OUTER-SPHERE ELECTRON-TRANSFER IN METHYLENE-CHLORIDE - CONCENTRATION,SALT, AND TEMPERATURE DEPENDENCES OF THE OXIDATION OF TRANS-REX(2)(CIS-1,2 BIS(DIPHENYLPHOSPHINO)ETHYLENE)(2) (X=CL, BR) BY THE CLATHROCHELATE O(1,2-CYCLOHEXANEDIONEDIOXIMATE)(3)(BBUTYL)(2)]BF4

The oxidation of ReCl2(cis-1,2 bis(diphenylphosphino)ethylene)(2) and ReBr2(cis-1,2 bis(diphenylphosphino) ethylenef 2 by the clathrochelate [Co(1,2-cyclohexanedione dioximate)(3)(BButyl)(2)]BF4 have been studi ed by the stopped-flow method as a function of temperature (-85 to -50 degrees C), added Bu(4)NBF(4) (0-0.1 M), and reactant concentration i n methylene chloride. The rate constants were fit to a mechanism invol ving separate paths for the free ion and the ion paired Co(III)) oxida nt. The result was the enthalpy and entropy of ion pairing for both Bu (4)NBF(4) and the oxidant, and the enthalpy and entropy of activation for both the free ion path and the ion paired path for each reaction. This study makes this one of the best characterized outer-sphere elect ron transfer reactions occurring in the low dielectric constant solven t methylene chloride. The results will allow comparison of the reactiv ity of these mononuclear complexes with that of metal-metal bonded dir henium complexes. Using the temperature dependences of the reduction p otentials of the Re and Co complexes as well as decamethylferrocene, a nd the kinetics of the reduction of the Co(III) complex by decamethylf errocene in methylene chloride, also as a function of added salt, esti mates of the high electron self-exchange rate constants of the two Re complexes have been made. They are both very similar and are ca 10(8) M(-1) s(-1) at 25 degrees C.