Macrocyclic Ligands - Web del Profesor

4 MACROCYCLIC LIGANDS
N
N
2.3.4 Catenands
Me
N OH N
N
OH
Me
(16)
O
O O
O
O
O
O O
O
O
(17)
Catenands (17) are interlocked macrocyclic ligands, which
complex a variety of metal ions. 29
2.4 Polyoxa Macrocycles
Polyoxa macrocycles, known more commonly as the crown
ethers, comprise an extensive area of research, with a repertoire
of types and variations. 30 Some of these macrocycles have
been utilized predominantly for purposes other than metal ion
complexation, and these will not be discussed in depth in this
review. Included in this latter category are the polycarbonyls, 31
polylactones, 32 polylactams 33 and carcerands. 34
2.4.1 Polyether Macrocycles
Polyether macrocycles (18) are the simplest of the polyoxa
macrocycles. The commonly used name for these macrocycles
is the crown ethers, due to their crown-like structure in the
solid state. These molecules have been extensively studied
N
O
O
N
N
O
O
O
O
(18)
as complexing agents for the alkali and alkaline earth metal
ions. 30
2.4.2 Lariat Ethers
The lariat ethers comprise a subset of the polyether
macrocycles, and are identified by their pendant chains. 35
They can be categorized as either N-pivot (19) orC-pivot
(20), depending on which type of atom the chain is attached.
As for their polyether parents, much of the focus on these
macrocycles has been on complexation of alkali and alkaline
earth metal ions.
O
O
O
O
(19)
N
O
2.4.3 Spherands and Hemispherands
O
O
O
O
O
O
(20)
O
O
MeO
These consist of an arrangement of phenyl groups which
provide a preorganized cavity for complexation, 36 e.g. (21)
and (22).
Me Me
Me
Me
OMe
OMe MeO
OMe MeO
OMe
Me
(21)
Me