1004 Inorganic Chemistry, VoZ. 10, No. 5, 1971
J. R. HUTCHISON, J. G. GORDON, 11, AND R. H . HOLM
CONTRIBUTION FROM THE DEPARTMEST OF CHEMISTRY, MASSACHUSETTS INSTITUTE O F TECHNOLOGY, CAMBRIDGE, L&~ASSACHUSETTS 02139
Intramolecular Rearrangement Reactions of Tris-Chelate Complexes. 1I.l Kinetics and Probable Mechanism of the Isomerization and Racemization of the “Fast” Complexes Tris(l-phenyl-5-methylhexane-2,4-dionato)aluminum(III) and -gallium(III) BY
J. R. HUTCHISOK;,~J. G. GORDON,
I I , ~ A N DR. H.
HOLM*
Received July 15, 1970 Rearrangement reactions of the title complexes, M(pmhd)3(2), have been investigated by proton resonance in chlorobenzene solution. These reactions were found to be intramolecular and to involve geometrical isomerization and inversion of the molecular configuration. The two processes occur simultaneously and were examined by means of the temperature dependencies of isopropyl methyl signals. Experimental spectra in the intermediate-exchange regions of both complexes were compared with those computed for various rearrangement mechanisms of the twist and bond rupture type. Microscopic rate constants for the mechanisms are presented. On the basis of full line shape analysis, a number of mechanisms have been excluded. Those regarded as most probable for Al(pmhd)3and Ga(pmhd)s are certain twist processes and bond rupture to form square-pyramidal-axial transition states. Activation parameters for these mechanisms are given. Tris(3-acetylpentane-2,4-dionato) complexes of aluminum and gallium were prepared and found not to undergo linkage isomerization at 180” in chlorobenzene. Arguments based on estimated lower limits of the rates of this process compared to the rates of rearrangement of pmhd complexes suggest that Ga(pmhd)S may rearrange by a twist mechanism. Rearrangement rates were found to increase with increasing ionic radius of the metal ion, viz., AI < Ga
