Catalysis

Boron

Boranes

Ammonia borane

Solvent

Hydrogen storage

Combinatorial chemistry

Hydrogen

Organic chemistry

Reagent

Amine gas treating

Borane

Computational chemistry

Transfer hydrogenation

Ruthenium

Chemistry

Angewandte Chemie International Edition

Transfer hydrogenation (TH) has historically been dominated by Meerwein–Ponndorf–Verley (MPV) reactions. However, with growing interest in amine–boranes, not least ammonia–borane (H 3 N⋅BH 3 ), as potential hydrogen storage materials, these compounds have also started to emerge as an alternative reagent in TH reactions. In this Review we discuss TH chemistry using H 3 N⋅BH 3 and their analogues (amine–boranes and metal amidoboranes) as sacrificial hydrogen donors. Three distinct pathways were considered: 1) classical TH, 2) nonclassical TH, and 3) hydrogenation. Simple experimental mechanistic probes can be employed to distinguish which pathway is operating and computational analysis can corroborate or discount mechanisms. We find that the pathway in operation can be perturbed by changing the temperature, solvent, amine–borane, or even the substrate used in the system, and subsequently assignment of the mechanism can become nontrivial.

Amine–Boranes as Transfer Hydrogenation and Hydrogenation Reagents: A Mechanistic Perspective