Trimer-dimer equilibrium studies of alkylaluminum alkoxides

摘要

The aluminum alkoxides [MeClAlOEt]_3 (1), [Et_2AlOMe]_3 (2), [Me_2AlOEt]_3 (3), and [EtClAlOEt]_3 (4) were investigated by ~1H NMR spectroscopy to study the o-dichlorobenzene solution equilibrium: 2 [R_2AlOR']_3 <-> 3 [R_2AlOR']_2. The complexes are shown to exist primarily as trimers at room temperature, but increasing concentrations of the dimeric form are observed at higher temperatures. Equilibrium constants, #DELTA#H, and #DELTA#S were determined for the trimer-dimer equilibrium. Values of #DELTA#H for the conversion of 2 moles of trimer are 63(4), 78(1), 85.0(8), and 99(6) kJ for 1,2,3, and 4, respectively. The corresponding values of #DELTA#S are 142(7), 184(3), 218(2), and 265(17) J/K, respectively. Thermodynamic parameters are compared with those reported for [Me_2AlOPr~n]_3 and [Me_2AlOPh]_3. The characterization of [EtClAlOMe]_3 is also reported.