Synthesis, structure, and host ability of macrocycles based on the structural diversity of 1,3-diene

Article abstract of DOI:10.1016/S0040-4039(00)02328-5

Macrocycles consisting of both a 1,3-diene unit and a polyether linkage were prepared by the reaction of muconic acid dichloride with diols containing a polyether linkage. The 1,3-diene moiety was complexed by iron carbonyl to furnish macrocycles bearing a (η⁴-diene)tricarbonyliron moiety. The structures of the macrocycles were determined by NMR and IR spectroscopy, and by X-ray structural analysis. The macrocycles formed complexes with some ammonium salts and their association constants varied according to whether the structure of the 1,3-diene moiety was complexed or uncomplexed. Ring-size effects of the macrocycles on the association constants were also studied.

Full text of DOI:10.1016/S0040-4039(00)02328-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 1699–1702
Synthesis, structure, and host ability of macrocycles based on
the structural diversity of 1,3-diene
Hiroshi Yamaguchi, Saburo Nakanishi, Nobuhiro Kihara and Toshikazu Takata*
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
Received 18 September 2000; revised 24 November 2000; accepted 15 December 2000
Abstract—Macrocycles consisting of both a 1,3-diene unit and a polyether linkage were prepared by the reaction of muconic acid
dichloride with diols containing a polyether linkage. The 1,3-diene moiety was complexed by iron carbonyl to furnish macrocycles
bearing a (h4-diene)tricarbonyliron moiety. The structures of the macrocycles were determined by NMR and IR spectroscopy, and
by X-ray structural analysis. The macrocycles formed complexes with some ammonium salts and their association constants varied
according to whether the structure of the 1,3-diene moiety was complexed or uncomplexed. Ring-size effects of the macrocycles
on the association constants were also studied. © 2001 Elsevier Science Ltd. All rights reserved.
Crown ethers and macrocyclic polyethers are typical
representatives of host molecules.1 A variety of syn-
thetic receptors capable of varying their structures by
external stimuli have been developed. These motifs
include alkenes,1g azobenzenes,1d,e and bipyridines1f
causing allosteric effects.1h,i 1,3-Dienes can be easily
complexed by iron carbonyls to give (h4-diene)Fe(CO)3
complexes, which are fairly stable toward water, air,
and heating.2 Decomplexation of (h4-diene)Fe(CO)3
complexes can also be readily conducted by photo- and
oxidation reactions leading to the original 1,3-dienes.3
These complexation and decomplexation are highly
selective, and can be reversible in the presence of vari-
ous substrates. Thus, the interconversion between 1,3-
diene and its Fe(CO)3 complex can be another
candidate of the driving force to realize allosteric
effects.
complexation with the Fe(CO)3 group. Further, the
transformation of the 1,3-diene to a (h4-diene)Fe(CO)3
complex results in an increase in the steric hindrance
around the 1,3-diene and a decrease in the electron
density of the diene unit. We now wish to report the
preparation, structure, and host ability of macrocycles
having both polyether linkages and 1,3-diene units, and
the change of host ability by the conversion to the
(h4-diene)Fe(CO)3 complex.
The synthesis of macrocycles 2, bearing both 1,3-diene
units and polyether linkages, is shown in Scheme 2.
Cyclization of muconic acid dichloride and diols 14
having polyether linkages were carried out under high
dilution conditions to afford 2 in moderate yields.5 The
1,3-diene units of 2 were complexed with diiron
nonacarbonyl to give macrocycles 5 bearing a (h4-
diene)tricarbonyliron moiety in good yields (Scheme
3).6 Complex 6a was obtained from 5a by ligand substi-
tution with triphenylphosphine.7
While the C2ꢀC3 single bond of the 1,3-diene rotates
freely to make the conformation flexible, the 1,3-diene
unit in the Fe(CO)3 complex is fixed by the s-cis form
so that the (h4-diene)Fe(CO)3 complex has a rigid,
planar structure (Scheme 1). Therefore, host molecules
bearing a 1,3-diene moiety can be preorganized by the
The structures of the macrocycles 2, 5 and 6 were
determined by the IR and NMR spectroscopy. The
Scheme 1.
Keywords: (h4-diene)Fe(CO)3 complex; s-cis, s-trans configurations; molecular recognition.
* Corresponding author. E-mail: takata@chem.osakafu-u.ac.jp
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)02328-5

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H. Yamaguchi et al. / Tetrahedron Letters 42 (2001) 1699–1702
Scheme 2.
complexed structure with a Fe(CO)3 moiety was con-
firmed by X-ray crystal structure analysis of 5a.8 The
(h4-diene)Fe(CO)3 moiety has an almost planar s-cis
structure, judging from the dihedral angle between the
C2ꢀC3 and C4ꢀC5 bonds (1.1°) (Fig. 1).
It was established from extraction experiments of
picrate that macrocycles 2 and 5 were able to form
complexes with some ammonium picrates derived from
4-methylaniline, benzylamine, 4-chloroaniline, and ani-
line. The complex-forming ability of the macrocycles
with 4-methylanilinium picrate 7 was evaluated in terms
of the structural diversity of a 1,3-diene. Job plots,
1
which were obtained from the H NMR spectra of a
mixture of host and 7, indicated that 2a, 5a, and 5b
furnish a 1:2 (host:guest) complex with 7, while the
complexing ratios for 2a, 5a, and 5b could not be
Figure 1. X-Ray crystal structure of 5a. Hydrogen atoms are
omitted for clarity.
Table 1. Association constants of 4-methylanilinium picrate 7 and macrocycles
Diene macrocycle (ring member) Association constant (Ka)a
Iron complex macrocycle (ring member)
Association constant (Ka)a
2a (22)
124 M−1
5a (22)
6a (22)
5b (28)
5c (34)
84 M−1
8 M−1
2b (28)
2c (34)
2.10×104 M−2
5.40×105 M−2
3.12×104 M−2
5.62×105 M−2
a Determined by extraction of 4-methylanilinium picrate 7 from the aqueous layer to the CHCl3 layer.

H. Yamaguchi et al. / Tetrahedron Letters 42 (2001) 1699–1702
1701
Scheme 3.
determined exactly because the changes in the NMR
chemical shifts were too small. Complexation ratios
were estimated as 1:2 for 5b and 1:1 for 2a and 5a,
referring to the ratios reported for macrocycles with 32
and 26 ring member hosts.9
In summary, we have demonstrated the synthesis, struc-
ture, and hosting ability of novel macrocycles contain-
ing 1,3-diene and (h4-diene)Fe(CO)3 complex moieties.
Structural variation of the 1,3-diene moiety, complexed
or uncomplexed, could control the host ability, while
the effect of the structural change of 1,3-diene depends
on the ring size and the structure of the macrocycles.
The Kas decreased in a series of 22 ring member hosts
(from 2a to 5a, negative allosteric effect), increased in
28 ring member (from 2b to 5b, positive allosteric
effect), and was approximately the same in a series of
34 ring member hosts (from 2c to 5c), due to the
transformation of a 1,3-diene to a (h4-diene)Fe(CO)3
complex. These results suggest that the structural
change of a 1,3-diene by ‘Fe(CO)3’ is very effective for
modifying the host ability of diene-containing macrocy-
cles. Further application of this structural diversity of
1,3-diene is under investigation.
Association constants (Ka) of the macrocycles with
4-methylanilinium picrate 7 were obtained by Cram’s
method in a CHCl3–water bilayer system (Table 1).10
The Kas were compared with those having the same
dimensions. For 2a and 5a, Ka decreased from 124 M−1
(2a) to 84 M−1 (5a) by the transformation of the
1,3-diene unit to a (h4-diene)Fe(CO)3 complex. The
decrease is probably due to steric hindrance of the
Fe(CO)3 unit. The Ka decreased further to 8 M−1 (6a)
by the introduction of a Ph3P group, which replaced the
CO group as the ligand, due to the steric bulkiness of
(h4-diene)Fe(CO)2PPh3. On the other hand, for 2b and
5b, the Ka increased from 2.10×104 M−2 (2b) to 3.12×104
M−2 (5b) by the transformation of the 1,3-diene unit to
a (h4-diene)Fe(CO)3 complex. The rigid, planar s-cis
h4-diene structure is more favorable for the complexa-
tion with 7 than the flexible 1,3-diene unit. As for
macrocycles 2c and 5c, the Ka values were approxi-
mately the same, indicating the effects of steric hind-
rance and preorganization were counterbalanced.
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.