N‐Heterocyclic Iod(az)olium Salts – Potent Halogen‐Bond Donors in Organocatalysis

Abstract

This article describes the application of N-heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono-and dicationic NHISs are described and utilized as potent XB-donors in halogen-bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon-and metal-chloride bonds as well as carbonyl and nitro groups was achieved. N-Methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB-donors based on iodine(I) and (III) and the strong Lewis acid BF3.

Halonium, chalconium, and pnictonium salts as noncovalent organocatalysts: a computational study on relative catalytic activity

“…For XB donors, it has been demonstrated that cationic iodine(I)-containing species C-in particular, iodoazoliums [30][31][32][33][34][35][36][37][38][39] -effectively catalyze an extensive series of organic transformations, whereas hypervalent iodine(III) derivatives F (i.e., diaryliodonium salts) featuring two σ-holes at the iodine atom possess a greater catalytic activity than azolium-based iodine(I) species. [40][41][42][43][44][45][46][47][48][49][50][51] It is worth mentioning that diarylbromonium salts (F; X = Br) have also been reported to exhibit high catalytic activity. [52][53][54][55] Organocatalysts based on ChB donors have gained increasing attention over the last five years.…”

“…, diaryliodonium salts) featuring two σ-holes at the iodine atom possess a greater catalytic activity than azolium-based iodine( i ) species. 40–51 It is worth mentioning that diarylbromonium salts ( F ; X = Br) have also been reported to exhibit high catalytic activity. 52–55…”

Diaryliodonium Tetracyanidometallates Self-Assemble into Halogen-Bonded Square-Like Arrays

“…Diaryliodonium cations (Ar 2 I + ) are multipurpose reagents in organic synthesis. They have received major attention as arylating agents − but attracted interest also as topochemical reagents and noncovalent catalysts. − Their ability to form attractive interaction was recognized long ago, when Alcock introduced the concept of secondary bonding . After the rationalization of these interactions as charge-assisted halogen bonds (HaBs), the use of diaryliodonium cations as tectons in crystal engineering became more and more common. , This increased interest was favored by the unique geometric features of these HaB donors with respect to other organic tectons.…”

Diaryliodoniums as Hybrid Hydrogen- and Halogen-Bond-Donating Organocatalysts for the Groebke–Blackburn–Bienaymé Reaction

“…Recently, it was shown that hypervalent iodine­(III) derivatives (i.e., diaryliodonium salts) featuring two σ-holes at the iodine atom exhibit remarkable Lewis acidity, , and they possess greater catalytic activity than azolium-based iodine­(I) derivatives. − Current progress in the development of efficient diaryliodonium-based noncovalent organocatalysts has focused on two complementary directions: (i) functionalization of the aryl rings in the cation, ,, as well as changing the aryl to heteroaryl moieties; and (ii) preparation of chelating dinuclear iodine­(III) species (Figure ). , It is worthwhile to mention that diarylbromonium salts were also reported to exhibit high catalytic activity recently. , …”