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

Authors
  • Kennedy, C Rose1
  • Zhong, Hongyu1
  • Joannou, Matthew V1
  • Chirik, Paul J1
  • 1 Princeton University, Department of Chemistry, Princeton, NJ 08544, United States. , (United States)
Type
Published Article
Journal
Advanced Synthesis & Catalysis
Publisher
Wiley
Publication Date
Jan 23, 2020
Volume
362
Issue
2
Pages
404–416
Identifiers
DOI: 10.1002/adsc.201901289
PMID: 32431586
Source
Medline
Keywords
Language
English
License
Unknown

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 implicates 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 occurs 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.

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