A Computational Investigation of the Nitrogen−Boron Interaction in o-(N,N-Dialkylaminomethyl)arylboronate Systems

Abstract

o-(N,N-Dialkylaminomethyl)arylboronate systems are an important class of compounds in diol-sensor development. We report results from a computational investigation of fourteen o-(N,N-dialkylaminomethyl)arylboronates using second-order Møller-Plesset (MP2) perturbation theory. Geometry optimizations were performed at the MP2/cc-pVDZ level and followed by single-point calculations at the MP2/aug-cc-pVDZ(cc-pVTZ) levels. These results are compared to those from density functional theory (DFT) at the PBE1PBE(PBE1PBE-D)/6-311++G(d,p)(aug-cc-pVDZ) levels, as well as to experiment. Results from continuum PCM and CPCM solvation models were employed to assess the effects of a bulk aqueous environment. Although the behaviour of o-(N,N-dialkylaminomethyl) free acid and ester proved to be complicated, we were able to extract some important trends from our calculations: 1) for the free acids the intramolecular hydrogen-bonded B-O-H⋯N seven-membered ring conformers 12 and 16 are found to be slightly lower in energy than the dative-bonded N→B five-membered ring conformers 10 and 14 while conformers 13 and 17, with no direct boron-nitrogen interaction, are significantly higher in energy than 12 and 16; 2) for the esters where no intramolecular B-O-H⋯N bonded form is possible, the N→B conformers 18 and 21 are significantly lower in energy than the no-interaction forms 20 and 23; 3) H2O insertion reactions into the N→B structures 10, 14, 18, and 21 leading to the seven-membered intermolecular hydrogen-bonded B⋯OH2⋯N ring structures 11, 15, 19, and 22 are all energetically favorable.

Boronic acid sensors for saccharides: A theoretical study

“…As found previously [7][8][9], the hydrogen bonded conformation e.g. structure I above is lower in energy than the structure indicating a BÁ Á ÁN interaction, shown below in III.…”

“…The actual difference in energy calculated varies with the method and basis set, see also previous reports [9], and the values obtained here for the pyrene system vary between 7 and 5 kcal/mol. Similarly, for the anthracene sensor the analogue of structure I is found to be lower than the analogue of III by 17 kcal/mol.…”

“…The calculated NÁ Á ÁH and O-H distances also differ slightly depending on the functional. The subject of small variations in the calculated ground state structures obtained with different methodologies has been covered in great detail in previous theoretical work which was solely devoted to the determination of the different groundstate geometries including those of type I and III, employing more elaborate methods than here [9]. The objectives of the present work lie in the PET process leading to suppression of fluorescence in the sensors.…”

“…However, significant enhancement of fluorescence is observed upon reaction of the boronic acid with 1,2 diols of saccharides to form complex (II), which has been proposed to involve donation of electronic charge to boron from nitrogen, [4], thus inhibiting any PET process. Theoretical investigations on model systems have been devoted mainly to the elucidation of the interaction between B and N in these sensors [7][8][9][10] and determination of the most stable conformer of the sensors and as shown in (I) structures involving intramolecular B-O-HÁ Á ÁN interaction are found to be generally lower in energy than those involving a B-N bond [7][8][9]. Inference on the photoinduced electron transfer capabilities and fluorescence properties of protonated and neutral sensor systems has been made on the basis of electron-density plots of the highest occupied (HOMO) and the lowest unoccupied molecular orbitals (LUMO) of protonated and neutral sensors molecules [11].…”

Thiophene‐Inserted Aryl–Dicyanovinyl Compounds: The Second Generation of Fluorescent Molecular Rotors with Significantly Redshifted Emission and Large Stokes Shift

“…DFT calculations have recently been used to study the photophysical properties of fluorescent dyes, [29] molecular probes, [18][19][20][30][31][32][33][34] and luminescent materials. [35][36][37][38][39] In this work we used DFT calculations to study the absorption and emission properties of the new molecular rotors to investigate the role of the thiophene moiety in the π conjugation of the molecular framework.…”