Thermochemical Considerations of Metal Enolates

Abstract

Introduction Group 1: Lithium, Sodium, Potassium, Rubidium and Cesium Group 2: Beryllium, Magnesium, Calcium, Strontium and Barium Group 13: Aluminum, Gallium, Indium and Thallium Group 14: Tin and Lead Group 11: Copper, Silver and Gold Group 12: Zinc, Cadmium and Mercury Group 3: Scandium, Yttrium and the Lanthanides Actinides Group 4: Titanium, Zirconium and Hafnium Group 5: Vanadium, Niobium and Tantalum Group 6: Chromium, Molybdenum and Tungsten Group 7: Manganese and Rhenium Group 8: Iron, Ruthenium and Osmium Group 9: Cobalt, Rhodium and Iridium Group 10: Nickel, Palladium and Platinum

VO2+ Complexation by Bioligands Showing Keto–Enol Tautomerism: A Potentiometric, Spectroscopic, and Computational Study

“…An examination of Scheme allows one to notice that, for dihydroxyfumaric and oxalacetic acid, the enol tautomer is more stable than the keto tautomer. In particular, for dhfH 2 , the cis isomer (dihydroxymaleic acid) is preferred, both in the gas phase and in water, with respect to the trans one: this confirms the results reported in the literature and justifies the complexing behavior of the ligand. For 3-hydroxy-2-butanone and pyruvic acid, the opposite situation is realized and the keto tautomer is favored.…”

“…Such an equilibrium is due to the existence of the keto forms, which allow for interconversion between the two configurational isomers. The crystalline structure of dhfH 2 has been reported, but in the literature, it has been pointed out that the cis arrangement is slightly more stable than the trans one …”

“…In the case of simple ketones, such an amount is very low; however, it can increase if other keto, aldehyde, ester, or carboxylic groups are present in the molecule. For example, it is reported that, for dihydroxyfumaric and oxalacetic acid, the enol form is more stable, − while for pyruvic acid and 3-hydroxy-2-butanone, the keto form has the lower energy . Therefore, it can be very interesting to investigate whether V IV is able to stabilize the enol tautomer; indeed, in aqueous solution, the enol can undergo deprotonation of the −OH group (see Scheme ) to yield enolate, which possesses a greater affinity with respect to the keto tautomer toward a hard metal ion like V IV .…”