New insights into the photochemistry of [CpFe(CO) 2 ] 2 using picosecond through microsecond time-resolved infrared spectroscopy (TRIR)

Picosecond to microsecond time-resolved infrared spectroscopy (TRIR) has been used to investigate the photochemistry of [CpFe(CO)2]2. The early-time TRIR spectra are dominated by vibrationally hot transient species and this leads to spectra with broad featureless bands. The majority (84%) of the well characterized Cp2Fe2(μ-CO)3, with a band at 1824cm−1, grows in on a timescale (15–20ps) similar to the cooling rate of many of the ν(CO) bands, and this arises from presumably the initially formed species, [CpFe(CO)(μ-CO)2FeCp] of which we were unable to find clear evidence. However, Cp2Fe2(μ-CO)3 is formed by two different processes and under CO the remaining slower formation (16%) occurs at the same rate (46±2ns) as a transient band at 1908cm−1 decays. The 1908cm−1 had been previously observed in an earlier study but its identity remained unclear. We find that this 1908cm−1 intermediate has no corresponding bridging ν(CO) band and is formed by a 1-photon process. This band is assigned to a dicarbonyl-loss photoproduct, [CpFe(CO)]2 and is a rare example of double CO loss occurring following a single-photon excitation in the condensed phase.