Iodonium salts as efficient iodine(iii)-based noncovalent organocatalysts for Knorr-type reactions

Abstract

The dibenziodolium cation displays high catalytic activity for the Knorr-type reactions via binding with the carbonyl O atom.

Predicting the catalytic activity of azolium-based halogen bond donors: an experimentally-verified theoretical study

“…The S-shape of the kinetic curves is caused by the initial accumulation of the intermediate. 41 Fig. 3 The molecular structure of [5]OTf determined by X-ray diffraction.…”

“…The generation of 1-benzoyl-3,5-dimethylpyrazole from acetyl acetone and benzoyl hydrazide (Knorr-type reac-tion; Scheme 2) was selected as the model reaction for the experimental confirmation of the theoretical data because it involved carbonyl activation and was deemed suitable in our group's previous study regarding the catalytic activity of iodine (III) derivatives. 41 Proton nuclear magnetic resonance ( 1 H-NMR) monitoring indicated that the most active species for the test reaction was the triazolium [7]OTf, and the imidazolium [6]OTf was less active (Fig. 4).…”

“…This level of theory was successfully applied by us in studies of very similar metal-free objects and processes. 41,42 No symmetry restrictions were applied during the geometry optimization procedure. The Hessian matrices were calculated analytically for all optimized model structures (i) to confirm the location of the correct minima or saddle points on the potential energy surface (no imaginary frequencies, or one imaginary frequency, respectively) and (ii) to estimate the thermodynamic parameters (calculated at 25°C) (see Tables S1 and S2 in the ESI †).…”

“…37 Recently, hypervalent iodine(III) derivatives (i.e., diaryliodonium salts) have been successfully employed for the living cationic polymerization of olefins, 38 halide abstractions, 39 and carbonyl activations. [39][40][41] Although diaryliodonium salts demonstrate comparable or greater organocatalytic activity than azolium-based iodine(I) derivatives for the studied reactions, 39 currently, the latter remains to be the most commonly studied type of XB-donating organocatalyst.…”

Iodine(III)‐Based Halogen Bond Donors: Properties and Applications

“…In addition to these typical XB model reactions involving neutral substrate activation, the catalysis of Knorr‐type reactions between acetylacetone and acyl hydrazides using iodolium 17 a was published recently by Bolotin and coworkers (Scheme 13). [105] Therein, it was shown that using 17 a salts (as OTf, TFA and NTf 2 salts) provided sufficient activation for the reaction to proceed. In contrast, neutral non‐hypervalent XB donors, as well as other iodine(III) compounds such as diphenyliodonium trifluoroacetate failed to promote the reaction.…”