Studies of Ring-Opening Reactions of Styrene Oxide by Chromium Tetraphenylporphyrin Initiators. Mechanistic and Stereochemical Considerations

Chromium(III) tetraphenylporphyrin chloride, TPPCrCl, in the presence of bis(triphenylphosphine)iminium chloride, PPN+Cl–, is shown to react catalytically with styrene oxide, SO, under various conditions to lead to poly(styrene oxide), PSO, poly(styrene carbonate), PSC, styrene carbonate, SC, poly(styrene succinate), PSS, and β-hydroxyester. The stereochemical consequences of the ring-opening event in this coordination catalysis have been investigated by NMR spectroscopy, polarimetry, and chiral HPLC, employing both rac- and R-SO. The ring-opening event occurs by attack at both the methylene and methine carbons and nucleophilic attack at the methine occurs preferentially with inversion. These findings concerning coordinate catalysis are compared with the more common ring-opening reactions in organic chemistry and the recent report on the cobalt-catalyzed formation of PSC by Darensbourg and co-workers.