Gas-phase reaction pathways of aluminum organometallic compounds with dimethylaluminum hydride and alane as model systems

Gas-phase molecular association reactions of dimethylaluminum hydride have been studied with density functional theory (DFT) and ab initio MP2 methods to understand the dimer reversible arrow trimer equilibrium. A mechanism involving DMAH oligomers from monomers through hexamers is proposed as the equilibrium reaction pathway, and the kinetics and thermodynamics of the mechanism have been investigated. Optimized structures, heats of reaction, and transition states have been computed for the proposed reaction pathways. For transition-state optimizations, alane oligomers (AlH3)(n) were used as model systems to simplify electronic structure calculations for quantification of the kinetics of DMAH reaction pathways. The proposed reaction pathways consist of a sequence of unimolecular and concerted bimolecular steps with activation barriers substantially less than for alternative ring-opening pathways. On the basis of the current results, experimental observations of a complex DMAH dimer reversible arrow trimer equilibrium can be understood in terms of a series of these slow bimolecular and relatively faster unimolecular reactions.