Carbon Monoxide Insertion Reactions. I. The Carbonylation of Methyl Manganese Pentacarbonyl and Decarbonylation of Acetyl Manganese Pentacarbonyl

The equilibrium and the rates of the forward and reverse reactions in the system CH3Mn(CO)(5) + CO = CH2COMn(CO)(6) have been studied at atmospheric pressure of carbon monoxide in various solvents and at several temperatures. The reaction is first order in both CH3Mn(CO)(3) and CO. In (CH3CH2OCH2CH2)(2)O, the solvent most used, the following data have been obtained: For the equilibrium at 30 degrees, K = 367 1. mole(-1), Delta H degrees = -12.6 kcal. mole(-1), Delta F degrees = -3.55 kcal. mole(-1), Delta S degrees = -30.0 cal. mole(-1) deg.(-1). For the forward reaction at 30 degrees, k(1) = 8.99 X 10(-3) l. mole(-1) sec.(-1), Delta H* = 14.2 kcal. mole(-1), Delta F* = 20.6 kcal. mole-1, Delta S* = -21.1 cal. mole(-1) deg.(-1). For the reverse reaction at 30 degrees, k(2) = 2.48 X 10(-5) sec.(-1), Delta H* approximate to 27 kcal. mole(-1), Delta F* approximate to 24 kcal. mole(-1), Delta S* approximate to 10.5 cal. mole(-1) deg.(-1). The effect of changing the solvent appears to be mainly a function of the bulk dielectric constant in stabilizing a somewhat polar transition state and specific, molecular solvent participation does not appear to be important in the solvents used. Possible mechanisms are discussed and one involving direct combination of CH3Mn(CO)(5) with CO is shown to fit all the known facts and is preferred although a mechanism involving the rapid pre-equilibrium CH3Mn(CO)(6) = CH3COMn(CO)(4) cannot be ruled out at this stage.