Binding Energies for Aluminium Atom Association Complexes with Dimethyl Ether, Diethyl Ether, and Tetrahydrofuran

Article abstract of DOI:10.1021/j100324a038

Aluminium atom association reactions with the title ethers in the gase phase are investigated by time-resolved fluorescence excitation of ground-state Al atoms following pulsed visible laser photolysis of trimethylaluminium in a gas cell.Ar buffer gas pressure effects on the reaction rates are observed and interpreted in terms of collision complex formation in termolecular reactions.The limiting high Ar pressure bimolecular rate constants approach gas kinetic values, implying small or negligible activation energy barriers and large Arrhenius preexponential factors for these reactions.For each of dimethyl ether (DME), diethyl ether (DEE), and tetrahydrofuran (THF), an equilibrium is observed between free Al atoms and bound Al atom-ether complexes.Equilibrium constants for the dissociation reaction are obtained through analysis of kinetic data at different reactant pressures.Binding energies are derived from observations of the temperature dependence of the equilibrium constant in the range 5-35 deg C for DME and 5-30.5 deg C for DEE or through estimation of the standard entropy change for the dissociation of all three ether complexes in conjunction with measurements of the equilibrium constant for dissociation at room temperature.Evidence is presented which indicates that Al atoms form monoligand complexes with these three ethers.Al atom binding energies (kcal mol^-1 are reported for Al-DME (9.2 +/- 0.6) and Al-DEE (9.2 +/- 1.2).The binding energy for Al-THF is estimated at 10.8 kcal mol^-1 based upon the room-temperature equilibrium constant.Trends in binding energy and bonding mechanisms are discussed with regard to known and calculated properties of metal atom complexes with water and Lewis acid complexes of ethers.