Visible-Light Photocatalytic C-H Amination of Arenes Utilizing Acridine-Lewis Acid Complexes.

This report describes the development of a visible-light photocatalytic system for C(sp2)-H amination that leverages in situ-generated photocatalysts. We demonstrate that the combination of acridine derivatives and Lewis acids forms potent photooxidants that promote the C-H amination of electronically diverse arenes upon irradiation with visible-light (440 nm). A first-generation photocatalyst composed of Sc(OTf)3 and acridine effects the C-H amination of substrates with oxidation potentials ≤ +2.5 V vs SCE with pyrazole, triazole, and pyridine nucleophiles. Furthermore, the simplicity and modularity of this system enable variation of both Lewis acid and acridine to tune reactivity. This enabled the rapid identification of two second-generation photocatalysts (derived from (i) Al(OTf)3 and acridine or (ii) Sc(OTf)3 and a pyridinium-substituted acridine) that catalyze a particularly challenging transformation: C(sp2)-H amination with benzene as the limiting reagent.

Photochemical C(sp2 )-H Pyridination via Arene-Pyridinium Electron Donor-Acceptor Complexes.

This report describes the development of a photochemical method for C(sp2 )-H pyridination that leverages the photoexcitation of electron donor-acceptor (EDA) complexes. Experimental and DFT studies show that black light (λmax ≈350 nm) irradiation of solutions of protonated pyridines (acceptors) and aromatic C-H substrates (donors) results in single electron transfer to form aryl radical cation intermediates that can be trapped with pyridine nucleophiles under aerobic conditions. With some modification of the reaction conditions, this EDA activation mode is also effective for promoting the oxidatively triggered SN Ar pyridination of aryl halides. Overall, this report represents an inexpensive and atom-economical approach to photochemical pyridination reactions that eliminates the requirement of an exogenous photocatalyst.

Formation of ethane from mono-methyl palladium(II) complexes.

This article describes the high-yielding and selective oxidatively induced formation of ethane from mono-methyl palladium complexes. Mechanistic details of this reaction have been explored via both experiment and computation. On the basis of these studies, a mechanism involving methyl group transmetalation between Pd(II) and Pd(IV) interediates is proposed.

Oxidatively induced reductive elimination from ((t)Bu2bpy)Pd(Me)2: palladium(IV) intermediates in a one-electron oxidation reaction.

This communication describes studies of oxidatively induced C-C bond-forming reductive elimination from ((t)Bu(2)bpy)Pd(II)(Me)(2). With the outer-sphere oxidant ferrocenium, the data are consistent with a mechanism involving Pd(III) and Pd(IV) intermediates, with C-C bond formation occurring from the latter. The reaction with Ag(+) appears to proceed via a Pd-Ag(+) adduct, which then undergoes inner sphere electron transfer to generate Pd(III). In contrast, the slower benzoquinone reaction forms ethane by a different pathway that does not involve methyl group scrambling and generates Pd(0) products.