M. Van der Auweraer, J.-P. Sauvage, J.-L. Pierre et al.
FULL PAPER
(s, 2H), 4.10 (m, 8H); 13C NMR (CDCl3): d 190.8 (s, 2C), 156.0 (s, 2C),
overestimates[40±43] the rate of energy transfer, especially for
Znphen2H and the Z conformer of Znbipy2H.
140.3 (s, 2C), 138.7 (s, 2C), 137.6 (d, 2C), 127.0 (d, 4C), 126.8 (d, 4C), 120.4
(d, 2C), 119.7 (d, 2C), 103.5 (d, 2C), 65.3 (t, 4C). FAB -MS: m/z: 453
The detailed analysis of the fluorescence decays suggests
furthermore that about 30% of Znbipy2H is present in the
less-stable Z conformer. When it is assumed that the slow-
decaying component of the fluorescence of Znphen2H at
582 nm is due to a reversible energy transfer, the ratio of the
forward and backward energy-transfer steps matches the free-
energy difference between the excited state of the zinc
porphyrin and the metal-free porphyrins as suggested by the
position of the 0 ± 0 transitions. For the major (E) conformer
of Znbipy2H, which is characterized by a three times slower
forward energy transfer and a similar free-energy difference
between both singlet excited states, the rate of the backward
transfer is so small that it does not yield values of cÅ2 that differ
appreciably from zero.
[MH] , 365, 307; calcd for C28H24N2O4: 452.6.
6,6'-di-(p-formylphenyl)-2,2'-bipyridine (2): A solution of 5% HCl in water
(ca. 5 mL) was added to 8 (0.300 g, 0.66 mmol), and the suspension was
stirred at room temperature for 12 h. A solid was recovered by filtration,
washed with cold water, and dried to yield the monohydrochloride salt of 2.
1H NMR (200 MHz, [D6]DMSO): d 10.10 (s, 2H), 8.64 (d, J 7.1 Hz,
2H), 8.50 (d, J 7.8 Hz, 4H), 8.21 (t, J 7.6 Hz, 4H), 8.08 (d, J 7.8 Hz,
4H), 7.21 (s, J 5.3 Hz, N2H ). A suspension of this salt in water was
neutralized with aq. NaHCO3, and extracted with CH2Cl2. The organic
layer was dried and concentrated in vacuo to afford 2, which was purified
by silicagel chromatography (CH2Cl2/MeOH, 0 ± 10%). Yield, 0.227 g
(94%); white solid, m.p. 2608C (decomp); 1H NMR (CDCl3, 200 MHz):
d 10.12 (s, 2H), 8.68 (dd, J 7.6, 0.8 Hz, H3,3'), 8.36 (d, J 8.3 Hz, 4H),
8.04 (d, J 8.3 Hz, 4H), 8.00 (t, J 7.7 Hz, H4,4'), 7.89 (dd, J 7.7, 0.8 Hz,
H5,5'); 13C NMR (CDCl3): d 192.0 (d, 2C), 155.9 (s, 2C), 154.9 (s, 2C),
144.8 (s, 2C), 138.0 (d, 2C), 136.5 (s, 2C), 130.2 (d, 4C), 127.5 (d, 4C), 121.2
(d, 2C), 120.6 (d, 2C); DCI-MS: m/z: 365 [MH] ; calcd for C24H16N2O2:
364.5.
Bis-porphyrin 2Hphen2H: Three drops of trifluoroacetic acid were added
to a solution of 1 (0.088 g, 0.224 mmol), 3 (0.390 g, 1.79 mmol), and 4
(0.514 g, 2.24 mmol) in CH2Cl2 (250 mL) under argon. The reaction
mixture was stirred at room temperature for 16 h. Subsequently, solid
chloranil (1.59 g, 6.88 mmol) was added, and the reaction mixture refluxed
for 1.5 h. It was quenched with 10% aqueous NaHCO3. The organic layer
was washed with water and evaporated to dryness. The crude product was
extracted with hexane and chromatographed on an alumina column and
eluted with a mixture of hexane and dichloromethane (130:70), providing
the bis-porphyrin 2Hphen2H in pure form. The residue, which contained
small amounts of bis-porphyrin was subjected to successive column
chromatographies on alumina and silica, using n-hexane/CH2Cl2 mixtures
as eluents. The total yield of 2Hphen2H was 0.055 g (15%). 1H NMR
(200 MHz, CDCl3): d 10.17 (s, 4H, meso), 9.02 (d, J 8.1 Hz, 4H; Ho),
8.52 (AB, DnÄ 4.5 Hz, J 7 Hz, 4H; H3,8, H4,7), 8.30 (d, J 8.1 Hz, 4H;
Hm), 7.96 (s, 2H; H5,6), 7.87 (d, J 1.7 Hz, 4H; Hop), 7.78 (t, J 1.8 Hz, 2H;
Hpp), 3.99 (m, 16H; CH2b, CH2c), 2.63 (s, 12H; CH3d), 2.41 (s, 12H; CH3a),
1.72 (t, J 7.4 Hz, 24H; CH3b, CH3c), 1.47 (s, 36H; tBu), 2.46 (s, 4H; NH).
Experimental Section
Synthesis: Dialdehyde 1,[9] 3,5-di-tert-butylbenzaldehyde (3),[9] 3,3'-diethyl-
4,4'-dimethyl-2,2'-dipyrrylmethane (4),[26, 27] and p-bromophenyl-1,3-dioxo-
lane (6) were prepared according to the literature procedures. All other
chemicals were of the best commercially available grade and were used
without further purification. Dry solvents were obtained by distillation
from P2O5 (CH2Cl2) or Na/benzophenone (Et2O and THF). UV/visible
spectra were recorded on a Kontron Instruments UVIKON 860 spectro-
photometer. 1H NMR spectra were recorded on Bruker WP200SY
spectrometer. Fast atom bombardment mass spectra (FAB-MS) were
obtained in the positive-ion mode with either a krypton primary atom beam
in conjunction with a 3-nitrobenzyl alcohol matrix and a Kratos MS80RF
mass spectrometer coupled to a DS90 system or a xenon primary atom
beam with the same matrix and a ZAB-HF mass spectrometer.
6-Bromo-2-(p-phenyl-1,3-dioxolane)pyridine (7): A solution of tert-butyl-
lithium in pentane (1.4m, 32.2 mL, 43.7 mmol) was added to a solution of p-
bromophenyl-1,3-dioxolane 6 (5.00 g, 21.8 mmol) in THF (100 mL) at
988C under argon and was stirred for 10 min at this temperature. Then a
saturated solution of MgBr2 (2.62m; prepared from 2.43 g of Mg and
8.9 mL of dibromoethane in 50 mL of Et2O) was added, and the mixture
was stirred at 08C for 30 min. 2,6-Dibromopyridine 5 (5.15 g, 21.8 mmol)
and Pd(PPh3)4 (0.250 g, 0.01 mmol%) were then directly added, and the
mixture was heated to reflux for 48 h. The course of the reaction was
followed by TLC (n-hexane/AcOEt, 4:1). Water was added at room
temperature, and the product was extracted with AcOEt. The solvents were
evaporated and the major product was purified by flash chromatography
(n-hexane/AcOEt, 5:1) to afford a yellow solid that was recrystallized in
pentane/CH2Cl2 to afford 4.40 g (66%) of pure 7. White solid, m.p. 91 ±
FAB -MS: m/z: 1663.0, 831.5; calcd for C116H128N10: 1664.4 [MH] , 832.0
([M2H] /2); UV/Vis (CH2Cl2): l 273, 409, 507, 540, 573, 625 nm (plus
an impurity at 654 nm).
Bis-porphyrin Znphen2H:
A solution of Zn(OAc)2 ´ 2H2O (0.0072 g,
0.033 mmol) in CH3OH (7 mL) was added to a refluxing solution of
2Hphen2H (0.055 g, 0.033 mmol) in CHCl3 (20 mL) under argon over
20 min. The reaction mixture was refluxed for 1.5 h. The solvents were
rotary evaporated, and the residue redissolved in CH2Cl2 (70 mL) and
shaken with a 5% aqueous solution in of NaHCO3 (80 mL). The organic
layer was washed with water and evaporated to dryness. Examination of the
residue by TLC (Al2O3, n-hexane/CH2Cl2, 50:50) showed three spots,
corresponding to the bis-porphyrins 2Hphen2H, Znphen2H, and
ZnphenZn in the order of increasing polarity. The products were separated
by successive column chromatographies on alumina and silica, with n-
hexane/CH2Cl2 mixtures as eluents. The yields obtained were 0.0137 g
(18%) for 2Hphen2H, 0.0147 g (25%) for ZnphenZn, and 0.0231 g (41%)
for Znphen2H.
1
928C; H NMR (200 MHz, CDCl3): d 8.00 (dt, J 8.4, 1.8, 1.8 Hz, 2H),
7.67 (dd, J 7.7, 1.1 Hz, 4H), 7.40 (dd, J 7.8, 1.0 Hz, 1H), 5.87 (s, 1H), 4.10
(m, 4H); MS (EI): m/z: 306, 304 [M H] , 235, 233, 154; calcd for
C14H12BrNO2: 306.2. 2,6-Di-(p-phenyl-1,3-dioxolane)pyridine (10%) and
4,4'-di-(1,3-dioxolane)biphenyl (5%) were also isolated as byproducts.
ZnphenZn: 1H NMR (200 MHz, CDCl3): d 10.13 (s, 4H, meso), 9.06 (d,
J 8.2 Hz, 4H; Ho), 8.56 (AB, DnÄ 15 Hz, J 8.6 Hz, 4H; H3,8, H4,7), 8.32
(d, J 8.2 Hz, 4H; Hm), 7.97 (s, 2H; H5,6), 7.87 (d, J 1.8 Hz, 4H; Hop), 7.77
(t, J 1.8 Hz, 2H; Hpp), 3.96 (m, 16H; CH2b, CH2c), 2.61 (s, 12H; CH3d),
2.38 (s, 12H, CH3a), 1.71 (t, J 7.5 Hz, 24H; CH3b, CH3c), 1.47 (s, 36H, tBu);
6,6'-Di-(p-phenyl-1,3-dioxolane)-2,2'-bipyridine (8): A solution of nBuLi
(1.6m, 1.44 mL, 2.1 mmol) in hexane was added to a solution of 7 (0.612 g,
2 mmol) in Et2O (20 mL) under argon at 608C, and the resulting mixture
was stirred for 30 min. Anhydrous CuCl2 (0.1484 g, 1.1 mmol) was then
added at 908C. The vigorously stirred suspension was allowed to warm up
to 708C; at this temperature an exothermic reaction took place. Stirring
was continued for 1 h, and dry oxygen was bubbled through the solution
until the brown suspension turned green (ca. 20 min). The suspension was
then hydrolyzed with water (ca. 10 mL), the ether was removed under
reduced pressure, and KCN was dissolved in the stirred aqueous solution to
remove all the copper. The precipitated solid was filtered off and purified
by silicagel chromatography (CH2Cl2/MeOH, 0 ± 2%) to yield 0.325 g
(72%) of product as a white solid. M.p. 3208C (decomp); 1H NMR
(200 MHz, CDCl3): d 8.59 (d, J 7.7 Hz, 2H), 8.18 (d, J 8.2 Hz, 4H),
7.91 (t, J 7.7 Hz, 2H), 7.78 (d, J 7.8 Hz, 2H), 7.62 (d, J 8.2 Hz, 4H), 5.92
FAB -MS: m/z: 1787.7, 894.3; calcd for C116H124N10Zn2: 1789.0 [MH] ,
894.5 ([M2H] /2); UV/Vis (CH2Cl2): l 273, 342, 413, 542, 575 nm.
Znphen2H: 1H NMR (200 MHz, CDCl3): d 10.17 (s, 2H; meso'), 10.14 (s,
2H; meso), 9.05 (d, J 8.3 Hz, 2H; Ho), 9.02 (d, J 8.3 Hz, 2H; Ho'), 8.55
(AB, 2H, H3,8), 8.52 (AB, 2H, H4,7), 8.33 (d, J 6.5 Hz, 2H; Hm), 8.30 (d,
J 8.1 Hz, 2H; Hm'), 7.95 (s, 2H; H5,6), 7.88 (d, J 1.8 Hz, 2H; Hop), 7.86 (d,
J 1.8 Hz, 2H; Hop'), 7.78 (t, 2H; Hpp, Hpp'), 3.97 (m, 16H; CH2b, CH2c
,
CH2b', CH2c'), 2.62 (s, 12H; CH3d, CH3d'), 2.41 (s, 6H, CH3a'), 2.39 (s, 6H,
CH3a), 1.72 (t, J 7.3 Hz, 12H; CH3b, CH3c, CH3b', and CH3c'), 1.47 (s, 18H;
tBu, tBu'), 2.65 (s, 2H; NH); FAB -MS: m/z: 1725.9, 862.9; calcd for
2098
ꢁ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
0947-6539/99/0507-2098 $ 17.50+.50/0
Chem. Eur. J. 1999, 5, No. 7