3. 3. 1.

Article abstract of DOI:10.1021/ja00366a027

The hydroboration of alkynes with 9-borabicyclo left bracket 3. 3. 1 right bracket nonane dimer, (9-BBN)//2, exhibits kinetics similar to those for the hydroboration of alkenes. For the more reactive alkynes such as 1-hexyne, 3-methyl-1-butyne, 3,3-dimethyl-1-butyne, and cyclohexylethyne, the reaction exhibits first-order kinetics, first order in (9-BBN)//2 only. For the less reactive alkynes, such as diphenylethyne, the reaction exhibits three-halves-order kinetics, first order in alkyne and one-half order in (9-BBN)//2. Intermediate kinetics between first and three-halves order were observed with phenylethyne. Apparently the reaction proceeds through the same mechanism as the hydroboration of alkenes. There is a prior dissociation of the 9-BBN dimer into the monomer, followed by the reaction of the monomer with the alkyne. The relative reactivities of the alkynes toward 9-BBN, as well as the relative reactivities between the alkynes and their monohydroboration products, were obtained by competitive studies.