Copper ions catalyse the reaction of diaquocobinamide with acetylene in aqueous solution at room temperature to give ethynylaquocobinamide as a mixture of the two isomers which differ in the relative orientation of the axial ligands. This leads to the first reported value for an equilibrium constant (axial ligands only given) involving the substitution of co-ordinated H2O by HC2- of K = [HC2-Co-OH2]/([H2O-Co-OH2] [HC2-]) ≥ 1023 dm3 mol-1. Equilibrium constants have been determined for the substitution of co-ordinated H2O in ethynylaquocobinamide by OH- (pK = 13.0 ± 0.1), CN- (log10K ≥ 6.8), and imidazole (log10K = 3.4), which confirm the position of HC2- between cyanide and vinyl in the trans-effect series for CoIII corrinoids.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|State||Published - 1983|
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