The poorly understood factors governing the small molecule activation reactions mediated by diazaborinines have been computationally explored in detail using quantum chemical tools. To this end, the activation of E-H σ-bonds (E = H, C, Si, N, P, O, S) has been investigated. These reactions, which proceed in a concerted manner, are exergonic and, in general, associated with relatively low activation barriers. In addition, the barrier becomes lower for the E-H bonds involving the heavier element in the same group (ΔG≠ : C>Si; N>P; O>S). This reactivity trend together with the mode of action of the diazaborinine system are quantitatively analyzed by means of the activation strain model of reactivity in combination with the energy decomposition analysis method.