Observation of the photogenerated CO-loss intermediate from [CpFe(CO)]2(μ-CO)(μ-CHCH3) via time-resolved IR spectroscopy

Nanosecond time-resolved IR (TRIR) measurements were performed for both [CpFe(CO)(μ-CO)]2 (1) and [CpFe(CO)]2(μ-CO)(μ-CHCH3) (4). The results obtained for 1 are consistent with those previously reported. The TRIR spectrum of 4 in cyclohexane at room temperature (λexc=355 nm) both under argon and in CO atmosphere is consistent with the formation of the triply-bridged intermediate [CpFe]2(μ-CO)2(μ-CHCH3) (5) that results from loss of CO. The IR absorption peaks observed at 1840 and 1808 cm−1 in the TRIR spectrum of 5 are similar to those previously reported in matrix isolation experiments and the lifetimes are consistent with published time-resolved data in the visible region. In addition, DFT calculations result in the calculated frequencies of 1842 and 1810 cm−1 for the predicted 3B2 ground state of the structurally related [CpFe]2(μ-CO)2(μ-CH2) complex.