Reactivity and Mechanisms of Methane, Ethane, and Benzene C–H Amination with an Iodine(III) Bistriflimide Complex

The
iodine(III) bistriflamide complex (C6F5)IIII(NTf2)2 in HNTf2 (bistriflimide
acid; (CF3SO2)2NH)
selectively aminates methane and ethane. At a 100 °C reaction
with methane after 3 h, it resulted in the exclusive formation of
MeNTf2 with a yield of approximately 40%. For ethane, at
100 °C in 2 h, a > 80% yield was found for a combination of
monofunctionalized
and difunctionalized amination products. In contrast to alkanes giving
functionalized products, the reaction of (C6F5)IIII(NTf2)2 with benzene resulted
in being stalled at (C6F5)IIII(Ph)(NTf2) with a <5% conversion to PhNTf2 even at 120
°C. PWPB95-D3(BJ) density functional theory calculations indicate
that C–H activation is the lowest energy pathway to break the
hydrocarbon bonds and is lower in energy than radical, electron-transfer,
proton-coupled electron-transfer, or hydride substitution pathways.
For methane, from the (C6F5)IIII(CH3)(NTf2) intermediate, there is a one-step amine
functionalization mechanism that avoids a carbocation intermediate.
For ethane, from the (C6F5)IIII(Et)(NTf2) intermediate, dynamics simulations suggest the possibility
of a competitive two-step functionalization pathway that involves
a short-lived carbocation intermediate. A reaction coordinate strain
analysis provides a straightforward model for understanding the relative
reactivity rates for alkyl versus aryl functionalization.