Initial gas phase reactions between Al(CH3)3/AlH3 and ammonia: theoretical study

Area of Science:

• Computational Chemistry
• Materials Science
• Inorganic Chemistry

Background:

• Understanding the initial reaction stages between trimethylaluminum (TMA) and ammonia is crucial for various chemical processes.
• Previous studies have not fully elucidated the detailed mechanisms and pathways involved in these gas-phase reactions.

Purpose of the Study:

• To investigate the mechanisms of initial gas-phase reactions between trimethylaluminum and ammonia.
• To determine the structures of intermediate species, donor-acceptor complexes, and dimerization products.
• To elucidate the reaction pathways for methane elimination.

Main Methods:

• Density Functional Theory (DFT) studies were employed to explore reaction mechanisms.
• Analysis of substitution reactions involving CH3 groups in AlMe3 and H atoms in ammonia.
• Identification of transition states, reaction pathways, and thermodynamic favorability of products.

Main Results:

• Structures of Al(CH3)x(NH2)3-x and NHx(Al(CH3)2)3-x (x = 0-3) species were obtained.
• The first methane elimination from the Al(CH3)3NH3 adduct has the highest transition state; subsequent steps are exothermic.
• Product formation depends on reactant ratios: [Al(NH2)3]2 in excess ammonia, N(AlMe2)3 in excess TMA, and [AlMe2NH2]2 dimer is highly favorable.

Conclusions:

• The study provides a detailed mechanistic understanding of trimethylaluminum-ammonia reactions.
• Reaction pathways and product distributions are predictable based on reactant stoichiometry.
• Model reactions with AlH3 suggest that hydrogen-substituted species can estimate reactivity in methyl-substituted systems.