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.