A convenient synthesis of porphodimethenes and their conversion to trans-porphyrins with two functionalized meso-naphthyl substituents

Article abstract of DOI:10.1039/a907992k

The Mac Donald-type 2 + 2 condensation of the readily available 5- mesityldipyrromethane with acenaphthenequinone leads to the trans (syn and anti) porphodimethenes, respectively, which, after treatment with KOH or NaOMe in THF and subsequent oxidation wi

Full text of DOI:10.1039/a907992k

A convenient synthesis of porphodimethenes and their conversion to
trans-porphyrins with two functionalized meso-naphthyl substituents
Michael Harmjanz and Michael J. Scott
Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA. E-mail: mjscott@chem.ufl.edu
Received (in Bloomington, IN, USA) 4th October 1999, Accepted 20th January 2000
The Mac Donald-type 2 + 2 condensation of the readily
available 5-mesityldipyrromethane with acenaphthenequi-
none leads to the trans (syn and anti) porphodimethenes,
respectively, which, after treatment with KOH or NaOMe in
THF and subsequent oxidation with air, yield the corre-
sponding trans-8-carboxynaphthylporphyrins or their es-
ters.
alumina, a mixture of the corresponding porphodimethene
isomers in 26% yield. Separation by column chromatography
yields the two isomers [1 (syn), 2 (anti)] in an almost 1+2
ratio.†
The porphodimethenes 1 and 2 are air-stable, bright orange
solids and they exhibit a characteristic absorption maxima in the
visible region at lmax/nm (log e) 440(4.97) (1) and 438(4.93)
(2), which when compared to previously described octaalk-
ylporphodimethenes (414–426 nm) are bathochromically
shifted.8 The N–H and CNO stretch frequencies can be found,
respectively, in the IR at 3345, 1732 cm21 for 1 and 3279,
1720 cm21 for 2. The absolute configuration has been
meso-Substituted porphyrins with rigid anthracene, bipheny-
lene or naphthalene spacers have been widely used to determine
the distance dependency of photo-induced electron transfer1 as
well as to prepare and examine cofacial diporphyrins2 or other
bridged porphyrins with well defined separations and varying
relative arrangements of the porphyrin rings.3 Porphyrins with a
functionalized anthracene or naphthalene group have also found
utility as building blocks for the synthesis of molecular
receptors and for the design of dinuclear complexes.4 Despite
the numerous potential applications for these types of com-
plexes, their development has been severely hampered by the
inability to prepare large quantities of the porphyrin precursors.
The syntheses, in general, require complex procedures for the
preparation of the aromatic side arm and/or a multistep
procedure for the porphyrin backbone. Chang et al.5 and
Therien and coworkers6 have reported the preparation of
porphyrins attached to the 1-position of an 8-functionalized
naphthalene but to the best of our knowledge, a straightforward
synthetic procedure for the synthesis of trans aa/ab porphyrins
bearing two 8-functionalized naphthalene derivatives has yet to
be reported.
1
determined by H NMR and by an X-ray structure analysis of
the metallated (Zn2+) porphodimethene 2b. Although the X-ray
structure analysis of 2 reveals a strong roof-like folded structure
of the porphodimethene core,9 only one type of acena-
1
phtheneoyl can be identified in the H NMR spectra of both 1
and 2, suggesting a fast up and down motion of the
acenaphtheneoyl groups together with a flexing of the two
dipyrromethane units along a line joining the two saturated
meso carbons. Even at 223 K, only minor changes were evident
in the NMR spectra of 2. Owing to the lack of aromaticity in the
macrocycle, the signal of the N–H protons appears downfield at
d 13.92 (1) and 14.00 (2), respectively, characteristic of
porphodimethenes.8,10 Metal insertion has been demonstrated
by reaction of 2 with Zn(OAc)2·2H2O in refluxing CHCl3–
MeOH. Complex formation can be easily monitored by UV–
VIS-spectroscopy [Fig. 1, lmax (log e) 475 nm (5.17) (2b)]. As
shown in Fig. 2, the Zn2+ in 2b is complexed by a nearly planar,
C2 symmetric, tetrapyrrole macrocycle, although the metal is
disordered over two positions in the solid-state structure. The
As part of our building block approach towards the
preparation of new di- and tri-nuclear porphyrin based com-
plexes, a general two-step synthesis, starting from 5-mesityldi-
pyrromethane, has been developed to provide convenient
amounts of the desired porphyrins. Reaction of commercially
available acenaphthenequinone with 5-mesityldipyrromethane
7
in the presence of catalytic amounts of BF3·OEt2 gives, after
oxidation with DDQ and subsequent filtration through neutral
Fig. 1 UV-VIS spectra of 2 upon addition of Zn(OAc)2 in boiling CHCl3–
MeOH. The arrows indicate the direction of change in peaks during
metallation. Spectra were measured at 5 min intervals.
Scheme 1 Reagents and conditions: i, 1. BF3·OEt2, CH2Cl2, room temp., 4
h, 2. DDQ, room temp., 1 h. R = mesityl.
DOI: 10.1039/a907992k
Chem. Commun., 2000, 397–398
This journal is © The Royal Society of Chemistry 2000
397

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slightly inclined back away from the porphyrin, lifting the two
oxygen atoms above the plane of the macrocycle by 2.667 Å
[O(2)] and 3.087 Å [O(1)], respectively.
In summary, we have demonstrated that acenaphthenone
substituted porphodimethenes can be generated from 5-mesi-
tyldipyrromethane and acenaphthenequinone. Ring cleavage
gives the desired porphyrins bearing two 8-functionalized
naphthalene groups. Work is in progress to extend this reaction
to other vicinale diketones. Other ring opening reactions are
also under investigation.
We thank the Deutsche Forschungsgemeinschaft and the
Research Corporation (Research Innovation Award) for provid-
ing financial support for this work. Support from the National
Science Foundation (CAREER Award) is also gratefully
acknowledged.
Fig. 2 Diagram of 2b; the porphodimethene resides on inversion symmetry
position, relating the prime and unprimed atoms. The zinc atom is
disordered over two positions and the symmetry equivalent Zn(1A) and
O(101A) atoms as well as all hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (°): Zn(1)–N(1) 2.116(4), Zn(1)–N(2)
2.197(4), Zn(1)–N(1A) 2.038(4), Zn(1)–N(2A) 2.063(4), Zn(1)–O(101)
2.175(7), N(1)–Zn(1)–N(2) 85.2(1), N(1)–Zn(1)–N(2A) 88.6(1), N(1A)–
Zn(1)–N(2) 87.0(1), N(1A)–Zn(1)–N(2A) 90.7(1), N(1)–Zn(1)–O(101)
97.9(2), N(2)–Zn(1)–O(101) 107.4(2), N(1A)–Zn(1)–O(101) 104.9(2),
N(2A)–Zn(1)–O(101) 94.3(2).
Notes and references
† 5-Mesityldipyrromethane was prepared as described before.12 The
formation of the porphodimethenes 1 and 2 and the porphyrins 5 and 6 were
carried out under a nitrogen atmosphere in dried and degassed solvents.
Satisfactory elemental analyses or HR-MS (MH+) were obtained for new
compounds. 1: Yield: 8%. lmax(CH2Cl2)/nm (log e) 440 (4.97). IR (KBr):
3345 (nN–H), 1732 cm21 (nCO). 2: Yield: 18%. lmax(CH2Cl2)/nm (log e)
438(4.93). IR (KBr): 3279 (nN–H), 1720 cm21 (nCO). 2b: Yield: 91%.
lmax(CH2Cl2)/nm (log e) 475(5.17). IR (KBr): 1720 cm21 (nCO) 3: Yield:
92%. lmax (CHCl3) 432 nm. IR (KBr): 3327 (nN–H), 1708 cm21 (nCO). 4
(potassium salt after recrystallization): Yield: 65%. lmax (MeOH) 431 nm.
IR (KBr): 1563 cm21 (nCO). 5: Yield: 69%. lmax (CHCl3) 425 nm. IR
(KBr): 3315 (nN-H), 1727 cm21 (nCO). 6: Yield: 59%. lmax(CHCl3) 425 nm.
IR (KBr): 3315 (nN–H), 1725 cm21 (nCO).
largest out of plane displacements are observed for the saturated
meso carbon atoms (0.11 Å) which are part of the five-
membered rings of the two 1-acenaphthenone moieties aligned
in an anti position. The Zn atom, coordinated by the four pyrrole
nitrogens and an axial water molecule, resides 0.404 Å above
the plane defined by the nitrogen donor set. The Zn–N bond
lengths vary considerably from 2.038(4) to 2.197(4) Å, but the
average distance of 2.10 Å is significantly larger than the
corresponding linkage in tetra meso-aryl substituted porphyrins
[mean: 2.036(6) Å; ZnTPP].11
Refluxing the porphodimethenes 1 and 2 in THF in the
presence of 30% KOH results in ring opening and formation of
the respective porphyrins without further oxidation by DDQ.
Subsequent protonation with 6 M HCl gives the free acids (3, 4)
in high yields. While the aa isomer 3 is soluble in CHCl3, the
ab atropisomer is virtually insoluble in most common organic
solvents, possibly owing to strong intermolecular hydrogen-
bonding interactions between the carboxylic acid groups.
Accordingly, the ab atropisomer has been fully characterized as
the dipotassium salt.
Porphyrin formation has also been accomplished by reaction
of 1 or 2 with NaOMe in THF–MeOH at room temp. After
bubbling air through the reaction mixture, the corresponding
esters (5, 6) were isolated in moderate yields.‡ All of the
porphyrins exhibit a characteristic Soret band between 425 and
432 nm in the UV–VIS spectra and they have been charac-
terized by IR, NMR and MS. In addition, the ab atropisomer 6
has been characterized by an X-ray structural analysis (Fig. 3),
and although most of the structural parameters of the porphyrin
core are indistinguishable from other meso-aryl substituted
porphyrins, a few particular details are worth noting. The two
mesityl residues are oriented nearly perpendicular to the
porphyrin plane (85.3°) while the naphthalene moieties exhibit
a twist of 61.8° relative to the macrocyclic ring. Owing to the
electronic repulsion of the ester group and the electron rich
porphyrin plane, the functionalized naphthalene groups are
‡ Crystal data: 2b·CHCl3: C61H45N4O3Cl3Zn, tetragonal, space group, I41/
a, a = 29.539(2), c = 12.104(1) Å, V = 10561(1) Å3 , T = 173 K, Z = 8,
Dc
= =
1.325 g cm23, m(Mo-Ka) 0.667 mm21, 27 497 reflections
collected, 4520 unique, of which 2954 with I > 2s(I) were used in the
refinement. The structure was solved by direct methods and refined using
full-matrix least squares refinement on F2 and difference Fourier synthesis.
Unless severely disordered, all non-hydrogen atoms were refined anisotrop-
ically; hydrogen atoms were included at calculated positions. At con-
vergence, R1 = 0.0704 [I > 2s(I)], wR2 = 0.2010, GOF = 1.029 for 381
parameters.
6·CH2Cl2: C63H52N4O4Cl2, monoclinic, space group C2/c,
a =
25.800(1), b = 12.7094(7), c = 17.6758(9) Å, b = 115.168(1)°, V =
5245.6(5) Å3, T = 173 K, Z = 4, Dc = 1.266 g cm23, m(Mo-Ka) = 0.177
mm21, data collection, refinement and solution as above, 11 105 reflections
collected, 3433 unique, of which 3006 with I > 2s(I) were used in all
calculations. R1 = 0.0611 [I > 2s(I)], wR2 = 0.1766, GOF = 1.047 for 357
parameters.
CCDC 182/1536. See http://www.rsc.org/suppdata/cc/a9/a907992k/ for
crystallographic files in .cif format.
1 H. A. Staab, B. Kratzer and S. Quazzotti, Eur. J. Org. Chem., 1998,
2149.
2 R. Guilard, M. A. Lopez, A. Tabard, P. Richard, C. Lecomte, S.
Brandes, J. E. Hutchison and J. P. Collman, J. Am. Chem. Soc., 1992,
114, 9877 and references therein.
3 Y. Naruta, M. Sasayama and K. Ichihara, Russ. J. Org. Chem., 1996, 32,
214.
4 Y. Liang and C. K. Chang, Tetrahedron Lett., 1995, 36, 3817; N. Bag,
S.-S. Chern, S.-M. Peng and C. K. Chang, Inorg. Chem., 1995, 34,
753.
5 C. K. Chang and M. P. Kondylis, J. Chem. Soc., Chem. Commun., 1986,
316.
6 A. G. Hyslop, M. A. Kellett, P. M. Iovine and M. J. Therien, J. Am.
Chem. Soc., 1998, 120, 12676.
7 B. J. Littler, Y. Ciringh and J. S. Lindsey, J. Org. Chem., 1999, 64,
2864.
8 A. Botulinski, J. W. Buchler, K.-L. Lay and H. Stoppa, Liebigs Ann.
Chem., 1984, 7, 1259.
9 M. Harmjanz and M. J. Scott, unpublished results.
10 M. Fontecave, J. P. Battioni and D. Mansuy, J. Am. Chem. Soc., 1984,
106, 5217.
11 W. R. Scheidt, M. E. Kastner and K. Hatano, Inorg. Chem., 1978, 17,
706.
12 C.-H. Lee and J. S. Lindsey, Tetrahedron, 1994, 50, 11427.
Fig. 3 Diagram of the structure of 6 outlining the atom numbering scheme.
Primed and unprimed atoms are related by a center of inversion. The
hydrogen atoms have been omitted for clarity.
Communication a907992k
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Chem. Commun., 2000, 397–398