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)-R12C-(C=NCHR 2CR12O)2] (cod = cycloocta-1,5-diene; R1 = H, R2 = CH2Ph or Pri; R1 = Me, R2 = Pri). 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)-R2C(C=NCHPriCR 2O)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 PriCO3H and that this carries out the epoxidation, either directly or by formation of oxo-ruthenium species.
S. M. Bennett et al., "Structure and Mechanism in Aerobic Alkene Epoxidations Promoted by Ruthenium Complexes of Bis(dihydrooxazole) Ligands," Journal of the Chemical Society, Dalton Transactions, Royal Society of Chemistry, Jan 1995.
The definitive version is available at http://dx.doi.org/10.1039/DT9950000367
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