Molecular mapping of the catalytic cycle of the cobalt-catalyzed hydromethoxycarbonylation of 1,3-butadiene in the presence of pyridine in methanol

László T. Mika, Róbert Tuba, Imre Tóth, Stephan Pitter, István T. Horváth

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

High-pressure in situ IR and NMR investigations of the hydromethoxycarbonylation of 1,3-butadiene (1) to methyl 3-pentenoate (2) in methanol in the presence of Co2(CO)8 and pyridine under carbon monoxide has revealed that the reaction starts by the methanol- and/or pyridine-assisted disproportionation of Co2(CO)8, followed by the establishment of equilibria involving the ionic species [Co(Py) 6]2+{[Co(CO)4]-}2, [Co(Py)6]2+[MeO]-[Co(CO)4] -, [PyH]+[Co(CO)4]-, and [MeOH 2]+[Co(CO)4]-. The addition of HCo(CO)4 (3) to pyridine or methanol results in the formation of [PyH]+[Co(CO)4]- and [MeOH2] +[Co(CO)4]-, respectively, and 3 is not detectable by either IR or NMR. The ionic 1,4-addition of [MeOH 2]+[Co(CO)4]- to 1 is the only pathway to 2-butenylcobalt tetracarbonyl, CH3CH=CHCH 2Co(CO)4 (4), via the protonation of 1 followed by the reaction of the C4 carbocation with the counteranion tetracarbonylcobaltate. In the absence of carbon monoxide, 4 could lose a coordinated carbon monoxide to form (η3-C4H 7)Co(CO)3 (7) in a reversible reaction. In the presence of carbon monoxide, 4 is converted to the acylcobalt tetracarbonyl species 5 via CO insertion into the Co-carbon bond of 4 followed by the reaction with CO. The pyridine-assisted methanolysis of 5 leads to the formation of the product methyl 3-pentenoate (2) and pyridinium tetracarbonylcobaltate. The key intermediates of the catalytic cycle were isolated and characterized.

Original languageEnglish
Pages (from-to)4751-4764
Number of pages14
JournalOrganometallics
Volume30
Issue number17
DOIs
Publication statusPublished - Sep 12 2011

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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