Abstract

Aluminyl anions are low-valent, anionic, and carbenoid aluminum species commonly found stabilized with potassium cations from the reaction of Al-halogen precursors and alkali compounds. These systems are very reactive toward the activation of sigma-bonds and in reactions with electrophiles. Various research groups have detected that the potassium atoms play a stabilization role via electrostatic and cationMIDLINE HORIZONTAL ELLIPSIS pi interactions with nearby (aromatic)-carbocyclic rings from both the ligand and from the reaction with unsaturated substrates. Since stabilizing KMIDLINE HORIZONTAL ELLIPSISH bonds are witnessed in the activation of this class of molecules, we aim to unveil the role of these metals in the activation of the smaller and less polarizable H-2 molecule, together with a comprehensive characterization of the reaction mechanism. In this work, the activation of H-2 utilizing a NON-xanthene-Al dimer, [K{Al(NON)}](2) (D) and monomeric, [Al(NON)](-) (M) complexes are studied using density functional theory and high-level coupled-cluster theory to reveal the potential role of K+ atoms during the activation of this gas. Furthermore, we aim to reveal whether D is more reactive than M (or vice versa), or if complicity between the two monomer units exits within the D complex toward the activation of H-2. The results suggest that activation energies using the dimeric and monomeric complexes were found to be very close (around 33 kcal mol(-1)). However, a partition of activation energies unveiled that the nature of the energy barriers for the monomeric and dimeric complexes are inherently different. The former is dominated by a more substantial distortion of the reactants (and increased interaction energies between them). Interestingly, during the oxidative addition, the distortion of the Al complex is minimal, while H-2 distorts the most, usually over 0.77 Delta Edist not equal . Overall, it is found here that electrostatic and induction energies between the complexes and H-2 are the main stabilizing components up to the respective transition states. The results suggest that the K+ atoms act as stabilizers of the dimeric structure, and their cooperative role on the reaction mechanism may be negligible, acting as mere spectators in the activation of H-2. Cooperation between the two monomers in D is lacking, and therefore the subsequent activation of H-2 is wholly disengaged.