Addition of amines and phenols to acrylonitrile derivatives catalyzed by the POCOP-type pincer complex [{κP,κC,κP-2,6-(i-Pr2PO)2C6H3}Ni(NCMe)][OSO2CF3]

The pincer-type complex [{κP,κC,κP-2,6-(i-Pr2PO)2C6H3}Ni(NCMe)][OSO2CF3] (1) can serve as a precatalyst for the regioselective, anti-Markovnikov addition of nucleophiles to activated olefins. The catalyzed additions of aliphatic amines to acrylonitrile, methacrylonitrile, and crotonitrile proceed at room temperature and give quantitative yields of products resulting from the formation of C–N bonds. On the other hand, aromatic amines or alcohols are completely inert toward methacrylonitrile and crotonitrile, and much less reactive toward acrylonitrile, requiring added base, heating, and extended reaction times to give good yields. The catalytic reactivities of 1 are thought to arise from the substitutional lability of the coordinated acetonitrile that allows competitive coordination of the nitrile moiety in the olefinic substrates; this binding enhances the electrophilicity of the CC moiety, rendering them more susceptible to attack by nucleophiles. In some cases, RCN → Ni binding results in double bond isomerization/migration (allyl cyanide) or attack of nucleophiles at the nitrile moiety (cinnamonitrile and 4-cyanostyrene). Reaction of morpholine with 1 at 60 °C led to formation of the amidine derivative 2 that has been characterized by X-ray crystallography.

The pincer type nickel complex promotes the anti-Markovnikov addition of primary and secondary amines and substituted phenols to acrylonitrile and its derivatives. With cinnamonitrile, 4-cyanostyrene, and acetonitrile, the nucleophilic attack by morpholine takes place on the nitrile moiety to give the corresponding amidine.Figure optionsDownload high-quality image (73 K)Download as PowerPoint slideResearch highlights▶ Greater range of amine substrates for hydroamination of acrylonitrile and its derivatives. ▶ First pincer-type nickel complex to promote hydroaryloxylation of acrylonitrile. ▶ Noted important role played by bases in promoting the hydroaryloxylation reaction. ▶ Obtained supporting evidence for the proposed mechanism of catalysis. ▶ Discovered the conversion of nitriles to amidines during the hydroamination catalysis.