Theoretical insights into the reaction of Cp*(Cl) Hf(diene) with isonitriles

摘要

The migratory insertion of isonitriles into a metal-C bond is a potentially important method for C-C bond construction in organic and pharmaceutical syntheses. In this context, the reaction mechanism of Cp*(Cl) Hf(diene) (Cp* = pentamethylcyclopentadienyl) with isonitriles was studied using density functional theory calculations. Hf-imido complexes and a-methylene cyclopentenimines are the confirmed products for N-tert-butyl-or N-1-adamantyl-substituted isonitriles. They are also the thermodynamically favored products of N-2,6-dimethylphenyl (Ar)-substituted isonitriles. The beta-H elimination reaction pathway is responsible for the formation of alpha-methylene cyclopentenimines. Its elementary reactions include the isomerization of Cp*(Cl) Hf(diene), migratory insertion of the first isonitrile into the Hf-C bond, C-C reductive elimination, beta-H elimination, migratory insertion of the second isonitrile into the Hf-H bond, C-C reductive coupling, addition of a Hf-H bond, and fragmentation of the six-membered hafnacycle. For methyl-, ethyl-, and Ar-substituted isonitriles, the kinetically favored products are diazahafnacyclopentanes ("sigma complexes"). These are formed via an isomerization reaction pathway that comprises isomerization of the Hf complex, C-C reductive coupling, and insertion of a C=N bond. The effects of different substituents on the isonitrile nitrogen on the main elementary reactions are discussed.