Quantum-chemical study on conformations of molecular complexes formed by 2-methyl-1,3,2-dioxaborinane with methylamine

Abstract

Conformations of 1 : 1 molecular complexes of 2-methyl-1,3,2-dioxaborinane with methylamine were studied in terms of restricted Hartree-Fock approximation using STO-3G, 3-21G, and 6-31G(d) bass sets. The results showed possible formation of two types of complexes, one with dative N→B bond, and the other with intermolecular hydrogen bond NH · · · O. Their relative stability and conformations are determined by both mutual orientation of the components and basis set used.The ability of boric acid esters to form molecular complexes with both lone electron pair (LEP) donors and acceptors [1] makes these compounds convenient models for computer simulation of mechanisms of interactions with various solvents. It was shown previously [2-7] that molecules of 2-alkyl-1,3,2-dioxaborinanes at room temperature undergo fast (on the NMR time scale) ring inversion with a relatively low barrier. In addition, the potential energy surface (PES) of 2-methyl-1,3,2-dioxaborinane (I) includes minima (energy-degenerate sofa conformers S) and a maximum corresponding to 2,5-twist conformer 2,5-T (Scheme 1) [8].culations, the formation of adducts by methyl-and phenylboronic acids with ammonia in solution is an endothermic processes [12]. In the present work we tried to simulate the potential energy surface of ester I in the presence of methylamine molecule in terms of the restricted Hartree-Fock approximation with STO-3G, 3-21G, and 6-31G(d) basis sets using HyperChem software package [13].We found that the molecular system 2-methyl-1,3,2-dioxaborinane (I)-methylamine (1 : 1) could give rise to numerous binary structures and that there are only two most stable associates with dative N→B bond (A) and intramolecular hydrogen bond H-N · · · O (B).