Cobalt nitrosation

Chemical complexes of various transition metals have been shown to promote N-nitrosation (28). These metal complexes include ferrocyanide, ferricyanide, cupric ion, molybate ion, cobalt species, and mercuric acetate. All of the reactions are thought to proceed by oxidation-reduction mechanisms. However, such promotion may not be characteristic of transition metal complexes in general, since ferricyanide ion has been shown to promote nitrosation in metalworking fluids, whereas ferric EDTA does not (2 0). Since the metalworking operation generates metal chips and fines which build up in the fluids, this reaction could be of significance in the promotion of nitrosamine formation in water-based metalworking fluids. 

The preparation of oximes from olefins is a valuable approach for the synthesis of nitrogen-containing compounds such as amino acids and heterocycles. Okamoto and colleagues have reported that a catalytic reduction-nitrosation of styrenes 31 with ethyl nitrite and tetrahydroborate anion by the use of bis(dimethylglyoximato)cobalt(II) complex afford the corresponding acetophenone oximes 32 (Scheme 23). 

Sugamoto and colleagnes have attempted the rednction-nitrosation of the conjn-gated olefins 33 by the nse of f-bntyl nitrite instead of oxygen (Scheme 24). Various olefins such as styrenes, a,-unsaturated carbonyl compounds and a, S,y,5-unsaturated carbonyl compounds were directly converted to the corresponding acetophenone oximes, a-hydroxyimino carbonyl compounds and y-hydroxyimino-a,/S-unsaturated carbonyl compounds in good or moderate yields by rednction-nitrosation with f-butyl nitrite and triethylsilane in the presence of cobalt(II) porphyrin as a catalyst (Scheme 24). 

The displacement of cobalt(m) and chromium(III) from pyridiomethylcobaltate ions and -cfaromium(III) ions by nitrosating agents... 

Styrenes, enolates, and dienoates 337 can be nitrosated using (tetraphenyl-porphyrin)cobalt(II) 326a as the catalyst (entry 17). Under these conditions oximes 345 were isolated in 31-94% yield. The mechanistic details of this reaction remain to be elucidated [397]. 

Nitrosation of [Co(diAMsar)]3+ cation in the presence of chloride anion led to the formation of cobalt dichlorosarcophaginate, the reduction of which with zinc dust and subsequent treatment with H2O2 and HCl gave the simplest [Co(sar)]Cl3 sarcophaginate [94, 101] ... 

Few cobalt complexes exist containing coordinated tetrahedral perchlorate, and those which do show weak coordination. Table 75 gives some structural data. Early reports on the isolation of [Co(OC10j)(NH3)5](C104)2 are erroneous but Sargeson and coworkers have prepared it as pink crystals by nitrosation of [CoNj(NHj)5](a04)2 in concentrated HCIO4. Coordinated perchlorate is rapidly displaced by water in aqueous solution (ri/2 7 s) and cobalt in any oxidation state prefers almost any other donor atom over perchlorate oxygen. 

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