Isolation and crystal structures of both enol and keto tautomer intermediates in a hydration of an alkyne-carboxylic acid ester catalyzed by iridium complexes in water

Hironobu Kanemitsu, Keiji Uehara, Shunichi Fukuzumi, Seiji Ogo

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

Hydration of tetrolic acid ethyl ester as an alkyne-carboxylic acid ester catalyzed by an Ir-aqua complex [IrIIICp*(bpy)(OH 2)]2+ (1, Cp* = η5-C 5Me5, bpy = 2,2′-bipyridine) in water provides ethyl acetoacetate as a β-keto acid ester. We report the successful isolation of both an Ir-enol tautomer intermediate [IrIIICp*(bpy){CH 3C(OH)=CC(O)OC2H5}]+ (2) and an Ir-keto tautomer intermediate [IrIIICp*(bpy){CH 3C(O)-CHC(O)OC2H5}]+ (3) in the catalytic hydration by optimizing the conditions of the isolation, such as pH of the solution, reaction time, and selection of counteranions. The structures of the enol and keto complexes with characteristic Ir-(sp2carbon) bond and Ir-(sp3 carbon) bond, respectively, were unequivocally determined by X-ray analysis, IR, electrospray ionization mass spectrometry (ESI-MS), and NMR studies including 1H, 13C, distortionless enhancement by polarization transfer (DEPT) and correlation spectroscopy (COSY) experiments. It was confirmed that the hydration of tetrolic acid ethyl ester catalyzed by 2 or 3 as initial catalysts provides ethyl acetoacetate. Mechanism of the catalytic hydration of tetrolic acid ethyl ester as an alkyne-carboxylic acid ester is discussed based on isotopic labeling experiments with the Ir-enol and Ir-keto tautomers.

Original languageEnglish
Pages (from-to)17141-17147
Number of pages7
JournalJournal of the American Chemical Society
Volume130
Issue number50
DOIs
Publication statusPublished - Dec 17 2008

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Iridium
Alkynes
Carboxylic Acids
Carboxylic acids
Hydration
Esters
Crystal structure
Water
Acids
Keto Acids
Electrospray ionization
Electrospray Ionization Mass Spectrometry
X ray analysis
Labeling
Mass spectrometry
Spectrum Analysis
Carbon
Experiments
Nuclear magnetic resonance
X-Rays

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Isolation and crystal structures of both enol and keto tautomer intermediates in a hydration of an alkyne-carboxylic acid ester catalyzed by iridium complexes in water. / Kanemitsu, Hironobu; Uehara, Keiji; Fukuzumi, Shunichi; Ogo, Seiji.

In: Journal of the American Chemical Society, Vol. 130, No. 50, 17.12.2008, p. 17141-17147.

Research output: Contribution to journalArticle

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