Catalytic 1,3‐H Atom Shift of a Terminal Benzylic Alkyne by Iron and Alkali Metal Silylamides – Switching between Allene and Internal Alkyne

Herein the examination of transformation alkynes by low-coordinate iron silylamides is presented. An anionic linear iron(I) ([Fe(N{Dipp}SiR3)2]−; Dipp=2,6-di-iso-propylphenyl, R=Me) acts as precatalyst for cyclotrimerization diphenyl acetylene but unable to transform internal with aliphatic substituents or terminal accordingly. For a benzylic, alkyne, however, 1,3-H-shift alkyne observed and proceeds via phenyl allene. Using 10 mol% complex, alkene selectively transformed allene within minutes, further fully 24 h. The retraced on stoichiometric level leads isolation π-alkyne complex shifted triple bond. Further, anionic, trigonal iron(II) silylamide [Fe(NR2)3]− also mediates catalytic conversion restricted formation. Overall, deprotonation/reprotonation mechanism assumed these transformations. This was ultimately proven using potassium hexamethyldisilazanide KNR2, which an even more active catalyst complete bond shift.