Cobalt pentamines

The kinetic effects of C02 in the base catalyzed hydrolysis of some carboxylato amine cobalt(III) complexes have been reported (80-82). In the base catalyzed hydrolysis of oxalatopentaammine-cobalt(III) (80), C02 retarded the reaction due to the formation of a virtually unreactive ion-pair, f (N H .) r, 2 2 COi ]. The equilibrium constant for formation of carbonate ion-pairs with (glycinato-O) (tetraethylene-pentamine)cobalt(III), (81) and (o-methoxybenzoato) (tetraethylenepentamine)cobalt(III) (82) were, however, much smaller than for the oxalatopentamminecobat(III) and a very weak rate retardation and virtually no effect was observed in the base catalyzed hydrolysis of the latter two complexes. 

The formation of 4-nitroimidazole complexes, such as pentamine-(4-nitroimida-zolato)cobalt chloride, involves no deformation of coplanarity between the nitro group and the imidazole ring [70],... 

Cobalt can also be separated from nickel in alkaline conditions by first adding ammonia and hydrogen peroxide to form cobalt(III) pentamine complex, and then crystallizing the bulk of the nickel as the sparingly soluble nickel ammonium sulfate (Figure 6.8). The separation of nickel from cobalt can be achieved by precipitation via oxidation to nickel(III) hydroxide with Caro s acid at near-neutral pH (Figure 6.9).257... 

It is quite clear that conversion between the fully oxidized and fully reduced forms of cytochrome oxidase is a four electron process126). In accord with the four electron accepting role of dioxygen, the titration of reduced oxidase with 02 (obtained in situ from /r-peroxo-bis (pentamine cobalt(II) tetranitrate) indicated complete oxidation of one reductant molecule by each molecule of 02127). There is no evidence for the liberation of intermediate oxidation states of oxygen such as peroxide or superoxide. The presence of two hemes and two coppers has lead to the assumption (but not without some strong exception, vide infra) that all four metal ions are involved in the red-ox process. 

The intramolecular condensation of monodentate aminomethylcarbonyl ligands, NH2CH2COR (R = H, Me, Ph), with quadridentate amines such as tren[tris(2-aminoethyl)amine] and tren(l,8-diamino-3,6-diazaoctane) bound to cobalt(III) has been studied. Chloride bound to the pentamine cobalt(III) directs the condensation to the amine site trans to it by base-catalyzed removal of a proton on the amine. The resultant carbinol amine complexes give imines (15), according to Eq. (4), which can be isolated and then reduced by BH4 to the fully saturated amine complexes without significant reduction of the Co(III) center. 

Cobalt chloride (anhydrous) was obtained from Aesar, L-histidine hydrochloride from Sigma, N-benzyl-L-histidine from Vega, tetraethylene pentamine (tetren) was obtained from Aldrich. Hater was deionized via a Barnstead Nanopure II ion exchange unit. Cells and electrodes for voltammetry were standard Bioanalytical Systems or Pine Instrument controlled by BAS lOOA, BAS-CV27 or Pine Instrument RDE4 potentiostats and instrumentation. Spectroelectrochemistry was accomplished using a standard... 

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