For a direct quantitative investigation of the Csp(2)-Csp(2) reductive elimination rate within a catalytic cycle, a novel oxidative coupling system in the presence of a Ni catalyst and desyl chloride as the oxidant is devised. The reaction progress profiles of arylzinc reagents exhibit zero-order kinetic behavior, and a reductive elimination step is confirmed as the rate-determining step. This allows direct measurement of the Csp(2)-Csp(2) reductive elimination rate constant within a catalytic cycle. The rate constants of p-MePhZnCl are obtained in the range 0.23 to 3.5 s(-1) from 0 to -35 degrees C, which are unusually fast reaction rates. According to the Arhenius equation, the values of Delta H-double dagger and Delta S-double dagger (Delta H-double dagger = 9.7 kcal mo(-1), Delta S-double dagger = 35 J mo(-1) K-1) are obtained. The small value of Delta H-double dagger reveals that the reductive elimination step of Csp(2)-Ni-Csp(2) is an extremely facile process.