Mechanistic Implications for the Ni(I)-Catalyzed Kumada Cross-Coupling Reaction

Abstract

Herein we report on the cross-coupling reaction of phenylmagnesium bromide with aryl halides using the well-defined tetrahedral Ni(I) complex, [(Triphos)NiICl] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane). In the presence of 0.5 mol % [(Triphos)NiICl], good to excellent yields (75–97%) of the respective coupling products within a reaction time of only 2.5 h at room temperature were achieved. Likewise, the tripodal Ni(II)complexes [(κ2-Triphos)NiIICl2] and [(κ3-Triphos)NiIICl](X) (X = ClO4, BF4) were tested as potential pre-catalysts for the Kumada cross-coupling reaction. While the Ni(II) complexes also afford the coupling products in comparable yields, mechanistic investigations by UV/Vis and electron paramagnetic resonance (EPR) spectroscopy indicate a Ni(I) intermediate as the catalytically active species in the Kumada cross-coupling reaction. Based on experimental findings and density functional theory (DFT) calculations, a plausible Ni(I)-catalyzed reaction mechanism for the Kumada cross-coupling reaction is presented.

Keywords

• nickel
• tripodal ligands
• cross-coupling
• EPR
• Grignard
• DFT