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Stereospecific synthesis and catalytic activity of L-histidylidene metal complexes
Date Issued
2012-05
Date Available
2015-05-25T10:31:01Z
Abstract
We report on the synthesis, metal coordination, and catalytic impact of histidylidene, a histidine-derived N-heterocyclic carbene (NHC) ligand. The histidinium salt 3, comprising methyl substituents at both heterocyclic nitrogens and protected at the C- and N-terminus of the amino acid, was rhodated and iridated by a transmetallation protocol using Ag2O. Ambient temperature and short reaction times were pivotal for full retention of configuration at the a-carbon. The stereospecificity of the reaction was conveniently probed by P-31 NMR spectroscopy after transmetallation with rhodium(I) and coordination of enantiopure (S)-Ph-binepine. The histidylidene rhodium complexes are highly efficient catalysts for the mild hydrosilylation of ketones. For the cationic complexes [Rh(cod)(histidylidene)(phosphine)](+), lowering the temperature shifted the rate-limiting step of the catalytic reaction to an earlier stage that is not enantioselective. Hence the asymmetric induction-which is governed by the chiral phosphine-did not improve at low temperature.
Sponsorship
European Research Council
Other Sponsorship
Swiss National Science Foundation
Type of Material
Journal Article
Publisher
Royal Society of Chemistry
Journal
Dalton Transactions
Volume
41
Issue
29
Start Page
8813
End Page
8821
Copyright (Published Version)
2012 The Royal Society of Chemistry
Language
English
Status of Item
Peer reviewed
This item is made available under a Creative Commons License
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