Understanding the Reactivity of "Naked" Acyclic Carbene-like Species Featuring a Group 13 Element in the [4+1]...

The chemical reactivity between benzene and the "naked" acyclic carbene-like (G13X₂)^- species, having two bulky N-heterocyclic boryloxy ligands at the Group 13 center, was theoretically assessed using density functional theory computations. Our theoretical studies show that (BX₂)^- preferentially undergoes C-H bond insertion with benzene, both kinetically and thermodynamically, whereas the (AlX₂)^- analogue favors a reversible [4 + 1] cycloaddition. Conversely, the heavier carbene analogues ((GaX₂)^-, (InX₂)^-, and (TlX₂)^-) are not expected to engage in a reaction with benzene. The activation strain model analysis suggests that the geometric deformation energy of benzene, driven by the relativistic effects of the central G13 element in the (G13X₂)^- molecule, is crucial in determining the chemical reactivity of the [4 + 1] cycloaddition with benzene. According to our theoretical analyses, the stronger forward bonding is specifically the sp²-σ-orbital (G13) → vacant protruding p-π* orbitals (bent benzene). In contrast, the weaker backward bonding is the empty p-π orbital (G13) ←-filled protruding p-π orbital (bent benzene). Moreover, our theoretical findings indicate that the singlet-triplet splitting of (G13X₂)^- can be used as a diagnostic measure to predict the barrier height and reaction energy for their [4 + 1] cycloaddition with benzene.