Organoboranes. 47. An extremely facile elimination of alkenes from dialkylhaloboranes. A comparative rate study with related trialkylboranes

Article abstract of DOI:10.1021/om00141a034

Dialkylhaloboranes reduce benzaldehyde at a rate much faster than does trialkylboranes. Whereas Ipc₂BCl reduces 2 equiv of benzaldehyde at room temperature almost instantaneously, the related trialkylborane Ipc₂B-n-Hex requires approximately 6 days. Sia₂BCl, 2-MeCpn₂BCl, Car₂BCl and Ipc₂BBr also reduce benzaldehyde rapidly, but 2-MeChx₂BCl reacts relatively slowly. A cyclic mechanism with a boat-like transition state is proposed, which can account for the major differences in the rates of reduction among the various dialkylhaloboranes.