NUCLEAR MAGNETIC RESONANCE STUDIES OF LIGAND-EXCHANGE PROCESSES .2. KINETICS OF CONFIGURATIONAL REARRANGEMENT FOR SOME MIXED BETA-DIKETONATE COMPLEXES OF GALLIUM(3)

Nmr studies of Ga(acac)2(hfac) in dichloromethane and of Ga(acac)2(bzbz) in benzene, where acac = acetylacetonate, hfac = hexafluoroacetylacetonate, and bzbz = dibenzoylmethanate, have shown that the molecules undergo intramolecular configurational rearrangement processes which result in exchange of nonequivalent terminal methyl groups on the acac ligands. First-order rate constants for the rearrangement processes have been determined by line-broadening techniques. The rate of methyl group exchange at 25° for Ga(acac)2(hfac) is ca. 104 times larger than the rate for Ga(acac)2(bzbz). Activation energies and activation entropies were found to be, respectively: 14.5 ± 1.1 kcal/mol and 1.7 ± 4.4 eu for Ga(acac)2(hfac); 20.6 ± 2.7 kcal/mol and 3.5 ± 8.0 eu for Ga(acac)2(bzbz). The activation energies are discussed briefly and are compared with available parameters for terminal group exchange in other group IIIb metal γ-diketonates. © 1969, American Chemical Society. All rights reserved.