Mechanisms of Pyrolysis of Tricarbonylcyclopentadienylmanganese and Tricarbonyl(methylcyclopentadienyl)manganese

The mechanisms of the gas-phase pyrolysis of tricarbonylcyclopentadienylmanganese (1) and tricarbonyl(methylcyclopentadienyl)manganese (2) have been investigated using a combination of IR laser-powered homogeneous pyrolysis, stirred flow reactor kinetic measurements, and matrix isolation ESR spectroscopy. The observations are consistent with initial stepwise loss of CO, followed ultimately by release of *C₅H₅ (for 1) or *C₅H₄CH₃ (for 2); the hydrocarbon radicals then abstract hydrogen from unreacted starting material. For 1, the resultant *C₅H₄Mn unit undergoes intramolecular rearrangement, yielding ethyne and a second species tentatively identified as a manganese carbide. For 2, the more rapid abstraction from the ring CH₃ group results in formation of the fulvene CH₂C₅H₄ followed by isomerization to benzene. These processes lead to heavy carbon contamination of deposited Mn films unless an alternative source of H atoms for abstraction by cyclopentadienyl radicals is present.