Catalytic 1, 3‐H Atom Shift of a Terminal Benzylic Alkyne by Iron and Alkali Metal Silylamides – Switching between Allene and Internal Alkyne. Issue 6 (20th January 2022)

• Record Type: Journal Article
• Authors: Weller, Ruth; Müller, Igor; Werncke, C. Gunnar
• Is Part Of: European journal of inorganic chemistry. Volume 2022:Issue 6(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-20
• Subjects: Alkynes -- Allenes -- Homogeneous catalysis -- Earth abundant metals -- Isomerization -- Silylamides; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.202100955
• Languages: English
• ISSNs: 1434-1948

Abstract

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