Hydrazones complexes

Because there are at least three ways in which the hydrazone ligand could attach itself to a transition metal and because hydrazone complexes of transition metals barely have been investigated, this type of compound is interesting to us. 

Hydrazone complexes of platinum(II) can be prepared by treating Zeise s salt wit hydrazones (equation 370).1205 Coordination is via the lone pair of electrons on nitrogen.120 The reaction between (phenylazo)acetaldoxime (HL) and PtCl gives two isomers of PtL. Th< cis isomer has been crystallographically confirmed.1207 These arylazoacetaldoximat ... 

Thermodynamic template reactions allow the formation of hydrazones from hydrazines and carbonyl compounds, in the same manner as simple imines are formed. However, in many cases it is more convenient to form hydrazones in non-template reactions, as they are generally easier carbonyl derivatives to isolate than are simple imines. Hydrazone complexes often are capable of further manipulation and both aspects of synthesis and reactivity will be combined in this section. 

The reaction of the nickel(II) perchlorate complex (89) with acetone and related ketones yields simple hydrazone complexes rather than macrocyclic complexes resulting from a Curtis-type reaction. Acetylacetone also fails to bridge the bis(hydrazine) and instead yields a pyrazole derivative (Scheme 37).197 198 In contrast to this result, 1,4-dihydrazinophthalazine undergoes a template reaction with 2,2-dimethoxypropane, a source of acetone, in the presence of nickel(II) fluoroborate and a trace of fluoroboric acid (Scheme 38).199... 

One subset of Schiff base complexes are the hydrazone complexes which have a R—C=N—N functional group instead of the R C=N—C functionality. These compounds have been prepared as models for bromoperoxidase389 and other biological systems.390 In the solid state, the hydrazones have coordination patterns similar to those of the Schiff bases and the majority of the complexes are oxovanadium(V) hexadentate or pentacoordinate complexes with tridentate 02N donor sets (see Table 5). While most structures contain alkoxide donors,390-403 complexes have been reported with diols and catechols,129,404,405 hydroxamic acids,288,391 hydroxy quinolinate,406, 7 and benzoylhydrazine.408 In addition, dioxo,375,409-412 oxo-bridged... 

Table 5 Summary of the structural features of the crystallographically characterized hydrazone complexes. ...

In this scheme A denotes a protonated hydrazone complex.) l nce the imine is formed at the electrode in protonated form, its halfwave potential does not depend on the pH value... 

Premkumar, T. and Govindarajan, S. (2002) The chemistry of hydrazine derivatives-thermal behavior and characterization of hydrazinium salts and metal hydrazone complexes of 4,5-imidazoledicarboxylic acid. Thermochimica Acta, 386, 35-42. 

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