Hydrogenations at Room Temperature and Atmospheric Pressure with Mesoionic Carbene-Stabilized Borenium Catalysts

1,2,3‐Triazolylidene‐based mesoionic carbene boranes have been synthesized in a convenient one‐pot protocol from the corresponding 1,2,3‐triazolium salts, base, and borane. Borenium ions are obtained by hydride ion and serve as catalysts in mild hydrogenation reactions of imines and unsaturated N‐heterocycles at ambient pressure and temperature. Size does matter after all: Tunable, comparatively robust mesoionic borenium ions catalyze the mild hydrogenation of N‐containing unsaturated organic functionalities at ambient temperature and ambient pressure. These reactions proceed through a mechanism reminiscent of frustrated Lewis pair chemistry.