title: Versatile Self-Adapting Boronic Acids for H-Bond Recognition: From Discrete to Polymeric Supramolecules.
abstract: Because of the peculiar dynamic covalent reactivity of boronic acids to form tetraboronate derivatives, interest in using their aryl derivatives in materials science and supramolecular chemistry has risen. Nevertheless, their ability to form H-bonded complexes has been only marginally touched. Herein we report the first solution and solid-state binding studies of the first double-H-bonded DD·AA-type complexes of a series of aromatic boronic acids that adopt a syn-syn conformation with suitable complementary H-bonding acceptor partners. The first determination of the association constant (Ka) of ortho-substituted boronic acids in solution showed that Kafor 1:1 association is in the range between 300 and 6900 M-1. Crystallization of dimeric 1:1 and trimeric 1:2 and 2:1 complexes enabled an in-depth examination of these complexes in the solid state, proving the selection of the -B(OH)2syn-syn conformer through a pair of frontal H-bonds with the relevant AA partner. Non-ortho-substituted boronic acids result in "flat" complexes. On the other hand, sterically demanding analogues bearing ortho substituents strive to retain their recognition properties by rotation of the ArB(OH)2moiety, forming "T-shaped" complexes. Solid-state studies of a diboronic acid and a tetraazanaphthacene provided for the first time the formation of a supramolecular H-bonded polymeric ribbon. On the basis of the conformational dynamicity of the -B(OH)2functional group, it is expected that these findings will also open new possibilities in metal-free catalysis or organic crystal engineering, where double-H-bonding donor boronic acids could act as suitable organocatalysts or templates for the development of functional materials with tailored organizational properties.
authors.affiliation: Department of Chemistry, University of Namur (UNamur) , Rue de Bruxelles 61, 5000 Namur, Belgium.
authors.forename: Irene
authors.initials: I
authors.lastname: Georgiou
authors.affiliation: Department of Chemistry, University of Namur (UNamur) , Rue de Bruxelles 61, 5000 Namur, Belgium.
authors.forename: Simon
authors.initials: S
authors.lastname: Kervyn
authors.affiliation: Department of Chemistry, University of Namur (UNamur) , Rue de Bruxelles 61, 5000 Namur, Belgium.|School of Chemistry, Cardiff University , Park Place, Main Building, Cardiff CF10 3AT, U.K.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Rossignon
authors.affiliation: Department of Chemistry, University of Namur (UNamur) , Rue de Bruxelles 61, 5000 Namur, Belgium.
authors.forename: Federica
authors.initials: F
authors.lastname: De Leo
authors.affiliation: Department of Chemistry, University of Namur (UNamur) , Rue de Bruxelles 61, 5000 Namur, Belgium.
authors.forename: Johan
authors.initials: J
authors.lastname: Wouters
authors.affiliation: Université Libre de Bruxelles , Ecole Polytechnique de Bruxelles, Campus du Solbosch, Avenue F. D. Roosevelt 50, 1050 Bruxelles, Belgium.
authors.forename: Gilles
authors.initials: G
authors.lastname: Bruylants
authors.affiliation: Department of Chemistry, University of Namur (UNamur) , Rue de Bruxelles 61, 5000 Namur, Belgium.|School of Chemistry, Cardiff University , Park Place, Main Building, Cardiff CF10 3AT, U.K.
authors.forename: Davide
authors.identifier: 0000-0001-5717-0121
authors.initials: D
authors.lastname: Bonifazi