Efficient nickel mediated carbon–carbon bond cleavage of organonitriles

Abstract

The reactions of the nickel complex [Ni₂(iPr₂Im)₄(COD)] 1 with organonitriles smoothly and irreversibly proceed via intermediates with η²-coordinated organonitrile ligands such as [Ni(iPr₂Im)₂(η²-(CN)-PhCN)] 2 and [Ni(iPr₂Im)₂(η²-(CN)-pTolCN)] 4 to yield aryl cyanide complexes of the type trans-[Ni(iPr₂Im)₂(CN)(Ar)] (Ar = Ph 3, pTol 5, 4-CF₃C₆H₄6, 2,4-(OMe)₂C₆H₃7, 2-C₄H₃O 8, 2-C₅H₄N 9). The compounds 3, 7, and 9 have been structurally characterized. For the conversion of 2 to 3 a free activation enthalpy ΔG^‡(328 K) of 103.47 ± 0.79 kJ mol⁻¹ was calculated from time dependent NMR spectroscopy. The analogous reaction of arylnitriles with electron releasing substituents or heteroaromatic organonitriles is significantly faster compared to the reaction with benzonitrile or toluonitrile. The reactions of 1 with acetonitrile or trimethylsilyl cyanide afforded [Ni(iPr₂Im)₂(CN)(Me)] 10 and structurally characterized [Ni(iPr₂Im)₂(CN)(SiMe₃)] 11. The usage of an organonitrile with a longer alkyl chain, adiponitrile, yielded [Ni(iPr₂Im)₂(η²-(CN)-NCC₄H₈CN)] 12 as well as the C–CN activation product [Ni(iPr₂Im)₂(CN)(C₄H₈CN)] 13 in thermal and photochemical reactions, although this pathway seems to be significantly interfered with by decomposition pathways under the formation of the dicyanide complex [Ni(iPr₂Im)₂(CN)₂] 14.