Self-Assembly of Bisporphyrins
FULL PAPER
The mixture was heated at 808C under argon atmosphere for 2 h. After
cooling to room temperature, tert-butyl methyl ether (50 mL) was added
and the solids were filtered through celite. The filtrate was washed with
HCl (1n) and brine, dried over Na2SO4, filtered and concentrated in
vacuo, to give the crude white solid dimethyl ester of 5-methoxy-1,3-ben-
zenedicarboxylic acid[27] (750 mg, 70%). 1H NMR (300 MHz, CDCl3): d
=8.28 (t, J=1.2 Hz, 1H,), 7.75 (d, J=1.2 Hz, 2H), 3.94 (s, 6H), 3.89 ppm
(s, 3H).
alumina eluting with CH2Cl2/CH3OH (99:1). The product was recrystal-
lized from CH2Cl2/CH3OH yielding the zinc–bisporphyrin 5 as a purple
powder.
Zn–bisporphyrin 5a: Yield 90%; m.p. 260–2688C; 1H NMR
(300 MHz,[D5]pyridine): d=9.19 (d, J=4.5 Hz, 8H), 9.10 (s, 2H), 9.01 (d,
J=4.9 Hz, 8H), 8.7 (s, 2H), 8.28 (m, 16H), 7.79 (t, J=7.5 Hz, 2H), 7.61
(m, 12H), 7.10 (s, 1H), 5.18 (s, 2H), 2.97 (t, J=7.5 Hz, 4H), 2.90 (t, J
=7.5 Hz, 8H), 1.85 (m,12H), 1.44 (m, 24H), 1.00 (t, J=7.1 Hz, 6H), 0.95
(t, J=7.1 Hz, 12H), 0.94 ppm (s, 3H); IR (KBr): n˜ =3416, 2925, 2854,
1639, 1617, 1384, 1079, 799, 621, 476 cmꢀ1; HRMS (ESI): m/z calcd for
C127H122N10O3Zn2Na: 1989.8187; found: 1989.8251.
Without any further purification, the crude product (750 mg, 3.3 mmol)
was suspended in an aqueous solution of sodium hydroxide (1n, 20 mL).
The suspension was heated at 708C under argon atmosphere overnight,
during which time the reaction mixture turned to a clear solution. The
mixture was allowed to reach room temperature and was diluted with
NaOH (1n, 30 mL). The aqueous solution was extracted with tert-butyl
methyl ether (3ꢅ20 mL). Concentrated HCl was added to the aqueous
layer to pH~3. The resulting white precipitate was collected by vacuum
filtration and dried in vacuo to give 5-methoxy-1,3-benzenedicarboxylic
Zn–bisporphyrin 5b: Yield 93%; m.p. 245–2508C; 1H NMR (300 MHz,
[D5]pyridine): d=11.43 (s, 2H), 9.30 (d, J=4.5 Hz 4H), 9.27 (d,
J
=5.0 Hz, 4H), 9.24 (d, J=4.5 Hz, 4H), 9.20 (d, J=5.0 Hz, 4H), 9.03 (s,
2H), 8.84 (s, 1H), 8.58 (d, J=7.8 Hz, 2H), 8.35 (m, 12H), 8.22 (d, J
=7.8 Hz, 2H), 8.04 (s, 2H), 7.78 (t, J=7.8 Hz, 2H), 7.60 (m, 12H), 3.56
(s, 3H), 2.92 (t, J=7.7 Hz, 4H), 2.88 (t, J=7.7 Hz, 8H), 1.82 (m, 12H),
1.43 (m, 24H), 0.97 (t, J=6.6 Hz 6H), 0.94 ppm (t, J=6.6 Hz, 12H); IR
acid as
a
white solid (570 mg, 88%). M.p. 260–2688C; 1H NMR
(KBr): n˜ =3415, 2926,1617, 1526, 1384, 1339, 1207, 1000, 797, 720 cmꢀ1
;
(300 MHz, CDCl3/[D6]DMSO): d=8.18 (t, J=1.4 Hz, 1H), 7.61 (d, J
=1.4 Hz, 2H), 3.75 ppm (s, 3H); 13C NMR (75 MHz, CDCl3/[D6]DMSO):
d=167.5, 159.4, 132.5, 123.4, 119.1, 55.6 ppm; IR (KBr): n˜ =3415, 1704,
HRMS (ESI): m/z calcd for C127H122N10O3Zn2Na: 1989.8187; found:
1989.8273.
1464, 1421, 1384, 1279, 1057, 760, 694 cmꢀ1
.
Zn–bisporphyrin 5c: Yield 94%; m.p. 295–3008C; 1H NMR (300 MHz,
CDCl3): d=8.99 (s, 8H), 8.98 (d, J=5.3 Hz, 4H), 8.96 (d, J=5.3 Hz,
4H), 8.26 (d, J=8.5 Hz, 4H), 8.19 (s, 2H), 8.12 (d, J=8.2 Hz, 4H), 8.11
(d, J=8.2 Hz, 8H), 7.94 (d, J=8.5 Hz, 4H), 7.82 (s, 1H), 7.57 (s, 2H),
7.56 (d, J=8.2 Hz, 4H), 7.53 (d, J=8.2 Hz, 8H), 3.96 (s, 3H), 2.95 (m,
12H), 1.92 (m, 12H), 1.50 (m, 24H), 1.02 ppm (m, 18H); IR (KBr): n˜
The crude diacid obtained above (570 mg, 2.9 mmol) was suspended in
thionyl chloride (2 mL, 27.4 mmol), and a catalytic amount of triphenyl-
phosphine was added. The mixture was refluxed under argon until the
solid was completely dissolved (3 h) and evaporated to dryness to give a
solid residue. The residue was dissolved in dry CH2Cl2 (5 mL) and the
solvent was evaporated under reduced pressure. This process was repeat-
ed three times. The final solid residue was purified by crystallization
from hexane to yield compound 3 (290 mg, 43%) as white needles.
=3409, 2924,1643, 1515, 1446, 1384, 1336, 1205, 1066, 796, 719 cmꢀ1
;
HRMS (ESI): m/z calcd for C127H122N10O3Zn2Na: 1989.8187; found:
1989.8251.
1H NMR (300 MHz, CDCl3): d=8.46 (t, J=1.2 Hz 1H), 7.89 (d,
J
1
Titrations and data analysis: H NMR and UV-visible titrations were per-
=1.2 Hz, 2H), 3.95 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d=165.5,
formed by adding solutions containing the ligand to a solution of the zinc
porphyrin in either a 5 mm NMR tube or a 1 cm path cuvette by using
microliter syringes. In both types of titration experiments the zinc–por-
phyrin was present in the guest solution at the same concentration as
that in the NMR tube or cuvette to avoid dilution effects. Deacidified
chloroform and deacidified deuterochloroform were used as solvents for
the UV-visible and 1H NMR titrations, respectively. In general, UV-visi-
ble spectrophotometric titrations were analyzed by fitting the whole
series of spectra at 1 nm intervals by using the software SPECFIT 3.0
from Spectrum Software Associates (PMB 361, 197M Boston Post Road
West, Marlborough, MA 01752, USA), which uses a global system with
expanded factor analysis and Marquardt least-squares minimization to
obtain globally optimized parameters. Titration curves with respect to the
simple binding model were also analyzed by fitting the data to the theo-
retically expected binding curve by using nonlinear curve-fitting pro-
grams developed by one of us (C.A.H.). In these simple cases the two
methods gave similar results, but the first method was more accurate. In
all the cases of the zinc–bis-porphyrins binding to DABCO, multivariate
global factor analysis was the only method used. The reported errors for
the stability constants directly calculated with SPECFIT, or any other fit-
ting program, were estimated as the square root of the sum of the square
of the standard deviations from at least three experimental values of the
binding constants determined in different titration experiments. Errors
for the stability constants and molarity effects computed using the values
determined directly for the stability constants were estimated by error
propagation analysis.[28]
158.6, 133.7, 124.4, 120.6, 54.5 ppm.
General procedure for the preparation of free-base bisporphyrins 4a–c:
A solution of aminoporphyrin 1 (220 mg, 0.26 mmol), freshly distilled dry
triethylamine (60 mL, 0.4 mmol), and a catalytic amount of 4-(dimethyl-
amino)pyridine (DMAP) in dry CH2Cl2 (30 mL) was cooled at 08C in an
ice-water bath, and diacid 3 (31 mg, 0.13 mmol) was added in one por-
tion. After stirring for 4 h at room temperature under argon atmosphere,
the organic layer was washed with saturated NaHCO3 and brine, dried
over Na2SO4, filtered, and concentrated in vacuo to yield a solid residue.
The product was separated from the unreacted porphyrin by flash chro-
matography of the residue on silica gel eluting with CH2Cl2:THF (99:1)
to recover first the aminoporphyrin 1 followed by the free-base bispo-
rhyrin 4 as a purple solid.
Free-base bis-porphyrin 4a: Yield 40%; 1H NMR (300 MHz, CDCl3): d
=8.82 (d, J=5.7 Hz, 4H), 8.78 (d, J=5.7 Hz, 4H), 8.66 (d, J=4.7 Hz,
4H), 8.49 (d, J=4.7 Hz, 4H), 8.26 (d, J=8.2, 2H), 8.11 (d, J=7.2 Hz,
2H), 7.98 (m, 8H), 7.86 (d, J=7.4 Hz, 4H), 7.67 (t, J=8.2 Hz, 2H), 7.59
(d, J=7.2 Hz, 4H), 7.49 (d, J=7.2 Hz, 4H), 7.44 (t, J=8.2 Hz, 2H),
7.37(d, J=7.2 Hz, 4H), 6.99 (s, 2H), 6.02 (s, 1H), 4.66 (s, 2H), 2.96 (t, J
=7.8 Hz, 4H), 2.90 (t, J=7.8 Hz, 8H), 1.86 (m, 12H), 1.51 (m, 24H),
1.03 (m, 18H), 1.0 (s, 3H), ꢀ2.94 ppm (s, 4H).
Free-base bis-porphyrin 4b: Yield 42%; 1H NMR (300 MHz, CDCl3): d
=8.86 (s, 8H), 8.83 (s, 8H), 8.32 (s, 2H), 8.1 (m, 16H), 7.5 (m, 19H), 3.8
(s, 3H), 2.95 (t, J=7.5 Hz, 4H), 2.88 (t, J=7.5 Hz, 8H), 1.85 (m, 12H),
1.51 (m, 24H), 1.02 (m, 18H), ꢀ2.75 ppm (s, 4H).
Free-base bis-porphyrin 4c: Yield 42%; 1H NMR (300 MHz, CDCl3): d
=8.89 (s, 8H), 8.87 (s, 8H), 8.35 (s, 2H), 8.29 (d, J=8.2 Hz, 4H), 8.26 (s,
2H), 8.12 (d, J=8.2 Hz, 4H), 8.11 (d, J=7.8 Hz, 12H), 7.84 (s, 2H), 7.55
(d, J=7.8 Hz, 12H), 2.94 (t, J=7.5 Hz, 12H,), 1.90(m, 12H), 1.52 (m,
24H), 1.02 (t, J=7 Hz, 18H), ꢀ2.75 ppm (s, 4H).
Computational methods: Semiempirical calculations were carried out at
the restricted Hartree–Fock (RHF) level using the AM1[29] method, as
implemented in MOPAC-93 package.[30] The geometry of all structures
was optimized and further refined by minimization of the gradient norm
to less than 0.418 kJꢆꢀ1 degꢀ1 by means of the Eigenvector Following
(EF) routine.[31] Side chains were assumed not to be attached to the por-
phyrins in order to keep the size of the calculation approachable.
General procedure for the preparation of the zinc–bisporphyrins 5a–c:
The free-base bisporphyrin
4 (100 mg, 0.05 mmol) was dissolved in
CH2Cl2/CH3OH (3:1, 30 mL) and zinc acetate (180 mg, 0.98 mmol) was
added. The reaction mixture was protected from light and stirred at
room temperature for 1 h. After removal of the solvents under reduced
pressure, the product was purified by column chromatography on basic
Chem. Eur. J. 2005, 11, 2196 – 2206
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