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NMR spectroscopic study of solution structure and complexational behaviour of bis-benzo crown ethers
J o u r n a l of
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular Structure 404 (1997) 273-290
NMR spectroscopic study of solution structure and complexational behaviour of bis-benzo crown ethers E. Kleinpeter a'*, I. Starke a, D. Str6hl b, H.-J.
Holdt c
~lnstitut fiir Organische Chemie und Strukturanalytik, Universitiit Potsdam, Am Neuen Palais 10, D-14469 Potsdam, Germany blnstitut fiir Organische Chemie, Martin-Luther-Universitiit Halle-Wittenberg, Weinbergweg 16, D-06122 Halle/Saale, Germany CChemische lnstitut, Universiti~t Rostock, Buchbinder Strasse 9, D-18055 Rostock, Germany
Received 29 June 1996; accepted 16 August 1996
Abstract The tH, t3C and tSN NMR spectra of a series of polymethylene-bridged carbonylhydrazone bis(benzo-15-crown-5 ethers) 1-9 (n = 0-8) and bis(benzo-18-crown-6 ethers) 10-11 (n = 1,5) were recorded and assigned by COSY, HMQC and HMBC 2D NMR experiments. The stereoisomerism of the bridging R - C H = N - N H - C ( = O ) - ( C H 2 ) , moieties was studied by various useful NMR parameters (rc-o, 3Jc.H, IJN-H, IJc H, 2Jc(=O)-NH)and intramolecular NOEs. Three isomers (E/E, E/Z and Z/Z, respectively) with respect to the amide bond proved to exist, NH and the imine lone pair were found in anti position. The -OCH2CH20- fragments occur as rapidly interconverting gauche conformations and the ot-CHz groups more or less in-plane with the adjacent phenyl ring moiety as concluded from the corresponding ~3C chemical shifts and NOEs, respectively. The solvent dependence of the amide isomerism was studied and the complexation of the bis-benzo crown ethers to Na + and K + cations carefully investigated. The conformation of the free and complexed bis-crown ethers was obtained. Both the complexation mechanism (sandwich, double-sandwich, inclusion and addition complex) and the conformational equilibrium about the =CH-Ph bond proved to be strongly dependent on the bis-benzo crown ethers 1-11 studied. The conformational study is accompanied and corroborated by molecular dynamics and quantum-chemical calculations. © 1997 Elsevier Science B.V. Keywords: NMR spectroscopy; Conformational isomerism; Bis-benzo crown ethers
I. Introduction Bis-benzo crown ethers have been widely studied owing to their ability to form complexes selectively with alkali metal cations [1-6]. These compounds consist of two crown ether units in the same molecule and provide, besides the conventional inclusion of the cations within the cavity of the crown ether moieties, also the opportunity to forming " s a n d w i c h " - l i k e * Corresponding author. Fax: +49 331 977 1516.
complexes with cations of radii larger than the cavity size of the single crown ether units [7-10]. The stability of these complexes is higher (due to the " b i s - c r o w n e f f e c t " ) than the stability of simple addition complexes where the cations, due to radii larger than the cavity size, are positioned only above the cavity of the crown ether units. Hereby the linking chain is also of deciding influence on both the formation and the stability of the " s a n d w i c h " - l i k e complexes; limited flexibility and the existence of preferred conformations can prevent the non-distorted
0022-2860/97/$17.00 Copyright © 1997 Elsevier Science B.V. All rights reserved PII S0022-2860(96)09444-6
274
E. Kleinpeter
et al./Journal
of Molecular
formation. It is the objective of this paper to test the - C H = N - N H - C O - ( C H 2 ) , - C O - N H - N = C H moiety as a linking chain for two benzo crown ether units in this respect. For this reason, the stereochemistry (isomerism, conformation) of a series of polymethylene-bridged carbonylhydrazone bis(benzo-15-crown-5 ethers) 1-9 (n = 0-8) and two bis(benzo-18-crown-6 ethers) 10-11 (n = 1,5) (cf. Scheme 1)was studied in solution both in the free and the Na ÷ (K ÷) complexed state employing the whole arsenal of 2D NMR methods, a variety of useful NMR parameters and intramolecular NOEs. Hereby, the complexation mechanism (inclusion, addition, "sandwich"-like and double-"sandwich"-like complex, respectively) was of special interest.
2. Experimental The synthesis of compounds 1-11 has been published already previously [11]. The alkali salts used for the complexation studies were dried over P40~0 and the solvents over Call2 or mole sieve. The ill, ~3C and ~SN NMR spectra were recorded at 300.13, 75.47 and 30.41 MHz, respectively (BRUKER ARX
R =
OH 2
Bis-benzo crown ether
compound
n
m
Bis(benzo- l 5-crown- 5+ether)
I
0
I
Isomer [~Eundl:Z
2
I
I
E,~-,EZundZZ
3
2
1
-"-
4
3
I
-"-
5
4
I
-<-
6
5
1
-"-
7
6
I
-"
8
7
I
-"-
9
8
I
-"-
Bis(benzo- 18-crown-6-ether)
1o
I'
II Scheme
5 1.
Structure
404 (1997)
273-290
300) in CDC13/CD3OD (4 : 1) solution (5 mm probe tubes, ambient temperature, deuterated solvents as internal lock); in cases of less soluble compounds also spectra at 600 and 750 MHz were recorded employing aRUKER DMX 600 and 750 NMR spectrometers. Typical conditions 13C: 30 ° pulse, 2 s repetition time, sufficient number of scans, 32K data points, 18750 Hz spectral range and 0.57 Hz per point digital resolution. The 15N NMR spectra were also recorded at 60.81 MHz (on a UNITY 600 VARIAN spectrometer) in natural abundance (solvent DMSO-d6 versus NO2CH3 as reference; 10 mm probe tubes at ambient temperature). Typical conditions: 45 ° pulse, 4 s repetition time, 32K data points, 9259 MHz spectral range and 0.28 Hz per point digital resolution. The 1H, 13Cand 15NNMR spectra were assigned by H,H-COSY, HMQC and HMBC 2D NMR experiments using the BRUKER standard software. Typical settings: (HMQC) sweep width in Fi 18 kHz and in F2 6.9 kHz, 8K data points in F2, 512 experiments in F2 (8 or 16 scans), relaxation delay 0.2 s, pulse width ( IH, 90 °) 11.0/~s, (13C) 9.5/zs, zero filling, filter function sine-bell in both dimensions. For the ~SN NMR spectra the sweep width in F ~is 1 kHz and in F2 7 kHz, pulse width P1 (90, 15N) 10.2/zs, 8K data points in F2 and 128 experiments in Fl. The 2D ROESY NMR experiments were processed in phase-sensitive mode (BRUKER standard software); the samples were degassed at least 3 times and sealed under argon. Typical conditions: sweep width in F~ and in F2 7 kHz, 1K data points in F I and 2K data points in F2, zero filling in Fl, relaxation delay 2 s, mixing time 200 ms, filter function sine-bell in both dimensions. The molecular dynamics calculations (simulated annealing) were carried out with the TRIPOS force field [12] starting at 1000 K and cooling down to 200 K for 1000 fs. The default setup used a constant N, V, T ensemble based on Berendsen's method [13]. Quantum-chemical calculations were carried out with MOPAC 7.0 program package [14] using Silicon Graphics work stations IRIS INDIGO XS 4000 [15].
3. Results and discussion 12 2
I'DE.E. Z u n d Z Z
-"-
The IH NMR spectra exhibit 4 characteristic absorption ranges: the NH protons at ~ = 9.75-
\ DO m
_ _ _ . _
< / .t / t /-
_
727
~ I 0
002
~-;~
~ \ \ k \ k \
I
9. B99 9. 829 7 999
7.96i
i
\m.
7. ?52 7.69,~
;j
7. 559
\ \
7.531 7 363 ; 263 7 23,d
\
\
\ \ \
\
\
d¸ "I
\I - J
z
~, 108
7.081 7.05~
z
6.881 68~9
6.822 6 ~99 r- ~ 223 ~ 209
0 e~
z 179
Z
3 g38
~
3 930 3 7~) 3689
< /
r
35~s
-----I- 3 373 . ~ 2 775
E
2 75~ 2 728
..~
r~
2 306 2 28g 2 266 ~ 760 ?38
I 6}96 1 474 J
] 431 I 408
K .........
~LE
L_ I 259
[i-
06~-FZE (/66I) #0/~ a.~nj.~nJ.~E.~OlnJdlOl4/ /o 1DuJ,ol'/'l D la Jdlddu!dlX "~
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
276
11.37 ppm, the OCH2 crown ether protons (H-10-H13 at ~i = 3.67-4.45 ppm), the H-3 methin protons (6 = 7.65-8.06 ppm), the aromatic protons H-5-H-9 at ~ = 6.77-7.68 ppm, and the methylene protons of the linking chain below 2.77 ppm (cf. Fig. 1 for 11). The latter protons are lowfield shifted dependent on their position to the adjacent carbonyl groups (the linking chain protons were assigned in detail by the corresponding H,H-COSY experiments). The aromatic protons H-5, H-8 and H-9 can be readily differentiated by the vicinal H,H coupling (H-8 at higher field due to the ortho-OR substituent);
the substitution pattern for the aromatic rings proved unequivocal. The multiplets of the crown ether fragments H-10H-13 are shifted to higher field with respect to the aromatic ring current effect; the H,H coupling constants as extracted from the AA'BB' subspectra indicate gauche fragments - O - C H 2 - C H 2 - O - , readily interconverting on the NMR time scale at ambient temperature. Due to the highfield position of both ot-OCH2 carbon resonances and those of C-5 and C-8, respectively, the more or less in-plane position of these fragments in the bis-crown ethers
Table 1 IH NMR spectra (6 (ppm) and JH,H (Hz)) of the bis-benzo crown ether 1 - 9 in CDCIflCD3OD (80 : 20) No.
NH
H-3
H-5
H-8
H-9
H-10
H-11
H-12
H-13
3j(H8,H9) 4j(H5,H9)
1 2 E/E E/Z
11.35
8.24
7.55
6.86
7.21
4.24
4.21
3.95
3.77
8.3
-
11.30 11.15 10.46 10.35
8.00 8.00 7.79 7.73
7.55 7.51 7.29 7.28
6.85 6.85 6.80 6.80
7.13 7.13 7.10 7.10
4.20
4.11
3.98
3.74
8.3 8.3 8.4 8.4
1,6 1,5 1,7 1,7
11.30 11.17 10,50 10.42
7.97 7.96 7.78 7.78
7.56 7.54 7.31 7.31
6.87 6.87 6.83 6.83
7.13 7.13 7.11 7.11
4.22
4.19
3.94
3.79
8.06 8.06 8.24 8.24
1.65 1.65 1.47 1.47
11.23 11.17 10.40 10.37
7.98 7.98 7.80 7.79
7.59 7.59 7.29 7.29
6.91 6.91 6.85 6.85
7.13 7.13 7.10 7.10
4.23
4.18
3.93
3.77
8.29 8.29 8.36 8.36
1.53 1.53 1.56 1.56
10.87 10.61 9.80 9.75
7.96 7.95 7.73 7.65
7.56 7.53 7.25 7.22
6.86 6.86 6.81 6.81
7.13 7.13 7.08 7.08
4.40
4.19
3.93
3.77
8.14 8.14 8.21 8.21
1.76 1.76 1.81 1.81
11.05 10.93 10.13 10.07
7.96 7.96 7.78 7.76
7.59 7.58 7.28 7.26
6.90 6.90 6.87 6.87
7.15 7.15 7.10 7.10
4.19
4.11
3.97
3.77
8.26 8.26 8.28 8.28
1.34 1.34 1.27 1.27
11.36 11.32 10.50 10.40
7.97 7.95 7.73 7.71
7.68 7.55 7.25 7.22
6.87 6.87 6.81 6.81
7.16 7.16 7.12 7.12
4.44
4.18
3.90
3.73
8.21 8.21 8.32 8.32
1.10 1.10 1.20 1.20
10.95 10.83 10.06 10.02
7.98 7.98 7.78 7.77
7.56 7.55 7.29 7.25
6.94 6.94 6.88 6.88
7.12 7.12 7.10 7.10
4.35 4.20
4.19 4.17
3.91
3.74
8.14 8.14 8.34 8.34
1.55 1.55 1.54 1.54
Z/Z 3 E/E E/Z Z/Z 5 E/E E/Z 7JZ 6 E/E E/Z
Z/Z 7 E/E E/Z Z/Z 8 E/E E/Z Z/Z 9 E/E E/Z Z/Z
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
277
Table 2 ~H NMR spectra (6 (ppm) and JH.H (Hz)) of the CH2 protons in the linking chain of the bis-benzo crown ethers 1-9 in CDCIflCD3OD (80 : 20) No.
CH2 A
CH2 B
CH2 C
CH2 D
CH2 D
CH2 C
CH2 B
CH2 A
3J(H,H)
1 2
E/E E/Z Z/Z
3.35 3.35 4.05
4.05
E/E E/Z Z/Z
2.67 2.67 3.19
2.67 3.19 3.19
7.15,7.20 7.15,7.20 7.14,7.15
E/E E/Z Z/Z
2.38 2.38 2.77
2.10 2.11 2.11
2.38 2.77 2.77
7.17,7.20 7.17,7.20 7.22,7.21
E/E E/Z Z/Z
2.34 2.36 2.82
1.77 1.77 1.82
1.77 1.82 1.82
2.34 2.80 2.82
7.16,7.20 7.16,7.20 -
E/E E/Z Z/Z
2.28 2.31 2.76
1.75 1.75 1.76
1.44 1.44 1.44
1.75 1.76 1.76
2.28 2.75 2.76
7.20,7.29 7.20,7.29 7.41,7.41
E/E E/Z Z/Z
2.27 2.27 2.74
1.76 1.76 1.76
1.44 1.44 1.44
1.44 1.44 1.44
1.76 1.76 1.76
2.27 2.74 2.74
7.26,7.23 7.26,7.23 7.47,7.56
E/E E/Z Z/Z
2.27 2.27 2.73
1.71 1.71 1.71
1.40 1.40 1.40
1.40 1.40 1.40
1.40 1.40 1.40
1.71 1.71 1.71
2.27 2.73 2.73
7.20,7.20 7.20,7.20 7.47,7.56
E/E E/Z Z/Z
2.26 2.29 2.73
1.69 1.69 1.70
1.35 1.35 1.35
1.35 1.35 1.35
1.35 1.35 1.35
1.69 1.70 1.70
2.26 2.72 2.73
7.37,7.37 7.37,7.37 7.17,7.17
1.35 1.35 1.35
a Overlapping signals.
Table 3 IH NMR spectra (6 (ppm) and the nJH.H (Hz)) of the bis-benzo crown ethers 10 and 11 in CDCIflCD3OD (80:20) No.
10
11
E/E E/Z Z/Z E/E E/Z Z/Z
NH
H-3
H-5
H-8
H-9
H-10
H-I 1
H-12
H-13
H-14
3J(H8,H9)
~J(H5,H9)
11.30 I 1.20 10.63 10.57 11.12 10.85 9.98 10.07
8.01 8.01 7.81 7.78 8.06 8.00 7.30 7.79
7.51 7.55 7.29 7.29 7.48 7.51 7.25 7.23
6.83 6.83 6.78 6.78 6.83 6.83 6.80 6.77
7.09 7.09 7.03 7.03 7.12 7.12 7.05 7.05
4.21
4.16
3.99
3.73
3.68
4.18
3.91
3.75
3.71
3.67
8.2 8.2 8.3 8.3 8.1 8.1 8.2 8.2
1.33 1.33 1.22 1.22 1.33 1.33 1.21 1.21
278
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
Table 4 ~H NMR spectra (¢5 (ppm), Jn.n (Hz)) of the protons in the linking chain of the bis-benzo crown ethers 10 and 11 in CDCI 3/CD3OD (80 : 20) No. 10
11
CH2 A
CH2 B
E/E E/Z Z/Z
3.39 3.39 4.02
4.02
E/E E/Z Z/Z
2.28 2.30 2.77
1.70 1.70 1.78
1-11 can be concluded [16]; from NOEs H-5/~-CH2 and H-8/t~-CH2 comes the same information. Proton chemical shifts and relevant coupling constants are given in Tables 1-4. Especially from the resonances of the H-3 and NH protons (4 each, two signals of same intensity), on the existence of the studied compounds in the 3 possible configurations with respect to the amide bonds can be readily concluded: E/E, E/Z and Z/Z, respectively (cf. 2 2). The same information comes from the resonances of the other protons of 1-11 which are also splitted into the correct number of signals. The presence of 3 different isomers in 1-11 can be also concluded from the corresponding number of signals for the carbonyl resonances but also the aromatic carbon atoms in the t3C NMR spectra; H I NR~N 4 H 2 ~ N
Eo
CH2 C
CH2 B
CH2 A
3j( H A,H A)
1.44 1.44 1.46
1.70 1.78 1.78
2.28 2.76 2.77
7.26,7.26 7.26,7.26 7.03,7.03
having the correct assignment of the IH NMR spectra in hand, the 13C NMR spectra were assigned by employing both HMQC and HMBC 2D NMR correlation experiments (cf. Tables 5-7). Especially the HMBC connectivities of NH/C=O, NH/C 3 and CH~/C=O, respectively, were very useful for assigning the three sets of resonances to the isomers. The quaternary carbon atoms C-6,7 were unequivocally assigned by employing the semi-selective INEPT experiment (optimized on nJc,H = 8 Hz) [17] by selectively irradiating the aromatic protons H-5, H-8 and H-9, respectively. For assigning the stereochemistry of the studied bis-benzo crown ethers 1-11 from both the IH and 13C NMR spectra, a number of useful NMR parameters were employed.
H I
H NR ' , N R "~N "~( C H 2~..,.."N x n
"NR
oE
E; NR I
I
H-N~CH2~NZ o
0
NOE - H R/
c~k
;z
NR
I
2.~/N
o
H Z
H O%c/N
I
c a?\ R
3j CI~.NH
< 0.5 Hz Scheme 2.
~7Hz
279
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
3.1. Isomerism of the amide bonds
3.1.1. 13C chemical shift of carbonyl carbon atoms
In order to prove this isomerism, the positions of the signals of both the C=O carbon and the NH proton were considered (cf. Scheme 2).
The 13C chemical shifts of the E/Z isomers of formamide and acetamide were assigned by DORMAN and BOVEY [18]; adequately the highfield carbonyl resonances (6 = 164.1-171.6 ppm) of the bis-benzo
Table 5 I~C chemical shifts b (ppm) of the bis-benzo crown ethers 1 - 9 in CDCI3/CD3OD (80: 20) No.
C-1
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
C-I 1
C-12
C-13
1
E/E Z/E Z/Z
155.5
149.5
126.9
110.9
152.1
152.7
112.7
124.4
68.7 68.9
69.6 69,7
70.5
71.0 71.1
2
E/E E/Z
164.1 164.1 169.9 170.7
149.8 148.8 145.8 144.7
127.7 127.4 127.3 127.1
110.7 110.6 110.4 110.4
149.8 149.8 149.4 149.4
151.5 151.4 151.3 151.1
112.9 112.9 112.7 112.7
123.7 123.5 122.9 122.7
68.7 68.9
69.7
70.3
70.9 71.0
169.8 170.1 175.1 175.4
148.9 148.2 145.1 144.7
127.8 127.8 127.6 127.6
110.9 110.9 110.8 110.8
149.4 149.4 149.4 149.4
151.4 151.3 151.2 151.2
113.0 113.0 112.8 112.8
123.5 123.4 122.7 122.6
68.6 68.8
69.4 69.6
70.5
71.0
170.6 170.7 175.9 176.0
148.6 148.1 144.9 144.4
127.8 127.6 127.4 127.4
111.7 111.4 111.2 110.8
149.5 149.4 148.6 148.1
152.3 152.3 151.5 151.5
113.2 113.0 112.9 112.9
123.4 123.3 122.4 122.3
68.8 69.0
69.6 69.7
70.5
71.1 71.2
171.1 171.3 176.6 176.6
148.7 148.3 145.0 144.7
127.7 127.6 127.5 127.5
110.9 110.9 110.7 110.7
149.3 149.3 149.3 149.3
151.3 151.2 151.1 151.1
113.0 113.0 112.7 112.7
123.4 122.5 122.4 122.4
68.6 68.7
68.9
69.5 70.4
70.9 71.0
171.2 171.3 176.6 176.7
148.3 148.1 144.7 144.5
127.6 127.4 127.5 127.5
110.9 110.9 110.5 110.5
149.3 149.3 149.2 149.2
151.2 151.0 150.9 150.9
113.0 113.0 112.6 112.6
123.2 123.2 122.2 122.2
68.5 68.8
69.3 69.4
70.2
70.7 70.9
171.4 171.6 176.9 177.0
148.5 148.2 144.8 144.6
128.7 127.8 127.7 127.7
111.1 111.1 110.7 110.7
149.5 149.5 149.4 149.4
151.3 151.3 151.2 151.2
113.2 113.2 112.7 112.7
123.5 123.5 122.6 122.4
68.7 68.8
69.1 69.6
70.5
71.1 71.1
171.4 171.6 177.0 177.0
148.3 148.2 144.7 144.6
127.7 127.7 127.5 127.5
110.9 110.9 110.5 110.5
149.3 149.3 149.2 149.2
151.2 151.0 150.9 150.9
113.0 113.0 112.6 112.6
123.3 123.3 122.4 122.4
68.6 69.1
69.7 69.8
70.3
71.1 71.2
171.5 171.6 177.0 177.0
148.2 148.1 144.5 144.4
127.8 127.7 127.6 127.6
111.5 111.2 111.1 110.8
149.4 149.4 149.3 149.3
151.3 151.3 151.2 151.2
113.1 113.1 112.8 112.8
123.2 123.1 122.4 122.3
68.7 68.9
69.6 69.7
70.3 70.5
71.0 71.1
Z/Z 3
E/E E/Z Z/Z
4
E/E E/Z Z/Z
5
E/E E/Z Z/Z
6
E/E E/Z Z/Z
7
E/E E/Z Z/Z
8
E/E E/Z Z/Z
9
E/E E/Z Z/Z
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
280
crown ethers 1-11 were assigned to the E isomers, the lowfield absorptions (t5 = 169.9-177.0 ppm) to the Z analogues.
3.1.2. Vicinal CH coupling between ot-CH2 carbon and NH proton The corresponding trans coupling constant 3Jc,H ( - 7 Hz) in Z configuration was found characteristically larger than the analogous cis coupling ( - < 0.5 Hz) in the E isomer [18,19] (cf. Scheme 2). Values detected for 2-11 are 5.9-7.7 Hz in cases of Z configuration; no cross peaks could be detected for
the corresponding E isomers, both in agreement with Ref. [19].
3.1.3. 15N chemical shift and direct N - H coupling constant Both the 15N chemical shifts [19] and the 1JN,H coupling constants [20] have been successfully employed in order to estimate the configuration at the amide bond in the case of planar arrangement [21]. The corresponding parameters for 1-11 were determined by HMQC- 15N,IH experiments: tS(15N) of the Z isomer was found at higher field ( - 201.6-
Table 6 t3C chemical shifts/~ (ppm), and Jc.H (Hz) coupling constants of the linking chains of the bis-benzo crown ethers 1-9 in CDCI3/CD3OD (80 : 20) No.
1
2 E/E E/Z Z/Z 3 E/E E/Z Z/Z 4 E/E E/Z Z/Z 5 E/E E/Z Z/Z 6 E/E E/Z Z/Z 7 E/E E/Z Z/Z
CH2 A
CH2 B
CH2 C
CH2 D
CH2 D
CH2 C
CH2 B
CH2 A
IJ(C3,H3)
IJ(CA,HA)
158.0
-
41.71 41.2 40.7
160.0 159.8 161.5,161.5
127.0
30.1 28.6 27.6
160.0 169.1 160.0,162.0
128.0
33.9 31.7 31.7
163.7 163.0 159.0,159.0
130.0
25.8 24.9 24.5
34.9 32.7 32.5
161.0 160.6 160.5,160.0
127.0
28.9 28.5 28.5
34.6 32.5 32.4
161.0 161.3 164.0,164.2
132.0
25.8 25.5 24.9
29.1 28.6 28.6
34.8 32.8 32.7
162.5 162.3 160.3,160.4
130.0
25.9 25.8 25.0
29.5 28.9 28.9
34.9 32.8 32.8
160.0 164.3 160.2,162.3
129.0
29.3 29.1 29.1
29.6 29.5 29.5
35.0 32.9 32.8
165.3 165.2 164.5,164.5
127.0
30.1 29.3 27.6 33.9 33.5 31.7
21.7 21.7 20.9
34.9 34.4 32.5
25.8 25.4 24.5
34.6 34.4 32.4
28.9 28.9 28.5
25.6 25.1 24.3
34.8 34.6 32.7
29.1 29.1 28.6
25.8 25.5 24.9
34.9 34.8 32.8
29.5 29.5 28.9
25.9 25.9 25.0
25.9 25.8 25.0
35.0 34.9 32.8
29.6 29.6 29.5
29.3 29.3 29.1
25.9 25.7 25.0
125.0
126.0
129.2
130.0
129.0
126.0
8
E/E E/Z Z/Z 9 E/E E/Z Z/Z
25.9 25.1 25.0
126.0
125.0
Z/Z
Z/Z 11 E/E E/Z
10 E/E E/Z
NO.
149.3 149.1 146.0 144.7
148.5 148.2 144.7 144.4
171.0 171.3 176.6 176.7
C-3
164.2 164.4 170.9 170.8
C-I
127.7 127.7 127.7 127.7
127.7 127.7 127.3 127.0
C-4
111.1 110.9 110.5 110.5
110.7 110.6 110.5 110.1
C-5
149.2 149.2 149.2 149.2
150.9 150.9 150.1 150.1
C-6
151.0 151.0 151.0 151.0
151.7 151.7 151.5 151.4
C-7
113.2 113.1 112.6 112.6
112.7 112.9 112.6 112.6
C-8
123.3 123.3 122.4 122.4
123.7 123.5 122.9 122.7
C-9
68.9
68.9
C-10
69.2
69.6
C-I 1
69.7
69.7
C-12
70.1
70.8
C-13
.
70.9
70.9
C-14
.
32.7 28.7 24.5 28.7 32.7
34.9 29.4 25.6 29.4 34.9 34.7 29.1 25.4 28.7 33.9
39.8
41.7 41.2
CH2 CH2 CH2 CH2 CH2
Table 7 13C chemical shifts 6 (ppm) and IJc.H (Hz) coupling constants of the bis-benzo crown ethers 10 and 11 in CDCI¢CD3OD (80 : 20)
161.1 160.4 161.8 161.1
159.5 161.2 163.8 162.1
IJ(C-3,H-3)
122.6 122.6 120.9 120.9
131.3 131.3 129.6 129.6
IJ(CA,HA)
t,o
"~,
,,....-
E. Kleinpeter et aL/Journal of Molecular Structure 404 (1997) 273-290
282
Table 8 ~H C h e m i c a l shift d i f f e r e n c e s At5 ( p p m ) o f the b i s - b e n z o c r o w n e t h e r s 1 - 9 d u r i n g the c o m p l e x a t i o n w i t h N a ÷ c a t i o n s No.
H-3 a
H-3 b
H-5 ~
H-5
H-8
H-8
H-9
H-9
H-10
H-11
H-12
H-13
CH2-Z
CH2-E
1 : N a ÷ = (1 : 1)
0.09
-
-0.03 d
_
0.03
-
0.06
--
0.04
--0.90
.
.
.
1 : N a ÷ = (1 : 2)
0.14
-
0.20
-
0.18
-
0.13
-
0.08
-0.90
.
.
.
2 : N a + = (1 : 1)
0.15
0.10
-0.11
-0.02
0.01
0.01
0.03
0.03
-0.06
-0.03
-
-
< 0.00
< 0.00
2 : N a ÷ = (1 : 2)
0.22
0.20
0.02
0.02
0.13
0.12
0.13
0.15
0.14
-0.03
-
-
< 0.00
< 0.00
3 : N a ÷ = (1 : 1)
-0.02
-0.02
-0.01
-0.02
-0.02
-0.01
-0.01
-0.01
-0.03
-0.01
-
-
0.00
-0.01
3 : N a + = (1 : 2)
0.11
0.05
0.15
0.16
0.18
0.14
0.16
0.14
0.07
- c
-
-
0.00
0.03
4 : N a + = (1 : 1)
0.20
0.10
0.13
0.06
0.06
0.08
0.05
0.06
0.03
0.03
-
-
0.00
0.07
4 : N a ÷ = (1 : 2)
0.31
0.17
0.17
0.17
0.19
0.21
0.14
0.15
0.05
0.06
-
-
0.00
0.08
5 : N a ÷ = (1 : 1)
0.06
0.02
0.05
0.02
0.05
0.05
0.05
0.06
-0.03
-0.03
-
-
0.00
0.03
5 : N a ÷ = (1 : 2)
0.13
0.04
0.13
0.08
0.16
0.16
0.12
0.12
0.07
0.01
-
-
0.00
0.05
6 : N a ÷ = (1 : 1)
0.11
0.23
0.04
0.06
0.04
0.05
0.06
0.07
0.00
-0.04
-
-
-0.02
0.06
6 : N a + = (1 : 2)
0.26
0.38
0.08
0.16
0.12
0.11
0.13
0.13
0.04
-0.05
-
-
-0.06
0.09
7 : N a ÷ = (1 : 1)
0.16
0.05
0.05
0.07
0.06
0.07
0.09
0.09
0.00
0.02
-
-
0.00
0.05
7 : N a + = (1 : 2)
0.30
0.10
0.14
0.14
0.13
0.13
0.16
0.17
0.03
0.05
-
-
0.00
0.08
8 : N a ÷ = (1 : 1)
0.26
0.06
0.04
0.07
0.07
0.06
0.04
0.05
-0.01
-0.02
-
-
-0.02
0.03
8 : N a ÷ = (1 : 2)
0.37
0.16
0.13
0.13
0.13
0.13
0.12
0.13
0.03
0.05
-
-
-0.06
0.09
9 : N a ÷ = (1 : 1)
0.07
0.04
0.08
0.05
0.06
0.07
0.03
0.05
0.03
-0.01
-
-
0.00
0.02
9:Na÷=
0.16
0.08
0.19
0.13
0.17
0.17
0.14
0.16
0.11
0.13
-
-
0.00
0.04
H-12
H-13
CH2-Z
CH2-E
(1:2)
. .
C h e m i c a l s h i f t s o f the E s i d e o f the E / E u n d E / Z i s o m e r s . b C h e m i c a l s h i f t s o f the Z s i d e o f the E / Z a n d Z / Z i s o m e r s . c Overlapping signals. a At5 < 0 m e a n s shifts to h i g h e r field.
Table 9 IH C h e m i c a l shifts A6 ( p p m ) o f the b i s - b e n z o c r o w n e t h e r s 1 - 9 d u r i n g the c o m p l e x a t i o n w i t h K ÷ c a t i o n s No.
H-3 a
H-3 b
H-5
H-5
1 : K + = (1 : 1)
0.40
0.01
-0.18 d
0.07
-0.01
0.01
-0.22
-0.04
-0.24
.
.
.
.
1 : K ÷ = ( l : 2)
0.40
0.03
-0.29
-
0.07
-0.01
0.01
-0.22
-0.05
-0.24
.
.
.
.
2 : K ÷= (l : l)
-0.24
-0.17
-0.31
-
-0.28
-0.22
-0.24
-0.20
-
-0.09
-
-
< 0.00
< 0.00
2 : K ÷ = (1 : 2)
-0.29
-0.18
-0.31
-
-0.28
-0.22
-0.27
-0.27
-
-0.09
-
-
< 0.00
< 0.00
3 : K ÷ = (1 : 1)
0.00
0.00
-0.08
-0.08
-0.07
-0.04
-0.02
-0.02
0.00
-0.01
-
0.00
0.02
3 : K + = (1 : 2)
-0.01
0.00
-0.10
-0.10
-0.07
-0.04
-0.02
-0.02
0.00
-0.01
-
4 : K + = (1 : 1)
-0.02
-0.06
-0.10
-0.10
-0.01
-0.07
-0.05
-0.06
-0.06
-0.01
-
4 : K + = (1 : 2)
-0.02
-0.07
-0.10
-0.10
-0.02
-0.08
-0.10
-0.08
-0.01
-0.01
5 : K + = (1 : 1)
0.03
0.06
-0.08
-0.10
-0.06
-
--0.05
-0.05
-0.03
-0.03
5 : K ÷ = (1 : 2)
0.05
0.07
-0.08
-0.10
-0.06
-
-0.05
-0.05
-
6 : K + = (1 : 1)
0.08
0.06
-0.14
-0.14
-0.12
-0.13
-0.03
-0.03
0.00
6 : K + = (1 : 2)
0.08
0.06
-0.14
-0.14
-0.12
-0.13
-0.03
-0.03
0.00
7 : K ÷ = (1 : 1)
0.04
0.00
-0.13
-0.08
-0.06
-0.07
0.01
0.01
7 : K ÷ = (1 : 2)
0.04
0.00
-0.13
-0.08
-0.06
-0.07
0.01
8 : K ÷ = (1 : 1)
0.07
0.03
0.00
-0.01
-0.04
-0.20
8 : K + = (1 : 2)
0.07
0.03
0.00
-0.01
-0.04
-0.20
9 : K + = (1 : 1)
0.04
0.00
-0.09
-0.07
-0.10
-0.12
0.00
-0.04
0.01
9 : K + = (1 : 2)
0.04
0.00
-0.09
-0.07
-0.10
-0.12
0.00
-0.04
0.03
-
c
-
H-8
a C h e m i c a l s h i f t s o f the E side o f the E / E a n d E / Z i s o m e r s . b C h e m i c a l s h i f t s o f the Z side o f the E / Z a n d Z / Z i s o m e r s . c Overlapping signals. 0 At5 < 0 m e a n s s h i f t s to h i g h e r field.
H-8
H-9
H-9
H-10
H-11
-0.02
0.07
0.00
0.03
-
0.00
0.05
-
-0.02
0.04
-
-0.02
0.06
-0.18
-
0.00
0.07
-0.18
-
0.00
0.09
-0.02
-0.04
-
0.00
0.04
0.01
-0.02
-0.04
-
0.00
0.06
-0.06
-0.01
0.00
-
-
0.00
0.07
-0.06
-0.01
0.00
-
-
0.00
0.07
0.00
0.03
0.00
0.05
-
-0.04 -
-
-
-
+=(2:
ll:Na
1)
0.23,
0.34
0.26
0.33
0.13
0.12, 0.03 0.30, 0.16 0.29, 0.05 0.33, 0.11
E/E H-5
0.02 0.01 0.02
0.02 0.05 0.04 0.06
0.20 0.12 0.21
0.01 0.11 0.05 0.15
0.07 - 0 . 0 2
Z/Z H-3
a Negative shift means shift to higher field. h A8 of multiplet given. O v e r l a p p i n g signals.
+=(1:1)
ll:Na
I)
+ = ( 1 : l)
II:K +=(2:
ll:K
1)
: 1)
10:Na÷=(l
10:Na +=(2:
1)
10:K ÷=(2:
0.10
10 : K + = (1 : 1)
E/Z H-3
-0.02 a 0.24 0.41, 0.04 0.16 0.30, -0.02 0.25 0.42, 0.02
E/E H-3
No.
0.00, 0.01 0.09, 0.11 0.05, 0.03 0.09, 0.10
0.04 0.05, 0.11 0.05, 0.05 0.07, 0.07
-0.01,
E/Z H-5
E/E H-8
0.10
0.03
0.10
0.00
0.12
0.08
0.08
0.05
0.01
0.06
0.00
0.07
0.02
0.05
0.00 - 0 . 0 1 b
Z/Z H-5
0.00, 0.00 0.06, 0.05 0.02, 0.03 0.06, 0.08
0.00, 0.03 0.06, 0.09 0.04, 0.04 0.07, 0.07
E/Z H-8
E/Z H-9
0.00 0.06 0.02 0.04
0.05 0.02 0.07
0.01, 0.00 0.06, 0.05 0.03, 0.03 0.06, 0.07
0.01, 0.02 0.10 0.07, 0.08 0.01 0.01, -0.01 0.03 0.04, 0.03
0.03
E/E H-9
0.00
0.07
0.04
0.08
0.02
Z/Z H-8 H-10
0.04
-0.04
0.01
0.10
0.06
0.02
0.01
0.08 - 0 . 0 1
0.02
0.05
0.01 - 0 . 0 3
0.08
0.01 - 0 . 0 4
Z/Z H-9
-0.03
-0.03
0.00
0.00
-0.011
-0.02
0.10
0.01
H-I 1
-0.01
-0.01
-0.02
-0.02
-0.19
-0.06
- ~
0.07
H-12
-
-0.04
-0.04
-
-
-
-
H-13
-
-0.10
0.00
-
-
H-14
-0.04
-0.04
-0.01
-0.01
-
-
-
0.04
Z CH2
0.09
0.07
0.06
-0.01
0.01
-0.01
-
0.00
E CH2
Table 10 IH Chemical shift differences A6 (ppm) o f the bis-benzo c r o w n ethers 10 and 11 in CDC13/CD O D during the c o m p l e x a t i o n with Na + and K ÷ cations (1 : 1) a n d (2 : 1)
t,~
-,q
4~
,--...
284
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
-202.3 ppm; in the E isomer at ~ = - 2 0 5 - - 2 0 6 . 4 ppm) and the corresponding N - H direct coupling constant proved to be smaller ( 1JN,H= 92--92.7 HZ) than in the E analogue (IJN,H = 94.0--96.5 HZ). Also the 1Jc,H of the ot-CH2 groups in 2 - 1 1 proved characteristically dependent on the amide bond configuration; e.g. for 2 1Jc.H(Z) = 125.0 Hz but lJc,rt(E) = 127.1 Hz (cf. Table 7). 3.1.4. NOEs between NH proton and ot-CH2 protons NOEs were found only in E configuration of the amide bond (cf. Scheme 2). 3.1.5. Geminal coupling constant between carbonyl carbon and N H proton In formamides the corresponding coupling constants proved to be dependent on the amide bond configuration [20,22]; in the E isomer 5.2 Hz, in the Z isomer 2.9 Hz has been measured [22]. In the case of the bis-benzo crown ethers studied 4.5-6.8 Hz (for the trans coupling constant) and 2.9-3.2 Hz for the corresponding cis coupling were detected, values sufficiently different to distinguish the present isomers in connection with arguments stated in Sections 3.1.1, 3.1.2, 3.1.3 and 3.1.4.
clearing the stereochemistry along the linking chain, the complexation of the bis-crown ethers 1-11 to K + and Na + cations, respectively, was studied. The variations of the IH chemical shifts of the corresponding protons at molar ratios 1-11 : K+/Na + = 1 : 1 and 1 : 2, respectively, are given in Tables 8-10. According to previous results [16], highfield shift of especially the aromatic protons during complexation was interpreted as formation of "sandwich"-like complexes due to intramolecular/intermolecular shielding of the two benzo crown ether moieties; from lowfield shifts, on the other hand, on conventional complexation of the cations within the cavity of the bis-crown moieties was concluded. With respect to these effects (cf. Tables 8-10) the following conclusions could be drawn. •
•
3.2. Syrdanti isomerism of the imine fragments 3.2.1. NOEs between the NH proton and the imine proton H-3 NOEs were found in 1-11 (in all the three isomers) and unequivocally prove the anti position of the NH proton and the imine nitrogen lone pair. • 3.2.2. Direct C(3)-H(3) coupling constant The corresponding direct C,H coupling constant for the anti arrangement expected proved to be 158164 Hz for 1-11; in case of the syn position values of > 185 Hz had to be expected [23-25]. Finally, no NMR parameter was found to determine the s-cis/s-trans isomerism of the carbonyl groups in 1; however, some indication was obtained from the quantum-chemical calculations (to be reported later in this paper). 3.3. Complexation of 1-11 to K÷/Na ÷ cations After assigning the various isomers of 1-11 and
The bis-benzo crown ethers 10-11 with the 18-crown-6 ether moieties complex both K + and Na + cations conventionally; 1 : 2 complexes proved to exist. Obviously, the cavity is sufficiently wide to host the two cations properly. The bis-benzo crown ethers 2 - 9 with the only 15-crown-5 ether moieties form "sandwich"like complexes to K ÷ cations; the cavities seem too small to host the K ÷ cations and the "bis-crown effect" was fully activated. The Na ÷ cations, on the other hand, are still sufficiently small to fix into the cavities of 2-9. For this reason, the formation of the conventional "filling" complexes 1 : 2 of 2 - 9 and Na ÷ cations could be concluded. The complexational behaviour of 1 (which proved to exist in E/E configuration only) to K + cations, due to the rigid molecular structure, was extraordinary: first, from highfield shifts of H-5-H-8 and lowfield shifts of H-9 during the complexation up to molar ratios of 1 : 1 on intermolecular complexation ("double-sandwich' '-like complex, cf. Scheme 3) was concluded. With further increasing the molar ratio 1 : K + up to 1 : 2 another set of signals of constant chemical shifts but growing intensity was obtained. From this behaviour, it was concluded that the 1:1 "sandwich"-like complex (Scheme 3) at those molar ratios will be
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
285
n=0 double
"sandwich"
complex of compound
I
"addition" complex "filling" complex
"sandwich"
- like structure
Scheme 3.
Table 11 t3C C h e m i c a l shift variations A6 (ppm) o f the bis-benzo c r o w n ethers 2, 4, 6 a n d 8 during the c o m p l e x a t i o n with Na + a n d K ÷ cations in CDCI 3/ C D 3 O D (80:20) No.
C-3
C-3
C-5
C-5
C-8
C-8
C-9
2 : Na + = (1 : 1) 2 : Na + = (1 : 2) 2 : K ÷ = (1 : 1) 2 : K + = (1 : 2) 4 : Na + = (1 : 1) 4 : Na + = (1 : 2) 4 : K + = (1 : 1) 4 : K + = (1 : 2) 6 : Na + = (1 : 1) 6 : Na ÷ = (1 : 2) 6 : K + = (1 : 1) 6 : K + = (1 : 2) 8 : Na + = (1 : 1) 8 : Na + = (1 : 2) 8 : K + = (1 : I) 8 : K + = (1 : 2)
-1.0 a -2.0 -0.4 -0.4 -0.1 -0.5 -0.6 -0.6 -0.6 -1.2 -0.2 -0.2 -0.6 -1.1 -0.3 -0.4
-0.2 -0.4 -0.7 -0.6 -0.1 -0.3 -0.8 -0.8 -0.1 -0.8 -0.2 -0.2 -0.2 -0.6 -0.1 -0.1
0.0 0.4 -0.6 -0.7 0.0 -0.1 -0.2 -0.2 0.0 0.2 -0.5 -0.6 0.1 0.2 -0.4 -0.4
0.0 0.4 -0.6 -0.7 0.1 0.1 -0.4 -0.4 0.2 0.4 -0.3 -0.3 0.3 0.6 -0.2 -0.2
0.2 0.3 -0.3 -0.5 0.2 0.4 -0.2 -0.2 0.2 0.2 -0.4 -0.4 0.2 0.3 -0.4 -0.4
0.2 0.3 0.3 -0.5 0.1 0.3 -0.6 -0.7 0.2 0.4 -0.3 -0.4 0.3 0.4 -0.6 -0.6
0.2 0.6 0.9 0.9 0.4 0.7 -0.1 -0.1 0.2 0.5 0.2 0.2 0.3 0.2 0.2 0.3
a
Negative A6 values m e a n shifts to higher fields.
C-9 0.3 0.6 0.9 0.9 0.4 0.7 0.1 0.1 0.2 0.4 0.0 0.0 0.1 0.3 0.0 0.0
C-10
C-11
C-12
C-13
-1.1 -1.2 -1.5 -1.6 -0.6 -1.4 -1.5 -1.7 -1.1 -1.6 -1.3 -1.5 -0.9 -1.7 -0.9 -1.2
-1.1 -1.6 -1.6 -1.7 -0.8 -1.5 -1.3 -1.5 -0.9 -1.6 -1.7 -1.8 -0.8 -1.5 -1.2 -1.3
-1.4 -1.7 -1.6 -1.7 -1.3 -1.7 -1.7 -1.9 -0.6 -1.8 -1.3 -1.5 -1.1 -1.7 -1.8 -1.8
-1.5 -2.1 -0.7 -0.9 -1.6 -2.1 -1.7 -2.0 -1.3 -2.1 -1.5 -1.5 -1.3 -2.2 -1.4 -1.5
286
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
Table 12 13C chemical shift variations A6 (ppm) of the bis-benzo crown ethers 10 and 11 in CDC13/CD 3OD (80 : 20) during their complexation with Na ÷ and K + cations No.
E/E
E/Z
Z/Z
E/E
E/Z
Z/Z
E/E
E/Z
Z/Z
E/E
E/Z
Z/Z
C-3
C-3
C-3
C-5
C-5
C-5
C-8
C-8
C-8
C-9
C-9
C-9
C-10
C-II
C-12
C-13
C-14
10 : KI (1 : 1)
-1. I a
-0.3
-0.5
-0.6
0.1
-0.6
-0.2
-0.2
-0.8
-0.4
-1.0
-1.1
-1.1
-0.8
0.1
0.l, 0.l 0.2, 0.0
0.1
-0.6
-0.6, -0.5 -0.9, -0.9
-0.5
-1.6
-0.6, -0.4 -1.1, -1.0
~).5
(2 : 1)
-1.0, 0.7 -1.4, 0.3
0.1
-1.1
-1.0
-0.3
-0.6
-0.4
10 : NaI (1 : l)
-0.8
-0.5
0.l
-0.8
-0.1
-1.0
-0.4
-0.8
-0.2
-0.4
-1.7
-1.7
-1.6
-1.3
-0.1
0.1, 0.1 -0.2, -0.4
0.l
-1.0
-0.6, -0.6 -1.4, -1.4
-0.7
-1.2
-0.9, -1.0 -1.8, -1.7
-0.8
(2 : 1)
-0.6, -0.7 -1.3, -1.7
-0.1
-2.1
-1.3
-0.3
-0.9
-1.3
ll:KI (1 : 1)
-0.3
-0.1
-0.5
-0.3
-0.3
-0.4
-1.1
-1.5
-0.5
-0.5
-1.4
-0.9
-0.8
-1.2
-0.2
-0.7, -0.7 -1.0, -1.0
-0.1
-0.6
-0.7, -0.7 -0.9, -0.9
-0.8
-0.7
-0.7, -0.7 -1.3, -1.3
-0.2
(2 : 1)
-0.2, -0.3 -0.3, -0.5
-0.1
-1.0
-1.7
-I.3
-0.9
-0.9
l l : NaI (1 : 1)
-0.5
-0.1
-1.1
-0.5
-1.7
-1.7
-0.9
-0.8
-0.6
-0.1
-2.1
-1.5
-1.4
0.2, -0.1 0.2, -0.2
0.7
-0.7
-0.9, -0.9 -1.9, -1.9
-0.9
(2 : 1)
-0.3, -0.3 -0.4, -0.1
0.6
-1.8
-1.7
-1.3
-0.9
-0.9
-0.2, -0.5 -0.4 -1.0,1 -0.9 -1.4
0.1 0.1
a A6 < 0 means shifts to higher field. and C3-H, respectively, of same intensity on
increasingly formed (and this on behalf of the former "double-sandwich'
the E/Z isomer could be readily concluded.
'-like association).
The additional set of arising and growing reso-
•
Also the bis-benzo crown ethers of lower link-
nances, on the other hand, proves another iso-
i n g c h a i n 2 - 4 s e e m to b e h a v e s i m i l a r l y t o N a +
m e r o f 1 to o r i g i n a t e ; f r o m t w o s i g n a l s o f N H
c a t i o n s at m o l a r r a t i o s u p to 1 : 1 as 1 to K +
113 112.5 ! ~ ..... : - - ~
'•
K +
111.5
"'~O
--
-0-
.......
-0
Na'
111
110.5 t "~
110 z
"E~ 109,5 •5
lO9
108,5
---e-
108 0
~ 0,5
q 1
i 1,5
..........
i 2
- ~
i 3
.........
-e
Na *
p 4
[Cationl:[Ugmzd] Fig. 2. Dependence of the 13Cchemical shifts of C-5 and C-8, respectively, of compound l l on the molar ratio [Na ÷] : [ l l ] (balls) and [K ÷] :[11] (squares).
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290 H i
cations, just aforementioned. First, up to molar ratios 2 - 3 : Na + = 1 : 1 highfield shifts reveal the formation of intermolecular 1 : 1 double"sandwich"-like association, only at molar ratios further increasing, lowfield shifts of the aromatic protons prove the conventional 1 : 2 "filling" complexation as mentioned already. In the cases of 2,4,6,8,10,11 also the 13C chemical shifts were followed during complexation (cf. Tables 11 and 12). The shapes of the corresponding curves (cf. Fig. 2 for 11) support previous conclusions [16,26]. In addition, from these studies for 10-11 could the Na + cations be concluded to better fit into the crown cavities than the K + cation: in the former case, the ~3C resonances within the ~,-fragments - C 5C6_O_C10_ and - C 8 - C 7 - O - C 1 ° - , respectively, shift stronger to highfield due to stronger in-plane interaction in order to form any useful topology for effectively complexing the Na + cations. The K + cations seem to be slightly too large for the present cavity and, therefore, only form association complexes as depicted in Scheme 3. Both in the free as well as in the K+/Na+-complexed state, the equilibrium of the three isomers E/E, E/Z and Z/Z proved more or less constant; variations when changing the solvent polarity were only minor and are related only to the preference of E/E on behalf of Z/Z (and the opposite way round), but the population of the E/Z isomer proved generally constant. Also the
H
(3
287
H-
t~
H
R / N ~ N ~
H.
H0
R/N'-N
H0
"'5 11
1
Scheme 4.
syn/anti isomerism of the imine fragments remains constant in the K+/Na + complexes studied. 3.4. Rotation about the CS-benzo crown ether moiety In order to study quantitatively the conformational equilibrium of the C3-aryl moiety, ROESY 2D NMR spectra [23,27] were recorded and the ROE cross peaks H-3/H-5 and H-3/H-9, respectively, volume integrated. Both these cross peaks were obtained; from this result, it was concluded that (i) the rotation about t h e C3-aryl bond is fast on the NMR time scale (the quantum-chemical calculations find the barrier to rotation to be below 2 kcal mo1-1) and that the two corresponding in-plane conformations (cf. Scheme 4) participate in the corresponding conformational equilibrium. The ROE values (in %: ROE(H-3/H-5) + ROE(H-3/ H-9) = 100%) thus obtained are shown in Tables 1315. Usually, in all isomers, conformation II proved to be the preferred one (from --50% up to 72%); only in the E/Z and Z/Z isomers of 4, I proved to be more
Table 13 Relative intensity of the R O E cross peaks of H - 3 / H - 5 a n d H-3/H-9, respectively, and of N - H / H - 3 moities obtained from R O E S Y 2D N M R spectra of the bis-benzo c r o w n ethers 1 - 9 Isomer
ROE
E/E
H I~ ~ H) ~ H~~ H~~ H~~ H~~ H ~~ H~~ NH ~
E/Z
Z/Z E/E E/Z Z/Z E/E E/Z Z/Z
1
2
3
4
5
6
7
8
9
30% 70%
NH ~ H ~ H5 ~ HI°
ROE ROE ROE ROE
50% 50% 40% 60% 50% 50% 50% 50% ROE ROE ROE ROE
23% 77% 37% 64% 28% 72% 30% 70% ROE ROE ROE ROE
40% 60% 38% 62% 46% 54% 67% 33% ROE ROE ROE ROE
31% 69% 40% 60e~ 40c~ 60% 33% 67% ROE ROE ROE ROE
45% 55% 45% 55% 50% 50% 50% 50% ROE ROE ROE ROE
42% 58% 29% 71% 30% 70% 40% 60% ROE ROE ROE ROE
38% 62% 33% 67% 50% 50% 50% 50% ROE ROE ROE ROE
28% 72% 31% 69% 31% 69% 30% 70% ROE ROE ROE ROE
H 8 ~ H I°
ROE
ROE
ROE
ROE
ROE
ROE
ROE
ROE
ROE
H5 H~ H5 H '~ H5 H~ 1-t5 H~ H~
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
288
Table 14 Relative intensity of the ROE cross peaks of H-3/H-5 and H-3/H-9, respectively, and of N-H/H-3 moities obtained from ROESY 2D NMR spectra of the bis-benzo crown ethers 1 - 9 complexed to K + cations (1 : 1) Isomer
ROE
E~
H 3~
H5
H 3~
H9
~Z
1
2
3
4
5
32% 68%
-~ ROE .
ROE
ROE -
. ROE .
H 3~ H5
NH ~ H 3 NH ~ H 3 NH ~ H 3 H 5 ~ H I°
20%
ROE ROE 50% 50% ROE ROE ROE ROE
H 8~ H m
80%
ROE
H 3~
H9
H3~ H5 H3 ~ H9 H3~ H5
~Z
H 3~
E~ E~ ~Z E~ E~ ~Z
H9
.
.
.
6 .
7
8
9
. ROE
ROE
ROE
ROE
ROE
ROE
ROE
ROE ROE ROE ROE ROE
ROE ROE ROE ROE ROE
ROE
ROE
. ROE .
. ROE ROE . ROE ROE ROE ROE ROE
ROE ROE ROE ROE ROE ROE ROE
ROE 50% 50% 50% 50% ROE ROE ROE ROE
ROE ROE ROE ROE ROE ROE ROE
ROE ROE . ROE ROE ROE ROE ROE
ROE
ROE
ROE
ROE
.
.
ROE
a No ROE obtained.
preferred
than II. In case of the corresponding
K÷
Section
3. U p to m o l a r
these
w a s o b t a i n e d (cf. T a b l e s 1 3 - 1 5 ) .
O b v i o u s l y , o n l y in
wich"-like
this conformational
any
change former conformational
arrangement
"sandwich"-
successfully
formed.
Further,
complexing this
conformation
seems
to
form
obviously
+ =
1 : 1,
double-"sand-
with no need
to
constructions. also confor-
be
m e r I I p r o v e d to b e i n c r e a s i n g p r e f e r r e d i n t h e K + / N a +
be
complexes compared with the non-complexed
species
(cf. T a b l e 15), b u t , e v e n w h e n b e i n g r e d u c e d , c o n f o r -
The exceptional behaviour of 1 and
m e r I is still p r e s e n t a n d w a s d e t e c t e d w i t h p o p u l a -
in t h e n o n - c o m p l e x e d
4 can also be understood complexational
could
complexes,
ethers
state of
already pre-organized these compounds.
the cations
crown
In the bis-benzo crown ethers 10-11
like topology of the bis-benzo crown ethers 2,3,5-9 for
bis-benzo
ratios of 1,4:K
c o m p l e x e s , e x c e p t f o r 1 a n d 4, o n l y t h i s c o n f o r m a t i o n
behaviour,
within
t i o n s o f at l e a s t 2 1 % . A l s o t h i s r e s u l t is in c o i n c i d e n c e
their exceptional
aforementioned
with the complexational
in
behaviour
of the bis-benzo
Table 15 Relative intensity of the ROE cross peaks of H-3/H-5 and H-3/H-9, respectively, and of N-H/H-3 moities obtained from ROESY 2D NMR spectra both in the free state of the bis-benzo crown ethers 10 and 11 and complexed to K + cations 10' and 11' (2 : 1) Isomer
ROE
10
10'
11
11'
E/E
H 3 ,-* H 5 H 3 ,--* H 9 H 3 '-* H 5
50% 50% 32% 68% 50% 50% 50% 50% ROE ROE ROE ROE ROE ROE
32% 68% 42% 58% 42% 58% 58% u.39% 42% U.61% ROE ROE ROE ROE ROE ROE
47% 53% 50% 50% 36% 64% 47% 53% ROE ROE ROE ROE ROE ROE
38% 62% 21% 79% 23% 77% 26% 74% ROE ROE ROE ROE ROE ROE
E/Z
H 3~
Z/Z E/E E/Z Z/Z E/E E/Z Z/Z
n 9
H3~ H5 H3~ H 9 H 3 *"* H 5 H 3 '--* H 9 NH ~ H 3 NH ~ H 3 NH ,--, H 3 H 5 '--' H ~0 H 8 ~ H ~0
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
crown ethers studied: conventional association and "filling" 1 ' 2 complexation (as aforementioned in Section 3) proved to be of only minor influence on the conformational preference of the C3-aryl moiety of 10-11. 3.5. Molecular dynamics simulations of the stereochemistry of 1-11 employing NOEs as constraints Various quantum-chemical and force field calculations of crown ethers and of their alkali cation complexes have been reported [28-31], even on the ab initio level [32,33]. As usual for flexible molecules of this size (dynamic NMR studies to lowest attainable temperatures revealed no line broadenings due to exchange phenomena) a large number of conformers will be obtained. In order to find out the preferred conformers of lowest energy for the bis-benzo crown ethers studied, the "simulated annealing" program of the TRIPOS software was employed, and, in the beginning, 1000 K was selected to be the plateau temperature. This temperature will be sufficient to surmount all the barriers to rotation present (plateau time I000 fs only). Then the systems (the ROEs measured were applied as constraints in order to find more realistic structures) were cooled down (in 1000 fs only in order to prevent the formation of non-realistic structures) to 200 K (100 cycles for each bis-benzo crown ether in order to find as many different conformations as possible) and the preferred conformers obtained by this method were energy optimized by the TRIPOS force field [12]. Within this frame for each of the E/E, E/Z and Z/Z isomers of the bisbenzo crown ether 1-11 5000 different conformers each were obtained. From these - 2 0 conformations of lowest energy but most different structure were selected for the energy optimization mentioned. The main conclusion from these results is that the three isomers of 1-11, in coincidence with the experimental results, are of nearly the same energy. Additionally, two general types of conformers, a stretched type (as useful for e.g. double-"sandwich"-like complexation (cf. Scheme 3) and a "sandwich"-like type (i.e. pre-organization of the bis-benzo crown ethers) were obtained. When comparing the corresponding energies of formation, the stretched type of conformation proved to be of higher energy (also in agreement
289
(a)
(b)
(c)
"
~
•
I
Fig. 3. Stereostuctures of compound 1: (a) E/E isomer (anti periplanar position of the two carbonyl groups; (b) E/E isomer (syn position of the two carbonyl groups; (c) E/Z isomer.
with the experiment where a "sandwich"-like topology of even the non-complexed bis-benzo crown ethers was found). Compound 1, having completely no linking chain, can exist in syn/anti conformation of the two carbonyl functions. Because of having no unequivocal argument in order to assign, this compound was theoretically studied in detail. From both methods very similar heats of formation were obtained (cf. Fig. 3), the anti arrangement slightly favoured in the preferred E/E isomer. At the same time, any "sandwich' '-like topology in the free state or in order to complex the alkali cations, proved to be hindered in this configuration. In the E/Z isomer, however, but in syn conformation of the carbonyl functions this "sandwich"-like topology becomes available and hereby the opportunity to complex alkali cations in this manner. The NMR study corroborates this complexational behaviour (as calculated by molecular mechanics and quantum-chemical calculations) by indicating another set of resonances (two NH and C 3 - H resonances each of same intensity) with proceeding K ÷ complexation of the 1.
References [1] J. Lekschas and D. Cech, Wiss. Fortschr., 38 (1988)4. [2] K. Gloe, P. Miihl, A.I. Kholkin, M. Meerbok and J. Berger, Isotopenpraxis, 18(1982) 170.
290
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
[3] G.W. Gokel, Crown Ethers and Cryptands, The Royal Society of Chemistry, Cambridge, 1991. [4] M. Hiraoka, Crown Compounds, Elsevier, Amsterdam, 1982. [5] S. Faulkner, R. Kataky, D. Parker and A. Teasdale, J. Chem. Soc., Perkin Trans., 2 (1995) 1761. [6] M. Eberstedt, G. Gemmecker, D.M. Thieske and H. Kessler, Angew. Chem., 107 (1995) 1813. [7] F. V6gtle, Supramolekulare Chemie, Teubner, Stuttgart, 1992. [8] C.J. Pederson, J. Am. Chem. Soc., 89 (1967) 7017. [9] G.W. Gokel, D.M. Dishong and C.J. Diamond, J. Chem. Soc., Chem. Commun. (1980) 1053. [10] A.E. Kaifer and L. Echegoyn, in Y. lnoue (Ed.) Cation Binding by Macrocycles, Dekker, New York, 1990, p. 364. [11] H.-J. Holdt, J. Aurich, J. Teller and G. Kuntosch, Patent 1988 DD 257 070 A1. [12] SYBYL, Molecular Modelling Software, Version 7.1, TRIPOS Inc., St. Louis, MO, 1995. [13] H.J. Berendson, J.M.P. Postman, W.F. Van Gunsteren, A. Dinola and J.R. Haak, J. Chem. Phys., 81 (1984) 3684. [14] J.J.P. Stewart, MOPAC7.0, QCPE-number 455. [15] J.J.P. Stewart, J. Comput. Aided Mol. Des., 4 (1990) 1. [16] S. Stoss, E. Kleinpeter and H.J. Holdt, Magn. Reson. Chem., 29 (1991) 999. [17] A. Bax, J. Magn. Reson., 57 (1984) 314. [18] D.E. Dorman and F.A. Bovey, J. Org. Chem., 38 (1973) 1719. [ 19] H.O. Kalinowski, S. Berger and S. Braun, ~3C-NMR-Spektroskopie, Thieme, Stuttgart, 1984.
[20] S. Berger, S. Braun and H.O. Kalinowski, NMR-Spektroskopie von Nichtmetallen, Bd. 2. tSN-NMR-Spektroskopie, Thieme, Stuttgart, 1992. [21] G,J. Martin, M.L. Martin and J.P. Gouesnard, tSN NMR-Spectroscopy, Springer, Berlin, 1981. [22] V. Barboiu and V. Petrescu, Org. Magn. Reson., 5 (1973)43. [23] V.M.S. Gil and W. v. Philippsborn, Magn. Reson. Chem., 27 (1989) 409. [24] R.R. Fraser and M. Bresse, Can. J. Chem., 61 (1983) 576. [25] H. Egli and W. v. Philippsborn, Helv. Chim. Acta, 64 (1981) 976. [26] I. Starke, A. Koch, H.J. Holdt and E. Kleinpeter, J. Mol. Struct., 356 (1995) 15. [27] A. Bax and D.G. Davis, J. Magn. Reson., 63 (1985) 207. [28] R.P. Hicks, J.K. Yong and D. Moskau, Concepts Magn. Reson., 6 (1994) 115. [29] A.K. Gohse, E.P. Jaeger, P.J. Kowalczyk, M.L. Peterson and A.M. Treasurywala, J. Comput. Chem., 14 (1993) 1050. [30] P.D.J. Groothenius and P.A. Kollmann, J. Am. Chem. Soc., 111 (1989) 2152. [31] Y. Sun and P.A. Kollmann, J. Am. Chem. Soc., 117 (1995) 3599. [32] E.D. Glendening, D. Feller and M.A. Thompson, J. Am. Chem. Soc., 116 (1994) 10657. [33] B.P. Hay, J.R. Rustard and C.J. Hostetler, J. Am. Chem. Soc., 115 (1993) 11 158.
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular Structure 404 (1997) 273-290
NMR spectroscopic study of solution structure and complexational behaviour of bis-benzo crown ethers E. Kleinpeter a'*, I. Starke a, D. Str6hl b, H.-J.
Holdt c
~lnstitut fiir Organische Chemie und Strukturanalytik, Universitiit Potsdam, Am Neuen Palais 10, D-14469 Potsdam, Germany blnstitut fiir Organische Chemie, Martin-Luther-Universitiit Halle-Wittenberg, Weinbergweg 16, D-06122 Halle/Saale, Germany CChemische lnstitut, Universiti~t Rostock, Buchbinder Strasse 9, D-18055 Rostock, Germany
Received 29 June 1996; accepted 16 August 1996
Abstract The tH, t3C and tSN NMR spectra of a series of polymethylene-bridged carbonylhydrazone bis(benzo-15-crown-5 ethers) 1-9 (n = 0-8) and bis(benzo-18-crown-6 ethers) 10-11 (n = 1,5) were recorded and assigned by COSY, HMQC and HMBC 2D NMR experiments. The stereoisomerism of the bridging R - C H = N - N H - C ( = O ) - ( C H 2 ) , moieties was studied by various useful NMR parameters (rc-o, 3Jc.H, IJN-H, IJc H, 2Jc(=O)-NH)and intramolecular NOEs. Three isomers (E/E, E/Z and Z/Z, respectively) with respect to the amide bond proved to exist, NH and the imine lone pair were found in anti position. The -OCH2CH20- fragments occur as rapidly interconverting gauche conformations and the ot-CHz groups more or less in-plane with the adjacent phenyl ring moiety as concluded from the corresponding ~3C chemical shifts and NOEs, respectively. The solvent dependence of the amide isomerism was studied and the complexation of the bis-benzo crown ethers to Na + and K + cations carefully investigated. The conformation of the free and complexed bis-crown ethers was obtained. Both the complexation mechanism (sandwich, double-sandwich, inclusion and addition complex) and the conformational equilibrium about the =CH-Ph bond proved to be strongly dependent on the bis-benzo crown ethers 1-11 studied. The conformational study is accompanied and corroborated by molecular dynamics and quantum-chemical calculations. © 1997 Elsevier Science B.V. Keywords: NMR spectroscopy; Conformational isomerism; Bis-benzo crown ethers
I. Introduction Bis-benzo crown ethers have been widely studied owing to their ability to form complexes selectively with alkali metal cations [1-6]. These compounds consist of two crown ether units in the same molecule and provide, besides the conventional inclusion of the cations within the cavity of the crown ether moieties, also the opportunity to forming " s a n d w i c h " - l i k e * Corresponding author. Fax: +49 331 977 1516.
complexes with cations of radii larger than the cavity size of the single crown ether units [7-10]. The stability of these complexes is higher (due to the " b i s - c r o w n e f f e c t " ) than the stability of simple addition complexes where the cations, due to radii larger than the cavity size, are positioned only above the cavity of the crown ether units. Hereby the linking chain is also of deciding influence on both the formation and the stability of the " s a n d w i c h " - l i k e complexes; limited flexibility and the existence of preferred conformations can prevent the non-distorted
0022-2860/97/$17.00 Copyright © 1997 Elsevier Science B.V. All rights reserved PII S0022-2860(96)09444-6
274
E. Kleinpeter
et al./Journal
of Molecular
formation. It is the objective of this paper to test the - C H = N - N H - C O - ( C H 2 ) , - C O - N H - N = C H moiety as a linking chain for two benzo crown ether units in this respect. For this reason, the stereochemistry (isomerism, conformation) of a series of polymethylene-bridged carbonylhydrazone bis(benzo-15-crown-5 ethers) 1-9 (n = 0-8) and two bis(benzo-18-crown-6 ethers) 10-11 (n = 1,5) (cf. Scheme 1)was studied in solution both in the free and the Na ÷ (K ÷) complexed state employing the whole arsenal of 2D NMR methods, a variety of useful NMR parameters and intramolecular NOEs. Hereby, the complexation mechanism (inclusion, addition, "sandwich"-like and double-"sandwich"-like complex, respectively) was of special interest.
2. Experimental The synthesis of compounds 1-11 has been published already previously [11]. The alkali salts used for the complexation studies were dried over P40~0 and the solvents over Call2 or mole sieve. The ill, ~3C and ~SN NMR spectra were recorded at 300.13, 75.47 and 30.41 MHz, respectively (BRUKER ARX
R =
OH 2
Bis-benzo crown ether
compound
n
m
Bis(benzo- l 5-crown- 5+ether)
I
0
I
Isomer [~Eundl:Z
2
I
I
E,~-,EZundZZ
3
2
1
-"-
4
3
I
-"-
5
4
I
-<-
6
5
1
-"-
7
6
I
-"
8
7
I
-"-
9
8
I
-"-
Bis(benzo- 18-crown-6-ether)
1o
I'
II Scheme
5 1.
Structure
404 (1997)
273-290
300) in CDC13/CD3OD (4 : 1) solution (5 mm probe tubes, ambient temperature, deuterated solvents as internal lock); in cases of less soluble compounds also spectra at 600 and 750 MHz were recorded employing aRUKER DMX 600 and 750 NMR spectrometers. Typical conditions 13C: 30 ° pulse, 2 s repetition time, sufficient number of scans, 32K data points, 18750 Hz spectral range and 0.57 Hz per point digital resolution. The 15N NMR spectra were also recorded at 60.81 MHz (on a UNITY 600 VARIAN spectrometer) in natural abundance (solvent DMSO-d6 versus NO2CH3 as reference; 10 mm probe tubes at ambient temperature). Typical conditions: 45 ° pulse, 4 s repetition time, 32K data points, 9259 MHz spectral range and 0.28 Hz per point digital resolution. The 1H, 13Cand 15NNMR spectra were assigned by H,H-COSY, HMQC and HMBC 2D NMR experiments using the BRUKER standard software. Typical settings: (HMQC) sweep width in Fi 18 kHz and in F2 6.9 kHz, 8K data points in F2, 512 experiments in F2 (8 or 16 scans), relaxation delay 0.2 s, pulse width ( IH, 90 °) 11.0/~s, (13C) 9.5/zs, zero filling, filter function sine-bell in both dimensions. For the ~SN NMR spectra the sweep width in F ~is 1 kHz and in F2 7 kHz, pulse width P1 (90, 15N) 10.2/zs, 8K data points in F2 and 128 experiments in Fl. The 2D ROESY NMR experiments were processed in phase-sensitive mode (BRUKER standard software); the samples were degassed at least 3 times and sealed under argon. Typical conditions: sweep width in F~ and in F2 7 kHz, 1K data points in F I and 2K data points in F2, zero filling in Fl, relaxation delay 2 s, mixing time 200 ms, filter function sine-bell in both dimensions. The molecular dynamics calculations (simulated annealing) were carried out with the TRIPOS force field [12] starting at 1000 K and cooling down to 200 K for 1000 fs. The default setup used a constant N, V, T ensemble based on Berendsen's method [13]. Quantum-chemical calculations were carried out with MOPAC 7.0 program package [14] using Silicon Graphics work stations IRIS INDIGO XS 4000 [15].
3. Results and discussion 12 2
I'DE.E. Z u n d Z Z
-"-
The IH NMR spectra exhibit 4 characteristic absorption ranges: the NH protons at ~ = 9.75-
\ DO m
_ _ _ . _
< / .t / t /-
_
727
~ I 0
002
~-;~
~ \ \ k \ k \
I
9. B99 9. 829 7 999
7.96i
i
\m.
7. ?52 7.69,~
;j
7. 559
\ \
7.531 7 363 ; 263 7 23,d
\
\
\ \ \
\
\
d¸ "I
\I - J
z
~, 108
7.081 7.05~
z
6.881 68~9
6.822 6 ~99 r- ~ 223 ~ 209
0 e~
z 179
Z
3 g38
~
3 930 3 7~) 3689
< /
r
35~s
-----I- 3 373 . ~ 2 775
E
2 75~ 2 728
..~
r~
2 306 2 28g 2 266 ~ 760 ?38
I 6}96 1 474 J
] 431 I 408
K .........
~LE
L_ I 259
[i-
06~-FZE (/66I) #0/~ a.~nj.~nJ.~E.~OlnJdlOl4/ /o 1DuJ,ol'/'l D la Jdlddu!dlX "~
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
276
11.37 ppm, the OCH2 crown ether protons (H-10-H13 at ~i = 3.67-4.45 ppm), the H-3 methin protons (6 = 7.65-8.06 ppm), the aromatic protons H-5-H-9 at ~ = 6.77-7.68 ppm, and the methylene protons of the linking chain below 2.77 ppm (cf. Fig. 1 for 11). The latter protons are lowfield shifted dependent on their position to the adjacent carbonyl groups (the linking chain protons were assigned in detail by the corresponding H,H-COSY experiments). The aromatic protons H-5, H-8 and H-9 can be readily differentiated by the vicinal H,H coupling (H-8 at higher field due to the ortho-OR substituent);
the substitution pattern for the aromatic rings proved unequivocal. The multiplets of the crown ether fragments H-10H-13 are shifted to higher field with respect to the aromatic ring current effect; the H,H coupling constants as extracted from the AA'BB' subspectra indicate gauche fragments - O - C H 2 - C H 2 - O - , readily interconverting on the NMR time scale at ambient temperature. Due to the highfield position of both ot-OCH2 carbon resonances and those of C-5 and C-8, respectively, the more or less in-plane position of these fragments in the bis-crown ethers
Table 1 IH NMR spectra (6 (ppm) and JH,H (Hz)) of the bis-benzo crown ether 1 - 9 in CDCIflCD3OD (80 : 20) No.
NH
H-3
H-5
H-8
H-9
H-10
H-11
H-12
H-13
3j(H8,H9) 4j(H5,H9)
1 2 E/E E/Z
11.35
8.24
7.55
6.86
7.21
4.24
4.21
3.95
3.77
8.3
-
11.30 11.15 10.46 10.35
8.00 8.00 7.79 7.73
7.55 7.51 7.29 7.28
6.85 6.85 6.80 6.80
7.13 7.13 7.10 7.10
4.20
4.11
3.98
3.74
8.3 8.3 8.4 8.4
1,6 1,5 1,7 1,7
11.30 11.17 10,50 10.42
7.97 7.96 7.78 7.78
7.56 7.54 7.31 7.31
6.87 6.87 6.83 6.83
7.13 7.13 7.11 7.11
4.22
4.19
3.94
3.79
8.06 8.06 8.24 8.24
1.65 1.65 1.47 1.47
11.23 11.17 10.40 10.37
7.98 7.98 7.80 7.79
7.59 7.59 7.29 7.29
6.91 6.91 6.85 6.85
7.13 7.13 7.10 7.10
4.23
4.18
3.93
3.77
8.29 8.29 8.36 8.36
1.53 1.53 1.56 1.56
10.87 10.61 9.80 9.75
7.96 7.95 7.73 7.65
7.56 7.53 7.25 7.22
6.86 6.86 6.81 6.81
7.13 7.13 7.08 7.08
4.40
4.19
3.93
3.77
8.14 8.14 8.21 8.21
1.76 1.76 1.81 1.81
11.05 10.93 10.13 10.07
7.96 7.96 7.78 7.76
7.59 7.58 7.28 7.26
6.90 6.90 6.87 6.87
7.15 7.15 7.10 7.10
4.19
4.11
3.97
3.77
8.26 8.26 8.28 8.28
1.34 1.34 1.27 1.27
11.36 11.32 10.50 10.40
7.97 7.95 7.73 7.71
7.68 7.55 7.25 7.22
6.87 6.87 6.81 6.81
7.16 7.16 7.12 7.12
4.44
4.18
3.90
3.73
8.21 8.21 8.32 8.32
1.10 1.10 1.20 1.20
10.95 10.83 10.06 10.02
7.98 7.98 7.78 7.77
7.56 7.55 7.29 7.25
6.94 6.94 6.88 6.88
7.12 7.12 7.10 7.10
4.35 4.20
4.19 4.17
3.91
3.74
8.14 8.14 8.34 8.34
1.55 1.55 1.54 1.54
Z/Z 3 E/E E/Z Z/Z 5 E/E E/Z 7JZ 6 E/E E/Z
Z/Z 7 E/E E/Z Z/Z 8 E/E E/Z Z/Z 9 E/E E/Z Z/Z
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
277
Table 2 ~H NMR spectra (6 (ppm) and JH.H (Hz)) of the CH2 protons in the linking chain of the bis-benzo crown ethers 1-9 in CDCIflCD3OD (80 : 20) No.
CH2 A
CH2 B
CH2 C
CH2 D
CH2 D
CH2 C
CH2 B
CH2 A
3J(H,H)
1 2
E/E E/Z Z/Z
3.35 3.35 4.05
4.05
E/E E/Z Z/Z
2.67 2.67 3.19
2.67 3.19 3.19
7.15,7.20 7.15,7.20 7.14,7.15
E/E E/Z Z/Z
2.38 2.38 2.77
2.10 2.11 2.11
2.38 2.77 2.77
7.17,7.20 7.17,7.20 7.22,7.21
E/E E/Z Z/Z
2.34 2.36 2.82
1.77 1.77 1.82
1.77 1.82 1.82
2.34 2.80 2.82
7.16,7.20 7.16,7.20 -
E/E E/Z Z/Z
2.28 2.31 2.76
1.75 1.75 1.76
1.44 1.44 1.44
1.75 1.76 1.76
2.28 2.75 2.76
7.20,7.29 7.20,7.29 7.41,7.41
E/E E/Z Z/Z
2.27 2.27 2.74
1.76 1.76 1.76
1.44 1.44 1.44
1.44 1.44 1.44
1.76 1.76 1.76
2.27 2.74 2.74
7.26,7.23 7.26,7.23 7.47,7.56
E/E E/Z Z/Z
2.27 2.27 2.73
1.71 1.71 1.71
1.40 1.40 1.40
1.40 1.40 1.40
1.40 1.40 1.40
1.71 1.71 1.71
2.27 2.73 2.73
7.20,7.20 7.20,7.20 7.47,7.56
E/E E/Z Z/Z
2.26 2.29 2.73
1.69 1.69 1.70
1.35 1.35 1.35
1.35 1.35 1.35
1.35 1.35 1.35
1.69 1.70 1.70
2.26 2.72 2.73
7.37,7.37 7.37,7.37 7.17,7.17
1.35 1.35 1.35
a Overlapping signals.
Table 3 IH NMR spectra (6 (ppm) and the nJH.H (Hz)) of the bis-benzo crown ethers 10 and 11 in CDCIflCD3OD (80:20) No.
10
11
E/E E/Z Z/Z E/E E/Z Z/Z
NH
H-3
H-5
H-8
H-9
H-10
H-I 1
H-12
H-13
H-14
3J(H8,H9)
~J(H5,H9)
11.30 I 1.20 10.63 10.57 11.12 10.85 9.98 10.07
8.01 8.01 7.81 7.78 8.06 8.00 7.30 7.79
7.51 7.55 7.29 7.29 7.48 7.51 7.25 7.23
6.83 6.83 6.78 6.78 6.83 6.83 6.80 6.77
7.09 7.09 7.03 7.03 7.12 7.12 7.05 7.05
4.21
4.16
3.99
3.73
3.68
4.18
3.91
3.75
3.71
3.67
8.2 8.2 8.3 8.3 8.1 8.1 8.2 8.2
1.33 1.33 1.22 1.22 1.33 1.33 1.21 1.21
278
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
Table 4 ~H NMR spectra (¢5 (ppm), Jn.n (Hz)) of the protons in the linking chain of the bis-benzo crown ethers 10 and 11 in CDCI 3/CD3OD (80 : 20) No. 10
11
CH2 A
CH2 B
E/E E/Z Z/Z
3.39 3.39 4.02
4.02
E/E E/Z Z/Z
2.28 2.30 2.77
1.70 1.70 1.78
1-11 can be concluded [16]; from NOEs H-5/~-CH2 and H-8/t~-CH2 comes the same information. Proton chemical shifts and relevant coupling constants are given in Tables 1-4. Especially from the resonances of the H-3 and NH protons (4 each, two signals of same intensity), on the existence of the studied compounds in the 3 possible configurations with respect to the amide bonds can be readily concluded: E/E, E/Z and Z/Z, respectively (cf. 2 2). The same information comes from the resonances of the other protons of 1-11 which are also splitted into the correct number of signals. The presence of 3 different isomers in 1-11 can be also concluded from the corresponding number of signals for the carbonyl resonances but also the aromatic carbon atoms in the t3C NMR spectra; H I NR~N 4 H 2 ~ N
Eo
CH2 C
CH2 B
CH2 A
3j( H A,H A)
1.44 1.44 1.46
1.70 1.78 1.78
2.28 2.76 2.77
7.26,7.26 7.26,7.26 7.03,7.03
having the correct assignment of the IH NMR spectra in hand, the 13C NMR spectra were assigned by employing both HMQC and HMBC 2D NMR correlation experiments (cf. Tables 5-7). Especially the HMBC connectivities of NH/C=O, NH/C 3 and CH~/C=O, respectively, were very useful for assigning the three sets of resonances to the isomers. The quaternary carbon atoms C-6,7 were unequivocally assigned by employing the semi-selective INEPT experiment (optimized on nJc,H = 8 Hz) [17] by selectively irradiating the aromatic protons H-5, H-8 and H-9, respectively. For assigning the stereochemistry of the studied bis-benzo crown ethers 1-11 from both the IH and 13C NMR spectra, a number of useful NMR parameters were employed.
H I
H NR ' , N R "~N "~( C H 2~..,.."N x n
"NR
oE
E; NR I
I
H-N~CH2~NZ o
0
NOE - H R/
c~k
;z
NR
I
2.~/N
o
H Z
H O%c/N
I
c a?\ R
3j CI~.NH
< 0.5 Hz Scheme 2.
~7Hz
279
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
3.1. Isomerism of the amide bonds
3.1.1. 13C chemical shift of carbonyl carbon atoms
In order to prove this isomerism, the positions of the signals of both the C=O carbon and the NH proton were considered (cf. Scheme 2).
The 13C chemical shifts of the E/Z isomers of formamide and acetamide were assigned by DORMAN and BOVEY [18]; adequately the highfield carbonyl resonances (6 = 164.1-171.6 ppm) of the bis-benzo
Table 5 I~C chemical shifts b (ppm) of the bis-benzo crown ethers 1 - 9 in CDCI3/CD3OD (80: 20) No.
C-1
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
C-I 1
C-12
C-13
1
E/E Z/E Z/Z
155.5
149.5
126.9
110.9
152.1
152.7
112.7
124.4
68.7 68.9
69.6 69,7
70.5
71.0 71.1
2
E/E E/Z
164.1 164.1 169.9 170.7
149.8 148.8 145.8 144.7
127.7 127.4 127.3 127.1
110.7 110.6 110.4 110.4
149.8 149.8 149.4 149.4
151.5 151.4 151.3 151.1
112.9 112.9 112.7 112.7
123.7 123.5 122.9 122.7
68.7 68.9
69.7
70.3
70.9 71.0
169.8 170.1 175.1 175.4
148.9 148.2 145.1 144.7
127.8 127.8 127.6 127.6
110.9 110.9 110.8 110.8
149.4 149.4 149.4 149.4
151.4 151.3 151.2 151.2
113.0 113.0 112.8 112.8
123.5 123.4 122.7 122.6
68.6 68.8
69.4 69.6
70.5
71.0
170.6 170.7 175.9 176.0
148.6 148.1 144.9 144.4
127.8 127.6 127.4 127.4
111.7 111.4 111.2 110.8
149.5 149.4 148.6 148.1
152.3 152.3 151.5 151.5
113.2 113.0 112.9 112.9
123.4 123.3 122.4 122.3
68.8 69.0
69.6 69.7
70.5
71.1 71.2
171.1 171.3 176.6 176.6
148.7 148.3 145.0 144.7
127.7 127.6 127.5 127.5
110.9 110.9 110.7 110.7
149.3 149.3 149.3 149.3
151.3 151.2 151.1 151.1
113.0 113.0 112.7 112.7
123.4 122.5 122.4 122.4
68.6 68.7
68.9
69.5 70.4
70.9 71.0
171.2 171.3 176.6 176.7
148.3 148.1 144.7 144.5
127.6 127.4 127.5 127.5
110.9 110.9 110.5 110.5
149.3 149.3 149.2 149.2
151.2 151.0 150.9 150.9
113.0 113.0 112.6 112.6
123.2 123.2 122.2 122.2
68.5 68.8
69.3 69.4
70.2
70.7 70.9
171.4 171.6 176.9 177.0
148.5 148.2 144.8 144.6
128.7 127.8 127.7 127.7
111.1 111.1 110.7 110.7
149.5 149.5 149.4 149.4
151.3 151.3 151.2 151.2
113.2 113.2 112.7 112.7
123.5 123.5 122.6 122.4
68.7 68.8
69.1 69.6
70.5
71.1 71.1
171.4 171.6 177.0 177.0
148.3 148.2 144.7 144.6
127.7 127.7 127.5 127.5
110.9 110.9 110.5 110.5
149.3 149.3 149.2 149.2
151.2 151.0 150.9 150.9
113.0 113.0 112.6 112.6
123.3 123.3 122.4 122.4
68.6 69.1
69.7 69.8
70.3
71.1 71.2
171.5 171.6 177.0 177.0
148.2 148.1 144.5 144.4
127.8 127.7 127.6 127.6
111.5 111.2 111.1 110.8
149.4 149.4 149.3 149.3
151.3 151.3 151.2 151.2
113.1 113.1 112.8 112.8
123.2 123.1 122.4 122.3
68.7 68.9
69.6 69.7
70.3 70.5
71.0 71.1
Z/Z 3
E/E E/Z Z/Z
4
E/E E/Z Z/Z
5
E/E E/Z Z/Z
6
E/E E/Z Z/Z
7
E/E E/Z Z/Z
8
E/E E/Z Z/Z
9
E/E E/Z Z/Z
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
280
crown ethers 1-11 were assigned to the E isomers, the lowfield absorptions (t5 = 169.9-177.0 ppm) to the Z analogues.
3.1.2. Vicinal CH coupling between ot-CH2 carbon and NH proton The corresponding trans coupling constant 3Jc,H ( - 7 Hz) in Z configuration was found characteristically larger than the analogous cis coupling ( - < 0.5 Hz) in the E isomer [18,19] (cf. Scheme 2). Values detected for 2-11 are 5.9-7.7 Hz in cases of Z configuration; no cross peaks could be detected for
the corresponding E isomers, both in agreement with Ref. [19].
3.1.3. 15N chemical shift and direct N - H coupling constant Both the 15N chemical shifts [19] and the 1JN,H coupling constants [20] have been successfully employed in order to estimate the configuration at the amide bond in the case of planar arrangement [21]. The corresponding parameters for 1-11 were determined by HMQC- 15N,IH experiments: tS(15N) of the Z isomer was found at higher field ( - 201.6-
Table 6 t3C chemical shifts/~ (ppm), and Jc.H (Hz) coupling constants of the linking chains of the bis-benzo crown ethers 1-9 in CDCI3/CD3OD (80 : 20) No.
1
2 E/E E/Z Z/Z 3 E/E E/Z Z/Z 4 E/E E/Z Z/Z 5 E/E E/Z Z/Z 6 E/E E/Z Z/Z 7 E/E E/Z Z/Z
CH2 A
CH2 B
CH2 C
CH2 D
CH2 D
CH2 C
CH2 B
CH2 A
IJ(C3,H3)
IJ(CA,HA)
158.0
-
41.71 41.2 40.7
160.0 159.8 161.5,161.5
127.0
30.1 28.6 27.6
160.0 169.1 160.0,162.0
128.0
33.9 31.7 31.7
163.7 163.0 159.0,159.0
130.0
25.8 24.9 24.5
34.9 32.7 32.5
161.0 160.6 160.5,160.0
127.0
28.9 28.5 28.5
34.6 32.5 32.4
161.0 161.3 164.0,164.2
132.0
25.8 25.5 24.9
29.1 28.6 28.6
34.8 32.8 32.7
162.5 162.3 160.3,160.4
130.0
25.9 25.8 25.0
29.5 28.9 28.9
34.9 32.8 32.8
160.0 164.3 160.2,162.3
129.0
29.3 29.1 29.1
29.6 29.5 29.5
35.0 32.9 32.8
165.3 165.2 164.5,164.5
127.0
30.1 29.3 27.6 33.9 33.5 31.7
21.7 21.7 20.9
34.9 34.4 32.5
25.8 25.4 24.5
34.6 34.4 32.4
28.9 28.9 28.5
25.6 25.1 24.3
34.8 34.6 32.7
29.1 29.1 28.6
25.8 25.5 24.9
34.9 34.8 32.8
29.5 29.5 28.9
25.9 25.9 25.0
25.9 25.8 25.0
35.0 34.9 32.8
29.6 29.6 29.5
29.3 29.3 29.1
25.9 25.7 25.0
125.0
126.0
129.2
130.0
129.0
126.0
8
E/E E/Z Z/Z 9 E/E E/Z Z/Z
25.9 25.1 25.0
126.0
125.0
Z/Z
Z/Z 11 E/E E/Z
10 E/E E/Z
NO.
149.3 149.1 146.0 144.7
148.5 148.2 144.7 144.4
171.0 171.3 176.6 176.7
C-3
164.2 164.4 170.9 170.8
C-I
127.7 127.7 127.7 127.7
127.7 127.7 127.3 127.0
C-4
111.1 110.9 110.5 110.5
110.7 110.6 110.5 110.1
C-5
149.2 149.2 149.2 149.2
150.9 150.9 150.1 150.1
C-6
151.0 151.0 151.0 151.0
151.7 151.7 151.5 151.4
C-7
113.2 113.1 112.6 112.6
112.7 112.9 112.6 112.6
C-8
123.3 123.3 122.4 122.4
123.7 123.5 122.9 122.7
C-9
68.9
68.9
C-10
69.2
69.6
C-I 1
69.7
69.7
C-12
70.1
70.8
C-13
.
70.9
70.9
C-14
.
32.7 28.7 24.5 28.7 32.7
34.9 29.4 25.6 29.4 34.9 34.7 29.1 25.4 28.7 33.9
39.8
41.7 41.2
CH2 CH2 CH2 CH2 CH2
Table 7 13C chemical shifts 6 (ppm) and IJc.H (Hz) coupling constants of the bis-benzo crown ethers 10 and 11 in CDCI¢CD3OD (80 : 20)
161.1 160.4 161.8 161.1
159.5 161.2 163.8 162.1
IJ(C-3,H-3)
122.6 122.6 120.9 120.9
131.3 131.3 129.6 129.6
IJ(CA,HA)
t,o
"~,
,,....-
E. Kleinpeter et aL/Journal of Molecular Structure 404 (1997) 273-290
282
Table 8 ~H C h e m i c a l shift d i f f e r e n c e s At5 ( p p m ) o f the b i s - b e n z o c r o w n e t h e r s 1 - 9 d u r i n g the c o m p l e x a t i o n w i t h N a ÷ c a t i o n s No.
H-3 a
H-3 b
H-5 ~
H-5
H-8
H-8
H-9
H-9
H-10
H-11
H-12
H-13
CH2-Z
CH2-E
1 : N a ÷ = (1 : 1)
0.09
-
-0.03 d
_
0.03
-
0.06
--
0.04
--0.90
.
.
.
1 : N a ÷ = (1 : 2)
0.14
-
0.20
-
0.18
-
0.13
-
0.08
-0.90
.
.
.
2 : N a + = (1 : 1)
0.15
0.10
-0.11
-0.02
0.01
0.01
0.03
0.03
-0.06
-0.03
-
-
< 0.00
< 0.00
2 : N a ÷ = (1 : 2)
0.22
0.20
0.02
0.02
0.13
0.12
0.13
0.15
0.14
-0.03
-
-
< 0.00
< 0.00
3 : N a ÷ = (1 : 1)
-0.02
-0.02
-0.01
-0.02
-0.02
-0.01
-0.01
-0.01
-0.03
-0.01
-
-
0.00
-0.01
3 : N a + = (1 : 2)
0.11
0.05
0.15
0.16
0.18
0.14
0.16
0.14
0.07
- c
-
-
0.00
0.03
4 : N a + = (1 : 1)
0.20
0.10
0.13
0.06
0.06
0.08
0.05
0.06
0.03
0.03
-
-
0.00
0.07
4 : N a ÷ = (1 : 2)
0.31
0.17
0.17
0.17
0.19
0.21
0.14
0.15
0.05
0.06
-
-
0.00
0.08
5 : N a ÷ = (1 : 1)
0.06
0.02
0.05
0.02
0.05
0.05
0.05
0.06
-0.03
-0.03
-
-
0.00
0.03
5 : N a ÷ = (1 : 2)
0.13
0.04
0.13
0.08
0.16
0.16
0.12
0.12
0.07
0.01
-
-
0.00
0.05
6 : N a ÷ = (1 : 1)
0.11
0.23
0.04
0.06
0.04
0.05
0.06
0.07
0.00
-0.04
-
-
-0.02
0.06
6 : N a + = (1 : 2)
0.26
0.38
0.08
0.16
0.12
0.11
0.13
0.13
0.04
-0.05
-
-
-0.06
0.09
7 : N a ÷ = (1 : 1)
0.16
0.05
0.05
0.07
0.06
0.07
0.09
0.09
0.00
0.02
-
-
0.00
0.05
7 : N a + = (1 : 2)
0.30
0.10
0.14
0.14
0.13
0.13
0.16
0.17
0.03
0.05
-
-
0.00
0.08
8 : N a ÷ = (1 : 1)
0.26
0.06
0.04
0.07
0.07
0.06
0.04
0.05
-0.01
-0.02
-
-
-0.02
0.03
8 : N a ÷ = (1 : 2)
0.37
0.16
0.13
0.13
0.13
0.13
0.12
0.13
0.03
0.05
-
-
-0.06
0.09
9 : N a ÷ = (1 : 1)
0.07
0.04
0.08
0.05
0.06
0.07
0.03
0.05
0.03
-0.01
-
-
0.00
0.02
9:Na÷=
0.16
0.08
0.19
0.13
0.17
0.17
0.14
0.16
0.11
0.13
-
-
0.00
0.04
H-12
H-13
CH2-Z
CH2-E
(1:2)
. .
C h e m i c a l s h i f t s o f the E s i d e o f the E / E u n d E / Z i s o m e r s . b C h e m i c a l s h i f t s o f the Z s i d e o f the E / Z a n d Z / Z i s o m e r s . c Overlapping signals. a At5 < 0 m e a n s shifts to h i g h e r field.
Table 9 IH C h e m i c a l shifts A6 ( p p m ) o f the b i s - b e n z o c r o w n e t h e r s 1 - 9 d u r i n g the c o m p l e x a t i o n w i t h K ÷ c a t i o n s No.
H-3 a
H-3 b
H-5
H-5
1 : K + = (1 : 1)
0.40
0.01
-0.18 d
0.07
-0.01
0.01
-0.22
-0.04
-0.24
.
.
.
.
1 : K ÷ = ( l : 2)
0.40
0.03
-0.29
-
0.07
-0.01
0.01
-0.22
-0.05
-0.24
.
.
.
.
2 : K ÷= (l : l)
-0.24
-0.17
-0.31
-
-0.28
-0.22
-0.24
-0.20
-
-0.09
-
-
< 0.00
< 0.00
2 : K ÷ = (1 : 2)
-0.29
-0.18
-0.31
-
-0.28
-0.22
-0.27
-0.27
-
-0.09
-
-
< 0.00
< 0.00
3 : K ÷ = (1 : 1)
0.00
0.00
-0.08
-0.08
-0.07
-0.04
-0.02
-0.02
0.00
-0.01
-
0.00
0.02
3 : K + = (1 : 2)
-0.01
0.00
-0.10
-0.10
-0.07
-0.04
-0.02
-0.02
0.00
-0.01
-
4 : K + = (1 : 1)
-0.02
-0.06
-0.10
-0.10
-0.01
-0.07
-0.05
-0.06
-0.06
-0.01
-
4 : K + = (1 : 2)
-0.02
-0.07
-0.10
-0.10
-0.02
-0.08
-0.10
-0.08
-0.01
-0.01
5 : K + = (1 : 1)
0.03
0.06
-0.08
-0.10
-0.06
-
--0.05
-0.05
-0.03
-0.03
5 : K ÷ = (1 : 2)
0.05
0.07
-0.08
-0.10
-0.06
-
-0.05
-0.05
-
6 : K + = (1 : 1)
0.08
0.06
-0.14
-0.14
-0.12
-0.13
-0.03
-0.03
0.00
6 : K + = (1 : 2)
0.08
0.06
-0.14
-0.14
-0.12
-0.13
-0.03
-0.03
0.00
7 : K ÷ = (1 : 1)
0.04
0.00
-0.13
-0.08
-0.06
-0.07
0.01
0.01
7 : K ÷ = (1 : 2)
0.04
0.00
-0.13
-0.08
-0.06
-0.07
0.01
8 : K ÷ = (1 : 1)
0.07
0.03
0.00
-0.01
-0.04
-0.20
8 : K + = (1 : 2)
0.07
0.03
0.00
-0.01
-0.04
-0.20
9 : K + = (1 : 1)
0.04
0.00
-0.09
-0.07
-0.10
-0.12
0.00
-0.04
0.01
9 : K + = (1 : 2)
0.04
0.00
-0.09
-0.07
-0.10
-0.12
0.00
-0.04
0.03
-
c
-
H-8
a C h e m i c a l s h i f t s o f the E side o f the E / E a n d E / Z i s o m e r s . b C h e m i c a l s h i f t s o f the Z side o f the E / Z a n d Z / Z i s o m e r s . c Overlapping signals. 0 At5 < 0 m e a n s s h i f t s to h i g h e r field.
H-8
H-9
H-9
H-10
H-11
-0.02
0.07
0.00
0.03
-
0.00
0.05
-
-0.02
0.04
-
-0.02
0.06
-0.18
-
0.00
0.07
-0.18
-
0.00
0.09
-0.02
-0.04
-
0.00
0.04
0.01
-0.02
-0.04
-
0.00
0.06
-0.06
-0.01
0.00
-
-
0.00
0.07
-0.06
-0.01
0.00
-
-
0.00
0.07
0.00
0.03
0.00
0.05
-
-0.04 -
-
-
-
+=(2:
ll:Na
1)
0.23,
0.34
0.26
0.33
0.13
0.12, 0.03 0.30, 0.16 0.29, 0.05 0.33, 0.11
E/E H-5
0.02 0.01 0.02
0.02 0.05 0.04 0.06
0.20 0.12 0.21
0.01 0.11 0.05 0.15
0.07 - 0 . 0 2
Z/Z H-3
a Negative shift means shift to higher field. h A8 of multiplet given. O v e r l a p p i n g signals.
+=(1:1)
ll:Na
I)
+ = ( 1 : l)
II:K +=(2:
ll:K
1)
: 1)
10:Na÷=(l
10:Na +=(2:
1)
10:K ÷=(2:
0.10
10 : K + = (1 : 1)
E/Z H-3
-0.02 a 0.24 0.41, 0.04 0.16 0.30, -0.02 0.25 0.42, 0.02
E/E H-3
No.
0.00, 0.01 0.09, 0.11 0.05, 0.03 0.09, 0.10
0.04 0.05, 0.11 0.05, 0.05 0.07, 0.07
-0.01,
E/Z H-5
E/E H-8
0.10
0.03
0.10
0.00
0.12
0.08
0.08
0.05
0.01
0.06
0.00
0.07
0.02
0.05
0.00 - 0 . 0 1 b
Z/Z H-5
0.00, 0.00 0.06, 0.05 0.02, 0.03 0.06, 0.08
0.00, 0.03 0.06, 0.09 0.04, 0.04 0.07, 0.07
E/Z H-8
E/Z H-9
0.00 0.06 0.02 0.04
0.05 0.02 0.07
0.01, 0.00 0.06, 0.05 0.03, 0.03 0.06, 0.07
0.01, 0.02 0.10 0.07, 0.08 0.01 0.01, -0.01 0.03 0.04, 0.03
0.03
E/E H-9
0.00
0.07
0.04
0.08
0.02
Z/Z H-8 H-10
0.04
-0.04
0.01
0.10
0.06
0.02
0.01
0.08 - 0 . 0 1
0.02
0.05
0.01 - 0 . 0 3
0.08
0.01 - 0 . 0 4
Z/Z H-9
-0.03
-0.03
0.00
0.00
-0.011
-0.02
0.10
0.01
H-I 1
-0.01
-0.01
-0.02
-0.02
-0.19
-0.06
- ~
0.07
H-12
-
-0.04
-0.04
-
-
-
-
H-13
-
-0.10
0.00
-
-
H-14
-0.04
-0.04
-0.01
-0.01
-
-
-
0.04
Z CH2
0.09
0.07
0.06
-0.01
0.01
-0.01
-
0.00
E CH2
Table 10 IH Chemical shift differences A6 (ppm) o f the bis-benzo c r o w n ethers 10 and 11 in CDC13/CD O D during the c o m p l e x a t i o n with Na + and K ÷ cations (1 : 1) a n d (2 : 1)
t,~
-,q
4~
,--...
284
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
-202.3 ppm; in the E isomer at ~ = - 2 0 5 - - 2 0 6 . 4 ppm) and the corresponding N - H direct coupling constant proved to be smaller ( 1JN,H= 92--92.7 HZ) than in the E analogue (IJN,H = 94.0--96.5 HZ). Also the 1Jc,H of the ot-CH2 groups in 2 - 1 1 proved characteristically dependent on the amide bond configuration; e.g. for 2 1Jc.H(Z) = 125.0 Hz but lJc,rt(E) = 127.1 Hz (cf. Table 7). 3.1.4. NOEs between NH proton and ot-CH2 protons NOEs were found only in E configuration of the amide bond (cf. Scheme 2). 3.1.5. Geminal coupling constant between carbonyl carbon and N H proton In formamides the corresponding coupling constants proved to be dependent on the amide bond configuration [20,22]; in the E isomer 5.2 Hz, in the Z isomer 2.9 Hz has been measured [22]. In the case of the bis-benzo crown ethers studied 4.5-6.8 Hz (for the trans coupling constant) and 2.9-3.2 Hz for the corresponding cis coupling were detected, values sufficiently different to distinguish the present isomers in connection with arguments stated in Sections 3.1.1, 3.1.2, 3.1.3 and 3.1.4.
clearing the stereochemistry along the linking chain, the complexation of the bis-crown ethers 1-11 to K + and Na + cations, respectively, was studied. The variations of the IH chemical shifts of the corresponding protons at molar ratios 1-11 : K+/Na + = 1 : 1 and 1 : 2, respectively, are given in Tables 8-10. According to previous results [16], highfield shift of especially the aromatic protons during complexation was interpreted as formation of "sandwich"-like complexes due to intramolecular/intermolecular shielding of the two benzo crown ether moieties; from lowfield shifts, on the other hand, on conventional complexation of the cations within the cavity of the bis-crown moieties was concluded. With respect to these effects (cf. Tables 8-10) the following conclusions could be drawn. •
•
3.2. Syrdanti isomerism of the imine fragments 3.2.1. NOEs between the NH proton and the imine proton H-3 NOEs were found in 1-11 (in all the three isomers) and unequivocally prove the anti position of the NH proton and the imine nitrogen lone pair. • 3.2.2. Direct C(3)-H(3) coupling constant The corresponding direct C,H coupling constant for the anti arrangement expected proved to be 158164 Hz for 1-11; in case of the syn position values of > 185 Hz had to be expected [23-25]. Finally, no NMR parameter was found to determine the s-cis/s-trans isomerism of the carbonyl groups in 1; however, some indication was obtained from the quantum-chemical calculations (to be reported later in this paper). 3.3. Complexation of 1-11 to K÷/Na ÷ cations After assigning the various isomers of 1-11 and
The bis-benzo crown ethers 10-11 with the 18-crown-6 ether moieties complex both K + and Na + cations conventionally; 1 : 2 complexes proved to exist. Obviously, the cavity is sufficiently wide to host the two cations properly. The bis-benzo crown ethers 2 - 9 with the only 15-crown-5 ether moieties form "sandwich"like complexes to K ÷ cations; the cavities seem too small to host the K ÷ cations and the "bis-crown effect" was fully activated. The Na ÷ cations, on the other hand, are still sufficiently small to fix into the cavities of 2-9. For this reason, the formation of the conventional "filling" complexes 1 : 2 of 2 - 9 and Na ÷ cations could be concluded. The complexational behaviour of 1 (which proved to exist in E/E configuration only) to K + cations, due to the rigid molecular structure, was extraordinary: first, from highfield shifts of H-5-H-8 and lowfield shifts of H-9 during the complexation up to molar ratios of 1 : 1 on intermolecular complexation ("double-sandwich' '-like complex, cf. Scheme 3) was concluded. With further increasing the molar ratio 1 : K + up to 1 : 2 another set of signals of constant chemical shifts but growing intensity was obtained. From this behaviour, it was concluded that the 1:1 "sandwich"-like complex (Scheme 3) at those molar ratios will be
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
285
n=0 double
"sandwich"
complex of compound
I
"addition" complex "filling" complex
"sandwich"
- like structure
Scheme 3.
Table 11 t3C C h e m i c a l shift variations A6 (ppm) o f the bis-benzo c r o w n ethers 2, 4, 6 a n d 8 during the c o m p l e x a t i o n with Na + a n d K ÷ cations in CDCI 3/ C D 3 O D (80:20) No.
C-3
C-3
C-5
C-5
C-8
C-8
C-9
2 : Na + = (1 : 1) 2 : Na + = (1 : 2) 2 : K ÷ = (1 : 1) 2 : K + = (1 : 2) 4 : Na + = (1 : 1) 4 : Na + = (1 : 2) 4 : K + = (1 : 1) 4 : K + = (1 : 2) 6 : Na + = (1 : 1) 6 : Na ÷ = (1 : 2) 6 : K + = (1 : 1) 6 : K + = (1 : 2) 8 : Na + = (1 : 1) 8 : Na + = (1 : 2) 8 : K + = (1 : I) 8 : K + = (1 : 2)
-1.0 a -2.0 -0.4 -0.4 -0.1 -0.5 -0.6 -0.6 -0.6 -1.2 -0.2 -0.2 -0.6 -1.1 -0.3 -0.4
-0.2 -0.4 -0.7 -0.6 -0.1 -0.3 -0.8 -0.8 -0.1 -0.8 -0.2 -0.2 -0.2 -0.6 -0.1 -0.1
0.0 0.4 -0.6 -0.7 0.0 -0.1 -0.2 -0.2 0.0 0.2 -0.5 -0.6 0.1 0.2 -0.4 -0.4
0.0 0.4 -0.6 -0.7 0.1 0.1 -0.4 -0.4 0.2 0.4 -0.3 -0.3 0.3 0.6 -0.2 -0.2
0.2 0.3 -0.3 -0.5 0.2 0.4 -0.2 -0.2 0.2 0.2 -0.4 -0.4 0.2 0.3 -0.4 -0.4
0.2 0.3 0.3 -0.5 0.1 0.3 -0.6 -0.7 0.2 0.4 -0.3 -0.4 0.3 0.4 -0.6 -0.6
0.2 0.6 0.9 0.9 0.4 0.7 -0.1 -0.1 0.2 0.5 0.2 0.2 0.3 0.2 0.2 0.3
a
Negative A6 values m e a n shifts to higher fields.
C-9 0.3 0.6 0.9 0.9 0.4 0.7 0.1 0.1 0.2 0.4 0.0 0.0 0.1 0.3 0.0 0.0
C-10
C-11
C-12
C-13
-1.1 -1.2 -1.5 -1.6 -0.6 -1.4 -1.5 -1.7 -1.1 -1.6 -1.3 -1.5 -0.9 -1.7 -0.9 -1.2
-1.1 -1.6 -1.6 -1.7 -0.8 -1.5 -1.3 -1.5 -0.9 -1.6 -1.7 -1.8 -0.8 -1.5 -1.2 -1.3
-1.4 -1.7 -1.6 -1.7 -1.3 -1.7 -1.7 -1.9 -0.6 -1.8 -1.3 -1.5 -1.1 -1.7 -1.8 -1.8
-1.5 -2.1 -0.7 -0.9 -1.6 -2.1 -1.7 -2.0 -1.3 -2.1 -1.5 -1.5 -1.3 -2.2 -1.4 -1.5
286
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
Table 12 13C chemical shift variations A6 (ppm) of the bis-benzo crown ethers 10 and 11 in CDC13/CD 3OD (80 : 20) during their complexation with Na ÷ and K + cations No.
E/E
E/Z
Z/Z
E/E
E/Z
Z/Z
E/E
E/Z
Z/Z
E/E
E/Z
Z/Z
C-3
C-3
C-3
C-5
C-5
C-5
C-8
C-8
C-8
C-9
C-9
C-9
C-10
C-II
C-12
C-13
C-14
10 : KI (1 : 1)
-1. I a
-0.3
-0.5
-0.6
0.1
-0.6
-0.2
-0.2
-0.8
-0.4
-1.0
-1.1
-1.1
-0.8
0.1
0.l, 0.l 0.2, 0.0
0.1
-0.6
-0.6, -0.5 -0.9, -0.9
-0.5
-1.6
-0.6, -0.4 -1.1, -1.0
~).5
(2 : 1)
-1.0, 0.7 -1.4, 0.3
0.1
-1.1
-1.0
-0.3
-0.6
-0.4
10 : NaI (1 : l)
-0.8
-0.5
0.l
-0.8
-0.1
-1.0
-0.4
-0.8
-0.2
-0.4
-1.7
-1.7
-1.6
-1.3
-0.1
0.1, 0.1 -0.2, -0.4
0.l
-1.0
-0.6, -0.6 -1.4, -1.4
-0.7
-1.2
-0.9, -1.0 -1.8, -1.7
-0.8
(2 : 1)
-0.6, -0.7 -1.3, -1.7
-0.1
-2.1
-1.3
-0.3
-0.9
-1.3
ll:KI (1 : 1)
-0.3
-0.1
-0.5
-0.3
-0.3
-0.4
-1.1
-1.5
-0.5
-0.5
-1.4
-0.9
-0.8
-1.2
-0.2
-0.7, -0.7 -1.0, -1.0
-0.1
-0.6
-0.7, -0.7 -0.9, -0.9
-0.8
-0.7
-0.7, -0.7 -1.3, -1.3
-0.2
(2 : 1)
-0.2, -0.3 -0.3, -0.5
-0.1
-1.0
-1.7
-I.3
-0.9
-0.9
l l : NaI (1 : 1)
-0.5
-0.1
-1.1
-0.5
-1.7
-1.7
-0.9
-0.8
-0.6
-0.1
-2.1
-1.5
-1.4
0.2, -0.1 0.2, -0.2
0.7
-0.7
-0.9, -0.9 -1.9, -1.9
-0.9
(2 : 1)
-0.3, -0.3 -0.4, -0.1
0.6
-1.8
-1.7
-1.3
-0.9
-0.9
-0.2, -0.5 -0.4 -1.0,1 -0.9 -1.4
0.1 0.1
a A6 < 0 means shifts to higher field. and C3-H, respectively, of same intensity on
increasingly formed (and this on behalf of the former "double-sandwich'
the E/Z isomer could be readily concluded.
'-like association).
The additional set of arising and growing reso-
•
Also the bis-benzo crown ethers of lower link-
nances, on the other hand, proves another iso-
i n g c h a i n 2 - 4 s e e m to b e h a v e s i m i l a r l y t o N a +
m e r o f 1 to o r i g i n a t e ; f r o m t w o s i g n a l s o f N H
c a t i o n s at m o l a r r a t i o s u p to 1 : 1 as 1 to K +
113 112.5 ! ~ ..... : - - ~
'•
K +
111.5
"'~O
--
-0-
.......
-0
Na'
111
110.5 t "~
110 z
"E~ 109,5 •5
lO9
108,5
---e-
108 0
~ 0,5
q 1
i 1,5
..........
i 2
- ~
i 3
.........
-e
Na *
p 4
[Cationl:[Ugmzd] Fig. 2. Dependence of the 13Cchemical shifts of C-5 and C-8, respectively, of compound l l on the molar ratio [Na ÷] : [ l l ] (balls) and [K ÷] :[11] (squares).
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290 H i
cations, just aforementioned. First, up to molar ratios 2 - 3 : Na + = 1 : 1 highfield shifts reveal the formation of intermolecular 1 : 1 double"sandwich"-like association, only at molar ratios further increasing, lowfield shifts of the aromatic protons prove the conventional 1 : 2 "filling" complexation as mentioned already. In the cases of 2,4,6,8,10,11 also the 13C chemical shifts were followed during complexation (cf. Tables 11 and 12). The shapes of the corresponding curves (cf. Fig. 2 for 11) support previous conclusions [16,26]. In addition, from these studies for 10-11 could the Na + cations be concluded to better fit into the crown cavities than the K + cation: in the former case, the ~3C resonances within the ~,-fragments - C 5C6_O_C10_ and - C 8 - C 7 - O - C 1 ° - , respectively, shift stronger to highfield due to stronger in-plane interaction in order to form any useful topology for effectively complexing the Na + cations. The K + cations seem to be slightly too large for the present cavity and, therefore, only form association complexes as depicted in Scheme 3. Both in the free as well as in the K+/Na+-complexed state, the equilibrium of the three isomers E/E, E/Z and Z/Z proved more or less constant; variations when changing the solvent polarity were only minor and are related only to the preference of E/E on behalf of Z/Z (and the opposite way round), but the population of the E/Z isomer proved generally constant. Also the
H
(3
287
H-
t~
H
R / N ~ N ~
H.
H0
R/N'-N
H0
"'5 11
1
Scheme 4.
syn/anti isomerism of the imine fragments remains constant in the K+/Na + complexes studied. 3.4. Rotation about the CS-benzo crown ether moiety In order to study quantitatively the conformational equilibrium of the C3-aryl moiety, ROESY 2D NMR spectra [23,27] were recorded and the ROE cross peaks H-3/H-5 and H-3/H-9, respectively, volume integrated. Both these cross peaks were obtained; from this result, it was concluded that (i) the rotation about t h e C3-aryl bond is fast on the NMR time scale (the quantum-chemical calculations find the barrier to rotation to be below 2 kcal mo1-1) and that the two corresponding in-plane conformations (cf. Scheme 4) participate in the corresponding conformational equilibrium. The ROE values (in %: ROE(H-3/H-5) + ROE(H-3/ H-9) = 100%) thus obtained are shown in Tables 1315. Usually, in all isomers, conformation II proved to be the preferred one (from --50% up to 72%); only in the E/Z and Z/Z isomers of 4, I proved to be more
Table 13 Relative intensity of the R O E cross peaks of H - 3 / H - 5 a n d H-3/H-9, respectively, and of N - H / H - 3 moities obtained from R O E S Y 2D N M R spectra of the bis-benzo c r o w n ethers 1 - 9 Isomer
ROE
E/E
H I~ ~ H) ~ H~~ H~~ H~~ H~~ H ~~ H~~ NH ~
E/Z
Z/Z E/E E/Z Z/Z E/E E/Z Z/Z
1
2
3
4
5
6
7
8
9
30% 70%
NH ~ H ~ H5 ~ HI°
ROE ROE ROE ROE
50% 50% 40% 60% 50% 50% 50% 50% ROE ROE ROE ROE
23% 77% 37% 64% 28% 72% 30% 70% ROE ROE ROE ROE
40% 60% 38% 62% 46% 54% 67% 33% ROE ROE ROE ROE
31% 69% 40% 60e~ 40c~ 60% 33% 67% ROE ROE ROE ROE
45% 55% 45% 55% 50% 50% 50% 50% ROE ROE ROE ROE
42% 58% 29% 71% 30% 70% 40% 60% ROE ROE ROE ROE
38% 62% 33% 67% 50% 50% 50% 50% ROE ROE ROE ROE
28% 72% 31% 69% 31% 69% 30% 70% ROE ROE ROE ROE
H 8 ~ H I°
ROE
ROE
ROE
ROE
ROE
ROE
ROE
ROE
ROE
H5 H~ H5 H '~ H5 H~ 1-t5 H~ H~
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
288
Table 14 Relative intensity of the ROE cross peaks of H-3/H-5 and H-3/H-9, respectively, and of N-H/H-3 moities obtained from ROESY 2D NMR spectra of the bis-benzo crown ethers 1 - 9 complexed to K + cations (1 : 1) Isomer
ROE
E~
H 3~
H5
H 3~
H9
~Z
1
2
3
4
5
32% 68%
-~ ROE .
ROE
ROE -
. ROE .
H 3~ H5
NH ~ H 3 NH ~ H 3 NH ~ H 3 H 5 ~ H I°
20%
ROE ROE 50% 50% ROE ROE ROE ROE
H 8~ H m
80%
ROE
H 3~
H9
H3~ H5 H3 ~ H9 H3~ H5
~Z
H 3~
E~ E~ ~Z E~ E~ ~Z
H9
.
.
.
6 .
7
8
9
. ROE
ROE
ROE
ROE
ROE
ROE
ROE
ROE ROE ROE ROE ROE
ROE ROE ROE ROE ROE
ROE
ROE
. ROE .
. ROE ROE . ROE ROE ROE ROE ROE
ROE ROE ROE ROE ROE ROE ROE
ROE 50% 50% 50% 50% ROE ROE ROE ROE
ROE ROE ROE ROE ROE ROE ROE
ROE ROE . ROE ROE ROE ROE ROE
ROE
ROE
ROE
ROE
.
.
ROE
a No ROE obtained.
preferred
than II. In case of the corresponding
K÷
Section
3. U p to m o l a r
these
w a s o b t a i n e d (cf. T a b l e s 1 3 - 1 5 ) .
O b v i o u s l y , o n l y in
wich"-like
this conformational
any
change former conformational
arrangement
"sandwich"-
successfully
formed.
Further,
complexing this
conformation
seems
to
form
obviously
+ =
1 : 1,
double-"sand-
with no need
to
constructions. also confor-
be
m e r I I p r o v e d to b e i n c r e a s i n g p r e f e r r e d i n t h e K + / N a +
be
complexes compared with the non-complexed
species
(cf. T a b l e 15), b u t , e v e n w h e n b e i n g r e d u c e d , c o n f o r -
The exceptional behaviour of 1 and
m e r I is still p r e s e n t a n d w a s d e t e c t e d w i t h p o p u l a -
in t h e n o n - c o m p l e x e d
4 can also be understood complexational
could
complexes,
ethers
state of
already pre-organized these compounds.
the cations
crown
In the bis-benzo crown ethers 10-11
like topology of the bis-benzo crown ethers 2,3,5-9 for
bis-benzo
ratios of 1,4:K
c o m p l e x e s , e x c e p t f o r 1 a n d 4, o n l y t h i s c o n f o r m a t i o n
behaviour,
within
t i o n s o f at l e a s t 2 1 % . A l s o t h i s r e s u l t is in c o i n c i d e n c e
their exceptional
aforementioned
with the complexational
in
behaviour
of the bis-benzo
Table 15 Relative intensity of the ROE cross peaks of H-3/H-5 and H-3/H-9, respectively, and of N-H/H-3 moities obtained from ROESY 2D NMR spectra both in the free state of the bis-benzo crown ethers 10 and 11 and complexed to K + cations 10' and 11' (2 : 1) Isomer
ROE
10
10'
11
11'
E/E
H 3 ,-* H 5 H 3 ,--* H 9 H 3 '-* H 5
50% 50% 32% 68% 50% 50% 50% 50% ROE ROE ROE ROE ROE ROE
32% 68% 42% 58% 42% 58% 58% u.39% 42% U.61% ROE ROE ROE ROE ROE ROE
47% 53% 50% 50% 36% 64% 47% 53% ROE ROE ROE ROE ROE ROE
38% 62% 21% 79% 23% 77% 26% 74% ROE ROE ROE ROE ROE ROE
E/Z
H 3~
Z/Z E/E E/Z Z/Z E/E E/Z Z/Z
n 9
H3~ H5 H3~ H 9 H 3 *"* H 5 H 3 '--* H 9 NH ~ H 3 NH ~ H 3 NH ,--, H 3 H 5 '--' H ~0 H 8 ~ H ~0
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
crown ethers studied: conventional association and "filling" 1 ' 2 complexation (as aforementioned in Section 3) proved to be of only minor influence on the conformational preference of the C3-aryl moiety of 10-11. 3.5. Molecular dynamics simulations of the stereochemistry of 1-11 employing NOEs as constraints Various quantum-chemical and force field calculations of crown ethers and of their alkali cation complexes have been reported [28-31], even on the ab initio level [32,33]. As usual for flexible molecules of this size (dynamic NMR studies to lowest attainable temperatures revealed no line broadenings due to exchange phenomena) a large number of conformers will be obtained. In order to find out the preferred conformers of lowest energy for the bis-benzo crown ethers studied, the "simulated annealing" program of the TRIPOS software was employed, and, in the beginning, 1000 K was selected to be the plateau temperature. This temperature will be sufficient to surmount all the barriers to rotation present (plateau time I000 fs only). Then the systems (the ROEs measured were applied as constraints in order to find more realistic structures) were cooled down (in 1000 fs only in order to prevent the formation of non-realistic structures) to 200 K (100 cycles for each bis-benzo crown ether in order to find as many different conformations as possible) and the preferred conformers obtained by this method were energy optimized by the TRIPOS force field [12]. Within this frame for each of the E/E, E/Z and Z/Z isomers of the bisbenzo crown ether 1-11 5000 different conformers each were obtained. From these - 2 0 conformations of lowest energy but most different structure were selected for the energy optimization mentioned. The main conclusion from these results is that the three isomers of 1-11, in coincidence with the experimental results, are of nearly the same energy. Additionally, two general types of conformers, a stretched type (as useful for e.g. double-"sandwich"-like complexation (cf. Scheme 3) and a "sandwich"-like type (i.e. pre-organization of the bis-benzo crown ethers) were obtained. When comparing the corresponding energies of formation, the stretched type of conformation proved to be of higher energy (also in agreement
289
(a)
(b)
(c)
"
~
•
I
Fig. 3. Stereostuctures of compound 1: (a) E/E isomer (anti periplanar position of the two carbonyl groups; (b) E/E isomer (syn position of the two carbonyl groups; (c) E/Z isomer.
with the experiment where a "sandwich"-like topology of even the non-complexed bis-benzo crown ethers was found). Compound 1, having completely no linking chain, can exist in syn/anti conformation of the two carbonyl functions. Because of having no unequivocal argument in order to assign, this compound was theoretically studied in detail. From both methods very similar heats of formation were obtained (cf. Fig. 3), the anti arrangement slightly favoured in the preferred E/E isomer. At the same time, any "sandwich' '-like topology in the free state or in order to complex the alkali cations, proved to be hindered in this configuration. In the E/Z isomer, however, but in syn conformation of the carbonyl functions this "sandwich"-like topology becomes available and hereby the opportunity to complex alkali cations in this manner. The NMR study corroborates this complexational behaviour (as calculated by molecular mechanics and quantum-chemical calculations) by indicating another set of resonances (two NH and C 3 - H resonances each of same intensity) with proceeding K ÷ complexation of the 1.
References [1] J. Lekschas and D. Cech, Wiss. Fortschr., 38 (1988)4. [2] K. Gloe, P. Miihl, A.I. Kholkin, M. Meerbok and J. Berger, Isotopenpraxis, 18(1982) 170.
290
E. Kleinpeter et al./Journal of Molecular Structure 404 (1997) 273-290
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