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

Abstract

The stability of a variety of linear and cyclic (BN) n (n = 1-3) adducts with N-heterocyclic carbene (ImMe 2; ImMe 2 = [(HCNMe) 2 C:]), N-heterocyclic olefin (ImMe 2 CH 2) and Wittig (Me 3 PCH 2) donors has been examined using M05-2X/cc-pVTZ computations. The strength and nature of the bonds have been investigated using natural bond orbital (NBO) and atoms-in-molecules (AIM) analyses. Complementary energy decomposition analysis (EDA-NOCV) has been carried out based on BP86/TZ2P computations. In agreement with NBO and AIM analyses, the orbital interaction energy obtained from EDA contributes at least 50% to the total attractive interactions for the carbon-boron bonds indicating their largely covalent nature. The feasibility of isolating monomeric (BN) n units using a donor/acceptor protocol was also investigated in a series of adducts of the general form: LB·(BN) n ·BH 3 and LB·(BN) n ·W(CO) 5 (n = 1-3; LB = Lewis bases). Moreover, EDA-NOCV analysis of ImMe 2 ·BN·W(CO) 5 and ImMe 2 ·B 3 N 3 ·W(CO) 5 shows that the carbene-boron bonds are stronger in the presence of W(CO) 5 as a Lewis acid mainly because of a dramatic decrease in the amount of Pauli repulsion rather than an increase in the electrostatic/orbital attraction terms.