The pK(R+) values for metal-stabilized carbocations [CP2M2(CO)(4)(mu-eta(2),eta(3)-HCdropCCR(1)R(2))](+) (M = Mo, W) containing primary (R-1 = R-2 = H), secondary (R-1 = H, R-2 = Me), or tertiary (R-1 = R-2 = Me) coordinated propargyl cations were measured in 50% aqueous acetonitrile, Their stability increases from the tertiary to primary cation, and the stability of the tungsten-containing cations is higher than that of the corresponding molybdenum analogs.