Schiff salicylaldimine ligands

In 1966, Nozaki et al. reported that the decomposition of o-diazo-esters by a copper chiral Schiff base complex in the presence of olefins gave optically active cyclopropanes (Scheme 58).220 221 Following this seminal discovery, Aratani et al. commenced an extensive study of the chiral salicylaldimine ligand and developed highly enantioselective and industrially useful cyclopropanation.222-224 Since then, various complexes have been prepared and applied to asymmetric cyclo-propanation. In this section, however, only selected examples of cyclopropanations using diazo compounds are discussed. For a more detailed discussion of asymmetric cyclopropanation and related reactions, see reviews and books.17-21,225... 

Structural motifs related to Schiff-base ligands have been explored. Three tridentate ligands have been coordinated to the VO (quin) fragment (quin = 8-quinolinato). The octahedral azobenzene complex VO (quin) (2-hydroxy-2 -carboxy-5-methylazobenzene) shown in Fig.22 has a reversible reduction (by CV and controlled potential electrolysis) at ca —0.31 V versus Cp2Fe/CH2Cl2. This potential is 0.58 V more positive than the potential found in the analogous Schiff-base VO (quin) (V-(l-hydroxyethyl)salicylaldimine) complex. The latter complex reduction is also... 

Fig. 111. (Top) Imidazo[4,5-f]l,10-phenanthroline ligands for metallomesogens. (Bottom) Salicylaldimine Schiff...

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