Manganese Carbonyl Compounds Reveal Ultrafast Metal–Solvent Interactions

Herein, we exemplify that time-resolved multiple-probe spectroscopy (TRMPS) with infrared detection can be used to observe and quantify the dynamic processes occurring during the solvation of a catalytically competent manganese­(I) carbonyl compound. TRMPS has been used to demonstrate that a manganese­(I) 2-phenylpyridyl (ppy) complex, [Mn­(ppy)­(CO)4], undergoes photochemically induced loss of a carbonyl ligand on a sub-picosecond time scale to give solvent (S) complexes of the type, fac-[Mn­(ppy)­(S)­(CO)3] (S = n-C7H16, CH2Cl2, NCMe, C6H5CH3, THF, 1,4-dioxane, n-Bu2O, and DMSO). An excited state, assigned as 3[Mn­(ppy)­(CO)4], with a lifetime, τ, of ca. 5 ps is also formed as a minor photoproduct. The vibrational modes of the carbonyl ligands in fac-[Mn­(ppy)­(S)­(CO)3] are diagnostic of the nature of the coordinated solvent and allow for the dynamics of solvation within the coordination of the metal to be observed. For example, in the case of THF, initial interactions with the metal occur through a C–H σ-interaction, assigned based on the similarity to the bands observed for the related heptane metal complex. Isomerization to the thermodynamically preferred O-binding mode was observed, τ ca. 18 ps, with similar behavior evident in 1,4-dioxane and nBu2O. The lifetime for the isomerization shows a correlation with the number of C–H bonds in the solvent. In 1,4-dioxane, there is no evidence for the initial formation of an O-bound complex which indicates that the solvent binding is not stochastic in nature and is likely determined by the topology of the first solvation shell of the metal complex. The insight into these ultrafast metal–solvent interactions is enabled by the dominant photoprocess, CO dissociation, being rapid (