Synthesis, Characterization, Catalytic Activity, and DFT Calculations of Zn(II) Hydrazone Complexes.

Temiloluwa T Adejumo,Božidar Čobeljić,Andrej Pevec,Leandros P Zorba,Nikolaos V Tzouras,Georgios C Vougioukalakis,Dragana Mitić,Dušanka Radanović,Iztok Turel,Katarina K Anđelković,Sonja Grubišić

doi:10.3390/molecules25184043

Abstract

Two new Zn(II) complexes with tridentate hydrazone-based ligands (condensation products of 2-acetylthiazole) were synthesized and characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction methods. The complexes 1, 2 and recently synthesized [ZnL3(NCS)2] (L3 = (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-aminium) complex 3 were tested as potential catalysts for the ketone-amine-alkyne (KA2) coupling reaction. The gas-phase geometry optimization of newly synthesized and characterized Zn(II) complexes has been computed at the density functional theory (DFT)/B3LYP/6–31G level of theory, while the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO and LUMO) energies were calculated within the time-dependent density functional theory (TD-DFT) at B3LYP/6-31G and B3LYP/6-311G(d,p) levels of theory. From the energies of frontier molecular orbitals (HOMO–LUMO), the reactivity descriptors, such as chemical potential (μ), hardness (η), softness (S), electronegativity (χ) and electrophilicity index (ω) have been calculated. The energetic behavior of the investigated compounds (1 and 2) has been examined in gas phase and solvent media using the polarizable continuum model. For comparison reasons, the same calculations have been performed for recently synthesized [ZnL3(NCS)2] complex 3. DFT results show that compound 1 has the smaller frontier orbital gap so, it is more polarizable and is associated with a higher chemical reactivity, low kinetic stability and is termed as soft molecule.

Highlights

Hydrazone ligands are one of the most important classes of flexible and versatile polydentate ligands which show very high efficiency in chelating various metal ions [1,2,3,4,5,6,7,8,9,10,11,12,13]
The HL3 Cl ligand was synthesized by the reaction of 2-acetylpyridine and Girard’s T reagent according to the previously described method [8]
All the density functional theory (DFT) calculations were performed in gas phase with the Gaussian 09 [55] program at B3LYP/6–31G level [56,57,58,59] of theory

Summary

Introduction

Hydrazone ligands are one of the most important classes of flexible and versatile polydentate ligands which show very high efficiency in chelating various metal ions [1,2,3,4,5,6,7,8,9,10,11,12,13]. Our interest in metal complexes with hydrazone-based ligands is partly due to their potential applications as catalysts [5,6] and molecular magnets [7]. In the other type of mononuclear structures two hydrazone ligand molecules occupy the coordination sphere of the central metal ion forming an octahedral coordination geometry (e.g., [CoL3 2 ][Co(NCS)4 ]BF4 [12]. Propargylic amines are frequently encountered as intermediates in organic synthesis, providing facile access to a variety of structurally complex organic compounds [14,15] Among these compounds, the subgroup of tetrasubstitutedpropargylamines is interesting, as it comprises the least studied family of propargylamines. The catalytic activity of 1 and 2 and the previously characterized [ZnL3 (NCS)2 ]·0.5MeOH [8] complex 3 has been evaluated in the ketone-amine-alkyne (KA2 ) coupling reaction.

Synthesis

Materials and Methods

X-Ray Crystallography

Catalysis General Procedure

DFT Calculations

Conclusions