2,6-Diacetylpyridine, transition metal ligands

Transition Metal Complexes with Bis(Hydrazone) Ligands of 2, 6-Diacetylpyridine. Hepta-Coordination of 3d Metals... 

TRANSITION METAL COMPLEXES WITH BIS(HYDRAZONE) LIGANDS OF 2,6-DIACETYLPYRIDINE. HEPTA-COORDINATION OF 3d METALS... 

So far, we have concentrated upon reactions resulting from discrepancies between the size of the metal ion and the size of the macrocyclic cavity. However, it is not only the size of the metal ion that may result in a mismatch what happens if the favoured conformation of the ligand does have an arrangement of donor atoms that matches with the preferred co-ordination geometry of the metal ion This is exactly the situation that we observe with metal complexes of some pentadentate macrocycles. We have previously observed the formation of tetraaza macrocycles from the template condensation of 2,6-diacetylpyridine with diamines in the presence of a transition metal ions. We also noted that if the size of the metal ion were incorrect, it was possible to get [2+2] or other products. Now let us look at this topic in a little more detail. 

Retrosynthetically, preparation of N-azolyl 2,6-bis(imino)pyridyl metal complexes as precatalysts for polymerization involves (i) synthesis of N-amino azoles, (ii) condensation of 2,6-diacetylpyridine with two equivalents of N-amino azole, and (iii) complexation of die appropriate transition metal halide with the terdentate ligands. The latter two reactions present no real challenge and are more or less analogous to fhe published preparation of N-aryl 2,6-bis(imino)pyridyl complexes [13], and fhe more demanding synthesis of N-amino-azoles was covered in a preceding section. 

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