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.
crystallographic files in .cif format.
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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
398
Chem. Commun., 2000, 397–398