Dehydrogenation of ketones by pincer-ligated iridium: Formation and reactivity of novel enone complexes |
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Authors: | Xiawei Zhang |
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Affiliation: | Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA |
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Abstract: | The transfer dehydrogenation of several ketones by (PCP)IrH2 (PCP = κ3-C6H3-2,6-(CH2PtBu2)2) (1) has been observed. Catalytic turnover was inhibited in most cases by the formation of stable metallacycles or the O-H oxidative addition of phenolic products. Catalytic transfer dehydrogenation of 3,3-dimethylcyclohexanone was achieved, giving the corresponding α,β-enone. The transfer dehydrogenation reaction of cycloheptanone with 1 was found to generate a surprisingly stable PCP-iridium troponyl hydride (9), which is stabilized by conjugation and possibly represents an unusual bicyclo[5.2.0]troponyliridium metalloaromatic structure. Complex 9 was found to catalyze the dimerization of tropone to give a fused tricyclic dihydrodicycloheptafuranol. A mechanism for this reaction is proposed wherein the coordinated troponyl group nucleophilically attacks a free tropone molecule. |
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Keywords: | Transfer dehydrogenation of ketones PCP pincer-ligated iridium complexes Organometallic homogeneous catalysis Tropone dimerization X-ray crystal structures |
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