Synthesis and characterization of new tetra-substituted porphyrins with exo-donor carboxylic groups as building blocks for supramolecular architectures. Catalytic and structural studies of their metalated derivatives

Article abstract of DOI:10.1142/S1088424610002641

We report herein the synthesis of the porphyrins 5,10,15,20-tetrakis(4- carboxybiphenyl)-porphyrin (H₂TCBP) and 5,10,15,20-tetrakis(4- carboxy-2,6-dimethylbiphenyl)porphyrin (H₂TCDMBP) bearing diphenyl units on meso-positions, and of

Full text of DOI:10.1142/S1088424610002641

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 804–814
DOI: 10.1142/S1088424610002641
Published at http://www.worldscinet.com/jpp/
Synthesis and characterization of new tetra-substituted
porphyrins with exo-donor carboxylic groups as building
blocks for supramolecular architectures. Catalytic and
structural studies of their metalated derivatives
Lucia Carlucci*a, Gianfranco Ciania, Simona Magginia, Davide M. Proserpioa,
Fabio Ragainib, Emma Gallo*b, Marco Ranocchiarib and Alessandro Casellib
a Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Università degli Studi di Milano,
Via G. Venezian 21, 20133 Milano, Italy
b Dipartimento di Chimica Inorganica, Metallorganica e Analitica “L. Malatesta”,
Università degli Studi di Milano, and ISTM-CNR, Via G. Venezian 21, 20133 Milano, Italy
Received 17 March 2010
Accepted 27 August 2010
ABSTRACT: We report herein the synthesis of the porphyrins 5,10,15,20-tetrakis(4-carboxybiphenyl)-
porphyrin (H2TCBP) and 5,10,15,20-tetrakis(4-carboxy-2,6-dimethylbiphenyl)porphyrin (H2TCDMBP)
bearing diphenyl units on meso-positions, and of their cobalt and silver derivatives. The silver complexes
of H2TCDMBP and of H2TCPP (H2TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) were
investigated by X-ray crystallography and their supramolecular organization elucidated. Co(TCBP) was
reacted with copper formate, yielding a polymeric compound that showed a catalytic activity in the
benzylic amination of hydrocarbons using arylazide as aminating agent.
KEYWORDS: coordination network, cobalt, silver, catalysis, amination.
coordinative bonds to the metals of identical neighbor-
INTRODUCTION
ing metalloporphyrin units [3–11], or bonds to external
The crystal engineering of functional coordination
metal centers [12–24]. The last strategy seems especially
networks [1] extensively exploited, in the past few
promising for the engineering of open networks. In prin-
years, the networking ability of tetra-meso-substituted
porphyrins and metalloporphyrins [2]. Open-lattice
zeolite-like species with large free-void volumes can be
ciple, these can be programmed by carefully selecting
both the different porphyrin meso-substituents and the
different external metal ions with suitable coordination
produced when porphyrin units act as tetradentate pla-
geometries. Many years ago, Robson and co-workers
nar donor nodes. More in general, porphyrin supramo-
showed that metalloporphyrins bearing four peripheral
lecular arrays show potential applications in many fields
pyridyl donors can produce coordination networks with
of materials chemistry, as photonic devices, conductive
polymers, chemical sensors and receptors for selective
catalysis.
the CdSO4 topology (cds) using Cd(II) centers as linear
spacers [12], or with the PtS topology (pts) using tetra-
hedral Cu(I) centers [13]. A variety of remarkable multi-
Multi-porphyrin architectures include networks
porphyrin architectures have been described by Goldberg
assembled through hydrogen bond bridges [2a,b],
and co-workers [2].
The two tetra-substituted porphyrins most widely inves-
tigated and characterized in the above context are surely
SPP full member in good standing
5,10,15,20-tetrakis(4-piridyl)porphyrin (H2TPYP) and
*Correspondence to: Lucia Carlucci, email: lucia.carlucci@
5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (H2TCPP),
according, at least, to the number of hits present in the
Cambridge Structural Database.
unimi.it, tel: +39 025-031-4446, fax: +39 025-031-4454 and
Emma Gallo, email: emma.gallo@unimi.it, tel: +39 025-031-
4372, fax: +39 025-031-4405
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Metalloporphyrins should be suitable building blocks
possibly produce frames with greater openings suitable
for catalytic applications.
for the synthesis of catalytic metal organic frameworks
(MOFs), thanks to their thermal and chemical stabil-
ity. However, few examples of catalytically active
porphyrin-strut-based MOFs have been reported so far
[25, 26]. This is mainly due to the difficulty to syn-
thesize MOFs with appropriate pores for catalysis that
do not collapse during the reaction solvent removal. It
is quite difficult to build networks with free-base por-
phyrins because of the great aptitude of the porphyrin
core to coordinate every metal present in the reaction
mixture. Nevertheless, the development of new meth-
odologies for the synthesis of porphyrin strut-based
MOFs is encouraged by the facility of porphyrin skel-
eton modifications and by the high catalytic activity of
metalloporphyrins.
The first report of porphyrin strut-based catalysis
described a MOF constituted by [tetrakis(phenyl-
carboxylate)porphyrin]Mn(III) complexes as building
blocks and trinuclear manganese clusters as second-
ary building blocks units (SBUs) [27]. The frame-
work, dubbed PIZA-3 (Porphyrinic Illinois Zeolite
Analogue-3), showed a non-interpenetrating structure
and was an effective catalyst in hydroxylation and epoxi-
dation reactions.
We report here the synthesis and characterization of
5,10,15,20-tetrakis(4-carboxy-2,6-dimethylbiphenyl)
porphyrin (H2TCDMBP) and an improvement of the
already published synthesis of 5,10,15,20-tetrakis(4-
carboxybiphenyl)porphyrin (H2TCBP) [28] (Fig. 1).
Both porphyrins have been used for the preparation of
metalated derivatives and as building blocks for net-
working. The Ag(II)-metalated derivatives [Ag(TCPP)]
(H2O)2(solv)x and [Ag(TCDMBP)](DMF)4(solv)x were
obtained as single crystals and their structures are here-
with reported.
The cobalt complex of H2TCBP was prepared and
reacted with Cu(HCOO)2(H2O)x to obtain a polymeric
material that showed catalytic properties in the benzylic
amination of toluene by p-NO2C6H4N3. The same reac-
tion was also catalyzed by PIZA-1 that was prepared
by reacting cobalt(III) tetra(p-carboxyphenyl)porphy-
rin (Co(TCPP)) with a linear trinuclear cobalt(II) clus-
ter according to the protocol reported by Suslick and
co-workers [29].
RESULTS AND DISCUSSION
We are currently interested in obtaining new porphy-
rins building blocks for the formation of extended arrays
in the form of open nanoporous framework or immo-
bilized on different supporting matrices for catalytic
purposes. Some of us have previously reported inves-
tigations on the ability of free-base H2TPYP and of its
ZnII-metalated derivative to give networks with different
silver(I) salts [23, 24]. We have now turned our attention
towards tetra-carboxyporphyrins, analogous to H2TCPP
but bearing longer donor side arms (see Fig. 1) in order to
Synthesis of 5,10,15,20-tetrakis(4-carboxybiphenyl)-
porphyrin (H2TCBP) (3)
The reported synthesis of H2TCBP [28], a modification
of Alder’s method [40], consists of a condensation in ace-
tic acid of pyrrole with 4′-formyl-biphenyl-4-carboxylic
acid. The latter was obtained by Suzuki coupling between
the corresponding arylbromide and arylboronic acid
using Pd(PPh3)4 as catalyst.
To improve the synthesis of H2TCBP we used a differ-
ent strategy to achieve 4′-formyl-biphenyl-4-carboxylic
acid employing 10% of Pd(OAc)2 as catalyst. The
sodium salt of the commercially available 4-iodobenzoic
acid was coupled with 4-formyl-phenylboronic acid in
water to form 4′-formyl-biphenyl-4-carboxylic acid (2)
in quantitative yield. It should be noted that up to now
2 was obtained starting from ester derivatives of 4-iodo-
benzoic acid and using palladium posphine complexes as
catalysts [41] or supporting the acid on PEG [42]. Con-
versely, we here report an almost quantitative synthesis
of 2 starting from commercially available compounds
using a cheap catalyst and a safe, economic and environ-
mentally benign solvent.
R
R
N
H
N
N
H
N
R
R
R = -COOH (H2TCPP)
(H TCBP)
R =
R =
COOH
2
Then, the corresponding porphyrin ligand was syn-
thesized in a good yield by using the usual methodology
(Scheme 1).
(H TCDMBP)
2
COOH
Synthesis of 5,10,15,20-tetrakis(4-carboxy-2,6-dimethyl-
biphenyl)porphyrin (H2TCDMBP) (8)
Fig. 1. 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (H2TCPP),
5,10,15,20-tetrakis(4-carboxybiphenyl)porphyrin (H2TCBP) and
5,10,15,20-tetrakis(4-carboxy-2,6-dimethylbiphenyl)porphyrin
(H2TCDMBP)
The novel 5,10,15,20-tetrakis(4-carboxy-2,6-dimethyl-
biphenyl)porphyrin (H2TCDMBP) was synthesized using
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I
B(OH)2
CHO
The two methyl groups of the 2,5-dibromo-m-xylene
control the regioselectivity of the process, leading to the
formation of a single compound.
The described synthesis of 5 was preferred to the
direct oxidation of 2-bromo-1,3,5-trimethylbenzene with
chromic acid (K2Cr2O7/H2SO4) which was characterized
by a lower yield (<10%) and required a more difficult
purification process.
The coupling reaction between 6 and 4-formyl-
phenylboronic acid was performed using 1 mol% of
bis(triphenylphosphine)palladium(II)succinimide as pre-
catalyst, following the procedure developed by Fairlamb
et al. [30]. Efficient cross-coupling catalysts for the
synthesis of biaryls starting from ortho-hindered aryl
bromides are not ordinary.
+
COONa
Pd(OAc)2
K2CO3
H2O
CHO
pyrrole
H2TCBP
3, 46%
CO2H
The catalytic system Pd2(dba)3/P(t-Bu)3/KF, developed
by Fu and co-workers [43], was tested in THF at room and
reflux temperature and even though it was very successful
with other sterically hindered aryl bromides, in this case
it gave only traces of the desired coupled product.
Attempts to effect the coupling using the catalytic sys-
tems Pd(PPh3)4/Na2CO3(aq.) or NaOH (aq.) or t-BuOK/
t-BuOH in refluxing DME were unsuccessful (in the case
of Na2CO3) or led to traces of 4′-formyl-2,6-dimethyl-
biphenyl-4-carboxylic acid (7) (in the other two cases).
Increasing the strength of the base was observed to
improve the performance of the reaction, in accordance
with what was expected.
2, 99%
Scheme 1. Synthesis of 5,10,15,20-tetrakis(4-carboxybiphenyl)-
porphyrin (H2TCBP) (3)
the Adler’s method by reacting 4′-formyl-2,6-dimethyl-
biphenyl-4-carboxylic acid with freshly distilled pyr-
role in refluxing propionic acid. The starting aldehyde
4′-formyl-2,6-dimethyl-biphenyl-4-carboxylic acid was
first synthesized from the commercial 4-bromo-2,6-
dimethylaniline through the four different steps shown in
Scheme 2 with an overall yield of 46%.
The first step involved a Sandemeyer reaction to trans-
form 4-bromo-2,6-dimethylaniline into 2,5-dibromo-m-
xylene (4). In the second step, n-BuLi was used in an
exchange reaction of the less hindered bromine of 2,5-
dibromo-m-xylene to form the corresponding organo-
lithium derivative, which was promptly reacted with CO2.
The methodology employed for the synthesis of 2,
Pd(OAc)2 as catalyst in water at 150 °C afforded 11% of
the desired product, but this was associated to extensive
catalyst decomposition.
The H2TCDMBP porphyrin was obtained in 15%
yield as a pure product at the end of the reaction and did
1
not require further purification. Its H NMR spectrum,
Br
NH2
acquired in DMSO, shows a broad signal at -2.83 ppm for
the pyrrolic NH groups and a singlet at 2.30 ppm for the
two methyl groups; the aromatic CH groups give dou-
Na(NO2)
H2SO4 conc.
1) n-BuLi, THF
2) CO2, HCl
CuBr, HBr 48%,
CH3CO2H
blets at 7.38 ppm (3JH-H = 7.15 Hz) and 8.10 ppm (3JH-H
=
Br
Br
Br
7.15 Hz) and a singlet at 7.86 ppm. The broad singlet at
12.89 ppm was assigned to COOH groups.
4, 52%
Br
NaOH
Pd(PPh3)2(N-succ)2
Na2CO3,THF/H2O
Synthesis of silver complexes of H2TCPP and
H2TCDMBP
CO2H
CO2Na
Despite the commercially available H2TCPP have
been widely employed both in the preparation of novel
metalated complexes and in the crystal engineering of
coordination networks, their silver derivatives have never
been reported. We have been able to obtain the silver-
metalated derivative of H2TCPP and characterized it by
X-ray analysis. The metalation was performed by react-
ing H2TCPP with Ag(O2CCH3) in pyridine/H2O/NH3
at 150 °C for four days. The resulting solution was left
to evaporate slowly at room temperature to obtain
small single crystals of the pyridine chlatrate complex
[Ag(TCPP)](H2O)2(solv)x (9).
5, 95%
6
(HO)2B
CHO
CHO
pyrrole
CH3CH2CO2H
H2TCDMBP
8, 15%
CO2H
7, 93%
Scheme 2. Synthesis of 5,10,15,20-tetrakis(4-carboxy-2,6-
dimethylbiphenyl)porphyrin (H2TCDMBP) (8)
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Similarly, single crystals of the silver-metalated
adjacent units. These bridges consist of chains of three
−COOH groups generating a T shaped node (see Fig. 2).
To describe the layer topology we observe that it is
comprised of two types of 3-conn nodes (the C atom of the
central −COOH group of the chains bridges in Fig. 2 and
the Ag ions, Ag···C edge lengths 9.20, 13.44, 13.53 Å).
It is an unprecedented uninodal 3-connected 2D net with
point symbol (Schläfli) 103 (Vertex Symbol: 102.104.104).
A special feature is the presence of self-catenation (illus-
trated in Fig. 4). The fourth side arms of the porphyrins
not involved in the hydrogen-bonding bridges protrude
on both sides of the layers, showing deep interdigitation
with the two adjacent layers (see Fig. 5). These thick lay-
ers superimpose in an ABAB sequence. A chlatrate water
molecule gives hydrogen-bonding bridges between the
carboxylic group of the dangling arm and the three-con-
nected node of an adjacent layer. If these hydrogen bonds
are also considered, the resulting framework is a complex
3D architecture. The other chlatrate water molecules are
involved in an intricate hydrogen-bonding pattern.
H2TCDMBP porphyrin (10) were obtained by slow dif-
fusion of a methanolic solution of Ag(O2CCH3) into a
solution of H2TCDMBP in DMF. This is the first exam-
ple of a crystal structure reported for a tetra-carboxylic
biphenyl porphyrin. Note that a very limited number
of Ag(II)-metalated porphyrin structures have been
reported [44].
Single crystal structure of [Ag(TCPP)](H2O)2(solv)x
(9)
The crystallographic analysis of 9, in spite of the poor
quality of the isolated single crystals, was carried out con-
sidering the limited number of reported silver-metalated
porphyrins.
The Ag(II)-porphyrinate complex shows a saddle-type
distortion of the tetrapyrrolic core with large deviations
from the mean plane of the pyrrolic rings that are in the
range 0.355–0.472 Å. The four Ag−N distances are in the
range 2.067(5)–2.078(5)Å, similar to previously reported
Ag−N bonds in metalated porphyrins [44]. The four car-
boxylic groups are protonated and the molecules form
an extended hydrogen bond pattern (O−H···O 2.613(6)–
3.036(7) Å, O−HO 123–168°) (Fig. 2). A rationaliza-
tion neglecting the chlatrate water molecules results in a
hydrogen-bonded unusual 2D layer illustrated in Fig. 3.
The porphyrinate units employ three of the four exo-
carboxylic groups to form hydrogen-bond bridges with
Crystal structure of [Ag(TCDMBP)](DMF)4(solv)x
(10)
The [Ag(TCDMBP)](DMF)4(solv)x crystallizes in
the triclinic P-1 space group, giving centrosymmetric
silver(II)-porphyrinate monomeric units. All the four car-
boxylic groups are protonated and their involvement in
stronghydrogenbonds(O−H···Ointherange2.55–2.56Å,
Fig. 2. A view of the hydrogen bonds involving the carboxylic groups in [Ag(TCPP)](H2O)2(solv)x (9)
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L. CarLuCCI et al.
Fig. 3. A top view of the 2D layer in [Ag(TCPP)](H2O)2(solv)x (9)
square-like rod packing (Fig. 7). The void left is only
12.3% of the cell volume and is mainly distributed in
channels along the a axis with an average cross-section
diameter of 3.3 Å.
Synthesis of cobalt complexes of H2TCPP and
H2TCDMBP
The porphyrin H2TCPP was employed to synthesize
the network PIZA-1 following Suslick’s procedure [29].
The compound PIZA-1, which molecular structure was
elucidated by X-ray analysis [29], is a neutral network
of cobalt(III) porphyrin cores linked to each other by
cobalt(II)-carboxylate clusters. The presence of large
internal cavities in the non-interpenetrating PIZA-1
framework allowed us to suppose a catalytic activity
of this compound in the benzylic amination of toluene,
a reaction efficiently catalyzed by monomeric cobalt
porphyrin complexes [45].
The reaction, shown in Scheme 3, was performed at
reflux temperature. The consumption of the azide was
followed by IR spectroscopy and the formation of the
corresponding benzylic amine by TLC.
Although PIZA-1 was insoluble in toluene, 70% of
azide conversion was observed after 48 h. Its catalytic
activity partially decreased when additional amounts of
the reagents were added; in 53 h only 35% of azide con-
version was achieved. The presence of the corresponding
benzylic imine was confirmed by GC-MS analysis of the
reaction mixture.
Fig. 4. A schematic view of the 2D layer showing self-catenation
in [Ag(TCPP)](H2O)2(solv)x (9)
O−H···O 179.5°) with a molecule of dimethylformamide
(DMF) prevents a possible extension of the hydrogen-
bonding pattern, giving discrete 1:4 porphyrinate:DMF
assembly (Fig. 6). The metalated tetrapyrrolic macrocy-
cle core is very flat and the deviation from the mean plane
is up to 0.015 Å. The Ag−N distances are 2.077(6) Å
and 2.085(6) Å and are in the typical range of the
Ag−porphyrinate systems [44]. The four side arms are
slightly oriented up or down with respect to the flat core
plane. As expected for steric reasons the presence of two
methyl groups in the 2,6-positions of the external phenyl
rings makes these groups almost orthogonal to the other
one (dihedral angles: 70.7° and 81.4°). The distances
between the silver atom and the H−bonded oxygen atom
of the carboxylic groups are respectively 13.85 Å and
13.92 Å. A side view of the molecule is also shown in
Fig. 6.
In order to build MOF with larger pores, H2TCBP
instead of H2TCPP was used as porphyrin ligand for the
synthesis of Co(TCBP) (11) (80% yield). Complex 11
The porphyrinate units are stacked down the crystal-
lographic a axes with an AAA sequence to generate a
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The solvotermic reaction between Cu(HCOO)2(H2O)x
and 11 yielded a brown powder whose elemental anal-
ysis is in accord with the formula {Cu2[Co(TCBP)]}n
(12) and its polymeric nature is proposed on the base of
extreme insolubility in any organic solvent. On this bulk
material we performed XRPD analysis that revealed an
amorphous powder. SEM images and EDS analyses on
the same sample showed a heterogeneous distribution of
copper and cobalt elements. Thermal gravimetric analy-
sis (TGA), performed in the range 50–650 °C, showed
a first weight loss of about 5% in the range 50–230 °C,
followed by an almost continual weight loss to 68% at
650 °C.
Unfortunately, attempts to obtain single crystals of 12
for a structure determination failed. However, this mate-
rial was tested as a catalyst in the reaction in Scheme 3
and within 48 h 63% of the azide was converted to
form the corresponding imine. A comparison of this
catalytic result with those illustrated above using com-
plex 11 as catalyst evidences a lower catalytic activity
for polymer 12. This is not unexpected as it is quite the
rule that heterogenized catalysts show lower activity than
their homogeneous counterpart. On the other hand, UV
spectroscopy of the solution at the end of the catalytic
reaction showed the absence of any porphyrin complex,
indicating that the catalyst is indeed heterogeneous and
easily recovered.
In order to exclude a catalytic role of the copper
atom, we repeated the reaction between toluene and
4-nitrophenylazide in the presence of Cu(TPP). We did
not observe any arylazide conversion after 20 h in reflux-
ing toluene. Then, to better investigate this catalytic
aspect, the porphyrin H2TCBP (3) was reacted with
Cu(HCOO)2(H2O)x in a 1:2 molar ratio using the same
experimental procedure employed for the synthesis of
12. The obtained compound was tested as catalyst in the
model reaction described above (Scheme 3). Again, no
Fig. 5. A schematic view of the packing in [Ag(TCPP)]-
(H2O)2(solv)x (9) showing the interdigitation and the inter-layer
hydrogen bonds
arylazide conversion was observed, strongly supporting
the catalytic inactivity of copper atoms.
was employed as catalyst in the amination of toluene
(R = H), ethylbenzene (R = CH3) and isopropylbenzene
(R = CH(CH3)2) by 4-nitrophenylazide and a complete
azide conversion was observed in 12, 8 and 9 h, respec-
tively. The GC-MS analyses of the reaction mixtures
revealed the presence of benzylic imine as the only ami-
nated compound (Scheme 4).
In view of the catalytic activity of complex 11 and of
the coordinative environment of the porphyrin periphery,
we employed 11 as a building block to synthesize a tri-
dimensional complex using Cu(HCOO)2(H2O)x as sec-
ondary building units (SBUs) [46]. Copper carboxylates
are often employed as SBUs in the assembling of MOFs
because they form dicopper units with a paddlewheel
structure that is well-suited for regular propagation of the
structural motif.
EXPERIMENTAL
General
The reaction solvents were of analytical grade and were
freshly distilled under a dry nitrogen atmosphere prior to
use. Tetrahydrofuran and toluene were purified by distil-
lation over sodium. Dichloromethane and pyrrole were
purified by distillation over calcium hydride. 5,10,15,20-
tetrakis(4-carboxyphenyl)porphyrin (H2TCPP) and the
other reagents were purchased from Sigma-Aldrich and
used without further purification. Bis(triphenylphosphine)
palladium(II)succinimide [30] and PIZA-1 [29] were
prepared according to the reported procedures.
All the reactions were monitored by thin-layer chro-
matography carried out on 0.2-mm Fluka silica gel plates
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Fig. 6. Front and side views of [Ag(TCDMBP)](DMF)4(solv)x (10)
Fig. 7. A view of the packing down the crystallographic a axis in [Ag(TCDMBP)](DMF)4(solv)x (10)
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811
N3
CH3
stirred for 30 min and then filtered. The recovered solid
was washed with H2O and dried by azeotropic distillation
with n-hexanes. The desired product was recovered as a
white solid (1.75 g, 99.0%). 1H NMR (300 MHz, DMSO):
δ, ppm 8.08–7.89 (m, 8H, Ar), 10.08 (s, 1H, CHO), 13.07
(brs, 1H, COOH). Anal. calcd. for C14H10O3: C, 74.33; H,
4.46%. Found: C, 74.34; H, 4.44.
+
NO2
PIZA-1 toluene
Preparation of 5,10,15,20-tetrakis(4-carboxybi-
phenyl)porphyrin (H2TCBP) (3). A solution of pyr-
role (1.30 mL, 18.7 mmol) in propionic acid (2.00 mL)
was added dropwise to a solution of 4′-formyl-biphenyl-
4-carboxylic acid (3.92 g, 17.3 mmol) in propionic acid
(25.0 mL). The resulting mixture was refluxed for 1 h
and then allowed to cool to room temperature. The result-
ing green solid was collected, washed with H2O, EtOH,
n-hexanes, and dried by azeotropic distillation with
n-hexanes (2.16 g, 46.0%). 1H NMR (300 MHz, DMSO):
δ, ppm 7.67–8.16 (m, 32H, Ar), 10.60 (brs, 8H, pyrrole),
12.80 (s, 4H, COOH). IR (nujol): νmax, cm-1 3428 (br),
1732 (m), 1716 (m), 1699 (m), 1651 (w), 1557 (w), 1260
(w). UV-vis (DMF): λmax, nm (log εΜ) 423 (5.60), 514
(4.27). Anal. calcd. for C72H46N4O8: C, 78.96; H, 4.23; N,
5.12%. Found: C, 78.55; H, 4.60; N, 5.30.
CH=N
NO2
Scheme 3. PIZA-catalyzed amination of toluene by 4-nitro-
phenylazide
R
complex 11
Ph
Ph
CH2R + 2 ArN3
+ ArNH2
NAr
C
R = H, CH3, CH(CH3)2; Ar = 4-NO2C6H4
Scheme 4. Complex 11-catalyzed amination of hydrocarbons
by 4-nitrophenylazide
using UV light as a detector. Column chromatographic
separations were performed using silica gel (Merck 60,
0.040–0.060 mm) and solvents of analytical grade as
1
eluents. H NMR spectra were recorded on a Bruker
DRX-300 instrument; δ values are given in ppm rela-
tive to tetramethylsilane. IR spectra were recorded on
PerkinElmer Paragon 1000 PC FTIR or Varian Scimi-
tar FTS 1000 spectrophotometers. Thermogravimetric
analysis (TGA) were performed on a PerkinElmer TGA
7 instrument under dynamic nitrogen (total flow rate
20 cm3/min). Powder patterns were recorded on a Philips
PW1820 diffractometer (Cu Kα radiation, λ = 1.5405 Å),
in the 5–35° 2θ range (0.02° and 2.5 s per step). Semi-
quantitative Scanning Electron Microcospy (SEM) analy-
ses were performed with a Jeol JSM-5500LV instrument
equipped with EDS spectrometer IXRF EDS 2000.
Synthesis of 5,10,15,20-tetrakis(4-carboxy-2,6-di-
methylbiphenyl)porphyrin (H2TCDMBP) (8)
Preparation of 1,4-dibromo-m-xylene (4). A solu-
tion of NaNO2 (1.08 g, 15.6 mmol) in conc. H2SO4 (12.0
mL) was prepared and maintained below 10 °C. A solu-
tion of 4-bromo-2,6-dimethylaniline (3.00 g, 15.0 mmol)
in acetic acid (12.0 mL) was added portionwise. The
mixture was stirred for 1 h below 10 °C and then added in
portions to a vigorously stirred solution of CuBr (2.27 g,
15.6 mmol) in 48.0% HBr (15.0 mL) and H2O (12.0 mL)
at 50 °C. The addition was made over 30 min. After the
addition was completed, the reaction mixture was heated
for 30 min at 70 °C. The mixture was left to cool to room
temperature, then H2O (120 mL) and n-hexane (180 mL)
were added. The organic phase was isolated, washed with
H2O (120 mL), and dried over MgSO4. The salt was fil-
tered off and the solvent was evaporated to dryness. The
residue was purified by chromatography column (silica
gel, elution with n-hexanes). The desired product was
obtained as a light yellow liquid which crystallized on
standing (2.06 g, 52.0%). Analytical data is in accord
with the literature [31].
Preparation of 4-bromo-3,5-dimethylbenzoic acid
(5). Under a nitrogen atmosphere, n-BuLi 2.5 M in
n-hexanes (19.5 mL, 48.7 mmol) at -78 °C was added
to a solution of 1,4-dibromo-m-xylene (10.7 g, 40.6
mmol) in anhydrous THF (100 mL). The mixture was
stirred at -78 °C for 1 h, and then was added dropwise
to an excess of dry ice. The reaction mixture was then
stirred for 3 h and allowed to warm to room temperature.
A solution of HCl 1 M was added to reach pH = 1–2.
The mixture was extracted with ethyl acetate (500 mL)
Synthesis of 5,10,15,20-tetrakis(4-carboxybiphenyl)-
porphyrin (H2TCBP) (3)
Preparation of sodium 4-iodo-benzoate (1). 4-iodo-
benzoic acid (5.08 g, 20.5 mmol) was added to a water
solution of NaOH 0.1 M (205 mL, 20.5 mmol). The mix-
ture was stirred at 70 °C until a solution was formed. The
solvent was evaporated to dryness and the residue was
dried by azeotropic distillation with n-hexanes using a
Dean-Stark apparatus. Sodium 4-iodo-benzoate was
quantitatively recovered as a white solid.
Preparation of 4′-formyl-biphenyl-4-carboxylic
acid (2). 4-formyl-phenylboronic acid (1.39 g, 9.25
mmol), Pd(OAc)2 (0.17 g, 0.77 mmol) and K2CO3 (2.69 g,
19.5 mmol) were added to a degassed solution of
sodium 4-iodo-benzoate (2.09 g, 7.75 mmol) in H2O (125
mL). The mixture was stirred at 70 °C for 2 h. The green
suspension was filtered through celite to remove palla-
dium and washed with H2O. The filtrate was treated with
conc. HCl to reach pH ~ 2. The resulting suspension was
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 811–814

812
L. CarLuCCI et al.
and the organic phase was washed with H2O (100 mL)
and dried over MgSO4. The salt was filtered off and the
solvent was evaporated to dryness to obtain 4-bromo-
3,5-dimethylbenzoic acid as a white solid (8.80 g, 95%).
Analytical data is in accord with the literature [32].
Preparation of sodium 4-bromo-3,5-methyl-
benzoate (6). A water solution (2.00 mL) of NaOH (17.6
mg, 0.44 mmol) was added to 4-bromo-3,5-dimethylben-
zoic acid (0.10 g, 0.44 mmol). The mixture was heated to
50 °C and stirred until the solid was fully dissolved. The
water was evaporated to dryness to quantitatively obtain
the product as a white solid.
The mixture was stirred at room temperature for 20 min,
then heated at 150 °C for four days and slowly cooled
(0.1 °C/min) to room temperature. The obtained solution
was slowly evaporated at atmospheric pressure and room
temperature. After two months, purple-green needles
formed. UV-vis (DMF): λmax, nm 420, 515, 549.
Synthesis of [Ag(TCDMBP)](DMF)4(solv)x (10)
Crystals suitable for X-ray analysis were obtained by
slow diffusion of a solution of Ag(O2CCH3) (1.80 mg,
11.0 × 103 mmol) in MeOH (4.00 mL) into a solution of
meso-tetrakis(4-carboxy-2,6-dimethylbiphenyl)porphy-
rin (H2TCDMBP) (2.00 mg, 1.70 × 10-3 mmol) in DMF
(4.00 mL), after a period of five months. UV-vis (DMF):
Preparation of 4′-formyl-2,6-dimethyl-biphenyl-
4-carboxylic acid (7). Sodium 4-bromo-3,5-methylben-
zoate (0.44 mmol), 4-formyl benzoic acid (0.07 g, 0.47
mmol), Na2CO3 (0.11 g, 1.00 mmol), H2O (1.00 mL), THF
(1.50 mL) and [(PPh3)2Pd(N-succ)2] (3.30 mg, 4.10 × 10-3
mmol) were degassed by freeze-pump-thaw method. The
reaction mixture was heated at 60 °C for 23 h. The sol-
vent was evaporated to dryness and H2O (60.0 mL) was
added. The water solution was washed with diethyl ether
(3 × 20.0 mL) and then treated with conc. HCl to reach
pH = 1. The product was extracted with ethyl acetate
(3 × 60.0 mL). The organic phases were combined and
dried over MgSO4. The salt was filtered off and the sol-
vent was evaporated to dryness to obtain the desired prod-
λmax, nm 425, 517, 446.
Synthesis of [Co(TCBP)] (11)
CoCl2(H2O)6 (109 mg, 4.60 × 10-1 mmol) was added to
a DMF (18.0 mL) solution of H2TCBP (502 mg, 4.60 ×
10-1 mmol) and the resulting suspension was refluxed for
1.5 h and cooled to room temperature. Then CoCl2(H2O)6
(109 mg, 4.60 × 10-1 mmol) was re-added to the reac-
tion mixture that was refluxed for another 1.5 h. The
mixture was cooled and water (40.0 mL) was added. The
resulting solid was collected in a filter and refluxed in
n-hexane to eliminate the residual water by azeotropic
distillation. The brown solid was collected in a filter and
dried in vacuo (417 mg, 80%). IR (nujol): νmax, cm-1 3447
(br), 1733 (m), 1717 (m), 1700 (m), 1653 (w), 1558 (w),
1377 (w). Anal. calcd. (%) for C72H44CoN4O8: C, 75.06;
H, 3.85; N, 4.86%. Found: C, 74.85; H, 4.12; N, 4.39.
UV-vis (DMF): λmax, nm (log εΜ) 430 (4.90), 540 (4.32).
uct as a white solid (104 mg, 93.0%). 1H NMR (300 MHz,
3
CDCl3): δ, ppm 2.11 (s, 6H, CH3), 7.36 (d, 2H, JH-H
=
8.04 Hz, ArH), 7.91 (s, 2H, ArH), 8.02 (d, 2H, 3JH-H = 8.04
Hz, ArH), 10.12 (s, 1H, CHO). Anal. calcd. for C16H14O3:
C, 75.57; H, 5.55%. Found: C, 75.71; H, 5.69.
Preparation of 5,10,15,20-tetrakis(4-carboxy-2,6-di-
methylbiphenyl)porphyrin (H2TCDMBP) (8). 4′-formyl-
2,6-dimethyl-biphenyl-4-carboxylic acid (500 mg, 1.97
mmol) and pyrrole (0.140 mL, 2.02 mmol) were added
dropwise to refluxing propionic acid (12.0 mL). After
the addition the reflux was maintained for 45 min. The
mixture was allowed to cool to room temperature, after
which the precipitated purple solid was collected in a fil-
ter, washed with hot H2O and MeOH, and dried under
Synthesis of {Cu2[Co(TCBP)]}n (12)
A mixture of HCOOH (0.20 mL, 5.30 mmol) and
Cu(HCOO)2(H2O)x (31.0 mg) was added to a suspen-
sion of Co(TCBP) (102 mg, 8.85 × 10-2 mmol) in CH3OH
(20.0 mL). The resulting brown suspension was placed in
a glass liner inside an autoclave. The autoclave was fro-
zen at dry ice temperature, evacuated and filled with dini-
trogen three times. N2 (10 bar) was then added at room
temperature and the autoclave was heated at 160 °C for
12 h. The reaction was cooled to room temperature and
the brown solid was collected in a filter, washed with
CH3OH, and dried under vacuum (85.0 mg). Anal. calcd.
(%) for C72H44Cu2CoN4O8: C, 67.60; H, 3.47; N, 4.38%.
1
reduced pressure (87.1 mg, 15%). H NMR (300 MHz,
DMSO): δ, ppm -2.83 (s, 1H, NH), 2.30 (s, 24H, CH3),
3
7.38 (d, 8H, JH-H = 7.15 Hz, ArH), 7.86 (s, 8H, ArH),
8.10 (d, 8H, 3JH-H = 7.15 Hz, ArH), 12.89 (s, 4H, COOH).
IR (nujol): νmax, cm-1 3434 (br), 3317 (w), 2697 (w), 2597
(w), 2525 (w), 1682 (s), 1606 (m), 1571 (w), 1508 (w),
1417 (w), 1392 (w), 1347 (w), 1306 (m), 1266 (w), 1236
(m), 1218 (m), 1182 (w), 1157 (w), 1104 (w). UV-vis
(DMF): λmax, nm (log εΜ) 420 (5.50), 515 (4.23). Anal.
calcd. for C80H62N4O8: C, 79.58; H, 5.18; N, 4.64%.
Found: C, 79.95; H, 5.29; N, 4.31.
Found: C, 67.35; H, 3.60; N, 4.55. UV-vis (DMF): λmax
,
nm (log εΜ) 421 (5.07), 533 (4.26). {Cu2[Co(TCBP)]}n
was analyzed by Scanning Electron Microscopy (SEM),
Thermal Gravimetric Analysis (TGA) and X-ray Powder
Diffraction (XRD) (see Results and Discussion sections).
Synthesis of [Ag(TCPP)](H2O)2(solv)x (9)
General procedure for catalytic reactions
H2TCPP (6.90 mg, 87.0 × 10-3 mmol), Ag(O2CCH3)
(4.50 mg, 27 × 10-3 mmol), 28% NH3 solution (0.50 mL),
and pyridine (0.80 mL) were added to a steel reactor.
Inatypicalrun,thecatalyst(1.22×10-2 mmol)wasadded
to a hydrocarbon (30.0 mL) solution of p-nitrophenylazide
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 812–814

SyntheSIS anD CharaCterIzatIOn Of neW tetra-SubStItuteD POrPhyrInS
813
(100 mg, 6.09 × 10-1 mmol). The resulting solution was
Fo > 4σ(Fo) for [Ag(TCPP)](H2O)2(solv)x and R1 =
0.1551 for 4797 Fo > 4σ(Fo) for [Ag(TCDMBP)](DMF)4.
Due to difficulty in the refinement, arising from the very
weak diffraction, anisotropic thermal parameters in
[Ag(TCPP)](H2O)2(solv)x were used only for the central
silver atom and in [Ag(TCDMBP)](DMF)4 all the atoms
were treated as anisotropic except for the 12 independent
atoms of the porphyrin ring. Further details are reported
in the .cif files (see Supporting Information section).
refluxed using a preheated oil bath. The consumption of
the arylazide was monitored by TLC up to the point that
its spot was no longer observable, and then by IR spectros-
copy measuring the N3 characteristic absorbance at 2120
cm-1. The solution was then analyzed by GC-MS.
Crystallography
Crystal data for all the compounds is listed in Table 1.
Data were collected on a APEX II-CCD Bruker dif-
fractometer with Mo-Kα λ = 0.71073 Å. Empirical
absorption corrections (SADABS) [33] were applied to
all data. The structures were solved by direct methods
(SIR97) [34] and refined by full-matrix least-squares on
F2 (SHELX-97) [35] with WINGX interface [36]. All
hydrogen atoms were placed in geometrically calculated
positions and thereafter refined using a riding model with
Uiso(H) = 1.2Ueq(C).All the diagrams were produced using
TOPOS program [37]. The accessible free voids were
calculated by PLATON [38]. Details on the refinements
can also be found in the cif file under _refine_special_
details. The crystals are unstable in air and were collected
under mineral oil. Both contain disordered solvents and
because it was difficult to refine a consistent model, their
contribution was subtracted from the observed structure
factors according to the BYPASS procedure [39], as
implemented in PLATON with the command SQUEEZE.
The R before the procedure was R1 = 0.1977 for 6884
CONCLUSION
In conclusion, we report the synthesis of the novel
5,10,15,20-tetrakis(4-carboxy-2,6-dimethylbiphenyl)-
porphyrin (H2TCDMBP) (8) and an improvement in the
synthesis of 5,10,15,20-tetrakis(4-carboxybiphenyl)por-
phyrin (H2TCBP) (3). Both porphyrins have long diphenyl
units on meso-positions and are suitable building blocks
to be used for the synthesis of porous MOFs. The porphy-
rins reactivity towards metal cations has been preliminar-
ily explored obtaining cobalt and silver derivatives. X-ray
analyses of the silver derivatives of 8 and of thecommercial
5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin(H2TCPP)
have been carried out considering that structurally charac-
terized Ag(II)-metalated porphyrins are scarce. The cobalt
derivative of 3 was reacted with Cu(HCOO)2(H2O)x to
yield [Cu2Co(TCBP)]n (12), a polymeric complex that
showed a catalytic activity in the benzylic amination of
hydrocarbons using arylazide as aminating agent.
Table 1. Crystallographic data for all compounds
Acknowledgements
Ag(TCPP) · 2H2O Ag(TCDMBP) · 4DMF
We thank MIUR (FIRB RBNE03JCR5) for financial
support.
Formula
C48H32AgN4O10
932.65
monoclinic
C2/c
C92H88AgN8O12
1605.57
triclinic
P-1
M
System
Supporting information
Space group
Crystallographic data have been deposited at the
Cambridge Crystallographic Data Center (CCDC) under
deposition numbers CCDC 769846–769847. Copies can
be obtained on request, free-of-charge, via www.ccdc.
cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data Center, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: +44 1223-336-033 or email:
deposit@ccdc.cam.ac.uk).
a, Å
46.612(8)
8.8465(15)
33.738(6)
90
7.7821(10)
12.2156(15)
24.305(3)
83.551(2)
87.161(2)
74.649(2)
2213.5(5)
1
b, Å
c, Å
α, °
β, °
131.705(2)
90
γ, °
U, Å3
10387(3)
8
Z
Temperature, K
Reflections collected
Indep. refls, R (int)
Crystal decay, %
150(2)
150(2)
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