Kinetics of dehalogenation of the bromobenzenes 4-RC6H4Br (R=F, Cl, H, CH3, Cn(3)O and N(CH3)(2)) with the title hydride (SDMA) and with SDMA in the presence of Co(acac)(2) have been examined. The rate constants of the debromination were correlated with Hammett substituent constants sigma (p) and E-1/2 reduction potentials of the bromobenzenes. rho values (+4.3 for SDMA reduction and +1.9 for the Co-catalyzed debromination) imply a negative charge concentration effect in transition states of both debrominations. Differences in the course of these reactions are discussed.