Pyridine-2-carbaldehyde Schiff bases

A number of representative nickel(II) complexes prepared with Schiff bases derived from pyridine-2-carbaldehyde, pyridine-2,6-dicarbaldehyde and related species are summarized in Table 98, together with some of their distinctive physicochemical properties and preparative routes. All of these complexes involve N and either O or S as donor atoms and exhibit various coordination numbers and geometries depending on the denticity of the ligands and on their steric and electronic requirements. 

In addition to its use in the preparation of the square pyramidal Mo and W complexes 38 and 39, the Schiff base derived from pyridine carbaldehyde-(2) and S-(—)-a-phenyl ethyl amine54 was also used for the synthesis of optically active Co complexes of the tetrahedral type60. Unlike the Mo and W compounds, the separated Co diastereoisomers 40a, 40b one of which is shown in Scheme 20, are optically stable. The rigidity of the tetrahedral Co complexes and the nonrigidity of the square pyramidal Mo and W complexes give a further indication of the intramolecular character of the epimerization of 38 and 39. 

Hi) Complexes with Schiff bases derived from pyridine-2-carbaldehyde and related species and with hydrazones... 

Epimerization of diastereoisomers of related complexes [M(CO)2(LL )( -C5H5)] (M = Mo or W) where LL is a bidentate ligand derived from Schiff bases of benz-aldehyde (5) follows first-order kinetics with the activation parameters given in Table 2. In these cases the epimerization process, as with pyridine carbaldehyde... 

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