Thermally Stable Redox Noninnocent Bathocuproine-Iron Complex for Cycloaddition Reactions

Abstract

In this work, we aim to formally design iron(0) complexes combined with a phenanthroline-type ligand (phen) and investigate their utility in cycloaddition catalysis. Owing to the strong noninnocence of the phen scaffold, its ligation to reduced iron oxidation states classically affords particularly unstable species. The reported examples of such well-defined coordination complexes are thus particularly scarce. We demonstrate herein that a strategic steric protection of the C4 and C7 positions of the phen ring leads to neutral (N,N)2Fe species, which exhibits an unprecedented thermal and kinetic stability, amenable to its easy use as an in situ generated precursor in catalytic processes. The electronic structure of this noninnocent complex has been fully rationalized, and its promising catalytic activity in alkyne [2 + 2 + 2] cyclizations is discussed. Given its intrinsic thermal stability due to the noninnocent behavior of the (N,N) ligand, (N,N)2Fe appears to be an efficient dormant state of the catalytic process, precluding deactivation of iron as nonreactive aggregates.

Photocatalytic CO2 Reduction Using Mixed Catalytic Systems Comprising an Iron Cation with Bulky Phenanthroline Ligands

“…Note that in the absence of TEOA, the system with Fe II ( MeHp )Cl 2 did not induce CO 2 reduction. This indicates that a singly reduced Fe II ( MeHp )Cl 2 , in which the added electron was localized on the MeHp ligands, i.e., Fe II ( MeHp •– )Cl 2 , could not induce CO 2 reduction. Thus, the production of MeHp H • and its interaction with the Fe ion are essential for the CO 2 reduction.…”

A Versatile, Functional Group‐Tolerant, and Bench‐Stable Iron Precatalyst for Building Arene and Triazine Rings by [2+2+2] Cycloadditions

“…Spectroscopic data matched with literature. [34] Typical procedure for cycloadditions A 10 mL round bottom two-necked flask was charged with (L 1 )FeCl 2 (29.2 mg, 0.06 mmol, 1.00 equiv.) and bathocuproine (L 1 ), 22.6 mg, 0.06 mmol, 1.00 equiv.).…”

“…We reported that (L 1 ) 2 Fe was an efficient alkyne [2 + 2 + 2] cycloaddition catalyst, albeit under thorough air-sensitive, glovebox conditions. [34] Because (L 1 )FeCl 2 is readily obtained in a single, quantitative step from commercially available ligand L 1 and can subsequently be stored with no need of specific air-sensitive procedures, it appears to be a particularly appealing catalyst for synthetic purposes, because the targeted transformations are carried out with no need of glovebox or drastic air-and moisture-free conditions. In this report, we demonstrate that cycloadditions mediated by in situ generated (L 1 ) 2 Fe can be achieved in such user-friendly conditions.…”

“…[30,31] From a synthetic standpoint, it is more convenient to handle stable precatalysts that are reduced in situ into catalytically active low oxidation states. Thus, numerous methods have been described using a well-defined, stable iron(II) or iron(III) precursor, and with Zn dust [18,19,20,32,33] or Grignard reagents [16,34] such as EtMgBr used most commonly as reductants. In some rare cases, iron(II) complexes activated by hydride donors such as pinacolborane remain the active species.…”

“…Substitution at the C4/C7 positions proved to be a crucial parameter, inhibiting the decomposition of the reduced L 1 ⋅ − moiety by radical pathways. We reported that ( L 1 ) 2 Fe was an efficient alkyne [2+2+2] cycloaddition catalyst, albeit under thorough air‐sensitive, glovebox conditions [34] …”