Abstract
Chiral racemic rhenium thiolate complexes [CpRe(NO)(PPh3)(SR)] were obtained under either acidic or basic conditions. Thus, when [CpRe(NO)(PPh3)(CH3)] (1) was treated with etheral HBF4 and HSR the thiolate complexes [CpRe(NO)(PPh3)(SR)] [SR = SCH2(2-furyl) (2), SCH2C(O)OEt (3)] were obtained after chromatographic workup. Ligand exchange reactions between [CpRe(NO)(PPh3)(OC4H8)]BF4 (4) and sodium thiolates yielded analogous complexes with SR = SH (5), SCH2CH2Ph (6), SCH2CH=CH2 (7). SR groups which tolerate strongly alkaline conditions may be introduced by treatment of 4 with HSR in the presence of sodium ethoxide as demonstrated by the high-yield synthesis of 2 as well as of complexes with SR = SCH2CH2NHAc (8), SCH2CH2C(O)OH (9). A milder synthesis using hydrated sodium carbonate as a base provided 8 and compounds with SR = SCH2CH2C(O)OMe (10), SCH2CH2C(O)NHCH2Ph (11) in high yields. Using similar methods, thiolate complexes of (R)-N-acetylcysteine (13), its methyl ester (14), (R)-N-phthaloylcysteine (16), and N-[(S)-3-mercapto-2-methylpropionyl]-S-proline (Captopril) (17) were obtained as diastereomeric pairs. The formation of 13 was preceded by the O-bonded isomer 12 which slowly rearranges in solution. 13 can be converted under acidic conditions into its methyl (14) or ethyl (15) esters. The diastereomers of 16 were separated by crystallization, and the structure of the (R,R)-isomer 16a determined.
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