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.
Highlights
Metal-catalyzed cross-coupling reactions are an essential tool for the formation of carbon–carbon bonds [1]
The first cross-coupling reactions of organomagnesium bromides described by Kumada or Corriu utilized nickel catalysts, for example, [Ni(dppe)Cl2] and Ni(acac)2 [2,3], the most efficient and commonly employed catalysts for such C–C coupling reactions nowadays are based on noble metals [4]
We observed that Ni(II) complexes 2–4 are suitable to catalyze the coupling of aryl iodides with phenylmagnesium bromide
Summary
Metal-catalyzed cross-coupling reactions are an essential tool for the formation of carbon–carbon bonds [1]. The first cross-coupling reactions of organomagnesium bromides described by Kumada or Corriu utilized nickel catalysts, for example, [Ni(dppe)Cl2] and Ni(acac)2 [2,3], the most efficient and commonly employed catalysts for such C–C coupling reactions nowadays are based on noble metals [4]. Ni(0), Ni(I), Ni(II) and Ni(III) complexes have been proposed as potential intermediates for various C–C coupling reactions including Heck, Hiyama, Kumada, Negishi, Suzuki–Miyaura, Sonogashira and Stille coupling techniques [6,7,8]. Along this line, Ni(I) as well as Ni(III)
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