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

Abstract

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.

Cross‐Dehydrogenative Alkynylation: A Powerful Tool for the Synthesis of Internal Alkynes

“…deduced that the reaction was perhaps a Cu I /Cu III process, however no further experimental evidence was provided, and the catalytic cycle was also not depicted. Following a similar idea, the ferrocene sp 2 C−H bonds were also alkynylated with 2 equivalents of Cu(OAc) 2 using 8‐aminoquinoline as a directing group …”

Copper-catalyzed monoselective C–H amination of ferrocenes with alkylamines

“…To note, this reaction showed excellent mono-selectivity and no diaminated ferrocenylamide was detected. The exclusive monoselectivity is most likely originated from the strong coordination of the amino group, which could form a tridentate copper complex and prevent the second C–H amination [ 34 , 50 ].…”

“…Meanwhile, Co(III)catalyzed ortho-C-H amidation of ferrocene derivatives were also developed by the groups of You [30], Ackermann [31] and Shi [32,33] with 1,4,2-dioxazol-5-ones as versatile amidating reagents. In 2019, the alkynylated ferrocenes were isolated in the formation of alkyne-Cu(I) π-complexes by the Tan group via Cu-mediated C-H alkynylations [34]. Later in 2020, an enantioselective C-H annulation of ferrocenylformamides with alkynes was achieved by the Ye group enabled by Ni-Al bimetallic catalysis and a chiral secondary phosphine oxide (SPO) ligand [35].…”

8‐Aminoquinoline‐Assisted Synthesis and Crystal Structure Studies of Ferrocenyl Aryl Sulfones

“…Shi group has shown a cobalt catalyzed amidation of ferrocene directed by thioamides . Recently, an elegant methodology has been developed for alkynylation of ferrocene using copper catalysts by Tan and co‐workers …”