Dimethylplatinum(II) complexes: computational insights into Pt-C bond protonolysis

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Reaction Mechanisms

Background:

• The electrophilic cleavage of platinum-carbon bonds in platinum(II) complexes is crucial in organometallic chemistry.
• Understanding the precise reaction mechanism (direct vs. stepwise) is essential for controlling chemical transformations.

Purpose of the Study:

• To elucidate the mechanism of protonation and methane elimination in dimethylplatinum(II) complexes using detailed density functional theory (DFT) calculations.
• To investigate the influence of ancillary ligands and solvents on the reaction pathways.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to study dimethylplatinum(II) complexes reacting with triflic acid in various solvents.
• Both direct one-step proton attack (S(E)2) and stepwise oxidative-addition/reductive elimination (S(E)(ox)) mechanisms were explored.

Main Results:

• The reaction mechanism is not solely determined by the donating properties of spectator ligands.
• Phosphorus-ligated complexes favor a direct protonolysis pathway (S(E)2).
• Nitrogen-based or hard, poor-donor ligands show varied behavior; solvent nucleophilicity and sterics can alter the preferred mechanism.
• Six-coordinate Pt(IV) hydride intermediates can form via direct protonation, but their presence doesn't confirm the S(E)(ox) pathway.
• Methane elimination consistently occurs via an associative mechanism, assisted by solvent or acid anion.

Conclusions:

• The mechanism of Pt-C bond cleavage in dimethylplatinum(II) complexes is complex and depends on multiple factors including ligand type and solvent properties.
• The study refutes the formation of five-coordinate Pt(IV) intermediates and clarifies the role of six-coordinate Pt(IV) hydrides.
• Methane elimination is an associative process, with solvent and counterion playing facilitating roles.