Mechanistic Study of Borylation of Nitriles Catalyzed by Rh–B and Ir–B Complexes via C–CN Bond Activation

Abstract

Recently the Chatani group reported the Rh(I)-catalyzed borylation of nitriles, which provided an efficient protocol for transformation of the C–CN bond to the C–B bond (J. Am. Chem. Soc.2012, 134, 115). Although an unconventional β-carbon elimination mechanism was proposed in their study, the other previously proposed mechanisms, i.e., oxidative addition, deinsertion, and initial C–H bond activation, cannot be excluded. To clarify the dominant mechanism of this reaction, a density functional theory study on borylation of PhCN and BnCN catalyzed by [Rh(XantPhos)(B(nep))] (nep = neopentylglycolate, XantPhos = 4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene) was conducted. The computational results indicated that the deinsertion mechanism (2,1-insertion of the Rh–B bond into the C≡N bond occurs first, followed by the insertion of the metal center into C–CN bond) is favored over oxidative addition, β-carbon elimination, and the initial C–H bond activation mechanism within all the investigated reactions. The ...