0.5)
643, 709 (10.9 ( 0.1)
18
20
22
24
409
aConcentration for all samples: 7.39 ꢀ 10-7 in THF. Laser: 370 nm (pulse <1 ns); 635 nm (<200 ps)
the lowest singlet excited state S1. Fluorescence lifetime
results are presented in Table 2.
We have compared the obtained results for the stannyl
porphyrins and the dimers with the lifetime of Foscan (2,3-
dihydro-5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin),
which is used as an approved drug in photodynamic ther-
apy.25 Photophysical properties were studied in THF at
the same concentrations. We found that the Q-bands in the
absorption spectra for the porphyrin synthesized and
the lifetimes of the novel compounds 22 and 24 are compar-
able to those of Foscan. Thus, their electronic absorption
properties and a longer fluorescence lifetime make these
novel porphyrin dimers promising test compounds for use
in PDT.
Conclusions
FIGURE 4. Emission spectra at the excitation energies of the Soret
bands for the porphyrins 9-11, 15, 16, 18, and 20.
We have shown that the novel stannyl porphyrins 10-13,
15, 16, 18, and 20 can be easily prepared and characterized
using the Stille coupling reaction in 21-67% yields. The
compounds are stable and can be stored in solid form for
several months. However, these materials are readily hydro-
lyzed on silica gel and can only be purified on aluminum
oxide or via recrystallization. These porphyrins can be used
further as building blocks in coupling reactions and thus
offer significant synthetic potential. In addition, this ap-
proach can also be applied for the synthesis of dimeric
porphyrins simply by reducing the equivalents of tin reagent.
As an illustration, dimers 22-24 were prepared in 21-50%
yields. Attempts to use conditions employing CuI/CsF for
the synthesis of these compounds led to complex mixtures of
the monomeric porphyrins and polymerization products.
We found that 119Sn NMR can easily be used for analysis
and characterization of the stannyl porphyrins. It gives a
narrow signal and can be recorded within a short period of
time. However, tin NMR active nuclei complicate 1H spec-
tra. A complex analysis including various NMR techniques
as well as a series of compounds with increasing spin-spin
complexity modes is necessary to reveal the mystery of the tin
influence. These investigations indicate that structural in-
formation can be gathered by a use of standard NMR
methods.
for directly bonded (Sn,C) are very large; the values of the J
1
(
117/119Sn-13C) are ca. 336 Hz for the J, ∼53 Hz for the
2J, and ∼21 Hz for the 3J, respectively.
3. Photophysical Studies of the Stannyl Porphyrins and
Porphyrin Dimers. Emission and absorption spectra, and the
fluorescence lifetime characteristics for the series of the
stannyl compounds prepared were recorded. All stannyl
porphyrins exhibited a large bathochromic shift of the last
Q-bands ∼650 nm in CH2Cl2 compared to ∼635 nm in THF.
However, due to their relative low solubility and in some
cases unwanted protonation (e.g., dication formation),
the spectra for these compounds were recorded in THF.
The stannyl compounds showed a much higher emission
intensity (90- to 110-fold) compared to the corresponding
bromides (as an example, the bromoporphyrin 9 is shown in
Figure 4).22
The porphyrins were excited at the energies of the Soret
bands, resulting in a deviation of the mirror image rules of
the emission spectra.23 Such exceptions of the mirror rules
are often associated with the different geometry of the
excited state compared to the ground states.23,24 The stannyl
porphyrins emitted in the UV-vis region, and in all cases
large Stokes shifts were observed (Table 2). Fluorescence
lifetime measurements were carried out in THF and excita-
tion of the porphyrins was performed by 635 nm laser with
pulse rate of <200 ps. The laser (635 nm) targeted the lower-
energy Q-band in absorption spectra, which originates from
Photophysical analyses were carried on for the series of the
stannyl porphyrins and dimers. Emission spectra for the
stannyl porphyrins were recorded in THF and showed an
increased intensity for the latter compared to the starting
(22) The intensity comparison of the tin bromides and corresponding
bromides were calculated as the integral function under the intensity curves.
(23) Lakowicz, J. R. Principles of Fluorescence Spectroscopy; Kluwer
Academic-Plenum Publishers: New York, 1999.
(25) (a) Kessel, D.; Dougherty, T. J. Rev. Contemp. Pharmacother. 1999,
€
10, 19–24. (b) Wiehe, A.; Simonenko, E. J.; Senge, M. O.; Roder, B. J.
Porphyrins Phthalocyanines 2001, 5, 758–761. (c) Wiehe, A.; Shaker, Y. M.;
Brandt, J. C.; Mebs, S.; Senge, M. O. Tetrahedron 2005, 61, 5535–5564.
(24) Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31, 1–13.
J. Org. Chem. Vol. 74, No. 18, 2009 7145

Sergeeva et al.
JOCArticle
bromides. The fluorescence lifetimes were measured for the
stannyl and dimeric porphyrins and compared with com-
monly used PDT drug Foscan.
Hz, 2H), 10.25 (s, 1H); 13C NMR (100.6 MHz, CDCl3) δ 9.9,
13.8, 27.4, 29.2, 104.7, 119.6, 121.4, 126.0, 126.8, 127.7, 130.6,
131.4, 134.2, 134.7, 135.7, 139.8, 141.8, 141.9, 142.6, 146.4;
UV-vis (THF) λmax (log ε) 412 (5.4), 440 (5.1), 509 (4.6), 545
(4.5), 585 (4.5), 643 (4.6) nm; TOF MS ESþ (C50H52N4Sn)
calcd for [M þ H] 829.3292, found 829.3292.
Experimental Section
All solvents were distilled prior to use. All reagents were
purchased from Sigma-Aldrich and were used without any
further purification. trans-1,2-Bis(tri-n-butylstannyl)ethylene 5
was purchased from TCI Europe. Bromoporphyrins 6-9, 17,
and 19 were synthesized according to the procedures previously
reported.7a,10c General experimental and analytical techniques
used were as described earlier.10d All photophysical measure-
ments were performed in THF at concentration for all samples:
7.39 ꢀ 10-7 M. All fluorescence spectra were recorded on
Perkin-Elmer Precisely LS55 spectrometer. Lifetime measure-
ments were carried out on Fluorolog Horiba Jobin Yvon
spectrometer using a laser beam: 370 nm (pulse <1 ns) and
635 nm (<200 ps). For the spectroscopic analyses statistical
measurements were carried out for each compound reported
(five times at the same concentrations) and average data were
collected and used.
General Procedure for the Synthesis of Mono- and Bis-tin
Reagents 2 and 4. To a solution of bromide 1 or 3 (8 mmol) in
anhydrous THF (35-50 mL) was added 11.8 mL (for mono-
bromide 1) or 18.8 mL (for dibromide 3) of tBuLi (1.7 M in
pentane) dropwise (40 min to 1 h) at -90 to -100 °C. A white or
yellow precipitation was observed. The mixture was stirred for 1
h, and tri(n-butyl)tin chloride (12 mmol for monobromide 1 and
27 mmol for dibromide 3) was added at -50 °C and stirred at the
same temperature for 30 min, resulting in a clear solution. The
cold bath was removed, and stirring was continued for 8-12 h.
The reaction mixture was quenched with NH4Cl (satd), ex-
tracted with ether (3 ꢀ 50 mL), and dried over Na2SO4. The
volatiles were removed, and n-hexane (50 mL) was added. The
solution was quickly passed through a silica plug and eluted with
n-hexane to give colorless or light yellow oils in 54-94% yield
(all tin compounds 2 and 4 have a high Rf (0.9-1)). Alterna-
tively, they can be purified by distillation.
2-[4-(Tri-n-butylstannyl)phenyl]-5,10,15,20-tetraphenylpor-
phyrin 12. Amorphous solid (35.3 mg, 30%); Rf 0.5 (CH2Cl2/
1
hexane, 2:3, v/v); H NMR (400 MHz, CDCl3) δ -2.60 (br,
2H), 1.02 (tr, J = 7.0 Hz, 9H), 1.14 (m, 6H), 1.46 (m, 6H), 1.66
(m, 6H), 7.28 (m, 5H), 7.56 (m, 1H), 7.77 (m, 10H), 7.93 (m,
2H), 8.25 (m, 6H), 8.79 (m, 7H); 13C NMR (100.6 MHz,
CDCl3) δ 9.6, 13.8, 27.6, 29.2, 119.7, 119.9, 120.4, 121.4,
126.0, 126.6, 126.7, 126.8, 127.4, 127.6, 127.7, 128.8, 129.8,
130.9, 132.5, 134.5, 134.6, 134.7, 135.5, 135.9, 139.0, 140.5,
141.9, 142.4, 142.6; UV-vis (CH2Cl2) λmax (log ε) 421 (5.3),
517 (4.2), 551 (4.0), 595 (3.9), 656 (3.9) nm; HRMS (C62
60N4Sn) calcd for [M þ H] 981.3918, found 981.4046.
(E)-5-[2-(Tri-n-butylstannyl)vinyl]-10,15,20-triphenylporphyr-
-
H
in 13. Purple solid (61.5 mg, 60%); Rf 0.5 (ethyl acetate/hexane,
1:7, v/v); 1H NMR (400 MHz, CDCl3) δ -2.65 (br, 2H), 1.09 (tr,
J = 7.3 Hz, 9H), 1.39 (m, 6H), 1.61 (m, 6H), 1.92 (m, 6H), 7.34
(d, J = 19.6 Hz, 1H), 7.83 (m, 9H), 8.27 (m, 6H), 8.88 (br, 4H),
8.96 (m, 2H), 9.54 (m, 3H); 13C NMR (100.6 MHz, CDCl3) δ
10.0, 13.5, 27.4, 29.4, 119.8, 120.0, 120.5, 126.55, 126.6, 127.5,
127.6, 130.9 (br), 134.4, 141.9, 142.1, 146.2, 149.1; UV-vis
(CH2Cl2) λmax (log ε) 422 (5.2), 520 (3.8), 557 (3.6), 595 (3.3),
656 (3.4) nm; HRMS (C52H54N4Sn) calcd for [M þ H] 855.3449,
found 855.3415.
5,15-Di(1-naphthalenyl)-10,20-diphenylporphyrin 14. Purple
solid (50.1 mg, 37%); mp >300 °C; Rf 0.4 (CH2Cl2/hexane,
2:3, v/v); 1H NMR (400 MHz, CDCl3) δ -2.48 (s, 2H), 7.15 (m,
4H), 7.52 (m, 2H), 7.74 (m, 6H), 7.90 (m, 2H), 8.20 (m, 6H), 8.32
(m, 4H), 8.61 (d, J = 3.9 Hz, 4H), 8.77 (d, J = 3.9 Hz, 4H); 13
C
NMR (100.6 MHz, CDCl3) δ117.2, 119.7, 123.8, 125.2, 125.8,
126.2, 127.2, 127.4, 128.2, 130.7 (br), 132.3 (m), 134.0, 136.4,
138.9, 141.5; UV-vis (THF) λmax (log ε) 419 (6.0), 514 (5.0), 547
(4.8), 590 (4.8) nm; TOF MS ESþ (C70H46N8) calcd for [M þ H]
715.2862, found 715.2862.
General Procedure for the Synthesis of the Stannyl Porphyrins
10-16, 18, and 20. A heterogeneous solution of a bromopor-
phyrin 6-9 (0.12 mmol), Pd(PPh3)4 (46.2 mg, 0.03 mmol) and
tin reagent 2 or 4 (0.24 mmol for monobromides and 0.48 mmol
for dibromides) in toluene (20 mL) was heated under argon at
90-110 °C for 24-72 h (TLC control). The reaction mixture
was filtered through a plug of aluminum oxide and washed with
ethyl acetate. After removal of the solvents under reduced
pressure the residue was chromotographed on aluminum oxide
or recrystallized from CH2Cl2/MeOH to give 10-16 in 21-60%
yields.
5,15-Bis[4-(tri-n-butylstannyl)phenyl]-10,20-diphenylporphyr-
in 15. Violet solid (40.1 mg, 28%); mp >300 °C; Rf 0.7 (CH2Cl2/
hexane, 2:3, v/v); 1H NMR (400 MHz, CDCl3) δ -2.75 (br, 2H),
1.03 (tr, J = 7.3 Hz, 18H), 1.30 (m, 12H), 1.50 (m, 12H), 1.76 (m,
12H), 7.82 (m, 10H), 8.23 (m, 8H), 8.89 (dþd, J = 4.7 Hz, 17.0
Hz, 8H); 13C NMR (100.6 MHz, CDCl3) δ 9.4, 13.4, 27.1, 28.9,
119.6, 119.9, 126.2, 126.3, 127.2, 130.8 (br), 133.8, 134.2, 134.3,
140.8, 141.2, 141.8; UV-vis (CH2Cl2) λmax (log ε) 420 (5.6), 517
(4.6), 552 (4.5), 593 (4.4), 648 (4.4) nm; TOF MS LDþ
(C68H82N4Sn2) calcd for [M þ H] 1195.4662, found 1195.4655.
5-[4-(Tri-n-butylstannyl)phenyl]-10,15,20-triphenylporphyrin
16. Violet solid (57.5 mg, 53%); mp >300 °C; Rf 0.6 (CH2Cl2/
(E)-5-[2-(Tri-n-butylstannyl)vinyl]-10,20-diphenylporphyrin
10. Violet solid (51.3 mg, 55%); mp 240 °C; Rf 0.6 (ethyl
acetate/hexane, 1:7, v/v); 1H NMR (400 MHz, CDCl3) δ
-2.87 (br, 2H), 1.06 (tr, J = 7.3 Hz, 9H), 1.34 (m, 6H), 1.58
(m, 6H), 1.88 (m, 6H), 7.25 (d, J = 19.0 Hz, 1H), 7.83 (m, 6H),
8.28 (m, 4H), 8.99 (dþd, J = 4.6 Hz, 4H), 9.32 (d, J = 4.6 Hz,
1
hexane, 3:2, v/v); H NMR (400 MHz, CDCl3) δ -2.59 (br,
2H), 1.05 (tr, J = 7.3 Hz, 9H), 1.35 (m, 6H), 1.53 (m, 6H), 1.80
(m, 6H), 7.87 (m, 9H), 8.24 (d, J = 7.8 Hz, 2H), 8.34 (m, 4H),
8.67 (m, 2H), 8.95 (br, 4H), 9.08 (br, 2H), 9.34 (br, 2H); 13C
NMR (100.6 MHz, CDCl3) δ 9.9, 13.9, 27.5, 29.3, 119.7, 120.3,
120.7, 126.8 (m), 127.8, 131.1 (br), 133.0, 134.3, 134.7 (m),
141.4, 141.7, 142.3; UV-vis (CH2Cl2) λmax (log ε) 421 (4.9), 514
(4.1), 549 (4.0), 592 (3.9), 647 (3.9) nm; HRMS (C56H56N4Sn)
calcd for [M þ H] 905.3605, found 905.3622.
2H), 9.53 (dþd, J = 4.6 Hz, 19.0 Hz, 3H), 10.17 (s, 1H); 13
C
NMR (100.6 MHz, CDCl3) δ 10.2, 13.9, 27.5, 29.5, 104.5,
119.6, 121.1, 126.8, 129.9, 130.7, 131.1, 131.4, 134.7, 141.9,
146.9, 148.7; UV-vis (THF) λmax (log ε) 415 (5.6), 513 (4.7),
549 (4.7), 591 (4.6) nm; HRMS (C46H50N4Sn) calcd for [M þ
H] 779.3136, found 779.3159.
5-[4-(Tri-n-butylstannyl)biphen-40-yl]-10-[4-(p-terphenyl)]por-
phyrin 18. Violet solid (79 mg, 67%); mp >300 °C; Rf 0.4
(CH2Cl2/hexane, 2:3, v/v); recrystallization (CH2Cl2/MeOH);
1H NMR (400 MHz, CDCl3) δ -3.27 (br, 2H), 0.98 (tr, J = 7.6
Hz, 9H), 1.19 (m, 6H), 1.44 (m, 6H), 1.66 (m, 6H), 7.51 (m, 3H),
7.77 (m, 4H), 7.90 (m, 4H), 8.03 (m, 6H), 8.36 (m, 4H), 9.08 (m,
2H), 9.17 (m, 2H), 9.42 (br, 2H), 9.51 (br, 2H), 10.30 (br, 2H);
13C NMR (100.6 MHz, CDCl3) δ 9.6, 13.6, 27.3, 29.0, 104.1,
5-[3-(Tri-n-butylstannyl)phenyl]-10,20-diphenylporphyrin 11.
Purple solid (25.0 mg, 21%); mp 198 °C; Rf 0.5 (CH2Cl2/
hexane, 2:3, v/v); 1H NMR (400 MHz, CDCl3) δ -2.95 (s,
2H), 0.91 (s, 9H), 1.18 (tr, J = 7.8 Hz, 6H), 1.37 (q, J = 7.8 Hz,
6H), 1.65 (m, 6H), 7.83 (m, 8H), 8.18 (d, J = 6.8 Hz, 1H), 8.29
(m, 5H), 8.94 (br, 4H), 9.06 (d, J = 4.9 Hz, 2H), 9.37 (d, J = 4.9
7146 J. Org. Chem. Vol. 74, No. 18, 2009

Sergeeva et al.
JOCArticle
125.1, 125.2, 126.7, 127.0, 127.25, 127.3, 122.75, 127.6, 127.62,
128.8, 128.9, 131.3, 135.0, 135.1, 137.0, 139.6, 139.8, 140.4, 140.5,
140.6, 140.7, 140.9, 141.1, 141.3; UV-vis (CH2Cl2) λmax (log ε)
410 (3.3), 504 (2.3), 537 (2.2), 578 (2.2), 634 (2.1) nm; HRMS
(C62H60N4Sn) calcd for [M þ H] 981.3918, found 981.3959.
(E)-5-[4-(1-Tri-n-butylstannylvinyl)phenyl]-2,3,7,8,12,13,17,18-
octaethylporphyrin 20. Violet amorphous solid (86 mg, 77%);
19.7, 19.8, 95.8, 97.0, 117.1, 128.6, 130.4, 130.5, 130.9, 134.1,
141.3, 142.0, 142.5, 143.1, 144.7, 146.0; UV-vis (CH2Cl2) λmax
(log ε) 407 (5.2), 505 (4.3), 540 (4.1), 573 (4.1), 624 (3.9) nm;
HRMS (C90H102N8) calcd for [M þ H] 1295.8300, found
1295.8304.
1,4-Bis[5-(10,15,20-triphenylporphyrinatonickel(II)yl)]benzene
23. Purple solid (76 mg, 50%); mp >300 °C; Rf 0.6 (CH2-
Cl2/hexane, 1:2, v/v); 1H NMR (600 MHz, CD2Cl2) δ 7.73 (m,
19H), 8.11 (m, 15H), 8.60 (d, J = 4.9 Hz, 4H), 8.86 (dd, J = 4.9
Hz, 8H); 13C NMR (150.9 MHz, CD2Cl2) δ 115.6, 119.8,
119.9, 126.6, 126.7, 126.8, 127.6, 127.7, 131.8, 132.1 (m), 133.5,
133.6 (m), 140.6, 140.7, 142.4, 142.7, 143.2, 146.7; UV-
vis (CH2Cl2) λmax (log ε) 413 (5.1), 443 (5.1), 535 (4.6) nm;
HRMS (C76H46N8Ni2) calcd for [Mþ] 1186.2567, found
1186.2552.
1,3-Bis[5-(10,20-diphenylporphyrinyl)]benzene 24. Purple so-
lid (17 mg, 28%); mp >300 °C; Rf 0.2 (CH2Cl2/hexane, 2:3, v/v);
1H NMR (400 MHz, CDCl3) δ -2.94 (br, 4H), 7.84 (m, 12H),
8.27 (m, 8H), 8.67 (m, 2H), 9.06 (dþd, J = 4.9 Hz, 8H), 9.37
(dþd, J = 3.9 Hz, 8H), 10.24 (s, 2H); 13C NMR (100.6 MHz,
CDCl3) δ 104.5, 119.3, 119.6, 124.3, 126.4, 127.3, 130.7, 130.9
(br), 133.3, 134.2 (m), 139.5, 140.4, 145.7 (br), 146.7 (br);
UV-vis (THF) λmax (log ε) 408 (5.8), 420 (5.7), 508 (4.9), 540
(4.7), 581 (4.7), 640 (4.5) nm; TOF MS ESþ (C70H46N8) calcd
for [M þ H] 999.3925 found 999.3924.
1
eluent (ethyl acetate/hexane, 1:10, v/v); H NMR (400 MHz,
CDCl3) δ -3.05 (br, 2H), 1.04 (tr, J = 7.3 Hz, 9H), 1.18 (m, 12H),
1.49 (m, 6H), 1.71 (m, 6H), 1.92 (m, 18H), 2.87 (m, 4H), 4.10 (m,
12H), 7.26 (m, 2H), 7.76 (d, J = 7.9 Hz, 2H), 8.20 (d, J = 7.9 Hz,
2H), 9.96 (s, 1H), 10.20 (s, 2H); 13C NMR (100.6 MHz, CDCl3) δ
9.8, 13.9, 18.1, 18.5, 18.55, 18.6, 19.8, 19.9, 20.9, 27.5, 29.3, 29.7,
95.3, 96.7, 118.8, 124.0, 124.2, 130.3, 133.6, 138.8, 141.0, 141.2,
141.9, 142.2, 142.6, 142.7, 142.8, 143.5, 144.1, 145.7, 146.1;
UV-vis (CH2Cl2) λmax (log ε) 406 (5.2), 506 (4.3), 537 (4.2),
570 (4.2), 622 (4.1) nm; HRMS (C56H78N4Sn) calcd for [M þ H]
927.5327, found 927.5303.
5-(4-Vinylphenyl)-2,3,7,8,12,13,17,18-octaethylporphyrin 21.
Violet solid; mp >219 °C; Rf 0.2 (CH2Cl2/hexane, 3:2, v/v);
1H NMR (600 MHz, CDCl3) δ -3.03 (br, 2H), 1.19 (tr, J = 7.6
Hz, 6H), 1.19 (m, 18H), 2.86 (m, 4H), 4.09 (m, 12H), 5.54 (d, J =
10.3 Hz, 1H), 6.12 (d, J = 17.6 Hz, 1H), 7.11 (m, 1H), 7.76 (d,
J = 7.3 Hz, 2H), 8.20 (d, J = 7.3 Hz, 2H), 9.96 (s, 1H), 10.20 (s,
2H); 13C NMR (150.9 MHz, CDCl3) δ 17.9, 18.2, 18.3, 18.4,
19.5, 19.6, 19.7, 20.7, 96.6, 114.1, 124.1, 133.5, 136.9, 137.5,
140.8, 141.8, 142.1, 142.5, 142.6, 143.3, 144.0, 145.6; UV-vis
(CH2Cl2) λmax (log ε) 407 (5.1), 506 (4.2), 538 (4.1), 572 (4.1), 622
(3.9) nm; HRMS (C44H52N4) calcd for [M þ H] 637.4265, found
637.4266.
Acknowledgment. This work was supported by grants
from Science Foundation Ireland (SFI Research Professor-
ship 04/RP1/B482) and the Health Research Board (HRB
Translational Research Award 2007 TRA/2007/11).
4,400-Bis[5-(2,3,7,8,12,13,17,18-octaethylporphyrinyl)]-p-ter-
phenyl 22. Violet solid (33 mg, 21%); mp >300 °C; Rf 0.3
(CH2Cl2/hexane, 3:2, v/v); 1H NMR (400 MHz, CDCl3) δ
-3.00 (br, 4H), 1.37 (m, 12H), 1.92 (m, 36H), 2.98 (m, 8H), 4.10
(m, 24H), 7.56 (m, 2H), 7.74 (m, 2H), 8.65 (m, 8H), 9.96 (s, 2H),
10.20 (s, 4H); 13C NMR (100.6 MHz, CDCl3) δ 18.2, 18.4, 18.5,
Supporting Information Available: Characterization data
including 1D and 2D NMR spectra of compounds 10-16, 18,
20-22, 24. This material is available free of charge via the
Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 74, No. 18, 2009 7147