Ultrafast vibrational spectroscopic analysis of the ubiquitous precatalyst [Mn2(CO)10] in different solvents

Abstract

Infrared (IR) absorption and time resolved IR (IRpump–IRprobe, 2D-IR) spectroscopies have been combined to study the vibrational dynamics and solvent interactions of the carbonyl ligand stretching vibrational modes of the photocatalyst dimanganese decacarbonyl, [Mn2(CO)10], in solvents with varying physical properties (heptane, cyclohexane, THF, MeCN, DMSO, iPrOH, and MeOH). The presence of a solvent-mediated symmetry breaking mechanism leading to a gain in oscillator strength of formally symmetry-forbidden modes was observed in all solvents, although the effect was more marked in polar solvents. Ultrafast vibrational energy dissipation was found to occur via two solvent dependent relaxation pathways, rapid intramolecular vibrational energy redistribution (IVR ∼ 0.3–1 ps) and relaxation to the ground vibrational state (T1 ∼ 80–250 ps). Accelerating factors for vibrational relaxation included hydrogen bonding and the presence of solvent vibrational modes resonant with the carbonyl modes of [Mn2(CO)10], while IVR timescales displayed an anticorrelation with vibrational relaxation times. Overall, a simple association of dynamic behavior with solvent properties could not be identified for any of the measured parameters. Rather, specific solvent properties were found to contribute to different extents in each case. Thus, our results highlight the need for careful consideration of solvent factors when attempting a rational selection of catalyst/solvent combinations or the implementation of sustainable replacement solvents.