Metal−Ligand Cooperation in C−H and H2 Activation by an Electron-Rich PNP Ir(I) System:  Facile Ligand Dearomatization−Aromatization as Key Steps

Unusual reactions are reported, in which the aromatic PNP ligand (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine) acts in concert with the metal in the activation of H2 and benzene, via facile aromatization/dearomatization processes of the ligand. A new, dearomatized electron-rich (PNP*)Ir(I)...

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Veröffentlicht in:Journal of the American Chemical Society 2006-12, Vol.128 (48), p.15390-15391
Hauptverfasser: Ben-Ari, Eyal, Leitus, Gregory, Shimon, Linda J. W, Milstein, David
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Sprache:eng
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Zusammenfassung:Unusual reactions are reported, in which the aromatic PNP ligand (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine) acts in concert with the metal in the activation of H2 and benzene, via facile aromatization/dearomatization processes of the ligand. A new, dearomatized electron-rich (PNP*)Ir(I) complex 2 (PNP* = deprotonated PNP) activates benzene to form the aromatic (PNP)Ir(I)Ph 4, which upon treatment with CO undergoes a surprising oxidation process to form (PNP*)Ir(III)(H)CO 6, involving proton migration from the ligand “arm” to the metal, with concomitant dearomatization. 4 undergoes stereoselective activation of H2 to exclusively form the trans-dihydride 7, rather than the expected cis-dihydride complex. Our evidence, including D-labeling, suggests the possibility that the Ir(I)−Ph complex is transformed to the dearomatized Ir(III)(Ph)(H) (independently prepared at low temperature), which may be the actual intermediate undergoing H2 activation.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja066411i