An easy one-pot desilylation/copper-free Sonogashira cross-coupling reaction assisted by tetra-butylammonium fluoride (TBAF): Synthesis of highly π-conjugated porphyrins

Article abstract of DOI:10.1016/j.tet.2013.04.092

Sonogashira cross-coupling is a key reaction for the synthesis of highly conjugated oligomers. However, its application has well known drawbacks; it requires drastic inert atmosphere conditions, generates homocoupling by-product of the terminal alkyne and others. In this paper, we describe a new and easy procedure using PdCl₂(PPh₃)₂ as catalyst assisted by TBAF in a one-pot desilylation/copper-free Sonogashira reaction for the synthesis of highly conjugated porphyrin oligomers.

Full text of DOI:10.1016/j.tet.2013.04.092

Tetrahedron 69 (2013) 5098e5103
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
An easy one-pot desilylation/copper-free Sonogashira
cross-coupling reaction assisted by tetra-butylammonium
fluoride (TBAF): synthesis of highly
p-conjugated porphyrins
Ahmad Jiblaoui a, Christine Baudequin b, Vincent Chaleix a, Guillaume Ducourthial c,
c
b
a
,
a
*
ꢀ
ꢀ
Frederic Louradour , Yvan Ramondenc , Vincent Sol , Stephanie Leroy-Lhez
a
ꢀ
Universite de Limoges, Laboratoire de Chimie des Substances Naturelles, EA 1069, 123 Avenue Albert Thomas, 87060 Limoges, France
Universite de Rouen, IRCOF, UMR CNRS 6014 COBRA, 1 rue Tesniere, 76131 Mont Saint Aignan, France
Universite de Limoges, XLIM, UMR CNRS 6172, Departement Photonique, 123 Avenue Albert Thomas, 87060 Limoges, France
b
ꢀ
ꢁ
c
ꢀ
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
Sonogashira cross-coupling is a key reaction for the synthesis of highly conjugated oligomers. However,
its application has well known drawbacks; it requires drastic inert atmosphere conditions, generates
homocoupling by-product of the terminal alkyne and others. In this paper, we describe a new and easy
procedure using PdCl2(PPh3)2 as catalyst assisted by TBAF in a one-pot desilylation/copper-free Sono-
gashira reaction for the synthesis of highly conjugated porphyrin oligomers.
Received 28 February 2013
Received in revised form 16 April 2013
Accepted 18 April 2013
Available online 25 April 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
One-pot
Copper-free Sonogashira coupling
TBAF
Porphyrin
Two-photon absorption ‘TPA’
1. Introduction
TPA cross section,8 in this context the synthesis of new molecular
systems specially designed for this purpose appears desirable.
Over the past few years, the development of highly conjugated
porphyrin oligomers with a strong two-photon absorption (TPA)
attracted great attention in a wide range of applications such as
chlorophyll antenna mimics,1 nonlinear optics,2 organic light-
emitting diodes3 and photodynamic therapy (PDT).4 PDT is
a promising treatment, that is, used clinically to destroy some types
of cancers. It relies on the use of a photosensitive drug activated by
light to induce cytotoxicity; the photosensitizer (PS) is harmless in
the dark.5 Penetration depth of light into tissue is critical, especially
when it comes to reach deep tumours. Unfortunately, the most
common PS used in PDT requires visible radiation (600e700 nm)
while the therapeutic window is located in the near infrared region
(700e950 nm).6 Two-photon excitation represents an attractive
alternative, since it not only allows a deeper penetration of exci-
tation light but also leads to a reduction in photothermal damage
caused by light intensity.7 Clinical porphyrin-based PDT photo-
sensitisers, such as PhotofrinÒ, Verteporfin or FoscanÒ have a low
Conjugated porphyrin oligomers have been well studied in the
literature and showed to exhibit good to strong TPA.8e12 The key
reaction to synthesize most of these
p-conjugated cores seems to
be Sonogashira cross-coupling. However, its application on tetra-
pyrrolic macrocycles has well known drawbacks that restricted its
use: a) it requires drastic inert atmosphere conditions to protect
unstable Pd(0) and terminal ethynyl porphyrin. b) The reaction is
slow and exceeds 14 h at reflux. c) Applying Pd(II) catalyst, such as
Pd2(PPh3)2Cl2, PdCl2 requests the use of a reducer, such as CuI that
often generates homocoupling product of the terminal alkyne
(Glaser cross-coupling).13 Frequently, Lindsey et al. copper-free
Sonogashira conditions that are based on use of Pd(0) (Pd2(dba)3)
as catalyst and triphenylarsine (AsPh3) as ligand are used to avoid
undesired by-product.14 However, although these conditions re-
duce the formation of Glaser product, they include additional
caution in handling unstable Pd2(dba)3. Also, Senge et al. have
applied these conditions to synthesize new ethynyl-linked por-
phyrin dimers with moderate to good yields (25e68%).9
Recently, Mori et al. have reported that tetra-butylammonium
fluoride (TBAF) is a useful promoter for palladium-catalyzed cop-
per-free Sonogashira cross-coupling reaction.15 Then, Li et al. have
* Corresponding author. Tel.: þ33 (0) 5 55 74 90; fax: þ33 (0) 5 55 72 02; e-mail
address: vincent.sol@unilim.fr (V. Sol).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.04.092

A. Jiblaoui et al. / Tetrahedron 69 (2013) 5098e5103
5099
shown that this combined system works solvent-free on aryl chlo-
rides with moderate yields.16 However, both teams have worked on
small aryl species, such as ethenylphenyl and halogenophenyl. TBAF
has also been used for deprotection of silylated arylethynyl in one-
pot desilylation/Sonogashira coupling reaction,17 yet authors have
applied classical conditions by using copper as co-catalyst (Pd(II)/
CuI). To the best of our knowledge, no paper has described the use of
TBAF as palladium’s promoter in one-pot desilylation/copper-free
Sonogashira cross-coupling reaction.
The aim of this work is to describe a simple and new procedure
to synthesize highly
p-conjugated porphyrins by using a one-pot
desilylation/copper-free Sonogashira reaction assisted by TBAF,
which can be use as both a desilylate reagent and a base. There is no
more need to work in inert atmosphere conditions, reaction time is
reduced to 4e6 h at reflux and easy to handle Pd(II) has been used
without any copper need. Firstly, various factors have been in-
vestigated to find the best conditions to synthesize ethynyl-linked
porphyrin dimer. Secondly, these best conditions have been applied
in the synthesis of trimeric porphyrin, subsequently a study has
been presented to decrease the quantity of TBAF and consequently
the amount of solvent used in the reaction.
2. Results and discussion
The key parent molecule of most highly
p-conjugated porphy-
rins reported in the literature is silylated meso-ethynyl
porphyrin,8e12 herein, we chose to work on porphyrin 4. It was
obtained in two steps starting from porphyrin 1 with one free meso
position. Compound 1 was accomplished according to Lindsey’s
method18 by reaction between dipyrromethane, mesityldipyrro-
methane with 2 equiv of mesitaldehyde (Scheme 1).
The first step involved halogenation of the free meso position,
where bromination19 or iodination20 routes are widely reported
and in both cases a radical mechanism seems to be the most ap-
propriate. We chose the iodination way described by Dolphin
where iodine and phenyliodine(III)bis(trifluoroacetate) (I2/PIFA)
are respectively used as reagent and catalyst to iodinate free-base
porphyrin.20 On the other hand, Jin et al. have already shown in
bromination case that Zn-metallated porphyrin has given better
yield than the free-base, so we investigated iodination of both
metallated and free-base porphyrins (Scheme 1).19 In the instance
of free-base porphyrin we have obtained product 2 with an overall
yield of iodination and Zn-metallation of 36%. In contrast, applying
Dolphin’s iodination on already Zn-metallated porphyrin has given
surprisingly meso,meso-linked porphyrin dimer 3 with a good yield
without appearance of the desired product on TLC. This simple
procedure to synthesize meso,meso-linked porphyrin dimers seems
to have been previously described by Chen et al.21 using PIFA as
catalyst, yet Senge’s oxidation or Osuka’s oxidation methods are
more commonly reported.22
Scheme 1. Reagents and conditions (i) BF3OEt2, CHCl3, 30 min, then DDQ, 1 h, rt, 17%;
(ii) (CF3CO2)2IC6H5, I2, CHCl3, 1 h, rt, then, Zn(OAc)2, CHCl3/MeOH, 3 h, reflux, 36%; (iii)
Zn(OAc)2, CHCl3/MeOH, 3 h, reflux, then, (CF3CO2)2IC6H5, I2, CHCl3, 5 min, rt, 75%; (iv)
PdCl2(PPh3)2, CuI, TMSA, toluene/TEA, 4 h, reflux, 75%.
authors,10e12 we have not succeeded to isolate compound 5 by silica
gel chromatography (substantial decomposition was observed),
and we have used this product immediately without purification.
Secondly, Li et al. conditions (Table 1, entry 2) have been ap-
plied,16 involving Pd2(PPh3)2Cl2 as catalyst assisted by an excess of
TBAF solution (100 equiv, 1 M in THF, 5% water) used too to dissolve
reagents, starting from porphyrins 2 and 4. Desired dimer 6 was
obtained with a low yield (28%), while by-product 7 was formed
with a significant yield (12%) resulting from Glaser reaction of
terminal ethynyl porphyrin even in copper-free conditions. This
kind of homocoupling was also observed during Hiyama cross-
coupling reaction.23 In order to minimize the formation of by-
product 7, AsPh3 was added to the reaction and used as a palla-
dium ligand. Starting from porphyrins 2 and 4 at reflux (60 ꢀC)
(Table 1, entry 3) the reaction time (4 h) and by-product 7 (6%) were
significantly declined and desired product 6 was obtained with
a good yield (57%).
Our explanation is that without ligand (AsPh3) deprotected silyl
reagent 5 has been employed in order to reduce Pd(II) to Pd(0)
(Scheme 2) and consequently formed the homocoupling product 7.
In fact, it has been shown that Pd(0) species could be readily gen-
erated from the reaction of Pd2(PPh3)2Cl2 with solvents, substrates,
additives, and/or ligands, etc.24
Finally, these results have been compared to those mentioned in
the literature, in Table 1 we have chosen the zinc(II) complex of 1,2-
bis(5,10,15-triphenylporphyrin-20-yl)ethyne dimer described by
Senge et al. (Table 1, entry 4).9 It is obvious that the new procedure
(entry 3) is better and easier to use than classical Sonogashira
The second step was Sonogashira cross-coupling using trime-
thylsilylacetylene (TMSA) under classical conditions (Pd(II)/CuI) to
attach silyl-protected acetylene on porphyrin 2; porphyrin 4 was
obtained with a good yield of 75%.
Several procedures have been then investigated (Table 1) to find
the most appropriate method to synthesize ethynyl-linked por-
phyrin dimer 6 (Scheme 3). Firstly, classical Sonogashira coupling
conditions have been applied (Table 1, entry 1) using Pd(II)
(Pd2(PPh3)2Cl2) as catalyst and copper(I) iodide (CuI) as palladium’s
reductant and co-catalyst, in anhydrous and degassed toluene/
triethylamine (TEA) at reflux for 18 h. Starting from iodo-porphyrin
2 and terminal ethynyl porphyrin 5, these conditions have given
product 6 with a low yield (26%). Reagent 5 has been obtained by
desilylation of porphyrin 4 using 1.1 equiv of TBAF (1 M in THF, 5%
water) in THF. It was used directly, after a simple pretreatment with
excess CaCl2 to give compound 6. Indeed, according to various

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A. Jiblaoui et al. / Tetrahedron 69 (2013) 5098e5103
Table 1
Conditions of synthetic routes for Sonogashira couplinga
Entry
Path
Catalyst
Step
Solvent
T (ꢀC)
Reaction time (h)
Yield (%)
6
7
1
2
3
A
B
B
A
PdCl2(PPh3)2/CuI
PdCl2(PPh3)2
PdCl2(PPh3)2/AsPh3
Pd2(dba)3/AsPh3
2
1
1
2
Toluene/TEA
Reflux
Reflux
Reflux
Reflux
18
5
4
26
28
57
47
17
12
6
TBAF (1 M in THF, 5% water)
TBAF (1 M in THF, 5% water)
THF/TEA
4b (literature)
16
Not reported
a
Path A summarizes the classical conditions or copper-free Lindsey conditions. Path B summarizes the new procedure.
b
Copper-free Lindsey conditions used by Senge et al. for the synthesis of Zinc(II) complex of 1,2-bis(5,10,15-triphenylporphyrin-20-yl)ethyne dimer.9
Scheme 2. Formation of homocoupling product by reducing Pd(II) to catalytically active Pd(0) through terminal alkyne.
Scheme 3. Synthetic routes for Sonogashira coupling. Path A illustrates the classical conditions or copper-free Lindsey conditions (i) TBAF, 15 min, rt, then excess CaCl2, 15 min, rt, (ii)
PdCl2(PPh3)2/CuI, toluene/TEA, 18 h, reflux, (iii) Pd2(dba3)2/Ph3As, THF/TEA, 16 h, reflux. Path B illustrates the new procedure, (iv) PdCl2(PPh3)2/Ph3As, TBAF (1 M in THF, 5% water),
4 h, reflux.
reaction conditions (entry 1) or Lindsey copper-free conditions
(entry 4): 1) It is a one-pot instead of 2-step reaction. 2) It is no
longer necessary to work in inert atmosphere neither to use
degassed anhydrous solvents. 3) Easy to handle Pd2Cl2(PPh3)2 has
been employed without copper(I), which often generate homo-
coupling product. 4) Yield is close or higher than the best ones
described in the literature. 5) Reaction time significantly decreased
to 4 h, compared to 16 h. It is worth noting that we tried to reduce
even more the reaction time by using microwave irradiation but all
assays have furthered Glaser reaction.
Once the best conditions have been obtained, they have been
committed in the synthesis of trimer 8 (Scheme 4). Starting from
tris(4-iodophenyl)amine and porphyrin 4, using PdCl2(PPh3)2 as
catalyst assisted by an excess of TBAF (100 equiv, 1 M in THF, 5%
water) at reflux for 6 h (Table 2, entry 1). However, in order to justify
TBAF excess, we decided to investigate the effect of the amount of
solution employed in the reaction. This large excess of TBAF is jus-
tified by experimental data collected in Table 2. The use of smaller
amounts of TBAF solution (1 M in THF, 5% water) resulted in drastic
yield reductions, particularly when the minimum necessary of
3.6 equiv was tested (entry 3); this amount corresponds to the total
quantity of silylporphyrin 4 used in the reaction. So, excess TBAF
(1 M in THF, 5% water) solution allowed solubilization of the
reagents, 100 equiv lead to completely dissolving of all species, but
the increase of this amount of TBAF did not give a better yield.
Moreover, TBAF permits also to activate the palladium catalyst. In-
deed, even if the mechanism of the Sonogashira reaction assisted by
TBAF is not well known,25 some works report that this ammonium
fluoride salt acts as a base and also as a stabilizer of possible active
palladium nanoparticles generated in the decomposition of the
catalyst.26,27
Photophysical analyses were carried out on all synthesized
porphyrins. Scheme 5 shows the UVevis absorption spectra of
oligomers 3, 6, 7, 8 and corresponding monomer 4 in CHCl3 at
298 K, selected data are reported in Table 3. As expected porphyrin
dimers 3, 6 and 7 show splitting of the Soret band, which is due to
the excitonic coupling between the two parallel strong dipole
transitions of each porphyrin ring.9,28 Absence of excitonic coupling
between porphyrin units in compound 8 explains why, in this in-
stance, the electronic spectrum does not display this splitting.28
Moreover, dimers 6, 7 and trimer 8 exhibit bathochromic shifts of
Q-bands compared to monomer 4; it can be explained by a decrease
of the energy gap between HOMO and LUMO as a result of the
extension of the p
-conjugated system.29
Emission measurements were carried out in order to study the
electronic interactions between the porphyrin subunits in the

A. Jiblaoui et al. / Tetrahedron 69 (2013) 5098e5103
5101
Scheme 4. Synthesis of trimer 8, (i) PdCl2(PPh3)2/Ph3As, TBAF (1 M in THF, 5% water), reflux, 6 h.
Table 2
Table 3
Effects of TBAF amount on reaction yield
Photophysical parameters of porphyrins: monomer 4 and oligomers 3, 6, 7 and 8 in
CHCl3
a
Entry
TBAF (1 M in THF, 5% water)
Yield (%)
Compound
labs [nm]
ε [10ꢁ3 Mꢁ1 cmꢁ1
]
lem [nm]
F
1
2
3
100 equiv
10 equiv
3.6 equiv
81
45
24
3
418
456
560
431
563
603
414
482
563
680
451
483
568
623
674
434
567
624
187
203
50
514
18
569
614
0.02
4
6
609
660
0.03
12
122
277
19
638
676
0.006
46
7
270
199
24
42
54
389
36
67
627
676
0.007
0.05
8
635
a
labs¼absorption peak wavelength; ε¼molar extinction coefficient;
lem¼emission peaks (lexc¼450 nm); ¼emission quantum yield versus cresyl violet
F
in methanol (0.5429).
Scheme 5. Normalized absorption spectra of monomer 4 and oligomers 3, 6, 7 and 8 in
CHCl3 at 298 K (c<10ꢁ6 M).
excited state. Fluorescence spectra of oligomers 3, 6, 7, 8 and cor-
responding monomer 4 in CHCl3 are presented in Scheme 6 and the
corresponding photophysical parameters are summarized in Table
3. Dimer 3 shows a broadening of the emission bands, but no
bathochromic shift was observed, compared, to monomer 4 as
there is no conjugation between the porphyrin units. On the other
hand, the emission maxima of oligomers 6, 7 and 8 have been red
shifted compared to monomer 4. Indeed, the enlargement of the p-
conjugation system in these three oligomers has significant in-
fluences on the emission characteristics. All these electronic ab-
sorption and emission spectra are the hallmarks of electronic
interactions between porphyrin units in oligomers 6, 7 and 8.
Scheme 6. Normalized emission spectra of monomer 4 and oligomers 3, 6, 7 and 8 in
CHCl3 at 298 K (c<10ꢁ6 M, lexc¼450 nm).

5102
A. Jiblaoui et al. / Tetrahedron 69 (2013) 5098e5103
3. Conclusion
(48 mg, 36%).1H NMR (CDCl3, 400 MHz)
d
ppm 9.70 (d, 2H, J¼4.6 Hz),
8.77 (d, 2H, J¼4.6 Hz), 8.66 (m, 4H), 7.27 (s, 4H), 7.25 (s, 2H), 2.63 (s,
A simple one-pot desilylation/copper-free Sonogashira cross-
6H), 2.60 (s, 3H),1.83 (s, 6H),1.81 (s,12H); 13C NMR (CDCl3, 400 MHz)
coupling reaction has been reported for the synthesis of highly
p-
d ppm 151.8, 150.7, 150.2, 139.2, 139.1, 138.7, 137.9, 137.5, 132.1, 131.5,
conjugated porphyrin oligomers. Pd2Cl2(PPh3)2 assisted by TBAF
has been used, yet results showed the importance of using Ph3As as
ligand in order to decrease the formation of Glaser by-product.
131.4, 127.6, 119.6, 79.8, 21.7, 21.6, 21.4; UVevis (CHCl3) lmax nm (ε,
L mmolꢁ1 cmꢁ1) 425 (477), 554 (21), 593 (4); MS(MALDI-TOF)
calcd for C47H41IN4Zn 852.166, [MþH]þ found: 853.203.
4. Experimental section
4.1. General
4.1.3. Zinc (II) dimer 3. 5,10,15-Trimesitylporphyrin 1 (50 mg,
0.075 mmol) and zinc(II) acetate (5 equiv, 83 mg, 0.37 mmol) were
dissolved in a solution of CHCl3/MeOH (10 mL/2 mL). The mixture
was stirred for 3 h at reflux and solvent was evaporated. The crude
was washed twice with water (100 mL) and dried over MgSO4.
Next, zinceporphyrin (53 mg, 0.073 mmol), iodine (0.6 equiv,
11 mg, 0.043 mmol) and bis-(trifluoroacetoxy)iodobenzene
(0.7 equiv, 22 mg, 0.051 mmol) were dissolved in CHCl3 (11 mL) and
the solution was stirred at room temperature for 5 min under ar-
gon. The resulting yellow-brown mixture was then washed several
times with water and dried with anhydrous MgSO4. The product
was purified by flash chromatography (silica gel, petroleum ether
with DCM, gradient ranging from 0 to 30%), to give 3 (35 mg, 75%).
All solvents and reagents were purchased from Aldrich, Prolabo
or Acros. Chloroform used in the UVevis and fluorescence mea-
surements is of spectroscopy quality and it was stored in a dark place
to avoid its acidification. Analytical thin layer chromatography (TLC)
was performed on Merck 60F254 silica gel. Column chromatography
was carried out with a CombiflashÒ COMPANIONÒ/TS using Grace-
ResolvÔ silica cartridges. 1H and 13C NMR spectroscopies were per-
€
formed with a Bruker DPX 400 spectrometer. Chemical shifts are
reported as
d (parts per million), downfield from internal TMS.
UVevis spectra were recorded on a SPECORDÒ 210 double beam
spectrophotometer using 10 mm quartz cells. Fluorescence spectra
were recorded on a PTI quanta master spectrofluorimeter equipped
with a xenon short arc lamp (Ushio) and a photomultiplier tube
1H NMR (CDCl3, 400 MHz)
d
ppm 8.74 (d, J¼4.5 Hz, 4H), 8.71 (d,
J¼4.5 Hz, 4H), 8.41 (d, J¼4.6 Hz, 4H), 8.02 (d, J¼4.6 Hz, 4H), 7.31 (s,
4H), 7.17 (s, 8H), 2.65 (s, 6H), 2.51 (s,12H),1.94 (s,12H),1.88 (s, 24H);
13C NMR (CDCl3, 400 MHz)
d ppm 154.8, 150.1, 149.6, 149.2, 139.3,
(Hamamatsu R1527P). Porphyrin fluorescence quantum yields (F)
139.2, 137.3, 137.1, 130.9, 130.6, 130.0, 127.6, 127.5, 119.3, 119.0, 118.8,
21.8, 21.5, 21.3; UVevis (CHCl3) lmax nm (ε, 10ꢁ3 L molꢁ1 cmꢁ1) 418
(187), 456 (203), 560 (50); MS(MALDI-TOF) calcd for C94H82N8Zn2
1454.523, [MþH]þ found: 1455.468.
were determined using cresyl violet in MeOH (
F
¼0.54) as a stan-
dard.30 MALDI-TOF mass spectra were recorded with a Voyager Elite
(Framingham MA, USA) time-off light mass spectrometer equipped
with a 337 nm nitrogen laser (VSL 337ND) (IRCOF, University of
Rouen e France). It was operated in the reflection-delayed extrac-
tion mode at an acceleration voltage of 20 kV.
4.1.4. (5,10,15-Trimesityl-20-trimethylsilylethynylporphyrinato)zinc
(II) (4). Porphyrin 2 (1 equiv, 220 mg, 0.26 mmol), PdCl2(PPh3)2
(0.2 equiv, 38 mg, 0.05 mmol), CuI (0.1 equiv, 6 mg, 0.03 mmol) and
TMSA(5equiv,128mg,1.3mmol)werecombinedina250-mLSchlenk
flask. Dry toluene and freshly distilled TEA (11 mL, 10:1) were added
and the solution was freezeepumpethaw degassed. Then, the mix-
ture was stirred for 4 h at 50 ꢀC. After solvent removing, the crude
product was dissolved in DCM, washed twice with water (75 mL) and
dried over MgSO4. The residue was purified by flash chromatography
(silica gel, petroleumether/DCM:gradient ranging from 0 to 30%). The
title compound was obtained as a dark green solid in 75% yield
4.1.1. 5,10,15-Trimesitylporphyrin (1). Dipyrromethane (1 equiv,
578 mg, 3.95 mmol), meso-mesityldipyrromethane (1 equiv,
1.045 g, 3.95 mmol) and mesitaldehyde (2 equiv, 1.2 g, 7.9 mmol)
were dissolved in 450 mL of dry chloroform under argon atmo-
sphere. BF3(OEt)2 (0.6 equiv, 242 mL, 2.37 mmol) was added to the
solution and the reaction was stirred in the dark for 30 min. Then,
DDQ (3 equiv, 2.7 g, 11.95 mmol) was added and the solution was
stirred for an additional 1 h at room temperature. The reaction was
quenched by addition of TEA (10 mL), the mixture was poured over
(169 mg).1H NMR (CDCl3, 400 MHz)
d
ppm 9.66 (d, J¼4.5 Hz, 2H), 8.78
silica (120 mm) and eluted with DCM until elution of all porphyrins.
(d, J¼4.5Hz, 2H),8.62(m, 4H), 7.27(s,4H),7.22(s, 2H), 2.63(s, 6H)2.60
(s,3H),1.84(s, 6H),1.82(s,12H),0.59(s,9H);UVevis(DCM)lmax nm(ε,
10ꢁ3 L molꢁ1 cmꢁ1) 431 (514), 563 (18), 603 (12). MS(MALDI-TOF)
calcd for C52H50N4SiZn 822.309, [MþH]þ found: 823.352.
Porphyrins were then separated by flash chromatography (silica
gel, petroleum ether/DCM: gradient ranging from 0 to 25%). Por-
phyrin 1 was obtained as a purple solid (450 mg, 17%): 1H NMR
(CDCl3, 400 MHz)
d
ppm 10.23 (s,1H), 9.39 (d, 2H, J¼4.6 Hz), 8.99 (d,
2H, J¼4.6 Hz), 8.86 (s, 4H), 7.46 (s, 4H), 7.43 (s, 2H), 2.78 (s, 6H), 2.76
(s, 3H), 2.03 (s, 18H), ꢁ2.60 (s, 2H); 13C NMR (CDCl3)
d ppm 139.4,
4.1.5. Zinc (II) complex of 1,2-bis(5,10,15-trimesitylporphyrin-20yl)
ethyne (6) and zinc (II) complex of 1,4-bis(5,10,15-trimesitylporphyrin
-20yl)-buta-1,3-diyne (7)
138.5, 137.9, 137.7, 131.5, 130.4, 130.1, 127.8, 127.7, 118.1, 117.4, 104.0,
21.7, 21.4; UVevis (CHCl3) lmax nm (ε, 10ꢁ3 L molꢁ1 cmꢁ1) 414 (431),
509 (17), 541 (4.6), 583 (5.0), 639 (1.1); MS(MALDI-TOF) calcd for
C47H44N4 664.356, [MþH]þ found: 665.459.
4.1.5.1. Classical procedure. Porphyrin
0.072 mmol) was dissolved in anhydrous THF (12 mL) under argon
atmosphere in a 25 mL-Schlenk flask. TBAF (1.4 equiv, 100 L, 1 M in
4 (1 equiv, 60 mg,
m
THF) was added in the solution and the mixture was stirred for
15 min at room temperature. Then, anhydrous calcium chloride
(3 g) was added and the solution was stirred for an additional
15 min. The mixture was filtered into another Schlenk flask and the
solvent was evaporated. Deprotected TMS compound 5 (1.4 equiv,
0.072 mmol) was combined with zinc-(II)5-iodo-10,15,20-
trimesitylporphyrin 2 (1 equiv, 41 mg, 0.049 mmol), PdCl2(PPh3)2
4.1.2. Zinc(II)
5-iodo-10,15,20-trimesitylporphyrin
(2). 5,10,15-
Trimesitylporphyrin 1(1 equiv, 103 mg, 0.155 mmol), CHCl3
(10 mL), bis-(trifluoroacetoxy)iodobenzene (0.7 equiv, 50 mg,
0.11 mmol) and iodine (0.6 equiv, 24 mg, 0.093 mmol) were stirred
for 1 h under argon at room temperature. The mixture was poured
into DCM, washed with saturated aqueous Na2S2O3 (200 mL) then
with water (300 mL) and dried over MgSO4. Next, the residue and
zinc (II) acetate (42 mg, 0.23 mmol) were dissolved in a solution of
CHCl3/MeOH (10 mL/2 mL). The mixture was heated to a gentle
reflux for 3 h. After solvent evaporation, the product was purified by
flash chromatography (silica gel, petroleum ether/DCM: gradient
ranging from 0 to 30%), to obtain compound 2 as a pale purple solid
(0.2 equiv,
7 mg, 0.009 mmol) and CuI (0.1 equiv, 1 mg,
0.005 mmol). Degassed anhydrous toluene/TEA (11 mL, 10/1) was
added and the mixture was stirred for 18 h under argon atmo-
sphere at reflux. Then, the solvent was removed; the crude product
was dissolved in DCM, washed twice with water (75 mL) and dried

A. Jiblaoui et al. / Tetrahedron 69 (2013) 5098e5103
5103
over MgSO4. The residue was purified by preparative silica gel
References and notes
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26%). The remainder of the material was a mixture of 6 and 7.
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0.0028 mmol), Ph3As (0.6 equiv, 3.5 mg, 0.011 mmol) and TBAF
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4.1.6. Zinc (II) complex of 1,2-bis(5,10,15-trimesitylporphyrin-20yl)
ethyne (6). 1H NMR (CDCl3, 400 MHz)
d
ppm 10.37 (d, J¼4.5 Hz, 4H),
8.96 (d, J¼4.5 Hz, 4H), 8.67 (s, 8H), 7.30 (s, 8H), 7.28 (s, 4H), 2.65 (s,
12H), 2.62 (s, 6H), 1.92 (s, 24H), 1.90(s, 12H); 13C NMR (CDCl3,
400 MHz) d ppm 152.6, 150.2, 149.9, 149.5, 139.2, 138.8, 137.5, 131.7,
131.3, 131.0, 127.7, 127.6, 120.1, 105.0, 21.8, 21.7 21.6; UVevis (CHCl3)
lmax nm (ε, 10ꢁ3 L molꢁ1 cmꢁ1) 414 (122), 482 (277), 563 (19), 680
(46); MS(MALDI-TOF) calcd for C96H82N8Zn2 1478.523, [MþH]þ
found: 1479.476.
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buta-1,3-diyne (7). 1H NMR (CDCl3, 400 MHz)
d ppm 9.91 (d,
13. (a) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int. Ed. 2000, 39,
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J¼4.5 Hz, 4H), 8.87 (d, J¼4.5 Hz, 4H), 8.63 (q, 8H), 7.3 (s, 12H), 2.64
(s, 12H), 2.62 (s, 6H), 1.87 (s, 24H), 1.86 (s, 12H); 13C NMR (CDCl3,
400 MHz)
d ppm 153.2, 150.4, 149.6, 149.4, 139.1, 138.7, 137.5, 131.9,
131.7, 131.4, 131.2, 131.1, 130.9, 128.4, 128.2, 127.7, 127.6, 120.3, 68,0
21.7, 21.6, 21.4; UVevis (CHCl3) lmax nm (ε, 10ꢁ3 L molꢁ1 cmꢁ1) 451
(5.43), 483 (5.29), 568 (4.37), 623 (4.62), 674 (4.73); MS(MALDI-
TOF) calcd for C98H82N8Zn2 1502.523, [MþH]þ found: 1503.386.
4.1.8. Zinc(II) trimer 8. It was obtained according to the new pro-
cedure, starting from tris(4-iodophenylamine) (5 mg, 0.008 mmol),
4
(3.6 equiv, 24 mg, 0.03 mmol), PdCl2(PPh3)2 (0.4 equiv,
2.2 mg,0.0032 mmol), Ph3As (1.5 equiv, 3.8 mg, 0.012 mmol) and
TBAF (100 equiv, 0.8 mL, 1 M in THF 5% water). The mixture was
stirred at reflux for 6 h. The reaction was quenched by adding DCM;
the solution was washed twice with water (100 mL) and dried over
MgSO4. The crude was purified by preparative silica gel (petroleum
ether/DCM: 50/50), to give 8 as a dark green solid (17 mg, 81%). 1H
21. Jin, L.-M.; Chen, L.; Yin, J.-J.; Guo, C.-C.; Chen, Q.-Y. Eur. J. Org. Chem. 2005,
3994e4001.
NMR (CDCl3, 400 MHz)
d
ppm 9.80 (d, J¼4.5 Hz, 6H), 8.83 (d,
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J¼4.5 Hz, 6H), 8.64 (q, 12H), 8.06 (d, J¼8.5 Hz, 6H), 7.52 (d, J¼8.5 Hz,
6H), 7.29 (s, 18H), 2.64 (s, 18H), 2.61 (s, 9H), 1.86 (s, 54H); 13C NMR
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winski, R. R. Angew. Chem., Int. Ed. 2003, 42, 1566e1568.
(CDCl3, 400 MHz)
d ppm 152.0, 150.1, 149.7, 149.4, 146.9, 139.2,
138.8, 137.4, 132.9, 131.4, 131.2, 131.0, 130.9, 127.6, 124.5, 120.2, 119.8,
119.3, 99.4, 95.8, 92.8, 21.7, 21.6, 21.4; UVevis (CHCl3) lmax nm (ε,
10ꢁ3 L molꢁ1 cmꢁ1) 434 (389), 567 (36), 624 (67); MS(MALDI-TOF)
calcd for C165H135N13Zn3 2495.884, [MþH]þ found: 2496.727.
ꢀ
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ꢀ
The authors thank the Conseil Regional du Limousin for financial
support and Dr. Michel Guilloton for his help in writing the
manuscript.