The development of strategies to access 2,2'-diaminobiaryl derivatives via transition-metal-catalyzed coupling
reaction from protecting-group-free starting materials is a challenging task to accomplish owing to the easy occurrence of
undesired side reactions. The exploitation of Ni-catalyzed direct homocoupling of unprotected 2-haloaniline analogs to
produce 2,2'-diaminobiaryls with a readily available and inexpensive bipyridine ligand has been described. This approach
was highlighted by its high chemoselectivity, broad substrate scope, and functional group compatibility. The mechanistic and
calculation studies indicated that Ni(0), Ni(I), Ni(II), and Ni(III) species might be involved in the catalytic cycle.