Photochemistry of (η ⁶-anisole)Cr(CO) ₃ and (η ⁶-thioanisole)Cr(CO) ₃: Evidence for a photoinduced haptotropic shift of the thioanisole ligand, a picosecond time-resolved infrared spectroscopy and density functional theory investigation

The photochemistry of (η ⁶-anisole)Cr(CO) ₃ and (η ⁶-thioanisole)Cr(CO) ₃ was investigated by picosecond time-resolved infrared spectroscopy in n-heptane solution at 298 K. Two independent excited states are populated following 400 nm excitation of each of these complexes. An excited state with some metal-to-CO charge-transfer character is responsible for the CO-loss process, which is slow compared to CO-loss from Cr(CO) ₆. Observed first order rate constants of 1.8 × 10 ¹⁰ s ^-1 and 2.5 × 10 ¹⁰ s ^-1 were obtained for the anisole and thioanisole complexes, respectively. The second excited state has metal-to-arene charge transfer character and results in a haptotropic shift of the thioanisole ligand. DFT calculations characterized the excited states involved and the nature of the haptotropic shift intermediate observed for the thioanisole species.