Tandem couplings of imines and other unsaturated organic compounds with a half-open titanocene

Abstract

The half-open titanocene Ti(C₅H₅)(2,4-C₇H₁₁)(PEt₃) (C₇H₁₁ = dimethylpentadienyl) has been found to incorporate a second equivalent of PhC(H)NMe more slowly than the first, with coupling occurring between the imine’s carbon atom and the dienyl’s terminal CH₂ groups. The structure of this complex has been confirmed through a diffraction study. The fact that a second imine could be incorporated has allowed mixed couplings involving initial incorporation of one equivalent of imine followed by another type of unsaturated compound. Thus, after addition and coupling of one equivalent of PhC(H)–NPrⁱ, addition of an excess of acetone or Bu^tNC leads to the respective incorporation of one or two equivalents of these species. X-Ray diffraction studies have been carried out for each, and reveal that one equivalent of ketone or nitrile has undergone coupling. A reaction involving the same imine and p-MeC₆H₄NC in the presence of Bu^tOH was found to lead to the incorporation of three equivalents of the isocyanide along with one equivalent of the alcohol. The nature of the coupled product has been revealed through a diffraction study, and a reasonable mechanism proposed for the product’s formation.