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

Abstract

The iodine(III) bistriflamide complex (C 6 F 5 ) III I(NTf 2 ) 2 in HNTf 2 (bistriflimide acid; (CF 3 SO 2 ) 2 NH) selectively aminates methane and ethane. At a 100 °C reaction with methane after 3 h, it resulted in the exclusive formation of MeNTf 2 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 (C 6 F 5 )I III (NTf 2 ) 2 with benzene resulted in being stalled at (C 6 F 5 )I III (Ph)(NTf 2 ) with a <5% conversion to PhNTf 2 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 (C 6 F 5 )I III (CH 3 )(NTf 2 ) intermediate, there is a one-step amine functionalization mechanism that avoids a carbocation intermediate. For ethane, from the (C 6 F 5 )I III (Et)(NTf 2 ) 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.

A decade of lessons in the activation of ArIL2 species

“… 38 Such activation has only very recently been reported by Periana and co-workers by C 6 F 5 -I(NTf 2 ) 2 on methane and ethane at elevated temperatures and pressures (see next section). 39 We surmised that the intermediate in these reactions was potentially p -NO 2 -C 6 H 4 -I(OTf)(H). To lend support to this hypothesis we reacted p -NO 2 -C 6 H 4 -I(OTf) 2 with adamantane and 1-fluoroadamantane.…”

“…Periana and co-workers recently reported the isolation of C 6 F 5 -I(NTf 2 ) 2 , albeit without obtaining a crystal structure. 39 They found that at elevated temperatures and pressures this compound could effect the activation of simple sp 3 C–H bonds in ethane and methane generating the corresponding simple alkyl-NTf 2 compounds. Given the above discussion regarding misidentification of reactive I( iii ) species, we isolated p -NO 2 -C 6 H 4 -I(NTf 2 ) 2 via reaction of p -NO 2 -C 6 H 4 -IF 2 with 2 equivalents of TMS-NTf 2 ( Scheme 12 ).…”

ArI(NTf2)2: the boundary of oxidative capacity for ArIL2?

“…While we were undertaking this study Periana and co-workers isolated and spectroscopically characterized C 6 F 5 –I(NTf 2 ) 2 and showed that at elevated temperatures and pressures direct C–H activation of simple alkanes is possible. 13 They did not however confirm the structure by X-ray crystallography and in light of the previous misidentifications of PhI(OTf) 2 , as well as other recent cases involving structural misassignment of I( iii ) complexes, 14–16 it is important that structural confirmation of ArI(NTf 2 ) 2 is obtained. In this report we structurally characterize NO 2 –C 6 H 4 –I(NTf 2 ) 2 and provide analysis that shows these NTf 2 ligated species are significantly stronger oxidizing agents than NO 2 –C 6 H 4 –I(OTf) 2 , representing the current frontier in the oxidative ability of ArIL 2 and possibly the limit for this class of compound.…”

“…Periana and co-workers generated C 6 F 5 –I(NTf 2 ) 2 in situ from C 6 F 5 –I(OTFA) 2 and HNTf 2 and were also able to isolate C 6 F 5 –I(NTf 2 ) 2 via a 4-cycle exchange between C 6 F 5 –I(OTFA) 2 and HNTf 2 . 13 We have previously found that TMS metathesis is an efficient one-step procedure for these types of transformations, 11 and examined if this would be effective for generation of NO 2 –C 6 H 4 –I(NTf 2 ) 2 . Reactions of NO 2 –C 6 H 4 –IF 2 and NO 2 –C 6 H 4 –I(OTFA) 2 were carried out with 2 equivalents of TMS-NTf 2 in CDCl 3 .…”

“…We also included C 6 F 5 –I(NTf 2 ) 2 reported by Periana and co-workers. 13 To evaluate oxidative capability we undertook a similar model used by Radzhabov and co-workers, 4 using the electronic energy change of the reaction ArIL 2 + 2 e − → ArI + 2 L − . We have previously found that the B3LYP/6-311+G(d,p) method used in that study models the geometry of bound triflate species poorly.…”