STRUCTURE AND MECHANISM IN AEROBIC ALKENE EPOXIDATIONS PROMOTED BY RUTHENIUM COMPLEXES OF BIS(DIHYDROOXAZOLE) LIGANDS

Reaction of [RuCl2(NCMe)(2)(cod)] with bis(dihydrooxazoles) gave [RuCl2(cod){(S,S)-R(2)(1)C-(C=NCHR(2)C(2)(1)O)(2)] (cod = cycloocta-1.5-diene; R(1) = H, R(2) = CH(2)Ph or Pr-i; R(1) = Me, R(2) = Pr-i). The benzyl complex has been crystallographically characterised. The IR spectra of the complex of the hexamethyl -substituted compound suggest that the ligand is relatively distorted and this is borne out by crystallographic comparison of the model complexes cis- [W(CO)(4){(S,S)-R(2)C(C=NCHPrCR(2)O)(2)}] (R = H or Me). Mechanistic studies of the epoxidation of styrene and stilbenes in the presence of isobutyraldehyde and molecular oxygen using the ruthenium complexes as catalysts in the presence and absence of 4-tert-butylcatechol as a radical trap revealed that the metals act as promoters for the production of (PrCO3H)-C-i and that this carries out the epoxidation, either directly or by formation of oxo-ruthenium species.