| Sumario: | The dimers {(¿n-ring)MCl}2(µ-Cl)2] ((¿n-ring)M = (¿5-C5Me5)Ir, (¿6-p-MeC6H4iPr)Ru) react with the modified cysteines S-benzyl-l-cysteine (HL1) or S-benzyl-a-methyl-l-cysteine (HL2) affording cationic complexes of the formula (¿n-ring)MCl(¿2N, S-HL)]Cl (1, 2) in good yield. Addition of NaHCO3 to complexes 1 and 2 gave equilibrium mixtures of neutral (¿n-ring)MCl(¿2N, O-L)] (3, 4) and cationic (¿n-ring)M(¿3N, O, S-L)]Cl (6Cl, 7Cl) complexes. Similar mixtures were obtained in one-pot reaction by successive addition of the modified cysteine and NaHCO3 to the above formulated dimers. Addition of the N-Boc substituted cysteine derivative S-benzyl-N-Boc-l-cysteine (HL3) and NaHCO3 to the dimers {(¿n-ring)MCl}2(µ-Cl)2] affords the neutral compounds (¿n-ring)MCl(¿2O, S-L3)] ((¿n-ring)M = (¿5-C5Me5)Ir (5a), (¿6-p-MeC6H4iPr)Ru (5b)). Complexes of the formula (¿n-ring)MCl(¿3N, O, S-L)]SbF6] (6Sb-8Sb), in which the cysteine derivative acts as a tridentate chelate ligand, can be prepared by adding one equivalent of AgSbF6 to the solutions of compounds 5 or to the mixtures of complexes 3/6Cl and 4/7Cl. The amide proton of compounds 8aSb and 8bSb can be removed by addition of NaHCO3 affording the neutral complexes (¿n-ring)M(¿3N, O, S-L3-H)] ((¿n-ring)M = (¿5-C5Me5)Ir (9a), (¿6-p-MeC6H4iPr)Ru (9b)). Complexes 9a and 9b can also be prepared by reacting the dimers {(¿n-ring)MCl}2(µ-Cl)2] with HL3 and two equivalents of NaHCO3. The absolute configuration of the complexes has been established by spectroscopic and diffractometric means including the crystal structure determination of (RIr, RC, RS)-(¿5-C5Me5)Ir(¿3N, O, S-L1)]SbF6] (6aSb). The thermodynamic parameters associated with the epimerization at sulphur that the iridium compound (¿5-C5Me5)Ir(¿3N, O, S-L3-H)] (9a) undergoes have been determined through variable temperature 1H NMR studies.
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