Kinetics and Mechanism of Molecular A-Frame Formation in Reactions of (PF6)2 with Diazomethane, Carbon Monoxide, Sulfur Dioxide, Sulfur, and Hydrogen Chloride

Article abstract of DOI:10.1021/ja00338a017

The mechanism of the formation of A frames of the type (PF6)2 (Y = CH2, CO, S, SO2) from (PF6)2 by reaction with CH2N2, CO, S, and SO2 (R) in CH2Cl2 and other organic solvents has been investigated by using kinetic studies and product analysis.Pseudo-first-order kinetic data (excess ₀) are consistent with either preequilibrium association of R with the complex prior to rate-limiting product formation or unimolecular formation of a common intermediate which is then attacked by R to form the A -frame product.Kinetic studies with _{0 0} substantiate the latter.The most likely intermediate leading to the products is one with a dangling dppm ligand formed by Pt-P bond heterolysis.When ₀ is very large, formation of this intermediate becomes rate limiting and is independent of the nature of R, with k = 2.73 +/-0.05E-2 s^-1 (at 25 deg C; ΔH^* = 25.0 kcal mol^-1 and ΔS^* = 18.5 cal mol^-1 K^-1).The same process and mechanism is observed for R = HCl, although with minor numerical differences; similar salt and solvent polarity effects occur in all of the reactions.