Carbon-oxygen bond cleavage by bis(imino)pyridine iron compounds

Catalyst deactivation pathways and observation of acyl C-O bond cleavage in esters

Ryan Trovitch, Emil Lobkovsky, Marco W. Bouwkamp, Paul J. Chirik

Research output: Contribution to journalArticle

67 Citations (Scopus)

Abstract

Investigations into the substrate scope of bis(imino)pyridine iron-catalyzed hydrogenation and [2π + 2π] diene cyclization reactions identified C-O bond cleavage as a principal deactivation pathway. Addition of diallyl or allyl ethyl ether to the bis(imino)pyridine iron dinitrogen complex, (iPrPDI)Fe(N2)2 (iPrPDI = 2,6-(2,6-iPr2-C6H3N=CMe) 2C5H3N, 1-(N2)2), under a dinitrogen atmosphere resulted in facile cleavage of the C-O bond and yielded a mixture of the corresponding paramagnetic iron allyl and alkoxide complexes. For ethyl vinyl ether, clean and selective formation of the iron ethoxide was observed with concomitant loss of the vinyl fragment. In situ monitoring of the catalytic hydrogenation of trans-methyl cinnamate established ester C-O bond cleavage as a competing process. Stoichiometric reactions between 1-(N 2)2 and allyl and vinyl acetate also produced facile C-O oxidative addition. For the latter, a six coordinate diamagnetic bis(imino)pyridine acetatoxy iron vinyl compound was obtained and characterized by X-ray diffraction. Phenyl acetate undergoes exclusive acyl C-O bond cleavage, while alkyl-substituted esters such as ethyl, pentyl, benzyl, isopropyl, cyclohexyl, and tert-butyl acetate undergo competing ester and acyl C-O bond cleavage accompanied by iron-promoted decarbonylation. Deuterium labeling studies established that reversible C-H activation and chelate cyclometalation occur prior to, but are not a prerequisite for, carbon-oxygen bond oxidative addition of ethyl acetate. The molecular and electronic structures of the ether and ester C-O bond cleavage products have been established and demonstrate that ligand- rather than metal-based oxidation accompanies substrate activation.

Original languageEnglish
Pages (from-to)6264-6278
Number of pages15
JournalOrganometallics
Volume27
Issue number23
DOIs
Publication statusPublished - Dec 8 2008

Fingerprint

Iron Compounds
iron compounds
Catalyst deactivation
deactivation
esters
cleavage
pyridines
Esters
Carbon
Iron
Oxygen
iron
catalysts
acetates
carbon
oxygen
ethers
Ether
Hydrogenation
hydrogenation

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Carbon-oxygen bond cleavage by bis(imino)pyridine iron compounds : Catalyst deactivation pathways and observation of acyl C-O bond cleavage in esters. / Trovitch, Ryan; Lobkovsky, Emil; Bouwkamp, Marco W.; Chirik, Paul J.

In: Organometallics, Vol. 27, No. 23, 08.12.2008, p. 6264-6278.

Research output: Contribution to journalArticle

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