Just before splitting: A mechanistic model has been proposed for H2 activation by sterically demanding phosphine–borane Lewis pairs. There is theoretical evidence for noncovalent intermolecular association of donor–acceptor molecules to form a flexible but energetically strained complex, which provides preorganized active centers for heterolytic HH bond cleavage (see picture).

The mechanism of enantioselective Michael addition of acetylacetone to a nitroolefin catalyzed by a thiourea-based chiral bifunctional organocatalyst is investigated using density functional theory calculations. A systematic conformational analysis is presented for the catalyst, and it is shown that both substrates coordinate preferentially via bidentate hydrogen bonds. The deprotonation of the enol form of acetylacetone by the amine of the catalyst is found to occur easily, leading to an ion pair characterized by multiple H-bonds involving the thiourea unit as well. Two distinct reaction pathways are explored toward the formation of the Michael product that differ in the mode of electrophile activation. Both reaction channels are shown to be consistent with the notion of noncovalent organocatalysis in that the transition states leading to the Michael adduct are stabilized by extensive H-bonded networks. The comparison of the obtained energetics for the two pathways allows us to propose an alternative mechanistic rationale for asymmetric C-C bond forming reactions catalyzed by bifunctional thiourea derivatives. The origin of enantioselectivity in the investigated reaction is also discussed.

In this paper, we report on the development of a bench-stable borane for frustrated Lewis pair catalyzed reduction of aldehydes, ketones and enones. The deliberate for finetuning of structural and electronic parameters of Lewis acid component and the choice of Lewis base provided for the first time, a moisture tolerant FLP catalyst. Related NMR and DFT studies underpinned the unique behavior of this FLP catalyst and gave insight into the catalytic activity of the resulting FLP catalyst.

Bevorstehende Scheidung: Ein theoretisches Modell für den Mechanismus der H2‐Aktivierung durch Lewis‐Paare aus sperrigen Phosphanen und Boranen liefert Hinweise auf eine nichtkovalente Anlagerung der Donor‐ und Akzeptormoleküle unter Bildung eines flexiblen, aber gespannten Komplexes mit präorganisierten aktiven Zentren für die heterolytische Spaltung der H‐H‐Bindung (siehe Bild).