Evidence for Carbene Intermediates in Isocyanide Homologation by Aluminium(I)

Abstract

AbstractThe C−C bond formation between C1 molecules plays an important role in chemistry as manifested by the Fischer–Tropsch (FT) process. Serving as models for the FT process, we report here the reactions between a neutral AlIcomplex (MeNacNac)Al (1,MeNacNac=HC[(CMe)(NDipp)]2, Dipp=2,6‐diisopropylphenyl) and various isocyanides. The step‐by‐step coupling mechanism was studied in detail by low‐temperature NMR monitoring, isotopic labeling, as well as quantum chemical calculations. Three different products were isolated in reaction of1with the sterically encumbered 2,6‐bis(benzhydryl)‐4‐Me‐phenyl isocyanide (BhpNC). These products substantiate carbene intermediates. The reaction between1and adamantyl isocyanide (AdNC) generated a trimerization product, and a corresponding carbene intermediate could be trapped in the form of a molybdenum(0) complex. Tri‐, tetra‐, and even pentamerization products were isolated with the sterically less congested phenyl andp‐methoxyphenyl isocyanides (PhNC and PMPNC) with concurrent construction of quinoline or indole heterocycles. Overall, this study provides evidence for carbene intermediates in FT‐type chemistry of aluminium(I) and isocyanides.