A theoretical study on the mechanism of the original Shilov reaction.

摘要

Theoretical studies have been conducted to investigate the mechanism and search of the optimal catalysts for the original Shilov reaction in which C-H bond in methane is activated by platinum tetrachloride (PtCl4 2-) in an acidic aqueous solution. As to the reaction mechanism, methane uptake instead of C-H bond activation is the rate-determining step. Solvent-substituted Pt catalysts are more active than the original catalyst PtCl42-, among which, PtCl3(H 2O)- is the most active due to its abundance in solution and low activation energy barrier. The inverse trans-labilizing effect reveals the importance of the trans-directing ability of the trans ligand to the reactivity of the catalysts. Trans ligands influence the overall reaction rate through affecting the type and abundance of the active solvent substituted Pt species produced in the solution. Such phenomenon is essentially related to the electronegativity of the trans-ligands. In order to improve the activity of the catalysts, Phosphine-, nitrogen-, and oxygen-based trans ligands are examined for their suitability as the trans ligand. A variety of weakly coordinating solvents are investigated as the leaving ligand. Nitrogen based trans ligand and fluorinated methanol solvent are recommended for optimal catalysts. M-C and C-H bond strengths of a variety of different alkanes are explored and the trend-setting factor is identified. Sterics are crucial for saturated hydrocarbons and orbital interaction energy between C fragments, and H is becoming more important for cyclo-unsaturated, and bulky alkanes.