Cooperative H₂ Activation by N,P- and N,N-Chelated Low-Valent Group 13 Complexes: A DFT Study

Herein, we present a computational mechanistic study on H₂ activation mediated by various N,P- and N,N-chelated low-valent Group 13 species, including mononuclear Al(I) complexes, dialumenes featuring Al-Al multiple bonds, and heterobimetallic Al(I)/In(I) carbenoid pairs. Density functional theory (DFT) calculations reveal that H-H bond cleavage preferentially proceeds via 1,2-hydrogenation across the bimetallic active centers Al(I)/Al(I) or Al(I)/In(I). This cooperative activation mechanism involves homolytic H-H bond splitting, characterized by synergistic electron donation from the Al-Al (or Al-In) π-bonding orbital into the H-H σ-antibonding orbital and from the H-H σ-bonding orbital into vacant Al (or In) p-orbitals. The computed free energy barriers (ΔG‡ = 14.9-24.6 kcal mol^-1) for this pathway are substantially lower than those (ΔG‡ = 38.6-44.6 kcal mol^-1) calculated for oxidative addition at a mononuclear Al(I) center. Energy decomposition analysis (EDA) on ligand effects indicates that N,P-amidophosphine coordination enhances Al-Al bond flexibility and reduces Pauli repulsion during H₂ addition, leading to lower activation barriers relative to N,N-amidinate-supported systems. Furthermore, our calculations validate that amidophosphine-stabilized In(I) carbenoid can efficiently catalyze the hydrogenation of both N,P- and N,N-chelated Al(I) monomers to yield the corresponding Al(III) dihydrides.