Correlating solvent dynamics and chemical reaction rates using binary solvent mixtures and two-dimensional infrared...

Area of Science:

• Physical Chemistry
• Spectroscopy
• Chemical Kinetics

Background:

• Vaska's complex (VC) is a key organometallic compound studied for its reactivity.
• Understanding solvent effects on reaction mechanisms is crucial in chemistry.
• Two-dimensional infrared (2D-IR) spectroscopy offers insights into molecular dynamics and solvation.

Purpose of the Study:

• To investigate the role of solvent dynamics in the oxygenation reaction of Vaska's complex.
• To correlate spectroscopic data from 2D-IR with kinetic measurements of oxygenation rates.
• To explore how binary solvent mixtures affect the reactivity and solvation shell of Vaska's complex.

Main Methods:

• Performed 2D-IR spectroscopy on Vaska's complex and its oxygen adduct in chloroform/d6-benzene and benzyl alcohol/d6-benzene mixtures.
• Measured second-order rate constants for the oxygenation reaction in the same binary solvent mixtures.
• Analyzed FTIR spectra of the carbonyl ligand and determined frequency-frequency correlation functions using 2D-IR.

Main Results:

• Oxygenation rate constants showed linear dependence on mole fraction in chloroform mixtures but nonlinear behavior in benzyl alcohol mixtures.
• A strong correlation was observed between reaction rate constants and homogeneous linewidths of the carbonyl vibration in the V C-O2 product.
• FTIR and 2D-IR data indicated increased solvent heterogeneity around the product, suggesting solvent dynamics play a role in reactivity.

Conclusions:

• Solvent dynamics, particularly in mixtures with benzyl alcohol, significantly influence the oxygenation reactivity of Vaska's complex.
• The study highlights a direct link between molecular-level solvent heterogeneity and macroscopic reaction rates.
• 2D-IR spectroscopy is a powerful tool for probing solvent-solute interactions and their impact on chemical transformations.