Phosphirenium ions as masked phosphenium catalysts : mechanistic evaluation and application in synthesis
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, 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.
Citation
Gasperini , D , Neale , S E , Mahon , M F , MacGregor , S A & Webster , R L 2021 , ' Phosphirenium ions as masked phosphenium catalysts : mechanistic evaluation and application in synthesis ' , ACS Catalysis , vol. 11 , no. 9 , pp. 5452-5462 . https://doi.org/10.1021/acscatal.1c01133
Publication
ACS Catalysis
Status
Peer reviewed
ISSN
2155-5435Type
Journal article
Description
The EPSRC is thanked for funding. S.E.N. thanks Heriot Watt University for the award of a James Watt scholarship.Collections
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