B2Pin2-Enabled Chemoselective Ni-Catalyzed Reductive Ar-Ar Coupling of Two Aryl Halides

A versatile Ni-catalyzed reductive coupling platform has been developed for the chemoselective cross-coupling of two distinct aryl (and heteroaryl) halides. The method employed B2Pin2 as a non-single-electron-transfer (non-SET) homogeneous reductant. The use of specific 2,9-dimethyl phenanthroline ligands (L1 and L2) and additives allows the protocol to be modulated, according to the electronic nature of the coupling partners. This includes the 1:1 coupling of electron-deficient aryl bromides with electron-rich aryl iodides, the coupling of two electronically similar (either rich or deficient) aryl halides, and reactions involving heteroaryl halides. These equimolar reactions afforded the biaryl scaffolds in moderate to good yields. Notably, a directing effect from nitrogen-containing heterocycles, such as 2-chloropyridine, 2chloropyrimidine and 8-bromoquinoline, further enhances chemoselectivity. Two proposals were implemented for the formation of a key Ar 1-LnNi I intermediate. One concerns Ni(I) reduction of Ar 1-LnNi II X generated from oxidative addition of Ar 1 X to LnNi 0 , the other emphasizes B2pin2-invoked reduction of Ar 1-LnNi III (X)2 generated from addition of Ar 1 X to LnNi I X. This cost-effective reductive system minimizes the need for an excess of one coupling partner in constructing biaryl scaffolds, and the mechanistic insights offer valuable guidance for the future development of cross-electrophile coupling methodologies.