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

The chemical reactivity between benzene and the "naked" acyclic carbene-like (G13X) 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 (BX) preferentially undergoes C-H bond insertion with benzene, both kinetically and thermodynamically, whereas the (AlX) analogue favors a reversible [4 + 1] cycloaddition. Conversely, the heavier carbene analogues ((GaX), (InX), and (TlX)) 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 (G13X) 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 sp-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 (G13X) can be used as a diagnostic measure to predict the barrier height and reaction energy for their [4 + 1] cycloaddition with benzene.