Reactive Intermediates in the Photodecarbonylation of the Cyclopentadienyl and Indenyl Complexes CpFe(CO)₂(C(O)CH₃) and IndFe(CO)₂(C(O)CH₃) (Cp = η⁵-C₅H₅; Ind = η⁵-C₉H₇)

Time-resolved infrared and time-resolved optical spectroscopy have been used to probe further into the spectra and dynamics of reactive intermediates I and I ind generated by flash photodecarbonylation of the respective acetyl complexes CpFe(CO) 2 (C(O)CH 3 ) ( A ) and IndFe(CO) 2 (C(O)CH 3 ) ( A ind ) (Cp = η 5 -C 5 H 5; Ind = η 5 -C 9 H 7 ). The competitive reaction dynamics of CH 3 migration to the metal, trapping by CO, and trapping by other ligands such as P(OCH 3 ) 3 were determined for these intermediates in various solvents. Hydrostatic pressure effects on the competitive photoreaction pathways for both A and A ind in hexane solutions were also examined, and it was found that the photosubstitution pathway has a significantly more negative activation volume than does the photoinduced methyl migration (although a less negative value was found than that previously reported from these laboratories). The indenyl intermediate I ind is about 5-fold more reactive toward methyl migration and toward trapping by various ligands than is the cyclopentadienyl analogue I, but these differences appear to be too small to support a ring-slip mechanism for either type of reaction. The overall picture points to solvento species, e.g., CpFe(CO)(Sol)(C(O)CH 3 ), as the most likely form of the intermediates for all solvent systems studied at ambient temperature, with the possible exception of the solutions in perfluoro(methylcyclohexane). The possible relevance of these species to mechanisms for migratory insertion of CO into the metal−alkyl bonds of the methyl complexes CpFe(CO) 2 CH 3 ( M) and IndFe(CO) 2 CH 3 ( M ind ) is discussed.