KINETICS AND MECHANISM FOR THE ELIMINATION OF HYDROGEN BETWEEN DIMETHYLALUMINUM HYDRIDE AND N-METHYLANILINE

The rate of elimination of hydrogen from dimethylaluminum hydride and N-methylaniline has been measured at -63 °C in toluene solution. Reaction conditions include equal concentrations of dimethylaluminum hydride and the amine and pseudo-first-order conditions with excess amine. The kinetics data are consistent with a second-order rate law which is complicated by an equilibrium. The following steps of the mechanism determine the rate of elimination of hydrogen:[formula omitted] Our results are consistent with the conclusion that adduct formation is a “dead-end” path for the elimination reaction. The elimination reaction is not a reaction of a preformed adduct. The factors responsible for the formation of only a dimeric aluminum-nitrogen product, [ (CH3)2A1N (C6H5) (CH3)]2, and the predominance of the cis isomer over the trans isomer (80/20%) are discussed. A 27πs + 2πa cycloaddition reaction which minimizes interactions between the bulky phenyl groups is proposed. © 1979, American Chemical Society. All rights reserved.