An Iridium-Stabilized Borenium Intermediate

Exploration of new organometallic systems based on polyhedral boron clusters has the potential to solve challenging chemical problems such as the stabilization of reactive intermediates and transition-state-like species postulated for E-H (E = H, B, C, Si) bond activation reactions. We report on facile and clean B-H activation of a hydroborane by a new iridium boron cluster complex. The product of this reaction is an unprecedented and fully characterized transition metal-stabilized boron cation or borenium. Moreover, this intermediate bears an unusual intramolecular B center dot center dot center dot H interaction between the hydrogen originating from the activated hydroborane and the cyclometallated metal-bonded boron atom of the boron cluster. This B center dot center dot center dot H interaction is proposed to be an arrested insertion of hydrogen into the B-cage-metal bond and the initiation step for iridium cage-walking around the upper surface of the boron cluster. The cage-walking process is supported by the hydrogen-deuterium exchange observed at the boron cluster, and a mechanism is proposed on the basis of theoretical methods with a special focus on the role of noncovalent interactions. All new compounds were isolated and fully characterized by NMR spectroscopy and elemental analysis. Key compounds were studied by single crystal X-ray diffraction and X-ray photoelectron spectroscopy.

Automated summary

This study reports on the activation of hydroborane by a new iridium boron cluster complex, leading to the formation of a stable boron cation. The reaction involves an unconventional intramolecular B center dot center dot center dot H interaction, and a mechanism is proposed based on theoretical methods and noncovalent interactions.