Are tetrahedral intermediates formed by addition of nucleophiles to organoboranes in the gas phase?
Abstract
Nucleophilic addition of CD3O– to Me2BOMe gives the same addition product as the corresponding reaction between Me2BOCD3 and MeO–, as evidenced by the identical collisional activation mass spectra of the products. This is interpreted in terms of exclusive formation of a boron product ion of tetrahedral geometry. The decompositions of the product involve loss of MeOH and CD3OH and the formation of MeO– and CD3O–. The major decompositions of (CD3)3B +–OCH2CH2XMe (X = O, S, or NMe2) are similar to those outlined above and may be explained by initial formation of (CD3)3 OCH2CH2XMe. However, there are some unusual fragmentations (e.g. loss of CH3D) which may occur through the alternative structure (CD3)3[graphic omitted](Me)CH2CH2O–. It is suggested that other ambident species may also react with Me3B to form several tetrahedral species, e.g. deprotonated methyl acetate could yield Me3CH2CO2Me, Me3OC(OMe)CH2, and Me3—[graphic omitted](Me)[graphic omitted]. The formation of the third structure is supported by the pronounced loss of ketene from this system.