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*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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, Hâ'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 electrondonating 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
Issue number9
Early online date20 Apr 2021
Publication statusPublished - 7 May 2021


  • Density functional theory
  • Hydrosilylation
  • Organocatalysis
  • Phosphenium ions
  • Phosphirenium ions
  • Reaction mechanism studies


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