New ligand systems for ions and molecules - and electronic effects upon complexation
Chromophore—ionophores are described, which upon complexation give ion—selective colour changes. Thus, dyestuffs can be influenced either in a hypsochromic or in a bathochromic way. Bond formation and bond cleavage reactions as well as organic catalysts are likewise electronically influenced by ion-selective complexation, so that an accurate steering of reactivities by ions is possible. Neutral guest molecules form definite complexes with crown ethers and their analogues. Crystalline phenyl hydrazine complexes can serve as stable reagents for the derivatisation of carbonyl compounds to the corresponding hydrazones in lipophilic solvents. Volatile toxic substances, which are used as reagents for alkylation and acy— lation reactions, can be converted into crystalline stoichiometric neutral complexes. It seems possible to develop receptor cavities for urea and other molecules of physiological interest. It has been shown that the complex stability towards particular metal cations can be influenced by suitable substituents X in the benzene nucleus of benzo crown comDounds [1]. For example, the complexation constant for alkali metal ions of benzo [18] crown-6 compounds [2], bearing electron—withdrawing substituents X,Y [cf. (2)] is lower than that of the unsubstituted benzo{18]crown—6 (!), owing to the electron-withdrawing effect which causes a reduction in the electron density and thereby in the donating power of the catechol oxygen atoms [3]. (!) : XY H () (2): X= Br, N07, Y H, Cl We are interested in the reverse aspect, namely, whether and how strong the electronic properties of functional groups Z in the benzene nucleus [come. (3)] can be influenced by the selective complexation of cations (Me) in the ionophore part of the molecule. The monocyclic ionophore structure in (3) may be