A Quantum Chemical Study of the Haptotropic Rearrangements of Cr(CO)<sub>3</sub> on Naphthalene and Phenanthrene Systems

First-principles gradient-corrected density functional theory electronic structure calculations of the haptotropic rearrangement of a Cr(CO)<sub>3</sub> unit on naphthalene and phenanthrene derivatives are reported. Coupled-cluster calibration studies of Cr(CO)<sub>3</sub> complexes with benzene and naphthalene derivatives confirm the accuracy of the applied Becke exchange and Perdew correlation functionals. Characteristic points on the energy hypersurface (reactants, products, intermediates, and transition states) were located for various substituents on the aromatic skeleton. It is argued that a −OH/−O<sup>-</sup> substituent may provide a means to steer the haptotropic shift depending on the pH value, i.e., to construct a molecular switch. In addition, the mechanism of the [3 + 2 + 1] benzannulation of chromium pentacarbonyl naphthylcarbene complexes with alkynes was investigated, and the preference of the angular benzannulation leading to phenanthrene complexes of Cr(CO)<sub>3</sub> over the linear benzannulation leading to corresponding anthracene complexes is explained.