Terminal cobalt(IV)–oxo (CoIV–O) species have been implicated as key intermediates in various cobalt-mediated oxidation reactions. Herein we report the photocatalytic generation of a mononuclear non-haem [(13-TMC)CoIV(O)]2+ (2) by irradiating [CoII(13-TMC)(CF3SO3)]+ (1) in the presence of [RuII(bpy)3]2+, Na2S2O8, and water as an oxygen source. The intermediate 2 was also obtained by reacting 1 with an artificial oxidant (that is, iodosylbenzene) and characterized by various spectroscopic techniques. In particular, the resonance Raman spectrum of 2 reveals a diatomic Co–O vibration band at 770 cm−1, which provides the conclusive evidence for the presence of a terminal Co–O bond. In reactivity studies, 2 was shown to be a competent oxidant in an intermetal oxygen atom transfer, C–H bond activation and olefin epoxidation reactions. The present results lend strong credence to the intermediacy of CoIV–O species in cobalt-catalysed oxidation of organic substrates as well as in the catalytic oxidation of water that evolves molecular oxygen.

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−Ncoupled 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.

A new, bidentate, chiral directing group derived from 2,2-dimethyl-1-(pyridin-2-yl)propan-1-amine was discovered, which enables stereoselective palladium(ii)-catalyzed intramolecular C(sp3)–O bond formation.