Computational chemistry methods were employed to study small boron containing reactive intermediates, such as borylenes, which are the analogs of carbenes and nitrenes, and borirenes and boriranes that are isoelectronic to cyclopropenyl and cyclopropyl cations, respectively. Density functional theory (DFT) was used to study the electronic and molecular structure of various substituted borylenes BR. The influence of substitution on the frontier molecular orbitals (FMO) energies, HOMO-LUMO energy gaps, and singlet-triplet energy splittings was also examined. In addition, two lowest singlet-singlet electronic transitions were computed using equation-of-motion coupled cluster singles and doubles (EOM-CCSD) and time-dependent density functional theory (TD-DFT). The reactivity of singlet borylenes towards unsaturated and saturated hydrocarbons was investigated. To study the mechanisms of the addition and insertion reactions, ethyne, ethene, and methane were chosen as model hydrocarbons. The philicity of borylenes was also studied in terms of geometrical parameters of the transition states calculated for the addition reactions. The aforementioned addition and insertion reactions involve weakly bound van der Waals complexes formed between hydrocarbons and borylenes that correspond to shallow minima on the potential energy surfaces. Spin-component scaled second-order Møller-Plesset perturbation theory (SCS-MP2) was used to study all complexes. Symmetry-adapted perturbation theory (SAPT) analysis was performed to study the nature of the interaction in borylene-hydrocarbon van der Waals complexes. The reactions of three-membered boron heterocycles (borirane and borirene) towards unsaturated hydrocarbons (ethyne and ethene) were investigated. Dimerization reactions of borirenes and boriranes were also studied using DFT and CCSD(T) methods
