Organotin Hydride Reduction of Benzyl Bromides

A Hammett study was carried out on the tributyltin hydride reduction of substituted benzyl bromides. Electron-withdrawing groups facilitate the reaction, whereas electron-releasing groups have little or no impact on the rate. This unusual effect creates a discontinuity in the Hammett plot. Electron-withdrawing groups stabilize both the free radical and polar character of the transition state. Electron-releasing groups, however, stabilize the free radical character but destabilize the polar character of the transition state.