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Catalyst poisoning in catalyzed imine hydrogenation: A novel zwitterionic Rh(I)/o-hydroxy-substituted imine complex

TitleCatalyst poisoning in catalyzed imine hydrogenation: A novel zwitterionic Rh(I)/o-hydroxy-substituted imine complex
Publication TypeJournal Article
Year of Publication2006
AuthorsMarcazzan, P, Patrick, BO, James, BR
JournalJournal of Molecular Catalysis a-Chemical
Volume257
Pagination26-30
Date PublishedSep
Type of ArticleArticle
ISBN Number1381-1169
Keywordsamine, BEHAVIOR, CATALYSIS, CATIONIC RHODIUM COMPLEXES, CHEMICALS, FINE, HYDROGENATION, HYDROLYSIS, imine complex, LIGAND, LIGANDS, OLEFINS, phosphine, RHODIUM COMPLEX, SCHIFF-BASES, SELECTIVE HYDROGENATION, zwitterion
Abstract

During investigation of the homogeneous H-2-hydrogenation of the ketimine (o-HOC6H4)C(Me)=NCH2Ph catalyzed by the [Rh(COD)(PPh3)(2)]PF6 precursor in MeOH at ambient conditions, we have isolated [Rh{eta(4)-(C6H4O)C(-)(Me)=N(+)(H)CHPh}(PPh3)(2)]PF6 (3), an unusual zwitterionic Rh complex in which the imine is coordinated via the C-4 part of the o-hydroxy-arene moiety in a quinoid form; this tautomer is generated via proton transfer from the O-atom to the N-atom within the molecular, benzenoid form. Precipitation of 3 from the MeOH solution, even under H-2, causes sequestration of the Rh and complete suppression of the catalytic activity. (In a previously studied system with the corresponding, non-hydroxy-substituted ketimine, PhC(Me) = NCH2Ph, the Rh was sequestered as an inactive o-metalated species). The solid state structure of 3 is retained in CH2Cl2 solution, but in MeOH and Me2CO reversible loss of the ketimine generates the cis-[Rh(PPh3)(2)(solvent)(2)]PF6 species. (c) 2006 Elsevier B.V. All rights reserved.

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