Spontaneous trans‐Selective Transfer Hydrogenation of Apolar Boron–Boron Double Bonds

The transfer hydrogenation of N‐heterocyclic carbene (NHC)‐supported diborenes with dimethylamine borane proceeds with high selectivity for the trans‐1,2‐dihydrodiboranes. DFT calculations, supported by kinetic studies and deuteration experiments, suggest a stepwise proton‐first‐hydride‐second reaction mechanism via an intermediate μ‐hydrodiboronium dimethylaminoborate ion pair. Game of borons: The transfer hydrogenation of apolar cis‐ and trans‐diborenes with dimethylamine borane as the hydrogen source proceeds with high selectivity for the corresponding trans‐1,2‐dihydrodiboranes. DFT calculations, supported by kinetic data, reveal a new reaction mechanism proceeding via a proton‐first‐hydride‐second pathway through an intermediate μ‐hydrodiboronium aminoborate ion pair.