Oxidative addition of amino acids to iridium(I) metal centers
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The oxidative addition of both monosubstituted and disubstituted a.-amino acids to [Ir(COD)(PMe3)3]Cl (COD = cyclooctadiene) was studied and the reactivity of the resulting complexes was examined. The reaction of [Ir(COD)(PMe3)3]CI with the disubstituted amino acids, diphenylglycine and methyl phenyl alanine, led to an almost exclusive facial product. Monosubstituted amino acid complexes were observed to be mixtures of the meridional and facial isomers with the meridional isomer largely predominating. The meridional isomer was found to convert to the facial isomer when heated for several days at 100Â°C. In fact, a predominantly meridional mixture was found to convert to a predominantly facial mixture upon heating. The facial isomer was therefore shown to be the thermodynamic product from the mixture. Small amounts of other isomers were observed in the hydride region of the proton NMR spectrum. One resonance at -23.75 ppm disappeared upon heating t-butyl acetylene with the amino acid complex. The disappearance of this hydride resonance may indicate the insertion of the unsaturate into the Ir-H bond, or alternatively, the conversion of this isomer to a more thermodynamically stable isomer. Reactions of these complexes with methylpropiolate and acrylamide were attempted but evidence of an insertion product was not found.
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