Catalytic Generation of Borenium Ions by Cooperative B–H Bond Activation: The Elusive Direct Electrophilic Borylation of Nitrogen Heterocycles with Pinacolborane
The B-H bond of typical boranes is heterolytically split by the polar Ru-S bond of a tethered ruthenium(II) thiolate complex, affording a ruthenium(II) hydride and borenium ions with a dative interaction with the sulfur atom. These stable adducts were spectroscopically characterized, and in one case, the B-H bond activation step was crystallographically verified, a snapshot of the σ-bond metathesis