Ancillary ligand effects on C-H bond activation reactions promoted by β-diiminate iridium complexes

Wesley H. Bernskoetter, Emil Lobkovsky, Paul J. Chirik

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A series of β-diiminate iridium(I) olefin, diolefin, and hydride complexes have been synthesized and evaluated in carbon-hydrogen bond activation reactions. Treatment of [Ir-(COE) 2Cl] 2 (COE = cyclooctene) with the lithio β-diiminate anions [Li(OEt 2)] [BDI] (BDI = ArNC(Me)CH(Me)CNAr; Ar = 2,6-Me 2C 6H 3, 2,6-Et 2C 6H 3, 2,6- iPr 2C 6H 3) under an N 2 atmosphere furnished the corresponding iridium(I) cycloctene dinitrogen complexes. Using a similar procedure, the analogous β-diiminate iridium(I) cyclooctadiene compounds have also been prepared and characterized. Addition of the sterically demanding β-diiminate anion (2,6-Me 2C 6H 3)NC(CMe 3)CH(CMe 3)CN(2,6-Me 2C 6H 3) to [Ir(COD)Cl] 2 (COD = 1,5-cyclooctadiene) yielded an unusual η 5-arene complex that is stabilized by a significant contribution from an iminocyclohexadienyl resonance form. The relative electronic influence of each β-diiminate ligand has been evaluated by preparation of the corresponding iridium dicarbonyl complexes and reveals little electronic perturbation among alkyl substituents on the aryl rings. With respect to C-H bond activation, warming the β-diiminate iridium(I) cyclooctene dinitrogen compounds to 50°C resulted in intramolecular dehydrogenation chemistry, the outcome of which is dependent on the β-diiminate aryl substituents. For the 2,6-dimethyl-substituted complex, transfer dehydrogenation of the cyclooctene ligand is observed, while for the larger diethyl- and diisopropyl-substituted variants, dehydrogenation of the aryl substituents occurs.

Original languageEnglish (US)
Pages (from-to)6250-6259
Number of pages10
Issue number25
StatePublished - Dec 5 2005
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry


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