Concurrent and competitive homolysis and elimination reactions of (.alpha.-phenylethyl)aquocobaloxime

The kinetics of decomposition of PhCH(CH/sub 3/)Co(dmgH)/sub 2/OH/sub 2/) in aqueous methanol were studied in acidic solution and suggest parallel reactions of the parent complex (k/sub b,298/ = 3.55 x 10/sup -3/ s/sup -1/, ..delta..H/sup double dagger/ = 28.6 +- 1.1 kcal mol/sup -1/, ..delta..S/sup double dagger/ = 25.7 +- 3.6 cal mol/sup -1/ K/sup -1/) and its conjugate acid (k/sub a,298/ = 1.48 x 110/sup -2/ s/sup -1/, ..delta..H/sup double dagger/ = 23.2 +- 0.2 kcal mol/sup -1/, ..delta..S/sup double dagger/ = 11.1 +- 0.7 cal mol/sup -1/ K/sup -1/), the two reactants differing by the extent of protonation of the oxime oxygens and interrelated by an equilibrium constant K/sub H/ = 8.1 +- 0.4 M/sup -1/. The products consist of Co/sup 2 +/, four dimers of PhCHCH/sub 3/ (including a quinoid from ..cap alpha..-to-para addition and 1,3-diphenylbutane as well as meso- and rac-2,3-diphenylbutanes) and styrene. The results suggest parallel homolytic (approx. 72%) and ..beta..-elimination (approx. 28%) pathways. The intermediacy of cobalt(II) cobaloxime was confirmed by experiments with added H/sub 2/O/sub 2/ and Co(NH/sub 3/)/sub 5/Br/sup 2 +/. These reagents do not alter the rate constant but do produce mixtures of Co/sup 2 +/ and (H/sub 2/O)/sub 2/Co(dmgH)/sub 2//sup +/ or BrCo(dmgH/sub 2/)/sub 2/OH/sub 2/, in ratios consistent with the rate constants determined independently for the Co(II) complex.