1.2- Cyclohexanedione dioxime, reaction

The structure of the 1,2-cyclohexanedione dioxime (niox) complex, [Fe(niox)2(imid)2] (54), which is more soluble than the analogous DMG complex, has also been determined,604 but because of disorder in the cyclohexyl rings some of the important structural parameters were ill defined. However, the Mossbauer spectra of [Fe(niox)2L2] (L = py, imid, NH3, BuNH2) and related complexes have been studied in detail and are consistent with considerable tetragonal distortion.605,606 [Fe(niox)2(imid)2] reacts with CN to give [Fe(niox)2(CN)2]2, and by using only one equivalent of CN" [Fe(niox)2(CN)(imid)] can be obtained.605 Reaction with CO affords [Fe(niox)2(imid)(CO)] as in Scheme 13. 

Ligand Replacement Unidentate by Multidentate.—1,2-Cyclohexanedione dioxime replaces the two chlorides of /rfl/w-[Co(en)2Cl2]+, in aqueous solution, by a complicated mechanism whose essential features are an 8- 2. reaction of the incoming ligand with the complex and a later intramolecular 5 n2 reaction in which chelate ring formation is synchronous with chloride expulsion. The evidence in favour of the bimolecularity of the first step is the activation entropy of — 11 cal deg mol the evidence in favour of the latter 5 2 step is that its rate is 100 times faster than normal... 

SCHEME 1.77 Reaction of 1,2-cyclohexanedione dioxime with acetylene. 

A detailed mechanistic study of the iron-templated reaction of 1,2-cyclohexanedione dioxime (37) with H3BO3 to form complexes of the cage ligand (38) has been reported. The first step appears to be the formation of the /w(oxime) complex, followed by a reversible association with H3BO3 and... 

This is encouragingly small, especially considering the experimental uncertainty for the dioxime enthalpy of formation, althongh we have no real idea how mnch repnlsion or stabilization we might expect from vicinal dioxime gronps. (We likewise lack snch information for vicinally substituted alicycUc diones—there are literature enthalpy of formation data for 1,3- and 1,4- but not 1,2-cyclohexanedione there are also data for 2,3-pentanedione but not 1,2-cyclopentanedione.) Consider now the reaction 33. 

Accordingly, we derive an enthalpy of formation of —49 kJ mol for the acyclic dioxime and so an endothermicity of 40 kJmol for the cyclohexane dioxime forming reaction 33—only 25 kJmol would have been expected from the above cyclohexanedione reaction if we assume that the cyclohexane dioxime is destabilized by 15 kJmol . ... 

When a metal ion such as nickel (II) is absent, thiazoles and mercaptals are formed. Such reactions have been carried out in which the diketone was biacetyl, 2,3-pentanedione, 2,3-octanedione, l-phenyl-l,2-propane-dione, and 1,2-cyclohexanedione (51). In like manner, the tris complexes of W,W -dimethyl-2,3-butane diimine with iron(II), cobalt(II), and nickel(II) may be prepared from methylamine and biacetyl when the appropriate metal ion (27j 28j 41) is present. Replacing methylamine with hydroxylamine causes the formation of a-dioximes (13). 

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