1.2- Diimines hydroxylation

The diimine-hydroxyl ligand poap, (48), undergoes self-assembly in the presence of Fe + to give Fes and Fee... 

Rate and equilibrium constant data, including substituent and isotope effects, for the reaction of [Pt(bpy)2]2+ with hydroxide, are all consistent with, and interpreted in terms of, reversible addition of the hydroxide to the coordinated 2,2 -bipyridyl (397). Equilibrium constants for addition of hydroxide to a series of platinum(II)-diimine cations [Pt(diimine)2]2+, the diimines being 2,2 -bipyridyl, 2,2 -bipyrazine, 3,3 -bipyridazine, and 2,2 -bipyrimidine, suggest that hydroxide adds at the 6 position of the coordinated ligand (398). Support for this covalent hydration mechanism for hydroxide attack at coordinated diimines comes from crystal structure determinations of binuclear mixed valence copper(I)/copper(II) complexes of 2-hydroxylated 1,10-phenanthroline and 2,2 -bipyridyl (399). 

Aromatic nitro compounds may generally be reduced in a four-electron reduction to hydroxylamines, which in acid solution at a more negative potential can be reduced further to amines. By choosing a suitable cathode potential it is thus possible to avoid the further reduction of the hydroxylamine to the amine. When a hydroxyl or amino group is ortho or para to the nitro group, it is not feasible to isolate the hydroxylamino compound, as it is too easily dehydrated to the reducible quinone mono- or diimine. It may, however, be possible to trap the intermediate. 

Oxygenation of ligands has also been observed. An a-diimine iron(II) complex has been effectively hydroxylated as a result of oxidation by cerixim(IV) (equation 63). Aerial oxidation in dimethylformamide of an iron(III) acetate complex results in the conversion of an ethano linkage to dioxo (equation 64). During the formation of the related nickel(II) complex (64), the modified complex (65) was isolated. It is likely that the product arose by reaction of 1,2-diaminoethane... 

While the rate of dissociation of Fe(phen)i" is not sensibly affected by hydrogen ions, hydroxyl (200) as well as cyanide and azide ions 201) greatly accelerate the rate of displacement of the diimine ligand. For the reaction with OH, the activation energy for the catalized path is lowered by ca. 6 kcal/mole 202). The preferred mechanism 201) consists in the replacement of water molecules in one of the pockets between the hgands, by the nucleophilic ion. Interaction between the i r-orbitals of the latter and the antibonding metal i-orbitals is believed to destabilize the metal-diimine bonds. 

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