Umpolung of B−H Bonds by Metal–Ligand Cooperation with Cyclopentadienone Iridium Complexes

In contrast to conventional metal–ligand cooperative cleavage of a B−H bond, which provides a B cation on the ligand and an H anion on the metal, we report herein the umpolung of B−H bonds by novel cyclopentadienone iridium complexes. The B−H bonds of 4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane (HBpin) and 1,8‐naphthalenediaminatoborane (HBdan) were cleaved to give a B anion on the metal and an H cation on the phenolic oxygen atom of the ligand. Mechanistic investigation by DFT calculations revealed that the alkoxycarbonyl‐substituted cyclopentadienone ligand facilitated deprotonation from Ir−H after oxidative addition of the B−H bond to give the umpolung product. The generated boryliridium complex was found to undergo borylation of an allyl halide in the presence of base, thus showing the nucleophilic nature of the boron atom. Conventional heterolytic cleavage of a B−H bond provides a B cation and an H anion. However, umpolung of the B−H bond in HBpin by novel cyclopentadienone iridium complexes led to cleavage into a B anion on the metal and an H cation on the phenolic oxygen atom of the ligand (see scheme).