Reactivity of bridgehead halides with pentacyanocobaltate(II)

Abstract

The kinetics of the reaction of pentacyanocobaltate(II) with 1-adamantyl iodide and 2,4-dimethyl-1-bicyclo[2.2.2]-octyl iodide are studied and found to be second order in pentacyanocobaltate(II) and first order in the iodide. When studied in the presence of acrylonitrile as a radical scavenger the kinetics then show the usual first-order dependence on each of pentacyanocobaltate(II) and organic iodide. A comparative study is also performed on the rates of reaction of other bridgehead halides e.g. 7,7-dimethyl-1-bicyclo[2.2.1]heptyl iodide and triptycyl iodides. The reactivities of the iodides decrease in the order of the relative stability of the bridgehead radicals (second-order rate constants at 25 °C in dm³ mol^–1 s^–1 given in parentheses): 1-adamantyl (2.47 × 10^–2) > 2,4-dimethyl-1-bicyclo[2.2.2]octyl (7.5 × 10^–3) > 7,7-dimethyl-1-bicyclo[2.2.1]heptyl (< 10^–6) > triptycyl (< 10^–6).