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Synthesis Structure and Complexation Properties of Amide-Substituted Derivatives of Norbornadiene and Quadricyclane.

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Angewandte
Chemie
Photoinduced Na+ Coordination
Synthesis, Structure, and Complexation
Properties of Amide-Substituted Derivatives of
Norbornadiene and Quadricyclane
Torsten Winkler, Ina Dix, Peter G. Jones, and
Rainer Herges*
The indirect coupling of external energy sources (e.g. light,
redox and proton gradients, and exergonic reactions) to
molecular switches[1] to drive a function is one of the most
interesting problems in supramolecular chemistry. To our
knowledge, light-driven, carrier-mediated, active transport
through a membrane against a concentration gradient has not
yet been achieved. To this end, we developed a photoswitchable ligand[2] based on the known norbornadieneQquadricyclane isomerization.[3] Quadricyclanes with electrondonating substitutents on the cyclobutane ring isomerize to
the norbornadienes with a concerted “grapplelike” motion,
which can be used to bind or release guests (cations). The
main advantage of these compounds is the large reisomerization energy. More than 20 kcal mol1 are released in forming
the norbornadiene, which makes the switching process almost
independent of the presence of a guest ion. Additional
prerequisites for the application of this photosystem as an
active ion carrier are the high lipophilicity of the ligand, a
considerable difference in the complexation energy of the two
isomers, and the high yields of the switching process. Amide
substituents are promising for this photoswitchable system
because they can act as chromophores for effective photoisomerization and are also efficient donor ligands for alkalimetal cations.[4] In this context calixarene derivatives[5] (some
of them even conformationally switchable[6]) have been
studied.
Norbornadiene tetramide 1 was prepared from the
corresponding tetracarboxylic acid 2 (Scheme 1). After generation of the acid chloride in situ by chlorination with oxalyl
dichloride, the reaction mixture was treated directly with
diisopropylamine. Quadricyclane tetramide 3 was synthesized
photochemically from 1. According to the 1H NMR spectra,
this conversion—a photochemical [2 + 2] cycloaddition—was
[*] Prof. Dr. R. Herges, Dr. T. Winkler
Institut f'r Organische Chemie
Christian-Albrechts-Universit,t Kiel
Otto Hahn-Platz 4, 24098 Kiel (Germany)
Fax: (+ 49) 431-880-1558
E-mail: rherges@oc.uni-kiel.de
I. Dix
Institut f'r Organische Chemie
Technische Universit,t Braunschweig
Hagenring 30, 38106 Braunschweig (Germany)
Prof. Dr. P. G. Jones
Institut f'r Anorganische und Analytische Chemie
Technischen Universit,t Braunschweig
Hagenring 30, 38106 Braunschweig (Germany)
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2003, 42, 3541 –3544
Scheme 1. Synthesis of norbornadiene and quadricyclanediisopropyl
tetramides 1 and 3 from tetracarboxylic acid 2. )))) = ultrasonic radiation.
almost quantitative (> 95 %, 85 % yield after purification by
chromatography); side products were not detected. The
cycloaddition proceeds with the same efficiency in the
presence of Na+ ions under the same conditions. The reverse
reaction (3!1, Scheme 2) was achieved with UV light of
shorter wavelength (mercury low-pressure lamp, quartz filter)
with a yield of 50 % (photostationary equilibrium). Upon
prolonged irradiation the elimination of propene (Norrish
Type-II reaction) was observed as a minor side reaction.
Scheme 2. Photoinduced interconversion of norbornadiene tetraamide
1 and quadricyclane tetramide 3.
In view of the complexation of metal cations, the spatial
arrangement of the substituents and the size of the cavity they
form is particularly interesting. The structures of tetramides 1
and 3 were elucidated by X-ray analysis. The symmetry of
norbornadiene tetramide 1 is lowered to C2, and quadricyclane tetramide 3 exhibits a similar, approximately C2-symmetrical structure. For steric reasons two carbonyl oxygen
atoms diagonal to each other point toward the center of the
cavity and the other two point outward. Consequently the
bulky diisopropyl groups assume a sterically favorable alternating orientation (Figure 1, top). The distance between the
two oxygen atoms pointing towards the interior is 5.66 = in 1
and 5.53 = in 3. In addition, the crystal of norbornadiene
tetramide 1 contains disordered solvent molecules (diethyl
ether or pentane).
DOI: 10.1002/anie.200350959
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3541
Communications
cavity and coordinate the Na+ ion. The Na+ ion in this
complex has the coordination number 5 and nearly squarepyramidal coordination geometry. The symmetry of the
complex is C2 ; the thiocyanate ion, the Na+ ion, and the two
carbon atoms of the isopropyl group lie exactly on the C2 axis.
The distances between the oxygen atoms and the Na+ ion are
2.40 and 2.49 =, that between the Na+ ion and the nitrogen
atom of the thiocyanate is 2.32 =; the O-Na-O angles between
the diagonally facing oxygen atoms are 135.1 and 142.38. The
four carbonyl oxygen atoms almost exactly define a plane,
which is located 0.44 = above the Na+ ion.
The complexation properties of the quadricyclane and
norbornadiene tetramides were investigated by the picrate
extraction method. A solution of the ligand in chloroform was
used to extract the yellow alkali-metal picrates (Li+Pic ,
Na+Pic , K+Pic , and Cs+Pic) from an aqueous solution.
UV/Vis spectroscopy was used for quantification. The extraction constant Kex and the association constant Kass were
determined according to the method of Cram et al. [7] This
method was also used to investigate the complexation
properties of ether-substituted quadricyclane und norbornadiene derivatives.[8] The Kex and Kass values for norbornadiene
tetramide 1 are always higher than those for quadricyclane
tetramide 3 (Table 1). In the experiments with 3 the
association constants increase with decreasing ion radius. In
Table 1: Extraction constants Kex and association constants Kass for the complexation of alkali-metal cations by 1 and 3 in chloroform.
Cation Kex [L2 mol2]
Kex [L2 mol2]
Kass [L1 mol1]
quadricyclane 3 norbornadiene 1 quadricyclane 3
Li+
Na+
K+
Cs+
13.90 0.54
8.57 0.25
5.13 0.32
6.87 0.25
14.06 0.38
23.31 1.07
6.22 0.16
18.54 0.46
Kass [L1 mol1]
norbornadiene 1
9786.80 281.04 9899.50 172.16
4925.86 120.74 13394.15 425.35
2013.43 83.45
2440.01 41.26
1040.72 30.50
2809.50 52.01
contrast, norbornadiene 1 binds most strongly to Na+,
indicating a cavity of a defined size. For Li+ the association
constants of 1 and 3 are almost identical, whereas the values
for Na+ coordination are distinctly different (Figure 2).
The size selectivity of the tertiary amides 1 and 3 in the
coordination of alkali-metal ions is opposite to that of the
Figure 1. Crystal structures of tetramides 3 and 1 and the complex
[1-NaSCN].
Can 1 assume a conformation in which all four carbonyl
oxygen atoms are available for coordination to a suitable
cation? This question was answered by the X-ray structure
analysis of a sodium complex of norbornadiene 1 (Figure 1,
bottom). In contrast to the arrangement in the free ligand all
four carbonyl oxygen atoms in [1-NaSCN] point into the
3542
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Figure 2. Association constants Kass for the complexation of alkalimetal ions by the tetramides 1 and 3 in chloroform.
www.angewandte.org
Angew. Chem. Int. Ed. 2003, 42, 3541 –3544
Angewandte
Chemie
ether-substituted norbornadienes and quadricyclanes.[8] The
association constants of the “open” form (norbornadiene) are
larger than those of the “closed” isomer (quadricyclane).
Apparently the cavity of quadricyclane 3 is too small for
binding cations larger than Li+. Moreover, the conformation
necessary for the complexation of a cation, in which all four
carbonyl oxygen atoms point towards the center of the cavity
and the bulky isopropyl groups are directed outwards, is less
favorable in the quadricyclane than in the norbonadiene
(Scheme 3).
Scheme 3. Representation of the switching and complexation processes of 1 and 3. The isopropyl groups are not shown for clarity. The
convergent orientation of all four carbonyl groups for the complexation
of Na+ in the interior of the ligand is more strongly hindered by the
bulky isopropyl groups in the quadricyclane 3 than in the norbornadiene 1. Moreover, the cavity in the quadricyclane 3 is considerably
smaller.
C-2,3,5,6), 98.31 (Cq, C-8), 56.30 (CH, C-1,4), 50.50, 45.48 (CH, C-11),
21.30, 21.02, 20.66, 20.26 (CH3, C-12) 18.37 ppm (CH3, C-9); MS (EI,
70 eV): m/z(%) = 640 (25) [M+], 541 (50), 498 (15), 442 (28), 413 (52),
355 (20), 313 (19), 260 (55), 218 (25), 176 (20), 158 (42), 100 (75), 86
(28), 58 (12), 43 (100); IR (KBr): ñ = 2961 (s), 2932 (m), 1628 (ss),
1440 (s), 1371 (m), 1344 (s), 1329 (s), 1208 (m), 1156 (w), 1136 (w),
1037 (m), 815 (w), 781 (w), 610 (w), 570 cm1 (w); HRMS:
C38H64N4O4 ; calcd for [M+]: 640.4927, found: 640.4913 3 ppm;
UV/Vis (CH2Cl2): lmax (e) = 250 nm (sh, 11 965), 285 nm (sh,
2680 L mol1 cm1); elemental analysis calcd (%) for C38H64N4O4 : C
71.21, H 10.06, N 8.74; found: C 71.31, H 10.20, N 8.76 %.
3: Compound 1 (150 mg, 0.23 mmol) was dissolved in anhydrous
THF (~ 5 mL). The solution was pipetted into five NMR tubes
(normal glass) and irradiated with a mercury high-pressure lamp
(150 W, Pyrex filter) for 2 h in an ice bath. The solvent was removed in
vacuo, and the remaining starting material was separated by flash
column chromatography (silca gel, cyclohexane/ethyl acetate 3:1,
Rf = 0.27). The colorless solid was dried in high vacuum. Yield:
125 mg (0.20 mmol, 85 %); m.p.: > 200 8C (decomp.); 1H NMR
(CDCl3): d = 4.09 (br, 4 H, 11-H), 3.38 (sept, 3J(H,H) = 6.8 Hz, 4 H,
11-H), 2.69 (s, 2 H, 2,4-H), 1,97 (s, 6 H, 9-H), 1.39 (d, 3J(H,H) = 6.8 Hz,
12 H, 12-H), 1.36 (d, 3J(H,H) = 6.8 Hz, 12 H, 12-H), 1.29 (br, 12 H, 12H), 1.11 ppm (d, 3J(H,H) = 6.3 Hz, 12 H, 12-H). 13C NMR (CDCl3):
d = 164.24 (Cq, C = O), 133.06 (Cq, C-8), 126.72 (Cq, C-3), 49.57, 47.54
(Cq, C-1,5,6,7), 46.02 (CH, C-1,4), 37.97 (CH, C-11), 22.58 (CH3, C-9),
21.53, 20.66, 20.57, 20.43 ppm (CH3, C-12); MS (EI, 70 eV): m/z(%) =
640 (15) [M+], 597 (9), 541 (29), 496 (33), 442 (19), 413 (45), 355 (26),
313 (17), 270 (22), 260 (52), 218 (26), 158 (44), 100 (100), 72 (68); IR
(KBr): ñ = 3447 (br), 2965 (s), 1638 (ss), 1438 (s), 1374 (m), 1325 (s),
1215 (m), 1038 cm1 (m); UV/Vis (EtOH): l (e) = 207 nm
(29 047 L mol cm1); HRMS: calcd for C38H64N4O4 : [M+]: 640.49276,
found 640.49250 3 ppm.
Reisomerization 3!1: A solution of 3 (20 mg, 0.03 mmol) in
anhydrous THF (1 mL) was irradiated in an NMR tube (normal glass)
with a low-pressure mercury lamp (15 W, quartz filter) for 4 h.
According to the 1H NMR spectrum (CDCl3), the conversion to 1 was
50 %. Upon prolonged irradiation (8 h) the norbornadiene/quadricyclane ratio does not change. However, small amounts (< 10 %) of 7isopropylidenenorborna-2,5-diene-2,3,5,6-tetracarboxylic acid tetrakis(isopropyl amide) were observed.
Received: January 16, 2003 [Z50959]
.
Keywords: amide ligands · association constants ·
photochemistry · sodium · valence isomerization
Experimental Section
1: Compound 2 (750 mg, 2.44 mmol) and potassium carbonate (3.00 g,
21.73 mmol) were suspended in anhydrous dichloromethane (25 mL)
and cooled to 0 8C with ice and water in an ultrasound bath. Upon
sonification oxalyl dichloride (0.9 mL, 10.39 mmol) and then dimethylformamide (2–3 drops) were added with a syringe. There was a
strong generation of gas in the cloudy mixture which ceased after
about an hour. A solid precipitated from the clear supernatant
yellow–green solution. Diisopropyl amine (5.0 mL, 48.42 mmol) was
added with a syringe to the solution of the acid chloride. A fine,
colorless precipitate formed thereafter. The mixture was stirred for
another 2 h and allowed to warm to room temperature. The
precipitate was filtered off and the filtrate was concentrated in
vacuo. The crude product was purified by column chromatography
(silica gel, cyclohexane/ethyl acetate 1:1, Rf = 0.60). Yield: 380 mg
(0.59 mmol, 24 %); m.p.: 212 8C; 1H NMR (CDCl3): d = 4.15 (s, 2 H,
1,4-H), 3.89 (sept, 3J(H,H) = 6.6 Hz, 4 H, 11-H), 3.40 (sept, 3J(H,H) =
6.8 Hz, 4 H, 11-H), 1.55 (s, 6 H, 9-H), 1.44 (d, 3J(H,H) = 6.8 Hz, 12 H,
12-H), 1.40 (d, 3J(H,H) = 6.8 Hz, 12 H, 12-H), 1.15 (d, 3J(H,H) =
6.9 Hz, 12 H, 12-H), 1.13 ppm (d, 3J(H,H) = 6.9 Hz, 12 H, 12-H);
13
C NMR (CDCl3): d = 166.50 (Cq, C-10), 162.14 (Cq, C-7), 144.01 (Cq,
Angew. Chem. Int. Ed. 2003, 42, 3541 –3544
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