Homolysis and acidolysis reactions of (.alpha.-hydroxyalkyl)- and (.alpha.-alkoxyalkyl)chromium(III) complexes: kinetics, steric effects, and bond energies

The rates of homolysis of 12 organochromium complexes were determined by the addition of oxidizing scavengers to prevent recombination of Cr/sup 2 +/ and the carbon-centered radicals. The rate constants for complexes derived from aliphatic alcohols span the range 3.7 x 10/sup -5/to approx. 3 x 10/sup 2/s/sup -1/ CrCH/sub 2/OH/sup 2 +/s/sup -1/ for CrC(CH/sub 3/)(t-C/sub 4/H/sub 9/)OH/sup 2 +/ at 25/sup 0/C. There is a good correlation between the free energies of activation for homolysis of the organochromium complexes and corresponding substituted symmetrical ethanes. On the basis of the activation parameters and the literature data, estimates of the Cr-C bond dissociation enthalpies were made. Rate constants for the acidolysis reaction, previously known for some of these complexes, were evaluated for the others. Means were developed, by control of reaction conditions, to permit independent measurements of homolysis and acidolysis. The organochromium complex derived from isopropyl ether, CrC(CH/sub 3/)/sub 2/OCH(CH/sub 3/)/sub 2//sup 2 +/, undergoes a rapid (0.05 < k < 2 s/sup -1/) conversion to CrC(CH/sub 3/)/sub 2/OH/sup 2 +/ in dilute perchloric acid. 5 figures, 6 tables.