Ligand rearrangement reactions of Cr(CO)6 in alcohol solutions: experiment and theory

The ligand rearrangement reaction of Cr(CO)6 is studied in a series of alcohol solutions using ultrafast infrared spectroscopy and Brownian dynamics simulations. Excitation with 266 nm light gives Cr(CO)5 which is quickly solvated by a ligand from the bath. In alcohol solutions, solvation by an alkyl or hydroxyl site can occur; all alkyl bound complexes eventually rearrange to hydroxyl bound complexes. This rearrangement has been described using both an intermolecular (stochastic) and intramolecular (chainwalk) mechanism. Experiments alone do not allow for characterization of the mechanism, and therefore, theoretical calculations were carried out for the first time by modeling the ligand rearrangement as a diffusive walk along a potential defined by the different interaction possibilities. Experiments and simulations were carried out for Cr(CO)6 in 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 2-methylbutanol, and 3-methylbutanol. The trends in the theoretical and experimental rearrangement times are similar for all simulations carried out indicating that the two mechanisms have very similar ensemble behavior when bath effects are taken into account. The nature of the mechanism responsible for motion along the alcohol chain is not of primary importance in isolating the kinetic behavior because of the highly diffusive nature of the reaction. Future experimental and theoretical work will be directed at identifying a definitive assignment of the reaction mechanism.