1.2- Dihydrazones reactions with formaldehyde

The metal-promoted reactions of 1,2-dihydrazones with formaldehyde (see Scheme 35) can be compared with the purely organic reactions of 1,2-dihydrazones with orthoesters, which lead directly to macrocyclic compounds from which complexes of structural type (85) can be prepared.189190... 

CLATHROCHELATES FORMED BY THE REACTION OF TRIS(2,3-BUTANEDIONE DIHYDRAZONE)-METAL COMPLEXES WITH FORMALDEHYDE [5,6,14,15,20,21-HEXAMETHYL-1,3,4,7,8,10,... 

The condensation of butanedione-2,3-dihydrazone with formaldehyde on a metal ion (Fe-, Co-" and Ni +) matrix (Scheme 74), performed by Goedken and Peng, led to the formation of clathrochelate [M(thz)](BFi)2 complexes. Direct reaction between the three components proved to be efficient only with iron(II) ion [183]. Therefore, nickel, cobalt, and iron(II) tris-dihydrazonates were preliminarily synthesized. It was noted that even when the reaction was carried out under nitrogen and cobalt(II) tris-dihydrazonate was used as the starting material, only cobalt(III) clathrochelate could be isolated from the reaction mixture. Its reduction with anhydrous hydrazine yielded cobalt(II) clathrochelate [95, 183]. 

The clathrochelate complexes, [M(ClgH30Ni2)] [BF4]2, are prepared by adding 5.0 g of 37% aqueous formaldehyde solution to a suspension of 5 g of the appropriate tris(2,3-butanedione dihydrazone)metal bis(tetrafluoroborate) complex in acetonitrile. The condensation reaction is catalyzed by the addition of 0.5 mL of concentrated tetrafluoroboric acid. An immediate darkening of the solutions is observed as the condensation reaction proceeds. The iron (II)-containing solution becomes a very intense purple the nickel(II) solution becomes very dark olive-brown. Precipitation of the clathrochelates requires the addition of approximately 30% by volume of diethyl ether and refrigeration. The products are filtered from the solution, washed with methanol, and air dried. The iron(II) complex is somewhat more soluble in acetonitrile than the other complexes, and increased yields can be obtained by the dropwise addition... 

The reaction of iron(ii) with butane-2,3-dione dihydrazone and formaldehyde is illustrated in Scheme 3 (M = Fe). The complex (55) is low-spin, with MeCN co-ordinated in the axial sites, (56) is also low-spin and very stable in acidic solution. ... 

---