Acetonitrile cobalt complexes

Alkali metal boratabenzenes may be liberated from bis (boratabenzene) cobalt complexes 7 and 13 by reductive degradation with elemental Li, sodium amalgam, or Na/K alloy (60), or alternatively by degradation with cyanides (61). The latter method has been developed in detail (Scheme 4). It produces spectroscopically pure ( H-NMR control) solutions of the products 26 the excess alkali metal cyanide and the undefined cyanocobalt compounds produced are essentially insoluble in acetonitrile. 

The catalysis of the selective oxidation of alkanes is a commercially important process that utilizes cobalt carboxylate catalysts at elevated (165°C, 10 atm air) temperatures and pressures (98). Recently, it has been demonstrated that [Co(NCCH3)4][(PF6)2], prepared in situ from CoCl2 and AgPF6 in acetonitrile, was active in the selective oxidation of alkanes (adamantane and cyclohexane) under somewhat milder conditions (75°C, 3 atm air) (99). Further, under these milder conditions, the commercial catalyst system exhibited no measurable activity. Experiments were reported that indicated that the mechanism of the reaction involves a free radical chain mechanism in which the cobalt complex acts both as a chain initiator and as a hydroperoxide decomposition catalyst. 

NC2H Acetonitrile cobalt, copper, and ruthenium complexes, 26 356, 359... 

Alkali metal 1-methyl- and 1-phenyl-borinates are also available from bis(borinato)cobalt complexes (see below) on treatment with sodium or potassium cyanide in an aprotic solvent like acetonitrile. Cobalt cyanide precipitates and the alkali borinate remains in solution. After addition of thallium(I) chloride to some complexes, thallium 1-methyl- or 1-phenyl-borinate could be isolated as pale yellow solids, the only main group borinates isolated hitherto. They are insoluble in most organic solvents but readily soluble in pyridine and DMSO. The solids are stable on treatment with water and aqueous potassium hydride, but are decomposed by acids <78JOM(153)265). 

Chelate cobalt complex was synthesized electrochemically by reacting 2-N-tosylamino (2 -hydroxybenzylidene)aniline with 2-amino-l-methylbenzimidazole on a cobalt anode (2x2 cm2 plate) at room temperature. A working acetonitrile solution (50 mL) contained azomethine (0.250 g), N-base (0.185 g), and Et4NC104 (0.01 g). Electrolysis was carried out in a special-purpose electrolytic cell at a direct current of 10 mA with a voltage of 20 V for 4 hr. The resulting green powder was filtered off and recrystallized from ethanol giving brown crystals. 

Analogously, the complex [(ti -C5H5)Fe(j/ -C5H4CHN(N) = C(S)NH2)]2Ni, an analog of the cobalt complex shown in Scheme 7-21, undergoes in acetonitrile solution a ferrocene-centered two-electron oxidation at +0.48 V. In DMF it also undergoes a nickel-centered, irreversible, two-electron reduction at —1.34 V. The same conclusions drawn for the corresponding cobalt complex hold [120]. 

Redox potentials (mV) of macrobicyclic cobalt complexes in acetonitrile. 

C2H,N, Acetonitrile, cobalt, copper, and ruthenium complexes, 26 356, 359 molybdenum, palladium, and tungsten complexes, 26 128-133 osmium complex, 26 290, 292 ruthenium(II) complexes, 26 69-72 C2H4, Ethene, molybdenum complex, 26 102-105... 

In contrast to the cobalt-based system, small amounts of H2 and no CO are produced when nickel cyclam or other saturated 14-membered tetraazamacrocycles (L) in Figure 3 are used to replace the cobalt complex in the above system [22]. Flash photolysis studies indicate that the electron-transfer rate constant (kn) for the reaction of the />-terphenyl radical anion with Nil (cyclam)2 is 4.3 x 10 M s. However, when CO2 is added to the solution, the decay of the TP anion becomes slower Flash photolysis studies of the acetonitrile solutions... 

Fig. 6.29 Mass spectra of the cobalt complexes in the presence of one equivalent nitrocefin measured in acetonitrile, a [Co2(C02EtH2Ll)(CH3COO)2]" was added to a solution of nitrocefin in acetonitrile (both 0.01 mM final concentration) and a color change from yellow to red was apparent after 1 min. The spectrum was recorded 5 min after mixing, b [Co2(C02EtL2)(CH3COO)2]" was added to a solution of nitrocefin in acetonitrile (both 0.01 mM final concentration). No color change was observed...

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