Browsing by Author "Jesus, A. J. Lopes"

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The Meta and Para OH Substitution Effect on C-Phenyl-Nitrilimine Bond-Shift Isomers
(Wiley-VCH Verlag GmbH, 2023) Ferreira, Gil A.; Nunes, Claudio M.; Jesus, A. J. Lopes; FAUSTO, RUI
The geometric and electronic structure of 1,3-dipolar species, in particular of nitrile imines, can be surprisingly intricate. A particular example is the C-phenyl-nitrilimine, which exists as two energy minima that constitute bond-shift isomers. To examine the effect of substituents in the phenyl ring, here we investigate the meta and para OH substituted derivatives. These two nitrile imines were generated in an argon matrix by UV-irradiation of 2H-tetrazole precursors and found to photoisomerize to carbodiimides via 1H-diazirines. The different effects of the OH substitution in meta and para positions on the bond-shift isomerism are rationalized with the support of Natural Resonance Theory and Hirshfeld atomic charges. The understanding of how substitution affects the structural characteristics of C-phenyl-nitrilimines, opens a door to modulate the chemistry of those compounds (e. g. in cycloaddition reactions) by appropriate tuning of their substitution (substituent type and position).
Open Access
A New Azide-Bridged Polymeric Manganese (III) Schiff Base Complex with an Allylamine-Derived Ligand: Structural Characterization and Activity Spectra
(MDPI, 2024) Talebi, Aynaz; Salehi, Mehdi; Jesus, A. J. Lopes; Kubicki, Maciej; FAUSTO, RUI; Golbedaghi, Reza
This paper reports the synthesis and structural characterization of a novel azide-bridged polymeric manganese (III) Schiff base complex, using 2-((allylimino)methyl)-6-ethoxyphenol as a ligand. The crystal structure of the synthesized compound, elucidated by single-crystal X-ray diffraction analysis, indicates that it crystallizes in the monoclinic space group P21/c. The complex is found to display an octahedral geometry in which the central manganese Mn(III) coordinates with two bidentate donor Schiff base ligands via oxygen and nitrogen atoms. In addition, the metallic centers are linked together to form a one-dimensional chain bridged by end-to-end azide ligands. To offer a more thorough characterization of the synthesized compound, the study incorporates experimental data from FT-IR, UV-Vis, and cyclic voltammetry, alongside computational results from Hirshfeld surface analysis and DFT calculations conducted for both the ligand and complex. The computational analyses provided valuable insights into the intrachain and interchain interactions within the crystal structure, clarified the conformational characteristics of the isolated ligand molecule, and aided in the interpretation of the experimental IR spectra. Furthermore, an assessment of the compound’s drug-like properties was conducted using activity spectra for substances (PASS) predictions, revealing potential pharmacological activities. © 2024 by the authors.
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On the Carbenic Nature of Nitrile Ylides: Experimental and Computational Characterization of Hydroxy and Amino Nitrile Ylides
(Wiley-VCH Verlag, 2024) Nunes, Claudio M.; Jesus, A. J. Lopes; Rosado, Mario T. S.; FAUSTO, RUI
Nitrile ylides are 1,3-dipolar species with structures that are commonly described by propargylic and/or allenic resonance forms. Nevertheless, certain nitrile ylides exhibit a tendency to form dimers, suggesting the existence of structures characterized by an important carbenic contribution. To address the nitrile ylide carbenic nature, here we investigate two derivatives with OH and NH2 electron-donating substituents. These nitrile ylides were generated in cryogenic matrices by UV-irradiation of 3-hydroxy- and 3-amino-isoxazole precursors and were found to photoisomerize to the corresponding oxazoles. The IR spectral characterization of the photogenerated nitrile ylides reveals the absence of the characteristic strong nu as(CNC) absorption, which is associated with allenic and propargylic type structures. Computed geometries for the two experimentally investigated nitrile ylides and for analogues with different substituents at C3 and C1, together with NBO and NRT electronic structure analyses, performed at the CCSD(T) level of theory, reveal substantial carbenic character exclusively for nitrile ylides bearing OH and NH2 substituents at C3. As a whole, the results shed light on the factors determining the structural features of nitrile ylides, which play a major role in defining the reactivity of these important elusive compounds.
Open Access
Photochemical Generation and Characterization of C-Aminophenyl-Nitrilimines: Insights on Their Bond-Shift Isomers by Matrix-Isolation IR Spectroscopy and Density Functional Theory Calculations
(MDPI, 2024) Jesus, A. J. Lopes; Nunes, Claudio M.; Ferreira, Gil A.; Keyvan, Kiarash; FAUSTO, RUI
The intriguing ability of C-phenyl-nitrilimine to co-exist as allenic and propargylic bond-shift isomers motivated us to investigate how substituents in the phenyl ring influence this behavior. Building on our previous work on the meta- and para-OH substitution, here we extended this investigation to explore the effect of the NH2 substitution. For this purpose, C-(4-aminophenyl)- and C-(3-aminophenyl)-nitrilimines were photogenerated in an argon matrix at 15 K by narrowband UV-light irradiation (lambda = 230 nm) of 5-(4-aminophenyl)- and 5-(3-aminophenyl)-tetrazole, respectively. The produced nitrilimines were further photoisomerized to carbodiimides via 1H-diazirines by irradiations at longer wavelengths (lambda = 380 or 330 nm). Combining IR spectroscopic measurements and DFT calculations, it was found that the para-NH2-substituted nitrilimine exists as a single isomeric structure with a predominant allenic character. In contrast, the meta-NH2-substituted nitrilimine coexists as two bond-shift isomers characterized by propargylic and allenic structures. To gain further understanding of the effects of phenyl substitution on the bond-shift isomerism of the nitrilimine fragment, we compared geometric and charge distribution data derived from theoretical calculations performed for C-phenyl-nitrilimine with those performed for the derivatives resulting from NH2 (electron-donating group) and NO2 (electron-withdrawing group) phenyl substitutions.