5-Iodo-1-Arylpyrazoles as Potential Benchmarks for Investigating the Tuning of the Halogen Bonding

Abstract

5-Iodo-1-arylpyrazoles are interesting templates for investigating the halogen bond propensity in small molecules other than the already well-known halogenated molecules such as tetrafluorodiiodobenzene. Herein, we present six compounds with different substitution on the aryl ring attached at position 1 of the pyrazoles and investigate them in the solid state in order to elucidate the halogen bonding significance to the crystallographic landscape of such molecules. The substituents on the aryl ring are generally combinations of halogen atoms (Br, Cl) and various alkyl groups. Observed halogen bonding types spanned by these six 5-iodopyrazoles included a wide variety, namely, C–I⋯O, C–I⋯π, C–I⋯Br, C–I⋯N and C–Br⋯O interactions. By single crystal X-ray diffraction analysis combined with the descriptive Hirshfeld analysis, we discuss the role and influence of the halogen bonds among the intermolecular interactions.

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

“…[11][12][13][14] The vast majority of XB-donors are based on monodentate iodine(I) derivatives with either a polyfluorinated or a N-heterocyclic backbone, for example, the triazolium derivative 1 or the pyridinium derivative 2 (Figure 1a), with cationic species being typically more reactive than neutral derivatives. [15][16][17][18][19][20][21][22][23] Bidentate XB-donors such as imidazolium 3 have been described as well and were found to have a significantly higher reactivity than monodentate analogues. [24] Besides iodine(I) species, hypervalent iodine(III) derivatives, in the form of (cyclic) diaryliodonium salts, received growing attention as XB-donors, due to the high Lewis acidity of the hypervalent iodine atom.…”

“…Next, we investigated the more challenging Diels-Alder reaction between cyclohexadiene (22) and MVK (20), in which the bidentate iodolium salts 5 was reported to be the so far only active XB-donor and nearly approached the activity of the strong Lewis acid BF 3 . [34] In contrast to the literature report, we started the investigation with a catalyst loading of 15 mol % instead of 30 mol %.…”

“…[ 11 , 12 , 13 , 14 ] The vast majority of XB‐donors are based on monodentate iodine(I) derivatives with either a polyfluorinated or a N‐heterocyclic backbone, for example, the triazolium derivative 1 or the pyridinium derivative 2 (Figure 1 a), with cationic species being typically more reactive than neutral derivatives. [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ] Bidentate XB‐donors such as imidazolium 3 have been described as well and were found to have a significantly higher reactivity than monodentate analogues. [24] …”

Recent Developments in Polymeric Assemblies and Functional Materials by Halogen Bonding

“…By the aid of 13 C NMR spectroscopy, they further demonstrated the binding of 1‐aryl‐5‐iodopyrazoles with different Lewis bases such as Et 3 N, pyridine, DABCO, DMSO and their influence in the shielding property of the iodo‐donor attached to the 5‐position of the pyrazole ring. Later on, the same group showed that by introducing an additional Br‐atom in the phenyl ring, other variety of XBs such as C−I⋅⋅⋅O, C−I⋅⋅⋅π, C−I⋅⋅⋅Br, C−Br⋅⋅⋅O, other than C−I⋅⋅⋅N were involved in dictating the supramolecular polymerization [103] . In another instance, two new di‐bromo halogenated systems were reported, namely 3‐(2‐isopropylphenyl) sydnones and 1‐(2‐isopropylphenyl) pyrazoles that produced 1D chains by Br⋅⋅⋅Br Type II halogen bonding and concomitant C−H⋅⋅⋅O hydrogen bonding [104] .…”

Synthesis of 1-(2-Fluorophenyl)pyrazoles by 1,3-Dipolar Cycloaddition of the Corresponding Sydnones

“…Moreover, (2-fluorophenyl)pyrazoles [ 35 , 36 ] were reported to present anticancer activity [ 37 ] and are important ligands for organometallic applications [ 38 ]. We have shown also that halogenated pyrazoles are important tools for studying the halogen bonding propensity [ 39 , 40 ] and it was interesting to investigate if the fluorine atom could also play a role among the intermolecular interactions.…”