Analysis of the relative stability of trigonal and tetrahedral boronate cyclic esters in terms of boronic acid and diol acidities and the strain release effect
Por:
Martinez-Aguirre, Mayte A., Medrano, Felipe, Ramirez-Rave, Sandra, Yatsimirsky, Anatoly K.
Publicada:
1 dic 2022
Ahead of Print:
1 ago 2022
Resumen:
Higher stability of tetrahedral hydroxyboronate cyclic esters of
1,2-diols in comparison with the respective trigonal esters and the
associated increased acidity of the trigonal esters in comparison with
free boronic acids are wellknown and important aspects of the
thermodynamics of boronate ester formation usually attributed to the
strain in O-B-O angle created in the trigonal esters and released in the
tetrahedral hydroxyboronates. The stability constants of tetrahedral
(K-tet) and trigonal (K-trig) boronate esters of several aliphatic and
aromatic 1,2- and 1,3-diols with a series of five boronic acids of
variable acidity were determined by potentiometric titrations in water.
The ratio K-tet/K(trig )varies from similar to 10 for
cis-1,2-cyclopentanediol to similar to 10(4) for catechol entirely due
to the increase in Ktet for more acidic diols and is weakly affected by
the acidity of boronic acids. Analysis of DFT minimized structures of
trigonal and tetrahedral esters of phenylboronic acid with
cis-1,2-cyclopentanediol, 1,4-anhydroerythritol, and catechol
demonstrates the absence of postulated strain release in the tetrahedral
esters. A global analysis of new and previously reported relevant data
on K-tet, K-trig, and K-tet/K-trig values for 1,2- and 1,3-diols and
different boronic acids in terms of the Bronsted-type correlations with
pK(a) values of the reaction components shows that K-tet/K-trig values
vary in a wide range from similar to 1 to similar to 10(6), and this
variation can be satisfactorily explained by the stabilization of
tetrahedral hydroxyboronate cyclic esters by more acidic diols without
invoking of the strain release effect.
Filiaciones:
Martinez-Aguirre, Mayte A.:
Univ Nacl Autonoma Mexico, Fac Quim, Mexico City 04510, DF, Mexico
Medrano, Felipe:
Univ Sonora, Dept Ciencias Quim Biol, Hermosillo, Sonora, Mexico
Ramirez-Rave, Sandra:
Univ Nacl Autonoma Mexico, Fac Quim, Mexico City 04510, DF, Mexico
Yatsimirsky, Anatoly K.:
Univ Nacl Autonoma Mexico, Fac Quim, Mexico City 04510, DF, Mexico
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