Kinetic parameters for the intramolecular environmental interchange of nonequivalent terminal groups on the like ligands of the following mixed β-diketonate complexes of aluminum(III) have been determined by nmr spectroscopy: Al(acac)-(hfac)2, Al(acac)2(hfac), and Al(acac)2(bzbz), where acac = acetylacetonate, hfac = hexafluoroacetylacetonate, and bzbz = dibenzoylmethanate. The rates of terminal CF3 group exchange for Al(hfac)2(acac) were studied in benzene, dichloromethane, and nitrobenzene; the activation energies (kcal/mol) and entropies (eu) at 25° are, respectively, 19.0 ± 1.3 and 2.9 ± 4.2 in C6H6, 21.3 ± 0.7 and 10.7 ± 2.2 in CH2Cl2, and 19.5 ± 0.6 and 5.7 ± 1.9 in C6H5NO2. For CH3 group exchange in Al(acac)2(hfac) in dichloromethane solution, Ea = 18.4 ± 0.7 kcal/mol and ΔS≠25° = 10.0 ± 2.4 eu, and for Al(acac)2-(bzbz) in o-dichlorobenzene, Ea = 22.0 ± 0.6 kcal/mol and ΔS±25° = 0.9 ± 1.5 eu. The results are evaluated in terms of a bond-rupture mechanism in which one metal-oxygen bond ruptures to give a five-coordinate intermediate.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry