Issue 19, 2007

Pentamethylcyclopentadienyl-iridium(iii) complexes with pyridylamino ligands: synthesis and applications as asymmetric catalysts for Diels–Alder reactions

Abstract

Reaction of the dimer [(Cp*IrCl)2(µ-Cl)2] with chiral pyridylamino ligands (pyam, L1L5) in the presence of NaSbF6 gave complexes [Cp*IrCl(pyam)][SbF6] 15 as diastereomeric mixtures, which have been fully characterised, including the X-ray molecular structure determination of the complexes (SIr,RN,RC)–[Cp*IrClL1][SbF6] 1a and (RIr,SN,SC)–[Cp*IrClL5][SbF6] 5a. Treatment of these cations with AgSbF6 affords the corresponding aqua species [Cp*Ir(pyam)(H2O)][SbF6]2610 which have been also fully characterised. The molecular structure of the complex (SIr,RN,RC)–[Cp*IrL1(H2O)][SbF6]26 has been determined by X-ray diffractometric methods. The aqua complexes [Cp*Ir(pyam)(H2O)][SbF6]2 (6, pyam = L2 (7), L3 (8)) evolve to the cyclometallated species [Cp*Ir{κ3(N,N′,C)-(R)-(C6H4)CH(CH3)NHCH2C5NH4}][SbF6] (11), [Cp*Ir{κ3(N,N′,C)-(R)-(C10H6)CH(CH3)NHCH2C5NH4)}][SbF6] (12), and [Cp*Ir{κ3(N,N′,C)-(R)-(C10H6)CH(CH3)NHCH2C9NH6)}][SbF6] (13) respectively, via intramolecular activation of an ortho C–H aryl bond. Complexes 610 are enantioselective catalysts for the Diels–Alder reaction between methacrolein and cyclopentadiene. Reaction occurs rapidly at room temperature with good exo : endo selectivity (from 81 : 19 to 98 : 2) and moderate enantioselectivity (up to 72%). The involved intermediate Lewis acid–dienophile compounds [Cp*Ir(pyam)(methacrolein)][SbF6]2 (pyam = L4 (14), L5 (15)) have been isolated and characterised.

Graphical abstract: Pentamethylcyclopentadienyl-iridium(iii) complexes with pyridylamino ligands: synthesis and applications as asymmetric catalysts for Diels–Alder reactions

Supplementary files

Article information

Article type
Paper
Submitted
22 Dec 2006
Accepted
20 Feb 2007
First published
21 Mar 2007

Dalton Trans., 2007, 1911-1921

Pentamethylcyclopentadienyl-iridium(III) complexes with pyridylamino ligands: synthesis and applications as asymmetric catalysts for Diels–Alder reactions

D. Carmona, M. P. Lamata, F. Viguri, R. Rodríguez, F. J. Lahoz, I. T. Dobrinovitch and L. A. Oro, Dalton Trans., 2007, 1911 DOI: 10.1039/B618720J

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