Borane Chemistry. II. Kinetics and Mechanism of Reaction of Chlorodipentylborane With Some Aldehydes

Abstract

Chlorodipentylborane causes extensive polymerization of aliphatic aldehydes , even in low concentrations and at 273 K, but its reaction with aromatic aldehydes is more controlled, and allows the study of the rates and products of its addition to a range of these aldehydes by using ¹H, ¹¹B and ¹³C n.m.r. spectroscopy. The second-order rate constant (282 K) for the formation of pent-1-ene increases as the para substituent in benzaldehyde changes in the sequence NMe₂, OMe , H, Cl , NO₂; the derived Hammett p value (1.6; CDCl₃, 282 K) suggests a transition state involving hydride ion transfer to carbonyl oxygen. The significance of an adduct as an intermediate in the reaction is discussed.