Two-Dimensional Infrared Spectroscopy of the Photoproduct of π-Cyclopentadienyliron Dicarbonyl Dimer

Equilibrium photoproduct of π-cyclopentadienyliron dicarbonyl dimer CpFe(CO)₂₂ in nonpolar solvent carbon tetrachloride (CCl₄) is investigated using time-resolved 2D IR spectroscopy. One of the several possible visible-light-driven photoreaction pathways is confirmedand the product is found to contain a di-carbonyl group that exhibits quantum beating between two equivalent transitions in time-resolved 2D IR spectra, which turns out to be the anti-symmetric and symmetric stretching of the terminal carbonyl stretching modes of CpFe(CO)₂Cl. This is the main product and its reaction pathway involves radical formation, followed by chloride addition. Quantum-chemistry computations support these experimental results. Our results indicate that 2D IR method can be used to identify in situ structures and dynamics of chemical species involved in condensed-phase chemical reactions