Synthesis of Ferrocenyl Alkyne–Cu(I) π‑Complexes via Copper-Promoted 8‑Aminoquinoline-Directed C–H Bond Alkynylations

A highly monoselective synthesis
of ferrocenyl alkynes was achieved
via Cu-promoted ferrocene C­(sp2)–H bond activations.
The reaction employs an 8-aminoquinoline group as the directing group
and terminal alkynes as the alkyne source. It was found the alkynylation
products actually complex with the in situ generated Cu­(I) ions to
give robust and stable alkyne π-copper complexes. In addition,
these alkyne π-copper complexes could be freed of the copper
ions to give various ferrocenyl alkynes in almost quantitative yields.
The test results also showed that the alkyne π-copper complexes
could be reformed from the free alkynes upon treating them with Cu­(I)
salts.