Transition Metal‐Free Catalytic C−H Zincation and Alumination

Milan Kumar Bisai, Justyna Losiewicz, Lia Sotorríos, Gary Nichol, Andrew Dominey, Michael Cowley, Stephen Thomas, Stuart Macgregor, Michael Ingleson

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Abstract

C−H metalation is the most efficient method to prepare aryl–zinc and –aluminium complexes that are ubiquitous nucleophiles. Virtually all C−H metalation routes to form Al/Zn organometallics require stoichiometric, strong Brønsted bases with no base-catalyzed reactions reported. Herein we present a catalytic in amine/ammonium salt (Et3N/[(Et3N)H]+) C−H metalation process to form aryl-zinc and aryl-aluminium complexes. Key to this approach is coupling an endergonic C−H metalation step with a sufficiently exergonic dehydrocoupling step between the ammonium salt by-product of C−H metalation ([(Et3N)H]+) and a Zn−H or Al−Me containing complex. This step, forming H2/MeH, makes the overall cycle exergonic while generating more of the reactive metal electrophile. Mechanistic studies supported by DFT calculations revealed metal-specific dehydrocoupling pathways, with the divergent reactivity due to the different metal valency (which impacts the accessibility of amine-free cationic metal complexes) and steric environment. Notably, dehydrocoupling in the zinc system proceeds through a ligand-mediated pathway involving protonation of the β-diketiminate Cγ position. Given this process is applicable to two disparate metals (Zn and Al), other main group metals and ligand sets are expected to be amenable to this transition metal-free, catalytic C−H metalation.

Original languageEnglish
Article numbere202404848
JournalAngewandte Chemie International Edition
Volume63
Issue number24
Early online date5 Apr 2024
DOIs
Publication statusPublished - 10 Jun 2024

Keywords

  • C−H functionalization
  • Frustrated Lewis pairs
  • Zinc
  • aluminium
  • beta-diketiminates

ASJC Scopus subject areas

  • General Chemistry
  • Catalysis

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