Synthesis, structure, and interconversion of chiral rhenium oxygen- and sulfur-bound sulfoxide complexes of formula [(eta(5)-C5H5)Re(NO)(PPh3)(OS(Me)R)](+) X-; diastereoselective oxidations of coordinated methyl alkyl sulfides

Reactions of the chiral chlorobenzene complex [(eta (5)-C5H5)Re(NO)(PPh3)(C lC6H5)]+BF4- (1(+) BF4-) and alkyl methyl sulfoxides O=S(Me)R (R = a, Me; b , Et; c, i-Pr or d, t-Bu), at -15 degreesC gave the oxygen-bound sulfoxide complexes [(eta (5)-C5H5)Re(NO)(PPh3)(O=S(Me)R)](+) BF4- (2a-2d(+)BF(4)(-); 94-56%). Above 0 degreesC, 2a-2d(+)BF(4)(-) rearrange to sulfur-bound link age isomers [(eta (5)-C5H5)Re(NO)(PPh3)(S(=O)(Me)R)]+BF4- (3a-3d(+)BF(4)(-) ; 96-20%). The triflate salts 2c,2d(+)TfO(-) and 3b,3c(+)TfO(-) are analogo usly prepared from (eta (5)-C5H5)Re(NO)(PPh3)(OTf). Complexes 2b-2d(+)X(-) and 3b-3d(+)X(-) can exist as two Re, S configurational diastereomers. Ster eochemistry is assigned from reactions of (S)- or (R)-1(+)BF(4)(-) with ena ntiomerically enriched sulfoxides (R)-b-d, and a crystal structure of (SReR S,RReSS)-2d(+)TfO(-).0.5CH(2)Cl(2). Relative diastereomer stabilities, and the basis for the divergent kinetic and thermodynamic oxygen/sulfur binding selectivities, are analysed. The alkyl methyl sulfide complexes [(eta (5)- C5H5)Re(NO)(PPh3)(S(Me)R)](+) X- and dimethyldioxirane react (acetone, -20 degreesC) to give 3a-3d(+)X(-). Diastereoselectivities (3b-3d(+)X(-)) are f air to good. However, some overoxidation to Ph3P=O occurs, lowering yields.