The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Chelate Effect in the Gas Phase. The Complexes of Ni(2,2,6,6-tetramethyl-3,5-heptanedionate)2 with Bidentate Ligands》. Authors are Emmenegger, Franzpeter; Schlaepfer, Carl Wilhelm; Stoeckli-Evans, Helen; Piccand, Michel; Piekarski, Henryk.The article about the compound:Bis(2,2,6,6-tetramethyl-3,5-heptanedionato)nickel(II)cas:14481-08-4,SMILESS:CC(C)(C1=O[Ni+2]2(O=C(C(C)(C)C)[CH-]1)O=C([CH-]C(C(C)(C)C)=O2)C(C)(C)C)C).Safety of Bis(2,2,6,6-tetramethyl-3,5-heptanedionato)nickel(II). Through the article, more information about this compound (cas:14481-08-4) is conveyed.
When a bidentate ligand L-L is added to the square planar Ni(tmhd)2 (tmhd = tetramethylheptanedionate), octahedral Ni(tmhd)2L-L (L-L = tetramethylethylenediamine (TEME), 2,2-bipyridine, dimethylaminomethoxyethane (MAO)) are formed. This reaction was studied by visible spectroscopy in toluene at 25° and in the gas phase between 150 and 350°. It allows the comparison on one hand of the chelate effect of three ligands forming five-membered chelate rings: (i) the flexible N-N ligand TEME; (ii) the rigid N-N ligand bpy; (iii) the flexible N-O ligand MAO. However, it allows the comparison of these ligands with the six-membered chelate ring-forming N-N ligand 1,3-tetramethylpropylenediamine (TEMP). From the temperature dependence of the gas-phase stability constants, enthalpies and entropies of the complex-forming reactions were derived. As there are no solvation effects in the gas phase, the reaction enthalpies are the metal-ligand bond enthalpies. This is of particular interest for the hemilabile ligand MAO. For the N-N ligands, the stability of the metal-ligand bonds decreases in the order TEME > bpy > TEMP. The entropy of the complex formation with the two flexible ligands TEME and MAO is the same, while it is slightly more pos. for the rigid bpy and a lot more pos. for TEMP. ΔformG°298 of the complexes is more neg. in the gas phase than in solution because the solvation energy of the reactants is more neg. than the solvation energy of the products. This is shown in detail for the formation of Ni(tmhd)2bpy where data of a complete thermodn. cycle are presented.
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Reference:
Ester – Wikipedia,
Ester – an overview | ScienceDirect Topics