Photochemistry of (η⁶-Anisole)Cr(CO)₃ and (η⁶-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

Abstract

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.