A synthesis of alkyl aryl ethers was achieved via the cross‐coupling of aryl halides with primary and secondary aliphatic alcohols catalyzed by a bench‐stable nickel complex supported by a monoanionic O,N,N‐tridentate ligand. This nickel ‐catalyzed reaction proceeds smoothly in the absence of a phosphine ligand, affording alkyl aryl ethers in moderate to good yields.
A β‐diketiminato‐based tridentate pincer‐type nickel(II) complex Ni‐NNP was prepared by the reaction of the nickel(II) precursor [NiCl2(2,4‐lutidine)2] with the lithiated NNP ligand, which was generated in situ by the reaction of the NNP pro‐ligand H‐NNP with nBuLi. H‐NNP was prepared by the condensation of 4‐[(2,4,6‐trimethylphenyl)amino]pent‐3‐en‐2‐one with 2‐(diphenylphosphanyl)ethylamine. Ni‐NNP was characterized spectroscopically and by X‐ray diffraction, revealing a slightly distorted square‐planar geometry around the nickel center. Density functional theory calculations indicated that the highest occupied molecular orbital in Ni‐NNP is located at higher energy than those of three other homologous nickel(II) complexes, i.e., Ni‐ONN, Ni‐ONP, and Ni‐NNN, which contain β‐aminoketonato‐ or β‐diketiminato‐based pincer‐type ligands. The electronic and steric properties of Ni‐NNP effectively facilitated the cross‐coupling of aryl fluorides with aryl Grignard reagents.
A cross-coupling reaction of allylic aryl ethers with arylmagnesium reagents was investigated using β-aminoketonato- and β-diketiminato-based pincer-type nickel(II) complexes as catalysts. An β-aminoketonato nickel(II) complex bearing a diphenylphosphino group as a third donor effectively catalyzed the reaction to afford the target cross-coupled products, allylbenzene derivatives, in high yield. The regioselective reaction of a variety of substituted cinnamyl ethers proceeded to give the corresponding linear products. In contrast, α- and γ-alkyl substituted allylic ethers afforded a mixture of the linear and branched products. These results indicated that the coupling reaction proceeded via a π-allyl nickel intermediate.
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