Ni(I) and Ni(II) ring-expanded N-heterocyclic carbene complexes: C-H activation, indole elimination and catalytic hydrodehalogenation.

Reaction of the bulky 6-membered N-heterocyclic carbene 6-Mes with Ni(cod)(2) gives a C-H activated 6-Mes nickel(II) complex, but the novel three-coordinate Ni(I) species Ni(6-Mes)(PPh(3))Br if the reaction is performed in the presence of Ni(PPh(3))(2)Br(2). The Ni(I) complex is a precursor for the catalytic hydrodehalogenation of aryl halides.