Ruthenium Complexes, Thioether, Sulfoxide, Epoxide, Dimethyldioxirane Halfsandwich ruthenium thiolate complexes bearing electron-withdrawing phosphite or phos phonite ligands were prepared from [CpRu(PPh3)2(SR)l (R = Ph, CH2Ph, Me) and triphenylphosphite or (5,5')-bis(binaphthylphosphonito)ethane (bbpe), respectively. Reaction with l-bromo-3-methyl-2-butene in the presence of NH4PF6 gave the corresponding allylthioether complexes [CpRu(PR'3)2(S(R)CH2CH=CMe2)]PF6. Treatment with an excess of dimethyl dioxirane (DMD) transformed the triphenylphosphite derivatives into diastereomeric (oxiranylmethyl)sulfoxide complexes with 18 -80% de. NMR monitoring of the reaction revealed that the oxidant attacks the sulfur atom and the C=C double bond with comparable rates. Sim ilar oxidation of the bbpe complexes gave mixtures of four diastereoisomers with ratios of (64 : 15 : 1 3 :8 ) and (51 : 24 : 15 : 10), respectively.