Pyridine(diimine) Iron Diene Complexes Relevant to Catalytic [2+2]-Cycloaddition Reactions

C. Rose Kennedy, Hongyu Zhong, Matthew V. Joannou, Paul J. Chirik

Research output: Contribution to journalArticle

Abstract

The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E)-piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicated the diamagnetic η4-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature 1H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e complexes occurred rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (Me(Et)PDI) Fe(η4-piperylene) (Me(Et)PDI=2,6-(2,6-Me2-C6H3N=CEt)2C5H3N) was determined by single-crystal X-ray diffraction and confirmed the s-trans coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed. (Figure presented.).

Original languageEnglish (US)
Pages (from-to)404-416
Number of pages13
JournalAdvanced Synthesis and Catalysis
Volume362
Issue number2
DOIs
StatePublished - Jan 23 2020

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

Keywords

  • cycloaddition
  • diene ligands
  • iron
  • metallacycles

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