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A Crystalline Boravinylidene from an Arrested Hydroboration Reaction
Manjur O Akram1, Kirk A French1, Kevin L Shuford1
1Baylor University, Department of Chemistry and Biochemistry, One Bear Place #97348, Waco, Texas 76798, United States.
None:
Boravinylidenes are intermediates in 1,1-hydroboration reactions of alkynes en route to vinyl boranes. Unlike transition metal-vinylidene complexes, boravinylidenes have hitherto, not been crystallographically characterized. Pairing bis(trimethylsilyl)ethyne with an extremely potent hydroboration reagent, bis(1-methyl-ortho-carboranyl)borane, enables crystallization and characterization of a boravinylidene. Solution multinuclear NMR experiments validate the boravinylidene and reveal it is in equilibrium with the starting materials. Density functional theory calculations indicate hyperconjugative interactions from the β-silyl groups and B-H bond stabilize this unusual species. Reaction of the feature compound with nitriles triggered an insertion and rearrangement to furnish an iminium-tethered borataallene.
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