Coordination Compounds of Indium. Part XIX. Ligand Exchange Studies with Indium(III) Complexes of Trifluoromethyl-β-diketonates

The ligand exchange reaction between InL₃ con plexes (L = CF_3•CO_•CH_•CO_•R⁻ anion; R = methyl, i-butyl, phenyl, 2-naphthyl, and 2-thienyl) and excess free ligand (HL) has been studied in the solvents diisopropyl ketone, acetonitrile, benzene, and dimethylsulfoxide. Studies of the lifetimes of the reactants as obtained from their ¹⁹F n.m.r. line-widths show that the exchange is first order in InL₃ concentration, but zero order in free ligand concentration. The coalescence temperature for the collapse of the n.m.r. ¹⁹F chemical shift between free and complexed ligand (~50 Hz) yields ΔG^≠ for the exchange. The results are in agreement with the known stereochemical properties of indium(III) complexes. The rate-controlling process in the exchange is identified as the. rotation of one monodentate ligand about a partial double bond prior to intramolecular proton transfer to a second monodentate ligand.