Mechanism of Palladium-Catalyzed C–N Coupling with 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) as a Base

The
mechanism of the Buchwald–Hartwig amination assisted
by the base 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU) is explored with
density functional theory (DFT) calculations. Whereas the previous
study indicates that the tight binding of DBU to the Pd­(II) center
could block the desired catalytic pathways, the recent work from Buchwald
and co-workers demonstrates that the bulkier ligands, such as AlPhos,
can overcome the catalyst deactivation by DBU and yield the C–N-coupled
product at room temperature. The results show that the bulkier ligands
sterically hinder DBU binding and enable the desired catalytic steps
by improving the Pd–substrate coordination. This study confirms
quantitatively and precisely how and at which step of the catalysis
the steric demands engineered into the phosphine ligands improve the
catalytic C–N coupling using an organic base.