Donor−Acceptor Complexes of Borazines

Abstract

Donor-acceptor complexes of borazine (BZ) and its substituted derivatives with Lewis acids (A = MCl(3), MBr(3); M = B, Al, Ga) and Lewis bases (D = NH(3), Py) have been theoretically studied at the B3LYP/TZVP level of theory. The calculations showed that complexes with Lewis bases only are unstable with respect to dissociation into their components, while complexes with Lewis acids only (such as aluminum and gallium trihalides) are stable. It was shown that formation of ternary D→BZ→A complexes may be achieved by subsequent introduction of the Lewis acid (acceptor A) and the Lewis base (donor D) to borazine. The nature of substituents in the borazine ring, their number, and position were shown to have only minor influence on the stability of ternary D→BZ→A complexes due to the compensation effect. Much weaker acceptor properties of borazine are explained in terms of large endothermic pyramidalization energy of the boron center in the borazine ring. In contrast to borazine, binary complexes of the isoelectronic benzene were predicted to be weakly bound even in the case of very strong Lewis acids; ternary DA complexes of benzene were predicted to be unbound. The donor-acceptor complex formation was predicted to significantly reduce both the endothermicity (by 70-95 kJ mol(-1)) and the activation energy (by 40-70 kJ mol(-1)) for the borazine hydrogenation. Thus, activation of the borazine ring by Lewis acids may be a facile way for the hydrogenation of borazines and polyborazines.

Interplay of donor–acceptor interactions in stabilizing boron nitride compounds: insights from theory

“…NICS data are sensitive to the position at which they are evaluated and to interference from other parts of the molecule, especially for non-planar compounds. 23 The changes in aromaticity/anti-aromaticity are discussed in terms of NICS (1.00) zz values, see Table S1, ESI † for complete NICS data.…”

“…[7][8][9][10][11][12][13][14][15] Moreover, donor-acceptor stabilization has been used to great success to isolate heavier group 13-15 element species, [16][17][18][19][20][21] while related computational studies have been reported. 22,23 More specifically, DFT predicted a significant thermodynamical stabilization of group 13-15 cubane systems (e.g., B 4 N 4 ) upon addition of NH 3 and BH 3 as donor and acceptor molecules, respectively. 22 In this work we present our analyses of the bonding within Lewis base-substituted boron nitride compounds in the presence and/or absence of Lewis acid.…”

Reduction of Borazines Mediated by Low‐Valent Chromium Species

“…[17] Note that diene-type products obtained by single H + addition are predicted to have limited thermodynamic stability relative to the corresponding borazine or monoene species. [5,18] Thus, we targeted a quench/trap method to capture unstable and reactive diene intermediates by derivatization. Because HX additions to borazine (X = Cl, Br) were previously reported, [19] we examined acids that feature coordinating anions as trapping reagents, and initiated our studies with H + donors featuring attenuated acidity relative to HCl.…”

Reduction of Borazines Mediated by Low‐Valent Chromium Species

“…Note that diene‐type products obtained by single H + addition are predicted to have limited thermodynamic stability relative to the corresponding borazine or monoene species 5. 18 Thus, we targeted a quench/trap method to capture unstable and reactive diene intermediates by derivatization. Because HX additions to borazine (X=Cl, Br) were previously reported,19 we examined acids that feature coordinating anions as trapping reagents, and initiated our studies with H + donors featuring attenuated acidity relative to HCl.…”