Alkali metal complexes Schiff bases

Crown ethers may also be used to functionalize salicylideneimine complexes.1179 The crown ether-functionalized tetra-t-butyl-salicylideneimines are useful in studies on the selective com-plexation and transport of cations (e.g., Na+ and K+). 4,5-Bis(3,5-di-/-butylsalicylideneimino) benzo-18-crown-6 coordinates Ni11 via the Schiff base N202 donor system and K+ or Cs+ at the crown site.1180 These Ni-alkali metal complexes are able to transport amino acids from acidic aqueous solution to pure water. 

In contrast to the extensive coverage of transition metal Schiff base complexes, there is a somewhat desultory presentation of alkali and alkaline earth metal complexes of these ligands. 

We have prepared a variety of new Schiff base bis crown ether ligands (98-100) that contain alkali and transition metal coordinating sites via the condensation of two or three equivalents of 4-formyl-benzo-15-crown-5 with an appropriate di- or triamine (Scheme 18). Homometallic copper(I), silver(I), and heteropolymetallic copper(I)-sodium, silver-(I)-sodium, and potassium complexes have been isolated. The singlecrystal X-ray structure of the [Cu(57)K](PF6)2 complex (100) is shown... 

The purification of sirupy ribose has in the past usually been carried out through the p-bromophenylhydrazone,1 7 27 a costly and laborious procedure. Recent studies of the arylamine ribosides have resulted in the discovery of a cheaper and more convenient method for the purification of ribose.28 29 30 The procedure is based upon the fact that ribose, dissolved in aqueous alcohol containing an arylamine such as aniline and an alkali metal salt such as sodium sulfate and having a pH of 4, is precipitated in high yield as a crystalline arylamine riboside-salt complex. The arylamine riboside may be extracted from this complex with dioxane and decomposed by boiling in water containing a trace of acetic acid. After the arylamine has been removed by steam distillation or through formation of a Schiff base with formaldehyde or benzaldehyde, the pure, crystalline ribose may be recovered. 

The nitrogen atom of a Schiff base or oxime can coordinate to various metal ions (alkali metal, alkaline earth metal, transition metal, heavy metal ion). In particular, chelates such as salen (bis(salicylidene)ethylenediamine), saloph (bis(salicylidene)-o-phenylenediamine), and salamo (bis(salicylideneaminooxy)ethane) afford stable metal complexes, which are utilized for a variety of molecular functions such as catalysis of organic reactions, magnetism, luminescence, etc. °... 

Addition of acid leads to protonation of the sidearm N and the formation of a new hydrogen bonding leads to o -state in solution at relatively mild conditions - p/Cj value of 26a in 5.89 in acetonitrile [67]. The on-off process is truly reversible in ground state, showing that controlled ground state tautomerism is possible in azonaphthols and structurally similar Schiff bases [15, 66]. The same effect is observed upon alkali and alkaline earth metal ions addition when piperidine unit in 26a is replaced by an aza-15-crown-5 [68]. The o/i-state is stabilized through 1 1 complex formation and the excess of metal ion leads to deprotonation of the tautomeric ligand as well as to 2 2 complexation. 

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