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Octahedral perfluoroalkyl complexes of Ir(III) formed by oxidative addition of perfluoroalkyl iodides to Ir(acac)(CO)2

Publication: Canadian Journal of Chemistry
January 2009

Abstract

Oxidative addition of primary, secondary, or benzylic perfluoroalkyl iodides (RF–I) to the phosphine free Ir(I) precursor Ir(acac)(CO)2 1 (acac = 2,4-pentanedionato) proceeds smoothly to afford octahedral Ir(III) products Ir(acac)(I)(RF)(CO)2, A combination of X-ray crystallographic studies and solution spectroscopy shows that these products are the result of overall trans-addition of the C–I bond to iridium, probably a result of thermodynamic control; evidence for a kinetic product resulting from net cis-addition is obtained in one case. Treatment of the Ir(III) compounds with AgOTf (Tf = CF3SO3) illustrates that the iodo ligand is replaced by triflate with retention of stereochemistry at Ir. The resulting triflate complexes are inert to displacement by H2O or H2. The Ir(III) products exhibit very high CO stretching frequencies in the IR, indicating that the CO ligands may be non-classical. A quantitative estimation of the degree of backbonding to the CO ligands in these compounds, and a comparison of the π-acceptor properties of CO and fluoroalkyl ligands, is made using an approach based on Density Functional Theory (DFT) and Natural Bond Orbital analyses.Key words: iridium, fluoroalkyl, oxidation, carbonyl, DFT.

Résumé

L’addition oxydante d’iodures primaires, secondaires ou benzyliques perfluoroalkylés (RF–I) sur le précurseur Ir(I) sans phosphine, Ir(acac)(CO)2 (1) (acac = 2,4-pentanedionato), s’effectue sans problème et elle conduit à la formation de produits Ir(III) octaédriques Ir(acac)((I)(RF)(CO)2. Des études cristallographiques par diffraction des rayons X et d’autres réalisées par spectroscopie en solution permettent de montrer que ces produits sont le résultat d’une addition nette trans de la liaison C–I sur l’iridium, probablement sous l’influence d’un contrôle thermodynamique; dans un cas, on a toutefois été en mesure de mettre en évidence d’un produit cinétique résultant d’une addition nette cis. Le traitement des composés Ir(III) avec du AgOTf (Tf = CF3SO3) permet d’illustrer que le ligand iodo est remplacé par le triflate avec rétention de la stéréochimie au niveau de l’iridium. Les complexes triflates qui en résultent sont inertes aux déplacements par l’eau ou l’hydrogène. Les produits Ir(III) présentent des spectres infrarouges dans lesquels les fréquences d’élongation du CO sont très élevées, ce qui suggère que les ligands CO ne sont pas classiques. Faisant appel à la théorie de la densité fonctionnelle et une analyse des orbitales de liaison naturelle, on a fait une évaluation quantitative du degré de retour de liaison vers les ligands CO dans ces composés ainsi qu’une comparaison des propriétés des ligands CO et fluoroalkyles comme accepteurs π.Mots-clés : iridium, fluoroalkyle, oxydation, carbonyle, théorie de la densité fonctionnelle (TDF).[Traduit par la Rédaction]

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Published In

cover image Canadian Journal of Chemistry
Canadian Journal of Chemistry
Volume 87Number 1January 2009
Pages: 151 - 160

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Version of record online: 5 February 2011

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