Tandem Mn–I Exchange and Homocoupling Processes Mediated by a Synergistically Operative Lithium Manganate

Abstract

Pairing lithium and manganese(II) to form lithium manganate [Li2Mn(CH2SiMe3)4] enables the efficient direct Mn–I exchange of aryliodides, affording transient (aryl)lithium manganate intermediates which in turn undergo spontaneous C−C homocoupling at room temperature to furnish symmetrical (bis)aryls in good yields under mild reaction conditions. The combination of EPR with X‐ray crystallographic studies has revealed the mixed Li/Mn constitution of the organometallic intermediates involved in these reactions, including the homocoupling step which had previously been thought to occur via a single‐metal Mn aryl species. These studies show Li and Mn working together in a synergistic manner to facilitate both the Mn–I exchange and the C−C bond‐forming steps. Both steps are carefully synchronized, with the concomitant generation of the alkyliodide ICH2SiMe3 during the Mn–I exchange being essential to the aryl homocoupling process, wherein it serves as an in situ generated oxidant.

The Anionic Pathway in the Nickel‐Catalysed Cross‐Coupling of Aryl Ethers

“…Moreover, the enhanced nucleophilicity of the higher order (2:1 Li/Ni) species is expected to lead to increased reactivity at Ni. This has been demonstrated in other studies with hetero‐bimetallic systems such as lithium manganates [55] …”

“…This has been demonstrated in other studies with heterobimetallic systems such as lithium manganates. [55] Taking our spectroscopic,structural, and kinetic data into account, together with related computational studies, [14,16] am echanistic proposal for the anionic pathway can be postulated (Scheme 7). Starting from Ni(COD) 2 (A), addition of PhLi(donor) n can form either a1 :1 (B)o r2:1 (F)l ithium…”

The Anionic Pathway in the Nickel‐Catalysed Cross‐Coupling of Aryl Ethers

“…This has been demonstrated in other studies with hetero‐bimetallic systems such as lithium manganates. [55] …”

Iron-Catalyzed Cross-Coupling of Thioesters and Organomanganese Reagents

“…[18] Another important feature of these reagents is their property to form higher substituted manganates (LiMnR3 or Li2MnR4), which led to the recent discovery of a tandem Mn-I exchange/homocoupling, a reactivity thought to be reserved for RLi or RMgX reagents. [19] These literature examples not only elucidate the high complexity of manganese organyles but also inspire further studies of their so far less known potential. Our herein presented methodology of a base metal-catalyzed cross-coupling reaction of b-hydrogen containing aliphatic organomanganese reagents with thioesters furnishing highly functionalized building blocks extends the known synthetic scope of these reagents.…”