Metal Triflimidates: Better than Metal Triflates as Catalysts in Organic Synthesis—The Effect of a Highly Delocalized Counteranion

Abstract

The continuously increasing need for novel and selective methods in organic synthesis to aid drug discovery and to address environmental concerns is a constant source of stimulation to develop novel and more efficient reaction systems. This has often resulted in a focus on transition metals, ligands, and additives, with much less attention paid to the counterion(s) of the metal cation. Recently, metal salts with one or more triflimidate counterion(s) have appeared as a unique class of catalysts that display outstanding σ- and π-Lewis acid character. The highly delocalized nature of the triflimidate counterion, combined with its high steric hindrance results in virtually no nucleophilic behavior and an extremely high positive charge density on the metal cation, thus enhancing its Lewis acid character. Consequently, these metal triflimidates often outperform their metal halide or triflate analogues. This Review describes general methods for the preparation of metal triflimidate salts and their use as catalysts.

First Evidence for the Existence of Hexafluoroantimonic(V) Acid

“…[6] On the other hand, the molecular species HSbF 6 has neverbeen observed. [7] Our research group is interested in the use of Lewis superacids [8] in molecular catalysis, notably N-heterocyclic carbene gallium complexes of type [(NHC)GaX 2 ][SbF 6 ]( X=Cl, Br,I ). [9,10] These compounds are typicallyp repared by mixing (NHC)GaX 3 and AgSbF 6 in 1,2-dichloroethane at room temperature.…”

Synthesis of N-heterocycles through cyclization-triggered tandem additions to alkynes and the study of promoters in ionic reactions.

“…We found that LiNTf2 slowed down the reaction in the beginning but could maintain its reactivity effect with time, probably due to the stabilizing effect of NTf2 -. 58,69 NaBARF enhanced the rate of the reaction significantly but only in the beginning. We attributed the time leveling effect of NaBARF to catalyst deactivation under the reaction conditions.…”

“…Our work is significant because this tandem chemistry is Recently, cationic metal salts containing triflimidate (NTf2 -) have appeared as a unique class of catalysts that display outstanding -and -Lewis acid character. 58 Consequently, these metal triflimidates often outperform their triflate analogues in catalysis. 58 In 2010, Dalla and Dunach published a review article in Angew.…”

“…58 Consequently, these metal triflimidates often outperform their triflate analogues in catalysis. 58 In 2010, Dalla and Dunach published a review article in Angew. Chem.…”

“…58 Despite intensive investigations, there is no concrete rationnle to explain benefits of triflimidates, chemists usually explain their higher performance to its more delocalized charge, higher steric hindrance and reduced nucleophilicity compared to triflate. 58 In the periodic table, N to in the left side of O, C is to the left side of N. If NTf2 -is better than OTf -and this trend continues, CTf3 -will be even better than NTf2 - (Figure 2). CTf3 -will have even more delocalized negative charge, bigger size, increased stability and reduced nucleophilicity.…”