RESUMEN
Existing methodologies for metal-catalyzed cross-couplings typically rely on preinstallation of reactive functional groups on both reaction partners. In contrast, C-H functionalization approaches offer promise in simplification of the requisite substrates; however, challenges from low reactivity and similar reactivity of various C-H bonds introduce considerable complexity. Herein, the oxidative cross dehydrogenative coupling of α-amino C(sp3)-H bonds and aldehydes to produce ketone derivatives is described using an unusual reaction medium that incorporates the simultaneous use of di-tert-butyl peroxide as an oxidant and zinc metal as a reductant. The method proceeds with a broad substrate scope, representing an attractive approach for accessing α-amino ketones through the formal acylation of C-H bonds α to nitrogen in N-heterocycles. A combination of experimental investigation and computational modeling provides evidence for a mechanistic pathway involving cross-selective nickel-mediated cross-coupling of α-amino radicals and acyl radicals.
RESUMEN
Electrocatalytic nitrogen reduction (N2R) mediated by well-defined molecular catalysts is poorly developed by comparison with other reductive electrocatalytic transformations. Herein, we explore the viability of electrocatalytic N2R mediated by a molecular Mo-PNP complex. A careful choice of acid, electrode material, and electrolyte mitigates electrode-mediated HER under direct electrolysis and affords up to 11.7 equiv of NH3 (Faradaic efficiency < 43%) at -1.89 V versus Fc+/Fc. The addition of a proton-coupled electron transfer (PCET) mediator has no effect. The data presented are rationalized by an initial electron transfer (ET) that sets the applied bias needed and further reveal an important impact of [Mo] concentration, thereby pointing to potential bimolecular steps (e.g., N2 splitting) as previously proposed during chemically driven N2R catalysis. Finally, facile reductive protonation of [Mo(N)Br(HPNP)] with pyridinium acids is demonstrated.
