Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts

Richard H. Perry, Kristen R. Brownell, Konstantin Chingin, Thomas J. Cahill, Robert M. Waymouth, Richard N. Zare

Research output: Contribution to journalArticlepeer-review

Abstract

Desorption electrospray ionization (DESI) coupled to high-resolution Orbitrap mass spectrometry (MS) was used to study the reactivity of a (β-amino alcohol)(arene)RuCl transfer hydrogenation catalytic precursor in methanol (CH 3OH). By placing [(p-cymene) RuCl 2] 2 on a surface and spraying a solution of β-amino alcohol in methanol, two unique transient intermediates having lifetimes in the submillisecond to millisecond range were detected. These intermediates were identified as Ru (II) and Ru (IV) complexes incorporating methyl formate (HCOOCH 3). The Ru (IV) intermediate is not observed when the DESI spray solution is sparged with Ar gas, indicating that O 2 dissolved in the solvent is necessary for oxidizing Ru (II) to Ru (IV). These proposed intermediates are supported by high-resolution and high mass accuracy measurements and by comparing experimental to calculated isotope profiles. Additionally, analyzing the bulk reaction mixture using gas chromatography-MS and nuclear magnetic resonance spectroscopy confirms the formation of HCOOCH 3. These results represent an example that species generated from the (β-amino alcohol)(arene)RuCl (II) catalytic precursor can selectively oxidize CH3OH to HCOOCH 3. This observation leads us to propose a pathway that can compete with the hydrogen transfer catalytic cycle. Although bifunctional hydrogen transfer with Ru catalysts has been well-studied, the ability of DESI to intercept intermediates formed in the first few milliseconds of a chemical reaction allowed identification of previously unrecognized intermediates and reaction pathways in this catalytic system.

Original languageEnglish (US)
Pages (from-to)2246-2250
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number7
DOIs
StatePublished - Feb 14 2012

Keywords

  • Kinetics
  • Organometallic catalysis
  • Reaction intermediates
  • Ruthenium

ASJC Scopus subject areas

  • General

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