Well‐Defined Ni(0) and Ni(II) Complexes of Bicyclic (Alkyl)(Amino)Carbene (MeBICAAC): Catalytic Activity and Mechanistic Insights in Negishi Cross‐Coupling Reaction

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Negishi cross‐coupling reaction of organozinc compounds as nucleophiles with aryl halides has drawn immense focus for C−C bond formation reactions. In comparison to the well‐established library of Pd complexes, the C−C cross‐coupling of this particular approach is largely primitive with nickel‐complexes. Herein, we describe the syntheses of Ni(II) complexes, [( Me BICAAC) 2 NiX 2 ] (X=Cl ( 1 ), Br ( 2 ), and I ( 3 )) by employing the bicyclic (alkyl)(amino)carbene ( Me BICAAC) ligand. The reduction of complexes 1 – 3 using KC 8 afforded the two coordinate low valent, Ni(0) complex, [( Me BICAAC) 2 Ni(0)] ( 4 ). Complexes 1 – 4 have been characterized by spectroscopic techniques and their solid‐state structures were also confirmed by X‐ray crystallography. Furthermore, complexes 1 – 4 have been applied in a direct and convenient method to catalyze the Negishi cross‐coupling reaction of various aryl halides with 2,6‐difluorophenylzinc bromide or phenylzinc bromide as the coupling partner in the presence of 3 mol % catalyst. Comparatively, among all‐pristine complexes, 1 exhibit high catalytic potential to afford value‐added C−C coupled products without the use of any additive. The UV‐vis studies and HRMS measurements of controlled stochiometric reactions vindicate the involvement of Ni(I)−NI(III) cycle featured with a penta‐coordinated Ni(III)‐aryl species as the key intermediate for 1 whereas Ni(0)/Ni(II) species are potentially involved in the catalytic cycle of 4 .