A method for the reduction of a manganese nitride to ammonia is reported, where light-driven proton-coupled electron transfer enables the formation of weak NH bonds. Photoreduction of (saltBu)­MnVN to ammonia and a Mn­(II) complex has been accomplished using 9,10-dihydroacridine and a combination of an appropriately matched photoredox catalyst and weak Brønsted acid. Acid-reductant pairs with effective bond dissociation free energies between 35 and 46 kcal/mol exhibited high efficiencies. This light-driven method may provide a blueprint for new approaches to catalytic homogeneous ammonia synthesis under ambient conditions.

Concepts for the thermodynamically challenging synthesis of weak N–H bonds by photoinduced proton coupled electron transfer are explored. By harvesting visible light as driving force, ammonia synthesis was achieved and mechanistically elucidated.

Pd-catalyzed C–H arylation of heteroarenes is an important and widely studied synthetic transformation; however, the regioselectivity is often substrate-controlled. Here, we report catalyst-controlled regioselectivity in the Pd-catalyzed oxidative coupling of N-(phenylsulfonyl)­indoles and aryl boronic acids using O2 as the oxidant. Both C2- and C3-arylated indoles are obtained in good yield with >10:1 selectivity. A switch from C2 to C3 regioselectivity is achieved by adding 4,5-diazafluoren-9-one or 2,2′-bipyrimidine as an ancillary ligand to a “ligand-free” Pd­(OTs)2 catalyst system. Density functional theory calculations indicate that the switch in selectivity arises from a change in the mechanism, from a C2-selective oxidative-Heck pathway to a C3-selective C–H activation/reductive elimination pathway.