OUTER-SPHERE ELECTRON-TRANSFER IN METHYLENE-CHLORIDE - CONCENTRATION,SALT, AND TEMPERATURE DEPENDENCES OF THE OXIDATION OF (2)X(4)(CIS-1,2-BIS(DIPHENYLPHOSPHINO)ETHYLENE)(2) (X=CL, BR) BY [CO(DIMETHYLGLYOXIMATE)(3)(BF)(2)]BF4 AND THE OXIDATION OF RE2BR4(PME(2)PH)(4) BY [CO(1,2-CYCLOHEXANEDIONE DIOXIMATE)(3)(BBU)(2)]BF4

The kinetics of the oxidation of beta-Re(2)X(4)(cis-1,2-bis (diphenylp hosphino) ethylene)(2) (X = Cl, Br) by the cobalt clathtrochelate [Co( dimethylglyoximate)(3)(BF)(2)]BF4 and the oxidation of Re2Br4(PMe(2)Ph )(4) by the cobalt clathrochelate [Co(1,2-cyclohexanedione dioximate)( 3)(BBu)(2)]BF4 have been studied by the stopped-flow method as a funct ion of temperature (-85 to -19 degrees C), added Bu(4)NBF(4) (0-0.100 M), and reactant concentration in the low dielectric solvent methylene chloride. For each reaction, similar to 100 different conditions were studied. The observed rate constants were well fit by a mechanism inv olving separate paths for free ion and the ion-paired Co(III) oxidant. The analysis yielded values for Delta H double dagger and Delta S dou ble dagger for each path of each reaction and consistent Delta H degre es and Delta S degrees values for the ion-pairing of the cationic reac tant and the electrolyte, In addition, temperature-dependent electroch emical measurements in 0.10 M Bu(4)NBF(4) yielded Delta H degrees and Delta S degrees for the electron transfer process. This is the first m easurement of the homogeneous electron transfer reactivity of the dirh enium complexes, and they showed the expected high reactivity. The mos t notable result is a very high inhibition (ca. 700-fold) by added sal t of only the [Co(dmg)(3)(BF)(2)]BF4 reactions. We attribute this to a change of rate-controlling step, for the ion-paired path, to one invo lving anion migration. This appears only to occur when the magnitude o f ion-pairing free energy is significantly greater than the magnitude of the free energy change for the electron transfer process.