Cobalt Azide Complexes

Cobalt Azide Complexes — Curtius Rissom (Ref 1) found that potassium cobaltoazoimide,... 

Cobalt Azide Complexes — Curtius Rissom (Ref 1) found that potassium cobaltoazoimide, [KNj-CofNjl ], pptd when strong solns of the two azides were mixed. This compd appeared as bright-blue crysts (pink in soln) which expl at 225°, The ammonium analogue, [(NHJN,(CO(N,)J, was similar in appearance and props (Ref 1). 

Electron transfer oxidation of 4-methoxyphenol using wjeio-tetraphenylporphyrin as the electron acceptor brings about dehydrodimerization of the phenol to yield 5. The presence of the radical cation of the phenol has been detected by CIDNP techniques. The same product is obtained by irradiation of the tetraphenylporphyrin/benzoquinone/p-methoxyphenol system . Pyrimidinopteridine Af-oxide has been used as a sensitizer to effect the hydroxylation of phenols, also involving the radical cation of the phenol. Thus phenol can be converted to catechol and hydroquinone while cresol yields 4-methyl-catechol . Hydroquinone can itself be oxidized by the cobalt azide complex in aqueous... 

With a view to determining the equilibrium constant for the isomerisation, the rates of reduction of an equilibrium mixture of cis- and rra/i5-Co(NH3)4(OH2)N3 with Fe have been measured by Haim S . At Fe concentrations above 1.5 X 10 M the reaction with Fe is too rapid for equilibrium to be established between cis and trans isomers, and two rates are observed. For Fe concentrations below 1 X lO M, however, equilibrium between cis and trans forms is maintained and only one rate is observed. Detailed analysis of the rate data yields the individual rate coefficients for the reduction of the trans and cis isomers by Fe (24 l.mole sec and 0.355 l.mole .sec ) as well as the rate coefficient and equilibrium constant for the cw to trans isomerisation (1.42 x 10 sec and 0.22, respectively). All these results apply at perchlorate concentrations of 0.50 M and at 25 °C. Rate coefficients for the reduction of various azidoammine-cobalt(lll) complexes are collected in Table 12. Haim discusses the implications of these results on the basis that all these systems make use of azide bridges. The effect of substitution in Co(III) by a non-bridging ligand is remarkable in terms of reactivity towards Fe . The order of reactivity, trans-Co(NH3)4(OH2)N3 + > rra/is-Co(NH3)4(N3)2" > Co(NH3)sN3 +, is at va-... 

See AZIDE COMPLEXES of cobalt(IH) See related metal azides... 

ACYL AZIDES, AMMINECOB ALT (III) AZIDES, AZIDE COMPLEXES OF COBALT(III)... 

The cobalt(I) complexes also react with organic aryl azides to form the terminal cobalt(III) imido complexes [(TIMEN" OCo(NAr )]Cl (Ar = xyl, mes, R — p-PhMe, p-PhOMe) at —35°C (Fig. 17). These deep-green complexes are fully characterized, including NMR, IR, UV-Vis spectroscopy, and combustion analysis 10). These are diamagnetic (d low-spin, S — 0), and the NMR spectra suggest a Ca-symmetry of these molecules in solution. 

As expected, azide addition to dimethyl maleate is very sluggish, and a triazoline is not isolated32 because the LUMOfumarale < LUMOmaleale.304a Recently, however, it has been found that azide coordinated in a cobalt chelate complex [N3Co(DH)2NH3] is sufficiently reactive to add to diethyl maleate, and 25% of the pure triazoline has been obtained (Scheme 80).30 5... 

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