Effect of beryllium bonds on the keto?enol tautomerism of formamide derivatives: a subtle basicity?acidity balance

HERRERA, BARABARA; LAMSABHI, AL MOKHTAR; MÓ, OTILIA; VALLEJOS, MARGARITA M.; YÁÑES, MANUEL

THEORETICAL CHEMISTRY ACCOUNTS

SPRINGER

Lugar: Berlin; Año: 2016 vol. 135 p. 1 - 9

1432-881X

The effects of theassociation of BeH2 to formamide derivatives have been investigatedthrough the use of G4 high-level ab initio calculations. The association takesplace preferentially at the carbonyl group of the amide in the keto tautomerand to the imino group in the enol form. In both cases, the complexes formedare stabilized through the formation of beryllium and dihydrogen bonds. Therelative stability of these complexes is the result of a subtle balance betweenthe changes induced by the formation of the beryllium bond on the intrinsicbasicity and acidity of the amide. One of the main consequences of this balanceis the significant stabilization of the enol tautomer due to the concomitantincrease in the basicity of the imino group with respect to the carbonyl groupand the significant acidity enhancement of the OH group, which leads to theformation of very strong BeH···HO dihydrogen bonds in the enol complexes. Forthe Cl-, Br- and NO2-formamide derivatives, this dihydrogen bond isso strong that a spontaneous formation of hydrogen molecule takes place. Theformation of the beryllium bond not only stabilizes the enol forms, but alsoleads to a significant decrease in the activation barriers involved in theenolization process.