Stability of Borane−Adduct Complexes:  A G-2 Molecular Orbital Study

Abstract

Complexation energies of H3BXH n and [H3BXH n - 1]- complexes (X = N, O, F, P, S, and Cl) (n = 3, 2, 1) have been computed at the G-2 level of theory. The formation of H3BXH3 (X = N, P) is found to be more favored than the formations of H3BXH2 (X = O, S) and H3BXH (X = F, Cl). The qualitative features of the molecular orbital interaction (the correlation diagrams) of H3BNH3 (C 3 v symmetry group), H3BOH2 (C s symmetry group), and H3BFH (C s symmetry group) complexes are presented. These diagrams show that the σ character of the B−X bond decreases and the π character increases when the electronegativity of X increases and indicate that the B−X bond cannot be treated only in terms of the simplest model of the HOMO−LUMO interaction (i.e., a two-level and two-electron model system). Two linear correlations were established and discussed. The first one was between proton affinities of the Lewis bases L (L = XH n and [XH n - 1]-, n = 3, 2, 1) and complexation energies of the H3BL compounds calculated at the G-2 level of theory. The second correlation was between the 11B NMR coupling constant 1 J B - H and the complexation energies of H3BL (L = OH-, PH2 - , SH-, Cl-, NH3, and PH3).

Computational study of the fluorination effect on nitrogen–boron bond

“…The optimized geometries of BX 3 Lewis acids (X ϭ H, F), NH 3 Lewis base and their complexes at the B3LYP/6-31G** level of theory are summarized in Table I. As can be seen in Table I, the B3LYP values are in excellent agreement with the experimental ones.…”

“…A typical property of electron-deficient boranes is their Lewis acidity, which reflects the fact that boron possesses fewer valence electrons than valence orbitals. As a result, boron hydride BH 3 and its halides BX 3 readily form donor-acceptor complexes with Lewis bases such as NH 3 and N(CH 3 ) 3 [1][2][3][4][5].…”

“…The knowledge of the structure and properties of these complexes is essential for understanding the mechanism of such processes. Numerous studies have been devoted to the H 3 N-BH 3 and H 3 N-BF 3 complexes [6 -10]. It is well-known that the Lewis acidities of boron trihalides increase in the order BF 3 Ͻ BCl 3 Ͻ BBr 3 .…”

“…Numerous studies have been devoted to the H 3 N-BH 3 and H 3 N-BF 3 complexes [6 -10]. It is well-known that the Lewis acidities of boron trihalides increase in the order BF 3 Ͻ BCl 3 Ͻ BBr 3 . This is opposite to what would be expected from the electro-negativities of the halogens.…”

A G2(MP2) theoretical study of substituent effects on H3BNHnCl3−n (n= 3-0) donor-acceptor complexes

“…Accurate knowledge of the thermodynamics of complexation energies would serve as a useful framework from which to build a detailed and quantitative understanding of borane reactivity and mechanism [1][2][3]. Many theoretical studies have been devoted to boron donor-acceptor complexes concerning their structural parameters, the nature of the bonding, the factors affecting their stability and other physical proprieties [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] where the methods used for analysis differ.…”