Table Of ContentHost Guest Complex
Chemistry
Macrocycles
Synthesis, Structures, Applications
Editors: F. V6gtle, E. Weber
With 174 Figures and 46 Tables
Springer-Verlag
Berlin Heidelberg New York Tokyo
1985
Professor Dr. Fritz Vogtle
Dr. Edwin Weber
Institut fUr Organische Chemie und Biochemie
Universitiit Bonn
Gerhard-Domagk-StraBe 1
5300 Bonn 1
ISBN -13: 978-3-540-13950-8 e-ISBN -13: 978-3-642-70108-5
DOl: 10.1007/978-3-642-70108-5
Library of Congress Cataloging in Pnblication Data. Main entry under title:
Host guest complex chemistry/macrocycles.
Bibliography: p. Includes index.
1. Electron don~r-acceptor complexes--Adresses, essays, lectures. I. VogUe, F. (Fritz), 1939 -
ll. Weber, E.
QD474.H67 1985 541.2'8 84-23569
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Table of Contens
Crown-Type Compounds - An Introductory Overview
E. Weber and F. Vogtle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Structural Chemistry of Natural and Synthetic Ionophores
and their Complexes with Cations
R. Hilgenberger and W. Saenger ............................ 43
Concept, Structure, and Binding in Complexation
D. J. Cram and K N. Trueblood. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 125
Analytical Applications of Crown Compounds and Cryptands
E. Blasius and K-P. Janzen ................................. 189
Crown Compounds as Alkali and Alkaline Earth
Metal Ion Selective Chromogenic Reagents
M. Takagi and K Ueno ..................................... 217
Photocontrol of Ion Extraction and Ion Transport
by Photofunctional Crown Ethers
S. Shinkai and O. Manabe .................................. 245
Bioorganic Modelling-Stereoseletive Reactions with
Chiral Neutral Ligand Complexes as Model Systems
for Enzyme Catalysis
R. M. Kellogg. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 283
Complexation of Uncharged Molecules and Anions
by Crown-'JYpe Host Molecules
F. Vogtle, H. Sieger and W. M. MUller ....................... 319
The Calixarenes
C. D. Gutsche ............................................. 375
Crown-Type Compounds - An Introductory Overview
Dr. Edwin Weber, Prof. Dr. Fritz Vogtle
Institut fUr Organische Chemie und Biochemie der Universitat Bonn, Gerhard-Domagk-Stra13e 1,
D-5300 Bonn 1, FRG
Table of Contents
1 Introduction . 3
2 Classification of Oligo-/Multidentate Neutral Ligands
and of their Complexes. . . . . . . . . . . . . . 3
3 Crown-Type Ligands. . . . . . . . . . . . 3
3.1 Historical Crown Ethers, Nomenclature . 3
3.2 Variation Possibilities with Coronands . 5
3.3 Cryptands. . . . . . . . . . . . . . 10
3.4 Podands (Open-Chain Crown Compounds and Cryptands,
Octopus Molecules). . . 11
3.5 Podandocoronands ... 14
3.6 Macrocyclic Oligoketones 15
3.7 Spherands. 16
4 Ligand Synthesis 16
4.1 Coronands 16
4.2 Cryptands. 17
4.3 Podands .. 17
5 Properties of Crown Compounds. 18
5.1 Hydrophilicity/Lipophilicity Balance 18
5.2 Crown Ethers as Cation Receptors . 18
5.2.1 Optimal Spatial Fit Concept and Circular Recognition. 18
5.2.2 Structure of Crystalline Complexes . . . 18
5.2.3 Complex Stability in Solution. . . . . . . . 19
5.2.4 Selectivity of Crown Ether Complexation. . . 19
5.3 Coronates - The Concept of Donor-Site Variation. 21
5.4 Complexation of Cryptands, Cryptate Effect and Spherical Recognition 22
5.5 Podates. . . . . . . . . . . . . . . . . . . . . . . . . . .. 23
Edwin Weber and Fritz VogUe
5.6 Complexation Kinetics of Neutral Ligands. 25
5.7 Recognition and Complexation of Molecular Cations 25
5.8 Chiral Crown Compounds and Chiral Recognition . 26
5.9 Multisite Receptors, Cascade Complexation and Ion-Pair Complexes 28
5.10 Anion Receptors and Neutral Molecular Complexes . . . . . . . . 29
6 Consequences of the Properties of Crown Compounds . 30
6.1 Lipophilisation and Phase Transfer of Ions 30
6.2 Ion-Pairing and Ion-Aggregation Effects. 31
6.3 Modifications in Chemical Reactivity. 31
6.3.1 Anion Activation . . . . . . . . 31
6.3.2 Nucleophilicity/Basicity Balance. . 32
6.3.3 Ambidency and Regioselectivity Control . 32
6.3.4 Effects of Cation Capture ..., . . . . 33
6.4 Modification of Reaction Mechanisms and of their Stereochemistry. 34
7 Application Possibilities 35
8 Acknowledgement . 35
9 References . . . . 35
2
Crown-Type Compounds
1 Introduction
The scientific and practical interest in coronands (crown ethers), cryptands, podands
as complexing agents for cations as well as for anions and neutral low molecular
species is undeniable 1,2). The chemistry of crown compounds is steadily increasing.
About 250 original papers dealing with crown chemistry appeared only in 1980.
New molecules· with crown ether properties are constantly synthesized and new
applications discov,?red.
Owing to lack of space, only a small number of the original publications is men
tioned here. Thus, in the literature compilation only some, but relevant works
are selected for each chapter. Whenever possible, reference is made to reviews or
review-like articles alone by means of which origin,al works can be consulted. The
reviews given under ref. are considered to be the most relevant. The formulae
1)
presented in the figures should be understood as representative structures outlining
a specific field.
2 Classification of Oligo-/Multidentate Neutral Ligands
and of their Complexes
Today, a distinction is made between the classical ring oligoethers (crown ethers) and
monocyclic coronands, oligocyclic spherical cryptands and the acyclic podands
with respect to topological aspects 3). This classification and the topology are
illustrated in Fig. 1, each figure representing the minimum number of donor atoms
and chain segments characteristic of each class of compounds. Multidentate mono
cyclic ligands with any type of donor atoms are called coronands ("crown
compounds"), while the term crown ether should be reserved for cyclic oligoethers
exclusively containing oxygen as donor atom. Moreover, a subdivision of each
of the three respectively four classes of ligands according to the number of arms or
bridges is possible.
Because of their ability to take up ions and to transfer them across a lipophilic
medium, these types of ligands also are often called ionophores, comparable to the
structurally related polyether antibiotics, the ionophoric behaviour of which had
been discovered first
4).
In order to differentiate the crown ether ligands from their metal ion complexes,
the terms coronand and coronate were suggested for the uncomplexed and com
plexed species, respectively 3). Analogously used are the terms cryptand/cryptate
and podand/podate (cf. Sects. 3.3. and 3.4.).
3 Crown-Type Ligands
3.1 Historical Crown Ethers, Nomenclature
The first synthetic ionophores described by Pedersen in 19675), were the cyclic
hexaethers 1 and 2, which have been simply called [18]crown-6 and dibenzo[18]
crown-62f), in contrast to their cumbersome and less illustrative IUPAC nomen
clature (Fig. 2).
6)
3
Edwin Weber and Fritz Vogtle
Podands (open -chain) Coronands (cyclic) Cryptands (spherical)
C-0~ ~O~
o~ 0~ 0 o 0 B-l.--0,J:,B
"---./ ~O;;
{I) Podand {MonopodandJ III Coronond (Monocoronond) (2) Cryptond
r+o~o
(0,(0, ko,fn-8~0~
0 0 B+ 01:0; "'8
A A
"to 0
~°'t!"-r°iJ ~Dr-B~in
V
{ 2 )P odond (Dipodond) ( 2 )C oronond I Oicoronond) (3) Cryptond I Tricryplond)
B~O-Tn)
( 'f-'-f' )
C+o~
~
r+o 0 0 0
BrT-o-1.0B
A (~A+D~
( "foDof" )
'ito0 ~/0 o )( 0
n
Yn V O
0'--f /f'o~B
"-r0~
{3 I Podond (Tripodond) { 3 I Coronond (Tricoronond ) { G IC ryptond (Tetrocryptand)
Fig, I. Topology and classification of organic neutral ligands 3) (D = donor atom, A = anchoring
group, n = chain segment without donor atom, B = bridgehead atom)
"Dibenzo" stands for both of the benzene nuclei annexed to the ring while
"[18]" in square brackets means the number of ring atoms. The class specification
"crown" is followed by the number of heteroatoms in the ring; in this case "6",
The above notation is now commonly accepted and generally serves to give a
rough characterisation of medium- to many-membered cyclic polyethers in which
the oxygen atoms are mostly connected via ethan a bridges and in which annexed
benzene and cyclohexane rings may also be present (Fig, 2),
7)
As Pedersen's crown notation is not unequivocally defined with regard to the
location of the donor atoms, the benzene nuclei, the cyclohexane units or other
ring components, even in simple cases, a more systematic and widely applicable
nomenclature covering all kinds of cyclic and noncyclic ligands and also their
complexes has been proposed recently (cf. Figs, I and 2) In principle, the same
3),
symbolisms are retained but in addition it is specified as follows: The number
preceding the angular brackets "( )" indicates the ring size. In the presence of
aromatic and heteroaromatic units in the ring, the shortest way to the next donor
atom is considered. The angular brackets contain in the order given: I) donor
4
0(0 10 :0
0
Structure: r I I
:::,.. 0 0 ~
~o-.J
Nr. 2
IUPAC-designation 1,4,7, 10, 13, 16-hexaoxa 2,5,8,15,18,21-hexaoxa 2,5,8,15,18,21-hexa
cyclooctadecane tricyclo[20.4.0.09•14] oxatricyclo
hexacosa- [20.4.0.09,14]
1(22),8,11,13,23,24· hexacosane
hexaene"
Short name [18]crown-6 dibenzo[18]crown-6 dicyclohexano[18]
(Pedersen's crown crown-6
nomenclature)
Notation [18]C-6 DB[18]C-6 DCH[18)C-6
New nomenclature 18( 06coronand -6) 18(06(1,2)benzeno.22· 18(0 6(1 ,2)cyclo
system (1,2)benzeno.22coro hexano .22.(1,2)
nand-6) cyclohexano.2 cbro
2
nand-6)
" Phane nomenclature: 1,4,7,14,17,20-hexaoxa[7.7] (l,2)benzenophane
Fig. 2. Nomenclature of crown ethers
heteroatoms expressed by elemental symbols; 2) bridges, i.e. C--C chains between
the donor atoms, denoted by numbers which correspond to the bridging C-atoms,
bridge units like aromatic nuclei or more complex groups (position marked in round
brackets). The designation "2" for ethano, the most common bridge, is omitted
if only this kind of bridge unit is present or if such a procedure does not curtail
the clarity of the structure (cf. 18< 06-coronand-6»); 3) the class name (e.g.
coronand), and 4) the total number of donor heteroatoms.
In the case of mixed O/N/S macrocycles where ether oxygens are successively
replaced by other heteroatoms (combinations s.b.), the sequence of donor sites
in the ligand skeleton is given by heteroelemental symbols arranged in the order
of priority laid down by the IUPAC rules. Heterocycles with donor sites (s.b.)
are treated as single atoms. The sequence for the chain segments without donor atoms
correspond to that of the heteroatoms, beginning with the donor atom of highest
priority (cf. structures 2 and 3 in Fig. 2).
Substituents and functional groups in the basic skeleton (class name) are
denoted by prefixes and suffixes. The numbering is principally carried out according
to the IUPAC rules (this is also valid for the cryptands but does not strictly apply
to podands; s.b.).
Altogether, the new proposal of nomenclature extended in Sections 3.3. and 3.4.
allows an essentially easier recognition of the ligand type and other characteristics
such as topology and donor centers.
3.2 Variation Possibilities with Coronands (Fig. 3-11)
Since the discovery of crown ethers efforts have not diminished to synthesize
8)
crown species with other distributions, numbers and types of donor heteroatoms
like nitrogen or sulfur 1.2):
5
Edwin Weber and Fritz Vogtle
(0")
r?y0 0)
~O 0
~OJ
S9a.101
Fig. 3. Stiffening of the [l81crown-6 skeleton by benzo condensation
r-\ 1\0 )
(0 0) \
0 0 J
Co
~oJ 0
l.....-0~
911al 1011bl 1111bl
Fig. 4. Crown ethers of different
1211bl ring size
a) Ring-stiffened aryl ether ligands (Fig. 3) 5.9-10): Basicity and donor ability of
the oxygen atoms are reduced (4-8).
b) Varied ring size (Fig. 4) 5,11): Every number of ring members and oxygen donors
is possible (9-13).
c) Geometric arrangement of the donor atoms in the ring (Fig. 5) 5,12): The oxygen
atoms can be separated (14, 15) or brought together (16-18).
d) Sulfur as -alternative donor site (Fig. 6) 13,14): All O,S-sequence combinations
(19-22) and even pure thiacrowns like 23 are possible.
e) Nitrogen as donor site (Fig. 7) 15): Incorporation of any number of N-atoms
into the ring and at any position is possible (24-28).
6
