A TMEDA–Iron Adduct Reaction Manifold in Iron‐Catalyzed C(sp2)−C(sp3) Cross‐Coupling Reactions. (18th February 2022)

• Record Type: Journal Article
• Authors: Bakas, Nikki J.; Sears, Jeffrey D.; Brennessel, William W.; Neidig, Michael L.
• Is Part Of: Angewandte Chemie. Volume 134:Number 15(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-18
• Subjects: C−C Coupling -- Homogeneous Catalysis -- Iron -- Ligand Effects -- Organometallics; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202114986
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Herein, we expand the current molecular‐level understanding of one of the most important and effective additives in iron‐catalyzed cross‐coupling reactions, N, N, N′, N′ ‐tetramethylethylenediamine (TMEDA). Focusing on relevant phenyl and ethyl Grignard reagents and slow nucleophile addition protocols commonly used in effective catalytic systems, TMEDA‐iron(II)‐aryl intermediates are identified via in situ spectroscopy, X‐ray crystallography, and detailed reaction studies to be a part of an iron(II)/(III)/(I) reaction cycle where radical recombination with FePhBr(TMEDA) (2Ph ) results in selective product formation in high yield. These results differ from prior studies with mesityl Grignard reagent, where poor product selectivity and low catalytic performance can be attributed to homoleptic iron–ate species. Overall, this study represents a critical advance in how amine additives such as TMEDA can modulate selectivity and reactivity of organoiron species in cross‐coupling. Abstract : Historically, the role of TMEDA in iron‐catalyzed C(sp 2 )−C(sp 3 ) cross‐coupling has been disputed due to a lack of insight into the iron species present during catalysis. In this report, low‐temperature synthesis, freeze‐trapped 57 Fe Mössbauer, X‐ray diffraction (XRD), and chemical‐quenched GC analysis were utilized to identify highly reactive and selective TMEDA‐ligated iron species responsible for C(sp 2 )−C(sp 3 ) cross‐coupling catalysis.