Mechanistic studies on the catalytic oxidative amination of alkenes by rhodium(I) complexes with hemilabile phosphines

Autor: Jesús J. Pérez-Torrente, M. Victoria Jiménez, Luis A. Oro, F. Javier Modrego, Daniel Gómez, M. Isabel Bartolomé
Přispěvatelé: Ministerio de Economía y Competitividad (España), Gobierno de Aragón, European Commission, Ministerio de Ciencia e Innovación (España), Universidad de Zaragoza, CSIC-UZA - Instituto de Síntesis Química y Catálisis Homogénea (ISQCH)
Rok vydání: 2013
Předmět:
Zdroj: Digital.CSIC. Repositorio Institucional del CSIC
instname
ISSN: 1867-3899
1867-3880
Popis: Cationic rhodium(I) complexes with P,O-functionalised arylphosphine ligands are efficient catalysts for the regioselective anti-Markovnikov oxidative amination of styrene with piperidine. The mechanism of the catalytic reaction has been investigated by spectroscopic means under stoichiometric and catalytic conditions. In the presence of piperidine, the catalyst precursor [Rh{κ2-P,O-Ph2P(CH2)3OEt}2]+ (5) gave the piperidine complex [Rh{κ1-P-Ph2P(CH2)3OEt}2(HNC5H10)2]+ (8) that was transformed into the neutral amido-piperidine species [Rh{κ1-P-Ph2P(CH2)3OEt}2(NC5H10)(HNC5H10)] (9) under thermal conditions. NMR studies performed in the presence of styrene under catalytic conditions showed that 9 is a key species in the catalytic oxidative amination of styrene. Related cyclooctadiene-containing catalyst precursors [Rh(cod){κ1-P-Ph2P(CH2)3OEt}n]+ (n=1, 2) also gave 9 under the same conditions. The proposed catalytic cycle has been established by a series of DFT calculations including the transition states of the key steps that have been identified and characterised. These studies have shown that, after elimination of the enamine, regeneration of catalytic active species takes place by direct transfer of the proton of a piperidine ligand to the alkyl group resulting from the insertion of styrene into the Rh-H bond and formation of ethylbenzene. Against the expectations, the formation of a dihydride intermediate by NH oxidative addition is a highly energy-demanding process. Catalyst 5 has also been applied for the oxidative amination of substituted vinylarenes with several secondary cyclic and acyclic amines. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Financial support from the Ministerio de Economía y Competitividad (MINECO/FEDER), projects CTQ2010-15221 and MULTICAT (CSD2009-00050), and Gobierno de Aragón/FSE (Group E07) is gratefully acknowledged. M.I.B. and D.G. thank the Spanish MICINN and the IUCH (Instituto Universitario de Catálisis Homogénea) for a predoctoral fellowship.
Databáze: OpenAIRE
Externí odkaz: