Copper-catalyzed oxidative dehydrogenative carboxylation of unactivated alkanes to allylic esters via alkenes.
We report copper-catalyzed oxidative dehydrogenative carboxylation (ODC) of unactivated alkanes with various substituted benzoic acids to produce the corresponding allylic esters. Spectroscopic studies (EPR, UV-vis) revealed that the resting state of the catalyst is [(BPI)Cu(O2CPh)] (1-O2CPh), formed from [(BPI)Cu(PPh3)2], oxidant, and benzoic acid. Catalytic and stoichiometric reactions of 1-O2CPh with alkyl radicals and radical probes imply that C-H bond cleavage occurs by a tert-butoxy radical. In addition, the deuterium kinetic isotope effect from reactions of cyclohexane and d12-cyclohexane in separate vessels showed that the turnover-limiting step for the ODC of cyclohexane is C-H bond cleavage. To understand the origin of the difference in products formed from copper-catalyzed amidation and copper-catalyzed ODC, reactions of an alkyl radical with a series of copper-carboxylate, copper-amidate, and copper-imidate complexes were performed. The results of competition experiments revealed that the relative rate of reaction of alkyl radicals with the copper complexes follows the trend Cu(II)-amidate > Cu(II)-imidate > Cu(II)-benzoate. Consistent with this trend, Cu(II)-amidates and Cu(II)-benzoates containing more electron-rich aryl groups on the benzamidate and benzoate react faster with the alkyl radical than do those with more electron-poor aryl groups on these ligands to produce the corresponding products. These data on the ODC of cyclohexane led to preliminary investigation of copper-catalyzed oxidative dehydrogenative amination of cyclohexane to generate a mixture of N-alkyl and N-allylic products.
Department of Chemistry, University of California , Berkeley, California 94720, United States.
Ba L
BL
Tran
Matthias
M
Driess
John F
JF
Hartwig
D000473:Alkanes / Q000737:chemistry*; D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry; D000498:Allyl Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D004952:Esters / Q000138:chemical synthesis* / Q000737:chemistry; D006865:Hydrogenation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*
D000473:Alkanes; D000475:Alkenes; D000498:Allyl Compounds; D004952:Esters; D009942:Organometallic Compounds; D003300:Copper