A kinetic study of the heterobimetallic dimer disruption of $PPN+^aCrMn(CO)_{10}$- by ligand L(L = CO, $PR_3$) is described. The rate was determined in several aprotic solvents. The results indicated that the reaction of $PPN+^aCrMn(CO)_{10}$- with $PR_3$ is of first order with respect to [$PPN+^aCrMn(CO)_{10}$-] and the heterolytic Cr-Mn bond dissociation energy is approximately 27 kcal/mol.