Tautomeric and conformational switching in a new versatile N-rich heterocyclic ligand

Parisi, Elio; Capasso, Domenica; Capobianco, Amedeo; Peluso, Andrea; Gaetano, Sonia Di; Fusco, Sabato; Manfredi, Carla; Mozzillo, Rosaria; Pinto, Gabriella; Centore, Roberto

doi:10.1039/d0dt02572k

Cited by 13 publications

(15 citation statements)

References 27 publications

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“…In particular, while crystallization of the pure neutral ligand yielded the most stable 2H-tautomer, as expected, crystallization of neutral TT9 in the presence of Zn II and Cu II salts yielded metal complexes of the neutral ligand, with a 1:1 metal-to-ligand ratio, in which the 3H-tautomer is present (Parisi et al, 2020). In order to further confirm metal complexation as a way of stabilizing the elusive 3H-tautomer, we report, in this article, structural data for the Zn II and Cu II complexes of TT9, with a 1:2 metal-to-ligand ratio (Fig.…”

Section: Figuresupporting

confidence: 74%

“…The tautomeric/conformational variability of the TT9 ligand, which possesses four different tautomers/conformers within a narrow energy range ÁE < 2 kcal mol À1 (Parisi et al, 2020), makes TT9 a reliable candidate for this target. In fact, we have considered the formation of hydrogen-bonded dimers for the four lowest-energy tautomers/conformers of TT9, shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The synthesis of the TT9 ligand was performed according to the procedure already described by us (Parisi et al, 2020). Prismatic green crystals of the complex Cu(TT9) 2 Br 2 Á3H 2 O, henceforth complex 1, were grown in 2 d by slow evaporation of a clear 50:50 (v/v) water-ethanol solution containing a 1:2 molar ratio of CuBr 2 dihydrate (13.0 mg, 7.63 Â 10 À5 mol) and TT9 (31.0 mg, 1.56 Â 10 À4 mol) at room temperature in a quantitative yield (53.0 mg).…”

Section: Synthesis and Crystallizationmentioning

confidence: 99%

“…We have recently described a new versatile nitrogenrich triazolotriazole ligand, 4-methyl-7-(pyrazin-2-yl)-2H,3H- [1,2,4]triazolo [3,2-c][1,2,4]triazole, henceforth TT9 (Fig. 2a), whose tautomeric behaviour is further enriched by the possibility of metal coordination (Parisi et al, 2020).…”

Section: Figurementioning

confidence: 99%

“…Figure 5Low-energy tautomers/conformers of TT9. Relative energies are taken fromParisi et al (2020) and are evaluated in water as the continuum polarizable medium.…”

mentioning

confidence: 99%

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Stabilization of an elusive tautomer by metal coordination

Parisi¹,

Centore²

2021

Acta Crystallogr C

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The solid-state isolation of the different tautomers of a chemical compound can be a challenging problem. In many cases, tautomers with an energy very close to the most stable one cannot be isolated (elusive tautomers). In this article, with reference to the 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole ligand, for which the elusive 3H-tautomer has an energy only 1.4 kcal mol−1 greater than the most stable 2H form, we show that metal complexation is a successful and reliable way for stabilizing the elusive tautomer. We have prepared two complexes of the neutral ligand with CuBr2 and ZnBr2, namely, aquabromidobis[4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]copper(II) bromide trihydrate, [CuBr(C8H7N7)2(H2O)]Br·3H2O, and dibromido[4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole][4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]zinc(II) monohydrate, [ZnBr2(C8H7N7)2]·H2O. The X-ray analysis shows that, in both cases, the elusive 3H-tautomer is present. The results of the crystallographic analysis of the two complexes reflect the different coordination preferences of CuII and ZnII. The copper(II) complex is homotautomeric as it only contains the elusive 3H-tautomer of the ligand. The complex can be described as octahedral with tetragonal distortion. Two 3H-triazolotriazole ligands are bis-chelated in the equatorial plane, while a water molecule and a bromide ion in elongated axial positions complete the coordination environment. The zinc(II) complex, on the other hand, is heterotautomeric and contains two bromide ions and two monodentate ligand molecules, one in the 2H-tautomeric form and the other in the 3H-tautomeric form, both coordinated to the metal in tetrahedral geometry. The observation of mixed-tautomer complexes is unprecedented for neutral ligands. The analysis of the X-ray molecular structures of the two complexes allows the deduction of possible rules for a rational design of mixed-tautomer complexes.

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Section: Figuresupporting

confidence: 74%

Section: Resultsmentioning

confidence: 99%

Section: Synthesis and Crystallizationmentioning

confidence: 99%

Section: Figurementioning

confidence: 99%

“…Figure 5Low-energy tautomers/conformers of TT9. Relative energies are taken fromParisi et al (2020) and are evaluated in water as the continuum polarizable medium.…”

mentioning

confidence: 99%

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Stabilization of an elusive tautomer by metal coordination

Parisi¹,

Centore²

2021

Acta Crystallogr C

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Competitive Intramolecular Hydrogen Bonding: Offering Molecules a Choice

Sun,

Morton,

Bhabha

et al. 2024

ChemPlusChem

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The conformational preferences of N‐((6‐methylpyridin‐2‐yl)carbamothioyl)benzamide were studied in solution, the gas phase and the solid state via a combination of NMR, density functional theory (DFT) and single crystal X‐ray techniques. This acyl thiourea derivative can adopt two classes of low energy conformation, each stabilized by a different 6‐membered intramolecular hydrogen bond (IHB) pseudoring. Analysis in different solvents revealed that the conformational preference of this molecule is polarity dependent, with increasingly polar environments yielding a higher proportion of the minor conformer containing an NH…N IHB. The calculated barrier to interconversion is consistent with dynamic behaviour at room temperature, despite the propensity of 6‐membered IHB pseudorings to be static. This work demonstrates that introducing competitive IHB pathways can render static IHBs more dynamic and that such systems could have potential as chameleons in drug design.

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High N‐H Photoacidity of a Nitrogen‐Rich Fused Ring Heteroaromatic Scaffold

et al. 2022

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It is shown that 4-methyl-7-(4-nitrophenyl)-triazolo[3,2-c]triazole exhibits a high photoacidity, unprecedented in neutral molecules in which the proton is delivered by a NH bond, which promotes acetalization of aldehydes under irradiation by a near-UV low power LED. Time dependent transient absorption spectroscopy shows a series of stimulated emission signals attributable to photo-tautomerization and formation of the deprotonated species, followed by broad positive absorption band which does not decay within the investigated timescale, compatible with the formation of a long living species, possibly the anion in the lowest energy triplet state. Computational analyses qualitatively confirm the strong photoacidity of the molecule in all its tautomeric forms, allow to assign transient absorption signals, and show that the first singlet excited state exhibits high spin-orbit couplings with excited triplet states which could promote a fast singlet-triplet transition, thus leading to a long living species able to photocatalyze chemical reactions.

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Tautomeric and conformational switching in a new versatile N-rich heterocyclic ligand

Abstract: The dancing of protons: five different tautomers/conformers of a new N-rich heterocyclic ligand were isolated and characterized.

Cited by 13 publications

References 27 publications

Stabilization of an elusive tautomer by metal coordination

Stabilization of an elusive tautomer by metal coordination

Competitive Intramolecular Hydrogen Bonding: Offering Molecules a Choice

High N‐H Photoacidity of a Nitrogen‐Rich Fused Ring Heteroaromatic Scaffold

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