Tridentate triamine

Most tridentate triamine ligands 165 and 166 command a high level of interest [285e,286,293-295,297,298]. In general, octahedral complexes have been obtained in which the existence of the three isomeric compounds 167—169 has been established by x-ray diffraction [28 5e] ... 

Pyridine-2,6-dicarbaldehyde and 2,6-diacetylpyridine have been widely used in the template synthesis of imine chelates ranging in complexity from linear tridentates, such as (17),38 39 to macrocyclic structures with a range of ring sizes, such as (18).40-42 The in situ formation of macrocyclic ligands of this type depends upon the ring size and the strength of complexation of the triamine by the metal ion at the pH of the reaction. Related complexes with an additional donor atom attached to R2 have been synthesized also.43 44... 

Research with tridentate ligands has been carried out for several fundamental coordinating groups, pyrazolyl-borates, aliphatic triamines and histidine-type ligands. Other ligands have also been investigated and some of the structures are shown in Scheme 15. 

Among unsolvated organolithium compounds only the alkyllithiums are soluble in noncoordinating solvents such as alkanes and arenes. Their states of aggregation depend on the structure close to lithium. Thus primary, tertiary and secondary alkyllithiums, all unsolvated, assemble into respectively hexamers, tetramers and equilibrium mixtures of hexamers and tetramers. Most organolithium compounds dissolve in and coordinate with donor compounds such as ethers and tertiary amines. The actual structures depend critically on the nature of the donor. Thus, diethyl ether solvates tend to be mainly cubic tetramers (with some dimers) while THF favors mixtures of monomers and dimers. Tertiary vicinal diamines such as TMEDA and 1,2-di-Af-piperidinoethane, DPE, favor bidentated coordinated dimers. Finally, in the presence of triamines such as pentamethyl-triethylenediamine PMDTA and l,4,7-trimethyl-l,4,7-triazacyclononane TMTAN, many organolithium compounds form tridentately complexed monomers. 

A series of five-coordinate Fe(II) complexes were thoroughly studied with tridentate ligands, including triamines, like N,N,N, N",N"-p>entamethyldiethylenetriamine (PMDETA) (Fe-25, R=CH3), pyridylamine (Fe-26), N-aminoethyl-pyridylimine... 

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