Potential energy mapping of the excited-states of (η6-arene)Cr(CO)3 complexes: the evolution toward CO-loss or haptotropic shift processes.

The potential energy profiles of the optically accessible excited states of two model (η(6)-arene)Cr(CO)(3) systems were explored using Time-Dependent Density Functional Theory. Two photochemical reactions were investigated, CO-loss and the haptotropic or ring-slip of the arene ligand. In both cases the photochemical reaction requires the surmounting of a small thermal barrier in the lowest energy excited state. In the case of (η(6)-benzene)Cr(CO)(3) only one excited state is populated following 400 nm excitation and this leads to the release of CO. The calculated energy barrier to this process is 13 kJ mol(-1). In the case of (η(6)-thiophenol)Cr(CO)(3) two excited states are accessible one leading to CO-loss while the other results in the ring-slip process. The calculated barrier to the ring-slip process is 11 kJ mol(-1). The calculations are consistent with the results of picosecond time-resolved infrared studies.