Phosphirenium Ions as Masked Phosphenium Catalysts: Mechanistic Evaluation and Application in Synthesis

Danila Gasperini, Samuel E. Neale, Mary F. Mahon, Stuart A. Macgregor, Ruth L. Webster

Research output: Contribution to journalArticlepeer-review

Abstract

The utilization of phosphirenium ions is presented; optimized and broadened three-membered ring construction is described together with the use of these ions as efficient pre-catalysts for metal-free carbonyl reduction with silanes. Full characterization of the phosphirenium ions is presented, and initial experimental and computational mechanistic studies indicate that these act as a "masked phosphenium"source that is accessed via ring opening. Catalysis proceeds via associative transfer of {Ph2P+} to a carbonyl nucleophile, H-SiR3 bond addition over the C=O group, and associative displacement of the product by a further equivalent of the carbonyl substrate, which completes the catalytic cycle. A competing off-cycle process leading to vinyl phosphine formation is detailed for the hydrosilylation of benzophenone for which an inverse order in [silane] is observed. Experimentally, the formation of side products, including off-cycle vinyl phosphine, is favored by electron-donating substituents on the phosphirenium cation, while catalytic hydrosilylation is promoted by electron-withdrawing substituents. These observations are rationalized in parallel computational studies.

Original languageEnglish
Pages (from-to)5452-5462
Number of pages11
JournalACS Catalysis
Volume11
Issue number9
Early online date20 Apr 2021
DOIs
Publication statusPublished - 7 May 2021

Keywords

  • density functional theory
  • hydrosilylation
  • organocatalysis
  • phosphenium ions
  • phosphirenium ions
  • reaction mechanism studies

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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