2 Homometallic Alkoxides

452 Alkoxo and Aryloxo Derivatives of Metals
(CH2) n
Me
N OH N
N OH N
Me
Me
N OH N
N OH N
Me
(CH2)m
2.3 Poly-aryloxides and Calixarenes
N
Me
N OH N
NH OH HN
Me
N OH N
N OH N
N
Me
Me
Scheme 6.6
O
O
Me
NH OH HN
NH OH HN
Me
Cl
N OH N
N OH N
The elaboration of routine synthetic methodologies such as the condensation reaction
of 2-formyl- or 2-acyl-phenols with primary amines, sometimes followed by
reduction, can be utilized in the synthesis of poly-aryloxide ligands including macrocyclic
examples. Some types of tris-aryloxides obtained in this way are shown in
Scheme 6.7 (A) and(B). 74,75 Examples of a nonmacrocyclic tetra-aryloxide (C), 76 and
a macrocyclic tetra-aryloxide (D) 77,78 are also shown. The connection of multiple catecholate
nuclei can also generate poly-aryloxides (see Section 2.2.1). An important
class of poly-phenoxides is the calix[n]arenes (n represents the number of phenol
units (Scheme 6.7) (E)), which can be readily obtained by the condensation of parasubstituted
phenols with formaldehyde. 79 The chemistry of the calixarene ligand has
been exhaustively reviewed. 80 An important aspect of the chemistry of these ligands
centres upon the various conformers that can be adopted and/or stabilized. In the case of
calix[4]arene there are four conformations: “cone” (all oxygen atoms on the same side
of the ring), “partial cone” (three up, one down), “1,2-alternate”, and“1,3-alternate”.
By blocking or linking phenoxide oxygens it is possible to generate unusual tris- and
bis-aryloxides. 81,82 There are eight possible conformers for calix[6]arene. 83
Cl
O
O