Carbon-hydrogen (C-H) bonds are ubiquitous in nature. Transition metal catalysis is a promising strategy for the activation/functionalization of the typically unreactive C-H bonds under mild conditions. An important aspect of this strategy is the ability to selectively activate and functionalize C-H bonds. Functional groups on a molecule can act as directing groups for selectively activating ortho C-H bonds via chelation assistance. An example of this is the coupling reaction between benzoic acid and alkynes to yield isocoumarins, which has been efficiently catalyzed by Cp*Ir(III) in our group. In this project the analogous reaction with the nitrogen derivate, benzamide, was studied. Two Cp*Ir(III) catalysts, [Cp*Ir(NHC)(H2O)2][OTf2] (A ) and [Cp*Ir(H2O)3][OTf2] (B ) (where NHC is N-heterocyclic carbene and OTf- is trifluoromethanesulfonate anion) were found to be efficient in the catalytic C-H functionalization of N-methyl and N-ethyl benzamide, when utilizing silver acetate as the external oxidant. Catalyst B   provided an enhancement in reactivity (a larger rate constant was observed), thus lower catalyst loadings could be employed. Additionally, the reaction catalyzed by B  can be performed in the absence of silver acetate, i.e. under air, O2, or N2, suggesting that the reaction can be performed in the absence of an external oxidant. Preliminary mechanistic studies suggest that the coupling reaction catalyzed by A   follows first order kinetics and has a kinetic isotope effect of 1.4. Mechanistic studies with catalyst B  are currently underway.

Cp*Ir(III)-catalyzed isoquinolone synthesis via selective oxidative C-H bond activation of benzamides

248th National Meeting (2014)

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